Effect of coincidence

Two types of error arise due to more than one particle being in the measurement zone at any one time. 

Primary Coincidence. Two or more particles in the measurement zone give rise to two or more overlapping pulses. Depending on their proximity and electrical resolution, these pulses may not be resolved, leading to loss of count. 

Secondary Coincidence Two or more very close particles, which individually give rise to pulses below the threshold level, may collectively generate a pulse above the level. Thus if the concentration is too high, oversize particles begin to appear. 

A coincidence correction can be applied for primary coincidence but it is preferable to use a concentration so low that this effect is negligible. Under this condition, secondary coincidence errors are also reduced. 

The correction for primary coincidence is derived through Poisson probabilities of finding multiple particles in different parts of the sensing zone simultaneously. This yields the following relationship between true count N and observed count n  

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Figure 2 Effect of coincidence upon count recorded.

One way to check the influence of coincidence is to perform a second measurement at a more dilute concentration. If the particle concentration ratio of the two measurements differs from the known dilution ratio of the two samples, some effects of coincidence in the first measurement are probable and the result should be discarded and a new dilution prepared to test the second sample. Progressive measurements should be made until the reported concentration ratio between two consecutive samples agrees with the toown dilution ratio. The highest concentration at which this occurs is then accepted as the uppermost concentration limit for the instrument used in measuring this material. No specific concentration limit can be specified since this will depend on the particle size distribution, instrument design, and the flow rate. The overall maximum concentration may range from a few particles to a few thousand particles per ml. 

Figure Bl.10.10. Schematic diagram of the effect of detector view angles on coincidence rate. The view angles of two detectors are shown along with the common view angle. Maximum signal collection efficiency is achieved when the individual view angles have the maximum overlap and when the overlap coincides with the maximum density of the incident beam.

The extreme influence water can exert on the Diels-Alder reaction was rediscovered by Breslow in 1980, much by coincidence . Whale studying the effect of p-cyclodextrin on the rate of a Diels-Alder reaction in water, accidentally, the addition of the cyclodextrin was omitted, but still rate constants were observed that were one to two orders of magnitude larger than those obtained in organic solvents. The investigations that followed this remarkable observation showed that the acceleration of Diels-Alder reactions by water is a general phenomenon. Table 1.2 contains a selection from the multitude of Diels-Alder reactions in aqueous media that have been studied Note that the rate enhancements induced by water can amount up to a factor 12,800 compared to organic solvents (entry 1 in Table 1.2). 

Mechanism of Action. P-Agonists stimulate skeletal muscle growth by accelerating rates of fiber hypertrophy and protein synthesis, but generally do not alter muscle DNA content in parallel with the increases in protein accretion (133—135). This is in contrast to the effects of anaboHc steroids and ST on skeletal muscle growth. Both of the latter stimulate fiber hypertrophy and muscle protein synthesis, but also increase muscle DNA content coincident with increased protein accretion. Whether the P-agonists decrease muscle protein degradation is equivocal. 

These values are determined by experiment. It is, however, by no means a trivial task to measure the lamina compressive and shear strengths (52,53). Also the failure of the first ply of a laminate does not necessarily coincide with the maximum load that the laminate can sustain. In many practical composite laminates first-ply failure may be accompanied by a very small reduction in the laminate stiffness. Local ply-level failures can reduce the stress-raising effects of notches and enhance fatigue performance (54). 

If an atom or covalent molecule is placed in an electric field there will be a displacement of the light electron cloud in one direction and a considerably smaller displacement of the nucleus in the other direction (Figure 6.1 (b)). The effect of the electron cloud displacement is known as electron polarisation. In these circumstances the centres of negative and positive charge are no longer coincident. 

Now we can adjust a until the calculated and observed AGPr coincide. This calibrated surface can then be used with confidence for studying the reaction in different solvents (and different environments), since a remains unchanged and only Ais recalculated. In this way, the error associated with the evaluation of does not affect the calculations of the relative effects of different solvents. 

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

While multiple signaling pathways are implicated in mediating the proliferative effects of CXCL12, only Akt activation, p38 activation, and suppression of cAMP levels have been shown to influence the survival response. Vlahakis et al. (2002) demonstrated that CXCL12 regulates survival in CD4-t T lymphocytes via the balance of pro-survival Akt activation and pro-apoptotic p38 activation. Whether the cellular response to CXCL12 was survival or apoptosis depended on coincident activation of these pathways by other factors. 

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