10,670 research outputs found
Existence of global strong solutions in critical spaces for barotropic viscous fluids
This paper is dedicated to the study of viscous compressible barotropic
fluids in dimension . We address the question of the global existence
of strong solutions for initial data close from a constant state having
critical Besov regularity. In a first time, this article show the recent
results of \cite{CD} and \cite{CMZ} with a new proof. Our result relies on a
new a priori estimate for the velocity, where we introduce a new structure to
\textit{kill} the coupling between the density and the velocity as in
\cite{H2}. We study so a new variable that we call effective velocity. In a
second time we improve the results of \cite{CD} and \cite{CMZ} by adding some
regularity on the initial data in particular is in . In this
case we obtain global strong solutions for a class of large initial data on the
density and the velocity which in particular improve the results of D. Hoff in
\cite{5H4}. We conclude by generalizing these results for general viscosity
coefficients
Five-Dimensional f(R) Braneworld Models
After incorporating the f(R) gravity into the general braneworld sum rules
scope, it is shown that some particular class of warped five dimensional
nonlinear braneworld models, which may be interesting for the hierarchy problem
solution, still require a negative tension brane. For other classes of warp
factors (suitable and not suitable for approaching the hierarchy problem) it is
not necessary any negative brane tension in the compactification scheme. In
this vein, it is argued that in the bulk f(R) gravity context, some types of
warp factors may be useful for approaching the hierarchy problem and for
evading the necessity of a negative brane tension in the compactification
scheme.Comment: 10 pages, references updated, small modifications. Accepted for
publication in Phys. Rev.
Bifurcation structures and transient chaos in a four-dimensional Chua model
A four-dimensional four-parameter Chua model with cubic nonlinearity is
studied applying numerical continuation and numerical solutions methods.
Regarding numerical solution methods, its dynamics is characterized on Lyapunov
and isoperiodic diagrams and regarding numerical continuation method, the
bifurcation curves are obtained. Combining both methods the bifurcation
structures of the model were obtained with the possibility to describe the {\it
shrimp}-shaped domains and their endoskeletons. We study the effect of a
parameter that controls the dimension of the system leading the model to
present transient chaos with its corresponding basin of attraction being
riddled.Comment: 9 figures, to appear in PL
Nutritional and cultural aspects of plant species selection for a controlled ecological life support system
The feasibility of using higher plants in a controlled ecological life support system is discussed. Aspects of this system considered important in the use of higher plants include: limited energy, space, and mass, and problems relating to cultivation and management of plants, food processing, the psychological impact of vegetarian diets, and plant propagation. A total of 115 higher plant species are compared based on 21 selection criteria
Machine vision based teleoperation aid
When teleoperating a robot using video from a remote camera, it is difficult for the operator to gauge depth and orientation from a single view. In addition, there are situations where a camera mounted for viewing by the teleoperator during a teleoperation task may not be able to see the tool tip, or the viewing angle may not be intuitive (requiring extensive training to reduce the risk of incorrect or dangerous moves by the teleoperator). A machine vision based teleoperator aid is presented which uses the operator's camera view to compute an object's pose (position and orientation), and then overlays onto the operator's screen information on the object's current and desired positions. The operator can choose to display orientation and translation information as graphics and/or text. This aid provides easily assimilated depth and relative orientation information to the teleoperator. The camera may be mounted at any known orientation relative to the tool tip. A preliminary experiment with human operators was conducted and showed that task accuracies were significantly greater with than without this aid
Ritualized Rhetoric and Historical Memory in German Foreign and Security Policy
Recent changes in German foreign policy behavior have led to questions about Germany\u27s European vocation. At the center of this inquiry is Germany\u27s struggle to resolve the intersection between historical memory and present day international responsibility, especially in cases involving the use of force. This dissertation examines how and when historical memory has influenced, shaped, and informed contemporary German foreign and security policy and rhetoric by examining cases within two policy areas: out of area operations and nuclear nonproliferation. Focusing on the case of Libya, this dissertation also considers the cases of Kosovo, Iraq, and Afghanistan. Nuclear nonproliferation, a global policy issue, highlights Germany\u27s role as an international actor by focusing on Germany\u27s voice and actions during the negotiations with Iran over its nuclear program. This dissertation hypothesizes that Germany has a ritualized foreign and security policy and rhetoric determined by historical memory. The argument is made that historical memory and ritualized rhetoric is used depending on policy area, allowing Germany to present reason, argument, and justification to a variety of international security challenges, either to support or oppose military involvement. This dissertation finds support for questions regarding Germany\u27s European vocation. However, Germany exercises self-interests precisely within the institutions of the European Union and the North Atlantic Treaty Organization. What has changed is that Germany is increasingly using rhetoric of memory and guilt in order to obscure that it is actually acting in its self-interests. German policy choices, as they relate to the future use of force will be critically guided by this rhetoric
Some remarks on the attractor behaviour in ELKO cosmology
Recent results on the dynamical stability of a system involving the
interaction of the ELKO spinor field with standard matter in the universe have
been reanalysed, and the conclusion is that such system does not exhibit
isolated stable points that could alleviate the cosmic coincidence problem.
When a constant parameter related to the potential of the ELKO field
is introduced in the system however, stable fixed points are found for some
specific types of interaction between the ELKO field and matter. Although the
parameter is related to an unknown potential, in order to satisfy the
stability conditions and also that the fixed points are real, the range of the
constant parameter can be constrained for the present time and the
coincidence problem can be alleviated for some specific interactions. Such
restriction on the ELKO potential opens possibility to apply the ELKO field as
a candidate to dark energy in the universe, and so explain the present phase of
acceleration of the universe through the decay of the ELKO field into matter.Comment: 17 pages, section III with minor changes and section IV rewritten
with a new analysi
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