Challenges for scale

The small synthetic scale used for production of many labeled compounds creates special challenges for product purification. Eirst, because of the need for use of micro or semimicro synthetic procedures, the yield of many labeled products such as high specific activity tritiated compounds is often low. In addition, under such conditions, side reactions can generate the buildup of impurities, many of which have chemical and physical properties similar to the product of interest. Also, losses are often encountered in simply handling the small amounts of materials in a synthetic mixture. As a consequence of these considerations, along with the variety of tracer chemicals of interest, numerous separation techniques are used in purifying labeled compounds. 

The scale-up challenges for microchannel reactors are addressed through integrated mathematical models to describe all elements of the physics. Integrated... 

Heat transfer in laminar single-phase, two-stream microchannels has been well described in the literature [33, 39-41]. The challenge for medium- to large-scale processes is an added complexity if more than two fluids are required and also the micromanifold region. 

However, time-resolved X-ray diffraction remains a young science. It is still impossible, or is at least very difficult, to attain time scales below to a picosecond. General characteristics of subpicosecond X-ray diffraction and absorption are hardly understood. To progress in this direction, free electron laser X-ray sources are actually under construction subject to heavy financial constraints. Nevertheless, this field is exceptionally promising. Working therein is a challenge for everybody ... 

These fundamental issues have not previously limited the scaling of transistors and represent a considerable challenge for the semiconductor industiy. There are currently no known solutions to these problems. To continue the performance trends of the past 20 years and maintain Moore s law of improvement will be the most difficult challenge the semiconductor industry has ever faced. 

Understanding of the soil-plant-microbe relationship probably remains one of the most difficult challenge for life sciences due to the integration of observations at many scales. New efforts relying more on holistic approaches are needed. 

The challenge for developing methods for synthesizing oligosaccharides, notably for complex oligosaccharides, that can be scaled up to an industrial level is obvious, based on the use of substrates and enzymes that are available at reasonable cost and purity. Strategies for oligosaccharides synthesis include ... 

Although the effect of nutrients and classical toxicants (e.g. heavy metals, herbicides) is well known, that of the so-called non-PS in biofilms is still largely unknown. Furthermore, the combination of effects, which operate at the basin scale, requires complex approaches. Therefore, the response of biofilms to these situations should trigger the development of new applications and higher standardisation in the use of biofilms. The standardisation of methods and procedures is a challenge for the future research on the use of natural and laboratory biofilms. 

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