Breit-Wheeler Process in Intense Short Laser Pulses

Energy-angular distributions of electron-positron pair creation in collisions of a laser beam and a nonlaser photon are calculated using the $S$-matrix formalism. The laser field is modeled as a finite pulse, similar to the formulation introduced in our recent paper in the context of Compton scattering [Phys. Rev. A {\bf 85}, 062102 (2012)]. The nonperturbative regime of pair creation is considered here. The energy spectra of created particles are compared with the corresponding spectra obtained using the modulated plane wave approximation for the driving laser field. A very good agreement in these two cases is observed, provided that the laser pulse is sufficiently long. For short pulse durations, this agreement breaks down. The sensitivity of pair production to the polarization of a driving pulse is also investigated. We show that in the nonperturbative regime, the pair creation yields depend on the polarization of the pulse, reaching their maximal values for the linear polarization. Therefore, we focus on this case. Specifically, we analyze the dependence of pair creation on the relative configuration of linear polarizations of the laser pulse and the nonlaser photon. Lastly, we investigate the carrier-envelope phase effect on angular distributions of created particles, suggesting the possibility of phase control in relation to the pair creation processes.Comment: 13 pages, 8 figure

Properties of a ceramic pyroelectric X-ray generator as dependent on residual-gas pressure

The properties of X-ray emission from a pyroelectric accelerator based on ferroelectric ceramics have been experimentally studied, including the maximum energy of X-ray photons and their maximum yield generated by accelerated electrons at various pressures of residual gas in the generator chambe

Muon pair creation from positronium in a circularly polarized laser field

We study elementary particle reactions that result from the interaction of an atomic system with a very intense laser wave of circular polarization. As a specific example, we calculate the rate for the laser-driven reaction $e^+e^- \to \mu^+\mu^-$, where the electron and positron originate from a positronium atom or, alternatively, from a nonrelativistic $e^+e^-$ plasma. We distinguish accordingly between the coherent and incoherent channels of the process. Apart from numerical calculations, we derive by analytical means compact formulas for the corresponding reaction rates. The rate for the coherent channel in a laser field of circular polarization is shown to be damped because of the destructive interference of the partial waves that constitute the positronium ground-state wave packet. Conditions for the observation of the process via the dominant incoherent channel in a circularly polarized field are pointed out

MUTUAL IMAGE TRANSFORMATION ALGORITHMS FOR VISUAL INFORMATION PROCESSING AND RETRIEVAL

Subject of Research. The paper deals with methods and algorithms for mutual transformation of related pairs of images in order to enhance the capabilities of cross-modal multimedia retrieval (CMMR) technologies. We have thoroughly studied the problem of mutual transformation of face images of various kinds (e.g. photos and drawn pictures). This problem is widely represented in practice. Research is this area is based on existing datasets. The algorithms we have proposed in this paper can be applied to arbitrary pairs of related images due to the unified mathematical specification. Method. We have presented three image transformation algorithms. The first one is based on principal component analysis and Karhunen-Loève transform (1DPCA/1DKLT). Unlike the existing solution, it does not use the training set during the transformation process. The second algorithm assumes generation of an image population. The third algorithm performs the transformation based on two-dimensional principal component analysis and Karhunen-Loève transform (2DPCA/2DKLT). Main Results. The experiments on image transformation and population generation have revealed the main features of each algorithm. The first algorithm allows construction of an accurate and stable model of transition between two given sets of images. The second algorithm can be used to add new images to existing bases and the third algorithm is capable of performing the transformation outside the training dataset. Practical Relevance. Taking into account the qualities of the proposed algorithms, we have provided recommendations concerning their application. Possible scenarios include construction of a transition model for related pairs of images, mutual transformation of the images inside and outside the dataset as well as population generation in order to increase representativeness of existing datasets. Thus, the proposed algorithms can be used to improve reliability of face recognition performed on images of various kinds. Moreover, these techniques can be applied to address a wide variety of other CMMR problems

Essential self-adjointness of magnetic Schr\"odinger operators on locally finite graphs

We give sufficient conditions for essential self-adjointness of magnetic Schr\"odinger operators on locally finite graphs. Two of the main theorems of the present paper generalize recent results of Torki-Hamza.Comment: 14 pages; The present version differs from the original version as follows: the ordering of presentation has been modified in several places, more details have been provided in several places, some notations have been changed, two examples have been added, and several new references have been inserted. The final version of this preprint will appear in Integral Equations and Operator Theor

Observation of X-rays during heating a pyroelectric crystal by an infrared laser

A pyroelectric X-ray source is proposed, in which a lithium tantalate crystal is heated by an infrared laser with a wavelength of 10.6 μm. X-ray spectra measured during irradiation of the crystal with infrared radiation and during natural cooling of the crystal include characteristic X-ray radiation of atoms contained in the structural parts of the source, as well as bremsstrahlung of electrons with energies above 50 keV. An 8 mm sodium chloride window was used to inject 64 W infrared radiation into a vacuum chamber with the pyroelectric crystal installe

To the problems of modeling the brain ischemia in small animals

In the review article the problems of modeling cerebral ischemia in small mammals are consecrated. The advantages of experimental studies that are based on the similarity of the blood circulation of the brain in humans and animals are indicated. Classification of experimental models for the study of acute and chronic disorders of cerebral circulation, mechanisms of their development and preclinical approbation of new drugs is given. The authors indicate that all experimental models of brain ischemia can be divided into two groups: to study risk factors and pathophysiological studies of brain ischemia. And in the second case, the models of focal and global ischemia are described. In conclusion, the authors point out the difficulties and shortcomings of certain methods of ischemia reproduction, which await researchers to solve the above problems

INVESTIGATION ON THE DISCRETIZATION OF THE REALISTIC IRREGULAR WAVE GENERATION REGION THROUGH THE WAVEMIMO METHODOLOGY

Aiming to contribute to the research related to the sea wave energy conversion, the present paper approaches an investigation of the discretization used in the region of imposition of the prescribed velocity boundary condition, which is necessary for the WaveMIMO methodology. This methodology is employed for the numeric generation of irregular waves based on realistic sea state data. These data (obtained from TOMAWAC software in the present study) are treated to obtain orbital profiles of wave propagation velocity, which are imposed as boundary conditions on the wave channel. In this study, the realistic data considered refers to a point close to the Molhes da Barra, located on the coast of the municipality of Rio Grande, Rio Grande do Sul, Brazil. The numerical simulations were performed in Fluent, a computational fluid dynamics (CFD) software based on the finite volume method (FVM). The volume of fluid (VOF) multiphase model was used on the treatment of the water-air interface. Free surface elevation data obtained when the region of imposition of the prescribed velocity boundary condition was subdivided into 8, 11 and 14 segments were compared. The results found show that the 14 segments discretization represents more precisely the free surface elevation of irregular waves

NUMERICAL STUDY COMPARING THE INCIDENCE INFLUENCE BETWEEN REALISTIC WAVE AND REGULAR WAVE OVER AN OVERTOPPING DEVICE

This work presents a numerical study to evaluate the difference between the fluid dynamic behavior of an overtopping device subjected to the incidence of a realistic wave when compared to a regular one; being this regular wave representative of the considered realistic sea state. To do so, the FLUENT software was employed, which is a Computational Fluid Dynamics package based on the Finite Volume Method. The regular wave was generated through a User Defined Function (UDF) that imposes its velocities components as boundary conditions of prescribed velocity. On the other hand, for the realistic wave it was used a methodology to impose the realistic components velocities from transient discrete values, named Table Data (TD) in FLUENT software. For both cases the Volume of Fluid (VOF) multiphase model was applied in the treatment of the water-air interaction. The results showed that the amount of water accumulated in the reservoir for the realistic sea state was 2.46 higher than for the regular wave. This is a relevant finding, since several researches about Overtopping device efficiency were promoted considering only the incidence of regular wave

WOOL PRODUCTIVITY AND QUALITY OF RUSSIAN MEAT MERINO SHEEP FROM INTRA- AND INTERLINE SELECTION

Line breeding is often used in purebred animal husbandry, although the combination of lines may affect undesirable result. Therefore, it is very important for animal breeders to know which lines of animals can be combined to produce highly productive offspring with high meat and wool properties. This article studies the influence of interline selection of Russian meat merino breed on wool productivity, quality and skin histostructure. We found that the highest clipping was in the animals of group III obtained from ME-50 line rams and AS-30 line ewes. Ewes exceeded their peers of group II from the intraline AC-30 selection and peers of group IV from AS-30 line rams and ME-50 line queens. At the same time, ewes of group III insignificantly exceeded peers of group I from intraline selection of ME-50 line animals by 2.0% (P>0.05). Animals of group III had rather high fleece indices in terms of the wool condition due to the influence of ME-50 rams. Moreover, they had the highest ratio of “fat:sweat” (0.84), which confirms the high technological wool properties of this genotype. The quality of sheepskins depends on the nature of the connection of collagen fibers in the reticular layer. In terms of the thickness of the skin reticular layer young ewes of the group III exceeded their peers in groups I, II and IV by 5.3% (P> 0.05), 21.9% ( P<0.01) and 12.0% (P<0.05) respectively