1,697 research outputs found
Intertemporal Indicator Evaluation: A Preliminary Note on Problems for Evaluating Time Stream Data for Environmental Policy Analysis
Assumptions regarding the aggregation of time stream data (e.g. "discounting") are crucial in the evaluation of regional development proposals and the assessment of environmental impacts. Nonetheless, present practice reflects a great deal of confusion, ambiguity, caprice, and downright error in the calculation and implementation of such assumptions. We present in this paper the outlines of an approach to inter-temporal indicator evaluation for use in the analysis of regional development alternatives. Our ultimate objective is pragmatic: We wish to develop a practical framework for the reduction and comparison of time stream data for evaluation of public programs and policies. As a foundation for this approach, however, it has been necessary critically to review the existing controversy on intertemporal aggregation in a public policy context, and to clarify the practical implications of the, points at issue. Three interrelated themes pervade this review and provide a conceptual focus for the work
Study of solid 4He in two dimensions. The issue of zero-point defects and study of confined crystal
Defects are believed to play a fundamental role in the supersolid state of
4He. We report on studies by exact Quantum Monte Carlo (QMC) simulations at
zero temperature of the properties of solid 4He in presence of many vacancies,
up to 30 in two dimensions (2D). In all studied cases the crystalline order is
stable at least as long as the concentration of vacancies is below 2.5%. In the
2D system for a small number, n_v, of vacancies such defects can be identified
in the crystalline lattice and are strongly correlated with an attractive
interaction. On the contrary when n_v~10 vacancies in the relaxed system
disappear and in their place one finds dislocations and a revival of the
Bose-Einstein condensation. Thus, should zero-point motion defects be present
in solid 4He, such defects would be dislocations and not vacancies, at least in
2D. In order to avoid using periodic boundary conditions we have studied the
exact ground state of solid 4He confined in a circular region by an external
potential. We find that defects tend to be localized in an interfacial region
of width of about 15 A. Our computation allows to put as upper bound limit to
zero--point defects the concentration 0.003 in the 2D system close to melting
density.Comment: 17 pages, accepted for publication in J. Low Temp. Phys., Special
Issue on Supersolid
Further Observations on the Use of Lipocaic in the Treatment of Psoriasis11Read before the 3rd Annual Meeting of the Society for Investigative Dermatology, New York, June 11, 1940.
Zero-point vacancies in quantum solids
A Jastrow wave function (JWF) and a shadow wave function (SWF) describe a
quantum solid with Bose--Einstein condensate; i.e. a supersolid. It is known
that both JWF and SWF describe a quantum solid with also a finite equilibrium
concentration of vacancies x_v. We outline a route for estimating x_v by
exploiting the existing formal equivalence between the absolute square of the
ground state wave function and the Boltzmann weight of a classical solid. We
compute x_v for the quantum solids described by JWF and SWF employing very
accurate numerical techniques. For JWF we find a very small value for the zero
point vacancy concentration, x_v=(1.4\pm0.1) x 10^-6. For SWF, which presently
gives the best variational description of solid 4He, we find the significantly
larger value x_v=(1.4\pm0.1) x 10^-3 at a density close to melting. We also
study two and three vacancies. We find that there is a strong short range
attraction but the vacancies do not form a bound state.Comment: 19 pages, submitted to J. Low Temp. Phy
Annealing Effect for Supersolid Fraction in He
We report on experimental confirmation of the non-classical rotational
inertia (NCRI) in solid helium samples originally reported by Kim and Chan. The
onset of NCRI was observed at temperatures below ~400 mK. The ac velocity for
initiation of the NCRI suppression is estimated to be ~10 m/sec. After an
additional annealing of the sample at K for 12 hours, ~ 10% relative
increase of NCRI fraction was observed. Then after repeated annealing with the
same conditions, the NCRI fraction was saturated. It differs from Reppy's
observation on a low pressure solid sample.Comment: to be published in J. of Low Temp. Phys. (QFS2006 proceedings
Two-body correlations and the superfluid fraction for nonuniform systems
We extend the one-body phase function upper bound on the superfluid fraction
in a periodic solid (a spatially ordered supersolid) to include two-body phase
correlations. The one-body current density is no longer proportional to the
gradient of the one-body phase times the one-body density, but rather it
depends also on two-body correlation functions. The equations that
simultaneously determine the one-body and two-body phase functions require a
knowledge of one-, two-, and three-body correlation functions. The approach can
also be extended to disordered solids. Fluids, with two-body densities and
two-body phase functions that are translationally invariant, cannot take
advantage of this additional degree of freedom to lower their energy.Comment: 13 page
The PER model of abstract non-interference
Abstract. In this paper, we study the relationship between two models of secure information flow: the PER model (which uses equivalence relations) and the abstract non-interference model (which uses upper closure operators). We embed the lattice of equivalence relations into the lattice of closures, re-interpreting abstract non-interference over the lattice of equivalence relations. For narrow abstract non-interference, we show non-interference it is strictly less general. The relational presentation of abstract non-interference leads to a simplified construction of the most concrete harmless attacker. Moreover, the PER model of abstract noninterference allows us to derive unconstrained attacker models, which do not necessarily either observe all public information or ignore all private information. Finally, we show how abstract domain completeness can be used for enforcing the PER model of abstract non-interference
Effective theory for wall-antiwall system
We propose a useful method for deriving the effective theory for a system
where BPS and anti-BPS domain walls coexist. Our method respects an
approximately preserved SUSY near each wall. Due to the finite width of the
walls, SUSY breaking terms arise at tree-level, which are exponentially
suppressed. A practical approximation using the BPS wall solutions is also
discussed. We show that a tachyonic mode appears in the matter sector if the
corresponding mode function has a broader profile than the wall width.Comment: LaTeX file, 30 page, 5 eps figures, references adde
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