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Ring patterns generated by an expanding colloidal meniscus. Phys Rev E 2020; 102:052608. [PMID: 33327138 DOI: 10.1103/physreve.102.052608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Accepted: 11/06/2020] [Indexed: 11/07/2022]
Abstract
The drop-and-dry is a common technique allowing for creation of periodic nanoparticle (NP) structures for sensing, photonics, catalysis, etc. However, the reproducibility and scalability of this approach for fabrication of NP-based structures faces serious challenges due to the complexity of the simple, at first glance, evaporation process. In this work we study the effect of the spatial confinement on the NP self-assembly under slow solvent evaporation, when the air-liquid-substrate contact line (CL) expands from the center towards the walls of a cylindrical cell, forming a toroid. Using in situ video monitoring of the stick-slip CL motion, we find regular hydrodynamic perturbations in the meniscus, and reveal fine details of the formation of quasiperiodic rings of close packed NP layers. We report that drying of the toroidal NP droplet has a number of important differences from drying of the classical hemispherical colloidal drops. In toroidal drops we observe linear-in-time average meniscus motion, in contrast to the hemispherical drops where the meniscus moves as a square root of time. While both droplet geometries produce NP ring patterns, the ring width for the toroidal drop decreases with increasing ring radius, while it decreases with decreasing the radius of the hemispherical drop. We suggest that free ligands are the main cause of the Marangoni instabilities driving the periodic vorticity in the meniscus. In addition, we show that the usually ignored contact line tension may yield a considerable contribution to the CL pinning causing the CL slip-stick motion and the ring formation.
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Abstract
Fascination with glassy states has persisted since Fisher introduced the vortex-glass as a new thermodynamic phase that is a true superconductor that lacks conventional long-range order. Though Fisher's original model considered point disorder, it was later predicted that columnar defects (CDs) could also induce glassiness - specifically, a Bose-glass phase. In YBa2Cu3O7-x (YBCO), glassy states can cause distinct behavior in the temperature (T ) dependent rate of thermally activated vortex motion (S). The vortex-glass state produces a plateau in S(T ) whereas a Bose-glass can transition into a state hosting vortex excitations called double-kinks that can expand, creating a large peak in S(T ). Although glass phases have been well-studied in YBCO, few studies exist of other materials containing CDs that could contribute to distinguishing universal behavior. Here, we report on the effectiveness of CDs tilted ~30° from the c-axis in reducing S in a NbSe2 crystal. The magnetization is 5 times higher and S is minimized when the field is parallel to the defects versus aligned with the c-axis. We see signatures of glassiness in both field orientations, but do not observe a peak in S(T ) nor a plateau at values observed in YBCO. Finally, we discuss the possibility that competing disorder induces a field-orientation-driven transition from a Bose-glass to an anisotropic glass involving both point and columnar disorder.
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Temperature-Dependent Three-Dimensional Anisotropy of the Magnetoresistance in WTe_{2}. PHYSICAL REVIEW LETTERS 2015; 115:046602. [PMID: 26252701 DOI: 10.1103/physrevlett.115.046602] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2015] [Indexed: 06/04/2023]
Abstract
Extremely large magnetoresistance (XMR) was recently discovered in WTe_{2}, triggering extensive research on this material regarding the XMR origin. Since WTe_{2} is a layered compound with metal layers sandwiched between adjacent insulating chalcogenide layers, this material has been considered to be electronically two-dimensional (2D). Here we report two new findings on WTe_{2}: (1) WTe_{2} is electronically 3D with a mass anisotropy as low as 2, as revealed by the 3D scaling behavior of the resistance R(H,θ)=R(ϵ_{θ}H) with ϵ_{θ}=(cos^{2}θ+γ^{-2}sin^{2}θ)^{1/2}, θ being the magnetic field angle with respect to the c axis of the crystal and γ being the mass anisotropy and (2) the mass anisotropy γ varies with temperature and follows the magnetoresistance behavior of the Fermi liquid state. Our results not only provide a general scaling approach for the anisotropic magnetoresistance but also are crucial for correctly understanding the electronic properties of WTe_{2}, including the origin of the remarkable "turn-on" behavior in the resistance versus temperature curve, which has been widely observed in many materials and assumed to be a metal-insulator transition.
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4
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Huge critical current density and tailored superconducting anisotropy in SmFeAsO₀.₈F₀.₁₅ by low-density columnar-defect incorporation. Nat Commun 2014; 4:2655. [PMID: 24189627 DOI: 10.1038/ncomms3655] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 09/22/2013] [Indexed: 11/09/2022] Open
Abstract
Iron-based superconductors could be useful for electricity distribution and superconducting magnet applications because of their relatively high critical current densities and upper critical fields. SmFeAsO₀.₈F₀.₁₅ is of particular interest as it has the highest transition temperature among these materials. Here we show that by introducing a low density of correlated nano-scale defects into this material by heavy-ion irradiation, we can increase its critical current density to up to 2 × 10⁷ A cm⁻² at 5 K--the highest ever reported for an iron-based superconductor--without reducing its critical temperature of 50 K. We also observe a notable reduction in the thermodynamic superconducting anisotropy, from 8 to 4 upon irradiation. We develop a model based on anisotropic electron scattering that predicts that the superconducting anisotropy can be tailored via correlated defects in semimetallic, fully gapped type II superconductors.
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Stripe domains and first-order phase transition in the vortex matter of anisotropic high-temperature superconductors. PHYSICAL REVIEW LETTERS 2014; 112:157001. [PMID: 24785065 DOI: 10.1103/physrevlett.112.157001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2013] [Indexed: 06/03/2023]
Abstract
We report the direct imaging of a novel modulated flux striped domain phase in a nearly twin-free YBCO crystal. These domains arise from instabilities in the vortex structure within a narrow region of tilted magnetic fields at small angles from the in-plane direction. By comparing the experimental and theoretically derived vortex phase diagrams we infer that the stripe domains emerge from a first-order phase transition of the vortex structure. The size of domains containing vortices of certain orientations is controlled by the balance between the vortex stray field energy and the positive energy of the domain boundaries. Our results confirm the existence of the kinked vortex chain phase in an anisotropic high temperature superconductor and reveal a sharp transition in the state of this phase resulting in regular vortex domains.
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Diagnostic Accuracy of Scintigraphy and Sonography for Biliary Atresia. HONG KONG JOURNAL OF RADIOLOGY 2013. [DOI: 10.12809/hkjr1313203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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7
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Realization of artificial ice systems for magnetic vortices in a superconducting MoGe thin film with patterned nanostructures. PHYSICAL REVIEW LETTERS 2013; 111:067001. [PMID: 23971602 DOI: 10.1103/physrevlett.111.067001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Indexed: 06/02/2023]
Abstract
We report an anomalous matching effect in MoGe thin films containing pairs of circular holes arranged in such a way that four of those pairs meet at each vertex point of a square lattice. A remarkably pronounced fractional matching was observed in the magnetic field dependences of both the resistance and the critical current. At the half matching field the critical current can be even higher than that at zero field. This has never been observed before for vortices in superconductors with pinning arrays. Numerical simulations within the nonlinear Ginzburg-Landau theory reveal a square vortex ice configuration in the ground state at the half matching field and demonstrate similar characteristic features in the field dependence of the critical current, confirming the experimental realization of an artificial ice system for vortices for the first time.
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Concentric left ventricular hypertrophy associated with 2-year cardiovascular related mortality in heart failure and preserved ejection fraction. Eur Heart J 2013. [DOI: 10.1093/eurheartj/eht310.p5745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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9
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Large magnetoresistance oscillations in mesoscopic superconductors due to current-excited moving vortices. PHYSICAL REVIEW LETTERS 2012; 109:057004. [PMID: 23006202 DOI: 10.1103/physrevlett.109.057004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Indexed: 06/01/2023]
Abstract
We show in the case of a superconducting Nb ladder that a mesoscopic superconductor typically exhibits magnetoresistance oscillations whose amplitude and temperature dependence are different from those stemming from the Little-Parks effect. We demonstrate that these large resistance oscillations (as well as the monotonic background on which they are superimposed) are due to current-excited moving vortices, where the applied current in competition with the oscillating Meissner currents imposes or removes the barriers for vortex motion in an increasing magnetic field. Because of the ever present current in transport measurements, this effect should be considered in parallel with the Little-Parks effect in low-critical temperature (T(c)) samples, as well as with recently proposed thermal activation of dissipative vortex-antivortex pairs in high-T(c) samples.
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Hydrogen gas sensing with networks of ultrasmall palladium nanowires formed on filtration membranes. NANO LETTERS 2011; 11:262-268. [PMID: 21114299 DOI: 10.1021/nl103682s] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Hydrogen sensors based on single Pd nanowires show promising results in speed, sensitivity, and ultralow power consumption. The utilization of single Pd nanowires, however, face challenges in nanofabrication, manipulation, and achieving ultrasmall transverse dimensions. We report on hydrogen sensors that take advantage of single palladium nanowires in high speed and sensitivity and that can be fabricated conveniently. The sensors are based on networks of ultrasmall (<10 nm) palladium nanowires deposited onto commercially available filtration membranes. We investigated the sensitivities and response times of these sensors as a function of the thickness of the nanowires and also compared them with a continuous reference film. The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of our fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.
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11
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P16-45. High avidity CD4+ T cell response directed to an immunodominant Gag epitope in HIV controllers: an ANRS EP36 study. Retrovirology 2009. [PMCID: PMC2767775 DOI: 10.1186/1742-4690-6-s3-p274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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12
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Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip. PHYSICAL REVIEW LETTERS 2008; 101:077003. [PMID: 18764568 DOI: 10.1103/physrevlett.101.077003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Indexed: 05/26/2023]
Abstract
We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.
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Acute myocardial infarction found by multi-detector computed tomography ordered for suspected aortic dissection. Hong Kong Med J 2008; 14:233-235. [PMID: 18525095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023] Open
Abstract
Urgent requests for contrast computed tomographic scans of the thorax are often performed for suspected aortic dissections and pulmonary embolisms, both of which have clinical features similar to those seen in acute myocardial infarction. We present two cases with computed tomographic scans showing decreased myocardial enhancement, suggestive of acute myocardial infarction, but no evidence of aortic dissection. Acute myocardial infarction was subsequently confirmed by coronary angiography.
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Abstract
A 12-year-old boy presented with large-bowel obstruction due to sigmoid volvulus. Temporary relief was achieved with rectal tube decompression. Elective laparoscopic-assisted sigmoid colectomy was performed. Post-operative recovery was uneventful. The patient remained well with no recurrence after 4 years of follow-up. Laparoscopic-assisted sigmoid colectomy may be the procedure of choice for selected children with sigmoid volvulus.
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Electrical stimulation and biofeedback exercise of pelvic floor muscle for children with faecal incontinence after surgery for anorectal malformation. Pediatr Surg Int 2006; 22:975-8. [PMID: 17001486 DOI: 10.1007/s00383-006-1790-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
We report our experience of electrical stimulation and biofeedback exercise of pelvic floor muscle for children with faecal incontinence after surgery for anorectal malformation (ARM). Electrical stimulation and biofeedback exercise of pelvic floor muscle were performed on children with post-operative faecal soiling following repair of intermediate or high type ARM. Children under the age of 5 years or with learning difficulties were excluded. They had 6 months supervised programme in the Department of Physiotherapy followed by 6 months home based programme. Bowel management including toilet training, dietary advice, medications and enemas were started before the pelvic floor muscle exercise and continued throughout the programme. Soiling frequency rank, Rintala continence score, sphincter muscle electromyography (EMG) and anorectal manometry were assessed before and after the programme. Wilcoxon signed rank test was performed for statistical analysis. From March 2001 to May 2006, 17 children were referred to the programme. Twelve patients (M:F = 10:2; age = 5-17 years) completed the programme. There was a trend of improvement in Rintala score at sixth month (p = 0.206) and at the end of programme (p = 0.061). Faecal soiling was significantly improved at sixth month (p = 0.01) and at the end of the programme (p = 0.004). Mean sphincter muscle EMG before treatment was 1.699 microV. Mean EMG at sixth month and after the programme was 3.308 microV (p = 0.034) and 3.309 microV (p = 0.002) respectively. After the programme, there was a mean increase in anal sphincter squeeze pressure of 29.9 mmHg (p = 0.007). Electrical stimulation and biofeedback exercise of pelvic floor muscle is an effective adjunct for the treatment of faecal incontinence in children following surgery for anorectal malformation.
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Direct observation of geometrical phase transitions in mesoscopic superconductors by scanning tunneling microscopy. PHYSICAL REVIEW LETTERS 2005; 95:167002. [PMID: 16241833 DOI: 10.1103/physrevlett.95.167002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Indexed: 05/05/2023]
Abstract
Using scanning tunneling microscopy, we mapped the distribution of the local density of states in a single crystal superconductor heterostructure with an array of submicron normal metal islands. We observe the coexistence of strongly interacting multiquanta vortex lattice with interstitial Abrikosov vortices. The newly formed composite magnetic flux structure undergoes a series of phase transitions between different topological configuration states. The vortex configuration states are strongly dependent on the number of flux quanta and the nanoscale confinement architecture of the mesoscopic superconductor. Here, we present images of vortex phase transitions due to confinement effects when the number of magnetic flux quanta in the system changes. The vortex dynamics in these systems could serve as a model for behavior of confined many-body systems when the number of particles changes.
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Laparoscopic mobilization of testicular vessels: an adjunctive step in orchidopexy for impalpable and redo undescended testis in children. Pediatr Surg Int 2005; 21:767-9. [PMID: 16096794 DOI: 10.1007/s00383-005-1495-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 06/23/2005] [Indexed: 10/25/2022]
Abstract
The testicular position after conventional inguinal orchidopexy for canalicular, "peeping" and redo undescended testes may not be satisfactory despite retroperitoneal dissection. Laparoscopy allows extensive mobilization of testicular vessels to gain additional length. We review our experience of using laparoscopic mobilization of testicular vessels (LMTV) in orchidopexy for these difficult undescended testes. From January 2003 to May 2004, LMTV was performed in 18 boys. The testicular vessels were mobilized from just proximal to the internal inguinal ring to the level of caecum and sigmoid colon respectively. Fifteen patients had clinically impalpable testes. Diagnostic laparoscopy revealed 13 "peeping" and 2 canalicular testes. LMTV was performed together with inguinal orchidopexy. There were three cases of redo orchidopexies because of unfavourable testicular position after previous surgery. LMTV was performed following inguinal dissection. The median follow-up period is 11.7 months. Sixteen testes are located at the base of scrotum, and two at mid-scrotum. The size is normal in 17 testes, whereas 1 testis is smaller than the contralateral one. LMTV is a safe and efficient adjunctive step in orchidopexy for impalpable and redo undescended testes.
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Abstract
We report synthesis of nanowires and nanoribbons of the charge-density-wave conductor NbSe(3) through direct reaction of Nb and Se powders. The transverse dimension of the obtained nanostructures, as identified with scanning/transmission electron microscopy, ranges from 20 to 700 nm. X-ray and selected area electron diffraction analyses indicate that these nanowires and nanoribbons are single crystalline. Four-probe resistivity measurements confirm the expected charge-density-wave transitions, and furthermore, we find significant enhancement in the depinning threshold fields, which we attribute to a confinement effect.
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Crystal-lattice coupling to the vortex-melting transition in YBa(2)Cu(3)O(7-delta). PHYSICAL REVIEW LETTERS 2003; 90:237002. [PMID: 12857281 DOI: 10.1103/physrevlett.90.237002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2002] [Indexed: 05/24/2023]
Abstract
Distinct discontinuities in the thermal expansion of the crystal lattice are observed at the melting transition of the vortex lattice in a naturally untwinned reversible YBa(2)Cu3O(7-delta) single crystal using high-resolution dilatometry. This coupling between the vortex transition and the crystal lattice demonstrates that the crystal lattice is more than a mere host for the vortices, and it is attributed to a strong pressure dependence of the superconducting transition temperature and thus to the condensation energy at the vortex-melting temperature.
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20
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Periodic and disordered structures in a modulated gas-driven granular layer. PHYSICAL REVIEW LETTERS 2003; 90:134301. [PMID: 12689292 DOI: 10.1103/physrevlett.90.134301] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2002] [Revised: 02/10/2003] [Indexed: 05/24/2023]
Abstract
Experiments with a thin gas-fluidized granular layer revealed a sequence of well-defined transitions as the amplitude and frequency of the gas flow modulation are varied. The observed patterns include subharmonic squares and stripes, quasiperiodic and disordered structures. The wavelength of subharmonic patterns increases with the mean flow rate and decreases with the modulation frequency.
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Abstract
The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV and Delta(2)=7.1 meV at 4.2 K. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multiband system. Temperature evolution of the tunneling spectra follows the BCS scenario [Phys. Rev. Lett. 3, 552 (1959)]] with both gaps vanishing at the bulk T(c). The data confirm the importance of Fermi-surface sheet dependent superconductivity in MgB2 proposed in the multigap model by Liu et al. [Phys. Rev. Lett. 87, 087005 (2001)]].
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Synthesis, ESR studies, band electronic structure, and superconductivity in the (BEDT-TTF)2M(NCS)2 system (M = copper, silver, gold, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) [Erratum to document cited in CA108(14):120961j]. Inorg Chem 2002. [DOI: 10.1021/ic00289a036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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23
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The first ambient pressure organic superconductor containing oxygen in the donor molecule, .beta.m-(BEDO-TTF)3Cu2(NCS)3, Tc = 1.06 K. Inorg Chem 2002. [DOI: 10.1021/ic00334a003] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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24
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Synthesis, ESR studies, band electronic structure, and superconductivity in the (BEDT-TTF)2M(NCS)2 system (M = copper, silver, gold, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene). Inorg Chem 2002. [DOI: 10.1021/ic00279a001] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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25
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A new ambient-pressure organic superconductor, .kappa.-(ET)2Cu[N(CN)2]Br, with the highest transition temperature yet observed (inductive onset Tc = 11.6 K, resistive onset = 12.5 K). Inorg Chem 2002. [DOI: 10.1021/ic00339a004] [Citation(s) in RCA: 567] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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26
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Superconductivity at 91 K in the magnetic oxide holmium barium copper oxide, HoBa2Cu3O6+x. Inorg Chem 2002. [DOI: 10.1021/ic00258a004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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27
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Medium Effects, Isotope Rate Factors, and the Mechanism of the Reaction of Diphenyldiazomethane with Carboxylic Acids in the Solvents Ethanol and Toluene. J Am Chem Soc 2002. [DOI: 10.1021/ja01078a031] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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28
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Scanning tunneling spectroscopy in MgB2. PHYSICAL REVIEW LETTERS 2001; 86:4374-4377. [PMID: 11328178 DOI: 10.1103/physrevlett.86.4374] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2001] [Indexed: 05/23/2023]
Abstract
We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39 K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter gamma. The value of the superconducting gap is 5 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair breaking as seen in the conductance spectra in fields up to 6 T.
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An unusual phase transition to a second liquid vortex phase in the superconductor YBa2Cu3O7. Nature 2001; 411:448-51. [PMID: 11373670 DOI: 10.1038/35078016] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A magnetic field penetrates a superconductor through an array of 'vortices', each of which carries one quantum of flux that is surrounded by a circulating supercurrent. In this vortex state, the resistivity is determined by the dynamical properties of the vortex 'matter'. For the high-temperature copper oxide superconductors (see ref.1 for a theoretical review), the vortex phase can be a 'solid', in which the vortices are pinned, but the solid can 'melt' into a 'liquid' phase, in which their mobility gives rise to a finite resistance. (This melting phenomenon is also believed to occur in conventional superconductors, but in an experimentally inaccessible part of the phase diagram.) For the case of YBa2Cu3O7, there are indications of the existence of a critical point, at which the character of the melting changes. But neither the thermodynamic nature of the melting, nor the phase diagram in the vicinity of the critical point, has been well established. Here we report measurements of specific heat and magnetization that determine the phase diagram in this material to 26 T, well above the critical point. Our results reveal the presence of a reversible second-order transition above the critical point. An unusual feature of this transition-namely, that the high-temperature phase is the less symmetric in the sense of the Landau theory-is in accord with theoretical predictions of a transition to a second vortex-liquid phase.
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Intraoperative pancreatoscopy for pancreatic duct stone debris distal to the common channel in choledochal cyst. J Pediatr Surg 2000; 35:1528-9. [PMID: 11051170 DOI: 10.1053/jpsu.16433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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31
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Experimental evidence for the vortex glass phase in untwinned, proton irradiated YBa2Cu3O7-delta. PHYSICAL REVIEW LETTERS 2000; 84:5852-5855. [PMID: 10991071 DOI: 10.1103/physrevlett.84.5852] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/1998] [Indexed: 05/23/2023]
Abstract
We report on magnetoresistance measurements of the effects of 9 MeV proton irradiation on a clean, untwinned single crystal of YBa2Cu3O7-delta. For the first time, evidence for a vortex glass transition is detected in an untwinned single crystal of YBa2Cu3O7-delta with induced pointlike disorder, in which the first order vortex melting transition is completely suppressed after proton irradiation. Our results suggest that a sufficiently high pinning disorder is required in order for the vortex glass phase to be observed.
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Vortex flow and transverse flux screening at the bose glass transition. PHYSICAL REVIEW LETTERS 2000; 84:4974-4977. [PMID: 10990845 DOI: 10.1103/physrevlett.84.4974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/1999] [Indexed: 05/23/2023]
Abstract
We study the vortex phase diagram in untwinned YBCO crystals with columnar defects. These randomly distributed defects are expected to induce a "Bose glass" phase of localized vortices exhibiting a vanishing resistance and Meissner effect for magnetic fields H( perpendicular) transverse to the columns. We directly observe the transverse Meissner effect using a Hall probe array. As predicted, the Meissner state breaks down at temperatures T(s) that decrease linearly as H( perpendicular) increases. However, T(s) lies far below the conventional melting temperature T(m) determined by a vanishing resistivity, suggesting a regime where vortices are effectively localized even when rotated off the columnar defects.
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Critical points in heavy ion irradiated untwinned YBa(2)Cu3O(7-delta) crystals. PHYSICAL REVIEW LETTERS 2000; 84:3706-3709. [PMID: 11019182 DOI: 10.1103/physrevlett.84.3706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/1999] [Indexed: 05/23/2023]
Abstract
The critical points in untwinned YBa(2)Cu(3)O(7-delta) crystals with dilute columnar defects are investigated. We find a convergence of a first order vortex melting line with an irreversibility line associated with the onset of the Bose glass critical regime at the lower critical point. In addition, we find that columnar defects raise the upper critical point, implying that vortex line meandering is a basic feature controlling its position.
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Abstract
A case of colonic atresia (CA) and aganglionosis is presented, which is probably the tenth in the English literature. The boy presented on day 3 of life with delayed passage of meconium, milk intolerance, and progressive abdominal distension. A barium enema study was complicated by barium peritonitis. Emergency peritoneal lavage was done and the intestinal obstruction was relieved by a proximal defunctioning ileostomy; type III CA (Grosfeld classification) was identified. The proximal atretic end was the blind-ending caecum and the distal atretic end commenced in the splenic area as a microcolon extending to the pelvis and replacing the normal colon. Total colonic aganglionosis (TCA) was confirmed by biopsies. This is the first case in the literature of TCA with CA documented before any attempts at colonic resection and anastomosis were made. This association highlights the recommendation for biopsy of the micro-colon and rectum when Type III CA (Grosfeld classification) is encountered in a newborn. The infant underwent a cholecystectomy and Duhamel-Martin operation at 14 months that was complicated by abdominal wound dehiscence; the ileostomy was closed at 22 months of age.
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Abstract
A total of 173 boys aged 10 to 179 months with previous unilateral inguinal herniotomy were called back for follow-up. Clinical and ultrasound examinations of the scrotum were performed. The interval between operation and follow-up was 6 to 123 months (mean 31.68 months). One boy (0.58%) had a more than 50% and 10 (5.8%) had a more than 25% decrease in testicular volume on the operated side when compared with the non-operated side.
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Should we perform early operations in children who have reducible inguinal hernia? Hong Kong Med J 1998; 4:337. [PMID: 11830695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023] Open
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Abstract
The influence of process conditions (substrate loading rate and detachment force) on the structure of biofilms grown on basalt particles in a Biofilm Airlift Suspension (BAS) reactor was studied. The structure of the biofilms (density, surface shape, and thickness) and microbial characteristics (biomass yield) were investigated at substrate loading rates of 5, 10, 15, and 20 kg COD/m3. day with basalt concentrations of 60 g/L, 150 g/L, and 250 g/L. The basalt concentration determines the number of biofilm particles in steady state, which is the main determining factor for the biofilm detachment in these systems. In total, 12 experimental runs were performed. A high biofilm density (up to 67 g/L) and a high biomass concentration was observed at high detachment forces. The higher biomass content is associated with a lower biomass substrate loading rate and therefore with a lower biomass yield (from 0.4 down to 0.12 gbiomass/gacetate). Contrary to general beliefs, the observed biomass detachment decreased with increasing detachment force. In addition, smoother (fewer protuberances), denser and thinner compact biofilms were obtained when the biomass surface production rate decreased and/or the detachment force increased. These observations confirmed a hypothesis, postulated earlier by Van Loosdrecht et al. (1995b), that the balance between biofilm substrate surface loading (proportional to biomass surface production rate, when biomass yield is constant) and detachment force determines the biofilm structure. When detachment forces are relatively high only a patchy biofilm will develop, whereas at low detachment forces, the biofilm becomes highly heterogeneous with many pores and protuberances. With the right balance, smooth, dense and stable biofilms can be obtained. Copyright 1998 John Wiley & Sons, Inc.
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Vortex localization in single crystals of Tl2Ba2CuO6+ delta with columnar defects. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:R12725-R12728. [PMID: 9985229 DOI: 10.1103/physrevb.54.r12725] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Thermodynamic evidence for a flux line lattice melting transition in YBa2 Cu3O7- delta. PHYSICAL REVIEW LETTERS 1996; 76:4809-4812. [PMID: 10061386 DOI: 10.1103/physrevlett.76.4809] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Vortex shear modulus and lattice melting in twin boundary channels of YBa2Cu3O7- delta. PHYSICAL REVIEW LETTERS 1996; 76:4596-4599. [PMID: 10061331 DOI: 10.1103/physrevlett.76.4596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Amplification of the c-axis vortex correlation by twin-boundary pinning at the vortex liquid-solid phase transition. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 53:R8895-R8897. [PMID: 9982479 DOI: 10.1103/physrevb.53.r8895] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Order of the fundamental vortex transformation in YBa2Cu3O7- delta. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 51:9148-9154. [PMID: 9977556 DOI: 10.1103/physrevb.51.9148] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Vortex liquid state in an electron irradiated untwinned YBa2Cu3O7- delta crystal. PHYSICAL REVIEW LETTERS 1995; 74:1210-1213. [PMID: 10058962 DOI: 10.1103/physrevlett.74.1210] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Peak effect as a precursor to vortex lattice melting in single crystal YBa2Cu3O7- delta. PHYSICAL REVIEW LETTERS 1994; 73:2614-2617. [PMID: 10057105 DOI: 10.1103/physrevlett.73.2614] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Suppression of the first order vortex melting transition by intrinsic pinning in YBa2Cu3O7- delta. PHYSICAL REVIEW LETTERS 1994; 72:1088-1091. [PMID: 10056614 DOI: 10.1103/physrevlett.72.1088] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Vortex liquid disorder and the first order melting transition in YBa2Cu3O7- delta. PHYSICAL REVIEW LETTERS 1994; 72:1092-1095. [PMID: 10056615 DOI: 10.1103/physrevlett.72.1092] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Anisotropy and Lorentz-force dependence of twin-boundary pinning and its effect on flux-lattice melting in single-crystal YBa2Cu3O7- delta. PHYSICAL REVIEW. B, CONDENSED MATTER 1993; 47:14448-14461. [PMID: 10005796 DOI: 10.1103/physrevb.47.14448] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Effect of gold impurities on the superconducting fluctuations and the upper critical field of YBa2Cu3O7- delta single crystals. PHYSICAL REVIEW. B, CONDENSED MATTER 1993; 47:12369-12372. [PMID: 10005429 DOI: 10.1103/physrevb.47.12369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Vortex lattice melting in untwinned and twinned single crystals of YBa2Cu3O7- delta. PHYSICAL REVIEW LETTERS 1992; 69:3370-3373. [PMID: 10046801 DOI: 10.1103/physrevlett.69.3370] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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