174 research outputs found
Inversion of Gamow's Formula and Inverse Scattering
We present a pedagogical description of the inversion of Gamow's tunnelling
formula and we compare it with the corresponding classical problem. We also
discuss the issue of uniqueness in the solution and the result is compared with
that obtained by the method of Gel'fand and Levitan. We hope that the article
will be a valuable source to students who have studied classical mechanics and
have some familiarity with quantum mechanics.Comment: LaTeX, 6 figurs in eps format. New abstract; notation in last
equation has been correcte
Recommended from our members
A statistical model for the prediction of wind-speed probabilities in the atmospheric surface layer
Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behavior of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The modelâs basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds showed a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on the knowledge of only a few simple flow statistics (mean wind speed, wind speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence
MODELLING THE CONCENTRATION FLUCTUATION AND INDIVIDUAL EXPOSURE IN COMPLEX URBAN ENVIRONMENTS
The concentrations fluctuations of a dispersing hazardous gaseous pollutant in the atmospheric boundary layer, and the
hazard associated with short-term concentration levels, demonstrate the necessity of estimating the magnitude of these fluctuations
using predicting models. Moreover the computation of concentration fluctuations and individual exposure in case of dispersion in
realistic situations, such as built-up areas or street canyons, is of special practical interest for hazard assessment purposes. In order to
predict or/and estimate the maximum expected dosage and the exposure time within which the dosage exceeds certain health limits,
the knowledge of the behaviour of concentration fluctuations at the point under consideration is needed. In this study the whole
effort is based on the âMock Urban Setting Test â MUSTâ, an extensive field test carried out on a test site of the US Army in the
Great Basin Desert in 2001 (Biltoft, 2001; Yee, 2004). The experimental data that was used for the model evaluation concerned the dispersion of a passive gas between street canyons which have been created by 120 standard size shipping containers. The
computational simulations have been performed using the laboratory CFD code ADREA, which has been developed for simulating
the dispersion and exposure of pollutants over complex geometries. The ADREA model is evaluated by comparing the modelâs
predictions with the observations utilizing statistical metrics and scatter plots. The present study has been performed in the frame of
the Action COST 732 âQuality Assurance and Improvement of Micro-Scale Meteorological Modelsâ
Modelling short-term maximum individual exposure from airborne hazardous releases in urban environments. Part ÎI: Validation of a deterministic model with wind tunnel experimental data
The capability to predict short-term maximum individual exposure is very important for several applications including, for example, deliberate/accidental release of hazardous substances, odour fluctuations or material flammability level exceedance. Recently, authors have proposed a simple approach relating maximum individual exposure to parameters such as the fluctuation intensity and the concentration integral time scale. In the first part of this study (Part I), the methodology was validated against field measurements, which are governed by the natural variability of atmospheric boundary conditions. In Part II of this study, an in-depth validation of the approach is performed using reference data recorded under truly stationary and well documented flow conditions. For this reason, a boundary-layer wind-tunnel experiment was used. The experimental dataset includes 196 time-resolved concentration measurements which detect the dispersion from a continuous point source within an urban model of semi-idealized complexity. The data analysis allowed the improvement of an important model parameter. The model performed very well in predicting the maximum individual exposure, presenting a factor of two of observations equal to 95%. For large time intervals, an exponential correction term has been introduced in the model based on the experimental observations. The new model is capable of predicting all time intervals giving an overall factor of two of observations equal to 100%
Applications of Partial Supersymmetry
I examine quantum mechanical Hamiltonians with partial supersymmetry, and
explore two main applications. First, I analyze a theory with a logarithmic
spectrum, and show how to use partial supersymmetry to reveal the underlying
structure of this theory. This method reveals an intriguing equivalence between
two formulations of this theory, one of which is one-dimensional, and the other
of which is infinite-dimensional. Second, I demonstrate the use of partial
supersymmetry as a tool to obtain the asymptotic energy levels in
non-relativistic quantum mechanics in an exceptionally easy way. In the end, I
discuss possible extensions of this work, including the possible connections
between partial supersymmetry and renormalization group arguments.Comment: 11 pages, harvmac, no figures; typo corrected in identifying info on
title pag
Greybody factors in a rotating black-hole background-II : fermions and gauge bosons
We study the emission of fermion and gauge boson degrees of freedom on the
brane by a rotating higher-dimensional black hole. Using matching techniques,
for the near-horizon and far-field regime solutions, we solve analytically the
corresponding field equations of motion. From this, we derive analytical
results for the absorption probabilities and Hawking radiation emission rates,
in the low-energy and low-rotation case, for both species of fields. We produce
plots of these, comparing them to existing exact numerical results with very
good agreement. We also study the total absorption cross-section and
demonstrate that, as in the non-rotating case, it has a different behaviour for
fermions and gauge bosons in the low-energy limit, while it follows a universal
behaviour -- reaching a constant, spin-independent, asymptotic value -- in the
high-energy regime.Comment: 22 pages, 8 figures, added reference
Form factors in the Bullough-Dodd related models: The Ising model in a magnetic field
We consider particular modification of the free-field representation of the
form factors in the Bullough-Dodd model. The two-particles minimal form factors
are excluded from the construction. As a consequence, we obtain convenient
representation for the multi-particle form factors, establish recurrence
relations between them and study their properties. The proposed construction is
used to obtain the free-field representation of the lightest particles form
factors in the perturbed minimal models. As a significant example
we consider the Ising model in a magnetic field. We check that the results
obtained in the framework of the proposed free-field representation are in
agreement with the corresponding results obtained by solving the bootstrap
equations.Comment: 20 pages; v2: some misprints, textual inaccuracies and references
corrected; some references and remarks adde
Shape Invariance in the Calogero and Calogero-Sutherland Models
We show that the Calogero and Calogero-Sutherland models possess an N-body
generalization of shape invariance. We obtain the operator representation that
gives rise to this result, and discuss the implications of this result,
including the possibility of solving these models using algebraic methods based
on this shape invariance. Our representation gives us a natural way to
construct supersymmetric generalizations of these models, which are interesting
both in their own right and for the insights they offer in connection with the
exact solubility of these models.Comment: Latex file, 23 pages, no picture
A review of methods for addressing components of interventions in meta-analysis
Many healthcare interventions are complex, consisting of multiple, possibly interacting, components. Several methodological articles addressing complex interventions in the metaanalytical context have been published. We hereby provide an overview of methods used to evaluate the effects of complex interventions with meta-analytical models. We summarized the methodology, highlighted new developments, and described the benefits, drawbacks, and potential challenges of each identified method. We expect meta-analytical methods focusing on components of several multicomponent interventions to become increasingly popular due to recently developed, easy-to-use, software tools that can be used to conduct the relevant analyses. The different meta-analytical methods are illustrated through two examples comparing psychotherapies for panic disorder. Copyright
- âŠ