Radiating dipole model of interference induced in spacecraft circuitry by surface discharges

Spacecraft in geosynchronous orbit can be charged electrically to high voltages by interaction with the space plasma. Differential charging of spacecraft surfaces leads to arc and blowoff discharging. The discharges are thought to upset interior, computer-level circuitry. In addition to capacitive or electrostatic effects, significant inductive and less significant radiative effects of these discharges exist and can be modeled in a dipole approximation. Flight measurements suggest source frequencies of 5 to 50 MHz. Laboratory tests indicate source current strengths of several amperes. Electrical and magnetic fields at distances of many centimeters from such sources can be as large as tens of volts per meter and meter squared, respectively. Estimates of field attenuation by spacecraft walls and structures suggest that interior fields may be appreciable if electromagnetic shielding is much thinner than about 0.025 mm (1 mil). Pickup of such fields by wires and cables interconnecting circuit components could be a source of interference signals of several volts amplitude

LEO high voltage solar array arcing response model

A series of mathematical models were developed that describe the electrical behavior of a large solar cell array floating electrically in the low Earth orbit (LEO) space plasma and struck by an arc at a point of negative bias. There are now three models in this series: ARCII, which is a fully analytical, linearized model; ARCIII, which is an extension of ARCIII that includes solar cell inductance as well as load reactance; Nonlinear ARC, which is a numerical model able to treat effects such as non-linearized, i.e., logarithmic solar cell I/V characteristics, conductance switching as a solar cell crosses plasma ground on a voltage excursion and non-ohmic plasma leakage current collection

Circuit transients due to negative bias arcs on a high-voltage solar array in low Earth orbit

Arcing to negatively biased, exposed solar cell interconnects on solar arrays placed in plasma environments was established. Arcing, however, may cause damaging interference with the operation of electrical power systems in spacecraft planned to be driven with high-voltage solar arrays. An analytical model was developed to estimate the effects of netagive bias arcs on solar array power system performance. Solar cell characteristics, plasma interactions, and power system features are modeled by a linear, lumped element transient circuit, and the time domain equations are solved. Numerical results for solar array common mode and load voltage transients are calculated for typical conditions. Acceptable load transients are found for a range of arc current amplitudes and time constants

Storage tests of nitrogen tetroxide and hydrazine in aluminum containers

Nitrogen tetroxide and hydrazine compatibility with aluminum alloy storage tank

Migrating the CERN PS control system to IBM workstations

The workstations used within the control system of the CERN PS accelerator complex are not produced any more. We had therefore to review the software primary used as user interface and we achieved a port to IBM workstations. We are also preparing the maintenance of this code for the next ten years with minimal staff. This implies a clear separation between general computing facilities, control system developments, and operation. In order to share our experience, we will try to summarize various aspects of this migration: - system installation principles used to speed-up error recovery time and long-term maintenance costs, - problems correlated with the coexistence of two different platforms during migration, - software problems due to the platform and operating system changes, - hidden dependencies from a specific manufacturer

LEO high voltage solar array arcing response model, continuation 5

The modeling of the Debye Approximation electron sheaths in the edge and strip geometries was completed. Electrostatic potentials in these sheaths were compared to NASCAP/LEO solutions for similar geometries. Velocity fields, charge densities and particle fluxes to the biased surfaces were calculated for all cases. The major conclusion to be drawn from the comparisons of our Debye Approximation calculations with NASCAP-LEO output is that, where comparable biased structures can be defined and sufficient resolution obtained, these results are in general agreement. Numerical models for the Child-Langmuir, high-voltage electron sheaths in the edge and strip geometries were constructed. Electrostatic potentials were calculated for several cases in each of both geometries. Velocity fields and particle fluxes were calculated. The self-consistent solution process was carried through one cycle and output electrostatic potentials compared to NASCAP-type input potentials

State Vehicle Electrification Mandates and Federal Preemption

By requiring that new vehicles sold after a certain date be electric, states can lower drivers’ vehicle operating costs, boost local employment, and lower electric rates. But there’s a widespread perception that states can’t take advantage of these opportunities because a state vehicle electrification mandate would be preempted by federal law. Not so. While the Federal Clean Air Act (CAA) prohibits state regulations “relating to” the control of emissions in motor vehicles, and the Federal Energy Policy and Conservation Act (EPCA) prohibits state regulations “related to” fuel economy standards, there is a strong rationale for federal courts to reject preemption of state vehicle electrification mandates. The Supreme Court has indicated repeatedly that state laws regulating a product or process “upstream” that have an effect “downstream” are not preempted by the federal law. A state law conditioning construction of nuclear power plants on adequate means for storage and disposal of nuclear waste is not preempted by a federal law regulating nuclear plant safety, although its effect is to advance nuclear plant safety. A state ban on uranium mining is not preempted by a federal law on uranium milling and tailing safety, although its effect is to advance uranium milling and tailing safety. Similarly, a state law requiring that cars run on electricity should not be preempted by federal law on emissions and fuel economy standards, although its effect is to reduce emissions and improve fuel economy. Moreover, there is no conflict between a state vehicle electrification law and the purposes of the CAA and EPCA. The purpose of the Clean Air Act is to clean the air. The relevant purpose of the Energy Policy and Conservation Act is to reduce energy demand. Neither statute has a purpose of ensuring that new vehicles have at least some emissions, nor that they continue to use gasoline. This Article concludes that state vehicle electrification legislation should not be preempted. Neither the CAA nor the EPCA directly regulates how vehicles are powered. Neither statute explicitly prohibits states from mandating electrification of vehicles. And legal precedent limiting regulation of vehicles based on emissions or fuel economy standards has never addressed vehicle electrification mandates. Further, states have compelling reasons for vehicle electrification mandates that have nothing to do with regulating emissions or improving fuel economy standards. Such reasons may be sufficient to avoid preemption. The Supreme Court’s increasingly preemption-skeptical jurisprudence, as articulated in Virginia Uranium v. Warren, limits courts’ ability to scrutinize state motives in passing vehicle electrification statutes. Thus, although preemption cannot be dismissed as a concern, the stage has been set for state-based vehicle electrification mandates

An importance–competence analysis of the roles and competencies of e-tutors at an open distance learning institution.

This study investigates the role of the e-tutor within an open distance learning (ODL) higher education institution in terms of perceptions of the work roles and assessment of the competencies of the e-tutor. As part of the universities’ strategic plan the importance of providing excellent service to learners is strongly emphasised. E-tutors are the learner’s first and foremost contact with the university; they invariably become the face of the ODL university for the geographically distant learner. E-tutors are therefore strategically important for the perceived quality and attractiveness of the university, however, they can also be a vulnerable link in the university’s educational chain. The process of online tutoring therefore becomes a critical success factor in learners’ acceptance of e-learning. The first phase of this research focuses on the e-tutor’s perspective, investigating the competencies required by e-tutors to function effectively in an online environment, as well as their perceived role. A survey was administered to e-tutors in the College of Economic and Management Sciences of the university to assess their perceived roles and competencies. Understanding the importance of these roles and identifying necessary tutoring skills is paramount for the success of e-learning solutions.Human Resource Managemen

Observing collapse in two colliding dipolar Bose-Einstein condensates

We study the collision of two Bose-Einstein condensates with pure dipolar interaction. A stationary pure dipolar condensate is known to be stable when the atom number is below a critical value. However, collapse can occur during the collision between two condensates due to local density fluctuations even if the total atom number is only a fraction of the critical value. Using full three-dimensional numerical simulations, we observe the collapse induced by local density fluctuations. For the purpose of future experiments, we present the time dependence of the density distribution, energy per particle and the maximal density of the condensate. We also discuss the collapse time as a function of the relative phase between the two condensates.Comment: 6 pages, 7 figure

Robust Entanglement through Macroscopic Quantum Jumps

We propose an entanglement generation scheme that requires neither the coherent evolution of a quantum system nor the detection of single photons. Instead, the desired state is heralded by a {\em macroscopic} quantum jump. Macroscopic quantum jumps manifest themselves as a random telegraph signal with long intervals of intense fluorescence (light periods) interrupted by the complete absence of photons (dark periods). Here we show that a system of two atoms trapped inside an optical cavity can be designed such that a dark period prepares the atoms in a maximally entangled ground state. Achieving fidelities above 0.9 is possible even when the single-atom cooperativity parameter C is as low as 10 and when using a photon detector with an efficiency as low as eta = 0.2.Comment: 5 pages, 4 figures, more detailed discussion of underlying physical effect, references update