Performance deterioration

Another matter of concern in pyrotechnic formulations is the possibiHty of exchange reactions occurring between components. Addition of ammonium salts to compositions containing nitrate oxidizers can produce ammonium nitrate, a very hygroscopic material. The composition then becomes quite prone to pick up water and its performance deteriorates. The addition of an ammonium salt to a chlorate-based formulation can lead to the... 

Gas-Barrier Properties. The oxygen-barrier properties of PVA at low humidity ate the best of any synthetic resin. However, barrier performance deteriorates above 60% th (Fig. 9). No additives or chemical modifiers are known that can effectively reduce moisture sensitivity. The gas-barrier performance is affected by the degree of hydrolysis and rapidly diminishes as the hydrolysis is decreased below 98%. 

While a single, low pressure compressor may require little or no treatment for pulsation control, the same machine with an increased gas density, pressure, or operational changes may develop a problem with pre, sure pulses or standing wave performance deterioration. As un installation becomes more complex, such as with an increase in the number of cylinders connected to one header and the use of multiple stages the possibility of a problem can increase. 

Impeller Since the Sundyne straight, radlal-bladed Impeller does not require close running clearances, It eliminates the necessity for over-sizing to compensate for performance deterioration common to conventional pumps. Clearance of the Sundyne Impeller Is 0.030 to 0.070 inch. 

Generous clearances of. 035 in. (.889 mm) elminate performance deterioration caused by wear and the need for mechanical adjustment. 

In addition to a large input dimension, complex processes also typically have a large output dimension (i.e., many possible plant behaviors). Although only a few events occur at any given time, identification of those few events requires consideration of a large subset of all possible events. Without careful management of both input and output dimensionality, interpretation performance deteriorates rapidly with scale and complexity. 

There are discrepancies in the amounts of harmful species tolerance that fuel cell developers establish, even for similar type fuel cells. These discrepancies are probably due to electrode design, microstructure differences, or in the way developers establish tolerance. There are some cases where the presence of certain harmful species causes immediate performance deterioration. More often, the degradation occurs over a long period of time, dependant on the developer s allowable voltage degradation rate on exposure to the specific harmful species. Here, the developer establishes an estimated cell life based on economics. The permissible amount of the harmful constituent is then determined based on its life effects. 

The existence of a maximum thickness beyond which the performance deteriorates is due to the concerted impact of oxygen and proton transport limitations. Considered separately, each of these limitations would only serve to define a minimum thickness below which performance worsens due to an insufficient electroactive surface. The thickness of the effective layer, in which current density is predominantly generated, is given by the reaction penetration depth ... 

One of the most important requirements that must be met is the membrane s ability to prevent excessive transfer of water from one half cell to the other. The preferential transfer of water can be a problem in the vanadium battery as one half-cell (the negative half cell in the case of cation exchange membranes) is flooded and becomes diluted, while the other becomes more concentrated, adversely affecting the overall operation of the cell. Most of the membranes show good initial water transfer properties, but their performance deteriorates with exposure to the vanadium solutions. Sukkar et al. ° evaluated various polyelectrolytes to determine whether they could improve the selectivity and stability of the membranes in the vanadium redox cell solutions. Both the cationic and anionic polyelectrolytes evaluated improved the water transfer properties of the membranes, although upon extended exposure to the vanadium electrolyte the modified membranes did not maintain their improved water transfer properties. The solvent based Nuosperse 657 modified membrane displayed exceptional properties initially but also failed to maintain its performance with extended exposure to the vanadium solutions. 

The question is similar to asking how many times one can strip and reuse a microarray before performance deteriorates. An alternative approach is provided by Hessner et al. (2003a) in which the cDNA probes are permanently labeled using fluorescein-labeled primers to the clone s vector insert region. Fluorescein is excited at 488 nm and emits at 508 nm, while Cy3 may be excited at 543 nm to reduce any spectral overlap with fluorescein. Thus, fluorescein-labeled cDNA probes may be printed down and the slide scanned for QC/QA purposes prior to hybridization. Since the same region is primer-labeled in each cDNA, a direct comparison between the relahve fluorescence units (RFUs) and the amount of cDNA probe can be defermined. 

The introduction of heteroatoms into the ligands via alkoxy and trisubstituted amino groups has been explored to improve initiator performance through electronic effects. This approach is not promising as initiator performance deteriorates with very few exceptions. The exceptions do not result in performance enhancements at best, performance is... 

Such conglomerations can grow to be as large as a human head, and are known as "mud balls." Coalescer performance deteriorates rapidly when this occurs. 

A certain minimum flow rate is necessary to set up the vortex motion and to establish centrifugal separation forces that grow in intensity as the flow rate increases and improve the separation efficiency. A point will be reached for a given set of conditions, however, beyond which further increases in flow rate will cause performance deterioration. This is caused principally by the following. 

The oxygen-barrier properties of PVA at low humidity are the best of any synthetic resin. However, barrier performance deteriorates above 60% rh,... 

Since pemoline is intended primarily as a treatment for ADHD, its effects on vigilance have not been well established. However, Orzack et al. (60) compared 25 mg and 50 mg pemoline to 100 mg and 200 mg caffeine, 15 mg methylphenidate, and placebo on the performance of a 2-hr psychomotor task (pressing keys corresponding to visual stimuli). They found that performance deteriorated as a function of time on task under the influence of placebo, but that 50 mg pemoline, 200 mg caffeine, and 15 mg methylphenidate maintained consistent performance throughout the 2 hr. 

A further unfortunate characteristic of the stirred vessel is that its mixing capability is also a strong function of its size. Scale-up usually proceeds on the basis of a constant impeller tip speed, and since the mean circulation speed in the vortices is broadly proportional to the tip speed chosen, the circulation time is proportional to the vessel diameter. Thus the turnover time of the vessel contents increases at the larger scale and the macro mixing performance deteriorates. 

Inspect probes for cracks, scratches, or salt crystallization probes age with use and their performance deteriorates. 

When the chloride ion concentration is above 100,000 ppm, system performance deteriorated with the increase of chloride ion concentration. In addition to the decreasing scrubbing solution pH and SO removal efficiency, the filter cake insoluble solids also decreased and resulted in increased liquor losses and sodium consumptions. 

The performance of a heat exchanger depends upon the transfer surfaces being clean and uncorroded. The performance deteriorates with time due to accumulation of deposits on the heat transfer surfaces. The layer of deposits represents additional resistance to heat transfer. In the design of heat exchangers, this added resistance is accounted for by a fouling factor or dirt factor, R. ... 

The magnitude of performance deterioration for failing to optimize any one of the steps described in sections 2 to 4 varies enormously, and from element to element. How painstaking you should be when setting up for a particular determination depends upon how close to the detection limit you will be working, and upon the degree of precision required. With experience, many shortcuts may be deemed perfectly acceptable. Where particular care is needed with optimization, a warning is provided in the element-by-element section of Chapter 7. 

Combustion instability that leads to performance deterioration and excessive mechanical loads, which could result in reduced life and premature failure, is an important issue with modern gas turbine engines and ramjet and scramjet combustors. Various techniques of passive and active control to reduce combustion instabilities and improve performance are addressed. Since extensive, promising research is being carried out to develop sensors and actuators, these techniques can be used in practical combustors in the near future. The topics covered in Section 3 provide the required chemical, kinetic, and fluid dynamic understanding to help the designer who is involved in active feedback control for combustion systems. 

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