797 research outputs found
Electron-phonon interaction in the solid form of the smallest fullerene C
The electron-phonon coupling of a theoretically devised carbon phase made by
assembling the smallest fullerenes C is calculated from first
principles. The structure consists of C cages in an {\it fcc} lattice
interlinked by two bridging carbon atoms in the interstitial tetrahedral sites
({\it fcc}-C). The crystal is insulating but can be made metallic by
doping with interstitial alkali atoms. In the compound NaC the
calculated coupling constant is 0.28 eV, a value much larger
than in C, as expected from the larger curvature of C. On the
basis of the McMillan's formula, the calculated =1.12 and a
assumed in the range 0.3-0.1 a superconducting T in the range 15-55 K is
predicted.Comment: 7 page
Mesoscopic Phase Fluctuations: General Phenomenon in Condensed Matter
General conditions for the occurrence of mesoscopic phase fluctuations in
condensed matter are considered. The description of different thermodynamic
phases, which coexist as a mixture of mesoscopically separated regions, is
based on the {\it theory of heterophase fluctuations}. The spaces of states,
typical of the related phases, are characterized by {\it weighted Hilbert
spaces}. Several models illustrate the main features of heterophase condensed
matter.Comment: 23 pages, Latex, no figure
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Over-winter persistence of supraglacial lakes on the Greenland Ice Sheet: Results and insights from a new model
AbstractWe present a newly developed 1-D numerical energy-balance and phase transition supraglacial lake model: GlacierLake. GlacierLake incorporates snowfall, in situ snow and ice melt, incoming water from the surrounding catchment, ice lid formation, basal freeze-up and thermal stratification. Snow cover and temperature are varied to test lake development through winter and the maximum lid thickness is recorded. Average wintertime temperatures of â2 toand total snowfall of 0 to 3.45 m lead to a range of the maximum lid thickness from 1.2 to 2.8 m afterdays, with snow cover exerting the dominant control. An initial ice temperature ofwith simulated advection of cold ice from upstream results in 0.6 m of basal freeze-up. This suggests that lakes with water depths above 1.3 to 3.4 m (dependent on winter snowfall and temperature) upon lid formation will persist through winter. These buried lakes can provide a sizeable water store at the start of the melt season, expedite future lake formation and warm underlying ice even in winter.NER
Displacement and emission currents from PLZT 8/65/35 and 4/95/5 excited by a negative voltage pulse at the rear electrode
It is shown that non-prepoled PLZT ceramics, both in ferroelectric and antiferroelectric phase, emit intense current bursts when a negative exciting voltage is applied to the rear surface of the cathode. The spontaneous polarization induced in the bulk by applying the field through the cathode disk, creates a sheet of negative charge on the diode boundary of the ferroelectric. This, in turn, induces such a high electric field at the diode dielectric surface that electrons are ejected out from the ceramic surface into the vacuum. The coherent behaviour of the displacement and emitted current shows clearly that the emission is due to a variation of spontaneous polarization. A second effect generated by the application of the high voltage pulse at the rear side is the formation of a surface plasma. Applying a positive voltage to the anode, electrons are readily transferred through the diode gap
Electron Emission from Ferroelectric/Antiferroelectric Cathodes Excited by Short High-Voltage Pulses
Un-prepoled Lead Zirconate Titanate Lanthanum doped-PLZT ferroelectric cathodes have emitted intense current pulses under the action of a high voltage pulse of typically 8 kV/cm for PLZT of 8/65/35 composition and 25 kV/cm for PLZT of 4/95/5 composition. In the experiments described in this paper, the exciting electric field applied to the sample is directed from the rear surface towards the emitting surface. The resulting emission is due to an initial field emission from the metal of the grid deposited over the emitting surface with the consequent plasma formation and the switching of ferroelectric domains. These electrons may be emitted directly form the crystal or from the plasma. This emission requires the material in ferroelectric phase. In fact, PLZT cathodes of the 8/65/35 type, that is with high Titanium content, showing ferroelectric-paraelectric phase sequence, emit at room temperature, while PLZT cathodes of the 4/95/5 type, that is with low Titanium content, having antiferro-ferro-paraelectric phase sequence, emit strongly at a temperature higher than 130°C
Sequence analysis of 16S rRNA, gyrB and catA genes and DNA-DNA hybridization reveal that Rhodococcus jialingiae is a later synonym of Rhodococcus qingshengii
The results of 16S rRNA, gyrB and catA gene sequence comparisons and reasserted DNAâDNA hybridization unambiguously proved that
Rhodococcus jialingiae
Wang et al. 2010 and
Rhodococcus qingshengii
Xu et al. 2007 represent a single species. On the basis of priority
R. jialingiae
must be considered a later synonym of
R. qingshengii
.</jats:p
The scaling limit of the critical one-dimensional random Schrodinger operator
We consider two models of one-dimensional discrete random Schrodinger
operators (H_n \psi)_l ={\psi}_{l-1}+{\psi}_{l +1}+v_l {\psi}_l,
{\psi}_0={\psi}_{n+1}=0 in the cases v_k=\sigma {\omega}_k/\sqrt{n} and
v_k=\sigma {\omega}_k/ \sqrt{k}. Here {\omega}_k are independent random
variables with mean 0 and variance 1.
We show that the eigenvectors are delocalized and the transfer matrix
evolution has a scaling limit given by a stochastic differential equation. In
both cases, eigenvalues near a fixed bulk energy E have a point process limit.
We give bounds on the eigenvalue repulsion, large gap probability, identify the
limiting intensity and provide a central limit theorem.
In the second model, the limiting processes are the same as the point
processes obtained as the bulk scaling limits of the beta-ensembles of random
matrix theory. In the first model, the eigenvalue repulsion is much stronger.Comment: 36 pages, 2 figure
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