No Transition Disk? Infrared Excess, PAH, H-2, And X-Rays From The Weak-Lined T Tauri Star DoAr 21

As part of a program to understand disk dispersal and the interplay between circumstellar disks and X-ray emission, we present new high-resolution mid-infrared (IR) imaging, high-resolution optical spectroscopy, and Chandra grating X-ray spectroscopy of the weak-lined T Tauri star DoAr 21. DoAr 21 (age \u3c 10(6) yr and mass similar to 2.2M(circle dot) based on evolutionary tracks) is a strong X-ray emitter, with conflicting evidence in the literature about its disk properties. It shows weak but broad H alpha emission (reported here for the first time since the 1950s); polarimetric variability; polycyclic aromatic hydrocarbon (PAH) and H-2 emission; and a strong, spatially resolved 24 mu m excess in archival Spitzer photometry. Gemini sub-arcsecond-resolution 9-18 mu m images show that there is little or no excess mid-IR emission within 100 AU of the star; the excess emission is extended over several arcseconds and is quite asymmetric. The extended emission is bright in the ultraviolet (UV)-excited lambda = 11.3 mu m PAH emission feature. A new high-resolution X-ray grating spectrum from Chandra shows that the stellar X-ray emission is very hard and dominated by continuum emission; it is well fit by a multi-temperature thermal model, typical of hard coronal sources, and shows no evidence of unusually high densities. A flare during the X-ray observation shows a temperature approaching 10(8) K. We argue that the far-UV emission from the transition region is sufficient to excite the observed extended PAH and continuum emission, and that the H-2 emission may be similarly extended and excited. While this extended emission may be a disk in the final stages of clearing, it also could be more akin to a small-scale photodissociation region than a protoplanetary disk, highlighting both the very young ages (\u3c10(6) yr) at which some stars are found without disks and the extreme radiation environment around even late-type pre-main-sequence stars

Contract and Exit Decisions in Finisher Hog Production

Finisher hog production in North America has seen a shift toward larger production units and contract-organized production since circa 1990. Given the efficiency gains and conversion costs associated with contract production, growers may have to choose between long term commitment through investments and atrophy with intent to exit in the intermediate term. A model is developed to show that growers with any of three efficiency attributes (lower innate hazard of exit, variable costs, or fixed contract adoption costs) are not only more likely to contract but will also produce more and expend more on lowering business survival risks. Using the 2004 U.S. Agricultural Resource Management Survey for hogs, a recursive bivariate probit model is estimated in which exit is affected directly, and also indirectly through the contract decision. It is confirmed that contracting producers are less likely to exit. Greater specialization and regional effects are important in increasing the probability of contracting. More education, having non-farm income and older production facilities are significant in increasing the expected rate of exit. The findings suggest further exits by non-contract producers.agricultural industrialization, hog production, occupation choice, production contracts, recursive bivariate probit, relationship-specific investments, sector dynamics., Agricultural and Food Policy, Demand and Price Analysis, Production Economics, D23, Q12, J26, J43.,

Systemic Failure in the Provision of Safe Food

Many deficiencies in the capacity of a food system to deliver safe products are systemic in nature. We suggest a taxonomy of four general ways in which a systemic failure might occur. One relates to the connectedness, or topology, of the system. Another arises from mistrust on the part of downstream parties concerning signals on product attributes, production processes, and the performance of regulatory mechanisms. A third arises when asymmetric information leads to low incentives for preserving food quality. Finally, inflexibilities in adapting to different states of nature may leave the system vulnerable to failures. Innovations in information technology and institutional design may ameliorate many problems, while appropriate trade, industrial organization, science, and public infrastructure policies also may fortify the system.

Quality Dispersion Among Organic Milk Channels

The most widely used measure of milk hygiene is Somatic Cell Count (SCC), where low SCC values indicate more wholesome milk. Dirt, often associated with grazing, carry bacteria and these bacteria can cause mastitis. Milk from cows with mastitis generally has higher SCC levels and cows with mastitis are most readily treated with antibiotics. Milk with high SCC is penalized by distributers as it is difficult to process and is not considered as wholesome in fluid markets. Grazing cows is common for many organic farmers. However, regulators prohibit antibiotic use under organic production. Intensive management protocols, maintaining equipment, and closely managing the herd’s environment offer substitutes for antibiotics use. Organic milk carries with it a substantial premium but may be at higher risk of discounts or penalties if the milk is more likely to have higher SCC levels. There are two forces at play concerning the quality of organic milk relative to conventional milk. For one, required and proscribed production practices create significant problems when managing milk quality. Secondly, a large premium exists to produce organic milk of high quality. This research seeks to better understand these and other determinants of SCC for conventional milk and for organic milk.milk, organic, quality, quantile, Food Consumption/Nutrition/Food Safety, Livestock Production/Industries,

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

Positron annihilation induced Auger electron spectroscopy

Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions

Window Characterization at 1550 nm

Author Institution: Los Alamos National LaboratoryAuthor Institution: Sandia National LaboratoriesSlides presented at the Heterodyne Velocimeter Workshop held at Lawrence Livermore National Laboratory, Livermore, California, July 20-21, 2006

Probing the exchange field of a quantum-dot spin valve by a superconducting lead

Electrons in a quantum-dot spin valve, consisting of a single-level quantum dot coupled to two ferromagnetic leads with magnetizations pointing in arbitrary directions, experience an exchange field that is induced on the dot by the interplay of Coulomb interaction and quantum fluctuations. We show that a third, superconducting lead with large superconducting gap attached to the dot probes this exchange field very sensitively. In particular, we find striking signatures of the exchange field in the symmetric component of the supercurrent with respect to the bias voltage applied between the ferromagnets already for small values of the ferromagnets' spin polarization.Comment: published version, 10 pages, 7 figure