1,391 research outputs found
Gauge Coupling Instability and Dynamical Mass Generation in N=1 Supersymmetric QED(3)
Using superfield Dyson-Schwinger equations, we compute the infrared dynamics
of the semi-amputated full vertex, corresponding to the effective running gauge
coupling, in N-flavour {\mathcal N}=1 supersymmetric QED(3). It is shown that
the presence of a supersymmetry-preserving mass for the matter multiplet
stabilizes the infrared gauge coupling against oscillations present in the
massless case, and we therefore infer that the massive vacuum is thus selected
at the level of the (quantum) effective action. We further demonstrate that
such a mass can indeed be generated dynamically in a self-consistent way by
appealing to the superfield Dyson-Schwinger gap equation for the full matter
propagator.Comment: 14 pages ReVTeX; four axodraw figures incorporate
Performance, combustion and emissions of a diesel engine operated with reformed EGR. Comparison of diesel and GTL fuelling
This is the post-print version of the final paper published in Fuel. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2008 Elsevier B.V.In this work, the effects of a standard ultra-low sulphur diesel (ULSD) fuel and a new, ultra-clean synthetic GTL (gas-to-liquid) fuel on the performance, combustion and emissions of a single-cylinder, direct injection, diesel engine were studied under different operating conditions with addition of simulated reformer product gas, referred to as reformed EGR (REGR). For this purpose various levels of REGR of two different compositions were tested. Tests with standard EGR were also carried out for comparison. Experiments were performed at four steady state operating conditions and the brake thermal efficiency, combustion process and engine emission data are presented and discussed. In general, GTL fuel resulted in a higher brake thermal efficiency compared to ULSD but the differences depended on the engine condition and EGR/REGR level and composition. The combustion pattern was significantly modified when the REGR level was increased. Although the extent of the effects of REGR on emissions depended on the engine load, it can be generally concluded that an optimal combination of GTL and REGR significantly improved both NOx and smoke emissions. In some cases, NOx and smoke emission reductions of 75% and 60%, respectively, were achieved compared to operation with ULSD without REGR. This offers a great potential for engine manufacturers to meet the requirements of future emission regulations.Shell Global Solutions UK, the Government of Castilla-La Mancha (Spain) and the Royal Thai Government
Saturn's icy satellites and rings investigated by Cassini - VIMS. III. Radial compositional variability
In the last few years Cassini-VIMS, the Visible and Infared Mapping
Spectrometer, returned to us a comprehensive view of the Saturn's icy
satellites and rings. After having analyzed the satellites' spectral properties
(Filacchione et al. (2007a)) and their distribution across the satellites'
hemispheres (Filacchione et al. (2010)), we proceed in this paper to
investigate the radial variability of icy satellites (principal and minor) and
main rings average spectral properties. This analysis is done by using 2,264
disk-integrated observations of the satellites and a 12x700 pixels-wide rings
radial mosaic acquired with a spatial resolution of about 125 km/pixel. The
comparative analysis of these data allows us to retrieve the amount of both
water ice and red contaminant materials distributed across Saturn's system and
the typical surface regolith grain sizes. These measurements highlight very
striking differences in the population here analyzed, which vary from the
almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to
the metal/organic-rich and red surfaces of Iapetus' leading hemisphere and
Phoebe. Rings spectra appear more red than the icy satellites in the visible
range but show more intense 1.5-2.0 micron band depths. The correlations among
spectral slopes, band depths, visual albedo and phase permit us to cluster the
saturnian population in different spectral classes which are detected not only
among the principal satellites and rings but among co-orbital minor moons as
well. Finally, we have applied Hapke's theory to retrieve the best spectral
fits to Saturn's inner regular satellites using the same methodology applied
previously for Rhea data discussed in Ciarniello et al. (2011).Comment: 44 pages, 27 figures, 7 tables. Submitted to Icaru
The Christiansen Effect in Saturn's narrow dusty rings and the spectral identification of clumps in the F ring
Stellar occultations by Saturn's rings observed with the Visual and Infrared
Mapping Spectrometer (VIMS) onboard the Cassini spacecraft reveal that dusty
features such as the F ring and the ringlets in the Encke and the Laplace Gaps
have distinctive infrared transmission spectra. These spectra show a narrow
optical depth minimum at wavelengths around 2.87 microns. This minimum is
likely due to the Christiansen Effect, a reduction in the extinction of small
particles when their (complex) refractive index is close to that of the
surrounding medium. Simple Mie-scattering models demonstrate that the strength
of this opacity dip is sensitive to the size distribution of particles between
1 and 100 microns across. Furthermore, the spatial resolution of the
occultation data is sufficient to reveal variations in the transmission spectra
within and among these rings. For example, in both the Encke Gap ringlets and F
ring, the opacity dip weakens with increasing local optical depth, which is
consistent with the larger particles being concentrated near the cores of these
rings. The strength of the opacity dip varies most dramatically within the F
ring; certain compact regions of enhanced optical depth lack an opacity dip and
therefore appear to have a greatly reduced fraction of grains in the few-micron
size range.Such spectrally-identifiable structures probably represent a subset
of the compact optically-thick clumps observed by other Cassini instruments.
These variations in the ring's particle size distribution can provide new
insights into the processes of grain aggregation, disruption and transport
within dusty rings. For example, the unusual spectral properties of the F-ring
clumps could perhaps be ascribed to small grains adhering onto the surface of
larger particles in regions of anomalously low velocity dispersion.Comment: 42 pages, 15 figures, accepted for publication in Icarus. A few small
typographical errors fixed to match correction in proof
Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)
International audienceOntario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and Radar in 2009 and 2010). In this study, we take advantage of each imaging dataset to establish a global survey of Ontario Lacus' environment from 2005 to 2010. We perform a geomorphological mapping and interpretation of Ontario Lacus, mainly based on a joint analysis of VIMS and Radar SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which closely resembles Titan's lakes: the pans of the Etosha Basin, located in Namibia. From this comparison, we infer that Ontario Lacus is an extremely flat depression where liquids, only located in the darkest areas in the Radar data, cover topographic lows where the "alkanofer" would raise above the depression floor. The rest of the depression appears rather as a muddy flat surface likely composed of a thick coating of photon-absorbing materials, explaining its still rather dark appearance in the infrared and radar data. We also determined whether surface changes occurred during the 5 years time interval between 2005 and 2010. We found that the depression contour is constant at the resolution of ISS and VIMS data, both being consistent with the depression contour derived from the Radar data. Our interpretation, in which the liquids are located only in some parts of Ontario Lacus, agrees with the lack of significant change of the depression contour between 2007 (and 2005 with more uncertainties) and 2010
Active Amplification of the Terrestrial Albedo to Mitigate Climate Change: An Exploratory Study
This study explores the potential to enhance the reflectance of solar
insolation by the human settlement and grassland components of the Earth's
terrestrial surface as a climate change mitigation measure. Preliminary
estimates derived using a static radiative transfer model indicate that such
efforts could amplify the planetary albedo enough to offset the current global
annual average level of radiative forcing caused by anthropogenic greenhouse
gases by as much as 30 percent or 0.76 W/m2. Terrestrial albedo amplification
may thus extend, by about 25 years, the time available to advance the
development and use of low-emission energy conversion technologies which
ultimately remain essential to mitigate long-term climate change. However,
additional study is needed to confirm the estimates reported here and to assess
the economic and environmental impacts of active land-surface albedo
amplification as a climate change mitigation measure.Comment: 21 pages, 3 figures. In press with Mitigation and Adaptation
Strategies for Global Change, Springer, N
AN EVALUATION OF MERCURY COOLED BREEDER REACTORS
Under the New Reactor Concepts Evaluation Program sponsored by the United States Atomic Energy Commission. Advanced Technology Laboratories (a Division of American Radiator & Standard Sanitary Corporation) has undertaken am investigation of the technical feasibility and economic potential of the use of boiling mercury as a coolant for fast breeder reactors The investigation was performed between January 1, 1959, and October 31. 1959. This is the final report on that investigation and is submitted in compliance with the terms of the program authorization, Contract Number AT(04-3)-109, Project Agreement Number 4. (auth
Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space
Astronomically, there are viable mechanisms for distributing organic material
throughout the Milky Way. Biologically, the destructive effects of ultraviolet
light and cosmic rays means that the majority of organisms arrive broken and
dead on a new world. The likelihood of conventional forms of panspermia must
therefore be considered low. However, the information content of dam-aged
biological molecules might serve to seed new life (necropanspermia).Comment: Accepted for publication in Space Science Review
Avaliação da sensibilidade do questionårio de triagem para dor orofacial e desordens temporomandibulares recomendado pela Academia Americana de Dor Orofacial
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