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Alagoz HS, Živković I, Chow KH, Jung J. Non-percolating small metallic clusters and sharp suppression of metallicity in RE 0.55Sr 0.45Mn 1−xRu xO 3manganites. Phys Chem Chem Phys 2018; 20:2431-2437. [DOI: 10.1039/c7cp02423a] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The origin of the anomalous sharp phase transition from a ferromagnetic metal into a ferromagnetic insulator has been investigated in ruthenium (Ru)-doped RE0.55Sr0.45Mn1−xRuxO3(0 ≤x≤ 0.25) manganites (RESRMO) with RE(A-site) = Sm, Eu and Gd.
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Affiliation(s)
- H. S. Alagoz
- Department of Physics
- University of Alberta
- Edmonton
- Canada
| | - I. Živković
- LQM, Institute of Physics
- Ecolé Polytechnique Fédérale de Lausanne
- CH-1015 Lausanne
- Switzerland
| | - K. H. Chow
- Department of Physics
- University of Alberta
- Edmonton
- Canada
| | - J. Jung
- Department of Physics
- University of Alberta
- Edmonton
- Canada
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2
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Jeon J, Jung J, Chow KH. Electron beam induced tunneling magnetoresistance in spatially confined manganite bridges. Nanoscale 2017; 9:19304-19309. [PMID: 29192923 DOI: 10.1039/c7nr04232a] [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: 06/07/2023]
Abstract
Certain manganites exhibit rich and technologically relevant transport properties which can often be attributed to the existence and changes of the intrinsic electronic phase competition within these materials. Here we demonstrate that a scanning electron beam can be used to artificially create domain configurations within La0.3Pr0.4Ca0.3MnO3 thin film microbridges that results in novel magneto-transport effects. In particular, the electron beam preferentially produces insulating regions within the narrow film and can be used to create a configuration consisting of ferromagnetic metallic domains separated by a potential barrier. This arrangement enables the spin-dependent tunneling of charge carriers and can produce large switching tunneling magnetoresistance effects which were initially absent. Hence, this work describes a new and potentially powerful method for engineering the electronic phase domains in manganites to generate functional transport properties that are important for spintronic devices.
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Affiliation(s)
- J Jeon
- Department of Physics, University of Alberta, Edmonton T6G 2E1, Canada.
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Ho PL, Cheung YY, Wang Y, Lo WU, Lai ELY, Chow KH, Cheng VCC. Characterization of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae from a healthcare region in Hong Kong. Eur J Clin Microbiol Infect Dis 2016; 35:379-85. [PMID: 26740321 DOI: 10.1007/s10096-015-2550-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 12/07/2015] [Indexed: 12/21/2022]
Abstract
Carbapenem-resistant Enterobacteriaceae represents a major public health issue. This study investigated the clonality and resistance mechanisms of 92 carbapenem-resistant E. coli (n = 21) and K. pneumoniae (n = 71) isolates collected consecutively from clinical specimens and patients at high risk of carriage between 2010 and 2012 in a healthcare region in Hong Kong. Combined disk tests (CDTs) and the Carba NP test were used for phenotypic detection of carbapenemases. PCR assays were used to detect carbapenemase genes. All isolates were intermediate or resistant to at least one carbapenem. Nine (9.8 %) isolates were genotypic carbapenemase producers and included six K. pneumoniae (one ST1306/bla IMP-4, one ST889/bla IMP-4, two ST11/bla KPC-2, one ST258/bla KPC-2, one ST483/bla NDM-1) and three E. coli (one ST131/bla IMP-4, two ST744/ bla NDM-1) isolates. All nine isolates carrying carbapenemase genes could be detected by the CDTs and the Carba NP test. PCR identified bla CTX-M and bla AmpC alone or in combination in 77.8 % (7/9) and 96.4 % (80/83) of the carbapenemase-producers and non-producers, respectively. Porin loss was detected in 22.2 % (2/9) and 59.0 % (49/83) of the carbapenemase-producers and non-producers, respectively. Overall, the E. coli clones were diverse (14 different STs), but 36.6 % (26/71) of the K. pneumoniae isolates belonged to ST11. In conclusion, the prevalence of carbapenemases among carbapenem-nonsusceptible E. coli and K. pneumoniae remained low in Hong Kong. Porin loss combined with AmpC and/or CTX-M type ESBL was the major mechanism of carbapenem resistance in the study population.
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Affiliation(s)
- P L Ho
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China.
| | - Y Y Cheung
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
| | - Y Wang
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
| | - W U Lo
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
| | - E L Y Lai
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
| | - K H Chow
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
| | - V C C Cheng
- Department of Microbiology, Queen Mary Hospital, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, SAR, People's Republic of China
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So BKL, Chu CCY, Ho PL, Chow KH, Leung JNS, Lee IYM, Lin CK, Lee CK. Evaluation of two chlorhexidine - alcohol-based skin disinfectants in blood donation setting. Vox Sang 2013; 106:316-21. [DOI: 10.1111/vox.12107] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- B. K. L. So
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
| | - C. C. Y. Chu
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
| | - P. L. Ho
- Carol Yu Center for Infection and Department of Microbiology; the University of Hong Kong; Hong Kong SAR China
| | - K. H. Chow
- Carol Yu Center for Infection and Department of Microbiology; the University of Hong Kong; Hong Kong SAR China
| | - J. N. S. Leung
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
| | - I. Y. M. Lee
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
| | - C. K. Lin
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
| | - C. K. Lee
- Hong Kong Red Cross Blood Transfusion Service; Hong Kong SAR China
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Prokscha T, Chow KH, Stilp E, Suter A, Luetkens H, Morenzoni E, Nieuwenhuys GJ, Salman Z, Scheuermann R. Photo-induced persistent inversion of germanium in a 200-nm-deep surface region. Sci Rep 2013; 3:2569. [PMID: 23995307 PMCID: PMC3759057 DOI: 10.1038/srep02569] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 08/19/2013] [Indexed: 11/17/2022] Open
Abstract
The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.
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Affiliation(s)
- T Prokscha
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, Villigen PSI, Switzerland.
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Ho PL, Chan J, Lo WU, Law PY, Li Z, Lai EL, Chow KH. Dissemination of plasmid-mediated fosfomycin resistance fosA3 among multidrug-resistant Escherichia coli from livestock and other animals. J Appl Microbiol 2012; 114:695-702. [PMID: 23216653 DOI: 10.1111/jam.12099] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Revised: 11/29/2012] [Accepted: 12/04/2012] [Indexed: 11/27/2022]
Abstract
AIMS To investigate plasmid-mediated fosfomycin resistance related to fosA3 in Escherichia coli isolates collected from different animals in Hong Kong, China, 2008-2010. METHODS AND RESULTS In total, 2106 faecal specimens from 210 cattle, 214 pigs, 460 chickens, 398 stray cats, 368 stray dogs and 456 wild rodents were cultured. The faecal colonization rates of fosfomycin-resistant E. coli were as follows: 11.2% in pigs, 8.6% in cattle, 7.3% in chickens, 2.4% in dogs, 0.8% in cats and 1.5% in rodents. The cultures yielded 1693 isolates of which 831 were extended-spectrum β-lactamases (ESBL) producers. Fosfomycin-resistant isolates were more likely than fosfomycin-susceptible isolates to be producers of ESBL and to have resistance to chloramphenicol, ciprofloxacin, cotrimoxazole, gentamicin and tetracycline. Of the 101 fosfomycin-resistant isolates, 97 (96.0%) isolates were fosA3 positive and 94 (93.1%) were bla(CTX) (-M) positive. PCR mapping showed that the fosA3-containing regions were flanked by IS26, both upstream and downstream in 81 (83.5%) isolates, and by an upstream bla(CTX-M-14) -containing transposon-like structure (ΔISEcp1-bla(CTX-M-14) -ΔIS903 or ISEcp1-IS10 -bla(CTX-M-14) -ΔIS903) and a downstream IS26 in 14 (14.4%) isolates. For the remaining two isolates, fosA3 was flanked by a downstream IS26 but the upstream part cannot be defined. In a random subset of 18 isolates, fosA3 was carried on transferable plasmids with sizes of 50-200 kb and the following replicons: F2:A-B- (n = 3), F16:A1:B- (n = 2), F24:A-B- (n = 1), N (n = 1), B/O (n = 1) and untypeable (n = 3). SIGNIFICANCE AND IMPACT OF THE STUDY This study demonstrates the emergence of fosA3-mediated fosfomycin resistance among multidrug-resistant E. coli isolates from various animals. IS26 transposon-like structures might be the main vehicles for dissemination of fosA3.
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Affiliation(s)
- P L Ho
- Department of Microbiology, University of Hong Kong, Pokfulam, Hong Kong, China.
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Salman Z, Ofer O, Radovic M, Hao H, Ben Shalom M, Chow KH, Dagan Y, Hossain MD, Levy CDP, Macfarlane WA, Morris GM, Patthey L, Pearson MR, Saadaoui H, Schmitt T, Wang D, Kiefl RF. Nature of weak magnetism in SrTiO3/LaAlO3 multilayers. Phys Rev Lett 2012; 109:257207. [PMID: 23368496 DOI: 10.1103/physrevlett.109.257207] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Revised: 09/20/2012] [Indexed: 06/01/2023]
Abstract
We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.
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Affiliation(s)
- Z Salman
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
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Ho PL, Chan J, Lo WU, Law PY, Chow KH. Plasmid-mediated fosfomycin resistance in Escherichia coli isolated from pig. Vet Microbiol 2012; 162:964-967. [PMID: 23078751 DOI: 10.1016/j.vetmic.2012.09.023] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 09/21/2012] [Accepted: 09/22/2012] [Indexed: 10/27/2022]
Abstract
Previous studies have reported plasmid-mediated fosA3 among Escherichia coli originating from human and companion animals. In this study, the plasmid, designated pHK23a originating from a multidrug-resistant E. coli isolate recovered from a slaughter pig in December 2008 in Hong Kong, China was sequenced. In conjugation, the plasmid readily transferred to E. coli J53 at high frequencies. It belongs to the narrow host range IncFII incompatibility group and is 73,607 bp in length. Sequence alignment showed that pHK23a has a 59.1 kb backbone which shares high homology with the prototype R100 plasmid and a 14.5 kb variable region. The variable region includes three genes mediating antimicrobial resistance (fosA3, Δbla(TEM-1), bla(CTX-M-3)), ten mobile genetic elements (four copies of IS26, insA, ΔinsB, ΔTn2, IS1, ΔISEcp1, Δintl1), the tir transfer inhibition protein, the pemI/pemK addiction system and eight ORFs of unknown functions (orf1, orf2, Δorf3, orf20, orf23, orf24, ycdA and ycdB). The three resistance genes were organized in a novel IS26-composite transposon-like structure. In conclusion, this is the first report of fosA3 containing plasmid in an isolate of pig origin. Since IncFII plasmids spread efficiently in Enterobacteriaceae, the detection of fosA3 with bla(CTX-M) is worrisome and might become a public health concern.
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Affiliation(s)
- P L Ho
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China; Carol Yu Center for Infection, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China.
| | - Jane Chan
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China
| | - W U Lo
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China
| | - Pierra Y Law
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China
| | - K H Chow
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, China
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Abstract
The outcome for patients with the most common primary brain tumor, glioblastoma multiforme (GBM), remains poor. Several immunotherapeutic approaches are actively being pursued including antibodies and cell-based therapies. While the blood-brain barrier protects brain tumor cells from therapeutic antibodies, immune cells have the ability to traverse the blood-brain barrier and migrate into GBM tumors to exert their therapeutic function. Results of Phase I clinical studies with vaccines to induce GBM-specific T cells are encouraging and Phase II clinical trials are in progress. Nonvaccine-based cell therapy for GBM has been actively explored over the last four decades. Here we will review past clinical experience with adoptive cell therapies for GBM and summarize current strategies on how to improve these approaches.
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Affiliation(s)
- K H Chow
- Texas Children's Cancer Center, Baylor College of Medicine, Houston, TX 77030, USA.
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Ho PL, Lo WU, Wong RCW, Yeung MK, Chow KH, Que TL, Tong AHY, Bao JYJ, Lok S, Wong SSY. Complete sequencing of the FII plasmid pHK01, encoding CTX-M-14, and molecular analysis of its variants among Escherichia coli from Hong Kong. J Antimicrob Chemother 2011; 66:752-6. [PMID: 21393220 DOI: 10.1093/jac/dkr010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
OBJECTIVES We characterized plasmids encoding CTX-M-14 β-lactamase originating from Escherichia coli isolates recovered from patients with uncomplicated cystitis or individuals with faecal colonization in Hong Kong from 2002 to 2004. METHODS Plasmids carrying CTX-M-14 were studied by conjugation, replicon typing, S1 nuclease-PFGE and plasmid PCR-restriction fragment length polymorphism (RFLP). The complete sequence of pHK01, a 70 kb plasmid encoding CTX-M-14 from an E. coli strain, was determined and the results compared with reference plasmids and aligned with GenBank data. RESULTS The blaCTX-M-14 plasmids could be transferred in 23 of 44 E. coli strains tested. Among the 23 transconjugants, the replicon types of the CTX-M-14-encoding plasmid were FII (n=13), I1-Iγ (n=4), F1B (n=2), FII and I1-Iγ (n=1), K (80 kb, n=1) and undetermined (n=2). Plasmid pHK01 (FII replicon) shares a high degree of homology with R100 except mainly for a 11 kb variable region containing blaCTX-M-14 (with an upstream ISEcp1 and a downstream truncated IS903), an iron transport system, an outer membrane protein (malB, maltoporin) and a putative toxin-antitoxin plasmid stability system (yacABC). It was highly related to blaCTX-M-14 (pKF3-70) and blaCTX-M-24 (pEG356) plasmids reported from mainland China in 2006 and Vietnam in 2007, respectively. Subtyping by a plasmid PCR-RFLP scheme showed that 10 of the 13 FII plasmids originating from isolates collected by multiple laboratories exhibited either identical or highly similar profiles. CONCLUSIONS This study showed that narrow host-range FII plasmids play important roles in the dissemination of CTX-M-14. FII plasmids closely related to pHK01 have disseminated widely in the Hong Kong community.
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Affiliation(s)
- P L Ho
- Department of Microbiology, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong, People's Republic of China.
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Ho PL, Chow KH, Lai EL, Lo WU, Yeung MK, Chan J, Chan PY, Yuen KY. Extensive dissemination of CTX-M-producing Escherichia coli with multidrug resistance to 'critically important' antibiotics among food animals in Hong Kong, 2008-10. J Antimicrob Chemother 2011; 66:765-8. [DOI: 10.1093/jac/dkq539] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Ho PL, Cheng VC, Chow KH. Decreasing prevalence of levofloxacin-resistant Streptococcus pneumoniae in Hong Kong, 2001 to 2007. J Antimicrob Chemother 2009; 63:836-8. [DOI: 10.1093/jac/dkp038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Abstract
We have determined locations for the donor and acceptor levels of muonium in six semiconductor materials (Si, Ge, GaAs, GaP, ZnSe, and 6H-SiC) as a test of defect-level pinning for hydrogen. Within theoretical band alignments, our results indicate a common energy for the equilibrium charge-transition level Mu(+/-) to within experimental uncertainties. However, this is nearly 0.5 eV higher than the energy at which the equivalent level for hydrogen was predicted to be pinned. Corrections for zero-point energy account for only about 10% of this difference. We also report experimental results for the (negative-U) difference between donor and acceptor levels for Mu to be compared with calculated values for H impurities in the same materials.
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Affiliation(s)
- R L Lichti
- Department of Physics, Texas Tech University, Lubbock, Texas 79409-1051, USA.
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Mansour AI, Salman Z, Chow KH, Fan I, King PJC, Hitti B, Jung J, Cottrell SP. Dynamics and reactivity of positively charged muonium in heavily doped Si:B and comparisons with hydrogen. Phys Rev Lett 2008; 100:257602. [PMID: 18643703 DOI: 10.1103/physrevlett.100.257602] [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: 10/08/2007] [Indexed: 05/26/2023]
Abstract
The detailed dynamics of the positively charged muonium (Mu+) in heavily doped p-type Si:B is reported. Below 200 K, Mu+ is static and isolated, and is located in a stretched Si-Si bond. Above approximately 200 K, Mu+ diffuses incoherently. At temperatures higher than 300 K, the Mu+-B- complex is formed while above 520 K, it starts to dissociate. There is significant enhancement of the diffusion of Mu+ in Si compared to H+ and D+-this is attributed to its smaller mass.
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Affiliation(s)
- A I Mansour
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2G7.
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Xu M, Hossain MD, Saadaoui H, Parolin TJ, Chow KH, Keeler TA, Kiefl RF, Morris GD, Salman Z, Song Q, Wang D, MacFarlane WA. Proximal magnetometry in thin films using betaNMR. J Magn Reson 2008; 191:47-55. [PMID: 18162424 DOI: 10.1016/j.jmr.2007.11.022] [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] [Received: 07/20/2007] [Revised: 11/22/2007] [Accepted: 11/27/2007] [Indexed: 05/25/2023]
Abstract
Low energy ion implantation of hyperpolarized radioactive magnetic resonance probes allows the NMR study of thin film heterostructures by enabling depth-resolved measurements on a nanometer lengthscale. By stopping the probe ions in a layer adjacent to a layer of interest, it is possible to study magnetic fields proximally. Here we show that, in the simplest case of a uniformly magnetized layer, this yields an unperturbed in situ frequency reference. We also discuss demagnetization contributions to measured shifts for this case. With a simple illustrative calculation, we show how a nonuniformly magnetized layer causes a strongly depth-dependent line broadening in an adjacent layer. We then give some experimental examples of resonance line broadening in heterostructures.
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Affiliation(s)
- M Xu
- TRIUMF, 4004 Wesbrook Mall, Vancouver, Canada V6T 2A3
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Mukai K, Ikedo Y, Nozaki H, Sugiyama J, Nishiyama K, Andreica D, Amato A, Russo PL, Ansaldo EJ, Brewer JH, Chow KH, Ariyoshi K, Ohzuku T. Magnetic phase diagram of layered cobalt dioxide LixCoO2. Phys Rev Lett 2007; 99:087601. [PMID: 17930981 DOI: 10.1103/physrevlett.99.087601] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2006] [Indexed: 05/25/2023]
Abstract
The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.
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Affiliation(s)
- K Mukai
- Toyota Central Research and Development Labs Inc, Nagakute, Aichi, Japan
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Salman Z, Chow KH, Miller RI, Morello A, Parolin TJ, Hossain MD, Keeler TA, Levy CDP, MacFarlane WA, Morris GD, Saadaoui H, Wang D, Sessoli R, Condorelli GG, Kiefl RF. Local magnetic properties of a monolayer of Mn12 single molecule magnets. Nano Lett 2007; 7:1551-5. [PMID: 17488049 DOI: 10.1021/nl070366a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled beta-detected nuclear magnetic resonance. A low-energy beam of spin-polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance line width varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the line width indicates that the magnetic properties of the Mn12 moments in this low-dimensional configuration differ from bulk Mn12.
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Affiliation(s)
- Z Salman
- Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU, UK.
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Ho PL, Poon WWN, Loke SL, Leung MST, Chow KH, Wong RCW, Yip KS, Lai EL, Tsang KWT. Community emergence of CTX-M type extended-spectrum β-lactamases among urinary Escherichia coli from women. J Antimicrob Chemother 2007; 60:140-4. [PMID: 17496058 DOI: 10.1093/jac/dkm144] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [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: 11/14/2022] Open
Abstract
OBJECTIVES To conduct a territory-wide study of extended-spectrum beta-lactamases (ESBLs) among community isolates of urinary Escherichia coli from women in Hong Kong. METHODS Up to 50 consecutive single-patient E. coli isolates, collected from 13 laboratories in 2004, were studied. The ESBLs were characterized by PCR sequencing using specific primers. The epidemiological relationship of the isolates was studied by PFGE and phylogenetic group PCRs. RESULTS Forty-two ESBL producers were found among 600 consecutive isolates tested. The ESBL prevalence was 7.3% (15/205) for women aged 18-35 years, 5% (11/219) for women aged 36-50 years, 6.3% (4/63) for women aged 51-64 years and 10.6% (12/113) for women aged >or=65 years (P=0.3). The ESBL-producing isolates were often multidrug-resistant and CTX-M-14 was found in 37 isolates, CTX-M-15 in 3 isolates and CTX-M-3 in 2 isolates. PFGE revealed no significant clusters among the ESBL producers. Overall, CTX-M-14 producers were significantly more likely to belong to group D than non-ESBL producers [18/37 (48.6%) versus 13/57 (22.8%), P=0.009]. However, 7 of 13 (53.8%) CTX-M-14 producers from women aged 18-35 years represented phylogenetic group B2, compared with 7 of 24 (29.2%) for women of all other ages (P=0.1). CONCLUSIONS The study documented the community emergence of CTX-M as the predominant ESBL type among urinary isolates from women. The spread of CTX-M enzymes among isolates from young women is concerning and deserves close monitoring.
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Affiliation(s)
- P L Ho
- Division of Infectious Diseases, Department of Microbiology and Centre of Infection, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region, China.
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Salman Z, Wang D, Chow KH, Hossain MD, Kreitzman SR, Keeler TA, Levy CDP, MacFarlane WA, Miller RI, Morris GD, Parolin TJ, Saadaoui H, Smadella M, Kiefl RF. Magnetic-field effects on the size of vortices below the surface of NbSe2 detected using low energy beta-NMR. Phys Rev Lett 2007; 98:167001. [PMID: 17501451 DOI: 10.1103/physrevlett.98.167001] [Citation(s) in RCA: 3] [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: 06/14/2006] [Indexed: 05/15/2023]
Abstract
A low energy radioactive beam of polarized 8Li has been used to observe the vortex lattice near the surface of superconducting NbSe2. The inhomogeneous magnetic-field distribution associated with the vortex lattice was measured using depth-resolved beta-detected NMR. Below Tc, one observes the characteristic line shape for a triangular vortex lattice which depends on the magnetic penetration depth and vortex core radius. The size of the vortex core varies strongly with the magnetic field. In particular, in a low field of 10.8 mT, the core radius is much larger than the coherence length. The possible origin of these giant vortices is discussed.
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Affiliation(s)
- Z Salman
- TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, Canada
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Parolin TJ, Salman Z, Chakhalian J, Song Q, Chow KH, Hossain MD, Keeler TA, Kiefl RF, Kreitzman SR, Levy CDP, Miller RI, Morris GD, Pearson MR, Saadaoui H, Wang D, MacFarlane WA. beta-NMR of isolated lithium in nearly ferromagnetic palladium. Phys Rev Lett 2007; 98:047601. [PMID: 17358812 DOI: 10.1103/physrevlett.98.047601] [Citation(s) in RCA: 2] [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: 08/23/2006] [Indexed: 05/14/2023]
Abstract
The temperature dependence of the frequency shift and spin-lattice relaxation rate of isolated, nonmagnetic (8)Li impurities implanted in a nearly ferromagnetic host (Pd) are measured by means of beta-detected nuclear magnetic resonance (beta-NMR). The shift is negative, very large, and increases monotonically with decreasing T in proportion to the bulk susceptibility of Pd for T > T* approximately 100 K. Below T*, an additional shift occurs which we attribute to the response of Pd to the defect. The relaxation rate is much slower than expected for the large shift and is linear with T below T*, showing no sign of additional relaxation mechanisms associated with the defect.
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Affiliation(s)
- T J Parolin
- Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
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Duan RS, Sit THC, Wong SSY, Wong RCW, Chow KH, Mak GC, Yam WC, Ng LT, Yuen KY, Ho PL. Escherichia coli Producing CTX-M β-Lactamases in Food Animals in Hong Kong. Microb Drug Resist 2006; 12:145-8. [PMID: 16922633 DOI: 10.1089/mdr.2006.12.145] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [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: 11/12/2022] Open
Abstract
A study was conducted to evaluate the occurrence of extended-spectrum beta-lactamases (ESBLs)-producing Escherichia coli from fecal samples of healthy food animals in Hong Kong. Rectal or cloacal swabs were obtained from cattle, pigs, chicken, ducks, geese, and pigeons in slaughterhouses or wholesale markets over a 5- month period in 2002. Antibiotic-containing medium was used for selective isolation of potentially ESBL-producing E. coli. Of 734 samples analyzed, six (2%) from pigs, three (3.1%) from cattle, and one (3%) from pigeons had E. coli strains with the ESBL phenotype. The ESBL content for the 10 isolates include CTXM- 3 (n = 4), CTX-M-13 (n = 3), CTX-M-14 (n = 2), and CTX-M-24 (n = 1). In five isolates, the bla (CTX-M) gene was encoded on transferable plasmids (60 or 90 kb), and the gene was found to transfer to E. coli (J53 or JP995) with frequencies of 10(7) to 10(3) per donor cells. The ten isolates had five distinct pulsotypes with some clonal spread. However, the isolates from the different kinds of animals were not clonally related. These findings imply that bacteria of animal origins may serve as reservoirs of some ESBL genes.
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Affiliation(s)
- R S Duan
- Division of Infectious Diseases, Department of Microbiology and Centre of Infection, University of Hong Kong, Hong Kong Special Administrative Region, China
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22
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Salman Z, Kiefl RF, Chow KH, Hossain MD, Keeler TA, Kreitzman SR, Levy CDP, Miller RI, Parolin TJ, Pearson MR, Saadaoui H, Schultz JD, Smadella M, Wang D, MacFarlane WA. Near-surface structural phase transition of SrTiO3 studied with zero-field beta-detected nuclear spin relaxation and resonance. Phys Rev Lett 2006; 96:147601. [PMID: 16712119 DOI: 10.1103/physrevlett.96.147601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Indexed: 05/09/2023]
Abstract
We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.
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Affiliation(s)
- Z Salman
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
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23
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Ho PL, Mak GC, Tse CWS, Chow KH, Cheung CHY. Invasive Haemophilus influenzae isolates with decreased levofloxacin susceptibility in Hong Kong. J Antimicrob Chemother 2005; 57:366. [PMID: 16387750 DOI: 10.1093/jac/dki466] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Schultz BE, Chow KH, Hitti B, Kiefl RF, Lichti RL, Cox SFJ. Local structure of isolated positively charged muonium as an analog for the hydrogen ion in p-type GaAs. Phys Rev Lett 2005; 95:086404. [PMID: 16196878 DOI: 10.1103/physrevlett.95.086404] [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: 05/15/2005] [Indexed: 05/04/2023]
Abstract
We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.
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Affiliation(s)
- B E Schultz
- Department of Physics, University of Alberta, Edmonton, Canada T6G 2J1
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Yam WC, Chan KH, Chow KH, Poon LLM, Lam HY, Yuen KY, Seto WH, Peiris JSM. Clinical evaluation of real-time PCR assays for rapid diagnosis of SARS coronavirus during outbreak and post-epidemic periods. J Clin Virol 2005; 33:19-24. [PMID: 15797361 PMCID: PMC7108323 DOI: 10.1016/j.jcv.2004.09.029] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2004] [Revised: 09/14/2004] [Accepted: 09/24/2004] [Indexed: 01/27/2023]
Abstract
BACKGROUND The protocols of WHO network laboratories facilitated development of rapid diagnosis for SARS coronavirus (CoV) using reverse transcription (RT)-PCR assays. However, several reports have shown that conventional and real-time PCR assays were very specific for SARS CoV but lack sensitivity depending on the assay, specimen, and time course of disease. OBJECTIVE To evaluate an automatic nucleic acid extraction system and two standardized real-time PCR assays for rapid diagnosis of SARS CoV during outbreak and post-epidemic periods in Hong Kong. STUDY DESIGN Specimens from clinically suspected SARS patients collected during outbreak and post-epidemic periods were tested by an automatic nucleic acid extraction system followed by our first generation conventional RT-PCR and two standardized real-time PCR assays (Artus GmbH, Germany and Roche Diagnostics, Germany). Paired serum samples were assayed for increasing titer against SARS CoV. RESULTS In the SARS epidemic, Artus and Roche PCR assays exhibited sensitivities of 87% and 85% for respiratory specimens (n = 64), 91% and 88% for stool (n = 44), and 82% for urine (n = 29). A specificity of 100% was exhibited by both PCR assays except Artus attained only a 92% specificity for stool. For post-epidemic period, no SARS CoV was identified among 56 respiratory specimens by all PCR assays. Inhibitors to PCR assays were detected at an average rate of 7-8% among 202 clinical specimens. CONCLUSION This study highlights the high throughput and performance of automatic RNA extraction in coordination with standardized real-time PCR assays suitable for large-scale routine diagnosis in case of future SARS epidemic. As no SARS CoV was detected among specimens collected during post-epidemic period, the positive predictive value of real-time PCR assays for detection of SARS CoV during low epidemic requires further evaluation.
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Affiliation(s)
- W C Yam
- Department of Microbiology, The University of Hong Kong, University Pathology Building, Queen Mary Hospital Compound, Pokfulam, Hong Kong SAR, PR China.
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26
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Ho PL, Ho AYM, Chow KH, Wong RCW, Duan RS, Ho WL, Mak GC, Tsang KW, Yam WC, Yuen KY. Occurrence and molecular analysis of extended-spectrum β-lactamase-producing Proteus mirabilis in Hong Kong, 1999–2002. J Antimicrob Chemother 2005; 55:840-5. [PMID: 15857942 DOI: 10.1093/jac/dki135] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [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: 11/14/2022] Open
Abstract
OBJECTIVES A study was conducted to evaluate the occurrence and characterization of extended-spectrum beta-lactamases (ESBLs) among blood isolates of Proteus mirabilis collected over a 4 year period in Hong Kong. METHODS Production of ESBLs among 99 consecutive and non-duplicate isolates was evaluated by the double-disc synergy test. The ESBLs were characterized by isoelectric focusing and PCR sequencing using specific primers. The epidemiological relationship of the isolates was studied by the Dienes test and PFGE. RESULTS ESBLs were identified in 13 isolates, from none in 1999-2000 and up to 18.5% (5/27) in 2001 and 25.8% (8/31) in 2002. The ESBL-producing isolates were more resistant to ceftriaxone than to ceftazidime, and were more likely than non-ESBL-producers to have resistance to ciprofloxacin (76.9% versus 14%) and gentamicin (38.5% versus 9.3%). The ESBL content included CTX-M-13 (n=8), CTX-M-14 (n=3), SHV-5 (n=2), TEM-11 (n=1), and an unidentified ESBL with a pI of 7.5. The Dienes test revealed that the genetic background in the 99 isolates was highly heterogeneous, with 54 distinct types among 92 isolates and seven were non-typeable. Among the 13 ESBL-producing isolates, five different backgrounds, including one cluster (Dienes-pulsotype A) with nine isolates, were identified by both Dienes test and PFGE, thus suggesting both clonal and multi-clonal spread of the CTX-M enzymes. CONCLUSIONS Our findings indicate the emergence of CTX-M enzymes among P. mirabilis in Hong Kong. More ESBL screening of this species is required to improve their recognition.
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Affiliation(s)
- P L Ho
- Division of Infectious Diseases, Department of Microbiology and Centre of Infection, The University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Pokfulam, Hong Kong Special Administrative Region, China.
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27
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Ho PL, Shek RHL, Chow KH, Duan RS, Mak GC, Lai EL, Yam WC, Tsang KW, Lai WM. Detection and characterization of extended-spectrum β-lactamases among bloodstream isolates of Enterobacter spp. in Hong Kong, 2000–2002. J Antimicrob Chemother 2005; 55:326-32. [PMID: 15681579 DOI: 10.1093/jac/dki010] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [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: 11/13/2022] Open
Abstract
OBJECTIVES A total of 139 consecutive and non-duplicate bloodstream isolates of Enterobacter spp. collected from inpatients in Hong Kong during 2000-2002 were studied for production of extended-spectrum beta-lactamases (ESBLs). METHODS All isolates were evaluated by the modified double-disc synergy test (m-DDST), the combined disc method (CDM) and the three-dimensional (3D) test. The m-DDST and CDM were modified by the use of cefepime discs. beta-Lactamases were characterized by isoelectric focusing and PCR sequencing using specific primers. RESULTS ESBLs were identified in nine isolates (overall 6.5%), including seven of 39 (17.9%) Enterobacter hormaechei, one of 27 (3.7%) Enterobacter aerogenes and the only Enterobacter intermedius strain. The E. intermedius strain was positive only in the 3D test but not in the other two tests. The other eight strains were positive in all three tests. No ESBL was detected in the other species, including non-hormaechei members of the Enterobacter cloacae complex (n=61), Enterobacter agglomerans (n=7), Enterobacter gergoviae (n=4) and Enterobacter sakazakii (n=1). The ESBL content included five different CTX-M enzymes (CTX-M-9, CTX-M-13, CTX-M-14, CTX-M-24 and a novel CTX-M-2-like beta-lactamase), SHV-12 (n=2) and unidentifiable ESBLs with a pI of 7.7 or 7.9 in two strains. The seven ESBL-producing E. hormaechei were genotyped by pulsed-field gel electrophoresis and were found to be unrelated to each other. In three of the CTX-M-producing strains, ISEcp1-like elements, including promoters for the beta-lactamase gene, were found. CONCLUSIONS Our data underscore the diversity of CTX-M enzymes among Enterobacter spp. in Hong Kong.
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Affiliation(s)
- P L Ho
- Division of Infectious Diseases, Department of Microbiology and Centre of Infection, United Christian Hospital, University of Hong Kong, Hong Kong SAR, China.
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Morris GD, Macfarlane WA, Chow KH, Salman Z, Arseneau DJ, Daviel S, Hatakeyama A, Kreitzman SR, Levy CDP, Poutissou R, Heffner RH, Elenewski JE, Greene LH, Kiefl RF. Depth-controlled beta-NMR of 8Li in a thin silver film. Phys Rev Lett 2004; 93:157601. [PMID: 15524941 DOI: 10.1103/physrevlett.93.157601] [Citation(s) in RCA: 14] [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: 10/17/2003] [Indexed: 05/24/2023]
Abstract
Depth-controlled beta-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field beta-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver.
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Affiliation(s)
- G D Morris
- Los Alamos National Laboratory, K764, Los Alamos, New Mexico 87545, USA
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Ho PL, Tse CWS, Mak GC, Chow KH, Ng TK. Community-acquired methicillin-resistant Staphylococcus aureus arrives in Hong Kong. J Antimicrob Chemother 2004; 54:845-6. [PMID: 15355941 DOI: 10.1093/jac/dkh426] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Shimomura K, Kadono R, Ohishi K, Mizuta M, Saito M, Chow KH, Hitti B, Lichti RL. Muonium as a shallow center in GaN. Phys Rev Lett 2004; 92:135505. [PMID: 15089625 DOI: 10.1103/physrevlett.92.135505] [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: 10/22/2003] [Indexed: 05/24/2023]
Abstract
A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the <0001> direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c axis. Its small ionization energy (<or=14 meV) and small hyperfine parameter (approximately 10(-4) times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.
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Affiliation(s)
- K Shimomura
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
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Zigment-Reed LM, Fairley CA, Chow KH, Yucel F, Cirakoglu B, Thompson KM, Suleyman S, Pinchuk GV. Cross-reaction of anti-simian immunodeficiency virus envelope protein antibodies with human immunoglobulins. Scand J Immunol 2003; 57:239-45. [PMID: 12641652 DOI: 10.1046/j.1365-3083.2003.01222.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [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: 11/20/2022]
Abstract
It has been recently established that retroviral envelope proteins (REPs) have structural features similar to those of immunoglobulins (Igs). In this study, we asked whether anti-REP antibodies cross-react with human Igs (hIgs). To this end, murine monoclonal antibodies (mMoAbs) that had been raised against a simian immunodeficiency virus (SIV) envelope protein, SIVMac251gp120, were screened for their ability to react with human monoclonal Igs (HMIgs). We show that two HMIgs, RFSJ2 (a rheumatoid factor) and PAMLN6 (a human anti-hIg V region antibody), but not a number of other HMIgs, could be weakly, but consistently, bound by anti-SIVMac251gp120 mMoAbs KK17 and KK46, as judged by indirect enzyme-linked immunosorbent assay and a liquid-phase inhibition immunoassay. Both mMoAbs are specific to amino acid residues in the V3 loop of the SIVMac251gp120. The RFSJ2 Ig heavy-chain V region (VH) is coded in part by a human VH gene, VH3-30.3 and includes the idiotope 7B4 (NKYY), which was previously shown to be present in the gp120 protein of a number of HIV-2 and SIV strains. However, an entirely different VH gene codes the PAMLN6 VH region, opening the possibility that epitope(s) shared between SIVMac251gp120 and hIgs may not be limited to the 7B4 idiotope.
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Affiliation(s)
- L M Zigment-Reed
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762, USA
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Chow KH, Hitti B, Kiefl RF, Lichti RL, Estle TL. Muonium analog of hydrogen passivation: observation of the Mu+-Zn- reaction in GaAs. Phys Rev Lett 2001; 87:216403. [PMID: 11736357 DOI: 10.1103/physrevlett.87.216403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2001] [Indexed: 05/23/2023]
Abstract
We report direct detection of the formation and subsequent breakup of a complex containing positively charged muonium ( Mu+) and a substitutional Zn(Ga) acceptor in heavily doped p-type GaAs:Zn. Mu+ diffuses above 200 K with a hop rate nu = nu(0)e(-E(nu)/k(B)T) where nu(0) = (7.7+/-2.0)x10(8) s(-1) and E(nu) = 0.15(4) eV. Above 350 K, it forms the complex with a trapping radius of 500+/-200 A. The Mu-Zn complex breaks up above 550 K with a dissociation energy of 0.88(7) eV and prefactor of (5+/-4)x10(12) s(-1). Above 750 K, the cyclic reaction Mu+<--> Mu0 takes place.
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Affiliation(s)
- K H Chow
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1
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Abstract
A PCR that amplifies a recently discovered Vibrio cholerae RTX (repeat in toxin) toxin gene was developed. Among 166 clinical and environmental isolates of V. cholerae causing epidemics and sporadic cases of cholera in various parts of the world, all were found to be toxigenic by both PCR and HEp-2 cell cytotoxicity assay. Standard strains of the classical biotype containing a deletion within the gene cluster exhibited negative results by both assays. This is the first rapid genotyping method for differentiation of V. cholerae O1 classical biotype strains from El Tor biotype strains as well as strains of other non-O1 serogroups including serogroup O139. The PCR assay that was developed also specifically detects RTX toxin genes in V. cholerae, as clinical isolates of Vibrio parahaemolyticus, diarrheagenic Escherichia coli, Aeromonas species, and Plesiomonas species were all negative by the RTX toxin-specific PCR as well as the HEp-2 cytotoxicity assay. These findings highlight the characteristics of the RTX toxins in V. cholerae. Their role in the pathogenicity of the bacterium requires further investigation.
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Affiliation(s)
- K H Chow
- Department of Microbiology, The University of Hong Kong, China
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Abstract
We report the direct detection of interstitial Ga by optical detection of electron paramagnetic resonance (ODEPR) in the photoluminescence of n-type GaN after irradiation in situ at 4.2 K with 2.5 MeV electrons. It is stable upon annealing until room temperature, where it becomes mobile and trapped to form a new defect which is observed to emerge as the interstitial disappears. The time constant of the process at room temperature is approximately 200 min. The emergence of another ODEPR center beginning at approximately 135 K suggests even easier migration of one of the other intrinsic defects in the GaN lattice.
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Affiliation(s)
- KH Chow
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
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Chow KH, Kiefl RF, Hitti B, Estle TL, Lichti RL. Novel behavior of bond-centered muonium in heavily doped n-type silicon: Curie-like spin susceptibility and charge screening. Phys Rev Lett 2000; 84:2251-2254. [PMID: 11017256 DOI: 10.1103/physrevlett.84.2251] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/1999] [Indexed: 05/23/2023]
Abstract
Bond-centered muonium ( Mu(0)(BC)) has been observed in very heavily doped n-type Si:P. It exhibits a Curie-like electronic spin susceptibility which leads to a giant negative shift in the muon spin precession frequency. At high dopant levels, the Mu(0)(BC) hyperfine parameters, deduced from a model involving spin exchange with free carriers, are significantly reduced from those in intrinsic Si. This indicates that the spin density distribution for Mu(0)(BC) in metallic Si:P is altered significantly by charge screening effects, likely a general phenomenon for deep impurities in materials with high carrier concentrations.
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Affiliation(s)
- K H Chow
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
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Ho PL, Que TL, Tsang DN, Ng TK, Chow KH, Seto WH. Emergence of fluoroquinolone resistance among multiply resistant strains of Streptococcus pneumoniae in Hong Kong. Antimicrob Agents Chemother 1999; 43:1310-3. [PMID: 10223962 PMCID: PMC89269 DOI: 10.1128/aac.43.5.1310] [Citation(s) in RCA: 192] [Impact Index Per Article: 7.7] [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: 11/20/2022] Open
Abstract
The MICs of 17 antimicrobial agents for 181 Streptococcus pneumoniae strains were determined by the E-test. Overall, 69.1% were penicillin resistant (MIC > 0.06 microgram/ml). Resistance to ciprofloxacin (MIC > 2 microgram/ml), levofloxacin (MIC > 2 microgram/ml), or trovafloxacin (MIC > 1 microgram/ml) was found in 12.1, 5.5, or 2.2% of the strains, respectively. These high rates of resistance raise concerns for the future.
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Affiliation(s)
- P L Ho
- Department of Microbiology, Division of Infectious Diseases, University of Hong Kong, Hong Kong.
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Ho PL, Chow KH, Yuen KY, Ng WS, Chau PY. Comparison of a novel, inhibitor-potentiated disc-diffusion test with other methods for the detection of extended-spectrum beta-lactamases in Escherichia coli and Klebsiella pneumoniae. J Antimicrob Chemother 1998; 42:49-54. [PMID: 9700527 DOI: 10.1093/jac/42.1.49] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [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: 11/12/2022] Open
Abstract
A novel, inhibitor-potentiated disc-diffusion test for detecting extended-spectrum beta-lactamases (ESBLs) in bacteria was evaluated. This test uses the principle of augmentation (by > or = 10 mm) of inhibition zones produced by ceftazidime, cefotaxime, ceftriaxone or aztreonam discs on Mueller-Hinton agar supplemented with clavulanate (4 mg/L). The test was initially compared with the double-disc synergy test, Kirby-Bauer disc-diffusion test and Etest ESBL screen with a panel of 45 reference strains with known resistance profiles. This panel consisted of 27 ESBL-positive Escherichia coli strains expressing 14 Bush group 2be enzymes and 18 other E. coli and Klebsiella pneumoniae strains (14 non-ESBL beta-lactamase producers and four non-beta-lactamase producers). The Kirby-Bauer disc-diffusion test was the least sensitive method: 11-44% of the ESBL-positive control strains were misclassified as susceptible to ceftazidime, cefotaxime, ceftriaxone or aztreonam when interpreted by National Committee for Clinical Laboratory Standards (NCCLS) criteria. The sensitivities of the inhibitor-potentiated disc-diffusion test, the double-disc synergy test (when discs were 25 or 30 mm apart) and the Etest ESBL screen (with a breakpoint of > 4-fold reduction in ceftazidime MIC in the presence of clavulanate) were 100%, 96% and 89-96%, respectively. The inhibitor-potentiated disc-diffusion test was further evaluated with 81 E. coli and K. pneumoniae clinical isolates, which were identified as putative ESBL-producers by the double-disc synergy test. For these isolates, the sensitivity of both the inhibitor-potentiated disc-diffusion test and the Etest ESBL screen was 100%. In conclusion, the inhibitor-potentiated disc-diffusion test is a sensitive, convenient and inexpensive method of screening for ESBLs in E. coli and K. pneumoniae isolates, with potential for incorporation into routine clinical laboratory service.
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Affiliation(s)
- P L Ho
- Department of Microbiology, University of Hong Kong.
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Affiliation(s)
- K H Chow
- University of California, Santa Barbara, USA
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Dunsiger SR, Kiefl RF, Chow KH, Gaulin BD, Gingras MJ, Greedan JE, Keren A, Kojima K, Luke GM, MacFarlane WA, Raju NP, Sonier JE, Uemura YJ, Wu WD. Muon spin relaxation investigation of the spin dynamics of geometrically frustrated antiferromagnets Y2Mo2O7 and Tb2Mo2O7. Phys Rev B Condens Matter 1996; 54:9019-9022. [PMID: 9984622 DOI: 10.1103/physrevb.54.9019] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Chow KH, Pattenden PA, Blundell SJ, Hayes W, Pratt FL, Jestädt T, Green MA, Millburn JE, Rosseinsky MJ, Hitti B, Dunsiger SR, Kiefl RF, Chen C, Chowdhury AJ. Muon-spin-relaxation studies of magnetic order in heavily doped La2-xSrxNiO4+ delta. Phys Rev B Condens Matter 1996; 53:R14725-R14728. [PMID: 9983340 DOI: 10.1103/physrevb.53.r14725] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Chow KH, Hitti B, Kiefl RF, Dunsiger SR, Lichti RL, Estle TL. Diffusion and charge dynamics of negatively charged muonium in n-type GaAs. Phys Rev Lett 1996; 76:3790-3793. [PMID: 10061110 DOI: 10.1103/physrevlett.76.3790] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Chow KH, Kiefl RF, MacFarlane WA, Schneider JW, Cooke DW, Leon M, Paciotti M, Estle TL, Hitti B, Lichti RL, Cox SF, Schwab C, Davis EA, Morrobel-Sosa A, Zavieh L. Erratum: Structure of negatively charged muonium in n-type GaAs. Phys Rev B Condens Matter 1995; 52:16939. [PMID: 9981107 DOI: 10.1103/physrevb.52.16939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Riseman TM, Brewer JH, Chow KH, Hardy WN, Kiefl RF, Kreitzman SR, Liang R, MacFarlane WA, Mendels P, Morris GD, Rammer J, Schneider JW, Niedermayer C, Lee SL. Ginzburg-Landau parameter in YBa2Cu3O6.95 below the irreversibility temperature as measured by micro+SR in high magnetic fields. Phys Rev B Condens Matter 1995; 52:10569-10580. [PMID: 9980110 DOI: 10.1103/physrevb.52.10569] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Cooke DW, Smith JL, Blundell SJ, Chow KH, Pattenden PA, Pratt FL, Cox SF, Brown SR, Morrobel-Sosa A, Lichti RL, Gupta LC, Nagarajan R, Hossain Z, Mazumdar C, Godart C. Competition between magnetism and superconductivity in TmNi2B2C observed by muon-spin rotation. Phys Rev B Condens Matter 1995; 52:R3864-R3867. [PMID: 9981613 DOI: 10.1103/physrevb.52.r3864] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Chow KH, Kiefl RF, MacFarlane WA, Schneider JW, Cooke DW, Leon M, Paciotti M, Estle TL, Hitti B, Lichti RL, Cox SF, Schwab C, Davis EA, Morrobel-Sosa A, Zavieh L. Structure of negatively charged muonium in n-type GaAs. Phys Rev B Condens Matter 1995; 51:14762-14765. [PMID: 9978422 DOI: 10.1103/physrevb.51.14762] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Kreitzman SR, Hitti B, Lichti RL, Estle TL, Chow KH. Muon-spin-resonance study of muonium dynamics in Si and its relevance to hydrogen. Phys Rev B Condens Matter 1995; 51:13117-13137. [PMID: 9978110 DOI: 10.1103/physrevb.51.13117] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Chow KH, Lichti RL, Kiefl RF, Dunsiger S, Estle TL, Hitti B, Kadono R, MacFarlane WA, Schneider JW, Schumann D, Shelley M. Identification of neutral bond-centered muonium in n-type semiconductors by longitudinal muon-spin relaxation. Phys Rev B Condens Matter 1994; 50:8918-8921. [PMID: 9974927 DOI: 10.1103/physrevb.50.8918] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Kadono R, Matsushita A, Nagamine K, Nishiyama K, Chow KH, Kiefl RF, MacFarlane A, Schumann D, Fujii S, Tanigawa S. Charge state and diffusivity of muonium in n-type GaAs. Phys Rev B Condens Matter 1994; 50:1999-2002. [PMID: 9976401 DOI: 10.1103/physrevb.50.1999] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Sonier JE, Kiefl RF, Brewer JH, Bonn DA, Carolan JF, Chow KH, Dosanjh P, Hardy WN, Liang R, MacFarlane WA, Mendels P, Morris GD, Riseman TM, Schneider JW. New muon-spin-rotation measurement of the temperature dependence of the magnetic penetration depth in YBa2Cu3O6.95. Phys Rev Lett 1994; 72:744-747. [PMID: 10056512 DOI: 10.1103/physrevlett.72.744] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Schneider JW, Kiefl RF, Chow KH, Johnston S, Sonier J, Estle TL, Hitti B, Lichti RL, Connell SH, Sellschop JP, Smallman CG, Anthony TR, Banholzer WF. Bond-centered muonium in diamond: Resolved nuclear hyperfine structure. Phys Rev Lett 1993; 71:557-560. [PMID: 10055306 DOI: 10.1103/physrevlett.71.557] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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