11,779 research outputs found
Choosing a basis that eliminates spurious solutions in k.p theory
A small change of basis in k.p theory yields a Kane-like Hamiltonian for the
conduction and valence bands of narrow-gap semiconductors that has no spurious
solutions, yet provides an accurate fit to all effective masses. The theory is
shown to work in superlattices by direct comparison with first-principles
density-functional calculations of the valence subband structure. A
reinterpretation of the standard data-fitting procedures used in k.p theory is
also proposed.Comment: 15 pages, 2 figures; v3: expanded with much new materia
When is an alternative possibility robust?
According to some, free will requires alternative possibilities. But not any old alternative possibility will do. Sometimes, being able to bring about an alternative does not bestow any control on an agent. In order to bestow control, and so be directly relevant qua alternative to grounding the agent's moral responsibility, alternatives need to be robust. Here, I investigate the nature of robust alternatives. I argue that Derk Pereboom's latest robustness criterion is too strong, and I suggest a different criterion based on the idea that what agents need to be able to do is keep open the possibility of securing their blamelessness, rather than needing to directly ensure their own blamelessness at the time of decision
Analysis of heavy spin--3/2 baryon--heavy spin--1/2 baryon--light vector meson vertices in QCD
The heavy spin--3/2 baryon--heavy spin--1/2 baryon vertices with light vector
mesons are studied within the light cone QCD sum rules method. These vertices
are parametrized in terms of three coupling constants. These couplings are
calculated for all possible transitions. It is shown that correlation functions
for these transitions are described by only one invariant function for every
Lorenz structure. The obtained relations between the correlation functions of
the different transitions are structure independent while explicit expressions
of invariant functions depend on the Lorenz structure.Comment: 17 Pages, 6 Figures and 4 Table
Stereoscopic observations of hard x ray sources in solar flares made with GRO and other spacecraft
Since the launch of the Gamma Ray Observatory (GRO) in Apr. 1991, the Burst and Transient Source Experiment (BATSE) instrument on GRO has recorded a large number of solar flares. Some of these flares have also been observed by the Gamma-Ray Burst Detector on the Pioneer Venus Orbiter (PVO) and/or by the Solar X-Ray/Cosmic Gamma-Ray Burst Experiment on the Ulysses spacecraft. A preliminary list of common flares observed during the period May-Jun. 1991 is presented and the possible joint studies are indicated
Is there a renormalization of the 1D conductance in Luttinger Liquid model?
Properties of 1D transport strongly depend on the proper choice of boundary
conditions. It has been frequently stated that the Luttinger Liquid (LL)
conductance is renormalized by the interaction as . To
contest this result I develop a model of 1D LL wire with the interaction
switching off at the infinities. Its solution shows that there is no
renormalization of the universal conductance while the electrons have a free
behavior in the source and drain reservoirs.Comment: 5 pages, RevTex 2.0, attempted repair of tex error
High-Field Electrical Transport in Single-Wall Carbon Nanotubes
Using low-resistance electrical contacts, we have measured the intrinsic
high-field transport properties of metallic single-wall carbon nanotubes.
Individual nanotubes appear to be able to carry currents with a density
exceeding 10^9 A/cm^2. As the bias voltage is increased, the conductance drops
dramatically due to scattering of electrons. We show that the current-voltage
characteristics can be explained by considering optical or zone-boundary phonon
emission as the dominant scattering mechanism at high field.Comment: 4 pages, 3 eps figure
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