303 research outputs found
Apparent finite-size effects in the dynamics of supercooled liquids
Molecular dynamics simulations are performed for a supercooled simple liquid
with changing the system size from N=108 to to examine possible
finite-size effects. Although almost no systematic deviation is detected in the
static pair correlation functions, it is demonstrated that the structural
relaxation in a small system becomes considerably slower than that in
larger systems for temperatures below at which the size of the
cooperative particle motions becomes comparable to the unit cell length of the
small system. The discrepancy increases with decreasing temperature.Comment: 4 pages 5 figure
Anisotropic s-wave superconductivity in single crystals CaAlSi from penetration depth measurements
In- and out-of-plane London penetration depths were measured in single
crystals CaAlSi (T_{c}=6.2 K and 7.3 K) using a tunnel-diode resonator. A full
3D BCS analysis of the superfluid density is consistent with a prolate
spheroidal gap, with a weak-coupling BCS value in the ab-plane and stronger
coupling along the c-axis. The gap anisotropy was found to significantly
decrease for higher T_{c} samples.Comment: 4 page
Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
We have investigated a gap structure in a newly-discovered superconductor,
MgB2 through the measurement of 11B nuclear spin-lattice relaxation rate,
^{11}(1/T_1). ^{11}(1/T_1) is proportional to the temperature (T) in the normal
state, and decreases exponentially in the superconducting (SC) state, revealing
a tiny coherence peak just below T_c. The T dependence of 1/T_1 in the SC state
can be accounted for by an s-wave SC model with a large gap size of 2\Delta
/k_BT_c \sim 5 which suggests to be in a strong-coupling regime.Comment: 2 pages with 1 figur
Evidence for High-frequency Phonon Mediated S-wave Superconductivity : 11B-NMR Study of Al-doped MgB2
We report B-NMR study on Al-doped MgB that addresses a possible
mechanism for a high superconducting (SC) transition temperature () of
K in recently discovered MgB. The result of nuclear spin lattice
relaxation rate in the SC state revealed that the size in the SC gap is
not changed by substituting Al for Mg. The reduction on by Al-doping is
shown to be due to the decrease of . According to the McMillan
equation, the experimental relation between and the relative change in
allowed us to estimate a characteristic phonon frequency K and an electron-phonon coupling constant . These
results suggest that the high- superconductivity in MgB is mediated by
the strong electron-phonon coupling with high-frequency phonons.Comment: 6pages, 3figure
Superconductivity in a new layered triangular-lattice system Li2IrSi2
We report on the crystal structure and superconducting properties of a novel iridium-silicide, namely Li2IrSi2. It has a Ag2NiO2-type structure (space group R-3m) with the lattice parameters a = 4.028 30(6) Ă
and c = 13.161 80(15) Ă
. The crystal structure comprises IrSi2 and double Li layers stacked alternately along the c-axis. The IrSi2 layer includes a two-dimensional Ir equilateral-triangular lattice. Electrical resistivity and static magnetic measurements revealed that Li2IrSi2 is a type-II superconductor with critical temperature (Tc) of 3.3 K. We estimated the following superconducting parameters: lower critical field Hc1(0) ~ 42 Oe, upper critical field Hc2(0) ~ 1.7 kOe, penetration depth λ0 ~ 265 nm, coherence length Ο0 ~ 44 nm, and GinzburgâLandau parameter ÎșGL ~ 6.02. The specific-heat data suggested that superconductivity in Li2IrSi2 could be attributed to weak-coupling Cooper pairs
The Role of Arabidopsis ABCG9 and ABCG31 ATP Binding Cassette Transporters in Pollen Fitness and the Deposition of Steryl Glycosides on the Pollen Coat
The pollen coat protects pollen grains from harmful environmental stresses such as drought and cold. Many compounds in the pollen coat are synthesized in the tapetum. However, the pathway by which they are transferred to the pollen surface remains obscure. We found that two Arabidopsis thaliana ATP binding cassette transporters, ABCG9 and ABCG31, were highly expressed in the tapetum and are involved in pollen coat deposition. Upon exposure to dry air, many abcg9 abcg31 pollen grains shriveled up and collapsed, and this phenotype was restored by complementation with ABCG9(pro):GFP:ABCG9. GFP-tagged ABCG9 or ABCG31 localized to the plasma membrane. Electron microscopy revealed that the mutant pollen coat resembled the immature coat of the wild type, which contained many electron-lucent structures. Steryl glycosides were reduced to about half of wild-type levels in the abcg9 abcg31 pollen, but no differences in free sterols or steryl esters were observed. A mutant deficient in steryl glycoside biosynthesis, ugt80A2 ugt80B1, exhibited a similar phenotype. Together, these results indicate that steryl glycosides are critical for pollen fitness, by supporting pollen coat maturation, and that ABCG9 and ABCG31 contribute to the accumulation of this sterol on the surface of pollen.X1133Ysciescopu
Theory for phonon-induced superconductivity in MgB
We analyze superonductivity in MgB observed below K resulting
from electron-phonon coupling involving a mode at meV and
most importantly the in-plane B-B vibration at
meV. The quasiparticles originating from - and -states couple
strongly to the low-frequency mode and the -vibrations respectively.
Using two-band Eliashberg theory, and , we calculate the gap functions (,
).
Our results provide an explanation of recent tunneling experiments.
We get .Comment: revised version, accepted for publication in PR
Indução da carcinogĂȘnese mamĂĄria experimental em ratas com 7,12-dimetilbenz(a)antraceno
PURPOSE: To test an experimental model of chemical mammary carcinogenesis induction in rats. METHODS: Twenty young virgin Sprague-Dawley female rats, aged 47 days, received 20 mg of 7,12-dimethylbenz(a)anthracene (DMBA) intragastrically by gavage. Afterwards, at 8 and 13 weeks, their mammary glands were examined. At the end of the experiment, the animals were sacrificed, and the mammary tumors were measured and weighed. Tumor fragments were analyzed using light microscopy. RESULTS: Eight weeks after DMBA injection, 16 rats presented at least 1 breast tumor (80%). After 13 weeks, all of them (100%) developed breast carcinomas that were confirmed by histopathological analysis. CONCLUSION: This experimental animal model of chemical mammary induced carcinogenesis is feasible and can be used in further experiments on the role of tumorigenic biomodulator substances.OBJETIVO: Testar um modelo experimental de indução quĂmica de carcinogĂȘnese mamĂĄria em ratas. MATERIAL E MĂTODOS: Com 47 dias de vida, 20 ratas Sprague-Dawley, jovens e virgens, receberam por gavagem intragĂĄstrica 20 mg de 7,12-dimetilbenz(a)antraceno (DMBA). Oito e 13 semanas depois da injeção de droga as mamas das ratas foram examinadas. Ao final os animais foram sacrificados e fragmentos dos tumores foram estudados ao microscĂłpio. RESULTADO: Oito semanas depois da injeção de DMBA 16 ratas apresentavam tumor nas mamas (80%). Com 13 semanas todas desenvolveram carcinomas de mama (100%), que foram confirmados por anĂĄlise histopatolĂłgica. CONCLUSĂO: Este modelo experimental de indução quĂmica de carcinogĂȘnese mamĂĄria Ă© factĂvel e pode ser empregado em futuras pesquisas para avaliar o papel de substĂąncias biomoduladoras da tumorigĂȘnese
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