A Deconvolution Technique for Determining the Intrinsic Fluorescence Decay Lifetimes of Crude Oils

1988 ◽  
Vol 42 (3) ◽  
pp. 406-410 ◽  
Author(s):  
M. F. Quinn ◽  
S. Joubian ◽  
F. Al-Bahrani ◽  
S. Al-Aruri ◽  
Oussama Alameddine

A simple deconvolution procedure using FT was developed for determining the average lifetime of samples excited by a nitrogen laser pumped dye laser operating at 428 nm. To overcome the noise limitations imposed by including higher frequency harmonics in the analysis, we used an alternative approach. This approach relied on taking the Fourier transform at 21 subharmonic frequencies and using an appropriate weighting procedure in the calculation of amplitude and lifetime of the sample impulse response. A single exponential decay was assumed.

2021 ◽  
pp. 204-268
Author(s):  
Victor Lazzarini

This chapter now turns to the discussion of filters, which extend the notion of spectrum beyond signals into the processes themselves. A gentle introduction to the concept of delaying signals, aided by yet another variant of the Fourier transform, the discrete-time Fourier transform, allows the operation of filters to be dissected. Another analysis tool, in the form of the z-transform, is brought to the fore as a complex-valued version of the discrete-time Fourier transform. A study of the characteristics of filters, introducing the notion of zeros and poles, as well as finite impulse response (FIR) and infinite impulse response (IIR) forms, composes the main body of the text. This is complemented by a discussion of filter design and applications, including ideas related to time-varying filters. The chapter conclusion expands once more the definition of spectrum.


1990 ◽  
Vol 80 (4) ◽  
pp. 832-856
Author(s):  
Hsi-Ping Liu

Abstract Impulse responses including near-field terms have been obtained in closed form for the zero-offset vertical seismic profiles generated by a horizontal point force acting on the surface of an anelastic half-space. The method is based on the correspondence principle. Through transformation of variables, the Fourier transform of the elastic impulse response is put in a form such that the Fourier transform of the corresponding anelastic impulse response can be expressed as elementary functions and their definite integrals involving distance, angular frequency, phase velocities, and attenuation factors. These results are used for accurate calculation of shear-wave arrival rise times of synthetic seismograms needed for data interpretation of anelastic-attenuation measurements in near-surface sediment.


Geophysics ◽  
1996 ◽  
Vol 61 (3) ◽  
pp. 815-820 ◽  
Author(s):  
Binzhong Zhou ◽  
Iain M. Mason ◽  
Stewart A. Greenhalgh

Dip moveout (DMO) processing is a partial prestack migration procedure that has been widely used in seismic data processing. The DMO process has been described in Deregowski (1986), Hale (1991) and Liner (1990). Many different DMO algorithms have been developed over the past decade. These algorithms have been designed to improve either the accuracy or the computational speed of the DMO process. Hale (1984) developed a method for performing DMO via Fourier transforms that is accurate for all reflector dips (assuming constant velocity). Hale’s method is computationally expensive because his DMO operator is temporally nonstationary, but its accuracy and simplicity have made it an industry standard. It has become a benchmark by which results from other DMO algorithms are judged. Of all the methods used to make the frequency‐domain DMO computationally efficient, the technique of logarithmic time stretching, first suggested in Bolondi et al. (1982), is widely used. After logarithmic stretching of the time axis, the DMO operator becomes temporally stationary which enables replacement of the slow temporal Fourier integration with a fast Fourier transform combined with a simple phase shift. Bale and Jakubowicz (1987) presented a log‐stretch DMO operator (hereafter referred to as Bale’s DMO) in the frequency‐wavenumber (F-K) domain without approximations, while Notfors and Godfrey (1987) suggested an approximate version of log‐stretch DMO operator (hereafter referred to as Notfors’s DMO). Surprisingly, Bale’s full log‐stretch DMO operator produces a less satisfactory impulse response than Notfors’s approximate log‐stretch DMO scheme (see Liner, 1990). Liner (1990) attributed this characteristic to the fact that Bale’s DMO derivation implicitly assumes that the Fourier transform frequency in the log‐stretch domain is not time‐dependant. He presented an exact log‐stretch DMO operator (hereafter referred to as Liner’s DMO) which was derived by transforming the time log‐stretched Hale’s (t, x) DMO impulse response into the Fourier domain. Its derivation is relatively complicated, but Liner has shown that his DMO does generate good DMO impulse responses.


1992 ◽  
Vol 46 (7) ◽  
pp. 1140-1142 ◽  
Author(s):  
S. Jarabo ◽  
M. A. Rebolledo ◽  
J.F. Calleja

In this paper the Fourier transform of the time-interval probability (FT-TIP) technique is applied to a fluorescence decay spectroscopy experiment in which a very small signal is detected. The lifetime of the 4 F9/2, level of Er3+ ions in an Er-doped glass is measured by the FT-TIP technique. It is concluded that this technique can be applied to lifetime measurement with small errors, in those experiments where standard techniques do not work well because of the small detected signal.


2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Mikhail Isaev ◽  
Roman G. Novikov

AbstractWe prove Hölder-logarithmic stability estimates for the problem of finding an integrable function v on {{\mathbb{R}}^{d}} with a super-exponential decay at infinity from its Fourier transform {\mathcal{F}v} given on the ball {B_{r}}. These estimates arise from a Hölder-stable extrapolation of {\mathcal{F}v} from {B_{r}} to a larger ball. We also present instability examples showing an optimality of our results.


2021 ◽  
Vol 12 (11) ◽  
pp. 947-962
Author(s):  
Sanjar M. Abrarov ◽  
Rehan Siddiqui ◽  
Rajinder K. Jagpal ◽  
Brendan M. Quine

2021 ◽  
Vol 11 (6) ◽  
pp. 2582
Author(s):  
Lucas M. Martinho ◽  
Alan C. Kubrusly ◽  
Nicolás Pérez ◽  
Jean Pierre von der Weid

The focused signal obtained by the time-reversal or the cross-correlation techniques of ultrasonic guided waves in plates changes when the medium is subject to strain, which can be used to monitor the medium strain level. In this paper, the sensitivity to strain of cross-correlated signals is enhanced by a post-processing filtering procedure aiming to preserve only strain-sensitive spectrum components. Two different strategies were adopted, based on the phase of either the Fourier transform or the short-time Fourier transform. Both use prior knowledge of the system impulse response at some strain level. The technique was evaluated in an aluminum plate, effectively providing up to twice higher sensitivity to strain. The sensitivity increase depends on a phase threshold parameter used in the filtering process. Its performance was assessed based on the sensitivity gain, the loss of energy concentration capability, and the value of the foreknown strain. Signals synthesized with the time–frequency representation, through the short-time Fourier transform, provided a better tradeoff between sensitivity gain and loss of energy concentration.


2021 ◽  
Vol 262 ◽  
pp. 117928
Author(s):  
Shusaku Nakajima ◽  
Shuhei Horiuchi ◽  
Akifumi Ikehata ◽  
Yuichi Ogawa

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