2,610 research outputs found
Finite size Spin Wave theory of the triangular Heisenberg model
We present a finite size spin wave calculation on the Heisenberg
antiferromagnet on the triangular lattice focusing in particular on the
low-energy part of the excitation spectrum. For s=1/2 the good agreement with
the exact diagonalization and quantum Monte Carlo results supports the
reliability of the spin wave expansion to describe the low-energy spin
excitations of the Heisenberg model even in presence of frustration. This
indicates that the spin susceptibility of the triangular antiferromagnet is
very close to the linear spin wave result.Comment: 6 pages (LateX), 2 ps-figure
Dirac constraints in field theory and exterior differential systems
The usual treatment of a (first order) classical field theory such as
electromagnetism has a little drawback: It has a primary constraint submanifold
that arise from the fact that the dynamics is governed by the antisymmetric
part of the jet variables. So it is natural to ask if there exists a
formulation of this kind of field theories which avoids this problem, retaining
the versatility of the known approach. The following paper deals with a family
of variational problems, namely, the so called non standard variational
problems, which intends to capture the data necessary to set up such a
formulation for field theories; moreover, we will formulate a multisymplectic
structure for the family of non standard variational problems, and we will
relate this with the (pre)symplectic structure arising on the space of sections
of the bundle of fields. In this setting the Dirac theory of constraints will
be studied, obtaining among other things a novel characterization of the
constraint manifold which arises in this theory, as generators of an exterior
differential system associated to the equations of motion and the chosen
slicing. Several examples of application of this formalism are discussed: Two
of them motivated from the physical point of view, that is, electromagnetism
and Poisson sigma models, and two examples of mathematical application. In the
case of electromagnetism, it is shown that this formulation avoids the problems
arising in the usual approach.Comment: 51 pages, aims; added examples and references, typos added, improved
some content, to appear in "Journal of Geometric Mechanics"
Non-Destructive Inspection of Impact Damage in Composite Aircraft Panels by Ultrasonic Guided Waves and Statistical Processing.
This paper discusses a non-destructive evaluation (NDE) technique for the detection of damage in composite aircraft structures following high energy wide area blunt impact (HEWABI) from ground service equipment (GSE), such as heavy cargo loaders and other heavy equipment. The test structures typically include skin, co-cured stringers, and C-frames that are bolt-connected onto the skin with shear ties. The inspection exploits the waveguide geometry of these structures by utilizing ultrasonic guided waves and a line scan approach. Both a contact prototype and a non-contact prototype were developed and tested on realistic test panels subjected to impact in the laboratory. The results are presented in terms of receiver operating characteristic curves that show excellent probability of detection with low false alarm rates for defects located in the panel skin and stringers
Miscommunication Of Uncertainties In Financial Statements: A Study Of Preparers And Users
The focus of this study is management's communication of uncertainty (attested to by auditors) and the potential for miscommunication due to the communication mode used in accounting disclosures. Two hypotheses are addressed to determine if financial statement users differentiate among three levels of uncertainty (using SFAS No. 5 as a vehicle for study), and whether their judgments differ when numerical probabilities replace the prescribed verbal expressions in communicating these uncertainties. The participants for this study are drawn from commercial loan officers from a major regional bank. Results lend evidence that both the level of uncertainty and the mode of communication are significant factors influencing the level of risk revision in an uncertainty exercise. Support is found that miscommunication may exist between the preparers and users of financial statements. However, support is not found that the “vagueness” of SFAS No. 5 verbal expressions of uncertainty is detrimental to users’ decision-making abilities
Comparing Fixed-amount and Progressive-amount DRO Schedules for Tic Suppression in Youth with Chronic Tic Disorders
Chronic tic disorders (CTDs) involve motor and/or vocal tics that often cause substantial distress and impairment. Differential reinforcement of other behavior (DRO) schedules of reinforcement produce robust, but incomplete, reductions in tic frequency in youth with CTDs; however, a more robust reduction may be needed to affect durable clinical change. Standard, fixedâamount DRO schedules have not commonly yielded such reductions, so we evaluated a novel, progressiveâamount DRO schedule, based on its ability to facilitate sustained abstinence from functionally similar behaviors. Five youth with CTDs were exposed to periods of baseline, fixedâamount DRO (DROâF), and progressiveâamount DRO (DROâP). Both DRO schedules produced decreases in tic rate and increases in intertic interval duration, but no systematic differences were seen between the two schedules on any dimension of tic occurrence. The DROâF schedule was generally preferred to the DROâP schedule. Possible procedural improvements and other future directions are discussed
ThermoScan: Semi-automatic Identification of Protein Stability Data From PubMed
open3noThis work was supported by the PRIN project, âIntegrative tools for defining the molecular basis of the diseases: Computational and Experimental methods for Protein Variant Interpretationâ of the Ministero Istruzione, UniversitĂ e Ricerca (201744NR8S).During the last years, the increasing number of DNA sequencing and protein mutagenesis studies has generated a large amount of variation data published in the biomedical literature. The collection of such data has been essential for the development and assessment of tools predicting the impact of protein variants at functional and structural levels. Nevertheless, the collection of manually curated data from literature is a highly time consuming and costly process that requires domain experts. In particular, the development of methods for predicting the effect of amino acid variants on protein stability relies on the thermodynamic data extracted from literature. In the past, such data were deposited in the ProTherm database, which however is no longer maintained since 2013. For facilitating the collection of protein thermodynamic data from literature, we developed the semi-automatic tool ThermoScan. ThermoScan is a text mining approach for the identification of relevant thermodynamic data on protein stability from full-text articles. The method relies on a regular expression searching for groups of words, including the most common conceptual words appearing in experimental studies on protein stability, several thermodynamic variables, and their units of measure. ThermoScan analyzes full-text articles from the PubMed Central Open Access subset and calculates an empiric score that allows the identification of manuscripts reporting thermodynamic data on protein stability. The method was optimized on a set of publications included in the ProTherm database, and tested on a new curated set of articles, manually selected for presence of thermodynamic data. The results show that ThermoScan returns accurate predictions and outperforms recently developed text-mining algorithms based on the analysis of publication abstracts. Availability: The ThermoScan server is freely accessible online at https://folding.biofold.org/thermoscan. The ThermoScan python code and the Google Chrome extension for submitting visualized PMC web pages to the ThermoScan server are available at https://github.com/biofold/ThermoScan.openTurina P.; Fariselli P.; Capriotti E.Turina P.; Fariselli P.; Capriotti E
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