Computer simulation studies of magnetic phase transitions

The advancements which have been made in the use of computer simulations to study magnetic-phase transitions and critical phenomena are reviewed. We describe how the use of a combination of sophisticated Monte Carlo simulation algorithms and reweighting (histogram) techniques have allowed the determination of the static critical behavior with unprecedented precision. The study of “dynamic” critical behavior in simple spin models by both Monte Carlo and spin dynamics methods is also reviewed. Recent estimates for dynamic critical exponents are given including those for true dynamics.     

Measurement of the Proton Structure Function F 2 at Low Q 2 and Very Low x with the ZEUS Beam Pipe Calorimeter at HERA

Three different kinds of scaling are observed in a toy model of turbulence (“GOY”). The first has a multifractal spectrum of exponents. The second is a simple static selfsimilarity solution. The third phase is dynamic but has simple scaling. This last previously unreported equipartition behavior is discussed. It is drastically different from the other two in terms of its scaling exponent(s) and emerges when the energy flux on the boundaries vanishes (no dissipation and no forcing).     

Study of Frozen Waves’ theory through a continuous superposition of Bessel beams

This paper presents a study of a recent solution to Maxwell's equation, the so-called “Frozen Waves”, whose main characteristics are to remain static in space, and to keep an arbitrary longitudinal field pattern previously chosen. These waves could be obtained by an adequate, but discrete, superposition of monochromatic Bessel beams. Contrary to that, we have here proposed a new way to get these waves through a continuous superposition of Bessel beams, and discussed some physical aspects and then exemplified for both loss and lossless media.     

Discrete Element Method studies of the collision of one rapid sphere on 2D and 3D packings

We performed numerical simulations of one-bead collision on the surface of a static granular medium. The simulations have been done for two- and three-dimensional packings of beads. The effect of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings and only disordered 3D packings. The 2D results are in good agreement with experimental available data. The 3D simulations give good preliminaries results about the shock-wave propagation through the stacking and provides new insights in the ejection process (“splash function”).     

The bubble cloud as an N-degree of freedom harmonic oscillator

The dynamics of a two-dimensional N-bubble static cloud is investigated and shown to be well described by an N-degree of freedom harmonic oscillator model, at least at low enough frequencies. Eigenmodes and eigenfrequencies are calculated and compared with experimental results obtained with an assembly of bubbles caught up under a net in a water tank. Accordance is found to be excellent in the frequency range of validity of the model, the limits of which are discussed. An interpretation of the low-frequency branch of Foldy’s dispersion relation in bubbly liquids is suggested in terms of “bubble waves” in a quasi-incompressible medium.     

Theoretical Studies on the Second Hyperpolarizabilities of Trithiapentalene and Its Donor and Acceptor Disubstituted Species

We study the third-order optical nonlinearity for some interesting ϖ-conjugated systems involving sulfur (S) atoms. The static second hyperpolarizabilities (γ) for l, 6, 6a-trithiapentalene and its donor-and acceptor-disubstituted species are calculated by ab initio molecular orbital and density functional methods. Using the second hyperpolarizability density analysis, these molecules are found to exhibit remarkable differences in spatial ϖ-electron contributions of unusual binding structure, i.e., S-S-S bridged structure, to the longitudinal γ.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED THECHNOLOGIES (NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Physics and Mombusho Grant-in Aid for Science Research on Priority Areas “Near-field Nano-optics” Project, sponsored by Japan Society for the Promotion of Science.     

Nucleation and growth mechanism for flame synthesis of MoO2 hollow microchannels with nanometer wall thickness

The growth and morphological evolution of molybdenum-oxide microstructures formed in the high temperature environment of a counter-flow oxy-fuel flame using molybdenum probes is studied. Experiments conducted using various probe retention times show the sequence of the morphological changes. The morphological row begins with micron size objects exhibiting polygonal cubic shape, develops into elongated channels, changes to large structures with leaf-like shape, and ends in dendritic structures. Time of probe–flame interaction is found to be a governing parameter controlling the wide variety of morphological patterns; a molecular level growth mechanism is attributed to their development. This study reveals that the structures are grown in several consecutive stages: material “evaporation and transportation”, “transformation”, “nucleation”, “initial growth”, “intermediate growth”, and “final growth”. XRD analysis shows that the chemical compositions of all structures correspond to MoO₂.     

Belting and pop, nonclassical approaches to the female middle voice: Some preliminary considerations

There is a commonly perceived difference in the sound produced in the approximate range D₄-D₅ by female singers in the western opera and concert tradition, on the one hand, and certain other styles, including rock, pop, folk, and some Broadway musicals, on the other. The term “belting” is sometimes used to refer to at least one approach to such “nonclassical” singing. In this study, based on spectrographic, electroglottographic, and sub- and supraglottal pressure measurements on representative voices of the “operatic” and “nonclassical” tradition, acoustic and laryngeal differences between the two traditions are described, and an objective, specific definition of “belting” is offered.     

K–K excitations on as “primary” superfields

We show that the K–K spectrum of IIB string on is described by “twisted chiral” superfields, naturally described in “harmonic superspace”, obtained by taking suitable gauge singlets polynomials of the D3-brane boundary superconformal field theory.To each p-order polynomial is associated a massive K–K short representation with states. The quadratic polynomial corresponds to the “supercurrent multiplet” describing the “massless” bulk graviton multiplet.     

On the theory of temporal aberrations for cathode lenses

A new approach to the theory of temporal aberration for cathode lenses is given in the present paper. A definition of temporal aberration is given in which a certain initial energy of electron emission along the axial direction ε_z1 (0ε_z1ε_0max) is considered. A new method to calculate the temporal aberration coefficients of cathode lenses named “direct integral method” is also presented. The “direct integral method” gives new expressions of the temporal aberration coefficients which are expressed in integral forms. The difference between “direct integral method” and “τ-variation method” is that the “τ-variation method” needs to solve the differential equations for the three of temporal geometrical aberration coefficients of second order, while the “direct integral method” only needs to carry out the integral calculation for all of these temporal aberration coefficients of second order.All of the formulae of the temporal aberration coefficients deduced from “direct integral method” and “τ-variation method” have been verified by an electrostatic concentric spherical system model, and contrasted with the analytical solutions. Results show that these two methods have got identical solutions and the solutions of temporal aberration coefficients of the first and second order are the same as with the analytical solutions. Although some forms of the results seem different, but they can be transformed into the same form. Thus, it can be concluded these two methods given by us are equivalent and correct, but the “direct integral method” is related to solve integral equations, which is more convenient for computation and could be suggested for use in practical design.     

Beyond nanosizing: an approach to shape analysis of fluorescent nanostructures by SMI-microscopy

Using spatially modulated illumination (SMI) light microscopy it is possible to measure the sizes of fluorescent structures that have an extension far below the conventional optical resolution limit (“subresolution size”). Presently, the sizes are determined as the object extension along the optical axis of the SMI microscope. For this, however, “a priori” assumptions on the fluorochrome distribution (“shape”) within the examined fluorescent structure have to be made. Usually it is assumed that the fluorochrome follows a Gauss-distribution or a spherical distribution. In this report we overcome the necessity to make an assumption on the shape of the fluorochrome distribution. We introduce two new experimentally obtained parameters which allow the determination of a shape measure to describe the spatial distribution of the fluorescent dye. This becomes possible by independent measurements with different excitation wavelengths. As an example, we present shape parameter measurements on individual fluorescent microspheres with a nominal geometrical diameter (“size”) of 190 nm. In the case investigated, the experimental shape correlated well with a homogeneous fluorochrome distribution (“spherical shape”) but not with a variety of other “shapes”.     

Feasibility of “intermittent” active control of combustion instabilities in liquid fueled combustors using a “smart” fuel injector

This paper describes an experimental investigation of the feasibility of an “intermittent” active control approach for suppressing combustion instabilities in liquid fueled combustors. The developed controller employs a “smart” fuel injector that can modify the spray properties in response to changes in combustor operating conditions. This action weakens or breaks up the coupling between the combustion process and combustor acoustic modes oscillations, thus preventing the excitation of large amplitude instabilities. This approach differs significantly from previously proposed active control methods, both in concept and implementation, as it requires only “intermittent” modification of the combustion process by a single control action as opposed to the continuous action required by most other active control methods. The “smart” fuel injector used in this study consisted of a double-staged, air-assisted atomizer in which counter swirling, primary (inner stage) and secondary (outer stage) air streams were supplied to the injector through separate sets of tangentially oriented orifices. Control of the ratio of air mass flow rates supplied to these two stages, by use of a diverter valve, resulted in significant changes in the spray shape and its axial, tangential, and radial velocity components. This variation in spray properties of the “smart” injector was characterized for different values of the inner to outer air flow rate ratio in cold flow tests with a PDPA system. These results were then correlated with the characteristics of the “intermittently” controlled combustor. Measured quantities included the instability amplitudes, axial dependence of the mean and oscillatory heat release amplitudes, and the characteristics of the recirculation zones, which were all shown to depend on the fuel spray properties. The results of this study demonstrate the feasibility of using “smart” fuel injectors with capabilities for varying the combustion process characteristics to reduce the amplitudes of detrimental combustion instabilities in real engines to acceptable levels.     

What is “Twang”?

A single female professional vocal artist and pedagogue sang examples of “twang” and neutral voice quality, which a panel of experts classified, in almost complete agreement with the singer's intentions. Subglottal pressure was measured as the oral pressure during the occlusion during the syllable /pae/. This pressure tended to be higher in “twang,” whereas the sound pressure level (SPL) was invariably higher. Voice source properties and formant frequencies were analyzed by inverse filtering. In “twang,” as compared with neutral, the closed quotient was greater, the pulse amplitude and the fundamental were weaker, and the normalized amplitude tended to be lower, whereas formants 1 and 2 were higher and 3 and 5 were lower. The formant differences, which appeared to be the main cause of the SPL differences, were more important than the source differences for the perception of “twanginess.” As resonatory effects occur independently of the voice source, the formant frequencies in “twang” may reflect a vocal strategy that is advantageous from the point of view of vocal hygiene.     

Simulation of Magnetic Resonance Static Powder Lineshapes: A Quantitative Assessment of Spherical Codes

Simulation of magnetic resonance static powder spectra is performed by a (possibly weighted) summation of single-crystal spectra computed for different orientations of the external field with respect to the principal axes of the magnetic interactions. The many available methods differ in the choice of the integration points (i.e., orientations) and weights, the set of which is called spherical code. There is continuing interest in minimizing the number of integration points necessary to a good simulation. Neglecting the possible interpolation of transition frequencies and intensities between integration points, we turn our attention to the efficiency of spherical codes themselves. To this end, an unbiased quantitative procedure to assess their efficiency in simulating magnetic resonance static powder spectra is proposed. To achieve an impartial judgement, the procedure has been designed by carefully taking into consideration the following points: choice of exact reference spectra; accurate definition of the merit figures; extended range of number of integration points; orientation dependence of the efficiency. The proposed procedure has been applied to an inclusive set of 23 spherical codes. It was found that most codes perform rather similarly. SPIRAL is the most efficient code, whereas Monte Carlo and “repulsive” codes show the best rotational invariance of the simulated lineshape with respect to the orientation of the spherical code.     

Quantum interference rectifier

Electron transport in bent quantum wire in the presence of a magnetic field which is orthogonal to the system plane is considered. Possible constructions of “quantum interference switch” and “quantum interference rectifier” are suggested.     

“Alternative medical therapy” use among singers: Prevalence and implications for the medical care of the singer

Singers are extremely conscious of health problems that affect their voices and well-being and often take an active role in seeking care for these problems. They frequently seek treatment from providers or with modalities considered “alternative” to traditional medical care. A survey of singers was completed to elucidate their attitudes and practices regarding “alternative modalities” of medical care. Frequently singers will self-medicate or take advice from people not well versed in the special needs of a professional voice user. They will fail to share this information with the physician when seeking “traditional” medical care. These practices may predispose the singer to suboptimal or even dangerous care. These results are discussed, as well as the implications for the medical physician treating the singer. The possible detrimental pharmacologic effects of “natural therapies” widely used by singers are presented, with special attention to the particular concerns for the professional singer     

Vague concept of “reversible cleavage” in the theory of the surface tension of solids

Numerous derivations of the well-known Shuttleworth equation have been based on the unclear concept of “reversible cleavage” leading to the decisive step in any derivation - equalization of the surface free energy and surface stress. This is the key concept in contemporary surface thermodynamics of solids. But “cleavage” is not a surface process and, in this field, it cannot be a reversible operation. Besides, the “reversible cleavage” has no formal definition in the domain of the surface tension of solids that is an abnormal for any exact science. Consequently, this concept and all its corollaries including the Shuttleworth and generalized Lippmann equations have to be recognized as incorrect.     

Phonetographic profiles and F0-SPL characteristics of untrained versus trained vocal groups

The phonetogram has been recommended as an international tool for voice analysis. However, the capability of this technique to distinguish between different vocal groups has not been clearly established. The purpose of this study was to examine untrained versus trained vocalists using the phonetogram and the fundamental frequency by intensity (F₀/SPL) information derived through that method. In this study, “musical” or “controlled” ranges of phonation were stressed rather than “physiological” ranges. Results indicated that (a) characteristic phonetographic profiles may be established for untrained versus trained vocalists, and (b) trained vocalists show significantly increased capability in terms of F₀ range and maximum, minimum, and comfortable SPL production. Elicitation of “controlled” phonations may be the key to revealing the underlying vocal capabilities of seemingly different vocal groups.