Noise band

The main problem has been a methodological one. The patch clamp analysis of single channels views the world of channels through a very small analytical window [10]. A single channel event (opening) needs to be sufficiently long-lived and sufficiently large to be picked up within the current noise band under optimized conditions, and with the low-pass filter set to say 2 kHz. The open time needs to be close to a millisecond and the current amplitude close to 0.5 pA to permit detection. 

The research was pioneered by the government funded department of Psycho-Correction at the Moscow Medical Academy. Acoustic psychocorrection, said the newspaper, involves the transmission of specific commands via static or white noise bands into the human subconscious without upsetting other intellectual functions. Exposure to the subliminal radio waves took less than one minute to achieve encouraging results. ... 

In an effort to improve signal quality by reducing baseline noise, a water-cooled particle impinger bar was installed immediately upstream of the path control probes. This bar directs a portion of the particulates around the beam path and reduces the interaction of particles with the beam. In this configuration, the TDL and extractive CO measurements agreed to within approximately 2% CO over a range of approximately 0 to 15% CO. The output of both instruments contains a noise band of approximately +1% CO. 

In the last decade, numerous applications of the WT have been proposed for chemical analysis. One of the main goals in analytical chemistry is to extract useful information from recorded data however, data gathered from experiments is contaminated with noise. Band-pass filtering behaviour of WT has been successfully applied to the removal of noise or trends, and smoothing (Alsberg et al. 1997). 

The peak-to-peak measurement must include all noise bands within the defined frequency window but is somewhat susceptible to what one might call operator optimism in the exclusion of spikes or glitches . Computational methods for determining noise have the advantage of removing such operator bias, and it is consistency of approach that is important for performance monitoring. 

In a noise spectrum (Fig. 5) the noise amplitude is plotted as a function of frequency [31]. White noise (Fig. 5 A) occurs over all frequencies and is almost always fundamental in origin, whereas for Mf noise (Fig. 5B) the amplitude decreases with the frequency and it is nonfundamental in origin. Discrete noise bands with well-defined causes may also occur (Fig. 5 C). These may stem from the source, caused by gas flow dynamics or contributions from the vacuum line, etc. Noise spectra are a powerful diagnostic tool to trace the sources of noise, and to study instrumental limitations to the power of detection. In atomic. spectrometry, it is important to determine if noise from the detector is predominant if so. it can be described by a Poisson distribution ... 

FIGURE 13.8 Noise-band chart for ECL. (Prepared by Pitch... 

By fitting the minima of each absorbance spectrum to a polynomial one gets complete independence from the BCP. However, in spite of getting rid of the BCP selection, the critical point now is the correct choice of the minima. This is accomplished by dividing the recorded spectral interval into a certain number of windows. From each window the local minima are selected as sampling points for the polynomial fit. Using only the absolute minima for the calculation would result in over-correction. As a fluctuation of the baseline around the zero line would be correct, not only the absolute minimum but also all values within a certain noise band above the minimum of each window have to be included. The... 

In addition, it has to be considered that the intensity is in general highest during the BOC scans, and the shot-noise therefore is at its minimum. Since the noise level increases with the decrease in intensity resulting from continuous background, the width of the noise band for each scan intensity correction factor ttscan of the individual scan ... 

Taking this into account, all pixels within a window with a value for uncorrected absorbance inside the noise band are included in the calculation. From these values the mean value of both absorbance values and positions is obtained thus for each window a mean absorbance value is correlated with a mean wavelength position. In this way, a certain number of sampling points is obtained for the polynomial fit (refer to Figure 8.52). 

For practical reasons, the signal domain is used to calculate the LOD on screen or printouts. In a chromatogram of a low concentration standard, the width of the noise band is determined, and from the average noise the peak height is taken. This can simply be done in centimeter or counts, or a suitable software routine used. 

Another approach to determine the LOD is based statistically on the results of a series of measurements on low concentration level. Especially with MS/MS instruments and HRMS accurate mass acquisitions, the noise band is not continuously accessible anymore due to the high selectivity of these analyser types and a very noise-free digital signal processing. With a noise band tending to zero, the S/N calculation becomes increasingly meaningless. 

Instrument detection limit, defined statistically as a measure for the potential instrument sensitivity at the 99% confidence level from the area precision (RSD%) of a series of measurements, applied in cases a S/N cannot be calculated due to the absence of a suitable noise band in modern digitally filtered MS systems. The IDL does not inform about the lowest detectable concentration LOD. 

Signal-to-noise ratio, the ratio of the peak height to the noise level. Peak height is measured from the average noise level to peak top. Noise is measured as the width of the noise band (typically 4 a), excluding known signals. 

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