6,709 research outputs found
Breaking arches with vibrations: the role of defects
We present experimental results about the stability of arches against
external vibrations. Two dimensional strings of mutually stabilizing grains are
geometrically analyzed and subsequently submitted to a periodic forcing at
fixed frequency and increasing amplitude. The main factor that determines the
granular arch resistance against vibrations is the maximum angle among those
formed between any particle of the arch and its two neighbors: the higher the
maximum angle is, the easier to break the arch. Based in an analysis of the
forces, a simple explanation is given for this dependence. From this,
interesting information can be extracted about the expected magnitudes of
normal forces and friction coefficients of the particles conforming the arches
Using automatic robot programming for space telerobotics
The interpreter of a task level robot programming system called Handey is described. Handey is a system that can recognize, manipulate and assemble polyhedral parts when given only a specification of the goal. To perform an assembly, Handey makes use of a recognition module, a gross motion planner, a grasp planner, a local approach planner and is capable of planning part re-orientation. The possibility of including these modules in a telerobotics work-station is discussed
Power scaling rules for charmonia production and HQEFT
We discuss the power scaling rules along the lines of a complete Heavy Quark
Effective Field Theory (HQEFT) for the description of heavy quarkonium
production through a color-octet mechanism. To this end, we firstly derive a
tree-level heavy quark effective Lagrangian keeping both particle-antiparticle
mixed sectors allowing for heavy quark-antiquark pair annihilation and
creation, but describing only low-energy modes around the heavy quark mass.
Then we show the consistency of using HQEFT fields in constructing four-fermion
local operators a la NRQCD, to be identified with standard color-octet matrix
elements. We analyze some numerical values extracted from charmonia production
by different authors and their hierarchy in the light of HQEFT.Comment: LaTeX, 19 pages, 3 EPS figure
The Near-Horizon Limit of the Extreme Rotating d=5 Black Hole as a Homogenous Spacetime
We show that the spacetime of the near-horizon limit of the extreme rotating
d=5 black hole, which is maximally supersymmetric in N=2,d=5 supergravity for
any value of the rotation parameter j in [-1,1], is locally isomorphic to a
homogeneous non-symmetric spacetime corresponding to an element of the
1-parameter family of coset spaces SO(2,1)x SO(3)/SO(2)_j in which the subgroup
SO(2)_j is a combination of the two SO(2) subgroups of SO(2,1) and SO(3).Comment: Some points clarified and misprints corrected. Version to be
published in Classical and Quantum Gravit
On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion
We study the chronocyclic character, i.e. the joint temporal and spectral
properties, of the single-photon constituents of photon pairs generated by
spontaneous parametric down conversion. In particular we study how single
photon properties, including purity and single-photon chirp, depend on photon
pair properties, including the type of signal-idler spectral and correlations
and the level of pump chirp.Comment: 13 pages, 6 figure
Integration of hydrothermal liquefaction and carbon capture and storage for the production of advanced liquid biofuels with negative CO2 emissions
The technical and economic feasibility to deliver sustainable liquid biocrude
through hydrothermal liquefaction (HTL) while enabling negative carbon dioxide
emissions is evaluated in this paper, looking into the potential of the process
in the context of negative emission technologies (NETs) for climate change
mitigation. In the HTL process, a gas phase consisting mainly of carbon dioxide
is obtained as a side product driving a potential for the implementation of
carbon capture and storage in the process (BECCS) that has not been explored
yet in the existing literature and is undertaken in this study. To this end,
the process is divided in a standard HTL base and a carbon capture add-on,
having forestry residues as feedstock. The Selexol technology is adapted in a
novel scheme to simultaneously separate the CO2 from the HTL gas and recover
the excess hydrogen for biocrude upgrading. The cost evaluation indicates that
the additional cost of the carbon capture can be compensated by revenues from
the excess process heat and the European carbon allowance market. The impact in
the MFSP of the HTL base case ranges from -7% to 3%, with -15% in the most
favorable scenario, with a GHG emissions reduction potential of 102-113%
compared to the fossil baseline. These results show that the implementation of
CCS in the HTL process is a promising alternative from technical, economic and
environmental perspective in future scenarios in which advanced liquid biofuels
and NETs are expected to play a role in the decarbonization of the energy
system
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 EPS figure
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