17,522 research outputs found
Object orientation and visualization of physics in two dimensions
We present a generalized framework for cellular/lattice based visualizations
in two dimensions based on state of the art computing abstractions. Our
implementation takes the form of a library of reusable functions written in C++
which hides complex graphical programming issues from the user and mimics the
algebraic structure of physics at the Hamiltonian level. Our toolkit is not
just a graphics library but an object analysis of physical systems which
disentangles separate concepts in a faithful analytical way. It could be
rewritten in other languages such as Java and extended to three dimensional
systems straightforwardly. We illustrate the usefulness of our analysis with
implementations of spin-films (the two-dimensional XY model with and without an
external magnetic field) and a model for diffusion through a triangular
lattice.Comment: 12 pages, 10 figure
Multi-wavelength observations of 3FGL J2039.6-5618: a candidate redback millisecond pulsar
We present multi-wavelength observations of the unassociated gamma-ray source
3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source
gamma-ray properties suggest that it is a pulsar, most likely a millisecond
pulsar, for which neither radio nor -ray pulsations have been detected
yet. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several
candidate X-ray counterparts within/close to the gamma-ray error box. The
brightest of these X-ray sources is variable with a period of 0.22450.0081
d. Its X-ray spectrum can be described by a power law with photon index
, and hydrogen column density cm, which gives an unabsorbed 0.3--10 keV X-ray flux of erg cm s. Observations with the Gamma-Ray Burst
Optical/Near-Infrared Detector (GROND) discovered an optical counterpart to
this X-ray source, with a time-average magnitude . The counterpart
features a flux modulation with a period of 0.227480.00043 d that
coincides, within the errors, with that of the X-ray source, confirming the
association based on the positional coincidence. We interpret the observed
X-ray/optical periodicity as the orbital period of a close binary system where
one of the two members is a neutron star. The light curve profile of the
companion star, with two asymmetric peaks, suggests that the optical emission
comes from two regions at different temperatures on its tidally-distorted
surface. Based upon its X-ray and optical properties, we consider this source
as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to
be a new redback system.Comment: 35 pages, 8 figures, accepted for publication on Astrophysical
Journa
Toward the End of Time
The null-brane space-time provides a simple model of a big crunch/big bang
singularity. A non-perturbative definition of M-theory on this space-time was
recently provided using matrix theory. We derive the fermion couplings for this
matrix model and study the leading quantum effects. These effects include
particle production and a time-dependent potential. Our results suggest that as
the null-brane develops a big crunch singularity, the usual notion of
space-time is replaced by an interacting gluon phase. This gluon phase appears
to constitute the end of our conventional picture of space and time.Comment: 31 pages, reference adde
Dynamical system analysis and forecasting of deformation produced by an earthquake fault
We present a method of constructing low-dimensional nonlinear models
describing the main dynamical features of a discrete 2D cellular fault zone,
with many degrees of freedom, embedded in a 3D elastic solid. A given fault
system is characterized by a set of parameters that describe the dynamics,
rheology, property disorder, and fault geometry. Depending on the location in
the system parameter space we show that the coarse dynamics of the fault can be
confined to an attractor whose dimension is significantly smaller than the
space in which the dynamics takes place. Our strategy of system reduction is to
search for a few coherent structures that dominate the dynamics and to capture
the interaction between these coherent structures. The identification of the
basic interacting structures is obtained by applying the Proper Orthogonal
Decomposition (POD) to the surface deformations fields that accompany
strike-slip faulting accumulated over equal time intervals. We use a
feed-forward artificial neural network (ANN) architecture for the
identification of the system dynamics projected onto the subspace (model space)
spanned by the most energetic coherent structures. The ANN is trained using a
standard back-propagation algorithm to predict (map) the values of the observed
model state at a future time given the observed model state at the present
time. This ANN provides an approximate, large scale, dynamical model for the
fault.Comment: 30 pages, 12 figure
A novel haptic model and environment for maxillofacial surgical operation planning and manipulation
This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone
Proceedings of the 2011 New York Workshop on Computer, Earth and Space Science
The purpose of the New York Workshop on Computer, Earth and Space Sciences is
to bring together the New York area's finest Astronomers, Statisticians,
Computer Scientists, Space and Earth Scientists to explore potential synergies
between their respective fields. The 2011 edition (CESS2011) was a great
success, and we would like to thank all of the presenters and participants for
attending. This year was also special as it included authors from the upcoming
book titled "Advances in Machine Learning and Data Mining for Astronomy". Over
two days, the latest advanced techniques used to analyze the vast amounts of
information now available for the understanding of our universe and our planet
were presented. These proceedings attempt to provide a small window into what
the current state of research is in this vast interdisciplinary field and we'd
like to thank the speakers who spent the time to contribute to this volume.Comment: Author lists modified. 82 pages. Workshop Proceedings from CESS 2011
in New York City, Goddard Institute for Space Studie
Motion clouds: model-based stimulus synthesis of natural-like random textures for the study of motion perception
Choosing an appropriate set of stimuli is essential to characterize the
response of a sensory system to a particular functional dimension, such as the
eye movement following the motion of a visual scene. Here, we describe a
framework to generate random texture movies with controlled information
content, i.e., Motion Clouds. These stimuli are defined using a generative
model that is based on controlled experimental parametrization. We show that
Motion Clouds correspond to dense mixing of localized moving gratings with
random positions. Their global envelope is similar to natural-like stimulation
with an approximate full-field translation corresponding to a retinal slip. We
describe the construction of these stimuli mathematically and propose an
open-source Python-based implementation. Examples of the use of this framework
are shown. We also propose extensions to other modalities such as color vision,
touch, and audition
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