积微分算子的迹公式

考虑了基于Dirchlet边界条件和Neumann边界条件下的含有积分项的Sturm-Liouville特征值的迹问题.将微分算子迹的计算化归为相关亚纯函数在回路上的渐近式计算,并采用留数公式,得到了Dirchlet边界条件和Neumann边界条件下该积微分算子的迹公式.     

龙门加工中心空运转与铣削工况热特性

文章讨论了机床切削的热源和边界条件的数学模型,建立了某龙门加工中心的有限元模型,给出了该加工中心的热边界条件,利用ANSYS软件对该加工中心在不同主轴转速下空运转及铣削时的整机温度场及加工中心上关键点的温升规律进行了分析,并通过对该加工中心在几种工况下温升的实测验证了理论分析的结果与实测结果有较好的一致性。     

周期性边界条件下的三方演化少数者博弈

提出并研究了周期性边界条件下的三方演化少数者博弈模型.在该模型中,每个经纪人有一组概率(p1,p2,p3=1-p1-p2),做决定时或者以概率p1(p3)选择去最近相同历史下的少数方(多数方),或者以概率p2选择去最近相同历史下的中间方.数值模拟结果显示,在周期性边界条件下系统的整体效益要比在反射边界条件下的好.边界条件对三方演化少数者博弈有影响.     

二维机织复合材料力学分析中的周期性边界条件研究

为了精确地进行二维机织复合材料力学性能的数值分析,需建立单胞模型的准确边界条件。基于周期边界条件理论,提出了简便通用的二维机织复合材料周期边界方程,并给出了周期边界条件下各弹性常数在有限元分析中的求解方法;为验证周期边界条件的正确性,建立了９ 个单胞构成的九宫格结构,取中央单胞作为参考单胞,对不同边界条件下独立单胞的变形和应力分布与参考单胞进行对比。研究结果表明：即使在单向拉伸载荷下,单胞各个边界面也不保持平面状态,而是出现凹凸翘曲变形,即存在边界周期性;通过边界周期性条件,可正确地获得二维机织织物的工程弹性常数。     

社区体育会所——筑起健康家园

分析了钢质燃气管道在多种内、外边界条件下的传热情况，对管道进行分段传热计算，得到了沿程管壁及燃气温度场。     

非稳态自然对流换热系数计算方法及其在防护服隔热预报中的运用

为得到相对精确的热防护服非稳态隔热性能预测数值,基于传热系统的非稳态传热模型,在防护服材料外表面分别为恒温边界条件和Howard模型对流边界条件下,利用有限差分法分别计算了2种边界条件下模拟皮肤处温度的时程曲线,所得结果均与实验测量值差别较大。在细致分析传热过程的基础上,综合运用傅里叶定律、牛顿冷却定律、以及Howard模型对流边界条件,在线化假设下提出了一种自然对流换热系数计算方法,代入非稳态模型后利用有限差分法进行了求解,随着时间步长的加密,计算结果迅速向实验测量值收敛,当时间步长为0.001 s时,计算结果与测量结果误差小于0.1 ℃。     

一类非线性抛物型方程组解的整体存在及爆破问题

研究了一类带有Dirichlet边界条件的非线性抛物型方程组解的整体存在及解在有限时刻爆破问题, 通过构造方程组的上、下解,得到了解整体存在的一个充分条件及解在有限时刻爆破的一个充分条件.     

一类非线性抛物型方程组解的整体存在及爆破

研究了一类带有非线性边界条件的非线性抛物型方程组解的整体存在及解在有限时刻爆破问题.通过构造方程组的上、下解,得到了解整体存在的一个充分条件及解在有限时刻爆破的一个充分条件.     

一类比率依赖捕食模型的局部分歧及稳定性

运用谱分析和分歧理论的方法,在齐次Dirichlet边界条件下,对一类比率依赖捕食模型的半平凡解的分歧及稳定性进行了研究.以增长率b为分歧参数,讨论了发自半平凡解的分歧,同时判定了分歧解的稳定性.     

二次及三次分市载荷作用下弹性体的多项式解答

求解受二次及三次连续分布载荷作用时的弹性平面问题,通常是采用三角级数解法.本文探讨了利用应力函数边界条件的性质,来建立受二次及三次分布载荷作用时弹性体内应力函数的解析方法.它是用应力函数边界条件代替应力边界条件,作为求解双调和方程式(?)~4φ=0的定解条件.其优点是设取应力函数初步形式直观且容易,并有一定的规律可循,即可以解析地求得由多项式表示的应力函数解答.     

支座位移作用下一对边支承矩形弹性薄板弯曲统一求解方法

对一对边支承一对边自由矩形板提出了一种统一的弯曲挠度表达式,该表达式切合板边界所能激发的弯曲变形形态和角点位移时导致的变形特点,可以计算一对边支承一对边自由矩形板在边界发生任意支座位移时的弯曲.     

考虑横向剪应力连续的复合材料面层夹层板精化理论

采用逐段光滑位移矢假设，考虑了横向剪应力在层间的连续及表面的协调，用最小位能原理建立了复合材料面层夹层析的精化理论，所得控制方程含有７个未知量。本文理论可视为Ｌｉｂｒｅｓｃｕ夹层板模型的精化形式，它可直接计算出数值甚小但工程上颇为重要的层间应力。     

Isolation of single yeast cells by optical trapping

Individual yeast cells can be successfully isolated and recultured on plates with a new isolation method making use of optical trapping with infrared laser light. The cells can be selected on morphological criteria by high resolution microscopy. The isolation device is constructed from two coverslips separated by spacers, in which selected cells are transferred to a plastic capillary, using the optical trap. To test the procedure, selection experiments were done with a mixture of two Saccharomyces cerevisiae strains, distinguishable both in fluorescence microscopy and on agar plates. These experiments showed that only selected cells were isolated, and close to 100% of the isolated stationary-phase cells formed colonies on agar plates, indicating a high recovery. A lower recovery was obtained with exponential-phase cells, possibly because of a higher sensitivity to laser irradiation. Applications for this method may include the isolation of mutants with altered morphology and the isolation of subpopulations of yeast cultures, for their separate investigation or for the initiation of pure cultures.     

Evaluation of the Petrifilm rapid coliform count plate method for coliform enumeration from surimi-based imitation crab slurry

The 3M Petrifilm rapid coliform count (RCC) plate method was compared with two conventional methods, namely violet red bile agar (VRBA) and desoxycholate lactose agar (DLA), for enumerating coliforms. The VRBA plating method is a reference method in the Bacteriological Analytical Manual and the DLA plating method is the method recommended by the Food Sanitation Law of Korea for enumeration of coliforms. Serratia sp., a coliform that was isolated from frozen surimi, was incubated in surimi-based imitation crab (SBIC) slurries and enumerated on the Petrifilm RCC, VRBA, and DLA plates. Results from the Petrifilm RCC plate were not significantly different from results from VRBA or DLA plates at P < 0.05 level. The correlation coefficient for Petrifilm RCC plates versus the VRBA method and for Petrifilm RCC plates versus the DLA method were 0.994 and 0.996, respectively. With the Petrifilm RCC plate method, we were able to estimate presumptive coliforms (except Serratia sp.) after 14 h and to enumerate confirmed coliforms (including Serratia sp.) after 24 h.     

关子钞版研究之六关子钞版的制作工艺

关子钞版的制作工艺与其性质、用途具有十分密切的关系.不论是铸造还是雕刻,都会留下一些特征性的痕迹.利用体视显微镜,寻找关子钞版上跟铸造或雕刻有关的特征性的痕迹,结果表明,关子钞版应是由铸造而成.     

A Convenient Surface Plate Method for Bacteriological Examination of Poultry

The surface plate method was compared with the more conventional pour plate method for the enumeration of mesophiles, psychrotrophs, lactobacilli, coliforms, and streptococci on poultry. Surface plates were prepared by drying freshly poured plates at 37°C for 3 days. These plates were stored at 5°C until 4 hr before use when they were re-dried at 37°C. Pour plates were made using standard methods. The two methods were highly correlated but there was a significant difference between the surface plate and pour plate methods for coliforms and psychrotrophic counts. Higher counts were obtained with the surface plate technique for these organisms.     

19—THE HIGH-CURVATURE CREASING BEHAVIOUR OF FABRICS

An alternative theoretical analysis is presented of an apparatus described by Skelton to measure the bending characteristics of fabrics by simultaneous rolling and compression of fabric loops between flat plates. At low values of θ, the angle between the direction of movement of the plates and the plate surfaces, the present analysis does not differ appreciably from that provided by Skelton. However, at higher values of θ, the differences are considerable. Other limitations of this method of obtaining bending parameters are discussed.     

非保守矩形板稳定性分析的幂级数法

采用Ｌｅｖｙ法和幂级数解法，对两对边简支，另两对边具有弹性约束的矩形薄板在切向均布随从力作用下的振动与稳定性进行了分析，讨论了弹性约束对方板的自振频率和临界载荷的影响。     

The use of Petrifilm™ for the enumeration of lactococci

Petrifilm^™ aerobic plate counts were compared to Elliker and M17 agar counts for the enumeration of Lactococcus strains. There were no significant differences between counts obtained with the three methods, which suggests that Petrifilm^™ plates can be used as a time-saving method for the determination of lactococci starter populations. The standard method of using Petrifilm^™, in which 1 ml of sample is analysed, can be modified to have multiple inoculations on the same dry medium culture plates, such that four aliquots of 0·1 ml are added to a single Petrifilm^™ plate. Counts obtained with the multiple inoculation method did not differ significantly from the standard single inoculation method recommended by the Petrifilm^™ manufacturer.     

Rapid Enumeration of Four Indicator Microorganisms in Ground Beef Using a Freeze-dried Four-culture Method

ABSTRACT: A recently reported, miniaturized method can simultaneously enumerate 4 critical indicator microorganisms in 24 h on a single 96-well microtiter plate, and is a convenient monitoring system for ensuring food plant hygiene. However, the utility of this method is limited by the necessity of plates being freshly prepared prior to each use. This study was undertaken to develop a method that would permit these plates to be prepared and stored in a stable form that could be conveniently used later. A microtiter plate filled with media dedicated to enumerating 4 specific classes of bacteria was freeze-dried. A given series was dedicated to enumerating either, total mesophilic bacteria, Gram-negative bacteria, coliform bacteria, or Escherichia coli . Freeze-dried plates were reconstituted simply by adding 100 μL of sterile water to each well. After adding samples, two-fold serial dilutions were performed, and the plate was incubated for 24 h at 32 °C. Growth of 4 indicator microorganisms was detected in each series using metabolic indicators. The numerical estimates that these procedures yielded correlated very closely with numbers gained from conventional spread-plating methods ( r ² > 0.90). Additionally, the estimates obtained from liquid media microtiter plates and freeze-dried media plates showed a significantly strong relationship ( r ² > 0.92). Analysis of commercial ground beef showed a highly associated relationship ( r ² > 0.94) between the liquid four-culture and freeze-dried four-culture plate methods. The greatly enhanced facility of using premanufactured, freeze-dried microtiter plates would make this a most convenient way to perform microbial food quality analysis.