大气：转动的热机

 地球是一个旋转的球体,它具有巨大的质量和强大的惯性。地球的旋转包括每日一圈的自转和每年一圈的公转,自转带来了大气运动的日变化,而公转则导致了大气运动的四季变化。普通人或许并不清楚,但对于地球科学领域的学者来说,由于地球自转而产生的地转偏向力具有无处不在的影响, 这种力施加在运动物体之上,在北半球指向运动方向的右侧,而在南半球则指向运动方向的左侧。这种偏向力也是大气运动中很多特殊现象背后的关键原因。     

Objective evaluation of target detectability in night vision color fusion images

An evaluation for objectively assessing the target detectability in night vision color fusion images is proposed.On the assumption that target detectability could be modeled as the perceptual color variation between the target and its optimal sensitive background region,we propose an objective target detectability metric in CIELAB color space defined by four color information features:target luminance,region perceptual luminance variation in human vision system,region hue difference,and region chroma difference.Experimental results show that this proposed metric is perceptually meaningful because it corresponds well with subjective evaluation.     

Cation mixing （Li0.5Fe0.5）2SO4F cathode material for lithium-ion batteries

We study the crystal structure of a triplite-structured (Li_0.5Fe_0.5)SO₄F with full Li⁺/Fe2⁺ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li⁺/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li⁺ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO₄ with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.     

A NEW HYBRID ELEMENT ANALYSIS FOR EXPONENTIALLY VARYING FGM BASED ON AN ASYMPTOTIC STRESS FIELD

A hybrid finite element for exponentially varying Fhnctionally Graded Material （FGM） is established based on a derived stress field for an intact plate. Elements with both single layer and two layers of gradient are presented. The general stress field is obtained through an asymptotic analysis coupled with Westergaard＇s stress function approach. With the aid of boundary collocation technique, convergence of the derived stress field is verified. Effectiveness and efficiency of the element is investigated through calculation and comparison. Based on that element, stress field of FGM plate under different loading cases is studied briefly.     

EFFECT OF TEMPERATURE-DEPENDENT PROPERTIES ON THERMOELASTIC PROBLEMS WITH THERMAL RELAXATIONS

Based on the generalized thermoelasticity proposed by Green and Lindsay, the dynamic response of generalized thermoelastic problems with temperature-dependent material properties is investigated. The governing equations are formulated and found to be nonlinear because of the temperature-dependence of properties. Owing to the nonlinearity of the governing equations, the finite element method is resorted to for solution. The results obtained show that the temperature-dependent properties influence the variables considered by reducing their magnitudes. This indicates that taking the temperature-dependence of properties into consideration in the investigation of generalized thermoelastic problems is necessary and practical for accurately predicting the thermoelastic behavior.     

带刚臂平面悬链线索单元的非线性分析

针对索梁混合结构中存在的索单元锚固点刚性连接问题,将锚固点的刚性连接视为刚臂,进行了带刚臂的平面悬链线索单元研究。一方面在已有文献的基础上,根据平面刚臂的受力和变形特点,基于微分方法导出了两端带任意刚臂的平面悬链线索单元切线刚度矩阵显式表达式;另一方面,为考虑温度变化对索单元计算的影响,基于索单元变形的几何与物理意义进行了考虑温度变化的索单元节点力计算方法的研究。通过与已有文献的对比,表明了本文研制的程序及导出的考虑温度变化的索单元计算方法的正确性;考虑温度变化下由本文方法得到的索水平张力与已有文献解析解最大仅相差0.862%。同时本文考虑的刚臂非线性因素更加全面,具体体现在:在非线性计算能力上,已有文献方法在荷载大于2.52kN时计算无法收敛,远小于本文方法能达到的35kN;在计算效率方面,在7个荷载增量步内已有文献方法所需的迭代步数为4~33,而本文方法的迭代步数保持在4不变。     

基于改进高斯模型的哈尔滨市PM_(2.5)扩散问题实证分析

2013年初以来,国内发生大范围持续雾霾天气,我国城市PM_(2.5)的污染问题引起了社会各界的关注和重视.根据风场和气象变化对高斯扩散模型进行适当改进,并提出基于高斯模型的PM_(2.5)扩散预测模型.以哈尔滨市PM_(2.5)近期实测数据为基础进行实证分析,对市区内10个地区的PM_(2.5)扩散和浓度变化做出合理的预测.     

Scattering for focusing combined power-type NLS

We consider the scattering of Cauchy problem for the focusing combined power-type Schr¨odinger equation. In the spirit of concentration-compactness method, we will show that, H1 solution will scatter under some condition on its energy and mass. We adapt some variance argument, following the idea of Ibrahim–Masmoudi–Nakanishi.     

Analysis of optical axis variations in monolithic nonplanar ring laser

A mathematical model of the mirror misalignment of a four-equal-sided nonplanar ring cavity is established in this letter.The variations in the optical axis are discussed through an augmented 6×6 ray matrix formulation.Numerical analysis shows that the self-consistence of the optical axis can always be obtained because of the thermal e?ects in any case of mirror misalignment.For a fabricated design,optical axis variations always appear.The influence of thermal e?ects(i.e.,pump power) on optical axis variations are studied.The tilt of the optical axis remains constant,whereas its decentration varies with pump power.Further analysis shows that the actual closing point of the optical axis moves close to the ideal point as the pump power increases.The theoretical analysis proposed is proven and validated by the experimental results.     

Effect of optical pump on the dielectric properties of SrTiO_3 in terahertz range

Tuning the dielectric permittivity spectra of strontium titanate （SrTiO3） single crystals in an extemal optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. The application of the optical field leads to an appreciable tuning of the permittivity, reaching up to 2.8%, with the dielectric loss changing about 3%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of the refractive index responds linearly to the applied light power. These findings are attributed to a linear electro-optical effect of the internal space charge field of the crystal.