1,537 research outputs found
The Milky Way rotation curve in Horava - Lifshitz theory
The Horava - Lifshitz (HL) theory has recently attracted a lot of interest as
a viable solution to some quantum gravity related problems and the presence of
an effective cosmological constant able to drive the cosmic speed up. We show
here that, in the weak field limit, the HL proposal leads to a modification of
the gravitational potential because of two additive terms (scaling respectively
as and ) to the Newtonian potential. We then derive a
general expression to compute the rotation curve of an extended system under
the assumption that the mass density only depends on the cylindrical
coordinates showing that the HL modification induces a dependence of
the circular velocity on the mass function which is a new feature of the
theory. As a first exploratory analysis, we then try fitting the Milky Way
rotation curve using its visible components only in order to see whether the HL
modified potential can be an alternative to the dark matter framework. This
turns out not to be the case so that we argue that dark matter is still needed,
but the amount of dark matter and the dark halo density profile have to be
revised according to the new HL potential.Comment: 10 pages, 1 figure, accepted for publication on MNRA
Homogenization of a 2D tidal dynamics equation
This work deals with the homogenization of two dimensions’ tidal equations. We study the asymptotic behavior of the sequence of the solutions using the sigma-convergence method. We establish the convergence of the sequence of solutions towards the solution of an equivalent problem of the same type
Optical Guidance System /OGS/ for rendezvous and docking Final report
Optical guidance system for Apollo rendezvous and dockin
Thermoconditional modulation of the pleiotropic sensitivity phenotype by the Saccharomyces cerevisiae PRP19 mutant allele pso4-1
The conditionally-lethal pso4-1 mutant allele of the spliceosomal-associated PRP19 gene allowed us to study this gene’s influence on pre-mRNA processing, DNA repair and sporulation. Phenotypes related to intron-containing genes were correlated to temperature. Splicing reporter systems and RT–PCR showed splicing efficiency in pso4-1 to be inversely correlated to growth temperature. A single amino acid substitution, replacing leucine with serine, was identified within the N-terminal region of the pso4-1 allele and was shown to affect the interacting properties of Pso4-1p. Amongst 24 interacting clones isolated in a two-hybrid screening, seven could be identified as parts of the RAD2, RLF2 and DBR1 genes. RAD2 encodes an endonuclease indispensable for nucleotide excision repair (NER), RLF2 encodes the major subunit of the chromatin assembly factor I, whose deletion results in sensitivity to UVC radiation, while DBR1 encodes the lariat RNA splicing debranching enzyme, which degrades intron lariat structures during splicing. Characterization of mutagen-sensitive phenotypes of rad2{Delta}, rlf2{Delta} and pso4-1 single and double mutant strains showed enhanced sensitivity for the rad2{Delta} pso4-1 and rlf2{Delta} pso4-1 double mutants, suggesting a functional interference of these proteins in DNA repair processes in Saccharomyces cerevisiae
Spiral galaxies rotation curves in the Horava - Lifshitz gravity theory
We focus on a modified version of Horava - Lifschitz theory and, in
particular, we consider the impact of its weak - field static spherically
symmetric limit on the galaxy dynamics. In a previous paper, we used the
modified gravitational potential obtained in this theory to evaluate the Milky
Way rotation curve using a spheroidal truncated power - law bulge and a double
exponential disc as the only sources of the gravitational field and showed that
the modified rotation curved is not in agreement with the data. Making a step
forward, we here include also the contribution from a dark matter halo in order
to see whether this helps fitting the rotation curve data. As a test case, we
consider a sample of spiral galaxies with smooth baryon matter distribution and
well measured circular velocity profiles. It turns out that, although a
marginal agreement with the data can be found, this can only be obtained if the
dark matter halo has an unrealistically small virial mass and incredibly large
concentration. Such results can be interpreted as a strong evidence against the
reliability of the gravitational potential obtained in the modified version of
Horava -Lifschitz theory that we consider.Comment: 9 pages, 1 figure, 2 tables, accepted for publication on MNRA
Some Experimental Investigations on Gas Turbine Cooling Performed with Infrared Thermography at Federico II
This paper reviews some experimental measurements of convective heat transfer coefficient distributions which are connected with the cooling of gas turbines, performed by the authors' research group at the University of Naples Federico II with infrared thermography. Measurements concern impinging jets, cooling of rotating disks, and gas turbine blades, which are either stationary or rotating. The heated thin foil sensor, associated with the detection of surface temperature by means of infrared thermography, is exploited to accurately measure detailed convective heat transfer coefficient maps. The paper also intends to show how to correctly apply the infrared technique in a variety of gas turbines cooling problems
Sprouted wheat as an alternative to conventional flour improvers in bread-making
Sprouting is a natural process that enhances the nutritional and sensory profile of cereal-based foods. The present work addressed the possibility of using refined flour from sprouted wheat (SWF) to improve the bread-making performance of some flours in place of conventional improvers - i.e. enzymatic improver (EI) and malt (M). Either 0.5% EI or M was added to the control flour (CTRL), as conventionally used in bakeries, whereas SWF was used up to 2%. Unlikely EI and M, 1.5% SWF showed a gluten aggregation strength similar to that of the CTRL, suggesting no worsening of the protein network characteristics. As for the leavening properties, dough development increased, thanks to the enrichment with 1.5% SWF. In addition, presence of SWF improved the amount of gas production during leavening-resulting in bread with high specific volume - and the crumb softness during storage. Addition of SWF may represent a valid alternative to enzymatic improvers or malt for improving the technological performance of wheat flours
Effects of Rayleigh Waves on the Essential Spectrum in Perturbed Doubly Periodic Elliptic Problems
We give an example of a scalar second order differential operator in the plane with double periodic coefficients and describe its modification, which causes an additional spectral band in the essential spectrum. The modified operator is obtained by applying to the coefficients a mirror reflection with respect to a vertical or horizontal line. This change gives rise to Rayleigh type waves localized near the line. The results are proven using asymptotic analysis, and they are based on high contrast of the coefficient functions.Peer reviewe
Constraining dark energy models using the lookback time to galaxy clusters and the age of the universe
An impressive amount of different astrophysical data converges towards the
picture of a spatially flat universe undergoing a today phase of accelerated
expansion. The nature of the dark energy dominating the energy content of the
universe is still unknown and a lot of different scenarios are viable
candidates to explain cosmic acceleration. Most of the methods employed to test
these cosmological models are essentially based on distance measurements to a
particular class of objects. A different method, based on the lookback time to
galaxy clusters and the age of the universe, is used here. In particular, we
constrain the characterizing parameters of three classes of dark energy
cosmological models to see whether they are in agreement with this kind of
data, based on time measurements rather than distance observations.Comment: 13 pages, 8 figures, accepted for publication on Physical Review
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