Search

Using an ab initio, time-dependent calculational method, we study the non-linear dynamics of a two-electron quantum dot in the presence of ultrashort Thz laser pulses. The analysis of the contribution of the various partial waves to two-electron joint radial and energy distribution patterns revealed strongly correlated electron ejection channels. In the double-ionization process, regardless of the photon energy, the two-electron wave packets are born and remain concentrated until the pulse's peak; at later times, and depending on the photon energy of the field, distinctly different patterns emerge. Our calculations also showed the gradual transition of the radial and energy patterns from a single-peak to a doubly peaked structure, associated with the direct and the sequential double-ionization mechanisms, respectively. [ABSTRACT FROM AUTHOR]

We investigate energy distributions of Frenkel–Kontorova-type atomic chains generated from large number of independent identically distributed (iid) random initial atomic positionings under two cases. In the first case, atoms at the free-end chains without dissipation (conservative case) are only coupled to one other atom, whereas each atom inside the bulk is coupled to its 2 nearest neighbours. Here, atoms located at the chain are all at the same type. Such kind of systems can be modelled by conservative standard map. We show that, when the coupling is non-linear (which leads chaotic arrangement of the atoms) for energy distribution, the Boltzmann–Gibbs statistical mechanics is constructed, namely, exponential form emerges as Boltzmann factor P (E) ∝ e − β E . However, when the coupling is linear (which leads linear arrangement of the atoms) the Boltzmann–Gibbs statistical mechanics fails and the exponential distribution is replaced by a q -exponential form, which generalizes the Boltzmann factor as P (E) ∝ e q − β q E = [ 1 − (1 − q) β q E ] 1 / (1 − q) . We also show for each type of atom localization with N number of atoms, β (or β q) values can be given as a function of 1 / N. In the second case, although the couplings among the atoms are exactly the same as the previous case, atoms located at the chain are now considered as being at different types. We show that, for energy distribution of such linear chains, each of the distributions corresponding to different dissipation parameters (γ) are in the q -exponential form. Moreover, we numerically verify that β q values can be given as a linear function of 1 / ∑ n = 1 N (1 − γ) (n − 2) . On the other hand, although energy distributions of the chaotic chains for different dissipation parameters are in exponential form, a linear scaling between β and γ values cannot be obtained. This scaling is possible if the energies of the chains are scaled with 1 / (1 − γ) − N . For both cases, clear data collapses among distributions are evident. • Energy distributions of Frenkel–Kontorova-type atomic chains are investigated. • The energy distributions for the chaotically located atoms are in exponential form. • The energy distributions for the linearly located atoms are in q-exponential form. [ABSTRACT FROM AUTHOR]

Detonation Shock Dynamics (DSD), involved in an underwater explosion scenario is numerically simulated by an in-house computer code, 'DSSDYN'. The simulation is based on Chapman-Jouguet (CJ) theory, formulated in Arbitrary Lagrangian Eulerian frame work. Specifically, the propagation of detonation front is simulated with'Burn Fraction Model'. The classical burn fraction model is improved for achieving better computational efficiency. The simulation capability of DSS-DYN is demonstrated through a case study on explosion of PETN charge under the deep-water medium.Through this study, the salient features of DSD with better insight have been brought out. Besides, the physical parameters, such as work potential of PETN, are predicted efficiently.The apportionment of energy distributions indicates that about 70 % of chemical energy of explosive is transmitted to the surrounding water that is the major contribution of damage potential of the explosive. The predictions of peak velocity and peak pressure values by DSS-DYN and LS-DYNA show satisfactory comparison.DSS-DYN consumes lesser computational time (~1h), compared to LS-DYNA (~3h). [ABSTRACT FROM AUTHOR]

Purpose: The adequate performance of radiobiological experiments using clinical proton beams typically requires substantial preparations to provide the appropriate setup for specific experiments. Providing radiobiologically interesting low‐energy protons is a particular challenge, due to various physical effects that become more pronounced with larger absorber thickness and smaller proton energy. This work demonstrates the generation of decelerated low‐energy protons from a clinical proton beam. Methods: Monte Carlo simulations of proton energy spectra were performed for energy absorbers with varying thicknesses to reduce the energy of the clinical proton beam down to the few‐MeV level corresponding to μm‐ranges. In this way, a setup with an optimum thickness of the absorber with a maximum efficiency of the proton fluence for the provisioning of low‐energy protons is supposed to be found. For the specific applications of 2.5–3.3 MeV protons and α‐particle range equivalent protons, the relative depth dose was measured and simulated together with the dose‐averaged linear energy transfer (LETd) distribution. Results: The resulting energy spectra from Monte Carlo simulations indicate an optimal absorber thickness for providing low‐energy protons with maximum efficiency of proton fluence at an user‐requested energy range for experiments. For instance, providing energies lower than 5 MeV, an energy spectrum with a relative total efficiency of 38.6% to the initial spectrum was obtained with the optimal setup. The measurements of the depth dose, compared to the Monte Carlo simulations, showed that the dosimetry of low‐energy protons works and protons with high LETd down to the range of α‐particles can be produced. Conclusions: This work provides a method for generating all clinically and radiobiologically relevant energies – especially down to the few‐MeV level – at one clinical facility with pencil beam scanning. Thereby, it enables radiobiological experiments under environmentally uniform conditions. [ABSTRACT FROM AUTHOR]

In this study, we developed an improved comprehensive pyrolysis scheme by modifying the bio-oil species and gas species fractions, increasing the carbon fraction in the char, and combining and changing the metaplastic decompositions for energy analysis. The two-fluid model (TFM) framework was used to simulate pyrolysis in a two-dimensional tubular reactor, and 10 g of 1500-μm-sized pinewood particles was used as biomass feedstock. Pyrolysis was performed at 400 °C−600 °C with an average heating rate of 115 °C/min. The improved scheme was evaluated against recent comprehensive pyrolysis schemes with respect to decomposition characteristics. The pyrolysis product yields and compositions predicted by the improved model accorded with experimental results. Moreover, the energy contents and distributions of pyrolysis products were successfully estimated, and the relative errors of bio-oil, gas, and char energies were 0.61%, 9.54%, and −3.76%, respectively. The energy distributions were more dominant influenced by the pyrolysis product yields than by the energy density. [Display omitted] • The improved comprehensive reaction scheme was developed for energy analysis of pyrolysis products. • This improved scheme had a closer bio-oil composition to the experiment with the heating value of 23.69 MJ/kg on dry basis. • The heating value of NCG and char of this improved scheme were in a range of 7.8–12.8 MJ/m3 and 27.1–30.7 MJ/kg, respectively. • The energy at 500 °C distributed to 56.3%, 9.6%, and 34.1% of bio-oil, NCG, and char predicted using this improved scheme. [ABSTRACT FROM AUTHOR]

Neutrinos in astrophysical environments, such as Supernovae (SNe), may interact through pair interactions. These interactions are density and temperature-dependent. Under certain conditions, a neutrino-condensate may form. In this work, we have adapted the separable nonlocal pairing interactions to the SN conditions and studied the temperature and density dependence of the pairing gap as well as the collective response with respect to these variables. We have applied the Bogoliubov transformations and solved the Bardeen, Cooper and Schrieffer (BCS) equations to construct the free quasi-particle sector of the Hamiltonian. The residual two-quasi-particle terms have been treated by applying the Tamm–Dancoff approximation (TDA) and random-phase approximation (RPA), suited to the extended neutrino media. With this, we have constructed neutrino energy distributions both in the superfluid and normal regimes and extracted critical values of the density and temperature. [ABSTRACT FROM AUTHOR]

• ·The differential characterization of AE signals from various fractures and the precursor law were investigated. • ·Proposed a novel approach to decompose the P- and S- waves of AE signals. • ·The criterion value of Es/Ep for laboratory differentiation between tensile and shear fracture is determined. Coal mining is going deeper into the ground, resulting in more intense and frequent mine dynamic disasters. To ensure the early warning of dynamic disasters, it is significant to accurately reveal the differences of acoustic emission (AE) signals generated by rock fractures. This paper focuses on studying how AEs average frequency (AF) and rise angle (RA) change in sandstone during loading, and examines the characteristics of waveform amplitude, energy, and frequency distribution of AE signals from different types of fractures. The findings reveal that the percentage of shear fracture gradually increases with increasing load, and the energy activity of the AE signal is significantly enhanced in the high stress stage. The occurrence of the main fracture was preceded by a large number of low-frequency tensile fracture AE signals, accompanied by a small decrease in RA and a small increase in AF. The spectra of different fracture signals were characterized as "low anomalous F" for shear fractures, "vertical F" for low-frequency tensile fractures, and "high anomalous F" for high-frequency tensile fractures. Their energy distribution in the frequency domain was respectively described as "peak-centered distribution", "pillar-shaped distribution" and "peak-skewed distribution". The outcomes of the decomposition and reconstruction from the P- and S-waves reveal that the P wave energy (Ep) dominates in the high-frequency tensile fracture AE signal, while the S wave energy (Es) is greater in the low-frequency tensile fracture and the shear fracture AE signals. The E S /E P threshold value for laboratory discrimination of tensile and shear fracture is 3, as the fracture extends and penetrates, the E S /E P value rises rapidly at the appearance of macroscopic fracture. The findings offer theoretical guidance for monitoring and early warning of coal and rock dynamic hazards as well as revealing the morphology of fracture source. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Energy flow in each component of a turbocharged diesel engine was analyzed. • More than 60% energy was lost by the coolant at low engine speed and load conditions. • The exhaust energy recycled by turbocharger increased with the engine power output. • The percentage of the recycled energy flowing into the cylinders was less than 2.7%. • Total thermal efficiency changed significantly if energy recoveries were applied. Abstract The impetus of the internal combustion engine developments is the reductions of the fuel consumptions and exhaust emissions. Thermal management is an efficient method to decrease the exhaust emissions and enhance fuel economy. In order to further optimize the thermal management of internal combustion engines, a detailed analysis of the energy flow in each component of internal combustion engines is indispensable. In this paper, the test bench of a heavy duty diesel engine was established to obtain the target parameters. The energy distributions in each component of the diesel engine, including compressor, intercooler, shaft power, turbine, coolant and exhaust, were calculated using tested parameters. The lubricating oil consumption was also taken into consideration. In addition, the potential influences of different turbochargers on the total thermal efficiency were analyzed. The results showed that the thermal efficiency of the diesel engine was more than 38% when the engine operated at 50%–100% engine load and 1000 rpm–1700 rpm conditions. The energy loss by coolant was more than 50% of the total fuel energy consumption in the low power output conditions. However, it was lower than 30% in high power output conditions, and the thermal loss was more than 150 kW around rated power conditions. The maximum proportion of the energy being consumed by turbine was ∼10% of the fuel energy; additionally, the exhaust energy distributions changed significantly after the turbine expansion. 1%–3% of the fuel energy was recycled by the turbocharger, then, flowed into the cylinders. The energy loss through the intercooler accounted for ∼6% of the fuel energy. Significant reductions of exhaust emissions and fuel consumptions can be achieved by optimizing the coolant and lubricating oil thermal conditions. Turbochargers presented a huge effect on exhaust temperature distributions at high power output conditions, and the total thermal efficiency changed significantly if all kinds of energy recovery approaches were applied. [ABSTRACT FROM AUTHOR]

By correlating the seismic noise, it is possible to recover one of the most important characteristics of the structure of the medium where seismic waves propagate, such characteristic is known as the Green's function. However, it's necessary to study the influence of the seismic noise distribution in order to estimate whether the recovered Green's function will be accurate. This work shows a formulation that allows obtaining the Green function for different distributions of seismic noise sources. First, the exact Green functions are used, and the energy contents of the P and SV waves are studied. Afterwards, the relationship of the exact Green function and that recovered by seismic noise is shown. Subsequently, several seismic source distributions are analyzed, mainly isotropic and collinear, and some elements that allow us to assess which of them can lead to obtain the Green's function with good approximation are exposed. [ABSTRACT FROM AUTHOR]

Vertex-frequency analysis of graph signals is a challenging topic for research and applications. Counterparts of the short-time Fourier transform, the wavelet transform, and the Rihaczek distribution have recently been introduced to the graph-signal analysis. In this letter, we have extended the energy distributions to a general reduced interference distributions class. It can improve the vertex-frequency representation of a graph signal while preserving the marginal properties. This class is related to the spectrogram of graph signals as well. Efficiency of the proposed representations is illustrated in examples. [ABSTRACT FROM AUTHOR]

• A coupled optical-electrical-thermal loss model of a photovoltaic (PV) module are developed. • Energy distributions of a PV module are evaluated qualitatively and quantitatively. • PV power output, optical and thermal losses are 16%, 16% and 68%, respectively. • A number of suggestions in theory are provided to optimize the PV technology. This paper develops a coupled optical-electrical-thermal loss model of a photovoltaic (PV) module under various conditions. Validation shows that the coupled optical-electrical-thermal loss model is accurate and effective, ranging from 0.17% to −1.88%, which are smaller than limit error in the IEC standard. The developed model is then applied to investigate energy distributions of a PV module under standard test conditions (STC) and dynamic conditions by qualitative and quantitative evaluations. Results show that the energy distributions under dynamic conditions are similar to those under STC. The power output, optical and thermal losses are 16%, 16% and 68%, respectively. The optical losses mainly result from transmission loss (43.4%), reflection loss at air-glass interface (25.5%) and reflection loss at PV layer (25%). As for complicated thermal losses, they are caused by thermalization loss (38.4%), sub-bandgap loss (21.6%), angle mismatch loss (12.9%) and voltage drop loss due to non-radiative recombination (11.6%). Furthermore, some optical suggestions (anti-reflection film, velvet surface and light trapping structure) and thermal suggestions (up conversion, down conversion, stacked structure, surface recombination optimization and the photovoltaic/thermal technology) are proposed to optimize the PV power output. [ABSTRACT FROM AUTHOR]

[Display omitted] • Opposed rotary piston engines deliver high power density. • Hydrogen direct injection applications to this novel engine are explored. • In-cylinder combustion and thermal efficiency are insensitive to early ignition. • Start of hydrogen injection avoiding the piston end faces is helpful for combustion. • Late hydrogen injection contributes to restraining the nitric oxides formations. Opposed rotary piston (ORP) engines as a new type of internal combustion engines are free of connecting-rod mechanisms, have small engine size and mass. ORP engines have the abilities of delivering high power density. Hydrogen fuel applications in internal combustion engines contribute to nearly zero carbon emissions in the combustion processes. In this paper, the effect of hydrogen direct injection strategies and ignition timing on hydrogen diffusion, in-cylinder combustion, energy distributions, and nitric oxide (NO x) emissions are investigated using a numerical simulation method regarding this novel internal combustion engine. The results showed that hydrogen was the most unevenly distributed in the combustion chambers for the start of injection (SoI) of −68.2° crank angle (CA) after top dead centre (aTDC) among the three hydrogen injection strategies; meantime, it presented the lowest combustion efficiency, being smaller than 98.5%. The peak in-cylinder pressure ranged from 40 bar to 83 bar for the given scenarios. The combustion durations were in the range of 20 °CA ~ 30 °CA for the ignition timing of −20.85 °CA aTDC ~ −11.06 °CA aTDC. The indicated thermal efficiency was higher than 38% over early ignition cases; the energy losses in total fuel energy by cylinder walls were lower than 15%. NO x emissions factors were lower than 36 g/kWh, and they were reduced by the retarded hydrogen injection. The engine performance and NO x emissions under early hydrogen injection scenarios are less sensitive to late ignition; additionally, the crank angle corresponding to the optimal efficiency was almost the same under different hydrogen injection strategies. [ABSTRACT FROM AUTHOR]

In order to clarify the transmission properties of an ion beam extracted with a large bore metal capillary into air, we measured the energy distributions of extracted 4.0 MeV alpha particles using a pinhole slit. The metal capillary we used is a conventional injection needle with 500 μ m inner diameter. As a result, we obtained two-dimensional intensity distributions of the ion beam extracted into air with this large bore metal capillary and the energy spectra at each position. We discuss the result of two-dimensional intensity distributions and report the difference of the energy spectra at the center part and at the edge. [ABSTRACT FROM AUTHOR]

We present experimental studies and computer simulations of the energy distributions of the particles sputtered from copper and molybdenum with gas cluster ions. Both experimental and simulated distributions were found to be narrower than ones known for atomic ion sputtering. It was shown that the distributions of sputtered atoms obtained by molecular dynamics simulations can be well described in frames of the thermal spike theory. For a given cluster energy, its size and the target material properties determine the parameters of the distributions. Including into consideration sequential cluster impacts on the target surface resulted in changes both in energy and angular distributions of sputtered matter and as well in total sputtering yield. Experimentally measured distributions well matched the ones simulated in "sequential" mode. Unlabelled Image • Simulated energy distributions can be described in lines of thermal spike model. • For cluster-bombarded surface the particles energy is lower for all emission angles. • Total yield is systematically lower for the bombarded surface than for the flat one. • Simulated distributions well match the experimental ones. [ABSTRACT FROM AUTHOR]