bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-wavelength stability analysis of a helical vortex tube
Authors: Hattori Y. , Fukumoto Y.
Published: January 2009

The stability of a helical vortex tube is studied by short-wavelength stability analysis. The ratio ϵ of the core to the curvature radius is assumed to be small but finite. The base flow of the helical vortex tube is obtained by perturbation expansion which exhibits rotational and translational motions as a whole. It is shown that the helical vortex tube is subject to curvature instability, which was first found for the vortex ring. The growth rates of the curvature instability are obtained both analytically and numerically. The effects of torsion and rotation are investigated. Both torsion and rotation appear as second-order correction to the growth rate of the curvature instability which is first order in ϵ. They break symmetry so that the maximal growth rates are larger than the vortex ring of which all the parameters but torsion and rotation are the same.
Role of noncollinear magnetization for the first-order electric-dipole hyperpolarizability at the four-component Kohn–Sham density functional theory level
Authors: Bast Radovan , Saue Trond , Henriksson Johan , Norman Patrick
Published: January 2009

The quadratic response function has been derived and implemented at the adiabatic four-component Kohn–Sham density functional theory level with inclusion of noncollinear spin magnetization and gradient corrections in the exchange-correlation functional—a work that is an extension of our previous report where magnetization dependencies in the exchange-correlation functional were ignored [J. Henriksson, T. Saue, and P. Norman, J. Chem. Phys. 128, 024105 (2008)]. The electric-field induced second-harmonic generation experiments on CF3Cl and CF3Br are addressed by a determination of β¯(−2ω;ω,ω) for a wavelength of 694.3 nm, and the same property is also determined for CF3I. The relativistic effects on the static hyperpolarizability for the series of molecules amount to 1%, 5%, and 9%, respectively. At the experimental wavelength, the contributions to β due to the magnetization dependence in the exchange-correlation functional are negligible for CF3Cl and CF3Br and small for CF3I. The noticeable effect of magnetization in the latter case is attributed to a near two-photon resonance with the excited state 1 E3 (nonrelativistic notation). It is emphasized, however, that the effect of magnetization on β for CF3I is negligible both in comparison to the total relativistic correction as well as to the effects of electron correlation. It is concluded that, in calculations of hyperpolarizabilities under nonresonant conditions, the magnetization dependence in the exchange-correlation functional may be ignored.
Role of heat flow direction, monolayer film thickness, and periodicity in controlling thermal conductivity of a Si–Ge superlattice system
Authors: Samvedi Vikas , Tomar Vikas
Published: January 2009

Superlattices are considered one of the most promising material systems for nanotechnological applications in fields such as high figure of merit (ZT) thermoelectrics, microelectronics, and optoelectronics owing to the possibility that these materials could be tailored to obtain desired thermal properties. Factors that could be adjusted for tailoring the thermal conductivity of the superlattices include the monolayer film thickness, periodicity, heat flow direction, straining, and temperature of operation. In the presented study, nonequilibrium molecular dynamics (NEMD) simulations are performed to obtain an understanding of the effect of such factors on the thermal conductivity of Si–Ge superlattices at three different temperatures (400, 600, and 800 K). The NEMD simulations are performed using Tersoff bond-order potential. The thermal conductivity is found to increase with an increase in the number of periods as well as with the increase in the period thickness. The dependence of thermal conductivity on the direction of heat flow is found to be sensitive to the extent of acoustic mismatch at the interface (i.e., heat flowing from Si to Ge versus heat flowing from Ge to Si in a single period). Superlattices with Ge–Si interfaces (heat flows from Ge monolayer to Si monolayer in a period) are found to have lower thermal conductivity than superlattices with Si–Ge interfaces (heat flows from Si monolayer to Ge monolayer in a period). The superlattices thermal conduction, therefore, can be considered to have a characteristic somewhat similar to a thermal diode. Both compressive and tensile strains are observed to be an important factor in tailoring the thermal conductivity of the analyzed superlattices. Particularly, straining can help in reducing the thermal conductivity. The influence of straining is found to increase with increasing period thickness and periodicity.
Sputter yields of single- and polycrystalline metals for application in focused ion beam technology
Authors: Stark Yuliya , Frömter Robert , Stickler Daniel , Oepen Hans Peter
Published: January 2009

In this paper we present results from quantitative sputter yield measurements for bombardment with 30 keV Ga+ ions, which are commonly used in focused ion beam systems. The sputter yields were obtained from measurements of the removed volume. We describe a technique that allows the precise geometric measurement of the material removed by multipass milling. Yield data for polycrystalline Permalloy and cobalt are measured as well as data for silicon and gallium arsenide. For iron and tungsten single crystals, the dependence of the sputter yield on the crystalline orientation has been investigated. Distinctive minima and maxima of the yield are observed as a function of the incidence angle, and vary up to a factor of 10. The positions of the minima coincide with low-Miller-index crystalline orientations and can thus be attributed to channeling of the Ga+ ions. A comparison with simulation results for amorphous materials shows that yield values from simulation are only applicable for those orientations without channeling.
Ion-size effect at the surface of a silica hydrosol
Authors: Tikhonov Aleksey M.
Published: January 2009

Using synchrotron x-ray reflectivity, I studied the ion-size effect for alkali ions (Na+, K+, Rb+, and Cs+), with densities as high as 4×1018–7×1018 m−2, suspended above the surface of a colloidal solution of silica nanoparticles in the field generated by the surface electric-double layer. I found that large alkali ions preferentially accumulate and replace smaller ones at the surface of the hydrosol, a result qualitatively agreeing with the dependence of the Kharkats–Ulstrup single-ion electrostatic free energy on the ion’s radius.
Engineering aspects of magnetohydrodynamics
Authors: Sutton George W.
Published: January 2009

The progress, or lack of progress in some cases, which is being made toward the practical utilization of magnetohydrodynamics was the subject of an all-inclusive meeting with the rather lengthy title of “Symposium on the Engineering Aspects of Magnetohydrodynamics”. The gathering, which was sponsored by the Basic Sciences Committee of the American Institute of Electrical Engineers, had the advantage of using the auditorium of the University Museum of the University of Pennsylvania. This auditorium was large, the seats were comfortable, free parking was available, and the acoustics and visibility were far superior to that of many recent meetings this writer has attended. The arrangements committee, under R. M. Showers, is to be congratulated. We hope this auditorium is used more often in the future.
The Governmental Science Administrator
Authors: Seitz Frederick
Published: January 2009

Like so many other physicists, I emerged into the postwar climate of our country in the fall of 1945, having spent nearly six years on work that bordered more nearly on applied than pure science. The first part of the war had been devoted to ordnance and ballistics, the intermediate part to the development of radar components, such as diodes and oscilloscope screens, and the last part to the Plutonium Project at Chicago—all climaxed by a number of months as one of the scientific intelligence officers in SHAEF. With my colleagues at the Carnegie Institute of Technology, plans were laid for research in the coming period. We hoped that we could find the funds to match our dreams even modestly.
2nd Symposium on the engineering aspects of magnetohydrodynamics
Authors: Sutton G. W. , Gloersen Per
Published: January 2009

During the past few years, plasma physics and magnetohydrodynamics have been the topics of many scientific meetings. In these meetings, the emphasis was placed mostly on the physical principles and scientific accomplishment with little discussion of the potential applications. For this reason, the Basic Sciences Committee of the American Institute of Electrical Engineers organized a meeting on the engineering aspects of magnetohydrodynamics last year with sessions on several different subjects. These helped to give to the audience a variegated view of the potential applications of MHD and the progress which is being made in each field. Last year's meeting attracted an audience of about four hundred.
New developments in high-magnetic field research
Authors: Bitter Francis
Published: January 2009

Three hundred and fifty years ago, long before Newton was born, at a time when the motions of freely falling bodies were first being carefully observed and analyzed, William Gilbert, the physician of Queen Elizabeth I, was collecting facts about magnets. These he published in his famous book De Magnete. Magnets were, at the time, thought of as curios having occult and magical properties. These Gilbert reviewed, but in addition he performed a most extraordinary feat of synthesis. He collected data on the orientation of compass needles carried around the surface of the earth earth by mariners and showed that the enormously varied observations could all be described by means of one basic assumption, that the earth itself was a magnet.
Plasma physics symposium
Authors: Morey D. R.
Published: January 2009

Properties of a plasma are described by parameters such as degree of ionization, conductivity, shielding length, and plasma frequency, as was learned by the more than 200 participants at the Symposium on Plasma Physics which was organized by the New York State Section of the American Physical Society and held last spring in Tarrytown, N.Y. The meeting itself, in terms of properties, turned out to have sparkle, interaction, idea frequency, and questionanswer density.
An independent-particle model of scientific salaries
Authors: Green Alex E. S.
Published: January 2009

During recent years there has been a remarkable correlation or explanation of a wide variety of experimental nuclear data in terms of the socalled independent-particle model (IPM) of the nucleus. This model, which encompasses both the shell model and the optical model, views a nucleon which interacts with the many other nucleons in a complex nucleus as interacting with the nucleus as a whole via an IPM potential. For nucleon-nuclear interactions the potentials which have been inferred by phenomenologists from a vast amount of data have the general form shown in Fig. 1. Here the vertical scale represents the IPM potential of a nucleon interacting with the nucleus as a whole and the horizontal scale represents the radial distance (r) from the center of the nucleus. The curves shown represent IPM potentials used to represent typical nuclei with mass numbers A = 50, 100, 150, 200, and 250. A convenient and frequently used form function for representing nuclear potentials is the Saxon potential f(r) = {1+exp[(r−R)/d]}−1, where R represents the radial distance to the point at which the potential reduces in magnitude to 0.5 of its central value and d is a parameter which determines the diffuseness or surface thickness of the potential. Experimental data with beams of deuterons, alpha particles, other nuclei, as well as pions and K mesons, all scattered by heavy nuclei, seem to be accounted for quite readily in terms of the optical-model form of the IPM. The success of the IPM seems so broad that one might be tempted to apply it to a great variety of physical phenomena and even sociological phenomena.
Waiting for Mr. Know-It-All or scientific information tools we could have now
Authors: Way K. , Gove N. B. , van Lieshout R.
Published: January 2009

The New York Times and Senator Humphrey have been talking about the plight of the poor scientists who find it easier to measure a quantity than to locate the results of earlier experimental work in the library. But instead of making a straightforward attack on the problems of handling the data explosion, everyone seems to be standing by for the day when that popular robot, Mr. Know-It-All, will roll himself into the laboratory and speak as follows:
1961 Midwest Solid State Conference
Authors: Phelps Fred T.
Published: January 2009

Increased interest in the Midwest Solid-State Conference was apparent at the ninth annual meeting held October 20–21 at the Argonne National Laboratory. One hundred and seventy scientists representing 29 institutions took part in the program, which consisted of a laboratory open house, followed by a banquet on Friday and the presentation of 23 contributed papers on Saturday. There were two invited papers: an after-banquet address by Charles Slichter of the University of Illinois and an after-luncheon talk by John Hulm of the Westinghouse Research Laboratory.
Objective tests—All bad?
Authors: Fornoff Frank J.
Published: January 2009

I am one of those people whose identity is hidden by the letters—ETS—which Dr. Banesh Hoffmann has attacked with such determination. My responsibility, shared directly with two colleagues and indirectly with many more, is the preparation of science tests. I have a doctorate in chemistry from the Ohio State University, and I spent a postdoctoral year at the University of California. I have been on the faculties of three good universities, Lehigh, Kansas State, and Rutgers, but I must admit that there are many things that I do not know. Contrary to Dr. Hoffmann's suspicion, I believe that my colleagues and I do know a few things.
The Earth as a man-controlled space ship
Authors: Froman Darol
Published: January 2009

I am very happy to have the opportunity tonight to express the pleasure of the Los Alamos Scientific Laboratory in cosponsoring this meeting on Plasma Physics. The fine facilities and cooperation of the Air Force and the excellent accommodations in this hotel certainty constitute a fitting environment for the scholarly papers and discussion I heard today.
Science on the march
Authors: Seitz Frederick
Published: January 2009

The various civilizations of mankind known to us are characterized both by remarkable similarities, stemming from the common problems of humanity in all environments, and by quite remarkable differences, related to differences in culture and environment. The differences may be of secondary importance, or they may be so important that they determine the fate of a given civilization in a major way.
Roundabout route to understanding
Authors: Brown F. C.
Published: January 2009

In 1905 the author became interested in selenium cells because of the unusual challenge to understanding which they presented. One of the bestknown selenium cells of that time was the Giltay Cell—a thin soapstone plate around which two parallel wires were wound, with selenium melted and crystallized between the wire electrodes. There were other types, but all had the same remarkable capacity to increase in electrical conductivity when exposed to light. By comparison, a metal, such as a blackened platinum foil, decreased in conductivity when exposed to light. Because of the light sensitivity, selenium cells had proved useful in several kinds of machines and instruments; for example, in the Optiphone and phonopticon, which could enable the blind to read the printed page.
Wiggleworm physics
Authors: Rothstein Jerome
Published: January 2009

WE know that our picture of the universe is very strongly influenced by our means of perception. Basically, we are eye-hand-coordinated animals. Perhaps our sensory and psychological apparatus prejudices us in favor of some particular picture of the universe, when in reality the picture is warped by being filtered through our particular sensory and nervous equipment. This is, of course, a very old philosophical problem, and one can say that the use of measuring apparatus sensitive to things we cannot observe directly would go a long way toward removing this kind of prejudice. The suspicion remains, however, that intelligent beings very differently endowed than we are might come up with a very different picture of the world. For example, the space-time of such a creature might have a dimensionality different from ours, or other concepts might be basic and lead to a whole different structure from the one we have so painfully evolved over the centuries—often by stripping away prejudices.
The interdisciplinary laboratory program in materials sciences
Authors: Yost Charles F. , Vicars Earl C.
Published: January 2009

IT seems particularly timely to offer a broad discussion of the background and implementation of the Interdisciplinary Materials Sciences Program of the Advanced Research Projects Agency. It is one which is unique in many respects and has attracted considerable interest within the scientific community. It is revolutionary in character, and there have been numerous inquiries concerning the program from the agencies of the government as well as from industry, research institutes, and university personnel engaged in or associated with materials research. Our purpose is to present some of the fundamental aspects of the program and to provide an insight from which the philosophy, objectives, and implementation will become a coherent pattern.
Shear induced structural ordering of a model metallic glass
Authors: Mokshin Anatolii V. , Barrat Jean-Louis
Published: January 2009

We report results of nonequilibrium molecular dynamics simulations of a one-component glassy system under the influence of a shear flow, with the aim of investigating shear-induced ordering of this system. In spite of the very low temperature, the system transforms into a strained crystalline state through well defined nucleation events. Various characteristics of the observed ordering at different strain rates and temperatures are discussed. We also define and discuss the transition rates.
Unbiased bases (Hadamards) for six-level systems: Four ways from Fourier
Authors: Skinner A. J. , Newell V. A. , Sanchez R.
Published: January 2009

In quantum mechanics some properties are maximally incompatible, such as the position and momentum of a particle or the vertical and horizontal projections of a two-level spin. Given any definite state of one property, the other property is completely random or unbiased. For N-level systems, the six-level ones are the smallest for which a tomographically efficient set of N+1 mutually unbiased bases has not been found. To facilitate the search, we numerically extend the classification of unbiased bases, or Hadamards, by incrementally adjusting relative phases in a standard basis. We consider the nonunitarity caused by small adjustments with a second order Taylor expansion and choose incremental steps within the four-dimensional null space of the curvature. In this way, we prescribe a numerical integration of a four-parameter set of Hadamards of order of 6.
Strongly interacting bumps for the Schrödinger–Newton equations
Authors: Wei Juncheng , Winter Matthias
Published: January 2009

We study concentrated bound states of the Schrödinger–Newton equations h2Δψ−E(x)ψ+Uψ=0, ψ>0, x∊R3; ΔU+12|ψ|2=0, x∊R3; ψ(x)→0, U(x)→0 as |x|→∞. Moroz et al. [“An analytical approach to the Schrödinger-Newton equations,” Nonlinearity 12, 201 (1999)] proved the existence and uniqueness of ground states of Δψ−ψ+Uψ=0, ψ>0, x∊R3; ΔU+12|ψ|2=0, x∊R3; ψ(x)→0, U(x)→0 as |x|→∞. We first prove that the linearized operator around the unique ground state radial solution (ψ0,U0) with ψ0(r)=(Ae−r/r)(1+o(1)) as r=|x|→∞, U0(r)=(B/r)(1+o(1)) as r=|x|→∞ for some A,B>0 has a kernel whose dimension is exactly 3 (corresponding to the translational modes). Using this result we further show that if for some positive integer K the points Pi∊R3, i=1,2…,K, with Pi≠Pj for i≠j are all local minimum or local maximum or nondegenerate critical points of E(P), then for h small enough there exist solutions of the Schrödinger–Newton equations with K bumps which concentrate at Pi. We also prove that given a local maximum point P0 of E(P) there exists a solution with K bumps which all concentrate at P0 and whose distances to P0 are at least O(h1/3).
George B. Pegram: Retiring Treasurer of the American Physical Society
Authors: Darrow K. K.
Published: January 2009

This is the last meeting at which George Braxton Pegram is the Treasurer of the American Physical Society. This Society as we know it is largely his own creation. When he entered the Society fifty-eight years ago at its second meeting, it had fewer than one hundred members. When he was first elected Treasurer thirty-eight years ago, the Society was still less than one-tenth as large as it is today. The volume of its publications was an even smaller fraction of their present volume, and nobody could have dared to say that our Physical Review is the most important journal of physics in the world, a claim that now might not appear unreasonable. Its meetings were so small that simultaneous sessions were unknown; now there are six or seven at a time. For all of these thirty-eight years George Pegram has served the Society without a break, by far the longest term of service ever accorded to us by anyone. Years of prosperity and depression, years of deflation and inflation, and now for a decade of unremitting expansion of physics and of the Society,—through all this time George Pegram has maintained the finances of the Society, and only twice in all this time have the vicissitudes of the years required an appeal for brief and transient help to surmount a temporary crisis. When Pegram began to be Treasurer he was at an age when most men are working full time in their own profession, and he himself, according to all that we hear, was working half again as hard as most men. He has continued to be Treasurer up to an age when most men want nothing but rest and ease, and when his own physician has long been urging him to relax and quit. And yet, immense as has been his service as Treasurer, it is but a small part of his total service. For longer than most of us can remember George Pegram has been the guide and the elder statesman of the Society, always concerning himself with everything that concerned the Society, always foresighted and always vigilant. Those who will be officers hereafter will feel like children who have lost the guidance of the wise and kindly father on whom they have always relied to lead them, to advise them, to keep them out of trouble, and to help them out of such troubles as they incurred on their own. Of course we count on the continuance of his good counsel. The American Physical Society will never be able to measure what it owes to George Braxton Pegram. He has been the Society incarnate. There will never be another like him.
The positive and negative Camassa–Holm-γ hierarchies, zero curvature representations, bi-Hamiltonian structures, and algebro-geometric solutions
Authors: Fan Engui
Published: January 2009

In this paper, we extend the Camassa–Holm-γ (CH-γ) equation to two different hierarchies of nonlinear evolution equations by resorting to two Lenard recursion sequences. One is of positive order CH-γ hierarchy including a Harry–Dym-type equation, while the other is of negative order CH-γ hierarchy of integrodifferential equations with nonzero integration constants including the CH-γ equation. We provide the zero curvature representations for both hierarchies by solving a key matrix equation. Moreover, the Lenard sequences are used to construct a Lax matrix that satisfies a stationary zero curvature equation, which enables us to establish bi-Hamiltonian structures for both hierarchies by applying trace identity. In addition, the Lenard sequence and Lax pair are used to systematically derive the Its–Matveev trace formula and the Dubrovin-type equations associated with the CH-γ equation. The hyperelliptic curve and Abel–Jacobi coordinates are then introduced to linearize the associated flow, from which the algebro-geometric solutions to the CH-γ equation are constructed by using standard Jacobi inversion technique.
Silicon carbide
Authors: O'Connor J. R.
Published: January 2009

There exists a need, especially in the cases of some military applications, for a stable, high-temperature semiconductor material. Active and passive devices fabricated from such a material could operate in a high-temperature ambient and simultaneously resist radiation damage. The most useful semiconductor materials, to date, have been the Group IV elements, germanium and silicon. Devices made from silicon, however, cannot be efficiently operated at temperatures in excess of 200 °C. Logically, one should next consider diamond, the cubic modification of carbon. At this time, however, the technological problems that one would encounter with diamond are formidable.
Physics in Israel
Authors: Jacobs Stephen F.
Published: January 2009

There are no liberal arts colleges in Israel. This fact became evident to me early in a recent visit to Israel. I was curious to learn how Israel's educational system differs from the American system, and what success Israel is having in this area. There are three institutions of higher learning which offer training in physics; one in or near each of the three major cities (see map).
Reactor physics
Authors: Okrent David
Published: January 2009

As I perused several back issues of Physics Today to get some feeling for how symposia were being reported, it soon became obvious that there just is no other conference like the Geneva “Atoms for Peace” Conference. More than 2000 papers were submitted for the proceedings. 600 of which were covered in oral presentations during the nearly 80 sessions held over a two-week period. The number of topics treated far exceeded the number of sessions, and the attendees exceeded the speakers by approximately 10:1, at least in registration.
Mechanical properties of nonmetallic solids
Authors: Hsiao C. C.
Published: January 2009

Early in April 1958 an opportunity developed for the writer to attend the Conference on The Mechanical Properties of Nonmetallic Solids sponsored by the International Union of Pure and Applied Physics and the Academy of Sciences of the USSR on May 19–26 in Leningrad, USSR. A letter of invitation from Academician A. F. Joffe who was the chairman of the Conference Organization Committee was received. In the letter it was stated that three physical problems would be discussed. They were: (1) defects in crystalline and amorphous solids, (2) plasticity of crystals, and (3) mechanical strength of solids. It was also indicated that the number of participants, as well as the number of reports at the conference, would be limited. The conference would chiefly proceed with the discussion of the reports.
Sources of experimental errors in the observation of nanoscale magnetism
Authors: Garcia M. A. , Fernandez Pinel E. , de la Venta J. , Quesada A. , Bouzas V. , Fernández J. F. , Romero J. J. , Martín González M. S. , Costa-Krämer J. L.
Published: January 2009

It has been recently reported that some nonmagnetic materials in bulk state exhibit magnetic behavior at the nanoscale due to surface and size effects. The experimental observation of these effects is based on the measurement of very small magnetic signals. Thus, some spurious effects that are not critical for bulk materials with large magnetic signals may become important when measuring small signals (typically below 10−4emu). Here, we summarize some sources of these small magnetic signals that should be considered when studying this new nanomagnetism.
Magnesium oxide nanowires synthesized by pulsed liquid-injection metal organic chemical vapor deposition
Authors: Lai Y. F. , Chaudouët P. , Charlot F. , Matko I. , Dubourdieu C.
Published: January 2009

Vertically aligned MgO nanowires were epitaxially grown at 600 °C on Au-coated MgO (001) substrates by metal organic chemical vapor deposition using Mg(tmhd)2 precursor. Discrete Au particles were embedded in the wires and distributed along the central axis. Scanning and transmission electron microscopy show that the orientation, diameter, and length of the wires strongly depend on the processing conditions such as oxygen partial pressure and reactive species flow rate as well as the starting Au thickness. Diameters down to 15–20 nm were obtained. The growth can be switched from vertical to horizontal wires by decreasing the period at which reactants are supplied.
Fatigue response of a PZT multilayer actuator under high-field electric cycling with mechanical preload
Authors: Wang Hong , Wereszczak Andrew A. , Lin Hua-Tay
Published: January 2009

An electric fatigue test system was developed for evaluating the reliability of piezoelectric actuators with a mechanical loading capability. Fatigue responses of a lead zirconate titanate (PZT) multilayer actuator with a platethrough electrode configuration were studied under an electric field (1.7 times that of the coercive field of PZT material) and a concurrent mechanical preload (30.0 MPa). A total of 109 cycles was carried out. Variations in charge density and mechanical strain under the high electric field and constant mechanical loads were observed during the fatigue test. The dc and the first harmonic (at 10 Hz) dielectric and piezoelectric coefficients were subsequently characterized using fast Fourier transformation. Both the dielectric and the piezoelectric coefficients exhibited a monotonic decrease prior to 2.86×108 cycles under certain preloading conditions, and then fluctuated. Both the dielectric loss tangent and the piezoelectric loss tangent also fluctuated after a decrease. The results are interpreted and discussed with respect to domain wall activities, microdefects, and other anomalies.
Coherent terahertz radiation from interaction of electron beam with rippled density plasma
Authors: Pathak Vishwa Bandhu , Dahiya Deepak , Tripathi V. K.
Published: January 2009

An alternative free electron laser concept for producing coherent terahertz radiation is investigated. A weakly relativistic electron beam impinged on a rippled underdense plasma, at an angle to the ripple wave vector, interacts with a seed terahertz signal to produce a space charge beam mode. The oscillatory electron velocity due to the beam mode beats with the density ripple to generate a coherent electromagnetic wave in the terahertz frequency range in forward direction. For an electron beam with 5 MW power, one can obtain ∼40 kW power at 1 THz frequency.
Impurity control in Co-doped ZnO films through modifying cooling atmosphere
Authors: Liu Yinglin , MacManus-Driscoll Judith L.
Published: January 2009

In order to understand the role of impurities in Co-doped ZnO, while at the same time minimizing the possibility of Co nanocluster formation, Zn1−xCoxO films were grown under relatively oxidizing conditions and then cooled under either N2 or air. Up to the highest doping level x=0.04, after cooling in N2 no measurable second phases were found whereas after cooling in air, ZnCo2O4 (nonferromagnetic at room temperature) appeared even for the lowest doping level x=0.0015. In addition, stronger ferromagnetism was observed in the N2 cooled samples, indicating an intrinsic origin to the ferromagnetism in Zn1−xCoxO.
A flyer-impact technique for measuring viscosity of metal under shock compression
Authors: Li Yilei , Liu Fusheng , Ma Xiaojuan , Li Yinglei , Yu Ming , Zhang Jichun , Jing Fuqian
Published: January 2009

A flyer-impact technique, different from the explosive method of [Sakharov et al., Sov. Phys. Dokl. 9, 1091 (1965)], is developed to investigate the viscosity of shocked metals. The shock wave with a front of sinusoidal perturbation is induced by the sinusoidal profile of the impact surface of the sample by use of two-stage light-gas gun. The oscillatory damping process of the perturbation amplitude is monitored by electric pins. Two damping curves (perturbation amplitude relative to its initial value versus propagated distance relative to the wavelength of sinusoidal perturbation) of aluminum are determined at 78 and 101 GPa. The effective shear viscosity coefficients are deduced to be about 1300 and 800 Pa s based on the Miller and Ahrens analytic solution for viscous fluid.
Normal and reversed tunable magnetoresistance in a NiOx/p-doped silicon diode
Authors: Céspedes Oscar , Viret Michel
Published: January 2009

Nonstoichiometric NiOx thin films fabricated by heating in air nickel thin films sputtered on p-doped silicon substrates show a superparamagnetic magnetization and frustrated magnetism with transition temperatures of 200–300 K. Transport measurements across the magnetic/semiconductor bilayer have a rectifying I-V and voltage dependent magnetoresistance, with maximum ratios at 77 K and 2 T of 70% and −17%. The effect is explained in terms of field dependent polarization in granular NiOx and highly efficient spin filtering/injection.
Spectral and angular distribution of Rayleigh scattering from plasmon-coupled nanohole chains
Authors: Alaverdyan Yury , Hempe Eva-Maria , Vamivakas A. Nick , E Haibo , Maier Stefan A. , Atatüre Mete
Published: January 2009

We experimentally investigate the optical properties of nanohole chains in 20nm gold films by measuring the far-field radiation patterns and scattering spectra using both white light and single-frequency laser excitations. We observe intensity enhancement in the frequency spectrum originating from resonantly coupled nanohole excitations via thin film surface plasmon polaritons. However, the angular distribution of the far-field pattern is identical to that of a chain of coherently radiating point dipoles both on and off the resonance frequency. We highlight a potential of the k-space imaging technique for studying far-field properties of ordered nanoscale structures.
Carrier transport properties in the vicinity of single self-assembled quantum dots determined by low-voltage cathodoluminescence imaging
Authors: Dupuy E. , Morris D. , Pauc N. , Aimez V. , Gendry M. , Drouin D.
Published: January 2009

We propose a method to investigate the carrier transport properties in the ultrathin wetting layer of a self-assembled quantum dot (QD) structure using low-voltage cathodoluminescence (CL) imaging. Measurements are performed on diluted InAs/InP QDs in order to spatially resolve them on CL images at temperature ranging from 5 to 300 K. The mean ambipolar diffusion length extracted from CL intensity profiles across different isolated bright spots is about 300 nm at 300 K. This gives an ambipolar carrier mobility of about 110 cm2/(V s). Temperature investigation reveals a maximum diffusion length near 120 K.
Loss of PKCλ/ι impairs Th2 establishment and allergic airway inflammation in vivo
Authors: Yang Jun-Qi , Leitges Michael , Duran Angeles , Diaz-Meco Maria T. , Moscat Jorge
Published: January 2009

The differentiation of T cells along different lineages is central to the control of immunity. Here we have used a conditional gene knockout system to delete
PKC
λ/ι selectively in activated T cells. With this system we have demonstrated that PKCλ/ι is necessary for T-helper cell (Th2) cytokine production and optimal T-cell proliferation and allergic airway inflammation in vivo. Our data demonstrate that the activation of the transcription factors nuclear factor of activated T cells and NF-κB is impaired in PKCλ/ι-deficient activated T cells. In addition, we present genetic knockout evidence in ex vivo experiments with primary T cells that PKCλ/ι is critical for the control of cell polarity during T-cell activation. Therefore PKCλ/ι emerges as a critical regulator of Th 2 activation.
Constitutional hypomorphic telomerase mutations in patients with acute myeloid leukemia
Authors: Calado Rodrigo T. , Regal Joshua A. , Hills Mark , Yewdell William T. , Dalmazzo Leandro F. , Zago Marco A. , Lansdorp Peter M. , Hogge Donna , Chanock Stephen J. , Estey Elihu H. , Falcão Roberto P. , Young Neal S.
Published: January 2009

Loss-of-function mutations in telomerase complex genes can cause bone marrow failure, dyskeratosis congenita, and acquired aplastic anemia, both diseases that predispose to acute myeloid leukemia. Loss of telomerase function produces short telomeres, potentially resulting in chromosome recombination, end-to-end fusion, and recognition as damaged DNA. We investigated whether mutations in telomerase genes also occur in acute myeloid leukemia. We screened bone marrow samples from 133 consecutive patients with acute myeloid leukemia and 198 controls for variations in
TERT
and
TERC
genes. An additional 89 patients from a second cohort, selected based on cytogenetic status, and 528 controls were further examined for mutations. A third cohort of 372 patients and 384 controls were specifically tested for one
TERT
gene variant. In the first cohort, 11 patients carried missense
TERT
gene variants that were not present in controls (
P
< 0.0001); in the second cohort,
TERT
mutations were associated with trisomy 8 and inversion 16. Mutation germ-line origin was demonstrated in 5 patients from whom other tissues were available. Analysis of all 3 cohorts (
n
= 594) for the most common gene variant (A1062T) indicated a prevalence 3 times higher in patients than in controls (
n
= 1,110;
P
= 0.0009). Introduction of
TERT
mutants into telomerase-deficient cells resulted in loss of enzymatic activity by haploinsufficiency. Inherited mutations in
TERT
that reduce telomerase activity are risk factors for acute myeloid leukemia. We propose that short and dysfunctional telomeres limit normal stem cell proliferation and predispose for leukemia by selection of stem cells with defective DNA damage responses that are prone to genome instability.
Using the Four-Questions Technique to Enhance Learning
Authors: Dietz-Uhler Beth , Lanter Jason R.
Published: January 2009

To assess the effect of a 4-question reflective learning technique on quiz performance, students engaged in an interactive activity, responded to 4 questions to encourage analyzing (i.e., what was learned), reflecting (i.e., why it is important), relating (i.e., how the material related to their personal lives), and generating (i.e., what questions they now have about the material), and took a quiz on the studied material. Quiz performance was better for students who responded to the 4 questions prior to the quiz than for those who did so after the quiz. Students also perceived the 4-question technique to be enjoyable and successful in meeting its objectives. We discuss how this simple technique effectively promotes students' understanding and memory.
Communicative gestures and vocabulary development in 36‐month‐old children with Down's syndrome
Authors: Zampini Laura , D'Odorico Laura
Published: January 2009

Background: Children with Down's syndrome seem to show a preference for the use of gestural rather than vocal productions during the first stages of language development. This ‘gestural advantage’ could actually be due to a developmental strategy used to compensate the difficulties in verbal production that are typical of language development in this population.

Aims: The principal aim of the present study is to analyse the relationships between gesture production and vocabulary development in children with Down's syndrome, verifying the existence of any similarities with the processes that characterize typical development.

Methods & Procedures: Twenty 36‐month‐old Italian children with Down's syndrome participated in the study. Each child's spontaneous gestural and vocal production was assessed during a mother‐and‐child play session. Their psychomotor development was evaluated using the Brunet–Lézine Scale of Infant Development; and their vocabulary size, with regards both production and comprehension, was assessed using the Italian version of the MacArthur Communicative Development Inventory (CDI). Following a longitudinal perspective, parents were requested to complete the inventory at 6 months after the first evaluation (i.e., at 42 months). Data analyses focused both on the concurrent relations of gesture production, vocabulary size and psychomotor development, and on the longitudinal relations between gesture production and subsequent vocabulary development.

Outcomes & Results: As regards concurrent relationships, gesture production appeared to be related both to psychomotor development and to word comprehension, but not to word production. Nevertheless, as regards longitudinal relationships, gesture production at 36 months was significantly correlated to the subsequent vocabulary production, assessed at 42 months using the MacArthur Communicative Development Inventory (CDI), though this relationship appeared to be mediated by word comprehension.

Conclusions & Implications: Two processes in the gesture production of children with Down's syndrome appear to be similar to those previously identified in typically developing children: (1) the role of gestures as a ‘bridge’ between word comprehension and word production; and (2) the predictive role of gestures, in association with comprehension, on vocabulary development.
Real‐word repetition as a predictor of grammatical competence in Italian children with typical language development
Authors: Dispaldro Marco , Benelli Beatrice , Marcolini Stefania , Stella Giacomo
Published: January 2009

Background: Non‐word repetition in children is a skill related to, but separable from grammatical ability. Lexical skill may bridge the gap between these two abilities.

Aims: The main aim was to determine whether real‐word‐repetition tasks could be better as predictors of grammatical ability than non‐word‐repetition tasks in children with typical language. This proposal was pursued because lexical knowledge was assumed to make performance in repetition tasks more representative of other language abilities, whereas non‐word‐repetition tasks are heavily influenced by phonological short‐term memory.

Methods & Procedures: In order to investigate this possibility, three repetition tasks (two real‐word lists characterized by different lexical knowledge and one non‐word list), were compared in three groups of three‐ to four‐year‐olds with typical language (42 children). Grammatical ability was tested through probes for third‐person plural inflection and direct‐object clitic use.

Outcomes & Results: Real words were repeated more accurately than non‐words and the non‐words were more sensitive to Syllable length than real words. Performance on all repetition tasks was correlated with grammatical ability, but real words predicted variance in grammatical ability to a greater extent than non‐words.

Conclusions & Implications: Given the lexical information contained in real words, repetition of such words was a better predictor of grammatical ability than non‐word repetition. Future research should replicate and extend these results. Tasks using real words may also have considerable clinical potential; for this reason, these tasks might also be included in studies of children with language impairment.
Influence of Extreme Temperatures During Grain Filling on Protein Fractions, and Its Relationship to Some Quality Characteristics in Bread, Biscuit, and Durum Wheat
Authors: Labuschagne M. T. , Elago O. , Koen E.
Published: January 2009

Extreme temperatures during grain filling have been identified as a major source of variation in wheat quality characteristics. In this study one biscuit, two bread, and one durum wheat cultivars were evaluated in two consecutive seasons for reaction to extreme high and low temperatures during grain filling. In both years, the soft biscuit wheat cultivar showed the largest reaction to low temperature stress, where the monomeric proteins were significantly increased and the polymeric proteins significantly decreased. The effect of temperature stress was more pronounced in the second year, with an earlier planting date. The durum wheat reacted to both heat and cold stress in the second year, where the small polymeric proteins were significantly reduced, and the small and large monomeric proteins were increased with stress. The effect of wheat type was much more pronounced than the effect of temperature treatments on the protein fractions. The protein fractions of the tetraploid durum wheat were very different from the hexaploid cultivars, with much less polymeric proteins, and more monomeric proteins. The soft biscuit wheat had significantly less large polymeric proteins and more large monomeric proteins than the bread wheat cultivars for both years.
Childhood Esophagitis: Then and Now
Authors: Lee Joyce J , Baker Robert D , Khan Abdur R , Baker Susan S
Published: January 2009

Objectives:

It is not known whether the prevalence of childhood esophagitis has changed over time. In children, the intraepithelial eosinophil is considered the hallmark of esophageal inflammation. This study compares the prevalence of intraepithelial eosinophils in esophageal biopsies obtained from 1980–1988 and 2001–2002.

Patients and Methods:

This study reevaluated all of the esophageal biopsies obtained at a single center during 2 periods: 1980–1988 and 2001–2002. Histological appearances were characterized and eosinophils per high‐power field were quantified.

Results:

In total, 1058 esophageal biopsies from 510 subjects were reviewed. Between 1980 and 1988, 247 biopsies from 188 subjects were evaluated. Of these, 62 subjects met the criteria for esophageal disease, and 106 had no specific pathological changes. Between 2001 and 2002, 811 biopsies from 322 subjects were evaluated. Of these, 132 subjects met the criteria for esophageal disease, and 182 had no specific pathological changes. A statistically significant increase in the prevalence of esophageal inflammatory disease was observed comparing the recent group with the remote group. Eosinophilic esophagitis is thought to be distinct from other types of esophagitis in pathogenesis, epidemiology, histology, and treatment. Some suggest the prevalence of eosinophilic esophagitis has increased in recent years. We sought evidence for an increase in histological changes consistent with eosinophilic esophagitis. No matter whether histology consistent with eosinophilic esophagitis was defined as 25, 20, 15, or 10 eosinophils per high‐power field, no increase in prevalence was found.

Conclusions:

This study demonstrated no evidence for a change in the density of eosinophilic infiltrates in esophageal biopsies during the 22‐year study period. The study showed a statistically significant increase in the prevalence of esophageal inflammatory disease across the same period.