Search results for "COPI"
showing 10 items of 2618 documents
Numerical investigation of one‐dimensional tunnel junction arrays at temperatures above the Coulomb blockade regime
1996
Arrays of tunnel junctions provide simple thermometric parameters in the limit where thermal excitations dominate over charging effects. We present numerical simulations for calculating the current versus voltage characteristics of an arbitrary one‐dimensional array at arbitrary temperatures on the premise of the ‘‘orthodox theory.’’ The purpose of the computer simulations is to investigate the suitability of tunnel junction arrays for thermometry at low temperatures when the analytical formulas do not hold and, specifically, to see the effect of background charges in this regime.
Intravalley spin-flip relaxation dynamics in single-layer WS2
2019
Two-dimensional Transition Metal Dichalcogenides (TMDs) have been widely studied because of the peculiar electronic band structure and the strong excitonic effects [1]. In these materials the large spin-orbit coupling lifts the spin degeneracy of the valence (VB) and the conduction band (CB) giving rise to the A and B interband excitonic transitions. In monolayer WS2, the spins of electrons in the lowest CB and in the highest VB at K/K' point of the Brillouin zone are antiparallel resulting in an intravalley dark exciton state at a lower energy than the bright exciton, see left panel of Fig.1. On the one hand, the presence of dark excitons has been revealed indirectly from the observation o…
LATTICE–BOLTZMANN SIMULATION OF DENSE NANOFLOWS: A COMPARISON WITH MOLECULAR DYNAMICS AND NAVIER–STOKES SOLUTIONS
2007
In a recent work, a dense fluid flow across a nanoscopic thin plate was simulated by means of Molecular Dynamics (MD) and Lattice Boltzmann (LB) methods. It was found that in order to recover quantitative agreement with MD results, the LB simulation must be pushed down to sub–nanoscopic scales, i.e. fractions of the range of molecular interactions. In this work, we point out that in this sub–nanoscopic regime, the LB method works outside the hydrodynamic limit at the level of a single cell spacing. A quantitative comparison with the Navier–Stokes (NS) solution shows however that LB and NS results are quite similar, thereby indicating that, apart for a small region past the plate, this nano…
High‐Resolution X‐Ray Spectroscopy of the Post–T Tauri Star PZ Telescopii
2004
We present an analysis of the Chandra High Energy Transmission Grating Spectrometer observation of the rapidly rotating P_(rot)=0.94 d post T Tauri (~20 Myr old) star PZ Telescopii, in the Tucana association. Using two different methods we have derived the coronal emission measure distribution, em(T), and chemical abundances. The em(T) peaks at log T = 6.9 and exhibits a significant emission measure at temperatures log T > 7. The coronal abundances are generally ~0.5 times the solar photospheric values that are presumed fairly representative of the composition of the underlying star. A minimum in abundance is seen at a first ionization potential (FIP) of 7-8 eV, with evidence for higher abu…
High Energy, High Resolution X-Ray Spectroscopy: Microcalorimeters For Nuclear Line Astrophysics
2005
We introduce focusing optics and microcalorimeter spectroscopy to nuclear line emission astrophysics with a balloon payload concept called, B‐MINE. It is designed to probe the deepest regions of a supernova explosion by detecting 44Ti emission at 68 keV with spatial and spectral resolutions that are sufficient to determine the velocity distribution of the 44Ti emitting region. B‐MINE has a thin plastic foil telescope multilayered to maximize the reflectivity in a 20 keV band centered at 68 keV and a microcalorimeter array optimized for the same energy band. This combination provides a reduced background, an energy resolution of 50 eV and a 3σ sensitivity in 106 s of 6 × 10−8 ph cm−2 s−1 at …
Paramagnetic-diamagnetic interplay in quantum dots for non-zero temperatures
2000
In the usual Fock-and Darwin-formalism with parabolic potential characterized by the confining energy $\eps_o := \hbar\omega_o= 3.37$ meV, but including explicitly also the Zeeman coupling between spin and magnetic field, we study the combined orbital and spin magnetic properties of quantum dots in a two-dimensional electron gas with parameters for GaAs, for N =1 and N >> 1 electrons on the dot. For N=1 the magnetization M(T,B) consists of a paramagnetic spin contribution and a diamagnetic orbital contribution, which dominate in a non-trivial way at low temperature and fields rsp. high temperature and fields. For N >> 1, where orbital and spin effects are intrinsically coupled in a subtle w…
High-resolution study of some doubly excited vibrational states of PH2D: the m1 + m2, m2 + m5, m2 + m3, and m2 + m6 bands
2004
Abstract The absorption bands ν 1 + ν 2 , ν 2 + ν 3 , and ν 2 + ν 6 of PH 2 D have been recorded for the first time using a high-resolution Bruker 120 HR interferometer, and rotationally analyzed. Some transitions belonging to the very weak band ν 2 + ν 5 and enhanced in intensity by strong interactions with the ν 1 + ν 2 band were also assigned. Sets of parameters obtained from the fit reproduce experimental line position of the bands ν 1 + ν 2 and ν 2 + ν 3 with about the experimental accuracy. The residuals of the ro-vibrational energies of the ν 2 + ν 6 band are about 10 times larger. Reasons for the poorer reproduction of the latter data are given.
Continuum constitutive laws to describe acoustic attenuation in glasses
2020
International audience; Nowadays metamaterials are at the focus of an intense research as promising for thermal and acoustic engineering. However, the computational cost associated to the large system size required for correctly simulating them imposes the use of finite-elements simulations, developing continuum models, able to grasp the physics at play without entering in the atomistic details. Still, a correct description should be able to reproduce not only the extrinsic scattering sources on waves propagation, as introduced by the metamaterial microstructure, but also the intrinsic wave attenuation of the material itself. This becomes dramatically important when the metamaterial is made…
Gap solitons in nonlinear electrical transmission lines
2005
We study theoretically and numerically the properties of monochromatic waves in a nonlinear electrical transmission line,whose capacitance has a periodic spatial variation.ln the continuum limit and weak amplitude limit we reduce the characteristic equations of this system to NLS equation. We find analytical solutions for the voltage envelope, which propagate with frequency in the gap induced by the capacitance periodicity. Our numerical experiments show that, when the input voltage increases, the transmissivity in the gap increases and the voltage envelope approaches the stationnary shape predicted by theory.
A Novel Method Of Measuring Light Absorption On A Self-Assembled Single Quantum Dot
2005
Abstract. We present a novel method by wich excitonic interband optical transitions within single InAs self-assembled quantum dots can be directly observed in a transmission experiment. Due to the extremely high resolution of the tecnique, individual peaks associated to single exciton absorption resonances in single quantum dots can be spectrally resolved. Using this technique we investigate the oscillator strength, homogeneous linewidth and fine structure splitting in a collection of such individual resonances.