Search results for "Computational physics"
showing 10 items of 725 documents
Time delay in binary systems
2005
The aim of this paper is to study the time delay on electromagnetic signals propagating across a binary stellar system. We focus on the antisymmetric gravitomagnetic contribution due to the angular momentum of one of the stars of the pair. Considering a pulsar as the source of the signals, the effect would be manifest both in the arrival times of the pulses and in the frequency shift of their Fourier spectra. We derive the appropriate formulas and we discuss the influence of different configurations on the observability of gravitomagnetic effects. We argue that the recently discovered PSR J0737-3039 binary system does not permit the detection of the effects because of the large size of the …
Modelling of the magnetic field structures and first measurements of heat fluxes for TEXTOR-DED operation
2004
The dynamic ergodic divertor (DED) was recently installed at the TEXTOR tokamak. One of the aims of the DED is to control and study heat and particle deposition on a plasma wall via modification of the plasma edge by external perturbation coils. Sixteen perturbation coils are mounted on the high-field side of the torus. The external magnetic perturbation creates a zone of chaotic field lines at the plasma edge by destroying several resonant surfaces. These structures have the properties of an open chaotic system while the field lines intersect the tokamak vessel. In order to study the topology of the field lines in different regimes, a set of tools called Atlas was created. Atlas uses a sym…
Fracture processes studied in CRESST
2005
In the early stages of running of the CRESST dark matter search with sapphire crystals as detectors, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time that the energy release in fracture has been accurately measured on a microscopic event-by-event basis. The energy distributions appear to follow a power law, dN/dE proportional to E-beta, similar to the Gutenberg-Richter power law for earthquake magnitudes, and after appropriat…
Estimating accidental coincidences for pixelated PET detectors and singles list-mode acquisition
2007
We have studied the validity of random estimation techniques for various low energy thresholds (LETs) and single list-mode data sets in small animal PET. While a LET below 255 keV helps to increase the sensitivity, it also results in an increase of random coincidences and inter-crystal scatter (ICS). The study is carried out for MADPET-II, a dual-layer positron emission tomography (PET) scanner prototype consisting of LSO crystals read out individually by APDs. The data are acquired in singles list-mode format, and coincidences are computed post-acquisition. To estimate randoms, we have used the delayed coincidence window method (DW), and the singles rate model (SR). Various phantoms were s…
Event-by-event hydrodynamics and elliptic flow from fluctuating initial states
2010
We develop a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow which is measured at different centralities in Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). Fluctuating initial energy density profiles, which here are the event-by-event analogues of the eWN profiles, are created using a Monte Carlo Glauber model. Using the same event plane method for obtaining $v_2$ as in the data analysis, we can reproduce both the measured centrality dependence and the $p_T$ shape of charged-particle elliptic flow up to $p_T\sim2$~GeV. We also consider the relation of elliptic flow to the initial state eccentricity using different reference planes, and di…
Even harmonics generation in plasma as a new tool of current evolution diagnostics
2005
It is shown that using even harmonics of a test wave it is possible to diagnose the fast time evolution of the current density.
High-frequency even harmonics generation in a plasma with electron heat flux
2004
It is shown that in a weakly nonuniform plasma with electron heat flux the generation of odd and even harmonics of high frequency radiation is possible. The even harmonics properties qualitatively differ as compared to those of odd harmonics and depend in an essential way on the heat flux value and orientation with respect to the fundamental wave polarization and propagation directions.
Event rates for CDM detectors from large-scale shell-model calculations
2006
Abstract We investigate the scattering of the CDM candidate LSP (Lightest Supersymmetric Particle) off nuclei. We have computed the associated event rates and annual modulation signals for the 23 Na, 71 Ga, 73 Ge and 127 I CDM detectors by using the nuclear shell model in realistic model spaces and exploiting microscopic effective two-body interactions. Large-scale computations had to be performed in order to achieve convergence of the results. We have tabulated the associated nuclear-structure coefficients for several LSP masses enabling easy interpolation of our results for any other mass. The relevance of the spin-dependent and coherent channels for the event rates is discussed, from bot…
FARCOS, a new array for femtoscopy and correlation spectroscopy
2012
Correlations between two or more particles can be used as a tool to explore the space-time features of nuclear reactions as well as spectroscopic properties of produced unbound clusters. In order to have new options to study the mentioned correlations, FARCOS (Femtoscope ARray for COrrelations and Spectroscopy) has been conceived as a compact high resolution array, composed of square telescopes. In this work the main features of FARCOS array as well as part of the physics cases are described. © Owned by the authors, 2012.
On the correlation between phase-locking modes and Vibrational Resonance in a neuronal model
2018
International audience; We numerically and experimentally investigate the underlying mechanism leading to multiple resonances in the FitzHugh-Nagumo model driven by a bichromatic excitation. Using a FitzHugh-Nagumo circuit, we first analyze the number of spikes triggered by the system in response to a single sinusoidal wave forcing. We build an encoding diagram where different phase-locking modes are identified according to the amplitude and frequency of the sinusoidal excitation. Next, we consider the bichromatic driving which consists in a low frequency sinusoidal wave perturbed by an additive high frequency signal. Beside the classical Vibrational Resonance phenomenon, we show in real ex…