Dendrites definition

Another definition, taking into account polymerization conversion, has been more recently proposed.192 Perfect dendrimers present only terminal- and dendritic-type units and therefore have DB = 1, while linear polymers have DB = 0. Linear units do not contribute to branching and can be considered as structural defects present in hyperbranched polymers but not in dendrimers. For most hyperbranched polymers, nuclear magnetic resonance (NMR) spectroscopy determinations lead to DB values close to 0.5, that is, close to the theoretical value for randomly branched polymers. Slow monomer addition193 194 or polycondensations with nonequal reactivity of functional groups195 have been reported to yield polymers with higher DBs (0.6-0.66 range). 

Schematic representation of the hematopoietic cascade in mice and human (hum). All the cells of the hematopoietic system are positive for antigen CD45. Based on this, the dynamics of surface antigen expression along development of different mature cells derived from the hematopoietic stem cell system can be observed. Rounded arrows indicate self-renewal potential. Smooth thinner arrows indicate directions of cellular differentiation. The identification of CDs (clusters definition) and other antigen cell markers are listed in the glossary. (LT-HSC - long term hematopoietic stem cell ST-HSC - short term hematopoietic stem cell MPP - multipotent progenitor CLP - common lymphoid precursor CMP - common myeloid precursor GMP - granulocyte-monocyte precursor MEP - megacaryocyte-erythrocyte precursor T - T lymphocyte B - B lymphocyte NK - natural killer cell DC - dendritic cell).

Avnir et al. llbl have examined the classical definitions and terminology of chirality and subsequently determined that they are too restrictive to describe complex objects such as large random supermolecular structures and spiral diffusion-limited aggregates (DLAs). Architecturally, these structures resemble chiral (and fractal) dendrimers therefore, new insights into chiral concepts and nomenclature are introduced that have a direct bearing on the nature of dendritic macromolecular assemblies, for example, continuous chirality measure44 and virtual enantiomers. ... 

Because of the one-step polymerization procedure, hyperbranched polymers often contain not only D and T but also L repeating units. This can be expressed by DB, which is an important structural parameter of hyperbranched polymers. DB is estimated as the sum of the D and T units divided by the sum of all the three structural units, that is, D, T and L [41]. By definition, a linear polymer has no dendritic units and its DB is zero, while a perfect dendrimer has no linear units and its DB is thus unity. Frey has pointed out that DB statistically approaches 0.5 in the case of polymerization of AB2 monomers, provided that all the functional groups possess the same reactivity [42]. The structures of the hb-PYs could be analyzed by spectroscopic methods such as NMR and FTIR. The DB value of the phosphorous-containing polymer hb-F21, for example, was estimated to be 53% from its 31P NMR chemical shifts (Chart 1). 

Denotations and connotations of the term "polymer" and its associated building block, termed "monomer", are probed. The nomenclature previously developed in order to canonically name finite length molecules is extended so as to apply to unlimited repeats of the monomer. A system of taxonomy based on dimension underlies the choice of canonical ordering of "polymers", as well as that aggregation of atoms which lacks the "regularity" to meet the proposed limitation to the definition of the term "polymer" (herein called "multimer") is introduced. The extension from Cartesian nomenclature to spherical nomenclature introduced in Chapter 6 is further developed for "dendritic" molecules. 

A large number of covalently linked systems are currently being synthesized and investigated, differing in the nature of A, B, and L, as well as in the number of functional units in the supramolecular system (nuclearity). It is common to call simple two-component donor-acceptor systems such as that of Eq. 2 dyads , and progressively more complex systems triads , tetrads , pentads , etc.. Systems where all the A and B units are organic molecules are dealt with in Chapter 1 of this section. The present chapter deals with systems where at least one of the A/B functional units is a transition metal coordination compound. From this definition, however, are excluded (a) systems where A and/or B are porphyrins or related species (dealt with in Chapter 2) and (b) systems of high nuclearity with dendritic structures (dealt with in Chapter 9). 

Dendritic deposits grow under mass transport-controlled electrodeposition conditions. These conditions involve low concentration of electrolyte and high current density. A dendrite is a skeleton of a monocrystal consisting of stem and branches. The shapes of the dendrites are mainly determined by the directions of preferred growth in the lattice. The simplest dendrites consist of the stem and primary branches. The primary branches may develop secondary and tertiary branches. The angles between the stem and the branches, or between different branches, assume certain definite values in accordance with the space lattice. Thus, dendrites can be two dimensional (2D) or three dimensional (3D). 

Histologically, freckles are characterized by a normal number of melanocytes in the basal layer. The melanocytes are, however, larger and more dendritic , and give up their melanosomes more readily to the keratinocytes. Freckles disappear completely and definitively with phenol. A TCA peel to the papillary dermis will also get rid of freckles. A local phenol peel is contraindicated on light skin phototypes - which in principle are a good indication for phenol - with freckles, as they will disappear where the phenol has been applied and will persist in the surrounding areas. A combination of local Lip Eyelid and Unideep (TCA to the papillary dermis) is suitable to avoid this freckle demarcation Hne. 

In a recent review article on the anatomy of autism Amaral et al. (2008) point out that in these studies by Casanova and his colleagues, only 14 cases of autism, 9 of which had seizures and at least 10 with mental retardation, have been examined for minicolumn pathology. Consequently, more studies using a greater number of autistic brains with fewer other complications need to be carried out before any definite conclusions can be reached about changes that can only be attributed to autism. It would also be appropriate to examine brains in which the apical dendritic clusters and myelinated axon bundles have been stained to confirm the sizes of the minicolumns as detected in digitized images from autistic brains. 

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