71 research outputs found
Analysis and Methodology to Characterize Heat Transfer Phenomena in Automotive Turbochargers
In the present work a comprehensive study of turbocharger heat transfer phenomena is discussed, showing their relevance compared to gas enthalpy variations through the turbomachinery. The study provides an experimental methodology to consider the different heat fluxes in the turbocharger and modeling them by means of a lumped capacitance heat transfer model (HTM). The input data required for the model are obtained experimentally by a proper combination of both steady and transient tests. These tests are performed in different test benches, in which incompressible fluids (oil) and compressible fluids (gas) are used in a given sequence. The experimental data allows developing heat transfer correlations for the different turbocharger elements. These correlations take into account all the possible heat fluxes, discriminating between internal and external heat transfer. In order to analyze the relative importance of heat transfer phenomena in the predictability of the turbocharger performance and the different related variables; model results, in hot and cold conditions, have been compared with those provided by the standard technique, consisting on using look up maps (LUM) of the turbocharger. The analysis of these results evidences the highly diabatic operative areas of the turbocharger and it provides clearly ground rules for using hot or cold turbocharger maps. In addition, paper discussion advises about using or not aHTM, depending on the turbocharger variables and the operative conditions that one desires to predict. Paper concludes that an accurate prediction of gas temperatures at turbine and compressor outlet and of fluid temperatures at water and oil ports outlet is not always possible without considering heat transfer phenomena in the turbocharger
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
The Crab Nebula and Pulsar between 500 GeV and 80 TeV: Observations with the HEGRA stereoscopic air Cherenkov telescopes
The Crab supernova remnant has been observed regularly with the stereoscopic
system of 5 imaging air Cherenkov telescopes that was part of the High Energy
Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hours of useful
data have been collected from 1997 until 2002. The spectrum extends up to
energies of 80 TeV and is well matched by model calculations in the framework
of inverse Compton scattering of various seed photons in the nebula including
for the first time a recently detected compact emission region at
mm-wavelengths. The observed indications for a gradual steepening of the energy
spectrum in data is expected in the inverse Compton emission model.The average
magnetic field in the emitting volume is determined to be
G. The presence of protons in
the nebula is not required to explain the observed flux and upper limits on the
injected power of protons are calculated being as low as 20 % of the total spin
down luminosity for bulk Lorentz factors of the wind in the range of
.The position and size of the emission region have been studied over
a wide range of energies. The position is shifted by 13\arcsec to the west of
the pulsar with a systematic uncertainty of 25\arcsec. No significant shift in
the position with energy is observed. The size of the emission region is
constrained to be less than 2\arcmin at energies between 1 and 10 TeV. Above 30
TeV the size is constrained to be less than 3\arcmin.No indications for pulsed
emission has been found and upper limits in differential bins of energy have
been calculated reaching typically 1-3 % of the unpulsed component.Comment: 53 pages, 12 figures. Accepted for publication in Astrophysical
Journa
Genome Sequence of the Pea Aphid Acyrthosiphon pisum
Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems
Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
In this contribution we review the recent progress in the modelling of Pulsar Wind Nebulae (PWN). We start with a brief overview of the relevant physical processes in the magnetosphere, the wind-zone and the inflated nebula bubble. Radiative signatures and particle transport processes obtained from 3D simulations of PWN are discussed in the context of optical and X-ray observations. We then proceed to consider particle acceleration in PWN and elaborate on what can be learned about the particle acceleration from the dynamical structures called GwispsG observed in the Crab nebula. We also discuss recent observational and theoretical results of gamma-ray flares and the inner knot of the Crab nebula, which had been proposed as the emission site of the flares. We extend the discussion to GeV flares from binary systems in which the pulsar wind interacts with the stellar wind from a companion star. The chapter concludes with a discussion of solved and unsolved problems posed by PWN
Quartz-Fiber Thermal Insulation: Infrared Radiative Properties and Calculation of Radiative-Conductive Heat Transfer
Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun
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