A methodology for exploiting parallelism in the finite element process

A methodology is described for developing a parallel system using a top down approach taking into account the requirements of the user. Substructuring, a popular technique in structural analysis, is used to illustrate this approach

Design, development and use of the finite element machine

Some of the considerations that went into the design of the Finite Element Machine, a research asynchronous parallel computer are described. The present status of the system is also discussed along with some indication of the type of results that were obtained

The role of center vortices in Gribov's confinement scenario

The connection of Gribov's confinement scenario in Coulomb gauge with the center vortex picture of confinement is investigated. For this purpose we assume a vacuum wave functional which models the infrared properties of the theory and in particular shows strict confinement, i.e. an area law of the Wilson loop. We isolate the center vortex content of this wave functional by standard lattice methods and investigate their contributions to various static propagators of the Hamilton approach to Yang-Mills theory in Coulomb gauge. We find that the infrared properties of these quantities, in particular the infrared divergence of the ghost form factor, are dominated by center vortices.Comment: 18 pages, 5 figure

Terrestrial locomotion imposes high metabolic requirements on bats

The evolution of powered flight involved major morphological changes in Chiroptera. Nevertheless, all bats are also capable of crawling on the ground and some are even skilled sprinters. We asked if a highly derived morphology adapted for flapping flight imposes high metabolic requirements on bats when moving on the ground. We measured the metabolic rate during terrestrial locomotion in mastiff bats, Molossus currentium, a species that is both a fast-flying aerial-hawking bat and an agile crawler on the ground. Metabolic rates of bats averaged 8.0±4.0 ml CO2 min–1 during a 1-min period of sprinting at 1.3±0.6 km h–1. With rising average speed, mean metabolic rates increased, reaching peak values that were similar to those of flying conspecifics. Metabolic rates of M. currentium were higher than those of similar-sized rodents that sprinted at similar velocities under steady-state conditions. When M. currentium sprinted at peak velocities, its aerobic metabolic rate was 3–5 times higher than those of rodent species running continuously in steady-state conditions. Costs of transport (J kg–1 m–1) were more than 10 times higher for running than for flying bats. We conclude that at the same speed bats experience higher metabolic rates during short sprints than quadruped mammals during steady-state terrestrial locomotion, yet running bats achieve higher maximal mass-specific aerobic metabolic rates than non-volant mammals such as rodents

Thermal conduction and reduced cooling flows in galaxy clusters

Conduction may play an important role in reducing cooling flows in galaxy clusters. We analyse a sample of sixteen objects using Chandra data and find that a balance between conduction and cooling can exist in the hotter clusters (T > 5 keV), provided the plasma conductivity is close to the unhindered Spitzer value. In the absence of any additional heat sources, a reduced mass inflow must develop in the cooler objects in the sample. We fit cooling flow models to deprojected data and compare the spectral mass deposition rates found to the values required to account for the excess luminosity, assuming Spitzer-rate heat transfer over the observed temperature gradients. The mass inflow rates found are lower than is necessary to maintain energy balance in at least five clusters. However, emission from cooling gas may be partially absorbed. We also compute the flux supplied by turbulent heat transport (Cho et al. 2003) and find conductivity profiles which follow a strikingly similar temperature dependence to the conductivity values required to prevent cooling. Finally, we show that the cluster radio luminosities vary by over five orders of magnitude in objects with X-ray luminosities differing by no more than a factor of a few. This suggests that there is unlikely to be a straightforward correlation between the mechanical power provided by the radio lobes and the rate of energy loss in cooling flow clusters.Comment: Submitted to MNRA

Galaxy cluster mass profiles

Accurate measurements of the mass distribution in galaxy and cluster halos are essential to test the cold dark matter (CDM) paradigm. The cosmological model predicts a universal shape for the density profile in all halos, independent of halo mass. Its profile has a `cuspy' centre, with no evidence for the constant density core. In this paper we carry out a careful analysis of twelve galaxy clusters, using Chandra data to compute the mass distribution in each system under the assumption of hydrostatic equilibrium. Due to their low concentration, clusters provide ideal objects for studying the central cusps in dark matter halos. The majority of the systems are consistent with the CDM model, but 4 objects exhibit flat inner density profiles. We suggest that the flat inner profile found for these clusters is due to an underestimation of the mass in the cluster centre (rather than any problem with the CDM model), since these objects also have a centrally peaked gas mass fraction. We discuss possible causes for erroneously low mass measurements in the cores of some systems.Comment: 16 pages, 10 figures, 4 tables, accepted for publication in MNRA

The FEM-2 design method

The FEM-2 parallel computer is designed using methods differing from those ordinarily employed in parallel computer design. The major distinguishing aspects are: (1) a top-down rather than bottom-up design process; (2) the design considers the entire system structure in terms of layers of virtual machines; and (3) each layer of virtual machine is defined formally during the design process. The result is a complete hardware/software system design. The basic design method is discussed and the advantages of the method are considered. A status report on the FEM-2 design is included

Ultrasonic studies of the magnetic phase transition in MnSi

Measurements of the sound velocities in a single crystal of MnSi were performed in the temperature range 4-150 K. Elastic constants, controlling propagation of longitudinal waves reveal significant softening at a temperature of about 29.6 K and small discontinuities at $\sim$28.8 K, which corresponds to the magnetic phase transition in MnSi. In contrast the shear elastic moduli do not show any softening at all, reacting only to the small volume deformation caused by the magneto-volume effect. The current ultrasonic study exposes an important fact that the magnetic phase transition in MnSi, occurring at 28.8 K, is just a minor feature of the global transformation marked by the rounded maxima or minima of heat capacity, thermal expansion coefficient, sound velocities and absorption, and the temperature derivative of resistivity.Comment: 4 pages, 4 figure

Photoproduction of calcium-47*

The irradiation of highly enriched Ca 48co3 with a bremsstrahlung beam of maximum energy 46 Mev produced Ca47 with a yield of 1. 1 to 3 . O uc/mg Ca48 at half-saturation. The half-life of a sample measured through aluminum absorber to eliminate the contribution by the sc47 daughter was 4. 51 ±. 0 . 02 days . By comparison with the Cu63( 7, n)Cu62 reaction the integrated cross section from 0 to 46 Mev for the sum of the reactions ca48( 7, n)Ca47 and Ca48( 7\u27, p)K47 was calculated to be 29 Mev-mbarn. The Ca46 content of the sample calculated to the end of the bombardment was,.. 0. 040/o, probably the result of the Ca 48 ( ?\u27, 3n) and ( 7, p2n) reactions