Shock formation in electron-ion plasmas: mechanism and timing

We analyse the full shock formation process in electron-ion plasmas in theory and simulations. It is accepted that electromagnetic shocks in initially unmagnetised relativistic plasmas are triggered by the filamentation instability. However, the transition from the first unstable phase to the quasi-steady shock is still missing. We derive a theoretical model for the shock formation time, taking into account the filament merging in the non-linear phase of the filamentation instability. This process is much slower than in electron-positron pair shocks, so that the shock formation is longer by a factor proportional to sqrt(m_i/m_e) ln(m_i/m_e)

Physics of collisionless shocks - theory and simulation

Collisionless shocks occur in various fields of physics. In the context of space and astrophysics they have been investigated for many decades. However, a thorough understanding of shock formation and particle acceleration is still missing. Collisionless shocks can be distinguished into electromagnetic and electrostatic shocks. Electromagnetic shocks are of importance mainly in astrophysical environments and they are mediated by the Weibel or filamentation instability. In such shocks, charged particles gain energy by diffusive shock acceleration. Electrostatic shocks are characterized by a strong electrostatic field, which leads to electron trapping. Ions are accelerated by reflection from the electrostatic potential. Shock formation and particle acceleration will be discussed in theory and simulations

UniquID: A Quest to Reconcile Identity Access Management and the Internet of Things

The Internet of Things (IoT) has caused a revolutionary paradigm shift in computer networking. After decades of human-centered routines, where devices were merely tools that enabled human beings to authenticate themselves and perform activities, we are now dealing with a device-centered paradigm: the devices themselves are actors, not just tools for people. Conventional identity access management (IAM) frameworks were not designed to handle the challenges of IoT. Trying to use traditional IAM systems to reconcile heterogeneous devices and complex federations of online services (e.g., IoT sensors and cloud computing solutions) adds a cumbersome architectural layer that can become hard to maintain and act as a single point of failure. In this paper, we propose UniquID, a blockchain-based solution that overcomes the need for centralized IAM architectures while providing scalability and robustness. We also present the experimental results of a proof-of-concept UniquID enrolment network, and we discuss two different use-cases that show the considerable value of a blockchain-based IAM.Comment: 15 pages, 10 figure

Viabilização da produção de leite em estabelecimentos familiares, com utilização de pacote tecnológico recomendado pela Embrapa Pecuária Sudeste.

O objetivo do estudo foi viabilizar economicamente a produção de leite em estabelecimentos familiares (EF) no município de São Carlos, SP, de 1998 a 2001, por meio de ações técnicas e gerenciais que intensificam os sistemas de produção de maneira sustentável. Utilizaram-se seis EFs, com área de 4,2 a 27,2 ha, que tinham a produção de leite como principal atividade econômica. As ações foram: Agropecuárias: a) alimentação: plantio e fornecimento de cana-de-açúcar + uréia na seca, alimentação suplementar de acordo com a produção da vaca e pastejo rotacionado sobre gramíneas tropicais nas águas; b) manejo: melhoria do conforto dos animais; c)reprodução: melhor controle reprodutivo do rebanho; d) sanidade: melhor controle sanitário do rebanho; e) melhoramento genético: uso de touro selecionado; Ambientais: recuperação e conservação de recursos naturais, melhoria da qualidade da água e recuperação da fertilidade do solo; e Gerenciais: controle zootécnico do rebanho, práticas de associativismo, descarte de animais improdutivos e análise econômica. Como as tecnologias foram implantadas ao longo dos anos, a avaliação foi feita tomando-se como base o ano inicial (1998). Nos seis EFS, as estimativas de produção de leite/ano, produção de leite/ha/ano, produção de leite/vaca, receita e patrimônio aumentaram 24%, 36%, 38%, 70% e 27%, respectivamente. O custo operacional e o custo total aumentaram 12% e 5% e o lucro aumentou 4%. Dos seis EFs estudados, dois tornaram-se modelos de sistemas de produção de leite familiar. Concluiu-se que o pacote tecnológico implantado foi eficiente nos diferentes sistemas de produção de leite familiar.bitstream/CPPSE/15938/1/PROCIDoc42AM2005.00187.pd

Applying blockchain to improve the integrity of the software development process

Software development is a complex endeavor that encompasses application and implementation layers with functional (refers to what is done) and non-functional (how is done) aspects. The efforts to scale agile software development practices are not wholly able to address issues such as integrity, which is a crucial non-functional aspect of the software development process. However, if we consider most software failures are Byzantine failures (i.e., where components may fail and there is imperfect information on which a component has failed.) that might impair the operation but do not completely disable the production line. In this paper, we assume software practitioners who cause defects as Byzantine participants and claim that most software failures can be mitigated by viewing software development as the Byzantine Generals Problem. Consequently, we propose a test-driven incentive mechanism based on a blockchain concept to orchestrate the software development process where production is controlled by a similar infrastructure based on the working principles of blockchain. We discuss the model that integrates blockchain with the software development process, and provide some recommendations for future work to address the issues while orchestrating software productio

Urban agriculture: a global analysis of the space constraint to meet urban vegetable demand

Urban agriculture (UA) has been drawing a lot of attention recently for several reasons: the majority of the world population has shifted from living in rural to urban areas; the environmental impact of agriculture is a matter of rising concern; and food insecurity, especially the accessibility of food, remains a major challenge. UA has often been proposed as a solution to some of these issues, for example by producing food in places where population density is highest, reducing transportation costs, connecting people directly to food systems and using urban areas efficiently. However, to date no study has examined how much food could actually be produced in urban areas at the global scale. Here we use a simple approach, based on different global-scale datasets, to assess to what extent UA is constrained by the existing amount of urban space. Our results suggest that UA would require roughly one third of the total global urban area to meet the global vegetable consumption of urban dwellers. This estimate does not consider how much urban area may actually be suitable and available for UA, which likely varies substantially around the world and according to the type of UA performed. Further, this global average value masks variations of more than two orders of magnitude among individual countries. The variations in the space required across countries derive mostly from variations in urban population density, and much less from variations in yields or per capita consumption. Overall, the space required is regrettably the highest where UA is most needed, i.e., in more food insecure countries. We also show that smaller urban clusters (i.e., <100 km2 each) together represent about two thirds of the global urban extent; thus UA discourse and policies should not focus on large cities exclusively, but should also target smaller urban areas that offer the greatest potential in terms of physical space