282,894 research outputs found
Parent Stars of Extrasolar Planets. XII. Additional evidence for trends with vsini, condensation temperature, and chromospheric activity
Several recent studies have reported differences in vsini,
abundance-condensation temperature trends, and chromospheric activity between
samples of stars with and without Doppler-detected planets. These findings have
been disputed, and the status of these results remains uncertain. We evaluate
these claims using additional published data and find support for all three.Comment: 4 pages, 4 figures; accepted for publication in MNRAS as a Lette
Cubical Cohomology Ring of 3D Photographs
Cohomology and cohomology ring of three-dimensional (3D) objects are
topological invariants that characterize holes and their relations. Cohomology
ring has been traditionally computed on simplicial complexes. Nevertheless,
cubical complexes deal directly with the voxels in 3D images, no additional
triangulation is necessary, facilitating efficient algorithms for the
computation of topological invariants in the image context. In this paper, we
present formulas to directly compute the cohomology ring of 3D cubical
complexes without making use of any additional triangulation. Starting from a
cubical complex that represents a 3D binary-valued digital picture whose
foreground has one connected component, we compute first the cohomological
information on the boundary of the object, by an incremental
technique; then, using a face reduction algorithm, we compute it on the whole
object; finally, applying the mentioned formulas, the cohomology ring is
computed from such information
"Männerbund" and "pistos hetairos". Well-being of the Epic Warrior
Männerbund, male solidarity between comrades in arms, has vital importance in war, at least in ancient warfare. In Homeric poetry we find clear examples of the importance of such ties, always between men, and observe a variety of possible overtones. Moreover, the bond that unites a couple as Achilles and Patroclus has an additional component, that of the friend as counsellor and confidant. The purpose of this paper is to analyze the role played by the pistos hetairos, the reliable friend, in the well-being of the warrior. The basis of this study will be the Iliad, epic in whose plot the couple Achilles-Patroclus is an excellent example of the positive function exercised by the existence of a friend, confidant and comrade absolutely faithful, as well as the dangers of that presence disappearing. Aside from the possibly erotic nature of the relationship between Achilles and Patroclus, the latter’s fundamental role is that of reliable counsellor to Achilles, the same role that Nestor plays in relation to Agamemnon, or Polydamas to Hector
AUGER-HiRes results and models of Lorentz symmetry violation
The implications of AUGER and HiRes results for patterns of Lorentz symmetry
violation (LSV) are examined, focusing on weak doubly special relativity
(WDSR). If the Greisen-Zatsepin-Kuzmin (GZK) cutoff is definitely confirmed,
the mass composition of the highest-energy cosmic-ray spectrum will be a
crucial issue to draw precise theoretical consequences from the experimental
results. Assuming that the observed flux suppression is due to the GZK
mechanism, data will allow in principle to exclude a significant range of LSV
models and parameters, but other important possibilities are expected to remain
open : Lorentz breaking can be weaker or occur at a scale higher than the
Planck scale, unconventional LSV effects can fake the GZK cutoff, threshold
phenomena can delay its appearance... Space experiments appear to be needed to
further test special relativity. We also examine the consequences of AUGER and
HiRes data for superbradyons. If such superluminal ultimate constituents of
matter exist in our Universe, they may provide new forms of dark matter and
dark energy.Comment: Talk given at the CRIS (Cosmic Ray International Seminar), La Malfa,
September 15-19, 2008. To be published in the Proceeding
Modular Curves Of Genus 2
We prove that there is only a finite number of genus 2 curves C defined over
Q such that there exists a nonconstant morphism pi:X_1(N) --->C defined over Q
and the jacobian of C, J(C), is a Q-factor of the new part of the jacobian of
X_1(N), J_1(N)^{new}. Moreover, we prove that there are only 149 genus two
curves of this kind with the additional requeriment that their jacobians are
Q-simple. We determine the corresponding newforms and present equations for all
these curves
A Study on the Integration of a High-Speed Flywheel as an Energy Storage Device in Hybrid Vehicles
The last couple of decades have seen the rise of the hybrid electric vehicle as a compromise between the outstanding specific energy of petrol fuels and its low-cost technology, and the zero tail-gate emissions of the electric vehicle. Despite this, considerable reductions in cost and further increases in fuel economy are needed for their widespread adoption.
An alternative low-cost energy storage technology for vehicles is the high-speed flywheel. The flywheel has important limitations that exclude it from being used as a primary energy source for vehicles, but its power characteristics and low-cost materials make it a powerful complement to a vehicle's primary propulsion system. This thesis presents an analysis on the integration of a high-speed flywheel for use as a secondary energy storage device in hybrid vehicles.
Unlike other energy storage technologies, the energy content of the flywheel has a direct impact on the velocity of transmission. This presents an important challenge, as it means that the flywheel must be able to rotate at a speed independent of the vehicle's velocity and therefore it must be coupled via a variable speed transmission. This thesis presents some practical ways in which to accomplish this in conventional road vehicles, namely with the use of a variator, a planetary gear set or with the use of a power-split continuously variable transmission. Fundamental analyses on the kinematic behaviour of these transmissions particularly as they pertain to flywheel powertrains are presented. Computer simulations were carried out to compare the performance of various transmissions, and the models developed are presented as well.
Finally the thesis also contains an investigation on the driving and road conditions that have the most beneficial effect on hybrid vehicle performance, with a particular emphasis on the effect that the road topography has on fuel economy and the significance of this
Parent Stars of Extrasolar Planets. XI. Trends with Condensation Temperature Revisited
We report the results of abundance analyses of new samples of stars with
planets and stars without detected planets. We employ these data to compare
abundance-condensation temperature trends in both samples. We find that stars
with planets have more negative trends. In addition, the more metal-rich stars
with planets display the most negative trends. These results confirm and extend
the findings of Ramirez et al. (2009) and Melendez et al. (2009), who
restricted their studies to solar analogs. We also show that the differences
between the solar photospheric and CI meteoritic abundances correlate with
condensation temperature.Comment: 7 pages, 11 figures; to be published in MNRA
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