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[en] Investigations of the excess current fluctuations from photomultipliers in a range of 10^-3-10^-1Hz are presented. The correlation and amplitude distributions of fluctuations in two types of photomultiplier tube (PMT) in different domains of the above frequency range are studied. To explain the data it is hypothesized that the excess noise is due to the accumulation of electrons on the inside surface of the PMT insulator which changes the potential relief within the tube due to the motion of the charge along the insulator surface in an electric field. The resulting current in the external circuit is a random value, and hence, the appearance of excess fluctuations. 9 refs., 5 figs., 2 tabs

[en] In this work we study the influence of the Newtonian noise on atom interferometers applied to the detection of gravitational waves, and we compute the resulting limits to the sensitivity in two different configurations: a single atom interferometer, or a pair of atom interferometers operated in a differential configuration. We find that for the instrumental configurations considered, and operating in the frequency range [0.1-10] Hz, the limits would be comparable to those affecting large scale optical interferometers. (orig.)

[en] A circuit is described which permits a hysteretic ratio to be graphed versus another experimental parameter. The hysteretic ratio can be defined either: (a) by the two discontinuities of the I--V response (or more exactly the two discontinuities in (dV/dt) or (b) by the two polarity changes (as in ferromagnetic B vs H curves). The circuit features a large dynamic range (>40 dB with no adjustments) and works well for modulation frequencies between 10^-3 and 300 Hz

[en] In space laser interferometer gravitational wave (G.W.) detection missions, the stability of the laser beam pointing direction has to be kept at 10 nrad/√Hz. Otherwise, the beam pointing jitter noise will dominate the noise budget and make the detection of G.W. impossible. Disturbed by the residue non-conservative forces, the fluctuation of the laser beam pointing direction could be a few μrad/√Hz at frequencies from 0.1 mHz to 10 Hz. Therefore, the laser beam pointing control system is an essential requirement for those space G.W. detection missions. An on-ground test of such beam pointing control system is performed, where the Differential Wave-front Sensing technique is used to sense the beams pointing jitter. An active controlled steering mirror is employed to adjust the beam pointing direction to compensate the jitter. The experimental result shows that the pointing control system can be used for very large dynamic range up to 5 μrad. At the interested frequencies of space G.W. detection missions, between 1 mHz and 1 Hz, beam pointing stability of 6 nrad/√Hz is achieved

[en] We have tested ten old novae for the presence of rapid oscillations similar to the 71-second periodicity in the old nova DQ Her. None of the novae displayed coherent periodicities, indicating that the 71-second oscillation of DQ Her must be considered exceptional rather than normal behavior. One of the novae, T Aur, is essentially identical with DQ Her in every respect save that it lacks a rapid oscillation. Thus, the 71-second oscillation does not appear to have, nor have had, any significant impact on the remaining properties of DQ Her

[en] In this paper, dual-frequency GPS data recorded at Varanasi (geographic latitude 25deg 16' N, longitude 82deg 59' E) have been analyzed to study the ionospheric perturbations in total electron content (TEC) due to two recent major earthquakes (M>5.0) whose main shocks occurred on 25 February and 12 March 2010. A monthly median of the TEC and associated inter-quartile range, upper bound and lower bound are utilized as a reference to identify abnormal signals during these two earthquakes. The results show anomalous depletions in the TEC. These pre-earthquake ionospheric anomalies appear within 6 days prior to the earthquakes. We have also analyzed the ELF and VLF spectra observed from the DEMETER micro-satellite above the epicenter of the earthquake to support the ionospheric anomalies prior to the earthquakes. A possible mechanism responsible for the ionospheric anomalies due to earthquakes is also discussed.

[en] It is known that electromagnetic ion cyclotron (EMIC) waves in the Pc 1 frequency range can be responsible for a large amount of energy transport within the magnetosphere, and for energy transfer between different particle populations. Because these waves can play such important roles in the magnetosphere, it is important to study the generation and propagation mechanisms for such waves. The authors make use to the HOTRAY ray tracing code, developed for a hot realistic multi-ion plasma representative of magnetospheric conditions during magnetic storms, to study the growth, propagation, and absorption of EMIC waves in the magnetosphere for L ≤ 7. They compare their calculational results with recent observations from satellite and ground based instrumentation

[en] The new type infrasonic condenser microphone has been made in Institute of Acoustics, CAS. It has many features, such as: the sensitivity is high, 0.1 μbar infrasound pressure can be received; frequency band is wide, cover all infrasonic frequency range, from 10 Hz to 0.001 Hz bellow; output volt is large, such as 400 mV/Pa, then can be directly converted by A/D; dynamic range is wide, the most high sound level ≥108 dB; frequency response is good flat in frequency band necessary; long-term stability of operation is good; the outside of back volume keeps vacuum and prevent with plastic (freedom from zero drift); consistent is good, the head capacitance C₀, the first resonance frequency of stress of membrane and circuit can be adjusted, so can be used to in the infrasound array; volume is small, φ80 x 220 mm, weight is light, 1.6 kg, and easy to potable and installation; membrane mass is small, freedom from vibration, no sense to shock; it forms a complete configuration, can be connected with PC and structured infrasound monitoring system. Adding triangle array, it can get infrasonic arrival time, the most amplitude and period of it, wave direct, wave horizontal tracing velocity and real-time 3D dynamic spectrum and so on

[en] Ground based GW detectors are limited at their lower frequency band (1-10 Hz) by settlement gravity gradients and seismic noise, and their sensitivity peaks at around 100 Hz. Sources in this band are mostly short duration signals, and their rates uncertain. Going down to milli-Hertz frequencies significantly increases the number and types of available sources. LISA was planned with the idea to explore a likely richer region of the GW spectrum, beyond that accessible to ground detectors; the latter are however expected to produce the first GW observations. In this paper I will present the main LISA concepts; in particular, emphasis will be placed on LISAPathFinder, the ESA precursor of LISA, in which our research group in Barcelona is heavily involved.