Parallel branch and bound on fine-grained hypercube multiprocessors

In this paper, we study parallel branch and bound on fine grained hypercube multiprocessors. Each processor in a fine grained system has only a very small amount of memory available. Therefore, current parallel branch and bound methods for coarse grained systems ( 1000 nodes) cannot be applied, since all these methods assume that every processor stores the path from the node it is currently processing back to the node where the process was created (the back-up path). Furthermore, the much larger number of processors available in a fine grained system makes it imperative that global information (e.g. the current best solution) is continuously available at every processor; otherwise the amount of unnecessary search would become intolerable. We describe an efficient branch-and-bound algorithm for fine grained hypercube multiprocessors. Our method uses a global scheme where all processors collectively store all back-up paths such that each processor needs to store only a constant amount of information. At each iteration of the algorithm, all current nodes may decide whether they need to create new children, be pruned, or remain unchanged. We describe an algorithm that, based on these decisions, updates the current back-up paths and distributes global information in O(log m) steps, where m is the current number of nodes. This method also includes dynamic allocation of search processes to processors and provides optimal load balancing. Even if very drastic changes in the set of current nodes occur, our load balancing mechanism does not suffer any slow down.     

Perfusion changes in hemodilution. The effect of extensive isovolemic hemodilution with gelatin and hydroxyethylstarch solutions on cerebral blood flow velocity and cutaneous microcirculation in humans

OBJECTIVE: Quantifying the influence of extreme isovolemic hemodilution (NH) with different colloids on cerebral blood flow velocities (transcranial Doppler sonography) and cutaneous microcirculatory blood flow (laser Doppler flowmetry) in healthy, non-premedicated volunteers was the aim of this study. METHODS: In seven volunteers (randomized cross-over design) 20 ml/kg blood was withdrawn within 30 min and simultaneously replaced with 6% hydroxyethyl starch (200,000/0.5, HES) or 3% gelatin (GEL). Thirty minutes later, the autologous blood was retransfused (RT) within 30 min. Due to a severe allergic reaction to gelatin in one volunteer, only 6 GEL-NH were evaluated. Recorded parameters were: mean blood flow velocities (Vm-MCA) as well as the pulsatility index (PI) and the resistance index (RI) over the middle cerebral artery. In addition laser Doppler flux (FLUX), cell velocity (SPEED), mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb) and hematocrit (Hc) were monitored. RESULTS: NH resulted in a withdrawal volume of 1498 +/- 85 ml (HES) and 1493 +/- 95 ml (GEL), (mean +/- SD) and induced a decrease in hemoglobin from 40.9 to 29.0% (HES) and from 39.8 to 30.0% (GEL). RT increased Hc to 34.2% (HES) and 34.5% (GEL). MAP and HR showed no significant alterations in both groups. Following NH, Vm-MCA rose almost the same way in either case (26% HES), 21% (GEL), but decreased continuously again during RT. After completing RT, only in the HES group Vm-MCA still remained higher than baseline values (14% HES, only 3% GEL). Similar inverse regression lines were found for the two groups between Hc and Vm-MCA: [Vm-MCAHES (cm/s) = -1.27 x Hc + 110.9; r = 0.98, P < 0.001 and Vm-MCAGEL (cm/s) = -1.32 x Hc + 110.9; r = 0.91, P < 0.001]. Furthermore, as a result of NH, FLUX and SPEED increased about 61% and 38% in the HES group and remained on higher values in comparison with starting positions (21% FLUX, 13% SPEED). However, the results in the GEL group were of a different kind: FLUX and SPEED increased stupendously to 291% and 114% combined with NH, but both were reduced by RT on a large scale (39 and 27% below baseline values). Whereas RI showed no group differences, there was a remarkable drop in PI during RT (17% HES, 12% GEL). CONCLUSION: The two plasma expanders studied show a close inverse correlation between the alterations of blood flow velocities in the middle cerebral artery and systemic hemoglobin and hematocrit values. In both groups the change in blood flow velocities is comparable. For the first time the results of relative changes in blood flow velocities following hemodilution and retransfusion in healthy volunteers are described that correspond closely by relative cerebral blood flow alterations found in animal studies as well. Moreover, a non-linear correlation of cutaneous microcirculation was shown by means of HES, but also by GEL. Obviously, there was the GEL group to be responsible for pronounced differences in cutaneous circulation.     

A Novel Method Facilitating the Simple and Low-Cost Preparation of Human Osteochondral Slice Explants for Large-Scale Native Tissue Analysis

For in vitro modeling of human joints, osteochondral explants represent an acceptable compromise between conventional cell culture and animal models. However, the scarcity of native human joint tissue poses a challenge for experiments requiring high numbers of samples and makes the method rather unsuitable for toxicity analyses and dosing studies. To scale their application, we developed a novel method that allows the preparation of up to 100 explant cultures from a single human sample with a simple setup. Explants were cultured for 21 days, stimulated with TNF-α or TGF-β3, and analyzed for cell viability, gene expression and histological changes. Tissue cell viability remained stable at >90% for three weeks. Proteoglycan levels and gene expression of COL2A1, ACAN and COMP were maintained for 14 days before decreasing. TNF-α and TGF-β3 caused dose-dependent changes in cartilage marker gene expression as early as 7 days. Histologically, cultures under TNF-α stimulation showed a 32% reduction in proteoglycans, detachment of collagen fibers and cell swelling after 7 days. In conclusion, thin osteochondral slice cultures behaved analogously to conventional punch explants despite cell stress exerted during fabrication. In pharmacological testing, both the shorter diffusion distance and the lack of need for serum in the culture suggest a positive effect on sensitivity. The ease of fabrication and the scalability of the sample number make this manufacturing method a promising platform for large-scale preclinical testing in joint research.     

Vergleich der Acrylamidaufnahme über die Nahrung bei Jugendlichen auf der Basis von Acrylamidgehalten von Januar 2003 und Oktober 2005

Auf der Basis von zwei Verzehrserhebungen – der Berliner Jugendstudie vom Herbst 2002 und der Nationalen Verzehrsstudie vom Ende der 80er Jahre – und Acrylamidwerten vom Stand Januar 2003 und Oktober 2005 wurde gesch?tzt, wie viel Acrylamid über die Nahrung aufgenommen worden ist. Ziel dieser Untersuchung war es, die Wirkung des Minimierungskonzepts des Bundesamtes für Verbraucherschutz und Lebensmittelsicherheit (BVL) in der betrachteten Bev?lkerungsgruppe zu belegen. Auf Basis der Verzehrsmengen der Berliner Jugendstudie ist eine Verringerung der mittleren t?glichen Acrylamidaufnahme durch den Verzehr der ausgew?hlten Lebensmittel von 1,08 μg auf 0,81 μg pro kg K?rpergewicht zu beobachten. Das entspricht einer Reduzierung um ca. 25%, die auf gesunkene Acrylamidwerte der betrachteten Produktgruppen zurückzuführen ist. Etwa identische Ergebnisse bezüglich der Reduzierung sind zu verzeichnen, wenn die Nationale Verzehrsstudie zugrunde gelegt wird. Auf Basis dieser Daten reduziert sich die mittlere t?gliche Acrylamidaufnahme pro kg K?rpergewicht von 0,91 μg auf 0,70 μg um ca. 23%.     

Clustering methods for geometric objects and applications to design problems

Clustering of geometric objects is a very familiar and important problem in many different areas of applications as well as in the theoretical foundation of some modern fields of computer science. This paper describes how design problems, especially the design of an assembly line, can be transformed into a clustering problem. In order to solve the problem for large sizes of input data we introduce a structure, called Voronoi Tree, which applied to our real world data (assembly line design) did not only reduce the time to get a feasible design of an assembly line dramatically, but additionally increased the value of the design by more than 30% (in comparison with standard design methods). In addition to this we introduce a clustering method which is of interest for those applications which can be transformed to planar clustering problems. In this particular case it is possible to compute an (hierarchically) optimized clustering with resp. to a large class of clustering measures in timeO(nn^1/2log³ n+U _F(n)nn^1/2+P _F(n)) [n: number of points;U _F(n), P_F(n) dependent on the chosen clustering measure].     

Controlled enzymatic protein hydrolysis in low pH areas. 1. Studies with bovine serum albumin

A method for the controlled enzymatic hydrolysis of proteins in the pH range 1.5-3.5 is described. The hydrolysis of the peptide bond at a constant pH value ("pH-stat") can be followed by the consumption of acid. This value is used for calculating the degree of protein hydrolysis. The degree of hydrolysis is in good accordance with the number of amino groups liberated during the course of hydrolysis. These experiments are carried out using bovine serum albumin as the substrate.     

Optical clustering

This paper presents a definition of ‘optical clusters’ which is derived from the concept of optical resolution. The clustering problem (induced by this definition) is transformed such that the application of well known Computational Geometry methods yields efficient solutions. One result (which can be extended to different classes of objects and metrices) is the following: Given a setS ofN disjoint line segments inE ².

1. The optical clusters with respect to a given separation parameterr∈R can be computed in timeO(Nlog² N).
2. Given an interval [a, b] for the numberm(S, r) of optical clusters which we want to compute, then timeO(N log² N)[O(Nlog² N+CN)] suffices to compute the interval [R(b),R(a)]={r∈R/m(S,r)∈[a,b]} [allC optical clusterings withR(b)≦ r≦R(a)].

     

Solving visibility and separability problems on a mesh-of-processors

In this paper we study parallel algorithms for the Mesh-of-Processors architecture to solve visibility and related separability problems for sets of simple polygons in the plane. In particular, we present the following algorithms:

- AnO( \(\sqrt N\) time algorithm for computing on a Mesh-of-Processors of size N the visibility polygon from a point located in anN-vertex polygon, possibly with holes.

-O( \(\sqrt N\) ) time algorithms for computing on a Mesh-of-Processors of sizeN the set of all points on the boundary of anN-vertex polygonP which are visible in a given directiond as well as the visibility hull ofP for a given directiond.

- AnO( \(\sqrt N\) ) time algorithm for detecting on a Mesh-of-Processors of size 2N whether twoN-vertex polygons are separable in a given direction and anO( \(\sqrt {MN}\) ) time algorithm for detecting on a Mesh-of-Processors of sizeMN whetherM N-vertex polygons are sequentially separable in a given direction.

All proposed algorithms are asymptotically optimal (for the Mesh-of-Processors) with respect to time and number of processors.