Optic parameters of a middle-focus Kumakhov lens for hard X-rays

Middle-focus Kumakhov polycapillary lenses for hard X-ray optic systems are created for the first time. The performance of such a lens has been studied for X-rays in the 20–65 keV range. The radiation energy density amplification coefficient of the lens in this energy range falls within four to two orders of magnitude. Thus, the upper boundary of the energy range for effective use of the Kumakhov polycapillary X-ray optics has been increased to over 60 keV.     

Structural,elastic, electronic and optical properties of new layered semiconductor BaGa2P2

We report the results of a detailed first-principles based density functional theory study of the structural, elastic, electronic and optical properties of a recently synthesized layered semiconductor BaGa₂P₂. The optimized structural parameters are in excellent agreement with the experimental structural findings, which validates the used theoretical method. The single crystal and polycrystalline elastic constants are numerically estimated using the strain–stress method and Voigt–Reuss–Hill approximations. Predicted values of the elastic constants suggest that the considered material is mechanically stable, brittle and very soft material. The three-dimensional surface and its planar projections of Young’s modulus are visualized to illustrate the elastic anisotropy. It is found that Young’s modulus of BaGa₂P₂ show strong dependence on the crystallographic directions. Band structure calculation reveals that BaGa₂P₂ is a direct energy band gap semiconductor. The effective masses of electrons and holes at the minimum of the conduction band and maximum of the valence band are numerically estimated. The density of state, charge density distribution and charge transfers are calculated and analyzed to determine the chemical bonding nature. Dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and electron-loss energy function spectra are computed for a wide photon energy range up to 20 eV. Calculated optical spectra exhibit a noticeable anisotropy.     

Emerging Nonaqueous Aluminum‐Ion Batteries: Challenges,Status, and Perspectives

Aluminum‐ion batteries (AIBs) are regarded as viable alternatives to lithium‐ion technology because of their high volumetric capacity, their low cost, and the rich abundance of aluminum. However, several serious drawbacks of aqueous systems (passive film formation, hydrogen evolution, anode corrosion, etc.) hinder the large‐scale application of these systems. Thus, nonaqueous AIBs show incomparable advantages for progress in large‐scale electrical energy storage. However, nonaqueous aluminum battery systems are still nascent, and various technical and scientific obstacles to designing AIBs with high capacity and long cycling life have not been resolved until now. Moreover, the aluminum cell is a complex device whose energy density is determined by various parameters, most of which are often ignored, resulting in failure to achieve the maximum performance of the cell. The purpose here is to discuss how to further develop reliable nonaqueous AIBs. First, the current status of nonaqueous AIBs is reviewed based on statistical data from the literature. The influence of parameters on energy density is analyzed, and the current situation and existing problems are summarized. Furthermore, possible solutions and concerns regarding the construction of reliable nonaqueous AIBs are comprehensively discussed. Finally, future research directions and prospects in the aluminum battery field are proposed.     

Ab initio study of the structural, elastic, electronic and optical properties of the antiperovskite SbNMg3

A theoretical study of structural, elastic, electronic and optical properties of the cubic antiperovskite SbNMg₃ is presented using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). Results are given for lattice constant, elastic constants and their pressure dependence. Band structure, density of states and pressure coefficients of energy gaps are also given. Furthermore, the optical reflectivity, refractive index, extinction coefficient, dielectric function and electron energy loss are calculated for radiation up to 30 eV. The results are compared with the available theoretical and experimental data.     

Theoretical description of the graphite,diamond, and liquid phases of carbon

A three-phase equation-of-state model, to be used in high-pressure high-density simulations of systems containing carbon, is described for the system graphite-diamond-liquid. The solid phases are represented by cold lattice and thermal energy terms. Simple additivity of the energy terms is assumed and the cold curve is a modified Birch form. Liquid states for diamond and graphite are obtained by a previously described scaling model. The actual Gibbs free energy of the liquid state uses the free energy of these liquids in a mixture model that includes an entropy of mixing and a pressure-dependent strain term. It is noted that the thermal expansion coefficient and the Grüneisen gamma increase faster above 3000 K than the usual approximation for the volume dependence would predict. The result is a phase diagram that fits all available data.     

FP-LAPW calculations of structural, electronic, and optical properties of alkali metal tellurides: M2Te [M: Li, Na, K and Rb]

Structural, electronic, and optical properties of alkali metal tellurides M₂Te [M: Li, Na, K, and Rb] are investigated in the framework of density functional theory within generalized gradient approximation. The calculated structural parameters are in excellent agreement with the experimental data. The electronic band structure calculations show that tellurides of Li, K, and Rb have an indirect fundamental energy band gap, whereas Na₂Te has a direct fundamental energy band gap. To explicate the contribution of anion and cation states to the electronic band structure, the electronic density of states for these compounds has been analyzed. Optical properties such as complex dielectric function, absorption coefficient, refractive index, extinction coefficient, and reflectivity are reported for a wide range of photon energy and are discussed on the basis of corresponding electronic band structure. Furthermore, the electron energy-loss functions for M₂Te compounds are also predicted. In order to validate the performance of the ab initio calculation reported herein, we systematically study the electronic and optical properties of wide band gap M₂Te compounds and compare them with available theoretical and experimental data of M₂O, M₂S, and M₂Se compounds.     

Time-dependent density functional study of field emission from nanotubes composed of C, BN, SiC, Si, and GaN

Field emission from various types of nanotubes is studied by propagating the electronic density in real space and time using time-dependent density functional theory. Capped (5, 5) C, BN, SiC, Si, and GaN nanotubes are considered. The GaN, SiC, and Si nanotubes were found to be significantly better field emitters than C and BN nanotubes, both in terms of current magnitude and sharpness of peaks in the energy spectra. By analyzing the electronic structure of the various systems it is seen that the nanotubes with the highest currents have electron densities that extend significantly from the nanotube in the emission direction.     

村镇滑移隔震建筑输入能量的参数敏感性分析

以村镇滑移隔震建筑为研究对象,以总输入能量为响应指标,采用正交试验的方法,研究了总输入能量对刚度比、第二阶段刚度系数、隔震层屈服位移、摩擦系数、质量比和上部结构固有周期的敏感性。研究表明:在该文所研究的参数范围内,总输入能量对参数的敏感性几乎均与地震动幅值和场地条件有关,各种条件下上部结构固有周期对总输入能量的影响都是最为显著的,当上部结构固有周期大约为0.1 s时,总输入能量受场地条件的影响比较小,当地震动幅值较大时,摩擦系数与总输入能量基本呈正比关系,刚度比、隔震层屈服位移、第二阶段刚度系数和质量比均对总输入能量有一定的影响,但影响程度相对较小。     

Measurement of effective piezoelectric coefficients of PZT thin films for energy harvesting application with interdigitated electrodes

Interdigitated electrode (IDE) systems with lead zirconate titanate (PZT) thin films play an increasingly important role for two reasons: first, such a configuration generates higher voltages than parallel plate capacitor-type electrode (PPE) structures, and second, the application of an electric field leads to a compressive stress component in addition to the overall stress state, unlike a PPE structure, which results in tensile stress component. Because ceramics tend to crack at relatively moderate tensile stresses, this means that IDEs have a lower risk of cracking than PPEs. For these reasons, IDE systems are ideal for energy harvesting of vibration energy, and for actuators. Systematic investigations of PZT films with IDE systems have not yet been undertaken. In this work, we present results on the evaluation of the in-plane piezoelectric coefficients with IDE systems. Additionally, we also propose a simple and measurable figure of merit (FOM) to analyze and evaluate the relevant piezoelectric parameter for harvesting efficiency without the need to fabricate the energy harvesting device. Idealized effective coefficients e(IDE) and h(IDE) are derived, showing its composite nature with about one-third contribution of the transverse effect, and about two-thirds contribution of the longitudinal effect in the case of a PZT film deposited on a (100)-oriented silicon wafer with the in-plane electric field along one of the <011> Si directions. Randomly oriented 1-μm-thick PZT 53/47 film deposited by a sol-gel technique, was evaluated and yielded an effective coefficient e(IDE) of 15 C???m(???2). Our FOM is the product between effective e and h coefficient representing twice the electrical energy density stored in the piezoelectric film per unit strain deformation (both for IDE and PPE systems). Assuming homogeneous fields between the fingers, and neglecting the contribution from below the electrode fingers, the FOM for IDE structures with larger electrode gap is derived to be twice as large as for PPE structures, for PZT-5H properties. The experiments yielded an FOM of the IDE structures of 1.25 × 10(10) J/m(3) and 14 mV/μ strain.     

First-principles study of electronic and optical properties of cubic perovskite CsSrF3

We present first principles calculations of the electronic, structural and optical properties of the cubic perovskite CsSrF₃ by using the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method with generalized gradient approximation (GGA) in the frame work of density functional theory. The calculated lattice constant is in a good agreement with the experimental result. The electronic band structure shows that the fundamental band gap is wide and direct at ?? point. The contribution of the different bands was analyzed from the total and partial density of states curves. The charge density plots show strong ionic bonding in Cs-F, ionic and weak covalent bonding between Sr and F. The calculated optical spectra viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0?C30 eV.     

Elastic, optoelectronic, and thermal properties of cubic CSi2N4: an ab initio study

The mechanical, optoelectronic, and thermodynamic properties of carbon silicon nitride spinel compound have been investigated using density functional theory. The exchange–correlation potential was treated with the local density approximation (LDA) and the generalized gradient approximation of Perdew–Burke and Ernzerhof (PBE-GGA). In addition, the Engel–Vosko generalized gradient approximation (EV-GGA) and the modified Becke–Johnson potential (TB-mBJ) were also applied to improve the electronic band structure calculations. The ground state properties, including lattice constants and bulk modulus, are in fairly good agreement with the available theoretical data. The elastic constants, Young’s modulus, shear modulus, and Poisson’s ratio have been determined by using the variation of the total energy with strain. From the elastic parameters, it is inferred that this compound is brittle in nature. The results of the electronic band structure show that CSi₂N₄ has a direct energy band gap (Γ–Γ). The TB-mBJ approximation yields larger fundamental band gaps compared to those of LDA, PBE-GGA, and EV-GGA. In addition, we have calculated the optical properties, namely, the real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, and energy loss function for radiation up to 40.0 eV. Using the quasi-harmonic Debye model which considers the phononic effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and the heat capacity for this compound were investigated for the first time.     

Electronic properties of nanotube-ribbon hybrid systems

In this work we use the tight-binding model to study the electronic properties of nanotube-ribbon hybrid systems. The nanotube-ribbon interactions will modify state energies, alter energy gaps, destroy state degeneracy, and create additional band-edge states. The bandstructures are asymmetric and symmetric about the Fermi energy when the interactions are turned on and off, respectively. The energy gap is found to vary sensitively with the nanotube location. Moreover, semiconductor-metal transition is predicted for nanotube-ribbon hybrid systems (I) and (III). For a zigzag ribbon, the partial flat bands at E(F) are almost unaffected by the nanotube-ribbon coupling although the bandstructures have been noticeably modified by such coupling; the energy gap of system (IV) is always zero. The effects of nanotube diameter and ribbon width on the energy gap and the density of states are also investigated. The semiconductor-metal transition can be accomplished by varying the nanotube location, the nanotube diameter or the ribbon width. The main features of the bandstructure are directly reflected in the density of states. The numbers, heights, and energies of the density of states peaks are strongly dependent on the nanotube-ribbon hoppings.     

Spectral density of oscillator with bilinear stiffness and white noise excitation

The power spectral density of an oscillator with bilinear stiffness excited by Gaussian white noise is considered. A method originally proposed by Krenk and Roberts [J Appl Mech 66 (1999) 225] relying on slowly changing energy for lightly damped systems is applied. In this method an approximate solution for the power spectral density at a given energy level is obtained by considering local similarity with the free undamped response. The total spectrum is obtained by integrating over all energy levels weighting each with the stationary probability density of the energy. The accuracy of the approximate analytical solution is demonstrated by comparing with results obtained by stochastic simulation. It is shown how the method successfully captures the broadening of the resonance peak and the presence of higher harmonics in the power spectral density of strongly non-linear systems.     

A direct energy balance method for approximating envelope decay of oscillating MEMS structures

The real pole component (envelope decay coefficient) of an oscillating microelectromechanical systems (MEMS) structure is calculated directly in the energy domain without using an equation of motion. Similar to the simplified Rayleigh frequency calculation in which maximum potential and kinetic energy are equated, our method equates the initial minus dissipated energy to present energy.     

Recent Advances in High‐Performance Microbatteries: Construction,Application, and Perspective

High‐performance miniaturized energy storage devices have developed rapidly in recent years. Different from conventional energy storage devices, microbatteries assume the main responsibility for micropower supply, functionalization, and characterization platforms. Evolving from the essential goals for battery design of high power density, high energy density, and long lifetime, further practical demands for microbatteries (MBs) have been raised for the microfabrication technique and device design. Numerous studies have generally focused on specific aspects of the microelectrode structures or certain microfabrication techniques, while the connection from techniques to functional applications is rarely involved. This Review generally fills such blanks from an application‐oriented perspective. First, some basic micromachining techniques with different compatible features are summarized. Afterward, device designs including diversified battery reaction types, configuration, and assembly are highlighted, as well as microbatteries serving powering resources or further complicated functional systems. Finally, through providing the overall design concept based on requirements in application, this Review offers innovative insights for further development of microbatteries.     

Seebeck effect in polycrystalline semiconductors

The paper deals with the interpretation of the Seebeck coefficient measured for a polycrystalline semiconductor. Polycrystalline semiconductors are considered to be composed of grains separated from one another by intergrain domains. An isotype heterojunction with a certain density of interface states is assumed to exist at the grain-intergrain domain interface.The general formula for the Seebeck coefficient under these conditions is derived. The relations valid for systems of practical interest are shown as limiting cases of the formula presented.     

First-principles study of structural,elastic, electronic and optical properties of orthorhombic NaAlF4

We have performed the ab initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study the structural parameters, elastic, electronic, chemical bonding and optical properties of orthorhombic NaAlF₄. The calculated lattice parameters are in good agreement with experimental work. The bulk, shear and Young’s modulus, Poisson’s coefficient, compressibility and Lamé’s constants are firstly obtained using Voigt–Reuss–Hill method and the Debye temperature is estimated using Debye-Grüneisen model. Band structure shows a direct band gap at Γ point. Density of states and charge density have been studied, which show the bonding between Na and F is mainly ionic as well as that between Al and F. In order to clarify the mechanism of optical transitions of orthorhombic NaAlF₄, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. The optical properties and origins of the structure have been analysed.     

Optical properties of laser ablated gallium lanthanum sulphide chalcogenide glass thin films prepared at different deposition laser energy densities

This paper describes the optical properties of GLS thin films deposited by laser ablation technique. These results complement the structural and compositional data on the same specimens reported in the preceding papers. A systematic investigation of the energy dependence of the refractive index, optical absorption edge, Urbach edge and optical gap has been carried out as a function of increasing deposition energy density. The optical absorption coefficient as a function of photon energy, deduced from transmission (T) and reflection (R) measurements, shows a very large shift of the edge towards lower energies relative to that of bulk glass with increasing deposition energy density. The optical gap, as determined by Tauc extrapolation, and Urbach parameter have been determined as a function of deposition energy density. The changes in optical properties are correlated with the structural data.     

High power rechargeable batteries

Energy and power density are the key figures of merit for most electrochemical energy storage systems. Considerable efforts worldwide have been made to improve the energy density of rechargeable (secondary) batteries, as this is critical for most applications. As the penetration of batteries into ever more demanding applications has increased, power density, the allowed rate of energy transfer per unit volume or mass, is becoming equally important. High power density batteries have the potential to be rapidly charged, possibly in a few minutes or less, and can also deliver high peak discharge powers. Normally increases in power density are only possible through significant reductions in energy density, however emerging materials research is showing this needs not to be the case. Here we discuss emerging concepts in high power batteries, with a particular focus on Li-ion based chemistries.     

In-situ imaging techniques for advanced battery development

Currently, the demand for clean energy to replace fossil energy is increasing dramatically, which is driving the fast development of lithium batteries and other advanced battery systems with high energy density, high power density, good safety and low price. On the way from laboratory to market, the problems of different materials and battery systems should be overcome first. Therefore, qualitative and quantitative techniques that can operate under real battery working conditions are urgently needed to determine the reasons for these limits and reveal the kinetics and mechanisms of electrochemical reactions. In this review, such in-situ imaging techniques are introduced in detail with the aim of obtaining a better understanding of their functions and limitations, and to promote their wide use to solve the existing problems in advanced batteries. The limitations of these techniques are also discussed.