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[en] This letter addresses the problem of stimulated Raman excitation of a hydrogen atom submitted to an ultrashort and intense laser pulse in the keV regime. The pulse central frequency ω of 55 a.u. (about 1.5 keV) is in the weakly relativistic regime, (c is the speed of light in vacuum and a 0 the Bohr radius) and the pulse duration is τ ≈ 18.85 a.u. (about 456 attoseconds). We solve the corresponding time-dependent Schrödinger equation (TDSE) using a spectral approach, retardation (or nondipole) effects are included up to , breaking the conservation of the magnetic quantum number m and forcing the resolution of the TDSE in a three-dimensional space. Due to the laser bandwidth, which is of the order of the ionization potential of hydrogen, stimulated Raman scattering populates nlm excited states (n and l are the principal and azimuthal quantum numbers, respectively). The populations of these excited states are calculated and analyzed in terms of l and m quantum numbers, this showing the contributions of the retardation effects and their relative importance. (letter)
[en] Highlights: • A new direct scheme for quantum dynamics simulations of photoexcited states. • Automatic generation of potential energy surfaces with machine learning. • Propagation of diabatic states enables direct grid-based quantum dynamics. • Requires fewer electronic structure evaluations than generation of fitted diabatic surfaces. We present a method for performing non-adiabatic, grid-based nuclear quantum dynamics calculations using diabatic potential energy surfaces (PESs) generated “on-the-fly”. Gaussian process regression is used to interpolate PESs by using electronic structure energies, calculated at points in configuration space determined by the nuclear dynamics, and diabatising the results using the propagation diabatisation method reported recently (Richings and Worth, 2015). Our new method is successfully demonstrated using a grid-based approach to model the non-adiabatic dynamics of the butatriene cation. Overall, our scheme offers a route towards accurate quantum dynamics on diabatic PESs learnt on-the-fly.
[en] We have studied the fission parameters of hot neutron-rich thermally fissile and nuclei within the temperature dependent effective field theory motivated relativistic mean field (E-TRMF) formalism by using the recently developed FSUGarnet and IOPB-I parameter sets. The results obtained by these two forces are compared with the results of the well known and widely accepted NL3 parameter set. The excitation energy , shell correction energy , single particle energy for neutrons and protons , level density parameter a, neutron skin thickness ΔR, two neutron separation energy , and asymmetry energy coefficient of these neutron-rich thermally fissile nuclei are calculated at finite temperature. The dependency of level density parameter and other observables on the temperature and the force parameters (interaction Lagrangian) are discussed.
[en] Highlights: • The efficiency of the MNITG at arbitrary power is analytically derived. • A universal bound on the efficiency of the MNITG with broken time-reversal symmetry and the arbitrary power is obtained. • Some system-specific characteristics are discussed and uncovered. • The broken time-reversal symmetry provides the physically allowed degrees of freedom for tuning the performance of heat devices. - Abstract: We investigate the performance at arbitrary power of minimally nonlinear irreversible thermoelectric generators (MNITGs) with broken time-reversal symmetry within linear irreversible thermodynamics, and the efficiency of MNITGs at arbitrary power is analytically derived. Furthermore, a universal bound on the efficiency of thermoelectric generators (TGs) with broken time-reversal symmetry and the arbitrary power is obtained. Some system-specific characteristics are discussed and uncovered. A large efficiency at arbitrary power can also be achieved via the cooperative mechanism between the system parameters. Our results indicate that the broken time-reversal symmetry provides the physically allowed degrees of freedom for tuning the performance of thermoelectric devices, and the physical trade-off region between the efficiency and the power output can also offer the appropriate space for optimizing the performance of TGs.
[en] The first (namely, inner) fission barriers for even-A N = 152 nuclei have been studied systematically in the framework of macroscopic-microscopic model by means of potential energy surface (PES) calculations in the three-dimensional () deformation space. Their collective properties, such as ground-state deformations, are compared with previous calculations and available observations, showing a consistent trend. In addition, it has been found that the microscopic shell correction energy plays an important role on surviving fission in these N = 152 deformed shell nuclei. The inclusion of non-axial symmetric degree of freedom γ will pull the fission barrier down more significantly with respect to the calculation involving in hexadecapole deformation β 4. Furthermore, the calculated Woods-Saxon (WS) single particle levels indicate that the large microscopic shell correction energies due to low level densities may be responsible for such a reduction on the inner fission barrier. (paper)
[en] The Hellmann–Feynman, virial and comparison theorems are three fundamental theorems of quantum mechanics. For the first two, counterparts exist for classical mechanics with relativistic or nonrelativistic kinetic energy. It is shown here that these three theorems are valid for classical mechanics with a nonstandard kinetic energy. This brings some information about the connections between the quantum and classical worlds. Constraints about the functional form of the kinetic energy are also discussed. (paper)
[en] In this paper, a model of irreversible three-electron-reservoir energy selective electron (ESE) cooling device with heat leakage is established. By utilizing the finite time thermodynamics, the optimal performance of the cooling device is studied and the influences of chemical potential differences of electron reservoirs, center energy level of energy filters and heat leakage on the optimal performances are discussed. On the basis of cooling rate and coefficient of performance (COP) analyses, the exergy-based ecological function and figure of merit are proposed as objective functions. The operation properties of ESE cooling device with different objective functions are investigated and the optimal performance region is obtained. Higher cooling rate and COP can both be attained for the ESE cooling device when it is working in the optimal performance region.
[en] Highlights: • A principle mechanism of temperature non-uniformities formation in shock-tube reactor is the boundary layer instability. • A key role in ignition kernels formation belongs to the interaction of reflected shock wave with roller vortices. • The origins of roller vortices are related with intrinsic boundary layer instability development behind the incident shock. • High-precision numerical simulations show similarity of the flow development in the tubes of round and square cross sections. - Abstract: The paper studies numerically the flow development behind the shock wave propagating inside the tube. The detailed analysis of the flow patterns behind the shock wave allows determination of the gas-dynamical origins of the temperature non-uniformities responsible for the subsequent localized start of chemical reactions in the test mixture. In particular, it is shown that the temperature field structure is determined mainly by the mechanisms of boundary layer instability development. The kinetic energy dissipation related to the flow deceleration inside boundary layer results in local heating of the test gas. At the same time, the heat losses to the tube wall lead to the cooling of the gas. Therefore the temperature stratification takes place on the scales of the boundary layer. As soon as the shock wave reflected from the end-wall of the tube interacts with the developed boundary layer the localized hot regions arise at a certain distance from the end wall. The position of these hot regions is associated with the zones of shock wave interaction with roller vortices at the margin between the boundary layer and the bulk flow. Formulated mechanism of the temperature field evolution can be used to explain the peculiarities of non-steady shock-induced ignition of combustible mixtures with moderate ignition delay times, where the ignition starts inside localized kernels at distance from the end wall.
[en] Decentralized control of DC microgrid (dcµG) using hybrid renewable energy sources (RES) and battery energy storage system (BESS) which operate with and without grid-connected mode is proposed in this paper. In dcµG integrated with multiple RES and BESS, fluctuating output characteristics of the distributed generations (DGs) due to changing input conditions and the dynamic interactions of the source and load interface converters are main factors which cause stability problem of DC bus voltage. Thus, to solve this problem, the decentralized control scheme which uses bus voltage level as communication link in the control law is proposed in this paper. Accordingly, the control method realizes different operating modes based on the available generations and load demand. Maximum power and constant voltage controls schemes are applied in the DGs interfacing control to regulate the power and voltage variations due to changing input conditions. Furthermore, in the control strategy, the source and battery interfacing converters are controlled autonomously using the bus voltage level without any communication. This maintains the reliability and flexibility of the system. The proposed system model is developed with Matlab/Simulink SimPowerSystem and simulated with real-time simulation using OPAL-RT.
[en] Using the generalized formalism of Dalibard, Dupont-Roc and Cohen-Tannoudji we investigate the spontaneous excitation of a static atom interacting with electromagnetic vacuum fluctuations outside an Einstein Gauss-Bonnet black hole in d-dimensions. It shows that spontaneous excitation does not occur in a Boulware vacuum, while exists in an Unruh vacuum and Hartle-Hawking vacuum. As to the total rate of change of the atomic energy, it does not receive the contribution from the coupling constant of the Gauss-Bonnet term at spatial infinity, only the dimensional parameter has the contribution to it. Near the event horizon, both the coupling constant and the dimension p contribute to the total rate of change of the atomic energy in all three kinds of vacuum. We discuss the contribution of the coupling constant and dimensional factor to the results in three different kinds of spacetime lastly. (authors)