412 research outputs found
The importance of safety on the bicycle friendliness of cities
In the framework of questions like climate protection, healthy lifestyles and more livable cities it is important to increase cycle use and replace motorized traffic. Safe cycling is one of the preconditions for the growth of cycle use, especially considering the more vulnerable user groups. But how important is safety in relation to other factors influencing bicycle friendliness like comfort of the cycle path and bike parking, accessibility or communication? And how is the relation between 'objective safety' - represented by the number of recorded accidents - and 'subjective safety' as the perceived safety feeling ofthe bike users? [From: Introduction
Quantification of Iodine Supply: Representative Data on Intake and Urinary Excretion of Iodine from the German Population in 1996
Background/Methods: In Germany, iodine deficiency is common. In a representative group of 2,500 Germans (age >13 years), using a specially designed food questionnaire, the iodine intake was calculated. In addition, iodine and creatinine concentrations in spot urine samples were determined in three groups with a possibly increased risk of iodine deficiency (769 conscripts, 886 pairs of mothers and newborns) or future hyperthyroidism (574 adults, age range 50-70 years) from 26 representative regions. In four groups of controls (young and older male and female adults; n = 91), 24-hour urine iodine and creatinine were measured in six diurnal fractions to calculate group- and period-specific factors for the estimation of the 24-hour iodine excretion from data of iodine/creatinine ratio and time of micturition in spot urine samples. Results: The mean calculated iodine intake (excretion) was 119 mug/day for the group of Germans above 13 years; it was 119 mug/day (125 mug/day) for adults aged 50-70 years, 137 mug/day (125 mug/day)for conscripts, and 162 mug/day for breast-feeding mothers. The median iodine concentration (iodine/creatinine ratio) was 9.4 mug/dl (83 mug/g) in 566 adults aged 50-70 years, 8.3 mug/dl (57 mug/g) in 772 conscripts. and 5.6 mug/dl (156 mug/g) in 739 breast-fed newborns. Conclusions: Compared to older data, the iodine intake in Germany has increased. In 1996, the meticulously quantified average deficit was about 30% of the recommended iodine intake. Copyright (C) 2002 S. Karger AG, Basel
Cosmological constant from quarks and torsion
We present a simple and natural way to derive the observed small, positive
cosmological constant from the gravitational interaction of condensing
fermions. In the Riemann-Cartan spacetime, torsion gives rise to the
axial-axial four-fermion interaction term in the Dirac Lagrangian for spinor
fields. We show that this nonlinear term acts like a cosmological constant if
these fields have a nonzero vacuum expectation value. For quark fields in QCD,
such a torsion-induced cosmological constant is positive and its energy scale
is only about 8 times larger than the observed value. Adding leptons to this
picture could lower this scale to the observed value.Comment: 4 pages; published versio
The Influence of Molecular Architecture on the Dynamics of H-Bonded Supramolecular Structures in Phenyl-Propanols
The relaxation behaviour of monohydroxy alcohols (monoalcohols) in broadband
dielectric spectroscopy (BDS) is usually dominated by the Debye process. This
process is regarded as a signature of the dynamics of transient supramolecular
structures formed by H-bonding. In phenyl propanols the steric hindrance of the
phenyl ring is assumed to influence chain formation and thereby to decrease or
even suppress the intensity of the Debye process. In the present paper we study
this effect in a systematic series of structural isomers of phenyl-1-propanol
in comparison with 1-propanol. It turns out that by combining BDS, Photon
Correlation Spectroscopy (PCS) and calorimetry the dynamics of supramolecular
structures can be uncovered. While light scattering spectra show the same
spectral shape of the main relaxation for all investigated monoalcohols, the
dielectric spectra differ in the Debye contribution. Thus it becomes possible
for the first time to unambiguously disentangle both relaxation modes in the
dielectric spectra. It turns out that the Debye relaxation gets weaker the
closer the position of phenyl ring is to the hydroxy group, in accordance with
the analysis of the Kirkwood-Fr\"ohlich correlation factor. Even in
1-phenyl-1-propanol, which has the phenyl group attached at the closest
position to the hydroxy group, we can separate a Debye-contribution in the
dielectric spectrum. From this we conclude that hydrogen bonds are not
generally suppressed by the increased steric hindrance of the phenyl ring, but
rather an equilibrium of ring and chain-like structures is shifted towards
ring-like shapes on shifting the phenyl ring closer to the hydroxy group.
Moreover, the shape of the alpha-relaxation as monitored by PCS and BDS remains
unaffected by the degree of hydrogen bonding and is the same among the
investigated alcohols.Comment: 9 pages, 7 figure
On the Nature of the Debye-Process in Monohydroxy Alcohols: 5-Methyl-2-Hexanol Investigated by Depolarized Light Scattering and Dielectric Spectroscopy
The slow Debye-like relaxation in the dielectric spectra of monohydroxy
alcohols is a matter of long standing debate. In the present work, we probe
reorientational dynamics of 5-methyl-2-hexanol with dielectric spectroscopy and
depolarized light scattering (DDLS) in the supercooled regime. While in a
previous study of a primary alcohol no indication of the Debye peak in the DDLS
spectra was found, we now for the first time report clear evidence of a Debye
contribution in a monoalcohol in DDLS. A quantitative comparison between the
dielectric and DDLS manifestation of the Debye peak reveals that while the
dielectric Debye process represents fluctuations in the end-to-end vector
dipole moment of the transient chains, its occurrence in DDLS shows a more
local signature and is related to residual correlations which occur due to a
slight anisotropy of the -relaxation caused by the chain formation.Comment: 5 pages, 5 figures; accepted in Phys. Rev. Let
Glassy dynamics in polyalcohols:intermolecular simplicity vs. intramolecular complexity
Using depolarized light scattering, we have recently shown that structural relaxation in a broad range of supercooled liquids follows, to good approximation, a generic line shape with high-frequency power law . We now continue this study by investigating a systematic series of polyalcohols (PAs), frequently used as model-systems in glass-science, , because the width of their respective dielectric loss spectra varies strongly along the series. Our results reveal that the microscopic origin of the observed relaxation behavior varies significantly between different PAs: while short-chained PAs like glycerol rotate as more or less rigid entities and their light scattering spectra follow the generic shape, long-chained PAs like sorbitol display pronounced intramolecular dynamic contributions on the time scale of structural relaxation, leading to systematic deviations from the generic shape. Based on these findings we discuss an important limitation for observing the generic shape in a supercooled liquid: the dynamics that is probed needs to reflect the intermolecular dynamic heterogeneity, and must not be superimposed by effects of intramolecular dynamic heterogeneity
- …