13,276 research outputs found
Predicting adaptive responses - simulating occupied environments
Simulation of building performance is increasingly being used in design practice to predict comfort of occupants in finished buildings. This is an area of great uncertainty: what actions does a person take when too warm or suffering from glare; how is comfort measured; how do groups of people interact to control environmental conditions, etc? An increasing attention to model these issues is evident in current research. Two issues are covered in this paper: how comfort can be assessed and what actions occupants are likely to make to achieve and maintain a comfortable status. The former issue describes the implementation of existing codes within a computational framework. This is non-trivial as information on local air velocities, radiant temperature and air temperature and relative humidity have to be predicted as they evolve over time in response to changing environmental conditions. This paper also presents a nascent algorithm for modelling occupant behaviour with respect to operable windows. The algorithm is based on results of several field studies which show the influence of internal and external temperatures on decision making in this respect. The derivation and implementation of the algorithm is discussed, highlighting areas where further effort could be of benefit
Jack polynomials with prescribed symmetry and hole propagator of spin Calogero-Sutherland model
We study the hole propagator of the Calogero-Sutherland model with SU(2)
internal symmetry. We obtain the exact expression for arbitrary non-negative
integer coupling parameter and prove the conjecture proposed by one of
the authors. Our method is based on the theory of the Jack polynomials with a
prescribed symmetry.Comment: 12 pages, REVTEX, 1 eps figur
Area products for stationary black hole horizons
Area products for multi-horizon stationary black holes often have intriguing
properties, and are often (though not always) independent of the mass of the
black hole itself (depending only on various charges, angular momenta, and
moduli). Such products are often formulated in terms of the areas of inner
(Cauchy) horizons and outer (event) horizons, and sometimes include the effects
of unphysical "virtual" horizons. But the conjectured mass-independence
sometimes fails. Specifically, for the Schwarzschild-de Sitter [Kottler] black
hole in (3+1) dimensions it is shown by explicit exact calculation that the
product of event horizon area and cosmological horizon area is not mass
independent. (Including the effect of the third "virtual" horizon does not
improve the situation.) Similarly, in the Reissner-Nordstrom-anti-de Sitter
black hole in (3+1) dimensions the product of inner (Cauchy) horizon area and
event horizon area is calculated (perturbatively), and is shown to be not mass
independent. That is, the mass-independence of the product of physical horizon
areas is not generic. In spherical symmetry, whenever the quasi-local mass m(r)
is a Laurent polynomial in aerial radius, r=sqrt{A/4\pi}, there are
significantly more complicated mass-independent quantities, the elementary
symmetric polynomials built up from the complete set of horizon radii (physical
and virtual). Sometimes it is possible to eliminate the unphysical virtual
horizons, constructing combinations of physical horizon areas that are mass
independent, but they tend to be considerably more complicated than the simple
products and related constructions currently being mooted in the literature.Comment: V1: 16 pages; V2: 9 pages (now formatted in PRD style). Minor change
in title. Extra introduction, background, discussion. Several additional
references; other references updated. Minor typos fixed. This version
accepted for publication in PRD; V3: Minor typos fixed. Published versio
Polarization-sensitive absorption of THz radiation by interacting electrons in chirally stacked multilayer graphene
We show that opacity of a clean multilayer graphene flake depends on the
helicity of the circular polarized electromagnetic radiation. The effect can be
understood in terms of the pseudospin selection rules for the interband optical
transitions in the presence of exchange electron-electron interactions which
alter the pseudospin texture in momentum space. The interactions described
within a semi-analytical Hartree--Fock approach lead to the formation of the
topologically different broken--symmetry states characterized by Chern numbers
and zero-field anomalous Hall conductivities.Comment: 6 pages, final versio
Coherent control of Snell's law at metasurfaces
It was recently demonstrated that the well-known Snell's law must be corrected for phase gradient metasurfaces to account for their spatially varying phase, leading to normal and anomalous transmission and reflection of light on such metasurfaces. Here we show that the efficiency of normal and anomalous transmission and reflection of light can be controlled by the intensity or phase of a second coherent wave. The phenomenon is illustrated using gradient metasurfaces based on V-shaped and rectangular apertures in a metal film. This coherent control effect can be exploited for wave front shaping and signal routing
On the Eigenvalue Density of Real and Complex Wishart Correlation Matrices
Wishart correlation matrices are the standard model for the statistical
analysis of time series. The ensemble averaged eigenvalue density is of
considerable practical and theoretical interest. For complex time series and
correlation matrices, the eigenvalue density is known exactly. In the real
case, however, a fundamental mathematical obstacle made it forbidingly
complicated to obtain exact results. We use the supersymmetry method to fully
circumvent this problem. We present an exact formula for the eigenvalue density
in the real case in terms of twofold integrals and finite sums.Comment: 4 pages, 2 figure
Spin-dependent Seebeck coefficients of Ni_{80}Fe_{20} and Co in nanopillar spin valves
We have experimentally determined the spin-dependent Seebeck coefficient of
permalloy (Ni_{80}Fe_{20}) and cobalt (Co) using nanopillar spin valve devices.
The devices were specifically designed to completely separate heat related
effects from charge related effects. A pure heat current through the nanopillar
spin valve, a stack of two ferromagnetic layers (F) separated by a non-magnetic
layer (N), leads to a thermovoltage proportional to the spin-dependent Seebeck
coefficient S_{S}=S_{\uparrow}-S_{\downarrow} of the ferromagnet, where
S_{\uparrow} and S_{\downarrow} are the Seebeck coefficient for spin-up and
spin-down electrons. By using a three-dimensional finite-element model (3D-FEM)
based on spin-dependent thermoelectric theory, whose input material parameters
were measured in separate devices, we were able to accurately determine a
spin-dependent Seebeck coefficient of -1.8 microvolt/Kelvin and -4.5
microvolt/Kelvin for cobalt and permalloy, respectively corresponding to a
Seebeck coefficient polarization P_{S}=S_{S}/S_{F} of 0.08 and 0.25, where
S_{F} is the Seebeck coefficient of the ferromagnet. The results are in
agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent
Seebeck and spin-dependent Peltier measurements in Ni_{80}Fe_{20}/Cu spin valve
structures
EPR and ferromagnetism in diluted magnetic semiconductor quantum wells
Motivated by recent measurements of electron paramagnetic resonance (EPR)
spectra in modulation-doped CdMnTe quantum wells, [F.J. Teran {\it et al.},
Phys. Rev. Lett. {\bf 91}, 077201 (2003)], we develop a theory of collective
spin excitations in quasi-two-dimensional diluted magnetic semiconductors
(DMSs). Our theory explains the anomalously large Knight shift found in these
experiments as a consequence of collective coupling between Mn-ion local
moments and itinerant-electron spins. We use this theory to discuss the physics
of ferromagnetism in (II,Mn)VI quantum wells, and to speculate on the
temperature at which it is likely to be observed in n-type modulation doped
systems.Comment: 4 pages, 1 figur
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