25,053 research outputs found
Modeling 3-D objects with planar surfaces for prediction of electromagnetic scattering
Electromagnetic scattering analysis of objects at resonance is difficult because low frequency techniques are slow and computer intensive, and high frequency techniques may not be reliable. A new technique for predicting the electromagnetic backscatter from electrically conducting objects at resonance is studied. This technique is based on modeling three dimensional objects as a combination of flat plates where some of the plates are blocking the scattering from others. A cube is analyzed as a simple example. The preliminary results compare well with the Geometrical Theory of Diffraction and with measured data
Away-side azimuthal distribution in a Markovian parton scattering model
An event generator is constructed on the basis of a model of multiple
scattering of partons so that the trajectory of a parton traversing a dense and
expanding medium can be tracked. The parameters in the code are adjusted to fit
the \Delta\phi azimuthal distribution on the far side when the trigger momentum
is in the non-perturbative region, p_T(trigger)<4 GeV/c. The dip-bump structure
for 1<p_T(assoc)<2.5 GeV/c is reproduced by averaging over the exit tracks of
deflected jets. An essential characteristic of the model, called Markovian
Parton Scattering (MPS) model, is that the scattering angle is randomly
selected in the forward cone at every step of a trajectory that is divided into
many discrete steps in a semi-classical approximation of the non-perturbative
scattering process. Energy loss to the medium is converted to thermal partons
which hadronize by recombination to give rise to the pedestal under the bumps.
When extended to high trigger momentum with \pt(trigger) >8 GeV/c, the model
reproduces the single-peak structure observed by STAR without invoking any new
dynamical mechanism.Comment: 20 pages + 3 figure
Approximating open quantum system dynamics in a controlled and efficient way: A microscopic approach to decoherence
We demonstrate that the dynamics of an open quantum system can be calculated
efficiently and with predefined error, provided a basis exists in which the
system-environment interactions are local and hence obey the Lieb-Robinson
bound. We show that this assumption can generally be made. Defining a dynamical
renormalization group transformation, we obtain an effective Hamiltonian for
the full system plus environment that comprises only those environmental
degrees of freedom that are within the effective light cone of the system. The
reduced system dynamics can therefore be simulated with a computational effort
that scales at most polynomially in the interaction time and the size of the
effective light cone. Our results hold for generic environments consisting of
either discrete or continuous degrees of freedom
The chemical equilibration volume: measuring the degree of thermalization
We address the issue of the degree of equilibrium achieved in a high energy
heavy-ion collision. Specifically, we explore the consequences of incomplete
strangeness chemical equilibrium. This is achieved over a volume V of the order
of the strangeness correlation length and is assumed to be smaller than the
freeze-out volume. Probability distributions of strange hadrons emanating from
the system are computed for varying sizes of V and simple experimental
observables based on these are proposed. Measurements of such observables may
be used to estimate V and as a result the degree of strangeness chemical
equilibration achieved. This sets a lower bound on the degree of kinetic
equilibrium. We also point out that a determination of two-body correlations or
second moments of the distributions are not sufficient for this estimation.Comment: 16 pages, 15 figures, revtex
Wiring Nanoscale Biosensors with Piezoelectric Nanomechanical Resonators
Nanoscale integrated circuits and sensors will require methods for unobtrusive interconnection with the macroscopic world to fully realize their potential. We report on a nanoelectromechanical system that may present a solution to the wiring problem by enabling information from multisite sensors to be multiplexed onto a single output line. The basis for this method is a mechanical Fourier transform mediated by piezoelectrically coupled nanoscale resonators. Our technique allows sensitive, linear, and real-time measurement of electrical potentials from conceivably any voltage-sensitive device. With this method, we demonstrate the direct transduction of neuronal action potentials from an extracellular microelectrode. This approach to wiring nanoscale devices could lead to minimally invasive implantable sensors with thousands of channels for in vivo neuronal recording, medical diagnostics, and electrochemical sensing
Renormalization group improved black hole space-time in large extra dimensions
By taking into account a running of the gravitational coupling constant with
an ultra violet fixed point, an improvement of classical black hole space-times
in extra dimensions is studied. It is found that the thermodynamic properties
in this framework allow for an effective description of the black hole
evaporation process. Phenomenological consequences of this approach are
discussed and the LHC discovery potential is estimated.Comment: 13 pages, 6 figure
- …