bluuebunny/crossref_metadata_2025 huggingface dataset:
Prometheus Chained
Authors: Drenth Pieter J.D.
Published: April 2003

The Chained Prometheus is introduced as a metaphor for the behavioral scientist. Science (including psychology and pedagogy) is no longer taken for granted. Society, politics, and the media pose critical questions and not infrequently demand censorship or at least control of science. An analysis is given of the types of criticism and skepticism with respect to science, and to psychology in particular. The (behavioral) scientist faces a dilemma: On the one hand, science cannot exist and develop without freedom; on the other hand, this does not mean the freedom to amass knowledge at any price and without any restrictions. Thus, we balance ourselves between freedom and ethical/social responsibility. This presentation reflects on the question of the social and ethical limitations of (behavioral) science: Who should control what and on which criteria?
The Professionalization of Psychology in Europe
Authors: Lunt Ingrid
Published: April 2003

Over the past 100 years psychology has become increasingly professionalized. Emerging from a scientific discipline at the beginning of the century, it has rapidly became a professional field with psychologists working in health, education, and organizational settings as practitioners. A number of measures of this increased professionalization are discussed: increased length of education and training, greater specialization and specialist training, pressures for regulation and laws for psychologists, the development of ethical codes, and a greater institutionalization of psychology. Professional organizations for psychologists play a key role in the professionalization of the discipline. However, the path followed is the traditional path of the traditional professions, and questions are raised about the appropriateness of this for the next century.
Studying, Working, and Living in Another EU Country
Authors: Mullet Etienne , Dej Véronique , Lemaire Isabelle , Raïff Philippe , Barthorpe Jolyon
Published: April 2003

This study assessed the willingness of French youth to go and study or work for some time in another EU country. We examined three types of questions: (a) What is the overall level of willingness to go in another EU country? Does age, gender or socioeconomic status (SES) of the family influence this overall level? Which country do French youth prefer to go to? (b) Is a four-factor Push-Anti-Push-Pull-Anti-Pull model able to account for data regarding attitudes toward other countries and attitudes toward France? (c) Is this model able to predict willingness to go and study or work in another EU country, both generally and for individual countries? The overall level of willingness to go to other EU countries was not very high. Except for the United Kingdom the mean response was always located closer to the “No” pole than to the “Quite possible” pole. Gender, age, and educational level of the father did not play a role. Participants clearly preferred the United Kingdom and Spain to Germany or The Netherlands. Exploratory factor analysis showed a clearly interpretable Push-Anti-Push-Pull-Anti-Pull solution, and confirmatory factor analysis showed that this structure fits the attitudes data very well according to the usual indices. This general model, however, did not explain much of the “intent-to-go” variance. In addition, specific Pull attractiveness considerations (liking and knowing the country) played, beyond the general Push-Pull model, a notable role in the determination of willingness to go and study or work in each of the 14 EU countries.
Does Delay Affect Prospective Memory Performance?
Authors: Nigro Giovanna , Cicogna Pier Carla
Published: April 2003

The aim of this study was to investigate the extent to which the retention interval between intention formation and the execution of the action affects the occurrence of remembering and its accuracy. 126 subjects (48 men and 78 women) between 18 and 24 years participated in a two-phase experiment. An event-based prospective memory task was assigned at the end of the first experimental session, which required reporting a message to the second experimenter at the beginning of the second experimental session. The length of the interval of time between the formation of the intention and its execution varied (10 minutes, 2 days, 2 weeks). Participants were randomly assigned to the three conditions (42 each). A post-experimental interview was carried out in order to find out the strategies that subjects employed to retrieve the message and the importance they attributed to the task. Results indicate that the delay affected neither the occurrence of remembering nor its accuracy, and that the importance attributed to the planned action improved the likelihood of prospective remembering. Furthermore, results seem to indicate that external reminders do not improve prospective memory. Further implications of the finding were discussed.
The Holistic-Interactionistic Paradigm: Some Directions for Empirical Developmental Research
Authors: Magnusson David
Published: April 2003

This article asserts the claim for linking methods to phenomena—and not vice versa—in research on individual development. It is argued that proper application of theory, design, and methodological tools in studies of specific problems requires strict consideration of four basic features of developmental processes: (1) the holistic-interactionistic nature of such processes, (2) individual development as a process of adaptation, (3) developmental change as transformation, and (4) synchronization and coordination of operating elements in developmental change. The research strategy and methodological consequences of this claim are discussed.
Developmental Processes and the Modern Typological Perspective
Authors: Bergman Lars R. , El-Khouri Bassam M.
Published: April 2003

Within the general theoretical framework of the holistic-interactionistic paradigm, the need for using methods reflecting the process characteristics of a developmental study is emphasized and certain limitations of current research practice in this regard are pointed out. We focus on a person-oriented approach that can be regarded as a modern typological approach, where patterns of values in relevant variables describing the individual are regarded as indivisible, so that the variable has a meaning only as a part of such a pattern. It is claimed that such an approach can be more process-oriented and more compatible with the holistic-interactionistic paradigm than conventional methods. Some relevant classification-based methods are briefly reviewed, and a new method (TYFO) is presented that aims at finding typical developmental patterns in data without striving for a complete classification. The procedure is illustrated with an empirical example.
Emotional Seesaw, Compliance, and Mindlessness
Authors: Dolinski Dariusz
Published: April 2003

Research on emotion conducted so far has ignored situations where the subject experiences a certain emotion, but where the external stimulus that evoked and upholds this emotion suddenly disappears. This kind of situation, however, is relatively common in everyday life. This article attempts to recognize certain consequences of those conditions under which the stimuli justifying our experience of such emotional states as fear or joy suddenly disappear. Research done to date by the author and colleagues indicates increased compliance of the subject when addressed with various requests, commands, or suggestions in the situation termed here “emotional seesaw.” The classical “live” example that illustrates this principle is the type of “good cop-bad cop” interrogation procedure. The probable mechanism underlying increased compliance under these conditions is connected with the fact that every emotion generates its own specific behavior program. When this program suddenly proves to be totally inadequate to new, modified external circumstances, the subject begins functioning “mindlessly.” This permits automatic reactions, which take no account for the peculiarity of the current situation. Another group of experiments presented in this article shows that the subject's cognitive functioning is disturbed under emotional seesaw conditions. Such a disturbance embraces not only simple cognitive operations like detection of facial expressions of emotion, but also more complex operations like arithmetical calculations done mentally. The article concludes that further research is needed regarding the consequences of sudden and unexpected withdrawal of stimuli that induce and uphold various emotions.
Genetic and Environmental Influences on Temperament
Authors: Zawadzki Bogdan , Strelau Jan , Oniszczenko Wodzimierz , Riemann Rainer , Angleitner Alois
Published: April 2003

Among the criteria for a personality paradigm the following three are the most crucial: biological basis (e. g., genetic contribution to the phenotypic variance), universality (existence of traits in different cultures) and reality (possibility to measure traits by different methods). The present study combines all three criteria to explore the impact of genetic and environmental factors on temperamental traits, as stipulated by Strelau 's regulative theory of temperament, across two culturally different samples (Polish and German), and by means of two diagnostic methods (self-report and peer-rating). The analysis was conducted on data obtained from 1009 same-sex pairs of twins (German sample) and 546 same-sex pairs of twins (Polish sample). For each subject the self-report as well as rating from two independent peers was recorded by both the Polish and German versions of the Formal Characteristics of Behavior-Temperament Inventory. Results demonstrate substantial heritability of temperamental traits, although average peer-rating tends to provide lower heritability estimates than self-report (for six traits M = 33% and M = 46% of the total variance, respectively). After separating the error variance from the effect of nonshared environment for both methods (self-report and peer-rating) and both samples, joint analysis indicated a very high impact of genetic factors (the average raised up to 66% of the total variance). No significant “sample” effect was found, so that we may allows to conclude that temperamental traits are determined in both cultures to the same extent by genetic factors.
Managing the Stress of Bringing the Economy in the Eastern German States to the Level of the Western German States
Authors: Kirkcaldy Bruce , Petersen Lars-Eric , Hübner Gundula
Published: April 2003

A select group of managers in the private and public sector working in the new and old German federal states were administered the German version of the Pressure Management Indicator (PMI; Williams, Kirkcaldy, & Cooper, 1999 ). Twenty-four scale scores were assessed encompassing diverse aspects of occupational stress, individual differences (type A, locus of control, and coping), and outcome variables (work satisfaction, physical and psychological health). Several differences were observed between those managers reared and educated in the former East Germany and those from the former West Germany. East-German managers, for example, were characterized by an external locus of control with regard to their jobs and revealed higher type A scores compared to their West-German counterparts. Furthermore, although there were no differences in the evaluation of working climate nor in subjectively perceived occupational stress, specific outcome variables such as self-reported physical and psychological health did differ between West- and East-German managers. The implications of these findings are discussed.
What Makes a Competent Psychologist?
Authors: Roe Robert A.
Published: April 2003

In developing European standards for the psychological profession, two main approaches to the definition of professional competence have been proposed. One focuses on the roles and functions psychologists should be able to perform (output model), the other on the educational curricula that should be followed in order to become a psychologist (input model). This article starts with a discussion of both approaches, which leads to the conclusion that neither of them offers a sufficient base for setting adequate professional standards. Next a comprehensive model of occupational competence is presented which comprises both input and output factors. It is indicated how this model can be utilized in defining competence profiles for the psychological specialties, as well as in developing and maintaining competence. Issues covered include: student selection, academic curriculum design, initial professional training, continued professional training, institutional and individual accreditation, and quality assurance.
Facilitating Mobility for Psychologists Through a Competency-Based Approach for Regulation and Accreditation: The Canadian Experiment
Authors: Gauthier Janel G.
Published: April 2003

Professionals in Canada are regulated by provincial/territorial bodies that have their own requirements for licensing and registration. Because these requirements vary tremendously across jurisdictions, the ability of Canadians to work anywhere in the country is greatly limited. In response to pressures for greater mobility, federal, provincial and territorial governments agreed in 1994 to take steps to remove or reduce barriers to the movement of workers in Canada. Under this agreement, regulatory bodies within each jurisdiction were asked to comply voluntarily with the obligations of the agreement or else the government would adopt and maintain measures to ensure such compliance. To address the issue of mobility, Canadian psychologists have taken a competency approach. This paper presents the template that provided a common framework or language for the mutual recognition of competencies for the purpose of mobility in Canada and the results of this process as reflected in the Mutual Recognition Agreement signed by the Canadian regulatory bodies of psychologists in June 2001. The paper also highlights the role of accreditation of training programs in the recognition of professional psychologists for the purpose of mobility and the influence that training programs may have on standards for licensure or registration.
Projecting a European Diploma in Psychology
Authors: Wilpert Bernhard
Published: April 2003

The paper presents an inside evaluation of the EuroPsyT project, funded by the EU Leonardo Program in 1999-2001. While standard research usually neglects to reflect on the internal and external constraints and opportunities under which research results are achieved, the paper stresses exactly those aspects: starting from a brief description of the overall objectives of the 11 countries project, the paper proceeds to describe the macro-context and the internal strengths and weaknesses of the project team, the internal procedures of cooperation,. and obstacles encountered during the research process. It winds up in noting some of the project's achievements and with a look towards future research.
Environmental Perception: Factor Profiles of Extreme Groups
Authors: Bogner Franz X. , Wiseman Michael
Published: April 2003

This paper describes an empirical survey of adolescent responses to two environmental perception batteries: “Environmental Perception” (ENV) and “New Environmental Paradigm” (NEP). The first was developed by the present authors for adolescents, while the second is already well-known within environmental psychology. The present study examines both batteries applied to a sample of over 800 German pupils. Responses to both batteries were subjected to factor analyses extracting the hypothesized 8 oblique factors. Groups were ranked according to their “Care with Resources” score, and the extreme groups were identified. Differences between these groups were examined in terms of the remaining seven factor scores, confirming the hypothesis that high scorers tend to enjoy nature, to favor a balanced nature and limits to growth, and to declare their intention to support conservation. Low scorers tend to do the opposite.
Neutrophils Induce Sequential Focal Changes in Endothelial Adherens Junction Components: Role of Elastase
Authors: Ionescu Carmen V. , Cepinskas Gediminas , Savickiene Jurate , Sandig Martin , Kvietys Peter R.
Published: April 2003

Objective: In vitro studies have indicated that polymorphonuclear leukocytes (PMNs) traverse endothelial cell monolayers via the paracellular pathway (i.e., through endothelial cell–cell junctions. Herein, we assessed whether the adherens junctions (AJs) are disrupted during PMN transendothelial cell migration.

Methods: Human umbilical vein endothelial cells (HUVECs) were grown to confluence on porous membranes and activated with interleukin‐1β, and PMN transendothelial migration was facilitated by formyl‐methionyl‐leucylphenylalanine. Using dual immunofluorescence staining and laser scanning confocal microscopy, we assessed the effects of PMN‐endothelial cell adhesive interactions (i.e., adhesion to and emigration across monolayers) on the AJ components vascular endothelial (VE)‐cadherin, β‐catenin, α‐catenin, and γ‐catenin.

Results: In the AJ immediately adjacent to the adherent PMN, there was a loss of staining for some of the AJ components. AJ components further away from HUVEC‐PMN adhesive interactions were unaffected. An iterative approach indicated that the four components were sequentially lost from the AJ. β‐catenin was lost first, followed by VE‐cadherin, α‐catenin, and, finally, γ‐catenin. In the absence of PMNs, the cross‐linking of VE‐cadherin, but not platelet endothelial cell adhesion molecule‐1 or intercellular adhesion molecule‐1, increased the cytoplasmic accumulation of β‐catenin. During PMN transendothelial migration, all of the junctional components under study were lost at the immediate site of monolayer penetration. Again, at regions removed from the actual site of PMN penetration of the monolayers, the AJ components were unaffected. PMN‐induced disorganization of the AJs was partially prevented by an elastase inhibitor.

Conclusions: These findings suggest that adherent PMNs induce a localized, sequential disassembly of AJs, which is partially mediated by PMN‐derived elastase and involves the initial loss of an intracellular component of AJs (i.e., β‐catenin).
Self-consistent Ornstein–Zernike approximation for a binary symmetric fluid mixture
Authors: Schöll-Paschinger Elisabeth , Kahl Gerhard
Published: April 2003

The self-consistent Ornstein–Zernike approximation (SCOZA) is an advanced microscopic liquid state method that is known to give accurate results in the critical region and for the localization of coexistence curves; this has been confirmed in several applications to continuous and discrete one component systems. In this contribution we present the extension of the SCOZA formalism to the case of a binary symmetric fluid mixture characterized by hard-core potentials with adjacent attractive interactions, given by linear combinations of Yukawa tails. We discuss the stability criteria for such a system and present results for the phase behavior: we recover the well-known three archetypes of phase diagrams, characterized by the different manners the second order demixing line (λ-line) intersects the first order liquid–vapor coexistence curve.
Frontiers of silicon-on-insulator
Authors: Celler G. K. , Cristoloveanu Sorin
Published: April 2003

Silicon-on-insulator (SOI) wafers are precisely engineered multilayer semiconductor/dielectric structures that provide new functionality for advanced Si devices. After more than three decades of materials research and device studies, SOI wafers have entered into the mainstream of semiconductor electronics. SOI technology offers significant advantages in design, fabrication, and performance of many semiconductor circuits. It also improves prospects for extending Si devices into the nanometer region (<10 nm channel length). In this article, we discuss methods of forming SOI wafers, their physical properties, and the latest improvements in controlling the structure parameters. We also describe devices that take advantage of SOI, and consider their electrical characteristics.
GaN Schottky diodes for piezoelectric strain sensing
Authors: Strittmatter R. P. , Beach R. A. , Brooke J. , Preisler E. J. , Picus G. S. , McGill T. C.
Published: April 2003

We report on the electromechanical response of Schottky diodes on n-GaN as a function of the strain frequency and the applied dc bias. These measurements reveal excellent strain detection sensitivity for frequencies above ∼10 Hz. The observed amplitude and phase of the electromechanical output can be largely explained using a simple model of piezoelectric charge generation on either side of the depletion layer. In addition, we report on the noise spectral density from these diodes under the same conditions and infer a signal to noise ratio for strain detection.
Electron attachment to C2Cl4 and Trojan horse ionization
Authors: Drexel H. , Sailer W. , Grill V. , Scheier P. , Illenberger E. , Märk T. D.
Published: April 2003

Electron attachment to tetrachloroethene (C2Cl4) has been studied in the energy range from ∼0 eV up to 9.5 eV, using a trochoidal electron monochromator with an energy resolution of about 70 meV. Production yields for the parent anion and various fragment anions are compared with previously published data in order to clarify some existent discrepancies. In particular, an inconsistency concerning the Cl−/C2Cl4 peak is investigated, and additional transitions leading to anion formation are presented. Moreover, a newly discovered mechanism for the production of a spurious anion signal at zero electron energy is presented. This mechanism appears when metastable anions that have been formed initially upon attachment undergo autodetachment in regions where electrostatic fields are present. Zero-energy peaks generated that way represent dangerous pitfalls and have to be taken into account, at least in electron attachment studies that are based on in-line instruments.
Electron ground state energy level determination of ZnSe self-organized quantum dots embedded in ZnS
Authors: Lu L. W. , Yang. C. L. , Wang J. , Sou I. K. , Ge W. K.
Published: April 2003

Optical and electrical characterization of the ZnS self-organized quantum dots (QDs) embedded in ZnS by molecular beam epitaxy have been investigated using photoluminescence (PL), capacitance–voltage (C−V), and deep level transient Fourier spectroscopy (DLTFS) techniques. The temperature dependence of the free exciton emission was employed to clarify the mechanism of the PL thermal quenching processes in the ZnSe QDs. The PL experimental data are well explained by a two-step quenching process. The C−V and DLTFS techniques were used to obtain the quantitative information on the electron thermal emission from the ZnSe QDs. The correlation between the measured electron emission from the ZnSe QDs in the DLTFS and the observed electron accumulation in the C−V measurements was clearly demonstrated. The emission energy for the ground state of the ZnSe QDs was determined to be at about 120 meV below the conduction band edge of the ZnS barrier, which is in good agreement with the thermal activation energy, 130 meV, obtained by fitting the thermal quenching process of the free exciton PL peak.
Effect of ion implantation on surface energy of ultrahigh molecular weight polyethylene
Authors: Chen J. S. , Sun Z. , Guo P. S. , Zhang Z. B. , Zhu D. Z. , Xu H. J.
Published: April 2003

The effect of ion implantation including ion species (N2+ and C3H8+) and the fluences (1×1014–5×1015 ions/cm2) on the surface energy of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The total surface energy increases significantly after implanting with the fluence of 1×1014 ions/cm2 regardless of ion species, then, the total surface energy slightly increases for N2+ implanted UHMWPE and decreases slightly for C3H8+ implanted UHMWPE with a further increase of fluence. The structural changes of UHMWPE with different fluence for different ion species are very similar. The linear chains of UHMWPE are damaged and cross linking is generated after implantation. As the fluence increases, the polymer surface becomes more disordered, and the surface becomes hydrogenated amorphous carbon when the fluence exceeds 1×1015 ions/cm2. The surface roughness increases with the increase of the fluence regardless of ion implantation species.
Interaction of NO(v=12) with LiF(001): Evidence for anomalously large vibrational relaxation rates
Authors: Wodtke Alec M. , Huang Yuhui , Auerbach Daniel J.
Published: April 2003

We report direct measurements of the vibrational survival probability of NO(v=12) suffering collisions with a LiF(001) crystalline surface. Survival probabilities are near unity in all cases. At the lowest reported incidence energies (5.3 kJ/mol) and surface temperatures (290 K), vibrational relaxation is enhanced, angular distributions approach cos(θ), and rotational temperatures of the scattered molecules approach the surface temperature. At higher incidence energies, rotational temperatures are higher than the surface temperature and angular distributions narrow approaching cos6(θ). These results suggest that trapping desorption is occurring at least at the lowest incidence energies and surface temperatures. Substantial vibrational relaxation appears to occur when residence time are as small as a few ps. This is many orders of magnitude faster than has been reported for diatomic molecules relaxing from v=1 on salt crystals.
An improved Polarflex water model
Authors: Jeon Jonggu , Lefohn Aaron E. , Voth Gregory A.
Published: April 2003

The three-site polarizable and flexible water potential employing the multistate empirical valence bond (MS–EVB) description for the electronic polarizability [A. E. Lefohn, M. Ovchinnikov, and G. A. Voth, J. Phys. Chem. B 105, 6628 (2001)] has been modified for better reproduction of liquid water properties under ambient conditions. The improvement of the potential model was accomplished by (i) replacing the point charge distribution associated with the atomic interaction sites in the original model with a diffuse Gaussian charge distribution and (ii) reparametrizing the molecular geometry, components of electronic polarizability tensor, the Lennard-Jones parameters, and the widths of the Gaussian charge distribution. Static and dynamic properties, such as the intermolecular interaction energy, radial distribution function, diffusion constant, and dielectric constant, have been used in the model parametrization and the resulting model well reproduces the experimental data. A closely related rigid version of the model is also developed and compared with the flexible one. For computational efficiency, the extended Lagrangian algorithm for the electronic degrees of freedom has been implemented in the MS–EVB molecular dynamics simulation and utilized in the calculations. Relations between the new features of the potential model, such as the Gaussian charge distribution and the anisotropy in the electronic polarizability, and the liquid properties are established and discussed.
Specifics of freezing of Lennard-Jones fluid confined to molecularly thin layers
Authors: Vishnyakov Aleksey , Neimark Alexander V.
Published: April 2003

Freezing of a Lennard-Jones fluid between solid surfaces was studied using grand canonical Monte Carlo and molecular dynamics simulations. We explored the formation of frozen phases of hexagonal and orthorhombic symmetry in mono-, bi-, and tri-layer structures. The freezing transition, the type of lattice, and translational and orientational ordering were identified on the basis of orientational order parameters, in-plane two-body and three-body translational correlation functions, orientational correlation functions, and analysis of molecular mobilities. We have found that the freezing temperature is a nonmonotonous function of the pore width: orthorhombic bi-layer freezes at lower temperatures than hexagonal monolayer and hexagonal bi-layer. As the pore width increases, the transition from a hexagonal monolayer to an orthorhombic bi-layer occurred via disordered liquidlike and quasi-long-range four-fold ordered bi-layers. The latter, “quadratic” structure is characterized by an algebraically decaying four-fold orientational correlation function. The transition from crystalline hexagonal bi-layer to orthorhombic tri-layer occurs through a bi-layer structure with two uncoupled hexagonal monolayers. The quadratic phase was observed also as an intermediate structure during freezing of a liquidlike bi-layer into an orthorhombic quasi-crystal. The formation of the quadratic phase was associated with step-wise densification of fluid, a sharp increase of the local orientational order parameter, and a significant reduction of fluid mobility. In the process of solidification, the system passed through a sequence of high-density jammed structures, in which the four-fold symmetry developed progressively, as the temperature decreased.
Phonon modes of GaN/AlN heterojunction field-effect transistor structures grown on Si(111) substrates
Authors: Pattada B. , Chen Jiayu , Manasreh M. O. , Guo S. , Gotthold D. , Pophristic M. , Peres B.
Published: April 2003

Phonon modes of GaN/AlN heterojunction field-effect transistor (HFET) structures were investigated using Fourier-transform infrared spectroscopy. The HFET structure was grown on Si(111) substrate with AlN-based buffer layers. The phonon modes were also investigated in structure without AlGaN cap layer. The phonon mode spectra were obtained at the normal incident, waveguide, and Brewster’s angle configurations. Several vibrational frequencies were observed and found to be strongly dependent on the angle of the incident light. In particular, a phonon frequency of ∼734 cm−1 was observed only in the spectra when the samples are in the Brewster’s angle configuration. Moreover, a phonon mode was observed at 880 cm−1 in both waveguide and Brewster’s angle configurations. Additionally, a phonon absorption band is observed around 576 cm−1 , which appears to be composed of two modes, was redshifted to ∼550 cm−1 when the spectra were recorded in the waveguide configuration.
Multiscale simulation of phonon transport in superlattices
Authors: Schelling P. K. , Phillpot S. R.
Published: April 2003

A particle-based model for phonon transport and the scattering of phonon wave packets at interfaces is developed. The model, which incorporates the interference effects associated with the wave nature of phonons, is parametrized with frequency-dependent scattering rates obtained from molecular-dynamics simulations of the interaction of phonon wave packets with a single interface. From simulations of scattering of phonon wave packets from superlattices, we find that when the interference effects are not included there is qualitative disagreement between the molecular-dynamics and particle simulations. Moreover, we show that such interference effects tend to result in a larger amount of energy being transmitted through a superlattice.
Theoretical characterization of the disilaethynyl anion (Si2H−)
Authors: Pak Chaeho , Sari Levent , Rienstra-Kiracofe Jonathan C. , Wesolowski Steven S. , Horný Ľuboš , Yamaguchi Yukio , Schaefer Henry F.
Published: April 2003

The singlet-state potential energy surface of the disilaethynyl anion (Si2H−) has been investigated using ab initio self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets. Four stationary points [cyclic (monobridged) A11 (C2v), linear Σ1 + (C∞v), bent A′1 (Cs), and quasilinear Σ1 + (Cs) structures] were located with the correlated wave functions, while only two stationary points [cyclic (monobridged) A11 (C2v) and linear Σ1 + (C∞v) structures] were found with the SCF method. The cyclic structure (C2v) is predicted to be the global minimum at all levels of theory. The linear structure (C∞v) is found to be a transition state between the two quasilinear structures (Cs) at the correlated levels of theory, while the SCF linear structure is predicted to be a transition state between the two cyclic structures. The quasilinear structure possesses a Si–Si–H bond angle similar to that of the monobridged Si2H2 molecule. The bent geometry is assigned to a transition state for the isomerization reaction between the cyclic and quasilinear structures. With the most reliable level of theory, augmented correlation-consistent polarized valence quadruple-ζ CCSD(T), the quasilinear structure is predicted to be 8.6 kcal/mol [7.9 kcal/mol with the zero-point vibrational energy (ZPVE) correction] above the cyclic (monobridged) structure, and the energy barrier for the cyclic→quasilinear isomerization reaction is determined to be 12.1 kcal/mol (11.0 kcal/mol with the ZPVE correction). The inversion reaction between the quasilinear and linear structures is found to have a very small energy barrier. With the estimated aug-cc-pCVQZ CCSD(T) method the electron affinity of Si2H is predicted to be 2.31 eV, which is in excellent agreement with the experimental value 2.31±0.01 eV.
High level ab initio studies of the excited states of sulfuric acid and sulfur trioxide
Authors: Robinson Timothy W. , Schofield Daniel P. , Kjaergaard Henrik G.
Published: April 2003

We have calculated the vertical excitation energies and oscillator strengths of the lowest energy electronic transitions in sulfuric acid (H2SO4) and sulfur trioxide (SO3) with a range of ab initio methods. We have found that the highest level calculations with the complete active space self-consistent field and multireference configuration interaction (MRCI) methods predict transition energies much lower than those previously calculated with the simpler configuration interaction-singles method. The MRCI calculated electronic transitions for SO3 are in good agreement with the experimental results, whereas electronic transitions in vapor phase H2SO4 have yet to be observed. Our MRCI results suggest that the lowest lying electronic excitation in H2SO4 occurs around 144 nm and that the cross section in the actinic region is very small.
Structure and spectroscopy of U4+ defects in Cs2ZrCl6: Ab initio theoretical studies on the 5f 2 and 5f 16d1 manifolds
Authors: Barandiarán Zoila , Seijo Luis
Published: April 2003

The ab initio model potential embedded cluster method, which combines the explicit treatment of quantum-mechanical embedding effects with electron correlation and spin–orbit coupling, has been applied to the calculation of the U–Cl equilibrium distances, totally symmetric vibrational frequencies, and 5f2→5f2, 5f2→5f16d1 electronic transitions of the (UCl6)2− defect cluster in the Cs2ZrCl6 host crystal. The 5f2→5f2 absorption spectrum of U4+ in gas phase has also been calculated. Comparison of the 5f2→5f2 spectra in gas phase and in Cs2ZrCl6 with experiments is used for establishing the accuracy of the methods and understanding the origins of the discrepancies between theory and experiments; the agreement between the calculated and experimental values are very satisfactory. The energies of the crystal levels of the 5f16d(t2g)1 and 5f16d(eg)1 manifolds are predicted to be 31 100–51 000 and 67 300–85 500 cm−1 above the ground state, respectively. The lowest electric dipole allowed zero-phonon absorption from the 5f2 ground state, 1 A1g→1 T1u, is calculated to be at 32 500 cm−1, whereas the highest electric dipole allowed zero-phonon emission from the first 5f16d(t2g)1 excited state, which is found to be 1 Eu→1 T1g, is calculated to be at 30 200 cm−1; this means that both of them should be observable before the sharp cutoff of the Cs2ZrCl6 host with a large gap of 2300 cm−1 between the zero-phonon absorption and emission lines. The combination of experimental spectroscopic data on Cs2ZrCl6:U4+, Cs2ZrCl6:UO22+, and Cs2UO2Cl4, with the calculated energy levels of the Cs2ZrCl6:U4+ 5f16d(t2g)1 manifold allows to discuss new possible mechanisms which could explain the observed green to blue upconversion emission of Cs2ZrCl6:U4+ crystals contaminated with UO22+. Altogether, the results in this paper demonstrate the potentiality of the wave function based methods of solid-state quantum chemistry for complementing experimental techniques in the study of actinide systems like U4+-doped Cs2ZrCl6 where hundreds of excited states are involved and their electronic structure is determined by strong spin–orbit and electron correlation interactions.
Generation–recombination noise in gallium nitride-based quantum well structures
Authors: Duran Rolando S. , Larkins Grover L. , Van Vliet Carolyne M. , Morkoç Hadis
Published: April 2003

Electronic noise has been investigated in AlxGa1−xN/GaN modulation-doped field-effect transistors of submicron dimensions, grown by molecular beam epitaxy techniques. Some 20 devices were grown on a sapphire substrate. Conduction takes place in the quasi-two-dimensional (2D) layer of the junction (xy plane) which is perpendicular to the triangular quantum well (z direction). A nondoped intrinsic buffer layer separates the Si-doped donors in the AlxGa1−xN layer from the 2D transistor plane. Since all contacts must reach through the AlxGa1−xN layer to connect internally to the 2D plane, parallel conduction through this layer is a feature of all modulation-doped devices. The excess noise has been analyzed as a sum of Lorentzian spectra and 1/fα noise. The Lorentzian noise is ascribed to trapping of the carriers in the AlxGa1−xN layer. The trap depths have been obtained from Arrhenius plots of log(τT 2) versus 1000/T. Comparison with previous noise results for GaAs devices shows that: (a) many more trapping levels are present in these nitride-based devices and (b) the traps are deeper (farther below the conduction band) than for GaAs, as expected for higher band-gap materials. Furthermore, the magnitude of the noise is strongly dependent on the level of depletion of the AlxGa1−xN donor layer. We also note that the trap-measured energies are in good agreement with the energies obtained by deep level transient spectroscopy.
Low-temperature behavior of capture rate constants for inverse power potentials
Authors: Dashevskaya E. I. , Maergoiz A. I. , Troe J. , Litvin I. , Nikitin E. E.
Published: April 2003

The energy dependence of the capture cross section and the temperature dependence of the capture rate constants for inverse power attractive potentials V∝−R−n is considered in the regime where the quantum character of the relative motion of colliding partners is important. For practically interesting cases n=4 and n=6, a simple formula for the cross section is suggested which interpolates between the classical and the quantum Bethe limits. We have shown that the classical approximation for the capture cross section performs well far below the simple estimations of the onset the quantum regime. This seemingly “classical” feature of the cross section and the rate constant is due to the large quantum effects of the waves in transmission through and reflection above the centrifugal potential barriers.
Identification of oxygen sites at the V2O5(010) surface by core-level electron spectroscopy: Ab initio cluster studies
Authors: Kolczewski C. , Hermann K.
Published: April 2003

Vanadium oxide contains differently coordinated oxygen sites which can participate in catalytic oxidation reactions of industrial relevance. For a full understanding of corresponding reaction steps an estimate of the relative importance of these oxygen sites for a given reaction at the surface is required. This may be possible using electron spectroscopy together with theoretical methods. We have performed density functional theory cluster calculations to describe the electronic structure at the V2O5(010) surface which possesses singly, doubly, and triply coordinated oxygen sites, O(1–3). For these sites we have evaluated O 1s core level excitation spectra using the transition state method. The analysis of the spectra based on atom projected densities-of-states of the unoccupied orbitals shows that all spectral features are determined by local V–O bonding. The spectra for different oxygen coordination differ enough to allow discrimination between the oxygen sites. In contrast, differences in the calculated O 1s core ionization potentials depend much less on coordination. A comparison of the theoretical O 1s core level excitation spectra with experimental NEXAFS and ELNES spectra yields rather good agreement and assists the interpretation of the latter. Further, the theoretical IP data are consistent with experimental XPS spectra.
Computing accurate forces in quantum Monte Carlo using Pulay’s corrections and energy minimization
Authors: Casalegno Mosé , Mella Massimo , Rappe Andrew M.
Published: April 2003

In order to overcome the difficulty of optimizing molecular geometry using quantum Monte Carlo methods, we introduce various approximations to the exact force expectation value. We follow Pulay’s suggestion [Mol. Phys. 17, 153 (1969)] to correct the Hellmann–Feynman estimator by introducing the contributions due to the changes in the wave function with respect to the nuclear positions. When used in conjunction with energy-optimized explicitly correlated trial wave functions for H2 and LiH, these approximations appear to yield accurate forces using both the variational and diffusion Monte Carlo methods. Also, the accuracy of the second-order estimate of the Hellmann–Feynman force estimator was investigated employing our energy-optimized trial wave functions, and an erratic behavior was uncovered for some of the studied bond lengths. The additional computational cost required to compute the corrections to the Hellmann–Feynman estimator was found to be only a small fraction of the cost for a simple mean energy calculation. The same approach could be exploited also in computing the derivative of other energy-dependent quantum-mechanical observables.
Role of achiral interactions on discrimination in racemates
Authors: Paci I. , Dunford J. , Cann N. M.
Published: April 2003

This article explores the competing effects of chiral and achiral interactions on discrimination in racemic fluids. For any racemate, the like–like (LL) and like–unlike (LU) interaction potentials can be divided into achiral (identical) and chiral (distinct) components. Clearly, if achiral interactions are dominant, then little discrimination is expected in the racemate. However, achiral interactions have the potential to increase discrimination by enhancing the probability of close contact, where the chiral component of the potential is largest. Intermolecular structure in a series of racemates is obtained from the molecule-based hypernetted-chain theory. This theory has previously been applied to hard chiral molecules [I. Paci and N. M. Cann, J. Chem. Phys. 115, 8489 (2001)]. In order to satisfactorily capture the molecular complexity of the enantiomers considered here, a modified closure relation has been derived and implemented. This modification incorporates the exact interaction potential, rather than an expansion, and will lead to a more accurate description of the intermolecular structure in any fluid. Intermolecular structure in a few racemates has also been examined with molecular dynamics simulations. We have found that elongated chiral molecules discriminate most readily with differences of up to 30% between the LL and LU distributions. We also find that a systematic increase in the achiral interactions is usually, but not always, accompanied by a corresponding systematic reduction in discrimination.
Dynamical critical exponents of a two-reaction model between monomers
Authors: da Costa E. C. , Figueiredo W.
Published: April 2003

We studied the dynamical critical behavior of a recently proposed competitive reaction model between monomers on a catalytic surface [E. C. da Costa and W. Figueiredo, J. Chem. Phys. 117, 331 (2002)]. The surface is represented by a square lattice and we consider the following reactions: A+A(B)→A2(AB) where A and B are two monomers that arrive at surface with probabilities yA and yB=1−yA, respectively. The model is studied in the adsorption controlled limit by an epidemic analysis, where the initial condition is close to the absorbing state. We have determined the dynamic critical exponents of the model, which are related to the asymptotic behavior of the survival probability, number of empty sites (the order parameter) and mean square displacement from origin. These exponents agree with that of the directed percolation.
Spectroscopic observation of the preferentially stabilized, linear He⋯ICl(X 1Σ+) complex
Authors: Bradke Matthew D. , Loomis Richard A.
Published: April 2003

Spectroscopic features attributed to rovibronic transitions from both the T-shaped and linear He⋯I35Cl(X) and He⋯I37Cl(X) ground-state complexes have been recorded in the ICl B 3Π0+–X 1Σ+, 2–0 and 3–0 spectral regions using laser-induced fluorescence spectroscopy. Experiments performed using varying expansion conditions indicate that the He⋯I35,37Cl(X) complex with a linear equilibrium orientation lies lower in energy than the separately localized T-shaped isomer even though the transition energies of the T-shaped and linear complexes are shifted by ∼3.5 and ∼14 cm−1 to higher energy than the I35,37Cl B–X band origins, respectively. Based on comparison with the excited state theoretical predictions of Waterland et al. [J. Chem. Phys. 92, 4261 (1990)], estimates of the binding energies for the ground state T-shaped and linear He⋯I35Cl(X) complexes are 17 and 21 cm−1, respectively, in qualitative agreement with the recently published predictions of 15.2 and 18.3 cm−1 obtained using high level ab initio theory for the ground state potential energy surface [J. Chem. Phys. 117, 7017 (2002)].
Probing highly excited vibrational eigenfunctions using a modified single Lanczos propagation method: Application to acetylene (HCCH)
Authors: Xu Dingguo , Chen Rongqing , Guo Hua
Published: April 2003

A modified version of the single Lanczos propagation method is proposed, which allows both energies and overlaps between multiple target functions and all eigenfunctions to be computed from a single Lanczos recursion with no explicit construction of the eigenfunctions. This method is employed to help assigning some highly excited bending levels of acetylene (HCCH) using a six-dimensional exact quantum Hamiltonian and target functions designed to extract information about the shape of the eigenfunctions. In the special case of the Ã-state vibrational eigenfunctions being the target functions, the Ã→X̃ resonance emission spectra are obtained. The assignments on the Bramley et al. [J. Mol. Spectrosc. 157, 301 (1993)] potential energy surface show a strong resemblance to the experimentally observed normal-to-local mode transition in the bending overtones, while that of Halonen et al. [Mol. Phys. 47, 1097 (1982)] supports no such transition in the same energy range.
Rashba spin-orbit effect on traversal time in ferromagnetic/semiconductor/ferromagnetic heterojunction
Authors: Wu Han-Chun , Guo Yong , Chen Xin-Yi , Gu Bing-Lin
Published: April 2003

Based on the group velocity concept, we investigated the traversal time of a quasi-one-dimensional waveguide that contains the ferromagnetic/semiconductor/ferromagnetic heterojunction in the presence of the Rashba spin-orbit interaction. The significant quantum size, quantum coherence, and Rashba spin-orbit interaction are considered simultaneously. The results indicate that as the strength of the spin-orbit coupling increases, the traversal time considerably decreases. The results also indicate that the traversal time is not prolonged linearly as the length of the semiconductor increases but shows step-like behavior.