1,392 research outputs found
Weak and strong electronic correlations in Fe superconductors
In this chapter the strength of electronic correlations in the normal phase
of Fe-superconductors is discussed. It will be shown that the agreement between
a wealth of experiments and DFT+DMFT or similar approaches supports a scenario
in which strongly-correlated and weakly-correlated electrons coexist in the
conduction bands of these materials. I will then reverse-engineer the realistic
calculations and justify this scenario in terms of simpler behaviors easily
interpreted through model results. All pieces come together to show that Hund's
coupling, besides being responsible for the electronic correlations even in
absence of a strong Coulomb repulsion is also the origin of a subtle emergent
behavior: orbital decoupling. Indeed Hund's exchange decouples the charge
excitations in the different Iron orbitals involved in the conduction bands
thus causing an independent tuning of the degree of electronic correlation in
each one of them. The latter becomes sensitive almost only to the offset of the
orbital population from half-filling, where a Mott insulating state is
invariably realized at these interaction strengths. Depending on the difference
in orbital population a different 'Mottness' affects each orbital, and thus
reflects in the conduction bands and in the Fermi surfaces depending on the
orbital content.Comment: Book Chapte
Practical private database queries based on a quantum key distribution protocol
Private queries allow a user Alice to learn an element of a database held by
a provider Bob without revealing which element she was interested in, while
limiting her information about the other elements. We propose to implement
private queries based on a quantum key distribution protocol, with changes only
in the classical post-processing of the key. This approach makes our scheme
both easy to implement and loss-tolerant. While unconditionally secure private
queries are known to be impossible, we argue that an interesting degree of
security can be achieved, relying on fundamental physical principles instead of
unverifiable security assumptions in order to protect both user and database.
We think that there is scope for such practical private queries to become
another remarkable application of quantum information in the footsteps of
quantum key distribution.Comment: 7 pages, 2 figures, new and improved version, clarified claims,
expanded security discussio
The Magic Number Problem for Subregular Language Families
We investigate the magic number problem, that is, the question whether there
exists a minimal n-state nondeterministic finite automaton (NFA) whose
equivalent minimal deterministic finite automaton (DFA) has alpha states, for
all n and alpha satisfying n less or equal to alpha less or equal to exp(2,n).
A number alpha not satisfying this condition is called a magic number (for n).
It was shown in [11] that no magic numbers exist for general regular languages,
while in [5] trivial and non-trivial magic numbers for unary regular languages
were identified. We obtain similar results for automata accepting subregular
languages like, for example, combinational languages, star-free, prefix-,
suffix-, and infix-closed languages, and prefix-, suffix-, and infix-free
languages, showing that there are only trivial magic numbers, when they exist.
For finite languages we obtain some partial results showing that certain
numbers are non-magic.Comment: In Proceedings DCFS 2010, arXiv:1008.127
First crystal structures of 1-deoxy-D-xylulose 5-phosphate synthase (DXPS) from Mycobacterium tuberculosis indicate a distinct mechanism of intermediate stabilization
The development of drug resistance by Mycobacterium tuberculosis and other pathogenic bacteria emphasizes the need for new antibiotics. Unlike animals, most bacteria synthesize isoprenoid precursors through the MEP pathway. 1-Deoxy-D-xylulose 5-phosphate synthase (DXPS) catalyzes the first reaction of the MEP pathway and is an attractive target for the development of new antibiotics. We report here the successful use of a loop truncation to crystallize and solve the first DXPS structures of a pathogen, namely M. tuberculosis (MtDXPS). The main difference found to other DXPS structures is in the active site where a highly coordinated water was found, showing a new mechanism for the enamine-intermediate stabilization. Unlike other DXPS structures, a "fork-like" motif could be identified in the enamine structure, using a different residue for the interaction with the cofactor, potentially leading to a decrease in the stability of the intermediate. In addition, electron density suggesting a phosphate group could be found close to the active site, provides new evidence for the D-GAP binding site. These results provide the opportunity to improve or develop new inhibitors specific for MtDXPS through structure-based drug design
First crystal structures of 1-deoxy-D-xylulose 5-phosphate synthase (DXPS) from Mycobacterium tuberculosis indicate a distinct mechanism of intermediate stabilization
The development of drug resistance by Mycobacterium tuberculosis and other pathogenic bacteria
emphasizes the need for new antibiotics. Unlike animals, most bacteria synthesize isoprenoid
precursors through the MEP pathway. 1-Deoxy-d-xylulose 5-phosphate synthase (DXPS) catalyzes the
frst reaction of the MEP pathway and is an attractive target for the development of new antibiotics.
We report here the successful use of a loop truncation to crystallize and solve the frst DXPS structures
of a pathogen, namely M. tuberculosis (MtDXPS). The main diference found to other DXPS structures
is in the active site where a highly coordinated water was found, showing a new mechanism for
the enamine-intermediate stabilization. Unlike other DXPS structures, a “fork-like” motif could be
identifed in the enamine structure, using a diferent residue for the interaction with the cofactor,
potentially leading to a decrease in the stability of the intermediate. In addition, electron density
suggesting a phosphate group could be found close to the active site, provides new evidence for
the D-GAP binding site. These results provide the opportunity to improve or develop new inhibitors
specifc for MtDXPS through structure-based drug design
Contribution of brown carbon to light absorption in emissions of European residential biomass combustion appliances
Residential biomass combustion significantly contributes to light-absorbing carbonaceous aerosols in the atmosphere, impacting the earth's radiative balance at regional and global levels. This study investigates the contribution of brown carbon (BrC) to the total particulate light absorption in the wavelength range of 370–950 nm (BrC370–950) and the particulate absorption Ångström exponents (AAE470/950) in 15 different European residential combustion appliances using a variety of wood-based fuels. BrC370–950 was estimated to be from 1 % to 21 % for wood log stoves and 10 % for a fully automatized residential pellet boiler. Correlations between the ratio of organic to elemental carbon (OC / EC) and BrC370–950 indicated that a one-unit increase in OC / EC corresponded to approximately a 14 % increase in BrC370–950. Additionally, BrC370–950 was clearly influenced by the fuel moisture content and the combustion efficiency, while the effect of the combustion appliance type was less prominent. AAE470/950 of wood log combustion aerosols ranged from 1.06 to 1.61. By examining the correlation between AAE470/950 and OC / EC, an AAE470/950 close to unity was found for pure black carbon (BC) particles originating from residential wood combustion. This supports the common assumption used to differentiate light absorption caused by BC and BrC. Moreover, diesel aerosols exhibited an AAE470/950 of 1.02, with BrC contributing only 0.66 % to the total absorption, aligning with the assumption employed in source apportionment. These findings provide important data to assess the BrC from residential wood combustion with different emission characteristics and confirm that BrC can be a major contributor to particulate UV and near-UV light absorption for northern European wood stove emissions with relatively high OC / EC ratios.</p
Genome variations: Effects on the robustness of neuroevolved control for swarm robotics systems
Manual design of self-organized behavioral control for swarms of robots is a complex task. Neuroevolution has proved a viable alternative given its capacity to automatically synthesize controllers. In this paper, we introduce the concept of Genome Variations (GV) in the neuroevolution of behavioral control for robotic swarms. In an evolutionary setup with GV, a slight mutation is applied to the evolving neural network parameters before they are copied to the robots in a swarm. The genome variation is individual to each robot, thereby generating a slightly heterogeneous swarm. GV represents a novel approach to the evolution of robust behaviors, expected to generate more stable and robust individual controllers, and bene t swarm behaviors that can deal with small heterogeneities in the behavior of other members in the swarm. We conduct experiments using an aggregation task, and compare the evolved solutions to solutions evolved under ideal, noise-free conditions, and to solutions evolved with traditional sensor noise.info:eu-repo/semantics/acceptedVersio
Simulating Kilobots within ARGoS: models and experimental validation
The Kilobot is a popular platform for swarm robotics research
due to its low cost and ease of manufacturing. Despite this, the effort to
bootstrap the design of new behaviours and the time necessary to develop
and debug new behaviours is considerable. To make this process less
burdensome, high-performing and flexible simulation tools are important.
In this paper, we present a plugin for the ARGoS simulator designed
to simplify and accelerate experimentation with Kilobots. First, the plugin
supports cross-compiling against the real robot platform, removing
the need to translate algorithms across different languages. Second, it is
highly configurable to match the real robot behaviour. Third, it is fast
and allows running simulations with several hundreds of Kilobots in a
fraction of real time. We present the design choices that drove our work
and report on experiments with physical robots performed to validate
simulated behaviours
Variation of Absorption Angstrom Exponent in Aerosols From Different Emission Sources
The absorption Angstrom exponent (AAE) describes the spectral dependence of light absorption by aerosols. AAE is typically used to differentiate between different aerosol types for example., black carbon, brown carbon, and dust particles. In this study, the variation of AAE was investigated mainly in fresh aerosol emissions from different fuel and combustion types, including emissions from ships, buses, coal-fired power plants, and residential wood burning. The results were assembled to provide a compendium of AAE values from different emission sources. A dual-spot aethalometer (AE33) was used in all measurements to obtain the light absorption coefficients at seven wavelengths (370-950 nm). AAE(470/950) varied greatly between the different emission sources, ranging from -0.2 +/- 0.7 to 3.0 +/- 0.8. The correlation between the AAE(470/950) and AAE(370-950) results was good (R-2 = 0.95) and the mean bias error between these was 0.02. In the ship engine exhaust emissions, the highest AAE(470/950) values (up to 2.0 +/- 0.1) were observed when high sulfur content heavy fuel oil was used, whereas low sulfur content fuels had the lowest AAE(470/950) (0.9-1.1). In the diesel bus exhaust emissions, AAE(470/950) increased in the order of acceleration (0.8 +/- 0.1), deceleration (1.1 +/- 0.1), and steady driving (1.2 +/- 0.1). In the coal-fired power plant emissions, the variation of AAE(470/950) was substantial (from -0.1 +/- 2.1 to 0.9 +/- 1.6) due to the differences in the fuels and flue gas cleaning conditions. Fresh wood-burning derived aerosols had AAE(470/950) from 1.1 +/- 0.1 (modern masonry heater) to 1.4 +/- 0.1 (pellet boiler), lower than typically associated with wood burning, while the burn cycle phase affected AAE variation.Peer reviewe
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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