4,967 research outputs found
Gas Absorption Detected from the Edge-on Debris Disk Surrounding HD32297
Near-infrared and optical imaging of HD32297 indicate that it has an edge-on
debris disk, similar to beta Pic. I present high resolution optical spectra of
the NaI doublet toward HD32297 and stars in close angular proximity. A
circumstellar absorption component is clearly observed toward HD32297 at the
stellar radial velocity, which is not observed toward any of its neighbors,
including the nearest only 0.9 arcmin away. An interstellar component is
detected in all stars >90 pc, including HD32297, likely due to the interstellar
material at the boundary of the Local Bubble. Radial velocity measurements of
the nearest neighbors, BD+07 777s and BD+07 778, indicate that they are
unlikely to be physically associated with HD32297. The measured circumstellar
column density around HD32997, log N(NaI) ~ 11.4, is the strongest NaI
absorption measured toward any nearby main sequence debris disk, even the
prototypical edge-on debris disk, beta Pic. Assuming that the morphology and
abundances of the gas component around HD32297 are similar to beta Pic, I
estimate an upper limit to the gas mass in the circumstellar disk surrounding
HD32297 of ~0.3 M_Earth.Comment: 13 pages, 2 figures; Accepted for publication in ApJ Letter
Policy responses to invasive native species: issues of social and private benefits and costs
Farm and catchment managers in Australia face decisions about controlling invasive native species (or scrub) which may infest agricultural land. The treatment of this land to remove the infestation and re-establish native pastures is likely to be expensive for landholders. Yet there are potential social benefits from such remediation and so a policy question arises of what to do to about facilitating such change. New South Wales state government legislation addresses this issue through regulations, and the Catchment Management Authorities are responsible for administering public funds to achieve associated natural resource improvements. However, the extent of the private costs and social benefits associated with such changes are not known, which precludes benefit-cost analyses using the traditional welfare economics framework. This paper reports results of a social and private economic analysis of the impacts of a typical infestation remediation decision. We show that for the landholder the private costs exceed the benefits achieved from increased livestock productivity. However, there are social benefits expressed by the willingness to pay by members of the local catchment community for improvements in native vegetation and biodiversity. When these social benefits are included, the economic analysis shows a positive social net benefit. This raises questions of how to reconcile the public and private accounting, and whether any changes to policies, regulations or procedures for natural resource management in New South Wales are warranted.Invasive native scrub, environmental values, choice modelling, financial, economic, Namoi catchment,
Assessing the Benefits of Public Research Within an Economic Framework: The Case of USDA's Agricultural Research Service
Evaluation of publicly funded research can help provide accountability and prioritize programs. In addition, Federal intramural research planning generally involves an institutional assessment of the appropriate Federal role, if any, and whether the research should be left to others, such as universities or the private sector. Many methods of evaluation are available, peer review—used primarily for establishing scientific merit—being the most common. Economic analysis focuses on quantifying ultimate research outcomes, whether measured in goods with market prices or in nonmarket goods such as environmental quality or human health. However, standard economic techniques may not be amenable for evaluating some important public research priorities or for institutional assessments. This report reviews quantitative methods and applies qualitative economic reasoning and stakeholder interviewing methods to the evaluation of economic benefits of Federal intramural research using three case studies of research conducted by USDA’s Agricultural Research Service (ARS). Differences among the case studies highlight the need to select suitable assessment techniques from available methodologies, the limited scope for comparing assessment results across programs, and the inherent difficulty in quantifying benefits in some research areas. When measurement and attribution issues make it difficult to quantify these benefits, the report discusses how qualitative insights based on economic concepts can help research prioritization.Agricultural Research Service, Federal intramural research, publicly funded research, Environmental Economics and Policy, Food Consumption/Nutrition/Food Safety, Livestock Production/Industries, Productivity Analysis,
On the fundamental group of the complement of a complex hyperplane arrangement
We construct two combinatorially equivalent line arrangements in the complex
projective plane such that the fundamental groups of their complements are not
isomorphic. The proof uses a new invariant of the fundamental group of the
complement to a line arrangement of a given combinatorial type with respect to
isomorphisms inducing the canonical isomorphism of the first homology groups.Comment: 12 pages, Latex2e with AMSLaTeX 1.2, no figures; this last version is
almost the same as published in Functional Analysis and its Applications 45:2
(2011), 137-14
On a Site of X-ray Emission in AE Aquarii
An analysis of recently reported results of XMM-Newton observations of AE Aqr
within a hypothesis that the detected X-ray source is located inside the Roche
lobe of the white dwarf is presented. I show this hypothesis to be inconsistent
with the currently adopted model of mass-transfer in the system. Possible
solutions of this problem are briefly discussed.Comment: 4 pages, accepted for publication in ApJ Letter
Error Avoiding Quantum Codes and Dynamical Stabilization of Grover's Algorithm
An error avoiding quantum code is presented which is capable of stabilizing
Grover's quantum search algorithm against a particular class of coherent
errors. This error avoiding code consists of states only which are factorizable
in the computational basis. Furthermore, its redundancy is smaller than the one
which is achievable with a general error correcting quantum code saturating the
quantum Hamming bound. The fact that this code consists of factorizable states
only may offer advantages for the implementation of quantum gates in the error
free subspace
Prospects for the Characterization and Confirmation of Transiting Exoplanets via the Rossiter-McLaughlin Effect
The Rossiter-McLaughlin (RM) effect is the distortion of stellar spectral
lines that occurs during eclipses or transits, due to stellar rotation. We
assess the future prospects for using the RM effect to measure the alignment of
planetary orbits with the spin axes of their parent stars, and to confirm
exoplanetary transits. We compute the achievable accuracy for the parameters of
interest, in general and for the 5 known cases of transiting exoplanets with
bright host stars. We determine the requirements for detecting the effects of
differential rotation. For transiting planets with small masses or long periods
(as will be detected by forthcoming satellite missions), the velocity anomaly
produced by the RM effect can be much larger than the orbital velocity of the
star. For a terrestrial planet in the habitable zone of a Sun-like star found
by the Kepler mission, it will be difficult to use the RM effect to confirm
transits with current instruments, but it still may be easier than measuring
the spectroscopic orbit.Comment: 18 pages, 8 figures, one table. Minor changes. Accepted to ApJ, to
appear in the Jan 20, 2007 issue (v655
The Computational Complexity of Knot and Link Problems
We consider the problem of deciding whether a polygonal knot in 3-dimensional
Euclidean space is unknotted, capable of being continuously deformed without
self-intersection so that it lies in a plane. We show that this problem, {\sc
unknotting problem} is in {\bf NP}. We also consider the problem, {\sc
unknotting problem} of determining whether two or more such polygons can be
split, or continuously deformed without self-intersection so that they occupy
both sides of a plane without intersecting it. We show that it also is in NP.
Finally, we show that the problem of determining the genus of a polygonal knot
(a generalization of the problem of determining whether it is unknotted) is in
{\bf PSPACE}. We also give exponential worst-case running time bounds for
deterministic algorithms to solve each of these problems. These algorithms are
based on the use of normal surfaces and decision procedures due to W. Haken,
with recent extensions by W. Jaco and J. L. Tollefson.Comment: 32 pages, 1 figur
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