11,445 research outputs found
The existence of time
Of those gauge theories of gravity known to be equivalent to general
relativity, only the biconformal gauging introduces new structures - the
quotient of the conformal group of any pseudo-Euclidean space by its Weyl
subgroup always has natural symplectic and metric structures. Using this metric
and symplectic form, we show that there exist canonically conjugate,
orthogonal, metric submanifolds if and only if the original gauged space is
Euclidean or signature 0. In the Euclidean cases, the resultant configuration
space must be Lorentzian. Therefore, in this context, time may be viewed as a
derived property of general relativity.Comment: 21 pages (Reduced to clarify and focus on central argument; some
calculations condensed; typos corrected
Tax in kind
Estimate and assessment of tax owed on pork: H. Wilson of Copiah County paid 104 pounds pork to the Confederate government, as a 10% tax on 1040 pounds assessed. Payment received by agent T. H. Wheeler at Depot No. 3, 4th Congressional District. Copiah County, Mississippi, 1865.https://scholarsjunction.msstate.edu/mss-ashley-collection/1001/thumbnail.jp
Changing trends in the labor force: a survey
The composition of the American workforce has changed dramatically over the past half century as a result of both the emergence of married women as a substantial component of the labor force and an increase in the number of minority workers. The aging of the population has contributed to this change as well. In this paper, the authors review the evidence of changing labor force participation rates, estimate the trends in labor force participation over the past 50 years, and find that aggregate participation has stabilized after a period of persistent increases. Moreover, they examine the disparate labor force participation experiences of different demographic groups. Finally, they survey some of the studies that have provided explanations for these differences.Labor supply ; Labor market
The economic performance of cities: a Markov-switching approach
This paper examines the determinants of employment growth in metro areas. To obtain growth rates, we use a Markov-switching model that separates a city’s growth path into two distinct phases (high and low), each with its own growth rate. The simple average growth rate over some period is, therefore, the weighted average of the high-phase and low-phase growth rates, with the weight being the frequency of the two phases. We estimate the effects of a variety of factors separately for the high-phase and low-phase growth rates, along with the frequency of the low phase. We find that growth in the high phase is related to human capital, industry mix, and average firm size. In contrast, we find that growth in the low phase is mostly related to industry mix, specifically, the relative importance of manufacturing. Finally, the frequency of the low phase appears to be related to the level of non-education human capital, but to none of the other variables. Overall, our results strongly reject the notion that city-level characteristics influence employment growth equally across the phases of the business cycle.Business cycles ; Cities and towns
New representation and a vacuum state for canonical quantum gravity
A new representation for canonical gravity and supergravity is presented,
which combines advantages of Ashtekar's and the Wheeler~DeWitt representation:
it has a nice geometric structure and the singular metric problem is absent. A
formal state functional can be given, which has some typical features of a
vacuum state in quantum field theory. It can be canonically transformed into
the metric representation. Transforming the constraints too, one recovers the
Wheeler~DeWitt equation up to an anomalous term. A modified Dirac quantization
is proposed to handle possible anomalies in the constraint algebra.Comment: 28 pages, LaTe
Some Heuristic Semiclassical Derivations of the Planck Length, the Hawking Effect and the Unruh Effect
The formulae for Planck length, Hawking temperature and Unruh-Davies
temperature are derived by using only laws of classical physics together with
the Heisenberg principle. Besides, it is shown how the Hawking relation can be
deduced from the Unruh relation by means of the principle of equivalence; the
deep link between Hawking effect and Unruh effect is in this way clarified.Comment: LaTex file, 6 pages, no figure
Revealing Relationships among Relevant Climate Variables with Information Theory
A primary objective of the NASA Earth-Sun Exploration Technology Office is to
understand the observed Earth climate variability, thus enabling the
determination and prediction of the climate's response to both natural and
human-induced forcing. We are currently developing a suite of computational
tools that will allow researchers to calculate, from data, a variety of
information-theoretic quantities such as mutual information, which can be used
to identify relationships among climate variables, and transfer entropy, which
indicates the possibility of causal interactions. Our tools estimate these
quantities along with their associated error bars, the latter of which is
critical for describing the degree of uncertainty in the estimates. This work
is based upon optimal binning techniques that we have developed for
piecewise-constant, histogram-style models of the underlying density functions.
Two useful side benefits have already been discovered. The first allows a
researcher to determine whether there exist sufficient data to estimate the
underlying probability density. The second permits one to determine an
acceptable degree of round-off when compressing data for efficient transfer and
storage. We also demonstrate how mutual information and transfer entropy can be
applied so as to allow researchers not only to identify relations among climate
variables, but also to characterize and quantify their possible causal
interactions.Comment: 14 pages, 5 figures, Proceedings of the Earth-Sun System Technology
Conference (ESTC 2005), Adelphi, M
Is there a relativistic nonlinear generalization of quantum mechanics?
Yes, there is. - A new kind of gauge theory is introduced, where the minimal
coupling and corresponding covariant derivatives are defined in the space of
functions pertaining to the functional Schroedinger picture of a given field
theory. While, for simplicity, we study the example of an U(1) symmetry, this
kind of gauge theory can accommodate other symmetries as well. We consider the
resulting relativistic nonlinear extension of quantum mechanics and show that
it incorporates gravity in the (0+1)-dimensional limit, where it leads to the
Schroedinger-Newton equations. Gravity is encoded here into a universal
nonlinear extension of quantum theory. The probabilistic interpretation, i.e.
Born's rule, holds provided the underlying model has only dimensionless
parameters.Comment: 10 pages; talk at DICE 2006 (Piombino, September 11-15, 2006); to
appear in Journal of Physics: Conference Series (2007
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
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