11,289 research outputs found
Improved CMB anisotropy constraints on primordial magnetic fields from the post-recombination ionization history
We investigate the impact of a stochastic background of Primordial Magnetic
Fields (PMF) generated before recombination on the ionization history of the
Universe and on the Cosmic Microwave Background radiation (CMB).
Pre-recombination PMFs are dissipated during recombination and reionization via
decaying MHD turbulence and ambipolar diffusion. This modifies the local matter
and electron temperatures and thus affects the ionization history and Thomson
visibility function. We use this effect to constrain PMFs described by a
spectrum of power-law type, extending our previous study (based on a
scale-invariant spectrum) to arbitrary spectral index. We derive upper bounds
on the integrated amplitude of PMFs due to the separate effect of ambipolar
diffusion and MHD decaying turbulence and their combination. We show that
ambipolar diffusion is relevant for whereas for MHD
turbulence is more important. The bound marginalized over the spectral index on
the integrated amplitude of PMFs with a sharp cut-off is nG. We discuss the quantitative relevance of the assumptions on
the damping mechanism and the comparison with previous bounds.Comment: 11 pages, 21 figures. Minor updates to match the published versio
advances in mechanical clinching employment of a rotating tool
Abstract In the recent years, high efforts have been spent concerning the development of fast mechanical joining processes. This is due to the growing employment of materials that are difficult to weld and hybrid structures involving different materials. Mechanical clinching enables to solving the major concerns in this field. However, the formability of the materials represent a limitation to the successful employment of the process. The present research illustrates a new concept of clinching, namely friction clinching that differs from the conventional process by the employment of a rotating tool, which heats up the sheet (by friction) during the process leading to an increase in the material formability. Preliminary tests were performed to verify the feasibility of the process and determine a sound processing window. The process was applied to join thin aluminium sheets and Carbon Fibre Reinforced Plastic (CFRP) laminate. Morphological analysis and mechanical characterization of the joints was performed in order to evaluate the suitability of such the rotating tool to increase the material formability and thus the aluminium sheet integrity. According to the achieved results, the employment of the rotating tool enables to avoid crack formation in the metal sheet, improves the material flow and reduces the joining forces
SiPM and front-end electronics development for Cherenkov light detection
The Italian Institute of Nuclear Physics (INFN) is involved in the
development of a demonstrator for a SiPM-based camera for the Cherenkov
Telescope Array (CTA) experiment, with a pixel size of 66 mm. The
camera houses about two thousands electronics channels and is both light and
compact. In this framework, a R&D program for the development of SiPMs suitable
for Cherenkov light detection (so called NUV SiPMs) is ongoing. Different
photosensors have been produced at Fondazione Bruno Kessler (FBK), with
different micro-cell dimensions and fill factors, in different geometrical
arrangements. At the same time, INFN is developing front-end electronics based
on the waveform sampling technique optimized for the new NUV SiPM. Measurements
on 11 mm, 33 mm, and 66 mm NUV SiPMs
coupled to the front-end electronics are presentedComment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Cosmological Parameters from a re-analysis of the WMAP-7 low resolution maps
Cosmological parameters from WMAP 7 year data are re-analyzed by substituting
a pixel-based likelihood estimator to the one delivered publicly by the WMAP
team. Our pixel based estimator handles exactly intensity and polarization in a
joint manner, allowing to use low-resolution maps and noise covariance matrices
in at the same resolution, which in this work is 3.6. We
describe the features and the performances of the code implementing our
pixel-based likelihood estimator. We perform a battery of tests on the
application of our pixel based likelihood routine to WMAP publicly available
low resolution foreground cleaned products, in combination with the WMAP
high- likelihood, reporting the differences on cosmological parameters
evaluated by the full WMAP likelihood public package. The differences are not
only due to the treatment of polarization, but also to the marginalization over
monopole and dipole uncertainties implemented in the WMAP 7 year pixel
likelihood code for temperature. The credible central value for the
cosmological parameters change below the 1 level with respect to the
evaluation by the full WMAP 7 year likelihood code, with the largest difference
in a shift to smaller values of the scalar spectral index .Comment: Revised to match the version on press in MNRAS. Different
interpretation of differences vs WMAP 7. 10 pages, 6 tables, 8 figure
Innovative nanomaterials for fuel cells fed with biogas
Challenges on sustainability promote research policy focused on renewable-energy technology development in order to enhance global energy security, local energy independence, environmental protection and economic growth. Biomass resources offer renewable energies that can play a key role in the current global strategies for reducing greenhouse gas emissions by partially replacing fossil fuels. The conversion of biomass chemical energy into electrical energy and cogenerated heat can be obtained by fuel cells. In particular, molten carbonate fuel cell (MCFC)
is the most suitable device for bioenergy production because it can be fed directly with biogas, whose primary constituents all improve the performance of the cell.
However hydrogen sulfide, which is the main biogas impurity, poisons the traditional nickel based anode, affecting the power and the endurance of the cell. In order to overcome this problem, an innovative anode material that resists against the sulfide corrosions has been developed. This material, made of a nanostructured and porous nickel support covered with a thin layer of ceria, exhibits high sulfur tolerance and recovering capability
Innovative nanomaterials for fuel cells fed with biogas
Challenges on sustainability promote research policy focused on renewable-energy technology development in order to enhance global energy security, local energy independence, environmental protection and economic growth. Biomass resources offer renewable energies that can play a key role in the current global strategies for reducing greenhouse gas emissions by partially replacing fossil fuels. The conversion of biomass chemical energy into electrical energy and cogenerated heat can be obtained by fuel cells. In particular, molten carbonate fuel cell (MCFC)
is the most suitable device for bioenergy production because it can be fed directly with biogas, whose primary constituents all improve the performance of the cell.
However hydrogen sulfide, which is the main biogas impurity, poisons the traditional nickel based anode, affecting the power and the endurance of the cell. In order to overcome this problem, an innovative anode material that resists against the sulfide corrosions has been developed. This material, made of a nanostructured and porous nickel support covered with a thin layer of ceria, exhibits high sulfur tolerance and recovering capability
Leaf water diffusion dynamics in vivo through a sub-terahertz portable imaging system
The development of terahertz based technology has given the opportunity for the realization of non destructive techniques capable of gaining meaningful information on delicate systems such as biological samples. Here, the health status of leaves in vivo has been monitored through a portable terahertz imaging system. The data have been extracted and analysed from the images acquired and compared with analogous results reported in the literature on similar systems. The possibilty of extracting additional information from the images regarding leaf details has also been explored
Cosmological effects of the Galileon term in Scalar-Tensor Theories
We study the cosmological effects of a Galileon term in scalar-tensor
theories of gravity. The subset of scalar-tensor theories considered are
characterized by a non-minimal coupling , a kinetic term with
arbitrary sign with , a potential
, and a Galileon term . In addition to the modified dynamics, the Galileon term provides a
screening mechanism to potentially reconcile the models with General Relativity
predictions inside a Vainshtein radius. Thanks to the Galileon term, the
stability conditions, namely ghost and Laplacian instabilities, in the branch
with a negative kinetic term () are fulfilled for a large volume of the
parameter space. Solving numerically the background evolution and linear
perturbations, we derive the constraints on the cosmological parameters in
presence of a Galileon term for different combination of the cosmic microwave
background (CMB) data from Planck, baryon acoustic oscillations (BAO)
measurements from BOSS, and supernovae from the Pantheon compilation. We find
that the Galileon term alters the dynamics of all the studied cases. For a
standard kinetic term (), we find that Planck data and a compilation of
BAO data constrain the Galileon term to small values that allow screening very
inefficiently. For a negative kinetic term (), a Galileon term and a
non-zero potential lead to an efficient screening in a physically viable regime
of the theory, with a value for the Hubble constant today which alleviates the
tension between its CMB and local determinations. For a vanishing potential,
the case with and the Galileon term driving the late acceleration of the
Universe is ruled out by Planck data.Comment: 23 pages, 15 figures, 4 table
- …