Baffle aperture design study of hollow cathode equipped ion thrusters

A simple theoretical model which can be used as an aid in the design of the baffle aperture region of a hollow cathode equipped ion thruster was developed. An analysis of the ion and electron currents in both the main and cathode discharge chambers is presented. From this analysis a model of current flow through the aperture, which is required as an input to the design model, was developed. This model was verified experimentally. The dominant force driving electrons through the aperture was the force due to the electrical potential gradient. The diffusion process was modeled according to the Bolm diffusion theory. A number of simplifications were made to limit the amount of detailed plasma information required as input to the model to facilitate the use of the model in thruster design. This simplified model gave remarkably consistant results with experimental results obtained with a given thruster geometry over substantial changes in operating conditions. The model was uncertain to about a factor of two for different thruster cathode region geometries. The design usefulness was limited by this factor of two uncertainty and by the accuracy to which the plasma parameters required as inputs to the model were specified

New Roles for an Old Molecule in Axon-Glial Interaction

AbstractAxons need to be above a minimum size before they can be ensheathed by myelin-forming glia. But it has generally been assumed that the axonal signals that initiate myelination, whatever they are, would act similarly in both the CNS and the PNS. The surprising finding of Chan et al. in this issue of Neuron is that NGF can act as a regulator of ensheathment but that it has opposite effects on CNS and PNS axons

PIPE Dreams? The Performance of Companies Issuing Equity Privately

Private Investments in Public Equity (PIPEs) have become an important source of financing for young, publicly traded firms whose poor operating performance may limit alternative financing options. We propose that firms are motivated to sell these securities to minimize costs associated with asymmetric information. We find that both the security structure and the investor composition of a PIPE security matter in the subsequent performance of the issuing firm. Poor post-issuance performance is associated with securities where investors obtain significant repricing rights, which protect them from future stock price declines. Furthermore, companies that obtain financing from hedge funds tend to under-perform companies that obtain financing from other institutional investors. We argue that hedge funds act as investors of last resort, playing an important role in the market for young, high-risk firms with substantial asymmetric information. Hedge funds are willing to fund such high-risk companies because they can protect against possible price declines in the issuing companies by either negotiating PIPE securities with repricing rights or by entering into short positions of the underlying stocks of the issuing companies.

Politics, Engineering and Aridity—Sustainable Use of Water in Arizona

26 pages (includes illustrations)

Politics, Engineering and Aridity—Sustainable Use of Water in Arizona

26 pages (includes illustrations)

Ion thruster performance model

A model of ion thruster performance is developed for high flux density, cusped magnetic field thruster designs. This model is formulated in terms of the average energy required to produce an ion in the discharge chamber plasma and the fraction of these ions that are extracted to form the beam. The direct loss of high energy (primary) electrons from the plasma to the anode is shown to have a major effect on thruster performance. The model provides simple algebraic equations enabling one to calculate the beam ion energy cost, the average discharge chamber plasma ion energy cost, the primary electron density, the primary-to-Maxwellian electron density ratio and the Maxwellian electron temperature. Experiments indicate that the model correctly predicts the variation in plasma ion energy cost for changes in propellant gas (Ar, Kr and Xe), grid transparency to neutral atoms, beam extraction area, discharge voltage, and discharge chamber wall temperature. The model and experiments indicate that thruster performance may be described in terms of only four thruster configuration dependent parameters and two operating parameters. The model also suggests that improved performance should be exhibited by thruster designs which extract a large fraction of the ions produced in the discharge chamber, which have good primary electron and neutral atom containment and which operate at high propellant flow rates

Neither Fear Nor Favour, Affection Or Ill Will: Modernisation of care proceedings and the use and value of independent social work expertise to senior judges

This is part two of an evaluation of the work of independent social work experts (ISWs) in care proceedings (stage I was published in April 2012). It takes forward findings from stage I exploring further the evidential base for views put to the Family Justice Review about the practice of courts. It examines the views, experiences and practices of a sample of senior judges in commissioning ISW assessments, placing these in the context of the timing, format and value of local authority assessments. Finally, judges? views about the implications of the modernisation programme for use of ISWs are explored - in the light of a need for earlier completion of cases, without loss of quality in assessments, and with regard to issues of fairness, justice and transparency in judicial decision making. In the report each section is followed by a summary of findings reflecting the key issue for policy and practice. The study is based on interviews with 23 senior judges (20 DFJs, 3 Circuit Judges) in 20/43 county courts in England and Wales. Interviews were held between February and April 2013. They include representation from all circuits, and courts with small and high volume case loads (less than 115, 251 - 900 applications in 12 months). They hear applications from just over half of authorities in England (59%) and just over one third (36%) in Wales

The contribution of experts in care proceedings : evaluation of independent social work reports on care proceedings

Several concerns surround the use of independent social work (ISW) assessments in care proceedings. Some result from the exclusion of this work from a review of legal aid for expert assessments in this field, a cap on ISW fees, and fears about a resulting reduction in the availability of ISWs. At the same time, submissions to the Family Justice Review (FJR) claimed that ISWs cause delay, simply duplicate existing local authority assessments, add nothing new and undermine confidence in social work assessments. It was also said that ISW reports result from parents utilising human rights claims to gain a second opinion of a local authority assessment ? and to which courts too readily accede. ... But while strong views have been expressed about the use of independent social work assessments, there is little hard evidence. This evaluation, commissioned following submissions to the FJR, begins to address that lack. It is based on 65 cases concerning 121 children and 82 reports for courts in England and Wales. The sample was drawn from the records of three independent agencies providing ISWs