Morphology of the nonspherically decaying radiation beam generated by a rotating superluminal source

We consider the nonspherically decaying radiation field that is generated by a polarization current with a superluminally rotating distribution pattern in vacuum, a field that decays with the distance R(P) from its source as R(P)(-1/2), instead of R(P)(-1). It is shown (i) that the nonspherical decay of this emission remains in force at all distances from its source independently of the frequency of the radiation, (ii) that the part of the source that makes the main contribution toward the value of the nonspherically decaying field has a filamentary structure whose radial and azimuthal widths become narrower (as R(P)(-2) and R(P)(-3), respectively) the farther the observer is from the source, (iii) that the loci on which the waves emanating from this filament interfere constructively delineate a radiation subbeam that is nondiffracting in the polar direction, (iv) that the cross-sectional area of each nondiffracting subbeam increases as R(P), instead of R(P)(2), so that the requirements of conservation of energy are met by the nonspherically decaying radiation automatically, and (v) that the overall radiation beam within which the field decays nonspherically consists, in general, of the incoherent superposition of such coherent nondiffracting subbeams. These findings are related to the recent construction and use of superluminal sources in the laboratory and numerical models of the emission from them. We also briefly discuss the relevance of these results to the giant pulses received from pulsars.     

Temperature distribution in a uniform medium heated by linear absorption of a Gaussian light beam

The linear-diffusion equation is considered for a positive half-space with heat sources represented by Gaussian functions in the transverse plane and by exponential decay along the longitudinal axis. The exact solution is presented as a single quadrature of the complementary error function (erfc). The approximate solution is suggested in the form of the product of two Gaussian functions and the hyperbolic secant function. Comparison with the exact solution shows that the error of this approximation is near 10%. The approximation may be used in different medical applications, e.g., laser angioplasty.     

Calculating the pressure force of the non-paraxial cylindrical Gaussian beam exerted upon a homogeneous circular-shaped cylinder

Forces exerted upon a dielectric cylinder of infinite length and arbitrary, or circular, cross-section by the non-paraxial cylindrical Gaussian beam are considered. The projections of the vector of the light force pressure exerted upon a dielectric cylinder of arbitrary and circular cross-section are expressed analytically. In particular, the pressure force is expressed through the coefficients of decomposition of the non-paraxial Gaussian beam into the cylindrical functions. Using numerical examples, a possibility to optically trap a circular-shaped cylinder in two oppositely directed Gaussian beams or a single non-paraxial Gaussian beam is demonstrated.     

Morphology of the nonspherically decaying radiation beam generated by a rotating superluminal source: comment

The same elementary disproof of the claimed "nonspherical" decay that I have given before applies. A comment asserting the correctness of the relevant formula from a standard text on electrodynamics is added at the end.     

Effect of stream swirling on the velocity and temperature distributions in a round tube

The results of a numerical study of the effect of stream swirling on the laminar flow structure and heat exchange in a round tube are presented.     

Formation of stable stacking zones in a flow stream for sample immobilization in microfluidic systems

Electrocapture is a multifunctional microfluidic tool that can be used for concentration, sample cleanup, multistep reactions, and separation of biomolecules. Herein, we investigate the mechanisms underlying the electrocapture principle. A microfluidic electrocapture device was found to be capable of generating regions of different electric field, which are maintained in the flow by electric and hydrodynamic forces, with the zones of lower electric field strength upstream of those with higher strength. In addition to detection of the local electric fields by direct measurements, the existence of the zones was observed by the capture of a solution containing Coomassie and myoglobin. The two molecules were captured at different spots in a steady-state manner and were released (separated) at different electric fields. Considering these observations and the experimental values for the electric field strengths, flow velocities, and electrophoretic mobilities of DNA, proteins, and peptides, it is concluded that the macromolecules are captured between the field zones by a stacking mechanism.     

The effect of thermal self-action of a light beam in a shear flow

The effect of thermal self-action in a shear gas flow transverse to the beam and containing a stagnation domain is investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 1, pp. 51–56, January, 1987.     

Electrochemistry in the presence of convective flow generated by acoustic streaming from a focused ultrasonic source

Limiting currents for the reduction of hexacyanoferrate-(III), i(lim), in aqueous solutions have been recorded in the presence of convective flow generated by a focused acoustic source with its main axis placed normal to the surface of a circular Au electrode embedded in a coplanar Teflon shroud. The results obtained could be fitted to a formula of the type -i(lim) = a(Uz(ss))b, where Uz(ss) is the axial velocity of the fluid along the center line of the lens evaluated at the focal point using computer simulation routines developed by Kamakura and co-workers (Kamakura, T.; Matsuda, K; Kumamoto, Y.; Breazeale, M. A. J. Acoust. Soc. Am. 1995, 97, 2740-2746). The fit yielded a value of b approximately 0.5 in agreement with that of rotating disk and impinging jet electrodes.     

Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator

We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.     

Influence of forward and multiple light scatter on the measurement of beam attenuation in highly scattering marine environments

Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1 degrees) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0 degrees and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m(-1), the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.     

Segregation behavior of particles with Gaussian distributions in the rotating drum with rolling regime

The mixing and segregation of granular materials are essential to provide valuable insights and references for practical industrial production. In this paper, the segregation behaviors of particles with Gaussian distributions and 40% filling level in the rotating drum with rolling regime were numerically studied by the discrete element method. The effects of rotation speed and particle size parameter λ (size ratio of the largest versus smallest particles) on the segregation behavior (mixing index, segregation rate), flow characteristics (particle velocity and trajectory, gyration degree and radius, particle size distributions) and the microscopic properties (collision, contact force, axial diffusion, and kinetic energy) of granular systems were systematically investigated. The results show that the segregation rate and degree of particles with Gaussian distributions gradually increase with the increase of the rotation speed and particle size parameter λ. The radial and axial segregation patterns become more obvious with the increase of λ. And the variation of the flow characteristics of particles with different sizes in the same system is also inconsistent. The microscopic properties of Gaussian-dispersed particles change with the rotation speed and λ. The rapid radial segregation depends on the larger pores existed in the granular system, which leads to a gradual increase of the axial dispersion coefficient of large particles and a gradual decrease of the axial dispersion coefficient of small particles.     

Effect of a gas stream on the wave flow of thin layers of a viscous liquid

An analytical study was undertaken of the effect of a gas stream on the wave flow characteristics of thin layers of a viscous liquid moving over a vertical surface. The results of the investigations are compared with experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 6, pp. 989–994, December, 1969.     

Accelerating the annihilation of an optical vortex dipole in a Gaussian beam

When a Gaussian beam with two oppositely charged vortices propagates in free space, these two vortices will move around on the transverse beam plane. They may either move toward each other and annihilate each other spontaneously or survive all the way depending on the conditions. Here, we investigate how to force vortex dipoles to annihilate. We find that the background phase function created by two oppositely charged vortices during beam propagation can cause the vortices to move together and annihilate each other. The background phase function on a transverse plane just beyond the point where a dipole annihilated is continuous and retains the potential that forces a dipole to annihilate. We use this background phase function to accelerate the annihilation of vortex dipoles. Numerical results are provided to show the acceleration of dipole annihilation in a Gaussian beam, using such a background phase function.     

Single Gaussian beam interaction with a Kerr microsphere: characteristics of the radiation force

We analyze the characteristics of the radiation force that is generated when a highly focused unpolarized Gaussian beam interacts with a nonabsorbing microsphere whose refractive index exhibits a first-order dependence on the beam intensity. The behavior of the force exerted on the sphere is analyzed as a function of beam power, axial distance, sphere radius, refractive-index difference between the sphere and the surrounding liquid, and wavelength. The force characteristics are compared with those of the radiation force that is generated when the electro-optic Kerr effect is absent. Our results show that a reversal in the net force direction is introduced when the Kerr effect becomes significant, which occurs at sufficiently high beam intensities.     

Forced flow of a vapor-liquid stream in a horizontal pipe with film boiling

The stream structure and flow regime during film boiling of liquid nitrogen in a horizontal pipe are investigated. Data on heat transfer are obtained and a model is proposed for calculating the parameters of the two-phase stream along the channel length.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 5, pp. 724–729, May, 1986.     

Analysis of the scatter growth in dispersive media with the use of dynamic light scattering

Analysis of the structure functions of intensity fluctuations of scattered laser light was applied to monitor the phase separation in probed disperse media. UV-cured mixtures of a liquid crystal and prepolymer were studied during the formation of the structure of dispersive polymer-liquid crystal (DPLC) composites. The experimentally observed features of light beating induced by dynamic light scattering in DPLC systems (the scaling properties of the structure functions, the narrowing of the beating spectrum for certain weight fractions of the liquid-crystalline component) were interpreted in terms of the discrete scattering model using the results of statistical modeling.     

Effect of scatter on reconstructed image quality in cone beam computed tomography: evaluation of a scatter-reduction optimisation function

The effect of scatter on reconstructed image quality in cone beam computed tomography was investigated and a function which can be used in scatter-reduction optimisation tasks was tested. Projections were calculated using the Monte Carlo method in an axially symmetric cone beam geometry consisting of a point source, water phantom and a single row of detector elements. Image reconstruction was performed using the filtered backprojection method. Image quality was assessed by the L2-norm-based difference relative to a reference image derived from (1) weighted linear attenuation coefficients and (2) projections by primary photons. It was found that the former function was strongly affected by the beam hardening artefact and did not properly reflect the amount of scatter but the latter function increased with increasing beam width, was higher for the larger phantom and exhibited properties which made it a good candidate for scatter-reduction optimisation tasks using polyenergetic beams.