2,086 research outputs found
Orbital correlations in the pseudo-cubic \emph{O} and rhombohedral -phases of LaMnO
The local and intermediate structure of stoichiometric LaMnO has been
studied in the pseudocubic and rhombohedral phases at high temperatures (300 to
1150 K). Neutron powder diffraction data were collected and a combined Rietveld
and high real space resolution atomic pair distribution function analysis
carried out. The nature of the Jahn-Teller (JT) transition around 750 K is
confirmed to be orbital order to disorder. In the high temperature orthorhombic
() and rhombohedral () phases the MnO octahedra are still fully
distorted locally. The data suggest the presence of local orbitally ordered
clusters of diameter \AA (four MnO octahedra) implying
strong nearest neighbor JT anti-ferrodistortive coupling.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Le
Scaling of the Fano effect of the in-plane Fe-As phonon and the superconducting critical temperature in BaKFeAs
By means of infrared spectroscopy we determine the temperature-doping phase
diagram of the Fano effect for the in-plane Fe-As stretching mode in
BaKFeAs. The Fano parameter , which is a
measure of the phonon coupling to the electronic particle-hole continuum, shows
a remarkable sensitivity to the magnetic/structural orderings at low
temperatures. More strikingly, at elevated temperatures in the
paramagnetic/tetragonal state we find a linear correlation between and
the superconducting critical temperature . Based on theoretical
calculations and symmetry considerations, we identify the relevant interband
transitions that are coupled to the Fe-As mode. In particular, we show that a
sizable orbital component at the Fermi level is fundamental for the Fano
effect and possibly also for the superconducting pairing.Comment: Supplemental materials are available upon reques
Study of temperature dependent atomic correlations in MgB
We have studied the evolution with temperature of the local as well as the
average crystal structure of MgB using the real-space atomic pair
distribution function (PDF) measured by high resolution neutron powder
diffraction. We have investigated the correlations of the B-B and B-Mg nearest
neighbor pair motion by comparing, in the wide temperature range from T=10 K up
to T=600 K, the mean-square displacements (MSD) of single atoms with the
mean-square relative displacements (MSRD) obtained from the PDF peak
linewidths. The results show that the single atom B and Mg vibrations are
mostly decoupled from each other, with a small predominance of positive (in
phase) correlation factor for both the B-B and B-Mg pairs. The small positive
correlation is almost temperature independent, in contrast with our theoretical
calculations; this can be a direct consequence of the strong decay processes of
the anharmonic phonons
High-mass star formation at high luminosities: W31 at >10^6 L_sun
Context: High-mass star formation has been a very active field over the last
decade, however, most studies targeted regions of luminosities between 10^4 and
10^5 L_sun. Methods: We selected the W31 star-forming complex with a total
luminosity of ~6x10^6 L_sun for a multi-wavelength spectral line and continuum
study covering wavelengths from the near- and mid-infrared via (sub)mm
wavelength observations to radio data in the cm regime. Results: While the
overall structure of the multi-wavelength continuum data resembles each other
well, there are several intriguing differences. The 24mum emission stemming
largely from small dust grains follows tightly the spatial structure of the cm
emission tracing the ionized free-free emission. Hence warm dust resides in
regions that are spatially associated with the ionized hot gas (~10^4 K) of the
HII regions. Furthermore, we find several evolutionary stages within the same
complexes, ranging from infrared-observable clusters, via deeply embedded
regions associated with active star formation traced by 24\,m and cm
emission, to at least one high-mass gas clump devoid of any such signature. The
13CO(2-1) and C18O(2-1) spectral line observations reveal a large kinematic
breadth in the entire region with a total velocity range of approximately 90
km/s. While the average virial mass ratio for W31 is close to unity, the line
width analysis indicates large-scale evolutionary differences between the
southern and northern sub-regions (G10.2-0.3 and G10.3-0.1) of the whole W31
complex. The clump mass function - tracing cluster scales and not scales of
individual stars - derived from the 875mum continuum data has a slope of
1.5+-0.3, consistent with previous cloud mass functions.Comment: 13 pages, 11 figures, accepted for Astronomy and Astrophysics,
high-resolution version of paper at
http://www.mpia.de/homes/beuther/papers.htm
The high-mass disk candidates NGC7538IRS1 and NGC7538S
Context: The nature of embedded accretion disks around forming high-mass
stars is one of the missing puzzle pieces for a general understanding of the
formation of the most massive and luminous stars. Methods: Using the Plateau de
Bure Interferometer at 1.36mm wavelengths in its most extended configuration we
probe the dust and gas emission at ~0.3",corresponding to linear resolution
elements of ~800AU. Results: NGC7538IRS1 remains a single compact and massive
gas core with extraordinarily high column densities, corresponding to visual
extinctions on the order of 10^5mag, and average densities within the central
2000AU of ~2.1x10^9cm^-3 that have not been measured before. We identify a
velocity gradient across in northeast-southwest direction that is consistent
with the mid-infrared emission, but we do not find a gradient that corresponds
to the proposed CH3OH maser disk. The spectral line data toward NGC7538IRS1
reveal strong blue- and red-shifted absorption toward the mm continuum peak
position. The red-shifted absorption allows us to estimate high infall rates on
the order of 10^-2 Msun/yr. Although we cannot prove that the gas will be
accreted in the end, the data are consistent with ongoing star formation
activity in a scaled-up low-mass star formation scenario. Compared to that,
NGC7538S fragments in a hierarchical fashion into several sub-sources. While
the kinematics of the main mm peak are dominated by the accompanying jet, we
find rotational signatures from a secondary peak. Furthermore, strong spectral
line differences exist between the sub-sources which is indicative of different
evolutionary stages within the same large-scale gas clump.Comment: 15 pages, 12 figures, accepted for A&
Dynamics of Flux Creep in Underdoped Single Crystals of Y_1-xPr_xBa_2Cu_3O_7-d
Transport as well as magnetic relaxation properties of the mixed state were
studied on strongly underdoped Y_1-xPr_xBa_2Cu_3O_7-d crystals. We observed two
correlated phenomena - a coupling transition and a transition to quantum creep.
The distribution of transport current below the coupling transition is highly
nonuniform, which facilitates quantum creep. We speculate that in the mixed
state below the coupling transition, where dissipation is nonohmic, the current
distribution may be unstable with respect to self-channeling resulting in the
formation of very thin current-carrying layers.Comment: 11 pages, 9 figures, Submitted to Phys. Rev.
Effect of AGM and Fetal Liver-Derived Stromal Cell Lines on Globin Expression in Adult Baboon (P. anubis) Bone Marrow-Derived Erythroid Progenitors
This study was performed to investigate the hypothesis that the erythroid micro-environment plays a role in regulation of globin gene expression during adult erythroid differentiation. Adult baboon bone marrow and human cord blood CD34+ progenitors were grown in methylcellulose, liquid media, and in co-culture with stromal cell lines derived from different developmental stages in identical media supporting erythroid differentiation to examine the effect of the micro-environment on globin gene expression. Adult progenitors express high levels of γ-globin in liquid and methylcellulose media but low, physiological levels in stromal cell co-cultures. In contrast, γ-globin expression remained high in cord blood progenitors in stromal cell line co-cultures. Differences in γ-globin gene expression between adult progenitors in stromal cell line co-cultures and liquid media required cell-cell contact and were associated with differences in rate of differentiation and γ-globin promoter DNA methylation. We conclude that γ-globin expression in adult-derived erythroid cells can be influenced by the micro-environment, suggesting new potential targets for HbF induction
All-cause mortality and risk factors in a cohort of retired military male veterans, Xi'an, China: an 18-year follow up study
<p>Abstract</p> <p>Background</p> <p>Risk factors of all-cause mortality have not been reported in Chinese retired military veterans. The objective of the study was to examine the risk factors and proportional mortality in a Chinese retired military male cohort.</p> <p>Methods</p> <p>A total of 1268 retired military men aged 55 or older were examined physically and interviewed using a standard questionnaire in 1987. The cohort was followed up every two years and the study censored date was June30, 2005 with a follow-up of up to 18 years. Death certificates were obtained from hospitals and verified by two senior doctors. Data were entered (double entry) by Foxbase, and analysis was carried out by SAS for Windows 8.2. Multivariate Cox proportional hazard regression model was used to compute hazard ratio (HR) and 95% confidence interval (CI).</p> <p>Results</p> <p>The total person-years of follow-up was 18766.28. Of the initial cohort of 1268 men, 491 had died, 748 were alive and 29 were lost to follow up. Adjusted mortality (adjusted for age, blood pressure, body mass index, cholesterol, triglycerides, alcohol, exercise, and existing disease) was 2,616 per 100,000 person years. The proportional mortality of cancer, vascular disease and Chronic Obstructive Pulmonary Disease (COPD) were 39.71%, 28.10% and 16.90% respectively. Multivariate analysis showed that age, cigarettes per day, systolic blood pressure, triglyceride, family history of diseases (hypertension, stroke and cancer), existing diseases (stroke, diabetes and cancer), body mass index, and age of starting smoking were associated with all-cause mortality, HR (95%CI) was1.083(1.062–1.104), 1.026(1.013–1.039), 1.009(1.003–1.015), 1.002(1.001–1.003), 1.330(1.005–1.759), 1.330(1.005–1.759), 1.444(1.103–1.890), 2.237(1.244–4.022), 1.462(1.042–2.051), 2.079(1.051–4.115), 0.963(0.931–0.996)and 0.988(0.978–0.999)respectively. Compared with never-smokers, current smokers had increased risks of total mortality [HR 1.369(1.083–1.731)], CHD [HR 1.805 (1.022–3.188)], and lung cancer [HR 2.939 (1.311–6.585)].</p> <p>Conclusion</p> <p>The three leading causes of diseases were cancer, CHD and stroke, and COPD. Aging, cigarette smoking, high systolic blood pressure, high triglyceride, family history of cancer, hypertension and stroke, existing cases recovering from stroke, diabetes and cancer, underweight, younger age of smoking were risk factors for all-cause mortality. Quitting cigarette smoking, maintaining normal blood pressure, triglyceride and weight are effect control strategies to prevent premature mortality in this military cohort.</p
Expression of Distal-less, dachshund, and optomotor blind in Neanthes arenaceodentata (Annelida, Nereididae) does not support homology of appendage-forming mechanisms across the Bilateria
The similarity in the genetic regulation of
arthropod and vertebrate appendage formation has been
interpreted as the product of a plesiomorphic gene
network that was primitively involved in bilaterian
appendage development and co-opted to build appendages
(in modern phyla) that are not historically related
as structures. Data from lophotrochozoans are needed to
clarify the pervasiveness of plesiomorphic appendage forming
mechanisms. We assayed the expression of three
arthropod and vertebrate limb gene orthologs, Distal-less
(Dll), dachshund (dac), and optomotor blind (omb), in
direct-developing juveniles of the polychaete Neanthes
arenaceodentata. Parapodial Dll expression marks premorphogenetic
notopodia and neuropodia, becoming restricted
to the bases of notopodial cirri and to ventral
portions of neuropodia. In outgrowing cephalic appendages,
Dll activity is primarily restricted to proximal
domains. Dll expression is also prominent in the brain. dac
expression occurs in the brain, nerve cord ganglia, a pair
of pharyngeal ganglia, presumed interneurons linking a
pair of segmental nerves, and in newly differentiating
mesoderm. Domains of omb expression include the brain,
nerve cord ganglia, one pair of anterior cirri, presumed
precursors of dorsal musculature, and the same pharyngeal
ganglia and presumed interneurons that express dac.
Contrary to their roles in outgrowing arthropod and
vertebrate appendages, Dll, dac, and omb lack comparable
expression in Neanthes appendages, implying independent
evolution of annelid appendage development. We infer
that parapodia and arthropodia are not structurally or
mechanistically homologous (but their primordia might
be), that Dll’s ancestral bilaterian function was in sensory
and central nervous system differentiation, and that
locomotory appendages possibly evolved from sensory
outgrowths
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