Energy Spectrum of Simply Constant Chromoelectric Flux Tubes

In this article we obtain the energy spectrum of colored, spinor particles in chromoelectric flux tubes. The chromoelectric field of the flux tubes considered here comes from simply constant gauge potentials rather than from covariantly constant gauge potential, as is usually the case. The energy spectrum of the simply constant flux tubes is different than that of the covariantly constant flux tubes. The spectrum is discrete due to the walls of the tube and with a plus/minus constant shift depending on the magnitude of the constant chromoelectric background. This goes against the classical intuition where one would expect a charged particle in a uniform “electric” field to accelerate with ever increasing velocity/energy i.e. there would be no constant energy eigenvalue.     

The solution of the cosmological constant problem from the inhomogeneous equation of state — a hint from modified gravity?

The cosmological constant problem is studied in a two component cosmological model. The universe contains a cosmological constant of an arbitrary size and sign and an additional component with an inhomogeneous equation of state. It is shown that, in a proper parameter regime, the expansion of the universe with a large absolute value of the cosmological constant may asymptotically tend to de Sitter space corresponding to a small effective positive cosmological constant. It is argued that such a behavior can be regarded as a solution of the cosmological constant problem in this model. The mechanism behind the relaxation of the cosmological constant is discussed. A connection with modified gravity theories is discussed and an example of a possible realization of the cosmological constant relaxation in f(R) modified gravity is described.     

Synthesis of highly ordered nanopores on alumina by two-step anodization process

Highly ordered anodic alumina was produced, on RF sputtered aluminium on a conductive glass substrate, by two step anodizing process in 0.4 M sulphuric acid at constant cell potentials of between 5 and 25 V and at a constant current density of 20 mA cm⁻². The temperature was kept constant at 15 °C during both anodization processes. The effects of the anodizing potential, current density, and time on the pore diameters were established. Longer anodization periods result in wider irregular pores with reduced porosity for both constant potential and constant current density anodization processes. The current density increases with increasing constant anodizing potential and generally remains constant with time after a sharp rise. Potential drop during constant current density anodization behaves in a similar manner. We confirm that sulphuric acid has a self-ordering potential of 25 V above which burning occurs.     

Axiomatic approach to the cosmological constant

A theory of the cosmological constant Λ is currently out of reach. Still, one can start from a set of axioms that describe the most desirable properties a cosmological constant should have. This can be seen in certain analogy to the Khinchin axioms in information theory, which fix the most desirable properties an information measure should have and that ultimately lead to the Shannon entropy as the fundamental information measure on which statistical mechanics is based. Here we formulate a set of axioms for the cosmological constant in close analogy to the Khinchin axioms, formally replacing the dependence of the information measure on probabilities of events by a dependence of the cosmological constant on the fundamental constants of nature. Evaluating this set of axioms one finally arrives at a formula for the cosmological constant given by , where G is the gravitational constant, m_e the electron mass, and α_el the low-energy limit of the fine structure constant. This formula is in perfect agreement with current WMAP data. Our approach gives physical meaning to the Eddington-Dirac large-number hypothesis and suggests that the observed value of the cosmological constant is not at all unnatural.     

Dark energy and gravity

I review the problem of dark energy focussing on cosmological constant as the candidate and discuss what it tells us regarding the nature of gravity. Section 1 briefly overviews the currently popular “concordance cosmology” and summarizes the evidence for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as a candidate and emphasizes why no other approach really solves the conceptual problems usually attributed to cosmological constant. Section 2 describes some of the approaches to understand the nature of the cosmological constant and attempts to extract certain key ingredients which must be present in any viable solution. In the conventional approach, the equations of motion for matter fields are invariant under the shift of the matter Lagrangian by a constant while gravity breaks this symmetry. I argue that until the gravity is made to respect this symmetry, one cannot obtain a satisfactory solution to the cosmological constant problem. Hence cosmological constant problem essentially has to do with our understanding of the nature of gravity. Section 3 discusses such an alternative perspective on gravity in which the gravitational interaction—described in terms of a metric on a smooth spacetime—is an emergent, long wavelength phenomenon, and can be described in terms of an effective theory using an action associated with normalized vectors in the spacetime. This action is explicitly invariant under the shift of the matter energy momentum tensor T _ab → T _ab + Λ _gab and any bulk cosmological constant can be gauged away. Extremizing this action leads to an equation determining the background geometry which gives Einstein’s theory at the lowest order with Lanczos–Lovelock type corrections. In this approach, the observed value of the cosmological constant has to arise from the energy fluctuations of degrees of freedom located in the boundary of a spacetime region.     

Temperature dependence of dielectric constant of crystals with fluorite structure

The experimental data on the temperature variation of dielectric constant of six crystals with fluorite structure are analysed using an approach proposed by Havinga and Bosman for ionic crystals. The temperature variation of dielectric constant is resolved in three components related to the thermal expansion, the pressure dependence of dielectric constant and the temperature variation of polarizability (theA, B, C terms). In the present work, theB term is calculated semiempirically, such that the analysis can be extended to crystals like EuF₂ for which high pressure dielectric constant data are not available. For the first time, such calculations have been made for EuF₂ and PbF₂ at elevated temperatures. TheC term, which is related to the temperature variation ofir polarizability is seen to play a dominant role in determining the temperature variation of dielectric constant.     

熔石英亚表面杂质颗粒附近光场调制的三维模拟

熔石英亚表面缺陷是光学材料低损伤阈值的主要因素之一.本文建立了熔石英亚表面三维球形杂质颗粒模型,采用三维时域有限差分方法对杂质附近的光场进行了数值模拟,分析了杂质的介电常数与尺寸对光强增强因子的影响,结果显示:介电常数小于熔石英的杂质,其光强增强因子不随尺寸、介电常数的改变而改变,均保持为4左右;当介电常数为6.0时,半径为1.5λ,2λ及2.5λ的杂质,相应的光强增强因子分别为50.1588,73.3904及102.9953,即增强因子随杂质尺寸的增大而增大;恰 关键词： 杂质颗粒 三维时域有限差分 数值计算 光强增强因子     

Cosmological constant—the weight of the vacuum

Recent cosmological observations suggest the existence of a positive cosmological constant Λ with the magnitude Λ(G/c³)≈10⁻¹²³. This review discusses several aspects of the cosmological constant both from the cosmological (Sections 1–6) and field theoretical (Sections 7–11) perspectives. After a brief introduction to the key issues related to cosmological constant and a historical overview, a summary of the kinematics and dynamics of the standard Friedmann model of the universe is provided. The observational evidence for cosmological constant, especially from the supernova results, and the constraints from the age of the universe, structure formation, Cosmic Microwave Background Radiation (CMBR) anisotropies and a few others are described in detail, followed by a discussion of the theoretical models (quintessence, tachyonic scalar field, …) from different perspectives. The latter part of the review (Sections 7–11) concentrates on more conceptual and fundamental aspects of the cosmological constant like some alternative interpretations of the cosmological constant, relaxation mechanisms to reduce the cosmological constant to the currently observed value, the geometrical structure of the de Sitter spacetime, thermodynamics of the de Sitter universe and the role of string theory in the cosmological constant problem.     

Localized modes due to U-centre in alkali halides

The vibration of H^?-ion impurity (U-centre) in alkali halide crystals is discussed with the help of nearest-neighbour effective force constant. A simple expression for the change in force constant involving effective force constant and localized mode frequency is obtained. Numerical results obtained for the relative force-constant-change are seen to be in agreement with the existing calculations.     

Rate constant of capture of electron charge carriers on a screened repulsive center

The rate constant of capture of electron charge carriers on a screened repulsive center are performed. Approximate expressions for the potential barrier width, the capture cross section, and rate constant are derived. It is shown that the increase in the concentration of free charge carriers in silver azide from 10¹⁶ to 10²⁰ cm^?3 results in an increase in the capture rate constant by four orders of magnitude. It is also shown that, with increasing concentration of free carriers, the temperature dependence of the rate constant weakens and the effective activation energy of capture in silver azide decreases from 0.18 to 0.01 eV.     

Giant Static Dielectric Constant of Strained PbTiO3

First-principles density functional perturbation calculations are employed to study the dielectric and piezoelectric properties of strained tetragonal PbTiO3. Lattice distortion, static dielectric constant, Born effective charge, zone-centre phonons, and piezoelectric constant are obtained. For the strained tetragonal PbTiO3, we obtain a giant static dielectric constant （3600） under a strain 0. 77%. Moreover, the calculated piezoelectric constant e15 of strained PbTiO3 reaches about 203 C/m^2 which is about 20 times of that of unstrained system. The giant static dielectric constant is mainly due to the softening of the lowest-frequency phonon mode and the reduce of Ti-O bond length. This work demonstrates a route to a giant static dielectrics for electrically microwave and other devices.     

Low temperature specific heat of 12442-type KCa2Fe4As4F2 single crystals

The Hubble constant H_0 represents the expansion rate of the Universe at present and is closely related to the age of the Universe.The accurate measurement of Hubble constant is crucial for modern cosmology.However,different cosmological observations give diverse values of Hubble constant in literature.Up to now,there are two methods to measure the Hubble constant.One is to directly measure the Hubble constant based on distance ladder estimates of Cepheids and so on.The other is to globally fit the Hubble constant under the assumption of a cosmological model,for example the "standard" ACDM model.Adopting the low-redshift observational datasets,including the Pantheon sample of Type Ⅰa supernovae,baryon acoustic oscillation measurements,and the tomographic Alcock-Paczynski method,we determine the Hubble constant to be 67.95_(-1.03)~(+0.78),69.81_(-2.70)~(+2.22) and66.75_(-4.23)~(+3.42) km s~(-1) Mpc~(-1) at 68% confidence level in the △CDM,wCDM and W_0W_a CDM models,respectively.Compared to the Hubble constant given by Riess et al.in 2019,we conclude that the new physics beyond the standard △CDM model is needed if all of these datasets are reliable.     

Pressure and temperature dependence of the static dielectric constant of KBr

The static dielectric constant and the temperature and pressure derivatives of the static dielectric constant of KBr have been measured at several temperatures between 4·3°K and room temperature. The sample was prepared in the form of a three-terminal parallel-plate capacitor and the dielectric constant was determined from measurements of the capacitance with a high precision bridge. The dielectric constant decreases with temperature as does the magnitude of the temperature dependence and the magnitude of the pressure dependence. The data were used to calculate the fixed-volume temperature derivative of the dielectric constant. This quantity, (? ln ε/?T)_v, exhibiting lattice-anharmonicity effects, decreases slightly from its room temperature value as the temperature is lowered, rises to a maximum value at about 33°K and then decreases rapidly at lower temperatures.     

Relaxational behavior of the piezoelectric constant and the electrostriction constant in polymers

Piezoelectricity in polymer films is classified by its mechanism into three groups: A-1, intrinsic piezoelectricity due to internal strain in nonpolar crystals; A-2, intrinsic piezoelectricity due to the strain-dependence of the spontaneous polarization in polar crystals; and B, piezoelectricity due to the heterogeneity of macroscopic strain.

The relaxational behavior of piezoelectricity in Type A-1 is discussed for two cases: (a) the piezoelectric phase is relaxing, and (b) the piezoelectric phase is nonrelaxing but the nonpiezoelectric phase is relaxing. For Case a, a thermody-namic theory is developed, yielding relations among relaxation strengths of piezoelectric constant, dielectric constant, and elastic modulus. For Case b, on the other hand, the inequalities e″/e′ < 0 and d″/d′ > 0 are verified for a generalized composite model of two phases, where e′ — ie” and d′ — id″ are complex piezoelectric stress and strain constants, respectively.

Relaxational behavior of the piezoelectric constant for Type A-2 and Type B is expected to reflect that of the electrostriction constant as suggested by theories. The complex electrostriction constant in a range from 30 Hz to 500 kHz is presented for unrolled and rolled poly(vinylidene fluoride) films. The frequency dependence of the complex electrostriction constant can explain the relaxational behavior of the piezoelectric constant of Types A-2 and B, and at the same time gives a new aspect of the relaxational character of polymers, the strain-dependence of the relaxation time, and its anisotropy.     

Laser induced air breakdown using 0.355, 0.532, and 1.06 µm radiation

Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06 μm radiation are reported. We observep ^−0.8 scaling ofI _th at 1.06 μm and a weak scaling ofp ^−0.4 at 0.532 and 0.355 μm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure is observed.     

Dielectric properties of CaCu3Ti4O12–silicone resin composites

CaCu₃Ti₄O₁₂ (CCTO)–silicone resin composites with various CCTO volume fractions were prepared. Relatively high dielectric constant (ε=119) and low loss (tanδ=0.35) of the composites with CCTO volume fraction of 0.9 were observed. Two theoretical models were employed to predict the dielectric constant of these composites; the dielectric constant obtained via the Maxwell–Garnett model was in close agreement with the experimental data. The dielectric constant of CCTO–silicone resin composites showed a weak frequency dependence at the measuring frequency range and the loss tangent apparently decreases with increase in frequency.     

金红石相纳米块材TiO2的介电特性

研究了不同制备压力下成型的以金红石相为主的纳米二氧化钛介电常数的频率谱和温度谱。在频率谱上发现,当频率ω<0.1kHz时,随着测量频率的下降,介电常数迅速升高,低频下的介电常数比高频区的介电常数高1—2个数量级。并且随着样品加压压力的提高,介电常数升高,在与之相对应的介电损耗谱上,随着样品加压压力的提高,损耗值下降,损耗峰向低频区位移。对1.0GPa压力下成型的样品,其介电常数随测量温度的升高,分别在50℃和300℃出现两个峰值。经分析得出,影响金红石相纳米二氧化钛介电行为的微观机制主要为晶粒内部的电子松弛极化和界面中的电偶极矩的转向极化,50℃峰对应于电于松弛极化,而300℃峰则对应于电偶极矩的转向极化。 关键词：     

Attenuation and propagation in various finline structures

The theory and numerical results of the asymmetric single and coupled bilateral and unilateral finlines and arbitrary antipodal finline considering the attenuation of the substrate are presented. Results are given to the complex propagation constant. The full wave analysis of the Transverse Transmission Line — TTL method is used in the FTD. Applying the moment method the complex propagation constant, including the attenuation constant and the phase constant, are obtained. The effective dielectric constant, _eff,, and the characteristic impedance are also calculated. The results are compared with the references, and news results are presented for these parameters.     

Electrodynamique stochastique et mécanique quantique

Numerous quantum-like results are obtained in stochastic electrodynamics. However, the latter has not the interpretation difficulties of quantum mechanics. K, a constant of stochastic electrodynamics is not a fundamental constant as is ?, the corresponding constant in quantum mechanics.