bluuebunny/crossref_metadata_2025 huggingface dataset:
Seven Steps Toward Freedom and Two Ways to Lose It
Authors: Kuhl Julius , Quirin Markus
Published: January 2011

Psychological approaches often conceptualize “free will” as self-determined decision-making. However, the functional mechanisms potentially underlying volitional freedom or its limitations have barely been elaborated. Starting from a functional definition of volition, we illustrate how personality systems interactions (PSI) theory may contribute to explaining underlying mechanisms of volitional freedom. Specifically, based on neurobiological evidence, this theory postulates that degrees of volitional freedom increase with an increasing involvement of more complex levels of psychological functioning (e.g., from habits and affective impulses toward motives, specific goals, intentions, and more global, personal goals). We will demonstrate how, at a psychological level, demand-related stress limits the pursuit of specific goals, whereas threat-related stress limits self-congruent choice of specific goals. Empirical evidence will be reported that relate to these two possible ways of losing volitional (“top-down”) control. In addition, we report on neurobiological findings supporting the present view of volitional freedom and its limitations.
Flow structures and hydrodynamic force during sediment entrainment
Authors: Dwivedi Ambuj , Melville Bruce W. , Shamseldin Asaad Y. , Guha Tushar K.
Published: January 2011

An experimental investigation of the role of coherent structures and their effect on hydrodynamic forces responsible for inception of sediment motion has been carried out using a laboratory flume. Two types of experiments, namely, movable and fixed ball, were conducted using spherical roughness element beds with particle image velocimetry used to measure the instantaneous flow velocity field. Movable ball experiments revealed the predominance of large sweep structures at the instant of entrainment for both shielded and exposed particles. Fixed ball experiments involving simultaneous measurements of hydrodynamic forces and velocity on the particle at entrainment conditions revealed the significance of impulse in initiating sediment entrainment such that an optimum combination of force and duration is required to produce the threshold impulse. Short‐duration lift forces of magnitudes greater than the submerged weight are thought to be responsible for partial lifting of the completely shielded particle. Quadrant analysis and probability distribution function plots of the dominant hydrodynamic force reveal the higher probability of occurrence of high‐magnitude force induced by sweep (Q4) events.
Analytical optimal hedging with explicit incorporation of reservoir release and carryover storage targets
Authors: Shiau Jenq‐Tzong
Published: January 2011

This study analytically derives optimal hedging for a water supply reservoir considering balance between beneficial release and carryover storage value. With the reservoir operation goal expressed as a weighted sum of loss functions (i.e., normalized deviations from targets) for current release and carryover storage, the derived optimal hedging is a linear function of water availability. This analytical optimal hedging is generalized to represent two‐point as well as one‐point hedging. The relationship between the weighting factor and the ratio of release target to total target can be used to detect two types of two‐point hedging. A factor called the inverse‐weighted target ratio (composed of a weighting factor and release and carryover storage targets) is developed to simplify derived optimal hedging and distinguish these two types of hedging, which are classified as the factors less than or equal to 1 and greater than or equal to 1, respectively. One‐point hedging is a special case where these two types of two‐point hedging coincide and this factor equals 1. By explicitly incorporating release and carryover storage targets as well as a weighting factor and an exponent of loss functions, effects of these components on reservoir hedging can be evaluated analytically. Since reservoir release is also a linear function of reservoir inflow, analytical assessment of hedging uncertainty induced by inflow is made possible. The proposed methodology is applied to the Shihmen Reservoir in northern Taiwan to illustrate effects of derived optimal hedging on reservoir performance in terms of shortage‐related indices and hedging uncertainty.
Inner‐membrane proteins PMI/TMEM11 regulate mitochondrial morphogenesis independently of the DRP1/MFN fission/fusion pathways
Authors: Rival Thomas , Macchi Marc , Arnauné‐Pelloquin Laetitia , Poidevin Mickael , Maillet Frédéric , Richard Fabrice , Fatmi Ahmed , Belenguer Pascale , Royet Julien
Published: January 2011

Mitochondria are highly dynamic organelles that can change in number and morphology during cell cycle, development or in response to extracellular stimuli. These morphological dynamics are controlled by a tight balance between two antagonistic pathways that promote fusion and fission. Genetic approaches have identified a cohort of conserved proteins that form the core of mitochondrial remodelling machineries. Mitofusins (MFNs) and OPA1 proteins are dynamin‐related GTPases that are required for outer‐ and inner‐mitochondrial membrane fusion respectively whereas dynamin‐related protein 1 (DRP1) is the master regulator of mitochondrial fission. We demonstrate here that the Drosophila PMI gene and its human orthologue TMEM11 encode mitochondrial inner‐membrane proteins that regulate mitochondrial morphogenesis. PMI‐mutant cells contain a highly condensed mitochondrial network, suggesting that PMI has either a pro‐fission or an anti‐fusion function. Surprisingly, however, epistatic experiments indicate that PMI shapes the mitochondria through a mechanism that is independent of drp1 and mfn. This shows that mitochondrial networks can be shaped in higher eukaryotes by at least two separate pathways: one PMI‐dependent and one DRP1/MFN‐dependent.
Ebolavirus VP35 suppresses IFN production from conventional but not plasmacytoid dendritic cells
Authors: Leung Lawrence W , Park Man‐Seong , Martinez Osvaldo , Valmas Charalampos , López Carolina B , Basler Christopher F
Published: January 2011

Ebolaviruses naturally infect a wide variety of cells including macrophages and dendritic cells (DCs), and the resulting cytokine and interferon‐α/β (IFN) responses of infected cells are thought to influence viral pathogenesis. The VP35 protein impairs RIG‐I‐like receptor‐dependent signaling to inhibit IFN production, and this function has been suggested to promote the ineffective host immune response characteristic of ebolavirus infection. To assess the impact of VP35 on innate immunity in biologically relevant primary cells, we used a recombinant Newcastle disease virus encoding VP35 (NDV/VP35) to infect macrophages and conventional DCs, which primarily respond to RNA virus infection via RIG‐I‐like pathways. VP35 suppressed not only IFN but also tumor necrosis factor (TNF)‐α secretion, which are normally produced from these cells upon NDV infection. Additionally, in cells susceptible to the activity of VP35, IRF7 activation is impaired. In contrast, NDV/VP35 infection of plasmacytoid DCs, which activate IRF7 and produce IFN through TLR‐dependent signaling, leads to robust IFN production. When plasmacytoid DCs deficient for TLR signaling were infected, NDV/VP35 was able to inhibit IFN production. Consistent with this, VP35 was less able to inhibit TLR‐dependent versus RIG‐I‐dependent signaling in vitro. These data demonstrate that ebolavirus VP35 suppresses both IFN and cytokine production in multiple primary human cell types. However, cells that utilize the TLR pathway can circumvent this inhibition, suggesting that the presence of multiple viral sensors enables the host to overcome viral immune evasion mechanisms.
Second harmonic generation probing of dopant type and density at the Si/SiO2 interface
Authors: Fiore Julie L. , Fomenko Vasiliy V. , Bodlaki Dora , Borguet Eric
Published: January 2011

Time-dependent second-harmonic generation (TD-SHG) is shown to be a sensitive, noncontact probe of dopant type and concentration at Si/SiO2 interfaces. TD-SHG signal magnitude increases for n-Si(111)/SiO2, while for p-Si(111)/SiO2 TD-SHG is nonmonotonic. This behavior is interpreted as a consequence of SHG sensitivity to electric fields induced by interfacial charge transfer and trapping.
C6H6/Au(111): Interface dipoles, band alignment, charging energy, and van der Waals interaction
Authors: Abad E. , Dappe Y. J. , Martínez J. I. , Flores F. , Ortega J.
Published: January 2011

We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.
Proton transport in biological systems can be probed by two-dimensional infrared spectroscopy
Authors: Liang Chungwen , Jansen Thomas L. C. , Knoester Jasper
Published: January 2011

We propose a new method to determine the proton transfer (PT) rate in channel proteins by two-dimensional infrared (2DIR) spectroscopy. Proton transport processes in biological systems, such as proton channels, trigger numerous fundamental biochemical reactions. Due to the limitation in both spatial and time resolution of the traditional experimental approaches, describing the whole proton transport process and identifying the rate limiting steps at the molecular level is challenging. In the present paper, we focus on proton transport through the Gramicidin A channel. Using a kinetic PT model derived from all-atom molecular dynamics simulations, we model the amide I region of the 2DIR spectrum of the channel protein to examine its sensitivity to the proton transport process. We demonstrate that the 2DIR spectrum of the isotope-labeled channel contain information on the PT rate, which may be extracted by analyzing the antidiagonal linewidth of the spectral feature related to the labeled site. Such experiments in combination with detailed numerical simulations should allow the extraction of site dependent PT rates, providing a method for identifying possible rate limiting steps for proton channel transfer.
On the construction of quasidiabatic state representations of bound adiabatic state potential energy surfaces coupled by accidental conical intersections: Incorporation of higher order terms
Authors: Dillon Joseph , Yarkony David R. , Schuurman Michael S.
Published: January 2011

The quadratic vibronic coupling model is an important computational tool for simulating photoelectron spectra involving strongly coupled electronic states in polyatomic molecules. However, recent work has indicated the need for higher order terms, with most of the initial studies focusing on molecules with symmetry-required degeneracies. In this study we report an extension of our approach for constructing fully quadratic representations of bound electronic states coupled by conical intersections, which allows for the inclusion of higher order terms, demonstrated here employing a quartic expansion. Procedures are developed that eliminate unphysical behavior for large displacements, a problem likely to be an endemic to anharmonic expansions. Following work on representing dissociative electronic states, Lagrange multipliers are used to constrain the constructed representation to reproduce exactly the energy, energy gradients, and/or derivative couplings at specific points, or nodes, in nuclear coordinate space. The approach is illustrated and systematically studied using the four lowest electronic states of triazolyl, (CH)2N3.
Reversible uptake of water on NaCl nanoparticles at relative humidity below deliquescence point observed by noncontact environmental atomic force microscopy
Authors: Bruzewicz Derek A. , Checco Antonio , Ocko Benjamin M. , Lewis Ernie R. , McGraw Robert L. , Schwartz Stephen E.
Published: January 2011

The behavior of NaCl nanoparticles as a function of relative humidity (RH) has been characterized using non-contact environmental atomic force microscopy (e-AFM) to measure the heights of particles deposited on a prepared hydrophobic surface. Cubic NaCl nanoparticles with sides of 35 and 80 nm were found to take up water reversibly with increasing RH well below the bulk deliquescence relative humidity (DRH) of 75% at 23 \documentclass[12pt]{minimal}\begin{document}$^{\circ }$\end{document}∘C, and to form a liquid-like surface layer of thickness 2 to 5 nm, with measurable uptake ( \documentclass[12pt]{minimal}\begin{document}$>$\end{document}>2 nm increase in particle height) beginning at 70% RH. The maximum thickness of the layer increased with increasing RH and increasing particle size over the range studied. The liquid-like behavior of the layer was indicated by a reversible rounding at the upper surface of the particles, fit to a parabolic cross-section, where the ratio of particle height to maximum radius of curvature increases from zero (flat top) at 68% RH to 0.7 ± 0.3 at 74% RH. These observations, which are consistent with a reorganization of mass on the solid NaCl nanocrystal at RH below the DRH, suggest that the deliquescence of NaCl nanoparticles is more complex than an abrupt first-order phase transition. The height measurements are consistent with a phenomenological model that assumes favorable contributions to the free energy of formation of a liquid layer on solid NaCl due both to van der Waals interactions, which depend partly upon the Hamaker constant, \documentclass[12pt]{minimal}\begin{document}$A_{\hbox{\it film}}$\end{document}Afilm, of the interaction between the thin liquid film and the solid NaCl, and to a longer-range electrostatic interaction over a characteristic length of persistence, ξ; the best fit to the data corresponded to \documentclass[12pt]{minimal}\begin{document}$A_{\hbox{\it film}} =$\end{document}Afilm= 1 kT and ξ = 2.33 nm.
Shedding light on a dark state: The energetically lowest quintet state of C$_2$2
Authors: Bornhauser P. , Sych Y. , Knopp G. , Gerber T. , Radi P. P.
Published: January 2011

In this work we present a deperturbation study of the $d\,^3\Pi _g, v=6$d3Πg,v=6 state of C$_{2}$2 by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system ($d^3\Pi _g-a\,^3\Pi _u$d3Πg−a3Πu) unveils the presence of the energetically lowest high-spin state of C$_{2}$2 in the vicinity of the $d\,^3\Pi _g, v=6$d3Πg,v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the $1\;^5\Pi _g$15Πg state at rotational quantum numbers N ⩽ 11. The spectral complexity for transitions to the v = 6 level of $d\,^3\Pi _g$d3Πg state is further enhanced by an additional perturbation at N = 19 and 21 owing to the $b\, ^3\Sigma _g^-, v=19$b3Σg−,v=19 state. The spectroscopic characterization of both dark states is accessible by the measurement of 122 “window” levels. A global fit of the positions to a conventional Hamiltonian for a linear diatomic molecule yields accurate molecular constants for the quintet and triplet perturber states for the first time. In addition, parameters for the spin-orbit and L-uncoupling interaction between the electronic levels are determined. The detailed deperturbation study unravels major issues of the so-called high-pressure bands of C$_{2}$2. The anomalous nonthermal emission initially observed by Fowler in 1910 [Mon. Not. R. Astron. Soc. 70, 484 (1910)] and later observed in numerous experimental environments are rationalized by taking into account “gateway” states, i.e., rotational levels of the $d\,^3\Pi _g, v=6$d3Πg,v=6 state that exhibit significant $^5\Pi _g$5Πg character through which all population flows from one electronic state to the other.
Is there a relation between excess volume and miscibility in binary liquid mixtures?
Authors: Amore S. , Horbach J. , Egry I.
Published: January 2011

Molecular dynamics computer simulations of various symmetrical Lennard-Jones (LJ) models are used to elucidate how the excess volume in dense binary liquids is related to the microscopic interactions between the particles. Both fully miscible systems and systems with a liquid–liquid phase separation are considered by varying systematically the parameters of the LJ potentials. The phase diagrams with the critical points of the demixing systems are determined by means of Monte Carlo simulations in the semigrandcanonical ensemble. The different LJ models are investigated by computing Bhatia–Thornton structure factors, enthalpy of mixing, and excess volume. For the demixing systems, the LJ models show a positive enthalpy of mixing while it is negative for the systems without miscibility gap. In contrast to that, the excess volume can be negative and positive for both demixing and fully miscible systems. This behavior is explained in terms of the interplay between the repulsive and attractive terms in the LJ potential. Whereas repulsions dominate the packing of particles as reflected by the number-density structure factor, the chemical ordering and thus the concentration structure factor are strongly affected by attractive interactions, leading to the “anomalies” of the excess volume.
Modified Fowler–Milne method for the spectroscopic determination of thermal plasma temperature without the measurement of continuum radiation
Authors: Ma Shuiliang , Gao Hongming , Wu Lin
Published: January 2011

A technique based on the Fowler–Milne method for the spectroscopic determination of thermal plasma temperatures without measuring continuum radiation is presented. This technique avoids the influence of continuum radiation with the combined line and continuum emission coefficients to derive the plasma temperatures. The amount of continuum emission coefficient is estimated by using an expression related to the Biberman factors. Parameters that affect the accuracy of the proposed technique and errors in the measured plasma temperatures are analyzed. It is shown that, by using the Ar I 696.5 nm line with a bandwidth of 3.27 nm without taking into account the continuum radiation, the plasma temperature measured will be lower on the order of up to 1000–3000 K for temperatures from 20 000 to 24 000 K. The theoretically predicted temperature errors are in good agreement with the experimental results, indicating that the proposed technique is reliable for plasma temperature measurement.
Thermal diffusivity of nonflat plates using the flash method
Authors: Salazar Agustín , Fuente Raquel , Apiñaniz Estibaliz , Mendioroz Arantza
Published: January 2011

The flash method is the standard technique to measure the thermal diffusivity of solid samples. It consists of heating the front surface of an opaque sample by a brief light pulse and detecting the temperature evolution at its rear surface. The thermal diffusivity is obtained by measuring the time corresponding to the half maximum of the temperature rise, which only depends on the sample thickness and thermal diffusivity through a simple formula. Up to now, the flash method has been restricted to flat samples. In this work, we extend the flash method to measure the thermal diffusivity of nonflat samples. In particular, we focus on plates with cylindrical and spherical shapes. The theoretical model indicates that the same expression for flat samples can also be applied to cylindrical and spherical plates, except for extremely curved samples. Accordingly, a curvature limit for the application of the expression for flat samples is established. Flash measurements on lead foils of cylindrical shape confirm the validity of the model.
Efficient moves for global geometry optimization methods and their application to binary systems
Authors: Sicher Michael , Mohr Stephan , Goedecker Stefan
Published: January 2011

We show that molecular dynamics based moves in the minima hopping method are more efficient than saddle point crossing moves. For binary systems we incorporate identity exchange moves in a way that allows one to avoid the generation of high energy configurations. Using this modified minima hopping method, we re-examine the binary Lennard-Jones benchmark system with up to 100 atoms and we find a large number of new putative global minima.
Imaginary time Gaussian dynamics of the Ar3 cluster
Authors: Cartarius Holger , Pollak Eli
Published: January 2011

Semiclassical Gaussian approximations to the Boltzmann operator have become an important tool for the investigation of thermodynamic properties of clusters of atoms at low temperatures. Usually, numerically expensive thawed Gaussian variants are applied. In this article, we introduce a numerically much cheaper frozen Gaussian approximation to the imaginary time propagator with a width matrix especially suited for the dynamics of clusters. The quality of the results is comparable to that of thawed Gaussian methods based on the single-particle ansatz. We apply the method to the argon trimer and investigate the dissociation process of the cluster. The results clearly show a classical-like transition from a bounded moiety to three free particles at a temperature T ≈ 20  K, whereas previous studies of the system were not able to resolve this transition. Quantum effects, i.e., differences with the purely classical case manifest themselves in the low-temperature behavior of the mean energy and specific heat as well as in a slight shift of the transition temperature. We also discuss the influence of an artificial confinement of the atoms usually introduced to converge numerical computations. The results show that restrictive confinements often implemented in studies of clusters can influence the thermodynamic properties drastically. This finding may have implications on other studies of atomic clusters.
Orientational relaxation dynamics in aqueous ionic solution: Polarization-selective two-dimensional infrared study of angular jump-exchange dynamics in aqueous 6M NaClO4
Authors: Ji Minbiao , Gaffney Kelly J.
Published: January 2011

The dynamics of hydrogen bond (H-bond) formation and dissociation depend intimately on the dynamics of water rotation. We have used polarization resolved ultrafast two-dimensional infrared (2DIR) spectroscopy to investigate the rotational dynamics of deuterated hydroxyl groups (OD) in a solution of 6M NaClO4 dissolved in isotopically mixed water. Aqueous 6M NaClO4 has two peaks in the OD stretching region, one associated with hydroxyl groups that donate a H-bond to another water molecule (ODW) and one associated with hydroxyl groups that donate a H-bond to a perchlorate anion (ODP). Two-dimensional IR spectroscopy temporally resolves the equilibrium inter conversion of these spectrally distinct H-bond configurations, while polarization-selective 2DIR allows us to access the orientational motions associated with this chemical exchange. We have developed a general jump-exchange kinetic theory to model angular jumps associated with chemical exchange events. We use this to model polarization-selective 2DIR spectra and pump-probe anisotropy measurements. We determine the H-bond exchange induced jump angle to be 49 ± 5° and the H-bond exchange rate to be 6 ± 1 ps. Additionally, the separation of the 2DIR signal into contributions that have or have not undergone H-bond exchange allows us to directly determine the orientational dynamics of the ODW and the ODP configurations without contributions from the exchanged population. This proves to be important because the orientational relaxation dynamics of the populations that have undergone a H-bond exchange differ significantly from the populations that remain in one H-bond configuration. We have determined the slow orientational relaxation time constant to be 6.0 ± 1 ps for the ODW configuration and 8.3 ± 1 ps for the ODP configuration. We conclude from these measurements that the orientational dynamics of hydroxyl groups in distinct H-bond configurations do differ, but not significantly.
Fiber based pathogen photoinactivating system
Authors: Chen Jie , Cesario Thomas C. , Rentzepis Peter M.
Published: January 2011

A new fiber based instrument described, which can be inserted through the nose, mouth, or other means into the body, has the potential to: (a) detect and image infected areas inside the body; (b) deliver drugs only onto the infected areas inside and outside the human body; (c) remove the excess drugs; (d) use the same fiber for both imaging and illumination with high intensity light of wavelengths varying from deep UV to IR to induce photoreactions of the drug with the pathogen of the infected area. This compact system utilizes much smaller quantities of drugs and radiation dose than conventional methods, eliminates the need for intravenous injection, and greatly decreases the toxic effects of drugs and irradiation to the human body including swelling, inflammation, nausea, fever, and sunlight sensitivity that lasts for about 30 days.
Stress-based control of magnetic nanowire domain walls in artificial multiferroic systems
Authors: Dean J. , Bryan M. T. , Schrefl T. , Allwood D. A.
Published: January 2011

Artificial multiferroic systems, which combine piezoelectric and piezomagnetic materials, offer novel methods of controlling material properties. Here, we use combined structural and magnetic finite element models to show how localized strains in a piezoelectric film coupled to a piezomagnetic nanowire can attract and pin magnetic domain walls. Synchronous switching of addressable contacts enables the controlled movement of pinning sites, and hence domain walls, in the nanowire without applied magnetic field or spin-polarized current, irrespective of domain wall structure. Conversely, domain wall-induced strain in the piezomagnetic material induces a local potential difference in the piezoelectric, providing a mechanism for sensing domain walls. This approach overcomes the problems in magnetic nanowire memories of domain wall structure-dependent behavior and high power consumption. Nonvolatile random access or shift register memories based on these effects can achieve storage densities >1 Gbit/In2, sub-10 ns switching times, and power consumption <100 keV per operation.
On the density scaling of liquid dynamics
Authors: Fragiadakis D. , Roland C. M.
Published: January 2011

Superpositioning of relaxation data as a function of the product variable TVγ, where T is temperature, V the specific volume, and γ a material constant, is an experimental fact demonstrated for approximately 100 liquids and polymers. Such scaling behavior would result from the intermolecular potential having the form of an inverse power law (IPL), suggesting that an IPL is a good approximation for certain relaxation properties over the relevant range of intermolecular distances. However, the derivation of the scaling property of an IPL liquid is based on reduced quantities, for example, the reduced relaxation time equal to T1/2V−1/3 times the actual relaxation time. The difference between scaling using reduced rather than unreduced units is negligible in the supercooled regime; however, at higher temperature the difference can be substantial, accounting for the purported breakdown of the scaling and giving rise to different values of the scaling exponent. Only the γ obtained using reduced quantities can be sensibly related to the intermolecular potential.
Instabilities and transition in flows between two porous concentric cylinders with radial flow and a radial temperature gradient
Authors: Kolesov V. V. , Shapakidze L. D.
Published: January 2011

Complex regimes arising after the loss of stability of a viscous fluid with radial flow and radial temperature gradient between two heated rotating permeable cylinders are investigated in a small neighborhood of the point of intersection of neutral curves of monotonic axisymmetric and oscillatory three-dimensional instabilities. Since by the linear theory we can form a judgment only of the first loss of instability, the development of complex flows is investigated by nonlinear analysis, which makes it possible to detect transitions with generation of both quasiperiodic oscillations and chaotic regimes.
Large heat capacity anomaly near the consolute point of the binary mixture nitromethane and 3-pentanol
Authors: Losada-Pérez Patricia , Tripathi Chandra Shekhar Pati , Leys Jan , Glorieux Christ , Thoen Jan
Published: January 2011

The large critical anomaly in the isobaric heat capacity $C_{p,x}(T)$Cp,x(T) of the binary mixture nitromethane + 3-pentanol is measured using high-resolution adiabatic scanning calorimetry. The unique features of this technique provided an alternative approach to the study of the critical behavior of $C_{p,x}(T)$Cp,x(T), providing further $C_{p,x}(T)$Cp,x(T) related quantities from which valuable information could be extracted. Our data are in full agreement with the predictions of the Modern Theory of Critical Phenomena; specifically, 3D-Ising model values for the critical exponent α and the universal amplitude ratio values of the leading critical amplitudes, as well as for the first correction-to-scaling ones, provide the optimum fits to represent the experimental data. Evidence for the need of higher-order terms, i.e., first correction-to-scaling term, is given. The large value of the coefficient E for the linear temperature dependence of the background obtained is ascribed to a possible contribution of the regular linear background term, of a higher-order asymmetry term, and of the second correction-to-scaling term. Internal consistency of $C_{p,x}(T)$Cp,x(T) and its related quantities is successfully checked.
Effect of surface tension on global modes of confined wake flows
Authors: Tammisola Outi , Lundell Fredrik , Söderberg L. Daniel
Published: January 2011

Many wake flows are susceptible to self-sustained oscillations, such as the well-known von Kármán vortex street behind a cylinder that makes a rope beat against a flagpole at a distinct frequency on a windy day. One appropriate method to study these global instabilities numerically is to look at the growth rates of the linear temporal global modes. If all growth rates for all modes are negative for a certain flow field then a self-sustained oscillation should not occur. On the other hand, if one growth rate for one mode is slightly positive, the oscillation will approximately obtain the frequency and shape of this global mode. In our study, we first introduce surface tension between two fluids to the wake-flow problem. Then we investigate its effects on the global linear instability of a spatially developing wake with two co-flowing immiscible fluids. The inlet profile consists of two uniform layers, which makes the problem easily parametrizable. The fluids are assumed to have the same density and viscosity, with the result that the interface position becomes dynamically important solely through the action of surface tension. Two wakes with different parameter values and surface tension are studied in detail. The results show that surface tension has a strong influence on the oscillation frequency, growth rate, and shape of the global mode(s). Finally, we make an attempt to confirm and explain the surface-tension effect based on a local stability analysis of the same flow field in the streamwise position of maximum reverse flow.
Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules
Authors: Holm A. I. S. , Johansson H. A. B. , Cederquist H. , Zettergren H.
Published: January 2011

We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H$^+$+-, C$_2$2H$_2$2-, and C$_2$2H$_2^+$2+-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion–PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAH$^{q+}$q+-molecules are thermodynamically stable for q ⩽ 2 (naphthalene, biphenylene, and anthracene), q ⩽ 3 (pyrene), and q ⩽ 4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H$^+$+-emissions from all five PAHs and for C$_2$2H$_2^{+}$2+-emission from naphthalene – the smallest PAH.
Dynamics of nearly unstable axisymmetric liquid bridges
Authors: Perales José M. , Vega José M.
Published: January 2011

The dynamics of a noncylindrical, axisymmetric, marginally unstable liquid bridge between two equal disks is analyzed in the inviscid limit. The resulting model allows for the weakly nonlinear description of both the (first stage of) breakage for unstable configurations and the (slow) dynamics for stable configurations. The analysis is made for both slender and short liquid brides. In the former range, the dynamics breaks reflection symmetry on the midplane between the supporting disks and can be described by a standard Duffing equation, while for short bridges reflection symmetry is preserved and the equation is still Duffing-like but exhibiting a quadratic nonlinearity. The asymptotic results compare well with existing experiments.
Kinetic solution of the structure of a shock wave in a nonreactive gas mixture
Authors: Josyula Eswar , Vedula Prakash , Bailey William F. , Suchyta Casimir J.
Published: January 2011

The multispecies Boltzmann equation is numerically integrated to characterize the internal structure of a Mach 3 shock wave in a hard sphere gas. The collision integral is evaluated by the conservative discrete ordinate method [F. G. Tcheremissine, Comput. Math. Math. Phys. 46, 315 (2006)]. There was excellent agreement of macroscopic variables [Kosuge et al.., Eur. J. Mech. B/Fluids 20, 87 (2001)]. The effect of species concentration and mass ratio on the behavior of macroscopic variables and distribution functions in the structure of the shock wave is considered for both two- and three-species gas mixtures. In a binary mixture of gases with different masses and varying concentrations, the temperature overshoot of the parallel component of temperature near the center of the shock wave is highest for the heavy component when the concentration of the heavy component is the smallest. The rise in the parallel component of temperature is revealed by the behavior of the distribution function.
The Rayleigh–Taylor instability of a surface of arbitrary cross section with pinned edges
Authors: Johns L. E. , Narayanan R.
Published: January 2011

We determine the critical points of the Rayleigh–Taylor instability of a surface of arbitrary cross section having pinned edges. Often these points coincide with the diffusion eigenvalues but sometimes they do not.
Experimental study of freely falling thin disks: Transition from planar zigzag to spiral
Authors: Zhong Hongjie , Chen Shiyi , Lee Cunbiao
Published: January 2011

Using a stereoscopic vision method, we have experimentally investigated the time evolution of a free thin disk motion with six degrees of freedom for the first time. It is found that, as the dimensionless moment of inertia I∗ decreases, the trajectory of the disk transits from planar to nonplanar. New types of free falling motions were identified for small I∗ values, including the spiral state and the transitional state. An extended Re−I∗ phase diagram corresponding to different flow regimes was given. The underlying physics associated with the transition is found to be connected to the interactions between the moving object and induced vortices.
Average characteristic polynomials in the two-matrix model
Authors: Delvaux Steven
Published: January 2011

The two-matrix model is defined on pairs of Hermitian matrices \documentclass[12pt]{minimal}\begin{document}$(M_1,M_2)$\end{document}(M1,M2) of size n × n by the probability measure \documentclass[12pt]{minimal}\begin{document}$\frac{1}{Z_n} \exp (\hbox{Tr} (-V(M_1)-W(M_2)+\tau M_1M_2))$\break $ dM_1\ dM_2,$\end{document}1Znexp(Tr(−V(M1)−W(M2)+τM1M2))dM1dM2, where V and W are given potential functions and \documentclass[12pt]{minimal}\begin{document}$\tau \in \mathbb {R}$\end{document}τ∈R. We study averages of products and ratios of characteristic polynomials in the two-matrix model, where both matrices \documentclass[12pt]{minimal}\begin{document}$M_1$\end{document}M1 and \documentclass[12pt]{minimal}\begin{document}$M_2$\end{document}M2 may appear in a combined way in both numerator and denominator. We obtain determinantal expressions for such averages. The determinants are constructed from several building blocks: the biorthogonal polynomials, \documentclass[12pt]{minimal}\begin{document}$p_n(x)$\end{document}pn(x) and \documentclass[12pt]{minimal}\begin{document}$q_n(y),$\end{document}qn(y), associated with the two-matrix model; certain transformed functions \documentclass[12pt]{minimal}\begin{document}$\widetilde{P}_n(w)$\end{document}P̃n(w) and \documentclass[12pt]{minimal}\begin{document}$\widetilde{Q}_n(v)$\end{document}Q̃n(v); and finally Cauchy-type transforms of the four Eynard–Mehta kernels \documentclass[12pt]{minimal}\begin{document}$K_{1,1}$\end{document}K1,1, \documentclass[12pt]{minimal}\begin{document}$K_{1,2}$\end{document}K1,2, \documentclass[12pt]{minimal}\begin{document}$K_{2,1}$\end{document}K2,1, and \documentclass[12pt]{minimal}\begin{document}$K_{2,2}$\end{document}K2,2. In this way, we generalize known results for the one-matrix model. Our results also imply a new proof of the Eynard–Mehta theorem for correlation functions in the two-matrix model, and they lead to a generating function for averages of products of traces.
Mg doped InN and confirmation of free holes in InN
Authors: Wang K. , Miller N. , Iwamoto R. , Yamaguchi T. , Mayer M. A. , Araki T. , Nanishi Y. , Yu K. M. , Haller E. E. , Walukiewicz W. , Ager J. W.
Published: January 2011

We report a systematic investigation on Mg doped InN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy. Electrolyte capacitance voltage (ECV) combined with thermopower measurements find p-type conduction over an Mg concentration range. For InN:Mg in this p-type “window” the Seebeck coefficients dramatically change their signs from negative to positive when the thickness of undoped InN interlayer decreases to zero. This notable sign change of Seebeck coefficient explains the previous inconsistency between ECV and thermopower results and confirms the existence of mobile holes in the InN:Mg. Taking into account the undoped InN interlayer, the hole density and mobility are extracted.
Gd-doping effect on performance of HfO2 based resistive switching memory devices using implantation approach
Authors: Zhang Haowei , Liu Lifeng , Gao Bin , Qiu Yuanjun , Liu Xiaoyan , Lu Jing , Han Ruqi , Kang Jinfeng , Yu Bin
Published: January 2011

An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.
Ab initio mass tensor molecular dynamics
Authors: Tsuchida Eiji
Published: January 2011

Mass tensor molecular dynamics method was first introduced by Bennett [J. Comput. Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of generalized atomic masses. Here, we show how to apply this method to ab initio molecular dynamics simulations with minimal computational overhead. Test calculations on liquid water show a threefold reduction in computational effort without making the fixed geometry approximation. We also present a simple recipe for estimating the optimal atomic masses using only the first derivatives of the potential energy.
Chemistry of defect induced photoluminescence in chalcopyrites: The case of CuAlS2
Authors: Liborio Leandro M. , Bailey Christine L. , Mallia Giuseppe , Tomić Stanko , Harrison Nicholas M.
Published: January 2011

Hybrid exchange density functional theory is used to study the wide band gap chalcopyrite CuAlS2. The formation energies of charged and neutral intrinsic defects are calculated for different environmental conditions, and it is shown that CuAlS2 is a p-type material that cannot be type inverted through the formation of intrinsic defects. The calculated band gap states associated with the different intrinsic defects are used to comment on the origin of the observed CuAlS2 photoluminescence emissions. The origin and stability of ordered defect compounds derived from CuAlS2 are investigated, and it is concluded that CuAl5S8 is a stable ordered defect compound, albeit in a small region of phase space.
Thermo-optic tuning of erbium-doped amorphous silicon nitride microdisk resonators
Authors: Hryciw Aaron C. , Kekatpure Rohan D. , Yerci Selçuk , Dal Negro Luca , Brongersma Mark L.
Published: January 2011

We demonstrate a technique to yield a direct and sensitive measurement of the thermo-optic coefficient (TOC) for light-emitting materials in optical microdisk resonators. Using photoluminescence from erbium-doped amorphous silicon nitride (a-SiNx:Er) as an example, we show how the TOC can be extracted from thermally induced shifts in the resonant microdisk modes. For the highest-performance a-SiNx:Er material composition, we find a TOC at 1.54 μm of ∼3×10−5 K−1 in the 300–500 K range. Additionally, our work demonstrates a convenient all-optical spectroscopic technique for sensitive temperature measurements, with a resolution of ∼30 mK in this temperature range.
A field-induced ferrielectric liquid crystal phase
Authors: Jaradat S. , Brimicombe P. D. , Osipov M. A. , Pindak R. , Gleeson H. F.
Published: January 2011

Understanding the structures and stability conditions of emerging liquid crystal (LC) phases brings us a step closer to the crucial understanding of delicate self-assembling nanoscale systems and the consequential impact on their macroscopic properties. We report experimental evidence and a theoretical model for a ferrielectric LC phase which has a three-layer repeat structure and is field-induced but exhibits a symmetry and electro-optical properties that are distinct from those of the known ferrielectric (SmC*FI1) phase. This discovery has implications for the ways in which LC phases are identified, and offers the potential for better control of ferroelectric LC devices.
Radial elasticity of single-walled carbon nanotube measured by atomic force microscopy
Authors: Yang Y. H. , Li W. Z.
Published: January 2011

Effective radial modulus (Eradial) of straight single-walled carbon nanotubes (SWCNTs) grown directly on quartz substrate have been measured by using well-calibrated tapping mode and contact mode atomic force microscopies. It is found that the measured Eradial decreases from 57 to 9 GPa as the diameter of the SWCNTs increases from 0.92 to 1.91 nm. The current experimental results are consistent with the recently reported simulation data in both the data pattern and values. The method used in this research can also be applied to measure the mechanical properties of other low-dimension nanostructures, such as nanowires and nanodots.
Accurate all-electron correlation energies for the closed-shell atoms from Ar to Rn and their relationship to the corresponding MP2 correlation energies
Authors: McCarthy Shane P. , Thakkar Ajit J.
Published: January 2011

All-electron correlation energies \documentclass[12pt]{minimal}\begin{document}$E_{\rm c}$\end{document}Ec are not very well-known for atoms with more than 18 electrons. Hence, coupled-cluster calculations in carefully designed basis sets are combined with fully converged second-order Møller–Plesset perturbation theory (MP2) computations to obtain fairly accurate, nonrelativistic \documentclass[12pt]{minimal}\begin{document}$E_{\rm c}$\end{document}Ec values for the 12 closed-shell atoms from Ar to Rn. These energies will be useful for the evaluation and parameterization of density functionals. The results show that MP2 overestimates \documentclass[12pt]{minimal}\begin{document}$\vert {E_{\rm c}}\vert$\end{document}|Ec| for heavy atoms. Spin-component scaling of the MP2 correlation energy is used to provide a simple explanation for this overestimation.
Two-cell circulation in a liquid meniscus driven by a swirling gas jet
Authors: Herrada Miguel A. , Shtern Vladimir N. , López-Herrera José María
Published: January 2011

A liquid issuing from a capillary needle adopts a cone-jet structure if the liquid is further driven by a coflowing gas jet. In the present work, flow patterns appearing in this cone-jet structure are studied by the volume-of-fluid numerical method. Axisymmetric motions of the liquid and gas, both treated as viscous incompressible fluids, are simulated. As the gas/liquid mass ratio increases, the meridional circulation develops in the meniscus region of the liquid flow. As the ratio exceeds a threshold, the flow becomes time periodic and droplet generating. Swirl, added in the gas jet, affects the liquid flow in two ways. First, the threshold value increases with swirl. Second, the circulation region transforms from the bubble-like into ring-like pattern and then becomes two-cellular. As swirl further increases, the cells separate, one cell disappears, and a new cell emerges being attached to the needle wall. The predicted metamorphoses of the flow topology might be important for atomization of a liquid fuel.
Photoabsorption and photoelectric process in Si nanocrystallites
Authors: Anchala  , Purohit S. P. , Mathur K. C.
Published: January 2011

Using the effective mass approximation, we investigate the photoabsorption and photoelectric process in the conduction band of a single electron charged spherical Si semiconductor quantum dot nanostructure embedded in the amorphous SiO2 matrix. We consider the potential barrier at the interface as of (i) infinite and (ii) finite heights. The effect of self-energy associated with surface polarization due to the charging of the quantum dot is also considered. Our results of photoabsorption coefficient for (1s-1p) transition are found to be in good agreement with the available experimental data.
Subgap optical conductivity in semihydrogenated graphene
Authors: Ang Yee Sin , Zhang C.
Published: January 2011

We report that for graphene with a finite band gap (such as semihydrogenated graphene or graphene with spin-orbit coupling), there exists a strong nonlinear optical response for energies lower than the band gap where the linear response is forbidden. At low temperatures, the nonlinear current in graphene with a gap is much stronger than that in gapless graphene. Our result suggests that semihydrogenated graphene can have a unique potential as a two-color nonlinear material in the terahertz frequency region. The relative intensity of the two colors can be tuned with the electric field.