5,965 research outputs found
Photoproduction of K^+ Mesons in Hydrogen
The photoproduction of K^+ mesons in hydrogen has been measured with the purpose of extending the previous CalTech measurements to smaller angles, and obtaining better absolute values for the cross sections. The technique of Donoho and Walker, using a magnetic spectrometer and a time-of-flight measurement to detect the K^+ mesons, was modified so as to achieve a better discrimination against pions and scattered protons. The results obtained are in fairly good agreement with the more extensive measurements made at Cornell by a somewhat different method
Metric approach to quantum constraints
A new framework for deriving equations of motion for constrained quantum
systems is introduced, and a procedure for its implementation is outlined. In
special cases the framework reduces to a quantum analogue of the Dirac theory
of constrains in classical mechanics. Explicit examples involving spin-1/2
particles are worked out in detail: in one example our approach coincides with
a quantum version of the Dirac formalism, while the other example illustrates
how a situation that cannot be treated by Dirac's approach can nevertheless be
dealt with in the present scheme.Comment: 13 pages, 1 figur
Post‐traumatic stress disorder\u27s relation with positive and negative emotional avoidance: The moderating role of gender
Post‐traumatic stress disorder (PTSD) is characterized by avoidance of trauma‐related emotions. Research indicates that this avoidance may extend to any emotional experience that elicits distress, including those that are unrelated to the trauma. Literature in this area has been limited in its exclusive focus on negative emotions. Despite evidence of gender differences in PTSD and emotional avoidance separately, no studies to date have examined gender as a moderator of their association. The goal of the current study was to extend research by exploring the moderating role of gender in the relation between PTSD symptom severity and positive and negative emotional avoidance. Participants were 276 trauma‐exposed individuals (65.9% female, 65.6% White, Mage = 19.24) from a university in the north‐eastern United States. Moderation results indicated a main effect for PTSD symptom severity on both positive (b = 0.07, p \u3c .001) and negative (b = 0.04, p = .03) emotional avoidance. The interaction of gender and PTSD symptom severity was significant for positive emotion avoidance (b = 0.97, p = .01). Analysis of simple slopes revealed that PTSD symptom severity was significantly associated with positive emotional avoidance for males (b = 0.13, p \u3c .001) but not females (b = 0.03, p = .08). Results suggest the importance of gender‐sensitive recommendations for assessment and treatment of emotional avoidance in PTSD
Nuclear Structure Calculations with Low-Momentum Potentials in a Model Space Truncation Approach
We have calculated the ground-state energy of the doubly magic nuclei 4He,
16O and 40Ca within the framework of the Goldstone expansion starting from
various modern nucleon-nucleon potentials. The short-range repulsion of these
potentials has been renormalized by constructing a low-momentum potential
V-low-k. We have studied the connection between the cutoff momemtum Lambda and
the size of the harmonic oscillator space employed in the calculations. We have
found a fast convergence of the results with a limited number of oscillator
quanta.Comment: 6 pages, 8 figures, to be published on Physical Review
Constrained quantum dynamics
We give an overview of the two different methods that have been introduced in
order to describe the dynamics of constrained quantum systems; the symplectic
formulation and the metric formulation. The symplectic method extends the work
of Dirac on constrained classical systems to quantum systems, whereas the
metric approach is purely a quantum mechanical method having no immediate
classical counterpart. Two examples are provided that illustrate the nonlinear
motion induced by the constraint.Comment: 8 pages, 4 figures. Based on the talk presented at the DICE2008
conference in Castiglioncello, September 200
Fundamental Limits on the Speed of Evolution of Quantum States
This paper reports on some new inequalities of
Margolus-Levitin-Mandelstam-Tamm-type involving the speed of quantum evolution
between two orthogonal pure states. The clear determinant of the qualitative
behavior of this time scale is the statistics of the energy spectrum. An
often-overlooked correspondence between the real-time behavior of a quantum
system and the statistical mechanics of a transformed (imaginary-time)
thermodynamic system appears promising as a source of qualitative insights into
the quantum dynamics.Comment: 6 pages, 1 eps figur
modCHIMERA: A novel murine closed-head model of moderate traumatic brain injury
AbstractTraumatic brain injury is a major source of global disability and mortality. Preclinical TBI models are a crucial component of therapeutic investigation. We report a tunable, monitored model of murine non-surgical, diffuse closed-head injury—modCHIMERA—characterized by impact as well as linear and rotational acceleration. modCHIMERA is based on the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) platform. We tested this model at 2 energy levels: 1.7 and 2.1 Joules—substantially higher than previously reported for this system. Kinematic analysis demonstrated linear acceleration exceeding injury thresholds in humans, although outcome metrics tracked impact energy more closely than kinematic parameters. Acute severity metrics were consistent with a complicated-mild or moderate TBI, a clinical population characterized by high morbidity but potentially reversible pathology. Axonal injury was multifocal and bilateral, neuronal death was detected in the hippocampus, and microglial neuroinflammation was prominent. Acute functional analysis revealed prolonged post-injury unconsciousness, and decreased spontaneous behavior and stimulated neurological scores. Neurobehavioral deficits were demonstrated in spatial learning/memory and socialization at 1-month. The overall injury profile of modCHIMERA corresponds with the range responsible for a substantial portion of TBI-related disability in humans. modCHIMERA should provide a reliable platform for efficient analysis of TBI pathophysiology and testing of treatment modalities.</jats:p
Martingale Models for Quantum State Reduction
Stochastic models for quantum state reduction give rise to statistical laws
that are in most respects in agreement with those of quantum measurement
theory. Here we examine the correspondence of the two theories in detail,
making a systematic use of the methods of martingale theory. An analysis is
carried out to determine the magnitude of the fluctuations experienced by the
expectation of the observable during the course of the reduction process and an
upper bound is established for the ensemble average of the greatest
fluctuations incurred. We consider the general projection postulate of L\"uders
applicable in the case of a possibly degenerate eigenvalue spectrum, and derive
this result rigorously from the underlying stochastic dynamics for state
reduction in the case of both a pure and a mixed initial state. We also analyse
the associated Lindblad equation for the evolution of the density matrix, and
obtain an exact time-dependent solution for the state reduction that explicitly
exhibits the transition from a general initial density matrix to the L\"uders
density matrix. Finally, we apply Girsanov's theorem to derive a set of simple
formulae for the dynamics of the state in terms of a family of geometric
Brownian motions, thereby constructing an explicit unravelling of the Lindblad
equation.Comment: 30 pages LaTeX. Submitted to Journal of Physics
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