2009年一次华北强桑拿天气过程的动力识别

本文数值模拟并诊断分析了2009年7月华北的一次桑拿天过程, 分析了高温高湿天气的环流特征, 温度、 湿度的水平和垂直分布特征, 位涡分布特征等. 分析发现, 此次桑拿天事件高层为反气旋性环流的高压控制, 水平分布图上, 低层相对湿度大. 垂直剖面上, 中低层为下沉气流和暖湿区, 有明显的水汽梯度和垂直温度梯度, 有倾斜的位涡分布. 既然桑拿天发生在夏季普遍高温的大环境之下, 因此靠单纯的温度或湿度来动力识别和诊断桑拿天, 有较大难度. 本文抓住华北地区桑拿天过程高温、 高湿、 高位涡的特点, 引入一个适合于桑拿天的湿热力位涡参数(MTPV, 它表示为▽ q · (▽ θ × ▽ Q), 这里q是湿度, 表示为大气或者云中水汽和所有水凝物的总和, θ 是位温, Q是位涡), 对桑拿天进行动力诊断分析, 并通过实际个例的计算分析作出简化. 个例分析发现, 此次高温高湿的桑拿天过程伴随MTPV的异常. 虽然2009年7月此次华北地区桑拿天过程有较高的温度, 较大的湿度和倾斜位涡发展, 但是单个变量的范围远大于我们要研究的华北地区桑拿天的爆发范围. 而结合这三个变量引入的MTPV及其简化形式, 无论从经向还是纬向剖面图来看, MTPV的异常大值区相对集中在北京及其周边的华北地区对流层的低层, 并维持. 因而, MTPV及其简化形式均能对此次高温高湿的桑拿天进行较好的动力识别。     

应力对La0.83Sr0.17MnO3薄膜输运性能的影响

采用溶胶-凝胶方法在Si(111)上制备了LSMO(x=0.17)薄膜.研究了块体材料和不同厚度薄膜R -T曲线、红外光谱和X射线衍射.结果表明，LSMO薄膜属于正交晶体结构，薄膜取向与膜厚度 有关，当膜厚度为450nm或680nm时，主要取向〈200〉，而膜厚度为900nm时取向为〈020〉 ：根据离子对相互作用能和谐振子模型，得到了红外吸收与Mn—O—Mn键长和键角关系式，6 00cm^-1附近红外吸收与晶格常数b的变化有关；块体与薄膜的金属—绝缘体转变 温度(T_MI)存在较大差别，薄膜转变温度显著低于块体，并与厚度有一定关系. 认为是LSMO薄膜中的应力诱导了晶格常数变化，引起键角改变及JT效应是转变温度变化的主 要原因. 关键词： 单晶硅 晶格常数 金属—绝缘体转变温度 应力诱导     

厄尔尼诺和南方涛动海气耦合模型中参数估计的变分方法

提出一种基于变分原理估计厄尔尼诺和南方涛动海气耦合模型中未知参数的方法. 首先将所研究的非线性海气耦合动力方程引入到目标泛函中; 接着利用变分方法导出伴随方程和待辨识参数泛函梯度的公式; 然后设计了估计未知参数的算法.数值试验结果表明变分方法是一 种能有效估计海气耦合非线性系统未知参数的方法.     

Increased Rigidity in Complexes Formed from Negatively Charged Lariat Ethers and Alkali Metal Cations

Abstract

C-13 NMR longitudinal relaxation times have been measured for lariat ether complexes in which a negative charge is present in the ligand but the system is diamagnetic. A -CH₂COO^? group connected to the nitrogen of aza-15-crown-5 results in drastically increased T₁'s in the presence of Li⁺ compared to the values for the free carboxylic acid and for the acid in the presence of LiClO₄. Longer relaxation times upon complexation show the ‘cryptand-like’ behavior of the complexes, resulting from overall molecular reorientation rates due to compression. These conclusions are supported by molecular mechanics calculations described herein.     

油水饱和球管孔隙模型弛豫的理论计算与计算机模拟

根据Brownstein-Tarr理论,采用特征函数展开法,通过求解基于扩散效应的Bloch控制方程,给出了油水饱和球管孔隙模型弛豫的理论计算公式.理论计算结果表明,在水润湿条件下,油的弛豫过程只与含油饱和度有关,而与岩石的孔隙结构无关.根据理论计算结果对球管模型中水的弛豫进行了数值模拟,模拟结果显示,球和管的主弛豫过程是一个单指数函数,其余部分与之相比可以忽略,即球管模型中水的弛豫可近似为一个双指数衰减过程. 关键词： 核磁共振 弛豫 球管孔隙模型 Bloch控制方程     

基于无人机高光谱特征参数和株高估算马铃薯地上生物量

地上生物量(above-ground biomass,AGB)是评价作物长势及其产量估测的重要指标,对指导农业管理具有重要的作用.因此,快速准确地获取生物量信息,对于监测马铃薯生长状况,提高产量具有重要的意义.于马铃薯现蕾期、块茎形成期、块茎增长期、淀粉积累期、成熟期获取成像高光谱影像、实测株高(heigh,H)、地上...     

Deuterium solid echo line shape study of poly(ethylene oxide) dynamics in a blend with poly(methyl methacrylate)

Deuterium solid echo line shapes were measured on deuterated poly(ethylene oxide) (d₄PEO) in a blend with protonated poly(methyl methacrylate) to characterize chain dynamics of this component in the blend. Line shapes were observed as a function of temperature from 183 to 243 K and echo delay times from 10 to 100 μs on a blend containing 20 wt % d₄PEO. The line shapes and the associated relative intensities were quantitatively interpreted in terms of segmental motion and libration. The results of the interpretation are compared to an earlier study of deuterium spin‐lattice relaxation times over the temperature range of 313 to 413 K. A combined interpretation of both sets of data is developed based on bimodal distribution of correlation times that are separated by about 2 orders of magnitude in time. The faster mode is 30% of the correlation function with a stretched exponent near one while the slower mode is characterized by an exponent of 0.5. The source of the bimodal character is not revealed by the line shape and relaxation data but is consistent with the presence of two glass transition temperatures in this miscible blend and anomalous translational diffusion of diethyl ether through the blend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2433–2444, 2005     

A cosmological study in massive gravity theory

A detailed study of the various cosmological aspects in massive gravity theory has been presented in the present work. For the homogeneous and isotropic FLRW model, the deceleration parameter has been evaluated, and, it has been examined whether there is any transition from deceleration to acceleration in recent past, or not. With the proper choice of the free parameters, it has been shown that the massive gravity theory is equivalent to Einstein gravity with a modified Newtonian gravitational constant together with a negative cosmological constant. Also, in this context, it has been examined whether the emergent scenario is possible, or not, in massive gravity theory. Finally, we have done a cosmographic analysis in massive gravity theory.     

Orientational order parameter studies on 3.Om and 3O.Om liquid crystals

Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/T_c) ^β, effective geometry parameter α_g and Vuks’ scaling factor S_C. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method.