1,757 research outputs found
Galaxy rotation curves from General Relativity with Renormalization Group corrections
We consider the application of quantum corrections computed using
renormalization group arguments in the astrophysical domain and show that, for
the most natural interpretation of the renormalization group scale parameter, a
gravitational coupling parameter varying of its value across a
galaxy (which is roughly a variation of per light-year) is
sufficient to generate galaxy rotation curves in agreement with the
observations. The quality of the resulting fit is similar to the Isothermal
profile quality once both the shape of the rotation curve and the mass-to-light
ratios are considered for evaluation. In order to perform the analysis, we use
recent high quality data from nine regular disk galaxies. For the sake of
comparison, the same set of data is modeled also for the Modified Newtonian
Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity
(STVG). At face value, the model based on quantum corrections clearly leads to
better fits than these two alternative theories.Comment: 35 pages, 12 PDF figures. v4: Version accepted in JCAP. Improved
comments on the galactic gas effects to our model, stressed the relevance of
our MOND and STVG fits, slightly extended discussion on our perspectives and
minor additional comments. Ref's added
Coulomb's law modification driven by a logarithmic electrodynamics
We examine physical aspects for the electric version of a recently proposed
logarithmic electrodynamics, for which the electric field of a point-like
charge is finite at the origin. It is shown that this electrodynamics displays
the vacuum birefringence phenomenon in the presence of external magnetic field.
Afterwards we compute the lowest-order modification to the interaction energy
by means of the gauge-invariant but path-dependent variables formalism. These
are shown to result in a long-range (-type) correction, in addition to a
linear and another logarithmic correction, to the Coulomb potential.Comment: 4 pages. arXiv admin note: text overlap with arXiv:1709.0386
The photino sector and a confining potential in a supersymetric Lorentz-symmetry-violating model
We study the spectrum of the minimal supersymmetric extension of the
Carroll-Field-Jackiw model for Electrodynamics with a topological
Chern-Simons-like Lorentz-symmetry violating term. We identify a number of
independent background fermion condensates, work out the gaugino dispersion
relation and propose a photonic effective action to consider aspects of
confinement induced by the SUSY background fermion condensates, which also
appear to signal Lorentz-symmetry violation in the photino sector of the
action. Our calculations of the static potential are carried out within the
framework of the gauge-invariant but path-dependent variables formalism which
are alternative to the Wilson loop approach. Our results show that the
interaction energy contains a linear term leading to the confinement of static
probe charges.Comment: 11 pages, photino dispersion relation is extended to included the
case the photino acquires mass through spontaneous SUSY breakin
Aspects of CPT-even Lorentz-symmetry violating physics in a supersymmetric scenario
Background fermion condensates in a landscape dominated by global SUSY are
reassessed in connection with a scenario where Lorentz symmetry is violated in
the bosonic sector (actually, the photon sector) by a -even -term. An
effective photonic action is discussed that originates from the supersymmetric
background fermion condensates. Also, the photino mass emerges in terms of a
particular condensate contrary to what happens in the -violation.
Finally, the interparticle potential induced by the effective photonic action
is investigated and a confining profile is identified.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1102.3777 by
other author
A robot design for wind generator support structure inspection
In recent time, the development of wind tower inspection has been very crucial for the overall performance of the wind turbine. In order to maintain, monitor and determine the life span of the tower, an investigation of robot design is discussed. It presents how to design and construct a robot that can climb the tower and rotate 360° . A ring system which is in a circular shape robot is designed that allows the device to fit in the structure of the wind generator tower. The rotational module is designed to allow the wheels to rotate and be able to go in a circular motion. Also it is designed with a suspension that allows the robot to go through any obstacle. This paper also presents the FEA spring stress analysis and Simulink control system model to find the optimal parameters that are required for the wind tower climbing robot
Envisioning and evolving: Future evolution of the concept and the practice of service design
ervice Design is evolving from an emerging field, breaking new ground in the design and service research areas, to a more mature stage, developing a set of fundamental concepts, methods and principles that can provide the foundation for its further significance and impact in both research and practice. This paper reflects on the roots and recent evolution of service design in terms of fundamental concepts, methods and outcomes, taking into account the papers in the Envisioning and Evolving track. It considers how the growing interrelation with close fields of service research is introducing useful âcontaminationsâ and reports how the Service perspective is revealing its potential to bring life to technical and entrenched systems. It goes on to argue that design should aim to bring services to life to prove its real, distinguishing value and contribution
Potential flows in a core-dipole-shell system: numerical results
Numerical solutions for: the integral curves of the velocity field
(streamlines), the density contours, and the accretion rate of a steady-state
flow of an ideal fluid with p=K n^(gamma) equation of state orbiting in a
core-dipole-shell system are presented. For 1 < gamma < 2, we found that the
non-linear contribution appearing in the partial differential equation for the
velocity potential has little effect in the form of the streamlines and density
contour lines, but can be noticed in the density values. The study of several
cases indicates that this appears to be the general situation. The accretion
rate was found to increase when the constant gamma decreases.Comment: RevTex, 8 pages, 5 eps figures, CQG to appea
Living bacteria rheology: population growth, aggregation patterns and cooperative behaviour under different shear flows
The activity of growing living bacteria was investigated using real-time and
in situ rheology -- in stationary and oscillatory shear. Two different strains
of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell
wall autolysis mutant -- were considered in this work. For low bacteria
density, strain COL forms small clusters, while the mutant, presenting
deficient cell separation, forms irregular larger aggregates. In the early
stages of growth, when subjected to a stationary shear, the viscosity of both
strains increases with the population of cells. As the bacteria reach the
exponential phase of growth, the viscosity of the two strains follow different
and rich behaviours, with no counterpart in the optical density or in the
population's colony forming units measurements. While the viscosity of strain
COL keeps increasing during the exponential phase and returns close to its
initial value for the late phase of growth, where the population stabilizes,
the viscosity of the mutant strain decreases steeply, still in the exponential
phase, remains constant for some time and increases again, reaching a constant
plateau at a maximum value for the late phase of growth. These complex
viscoelastic behaviours, which were observed to be shear stress dependent, are
a consequence of two coupled effects: the cell density continuous increase and
its changing interacting properties. The viscous and elastic moduli of strain
COL, obtained with oscillatory shear, exhibit power-law behaviours whose
exponent are dependent on the bacteria growth stage. The viscous and elastic
moduli of the mutant have complex behaviours, emerging from the different
relaxation times that are associated with the large molecules of the medium and
the self-organized structures of bacteria. These behaviours reflect
nevertheless the bacteria growth stage.Comment: 9 pages, 10 figure
Positive radial solutions to a âsemilinearâ equation involving the Pucci's operator
AbstractIn this article we prove existence of positive radially symmetric solutions for the nonlinear elliptic equationMλ,Î+(D2u)âÎłu+f(u)=0inBR,u=0onâBR,where Mλ,Î+ denotes the Pucci's extremal operator with parameters 0<λ⩜Πand BR is the ball of radius R in RN, Nâ©Ÿ3. The result applies to a wide class of nonlinear functions f, including the important model cases: (i) Îł=1 and f(s)=sp, 1<p<pâ+. (ii) Îł=0, f(s)=αs+sp, 1<p<pâ+ and 0⩜α<ÎŒ1+. Here pâ+ is critical exponent for Mλ,Î+ and ÎŒ1+ is the first eigenvalue of Mλ,Î+ in BR. Analogous results are obtained for the operator Mλ,Îâ
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