Extrinsic noise

It is evidently insufficient to consider only the response of a detector when analysing its usefulness for a particular application. It is generally necessary to analyse both intrinsic and extrinsic noise signals and compare them with the response. The result of this comparison can be expressed in many different ways. One of the most useful is the noise-equivalent power nep which is the power of an rms signal input (in watts) required to give a response equal to the total rms noise voltage AVN. Then ... 

Scott, M. Ingalls, B. Kaem, M. Estimations of intrinsic and extrinsic noise in models of nonlinear genetic networks. Chaos 2006,16 026107. 

A similar approach was used to discriminate between intrinsic noise, stochastic fluctuations that arise from fluctuations of the molecules directly involved in gene expression, and extrinsic contributions that arise form fluctuations in other molecules that regulate or otherwise contribute to the process [22]. The latter are uniform within a cell but vary from cell to cell while the former produce fluctuations over time within an individual cell. The two forms of noise were distinguished by determining the extent of correlation between the expression of cyan and yellow fluorescent proteins under the control of identical promoters in the same cell. The intrinsic noise was measured as the difference in fluorescence intensity of the YFP and CFP. The extrinsic noise was determined by using the fact that the square of the total noise equals the sum of the squares of the intrinsic and extrinsic noises. The results show that both types of noise contribute significantly. 

As femtomolar detection of analytes become more routine, the goal is to achieve attomolar (10 molar) analyte detection, corresponding to the detection of thousands of molecules. Detection sensitivity is enhanced if the noise in the analytical system can be reduced. System noise consists of two types, extrinsic and intrinsic. Intrinsic noise, which represents a fundamental limitation Hnked to the probabiHty of finding the analyte species within the excitation and observation regions of the instmment, cannot be eHrninated. However, extrinsic noise, which stems from light scattering and/or transient electronic sources, can be alleviated. 

Under these assumptions, the formulation of cell division as an FPT problem requires that the following be specified (i) a stochastic model for how cell size, s, increases with time, t, between divisions (ii) the function of the cell size, s, that attains critical or threshold value, 6, at division and (iii) appropriate initial conditions, including the initial distribution of cell sizes. While in all previous cases considered, every member of the ensemble (i.e., each cell in the population) was assumed to be subjected to identical initial conditions, in this section we relax that condition to allow different cells to experience different initial conditions (i.e., different freshly divided cells having different sizes). This is an added source of stochasticity, namely, extrinsic noise in addition to the intrinsic fluctuations encoded in stochastic growth for a given initial condition. 

Ideal Performance and Cooling Requirements. Eree carriers can be excited by the thermal motion of the crystal lattice (phonons) as well as by photon absorption. These thermally excited carriers determine the magnitude of the dark current,/ and constitute a source of noise that defines the limit of the minimum radiation flux that can be detected. The dark carrier concentration is temperature dependent and decreases exponentially with reciprocal temperature at a rate that is determined by the magnitude of or E for intrinsic or extrinsic material, respectively. Therefore, usually it is necessary to operate infrared photon detectors at reduced temperatures to achieve high sensitivity. The smaller the value of E or E, the lower the temperature must be. 

The photon-economy depends on extrinsic sources of noise, the characteristics and settings of the instrument and also on the analysis method. Usually, the photon-economy depends on the lifetime therefore it is instructive to construct graphs of F as a function of the lifetime. The photon-economy of time-domain techniques has been extensively characterized [10, 14, 32, 33],... 

Consider first the simple extrinsic photoconductor. Here the sample is a semiconductor containing a single impurity level, the source of the free electrons (or holes) present in the sample. Thus the fluctuation in the number of the free carriers arises from the fluctuation in the generation and recombination rates through that level. If it is assumed that the temperature is so low that very few of the extrinsic centers are thermally ionized (which is valid for most extrinsic cooled photoconductive infrared detectors), then the short circuit g—r noise current and the open circuit g — r noise voltage which appear only in the presence of a bias current Ig, are given by... 

Nonlinear optical materials are recognized as the key element for future photonic applications. Photonics, a technology that uses photons rather than electrons to carry information, offers several advantages over electronics. Advantages include larger bandwidths, faster response times, and less noise from extrinsic electromagnetic fields (361). Several approaches using EAPs for photonics applications have been reported (362). 

The resistance of potentiometric sensors does not seem to be a cracial point a priori. Membranes with a very low conductivity (lower than 10S cm- ) are sometimes used in ISE devices. Nevertheless, a too-high resistance leads to a capacitive behavior of the sensor. The parasitic charges which appear in the circuit or electrical noise (intrinsic or extrinsic) may lead to erroneous results. To avoid this disadvantage, thin sensitive membranes may be used (pH or pNa glass membranes), but they are very fragile. Generally, a conductivity of about 10- to 10- S cm- is required. Miniaturization of devices allows a lower resistance of the SIC to be obtained, but the interface impedance is not fundamentally modified because it depends on the electrochemical kinetics, which is a function of the interfacial area. 

In previous theoretical works [17-21] we studied the time behavior of nano-sized reacting vesicles by using a stochastic approach in order to elucidate the role of intrinsic fluctuations, i.e. fluctuations in the reactions occurring time intrinsic stochasticity). On the other hand, two deterministic approaches are instead suitable for modelling enzymatic pathways taking place in micrometer-sized GVs the OD and the 3D approach respectively. Both assume that intrinsic noise is negligible in first approximation and that random fluctuations observed in the time behavior of a vesicle population are mainly due to extrinsic stochasticity, i.e., due to the different sizes and different composition of the reacting comportments as shown by Fig. 1. 

Due to these characteristics, the possibility to build databases of NMR-based metabolic profiles of foodstuffs, in order to assess their quality, is becoming more and more actual [9]. However, when we apply multivariate analysis to our data fields or wish to compare databases obtained by NMR spectroscopy by other researchers, it is very important to consider the source of extrinsic variability originated by the employed experimental conditions, in terms of sample preparation, NMR acquisition parameters, signal-to-noise ratio, NMR spectral pre-treatment, NMR data pre-processing, as well as the strategy for NMR-based metabolomics (for an exhaustive introduction to the reported critical cmicepts see the manual by Axelson [10]). 

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