Other important design issues

Other important issues are to do with the basic structure of trials. For example, what are the appropriate comparator treatments How many should be studied simultaneously Will the object of the trial be to find differences or to demonstrate equivalence Should a parallel group study or a cross-over trial be used How many centres should be used What should the block size be If a cross-over trial is employed will it be necessary to use incomplete blocks (These are designs in which each patient receives only a subset of the treatments being studied.) How long should the treatments be applied When should values be measured How should they be combined Should the results be analysed sequentially If the trial is to be blinded, how should this be achieved Is stratification desired What factors should be included in the analysis What is the general approach to be adopted What is the strategy for dealing with multiplicity of outcomes  

It is also important to appreciate that a clinical trial protocol will have to include a detailed specification of the intended analysis as well, of course, as the attendant sample size justification. Indeed, these statements will be needed in order to get ethical approval and, since there is an intimate relationship between design and analysis, it is necessary to know the intended analysis to judge the suitability of the design (Bailey, 1981). 

The statistician has to ensure that the randomization is prepared according to the study design. The key features of the schedule such as block size have to be approved by the statistician. Typically for a double blind trial, only those involved in the packing of the supplies are aware of the final treatment assignments. 

Two approaches to randomization are common pre-allocation and post-allocation (Senn, 2004). In pre-allocation, treatment packs that are identical in appearance are prepared in random sequences and delivered to the centres. As each patient is recruited. 

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Manufacturers and other bodies have issued their own designations, which may be encountered occasionally. Most important is the US Military specification MIL-L-2105D (which replaced M1L-L-2105C) corresponding to API GL-5, and introduced approval for multi-grade gear oils. 

It is now possible to model the wafer-level performance for most CMP processes. These models cover only some of the important tool or process design issues, such as relative velocities and pressure dependencies additional work is needed to predict the results for other parameters such as slurry composition or particle size, temperature dependencies, pad properties, and other effects. Die-level modeling has been used effectively to identify... 

A continuous counter-current reactor system has shown great promise as a process reactor in the dilute acid hydrolysis of cellulose. However, the findings on this unique reactor system have been limited to the theoretical aspects and the proof-of-concept laboratory experiments. It has to be developed into an upscale process reactor before it is adopted into the biomass conversion process. To this end, a pilot-scale process study is being conducted at NREL. This is only the first step. To be noted here is that reactors of similar design are being used in industry it took years of developmental work, however, before they were put into commercial service. It would probably take about the same degree of investment in this case. In addition to the reactor issue, there are other important issues that need to be addressed in the dilute acid process. 

In this article, we review the most recent research on such issues as the design and synthesis of novel electroluminescent polymers with high electron affinity, and of polymeric oxadiazoles with a strong tendency for n-doping, as well as those having high photoluminescence efficiency. Although most of this work was done in our latoratory, other important work is also included. 

Gas distributors are also an important component of packed bed columns and influence phase distribution. The design issue is to ensure a uniform gas flow distribution through the reactor or a necessary gas flow ratio relative to the liquid phase. The liquid-gas ratio is only important if the process requires a chemical reaction of the liquid phase induced by the gas phase. The packing, on the other hand, is responsible for the pressure drop profile and, hence, the downstream gas-phase distribution. 

Design considerations for vascular access devices include ease of handling, insertion, and use minimal thrombotic and other biocompatibility-related complications stmctural and operational reliability over time and optimization for application-specific performance issues (Canaud et al., 2000). Three different catheter tips are shown in Fig. 20.10 to illustrate these variations in design and structure. Because of the distinct characteristics of the different treatments and agents deployed through catheters, it is not practical to provide specific values for flow rates, pressure drops, viscosities, and other important transport properties. 

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