3,058 research outputs found
A liquid crystal analogue of the cosmic string
We consider the propagation of light in a anisotropic medium with a
topological line defect in the realm of geometrical optics. It is shown that
the effective geometry perceived by light propagating in such medium is that of
a spacial section of the cosmic string spacetime.Comment: 3 pages, 2 figures. Modern Physics Letters A, accepted for
publicatio
Umbilical Cord Mercury Concentration as Biomarker of Prenatal Exposure to Methylmercury
Biomarkers are often applied to assess prenatal exposure to methylmercury in research and surveillance. In a prospective study in the Faroe Islands, the main exposure biomarkers were the mercury concentrations in cord blood and maternal hair obtained at parturition. We have now supplemented these exposure biomarkers with mercury analyses of umbilical cord tissue from 447 births. In particular, when expressed in relation to the dry weight of the tissue, the cord mercury concentration correlated very well with that in cord blood. Structural equation model analysis showed that these two biomarkers have average total imprecision of about 30%, which is much higher than the laboratory error. The imprecision of the dry-weight–based concentration was lower than that of the wet-weight–based parameter, and it was intermediate between those of the cord blood and the hair biomarkers. In agreement with this finding, regression analyses showed that the dry-weight cord mercury concentration was almost as good a predictor of methylmercury-associated neuropsychologic deficits at 7 years of age as was the cord-blood mercury concentration. Cord mercury analysis can therefore be used as a valid measure of prenatal methylmercury exposure, but appropriate adjustment for the imprecision should be considered
The relative fitness of drug-resistant Mycobacterium tuberculosis: a modelling study of household transmission in Peru.
The relative fitness of drug-resistant versus susceptible bacteria in an environment dictates resistance prevalence. Estimates for the relative fitness of resistant Mycobacterium tuberculosis (Mtb) strains are highly heterogeneous and mostly derived from in vitro experiments. Measuring fitness in the field allows us to determine how the environment influences the spread of resistance. We designed a household structured, stochastic mathematical model to estimate the fitness costs associated with multidrug resistance (MDR) carriage in Mtb in Lima, Peru during 2010-2013. By fitting the model to data from a large prospective cohort study of TB disease in household contacts, we estimated the fitness, relative to susceptible strains with a fitness of 1, of MDR-Mtb to be 0.32 (95% credible interval: 0.15-0.62) or 0.38 (0.24-0.61), if only transmission or progression to disease, respectively, was affected. The relative fitness of MDR-Mtb increased to 0.56 (0.42-0.72) when the fitness cost influenced both transmission and progression to disease equally. We found the average relative fitness of MDR-Mtb circulating within households in Lima, Peru during 2010-2013 to be significantly lower than concurrent susceptible Mtb If these fitness levels do not change, then existing TB control programmes are likely to keep MDR-TB prevalence at current levels in Lima, Peru
Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies
The effect of a tunable, externally coupled Fabry-P\'{e}rot cavity to
resonantly enhance the optical Hall effect signatures at terahertz frequencies
produced by a traditional Drude-like two-dimensional electron gas is shown and
discussed in this communication. As a result, the detection of optical Hall
effect signatures at conveniently obtainable magnetic fields, for example by
neodymium permanent magnets, is demonstrated. An AlInN/GaN-based high electron
mobility transistor structure grown on a sapphire substrate is used for the
experiment. The optical Hall effect signatures and their dispersions, which are
governed by the frequency and the reflectance minima and maxima of the
externally coupled Fabry-P\'{e}rot cavity, are presented and discussed. Tuning
the externally coupled Fabry-P\'{e}rot cavity strongly modifies the optical
Hall effect signatures, which provides a new degree of freedom for optical Hall
effect experiments in addition to frequency, angle of incidence and magnetic
field direction and strength
A Magnetic and Moessbauer Spectral Study of Core/Shell Structured Fe/Au Nanoparticles
Fe/Au nanoparticles have been chemically synthesized through a reverse
micelle reaction and investigated by both conventional and synchrotron based
x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder
x-ray diffraction patterns reveal both the presence of crystalline alpha-iron
and gold and the absence of any crystalline iron oxides or other crystalline
products. First-order reversal curves, along with the major hysteresis loops of
the Fe/Au nanoparticles have been measured as a function of time in order to
investigate the evolution of their magnetic properties. The iron-57 Moessbauer
spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have
been measured at 78 and 295 K and indicate that two major iron containing
components are present, namely the expected alpha-iron and the unexpected
amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide
components as well as paramagnetic iron(II) and iron(III) components are also
observed. These results indicate that the Fe-core/Au-shell nanoparticles
synthesized through reverse micelles are far more complex that had been
believed.Comment: 31 pages, 1 table, 8 figures, to appear in Chemistry of Material
A Second-Generation Janus Scorpionate Ligand: Controlling Coordination Modes in Iron(II) Complexes by Steric Modulation
The second-generation Janus scorpionate ligand [HB(mtdaMe)3−] containing methyl-mercaptothiadiazolyl (mtdaMe) heterocyclic rings and (N,N,N-) and (S,S,S-) binding pockets has been prepared. The effect of methyl substitution versus the unsubstituted first-generation Janus scorpionate [HB(mtda)3]− on the coordination chemistry with alkali metals and on the binding preferences and on the ground spin state of iron(II) complexes has been studied structurally and by 57Fe Mossbauer Spectroscopy
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