964 research outputs found
Causes of accidents on construction sites: the case of a large construction contractor in Great Britain
In the construction industry in Great Britain, it is estimated that workplace accidents and work-related ill-health cost society £3 billion – this is equivalent to 4% of the construction industry revenue of about £75 billion. Thus, the need to study, understand and effectively manage health and safety (H&S) on construction sites cannot be overemphasised. This paper presents an analysis of accident data recorded by a large construction contractor in Great Britain. The data cover a period of 36 months from April 2004 to March 2007. Pareto analysis was used to determine the relative importance of the causes of accidents on the basis of number of workdays lost. Differences between the four sectors (highways, infrastructure, rail and utilities)
in which the company operates were investigated. The case study suggests that the main causes of accidents on construction sites relate to individual attitudes towards
H&S. Ability and willingness to implement safe approaches to working and an awareness of their own and others’ H&S can contribute to safe performances. It is suggested that the company could increase awareness of H&S issues among the workforce. This should be done on a regular basis through effective training, briefing
and debriefing
An evaluation of health and safety management in small construction enterprises in the United Kingdom
The United Kingdom (UK) construction industry has one of the best safety records
within the European Union, with fatalities and serious injuries being about one third
of the European average. However, despite a number of recent initiatives, accidents
still regularly occur on UK construction sites. A disproportionate number of fatalities
occur in small construction enterprises employing fifteen operatives or less. In 2007,
a survey of small construction enterprises in Southern England was carried out to
identify factors which contribute to this relatively poor safety record. The survey was
based on prior research which had identified three interrelated factors that influence
health and safety (H&S) management: the individual’s competence and attitude; the
job tasks and environment; and the organisational culture and leadership. It was
found that project managers on small construction sites had limited knowledge of
H&S requirements which often resulted in a poor or potentially dangerous work
environment and a poor safety attitude within the workforce. It was concluded that
increased awareness and training of project managers in small construction
enterprises should be a priority for all who seek to improve H&S on construction
sites
The complexity of linear-time temporal logic over the class of ordinals
We consider the temporal logic with since and until modalities. This temporal
logic is expressively equivalent over the class of ordinals to first-order
logic by Kamp's theorem. We show that it has a PSPACE-complete satisfiability
problem over the class of ordinals. Among the consequences of our proof, we
show that given the code of some countable ordinal alpha and a formula, we can
decide in PSPACE whether the formula has a model over alpha. In order to show
these results, we introduce a class of simple ordinal automata, as expressive
as B\"uchi ordinal automata. The PSPACE upper bound for the satisfiability
problem of the temporal logic is obtained through a reduction to the
nonemptiness problem for the simple ordinal automata.Comment: Accepted for publication in LMC
Recommended from our members
Flight behaviour and migration of insect pests: Radar studies in developing countries (NRI Bulletin 71)
The use of radar to make direct observations of insects flying at altitude has provided many new insights into the phenomenon of long-range insect migration. In particular, the technique has produced a wealth of quantitative information on the spatial and temporal distribution of migrants in the air, on the direction, speed and duration of their displacements, and on their orientation behaviour. These data could not have been obtained by any other means, and it is probably fair to claim that our present knowledge of the magnitude and importance of high altitude insect movement stems very largely from radar observations. The pioneering field studies using the first specially designed entomological radar were undertaken in 1968, with the support of the UK Overseas Development Administration (ODA), and since that time ODA has been responsible for funding almost all of the applications of the technique in developing countries. The motivation for this work was the assumption that it was impossible to design efficient management strategies for migrant pest insects without a good knowledge of their migratory behaviour, and of the role which this played in their population dynamics. The ODA-funded studies thus focused primarily on pest species, and were carried out by the Radar Entomology Unit of the Natural Resources Institute (NRI) and its precursors. In this Bulletin, we give a brief account of the history of radar entomology, with emphasis on studies of insect pests. Next, the different types of entomological radar and some associated analysis methods are outlined, together with descriptions of some ancillary measurement techniques. We then describe in some detail the contributions made by the NRI Radar Unit to current knowledge of the flight patterns of a variety of major insect pests of agriculture and of human health. These pests include: grasshoppers and locusts, the African Armyworm moth, the Rice Brown Planthopper and other rice pests, the Old World Bollworm, and some mosquito vectors of human diseases. Recent developments directed towards long-term monitoring of insect aerial faunas (for environmental impact, biodiversity and conservation purposes), and towards observations of low-altitude flight, are included. The Bulletin concludes with a short overview, in which we speculate how the technique might find application in the future
Dialogue on nanotech :the South Carolina Citizens’ School of Nanotechnology
Theory and experience emphasize that science communications between experts and nonexperts should be dialogue, not monologue. This principle guides a nanotechnology outreach program at the University of South Carolina which enables the participants to express their values and concerns to experts, and to question them. It is intended that the knowledge and confidence generated by this program will enhance the participants’ ability to have active and constructive roles in nanotech policy
Highlighting when animals expend excessive energy for travel using dynamic body acceleration
Travel represents a major cost for many animals so there should be selection pressure for it to be efficient – at minimum cost. However, animals sometimes exceed minimum travel costs for reasons that must be correspondingly important. We use Dynamic Body Acceleration (DBA), an acceleration-based metric, as a proxy for movement-based power, in tandem with vertical velocity (rate of change in depth) in a shark (Rhincodon typus) to derive the minimum estimated power required to swim at defined vertical velocities. We show how subtraction of measured DBA from the estimated minimum power for any given vertical velocity provides a “proxy for power above minimum” metric (PPAmin), highlighting when these animals travel above minimum power. We suggest that the adoption of this metric across species has value in identifying where and when animals are subject to compelling conditions that lead them to deviate from ostensibly judicious energy expenditure
Magnetic fields in supernova remnants and pulsar-wind nebulae
We review the observations of supernova remnants (SNRs) and pulsar-wind
nebulae (PWNe) that give information on the strength and orientation of
magnetic fields. Radio polarimetry gives the degree of order of magnetic
fields, and the orientation of the ordered component. Many young shell
supernova remnants show evidence for synchrotron X-ray emission. The spatial
analysis of this emission suggests that magnetic fields are amplified by one to
two orders of magnitude in strong shocks. Detection of several remnants in TeV
gamma rays implies a lower limit on the magnetic-field strength (or a
measurement, if the emission process is inverse-Compton upscattering of cosmic
microwave background photons). Upper limits to GeV emission similarly provide
lower limits on magnetic-field strengths. In the historical shell remnants,
lower limits on B range from 25 to 1000 microGauss. Two remnants show
variability of synchrotron X-ray emission with a timescale of years. If this
timescale is the electron-acceleration or radiative loss timescale, magnetic
fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition
arguments and dynamical modeling can be used to infer magnetic-field strengths
anywhere from about 5 microGauss to 1 mG. Polarized fractions are considerably
higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field
geometries often suggest a toroidal structure around the pulsar, but this is
not universal. Viewing-angle effects undoubtedly play a role. MHD models of
radio emission in shell SNRs show that different orientations of upstream
magnetic field, and different assumptions about electron acceleration, predict
different radio morphology. In the remnant of SN 1006, such comparisons imply a
magnetic-field orientation connecting the bright limbs, with a non-negligible
gradient of its strength across the remnant.Comment: 20 pages, 24 figures; to be published in SpSciRev. Minor wording
change in Abstrac
Gamma-ray emission expected from Kepler's SNR
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants (SNRs) is used to investigate the properties of Kepler's SNR and, in
particular, to predict the gamma-ray spectrum expected from this SNR.
Observations of the nonthermal radio and X-ray emission spectra as well as
theoretical constraints for the total supernova (SN) explosion energy E_sn are
used to constrain the astronomical and particle acceleration parameters of the
system. Under the assumption that Kepler's SN is a type Ia SN we determine for
any given explosion energy E_sn and source distance d the mass density of the
ambient interstellar medium (ISM) from a fit to the observed SNR size and
expansion speed. This makes it possible to make predictions for the expected
gamma-ray flux. Exploring the expected distance range we find that for a
typical explosion energy E_sn=10^51 erg the expected energy flux of TeV
gamma-rays varies from 2x10^{-11} to 10^{-13} erg/(cm^2 s) when the distance
changes from d=3.4 kpc to 7 kpc. In all cases the gamma-ray emission is
dominated by \pi^0-decay gamma-rays due to nuclear CRs. Therefore Kepler's SNR
represents a very promising target for instruments like H.E.S.S., CANGAROO and
GLAST. A non-detection of gamma-rays would mean that the actual source distance
is larger than 7 kpc.Comment: 6 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysics, minor typos correcte
Properties of low-lying states in some high-nuclearity Mn, Fe and V clusters: Exact studies of Heisenberg models
Using an efficient numerical scheme that exploits spatial symmetries and spin
parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}.
The largest calculation involves the Mn_{12} cluster which spans a Fock space
of a hundred million. Our results show that the earlier estimates of the
exchange constants need to be revised for the Mn_{12} cluster to explain the
level ordering of low-lying eigenstates. In the case of the Fe_8 cluster,
correct level ordering can be obtained which is consistent with the exchange
constants for the already known clusters with butterfly structure. In the
V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the
eight low-lying eigenvalues of the full Hamiltonian.Comment: Revtex, 12 pages, 16 eps figures; this is the final published versio
- …