327 research outputs found
Critical Point Field Mixing in an Asymmetric Lattice Gas Model
The field mixing that manifests broken particle-hole symmetry is studied for
a 2-D asymmetric lattice gas model having tunable field mixing properties.
Monte Carlo simulations within the grand canonical ensemble are used to obtain
the critical density distribution for different degrees of particle-hole
asymmetry. Except in the special case when this asymmetry vanishes, the density
distributions exhibit an antisymmetric correction to the limiting
scale-invariant form. The presence of this correction reflects the mixing of
the critical energy density into the ordering operator. Its functional form is
found to be in excellent agreement with that predicted by the mixed-field
finite-size-scaling theory of Bruce and Wilding. A computational procedure for
measuring the significant field mixing parameter is also described, and its
accuracy gauged by comparing the results with exact values obtained
analytically.Comment: 10 Pages, LaTeX + 8 figures available from author on request, To
appear in Z. Phys.
Smoking Cessation and Low-Dose Computed Tomography Screening: A Necessary Pair
The primary health benefits of cancer screening are realized by improved cancer-specific or overall mortality. Low-dose computed tomography (LDCT) screening is a relatively recent addition to the repertoire of methods that the health care system uses to improve mortality from lung cancer
Moduli and (un)attractor black hole thermodynamics
We investigate four-dimensional spherically symmetric black hole solutions in
gravity theories with massless, neutral scalars non-minimally coupled to gauge
fields. In the non-extremal case, we explicitly show that, under the variation
of the moduli, the scalar charges appear in the first law of black hole
thermodynamics. In the extremal limit, the near horizon geometry is
and the entropy does not depend on the values of moduli at
infinity. We discuss the attractor behaviour by using Sen's entropy function
formalism as well as the effective potential approach and their relation with
the results previously obtained through special geometry method. We also argue
that the attractor mechanism is at the basis of the matching between the
microscopic and macroscopic entropies for the extremal non-BPS Kaluza-Klein
black hole.Comment: 36 pages, no figures, V2: minor changes, misprints corrected,
expanded references; V3: sections 4.3 and 4.5 added; V4: minor changes,
matches the published versio
Hidden symmetry of hyperbolic monopole motion
Hyperbolic monopole motion is studied for well separated monopoles. It is
shown that the motion of a hyperbolic monopole in the presence of one or more
fixed monopoles is equivalent to geodesic motion on a particular submanifold of
the full moduli space. The metric on this submanifold is found to be a
generalisation of the multi-centre Taub-NUT metric introduced by LeBrun. The
one centre case is analysed in detail as a special case of a class of systems
admitting a conserved Runge-Lenz vector. The two centre problem is also
considered. An integrable classical string motion is exhibited.Comment: 39 pages, 7 figures, references added, minor changes to section
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Biogenic Versus Anthropogenic Sources of CO in the United States
Aircraft observations of carbon monoxide (CO) from the ICARTT campaign over the eastern United States in summer 2004 (July 1âAugust 15), interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem), show that the national anthropogenic emission inventory from the U.S. Environmental Protection Agency (93 Tg CO yâ1) is too high by 60% in summer. Our best estimate of the CO anthropogenic source for the ICARTT period is 6.4 Tg CO, including 4.6 Tg from direct emission and 1.8 Tg CO from oxidation of anthropogenic volatile organic compounds (VOCs). The biogenic CO source for the same period from the oxidation of isoprene and other biogenic VOCs is 8.3 Tg CO, and is independently constrained by ICARTT observations of formaldehyde (HCHO). Anthropogenic emissions of CO in the U.S. have decreased to the point that they are now lower than the biogenic source in summer.Earth and Planetary SciencesEngineering and Applied Science
Endothelial Cell-Astrocyte Interactions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75690/1/j.1749-6632.1988.tb51417.x.pd
On Thermalization in de Sitter Space
We discuss thermalization in de Sitter space and argue, from two different
points of view, that the typical time needed for thermalization is of order
, where is the radius of the de Sitter space in question.
This time scale gives plenty of room for non-thermal deviations to survive
during long periods of inflation. We also speculate in more general terms on
the meaning of the time scale for finite quantum systems inside isolated boxes,
and comment on the relation to the Poincar\'{e} recurrence time.Comment: 14 pages, 2 figures, latex, references added. Improved discussion in
section 3 adde
Black hole partition functions and duality
The macroscopic entropy and the attractor equations for BPS black holes in
four-dimensional N=2 supergravity theories follow from a variational principle
for a certain `entropy function'. We present this function in the presence of
R^2-interactions and non-holomorphic corrections. The variational principle
identifies the entropy as a Legendre transform and this motivates the
definition of various partition functions corresponding to different ensembles
and a hierarchy of corresponding duality invariant inverse Laplace integral
representations for the microscopic degeneracies. Whenever the microscopic
degeneracies are known the partition functions can be evaluated directly. This
is the case for N=4 heterotic CHL black holes, where we demonstrate that the
partition functions are consistent with the results obtained on the macroscopic
side for black holes that have a non-vanishing classical area. In this way we
confirm the presence of a measure in the duality invariant inverse Laplace
integrals. Most, but not all, of these results are obtained in the context of
semiclassical approximations. For black holes whose area vanishes classically,
there remain discrepancies at the semiclassical level and beyond, the nature of
which is not fully understood at present.Comment: 36 pages, Late
Separation of Attractors in 1-modulus Quantum Corrected Special Geometry
We study the attractor equations for a quantum corrected prepotential
F=t^3+i\lambda, with \lambda \in R,which is the only correction which preserves
the axion shift symmetry and modifies the geometry.
By performing computations in the ``magnetic'' charge configuration, we find
evidence for interesting phenomena (absent in the classical limit of vanishing
\lambda). For a certain range of the quantum parameter \lambda we find a
``separation'' of attractors, i.e. the existence of multiple solutions to the
Attractor Equations for fixed supporting charge configuration. Furthermore, we
find that, away from the classical limit, a ``transmutation'' of the
supersymmetry-preserving features of the attractors takes place when \lambda
reaches a particular critical value.Comment: 1+24 pages, 11 figures; v2: new section added; v3: change in title,
minor updates, published versio
Spin interactions and switching in vertically tunnel-coupled quantum dots
We determine the spin exchange coupling J between two electrons located in
two vertically tunnel-coupled quantum dots, and its variation when magnetic (B)
and electric (E) fields (both in-plane and perpendicular) are applied. We
predict a strong decrease of J as the in-plane B field is increased, mainly due
to orbital compression. Combined with the Zeeman splitting, this leads to a
singlet-triplet crossing, which can be observed as a pronounced jump in the
magnetization at in-plane fields of a few Tesla, and perpendicular fields of
the order of 10 Tesla for typical self-assembled dots. We use harmonic
potentials to model the confining of electrons, and calculate the exchange J
using the Heitler-London and Hund-Mulliken technique, including the long-range
Coulomb interaction. With our results we provide experimental criteria for the
distinction of singlet and triplet states and therefore for microscopic spin
measurements. In the case where dots of different sizes are coupled, we present
a simple method to switch on and off the spin coupling with exponential
sensitivity using an in-plane electric field. Switching the spin coupling is
essential for quantum computation using electronic spins as qubits.Comment: 13 pages, 9 figure
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