Search

The spacio—geotnetric characteristics of macromolecular chains are discussed from the point of view of the essential connections they provide between chemical constitution and properties. Quantities such as molecular weight, radius of gyration, degree of branching, etc., that characterize the molecule as a whole do not suffice for an understanding of the virtually endless variations in the properties that distinguish one polymer from another. For this purpose it is necessary to examine the chemical structures of the constituent units, taking into account the geometric parameters pertaining to chemical bonds, the conformations accessible to the chain skeleton and the resulting spatial configurations. The physical principles underlying the statistical mechanical treatment of conformations of long chain molecules and of their configuration—dependent properties are summarized. Correlations between bonds of the chain and the range of such correlations provide insights into the spatial characteristics of polymer chains. Persistences expressing the configurational averages of vectors spanning sequences of chain units are particularly useful in this connection. Experimental methods that provide quantitative information on conformation and the correlations between units of the chain are briefly discussed.

Die Indikation zur O/C-Fusion ist gegeben bei Tumordestruktion, bei pathologischen Instabilitaten und bei bestimmten Luxationsfrakturen dieser Region. Wir bevorzugen die Verbundfusion mit Drahtzuggurtung bei palliativer Stabilisierung und das Einfalzen eines massiven cortico-spongiosen Knochenblockes bei kurativem Vorgehen. Zur occipitalen Verankerung wird eine epidurale Drahtfuhrung uber 2 Bohrlocher empfohlen, fur die cervicale Verankerung eine Drahtumschlingung der Bogenwurzeln.

A partition function for a system of rigid rod-like particles with partial orientation about an axis is derived through the use of a modified lattice model. In the limit of perfect orientation the partition function reduces to the ideal mixing law ; for complete disorientation it corresponds to the polymer mixing law for rigid chains. A general expression is given for the free energy of mixing as a function of the mole numbers, the axis ratio of the solute particles, and a disorientation parameter. This function passes through a minimum followed by a maximum with increase in the disorientation parameter, provided the latter exceeds a critical value which is 2e for the pure solute and which increases with dilution. Assigning this parameter the value which minimizes the free energy, the chemical potentials display discontinuities a t the concentration a t which the minimum first appears. Separation into an isotropic phase and a some what more concentrated anisotropic phase arises because of the discontinuity, in confirmation of the theories of Onsager and Isihara, which treat only the second virial coefficient. Phase separation thus arises as a consequence of particle asymmetry, unassisted by an energy term . Whereas for a large-particle asymmetry both phases in equilibrium are predicted to be fairly dilute when mixing is athermal, a comparatively small positive energy of interaction causes the concentration in the anisotropic phase to increase sharply, while the concentration in the isotropic phase becomes vanishingly small. The theory offers a statistical mechanical basis for interpreting precipitation of rod-like colloidal particles with the formation of fibrillar structures such as are prominent in the fibrous proteins. The asymmetry of tobacco mosaic virus particles (with or without inclusion of their electric double layers) is insufficient alone to explain the well-known phase separation which occurs from their dilute solutions at very low ionic strengths. Higher-order interaction between electric double layers appears to be a major factor in bringing about dilute phase separation for these and other asymmetric colloidal particles bearing large charges, as was pointed out previously by Oster.

Geometrical and spatial characteristics of macromolecular chains are determined by bond lengths, bond angles and hindrances to rotations about skeletal bonds as expressed by the conformational energies associated therewith. The presence of cyclic structures or of double bonds within the backbone may alter the configurational behaviour markedly. The structures of familiar polymeric substances present wide variations in these respects. Mathematical methods now available enable one to evaluate average properties of randomly coiled polymer chains of almost any description, full account being taken of all configurations of the molecule. These methods are exact, being subject only to the scheme adopted for describing bond conformations. The rotational isomeric scheme is generally applicable for this purpose, although more refined models may be employed for complicated chains such as the polypeptides and poiynucleotides. The nature of the methods is described and configurational characteristics of representative chains are reviewed. Artificial models such as the freely jointed chain and the wormlike chain are incapable of representing the diversity of chemical structures that are of interest. These models tend to obscure rather than clarify the connections between properties and structure of polymeric chain molecules, which can now be treated in realistic fashion by newer methods.

Operationsindikationen fur primarye and metastatische Tumoren der Wirbelsaule bestehen zur Diagnosesicherung, bei spinaler and radicularer Kompression Bowie drohender oder manifester Instabilitat. Behandlungsziele sind die Tumorresektion and -reduction, die Dekompression und Wiederherstellung der Stabilitat. Bei benignen Tumoren gelingt die Heilung, neurologische Komplikationen werden verhindert. Bei malignen Systemerkrankungen erreicht die Tumorexcision in Kombination mit Chemo- and/oder Strahlentherapie beeindruckende Remissionen. Bei metastatischem Befall erbringt die Palliation trotz unveranderter kurzer Uberlebenszeit eine Verbesserung der Lebensqualitat and der Pflegesituation.

Seine Grosse und sein langer Gefassstiel empfehlen den M. latissimus dorsi als Spendermuskel bei ausgedehnten Weichteildefekten mit schlechter Vascularisation des Empfangergebietes. Der Muskel kann als alleiniger Muskellappen mit einem Spalthauttransplantat oder als myocutaner Lappen mit defektangepassten Hautinseln transferiert werden. Anhand unserer Erfahrungen mit 83 freien Muskelverpflanzungen stellen wir Vorgehen und Ergebnisse bei Patienten mit traumatischem Weichteilverlust, Verbrennungen, chronischen Infekten und Tumoren vor. Abhangig vom verwandten Gefassstiel werden verschiedene Moglichkeiten der Lappengestaltung gezeigt.

Bei den jahrlich ca. 40 Motorradrennen, die in Deutschland fur uber 3000 Lizenzfahrer veranstaltet werden, sturzen jeweils 10% der Fahrer. Die Verletzungsschwerpunkte liegen im Schultergurtel-, Handgelenks- und Unterschenkel-Fusbereich. Normale Strasenmotorradfahrer verunfallen statistisch haufiger. Eine vergleichende Analyse zeigt fur die Verletzungen der unteren Extremitat einen hoheren Anteil an komplizierten und offenen Frakturen. Das gunstigere Abschneiden der Rennfahrer erklart sich aus einer wesentlich besseren Unfallprevention.