15,527 research outputs found
Safer in the Clouds (Extended Abstract)
We outline the design of a framework for modelling cloud computing
systems.The approach is based on a declarative programming model which takes
the form of a lambda-calculus enriched with suitable mechanisms to express and
enforce application-level security policies governing usages of resources
available in the clouds. We will focus on the server side of cloud systems, by
adopting a pro-active approach, where explicit security policies regulate
server's behaviour.Comment: In Proceedings ICE 2010, arXiv:1010.530
Search for synchrotron emission from secondary leptons in dense cold starless cores
We report radio continuum observations with the Australia Telescope Compact
Array of two molecular clouds. The impetus for these observations is a search
for synchrotron radiation by cosmic ray secondary electrons/positrons in a
region of enhanced density and possibly high magnetic field. We present
modelling which shows that there should be an appreciable flux of synchrotron
above the more diffuse, galactic synchrotron background.
The starless core G333.125-0.562 and infrared source IRAS 15596-5301 were
observed at 1384 and 2368 MHz. For G333.125-0.562, we find no significant
levels of radio emission from this source at either frequency, nor any
appreciable polarisation: we place an upper limit on the radio continuum flux
from this source of 0.5 mJy per beam at both 1384 and 2368 MHz. Due to the
higher than expected flux density limits, we also obtained archival ATCA data
at 8640 MHz for this cloud and place an upper limit on the flux density of 50
micro-Jy per beam. Assuming the cosmic ray spectrum is similar to that near the
Sun, and given the cloud's molecular density and mass, we place an upper limit
on the magnetic field of 500 micro-G. IRAS 15596-5301, with an RMS of 50
micro-Jy per beam at 1384 MHz, shows an HII region consistent with optically
thin free-free emission already detected at 4800 MHz. We use the same
prescription as G333 to constrain the magnetic field from this cloud to be less
than 500 micro-G. We find that these values are not inconsistent with the view
that magnetic field values scale with the average density of the molecular
cloud.Comment: 6 pages, 5 pdf figures, accepted for publication in PAS
Recommended from our members
New safety model for the commercial human spaceflight industry
The aviation and space domains have safety guidelines and recommended practices for Design Organisations (DOs) and Operators alike. In terms of Aerospace DOs there are certification criteria to meet and to demonstrate compliance there are Advisory Circulars or Acceptable Means of Compliance to follow. Additionally there are guidelines such as Aerospace Recommended Practices (ARP), Military Standards (MIL-STD 882 series) and System Safety Handbooks to follow in order to identify and manage failure conditions. In terms of Operators there are FAA guidelines and a useful ARP that details many tools and techniques in understanding Operator Safety Risks. However there is currently no methodology for linking the DO and Operator safety efforts. In the space domain NASA have provided safety standards and guidelines to follow and also within Europe there are European Co-operation of Space Standardization (ECSS) to follow. Within the emerging Commercial Human Spaceflight Industry, the FAA’s Office of Commercial Space Transportation has provided hazard analysis guidelines. However all of these space domain safety documents are based on the existing aerospace methodology and once again, there is no link between the DO and Operator’s safety effort.
This paper addresses the problematic issue and presents a coherent methodology of joining up the System Safety effort of the DOs to the Operator Safety Risk Management such that a ‘Total System’ approach is adopted. Part of the rationale is that the correct mitigation (control) can be applied within the correct place in the accident sequence. Also this contiguous approach ensures that the Operator is fully aware of the safety risks (at the accident level) and therefore has an appreciation of the Total System Risk.
The authors of this paper contend that it is better practice to have a fully integrated safety model as opposed to disparate requirements or guidelines. Our methodology is firstly to review ‘best practice’ approaches from the aviation and space industries, and then to integrate these approaches into a contiguous safety model for the commercial human spaceflight industry
Supernova remnants and gamma-ray sources
A review of the possible relationship between gamma-ray sources and supernova
remnants (SNRs) is presented. Particular emphasis is given to the analysis of
the observational status of the problem of cosmic ray acceleration at SNR shock
fronts. All positional coincidences between SNRs and unidentified gamma-ray
sources listed in the Third EGRET Catalog at low Galactic latitudes are
discussed on a case by case basis. For several coincidences of particular
interest, new CO(J=1-0) and radio continuum maps are shown, and the mass
content of the SNR surroundings is determined. The contribution to the
gamma-ray flux observed that might come from cosmic ray particles (particularly
nuclei) locally accelerated at the SNR shock fronts is evaluated. We discuss
the prospects for future research in this field and remark on the possibilities
for observations with forthcoming gamma-ray instruments.Comment: Final version of a review article, to appear in the Physics Reports
(82 pages, 31 figures). Figures requiring high quality are just too large and
too many to be included here. Please download them from
http://www.angelfire.com/id/dtorres/down3.htm
Molecular Lines of 13 Galactic Infrared Bubble Regions
We investigated the physical properties of molecular clouds and star
formation processes around infrared bubbles which are essentially expanding HII
regions. We performed observations of 13 galactic infrared bubble fields
containing 18 bubbles. Five molecular lines, 12CO (J=1-0), 13CO (J=1-0),
C18O(J=1-0), HCN (J=1-0), and HCO+ (J=1-0), were observed, and several publicly
available surveys, GLIMPSE, MIPSGAL, ATLASGAL, BGPS, VGPS, MAGPIS, and NVSS,
were used for comparison. We find that these bubbles are generally connected
with molecular clouds, most of which are giant. Several bubble regions display
velocity gradients and broad shifted profiles, which could be due to the
expansion of bubbles. The masses of molecular clouds within bubbles range from
100 to 19,000 solar mass, and their dynamic ages are about 0.3-3.7 Myr, which
takes into account the internal turbulence pressure of surrounding molecular
clouds. Clumps are found in the vicinity of all 18 bubbles, and molecular
clouds near four of these bubbles with larger angular sizes show shell-like
morphologies, indicating that either collect-and-collapse or radiation-driven
implosion processes may have occurred. Due to the contamination of adjacent
molecular clouds, only six bubble regions are appropriate to search for
outflows, and we find that four of them have outflow activities. Three bubbles
display ultra-compact HII regions at their borders, and one of them is probably
responsible for its outflow. In total, only six bubbles show star formation
activities in the vicinity, and we suggest that star formation processes might
have been triggered.Comment: 55 Pages, 32 figures. Accepted for publication in A
Remote sensing data from CLARET: A prototype CART data set
The data set containing radiation, meteorological , and cloud sensor observations is documented. It was prepared for use by the Department of Energy's Atmospheric Radiation Measurement (ARM) Program and other interested scientists. These data are a precursor of the types of data that ARM Cloud And Radiation Testbed (CART) sites will provide. The data are from the Cloud Lidar And Radar Exploratory Test (CLARET) conducted by the Wave Propagation Laboratory during autumn 1989 in the Denver-Boulder area of Colorado primarily for the purpose of developing new cloud-sensing techniques on cirrus. After becoming aware of the experiment, ARM scientists requested archival of subsets of the data to assist in the developing ARM program. Five CLARET cases were selected: two with cirrus, one with stratus, one with mixed-phase clouds, and one with clear skies. Satellite data from the stratus case and one cirrus case were analyzed for statistics on cloud cover and top height. The main body of the selected data are available on diskette from the Wave Propagation Laboratory or Los Alamos National Laboratory
- …