1,012 research outputs found
Virtual Reality Techniques for 3D Data-Warehouse Exploration
This paper focuses on the evaluation of virtual reality (VR) interaction techniques for exploration of data warehouse (DW). The experimental DW involves hierarchical levels and contains information about customers profiles and related purchase items. A user study has been carried out to compare two navigation and selection techniques. Sixteen volunteers were instructed to explore the DW and look for information using the interaction techniques, involving either a single WiimoteTM (monomanual) or both WiimoteTM and NunchuckTM (bimanual). Results indicated that the bimanual interaction technique is more efficient in terms of speed and error rate. Moreover, most of the participants preferred the bimanual interaction technique and found it more appropriate for the exploration task. We also observed that males were faster and made less errors than females for both interaction techniques
Complex Behavior in Simple Models of Biological Coevolution
We explore the complex dynamical behavior of simple predator-prey models of
biological coevolution that account for interspecific and intraspecific
competition for resources, as well as adaptive foraging behavior. In long
kinetic Monte Carlo simulations of these models we find quite robust 1/f-like
noise in species diversity and population sizes, as well as power-law
distributions for the lifetimes of individual species and the durations of
quiet periods of relative evolutionary stasis. In one model, based on the
Holling Type II functional response, adaptive foraging produces a metastable
low-diversity phase and a stable high-diversity phase.Comment: 8 pages, 5 figure
Entanglement of a microcanonical ensemble
We replace time-averaged entanglement by ensemble-averaged entanglement and
derive a simple expression for the latter. We show how to calculate the
ensemble average for a two-spin system and for the Jaynes-Cummings model. In
both cases the time-dependent entanglement is known as well so that one can
verify that the time average coincides with the ensemble average.Comment: 10 page
Genericity aspects in gravitational collapse to black holes and naked singularities
We investigate here the genericity and stability aspects for naked
singularities and black holes that arise as the final states for a complete
gravitational collapse of a spherical massive matter cloud. The form of the
matter considered is a general Type I matter field, which includes most of the
physically reasonable matter fields such as dust, perfect fluids and such other
physically interesting forms of matter widely used in gravitation theory. We
first study here in some detail the effects of small pressure perturbations in
an otherwise pressure-free collapse scenario, and examine how a collapse
evolution that was going to the black hole endstate would be modified and go to
a naked singularity, once small pressures are introduced in the initial data.
This allows us to understand the distribution of black holes and naked
singularities in the initial data space. Collapse is examined in terms of the
evolutions allowed by Einstein equations, under suitable physical conditions
and as evolving from a regular initial data. We then show that both black holes
and naked singularities are generic outcomes of a complete collapse, when
genericity is defined in a suitable sense in an appropriate space.Comment: 24 pages, 6 figures, some changes in text and figures to match the
version accepted for publication by IJMP
The self-consistent gravitational self-force
I review the problem of motion for small bodies in General Relativity, with
an emphasis on developing a self-consistent treatment of the gravitational
self-force. An analysis of the various derivations extant in the literature
leads me to formulate an asymptotic expansion in which the metric is expanded
while a representative worldline is held fixed; I discuss the utility of this
expansion for both exact point particles and asymptotically small bodies,
contrasting it with a regular expansion in which both the metric and the
worldline are expanded. Based on these preliminary analyses, I present a
general method of deriving self-consistent equations of motion for arbitrarily
structured (sufficiently compact) small bodies. My method utilizes two
expansions: an inner expansion that keeps the size of the body fixed, and an
outer expansion that lets the body shrink while holding its worldline fixed. By
imposing the Lorenz gauge, I express the global solution to the Einstein
equation in the outer expansion in terms of an integral over a worldtube of
small radius surrounding the body. Appropriate boundary data on the tube are
determined from a local-in-space expansion in a buffer region where both the
inner and outer expansions are valid. This buffer-region expansion also results
in an expression for the self-force in terms of irreducible pieces of the
metric perturbation on the worldline. Based on the global solution, these
pieces of the perturbation can be written in terms of a tail integral over the
body's past history. This approach can be applied at any order to obtain a
self-consistent approximation that is valid on long timescales, both near and
far from the small body. I conclude by discussing possible extensions of my
method and comparing it to alternative approaches.Comment: 44 pages, 4 figure
Stability of Naked Singularity arising in gravitational collapse of Type I matter fields
Considering gravitational collapse of Type I matter fields, we prove that,
given an arbitrary - mass function and a -
function (through the corresponding - metric function
), there exist infinitely many choices of energy distribution
function such that the `true' initial data () leads
the collapse to the formation of naked singularity. We further prove that the
occurrence of such a naked singularity is stable with respect to small changes
in the initial data. We remark that though the initial data leading to both
black hole and naked singularity form a "big" subset of the true initial data
set, their occurrence is not generic. The terms `stability' and `genericity'
are appropriately defined following the theory of dynamical systems. The
particular case of radial pressure has been illustrated in details
to get clear picture of how naked singularity is formed and how, it is stable
with respect to initial data.Comment: 16 pages, no figure, Latex, submitted to Praman
Fluctuations and correlations in an individual-based model of biological coevolution
We extend our study of a simple model of biological coevolution to its
statistical properties. Staring with a complete description in terms of a
master equation, we provide its relation to the deterministic evolution
equations used in previous investigations. The stationary states of the
mutationless model are generally well approximated by Gaussian distributions,
so that the fluctuations and correlations of the populations can be computed
analytically. Several specific cases are studied by Monte Carlo simulations,
and there is excellent agreement between the data and the theoretical
predictions.Comment: 25 pages, 2 figure
An exact analytical solution for generalized growth models driven by a Markovian dichotomic noise
Logistic growth models are recurrent in biology, epidemiology, market models,
and neural and social networks. They find important applications in many other
fields including laser modelling. In numerous realistic cases the growth rate
undergoes stochastic fluctuations and we consider a growth model with a
stochastic growth rate modelled via an asymmetric Markovian dichotomic noise.
We find an exact analytical solution for the probability distribution providing
a powerful tool with applications ranging from biology to astrophysics and
laser physics
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