Noise coherent

In pulse NMR, there is always noise coherent with the pulse sequence because of the transient nature of the experiment. This is in addition to the usual random noise as well as other systematic noises such as the 50 or 60 Hz "hum from the ac source which are not synchronized with the pulses. These non-synchronous components of noise can be reduced either by appropriate filtering or by multiscan averaging or both. In this section we will deal with noise coherent with the pulse sequence. Even if such noises were very small, they will add upon signal averaging (just like the desired signal) and may, therefore, be troublesome in experiments where very many FID s are accumulated due to inherently poor S/N. 

Since the noise coherent with the FID is usually a ringing of some kind generated by the high intensity rf pulse, such ringing must be suppressed as much as possible. Some of the major sources of ringing were discussed in section VI.B.5. 

Ringler AT, Hutt CR (2010) Self-noise models of seismic instruments. Seismol Res Lett 81 972-983 Ringler AT, Hutt CR, Evans JR, Sandoval LD (2011) A comparison of seismic instrument noise coherence analysis techniques. Bull Seismol Soc Am 101 558-567... 

Enloe, Noise-like structure in the image of diffusely reflecting objets in coherent illumination . Bell Syst. Tech. I., vol. 46, p.1479(1967). 

A connnon teclmique used to enliance the signal-to-noise ratio for weak modes is to inject a local oscillator field polarized parallel to the RIKE field at the detector. This local oscillator field is derived from the probe laser and will add coherently to the RIKE field [96]. The relative phase of the local oscillator and the RIKE field is an important parameter in describing the optical heterodyne detected (OHD)-RIKES spectrum. If the local oscillator at the detector is in phase with the probe wave, the heterodyne mtensity is proportional to... 

Adaptive optics requires a reference source to measure the phase error distribution over the whole telescope pupil, in order to properly control DMs. The sampling of phase measurements depends on the coherence length tq of the wavefront and of its coherence time tq. Both vary with the wavelength A as A / (see Ch. 1). Of course the residual error in the correction of the incoming wavefront depends on the signal to noise ratio of the phase measurements, and in particular of the photon noise, i.e. of the flux from the reference. This residual error in the phase results in the Strehl ratio following S = exp —a ). 

A simple expression for the signal-to-noise ratio (SNR) of a measurement of visibility amplitude involves several parameters relating to interferometer and source properties. The formula presented here provides the fundamental sensitivity limit. Contrast loss arising from instrumental jitter and seeing are summarised in a common factor system Strehl , which is the ratio of the number of photons which can be used for a coherent measurement to the... 

Keywords coherent detection, incoherent source, thermal emission, Shottky noise, photon... 

These data indicate that thermal losses during unsteady flame-wall interactions constitute an intense source of combustion noise. This is exemplified in other cases where extinctions result from large coherent structures impacting on solid boundaries, or when a turbulent flame is stabilized close to a wall and impinges on the boundary. However, in many cases, the flame is stabilized away from the boundaries and this mechanism may not be operational. 

Increasing the number of dimensions from two to three may result in a reduction in the signal/noise (S/N) ratio. This may be due either to the distribution of the intensity of the multiplet lines over three dimensions or to some of the coherence transfer steps being inefficient, resulting in weak 3D cross-peaks. 

The fourth-order coherent Raman spectrum of a liquid surface was observed by Fujiyoshi et al. [28]. The same authors later reported a spectrum with an improved signal-to-noise ratio and different angle of incidence [27]. A water solution of oxazine 170 dye was placed in air and irradiated with light pulses. The SH generation at the oxazine solution was extensively studied by Steinhurst and Owrutsky [24]. The pump and probe wavelength was tuned at 630 nm to be resonant with the one-photon electronic transition of the dye. The probability of the Raman transition to generate the vibrational coherence is enhanced by the resonance. The efficiency of SH generation is also enhanced. 

Two-dimensional constant matrix, transition state trajectory, white noise, 203-207 Two-pathway excitation, coherence spectroscopy atomic systems, 170-171 channel phases, 148-149 energy domain, 178-182 extended systems and dissipative environments, 177-185 future research issues, 185-186 isolated resonance, coupled continuum, 168-169... 

Y. Xu, R. M. Narayanan, X. Xu, and J. O. Curtis, Polarimetric processing of coherent random noise radar data for buried object detection , IEEE Trans. Geosci. Remote Sensing, vol. 39, no. 3, pp. 467-478, Mar. 2001. 

R. M. Narayanan and M. Dawood, Doppler estimation using a coherent ultra wide-band random noise radar , IEEE Trans. Antennas Propagat., vol. 48, pp. 868-878, June 2000. 

Only deterministic models for cellular rhythms have been discussed so far. Do such models remain valid when the numbers of molecules involved are small, as may occur in cellular conditions Barkai and Leibler [127] stressed that in the presence of small amounts of mRNA or protein molecules, the effect of molecular noise on circadian rhythms may become significant and may compromise the emergence of coherent periodic oscillations. The way to assess the influence of molecular noise on circadian rhythms is to resort to stochastic simulations [127-129]. Stochastic simulations of the models schematized in Fig. 3A,B show that the dynamic behavior predicted by the corresponding deterministic equations remains valid as long as the maximum numbers of mRNA and protein molecules involved in the circadian clock mechanism are of the order of a few tens and hundreds, respectively [128]. In the presence of molecular noise, the trajectory in the phase space transforms into a cloud of points surrounding the deterministic limit cycle. 

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