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Williams JR, Aghion DM, Doberstein CE, Cosgrove GR, Asaad WF. Penetrating brain injury after suicide attempt with speargun: case study and review of literature. Front Neurol 2014; 5:113. [PMID: 25071701 PMCID: PMC4083241 DOI: 10.3389/fneur.2014.00113] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 06/16/2014] [Indexed: 11/16/2022] Open
Abstract
Penetrating cranial injury by mechanisms other than gunshots are exceedingly rare, and so strategies and guidelines for the management of PBI are largely informed by data from higher-velocity penetrating injuries. Here, we present a case of penetrating brain injury by the low-velocity mechanism of a harpoon from an underwater fishing speargun in an attempted suicide by a 56-year-old Caucasian male. The case raised a number of interesting points in management of low-velocity penetrating brain injury (LVPBI), including benefit in delaying foreign body removal to allow for tamponade; the importance of history-taking in establishing the social/legal significance of the events surrounding the injury; the use of cerebral angiogram in all cases of PBI; advantages of using dual-energy CT to reduce artifact when available; and antibiotic prophylaxis in the context of idiosyncratic histories of usage of penetrating objects before coming in contact with the intracranial environment. We present here the management of the case in full along with an extended discussion and review of existing literature regarding key points in management of LVPBI vs. higher-velocity forms of intracranial injury.
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Williams JR, Sprumont D, Hirtle M, Adebamowo C, Braunschweiger P, Bull S, Burri C, Czarkowski M, Te Fan C, Franck C, Gefenas E, Geissbuhler A, Klingmann I, Kouyaté B, Kraehenbhul JP, Kruger M, Moodley K, Ntoumi F, Nyirenda T, Pym A, Silverman H, Tenorio S. Consensus standards for introductory e-learning courses in human participants research ethics. JOURNAL OF MEDICAL ETHICS 2014; 40:426-428. [PMID: 23959838 PMCID: PMC4391623 DOI: 10.1136/medethics-2013-101572] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This paper reports the results of a workshop held in January 2013 to begin the process of establishing standards for e-learning programmes in the ethics of research involving human participants that could serve as the basis of their evaluation by individuals and groups who want to use, recommend or accredit such programmes. The standards that were drafted at the workshop cover the following topics: designer/provider qualifications, learning goals, learning objectives, content, methods, assessment of participants and assessment of the course. The authors invite comments on the draft standards and eventual endorsement of a final version by all stakeholders.
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Amet F, Williams JR, Watanabe K, Taniguchi T, Goldhaber-Gordon D. Selective equilibration of spin-polarized quantum Hall edge states in graphene. PHYSICAL REVIEW LETTERS 2014; 112:196601. [PMID: 24877955 DOI: 10.1103/physrevlett.112.196601] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Indexed: 06/03/2023]
Abstract
We report on transport measurements of dual-gated, single-layer graphene devices in the quantum Hall regime, allowing for independent control of the filling factors in adjoining regions. Progress in device quality allows us to study scattering between edge states when the fourfold degeneracy of the Landau level is lifted by electron correlations, causing edge states to be spin and/or valley polarized. In this new regime, we observe a dramatic departure from the equilibration seen in more disordered devices: edge states with opposite spins propagate without mixing. As a result, the degree of equilibration inferred from transport can reveal the spin polarization of the ground state at each filling factor. In particular, the first Landau level is shown to be spin polarized at half filling, providing an independent confirmation of a conclusion of Young et al. [Nat. Phys. 8, 550 (2012). The conductance in the bipolar regime is strongly suppressed, indicating that copropagating edge states, even with the same spin, do not equilibrate along PN interfaces. We attribute this behavior to the formation of an insulating ν = 0 stripe at the PN interface.
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Mitchell KM, Foss AM, Prudden HJ, Mukandavire Z, Pickles M, Williams JR, Johnson HC, Ramesh BM, Washington R, Isac S, Rajaram S, Phillips AE, Bradley J, Alary M, Moses S, Lowndes CM, Watts CH, Boily MC, Vickerman P. Who mixes with whom among men who have sex with men? Implications for modelling the HIV epidemic in southern India. J Theor Biol 2014; 355:140-50. [PMID: 24727187 PMCID: PMC4064301 DOI: 10.1016/j.jtbi.2014.04.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 04/01/2014] [Accepted: 04/02/2014] [Indexed: 11/19/2022]
Abstract
In India, the identity of men who have sex with men (MSM) is closely related to the role taken in anal sex (insertive, receptive or both), but little is known about sexual mixing between identity groups. Both role segregation (taking only the insertive or receptive role) and the extent of assortative (within-group) mixing are known to affect HIV epidemic size in other settings and populations. This study explores how different possible mixing scenarios, consistent with behavioural data collected in Bangalore, south India, affect both the HIV epidemic, and the impact of a targeted intervention. Deterministic models describing HIV transmission between three MSM identity groups (mostly insertive Panthis/Bisexuals, mostly receptive Kothis/Hijras and versatile Double Deckers), were parameterised with behavioural data from Bangalore. We extended previous models of MSM role segregation to allow each of the identity groups to have both insertive and receptive acts, in differing ratios, in line with field data. The models were used to explore four different mixing scenarios ranging from assortative (maximising within-group mixing) to disassortative (minimising within-group mixing). A simple model was used to obtain insights into the relationship between the degree of within-group mixing, R0 and equilibrium HIV prevalence under different mixing scenarios. A more complex, extended version of the model was used to compare the predicted HIV prevalence trends and impact of an HIV intervention when fitted to data from Bangalore. With the simple model, mixing scenarios with increased amounts of assortative (within-group) mixing tended to give rise to a higher R0 and increased the likelihood that an epidemic would occur. When the complex model was fit to HIV prevalence data, large differences in the level of assortative mixing were seen between the fits identified using different mixing scenarios, but little difference was projected in future HIV prevalence trends. An oral pre-exposure prophylaxis (PrEP) intervention was modelled, targeted at the different identity groups. For intervention strategies targeting the receptive or receptive and versatile MSM together, the overall impact was very similar for different mixing patterns. However, for PrEP scenarios targeting insertive or versatile MSM alone, the overall impact varied considerably for different mixing scenarios; more impact was achieved with greater levels of disassortative mixing. Different mixing scenarios are explored for 3 groups of role-segregated MSM. Models show that the mixing scenario affects both R0 and endemic HIV prevalence. When models are fit to data, predicted HIV trends are unaffected by mixing. Impact of targeted (but not non-targeted) interventions can be affected by mixing.
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Bloom BJ, Nicholson TL, Williams JR, Campbell SL, Bishof M, Zhang X, Zhang W, Bromley SL, Ye J. An optical lattice clock with accuracy and stability at the 10(-18) level. Nature 2014; 506:71-5. [PMID: 24463513 DOI: 10.1038/nature12941] [Citation(s) in RCA: 210] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Accepted: 12/04/2013] [Indexed: 11/09/2022]
Abstract
Progress in atomic, optical and quantum science has led to rapid improvements in atomic clocks. At the same time, atomic clock research has helped to advance the frontiers of science, affecting both fundamental and applied research. The ability to control quantum states of individual atoms and photons is central to quantum information science and precision measurement, and optical clocks based on single ions have achieved the lowest systematic uncertainty of any frequency standard. Although many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 16 times worse. Here we demonstrate a many-atom system that achieves an accuracy of 6.4 × 10(-18), which is not only better than a single-ion-based clock, but also reduces the required measurement time by two orders of magnitude. By systematically evaluating all known sources of uncertainty, including in situ monitoring of the blackbody radiation environment, we improve the accuracy of optical lattice clocks by a factor of 22. This single clock has simultaneously achieved the best known performance in the key characteristics necessary for consideration as a primary standard-stability and accuracy. More stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units, the search for time variation of fundamental constants, clock-based geodesy and other precision tests of the fundamental laws of nature. This work also connects to the development of quantum sensors and many-body quantum state engineering (such as spin squeezing) to advance measurement precision beyond the standard quantum limit.
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Santhi C, Kannan N, White M, Di Luzio M, Arnold JG, Wang X, Williams JR. An integrated modeling approach for estimating the water quality benefits of conservation practices at the river basin scale. JOURNAL OF ENVIRONMENTAL QUALITY 2014; 43:177-198. [PMID: 25602551 DOI: 10.2134/jeq2011.0460] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The USDA initiated the Conservation Effects Assessment Project (CEAP) to quantify the environmental benefits of conservation practices at regional and national scales. For this assessment, a sampling and modeling approach is used. This paper provides a technical overview of the modeling approach used in CEAP cropland assessment to estimate the off-site water quality benefits of conservation practices using the Ohio River Basin (ORB) as an example. The modeling approach uses a farm-scale model, Agricultural Policy Environmental Extender (APEX), and a watershed scale model (the Soil and Water Assessment Tool [SWAT]) and databases in the Hydrologic Unit Modeling for the United States system. Databases of land use, soils, land use management, topography, weather, point sources, and atmospheric depositions were developed to derive model inputs. APEX simulates the cultivated cropland, Conserve Reserve Program land, and the practices implemented on them, whereas SWAT simulates the noncultivated land (e.g., pasture, range, urban, and forest) and point sources. Simulation results from APEX are input into SWAT. SWAT routes all sources, including APEX's, to the basin outlet through each eight-digit watershed. Each basin is calibrated for stream flow, sediment, and nutrient loads at multiple gaging sites and turned in for simulating the effects of conservation practice scenarios on water quality. Results indicate that sediment, nitrogen, and phosphorus loads delivered to the Mississippi River from ORB could be reduced by 16, 15, and 23%, respectively, due to current conservation practices. Modeling tools are useful to provide science-based information for assessing existing conservation programs, developing future programs, and developing insights on load reductions necessary for hypoxia in the Gulf of Mexico.
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Sellers EL, Fearon PV, Ripley C, Vincent A, Barnard S, Williams JR. The introduction of rib fracture fixation for traumatic flail chest injury: A single centre experience. TRAUMA-ENGLAND 2013. [DOI: 10.1177/1460408613497146] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Introduction High energy chest trauma resulting in flail chest injury or multiple rib fractures is associated with increased rates of patient morbidity and mortality. Operative fixation of acute rib fractures causing flail chest is thought to reduce morbidity by reducing pain and improving chest mechanics enabling earlier ventilator weaning. A variety of operative techniques have been described historically and we report on our unit’s experience of the introduction of acute rib fracture fixation using contoured locking plates. Methods Between December 2010 and 2011, 10 patients underwent acute rib fracture fixation under the joint care of orthopaedic and thoracic surgeons. Outcome measures included patient demographics, time ventilated pre-operatively, time ventilated post-operatively and time spent on intensive treatment unit/high dependency unit (ITU/HDU) post operatively. Results The median time from presentation to surgery was 5 days (range 2–12 days), the median time ventilated post-operatively was 2 days (range 1–4 days) and the median number of days spent on ITU/HDU post-operatively was 6 days (range 2–11 days). All but two patients, who did not require post-operative ventilation, were weaned off the ventilator within 4 days of surgery. Conclusions Our results appear positive in terms of time spent ventilated post-operatively but no conclusion can be drawn as we have no comparable non-operative group. We have however shown that rib fracture fixation can be carried out successfully and safely in a trauma centre with few post-operative complications reported to date. Further evidence on rib fracture fixation is required from a large, multi-centre randomised controlled trial.
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Amet F, Williams JR, Watanabe K, Taniguchi T, Goldhaber-Gordon D. Insulating behavior at the neutrality point in single-layer graphene. PHYSICAL REVIEW LETTERS 2013; 110:216601. [PMID: 23745906 DOI: 10.1103/physrevlett.110.216601] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Revised: 01/15/2013] [Indexed: 06/02/2023]
Abstract
The fate of the low-temperature conductance at the charge-neutrality (Dirac) point in a single sheet of graphene on boron nitride is investigated down to 20 mK. As the temperature is lowered, the peak resistivity diverges with a power-law behavior and becomes as high as several megohms per square at the lowest temperature, in contrast with the commonly observed saturation of the conductivity. As a perpendicular magnetic field is applied, our device remains insulating and directly transitions to the broken-valley-symmetry, ν=0 quantum Hall state, indicating that the insulating behavior we observe at zero magnetic field is a result of broken valley symmetry. Finally we discuss the possible origins of this effect.
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Nicholson TL, Martin MJ, Williams JR, Bloom BJ, Bishof M, Swallows MD, Campbell SL, Ye J. Comparison of two independent Sr optical clocks with 1×10(-17) stability at 10(3) s. PHYSICAL REVIEW LETTERS 2012; 109:230801. [PMID: 23368177 DOI: 10.1103/physrevlett.109.230801] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Indexed: 06/01/2023]
Abstract
Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise. However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two ^{87}Sr lattice systems using a laser with a thermal noise floor of 1×10(-15), we remove classically correlated laser noise from the intercomparison, but this does not demonstrate independent clock performance. With an improved optical oscillator that has a 1×10(-16) thermal noise floor, we demonstrate an order of magnitude improvement over the best reported stability of any independent clock, achieving a fractional instability of 1×10(-17) in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined quantum projection noise limit for a 160 ms probe time with ~10(3) atoms in each clock. We further demonstrate that even at this high precision, the overall systematic uncertainty of our clock is not limited by atomic interactions. For the second Sr clock, which has a cavity-enhanced lattice, the atomic-density-dependent frequency shift is evaluated to be -3.11×10(-17) with an uncertainty of 8.2×10(-19).
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Martin CJ, Sutton DG, Magee J, McVey S, Williams JR, Peet D. Derivation of factors for estimating the scatter of diagnostic x-rays from walls and ceiling slabs. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2012; 32:373-396. [PMID: 23006642 DOI: 10.1088/0952-4746/32/4/373] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Computed tomography (CT) scanning rooms and interventional x-ray facilities with heavy workloads may require the installation of shielding to protect against radiation scattered from walls or ceiling slabs. This is particularly important for the protection of those operating x-ray equipment from within control cubicles who may be exposed to radiation scattered from the ceiling over the top of the protective barrier and round the side if a cubicle door is not included. Data available on the magnitude of this tertiary scatter from concrete slabs are limited. Moreover, there is no way in which tertiary scatter levels can be estimated easily for specific facilities. There is a need for a suitable method for quantification of tertiary scatter because of the increases in workloads of complex x-ray facilities. In this study diagnostic x-ray air kerma levels scattered from concrete and brick walls have been measured to verify scatter factors. The results have been used in a simulation of tertiary scatter for x-ray facilities involving summation of scatter contributions from elements across concrete ceiling slabs. The majority of the ceiling scatter air kerma to which staff behind a barrier will be exposed arises from the area between the patient/x-ray tube and the staff. The level depends primarily on the heights of the ceiling and protective barrier. A method has been developed to allow tertiary scatter levels to be calculated using a simple equation based on a standard arrangement for rooms with different ceiling and barrier heights. Coefficients have been derived for a CT facility and an interventional suite to predict tertiary scatter levels from the workload, so that consideration can be given to the protection options available.
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Williams JR, Bestwick AJ, Gallagher P, Hong SS, Cui Y, Bleich AS, Analytis JG, Fisher IR, Goldhaber-Gordon D. Unconventional Josephson effect in hybrid superconductor-topological insulator devices. PHYSICAL REVIEW LETTERS 2012; 109:056803. [PMID: 23006196 DOI: 10.1103/physrevlett.109.056803] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Indexed: 06/01/2023]
Abstract
We report on transport properties of Josephson junctions in hybrid superconducting-topological insulator devices, which show two striking departures from the common Josephson junction behavior: a characteristic energy that scales inversely with the width of the junction, and a low characteristic magnetic field for suppressing supercurrent. To explain these effects, we propose a phenomenological model which expands on the existing theory for topological insulator Josephson junctions.
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Sutton DG, Martin CJ, Peet D, Williams JR. The characterization and transmission of scattered radiation resulting from x-ray beams filtered with zero to 0.99 mm copper. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2012; 32:117-129. [PMID: 22555158 DOI: 10.1088/0952-4746/32/2/117] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The specification of shielding for fluoroscopic facilities in the UK is based on the determination of scatter incident on a barrier using a simple formula linking kerma area product and scatter kerma. Over the last few years there has been a move to incorporate additional copper filtration in equipment used for high dose fluoroscopic and interventional examinations, and the existing formula does not take this into account. The spectral and transmission characteristics of the scattered radiation resulting from a primary x-ray beam filtered with additional copper are not known. In this study, the relationship between primary and scattered radiation in these beams has been investigated as have their transmission characteristics. The scatter kerma area product from filtered beams is shown to be greater than that from conventional x-rays and a simple numerical correction linking the two has been derived. The implications for shielding calculations have been assessed and the impact of the correction on calculated barrier thickness has been shown to be relatively small. The broad beam transmission characteristics of the radiation scattered from the filtered beams have been simulated using Monte Carlo methods and found to be adequately described by the standard transmission equation using conventional coefficients.
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Turro NJ, Gagosian RB, Edelson SE, Darling TR, Williams JR, Hammond WB. CHEMISTRY OF CYCLOPROPANONE AND SOME OF ITS ALKYL DERIVATIVES*†. ACTA ACUST UNITED AC 2012. [DOI: 10.1111/j.2164-0947.1971.tb02609.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Williams JR, Hirsch ES, Anderson K, Bush AL, Goldstein SR, Grill S, Lehmann S, Little JT, Margolis RL, Palanci J, Pontone G, Weiss H, Rabins P, Marsh L. A comparison of nine scales to detect depression in Parkinson disease: which scale to use? Neurology 2012; 78:998-1006. [PMID: 22422897 DOI: 10.1212/wnl.0b013e31824d587f] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE The Methods of Optimal Depression Detection in Parkinson's Disease (MOOD-PD) study compared the psychometric properties of 9 depression scales to provide guidance on scale selection in Parkinson disease (PD). METHODS Patients with PD (n = 229) from community-based neurology practices completed 6 self-report scales (Beck Depression Inventory [BDI]-II, Center for Epidemiologic Studies Depression Rating Scale-Revised [CESD-R], 30-item Geriatric Depression Scale [GDS-30], Inventory of Depressive Symptoms-Patient [IDS-SR], Patient Health Questionnaire-9 [PHQ-9], and Unified Parkinson's Disease Rating Scale [UPDRS]-Part I) and were administered 3 clinician-rated scales (17-item Hamilton Depression Rating Scale [HAM-D-17], Inventory of Depressive Symptoms-Clinician [IDS-C], and Montgomery-Åsberg Depression Rating Scale [MADRS] and a psychiatric interview. DSM-IV-TR diagnoses were established by an expert panel blinded to the self-reported rating scale data. Receiver operating characteristic curves were used to estimate the area under the curve (AUC) of each scale. RESULTS All scales performed better than chance (AUC 0.75-0.85). Sensitivity ranged from 0.66 to 0.85 and specificity ranged from 0.60 to 0.88. The UPDRS Depression item had a smaller AUC than the BDI-II, HAM-D-17, IDS-C, and MADRS. The CESD-R also had a smaller AUC than the MADRS. The remaining AUCs were statistically similar. CONCLUSIONS The GDS-30 may be the most efficient depression screening scale to use in PD because of its brevity, favorable psychometric properties, and lack of copyright protection. However, all scales studied, except for the UPDRS Depression, are valid screening tools when PD-specific cutoff scores are used.
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Wallace H, Martin CJ, Sutton DG, Peet D, Williams JR. Establishment of scatter factors for use in shielding calculations and risk assessment for computed tomography facilities. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2012; 32:39-50. [PMID: 22327169 DOI: 10.1088/0952-4746/32/1/39] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The specification of shielding for CT facilities in the UK and many other countries has been based on isodose scatter curves supplied by the manufacturers combined with the scanner's mAs workload. Shielding calculations for radiography and fluoroscopy are linked to a dose measurement of radiation incident on the patient called the kerma-area product (KAP), and a related quantity, the dose-length product (DLP), is now employed for assessment of CT patient doses. In this study the link between scatter air kerma and DLP has been investigated for CT scanners from different manufacturers. Scatter air kerma values have been measured and scatter factors established that can be used to estimate air kerma levels within CT scanning rooms. Factors recommended to derive the scatter air kerma at 1 m from the isocentre are 0.36 µGy (mGy cm)(-1) for the body and 0.14 µGy (mGy cm)(-1) for head scans. The CT scanner gantries only transmit 10% of the scatter air kerma level and this can also be taken into account when designing protection. The factors can be used to predict scatter air kerma levels within a scanner room that might be used in risk assessments relating to personnel whose presence may be required during CT fluoroscopy procedures.
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Li D, Truong TV, Bills TM, Holt BC, VanDerwerken DN, Williams JR, Acharya A, Robison RA, Tolley HD, Lee ML. GC/MS Method for Positive Detection of Bacillus anthracis Endospores. Anal Chem 2012; 84:1637-44. [DOI: 10.1021/ac202606x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Lee M, Williams JR, Zhang S, Frisbie CD, Goldhaber-Gordon D. Electrolyte gate-controlled Kondo effect in SrTiO3. PHYSICAL REVIEW LETTERS 2011; 107:256601. [PMID: 22243097 DOI: 10.1103/physrevlett.107.256601] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Indexed: 05/31/2023]
Abstract
We report low-temperature, high-field magnetotransport measurements of SrTiO(3) gated by an ionic gel electrolyte. A saturating resistance upturn and negative magnetoresistance that signal the emergence of the Kondo effect appear for higher applied gate voltages. This observation, enabled by the wide tunability of the ionic gel-applied electric field, promotes the interpretation of the electric field-effect-induced 2D electron system in SrTiO(3) as an admixture of magnetic Ti(3+) ions, i.e., localized and unpaired electrons, and delocalized electrons that partially fill the Ti 3d conduction band.
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Blatt S, Nicholson TL, Bloom BJ, Williams JR, Thomsen JW, Julienne PS, Ye J. Measurement of optical Feshbach resonances in an ideal gas. PHYSICAL REVIEW LETTERS 2011; 107:073202. [PMID: 21902391 DOI: 10.1103/physrevlett.107.073202] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Indexed: 05/31/2023]
Abstract
Using a narrow intercombination line in alkaline earth atoms to mitigate large inelastic losses, we explore the optical Feshbach resonance effect in an ultracold gas of bosonic (88)Sr. A systematic measurement of three resonances allows precise determinations of the optical Feshbach resonance strength and scaling law, in agreement with coupled-channel theory. Resonant enhancement of the complex scattering length leads to thermalization mediated by elastic and inelastic collisions in an otherwise ideal gas. Optical Feshbach resonance could be used to control atomic interactions with high spatial and temporal resolution.
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Williams JR, Marcus CM. Snake states along graphene p-n junctions. PHYSICAL REVIEW LETTERS 2011; 107:046602. [PMID: 21867027 DOI: 10.1103/physrevlett.107.046602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2010] [Indexed: 05/31/2023]
Abstract
We investigate transport in locally gated graphene devices, where carriers are injected and collected along, rather than across, the gate edge. Tuning densities into the p-n regime significantly reduces resistance along the p-n interface, while resistance across the interface increases. This provides an experimental signature of snake states, which zigzag along the p-n interface and remain stable as applied perpendicular magnetic field approaches zero. Snake states appear as a peak in transverse resistance measured along the p-n interface. The generic role of snake states in disordered graphene is also discussed.
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Nakaharai S, Williams JR, Marcus CM. Gate-defined graphene quantum point contact in the quantum Hall regime. PHYSICAL REVIEW LETTERS 2011; 107:036602. [PMID: 21838385 DOI: 10.1103/physrevlett.107.036602] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Indexed: 05/31/2023]
Abstract
We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5h/e2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.
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Williams JR, Low T, Lundstrom MS, Marcus CM. Gate-controlled guiding of electrons in graphene. NATURE NANOTECHNOLOGY 2011; 6:222-225. [PMID: 21317890 DOI: 10.1038/nnano.2011.3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Accepted: 01/06/2011] [Indexed: 05/30/2023]
Abstract
Ballistic semiconductor structures have allowed the realization of optics-like phenomena in electronic systems, including the magnetic focusing and electrostatic lensing of electrons. An extension that appears unique to graphene is to use both n and p carrier types to create electronic analogues of optical devices with both positive and negative indices of refraction. Here, we use the gate-controlled density of both p and n carrier types in graphene to demonstrate the electronic analogue of fibre-optic guiding. Two basic effects are investigated: bipolar p-n junction guiding, based on the principle of angle-selective transmission through the interface between the graphene and the p-n junction; and unipolar fibre-optic guiding, using total internal reflection controlled by carrier density. We also demonstrate modulation of the guiding efficiency through gating, and comparison of these data with numerical simulations indicates that guiding performance is limited by the roughness of the interface. The development of p-n and fibre-optic guiding in graphene may lead to electrically reconfigurable wiring in high-mobility devices.
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Williams JR, Pillay AE. Metals, Metalloids and Toxicity in Date Palms: Potential Environmental Impact. ACTA ACUST UNITED AC 2011. [DOI: 10.4236/jep.2011.25068] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
The history of bioethics in Canada has yet to be written. When that happens, an important issue to be considered will be the influence of American bioethics. In what follows, I offer some suggestions to the author of the history about what should be included. I will limit my discussion to the formative years of 1970-2000 and leave later developments for another occasion. My article will be structured as follows: individuals, institutions, issues, bioethics education and a conclusion.
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Duarte MC, Cardona N, Poblete F, González K, García M, Pacheco M, Botto C, Pujol FH, Williams JR. A comparative epidemiological study of hepatitis B and hepatitis D virus infections in Yanomami and Piaroa Amerindians of Amazonas State, Venezuela. Trop Med Int Health 2010; 15:924-33. [PMID: 20561309 DOI: 10.1111/j.1365-3156.2010.02560.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
OBJECTIVES To report the prevalences of hepatitis B (HBV) and hepatitis D (HDV) infections in remote and more accessible Yanomami and Piaroa Venezuelan Amazonian Amerindian populations; to estimate incidence per susceptible. METHODS Clinico-epidemiological evaluation was carried out in 9 Piaroa villages. Blood samples were tested for HBV core antibody (anti-HBc), surface antigen (HBsAg) and HDV antibody (anti-HDV). Results were analysed using logistic regression, and estimates made of HBV forces of infection (FOI). Prevalences and FOI were also estimated for 4 Yanomami villages. RESULTS Mean Piaroa anti-HBc and HBsAg prevalences were 27.4% and 5.1%, respectively (up to 53% and 19% in the remote Autana region). Mean Yanomami anti-HBc and HBsAg prevalences were, respectively, 58.0% (range 43-70%) and 14.3% (31% in the village with highest HBsAg). No significant difference was found between sexes, with age and maternal HBsAg the only risk factors for HBV identified in multivariate regression of Piaroa data. Only 4 Piaroa and 2 Yanomami individuals were anti-HDV positive. CONCLUSION Piaroa HBV prevalences were generally higher in remote villages than in less remote ones, with prevalences in Yanomami villages even higher. Anti-HBc prevalence was 47% in one Yanomami village with a history of HBV vaccination but no HBsAg cases were identified, suggestive of previously cleared or possibly transient infection or vaccine escape. Despite a past history of HDV epidemic outbreaks and HBsAg levels in some villages appearing sufficient to facilitate HDV transmission, anti-HDV prevalence was low; it remains to be established why no recent outbreaks have been reported.
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Bell DC, Lemme MC, Stern LA, Williams JR, Marcus CM. Precision cutting and patterning of graphene with helium ions. NANOTECHNOLOGY 2009; 20:455301. [PMID: 19822934 DOI: 10.1088/0957-4484/20/45/455301] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report nanoscale patterning of graphene using a helium ion microscope configured for lithography. Helium ion lithography is a direct-write lithography process, comparable to conventional focused ion beam patterning, with no resist or other material contacting the sample surface. In the present application, graphene samples on Si/SiO2 substrates are cut using helium ions, with computer controlled alignment, patterning, and exposure. Once suitable beam doses are determined, sharp edge profiles and clean etching are obtained, with little evident damage or doping to the sample. This technique provides fast lithography compatible with graphene, with approximately 15 nm feature sizes.
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