Force indeterminacy in the jammed state of hard disks

Granular packings of hard discs are investigated by means of contact dynamics which is an appropriate technique to explore the allowed force-realizations in the space of contact forces. Configurations are generated for given values of the friction coefficient, and then an ensemble of equilibrium forces is found for fixed contacts. We study the force fluctuations within this ensemble. In the limit of zero friction the fluctuations vanish in accordance with the isostaticity of the packing. The magnitude of the fluctuations has a non-monotonous friction dependence. The increase for small friction can be attributed to the opening of the angle of the Coulomb cone, while the decrease as friction increases is due to the reduction of connectivity of the contact-network, leading to local, independent clusters of indeterminacy. We discuss the relevance of indeterminacy to packings of deformable particles and to the mechanical response properties.Comment: 4 pages, 3 figures. Minor changes, journal reference adde

Digital Preservation and Access of Natural Resources Documents

Digitization and preservation of natural resource documents were reviewed and the current status of digitization presented for a North American university. It is important to present the status of the digitation process for natural resources and to advocate for increased collections of digital material for ease of reference and exchange of information. Digital collections need to include both published documents and ancillary material for research projects and data for future use and interpretation. The methods in this paper can be applied to other natural resource collections increasing their use and distribution. The process of decision making for documents and their preservation and inclusion in ScholarWorks is presented as a part of the Forest Sciences Commons as a subset of the Life Sciences Commons of the Digital Commons Open Network launched and maintained by bepress. Digitization has increased the roles and skillsets needed for librarians and from libraries. This creates new challenges and opportunities for the library as publisher and as an advocate for open access. Digital curation melds together digitization and knowledge management and enhances community engagement. Digitization of collections are reviewed and natural resource documentation presented for faculty publications, Research Projects and Centers, eBooks, Journals, Galleries and electronic Theses and Dissertations (ETDs). Recommendations are made to increase the digital curation of the collection by encouraging community participation and use. Digital archives are important to natural resource professionals as society-ready natural resource graduates need to deal effectively with complex ecological, economic and social issues of current natural resources management. Natural resource research for the future needs to ensure that professionals have a greater breath of knowledge as they interpret and apply new knowledge, understanding, and technology to complex, transdisciplinary social and biological issues and challenges

Низкие затраты, низкие выплаты? – усовершенствование проблемы в группах средством электронной помощи

У статті розглядаються дослідження груп за допомогою техніки модерацій (PROMOD). У дослідженні було протестовано, чи може PROMOD покращити показник працездатності як групи, так й окремої одиниці.The aim of this study was to investigate whether PROMOD can also improve performance of teams and individuals in a virtual setting (N =180). Subjects had to solve an interpolation-problem (see Dörner, 1976) under facilitated and non-facilitated conditions while using a chat-program and electronic forms. Improvements were found to be significant in one of two performance-measures (p = .0245).В этом исследовании было протестировано, может ли PROMOD улучшить показатель трудоспособности так группы, как и отдельной единицы (N=180). К тому же, проблема интерполяции решалась в модерированых, а также немодерированых условиях при использовании чат-программ и электронных формуляров. Этот эффект можно было наблюдать в одном из двух тестов трудоспособности (p = .0245)

Processing and Transmission of Information

Contains reports on two research projects.Lincoln Laboratory, Purchase Order DDL-B158Department of the ArmyDepartment of the NavyDepartment of the Air Force under Contract AF 19(122)-45

Body burden of polycyclic aromatic hydrocarbons and tributyltin in hard clams, Mercenaria mercenaria from the Elizabeth River, Va

The Elizabeth River, contaminated with PAH, TBT, and heavy metals, is potentially home to a variety of estuarine invertebrates of commercial importance, notably oysters, hard clams, and crabs. Harvestable oysters have virtually disappeared from the system, but it has been rumored among commercial fishermen that a population of small (little neck to cherrystone) hard clams (Mercenaria mercenaria) exists within the Elizabeth River system. These clams are of serious interest to commercial clammers in the area as a previously unharvested source of market-size clams. Crabs of a harvestable size are also reasonably abundant throughout this river according to local fishermen. The Elizabeth River is presently closed to any type of commercial bivalve harvest because of bacterial and chemical contamination. Chemical contaminants of concern include heavy metals (including organotin compounds), pesticides, and PAHs. If these factors, bacterial or chemical, were shown to pose no human health risk after suitable depuration, the river could conceivably be opened to the taking of bivalve species