Analyzing Farmer Participation Intentions and Enrollment Rates for the Average Crop Revenue Election (ACRE) Program

The 2008 Farm Bill created the Average Crop Revenue Election (ACRE) program as a new commodity support program. Using a multinomial logit model to analyze a mail survey administered before the ACRE sign-up deadline, we identify factors driving farmer intentions regarding ACRE participation. Using a two-limit Tobit model to analyze actual county-level ACRE enrollment rates, we assess the effect of similar factors on actual farmer decisions. Results suggest that primary crops, risk perceptions, risk aversion, and program complexity were important factors. Farmer beliefs and attitudes also played key roles and were evolving during the months before the ACRE deadline.

Improved large-mode area endlessly single-mode photonic crystal fibers

We numerically study the possibilities for improved large-mode area endlessly single mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared to the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by ~30 % without a corresponding increase in the attenuation.Comment: 3 pages including 3 eps-figures. Accepted for Optics Letter

Mountain Pine Beetle Outbreaks in the Rocky Mountains: Regulators of Primary Productivity?

We consider the hypothesis that mountain pine beetles function as cybernetic regulators of primary productivity in ecosystems of lodgepole pine forest through their selective killing of dominant trees and the subsequent redistribution of resources. Following a recent major beetle outbreak in Yellowstone and Grand Teton national parks, surviving trees did grow significantly faster (P \u3c .1); wood production was redistributed among canopy, subcanopy, and understory trees; and annual wood production per hectare usually returned to pre-attack levels or exceeded them within 10-15 yr. However, reconstructions of annual wood production over the last 70-80 yr indicate that the beetle outbreak did not reduce the variation in productivity; rather, the beetles introduced more variation than would have existed in their absence. Hence, our results do not support the hypothesis that the beetles function as cybernetic regulators (in the strict sense). Nevertheless, the beetle-pine system that we studied shows great resilience, and the effects of beetles on primary productivity do not appear to be as severe as conventional wisdom maintains. Annual wood production per hectare returned quickly to previous levels in the stands we studied, and associated ecological changes can be considered generally benign or even beneficial

Water and Nutrient Outflow From Contrasting Lodgepole Pine Forests in Wyoming

Factors affecting water and nutrient outflow beyond the rooting zone were studied during a 3—yr period, using data from eight contrasting stands of lodgepole pine (Pinus contorta ssp. latifolia) forest in southeastern Wyoming and the output of a hydrologic simulation model (H2OTRANS) based on tree physiology. Nutrient outflow during a specific time period was estimated by multiplying simulated water outflow times element concentrations in the soil solution, the latter determined from samples collected periodically near the bottom of the rooting zone. Estimates of actual evapotranspiration (ET) for the period from early spring to late fall ranged from 21 to 53 cm, which was 33—95% (x = 73%) of total annual precipitation. For all stands and years, transpiration accounted for 50—61% of ET, and 9—44% of the transpiration occurred during the spring drainage period (vernal transpiration, VT). Estimated VT and outflow varied considerably among the stands, with VT accounting for 4—20% of the snow water. Outflow occurred only during the snow melt period and accounted for 0—80% of the snow water. Snow water equivalent varied annually by 300% or more. Nutrient outflow from the different stands also varied greatly. Ratios between simulated annual outflow and atmospheric inputs (bulk precipitation) were consistently \u3e1.0 for Ca, Na, and Mg; were consistently \u3c1.0 for N; and ranged from 0.3 to 2.0 for P and from 0.2 to 3.3 for K. Much of the variability in water and nutrient outflow can be attributed to the degree of biotic control, with water outflow affected by a different combination of factors than nutrient outflow. H2OTRANS was used to simulate the effects on outflow of different snow water equivalents and different total leaf areas. One result of the simulations was that nitrogen appears to be retained even at the highest levels of water outflow. Another was that increases in water outflow following reduction in leaf area were proportional to the leaf area removed. The results indicate that stands differing in site or habitat type experience different rates of water and element losses at different times during the snow melt season, and contribute differentially to streamwater quality and hydrograph shape. Factors affecting outflow are discussed in the context of successional trends, common perturbations including timber harvest, and hypotheses pertaining to nutrient conservation in terrestrial ecosystems. Nutrient retention in the snow—dominated lodgepole pine ecosystem appears to be primarily dependent on evergreen leaf area, duration of the VT period, and high carbon/nutrient ratios of the forest floor. Net losses of limiting nutrients probably occur primarily in pulses after abiotic perturbations such as fire

Kinetic pinning and biological antifreezes

Biological antifreezes protect cold-water organisms from freezing. An example are the antifreeze proteins (AFPs) that attach to the surface of ice crystals and arrest growth. The mechanism for growth arrest has not been heretofore understood in a quantitative way. We present a complete theory based on a kinetic model. We use the `stones on a pillow' picture. Our theory of the suppression of the freezing point as a function of the concentration of the AFP is quantitatively accurate. It gives a correct description of the dependence of the freezing point suppression on the geometry of the protein, and might lead to advances in design of synthetic AFPs.Comment: 4 pages, 4 figure

Locating the source of projectile fluid droplets

The ill-posed projectile problem of finding the source height from spattered droplets of viscous fluid is a longstanding obstacle to accident reconstruction and crime scene analysis. It is widely known how to infer the impact angle of droplets on a surface from the elongation of their impact profiles. However, the lack of velocity information makes finding the height of the origin from the impact position and angle of individual drops not possible. From aggregate statistics of the spatter and basic equations of projectile motion, we introduce a reciprocal correlation plot that is effective when the polar launch angle is concentrated in a narrow range. The vertical coordinate depends on the orientation of the spattered surface, and equals the tangent of the impact angle for a level surface. When the horizontal plot coordinate is twice the reciprocal of the impact distance, we can infer the source height as the slope of the data points in the reciprocal correlation plot. If the distribution of launch angles is not narrow, failure of the method is evident in the lack of linear correlation. We perform a number of experimental trials, as well as numerical calculations and show that the height estimate is insensitive to aerodynamic drag. Besides its possible relevance for crime investigation, reciprocal-plot analysis of spatter may find application to volcanism and other topics and is most immediately applicable for undergraduate science and engineering students in the context of crime-scene analysis.Comment: To appear in the American Journal of Physics (ms 23338). Improved readability and organization in this versio

Photon polarisation entanglement from distant dipole sources

It is commonly believed that photon polarisation entanglement can only be obtained via pair creation within the same source or via postselective measurements on photons that overlapped within their coherence time inside a linear optics setup. In contrast to this, we show here that polarisation entanglement can also be produced by distant single photon sources in free space and without the photons ever having to meet, if the detection of a photon does not reveal its origin -- the which way information. In the case of two sources, the entanglement arises under the condition of two emissions in certain spatial directions and leaves the dipoles in a maximally entangled state.Comment: 7 pages, 2 figures, revised version, accepted for publication in J. Phys.