bluuebunny/crossref_metadata_2025 huggingface dataset:
Physicists and the revolt against science in the 1930's
Authors: Kevles Daniel J.
Published: April 2009

To most people the main link between the abstrusities of science and the wonders of modern life is technology, seen as tangible machines that spew forth goods or ease the burden of labor. After the crash of 1929 many Americans began to ask whether chemistry produced more than consumers could absorb, whether machines destroyed more jobs than they created. Going beyond earlier humanist critiques, thoughtful citizens wondered whether science was not responsible, at least in part, for the end of the miracle, for the failure of machine civilization. In this context, an emotionally charged dispute between two physicists about the origin of cosmic rays became a focal point in the public reaction against science. The principals in this unprecedented and highly publicized debate were two Nobel laureates, Arthur Holly Compton and Robert A. Millikan. The repercussions of this dispute and the attendant revolt against science exposed difficulties in physics in the US that remain with us to the present day.
The electric lamp: 100 years of applied physics
Authors: Anderson John M. , Saby John S.
Published: April 2009

Night-time in 1879, but a scant 100 years ago, was considerably darker than the nocturnal world of today. Artificial illumination was limited to kerosene lamps, illuminating gas, the just-emerging arc lamp for street lighting and a few lingering candles.
The fusion hybrid
Authors: Bethe Hans A.
Published: April 2009

In the last few years nuclear fusion by magnetic confinement has made great progress. However, an economical pure fusion power plant is still many years away. In this article I will discuss how a combination of fusion and fission power might be much closer, and might be very helpful both to fission and fusion power.
The anomalous Hall effect
Authors: Bergmann Gerd
Published: April 2009

The Hall effect is observed when a magnetic field is applied to a metal through which a current flows: The current carriers are deflected in the field, giving rise to a transverse electric field. In a ferromagnetic metal the embedded magnetic moments produce an anomalous Hall effect. Because it depends on both electronic and magnetic properties of the metal, the anomalous Hall effect has become a useful experimental tool for solid-state physicists. In our laboratory in Jülich, for example, we have used the effect to study extremely thin magnetic layers and to observe the propagation of conduction electrons in a metal.
Optical Society of America meets in Boston
Authors: Dodd Patricia
Published: April 2009

Historic Boston will be the site of the annual meeting of the Optical Society of America, to be held at the Sheraton Boston Hotel on 21–24 October. Eleven symposia held throughout the four-day meeting will cover topics as diverse as molecular spectroscopy, laser speckle and visual perception.
Welcome to the post-industrial society
Authors: Bell Daniel
Published: April 2009

A number of countries in the West, the United States among them, are now passing from an industrial into a post-industrial phase of society. The change primarily affects the socio-technical dimensions of society and is generally independent of the nature of political change or political structure. The main difference between an industrial and a post-industrial society is that the sources of innovation in a post-industrial society are derived increasingly from the codification of theoretical knowledge, rather than from “random” inventions. Every society in human history has been dependent upon knowledge, but it is only in recent years that the accumulation and distribution of theoretical knowledge has come to the fore as a directive force of innovation and change.
Dynamics of electron excitation
Authors: Fano Ugo
Published: April 2009

A key step in any chemical reaction is the transition of bonding electrons from one stable wave-mechanical state to another. A complete description of the evolution of states in the course of such transitions remains a distant goal—in spite of our rather extensive knowledge of chemical reactions. This article reviews a start on this problem that has been made in recent years.
Pre-college: The PSSC course
Authors: Haber-Schaim Uri
Published: April 2009

TODAY, TEN YEARS after the formation of the Physical Science Study Committee, the PSSC course in physics is used in its entirety by more than half the high-school students taking physics in the United States. The laboratory equipment and films have found their way into many classrooms where other texts are used. There are 18 foreign editions of the PSSC text and laboratory guide in 15 languages. The course is being tried intensively in several countries and is already beyond that stage in some English-speaking countries. PSSC equipment is being manufactured and labeled as such in Asia, Latin America and Europe. Films have been successfully provided with synchronized translations. In this country, the second commercial edition of the printed material is on the market as well as an advanced-topics supplement. A college edition of the course, incorporating the advanced topics and deleting some elementary topics that are now taken up in earlier grades, is now in the editing stage. How did all this come about?
Transuranic elements and the high-flux isotope reactor
Authors: Weinberg Alvin
Published: April 2009

A TRANSURANIC-ELEMENTS research and production facility is being completed at Oak Ridge National Laboratory. Its three principal components are a High Flux Isotope Reactor (HFIR), an elaborate radiochemical processing plant called TRU and a transuranic research laboratory. Built over the past eight years at a cost of more than $24.5 million, this facility provides scientists from many different institutions with tools to advance understanding of the chemistry and nuclear physics of the transuranics and also to advance the technology of highflux reactors.
Ultracold neutrons
Authors: Luschikov V. I.
Published: April 2009

Nearly twenty years ago Ya. B. Zeldovich pointed out that free neutrons, if sufficiently slow, could in principle be stored in a closed “bottle”—presumably for periods up to the beta decay lifetime, about 103 seconds. Apparently, according to Bruno Pontecorvo, Enrico Fermi had mentioned this possibility as early as the middle 1930's, but Zeldovich's paper was the first published discussion. The basis for the belief that neutrons could be stored in this way was the behavior of the effective potential for the interaction of neutrons with matter, which for many substances becomes repulsive when the neutrons are sufficiently slow. Thus there is a strong suppression of inelastic processes for these very slow neutrons (energies below about 10−7 eV), and they are totally reflected upon collisions with, for example, container walls.
Computerized tomography: taking sectional x rays
Authors: Swindell William , Barrett Harrison H.
Published: April 2009

An important new diagnostic technique is making its appearance in our major hospitals. The technique, which uses x rays to render visible thin slices through any section of the human body, has been so dramatic in its development that no general agreement has yet been reached on its name—it has been called “computed tomography,” “computerized axial tomography,” “transaxial tomography” and “reconstruction from projections.” Figure 1 shows one version of the apparatus in a clinical setting.
Critical-point universality and fluids
Authors: Sengers Anneke Levelt , Hocken Robert , Sengers Jan V.
Published: April 2009

The similarity of critical behavior in dissimilar systems has long fascinated scientists. When Pierre Curie, in 1895, measured the magnetic equation of state of nickel, he was struck by how much the curves he obtained by plotting magnetization against temperature looked like the density–temperature isobars of carbon dioxide near the critical point. In 1907 Pierre Weiss fashioned his mean-field theory describing the equation of state of nickel after Van der Waals's equation for fluids.
The MIT technical information project
Authors: Kessler M. M.
Published: April 2009

The Technical Information Project at MIT is an experiment in information-system design. It is intended to provide a test-bed facility to evaluate search strategies, to learn from direct experience what contributions modern technology can make in solving the problems of scientific exchange, and to localize those areas in the information process where technological improvements are most likely to succeed. The present paper describes the system.
Performance prediction of a small-sized herringbone-grooved bearing with ferrofluid lubrication considering cavitation
Authors: Kao Yung-Yuan , Chao Paul C.-P. , Liu Zong-Bin , Wang Zhi-Kuan , Liu Po-Wen , Huang Jeng-Shen , Chang Chang-Chun
Published: April 2009

The small-sized herringbone groove journal bearing (HGJB), i.e., so-called “magnetic bearing,” filled with Newtonian ferrofluid lubrication is investigated via finite difference analysis (FDA), with consideration of cavitation zones in HGJB. The FDA starts with constructing the mass flux equations of the HGJB filled with ferrofluid. Discretization for FDA is next performed over the bearing clearance domain, from which algebraic finite difference equations based on the mass flow balance over the clearance domain are derived. Solving the equations, rotordynamic coefficients, cavitation zones, and side leakage rate are successfully predicted to show effectiveness in enhancing bearing performance by ferrofluid.
Effect of magnetic softness in a soft layer on media properties of hard/soft stacked composite perpendicular media
Authors: Jung H. S. , Malhotra S. S. , Acharya B. R. , Bertero G. , Suess D.
Published: April 2009

Adding Pt into CoCr-oxide alloy for controlling magnetic softness in a soft layer on hard/soft (H/S) stacked composite media significantly affects magnetic properties and microstructure. Hc values for capping layer (CL) media with a relatively high-Hk soft layer initially increase with increasing tcap. However, Hc values are relatively constant for H/S media with Pt 3% and 10% soft layers and reduced for the media with a CoTaZr–SiO2 soft layer having in-plane Hk. The simulation results explain these experimental Hc trends by the compensation effect between the decrease in average Ku due to the use of less-Ku soft layer and the increases in volume with increasing tsoft. Reduction in Hc with increasing tsoft is anticipated when Ku in a soft layer reduces by >27%. As the Pt content in a soft layer increases from 3% to 18%, higher Hc and Hn but lower Hs are observed. Plan-view transmission electron microscopy images for the medium with Pt 18% soft layer show no subgrains and thinner grain boundary width and explain the significant increase in lateral Aex. Thus, the Pt content in a soft layer needs to be optimized. Compared to CL media, H/S composite media with the Pt 5% and 8% soft layers improve both SNRme and media writability.
Calculation of eddy-current loss in multilayer magnetic films considering displacement current
Authors: Yao Di , Sullivan Charles R.
Published: April 2009

At high frequency, displacement current in dielectric layers of multilayer magnetic thin films becomes significant, and eddy-current loss can be much worse than would be predicted without considering displacement current. Two-dimensional finite-element method simulations were used to study the behavior of eddy-current loss in multilayer thin films from 1 kHz to 1 GHz. A closed-form expression for accurate loss prediction with error less than 10% was developed, and its consistency with experimental measurements on Co–Zr–O/ZrO2 multilayer films was checked.
Electro-optical characteristics of omnidirectional liquid crystal domain mode using doughnut-shaped slit electrodes
Authors: Gwag Jin Seog , Bae Kwang-Soo , Lee You-Jin , Kim Jae-Hoon
Published: April 2009

This paper proposes a liquid crystal (LC) display (LCD) mode, characterized by an azimuthally continuous nematic domain, driven by patterned electrodes with circular- and doughnut-shaped slits producing conelike fields, as a vertically aligned (VA) nematic LC mode. This proposed mode is focused on achieving a high transmittance display with omnidirectionally uniform optical characteristics by utilizing the proposed electrode structure. Consequently, the experimental results of the proposed LCD mode show high brightness and wide viewing angles that correlate well to numerical calculations. Other electro-optics characteristics of this mode correspond to the patterned VA LC mode.
A molecular dynamics simulation study of the pressure-volume-temperature behavior of polymers under high pressure
Authors: Hooper Justin B. , Bedrov Dmitry , Smith Grant D. , Hanson Ben , Borodin Oleg , Dattelbaum Dana M. , Kober Edward M.
Published: April 2009

Isothermal compression of poly (dimethylsiloxane), 1,4-poly(butadiene), and a model Estane® (in both pure form and a nitroplasticized composition similar to PBX-9501 binder) at pressures up to 100kbars has been studied using atomistic molecular dynamics (MD) simulations. Comparison of predicted compression, bulk modulus, and Us−up behavior with experimental static and dynamic compression data available in the literature reveals good agreement between experiment and simulation, indicating that MD simulations utilizing simple quantum-chemistry-based potentials can be used to accurately predict the behavior of polymers at relatively high pressure. Despite their very different zero-pressure bulk moduli, the compression, modulus, and Us−up behavior (including low-pressure curvature) for the three polymers could be reasonably described by the Tait equation of state (EOS) utilizing the universal C parameter. The Tait EOS was found to provide an excellent description of simulation PVT data when the C parameter was optimized for each polymer. The Tait EOS parameters, namely, the zero-pressure bulk modulus and the C parameter, were found to correlate well with free volume for these polymers as measured in simulations by a simple probe insertion algorithm. Of the polymers studied, PDMS was found to have the most free volume at low pressure, consistent with its lower ambient pressure bulk modulus and greater increase in modulus with increasing pressure (i.e., crush-up behavior).
Numerical study of effective permeability of soft-magnetic composites with conductive inclusions
Authors: Drnovšek Boštjan , Bregar Vladimir B. , Pavlin Mojca
Published: April 2009

We used three-dimensional finite-element modeling in order to study the effect of the microstructure (random, agglomerated, and percolated distributions of inclusions) on the effective permeability of a magnetic composite with incorporation of complex intrinsic properties in a frequency domain. The study includes the effect of the inclusions’ conductivity and eddy currents on the difference in the permeability. The results show a significant effect of inclusions distribution on the effective permeability of the composites for both nonconductive and conductive particles. We further show that in larger agglomerates with well connected conductive particles the eddy currents shield inner particles and significantly increase the imaginary effective permeability. Comparison with our experimental data from a composite with carbonyl iron inclusions showed that the particle agglomeration at small volume fractions gives similar frequency dependence for the effective permeability as in the case of composites with well distributed inclusions at larger volume fraction.
Coil geometry for efficient active compensation with separated magnetic shields
Authors: Nakashima Yoshihiro , Sasada Ichiro
Published: April 2009

We have already proposed a new method of magnetic shielding aiming for magnetocardiography, in which magnetic shells are separated and a new compensation scheme is employed to allow for wide space between them. Each magnetic shell that consists of a half of the cylinder (diameter=20 cm and length=60 cm) and two flanges at both ends of the half cylinder extending along the radial direction has a saddle coil on its outer surface with the coil’s long straight section running parallel to the axis of the cylinder. In this paper, the relationship between the width of the long straight sections of the saddle coil and the efficiency of the active compensation is investigated by the finite element method (FEM) analysis and by experiments. A magnetic shield used in this study is a double shell structure where each shell is made of stacked amorphous tapes and the outer shell has a magnetic shaking coil for the enhancement of the permeability. We have found that for a given magnetic field, the compensation current necessary for a given magnetic field varies by a factor of 3 depending on the width of a saddle coil and that its value monotonically decreases with increasing the width. We have also confirmed that the phase delay of the compensation magnetic field experienced while it comes in the magnetic shell is small.
An exploration of electronic structure and nuclear dynamics in tropolone: II. The Ã B12 (π∗π) excited state
Authors: Burns Lori A. , Murdock Daniel , Vaccaro Patrick H.
Published: April 2009

The first excited singlet state of tropolone (Ã B12) and the attendant π∗←π electronic transition have been examined computationally by applying several quantum chemical treatments built upon the aug-cc-pVDZ basis set, including time-dependent density functional theory (TDDFT/B3LYP), configuration interaction singles with perturbative corrections [CIS and CIS(D)], and equation-of-motion coupled-cluster schemes [EOM-CCSD and CR-EOMCCSD(T)]. As in the case of the X̃ A11 ground state [L. A. Burns, D. Murdock, and P. H. Vaccaro, J. Chem. Phys. 124, 204307 (2006)], geometry optimization procedures and harmonic force-field calculations predict the electronically excited potential surface to support a global minimum-energy configuration of rigorously planar (Cs) symmetry. Minimal Hartree–Fock (HF/CIS) and density-functional (DFT/TDDFT) approaches yield inconsistent results for the X̃ A11 and Ã B12 manifolds; however, coupled-cluster (CCSD/EOM-CCSD) methods give fully relaxed proton-transfer barrier heights of ΔEptX̃=3296.1 cm−1 and ΔEptÃ=1270.6 cm−1 that are in accordance with the experimentally observed increase in vibrationless tunneling splitting upon electronic excitation. Detailed analyses show that this reduction in ΔEpt stems from a variety of complementary factors, most notably an overall contraction of the proton-transfer reaction site (whereby the equilibrium O⋯O donor-acceptor distance decreases from 2.53 to 2.46 Å) and a concomitant shortening of the intramolecular hydrogen bond. Further refinement of Ã B12 energies through single-point perturbative triples corrections [CR–EOMCCSD(T)] leads to 1316.1 cm−1 as the best current estimate for ΔEptÃ. Direct comparison of the lowest-lying out-of-plane torsional mode [ν39(a2)] for X̃ A11 and Ã B12 tropolone reveals that its disparate nature (cf. ν39X̃=101.2 cm−1 and ν39Ã=42.0 cm−1) mediates vibrational-averaging effects which can account for inertial defects extracted by rotationally resolved spectroscopic measurements.
Effect of phosphonic acid surface modifiers on the work function of indium tin oxide and on the charge injection barrier into organic single-layer diodes
Authors: Sharma Asha , Haldi Andreas , Hotchkiss Peter J. , Marder Seth. R. , Kippelen Bernard
Published: April 2009

We investigate the use of several phosphonic acid surface modifiers in order to increase the indium tin oxide (ITO) work function in the range of 4.90–5.40 eV. Single-layer diodes consisting of ITO/modifier/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′ biphenyl-4,4″ diamine (α-NPD)/Al and ITO/modifier/pentacene/Al were fabricated to see the influence of the modified ITO substrates with different work functions on the charge injection. To calculate the charge injection barrier with different surface modifiers, the experimentally measured current density-voltage (J-V) characteristics at different temperatures are fitted using an equivalent circuit model that assumes thermionic emission across the barrier between the ITO work function and the highest occupied molecular orbital of the organic material. The charge injection barrier height extracted from the model for various surface modifier-based diodes is independent of the ITO work function within the range of changes achieved through modifiers for both α-NPD and pentacene-based single-layer diodes.
Thermal conductivity of carbon nanotubes
Authors: Sun Ke , Stroscio Michael A. , Dutta Mitra
Published: April 2009

This paper addresses the problem of modeling the thermal conductivity of carbon nanotubes (CNTs) of submicron length that have relatively low point-defect concentrations. Point defects are taken into account at the ends of these CNTs to model the commonly encountered situation where point defects are introduced unintentionally at the ends of the CNT under prevailing fabrication methods. Herein, previous models for thermal transport in graphite are adapted to investigate the thermal transport properties of CNTs.
Superintegrability with third order integrals of motion, cubic algebras, and supersymmetric quantum mechanics. II. Painlevé transcendent potentials
Authors: Marquette Ian
Published: April 2009

We consider a superintegrable quantum potential in two-dimensional Euclidean space with a second and a third order integral of motion. The potential is written in terms of the fourth Painlevé transcendent. We construct for this system a cubic algebra of integrals of motion. The algebra is realized in terms of parafermionic operators and we present Fock-type representations which yield the corresponding energy spectra. We also discuss this potential from the point of view of higher order supersymmetric quantum mechanics and obtain ground state wave functions.
Multidimensional theory of protein folding
Authors: Itoh Kazuhito , Sasai Masaki
Published: April 2009

Theory of multidimensional representation of free energy surface of protein folding is developed by adopting structural order parameters of multiple regions in protein as multiple coordinates. Various scenarios of folding are classified in terms of cooperativity within individual regions and interactions among multiple regions and thus obtained classification is used to analyze the folding process of several example proteins. Ribosomal protein S6, src-SH3 domain, CheY, barnase, and BBL domain are analyzed with the two-dimensional representation by using a structure-based Hamiltonian model. The extension to the higher dimensional representation leads to the finer description of the folding process. Barnase, NtrC, and an ankyrin repeat protein are examined with the three-dimensional representation. The multidimensional representation allows us to directly address questions on folding pathways, intermediates, and transition states.
The intersystem crossing process of p-bromofluorobenzene studied with time-resolved photoelectron imaging
Authors: Cao Zhenzhou , Wei Zhengrong , Hua Linqiang , Hu Changjin , Zhang Song , Zhang Bing
Published: April 2009

Ultrafast processes of p-bromofluorobenzene are studied with femtosecond time-resolved photoelectron imaging spectroscopy. The photoelectron image revealed four photoelectron rings centered at 0.39, 0.86, 1.13, and 1.61 eV, respectively. The inner rings are more anisotropic than the outer rings. The decay traces of the different rings were recorded separately. Sharp photoelectron energy distributions and different anisotropy parameters extracted from the images indicated resonances with Rydberg states at the (1+1′) photon energy. The quantum defect values of the four Rydberg states were determined to be 0.75, 0.52, 0.36, and ∼0, respectively, with principal quantum number of 3. The electron dephasing mechanism of the S1(B2) state corresponds to the intersystem crossing from the S1(B2) to T1(B2) state and the predissociation of the S1(B2) state via the T1(B1) state. The lifetimes of S1(B2) and T1(B2) are determined from the decay of the photoelectron signals to be 40 and 33 ps, respectively. The variety of time-dependent anisotropy parameters in the first 5 ps shows the rotational wave coherences of p-bromofluorobenzene at the S1(B2) state.
Conditioning Schramm–Loewner evolutions and loop erased random walks
Authors: Bauer Michel , Bernard Denis , Kennedy Tom
Published: April 2009

We discuss properties of dipolar Schramm–Loewner evolution (SLEκ) under conditioning. We show that κ=2, which describes continuum limits of loop erased random walks, is characterized as being the only value of κ such that dipolar SLE conditioned to stop on an interval coincides with dipolar SLE on that interval. We illustrate this property by computing a new bulk passage probability for SLE2.
Plasma “anti-assistance” and “self-assistance” to high power impulse magnetron sputtering
Authors: Anders André , Yushkov Georgy Yu.
Published: April 2009

A plasma assistance system was investigated with the goal to operate high power impulse magnetron sputtering (HiPIMS) at lower pressure than usual, thereby to enhance the utilization of the ballistic atoms and ions with high kinetic energy in the film growth process. Gas plasma flow from a constricted plasma source was aimed at the magnetron target. Contrary to initial expectations, such plasma assistance turned out to be contraproductive because it led to the extinction of the magnetron discharge. The effect can be explained by gas rarefaction. A better method of reducing the necessary gas pressure is operation at relatively high pulse repetition rates where the afterglow plasma of one pulse assists in the development of the next pulse. Here we show that this method, known from medium-frequency (MF) pulsed sputtering, is also very important at the much lower pulse repetition rates of HiPIMS. A minimum in the possible operational pressure is found in the frequency region between HiPIMS and MF pulsed sputtering.
Thermal models and noise in transition edge sensors
Authors: Goldie D. J. , Audley M. D. , Glowacka D. M. , Tsaneva V. N. , Withington S.
Published: April 2009

Detectors based on transition edge sensors (TESs) must achieve theoretically predicted noise levels if they are to be suitable for the next generation of space-borne astronomical telescopes. The noise of an ideal detector is determined by the sum of three contributions: (i) thermal-fluctuation noise in the heat link to the bath, (ii) Johnson noise in the sensor itself, and (iii) noise in the electrical read-out circuit. Many groups have reported TESs with noise levels significantly above the theoretical predictions. We use two well-defined experimental configurations to measure the read-out noise spectra of Mo–Cu TESs with transition temperatures of 370 and 200mK. The TESs are geometrically simple, comprising superconducting and normal metal films on a silicon nitride (SiNx) membrane. The measurements are compared with a multiparameter noise model, which is based on a physical model of the thin-film devices. Taking into consideration separate, accurate measurements of the heat capacity of identical SiNx membranes, we are able to provide a good account of both the magnitude and frequency dependences of the measured current-noise spectra. We find that an important excess noise mechanism involves the random exchange of heat between the heat capacity of the bilayer and the heat capacity of the nitride membrane, with either the thermal conductance of the membrane, or in some cases the thermal conductance of the bilayer, being the mediating path. Clear design recommendations are given to achieve the best possible noise performance.
Mössbauer investigation on Ni–Zn nanoferrite with the highest saturation magnetization
Authors: Kumar A. Mahesh , Rao K. H. , Greneche J. M.
Published: April 2009

The highest value of saturation magnetization (80 emu/g) ever reported has been achieved in Ni0.65Zn0.35Fe2O4 at lower sintering temperatures through sol-gel synthesis. The observed highest value of saturation magnetization has been explained on the basis of core-surface magnetic interactions facilitated through low temperature and in-field Mössbauer investigation of the system. Cation distribution for this composition has also been proposed and verified quantitatively by calculating the intensity of each peak of x-ray diffraction and estimating the lattice constant.
Formation of weakly bound, ordered adlayers of CO on rutile TiO2(110): A combined experimental and theoretical study
Authors: Kunat M. , Traeger F. , Silber D. , Qiu H. , Wang Y. , van Veen A. C. , Wöll Ch. , Kowalski P. M. , Meyer B. , Hättig C. , Marx D.
Published: April 2009

The adsorption of CO on the rutile TiO2(110) surface was investigated using He atom scattering (HAS), high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and different types of ab initio electronic structure calculations. The experimental and theoretical results allow to put forward a consistent picture for this rather complicated adsorbate system. At 70 K a (2×1) adlayer with a glide symmetry plane is formed, containing two molecules per unit cell which are tilted in alternate directions by about 20° relative to the surface normal. For this high density phase, the theoretical calculations reveal a substantial repulsion between CO molecules on neighboring lattice sites, in accord with the results of a detailed analysis of the experimental TDS data. The CO binding energy depends strongly on coverage and varies between 0.20 eV for the saturated monolayer and 0.36 eV for isolated molecules. The CO–CO repulsion leads to the desorption of about half of the CO molecules above 70 K and the formation of low density phases. HAS gave no indication of ordered adlayers at these lower coverages. For the internal stretching vibration of the CO molecules a value of 273 meV was determined by HREELS, in very good agreement with the theoretical calculations.
Sum rules and density waves spectrum for nonrelativistic fermions
Authors: Cintio A. , Morchio G.
Published: April 2009

Frequency sum rules are derived in extended quantum systems of nonrelativistic fermions from a minimal set of assumptions on dynamics in infinite volume, for ground and thermal states invariant under space translations or a lattice subgroup. For the jellium Coulomb model, they imply the one point result for the plasmon energy spectrum in the zero momentum limit. In the presence of a uniform magnetic field, they allow for a rigorous derivation of the gyroplasmon spectrum, as a pure point spectrum, in the same limit. For all potentials with integrable second derivatives, the density wave energy spectrum is shown to converge, in the limit of large wavelength, to a point measure at zero frequency, for any number of fermion fields. ⟨ω2(k)⟩∼k2 for potentials with r2∂i∂jV integrable, ⟨ω2(k)⟩∼kα−d+2 for potentials decaying at infinity as 1/rα, d−2<α<d, d the space dimensions. For one component models with short range interactions, the fourth moment of the frequency is derived and expressed, at lowest order in k, in terms of the three point correlation function of the density.
Discussion on a mechanical equilibrium condition of a sessile drop on a smooth solid surface
Authors: Yonemoto Yukihiro , Kunugi Tomoaki
Published: April 2009

Young’s equation describes an interfacial equilibrium condition of a liquid droplet on a smooth solid surface. This relation is derived by Thomas Young in 1805. It has been discussed until today after his work. In general, Young’s equation is discussed from the viewpoint of thermodynamics and derived by minimizing the total free energy of the system with intensive parameters in the total free energy kept constant, i.e., the variation in the total free energy is zero. In the derivation, the virtual work variations in the horizontal and vertical directions of the droplet on the smooth solid are considered independently. However, the virtual work variation at the droplet surface depends on the variation of the horizontal and vertical directions, which are related to an incline of the droplet surface. This point has been overlooked in past studies. In this study, by considering this directional dependency, we derive the modified Young’s equation based on the thermodynamics. Finally, we evaluate the modified Young’s equation by comparing the analytical solution of the relationship between a contact angle and the contact line radii of the droplet with some experimental data. Moreover, we investigated the line tension itself.
Dynamics of nonlinearly interacting magnetic electron drift vortex modes in a nonuniform plasma
Authors: Eliasson B. , Shukla P. K. , Pavlenko V. P.
Published: April 2009

A simulation study of dynamical evolution of nonlinearly interacting two-dimensional magnetic electron drift vortex (MEDV) modes in a nonuniform plasma is presented. Depending on the equilibrium density and temperature gradients, the system can either be stable or unstable. The unstable system reveals spontaneous generation of magnetic fields from noise level, and large-scale magnetic field structures are formed. When the system is linearly stable, one encounters MEDV mode turbulence in which there is a competition between zonons (zonal flows) and streamers. For large MEDV mode amplitudes, one encounters the formation of localized and small-scale magnetic vortices and vortex pairs with scale sizes of the order of the electron skin depth. The MEDV turbulence exhibits nonuniversal (non-Kolmogorov-type) spectra for different sets of plasma parameters. The relevance of this work to laboratory and cosmic plasmas is briefly mentioned.
A strategy to eliminate all nonlinear effects in constant-voltage hot-wire anemometry
Authors: Berson Arganthaël , Blanc-Benon Philippe , Comte-Bellot Geneviève
Published: April 2009

A constant-voltage anemometer is subject to nonlinear effects when the operating hot wire is exposed to large velocity fluctuations in the incident flow. This results in the generation of undesirable higher harmonics, just as in the two classic systems, constant-current and constant-temperature anemometers, for which no attempts are normally made to correct the nonlinearities. The present investigation shows that these undesirable higher harmonics can be suppressed in the case of a constant-voltage anemometer. A new approach to process experimental data is proposed. It is based on three explicit equations established and solved with all terms included, i.e., without linearization. These are (1) the first-order differential equation that describes the electronic circuit of a constant-voltage anemometer—this equation permits to deduce the instantaneous resistance of the hot wire from the output voltage of the anemometer; (2) the first-order differential equation that expresses the thermal lag behavior of the hot wire when used in a constant-voltage mode—this equation permits to restore the instantaneous resistance that an ideal wire would have without thermal inertia in the same flow conditions; and (3) the algebraic relation that expresses the heat-transfer law of an ideal wire, according to King’s law, a look-up table, or a polynomial fit—this relation permits to deduce the instantaneous flow velocity from the instantaneous resistance of the ideal wire. The proposed method is easily implemented on a personal computer and permits odd turbulence moments, such as skewness factors, to be obtained satisfactorily.
Efficient simulation of noncrossing fibers and chains in a hydrodynamic solvent
Authors: Padding J. T.
Published: April 2009

An efficient simulation method is presented for Brownian fiber suspensions, which includes both uncrossability of the fibers and hydrodynamic interactions between the fibers mediated by a mesoscopic solvent. To conserve hydrodynamics, collisions between the fibers are treated such that momentum and energy are conserved locally. The choice of simulation parameters is rationalized on the basis of dimensionless numbers expressing the relative strength of different physical processes. The method is applied to suspensions of semiflexible fibers with a contour length equal to the persistence length, and a mesh size to contour length ratio ranging from 0.055 to 0.32. For such fibers the effects of hydrodynamic interactions are observable, but relatively small. The noncrossing constraint, on the other hand, is very important and leads to hindered displacements of the fibers, with an effective tube diameter in agreement with recent theoretical predictions. The simulation technique opens the way to study the effect of viscous effects and hydrodynamic interactions in microrheology experiments where the response of an actively driven probe bead in a fiber suspension is measured.
Optical properties of β-Sn films
Authors: Takeuchi Katsuki , Adachi Sadao
Published: April 2009

Optical properties of white tin (β-Sn) have been investigated using spectroscopic ellipsometry in the photon-energy range between 0.6 and 6.5 eV at room temperature. The β-Sn films are deposited by vacuum evaporation on Si(001) substrates. The structural properties of the films are evaluated by x-ray diffraction and ex situ atomic force microscopy. The measured ε(E) spectra reveal distinct structures at several interband critical points in the Brillouin zone of β-Sn. These spectra are analyzed on the basis of a simplified model of the interband transitions, including the free-carrier absorption between the filled and empty electronic states. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of bulk β-Sn films are also presented.
Optical force enhanced by plasmon resonance allowing position-sensitive synthesis and immobilization of single Ag nanoparticles on glass surfaces
Authors: Itoh Tamitake , Biju Vasudevanpillai , Ishikawa Mitsuru , Ito Syoji , Miyasaka Hiroshi
Published: April 2009

Focused laser light in an aqueous solution of silver nitrate and disodium citrate allowed the synthesis and immobilization of single Ag particles on a glass surface. The as-synthesized Ag particles were free from aggregation. Rayleigh scattering spectra of the Ag particles showed a plasmon resonance band at ∼490 nm. Analysis of the spectra revealed that the Ag particles have oblate-spindle shapes with ∼30 nm diameter. The polarizability of the Ag nanoparticles demonstrated that soon after the formation of the particles at the focal point, optical force repels them out of the focal point and immobilizes on the glass surface.
Partitioning scheme for density functional calculations of extended systems
Authors: He Jiangping , Di Paola C. , Kantorovich L.
Published: April 2009

We show that, at least for the ground electronic state of systems treated using semilocal density functionals (like in local density or generalized gradient approximations), a calculation of the entire extended nonperiodic system consisting of several well distinguished parts (e.g., a collection of molecules) can be replaced with a finite set of calculations on specifically chosen smaller subsystems that overlap with each other. Every subsystem is terminated with link (or pseudo) atoms (or groups of atoms) to reduce the effect of the termination. However, because of the particular choice of the subsystems, the effect of the link atoms is largely compensated in the final total energy if the subsystems are chosen sufficiently large. In fact, we prove that the proposed method should result in nearly the same total energy, electronic density and atomic forces as a single (considered as a reference) density functional calculation on the entire system. Our method, however, should be much more efficient due to unfavorable scaling of the modern electronic structure methods with the system size. The method is illustrated on examples of serine water, lysine-water and lysine dimer systems. We also discuss possible approximate applications of our method for quantum-classical calculations of extended systems, when, as compared to widely used quantum-mechanical/molecular-mechanical methods, the problem of the quantum cluster boundary can be eliminated to a large degree.
Fast magnetic reconnection in a kinked current sheet
Authors: Fujimoto Keizo
Published: April 2009

Magnetic reconnection processes in a kinked current sheet are investigated using three-dimensional electromagnetic particle-in-cell simulations in a large system where both the tearing and kink modes are able to be captured. The spatial resolution is efficiently enhanced using the adaptive mesh refinement and particle splitting-coalescence method. The kink mode scaled by the current sheet width such as kyL∼1 is driven by the ions that are accelerated due to the reconnection electric field in the ion-scale diffusion region. Although the kink mode deforms the current sheet structure drastically, the gross rate of reconnection is almost identical to the case without the kink mode and fast magnetic reconnection is achieved. The magnetic dissipation mechanism is, however, found very different between the cases with and without the kink mode. The kink mode broadens the current sheet width and reduces the electron flow velocity, so that the electron inertia resistivity is decreased. Nevertheless, anomalous dissipation through the electron thermalization compensates the decrease in the inertia resistivity so as to keep a high reconnection rate. This suggests that the electron dynamics in the electron diffusion region is automatically adjusted so as to generate sufficient dissipation for fast magnetic reconnection. The electron thermalization occurs effectively because the electron meandering scale along the current sheet is comparable to the wavelength of the kink mode. On the other hand, two-dimensional simulations in the plane orthogonal to the magnetic field shows that in higher mass ratio cases with mi/me>100 the electron thermalization is caused due to a hybrid-scale mode with wavelength intermediate between the ion and electron inertia lengths kyλiλe∼1 rather than the large-scale kink mode with kyL∼1, because the electron meandering scale is shortened as the mass ratio increases.
Fluctuations in electron-positron plasmas: Linear theory and implications for turbulence
Authors: Gary S. Peter , Karimabadi Homa
Published: April 2009

Linear kinetic theory of electromagnetic fluctuations in a homogeneous, magnetized, collisionless electron-positron plasma predicts two lightly damped modes propagate at relatively long wavelengths: an Alfvén-like mode with dispersion ωr=k∥ṽA and a magnetosonic-like mode with dispersion ωr≃kṽA if βe⪡1. Here ṽA is the Alfvén speed in an electron-positron plasma and ∥ refers to the direction relative to the background magnetic field Bo. Both modes have phase speeds ωr/k which monotonically decrease with increasing wavenumber. The Alfvén-like fluctuations are almost incompressible, but the magnetosonic-like fluctuations become strongly compressible at short wavelengths and propagation sufficiently oblique to Bo. Using the linear dispersion properties of these modes, scaling relations are derived which predict that turbulence of both modes should be relatively anisotropic, with fluctuating magnetic energy preferentially cascading in directions perpendicular to Bo. Turbulent spectra in the solar wind show two distinct power-law regimes separated by a distinct breakpoint in observed frequency; this characteristic should not be present in electron-positron turbulence because of the absence of whistler-like dispersion. Linear theory properties of the cyclotron and mirror instabilities driven by either electron or positron temperature anisotropies are generally analogous to those of the corresponding instabilities in electron-proton plasmas.
The multistate multimode vibronic dynamics of benzene radical cation with a realistic model Hamiltonian using a parallelized algorithm of the quantumclassical approach
Authors: Sardar Subhankar , Paul Amit Kumar , Sharma Rahul , Adhikari Satrajit
Published: April 2009

We demonstrate the workability of a parallelized algorithm of the time-dependent discrete variable representation (TDDVR) method to explore the detailed dynamical aspects of vibronic interaction in two three-state model Hamiltonians (X 2E1g, B 2E2g, C 2A2u and B 2E2g, D 2E1u, E 2B2u) of benzene radical cation along with a preliminary investigation on its five electronic states (X 2E1g, B 2E2g, C 2A2u, D 2E1u, and E2B2u). Since those electronic states are interconnected through a series of conical intersections, we have used six and nine vibronically important modes for the three- and five-state Hamiltonians, respectively, in order to perform the quantum dynamics on such system. The population profiles calculated by using our TDDVR approach show reasonably good agreement with the results obtained by exact quantum mechanical (multiconfiguration time-dependent Hartree) method, whereas the corresponding (calculated) photoabsorption spectra originating from various electronic states agree well with the experimental ones. It is important to note that the parallelized algorithm of our TDDVR approach reduces the computation cost by more than an order of magnitude compared to its serial analog. The TDDVR approach appears to be a good compromise between accuracy and speed for such large molecular system, where quantum mechanical description is needed in a restricted region.
Numerical analysis of two homogeneous discharge modes at atmospheric pressure with a self-consistent model
Authors: Wang Qi , Sun Jizhong , Wang Dezhen
Published: April 2009

Two homogeneous discharge modes, Townsend discharge and glow discharge, can be obtained in dielectric barrier discharges at atmospheric pressure when an external voltage with an appropriate frequency is applied to the electrodes. In this paper, a one-dimensional self-consistent model was used to investigate the transition and the difference in characteristics of these two modes. The simulation results showed that the spatiotemporal distributions of the electron temperature in the two discharge modes differed noticeably. In the glow discharge, the electron temperature in the cathode fall was several times higher than that in any of the other regions; in contrast, the electron temperature in the Townsend discharge was approximately spatially uniform. The electron energy distribution functions (EEDFs) at different locations in the discharge gap at the discharge current peaks were given and analyzed. In the glow discharge, the EEDF in the cathode fall region contained the largest percentage of high energy in all regions, and the majority of the electrons in the negative glow region possessed very low energy. However in the Townsend discharge, the EEDFs at different locations were similar to each other. In addition, both the discharge current density and the voltage drop on the discharge gas versus the applied voltage were also examined. It was found that when the applied voltage was over a critical value, the Townsend discharge turned into the glow discharge, the peak magnitude of the discharge current density increased abruptly. The maximum of the discharge current density was nearly a linear function of the applied voltage, while the voltage drop on the discharge gas was approximately a constant. Also, we found that there was a minimum of the applied voltage leading to the transition from the Townsend discharge to the glow discharge as the discharge gap spacing varied.
Path-integral Monte Carlo simulation of ν3 vibrational shifts for CO2 in (He)n clusters critically tests the He–CO2 potential energy surface
Authors: Li Hui , Blinov Nicholas , Roy Pierre-Nicholas , Le Roy Robert J.
Published: April 2009

Path-integral Monte Carlo simulations of the ν3 vibrational band origin frequency shifts of CO2 in (He)n clusters for n=1–40 show that although only the asymmetric-stretch mode of CO2 is being excited, the effect of the associated change in the average value of Q1 cannot be ignored. When this fourth degree of freedom is taken into account, the resulting predicted vibrational frequency shifts are in excellent agreement with experiment across this whole range of cluster size. It is also shown that the quality of predictions obtained from simulations on a given potential energy surface can depend significantly on the choice of the analytic function used to represent it.