11,969 research outputs found
Widespread abiotic methane in chromitites
Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars
The 2010 M 87 VHE flare and its origin: the multi-wavelength picture
The giant radio galaxy M 87, with its proximity (16 Mpc) and its very massive
black hole ((3 - 6) \times 10^9 M_solar), provides a unique laboratory to
investigate very high energy (E>100 GeV; VHE) gamma-ray emission from active
galactic nuclei and, thereby, probe particle acceleration to relativistic
energies near supermassive black holes (SMBH) and in relativistic jets. M 87
has been established as a VHE gamma-ray emitter since 2005. The VHE gamma-ray
emission displays strong variability on timescales as short as a day. In 2008,
a rise in the 43 GHz Very Long Baseline Array (VLBA) radio emission of the
innermost region (core; extension of < 100 Rs ; Schwarzschild radii) was found
to coincide with a flaring activity at VHE. This had been interpreted as a
strong indication that the VHE emission is produced in the direct vicinity of
the SMBH. In 2010 a flare at VHE was again detected triggering further
multi-wavelength (MWL) observations with the VLBA, Chandra, and other
instruments. At the same time, M 87 was also observed with the Fermi-LAT
telescope at MeV/GeV energies, the European VLBI Network (EVN), and the
Liverpool Telescope (LT). Here, preliminary results from the 2010 campaign will
be reported.Comment: 6 pages, 2 figures; Procceedings of the workshop "High Energy
Phenomena in Relativistic Outflows III" (HEPRO III), Barcelona, June 27 -
July 1, 201
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A novel design process of low cost 3D printed ambidextrous finger designed for an ambidextrous robotic hand
This paper presents the novel mechanical design of an ambidextrous finger specifically designed for an ambidextrous anthropomorphic robotic hand actuated by pneumatic artificial muscles. The ambidextrous nature of design allows fingers to perform both left and right hand movements. The aim of our design is to reduce the number of actuators, increase the range of movements with best possible range ideally greater than a common human finger. Four prototypes are discussed in this paper; first prototype is focused on the choice of material and to consider the possible ways to reduce friction. Second prototype is designed to investigate the tendons routing configurations. Aim of third and fourth prototype is to improve the overall performance and to maximize the grasping force. Finally, a unified design (Final design) is presented in great detail. Comparison of all prototypes is done from different angles to evaluate the best design. The kinematic features of intermediate mode have been analysed to optimize both the flexibility and the robustness of the system, as well as to minimize the number of pneumatic muscles. The final design of an ambidextrous finger has developed, tested and 3D printed
Dilepton and Photon Emission Rates from a Hadronic Gas
We analyze the dilepton and photon emission rates from a hadronic gas using
chiral reduction formulas and a virial expansion. The emission rates are
reduced to pertinent vacuum correlation functions, most of which can be
assessed from experiment. Our results indicate that in the low mass region, the
dilepton and photon rates are enhanced compared to most of the calculations
using chiral Lagrangians. The enhancement is further increased through a finite
pion chemical potential. An estimate of the emission rates is also made using
Haag's expansion for the electromagnetic current. The relevance of these
results to dilepton and photon emission rates in heavy-ion collisions is
discussed.Comment: 7 pages, LaTeX using revTeX, 6 figures imbedded in text. Figures
slightly changed, text left unchange
Brown Dwarfs in the Pleiades Cluster. III. A deep IZ survey
We present the results of a deep CCD-based IZ photometric survey of a ~1 sq.
deg area in the central region of the Pleiades Galactic open cluster. The
magnitude coverage of our survey (from I~17.5 down to 22) allows us to detect
substellar candidates with masses between 0.075 and 0.03 Msol. Details of the
photometric reduction and selection criteria are given. Finder charts prepared
from the I-band images are provided.Comment: 11 pages with 8 figures, 4 of them are finder charts given in gif
format. Accepted for publication in A&AS. Also available at
http://www.iac.es/publicaciones/preprints.htm
Correlation between clustering and degree in affiliation networks
We are interested in the probability that two randomly selected neighbors of
a random vertex of degree (at least) are adjacent. We evaluate this
probability for a power law random intersection graph, where each vertex is
prescribed a collection of attributes and two vertices are adjacent whenever
they share a common attribute. We show that the probability obeys the scaling
as . Our results are mathematically rigorous. The
parameter is determined by the tail indices of power law
random weights defining the links between vertices and attributes
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