1,555 research outputs found
Orbits for eighteen visual binaries and two double-line spectroscopic binaries observed with HRCAM on the CTIO SOAR 4m telescope, using a new Bayesian orbit code based on Markov Chain Monte Carlo
We present orbital elements and mass sums for eighteen visual binary stars of
spectral types B to K (five of which are new orbits) with periods ranging from
20 to more than 500 yr. For two double-line spectroscopic binaries with no
previous orbits, the individual component masses, using combined astrometric
and radial velocity data, have a formal uncertainty of ~0.1 MSun. Adopting
published photometry, and trigonometric parallaxes, plus our own measurements,
we place these objects on an H-R diagram, and discuss their evolutionary
status. These objects are part of a survey to characterize the binary
population of stars in the Southern Hemisphere, using the SOAR 4m
telescope+HRCAM at CTIO. Orbital elements are computed using a newly developed
Markov Chain Monte Carlo algorithm that delivers maximum likelihood estimates
of the parameters, as well as posterior probability density functions that
allow us to evaluate the uncertainty of our derived parameters in a robust way.
For spectroscopic binaries, using our approach, it is possible to derive a
self-consistent parallax for the system from the combined astrometric plus
radial velocity data ("orbital parallax"), which compares well with the
trigonometric parallaxes. We also present a mathematical formalism that allows
a dimensionality reduction of the feature space from seven to three search
parameters (or from ten to seven dimensions - including parallax - in the case
of spectroscopic binaries with astrometric data), which makes it possible to
explore a smaller number of parameters in each case, improving the
computational efficiency of our Markov Chain Monte Carlo code.Comment: 32 pages, 9 figures, 6 tables. Detailed Appendix with methodology.
Accepted by The Astronomical Journa
Coupling of morphology to surface transport in ion-beam irradiated surfaces. I. Oblique incidence
We propose and study a continuum model for the dynamics of amorphizable
surfaces undergoing ion-beam sputtering (IBS) at intermediate energies and
oblique incidence. After considering the current limitations of more standard
descriptions in which a single evolution equation is posed for the surface
height, we overcome (some of) them by explicitly formulating the dynamics of
the species that transport along the surface, and by coupling it to that of the
surface height proper. In this we follow recent proposals inspired by
``hydrodynamic'' descriptions of pattern formation in aeolian sand dunes and
ion-sputtered systems. From this enlarged model, and by exploiting the
time-scale separation among various dynamical processes in the system, we
derive a single height equation in which coefficients can be related to
experimental parameters. This equation generalizes those obtained by previous
continuum models and is able to account for many experimental features of
pattern formation by IBS at oblique incidence, such as the evolution of the
irradiation-induced amorphous layer, transverse ripple motion with non-uniform
velocity, ripple coarsening, onset of kinetic roughening and other.
Additionally, the dynamics of the full two-field model is compared with that of
the effective interface equation.Comment: 23 pages, 14 figures. Movies of figures 6, 7, and 8 available at
http://gisc.uc3m.es/~javier/Movies
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Intrathecal enzyme replacement for Hurler syndrome: biomarker association with neurocognitive outcomes.
PurposeAbnormalities in cerebrospinal fluid (CSF) have been reported in Hurler syndrome, a fatal neurodegenerative lysosomal disorder. While no biomarker has predicted neurocognitive response to treatment, one of these abnormalities, glycosaminoglycan nonreducing ends (NREs), holds promise to monitor therapeutic efficacy. A trial of intrathecal enzyme replacement therapy (ERT) added to standard treatment enabled tracking of CSF abnormalities, including NREs. We evaluated safety, biomarker response, and neurocognitive correlates of change.MethodsIn addition to intravenous ERT and hematopoietic cell transplantation, patients (N = 24) received intrathecal ERT at four peritransplant time points; CSF was evaluated at each point. Neurocognitive functioning was quantified at baseline, 1 year, and 2 years posttransplant. Changes in CSF biomarkers and neurocognitive function were evaluated for an association.ResultsOver treatment, there were significant decreases in CSF opening pressure, biomarkers of disease activity, and markers of inflammation. Percent decrease in NRE from pretreatment to final intrathecal dose posttransplant was positively associated with percent change in neurocognitive score from pretreatment to 2 years posttransplant.ConclusionIntrathecal ERT was safe and, in combination with standard treatment, was associated with reductions in CSF abnormalities. Critically, we report evidence of a link between a biomarker treatment response and neurocognitive outcome in Hurler syndrome
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Selective photocatalytic CO reduction in water through anchoring of a molecular Ni catalyst on CdS nanocrystals
Photocatalytic conversion of CO into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H generation. In this work, we demonstrate selective visible-light-driven CO reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO reduction over H evolution in aqueous solution.Christian Doppler Research Association, OMV group, Isaac Newton Trust, the German Research Foundation, the World Premier International Research Center Initiative, MEXT, Japa
Wavelength Tunability of Ion-bombardment Induced Ripples on Sapphire
A study of ripple formation on sapphire surfaces by 300-2000 eV Ar+ ion
bombardment is presented. Surface characterization by in-situ synchrotron
grazing incidence small angle x-ray scattering and ex-situ atomic force
microscopy is performed in order to study the wavelength of ripples formed on
sapphire (0001) surfaces. We find that the wavelength can be varied over a
remarkably wide range-nearly two orders of magnitude-by changing the ion
incidence angle. Within the linear theory regime, the ion induced viscous flow
smoothing mechanism explains the general trends of the ripple wavelength at low
temperature and incidence angles larger than 30. In this model, relaxation is
confined to a few-nm thick damaged surface layer. The behavior at high
temperature suggests relaxation by surface diffusion. However, strong smoothing
is inferred from the observed ripple wavelength near normal incidence, which is
not consistent with either surface diffusion or viscous flow relaxation.Comment: Revtex4, 19 pages, 10 figures with JPEG forma
Residual-based scheme for detection and characterization of faults in lithium-ion batteries
This work proposes a real-time scheme to monitor the occurrence of faults and perform fault characterization. Faults, in this context, correspond to changes in the parameters of the system being monitored. The method relies on the concept of Analytical Redundancy Relation (ARR), which can be defined as the evaluation of the mathematical constraints of the physical model of the system given the real, noisy measurements. The algorithm consists of two modules: a detection strategy that relies on the regular application of an ARR-based hypothesis test in discrete time-steps; and an optimization procedure to estimate the changes undergone after a fault. By selecting a set of feasible solutions from the output of the optimization algorithm, the method also sheds some light on the uncertainty associated to the estimated quantities. The methodology is tested on simulated data of lithium-ion batteries in unmanned aerial vehicles
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