6,473 research outputs found
Simulation of merging binary neutron stars in full general relativity: case
We have performed 3D numerical simulations for merger of equal mass binary
neutron stars in full general relativity. We adopt a -law equation of
state in the form where P, , \varep and
are the pressure, rest mass density, specific internal energy, and the
adiabatic constant with . As initial conditions, we adopt models of
corotational and irrotational binary neutron stars in a quasi-equilibrium state
which are obtained using the conformal flatness approximation for the three
geometry as well as an assumption that a helicoidal Killing vector exists. In
this paper, we pay particular attention to the final product of the
coalescence. We find that the final product depends sensitively on the initial
compactness parameter of the neutron stars : In a merger between sufficiently
compact neutron stars, a black hole is formed in a dynamical timescale. As the
compactness is decreased, the formation timescale becomes longer and longer. It
is also found that a differentially rotating massive neutron star is formed
instead of a black hole for less compact binary cases, in which the rest mass
of each star is less than 70-80% of the maximum allowed mass of a spherical
star. In the case of black hole formation, we roughly evaluate the mass of the
disk around the black hole. For the merger of corotational binaries, a disk of
mass may be formed, where M_* is the total rest mass of the
system. On the other hand, for the merger of irrotational binaries, the disk
mass appears to be very small : < 0.01M_*.Comment: 27 pages, to appear in Phys. Rev.
The design-by-adaptation approach to universal access: learning from videogame technology
This paper proposes an alternative approach to the design of universally accessible interfaces to that provided by formal design frameworks applied ab initio to the development of new software. This approach, design-byadaptation, involves the transfer of interface technology and/or design principles from one application domain to another, in situations where the recipient domain is similar to the host domain in terms of modelled systems, tasks and users. Using the example of interaction in 3D virtual environments, the paper explores how principles underlying the design of videogame interfaces may be applied to a broad family of visualization and analysis software which handles geographical data (virtual geographic environments, or VGEs). One of the motivations behind the current study is that VGE technology lags some way behind videogame technology in the modelling of 3D environments, and has a less-developed track record in providing the variety of interaction methods needed to undertake varied tasks in 3D virtual worlds by users with varied levels of experience. The current analysis extracted a set of interaction principles from videogames which were used to devise a set of 3D task interfaces that have been implemented in a prototype VGE for formal evaluation
Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows
We find and investigate via numerical simulations self-sustained
two-dimensional turbulence in a magnetohydrodynamic flow with a maximally
simple configuration: plane, noninflectional (with a constant shear of
velocity) and threaded by a parallel uniform background magnetic field. This
flow is spectrally stable, so the turbulence is subcritical by nature and hence
it can be energetically supported just by transient growth mechanism due to
shear flow nonnormality. This mechanism appears to be essentially anisotropic
in spectral (wavenumber) plane and operates mainly for spatial Fourier
harmonics with streamwise wavenumbers less than a ratio of flow shear to the
Alfv\'{e}n speed, (i.e., the Alfv\'{e}n frequency is lower than
the shear rate). We focused on the analysis of the character of nonlinear
processes and underlying self-sustaining scheme of the turbulence, i.e., on the
interplay between linear transient growth and nonlinear processes, in spectral
plane. Our study, being concerned with a new type of the energy-injecting
process for turbulence -- the transient growth, represents an alternative to
the main trends of MHD turbulence research. We find similarity of the nonlinear
dynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass}
concept of subcritical turbulence. The essence of the analyzed nonlinear MHD
processes appears to be a transverse redistribution of kinetic and magnetic
spectral energies in wavenumber plane [as occurs in the related hydrodynamic
flow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differs
fundamentally from the existing concepts of (anisotropic direct and inverse)
cascade processes in MHD shear flows.Comment: 19 pages, 7 figures, published in Phys. Rev. E 89, 043101 (2014
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Soft reboot : the making of Hard Reset
textDirector, Writer and MFA Candidate Deepak Chetty will discuss his history as a filmmaker from an early age up until present day as well as the entire process of conceptualizing, creating, producing and finishing Hard Reset. Hard Reset, a science fiction thriller is the first short film out of UT3D and the first graduate thesis film shot natively in stereoscopic 3D in North America.Radio-Television-Fil
Repurpose 2D Character Animations for a VR Environment Using BDH Shape Interpolation.
Virtual Reality technology has spread rapidly in recent years.
However, its growth risks ending soon due to the absence of quality content, except for few exceptions. We present an original framework that allows artists to use 2D characters and animations in a 3D Virtual Reality environment, in order to give an easier access to the production of content for the platform. In traditional platforms, 2D animation represents a more economic and immediate alternative to 3D. The challenge in adapting 2D characters to a 3D environment is to interpret the missing depth information. A 2D character is actually flat, so there is not any depth information, and every body part is at the same level of the others. We exploit mesh interpolation, billboarding and parallax scrolling to simulate the depth between each body segment of the character. We have developed a prototype of the system, and extensive tests with a 2D animation production show the effectiveness of our framework
Repurpose 2D Animations for a VR Environment using BDH Shape Interpolation
Virtual Reality technology has spread rapidly in recent years. However, its growth risks ending soon due to the absence of quality content, except for few exceptions. We present an original framework that allows artists to use 2D characters and animations in a 3D Virtual Reality environment, in order to give an easier access to the production of content for the platform. In traditional platforms, 2D animation represents a more economic and immediate alternative to 3D. The challenge in adapting 2D characters to a 3D environment is to interpret the missing
depth information. A 2D character is actually flat, so there is not any depth information, and every body part is at the same level of the others. We exploit mesh interpolation, billboarding and parallax scrolling to simulate the depth between each body segment of the character. We have developed a prototype of the system, and extensive tests with a 2D animation production show the effectiveness of our framework
Strong electronic correlations in superconducting organic charge transfer salts
We review the role of strong electronic correlations in
quasi--two-dimensional organic charge transfer salts such as (BEDT-TTF),
(BETS) and -[Pd(dmit)]. We begin by defining minimal
models for these materials. It is necessary to identify two classes of
material: the first class is strongly dimerised and is described by a
half-filled Hubbard model; the second class is not strongly dimerised and is
described by a quarter filled extended Hubbard model. We argue that these
models capture the essential physics of these materials. We explore the phase
diagram of the half-filled quasi--two-dimensional organic charge transfer
salts, focusing on the metallic and superconducting phases. We review work
showing that the metallic phase, which has both Fermi liquid and `bad metal'
regimes, is described both quantitatively and qualitatively by dynamical mean
field theory (DMFT). The phenomenology of the superconducting state is still a
matter of contention. We critically review the experimental situation, focusing
on the key experimental results that may distinguish between rival theories of
superconductivity, particularly probes of the pairing symmetry and measurements
of the superfluid stiffness. We then discuss some strongly correlated theories
of superconductivity, in particular, the resonating valence bond (RVB) theory
of superconductivity. We conclude by discussing some of the major challenges
currently facing the field.Comment: A review: 52 pages; 10 fig
Rotating Higher Spin Partition Functions and Extended BMS Symmetries
We evaluate one-loop partition functions of higher-spin fields in thermal
flat space with angular potentials; this computation is performed in arbitrary
space-time dimension, and the result is a simple combination of Poincar\'e
characters. We then focus on dimension three, showing that suitable products of
one-loop partition functions coincide with vacuum characters of higher-spin
asymptotic symmetry algebras at null infinity. These are extensions of the
bms_3 algebra that emerges in pure gravity, and we propose a way to build their
unitary representations and to compute the associated characters. We also
extend our investigations to supergravity and to a class of gauge theories
involving higher-spin fermionic fields.Comment: 58 pages; clarifications and references added; version to be
published in JHE
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