Critical and sustainable fluxes: theory, experiments and applications

Over the last ten years, numerous membrane filtration data have been viewed in the light of the concept of critical flux. This concept, used in a number of different ways often without explicit redefinition, is here clarified both from a theoretical and from an experimental viewpoint. Also, a link is make with the sustainable fluxes. Also covered are the various methods of measurement and the influence of membrane and suspension properties on the critical flux. Over the same period of time, models have been developed to explain the observed behaviour. Those for stable colloidal suspensions are based on the existence of repulsive interactions between soft matter constituents. The assumptions and usefulness of various models are discussed. The concept of a critical concentration for phase transition is introduced into the theoretical discussion. For theoreticians and experimentalist, this and the clarified concept of a small set of critical fluxes will continue to provide a valuable framework. For membrane users dealing with most industrial process streams (mixtures and complex fluid) the concept of a sustainable flux (shown as being derived from critical flux) is of a great utility; above a certain key flux (dependent on hydrodynamics, feed conditions and process time) the rate of fouling is economically and environmentally unsustainable. For many, knowledge of the point below which no major irreversible fouling occurs (the critical flux) in a membrane separation will always be of greatest utility

Strengthening the Anonymity of Anonymous Communication Systems

In this work, we examine why a popular anonymity network, Tor, is vulnerable to timing side-channel attacks. We explore removing this vulnerability from Tor without sacrificing its low-latency which is important for usability. We find that Tor is vulnerable because inter-packet delays propagate along the network path from the source to the destination. This provides an easily detected signature. We explore techniques for making the timing signature either expensive or impossible to detect. If each packet took a unique, disjoint path from source to destination the inter-packet delay signature would be undetectable. Jitter and latency would change packet arrival orders. This is impractical since the overhead for constructing these circuits would be prohibitive. We scaled this idea back to reflect how the BitTorrent protocol creates a large number of possible paths from a small number of nodes. We form a fully connected network with the source, destination, and a small number of nodes. The number of paths through this network from source to destination grows quickly with the addition of each node. Paths do not have to include every node, so the delay of each path is different. By transmitting consecutive packets on different paths, the network delays will mask the inter-packet delay signature

S-band antenna phased array communications system

The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module

Structural changes in economics during the last fifty years

This essay portrays the major currents in recent economic thinking against the orthodoxy and dogmatism of neoclassical economics. It places behavioral economics, experimental economics, evolutionary economics, ecological economics, new institutional economics, agent-based computational economics and post-autistic economics vis-à-vis the classical and the neoclassical economics. It concludes that we may expect a synthesis of all these strands of economic thinking in the near future that will replace neoclassical economics from the citadel of mainstream. Teaching of these strands of new economics has already begun in many universities, although in an un-integrated manner. However, until the neoclassical microeconomics and macroeconomics are replaced by their alternatives and necessary as well as convincing tools of economic analysis are developed, neoclassicism would not give way to modern economics.Behavioral; experimental; evolutionary; ecological; new institutional; agent-based computational; post-autistic; classical; neoclassical, economics; bounded rationality; heterodox; individualism; pluralism

Thermal Management for High Power Cubesats

Thermal management systems for small satellites have traditionally been neglected entirely or only considered as an afterthought. This approach to small satellite systems design is no longer acceptable as technology has matured over the past decade and payload operational power has increased. Higher power leads to an increase in waste heat generated on-orbit. Trends in industry indicate that power demand for small satellite class (10-100 kg) can reach up to kilowatt range in the near future. A scalable Thermal Management System (TMS) has been developed which is applicable to small satellites ranging from CubeSats to ESPA class spacecraft. The TMS can handle up to 1 kW of waste heat. The TMS solution leverages breakthroughs in additive manufacturing, flexible heat pipes, and material science to dissipate extremely large quantities of waste heat in a small SWaP system. The system consists of: A rollout deployable radiator maximizing radiation of heat into space. Structurally integrated heat pipes for efficient heat transport; Energy storage based on a Phase Change Material (PCM) for mitigation of extreme temperature excursions to peak power The TMS is a modular system, flexible to be customized to particular mission requirements and spacecraft form factor. The paper discusses the TMS concept, components, and challenges. Performance evaluation is demonstrated. The TMS development has been sponsored by the United States Air Force Research Laboratory

Negative Evidence in Linguistics: The case of Wagiman Complex Predicates

In this thesis I will justify the use of negative forms of evidence as a permissible means of analysing grammatical constructions. I do this by presenting a test case, a grammatical construction that is not entirely understood, and attempting to understand and explain further aspects of it by appealing to negative forms of evidence. The constructions that form the object of this investigation are complex predicates in the Wagiman language. It will be necessary first, to provide a detailed explanation of Wagiman complex predicates; the elements that comprise them, the way those elements combine and the limitations that hold on them. Following that, negative evidence of the combinations that are possible and combinations that are impossible will provide the means by which to identify the constraints that limit complex predicates

Negative Evidence in Linguistics: The case of Wagiman Complex Predicates

In this thesis I will justify the use of negative forms of evidence as a permissible means of analysing grammatical constructions. I do this by presenting a test case, a grammatical construction that is not entirely understood, and attempting to understand and explain further aspects of it by appealing to negative forms of evidence. The constructions that form the object of this investigation are complex predicates in the Wagiman language. It will be necessary first, to provide a detailed explanation of Wagiman complex predicates; the elements that comprise them, the way those elements combine and the limitations that hold on them. Following that, negative evidence of the combinations that are possible and combinations that are impossible will provide the means by which to identify the constraints that limit complex predicates