1,672 research outputs found
Alloying, de-alloying and reentrant alloying in (sub-)monolayer growth of Ag on Pt(111)
An in-situ nanoscopic investigation of the prototypical surface alloying
system Ag/Pt(111) is reported. The morphology and the structure of the
ultrathin Ag-Pt film is studied using Low Energy Electron Microscopy during
growth at about 800 K. An amazingly rich dynamic behaviour is uncovered in
which stress relieve plays a governing role. Initial growth leads to surface
alloying with prolonged and retarded nucleation of ad-islands. Beyond 50%
coverage de-alloying proceeds, joined by partial segregation of Pt towards the
centre of large islands in violent processes. Upon coalescence the irregularly
shaped vacancy clusters are filled by segregating Pt, which then take a compact
shape (black spots). As a result at around 85% coverage the strain of the
initially pseudo-morphological film is almost completely relieved and
Pt-segregation is at its maximum. Further deposition of Ag leads to transient
re-entrant alloying and recovery of the pseudo-morphological layer. The black
spots persist even in/on several layers thick films. Ex-situ atomic force
microscopy data confirm that these are constituted by probably amorphous
Pt(-rich) structures. The (sub-)monolayer films are very much heterogeneous
Debye mass and heavy quark potential in a PNJL quark plasma
We calculate the Debye mass for the screening of the heavy quark potential in
a plasma of massless quarks coupled to the temporal gluon background governed
by the Polyakov loop potential within the PNJL model in RPA approximation. We
give a physical motivation for a recent phenomenological fit of lattice data by
applying the calculated Debye mass with its suppression in the confined phase
due to the Polyakov-loop to a description of the temperature dependence of the
singlet free energy for QCD with a heavy quark pair at infinite separation. We
compare the result to lattice data.Comment: 6 pages, 1 figure, contribution to Proceedings of the 6th
International Conference on "Critical Point and Onset of Deconfinement", to
appear in Phys. At. Nucl., vol. 7
Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision
Helium Ion Microscopy is known for its surface sensitivity and high lateral
resolution. Here, we present results of a Helium Ion Microscopy based
investigation of a surface confined alloy of Ag on Pt(111). Based on a change
of the work function of 25\,meV across the atomically flat terraces we can
distinguish Pt rich from Pt poor areas and visualize the single atomic layer
high steps between the terraces. Furthermore, dechanneling contrast has been
utilized to measure the periodicity of the hcp/fcc pattern formed in the 2--3
layers thick Ag/Pt alloy film. A periodicity of 6.65\,nm along the
surface direction has been measured. In terms of
crystallography a hcp domain is obtained through a lateral displacement of a
part of the outermost layer by of a nearest neighbour spacing
along . This periodicity is measured with atomic
precision: coincidence between the Ag and the Pt lattices is observed for 23 Ag
atoms on 24 Pt atoms. The findings are perfectly in line with results obtained
with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy.Comment: 15 pages, 7 figure
Limits on the Mass, Velocity and Orbit of PSR J19336211
We present a high-precision timing analysis of PSR J19336211, a
millisecond pulsar (MSP) with a 3.5-ms spin period and a white dwarf (WD)
companion, using data from the Parkes radio telescope. Since we have accurately
measured the polarization properties of this pulsar we have applied the matrix
template matching approach in which the times of arrival are measured using
full polarimetric information. We achieved a weighted root-mean-square timing
residuals (rms) of the timing residuals of 1.23 , 15.5
improvement compared to the total intensity timing analysis. After studying the
scintillation properties of this pulsar we put constraints on the inclination
angle of the system. Based on these measurements and on mapping we put
a 2- upper limit on the companion mass (0.44 M). Since this
mass limit cannot reveal the nature of the companion we further investigate the
possibility of the companion to be a He WD. Applying the orbital period-mass
relation for such WDs, we conclude that the mass of a He WD companion would be
about 0.260.01 M which, combined with the measured mass function
and orbital inclination limits, would lead to a light pulsar mass
1.0 M. This result seems unlikely based on current neutron star
formation models and we therefore conclude that PSR J19336211 most likely
has a CO WD companion, which allows for a solution with a more massive pulsar
A New 5 Flavour NLO Analysis and Parametrizations of Parton Distributions of the Real Photon
New, radiatively generated, NLO quark (u,d,s,c,b) and gluon densities in a
real, unpolarized photon are presented. We perform three global fits, based on
the NLO DGLAP evolution equations for Q^2>1 GeV^2, to all the available
structure function F_2^gamma(x,Q^2) data. As in our previous LO analysis we
utilize two theoretical approaches. Two models, denoted as FFNS_{CJK}1 & 2 NLO,
adopt the so-called Fixed Flavour-Number Scheme for calculation of the
heavy-quark contributions to F_2^gamma(x,Q^2), the CJK NLO model applies the
ACOT(chi) scheme. We examine the results of our fits by a comparison with the
LEP data for the Q^2 dependence of the F_2^gamma, averaged over various
x-regions, and the F_2,c^gamma. Grid parametrizations of the parton densities
for all fits are provided.Comment: 49 pages, 27 postscript figures; FORTRAN programs available at
http://www.fuw.edu.pl/~pjank/param.htm
Admission glucose, baseline glucose control, and mortality after acute myocardial infarction in diabetic patients
Crossing barriers in planetesimal formation: The growth of mm-dust aggregates with large constituent grains
Collisions of mm-size dust aggregates play a crucial role in the early phases of planet formation. It is for example currently unclear whether there is a bouncing barrier where millimeter aggregates no longer grow by sticking. We developed a laboratory setup that allowed us to observe collisions of dust aggregates levitating at mbar pressures and elevated temperatures of 800 K. We report on collisions between basalt dust aggregates of from 0.3 to 5 mm in size at velocities between 0.1 and 15 cm/s. Individual grains are smaller than 25 μm in size. We find that for all impact energies in the studied range sticking occurs at a probability of 32.1 ± 2.5% on average. In general, the sticking probability decreases with increasing impact parameter. The sticking probability increases with energy density (impact energy per contact area). We also observe collisions of aggregates that were formed by a previous sticking of two larger aggregates. Partners of these aggregates can be detached by a second collision with a probability of on average 19.8 ± 4.0%. The measured accretion efficiencies are remarkably high compared to other experimental results. We attribute this to the relatively large dust grains used in our experiments, which make aggregates more susceptible to restructuring and energy dissipation. Collisional hardening by compaction might not occur as the aggregates are already very compact with only 54 ± 1% porosity. The disassembly of previously grown aggregates in collisions might stall further aggregate growth. However, owing to the levitation technique and the limited data statistics, no conclusive statement about this aspect can yet be given. We find that the detachment efficiency decreases with increasing velocities and accretion dominates in the higher velocity range. For high accretion efficiencies, our experiments suggest that continued growth in the mm-range with larger constituent grains would be a viable way to produce larger aggregates, which might in turn form the seeds to proceed to growing planetesimals. © 2012 ESO
The enzymatic activity of the VEGFR2-receptor for the biosynthesis of dinucleoside polyphosphates
The group of dinucleoside polyphosphates encompasses a large number of molecules consisting of two nucleosides which are connected by a phosphate chain of variable length. While the receptors activated by dinucleoside polyphosphates as well as their degradation have been studied in detail, its biosynthesis has not been elucidated so far. Since endothelial cells released the dinucleoside polyphosphate uridine adenosine tetraphosphate (Up4A), we tested cytosolic proteins of human endothelial cells obtained from dermal vessels elicited for enzymatic activity. When incubated with ADP and UDP, these cells showed increasing concentrations of Up4A. The underlying enzyme was isolated by chromatography and the mass spectrometric analysis revealed that the enzymatic activity was caused by the vascular endothelial growth factor receptor 2 (VEGFR2). Since VEGFR2 but neither VEGFR1 nor VEGFR3 were capable to synthesise dinucleoside polyphosphates, Tyr-1175 of VEGFR2 is most likely essential for the enzymatic activity of interest. Further, VEGFR2-containing cells like HepG2, THP-1 and RAW264.7 were capable of synthesising dinucleoside polyphosphates. VEGFR2-transfected HEK 293T/17 but not native HEK 293T/17 cells synthesised dinucleoside polyphosphates in vivo too. The simultaneous biosynthesis of dinucleoside polyphosphates could amplify the response to VEGF, since dinucleoside polyphosphates induce cellular growth via P2Y purinergic receptors. Thus the biosynthesis of dinucleoside polyphosphates by VEGFR2 may enhance the proliferative response to VEGF. Given that VEGFR2 is primarily expressed in endothelial cells, the biosynthesis of dinucleoside polyphosphates is mainly located in the vascular system. Since the vasculature is also the main site of action of dinucleoside polyphosphates, activating vascular purinoceptors, blood vessels appear as an autocrine system with respect to dinucleoside polyphosphates. We conclude that VEGFR2 receptor is capable of synthesising dinucleoside polyphosphates. These mediators may modulate the effects of VEGFR2 due to their proliferative effects
Increased plasma phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression
The UTMOST pulsar timing programme I: overview and first results
We present an overview and the first results from a large-scale pulsar timing
programme that is part of the UTMOST project at the refurbished Molonglo
Observatory Synthesis Radio Telescope (MOST) near Canberra, Australia. We
currently observe more than 400 mainly bright southern radio pulsars with up to
daily cadences. For 205 (8 in binaries, 4 millisecond pulsars) we publish
updated timing models, together with their flux densities, flux density
variability, and pulse widths at 843 MHz, derived from observations spanning
between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve
the precision of the rotational and astrometric parameters for 123 pulsars, for
47 by at least an order of magnitude. The time spans between our measurements
and those in the literature are up to 48 yr, which allows us to investigate
their long-term spin-down history and to estimate proper motions for 60
pulsars, of which 24 are newly determined and most are major improvements. The
results are consistent with interferometric measurements from the literature. A
model with two Gaussian components centred at 139 and fits the transverse velocity distribution best. The pulse duty
cycle distributions at 50 and 10 per cent maximum are best described by
log-normal distributions with medians of 2.3 and 4.4 per cent, respectively. We
discuss two pulsars that exhibit spin-down rate changes and drifting subpulses.
Finally, we describe the autonomous observing system and the dynamic scheduler
that has increased the observing efficiency by a factor of 2-3 in comparison
with static scheduling.Comment: 31 pages, 14 figures, 6 tables, accepted for publication in MNRA
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