4,581 research outputs found
Fluid injection device for high-pressure systems
Screw activated device, consisting of a compressor, shielded replaceable ampules, a multiple-element rubber gland, and a specially constructed fluid line fitting, injects measured amounts of fluids into a pressurized system. It is sturdy and easily manipulated
Stabilizing the Dilaton in Superstring Cosmology
We address the important issue of stabilizing the dilaton in the context of
superstring cosmology. Scalar potentials which arise out of gaugino condensates
in string models are generally exponential in nature. In a cosmological setting
this allows for the existence of quasi scaling solutions, in which the energy
density of the scalar field can, for a period, become a fixed fraction of the
background density, due to the friction of the background expansion. Eventually
the field can be trapped in the minimum of its potential as it leaves the
scaling regime. We investigate this possibility in various gaugino condensation
models and show that stable solutions for the dilaton are far more common than
one would have naively thought.Comment: 13 pages, LaTex, uses psfig.sty with 3 figure
Constraints on string networks with junctions
We consider the constraints on string networks with junctions in which the
strings may all be different, as may be found for example in a network of
cosmic superstrings. We concentrate on three aspects of junction
dynamics. First we consider the propagation of small amplitude waves across a
static three-string junction. Then, generalizing our earlier work, we determine
the kinematic constraints on two colliding strings with different tensions. As
before, the important conclusion is that strings do not always reconnect with a
third string; they can pass straight through one another (or in the case of
non-abelian strings become stuck in an X configuration), the constraint
depending on the angle at which the strings meet, on their relative velocity,
and on the ratios of the string tensions. For example, if the two colliding
strings have equal tensions, then for ultra-relativistic initial velocities
they pass through one another. However, if their tensions are sufficiently
different they can reconnect. Finally, we consider the global properties of
junctions and strings in a network. Assuming that, in a network, the incoming
waves at a junction are independently randomly distributed, we determine the
r.m.s. velocities of strings and calculate the average speed at which a
junction moves along each of the three strings from which it is formed. Our
findings suggest that junction dynamics may be such as to preferentially remove
the heavy strings from the network leaving a network of predominantly light
strings. Furthermore the r.m.s. velocity of strings in a network with junctions
is smaller than 1/\sqrt{2}, the result for conventional Nambu-Goto strings
without junctions in Minkowski spacetime.Comment: 12 pages, 6 figures. Version to appear in PRD. (2 new references and
slightly extended discussion in section VII
Stretching Wiggly Strings
How does the amplitude of a wiggle on a string change when the string is
stretched? We answer this question for both longitudinal and transverse wiggles
and for arbitrary equation of state, {\it i.e.}, for arbitrary relation between
the tension and the energy per unit length of the string.
This completes our derivation of the renormalization of string parameters which
results from averaging out small scale wiggles on a string. The program is
presented here in its entirety.Comment: Written with ReVTeX 3.0 package. Two figures are not included.
Complete paper with postscript figures can be retrieved through anonymous ftp
@quark.phys.ufl.edu. Get /preprints/ifthep94_4.tar.gz, gunzip and tar it.
UFIFT-HEP-94-
Cosmological perturbation spectra from SL(4,R)-invariant effective actions
We investigate four-dimensional cosmological vacuum solutions derived from an
effective action invariant under global SL(n,R) transformations. We find the
general solutions for linear axion field perturbations about homogeneous
dilaton-moduli-vacuum solutions for an SL(4,R)-invariant action and find the
spectrum of super-horizon perturbations resulting from vacuum fluctuations in a
pre big bang scenario. We show that for SL(n,R)-invariant actions with n>3
there exists a regime of parameter space of non-zero measure where all the
axion field spectra have positive spectral tilt, as required if light axion
fields are to provide a seed for anisotropies in the microwave background and
large-scale structure in the universe.Comment: 8 pages, 3 figures, revtex plus epsf, minor typos corrected, version
to appear in Physical Review
Investigations into the Sarcomeric Protein and Ca2+-Regulation Abnormalities Underlying Hypertrophic Cardiomyopathy in Cats (Felix catus).
Hypertrophic cardiomyopathy (HCM) is the most common single gene inherited cardiomyopathy. In cats (Felix catus) HCM is even more prevalent and affects 16% of the outbred population and up to 26% in pedigree breeds such as Maine Coon and Ragdoll. Homozygous MYBPC3 mutations have been identified in these breeds but the mutations in other cats are unknown. At the clinical and physiological level feline HCM is closely analogous to human HCM but little is known about the primary causative mechanism. Most identified HCM causing mutations are in the genes coding for proteins of the sarcomere. We therefore investigated contractile and regulatory proteins in left ventricular tissue from 25 cats, 18 diagnosed with HCM, including a Ragdoll cat with a homozygous MYBPC3 R820W, and 7 non-HCM cats in comparison with human HCM (from septal myectomy) and donor heart tissue. Myofibrillar protein expression was normal except that we observed 20–44% MyBP-C haploinsufficiency in 5 of the HCM cats. Troponin extracted from 8 HCM and 5 non-HCM cat hearts was incorporated into thin filaments and studied by in vitro motility assay. All HCM cat hearts had a higher (2.06 ± 0.13 fold) Ca2+-sensitivity than non-HCM cats and, in all the HCM cats, Ca2+-sensitivity was not modulated by troponin I phosphorylation. We were able to restore modulation of Ca2+-sensitivity by replacing troponin T with wild-type protein or by adding 100 μM Epigallocatechin 3-gallate (EGCG). These fundamental regulatory characteristics closely mimic those seen in human HCM indicating a common molecular mechanism that is independent of the causative mutation. Thus, the HCM cat is a potentially useful large animal model
Kinks and small-scale structure on cosmic strings
We discuss some hitherto puzzling features of the small-scale structure of
cosmic strings. We argue that kinks play a key role, and that an important
quantity to study is their sharpness distribution. In particular we suggest
that for very small scales the two-point correlation function of the string
tangent vector varies linearly with the separation and not as a fractional
power, as proposed by Polchinski and Rocha [Phys. Rev. D 74, 083504 (2006)].
However, our results are consistent with theirs, because the range of scales to
which this linearity applies shrinks as evolution proceeds.Comment: 10pages, revtex file, minor errors correcte
Qualitative analysis of a scalar-tensor theory with exponential potential
A qualitative analysis of a scalar-tensor cosmological model, with an
exponential potential for the scalar field, is performed. The phase diagram for
the flat case is constructed. It is shown that solutions with an initial and
final inflationary behaviour appear. The conditions for which the scenario
favored by supernova type Ia observations becomes an attractor in the space of
the solutions are established.Comment: Latex file, 9 pages, 1 figur
Curvaton reheating: an application to braneworld inflation
The curvaton was introduced recently as a distinct inflationary mechanism for
generating adiabatic density perturbations. Implicit in that scenario is that
the curvaton offers a new mechanism for reheating after inflation, as it is a
form of energy density not diluted by the inflationary expansion. We consider
curvaton reheating in the context of a braneworld inflation model, {\em steep
inflation}, which features a novel use of the braneworld to give a new
mechanism for ending inflation. The original steep inflation model featured
reheating by gravitational particle production, but the inefficiency of that
process brings observational difficulties. We demonstrate here that the
phenomenology of steep inflation is much improved by curvaton reheating.Comment: 8 pages RevTeX4 file with two figures incorporated. Improved
referencing, matches PRD accepted versio
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