1,995 research outputs found
Pollutant emissions in common-rail diesel engines in extraurban cycle: rapeseed oils vs diesel fuel
The new energy strategy of EU (i.e., Directive 2009/28/EC) requires increasing the use of biofuels in transports up to
at least 10% of the total fuel consumption. In the last years, the share of Diesel engines in automotive applications
reached about 55% in EU market, thus trying to widen the alternatives to Diesel fuel is very important. In this
framework straight vegetable oils (SVO) can represent one of the available possibilities at least in some specific
applications (i.e., public transportation, hybrid or marine propulsion, etc.). SVO properties may be very different
form Diesel fuel, thus operating a Diesel engine with SVO might result in some problems, especially in automotive
configuration where the electronic unit acts as if it is working with Diesel fuel. This reflects in possible engine power
and torque reduction, maintenance problems, and pollutant emissions during vehicles running. The latter aspect is the
focus of the present paper. In this work, we used a turbocharged, four stroke, four cylinders, water cooled, commonrail
multijet Diesel engine in automotive configuration to simulate the extraurban cycle according to the EU standard,
comparing pollutant emissions in case of SVO and gasoil fuelling
Stellar Populations, Bars and Secular Evolution in Late-Type Galaxies
We have done a robust statistical analysis of UBV color profiles of 257 Sbc
barred and unbarred galaxies. We found that there is an excess of barred
galaxies among the objects with null or positive (bluish inward) color
gradients, which seems to indicate that bars act as a mechanism of
homogenization of the stellar population along galaxies. Moreover, the
relationship found between total and bulge colors shows that, in the process of
homogenization, the stellar population of bulges are getting bluer, whereas the
total color of galaxies remains the same. These characteristics are expected in
a secular evolutionary scenario, and seem incompatible with both the monolithic
and the hierarchical scenarios for spiral galaxy formation.Comment: 2 pages, 1 table, no figures. To appear in ASP Conference Series,
"Galaxy Disks and Disk Galaxies", J. G. Funes S. J. and E. M. Corsini, ed
Temperature - Emissivity separation assessment in a sub-urban scenario
In this paper, a methodology that aims at evaluating the effectiveness of different TES strategies is presented. The methodology takes into account the specific material of interest in the monitored scenario, sensor characteristics, and errors in the atmospheric compensation step. The methodology is proposed in order to predict and analyse algorithms performances during the planning of a remote sensing mission, aimed to discover specific materials of interest in the monitored scenario. As case study, the proposed methodology is applied to a real airborne data set of a suburban scenario. In order to perform the TES problem, three state-of-the-art algorithms, and a recently proposed one, are investigated: Temperature-Emissivity Separation'98 (TES-98) algorithm, Stepwise Refining TES (SRTES) algorithm, Linear piecewise TES (LTES) algorithm, and Optimized Smoothing TES (OSTES) algorithm. At the end, the accuracy obtained with real data, and the ones predicted by means of the proposed methodology are compared and discussed
Statistical analysis of hyper-spectral data: a non-Gaussian approach
We investigate the statistical modeling of hyper-spectral data. The accurate modeling of experimental data is critical in target detection and classification applications. In fact, having a statistical model that is capable of properly describing data variability leads to the derivation of the best decision strategies together with a reliable assessment of algorithm performance. Most existing classification and target detection algorithms are based on the multivariate Gaussian model which, in many cases, deviates from the true statistical behavior of hyper-spectral data. This motivated us to investigate the capability of non-Gaussian models to represent data variability in each background class. In particular, we refer to models based on elliptically contoured (EC) distributions. We consider multivariate EC-t distribution and two distinct mixture models based on EC distributions. We describe the methodology adopted for the statistical analysis and we propose a technique to automatically estimate the unknown parameters of statistical models. Finally, we discuss the results obtained by analyzing data gathered by the multispectral infrared and visible imaging spectrometer (MIVIS) sensor
Estimation of directional sea wave spectra from radar images: a Mediterranean sea case study
An inversion technique for estimating sea wave directional spectra from Synthetic Aperture Radar (SAR) images is applied to a set of ERS-1 data relevant to selected Mediterranean areas. The approach followed is based on the
analytical definition of the transform which maps the sea wave spectrum onto the corresponding SAR image spectrum. The solution of the inverse problem is determined through a numerical procedure which minimises a proper functional. A suitable iterative scheme is adopted, involving the use of the above transform. Although widely applied to the ocean case, the method has not been yet extensively tested in smaller scale basins, as for instance the Mediterranean sea. The results obtained demonstrate the effectiveness of the numerical procedure discussed for retrieving the sea wave spectrum from SAR images. This work provides new experimental data relevant to the Mediterranean Sea, discusses the results obtained by the above inversion technique and compares them with buoy derived sea truth measurements
The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698
The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner
region of the bulge structure is elongated perpendicularly to the major axis of
the disk, this is also true for the outer parts of the bulge if a parametric
photometric decomposition is adopted. At the same time the stellar component is
characterized by an inner velocity gradient and a central zero-velocity plateau
along the minor and major axis of the disk respectively. This remarkable
geometric and kinematic decoupling suggests that a second event occurred in the
formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication
in The Astrophysical Journal Letter
On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies
In order to investigate the correlation between the circular velocity Vc and
the central velocity dispersion of the spheroidal component sigma_c, we
analyzed these quantities for a sample of 40 high surface brightness disc
galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies
(hereafter LSB), and 24 elliptical galaxies characterized by flat rotation
curves. We find that the Vc-sigma_c relation is descri ed by a linear law out
to velocity dispersions as low as sigma_c~50km/s, while in previous works a
power law was adopted for galaxies with sigma_c>80k/ms.
Elliptical galaxies with Vc based on dynamical models or directly derived
from the HI rotation curves follow the same relation as the HSB galaxies in the
Vc-sigma_c plane. On the contrary, the LSB galaxies follow a different
relation, since most of them show either higher Vc (or lower sigma_c) with
respect to the HSB galaxies. This argues against the relevance of baryon
collapse in the radial density profile of the dark matter haloes of LSB
galaxies. (abridged)Comment: 18 pages, 4 figures, ApJ in pres
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