Close-coupled nozzle atomization integral simulation and powder preparation using vacuum induction gas atomization technology

We simulate the gas-atomization process of a close-coupled annular nozzle for vacuum induction gas atomization at a three-dimensional scale.Moreover,the relationship between the simulated droplet type and experimentally metallic powder is established by comparing the morphology of droplets with powders.Herein,the primary atomization process is described by the volume-of-fluid(VOF)approach,whereas the prediction of powder diameter after secondary atomization is realized by the VOF-Lagrangian method.In addition,to completely reflect the breaking and deformation process of the metallic flow,we employ the VOF model to simulate the secondary atomization process of a single ellipsoidal droplet.The results show that the primary atomization process includes the formation of surface liquid film,appearance of serrated ligaments,and shredding of ligaments.Further,gas recirculation zone plays an important role in formation of the umbrella-shaped liquid film.The secondary atomization process is divided into droplet convergence and dispersion stages,and the predicted powder diameter is basically consistent with the experiment.In general,the four main powder shapes are formed by the interaction of five different typical droplets.     

Three-loop mixing of dipole operators

We calculate the complete three-loop O(alpha(3)(s)) anomalous dimension matrix for the dimension-five dipole operators that arise in the standard model after integrating out the top quark and the heavy electroweak bosons. Our computation completes the three-loop anomalous dimension matrix of operators that govern low-energy |DeltaF| = 1 flavor-changing processes, and represents an important ingredient of the next-to-next-to-leading order QCD analysis of the B--> X(s)gamma decay.     

Three-loop beta-function of the Wess-Zumino-Witten model

The three-loop beta function for the Wess-Zumino-Witten model is presented. Dimensional regularization is used in the calculation. The result agrees with the exact solution.     

Three-loop counterterms for extended supergravity

An invariant three-loop counterterm is exhibited for O(2) supergravity; its presence would imply nonrenormalizability. The analogous one-loop invariant due to O(2) supermatter coupling is also given. Involved are new conserved quantities due to the internal symmetry and to symmetry between fields separated by one spin unit.     

Three-loop vanishing of the superstring cosmological constant

We employ a holomorphic unitary gauge to evaluate the genus-three partition function for closed superstrings in ten-dimensional flat space in the picture-changing representation. The Riemann identity leads to a pointwise vanishing measure in moduli space which trivially avoids global ambiguities.     

Three-loop corrections in a covariant effective field theory

Chiral effective field theories have been used with success in the study of nuclear structure. It is of interest to systematically improve these energy functionals (particularly that of quantum hadrodynamics) through the inclusion of many-body correlations. One possible source of improvement is the loop expansion. Using the techniques of Infrared Regularization, the short-range, local dynamics at each order in the loops is absorbed into the parameterization of the underlying effective Lagrangian. The remaining nonlocal, exchange correlations must be calculated explicitly. Given that the interactions of quantum hadrodynamics are relatively soft, the loop expansion may be manageable or even perturbative in nuclear matter. This work investigates the role played by the three-loop contributions to the loop expansion for quantum hadrodynamics.     

Three-dimensional integral imaging with improved visualization using subpixel optical ray sensing

In this Letter, we propose an improved three-dimensional (3D) image reconstruction method for integral imaging. We use subpixel sensing of the optical rays of the 3D scene projected onto the image sensor. When reconstructing the 3D image, we use a calculated minimum subpixel distance for each sensor pixel instead of the average pixel value of integrated pixels from elemental images. The minimum subpixel distance is defined by measuring the distance between the center of the sensor pixel and the physical position of the imaging lens point spread function onto the sensor, which is projected from each reconstruction point for all elemental images. To show the usefulness of the proposed method, preliminary 3D imaging experiments are presented. Experimental results reveal that the proposed method may improve 3D imaging visualization because of the superior sensing and reconstruction of optical ray direction and intensity information for 3D objects.     

Multiple scattering using the Foldy-Twersky integral equation

The importance of multiple scattering processes for the propagation of ultrasound through dispersions is assessed. Under certain well defined conditions, the Foldy-Twersky integral equation can be used to find a value for the amplitude and complex wavenumber of the multiply scattered plane wave collected by either the receiving or the emitting transducer. Expressions for the amplitude and wavenumber are evaluated in terms of particle number density, wavelength of ultrasound and the forward and backward scattering amplitudes. In the case where the wavelength is much greater than the particle size, explicit expressions for the real and imaginary parts of the wavenumber are provided, in terms of the scattering and absorption cross-sections, as far as terms in the square of the number density of particles.     

Three-loop ß-functions of non-linear σ models on symmetric spaces

It is shown that the renormalization group ß-functions of the two-dimensional non-linear σ models on various symmetric spaces are determined up to three-loop order by the isomorphic relations between the classical groups.     

Three-loop anomalous dimension of the non-singlet transversity operator in QCD

We calculate the three-loop anomalous dimension of the non-singlet transverse operator from N=1$N=1$ to N=15$N=15$. Using some guess we have reconstructed a general form of three-loop anomalous dimension for arbitrary Mellin moment N. Obtained result is transformed into Bjorken-x space by an inverse Mellin transformation. The final expressions are presented in both Mellin-N and Bjorken-x space.     

Three-loop corrections in a new variational treatment ofλφ 4

We present the three-loop calculation of the effective potential forλφ ⁴ in 3+1 dimensions, based on a new variational approach to quantum field theory. This formulation is based on a 2PPI loop expansion of an effective action for local composite operators and yields non-perturbative results. Renormalisation is carried out for both the trivial and the precarious phase using dimensional regularisation. The three-loop result is seen to be similar to the one-loop result (which coincides with the G.E.P.) and only one numerical constant in the effective potential has to be changed.     

Giant magnetoresistive coatings using thermionic vacuum arc technology

Giant magnetoresistive (GMR) coatings on silicon, glass and Kapton were prepared by simultaneous thermionic vacuum arc (TVA) discharges in high vacuum conditions. The magnetic metal or alloy (Fe, Co, Ni, Permalloy) together with the noble non magnetic metal were deposited on substrates having different positions relative to the discharges. Local magnetic interactions and Fe-phase composition were obtained by Mössbauer spectroscopy whereas the magnetoresistance effects were measured by a dc method using a four-point configuration with perpendicular to plane magnetic fields up to 0.8 T. The surface morphology of the coatings was characterized by atomic force microscopy (AFM) in contact mode.     

Three-loop calculation of the beta-function for the purely metric non-linear sigma-model

We present the results of an explicit calculation of the ultraviolet divergences, up to three loops in perturbation theory, of the non-linear sigma-model in two dimensions. The beta-function is computed and shown to derive from the string effective action.     

Stokes–Darcy boundary integral solutions using preconditioners

In a system where a free fluid flow is coupled to flow in a porous medium, different PDEs are solved simultaneously in two subdomains. We consider steady Stokes equations in the free region, coupled across a fixed interface to Darcy equations in the porous substrate. Recently, the numerical solution of this system was obtained using the boundary integral formulation combined with a regularization-correction procedure. The correction process also results in the improvement of the condition number of the linear system. In this paper, an appropriate preconditioner based on the singular part of corrections is introduced to improve the convergence of a Krylov subspace method applied to solve the integral formulation.     

Detection of vacuum birefringence using intense laser pulses

We propose a novel technique that promises hope of being the first to directly detect a polarization of the quantum electrodynamic (QED) vacuum. The technique exploits the high fields associated with ultra-short pulses of light stored in low dispersion optical resonators. We show that the technique circumvents the need for large-scale liquid helium cooled magnets, and more importantly avoids the experimental pitfalls that plague existing experimental approaches that use these magnets. The new technique has a predicted birefringence measurement sensitivity of Δn10⁻²⁰ in a 1 s measurement. Currently available optics and lasers will enable observation of vacuum polarization in an experiment of only a few days in duration.     

One electron atoms in both a squeezed vacuum and a magnetic field via path integral methods

In the present paper we study the dynamics of one-electron atoms in the presence of both a linearly polarized squeezed vacuum and a magnetic field along the polarization vector of the photonic field. We adopt the dipole approximation and approach the problem via path integral methods. After integrating over the light variables for certain initial and final squeezed vacuum states we treat the path integral over the spatial variables via Monte-Carlo methods. As an application we calculate the survival probability of the ground state of a one-electron atom for various values of the magnetic field. Received 30 November 2000 and Received in final form 15 February 2001