Assembly Experiments

Critical-Mass Measurements on Beryllium-Reflected, Enriched-Uranium, Spherical Systems, by O. Kolar and H, R. Ralston (VCBL-L). A scries of critical mass determinations has been made for spherical beryllium reflected systems. Cores were enriched (93.17S U-235) uranium spheres ranging in mass from 10.6 to 32.6 kg. The corresponding reflector thicknesses were 20.3 to 2.2 cm. All results were nonnalized to a core density of 18.6 g/cc. Some Los Alamos data are included for completeness and have been similarly normalized. These two sets of experiments were found to be in good agreement. The experiments and results arc discussed, together with the fit to the experimental data obtained with the spherical Si, 5-group code in use at UCRL. 

An expression for p is derived for rectangular slabs at right anodes h each odier. From diis expression values of p for parallel rectangular slabs with identical faces are obtained. These results are used tor cylinders as well as for slabs by approxiinating circular cylinders by square cylinders with die same base area and die same axis-to-axis separation. 

Equations are derived for multicomponent systems where the components need not be identical or equally spaced. Special precautions are necessary when the interacting frees are of unequal area, and a procedure is outlined for such situations. A procedure is outlined for allowing for the fraction of neutrons that is intercepted by intervening units. 

An expression for p for the self-interaction in an annulus is derived and evaluations of die expression are plotted. Expressions for p for the case of a disc or. of an infinite slab of finite height parallel to an infinite plane reflector are derived and evaluated. These results may be applied to any slab by taking whi ever p is smaller, that for a disc of the same area or that for an infinite slab of the same height. Expressions are also derived for p for the situation in which a fissile unit is completely surrounded by a reflector. 

Detailed flux distribution measurements throughout a representative cell have yielded a value of 1.10 0.02 for the disadvantage factor for a single fuel pin in a li-in. triangular lattice. Similar measurements in the clustered geometry gave 1.4. 

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Fig. 4. Schematic of the single-molecule chromatin assembly experiments, (a) The fluorescence videomicroscopy experiments of Ladoux et al. [64] (for details see text), (b) The chromatin assembly experiments of Bennink et al. [65] a single >.-DNA molecule suspended between two micron-sized beads is being assembled with the help of Xenopus egg extract containing core histones and assembly factors (for details see text), (c) Example assembly curve at 1 pN (redrawn from Ref. [65]).

Consider the case where the protein consists of o /3 dimers exclusively at the very beginning of an assembly experiment. Suppose further that spontaneous nucleation is sufficiently infrequent as the polymerization reaction reaches 5-10% of its maximal amplitude achieved over the remaining course of elongation. In this case, a reduction of the protomer concentration from about 20 to 18 JU.M would reduce the apparent extent of nucleation by a factor of about 10-20, such that the polymer number concentration remains fixed throughout the ensuing elongation phase. If nucleation were viewed as a one-step cooperative event, then the rate of nucleation would be proportional to the ith power of the protomer concentration if /protomers cooperatively form the polymerization nucleus ... 

The self-catalyzed model is a simplification of the actin polymerization model of Oosawa and Kasai (1962) [and more recent elaborations of it (Niranjan et al., 2003)], and both equilibrium constants K and Kn, and hence the free energies g and ga can in principle be obtained by fitting the theory to assembly experiments. Typical values of g for, for example, actin vary between —10 and —20 kBT and ga between +2 and +3 kBT (Oosawa and Asakura, 1975 Oosawa and Kasai, 1962). For the biomimetic compound oligo(phenylene vinylene) similar to compound 2 shown in Figure 6, dissolved in alkane solvents, similar values were found for g but much larger ones for ga of +8 to +10 kBT, making the supramolecular polymerization of this compound an extremely highly co-operative process (Jonkheijm et al., 2006). 

The transcribed mRNA is bound by a particle called a ribosome. Ribosomes are huge complexes consisting of fifty-two separate proteins (of which several are present in multiple copies) and three pieces of RNA with lengths of 120,1,542, and 2,904 nucleotides. The ribosome can be readily broken down into two large pieces, called the 30S sub-unit and the 50S subunit.6 Incredibly, the ribosome is self-assembling. Experiments have shown that when ribosomes are separated into their components and then remixed, under the right conditions the components will spontaneously reform ribosomes. 

Although electron microscopy is always interpreted with care and caution, because of the possibility of artifacts, a picture is always of value in developing models of self-assembly products. In self-assembly experiments it is important to stop the process of self-assembly so that direct visualization... 

A typical assembly experiment consisted of placing molded pieces of polyurethane in a flask, coating the pieces with liquid, and rotating the flask to tumble the pieces. Deposition of liquid films required adding a mixture of ethanol and the lubricant to cover the pieces. Gradual addition of water to an ethanol solution containing the lubricant then precipitated the lubricant onto the pieces. In both cases, we carefully minimized the introduction of bubbles that could interfere with assembly. 

HSV-1 and T4 are by far the best understood of the large viruses and their assembly processes may provide pointers to some of the mechanisms likely to occur in other virus families. In both HSV-1 and T4, the first product of assembly is not the capsid described above but rather a precursor, the procapsid. The formation of procapsids and their role in the capsid assembly pathway have long been known in T4 (see Black et al, 1994). However, in HSV-1, procapsids have been described only relatively recently. Although they were initially identified as the products of in vitro capsid assembly experiments (Newcomb et al, 1994), their role in infected cells is now firmly established (Church and Wilson, 1997 Newcomb et al, 2000 Preston et al, 1983 Rixon and McNab, 1999). Procapsids are formed by polymerization of capsid shell proteins around an internal structure called the scaffold. The scaffold has a number of possible functions but a major purpose is to determine the size and assure the fidelity of the capsid shell (see Fane and Prevelige, This volume). This function is likely to be particularly important for large capsid shells, where the possibility of incorrect interactions is multiplied by the increased number of subunits involved. 

In this chapter we introduce compounds which have been successfully applied in the construction of supramolecular assemblies. Only the amphiphiles which have been prepared in sufficient quantities have been admitted milligram quantities being considered unacceptable as starting materials for the preparation, analysis and application of assemblies. Experience proves that complicated dyes, pore builders, receptors etc. never reappear in the literature after their syntheses and spectroscopic properties have been reported. On the other hand, such easily attainable synkinons and surfactants around the ten gram scale need not, of course, be too simple. On the contrary, they may contain all the components of the chiral pool, i.e. amino acids, carbohydrates, steroids etc., as well as all commercial dyes of interest such as protoporphyrin, phthalo-cyanines, carotenes, viologen and quinones. 

Fig. 4. Time-resolved assembly experiment, showing (from top to bottom) the time course of the intensities in the scattering regions C (top), R (middle), and M (bottom, compare Fig. 2) the solid trace below the experimental curves is the temperature T. Note the pronounced undershoot in the top curve accompanying the temperature jump, due to the disappearance of ring oligomers. The subsequent rise in the first and third curve is due to the nucleation and growth of microtubules. From [11]...

Shimokawa K (1997) Transforming automobile assembly. Experience in automation and work organization. Springer, Berlin... 

The k, meter is a cross-shaped subcritical assembly into which a spent-fuel assembly is placed and its k,. determined by the change it produces in the multiplication of the subcritical assembly. Experiments have been performed with the PSBR to verify the multiplication characteristics of a cross-shaped subcritical assembly, as shown in Fig. 1, which is similar to the one proposed in the k , meter. Glumes in the source multiplication as observed by fission counters are compared with the nucleonic code calculations used to design the k,. meter. Multiplication experiments are also performed using a mctangularshaped assembly. The rectangle has the approximate dimensions of two PWR fuel assemblies. Only relative count rates are considered in these measurements because only r tive count rates are used by the k,. meter. 

Figure 3. a) Yields y and b) error rates (p of capillary assembly experiments with monomodal colloids plotted versus the trap type. Note the different scales of the y axes (a 100%, b 5%). 200-nm (P200), 350-nm (P350), and 500-nm particles (P500) were predominantly assembled in their corresponding trap types. 

Mechanically Induced Failures. PCBs may be mechanically loaded by test fixtures or processing equipment, when PCAs are loaded into card cages or fixtured into place with brackets, or when the assembly experiences mechanical shock or vibration in use. In general, once the PCA has been assembled, the interconnects to the components are the weak links in mechanical loading situations, not the boards themselves. 

Winfree, E. 2000. Algorithmic/self-assembly of DNA theoretical motivation and 2D assembly experiments. Journal of Biomolecular Structure and Dynamics 11 263-270. 

Figure 15.7 Influence of the evaporation rate on the convective flow involved in convective assembly. Experiment was performed on an oxygen plasma-treated PDMS surface [500 nm PS particles, 0.2% solid content].

Within the BWR core region, the jet pump assemblies experience high velocity as well as restricted flow regions. Since the flow in other regions is lower, consequences of erosion corrosion of less concern and an accompanying reduction in section has little impact. There has been no evidence of erosion corrosion in the jet pump throat area which would be... 

Electrostatic Self-Assembly Experiments (Adapted from Pelesk, 2009)... 

Wk8 Ch3 Student lectures experiments Wk9 Ch4 Terpenoids WklO Ch4 Student lectures experiments Wkll Ch5 Carbohydrates Wkl2 Ch5 Student lectures experiment Wkl3 Ch6 Lignins experiments Wkl4 Ch7 Self-assembly experiments wrap up. Wkl5 Final exam... 

The pentagon shape worked very well, and the idea of fitting parts together was also excellent. Fitting parts of dissimilar materials was virtually impossible. Minimum radiuses need to be developed so that students do not specify impractical sizes. The extrusion that held the pieces together was not robust enough to allow for small size mismatches. A more ductile material, such as plasticized polyvinyl chloride would probably enhance the assembly experience. Practical limits also need to be developed for the shapes students are allowed to put in or on the pentagons. 

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