643 research outputs found
Microscopic theory of atom-molecule oscillations in a Bose-Einstein condensate
In a recent experiment at JILA [E.A. Donley et al., Nature (London) 417, 529
(2002)] an initially pure condensate of Rb-85 atoms was exposed to a specially
designed time dependent magnetic field pulse in the vicinity of a Feshbach
resonance. The production of new components of the gas as well as their
oscillatory behavior have been reported. We apply a microscopic theory of the
gas to identify these components and determine their physical properties. Our
time dependent studies allow us to explain the observed dynamic evolution of
all fractions, and to identify the physical relevance of the pulse shape. Based
on ab initio predictions, our theory strongly supports the view that the
experiments have produced a molecular condensate.Comment: 18 pages, 20 figure
Absolute Calibration of a 200 MeV Proton Polarimeter for Use with the Brookhaven Linac
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter
We apply the closed-time path integral formalism to study the medium effects
of non-equilibrium gluon matter. We derive the medium modified resummed gluon
propagator to the one loop level in non-equilibrium in the covariant gauge. The
gluon propagator we derive can be used to remove the infrared divergences in
the secondary parton collisions to study thermalization of minijet parton
plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification,
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Size-dependent particle activation properties in fog during the ParisFog 2012/13 field campaign
Fog-induced visibility reduction is responsible for a variety of hazards in the transport sector. Therefore there is a large demand for an improved understanding of fog formation and thus improved forecasts. Improved fog forecasts require a better understanding of the numerous complex mechanisms during the fog life cycle. During winter 2012/13 a field campaign called ParisFog aiming at fog research took place at SIRTA (Instrumented Site for Atmospheric Remote Sensing Research). SIRTA is located about 20 km southwest of the Paris city center, France, in a semi-urban environment. In situ activation properties of the prevailing fog were investigated by measuring (1) total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems; (2) interstitial hydrated aerosol and fog droplet size distributions at ambient conditions; and (3) cloud condensation nuclei (CCN) number concentration at different supersaturations (SS) with a CCN counter. The aerosol particles were characterized regarding their hygroscopic properties, fog droplet activation behavior and contribution to light scattering for 17 developed fog events. Low particle hygroscopicity with an overall median of the hygroscopicity parameter, κ, of 0.14 was found, likely caused by substantial influence from local traffic and wood burning emissions. Measurements of the aerosol size distribution at ambient RH revealed that the critical wet diameter, above which the hydrated aerosols activate to fog droplets, is rather large (with a median value of 2.6μm) and is highly variable (ranging from 1 to 5μm) between the different fog events. Thus, the number of activated fog droplets was very small and the non-activated hydrated particles were found to contribute significantly to the observed light scattering and thus to the reduction in visibility. Combining all experimental data, the effective peak supersaturation, SSpeak, a measure of the peak supersaturation during the fog formation, was determined. The median SSpeak value was estimated to be in the range from 0.031 to 0.046% (upper and lower limit estimations), which is in good agreement with previous experimental and modeling studies of fog
DCE-MRI biomarkers of tumour heterogeneity predict CRC liver metastasis shrinkage following bevacizumab and FOLFOX-6
Background:
There is limited evidence that imaging biomarkers can predict subsequent response to therapy. Such prognostic and/or predictive biomarkers would facilitate development of personalised medicine. We hypothesised that pre-treatment measurement of the heterogeneity of tumour vascular enhancement could predict clinical outcome following combination anti-angiogenic and cytotoxic chemotherapy in colorectal cancer (CRC) liver metastases.
Methods:
Ten patients with 26 CRC liver metastases had two dynamic contrast-enhanced MRI (DCE-MRI) examinations before starting first-line bevacizumab and FOLFOX-6. Pre-treatment biomarkers of tumour microvasculature were computed and a regression analysis was performed against the post-treatment change in tumour volume after five cycles of therapy. The ability of the resulting linear model to predict tumour shrinkage was evaluated using leave-one-out validation. Robustness to inter-visit variation was investigated using data from a second baseline scan.
Results:
In all, 86% of the variance in post-treatment tumour shrinkage was explained by the median extravascular extracellular volume (ve), tumour enhancing fraction (EF), and microvascular uniformity (assessed with the fractal measure box dimension, d0) (R2=0.86, P<0.00005). Other variables, including baseline volume were not statistically significant. Median prediction error was 12%. Equivalent results were obtained from the second scan.
Conclusion:
Traditional image analyses may over-simplify tumour biology. Measuring microvascular heterogeneity may yield important prognostic and/or predictive biomarkers
Hierarchical Neutrino Mass Matrices, CP violation and Leptogenesis
In this work we study examples of hierarchical neutrino mass matrices
inspired by family symmetries, compatible with experiments on neutrino
oscillations, and for which there is a connection among the low energy CP
violation phase associated to neutrino oscillations, the phases appearing in
the amplitude of neutrinoless double beta decay, and the phases relevant for
leptogenesis. In particular, we determine the predictions from a texture based
on an underlying SU(3) family symmetry together with a GUT symmetry, and a
strong hierarchy for the masses of the heavy right handed Majorana masses. We
also give some examples of inverted hierarchies of neutrino masses, which may
be motivated in the context of U(1) family symmetries.Comment: 34 pages. Replaced with published version -typos, corrections and
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The Conformal Spin and Statistics Theorem
We prove the equality between the statistics phase and the conformal
univalence for a superselection sector with finite index in Conformal Quantum
Field Theory on . A relevant point is the description of the PCT symmetry
and the construction of the global conjugate charge.Comment: plain tex, 22 page
Relating the Lorentzian and exponential: Fermi's approximation,the Fourier transform and causality
The Fourier transform is often used to connect the Lorentzian energy
distribution for resonance scattering to the exponential time dependence for
decaying states. However, to apply the Fourier transform, one has to bend the
rules of standard quantum mechanics; the Lorentzian energy distribution must be
extended to the full real axis instead of being bounded from
below (``Fermi's approximation''). Then the Fourier transform
of the extended Lorentzian becomes the exponential, but only for times , a time asymmetry which is in conflict with the unitary group time evolution
of standard quantum mechanics. Extending the Fourier transform from
distributions to generalized vectors, we are led to Gamow kets, which possess a
Lorentzian energy distribution with and have exponential
time evolution for only. This leads to probability predictions
that do not violate causality.Comment: 23 pages, no figures, accepted by Phys. Rev.
Jet color chemistry and anomalous baryon production in -collisions
We study anomalous high- baryon production in -collisions due to
formation of the two parton collinear system in the anti-sextet color
state for quark jets and system in the decuplet/anti-decuplet color states
for gluon jets. Fragmentation of these states, which are absent for
-collisions, after escaping from the quark-gluon plasma leads to baryon
production. Our qualitative estimates show that this mechanism can be
potentially important at RHIC and LHC energies.Comment: 20 pages, 4 figures, Eur.Phys.J. versio
Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations
The infrared behaviour of the medium modified gluon propagator in
non-equilibrium situations is studied in the covariant gauge using the
Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic
screening mass is non-zero at the one loop level whenever the initial gluon
distribution function is non isotropic with the assumption that the
distribution function of the gluon is not divergent at zero transverse
momentum. For isotropic gluon distribution functions, such as those describing
local equilibrium, the magnetic mass at one loop level is zero which is
consistent with finite temperature field theory results. Assuming that a
reasonable initial gluon distribution function can be obtained from a
perturbative QCD calculation of minijets, we determine these out of equilibrium
values for the initial magnetic and Debye screening masses at energy densities
appropriate to RHIC and LHC. We also compare the magnetic masses obtained here
with those obtained using finite temperature lattice QCD methods at similar
temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys.
Rev.
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