8,556 research outputs found
Spinor fields without Lorentz frames in curved spacetime using complexified quaternions
Using complexified quaternions, a formalism without Lorentz frames, and
therefore also without vierbeins, for dealing with tensor and spinor fields in
curved spacetime is presented. A local U(1) gauge symmetry, which, it is
speculated, might be related to electromagnetism, emerges naturally.Comment: 14 pages; v2: minor corrections; v3: note added concerning unified
treatment of local Lorentz transformations and local U(1) gauge
transformations; v4: published in J. Math. Phys. 50 083507 (2009
The String Coupling Accelerates the Expansion of the Universe
Generic cosmological models in non-critical string theory have a
time-dependent dilaton background at a late epoch. The cosmological
deceleration parameter Q_0 is given by the square of the string coupling,
g_s^2, up to a negative sign. Hence the expansion of the Universe must
accelerate eventually, and the observed value of Q_0 coresponds to g_s^2 ~ 0.6.
In this scenario, the string coupling is asymptotically free at large times,
but its present rate of change is imperceptibly small.Comment: 7 page
Multiparty Politics in America (First Edition)
In the wake of Ross Perot, Ralph Nader, and other third party and independent candidates that ran in the 1996 election, this collection of original essays by leading political scientists and third party officials is must reading for individuals interested in American politics. Multiparty Politics in America examines the roles that third parties have played in U.S. elections past and present and their prospects for the future. It presents unique and detailed coverage of the Reform, Green, and Libertarian parties\u27 goals and campaign strategies; discusses the kinds of reforms that would help them become more viable; and advances the debate over whether the U.S. should have a two-party or multiparty system.https://ideaexchange.uakron.edu/multiparty_politics1/1000/thumbnail.jp
The X-ray Iron Emission from Tycho's Supernova Remnant
We present the results of broadband fits to the X-ray spectrum of Tycho's
supernova remnant obtained by the Solid-State Imaging Spectrometers on the ASCA
Observatory. We use single-temperature, single-ionization-age, nonequilibrium
ionization models to characterize the ejecta and the blast-shocked interstellar
medium. Based on the Fe K emission at 6.5 keV, previous spectral studies have
suggested that the Fe ejecta in this Type Ia remnant are stratified interior to
the other ejecta. The ASCA data provide important constraints from the Fe L
emission near 1 keV as well as the Fe K emission. We find that the simplest
models, with emission from the ejecta and blast wave each at a single
temperature and ionization age, severely underestimate the Fe K flux. We show
that there is little Fe emission associated with the Si and S ejecta shell. The
blast-shocked interstellar medium has abundances roughly 0.3 times the solar
value, while the ejecta, with the exception of Fe, have relative abundances
that are typical of Type Ia supernovae. The addition of another component of Fe
emission, which we associate with ejecta, at a temperature at least two times
higher and an ionization age 100 times lower than the Si ejecta, does
provide a good fit to the spectrum. This model is consistent with X-ray imaging
results. Although fluorescent emission from dust in the remnant may contribute
to the Fe K flux, we conclude that it is unlikely to dominate.Comment: 23 pages, LaTex; 4 postscript figures, 2 postscript tables. To appear
in ApJ, vol 49
Open problems in artificial life
This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated
Hemiparasitic plant impacts animal and plant communities across four trophic levels
1.Understanding the impact of species on community structure is a fundamental question in ecology. There is a growing body of evidence that suggests that both sub-dominant species and parasites can have a disproportionately large impact.
2.Here we report the impacts of an organism that is both subdominant and parasitic, the hemiparasite Rhinanthus minor. Whilst the impact of parasitic angiosperms on their hosts and, to a lesser degree, co-existing plant species, have been well characterized, much less is known about their impacts on higher trophic levels.
3.We experimentally manipulated field densities of the hemiparasite Rhinanthus minor in a species rich grassland, comparing the plant and invertebrate communities in plots where it was removed, at natural densities or at enhanced densities.
4.Plots with natural and enhanced densities of R. minor had lower plant biomass than plots without the hemiparasite, but enhanced densities almost doubled the abundance of invertebrates within the plots across all trophic levels, with effects evident in herbivores, predators and detritivores.
5.The hemiparasite R. minor, despite being a sub-dominant and transient component within plant communities that it inhabits, has profound effects on four different trophic levels. These effects persist beyond the life of the hemiparasite,
emphasizing its role as a keystone species in grassland communitie
A new mechanism for exchange processes observed in the compounds [M(η-C_5H_5)_2(exo-η-RCH = CH_2)H], M = Nb and Ta
Dynamic n.m.r. studies of the exchange processes in the complexes [M(η-C_5H_5)(exo-η-RCH=CH_2)H], M = Nb, Ta, lead to the proposal of a new mechanism involving intermediates with agostic bonding
The Statistical Mechanical Theory of Transport Processes. III. The Coefficients of Shear and Bulk Viscosity of Liquids
A molecular theory of the coefficients of shear and bulk viscosity of monatomic liquids is developed on the basis of the general theory of transport processes presented in the first article of this series. With the use of the Lennard-Jones potential and a reasonable analytic approximation to the experimental radial distribution function, calculations of the coefficients of shear and bulk viscosity of liquid argon at 89°K have been carried out. The theory leads explicitly to ratios of the coefficients to the friction constant of the theory of Brownian motion. With a preliminary estimate of the friction constant, a value of the shear viscosity of liquid argon in moderately good agreement with experiment is obtained
Geology of the Lower Paleozoic Rocks in the Boundary Mountain Anticlinorium
Guidebook for field trips in the Rangeley Lakes - Dead River Basin region, western Maine: 62nd annual meeting October 2, 3, and 4, 1970: Trip A-
The Journal of the Friends' Historical Society volume 1, no. 1
1. Foreword
2. Notes and Queries
3. The Handwriting of George Fox (illustrated) By Isaac Sharp, B.A.
4. Grangerised Books By The Editors
5. Our Recording Clerks: I. Ellis HookesBy Norman Penney
6. The Case of William Gibson (illustrated) By The Editor
7. Two Quotations in the London Y.M. Epistle, 1903 By The Editors
8. The Quaker Family of Owen I By Joseph J. Green
9. Letters of Wm. Dewsbury and John Whitehead By The Editors
10. Friends' Reference Library, Devonshire House
11. Book Notes By Norman Penney
12. List of Member
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