9,132 research outputs found
Spacetime-Filling Branes and Strings with Sixteen Supercharges
We discuss branes whose worldvolume dimension equals the target spacetime
dimension, i.e. ``spacetime-filling branes''. In addition to the D9-branes,
there are 9-branes in the NS-NS sectors of both the IIA and IIB strings. The
worldvolume actions of these branes are constructed, via duality, from the
known actions of branes with codimension larger than zero. Each of these types
of branes is used in the construction of a string theory with sixteen
supercharges by modding out a type II string by an appropriate discrete
symmetry and adding 32 9-branes. These constructions are related by a web of
dualities and each arises as a different limit of the Horava-Witten
construction.Comment: 43 pages, LaTeX, 8 figures, uses html.sty, version to appear in Nucl.
Phys.
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
On the Use of Second Order Neighbors to Escape from Local Optima
Designing efficient local search based algorithms requires to consider the specific properties of the problems. We introduce a simple and effi- cient strategy, the Extended Reach, that escapes from local optima ob- tained from a best improvement local search and apply it to the linear ordering problem (LOP), the traveling salesperson problem (TSP) and the quadratic assignment problem (QAP). This strategy is based on two landscape properties observed in the literature. First, it considers that a local optimum is usually located in the frontier of its own attraction basin, and thus, it is enough to inspect the second order neighbors to reach a (better) solution inside an attraction basin of a better local optimum. Second, taking into account that for the LOP and specific neighborhoods it is possible to discard solutions without the need of being evaluated, we extend this result to the TSP with the 2-opt neighborhood to avoid the unnecessary evaluation of solutions. Efficient ways of evaluating the second order neighbors are also presented, based on the cost differences, reducing significantly the computation cost. Experimental results on ran- dom and benchmark instances show that our strategy, indeed, escapes from local optima despite its simplicity.PID2019-104966GB-I00
AXA Research Fun
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
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
New design model for brittle failure in the parallel-to-grain direction of timber connections with large diameter fasteners
Timber connections with steel dowel-type fasteners may fail in ductile or brittle ways. The design of this joints was traditionally focused on ductile failure, assuming that brittle failure could be avoided by means of
geometrical limitations. However, recent studies demonstrated that these assumptions do not always guarantee ductile failure. A new design model for timber connections with small diameter dowel-type fasteners is provided in this paper. Its improved accuracy is demonstrated by analysing an extensive database of experimental tests and comparing its prediction accuracy to that of existing models
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
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