近50年来西藏极端降水时空变化特征

利用1961~2010年西藏地区9个气象站点逐日降水资料,结合百分位方法定义的极端降水阈值,分析了该地区极端雨日及其平均降水强度、不同持续时间的极端降水事件、气候变化对极端降水的时空变化特征的影响。结果表明:(1)92°E以西的地区,极端雨日平均降水强度呈现出增加的趋势,而在92°E以东的地区,呈现出减小的趋势;(2)极端降水事件以持续1 d为主,其频率一般在4.3次/年以上,强度一般在20 mm/d以上,林芝站和波密站为频率和强度高值区;(3)气候变化背景下,极端降水的频率、强度表现出西移的态势。     

Cycle-by-cycle combustion variation in a DISI engine fueled with methanol

The effects of injection and ignition timings, engine speed and load, compression ratio and injector configuration on cycle-by-cycle combustion variation in a direct-injection spark ignition (DISI) engine fueled with methanol have been studied experimentally. The coefficient of variation (COV) of the maximum in-cylinder pressure was used to evaluate the cycle-by-cycle combustion variation. The results showed that these factors significantly affect the cycle-by-cycle combustion variation. The COV reaches the least at an optimal injection and ignition timings. The COV at a compression ratio of 14:1 is less than that at a compression ratio of 16:1 at light load, and vice versa at high load. The COV using injector type A is significantly less than that when using types B and C.     

基于排队分析的端到端路径可用带宽的测量

端到端路径可用带宽是衡量网络性能的重要指标.目前,大多数对可用带宽测量的研究都集中在自拥塞方法上,但自拥塞方法会严重影响路径上的原有流量,因此,提出了一种基于模型的方法,将Internet视为一个具有单一服务单元且服务两种流量(探测流量和背景流量)的排队系统,通过分析探测流量离开排队系统的过程,在路径的负载与探测流量离去间隔的变异系数之间建立了对应关系,并在此基础上获得可用带宽值.与自拥塞方法相比,不会造成路径拥塞且具有较好的准确性.     

门楼水库时段降水序列展延模型的选择

针对动态汛限水位应用时存在的问题 ,结合门楼水库动态汛限水位过程线的研究 ,对季节性自回归模型、相关解集模型、正则展开模型、多变量序列模拟的正交变换法和多变量AR(1)模型五个常用多变量生成模型进行了分析试验 ,通过对比研究 ,指出多变量AR(1)模型最适合时段降水序列的展延     

Genome-Wide Investigation of Multifocal and Unifocal Prostate Cancer—Are They Genetically Different?

Prostate cancer is widely observed to be biologically heterogeneous. Its heterogeneity is manifested histologically as multifocal prostate cancer, which is observed more frequently than unifocal prostate cancer. The clinical and prognostic significance of either focal cancer type is not fully established. To investigate prostate cancer heterogeneity, the genetic profiles of multifocal and unifocal prostate cancers were compared. Here, we report observations deduced from tumor-tumor comparison of copy number alteration data of both focal categories. Forty-one fresh frozen prostate cancer foci from 14 multifocal prostate cancers and eight unifocal prostate cancers were subjected to copy number variation analysis with the Affymetrix SNP 6.0 microarray tool. With the investigated cases, tumors obtained from a single prostate exhibited different genetic profiles of variable degrees. Further comparison identified no distinct genetic pattern or signatures specific to multifocal or unifocal prostate cancer. Our findings suggest that samples obtained from multiple sites of a single unifocal prostate cancer show as much genetic heterogeneity and variability as separate tumors obtained from a single multifocal prostate cancer.     

四氧化三锰的制备及其对奥克托今的热分解行为研究

以氯化锰为锰源、六次甲基四胺(HMT)为沉淀剂,采用均相沉淀法在90℃制备了Mn3O4,用X-射线衍射、扫描电镜和透射电镜等对产物的结构和形貌进行表征,利用DSC技术研究了产物对奥克托今(HMX)的热分解行为的影响。结果表明,制备产物为四方结构Mn3O4,直径约为300 nm的近似球形。Mn3O4的加入,对HMX的分解峰形变化不大,但分解温度增大,分解活化能增加。     

DRYING OF BIOLOGICAL PRODUCTS WITH SIGNIFICANT VOLUME VARIATION. EXPERIMENTAL AND MODELING RESULTS FOR POTATO DRYING.

ABSTRACT

This work is devoted to the experimental investigation and theoretical modeling of biological products with high initial moisture content which implies significant volume contraction. Firstly, experimental equipment which was designed to continuously determine variations in the global moisture content and in the temperature of the sample is introduced. Furthermore, the equipment is controlled by a PC which records experimental information in real time. In particular, measurement of the radial and temporal distributions of moisture content and temperature during the drying process of the homogeneous porous media potato are given. The mean moisture content and temperature curves are also given.     

Interval Estimation Approach to Counting by Weighing: A Sequential Scheme

Abstract

Considerable time and energy involved in complete counting of large, but pre-specified, batch of N _s items could be saved by using weights of items. This article considers the case when the underlying distribution of weights, and its mean and variance are unknown. The problem is then reduced to that of finding an estimator of the mean and an optimal (small) sample size based on which a number [Ncirc] _n of items in the batch can be determined. Using a fixed-width interval criterion, Nickerson [Nickerson, D.M. Another look at counting by weighing. Commun. Statist. Simula. 1993, 22 (2), 323–343] derived an optimal sample size, but it depends on the unknown coefficient of variation. For this case, we propose a batch-type sequential sampling scheme which requires substantially fewer sampling operations and no prior knowledge of the coefficient of variation, but performs as well as Nickerson's and other available procedures in the literature. This shows that a little bit of sampling using substantially fewer sampling operations can significantly reduce the effort of complete counting.     

Sequential estimation of the mean of the negative binomial distribution

Insect population counts are often fit well by the negative binomial distribution. Estimation of the mean is of primary interest, and thus Anscombe's parameterization in terms of the mean, μ, and k has become almost standard. A common assumption is that k is known or a precise estimate of k is available. In this paper, sequential estimation of the mean with a prescribed degree of precision is investigated. The limiting behavior of each procedure is studied and Monte Carlo methods are employed to determine the behavior under moderate levels of precision.     

Variability of Phytosterols in Jatropha curcas Germplasm

Jatropha curcas L. has great potential for biofuel and phytosterol production. The objective of this research was to evaluate G × E variability for kernel phytosterol content and composition in Jatropha germplasm. Freshly matured seeds from 21 accessions grown in Málaga, Spain were collected at two stages of development. Significant genetic variation was detected for total kernel phytosterol content, which ranged from 2,246 to 2,883 mg kg^?1; and stigmasterol concentration, which ranged from 7.6 to 11.5 % of the total phytosterols. An accession with 9.2 % Δ⁵‐avenasterol was also identified. The coefficient of variation for kernel phytosterol content and stigmasterol concentration was 6.2 and 14.0 % respectively between accessions and 7.2 and 10.2 % respectively within accessions. Accordingly, evaluation of plant to plant variation is advisable. The existence of variability for kernel phytosterol content and composition in Jatropha will enable breeding for enhanced levels of these compounds.