727 research outputs found
A study of the entanglement in systems with periodic boundary conditions
We define the local periodic linking number, LK, between two oriented closed
or open chains in a system with three-dimensional periodic boundary conditions.
The properties of LK indicate that it is an appropriate measure of entanglement
between a collection of chains in a periodic system. Using this measure of
linking to assess the extent of entanglement in a polymer melt we study the
effect of CReTA algorithm on the entanglement of polyethylene chains. Our
numerical results show that the statistics of the local periodic linking number
observed for polymer melts before and after the application of CReTA are the
same.Comment: 11 pages, 11 figure
Improved Exploration for Safety-Embedded Differential Dynamic Programming Using Tolerant Barrier States
In this paper, we introduce Tolerant Discrete Barrier States (T-DBaS), a
novel safety-embedding technique for trajectory optimization with enhanced
exploratory capabilities. The proposed approach generalizes the standard
discrete barrier state (DBaS) method by accommodating temporary constraint
violation during the optimization process while still approximating its safety
guarantees. Consequently, the proposed approach eliminates the DBaS's safe
nominal trajectories assumption, while enhancing its exploration effectiveness
for escaping local minima. Towards applying T-DBaS to safety-critical
autonomous robotics, we combine it with Differential Dynamic Programming (DDP),
leading to the proposed safe trajectory optimization method T-DBaS-DDP, which
inherits the convergence and scalability properties of the solver. The
effectiveness of the T-DBaS algorithm is verified on differential drive robot
and quadrotor simulations. In addition, we compare against the classical
DBaS-DDP as well as Augmented-Lagrangian DDP (AL-DDP) in extensive numerical
comparisons that demonstrate the proposed method's competitive advantages.
Finally, the applicability of the proposed approach is verified through
hardware experiments on the Georgia Tech Robotarium platform
Team identification more than organizational identification predicts counterproductive work behavior and organizational citizenship behavior and mediates influences of communication climate and perceived external prestige
Organizational identification has been linked to both positive behavior and negative behavior at work. Based on theory and research that suggest that for many organizational behaviors, team identification may be a more important influence than organizational identification, we advance a research model proposing that team identification, more than organizational identification, predicts counterproductive work behavior and organizational citizenship behavior and is the more important mediator of the influence of communication climate (CC) and perceived external prestige (PEP) on these outcomes. This research model was tested in a survey of N = 300 employees of four Italian organizations from different sectors. Results show that team identification, but not organizational identification, predicts counterproductive behavior and citizenship behavior and mediates the influence of CC and PEP. To enhance team identification for sustaining positive voluntary behavior at work, two possible strategies could be considered: improving perceived external prestige and promoting a good communication climate
Marine alien species in Greek Seas: Additions and amendments by 2010
An update of the inventory of alien marine species from the coastal and offshore waters of Greece is presented. Records were compiled based on the existing scientific and grey literature, including the HCMR database of Greek alien species (ELNAIS), technical reports, scientific congresses, academic dissertations, websites, and unpublished/personal observations. 47 species were added to the inventory, including 34 invertebrates, one vertebrate (fish), three plants, eight protozoa, and one cyanobacterium. With the new records, the inventory of alien marine species of Greece now includes a total of 237 species (33 macrophytes, 131 invertebrates, 42 vertebrates, two bacteria and 29 protozoans). Among these, the presence of the gastropodHypselodoris infucata, the bivalvesDendrostrea frons and Septifer forskaliand the chondrichthyan Rhizoprionodon acutus is reported here for the first time. Based on molecular analysis, the occurrence of Bulla arabica in Greek waters is confirmed, and the suggestion that previous records of Bulla ampulla in the Mediterranean should be considered as misidentification of B. arabica is further supported. The acclimitization status of earlier records was revised in the light of new data, and thus the fishEnchelycore anatina, Seriola fasciata andTylerius spinosissimus, the red algaeHypnea cornuta and Sarconema scinaioides, the scyphomedusaCassiopea andromeda, the cephalopodSepioteuthis lessoniana, the nudibranchChromodoris annulata and the bivalvesGastrochaena cymbium andPseudochama corbieri were upgraded from casual records to established populations. The increased rate of introductions of warm water species confirms previous findings, which link the rate of introduction in the eastern Mediterranean to climate change
Numerical renormalization-group study of spin correlations in one-dimensional random spin chains
We calculate the ground-state two-spin correlation functions of spin-1/2
quantum Heisenberg chains with random exchange couplings using the real-space
renormalization group scheme. We extend the conventional scheme to take account
of the contribution of local higher multiplet excitations in each decimation
step. This extended scheme can provide highly accurate numerical data for large
systems. The random average of staggered spin correlations of the chains with
random antiferromagnetic (AF) couplings shows algebraic decay like ,
which verifies the Fisher's analytic results. For chains with random
ferromagnetic (FM) and AF couplings, the random average of generalized
staggered correlations is found to decay more slowly than a power-law, in the
form close to . The difference between the distribution functions of
the spin correlations of the random AF chains and of the random FM-AF chains is
also discussed.Comment: 14 pages including 8 figures, REVTeX, submitted to Physical Review
WIRED: World Wide Web Interactive Remote Event Display
WIRED is a framework, written in Java, to build High Energy Physics event displays that can be used across the network. To guarantee portability across all platforms, WIRED is implemented in the Java language and uses the Swing user interface component set. It can be used as a stand-alone application or as an applet inside a WWW browser. The graphical user interface allows for multiple views and for multiple controls acting on those views. A detector tree control is available to toggle the visibility of parts of the events and detector geometry. XML (Extensible Markup Language), RMI (Remote Method Invocation) and CORBA loaders can be used to load event data as well as geometry data, and to connect to FORTRAN, C, C++ and Java reconstruction programs. Non-linear and non-Cartesian projections (e.g. fish-eye, rho-phi, rho-Z, phi-Z) provide special views to get a better understanding of events. WIRED has grown to be a framework in use and under development in several HEP experiments (ATLAS, CHORUS, DELPHI, LHCb, BaBar, D0 and ZEUS). WIRED event displays have also proven to be useful to explain High Energy Physics to the general public. Both CERN, in its travelling exhibition and MicroCosm, and RAL, during its open days, have displays set up
Density of states in d-wave superconductors disordered by extended impurities
The low-energy quasiparticle states of a disordered d-wave superconductor are
investigated theoretically. A class of such states, formed via tunneling
between the Andreev bound states that are localized around extended impurities
(and result from scattering between pair-potential lobes that differ in sign)
is identified. Its (divergent) contribution to the total density of states is
determined by taking advantage of connections with certain one-dimensional
random tight-binding models. The states under discussion should be
distinguished from those associated with nodes in the pair potential.Comment: 5 pages, 1 figur
Delocalization and conductance quantization in one-dimensional systems
We investigate the delocalization and conductance quantization in finite
one-dimensional chains with only off-diagonal disorder coupled to leads. It is
shown that the appearence of delocalized states at the middle of the band under
correlated disorder is strongly dependent upon the even-odd parity of the
number of sites in the system. In samples with inversion symmetry the
conductance equals for odd samples, and is smaller for even parity.
This result suggests that this even-odd behaviour found previously in the
presence of electron correlations may be unrelated to charging effects in the
sample.Comment: submitted to PR
Potential for energy production from farm wastes using anaerobic digestion in the UK : An economic comparison of different size plants
Anaerobic digestion (AD) plants enable renewable fuel, heat, and electricity production, with their efficiency and capital cost strongly dependent on their installed capacity. In this work, the technical and economic feasibility of different scale AD combined heat and power (CHP) plants was analyzed. Process configurations involving the use of waste produced in different farms as feedstock for a centralized AD plant were assessed too. The results show that the levelized cost of electricity are lower for large-scale plants due to the use of more efficient conversion devices and their lower capital cost per unit of electricity produced. The levelized cost of electricity was estimated to be 4.3 p/kWhe for AD plants processing the waste of 125 dairy cow sized herds compared to 1.9 p/kWhe for AD plants processing waste of 1000 dairy cow sized herds. The techno-economic feasibility of the installation of CO2 capture units in centralized AD-CHP plants was also undertaken. The conducted research demonstrated that negative CO2 emission AD power generation plants could be economically viable with currently paid feed-in tariffs in the UK
Optimal control as a graphical model inference problem
We reformulate a class of non-linear stochastic optimal control problems
introduced by Todorov (2007) as a Kullback-Leibler (KL) minimization problem.
As a result, the optimal control computation reduces to an inference
computation and approximate inference methods can be applied to efficiently
compute approximate optimal controls. We show how this KL control theory
contains the path integral control method as a special case. We provide an
example of a block stacking task and a multi-agent cooperative game where we
demonstrate how approximate inference can be successfully applied to instances
that are too complex for exact computation. We discuss the relation of the KL
control approach to other inference approaches to control.Comment: 26 pages, 12 Figures; Machine Learning Journal (2012
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