Dynamic behaviour of gas jets in laser cutting

The efficiency and overall quality of a laser cutting operation is highly dependent on the assist gas parameters. The desire to cut thicker material has led to the observation of small process operating windows for thicker sections. The gas jet delivery and subsequent dynamical behaviour have significant effects on the cutting operation as the sample thickness increases. To date, few workers have examined the dynamical behaviour of the gas jet. This paper examines the characteristics of oxygen gas jets during CO2 laser cutting of steel. Particular emphasis is placed on the mass transfer effects that are operating within the kerf. Oxygen concentration levels within a model kerf are measured for various laser cutting set-ups. The results show a substantial reduction in oxygen concentration within the kerf. A system for oxygen concentration maintenance is described and cutting results from this system are compared with conventional techniques for cutting steels in the range 10 to 20mm thick. A theoretical analysis of turbulent mass transfer within a kerf is presented and compared with experiment.

IPLR: An online resource for Greek word-level and sublexical information

We present a new online psycholinguistic resource for Greek based on analyses of written corpora combined with text processing technologies developed at the Institute for Language & Speech Processing (ILSP), Greece. The "ILSP PsychoLinguistic Resource" (IPLR) is a freely accessible service via a dedicated web page, at http://speech.ilsp.gr/iplr. IPLR provides analyses of user-submitted letter strings (words and nonwords) as well as frequency tables for important units and conditions such as syllables, bigrams, and neighbors, calculated over two word lists based on printed text corpora and their phonetic transcription. Online tools allow retrieval of words matching user-specified orthographic or phonetic patterns. All results and processing code (in the Python programming language) are freely available for noncommercial educational or research use. © 2010 Springer Science+Business Media B.V.

微波蒸馏-顶空固相微萃取-气质联用检测鱼体中土霉味化合物

采用微波蒸馏-顶空固相微萃取-气质联用检测鱼体中常见的两种土霉味化合物,即2-甲基异茨醇(2-MIB)和土腥素(Geosmin)。研究并优化了微波蒸馏萃取过程的关键参数(微波蒸馏时间、载气流量),结果表明微波蒸馏6min、载气流70mL/min为土霉味化合物微波蒸馏萃取的最佳条件。在此优化的条件下,土霉味化合物能够充分地从鱼体中蒸馏出来,再采用顶空固相微萃取的方法使馏分中的土霉味化合物吸附于纤维涂层上,将其在250℃高温下解吸,并用GC-MS分析。基于此测定方法,鱼肉中2-甲基异茨醇和土腥素的检测限均达到

灰盔累枝虫形态学及表膜下纤维系的研究

利用活体观察及蛋白银染色技术对灰盔累枝虫(Epistylisgalea)的形态学及表膜下纤维系进行了研究。该种主要鉴别特征为:活体个员的表膜柔软,虫体充分伸展时呈倒长锥形,体长200—300μm,体宽70—90μm;大核“J”字形,呈纵位。单一伸缩泡,直径21—25μm,背位。纵向纤维细密。口围盘纤维呈网状,与纵向纤维直接相连,并在整体上呈兜网状。与本属其他相近种相比,本种第3咽膜(P3)明显要长,其后1/3超出第1咽膜后继续向下呈弧形弯曲。本文对该种上述特征在分类学上的意义及其与相近种类之间的关系进行了

养殖乌鳢类立克次体分离纯化的初步研究

国家自然科学基金 (No.3 0 3 710 91)资助

Can, and should, behavioural neuroscience influence public policy?

Recent years have seen enormous demand amongst policy makers for new insights from the behavioural sciences, especially neuroscience. This demand is matched by an increasing willingness on behalf of behavioural scientists to translate the policy implications of their work. But can neuroscience really help shape the governance of a nation? Or does this represent growing misuse of neuroscience to attach scientific authority to policy, plus a clutch of neuroscientists trying to overstate their findings for a taste of power?. © 2012.

光合率作为藻类毒理测试指标

以氧电极法的光合率作为藻类毒性测试指标．整个测试过程准确，简便，快速．能够随时测定受试毒物对藻类光合作用的效应，与常规毒性试验比较，测定时间由96h缩短到2h．灵敏度约提高了一倍，Cu2＋对光合作用的半数效应浓度（EC50）是0．105mg／L，比Cu2＋对藻的急性毒性试验的EC50（0．204mg／L）少了一倍．

光合率作为藻类毒理测试指标

以氧电极法的光合率作为藻类毒性测试指标。整个测试过程准确,简便,快速。能够随时测定受试毒物对藻类光合作用的效应,与常规毒性试验比较,测定时间由96h缩短到2h。灵敏度约提高了一倍,Cu~(2+)对光合作用的半数效应浓度(EC_(50))是0.105mg/L,比Cu~(2+)对藻的急性毒性试验的EC_(50)(0.204mg/L)少了一倍。

流域生态学——新学科、新思想、新途径

在评述流域生态学定义、来源及有关认识的基础上，论述了流域生态学作为一门学科的意义和主要研究内容．文章认为流域生态学的研究与应用是流域社会、经济可持续发展的有效途径，有必要尽快地系统开展相关研究

江汉平原47号钻孔中化石硅藻的新种类

在江汉平原47号钻孔中的46.60—2.20m层位上(上更新统到全新统),含有丰富的化石硅藻,经鉴定有4个新种类,即Cymbella jianghanensis sp.nov.,C.tenuistriata sp.nov.,C.cistula(Hempr.) Grun.var.retcta var.nov.,Gomphonema tropicale Brun var.nonpunctatum var.nov..同时,对一个变种进行了重新命名和特征修改,即Eunotia clevei Grun.var.ob

氯化高汞对大型溞的慢性毒性

在换水静置条件下(25℃),氯化高汞(以Hg~(++)计)对大型溞的48小时LC_(50)值及其可信限为13.5(±2.1)微克/升。试验个体饲以斜生栅藻单个培养,在汞含量为1—21微克/升浓度下,产仔总数经方差分析表明组间差异显著(F>F_(0.05))。各浓度组(X)与产仔总数(Y)的关系为:Y=-51.823X+4320.960(r=-0.904,p<0.01)。净增殖率(R_0)随浓度升高而逐渐下降。存活和生长用方差分析及D值检验表明对照组与各浓度组之间(差异数分别小于各自的D值20.89和0.1

Age and Growth of an Endemic Tibetan Fish, Schizothorax o'connori, in the Yarlung Tsangpo River

We investigated the age and growth of Schizothorax o'connori in the Yarlung Tsangpo River by examination of annuli from otoliths. The von Bertalanffy model was the most acceptable statistical growth model. Its parameters were as follows: SL infinity = 492.4 mm, K = 0.1133, t(0) = -0.5432 year and W-infinity = 1748.9 g for females; SL infinity = 449.0 mm, K = 0.1260, t(0) = -0.4746 year and W-infinity = 1287.0 g for males. Theoretical longevity was 25.9 years for the female and 23.3 years for the male. Moreover, females had larger asymptotic length and weight compared with males.

Dose-dependent effects of extracted microcystins on embryonic development, larval growth and histopathological changes of southern catfish (Silurus meridionalis)

A laboratory toxic experiment was conducted to examine dose-dependent effects of extracted microcystins (MCs) on embryonic development, larval growth and histopathological changes of southern catfish (Silurus meridionalis). Fertilized eggs were incubated in solutions with four concentrations of MCs (0, 1, 10, 100 mu g MC-LReq l(-1)). Higher MCs retarded egg development (2-10 h delays) and larval growth, reduced hatching rate (up to 45%), and caused high malformation rate (up to 15%) and hepatocytes damage (characterized by disorganization of cell structure and a loss of adherence between hepatocytes, cellular degeneration with vacuolar hepatocytes and marginal nuclei, even hepatocellular necrosis). A 10 mu g MC-LReql(-1) is close to a high concentration in natural cyanobacterial blooms, suggesting a possible existence of such toxic effects in eutrophic waters. (c) 2007 Elsevier Ltd. All rights reserved.

Vertical distribution and migration of planktonic rotifers in Xiangxi Bay of the three Gorges Reservoir, China

We investigated diel vertical migrations (DVM) and distributions of rotifers in summer, 2004 and spring, 2005, in Xiangxi Bay of the Three Gorges Reservoir, China. Water temperature, pH, conductivity, and phytoplankton were closely related to rotifer vertical distribution, while dissolved oxygen had no relationship with the vertical distribution of rotifers. The species composition and population density of rotifers changed significantly between seasons. However, rotifer vertical distributions in both seasons were similar. They aggregated at specific depths in the water column. All the rotifer species inhabited the surface layers (0.5-5 m). Generally, the rotifers did not display DVM except for Polyarthra vulgaris (in summer), which performed reverse migration. The reason that rotifers did not perform DVM may be explained by the low abundance of competitors and predators and the high density of food resources at the surface strata.