Determination of nitrie in human blood by combination of a specific sample preparation with high-performance anion-exchange chromatography and electrochemical detection

All photometric or HPLC methods described to date have been unable to detect nitrite, a reliable marker of NO synthase activity, in human blood because of its rapid metabolism within the erythrocytes. We now elaborate on method to prevent nitrite degradation during sample preparation which in combination with high-performance anion-exchange chromatography and electrochemical detection allows a sensitive measurement of nitrite. A linear current response in the concentration range of 10–1000 nmol/l nitrite was observed yielding a correlation coefficient of 0.99. In addition, the combination of the electrochemical with a UV detector allowed us to simultaneously quantify nitrate one analytical run, which is the end product of NO/nitrite metabolism. Basal levels for nitrate and nitrite in human blood were determined with 25±4 μmol/l and 578±116 nmol/l (n=8), respectively and thus were in the same concentration range as expected from NO measurement in saline perfused isolated organs or cultured endothelial cells. Therefore, the presented method may be used to assess activity of endothelial constitutive NO synthase in humans under physiological and pathophysiological conditions.     

Semi-automated liquid--liquid back-extraction in a 96-well format to decrease sample preparation time for the determination of dextromethorphan and dextrorphan in human plasma

A semi-automated, 96-well based liquid-liquid back-extraction (LLE) procedure was developed and used for sample preparation of dextromethorphan (DEX), an active ingredient in many over-the-counter cough formulations, and dextrorphan (DOR), an active metabolite of DEX, in human plasma. The plasma extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The analytes were isolated from human plasma using an initial ether extraction, followed by a back extraction from the ether into a small volume of acidified water. The acidified water isolated from the back extraction was analyzed directly by LC-MS-MS, eliminating the need for a dry down step. A liquid handling system was utilized for all aspects of liquid transfers during the LLE procedure including the transfer of samples from individual tubes into a 96-well format, preparation of standards, addition of internal standard and the addition and transfer of the extraction solvents. The semi-automated, 96-well based LLE procedure reduced sample preparation time by a factor of four versus a comparable manually performed LLE procedure.     

Evaluation of saliva as a source of human DNA for population and association studies

A simple noninvasive procedure for saliva sample collection and DNA extraction was developed. On average, the amount of human DNA (as measured by a TaqMan-based assay) was about 11.4 microg/mL saliva, which is more than can be obtained from other noninvasive samples such as cheek swabs. However, the presence of large amounts of nonhuman DNA (up to 90% of the total extracted DNA) in saliva samples does necessitate DNA quantitation methods that are specific for human DNA. We were able to reliably and accurately type different genetic markers (mDNA sequences, Y-chromosomal single-nucleotide polymorphisms, and autosomal microsatellite loci) from saliva samples stored for up to 30 days at 37 degrees C, making this method well-suited for field conditions and convenient transportation of samples back to the laboratory. Thus, saliva can be considered a reliable source of DNA for a wide variety of genetic studies.     

不同样本中甲螨的分离方法

采用电热分离法、清水漂浮法和振动分离法对不同样本中甲螨的分离时间、数量,样本的放置时间及电热分离所用热光源作了比较,结果证明,分离土壤甲螨时,土壤放置7d与立即分离所获甲螨数无差别,少量土样宜用清水漂浮法,大量土样宜用电热分离法,而植被样本宜用振动分离法。     

Interval estimation for a difference between intraclass kappa statistics

Model-based inference procedures for the kappa statistic have developed rapidly over the last decade. However, no method has yet been developed for constructing a confidence interval about a difference between independent kappa statistics that is valid in samples of small to moderate size. In this article, we propose and evaluate two such methods based on an idea proposed by Newcombe (1998, Statistics in Medicine, 17, 873-890) for constructing a confidence interval for a difference between independent proportions. The methods are shown to provide very satisfactory results in sample sizes as small as 25 subjects per group. Sample size requirements that achieve a prespecified expected width for a confidence interval about a difference of kappa statistic are also presented.     

Sample Size Calculations for the Mean in a Two Component Nonstandard Mixture Distribution

We are concerned with calculating the sample size required for estimating the mean of the continuous distribution in the context of a two component nonstandard mixture distribution (i.e., a mixture of an identifiable point degenerate function F at a constant with probability P and a continuous distribution G with probability 1 – P). A common ad hoc procedure of escalating the naïve sample size n (calculated under the assumption of no point degenerate function F) by a factor of 1/(1 – P), has about 0.5 probability of achieving the pre‐specified statistical power. Such an ad hoc approach may seriously underestimate the necessary sample size and jeopardize inferences in scientific investigations. We argue that sample size calculations in this context should have a pre‐specified probability of power ≥1 – β set by the researcher at a level greater than 0.5. To that end, we propose an exact method and an approximate method to calculate sample size in this context so that the pre‐specified probability of achieving a desired statistical power is determined by the researcher. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Use of the Upper Confidence Limit for the Variance from a Pilot Sample for Sample Size Determination

In a recent paper, Browne (1995) investigated the use of a pilot sample for sample size calculation. Monte Carlo simulations indicated that using a 100 · (1 — γ) per cent upper one-sided confidence limit on the population varíance σ² leads to a sample size that guarantees the planned power with a probability of at least 1 ? γ. The purpose of this paper is to get further insight into the results of Browne by analytical considerations. Furthermore, the expected power is investigated when applying the strategy and recommendations for the choice of the pilot sample size are given.     

Estimating the probability that the sample mean is within a desired fraction of the standard deviation of the true mean

The use of small sample sizes in human and primate evolutionary research is commonplace. Estimating how well small samples represent the underlying population, however, is not commonplace. Because the accuracy of determinations of taxonomy, phylogeny, and evolutionary process are dependant upon how well the study sample represents the population of interest, characterizing the uncertainty, or potential error, associated with analyses of small sample sizes is essential. We present a method for estimating the probability that the sample mean is within a desired fraction of the standard deviation of the true mean using small (n < 10) or very small (n ≤ 5) sample sizes. This method can be used by researchers to determine post hoc the probability that their sample is a meaningful approximation of the population parameter. We tested the method using a large craniometric data set commonly used by researchers in the field. Given our results, we suggest that sample estimates of the population mean can be reasonable and meaningful even when based on small, and perhaps even very small, sample sizes.     

Inconstancy of Taylor'sb: Simulated sampling with different quadrat sizes and spatial distributions

Taylor 's power law, s²=am^b, provides a precise summary of the relationship between sample variance (s²) and sample mean (m) for many organisms. The coefficient b has been interpreted as an index of aggregation, with a characteristic value for a given species in a particular environment, and has been thought to be independent of the sample unit. Simulation studies were conducted that demonstrate that the value of b may vary with the size of the sample unit in quadrat sampling, and this relationship, in turn, depends on the underlying spatial distribution of the population. For example, simulated populations with hierarchical aggregation on a large scale produced values of b that increased with the size of the sample unit. In contrast, for a simulated population with randomly distributed clusters of individuals, the value of b eventually decreased with increasing quadrat size, as sample counts became more uniform. A single value ofTaylor 's b, determined with a particular sample unit, provides neither a fixed index of aggregation nor a complete picture of a species' spatial distribution. Rather, it describes a consistent relationship between sample variance and sample mean over a range of densities, on a spatial scale related to the size of the sample unit. This relationship may reflect, but not uniquely define, density-dependent population and behavioral processes governing the spatial distribution of the organism. Interpretation ofTaylor 'sb for a particular organism should be qualified by reference to the sample unit, and comparisons should not be made between cases in which different sample units were used. Whenever possible, a range of sample units should be used to provide information about the pattern of distribution of a population on various spatial scales.     

Importance of inlet air velocity in fluid bed dyring of a granulation prepared in a high shear granulator

Conclusions  This report shows that inlet air velocity can play a critical role in maintaining proper fluidization and, ultimately, uniform drying. The mechanism by which air velocity affects fluidization has been discussed by various researchers [4–5]. An indication of good fluidization is a free downward flow of the granules at the sight glass of the drying bowl, but such limited observation could be misleading. In such cases, the exhaust air temperature can be used to detect poor fluidization. If the exhaust air temperature rises more rapidly than anticipated, as seen with process 1 (Figure 1), it is an indication that fluidization is incomplete. In conclusion, a fundamental understanding of the mechanism of fluidization by inlet air will help in the development of a fluid bed drying process that produces uniformly dried granules and minimizes the number of process problems encountered.     

Plate Colony Sample Sizes Required for Inferences about the Uniqueness of a Lactobacillus Strain within a Human Volunteer

Making inferences about the spectrum of bacterial strains on a plate as a consequence of observing only one strain in a random sample of colonies from the plate is relatively straightforward whereas making inferences about the spectrum of strains within a human volunteer as a consequence of observing only one strain in a random sample from the plate requires some care. The issue of the appropriate number of colonies to sample from a plate to make inferences about strain uniqueness within a human volunteer is examined and illustrated with an example     

A note on comparing exposure data to a regulatory limit in the presence of unexposed and a limit of detection

In some occupational health studies, observations occur in both exposed and unexposed individuals. If the levels of all exposed individuals have been detected, a two-part zero-inflated log-normal model is usually recommended, which assumes that the data has a probability mass at zero for unexposed individuals and a continuous response for values greater than zero for exposed individuals. However, many quantitative exposure measurements are subject to left censoring due to values falling below assay detection limits. A zero-inflated log-normal mixture model is suggested in this situation since unexposed zeros are not distinguishable from those exposed with values below detection limits. In the context of this mixture distribution, the information contributed by values falling below a fixed detection limit is used only to estimate the probability of unexposed. We consider sample size and statistical power calculation when comparing the median of exposed measurements to a regulatory limit. We calculate the required sample size for the data presented in a recent paper comparing the benzene TWA exposure data to a regulatory occupational exposure limit. A simulation study is conducted to investigate the performance of the proposed sample size calculation methods.     

大窑遗址二道沟地点石制品研究的抽样方法设计

结合简单随机抽样、整群抽样和连续重复抽样的特点,基于中心极限定理,本文设计了适用于大批量石制品抽样调查的具体方案,通过边抽样、边评价的方式,利用有限的样本量推断总体特征,并将其实际应用到大窑遗址二道沟地点石制品的研究中,取得了良好的效果。此外,该抽样方案对于石制品的物源追溯、遗址区域调查等也有一定的实用价值。     

某医院2014-2017年耐碳青霉烯类革兰阴性杆菌分布及耐药性

摘要：目的了解2014-2017年玉溪市人民医院耐碳青霉烯类革兰阴性杆菌在临床标本及科室中的检出情况及耐药情况,为防治耐碳青霉烯类革兰阴性杆菌提供依据。方法采用VITEK2 COMPACT微生物分析仪对细菌进行鉴定和药敏试验。结果共检出952株耐碳青霉烯类革兰阴性杆菌,涉及17个菌属30个菌种,主要来自痰样本（669株,72.27%）、尿液（90株,9.45%）和体表分泌物（54株,5.67%）。科室分布显示重症医学科有309株（32.46%）,急诊内科121株（12.71%）,神经内科113株（11.87%）,呼吸内科83株（8.72%）。检出细菌中鲍曼不动杆菌仅对庆大霉素和左氧氟沙星的耐药率小于40.00%;大肠埃希菌仅对阿米卡星和呋喃妥因的耐药率小于40.00%;铜绿假单胞菌对哌拉西林、头孢吡肟、氨曲南、阿米卡星、庆大霉素、左氧氟沙星和环丙沙星的耐药率低于40.00%;肺炎克雷伯菌肺炎亚种对厄他培南、阿米卡星、四环素、复方新诺明的耐药率小于40.00%。结论耐碳青霉烯类革兰阴性杆菌分布较广,不同细菌对抗菌药物的耐药状况不同。鲍曼不动杆菌和大肠埃希菌的耐药性较高,应重视监测细菌耐药情况,指导临床合理使用抗菌药物,更好地控制耐药菌株的产生及传播。     

Ultrasound-assisted digestion: a useful alternative in sample preparation

Ultrasound-assisted digestion is a promising alternative in the analysis of solid samples when either simple dissolution or direct analysis is not applicable. However, the field of application of ultrasonic sample digestion is still small in comparison with classical digestion alternatives and, particularly, with microwave-assisted digestion. This fact can be justified by the scant knowledge analytical chemists have about the advantages ultrasonic energy provides to digestion. Among these, the strict control at low temperatures of ultrasound applications allows the implementation of ultrasonic-assisted steps in biochemical analyses. In this connection, two specific biological applications, ultrasonic enzymatic digestion and assistance of ultrasound for cell disruption, are also reviewed.     

Bounded random walks as a null model for evaluating population trends

Management of wildlife and protection of endangered species depend on determination of population trends. Because population changes are stochastic and autoregressive, there is reason to believe that population trends might not be properly determined by simple regression over short time periods. A bounded random walk (BRW) model is introduced as a null model for evaluating population trends. The BRW model shows long-term stability but rising and falling sequences of up to many decades. For a given variability and survey length, there will be an expected probability of finding a greater than X% slope simply by chance. This false positive probability needs to be considered when evaluating trends. Breeding Bird Survey data for 128 species over 46 years for two states were analyzed for trends for different series lengths. Trends estimated from short series were likely to not agree with the 46-year trends. Very short series (e.g., 5 years) tended to indicate no trend due to loss of statistical power. A 101-year series for sandwich term (Sterna sandvicensis) revealed that even for 40 year-long series, 33% of subset series had a negative trend compared to the strong 101 year full series positive trend. The BRW model simulations and both data sets pointed to 20 years as a minimum time period for estimating trends reliably, though this can be longer for species that tend to cycle. Proper inference should thus consider the implications of inherent time series variability.     

The effects of dominance,species ranking and species matching on some similarity indices

Abstract. The performance of certain indices of sample similarity was explored with respect to variation in species matching, species ranking and dominance of simulated samples. An index of similarity is suggested which accounts for variation in species matching and ranking rather than for differences in dominance.