426 research outputs found
Study on joint thermal conductance in vacuum Final report
Bright leveling copper plating for improvement of thermal conductance in mechanical joints in vacuu
Critical Exponents of the Four-State Potts Model
The critical exponents of the four-state Potts model are directly derived
from the exact expressions for the latent heat, the spontaneous magnetization,
and the correlation length at the transition temperature of the model.Comment: LaTex, 7 page
Equation of Motion for a Spin Vortex and Geometric Force
The Hamiltonian equation of motion is studied for a vortex occuring in
2-dimensional Heisenberg ferromagnet of anisotropic type by starting with the
effective action for the spin field formulated by the Bloch (or spin) coherent
state. The resultant equation shows the existence of a geometric force that is
analogous to the so-called Magnus force in superfluid. This specific force
plays a significant role for a quantum dynamics for a single vortex, e.g, the
determination of the bound state of the vortex trapped by a pinning force
arising from the interaction of the vortex with an impurity.Comment: 13 pages, plain te
Axion Detection via Atomic Excitations
The possibility of axion detection by observing axion induced atomic
excitations as recently suggested by Sikivie is discussed. The atom is cooled
at low temperature and it is chosen to posses three levels. The first is the
ground state, the second is completely empty chosen so that the energy
difference between the two is close to the axion mass. Under the spin induced
axion-electron interaction an electron is excited from the first to the second
level. The presence of such an electron there can be confirmed by exciting it
further via a proper tunable laser beam to a suitably chosen third level, which
is also empty, and lies at a higher excitation energy. From the observation of
its subsequent de-excitation one infers the presence of the axion. In addition
the presence of the axion can be inferred from the de-excitation of the second
level to the ground state. The system is in a magnetic field so that the
energies involved can be suitably adjusted. Reasonable axion absorption rates
have been obtained.Comment: 11 pages, six figures, 3 tables, more references adde
Channeling Effects in Direct Dark Matter Detectors
The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger signal
than otherwise expected. We give estimates of the fraction of channeled
recoiling ions in NaI (Tl), Si and Ge crystals using analytic models produced
since the 1960's and 70's to describe channeling and blocking effects. We find
that the channeling fraction of recoiling lattice nuclei is smaller than that
of ions that are injected into the crystal and that it is strongly temperature
dependent.Comment: 8 pages, 12 figures, To appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
Fisher zeros of the Q-state Potts model in the complex temperature plane for nonzero external magnetic field
The microcanonical transfer matrix is used to study the distribution of the
Fisher zeros of the Potts models in the complex temperature plane with
nonzero external magnetic field . Unlike the Ising model for
which has only a non-physical critical point (the Fisher edge singularity), the
Potts models have physical critical points for as well as the
Fisher edge singularities for . For the cross-over of the Fisher
zeros of the -state Potts model into those of the ()-state Potts model
is discussed, and the critical line of the three-state Potts ferromagnet is
determined. For we investigate the edge singularity for finite lattices
and compare our results with high-field, low-temperature series expansion of
Enting. For we find that the specific heat, magnetization,
susceptibility, and the density of zeros diverge at the Fisher edge singularity
with exponents , , and which satisfy the scaling
law .Comment: 24 pages, 7 figures, RevTeX, submitted to Physical Review
Error-Tolerant Version Space Algebra
ABSTRACT Application customization has been extensively researched in the field of Programming by Demonstration (PBD), and Version Space Algebra has proven itself to be a viable means of quickly learning precise action sequences from user demonstrations. However, this technique is not capable of handling user error in domains with actions that depend on parameters that accept myriad values. Activities such as image, audio and video editing require user actions that are difficult for users to precisely replicate in different circumstances. Demonstrations that are off by a single pixel or a split-second cause traditional composite Version Spaces to collapse. We present a method of incorporating error tolerance into Version Space algebra. This approach, termed Error-Tolerant Version Spaces, adapts Version Space Algebra to domains where the tactile capabilities of the user have a much greater chance of prematurely collapsing the hypothesis space that is being learned. The resulting framework is capable of quickly learning in domains where perfectly consistent user input can not be expected. We have successfully applied our technique in the domain of image redaction, allowing our users to quickly specify redactions that can be reliably applied to many images without the entry of explicit parameters
Evaluating the performance of a climate-driven mortality model during heat waves and cold spells in Europe.
The impact of climate change on human health is a serious concern. In particular, changes in the frequency and intensity of heat waves and cold spells are of high relevance in terms of mortality and morbidity. This demonstrates the urgent need for reliable early-warning systems to help authorities prepare and respond to emergency situations. In this study, we evaluate the performance of a climate-driven mortality model to provide probabilistic predictions of exceeding emergency mortality thresholds for heat wave and cold spell scenarios. Daily mortality data corresponding to 187 NUTS2 regions across 16 countries in Europe were obtained from 1998-2003. Data were aggregated to 54 larger regions in Europe, defined according to similarities in population structure and climate. Location-specific average mortality rates, at given temperature intervals over the time period, were modelled to account for the increased mortality observed during both high and low temperature extremes and differing comfort temperatures between regions. Model parameters were estimated in a Bayesian framework, in order to generate probabilistic simulations of mortality across Europe for time periods of interest. For the heat wave scenario (1-15 August 2003), the model was successfully able to anticipate the occurrence or non-occurrence of mortality rates exceeding the emergency threshold (75th percentile of the mortality distribution) for 89% of the 54 regions, given a probability decision threshold of 70%. For the cold spell scenario (1-15 January 2003), mortality events in 69% of the regions were correctly anticipated with a probability decision threshold of 70%. By using a more conservative decision threshold of 30%, this proportion increased to 87%. Overall, the model performed better for the heat wave scenario. By replacing observed temperature data in the model with forecast temperature, from state-of-the-art European forecasting systems, probabilistic mortality predictions could potentially be made several months ahead of imminent heat waves and cold spells
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