P. Sigray - Academia.edu (original) (raw)

Papers by P. Sigray

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1993

We have developed a novel, nondestructive, beam-profile monitor for ion storage rings. The horizo... more We have developed a novel, nondestructive, beam-profile monitor for ion storage rings. The horizontal profile of the stored ton beam is determined by detecting electrons from the ionization of the residual gas with a two-dimensional position sensitive detector . The strong magnetic field, provided by one of the bending magnets, conserves the information on the initial horizontal positions of ionized electrons during their transport to the detector by means of a vertical electric field. The monitor is tested at the storage ring CRYRING in Stockholm for a 6 MeV/amu D + beam . We show that in this case, where the lifetime of the stored beam is restricted by single scattering on the residual gas, a reduction of the lifetime occurs due to the reduced angular acceptance .

ABSTRACT In this work we demonstrate information theoretic `resonance' type phenomena in ... more ABSTRACT In this work we demonstrate information theoretic `resonance' type phenomena in the performance of a simple static magneto-resistive device. We focus on signal detection applications where probability of detection together with so called phi-divergences, computed for the output, are used as performance measures. In particular we show that, when detecting a DC signal injected on the input under constant SNR, for all but very small input noise levels the performance deteriorates very rapidly with increased noise level. However, using nonlinear theory and by applying an appropriate bias one can `tune' the device to give high performance for a whole range of noise strengths. Maximization of statistical information processing capabilities as a performance criteria for a nonlinear system represents a new approach to sensor/device design. Such an approach is more appropriate than the classical linearization approach in applications where the system is expected to be `noise saturated.' .

Proceedings of the IEEE Signal Processing Workshop on Higher-Order Statistics. SPW-HOS '99, 1999

In this paper we investigate higher-order spectral properties of an electromagnetic (EM) transmis... more In this paper we investigate higher-order spectral properties of an electromagnetic (EM) transmission channel. We compare conventional ensemble averaging to higher-order signal reconstruction for signal to noise enhancement of received real underwater EM pulses. The reconstructed signal is estimated from the bicepstrum and are shown to outperform conventional stacking techniques. Appropriate features based on higher-order moments, bicoherence and cross-bispectrum for object classification are discussed. We use bicoherence for estimation of nonlinear properties in the received pulses. There are no significant quadratic nonlinear contributions in the signal. The nonlinearities are essentially around the power supply frequency and at a region above 17 kHz. The transmission channel transfer function is investigated based on the cross-bispectrum. It is found that several frequencies in the signal bandwidth contain a significant part with a nonlinear gain.

Science, 1994

Knowledge of the abundance of H3+ is needed in interstellar and planetary atmospheric chemistry. ... more Knowledge of the abundance of H3+ is needed in interstellar and planetary atmospheric chemistry. An important destruction mechanism of H3+ is low-energy electron impact followed by dissociation, but estimates of the reaction rate span several orders of magnitude. As an attempt to resolve this uncertainty, the cross section for dissociative recombination of vibrationally cold H3+ has been measured with an ion storage ring down to collision energies below 1 millielectron volt. A rate coefficient of 1.15 x lo-' cubic centimeters per second at 300 kelvin was deduced. The cross section scaled with collision energy according to E-'.I5, giving the rate a temperature dependence of T-0.65.

$Research paper thumbnail of Increase of true double-electron-capture cross sections in slow Xe^{q+}-(Xe,He) collisions at very high q$

Physical Review A, 1992

... However, close similarities of Prad(q) for double Rydberg states of Xe1q-2)+(n1,n'1&#x27... more ... However, close similarities of Prad(q) for double Rydberg states of Xe1q-2)+(n1,n'1'), populated in collisions with Xe and He, suggest that the electronic structure of the incoming projectile rather than the exact nature of the initial cap-ture state (which depends on the initial ...

Journal of Atmospheric and Oceanic Technology, 2004

ABSTRACT Transports between the Swedish mainland and the island of Gotland were studied by means ... more ABSTRACT Transports between the Swedish mainland and the island of Gotland were studied by means of motionally induced voltages. The copper mantle of an existent fiber-optic telecommunications cable was grounded on Gotland, and the data acquisition system was installed on the mainland, whereby the bulk flow over the section could be observed. The magnetic field was simultaneously measured so as to permit a comparison with the induced voltage. It was found that geomagnetic fluctuations only weakly affected the observed voltage differences at subinertial frequencies, whereas in the superinertial range a considerable degree of geomagnetic influence was detected. The induced-voltage results were also compared to the geostrophic transports determined using tidal gauge data, analysis of which showed that the stratification of the western Gotland basin affected both types of calculations. Transport adjustments, based on taking into account the effects of stratification as well as the bedrock geological characteristics, were thus carried out. It was found that the best correspondence between the two independent estimates of the transport was obtained by locating the main halocline at a depth of 78 m, in good agreement with hydrographic results from the region.

Chemical Physics Letters, 1988

ABSTRACT The MgCl+ cation has been observed with spectroscopic methods for the first time. The fa... more ABSTRACT The MgCl+ cation has been observed with spectroscopic methods for the first time. The fast ion beam laser technique was used to record an absorption spectrum due to MgCl+ in the wavelength range 580–620 nm. No banded structure could be observed, indicating that the upper state is purely repulsive or weakly bound. The observed spectrum is ascribed to the A 1Π-X 1Σ+ transition. Calculations of Franck-Condon densities and differential oscillator strengths based on recent ab initio calculated potential curves of MgCl+ by Åkeby and Pettersson are consistent with this interpretation.

Journal of Geophysical Research, 2004

ABSTRACT An evaluation of different bottom friction parameterizations has been performed with a n... more ABSTRACT An evaluation of different bottom friction parameterizations has been performed with a nonlinear barotropic shallow water model. The model was set up for the Baltic Sea and forced with meteorological data during 1 year. The simulations were validated using hourly observations from 38 tide gauge stations around the Baltic. A new parameterization with friction proportional to the scalar product between the flow velocity and the bottom slope was tested and compared with parameterizations using Rayleigh friction, Ekman friction, Laplacian viscosity, or quadratic bottom friction. The new parameterization consistently gave both a smaller error and a better correlation with the observations. The average error with slope friction was 5.0 cm, as compared with 5.2 cm using quadratic bottom friction, the best of the other parameterizations. The correlation using slope friction was 0.92, as compared with 0.91 using quadratic bottom friction. The results were slightly improved by combining slope friction and Rayleigh friction.