148,434 research outputs found
Evaluating A+B=K conditions in constant time
The authors consider a type of condition that can be evaluated without requiring a complete ALU (arithmetic logic unit) operation. The circuit that is presented detects the condition A+B=K (n-bit numbers) in constant time, avoiding the carry propagation delay. This circuit can be used to detect a wide spectrum of conditions in branch instructions. It can improve the processor performance by advancing the evaluation of conditions and eliminating the pipeline delays produced by these operations.Peer ReviewedPostprint (published version
Parallel Algorithms for Summing Floating-Point Numbers
The problem of exactly summing n floating-point numbers is a fundamental
problem that has many applications in large-scale simulations and computational
geometry. Unfortunately, due to the round-off error in standard floating-point
operations, this problem becomes very challenging. Moreover, all existing
solutions rely on sequential algorithms which cannot scale to the huge datasets
that need to be processed.
In this paper, we provide several efficient parallel algorithms for summing n
floating point numbers, so as to produce a faithfully rounded floating-point
representation of the sum. We present algorithms in PRAM, external-memory, and
MapReduce models, and we also provide an experimental analysis of our MapReduce
algorithms, due to their simplicity and practical efficiency.Comment: Conference version appears in SPAA 201
Good practice guide for calibrating a hydrophone "in situ" with a non-omnidirectional source at 10 kHz (26-34)
The aim of this paper is to provide the basis for the calibration of a hydrophonePeer ReviewedPostprint (published version
A Simple and Robust Dissemination Protocol for VANETs
Several promising applications for Vehicular Ad-hoc Networks (VANETs) exist. For most of these applications, the communication among vehicles is envisioned to be based on the broadcasting of messages. This is due to the inherent highly mobile environment and importance of these messages to vehicles nearby. To deal with broadcast communication, dissemination protocols must be defined in such a way as to (i) prevent the so-called broadcast storm problem in dense networks and (ii) deal with disconnected networks in sparse topologies. In this paper, we present a Simple and Robust Dissemination (SRD) protocol that deals with these requirements in both sparse and dense networks. Its novelty lies in its simplicity and robustness. Simplicity is achieved by considering only two states (cluster tail and non- tail) for a vehicle. Robustness is achieved by assigning message delivery responsibility to multiple vehicles in sparse networks. Our simulation results show that SRD achieves high delivery ratio and low end-to-end delay under diverse traffic conditions
Analysing Temporal Relations – Beyond Windows, Frames and Predicates
This article proposes an approach to rely on the standard
operators of relational algebra (including grouping and ag-
gregation) for processing complex event without requiring
window specifications. In this way the approach can pro-
cess complex event queries of the kind encountered in appli-
cations such as emergency management in metro networks.
This article presents Temporal Stream Algebra (TSA) which
combines the operators of relational algebra with an analy-
sis of temporal relations at compile time. This analysis de-
termines which relational algebra queries can be evaluated
against data streams, i. e. the analysis is able to distinguish
valid from invalid stream queries. Furthermore the analysis
derives functions similar to the pass, propagation and keep
invariants in Tucker's et al. \Exploiting Punctuation Seman-
tics in Continuous Data Streams". These functions enable
the incremental evaluation of TSA queries, the propagation
of punctuations, and garbage collection. The evaluation of
TSA queries combines bulk-wise and out-of-order processing
which makes it tolerant to workload bursts as they typically
occur in emergency management. The approach has been
conceived for efficiently processing complex event queries on
top of a relational database system. It has been deployed
and tested on MonetDB
Bit error rate measurement of free space optical communication links under laboratory controlled conditions
This paper outlines the experimental investigation of the fog effect on the bit error rate (BER) performance of the free space optical (FSO) communication link under a controlled laboratory environment. The link transmittance and the received signal Q-factor are measured against different levels of fog densities. The link visibility derived from fog attenuation measurement is used to characterize the fog within the chamber. Moreover, the effect of using different average transmitted optical communication power (Popt) on the transmittance and received Q-factor of the link is also studied for light and dense fog densities
A good practice guide on the sources and magnitude of uncertainty arising in the practical measurement of environmental noise
A brief introduction to measurement uncertainty, uncertainty budgets, and inter-comparison exercises (repeated measurements), is provided in Chapter 2. The procedure forformulating an uncertainty budget and evaluating magnitudes is outlined in greater detail in Chapter 3. A flow chart summarising this process, and a checklist for the identification of sources of measurement uncertainty are included at the end of the chapter. Two example measurement exercises with corresponding uncertainty budgets are presented in Chapter 4.
Some of the more commonly encountered sources of measurement uncertainty are outlined in Chapter5. Where possible, information on magnitudes or pointers to where that information can be found are included. The more important sources of uncertainty are highlighted, and “good practice guidelines” provided to help the practitioner identify means of reducing their effect.
Case studies illustrating some of the points made in Chapter 5,and listing of relevant guidelines and further reading are provided in the Appendices
Ignition and flame sptead in laminar mixing layers
In order to identify some of the mathematical problems encoun-tered in analyzing the ignition and ñame spread in mixing layéis, \ve shall describe the structure of the laminar mixing layer between two parallel streams of a fu el and air, initially separated by a splitter píate, undergoing an Arrhenius reaction.
If the activation energy of the reaction is lower than a critical valué, there is only one steady solution of the problein, showing a transition from nearly frozen mixing to diffusion controlled combustión
downstream of the píate.
For higher, typical, valúes of the activation energy we may find a multiplicity of solutions, depending on the valué of the Damkohler number D, characterized by the temperature of the hotter of the two streams. For valúes of the Damkohler number lower than a critical valué Dc, there is a solution where a thermal runaway is found to oceur, after an induction length, at a point that serves as the origin of premixed flames that do not propágate upstream. For valúes of D larger than a critical lift-ofif valué D¡(< Dc) we find a solution with diffusion controlled combustión in a diffusion fíame. This fíame is anchored, with a triple-fíame structure, in the near wake of the splitter píate, where upstream heat conduction to the píate plays a dominant role.
In the interval D¡ < D < Dc there is a third, unstable, solution. This solution determines where an external ignition source shonld be placed so that, by means of upstream triple-flame propagation to the splitter píate, transition to diffusion controlled combustión can take plac
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