11,481 research outputs found
Generalized Korn's inequality and conformal Killing vectors
Korn's inequality plays an important role in linear elasticity theory. This
inequality bounds the norm of the derivatives of the displacement vector by the
norm of the linearized strain tensor. The kernel of the linearized strain
tensor are the infinitesimal rigid-body translations and rotations (Killing
vectors). We generalize this inequality by replacing the linearized strain
tensor by its trace free part. That is, we obtain a stronger inequality in
which the kernel of the relevant operator are the conformal Killing vectors.
The new inequality has applications in General Relativity.Comment: 8 page
Birth, life and death of a cyclonic eddy in the Southern Ocean
The ACC is a climatically relevant frontal structure of global importance that regularly develops instabilities which grow into meanders that eventually evolve into long-lived cyclonic eddies. These eddies exhibit sustain primary productivity that can last several months fuelled by local resupply of nutrients. During April-May 2015 we conducted an intensive field experiment in the Southern Ocean (SMILES) where we sampled and tracked an ACC meander as it developed into an eddy and later vanished some 90 days later. The meander and later eddy physical characteristics were observed with a combination of high resolution hydrography, ADCP and turbulence observations in addition to surface and depth resolved biogeochemical observations of nutrients and phytoplankton. The life and death of the eddy was subsequently tracked through ARGO, BIO-ARGO and remote sensing
From E_8 to F via T
We argue that T-duality and F-theory appear automatically in the E_8 gauge
bundle perspective of M-theory. The 11-dimensional supergravity four-form
determines an E_8 bundle. If we compactify on a two-torus, this data specifies
an LLE_8 bundle where LG is a centrally-extended loopgroup of G. If one of the
circles of the torus is smaller than sqrt(alpha') then it is also smaller than
a nontrivial circle S in the LLE_8 fiber and so a dimensional reduction on the
total space of the bundle is not valid. We conjecture that S is the circle on
which the T-dual type IIB theory is compactified, with the aforementioned torus
playing the role of the F-theory torus. As tests we reproduce the T-dualities
between NS5-branes and KK-monopoles, as well as D6 and D7-branes where we find
the desired F-theory monodromy. Using Hull's proposal for massive IIA, this
realization of T-duality allows us to confirm that the Romans mass is the
central extension of our LE_8. In addition this construction immediately
reproduces the conjectured formula for global topology change from T-duality
with H-flux.Comment: 25 pages, 4 eps figure
Towards a Non-Relativistic Holographic Superfluid
We explore the phase structure of a holographic toy model of superfluid
states in non-relativistic conformal field theories. At low background mass
density, we find a familiar second-order transition to a superfluid phase at
finite temperature. Increasing the chemical potential for the probe charge
density drives this transition strongly first order as the low-temperature
superfluid phase merges with a thermodynamically disfavored high-temperature
condensed phase. At high background mass density, the system reenters the
normal phase as the temperature is lowered further, hinting at a
zero-temperature quantum phase transition as the background density is varied.
Given the unusual thermodynamics of the background black hole, however, it
seems likely that the true ground state is another configuration altogether.Comment: 13+5 pages, late
Mass production of volume phase holographic gratings for the VIRUS spectrograph array
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline
array of 150 copies of a simple, fiber-fed integral field spectrograph that
will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first
optical astronomical instrument to be replicated on an industrial scale, and
represents a relatively inexpensive solution for carrying out large-area
spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each
spectrograph contains a volume phase holographic (VPH) grating with a 138 mm
diameter clear aperture as its dispersing element. The instrument utilizes the
grating in first-order for 350-550 nm. Including witness samples, a suite of
170 VPH gratings has been mass produced for VIRUS. Here, we present the design
of the VIRUS VPH gratings and a discussion of their mass production. We
additionally present the design and functionality of a custom apparatus that
has been used to rapidly test the first-order diffraction efficiency of the
gratings for various discrete wavelengths within the VIRUS spectral range. This
device has been used to perform both in-situ tests to monitor the effects of
adjustments to the production prescription as well as to carry out the final
acceptance tests of the gratings' diffraction efficiency. Finally, we present
the as-built performance results for the entire suite of VPH gratings.Comment: 16 pages, 11 figures, 2 tables. To be published in Proc. SPIE, 2014,
"Advances in Optical and Mechanical Technologies for Telescopes and
Instrumentation", 9151-53. The work presented in this article follows from
arXiv:1207:448
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
On the CSFT approach to localized closed string tachyons
We compute the potential for localized closed string tachyons in bosonic
string theory on the orbifold C/Z_4 using level-truncated closed string field
theory. The critical points of the potential exhibit features which agree with
their conjectured identification as lower-order orbifolds. However this case
also raises some questions regarding the quantitative predictions associated
with these conjectures.Comment: 20 pages, 3 figures, v2: The relation between the flat space and
orbifold gravitational constants has been corrected. This resolves the puzzle
of multiple predictions, but worsens the agreement between the depth of the
potential and the change in the deficit angl
R^2 Corrections to Asymptotically Lifshitz Spacetimes
We study corrections to five-dimensional asymptotically Lifshitz
spacetimes by adding Gauss-Bonnet terms in the effective action. For the
zero-temperature backgrounds we obtain exact solutions in both pure
Gauss-Bonnet gravity and Gauss-Bonnet gravity with non-trivial matter. The
dynamical exponent undergoes finite renormalization in the latter case. For the
finite-temperature backgrounds we obtain black brane solutions perturbatively
and calculate the ratio of shear viscosity to entropy density . The KSS
bound is still violated but unlike the relativistic counterparts, the causality
of the boundary field theory cannot be taken as a constraint.Comment: 24 pages, Latex, typos fixed, accepted by JHE
The three-item ALERT-B questionnaire provides a validated screening tool to detect chronic gastrointestinal symptoms after pelvic radiotherapy in cancer survivors
Aims: Although pelvic radiotherapy is an effective treatment for various malignancies, around half of patients develop significant gastrointestinal problems. These symptoms often remain undetected, despite the existence of effective treatments. This study developed and refined a simple screening tool to detect common gastrointestinal symptoms in outpatient clinics. These symptoms have a significant effect on quality of life. This tool will increase detection rates and so enable access to specialist gastroenterologists, which will in turn lead to improved symptom control and quality of life after treatment. Materials and methods: A literature review and expert consensus meeting identified four items for the ALERT-B (Assessment of Late Effects of RadioTherapy - Bowel) screening tool. ALERT-B was face tested for its usability and acceptability using cognitive interviews with 12 patients experiencing late gastrointestinal symptoms after pelvic radiotherapy. Thematic analysis and probe category were used to analyse interview transcripts. Interview data were presented to a group of experts to agree on the final content and format of the tool. ALERT-B was assessed for reliability and tested for validity against the Gastrointestinal Symptom Rating Scale in a clinical study (EAGLE). Results: Overall, the tool was found to be acceptable in terms of wording, response format and completion time. Participant-reported experiences, including lifestyle modifications and the psychological effect of the symptoms, led to further modifications of the tool. The refined tool includes three questions covering rectal bleeding, incontinence, nocturnal bowel movements and impact on quality of life, including mood, relationships and socialising. ALERT-B was successfully validated against the Gastrointestinal Symptom Rating Scale in the EAGLE study with the tool shown broadly to be internally consistent (Cronbach’s alpha=0.61 and all item-subscale correlation [Spearman] coefficients are > 0.6). Conclusion: The ALERT-B screening tool can be used in clinical practice to improve post-treatment supportive care by triggering the clinical assessment of patients suitable for referral to a gastroenterologist
Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4
An energetic electron passing through liquid helium causes ionization along
its track. The ionized electrons quickly recombine with the resulting positive
ions, which leads to the production of prompt scintillation light. By applying
appropriate electric fields, some of the ionized electrons can be separated
from their parent ions. The fraction of the ionized electrons extracted in a
given applied field depends on the separation distance between the electrons
and the ions. We report the determination of the mean electron-ion separation
distance for charge pairs produced along the tracks of beta particles in
superfluid helium at 1.5 K by studying the quenching of the scintillation light
under applied electric fields. Knowledge of this mean separation parameter will
aid in the design of particle detectors that use superfluid helium as a target
material.Comment: 10 pages, 8 figure
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