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Gul Y, Holmes SN, Cho CW, Piot B, Myronov M, Pepper M. Two-dimensional localization in GeSn. J Phys Condens Matter 2022; 34:485301. [PMID: 36202078 DOI: 10.1088/1361-648x/ac9814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 10/06/2022] [Indexed: 06/16/2023]
Abstract
Localization behaviour is a characteristic feature of thep-type GeSn quantum well (QW) system in a metal-insulator-semiconductor device. The transition to strongly localized behaviour is abrupt with thermally activated conductivity and a high temperature intercept of 0.12 ×e2ħ-1at a hole carrier density 1.55 × 1011cm-2. The activation energy for the conductivity in the localized state is 0.40 ± 0.05 meV compared to an activation energy of ∼0.1 meV for conductivity activation to a mobility edge at carrier densities >1.55 × 1011cm-2. Insulating behaviour can occur from a system that behaves as though it is in a minimum metallic state, albeit at high temperature, or from a conductivity greater than a minimum metallic state behaviour showing that local disorder conditions with local differences in the density of states are important for the onset of localization. In the presence of a high magnetic field, thermally activated conductivity is present down to Landau level filling factor <1/2but without a magnetic-field-dependent carrier density or a variable range hopping (VRH) transport behaviour developing even with conductivity ≪e2h-1. In the localized transport regime inp-type doped Ge0.92Sn0.08QWs the VRH mechanism is suppressed at temperatures >100 mK and this makes this two-dimensional system ideal for future many body localization studies in disordered hole gases that can be thermally isolated from a temperature reservoir.
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Affiliation(s)
- Y Gul
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - S N Holmes
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | | | - B Piot
- LNCMI-CNRS, Grenoble 38042, France
| | - M Myronov
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - M Pepper
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
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DeMaria KA, Fink C, Pepper M, Rieger K, Tan SY, Namjoshi SS. Intestinal Failure in Junctional Epidermolysis Bullosa: Mild Skin Disease, Severe Diarrhea. Dig Dis Sci 2022; 67:1740-1743. [PMID: 35147818 DOI: 10.1007/s10620-022-07410-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/14/2022] [Indexed: 12/09/2022]
Affiliation(s)
- Karen A DeMaria
- Division of Pediatric Gastroenterology, Stanford University School of Medicine & the Lucile Packard Children's Hospital, 750 Welch Road- Suite 116, Palo Alto, CA, 94304, USA.
| | - Christopher Fink
- Division of Pediatric Gastroenterology, Stanford University School of Medicine & the Lucile Packard Children's Hospital, 750 Welch Road- Suite 116, Palo Alto, CA, 94304, USA
| | - Michael Pepper
- Department of Pathology, Stanford University School of Medicine, Palo Alto, USA
| | - Kerri Rieger
- Department of Pathology, Stanford University School of Medicine, Palo Alto, USA
| | - Serena Y Tan
- Department of Pathology, Stanford University School of Medicine, Palo Alto, USA
| | - Shweta S Namjoshi
- Division of Pediatric Gastroenterology, Stanford University School of Medicine & the Lucile Packard Children's Hospital, 750 Welch Road- Suite 116, Palo Alto, CA, 94304, USA
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Abou Mehrem A, Al Awad E, Anninck K, Au-Young S, Aydinol N, Bartmann P, Benders M, Benlamri A, Bolderheij L, Celik Y, Chan N, Chau C, Chau V, Chen X, Chetcuti Ganado C, Coetser A, Cools F, Da Rocha G, Deigner HP, Dereymaeker A, Deshmukh L, Domonoske R, Dossani S, Dsouza JM, El Gamal M, Eshemokhai P, Esser M, Fiedrich E, Franz A, Ghosh A, Groenendaal F, Grunau RE, Venkata SKRG, Hamitoglu S, Hellström-Westas L, Irvine L, Jansen K, Javadyan A, Jenkin G, Kamanga N, Kaur N, Keles E, Keller M, Kelly E, Kesting SJ, Kgwadi D, Kim B, Kohl M, Kowal D, Kricitober JD, Leijser L, LePine M, Lim YP, Lodha A, Londhe A, Ly L, Maes E, Malhotra A, Marlow N, Mathew JL, McDonald C, McLean M, Metcalfe C, Meyer R, Miller SP, Miller S, Mogajane T, Mohammad K, Momin S, Montpetit J, Mukiza N, Murthy P, Scott JN, Nakibuuka V, Nakwa F, Naulaers G, Noort J, Ntuli N, Ondongo-Ezhet C, Paul R, Pepper M, Plum A, Rombough B, Saugstad O, Scotland J, Scott J, Seake K, Sebunya R, Selvanathan T, Sepeng L, Simsek H, Steins-Rang C, Stonestreet B, Tang S, Taskin E, Thewissen L, Thomas S, Thomas R, van Kwawegen A, van Rensburg J, Velaphi S, Wu Y, Yaman A, Yapicioglu-Yildizdas H, Yawno T, Zaki P, Zein H, Zhou L. Proceedings of the 13th International Newborn Brain Conference: Neuroprotection strategies in the neonate. J Neonatal Perinatal Med 2022; 15:427-439. [PMID: 35431186 DOI: 10.3233/npm-229003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
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Kumar S, Pepper M. Interactions and non-magnetic fractional quantization in one-dimension. Appl Phys Lett 2021; 119:110502. [PMID: 35382142 PMCID: PMC8970604 DOI: 10.1063/5.0061921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 08/27/2021] [Indexed: 06/14/2023]
Abstract
In this Perspective article, we present recent developments on interaction effects on the carrier transport properties of one-dimensional (1D) semiconductor quantum wires fabricated using the GaAs/AlGaAs system, particularly the emergence of the long predicted fractional quantization of conductance in the absence of a magnetic field. Over three decades ago, it was shown that transport through a 1D system leads to integer quantized conductance given by N·2e2/h, where N is the number of allowed energy levels (N = 1, 2, 3, …). Recent experiments have shown that a weaker confinement potential and low carrier concentration provide a testbed for electrons strongly interacting. The consequence leads to a reconfiguration of the electron distribution into a zigzag assembly which, unexpectedly, was found to exhibit quantization of conductance predominantly at 1/6, 2/5, 1/4, and 1/2 in units of e2/h. These fractional states may appear similar to the fractional states seen in the Fractional Quantum Hall Effect; however, the system does not possess a filling factor and they differ in the nature of their physical causes. The states may have promise for the emergent topological quantum computing schemes as they are controllable by gate voltages with a distinct identity.
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Affiliation(s)
- S. Kumar
- Author to whom correspondence should be addressed:
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Brown S, Pepper M, Gunn A, Caridi T, Varma R, Liu R, El Khudari H, Salei A, Huang J. Abstract No. 88 CSI IR style: lawsuits involving interventional radiologists. J Vasc Interv Radiol 2021. [DOI: 10.1016/j.jvir.2021.03.514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Mlambo T, Roussel-Gervais A, Ilmjärv S, Sakic A, Myburgh R, Bredl S, Salmon P, Pepper M, Krause K, Speck R, Alessandrini M. Development of an off-the-shelf CAR T-cell therapy for HIV: a step towards a universally accessible advanced therapy. Cytotherapy 2021. [DOI: 10.1016/s1465324921004357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Fang Y, Dilworth JR, Pepper M, Edwards PP. Investigations of the optical and electronic effects of silicon and indium co-doping on ZnO thin films deposited by spray pyrolysis. ACTA ACUST UNITED AC 2020. [DOI: 10.1515/znb-2019-0196] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Silicon and indium co-doped ZnO thin films with both high optical and electrical performances have been successfully synthesised for the first time by the technique of spray pyrolysis. We find that this co-doping strategy can achieve comparable Figures-of-Merit performances to indium zinc oxide itself, but with, importantly, a significant saving in the indium content. The properties of the co-doped films are compared with those of either single indium or silicon doping.
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Affiliation(s)
- Yiwen Fang
- Inorganic Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QR , UK
| | - Jonathan R. Dilworth
- Inorganic Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QR , UK
| | - Michael Pepper
- London Centre for Nanotechnology and Department of Electronic and Electrical Engineering , University College London , Torrington Place , London, WC1E 7JE , UK
| | - Peter P. Edwards
- Inorganic Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QR , UK
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Khan FA, Mohammed AE, Poongkunran M, Chimakurthy A, Pepper M. Wearing Off Effect of OnabotulinumtoxinA Near the End of Treatment Cycle for Chronic Migraine: A 4-Year Clinical Experience. Headache 2019; 60:430-440. [PMID: 31758548 DOI: 10.1111/head.13713] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/30/2019] [Indexed: 01/11/2023]
Abstract
INTRODUCTION The injection interval for onabotulinumtoxinA (BoNTA) in the management of chronic migraine (CM) is 12 weeks (78-84 days). The aim of this study was to review patient-reported wearing off effect (WOE) of the therapeutic benefit of BoNTA near the end of the treatment cycle. We intended to describe the demographics of patients at baseline and compare groups of patients with multiple episodes of WOE. METHODS We conducted a retrospective review of patients with CM who received uninterrupted BoNTA therapy from January 2014 to March 2018. The data from patient-reported WOE (worsening headache variables and neck pain) that occurred during the 4 weeks (28 days) prior to the scheduled re-injection of BoNTA for treatment cycles with injection interval ≤13 weeks and without obvious confounding factors were reviewed. RESULTS We identified 98 eligible patients and analyzed 471 treatment cycles. Forty-three unique patients reported at least 1 occurrence of WOE. About 24/43 patients reported 1 WOE event and 19/43 patients reported ≥2 WOE events. Between the 2 groups, anxiety disorder and opioid use for headache were statistically significantly different. In the former group, the median interquartile range (IQR) dose of BoNTA was 165 (155, 175) units and the median IQR duration of the antinociceptive effect of BoNTA was 66.5 (63, 71.5) days. In the latter group, the median IQR dose of BoNTA was 167 (155, 173.3) units and the median IQR duration of the antinociceptive effect of BoNTA was 65.3 (62.5, 68.8) days. Up to 32% of these patients reported an increase in the use of abortive therapies to manage the symptoms of WOE. DISCUSSION The primary goal of BoNTA in the treatment of CM is to mitigate the development of central sensitization. Since the 12-week injection paradigm may not provide sustained antinociceptive effect in all patients, it may account for the failure of response to BoNTA. Repeated occurrences of the WOE can potentially lead to medication overuse and impact quality of life.
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Affiliation(s)
- Fawad A Khan
- McCasland Family Comprehensive Headache Center, Ochsner Neuroscience Institute, Ochsner Clinic Foundation, New Orleans, LA, USA.,The University of Queensland School of Medicine, Ochsner Clinical School, New Orleans, LA, USA.,Tulane University School of Medicine, New Orleans, LA, USA
| | - Alaa E Mohammed
- Center for Outcomes and Health Services Research, Ochsner Clinic Foundation, New Orleans, LA, USA
| | - Mugilan Poongkunran
- McCasland Family Comprehensive Headache Center, Ochsner Neuroscience Institute, Ochsner Clinic Foundation, New Orleans, LA, USA
| | - Anilkumar Chimakurthy
- McCasland Family Comprehensive Headache Center, Ochsner Neuroscience Institute, Ochsner Clinic Foundation, New Orleans, LA, USA
| | - Michael Pepper
- McCasland Family Comprehensive Headache Center, Ochsner Neuroscience Institute, Ochsner Clinic Foundation, New Orleans, LA, USA.,The University of Queensland School of Medicine, Ochsner Clinical School, New Orleans, LA, USA
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Pepper M, Wayland J, Elwood A, Walser S, Tran V, Posas J. Prevalence of Concussion in Quidditch. Neurology 2019. [DOI: 10.1212/01.wnl.0000581032.51679.e1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
ObjectiveThe aim of our study is to assess the rate of concussion occurring while engaging in nontraditional sports such as Quidditch, and the effects that injury during a novelty sport may have on concussion detection when compared to more traditional sports.BackgroundConcussions, once dismissed as nonconsequential, are rapidly attracting notice for acute and long-term health effects. Rates of recovery with repeated trauma is known to decrease with each occurrence. In novelty sports, regulation of concussions and proper return-to-play(RTP) protocol are not routinely enforced, resulting in repetitive injury to the detriment of players.Design/MethodsIRB approval was obtained prior to survey distribution to all players associated with Major League Quidditch (MLQ). Responses were recorded and analyzed.Results157 responses were received. 63% were male and 37% female with mean age 22.9. 146 (93%) respondents confirmed or denied quidditch-related head injury. 22 (15%) denied head injury and 124 (85%) indicated hitting their heads while participating in the sport. 19% of respondents indicated >10 head injuries. 67 (54%) reported suspected concussion with an additional 41 (33%) reporting formal diagnosis with at least one concussion. EMS reported 18 injuries at MLQ matches. 5 (27.8%) were preliminarily diagnosed with concussion. 3 had no further treatment, 1 RTP and 1 received basic care. 0 recieved formal neurologic evaluation. Players were also asked about head injuries sustained in non-quidditch activities for comparison. 43 (27%) reported having medically diagnosed concussions outside of quidditch. 53 (34%) reported at least one suspected concussion without formal diagnosis. 24 (15%) answered maybe.ConclusionsOur data supports that concussion is a significant burden in novelty sports such as quidditch. It is vital to recognize that with the rise of nontraditional sports, the prevalence of concussions in younger nontraditional athletes may be underreported and that concussion specialists must be cognizant of both traditional and novelty sports when evaluating long term effects of head trauma.
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Gul Y, Creeth GL, English D, Holmes SN, Thomas KJ, Farrer I, Ellis DJ, Ritchie DA, Pepper M. Conductance quantisation in patterned gate In 0.75Ga 0.25As structures up to 6 × (2e 2/h). J Phys Condens Matter 2019; 31:104002. [PMID: 30625452 DOI: 10.1088/1361-648x/aafd05] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We present electrical measurements from In0.75Ga0.25As 1D channel devices with Rashba-type, spin-orbit coupling present in the 2D contact regions. Suppressed backscattering as a result of the time-reversal asymmetry at the 1D channel entrance results in enhanced ballistic transport characteristics with clear quantised conductance plateaus up to 6 × (2e 2/h). Applying DC voltages between the source and drain ohmic contacts and an in-plane magnetic field confirms a ballistic transport picture. For asymmetric patterned gate biasing, a lateral spin-orbit coupling effect is weak. However, the Rashba-type spin-orbit coupling leads to a g-factor in the 1D channel that is reduced in magnitude from the 2D value of 9 to ~6.5 in the lowest subband when the effective Rashba field and the applied magnetic field are perpendicular.
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Affiliation(s)
- Y Gul
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
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Kumar S, Pepper M, Holmes SN, Montagu H, Gul Y, Ritchie DA, Farrer I. Zero-Magnetic Field Fractional Quantum States. Phys Rev Lett 2019; 122:086803. [PMID: 30932620 DOI: 10.1103/physrevlett.122.086803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Indexed: 06/09/2023]
Abstract
Since the discovery of the fractional quantum Hall effect in 1982 there has been considerable theoretical discussion on the possibility of fractional quantization of conductance in the absence of Landau levels formed by a quantizing magnetic field. Although various situations have been theoretically envisaged, particularly lattice models in which band flattening resembles Landau levels, the predicted fractions have never been observed. In this Letter, we show that odd and even denominator fractions can be observed, and manipulated, in the absence of a quantizing magnetic field, when a low-density electron system in a GaAs based one-dimensional quantum wire is allowed to relax in the second dimension. It is suggested that such a relaxation results in formation of a zigzag array of electrons with ring paths which establish a cyclic current and a resultant lowering of energy. The behavior has been observed for both symmetric and asymmetric confinement but increasing the asymmetry of the confinement potential, to result in a flattening of confinement, enhances the appearance of new fractional states. We find that an in-plane magnetic field induces new even denominator fractions possibly indicative of electron pairing. The new quantum states described here have implications both for the physics of low dimensional electron systems and also for quantum technologies. This work will enable further development of structures which are designed to electrostatically manipulate the electrons for the formation of particular configurations. In turn, this could result in a designer tailoring of fractional states to amplify particular properties of importance in future quantum computation.
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Affiliation(s)
- S Kumar
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - M Pepper
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - S N Holmes
- Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, United Kingdom
| | - H Montagu
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - Y Gul
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - D A Ritchie
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
| | - I Farrer
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
- Now at Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom
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Johnson N, Emary C, Ryu S, Sim HS, See P, Fletcher JD, Griffiths JP, Jones GAC, Farrer I, Ritchie DA, Pepper M, Janssen TJBM, Kataoka M. LO-Phonon Emission Rate of Hot Electrons from an On-Demand Single-Electron Source in a GaAs/AlGaAs Heterostructure. Phys Rev Lett 2018; 121:137703. [PMID: 30312059 DOI: 10.1103/physrevlett.121.137703] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Revised: 05/17/2018] [Indexed: 06/08/2023]
Abstract
Using a recent time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we develop a method to measure the longitudinal-optical-phonon emission rate of hot electrons traveling along a depleted edge of a quantum Hall bar. Comparison to a single-particle model implies the scattering mechanism involves a two-step process via an intra-Landau-level transition. We show that this can be suppressed by control of the edge potential profile, and a scattering length >1 mm can be achieved, allowing the use of this system for scalable single-electron device applications.
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Affiliation(s)
- N Johnson
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
- London Centre for Nanotechnology, and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
| | - C Emary
- Joint Quantum Centre Durham-Newcastle, School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - S Ryu
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
| | - H-S Sim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
| | - P See
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - J D Fletcher
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - J P Griffiths
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - G A C Jones
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - I Farrer
- Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom
| | - D A Ritchie
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - M Pepper
- London Centre for Nanotechnology, and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
| | - T J B M Janssen
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - M Kataoka
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
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Ho SC, Chang HJ, Chang CH, Lo ST, Creeth G, Kumar S, Farrer I, Ritchie D, Griffiths J, Jones G, Pepper M, Chen TM. Imaging the Zigzag Wigner Crystal in Confinement-Tunable Quantum Wires. Phys Rev Lett 2018; 121:106801. [PMID: 30240231 DOI: 10.1103/physrevlett.121.106801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Revised: 07/03/2018] [Indexed: 06/08/2023]
Abstract
The existence of Wigner crystallization, one of the most significant hallmarks of strong electron correlations, has to date only been definitively observed in two-dimensional systems. In one-dimensional (1D) quantum wires Wigner crystals correspond to regularly spaced electrons; however, weakening the confinement and allowing the electrons to relax in a second dimension is predicted to lead to the formation of a new ground state constituting a zigzag chain with nontrivial spin phases and properties. Here we report the observation of such zigzag Wigner crystals by use of on-chip charge and spin detectors employing electron focusing to image the charge density distribution and probe their spin properties. This experiment demonstrates both the structural and spin phase diagrams of the 1D Wigner crystallization. The existence of zigzag spin chains and phases which can be electrically controlled in semiconductor systems may open avenues for experimental studies of Wigner crystals and their technological applications in spintronics and quantum information.
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Affiliation(s)
- Sheng-Chin Ho
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Heng-Jian Chang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Chia-Hua Chang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Shun-Tsung Lo
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Graham Creeth
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Sanjeev Kumar
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Ian Farrer
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
- Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom
| | - David Ritchie
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Jonathan Griffiths
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Geraint Jones
- Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Michael Pepper
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - Tse-Ming Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
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Ragot N, Pepper M. The adapt European project: The transdisciplinary development of assistive technology for the benefit of the disabled people. Ann Phys Rehabil Med 2018. [DOI: 10.1016/j.rehab.2018.05.1148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Yan C, Kumar S, Thomas K, See P, Farrer I, Ritchie D, Griffiths J, Jones G, Pepper M. Coherent Spin Amplification Using a Beam Splitter. Phys Rev Lett 2018; 120:137701. [PMID: 29694224 DOI: 10.1103/physrevlett.120.137701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Indexed: 06/08/2023]
Abstract
We report spin amplification using a capacitive beam splitter in n-type GaAs where the spin polarization is monitored via a transverse electron focusing measurement. It is shown that partially spin-polarized current injected by the emitter can be precisely controlled, and the spin polarization associated with it can be amplified by the beam splitter, such that a considerably high spin polarization of around 50% can be obtained. Additionally, the spin remains coherent as shown by the observation of quantum interference. Our results illustrate that spin-polarization amplification can be achieved in materials without strong spin-orbit interaction.
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Affiliation(s)
- Chengyu Yan
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - Sanjeev Kumar
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - Kalarikad Thomas
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - Patrick See
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - Ian Farrer
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
| | - David Ritchie
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
| | - Jonathan Griffiths
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
| | - Geraint Jones
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom
| | - Michael Pepper
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
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16
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Abstract
We have investigated hole transport in quantum wires formed by electrostatic confinement in strained germanium two-dimensional layers. The ballistic conductance characteristics show the regular staircase of quantum levels with plateaux at n2e 2/h, where n is an integer, e is the fundamental unit of charge and h is Planck's constant. However as the carrier concentration is reduced, the quantised levels show a behaviour that is indicative of the formation of a zig-zag structure and new quantised plateaux appear at low temperatures. In units of 2e 2/h the new quantised levels correspond to values of n = 1/4 reducing to 1/8 in the presence of a strong parallel magnetic field which lifts the spin degeneracy but does not quantise the wavefunction. A further plateau is observed corresponding to n = 1/32 which does not change in the presence of a parallel magnetic field. These values indicate that the system is behaving as if charge was fractionalised with values e/2 and e/4, possible mechanisms are discussed.
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Affiliation(s)
- Y Gul
- London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
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17
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Yan C, Kumar S, Thomas K, See P, Farrer I, Ritchie D, Griffiths J, Jones G, Pepper M. Engineering the spin polarization of one-dimensional electrons. J Phys Condens Matter 2018; 30:08LT01. [PMID: 29334361 DOI: 10.1088/1361-648x/aaa7ce] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We present results of magneto-focusing on the controlled monitoring of spin polarization within a one-dimensional (1D) channel, and its subsequent effect on modulating the spin-orbit interaction (SOI) in a 2D GaAs electron gas. We demonstrate that electrons within a 1D channel can be partially spin polarized as the effective length of the 1D channel is varied in agreement with the theoretical prediction. Such polarized 1D electrons when injected into a 2D region result in a split in the odd-focusing peaks, whereas the even peaks remain unaffected (single peak). On the other hand, the unpolarized electrons do not affect the focusing spectrum and the odd and even peaks remain as single peaks, respectively. The split in odd-focusing peaks is evidence of direct measurement of spin polarization within a 1D channel, where each sub-peak represents the population of a particular spin state. Confirmation of the spin splitting is determined by a selective modulation of the focusing peaks due to the Zeeman energy in the presence of an in-plane magnetic field. We suggest that the SOI in the 2D regime is enhanced by a stream of polarized 1D electrons. The spatial control of spin states of injected 1D electrons and the possibility of tuning the SOI may open up a new regime of spin-engineering with application in future quantum information schemes.
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Affiliation(s)
- C Yan
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom. Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
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18
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Pepper M, Pal A, Papic Z, Schneider U, Simon S. Breakdown of ergodicity in quantum systems: from solids to synthetic matter. Philos Trans A Math Phys Eng Sci 2017; 375:20170264. [PMID: 29084887 PMCID: PMC5665788 DOI: 10.1098/rsta.2017.0264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/11/2017] [Indexed: 06/07/2023]
Affiliation(s)
- Michael Pepper
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, UK
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK
| | - Arijeet Pal
- Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK
| | - Zlatko Papic
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - Ulrich Schneider
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - Steven Simon
- Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK
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19
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Abstract
SummaryExtracellular proteolysis is an absolute requirement for new blood vessel formation, a process known as angiogenesis. This review will examine the role of the matrix metalloproteinase and plasminogen activator/plasmin systems during angiogenesis. Extracellular proteolysis has also been implicated in the generation of molecules with angioregulatory activity. These include, but are not limited to, angiostatin and endostatin. However, despite an abundance of data on their bioactivity, the molecular mechanisms by which these molecules achieve their effects are unknown. Anti-proteolysis, particularly in the context of angiogenesis, has become a key target in therapeutic strategies aimed at inhibiting tumor growth and other diseases associated with neovascularization.
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20
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Rosnoblet C, Sanza CD, Kruithof E, Pepper M. Synergistic Induction of t-PA by Vascular Endothelial Growth Factor and Basic Fibroblast Growth Factor and Localization of t-PA to Weibel-Palade Bodies in Bovine Microvascular Endothelial Cells. Thromb Haemost 2017. [DOI: 10.1055/s-0037-1616107] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
SummaryEndothelial cell migration is stimulated by members of the vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) families, and is dependent on extracellular proteolytic activity provided by enzymes of the plasminogen activator (PA) system. Here we report that in bovine microvascular endothelial cells (BME cells), bFGF principally increased urokinase-type PA (u-PA) while tissue-type PA (t-PA) was increased mainly by VEGF. In bovine aortic endothelial cells (BAE cells), bFGF increased u-PA, whereas VEGF had no effect. Co-added bFGF and VEGF increased t-PA mRNA levels and enzyme activity in both cell types in a synergistic manner. Tissue-type plasminogen activator (t-PA) immunoreactivity colocalized with von Willebrand factor, a marker for Weibel-Palade bodies. Co-added bFGF and VEGF increased the number of t-PA-positive cells as well as the number of t-PA-positive granules per cell. Localization of t-PA in regulated storage granules endows endothelial cells with the potential to rapidly increase proteolytic activity in the pericellular environment.
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21
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Lijnen H, Suffredini A, Pepper M, Steinberg K, Martin T, Pugin J, Lucas R. Increased Angiostatin Levels in Bronchoalveolar Lavage Fluids from ARDS Patients and from Human Volunteers after Lung Instillation of Endotoxin. Thromb Haemost 2017. [DOI: 10.1055/s-0037-1613119] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
SummaryAcute respiratory distress syndrome (ARDS) is characterized by a disruption of the alveolar-capillary barrier, due to both an epithelial and an endothelial dysfunction. Whereas epithelial apoptosis seems to be mainly mediated by Fas ligand, the mediators of endothelial damage remain to be identified. Angiostatin, a powerful inhibitor of angiogenesis in vivo, also specifically induces apoptosis in endothelial cells. The concentration of various enzymes that cleave angiostatin from plasminogen was reported to be significantly increased in bronchalveolar lavage (BAL) fluids from patients with ARDS. Therefore, in this study, we investigated whether angiostatin was generated during the pulmonary inflammatory response of both healthy subjects challenged with endobronchial endotoxin and in patients with ARDS. We found significantly elevated angiostatin levels in BAL fluids from patients at risk for and with early ARDS (up to 0.022% and 0.018% of total protein, respectively), as well as in BAL fluids from volunteers treated with endotoxin (up to 1.17% of total protein), as compared to BAL fluids from control patients (<0.005% of total protein). These data suggest that angiostatin may contribute to the endothelial damage observed in ARDS, probably via an increased permeability of the alveolar capillary barrier, allowing for an intra-alveolar processing of its precursor plasminogen.
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22
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Buxbaum JL, Hormozdi D, Dinis-Ribeiro M, Lane C, Dias-Silva D, Sahakian A, Jayaram P, Pimentel-Nunes P, Shue D, Pepper M, Cho D, Laine L. Narrow-band imaging versus white light versus mapping biopsy for gastric intestinal metaplasia: a prospective blinded trial. Gastrointest Endosc 2017; 86:857-865. [PMID: 28366441 DOI: 10.1016/j.gie.2017.03.1528] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Accepted: 03/19/2017] [Indexed: 02/07/2023]
Abstract
BACKGROUND AND AIMS Gastric intestinal metaplasia (GIM) is a gastric cancer precursor. Narrow-band imaging (NBI) may improve detection of GIM. We compared detection of GIM with high-definition white-light (HD-WL) endoscopy, NBI, and mapping biopsies in a population with increased gastric cancer risk. METHODS Patients undergoing upper endoscopy had HD-WL examination by 1 endoscopist, followed by an NBI examination by a second endoscopist blinded to HD-WL findings. The location of abnormalities detected by HD-WL and NBI were recorded by a research coordinator, and targeted biopsies of abnormal areas were performed after NBI. Subsequently, 5 mapping biopsies were performed per patient. Biopsy specimens were read by a pathologist blinded to mode of acquisition. The primary outcome was the proportion of patients with GIM. RESULTS We enrolled 112 patients: 107 (96%) were Hispanic or Asian, and 34 (30%) had GIM. Higher proportions of patients with GIM were detected by NBI (22/34 [65%]) and mapping (26/34 [76%]) versus HD-WL (10/34 [29%]) (P < .005 for both comparisons). GIM was detected by NBI in only 6 patients and only by mapping biopsy in 10 patients; no patient had GIM detected solely by HD-WL. Higher proportions of sites with GIM also were detected with NBI (30/57 [53%]) and mapping biopsies (38/57 [67%]) than HD-WL (16/57 [28%]) (P < .005 for both comparisons). The median number of biopsies per patient with mapping biopsies (5) was significantly higher than with NBI (2) or HD-WL (1). CONCLUSIONS HD-WL endoscopy is insufficient for detection of GIM in patients at increased risk for gastric cancer. NBI-targeted biopsies plus mapping biopsies should be used. (Clinical trial registration number: NCT02197351.).
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Affiliation(s)
- James L Buxbaum
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - David Hormozdi
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Mario Dinis-Ribeiro
- Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Christianne Lane
- Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Diogo Dias-Silva
- Department of Preventive Medicine, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Ara Sahakian
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Preeth Jayaram
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | | | - Daniel Shue
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Michael Pepper
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Daniel Cho
- Division of Gastroenterology, University of Southern California, Keck School of Medicine, Los Angeles, California, USA
| | - Loren Laine
- Section of Digestive Diseases, Yale School of Medicine, New Haven, Connecticut and Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut, USA
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23
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Yan C, Kumar S, Pepper M, See P, Farrer I, Ritchie D, Griffiths J, Jones G. Temperature Dependence of Spin-Split Peaks in Transverse Electron Focusing. Nanoscale Res Lett 2017; 12:553. [PMID: 28952141 PMCID: PMC5615081 DOI: 10.1186/s11671-017-2321-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 09/16/2017] [Indexed: 06/07/2023]
Abstract
We present experimental results of transverse electron-focusing measurements performed using n-type GaAs. In the presence of a small transverse magnetic field (B⊥), electrons are focused from the injector to detector leading to focusing peaks periodic in B⊥. We show that the odd-focusing peaks exhibit a split, where each sub-peak represents a population of a particular spin branch emanating from the injector. The temperature dependence reveals that the peak splitting is well defined at low temperature whereas it smears out at high temperature indicating the exchange-driven spin polarisation in the injector is dominant at low temperatures.
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Affiliation(s)
- Chengyu Yan
- London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom.
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom.
| | - Sanjeev Kumar
- London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
| | - Michael Pepper
- London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom
- Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
| | - Patrick See
- National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom
| | - Ian Farrer
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - David Ritchie
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - Jonathan Griffiths
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
| | - Geraint Jones
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom
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24
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Grootendorst MR, Fitzgerald AJ, Brouwer de Koning SG, Santaolalla A, Portieri A, Van Hemelrijck M, Young MR, Owen J, Cariati M, Pepper M, Wallace VP, Pinder SE, Purushotham A. Use of a handheld terahertz pulsed imaging device to differentiate benign and malignant breast tissue. Biomed Opt Express 2017; 8:2932-2945. [PMID: 28663917 PMCID: PMC5480440 DOI: 10.1364/boe.8.002932] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Accepted: 05/02/2017] [Indexed: 05/19/2023]
Abstract
Since nearly 20% of breast-conserving surgeries (BCS) require re-operation, there is a clear need for developing new techniques to more accurately assess tumor resection margins intraoperatively. This study evaluates the diagnostic accuracy of a handheld terahertz pulsed imaging (TPI) system to discriminate benign from malignant breast tissue ex vivo. Forty six freshly excised breast cancer samples were scanned with a TPI handheld probe system, and histology was obtained for comparison. The image pixels on TPI were classified using (1) parameters in combination with support vector machine (SVM) and (2) Gaussian wavelet deconvolution in combination with Bayesian classification. The results were an accuracy, sensitivity, specificity of 75%, 86%, 66% for method 1, and 69%, 87%, 54% for method 2 respectively. This demonstrates the probe can discriminate invasive breast cancer from benign breast tissue with an encouraging degree of accuracy, warranting further study.
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Affiliation(s)
- Maarten R Grootendorst
- King's College London, Division of Cancer Studies, London, UK
- Department of Breast Surgery, Guy's and St Thomas' NHS Foundation Trust, London, UK
- Contributed equally
| | - Anthony J Fitzgerald
- School of Physics, University of Western Australia, Perth, Australia
- Contributed equally
| | - Susan G Brouwer de Koning
- King's College London, Division of Cancer Studies, London, UK
- Department of Breast Surgery, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | | | | | - Matthew R Young
- Department of Breast Surgery, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Julie Owen
- King's College London, Division of Cancer Studies, King's Health Partners Cancer Biobank and Breast Pathology Research Group, London, UK
| | - Massi Cariati
- King's College London, Division of Cancer Studies, London, UK
- Department of Breast Surgery, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Michael Pepper
- Teraview Ltd., Cambridge, UK
- London Centre for Nanotechnology, University College London, UK
| | - Vincent P Wallace
- School of Physics, University of Western Australia, Perth, Australia
| | - Sarah E Pinder
- King's College London, Division of Cancer Studies, King's Health Partners Cancer Biobank and Breast Pathology Research Group, London, UK
| | - Arnie Purushotham
- King's College London, Division of Cancer Studies, London, UK
- Department of Breast Surgery, Guy's and St Thomas' NHS Foundation Trust, London, UK
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25
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Pepper M, Thornton TJ, Wharam DA. Early work on semiconductor quantum nanoelectronics in the Cavendish Laboratory. J Phys Condens Matter 2016; 28:421003. [PMID: 27557363 DOI: 10.1088/0953-8984/28/42/421003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Affiliation(s)
- M Pepper
- London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK. School of Electrical, Computer, and Energy Engineering, Arizona State University, PO Box 875706, Tempe, AZ 85287-5706, USA. Eberhard-Karls-University Tübingen, Institute of Applied Physics, Auf der Morgenstelle 10, D-72076 Tübingen, Germany
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26
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Kataoka M, Johnson N, Emary C, See P, Griffiths JP, Jones GAC, Farrer I, Ritchie DA, Pepper M, Janssen TJBM. Time-of-Flight Measurements of Single-Electron Wave Packets in Quantum Hall Edge States. Phys Rev Lett 2016; 116:126803. [PMID: 27058091 DOI: 10.1103/physrevlett.116.126803] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Indexed: 06/05/2023]
Abstract
We report time-of-flight measurements on electrons traveling in quantum Hall edge states. Hot-electron wave packets are emitted one per cycle into edge states formed along a depleted sample boundary. The electron arrival time is detected by driving a detector barrier with a square wave that acts as a shutter. By adding an extra path using a deflection barrier, we measure a delay in the arrival time, from which the edge-state velocity v is deduced. We find that v follows 1/B dependence, in good agreement with the E[over →]×B[over →] drift. The edge potential is estimated from the energy dependence of v using a harmonic approximation.
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Affiliation(s)
- M Kataoka
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - N Johnson
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
- London Centre for Nanotechnology, and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - C Emary
- Department of Physics and Mathematics, University of Hull, Kingston-upon-Hull HU6 7RX, United Kingdom
| | - P See
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
| | - J P Griffiths
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - G A C Jones
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - I Farrer
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - D A Ritchie
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - M Pepper
- London Centre for Nanotechnology, and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
| | - T J B M Janssen
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
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27
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Moritz C, Fujita MK, Rosauer D, Agudo R, Bourke G, Doughty P, Palmer R, Pepper M, Potter S, Pratt R, Scott M, Tonione M, Donnellan S. Multilocus phylogeography reveals nested endemism in a gecko across the monsoonal tropics of Australia. Mol Ecol 2016; 25:1354-66. [DOI: 10.1111/mec.13511] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 11/16/2015] [Accepted: 11/24/2015] [Indexed: 11/30/2022]
Affiliation(s)
- C. Moritz
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - M. K. Fujita
- Department of Biology; University of Texas at Arlington; Arlington TX 76019 USA
| | - D. Rosauer
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - R. Agudo
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - G. Bourke
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - P. Doughty
- Western Australian Museum; Welshpool WA 6986 Australia
| | - R. Palmer
- Science & Conservation Division; Department of Parks and Wildlife; Woodvale WA 6026 Australia
| | - M. Pepper
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - S. Potter
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - R. Pratt
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - M. Scott
- Research School of Biology; The Australian National University; Acton ACT 2601 Australia
- Centre for Biodiversity Analysis; Acton ACT 2601 Australia
| | - M. Tonione
- Museum of Vertebrate Zoology; University of California; Berkeley CA 94720-3102 USA
| | - S. Donnellan
- South Australian Museum; Adelaide SA 5000 Australia
- School of Biological Sciences; The University of Adelaide; Adelaide SA 5000 Australia
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28
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Backes D, Hall R, Pepper M, Beere H, Ritchie D, Narayan V. 'Metal'-like transport in high-resistance, high aspect ratio two-dimensional electron gases. J Phys Condens Matter 2016; 28:01LT01. [PMID: 26647878 DOI: 10.1088/0953-8984/28/1/01lt01] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We investigate the striking absence of strong localisation observed in mesoscopic two-dimensional electron gases (2DEGs) (Baenninger et al 2008 Phys. Rev. Lett. 100 016805, Backes et al 2015 arXiv:1505.03444) even when their resistivity [Formula: see text]. In particular, we try to understand whether this phenomenon originates in quantum many-body effects, or simply percolative transport through a network of electron puddles. To test the latter scenario, we measure the low temperature (low-T) transport properties of long and narrow 2DEG devices in which percolation effects should be heavily suppressed in favour of Coulomb blockade. Strikingly we find no indication of Coulomb blockade and that the high-ρ, low-T transport is exactly similar to that previously reported in mesoscopic 2DEGs with different geometries. Remarkably, we are able to induce a 'metal'-insulator transition (MIT) by applying a perpendicular magnetic field B. We present a picture within which these observations fit into the more conventional framework of the 2D MIT.
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Affiliation(s)
- Dirk Backes
- Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
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29
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Antonio B, Bayat A, Kumar S, Pepper M, Bose S. Self-Assembled Wigner Crystals as Mediators of Spin Currents and Quantum Information. Phys Rev Lett 2015; 115:216804. [PMID: 26636865 DOI: 10.1103/physrevlett.115.216804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Indexed: 06/05/2023]
Abstract
Technological applications of many-body structures that emerge in gated devices under minimal control are largely unexplored. Here we show how emergent Wigner crystals in a semiconductor quantum wire can facilitate a pivotal requirement for a scalable quantum computer, namely, transmitting quantum information encoded in spins faithfully over a distance of micrometers. The fidelity of the transmission is remarkably high, faster than the relevant decohering effects, independent of the details of the spatial charge configuration in the wire, and realizable in dilution refrigerator temperatures. The transfer can evidence near unitary many-body nonequilibrium dynamics hitherto unseen in a solid-state device. It could also be useful in spintronics as a method for pure spin current over a distance without charge movement.
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Affiliation(s)
- Bobby Antonio
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Abolfazl Bayat
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Sanjeev Kumar
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Michael Pepper
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
- London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Sougato Bose
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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30
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Dandara C, Mpye K, Agenbag G, Skelton M, Zaahl M, Masimirembwa C, Mulder N, Warnich L, Pepper M. Biotechnology Innovators To Convene in Cape Town, South Africa: Pharmacogenetics and Precision Medicine Conference (April 7-9, 2016). OMICS 2015; 19:731-2. [PMID: 26575827 DOI: 10.1089/omi.2015.0160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Collet Dandara
- 1 Division of Human Genetics, Department of Pathology, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town , South Africa
| | - Keleabetswe Mpye
- 1 Division of Human Genetics, Department of Pathology, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town , South Africa
| | - Gloudi Agenbag
- 1 Division of Human Genetics, Department of Pathology, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town , South Africa
| | - Michelle Skelton
- 1 Division of Human Genetics, Department of Pathology, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town , South Africa
| | | | - Collen Masimirembwa
- 3 African Institute of Biomedical Sciences and Technology (AiBST), Wilkins Hospital , Harare, Zimbabwe
| | - Nicola Mulder
- 4 Computational Biology Division, Department of Integrative Biomedical Sciences, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town , South Africa
| | - Louise Warnich
- 5 Department of Genetics, Faculty of Science, Stellenbosch University , Stellenbosch, South Africa
| | - Michael Pepper
- 6 Institute for Cellular and Molecular Medicine, Department of Immunology, Faculty of Health Sciences, University of Pretoria , Pretoria, South Africa
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Grootendorst M, de Koning SB, Fitzgerald T, Portieri A, Santaolalla A, Cariati M, Pepper M, Wallace V, Pinder S, Purushotham A. 5. The use of a handheld Terahertz pulsed imaging device to differentiate benign and malignant breast tissue with a view to reducing re-operation rates in breast-conserving surgery. Eur J Surg Oncol 2015. [DOI: 10.1016/j.ejso.2015.08.036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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32
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Chuang P, Ho SC, Smith LW, Sfigakis F, Pepper M, Chen CH, Fan JC, Griffiths JP, Farrer I, Beere HE, Jones GAC, Ritchie DA, Chen TM. All-electric all-semiconductor spin field-effect transistors. Nat Nanotechnol 2015; 10:35-39. [PMID: 25531088 DOI: 10.1038/nnano.2014.296] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Accepted: 11/11/2014] [Indexed: 06/04/2023]
Abstract
The spin field-effect transistor envisioned by Datta and Das opens a gateway to spin information processing. Although the coherent manipulation of electron spins in semiconductors is now possible, the realization of a functional spin field-effect transistor for information processing has yet to be achieved, owing to several fundamental challenges such as the low spin-injection efficiency due to resistance mismatch, spin relaxation and the spread of spin precession angles. Alternative spin transistor designs have therefore been proposed, but these differ from the field-effect transistor concept and require the use of optical or magnetic elements, which pose difficulties for incorporation into integrated circuits. Here, we present an all-electric and all-semiconductor spin field-effect transistor in which these obstacles are overcome by using two quantum point contacts as spin injectors and detectors. Distinct engineering architectures of spin-orbit coupling are exploited for the quantum point contacts and the central semiconductor channel to achieve complete control of the electron spins (spin injection, manipulation and detection) in a purely electrical manner. Such a device is compatible with large-scale integration and holds promise for future spintronic devices for information processing.
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Affiliation(s)
- Pojen Chuang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Sheng-Chin Ho
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - L W Smith
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - F Sfigakis
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - M Pepper
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, UK
| | - Chin-Hung Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Ju-Chun Fan
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - J P Griffiths
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - I Farrer
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - H E Beere
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - G A C Jones
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - D A Ritchie
- Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - Tse-Ming Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
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33
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Yeoh LA, Srinivasan A, Klochan O, Winkler R, Zülicke U, Simmons MY, Ritchie DA, Pepper M, Hamilton AR. Noncollinear paramagnetism of a GaAs two-dimensional hole system. Phys Rev Lett 2014; 113:236401. [PMID: 25526140 DOI: 10.1103/physrevlett.113.236401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2014] [Indexed: 06/04/2023]
Abstract
We have performed transport measurements in tilted magnetic fields in a two-dimensional hole system grown on the surface of a (311)A GaAs crystal. A striking asymmetry of Shubnikov-de Haas oscillations occurs upon reversing the in-plane component of the magnetic field along the low-symmetry [2[over ¯]33] axis. As usual, the magnetoconductance oscillations are symmetric with respect to reversal of the in-plane field component aligned with the high-symmetry [011[over ¯]] axis. Our observations demonstrate that an in-plane magnetic field can generate an out-of-plane component of magnetization in a low-symmetry hole system, creating new possibilities for spin manipulation.
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Affiliation(s)
- L A Yeoh
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - A Srinivasan
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - O Klochan
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - R Winkler
- Department of Physics, Northern Illinois University, De Kalb, Illinois 60115, USA
| | - U Zülicke
- School of Chemical and Physical Sciences and MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6140, New Zealand
| | - M Y Simmons
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - D A Ritchie
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - M Pepper
- Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
| | - A R Hamilton
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
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Vai AT, Kuznetsov VL, Jain H, Slocombe D, Rashidi N, Pepper M, Edwards PP. The Transition to the Metallic State in Polycrystallinen-type Doped ZnO Thin Films. Z Anorg Allg Chem 2014. [DOI: 10.1002/zaac.201400042] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Haaser M, Karrout Y, Velghe C, Cuppok Y, Gordon K, Pepper M, Siepmann J, Rades T, Taday P, Strachan C. Application of terahertz pulsed imaging to analyse film coating characteristics of sustained-release coated pellets. Int J Pharm 2013; 457:521-6. [DOI: 10.1016/j.ijpharm.2013.05.039] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Revised: 04/29/2013] [Accepted: 05/04/2013] [Indexed: 11/28/2022]
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36
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Fletcher JD, See P, Howe H, Pepper M, Giblin SP, Griffiths JP, Jones GAC, Farrer I, Ritchie DA, Janssen TJBM, Kataoka M. Clock-controlled emission of single-electron wave packets in a solid-state circuit. Phys Rev Lett 2013; 111:216807. [PMID: 24313516 DOI: 10.1103/physrevlett.111.216807] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Revised: 08/09/2013] [Indexed: 06/02/2023]
Abstract
We demonstrate the energy- and time-resolved detection of single-electron wave packets from a clock-controlled source transmitted through a high-energy quantum Hall edge channel. A quantum dot source is loaded with single electrons which are then emitted ~150 meV above the Fermi energy. The energy spectroscopy of emitted electrons indicates that at high magnetic field these electrons can be transported over several microns without inelastic electron-electron or electron-phonon scattering. Using a time-resolved spectroscopic technique, we deduce the wave packet size at picosecond resolution. We also show how this technique can be used to switch individual electrons into different electron waveguides (edge channels).
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Affiliation(s)
- J D Fletcher
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
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37
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Seeds AJ, Fice MJ, Balakier K, Natrella M, Mitrofanov O, Lamponi M, Chtioui M, van Dijk F, Pepper M, Aeppli G, Davies AG, Dean P, Linfield E, Renaud CC. Coherent terahertz photonics. Opt Express 2013; 21:22988-23000. [PMID: 24104182 DOI: 10.1364/oe.21.022988] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present a review of recent developments in THz coherent systems based on photonic local oscillators. We show that such techniques can enable the creation of highly coherent, thus highly sensitive, systems for frequencies ranging from 100 GHz to 5 THz, within an energy efficient integrated platform. We suggest that such systems could enable the THz spectrum to realize its full applications potential. To demonstrate how photonics-enabled THz systems can be realized, we review the performance of key components, show recent demonstrations of integrated platforms, and give examples of applications.
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Abstract
Terahertz Pulsed Imaging(TPI) is a new medical imaging modality forthe detection of epithelial cancers. Overthe last two years this technique has beenapplied to the study of in vitrobasal cell carcinoma (BCC). Usingtime-domain analysis the contrast betweendiseased and normal tissue has been shownto be statistically significant, andregions of increased terahertz (THz)absorption correlated well with thelocation of the tumour sites in histology.Understanding the source of this contrastthrough frequency-domain analysis mayfacilitate the diagnosis of skin cancer andrelated skin conditions using TPI. Wepresent the first frequency-domain analysisof basal cell carcinoma in vitro,with the raw power spectrum giving aninsight into the surface features of theskin. Further data manipulation is requiredto determine whether spectral informationcan be extrapolated at depth. These resultshighlight the complexity of working inreflection geometry.
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Affiliation(s)
- R M Woodward
- TeraView Limited, 302/304 Science Park, Milton Road, Cambridge, CB4 OWG UK ; Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 OHE UK
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Mehonic A, Vrajitoarea A, Cueff S, Hudziak S, Howe H, Labbé C, Rizk R, Pepper M, Kenyon AJ. Quantum conductance in silicon oxide resistive memory devices. Sci Rep 2013; 3:2708. [PMID: 24048282 PMCID: PMC3776960 DOI: 10.1038/srep02708] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 08/27/2013] [Indexed: 11/16/2022] Open
Abstract
Resistive switching offers a promising route to universal electronic memory, potentially replacing current technologies that are approaching their fundamental limits. In many cases switching originates from the reversible formation and dissolution of nanometre-scale conductive filaments, which constrain the motion of electrons, leading to the quantisation of device conductance into multiples of the fundamental unit of conductance, G0. Such quantum effects appear when the constriction diameter approaches the Fermi wavelength of the electron in the medium - typically several nanometres. Here we find that the conductance of silicon-rich silica (SiOx) resistive switches is quantised in half-integer multiples of G0. In contrast to other resistive switching systems this quantisation is intrinsic to SiOx, and is not due to drift of metallic ions. Half-integer quantisation is explained in terms of the filament structure and formation mechanism, which allows us to distinguish between systems that exhibit integer and half-integer quantisation.
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Affiliation(s)
- A. Mehonic
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
| | - A. Vrajitoarea
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
| | - S. Cueff
- Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), UMR 6252 CNRS/CEA/Ensicaen/UCBN, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France
- Brown University, School of Engineering, Providence, Rhode Island 02912, USA
| | - S. Hudziak
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
| | - H. Howe
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
| | - C. Labbé
- Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), UMR 6252 CNRS/CEA/Ensicaen/UCBN, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France
| | - R. Rizk
- Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), UMR 6252 CNRS/CEA/Ensicaen/UCBN, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France
| | - M. Pepper
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
| | - A. J. Kenyon
- Department of Electronic & Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, UK
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40
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Chen TM, Pepper M, Farrer I, Jones GAC, Ritchie DA. All-electrical injection and detection of a spin-polarized current using 1D conductors. Phys Rev Lett 2012; 109:177202. [PMID: 23215217 DOI: 10.1103/physrevlett.109.177202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Revised: 09/06/2012] [Indexed: 06/01/2023]
Abstract
All-electrical control of spin transport in nanostructures has been the central interest and challenge of spin physics and spintronics. Here we demonstrate on-chip spin polarizing or filtering actions by driving the gate-defined one dimensional (1D) conductor, one of the simplest geometries for integrated quantum devices, away from the conventional Ohmic regime. Direct measurement of the spin polarization of the emitted current was performed when the momentum degeneracy was lifted, wherein both the 1D polarizer for spin injection and the analyzer for spin detection were demonstrated. The results showed that a configuration of gates and applied voltages can give rise to a tunable spin polarization, which has implications for the development of spintronic devices and future quantum information processing.
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Affiliation(s)
- T-M Chen
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan.
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Abstract
Scientific interest in genomics in Africa is on the rise with a number of funding initiatives aimed specifically at supporting research in this area. Genomics research on material of African origin raises a number of important ethical issues. A prominent concern relates to sample export, which is increasingly seen by researchers and ethics committees across the continent as being problematic. The concept of genomic sovereignty proposes that unique patterns of genomic variation can be found in human populations, and that these are commercially, scientifically or symbolically valuable and in need of protection against exploitation. Although it is appealing as a response to increasing concerns regarding sample export, there are a number of important conceptual problems relating to the term. It is not clear, for instance, whether it is appropriate that ownership over human genomic samples should rest with national governments. Furthermore, ethnic groups in Africa are frequently spread across multiple nation states, and protection offered in one state may not prevent researchers from accessing the same group elsewhere. Lastly, scientific evidence suggests that the assumption that genomic data is unique for population groups is false. Although the frequency with which particular variants are found can differ between groups, such genes or variants per se are not unique to any population group. In this paper, the authors describe these concerns in detail and argue that the concept of genomic sovereignty alone may not be adequate to protect the genetic resources of people of African descent.
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Affiliation(s)
- Jantina de Vries
- Division of Human Genetics, Faculty of Health Sciences, University of Cape Town, Cape Town 7925, South Africa.
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Liu H, Liu B, Zhao C, Pepper M, Lin C. The action mechanisms of plant cryptochromes. Trends Plant Sci 2011; 16:684-91. [PMID: 21983106 PMCID: PMC3277817 DOI: 10.1016/j.tplants.2011.09.002] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2011] [Revised: 08/01/2011] [Accepted: 09/05/2011] [Indexed: 05/12/2023]
Abstract
Cryptochromes (CRY) are blue-light receptors that mediate various light responses in plants. The photoexcited CRY molecules undergo several biophysical and biochemical changes, including electron transfer, phosphorylation and ubiquitination, resulting in conformational changes to propagate light signals. Two modes of CRY signal transduction have recently been discovered: the cryptochrome-interacting basic-helix-loop-helix 1 (CIB)-dependent CRY2 regulation of transcription; and the SUPPRESSOR OF PHYA1/CONSTITUTIVELY PHOTOMORPHOGENIC1 (SPA1/COP1)-dependent cryptochrome regulation of proteolysis. Both CRY signaling pathways rely on blue light-dependent interactions between the CRY photoreceptor and its signaling proteins to modulate gene expression changes in response to blue light, leading to altered developmental programs in plants.
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Affiliation(s)
- Hongtao Liu
- Department of Molecular, Cell & Developmental Biology, University of California, Los Angeles, CA 90095, USA
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Ammar A, Mohammed RAA, Salmi M, Pepper M, Paish EC, Ellis IO, Martin SG. Lymphatic expression of CLEVER-1 in breast cancer and its relationship with lymph node metastasis. Anal Cell Pathol (Amst) 2011; 34:67-78. [PMID: 21483103 PMCID: PMC4605559 DOI: 10.3233/acp-2011-0002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Background: Mechanisms regulating breast cancer lymph node metastasis are unclear. Staining of CLEVER-1 (common lymphatic endothelial and vascular endothelial receptor-1) in human breast tumors was used, along with in vitro techniques, to assess involvement in the metastatic process. Methods: 148 sections of primary invasive breast cancers, with 10 yr follow-up, were stained with anti-CLEVER-1. Leukocyte infiltration was assessed, along with involvement of specific subpopulations by staining with CD83 (mature dendritic cells, mDC), CD209 (immature DC, iDC) and CD68 (macrophage, M&phis;). in vitro expression of CLEVER-1 on lymphatic (LEC) and blood endothelial cells (BEC) was examined by flow cytometry. Results: in vitro results showed that although both endothelial cell types express CLEVER-1, surface expression was only evident on LEC. In tumour sections CLEVER-1 was expressed in blood vessels (BV, 61.4% of samples), lymphatic vessels (LV, 18.2% of samples) and in M&phis;/DCs (82.4% of samples). However, only CLEVER-1 expression in LV was associated with LN metastasis (p = 0.027) and with M&phis; indices (p = 0.021). Although LV CLEVER-1 was associated with LN positivity there was no significant correlation with recurrence or overall survival, BV CLEVER-1 expression was, however, associated with increased risk of recurrence (p = 0.049). The density of inflammatory infiltrate correlated with CLEVER-1 expression in BV (p < 0.001) and LV (p = 0.004). Conclusions: The associations between CLEVER-1 expression on endothelial vessels and macrophage/leukocyte infiltration is suggestive of its regulation by inflammatory conditions in breast cancer, most likely by macrophage-associated cytokines. Its upregulation on LV, related surface expression, and association with LN metastasis suggest that it may be an important mediator of tumor cell metastasis to LN.
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Affiliation(s)
- Aula Ammar
- Department of Clinical Oncology, University of Nottingham, UK
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44
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Smith LW, Hamilton AR, Thomas KJ, Pepper M, Farrer I, Griffiths JP, Jones GAC, Ritchie DA. Compressibility measurements of quasi-one-dimensional quantum wires. Phys Rev Lett 2011; 107:126801. [PMID: 22026783 DOI: 10.1103/physrevlett.107.126801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2011] [Indexed: 05/31/2023]
Abstract
We report measurements of the compressibility of a one-dimensional quantum wire, defined in the upper well of a GaAs/AlGaAs double quantum well heterostructure. A wire defined simultaneously in the lower well probes the ability of the upper wire to screen the electric field from a biased surface gate. The technique is sensitive enough to resolve spin splitting of the subbands in the presence of an in-plane magnetic field. We measure a compressibility signal due to the 0.7 structure and study its evolution with increasing temperature and magnetic field. We see no evidence of the formation of the quasibound state predicted by the Kondo model, instead our data are consistent with theories which predict that the 0.7 structure arises as a result of spontaneous spin polarization.
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Affiliation(s)
- L W Smith
- Cavendish Laboratory, J. J. Thomson Avenue, Cambridge, CB3 OHE, United Kingdom.
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45
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Pepper M. Visions of the future for the Royal Society's 350th anniversary year. Philos Trans A Math Phys Eng Sci 2010; 368:3487-3489. [PMID: 20603362 DOI: 10.1098/rsta.2010.0131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
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46
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Chen TM, Graham AC, Pepper M, Farrer I, Anderson D, Jones GAC, Ritchie DA. Direct observation of nonequilibrium spin population in quasi-one-dimensional nanostructures. Nano Lett 2010; 10:2330-2334. [PMID: 20560608 DOI: 10.1021/nl903314j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Observation of the interplay between interacting energy levels of two spin species is limited by the difficulties in continuously tracking energy levels and thus leaves spin transport in quantum wires still not well understood. We present a dc conductance feature in the nonequilibrium transport regime, a direct indication that the first one-dimensional subband is filled mostly by one spin species only. How this anomalous spin population changes with magnetic field and source-drain bias is directly measured. We show the source-drain bias changes spin polarization in semiconductor nanowires, providing a fully electrical method for the creation and manipulation of spin polarization as well as spin-polarized currents.
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Affiliation(s)
- T-M Chen
- Cavendish Laboratory, Cambridge, United Kingdom.
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47
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McNeil RPG, Schneble RJ, Kataoka M, Ford CJB, Kasama T, Dunin-Borkowski RE, Feinberg JM, Harrison RJ, Barnes CHW, Tse DHY, Trypiniotis T, Bland JAC, Anderson D, Jones GAC, Pepper M. Localized magnetic fields in arbitrary directions using patterned nanomagnets. Nano Lett 2010; 10:1549-1553. [PMID: 20377235 DOI: 10.1021/nl902949v] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Control of the local magnetic fields desirable for spintronics and quantum information technology is not well developed. Existing methods produce either moderately small local fields or one field orientation. We present designs of patterned magnetic elements that produce remanent fields of 50 mT (potentially 200 mT) confined to chosen, submicrometer regions in directions perpendicular to an external initializing field. A wide variety of magnetic-field profiles on nanometer scales can be produced with the option of applying electric fields, for example, to move a quantum dot between regions where the magnetic-field direction or strength is different. We have confirmed our modeling by measuring the fields in one design using electron holography.
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48
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Pepper M. Editor's introduction to 'Personal perspectives in the physical sciences for the Royal Society's 350th anniversary'. Philos Trans A Math Phys Eng Sci 2010; 368:911. [PMID: 20123739 PMCID: PMC3263807 DOI: 10.1098/rsta.2009.0244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
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49
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Abstract
In this article, we present a summary of the current status of the study of the transport of electrons confined to one dimension in very low disorder GaAs-AlGaAs heterostructures. By means of suitably located gates and application of a voltage to 'electrostatically squeeze' the electronic wave functions, it is possible to produce a controllable size quantization and a transition from two-dimensional transport. If the length of the electron channel is sufficiently short, then transport is ballistic and the quantized subbands each have a conductance equal to the fundamental quantum value 2e(2)/h, where the factor of 2 arises from the spin degeneracy. This mode of conduction is discussed, and it is shown that a number of many-body effects can be observed. These effects are discussed as in the spin-incoherent regime, which is entered when the separation of the electrons is increased and the exchange energy is less than kT. Finally, results are presented in the regime where the confinement potential is decreased and the electron configuration relaxes to minimize the electron-electron repulsion to move towards a two-dimensional array. It is shown that the ground state is no longer a line determined by the size quantization alone, but becomes two distinct rows arising from minimization of the electrostatic energy and is the precursor of a two-dimensional Wigner lattice.
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Affiliation(s)
- K.-F. Berggren
- Theory and Modelling, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden
| | - M. Pepper
- London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 6BT, UK
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50
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Zeitler JA, Taday PF, Newnham DA, Pepper M, Gordon KC, Rades T. Terahertz pulsed spectroscopy and imaging in the pharmaceutical setting - a review. J Pharm Pharmacol 2010; 59:209-23. [PMID: 17270075 DOI: 10.1211/jpp.59.2.0008] [Citation(s) in RCA: 157] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Abstract
Terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) are two novel techniques for the physical characterization of pharmaceutical drug materials and final solid dosage forms, utilizing spectral information in the far infrared region of the electromagnetic spectrum. This review focuses on the development and performance of pharmaceutical applications of terahertz technology compared with other tools for physical characterization. TPS can be used to characterize crystalline properties of drugs and excipients. Different polymorphic forms of a drug can be readily distinguished and quantified. Recent developments towards a better understanding of the fundamental theory behind spectroscopy in the far infrared have been discussed. Applications for TPI include the measurement of coating thickness and uniformity in coated pharmaceutical tablets, structural imaging and 3D chemical imaging of solid dosage forms.
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Affiliation(s)
- J Axel Zeitler
- School of Pharmacy, University of Otago, P.O. Box 56, Dunedin, New Zealand
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