混合Weibull分布在棉纤维长度分布表征上的应用

利用含参数的概率密度函数来表征棉纤维的长度分布,不仅有利于纤维长度指标的计算,而且能够全面度量纤维的长度分布状态。本文基于USTER 的AFIS单纤维测试仪测得的纤维长度分布直方图,依据现有的混合Weibull分布模型,选用两组分与三组分的混合分布对其进行了拟合,并计算了相应的长度指标。结果表明：利用Weibull分布构建的混合分布模型能很好地拟合棉纤维的重量及根数加权长度分布。此外,通过指标计算值与实测值的对比,一般情况下二组分混合模型优于三组分模型。     

基于混合韦伯分布的碳纤维针刺毡结构表征

为研究碳纤维针刺毡的结构并对其参数化表征,基于混合（Weibull）分布分析了3种碳纤维针刺毡的结构参数。对碳纤维针刺毡的纤维长度分布进行了拟合,并分析了造成纤维长度分布规律不同的原因。采用纯弯梁模型模拟碳纤维在针刺毡中的弯曲状态,并对弯曲参数进行了统计分析。结果表明,采用混合Weibull分布模型分析碳纤维针刺毡的内部结构,可真实反映参数指标的分布规律。无论是纤维长度还是纤维的弯曲参数,拟合曲线都有较高的拟合度。此外,采用纯弯梁模型模拟弯曲的碳纤维,不仅可以模拟纤维在针刺毡中的弯曲形貌,还可以将测量结果用于碳纤维针刺毡的参数化建模。     

逆χ^2分布下正态模型参数的后验分布及其抽样

当正态线性模型中的参数取逆χ^2先验分布时,得出了回归系数和误差方差的联合后验分布和边际后验分布,特别导出了回归系数二次型的分布。利用回归系数和误差方差联合后验分布的分解形式,给出了一种抽样方案。     

降膜蒸发器用制冷剂分布器设计参数讨论

文章针对水平管降膜蒸发器用筛板式制冷剂分布器的操作流量、开孔数目、开孔大小、孔口流出系数、分布均匀度等设计参数展开讨论,由此总结了制冷剂分布器各设计参数的确定方法,以及制冷剂分布器的理论设计思路;文章针对筛板式制冷剂分布器设计参数的讨论也适用于其他类型的分布器.     

基于Weibull分布函数的浆板热风干燥特性

以未漂硫酸盐针叶木浆为干燥对象,研究了热风温度和风速对浆板干燥特性的影响。利用Weibull分布函数对浆板的干燥特性曲线进行了模拟,并建立热风温度、风速与模型中参数(尺度参数α、形状参数β)的定量关系。结果表明,Weibull分布函数可以很好地模拟浆板的热风干燥过程;模型的尺度参数α与热风温度和风速有关,并且随热风温度和风速的升高而降低;模型的形状参数β与热风风速有关,随热风风速的升高而降低;浆板热风干燥过程的估算水分扩散系数在2. 116×10-7～3. 251×10-7m2/s之间,干燥活化能为14. 8 kJ/mol。     

压力棒牵伸区中的纤维数量分布模型

牵伸区中纤维的运动状态受与其接触纤维状态的影响,为研究牵伸区中纤维的运动状态,对上托式压力棒牵伸区中各类纤维的数量分布进行了研究。分析了牵伸区中各类纤维的理论分布,测量了牵伸区中的各类纤维数量分布,简化了纤维数量分布曲线。再通过均匀设计,测试了不同牵伸参数下的变细曲线,建立了变细曲线与牵伸参数之间的回归方程,最终得到了牵伸区中的纤维数量分布模型。结果表明：牵伸区中各类纤维的数量分布受牵伸倍数、罗拉握持距、纤维长度、压力棒位置等牵伸参数的显著影响,纤维的数量分布可基于总纤维、前纤维和后纤维的数量分布得到。回归方程的平均拟合误差在7%以内,所建立的纤维数量分布模型适用于涤纶和粘胶纤维。     

牵伸区须内浮游纤维运动变速点分布的研究

本文通过牵伸区中浮游纤维运动变速点的测试，研究其变速点的分布及其特征，各特征值与工艺参数的关系。     

双螺杆挤压过程中停留时间分布的测定及影响因素研究

停留时间分布是表征双螺杆挤压过程中物料流动状态的重要参数,与挤压食品品质的形成密切相关。文章着重介绍了指示剂测定停留时间分布的方法及相关参数,分析了温度、水分、螺杆构型、模孔、喂料速度和螺杆转速等操作参数对双螺杆挤压过程中停留时间分布的影响。由于淀粉、蛋白等营养组分结构比较复杂,现有关于停留时间分布的研究成果不够完善,还需要进一步的深入细化。     

对颗粒状粮食湿度分布检测的理论研究

建立了利用微波反射法检测颗粒状粮食内部湿度分布的理论模型.结合该模型的特点给出了合适的测量仪器及相关参数.该模型为粮食储藏、运输过程中的发霉、变质问题提供了新的解决方法.     

牵伸区须条内浮游纤维运动变速点分布的研究

本文通过牵伸区中浮游纤维运动变速点的测试，研究其变速点的分布及其特征，各特征值与工艺参数的关系。     

Air quality model evaluation data for organics. 6. C3-C24 organic acids

The atmospheric concentrations of 47 carboxylic acids in the semivolatile and particle phases are quantified in the Los Angeles area, as part of a larger study of the vapor-phase, semivolatile, and particle-phase organic compounds. Variations in the spatial and temporal distributions of acid concentrations are analyzed to determine whether atmospheric formation or primary emissions are responsible for the observed levels. Relatively low molecular weight aliphatic dicarboxylic acids (e.g., butanedioic acid, hexanedioic acid, and propanedioic acid) and some n-alkanoic acids (e.g., n-octanoic acid and n-nonanoic acid) are found at an offshore sampling location at levels comparable to urban area concentrations indicating that these compounds or their atmospheric precursors may be derived from long-range transport or natural background sources. Some aromatic carboxylic acids (e.g., benzoic acid and 1,2-benzenedicarboxylic acid) have spatial and temporal distributions suggesting that formation from anthropogenic emissions of gaseous precursors dominates their atmospheric concentrations. Additionally, the distributions of aliphatic carboxylic acid concentrations known to be emitted from primary sources (e.g., hexadecanoic acid and octadecanoic acid) are consistent with direct emissions as the dominant source of these compounds.     

Microbial risk assessment of staphylococcal food poisoning in Korean kimbab

The objective of this study was to conduct a preliminary microbial risk assessment for Staphylococcus aureus in kimbab, and then propose appropriate guidelines for its preparation and storage. Kimbab is a ready-to-eat product, popular in Korea, made of various foods surrounded by rice and seaweed. Because it is usually prepared by hand and stored at room temperature, it can be contaminated with S. aureus. Data on the prevalence, concentration and growth of S. aureus in kimbab as well as typical ambient temperatures in Seoul were collected; probability distributions were then selected to describe these data. A Monte Carlo simulation model was created using @risk. When current Korean retail data on S. aureus prevalence and concentration were used as inputs, the simulation predicted that the S. aureus concentration would be between 4.0 and 4.9 log CFU/g after 1 h of storage at ambient temperature during the warmest part of the year (March through November). Conversely, by assuming a starting concentration of 1 cell/g, the simulation predicted that the S. aureus concentration would reach 4.4 log CFU/g after 5 h of ambient storage in May and 3.4 log CFU/g in October. Our results suggest that, given the current prevalence and concentration of S. aureus found in kimbab at retail outlets, the product should be consumed within 1 h of purchase. Our results also indicate that if Korean consumers wish to safely store kimbab for 5 h at ambient temperature, S. aureus concentration should not exceed 1 CFU/g at the time of preparation.     

酶解中国毛虾制备低分子肽的研究

以中国毛虾为原料,采用酶法制备低分子肽。利用响应面法优化了Alcalase4L酶水解中国毛虾的工艺参数:温度57.1℃、pH8.0、加酶量为46mL/kg,酶解产物的平均肽链长从0.5h的14.02逐渐降低到8h的3.96。采用凝胶层析法测定了酶解产物的分子质量分布,不同时间酶解产物的SephadexG-15凝胶色谱图中均出现3个吸收峰,前2个峰的分子质量在18722～641u和641～35u之间。从峰值变化可以判断出,随着酶解的进行,低分子肽的量逐渐增加。     

Variability of apparent particle density of an urban aerosol

The day to day and diurnal variation of apparent particle density was studied using highly time-resolved measurements of particle number distribution and fine-particle mass concentration. The study was conducted in Erfurt, Germany, from January 1, 1999, to November 22, 2000. A setup consisting of a differential mobility particle spectrometer and a laser aerosol spectrometer was used for particle number distribution measurements. PM2.5 particle mass was measured in parallel on an hourly basis using a tapered element oscillating microbalance (TEOM) and on daily base by using a Harvard marple impactor (HI). For the estimation of the mean apparent density of particles, number size distributions were converted into volume size distributions, assuming that the particles were spherically shaped. The volume size distributions were integrated over the range of 10 nm to 2.03 microm Stokes equivalent diameter to obtain volume concentrations. Mean apparent particle density was calculated as ratio of mass concentration and volume concentration. The mean apparent particle density, determined from HI and number size distribution on a daily basis was 1.6 +/- 0.5 g cm(-3). We found a strong day-to-day variation of apparent density ranging from 1.0 to 2.5 g cm(-3) (5th and 95th percentile). Furthermore, the apparent density showed pronounced diurnal pattern both in summer and in winter and also on weekdays and weekends. The apparent density was lowest in the morning and highest in the afternoon. The mean apparent density on an hourly basis was 1.4 +/- 0.5 and 1.5 +/- 0.5 g cm(-3) for PM2.5TEOM and corrected PM2.5TEOM using regression equation between daily mass concentration of HI and TEOM, respectively. The strong diurnal variation of apparent particle density was associated predominantly with the vertical temperature inversion and with traffic intensity. Thus, the apparent particle density depends on the physical particle properties and might be related to chemical composition of the sampled particle.     

Oyster-to-oyster variability in levels of Vibrio parahaemolyticus

This study examined the variability in the levels of total and pathogenic Vibrio parahaemolyticus in individual oysters. Twenty oysters were collected on three occasions (in June, July, and September 2001) from a site near Mobile Bay, Ala. Ten of these oysters were tested immediately, and 10 were tested after 24 h of storage at 26 degrees C. Levels of total and pathogenic V. parahaemolyticus were determined by alkaline phosphatase-labeled DNA probe procedures targeting the thermolabile hemolysin and thermostable direct hemolysin genes, respectively. Similar V. parahaemolyticus levels (200 to 2,000 CFU/g) were found in nearly 90% of the oysters (for all sampling occasions) prior to storage. The log-transformed densities (means +/- standard deviations) of V. parahaemolyticus in oysters immediately after harvest were 2.90 +/- 0.91, 2.88 +/- 0.36, and 2.47 +/- 0.26 log10 CFU/g for June, July, and September, respectively. After storage for 24 h at 26 degrees C, the mean V. parahaemolyticus densities increased approximately 13- to 26-fold. Before storage, pathogenic V. parahaemolyticus was detected in 40% (10 to 20 CFU/g) of the oysters collected in June and July but was not detected in any oysters collected in September. After storage, pathogenic V. parahaemolyticus was detected in some oysters at levels of > 100 CFU/g. These data should aid in the development of sampling protocols for oyster monitoring programs and in the determination of exposure distributions associated with raw oyster consumption.     

Short communication: Alteration of priors for random effects in Gaussian linear mixed models

Linear mixed models, for which the prior multivariate normal distributions of random effects are assumed to have a mean equal to 0, are commonly used in animal breeding. However, some statistical analyses (e.g., the consideration of a population under selection into a genomic scheme breeding, multiple-trait predictions of lactation yields, and Bayesian approaches integrating external information into genetic evaluations) need to alter both the mean and (co)variance of the prior distributions and, to our knowledge, most software packages available in the animal breeding community do not permit such alterations. Therefore, the aim of this study was to propose a method to alter both the mean and (co)variance of the prior multivariate normal distributions of random effects of linear mixed models while using currently available software packages. The proposed method was tested on simulated examples with 3 different software packages available in animal breeding. The examples showed the possibility of the proposed method to alter both the mean and (co)variance of the prior distributions with currently available software packages through the use of an extended data file and a user-supplied (co)variance matrix.     

酿酒酵母发酵生产谷胱甘肽的研究

以诱变获得的酿酒酵母突变株YF(ZnCl2r,Ethr)为试验菌株,通过摇瓶发酵、发酵罐补料分批发酵,对突变株发酵生产谷胱甘肽进行研究.确定发酵罐分批发酵的最佳培养条件为:温度30℃,pH 6.0,接种量为20%,搅拌转速为150 r/min,通气量为250 L/h.在补料分批操作方式下,分别考察了摇瓶培养、发酵罐培养...     

Amines compounds as inhibitors of PCDD/Fs de novo formation on sintering process fly ash

The polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic compounds produced by some natural processes and different human activities. Waste incineration as well as steel and iron industries, in particular, the sintering process, are among the principal sources of these pollutants. In this paper, two inhibitors, triethanolamine (TEA) and monoethanolamine (MEA) are tested relating to their abilityto prevent the de novo formation of PCDD/Fs on sinter plant fly ash. The amounts of both PCDDs and PCDFs, formed by thermal treatment of the fly ash, decrease when inhibitors are added. The best results, up to 90% reduction of the PCDD/ Fs formation, are obtained when MEA is mixed with the fly ash at the highest concentration tested (2 wt %). The addition of inhibitors modifies the PCDFs/PCDDs ratios and, under some experimental conditions, the PCDD/Fs homologue distributions, suggesting that more than one pathway for the de novo formation of PCDD/Fs exist. On the other hand, no modification in the PCDD/Fs isomer distributions is observed as a result of the addition of inhibitors, in accordance with the possible thermodynamic control of these distributions. The temperature tested, 325 and 400 degrees C, does not affect the inhibition activity; however, longer reaction times (4 h instead of 2 h) give better percentages of PCDD/Fs reduction. The results suggest that the two inhibitors and especially MEA can reduce the PCDD/Fs formation on sinter plant fly ash under various conditions of temperature and reaction time, making them suitable for use in the real process. Tests performed in parallel at a real sinter plant are in good agreement with the laboratory experiments and confirm that the use of inhibitors is an appropriate technique for the prevention of PCDD/Fs emissions from sintering processes.     

Policy implications of uncertainty in modeled life-cycle greenhouse gas emissions of biofuels

Biofuels have received legislative support recently in California's Low-Carbon Fuel Standard and the Federal Energy Independence and Security Act. Both present new fuel types, but neither provides methodological guidelines for dealing with the inherent uncertainty in evaluating their potential life-cycle greenhouse gas emissions. Emissions reductions are based on point estimates only. This work demonstrates the use of Monte Carlo simulation to estimate life-cycle emissions distributions from ethanol and butanol from corn or switchgrass. Life-cycle emissions distributions for each feedstock and fuel pairing modeled span an order of magnitude or more. Using a streamlined life-cycle assessment, corn ethanol emissions range from 50 to 250 g CO(2)e/MJ, for example, and each feedstock-fuel pathway studied shows some probability of greater emissions than a distribution for gasoline. Potential GHG emissions reductions from displacing fossil fuels with biofuels are difficult to forecast given this high degree of uncertainty in life-cycle emissions. This uncertainty is driven by the importance and uncertainty of indirect land use change emissions. Incorporating uncertainty in the decision making process can illuminate the risks of policy failure (e.g., increased emissions), and a calculated risk of failure due to uncertainty can be used to inform more appropriate reduction targets in future biofuel policies.     

Isolation and characterization of mutants from levan-producing Zymomonas mobilis

Levan is a fructose polymer with potential importance as a fructose source and as a thickening agent in food technology. By N-methyl N'-nitro N-nitroso guanidine (NTG) mutagenesis and selection, two mutants, ZML1 and ZML2, of Zymomonas mobilis B4286 overproducing levan (21.6 and 20.0 g/l at 24 h) were isolated. Despite showing similar rates of sucrose hydrolysis (2.38 g/l/h) in fermentation, these mutants exhibited higher rates of levan production (1.72 and 1.68 g/l/h, respectively) than their parent strain (0.69 g/l/h). In contrast, these mutants showed lower rates of ethanol production (1.06 and 1.55 g/l/h respectively) than the parent strain (3.75 g/l/h). The maximum levansucrase activity in the mutants was higher (30.6 and 36 U/mg, respectively, at 24 h) than in their parent strain (12.6 U/mg). Therefore, the increased rates of levan production by the mutants are attributed to their higher levansucrase activity.