measurement of noise power spectrum in photon counting PMT's and the effect of the observed (1/f) noise on astronomical photometry

In astronomical photometry, the sensitivity of observations is limited by the dark counts of the photomultiplier tube. In the present work, the effect of dark count noise in photon counting systems is investigated by theory and experimental measurements. Dark counts are considered to be originating from two sources, namely: dc fluctuations and random pulses.Experimental measurements were carried out to determine noise effects in different operating regions of noise dominance. The results provide strong evidence that: in normal operating mode, where the effect of random pulses is dominant, dark counts do not follow Poisson statistics. The observed noise shows strong (1/f) power spectrum, where the observed noise power is found to increase with time of observation.The results are important in photon counting systems operating under dark count limited mode. The conclusions drawn can be useful in obtaining more accurate error estimates and in assessing astronomical photometric observations and data reduction techniques.     

The First Recorded Occurrences and the Distribution of Physalia physalis (Hydrozoa: Physaliidae) in Algerian Waters

Ocean Science Journal - Recently, there have been recorded findings of the pleustonic siphonophore Physalia physalis Linnæus, 1758, in different regions of Algeria. Several colonies washed...     

Mixed mode crack propagation in low brittle rock-like materials

Mixed mode fracture is quite common in rock structures. Numerous investigators have used the Brazilian disk specimens with a central crack for investigating modes I, II, and mixed fracture toughness in brittle materials. In this study, analytical, experimental, and numerical investigations were planned and performed on Central Straight Through Crack Brazilian Disk (CSCBD) specimens. Ranking of geometrical parameters effective on the value of stress intensity factors (SIFs) of CSCBD specimens were obtained using stochastic analysis. Furthermore, experimental tests were undertaken in order to evaluate the crack propagation in rock-like material of low brittleness. Finally, numerical modeling was performed to assess the effect of crack length on the failure mode of CSCBD specimens. Analytical analyses revealed that the inclination angle of the crack with respect to the diametrical load has the most important impact on the SIFs among the geometrical parameters of CSCBD specimen. Performed experimental and numerical analyses also confirmed the effect of inclination angle and crack length and their impact on the mode of failure of the tested specimen.     

Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors

Abstract

This paper refers to the quantification and prediction of the sedimentation rate of 26 hillside-dam reservoirs in Central Tunisia. The objectives of the study are to develop a simple and practical methodology to identify controlling factors of sedimentation, and to propose a regionalization from the study sites. Principal component analysis (PCA) and complementary multi-dimensional statistical methods are used to relate highly variable area-specific sediment yield to hydro-morphometric, lithological, geomorphological and anthropogenic characteristics of catchments. It appears that catchment area is not the main controlling factor of sedimentation in the studied area. The overall slope index, drainage network characteristics and runoff parameters are also important in characterizing sediment yield. Applied to the annual sedimentation rate series, PCA resulted in retaining the first three principal axes, explaining 65% of the total variance. Statistical methods showed that the overall slope index, the total drainage length, the compacity index and the runoff parameters are as important for the sedimentation quantification. This allowed a graphical clustering of the study zone into three distinct groups having similar behaviours: (i) watersheds characterized by high sediment transport rates and high runoff coefficients, (ii) basins distinguished by relatively low values of both flow discharge and sediment transport rates, and (iii) watersheds with an intermediate sediment yield, especially characterized by relatively high relief. In a second step, a multiple regression model including the four characteristic catchment properties was developed, presenting a valuable tool to predict area-specific sediment yield from catchments in central Tunisia. This model shows reasonable efficiency with an absolute prediction error of 81%.

Citation Ayadi, I., Abida, H., Djebbar, Y. & Mahjoub, M. R. (2010) Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors. Hydrol. Sci. J. 55(3), 446–458.     

Magnetosonic rogons in electron-ion plasma

Magnetosonic rogue waves (rogons) are investigated in an electron-ion plasma by deriving the nonlinear Schrödinger (NLS) equation for low frequency limit. The first- and second-order rogue wave solutions of the NLS equation are obtained analytically and examined numerically. It is found that for dense plasma and stronger magnetic field the nonlinearity decreases, which causes the rogon amplitude becomes shorter. However, the electron temperature pumping more energy to the background waves which are sucked to create rogue waves with taller amplitudes.     

Investigation of the 600-km discontinuity under France through travel-time and amplitude anomalies

In this paper, we give a model of the 600-km discontinuity under France, which explains large travel-time and amplitude anomalies on teleseisms as recorded in the French network. It features a large descent from the Ardennes to the Pyrénées, of which tectonic implications are discussed.