基于输电线路垂直档距变化特征的等值覆冰厚度模型研究

针对电网防冰抗冰各业务的具体需求及现有覆冰监测终端受环境的影响使得多个测量值不够准确,从而增加架空线覆冰厚度观测值误差的问题,利用覆冰监测终端历史拉力值、气象因子测量数据,经过对历史拉力值数据合理的质量控制,采用相对值方法并结合实际测量技术手段,建立了考虑线路设计冰厚、垂直档距实时变化特征的更加精确的输电线路等值覆冰厚度计算模型,用于模拟两个冰期内线路等值覆冰厚度,并与实际观测结果进行对比。结果表明,AB相、地线垂直档距随覆冰厚度均呈非线性变化趋势,总体呈现出随覆冰厚度的增加而逐渐减小的变化趋势,且地线变化幅度大于AB相线;线路等值覆冰厚度与监测终端拉力值呈正相关性关系,计算出的线路等值覆冰厚度与同期的气象因子覆冰条件相一致,且模拟结果与实际观测结果误差较小。     

改进的经验小波变换在滚动轴承故障诊断中的应用

经验小波变换是一种基于Fourier 频谱特性,通过构建自适应小波滤波器组来分析复杂多分量信号的方法。该方法能够有效识别信号中的不同模态分量,但由于其Fourier 频谱分割问题,在处理噪声及不稳定信号方面有所欠缺。针对这一问题,采用改进的经验小波变换方法,将信号分解为具有物理意义的经验模态。改进的经验小波变换主要考虑被处理信号的频谱形状,通过采用基于顺序统计滤波器（OSF）的包络方法以及遵循三个准则来获取有效峰值的方法,改进Fourier 频谱分割过程。将改进的方法应用于滚动轴承故障诊断中,由于改进的经验小波变换能够将振动信号分解为一系列单分量成分,因此在轴承振动信号包络谱中能够清晰的发现故障特征。通过对滚动轴承振动模拟信号和实验信号的分析验证了该方法的有效性。     

The initial freezing temperature of foods at high pressure

The Pure water (P,T)-phase diagram is known in the form of empirical equations or tables from nearly a century as a result of Bridgman's work. However, few data are available on other aqueous systems probably due to the difficulty of high-pressure measurements. As an alternative, six approaches are presented here to obtain the food phase diagrams in the range of pressure 0.1-210 MPa. Both empirical and theoretical methods are described including the use of an artificial neural network (ANN). Experimental freezing points obtained at the laboratory of the authors and from literature are statistically compared to the calculated ones. About 400 independent freezing data points of aqueous solutions, gels, and foods are analysed. A polynomial equation is the most accurate and simple method to describe the entire melting curve. The ANN is the most versatile model, as only one model allows the calculation of the initial freezing point of all the aqueous systems considered. Robinson and Stokes' equation is successfully extended to the high pressures domain with an average prediction error of 0.4 degrees C. The choice of one approach over the others depends mainly on the availability of experimental data, the accuracy required and the intended use for the calculated data.     

Oxygen flux as an indicator of physiological stress in fathead minnow (Pimephales promelas) embryos: a real-time biomonitoring system of water quality

The detection of harmful chemicals and biological agents in real time is a critical need for protecting freshwater ecosystems. We studied the real-time effects of five environmental contaminants with differing modes of action (atrazine, cadmium chloride, pentachlorophenol, malathion, and potassium cyanide) on respiratory oxygen consumption in 2-day postfertilization fathead minnow (Pimephales promelas) eggs. Our objective was to assess the sensitivity of fathead minnow eggs using the self-referencing micro-optrode technique to detect instantaneous changes in oxygen consumption after brief exposures to low concentrations of contaminants. Oxygen consumption data indicated that the technique is indeed sensitive enough to reliably detect physiological alterations induced by four of the five contaminants. After 2 h of exposure, we identified significant increases in oxygen consumption upon exposure to pentachlorophenol (100 and 1000 microg/L), cadmium chloride (0.0002 and 0.002 microg/L), and atrazine (150 microg/L). In contrast, we observed a significant decrease in oxygen flux after exposuresto potassium cyanide (44 and 66 microg/L) and atrazine (1500 microg/L). No effects were detected after exposures to malathion (200 and 340 microg/L). Our work is the first step in development of a new technique for physiologically coupled biomonitoring as a sensitive and reliable tool for the detection of environmental toxicants.     

Modification of the volatile compound profile of cheese, by a Lactococcus lactis strain expressing a mutant oligopeptide binding protein

Lactococcus lactis strain AMP2I expresses OppA(D471R), a mutant oligopeptide binding OppA protein in which the aspartyl residue at position 471 was replaced by arginine. As a consequence of a different peptide transport in this strain, experimental Hispánico cheese made with Lc. lactis AMP2I had a higher content of total free amino acids than control cheese made with Lc. lactis AMP1I, an isogenic strain expressing wild-type OppA (Picon et al. 2005, 2007). In this work higher levels of diketones, hydroxy-ketones and, to a lesser extent, branched chain aldehydes were recorded for experimental cheese compared with control cheese. These differences levelled off as ripening proceeded. Strong correlations support the hypothesis that the increased levels of these volatile compounds in cheese made with Lc. lactis AMP2I are linked to higher concentrations of free amino acids threonine, valine and leucine.     

Diet and genotype effects on the quality index of beef produced in the Argentine Pampeana region

Steers of varying genotypes (Aberdeen Angus, Charolais x AA and Argentine Holstein) in four feeding systems were evaluated. Feeding systems were: S1=a diet based on pastures only; S2=a similar forage base as S1 plus a daily supplementation with cracked corn, at 0.7% of l.w./head/day; S3=a similar forage base as S1 plus a daily supplementation with cracked corn, at 1.0% of l.w./head/day; and S4=a regular feedlot diet. Tenderness and marbling were not affected by the feeding system. Feedlot meat showed an n-6/n-3 ratio significantly higher than meat produced with the diets based on pastures (S1=2.1; S2=3.1; S3=4.5; S4=14.2) (P<0.05), whereas CLA content had an inverse behavior, showing S1 (0.67%) and S2 (0.64%) higher concentrations than S3 (0.55%) and S4 (0.28%) (P<0.05). Diet based on pastures plus a low level of supplementation produced meat with better nutritional characteristics than other productive alternatives, without significant effects of the biotypes.     

Extraordinary all-dielectric light enhancement over large volumes

We present resonant dielectric structures exhibiting arbitrarily large optical field enhancement, only limited by fabrication imperfections. Three different arrangements are investigated, based upon dielectric waveguides, dielectric particle arrays, and a combination of these two structures. Experimental confirmation of enhancement in a waveguide resonator is achieved by measuring the luminescence of quantum dots dispersed in the hot optical region of the structure. The performance of these systems can be readily controlled by simply changing geometrical parameters, which allows obtaining remarkable values of the intensity enhancement approaching 105 relative to the incident intensity over large volumes under feasible experimental conditions. This opens new avenues for all-optical switching and biosensing.     

Controlling light localization and light-matter interactions with nanoplasmonics

Nanoplasmonics is the emerging research field that studies light-matter interactions mediated by resonant excitations of surface plasmons in metallic nanostructures. It allows the manipulation of the flow of light and its interaction with matter at the nanoscale (10(-9) m). One of the most promising characteristics of plasmonic resonances is that they occur at frequencies corresponding to typical electronic excitations in matter. This leads to the appearance of strong interactions between localized surface plasmons and light emitters (such as molecules, dyes, or quantum dots) placed in the vicinity of metals. Recent advances in nanofabrication and the development of novel concepts in theoretical nanophotonics have opened the way to the design of structures aimed to reduce the lifetime and enhance the decay rate and quantum efficiency of available emitters. In this article, some of the most relevant experimental and theoretical achievements accomplished over the last several years are presented and analyzed.     

绕丝对超临界流体热输运影响的CFD分析

高性能轻水反应堆（HPLWR）采用超临界水（SCW）作为冷却剂。在临界和拟临界点附近,这类超临界流体的热物性将遭受剧烈的变化,文献[1】和【2】报道了此类流体而致的正常传热、强化传热和传热恶化。大量的数值研究已经证明了以CFD方法为基础的雷诺平均纳维斯托克斯（RANS）在计算超临界二氧化碳（SC—CO2）和超临界水（SCW）热输运方面的能力。本文描述了绕丝对SC—CO2传热的影响。第一步,本文选取不带绕丝的环形通道内的SC—CO2流动作为研究对象,韩国原子能研究院（KAERI）曾在某次实验中采用过此类实验本体。质量流密度为400kg／m2、内管或棒热流密度为120kW／m2下的计算发现局部非常高的内壁温度,这种现象的出现可能是受到传热恶化的影响。第二步,在出现传热恶化的区域,有意识地在环形通道内圆柱体外表面引入正方形和半圆环形丝或障碍物。分析表明,通过增强环形障碍物后部的湍流生成,传热恶化现象得到了一定程度的缓解。尽管如此,研究还发现环形障碍物的形状对传热恶化的前部区域几乎没有影响。最后,分析了环形窄缝通道内圆柱螺旋绕丝对传热恶化的影响,结果表明,螺旋绕丝极大程度地缓解了传热恶化的影响。与光滑棒体相比,螺旋绕丝对强化传热的积极影响应归结于较高的湍动能生成,这也可以通过对燃料棒计算流线的分析推断得到,由此表明了绕丝对沿丝流动的扫掠效应。