1,820 research outputs found
Precise determination of graphene functionalization by in situ Raman spectroscopy
The verification of a successful covalent functionalization of graphene and
related carbon allotropes can easily be carried out by Raman spectroscopy.
Nevertheless, the unequivocal assignment and resolution of individual lattice
modes associated with the covalent binding of addends was elusive up to now.
Here we present an in situ Raman study of a controlled functionalization of
potassium intercalated graphite, revealing several new bands appearing in the
D-region of the spectrum. The evolution of these bands with increasing degree
of functionalization from low to moderate levels provides a basis for the
deconvolution of the different components towards quantifying the extent of
functionalization. By complementary DFT calculations we were able to identify
the vibrational changes in the close proximity of the addend bearing lattice
carbon atoms and to assign them to specific Raman modes. The experimental in
situ observation of the developing functionalization along with the
reoxidation of the intercalated graphite represents an important step towards
an improved understanding of the chemistry of graphene
Simulations of the High-Energy Beam-Transport (HEBT) section at FRANZ
The neutron source FRANZ (Frankfurter Neutronenquelle am
Stern-Gerlach-Zentrum), which is currently under construction, will be the neutron source with the highest intensity in the nuclear-astrophysically relevant energy
region. The TraceWin code was used to design the High-Energy Beam-Transport section with regard to the experimental requirements at different target positions
Poly(alkyl methacrylate) tooth coatings for dental care: evaluation of the demineralisation-protection benefit using a time-resolved in vitro method
An in vitro method for the time-resolved quantification of acid-mediated tooth demineralisation has been developed and evaluated against putative non-permanent protective formulations based on a series of poly(alkyl methacrylate)s. Using a thermostatted carousel, dentally relevant substrates consisting of hydroxyapatite discs or sections of bovine teeth have been exposed to aqueous citric acid under controlled conditions, before and after being treated with the polymeric coatings. The dissolution of phosphate was monitored by the determination of 31P by Inductively Coupled Plasma—Mass Spectrometry and by the spectrophotometric phosphovanadomolybdate method. Dose-response plots constructed for both groups of treated substrates have revealed that the coatings significantly reduce erosion rates but are less effective at inhibiting tooth demineralisation than the standard fluoride treatment. The approach has enabled an evaluation of the erosion-protection efficiency of each coating
Nuclear spin driven quantum relaxation in LiY_0.998Ho_0.002F_4
Staircase hysteresis loops of the magnetization of a LiY_0.998Ho_0.002F_4
single crystal are observed at subkelvin temperatures and low field sweep
rates. This behavior results from quantum dynamics at avoided level crossings
of the energy spectrum of single Ho^{3+} ions in the presence of hyperfine
interactions. Enhanced quantum relaxation in constant transverse fields allows
the study of the relative magnitude of tunnel splittings. At faster sweep
rates, non-equilibrated spin-phonon and spin-spin transitions, mediated by weak
dipolar interactions, lead to magnetization oscillations and additional steps.Comment: 5 pages, 5 eps figures, using RevTe
A radio catalog of Galactic HII regions for applications from decimeter to millimeter wavelengths
By collecting the information from 24 previously published lists and
catalogs, we produce a comprehensive catalog (Master Catalog) of 1442 Galactic
HII regions. For each object, we quote the original fluxes and diameters as
well as the available information on radio line velocities, line widths and
line temperatures and the errors on these quantitities. References to the
original works are also reported. By exploiting all these data we produce a
Synthetic Catalog of fluxes and diameters (with corresponding errors) at 2.7
GHz. This choice is motivated by the extensive, although not complete,
information available at this frequency, widely spread among many different
catalogs, and by its relevance for both detailed studies on Galactic HII
regions and the extrapolation up to millimetric wavelengths. The catalog can be
used for detailed studies of Galactic HII regions and, by extrapolation, for
investigations of HII regions up to millimetric wavelengths. In particular, we
discuss the study of the effects of microwave emission from HII regions on the
new generation of Cosmic Microwave Background (CMB) experiments. We present
simulations of the detection of HII regions in the high resolution CMB survey,
and briefly analize some of the typical applications of our catalog to the
evaluation of CMB anisotropy experiments such as calibration, beam
reconstruction and straylight effects. The Master Catalog and the Synthetic
Catalog are available via ftp at: cdsarc.u-strasbg.fr. This work is related to
Planck-LFI activities.Comment: 14 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Measurement of corrosion content of archaeological lead artifacts by their Meissner response in the superconducting state; a new dating method
Meissner fraction in the superconducting state of lead archaeological
artifacts is used to evaluate the mass of the uncorroded metal in the sample.
Knowing the total mass of the sample the mass of all corrosion products is
established. It is shown that this mass correlates with the archaeological age
of the lead artifacts over a time span of ~2500 years. Well-dated untreated
lead samples from Tel-Dor, the Persian period, Caesarea, the Byzantine and the
Crusader periods as well as contemporary data were used to establish the dating
correlation. This new chemical dating method is apparently applicable to lead
artifacts buried in soils with the pH>6.5. In such soils the corrosion process
is very slow and the corrosion products, mainly PbO and PbCO3, accumulate over
hundreds of years. The method presented is in principle non-destructive.
(corresponding author: )Comment: File ARCH_4.pdf 14 pages including 1 table and 5 figure
Presymptomatic risk assessment for chronic non-communicable diseases
The prevalence of common chronic non-communicable diseases (CNCDs) far
overshadows the prevalence of both monogenic and infectious diseases combined.
All CNCDs, also called complex genetic diseases, have a heritable genetic
component that can be used for pre-symptomatic risk assessment. Common single
nucleotide polymorphisms (SNPs) that tag risk haplotypes across the genome
currently account for a non-trivial portion of the germ-line genetic risk and
we will likely continue to identify the remaining missing heritability in the
form of rare variants, copy number variants and epigenetic modifications. Here,
we describe a novel measure for calculating the lifetime risk of a disease,
called the genetic composite index (GCI), and demonstrate its predictive value
as a clinical classifier. The GCI only considers summary statistics of the
effects of genetic variation and hence does not require the results of
large-scale studies simultaneously assessing multiple risk factors. Combining
GCI scores with environmental risk information provides an additional tool for
clinical decision-making. The GCI can be populated with heritable risk
information of any type, and thus represents a framework for CNCD
pre-symptomatic risk assessment that can be populated as additional risk
information is identified through next-generation technologies.Comment: Plos ONE paper. Previous version was withdrawn to be updated by the
journal's pdf versio
Foreground simulations for the LOFAR - Epoch of Reionization Experiment
Future high redshift 21-cm experiments will suffer from a high degree of
contamination, due both to astrophysical foregrounds and to non-astrophysical
and instrumental effects. In order to reliably extract the cosmological signal
from the observed data, it is essential to understand very well all data
components and their influence on the extracted signal. Here we present
simulated astrophysical foregrounds datacubes and discuss their possible
statistical effects on the data. The foreground maps are produced assuming 5
deg x 5 deg windows that match those expected to be observed by the LOFAR
Epoch-of-Reionization (EoR) key science project. We show that with the expected
LOFAR-EoR sky and receiver noise levels, which amount to ~52 mK at 150 MHz
after 300 hours of total observing time, a simple polynomial fit allows a
statistical reconstruction of the signal. We also show that the polynomial
fitting will work for maps with realistic yet idealised instrument response,
i.e., a response that includes only a uniform uv coverage as a function of
frequency and ignores many other uncertainties. Polarized galactic synchrotron
maps that include internal polarization and a number of Faraday screens along
the line of sight are also simulated. The importance of these stems from the
fact that the LOFAR instrument, in common with all current interferometric EoR
experiments has an instrumentally polarized response.Comment: 18 figures, 3 tables, accepted to be published in MNRA
Foregrounds for observations of the cosmological 21 cm line: I. First Westerbork measurements of Galactic emission at 150 MHz in a low latitude field
We present the first results from a series of observations conducted with the
Westerbork telescope in the 140--160 MHz range with a 2 arcmin resolution aimed
at characterizing the properties of the foregrounds for epoch of reionization
experiments. For the first time we have detected fluctuations in the Galactic
diffuse emission on scales greater than 13 arcmin at 150 MHz, in the low
Galactic latitude area known as Fan region. Those fluctuations have an of
14 K. The total intensity power spectrum shows a power--law behaviour down to
with slope . The detection of
diffuse emission at smaller angular scales is limited by residual point
sources. We measured an confusion noise of 3 mJy beam.
Diffuse polarized emission was also detected for the first time at this
frequency. The polarized signal shows complex structure both spatially and
along the line of sight. The polarization power spectrum shows a power--law
behaviour down to with slope .
The of polarization fluctuations is 7.2 K on 4 arcmin scales. By
extrapolating the measured spectrum of total intensity emission, we find a
contamination on the cosmological signal of K on 5 arcmin scales and a corresponding value
of 18.3 K at the same angular scale. The level of the polarization power
spectrum is K on 5 arcmin scales. Given its exceptionally
bright polarized signal, the Fan region is likely to represent an upper limit
on the sky brightness at moderate and high Galactic latitude.Comment: Minor corrections made to match the final version printed on A&A. A
version with high resolution figures is available at
http://www.astro.rug.nl/~bernardi/FAN/fan.pd
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