Analysis Of Low-frequency Spectra Research Articles

Capture the variation of the pore pressure with different geological age from seismic inversion study in the Jaisalmer sub-basin, India

Geoscientific evidence shows that various parameters such as compaction, buoyancy effect, hydrocarbon maturation, gas effect and tectonic activities control the pore pressure of sub-surface geology. Spatially controlled geoscientific data in the tectonically active areas is significantly useful for robust estimation of pre-drill pore pressure. The reservoir which is tectonically complex and pore pressure is changing frequently that circumference motivated us to conduct this study. The changes in pore pressure have been captured from the fine-scale to the broad scale in the Jaisalmer sub-basin. Pore pressure variation has been distinctly observed in pre- and post-Jurassic age based on the current study. Post-stack seismic inversion study was conducted to capturing the variation of pore pressure. Analysis of low-frequency spectrum and integrated interval velocity model provided a detailed feature of pore pressure in each compartment of the study area. Pore pressure estimated from well log data was correlated with seismic inversion based result. Based on the current study one well has been proposed where pore pressure was estimated and two distinguished trends are identified in the study zone. The approaches of the current study were analysed thoroughly and it will be highly useful in complex reservoir condition where pore pressure varies frequently.

Josephson Arbitrary Waveform Synthesizer as a Reference Standard for the Measurement of the Phase of Harmonics in Distorted Waveforms.

We have used the Josephson arbitrary waveform synthesizer (JAWS) to provide traceability for the phase of the harmonics, relative to their fundamental frequency, of a distorted waveform. For distorted waveforms with rms values from 0.154 to 0.2 V and harmonic magnitudes from 5% to 40% of the fundamental, our system can generate odd harmonics up to the 39th with best phase uncertainties from 0.001° to 0.010° (k = 2.0), depending on the harmonic number and harmonic magnitude. We anticipate that the ability of the JAWS to generate distorted waveforms with the lowest possible uncertainty in the magnitude, and phase spectra will make it a unique tool for low-frequency spectrum analysis.

Generation of low-frequency squeezed states

Squeezed state of light is an important resource of optical measuerments below the shot noise limit and has been used to improve measurement sensitivity in many areas such as gravitational wave detection, especially in audio frequency region. Compared with the high-frequency squeezed states, the generation of the low-frequency squeezed states is more difficult, because it is limited by several technical noise sources. In this paper we report the observation of more than 2 dB of vacuum squeezing at 1064 nm in the gravitational-wave detection band down to 3 kHz with a double-resonant optical parametric oscillator (OPO). The OPO has a configuration of linear cavity consisting of an input coupling mirror with a transmission of 11% at 532 nm and an output coupling mirror with the transmission of 12% at 1064 nm. The nonlinear materials in the OPO is type-I periodically poled potassium titanyl phosphate (PPKTP) crystal which is chosen for this experiment due to its higher nonlinearity, broader phase matching temperature, and smaller photo-thermal effect. The OPO is pumped by the light of 532 nm from Nd: YVO4/KTP solid-state laser of maximum optical power 3 W. To avoid various noise coupled from the seed beam, the OPO is seeded by vacuum fluctuations instead of coherent field at the fundamental wavelength (1064 nm). A Pound-Drever-Hall (PDH) locking scheme is used to lock the OPO cavity length with the signal derived from the reflected pump beam, so as to lock the pump field and also lock the fundamental field. To make both the pump and seed beams resonant simultaneously, the temperature of the PPKTP is carefully adjusted. The squeezed state can be detected on a homodyne detection by interfering it with the local oscillator (LO) and detected by a balanced detector with two photodiodes (EXT500 T) but having the same quantum efficiency of 86% at 1064 nm. The subsequent electronic noise is analyzed with a low-frequency spectrum analyzer, which shows that the audio noise sources from lab enviroment, locking quality, escape efficiency, propagation loss, homodyne efficiency and detection efficiency have effect on the squeezing pruced by an OPO.

Terahertz Vibrations of Crystalline Acyclic and Cyclic Diglycine: Benchmarks for London Force Correction Models

Terahertz spectroscopy provides direct information concerning weak intermolecular forces in crystalline molecular solids and therefore acts as an excellent method for calibrating and evaluating computational models for noncovalent interactions. In this study, the low-frequency vibrations of two dipeptides were compared, acyclic diglycine and cyclic diglycine, as benchmark systems for gauging the performance of semiempirical London force correction approaches. The diglycine samples were investigated using pulsed terahertz spectroscopy from 10 to 100 cm(-1) and then analyzed using solid-state density functional theory (DFT) augmented with existing London force corrections, as well as a new parametrization (DFT-DX) based on known experimental values. The two diglycine molecules provide a useful test for the applied models given their similarities, but more importantly the differences in the intermolecular forces displayed by each. It was found that all of the considered London force correction models were able to generate diglycine crystal structures of similar accuracy, but considerable variation occurred in their abilities to predict terahertz frequency vibrations. The DFT-DX parametrization was particularly successful in this investigation and shows promise for the improved analysis of low-frequency spectra.

The influence of transistor nonlinearities on noise properties

A nonlinear field-effect transistor equivalent-circuit model is examined to identify the fundamental mechanisms that up-convert baseband 1/f noise to near-carrier sideband noise when the device is operated in the large-signal regime. This model captures all physical noise sources and nonlinearities in the transistor, and thereby allows a general cause-and-effect treatment. The noise sources in the equivalent-circuit model are determined using low-frequency spectrum analyzer and microwave noise-figure meter data. Using the example of an AlGaN/GaN high electron-mobility transistor, the developed model correctly describes both the measured near-carrier sideband amplitude and phase noise simultaneously.

Influence of bromine on the incomplete devil’s staircase behavior of betaine calcium chloride dihydrate

The results of a comparative Raman study of pure and ${\mathrm{Br}}^{\ensuremath{-}}$-doped betaine calcium chloride dihydrate in the temperature interval 12--292 K are presented. The analysis of the low-frequency Raman spectra at room temperature revealed that the lowest-frequency phonons are associated with the betaines' vibrations whereas the lattice modes sensitive to ${\mathrm{Cl}}^{\ensuremath{-}}/{\mathrm{Br}}^{\ensuremath{-}}$ substitution are found above 44 ${\mathrm{cm}}^{\ensuremath{-}1}.$ The mechanisms responsible for the incommensurate phase are not strongly affected by bromination in contrast with what happens in the commensurate phases. It is shown that bromine weakens hydrogen bonding, preventing the localization of protons related to the onset of the nonmodulated ferroelectric phase. A quantitative analysis of low-frequency spectra provides evidence for a correlation between the anomalous increase of the damping parameter of the activated acoustic mode and the freezing of the random distribution of solitons at low temperatures.

The stability of some Zener-diode-based voltage standards

We report on a study, carried out from the point of view of users of Josephson array voltage standards, of factors limiting the precision of Zener-diode-based electronic voltage reference standards of the type (Fluke 732A) most widely used for Josephson voltage measurements. Frequency-dependent voltage noise was studied with a very low-frequency spectrum analyzer, and was found to be the major factor limiting short-term stability to about one part in 10/sup 8/. For two of the three reference standards tested, humidity effects were the principal factors limiting the medium- and long-term stability of the 1.018 V outputs. These effects were studied by subjecting the standards to step-function changes in relative humidity. For example, increases in ambient relative humidity of 0.01 were found to provoke decreases of 0.05-0.15 /spl mu/V in the 1.018 V output of one Zener. The time lag between the humidity change and the voltage change is characterized by a time constant /spl ges/19 days.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Digital measurement of resistance fluctuations

We describe a digital technique for measuring the spectral density of resistance fluctuations with simultaneous background subtraction. The technique implements either of two equivalent ac bridge techniques that rely on extremely good orthogonality between the two channels of a dual-phase lock-in amplifier. We use a digital signal processor (DSP) chip and a personal computer in place of both the lock-in amplifier and spectrum analyzer. The digital system can measure sample 1/f noise that is 100 times smaller than the experimental background noise; this performance equals or surpasses that of any analog system. The system is low cost, very flexible, and can function as a stand-alone digital lock-in amplifier or low-frequency spectrum analyzer.

PC-based spectrum analyzer

The design and performance analysis of a low-cost, low-frequency spectrum analyzer are described. This instrument has been conceived as a plug-in board to be incorporated in an IBM PC. Although intended primarily for educational purposes, this analyzer is suitable for other applications such as audio, vibrations, etc. The frequency synthesizer, superheterodyne, and harmonics identifier used in the spectrum analyzer are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A low-frequency digital spectrum analyzer for laboratory instruction

The design and implementation of a low-frequency spectrum analyzer is described. The design features a low-cost spectrum analyzer for use in the electrical engineering senior year communications laboratory. The frequency range of the spectrum analyzer extends from under 1 Hz up to 20 kHz. It covers the spectral region of interest in speech processing and baseband data transmission, and provides the students with a flexible signal analysis tool.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-Frequency Spectral Analysis Using a Dynamometer-Type Wattmeter

Two laboratory experiments using the dynamometer-type wattmeter as a low-frequency spectrum analyzer are presented. These experiments are simple, inexpensive, and easily understood by students. The wattmeter spectrum analyzer technique is capable of measuring frequencies from dc to approximately 500 Hz with immediate and meaningful results.