排序方式: 共有73条查询结果,搜索用时 31 毫秒
21.
B.B. Baker R.L. Lichti Y.G. Celebi P.W. Mengyan H.N. Bani-Salameh 《Physica B: Condensed Matter》2012,407(15):2864-2866
We report on a study of the motional characteristics of positively charged muonium defect centers in ZnO as an analog for H+ behavior. Muon spin depolarization measurements at zero applied magnetic field were completed from 20 K to 400 K, with preliminary results to 750 K. Results at the lower temperatures imply that Mu+ occupied two sites, and indicate local motion as thermally assisted tunneling with a characteristic energy of ∼60 meV, as well as a site change transition above 200 K with barrier energy ∼440 meV. Based on theoretical results, we have tentatively assigned these features to tunneling among three equivalent oxygen anti-bonding sites (AB⊥) and a transition to a lower-energy bond-centered site (BC‖) oriented along the c-axis. Preliminary fits suggest that global diffusion of muonium occurs above 400 K, with a diffusion barrier energy of ∼0.7 eV. 相似文献
22.
We report muon spin rotation spectra in the narrow-gap semiconductors FeGa(3) and FeSb(2) consistent with a narrow band of small spin polarons (SPs). The characteristic sizes obtained for these SPs are R(FeGa(3)) ≈ 0.3-0.6 nm and R(FeSb (2)) ≈ 0.3 nm, respectively. Such SP states are expected to originate from the exchange correlations between localized and itinerant electrons. Our data suggest that SP bands are formed at low temperature, but are destroyed by thermal fluctuations above 10 K in FeGa(3) and above 7 K in FeSb(2). Formation of such SP band states can explain many of the low-temperature properties of these materials. 相似文献
23.
Chen ZW Chen LH Akentieva N Lichti CF Darbandi R Hastings R Covey DF Reichert DE Townsend RR Evers AS 《Electrophoresis》2012,33(4):666-674
Previous studies have shown that the neurosteroid analogue, 6-Azi-pregnanolone (6-AziP), photolabels voltage-dependent anion channels and proteins of approximately 55 kDa in rat brain membranes. The present study used two-dimensional electrophoresis and nanoelectrospray ionization ion-trap mass spectrometry (nano-ESI-MS) to identify the 55 kDa proteins (isoelectric point 4.8) as isoforms of β-tubulin. This identification was confirmed by immunoblot and immunoprecipitation of photolabeled protein with anti-β-tubulin antibody and by the demonstration that 6-AziP photolabels purified bovine brain tubulin in a concentration-dependent pattern. To identify the photolabeling sites, purified bovine brain tubulin was photolabeled with 6-AziP, digested with trypsin, and analyzed by matrix-assisted laser desorption/ionization MS (MALDI). A 6-AziP adduct of TAVCDIPPR(m/z?= 1287.77), a β-tubulin specific peptide, was detected by MALDI. High-resolution liquid chromatography-MS/MS analysis identified that 6-AziP was covalently bound to cysteine 354 (Cys-354), previously identified as a colchicine-binding site. 6-AziP photolabeling was inhibited by 2-methoxyestradiol, an endogenous derivative of estradiol thought to bind to the colchicine site. Structural modeling predicted that neurosteroids could dock in this colchicine site at the interface between α- and β-tubulin with the photolabeling group of 6-AziP positioned proximate to Cys-354. 相似文献
24.
Alberto H. V. Vilão R. C. Piroto Duarte J. Gil J. M. Ayres de Campos N. Lichti R. L. Davis E. A. Cottrell S. P. Cox S. F. J. 《Hyperfine Interactions》2001,136(3-8):471-477
The hyperfine spectroscopy of muonium in II–VI semiconductors is reviewed, suggesting that whereas hydrogen is a deep-level
defect in ZnS, ZnSe and ZnTe, it constitutes a shallow donor in ZnO, CdS, CdSe and CdTe. Shallow and deep states coexist in
CdTe. Using new data for ZnO, it is shown that the principal values of the muonium hyperfine tensor may be obtained with equal
facility from measurements in longitudinal or in transverse magnetic field, and from samples that are polycrystalline powders
or single crystals. Spin density on the central muon in the shallow states correlates with the electron binding energy or
donor depth.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
25.
W. K. Dawson C. H. Halim S. P. Weathersby J. A. Flint J. C. Lam T. J. Hoffman C. Boekema KC. B. Chan R. L. Lichti D. W. Cooke M. S. Jahan J. E. Crow 《Hyperfine Interactions》1991,63(1-4):219-226
Key results of zero-field (ZF) and transverse-field (TF) muon-spin-relaxation (μSR) experiments on superconducting and insulating
RBa2Cu3O
y
(R123
y
, with R=Eu, Gd, Pr and Pr/Y:y=6, 7) are examined. The chemical behavior of the positive muon probe is addressed, and muon-oxygen bonding is shown to occur
in all these cuprates. To explain magnetic fields at muon-probe sites in Pr
x
Y1−x
Ba2Cu3O
y
(0<=x<0.5,y=7 andx=0,y=6) samples, improvements on the reported magnetic structures from neutron diffraction are necessary. Cu magnetism in Pr123y (y=6,7) is observed belowT
N1, which is near RT. The magnetism seen belowT
N2 can be interpreted assuming an additional ordering in the Cutt-O chain layers. Alternatively, Pr ordering is also considered
as the cause of the second phase transition. Considering the specific muon-probe location, a more detailed interpretation
can be provided for the μSR parameters, measured in the normal and mixed states of these unconventional superconductors. 相似文献
26.
K.H. Chow S.F.J. Cox E.A. Davis S.R. Dunsiger T.L. Estle B. Hitti R.F. Kiefl R.L. Lichti 《Hyperfine Interactions》1997,105(1-4):309-314
The diamagnetic muonium states in heavily doped GaAs are investigated with a combination of transverse‐field and longitudinal‐field
μSR techniques. In metallic n‐type GaAs, formation of Mu- occurs because of the high Fermi energy. This analog of the hydride ion (H-) is located in a TGa interstice where it is essentially immobile up to about 500 K. At higher temperatures, MuT acts as an electron–hole recombination center. In p‐type GaAs, Mu+ traps at two different sites, one at low temperatures and a second at higher temperatures after detrapping from the first.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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29.
The functional Ito formula, in the form df() = f( + d ) f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25. 相似文献
30.
M. A. Paciotti D. W. Cooke M. Leon B. L. Bennett C. Pillai O. M. Rivera B. Hitti T. L. Estle S. F. J. Cox R. L. Lichti T. R. Adams C. D. Lamp A. Morrobel-Sosa O. Richter C. Boekema J. Lam S. Alves J. Oostens E. A. Davis 《Hyperfine Interactions》1994,87(1):1111-1116
It has long been recognized thatLCR could profitably be done with the high intensity surface beam at LAMPF [1]. A spectrometer has been built that is matched to the LAMPF beam characteristics. The polarization information is obtained from a downstream array of counters while side counters, containing no polarization signal, monitor the
+ beam. Degraders select higher energy e+, thereby reducing rates and required counter segmentation while maintaining information content. We apply a ramped longitudinal field in addition to the static one to average over instabilities in the
+ beam. This field scan allows direct interpretation of data and does not require a prior estimate of the resonance structure of a sample. Flux coils monitor the applied ramp field and eddy-current induced fields. High average rate (2×107
+/s). good stability, and the versatile field scan permitted useful data to be collected from Cu, Al(Cu), Al, Si(Al), and polycrystalline Si targets. 相似文献