32,138 research outputs found
Field support, data analysis and associated research for the acoustic grenade sounding program
Temperature and horizontal winds in the 30 to 90 km altitude range of the upper atmosphere, were determined by acoustic grenade soundings conducted at Wallops Island, Virginia and Kourou, French Guiana. Field support provided at these locations included deployment of the large area microphone system, supervision, maintenance and operation of sound ranging stations; and coordination of activities. Data analysis efforts included the analysis of field data to determine upper atmospheric meteorological parameters. Profiles for upper atmospheric temperature, wind and density are provided in plots and tables for each of the acoustic grenade soundings conducted during the contract period. Research efforts were directed toward a systematic comparison of temperature data from acoustic grenade with other meteorological sensor probes in the upper atmosphere
Advanced Architectures for Astrophysical Supercomputing
Astronomers have come to rely on the increasing performance of computers to
reduce, analyze, simulate and visualize their data. In this environment, faster
computation can mean more science outcomes or the opening up of new parameter
spaces for investigation. If we are to avoid major issues when implementing
codes on advanced architectures, it is important that we have a solid
understanding of our algorithms. A recent addition to the high-performance
computing scene that highlights this point is the graphics processing unit
(GPU). The hardware originally designed for speeding-up graphics rendering in
video games is now achieving speed-ups of in general-purpose
computation -- performance that cannot be ignored. We are using a generalized
approach, based on the analysis of astronomy algorithms, to identify the
optimal problem-types and techniques for taking advantage of both current GPU
hardware and future developments in computing architectures.Comment: 4 pages, 1 figure, to appear in the proceedings of ADASS XIX, Oct 4-8
2009, Sapporo, Japan (ASP Conf. Series
Freely decaying turbulence in two-dimensional electrostatic gyrokinetics
In magnetized plasmas, a turbulent cascade occurs in phase space at scales
smaller than the thermal Larmor radius ("sub-Larmor scales") [Phys. Rev. Lett.
103, 015003 (2009)]. When the turbulence is restricted to two spatial
dimensions perpendicular to the background magnetic field, two independent
cascades may take place simultaneously because of the presence of two
collisionless invariants. In the present work, freely decaying turbulence of
two-dimensional electrostatic gyrokinetics is investigated by means of
phenomenological theory and direct numerical simulations. A dual cascade
(forward and inverse cascades) is observed in velocity space as well as in
position space, which we diagnose by means of nonlinear transfer functions for
the collisionless invariants. We find that the turbulence tends to a
time-asymptotic state, dominated by a single scale that grows in time. A theory
of this asymptotic state is derived in the form of decay laws. Each case that
we study falls into one of three regimes (weakly collisional, marginal, and
strongly collisional), determined by a dimensionless number D*, a quantity
analogous to the Reynolds number. The marginal state is marked by a critical
number D* = D0 that is preserved in time. Turbulence initialized above this
value become increasingly inertial in time, evolving toward larger and larger
D*; turbulence initialized below D0 become more and more collisional, decaying
to progressively smaller D*.Comment: 12 pages, 12 figures; replaced to match published versio
Origin and Dynamics of the Mutually Inclined Orbits of Upsilon Andromedae c and d
We evaluate the orbital evolution and several plausible origins scenarios for
the mutually inclined orbits of Upsilon Andromedae c and d. These two planets
have orbital elements that oscillate with large amplitudes and lie close to the
stability boundary. This configuration, and in particular the observed mutual
inclination, demands an explanation. The planetary system may be influenced by
a nearby low-mass star, Upsilon And B, which could perturb the planetary
orbits, but we find it cannot modify two coplanar orbits into the observed
mutual inclination of ~30 deg. However, it could incite ejections or collisions
between planetary companions that subsequently raise the mutual inclination to
>30 deg. Our simulated systems with large mutual inclinations tend to be
further from the stability boundary than Upsilon And, but we are able to
produce similar systems. We conclude that scattering is a plausible mechanism
to explain the observed orbits of Upsilon And c and d, but we cannot determine
whether the scattering was caused by instabilities among the planets themselves
or by perturbations from Upsilon And B. We also develop a procedure to
quantitatively compare numerous properties of the observed system to our
numerical models. Although we only implement this procedure to Upsilon And, it
may be applied to any exoplanetary system.Comment: 19 pages, 5 figures, accepted to Astrophysical Journa
Web 2.0 and micro-businesses: An exploratory investigation
This is the author's final version of the article. This article is (c) Emerald Group Publishing and permission has been granted for this version to appear here. Emerald does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from Emerald Group Publishing Limited.This article was chosen as a Highly Commended Award Winner at the Emerald Literati Network Awards for Excellence 2013.Purpose â The paper aims to report on an exploratory study into how small businesses use Web 2.0 information and communication technologies (ICT) to work collaboratively with other small businesses. The study had two aims: to investigate the benefits available from the use of Web 2.0 in small business collaborations, and to characterize the different types of such online collaborations.
Design/methodology/approach â The research uses a qualitative case study methodology based on semi-structured interviews with the owner-managers of 12 UK-based small companies in the business services sector who are early adopters of Web 2.0 technologies.
Findings â Benefits from the use of Web 2.0 are categorized as lifestyle benefits, internal operational efficiency, enhanced capability, external communications and enhanced service offerings. A 2Ă2 framework is developed to categorize small business collaborations using the dimensions of the basis for inter-organizational collaboration (control vs cooperation) and the level of Web 2.0 ICT use (simple vs sophisticated).
Research limitations/implications â A small number of firms of similar size, sector and location were studied, which limits generalizability. Nonetheless, the results offer a pointer to the likely future use of Web 2.0 tools by other small businesses.
Practical implications â The research provides evidence of the attraction and potential of Web 2.0 for collaborations between small businesses.
Originality/value â The paper is one of the first to report on use of Web 2.0 ICT in collaborative working between small businesses. It will be of interest to those seeking a better understanding of the potential of Web 2.0 in the small business community.WestFocu
Optimisation of confinement in a fusion reactor using a nonlinear turbulence model
The confinement of heat in the core of a magnetic fusion reactor is optimised
using a multidimensional optimisation algorithm. For the first time in such a
study, the loss of heat due to turbulence is modelled at every stage using
first-principles nonlinear simulations which accurately capture the turbulent
cascade and large-scale zonal flows. The simulations utilise a novel approach,
with gyrofluid treatment of the small-scale drift waves and gyrokinetic
treatment of the large-scale zonal flows. A simple near-circular equilibrium
with standard parameters is chosen as the initial condition. The figure of
merit, fusion power per unit volume, is calculated, and then two control
parameters, the elongation and triangularity of the outer flux surface, are
varied, with the algorithm seeking to optimise the chosen figure of merit. A
two-fold increase in the plasma power per unit volume is achieved by moving to
higher elongation and strongly negative triangularity.Comment: 32 pages, 8 figures, accepted to JP
Bibliography of titles of articles in the field of nuclear quadrupole resonance spectroscopy of solids
This bibliography lists the titles of literature articles in the field of nuclear quadrupole resonance spectroscopy of solids. This field has been taken to include the area of quadrupolar effects in nuclear magnetic resonance as well as 3 the basic area of nuclear quadrupole resonance in zero magnetic field. Articles published not later than January 1, 1958 have been included. Twenty-one journals are represented, and in addition, eleven books which contain chapters or sections dealing with this subject are included
Double potential step chronoamperometry at a microband electrode: Theory and experiment
Numerical simulation is used to characterise double potential step
chronoamperometry at a microband electrode for a simple redox process A + e-
goes to B, under conditions of full support such that diffusion is the only
active form of mass transport. The method is shown to be highly sensitive for
the measurement of the diffusion coefficient of both A and B, and is applied to
the one electron reduction of decamethylferrocene (DMFc), DMFc - e- goes to
DMFc+, in the room temperature ionic liquid 1-propyl-3-methylimidazolium
bistrifluoromethylsulfonylimide. Theory and experiment are seen to be in
excellent agreement and the following values of the diffusion coefficients were
measured at 298 K: D_(DMFc) = 2.50 x 10^(-7) cm^(2) s^(-1) and D_(DMFc+) = 9.50
x 10^(-8) cm^(2) s^(-1)
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