8,189 research outputs found
Evaluating Alternative Safety Net Programs in Alberta: A Firm-level Simulation Analysis
This paper examines alternative risk management strategies in terms of their effectiveness for three representative Alberta farm operations. Stochastic dynamic simulation methods are used to model financial performance for these farms, and alternative risk management programs are compared in terms of their ability to stabilize returns, support income and reduce the probability of bankruptcy. The results suggest that government programs such as the Net Income Stabilization Account (NISA) program or the Farm Income Disaster Program (FIDP) in Alberta have some benefits in terms of supporting income levels and reducing the chances of farm failure. Neither program is very effective, however, in stabilizing year to year income or cash flow for the farm operations. As a risk management program, FIDP is more effective than NISA but this improved performance comes at the price of higher government costs. Performance of NISA and FIDP, relative to alternative risk management programs and strategies such as forward contracting or crop insurance, is mixed. In some cases, NISA does not seem to provide benefits beyond those available from other strategies, while FIDP tends to perform better than the alternatives. Finally, while increased debt load weakens firm financial performance, NISA and FIDP still provide some benefits in terms of supporting income and reducing the probability of bankruptcy.Farm Management, Risk and Uncertainty,
Towards beating the curse of dimensionality for gravitational waves using Reduced Basis
Using the Reduced Basis approach, we efficiently compress and accurately
represent the space of waveforms for non-precessing binary black hole
inspirals, which constitutes a four dimensional parameter space (two masses,
two spin magnitudes). Compared to the non-spinning case, we find that only a
{\it marginal} increase in the (already relatively small) number of reduced
basis elements is required to represent any non-precessing waveform to nearly
numerical round-off precision. Most parameters selected by the algorithm are
near the boundary of the parameter space, leaving the bulk of its volume
sparse. Our results suggest that the full eight dimensional space (two masses,
two spin magnitudes, four spin orientation angles on the unit sphere) may be
highly compressible and represented with very high accuracy by a remarkably
small number of waveforms, thus providing some hope that the number of
numerical relativity simulations of binary black hole coalescences needed to
represent the entire space of configurations is not intractable. Finally, we
find that the {\it distribution} of selected parameters is robust to different
choices of seed values starting the algorithm, a property which should be
useful for indicating parameters for numerical relativity simulations of binary
black holes. In particular, we find that the mass ratios of
non-spinning binaries selected by the algorithm are mostly in the interval
and that the median of the distribution follows a power-law behavior
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
Epitaxial Frustration in Deposited Packings of Rigid Disks and Spheres
We use numerical simulation to investigate and analyze the way that rigid
disks and spheres arrange themselves when compressed next to incommensurate
substrates. For disks, a movable set is pressed into a jammed state against an
ordered fixed line of larger disks, where the diameter ratio of movable to
fixed disks is 0.8. The corresponding diameter ratio for the sphere simulations
is 0.7, where the fixed substrate has the structure of a (001) plane of a
face-centered cubic array. Results obtained for both disks and spheres exhibit
various forms of density-reducing packing frustration next to the
incommensurate substrate, including some cases displaying disorder that extends
far from the substrate. The disk system calculations strongly suggest that the
most efficient (highest density) packings involve configurations that are
periodic in the lateral direction parallel to the substrate, with substantial
geometric disruption only occurring near the substrate. Some evidence has also
emerged suggesting that for the sphere systems a corresponding structure doubly
periodic in the lateral directions would yield the highest packing density;
however all of the sphere simulations completed thus far produced some residual
"bulk" disorder not obviously resulting from substrate mismatch. In view of the
fact that the cases studied here represent only a small subset of all that
eventually deserve attention, we end with discussion of the directions in which
first extensions of the present simulations might profitably be pursued.Comment: 28 pages, 14 figures; typos fixed; a sentence added to 4th paragraph
of sect 5 in responce to a referee's comment
Total ozone changes in the 1987 Antarctic ozone hole
The development of the Antarctic ozone minimum was observed in 1987 with the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) instrument. In the first half of August the near-polar (60 and 70 deg S) ozone levels were similar to those of recent years. By September, however, the ozone at 70 and 80 deg S was clearly lower than any previous year including 1985, the prior record low year. The levels continued to decrease throughout September until October 5 when a new record low of 109 DU was established at a point near the South Pole. This value is 29 DU less than the lowest observed in 1985 and 48 DU less than the 1986 low. The zonal mean total ozone at 60 deg S remained constant throughout the time of ozone hole formation. The ozone decline was punctuated by local minima formed away from the polar night boundary at about 75 deg S. The first of these, on August 15 to 17, formed just east of the Palmer Peninsula and appears to be a mountain wave. The second major minimum formed on September 5 to 7 again downwind of the Palmer Peninsula. This event was larger in scale than the August minimum and initiated the decline of ozone across the polar region. The 1987 ozone hole was nearly circular and pole centered for its entire life. In previous years the hole was perturbed by intrusions of the circumpolar maximum into the polar regions, thus causing the hole to be elliptical. The 1987 hole also remained in place until the end of November, a few days longer than in 1985, and this persistence resulted in the latest time for recovery to normal values yet observed
Single Bidders and Tacit Collusion in Highway Procurement Auctions
Collusion in auctions can take different forms, one of which is refraining from bidding. Such behavior may be overt or tacit.Certain aspects of highway procurement auctions facilitate collusive outcomes. We collect data on asphalt paving auctions conducted by the Kentucky Transportation Cabinet from 2005 to 2007. We analyze both the bid participation decision and the pricing decision. We include variables that affect firm’s’ costs as well as variables that capture competitive and strategic effects. Most importantly, we determine the potential service area of each asphalt plant and use that information to determine the potential bidders for each paving project. We find that, in geographic markets with only a few feasible suppliers, county boundaries serve as a coordinating mechanism for softening competition, significantly influencing firms’ decisions whether and how much to bid
Negative Differential Resistivity and Positive Temperature Coefficient of Resistivity effect in the diffusion limited current of ferroelectric thin film capacitors
We present a model for the leakage current in ferroelectric thin- film
capacitors which explains two of the observed phenomena that have escaped
satisfactory explanation, i.e. the occurrence of either a plateau or negative
differential resistivity at low voltages, and the observation of a Positive
Temperature Coefficient of Resistivity (PTCR) effect in certain samples in the
high-voltage regime. The leakage current is modelled by considering a
diffusion-limited current process, which in the high-voltage regime recovers
the diffusion-limited Schottky relationship of Simmons already shown to be
applicable in these systems
Nonlinear Schroedinger Equation in the Presence of Uniform Acceleration
We consider a recently proposed nonlinear Schroedinger equation exhibiting
soliton-like solutions of the power-law form , involving the
-exponential function which naturally emerges within nonextensive
thermostatistics [, with ]. Since
these basic solutions behave like free particles, obeying , and (), it is relevant to investigate how they
change under the effect of uniform acceleration, thus providing the first steps
towards the application of the aforementioned nonlinear equation to the study
of physical scenarios beyond free particle dynamics. We investigate first the
behaviour of the power-law solutions under Galilean transformation and discuss
the ensuing Doppler-like effects. We consider then constant acceleration,
obtaining new solutions that can be equivalently regarded as describing a free
particle viewed from an uniformly accelerated reference frame (with
acceleration ) or a particle moving under a constant force . The latter
interpretation naturally leads to the evolution equation with .
Remarkably enough, the potential couples to , instead of coupling
to , as happens in the familiar linear case ().Comment: 4 pages, no figure
U.S. Agricultural Policy Effectiveness: An Analysis of Income and Capital Gain Returns Impacts
This paper examines the effects of agricultural policy upon the first three moments (mean, variance, and skewness) of aggregate farm income distributions. For the income variables examined, the program period distributions were positively skewed relative to the nonprogram period. However, it appears that the significant impact of the programs on risk reduction encourages the asset and product markets to shift the distribution of total returns toward asset appreciation rather than income enhancement
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