48,389 research outputs found
A Note on the Relativistic Covariance of the Cyclic Relations
It is shown that the Evans-Vigier modified electrodynamics is compatible with
the Relativity Theory.Comment: ReVTeX file, 14pp., no figure
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
Design and simulation of InGaAs/AlAsSb quantum-cascade lasers for short wavelength emission
The design and simulation of an In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade laser emitting in the near infrared is presented. Designed using a self-consistent rate equation solver coupled with an energy balance rate equation, the proposed laser has a calculated population inversion of ~20% at 77 K and sufficient gain to achieve room-temperature laser emission at λ ~2.8 µm. Threshold currents in the range 4–8 kA/cm2 are estimated as the temperature increases from 77 K to 300 K. The output characteristics of the proposed laser are compared to an existing λ ~3.1 µm In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade structure presented in the literature
Another Majorana Idea: Real and Imaginary in the Weinberg Theory
The Majorana discernment of neutrality is applied to the solutions of
Weinberg equations in the representation of the Poincar\`e
group.Comment: ReVTeX file, 6pp., no figure
Spontaneous Symmetry Breaking in a Non-Conserving Two-Species Driven Model
A two species particle model on an open chain with dynamics which is
non-conserving in the bulk is introduced. The dynamical rules which define the
model obey a symmetry between the two species. The model exhibits a rich
behavior which includes spontaneous symmetry breaking and localized shocks. The
phase diagram in several regions of parameter space is calculated within
mean-field approximation, and compared with Monte-Carlo simulations. In the
limit where fluctuations in the number of particles in the system are taken to
zero, an exact solution is obtained. We present and analyze a physical picture
which serves to explain the different phases of the model
Annihilation of Immobile Reactants on the Bethe Lattice
Two-particle annihilation reaction, A+A -> inert, for immobile reactants on
the Bethe lattice is solved exactly for the initially random distribution. The
process reaches an absorbing state in which no nearest-neighbor reactants are
left. The approach of the concentration to the limiting value is exponential.
The solution reproduces the known one-dimensional result which is further
extended to the reaction A+B -> inert.Comment: 12 pp, TeX (plain
A Nonlinear Super-Exponential Rational Model of Speculative Financial Bubbles
Keeping a basic tenet of economic theory, rational expectations, we model the
nonlinear positive feedback between agents in the stock market as an interplay
between nonlinearity and multiplicative noise. The derived hyperbolic
stochastic finite-time singularity formula transforms a Gaussian white noise
into a rich time series possessing all the stylized facts of empirical prices,
as well as accelerated speculative bubbles preceding crashes. We use the
formula to invert the two years of price history prior to the recent crash on
the Nasdaq (april 2000) and prior to the crash in the Hong Kong market
associated with the Asian crisis in early 1994. These complex price dynamics
are captured using only one exponent controlling the explosion, the variance
and mean of the underlying random walk. This offers a new and powerful
detection tool of speculative bubbles and herding behavior.Comment: Latex document of 24 pages including 5 eps figure
Thermal modeling of terahertz quantum-cascade lasers: comparison of optical waveguides
We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappaperp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappaperp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model
An Infinite Dimensional Symmetry Algebra in String Theory
Symmetry transformations of the space-time fields of string theory are
generated by certain similarity transformations of the stress-tensor of the
associated conformal field theories. This observation is complicated by the
fact that, as we explain, many of the operators we habitually use in string
theory (such as vertices and currents) have ill-defined commutators. However,
we identify an infinite-dimensional subalgebra whose commutators are not
singular, and explicitly calculate its structure constants. This constitutes a
subalgebra of the gauge symmetry of string theory, although it may act on
auxiliary as well as propagating fields. We term this object a {\it weighted
tensor algebra}, and, while it appears to be a distant cousin of the
-algebras, it has not, to our knowledge, appeared in the literature before.Comment: 14 pages, Plain TeX, report RU93-8, CTP-TAMU-2/94, CERN-TH.7022/9
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