657 research outputs found
Children’s travel as pedestrians: an international survey of policy and practice
A survey of OECD member countries was carried out to provide high level data on a consistent basis to identify and account for current patterns of child road safety . This paper reports the findings relating to children, aged 0-14 years, as pedestrians. Key survey elements included analyses of fatality data, relationships between socio-economic, demographic factors and fatality rates, and a questionnaire based survey.
League tables based on average child pedestrian fatality rates were constructed for each OECD member country participating in our questionnaire enabling identification of the top five countries with the lowest pedestrian fatality rate as Sweden, The Netherlands, Finland, Germany, and Denmark.
Few countries had quantitative information about children’s travel and its absence means that assessments are difficult about children’s safety and the relative risks they face, especially as pedestrians. There are large variations in the amount of walking between countries and growing car use is becoming an issue in one third of OECD countries.
The main findings from the questionnaire survey were that the majority of countries did not have information on high risk groups but of those that did, the cross cutting themes of socio-economic and ethnic minority groups, young children and urban areas were identified.
Three characteristics distinguish top countries in the League table from those doing less well: a strong approach to the introduction of infrastructure measures for pedestrian safety, including low speed limits in residential areas; conducting road safety campaigns at least once a year; and having legislation which assumes driver responsibility in an accident involving a child pedestrian.
Having compulsory road safety education for children aged 6-9 years was a characteristic shared by most countries, as was the promotion of child pedestrian education and training initiatives and the commissioning of research. However there is lower research activity in less well performing countries
Determination of |Vud| from nuclear mirror transitions
The Vud element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix has
traditionally been determined from the analysis of data in nuclear superallowed
0+ to 0+ transitions, neutron decay and pion beta decay. We show here that this
element can independently be determined from nuclear mirror transitions. The
extracted value, |Vud| = 0.9719 +- 0.0017, is at 1.2 combined standard
deviations from the value obtained in superallowed 0+ to 0+ transitions and has
a similar precision than the value obtained from neutron decay experiments. We
discuss some prospects to improve its precision through experiments in nuclear
mirror transitions.Comment: 4 pages, 2 figure
Superallowed 0+ to 0+ nuclear beta decays: A new survey with precision tests of the conserved vector current hypothesis and the standard model
A new critical survey is presented of all half-life, decay-energy and
branching-ratio measurements related to 20 0+ to 0+ beta decays. Compared with
our last review, there are numerous improvements: First, we have added 27
recently published measurements and eliminated 9 references; of particular
importance, the new data include a number of high-precision Penning-trap
measurements of decay energies. Second, we have used the recently improved
isospin symmetry-breaking corrections. Third, our calculation of the
statistical rate function now accounts for possible excitation in the daughter
atom. Finally, we have re-examined the systematic uncertainty associated with
the isospin symmetry-breaking corrections by evaluating the radial-overlap
correction using Hartree-Fock radial wave functions and comparing the results
with our earlier calculations, which used Saxon-Woods wave functions; the
provision for systematic uncertainty has been changed as a consequence. The new
corrected Ft values are impressively constant and their average, when combined
with the muon liftime, yields the up-down quark-mixing element of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix, V_{ud} = 0.97425(22). The unitarity
test on the top row of the matrix becomes |V_{ud}|^2 + |V_{us}|^2 + |V_{ub}|^2
= 0.99995(61). Both V_{ud} and the unitarity sum have significantly reduced
uncertainties compared with our previous survey, although the new value of
V_{ud} is statistically consistent with the old one. From these data we also
set limits on the possible existence of scalar interactions, right-hand
currents and extra Z bosons. Finally, we discuss the priorities for future
theoretical and experimental work with the goal of making the CKM unitarity
test even more definitive.Comment: 36 pages, 11 tables, 9 figure
Isospin-mixing corrections for fp-shell Fermi transitions
Isospin-mixing corrections for superallowed Fermi transitions in {\it
fp}-shell nuclei are computed within the framework of the shell model. The
study includes three nuclei that are part of the set of nine accurately
measured transitions as well as five cases that are expected to be measured in
the future at radioactive-beam facilities. We also include some new
calculations for C. With the isospin-mixing corrections applied to the
nine accurately measured values, the conserved-vector-current hypothesis
and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are
tested.Comment: 13 pages plus five tables. revtex macro
Measurement of the -asymmetry parameter of Cu in search for tensor type currents in the weak interaction
Precision measurements at low energy search for physics beyond the Standard
Model in a way complementary to searches for new particles at colliders. In the
weak sector the most general decay Hamiltonian contains, besides vector
and axial-vector terms, also scalar, tensor and pseudoscalar terms. Current
limits on the scalar and tensor coupling constants from neutron and nuclear
decay are on the level of several percent.
The goal of this paper is extracting new information on tensor coupling
constants by measuring the -asymmetry parameter in the pure Gamow-Teller
decay of Cu, thereby testing the V-A structure of the weak interaction.
An iron sample foil into which the radioactive nuclei were implanted was cooled
down to milliKelvin temperatures in a He-He dilution refrigerator. An
external magnetic field of 0.1 T, in combination with the internal hyperfine
magnetic field, oriented the nuclei. The anisotropic radiation was
observed with planar high purity germanium detectors operating at a temperature
of about 10\,K. An on-line measurement of the asymmetry of Cu
was performed as well for normalization purposes. Systematic effects were
investigated using Geant4 simulations.
The experimental value, = 0.587(14), is in agreement with the
Standard Model value of 0.5991(2) and is interpreted in terms of physics beyond
the Standard Model. The limits obtained on possible tensor type charged
currents in the weak interaction hamiltonian are -0.045
0.159 (90\% C.L.). The obtained limits are comparable to limits from other
correlation measurements in nuclear decay and contribute to further
constraining tensor coupling constants
Semileptonic Hyperon Decays and CKM Unitarity
Using a technique that is not subject to first-order SU(3) symmetry breaking
effects, we determine the element of the CKM matrix from data on
semileptonic hyperon decays. We obtain =0.2250(27). This value is of
similar precision to the one derived from , but higher and in better
agreement with the unitarity requirement, .Comment: 3 pages, 1 tabl
Ft values of the T = 1/2 mirror beta transitions
A complete survey is presented of all half-life and branching-ratio
measurements related to the isospin T = 1/2 mirror beta transitions ranging
from 3He to 83Mo. No measurements are ignored, although some are rejected for
cause. Using the decay energies obtained in the 2003 Mass Evaluation
experimental ft values are then determined for the transitions up to 45V. For
the first time also all associated theoretical corrections needed to convert
these results into "corrected" Ft values, similar to the superallowed 0+ -> 0+
pure Fermi beta transitions, were calculated. Precisions of the resulting
values are in most cases between 0.1 % and 0.4 %. These Ft(mirror) values can
now be used to extract precise weak interaction information from past and
ongoing correlation measurements in the beta decay of the T = 1/2 mirror beta
transitions
Branching ratios for the beta decay of 21Na
We have measured the beta-decay branching ratio for the transition from 21Na
to the first excited state of 21Ne. A recently published test of the standard
model, which was based on a measurement of the beta-nu correlation in the decay
of 21Na, depended on this branching ratio. However, until now only relatively
imprecise (and, in some cases, contradictory) values existed for it. Our new
result, 4.74(4)%, reduces but does not remove the reported discrepancy with the
standard model.Comment: Revtex4, 2 fig
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