544 research outputs found
Information driven SDLC concepts
Although software engineering has matured greatly over the years, a large number of ICT projects continue to fail. Studies continue to identify non-technical issues such as poor communication, shifting requirements and poor executive involvement as the main causes of these failures. In a previous paper, the authors identified such causes and posed the question as to why currently available software development life cycles fall short of dealing with them. They also proposed the development of an information driven software development life cycle. In this paper, the concept of an information driven SDLC is explored further and a number of concepts are discussed in this regard.peer-reviewe
Lifelong verification of software systems
Computers systems are increasingly interacting with our day-to-day life, but for this interaction to be facilitating and supporting, rather than interfering with our actions, these systems have to be dependable and trustworthy. The area of system verification and validation has a long history in computer science, but scaling up existing approaches to complex and large real-life systems is still an open-ended research question. In this paper we summarise and relate several ongoing research projects and tool development efforts in this field taking place within the Department of Computer Science.peer-reviewe
Wake skew angle variation with rotor thrust for wind turbines in yaw based on the MEXICO experiment
The primary objective of the MEXICO (Model Experiments in Controlled Conditions) project
was to generate experimental data from which the uncertainties of the computational tools
employed to predict wind turbine performance and loads. Pressure sensors were used for
pressure measurements while PIV was used with the major aim of tracking the tip vortex
trajectory. The aerodynamic forces on the blades were derived found from the pressure
measurements and were used in an inverse free wake lifting line model to compute the
positions of the tip vortices. From these the wake skew angle was derived. A relationship
between the skew angle and the thrust coefficient was thus drawn.peer-reviewe
The influence of photovoltaics on roof thermal performance - an analysis of convective heat transfer coefficients
In a Mediterranean climate, given the absence of snow, flat roofs are typical of both vernacular and modern architecture. Thermal mass, cross ventilation and night time cooling are standard passive design aids that inhibit indoor temperature build-up on hot summer days. Such flat roofs provide a golden opportunity for free-orientation of PV (photovoltaic) panels, unlike pitched roofs. There is established scientific evidence that their presence on flat roofs also helps curtail surface temperatures of the heavy mass structure, by means of (i) solar shading and (ii) convective cooling at given angles. Both factors in turn lower the convective heat transfer coefficient (CHTC) of the roof structure, thus inhibiting early seasonal temperature build-up. This contributes to lower cooling loads, thus reducing both the carbon footprint of the building as well as lowering energy costs for the owners. Such a holistic contribution is deemed to uphold the social, environmental and economic challenges of today. This study purports to do just that. Through CFD (computational fluid dynamics) this study investigates the effect of flow fields over a typical flat roof building mass in a free field for a range of wind velocities. Results indicate that for a higher wind speed, the convective cooling is more significant than at lower wind speeds. This will in turn influence the elemental U-value of the roof structure, thus reducing cooling loads indoors.peer-reviewe
On the Design of a Linear Delay Element for the Triggering Module at CERN LHC
This paper presents an analytical model of a linear delay element circuit to be employed in the triggering module for the High Momentum Particle Identification Detector (HMPID) at the CERN Large Hadron Collider (LHC). The aim of the analytical model is to facilitate the design of the linear delay element circuit, while maximizing its linearity and delay range. The analytical model avoids the need of time consuming parametric sweeps on the aspect ratios of the various transistors of the delay element in order to optimize it. In addition, the analytical model can be used to predict the variation of the delay with the input tuning voltage. The proposed analytical model is verified via the simulation of the delay element circuit using the 0.18 ÎŒm X-FAB technology
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
Search for astrophysical sources of neutrinos using cascade events in IceCube
The IceCube neutrino observatory has established the existence of a flux of
high-energy astrophysical neutrinos inconsistent with the expectation from
atmospheric backgrounds at a significance greater than . This flux has
been observed in analyses of both track events from muon neutrino interactions
and cascade events from interactions of all neutrino flavors. Searches for
astrophysical neutrino sources have focused on track events due to the
significantly better angular resolution of track reconstructions. To date, no
such sources have been confirmed. Here we present the first search for
astrophysical neutrino sources using cascades interacting in IceCube with
deposited energies as small as 1 TeV. No significant clustering was observed in
a selection of 263 cascades collected from May 2010 to May 2012. We show that
compared to the classic approach using tracks, this statistically-independent
search offers improved sensitivity to sources in the southern sky, especially
if the emission is spatially extended or follows a soft energy spectrum. This
enhancement is due to the low background from atmospheric neutrinos forming
cascade events and the additional veto of atmospheric neutrinos at declinations
.Comment: 14 pages, 9 figures, 1 tabl
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