Computer networks as social networks

Computer networks are inherently social networks, linking people, organizations, and knowledge. They are social institutions that should not be studied in isolation but as integrated into everyday lives. The proliferation of computer networks has facilitated a deemphasis on group solidarities at work and in the community and afforded a turn to networked societies that are loosely bounded and sparsely knit. The Internet increases people's social capital, increasing contact with friends and relatives who live nearby and far away. New tools must be developed to help people navigate and find knowledge in complex, fragmented, networked societies.     

Identity and search in social networks

Social networks have the surprising property of being "searchable": Ordinary people are capable of directing messages through their network of acquaintances to reach a specific but distant target person in only a few steps. We present a model that offers an explanation of social network searchability in terms of recognizable personal identities: sets of characteristics measured along a number of social dimensions. Our model defines a class of searchable networks and a method for searching them that may be applicable to many network search problems, including the location of data files in peer-to-peer networks, pages on the World Wide Web, and information in distributed databases.     

社会阶层变迁对休闲体育的影响因素分析

中国20余年来的变化使国家的社会结构发生了巨大的变迁，其中一个突出的特点就是逐渐形成了社会阶层的差异。通过对当代中国社会阶层的了解，力求以社会学的观点来分析和探讨当代中国社会阶层演进中的休闲体育，提出从社会阶层的视角来研究休闲体育的发展。     

Understanding agri-food networks as social relations

Actor network theory and supply chainmanagement theory provide suggestive researchdirections for understanding regional agri-foodnetworks. These theories claim that relationshipsbased upon trust and cooperation are critical to thestrength and vitality of the network. This means thatexploring and detailing these relationships among thesuppliers, producers, workers, processors, brokers,wholesalers, and retailers within specific regionalgeographies of these networks are critical forfurthering cooperation and trust. Key areas ofcooperation include resource sharing andapprenticeship programs. Employing food networks as akey unit of contextual analysis will deepen ourunderstanding of how to enhance their resiliency andvibrancy. Important questions can be raised about thedifference gender makes for farmers, brokers,entrepreneurs, and workers in local food networks.     

An experimental study of search in global social networks

We report on a global social-search experiment in which more than 60,000 e-mail users attempted to reach one of 18 target persons in 13 countries by forwarding messages to acquaintances. We find that successful social search is conducted primarily through intermediate to weak strength ties, does not require highly connected "hubs" to succeed, and, in contrast to unsuccessful social search, disproportionately relies on professional relationships. By accounting for the attrition of message chains, we estimate that social searches can reach their targets in a median of five to seven steps, depending on the separation of source and target, although small variations in chain lengths and participation rates generate large differences in target reachability. We conclude that although global social networks are, in principle, searchable, actual success depends sensitively on individual incentives.     

Identifying important factors influencing corn yield and grain quality variability using artificial neural networks

Soil, landscape and hybrid factors are known to influence yield and quality of corn (Zea mays L.). This study employed artificial neural network (ANN) analysis to evaluate the relative importance of selected soil, landscape and seed hybrid factors on yield and grain quality in two Illinois, USA fields. About 7 to 13 important factors were identified that could explain from 61% to 99% of the observed yield or quality variability in the study site-years. Hybrid was found to be the most important factor overall for quality in both fields, and for yield as well in Field 1. The relative importance of soil and landscape factors for corn yield and quality and their relationships differed by hybrid and field. Cation exchange capacity (CEC) and relative elevation were consistently identified as among the top four most important soil and landscape factors for both corn yield and quality in both fields in 2000. Aspect and Zn were among the top five most important factors in Fields 1 and 2, respectively. Compound topographic index (CTI), profile curvature and tangential curvature were, in general, not important in the study site-years. The response curves generated by the ANN models were more informative than simple correlation coefficients or coefficients in multiple regression equations. We conclude that hybrid was more important than soil and landscape factors for consideration in precision crop management, especially when grain quality was a management objective.     

The rural crisis in Minnesota: Identifying social and economic vulnerability and new directions for the future

The rural crisis of the 1980s is described in terms of the economic and social vulnerability of rural farm areas. The crisis is shown spreading from farms through families to rural communities, schools, churches, counties and beyond. Rural communities are shown to be undergoing dramatic and non-cyclical change. Criteria are defined to identify rural counties vulnerable to further economic losses and include: dependence on agriculture for jobs, inadequate off farm income, population losses, declines in residential and commercial property value, and county fiscal crises due to loss of the tax base, delinquincies, and additional federal and state program changes and cutbacks. Social and economic distress are so extensive as to overwhelm conventional emergency intervention efforts to provide food, shelter, access to health care, and professional counseling. Peer support programs have been found to be effective at reaching farm families and helping them seek out the assistance of farm financial advisors, counselors, food shelves, and public assistance. Emerging attempts to link politically contending parties are discussed, specifically the Reinvest in Minnesota Coalition and the Rural Strategy Task Force consisting of major farm, church, and lending organizations. A strategy process and stakeholder analysis for local communities are presented together with recommendations for action that include creating a rural trend watch capability.     

Fairness in alternative food networks: an exploration with midwestern social entrepreneurs

The notion of fairness is frequently invoked in the context of food and agriculture, whether in terms of a fair marketplace, fair treatment of workers, or fair prices for consumers. In 2009, the Kellogg Foundation named fairness as one of four key characteristics of a “good” food system. The concept of fairness, however, is difficult to define and measure. The purpose of this study is to explore the notion of fairness, particularly as it is understood within alternative food dialogues. Specifically, we wanted to answer the question of how alternative food entrepreneurs who are working to actualize fairness within local food networks understand this abstract notion. Using a multiple case study approach, the research for this project draws on semi-structured interviews that were conducted with key stakeholders in four alternative food businesses throughout the Midwest.     

社会网络、定居意愿对农民工城市心理融入的影响

基于3 167份农民工调查数据,采用有序Logistic模型计量分析方法,探讨农民工社会网络、定居意愿对其城市认同和身份认同等城市心理融入的影响。结果表明：初级社会网络、次级社会网络和社会网络强度都与城市认同和身份认同水平显著正向相关,城市认同对身份认同起到间接影响;定居意愿显著正向影响城市心理融入水平,同时定居意愿与社会网络存在交互影响。在独居和半迁移模式中,初级社会网络、次级社会网络和社会网络强度都显著正向影响身份认同和城市认同水平;而对于全家迁移的农民工来说,社会网络强度没有显著影响身份认同和城市认同水平,表明全家迁移对农民工社会关系具有部分替代作用。     

油桐果实破壳力学特性及主要影响因素研究

为研究油桐果实的破壳力学特性和影响因素,通过对油桐果实的物理特征进行测定,开展油桐整果和果瓣压缩试验,研究其破壳力学特性,在此基础上建立油桐果实破壳力学模型,拟合油桐果实破壳力学曲线,并分析破壳过程中的影响因素。结果表明:油桐果实的球度在0.95以上,各个部位外壳厚度基本相同,在进行力学分析时可以将油桐果实简化为均匀薄球壳,油桐果实外壳上的应力状态为二向应力状态。油桐果实的破壳力和所需功耗受油桐果实大小等级和加载部位的影响较明显,破壳力和功耗随着油桐大小等级的增大而增加,顶压方式所需破壳力和功耗明显小于中压方式。     

葡萄抗、感白粉病植株叶片蛋白质组差异比较

【目的】运用蛋白质组学比较研究白粉病不同抗病性葡萄蛋白质组构成的差异,找出白粉病感病蛋白和抗病蛋白。【方法】以抗病葡萄植株“6-12-4”和感病植株“6-12-2”为材料,在人工接种白粉菌后0（接种前）,2,4 d取叶片样品,提取其总蛋白,通过双向电泳技术,找到不同抗病性葡萄接种白粉菌后不同时间表达有差异的蛋白质点,对其中表达差异明显的蛋白质点进行回收和纯化,并进行MALDI-TOF质谱鉴定。【结果】从供试样品中共获得26个差异表达的蛋白质点,其中10个表达有明显差异的蛋白质经质谱鉴定后有7个为阳性斑点,3个为阴性斑点。蛋白质肽质量指纹鉴定结果表明,7个阳性斑点中有2个是假定蛋白,2个是未命名蛋白,差异蛋白质点5411为33 ku光系统Ⅱ放氧复合体外周蛋白,差异蛋白质点5625为核酮糖1,5-二磷酸羧化酶/加氧酶,差异蛋白质点7121为病程相关蛋白PR10。【结论】这些差异表达的蛋白可能与葡萄植株抗、感白粉病的特性有一定关联。     

Southern corn leaf blight: susceptible and resistant mitochondria

Mitochondria isolated from etiolated shoots of blight-susceptible and blight-resistant corn plants were subjected, in various respiratory states, to the pathotoxin released by Helminthosporium maydis (race T). The addition of the pathotoxin to susceptible mitochondria caused respiratory rate and oxidative phosphorylation changes. The addition of pathotoxin to susceptible mitochondria suspended in a potassium chloride reaction medium induced an immediate and irreversible swelling regardless of the respiratory state of the mitochondria. This membrane swelling correlates with the observed respiratory and coupling effects of the pathotoxin. In all instances, mitochondria isolated from blightresistant corn failed to exhibit any of the above responses to the pathotoxin.     

白细胞介素17及其家族

人白细胞介素17(hIL-17)是一种炎症前因子,因能诱导产生炎症介质,从而与许多疾病密切相关。文章就IL-17的分子结构、生物学功能及其家族成员加以综述。     

牛瘤胃微生物菌群变化及其影响因素

牛的瘤胃中富含各种微生物,微生物与瘤胃之间互生互利,对于牛的生长发育具有重要作用。本研究对牛瘤胃中常见的微生物菌群及其变化特征进行了综述,对影响牛瘤胃中微生物菌群变化的因素进行分析,以期为牛的生长发育、疾病防控和质量安全提供科学有效的指导。     

污泥砖的研制及其影响因素研究

【目的】以城市污水处理厂干化污泥为掺料制备污泥砖,并对影响砖体性能的因素进行分析,为降低污水处理厂运行成本,消除污泥对环境的潜在危害提供理论依据。【方法】以粘土和污泥为原料制备污泥砖,研究不同污泥掺量、成型压力、烧结温度及保温时间下砖体抗压强度及吸水率的变化,以得出污泥砖制备的最佳条件。【结果】当污泥掺量为0~200 g/kg时,随着污泥掺量的增加,污泥砖的抗压强度明显降低,吸水率却随之增大;当成型压力为20~80 MPa时,污泥砖的抗压强度随着成型压力的增大先升高后降低,而吸水率则先减小后增大;当烧结温度为900~1 100℃时,随着烧结温度的升高,污泥砖的抗压强度逐渐增强,吸水率逐渐降低;当保温时间≥1.5 h时,随着保温时间的延长,污泥砖的抗压强度降低,吸水率逐渐增大。【结论】兼顾污泥砖性能与节能环保原则,制备污泥砖的最佳条件为:污泥掺量100 g/kg,成型压力控制60 MPa,烧结温度1 050℃,保温时间1.5 h。     

纤维素酶酶活的影响因子初探

试验结果表明:在绿色木霉的纤维素酶酶活培养基中添加氮源为(NH4)2SO40 5%,无机盐组合为MgSO4·7H2O0 05%、KH2PO40 3%、CaCl20 06%,表面活性剂吐温-800 05%后,纤维素酶的酶活性达到较高水平,可为工业化生产纤维素酶提供依据。     

耕地细碎化的影响效应及对策研究进展

运用文献资料法和对比分析法,全面综述国内外关于耕地细碎化的影响效应及对策的研究文献,结果表明：耕地细碎化对农业的种植结构、粮食产出、生产技术效率、劳动力、土地利用格局及土地市场等方面产生影响,但整体上看,其负面效应突出。为应对耕地细碎化问题,不同地区从农村市场化、土地综合整治及法律制度保障3 个主要层面制定相应对策。在坚持农田生态稳定和民众广泛参与的前提下,耕地细碎化问题的解决对于农业的可持续发展及农民生活的改善具有重要意义。