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

Homogenization of Maxwell's equations in periodic composites

We consider the problem of homogenizing the Maxwell equations for periodic composites. The analysis is based on Bloch-Floquet theory. We calculate explicitly the reflection coefficient for a half-space, and derive and implement a computationally-efficient continued-fraction expansion for the effective permittivity. Our results are illustrated by numerical computations for the case of two-dimensional systems. The homogenization theory of this paper is designed to predict various physically-measurable quantities rather than to simply approximate certain coefficients in a PDE.Comment: Significantly expanded compared to v1. Accepted to Phys.Rev.E. Some color figures in this preprint may be easier to read because here we utilize solid color lines, which are indistinguishable in black-and-white printin

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

Strain Hardening of Polymer Glasses: Entanglements, Energetics, and Plasticity

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are pulled taut between entanglements rather than a change in entropy. A weak entropic stress is only observed in shape recovery of deformed samples when heated above the glass transition. While short chains do not form an entangled network, they exhibit partial shape recovery, orientation, and strain hardening. Stresses for all chain lengths collapse when plotted against a microscopic measure of chain stretching rather than the macroscopic stretch. The thermal contribution to the stress is directly proportional to the rate of plasticity as measured by breaking and reforming of interchain bonds. These observations suggest that the correct microscopic theory of strain hardening should be based on glassy state physics rather than rubber elasticity.Comment: 15 pages, 12 figures: significant revision

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

Numerical study of oil spill in the Patos lagoon under flood and ebb conditions

Facing great obstacles to eradicate environmental hazards generated by oil spills, it is crucial to establish actions against such accidents. In this context, the focus of this study is to analyze oil spills at the harbor region of Rio Grande, Rio Grande do Sul. The Easy Coupling Oil System (ECOS) model was used to model the oil spills under different environmental conditions simulated by the hydrodynamic model Telemac-3D, with the intention to identify the main forces controlling the movement of the oil slicks over a year of averaged hydrodynamic conditions from 2003 to 2015. The computational domain comprises the Patos Lagoon, the harbor area of Rio Grande and the Southern Brazilian Shelf. For the oil spill simulations, eight distinct events were defined considering both flood and ebb conditions in the estuarine region of the Patos Lagoon. The oil spill simulations showed that, in ebb conditions, the oil slick movement is mainly ruled by the currents, moving towards the outflow. After a few hours, the wind action makes the slick move towards the margins of the waterway. In flood conditions, on the other hand, the oil slick drifts to the interior of the estuary, following the dominant currents and the local winds

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

Numerical Analysis of an Overtopping Wave Energy Converter Subjected to the Incidence of Irregular and Regular Waves from Realistic Sea States

The present study aims to evaluate the difference in the fluid-dynamic behavior of an overtopping wave energy converter under the incidence of irregular waves based on a realistic sea state when compared to the incidence of regular waves, representative of this sea state. Thus, the sea data of three regions from the Rio Grande do Sul coast, Brazil, were considered. Fluent software was employed for the computational modeling, which is based on the finite volume method (FVM). The numerical generation of waves occurred through the imposition of the velocity boundary conditions using transient discrete values through the WaveMIMO methodology. The volume of fluid (VOF) multiphase model was applied to treat the water–air interaction. The results for the water amount accumulated in the device reservoir showed that the fluid-dynamic behavior of the overtopping converter has significant differences when comparing the two proposed approaches. Differences up to 240% were found for the water mass accumulated in the overtopping device reservoir, showing evidence that the results can be overestimated when the overtopping device is analyzed under the incidence of the representative regular waves. Furthermore, for all studied cases, it was possible to approximate the water volume accumulated over time in the overtopping reservoir through a first-degree polynomial function

Clinical Efficacy and Safety of Empagliflozin in Patients with Acute Heart Failure from the First Day of Hospitalization

Aim. Evaluation of the safety, clinical and hemodynamic effects of empagliflozin in patients with acute decompensated heart failure (ADHF) from the first day of hospitalization in the absence of signs of hemodynamic instability.Material and methods. A prospective, comparative, randomized study included 46 patients admitted to the hospital in connection with ADHF in the absence of signs of hemodynamic instability. Inclusion in the study and randomization to receive empagliflozin was carried out in the first 24 hours from the moment of admission to the hospital. The main group (n=23) from the first day of hospitalization and the entire subsequent follow-up period took empagliflozin at a daily dose of 10 and 25 mg (for patients with type 2 diabetes mellitus) in addition to basic therapy, the control group (n=23) received standard therapy without gliflozines. The observation period was 3 months and included 3 control points: 1st day of hospitalization, 7th-12th day, 3rd month of observation. Clinical, anamnestic and instrumental data were evaluated at all control points.Results. In the hospital period, by the 7th-12th day, only in the main group there was an improvement in all clinical indicators (p<0.01), an increase in the rate of diuresis (p><0.01), a decrease in the daily dose of the parenteral diuretic furosemide from 54 mg to 26 mg (p><0.01). A decrease in systolic blood pressure (SBP) occurred in both groups (p><0.01), but it was more pronounced in the comparison group [from 141 (110; 160) to 110 (90; 120) mm Hg) compared to the main group [from 140 (120; 160) to 120 (110; 130) mm Hg]. According to echocardiography data in the main group, there was a decrease in the indexed volume of the right atrium, the end-systolic volume of the left ventricle (LV ESV) and systolic pressure in the pulmonary artery, an increase in the LV ejection fraction (LV EF) (p><0.05). In the comparison group, only an increase in LV ESV was noted (p=0.04). The index of the indexed volume of the left atrium did not show significant dynamics in the main group (p=0.79), but showed a significant decrease>˂0.01), a decrease in the daily dose of the parenteral diuretic furosemide from 54 mg to 26 mg (p<0.01). A decrease in systolic blood pressure (SBP) occurred in both groups (p>˂0.01), but it was more pronounced in the comparison group [from 141 (110; 160) to 110 (90; 120) mm Hg) compared to the main group [from 140 (120; 160) to 120 (110; 130) mm Hg]. According to echocardiography data in the main group, there was a decrease in the indexed volume of the right atrium, the end-systolic volume of the left ventricle (LV ESV) and systolic pressure in the pulmonary artery, an increase in the LV ejection fraction (LV EF) (p˂0.05). In the comparison group, only an increase in LV ESV was noted (p=0.04). The index of the indexed volume of the left atrium did not show significant dynamics in the main group (p=0.79), but showed a significant decrease in the 2nd and 3rd control points compared to the control group (p=0.01 and p=0.02). Complications, against the background of taking empagliflozin, were not noted: there were no episodes of hypotension (SBP˂90 mm Hg), hypoglycemia, acute kidney injury.Conclusion. The results obtained indicate the safety of empagliflozin in patients with ADHF, regardless of the status of carbohydrate metabolism and LV EF, as well as taking into account the clinical (more intense positive dynamics of clinical symptoms of ADHF) and hemodynamic (smooth decrease in SBP, increased diuretic effect) effects of empagliflozin, this drug should be considered as an effective and safe supplement to the main therapy from the first day of hospitalization in patients with stable hemodynamic parameters

RNA-Seq identifies SPGs as a ventral skeletal patterning cue in sea urchins

The sea urchin larval skeleton offers a simple model for formation of developmental patterns. The calcium carbonate skeleton is secreted by primary mesenchyme cells (PMCs) in response to largely unknown patterning cues expressed by the ectoderm. To discover novel ectodermal cues, we performed an unbiased RNA-Seq-based screen and functionally tested candidates; we thereby identified several novel skeletal patterning cues. Among these, we show that SLC26a2/7 is a ventrally expressed sulfate transporter that promotes a ventral accumulation of sulfated proteoglycans, which is required for ventral PMC positioning and skeletal patterning. We show that the effects of SLC perturbation are mimicked by manipulation of either external sulfate levels or proteoglycan sulfation. These results identify novel skeletal patterning genes and demonstrate that ventral proteoglycan sulfation serves as a positional cue for sea urchin skeletal patterning