8,278 research outputs found
Non trivial generalizations of the Schwinger pair production result II
It is suggested that Schwinger's (1951) vacuum persistence probability
against pair production by an intense but constant electric field is a very
good approximation to the corresponding quantity if the field does not vary
appreciably over distances less than m/e/E/5 pagesComment: 5 page
Determination of complex dielectric functions of ion implanted and implanted‐annealed amorphous silicon by spectroscopic ellipsometry
Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ϵ = ϵ1 + iϵ2) of different kinds of amorphous silicon prepared by self‐implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a‐Si (i‐a‐Si) differs from that of relaxed (annealed) a‐Si (r‐a‐Si). Moreover, its ϵ differs from the ϵ of evaporated a‐Si (e‐a‐Si) found in the handbooks as ϵ for a‐Si. If we use this ϵ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ϵ2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i‐a‐Si), 1.12 eV (e‐a‐Si), 1.30 eV (r‐a‐Si). We attribute the optical change to annihilation of point defects
Nighttime Catches of Fishes in a Tidal Cove in Montsweag Bay Near Wiscasset Maine
Summer nighttime abundance and localized distribution of fishes in a tidal cove were studied by beach seining for comparison with a previous daytime study. American eels were relatively abundant at night and absent during the day. Alewife, blueback herring, and Atlantic silver-side were more abundant in the cove at night. Although mummichog numbers were greatly reduced at night, they remained an important constituent of the night fauna. Lesser components of the night fauna included Atlantic herring, Atlantic tomcod, smooth flounder, winter flounder, and rainbow smelt
The Double Quasar Q2138-431: Lensing by a Dark Galaxy?
We report the discovery of a new gravitational lens candidate Q2138-431AB,
comprising two quasar images at a redshift of 1.641 separated by 4.5 arcsecs.
The spectra of the two images are very similar, and the redshifts agree to
better than 115 km.sec. The two images have magnitudes and
, and in spite of a deep search and image subtraction procedure, no
lensing galaxy has been found with . Modelling of the system
configuration implies that the mass-to-light ratio of any lensing galaxy is
likely to be around , with an absolute lower limit of
for an Einstein-de Sitter universe. We conclude that
the most likely explanation of the observations is gravitational lensing by a
dark galaxy, although it is possible we are seeing a binary quasar.Comment: 17 pages (Latex), 8 postscript figures included, accepted by MNRA
Stellar Dynamics and the implications on the merger evolution in NGC6240
We report near-infrared integral field spectroscopy of the luminous merging
galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by
1.6arcsec are the central parts of inclined, rotating disk galaxies with equal
mass bulges. The dynamical masses of the nuclei are much larger than the
stellar mass derived from the K-band light, implying that the progenitor
galaxies were galaxies with massive bulges. The K-band light is dominated by
red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years
ago, possibly by the most recent perigalactic approach. Strong feedback effects
of a superwind and supernovae are responsible for a short duration burst
(~5x10^6 years) which is already decaying. The two galaxies form a
prograde-retrograde rotating system and from the stellar velocity field it
seems that one of the two interacting galaxies is subject to a prograde
encounter. Between the stellar nuclei is a prominent peak of molecular gas
(H_2, CO). The stellar velocity dispersion peaks there indicating that the gas
has formed a local, self-gravitating concentration decoupled from the stellar
gravitational potential. NGC 6240 has previously been reported to fit the
paradigm of an elliptical galaxy formed through the merger of two galaxies.
This was based on the near-infrared light distribution which follows a
r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far
not relaxed, rotation plays an important role, as does self-gravitating gas,
and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the
Astrophysical Journal, revised versio
The differential influence of life stress on individual symptoms of depression
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111765/1/acps12395.pd
Casimir forces from a loop integral formulation
We reformulate the Casimir force in the presence of a non-trivial background.
The force may be written in terms of loop variables, the loop being a curve
around the scattering sites. A natural path ordering of exponentials take place
when a particular representation of the scattering centres is given. The basic
object to be evaluated is a reduced (or abbreviated) classical pseudo-action
that can be operator valued.Comment: references added, text clarified in place
Probability distributions for quantum stress tensors in four dimensions
We treat the probability distributions for quadratic quantum fields, averaged
with a Lorentzian test function, in four-dimensional Minkowski vacuum. These
distributions share some properties with previous results in two-dimensional
spacetime. Specifically, there is a lower bound at a finite negative value, but
no upper bound. Thus arbitrarily large positive energy density fluctuations are
possible. We are not able to give closed form expressions for the probability
distribution, but rather use calculations of a finite number of moments to
estimate the lower bounds, the asymptotic forms for large positive argument,
and possible fits to the intermediate region. The first 65 moments are used for
these purposes. All of our results are subject to the caveat that these
distributions are not uniquely determined by the moments. However, we also give
bounds on the cumulative distribution function that are valid for any
distribution fitting these moments.We apply the asymptotic form of the
electromagnetic energy density distribution to estimate the nucleation rates of
black holes and of Boltzmann brains.Comment: 26 pages, 2 figure
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