共查询到20条相似文献，搜索用时 31 毫秒
1.
天山巩乃斯河谷积雪深度及季节冻土温度对气温变化的响应 总被引：2，自引：1，他引：1
气候变化影响着积雪的时空变化和季节冻土的水热变化,同时积雪变化对季节冻土的水热状态也有着重要的影响。为了分析积雪和气温对季节冻土热状况的影响,本文使用基于TFACE原理的试验装置在天山积雪与雪崩研究站进行了野外空气增温控制试验。野外试验设置了三种处理：自然状态、增温Ⅰ和增温Ⅱ。自然状态为无人为干扰的纯自然状态,增温Ⅰ为距积雪或土壤表层10cm气温增温约2℃,增温Ⅱ为距积雪或土壤表层10cm气温增温约4℃。结果表明：气温增加对积雪消融有显著的影响。在初始雪深为128cm条件下,增温I和增温II处理下的积雪消融时间比自然状态下分别提前19天和25天。在融雪期,气温、最大雪深和最大雪深发生的日期是影响季节冻土温度的重要因子。积雪覆盖条件下,季节冻土从深层开始解冻。而积雪的消失使土壤直接接受太阳辐射,土壤温度则迅速升高,从而使增温I和增温II处理下的季节冻土提前解冻。积雪消失后,季节冻土解冻的方向是从表层开始逐渐到深层。若积雪深度超过100cm时,积雪和土壤交界面的热交换基本达到平衡,此时土壤热通量损失达到最小值。融雪水对土壤温度特别是深层未冻结土壤有制冷作用。停止增温后,三个室外试验处理下的土壤温度随着时间逐渐趋于一致,并且土壤温度随着气温的波动而显著变化。 相似文献
2.
即兴与拼凑是中小企业经常应用的两类重要行为策略,但是它们对于创新的作用尚存在争议而需要进一步验证。本文构建由即兴、拼凑的主效应以及二者交互效应、资源结构调节效应组成的中小企业创新影响因素模型,利用242家科技型中小企业的问卷数据,采用普通最小二乘法,证实即兴、拼凑策略和中小企业创新之间分别呈倒U型和正相关关系,即兴和拼凑交互效应显示二者会弱化彼此的作用,维持更多的沉淀资源正向调节即兴对创新的作用。在证实即兴、拼凑作用的同时,从创新的角度为中小企业如何选用这些策略或者策略组合以及配置资源提供了思路。 相似文献
3.
R. T. Narendhirakannan M. Angeline Christie Hannah 《Indian journal of clinical biochemistry : IJCB》2013,28(2):110-115
Skin is the largest body organ that serves as an important environmental interface providing a protective envelope that is crucial for homeostasis. On the other hand, it is a major target for toxic insult by a broad spectrum of physical and chemical agents that are capable of altering its structure and function. There are a large number of dietary contaminants and drugs can manifest their toxicity in skin. These environmental toxicants or their metabolites are inherent oxidants and/or directly or indirectly drive the production of a variety of reactive oxidants also known as reactive oxygen species. These are short-lived entities that are continuously generated at low levels during the course of normal aerobic metabolism. These are believed to activate proliferative and cell survival signaling that can alter apoptotic pathways that may be involved in the pathogenesis of a number of skin disorders. The skin possesses an array of antioxidant defense mechanisms that interact with toxicants to obviate their deleterious effect. The “antioxidant power” of a food is an expression of its capability both to defend the human organism from the action of the free radicals and to prevent degenerative disorders. Plants like olive trees have their own built-in protection against the oxidative damage of the sun, and these built-in protectors function as cell protectors in our own body. Although many antioxidants have shown substantive efficacy in cell culture systems and in animal models of oxidant injury, unequivocal confirmation of their beneficial effects in human populations has proven elusive. 相似文献
4.
Simona Cernea Minodora Dobreanu 《Biochemia medica : ?asopis Hrvatskoga dru?tva medicinskih biokemi?ara / HDMB》2013,23(3):266-280
Diabetes is a complex, heterogeneous condition that has beta cell dysfunction at its core. Many factors (e.g. hyperglycemia/glucotoxicity, lipotoxicity, autoimmunity, inflammation, adipokines, islet amyloid, incretins and insulin resistance) influence the function of pancreatic beta cells. Chronic hyperglycaemia may result in detrimental effects on insulin synthesis/secretion, cell survival and insulin sensitivity through multiple mechanisms: gradual loss of insulin gene expression and other beta-cell specific genes; chronic endoplasmic reticulum stress and oxidative stress; changes in mitochondrial number, morphology and function; disruption in calcium homeostasis. In the presence of hyperglycaemia, prolonged exposure to increased free fatty acids result in accumulation of toxic metabolites in the cells (“lipotoxicity”), finally causing decreased insulin gene expression and impairment of insulin secretion. The rest of the factors/mechanisms which impact on the course of the disease are also discusses in detail.The correct assessment of beta cell function requires a concomitant quantification of insulin secretion and insulin sensitivity, because the two variables are closely interrelated. In order to better understand the fundamental pathogenetic mechanisms that contribute to disease development in a certain individual with diabetes, additional markers could be used, apart from those that evaluate beta cell function.The aim of the paper was to overview the relevant mechanisms/factors that influence beta cell function and to discuss the available methods of its assessment. In addition, clinical considerations are made regarding the therapeutical options that have potential protective effects on beta cell function/mass by targeting various underlying factors and mechanisms with a role in disease progression. 相似文献
5.
大气污染和气候变化同为中国面临的两大严峻环境问题，其对我国经济、社会发展的影响将变得越来越严重。在治理机制上，过去一直由环保部门和发改部门分而治之。随着相关治理工作的推进，分而治之的机制逐渐暴露出一系列政策重叠乃至互为掣肘的弊端，相应的治理机制创新也因此形成了重大需求。2018年，中国国务院实施机构改革，应对气候变化的职能被划转到生态环境部。生态环境部随即明确了大气污染和气候变化协同治理的战略目标。建立怎样的机制才能切实保障战略目标的实现？这是政界、学界、业界普遍关心的问题。针对这项需求，本文基于对大气污染和气候变化的影响范围和危害形式差异较大，但却“同根同源”的特性分析，阐述了两者协同治理的科学基础，提出了协同治理的机制模型，为我国有效实施绿色创新战略，积极融入应对气候变化全球治理体系打开了新思路。 相似文献
6.
Soma Gupta K. K. Singh V. J. Vyas V. N. Chaturvedi M. V. R. Reddy B. C. Harinath 《Indian journal of clinical biochemistry : IJCB》2000,15(1):52-55
Oxidative stress was studied by estimating plasma levels of malondialdehyde (MDA), beta carotene, vitamin E and erythrocytic
superoxide dismutase(E-SOD) activity in 50 cases of carcinoma of upper digestive tract which included carcinoma of oral cavity,
pharynx and oesophagus. While plasma MDA level was found to be increased (3.5±1.0 nmole/ml), a significant decrease in beta
carotene (81.2±14.5mg%), vitamin E (8.5±1.1 mg/L) level and E-SOD activity (657.0±80.6 U/G Hb) were observed in carcinoma
of upper digestive tract. Patients were treated with radiotherapy which itself was toxic enough and produced its deleterious
effects by generation of reactive oxygen species (ROS). As antioxdiants can detoxify ROS, beneficial effect if any, of antioxidant
administration during radiotherapy was studied in two groups of patients, group A (n=5, supplemented with antioxidants) and
group B (n=5, without antioxidant supplementation). Plasma MDA level was found to be elevated in both the groups but the increase
in group B was significant, compared to pretreatment level. Further, body weight was found to be significantly decreased in
group B patients, which was maintained in group A patients. Moreover, group A patients showed significant elevation in beta
carotene concentration, thus showing beneficial effect of administration of antioxidants during radiotherapy without disturbing
the desirable therapeutic effect of radiotherapy. 相似文献
7.
我国地热资源相当丰富,应用潜力巨大,因此,大力发展地热能能够缓解能源供应紧张局面,很大程度上解决因大量使用化石能源所造成严重的空气污染问题。在我国,应根据资源分布特点制定地热发展规划,在资源品质较好的地区发展地热发电,在有条件的地区发展各种地热直接利用技术,采用综合梯级利用提高资源利用效率。今后开发利用地热能,政府应加大对地热能利用的政策支持,鼓励企业加大资金投入;同时开发商应做好规划和布局,优选技术路线,使得地热能的利用由无序变有序,朝着更加科学合理的方向发展。 相似文献
8.
R. Ponalagusamy R. Tamil Selvi A.K. Banerjee 《Journal of The Franklin Institute》2012,349(5):1681-1698
The effects of rheological behavior of blood and pulsatility on flow through an artery with stenosis have been investigated. Blood has been represented by a non-Newtonian fluid obeying Herschel–Bulkley equation. Using the Reynolds number as the perturbation parameter, a perturbation technique is adopted to solve the resulting quasi-steady non-linear coupled implicit system of differential equations. Analytical expressions for velocity distribution, wall shear stress, volumetric flow rate and the mean flow resistance have been obtained. It is observed that the wall shear stress and flow resistance increase for increasing value of yield stress with other parameters held fixed. One of the remarkable results of the present analysis is not only to bring out the effect of the size of the stenosis but also to study the influence of the shape of the stenosis. The change in the shape of the stenosis brings out a significant change in the value of flow resistance but it has no effect on the variation of wall shear stress except shifting the point (where it attains its maximum value) towards downstream. It is pertinent to point out that pulsatile flow of Newtonian fluid, Bingham plastic fluid and Power-law fluid become particular cases of the present model. The present approach has general validity in comparison with many mathematical models developed by others and may be applied to any mathematical model by taking into account of any type of rheological property of blood. The obtained velocity profiles have been compared with the experimental data and it is observed that blood behaves like a Herschel–Bulkley fluid rather than Power-law and Bingham fluids. Finally, some biorheological applications of the present model have briefly been discussed. 相似文献
9.
蔬菜出口产地的农药使用行为及其对农民健康的影响——来自山东省莱阳、莱州和安丘三市的调研证据 总被引：4，自引：0，他引：4
近年来,蔬菜的农药残留问题日益成为食品安全中备受关注的焦点.尽管国内外学者对此已有一定研究.但针对蔬菜出口产地的农药使用行为及其对农民健康影响方面的实证研究却相当缺乏.本文根据在山东省取得的调研数据,深入研究了蔬菜出口产地的农药使用行为及其对农民健康的危害.结果表明,农民在使用农药的过程中存在着未能严格按照标签对农药进行稀释等一系列不规范的使用行为;而且不规范地使用农药和缺乏相应的保护措施对农民的整体健康造成了不可忽视的负面影响,其中是否采取保护措施对农民的皮肤健康有着显著的影响;喷洒次数对农民的呼吸系统具有显著的负面影响.在此基础上,本文提出了加大力度宣传正确使用农药的方法以及强化对农药使用的监控措施等相关政策建议. 相似文献
10.
《Information processing & management》2022,59(6):103064
Occupational stress has a significant adverse effect on workers’ well-being, productivity, and performance and is becoming a major concern for both individual companies and the overall economy. To reduce negative consequences, early detection of stress is a key factor. In response several stress prediction methods have been proposed, whose primary aim is to analyse physiological and behavioural data. However, evidence suggests that solutions based on physiological and behavioural data alone might be challenging when implemented in real-world settings. These solutions are sensitive to data problems arising from losses in signal quality or alterations in body responses, which are common in everyday activities. The contagious nature of stress and its sensitivity to the surroundings can be used to improve these methods. In this study, we sought to investigate automatic stress prediction using both surrounding stress data, which we define as close colleagues’ stress levels and the stress level history of the individuals. We introduce a real-life, unconstrained study conducted with 30 workers monitored over 8 weeks. Furthermore, we propose a method to investigate the effect of stress levels of close colleagues on the prediction of an individual’s stress levels. Our method is also validated on an external, independent dataset. Our results show that surrounding stress can be used to improve stress prediction in the workplace, where we achieve 80% of F-score in predicting individuals’ stress levels from the surrounding stress data in a multiclass stress classification. 相似文献
11.
研究了细胞内存在的分子伴侣、蛋白质聚集和大分子拥挤环境对蛋白质折叠的影响.首先,发现分子伴侣GroEL与底物蛋白的结合有"半位"和"全位"两种模式,它是由底物蛋白的分子形状、分子大小以及与GroEL的相互作用性质决定的.接着,发现两种不同的蛋白质一起复性时相互不干扰,提示细胞内蛋白质折叠可能不受其他蛋白聚集的影响;后又发现α-乳清蛋白的前熔球态不仅是分子伴侣也是蛋白质聚集体的作用对象.最后,研究大分子拥挤环境对蛋白质折叠热力学和动力学的影响,揭示了这种影响的复杂性和多样性. 相似文献
12.
在市政污水处理过程中总不可避免地产生恶臭。一些恶臭气体被归类为有毒污染物,其排放受到有关空气污染法规的约束。为了保护和提高各类处理现场及周围环境卫生质量,减少对空气造成二次污染,对恶臭进行有效的控制已势在必行。本文着重讨论市政污水、污泥处理过程产生的臭味,及其分布情况和除臭方法的概述。 相似文献
13.
采用盆栽法考察不同质量浓度的Cd、Zn、Cu、Pb、As 5种重金属复合胁迫对酢酱草抗氧化酶活性的影响。结果显示随着重金属处理浓度梯度的增加,酢酱草过氧化物酶(POD)活性、抗坏血酸过氧化物酶(APX)活性、脯氨酸(PRO)含量及谷胱甘肽(GSH)含量先升高后降低;而超氧化物歧化酶(SOD)活性和过氧化氢酶(CAT)酶活性逐渐下降。结果表明酢酱草在重金属复合胁迫下能防御性的增加POD酶活性、SOD酶活性、PRO含量及GSH含量以减少逆环境的伤害,而重金属复合胁迫浓度过高则会导致酢酱草抗氧化酶系统受到明显损害,生长受到很大程度的抑制。 相似文献
14.
15.
Zn/Cd超富集植物天蓝遏蓝菜(Thlaspi caerulescens)中TcCaM2基因的克隆及在酵母中的重金属耐受性分析 总被引：1，自引：0，他引：1
从重金属超富集植物天蓝遏蓝菜(T. caerulescens)Cd胁迫的cDNA文库中，通过基因表达的差异筛选得到的阳性克隆之一，核苷酸序列分析表明与拟南芥CaM2的相似性高达92%，故命名为TcCaM2(T. caerulescens CaM2, GenBank No. EF053035)。其核苷酸序列与迄今已知的钙调蛋白基因同源率在83%以上，其氨基酸序列同源性高达95%以上，与大多数高等植物的CaM，如印度芥菜、拟南芥、水稻等同源性则更高。将TcCaM2基因置于酵母表达启动子之下，构建酵母表达载体，并将其转入重金属敏感型酵母突变菌株，酵母重金属耐受实验表明，TcCaM2在酵母中的过量表达提高了酵母对Co2+或Ni2+的耐受性，增加了对Cd2+的敏感性，对Zn2+胁迫抗性稍有增加但差异不显著；说明TcCaM2通过其对重金属离子的结合作用及在信号转导系统中的功能，在植物细胞对重金属的富集、耐性中发挥了重要的调节作用。 相似文献
16.
A new subspecies, Primula obconica subsp. fujianensis, is described. The genus
Primula is widely distributed throughout China, but it has never been previously recorded in Fujian
and Jiangsu. Recently the authors collected a specimen of the genus from Fujian for the first time. It
is obviously closely related to P. obconica, which is one of the most common species in China,
ranging from western Yunnan and Sichuan through Guizhou, Hubei to Hunan and northern Guang-
dong, with its most easterly extension in southern Jiangxi. Morphologically, the Fujian plant is char-
acterized by its much smaller stature and by the scapes being shorter than the leaf rosette, and in
many ways it is more closely related to P. obconica subsp. parva, but can be easily distinguished
by its smaller, white and homostylous flowers. As it is isolated both in distribution and reproductionwith other subspecies of P. obconica, here it is described as a new subspecies. 相似文献
17.
企业技术效率国际比较研究——以中国航空运输企业为例 总被引：1，自引：0，他引：1
本文以中国航空运输企业为例,对中国企业技术效率进行探讨。用随机前沿函数方法估计了国内外航空公司的技术效率,并对估计结果进行比较分析。研究结果显示,中国航空公司的技术效率远低于全球按运营收入排名前100家的其它航空公司的技术效率, 这反映出中国航空运输企业在经营管理机制和方式及其生存发展的制度环境等方面存在着不足,从而导致其资源配置和技术的无效率。因此,提高中国航空运输业国际竞争力,既要从制度环境层面做出改进,更需要在微观层面上改进企业的经营管理机制和方式。中国航空运输企业技术效率状况在一定程度上反映了中国企业的共性问题。 相似文献
18.
中国华东及其周边地区NDVI对气温和降水的季节响应 总被引：6，自引：0，他引：6
地表植被与大气的相互作用过程是地球科学领域的研究重点和热点。本文基于SPOTVGT-NDVI数据和气象站点的气温和降水资料,采用时滞相关分析法,研究了1998年-2011年我国华东及其周边地区四季NDVI对气温和降水的时空响应特征。结果表明,在整个研究区,气温对NDVI的影响大于降水,NDVI与气温在夏季和秋季相关性较高,与降水在秋季和春季相关性较高,冬季NDVI与气温和降水相关性都最低。NDVI对气温响应的滞后期在春季和秋季较短,对降水响应的滞后期在冬季较短,夏季NDVI对气温和降水响应的滞后期都较长。在冬季、春季和秋季,NDVI对气温和降水最大相关系数的空间分布在研究区的南北部差异不明显,在夏季则具有较明显的南北差异。NDVI对气温变化响应的滞后期在春季、夏季和秋季具有较明显的南北差异,对降水变化响应的滞后期除在夏季具有一定的南北差异外,在其他季节空间分布规律性不显著。 相似文献
19.
Strong, Weak, and Latent Ties and the Impact of New Media 总被引：2，自引：0，他引：2
Caroline Haythornthwaite 《The Information Society》2002,18(5):385-401
This article argues that consideration of the strength of ties between communicators can help reconcile disparate results on the impact of new media on social relations. It is argued from the research literature and studies by the author that where ties are strong, communicators can influence each other to adapt and expand their use of media to support the exchanges important to their tie, but where ties are weak, communicators are dependent on common, organizationally established means of communication and protocols established by others. Due to this differential use of media, a new medium that adds means and opportunities for previously unconnected others to communicate will have positive effects on weak ties and weak-tie networks, in particular by laying an infrastructure of latent ties (ones that exist technically but have not yet been activated), and providing an opportunity for weak ties to develop and strengthen. A new medium may also have positive effects on strongly tied pairs where it adds another means of communicating and supports the communication needs and tasks of the pair. However, where a new medium replaces a former, common means of communication, the dependence of weak ties on a common medium makes weak-tie networks highly susceptible to dissolution. In contrast, strong-tie networks, with their connections via multiple relations and multiple media, can be expected to be more robust under conditions of change. 相似文献
20.
不同轮作模式下设施菜地土壤和蔬菜中砷汞镉铬铅的分布特征 总被引：3，自引：0，他引：3
以沈阳市大民屯镇蔬菜生产示范基地为平台,进行为期一年的设施蔬菜轮作试验,结果表明:该地区土壤和蔬菜中的As、Hg、Cr、Pb含量均处在安全范围;Cd由于输入量较大,在土壤表层呈现富集状况,直接增加了该地区重金属污染风险.菠菜-西红柿-芸豆轮作模式可在一定程度上减小土壤中Cd含量,降低土壤综合污染指数.菠菜体内Cd含量超标,不宜在该地区种植.建议将轮作模式改为油麦菜(或油菜)-西红柿-芸豆. 相似文献