On the positronium yield enhancement in polyethylene in high electric fields

The enhancement of the positronium (Ps) formation in polyethylene on the application of an electric field above 0.35 MV cm^-1, measured by Bisi et al., is discussed in terms of the spur model of Ps formation. Apparently, two effects can explain the results, namely (1) Ps formation by positron reaction with electrons injected in the charging processes at a high field, and (2) field dependent thermionic emission of excess electrons and positron trapped in the positron spur. The Ps enhancement in high fields does not disprove the spur model, even if the heating up of the positrons in high fields is assumed to take place.     

Final-state interaction as the origin of the Cronin effect

The Cronin effect that refers to the enhancement of hadron spectra at intermediate p(T) with increasing A in pA collisions is traditionally explained in terms of the broadening of the parton transverse momentum in the initial state. We show that recent data on the nuclear modification factor at eta=0 for d+Au collisions can be understood in terms of the recombination of soft and shower partons in the final state. It is the centrality dependence of the soft parton density that leads to the Cronin effect.     

Rigorous bounds on the radiative interaction between real gases and scattering particles

The radiative interaction due to the simultaneous presence of a real (non-gray) gas and isotropically scattering particles is examined rigorously for an isothermal plane layer, allowing completely general, frequency-dependent gas and particle radiative properties. A correction factor is defined to characterize the effects of interaction on the total hemispherical emittance of the layer, and rigorous bounds on the correction factor are determined, using the exact normal mode expansion technique of Case. It is shown that, under certain conditions for high albedo particles, interaction effects may lead to a slight enhancement of the total hemispherical emittance of the gas/particle mixture, compared to the sum of the emittances for the gas and particles considered separately, with the maximum enhancement possible being 3.2%. Under most conditions, however, the presence of the particles would be expected to shield the gas emittance. These rigorous bounds on the extent of the interaction effects are in contrast to the results of a previous numerical study, which predicted strong enhancement effects (nearly 100% enhancement for some cases) due to gas/particle radiative interaction.     

(π, d) Pick-up reaction

The reaction π + A → d + B at low energy is studied in a one-step DWBA framework. The nuclear structure aspects of the reaction are investigated. The reaction involves mostly neutron or proton pairs of the target nucleus with large total momentum and with total spin equal to zero. In the case of even-even nuclei with a partially filled shell, the coherence of the contributions from different orbitals produces an enhancement of the ground state to ground state transitions. Distortion effects are found to be very large. The final-state interaction is crucial in bringing the magnitude of the differential cross section into satisfactory agreement with the experimental value.     

Relativistic deuterons: Their dynamics and structure in collisions with nucleons and nuclei

A wide range of problems associated with investigating the structure and dynamics of relativistic deuterons in (d,p) processes on protons and atomic nuclei are considered. Experimental data include the proton momentum distributions and tensor analyzing power of these reactions on various nuclei and at various energies measured in beams of unpolarized and polarized deuterons at the JINR synchrophasotron. The experimental results are interpreted with an emphasis on using the light-front dynamics, which is well-suited for analyzing the data in terms of the wave function. The application of this approach for analyzing the A(d,p)X reaction is shown to be convenient for obtaining new important information on the deuteron structure at small distances and describing adequately its behavior at relativistic energies. The difficulties arising in this approach are also indicated. The suggestions for setting up new experiments in the designed polarized deuterons beam at Nuclotron are made.     

Effects of charge and structure of surfactants on kinetics of water reactions: the pH-independent hydrolysis of bis (2,4-dinitrophenyl) carbonate

The pH-independent hydrolysis of bis (2,4-dinitrophenyl) carbonate in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl GROUP = cetyl and dodecyl), and polyoxyethylene (9) nonylphenyl ether has been studied spectrophotometrically. Observed rate constants, k_obs, decrease in the following order: alkyldimethylbenzylammonium chlorides> bulk water ≈ alkyltrimethyl- ammonium chlorides> nonionic micelles> anionic micelles. Surfactant-substrate association constants have been determined from the dependence of k_obs on [surfactant]. ¹H NMR study of the solubilization of a model compound, phenyl-2,4-dinitrophenyl carbonate, showed that all surfactant segments are affected by the solubilizate, and that the ester penetrates deeper in micelles of alkyldimethylbenzylammonium chlorides relative to the corresponding alkyltrimethylammonium chlorides. Micellar effects on k_obs are analyzed in terms of “medium” and “electrostatic” effects. The lower microscopic polarity at the reaction site cause rate decrease, whereas electrostatic interactions of the dipolar transition state with the charged interface result in rate decrease by anionic micelles, and rate enhancement by cationic ones.     

The influence of strongly coupled pickup channels on proton elastic scattering

We show that the influence of strongly coupled deuteron channels on proton elastic scattering is large. The effect is to increase the total reaction cross section by an amount which is several times the pickup cross section. The effect is particularly large for light nuclei suggesting a reason for the breakdown of the folding model for these nuclei. We have carried out model calculations which make these results plausible in terms of the deuteron acting as a doorway for proton absorption. The effect on the real potential is considerable for lighter nuclei and consistently repulsive. Results are also presented concerning the applicability of DWBA for pickup and which illuminate the adiabatic model of Johnson and Soper. Uncertainty in very low energy deuteron propagation makes the observation of experimental effects at (p, d) threshold somewhat doubtful.     

Analysis of the reaction np → dπ+π− below 3.5 GeV/c

The reaction np → dπ⁺π^? was studied from threshold up to 3.5 GeV/c neutron beam momentum. Cross-section values for this reaction are evaluated as a function of the beam momentum. The deuteron production features and the enhancement observed in the dπ mass spectrum at 2.17 GeV are adequately described in terms of an OPE model and nucleon-nucleon final-state interactions.     

Acoustically assisted removal of nitrogen oxide from high temperature flue gas

The present study focuses on a possibility for improving NO removal efficiency from flue gas by application of powerful sound waves. The sound waves (frequency 6.9-17.2kHz, intensity 144-160dB) are propagated from Hartmann sound generators to a preheated graphite disk inside a vertical reaction tube (height 1.8m, I.D. 105mm). An Ar-NO synthetic mixture (NO 911-934ppm) is blown onto the disk surface to perform reactions in the system C-NO. It is found that the NO reduction rate can be significantly enhanced by the sound waves but the enhancement effect is dependent on the sound frequency, intensity and temperature of disk surface. The better effects are obtained at a temperature of 973K and sound frequencies between 9.6 and 12.4kHz. Under these conditions, the sound application results in 3-5-fold enhancement of NO reduction rate. The obtained effects are explained in terms of gas-phase mass transfer controlling mechanism and of near surface turbulent diffusivity.     

Effect of surface acoustic waves on activity in heterogeneous catalysis

A synopsis of the recent developments in acoustically influencing and controlling gas-surface interactions is presented. The cleaning effect of ultrasound and its surface activation play an important role for the sonochemical enhancement of reactivity in chemical processes involving solid and liquid phases. So far, there have only been a few studies on the effects of surface acoustic waves on surface chemical reactions under high-vacuum conditions by the application of piezoelectric surface acoustic wave transducers. Very recently, metal films deposited between InterDigital Transducer (IDT) electrodes on a LiNbO₃ substrate have shown a significant inerease in catalytic activity during surface acoustic excitation and Edge-Bonded Transducers (EBT) with a metal single crystal as a substrate have been used to acoustically influence the rate in the oscillatory reaction for CO oxidation. Tunable narrowband surface acoustic excitation is anticipated to be an efficient route to control catalytic processes, and in our work this approach is being used to investigate the physical basis of this process.     

The effects of electron screening and resonances in (p, α) reactions on10B and11B at thermal energies

The fusion reactions¹⁰B(p, α)⁷Be and¹¹B(p, α)⁸Be have been studied over the c.m. energy range E=17 to 134 keV using intense proton beams and thick solid targets. In the case of¹¹B(p, α)⁸Be the low-energy data in terms of the astrophysical S(E) factor show an exponential enhancement (up to a factor of 1.9) due to the effects of electron screening, where the deduced screening potential is larger than expected. In the case of¹⁰B(p, α)⁷Be the low-energy data exhibit an enhancement by more than a factor of 200, which cannot be explained by the effects of electron screening. The enhancement arises here from the high-energy tail of an expecteds-wave resonance at E_R=10 keV. The results offer an improved prospect for this reaction as advanced fuel in future fusion reactors than previously envisioned.     

Steady state convergence acceleration of the generalized lattice Boltzmann equation with forcing term through preconditioning

Several applications exist in which lattice Boltzmann methods (LBM) are used to compute stationary states of fluid motions, particularly those driven or modulated by external forces. Standard LBM, being explicit time-marching in nature, requires a long time to attain steady state convergence, particularly at low Mach numbers due to the disparity in characteristic speeds of propagation of different quantities. In this paper, we present a preconditioned generalized lattice Boltzmann equation (GLBE) with forcing term to accelerate steady state convergence to flows driven by external forces. The use of multiple relaxation times in the GLBE allows enhancement of the numerical stability. Particular focus is given in preconditioning external forces, which can be spatially and temporally dependent. In particular, correct forms of moment projections of source/forcing terms are derived such that they recover preconditioned Navier–Stokes equations with non-uniform external forces. As an illustration, we solve an extended system with a preconditioned lattice kinetic equation for magnetic induction field at low magnetic Prandtl numbers, which imposes Lorentz forces on the flow of conducting fluids. Computational studies, particularly in three-dimensions, for canonical problems show that the number of time steps needed to reach steady state is reduced by orders of magnitude with preconditioning. In addition, the preconditioning approach resulted in significantly improved stability characteristics when compared with the corresponding single relaxation time formulation.     

Low-energy enhancement in the photon strength of 95Mo

A new experimental technique is presented using proton-γ-γ correlations from (94)Mo(d,p)(95)Mo reactions which allows for the model-independent extraction of the photon strength function at various excitation energies using primary γ-ray decay from the quasicontinuum to individual low-lying levels. Detected particle energies provide the entrance excitation energies into the residual nucleus while γ-ray transitions from low-lying levels specify the discrete states being fed. Results strongly support the existence of the previously reported low-energy enhancement in the photon strength function.     

Entanglement entropy of black holes and anti-de Sitter space/conformal-field-theory correspondence

A recent proposal by Ryu and Takayanagi for a holographic interpretation of entanglement entropy in conformal field theories dual to supergravity on anti-de Sitter space is generalized to include entanglement entropy of black holes living on the boundary of anti-de Sitter space. The generalized proposal is verified in boundary dimensions d=2 and d=4 for both the uv-divergent and uv-finite terms. In dimension d=4 an expansion of entanglement entropy in terms of size L of the subsystem outside the black hole is considered. A new term in the entropy of dual strongly coupled conformal-field theory, which universally grows as L(2)lnL and is proportional to the value of the obstruction tensor at the black hole horizon, is predicted.     

High-p(T) Tomography of d+Au and Au+Au at SPS,RHIC, and LHC

The interplay of nuclear effects on the p(T)>2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at sqrt[s(NN)]=17, 200, and 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can be used to disentangle the initial and final state effects.     

Enhanced Raman scattering from individual semiconductor nanocones and nanowires

We report strong enhancement (approximately 10(3)) of the spontaneous Raman scattering from individual silicon nanowires and nanocones as compared with bulk Si. The observed enhancement is diameter (d), excitation wavelength (lambda(laser)), and incident polarization state dependent, and is explained in terms of a resonant behavior involving incident electromagnetic radiation and the structural dielectric cross section. The variation of the Raman enhancement with d, lambda(laser), and polarization is shown to be in good agreement with model calculations of scattering from an infinite dielectric cylinder.     

The3He(d,p) α reaction at astrophysical energies

We have performed a microscopic study of the³He(d,p) α reaction at astrophysical energies within the framework of the Resonating Group Method adopting three different effective nucleon-nucleon interactions. The calculations suggest that the low-energy³He(d,p) α cross section is in good approximation given by the contribution arising from the 3/2⁺ resonant state atE _R =245 keV. In fact, the low-energy data can be better (and more physically) described by a single Breit-Wigner resonance parametrization than by a polynomial fit. Our fit to the³He(d,p) α cross section results in a noticeable reduction in the uncertainties of the resonance parameters of the 3/2⁺ resonant state as well as in a significantly improved extrapolation of the data to astrophysically important energies. On the basis of this extrapolation we were able to quantitatively deduce the enhancement of the low-energy cross section due to electron screening effects from the data of Krauss et al. and Engstler et al. These experimental enhancement factors were compared with various theoretical models which are all based on the Born-Oppenheimer approximation. As the models underestimate the observed enhancement we suggest that the theoretical study of electron screening effects requires a dynamical treatment.     

水中金属丝爆引燃铝粉悬浮液冲击波增强效应

开展了水中铜丝电爆炸引燃铝粉悬浮液的实验研究,将铝粉悬浮液置于有机玻璃管中,同轴心方向穿过200 μm的金属铜丝,经脉冲功率驱动后快速相变发生电爆炸为铝粉爆燃提供反应条件。通过比对不同质量球状铝粉（μm粒径）的悬浮液在相同脉冲电容器储能条件下的放电和冲击波参数,获得了电爆炸驱动铝粉放电特性和冲击波增强效应的规律。实验发现,电爆炸起爆铝粉的冲击波有两个明显的波峰,分别对应于金属丝电爆炸（一次冲击波）和由产物气体胀裂管壁产生的二次冲击波,且铝粉爆燃对二次冲击波的增强效应非常显著,在300 mg铝粉的悬浮液环境中,二次冲击波峰值达到2.77 MPa,是无铝粉添加环境中二次冲击波的2.25倍,冲击波冲量增强了约50%。对不同储能条件下200 mg铝粉的悬浮液环境中金属丝爆的冲击波进行了对比研究,发现随着驱动源储能的增加,电爆炸引发的主冲击波和二次冲击波压力均逐渐增大,600 J时分别达到了3.17和1.91 MPa,冲击波冲量也随储能增加而增加,在600 J储能条件时的冲量为41.12 Pa·s,储能条件约300 J时20.24 Pa·s冲量的2倍。     

Numerical Investigation of Exergy Loss of Ammonia Addition in Hydrocarbon Diffusion Flames

In this paper, a theoretical numerical analysis of the thermodynamics second law in ammonia/ethylene counter-flow diffusion flames is carried out. The combustion process, which includes heat and mass transfer, as well as a chemical reaction, is simulated based on a detailed chemical reaction model. Entropy generation and exergy loss due to various reasons in ammonia/ethylene and argon/ethylene flames are calculated. The effects of ammonia addition on the thermodynamics efficiency of combustion are investigated. Based on thermodynamics analysis, a parameter, the lowest emission of pollutant (LEP), is proposed to establish a relationship between the available work and pollutant emissions produced during the combustion process. Chemical reaction paths are also analyzed by combining the chemical entropy generation, and some important chemical reactions and substances are identified. The numerical results reveal that ammonia addition has a significant enhancement on heat transfer and chemical reaction in the flames, and the total exergy loss rate increases slightly at first and then decreases with an increase in ammonia concentration. Considering the factors of thermodynamic efficiency, the emissions of CO₂ and NOx reach a maximum when ammonia concentration is near 10% and 30%, respectively. In terms of the chemical reaction path analysis, ammonia pyrolysis and nitrogen production increase significantly, while ethylene pyrolysis and carbon monoxide production decrease when ammonia is added to hydrocarbon diffusion flames.     

Thermoelectric transport in strained Si and Si/Ge heterostructures

The anisotropic thermoelectric transport properties of bulk silicon strained in the [111]-direction were studied by detailed first-principles calculations focusing on a possible enhancement of the power factor. Electron and hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high-temperature and high-doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of a [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole doping was drastically suppressed due to quantum-well effects, while under electron doping an enhanced power factor was found. For this, we state figures of merit of ZT?=?0.2 and 1.4 at T?=?300?and 900?K for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features.