Standing cones and lying cones

Summary It can be demonstrated in reconstructive surgery when using a fusiform excision that as the ratio of its lengthL to widthW is increased, the probability of a satisfactory closure is also increased. It is found that there is a minimum value ofL/W for a given area of skin beyond which small standing cones appear at the ends of the excision on closure. This indicates that there is a maximum value of the angle, included at the ends of the excision by its two sides, that can be closed satisfactorily. In other surgical procedures not only standing cones may form but also lying cones when the prodecure involves opening an angle instead of closing it.The phenomena of these standing and lying cones in human skin subject to reconstructive surgery are shown to be dependent on the characteristics of the tissue in uniaxial compression. It can be demonstrated that there is a critical value of this compression before the skin in vivo buckles into a ridge or cone.A semi empirical procedure is outlined that allows the surgeon to predict the maximum excisional angles which may be closed or opened without causing the formation of standing or lying cones.

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Zusammenfassung Es wird gezeigt, daß in der Wiederherstellungschirurgie bei Benutzung spindelförmiger Exzisionen mit Steigerung des Verhältnisses Länge L/DurchmesserW die Wahrscheinlichkeit eines zufriedenstellenden Verschlusses erhöht wird. Die Ergebnisse zeigen, daß es einen Minimalwert für das VerhältnisL/W bei einem vorgegebenen Hautbereich gibt, bei dessen Unterschreitung an den Enden der Exzision bei Verschluß kleine stehende Kegel auftreten. Das läßt den Schluß zu, daß es ein Maximum für den Winkel gibt, der am Ende der Exzision durch deren beide Seiten gebildet wird, welcher noch zufriedenstellend verschlossen werden kann. Bei anderen chirurgischen Verfahren können sich nicht nur stehende, sondern auch liegende Kegel bilden, wenn bei dem Verfahren ein Winkel geöffnet statt geschlossen werden muß.Die Erscheinung dieser stehenden und liegenden Kegel in menschlicher Haut, die der Wiederherstellungschirurgie ausgesetzt ist, ist, wie die Untersuchungen zeigen, abhängig von den Eigenschaften des Gewebes bei einachsiger Kompression. Für diese Kompression wird ein kritischer Wert abgeleitet, ehe sich die Haut in vivo zu einem Grat oder Kegel verzieht.Es wird ein halbempirisches Verfahren entwickelt, mit dessen Hilfe der Chirurg den maximalen Exzisionswinkel vorherzusagen vermag, der ohne die Bildung von stehenden oder liegenden Kegeln geschlossen werden kann.

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Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14–16, 1970.     

On the capacity of channels with unknown interference

The process of communicating in the presence of interference that is unknown or hostile is modeled as a two-person zero-sum game with the communicator and the jammer as the players. The objective function considered is the rate of reliable communication. The communicator's strategies are encoders and distributions on a set of quantizers. The jammer's strategies are distributions on the noise power subject to certain constraints. Various conditions are considered on the jammer's strategy set and on the communicator's knowledge. For the case where the decoder is uninformed of the actual quantizer chosen, it is shown that, from the communicator's perspective, the worst-case jamming strategy is a distribution concentrated on a finite number of points, thereby converting a functional optimization problem into a nonlinear programming problem. Moreover, the worst-case distributions can be characterized by means of necessary and sufficient conditions which are easy to verify. For the case where the decoder is informed of the actual quantizer chosen, the existence of saddle-point strategies is demonstrated. The analysis is also seen to be valid for a number of situations where the jammer is adaptive     

Experimental analysis of high-efficiency avalanche-resonance pumped oscillators

Silicon avalanche diodes yielded efficiencies of 10, 20 and 45% at the first, second and seventh subharmonic of an essential self-generated pump signal close to the diode's avalanche resonance. Measured large-signal impedances and dynamic characteristics explain the efficiency degradation at higher frequencies and suggest measures for further improvement.     

Zur Feldemission der Metalle Titan,Zirkon und Hafnium

The field emission of titanium, zirconium, and hafnium single crystals has been investigated. The patterns were found to agree with those obtained by clean tungsten and rhenium emitters.     

Control of thiolate nucleophilicity and specificity in zinc metalloproteins by hydrogen bonding: lessons from model compound studies

A single hydrogen bond between an amide N-H and a thiolate sulfur in model complexes designed to mimic the binding site of zinc thiolate proteins, is shown to reduce the reactivity of the thiolate toward electrophiles by up to 2 orders of magnitude. In addition a single such bond is also sufficient to achieve nearly 100% regiospecificity of reaction between a strong, and hence inherently indiscriminate, alkylating agent like trimethyl oxonium tetrafluoroborate and a single sulfur in a dithiolate construct. The importance of these results in understanding how two systems such as the zinc fingers of the GATA family and the Escherichia coli DNA repair protein Ada which share the same pseudotetrahedral structure and tetrascysteinyl ligation around the zinc can fulfill such widely divergent (structural vs reactive) roles and how specificity of reaction in multithiolate-containing systems can be achieved is discussed.     

H-bonding interactions and control of thiolate nucleophilicity and specificity in model complexes of zinc metalloproteins

It is shown in model complexes designed to mimic the binding site of zinc-thiolate proteins that a single hydrogen bond between an amide N-H and a Zn-coordinated thiolate reduces its reactivity toward electrophiles by up to 2 orders of magnitude. In addition, we show that a single N-H...S hydrogen bond is sufficient to achieve near 100% regiospecificity of reaction between a strong, and hence inherently indiscriminate, alkylating agent like trimethyloxonium tetraflouroborate and a single sulfur in a dithiolate construct. The importance of these results in understanding how systems such as the zinc fingers of the GATA family and the E. coli DNA repair protein Ada, which share the same pseudotetrahedral structure and tetracysteinyl ligation around the zinc, can fulfill such widely divergent (structural vs reactive) roles and how specificity of reaction in such multi-thiolate containing systems can be achieved is discussed.