11,568 research outputs found
Next--to--Leading Order QCD corrections for the --mixing with an extended Higgs sector
We present a calculation of the B0-B0--mixing including Next--to--Leading
Order (NLO) QCD corrections within the Two Higgs Doublet Model (2HDM). The QCD
corrections at NLO are contained in the factor denoted by eta_2 which modifies
the result obtained at the lowest order of perturbation theory. In the Standard
Model case, we confirm the results for eta_2 obtained by Buras, Jamin and
Weisz. The factor eta_2 is gauge and renormalization prescription invariant and
it does not depend on the infrared behaviour of the theory, which constitutes
an important test of the calculations. The NLO--calculations within the 2HDM
enhance the LO--result up to 18%, which affects the correlation between M_H and
V_{td}.Comment: 22 pages (LaTeX), 22 Postscript figures, version to appear in Nucl.
Phys. B, corrected some typos and a sign in the program, which results in
changes in Eqs. (71), (74) and (75). Due to these changes Eqs. (23) and (34)
may be written in a more compact wa
Simulated testing of an adaptive multimedia information retrieval system
The Semantic Gap is considered to be a bottleneck in image and video retrieval. One way to increase the communication between user and system is to take advantage of the user's action with a system, e.g. to infer the relevance or otherwise of a video shot viewed by the user. In this paper we introduce a novel video retrieval system and propose a model of implicit information for interpreting the user's actions with the interface. The assumptions on which this model was created are then analysed in an experiment using simulated users based on relevance judgements to compare results of explicit and implicit retrieval cycles. Our model seems to enhance retrieval results. Results are presented and discussed in the final section
Brane Cosmology and KK Gravitinos
The cosmology of KK gravitinos in models with extra dimensions is considered.
The main result is that the production of such KK modes is not compatible with
an epoch of non--standard expansion after inflation. This is so because the BBN
constraint on the zero mode forces the reduced five dimensional Planck mass
down to values much smaller than the usual four dimensional one, but this
in turn implies many KK states available for a given temperature. Once these
states are taken into account one finds that there is no for which the
produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion
holds for both flat and warped models in which only gravity propagates in the
full spacetime.Comment: 19 pages, references added, IoP styl
Electronic and atomic shell structure in aluminum nanowires
We report experiments on aluminum nanowires in ultra-high vacuum at room
temperature that reveal a periodic spectrum of exceptionally stable structures.
Two "magic" series of stable structures are observed: At low conductance, the
formation of stable nanowires is governed by electronic shell effects whereas
for larger contacts atomic packing dominates. The crossover between the two
regimes is found to be smooth. A detailed comparison of the experimental
results to a theoretical stability analysis indicates that while the main
features of the observed electron-shell structure are similar to those of
alkali and noble metals, a sequence of extremely stable wires plays a unique
role in Aluminum. This series appears isolated in conductance histograms and
can be attributed to "superdeformed" non-axisymmetric nanowires.Comment: 15 pages, 9 figure
Tackling Challenges in Seebeck Coefficient Measurement of Ultra-High Resistance Samples with an AC Technique
Seebeck coefficient is a widely studied semiconductor property. Conventional Seebeck coefficient measurements are based on DC voltage measurement. Normally this is performed on samples with moderate resistances (e.g., below a few MΩ level). Certain semiconductors are intrinsic and highly resistive. Many examples can be found in optical and photovoltaic materials. The hybrid halide perovskites that have gained extensive attention recently are a good example. Despite great attention from the materials and physics communities, few successful studies exist of the Seebeck coefficient of these compounds, for example CH3NH3PbI3. An AC-technique-based Seebeck coefficient measurement is reported, which makes high-quality Seebeck voltage measurements on samples with resistances up to the 100 GΩ level. This is achieved through a specifically designed setup to enhance sample isolation and increase capacitive impedance. As a demonstration, Seebeck coefficient measurement of a CH3NH3PbI3 thin film is performed at dark, with sample resistance 150 GΩ, and found S = +550 µV K−1. The strategy reported could be applied to the studies of fundamental transport parameters of all intrinsic semiconductors that have not been feasible
Compositional optimization of hard-magnetic phases with machine-learning models
Machine Learning (ML) plays an increasingly important role in the discovery
and design of new materials. In this paper, we demonstrate the potential of ML
for materials research using hard-magnetic phases as an illustrative case. We
build kernel-based ML models to predict optimal chemical compositions for new
permanent magnets, which are key components in many green-energy technologies.
The magnetic-property data used for training and testing the ML models are
obtained from a combinatorial high-throughput screening based on
density-functional theory calculations. Our straightforward choice of
describing the different configurations enables the subsequent use of the ML
models for compositional optimization and thereby the prediction of promising
substitutes of state-of-the-art magnetic materials like NdFeB with
similar intrinsic hard-magnetic properties but a lower amount of critical
rare-earth elements.Comment: 12 pages, 6 figure
Dynamics of a trapped Fermi gas in the BCS phase
We derive semiclassical transport equations for a trapped atomic Fermi gas in
the BCS phase at temperatures between zero and the superfluid transition
temperature. These equations interpolate between the two well-known limiting
cases of superfluid hydrodynamics at zero temperature and the Vlasov equation
at the critical one. The linearized version of these equations, valid for small
deviations from equilibrium, is worked out and applied to two simple examples
where analytical solutions can be found: a sound wave in a uniform medium and
the quadrupole excitation in a spherical harmonic trap. In spite of some
simplifying approximations, the main qualitative results of quantum mechanical
calculations are reproduced, which are the different frequencies of the
quadrupole mode at zero and the critical temperature and strong Landau damping
at intermediate temperatures. In addition we suggest a numerical method for
solving the semiclassical equations without further approximations.Comment: 15 pages, 4 figures; v2: discussion and references adde
Glasgow University at TRECVID 2006
In the first part of this paper we describe our experiments in the automatic and interactive search tasks of TRECVID 2006. We submitted five fully automatic runs, including a text baseline, two runs based on visual features, and two runs that combine textual and visual features in a graph model. For the interactive search, we have implemented a new video search interface with relevance feedback facilities, based on both textual and visual features.
The second part is concerned with our approach to the high-level feature extraction task, based on textual information extracted from speech recogniser and machine translation outputs. They were aligned with shots and associated with high-level feature references. A list of significant words was created for each feature, and it was in turn utilised for identification of a feature during the evaluation
Jahn-Teller Distortions and the Supershell Effect in Metal Nanowires
A stability analysis of metal nanowires shows that a Jahn-Teller deformation
breaking cylindrical symmetry can be energetically favorable, leading to stable
nanowires with elliptic cross sections. The sequence of stable cylindrical and
elliptical nanowires allows for a consistent interpretation of experimental
conductance histograms for alkali metals, including both the shell and
supershell structures. It is predicted that for gold, elliptical nanowires are
even more likely to form since their eccentricity is smaller than for alkali
metals. The existence of certain metastable ``superdeformed'' nanowires is also
predicted
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