5,530 research outputs found
Vibration isolation system for the Stratospheric Observatory For Infrared Astronomy (SOFIA)
The Vibration Isolation System for the Stratospheric Observatory for Infrared Astronomy (SOFIA) is studied. Included are discussions of the various concepts, design goals, concerns, and the proposed configuration for the Vibration Isolation System
Why we need to see the dark matter to understand the dark energy
The cosmological concordance model contains two separate constituents which
interact only gravitationally with themselves and everything else, the dark
matter and the dark energy. In the standard dark energy models, the dark matter
makes up some 20% of the total energy budget today, while the dark energy is
responsible for about 75%. Here we show that these numbers are only robust for
specific dark energy models and that in general we cannot measure the abundance
of the dark constituents separately without making strong assumptions.Comment: 4 pages, to be published in the Journal of Physics: Conference Series
as a contribution to the 2007 Europhysics Conference on High Energy Physic
Vision-Based Control of a Full-Size Car by Lane Detection
Autonomous driving is an area of increasing investment for researchers and auto manufacturers. Integration has already begun for self-driving cars in urban environments. An essential aspect of navigation in these areas is the ability to sense and follow lane markers. This thesis focuses on the development of a vision-based control platform using lane detection to control a full-sized electric vehicle with only a monocular camera. An open-source, integrated solution is presented for automation of a stock vehicle. Aspects of reverse engineering, system identification, and low-level control of the vehicle are discussed. This work also details methods for lane detection and the design of a non-linear vision-based control strategy
On Axially Symmetric Solutions in the Electroweak Theory
We present the general ansatz, the energy density and the Chern-Simons charge
for static axially symmetric configurations in the bosonic sector of the
electroweak theory. Containing the sphaleron, the multisphalerons and the
sphaleron-antisphaleron pair at finite mixing angle, the ansatz further allows
the construction of the sphaleron and multisphaleron barriers and of the
bisphalerons at finite mixing angle. We conjecture that further solutions
exist.Comment: 17 pages, latex, THU-94/0
On the detectability of non-trivial topologies
We explore the main physical processes which potentially affect the
topological signal in the Cosmic Microwave Background (CMB) for a range of
toroidal universes. We consider specifically reionisation, the integrated
Sachs-Wolfe (ISW) effect, the size of the causal horizon, topological defects
and primordial gravitational waves. We use three estimators: the information
content, the S/N statistic and the Bayesian evidence. While reionisation has
nearly no effect on the estimators, we show that taking into account the ISW
strongly decreases our ability to detect the topological signal. We also study
the impact of varying the relevant cosmological parameters within the 2 sigma
ranges allowed by present data. We find that only Omega_Lambda, which
influences both ISW and the size of the causal horizon, significantly alters
the detection for all three estimators considered here.Comment: 11 pages, 9 figure
Strange Multiskyrmions
Using the recently proposed approximation for multiskyrmion fields based on
rational maps we study the masses and baryonic radii of some strange
multibaryons within the bound state soliton model. We find the tetralambda
binding to be stronger than previously expected. In addition, the model
predicts the existence of a ``heptalambda'' which is stable against strong
decays.Comment: 8 pages, Latex, no figure
The HBI in a quasi-global model of the intracluster medium
In this paper we investigate how convective instabilities influence heat
conduction in the intracluster medium (ICM) of cool-core galaxy clusters. The
ICM is a high-beta, weakly collisional plasma in which the transport of
momentum and heat is aligned with the magnetic field. The anisotropy of heat
conduction, in particular, gives rise to instabilities that can access energy
stored in a temperature gradient of either sign. We focus on the heat-flux
buoyancy-driven instability (HBI), which feeds on the outwardly increasing
temperature profile of cluster cool cores. Our aim is to elucidate how the
global structure of a cluster impacts on the growth and morphology of the
linear HBI modes when in the presence of Braginskii viscosity, and ultimately
on the ability of the HBI to thermally insulate cores. We employ an idealised
quasi-global model, the plane-parallel atmosphere, which captures the essential
physics -- e.g. the global radial profile of the cluster -- while letting the
problem remain analytically tractable. Our main result is that the dominant HBI
modes are localised to the the innermost (~<20%) regions of cool cores. It is
then probable that, in the nonlinear regime, appreciable field-line insulation
will be similarly localised. Thus, while radio-mode feedback appears necessary
in the central few tens of kpc, heat conduction may be capable of offsetting
radiative losses throughout most of a cool core over a significant fraction of
the Hubble time. Finally, our linear solutions provide a convenient numerical
test for the nonlinear codes that tackle the saturation of such convective
instabilities in the presence of anisotropic transport.Comment: MNRAS, in press; minor modifications from v
O(\alpha_s^2) corrections to the running top-Yukawa coupling and the mass of the lightest Higgs boson in the MSSM
In this paper we propose a method to compute the running top-Yukawa coupling
in supersymmetric models with heavy mass spectrum based on the "running" and
"decoupling" procedure. In order to enable this approach we compute the
two-loop SUSY-QCD radiative corrections required in the decoupling process. The
method has the advantage that large logarithmic corrections are automatically
resummed through the Renormalization Group Equations. As phenomenological
application we study the effects of this approach on the prediction of the
lightest Higgs boson mass at three-loop accuracy. We observe a significant
reduction of the renormalization scale dependence as compared to the direct
method, that is based on the conversion relation between the running and pole
mass for the top quark. The effect of resummation of large logarithmic
contributions consists in an increased prediction for the Higgs boson mass, an
observation in agreement with the previous analyses.Comment: 24 pages, 9 figures; one more figure added; reference list extende
Bayesian estimation applied to multiple species
Observed data are often contaminated by undiscovered interlopers, leading to biased parameter estimation. Here we present BEAMS (Bayesian estimation applied to multiple species) which significantly improves on the standard maximum likelihood approach in the case where the probability for each data point being âpureâ is known. We discuss the application of BEAMS to future type-Ia supernovae (SNIa) surveys, such as LSST, which are projected to deliver over a million supernovae light curves without spectra. The multiband light curves for each candidate will provide a probability of being Ia (pure) but the full sample will be significantly contaminated with other types of supernovae and transients. Given a sample of N supernovae with mean probability, âšPâ©, of being Ia, BEAMS delivers parameter constraints equal to NâšPâ© spectroscopically confirmed SNIa. In addition BEAMS can be simultaneously used to tease apart different families of data and to recover properties of the underlying distributions of those families (e.g. the type-Ibc and II distributions). Hence BEAMS provides a unified classification and parameter estimation methodology which may be useful in a diverse range of problems such as photometric redshift estimation or, indeed, any parameter estimation problem where contamination is an issue
Dispositivo indicador de troca de filtro para biogĂĄs (Embrapa BiogĂĄs TF-01)
bitstream/item/58044/1/CUsersPiazzonDocuments478.pdfProjeto/Plano de Ação: 02.07.06.007-0
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