12,259 research outputs found
A novel CMB polarization likelihood package for large angular scales built from combined WMAP and Planck LFI legacy maps
We present a CMB large-scale polarization dataset obtained by combining WMAP
Ka, Q and V with Planck 70 GHz maps. We employ the legacy frequency maps
released by the WMAP and Planck collaborations and perform our own Galactic
foreground mitigation technique, which relies on Planck 353 GHz for polarized
dust and on Planck 30 GHz and WMAP K for polarized synchrotron. We derive a
single, optimally-noise-weighted, low-residual-foreground map and the
accompanying noise covariance matrix. These are shown, through
analysis, to be robust over an ample collection of Galactic masks. We use this
dataset, along with the Planck legacy Commander temperature solution, to build
a pixel-based low-resolution CMB likelihood package, whose robustness we test
extensively with the aid of simulations, finding excellent consistency. Using
this likelihood package alone, we constrain the optical depth to reionazation
at C.L., on 54\% of the sky. Adding the
Planck high- temperature and polarization legacy likelihood, the Planck
lensing likelihood and BAO observations we find
in a full CDM exploration. The
latter bounds are slightly less constraining than those obtained employing
\Planck\ HFI CMB data for large angle polarization, that only include EE
correlations. Our bounds are based on a largely independent dataset that does
include also TE correlations. They are generally well compatible with Planck
HFI preferring slightly higher values of . We make the low-resolution
Planck and WMAP joint dataset publicly available along with the accompanying
likelihood code.Comment: The WMAP+LFI likelihood module is available on
\http://www.fe.infn.it/u/pagano/low_ell_datasets/wmap_lfi_legacy
Interplay between bending and stretching in carbon nanoribbons
We investigate the bending properties of carbon nanoribbons by combining
continuum elasticity theory and tight-binding atomistic simulations. First, we
develop a complete analysis of a given bended configuration through continuum
mechanics. Then, we provide by tight-binding calculations the value of the
bending rigidity in good agreement with recent literature. We discuss the
emergence of a stretching field induced by the full atomic-scale relaxation of
the nanoribbon architecture. We further prove that such an in-plane strain
field can be decomposed into a first contribution due to the actual bending of
the sheet and a second one due to edge effects.Comment: 5 pages, 6 figure
Nanofriction behavior of cluster-assembled carbon films
We have characterized the frictional properties of nanostructured (ns) carbon
films grown by Supersonic Cluster Beam Deposition (SCBD) via an Atomic
Force-Friction Force Microscope (AFM-FFM). The experimental data are discussed
on the basis of a modified Amonton's law for friction, stating a linear
dependence of friction on load plus an adhesive offset accounting for a finite
friction force in the limit of null total applied load. Molecular Dynamics
simulations of the interaction of the AFM tip with the nanostructured carbon
confirm the validity of the friction model used for this system. Experimental
results show that the friction coefficient is not influenced by the
nanostructure of the films nor by the relative humidity. On the other hand the
adhesion coefficient depends on these parameters.Comment: 22 pages, 6 figures, RevTex
Orbital dynamics of "smart dust" devices with solar radiation pressure and drag
This paper investigates how perturbations due to asymmetric solar radiation pressure, in the presence of Earth shadow, and atmospheric drag can be balanced to obtain long-lived Earth centred orbits for swarms of micro-scale 'smart dust' devices, without the use of active control. The secular variation of Keplerian elements is expressed analytically through an averaging technique. Families of solutions are then identified where Sun-synchronous apse-line precession is achieved passively to maintain asymmetric solar radiation pressure. The long-term orbit evolution is characterized by librational motion, progressively decaying due to the non-conservative effect of atmospheric drag. Long-lived orbits can then be designed through the interaction of energy gain from asymmetric solar radiation pressure and energy dissipation due to drag. In this way, the usual short drag lifetime of such high area-to-mass spacecraft can be greatly extended (and indeed selected). In addition, the effect of atmospheric drag can be exploited to ensure the rapid end-of-life decay of such devices, thus preventing long-lived orbit debris
Numerical simulation of oil-water two-phase flow in a horizontal duct with a Venturi flow meter
The progressive depletion of on-shore and light-oil reserves is forcing an increased use of transitional and heavy oils, which implies new challenges both during the extraction and the transportation. Focusing on the latter, a technique to reduce the pressure drop is water injection in the oil stream to create the so-called core annular flow (CAF), a flow regime with an oil core enveloped in a water annulus wetting the pipe wall, so that the apparent viscosity of the mixture is considerably reduced. Behaviour of CAF in ducts with non-uniform sections is still under research. This work is devoted to a CFD investigation about the pressure drop, pressure gradients, velocity profiles and in situ volume fractions in a duct including a Venturi flow meter. Unsteady RANS simulations were carried out using the Volume-Of-Fluid interFoam solver of OpenFOAM. Numerical results were experimentally validated for oil superficial velocities in the range 0.25-0.75 m/s and water superficial velocities in the range 0.44-1.10 m/s and comparisons between different approaches and sensitivity analyses were performed. Satisfactory agreement was found for the pressure drop and pressure gradients, and also for the in situ volume fraction with respect to the predictions of the Arney correlation
Optimized Large-Scale CMB Likelihood And Quadratic Maximum Likelihood Power Spectrum Estimation
We revisit the problem of exact CMB likelihood and power spectrum estimation
with the goal of minimizing computational cost through linear compression. This
idea was originally proposed for CMB purposes by Tegmark et al.\ (1997), and
here we develop it into a fully working computational framework for large-scale
polarization analysis, adopting \WMAP\ as a worked example. We compare five
different linear bases (pixel space, harmonic space, noise covariance
eigenvectors, signal-to-noise covariance eigenvectors and signal-plus-noise
covariance eigenvectors) in terms of compression efficiency, and find that the
computationally most efficient basis is the signal-to-noise eigenvector basis,
which is closely related to the Karhunen-Loeve and Principal Component
transforms, in agreement with previous suggestions. For this basis, the
information in 6836 unmasked \WMAP\ sky map pixels can be compressed into a
smaller set of 3102 modes, with a maximum error increase of any single
multipole of 3.8\% at , and a maximum shift in the mean values of a
joint distribution of an amplitude--tilt model of 0.006. This
compression reduces the computational cost of a single likelihood evaluation by
a factor of 5, from 38 to 7.5 CPU seconds, and it also results in a more robust
likelihood by implicitly regularizing nearly degenerate modes. Finally, we use
the same compression framework to formulate a numerically stable and
computationally efficient variation of the Quadratic Maximum Likelihood
implementation that requires less than 3 GB of memory and 2 CPU minutes per
iteration for , rendering low- QML CMB power spectrum
analysis fully tractable on a standard laptop.Comment: 13 pages, 13 figures, accepted by ApJ
Characterization of plug and slug multiphase flows by means of image analysis
Multiphase flow is involved in a wide range of applications, and among the flow patterns that a multiphase mixture may develop in its flow, the intermittent one is particularly complex both in behaviour and for analysis. Experimental analysis about the characteristics of the flow structures (plugs and slugs) is therefore still mandatory for a detailed description of the phenomenon. In this work an image-based technique for the determination of the plug/slug characteristics was applied to air-water, oil-air and three-phase oil-water-air flows in horizontal ducts with different diameters, with superficial velocities of the phases in the range 0.2-2.1 m/s. The technique is based on the acquisition of a video of the flow and the conversion of each frame (or part of it) into a Boolean signal, in which the non-zero part represents the structure of interest. Concatenation of such signals along the singleton dimension creates a space-time representation of the flow, from which information about the flow velocities, the structure lengths and frequencies and the void fraction can be extracted. Focus here is particularly on the performances of the technique when using high-speed videos. The results were also compared with the predictions of the drift-flux model
SPARC is a new myeloid-derived suppressor cell marker licensing suppressive activities
Myeloid-derived suppressor cells (MDSC) are well-known key negative regulators of the immune response during tumor growth, however scattered is the knowledge of their capacity to influence and adapt to the different tumor microenvironments and of the markers that identify those capacities. Here we show that the secreted protein acidic and rich in cysteine (SPARC) identifies in both human and mouse MDSC with immune suppressive capacity and pro-tumoral activities including the induction of epithelial-to-mesenchymal transition (EMT) and angiogenesis. In mice the genetic deletion of SPARC reduced MDSC immune suppression and reverted EMT. Sparcâ/â MDSC were less suppressive overall and the granulocytic fraction was more prone to extrude neutrophil extracellular traps (NET). Surprisingly, arginase-I and NOS2, whose expression can be controlled by STAT3, were not down-regulated in Sparcâ/â MDSC, although less suppressive than wild type (WT) counterpart. Flow cytometry analysis showed equal phosphorylation of STAT3 but reduced ROS production that was associated with reduced nuclear translocation of the NF-kB p50 subunit in Sparcâ/â than WT MDSC. The limited p50 in nuclei reduce the formation of the immunosuppressive p50:p50 homodimers in favor of the p65:p50 inflammatory heterodimers. Supporting this hypothesis, the production of TNF by Sparcâ/â MDSC was significantly higher than by WT MDSC. Although associated with tumor-induced chronic inflammation, TNF, if produced at high doses, becomes a key factor in mediating tumor rejection. Therefore, it is foreseeable that an unbalance in TNF production could skew MDSC toward an inflammatory, anti-tumor phenotype. Notably, TNF is also required for inflammation-driven NETosis. The high level of TNF in Sparcâ/â MDSC might explain their increased spontaneous NET formation as that we detected both in vitro and in vivo, in association with signs of endothelial damage. We propose SPARC as a new potential marker of MDSC, in both human and mouse, with the additional feature of controlling MDSC suppressive activity while preventing an excessive inflammatory state through the control of NF-kB signaling pathway
Convective condensation of R134a and R1234ze(E) inside microfin tube
Environmental concerns are forcing the replacement of the commonly used refrigerants and finding new fluids is a top priority. The hydro-fluoro-olefin (HFO) R1234ze(E), because of its smaller global warming potential (GWP) and shorter atmospheric lifetime, replaced R134a. Accordingly, for HVAC systems design, a detailed knowledge of the thermo-fluid-dynamic characteristics of the fluids and reliable predictive models are required. To improve the understanding, R134a and R1234ze(E) were employed in convective condensation experiments (saturation temperature Tsat = 35°C, mean quality xm = 0.1~0.9, quality changes Îx = 0.05~0.6, mass flux G = 43~444 kg·m-2s-1) inside a microfin tube (outer
diameter D = 9.52 mm, fin number n = 60, fin height H = 0.2 mm). The results were used for two goals: the former is the comparison of the heat transfer features of the two fluids, while the latter aims at testing the performance of prediction models available in the open literature. At the saturation temperature T = 35°C, the two fluids show small differences in the thermal properties so that, as expected, the experiments highlighted a very similar behavior in the typical operating conditions of HVAC systems. In fact, for all the operating conditions marginal differences were observed in the pressure drop, the heat transfer coefficient and the flow pattern maps. The issue of prediction reliability, however, is still open. Actually, not all the models achieving good results for R134a show the same performance for R1234ze(E), especially for the pressure drop
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