1,216 research outputs found
Empirical Studies of Evolving Systems
This paper describes the results of the working group investigating the issues of empirical studies for
evolving systems. The groups found that there were many issues that were central to successful evolution and this
concluded that this is a very important area within software engineering. Finally nine main areas were selected for consideration. For each of these areas the central issues were identified as well as success factors. In some cases success stories were also described and the critical factors accounting for the success analysed. In some cases it was later found that a number of areas were so tightly coupled that it was important to discuss them together
Clinical investigation of an outbreak of alveolitis and asthma in a car engine manufacturing plant
Background Exposure to metal working fluid (MWF) has been associated with outbreaks of EAA in the US, with bacterial contamination of MWF being a possible cause, but was uncommon in the UK. Twelve workers developed extrinsic allergic alveolitis (EAA) in a car engine manufacturing plant in the UK, presenting clinically between December 2003 and May 2004. This paper reports the subsequent epidemiological investigation of the whole workforce. This had three aims:-
• To measure the extent of the outbreak by identifying other workers who may have developed EAA or other work-related respiratory diseases.
• To provide case-detection so that those affected can be treated.
• To provide epidemiological data to identify the cause of the outbreak.
Methods The outbreak was investigated in a three-phase cross-sectional survey of the workforce.
Phase I A respiratory screening questionnaire was completed by 808/836 workers (96.7%) in May 2004.
Phase II 481 employees with at least one respiratory symptom on screening and 50 asymptomatic controls were invited for investigation at the factory in June 2004. This included a questionnaire, spirometry and clinical opinion. 454/481(94.4%) responded along with 48/50(96%) controls. Workers were identified who needed further investigation and serial measurements of peak expiratory flow (PEF).
Phase III 162 employees were seen at the Birmingham Occupational Lung Disease clinic. 198 employees returned PEF records, including 141 of the 162 who attended for clinical investigation. Case definitions for diagnoses were agreed.
Results 87 workers (10.4% of workforce) met case definitions for occupational lung disease, comprising EAA(19), occupational asthma(74) and humidifier fever(7). 12 workers had more than one diagnosis. The peak onset of work-related breathlessness was Spring 2003. The proportion of workers affected was higher for those using metal working fluid (MWF) from a large sump(27.3%) compared with working all over the manufacturing area (7.9%) (OR=4.39,p<0.001). Two workers had positive specific provocation tests to the used but not the unused MWF solution.
Conclusions Extensive investigation of the outbreak of EAA detected a large number of affected workers, not only with EAA but also occupational asthma. This is the largest reported outbreak in Europe. Mist from used MWF is the likely cause. In workplaces using MWF, there is a need to carry out risk assessments, to monitor and maintain fluid quality, to control mist and to carry out respiratory health surveillance
Chaotic Friedmann-Robertson-Walker Cosmology
We show that the dynamics of a spatially closed Friedmann - Robertson -
Walker Universe conformally coupled to a real, free, massive scalar field, is
chaotic, for large enough field amplitudes. We do so by proving that this
system is integrable under the adiabatic approximation, but that the
corresponding KAM tori break up when non adiabatic terms are considered. This
finding is confirmed by numerical evaluation of the Lyapunov exponents
associated with the system, among other criteria. Chaos sets strong limitations
to our ability to predict the value of the field at the Big Crunch, from its
given value at the Big Bang. (Figures available on request)Comment: 28 pages, 11 figure
Collective traffic-like movement of ants on a trail: dynamical phases and phase transitions
The traffic-like collective movement of ants on a trail can be described by a
stochastic cellular automaton model. We have earlier investigated its unusual
flow-density relation by using various mean field approximations and computer
simulations. In this paper, we study the model following an alternative
approach based on the analogy with the zero range process, which is one of the
few known exactly solvable stochastic dynamical models. We show that our theory
can quantitatively account for the unusual non-monotonic dependence of the
average speed of the ants on their density for finite lattices with periodic
boundary conditions. Moreover, we argue that the model exhibits a continuous
phase transition at the critial density only in a limiting case. Furthermore,
we investigate the phase diagram of the model by replacing the periodic
boundary conditions by open boundary conditions.Comment: 8 pages, 6 figure
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Measurements in Film Cooling Flows: Hole L/D and Turbulence Intensity Effects
Hot-wire anemometry of simulated film cooling was used to study the influence of freestream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and turbulence intensity. Measurements were made in the zone where the coolant and freestream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35{degree} and no lateral injection and with a coolant- to-freestream flow velocity ratio of 1.0 was investigated under freestream turbulence levels of 0.5 and 12%. Coolant-to-freestream density ratio was unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. Results show that under low freestream turbulence conditions, pronounced differences exist in the flowfield between L/D=7.0 and 2.3; the differences are less prominent at high freestream turbulence intensities. Generally, short-L/D injection results in ``jetting`` of the coolant further into the freestream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in freestream turbulence intensity to engine- representative conditions are documented. 15 figs, 2 tabs, refs
A model of the Universe including Dark Energy accounted for by both a Quintessence Field and a (negative) Cosmological Constant
In this work we present a model of the universe in which dark energy is
modelled explicitely with both a dynamical quintessence field and a
cosmological constant. Our results confirm the possibility of a future
collapsing universe (for a given region of the parameter space), which is
necessary for a consistent formulation of string theory and quantum field
theory. We have also reproduced the measurements of modulus distance from
supernovae with good accuracy.Comment: 11 pages, 4 figures, only the results for the single exponential
potential are preserved. One author added. Some changes in the reference
section. Submitted to Physical Review
Qualitative Analysis of Causal Anisotropic Viscous Fluid Cosmological Models
The truncated Israel-Stewart theory of irreversible thermodynamics is used to
describe the bulk viscous pressure and the anisotropic stress in a class of
spatially homogeneous viscous fluid cosmological models. The governing system
of differential equations is written in terms of dimensionless variables and a
set of dimensionless equations of state is utilized to complete the system. The
resulting dynamical system is then analyzed using standard geometric
techniques. It is found that the presence of anisotropic stress plays a
dominant role in the evolution of the anisotropic models. In particular, in the
case of the Bianchi type I models it is found that anisotropic stress leads to
models that violate the weak energy condition and to the creation of a periodic
orbit in some instances. The stability of the isotropic singular points is
analyzed in the case with zero heat conduction; it is found that there are
ranges of parameter values such that there exists an attracting isotropic
Friedmann-Robertson-Walker model. In the case of zero anisotropic stress but
with non-zero heat conduction the stability of the singular points is found to
be the same as in the corresponding case with zero heat conduction; hence the
presence of heat conduction does not apparently affect the global dynamics of
the model.Comment: 35 pages, REVTeX, 3 Encapsulated PostScript Figure
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