减振复合板阻尼测试样品模态分析及尺寸确定

针对减振复合板样品在阻尼测试中样品尺寸标准不一,样品尺寸在确定时缺乏理论依据,无法确定测试样品尺寸的问题,利用有限元方法对减振复合板进行模态分析,用悬臂梁法进行阻尼实测。有限元模拟结果表明,在一定的宽度和厚度下,随着试样长度的增加,其1阶到6阶共振频率均出现降低的规律;在一定的长度和厚度下,随着样品宽度的增加,前4阶共振频率有略微增加的趋势;在一定的长度和宽度下,随着样品厚度的增加,1阶到3阶的共振频率基本保持稳定。实测结果表明,选取自由端长度为216 mm、宽度为12.7 mm的样品,利用2阶和3阶共振频率下的损耗因子进行阻尼表征较为合理。     

Multiple correlation: Exact power and sample size calculations.

This article discusses power and sample size calculations for observational studies in which the values of the independent variables cannot be fixed in advance but are themselves outcomes of the study. It reviews the mathematical framework applicable when a multivariate normal distribution can be assumed and describes a method for calculating exact power and sample sizes using a series expansion for the distribution of the multiple correlation coefficient. A table of exact sample sizes for level .05 tests is provided. Approximations to the exact power are discussed, most notably those of J. Cohen (1977). A rigorous justification of Cohen's approximations is given. Comparisons with exact answers show that the approximations are quite accurate in many situations of practical interest. More extensive tables and a computer program for exact calculations can be obtained from the authors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Establishing equivalence of two treatments and sample size requirements in matched-pairs design

To investigate the role of putative virulence factors of Streptococcus pyogenes (group A streptococcus; GAS) in causing disease, we introduced specific mutations in GAS strain B514, a natural mouse pathogen, and tested the mutant strains in two models of infection. To study late stages of disease, we used our previously described mouse model (C3HeB/FeJ mice) in which pneumonia and systemic spread of the streptococcus follow intratracheal inoculation. To study the early stages of disease, we report here a model of long-term (at least 21 days) throat colonization following intranasal inoculation of C57BL/10SnJ mice. When the three emm family genes of GAS strain B514-Sm were deleted, the mutant showed no significant difference from the wild type in induction of long-term throat colonization or pneumonia. We inactivated the scpA gene, which encodes a complement C5a peptidase, by insertion of a nonreplicative plasmid and found no significant difference from the wild type in the incidence of throat colonization. However, there was a small but statistically significant decrease in the incidence of pneumonia caused by the scpA mutant. Finally, we demonstrated a very important effect of the hyaluronic acid capsule in both models. Following intranasal inoculation of mice with a mutant in which a nonreplicative plasmid was inserted into the hasA gene, which encodes hyaluronate synthase, we found that all bacteria recovered from the throats of the mice were encapsulated revertants. Following intratracheal inoculation with the hasA mutant, the incidence of pneumonia within 72 h was significantly reduced from that of the control strain (P = 0.006). These results indicate that the hyaluronic acid capsule of S. pyogenes B514 confers an important selective advantage for survival of the bacteria in the upper respiratory tract and is also an important determinant in induction of pneumonia in our model system.     

Power analysis and determination of sample size for covariance structure modeling.

A framework for hypothesis testing and power analysis in the assessment of fit of covariance structure models is presented. We emphasize the value of confidence intervals for fit indices, and we stress the relationship of confidence intervals to a framework for hypothesis testing. The approach allows for testing null hypotheses of not-good fit, reversing the role of the null hypothesis in conventional tests of model fit, so that a significant result provides strong support for good fit. The approach also allows for direct estimation of power, where effect size is defined in terms of a null and alternative value of the root-mean-square error of approximation fit index proposed by J. H. Steiger and J. M. Lind (1980). It is also feasible to determine minimum sample size required to achieve a given level of power for any test of fit in this framework. Computer programs and examples are provided for power analyses and calculation of minimum sample sizes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A statistics primer. Power analysis and sample size determination

Gynecologic-oncologic patients are at increased risk for complications with closed laparoscopy. Open laparoscopy eliminates the steps of blind insufflation and trocar insertion. This study is the first large series of open laparoscopies to assess the feasibility and safety of the open laparoscopy technique in patients with gynecologic malignancies. We performed 90 open laparoscopies in 89 oncologic patients with previous major surgery (65%) and/or radiotherapy (17%) or a large omental cake (18%). Complications due to the laparoscopic access technique occurred in one patient (1%) for whom a laparotomy was performed for a small bowel perforation. The incidence of complications of the open laparoscopy technique (1%) is favorable compared to the complication rate of closed laparoscopy in gynecologic-oncologic patients. It is concluded that open laparoscopy is a safe and feasible technique in gynecologic-oncologic patients.     

A note on sample size determination for bioequivalence studies with high-order crossover designs

Similar to Liu and Chow, approximate formulas for sample size determination are derived based on Schuirmann's two one-sided tests procedure for bioequivalence studies for the additive and the multiplicative models under various higher order crossover designs for comparing two formulations of a drug product. The higher order crossover designs under study include Balaam's design, the two-sequence dual design, and two four-period designs (with two and four sequences), which are commonly used for assessment of bioequivalence between formulations. The derived formulas are simple enough to be carried out with a pocket calculator. The number of subjects required for each of the four higher order designs are tabulated for selected powers and various parameter values.     

Measure and statistical test for cross-correlation between paired neuronal spike trains with small sample size

Recent development of multi-unit recording techniques such as optical recording and multi-electrode arrays makes it possible to record neuronal activities from tens or hundreds of neurons simultaneously. To analyze functional connections between these neurons, cross-correlation analysis has been most commonly applied to the hundreds to thousands of pairs of these neurons. However, conventional cross-correlation data needs statistical tests for significance especially when the sample size of recorded spike trains is small. Here, a multiple hypergeometric model based on a transformation of the cross-correlogram data to a 2 x J table has been suggested. The exact p value for significance can be obtained by the generalized Fisher's method with small sample size and a cross-correlation coefficient for the strength of cross-correlation can be obtained based on the R-square analogue for nominal data. For large sample size, chi 2 test can be applied based on the same transformation. Examples of real spike train data set and simulation show that the methods are applicable to the data of multi-unit activity with only tens of spikes. These methods are especially useful when thousands of cross-correlograms need to be screened quickly and automatically.     

超低碳钢的取样和制样方法

近年来 ,武钢大力推进精品、名牌战略 ,品种结构不断优化 ,科技含量和附加值高的产品越来越多 ,如轿车用钢和阴罩框架钢等。它们的冶炼过程十分复杂 ,尤其对超低碳的控制很严格 ,一般都要求Ｃ≤ 0 0 0 5 0 % ,这使得化验室的快速准确分析更为必要。本文结合武钢第三炼钢厂取样制样方法以及化验室的制样和分析设备 ,探讨了两种取样方法和四种制样方法对超低碳分析结果的影响 ,并研制出用于超低碳钢的厚薄取样器 ,可以替代进口产品用于生产中。1　实验部分1 1　仪器和设备Ｚ5 1 2 5Ａ型方柱式钻床 (国产 ) ;ＨＳ -ＭＡＴ全自动磨样机 (德国…     

Power and sample size calculations for studies involving linear regression

This article presents methods for sample size and power calculations for studies involving linear regression. These approaches are applicable to clinical trials designed to detect a regression slope of a given magnitude or to studies that test whether the slopes or intercepts of two independent regression lines differ by a given amount. The investigator may either specify the values of the independent (x) variable(s) of the regression line(s) or determine them observationally when the study is performed. In the latter case, the investigator must estimate the standard deviation(s) of the independent variable(s). This study gives examples using this method for both experimental and observational study designs. Cohen's method of power calculations for multiple linear regression models is also discussed and contrasted with the methods of this study. We have posted a computer program to perform these and other sample size calculations on the Internet (see http://www.mc.vanderbilt.edu/prevmed/psintro+ ++.htm). This program can determine the sample size needed to detect a specified alternative hypothesis with the required power, the power with which a specific alternative hypothesis can be detected with a given sample size, or the specific alternative hypotheses that can be detected with a given power and sample size. Context-specific help messages available on request make the use of this software largely self-explanatory.     

Clinical evaluation of a test for immediate and quantitative determination of urinary albumin-to-creatinine ratio. A brief report

A technique is proposed for positioning the nasal oxygen cannula during facial surgery performed under local anesthesia and intravenous sedation. By placing the nasal prongs in the nostrils, and passing the tubing along the alar grooves, nasal dorsum, and forehead, the surgeon has full access to the preauricular areas, temporal regions, cheeks, nasolabial folds, and oral commissures. This method is easy to perform, provides secure positioning of the nasal oxygen, and allows access to areas of the face not possible with conventional placement of the oxygen cannula.     

散装红土镍矿取制样方法研究

针对红土镍矿的地质化学特性,结合我国进口的红土镍矿主要为高铁低镁的褐铁矿型特点, 参照ISO、中国和日本相关制取样标准,通过大量现场试验的统计数据,建立了精密度较高、科学可行的散装红土镍矿取制样方法。用该方法对一船由印尼进口的红土镍矿制取样,然后进行检测,根据样品中镍、铁、水分检测结果得到的制取样方法精密度（β_S）值和总精密度（β_SPM）值均较小,且符合货物的品质波动规律,表明制得的样品具有较好代表性和可靠性,方法可用于我国进口的红土镍矿取制样。     

超声粒度检测建模及其粒度分布反演计算

提出了在矿砂粒径尺寸级配情况下,不同粒径的筛下累积含量公式.在分析超声衰减基本理论模型的基础上,将不同粒径的筛下累积含量集成到超声波衰减模型中,推导出超声波衰减与矿浆浓度、粒度之间的关系模型.将所推导的模型结合实验和数据分析以确定超声波衰减与粒度分布的关系,且采用遗传算法反演计算获得矿浆中粒的粒度分布.结果表明,反演的计算结果精度较高.     

Determining sample size for a test of the equality of alpha coefficients when the number of part-tests is small.

In some measurement studies, the researcher seeks to compare the internal consistency reliability coefficients (α? and α?) of 2 rating scales or 2 observational techniques. In planning such studies, the investigator must determine the sample size (e.g., the number of participants or raters) that should be used if the power of the test of the null hypothesis is to be adequate. In this article, tables are derived that enable the researcher to determine what sample sizes are required to attain a specified power against a given alternative to the hypothesis of equality of 2 values of Cronbach's alpha coefficient. The tables cover situations in which either independent or dependent samples of participants or raters are used to estimate the reliability coefficients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The partial testing design: a less costly way to test equivalence for sensitivity and specificity

We propose a new, less costly, design to test the equivalence of digital versus analogue mammography in terms of sensitivity and specificity. Because breast cancer is a rare event among asymptomatic women, the sample size for testing equivalence of sensitivity is larger than that for testing equivalence of specificity. Hence calculations of sample size are based on sensitivity. With the proposed design it is possible to achieve the same power as a completely paired design by increasing the number of less costly analogue mammograms and not giving the more expensive digital mammograms to some randomly selected subjects who are negative on the analogue mammogram. The key idea is that subjects who are negative on the analogue mammogram are unlikely to have cancer and hence contribute less information for estimating sensitivity than subjects who are positive on the analogue mammogram. To ascertain disease state among subjects not biopsied, we propose another analogue mammogram at a later time determined by a natural history model. The design differs from a double sampling design because it compares two imperfect tests instead of combining information from a perfect and imperfect test.     

Employment test validation for minority and nonminority clerks with work sample criteria.

10 tests of intellectual ability and perceptual speed and accuracy were validated against specially developed clerical work samples of telephone company employees, using a newly hired sample of 143 Blacks, 74 Spanish-surnamed, and 195 Whites. Most validity coefficients were statistically significant, and in only 2 out of 36 comparisons were ethnic sample validity coefficients significantly different. A combination of 4 tests was significantly predictive of clerical proficiency for each ethnic sample and for the total combined sample. Comparisons of ethnic sample regression equations indicated that the slopes were essentially the same but that the intercepts differed significantly. The total sample regression equation did not underpredict prospective proficiency levels for minority clerks. A composite predictor found to be appropriate for minority and nonminority applicants for clerical jobs is recommended for employment office use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directional decisions for two-tailed tests: Power, error rates, and sample size.

One imposing directional decisions on nondirectional tests will overestimate power, underestimate sample size, and ignore the risk of Type III error (getting the direction wrong) if traditional calculations—those applying to nondirectional decisions—are used. Usually trivial with the z test, the errors might be important where α is large and effect size is small or with tests using other distributions. One can avoid the errors by using calculations that apply to directional decisions or by using a directional two-tailed test at the outset, a conceptually simpler solution. With a revised concept of power, this article shows calculations for the test; explains how to find its power, Type III error risk, and sample size in statistical tables for traditional tests; compares it to conventional one- and two-tailed tests and to one- and two-sided confidence intervals; and concludes that when a significance test is planned it is the best choice for most purposes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

中型厂H型钢性能试验试样取样部位的研究与探讨

通过对中型厂轧制与冷却工艺的研究,对不同规格进行取样分析,找出了H型钢不同部位组织、力学性能的内在规律,为H型钢取样具有准确性和代表性提供依据。     

电感耦合等离子体质谱法测定硒时多元素干扰的碰撞/反应研究及其在地质样品中的应用

采用电感耦合等离子体质谱仪(ICP-MS)在常规模式下测定硒时,由等离子体中大量氩原子所形成的多原子离子干扰不容忽视,使得硒的准确测定成为难题。控制碰撞气流量为4.5 mL/min,载气流量为0.85 L/min,ICP功率为1 300 W,采用碰撞/反应模式,以氢氦(体积比为7∶93)混合气为碰撞气体,⁸⁰Se为测定同位素,降低了多原子离子的干扰,建立了一种电感耦合等离子体质谱法测定地质样品中硒的分析方法。在优化的实验条件下,方法检出限为0.08 μg/g。采用实验方法对地质样品标准物质GBW07106、GBW07401、GBW07404及实际样品中的硒进行测定,结果与认定值或标准方法NY/T1104—2006测定值基本一致,相对标准偏差(RSD,n=5)不大于6.0%。