44,751 research outputs found
The radial structure of protostellar accretion disks: influence of jets
The radial structure of accretion disks is a fundamental issue regarding star
and planet formation. Many theoretical studies, focussing on different aspects
such as e.g. disk emissivity or ionization, have been conducted in the context
of the Standard Accretion Disk (SAD) model, where no jet is present. We wish to
calculate the structure of YSO accretion disks in an approach that takes into
account the presence of the protostellar jets. The radial structure of these
Jet Emitting Disks (JED) should then be compared to that of standard accretion
disks. The analytical treatment used in this work is very similar to that of
standard accretion disks but is using the parameter space of Magnetised
Accretion-Ejection Structures that include the jet torque on the underlying
disk. In this framework, the analytical expressions of key quantities, such as
mid-plane temperatures, surface densities or disk aspect ratio are derived. It
is found that JEDs present a structure very different from the SADs and that
can be observationally tested. The implications on planet formation in the
inner regions of accretion disks are briefly discussed. We also supply sets of
analytical formulae, valid in different opacity regimes, for the disk
quantities. These expressions can be readily used for any work where the disk
structure is needed as an input for the model.Comment: 11 pages, 4 figures. Accepted for publication in A&
Global-String and Vortex Superfluids in a Supersymmetric Scenario
The main goal of this work is to investigate the possibility of finding the
supersymmetric version of the U(1)-global string model which behaves as a
vortex-superfluid. To describe the superfluid phase, we introduce a
Lorentz-symmetry breaking background that, in an approach based on
supersymmetry, leads to a discussion on the relation between the violation of
Lorentz symmetry and explicit soft supersymmetry breakings. We also study the
relation between the string configuration and the vortex-superfluid phase. In
the framework we settle down in terms of superspace and superfields, we
actually establish a duality between the vortex degrees of freedom and the
component fields of the Kalb-Ramond superfield. We make also considerations
about the fermionic excitations that may appear in connection with the vortex
formation.Comment: 9 pages. This version presented the relation between Lorentz symmetry
violation by the background and the appearance of terms that explicitly break
SUS
A mass-transportation approach to a one dimensional fluid mechanics model with nonlocal velocity
We consider a one dimensional transport model with nonlocal velocity given by
the Hilbert transform and develop a global well-posedness theory of probability
measure solutions. Both the viscous and non-viscous cases are analyzed. Both in
original and in self-similar variables, we express the corresponding equations
as gradient flows with respect to a free energy functional including a singular
logarithmic interaction potential. Existence, uniqueness, self-similar
asymptotic behavior and inviscid limit of solutions are obtained in the space
of probability measures with finite second
moments, without any smallness condition. Our results are based on the abstract
gradient flow theory developed in \cite{Ambrosio}. An important byproduct of
our results is that there is a unique, up to invariance and translations,
global in time self-similar solution with initial data in
, which was already obtained in
\textrm{\cite{Deslippe,Biler-Karch}} by different methods. Moreover, this
self-similar solution attracts all the dynamics in self-similar variables. The
crucial monotonicity property of the transport between measures in one
dimension allows to show that the singular logarithmic potential energy is
displacement convex. We also extend the results to gradient flow equations with
negative power-law locally integrable interaction potentials
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Hybrid Prototypes to Assist Modeling Automotive Seats
The development of new modular seats is an important issue in the automotive industry.
However, is very time consuming and costly. Virtual models and hybrid prototypes could
accelerate the car seats development process. The hybrid prototypes are mainly manufactured by
rapid prototyping with multi materials. The objective of this paper is to establish a methodology
to develop innovative lightweight multi-functional, modular car seats to be used in Multi-Purpose
Vehicles (MPV), by means of FEA simulation and rapid prototyping additive/subtractive
technologies utilizing multi materials. A case study is presented to validate the developed
methodology. The manufactured hybrid prototype’s reproduces the main functionalities of the
MPV modular seat, namely its three key positions: normal, stored and table.Mechanical Engineerin
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