Aspects of k-k-Routing in Meshes and OTIS Networks

Aspects of k-k Routing in Meshes and OTIS-Networks Abstract Efficient data transport in parallel computers build on sparse interconnection networks is crucial for their performance. A basic transport problem in such a computer is the k-k routing problem. In this thesis, aspects of the k-k routing problem on r-dimensional meshes and OTIS-G networks are discussed. The first oblivious routing algorithms for these networks are presented that solve the k-k routing problem in an asymptotically optimal running time and a constant buffer size. Furthermore, other aspects of the k-k routing problem for OTIS-G networks are analysed. In particular, lower bounds for the problem based on the diameter and bisection width of OTIS-G networks are given, and the k-k sorting problem on the OTIS-Mesh is considered. Based on OTIS-G networks, a new class of networks, called Extended OTIS-G networks, is introduced, which have smaller diameters than OTIS-G networks.Für die Leistungfähigkeit von Parallelrechnern, die über ein Verbindungsnetzwerk kommunizieren, ist ein effizienter Datentransport entscheidend. Ein grundlegendes Transportproblem in einem solchen Rechner ist das k-k Routing Problem. In dieser Arbeit werden Aspekte dieses Problems in r-dimensionalen Gittern und OTIS-G Netzwerken untersucht. Es wird der erste vergessliche (oblivious) Routing Algorithmus vorgestellt, der das k-k Routing Problem in diesen Netzwerken in einer asymptotisch optimalen Laufzeit bei konstanter Puffergröße löst. Für OTIS-G Netzwerke werden untere Laufzeitschranken für das untersuchte Problem angegeben, die auf dem Durchmesser und der Bisektionsweite der Netzwerke basieren. Weiterhin wird ein Algorithmus vorgestellt, der das k-k Sorting Problem mit einer Laufzeit löst, die nahe an der Bisektions- und Durchmesserschranke liegt. Basierend auf den OTIS-G Netzwerken, wird eine neue Klasse von Netzwerken eingeführt, die sogenannten Extended OTIS-G Netzwerke, die sich durch einen kleineren Durchmesser von OTIS-G Netzwerken unterscheiden

SCUBA Observations of Dust around Lindroos Stars: Evidence for a Substantial Submillimetre Disc Population

We have observed 22 Lindroos stars with SCUBA on the JCMT to search for evidence of dust discs. Stars in this sample are the less massive companions of B-type primaries and have ages of 10-170Myr. Dust was detected around three of these stars (HD74067, HD112412 and HD99803B). The emission around HD74067 is centrally peaked and is approximately symmetrically distributed out to ~70". This emission either arises from a two component disc, one circumstellar and the other circumbinary with dust masses of 0.3 and >27Mearth respectively, or an unrelated background object. The other two detections we attribute to circumsecondary discs with masses of 0.04 and 0.3Mearth; a circumprimary disc is also present around HD112413 with a similar mass to that around the companion HD112412. Cross-correlation of our sample with the IRAS catalogs only showed evidence for dust emission at 25um and 60um toward one star (HD1438); none of the sub-mm detections were evident in the far-IR data implying that these discs are cold (<40K assuming beta=1). Our sub-mm detections are some of the first of dust discs surrounding evolved stars that were not detected by IRAS or ISO and imply that 9-14% of stars could harbour previously undetected dust discs that await discovery in unbiased sub-mm surveys. If these discs are protoplanetary remnants, rather than secondary debris discs, dust lifetime arguments show that they must be devoid of small <0.1mm grains. Thus it may be possible to determine the origin of these discs from their spectral energy distributions. The low dust masses for this sample support the picture that protoplanetary dust discs are depleted to the levels of the brightest debris discs (~1Mearth) within 10Myr.Comment: 14 pages, 4 figures, accepted by MNRA

The theory of the firm and its critics: a stocktaking and assessment

Includes bibliographical references."Prepared for Jean-Michel Glachant and Eric Brousseau, eds. New Institutional Economics: A Textbook, Cambridge, Cambridge University Press.""This version: August 22, 2005."Since its emergence in the 1970s the modern economic or Coasian theory of the firm has been discussed and challenged by sociologists, heterodox economists, management scholars, and other critics. This chapter reviews and assesses these critiques, focusing on behavioral issues (bounded rationality and motivation), process (including path dependence and the selection argument), entrepreneurship, and the challenge from knowledge-based theories of the firm

Optimal Oblivious Routing on D-Dimensional Meshes

In this work we consider deterministic oblivious k-k routing algorithms with buffer size O(k). Our main focus lie is the design of algorithms for d- dimensional n n meshes, d &gt; 1. For these networks we present asymptotically optimal O(k d ) step oblivious k-k routing algorithms for all k and d &gt; 1

A True Random Number Generator with Built-in Attack Detection

True random number generators (TRNGs) are extensively used in cryptography, simulations and statistics. Metastability is a way to generate true random numbers. By using electromagnetic radiation, a flip-flop in a metastable state can be manipulated to a known state. In this work, we introduce and analyze the concept of a randomized bit-cell, being able to simultaneously produce random numbers and detect active nonintrusive attacks. The experimental comparison with a standard TRNG yields an 11.5 times better distribution of zeros and ones while the TRNGs are under attack. The concept is extended by using a corrector. A perfect distribution can be gained at the expense of a delay which is proportional to the quality of the random source

k-k Sorting on the Multi-Mesh

. We present sorting algorithms on the recently introduced multi-mesh, a network consisting of n 2 meshes of size n \Theta n which are connected by the free marginal links of the meshes. Our algorithm takes 41n+ o(n) steps which is a significant improvement to previously known algorithms. The sorting algorithm is based on a technique using interchange of data between the n \Theta n submeshes to distribute information uniformly, an approach which is similar to an all-to-all mapping. Furthermore, with this approach we can also handle k-k problems on the multi-mesh, where each processor contains k elements initially and finally. We show that the k-k sorting problem can be solved in about 9:5kn steps, provided k 12. 1 Introduction Several models for parallel machines have been proposed and studied in the past and it has turned out that no model ideally fits all applications. One of the best studied topologies is the mesh of processors or mesh-connected array which is a simple architect..