203 research outputs found
Time-dependent evolution of two coupled Luttinger liquids
We consider two disconnected Luttinger liquids which are coupled at
through chiral density-density interactions. Both for and the
system is exactly solvable by means of bosonization and this allows to evaluate
analytically the time-dependence of correlation functions. We find that in the
long-time limit the critical exponent governing the one-particle correlation
function differs from the exponent dictated by the equilibrium ground state of
the coupled system. We also discuss how this reflects on some physical
quantities which are accessible in real experiments.Comment: 6 pages, 1 eps fig, revised version accepted for publication in Phys.
Rev.
A generalized drift-diffusion model for rectifying Schottky contact simulation
We present a discussion on the modeling of Schottky barrier rectifying contacts (diodes) within the framework of partial-differential-equation-based physical simulations. We propose a physically consistent generalization of the drift-diffusion model to describe the boundary layer close to the Schottky barrier where thermionic emission leads to a non-Maxwellian carrier distribution, including a novel boundary condition at the contact. The modified drift-diffusion model is validated against Monte Carlo simulations of a GaAs device. The proposed model is in agreement with the Monte Carlo simulations not only in the current value but also in the spatial distributions of microscopic quantities like the electron velocity and concentratio
Suppression of electron-electron repulsion and superconductivity in Ultra Small Carbon Nanotubes
Recently, ultra-small-diameter Single Wall Nano Tubes with diameter of have been produced and many unusual properties were observed, such as
superconductivity, leading to a transition temperature , much
larger than that observed in the bundles of larger diameter tubes.
By a comparison between two different approaches, we discuss the issue
whether a superconducting behavior in these carbon nanotubes can arise by a
purely electronic mechanism. The first approach is based on the Luttinger Model
while the second one, which emphasizes the role of the lattice and short range
interaction, is developed starting from the Hubbard Hamiltonian. By using the
latter model we predict a transition temperature of the same order of magnitude
as the measured one.Comment: 7 pages, 3 figures, to appear in J. Phys.-Cond. Ma
An Instruction to Accelerate Software Caches
In this paper we propose an instruction to accelerate software caches. While DMAs are very efficient for predictable data sets that can be fetched before they are needed, they introduce a large latency overhead for computations with unpredictable access behavior. Software caches are advantageous when the data set is not predictable but exhibits locality. However, software caches also incur a large overhead. Because the main overhead is in the access function, we propose an instruction that replaces the look-up function of the software cache. This instruction is evaluated using the Multidimensional Software Cache and two multimedia kernels, GLCM and H.264 Motion Compensation. The results show that the proposed instruction accelerates the software cache access time by a factor of 2.6. This improvement translates to a 2.1 speedup for GLCM and 1.28 for MC, when compared with the IBM software cache
The detached dust shells of AQ And, U Ant, and TT Cyg
Detached circumstellar dust shells are detected around three carbon variables
using Herschel-PACS. Two of them are already known on the basis of their
thermal CO emission and two are visible as extensions in IRAS imaging data. By
model fits to the new data sets, physical sizes, expansion timescales, dust
temperatures, and more are deduced. A comparison with existing molecular CO
material shows a high degree of correlation for TT Cyg and U Ant but a few
distinct differences with other observables are also found.Comment: Letter accepted for publication on the A&A Herschel Special Issu
Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy
Magnetic, transport, and x-ray diffraction measurements of ferromagnetic
shape memory alloy NiMnGa revealed that this alloy undergoes
an intermartensitic transition upon cooling, whereas no such a transition is
observed upon subsequent heating. The difference in the modulation of the
martensite forming upon cooling from the high-temperature austenitic state
[5-layered (5M) martensite], and the martensite forming upon the
intermartensitic transition [7-layered (7M) martensite] strongly affects the
magnetic and transport properties of the alloy and results in a large thermal
hysteresis of the resistivity and magnetization . The
intermartensitic transition has an especially marked influence on the transport
properties, as is evident from a large difference in the resistivity of the 5M
and 7M martensite, , which is larger than the jump of resistivity at
the martensitic transition from the cubic austenitic phase to the monoclinic 5M
martensitic phase. We assume that this significant difference in between
the martensitic phases is accounted for by nesting features of the Fermi
surface. It is also suggested that the nesting hypothesis can explain the
uncommon behavior of the resistivity at the martensitic transition, observed in
stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.Comment: 7 pages, 6 figures, REVTEX
Stabilizing single atom contacts by molecular bridge formation
Gold-molecule-gold junctions can be formed by carefully breaking a gold wire
in a solution containing dithiolated molecules. Surprisingly, there is little
understanding on the mechanical details of the bridge formation process and
specifically on the role that the dithiol molecules play themselves. We propose
that alkanedithiol molecules have already formed bridges between the gold
electrodes before the atomic gold-gold junction is broken. This leads to
stabilization of the single atomic gold junction, as observed experimentally.
Our data can be understood within a simple spring model.Comment: 14 pages, 3 figures, 1 tabl
Galaxies and Cladistics
The Hubble tuning fork diagram, based on morphology and established in the
1930s, has always been the preferred scheme for classification of galaxies.
However, the current large amount of multiwavelength data, most often spectra,
for objects up to very high distances, asks for more sophisticated statistical
approaches. Interpreting formation and evolution of galaxies as a ?transmission
with modification' process, we have shown that the concepts and tools of
phylogenetic systematics can be heuristically transposed to the case of
galaxies. This approach, which we call ?astrocladistics', has successfully been
applied on several samples. Many difficulties still remain, some of them being
specific to the nature of both galaxies and their diversification processes,
some others being classical in cladistics, like the pertinence of the
descriptors in conveying any useful evolutionary information.Comment: Talk given at the "12th Evolutionary Biology Meeting" held in
Marseille, France, Sept. 24-26, 200
- âŠ