6,281 research outputs found
An optical linewidth study of a chromoprotein-C-phycocyanin in a low-temperature glass
The temperature dependence of spectral holes burnt into a phycocyanin-doped ethylene glycol/water glass is investigated in the temperature range between 1.5 and 15 K. The data are well described by a power law with an exponent of 1.16 ± 0.1. Chromoproteins thus behave very much the same as glasses doped with small impurity molecules
Lattice and polarizability mediated spin activity in EuTiO_3
EuTiO_3 is shown to exhibit novel strong spin-charge-lattice coupling deep in
the paramagnetic phase. Its existence is evidenced by an, until now, unknown
response of the paramagnetic susceptibility at temperatures exceeding the
structural phase transition temperature T_S = 282K. The "extra" features in the
susceptibility follow the rotational soft zone boundary mode temperature
dependence above and below T_S. The theoretical modeling consistently
reproduces this behavior and provides reasoning for the stabilization of the
soft optic mode other than quantum fluctuations.Comment: 8 pages, 4 figure
The search for planetary mass companions to field brown dwarfs with HST/NICMOS
We present the results of a high-resolution spectral differential imaging
survey of 12 nearby, relatively young field L dwarfs (<1 Gyr) carried out with
HST/NICMOS to search for planetary mass companions at small physical
separations from their host. The survey resolved two brown dwarf binaries: the
L dwarf system Kelu-1AB and the newly discovered L/T transition system 2MASS
J031059+164815AB. For both systems common proper motion has already been
confirmed in follow-up observations which have been published elsewhere. The
derived separations of the binaries are smaller than 6 AU and consistent with
previous brown dwarf binary statistics. Their mass ratios of q > 0.8 confirm
the preference for equal mass systems similar to a large number of other
surveys. Furthermore, we found tentative evidence for a companion to the L4
dwarf 2MASS W033703-175807, straddling the brown dwarf/planetary mass boundary
and revealing an uncommonly low mass ratio system (q ~ 0.2) compared to the
vast majority of previously found brown dwarf binaries. With a derived minimum
mass of 10 - 15 Mjup, a planetary nature of the secondary cannot be ruled out
yet. However, it seems more likely to be a very low mass brown dwarf secondary
at the border of the spectral T/Y transition regime, primarily due to its
similarities to recently found very cool T dwarfs. This would make it one of
the closest resolved brown dwarf binaries (0.087" 0.015", corresponding
to 2.52 0.44 AU at a distance of 29 pc) with the coolest (Teff ~ 600-630
K) and least massive companion to any L or T dwarf.Comment: 33 pages, 8 figures, 2 tables, accepted for publication by Ap
Hybrid paramagnon phonon modes at elevated temperatures in EuTiO3
EuTiO3 (ETO) has recently experienced an enormous revival of interest because
of its possible multiferroic properties which are currently in the focus of
research. Unfortunately ETO is an unlikely candidate for enlarged
multifunctionality since the mode softening - typical for ferroelectrics -
remains incomplete, and the antiferromagnetic properties appear at 5.5K only.
However, a strong coupling between lattice and Eu spins exists and leads to the
appearance of a magnon-phonon-hybrid mode at elevated temperatures as evidenced
by electron paramagnetic resonance (EPR), muon spin rotation ({\mu}SR)
experiments and model predictions based on a coupled spin-polarizability
Hamiltonian. This novel finding supports the notion of strong
magneto-dielectric (MD) effects being realized in ETO and opens new strategies
in material design and technological applications.Comment: 9 pages, 4 figure
Star formation environments and the distribution of binary separations
We have carried out K-band speckle observations of a sample of 114 X-ray
selected weak-line T Tauri stars in the nearby Scorpius-Centaurus OB
association. We find that for binary T Tauri stars closely associated to the
early type stars in Upper Scorpius, the youngest subgroup of the OB
association, the peak in the distribution of binary separations is at 90 A.U.
For binary T Tauri stars located in the direction of an older subgroup, but not
closely associated to early type stars, the peak in the distribution is at 215
A.U. A Kolmogorov-Smirnov test indicates that the two binary populations do not
result from the same distibution at a significance level of 98%. Apparently,
the same physical conditions which facilitate the formation of massive stars
also facilitate the formation of closer binaries among low-mass stars, whereas
physical conditions unfavorable for the formation of massive stars lead to the
formation of wider binaries among low-mass stars. The outcome of the binary
formation process might be related to the internal turbulence and the angular
momentum of molecular cloud cores, magnetic field, the initial temperature
within a cloud, or - most likely - a combination of all of these. We conclude
that the distribution of binary separations is not a universal quantity, and
that the broad distribution of binary separations observed among main-sequence
stars can be explained by a superposition of more peaked binary distributions
resulting from various star forming environments. The overall binary frequency
among pre-main-sequence stars in individual star forming regions is not
necessarily higher than among main-sequence stars.Comment: 7 pages, Latex, 4 Postscript figures; also available at
http://spider.ipac.caltech.edu/staff/brandner/pubs/pubs.html ; accepted for
publication in ApJ Letter
Field and Temperature Dependence of the Superfluid Density in LaO_{1-x}F_xFeAs Superconductors: A Muon Spin Relaxation Study
We present zero field and transverse field \muSR experiments on the recently
discovered electron doped Fe-based superconductor LaO_{1-x}F_xFeAs. The zero
field experiments on underdoped (x=0.075) and optimally doped (x=0.1) samples
rule out any static magnetic order above 1.6 K in these superconducting
samples. From transverse field experiments in the vortex phase we deduce the
temperature and field dependence of the superfluid density. Whereas the
temperature dependence is consistent with a weak coupling BCS s-wave or a dirty
d-wave gap function scenario, the field dependence strongly evidences
unconventional superconductivity. We obtain the in-plane penetration depth of
\lambda_{ab} (0) = 254(2)nm for LaO_{0.9}F_{0.1}FeAs and \lambda_{ab} (0) =
364(8)nm for LaO_{0.925}F_{0.075}FeAs. Further evidence for unconventional
superconductivity is provided by the ratio of T_c versus the superfluid
density, which is close to the Uemura line of hole doped high-T_c cuprates.Comment: 5 pages, 5 figure
The effect of heavy metals on the expression of hsp 70 in soil invertebrates
Stress proteins from the hsp 70 (stress- 70) family usually are induced by different environmental factors and stress situations in order to protect proteotoxicity (protein denaturation).In the present paper, hsp 70 expression in response to heavy metal contamination was qualified and semi-quantified by biochemical and immunological techniques.Die Auswirkung von Schwermetallen auf die hsp 70 -Expression in Bodeninvertebrate
The spectrum of phenotypes associated with mutations in steroidogenic factor 1 (SF-1, NR5A1, Ad4BP) includes severe penoscrotal hypospadias in 46,XY males without adrenal insufficiency
OBJECTIVE. Hypospadias is a frequent congenital anomaly but in most cases an underlying cause is not found. Steroidogenic factor 1 (SF-1, NR5A1, Ad4BP) is a key regulator of human sex development and an increasing number of SF-1 (NR5A1) mutations are reported in 46,XY disorders of sex development (DSD). We hypothesized that NR5A1 mutations could be identified in boys with hypospadias.
DESIGN AND METHODS. Mutational analysis of NR5A1 in 60 individuals with varying degrees of hypospadias from the German DSD network.
RESULTS. Heterozygous NR5A1 mutations were found in three out of 60 cases. These three individuals represented the most severe end of the spectrum studied as they presented with penoscrotal hypospadias, variable androgenization of the phallus and undescended testes (three out of 20 cases (15%) with this phenotype). Testosterone was low in all three patients and inhibin B/anti-Müllerian hormone (AMH) were low in two patients. Two patients had a clear male gender assignment. Gender re-assignment to male occurred in the third case. Two patients harbored heterozygous nonsense mutations (p.Q107X/WT, p.E11X/WT). One patient had a heterozygous splice site mutation in intron 2 (c.103-3A/WT) predicted to disrupt the main DNA-binding motif. Functional studies of the nonsense mutants showed impaired transcriptional activation of an SF-1-responsive promoter (Cyp11a). To date, adrenal insufficiency has not occurred in any of the patients.
CONCLUSIONS. SF-1 (NR5A1) mutations should be considered in 46,XY individuals with severe (penoscrotal) hypospadias, especially if undescended testes, low testosterone, or low inhibin B/AMH levels are present. SF-1 mutations in milder forms of idiopathic hypospadias are unlikely to be common
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