Search results for "Distributed"
showing 10 items of 1260 documents
The Max-Product Algorithm Viewed as Linear Data-Fusion: A Distributed Detection Scenario
2019
In this paper, we disclose the statistical behavior of the max-product algorithm configured to solve a maximum a posteriori (MAP) estimation problem in a network of distributed agents. Specifically, we first build a distributed hypothesis test conducted by a max-product iteration over a binary-valued pairwise Markov random field and show that the decision variables obtained are linear combinations of the local log-likelihood ratios observed in the network. Then, we use these linear combinations to formulate the system performance in terms of the false-alarm and detection probabilities. Our findings indicate that, in the hypothesis test concerned, the optimal performance of the max-product a…
MAC Design for WiFi Infrastructure Networks: A Game-Theoretic Approach
2011
In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios because of non-standard configurations of the nodes. Due to the proliferation of open source drivers and programmable cards, enabling an easy customization of the channel access policies, we propose a game-theoretic analysis of random access schemes. Assuming that each node is rational and implements a best response strategy, we show that…
Microreflectivity studies of wavelength control in oxidised AlGaAs microcavities
2003
Wet oxidation of GaAs/AlGaAs structures is an important technique in the processing of advanced devices such as vertical cavity surface emitting lasers (VCSELs). In one VCSEL application, the low-index and electrically-insulating AlxOy layers have been used to obtain high-reflectivity and broad bandwidth distributed Bragg reflector mirrors (DBRs). A further recent development has shown that combined lateral–vertical oxidation of intracavity AlGaAs layers can be used to tune the resonant wavelength of a semiconductor microcavity. The slow oxidation rate limits the lateral scale of practical wet oxidation to mesas structures of 50–100 μm in width. Therefore post-processing assessment of spect…
GekkoFS - A Temporary Distributed File System for HPC Applications
2018
We present GekkoFS, a temporary, highly-scalable burst buffer file system which has been specifically optimized for new access patterns of data-intensive High-Performance Computing (HPC) applications. The file system provides relaxed POSIX semantics, only offering features which are actually required by most (not all) applications. It is able to provide scalable I/O performance and reaches millions of metadata operations already for a small number of nodes, significantly outperforming the capabilities of general-purpose parallel file systems. The work has been funded by the German Research Foundation (DFG) through the ADA-FS project as part of the Priority Programme 1648. It is also support…
Sorted deduplication: How to process thousands of backup streams
2016
The requirements of deduplication systems have changed in the last years. Early deduplication systems had to process dozens to hundreds of backup streams at the same time while today they are able to process hundreds to thousands of them. Traditional approaches rely on stream-locality, which supports parallelism, but which easily leads to many non-contiguous disk accesses, as each stream competes with all other streams for the available resources. This paper presents a new exact deduplication approach designed for processing thousands of backup streams at the same time on the same fingerprint index. The underlying approach destroys the traditionally exploited temporal chunk locality and cre…
DelveFS - An Event-Driven Semantic File System for Object Stores
2020
Data-driven applications are becoming increasingly important in numerous industrial and scientific fields, growing the need for scalable data storage, such as object storage. Yet, many data-driven applications cannot use object interfaces directly and often have to rely on third-party file system connectors that support only a basic representation of objects as files in a flat namespace. With sometimes millions of objects per bucket, this simple organization is insufficient for users and applications who are usually only interested in a small subset of objects. These huge buckets are not only lacking basic semantic properties and structure, but they are also challenging to manage from a tec…
Challenges and Solutions for Tracing Storage Systems
2018
IBM Spectrum Scale’s parallel file system General Parallel File System (GPFS) has a 20-year development history with over 100 contributing developers. Its ability to support strict POSIX semantics across more than 10K clients leads to a complex design with intricate interactions between the cluster nodes. Tracing has proven to be a vital tool to understand the behavior and the anomalies of such a complex software product. However, the necessary trace information is often buried in hundreds of gigabytes of by-product trace records. Further, the overhead of tracing can significantly impact running applications and file system performance, limiting the use of tracing in a production system. In…
Financial measures for supporting wind power systems in Europe: A comparison between green tags and feed’in tariffs
2008
Distributed Generation demonstrates to be able to significantly influence the electric power system, bringing considerable benefits to the quality of service and improving the energetic efficiency of the distribution network. In particular, in the last few years, Distributed Generation from renewable energy sources is considerably increased thanks to the many support policies promoted worldwide with the aim of facing the environmental issue and the problem of the permanent rise of prices of the fossil energy. In this contest, after a brief review on the financing strategies carried out in Europe in the last decade for promoting the recourse to renewable energy, the paper presents a comparis…
Regulation of security tokens as financial instruments in the EU: is there a need for amendments?
2022
In 2020 the European Commission proposed laws on crypto-assets and DLT. The EU treats security tokens as financial instruments, provided that they fall into the MiFID II definition. This Thesis aims to provide classification for crypto-asset as a financial instrument, to identify regulatory gaps in the EU legislation applicable to crypto-assets that qualify as financial instruments (security tokens), and to provide recommendations in relation to security tokens regulation in the EU. The results indicate that Amending Directive will harmonize the procedure for classification of a crypto-asset as a financial instrument across the EU, but the requirement for the expected profit to be derived f…
Distributed leadership in Finnish and Shanghai schools
2016
The present research employed mixed-methods approach to further theorise distributed leadership and to investigate its manifestations in Finnish and Shanghai schools. The whole research comprised two phases. The first phase contained a meta-analysis (Sub-study I), which systematically reviewed 85 key distributed leadership articles published between 2002 and 2013. The meta-analysis identified two main research paradigms: the descriptive-analytical paradigm and the prescriptive-normative paradigm. It also yielded a resource–agency duality model of distributed leadership. In this model, distributed leadership is seen as a process with both organisational and individual perspectives. From the …