bluuebunny/crossref_metadata_2025 huggingface dataset:
Why Fiction May be Twice as True as Fact: Fiction as Cognitive and Emotional Simulation
Authors: Oatley Keith
Published: September 2005

Although fiction treats themes of psychological importance, it has been excluded from psychology because it is seen as involving flawed empirical method. But fiction is not empirical truth. It is simulation that runs on minds of readers just as computer simulations run on computers. In any simulation, coherence truths have priority over correspondences. Moreover, in the simulations of fiction, personal truths can be explored that allow readers to experience emotions—their own emotions—and understand aspects of them that are obscure, in relation to contexts in which the emotions arise.
Can Prenatal Caffeine Exposure Affect Behavioral Inhibition?
Authors: Reznick J. Steven
Published: September 2005

Given the widespread use of caffeine and its potential nonoptimal effects during pregnancy, it is remarkable and distressing that almost nothing is known about the long-term effects of prenatal caffeine exposure in humans. Research on nonhumans reveals that prenatal caffeine exposure is associated with an enduring tendency toward a profile of fearfulness, hypoactivity, and exaggerated stress in uncertain situations. A similar pattern of behavioral inhibition has been observed in humans and has been attributed to various causes such as inborn temperament or environmental influences. The author's conjecture is that prenatal caffeine exposure could be an additional factor contributing to the tendency toward behavioral inhibition. One mechanism for this effect is that caffeine causes an upregulation of adenosine receptors, thus creating a vulnerability to adenosine-induced inhibition of neuronal firing and neurotransmitter release.
A Propulsion Model of Types of Creative Contributions
Authors: Sternberg Robert J.
Published: September 2005

This article proposes a propulsion model characterizing 7 different types of creative contributions in any domain. Four of these types of creativity accept current paradigms of work; 3 of the types reject these current paradigms. The basic notion is that creative contributions differ not only in the amounts of creativity they display but also in the types of creativity they display. The article discusses (a) creative contributions and why there is a need for a taxonomy of them, (b) some existing models of creative contributions, (c) a propulsion model for understanding creative contributions and 7 types of contributions that follow from the propulsion model, (d) why such a model can be useful in evaluating creative work, and (e) some phenomena that have been observed in the field of creativity and how they can be explained in terms of the model.
Generalization and Transfer: An Interrelation of Paradigms and a Taxonomy of Knowledge Extension Processes
Authors: Howard Robert W.
Published: September 2005

This article integrates work on generalization and transfer into a coherent framework. It analyzes the evolutionary problem with which generalization deals and then outlines a model of responses to a situation requiring generalization and a taxonomy of generalization and transfer processes. Key tenets are that many different generalization processes exist, that there are wide individual differences in which processes may occur, and that generalization of declarative knowledge usually involves concepts. Three experiments tested 2 tenets. One experiment suggested that generalization gradients found in the specialized paradigm used to study human stimulus generalization simply represent failure to perceptually discriminate between stimuli. The other experiments, involving a different paradigm, found step functions along dimensions instead of decremental gradients. They show that the traditional stimulus generalization paradigm is a type of concept learning paradigm. Participants generalize along a continuum by placing stimuli into categories. The experiments also show many different responses to a situation requiring generalization.
Nature and Mechanisms of Loss of Motivation
Authors: Miceli Maria , Castelfranchi Cristiano
Published: September 2005

Loss of motivation refers either to the weakening of a motive q or to the loss of energy and persistence with which some subordinate goal p is planned for and pursued in view of q. Although interrelated, such aspects can be kept distinct, and the present work focuses on the loss of strength of the subordinate goal. An analysis is provided of such mental attitudes as subjective frustration, negative expectation, disappointment, and discouragement so as to clarify their respective roles in favoring loss of motivation. The necessary cognitive conditions for the occurrence of loss of motivation are singled out; namely, goal p should be an intention, and a disappointment should occur in regard to the instrumental relationship between p and q, p‘s attainability, or p‘s convenience. Both advantages and limits of the model are discussed.
The Slave of the Passions: Experiencing Problems and Selecting Solutions
Authors: Overskeid Geir
Published: September 2005

This article argues that problem solving is motivated by feelings. The proposition is made that a person will experience a problem and engage in problem solving only if the person is in a state that feels aversive or if a mentally represented state becomes a goal by eliciting feelings more pleasurable than those that currently dominate. When people solve problems, the criteria they use in evaluating alternative solutions cannot in themselves motivate the choosing of an alternative. On evaluation, each alternative elicits a feeling that can be placed somewhere on a hedonic continuum. Whether rational or irrational, and even if the problem solver regards another alternative as correct, the alternative that produces the best feeling will always be selected as the solution to the problem.
Gestalt Perspectives on Cognitive Science and on Experimental Psychology
Authors: Sharps Matthew J. , Wertheimer Michael
Published: September 2005

At the 1st author's request, the 2nd author was interviewed on Gestalt psychology's origins and utility for modern experimental psychology. Wertheimer's connections with Gestalt psychologists Max Wertheimer and Wolfgang Köhler and his study of Gestalt problems and methods, give him a special perspective on these issues. Several points for modern psychology emerge from the Gestalt perspective. Phenomena should be studied within their full context; there is a need to acknowledge the domain specificity of principles in experimental psychology; it is wise to study phenomena that either exist in the real world or have close real-world analogues; psychology must recognize interchanges between organisms and surroundings as determinants of behavior; and a data-driven perspective must complement, and sometimes replace, theory-driven searches for broadly applicable, nondomain-specific principles.
Experimental Validity: Brunswik, Campbell, Cronbach, and Enduring Issues
Authors: Albright Linda , Malloy Thomas E.
Published: September 2005

Donald Campbell and Lee Cronbach had a long history of mutual respect for and fundamental disagreement with each other's ideas about experimental validity. Issues that Campbell labeled as external validity, Cronbach labeled internal validity. Issues that Campbell labeled internal validity, Cronbach suggested are trivial. Nevertheless, these methodological pioneers share much common ground, in part because of their alliance with Egon Brunswik. As science moved from a deterministic to a probabilistic paradigm, all 3 endeavored to protect behavioral science from validity-threatening practices that could result from naive use of the Fisherian approach to scientific investigation. This review shows that issues concerning the prioritization of types of validity still need to be resolved and that most social scientists do not understand internal validity. Several empirical practices for enhancing validity are suggested.
Adult Crying: A Model and Review of the Literature
Authors: Vingerhoets Ad J. J. M. , Cornelius Randolph R. , Van Heck Guus L. , Becht Marleen C.
Published: September 2005

Crying is one of the most powerfully compelling forms of human emotional expression, and yet, until recently, crying has received little attention from behavioral scientists. In this article, a model of adult crying is presented that describes the situations and emotions that elicit crying and characterizes the possible moderating effects of environmental, personal, and cultural factors on crying. Empirical data relevant to the model are summarized, and areas in need of further investigation are identified. In addition, the question of whether and how crying may affect mood and health is considered. It is concluded that the literature is full of ungrounded speculation and that research until now has been rather unsystematic and not sufficiently theory driven. Recently available data, however, pave the way for formulating a more comprehensive theoretical framework for generating testable hypotheses about crying.
Requirement of the MEK5–ERK5 pathway for neural differentiation in Xenopus embryonic development
Authors: Nishimoto Satoko , Kusakabe Morioh , Nishida Eisuke
Published: September 2005

Although previous studies have identified several key transcription factors in the generation process of the vertebrate nervous system, the intracellular signalling pathways that function in this process have remained unclear. Here we identify the evolutionarily conserved mitogen‐activated protein kinase kinase 5 (MEK5)–extracellular signal‐regulated kinase 5 (ERK5) pathway as an essential regulator in neural differentiation. Knockdown of Xenopus ERK5 or Xenopus MEK5 with antisense morpholino oligonucleotides results in the reduced head structure and inhibition of neural differentiation. Moreover, forced activation of the MEK5–ERK5 module on its own induces neural differentiation. In addition, we show that the MEK5–ERK5 pathway is necessary for the neuralizing activity of SoxD, a regulator of neural differentiation, and is sufficient for the expression of Xngnr1, a proneural gene. These results show that the MEK5–ERK5 pathway has an essential role in the regulation of neural differentiation downstream of SoxD and upstream of Xngnr1.
Depletion of licensing inhibitor geminin causes centrosome overduplication and mitotic defects
Authors: Tachibana Kiku‐e K , Gonzalez Michael A , Guarguaglini Giulia , Nigg Erich A , Laskey Ronald A
Published: September 2005

Metazoans limit origin firing to once per cell cycle by oscillations in cyclin‐dependent kinases and the replication licensing inhibitor geminin. Geminin inhibits pre‐replication complex assembly by preventing Cdt1 from recruiting the minichromosome maintenance proteins to chromatin. Geminin depletion results in genomic over‐replication in Drosophila and human cell lines. Here, we show that loss of geminin affects other cell cycle‐dependent events in addition to DNA replication. Geminin inactivation causes centrosome overduplication without passage through mitosis in human normal and cancer cells. Centrosomes are microtubule‐organizing centres that are duplicated during S phase and have an important role in the fidelity of chromosome transmission by nucleating the mitotic spindle. Consistent with this, geminin‐depleted cells show multiple mitotic defects, including multipolar spindles, when driven into mitosis by checkpoint abrogation. These results show that the consequences of geminin loss exceed its immediate role in DNA replication and extend to promoting chromosome mis‐segregation in mitosis.
Effective interactions in the colloidal suspensions from hypernetted-chain theory
Authors: Léger Daniel , Levesque Dominique
Published: September 2005

The hypernetted-chain (HNC) Ornstein-Zernike integral equations are used to determine the properties of simple models of colloidal solutions where the colloids and ions are immersed in a solvent considered as a dielectric continuum and have a size ratio equal to 80 and a charge ratio varying between 1 and 4000. At an infinite dilution of colloids, the effective interactions between colloids and ions are determined for ionic concentrations ranging from 0.001to0.1mol∕l and compared to those derived from the Poisson-Boltzmann theory. At finite concentrations, we discuss on the basis of the HNC results the possibility of an unambiguous definition of the effective interactions between the colloidal molecules.
Density-functional theory-based chemical reactivity indices in the Hartree-Fock method. I. Unrestricted Hartree-Fock method for a noninteger number of electrons
Authors: Balawender Robert , Geerlings Paul
Published: September 2005

Correct evaluation of the reactivity indices, such as chemical potential, hardness, and Fukui function demands for the extension of the formalism beyond the integer particle picture. An ensemble approach is used as an extension of the unrestricted Hartree-Fock (UHF) method for noninteger electron number systems. A prescription is given for the construction of an ensemble Fock operator for a system with partially filled spin-orbitals. The comparison between the ensemble HF method and the hyper-HF method in terms of density matrices and spin-orbitals is presented. The equivalence of the equiensemble case and the ensemble UHF case with unequal weight factors is shown.
Spectroscopic effects of first-order relativistic vibronic coupling in linear triatomic molecules
Authors: Mishra Sabyashachi , Vallet Valerie , Poluyanov Leonid V. , Domcke Wolfgang
Published: September 2005

It has recently been shown that there exists, in addition to the well-known nonrelativistic Renner-Teller coupling, a linear (that is, of the first order in the bending distortion) vibronic-coupling mechanism of relativistic (that is, spin-orbit) origin in Π2 electronic states of linear molecules [L. V. Poluyanov and W. Domcke, Chem. Phys. 301, 111 (2004)]. The generic aspects of the relativistic linear vibronic-coupling mechanism have been analyzed in the present work by numerical calculations of the vibronic spectrum for appropriate models. The vibronic and spin-orbit parameters have been determined by accurate ab initio electronic-structure calculations for the X̃Π2 states of a series of triatomic radicals and radical cations. It is shown for the example of GeCH that the relativistic linear vibronic-coupling mechanism provides a quantitative explanation of the pronounced perturbations in the vibronic spectrum of the X̃Π2 state of GeCH, which previously have been termed “Sears resonances” [S.-G. He, H. Li, T. C. Smith, D. J. Clouthier, and A. J. Merer, J. Chem. Phys. 119, 10115 (2003)]. The X̃Π2 vibronic spectra of the series BS2, CS2+, OCS+, and OBS illustrate the interplay of nonrelativistic and relativistic vibronic-coupling mechanisms in Renner-Teller systems.
A sequential Monte Carlo quantum mechanics study of the hydrogen-bond interaction and the solvatochromic shift of the n–π* transition of acrolein in water
Authors: Georg Herbert C. , Coutinho Kaline , Canuto Sylvio
Published: September 2005

The sequential Monte Carlo (MC) quantum mechanics (QM) methodology, using time-dependent density-functional theory (TD-DFT), is used to study the solvatochromic shift of the n–π* transition of trans-acrolein in water. Using structures obtained from the isothermal-isobaric Metropolis MC simulation TD-DFT calculations, within the B3LYP functional, are performed for the absorption spectrum of acrolein in water. In the average acrolein makes one hydrogen bond with water and the hydrogen-bond shell is responsible for 30% of the total solvatochromic shift, considerably less than the shift obtained for the minimum-energy configurations. MC configurations are sampled after analysis of the statistical correlation and 100 configurations are extracted for subsequent QM calculations. All-electron TD-DFT B3LYP calculations of the absorption transition including acrolein and all explicit solvent molecules within the first hydration shell, 26 water molecules, give a solvatochromic shift of 0.18±0.11eV. Using simple point charges to represent the solvent the shifts are calculated for the first, second, and third solvation shells. The results converge for the calculated shift of 0.20±0.10eV in very good agreement with the experimentally inferred result of 0.20±0.05eV. All average results presented are statistically converged.
Elastic, quasielastic, and inelastic neutron-scattering studies on the charge-transfer hexamethylbenzene-tetracyanoquinodimethane complex
Authors: Sawka-Dobrowolska Wanda , Bator Grażyna , Sobczyk Lucjan , Pawlukojć Andrzej , Ptasiewicz-Bak Halina , Rundlöf Håkan , Krawczyk Jan , Nowina-Konopka Małgorzata , Jagielski Piotr , Janik Jerzy A. , Prager Michael , Steinsvoll Olav , Grech Eugeniusz , Nowicka-Scheibe Joanna
Published: September 2005

The 1:1 hexamethylbenzene (HMB)-tetracyanoquinodimethane (TCNQ) complex shows a first-order phase transition at 230∕218K (heating/cooling) with no change of the space group. The neutron-diffraction studies reveal that this transition is related to a freezing of the rotation of methyl groups. The results for 100K enabled precise determination of configuration of HMB⋅TCNQ complexes. The planes of HMB and TCNQ molecules from small angle (6°) so that the dicyanomethylene group approaches the HMB molecule to a distance of 3.34Å. The conformation of methyl groups was exactly determined. The quasielastic neutron-scattering spectra can be interpreted in terms of 120° jumps with different activation barrier in low- and high-temperature phases, equal to 3.7 and 1.8kJ∕mol, respectively. These values are lower than that for neat HMB (6kJ∕mol). The conclusion can be drawn that the methyl groups can reorient more freely in the complex. This conclusion is in agreement with the results of inelastic neutron-scattering studies of low-frequency modes assigned to torsional vibrations of methyl groups. These frequencies are lower than those for neat HMB. The analyzed increase of frequencies of these modes as compared with free molecules can be interpreted as due to formation of unconventional C–H…Y hydrogen bonds which are more pronounced in crystals of neat HMB than in those of HMB⋅TCNQ. The low-frequency librational modes can be treated as a sensitive measure of unconventional hydrogen bonds formed by the CH3 groups.
Local environment and dynamics of PO4 tetrahedra in Na–Al–PO3 glasses and melts
Authors: Mamedov S. , Stachel D. , Soltwisch M. , Quitmann D.
Published: September 2005

Glasses and melts in the system (NaPO3)(1−x)(Al(PO3)3)x were studied with the aim of obtaining information about the structure on the next larger scale beyond the PO4 group. Magic angle spinning NMR was applied to the pure NaPO3 glass and Raman scattering to systems with x=0.00, 0.03, 0.06, 0.15, and 0.60 in the temperature range T=300–1100K. Comparison of the P31 chemical shift between glass and crystalline forms revealed that polymerization of the metaphosphate into tricyclophosphatelike (PO3)33− rings is the dominant structure, ca. 80%, formed by the twofold vertex-joined PO4 groups in the glass. In the Raman study we focused on the prominent polarized band at ca. 1170cm−1 which is due to the symmetric breathing mode of the tetrahedral PO4 group. This band was decomposed into a few Gaussian lines. These component lines could be identified using the NMR results: two narrow components are due to PO4 groups in the tricyclophosphatelike rings, which have either a Na or an Al counterion and a third broad component is due to chain-polymerized (PO3−)n. The variations of the component lines (peak positions, widths, and intensities) with respect to x and T are presented. We derive the shifts of the symmetric breathing mode frequency which are caused by Na or Al counterions, by ring closure, by x>0, etc. The relative intensities of the narrow and broad components in the 1170-cm−1 band of the Raman spectra are discussed. The amount of ring-to-chain transformation on addition of Al3+, and as functions of T and x, is derived. Indications for ordering on a next larger scale, derivable from Raman, NMR, and thermodynamics, are compared.
Integral equation theory for hard spheres confined on a cylindrical surface: Anisotropic packing entropically driven
Authors: Iwaki Takafumi , Shew Chwen-Yang , Gumbs Godfrey
Published: September 2005

The structure of two-dimensional (2D) hard-sphere fluids on a cylindrical surface is investigated by means of the Ornstein-Zernike integral equation with the Percus-Yevick and the hypernetted-chain approximation. The 2D cylindrical coordinate breaks the spherical symmetry. Hence, the pair-correlation function is reformulated as a two-variable function to account for the packing along and around the cylinder. Detailed pair-correlation function calculations based on the two integral equation theories are compared with Monte Carlo simulations. In general, the Percus-Yevick theory is more accurate than the hypernetted-chain theory, but exceptions are observed for smaller cylinders. Moreover, analysis of the angular-dependent contact values shows that particles are preferentially packed anisotropically. The origin of such an anisotropic packing is driven by the entropic effect because the energy of all the possible system configurations of a dense hard-sphere fluid is the same. In addition, the anisotropic packing observed in our model studies serves as a basis for linking the close packing with the morphology of an ordered structure for particles adsorbed onto a cylindrical nanotube.
Characteristics of the plasma impedance probe with constant bias
Authors: Blackwell David D. , Walker David N. , Messer Sarah J. , Amatucci William E.
Published: September 2005

The impedance of a small spherical probe immersed in a uniform plasma is measured by recording the reflection coefficient of an applied signal using a network analyzer. This impedance has a resonance at the plasma frequency where the imaginary part goes to zero, a feature that has made this measurement a good way of determining electron density. When the plasma potential is positive with respect to the sphere—for example, if the sphere is electrically floating or grounded, a second resonance occurs at ω<ωpe due to the capacitance created by the depleted electron density in the sheath. A greatly increased power deposition occurs at this lower resonance, whose frequency can be controlled by applying a dc bias which changes the sheath width. As the bias is increased the value of this frequency becomes smaller until the resonance disappears completely at Vprobe=Vplasma. As the bias is further increased past the plasma potential, an electron sheath forms with its own resonance, which is at a lower frequency than the resonance associated with the ion sheath. The impedance of the electron sheath can be approximated using sheath transit time perturbation theory for a space charge limited diode. As with the ion sheath resonance, the largest energy deposition occurs at the lower of the two resonant frequencies.
Effects of nonlinear left-hand circularly polarized waves supported by a proton beam on linear beam-plasma instabilities
Authors: Gomberoff L. , Hoyos J.
Published: September 2005

This paper studies the effect of nonlinear left-hand polarized waves supported by a proton beam on the linear circularly polarized instabilities driven by the same beam. It shows that the nonlinear wave can either stabilize or destabilize the linear instabilities. The effects depend on the amplitude of the nonlinear wave and on the temperature of the system. It also shows that purely electrostatic ion-acoustic-like waves, can be destabilized by the large amplitude wave. The latter instabilities do not occur in the absence of the nonlinear waves.
Evidence of PVT anomaly boundaries of water at high pressure from compression and NaCl∙2H2O dehydration experiments
Authors: Mirwald P. W.
Published: September 2005

Isothermal compression experiments on water have been performed between 0 to 80 °C and up to 1.3 GPa pressure. The compressibilities derived from the water compression experiments reveal a nonsmooth PVT behavior forming two anomaly boundaries. These boundaries originate at the melting line of ice III at about 0.25GPa∕−20°C, and of ice VI at about 0.8GPa∕13°C. Both boundaries have a positive sloped course separating three areas of different PVT properties of water. However, this P-T topology is obscured by an unresolved complication in the temperature range of 40–60 °C, which allows different topological interpretations of the data. As a cross-check for the compression experiment the dehydration boundary of sodium chloride-dihydrate (NaCl∙2H2O) has been determined up to 1.5 GPa. The dehydration curve of NaCl∙2H2O which traverses the two anomaly boundaries shows two inflections at the intersection, at 0.27GPa∕12°C and at 0.77GPa∕22°C, respectively. While the isothermal compressibility curves as well as the dP∕dT course of the two anomaly boundaries give evidence of two densifications of water, the slope analysis of the inflections of the NaCl∙2H2O dehydration curve suggests that the entropy change plays an important role. A recent model of water at high pressure conditions proposes a gradual structural transition from a low density water (LDW) at low pressures to a high density water (HDW) at high pressures. The compression data as well as the inflections of the dehydration boundary indicate, however, two discrete structural changes of water. Data comparison with that model suggests that the anomaly boundary at lower pressure corresponds to a volume fraction [VHDW∕(VLDW+VHDW)] of 0.8, while the upper one approaches a volume fraction of 1.
Scission-induced bounds on maximum polymer drag reduction in turbulent flow
Authors: Vanapalli Siva A. , Islam Mohammad T. , Solomon Michael J.
Published: September 2005

We report the direct quantification of molar mass degradation in the drag-reducing polymers polyethylene oxide (PEO) and polyacrylamide (PAM) in turbulent pipe flows with an upstream tapered contraction. We find that entrance effects associated with the upstream contraction dominate the polymer degradation. Quantifying degradation according to the scaling relationship γ̇w∝Mws−n, the exponent n is determined to be −2.20±0.21 and −2.73±0.18 for PEO and PAM, respectively. Here Mws is the steady-state (or limiting) weight-average scission molar mass. A methodology is devised to circumvent polymer degradation due to the upstream contraction and thereby conduct degradation experiments in which only the turbulent flow in the pipe is responsible for chain scission. In this case, the scission-scaling relationship for PEO is γ̇w∝Mw−3.20±0.28. Here Mw is the degraded weight-average molar mass after one pass through the 1.63-m length of pipe. Based on these scaling relationships we obtain a new upper limit for polymer drag reduction that is determined by chain scission rather than the maximum drag reduction asymptote.
The driven cavity flow over the whole range of the Knudsen number
Authors: Naris Stergios , Valougeorgis Dimitris
Published: September 2005

The flow of a rarefied gas in a rectangular enclosure due to the motion of the upper wall is solved over the whole range of the Knudsen number. The formulation is based on the two–dimensional linearized Bhatnagar-Gross-Krook (BGK) kinetic equation with Maxwell diffuse-specular boundary conditions. The integro-differential equations are solved numerically implementing the discrete velocity method. The discontinuity at the boundaries between stationary and moving walls is treated accordingly. A detailed investigation of the rarefaction effects on the flow pattern and quantities is presented over the whole range of the Knudsen number and various aspect (height/width) ratios. Numerical results of flow characteristics, including the streamlines, the velocity profiles, the pressure and temperature contours, and the drag force of the moving wall, are presented for different aspect ratios and various degrees of gas rarefaction from the free molecular through the transition up to the continuum limit. On several occasions, depending upon the flow parameters, in addition to the main vortex, corner eddies are created. As the depth of the cavity is increased, these eddies grow and merge into additional vortices under the top one. The mesoscale kinetic-type approach proves to be efficient and suitable for problems that incorporate multiscale physics, such as the present nonequilibrium flow.
Comparison of backwards and forwards relative dispersion in turbulence
Authors: Sawford Brian L. , Yeung P. K. , Borgas Michael S.
Published: September 2005

We use Lagrangian stochastic models and direct numerical simulation for stationary isotropic turbulence to calculate backwards relative dispersion statistics, that is, the statistics of the earlier locations of particle pairs that at a later time are located at prescribed locations. We find that, in general, backwards relative dispersion proceeds at a much faster rate than relative dispersion forwards in time, and the difference between the two is sensitive to the nature of the flow field. The difference vanishes for Gaussian flows and for white-noise (in time) flows (for which relative dispersion can be described by a diffusion equation), suggesting that theories such as two-point closure and kinematic simulation do not differentiate between backwards and forwards dispersion. Backwards relative dispersion is very sensitive to the details of the tails of the probability density function for the Eulerian velocity difference between two points.
Model for two-beam coupling during the formation of holographic gratings with a nematic film-polymer-slice sequence structure
Authors: Caputo Roberto , De Sio Luciano , Veltri Alessandro , Umeton Cesare , Sukhov Andrey V.
Published: September 2005

We present a model accounting for the main features of the wave coupling process that takes place during the UV curing of diffraction gratings made of liquid crystal films separated by slices of polymeric material. The effect depends on the phase shift between the curing interference pattern and the grating being cured. For a unit ratio of the impinging beam intensities, the model confirms the absence of energy transfer, as experimentally observed. When the ratio is not at its unit value, the beam coupling tends to equalize the intensities of the two beams as they propagate inside the sample.
Ultraviolet light-assisted domain inversion in magnesium-doped lithium niobate crystals
Authors: Wengler M. C. , Heinemeyer U. , Soergel E. , Buse K.
Published: September 2005

The influence of ultraviolet (UV) light (wavelengths λ=334 and 305nm) on the ferroelectric domain inversion of lithium niobate crystals doped with different amounts of magnesium ranging from 0to7.5mol% is investigated. Illumination at λ=334nm leads to a coercive field reduction of up to 50%, but only in samples doped with a magnesium concentration above the so-called optical damage threshold. For λ=305nm the effective coercive field is reduced significantly in all samples. Different behavior of the coercive field reduction at both wavelengths indicates the presence of two mechanisms. To explain the effect occurring for 305nm illumination a model is presented in which an UV-induced photoconductivity alters the electric-field distribution through the crystal thickness. Utilizing an UV-interference pattern and a suitable homogeneous external electrical field, periodically poled lithium niobate with a period length of 55μm is produced.
Verification of a model for the piezoelectric d33 coefficient of cellular electret films
Authors: Hillenbrand Joachim , Sessler Gerhard M. , Zhang Xiaoqing
Published: September 2005

An existing model for the piezoelectric thickness coefficient (d33 coefficient) of cellular polymers is tested with experimental data obtained from two differently manufactured cellular polypropylene (PP) materials. The model assumes the cellular film to consist of plane parallel solid and gaseous layers charged at their interfaces. The cellular PP films are expanded by a pressure treatment. Subsequently, due to viscoelastic relaxation, the thickness of the films decreases, thus causing a change of their Young’s modulus Y with time. The values of Y are obtained from interferometric measurements of the resonance frequency of the films. Together with the measured thickness of the solid layers and air layers in the material, the d33 coefficients can be determined from the model. These values are compared with experimental results for d33 also obtained interferometrically by means of the inverse piezoelectric effect. A very good agreement between the measured and calculated d33 coefficients as a function of film thickness is obtained for all investigated films.
Dielectric properties of Ba0.6Sr0.4TiO3∕Mg2SiO4∕MgO composite ceramics
Authors: Chen Ying , Dong Xian-Lin , Liang Rui-Hong , Li Jian-Tong , Wang Yong-Ling
Published: September 2005

The dielectric properties of BSTO∕Mg2SiO4∕MgO composite ceramics have been investigated systematically. The dielectric properties of BSTO composites under a dc bias field can be interpreted by the “soft-mode” theory near the phase transition and Johnson’s phenomenological equation far above the transition temperature. Compared with most of the other BSTO composite ceramics, BSTO∕Mg2SiO4∕MgO not only can be sintered at a lower temperature but also keep a higher dielectric tunability versus a lower dielectric constant. For example, BSTO∕35wt.%Mg2SiO4∕15wt.%MgO has a dielectric tunability ∼13.18% (under 2kV∕mm biasing) versus a dielectric constant εr(0)∼118.40 at 25°C. It suggests that the dielectric properties are influenced to a great extent by the microstructure, and the dielectric tunability is enhanced when more continuous BSTO phase is obtained.
High-power SiO2∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors
Authors: Kordoš P. , Heidelberger G. , Bernát J. , Fox A. , Marso M. , Lüth H.
Published: September 2005

We report on SiO2∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs), which exhibit a 6.7W∕mm power density at 7GHz. Unpassivated and SiO2-passivated heterostructure field-effect transistors (HFETs) were also investigated for comparison. Deposited 12nm thick SiO2 yielded an increase of the sheet carrier density from 7.6×1012to9.2×1012cm−2 and a subsequent increase of the static drain saturation current from 0.75to1.09A∕mm. The small-signal rf characterization of the MOSHFETs showed an extrinsic current gain cutoff frequency fT of 24GHz and a maximum frequency of oscillation fmax of 40GHz. The output power of 6.7W∕mm of the MOSHFETs measured at 7GHz is about two times larger than that of HFETs. The results obtained demonstrate the suitability of GaN-based MOSHFETs for high-power electronics.
Above-room-temperature ferromagnetism in half-metallic Heusler compounds NiCrP, NiCrSe, NiCrTe, and NiVAs: A first-principles study
Authors: Şaşıoğlu E. , Sandratskii L. M. , Bruno P.
Published: September 2005

We study the interatomic exchange interactions and Curie temperatures in half-metallic semi-Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study is performed within the framework of density functional theory. The calculation of exchange parameters is based on the frozen-magnon approach. It is shown that the exchange interactions in NiCrZ vary strongly depending on the Z constituent. The Curie temperature is calculated within mean field and random phase approximations. The difference between two estimated values is related to the properties of the exchange interactions. The predicted Curie temperatures of all four systems are considerably above room temperature. The relation between half-metallicity and the value of the Curie temperature is discussed. The combination of a high spin polarization of charge carriers and a high Curie temperature makes these Heusler alloys interesting candidates for spintronics applications.
Patterning of nanostructured thin films by structured light illumination
Authors: Haro-Poniatowski E. , Fort E. , Lacharme J. P. , Ricolleau C.
Published: September 2005

Light-induced reshaping of silver nanostructured films near the percolation threshold are investigated using a KrF excimer laser emitting at 248 nm. Depending on the laser intensity and the number of pulses, striking effects are observed for which the irregular particles melt and transform into spherical shaped particles. We show that the laser-induced modifications can be spatially designed by irradiating through masks and gratings taking advantage of their respective diffractive properties. This permits an easy and well controlled way to produce a variety of submicron patterning. The induced patterns accurately coincide with the intensity variations of the illumination field.
Large-scale, unidirectional convection during phase separation of a density-matched liquid mixture
Authors: Califano Filomena , Mauri Roberto , Shinnar Reuel
Published: September 2005

Complete phase segregation may occur on a 10cm scale even in the absence of buoyancy due to unidirectional, large-scale rapid bulk flow. Using a hexadecane-acetone nearly density-matched liquid mixture in a 20-cm-long condenser tube with a 1cm diameter, we observed the rapid axial migration of the acetone-rich drops towards the warmer regions of the condenser. Conversely, the hexadecane-rich drops moved in the opposite direction, therefore ruling out thermocapillary effects as a possible explanation of the phenomenon. These flows lead to a complete phase segregation within 10s, with the formation of a single interface perpendicular to the axial direction. Changing the temperature gradient along the tube from 0.25 to 1°C∕cm no change was detected, with typical drop speeds up to 6cm∕s, irrespective of the distance of the drop from the wall, showing that the phenomenon is not due to a flow instability.
Determination of crystallographic polarity of ZnO layers
Authors: Tampo H. , Fons P. , Yamada A. , Kim K.-K. , Shibata H. , Matsubara K. , Niki S. , Yoshikawa H. , Kanie H.
Published: September 2005

The crystallographic polarity of ZnO epilayers was determined by x-ray diffraction (XRD) using anomalous dispersion near the Zn K edge. The method is not destructive and is straightforward to carry out using a typical XRD measurement system. The polarity difference between the Zn (0001) and O (0001¯) surfaces could be easily determined using a {0002} diffraction peak and the Bremstrahlung radiation from a Cu rotating anode source. By using the normalized pre- and post-Zn K-edge diffraction intensity ratios of the (0002) diffraction peak, Zn polar and O polar ZnO layers could always be distinguished but, the absolute value of the ratio was found to change with layer thickness. The absolute value of the ratio with layer thickness was found to have a linear dependence on layer thickness allowing determination of the polarity of (0001) ZnO epilayers with a single x-ray measurement and the known layer thickness in conjunction with standard data. Acid etching results confirmed the veracity of the polarity determination of the XRD measurement. To test the technique, Zn and O polar ZnO layers were grown by radical source molecular beam epitaxy (RS MBE) on MgO buffer layers on c-sapphire substrate and O polar ZnO layers were grown on a-plane substrates and measured using the x-ray technique with excellent agreement.
Microcavity plasma photodetectors: Photosensitivity, dynamic range, and the plasma-semiconductor interface
Authors: Ostrom N. P. , Eden J. G.
Published: September 2005

Detailed measurements of the photosensitivity of Si microcavity plasma photodetectors in the visible and near-infrared (420–1100 nm) are reported for input optical intensities to a 100×100μm2 inverted pyramid device varied over three orders of magnitude (10−5–10−2Wcm−2). By resolving the contribution to the overall device response from the plasma/semiconductor interaction, as opposed to bulk Si photoconductivity, the photosensitivity of the plasma photodetector operating in 500 Torr of Ne was determined to range from (2.2±0.4)A∕W for 2 nW of input power (at λ=780nm) to (1.3±0.2)A∕W at ∼0.65μW. The spectral response profile of the hybrid plasma/semiconductor detector is similar to that of a conventional pn junction photodiode, but is blueshifted by ∼60nm. Also, the peak photosensitivity (3.5A∕W at λ≃900nm) of a Si microplasma device having a 50×50μm2 aperture is approximately twice that for its larger (100×100μm2) counterpart under identical conditions. Analysis of the data suggest that bandbending at the p-Si surface is sufficiently strong for a thin n-type region to form, thereby resembling a metal-oxide-semiconductor capacitor in the inversion mode. Electrons in this thin layer tunnel through the vacuum (Si-plasma) barrier, followed by electron avalanche in the nonequilibrium plasma. These results illustrate the potential for novel optoelectronic devices when interfacing a plasma with a semiconductor and coupling the two media with a strong electric field imposed across the interface.
Atomic structure of epitaxial SrTiO3–GaAs(001) heterojunctions
Authors: Klie R. F. , Zhu Y. , Altman E. I. , Liang Y.
Published: September 2005

We have examined the atomic and electronic structures of epitaxial SrTiO3 thin films on GaAs (001) deposited under different growth conditions in order to understand the interfacial structure-property relationships. High-resolution Z-contrast images show an atomically sharp heterointerface with SrTiO3[110] in perfect registry with GaAs [100] and the interfacial structure remains unchanged if a submonolayer of Ti was deposited prior to the SrTiO3 film growth. X-ray photoelectron spectroscopy shows that the Fermi level was pinned during the initial stage of growth when a submonolayer of Ti was deposited on As-terminated GaAs(001); subsequent SrTiO3 growth alleviated this pinning. These results indicate a self-driven interfacial atomic structure formation, independent of the initial stage of growth.
Surface enhanced infrared absorption by coupling phonon and plasma resonance
Authors: Anderson Mark S.
Published: September 2005

A gold and silicon carbide particle matrix is presented that concentrates light to its surface using a combination of phonon and plasmon resonance mechanisms. The enhanced infrared absorption spectrum of absorbed molecules is used to probe the coupled phonon and plasmon surface resonances. Sensitive molecular detection is achieved by measuring the enhanced infrared absorption or the frequency shift in the surface modes of the coated matrix. This work demonstrates that hybrid polariton resonance structures using metallic and polar dielectric materials are feasible for applications in near-field microscopy, nano-optical devices, and trace chemical sensing.
Influence of edge diffusion on the growth mode on vicinal surfaces
Authors: Ratsch C. , Garcia J. , Caflisch R. E.
Published: September 2005

Growth on vicinal surfaces typically occurs via nucleation and growth of islands or via step flow. In this letter, we present computational results based on an island dynamics model that employs the level-set technique that study the transition between these two competing mechanisms. Our results demonstrate that the rate of diffusion of atoms along step edges is an additional parameter that controls the competition between these mechanisms. We make suggestions about how one might be able to exploit these results experimentally.
Linear magnetic flux amplifier
Authors: Golubović D. S. , Moshchalkov V. V.
Published: September 2005

By measuring the critical current versus the applied magnetic field Ic(Φ) of an Al superconducting loop enclosing a soft Permalloy magnetic dot, we demonstrate that it is feasible to design a linear magnetic flux amplifier for applications in superconducting quantum interference devices. The selected dimensions of a single-domain Permalloy dot provide that the preferential orientation of the magnetization is rotated from the perpendicular direction. By increasing an applied magnetic field, the magnetization of the dot coherently rotates toward the out-of-plane direction, thus providing a flux gain and an enhancement of the sensitivity. As a result of a pronounced shape anisotropy, the flux gain generated by the dot can be tuned by adjusting the dimensions of the dot.
Characterization and reduction of twist in Ge on insulator produced by localized liquid phase epitaxy
Authors: Tweet Douglas J. , Lee Jong Jan , Maa Jer-Shen , Hsu Sheng Teng
Published: September 2005

Conditions for producing high-quality localized Ge-on-insulator film stacks on Si substrates by liquid phase epitaxy are discussed. In particular, we have found that the resulting Ge crystal planes have a tendency to exhibit a twist about the long axis of the crystal. If the wafer is heated much above the Ge melting temperature, this twist can be quite large (∼10°). The twist can be minimized by heating to just above the melting temperature and by using thicker Ge films. In spite of this twist, the Ge regions on top of the insulating Si3N4 are observed to be free of dislocations and stacking faults.
Varistors made of indium tin oxide∕Si multilayers on p-type GaN substrates
Authors: Yang S. Y. , Su P. P. , Chiu Y. C. , Hong Chin-Yih , Yang H. C. , Liu W. H. , Lee B. J.
Published: September 2005

Varistors are important devices in the prevention of electric circuits from electric surges or in the stabilization of the operation current. Instead of the conventional granular type, varistors consisting of conductor/semiconductor multilayers grown on p-type semiconductor substrates are developed. In this work, the conductor used is indium tin oxide (ITO), the semiconductor is Si and the substrate is of p-type GaN. It was found that symmetric and nonlinear current-voltage curves are available by cascading two (ITO∕Si)N∕p-GaN films with a bridging Ag film. Furthermore, the current-voltage characteristics can be manipulated by depositing various periods of ITO∕Si multilayers on the p-type GaN substrates. The details of the design principle and the characterizations of the cascading (ITO∕Si)N∕p-GaN thin-film varistors are also discussed.
Photoluminescence characteristics of coupled CdSe∕ZnS quantum dots on self-assembled silica nanospheres
Authors: Kang K. S. , Ju H. L. , Han W. H. , Lee J. H. , Choi J. G. , Boo D. W.
Published: September 2005

The photoluminescence (PL) characteristics of the self-assembled silica nanospheres containing coupled CdSe∕ZnS core-shell quantum dots (QDs) on the surface of the sphere were studied. The degree of QD-coupling and the distribution of the coupled QDs were controlled by generating spatially separated QD-binding sites on the surface of the spheres and varying the QD concentration during the attachment process. When the sizes of QD spots on the surface probed by atomic force microscopy gradually increased, the band gap energy shifted to lower energy via strong Förster energy transfer between nearby QDs, and when UV-exposure time increased, the band gap energy shifted to slightly higher energy, accompanied by a large enhancement in the emission intensity. Moreover, the Bragg diffraction of the self-assembled crystal structure of the spheres affected the PL characteristics of QDs by shifting the entire emission spectra toward longer wavelength as the incident angles were increased.
In situ transmission electron microscope observations of electromigration in copper lines at room temperature
Authors: Liao C. N. , Chen K. C. , Wu W. W. , Chen L. J.
Published: September 2005

Atomic-scale electromigration (EM) in unpassivated copper metal lines was directly observed in ultrahigh vacuum at room temperature by transmission electron microscopy. It was found that copper atoms on a (211) crystal plane vanished directionally within half an hour when applying an electric current with a density of 2×106A∕cm2 through the tested Cu line. The EM-induced atomic migration appeared to be anisotropic, and the combination of {111} planes and ⟨110⟩ directions was suggested to be the easiest electromigration system for crystalline copper. EM-induced mass transport was also found to be responsible for the weakening (111) texture of the Cu lines after electric current stressing.