1,443 research outputs found
A new interpretation of dielectric data in molecular glass formers
Literature dielectric data of glycerol, propylene carbonate and
ortho-terphenyl (OTP) show that the measured dielectric relaxation is a decade
faster than the Debye expectation, but still a decade slower than the breakdown
of the shear modulus. From a comparison of time scales, the dielectric
relaxation seems to be due to a process which relaxes not only the molecular
orientation, but the entropy, the short-range order and the density as well. On
the basis of this finding, we propose an alternative to the
Gemant-DiMarzio-Bishop extension of the Debye picture.Comment: 7 pages, 4 figures, 68 references; 3. version extended following
referee advic
Crystal structure, incommensurate magnetic order and ferroelectricity in mncuwo (x=0-0.19)
We have carried out a systematic study on the effect of Cu doping on nuclear,
magnetic, and dielectric properties in MnCuWO for
by a synergic use of different techniques, viz, heat
capacity, magnetization, dielectric, and neutron powder diffraction
measurements. Via heat capacity and magnetization measurements we show that
with increasing Cu concentration magnetic frustration decreases, which leads to
the stabilization of commensurate magnetic ordering. This was further verified
by temperature-dependent unit cell volume changes derived from neutron
diffraction measurements which was modeled by the Gr\"{u}neisen approximation.
Dielectric measurements show a low temperature phase transition below about
9-10 K. Further more, magnetic refinements reveal no changes below this
transition indicating a possible spin-flop transition which is unique to the Cu
doped system. From these combined studies we have constructed a magnetoelectric
phase diagram of this compound.Comment: 9 pages, 9 figures, accepted for publication in PR
Minimal Gauge Invariant Classes of Tree Diagrams in Gauge Theories
We describe the explicit construction of groves, the smallest gauge invariant
classes of tree Feynman diagrams in gauge theories. The construction is valid
for gauge theories with any number of group factors which may be mixed. It
requires no summation over a complete gauge group multiplet of external matter
fields. The method is therefore suitable for defining gauge invariant classes
of Feynman diagrams for processes with many observed final state particles in
the standard model and its extensions.Comment: 13 pages, RevTeX (EPS figures
D-Meson Mixing in Broken SU(3)
A fit of amplitudes to the experimental branching ratios to two mesons is
used to construct a new estimate of neutral mixing which includes
breaking. The result is dominated by the experimental uncertainties. This
suggests that the charm sector may not be as sensitive to new physics as
previously thought and that long-distance calculations may not be useful.Comment: 12 pages, LaTeX, no figure
Birth and growth of cavitation bubbles within water under tension confined in a simple synthetic tree
Water under tension, as can be found in several systems including tree
vessels, is metastable. Cavitation can spontaneously occur, nucleating a
bubble. We investigate the dynamics of spon- taneous or triggered cavitation
inside water filled microcavities of a hydrogel. Results show that a stable
bubble is created in only a microsecond timescale, after transient
oscillations. Then, a diffusion driven expansion leads to filling of the
cavity. Analysis reveals that the nucleation of a bubble releases a tension of
several tens of MPa, and a simple model captures the different time scales of
the expansion process
Ethnicity and age as factors in sildenafil treatment of erectile dysfunction
IntroductionSildenafil has been evaluated in >16Â 000 men with erectile dysfunction (ED) in doubleâ blind, placeboâ controlled trials.AimTo assess efficacy and safety of sildenafil in ED by ethnicity (white, black Asian) and age (â ¤45, 46â 60, â ¥61Â years).MethodsData were pooled from 38 doubleâ blind, placeboâ controlled, flexibleâ dose trials. Most had starting sildenafil doses of 50Â mg once daily, ~1Â hour before sexual activity, with adjustment to 100 or 25Â mg as needed.Main Outcome MeasuresChange from baseline in International Index of Erectile Function erectile function (IIEFâ EF) domain score assessed with analysis of covariance and a Global Assessment Question (GAQ; â Did the treatment improve your erections?â ) at endpoint assessed with logistic regression analysis.Results4120 and 3714 men received sildenafil and placebo, respectively (2740 and 2671 White; 407 and 385 Black; 973 and 658 Asian). For sildenafil vs. placebo groups, overall treatment differences for IIEFâ EF domain and GAQ were significant for each ethnic and age group (P<.0001); significant treatmentâ byâ ethnicity and treatmentâ byâ age interactions were also observed for change in IIEFâ EF domain scores (P<.05), with differences significantly greater for White vs. Black (P<.0001), White vs. Asian (P=.0163), and Asian vs. Black (P=.0036) men. A significant treatmentâ byâ ethnicity interaction was observed for GAQ (P=.0004). The OR comparison for GAQ was significantly greater (P=.0001) with sildenafil vs. placebo in White (OR=11.2) or Asian (OR=12.4) men vs. Black men (OR=5.1). Adverseâ event rates were generally similar, with some age variations.ConclusionsSildenafil is effective and wellâ tolerated regardless of ethnicity or age; however, treatment effects can vary.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137386/1/ijcp12945_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137386/2/ijcp12945.pd
A Completely Invariant SUSY Transform of Supersymmetric QED
We study the SUSY breaking of the covariant gauge-fixing term in SUSY QED and
observe that this corresponds to a breaking of the Lorentz gauge condition by
SUSY. Reasoning by analogy with SUSY's violation of the Wess-Zumino gauge, we
argue that the SUSY transformation, already modified to preserve Wess-Zumino
gauge, should be further modified by another gauge transformation which
restores the Lorentz gauge condition. We derive this modification and use the
resulting transformation to derive a Ward identitiy relating the photon and
photino propagators without using ghost fields. Our transformation also
fulfills the SUSY algebra, modulo terms that vanish in Lorentz gauge
Spacetime Noncommutativity in Models with Warped Extradimensions
We construct consistent noncommutative (NC) deformations of the
Randall-Sundrum spacetime that solve the NC Einstein equations with a
non-trivial Poisson tensor depending on the fifth coordinate. In a class of
these deformations where the Poisson tensor is exponentially localized on one
of the branes (the NC-brane), we study the effects on bulk particles in terms
of Lorentz-violating operators induced by NC-brane interactions. We sketch two
models in which massive bulk particles mediate NC effects to an
almost-commutative SM-brane, such that observables at high energy colliders are
enhanced with respect to low energy and astrophysical observables.Comment: 15 pages, LaTeX, pdf figures included, to appear in JHE
Pupil Alignment Considerations for Large, Deployable Space Telescopes
For many optical systems the properties and alignment of the internal apertures and pupils are not critical or controlled with high precision during optical system design, fabrication or assembly. In wide angle imaging systems, for instance, the entrance pupil position and orientation is typically unconstrained and varies over the system s field of view in order to optimize image quality. Aperture tolerances usually do not receive the same amount of scrutiny as optical surface aberrations or throughput characteristics because performance degradation is typically graceful with misalignment, generally only causing a slight reduction in system sensitivity due to vignetting. But for a large deployable space-based observatory like the James Webb Space Telescope (JWST), we have found that pupil alignment is a key parameter. For in addition to vignetting, JWST pupil errors cause uncertainty in the wavefront sensing process that is used to construct the observatory on-orbit. Furthermore they also open stray light paths that degrade the science return from some of the telescope s instrument channels. In response to these consequences, we have developed several pupil measurement techniques for the cryogenic vacuum test where JWST science instrument pupil alignment is verified. These approaches use pupil alignment references within the JWST science instruments; pupil imaging lenses in three science instrument channels; and unique pupil characterization features in the optical test equipment. This will allow us to verify and crosscheck the lateral pupil alignment of the JWST science instruments to approximately 1-2% of their pupil diameters
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