20,594 research outputs found
A Comment on General Formulae for Polarization Observables in Deuteron Electrodisintegration and Linear Relations
We establish a simple, explicit relation between the formalisms employed in
the treatments of polarization observables in deuteron two-body
electrodisintegration published by Arenh\"ovel, Leidemann, and Tomusiak in
Few-Body Systems {\bf 15}, 109 (1993) and the results of the present authors
published in Phys.~Rev.~C {\bf 40}, 2479 (1989). We comment on the overlap
between the two sets of results.Comment: 9 pages, no figure
Discrimination of Coastal Vegetation and Biomass Using AIS Data
The Airborne Imaging Spectrometer (AIS) was flown over a coastal wetlands region near Lewes, Delaware, adjacent to the Delaware Bay on 16 August 1984. Using the AIS data, it was possible to discriminate between four different types of wetland vegetation canopies: (1) trees; (2) broadleaf herbaceous plants (e.g., Acnida cannabina, Hisbiscus moscheutos); (3) the low marsh grass Spartina alterniflora; and (4) the high marsh grasses Distichlis spicata and Spartina patens. The single most useful region of the spectrum was that between 1.40 and 1.90 microns, where slopes of portions of the radiance curve and ratios of radiance at particular wavelengths were significantly different for the four canopy types. The ratio between the highest digital number in the 1.40 to 1.90 microns and .84 to .94 microns regions and a similar ratio between the peaks in radiance in the 1.12 to 1.40 microns and .84 to .94 microns spectral regions were also very effective at discriminating between vegetation types. Differences in radiance values at various wavelengths between samples of the same vegetation type could potentially be used to estimate biomass
Freeze-out Configuration in Multifragmentation
The excitation energy and the nuclear density at the time of breakup are
extracted for the reaction at beam energies of 1 and 3.6
GeV/nucleon. These quantities are calculated from the average relative velocity
of intermediate mass fragments (IMF) at large correlation angles as a function
of the multiplicity of IMFs using a statistical model coupled with many-body
Coulomb trajectory calculations. The Coulomb component and
thermal component are found to depend oppositely on the
excitation energy, IMFs multiplicity, and freeze-out density. These
dependencies allow the determination of both the volume and the mean excitation
energy at the time of breakup. It is found that the volume remained constant as
the beam energy was increased, with a breakup density of about ,
but that the excitation energy increased to about 5.5 MeV/nucleon.Comment: 12 pages, 2 figures available upon resues
Measurement of binding energy of negatively charged excitons in GaAs/AlGaAs quantum wells
We report a photoluminescence study of electron-hole complexes in specially
designed semiconductor heterostructures. Placing a remote dilute layer of
donors at different distances \itshape d \normalfont from the quantum well
leads to the transformation of luminescence spectra of neutral () and
negatively charged () excitons. The onset of an additional spectral line
and its energy dependence on \itshape d \normalfont allows us to unambiguously
relate the so-called trion state with charged excitons bound on charged
donors in a barrier. The results indicate the overestimation in free-trion
binding energies from previous studies of GaAs/AlGaAs quantum
wells, and give their corrected values for QWs of width 200 and 300 \AA \space
in the limiting case of infinitely distant donors.Comment: 5 pages, 4 figure
Tables of X-coefficients and Lambda-factors for Triple Angular Correlation Analysis
Tables of x-coefficients and lambda-factors for triple angular correlation measurements in nuclear reaction studie
Thermodynamics of rotating self-gravitating systems
We investigate the statistical equilibrium properties of a system of
classical particles interacting via Newtonian gravity, enclosed in a
three-dimensional spherical volume. Within a mean-field approximation, we
derive an equation for the density profiles maximizing the microcanonical
entropy and solve it numerically. At low angular momenta, i.e. for a slowly
rotating system, the well-known gravitational collapse ``transition'' is
recovered. At higher angular momenta, instead, rotational symmetry can
spontaneously break down giving rise to more complex equilibrium
configurations, such as double-clusters (``double stars''). We analyze the
thermodynamics of the system and the stability of the different equilibrium
configurations against rotational symmetry breaking, and provide the global
phase diagram.Comment: 12 pages, 9 figure
Emergence of hierarchical networks and polysynchronous behaviour in simple adaptive systems
We describe the dynamics of a simple adaptive network. The network
architecture evolves to a number of disconnected components on which the
dynamics is characterized by the possibility of differently synchronized nodes
within the same network (polysynchronous states). These systems may have
implications for the evolutionary emergence of polysynchrony and hierarchical
networks in physical or biological systems modeled by adaptive networks.Comment: 4 pages, 4 figure
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
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