Scaling Studies Of Spheromak Formation And Equilibrium

Formation and equilibrium studies have been performed on the Swarthmore Spheromak Experiment (SSX). Spheromaks are formed with a magnetized coaxial plasma gun and equilibrium is established in both small (d(small)=0.16 m) and large (d(large)=3d(small)=0.50 m) copper flux conservers. Using magnetic probe arrays it has been verified that spheromak formation is governed solely by gun physics (in particular the ratio of gun current to flux, mu(0)I(gun)/Phi(gun)) and is independent of the flux conserver dimensions. It has also been verified that equilibrium is well described by the force free condition del xB=lambda B (lambda=constant), particularly early in decay. Departures from the force-free state are due to current profile effects described by a quadratic function lambda=lambda(psi). Force-free SSX spheromaks will be merged to study magnetic reconnection in simple magnetofluid structures. (C) 1998 American Institute of Physics

Generalized Ohm\u27s Law In A 3-D Reconnection Experiment

We report the measurement of non-ideal terms of the generalized Ohm\u27s law at a reconnection site of a weakly collisional laboratory magnetohydrodynamic plasma. Results show that the Hall term dominates the measured terms; resistive and electron inertia terms are small. We suggest that electron pressure (not measured) supports the observed quasistatic reconnection rate, and that anomalous resistivity, while not ruled out, is not required to account for the results

Three-Dimensional Structure Of Magnetic Reconnection In A Laboratory Plasma

The local three-dimensional structure of magnetic reconnection has been measured for the first time in a magnetohydrodynamic (MHD) laboratory plasma at the Swarthmore Spheromak Experiment. An array of 600 magnetic probes which resolve ion inertial length and MHD time scale dynamics on a single shot basis measured the magnetic structure of partial spheromak merging events. Counter-helicity spheromaks merge rapidly, and reconnection activity clearly self-generates a local component of B which breaks the standard 2D symmetry at the ion inertial scale. Consistent with prior results, no reconnection is observed for co-helicity merging

Decision making in NICE single technological appraisals (STAs): How does NICE incorporate patient perspectives?

The National Institute for Health and Care Excellence (NICE) provides guidance and recommendations on the use of new and existing medicines and treatments within the NHS, basing its decisions on a review of clinical and economic evidence principally, at least for STAs, provided by the drug manufacturer. The advice provided by NICE is aimed at overcoming the previously ad hoc, discretionary decisions in order to standardise access to healthcare technologies across England based on evidence. A Single Technological Appraisal (STA) is one element of NICE’s decision-making processes in which evidence about a selected technology (often medicines) is evaluated in 3 distinct phases (scoping, assessment and appraisal). In the last phase of this process an independent Appraisal Committee evaluates evidence in a meeting, partly held in public with the latter half taking place in a ‘closed’ session. During the meeting, the Appraisal Committee considers evidence based on clinical and cost-effectiveness, as well as from statements expressed by patients, commissioning experts and clinical specialists. The Institute encourages experts attending the meeting to provide both written and oral commentary about their personal view in the current management of the condition and the expected role and use of the technology – in particular how it might provide benefit to patients. Yet, NICE and its committees find themselves in a potentially incongruous position: how to take on board the experiential evidence from individual experts along with the evidence on cost-effectiveness when reaching a decision, about whether or not to recommend a treatment on cost-effectiveness grounds. This paper considers how NICE committees incorporate the views of patient perspectives in making rationing decisions about STAs. The findings from the study will discuss where points of tension / conflict arise during meetings and how Committee members navigate experiential accounts with scientific data, which types of patient perspectives are regarded favourably and which perspectives are treated with greater caution (tension between representing patients views vs tokenism), and will highlight how Committee members in fact reflect upon their own personal experience and background in the appraisal process, and thereby are at odds with retaining an element of neutrality in decision-making, as they contend with combining their own subjective views alongside considerations of rationing in the STA process. The analysis is drawn from an ESRC funded study which used an ethnographic approach to understand the decision making process within STAs involving three contrasting pharmaceutical products. Data collection methods included analysis of documentary evidence released by NICE, non-participant unstructured observations of nine STA meetings, and qualitative interviews with key informants (n=41) involved in each of the three case studies

Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma

Magnetic reconnection is widely believed responsible for heating the solar corona as well as for generating X-rays and energetic particles in solar flares. On astrophysical scales, reconnection in the intergalactic plasma is a prime candidate for a local source (Mpc) of cosmic rays exceeding the Greisen-Zatsepin-Kuzmin cutoff (∼10(19) eV). In a laboratory astrophysics experiment, we have made the first observation of particles accelerated by magnetic reconnection events to energies significantly above both the thermal and the characteristic magnetohydrodynamic energies. These particles are correlated temporally and spatially with the formation of three-dimensional magnetic structures in the reconnection region

Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33

We present far-ultraviolet (far-UV) images of the rich galaxy cluster ZwCl1358.1+6245, taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). When combined with archival HST observations, our data provide a measurement of the UV-to-optical flux ratio in 8 early-type galaxies at z=0.33. Because the UV flux originates in a population of evolved, hot, horizontal branch (HB) stars, this ratio is potentially one of the most sensitive tracers of age in old populations -- it is expected to fade rapidly with lookback time. We find that the UV emission in these galaxies, at a lookback time of 3.9 Gyr, is significantly weaker than it is in the current epoch, yet similar to that in galaxies at a lookback time of 5.6 Gyr. Taken at face value, these measurements imply different formation epochs for the massive ellipticals in these clusters, but an alternative explanation is a "floor" in the UV emission due to a dispersion in the parameters that govern HB morphology.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty and apjfonts.sty (included). Accepted for publication in ApJ Letter

Test Particle Acceleration In Three-Dimensional Magnetohydrodynamic Turbulence

We perform numerical experiments of test particle acceleration on turbulent magnetic and electric fields obtained from pseudospectral direct numerical solutions of the compressible three-dimensional MHD equations. We find consistent acceleration of the particles to many times the plasma characteristic (Alfven) speed and extended power laws in the density distribution of energies. Scaling laws of maximum and mean energy of particles with the nominal gyrofrequency and the MHD electric field are observed and a simple estimate is presented

Supercomputing with MPI meets the Common Workflow Language standards: an experience report

Use of standards-based workflows is still somewhat unusual by high-performance computing users. In this paper we describe the experience of using the Common Workflow Language (CWL) standards to describe the execution, in parallel, of MPI-parallelised applications. In particular, we motivate and describe the simple extension to the specification which was required, as well as our implementation of this within the CWL reference runner. We discuss some of the unexpected benefits, such as simple use of HPC-oriented performance measurement tools, and CWL software requirements interfacing with HPC module systems. We close with a request for comment from the community on how these features could be adopted within versions of the CWL standards.Comment: Submitted to 15th Workshop on Workflows in Support of Large-Scale Science (WORKS20

Experimental Observation Of Correlated Magnetic Reconnection And Alfvénic Ion Jets

Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfvenic. As the spheromaks form equilibria and decay, the flow is substantially reduced

The resurrection of group selection as a theory of human cooperation

Two books edited by members of the MacArthur Norms and Preferences Network (an interdisciplinary group, mainly anthropologists and economists) are reviewed here. These books in large part reflect a renewed interest in group selection that has occurred among these researchers: they promote the theory that human cooperative behavior evolved via selective processes which favored biological and/or cultural group-level adaptations as opposed to individual-level adaptations. In support of this theory, an impressive collection of cross-cultural data are presented which suggest that participants in experimental economic games often do not behave as self-interested income maximizers; this lack of self-interest is regarded as evidence of group selection. In this review, problems with these data and with the theory are discussed. On the data side, it is argued that even if a behavior seems individually-maladaptive in a game context, there is no reason to believe that it would have been that way in ancestral contexts, since the environments of experimental games do not at all resemble those in which ancestral humans would have interacted cooperatively. And on the theory side, it is argued that it is premature to invoke group selection in order to explain human cooperation, because more parsimonious individual-level theories have not yet been exhausted. In summary, these books represent ambitious interdisciplinary contributions on an important topic, and they include unique and useful data; however, they do not make a convincing case that the evolution of human cooperation required group selection