bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictors of physical activity change during adolescence: a 3·5-year follow-up
Authors: Dumith Samuel C , Gigante Denise P , Domingues Marlos R , Hallal Pedro C , Menezes Ana MB , Kohl Harold W
Published: March 2012

Objective

To investigate the predictors of change in physical activity (PA) from early to mid adolescence in a cohort of adolescents.

Design

Prospective, population-based birth cohort study. PA level was evaluated by means of questionnaire, and was analysed in continuous form (min/week) and as a trajectory (inactive–inactive, inactive–active, active–inactive, active–active) based on the cut-off point of 300 min/week.

Setting

Pelotas, a city of 340 000 inhabitants in southern Brazil.

Subjects

Adolescents (n4120) followed from 11 to 15 years of age.

Results

Maternal PA change and more exposure to outdoors were directly associated with a positive change in PA level (min/week) for both genders. Higher maturation status (among boys) and later menarche were also associated with positive PA change in min/week. Predictors to remain inactive were: maternal PA change (inverse association), more exposure to outdoors, higher socio-economic level, fear of living in the neighbourhood and non-overweight girls. Predictors to become inactive were higher socio-economic level among boys and increase in screen time among girls.

Conclusions

The study demonstrates that social, family, biological, behavioural and environmental factors exert an important role in the PA change among youngsters as they move into adolescence. These findings may be relevant to the design of policies and intervention programmes aimed at promoting PA in teenagers.
Wie lässt sich der Einfluss von Kultur auf Erleben und Verhalten messen?
Authors: Freund Henning , Zimmermann Johannes , Pfeiffer Nils , Conradi Ania , Hunger Christina , Riedel Fanja , Boysen Folke , Schwinn Lisa , Rost Rebekka , Cierpka Manfred , Kämmerer Annette
Published: March 2012

Zusammenfassung. Die Frage nach dem Einfluss von Kultur auf Erleben und Verhalten hat innerhalb der quantitativen Psychologie erheblich an Bedeutung gewonnen. Im vorliegenden Artikel wird zunächst geklärt, was unter „Kultur” theoretisch und forschungspraktisch zu verstehen ist, wie sich psychologisch relevante Einflüsse von Kultur nachweisen lassen und welche Variablen diesen Einfluss vermitteln. Der empirische Schwerpunkt des Artikels liegt auf der deutschsprachigen Adaption der „Self-Construal Scale” (SCS; Singelis, 1994 ), der „Sex-Role Ideology Scale” (SRIS; Kalin & Tilby, 1978 ) und der „Tightness-Looseness Scale” (TLS; Gelfand et al., 2007 ), die ein breites Spektrum an kulturvermittelnden Variablen erfassen. Die adaptierten Skalen wurden innerhalb einer heterogenen Stichprobe (N = 515) hinsichtlich ihrer faktoriellen Struktur, Reliabilitäten und Validitätsindikatoren untersucht. Die psychometrischen Eigenschaften sind zufriedenstellend bis gut und mit den Originalskalen gut vergleichbar. Zusammengenommen bilden die Skalen, erstmals im deutschsprachigen Bereich, eine reliable, multidimensionale Fragebogenbatterie, die den Einfluss von Kultur in testökonomisch vertretbarer Weise messbar macht.
Faktoren psychosozialer Beeinträchtigung
Authors: Tran Ulrich S. , Walter Thomas , Remmel Andreas
Published: March 2012

Zusammenfassung. Routinemäßige Qualitätssicherung und Erfolgsforschung in der Psychotherapie sollte nach Expertenmeinung mehrdimensional erfolgen. Dazu können einerseits eigens entworfene klinische Instrumente („core batteries”) oder Batterien etablierter Einzelinstrumente eingesetzt werden. Empirisch zeigt sich jedoch, dass „core batteries” meist durch einen Generalfaktor dominiert werden, ähnlich wie die weit verbreitete und ebenso mehrdimensional konzipierte SCL-90-R. Anhand einer Stichprobe psychosomatischer Patienten mit heterogenen Diagnosen (N = 1285) wird demonstriert, dass dies ebenso für eine Batterie anderer klinischer Skalen (BDI, IIP-D, SF-36, SOC-29, STAI, STAXI, TAS-26) zutrifft. Der Raum, der zudem durch diese Skalen mit der SCL-90-R gebildet wird, ist vierdimensional und wird durch „psychische Belastung” sowie drei Faktoren zum interpersonellen Verhalten und Problemen aufgespannt. Die Bedeutung dieser Ergebnisse für die klinische Forschung und Theoriebildung, wie für die mehrdimensionale Evaluation wird diskutiert.
Optimismus und Pessimismus bei Vorschulkindern
Authors: Lemola Sakari , von Suchodoletz Antje , Räikkönen Katri , Gunzenhauser Catherine
Published: March 2012

Zusammenfassung. Ziel der vorliegenden Studie ist die Untersuchung der psychometrischen Eigenschaften, faktoriellen Struktur und konvergenten Validität der deutschsprachigen Version des Parent Rated Life Orientation Test of Children (PLOT) zur Messung von Optimismus und Pessimismus bei 4 bis 6-jährigen Vorschulkindern. Eltern von 145 Kindergartenkindern (77 Mädchen; Alter: M = 5.0, SD = 0.6 Jahre) schätzten Optimismus und Pessimismus sowie Emotionsregulation der Kinder ein. Außerdem wurde das Problemverhalten der Kinder (Eltern- und Erzieherinneneinschätzung) erfasst. Konsistent zu Studien mit Schulkindern und Jugendlichen zeigte sich eine zweidimensionale Faktorenstruktur mit einem Optimismus- und einem Pessimismusfaktor. Die Ergebnisse ergaben theoriekonforme Zusammenhänge mit Problemverhalten und Emotionsregulation der Kinder. Insgesamt weisen die gefundenen Reliabilitäts- und Validitätswerte auf eine gute Verwendbarkeit des PLOT bei Vorschulkindern hin. Das neue Messverfahren kann einen Beitrag zum besseren Verständnis von Zukunftserwartungen bei Vorschulkindern leisten und als Screening-Instrument zur Identifikation von Kindern mit einem Entwicklungsrisiko dienen.
Phytoplankton niche generation by interspecific stoichiometric variation
Authors: Göthlich L. , Oschlies A.
Published: March 2012

For marine biogeochemical models used in simulations of climate change scenarios, the ability to account for adaptability of marine ecosystems to environmental change becomes a concern. The potential for adaptation is expected to be larger for a diverse ecosystem compared to a monoculture of a single type of (model) algae, such as typically included in biogeochemical models. Recent attempts to simulate phytoplankton diversity in global marine ecosystem models display remarkable qualitative agreement with observed patterns of species distributions. However, modeled species diversity tends to be systematically lower than observed and, in many regions, is smaller than the number of potentially limiting nutrients. According to resource competition theory, the maximum number of coexisting species at equilibrium equals the number of limiting resources. By simulating phytoplankton communities in a chemostat model and in a global circulation model, we show here that a systematic underestimate of phytoplankton diversity may result from the standard modeling assumption of identical stoichiometry for the different phytoplankton types. Implementing stoichiometric variation among the different marine algae types in the models allows species to generate different resource supply niches via their own ecological impact. This is shown to increase the level of phytoplankton coexistence both in a chemostat model and in a global self‐assembling ecosystem model.
On the influence of solar wind conditions on the outer‐electron radiation belt
Authors: Kellerman A. C. , Shprits Y. Y.
Published: March 2012

The dependence of outer‐radiation belt electron fluxes upon solar wind velocity and density is investigated using the OMNI solar wind database and LANL‐GEO geosynchronous satellites for a period spanning over 20 years. Two dimensional probability distribution functions (PDF) of the flux‐solar wind velocity (Vsw) and flux‐solar wind density are calculated for electron energies in the 10's of keV to MeV range. The PDF's are normalized by Vsw and density and reveal new distinct relationships. Triangle‐shaped flux‐Vsw distributions become non‐linear PDF's, and the most probable flux increases with Vsw. The only significant saturation of fluxes observed with an increase in Vsw occurs for the lower energy electron fluxes (31.7 keV). The low energy fluxes exhibit a positive correlation with solar wind density, while mid‐to‐high energy electron fluxes are anti‐correlated with density. The maximum probability in the PDF's depends upon both velocity and density, the probability is higher for larger Vsw, and the maximum probability is larger for a given Vsw than for density. The results indicate that Vsw may be more important for determination of fluxes than density, especially for periods of high Vsw if suitable mixed delay times are applied to each solar wind parameter. It is shown that the source population of relativistic electrons of tens of keV exhibit a 2‐D normalized flux‐Vsw PDF, which is strikingly similar to that of the relativistic electrons. The findings support a model whereby solar wind velocity drives convective transport of source and seed electrons, to the inner magnetosphere, where local acceleration and subsequent radial diffusion is responsible for the enhanced fluxes. The results of this study also indicate that, statistically, ULF waves driven by dynamic pressure variations may act as a significant cause of loss for electrons in the 100's of keV to MeV range.
Magnetic signature of the lunar South Pole‐Aitken basin: Character, origin, and age
Authors: Purucker Michael E. , Head James W. , Wilson Lionel
Published: March 2012

A new magnetic map of the Moon, based on Lunar Prospector magnetometer observations, sheds light on the origin of the South Pole‐Aitken basin (SPA), the largest and oldest of the recognized lunar basins. A set of WNW‐trending linear to arcuate magnetic features, evident in both the radial and scalar observations, covers much of a 1000 km wide region centered on the NW portion of SPA. The source bodies are not at the surface because the magnetic features show no first‐order correspondence to any surface topographic or structural feature. Patchy mare basalts of possible late Imbrian‐age are emplaced within SPA and are inferred to have been emplaced through dikes, directly from mantle sources. We infer that the magnetic features represent dike swarms that served as feeders for these mare basalts, as evident from the location of the Thomson/Mare Ingenii, Van de Graaff, and Leeuwenhoek mare basalts on the two largest magnetic features in the region. Modeling suggests that the dike zone is between 25 and 50 km wide at the surface, and dike magnetization contrasts are in the range of 0.2 A/m. We theorize that the basaltic dikes were emplaced in the lunar crust when a long‐lived dynamo was active. Based on pressure, temperature, and stress conditions prevalent in the lunar crust, dikes are expected to be a dominantly subsurface phenomenon, consistent with the observations reported here.
Paleoceanography of the Atlantic‐Mediterranean exchange: Overview and first quantitative assessment of climatic forcing
Authors: Rogerson M. , Rohling E. J. , Bigg G. R. , Ramirez J.
Published: March 2012

The Mediterranean Sea provides a major route for heat and freshwater loss from the North Atlantic and thus is an important cause of the high density of Atlantic waters. In addition to the traditional view that loss of fresh water via the Mediterranean enhances the general salinity of the North Atlantic, and the interior of the eastern North Atlantic in particular, it should be noted that Mediterranean water outflowing at Gibraltar is in fact cooler than compensating inflowing water. The consequence is that the Mediterranean is also a region of heat loss from the Atlantic and contributes to its large‐scale cooling. Uniquely, this system can be understood physically via the constraints placed on it by a single hydraulic structure: the Gibraltar exchange. Here we review the existing knowledge about the physical structure of the Gibraltar exchange today and the evidential basis for arguments that it has been different in the past. Using a series of quantitative experiments, we then test prevailing concepts regarding the potential causes of these past changes. We find that (1) changes in the vertical position of the plume of Mediterranean water in the Atlantic are controlled by the vertical density structure of the Atlantic; (2) a prominent Early Holocene “contourite gap” within the Gulf of Cadiz is a response to reduced buoyancy loss in the eastern Mediterranean during the time of “sapropel 1” deposition; (3) changes in buoyancy loss from the Mediterranean during MIS3 caused changes in the bottom velocity field in the Gulf of Cadiz, but we note that the likely cause is reduced freshwater loss and not enhanced heat loss; and (4) strong exchange at Gibraltar during Atlantic freshening phases implies that the Gibraltar exchange provides a strong negative feedback to reduced Atlantic meridional overturning. Given the very counterintuitive way in which the Strait of Gibraltar system behaves, we recommend that without quantitative supporting work, qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust.
Pore scale mechanisms for enhanced vapor transport through partially saturated porous media
Authors: Shahraeeni Ebrahim , Or Dani
Published: March 2012

Recent theoretical and experimental studies of vapor transport through porous media question the existence and significance of vapor transport enhancement mechanisms postulated by Philip and de Vries. Several enhancement mechanisms were proposed to rectify shortcomings of continuum models and to reconcile discrepancies between predicted and observed vapor fluxes. The absence of direct experimental and theoretical confirmation of these commonly invoked pore scale mechanisms prompted alternate explanations considering the (often neglected) role of transport via capillary connected pathways. The objective of this work was to quantify the specific roles of liquid bridges and of local thermal and capillary gradients on vapor transport at the pore scale. We considered a mechanistic pore scale model of evaporation and condensation dynamics as a building block for quantifying vapor diffusion through partially saturated porous media. Simulations of vapor diffusion in the presence of isolated liquid phase bridges reveal that the so‐called enhanced vapor diffusion under isothermal conditions reflects a reduced gaseous diffusion path length. The presence of a thermal gradient may augment or hinder this effect depending on the direction of thermal relative to capillary gradients. As liquid phase saturation increases, capillary transport becomes significant and pore scale vapor enhancement is limited to low water contents as postulated by Philip and deVries. Calculations show that with assistance of a mild thermal gradient water vapor flux could be doubled relative to diffusion of an inert gas through the same system.
Tilt prior to explosions and the effect of topography on ultra‐long‐period seismic records at Fuego volcano, Guatemala
Authors: Lyons John J. , Waite Gregory P. , Ichihara Mie , Lees Jonathan M.
Published: March 2012

Ground tilt is measured from broadband seismic records prior to frequent explosions at Fuego volcano, Guatemala. We are able to resolve tilt beginning 20–30 minutes prior to explosions, followed by a rapid reversal in deformation coincident with explosion onsets. The tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of Fuego appears to affect the ultra‐long‐period signals. We account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite‐difference modeling. The results indicate a shallow spherical pressure source, and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography. The tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release.
Tricritical points attract workers in critical phenomena
Authors: Lubkin Gloria B.
Published: March 2012

Many workers in critical phenomena have become interested in the study of tricritical points; such a point is the intersection of three lines of critical points. With the introduction of the concept in 1970 by Robert B. Griffiths (Carnegie Mellon University), tricritical points have been identified in several materials. Griffiths feels that the topic offers the opportunity to study a phenomenon that is basically different and more complicated than ordinary critical points.
A new look at catalysis
Authors: Fischer Traugott E.
Published: March 2012

Our rapidly expanding demand for fuel has exceeded the amount now available to us with existing technology. In the long run, nonexhaustible sources of energy will have to be found and exploited. Solar and geothermal energy are being explored, as are breeder reactors, but none of these sources is expected to furnish a significant amount of energy within the next 50 years. Fission reactors are now providing nuclear energy, but by the end of the century they will still contribute less than one quarter of the total energy needed (see figure 1). How shall we provide the needed energy for the next 30 to 50 years?
Physicists and public policy: the “Forum” and the APS
Authors: Casper Barry M.
Published: March 2012

Since World War II physicists have played a prominent role in developing weapons policy and science policy for our country. This interaction with the government has been carried out largely behind the scenes, beyond the public view, by an elite group of established and renowned physicists working through such institutions as the President's Science Advisory Committee, the National Academy of Sciences and the JASON program of the Institute for Defense Analyses. By and large most physicists have had no role in this process. In the past the physics profession has not encouraged physicists to involve themselves in public policy. It has not provided reward and recognition for this kind of activity.
Nonlinear electrostatic shock waves in inhomogeneous plasmas with nonthermal electrons
Authors: Masood W. , Rizvi H. , Hasnain H.
Published: March 2012

Density inhomogeneity driven linear and nonlinear ion drift waves are investigated in a plasma consisting of heavy ions and non-thermal electrons. The dissipation is introduced in the system by the ion-neutral collision frequency. The nonlinear Korteweg de Vries Burgers (KdVB) and Burgers like equations are derived in the small amplitude limit, and the solution is obtained using the tangent hyperbolic method. It is found that the system under consideration admits rarefactive shock structures. It is observed that the ion-neutral collision frequency, nonthermal electron population, inverse density inhomogeneity scalelength, and the ambient magnetic field affect the propagation characteristics of the drift shock waves. The present study may be applicable in regions of space where nonthermal electrons and heavy ions have been observed.
Surface limitations to the electro-mechanical tuning range of negative dielectric anisotropy cholesteric liquid crystals
Authors: Bailey C. A. , Tondiglia V. T. , Natarajan L. V. , Bricker R. , Cui Y. , Yang D. K. , Bunning T. J.
Published: March 2012

Recent work on negative dielectric anisotropy cholesteric liquid crystals (CLCs) showed that externally applied dc voltages resulted in blue tuning of the reflection band position up to 20% of its original position. These results also showed that the observed shift in reflection band position was not caused by a direct interaction between the CLC and the applied voltage, but indirectly through electromechanical stresses that deformed the conductive glass substrates, in turn deforming the liquid crystal. In this work, the goal is to clarify that the major limiting factors on the tuning range limit result from the magnitude of the surface anchoring energy and surface induced hysteresis effects. An analytic solution for the tuning range limit and its dependence on the surface and bulk properties is derived that agrees well with the experimental data. Using this model, it was shown that tuning range limits in excess of 35% of the notch position should be expected with typically available alignment materials, and that with proper CLC/surface optimizations, values in the range of 75% are possible.
Onset of space charge limited current for field emission from a single sharp tip
Authors: Sun S. , Ang L. K.
Published: March 2012

A protrusive model of the Child-Langmuir (CL) law is proposed for non-uniform electron field emission from a sharp tip of either Lorentzian or hyperboloid shape. The model is expressed as Jc = μ×J1D at large electric field higher than a critical value Ec, and J1D is the classical one-dimensional CL law. It is found that the enhancement μ over the 1D CL law depends only on the calculated field enhancement factor (β) of the emitter and is independent of the work function and gap spacing. In particular, μ increases with β and it converges to a constant at β≫ 1 for a very sharp tip with small emission area.
Spontaneous soliton generation in the higher order Korteweg–de Vries equations on the half-line
Authors: Burde G. I.
Published: March 2012

Some new effects in the soliton dynamics governed by higher order Korteweg–de Vries (KdV) equations are discussed based on the exact explicit solutions of the equations on the positive half-line. The solutions describe the process of generation of a soliton that occurs without boundary forcing and on the steady state background: the boundary conditions remain constant and the initial distribution is a steady state solution of the problem. The time moment when the soliton generation starts is not determined by the parameters present in the problem formulation, the additional parameters imbedded into the solution are needed to determine that moment. The equations found capable of describing those effects are the integrable Sawada–Kotera equation and the KdV–Kaup–Kupershmidt (KdV-KK) equation which, albeit not proven to be integrable, possesses multi-soliton solutions.
Electronic properties of W-encapsulated Si cluster film on Si (100) substrates
Authors: Park S. J. , Uchida N. , Tada T. , Kanayama T.
Published: March 2012

We have fabricated thin films composed of W-encapsulated Si clusters (WSi10) on Si substrates and investigated their electronic properties using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). An epitaxial layer was observed at the interface with the Si substrate, and an amorphous layer was on top. The bulk plasmon of the WSi10 cluster film was measured and compared with those of crystalline Si (c-Si) and WSi2 films. We found similar plasmon energies in the epitaxial and amorphous layers of the WSi10 cluster film. The plasmon peak of the WSi10 cluster film is shifted to higher energy compared with that of c-Si, which is related to the electron density increase in the valence band. The Si-L23 absorption edge spectra show that the conduction-band density of states in Si was modified by hybridization between Si and W atoms.
Atomistic modeling of electron-phonon interaction and electron mobility in Si nanowires
Authors: Yamada Y. , Tsuchiya H. , Ogawa M.
Published: March 2012

We investigate the electron mobility of Si nanowires with 〈100〉, 〈110〉, and 〈111〉 crystalline orientations by considering atomistic electron-phonon interactions. We calculate the electron band structures based on a semiempirical sp3d5s* tight-binding approach and the phonon band structures based on the Keating potential model. Then, by combining the electron and phonon eigenstates based on Fermi’s golden rule and solving the linearized Boltzmann transport equation while considering Pauli’s exclusion principle, we evaluate the electron mobility of Si nanowires. As expected, phonons in Si nanowires are found to behave quite differently from phonons in bulk Si because of phonon confinement. However, electron mobility in Si nanowires is primarily governed by the variation in the electron effective mass rather than that of the phonon eigenstates. As a result, the 〈110〉-oriented Si nanowires showed the highest electron mobility, because they have the smallest electron effective mass among the three orientations.
Inertial confinement fusion implosions with imposed magnetic field compression using the OMEGA Laser
Authors: Hohenberger M. , Chang P.-Y. , Fiksel G. , Knauer J. P. , Betti R. , Marshall F. J. , Meyerhofer D. D. , Séguin F. H. , Petrasso R. D.
Published: March 2012

Experiments applying laser-driven magnetic-flux compression to inertial confinement fusion (ICF) targets to enhance the implosion performance are described. Spherical plastic (CH) targets filled with 10 atm of deuterium gas were imploded by the OMEGA Laser, compare Phys. Plasmas 18, 056703 or Phys. Plasmas 18, 056309. Before being imploded, the targets were immersed in an 80-kG magnetic seed field. Upon laser irradiation, the high implosion velocities and ionization of the target fill trapped the magnetic field inside the capsule, and it was amplified to tens of megagauss through flux compression. At such strong magnetic fields, the hot spot inside the spherical target was strongly magnetized, reducing the heat losses through electron confinement. The experimentally observed ion temperature was enhanced by 15%, and the neutron yield was increased by 30%, compared to nonmagnetized implosions [P. Y. Chang et al., Phys. Rev. Lett. 107, 035006 (2011)]. This represents the first experimental verification of performance enhancement resulting from embedding a strong magnetic field into an ICF capsule. Experimental data for the fuel-assembly performance and magnetic field are compared to numerical results from combining the 1-D hydrodynamics code LILAC with a 2-D magnetohydrodynamics postprocessor.
Laminar-turbulent separatrix in a boundary layer flow
Authors: Biau Damien
Published: March 2012

The transitional boundary layer flow over a flat plate is investigated. The boundary layer flow is known to develop unstable Tollmien-Schlichting waves above a critical value of the Reynolds number. However, it is also known that this transition can be observed for sub-critical Reynolds numbers. In that case, the basin of attraction of the laminar state coexists with the sustained turbulence. In this article, the trajectory on the separatrix between these two states is simulated. The state on the separatrix is independent from the initial condition and is dynamically connected to both the laminar flow and the turbulence. Such an edge state provides information regarding the basic features of the transitional flow. The solution takes the form of a low speed streak, flanked by two quasi-streamwise sinuous vortices. The shape of the streaks is close to that simulated with the linear optimal perturbation method. This solution is compared to existing results concerning streak breakdown. The simulations are realized in a temporal framework for a local boundary layer, with periodic boundary conditions in the streamwise direction. A dedicated model, based on a scale separation, is presented. The mean flow is a solution of the Prandtl boundary layer equations while the superposed small-scale fluctuations are a solution of the periodic Navier-Stokes equations. The model is validated with turbulent flow simulations and satisfactorily reproduces the physical characteristics of a boundary layer flow, especially in the outer region, where external fluid is entrained toward the boundary layer.
Influence of stress state and strain rate on structural amorphization in boron carbide
Authors: Ghosh Dipankar , Subhash Ghatu , Zheng James Q. , Halls Virginia
Published: March 2012

The reduced performance of B4C armor plate for impact against tungsten carbide penetrators beyond a critical velocity has been attributed in the literature to localized amorphization. However, it is unclear if this reduction in strength is a consequence of high pressure or high velocity. Despite numerous fundamental studies of B4C under indentation and impact, the roles of strain rate and pressure on amorphization have not been fully established. Toward this end, rate dependent uniaxial compressive strength and rate dependent indentation hardness, along with Raman spectroscopy, have been employed to show that high strain rate deformation alone (without concurrent high pressure) cannot trigger localized amorphization in B4C. Based on our analysis, it is also suggested that rate dependent indentation hardness can be used to reveal if a given B4C ceramic exhibits amorphization under high pressure and high strain rate loading. It is argued that when amorphization does occur in B4C, its dynamic inelastic properties degrade more severely than its static properties. Finally, it is suggested that dynamic hardness, in conjunction with static hardness, can be used as a measurable mechanical property to reveal the incidence of amorphization in B4C without the need for postmortem TEM or Raman spectroscopy analyses.
Time-resolved monitoring of cavitation activity in megasonic cleaning systems
Authors: Hauptmann M. , Brems S. , Struyf H. , Mertens P. , Heyns M. , De Gendt S. , Glorieux C.
Published: March 2012

The occurrence of acoustic cavitation in the cleaning liquid is a crucial precondition for the performance of megasonic cleaning systems. Hence, a fundamental understanding of the impact of different parameters of the megasonic process on cavitation activity is necessary. A setup capable of synchronously measuring sonoluminescence and acoustic emission originating from acoustically active bubbles is presented. The system also includes a high-speed-stroboscopic Schlieren imaging system to directly visualize the influence of cavitation activity on the Schlieren contrast and resolvable bubbles. This allows a thorough characterization of the mutual interaction of cavitation bubbles with the sound field and with each other. Results obtained during continuous sonication of argon-saturated water at various nominal power densities indicate that acoustic cavitation occurs in a cyclic manner, during which periods of stable and inertial cavitation activity alternate. The occurrence of higher and ultraharmonics in the acoustic emission spectra is characteristic for the stable cavitation state. The inertial cavitation state is characterized by a strong attenuation of the sound field, the explosive growth of bubbles and the occurrence of broadband components in the acoustic spectra. Both states can only be sustained at sufficiently high intensities of the sound field. At lower intensities, their occurrences are limited to short, random bursts. Cleaning activity can be linked to the cavitation activity through the measurement of particle removal on standard 200 mm silicon wafers. It is found that the particle removal efficiency is reduced, when a continuous state of cavitation activity ceases to exist.
Quasi-monochromatic pencil beam of laser-driven protons generated using a conical cavity target holder
Authors: Nishiuchi M. , Pirozhkov A. S. , Sakaki H. , Ogura K. , Zh. Esirkepov T. , Tanimoto T. , Kanasaki M. , Yogo A. , Hori T. , Sagisaka A. , Fukuda Y. , Matsumoto Y. , Entani S. , Sakai S. , Brenner C. M. , Neely D. , Yamauchi T. , Bulanov S. V. , Kondo K.
Published: March 2012

A 7 MeV proton beam collimated to 16 mrad containing more than 106 particles is experimentally demonstrated by focusing a 2 J, 60 fs pulse of a Ti:sapphire laser onto targets of different materials and thicknesses placed in a millimeter scale conical holder. The electric potential induced on the target holder by laser-driven electrons accelerates and dynamically controls a portion of a divergent quasi-thermal proton beam originated from the target, producing a quasi-monoenergetic “pencil” beam.
Development and characterization of very dense submillimetric gas jets for laser-plasma interaction
Authors: Sylla F. , Veltcheva M. , Kahaly S. , Flacco A. , Malka V.
Published: March 2012

We report on the characterization of recently developed submillimetric He gas jets with peak density higher than 1021 atoms/cm3 from cylindrical and slightly conical nozzles of throat diameter of less than 400 μm. Helium gas at pressure 300−400 bar has been developed for this purpose to compensate the nozzle throat diameter reduction that affects the output mass flow rate. The fast-switching electro-valve enables to operate the jet safely for multi-stage vacuum pump assembly. Such gaseous thin targets are particularly suitable for laser-plasma interaction studies in the unexplored near-critical regime.
The source of the Ti 3d defect state in the band gap of rutile titania (110) surfaces
Authors: Mitsuhara K. , Okumura H. , Visikovskiy A. , Takizawa M. , Kido Y.
Published: March 2012

The origin of the Ti 3d defect state seen in the band gap for reduced rutile TiO2(110) surfaces has been excitingly debated. The probable candidates are bridging O vacancies (VO) and Ti interstitials (Ti-int) condensed near the surfaces. The aim of this study is to give insights into the source of the gap state via photoelectron spectroscopy combined with ion scattering and elastic recoil detection analyses. We have made three important findings: (i) The intensity of the gap state observed is well correlated with the sheet resistance measured with a 4-point probe, inversely proportional to the density of Ti-int. (ii) Sputter/annealing cycles in ultrahigh vacuum (UHV) lead to efficient VO creation and condensation of Ti-int near the surface, while only annealing below 870 K in UHV condenses subsurface Ti-int but does not create VO significantly. (iii) The electronic charge to heal a VO is almost twice that to create an O adatom adsorbed on the 5-fold Ti row. The results obtained here indicate that both the VO and Ti-interstitials condensed near the surface region contribute to the gap state and the contribution to the gap state from the Ti-int becomes comparable to that from VO for the substrates with low sheet resistance less than ∼200 Ω/□.
Electron correlation contribution to the physisorption of CO on $\rm {Mg}{\rm F}_2$ Mg F2(110)
Authors: Hammerschmidt Lukas , Müller Carsten , Paulus Beate
Published: March 2012

We have performed CCSD(T), MP2, and DF-LMP2 calculations of the interaction energy of CO on the \documentclass[12pt]{minimal}\begin{document}$\rm {Mg}{\rm F}_2$\end{document} Mg F2(110) surface by applying the method of increments and an embedded cluster model. In addition, we performed periodic HF, B3LYP, and DF-LMP2 calculations and compare them to the cluster results. The incremental CCSD(T) calculations predict an interaction energy of Eint = −0.37 eV with a C-down orientation of CO above a \documentclass[12pt]{minimal}\begin{document}$\rm {Mg^{2+}}$\end{document} Mg 2+ ion at the surface with a basis set of VTZ quality. We find that electron correlation constitutes about 50% of the binding energy and a detailed evaluation of the increments shows that the largest contribution to the correlation energy originates from the CO interaction with the closest F ions on the second layer.
On the generation and disruption of a picosecond runaway electron beam during the breakdown of an atmospheric-pressure gas gap
Authors: Barengolts S. A. , Mesyats G. A. , Tsventoukh M. M. , Uimanov I. V.
Published: March 2012

The generation and disruption of the picosecond runaway electron beam in atmospheric pressure strongly overvolted gas gap is considered with emphasis on the runaway kinetics, the increase in emission current and plasma density, and beam instabilities. It has been shown that a few-nanosecond ten-kV prepulse gives rise to a streamer. Application of the main pulse (∼2 MV/ns) results in the runaway electron beam generation with the streamer electrons involved in the acceleration, and in increase of the electron emission from the cathode and the plasma density. At the high enough plasma density, fast beam instability disrupts the runaway electron beam.
Piezoelectric properties and temperature stability of Mn-doped Pb(Mg1/3Nb2/3)-PbZrO3-PbTiO3 textured ceramics
Authors: Yan Yongke , Cho Kyung-Hoon , Priya Shashank
Published: March 2012

In this letter, we report the electromechanical properties of textured 0.4Pb(Mg1/3Nb2/3)O3–0.25PbZrO3–0.35PbTiO3 (PMN-PZT) composition which has relatively high rhombohedral to tetragonal (R-T) transition temperature (TR-T of 160 °C) and Curie temperature (TC of 234 °C) and explore the effect of Mn-doping on this composition. It was found that MnO2-doped textured PMN-PZT ceramics with 5 vol. % BaTiO3 template (T-5BT) exhibited inferior temperature stability. The coupling factor (k31) of T-5BT ceramic started to degrade from 75 °C while the random counterpart showed a very stable tendency up to 180 °C. This degradation was associated with the “interface region” formed in the vicinity of BT template. MnO2 doped PMN-PZT ceramics textured with 3 vol. % BT and subsequently poled at 140 °C (T-3BT140) exhibited very stable and high k31 (>0.53) in a wide temperature range from room temperature to 130 °C through reduction in the interface region volume. Further, the T-3BT140 ceramic exhibited excellent hard and soft combinatory piezoelectric properties of d33 = 720 pC/N, k31 = 0.53, Qm = 403, tan δ = 0.3% which are very promising for high power and magnetoelectric applications.
Physical basis for constrained lattice density functional theory
Authors: Men Yumei , Zhang Xianren
Published: March 2012

To study nucleation phenomena in an open system, a constrained lattice density functional theory (LDFT) method has been developed before to identify the unstable directions of grand potential functional and to stabilize nuclei by imposing a suitable constraint. In this work, we answer several questions about the method on a fundamental level, and give a firmer basis for the constrained LDFT method. First, we demonstrate that the nucleus structure and free energy barrier from a volume constraint method are equivalent to those from a surface constraint method. Then, we show that for the critical nucleus, the constrained LDFT method in fact produces a bias-free solution for both the nucleus structure and nucleation barrier. Finally, we give a physical interpretation of the Lagrange multiplier in the constraint method, which provides the generalized force to stabilize a nucleus in an open system. The Lagrange multiplier is found to consist of two parts: part I of the constraint produces an effective pressure, and part II imposes a constraint to counteract the supersaturation.
Rippled nanocarbons from periodic arrangements of reordered bivacancies in graphene or nanotubes
Authors: Leyssale Jean-Marc , Vignoles Gérard L. , Villesuzanne Antoine
Published: March 2012

We report on various nanocarbons formed from a unique structural pattern containing two pentagons, three hexagons, and two heptagons, resulting from local rearrangements around a divacancy in pristine graphene, or nanotubes. This defect can be inserted in sheets or tubes either individually or as extended defect lines. Sheets or tubes containing only this defect as a pattern can also be obtained. These fully defective sheets, and most of the tubes, present a very pronounced rippled (wavy) structure and their energies are lower than other structures based on pentagons and heptagons published so far. Another particularity of these rippled carbon sheets is their ability to fold themselves into a two-dimensional porous network of interconnected tubes upon heat treatment as shown by hybrid Monte Carlo simulations. Finally, contrary to the common belief that pentagon/heptagon based structures are metallic, this work shows that this defect pattern should give rise to semimetallic conduction.
Effect of sputtered lanthanum hexaboride film thickness on field emission from metallic knife edge cathodes
Authors: Kirley M. P. , Novakovic B. , Sule N. , Weber M. J. , Knezevic I. , Booske J. H.
Published: March 2012

We report experiments and analysis of field emission from metallic knife-edge cathodes, which are sputter-coated with thin films of lanthanum hexaboride (LaB6), a low-work function material. The emission current is found to depend sensitively on the thickness of the LaB6 layer. We find that films thinner than 10 nm greatly enhance the emitted current. However, cathodes coated with a thicker layer of LaB6 are observed to emit less current than the uncoated metallic cathode. This result is unexpected due to the higher work function of the bare metal cathode. We show, based on numerical calculation of the electrostatic potential throughout the structure, that the external (LaB6/vacuum) barrier is reduced with respect to uncoated samples for both thin and thick coatings. However, this behavior is not exhibited at the internal (metal/LaB6) barrier. In thinly coated samples, electrons tunnel efficiently through both the internal and external barrier, resulting in current enhancement with respect to the uncoated case. In contrast, the thick internal barrier in thickly coated samples suppresses current below the value for uncoated samples in spite of the lowered external barrier. We argue that this coating thickness variation stems from a relatively low (no higher than 1018 cm−3) free carrier density in the sputtered polycrystalline LaB6.
Shearing radiative collapse with expansion and acceleration
Authors: Thirukkanesh S. , Rajah S. S. , Maharaj S. D.
Published: March 2012

We investigate the behaviour of a relativistic spherically symmetric radiative star with an accelerating, expanding and shearing interior matter distribution in the presence of anisotropic pressures. The junction condition can be written in standard form in three cases: linear, Bernoulli, and Riccati equations. We can integrate the boundary condition in each case and three classes of new solutions are generated. For particular choices of the metric we investigate the physical properties and consider the limiting behaviour for large values of time. The causal temperature can also be found explicitly.
Electromigration study of copper lines on steps prepared by a plasma-based etch process
Authors: Lin Chi-Chou , Kuo Yue
Published: March 2012

The electromigration phenomenon of the copper line etched with a plasma-based process over the SiNx step has been investigated. Two important factors, i.e., the dielectric topography and the stress temperature, were examined using the accelerated isothermal electromigration method. The activation energy of 0.73 eV to 0.89 eV indicates two possible mass transport pathways: interfacial and copper surface diffusions. The copper line on the SiNx step has a shorter lifetime and a smaller activation energy than the copper line on the flat surface has. For the former, voids were formed at the cusp region and perpendicular to the current flow direction. For the latter, voids were formed in series and parallel to the current flow direction. The “neck” structure at the cusp region, which is a result of the inappropriate etching condition, further decreased the lifetime and the activation energy. The lifetime of the “neck-free” copper line over the SiNx step was estimated to be 7.1 × 109 s under the high-speed IC operation condition. The thermal stress mismatch between the copper layer and TiW barrier layer as well as the underneath dielectric layer facilitated the void formation. The step effect on the lifetime was reduced when the test temperature was high because of the change of the local stress. In summary, the topography and the test temperature are critical factors for the copper line’s lifetime.
Highly transparent polymer light-emitting diode using modified aluminum-doped zinc oxide top electrode
Authors: Heum Park Sung , Hoon Lee Byoung , Moon Shin Jong , Jeong Se-Young , Song Suhee , Suh Hongsuk , Lee Kwanghee
Published: March 2012

We report a novel approach that leads to a significant improvement in the performance of transparent polymer light-emitting diodes (TPLEDs). By introducing a solution-based titanium oxide (TiOx) layer, we have demonstrated that the device performance of TPLEDs using aluminum-doped zinc oxide (AZO) top electrodes is enhanced. The TiOx layer lowers the energy barrier between the luminescent polymer and the AZO top electrode by modifying the WF of the top AZO electrodes. Moreover, the TiOx layer prevents the damage caused by UV radiation and by highly energetic ions generated during the AZO sputtering.
Photo-thermal polymerization of nanotube/polymer composites: Effects of load transfer and mechanical strength
Authors: Xu Peng , Loomis James , Panchapakesan Balaji
Published: March 2012

The authors report a method where in-situ photon assisted heating of multi-wall carbon nanotubes was utilized for enhanced polymerization of the nanotube/polydimethylsiloxane interface that resulted in significant load transfer and improved mechanical properties. Large Raman shifts (20 cm−1 wavenumbers) of the 2D bands were witnessed for near-infrared light polymerized samples, signifying increased load transfer to the nanotubes for up to ∼80% strains. An increase in elastic modulus of ∼130% for 1 wt. % composites is reported for photon assisted crosslinking.
Dielectric properties of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 giant permittivity ceramics at microwave frequencies
Authors: Li Lei , Zhang Wei , Chen Xiang Ming , Zhu Hai Yan
Published: March 2012

The dielectric properties of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 giant permittivity ceramics were evaluated at microwave frequencies using a modified resonant cavity method. In the frequency range between 3.4 and 9.5 GHz, the permittivities of the three ceramics were around 84.6, 43.9, and 40.4 at 20 °C and were nearly independent of frequency. The dielectric losses decreased and the Qf values increased significantly with increasing frequency. The temperature dependence of the dielectric properties was also investigated at about 6.02 GHz. With increasing temperature from −60 °C to 80 °C, the permittivities of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 ceramics varied nearly linearly, and the corresponding temperature coefficients of permittivity were −700, 175, and 164 ppm/ °C, respectively.
The influence of Mn substitution on the local structure of Na0.5Bi0.5TiO3 crystals: Increased ferroelectric ordering and coexisting octahedral tilts
Authors: Yao Jianjun , Ge Wenwei , Yan Li , Reynolds William T. , Li Jiefang , Viehland D. , Kiselev D. A. , Kholkin A. L. , Zhang Qinhui , Luo Haosu
Published: March 2012

The ferroelectric domain structure of pure Na1/2Bi1/2TiO3 (NBT) and 1 at.% Mn-doped NBT (Mn-NBT) crystals was investigated by piezoresponse force microscopy. The correlation length of the polar regions was found to increase upon Mn substitution. High resolution transmission electron microscopy revealed that the coherency of the lattice across the domain boundaries between polar regions was also enhanced. Selected area electron diffraction showed that Mn favored coexisting 1/2 (ooo) and 1/2 (ooe) oxygen octahedral tiltings, over only 1/2 (ooo) for pure NBT.
Piezoresponse force microscopy and vibrating sample magnetometer study of single phased Mn induced multiferroic BiFeO3 thin film
Authors: Gupta Surbhi , Sharma Anjali , Tomar Monika , Gupta Vinay , Pal Madhuparna , Guo Ruyan , Bhalla Amar
Published: March 2012

The effect of Bi excess (0 to 15%) and subsequently Mn doping (0 to 20%) on the structural, ferroelectric, and magnetic properties of BiFeO3 (BFO) thin films deposited by chemical solution deposition technique on low cost substrates are reported in the present work. No significant changes in crystallographic structure of BFO were observed with 5% excess Bi. With further increasing the Bi concentrations (> 10%), however, rhombohedral phase transformation occurs with appearance of the other Bi excess phases. Piezoresponse force microscopy studies show that the BFO thin film having 5% excess Bi and 10% Mn yields good ferroelectric behavior. The ferromagnetic behavior of 10% Mn doped BFO thin film is confirmed with vibrating sample magnetometer studies. The results indicate that the 10% Mn doped BFO thin films deposited by chemical solution deposition technique on low cost substrate exhibit very good multiferroic properties, suitable for magnetic memories applications.