Electron holography with atomic focusers

In a modified form of electron holography, as originally proposed by Gabor, a specimen illuminated by the focused, convergent beam of a scanning transmission electron microscope is followed by a thin crystal which acts as a periodic array of atomic focusers. Each of the broad diffraction spots of the crystal then contains a magnified image of the specimen with a resolution limit of 0.05 nm or less. The method is illustrated by images of crystal lattice planes and tungsten atoms in the diffraction patterns formed by crystals in the walls of carbon nanoshells.     

Republication of: Observations in cosmology

This is a reprinting of a paper by Jerome Kristian and Rainer K. Sachs, first published in 1966, in which they proposed a power-series scheme for reading out various parameters of the Universe directly from observations in a model-independent way. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by George Ellis and by a brief biography of J. Kristian, compiled by A. Krasiński from internet sources.     

A new method for predicting nonlinear structural vibrations induced by ground impact loading

Based on nonlinear theory and field measurements, a hybrid method for modeling the time history of structural vibrations resulting from impact loading in the vicinity of a structure is presented in this paper. The characteristics of the medium present between the impact source and a measured location inside of a structure are depicted by a nonlinear system that can be modeled by a Volterra functional series. The nonlinear system can be identified by the inputs and the corresponding output signals, which can be obtained by performing in situ experiments. Then, the predicted signal induced by a known impact loading at the measured location can be calculated using the identified Volterra functional series. Moreover, the structural vibration under a known impulse train can be controlled by adjusting the delay period according to the predicted results. In addition, the method has been verified by applying it in two practical applications: the cases of impact loading induced by either the impact of a hammer or blasting. The results show that the method features convenient application, high precision and extensive applicability for various types of impact loadings.     

Specification of spectral line shape and multiplex dispersion by self-imaging and moiré technique

Due to finite width of a spectral line, the visibility of the moiré fringes formed by a grating and the self-image of another similar grating reduces by the increase of the self-image order. This effect is exploited to specify the spectral line shape by evaluating the Fourier transform of a function related to the visibility. Even, by using in-expensive optics, the technique can provide the spectral line shapes of rather broad widths—of the order of nanometer and more—by precisions that are comparable by those obtained by expensive Fourier transform spectrometers.Besides, it is shown that by comparing the line shapes obtained with and without a dispersive medium between the gratings, one can specify the dispersion function of the medium in the wavelength range covered by the spectrum.     

A method to predict the transmission of sound through corridors

This paper describes research carried out to provide a method by means of which sound levels in rooms adjacent to a corridor, produced by the transmission of sound through the corridor from another room, can be predicted. This has been done by using an acoustic scale model to show how the physical parameters of the corridor affect the transmission of sound into, out of and along the corridor. From analysis of the experimental results, empirical formulae are obtained to predict: (1) sound levels along a corridor produced by a sound source in the corridor or an adjacent room, (2) sound levels along a side corridor produced by a sound source in the main corridor and (3) sound levels in rooms adjacent to the corridor produced by a sound source in another room.     

Suppression of thermoelastic damping in MEMS beam resonators by piezoresistivity

Microelectronic mechanical (MEM) beam resonators with high quality factors are always preferred in practical applications. As one of the damping sources, thermoelastic damping (TED) caused by irreversible heat flows is usually considered as an upper limit of the overall damping effect. A new method is proposed in this work to compensate TED by taking advantage of the piezoresistive effect. Such a method is implemented by applying an electrostatic field along the beam length with a negative piezoresistive coefficient. During a resonance, the stretched part of the beam generates a higher electrical power density and thus a higher temperature, while the compressed region leads to a lower temperature. Such a temperature distribution is opposite to the temperature change caused by the thermoelastic effect. The working principle is described by a set of coupled differential equations, which are subsequently solved by the finite element method. The result indicates that the TED in the beam resonators can be completely compensated when the strength of electrical field is tuned to a critical value, namely CEF. The value of the CEF is further analyzed by a series of parametric studies on various material properties and geometric factors.     

Coarsening and pearling instabilities in silver nanofractal aggregates

We investigate the morphological changes of 3D supported fractal aggregates generated through the deposition of silver clusters on graphite. The fractal relaxation, activated after their formation by perturbing them either by thermal annealing or by using a surfactant, as oxide molecules, carried by silver clusters in a subsequent deposition, shows evidence of two distinct fragmentation patterns. The post coarsening, driven by thermal heating, gives a broad asymmetrical distribution of fragments in agreement with a random process, whereas the entire silver fractal pearling fragmentation is driven by chemical adjunction of the surfactant.     

A short proof of a Kupershmidt-Wilson theorem

This is a short elementary proof of a statement originally observed by Adler, then pursued by the author, by Kupershmidt and Wilson, and in a more general setting by Drinfeld and Sokolov.     

Plasma generated from collision of cluster beams

Processes are analyzed in the course of production of a microplasma as a result of the collision of two dense cluster beams. In reality, this microplasma is characterized by a lifetime of ～1 ns, by a size of ～0.01 cm, by a number density of electrons of ～10²⁰ cm^?3, by an electron temperature of several tens of eV, and by a charge of its multicharged ions of up to z = 10. Under contemporary conditions, the laser method allows one to create a hot microplasma with a higher electron temperature and charge of atomic ions.     

Pulse shaper in a loop: demonstration of cascadable ultrafast all-optical code translation

We experimentally demonstrate repetitive M-ary spectral phase pulse shaping by placing a programmable pulse shaper driven by a 10-GHz source in a closed loop. This permits generation of encoded and decoded signals in the same apparatus by forming a closed loop to circulate a part of the output back into the pulse shaper. As a result, a series of M - 1 distinct encoded waveforms is sequentially generated, followed by generation of a properly decoded pulse.     

3D shape from phase errors by using binary fringe with multi-step phase-shift technique

A three-dimensional shape measurement method is presented, which is a uniaxial measurement by measuring phase errors instead of the well-known phase, modulation or contrast. A sequence of exposures are captured by using a multi-step phase-shift technique with the binary fringes. Then the high-accuracy phases can be obtained by using all the exposures, meanwhile, a set of low-accuracy phases can be calculated by dividing those exposures into a set of four-step phase-shift measurements. For each pixel there will be a set of phase errors by subtracting low-accuracy phases from the high-accuracy ones. And the weighted phase error of every pixel can be calculated. Meanwhile the phase error caused by the improperly defocused binary fringes has a unique relationship with the depth z. Therefore, the 3D information of every pixel can be obtained by analyzing the phase errors. It will be promising for a uniaxial measurement, such as deep holes.     

Scattering and absorption of particles by a black hole involving a global monopole

Under the conditions that the wavelength of a particle is much larger than its radius of central mass, and the Schwarzschild field is weak, the scattering of a particle has been studied by many researchers. They obtained that scalar and vector particles abide by Rutherford’s angle distribution by using the low level perturbation method and the scattered field’s approximation in a weak field. The scattering cross section of a photon coincides with the section in Newton’s field of point mass. We can obtain the photon’s polarization effect by calculating the second-order perturbation in the linear Schwarzschild field. This article discusses the scattering and absorption of a particle by a black hole involving a global monopole by using the aforesaid method.     

Effect of interference pattern on femtosecond laser-induced ripple structure

Combined structures composed of a micron-sized periodic structure and a nano-sized quasi-periodic ripple structure were generated by a single process of multiple shots of an interfering femtosecond laser. The former structure was generated by an interference pattern and controlled by a number of beams. The latter structure was generated by a multiple shot method. As a result, multiple periodic structures were generated. The periodicity of the structures was analyzed by two-dimensional (2D) fast Fourier transform (FFT). The most probable period of ripple structure was downsized to 177 nm by restricting irradiated region by a TM wave interference pattern. The smallest period was 105 nm. The dispersion angle of a ripple decreased to about 50%. The period and direction of the ripples were for a first time controlled by using interference.     

Failure of a proposed superluminal scheme

We consider a “superluminal quantum Morse telegraph”, recently proposed by Garuccio, involving a polarization-correlated photon pair and a Michelson interferometer in which one of the mirrors is replaced by a phase-conjugating mirror (PCM). Superluminal information transfer in this scheme is precluded by the impossibility of distinguishing between unpolarized photons prepared by mixing linear polarization states or by mixing circular polarization states.     

Evolutionary games with two timescales

We consider a two timescale model of learning by economic agents wherein active or ‘ontogenetic’ learning by individuals takes place on a fast scale and passive or ‘phylogenetic’ learning by society as a whole on a slow scale, each affecting the evolution of the other. The former is modelled by the Monte Carlo dynamics of physics, while the latter is modelled by the replicator dynamics of evolutionary biology. Various quanlitative aspects of the dynamics are studied in some simple cases, both analytically and numerically, and its role as a useful modelling device is emphasized. rights reserved.     

A Diffusion Limit for a Test Particle in a Random Distribution of Scatterers

We consider a point particle moving in a random distribution of obstacles described by a potential barrier. We show that, in a weak-coupling regime, under a diffusion limit suggested by the potential itself, the probability distribution of the particle converges to the solution of the heat equation. The diffusion coefficient is given by the Green–Kubo formula associated to the generator of the diffusion process dictated by the linear Landau equation.     

Generation of terahertz radiation by the optical breakdown induced by a bichromatic laser pulse

Experimental results are presented on generation of terahertz radiation by the air breakdown induced by a high-intensity laser pulse having not only a fundamental component, but also a second-harmonic one. A theoretical explanation of the experimental data is proposed, based on a model of field ionization of a gas by a bichromatic laser.     

Design and calibration of a piezoelectric actuator for interferometric applications

The present work reports a possible solution for a low-cost piezoelectric actuator available for interferometric applications. In the paper the design, the assembly and the calibration of the actuator are described in detail.

The solution adopted consists of a machined stainless steel case deformed by three low-voltage multilayer plumbum zirconate titanate (PZT) ceramic blocks. In the proposed arrangement a three degree of freedom device is obtained, by which a translation and two rotations can be performed.

The PZTs are driven by a supply voltage provided by a 16 bit D/A converter directly connected to the parallel port of a personal computer which guarantees a very accurate output. This voltage is applied on each ceramic by means of a variable resistor, by which it is possible to adjust the maximum driving voltage for the single block. This electrical solution allows to match up the strokes of the ceramics in order to obtain a straight expansion of the whole actuator.

After the mechanical and electrical set-up of the actuator, a static calibration was carried out by inserting it along one arm of a Michelson speckle interferometer. The calibration procedure had emphasized the hysteresis loop and the non-linearity of the electromechanical behaviour of the actuator.     

Friedmann cosmology with decaying vacuum density

Among the several proposals to solve the incompatibility between the observed small value of the cosmological constant and the huge value obtained by quantum field theories, we can find the idea of a decaying vacuum energy density, leading from high values at early times of universe evolution to the small value observed nowadays. In this paper we consider a variation law for the vacuum density recently proposed by Schützhold on the basis of quantum field estimations in the curved, expanding background, characterized by a vacuum density proportional to the Hubble parameter. We show that, in the context of an isotropic and homogeneous, spatially flat model, the corresponding solutions retain the well established features of the standard cosmology, and, in addition, are in accordance with the observed cosmological parameters. Our scenario presents an initial phase dominated by radiation, followed by a dust era long enough to permit structure formation, and by an epoch dominated by the cosmological term, which tends asymptotically to a de Sitter universe. Taking the matter density equals to half of the vacuum energy density, as suggested by observation, we obtain a universe age given by Ht = 1.1, and a decelerating parameter equals to −1/2.     

The Bragg Diffraction of Light at Acoustophotorefractive Holographic Gratings in Gyrotropic Cubic Crystals

We investigate diffraction of light at phase holographic-type gratings recorded by a piezoactive ultrasonic wave in gyrotropic cubic photorefractive crystals. We show that the efficiency of diffraction at a holographic grating can be increased substantially by applying a d.c. field to a crystal under the conditions of a longitudinal electrooptical effect; elliptical polarization of diffracted light is determined by electrically induced anisotropy of a crystal in the piezofield of a photorefractive grating, by the external electric field, detuning of phase synchronism, gyrotropy of the crystal, ultrasound frequency, and the time of recombination of charge carriers.