Search

Computations involving air plasma chemistry are often confronted with the necessity to deal with a large number of chemical species and reactions. In this article, an algorithm is demonstrated, which efficiently identifies and eliminates unimportant species and reactions, which can lead to a computational speedup of up to an order of magnitude. The proposed reduction method is independent of and can be combined with other time-saving algorithms, such as adaptive time stepping. The method was applied to two test cases: relaxation of plasma with hot neutrals (initial $T_{g} \gg T_{e}$ ), which may occur due to shock-induced heating during meteor reentry at high altitude and the relaxation of atmospheric pressure plasma with hot electrons (initial $T_{e} \gg T_{g}$ ), which may result from a laser-induced plasma breakdown. In the first scenario, the full set of 54 species and 1010 reactions was reduced to ten species and 106 reactions while achieving less than 3% error in the electron density. For the second case, a set containing 16 species and 195 reactions was sufficient. The test cases demonstrate that the directed relational graph method can reduce significantly the number of chemical species and reactions, thus streamlining computations. The algorithm is expected to have wider application and a strong impact on the reduction of extremely large data sets, e.g., hydrocarbons, chemistry with large dynamic time scales, and computations involving plasma chemistry in multidimensional simulations.

The existing “quotidian equation of state (QEOS)” model [More et al., Phys. Fluids 31, 3059 (1988)] has been revised, and an alternative set of formulas is provided for the Helmholtz free energy, internal energy, heat capacity, and pressure. A novel scheme for constructing the ion equation-of-state is proposed based on the additive of solid and fluid components that act throughout the temperature range, in contrast to the QEOS that matches the thermodynamic parameters at selected interfaces. These components are continuous along with their first and second derivatives and obey limiting cases and thermodynamics laws (Lindemann melting, Dulong–Petit law, Grüneisen pressure law, and ideal gas law). Thus, the new scheme eliminates discontinuities in thermodynamics parameters across interfaces and ensures that the thermodynamics parameters are consistent with each other. The Helmholtz free energy, internal energy, heat capacity, and pressure have been approximated with computationally efficient formulas that can be used as parts of other models, e.g., hydro-simulations.

The Thomas–Fermi–Dirac-Weizsäcker model for finite temperature is presented. Starting with the free energy density, consistent expressions for the Helmholtz free energy, total energy, pressure and virial theorem are derived. The exchange and correlation terms are cast in a form that is suitable for derivation of their contributions to energy and pressure. The Euler–Lagrange equation is written in Schrödinger-like form and solved in spherical symmetry in a Wigner–Seitz cell. The challenges associated with its numerical solution are discussed and a viable approach to obtain a non-negative solution is proposed. The model is benchmarked for two materials, Al and Cu, by comparing the pressure at solid density in the temperature range 0.1 < T e < 10 eV , as well as the cold pressure curves.

The US Naval Research Laboratory (NRL) is the world leader in the development of high energy excimer laser science and technology [1] . The argon fluoride (ArF*) laser can be scaled in power and energy to become a good candidate for direct or indirect driver for inertial confinement fusion (ICF). The deep UV light (193 nm) provides uniform target irradiation and broad native bandwidth (5 to 10 THz), suppresses laser plasma instabilities, and has intrinsic efficiency of more than 16 %. In this work we present the progress in modeling the kinetics and radiation of an electron beam ( e -beam) pumped ArF* laser relevant to NRL Electra facility. The modeling is based on the NRL Orestes suit of codes. The most important parameters used for guiding the experiments and monitoring the Orestes predictive capabilities are the laser yield and ASE. Here we present some numerical simulations for 0.5–1 MW⁄cm 3 e -beam power and total pressure 12–20 psi. We scan the range of pressures for which experiments are typically performed [2] . The ASE is a small fraction of the laser yield, on the order of 1-10 %. The numerical simulations show that the laser yield is not very sensitive to total pressure, which should be close to 1 atm, but very sensitive to F 2 content: maximum lasing is observed at 0.5±0.2% F 2 in Ar. The laser yield increases with e -beam power deposition until it reaches an optimum e -beam power beyond which the lasing decreases because most of the ArF* molecules are dissociated by electron impact or lost in neutral-neutral collisons with Ar and F 2 .

We present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

Laser-driven ion acceleration is often analyzed assuming that ionization reaches a steady state early in the interaction of the laser pulse with the target. This assumption breaks down for materials of high atomic number for which the ionization occurs concurrently with the acceleration process. Using particle-in-cell simulations, we have examined acceleration and simultaneous field ionization of copper ions in ultra-thin targets (20–150 nm thick) irradiated by a laser pulse with intensity 1 × 1021 W/cm2. At this intensity, the laser pulse drives strong electric fields at the rear side of the target that can ionize Cu to charge states with valence L-shell or full K-shell. The highly-charged ions are produced only in a very localized region due to a significant gap between the M- and L-shells’ ionization potentials and can be accelerated by strong, forward-directed sections of the field. Such an “ionization injection” leads to well-pronounced bunches of energetic, highly-charged ions. We also find that for the thinnest target (20 nm) a push by the laser further increases the ion energy gain. Thus, the field ionization, concurrent with the acceleration, offers a promising mechanism for the production of energetic, high-charge ion bunches.

A numerical model for laser-matter interactions in the warm dense matter regime is presented with broad applications, e.g., ablation, thermionic emission, and radiation. A unique approach is adopted, in which a complete set of collisional and transport data is calculated using a quantum model and incorporated into the classical two-temperature model for the electron and lattice-ion temperatures. The data set was produced by the average atom model that combines speed, conceptual simplicity, and straightforward numerical development. Such data are suitable for use in the warm dense matter regime, where most of the laser-matter interactions at moderate intensities occur, thus eliminating deficiencies of previous models, e.g., interpolation between solid and ideal plasma regimes. In contrast to other works, we use a more rigorous definition of solid and plasma states of the metal, based on the physical condition of the lattice, crystalline (ordered) versus melted (disordered), rather than a definition based on electron temperature. The synergy between the two-temperature and average atom models has been demonstrated on a problem involving heating and melting of the interior of Al by a short-pulse laser with duration 0.1--1 ps and laser fluences $1\ifmmode\times\else\texttimes\fi{}{10}^{3}\ensuremath{-}3\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{J}/{\mathrm{m}}^{2}(0.1\text{--}3\phantom{\rule{0.16em}{0ex}}\mathrm{J}/\mathrm{c}{\mathrm{m}}^{2})$. The melting line, which separates the solid and plasma regimes, has been tracked in time and space. The maximum melting depth has been determined as a function of laser fluence: ${l}_{\mathrm{melt}}(\ensuremath{\mu}\mathrm{m})\ensuremath{\cong}4\ifmmode\times\else\texttimes\fi{}{10}^{3}F\phantom{\rule{4pt}{0ex}}(\frac{\mathrm{J}}{{\mathrm{m}}^{2}})$.

The development of laser wakefield accelerators (LWFA) over the past several years has led to an interest in very compact sources of X-ray radiation – such as “table-top” free electron lasers. However, the use of conventional undulators using permanent magnets also implies system sizes which are large. In this work, we assess the possibilities for the use of novel mini-undulators in conjunction with a LWFA so that the dimensions of the undulator become comparable with the acceleration distances for LWFA experiments (i.e., centimeters). The use of a prototype undulator using laser machining of permanent magnets for this application is described and the emission characteristics and limitations of such a system are determined. Preliminary electron propagation and X-ray emission measurements are taken with a LWFA electron beam at the University of Michigan.

Thermionic emission of electrons is a process fundamental to our understanding of laser–matter interactions in the ultra-short pulse regime. Charge collected from an emission process, as well the secondary radiation generated by their collective motion, provides avenues for diagnosing and verifying existing laser–solid interaction models. Laser fluences (∼104 J/m2) are of particular interest as they heat the surface electrons to temperatures on the order of a few electron volts (eV), placing it in the warm dense matter regime where much underlying physics is yet to be fully understood. However, even at such moderate fluences the conventional Richardson–Dushman formula for the emission rate becomes invalid. We consider an additional barrier potential on the surface that appears due to space-charge effects, which then limits the thermionic emission. This provides feedback leading to a self-consistent solution with the emission rate. Unlike the work function, this barrier dynamically evolves during the emission process. Here, we present the first calculation of the barrier potential on the surface, along with analytical expression, from a one-dimensional electrostatic model. The result is a generalization of the Richardson–Dushman picture to moderate laser fluences. The potential barrier has been incorporated into a two-temperature model for thermionic emission from an Al target irradiated by a femtosecond laser. The collisional and transport data for Al have been obtained using an average atom model.

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma, where unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (~ keV) electron beam. The resulting plasmas are characterized by large electron densities (10 10 –10 11 cm − 3 ) and low electron temperatures (0.3–1.0 eV). Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies of only a few eV, a feature that can be attractive to processing applications that require low damage and atomic layer precision. This work describes the salient features of these plasmas produced in mixtures of argon and sulfur hexafluoride (SF 6 ) and their use in silicon nitride etching, with particular attention paid to developing processing parameters relevant to atomic layer processing.

Complex development of the motive qualities set up the issue of evaluation and control of the specific functional preparedness of the competitors. For the purpose, many researchers develop specific volleyball tests and indicators. The purpose of the study is the optimization of the training process of highly qualified volleyball players from „Lokomotiv”, Novosibirsk, volleyball team by analyzing their physical development and specific preparedness. The present study was processed during the period of July until September 2017. Subject of the study are the physical development and the specific workability of professional volleyball players. Tested were 13 volleyball players subjected to 24 indicators For realizing the purpose and the aims are applied the following methods of research: review study, anthropometry, expert evaluation and sport-pedagogical testing. The results of the study have been subjected to mathematical and statistical procession by: variation analysis and index method. The results show that both groups under research are homogeneous as a whole and relatively homogeneous in relation of all physical development and specific workability signs under study but negative percentage of relative homogeneity is recorded for the realization skills of the players.

Laser-driven ion acceleration has been an active research area in the past two decades with the prospects of designing novel and compact ion accelerators. Many potential applications in science and industry require high-quality, energetic ion beams with low divergence and narrow energy spread. Intense laser ion acceleration research strives to meet these challenges and may provide high charge state beams, with some successes for carbon and lighter ions. Here we demonstrate the generation of well collimated, quasi-monoenergetic titanium ions with energies ∼145 and 180 MeV in experiments using the high-contrast (−9) and high-intensity ( 6 × 10 20 W cm − 2 ) Trident laser and ultra-thin (∼100 nm) titanium foil targets. Numerical simulations show that the foils become transparent to the laser pulses, undergoing relativistically induced transparency (RIT), resulting in a two-stage acceleration process which lasts until ∼2 ps after the onset of RIT. Such long acceleration time in the self-generated electric fields in the expanding plasma enables the formation of the quasi-monoenergetic peaks. This work contributes to the better understanding of the acceleration of heavier ions in the RIT regime, towards the development of next generation laser-based ion accelerators for various applications.

The U.S. Naval Research Laboratory (NRL) has converted the repetitively pulsed Electra krypton fluoride (KrF) laser system to an electron-beam (e-beam) pumped argon fluoride (ArF) laser. Operating at 193 nm, ArF has the potential of being the most efficient excimer laser. Due to the shorter ultraviolet (UV) wavelength and broad native bandwidth, the ArF laser is a compelling candidate for an inertial confinement fusion (ICF) driver. Experiments conducted in amplifier and oscillator configurations have produced initial data on the small signal gain, intrinsic efficiency, and laser yield. These measurements are compared with the ArF kinetics code Orestes, under development at NRL.

Experiments of x-ray emission from Ar, Kr, and Ar/Kr gas jet mixture were performed at the UNR Leopard Laser Facility operated with 350 fs pulses at laser intensity of 2 × 1019 W/cm2 and 0.8 ns pulses at an intensity of 1016 W/cm2. Debris free x-ray source with supersonic linear nozzle generated clusters/monomer jet with an average density of ≥1019 cm−3 was compared to cylindrical tube subsonic nozzle, which produced only monomer jet with average density 1.5–2 times higher. The linear (elongated) cluster/gas jet provides the capability to study x-ray yield anisotropy and laser beam self-focusing with plasma channel formation that are interconnecting with efficient x-ray generation. Diagnostics include x-ray diodes, pinhole cameras and spectrometers. It was observed that the emission in the 1–9 keV spectral region was strongly anisotropic depending on the directions of laser beam polarization for sub-ps laser pulse and supersonic linear jet. The energy yield in the 1–3 keV region produced by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models and 3D molecular dynamic simulations of Ar and Kr clusters irradiated by sub-ps laser pulses have been implemented to analyze obtained data. A potential evidence of electron beam generation in jets' plasma was discussed. Note that the described debris-free gas-puff x-ray source can generate x-ray pulses in a high repetition regime. This is a great advantage compared to solid laser targets.

The U.S. Naval Research Laboratory (NRL) has built a 137 J electron beam pumped argon fluoride (ArF) laser operating at 193 nm utilizing the Electra facility. This paper highlights initial ArF oscillator measurements in the context of significant benefits of ArF laser characterization for inertial confinement fusion target performance and development of a kinetics code with predictive capabilities. Other aspects of NRL's ArF laser development program, including large scale electron beam pumped ArF amplifier development and ArF optical transport, are discussed. Initial measurements were made utilizing a quadruple pass oscillator configuration constructed in the Electra facility with a nominal 100 cm2 aperture. Laser yields between 80 and 100 J, time-dependent laser intensity, and amplified spontaneous emission (ASE) are reported over a range of gas pressure (0.8–1.4 atmospheres). Higher laser yields, 137 J, were attained in a non-optimized dual ArF oscillator configuration wherein the optical axis was rotated to conform to the measured electron beam deposition in the laser gas mixture.

The generation of low-frequency radiation from a short pulse (∼100 fs) laser with mJ energy incident on a metal surface is investigated. The electrons within the metal surface absorb energy from the laser pulse, increasing in temperature to a few electron volts and resulting in some at the high-energy tail of the distribution to overcome the work function barrier. Emission of these electrons from the surface contributes to a surface current which sources secondary radiation emission. The Richardson–Dushman emission picture breaks down due to Coulombic effects and a modified emission model is presented. Previous precedence exists for modified thermionic emission models for laser–metal interactions of a similar nature, such as the one presented by Riffe et al. [J. Opt. Soc. Am. B 10, 1424–1435 (1993)] upon which we elaborate. Surface currents generated by such a mechanism are modeled with a particle-in-cell (PIC) simulation together with a Monte Carlo treatment of electron–neutral collisions with air molecules. The modified emission model, together with the PIC model, provides a numerical basis from which the radiated spectra are estimated due to the time-varying currents emitted from the surface of the metal. Experiments and numerical simulations for air pressure between 0.1 and 1 atm show qualitative agreement as to the pressure dependence of the measured signal energy from the secondary radiation, with E measured ∝ P air − α for some α near but less than 1. Quantitative agreement between experiments and simulations is improved by including the effect of an additional contribution to secondary emission energy arising from inverse-bremsstrahlung collisions within a nm-scale vapor layer.

The generation of low-frequency radiation from sub-picosecond laser pulses incident on metal targets is investigated. The laser field drives time-varying currents in a thin sub-surface layer of the metal, which emits broadband radiation that peaks at terahertz frequencies. We present a one-dimensional electrostatic model for copper appropriate for the interaction of laser pulses at normal incidence combined with a radiation model for an infinitely thin disk. The latter uses as input a single parameter, the temporal dependence of the integrated current density on axis, which is derived from the electrostatic model. The salient characteristics of the emitted radiation, such as power, energy, and spectra, are calculated for laser pulses with various intensities and pulse durations. The radiated energy per unit solid angle peaks at a small angle off the target normal and tapers off at larger angles. Analytical scaling of radiated energy with incident laser energy, in the low frequency limit, is obtained in the form e rad ∼ e laser 3 / 2. For accurate results, it is imperative to use the full expression for the heat capacity of electrons, in both the degenerate and ideal gas limits. Failure to do so may result in inaccuracies for the computed radiated energy, as large as one order of magnitude. A comparison of calculated and measured radiation energy in the 8–12 GHz frequency range indicates a similar trend with laser energy and comparable magnitude (∼1 fJ).

Ion acceleration by a high intensity (> 1018 W/cm2) laser pulse interacting with a solid target has been an active research area. The major interest stems from the prospects of designing and building a novel laser-driven ion source that is significantly more compact in size and shorter in duration than conventional ion accelerators, to enable applications requiring high power such as isochoric heating.

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma. Unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (∼ few keV) electron beam, an approach that can be attractive to atomic layer processing applications. In particular, high electron densities (10101011 cm−3) can be produced in electron beam generated plasmas, where the electron temperature remains between 0.3 and 1.0 eV. Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies in the range of 1 to 5 eV. This provides the potential for controllably etching and/or engineering both the surface morphology and chemistry with monolayer precision. This work describes the electron beam driven plasma processing system, with particular attention paid to system characteristics and the ability to control the generation and delivery of ions to the surface and their energies. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0071506jss] All rights reserved.

In this work we compute the main features of a surface-wave-driven plasma in argon at atmospheric pressure in view of a better understanding of the contraction phenomenon. We include the detailed chemical kinetics dynamics of Ar and solve the mass conservation equations of the relevant neutral excited and charged species. The gas temperature radial profile is calculated by means of the thermal diffusion equation. The electric field radial profile is calculated directly from the numerical solution of the Maxwell equations assuming the surface wave to be propagating in the TM_{00} mode. The problem is considered to be radially symmetrical, the axial variations are neglected, and the equations are solved in a self-consistent fashion. We probe the model results considering three scenarios: (i) the electron energy distribution function (EEDF) is calculated by means of the Boltzmann equation; (ii) the EEDF is considered to be Maxwellian; (iii) the dissociative recombination is excluded from the chemical kinetics dynamics, but the nonequilibrium EEDF is preserved. From this analysis, the dissociative recombination is shown to be the leading mechanism in the constriction of surface-wave plasmas. The results are compared with mass spectrometry measurements of the radial density profile of the ions Ar^{+} and Ar_{2}^{+}. An explanation is proposed for the trends seen by Thomson scattering diagnostics that shows a substantial increase of electron temperature towards the plasma borders where the electron density is small.

We present a theoretical study of heavy ion acceleration from ultrathin (20 nm) gold foil irradiated by high-intensity sub-picosecond lasers. Using two-dimensional particle-in-cell simulations, three laser systems are modeled that cover the range between femtosecond and picosecond pulses. By varying the laser pulse duration we observe a transition from radiation pressure acceleration (RPA) to the relativistic induced transparency (RIT) regime for heavy ions akin to light ions. The underlying physics of beam formation and acceleration is similar for light and heavy ions, however, nuances of the acceleration process make the heavy ions more challenging. A more detailed study involving variation of peak laser intensity I-0 and pulse duration tau(FWHM) revealed that the transition point from RPA to RIT regime depends on the peak laser intensity on target and occurs for pulse duration tau(RPA -> RIT)(FWHM) [fs] congruent to 210/root I-0 [W cm (2)]/10(21) The most abundant gold ion and charge-to-mass ratio are Au51+ and q/M approximate to 1/4, respectively, half that of light ions. For ultrathin foils, on the order of one skin depth, we established a linear scaling of the maximum energy per nucleon (E/M)(max) with (q/M)(max), which is more favorable than the quadratic one found previously. The numerical simulations predict heavy ion beams with very attractive properties for applications: high directionality (10(11) ions sr(-1)) and energy (>20 MeV/nucleon) from laser systems delivering >20 J of energy on target.

Atmospheric pressure plasmas have certain advantage in materials synthesis and processing that are not available with other approaches including low-pressure plasmas. In particular, the breadth of reactions afforded by non-equilibrium, low temperature plasmas is unique; plasmas produced in full density air allows one to extend the application space to systems and materials that are not vacuum compatible. Non-equilibrium, atmospheric pressure plasma jet devices are well-suited for such applications given their relatively simple design and modest power requirements. However, their size tends to limit their utility to small scale processes and treatments. In this work, we describe approaches to extend the volume of non-equilibrium, atmospheric pressure plasma jets and thus, surface area that can be treated. In particular, we consider geometric and gas flow solutions to increase volume. We use high-speed cameras, optical emission spectroscopy (OES), current and voltage measurements, and simulations to characterize the results and understand the potential for and/or limitations to scale-up. This work is supported by the Naval Research Laboratory base program.

An intense, short laser pulse incident on a dielectric can excite electrons from valence to the conduction band. As these electrons undergo scattering, from both ion centers and acoustic phonons, they emit Bremsstrahlung radiation. Here we present 1D model that describes the laser pulse dielectric interaction and the resulting Bremsstrahlung emission. Characteristics of the radiation (power, energy and spectra) are computed for arbitrary ratios of electron collision frequency to radiation frequency [1]. The conversion efficiency of laser pulse energy into bremsstrahlung radiation depends strongly on both the fluence and duration of the pulse, saturating at values of about $10 ^{-5}$. Depending on whether the fluence is above or below the damage threshold of the material, the emission can originate either from the surface or the bulk of the dielectric. The radiation may provide a broadband light source for diagnostics.

We present here initial efforts to advance the modeling of electron-beam-pumped ArF lasers. These efforts will be tested against experiments using the NRLElectrafacility. The advantages of using ArF as a driver for direct drive laser fusion compared to KrF [1]are: shorter wavelength (193 nm for ArF* vs. 248 nm for KrF*) and broader bandwidth. Use of ArF driver should lead to more robust higher-energy-gain fusion implosions than KrF, with an even larger advantage over the 351 nm laser technology used on NIF. The smaller absorption cross section by F2 with ArF [2]is an advantage in constructing large, high-energy amplifiers. In addition, it may have higher intrinsic efficiency than KrF [3]. A theoretical model of an e-beam pumped ArF* excimer laser is under development. One of the goals of this work is to understand the energy deposition in Ar-F 2 mixture for ArF lasers and compare to Ar-Kr-F 2 mixture for KrF lasers [4, 5]. The collisional rates with electrons are obtained as a function of F 2 concentration and power deposition by solving the steady-state Boltzmann equation for the electron energy distribution function. We use the concept of excitation-to-ionization ratios to obtain slowly varying rates over a wide range of input parameters such as beam power, gas pressure, and initial gas composition. These rates are coupled to a 1D time-dependent plasma chemistry based on NRLOrestessuite of numerical models. It includes plasma chemistry reactions and vibrational population kinetics of ArF* molecules, coupled to a 3D-radiation transport for the amplified spontaneous emission (ASE). The input parameters are the e-beam temporal profile, gas composition, and system geometry (type of laser amplifier configuration with initial laser seed characteristics). Measurable plasma parameters, such as species concentrations, electron and gas temperatures, as well as laser parameters, such as small signal gain, non-saturable absorption, saturated laser intensity, and AES are calculated as a function of input power and gas composition in the e-beam high-power regime. The model results are compared with the limited experimental measurement literature for ArF lasers.

An intense, short laser pulse incident on a transparent dielectric can excite electrons from the valence to the conduction band. As these electrons undergo scattering, both from phonons and ions, they emit bremsstrahlung. Here we present a theory of bremsstrahlung emission appropriate for the interaction of laser pulses with dielectrics. Simulations of the interaction, incorporating this theory, illustrate characteristics of the radiation (power, energy, and spectra) for arbitrary ratios of electron collision frequency to radiation frequency. The conversion efficiency of laser pulse energy into bremsstrahlung depends strongly on both the intensity and duration of the pulse, saturating at values of about 10^{-5}. Depending on whether the intensity is above or below the damage threshold of the material, the emission can originate either from the surface or the bulk of the dielectric, respectively. The bremsstrahlung emission may provide a broadband light source for diagnostics.

Purpose To identify barriers to implementation of an evidence based integrated care pathway (ICP) for seizure management in the Emergency Department (ED). Methods A site specific bespoke questionnaire was designed to solicit anonymous responses from all grades of ED medical and nursing staff to a series of questions regarding utility, feasibility, significance and implementation of a locally designed and championed ICP for seizure management and onward referral. Results While 95% of respondents agreed that the pathway ensured patients were treated according to best practice, a number of human factors were identified as barriers to use. These fell into three categories 1) environmental 2) pathway design/process and 3) user related issues. Conclusions Most respondents understood and endorsed the evidence based utility of the pathway. Barriers to use, however, are broad with interactions involving many complex human factors. Nevertheless, solutions can be relatively easily formulated but departmental-wide effort is required to comprehensively address all issues.

Aims The effectiveness of stress cardiac magnetic resonance (CMR) as a gatekeeper for coronary angiography (CA) has been established. Level five HTA studies according to the hierarchical model of diagnostic test evaluation are not available. Methods This cohort study included 1,158 consecutive patients (mean age 63 ± 11 years, 42 % women) presenting at our institution between January 1, 2003 and December 31, 2004 with suspected coronary artery disease (CAD) for an elective CA. The patients were assessed for eligibility and propensity score matching was applied to address selection bias regarding the patients’ allocation to CMR or direct CA. Median patient follow-up was 7.9 years (95 % CI 7.8–8.0 years). The primary effect was calculated as relative survival difference. The cost unit calculation (per patient) at our institute was the source of costs. Results Survival was similar in CMR and CA (p = 0.139). Catheterizations ruling out CAD were significantly reduced by the CMR gate-keeper strategy. Patients with prior CMR had significantly lower costs at the initial hospital stay and at follow-up (CMR vs. CA, initial: 2,904€ vs. 3,421€, p = 0.018; follow-up: 2,045€ vs. 3,318€, p = 0.037). CMR was cost-effective in terms of a contribution of 12,466€ per life year to cover a part of the CMR costs. Conclusion Stress CMR prior to CA was saving 12,466€ of hospital costs per life year. Lower costs at follow-up suggest sustained cost-effectiveness of the CMR-guided strategy. Electronic supplementary material The online version of this article (doi:10.1007/s00392-014-0793-0) contains supplementary material, which is available to authorized users.

Aims Women with aortic stenosis develop a more concentric form of LV hypertrophy than men. However, the molecular factors underlying sex differences in LV remodelling are incompletely understood. We took an unbiased approach to identify sex-specific patterns in gene expression and pathway regulation, and confirmed the most prominent findings in human hearts. Methods and results Echocardiography was performed in 104 patients (53.8% women) with aortic stenosis before aortic valve replacement. LV mass, LV end-diastolic diameter, and relative wall thickness were included in a factor analysis to generate an index classifying LV remodelling as adaptive or maladaptive. Maladaptive remodelling was present in 64.6% of male and in 32.7% of female patients (P < 0.01). Genome-wide expression profiling of LV samples was performed in a representative subgroup of 19 patients (52.6% women) compared with samples from healthy controls (n = 18). Transcriptome characterization revealed that fibrosis-related genes/pathways were induced in male overloaded ventricles, while extracellular matrix-related and inflammatory genes/pathways were repressed in female overloaded ventricles (adjusted P < 0.05). We confirmed gene regulation by quantitative real-time reverse transcription–polymerase chain reaction and immunoblotting analysis, and we further demonstrate the relevance of our findings by histological documentation of higher fibrosis in men than in women. Conclusion We conclude that in pressure overload distinct molecular processes are regulated between men and women. Maladaptive LV remodelling occurs more frequently in men and is associated with greater activation of profibrotic and inflammatory markers. Collectively, sex-specific regulation of these processes may contribute to sex differences in the progression to heart failure.

We make direct observations of localized light absorption in a single nanostructure irradiated by a strong femtosecond laser field, by developing and applying a technique that we refer to as plasma explosion imaging. By imaging the photoion momentum distribution resulting from plasma formation in a laser-irradiated nanostructure, we map the spatial location of the highly localized plasma and thereby image the nanoscale light absorption. Our method probes individual, isolated nanoparticles in vacuum, which allows us to observe how small variations in the composition, shape, and orientation of the nanostructures lead to vastly different light absorption. Here, we study four different nanoparticle samples with overall dimensions of ∼100 nm and find that each sample exhibits distinct light absorption mechanisms despite their similar size. Specifically, we observe subwavelength focusing in single NaCl crystals, symmetric absorption in TiO2 aggregates, surface enhancement in dielectric particles containing a single gold nanoparticle, and interparticle hot spots in dielectric particles containing multiple smaller gold nanoparticles. These observations demonstrate how plasma explosion imaging directly reveals the diverse ways in which nanoparticles respond to strong laser fields, a process that is notoriously challenging to model because of the rapid evolution of materials properties that takes place on the femtosecond time scale as a solid nanostructure is transformed into a dense plasma.

This paper presents an unconventional approach for object racking using image statistical criteria and 3D image entropy sequence analysis. The experimental results prove that the relationship between statistical characteristics of the 3D image entropy sequences and process of motion estimation is a guarantee for creating reliable and high precision target detection and tracking system. Using 2D and 3D multistage entropy functions analysis provide us a better way to reduce sequence channels for tracking moving and non moving objects. Vector based approach is used for object searching and detection inside image sequences. This way we provide necessary information for object based image sequences compression format that is much more efficient than standard MGEG video stream. Object based compression format is much more acceptable for high demanding security and military systems.

This paper presents an unconventional approach for motion detection using 3D image histogram sequence analysis. The idea of this approach is to remove the process of motion estimation into the field of 3D image histogram sequences by analysis of their statistical characteristics. A functional and statistical model of a system for motion detection has been created. The experimental results prove that the relationship between statistical characteristics of the 3D image histograms sequences and process of motion estimation is a guarantee for creating a reliable and high precision motion detection system as well as for image compression using 3D entropy functions analysis. Such a system can be used for security control of banks, airports, military objects, embassies, shops etc.

We report on the unique clinical course of a 44-year-old male HIV-positive heart transplant recipient, who was bridged by mechanical circulatory support (MCS). The patient was admitted with acute ischemic heart failure due to severe myocardial infarction. After emergency coronary artery bypass grafting and nine days of extracorporeal life support, we implanted a left ventricular assist device. As HIV infection was effectively treated and other contraindications were not present, we decided to perform a heart transplantation (HTX). At the current time, 34 months after unremarkable HTX, rejection or opportunistic infections have not occurred.

We have developed a non-equilibrium time-dependent plasma chemistry model to describe NOx remediation from flue gas (82% N2, 6% O2, and 12% CO2) using the NRL Electra e-beam facility. Currently, this is a single shot model, in which the pulse width varies between 70 ns to 1.5 μs and the power deposition vary from 0.005 J/cm3 to 0.5 J/cm3. During the e-beam irradiation, the energetic electrons generate chemically active species, which then react with NOx to form harmless substances. The created plasma strongly deviates from thermodynamic equilibrium: after the beam is terminated a new equilibrium state is established in which the NOx amount have been substantially reduced. The relaxation process is due to a large number of plasmo-chemical reactions and proceeds on a time-scale from nanoseconds to tens of seconds. It was found that short (ns) e-beam pulses are the most efficient for NOx removal. Removal efficiency over 95% NOx with initial concentration of 200–1000 ppm range in a balance of 1.16 atm N2 was achieved [1]. In a simulated flue mixture at 1.2 atm, the initial 100 ppm NOx content has been reduced below the required level of EPA regulations [2]. Additional study is required on NOx reduction at elevated temperatures (> 500 C) and increased water vapor concentration.

Theoretical study of heavy ion acceleration from sub-micron gold foils irradiated by a short pulse laser is presented. Using two dimensional particle-in-cell simulations, the time history of the laser pulse is examined in order to get insight into the laser energy deposition and ion acceleration process. For laser pulses with intensity 3 x 10(21) W/cm(2), duration 32 fs, focal spot size 5 mu m, and energy 27 J, the calculated reflection, transmission, and coupling coefficients from a 20 nm foil are 80%, 5%, and 15%, respectively. The conversion efficiency into gold ions is 8%. Two highly collimated counter-propagating ion beams have been identified. The forward accelerated gold ions have average and maximum charge-to-mass ratio of 0.25 and 0.3, respectively, maximum normalized energy 25MeV/nucleon, and flux 2 x 10(11) ions/sr. An analytical model was used to determine a range of foil thicknesses suitable for acceleration of gold ions in the radiation pressure acceleration regime and the onset of the target normal sheath acceleration regime. The numerical simulations and analytical model point to at least four technical challenges hindering the heavy ion acceleration: low charge-to-mass ratio, limited number of ions amenable to acceleration, delayed acceleration, and high reflectivity of the plasma. Finally, a regime suitable for heavy ion acceleration has been identified in an alternative approach by analyzing the energy absorption and distribution among participating species and scaling of conversion efficiency, maximum energy, and flux with laser intensity. Published by AIP Publishing.

A gas jet containing a mixture of monomers and clusters was characterized and studied as an x-ray radiation source produced by a TW-class laser pulse. Gas jet parameters such as average density and cluster size were measured at the UNR Radiation Physics Laboratory using both optical interferometry and Rayleigh scattering techniques, respectively. Several noble gases were used in the gas jet: Ar, Kr, and Xe. Additionally, mixtures of two or three of those gases were also tested. By changing the gas jet backing pressure as well as the gas delay time between jet initiation and laser interaction with the jet, both the density and cluster size of the gas jets can be varied. Having control over the composition, density, and cluster size of the gas jets is important when considering them as targets for intense laser pulses. Our gas jets were irradiated with the 1057 nm short pulse (350 fs) UNR Leopard laser with an intensity of 1019 W/cm2 in the focus spot. Time resolved diagnostics included filtered Si-diode detectors (1.4–9 keV), filtered absolutely calibrated PCDs (>2.4 keV), and Faraday cups. An x-ray spectrometer and two three-channel x-ray pinhole cameras provided time integrated diagnostics on the gas jet plasma. Anisotropy of x-ray radiation with respect to laser beam polarization was observed in all spectral regions. The coefficient of conversion of laser energy into x-rays was measured with a maximum of 10−3. Most importantly, the mixtures of two or three gases each produced higher x-ray yields than the pure gases. Non-LTE modelling and a molecular dynamics (MD) code have been employed to determine plasma and cluster parameters. Electron temperatures and densities of the laser plasma of the mixed gases were higher than the pure gases.

Many aspects of physical phenomena occurring when an intense laser pulse with subpicosecond duration and an intensity of ${10}^{18}--{10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ heats an underdense plasma in a supersonic clustered gas jet are studied to determine the relative contribution of thermal and nonthermal processes to soft- and hard-x-ray emission from debris-free plasmas. Experiments were performed at the University of Nevada, Reno (UNR) Leopard laser operated with a 15-J, 350-fs pulse and different pulse contrasts (${10}^{7}$ or ${10}^{5}$). The supersonic linear (elongated) nozzle generated Xe cluster-monomer gas jets as well as jets with Kr-Ar or Xe-Kr-Ar mixtures with densities of ${10}^{18}--{10}^{19}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Prior to laser heating experiments, all jets were probed with optical interferometry and Rayleigh scattering to measure jet density and cluster distribution parameters. The supersonic linear jet provides the capability to study the anisotropy of x-ray yield from laser plasma and also laser beam self-focusing in plasma, which leads to efficient x-ray generation. Plasma diagnostics included x-ray diodes, pinhole cameras, and spectrometers. Jet signatures of x-ray emission from pure Xe gas, as well as from a mixture with Ar and Kr, was found to be very different. The most intense x-ray emission in the 1--9 KeV spectral region was observed from gas mixtures rather than pure Xe. Also, this x-ray emission was strongly anisotropic with respect to the direction of laser beam polarization. Non-local thermodynamic equilibrium (Non-LTE) models have been implemented to analyze the x-ray spectra to determine the plasma temperature and election density. Evidence of electron beam generation in the supersonic jet plasma was found. The influence of the subpicosecond laser pulse contrast (a ratio between the laser peak intensity and pedestal pulse intensity) on the jets' x-ray emission characteristics is discussed. Surprisingly, it was found that the x-ray yield was not sensitive to the prepulse contrast ratio.

Background Estrogen improves cardiac recovery after ischemia/reperfusion (I/R) by yet incompletely understood mechanisms. Mitochondria play a crucial role in I/R injury through cytochrome c-dependent apoptosis activation. We tested the hypothesis that 17β-estradiol (E2) as well as a specific ERβ agonist improve cardiac recovery through estrogen receptor (ER)β-mediated mechanisms by reducing mitochondria-induced apoptosis and preserving mitochondrial integrity. Methods We randomized ovariectomized C57BL/6N mice 24h before I/R to pre-treatment with E2 or a specific ERβ agonist (ERβA). Isolated hearts were perfused for 20min prior to 30min global ischemia followed by 40min reperfusion. Results Compared with controls, ERβA and E2 treated groups showed a significant improvement in cardiac recovery, i.e. an increase in left ventricular developed pressure, dP/dtmax and dP/dtmin. ERβA and E2 pre-treatment led to a significant reduction in apoptosis with decreased cytochrome c release from the mitochondria and increased mitochondrial levels of anti-apoptotic Bcl2 and ACAA2. Protein levels of mitochondrial translocase inner membrane (TIM23) and mitochondrial complex I of respiratory chain were increased by ERβA and E2 pre-treatment. Furthermore, we found a significant increase of myosin light chain 2 (MLC2) phosphorylation together with ERK1/2 activation in E2, but not in ERβA treated groups. Conclusions Activation of ERβ is essential for the improvement of cardiac recovery after I/R through the inhibition of apoptosis and preservation of mitochondrial integrity and can be a achieved by a specific ERβ agonist. Furthermore, E2 modulates MLC2 activation after I/R independent of ERβ. Electronic supplementary material The online version of this article (doi:10.1186/s13293-016-0104-8) contains supplementary material, which is available to authorized users.

In earlier work, a time-dependent, ionization dynamic model of a cluster of xenon atoms was constructed [2] , [3] in an effort to determine conditions under which the X-ray line amplification data that was observed experimentally at wavelengths between 2.71 and 2.88 A [1] could be replicated. Model calculations showed that, at laser intensities greater than 1019 W/cm2, the outermost N-shell electrons of xenon would be stripped away by tunnel ionization in less than a femtosecond. They also showed that L-shell electrons within the resulting cluster of Ni-like ions could be photoionized at a sufficient rate as to generate population inversions between these hole states and the states they radiatively decayed into. These inversions only lasted for several femtoseconds, and they were generated early in time when the cluster was being rapidly heated and the cluster's density was rapidly evolving, but was still high. They were seen to depend on the heating and expansion dynamics of the cluster, which had not been modeled in detail in this early work. In this paper, molecular dynamics calculations are described in which the rapidly evolving temperatures and ion densities of an intensely laser-heated cluster are calculated for different peak laser intensities and for two different sized xenon nano-clusters. This data is then used as an input to the ionization dynamic calculations in order to determine the influence of cluster size and of peak laser intensity on the gain coefficient calculations. In these calculations, inner-shell photoionization rates are shaped by the temperature and density dependence of the bremsstrahlung emissions under the assumption that these emissions drive the photoionizations. This shaping produces calculated gain coefficients that agree well with the measured ones.