41,945 research outputs found
Determining the Nature of Late Gunn-Peterson Troughs with Galaxy Surveys
Recent observations have discovered long (up to ~110 Mpc/h), opaque
Gunn-Peterson troughs in the z ~ 5.5 Lyman-alpha forest, which are challenging
to explain with conventional models of the post-reionization intergalactic
medium. Here we demonstrate that observations of the galaxy populations in the
vicinity of the deepest troughs can distinguish two competing models for these
features: deep voids where the ionizing background is weak due to fluctuations
in the mean free path of ionizing photons would show a deficit of galaxies,
while residual temperature variations from extended, inhomogeneous reionization
would show an overdensity of galaxies. We use large (~550 Mpc/h) semi-numerical
simulations of these competing explanations to predict the galaxy populations
in the largest of the known troughs at z ~ 5.7. We quantify the strong
correlation of Lyman-alpha effective optical depth and galaxy surface density
in both models and estimate the degree to which realistic surveys can measure
such a correlation. While a spectroscopic galaxy survey is ideal, we also show
that a relatively inexpensive narrowband survey of Lyman-alpha-emitting
galaxies is ~90% likely to distinguish between the competing models.Comment: 12 pages, 16 figures. Submitted to Ap
Winners and Losers: Formula versus Competitive Funding of Agricultural Research
Research and Development/Tech Change/Emerging Technologies, O3, O4, Q16,
Adoption of Best Management Practices to Control Weed Resistance By Cotton, Corn, and Soybean Growers
This study examined adoption of ten best management practices (BMPs) to control weed resistance to herbicides. Using data from a survey of 1,205 U.S. cotton, corn, and soybean growers, count data models were estimated to explain the total number of practices frequently adopted. Ordered probit regressions were used to explain the frequency of individual BMP adoption. Growers practicing a greater number of BMPs frequently (a) had more education, but less farming experience; (b) grew cotton, (c) expected higher yields relative to the county average; and (d) farmed in counties with a lower coefficient of variation (CV) for yield of their primary crop. Yield expectations and variability were significant predictors of the frequency of adoption of individual BMPs. Most growers frequently adopted the same seven BMPs. Extension efforts may be more effective if they target a minority of growers and the three practices with low adoption rates. Counties with a high yield CV would be areas to look for low BMP adoption.weeds, herbicide, resistance management, corn, cotton, soybeans, adoption, Crop Production/Industries, Farm Management, Production Economics, Research and Development/Tech Change/Emerging Technologies, Q12, Q16,
Thermodynamic curvature measures interactions
Thermodynamic fluctuation theory originated with Einstein who inverted the
relation to express the number of states in terms of entropy:
. The theory's Gaussian approximation is discussed in most
statistical mechanics texts. I review work showing how to go beyond the
Gaussian approximation by adding covariance, conservation, and consistency.
This generalization leads to a fundamentally new object: the thermodynamic
Riemannian curvature scalar , a thermodynamic invariant. I argue that
is related to the correlation length and suggest that the sign of
corresponds to whether the interparticle interactions are effectively
attractive or repulsive.Comment: 29 pages, 7 figures (added reference 27
Scattered Lyman-alpha Radiation Around Sources Before Cosmological Reionization
The spectra of the first galaxies and quasars in the Universe should be
strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by
neutral hydrogen (HI) in the intervening intergalactic medium. However, the
Lyman-alpha line photons emitted by these sources are not eliminated but rather
scatter until they redshift out of resonance and escape due to the Hubble
expansion of the surrounding intergalactic HI. We calculate the resulting
brightness distribution and the spectral shape of the diffuse Lyman-alpha line
emission around high redshift sources, before the intergalactic medium was
reionized. Typically, the Lyman-alpha photons emitted by a source at z=10
scatter over a characteristic angular radius of order 15 arcseconds around the
source and compose a line which is broadened and redshifted by about a thousand
km/s relative to the source. The scattered photons are highly polarized.
Detection of the diffuse Lyman-alpha halos around high redshift sources would
provide a unique tool for probing the neutral intergalactic medium before the
epoch of reionization. On sufficiently large scales where the Hubble flow is
smooth and the gas is neutral, the Lyman-alpha brightness distribution can be
used to determine the cosmological mass densities of baryons and matter.Comment: 21 pages, 5 Postscript figures, accepted by ApJ; figures 1--3
corrected; new section added on the detectability of Lyman alpha halos;
conclusions update
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Improving Linear Weld Density in Ultrasonically Consolidated Parts
Ultrasonic consolidation is a novel additive manufacturing process with immense
potential for fabrication of complex shaped three-dimensional metallic objects from metal foils.
The proportion of bonded area to unbonded area along the layer interface, termed linear weld
density (LWD), is perhaps the most important quality attribute of ultrasonically consolidated
parts. Part mechanical properties largely depend on LWD and a high level of LWD must be
ensured in parts intended for load-bearing structural applications. It is therefore necessary to
understand what factors influence LWD or defect formation and devise methods to enhance bond
formation during ultrasonic consolidation. The current work examines these issues and proposes
strategies to ensure near 100% LWD in ultrasonically consolidated aluminum alloy 3003 parts.
The work elucidates the effects of various process parameters on LWD and a qualitative
understanding of the effects of process parameters on bond formation during ultrasonic
consolidation is presented. The beneficial effects of using elevated substrate temperatures and its
implications on overall manufacturing flexibility are discussed. A preliminary understanding of
defect morphologies and defect formation is presented, based on which a method (involving
surface machining) for minimizing defect incidence during ultrasonic consolidation is proposed
and demonstrated. Finally, trade-offs between part quality and build time are discussed.Mechanical Engineerin
Assessing Domestic Demand for Organic and ‘Locally Grown' Produce on An ‘Organic Island': Dominica's Dilemma
The economy of Dominica faces a unique set of challenges. As with many other Caribbean nations, Dominica has historically been dependent upon agriculture. Over the past several hundred years, the island's economy has been largely supported through the concentrated mono-cropping of a variety of export-oriented crops including coffee, limes, vanilla, and bananas (FAVACA, 2008). Today, approximately 45% of Dominica's labor force is employed in the agricultural sector (FAVACA, 2008). While neighboring countries have economically benefited from tourism, due to its lack of white sand beaches, Dominica is not a typical tourist destination. Taking advantage of its landscape, rainforests, and diversity of natural wildlife, in an effort to diversify its economy Dominica has instead catered to eco-/wellness tourists. Bridging its agricultural foundations with the ecological preservation needed to support its tourist industry, the government of Dominica has signaled its interest in transforming Dominica into an Organic Island (‘Organic Dominica') by 2015. Through this initiative, sustainable, organic agricultural production methods will be encouraged. Complementing this, a ‘Buy Organic, Locally Grown' campaign has been proposed to encourage domestic and regional consumption of Dominica's agricultural outputs and food products. As such, ‘Organic Dominica' has the potential to simultaneously address ongoing national concerns surrounding food security, foreign exchange availability, domestic un/underemployment, and environmental preservation. Before and since proposing this policy, surveys were conducted to identity the major stakeholders in (organic) agricultural production, and current and potential markets for organic production. It remains, however, to quantify Dominica's capacity to produce organic goods, the scale of the potential market, and the price premia that organic production could command. This information is critical to determining the appropriate initial level of producer support and marketing programs required to successfully promote the production and consumption of Dominica's organic outputs and propel Dominica toward the desired status of a model ‘Organic Island'.contingent valuation, willingness to pay, Caribbean, organic, locally grown, food, Agricultural and Food Policy, International Development, Marketing, O13, O54, Q01, Q13, Q18,
Valuing the Roundup Ready® Soybean Weed Management Program
This study examines soybean grower adoption of the Roundup Ready® (RR) weed management program with and without a residual herbicide application, and grower concerns regarding weed resistance to herbicides using telephone survey data from of 357 growers in 2007. It also estimates the pecuniary and non-pecuniary benefits enjoyed by growers from their RR program. The results indicate that soybean growers planned to treat 29 percent of their RR acres with a residual herbicide in 2008. More than half (53%) of the growers survey were concerned about weed resistance. The estimated expected benefit of the RR program in 2008 was 727 million with 75.7 million acres of soybean in the U.S. in 2008. The estimated value per acre of the RR program with and without a residual was 12.83. The estimates also suggest that if growers were not using residual herbicides with the RR program, their benefits would be 28.4% lower. Alternatively, if all growers were required to use residual herbicides on their RR acres, the value of the RR program would be 46% lower. Simply increasing grower weed resistance concerns could increase residual herbicide use on RR acres by up to 7%. The same increase in residual herbicide use could be accomplished by decreasing the cost of residual herbicide applications on RR acres by $0.81 per acre.Roundup Ready, Soybean, Glyphosate, Weed Resistance, Benefits, Crop Production/Industries, Demand and Price Analysis, Farm Management, Research and Development/Tech Change/Emerging Technologies,
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