2,128 research outputs found
Type I singularities and the Phantom Menace
We consider the future dynamics of a transient phantom dominated phase of the
universe in LQC and in the RS braneworld, which both have a non-standard
Friedmann equation. We find that for a certain class of potentials, the Hubble
parameter oscillates with simple harmonic motion in the LQC case and therefore
avoids any future singularity. For more general potentials we find that damping
effects eventually lead to the Hubble parameter becoming constant. On the other
hand in the braneworld case we find that although the type I singularity can be
avoided, the scale factor still diverges at late times.Comment: More references added. Final PRD versio
Probing the Stochastic Dynamics of Coronaviruses: Machine Learning Assisted Deep Computational Insights with Exploitable Dimensions
A machine learning assisted efficient, yet comprehensive characterization ofthe dynamics of coronaviruses, in conjunction with finite element (FE)approach, is presented. Without affecting the accuracy of prediction inlow-frequency vibration analysis, an equivalent model for the FE analysis isproposed, based on which the natural frequencies corresponding to first threenon-rigid modes are analyzed. To quantify the inherent system-uncertaintyefficiently, Monte Carlo simulation is proposed in conjunction with themachine learning based FE computational framework for obtaining completeprobabilistic descriptions considering both individual and compound effect ofstochasticity. A variance based sensitivity analysis is carried out to enumeratethe relative significance of different material parameters corresponding tovarious constituting parts of the coronavirus structure. Using the modalcharacteristics like natural frequencies and mode shapes of the virus structureincluding their stochastic bounds, it is possible to readily identifycoronaviruses by comparing the experimentally measured dynamic responsesin terms of the peaks of frequency response function. Results from this first ofits kind study on coronaviruses along with the proposed generic machinelearning based approach will accelerate the detection of viruses and createefficient pathways toward future inventions leading to cure and containmentin the field of virology
Proactive and retroactive interference with associative memory consolidation in the snail Lymnaea is time and circuit dependent
Interference-based forgetting occurs when new information acquired either before or after a learning event attenuates memory expression (proactive and retroactive interference, respectively). Multiple learning events often occur in rapid succession, leading to competition between consolidating memories. However, it is unknown what factors determine which memory is remembered or forgotten. Here, we challenge the snail, Lymnaea, to acquire two consecutive similar or different memories and identify learning-induced changes in neurons of its well-characterized motor circuits. We show that when new learning takes place during a stable period of the original memory, proactive interference only occurs if the two consolidating memories engage the same circuit mechanisms. If different circuits are used, both memories survive. However, any new learning during a labile period of consolidation promotes retroactive interference and the acquisition of the new memory. Therefore, the effect of interference depends both on the timing of new learning and the underlying neuronal mechanisms
Perturbations on steady spherical accretion in Schwarzschild geometry
The stationary background flow in the spherically symmetric infall of a
compressible fluid, coupled to the space-time defined by the static
Schwarzschild metric, has been subjected to linearized perturbations. The
perturbative procedure is based on the continuity condition and it shows that
the coupling of the flow with the geometry of space-time brings about greater
stability for the flow, to the extent that the amplitude of the perturbation,
treated as a standing wave, decays in time, as opposed to the amplitude
remaining constant in the Newtonian limit. In qualitative terms this situation
simulates the effect of a dissipative mechanism in the classical Bondi
accretion flow, defined in the Newtonian construct of space and time. As a
result of this approach it becomes impossible to define an acoustic metric for
a conserved spherically symmetric flow, described within the framework of
Schwarzschild geometry. In keeping with this view, the perturbation, considered
separately as a high-frequency travelling wave, also has its amplitude reduced.Comment: 8 pages, no figur
Curvaton Dynamics in Brane-worlds
We study the curvaton dynamics in brane-world cosmologies. Assuming that the
inflaton field survives without decay after the end of inflation, we apply the
curvaton reheating mechanism to Randall-Sundrum and to its curvature
corrections: Gauss-Bonnet, induced gravity and combined Gauss-Bonnet and
induced gravity cosmological models. In the case of chaotic inflation and
requiring suppression of possible short-wavelength generated gravitational
waves, we constraint the parameters of a successful curvaton brane-world
cosmological model. If density perturbations are also generated by the curvaton
field then, the fundamental five-dimensional mass could be much lower than the
Planck massComment: 47 pages, 1 figure, references added, to be published in JCA
Cosmological evolution of interacting phantom (quintessence) model in Loop Quantum Gravity
The dynamics of interacting dark energy model in loop quantum cosmology (LQC)
is studied in this paper. The dark energy has a constant equation of state
and interacts with dark matter through a form . We
find for quintessence model () the cosmological evolution in LQC is the
same as that in classical Einstein cosmology; whereas for phantom dark energy
(), although there are the same critical points in LQC and classical
Einstein cosmology, loop quantum effect reduces significantly the parameter
spacetime () required by stability. If parameters and satisfy
the conditions that the critical points are existent and stable, the universe
will enter an era dominated by dark energy and dark matter with a constant
energy ratio between them, and accelerate forever; otherwise it will enter an
oscillatory regime. Comparing our results with the observations we find at
confidence level the universe will accelerate forever.Comment: 15 pages, 8 figures, to appear in JCA
A Quintessentially Geometric Model
We consider string inspired cosmology on a solitary -brane moving in the
background of a ring of branes located on a circle of radius . The motion of
the -brane transverse to the plane of the ring gives rise to a radion field
which can be mapped to a massive non-BPS Born-Infeld type field with a cosh
potential. For certain bounds of the brane tension we find an inflationary
phase is possible, with the string scale relatively close to the Planck scale.
The relevant perturbations and spectral indices are all well within the
expected observational bounds. The evolution of the universe eventually comes
to be dominated by dark energy, which we show is a late time attractor of the
model. However we also find that the equation of state is time dependent, and
will lead to late time Quintessence.Comment: 11 pages, 3 figures. References and comments adde
Interneuronal mechanism for Tinbergen's hierarchical model of behavioral choice
Recent studies of behavioral choice support the notion that the decision to carry out one behavior rather than another depends on the reconfiguration of shared interneuronal networks. We investigated another decision-making strategy, derived from the classical ethological literature, which proposes that behavioral choice depends on competition between autonomous networks. According to this model, behavioral choice depends on inhibitory interactions between incompatible hierarchically organized behaviors. We provide evidence for this by investigating the interneuronal mechanisms mediating behavioral choice between two autonomous circuits that underlie whole-body withdrawal and feeding in the pond snail Lymnaea. Whole-body withdrawal is a defensive reflex that is initiated by tactile contact with predators. As predicted by the hierarchical model, tactile stimuli that evoke whole-body withdrawal responses also inhibit ongoing feeding in the presence of feeding stimuli. By recording neurons from the feeding and withdrawal networks, we found no direct synaptic connections between the interneuronal and motoneuronal elements that generate the two behaviors. Instead, we discovered that behavioral choice depends on the interaction between two unique types of interneurons with asymmetrical synaptic connectivity that allows withdrawal to override feeding. One type of interneuron, the Pleuro-Buccal (PlB), is an extrinsic modulatory neuron of the feeding network that completely inhibits feeding when excited by touch-induced monosynaptic input from the second type of interneuron, Pedal-Dorsal12 (PeD12). PeD12 plays a critical role in behavioral choice by providing a synaptic pathway joining the two behavioral networks that underlies the competitive dominance of whole-body withdrawal over feeding
Coupled dark energy: Towards a general description of the dynamics
In dark energy models of scalar-field coupled to a barotropic perfect fluid,
the existence of cosmological scaling solutions restricts the Lagrangian of the
field \vp to p=X g(Xe^{\lambda \vp}), where X=-g^{\mu\nu} \partial_\mu \vp
\partial_\nu \vp /2, is a constant and is an arbitrary function.
We derive general evolution equations in an autonomous form for this Lagrangian
and investigate the stability of fixed points for several different dark energy
models--(i) ordinary (phantom) field, (ii) dilatonic ghost condensate, and
(iii) (phantom) tachyon. We find the existence of scalar-field dominant fixed
points (\Omega_\vp=1) with an accelerated expansion in all models
irrespective of the presence of the coupling between dark energy and dark
matter. These fixed points are always classically stable for a phantom field,
implying that the universe is eventually dominated by the energy density of a
scalar field if phantom is responsible for dark energy. When the equation of
state w_\vp for the field \vp is larger than -1, we find that scaling
solutions are stable if the scalar-field dominant solution is unstable, and
vice versa. Therefore in this case the final attractor is either a scaling
solution with constant \Omega_\vp satisfying 0<\Omega_\vp<1 or a
scalar-field dominant solution with \Omega_\vp=1.Comment: 21 pages, 5 figures; minor clarifications added, typos corrected and
references updated; final version to appear in JCA
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