Noise intrinsic

TES are based on the steep temperature dependence of the resistance of superconducting metallic films. The useful temperature range is very narrow. These thermometers which may have a very low intrinsic noise, are fabricated by a vacuum deposition process at very low pressure and are patterned either by photolithography technique (see e.g. ref. [21]) or by micromechanical machining (see e.g. ref. [22]). The dimensionless parameter a = T/R-dR/dT defines the DC quality of a sensor. TES with a as high as 1000 have been built [23],... 

Internal or intrinsic noise is caused by the fact that the system itself consists of discrete particles it is inherent in the very mechanism by which the system evolves, as described in III.2. All our examples concerning chemical reactions, emission and absorption of light, growth of populations, etc., were of this type. Internal noise cannot be switched off and it is therefore impossible to identify A(y) as the evolution equation for the system in isolation. One usually identifies it... 

Intrinsic noise can only be minimized by selecting low noise components or by using statistical methods if it is possible to make repeated measurements. Normally, the user of a data acquisition system has no influence on its construction. Therefore we will only consider the interference noise in the discussion below. A short survey on methods for noise reduction is given by Smit (ref. 9). 

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. 

An advantage of these over film is that the absorption efficiency is higher (Amemiya et al 1987), particularly in the short wavelength region. Also, the intrinsic noise is lower (compared with film chemical fog), the DQE is also better and the dynamic range is larger. However, spatial resolution is substantially worse than film (Amemiya et al 1987). Film and IPs are recording media which are off-line. 

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. 

F. 1. Level of the intrinsic noise of the recording system combined with the cosmic component ofthebacl ound(l) and the effect of the scattering by air (2). Curve 3 represents the diffuse back und maximum of liquid mercury. 

The third noise component is the intrinsic noise of the pipette itself [11]. The pipette noise consists of two different Johnson noise components ... 

Last but not least the contribution of noise is important The most significant source of noise is the imperfect control of the temperature of the column effluent reaching the conductivity celL Even with excellent temperature control, a tolerance of 0.005 °C has to be assimied. Taking the temperature coefficient of conductivity of about 2%/°C into accoimt, the imcertainty in conductivity is 0.01%. The intrinsic noise of the detector is estimated to be 0.01 pS/cm. 

The second limitation of the resistive feedback preamplifier is that the feedback resistor has an intrinsic noise associated with it Johnson noise) and this can be a significant problem with pulses of very small size. In order to minimize this source of noise the value of is chosen to be high. This, in turn, means that the decay time of the output pulse is long, which exacerbates the pile-up problem. In principle, it would be possible to reduce the time constant by reducing Cf but doing that would affect the linearity of the preamplifier. There is, however, scope for reducing the value of Rf, in order to trade off resolution for count rate performance and this will be referred to in Chapter 14, Section 14.3.2. 

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