822,940 research outputs found
The State of Theoretical Diversity
Theory provides the medium for organizing and communicating knowledge that enables scientific collaboration. Review of five years of published work in two major IS journals, Management Information Systems Quarterly and Journal of Management Information Systems, describes the nature of this theoretical diversity in IS research. Two-hundred-seventy-three articles were evaluated for theoretical citations to identify the range of theories in Information Systems. Approximately half of the papers explicitly cited one of the 111 theories identified. Thirty of the theories were cited multiple times, representing 55% of the citations. The large number of theories used and the small number used more than once indicate that theoretical diversity clearly exists in information systems research. Based on the results, no theory emerged as a potential candidate for the role of grand/unified theory of information systems
DMRG Study of the Ground State at Higher Landau Levels - Stripes, Bubbles and the Wigner Crystal
Hartree-Fock theory predicted stripe or bubble phase in the third and higher
Landau levels for two-dimensional electrons, and experimental evidences has
been accumulated. In this paper theoretical confirmation of the stripe phase
and bubble phase in higher Landau level is given by means of the density matrix
renormalization group (DMRG) method, which can give essentially exact ground
state for electron systems with up to 18 electrons. From the study of the pair
correlation function, the stripe phase, bubble phase, and the Wigner crystal
phase are identified, and phase diagram is obtained. The reentrant integer
quantum Hall state is identified as the bubble state. The phase diagram of the
fourth Landau level shows more diversity than the third level.Comment: submitted to EP2DS-14, 3 pages, RevTex, two figures included in the
tex
Symmetry, Entropy, Diversity and (why not?) Quantum Statistics in Society
We describe society as a nonequilibrium probabilistic system: N individuals
occupy W resource states in it and produce entropy S over definite time
periods. Resulting thermodynamics is however unusual because a second entropy,
H, measures a typically social feature, inequality or diversity in the
distribution of available resources. A symmetry phase transition takes place at
Gini values 1/3, where realistic distributions become asymmetric. Four
constraints act on S: expectedly, N and W, and new ones, diversity and
interactions between individuals; the latter result from the two coordinates of
a single point in the data, the peak. The occupation number of a job is either
zero or one, suggesting Fermi-Dirac statistics for employment. Contrariwise, an
indefinite nujmber of individuals can occupy a state defined as a quantile of
income or of age, so Bose-Einstein statistics may be required.
Indistinguishability rather than anonymity of individuals and resources is thus
needed. Interactions between individuals define define classes of equivalence
that happen to coincide with acceptable definitions of social classes or
periods in human life. The entropy S is non-extensive and obtainable from data.
Theoretical laws are compared to data in four different cases of economical or
physiological diversity. Acceptable fits are found for all of them.Comment: 13 pages, 2 figure
Nuclear Astrophysics
Nuclear astrophysics is that branch of astrophysics which helps understanding
some of the many facets of the Universe through the knowledge of the microcosm
of the atomic nucleus. In the last decades much advance has been made in
nuclear astrophysics thanks to the sometimes spectacular progress in the
modelling of the structure and evolution of the stars, in the quality and
diversity of the astronomical observations, as well as in the experimental and
theoretical understanding of the atomic nucleus and of its spontaneous or
induced transformations. Developments in other sub-fields of physics and
chemistry have also contributed to that advance. Many long-standing problems
remain to be solved, however, and the theoretical understanding of a large
variety of observational facts needs to be put on safer grounds. In addition,
new questions are continuously emerging, and new facts endanger old ideas. This
review shows that astrophysics has been, and still is, highly demanding to
nuclear physics in both its experimental and theoretical components. On top of
the fact that large varieties of nuclei have to be dealt with, these nuclei are
immersed in highly unusual environments which may have a significant impact on
their static properties, the diversity of their transmutation modes, and on the
probabilities of these modes. In order to have a chance of solving some of the
problems nuclear astrophysics is facing, the astrophysicists and nuclear
physicists are obviously bound to put their competence in common, and have
sometimes to benefit from the help of other fields of physics, like particle
physics, plasma physics or solid-state physics.Comment: LaTeX2e with iopart.cls, 84 pages, 19 figures (graphicx package), 374
updated references. Published in Reports on Progress in Physics, vol.62, pp.
395-464 (1999
Populations of Supersoft X-ray Sources: Novae, tidal disruption, Type Ia supernovae, accretion-induced collapse, ionization, and intermediate-mass black holes?
Observations of hundreds of supersoft x-ray sources (SSSs) in external
galaxies have shed light on the diversity of the class and on the natures of
the sources. SSSs are linked to the physics of Type Ia supernovae and
accretion-induced collapse, ultraluminous x-ray sources and black holes, the
ionization of the interstellar medium, and tidal disruption by supermassive
black holes. The class of SSSs has an extension to higher luminosities:
ultraluminous SSSs have luminosities above 10^39 erg/s. There is also an
extension to higher energies: quasisoft x-ray sources (QSSs) emit photons with
energies above 1 eV, but few or none with energies above 2 keV. Finally, a
significant fraction of the SSSs found in external galaxies switch states
between observations, becoming either quasisoft or hard. For many systems
``supersoft'' refers to a temporary state; SSSs are sources, possibly including
a variety of fundamentally different system types, that pass through such a
state. We review those results derived from extragalactic data and related
theoretical work that are most surprising and that suggest directions for
future research.Comment: submitted to Astron.Nachr.; latex, 6 figure
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