59,160 research outputs found
Continuity of the spectra for families of magnetic operators on Z^d
For families of magnetic self-adjoint operators on whose
symbols and magnetic fields depend continuously on a parameter , it
is shown that the main spectral properties of these operators also vary
continuously with respect to . The proof is based on an algebraic
setting involving twisted crossed product C*-algebras.Comment: 13 page
Effect of Night Blinds on Open Integral Display Cabinets
The impact of night blinds on the product temperature performance and electrical energy consumption of an integral open multi-deck cabinet is investigated in this paper. The cabinet was tested at various environmental conditions to establish the impact of ambient temperature on the effectiveness of the blind in reducing the energy consumption of the cabinet during night-time operation. The cabinet was tested over a range of temperatures between 20 °C and 35 °C at a constant moisture content. The results indicate that the use of night blinds could produce energy savings of between 10% and 22% calculated on the basis of a 24 hour period of operation with the blind lowered for 12 hours out of the 24 hours. These energy savings lead to pay-back periods of between 2 and 4 years. The savings reduced with increasing ambient temperature due to the increase in the impact of infiltration and conduction across the blind at higher temperatures
A spectral scheme for Kohn-Sham density functional theory of clusters
Starting from the observation that one of the most successful methods for
solving the Kohn-Sham equations for periodic systems -- the plane-wave method
-- is a spectral method based on eigenfunction expansion, we formulate a
spectral method designed towards solving the Kohn-Sham equations for clusters.
This allows for efficient calculation of the electronic structure of clusters
(and molecules) with high accuracy and systematic convergence properties
without the need for any artificial periodicity. The basis functions in this
method form a complete orthonormal set and are expressible in terms of
spherical harmonics and spherical Bessel functions. Computation of the occupied
eigenstates of the discretized Kohn-Sham Hamiltonian is carried out using a
combination of preconditioned block eigensolvers and Chebyshev polynomial
filter accelerated subspace iterations. Several algorithmic and computational
aspects of the method, including computation of the electrostatics terms and
parallelization are discussed. We have implemented these methods and algorithms
into an efficient and reliable package called ClusterES (Cluster Electronic
Structure). A variety of benchmark calculations employing local and non-local
pseudopotentials are carried out using our package and the results are compared
to the literature. Convergence properties of the basis set are discussed
through numerical examples. Computations involving large systems that contain
thousands of electrons are demonstrated to highlight the efficacy of our
methodology. The use of our method to study clusters with arbitrary point group
symmetries is briefly discussed.Comment: Manuscript submitted (with revisions) to Journal of Computational
Physic
Multi-Market Trading for Cooperative Resource Management: An Application to Water Pollution and Fisheries
Increasingly, environmental problems are recognized to involve linkages across multiple environmental variables (e.g., pollution and a fishery). Prior work on managing these complex, linked systems generally focuses on efficiency rather than implementation. However, implementation is important and will generally involve changing human behaviors within the multiple economic sectors that impact upon the multiple environmental variables. Tradable permit markets are generally seen as a coordinating mechanism, within a particular regulated sector, that enhances efficiency by incentivizing agents to respond to behavioral choices of others within the sector. However, prior work stops short of coordinating behaviors across multiple sectors for cases where society benefits from regulation in both sectors and one sector harms the other. We analyze a multi-sector permit market involving both the externality-generating sector and the affected sector. This multi-sector market provides a mechanism for agents in one sector to respond to environmental behaviors made within the other sector. Moreover, unlike traditional permit markets in which the regulated externality sector incurs only costs, we show that the multi-sector market generates efficiency gains that may be redistributed using appropriate allocations of initial endowments. Accordingly, the multi-sector market may generate gains that benefit both sectors, resulting in a win-win outcome for both sectors. We use a simple example of a polluted fishery to illustrate the approach.Permit trading, fisheries, pollution, Shapley values, bioeconomics, Environmental Economics and Policy, Resource /Energy Economics and Policy,
Liquid Crystal Polarimetry for Metastability Exchange Optical Pumping of 3He
We detail the design and operation of a compact, discharge light polarimeter
for metastability exchange optical pumping of 3He gas near 1 torr under a low
magnetic field. The nuclear polarization of 3He can be discerned from its
electron polarization, measured via the circular polarization of 668 nm
discharge light from an RF excitation. This apparatus measures the circular
polarization of this very dim discharge light using a nematic liquid crystal
wave retarder (LCR) and a high-gain, transimpedance amplified Si photodiode. We
outline corrections required in such a measurement, and discuss contributions
to its systematic error
Monoclinic and triclinic phases in higher-order Devonshire theory
Devonshire theory provides a successful phenomenological description of many
cubic perovskite ferroelectrics such as BaTiO3 via a sixth-order expansion of
the free energy in the polar order parameter. However, the recent discovery of
a novel monoclinic ferroelectric phase in the PZT system by Noheda et al.
(Appl. Phys. Lett. 74, 2059 (1999)) poses a challenge to this theory. Here, we
confirm that the sixth-order Devonshire theory cannot support a monoclinic
phase, and consider extensions of the theory to higher orders. We show that an
eighth-order theory allows for three kinds of equilibrium phases in which the
polarization is confined not to a symmetry axis but to a symmetry plane. One of
these phases provides a natural description of the newly observed monoclinic
phase. Moreover, the theory makes testable predictions about the nature of the
phase boundaries between monoclinic, tetragonal, and rhombohedral phases. A
ferroelectric phase of the lowest (triclinic) symmetry type, in which the
polarization is not constrained by symmetry, does not emerge until the
Devonshire theory is carried to twelfth order. A topological analysis of the
critical points of the free-energy surface facilitates the discussion of the
phase transition sequences.Comment: 10 pages, with 5 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/dv_pzt/index.htm
Hydrologic Properties of Subarctic Organic Soils
Completion Report
for
U. S. Forest Service
Institute of Northern Forestry
Cooperative Agreement No. 16 USC 581; 581a-581iThe need for understanding the natural system and how it responds
to various stresses is important; this is especially so in an environment
where the climate not only sustains permafrost, but develops
massive seasonal frost as well. Consequently, the role of the shallow
surface organic layer is also quite important. Since a slight change in
the soil thermal regime may bring about a phase change in the water or
ice, therefore, the system response to surface alterations such as
burning can be quite severe. The need for a better understanding of the
behavior and properties of the organic layer is, therefore, accentuated.
The central theme of this study was the examination of the hydrologic
and hydraulic properties of subarctic organic soils. Summarized
in this paper are the results of three aspects of subarctic organic soil
examinations conducted during the duration of the project. First, a
field site was set up in Washington Creek with the major emphasis on
measuring numerous variables of that soil system during the summer. The
greatest variations in moisture content occur in the thick organic soils
that exist at this site. Our major emphasis was to study the soil
moisture levels in these soils. This topic is covered in the first
major section, including associated laboratory studies. Those laboratory
studies include investigations of several hydraulic and hydrologic
properties of taiga organic and mineral soils. Second, some field data
on organic moisture levels was collected at the site of prescribed burns
in Washington Creek to ascertain the sustainability of fires as a function
of moisture levels. This portion of the study is described under the
second major heading. The last element of this study was a continued
application of the two-dimensional flow model that was developed in an
earlier study funded by the U. S. Forest Service, Institute of Northern
Forestry, and reported by Kane, Luthin, and Taylor (1975a).
Many of the results and concepts gathered in the field work were
integrated into the modeling effort, which is aimed at producing better
estimates of the hydrologic effects of surface disturbances in the black
spruce taiga subarctic ecosystem. This knowledge should also contribute
to better fire management decisions of the same system.The work upon which this report is based was made possible by a
cooperative aid agreement funded by the U. S. Forest Service, Institute
of Northern Forestry, Fairbanks, Alaska. Contribution to this study was
also made by Ohio State University
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