Effects of grain shape on packing and dilatancy of sheared granular materials

Granular material exposed to shear shows a variety of unique phenomena: Reynolds dilatancy, positional order and orientational order effects may compete in the shear zone. We study granular packings consisting of macroscopic prolate, oblate and spherical grains and compare their behaviour. X-ray tomography is used to determine the particle positions and orientations in a cylindrical split bottom shear cell. Packing densities and the arrangements of individual particles in the shear zone are evaluated. For anisometric particles, we observe the competition of two opposite effects. One the one hand, the sheared granulate is dilated, but on the other hand the particles reorient and align with respect to the streamlines. Even though aligned cylinders in principle may achieve higher packing densities, this alignment compensates for the effect of dilatancy only partially. The complex rearrangements lead to a depression of the surface above the well oriented region while neigbouring parts still show the effect of dilation in the form of heaps. For grains with isotropic shapes, the surface remains rather flat. Perfect monodisperse spheres crystallize in the shear zone, whereby positional order partially overcompensates dilatancy effects. However, already slight deviations from the ideal monodisperse sphere shape inhibit crystallization.Comment: 12 pages, 13 figures, accepted in Soft Matte

Минералого-петрохимические и геохимические черты околорудного метасоматизма в Западном золоторудном месторождении (Северное Забайкалье)

Приведены данные об условиях залегания, морфологии рудных тел, минеральном составе, физико-химических и термодинамических режимах образования руд Западного золоторудного месторождения Северного Забайкалья. Впервые показаны порядок минеральной зональности (структура) и минералого-петрохимические черты аподолеритовых околожильных метасоматических ореолов. Доказывается принадлежность последних к березитовой метасоматической формации, а месторождения - к золотой субформации золото-уран-полиметаллической березитовой рудной формации. Слабо контрастные аномалии золота, серебра, ртути приурочены к тыловым зонам околожильных метасоматических ореолов в непосредственном обрамлении слабозолотоносных (первые г/т) интервалов кварцевых жил. Аргументируются генетические связи околожильных метасоматических и геохимических ореолов с рудами и образование их в рудообразующем процессе позднепалеозойской металлогенической эпохи. Основные минералого-петрохимические и геохимические черты околожильного метасоматизма рассмотрены в сравнении с таковыми других месторождений Северо-Забайкальского золоторудного района

Evolution of shear zones in granular materials

The evolution of wide shear zones (or shear bands) was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains (e.g. sand) and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g. sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rod like particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear induced density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.Comment: 11 pages, 12 figures, submitted to Phys. Rev.

Expression of Human Immunodeficiency Virus Type 1 Gag Protein Precursor and Envelope Proteins from a Vesicular Stomatitis Virus Recombinant: High-Level Production of Virus-like Particles Containing HIV Envelope

AbstractRecombinant vesicular stomatitis viruses have been developed as high-level expression vectors which serve as effective vaccine vectors in animals (Roberts et al., 1998, J. Virol. 72, 4704–4711; Roberts et al., 1999, J. Virol. 73, 3723–3732). Here we show that two genes can be expressed simultaneously from a single, live-attenuated VSV recombinant. The genes used encode the Pr55gag protein precursor of HIV-1 (1.7-kb gene) and an HIV-1 envelope (Env) protein (2.4 kb gene). Our results show that VSV can accommodate up to a 40% increase in genome size with only a threefold reduction in virus titer. Recombinants expressing the Pr55gag protein precursor with or without Env protein produced abundant HIV virus-like particles (VLPs) in addition to bullet-shaped VSV particles. HIV Env protein expressed from a VSV recombinant also expressing Gag was specifically incorporated into the HIV VLPs but not into the VSV particles. In contrast, VSV G protein was found in both VSV particles and in HIV VLPs. Such VSV/HIV recombinants producing HIV VLPs with Env protein could be an effective source of HIV-like particles inducing both cellular and antibody-mediated immunity to HIV-1

The Metropolis and Evangelical Life: Coherence and Fragmentation in the ‘Lost City of London’

This article examines the interplay of different processes of cultural and subjective fragmentation experienced by conservative evangelical Anglicans, based on an ethnographic study of a congregation in central London. The author focuses on the evangelistic speaking practices of members of this church to explore how individuals negotiate contradictory norms of interaction as they move through different city spaces, and considers their response to tensions created by the demands of their workplace and their religious lives. Drawing on Georg Simmel’s ‘The Metropolis and Mental Life’, the author argues that their faith provides a sense of coherence and unity that responds to experiences of cultural fragmentation characteristic of everyday life in the city, while simultaneously leading to a specific consciousness of moral fragmentation that is inherent to conservative evangelicalism

Untersuchung der Praxistauglichkeit eines Ortungssystems zur Verbesserung des Herdenmanagements eines Milchviehbetriebes

Ziel dieses Versuches, der im Rahmen eines Praxisprojektes durchgeführt wurde, war die Überprüfung der Praxistauglichkeit des Real Time Location Systems (RTLS) Ubisense 7000 für das Herdenmanagement. Neben der Überprüfung der Genauigkeit der mit dem Ortungssystems erhobenen Daten, wurden Daten, zur Aktivitätsmessung, Brunsterkennung, Aufenthaltsdauer in den Funktionsbereichen sowie Laufverhalten mithilfe von Pedometern und Videobeobachtung erfasst

Prospects for e-democracy in Europe

The drivers behind e-participation are digitalisation, the development of digital tools that can be usedfor citizen involvement – social media, deliberative software, e-voting systems, etc. – and growingaccess to the internet. In European countries, especially those that rank prominently among the top 50performers, citizens have more and more opportunities to have their say in government and politics.According to the UN, the largest share of e-participation initiatives relates to central and localgovernments giving access to public sector information and public consultation via digital tools.Recently there has been a growing focus on citizen involvement in policy making, although progressin this field has been modest so far