Interface energy of semicoherent metal-ceramic interfaces

An ab initio based approach to determine energies and structures for semicoherent interfaces is developed and applied to the Fe(001)/VN(001) system. To account for elastic displacements resulting from the lattice misfit, we compare an atomistic approach using a model potential (embedded-atom method) with a continuum approach using the Peierls-Nabarro model. The total interface energy of the atomistic modeling is found to be well reproduced by the Peierls-Nabarro model, demonstrating that accurate interface energies of semicoherent interfaces can be obtained by combining first principles for the chemical part of the energy and a Peierls-Nabarro model to account for the elasticity of the media.     

Multilayered perceptron neural networks to compute energy losses in magnetic cores

This paper presents a new approach based on multilayered perceptrons (MLPs) to compute the specific energy losses of toroidal wound cores built from 3% SiFe 0.27 mm thick M4, 0.1  and 0.08 mm thin gauge electrical steel strips. The MLP has been trained by a back-propagation and extended delta-bar-delta learning algorithm. The results obtained by using the MLP model were compared with a commonly used conventional method. The comparison has shown that the proposed model improved loss estimation with respect to the conventional method.     

基于扩散势能和自由体积的自扩散系数模型

在考虑自由体积和局部临界扩散势能的基础上,提出一种新的计算自扩散系数模型,并给出新模型中各个因子物理含义．同时还提出一种计算局部临界扩散势能的新方法,并应用于新模型．另外将衍生van der Waals状态方程应用于求解自由体积,式中所需径向分布函数由Morsali-Goharshadi方程得到．在相同条件下,新模型比原自由体积模型更准确．     

A local approach to the computation of correlation energies of molecules

A new variational approach is introduced for the calculation of correlation energies of molecules. It is based on the local character of the correlated electron motion. Based on the approach we calculate correlation energies for simple systems. These include various Hubbard models as well as a model of the H₆-ring for which exact results are available. Our finding is that the proposed approach appears to be simpler and more economical for numerical work than conventional CI-methods. More than 90% of the correlation energy is obtained in all cases considered.     

Additivity rule for the softness parameter in alkali halides

In the present communication we report an additivity rule for the repulsive potential softness parameter in alkali halides derived from the values of overlap integrals. This rule provides a new interpretation for the repulsive interactions between different ion pairs and reduces the number of parameters. The use of additivity rule eliminates the assumption that the anion-anion, anion-cation and cation-cation softness parameters are equal. Using the new model for repulsive interactions we have calculated the cohesive energy and compressibility of sixteen alkali halides with NaCl structure. The results obtained in the present study are in better agreement with experiment than those obtained earlier with the help of a traditional approach based on the Born model.     

Modal analysis of IncGaAsP-InP, GaAs/AlGaAs-GaAs, and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.     

A keyhole volumetric model for weld pool analysis in Nd:YAG pulsed laser welding

This study presents a new model for analyzing the temperature distribution and weld pool shape in Nd:YAG pulsed laser welding. In the proposed approach, a surface flux heat transfer model is applied in the low laser energy intensity region of the weld, while a keyhole heat transfer model based on a volumetric heat source is applied in the high laser energy intensity region of the weld. The correlation between the intensity of the laser input energy and the geometric parameters of the volumetric heat source is derived experimentally. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the shape and size of the weld pool given different laser energy intensities. A good agreement is observed between the simulation results and the experimental results obtained under equivalent single pulse welding conditions. Thus, the basic validity of the proposed model is confirmed.     

The quasibound state model for self-consistent characteristics of semiconductor intersubband devices

The quasibound state model (QBSM) for determining the self-consistent conduction band profile and space charge density of semiconductor intersubband devices is presented. This new method is based on the quasibound (QB) state resonances of quantum structures. For heterostructures, the traditional self-consistent energy continuum model (ECM) calculates space charge by integration over the entire energy continuum, weighted by Fermi–Dirac statistics. In the present approach, the continuum of energy states of the heterostructure is accurately represented by a small number of QB states, and the space charge calculations are performed only at these eigen-energies. This approach significantly reduces the computational burden associated with all self-consistent algorithms. Theoretical formulation of QBSM is compared with the traditional ECM approach. The bound (B) and QB eigenenergies of the structure are obtained by solving the single-band effective-mass Schrödinger equation using the argument principle method. The performance and the accuracy of the QBSM are evaluated for a double-barrier resonant structure and an asymmetric Fabry–Perot electron-wave interference filter. The self-consistent electron density and potential profiles calculated by the present method are shown to be in excellent agreement with the results obtained from the traditional ECM model. In addition to requiring less computational time, the present method is easily implemented and may be applied equally well to biased/unbiased, symmetric/asymmetric heterostructures.     

A new approach to the calculation of the gain of an energy amplifier

A new view upon an energy amplifier (based on a subcritical reactor driven by an accelerator motivated source of neutrons) as a system united by the energy flow between the accelerator and the subcritical reactor is given in the paper. A new approach to the calculation of the gain of the energy amplifier using the neutron balance equation is also introduced. The expression for the gain obtained here is compared with an expression derived earlier [C. Rubbia et al.: Rep. ISC 93-31, ISC/P 57, CERN, 1993].     

Fusion of the extended modified liquid drop model for nucleation and dynamical nucleation theory

We present a new phenomenological approach to nucleation, based on the combination of the "extended modified liquid drop" model and dynamical nucleation theory. The new model proposes a new cluster definition, which properly includes the effect of fluctuations, and it is consistent both thermodynamically and kinetically. The model is able to predict successfully the free energy of formation of the critical nucleus, using only macroscopic thermodynamic properties. It also accounts for the spinodal and provides excellent agreement with the result of recent simulations.     

Simulation of the behavior of the cutting force during ultrasonic rotary machining of materials using structure-time fracture mechanics

An analytical model is developed for the behavior of the cutting force during ultrasonic rotary polishing, and it is based on the concepts of dynamic fracture mechanics and the solution to the problem of impact surface fracture. The dependence of the threshold fracture energy obtained in the problem of erosion using a structure-time approach is used to construct the cutting force model. The dependences of the cutting force on the material feed rate and the rate of tool rotation are obtained, and the developed model is shown to be efficient to explain the effects observed in experiments.     

Modeling of light coupling effect using tunneling theory based on particle properties of light

Based on the wave-particle duality of light, the Schrödinger equation for a photon as a particle is established to treat the light coupling effect by introducing concepts of the virtual mass and potential for a photon, which is different from the previous method that uses the analogy with quantum mechanics. The virtual mass is physically correlated to the kinetic energy according to Einstein’s energy–momentum relation. As a consequence, this new model has merits of physical simplicity and analytic nature. This new model can well explain the exponential dependence of the light coupling effect on the physical parameters in coupled waveguides on, which can be observed in the experimental and simulation data reported in the literature. Moreover, an explicit expression for the coupling length (coefficient) on the effects of physical parameters can be obtained by virtue of this new model, whereas the previous modal approach and the coupled-wave model resulted in implicit expressions. This new model does not only give a better physical understanding but also offers a possibility to design and fabricate optic devices based on the light coupling effect by optimizing the physical parameters.     

Kinetic component of the correlation energy density functional: a quantitative description from information theory

In the framework of information theory, a new method to determine T _c , the kinetic energy component of the correlation energy density functional for atoms, is presented. This approach is based on Shannon entropy and information energy that are obtained by fractional occupation probabilities of natural atomic orbitals. It is indicated that the calculated Shannon entropy using discrete probabilities is an increasing function while information energy is a decreasing function of the number of electrons. An expression is proposed with explicit dependence on the Shannon entropy or information energy and atomic number for the purpose. Applications of formulas for estimation of T _c values for neutral atoms up to Xe and their first positive and negative ions are then examined and validity of the proposed approach is numerically verified.     

A New Expression for Nuclear Rotational Spectra

A new formula, which is derived from a deformed rotor model for describing nuclear rotational spectra, is analyzed. The ground band of most even-even rare-earth and actinide nuclei are accurately reproduced using a damped nonlinear least-square fitting procedure for determining parameters of the theory. The results show that energy spectra obtained from a deformed rotor model are more accurate than those from a three-parameter formula based on perturbation theory.     

Gain and bandwidth in stagger-tuned gyroklystrons and gyrotwystrons

This paper describes an analytical approach to consideration of the tradeoff between the gain and the bandwidth in gyroklystrons and gyrotwystrons with stagger-tuned cavities. This approach is based on the “point-gap” model, in which short cavities are responsible for electron energy modulation only, while orbital phase bunching caused by this modulation proceeds in long drift sections. The paper contains a review of results of the analysis of stagger-tuned gyroklystrons and gyrotwystrons obtained previously. It also includes new results of the study of gyroklystrons in which different cavities operate at different cyclotron harmonics     

Gated photoluminescence study of oxide-free InP MIS structure having an ultrathin silicon interface control layer

In order to investigate the effectiveness of a novel oxide-free surface passivation approach for InP, using an ultrathin silicon interface control layer (Si ICL), gated photoluminescence characteristics of the Si₃N₄/Si ICL/n-InP metal–semiconductor–insulator (MIS) structure were studied at room temperature. As compared with gated PL spectra of Si₃N₄/n-InP MIS without Si ICL, PL intensities of the sample with Si ICL were much more strongly modulated by the gate voltage. The interface state density distribution was estimated by an optical analog of the Terman’s C–V analysis and a good agreement with the C–V analysis was obtained. The result indicates complete removal of Fermi level pinning over the entire bandgap in the novel oxide-free MIS structure.     

Advances towards using finger/toenail dosimetry to triage a large population after potential exposure to ionizing radiation

Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails.     

Experimental determination of vibrational anharmonic contributions

This article deals with the experimental determination of separate vibrational anharmonic contributions to the self‐energy of phonons in any crystals based on temperature dependence of their Raman spectra. We propose a new approach to find each anharmonic contribution by using special temperature points. We apply the approach to diamond, silicon, and crystalline α‐S₈ and show that our results for summarized anharmonicity in diamond and silicon are in good agreement with the values obtained previously for these systems by other researchers. Copyright © 2013 John Wiley & Sons, Ltd.     

Size-asymmetric primitive model at low temperature: description of ion pairing and location of the critical point

We argue that Bjerrum's approach to ion pairing is inappropriate for the size-asymmetric primitive model in the neighborhood of its critical point, and propose a new approach based on the Stillinger-Lovett pairing procedure. The new approach recursively scales up the ion size until linear approximations are suitable for analyzing such a model. To locate the critical point, a residual van der Waals interaction between pairs is added, with an energy cutoff adjusted to match the critical temperature of the restricted primitive model. The locations and downward trends of T(c) and rho(c) with asymmetry are found to compare favorably with simulations.     

EPR dosimetry in chemically treated fingernails

By using EPR measurements of radiation-induced radicals it is possible to utilize human fingernails to estimate radiation dose after-the-fact. One of the potentially limiting factors in this approach is the presence of artifacts due to mechanically induced EPR signals (MIS) caused by mechanical stress during the collection and preparation of the samples and the so-called background (non-radiation) signal (BKS). The MIS and BKS have spectral parameters (shape, g-factor and linewidth) that overlap with the radiation-induced signal (RIS) and therefore, if not taken into account properly, could result in a considerable overestimation of the dose. We have investigated the use of different treatments of fingernails with chemical reagents to reduce the MIS and BKS. The most promising chemical treatment (20 min with 0.1 M dithiothreitol aqueous solution) reduced the contribution of MIS and BKS to the total intensity of EPR signal of irradiated fingernails by a factor of 10. This makes it potentially feasible to measure doses as low as 1 Gy almost immediately after irradiation. However, the chemical treatment reduces the intensity of the RIS and modifies dose dependence. This can be compensated by use of an appropriate calibration curve for assessment of dose. On the basis of obtained results it appears feasible to develop a field-deployable protocol that could use EPR measurements of samples of fingernails to assist in the triage of individuals with potential exposure to clinically significant doses of radiation.