Using information theory to assess the diversity, complexity, and development of communicative repertoires.

The application of quantitative and comparative measures from information theory on animal communication can provide novel insights into the ecological, environmental, social, and contextual properties that shape the structure, organization, and function of signal repertoires. Using 2 phylogenetically different mammalian species that share similar ecological and social constraints as examples, the authors quantitatively examined the internal structure and development of a subsystem of these species' vocal repertoires in comparison with that of human language and illustrated that these species exhibit convergent developmental processes. The authors also discussed how predictions on the structure and organization of animal communication systems can be made from this new application of information theoretic measures with respect to behavioral ecology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive aspects of chronic depression.

Previous research on chronic depression has focused on its link with other mood disorders and Axis II personality disorders. However, there are few data examining whether the cognitive perspective applies to this condition. In this cross-sectional study, 42 outpatients with chronic depression were compared with 27 outpatients with nonchronic major depressive disorder and 24 never psychiatrically ill controls on cognitive variables thought to be related to vulnerability to depression (e.g., dysfunctional attitudes, attributional style, a ruminative response style, and maladaptive core beliefs). Both depressed groups were more elevated than a never-ill comparison group. However, chronically depressed individuals were generally more elevated on measures of cognitive variables than those with major depressive disorders even after controlling for mood state and personality disorder symptoms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scalar expectancy theory and peak-interval timing in humans.

The properties of the internal clock, temporal memory, and decision processes used to time short durations were investigated. The peak-interval procedure was used to evaluate the timing of 8-, 12-, and 21-s intervals, and analyses were conducted on the mean response functions and on individual trials. A distractor task prevented counting, and visual feedback on accuracy and precision was provided after each trial. Mean response distributions were (a) centered at the appropriate real-time criteria, (b) highly symmetrical, and (c) scalar in their variability. Analysis of individual trials indicated more memory variability relative to response threshold variability. Taken together, these results demonstrate that humans show the same qualitative timing properties that other animals do, but with some quantitative differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for Self-Organized Sentence Processing: Digging-In Effects.

Dynamical, self-organizing models of sentence processing predict "digging-in" effects: The more committed the parser becomes to a wrong syntactic choice, the harder it is to reanalyze. Experiment 1 replicates previous grammaticality judgment studies (F. Ferreira & J. M. Henderson, 1991b, 1993), revealing a deleterious effect of lengthening the ambiguous region of a garden-path sentence. The authors interpret this result as a digging-in effect. Experiment 2 finds a corresponding effect on reading times. Experiment 3 finds that making 2 wrong attachments is worse than making 1. Non-self-organizing models require multiple stipulations to predict both kinds of effects. The authors show that, under an appropriately formulated self-organizing account, both results stem from self-reinforcement of node and link activations, a feature that is needed independently. An implemented model is given. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A weak cipher that generates the symmetric group

There has been recent interest in the permutation group generated by the round functions of a block cipher. In this paper we present a cautionary example of a block cipher which generates the full symmetric group yet is very weak.     

Effects of Solute and Second-Phase Particles on the Texture of Nd-Containing Mg Alloys

Hot-rolled, binary Mg-Nd alloys with compositions ≥0.095 at. pct undergo the texture weakening phenomenon that has been reported in a number of Mg–rare earth (RE) alloys. However, alloys with compositions ≤0.01 at. pct retain a strong basal texture typical of pure Mg and other Mg alloys. Measurements of intragranular misorientation axes obtained using electron backscatter diffraction (EBSD) show that more dilute alloys contain predominantly basal $ < a > $ < a > dislocations, while richer alloys contain primarily prismatic $ < a > $ < a > dislocations. It is suggested that this change in dislocation content is related to a change in the dynamic recrystallization (DRX) mechanism. Metastable second-phase Mg _x Nd_1–x intermetallic particles are present within the alloys, and an annealing study indicates that the alloys undergoing texture weakening have grain sizes well predicted by classical Zener drag theory. Even though the more dilute alloys also contain second-phase particles, they are not sufficient to induce pinning. The promotion of nonbasal slip and the reduction in grain boundary mobility due to Zener drag are suggested as controlling mechanisms that promote the observed texture weakening phenomena.     

Crack Growth Modeling and Life Prediction of Pipeline Steels Exposed to Near-Neutral pH Environments: Stage II Crack Growth and Overall Life Prediction

This investigation was initiated to provide governing equations for crack initiation, crack growth, and service life prediction of pipeline steels in near-neutral pH (NNpH) environments. This investigation develops a predictive model considering loading interactions occurring during oil and gas pipeline operation with underload-type variable pressure fluctuations. This method has predicted lifetimes comparable to the actual service lives found in the field. This is in sharp contrast with the predictions made by existing methods that are either conservative or inconsistent with the field observations. It has been demonstrated that large slash loads (R-ratio is 0.05), often seen during gas pipeline operation, are a major life-limiting factor and should be avoided where possible. Oil pipelines have shorter lifetime because of their more frequent pressure fluctuations and larger amplitude load cycles. The accuracy of prediction can be improved if pressure data with appropriate sampling intervals are used. The sampling interval error is much larger in the prediction of oil pipelines than gas pipelines because of their different compressibility but is minimized if the pressure sampling rate for the data is at or less than one minute.     

DIRAC: A new version of computer algebra tools for studying the properties and behavior of hydrogen-like ions

During recent years, the Dirac package has proved to be an efficient tool for studying the structural properties and dynamic behavior of hydrogen-like ions. Originally designed as a set of Maple procedures, this package provides interactive access to the wave and Green's functions in the non-relativistic and relativistic frameworks and supports analytical evaluation of a large number of radial integrals that are required for the construction of transition amplitudes and interaction cross sections. We provide here a new version of the Dirac program which is developed within the framework of Mathematica (version 6.0). This new version aims to cater to a wider community of researchers that use the Mathematica platform and to take advantage of the generally faster processing times therein. Moreover, the addition of new procedures, a more convenient and detailed help system, as well as source code revisions to overcome identified shortcomings should ensure expanded use of the new Dirac program over its predecessor.

New version program summary

Program title: DIRACCatalogue identifier: ADUQ_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADUQ_v2_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 45 073No. of bytes in distributed program, including test data, etc.: 285 828Distribution format: tar.gzProgramming language: Mathematica 6.0 or higherComputer: All computers with a license for the computer algebra package Mathematica (version 6.0 or higher)Operating system: Mathematica is O/S independentClassification: 2.1Catalogue identifier of previous version: ADUQ_v1_0Journal reference of previous version: Comput. Phys. Comm. 165 (2005) 139Does the new version supersede the previous version?: YesNature of problem: Since the early days of quantum mechanics, the “hydrogen atom” has served as one of the key models for studying the structure and dynamics of various quantum systems. Its analytic solutions are frequently used in case studies in atomic and molecular physics, quantum optics, plasma physics, or even in the field of quantum information and computation. Fast and reliable access to functions and properties of the hydrogenic systems are frequently required, in both the non-relativistic and relativistic frameworks. Despite all the knowledge about one-electron ions, providing such an access is not a simple task, owing to the rather complicated mathematical structure of the Schrödinger and especially Dirac equations. Moreover, for analyzing experimental results as well as for performing advanced theoretical studies one often needs (apart from the detailed information on atomic wave- and Green's functions) to be able to calculate a number of integrals involving these functions. Although for many types of transition operators these integrals can be evaluated analytically in terms of special mathematical functions, such an evaluation is usually rather involved and prone to mistakes.Solution method: A set of Mathematica procedures is developed which provides both the non-relativistic and relativistic solutions of the “Hydrogen atom model”. It facilitates, moreover, the symbolic evaluation of integrals involved in the calculations of cross sections and transition amplitudes. These procedures are based on a large number of relations among special mathematical functions, information about their integral representations, recurrence formulae and series expansions. Based on this knowledge, the DIRAC tools provide a fast and reliable algebraic (and if necessary, numeric) manipulation of functions and properties of one-electron systems, thus helping to obtain further insight into the behavior of quantum physical systems.Reasons for new version: The original version of the DIRAC program was developed as a toolbox of Maple procedures and was submitted to the CPC library in 2004 (cf. Ref. [1]). Since then DIRAC has found its niche in advanced theoretical studies carried out in realm of heavy ion physics. With the help of this program detailed analysis has been performed, in particular, for the various excitation and ionization processes occurring in relativistic ion-atom collisions [2], the polarization of the characteristic X-ray radiation following radiative electron capture [3], the correlation properties of the two-photon emission from few-electron heavy ions [4], the spin entanglement phenomena in atomic photoionization [5] and even for exploring the vibrational excitations of the heavy nuclei [6]. Although these studies have conclusively proven the potential of the program, they have also illuminated routes for its further enhancement. Apart from certain source code revisions, demand has grown for a new version of DIRAC compatible with the Mathematica platform. The version presented here includes a wider ranging and more user friendly interactive help system, a number of new procedures and reprogramming for greater computational efficiency.Summary of revisions: The most important new capabilities of the DIRAC program since the previous version are:

1.

The utilization of the Mathematica (version 6.0) platform.

2.

The addition of a number of new procedures. Since the complete list of the new (and updated) procedures can be found in the interactive help library of the program, we mention here only the most important ones:

○

DiracGlobal[] - Displays a list of the current global settings which specify the framework, nuclear charge and the units which are to be used by the DIRAC program.

○

DiracRadialOrbitalMomentum[] - Returns a non-relativistic radial orbital in momentum space for both, the bound and free electron states.

○

DiracSlaterRadial[] - Evaluates the radial Slater integral both, with the non-relativistic and relativistic wavefunctions. In the previous version of the program this procedure was restricted to the non-relativistic framework only.

○

DiracGreensIntegralRadial[] - Evaluates the two-dimensional radial integrals with the wave- and Green's functions both in non-relativistic and relativistic frameworks.

○

DiracAngularMatrixElement[] - Calculates the angular matrix elements for various irreducible tensor operators.

3.

The elimination of some redundant procedures. In particular, the previous version supported evaluation of the spherical Bessel functions, Wigner 3j symbols, Clebsch-Gordan coefficients and spherical harmonics functions. These tools are now superseded by in-built procedures of Mathematica.

4.

The development of a full featured interactive help system which follows the style of the Mathematica Help Pages.

5.

Extensive revision of the source code in order to correct a number of bugs and inconsistencies that have been identified during use of the previous version of Dirac.

The DIRAC package is distributed as a compressed tar file from which the DIRAC root directory can be (re-)generated. The root directory contains the source code and help libraries, a “Readme” file, Dirac_Installation_Instructions, as well as the notebook DemonstrationNotebook.nb that includes a number of test cases to illustrate the use of the program. These test cases, which concern the theoretical analysis of wavefunctions and the fine-structure of hydrogen-like ions, has already been discussed in detail in Ref. [1] and are provided here in order to underline the continuity between the previous (Maple) and new (Mathematica) versions of the DIRAC program.Unusual features: Even though all basic features of the previous Maple version have been retained in as close to the original form as possible, some small syntax changes became necessary in the new version of DIRAC in order to follow Mathematica standards. First of all, these changes concern naming conventions for DIRAC's procedures. As was discussed in Ref. [1], previously rather long names were employed in which each word was separated by an underscore. For example, when running the Maple version of the program one had to call the procedure Dirac_Slater_radial() in order to evaluate the Slater integral. Such a naming convention however, cannot be used in the Mathematica framework where the underscore character is reserved to represent Blank, a built-in symbol. In the new version of DIRAC we therefore follow the Mathematica convention of delimiting each word in a procedure's name by capitalization. Evaluation of the Slater determinant can be accomplished now simply by entering DiracSlaterRadial[]. Besides procedure names, a new convention is introduced to represent fundamental physical constants. In this version of DIRAC the group of (preset) global variables has changed to resemble their conventional symbols, specifically α, a₀, ec, me, c and ?, being the fine structure constant, Bohr radius, electron charge, electron mass, speed of light and the Planck constant respectively. If the numerical evaluator N is wrapped around any of these constants, their numerical values are returned.Running time: Although the program replies promptly upon most requests, the running time also depends on the particular task. For example, computation of (radial) matrix elements involving components of relativistic wavefunctions might require a few seconds of a runtime. A number of test calculations performed regarding this and other tasks clearly indicate that the new version of Dirac requires up to 90% less evaluation time compared to its predecessor.References:

[1]

A. Surzhykov, P. Koval, S. Fritzsche, Comput. Phys. Comm. 165 (2005) 139.

[2]

H. Ogawa, et al., Phys. Rev. A 75 (2007) 1.

[3]

A.V. Maiorova, et al., J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 125003.

[4]

L. Borowska, A. Surzhykov, Th. Stöhlker, S. Fritzsche, Phys. Rev. A 74 (2006) 062516.

[5]

T. Radtke, S. Fritzsche, A. Surzhykov, Phys. Rev. A 74 (2006) 032709.

[6]

A. Pálffy, Z. Harman, A. Surzhykov, U.D. Jentschura, Phys. Rev. A 75 (2007) 012712.