A Numerical Treatment of Melt/Solid Segregation: Size of the Eucrite Parent Body and Stability of the Terrestrial Low-Velocity Zone

Crystal sinking to form cumulates and melt percolation toward segregation in magma pools can be treated with modifications of Stokes' and Darcy's laws, respectively. The velocity of crystals and melt depends, among other things, on the force of gravity (g) driving the separations and the cooling time of the environment. The increase of g promotes more efficient differentiation, whereas the increase of cooling rate limits the extent to which crystals and liquid can separate. The rate at which separation occurs is strongly dependent on the proportion of liquid that is present. As a result, cumulate formation is a process with a negative feedback; the more densely aggregated the crystals become, the slower the process can proceed. In contrast, melt accumulation is a process with a positive feedback; partial accumulation of melt leads to more rapid accumulation of subsequent melt. This positive feedback can cause melt accumulation to run rapidly to completion once a critical stability limit is passed. The observation of cumulates and segregated melts among the eucrite meteorites is used as a basis for calculating the g (and planet size) required to perform these differentiations. The eucrite parent body was probably at least 10-100 km in radius. The earth's low velocity zone (LVZ) is shown to be unstable with respect to draining itself of excess melt if the melt forms an interconnecting network. A geologically persistent LVZ with a homogeneous distribution of melt can be maintained with melt fractions only on the order of 0.1% or less

HRXRD study of the theoretical densities of novel reactive sintered boride candidate neutron shielding materials

Reactive Sintered Borides (RSBs) are novel borocarbide materials derived from FeCr-based cemented tungsten (FeCr-cWCs) show considerable promise as compact radiation armour for proposed spherical tokamak,[1],[2],[3],[4],[5]. Six candidate compositions (four RSBs, two cWCs) were evaluated by high-resolution X-ray diffraction (XRD), inductively coupled plasma (ICP), energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM) to determine the atomic composition, phase presence, and theoretical density. RSB compositions were evaluated with initial boron contents equivalent to 25 at% 30 at%. All RSB compositions showed delamination and carbon enrichment in the bulk relative to the surface, consistent with non-optimal binder removal and insufficient sintering time. Phase abundance within RSBs derived from powder XRD was dominated by iron tungsten borides (FeWB/FeW2B2), tungsten borides (W2B5/WB) and iron borides. The most optimal RSB composition (B5T522W) with respect to physical properties and highest ρ/ρtheo had ρtheo = 12.59 ± 0.01 g cm-3 for ρ/ρtheo = 99.3% and had the weigh-in and post-sintered W : B : Fe abundance closest to 1 : 1 : 1. This work indicates that despite their novelty, RSB materials can be optimized and in principle be processed using existing cWC processing routes

Constructing transportable behavioural models for nonlinear electronic devices

We use radial basis functions to model the input--output response of an electronic device. A new methodology for producing models that accuratly describe the response of the device over a wide range of operating points is introduced. A key to the success of the method is the ability to find a polynomial relationship between the model parameters and the operating points of the device.Comment: The file is in Revtex, it is 7 pages (two collumn format) with 13 figures in eps forma

Rapidly self-deoxygenating controlled radical polymerization in water via in situ disproportionation of Cu(i)

Rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. The disproportionation of Cu(I)/Me6Tren in water towards Cu(II) and highly reactive Cu(0) leads to O2-free reaction environments within the first seconds of the reaction, even when the reaction takes place in the open-air. By leveraging this significantly fast O2-reducing activity of the disproportionation reaction, a range of well-defined water-soluble polymers with narrow dispersity are attained in a few minutes or less. This methodology provides the ability to prepare block copolymers via sequential monomer addition with little evidence for chain termination over the lifetime of the polymerization and allows for the synthesis of star-shaped polymers with the use of multi-functional initiators. The mechanism of self-deoxygenation is elucidated with the use of various characterization tools, and the species that participate in the rapid oxygen consumption is identified and discussed in detail

Active Shooter Events: The Guardian Plan

The decision on how to protect the children and youth while at schools is a serious conversation with varying agreements on the best practices. Some feel that school personnel should not be trained nor expected to be able to react to an armed person while others believe that training of school personnel and allowing them to be armed will deter armed assailants in schools. Ultimately, each school board and district leadership need to choose an emergency safety plan that fits their community. The number of school shootings has brought emergency safety discussions to the forefront again. One school district, highlighted in this article, chose the implementation of a plan called the Guardian Plan

Managerial Power and Rent Extraction in the Design of Executive Compensation

This paper develops an account of the role and significance of managerial power and rent extraction in executive compensation. Under the optimal contracting approach to executive compensation, which has dominated academic re-search on the subject, pay arrangements are set by a board of directors that aims to maximize shareholder value. In contrast, the managerial power approach suggests that boards do not operate at arm's length in devising executive compensation arrangements; rather, executives have power to influence their own pay, and they use that power to extract rents. Furthermore, the desire to camouflage rent extraction might lead to the use of inefficient pay arrangements that provide suboptimal incentives and thereby hurt shareholder value. The authors show that the processes that produce compensation arrangements, and the various market forces and constraints that act on these processes, leave managers with considerable power to shape their own pay arrangements. Examining the large body of empirical work on executive compensation, the authors show that managerial power and the desire to camouflage rents can explain significant features of the executive compensation landscape, including ones that have long been viewed as puzzling or problematic from the optimal contracting perspective. The authors conclude that the role managerial power plays in the design of executive compensation is significant and should be taken into account in any examination of executive pay arrangements or of corporate governance generally.

Resource Allocation Contests: Experimental Evidence

Across many forms of rent seeking contests, the impact of risk aversion on equilibrium play is indeterminate. We design an experiment to compare individuals’ decisions across three contests which are isomorphic under risk-neutrality, but are typically not isomorphic under other risk preferences. The pattern of individual play across our contests is not consistent with a Bayes-Nash equilibrium for any distribution of risk preferences. We show that replacing the Bayes-Nash equilibrium concept with the quantal response equilibrium, along with heterogeneous risk preferences can produce equilibrium patterns of play that are very similar to the patterns we observe.rent seeking, experiments, risk aversion, game theory

Cured fish in Bangladesh. Report on a visit to Bangladesh, November 1990, on behalf of ODA Post-Harvest Fisheries Project, Bay of Bengal Programme, Madras, India

This report is based on a three week visit to Bangladesh in November 1990 by David Walker (Fish Processing and Infestation Technologist) and Martin Greeley (Marketing Economist) to examine the incidence of insect infestation in cured fish and report on both the technical and economic features of current insect control methods including the potential for improved post-harvest practices. The assignment was made on behalf of ODA for the Bay of Bengal Programme (BOBP) and included a debriefing visit to BOBP, Madras. In Bangladesh, the team included two local counterparts - S H Shamim, a socio-economist from a local research organisation, UBINIG, and Md Kador Ahmed an Inspector from the Chittagong Quality Control Office of the Department of Fisheries. The team made visits to cured fish production sites at Cox's Bazar and on islands in the Bay of Bengal including Sonadia, Dubla and Afatia Char. They observed production of cured fresh water fish in villages in Sunamganj district. They visited retail and wholesale markets in several towns including visits on three days to the major wholesale market for cured marine fish at Asadganj, Chittagong. These visits provided the opportunity to observe directly the problems of blowfly and beetle infestation and to discuss control practices with workers, managers, traders and entrepreneurs within the cured fish industry. In addition to the Ministry of Fisheries the team also visited a number of public sector agencies involved, inter alia, in research on or regulation of the Bangladesh fisheries. In practice there has been very little research or regulation of the cured fish industry. Indeed, there is not a comprehensive descriptive account of the location, organization and scale of cured fish production in Bangladesh. This is the justification for this report to include a fairly basic description of cured fish production in Bangladesh prior to discussion of insect infestation problems and controls. Many gaps remain in this description because of the lack of data on most aspects of the industry including the output levels for each product type; exported jewfish excepted. Beyond this general appreciation of the cured fish industry, the main focus of our visits and of this report is on control of insects and of possible project opportunities in this area. Our findings are that insect loss control practices being employed seem relatively effective and are economically beneficial given the sensitivity of price to quality. However, in some cases e.g. the non-approved use of DDT - current practice is potentially hazardous to the health of consumers with high measured residue levels in samples of cured fish purchased in the wholesale and retail market. There is very widespread use of dichlorvos, an insecticide similarly not approved for use on fish but there is some doubt whether a health hazard exists. Research on the potential hazards constitute the main recommendations of this mission and specific proposals have been incorporated in this report. Otherwise, no specific interventions are proposed. The socio-economic discussion highlights the difficulties of targeting project interventions to the benefit of the poor. Given the structure of economic interests in the cured fish industry, long-term programmes of human resource development and local institutional strengthening are necessary prerequisites for effective poverty alleviation programmes