443 research outputs found
Structure development and control of injection-molded hydroxylapatite-reinforced starch/EVOH composites
This article reports on the development of novel composites of starch-based polymers reinforced with hydroxylapatite (HA). Two different grades of blends of starch and ethylene vinyl alcohol copolymers were reinforced with up to 30% (wt) of sintered and nonsintered HA. The initial compounding stage was carried out either in a rotating drum or by twin-screw extrusion (TSE). Compounds were injection molded using both conventional molding and a shear-controlled orientation in injection molding (Scorim) technique. It was possible to obtain composites with very good mechanical properties, approaching those of cortical bone. The best results were achieved for 30% sintered HA composites processed by TSE and Scorim, due to the in situ formation of HA fibers, and the development of molecular orientation and more compact microstructures in the moldings. This was confirmed by SEM analysis of the fracture surfaces, x-ray diffraction, and Raman spectroscopy. The biodegradability of the composites was also assessed and was found to be faster than that of the matrixPRAXIS XXI Programm
Geodesic motion in the space-time of a cosmic string
We study the geodesic equation in the space-time of an Abelian-Higgs string
and discuss the motion of massless and massive test particles. The geodesics
can be classified according to the particles energy, angular momentum and
linear momentum along the string axis. We observe that bound orbits of massive
particles are only possible if the Higgs boson mass is smaller than the gauge
boson mass, while massless particles always move on escape orbits. Moreover,
neither massive nor massless particles can ever reach the string axis for
non-vanishing angular momentum. We also discuss the dependence of light
deflection by a cosmic string as well as the perihelion shift of bound orbits
of massive particles on the ratio between Higgs and gauge boson mass and the
ratio between symmetry breaking scale and Planck mass, respectively.Comment: 20 pages including 14 figures; v2: references added, discussion on
null geodesics extended, numerical results adde
Quantitative Chemically-Specific Coherent Diffractive Imaging of Buried Interfaces using a Tabletop EUV Nanoscope
Characterizing buried layers and interfaces is critical for a host of
applications in nanoscience and nano-manufacturing. Here we demonstrate
non-invasive, non-destructive imaging of buried interfaces using a tabletop,
extreme ultraviolet (EUV), coherent diffractive imaging (CDI) nanoscope. Copper
nanostructures inlaid in SiO2 are coated with 100 nm of aluminum, which is
opaque to visible light and thick enough that neither optical microscopy nor
atomic force microscopy can image the buried interfaces. Short wavelength (29
nm) high harmonic light can penetrate the aluminum layer, yielding
high-contrast images of the buried structures. Moreover, differences in the
absolute reflectivity of the interfaces before and after coating reveal the
formation of interstitial diffusion and oxidation layers at the Al-Cu and
Al-SiO2 boundaries. Finally, we show that EUV CDI provides a unique capability
for quantitative, chemically-specific imaging of buried structures, and the
material evolution that occurs at these buried interfaces, compared with all
other approaches.Comment: 12 pages, 8 figure
Comorbidity clusters in people with gout: an observational cohort study with linked medical record review
Objective. To investigate how comorbid conditions cluster in patients with gout in a UK primary care population.
Methods. A cross-sectional study was performed using baseline data from a primary-care-based prospective observational cohort of people aged >= 18 years with gout. Participants with gout were identified through primary care medical records. Factor analysis was performed to obtain distinct clusters of comorbidity variables including obesity, hypertension, diabetes mellitus, hyperlipidaemia, coronary heart disease, heart failure, chronic kidney disease (CKD) and cancer. Hierarchical cluster analysis of patient observations was also performed to identify homogenous subgroups of patients based on combinations of their comorbidities.
Results. Four distinct comorbidity clusters (C1-C4) were identified in 1079 participants [mean (S.D.) age 65.5 years (12.5); 909 (84%) male]. Cluster C1 (n = 197, 18%) was the oldest group and had the most frequent attacks of gout; 97% had CKD. Participants in C2 (n = 393, 36%) had isolated gout with few comorbidities but drank alcohol more frequently. In cluster C3 (n = 296, 27%), hypertension, diabetes mellitus, hyperlipidaemia, coronary heart disease and/or CKD were prevalent, and urate-lowering therapy was prescribed more frequently than in other clusters. All patients in C4 (193, 18%) had hypertension and were more likely to be obese than other clusters.
Conclusion. Four distinct comorbidity clusters were identified. People with multiple comorbidities were more likely to receive allopurinol. Tailoring of treatments depending on cluster and comorbidities should be considered
Constraints on Brane Inflation and Cosmic Strings
By considering simple, but representative, models of brane inflation from a
single brane-antibrane pair in the slow roll regime, we provide constraints on
the parameters of the theory imposed by measurements of the CMB anisotropies by
WMAP including a cosmic string component. We find that inclusion of the string
component is critical in constraining parameters. In the most general model
studied, which includes an inflaton mass term, as well as the brane-antibrane
attraction, values n_s < 1.02 are compatible with the data at 95 % confidence
level. We are also able to constrain the volume of internal manifold (modulo
factors dependent on the warp factor) and the value of the inflaton field to be
less than 0.66M_P at horizon exit. We also investigate models with a mass term.
These observational considerations suggest that such models have r < 2*10^-5,
which can only be circumvented in the fast roll regime, or by increasing the
number of antibranes. Such a value of r would not be detectable in CMB
polarization experiment likely in the near future, but the B-mode signal from
the cosmic strings could be detectable. We present forecasts of what a similar
analysis using PLANCK data would yield and find that it should be possible to
rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.Comment: 11 pages, 3 figures, revtex4, typos corrected, references adde
Cosmic microwave anisotropies from BPS semilocal strings
We present the first ever calculation of cosmic microwave background CMB
anisotropy power spectra from semilocal cosmic strings, obtained via
simulations of a classical field theory. Semilocal strings are a type of
non-topological defect arising in some models of inflation motivated by
fundamental physics, and are thought to relax the constraints on the symmetry
breaking scale as compared to models with (topological) cosmic strings. We
derive constraints on the model parameters, including the string tension
parameter mu, from fits to cosmological data, and find that in this regard BPS
semilocal strings resemble global textures more than topological strings. The
observed microwave anisotropy at l = 10 is reproduced if Gmu = 5.3x10^{-6} (G
is Newton's constant). However as with other defects the spectral shape does
not match observations, and in models with inflationary perturbations plus
semilocal strings the 95% confidence level upper bound is Gmu<2.0x10^{-6} when
CMB data, Hubble Key Project and Big Bang Nucleosynthesis data are used (c.f.
Gmu<0.9x10^{-6} for cosmic strings). We additionally carry out a Bayesian model
comparison of several models with and without defects, showing models with
defects are neither conclusively favoured nor disfavoured at present.Comment: 15 pages, 13 figures. Minor correction of numerical results, matches
published versio
Cosmic string parameter constraints and model analysis using small scale Cosmic Microwave Background data
We present a significant update of the constraints on the Abelian Higgs
cosmic string tension by cosmic microwave background (CMB) data, enabled both
by the use of new high-resolution CMB data from suborbital experiments as well
as the latest results of the WMAP satellite, and by improved predictions for
the impact of Abelian Higgs cosmic strings on the CMB power spectra. The new
cosmic string spectra (presented in a previous work) were improved especially
for small angular scales, through the use of larger Abelian Higgs string
simulations and careful extrapolation. If Abelian Higgs strings are present
then we find improved bounds on their contribution to the CMB anisotropies,
f10< 0.095, and on their tension, G\mu< 0.57 x 10^-6, both at 95% confidence
level using WMAP7 data; and f10 < 0.048 and G\mu < 0.42 x 10^-6 using all the
CMB data. We also find that using all the CMB data, a scale invariant initial
perturbation spectrum, ns=1, is now disfavoured at 2.4\sigma\ even if strings
are present. A Bayesian model selection analysis no longer indicates a
preference for strings.Comment: 8 pages, 3 figures; Minor corrections, matches published versio
Textures and Semi-Local Strings in SUSY Hybrid Inflation
Global topological defects may account for the large cold spot observed in
the Cosmic Microwave Background. We explore possibilities of constructing
models of supersymmetric F-term hybrid inflation, where the waterfall fields
are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged,
there arise Goldstone bosons and additional moduli, which are lifted only by
masses of soft-supersymmetry breaking scale. The model predicts the existence
of global textures, which can become semi-local strings if the waterfall fields
are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating
proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of
the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed
by normalisation of the power spectrum generated from inflation coincides with
the energy scale required to explain the most prominent of the cold spots. In
this case, the spectrum of density fluctuations is close to scale-invariant
which can be reconciled with measurements of the power spectrum by the
inclusion of the sub-dominant component due to the topological defects.Comment: 29 page
Towards Constraining Glacial Isostatic Adjustment in Greenland Using ICESat and GPS Observations
Constraining glacial isostatic adjustment (GIA) i.e. the Earth’s viscoelastic response to past ice changes, is an important task, because GIA is a significant correction in gravity-based ice sheet mass balance estimates. Here, we investigate how temporal variations in the observed and modeled crustal displacements due to the Earth’s response to ongoing ice mass changes can contribute to the process of constraining GIA. We use mass change grids of the Greenland ice sheet (GrIS) derived from NASA’s high resolution Ice, Cloud and land Elevation Satellite (ICESat) data in three overlapping time spans covering the period 2004–2009 to estimate temporal variations in the elastic response due to present day ice mass loss. The modeled crustal displacements (elastic + GIA) are compared with GPS time series from five permanent sites (KELY, KULU, QAQ1, THU2, and SCOR). We find, that the modeled pattern of elastic crustal displacements shows pronounced variation during the observation period, where an increase in elastic displacement is found at the northwest coast of Greenland, while a decrease is found at the southeast coast. This pattern of temporal changes is supported by the GPS observations. We find, that the temporal behavior of the ICESat-based modeled elastic response agrees well with the GPS observations at the sites KELY, QAQ1, and SCOR. This suggests, that our elastic models are able to resolve the temporal changes in the observed uplift, which indicates that the elastic uplift models are reliable at these sites. Therefore, we conclude that these sites are useful for constraining GIA
The status of GNSS data processing systems to estimate integrated water vapour for use in numerical weather prediction models
Modern Numerical Weather Prediction (NWP) models make use of the GNSS-derived Zenith Total Delay (ZTD) or Integrated Water Vapour (IWV) estimates to enhance the quality of their forecasts. Usually, the ZTD is assimilated into the NWP models on 3- hourly to 6-hourly intervals but with the advancement of NWP models towards higher update rates e.g. 1-hourly cycling in the Rapid Update Cycle (RUC) NWP, it has become of high interest to estimate ZTD on sub-hourly intervals. In turn, this imposes requirements related to the timeliness and accuracy of the ZTD estimates and has lead to a development of various strategies to process GNSS observations to obtain ZTD with different latencies and accuracies. Using present GNSS products and tools, ZTD can be estimated in real-time (RT), near real-time (NRT) and post-processing (PP) modes. The aim of this study is to provide an overview and accuracy assessment of various RT, NRT, and PP IWV estimation systems and comparing their achieved accuracy with the user requirements for GNSS meteorology. The NRT systems are based on Bernese GPS Software 5.0 and use a double-differencing strategy whereas the PP system is based on the Bernese GNSS Software 5.2 using the precise point positioning (PPP) strategy. The RT systems are based on the BKG Ntrip Client 2.7 and the PPPWizard both using PPP. The PPP-Wizard allows integer ambiguity resolution at a single station and therefore the effect of fixing integer ambiguities on ZTD estimates will also be presented
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