23,494 research outputs found
G181.1+9.5, a new high-latitude low-surface brightness supernova remnant
More than 90% of the known Milky Way supernova remnants are within 5 degrees
of the Galactic Plane. We present the discovery of the supernova remnant
G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing
survey of the Galactic Anti-centre High-Velocity Cloud complex, observed with
the DRAO Synthesis Telescope in the 21~cm radio continuum and HI spectral line.
We use radio continuum observations (including the linearly polarized
component) at 1420~MHz (observed with the DRAO ST) and 4850~MHz (observed with
the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its
nature as a SNR. High-resolution 21~cm HI line observations and HI emission and
absorption spectra reveal the physical characteristics of its local
interstellar environment. Finally, we estimate the basic physical parameters of
G181.1+9.5 using models for highly-evolved SNRs. G181.1+9.5 has a circular
shell-like morphology with a radius of about 16~pc at a distance of 1.5 kpc
some 250 pc above the mid-plane. The radio observations reveal highly linearly
polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data
reveal high-energy emission from the interior of G181.1+9.5 indicative of the
presence of shock-heated ejecta. The SNR is in the advanced radiative phase of
SNR evolution, expanding into the HVC inter-cloud medium with a density of
1^{-3}$. Basic physical attributes of G181.1+9.5 calculated with radiative
SNR models show an upper-limit age of 16,000 years, a swept-up mass of more
than 300 solar masses, and an ambient density in agreement with that estimated
from HI observations. G181.1+9.5 shows all characteristics of a typical mature
shell-type SNR, but its observed faintness is unusual and requires further
study.Comment: A&A accepted, 11 pages, 13 figure
Variable mixer propulsion cycle
A design technique, method and apparatus are delineated for controlling the bypass gas stream pressure and varying the bypass ratio of a mixed flow gas turbine engine in order to achieve improved performance. The disclosed embodiments each include a mixing device for combining the core and bypass gas streams. The variable area mixing device permits the static pressures of the core and bypass streams to be balanced prior to mixing at widely varying bypass stream pressure levels. The mixed flow gas turbine engine therefore operates efficiently over a wide range of bypass ratios and the dynamic pressure of the bypass stream is maintained at a level which will keep the engine inlet airflow matched to an optimum design level throughout a wide range of engine thrust settings
The Adsorption and Collapse Transitions in a Linear Polymer Chain near an Attractive Wall
We deduce the qualitative phase diagram of a long flexible neutral polymer
chain immersed in a poor solvent near an attracting surface using
phenomenological arguments. The actual positions of the phase boundaries are
estimated numerically from series expansion up to 19 sites of a self-attracting
self avoiding walk in three dimensions. In two dimensions, we calculate
analytically phase boundaries in some cases for a partially directed model.
Both the numerical as well as analytical results corroborate the proposed
qualitative phase diagram.Comment: 8 pages, 8 figures, revte
Gravitational waves in general relativity: XIV. Bondi expansions and the ``polyhomogeneity'' of \Scri
The structure of polyhomogeneous space-times (i.e., space-times with metrics
which admit an expansion in terms of ) constructed by a
Bondi--Sachs type method is analysed. The occurrence of some log terms in an
asymptotic expansion of the metric is related to the non--vanishing of the Weyl
tensor at Scri. Various quantities of interest, including the Bondi mass loss
formula, the peeling--off of the Riemann tensor and the Newman--Penrose
constants of motion are re-examined in this context.Comment: LaTeX, 28pp, CMA-MR14-9
Corner transfer matrix renormalization group method for two-dimensional self-avoiding walks and other O(n) models
We present an extension of the corner transfer matrix renormalisation group
(CTMRG) method to O(n) invariant models, with particular interest in the
self-avoiding walk class of models (O(n=0)). The method is illustrated using an
interacting self-avoiding walk model. Based on the efficiency and versatility
when compared to other available numerical methods, we present CTMRG as the
method of choice for two-dimensional self-avoiding walk problems.Comment: 4 pages 7 figures Substantial rewrite of previous version to include
calculations of critical points and exponents. Final version accepted for
publication in PRE (Rapid Communications
The competition of hydrogen-like and isotropic interactions on polymer collapse
We investigate a lattice model of polymers where the nearest-neighbour
monomer-monomer interaction strengths differ according to whether the local
configurations have so-called ``hydrogen-like'' formations or not. If the
interaction strengths are all the same then the classical -point
collapse transition occurs on lowering the temperature, and the polymer enters
the isotropic liquid-drop phase known as the collapsed globule. On the other
hand, strongly favouring the hydrogen-like interactions give rise to an
anisotropic folded (solid-like) phase on lowering the temperature. We use Monte
Carlo simulations up to a length of 256 to map out the phase diagram in the
plane of parameters and determine the order of the associated phase
transitions. We discuss the connections to semi-flexible polymers and other
polymer models. Importantly, we demonstrate that for a range of energy
parameters two phase transitions occur on lowering the temperature, the second
being a transition from the globule state to the crystal state. We argue from
our data that this globule-to-crystal transition is continuous in two
dimensions in accord with field-theory arguments concerning Hamiltonian walks,
but is first order in three dimensions
DEVELOPMENT OF A STOCHASTIC MODEL TO EVALUATE PLANT GROWERS' ENTERPRISE BUDGETS
Increased domestic concentration and international competition in the floricultural industry are forcing growers to improve resource management efficiency. Cost management and cost accounting methods are becoming key tools as growers attempt to reduce costs. These tools allow growers to allocate costs for each crop, increasing their greenhouse planning abilities. Growers have a relative high degree of risk due to potential crop and market failure. Individual growers have different tolerance for risk and risk bearing capacity. Growers need a cost accounting system that incorporates production and market risk, a system that allows them to make informed business decisions. The research reported in this paper developed a greenhouse budgeting model that incorporated risk to allow growers to compare production costs for flowers with different genetics and production technologies. This enables greenhouse growers to make production management decisions that incorporate production and market risk. The model gives growers the option of imputing their own production data to evaluate how various yield and price assumptions influence income and expense projections, and ultimately, profit. The model allows growers to compare total production cost and revenue varying grower type, production time, geographical location, operation size, and cost structure. The model evaluates budgets for growers who market to mass-market retail operations or wholesale intermediaries who sell to merchandisers or flower shops distribution channels. The model was demonstrated with sample data to illustrate how incorporating risk analysis into a grower's greenhouse budget model effects resource allocation and production decisions as compare to a budget model that does not incorporate risk. Deterministic and stochastic models were used to demonstrate differences in production decisions under various assumptions. The stochastic model introduced prices and flowering characteristics variability. The @Risk software was used to generate the random number simulation of the stochastic model, and stochastic dominance analysis was used to rank the alternatives. The result for both the deterministic and stochastic models identified the same cultivar as most profitable. However, there were differences in crop profits levels and rankings for subsequent cultivars that could influence growers' production choice decisions. The grower's risk aversion level influenced his/her choice of the most profitable cultivars in the stochastic model. The model summarizes the sources of variability that affect cost and revenue. The model enables the grower to measure effects that change in productivity might have on profit. Growers can identify items in their budget that have a greater effect on profitability, and make adjustments. The model can be used to allocate cost across activities, so the grower would be able to measure the economic impact of an item on the budget.Crop Production/Industries,
A Level-Set Hit-And-Run Sampler for Quasi-Concave Distributions
We develop a new sampling strategy that uses the hit-and-run algorithm within level sets of a target density. Our method can be applied to any quasi-concave density, which covers a broad class of models. Standard sampling methods often perform poorly on densities that are high-dimensional or multi-modal. Our level set sampler performs well in high-dimensional settings, which we illustrate on a spike-and-slab mixture model. We also extend our method to exponentially-tilted quasi-concave densities, which arise in Bayesian models consisting of a log-concave likelihood and quasiconcave prior density. We illustrate our exponentially-tilted level-set sampler on a Cauchy-normal model where our sampler is better able to handle a high-dimensional and multi-modal posterior distribution compared to Gibbs sampling and Hamiltonian Monte Carlo
GSM-enabled remote monitoring of rural handpumps: A proof-of-concept study
The continued expansion of mobile network coverage in rural Africa provides an opportunity for simple and low-cost hydroinformatic innovations to measure and transmit data on handpump use for policy and management improvements. We design, build and test a Waterpoint Data Transmitter to determine its robustness, functionality and scalability. Results demonstrate that this novel application using simple microprocessor, accelerometer and global system for mobile communications (GSM) components has significant potential in recording graduated time-step information flows of lever pumps which can be modelled into a reasonable water volume use approximation. Given the systemic informational deficit for rural waterpoints in Africa, where one in three handpumps is likely to be non-functioning, this innovation has the potential to provide universal, low-cost and immediate data to guide timely maintenance responses and planning decisions, as well as drive greater accountability and transparency in donor and government behaviour. © IWA Publishing 2012
Is silence golden? of mobiles, monitoring,and rural water supplies
Reliable and cost-effective monitoring of rural water supply infrastructure has long been hampered by the geographical curse of dispersed and low-income populations, and weak institutional performance. Recent advances in monitoring technology combined with mobile network expansion into rural areas has created an opportunity to bypass these seemingly intractable challenges. Mobile-enhanced technologies have the potential to produce data that is orders of magnitude richer, faster, and cheaper than that provided by traditional monitoring methods, which require costly field visits. However, more data does not equate to better data; information generated by crowdsourced and automated systems each has its respective limitations. We propose a framework for analysing monitoring and surveillance systems, which can help assess the strengths and weaknesses of different emerging approaches. We suggest that these advancements present an opportunity to fundamentally change the way we consider and conduct rural water supply monitoring. © Practical Action Publishing, 2012
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