640 research outputs found
The effect of oxygenate fuels on PN emissions from a highly boosted GDI engine
Gasoline Direct Injection (GDI) engines are increasingly available in the market. Such engines are known to emit more Particulate Matter (PM) than their port-fuel injected predecessors. There is also a widespread use of oxygenate fuels in the market, up to blends of E85, and their impact on PN emissions is widely studied. However the impact of oxygenate fuels on PN emissions from downsized, and hence highly-boosted engines is not known. In this work, PN emissions from a highly boosted engine capable of running at up to 35 bar Brake Mean Effective Pressure (BMEP) have been measured from a baseline gasoline and three different oxygenate fuels (E20, E85, and GEM – a blend of gasoline, ethanol, and methanol) using a DMS500. The engine has been run at four different operating points, and a number of engine parameters relevant to highly-boosted engines (such as EGR, exhaust back pressure, and lambda) have been tested – the PN emissions and size distributions have been measured from all of these. The results show that the oxygenate content of the fuel has a very large impact on its PN emissions, with E85 giving low levels of PN emissions across the operating range, and GEM giving very low and extremely high levels of PN emissions depending on operating point. These results have been analysed and related back to key fuel properties
Cosmic microwave background: polarization and temperature anisotropies from symmetric structures
I consider the case of anisotropies in the Cosmic Microwave Background (CMB)
from one single ordered perturbation source, or seed, existing well before
decoupling between matter and radiation. Such structures could have been left
by high energy symmetries breaking in the early universe.
I focus on the cases of spherical and cylindrical symmetry of the seed. I
give general analytic expressions for the polarization and temperature linear
perturbations, factoring out of the Fourier integral the dependence on the
photon propagation direction and on the geometric coordinates describing the
seed. I show how the CMB perturbations manifestly reflect the symmetries of
their seeds. CMB anisotropies are obtained with a line of sight integration.
This treatment highlights the undulatory properties of the CMB. I show with
numerical examples how the polarization and temperature perturbations propagate
beyond the size of their seeds, reaching the CMB sound horizon at the time
considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy
from a seed intersecting the last scattering surface appears as a series of
temperature and polarization waves surrounding the seed, extending on the scale
of the CMB sound horizon at decoupling, roughly in the sky. Each wave
is characterized by its own value of the CMB perturbation, with the same mean
amplitude of the signal coming from the seed interior.
These waves could allow to distinguish relics from high energy processes of
the early universe from point-like astrophysical sources, because of their
angular extension and amplitude. Also, the marked analogy between polarization
and temperature signals offers cross correlation possibilities for the future
Planck Surveyor observations.Comment: 21 pages, seven postscript figures, final version accepted for
publication in Phys.Rev.
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
Antarctic Climate Change and the Environment
The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment
Trading Methods and Family Strategies of Genoese People. Almería, XVIII century
Artículo de la sección: EstudiosEnfatizar la importancia de la documentación notarial para el estudio de un grupo
social parece una valoración innecesaria. Este estudio pretende, a partir fundamentalmente de los protocolos notariales como núcleo de la investigación y del Catastro de Ensenada, complementados con otras fuentes, libros de Contadurías e Hipotecas de la sección de hacienda del Archivo Histórico Provincial de Almería, documentos de hidalguía y matrícula de extranjeros del Archivo Municipal de Almería, acercarse al flujo de mercaderes genoveses que, durante el siglo XVIII, se avecinda en la ciudad de Almería.
La investigación se centra en los mecanismos que cuatro familias genovesas,
domiciliadas en la ciudad de Almería durante el Setecientos: Schiafino-Aste, Schiafino-
Schiafino, Schiafino-Ansaldo e Iluminatti-Marín, desarrollaron para conseguir la intervención en la administración local y la creación de unas prácticas mercantiles que,
desde la ciudad de Almería y su jurisdicción, se extenderían hacia las villas del interior de la provincia y hacia una importante ramificación a lo largo de las costas del levante peninsular y de Andalucía occidental. No olvidaremos las relaciones que el grupo ligur almeriense mantuvo durante el siglo con su Génova natal, que cristalizaron en la creación de una compañía mercantil desarrollada en base a los intereses económicos de familias genovesas de Santa María de Camogli y de la ciudad de Almería.
El análisis es un acercamiento, más que hacia aspectos económicos y al mundo
del comercio, a la relación que se establece entre la formación de las familias y la
creación de estrategias mercantiles que les llevará a la intervención en los mercados.To emphasize the notarial documentation for the study of a social group it seems
to be an unnecessary valuation. This research expects basically, from the notarial
protocols as the essence of the research work and from the Catastro of Ensenada,
completed with other sources, Accountancy books and Mortgages of the section of
finance from the Almerías 's Provincial Historical Record Office, nobility documents,
and registration of foreigners from the Almería"s Town Record Office, to approach to
the flow of Genoese merchants who, during the 18th century, comes near the town of
Almería.
The investigation is centred in the processes that four Genoese families established in the town of Almería during the Seven hundred, Schiafino-Aste, Shiafino-Shiafino,Shiafino-Ansaldo and Iluminatti-Marin, developped to get the participation in the local administration and the establishment of some trading methods which, from the city of Almería and its jurisdiction, would be spread over the inner small towns of the province and towards an important branch along the levant peninsular coasts and the west of Andalucía. We must not forget the relationship that the almeriense ligur group kept up during the century with its home town Genoa, crystallizing in the establishment
of a trading company developped on tha basis of economical interests of Genoese
families from Santa Maria of Camogli and the city of Almería.
The analysis is a approach, more than to economical aspects and the business
world, to the relationship that it is set up between the formation of the families and the
establishment of trading strategies that will take them to the participation in the
markets.Departamento de Historia Moderna y de América, Universidad de Granad
The Minimal Model of Nonbaryonic Dark Matter: A Singlet Scalar
We propose the simplest possible renormalizable extension of the Standard
Model - the addition of just one singlet scalar field - as a minimalist model
for non-baryonic dark matter. Such a model is characterized by only three
parameters in addition to those already appearing within the Standard Model: a
dimensionless self-coupling and a mass for the new scalar, and a dimensionless
coupling, \lambda, to the Higgs field. If the singlet is the dark matter, these
parameters are related to one another by the cosmological abundance constraint,
implying that the coupling of the singlet to the Higgs field is large, \lambda
\sim O(0.1 - 1). Since this parameter also controls couplings to ordinary
matter, we obtain predictions for the elastic cross section of the singlet with
nuclei. The resulting scattering rates are close to current limits from both
direct and indirect searches. The existence of the singlet also has
implications for current Higgs searches, as it gives a large contribution to
the invisible Higgs width for much of parameter space. These scalars can be
strongly self-coupled in the cosmologically interesting sense recently proposed
by Spergel and Steinhardt, but only for very low masses (< 1 GeV), which is
possible only at the expense of some fine-tuning of parameters.Comment: 26 pages, latex. Minor revisions, few references adde
Direct amplification of nodD from community DNA reveals the genetic diversity of Rhizobium leguminosarum in soil
Sequences of nodD, a gene found only in rhizobia, were amplified from total community DNA isolated from a pasture soil. The polymerase chain reaction (PCR) primers used, Y5 and Y6, match nodD from Rhizobium leguminosarum biovar trifolii, R. leguminosarum biovar viciae and Sinorhizobium meliloti. The PCR product was cloned and yielded 68 clones that were identified by restriction pattern as derived from biovar trifolii [11 restriction fragment length polymorphism (RFLP) types] and 15 clones identified as viciae (seven RFLP types). These identifications were confirmed by sequencing. There were no clones related to S. meliloti nodD. For comparison, 122 strains were isolated from nodules of white clover (Trifolium repens) growing at the field site, and 134 from nodules on trap plants of T. repens inoculated with the soil. The nodule isolates were of four nodD RFLP types, with 77% being of a single type. All four of these patterns were also found among the clones from soil DNA, and the same type was the most abundant, although it made up only 34% of the trifolii-like clones. We conclude that clover selects specific genotypes from the available soil population, and that R. leguminosarum biovar trifolii was approximately five times more abundant than biovar viciae in this pasture soil, whereas S. meliloti was rare
Invisible Axions and Large-Radius Compactifications
We study some of the novel effects that arise when the QCD axion is placed in
the ``bulk'' of large extra spacetime dimensions. First, we find that the mass
of the axion can become independent of the energy scale associated with the
breaking of the Peccei-Quinn symmetry. This implies that the mass of the axion
can be adjusted independently of its couplings to ordinary matter, thereby
providing a new method of rendering the axion invisible. Second, we discuss the
new phenomenon of laboratory axion oscillations (analogous to neutrino
oscillations), and show that these oscillations cause laboratory axions to
``decohere'' extremely rapidly as a result of Kaluza-Klein mixing. This
decoherence may also be a contributing factor to axion invisibility. Third, we
discuss the role of Kaluza-Klein axions in axion-mediated processes and decays,
and propose several experimental tests of the higher-dimensional nature of the
axion. Finally, we show that under certain circumstances, the presence of an
infinite tower of Kaluza-Klein axion modes can significantly accelerate the
dissipation of the energy associated with cosmological relic axion
oscillations, thereby enabling the Peccei-Quinn symmetry-breaking scale to
exceed the usual four-dimensional relic oscillation bounds. Together, these
ideas therefore provide new ways of obtaining an ``invisible'' axion within the
context of higher-dimensional theories with large-radius compactifications.Comment: 43 pages, LaTeX, 6 figure
Can a matter-dominated model with constant bulk viscosity drive the accelerated expansion of the universe?
We test a cosmological model which the only component is a pressureless fluid
with a constant bulk viscosity as an explanation for the present accelerated
expansion of the universe. We classify all the possible scenarios for the
universe predicted by the model according to their past, present and future
evolution and we test its viability performing a Bayesian statistical analysis
using the SCP ``Union'' data set (307 SNe Ia), imposing the second law of
thermodynamics on the dimensionless constant bulk viscous coefficient \zeta and
comparing the predicted age of the universe by the model with the constraints
coming from the oldest globular clusters.
The best estimated values found for \zeta and the Hubble constant Ho are:
\zeta=1.922 \pm 0.089 and Ho=69.62 \pm 0.59 km/s/Mpc with a \chi^2=314. The age
of the universe is found to be 14.95 \pm 0.42 Gyr. We see that the estimated
value of Ho as well as of \chi^2 are very similar to those obtained from LCDM
model using the same SNe Ia data set. The estimated age of the universe is in
agreement with the constraints coming from the oldest globular clusters.
Moreover, the estimated value of \zeta is positive in agreement with the second
law of thermodynamics (SLT).
On the other hand, we perform different forms of marginalization over the
parameter Ho in order to study the sensibility of the results to the way how Ho
is marginalized. We found that it is almost negligible the dependence between
the best estimated values of the free parameters of this model and the way how
Ho is marginalized in the present work. Therefore, this simple model might be a
viable candidate to explain the present acceleration in the expansion of the
universe.Comment: 31 pages, 12 figures and 2 tables. Accepted to be published in the
Journal of Cosmology and Astroparticle Physics. Analysis using the new SCP
"Union" SNe Ia dataset instead of the Gold 2006 and ESSENCE datasets and
without changes in the conclusions. Added references. Related works:
arXiv:0801.1686 and arXiv:0810.030
Magnetic fields in protoplanetary disks
Magnetic fields likely play a key role in the dynamics and evolution of
protoplanetary discs. They have the potential to efficiently transport angular
momentum by MHD turbulence or via the magnetocentrifugal acceleration of
outflows from the disk surface, and magnetically-driven mixing has implications
for disk chemistry and evolution of the grain population. However, the weak
ionisation of protoplanetary discs means that magnetic fields may not be able
to effectively couple to the matter. I present calculations of the ionisation
equilibrium and magnetic diffusivity as a function of height from the disk
midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling
by soaking up electrons and ions from the gas phase and reducing the
conductivity of the gas by many orders of magnitude. However, once grains have
grown to a few microns in size their effect starts to wane and magnetic fields
can begin to couple to the gas even at the disk midplane. Because ions are
generally decoupled from the magnetic field by neutral collisions while
electrons are not, the Hall effect tends to dominate the diffusion of the
magnetic field when it is able to partially couple to the gas.
For a standard population of 0.1 micron grains the active surface layers have
a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated
to 3 microns the active surface density is 80 g/cm^2. In the absence of grains,
x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150
g/cm^2). At 5 AU the entire disk thickness becomes active once grains have
aggregated to 1 micron in size.Comment: 11 pages, 11 figs, aastex.cls. Accepted for publication in
Astrophysics & Space Science. v3 corrects bibliograph
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