Vorwort

Ohne Zusammenfassung     

Optimizing counter-terror operations: Should one fight fire with “fire” or “water”?

This paper deals dynamically with the question of how recruitment to terror organizations is influenced by counter-terror operations. This is done within an optimal control model, where the key state is the (relative) number of terrorists and the key controls are two types of counter-terror tactics, one (“water”) that does not and one (“fire”) that does provoke recruitment of new terrorists. The model is nonlinear and does not admit analytical solutions, but an efficient numerical implementation of Pontryagin's minimum principle allows for solution with base case parameters and considerable sensitivity analysis. Generally, this model yields two different steady states, one where the terror organization is nearly eradicated and one with a high number of terrorists. Whereas water strategies are used at almost any time, it can be optimal not to use fire strategies if the number of terrorists is below a certain threshold.     

Approximating curves and their offsets using biarcs and Pythagorean hodograph quintics

This paper compares two techniques for the approximation of the offsets to a given planar curve. The two methods are based on approximate conversion of the planar curve into circular splines and Pythagorean hodograph (PH) splines, respectively. The circular splines are obtained using a novel variant of biarc interpolation, while the PH splines are constructed via Hermite interpolation of C¹ boundary data.We analyze the approximation order of both conversion procedures. As a new result, the C¹ Hermite interpolation with PH quintics is shown to have approximation order 4 with respect to the original curve, and 3 with respect to its offsets. In addition, we study the resulting data volume, both for the original curve and for its offsets. It is shown that PH splines outperform the circular splines for increasing accuracy, due to the higher approximation order.     

Successful treatment of a heterotopic pregnancy by sonographically guided instillation of hyperosmolar glucose

A potassium channel toxin (AeK) was isolated from the sea anemone Actinia equina by gel filtration on Sephadex G-50 and reverse-phase HPLC on TSKgel ODS-120T. AeK and alpha-dendrotoxin inhibited the binding of 125I-alpha-dendrotoxin to rat synaptosomal membranes with IC50 of 22 and 0.34 nM, respectively, indicating that AeK is about sixty-five times less toxic than alpha-dendrotoxin. The complete amino acid sequence of AeK was elucidated; it is composed of 36 amino acid residues including six half-Cys residues. The determined sequence showed that AeK is analogous to the three potassium channel toxins from sea anemones (BgK from Bunodosoma granulifera, ShK from Stichodactyla helianthus and AsKS from Anemonia sulcata), with an especially high sequence homology (86%) with AsKS.     

Clinical application of volume estimation based on three-dimensional ultrasonography

The development of three-dimensional sonography represents a milestone in the history of diagnostic ultrasound. It has become possible to evaluate a region of interest not only in the horizontal and vertical planes but also in a third, i.e. the frontal, plane. Among other possible applications, this technique greatly facilitates volume estimation. The objective of the present study was to evaluate the accuracy and precision of volumetry based on three-dimensional sonography. The results demonstrate a good correlation between estimated volumes and the volumes measured by transvaginal needle-guided follicle aspiration performed under sonographic visualization. Our findings confirm the conclusion of previous studies that three-dimensional sonography is making a valuable contribution to imaging techniques.     

Buchbesprechungen

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Optimal modification of machine reliability by maintenance and production

Summary The purpose of the following paper is to extend the optimal maintenance model of Kamien and Schwartz [8] by including the production rate as an additional control variable. Two models are considered: the first model deals with the optimal allocation of preventive maintenance of a machine and production, whereas in the second case both activities may be carried out independently and simultaneously. Using the maximum principle it is shown that for the optimal life time of the machine the optimal production rate increases monotonically with the age of the machine, whereas the optimal maintenance rate is decreasing. Thus, under the assumptions made it is, e.g.,not optimal to counteract a decrease in the machine's survival probability arising from an increasing production rate by a higher maintenance rate.

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Zusammenfassung Zweck des vorliegendes Aufsatzes ist es, ein optimales Instandhaltungsmodell von Kamien und Schwartz [8] durch Einbeziehung der Produktionsrate als zusätzliche Steuervariable zu erweitern. Zwei Modelle werden untersucht: beim ersten handelt es sich um die optimale Aufteilung von vorbeugenden Instandhaltungsmaßnahmen an einer Maschine und Produktion, während im zweiten Fall die Aktivitäten unabhängig voneinander simultan ausübbar sind.Unter Benützung des Pontrjaginschen Maximumprinzips wird u. a. gezeigt, daß bei optimaler Einsatzdauer der Maschine die optimale Produktionsrate mit dem Alter der Anlage monoton steigt, während die optimale Rate der Instandhaltung abnimmt. Unter den gesetzten Modellannahmen erweist es sich also etwa alssuboptimal, einer Abnahme der Maschinenzuverlässigkeit infolge gesteigerter Produktion durch erhöhte Aufwendungen für die Instandhaltung zu begegnen.

     

Buchbesprechungen

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