1,920 research outputs found
Flavor and chiral oscillations with Dirac wave packets
We report about recent results on Dirac wave packets in the treatment of
neutrino flavor oscillation where the initial localization of a spinor state
implies an interference between positive and negative energy components of
mass-eigenstate wave packets. A satisfactory description of fermionic particles
requires the use of the Dirac equation as evolution equation for the
mass-eigenstates. In this context, a new flavor conversion formula can be
obtained when the effects of chiral oscillation are taken into account. Our
study leads to the conclusion that the fermionic nature of the particles, where
chiral oscillations and the interference between positive and negative
frequency components of mass-eigenstate wave packets are implicitly assumed,
modifies the standard oscillation probability. Nevertheless, for
ultra-relativistic particles and sharply peaked momentum distributions, we can
analytically demonstrate that these modifications introduce correction factors
proportional to (m12/p0) square which are practically un-detectable by any
experimental analysisComment: 16 pages, 2 figure
Additional time-dependent phase in the flavor-conversion formulas
In the framework of intermediate wave-packets for treating flavor
oscillations, we quantify the modifications which appear when we assume a
strictly peaked momentum distribution and consider the second-order corrections
in a power series expansion of the energy. By following a sequence of analytic
approximations, we point out that an extra time-dependent phase is merely the
residue of second-order corrections. Such phase effects are usually ignored in
the relativistic wave-packet treatment, but they do not vanish
non-relativistically and can introduce some small modifications to the
oscillation pattern even in the ultra-relativistic limit.Comment: 9 pages, 3 figure
Coherence of neutrino flavor mixing in quantum field theory
In the simplistic quantum mechanical picture of flavor mixing, conditions on
the maximum size and minimum coherence time of the source and detector regions
for the observation of interference---as well as the very viability of the
approach---can only be argued in an ad hoc way from principles external to the
formalism itself. To examine these conditions in a more fundamental way, the
quantum field theoretical -matrix approach is employed in this paper,
without the unrealistic assumption of microscopic stationarity. The fully
normalized, time-dependent neutrino flavor mixing event rates presented here
automatically reveal the coherence conditions in a natural, self-contained, and
physically unambiguous way, while quantitatively describing the transition to
their failure.Comment: 12 pages, submitted to Phys. Rev.
Starvation Resistance is Associated with Developmentally Specified Changes in Sleep, Feeding and Metabolic Rate
Food shortage represents a primary challenge to survival, and animals have adapted diverse developmental, physiological and behavioral strategies to survive when food becomes unavailable. Starvation resistance is strongly influenced by ecological and evolutionary history, yet the genetic basis for the evolution of starvation resistance remains poorly understood. The fruit fly Drosophila melanogaster provides a powerful model for leveraging experimental evolution to investigate traits associated with starvation resistance. While control populations only live a few days without food, selection for starvation resistance results in populations that can survive weeks. We have previously shown that selection for starvation resistance results in increased sleep and reduced feeding in adult flies. Here, we investigate the ontogeny of starvation resistance-associated behavioral and metabolic phenotypes in these experimentally selected flies. We found that selection for starvation resistance resulted in delayed development and a reduction in metabolic rate in larvae that persisted into adulthood, suggesting that these traits may allow for the accumulation of energy stores and an increase in body size within these selected populations. In addition, we found that larval sleep was largely unaffected by starvation selection and that feeding increased during the late larval stages, suggesting that experimental evolution for starvation resistance produces developmentally specified changes in behavioral regulation. Together, these findings reveal a critical role for development in the evolution of starvation resistance and indicate that selection can selectively influence behavior during defined developmental time points
Preoperative Exercise Training to Prevent Postoperative Pulmonary Complications in Adults Undergoing Major Surgery. A Systematic Review and Meta-analysis with Trial Sequential Analysis.
Rationale: Poor preoperative physical fitness and respiratory muscle weakness are associated with postoperative pulmonary complications (PPCs) that result in prolonged hospital length of stay and increased mortality.Objectives: To examine the effect of preoperative exercise training on the risk of PPCs across different surgical settings.Methods: We searched MEDLINE, Web of Science, Embase, the Physiotherapy Evidence Database, and the Cochrane Central Register, without language restrictions, for studies from inception to July 2020. We included randomized controlled trials that compared patients receiving exercise training with those receiving usual care or sham training before cardiac, lung, esophageal, or abdominal surgery. PPCs were the main outcome; secondary outcomes were preoperative functional changes and postoperative mortality, cardiovascular complications, and hospital length of stay. The study was registered with PROSPERO (International Prospective Register of Systematic Reviews).Results: From 29 studies, 2,070 patients were pooled for meta-analysis. Compared with the control condition, preoperative exercise training was associated with a lower incidence of PPCs (23 studies, 1,864 patients; relative risk, 0.52; 95% confidence interval [CI], 0.41 to 0.66; grading of evidence, moderate); Trial Sequential Analysis confirmed effectiveness, and there was no evidence of difference of effect across surgeries, type of training (respiratory muscles, endurance or combined), or preoperative duration of training. At the end of the preoperative period, exercise training resulted in increased peak oxygen uptake (weighted mean difference [WMD], +2 ml/kg/min; 99% CI, 0.3 to 3.7) and higher maximal inspiratory pressure (WMD, +12.2 cm H <sub>2</sub> O; 99% CI, 6.3 to 18.2). Hospital length of stay was shortened (WMD, -2.3 d; 99% CI, -3.82 to -0.75) in the intervention group, whereas no difference was found in postoperative mortality.Conclusions: Preoperative exercise training improves physical fitness and reduces the risk of developing PPCs while minimizing hospital resources use, regardless of the type of intervention and surgery performed.Systematic review registered with https://www.crd.york.ac.uk/prospero/ (CRD 42018096956)
An Analytic Approach to the Wave Packet Formalism in Oscillation Phenomena
We introduce an approximation scheme to perform an analytic study of the
oscillation phenomena in a pedagogical and comprehensive way. By using Gaussian
wave packets, we show that the oscillation is bounded by a time-dependent
vanishing function which characterizes the slippage between the mass-eigenstate
wave packets. We also demonstrate that the wave packet spreading represents a
secondary effect which plays a significant role only in the non-relativistic
limit. In our analysis, we note the presence of a new time-dependent phase and
calculate how this additional term modifies the oscillating character of the
flavor conversion formula. Finally, by considering Box and Sine wave packets we
study how the choice of different functions to describe the particle
localization changes the oscillation probability.Comment: 16 pages, 7 figures, AMS-Te
Diffusion with critically correlated traps and the slow relaxation of the longest wavelength mode
We study diffusion on a substrate with permanent traps distributed with
critical positional correlation, modeled by their placement on the perimeters
of a critical percolation cluster. We perform a numerical analysis of the
vibrational density of states and the largest eigenvalue of the equivalent
scalar elasticity problem using the method of Arnoldi and Saad. We show that
the critical trap correlation increases the exponent appearing in the stretched
exponential behavior of the low frequency density of states by approximately a
factor of two as compared to the case of no correlations. A finite size scaling
hypothesis of the largest eigenvalue is proposed and its relation to the
density of states is given. The numerical analysis of this scaling postulate
leads to the estimation of the stretch exponent in good agreement with the
density of states result.Comment: 15 pages, LaTeX (RevTeX
Extended Source Diffraction Effects Near Gravitational Lens Fold Caustics
Calculations are presented detailing the gravitational lens diffraction due
to the steep brightness gradient of the limb of a stellar source. The lensing
case studied is the fold caustic crossing. The limb diffraction signal greatly
exceeds that due to the disk as a whole and should be detectable for white
dwarf sources in our Galaxy and it's satellites with existing telescopes.
Detection of this diffraction signal would provide an additional mathematical
constraint, reducing the degeneracy among models of the lensing geometry. The
diffraction pattern provides pico-arcsecond resolution of the limb profile.Comment: 19 pages including 17 figures, Accepted for publication in ApJ, Minor
conceptual change from previous versio
Phenotype and genotype associations of lung carcinoma with atypical adenomatoid hyperplasia, squamous cell dysplasia, and chromosome alterations in non-neoplastic bronchial mucosa
Abstract The frequency of preneoplastic lesions of the lung and bronchial mucosa as well as potential genotype alterations in spatial relationship to pulmonary malignancies still need intensive investigations in order to understand the occurrence and manifestation of lung cancer in detail. To investigate the contemporary manifestation of lung cancer precursor lesions, peripheral (non-neoplastic) lung parenchyma and bronchial mucosa of operated lung carcinomas were analyzed at distinct distances (1, 2, 3, and 4 cm) from the tumor boundary for pre-neoplastic lesions -atypical adenomatoid hyperplasia (AAH) and squamous cell dysplasia (SCD), in 150 surgical specimens. Short-term tissue cultures of additional 55 primary and secondary lung tumors and their surrounding non-neoplastic bronchial mucosa were performed at the same distances in order to search for chromosome alterations, i.e. genotype aberrations. In phenotype observations, atypical adenomatoid hyperplasia was noted in 19/150 (13%) cases, and squamous cell dysplasia in 46/150 (31%) cases. The degree of cellular atypia decreased with increasing distance from the tumor boundary in both AAH and SCM. AAH was observed more frequently in adenocarcinomas, SCQ more frequently in squamous cell carcinomas. In genotype observations, the average number of abnormal metaphases measured 4.5/10 high power fields (HPF) in primary lung carcinomas, and only 2/10 in metastases. Data indicate that the so-called preneoplastic lesions in the lung are not completely tumor-precursor lesions, but, in addition, induced by the tumor itself
Exploring CP Violation with B_d -> D K_s Decays
We (re)examine CP violation in the decays B_d -> D K_s, where D represents
D^0, D(bar), or one of their excited states. The quantity can be extracted from the time-dependent rates for and , where the decays to
. If one considers a non-CP-eigenstate hadronic final state to
which both D(bar) and D^0 can decay (e.g. ), then one can obtain two
of the angles of the unitarity triangle from measurements of the time-dependent
rates for and .
There are no penguin contributions to these decays, so all measurements are
theoretically clean.Comment: 15 pages, LaTeX, no figure
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