153,476 research outputs found
Super-rigidity for CR embeddings of real hypersurfaces into hyperquadrics
Let Q^N_l\subset \bC\bP^{N+1} denote the standard real, nondegenerate
hyperquadric of signature and M\subset \bC^{n+1} a real, Levi
nondegenerate hypersurface of the same signature . We shall assume that
there is a holomorphic mapping H_0\colon U\to \bC\bP^{N_0+1}, where is
some neighborhood of in \bC^{n+1}, such that
but . We show that if then, for any , any holomorphic mapping H\colon U\to \bC\bP^{N+1} with and must be the standard linear embedding
of into up to conjugation by automorphisms of
and
HOW DAIRY PRICE CHANGES INFLUENCE THE CONSUMERS' WELFARE
The Hicksian compensating variation is used to evaluate the consumers' welfare effects of price changes because of some hypothesized removals of Federal dairy policies and programs. The results indicate that consumers would reduce dairy expenditures from about one to two billion dollars nationally.compensating variation, dairy demand elasticities, dairy policies and programs., Demand and Price Analysis,
Effects of collisions against thermal impurities in the dynamics of a trapped fermion gas
We present a theoretical study of the dynamical behavior of a gas made of
ultracold fermionic atoms, which during their motions can collide with a much
smaller number of thermal bosonic impurities. The atoms are confined inside
harmonic traps and the interactions between the two species are treated as due
to s-wave scattering with a negative scattering length modeling the 40K-87Rb
fermion-boson system. We set the fermions into motion by giving a small shift
to their trap center and examine two alternative types of initial conditions,
referring to (i) a close-to-equilibrium situation in which the two species are
at the same temperature (well below the Fermi temperature and well above the
Bose-Einstein condensation temperature); and (ii) a far-from-equilibrium case
in which the impurities are given a Boltzmann distribution of momenta while the
fermions are at very low temperatures. The dynamics of the gas is evaluated by
the numerical solution of the Vlasov-Landau equations for the one-body
distribution functions, supported by some analytical results on the collisional
properties of a fermion gas. We find that the trapped gaseous mixture is close
to the collisionless regime for values of the parameters corresponding to
current experiments, but can be driven towards a collisional regime even
without increasing the strength of the interactions, either by going over to
heavier impurity masses or by matching the width of the momentum distribution
of the impurities to the Fermi momentum of the fermion gas.Comment: 7 pages, 4 figures, RevTeX 4, accepted in PR
Negative refraction and plano-concave lens focusing in one-dimensional photonic crystals
Negative refraction is demonstrated in one-dimensional (1D) dielectric
photonic crystals (PCs) at microwave frequencies. Focusing by plano-concave
lens made of 1D PC due to negative refraction is also demonstrated. The
frequency-dependent negative refractive indices, calculated from the
experimental data matches very well with those determined from band structure
calculations. The easy fabrication of one-dimensional photonic crystals may
open the door for new applications.Comment: 3 pages and 5 figure
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Dirac cohomology, elliptic representations and endoscopy
The first part (Sections 1-6) of this paper is a survey of some of the recent
developments in the theory of Dirac cohomology, especially the relationship of
Dirac cohomology with (g,K)-cohomology and nilpotent Lie algebra cohomology;
the second part (Sections 7-12) is devoted to understanding the unitary
elliptic representations and endoscopic transfer by using the techniques in
Dirac cohomology. A few problems and conjectures are proposed for further
investigations.Comment: This paper will appear in `Representations of Reductive Groups, in
Honor of 60th Birthday of David Vogan', edited by M. Nervins and P. Trapa,
published by Springe
An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
The new BABAR data on the pion-photon transition form factor arouses people's
new interests on the determination of pion distribution amplitude. To explain
the data, we take both the leading valence quark state's and the non-valence
quark states' contributions into consideration, where the valence quark part up
to next-to-leading order is presented and the non-valence quark part is
estimated by a phenomenological model based on its limiting behavior at both
and . Our results show that to be consistent with the
new BABAR data at large region, a broader other than the asymptotic-like
pion distribution amplitude should be adopted. The broadness of the pion
distribution amplitude is controlled by a parameter . It has been found that
the new BABAR data at low and high energy regions can be explained
simultaneously by setting to be around 0.60, in which the pion distribution
amplitude is closed to the Chernyak-Zhitnitsky form.Comment: 19 pages, 6 figures, 2 tables. Slightly changed, references updated.
To be published in Phys.Rev.
Single-Walled Carbon Nanotubes as Shadow Masks for Nanogap Fabrication
We describe a technique for fabricating nanometer-scale gaps in Pt wires on
insulating substrates, using individual single-walled carbon nanotubes as
shadow masks during metal deposition. More than 80% of the devices display
current-voltage dependencies characteristic of direct electron tunneling. Fits
to the current-voltage data yield gap widths in the 0.8-2.3 nm range for these
devices, dimensions that are well suited for single-molecule transport
measurements
Three-dimensional central-moments-based lattice Boltzmann method with external forcing: A consistent, concise and universal formulation
The cascaded or central-moments-based lattice Boltzmann method (CM-LBM) is a
robust alternative to the more conventional BGK-LBM for the simulation of
high-Reynolds number flows. Unfortunately, its original formulation makes its
extension to a broader range of physics quite difficult. To tackle this issue,
a recent work [A. De Rosis, Phys. Rev. E 95, 013310 (2017)] proposed a more
generic way to derive concise and efficient three-dimensional CM-LBMs. Knowing
the original model also relies on central moments that are derived in an adhoc
manner, i.e., by mimicking those of the Maxwell-Boltzmann distribution to
ensure their Galilean invariance a posteriori, a very recent effort [A. De
Rosis and K. H. Luo, Phys. Rev. E 99, 013301 (2019)] was proposed to further
generalize their derivation. The latter has shown that one could derive
Galilean invariant CMs in a systematic and a priori manner by taking into
account high-order Hermite polynomials in the derivation of the discrete
equilibrium state. Combining these two approaches, a compact and mathematically
sound formulation of the CM-LBM with external forcing is proposed. More
specifically, the proposed formalism fully takes advantage of the D3Q27
discretization by relying on the corresponding set of 27 Hermite polynomials
(up to the sixth order) for the derivation of both the discrete equilibrium
state and the forcing term. The present methodology is more consistent than
previous approaches, as it properly explains how to derive Galilean invariant
CMs of the forcing term in an a priori manner. Furthermore, while keeping the
numerical properties of the original CM-LBM, the present work leads to a
compact and simple algorithm, representing a universal methodology based on CMs
and external forcing within the lattice Boltzmann framework.Comment: Published in Phys. Fluids as Editor's Pic
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