349 research outputs found
Simultaneous quantification of antioxidants paraxanthine and caffeine in human saliva by electrochemical sensing for CYP1A2 phenotyping
The enzyme CYP1A2 is responsible for the metabolism of numerous antioxidants in the body, including caffeine, which is transformed into paraxanthine, its main primary metabolite. Both molecules are known for their antioxidant and pro-oxidant characteristics, and the paraxanthine-to-caffeine molar ratio is a widely accepted metric for CYP1A2 phenotyping, to optimize dose\u2013 response effects in individual patients. We developed a simple, cheap and fast electrochemical based method for the simultaneous quantification of paraxanthine and caffeine in human saliva, by differential pulse voltammetry, using an anodically pretreated glassy carbon electrode. Cyclic voltammetry experiments revealed for the first time that the oxidation of paraxanthine is diffusion controlled with an irreversible peak at ca. +1.24 V (vs. Ag/AgCl) in a 0.1 M H2 SO4 solution, and that the mechanism occurs via the transfer of two electrons and two protons. The simultaneous quantification of paraxanthine and caffeine was demonstrated in 0.1 M H2 SO4 and spiked human saliva samples. In the latter case, limits of detection of 2.89 \ub5M for paraxanthine and 5.80 \ub5M for caffeine were obtained, respectively. The sensor is reliable, providing a relative standard deviation within 7% (n = 6). Potential applicability of the sensing platform was demonstrated by running a small scale trial on five healthy volunteers, with simultaneous quantification by differential pulse voltammetry (DPV) of paraxanthine and caffeine in saliva samples collected at 1, 3 and 6 h postdose administration. The results were validated by ultra-high pressure liquid chromatography and shown to have a high correlation factor (r = 0.994)
Pd@TiO2/carbon nanohorn electrocatalysts: reversible CO2 hydrogenation to formic acid
Direct conversion of carbon dioxide to formic acid at thermodynamic equilibrium is an advantage of enzymatic catalysis, hardly replicated by synthetic analogs, but of high priority for carbon-neutral energy schemes. The bio-mimetic potential of totally inorganic Pd@TiO2 nanoparticles is envisioned herein in combination with Single Walled Carbon NanoHorns (SWCNHs). The high surface nano-carbon entanglement templates a wide distribution of \u201chard-soft\u201d bimetallic sites where the small Pd nanoparticles (1.5 nm) are shielded within the TiO2 phase (Pd@TiO2), while being electrically wired to the electrode by the nanocarbon support. This hybrid electrocatalyst activates CO2 reduction to formic acid at near zero overpotential in the aqueous phase (onset potential at E < 120.05 V vs. RHE, pH = 7.4), while being able to evolve hydrogen via sequential formic acid dehydrogenation. The net result hints at a unique CO2 \u201ccircular catalysis\u201d where formic acid versus H2 selectivity is addressable by flow-reactor technology
The impact of urea-induced unfolding on the redox process of immobilised cytochrome c
We have studied the effect of urea-induced unfolding on the electron transfer process of yeast iso-1-cytochrome c and its mutant K72AK73AK79A adsorbed on electrodes coated by mixed 11-mercapto-1-undecanoic acid/11-mercapto-1-undecanol self-assembled monolayers. Electrochemical measurements, complemented by surface enhanced resonance Raman studies, indicate two distinct states of the adsorbed proteins that mainly differ with respect to the ligation pattern of the haem. The native state, in which the haem is axially coordinated by Met80 and His18, displays a reduction potential that slightly shifts to negative values with increasing urea concentration. At urea concentrations higher than 6 M, a second state prevails in which the Met80 ligand is replaced by an additional histidine residue. This structural change in the haem pocket is associated with an approximately 0.4 V shift of the reduction potential to negative values. These two states were found for both the wild-type protein and the mutant in which lysine residues 72, 73 and 79 had been substituted by alanines. The analysis of the reduction potentials, the reaction enthalpies and entropies as well as the rate constants indicates that these three lysine residues have an important effect on stabilising the protein structure in the adsorbed state and facilitating the electron transfer dynamics
Simultaneous Planck, Swift, and Fermi observations of X-ray and gamma-ray selected blazars
We present simultaneous Planck, Swift, Fermi, and ground-based data for 105
blazars belonging to three samples with flux limits in the soft X-ray, hard
X-ray, and gamma-ray bands. Our unique data set has allowed us to demonstrate
that the selection method strongly influences the results, producing biases
that cannot be ignored. Almost all the BL Lac objects have been detected by
Fermi-LAT, whereas ~40% of the flat-spectrum radio quasars (FSRQs) in the
radio, soft X-ray, and hard X-ray selected samples are still below the
gamma-ray detection limit even after integrating 27 months of Fermi-LAT data.
The radio to sub-mm spectral slope of blazars is quite flat up to ~70GHz, above
which it steepens to ~-0.65. BL Lacs have significantly flatter spectra
than FSRQs at higher frequencies. The distribution of the rest-frame
synchrotron peak frequency (\nupS) in the SED of FSRQs is the same in all the
blazar samples with =10^13.1 Hz, while the mean inverse-Compton peak
frequency, , ranges from 10^21 to 10^22 Hz. The distributions of \nupS
and of \nupIC of BL Lacs are much broader and are shifted to higher energies
than those of FSRQs and strongly depend on the selection method. The Compton
dominance of blazars ranges from ~0.2 to ~100, with only FSRQs reaching values
>3. Its distribution is broad and depends strongly on the selection method,
with gamma-ray selected blazars peaking at ~7 or more, and radio-selected
blazars at values ~1, thus implying that the assumption that the blazar power
is dominated by high-energy emission is a selection effect. Simple SSC models
cannot explain the SEDs of most of the gamma-ray detected blazars in all
samples. The SED of the blazars that were not detected by Fermi-LAT may instead
be consistent with SSC emission. Our data challenge the correlation between
bolometric luminosity and \nupS predicted by the blazar sequence.Comment: Version accepted by A&A. Joint Planck, Swift, and Fermi
collaborations pape
Planck 2013 results. XXII. Constraints on inflation
We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be ns = 0:9603 _ 0:0073, ruling out exact scale invariance at over 5_: Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0:11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models, preferring potentials with V00 < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n _ 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dns=dln k = 0:0134 _ 0:0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by __2 e_ _ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the _2 e_ by approximately 4 as a result of slightly lowering the theoretical prediction for the ` <_ 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions
A coherent polarimeter array for the Large Scale Polarization Explorer balloon experiment
We discuss the design and expected performance of STRIP (STRatospheric
Italian Polarimeter), an array of coherent receivers designed to fly on board
the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP
focal plane array comprises 49 elements in Q band and 7 elements in W-band
using cryogenic HEMT low noise amplifiers and high performance waveguide
components. In operation, the array will be cooled to 20 K and placed in the
focal plane of a meter telescope providing an angular resolution of
degrees. The LSPE experiment aims at large scale, high sensitivity
measurements of CMB polarization, with multi-frequency deep measurements to
optimize component separation. The STRIP Q-band channel is crucial to
accurately measure and remove the synchrotron polarized component, while the
W-band channel, together with a bolometric channel at the same frequency,
provides a crucial cross-check for systematic effects.Comment: In press on the Proceedings of the SPIE Conference Astronomical
Telescopes + instrumentation 2012, Amsterdam, paper 8446-27
BeyondPlanck II. CMB map-making through Gibbs sampling
We present a Gibbs sampling solution to the map-making problem for CMB
measurements, building on existing destriping methodology. Gibbs sampling
breaks the computationally heavy destriping problem into two separate steps;
noise filtering and map binning. Considered as two separate steps, both are
computationally much cheaper than solving the combined problem. This provides a
huge performance benefit as compared to traditional methods, and allows us for
the first time to bring the destriping baseline length to a single sample. We
apply the Gibbs procedure to simulated Planck 30 GHz data. We find that gaps in
the time-ordered data are handled efficiently by filling them with simulated
noise as part of the Gibbs process. The Gibbs procedure yields a chain of map
samples, from which we may compute the posterior mean as a best-estimate map.
The variation in the chain provides information on the correlated residual
noise, without need to construct a full noise covariance matrix. However, if
only a single maximum-likelihood frequency map estimate is required, we find
that traditional conjugate gradient solvers converge much faster than a Gibbs
sampler in terms of total number of iterations. The conceptual advantages of
the Gibbs sampling approach lies in statistically well-defined error
propagation and systematic error correction, and this methodology forms the
conceptual basis for the map-making algorithm employed in the BeyondPlanck
framework, which implements the first end-to-end Bayesian analysis pipeline for
CMB observations.Comment: 11 pages, 10 figures. All BeyondPlanck products and software will be
released publicly at http://beyondplanck.science during the online release
conference (November 18-20, 2020). Connection details will be made available
at the same website. Registration is mandatory for the online tutorial, but
optional for the conferenc
BeyondPlanck VII. Bayesian estimation of gain and absolute calibration for CMB experiments
We present a Bayesian calibration algorithm for CMB observations as
implemented within the global end-to-end BeyondPlanck (BP) framework, and apply
this to the Planck Low Frequency Instrument (LFI) data. Following the most
recent Planck analysis, we decompose the full time-dependent gain into a sum of
three orthogonal components: One absolute calibration term, common to all
detectors; one time-independent term that can vary between detectors; and one
time-dependent component that is allowed to vary between one-hour pointing
periods. Each term is then sampled conditionally on all other parameters in the
global signal model through Gibbs sampling. The absolute calibration is sampled
using only the orbital dipole as a reference source, while the two relative
gain components are sampled using the full sky signal, including the orbital
and Solar CMB dipoles, CMB fluctuations, and foreground contributions. We
discuss various aspects of the data that influence gain estimation, including
the dipole/polarization quadrupole degeneracy and anomalous jumps in the
instrumental gain. Comparing our solution to previous pipelines, we find good
agreement in general, with relative deviations of -0.84% (-0.67%) for 30 GHz,
-0.14% (0.02%) for 44 GHz and -0.69% (-0.08%) for 70 GHz, compared to Planck
2018 (NPIPE). The deviations we find are within expected error bounds, and we
attribute them to differences in data usage and general approach between the
pipelines. In particular, the BP calibration is performed globally, resulting
in better inter-frequency consistency. Additionally, WMAP observations are used
actively in the BP analysis, which breaks degeneracies in the Planck data set
and results in better agreement with WMAP. Although our presentation and
algorithm are currently oriented toward LFI processing, the procedure is fully
generalizable to other experiments.Comment: 18 pages, 15 figures. All BeyondPlanck products and software will be
released publicly at http://beyondplanck.science during the online release
conference (November 18-20, 2020). Connection details will be made available
at the same website. Registration is mandatory for the online tutorial, but
optional for the conferenc
BeyondPlanck XII. Cosmological parameter constraints with end-to-end error propagation
We present cosmological parameter constraints as estimated using the Bayesian
BeyondPlanck (BP) analysis framework. This method supports seamless end-to-end
error propagation from raw time-ordered data to final cosmological parameters.
As a first demonstration of the method, we analyze time-ordered Planck LFI
observations, combined with selected external data (WMAP 33-61GHz, Planck HFI
DR4 353 and 857GHz, and Haslam 408MHz) in the form of pixelized maps which are
used to break critical astrophysical degeneracies. Overall, all results are
generally in good agreement with previously reported values from Planck 2018
and WMAP, with the largest relative difference for any parameter of about 1
sigma when considering only temperature multipoles between 29<l<601. In cases
where there are differences, we note that the BP results are generally slightly
closer to the high-l HFI-dominated Planck 2018 results than previous analyses,
suggesting slightly less tension between low and high multipoles. Using low-l
polarization information from LFI and WMAP, we find a best-fit value of
tau=0.066 +/- 0.013, which is higher than the low value of tau=0.051 +/- 0.006
derived from Planck 2018 and slightly lower than the value of 0.069 +/- 0.011
derived from joint analysis of official LFI and WMAP products. Most
importantly, however, we find that the uncertainty derived in the BP processing
is about 30% larger than when analyzing the official products, after taking
into account the different sky coverage. We argue that this is due to
marginalizing over a more complete model of instrumental and astrophysical
parameters, and this results in both more reliable and more rigorously defined
uncertainties. We find that about 2000 Monte Carlo samples are required to
achieve robust convergence for low-resolution CMB covariance matrix with 225
independent modes.Comment: 13 pages, 10 figure
BeyondPlanck X. Planck LFI frequency maps with sample-based error propagation
We present Planck LFI frequency sky maps derived within the BeyondPlanck
framework. This framework draws samples from a global posterior distribution
that includes instrumental, astrophysical and cosmological parameters, and the
main product is an entire ensemble of frequency sky map samples. This ensemble
allows for computationally convenient end-to-end propagation of low-level
instrumental uncertainties into higher-level science products. We show that the
two dominant sources of LFI instrumental systematic uncertainties are
correlated noise and gain fluctuations, and the products presented here support
- for the first time - full Bayesian error propagation for these effects at
full angular resolution. We compare our posterior mean maps with traditional
frequency maps delivered by the Planck collaboration, and find generally good
agreement. The most important quality improvement is due to significantly lower
calibration uncertainties in the new processing, as we find a fractional
absolute calibration uncertainty at 70 GHz of , which is nominally 40 times smaller than that reported by Planck
2018. However, the original Planck 2018 estimate has a non-trivial statistical
interpretation, and this further illustrates the advantage of the new framework
in terms of producing self-consistent and well-defined error estimates of all
involved quantities without the need of ad hoc uncertainty contributions. We
describe how low-resolution data products, including dense pixel-pixel
covariance matrices, may be produced directly from the posterior samples
without the need for computationally expensive analytic calculations or
simulations. We conclude that posterior-based frequency map sampling provides
unique capabilities in terms of low-level systematics modelling and error
propagation, and may play an important role for future CMB B-mode experiments.
(Abridged.)Comment: 32 pages, 23 figures, data available from
https://www.cosmoglobe.uio.no
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