225 research outputs found
The external gamma radiation environment from the Kiwi Phoebus, and Pewee reactors
During the past few years, ground tests of high-powered propulsion-prototype reactors have provided several opportunities to observe the external radiation environment. Reactor tests have been conducted in free air and inside of open well shields. Measurements were taken over distances ranging from contact with the pressure vessel out to greater than 5000' both during operation and after shutdown. Some measurements characteristic of each of the systems are presented and compared with results of calculations
Exact two-particle eigenstates in partially reduced QED
We consider a reformulation of QED in which covariant Green functions are
used to solve for the electromagnetic field in terms of the fermion fields. It
is shown that exact few-fermion eigenstates of the resulting Hamiltonian can be
obtained in the canonical equal-time formalism for the case where there are no
free photons. These eigenstates lead to two- and three-body Dirac-like
equations with electromagnetic interactions. Perturbative and some numerical
solutions of the two-body equations are presented for positronium and
muonium-like systems, for various strengths of the coupling.Comment: 33 pages, LaTex 2.09, 4 figures in EPS forma
The bound mu+ mu- system
We consider the hyperfine structure, the atomic spectrum and the decay
channels of the bound mu+ mu- system (dimuonium). The annihilation lifetimes of
low-lying atomic states of the system lie in the nanosecond range range. The
decay rates could be measured by detection of the decay products (high energy
photons or electron-positron pairs). The hyperfine structure splitting of the
dimuonic system and its decay rate are influenced by electronic vacuum
polarization effects in the far time-like asymptotic region. This constitutes a
previously unexplored kinematic regime. We evaluate next--to-leading order
radiative corrections to the decay rate of low-lying atomic states. We also
obtain order alpha^5 corrections to the hyperfine splitting of the 1S and 2S
levels.Comment: 10 figures (eps format) attached, Scheduled tentatively by PRA for
Nov/Dec 199
Protection of pregnant women at work in Switzerland: implementation and experiences of maternity protection legislation
Objectives. Like most industrialized countries, Switzerland has introduced legislation to protect the health of pregnant workers and their unborn children from workplace hazards. This study aims to assess legislation’s degree of implementation in the French-speaking part of Switzerland and understand the barriers to and resources supporting its implementation.
Methods. Data were collected using mixed methods: (1) an online questionnaire send to 333 gynecologist-obstetricians (GOs) and 637 midwives; (2) exploratory semi-structured interviews with 5 workers who had had a pregnancy in the last 5 years.
Results. Questionnaire response rates were 32% for GOs and 54% for midwives. Data showed that several aspects of the implementation of maternity protection policies could be improved. Where patients encounter workplace hazards, GOs and midwives estimated that they only received a risk assessment from the employer in about 5% and 2% of cases, respectively. Preventive leave is underprescribed: 32% of GOs reported that they “often” or “always” prescribed preventive leave in cases involving occupational hazards; 58% of GOs reported that they “often” or “always” prescribed sick leave instead.
Interviews with workers identified several barriers to the implementation of protective policies in workplaces: a lack of information about protective measures and pregnancy rights; organizational problems triggered by job and schedule adjustments; and discrepancies between some safety measures and their personal needs.
Conclusions. Results demonstrate the need to improve the implementation and appropriateness of maternity protection legislation in Switzerland. More research is required to identify the factors affecting its implementation
Assessment of Daily Life Physical Activities in Pulmonary Arterial Hypertension
Background: In pulmonary arterial hypertension (PAH), the six-minute walk test (6MWT) is believed to be representative of patient’s daily life physical activities (DLPA). Whether DLPA are decreased in PAH and whether the 6MWT is representative of patient’s DL PA remain unknown. Methods: 15 patients with idiopathic PAH (IPAH) and 10 patients with PAH associated with limited systemic sclerosis (PAH-SSc) were matched with 15 healthy control subjects and 10 patients with limited systemic sclerosis without PAH. Each subject completed a 6MWT. The mean number of daily steps and the mean energy expenditure and duration of physical activities.3 METs were assessed with a physical activity monitor for seven consecutive days and used as markers of DLPA. Results: The mean number of daily steps and the mean daily energy expenditure and duration of physical activities.3 METs were all reduced in PAH patients compared to their controls (all p,0.05). The mean number of daily steps correlated with the 6MWT distance for both IPAH and PAH-SSc patients (r = 0.76, p,0.01 and r = 0.85, p,0.01), respectively. Conclusion: DLPA are decreased in PAH and correlate with the 6MWT distance. Functional exercise capacity may thus be a useful surrogate of DL PA in PAH
Rigorous QCD-Potential for the -System at Threshold
Recent evidence for the top mass in the region of 160 for the first
time provides an opportunity to use the full power of relativistic quantum
field theoretical methods, available also for weakly bound systems. Because of
the large decay width \G of the top quark individual energy-levels in
"toponium" will be unobservable. However, the potential for the
system, based on a systematic expansion in powers of the strong coupling
constant \a_s can be rigorously derived from QCD and plays a central role in
the threshold region. It is essential that the neglect of nonperturbative
(confining) effects is fully justified here for the first time to a large
accuracy, also just {\it because} of the large \G. The different
contributions to that potential are computed from real level corrections near
the bound state poles of the -system which for \G \ne 0 move into
the unphysical sheet of the complex energy plane. Thus, in order to obtain the
different contributions to that potential we may use the level corrections at
that (complex) pole. Within the relevant level shifts we especially emphasize
the corrections of order O(\a_s^4 m_t) and numerically comparable ones to
that order also from electroweak interactions which may become important as
well.Comment: 36 pages (mailer uncorrupted version), TUW-94-1
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