Economic Impact of the Conservation Reserve Program in North Dakota

Environmental Economics and Policy, Land Economics/Use,

Financial, Managerial, and Attitudinal Characteristics of North Dakota Farm Families: Results of the 1986 Farm Survey

Agricultural Finance, Farm Management,

Rank-Ordering Statistics of Extreme Events: Application to the Distribution of Large Earthquakes

Rank-ordering statistics provides a perspective on the rare, largest elements of a population, whereas the statistics of cumulative distributions are dominated by the more numerous small events. The exponent of a power law distribution can be determined with good accuracy by rank-ordering statistics from the observation of only a few tens of the largest events. Using analytical results and synthetic tests, we quantify the systematic and the random errors. We also study the case of a distribution defined by two branches, each having a power law distribution, one defined for the largest events and the other for smaller events, with application to the World-Wide (Harvard) and Southern California earthquake catalogs. In the case of the Harvard moment catalog, we make more precise earlier claims of the existence of a transition of the earthquake magnitude distribution between small and large earthquakes; the $b$-values are $b_2 = 2.3 \pm 0.3$ for large shallow earthquakes and $b_1 = 1.00 \pm 0.02$ for smaller shallow earthquakes. However, the cross-over magnitude between the two distributions is ill-defined. The data available at present do not provide a strong constraint on the cross-over which has a $50\%$ probability of being between magnitudes $7.1$ and $7.6$ for shallow earthquakes; this interval may be too conservatively estimated. Thus, any influence of a universal geometry of rupture on the distribution of earthquakes world-wide is ill-defined at best. We caution that there is no direct evidence to confirm the hypothesis that the large-moment branch is indeed a power law. In fact, a gamma distribution fits the entire suite of earthquake moments from the smallest to the largest satisfactorily. There is no evidence that the earthquakes of the Southern California catalog have a distribution with tw

Disappearance of the extended main sequence turn-off in intermediate age clusters as a consequence of magnetic braking

Context. Extended main sequence turn-offs are features commonly found in the colour-magnitude diagrams of young and intermediate age (less than about 2 Gyr) massive star clusters, where the main sequence turn-off is broader than can be explained by photometric uncertainties, crowding, or binarity. Rotation is suspected to be the cause of this feature, by accumulating fast rotating stars, strongly affected by gravity darkening and rotation-induced mixing, near the main sequence turn-off. This scenario successfully reproduces the tight relation between the age and the actual extent in luminosity of the extended main sequence turn-off of observed clusters. Aims. Below a given mass (dependent on the metallicity), stars are efficiently braked early on the main sequence due to the interaction of stellar winds and the surface magnetic field, making their tracks converge towards those of non-rotating tracks in the Hertzsprung-Russell diagram. When these stars are located at the turn-off of a cluster, their slow rotation causes the extended main sequence turn-off feature to disappear. We investigate the maximal mass for which this braking occurs at different metallicities, and determine the age above which no extended main sequence turn-off is expected in clusters. Methods. We used two sets of stellar models (computed with two different stellar evolution codes: STAREVOL and the Geneva stellar evolution code) including the effects of rotation and magnetic braking, at three different metallicities. We implemented them in the SYCLIST toolbox to compute isochrones and then determined the extent of the extended main sequence turn-off at different ages. Results. Our models predict that the extended main sequence turn-off phenomenon disappears at ages older than about 2 Gyr. There is a trend with the metallicity, the age at which the disappearance occurs becoming older at higher metallicity. These results are robust between the two codes used in this work, despite some differences in the input physics and in particular in the detailed description of rotation-induced internal processes and of angular momentum extraction by stellar winds. Conclusions. Comparing our results with clusters in the Large Magellanic Cloud and Galaxy shows a very good fit to the observations. This strengthens the rotation scenario to explain the cause of the extended main sequence turn-off phenomenon

Resolving Vega and the inclination controversy with CHARA/MIRC

Optical and infrared interferometers definitively established that the photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u,v)-coverage, we find Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and also consistent with the possible rotational period of ~0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15 Msun and an age 700-75+150 Myrs, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z=0.006+0.003-0.002).Comment: Accepted for publication in ApJ Letter

Retarded long-range potentials for the alkali-metal atoms and a perfectly conducting wall

The retarded long-range potentials for hydrogen and alkali-metal atoms in their ground states and a perfectly conducting wall are calculated. The potentials are given over a wide range of atom-wall distances and the validity of the approximations used is established.Comment: RevTeX, epsf, 11 pages, 2 fig

High-precision calculations of dispersion coefficients, static dipole polarizabilities, and atom-wall interaction constants for alkali-metal atoms

The van der Waals coefficients for the alkali-metal atoms from Na to Fr interacting in their ground states, are calculated using relativistic ab initio methods. The accuracy of the calculations is estimated by also evaluating atomic static electric dipole polarizabilities and coefficients for the interaction of the atoms with a perfectly conducting wall. The results are in excellent agreement with the latest data from ultra-cold collisions and from studies of magnetic field induced Feshbach resonances in Na and Rb. For Cs we provide critically needed data for ultra-cold collision studies

The AMANDA Neutrino Telescope and the Indirect Search for Dark Matter

With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the first of a new generation of high energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We describe its performance, focussing on the capability to detect halo dark matter particles via their annihilation into neutrinos.Comment: Latex2.09, 16 pages, uses epsf.sty to place 15 postscript figures. Talk presented at the 3rd International Symposium on Sources and Detection of Dark Matter in the Universe (DM98), Santa Monica, California, Feb. 199

The heteronomy of choice architecture

Choice architecture is heralded as a policy approach that does not coercively reduce freedom of choice. Still we might worry that this approach fails to respect individual choice because it subversively manipulates individuals, thus contravening their personal autonomy. In this article I address two arguments to this effect. First, I deny that choice architecture is necessarily heteronomous. I explain the reasons we have for avoiding heteronomous policy-making and offer a set of four conditions for non-heteronomy. I then provide examples of nudges that meet these conditions. I argue that these policies are capable of respecting and promoting personal autonomy, and show this claim to be true across contrasting conceptions of autonomy. Second, I deny that choice architecture is disrespectful because it is epistemically paternalistic. This critique appears to loom large even against non-heteronomous nudges. However, I argue that while some of these policies may exhibit epistemically paternalistic tendencies, these tendencies do not necessarily undermine personal autonomy. Thus, if we are to find such policies objectionable, we cannot do so on the grounds of respect for autonomy