22 research outputs found
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 > 1. For these networks we present asymptotically optimal O(k d ) step oblivious k-k routing algorithms for all k and d > 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..