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Low-frequency Noise (low-frequency + noise)

Distribution by Scientific Domains

Physics and Astronomy	42%
Life Sciences	28%

Selected Abstracts

Low-frequency noise in structures with porous silicon in different gas media

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007
Z. H. Mkhitaryan
Abstract Noise properties of porous silicon/single-crystalline silicon structures under exposure to active gases are investigated for the first time. Current-voltage and noise characteristics of samples are measured. The Al/porous silicon/single-crystalline Si/Al sandwich-structures were placed in a special chamber and the influence of adsorption of various gases on low-frequency noise of the samples was revealed. The adsorption changes the dynamics of the interaction of charge carriers with traps, i.e. the noise characteristics of the samples. The results are encouraging for practical applications of porous silicon structures as gas sensors using measurements of low-frequency noise characteristics. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach

HUMAN BRAIN MAPPING, Issue 3 2006
Douglas Cheyne
Abstract We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude ,50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of ,150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data. Hum. Brain Mapping 2005. © 2005 Wiley-Liss, Inc. [source]

Low-frequency noise conversion modeling in RF devices under forced nonlinear operation

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2006
Gabriele Conte
Abstract The article addresses the frequency conversion of low-frequency noise deriving from trap-assisted generation-recombination (GR) noise in RF devices under forced, nonlinear operation through a physics-based noise model. The superposition of the stationary (small-signal) GR spectra originating from noninteracting trap levels with properly distributed energies is shown, in simple yet significant device case studies, to yield a 1/f or 1/f -like behaviour over a prescribed frequency range. The same trap distribution is also exploited for large-signal, cyclostationary noise simulation in forced periodic conditions. In this case, low-frequency 1/f -like noise is shown to be upconverted from the baseband to all noise sidebands. Circuit-level compact modeling strategies for noise-frequency conversion based on the modulation of small-signal low-frequency noise are also investigated and compared to the fundamental approach. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source]

Timing stability of millisecond pulsars and prospects for gravitational-wave detection

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
J. P. W. Verbiest
ABSTRACT The analysis of high-precision timing observations of an array of ,20 millisecond pulsars (a so-called ,timing array') may ultimately result in the detection of a stochastic gravitational-wave background. The feasibility of such a detection and the required duration of this type of experiment are determined by the achievable rms of the timing residuals and the timing stability of the pulsars involved. We present results of the first long-term, high-precision timing campaign on a large sample of millisecond pulsars used in gravitational-wave detection projects. We show that the timing residuals of most pulsars in our sample do not contain significant low-frequency noise that could limit the use of these pulsars for decade-long gravitational-wave detection efforts. For our most precisely timed pulsars, intrinsic instabilities of the pulsars or the observing system are shown to contribute to timing irregularities on a 5-year time-scale below the 100 ns level. Based on those results, realistic sensitivity curves for planned and ongoing timing array efforts are determined. We conclude that prospects for detection of a gravitational-wave background through pulsar timing array efforts within 5 years to a decade are good. [source]

Low-frequency noise in structures with porous silicon in different gas media

Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales

ANIMAL CONSERVATION, Issue 1 2001
Donald A. Croll
The human contribution to ambient noise in the ocean has increased over the past 50 years, and is dominated by low-frequency (LF) sound (frequencies <1000 Hz) from shipping, oil and gas development, defence-related and research activities. Mysticete whales, including six endangered species, may be at risk from this noise pollution because all species produce and probably perceive low-frequency sound. We conducted a manipulative field experiment to test the effects of loud, LF noise on foraging fin blue (B. musculus) and (Balaenoptera physalus) whales off San Nicolas Island, California. Naive observers used a combination of attached tracking devices, ship-based surveys, aerial surveys, photo-identification and passive monitoring of vocal behaviour to examine the behaviour and distribution of whales when a loud LF source (US Navy SURTASS LFA) was and was not transmitting. During transmission, 12-30% of the estimated received levels of LFA of whales in the study area exceeded 140 dB re 1 ,Pa. However, whales continued to be seen foraging in the region. Overall, whale encounter rates and diving behaviour appeared to be more strongly linked to changes in prey abundance associated with ceanographic parameters than to LF sound transmissions. In some cases, whale vocal behaviour was significantly different between experimental and non-experimental periods. However, these differences were not consistent and did not appear to be related to LF sound transmissions. At the spatial and temporal scales examined, we found no obvious responses of whales to a loud, anthropogenic, LF sound. We suggest that the cumulative effects of anthropogenic LF noise over larger temporal and spatial scales than examined here may be a more important consideration for management agencies. [source]