14,550 research outputs found
Structure formation by cosmic strings with a cosmological constant
Final published version.Comment: 4 Page
Thermo-mechanic-electrical coupling in phospholipid monolayers near the critical point
Lipid monolayers have been shown to represent a powerful tool in studying
mechanical and thermodynamic properties of lipid membranes as well as their
interaction with proteins. Using Einstein's theory of fluctuations we here
demonstrate, that an experimentally derived linear relationship both between
transition entropy S and area A as well as between transition entropy and
charge q implies a linear relationships between compressibility \kappa_T, heat
capacity c_\pi, thermal expansion coefficient \alpha_T and electric capacity
CT. We demonstrate that these couplings have strong predictive power as they
allow calculating electrical and thermal properties from mechanical
measurements. The precision of the prediction increases as the critical point
TC is approached
Varying c cosmology and Planck value constraints
It has been suggested that by increasing the speed of light during the early
universe various cosmological problems of standard big bang cosmology can be
overcome, without requiring an inflationary phase. However, we find that as the
Planck length and Planck time are then made correspondingly smaller, and
together with the need that the universe should not re-enter a Planck epoch,
the higher models have very limited ability to resolve such problems. For a
constantly decreasing the universe will quickly becomes quantum
gravitationally dominated as time increases: the opposite to standard cosmology
where quantum behaviour is only ascribed to early times.Comment: extended versio
QCD-based description of one-particle inclusive B decays
We discuss one-particle inclusive B decays in the limit of heavy b and c
quarks. Using the large-N_C limit we factorize the non-leptonic matrix
elements, and we employ a short distance expansion. Modeling the remaining
nonperturbative matrix elements we obtain predictions for various decay
channels and compare them with existing data.Comment: LaTeX, 22 pages, 6 figures (eps); analytical and numerical results
unchanged, misrepresentation of experimental data in Fig. 5 corrected, final
published versio
Ab initio Green's function formalism for band structures
Using the Green's function formalism, an ab initio theory for band structures
of crystals is derived starting from the Hartree-Fock approximation. It is
based on the algebraic diagrammatic construction scheme for the self-energy
which is formulated for crystal orbitals (CO-ADC). In this approach, the poles
of the Green's function are determined by solving a suitable Hermitian
eigenvalue problem. The method is not only applicable to the outer valence and
conduction bands, it is also stable for inner valence bands where strong
electron correlations are effective. The key to the proposed scheme is to
evaluate the self-energy in terms of Wannier orbitals before transforming it to
a crystal momentum representation. Exploiting the fact that electron
correlations are mainly local, one can truncate the lattice summations by an
appropriate configuration selection scheme. This yields a flat configuration
space; i.e., its size scales only linearly with the number of atoms per unit
cell for large systems and, under certain conditions, the computational effort
to determine band structures also scales linearly. As a first application of
the new formalism, a lithium fluoride crystal has been chosen. A minimal basis
set description is studied, and a satisfactory agreement with previous
theoretical and experimental results for the fundamental band gap and the width
of the F 2p valence band complex is obtained.Comment: 20 pages, 3 figures, 1 table, RevTeX4, new section on lithium
fluorid
EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary
We have discovered a doubly eclipsing, bound, quadruple star system in the
field of K2 Campaign 7. EPIC 219217635 is a stellar image with that
contains an eclipsing binary (`EB') with d and a second EB with
d. We have obtained followup radial-velocity (`RV')
spectroscopy observations, adaptive optics imaging, as well as ground-based
photometric observations. From our analysis of all the observations, we derive
good estimates for a number of the system parameters. We conclude that (1) both
binaries are bound in a quadruple star system; (2) a linear trend to the RV
curve of binary A is found over a 2-year interval, corresponding to an
acceleration, cm s; (3) small
irregular variations are seen in the eclipse-timing variations (`ETVs')
detected over the same interval; (4) the orbital separation of the quadruple
system is probably in the range of 8-25 AU; and (5) the orbital planes of the
two binaries must be inclined with respect to each other by at least
25. In addition, we find that binary B is evolved, and the cooler and
currently less massive star has transferred much of its envelope to the
currently more massive star. We have also demonstrated that the system is
sufficiently bright that the eclipses can be followed using small ground-based
telescopes, and that this system may be profitably studied over the next decade
when the outer orbit of the quadruple is expected to manifest itself in the ETV
and/or RV curves.Comment: Accepted for publication in MNRA
Doppler peaks from active perturbations
We examine how the qualitative structure of the Doppler peaks in the angular
power spectrum of the cosmic microwave anisotropy depends on the fundamental
nature of the perturbations which produced them. The formalism of Hu and
Sugiyama is extended to treat models with cosmic defects. We discuss how
perturbations can be ``active'' or ``passive'' and ``incoherent'' or
``coherent'', and show how causality and scale invariance play rather different
roles in these various cases. We find that the existence of secondary Doppler
peaks and the rough placing of the primary peak unambiguously reflect these
basic properties.Comment: uufile, 8pages, 3 figures. Now available at
http://euclid.tp.ph/Papers/index.html; Changes: URL added, Eqn. (8) expanded,
grant numbers include
Opportunities for future supernova studies of cosmic acceleration
We investigate the potential of a future supernova dataset, as might be
obtained by the proposed SNAP satellite, to discriminate among different ``dark
energy'' theories that describe an accelerating Universe. We find that many
such models can be distinguished with a fit to the effective
pressure-to-density ratio, , of this energy. More models can be
distinguished when the effective slope, , of a changing is also fit,
but only if our knowledge of the current mass density, , is improved.
We investigate the use of ``fitting functions'' to interpret luminosity
distance data from supernova searches, and argue in favor of a particular
preferred method, which we use in our analysis.Comment: Four pages including figures. Final published version. No significant
changes from v
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