13,136 research outputs found
Simulations of dual morphology in spiral galaxies
Gas and stars in spiral galaxies are modelled with the DUAL code, using
hydrodynamic and N-body techniques. The simulations reveal morphological
differences mirroring the dual morphologies seen in B and K' band observations
of many spiral galaxies. In particular, the gaseous images are more flocculent
with lower pitch angles than the stellar images, and the stellar arm-interarm
contrast correlates with the degree of morphological decoupling.Comment: 4 pages, 4 figures, to appear in Disk of Galaxies: Kinematics,
Dynamics and Perturbations, ASP Conf. Series, 200
New optical and radio frequency angular tropospheric refraction models for deep space applications
The development of angular tropospheric refraction models for optical and radio frequency usage is presented. The models are compact analytic functions, finite over the entire domain of elevation angle, and accurate over large ranges of pressure, temperature, and relative humidity. Additionally, FORTRAN subroutines for each of the models are included
On the Creation of the Universe out of Nothing
We explain how the Universe was created with no expenditure of energy or
initial mass.Comment: To be presented at IWARA 2009 (4th International Workshop on
Astronomy and Relativistic Astrophysics), to be held in Brazil, October 200
Relaxation and Zeno effect in qubit measurements
We consider a qubit interacting with its environment and continuously
monitored by a detector represented by a point contact. Bloch-type equations
describing the entire system of the qubit, the environment and the detector are
derived. Using these equations we evaluate the detector current and its noise
spectrum in terms of the decoherence and relaxation rates of the qubit. Simple
expressions are obtained that show how these quantities can be accurately
measured. We demonstrate that due to interaction with the environment, the
measurement can never localize a qubit even for infinite decoherence rate.Comment: some clarifications added, to appear in Phys. Rev. Let
Dispersion management using betatron resonances in an ultracold-atom storage ring
Specific velocities of particles circulating in a storage ring can lead to
betatron resonances at which static perturbations of the particles' orbit yield
large transverse (betatron) oscillations. We have observed betatron resonances
in an ultracold-atom storage ring by direct observation of betatron motion.
These resonances caused a near-elimination of the longitudinal dispersion of
atomic beams propagating at resonant velocities, an effect which can improve
the performance of atom interferometric devices. Both the resonant velocities
and the strength of the resonances were varied by deliberate modifications to
the storage ring.Comment: 4 pages, 5 figures. Also available at
http://physics.berkeley.edu/research/ultracol
Corporate Social Performance and Economic Cycles
Do firms respond to changes in economic growth by altering their corporate social responsibility programs? If they do respond, are their responses simply neglect of areas associated with corporate social performance (CSP) or do they also cut back on positive programs such as profit sharing, public/private housing programs, or charitable contributions? In this paper we argue that because CSP-related actions and programs tend to be discretionary, they are likely to receive less attention during tough economic times, a result of cost-cutting efforts. However, the various CSP performance areas vary in terms of their resource requirements and their influence on financial performance (short- and long-term), which suggests that firms may respond differently depending on area. Consequently, in addition to examining CSP concerns separately from positive actions and programs (CSP strengths), we also examine the influence of economic growth across the five areas of diversity, employee relations, the environment, product quality/safety, and the community.
Based on data from 837 firms over fifteen years, our results suggest that firms neglect some areas associated with CSP during economic downturns, resulting in increased concerns about community and employee relations, product safety/quality, and the environment. However, this relationship does not apply to positive actions and programs. Instead, firms tend to increase their positive CSP programs in areas such as diversity, employee relations, and the environment during periods of slow economic growth and reduce them when the economy picks up. We offer potential explanations for our findings and discuss their importance to research on CSP
Dynamical Stability and Quantum Chaos of Ions in a Linear Trap
The realization of a paradigm chaotic system, namely the harmonically driven
oscillator, in the quantum domain using cold trapped ions driven by lasers is
theoretically investigated. The simplest characteristics of regular and chaotic
dynamics are calculated. The possibilities of experimental realization are
discussed.Comment: 24 pages, 17 figures, submitted to Phys. Rev
Sub Shot-Noise Phase Sensitivity with a Bose-Einstein Condensate Mach-Zehnder Interferometer
Bose Einstein Condensates, with their coherence properties, have attracted
wide interest for their possible application to ultra precise interferometry
and ultra weak force sensors. Since condensates, unlike photons, are
interacting, they may permit the realization of specific quantum states needed
as input of an interferometer to approach the Heisenberg limit, the supposed
lower bound to precision phase measurements. To this end, we study the
sensitivity to external weak perturbations of a representative matter-wave
Mach-Zehnder interferometer whose input are two Bose-Einstein condensates
created by splitting a single condensate in two parts. The interferometric
phase sensitivity depends on the specific quantum state created with the two
condensates, and, therefore, on the time scale of the splitting process. We
identify three different regimes, characterized by a phase sensitivity scaling with the total number of condensate particles as i) the
standard quantum limit , ii) the sub shot-noise
and the iii) the Heisenberg limit . However, in a realistic dynamical BEC splitting, the 1/N limit
requires a long adiabaticity time scale, which is hardly reachable
experimentally. On the other hand, the sub shot-noise sensitivity can be reached in a realistic experimental setting. We
also show that the scaling is a rigorous upper bound in the limit
, while keeping constant all different parameters of the bosonic
Mach-Zehnder interferometer.Comment: 4 figure
- …