4,126 research outputs found
Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales
We use high-resolution Herschel-PACS data of 2 nearby elliptical galaxies,
IC1459 & NGC2768 to characterize their dust and stellar content. IC1459 &
NGC2768 have an unusually large amount of dust for elliptical galaxies (1-3 x
10^5 Msun), this dust is also not distributed along the stellar content. Using
data from GALEX (ultraviolet) to PACS (far-infrared), we analyze the spectral
energy distribution (SED) of these galaxies with CIGALEMC as a function of the
projected position, binning images in 7.2" pixels. From this analysis, we
derive maps of SED parameters, such as the metallicity, the stellar mass, the
fraction of young star and the dust mass. The larger amount of dust in FIR maps
seems related in our model to a larger fraction of young stars which can reach
up to 4% in the dustier area. The young stellar population is fitted as a
recent (~ 0.5 Gyr) short burst of star formation for both galaxies. The
metallicities, which are fairly large at the center of both galaxies, decrease
with the radial distance with fairly steep gradient for elliptical galaxies.Comment: 14 pages, 26 figures, to be published in Ap
Men and Books in fourth-century BC Athens
Analisi delle testimonianze relative alla circolazione e conservazione dei libri e al lavoro sui libri nell'Atene del IV secolo a.C.This paper is concerned with books as “working tools” in 4th century BC Athens and aims to collect and discuss evidence for the existence of private book collections. In this period literacy seems to have improved, the book trade to have developed and books appear to have a wider variety of functions than before. The development of new genres of prose, the establishment of schools of higher education and the search by cultural and political figures for consensus are some of the reasons that may explain the rise of a new attitude towards books, their collection and their use for intellectual purposes; there was a gradual move away from the previously accepted idea of book conservation as a kind of sacred act. The way in which 4th century authors describe people reading , working with books and writing and, at the same time, the way in which their own works are built up contain interesting clues to this cultural change and to the birth of the idea of “library” in the Greek world
Experimental proof of the reciprocal relation between spin Peltier and spin Seebeck effects in a bulk YIG/Pt bilayer
We verify for the first time the reciprocal relation between the spin Peltier
and spin Seebeck effects in a bulk YIG/Pt bilayer. Both experiments are
performed on the same YIG/Pt device by a setup able to accurately determine
heat currents and to separate the spin Peltier heat from the Joule heat
background. The sample-specific value for the characteristics of both effects
measured on the present YIG/Pt bilayer is (6.2 \pm 0.4)\times 10^{-3} \,\,
\mbox{KA^{-1}}. In the paper we also discuss the relation of both effects
with the intrinsic and extrinsic parameters of YIG and Pt and we envisage
possible strategies to optimize spin Peltier refrigeration.Comment: 11 pages, 3 figure
Wheel – Rail interaction based on roughness calculation
Rolling noise is a relevant source in railway applications. The rolling noise is generated by the contact force the wheel, and the rail, exchange each other during relative motion. The interaction force between wheel and rail is generated by their roughness. Wheel and rail surfaces are not perfectly flat, they have a lot of small micro imperfections due to usage, damages, manufacturing. The whole of these imperfection is the roughness of the two surfaces. In the following a new interaction model will be shown where the roughness in kept in account to simulate the real case application. The model, based on previously studies, is improved introducing the rail and wheel real roughness for interaction force calculation. A real case study will be kept in account for model application and its application
On the Discrepancy between Theoretical and X-Ray Concentration-Mass Relations for Galaxy Clusters
[Abridged] In the past 15 years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
has this relation been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
We analyzed 52 objects, simulated each time with different physical recipes
for the baryonic component, as well as 60 synthetic X-ray images, to determine
if these discrepancies are real or artificial. In particular, we investigate
how the simulated concentration-mass relation depends (1) on the radial range
used to derive the concentration, (2) on the presence of baryons in the
simulations, and on the prescription used to reproduce the gas. Finally, we
evaluate (3) how the results differ when adopting an X-ray approach for the
analysis and (4) how the selection functions based on X-ray luminosity can
impact the results. All effects studied go in the direction of alleviating the
discrepancy between observations and simulations, although with different
significance: while the fitting radial range and the baryonic component play
only a minor role, the X-ray approach and selection function have profound
repercussion on the resulting concentration-mass relation.Comment: 15 pages, 11 figures, 3 tables, ApJ in press. Significant extension
of the study of the selection-function influence and more attentive treatment
of errors (results unchanged
Non-equilibrium thermodynamics of the spin Seebeck and spin Peltier effects
We study the problem of magnetization and heat currents and their associated
thermodynamic forces in a magnetic system by focusing on the magnetization
transport in ferromagnetic insulators like YIG. The resulting theory is applied
to the longitudinal spin Seebeck and the spin Peltier effects. By focusing on
the specific geometry with one YIG layer and one Pt layer, we obtain the
optimal conditions for generating large magnetization currents into Pt or large
temperature effects in YIG. The theoretical predictions are compared with
experiments from the literature permitting to derive the values of the
thermomagnetic coefficients of YIG: the magnetization diffusion length m and the absolute thermomagnetic power coefficient TK.Comment: accepted for publication on Physical Review
Non-equilibrium thermodynamics of the longitudinal spin Seebeck effect
In this paper we employ non equilibrium thermodynamics of fluxes and forces
to describe magnetization and heat transport. By the theory we are able to
identify the thermodynamic driving force of the magnetization current as the
gradient of the effective field . This definition permits to define
the spin Seebeck coefficient which relates and the
temperature gradient . By applying the theory to the geometry of the
longitudinal spin Seebeck effect we are able to obtain the optimal conditions
for generating large magnetization currents. Furthermore, by using the results
of recent experiments, we obtain an order of magnitude for the value of
TK for yttrium iron garnet
(YFeO).Comment: accepted for publication on Physics Procedi
Experimental Validation Of An Innovative Procedure For The Rolling Noise Correction
Among the wide contest of the train vehicles rolling noise evaluation, the aim of the paper is the development, implementation and experimental testing of a new method for roughness calculation according to FprCEN/TR 16891:2015 and the successive evaluation of the correction parameters of the measured rolling noise due to the presence of not compliant rail roughness. It is, in-fact, a very often operative condition, the execution of rolling noise tests over standard in-operation rails that are characterized by roughness profiles very different from standard one as those prescribed within the ISO 3095 procedure. Very often, this difference lead to the presence of an exceeding noise that needs to be evaluated and revised for a correct definition of the phenomena. Within the paper, the procedure implementation is presented and later on verified in operative experimental contest; forecasted and measured data are compared and successively commented
An Innovative Procedure for the Rolling Noise Evaluation
Noise is often generated by pressure changes in the air induced by mechanical vibrations. The study of these
phenomena is known as structural acoustics or, in a more fashionable way, virboacoustics. Vibroacoustics is the study
of the mechanical waves in structures and how they interact with, and radiate into, adjacent media. In railway the most
important noise source, based on fluid and structure interaction is the rolling noise. The aim of the paper is the
development and implementation of a numerical method for the rail decay rate and combined roughness calculation
according to the FprCEN/TR 16891:2015 and a subsequent evaluation of the excess noise level in accordance with the
ISO/FDIS 3095: 2013. The tool, as a final results, will make possible the evaluation of the rail parameters without the
involvement of long and expensive test campaign based on classical roughness measurement methods and will permit
the compensation of the roughness induced excess noise level for a comparative comprehension of the acoustic
experimental data
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