3,878 research outputs found
Technology as an economic catalyst in rural and depressed places in Massachusetts
This paper uses case studies, including two cities (Lynn and New Bedford), a sub-city district (Roxbury) and two towns in rural Franklin County (Greenfield and Orange), to examine the role of technology as a potential economic catalyst in rural and depressed places in Massachusetts. Though the five target areas vary in size, density, geographic area, demographic characteristics and economic resources, each exhibits chronic patterns of economic distress related to the decline of manufacturing, construction and other key industries
Shot noise of interference between independent atomic systems
We study shot (counting) noise of the amplitude of interference between
independent atomic systems. In particular, for the two interfering systems the
variance of the fringe amplitude decreases as the inverse power of the number
of particles per system with the coefficient being a non-universal number. This
number depends on the details of the initial state of each system so that the
shot noise measurements can be used to distinguish between such states. We
explicitly evaluate this coefficient for the two cases of the interference
between bosons in number states and in broken symmetry states. We generalize
our analysis to the interference of multiple independent atomic systems. We
show that the variance of the interference contrast vanishes as the inverse
power of the number of the interfering systems. This result, implying high
signal to noise ratio in the interference experiments, holds both for bosons
and for fermions.Comment: 5 pages, 1 figure, final version, added a simple quantum-mechanical
argument why two independent condensates with fixed number of particles in
each must interfere in a generic experimental setu
The origin of phase in the interference of Bose-Einstein condensates
We consider the interference of two overlapping ideal Bose-Einstein
condensates. The usual description of this phenomenon involves the introduction
of a so-called condensate wave functions having a definite phase. We
investigate the origin of this phase and the theoretical basis of treating
interference. It is possible to construct a phase state, for which the particle
number is uncertain, but phase is known. However, how one would prepare such a
state before an experiment is not obvious. We show that a phase can also arise
from experiments using condensates in Fock states, that is, having known
particle numbers. Analysis of measurements in such states also gives us a
prescription for preparing phase states. The connection of this procedure to
questions of ``spontaneously broken gauge symmetry'' and to ``hidden
variables'' is mentioned.Comment: 22 pages 4 figure
Exclusion Statistics in a two-dimensional trapped Bose gas
We briefly explain the notion of exclusion statistics and in particular
discuss the concept of an ideal exclusion statistics gas. We then review a
recent work where it is demonstrated that a {\em two-dimensional} Bose gas with
repulsive delta function interactions obeys ideal exclusion statistics, with a
fractional parameter related to the interaction strength.Comment: 10 pages, RevTeX. Proceedings of the Salerno workshop "Theory of
Quantum Gases and Quantum Coherence", to appear in a special issue of J.Phys.
B, Dec. 200
Imperfect Homoclinic Bifurcations
Experimental observations of an almost symmetric electronic circuit show
complicated sequences of bifurcations. These results are discussed in the light
of a theory of imperfect global bifurcations. It is shown that much of the
dynamics observed in the circuit can be understood by reference to imperfect
homoclinic bifurcations without constructing an explicit mathematical model of
the system.Comment: 8 pages, 11 figures, submitted to PR
Anisotropic Spin Diffusion in Trapped Boltzmann Gases
Recent experiments in a mixture of two hyperfine states of trapped Bose gases
show behavior analogous to a spin-1/2 system, including transverse spin waves
and other familiar Leggett-Rice-type effects. We have derived the kinetic
equations applicable to these systems, including the spin dependence of
interparticle interactions in the collision integral, and have solved for
spin-wave frequencies and longitudinal and transverse diffusion constants in
the Boltzmann limit. We find that, while the transverse and longitudinal
collision times for trapped Fermi gases are identical, the Bose gas shows
diffusion anisotropy. Moreover, the lack of spin isotropy in the interactions
leads to the non-conservation of transverse spin, which in turn has novel
effects on the hydrodynamic modes.Comment: 10 pages, 4 figures; submitted to PR
Martian glaciation and the flow of solid CO2
The flow law determined experimentally for solid CO2 establishes that a hypothesis of glacial flow of CO2 at the Martian poles is not physically unrealistic. Compression experiments carried out under 1 atm pressure and constant strain rate demonstrate that the strength of CO2 near its sublimation point is considerably less than the strength of water ice near its melting point. The data fit a power law "creep" equation of the form , where is compressive strain rate (sec-1), [sigma] is compressive stress (bars), R is the gas constant in calories per mole, and T is absolute temperature. The exponent of [sigma] of 3.9 contrasts with a value near 3.1 for water ice, and indicates that the strain rate is somewhat more sensitive to stress for CO2 than for water. Likewise, the low activation energy for creep, 12 200 cal mole-1, illustrates that CO2 is not highly sensitive to temperature and is thus likely to flow over a broad range of temperatures below its melting point. Strength values for CO2 are of the order of one-tenth to one-third the strength of ice under equivalent conditions.A plausible glacial model for the Martian polar caps can be constructed and is helpful in explaining the unique character of the polar regions. CO2-rich layers deposited near the pole would have flowed outward laterally to relieve high internal shear stresses. The topography of the polar caps, the uniform layering of the layered deposits, and the general extent of the polar "sediments" could all be explained using this model. Flow of CO2 rather than water ice greatly reduces the problems with Martian glaciation. Nevertheless, problems do remain, in particular the large amounts of CO2 necessary, the need to increase vapor pressure and temperature with depth in the polar deposits, and the lack of good observational evidence of flor features. Within the limits of the present knowledge of surface conditions of Mars, CO2 glaciation appears to be a realistic alternate working hypothesis for the origin of the polar features.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21831/1/0000234.pd
Numerical study of the spherically-symmetric Gross-Pitaevskii equation in two space dimensions
We present a numerical study of the time-dependent and time-independent
Gross-Pitaevskii (GP) equation in two space dimensions, which describes the
Bose-Einstein condensate of trapped bosons at ultralow temperature with both
attractive and repulsive interatomic interactions. Both time-dependent and
time-independent GP equations are used to study the stationary problems. In
addition the time-dependent approach is used to study some evolution problems
of the condensate. Specifically, we study the evolution problem where the trap
energy is suddenly changed in a stable preformed condensate. In this case the
system oscillates with increasing amplitude and does not remain limited between
two stable configurations. Good convergence is obtained in all cases studied.Comment: 9 latex pages, 7 postscript figures, To appear in Phys. Rev.
Reduction and Emergence in Bose-Einstein Condensates
A closer look at some proposed Gedanken-experiments on BECs promises to shed
light on several aspects of reduction and emergence in physics. These include
the relations between classical descriptions and different quantum treatments
of macroscopic systems, and the emergence of new properties and even new
objects as a result of spontaneous symmetry breaking
Advanced power sources for space missions
Approaches to satisfying the power requirements of space-based Strategic Defense Initiative (SDI) missions are studied. The power requirements for non-SDI military space missions and for civil space missions of the National Aeronautics and Space Administration (NASA) are also considered. The more demanding SDI power requirements appear to encompass many, if not all, of the power requirements for those missions. Study results indicate that practical fulfillment of SDI requirements will necessitate substantial advances in the state of the art of power technology. SDI goals include the capability to operate space-based beam weapons, sometimes referred to as directed-energy weapons. Such weapons pose unprecedented power requirements, both during preparation for battle and during battle conditions. The power regimes for these two sets of applications are referred to as alert mode and burst mode, respectively. Alert-mode power requirements are presently stated to range from about 100 kW to a few megawatts for cumulative durations of about a year or more. Burst-mode power requirements are roughly estimated to range from tens to hundreds of megawatts for durations of a few hundred to a few thousand seconds. There are two likely energy sources, chemical and nuclear, for powering SDI directed-energy weapons during the alert and burst modes. The choice between chemical and nuclear space power systems depends in large part on the total duration during which power must be provided. Complete study findings, conclusions, and eight recommendations are reported
- …