Opin vísindi
Opin vísindi er varðveislusafn vísindaefnis og doktorsritgerða í opnum aðgangi á vegum íslenskra háskóla og Landsbókasafns Íslands - Háskólabókasafns.
Opinn aðgangur að rannsóknaniðurstöðum er í samræmi við 10. gr. laga nr. 3/2003 um opinberan stuðning við vísindarannsóknir sem og kröfur innlendra og erlendra rannsóknasjóða. Markmiðið með opnum aðgangi er að niðurstöður rannsókna séu aðgengilegar sem flestum óhindrað og án endurgjalds á rafrænu formi. Vistun í varðveislusafninu er varanleg og ætlað að tryggja aðgang að vísindaefni íslenskra háskóla í opnum aðgangi um ókomna tíð. Varðveislusafnið Opin vísindi er tengt við rannsóknagáttina IRIS og rannsóknaniðurstöður í opnum aðgangi sem eru skráðar í IRIS eru um leið vistaðar og gerðar aðgengilegar til framtíðar í varðveislusafninu. Með því að safna þessu efni saman í eitt safn verður aðgangur að því einfaldur og þægilegur fyrir alla sem vilja kynna sér það og geta þannig notið þess öfluga vísindastarfs sem fram fer í háskólum landsins.
Varðveislusafnið er OpenAIRE / OpenAIREplus samhæft og samrýmist kröfum sem gerðar eru um birtingu rannsóknaniðurstaðna úr verkefnum sem styrkt eru úr evrópsku rannsóknaáætlununum FP7 og H2020.
Varðveislusafnið notar opna hugbúnaðinn DSpace.
Opinn aðgangur að rannsóknaniðurstöðum er í samræmi við 10. gr. laga nr. 3/2003 um opinberan stuðning við vísindarannsóknir sem og kröfur innlendra og erlendra rannsóknasjóða. Markmiðið með opnum aðgangi er að niðurstöður rannsókna séu aðgengilegar sem flestum óhindrað og án endurgjalds á rafrænu formi. Vistun í varðveislusafninu er varanleg og ætlað að tryggja aðgang að vísindaefni íslenskra háskóla í opnum aðgangi um ókomna tíð. Varðveislusafnið Opin vísindi er tengt við rannsóknagáttina IRIS og rannsóknaniðurstöður í opnum aðgangi sem eru skráðar í IRIS eru um leið vistaðar og gerðar aðgengilegar til framtíðar í varðveislusafninu. Með því að safna þessu efni saman í eitt safn verður aðgangur að því einfaldur og þægilegur fyrir alla sem vilja kynna sér það og geta þannig notið þess öfluga vísindastarfs sem fram fer í háskólum landsins.
Varðveislusafnið er OpenAIRE / OpenAIREplus samhæft og samrýmist kröfum sem gerðar eru um birtingu rannsóknaniðurstaðna úr verkefnum sem styrkt eru úr evrópsku rannsóknaáætlununum FP7 og H2020.
Varðveislusafnið notar opna hugbúnaðinn DSpace.
Nýlega bætt við
Distributed distance computation and routing with small messages
(2019-04-08) Lenzen, Christoph; Patt-Shamir, Boaz; Peleg, David; Department of Computer Science
We consider shortest paths computation and related tasks from the viewpoint of network algorithms, where the n-node input graph is also the computational system: nodes represent processors and edges represent communication links, which can in each time step carry an O(log n) -bit message. We identify several basic distributed distance computation tasks that are highly useful in the design of more sophisticated algorithms and provide efficient solutions. We showcase the utility of these tools by means of several applications.
Self-Stabilizing Byzantine Clock Synchronization with Optimal Precision
(2019-02-15) Khanchandani, Pankaj; Lenzen, Christoph; Department of Computer Science
In the Byzantine-tolerant clock synchronization problem, the goal is to synchronize the clocks of n fully connected nodes. The clocks run at rates between 1 and > 1, and messages have a delay (including computation) between d − U and d. Moreover, up to f < n/3 of the nodes can fail by deviating arbitrarily from the protocol, i.e., are Byzantine. Despite this interference, correct nodes need to generate distinguished events (or pulses) almost simultaneously and periodically. The quality of the solution is measured by the skew, which is the maximum real time difference between corresponding pulses. In the self-stabilizing setting, in addition we allow for transient failures, possibly of all nodes. Once transient faults have ceased and at most f nodes remain faulty, the system should start generating synchronized pulses again. We design a self-stabilizing solution to this problem with asymptotically optimal skew. We achieve our goal by refining and extending the protocol of Lynch and Welch and make the following contributions in the process.We give a simple analysis of the Lynch and Welch protocol with improved bounds on skew and tolerable difference in clock rates by rebuilding upon the main ingredient of their protocol, called approximate agreement.We give a modified version of the protocol so that the frequency and amount of communication between the nodes is reduced. The modification adds a step to adjust the clock rates by another application of approximate agreement. The skew bound achieved is asymptotically optimal for suitable choices of parameters.We present a method to add self-stabilization to the above protocols while preserving their skew bounds. The heart of the method is a coupling scheme that leverages a self-stabilizing protocol with a larger skew.
A dual-band planar quasi yagi-uda antenna with optimized gain for LTE applications
(2019) Elahi, Manzoor; Irfanullah; Khan, Rizwan; Al-Hadi, Azremi Abdullah; Usman, Saeeda; Soh, Ping Jack; Department of Engineering
A printed Yagi-Uda antenna with two closely-spaced driven dipole elements and truncated ground plane is presented for dual-band operation. It is designed on a low-cost FR4 substrate with a dielectric constant 4.6, loss tangent of 0.02, and thickness of 1.6mm. The dipole, operating in the lower band (centered at 1.8GHz), is elliptical-bow-tie in shape with rounded edges, whereas a J-shaped dipole enables its operation in the upper band (centered at 2.6 GHz). A trapezoid-shaped director is employed to achieve maximum gain over the required frequency bands. Measurements indicate that the antenna operates from 1.71 to 1.9GHz and from 2.5 to 2.7GHz with |S11| < -10 dB. The behavior of the proposed antenna has been investigated by studying different parameters to achieve the maximum gains of 6 and 7.7 dB in LTE band 3 and band 7, respectively, with optimal size. It is found that the experimental results of the final packaged antenna agree with the simulated ones in terms of reflection coefficients, gain, and radiation patterns.
Parallel metric tree embedding based on an algebraic view on moore-bellman-ford
(2018-11) Friedrichs, Stephan; Lenzen, Christoph; Department of Computer Science
A metric tree embedding of expected stretch a ≥ 1 maps a weighted n-node graph G = (V, E,ω) to a weighted tree T = (VT , ET ,ωT ) with V ⊆ VT such that, for all v,w ∈ V , dist(v,w,G) ≤ dist(v,w,T ), and E[dist(v,w,T )] = a dist(v,w,G). Such embeddings are highly useful for designing fast approximation algorithms as many hard problems are easy to solve on tree instances. However, to date, the best parallel (polylogn)-depth algorithm that achieves an asymptotically optimal expected stretch of α ∈ O(logn) requires Ω(n2) work and a metric as input. In this article, we show how to achieve the same guarantees using polylogn depth and O-(m1+ϵ ) work, where m = |E| and ϵ > 0 is an arbitrarily small constant. Moreover, one may further reduce the work to O-(m + n1+ϵ ) at the expense of increasing the expected stretch to O(ϵ-1 logn). Our main tool in deriving these parallel algorithms is an algebraic characterization of a generalization of the classic Moore-Bellman-Ford algorithm. We consider this framework, which subsumes a variety of previous "Moore-Bellman-Ford-like" algorithms, to be of independent interest and discuss it in depth. In our tree embedding algorithm, we leverage it to provide efficient query access to an approximate metric that allows sampling the tree using polylogn depth and O-(m) work. We illustrate the generality and versatility of our techniques by various examples and a number of additional results. Specifically, we (1) improve the state of the art for determining metric tree embeddings in the Congest model, (2) determine a (1 + ϵ- )-approximate metric regarding the distances in a graph G in polylogarithmic depth and Õ (n(m + n1+ϵ )) work, and (3) improve upon the state of the art regarding the k-median and the buy-at-bulk network design problems.
Performance analysis of hyperledger fabric platforms
(2018) Nasir, Qassim; Qasse, Ilham A.; Abu Talib, Manar; Nassif, Ali Bou; Department of Computer Science
Blockchain is a key technology that has the potential to decentralize the way we store, share, and manage information and data. One of the more recent blockchain platforms that has emerged is Hyperledger Fabric, an open source, permissioned blockchain that was introduced by IBM, first as Hyperledger Fabric v0.6,and then more recently, in 2017, IBM released Hyperledger Fabric v1.0. Although there are many blockchain platforms, there is no clear methodology for evaluating and assessing the different blockchain platforms in terms of their various aspects, such as performance, security, and scalability. In addition, the new version of Hyperledger Fabric was never evaluated against any other blockchain platform. In this paper,we will first conduct a performance analysis of the two versions of Hyperledger Fabric,v0.6 and v1.0. The performance evaluation of the two platforms will be assessed in terms of execution time,latency,and throughput, by varying the workload in each platform up to 10,000 transactions.Second,we will analyze the scalability of the two platforms by varying the number of nodes up to 20 nodes in each platform. Overall, the performance analysis results across all evaluation metrics, scalability, throughput, execution time, and latency, demonstrate that Hyperledger Fabric v1.0 consistently outperforms Hyperledger Fabric v0.6.However, Hyperledger Fabric v1.0 platform performance did not reach the performance level in current traditional database systems under high workload scenarios.
Flokkar í Opnum vísindum
Veldu flokk til að skoða.
- University of Iceland
- University of Akureyri
- Bifröst University
- Hólar University College
- IRIS
- Agricultural University of Iceland
- National and University Library of Iceland
- Iceland University of the Arts