155 research outputs found
Occurrence and causes of occupational asthma in South Africa - results from SORDSA's occupational asthma registry, 1997 - 1999
Objective. To present results for the first 3 years of the occupational asthma registry of the Surveillance of Workrelated and Occupational Respiratory Diseases in South Africa (SORDSA) programme, ending December 1999.Design. Surveillance was accomplished by collecting voluntary reports of occupational asthma cases from pulmonologists, occupational medicine practitioners and occupational health nurses.Setting. Medical and occupational health referral centres in the nine provinces of South Africa.Subjects. Patients diagnosed with new-onset occupational asthma with latency or irritant-induced asthma, reported to SORDSA during 1997 - 1999. Outcome measures. Frequencies of cases, causative agents, industries causing exposure and diagnostic methods. Average annual incidence rates by province and by occupation.Results. During this period 324 cases of occupational asthma were reported. The average annual incidence rate of occupational asthma was estimated in the three bestreporting provinces, namely Gauteng, KwaZulu-Natal and the Western Cape, as 17.5 per million employed people annually. This rate was highest in the Western Cape (25.1 per million). Semi-skilled operators had the highest incidence rate of 68.7 per million annually in the three provinces. Isocyanates and latex were the most common agents. Low molecular weight causative agents predominated (68.8%) over high molecular weight agents. Health care was the most frequently reported workplace for occupational asthma (OA) development. Serial peak flow testing was the method most often used for diagnosis. One fifth of the cases were still occupationally exposed to the causative agent at time of diagnosis.Conclusion. Despite underreporting, SORDSA's estimate of the occupational asthma incidence rate was similar to that of the UK. SORDSA has also demonstrated that surveillance programmes in a developing country can provide useful information on which to base prevention activities
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
In 1930 Einstein argued against consistency of the time-energy uncertainty
relation by discussing a thought experiment involving a measurement of mass of
the box which emitted a photon. Bohr seemingly triumphed over Einstein by
arguing that the Einstein's own general theory of relativity saves the
consistency of quantum mechanics. We revisit this thought experiment from a
modern point of view at a level suitable for undergraduate readership and find
that neither Einstein nor Bohr was right. Instead, this thought experiment
should be thought of as an early example of a system demonstrating nonlocal
"EPR" quantum correlations, five years before the famous
Einstein-Podolsky-Rosen paper.Comment: 11 pages, revised, accepted for publication in Eur. J. Phy
Setting the scene for SORDSA - the importance of occupational respiratory disease surveillance in South Africa
No Abstrac
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
Spin-orbit coupling and the conservation of angular momentum
In nonrelativistic quantum mechanics, the total (i.e. orbital plus spin)
angular momentum of a charged particle with spin that moves in a Coulomb plus
spin-orbit-coupling potential is conserved. In a classical nonrelativistic
treatment of this problem, in which the Lagrange equations determine the
orbital motion and the Thomas equation yields the rate of change of the spin,
the particle's total angular momentum in which the orbital angular momentum is
defined in terms of the kinetic momentum is generally not conserved. However, a
generalized total angular momentum, in which the orbital part is defined in
terms of the canonical momentum, is conserved. This illustrates the fact that
the quantum-mechanical operator of momentum corresponds to the canonical
momentum of classical mechanics.Comment: 10 pages, as published by Eur. J. Phy
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
Vector Theory of Gravity
We proposed a gravitation theory based on an analogy with electrodynamics on
the basis of a vector field. For the first time, to calculate the basic
gravitational effects in the framework of a vector theory of gravity, we use a
Lagrangian written with gravitational radiation neglected and generalized to
the case of ultra-relativistic speeds. This allows us to accurately calculate
the values of all three major gravity experiments: the values of the perihelion
shift of Mercury, the light deflection angle in the gravity field of the Sun
and the value of radar echo delay. The calculated values coincide with the
observed ones. It is shown that, in this theory, there exists a model of an
expanding Universe.Comment: 9 page
Silicose em trabalhadores de quartzito da região de São Thomé das Letras - Minas Gerais: dados iniciais indicam um grave problema de saúde pública
Forces between electric charges in motion: Rutherford scattering, circular Keplerian orbits, action-at-a-distance and Newton's third law in relativistic classical electrodynamics
Standard formulae of classical electromagnetism for the forces between
electric charges in motion derived from retarded potentials are compared with
those obtained from a recently developed relativistic classical electrodynamic
theory with an instantaneous inter-charge force. Problems discussed include
small angle Rutherford scattering, Jackson's recent `torque paradox' and
circular Keplerian orbits. Results consistent with special relativity are
obtained only with an instantaneous interaction. The impossiblity of stable
circular motion with retarded fields in either classical electromagnetism or
Newtonian gravitation is demonstrated.Comment: 26 pages, 5 figures. QED and special relativity forbid retarded
electromagnetic forces. See also physics/0501130. V2 has typos corrected,
minor text modifications and updated references. V3 has further typos removed
and added text and reference
Singular behaviour of the electromagnetic field
The singularities of the electromagnetic field are derived to include all the
point-like multipoles representing an electric charge and current distribution.
Firstly derived in the static case, the result is generalized to the dynamic
one. We establish a simple procedure for passing from the first, to the second
case.Comment: Latex, 21.pages, no figure
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