25,232 research outputs found
Developing a Holistic Fire Risk Assessment Framework for Building Construction Sites in Hong Kong
Amongst all types of construction accidents, industrial practitioners tend to pay less attention to the prevention of fires at construction sites. Although fires may not occur frequently on construction sites, statistics show that when they do, the consequences are very serious; involving fatalities, injuries, serious project delays and financial loss. There are many reasons why fires occur on sites, but a simple lack of awareness of the risks of fire is a major contributor. Fire risk assessment is not commonly performed on sites. Hence, it is believed that an appropriate assessment method for evaluating potential fire risk is required in order to improve the awareness of fire risk on construction sites. This paper reports on the key findings of a research project which aims to develop a comprehensive, objective, reliable, and practical fire risk assessment framework for building construction sites based in Hong Kong. A comprehensive list of those factors (or conditions) which may constitute a fire risk was compiled using desktop research and structured face-to-face interviews with experienced site personnel. This list of factors was then used to develop a questionnaire survey form and the Reliability Interval Method (RIM) was used to analyse the survey results and determine the relative importance and rankings of the various fire risk factors at a broad level and risk sub-factors at a detailed level. It was found that the fire risk factor of “Fire Services Equipment and Installations” has the greatest impact on construction site fire safety, with “Means of Escape in Case of Fire” being the second, and “Attitude of Main Contractor towards Fire Safety” being the third. In fact, it is the main contractor who plays the pivotal role in maintaining construction site fire safety, which is in line with the high ranking given to the fire risk factor of “Attitude of Main Contractor towards Fire Safety”. The proposed fire risk assessment framework can be used to develop a useful checklist for assessing the overall level of fire risk for a construction site, and to identify any areas needing improvement. Although the fire risk assessment framework was developed locally in Hong Kong, the research methodology could be replicated in other countries to produce similar frameworks for international comparison. Such an extension would aid the understanding of the management of fire risk on construction sites and help discover differences between countries
Possible role of 3He impurities in solid 4He
We use a quantum lattice gas model to describe essential aspects of the
motion of 4He atoms and of 3He impurities in solid 4He. This study suggests
that 3He impurities bind to defects and promote 4He atoms to interstitial sites
which can turn the bosonic quantum disordered crystal into a metastable
supersolid. It is suggested that defects and interstitial atoms are produced
during the solid 4He nucleation process where the role of 3He impurities (in
addition to the cooling rate) is known to be important even at very small (1
ppm) impurity concentration. It is also proposed that such defects can form a
glass phase during the 4He solid growth by rapid cooling.Comment: 4 two-column Revtex pages, 4 figures. Europhysics Letters (in Press
The Casimir force on a surface with shallow nanoscale corrugations: Geometry and finite conductivity effects
We measure the Casimir force between a gold sphere and a silicon plate with
nanoscale, rectangular corrugations with depth comparable to the separation
between the surfaces. In the proximity force approximation (PFA), both the top
and bottom surfaces of the corrugations contribute to the force, leading to a
distance dependence that is distinct from a flat surface. The measured Casimir
force is found to deviate from the PFA by up to 15%, in good agreement with
calculations based on scattering theory that includes both geometry effects and
the optical properties of the material
Magnetic, thermodynamic, and electrical transport properties of the noncentrosymmetric B20 germanides MnGe and CoGe
We present magnetization, specific heat, resistivity, and Hall effect
measurements on the cubic B20 phase of MnGe and CoGe and compare to
measurements of isostructural FeGe and electronic structure calculations. In
MnGe, we observe a transition to a magnetic state at K as identified
by a sharp peak in the ac magnetic susceptibility, as well as second phase
transition at lower temperature that becomes apparent only at finite magnetic
field. We discover two phase transitions in the specific heat at temperatures
much below the Curie temperature one of which we associate with changes to the
magnetic structure. A magnetic field reduces the temperature of this transition
which corresponds closely to the sharp peak observed in the ac susceptibility
at fields above 5 kOe. The second of these transitions is not affected by the
application of field and has no signature in the magnetic properties or our
crystal structure parameters. Transport measurements indicate that MnGe is
metal with a negative magnetoresistance similar to that seen in isostructural
FeGe and MnSi. Hall effect measurements reveal a carrier concentration of about
0.5 carriers per formula unit also similar to that found in FeGe and MnSi. CoGe
is shown to be a low carrier density metal with a very small, nearly
temperature independent diamagnetic susceptibility.Comment: 16 pages 23 figure
Forced Symmetry Breaking from SO(3) to SO(2) for Rotating Waves on the Sphere
We consider a small SO(2)-equivariant perturbation of a reaction-diffusion
system on the sphere, which is equivariant with respect to the group SO(3) of
all rigid rotations. We consider a normally hyperbolic SO(3)-group orbit of a
rotating wave on the sphere that persists to a normally hyperbolic
SO(2)-invariant manifold . We investigate the effects of this
forced symmetry breaking by studying the perturbed dynamics induced on
by the above reaction-diffusion system. We prove that depending
on the frequency vectors of the rotating waves that form the relative
equilibrium SO(3)u_{0}, these rotating waves will give SO(2)-orbits of rotating
waves or SO(2)-orbits of modulated rotating waves (if some transversality
conditions hold). The orbital stability of these solutions is established as
well. Our main tools are the orbit space reduction, Poincare map and implicit
function theorem
Competing magnetic states, disorder, and the magnetic character of Fe3Ga4
The physical properties of metamagnetic FeGa single crystals are
investigated to explore the sensitivity of the magnetic states to temperature,
magnetic field, and sample history. The data reveal a moderate anisotropy in
the magnetization and the metamagnetic critical field along with features in
the specific heat at the magnetic transitions K and K. Both
and are found to be sensitive to the annealing conditions of the
crystals suggesting that disorder affects the competition between the
ferromagnetic (FM) and antiferromagnetic (AFM) states. Resistivity measurements
reveal metallic transport with a sharp anomaly associated with the transition
at . The Hall effect is dominated by the anomalous contribution which
rivals that of magnetic semiconductors in magnitude ( cm at 2 T
and 350 K) and undergoes a change of sign upon cooling into the low temperature
FM state. The temperature and field dependence of the Hall effect indicate that
the magnetism is likely to be highly itinerant in character and that a
significant change in the electronic structure accompanies the magnetic
transitions. We observe a contribution from the topological Hall effect in the
AFM phase suggesting a non-coplanar contribution to the magnetism. Electronic
structure calculations predict an AFM ground state with a wavevector parallel
to the crystallographic -axis preferred over the experimentally measured FM
state by 50 meV per unit cell. However, supercell calculations with a
small density of Fe-antisite defects introduced tend to stabilize the FM over
the AFM state indicating that antisite defects may be the cause of the
sensitivity to sample synthesis conditions.Comment: 13 pages, 14 figures, and 4 supplementary table
Most self-touches are with the nondominant hand
Self-touch may promote the transfer of microorganisms between body parts or surfaces to mucosa. In overt videography of a post-graduate office, students spent 9% of their time touching their own hair, face, neck, and shoulders (HFNS). These data were collected from 274,000 s of surveillance video in a Chinese graduate student office. The non-dominant hand contributed to 66.1% of HFNS-touches. Most importantly, mucous membranes were touched, on average, 34.3 (SE = 2.4) times per hour, which the non-dominant hand contributed to 240% more than the dominant hand. Gender had no significant effect on touch frequency, but a significant effect on duration per touch. The duration per touch on the HFNS was fitted with a log–log linear distribution. Touch behaviour analysis included surface combinations and a probability matrix for sequential touches of 20 sub-surfaces. These findings may partly explain the observed variation in the literature regarding the microbiome community distribution on human skin, supporting the importance of indirect contact transmission route in some respiratory disease transmission and providing data for risk analysis of infection spread and control
Universality class of the restricted solid-on-solid model with hopping
We study the restricted solid-on-solid (RSOS) model with finite hopping
distance , using both analytical and numerical methods. Analytically, we
use the hard-core bosonic field theory developed by the authors [Phys. Rev. E
{\bf 62}, 7642 (2000)] and derive the Villain-Lai-Das Sarma (VLD) equation for
the case which corresponds to the conserved RSOS (CRSOS) model
and the Kardar-Parisi-Zhang (KPZ) equation for all finite values of .
Consequently, we find that the CRSOS model belongs to the VLD universality
class and the RSOS models with any finite hopping distance belong to the KPZ
universality class. There is no phase transition at a certain finite hopping
distance contrary to the previous result. We confirm the analytic results using
the Monte Carlo simulations for several values of the finite hopping distance.Comment: 13 pages, 3 figure
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