Thermische Anmerkungen zu Zeitkonstanten von Wänden

Zusammenfassung Man erh?lt kompakte Approximationen von Laplace-übergangsfunktionen, wenn die Koeffizienten des Nenners aus den Zeitkonstanten des Systems abgeleitet werden. (üblicherweise führt dies auf das Problem der Nullstellensuche einer transzendenten Funktion.) Es ist bekannt (Gough [1], Stephenson [2]), da? für die meisten W?nde drei Zeitkonstanten ausreichen, um hinreichend genaue übergansfunktionen zu erhalten. Die Taylor-Entwicklung der Kettenmatrix im Laplaceraum wird für beliebige W?nde mit eindimensionalem W?rmestrom mit der Picard'schen Methode berechnet. Für ebene Mehrschichtw?nde ist dafür eine explizite L?sung angegeben. Die ersten N Zeitkonstanten werden n?herungsweise aus der (N+1). Ordnung der Partial-Summe der Taylor-Entwicklung berechnet. Dies wird mit einer generalisierten Pade-Approximation bewerkstelligt, die eine Totzeit enth?lt und direkt auf ein Nennerpolynom führt (ohne transzendente Wurzeln). Die Wurzeln konvergieren geometrisch zu den Eigenwerten mit wachsendem N (die Eigenwerte stellen die reziproken Zeitkonstanten dar). Die Komplexit?t der gesamten Prozedur liegt kaum über derjenigen für ein System mit konzentrierten Parametern der Ordnung N+1. Es werden Beispiele angegeben, um mit den „exakten” Frequenzg?ngen zu vergleichen.     

Symbolic parametrization of curves

If algebraic varieties like curves or surfaces are to be manipulated by computers, it is essential to be able to represent these geometric objects in an appropriate way. For some applications an implicit representation by algebraic equations is desirable, whereas for others an explicit or parametric representation is more suitable. Therefore, transformation algorithms from one representation to the other are of utmost importance.We investigate the transformation of an implicit representation of a plane algebraic curve into a parametric representation. Various methods for computing a rational parametrization, if one exists, are described. As a new idea we introduce the concept of working with classes of conjugate (singular or simple) points on curves. All the necessary operations, like determining the multiplicity and the character of the singular points or passing a linear system of curves through these points, can be applied to such classes of conjugate points. Using this idea one can parametrize a curve if one knows only one simple point on it. We do not propose any new method for finding such a simple point. By classical methods a rational point on a rational curve can be computed, if such a point exists. Otherwise, one can express the coordinates of such a point in an algebraic extension of degree 2 over the ground field.     

Modelling asymmetry in the peripheral auditory system of the lizard

The ears of lizards are highly directional. The directionality is generated by strong acoustical coupling of the eardrums. A simple lumped-parameter model of the ear followed by binaural comparisons has been shown to perform successful phonotaxis in robot implementations. However, such a model will produce localization errors in the form of response bias if the ears are asymmetrical. We have evaluated how large errors are generated by asymmetry using simulations of the ear model in Mathematica 5.2. The study shows that the effect of asymmetry is minimal around the most directional frequency of the ear, but that biases reduce the useful bandwidth of localization. This work was presented in part at the First European Workshop on Artificial Life and Robotics, Vienna, Austria, July 12–13, 2007     

Hypertension and pulmonary edema associated with subconjunctival phenylephrine in a 2-month-old child during cataract extraction

We have analysed trends in male:female ratios among newborns between 1950 and 1990 in 29 countries from five continents. The numbers of liveborn males and females over the period 1950-1994 were derived from the World Health Organization (WHO) database. Countries for which reliable data were available included 20 major European countries (excluding the former Soviet Union, Albania and a few small countries), Canada, the USA, selected countries of Central and South America, Japan, Australia and New Zealand. From the original numbers of males and females, we computed the proportion of males among liveborns for each country and for selected broader areas within Europe. In most countries the proportion of male liveborns was constant during the study period. In particular, the proportion of male newborns in the European Union was 0.515 in 1950-1954, 0.514 in 1970-1974 and 0.514 in 1990-1994. In the USA, corresponding values were 0.513, 0.513 and 0.512. In Japan the ratios were 0.513 in 1950-1954, 0.516 and 1970-1974 and 0.514 in 1990-1994. Decreasing ratios were observed in some northern and eastern European countries plus Greece and Portugal and, particularly, in Mexico. In contrast, the proportion of male liveborns tended to increase in southern Europe and Australia. Overall, among the 29 countries considered, the proportion of males declined in 16, increased in six, and remained stable in seven.     

Table-Free Bridging

Simple interconnection of high-speed local area networks (LAN's) can be accomplished without special technology through the use of table-free bridges. Self-guided frame routing allows frames to trace specific routes through bridged LAN's without requiring bridges to maintain address tables or perform table lookups. As a result, the technique applies to networks regardless of their operating speed or topological configuration and requires no interbridge protocols. The paper discusses a method known as source routing that provides tablefree bridging and self-guided frame routing for LAN's. Participation by the bridges that interconnect pairs of LAN's and by the stations whose frames they forward is described. Possible frame formats are shown as enhancements to the standard frame formats of the IEEE 802 and ISO 8802 local area networks.     

Tumor size and prognosis in aggressively treated osteosarcoma

PURPOSE: The aim of this retrospective analysis was to investigate the prognostic significance and optimal measures of tumor size in osteosarcoma treated with intensive neoadjuvant chemotherapy. PATIENTS AND METHODS: Initial anterior-posterior (AP) and lateral x-ray films of 128 patients treated within the trials Cooperative Osteosarcoma Study (COSS)-80, -82, and -86, were evaluated for the following three tumor diameters: length, width, and depth. Metastasis-free survival (MFS) analyses were performed in univariate and multivariate models with one, two, and three dimensions of the tumor as absolute or relative measures (tumor length, referred to bone length, plane and volume to body-surface area). RESULTS: Univariate analyses of MFS showed a high prognostic significance of all absolute measures. Relative measures, at best, showed a comparable predictive value. Cox regression analysis indicated the high prognostic significance of absolute tumor volume (ATV; P < .0001) and histologic response (P < .0001). None of 19 patients with an ATV < or = 70 cm3 and only four of 53 with an ATV < or = 150 cm3 relapsed, while in patients with an ATV more than 150 cm3, the relapse rate remained 40% to 60%, irrespective of further increase in volume. CONCLUSION: Initial tumor size is an important and easily obtainable prognostic factor in osteosarcoma and may serve as a basis for risk-adapted therapy. It is best represented by the absolute three-dimensional measure ATV. There is a cut-off point regarding the incidence of metastases at a tumor volume of approximately 150 cm3 as calculated from two-plane x-ray films.