566 research outputs found

### Microlensing Parallax for Observers in Heliocentric Motion

Motivated by the ongoing Spitzer observational campaign, and the forecoming
K2 one, we revisit, working in an heliocentric reference frame, the geometrical
foundation for the analysis of the microlensing parallax, as measured with the
simultaneous observation of the same microlensing event from two observers with
relative distance of order AU. For the case of observers at rest we discuss the
well known fourfold microlensing parallax degeneracy and determine an equation
for the degenerate directions of the lens trajectory. For the case of observers
in motion, we write down an extension of the Gould (1994) relationship between
the microlensing parallax and the observable quantities and, at the same time,
we highlight the functional dependence of these same quantities from the
timescale of the underlying microlensing event. Furthermore, through a series
of examples, we show the importance of taking into account the motion of the
observers to correctly recover the parameters of the underlying microlensing
event. In particular we discuss the cases of the amplitude of the microlensing
parallax and that of the difference of the timescales between the observed
microlensing events, key to understand the breaking of the microlensing
parallax degeneracy. Finally, we consider the case of the simultaneous
observation of the same microlensing event from ground and two satellites, a
case relevant for the expected joint K2 and Spitzer observational programs in
2016.Comment: Accepted for publication in Ap

### Generalized Uncertainty Principle from Quantum Geometry

The generalized uncertainty principle of string theory is derived in the
framework of
Quantum Geometry by taking into account the existence of an upper limit on
the acceleration of massive particles.Comment: 9 pages, LATEX file, to appear in Int. Jou. Theor. Phy

### Glassy behavior of the site frustrated percolation model

The dynamical properties of the site frustrated percolation model are
investigated and compared with those of glass forming liquids. When the density
of the particles on the lattice becomes high enough, the dynamics of the model
becomes very slow, due to geometrical constraints, and rearrangement on large
scales is needed to allow relaxation. The autocorrelation functions, the
specific volume for different cooling rates, and the mean square displacement
are evaluated, and are found to exhibit glassy behavior.Comment: 8 pages, RevTeX, 11 fig

### Effects of Noise in a Cortical Neural Model

Recently Segev et al. (Phys. Rev. E 64,2001, Phys.Rev.Let. 88, 2002) made
long-term observations of spontaneous activity of in-vitro cortical networks,
which differ from predictions of current models in many features. In this paper
we generalize the EI cortical model introduced in a previous paper (S.Scarpetta
et al. Neural Comput. 14, 2002), including intrinsic white noise and analyzing
effects of noise on the spontaneous activity of the nonlinear system, in order
to account for the experimental results of Segev et al.. Analytically we can
distinguish different regimes of activity, depending from the model parameters.
Using analytical results as a guide line, we perform simulations of the
nonlinear stochastic model in two different regimes, B and C. The Power
Spectrum Density (PSD) of the activity and the Inter-Event-Interval (IEI)
distributions are computed, and compared with experimental results. In regime B
the network shows stochastic resonance phenomena and noise induces aperiodic
collective synchronous oscillations that mimic experimental observations at 0.5
mM Ca concentration. In regime C the model shows spontaneous synchronous
periodic activity that mimic activity observed at 1 mM Ca concentration and the
PSD shows two peaks at the 1st and 2nd harmonics in agreement with experiments
at 1 mM Ca. Moreover (due to intrinsic noise and nonlinear activation function
effects) the PSD shows a broad band peak at low frequency. This feature,
observed experimentally, does not find explanation in the previous models.
Besides we identify parametric changes (namely increase of noise or decreasing
of excitatory connections) that reproduces the fading of periodicity found
experimentally at long times, and we identify a way to discriminate between
those two possible effects measuring experimentally the low frequency PSD.Comment: 25 pages, 10 figures, to appear in Phys. Rev.

### Neutrino Oscillations in Caianiello's Quantum Geometry Model

Neutrino flavor oscillations are analyzed in the framework of Quantum
Geometry model proposed by Caianiello. In particular, we analyze the
consequences of the model for accelerated neutrino particles which experience
an effective Schwarzschild geometry modified by the existence of an upper limit
on the acceleration, which implies a violation of the equivalence principle. We
find a shift of quantum mechanical phase of neutrino oscillations, which
depends on the energy of neutrinos as E^3. Implications on atmospheric and
solar neutrinos are discussed.Comment: 11 page

### A new view on relativity: Part 2. Relativistic dynamics

The Lorentz transformations are represented on the ball of relativistically
admissible velocities by Einstein velocity addition and rotations. This
representation is by projective maps. The relativistic dynamic equation can be
derived by introducing a new principle which is analogous to the Einstein's
Equivalence Principle, but can be applied for any force. By this principle, the
relativistic dynamic equation is defined by an element of the Lie algebra of
the above representation. If we introduce a new dynamic variable, called
symmetric velocity, the above representation becomes a representation by
conformal, instead of projective maps. In this variable, the relativistic
dynamic equation for systems with an invariant plane, becomes a non-linear
analytic equation in one complex variable. We obtain explicit solutions for the
motion of a charge in uniform, mutually perpendicular electric and magnetic
fields. By the above principle, we show that the relativistic dynamic equation
for the four-velocity leads to an analog of the electromagnetic tensor. This
indicates that force in special relativity is described by a differential
two-form

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