122 research outputs found
Performability Modeling Based on Real Data: A Case Study
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryNASA / NAG-1-613IBM CorporationJoint Services Electronics Program / N00014-84-C-0149Air Force Office of Scientific Research / AFOSR-84-013
On modelling the performance and reliability of multimode computer systems
We present an effective technique for the combined performance and reliability analysis of multi-mode computer systems. A reward rate (or a performance level) is associated with each mode of operation. The switching between different modes is characterized by a continuous time Markov chain. Different types of service-interruption interactions (as a result of mode switching) are considered. We consider the execution time of a given job on such a system and derive the distribution of its completion time. A useful dual relationship, between the completion time of a given job and the accumulated reward up to a given time, is noted. We demonstrate the use of our technique by means of a simple example
Towards the Formal Reliability Analysis of Oil and Gas Pipelines
It is customary to assess the reliability of underground oil and gas
pipelines in the presence of excessive loading and corrosion effects to ensure
a leak-free transport of hazardous materials. The main idea behind this
reliability analysis is to model the given pipeline system as a Reliability
Block Diagram (RBD) of segments such that the reliability of an individual
pipeline segment can be represented by a random variable. Traditionally,
computer simulation is used to perform this reliability analysis but it
provides approximate results and requires an enormous amount of CPU time for
attaining reasonable estimates. Due to its approximate nature, simulation is
not very suitable for analyzing safety-critical systems like oil and gas
pipelines, where even minor analysis flaws may result in catastrophic
consequences. As an accurate alternative, we propose to use a
higher-order-logic theorem prover (HOL) for the reliability analysis of
pipelines. As a first step towards this idea, this paper provides a
higher-order-logic formalization of reliability and the series RBD using the
HOL theorem prover. For illustration, we present the formal analysis of a
simple pipeline that can be modeled as a series RBD of segments with
exponentially distributed failure times.Comment: 15 page
Decompositional analysis of Kronecker structured Markov chains
This contribution proposes a decompositional iterative method with low memory requirements for the steadystate analysis ofKronecker structured Markov chains. The Markovian system is formed by a composition of subsystems using the Kronecker sum operator for local transitions and the Kronecker product operator for synchronized transitions. Even though the interactions among subsystems, which are captured by synchronized transitions, need not be weak, numerical experiments indicate that the solver benefits considerably from weak interactions among subsystems, and is to be recommended specifically in this case. © 2008, Kent State University
Approximate conditional distributions of distances between nodes in a two-dimensional sensor network
When we represent a network of sensors in Euclidean space by a graph, there
are two distances between any two nodes that we may consider. One of them is
the Euclidean distance. The other is the distance between the two nodes in the
graph, defined to be the number of edges on a shortest path between them. In
this paper, we consider a network of sensors placed uniformly at random in a
two-dimensional region and study two conditional distributions related to these
distances. The first is the probability distribution of distances in the graph,
conditioned on Euclidean distances; the other is the probability density
function associated with Euclidean distances, conditioned on distances in the
graph. We study these distributions both analytically (when feasible) and by
means of simulations. To the best of our knowledge, our results constitute the
first of their kind and open up the possibility of discovering improved
solutions to certain sensor-network problems, as for example sensor
localization
New Models of Gauge and Gravity Mediated Supersymmetry Breaking
We show that supersymmetry breaking in a class of theories with SU(N) x
SU(N-2) gauge symmetry can be studied in a calculable sigma model. We use the
sigma model to show that the supersymmetry breaking vacuum in these theories
leaves a large subgroup of flavor symmetries intact, and to calculate the
masses of the low-lying states. By embedding the Standard Model gauge groups in
the unbroken flavor symmetry group we construct a class of models in which
supersymmetry breaking is communicated by both gravitational and gauge
interactions. One distinguishing feature of these models is that the messenger
fields, responsible for the gauge mediated communication of supersymmetry
breaking, are an integral part of the supersymmetry breaking sector. We also
show how, by lowering the scale that suppresses the nonrenormalizable
operators, a class of purely gauge mediated models with a combined
supersymmetry breaking-cum-messenger sector can be built. We briefly discuss
the phenomenological features of the models we construct.Comment: Revised discussion of communication of supersymmetry breaking, 24
pages, LaTe
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
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