6,534 research outputs found
Experimental Flow Models for SSME Flowfield Characterization
Full scale flow models with extensive instrumentation were designed and manufactured to provide data necessary for flow field characterization in rocket engines of the Space Shuttle Main Engine (SSME) type. These models include accurate flow path geometries from the pre-burner outlet through the throat of the main combustion chamber. The turbines are simulated with static models designed to provide the correct pressure drop and swirl for specific power levels. The correct turbopump-hot gas manifold interfaces were designed into the flow models to permit parametric/integration studies for new turbine designs. These experimental flow models provide a vehicle for understanding the fluid dynamics associated with specific engine issues and also fill the more general need for establishing a more detailed fluid dynamic base to support development and verification of advanced math models
Ultrasound-guided trans-rectal high-intensity focused ultrasound (HIFU) for advanced cervical cancer ablation is feasible: a case report.
High-intensity focused ultrasound (HIFU) is an ablative treatment undergoing assessment for the treatment of benign and malignant disease. We describe the first reported intracavitary HIFU ablation for recurrent, unresectable and symptomatic cervical cancer.A 38 year old woman receiving palliative chemotherapy for metastatic cervical adenocarcinoma was offered ablative treatment from an intracavitary trans-rectal HIFU device (Sonablate® 500). Pre-treatment symptoms included vaginal bleeding and discharge that were sufficient to impede her quality of life. No peri-procedural adverse events occurred. Symptoms resolved completely immediately post-procedure, reappeared at 7 days, increasing to pre-procedural levels by day 30.This first time experience of intracavitary cervical HIFU suggests that it is feasible for palliation of advanced cervical cancer, with no early evidence of unexpected toxicity. Ethical approval had also been granted for the use of per-vaginal access if appropriate. This route, alone or in combination with the rectal route, may provide increased accessibility in future patients with a redesigned device more suited to trans-vaginal ablations.Intracavitary HIFU is a potentially safe procedure for the treatment of cervical cancer and able to provide symptomatic improvement in the palliative setting
Instanton induced charged fermion and neutrino masses in a minimal Standard Model scenario from intersecting D-branes
String instanton Yukawa corrections from Euclidean D-branes are investigated
in an effective Standard Model theory obtained from the minimal U(3)xU(2)xU(1)
D-brane configuration. In the case of the minimal chiral and Higgs spectrum, it
is found that superpotential contributions are induced by string instantons for
the perturbatively forbidden entries of the up and down quark mass matrices.
Analogous non-perturbative effects generate heavy Majorana neutrino masses and
a Dirac neutrino texture with factorizable Yukawa couplings. For this latter
case, a specific example is worked out where it is shown how this texture can
reconcile the neutrino data.Comment: 17 pages, 3 figure
String Thermodynamics in D-Brane Backgrounds
We discuss the thermal properties of string gases propagating in various
D-brane backgrounds in the weak-coupling limit, and at temperatures close to
the Hagedorn temperature. We determine, in the canonical ensemble, whether the
Hagedorn temperature is limiting or non-limiting. This depends on the
dimensionality of the D-brane, and the size of the compact dimensions. We find
that in many cases the non-limiting behaviour manifest in the canonical
ensemble is modified to a limiting behaviour in the microcanonical ensemble and
show that, when there are different systems in thermal contact, the energy
flows into open strings on the `limiting' D-branes of largest dimensionality.
Such energy densities may eventually exceed the D-brane intrinsic tension. We
discuss possible implications of this for the survival of Dp-branes with large
values of p in an early cosmological Hagedorn regime. We also discuss the
general phase diagram of the interacting theory, as implied by the holographic
and black-hole/string correspondence principles.Comment: 50 pages, LaTeX, 4 eps figures. Added discussion of random walk
picture. Corrected technical error in the treatment of ND strings (notice
some formulas are rewritten). Conclusions unchange
Some Thermodynamical Aspects of String Theory
Thermodynamical aspects of string theory are reviewed and discussed.Comment: 22 Pages plain latex; based on contributions to Golfand Memorial
Volume and Englertfest by E.Rabinovic
X-ray Scattering Study of the spin-Peierls transition and soft phonon behavior in TiOCl
We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using
single crystal x-ray diffraction and inelastic x-ray scattering techniques. The
Ti ions form staggered spin chains which dimerize below Tc1 = 66 K and have an
incommensurate lattice distortion between Tc1 and Tc2 = 92 K. Based on our
measurements of the intensities, wave vectors, and harmonics of the
incommensurate superlattice peaks, we construct a model for the incommensurate
modulation. The results are in good agreement with a soliton lattice model,
though some quantitative discrepancies exist near Tc2. The behavior of the
phonons has been studied using inelastic x-ray scattering with ~2 meV energy
resolution. For the first time, a zone boundary phonon which softens at the
spin-Peierls temperature Tsp has been observed. Our results show reasonably
good quantitative agreement with the Cross-Fisher theory for the phonon
dynamics at wave vectors near the zone boundary and temperatures near Tsp.
However, not all aspects of the data can be described, such as the strong
overdamping of the soft mode above Tsp. Overall, our results show that TiOCl is
a good realization of a spin-Peierls system, where the phonon softening allows
us to identify the transition temperature as Tsp=Tc2=92 KComment: 14 pages, 14 figure
Fermion Masses and Mixing in Four and More Dimensions
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. Mass matrix ansatze are considered within the SM and
SUSY GUTs where some predictive frameworks based on SU(5) and SO(10) are
reviewed. We describe a variety of schemes to construct quark mass matrices in
extra dimensions focusing on four major classes: models with the SM residing on
3-brane, models with universal extra dimensions, models with split fermions and
models with warped extra dimensions. We outline how realistic patterns of quark
mass matrices could be derived from orbifold models in heterotic superstring
theory. Finally, we address the fermion mass problem in intersecting D-branes
scenarios, and present models with D6-branes able to give a good quantitatively
description of quark masses and mixing. The role of flavor/CP violation problem
as a probe of new physics is emphasized.Comment: a review based on seminars presented by S.K. in different places, 34
pages, late
Cosmic Reionisation by Stellar Sources: Population II Stars
We study the reionisation of the Universe by stellar sources using a
numerical approach that combines fast 3D radiative transfer calculations with
high resolution hydrodynamical simulations. Ionising fluxes for the sources are
derived from intrinsic star formation rates computed in the underlying
hydrodynamical simulations. Our mass resolution limit for sources is M~ 4.0 x
10^7 h^-1 M_sol, which is roughly an order of magnitude smaller than in
previous studies of this kind. Our calculations reveal that the reionisation
process is sensitive to the inclusion of dim sources with masses below ~10^9
h^-1 M_sol. We present the results of our reionisation simulation assuming a
range of escape fractions for ionising photons and make statistical comparisons
with observational constraints on the neutral fraction of hydrogen at z~6
derived from the z=6.28 SDSS quasar of Becker and coworkers. Our best fitting
model has an escape fraction of ~20% and causes reionisation to occur by z~8,
although the IGM remains fairly opaque until z~6. In order to simultaneously
match the observations from the z=6.28 SDSS quasar and the optical depth
measurement from WMAP with the sources modeled here, we require an evolving
escape fraction that rises from f_esc=0.20 near z~6 to f_esc>~10 at z~18.Comment: 42 pages, 13 figure
Coulomb's law corrections from a gauge-kinetic mixing
We study the static quantum potential for a gauge theory which includes the
mixing between the familiar photon and a second massive gauge
field living in the so-called hidden-sector . Our discussion is carried
out using the gauge-invariant but path-dependent variables formalism, which is
alternative to the Wilson loop approach. Our results show that the static
potential is a Yukawa correction to the usual static Coulomb potential.
Interestingly, when this calculation is done inside a superconducting box, the
Coulombic piece disappears leading to a screening phase.Comment: 4 page
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