Showing papers on "Noise (radio) published in 1996"
TL;DR: In this paper, the authors present a technique for isolating climate signals in time series with a characteristic "red" noise background which arises from temporal persistence, which is estimated by a robust procedure that is largely unbiased by the presence of signals immersed in the noise.
Abstract: We present a new technique for isolating climate signals in time series with a characteristic ‘red’ noise background which arises from temporal persistence. This background is estimated by a ‘robust’ procedure that, unlike conventional techniques, is largely unbiased by the presence of signals immersed in the noise. Making use of multiple-taper spectral analysis methods, the technique further provides for a distinction between purely harmonic (periodic) signals, and broader-band (‘quasiperiodic’) signals. The effectiveness of our signal detection procedure is demonstrated with synthetic examples that simulate a variety of possible periodic and quasiperiodic signals immersed in red noise. We apply our methodology to historical climate and paleoclimate time series examples. Analysis of a ≈ 3 million year sediment core reveals significant periodic components at known astronomical forcing periodicities and a significant quasiperiodic 100 year peak. Analysis of a roughly 1500 year tree-ring reconstruction of Scandinavian summer temperatures suggests significant quasiperiodic signals on a near-century timescale, an interdecadal 16–18 year timescale, within the interannual El Nino/Southern Oscillation (ENSO) band, and on a quasibiennial timescale. Analysis of the 144 year record of Great Salt Lake monthly volume change reveals a significant broad band of significant interdecadal variability, ENSO-timescale peaks, an annual cycle and its harmonics. Focusing in detail on the historical estimated global-average surface temperature record, we find a highly significant secular trend relative to the estimated red noise background, and weakly significant quasiperiodic signals within the ENSO band. Decadal and quasibiennial signals are marginally significant in this series.
1,143 citations
TL;DR: In this paper, a family of silicon nitride cantilevers ranging in length from 23 to 203 μm were designed and tested, and the frequency spectrum of thermal motion in air and water was measured.
Abstract: We have designed and tested a family of silicon nitride cantilevers ranging in length from 23 to 203 μm. For each, we measured the frequency spectrum of thermal motion in air and water. Spring constants derived from thermal motion data agreed fairly well with the added mass method; these and the resonant frequencies showed the expected increase with decreasing cantilever length. The effective cantilever density (calculated from the resonant frequencies) was 5.0 g/cm3, substantially affected by the mass of the reflective gold coating. In water, resonant frequencies were 2 to 5 times lower and damping was 9 to 24 times higher than in air. Thermal motion at the resonant frequency, a measure of noise in tapping mode atomic force microscopy, decreased about two orders of magnitude from the longest to the shortest cantilever. The advantages of the high resonant frequency and low noise of a short (30 μm) cantilever were demonstrated in tapping mode imaging of a protein sample in buffer. Low‐noise images were tak...
515 citations
01 Jan 1996
TL;DR: In this paper, two similarity spectra, one for the noise from the large turbulence structures/instability waves of the jet flow, the other for the fine-scale turbulence, are identified.
Abstract: It is argued that because of the lack of intrinsic length and time scales in the core part of the jet flow, the radiated noise spectrum of a high-speed jet should exhibit similarity. A careful analysis of all the axisymmetric supersonic jet noise spectra in the data-bank of the Jet Noise Laboratory of the NASA Langley Research Center has been carried out. Two similarity spectra, one for the noise from the large turbulence structures/instability waves of the jet flow, the other for the noise from the fine-scale turbulence, are identified. The two similarity spectra appear to be universal spectra for axisymmetric jets. They fit all the measured data including those from subsonic jets. Experimental evidence are presented showing that regardless of whether a jet is supersonic or subsonic the noise characteristics and generation mechanisms are the same. There is large turbulence structures/instability waves noise from subsonic jets. This noise component can be seen prominently inside the cone of silence of the fine-scale turbulence noise near the jet axis. For imperfectly expanded supersonic jets, a shock cell structure is formed inside the jet plume. Measured spectra are provided to demonstrate that the presence of a shock cell structure has little effect on the radiated turbulent mixing noise. The shape of the noise spectrum as well as the noise intensity remain practically the same as those of a fully expanded jet. However, for jets undergoing strong screeching, there is broadband noise amplification for both turbulent mixing noise components. It is discovered through a pilot study of the noise spectrum of rectangular and elliptic supersonic jets that the turbulent mixing noise of these jets is also made up of the same two noise components found in axisymmetric jets. The spectrum of each individual noise component also fits the corresponding similarity spectrum of axisymmetric jets.
459 citations
IBM1
TL;DR: Noise as it pertains to digital systems is defined and a metric referred to as noise stability is defined, and a static noise analysis methodology based on this metric is introduced to demonstrate how noise can be analyzed systematically.
Abstract: As technology scales into the deep submicron regime, noise immunity is becoming a metric of comparable importance to area, timing, and power for the analysis and design of VLSI systems. This paper defines noise as it pertains to digital systems and addresses the technology trends which are bringing noise issues to the forefront. The noise sources which are plaguing digital systems are explained. A metric referred to as noise stability is defined, and a static noise analysis methodology based on this metric is introduced to demonstrate how noise can be analyzed systematically. Analysis issues associated with on-chip interconnect are also considered. This paper concludes with a discussion of the device, circuit, layout, and logic design issues associated with noise.
333 citations
TL;DR: Noise enhanced stability in an unstable physical system is experimentally detected and the average escape time has a maximum for a finite value of the noise intensity.
Abstract: We experimentally detect noise enhanced stability in an unstable physical system. The average escape time from a metastable, periodically driven, system is measured in the stable and unstable regimes in a noisy environment. In the unstable regime, we measure that the average escape time has a maximum for a finite value of the noise intensity. The scaling properties of the average escape time and of the variance of escape times are compared with the predictions obtained for a system in a marginal state.
267 citations
212 citations
TL;DR: These experiments indicate that the noise is generated by spontaneous activation of cGMP phosphodiesterase (PDE) through a process that does not involve transducin, indicating that endogenous gamma does not completely dissociate from the catalytic subunit of PDE during spontaneous activation.
176 citations
TL;DR: In this paper, it was shown explicitly how, at high power, both the laser field and the laser noise source become classical and that the increase in noise in lasers with open cavities is not due to enhanced spontaneous emission as once thought, but to single-pass amplification.
Abstract: The basic equations governing noise phenomena are derived from first principles and applied to examples in optical communications. Quantum noise arises from two sources, the momentum fluctuations of electrons at optical frequencies and the uncertainty-related fluctuations of the electromagnetic field. Shot noise results from the beating of the noise sources with the signal field. In high-gain amplifiers, the spontaneous-emission noise dominates shot noise and results in a noise figure of at least 3 dB. It is shown explicitly how, at high power, both the laser field and the laser noise source become classical. The increase in noise in lasers with open cavities is not due to enhanced spontaneous emission as once thought, but to single-pass amplification. The noise fields and spontaneous currents have Gaussian distributions, while nonlasing modes have exponential photon-number distributions. Low-frequency intensity fluctuations arise from the electric current driving the laser and can be sub-Poissonian, in contrast to shot noise, which has a Poissonian distribution. The calculational tools are a wave equation for the field operator and a rate equation for the carrier-number operator, each containing spontaneous current noise sources. The correlation functions of these sources are determined by the fluctuation-dissipation theorem. [S0034-6861(96)00503-X]
150 citations
TL;DR: In this article, the authors used a deep (1500 m) cased borehole near the town of Datil in west-central New Mexico to study high-frequency (>1 Hz) seismic noise characteristics.
Abstract: We used a deep (1500 m) cased borehole near the town of Datil in west-central New Mexico to study high-frequency (>1 Hz) seismic noise characteristics. The remote site had very low levels of cultural noise, but strong winds (winter and spring) made the site an excellent candidate to study the effects of wind noise on seismograms. Along with a three-component set of surface sensors (Teledyne Geotech GS-13), a vertical borehole seismometer (GS-28) was deployed at a variety of depths (5, 43, and 85 m) to investigate signal and noise variations. Wind speed was measured with an anemometer. Event-triggered and time-triggered data streams were recorded on a RefTek 72-02 data acquisition system located at the site. Our data show little cultural noise and a strong correlation between wind speed and seismic background noise. The minimum wind speed at which the seismic background noise appears to be influenced varies with depth: 3 m/sec at the surface, 3.5 m/sec at 43 m in depth, and 4 m/sec at 85 m in depth. For wind speed below 3 to 4 m/sec, we observe omni-directional background noise that is coherent at frequencies below 15 Hz. This coherence is destroyed when wind speeds exceed 3 to 4 m/sec. We use a test event ( Md ∼ 1.6) and superimposed noise to investigate signal-to-noise ratio (SNR) improvement with sensor depth. For the low Q valley fill of the Datil borehole (DBH) site, we have found that SNR can be improved by as much as 20 to 40 dB between 23 and 55 Hz and 10 to 20 dB between 10 and 20 Hz, by deploying at a 43-m depth rather than at the surface. At the surface, there is little signal above noise in the 23- to 55-Hz frequency band for wind speeds greater than 8 m/sec. Thus, high-frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m. Because we observe only minor further reductions in seismic background noise (SBN) at deeper depths, 40 m is likely to be a reasonable deployment depth for other high-frequency-monitoring sites in similar environmental and geologic conditions.
144 citations
01 Jun 1996
TL;DR: A preconditioned recycled Krylov-subspace method to accelerate a recently developed approach for ac and noise analysis of linear periodically-varying communication circuits and is shown to be up to forty times faster than the standard optimized direct methods.
Abstract: In this paper we present a preconditioned recycled Krylov-subspace method to accelerate a recently developed approach for ac and noise analysis of linear periodically-varying communication circuits. Examples are given to show that the combined method can be used to analyse switching filter frequency response, mixer 1/f noise frequency translation, and amplifier intermodulation distortion. In addition, it is shown that for large circuits the preconditioned recycled Krylov-subspace method is up to forty times faster than the standard optimized direct methods.
135 citations
TL;DR: This work evaluates the precision with which Ω can be determined by a CMB map as a function of sky coverage, pixel noise, and beam size.
Abstract: Variations in Ω, the total density of the Universe, leave an imprint on the power spectrum of temperature fluctuations in the cosmic microwave background (CMB). We evaluate the precision with which Ω can be determined by a CMB map as a function of sky coverage, pixel noise, and beam size. Assuming only that the primordial density perturbations were adiabatic and with no prior information on the values of any other cosmological parameters, a full-sky CMB map at 0.5° angular resolution and a noise level of 15 μK per pixel can determine Ω with a standard error of 5%. If all other cosmological parameters are fixed, Ω can be measured to better than 1%.
TL;DR: In this paper, two microbarometers have been installed in the seismic vault of two different GEOSCOPE stations, one at SSB and the other at TAM, to correct the seismic signals from the atmospheric pressure noise, a transfer function between the pressure data and the seismic data is inverted.
Abstract: Seismic investigations are mainly limited by seismic noise. Two microbarometers have been installed in the seismic vault of two different GEOSCOPE stations, one at SSB and the other at TAM. All vertical components and most of the horizontal components show a significant correlation with pressure. In order to correct the seismic signals from the atmospheric pressure noise, a transfer function between the pressure data and the seismic data is inverted. Results show that, after correction, the noise levels reached on the horizontal components are similar between the two stations, and the vertical components display noise levels below the low-noise model as defined by Peterson (1993). This technique reduces part of the noise and allows detection of small earthquakes and a better extraction of normal modes. The analysis of the lowest normal modes of the Earth excited by the M_S = 8.2 Macquarie Island earthquake is given to illustrate the perspectives of the method.
TL;DR: In this paper, the authors present a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses and demonstrate that there is a definite "size effect" for multiplication regions less than approximately 0.5 μm.
Abstract: It is well known that the gain‐bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This letter presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite ‘‘size effect’’ for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process.
TL;DR: In this paper, a balanced photoreceiver was used to reject both laser intensity noise and noise added by an erbium-doped fiber amplifier, and the results of a 12-GHz downconverting optical link were presented that demonstrate shot-noise-limited performance at a maximum total photore receiver current of 72 mA.
Abstract: Experimental results of a 12-GHz downconverting optical link are presented that demonstrate shot-noise-limited performance at a maximum total photoreceiver current of 72 mA. A balanced photoreceiver is utilized to reject both laser intensity noise and noise added by an erbium-doped fiber amplifier. The receiver was constructed of four commercial 2-GHz photodetectors, each capable of detecting greater than 20 mA of average photocurrent with less than I-dB compression in received RF power.
TL;DR: In this paper, the effects of a hot fluid in motion immersed in an external medium at rest are used to predict the noise power radiated from a gaseous hot turbulent jet, provided the jets are fully expanded and are devoid of shock waves.
TL;DR: In this paper, a 1 THz quasioptical SIS mixer using a twin-slot antenna, an antireflection-coated silicon hyperhemispherical lens, Nb/Aloxide/Nb tunnel junctions, and an aluminum normal-metal tuning circuit in a two-junction configuration is described.
Abstract: We describe a 1 THz quasioptical SIS mixer which uses a twin-slot antenna, an antireflection-coated silicon hyperhemispherical lens, Nb/Al-oxide/Nb tunnel junctions, and an aluminum normal-metal tuning circuit in a two-junction configuration. Since the mixer operates substantially above the gap frequency of niobium (nu >~ 2 Delta/h ~ 700 GHz), a normal metal is used in the tuning circuit in place of niobium to reduce the Ohmic loss. The frequency response of the device was measured using a Fourier transform spectrometer and agrees reasonably well with the theoretical prediction. At 1042 GHz, the uncorrected double-sideband receiver noise temperature is 840 K when the physical temperature of the mixer is 2.5 K. This is the first SIS mixer which outperforms GaAs Schottky diode mixers by a large margin at 1 THz.
TL;DR: In this paper, a distributed Josephson junction parametric amplifier with active gain medium consisting of a series array of 1000 Josephson junctions embedded in a coplanar waveguide is presented.
Abstract: We have obtained parametric gain at 19 GHz from a distributed Josephson junction parametric amplifier whose active gain medium consists of a series array of 1000 Josephson junctions embedded in a coplanar waveguide. When cooled to 1.7 K the amplifier provides 16 dB gain in a mode where the internally generated double sideband noise referred to input is 0.5±0.1 K. This noise is consistent with Nyquist noise generated from the losses. An instantaneous bandwidth of 125 MHz has been observed with a peak gain of 12 dB. The 3 dB compression point with a peak gain of 14.6 dB is ‐90.5 dB and the dynamic range is 38 dB.
TL;DR: An active noise control stethoscope enables a physician or paramedic to check vital signs in the presence of high background noise levels as mentioned in this paper. But it is not suitable for use in medical applications.
Abstract: An active noise control stethoscope enables a physician or paramedic to check vital signs in the presence of high background noise levels. A digital processing technique is used to remove noise from the output of a main detection sensor, the detector being impedance mismatched with air and therefore less sensitive to external airborne noise. Instead of a microphone, the detector uses a piezoceramic transflexural actuator mounted in a cylindrical piece of brass, with a polyurethane coating placed over the active side of the sensor to keep the sensor waterproof and broaden the response of the sensor. An identical sensor is placed above the device to detect background noise adjacent the device, the signals being combined to obtain a signal free of background noise. A third sensor is also used to electronically remove noise detected by the main sensor, the third sensor being positioned to pick-up noise coupled through the patient's body. The time varying voltages from signals output by these sensors are digitized and processed by the digital signal processor, and the output used to drive the speakers in the headset. The digital signal processor uses a least mean squared algorithm to digitally subtract out the part of the detector signal that is correlated to the signals from the second and third sensors. In addition, noise penetrating the earcups of the headset is reduced by using the speakers to generate antinoise. The antinoise is generated by a filtered X-adaptive digital algorithm, and also by a random noise cancellation system which sets up an infinite impulse response filter in which the coefficients are continually updated for minimizing an ear sensitivity weighted sound pressure level detected by a microphone inside the headset.
TL;DR: In this article, a longwavelength InAs1−xSbx/p−InSb heterostructures are derived from GaAs substrates by low pressure metalorganic chemical vapor deposition (LP•MOCVD).
Abstract: Long‐wavelength InAs1−xSbx photoconductors operated without cryogenic cooling are reported. The devices are based on p‐InAs1−xSbx/p‐InSb heterostructures grown on (100) semi‐insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP‐MOCVD). Photoreponse up to 14 μm has been obtained in a sample with x=0.77 at 300 K, which is in good agreement with the measured infrared absorption spectra. The corresponding effective lifetime of ≊0.14 ns at 300 K has been derived from stationary photoconductivity. The Johnson noise limited detectivity at λ=10.6 μm is estimated to be about 3.27×107 cm Hz1/2/W at 300 K.
TL;DR: The cardiac Na+, Ca2+ exchanger (NCX1) is thought to achieve a high turnover rate, but all estimates to date are indirect, so two new strategies demonstrate that maximum unitary exchange currents are about 1 fA and that they fluctuate between on and off levels similar to ion channel currents.
TL;DR: In this article, an integrated quasioptical receiver consisting of a planar double dipole antenna, superconductor insulator-superconductor mixer and a superconducting local oscillator (LO) with matching circuits has been designed, fabricated and tested in the frequency range 360-490 GHz.
Abstract: An integrated quasioptical receiver consisting of a planar double dipole antenna, superconductor‐insulator‐superconductor mixer and a superconducting local oscillator (LO) with matching circuits has been designed, fabricated and tested in the frequency range 360–490 GHz. A flux‐flow oscillator (FFO) based on unidirectional and viscous flow of magnetic vortexes in a long Josephson tunnel junction, is employed as a local oscillator. All components of the receiver are integrated on a 4 mm×4 mm×0.2 mm crystalline quartz substrate using a single Nb–AlOx–Nb trilayer. The lowest DSB noise temperature of 470–560 K has been achieved within a frequency range of 425–455 GHz.
TL;DR: A fully automatic, hands‐off algorithm for calculation of a noise model is developed and replaces the previous manual and subjective weeding out of poor data which was based on the experience of the interpreter.
Abstract: Knowledge of the noise level and the nature of the noise is critical when processing transient electromagnetic (TEM) sounding data. An inadequate noise estimation may result in an erroneous interpr...
TL;DR: The Kirchhoff method as discussed by the authors consists of the calculation of the nonlinear near and midfields, usually numerically, with the far-field solutions found from a linear KF formulation evaluated on a surface D surrounding the non-linear field.
Abstract: The Kirchhoff method consists of the calculation of the nonlinear near- and midfields, usually numerically, with the far-field solutions found from a linear Kirchhoff formulation evaluated on a surface D surrounding the nonlinear field. The surface S is assumed to include all the nonlinear flow effects and noise sources
Patent•
04 Jun 1996
TL;DR: In this article, a rotating cylindrical collimator limits the X rays to a pencil-beam, which is directed across and through an object prior to interception by a detector.
Abstract: An improved X-ray inspection system comprises a pulsed X-ray source configured to emit short, X-ray pulses for reducing afterglow noise. A rotating cylindrical collimator limits the X rays to a pencil-beam, which is directed across and through an object prior to interception by a detector. The detector comprises a plurality of scintillating screens optically coupled to photoemissive detecting elements. When the short X-ray pulses generated by the source are intercepted by the detector, the outputs of the detecting elements are sampled for only a short period of time, which sampling period is immediately followed by a substantially longer quiescent period of time during which the elements are not sampled. Therefore, only a slight portion of the typical afterglow noise occurs during measurement of a useful X-ray signal.
TL;DR: In this paper, surface and subsurface high-frequency (>1 Hz) noise data were recorded using nearly identical instrumentation at three widely separated sites in the United States (Amarillo, Texas, Datil, New Mexico; and Pinedale, Wyoming) for extended periods of time under varying wind conditions.
Abstract: Surface and subsurface high-frequency (>1 Hz) noise data were recorded using nearly identical instrumentation at three widely separated sites in the United States (Amarillo, Texas; Datil, New Mexico; and Pinedale, Wyoming) for extended periods of time under varying wind conditions. While the sites are geologically distinct, the near-surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site. Noise levels seen at or near the surface (5 m or less) are much higher (up to 30 dB) and much more variable (power range up to 44 dB) than those seen at depth (the smallest range was 9 dB for 1951 m at Amarillo). The greatest gains in noise level reduction are realized within the first 100 m and probably much shallower (
TL;DR: Experimental results that illustrate how laser intensity noise near the quantum-noise limit is transferred in an injection-locked cw Nd:(yttrium aluminum garnet) nonplanar ring-oscillator laser are presented and it is shown that the injection- Locked laser can generate and preserve nonclassical states.
Abstract: We present experimental results that illustrate how laser intensity noise near the quantum-noise limit is transferred in an injection-locked cw Nd:(yttrium aluminum garnet) nonplanar ring-oscillator laser. We show that these results are in extremely good agreement with our quantum-mechanical model describing the injection locking process [T. C. Ralph, C. C. Harb, and H.-A. Bachor, Phys. Rev. A]. Three regions in the intensity-noise spectrum are identified and we show that different minimum noise levels exist in these regions. Finally, we show that the injection-locked laser can generate and preserve nonclassical states. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the amplitude and phase differences of the reconstructed electron wave are compared with the existing theory, and the results of statistical evaluations collected from experimental holograms are compared to the existing theories.
TL;DR: In this article, the cyclotron instability of an anisotropic smooth energetic electron distribution is shown to create a step-like deformation of the distribution function at the boundary between resonant and nonresonant electrons.
Abstract: It is shown that quasi-monochromatic whistler waves (wavelets) can be caused by the strong cyclotron instability, stimulated by hiss emissions. The hiss, generated by the cyclotron instability of an anisotropic smooth energetic electron distribution, creates a step-like deformation of the distribution function at the boundary between resonant and nonresonant electrons. This deformation leads to the strong amplification of the wavelet whose frequency corresponds to that for cyclotron resonance with electrons at the step. Analytical calculations for this amplification have been made using the rigorous theory of the cyclotron instability in an inhomogeneous magnetic field. The wave amplification can be 2 orders of magnitude greater than that for a smooth distribution function. A self-consistent computational analysis of the cyclotron instability is developed on the basis of quasi-linear theory. This confirms both the formation of the step-like deformation of the distribution function and the wavelet generation.
TL;DR: In this paper, the low-frequency noise behavior of devices fabricated in silicon-on-insulator technologies is described and illustrated by experimental results, mainly obtained on MOSFETs.
Abstract: In this overview, the low-frequency noise behaviour of devices fabricated in silicon-on-insulator technologies is described. The different potential noise sources are analysed and illustrated by experimental results, mainly obtained on MOSFETs. Some SOI-specific noise behaviour is highlighted, as for instance the kink-related excess low-frequency noise overshoot. It is shown furthermore that SOI MOSFETs suffer from so-called random telegraph signals, which can originate from the front- or the back-gate dielectric, or from defects located in the thin Si active layer. The impact of the substrate type (SIMOX, bonded, ZMR,…) is discussed. At the same time, it is shown that the used technology and device structure can have a pronounced effect on the LF noise performance. Finally, the response of SOI MOSFETs on ionizing radiation (γs, X-rays,…) is studied through the LF noise degradation, in view of radiation-hardened applications.