Alpha decay rate enhancement in metals: An unlikely scenario

It has been recently suggested that one might drastically shorten the alpha lifetime of nuclear waste products, if these are embedded in metals at low temperatures. Using quantum mechanical tunneling arguments, we show that such an effect is likely to be very small, if present at all.     

A class of subgrid-scale models preserving the symmetry group of Navier–Stokes equations

Navier–Stokes equations (NS) admit transformations which transform a solution to another solution (galilean transformation, scaling transformation, …). They also admit viscosity dependent transformations which transform a solution to a solution of another NS with different viscosity. These particular transformations are called symmetries of NS. Each of them has a physical role (such as conservation laws, …). A consistent turbulence model should then remain invariant under these symmetry transformations. Unfortunately, this is not the case of several models.In this article, a class of subgrid-scale models preserving the symmetries of NS is built. This class is then refined such that the models respect the second law of thermodynamics. One of the simplest models of the class is tested to the flow in a ventilated room. Better results than those provided by Smagorinsky and dynamic models are obtained.     

Amplification without population inversion in a three-level Λ-type system with an external coherent magnetic field

In this Letter, we investigate the amplification without inversion (AWI) in a new scheme, a three-level Λ-type system which the two lower states are coupled by an external magnetic field. We find that, owing to the presence of the external magnetic field, the absorption of the probing field is very sensitive to the relative phase of the probing and the pumping fields. By appropriately choosing the Rabi frequency of the pumping field, the Lamor frequency of the external magnetic field and the relative phase, AWI can be realized.     

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C1–C4 aliphatic alcohols near ambient pressure

Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.     

光谱流量标准化的高效计算

流量标准化是光谱数据挖掘中的一个基本环节,他对挖掘结果的精度和系统的效率均有重要影响,常用方法存在效率较低的问题,为此研究了光谱数据挖掘中流量标准化的算法设计和效率比较问题。首先,探讨了光谱流量标准化技术不同实现方案的渐进效率,给出了实现高效计算的算法,并分析了它们的时间复杂度和空间复杂度。然后,通过SDSS(sloan digital sky survey)的实测光谱数据,横向比较了不同流量标准化算法的效率差异。在光谱流量标准化算法的纵向理论研究中,主要考虑的是计算效率随数据规模增长的变化规律,是在极限意义下进行探讨。在横向实验比较中,考虑重点是不同算法中基本操作时间复杂度的差异及其对算法效率的影响。理论研究和实验结果表明,虽然四种标准化方法Smax,Smedian,Smean和Sunit的渐进效率的类型相同,但对常见的观测规模光谱数据来说,Smax和Smean的效率远远高于Sunit和Smedian,且常用的Sunit标准化方法效率最低。该研究对于在光谱数据挖掘和开发中,如何根据数据的规模,具体需求,从整体上考虑精度和效率的折衷,以确定合适的流量标准化方法有重要的参考价值。     

Graphitization of activated carbon under high pressures and high temperatures

Activated carbon was treated at 5.0 GPa up to 1600 ^°C and the structural evolution in the graphitization process was investigated. The graphitization temperature is reduced to 1200 ^°C at 5 GPa, as reflected by x-ray diffraction patterns. Honeycomb-like structures come into being in the high-pressure sintering temperature range of 1000–1100 ^°C and slice-like structures appear after graphitization. Raman frequency and half width drop drastically near the graphitization temperature, and the appearance of D and D′ lines indicates there are still some disorder structures in the graphitized activated carbon.     

Incoherently coupled Hermite-Gaussian breather and soliton pairs in strongly nonlocal nonlinear media

We theoretically investigate the propagation of incoherently coupled Hermite-Gaussian breather and soliton pairs in strongly nonlocal nonlinear media. It is found that multipole-mode soliton pairs with arbitrary different orders of Hermite-Gaussian shape can exist when the total power of two beams equals the critical power and the ratio of the beam widths for the Gaussian part is inversely proportional to the square root of the ratio of the wave numbers. When the total power does not equal the critical power, the Hermite-Gaussian breather pair exists and their beam widths evolve analogously. For general cases where the ratio of the beam widths is arbitrary, soliton-breather pairs or breather-breather pairs can be formed and their beam widths evolve synchronously in-phase or out-of-phase. Numerical simulations directly based on the nonlocal nonlinear Schrödinger equation are conducted for comparison with our theoretical predictions. The numerical stability analysis shows the higher-order Hermite-Gaussian solitons can not be stable for small nonlocality or for some media like liquid crystals.     

Elliptic incoherent spatial solitons and their interactions in strongly nonlocal media with an anisotropic nonlocality

We investigate the propagation and interaction of elliptic incoherent spatial solitons (EISS) in strongly nonlocal kerr media with an anisotropic nonlocality based on the coherent density approach. An exact analytical solution of such EISS is obtained; the results show that such EISS can form with both isotropic and anisotropic coherence. Moreover, we find that the interaction properties of EISS are very similar to that of their coherent counterpart. Some numerical examples are presented and pertinent physics features are addressed.     

Lagrangian approach for dark soliton in nonlocal nonlinear media

We theoretically investigate the dynamics of dark solitons as well as their interaction in nonlocal media. Approximate equations describing the evolution of the beams are obtained via suitable trial functions of amplitude u and refractive index n in an averaged Lagrangian. Our results reveal that out-of-phase dark solitons can evolve into stable bound states in nonlocal materials. Moreover, it is found that the separations in the bound state monotonically increase with the degree of nonlocality in nonlocal limit. These results are in excellent agreement with the numerical simulations.     

Structural and optical properties of ZnO thin films on (111) CaF2 substrates grown by magnetron sputtering

ZnO thin films were grown on (111) CaF₂ substrates by magnetron sputtering at room temperature. Structural and optical properties of the ZnO thin films were studied. XRD analysis showed that the ZnO thin films had the (002) preferential orientation. The transmittance of ZnO thin films was over 80% in the visible range. The optical band gap of the ZnO thin films was 3.26 eV. The optical constants (n,k)$(n,k)$ of the ZnO thin films in the wavelength range 300–1000 nm were obtained by infrared spectroscopic ellipsometry measurement. PL spectra of ZnO thin films showed strong UV near-band-edge emission peak at 376.5 nm and weak visible red emission at 643.49 nm using He–Cd laser as the light source, using a synchrotron radiation light source PL spectra showed three emission peak at 320 nm, 410 nm and 542 nm respectively.