Large internal loop

To date, only two applications of complete relaxation matrix derived distance restraints have been reported for RNA. MARDIGRAS provided "precise" distance restraints for the structure determination of a 17mer RNA with a flexible loop (26) and a 31mer hairpin with a large internal loop (18). For the latter, assignments and NOE volume extraction was made feasible through deuteration of all cytosines. 

There are two types of sample valve commonly used in LC, the internal loop valve and the external loop valve. In order to improve the seating and eliminate leaks, the valve faces are sometimes made from appropriate ceramics. The internal loop valves are largely used with small bore columns, that is to say columns having internal diameters of less than 1.5 mm. The external loop valves are used for larger diameter columns up to semi-preparative columns. 

Following the arguments given above, micro mixers are valuable tools for bench-scale continuous processing to fill the recycle loop. For first tests on feasibility, the total volume of the recycle loop has to be kept small, demanding also for small-scale processing units. Conventional devices would probably suffer here from too large internal volumes. 

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

The loop reactor is sometimes used to model conventionally agitated stirred tanks. The ratio of internal circulation to net throughput in a large, internally agitated vessel... 

Extra column dispersion, as would result from large injection volumes > 1 pi and dead volumes introduced by frits and fittings must be reduced to obtain optimum performance. A variety of injection systems have been reported, including those of split injection, internal loop-rotary valve, microfeeder and pneumatic microsyringes [130]. Considerable advances have been made in quantitative reproducibility. Dead volumes have been minimised by locating the columns directly into the injection and detector systems. 

The NMR constructs for domain IV RNA are depicted in Figure 1. Recent low resolution models (12, 13) suggest that domain IV folds back on domain II making tertiary interactions, which would require domain IV to make a U-turn. The flexibility for this turn could be associated with the asymmetrical internal loop. Besides determining the structure of the fairly large 43 nucleotide RNA, it seemed prudent to also study the structure of domain IV by isolating the two internal loops and thus their contribution to a potential bend. 

Our recent NMR study of the 24mer hairpin motif comprising largely the symmetrical internal loop revealed that a unique and stable structure is formed only in the presence of Mg2+ ions, which seem to bind specifically in the internal loop region. Unfortunately, this construct had a large propensity for duplex formation and we did not consider the NMR data of sufficient quality to allow a high resolution structure determination. This particular problem could be circumvented by making the transition from the kinetically favored hairpin... 

To minimize the effect of sample volume on dispersion, and ensure that there was minimum dispersion from the valve and valve connections, a 0.2 jxl Valeo internal loop valve was employed to place the sample on the column. In addition, the sample valve was used with an intra-column injection system [2] that ensured the sample was placed in the center of the column about 5 mm below the packing surface. TMs device also determined that, even if the packing settled, there would be no void above the point of injection and the effective length of the column was not changed. All connecting tubes were 0.007 in. I.D. and their lengths were kept to a minimum (Le., <5 cm). The detector employed was the Perkin Elmer LC-85B fitted with a cell 1.4 pi volume and was used in conjunction with an electronic amplifier that had an effective time constant of 24 millisec. The columns employed had internal diameters of 8-9 mm to ensure the peak volumes were very large compared to any dispersion introduced by extra-column dispersion. As a result, the extra-column dispersion was maintained at a level of less than 2% of the peak volume for all measurements and, in most instances, was maintained at a level of less than 1%. 

Korea has been actively engaged in international collaborative research activities. As part of this effort, Korea has been actively participating in collaborative research and development (R D) activities of the Gen-IV International Forum (GIF). Large experimental facihties have been constmcted to conduct various experiments to validate thermal—hydrauhc phenomena and a large sodium loop, called Sodium Test Loop for Safety Simulation and Assessment (STELLA)-1, for the test of key decay heat removal system (DHRS) components, started its operation in 2014. Design work started in early 2015 for STELLA-2, which is an integral test loop for a simulation of the thermal—hydraulic characteristics of the PGSFR primary and intermediate heat transport systems. 

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