Aggregation of nuclei

Formation of domains tiirongh tile cooperative aggregation of folding nuclei... 

This step is termed nucleation and leads to the formation of primary particles. The nuclei, the smallest particles formed in the nucleation step, are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. 

I have found that the assumption that in atomic nuclei the nucleons are in large part aggregated into clusters arranged in closest packing leads to simple explanations of many properties of nuclei. Some aspects of the closest-packing theory of nuclear structure are presented in the following paragraphs.1... 

Summary.—The assumption that atomic nuclei consist of closely packed spherons (aggregates of neutrons and protons in localized Is orbitals—mainly helions and tritions) in concentric layers leads to a simple derivation of a subsubshell occupancy diagram for nucleons and a simple explanation of magic numbers. Application of the close-packed-spheron model of the nucleus to other problems, including that of asymmetric fission, will be published later.13... 

The close-packed-spheron theory8 incorporates some of the features of the shell model, the alpha-particle model, and the liquid-drop model. Nuclei are considered to be close-packed aggregates of spherons (helicons, tritons, and dineutrons), arranged in spherical or ellipsoidal layers, which are called the mantle, the outer core, and the inner core. The assignment of spherons, and hence nucleons, to the layers is made in a straightforward way on... 

The close-packed-spheron theory of nuclear structure may be described as a refinement of the shell model and the liquid-drop model in which the geometric consequences of the effectively constant volumes of nucleons (aggregated into spherons) are taken into consideration. The spherons are assigned to concentric layers (mantle, outer core, inner core, innermost core) with use of a packing equation (Eq. I), and the assignment is related to the principal quantum number of the shell model. The theory has been applied in the discussion of the sequence of subsubshells, magic numbers, the proton-neutron ratio, prolate deformation of nuclei, and symmetric and asymmetric fission. 

The aggregation of oligomers requires a lower average degree of polymerization for nuclei formation than the self-nucleation model where a larger individual chain is required. 

Muscle biopsy with full histochemical and ultrastructural investigation is necessary for the confirmation of a diagnosis of IBM. The inclusions which are the hallmark of this disorder are to be found in three locations (a) basophilic granular inclusions are found at the periphery of vacuoles within the cytoplasm of muscle fibers (b) eosinophilic hyaline inclusions are also found in the cytoplasm but are not associated with vacuoles and (c) intranuclear inclusions consisting of aggregates of filamentous microtubules are found in a variable percentage of muscle nuclei. Inclusions of the first two types are visible at light microscope level, whereas the third type is detectable at the electron microscope level only. Ultrastructural... 

Figure 3 Effect of seeding and inhibitors on aggregation reaction. The lag phase (curve c) is characteristic of reactions in which formation of nuclei for polymerization is an unfavorable process. Addition of preformed nuclei or seeds" (curve a) abolishes the lag phase. Inhibitors may affect the formation of nuclei and influence eitherthe lag phase, the extension of the nuclei changing the growth phase, or both (curve d). The inhibitor example (curve d) acts more strongly at nuclei formation than on the slope or plateau level of the growth phase.

Thus, ultrasound and surface active agents together help in reducing the aggregation of particles because of the fact that the bonds between them are extended due to cavitation. Additives inhibit the agglomeration during nucleation process by reducing the surface tension. Ultrasound and additives both reduce population of local nuclei hence reduction in particle size [43]. 

The initial transition of dissolved silicate molecules into solid nanoparticles is perhaps the least explored step in the synthesis of zeolites. One impediment to understanding this mysterious step is the poorly elucidated molecular composition of dissolved particles. The major mechanistic ideas for the formation of zeolites approach these structures differently i) many researchers believe that secondary building units (SBU) must be present to form initial nanoslabs [1,2] ii) some others prioritize the role of monomers to feed artificially introduced crystal nuclei or assume that even these nuclei form via appropriate aggregation of monomers [3] iii) silicate solutions are also frequently viewed as random mixtures of various siloxane polymers which condense first into an irregular gel configuration which can rearrange subsequently into a desired crystal nucleus at appropriate conditions [4,5],... 

Thus, the source terms for each environment S(c) and Sk ((/)) will be closed. Of particular interest are the local nucleation rates /(c ). As discussed in Wang and Fox (2004), due to poor micromixing the local nucleation rates can be much larger than those predicted by the average concentrations /((c)). This results in a rapid increase in the local particle number density mo due to the creation of a very large number of nuclei. As discussed below, this will have significant consequences on the local rate of aggregation. 

Dl) A molecular unit is an aggregate of atoms that is linked by a topologically connected network of covalent bonds equivalently, an electronic distribution that links a collection of nuclei by a contiguous network of covalent bonds. 

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