Showing papers by "Jožef Stefan Institute published in 2017"

Advanced capabilities for materials modelling with Quantum ESPRESSO.

Abstract: Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software

Advanced capabilities for materials modelling with Quantum ESPRESSO

Abstract: Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

Averages of B-Hadron, C-Hadron, and tau-lepton properties as of early 2012

Abstract: This article reports world averages of measurements of b-hadron, c-hadron, and tau-lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through the end of 2011. In some cases results available in the early part of 2012 are included. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays and CKM matrix elements.

Domain-wall conduction in ferroelectric BiFeO3 controlled by accumulation of charged defects.

Abstract: Mobile charged defects, accumulated in the domain-wall region to screen polarization charges, have been proposed as the origin of the electrical conductivity at domain walls in ferroelectric materials. Despite theoretical and experimental efforts, this scenario has not been directly confirmed, leaving a gap in the understanding of the intriguing electrical properties of domain walls. Here, we provide atomic-scale chemical and structural analyses showing the accumulation of charged defects at domain walls in BiFeO3. The defects were identified as Fe4+ cations and bismuth vacancies, revealing p-type hopping conduction at domain walls caused by the presence of electron holes associated with Fe4+. In agreement with the p-type behaviour, we further show that the local domain-wall conductivity can be tailored by controlling the atmosphere during high-temperature annealing. This work has possible implications for engineering local conductivity in ferroelectrics and for devices based on domain walls.

The Role of Interferons in Inflammation and Inflammasome Activation.

Abstract: Inflammation is an essential physiological process which enables survival during infection and maintains tissue homeostasis. Interferons and pro- and anti- inflammatory cytokines are crutial for appropriate response to pathogens, damaged cells or irritants in inflamamtory response. The inflammasom is multiprotein complex which initiates cleavage of pro-inflammatory cytokines IL-1β and IL-18 into active forms. In addition, inflammasomes initiate pyroptotic cell death. In the present review I summarize and analyze recent findings regarding the crosstalk of interferons and inflammasomes.

A high-temperature quantum spin liquid with polaron spins

Abstract: The existence of a quantum spin liquid (QSL) in which quantum fluctuations of spins are sufficiently strong to preclude spin ordering down to zero temperature was originally proposed theoretically more than 40 years ago, but its experimental realization turned out to be very elusive. Here we report on an almost ideal spin liquid state that appears to be realized by atomic-cluster spins on the triangular lattice of a charge-density wave state of 1T-TaS2. In this system, the charge excitations have a well-defined gap of ∼0.3 eV, while nuclear quadrupole resonance and muon-spin-relaxation experiments reveal that the spins show gapless QSL dynamics and no long-range magnetic order at least down to 70 mK. Canonical T2 power-law temperature dependence of the spin relaxation dynamics characteristic of a QSL is observed from 200 K to Tf = 55 K. Below this temperature, we observe a new gapless state with reduced density of spin excitations and high degree of local disorder signifying new quantum spin order emerging from the QSL. In the charge-density wave state of tantalum sulfide, tantalum atoms group into a Star-of-David arrangement. Experiments show that the polaron spins associated with these atomic clusters can form a quantum spin liquid.

Overview of the JET results in support to ITER

Abstract: The 2014-2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L-H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at β N ∼ 1.8 and n/n GW ∼ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D-T campaign and 14 MeV neutron calibration strategy are reviewed.

The role of the S 3 GUT leptoquark in flavor universality and collider searches

Abstract: We investigate the ability of the S 3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S 3 leptoquark with quantum numbers $$ \left(\overline{\mathbf{3}},\mathbf{3},1/3\right) $$ naturally emerges in the context of an SU(5) GUT model without any conflict with the stringent limits from observed nucleon stability. Scalar leptoquark S 3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both R K(∗) and R D(∗) . We quantify this suitability with numerical fits to a plethora of relevant flavor observables. The proposed SU(5) model calls for a second leptoquark state, i.e., $$ {\tilde{R}}_2 $$ with quantum numbers (3 , 2 , 1/6), if one is to generate gauge coupling unification and neutrino mass. We accordingly include it in our study to investigate $$ {\tilde{R}}_2 $$ ’s ability to offset adverse effects of S 3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S 3 to τ leptons are preferred. We furthermore identify $$ B\to {K}^{\left(\ast \right)}\overline{ u} u $$ as the most sensitive channel to probe the preferred region of parameter space. Large couplings of S 3 to τ leptons are finally confronted with the experimental searches for τ final states at the Large Hadron Collider. These searches comprise a study of decay products of the leptoquark pair production, as well as, and more importantly, an analysis of the high-mass ττ finalstates.

Mycotoxin Decontamination of Food: Cold Atmospheric Pressure Plasma versus “Classic” Decontamination

Abstract: Mycotoxins are secondary metabolites produced by several filamentous fungi, which frequently contaminate our food, and can result in human diseases affecting vital systems such as the nervous and immune systems. They can also trigger various forms of cancer. Intensive food production is contributing to incorrect handling, transport and storage of the food, resulting in increased levels of mycotoxin contamination. Mycotoxins are structurally very diverse molecules necessitating versatile food decontamination approaches, which are grouped into physical, chemical and biological techniques. In this review, a new and promising approach involving the use of cold atmospheric pressure plasma is considered, which may overcome multiple weaknesses associated with the classical methods. In addition to its mycotoxin destruction efficiency, cold atmospheric pressure plasma is cost effective, ecologically neutral and has a negligible effect on the quality of food products following treatment in comparison to classical methods.

A rule-based named-entity recognition method for knowledge extraction of evidence-based dietary recommendations.

Abstract: Evidence-based dietary information represented as unstructured text is a crucial information that needs to be accessed in order to help dietitians follow the new knowledge arrives daily with newly published scientific reports. Different named-entity recognition (NER) methods have been introduced previously to extract useful information from the biomedical literature. They are focused on, for example extracting gene mentions, proteins mentions, relationships between genes and proteins, chemical concepts and relationships between drugs and diseases. In this paper, we present a novel NER method, called drNER, for knowledge extraction of evidence-based dietary information. To the best of our knowledge this is the first attempt at extracting dietary concepts. DrNER is a rule-based NER that consists of two phases. The first one involves the detection and determination of the entities mention, and the second one involves the selection and extraction of the entities. We evaluate the method by using text corpora from heterogeneous sources, including text from several scientifically validated web sites and text from scientific publications. Evaluation of the method showed that drNER gives good results and can be used for knowledge extraction of evidence-based dietary recommendations.

Mechanistic Study of Magnesium–Sulfur Batteries

Abstract: Magnesium–sulfur batteries are considered as attractive energy-storage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the mechanism of a Mg–S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS (resonant inelastic X-ray scattering), and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystallizes in the rock-salt structure with octahedral coordination of magnesium.

Hypoxia-Induced Oxidative Stress Modulation with Physical Activity

Abstract: Increased oxidative stress, defined as an imbalance between prooxidants and antioxidants, resulting in molecular damage and disruption of redox signaling, is associated with numerous pathophysiological processes and known to exacerbate chronic diseases. Prolonged systemic hypoxia, induced either by exposure to terrestrial altitude or a reduction in ambient O2 availability is known to elicit oxidative stress and thereby alter redox balance in healthy humans. The redox balance modulation is also highly dependent on the level of physical activity. For example, both high-intensity exercise and inactivity, representing the two ends of the physical activity spectrum, are known to promote oxidative stress. Numerous to-date studies indicate that hypoxia and exercise can exert additive influence upon redox balance alterations. However, recent evidence suggests that moderate physical activity can attenuate altitude/hypoxia-induced oxidative stress during long-term hypoxic exposure. The purpose of this review is to summarize recent findings on hypoxia-related oxidative stress modulation by different activity levels during prolonged hypoxic exposures and examine the potential mechanisms underlying the observed redox balance changes. The paper also explores the applicability of moderate activity as a strategy for attenuating hypoxia-related oxidative stress. Moreover, the potential of such moderate intensity activities used to counteract inactivity-related oxidative stress, often encountered in pathological, elderly and obese populations is also discussed. Finally, future research directions for investigating interactive effects of altitude/hypoxia and exercise on oxidative stress are proposed.

Ferromagnetic nematic liquid crystals

Abstract: This review presents experimental realization and behaviour of the ferromagnetic nematic phase, which is observed in different suspensions of magnetic nanoplatelets. After a general introduction, the challenges in the synthesis of magnetic nanoplatelets and preparation of the nematic suspensions are discussed. A brief explanation of a simple macroscopic theory, which can be used to understand the main features of the ferromagnetic phase, follows. In the main part, four different ferromagnetic nematic systems are presented: (i) ferromagnetic suspensions of the platelets in nematic liquid crystals, (ii) dense suspensions in an isotropic solvent – ferromagnetic ferrofluids, (iii) biaxial ferromagnetic nematic suspensions, and (iv) chiral ferromagnetic suspensions. The main focus is on the formation of the ferromagnetic phases and the growth of the magnetic domains. At the end, dynamics of ferromagnetic liquid crystals and methods for their observation are briefly discussed.

Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron Elettra

Abstract: X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure.

Stance and influence of Twitter users regarding the Brexit referendum

Abstract: Social media are an important source of information about the political issues, reflecting, as well as influencing, public mood. We present an analysis of Twitter data, collected over 6 weeks before the Brexit referendum, held in the UK in June 2016. We address two questions: what is the relation between the Twitter mood and the referendum outcome, and who were the most influential Twitter users in the pro- and contra-Brexit camps? First, we construct a stance classification model by machine learning methods, and are then able to predict the stance of about one million UK-based Twitter users. The demography of Twitter users is, however, very different from the demography of the voters. By applying a simple age-adjusted mapping to the overall Twitter stance, the results show the prevalence of the pro-Brexit voters, something unexpected by most of the opinion polls. Second, we apply the Hirsch index to estimate the influence, and rank the Twitter users from both camps. We find that the most productive Twitter users are not the most influential, that the pro-Brexit camp was four times more influential, and had considerably larger impact on the campaign than the opponents. Third, we find that the top pro-Brexit communities are considerably more polarized than the contra-Brexit camp. These results show that social media provide a rich resource of data to be exploited, but accumulated knowledge and lessons learned from the opinion polls have to be adapted to the new data sources.

Search for photons with energies above 10$^{18}$ eV using the hybrid detector of the Pierre Auger Observatory

Abstract: A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1 - 2 EeV are found, which is compatible with the expected hadroninduced background. Upper limits on the integral flux of ultra-high energy photons of 0.027, 0.009, 0.008, 0.008 and 0.007 km -2 sr -1 yr -1 are derived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10 EeV. These limits bound the fractions of photons in the all-particle integral flux below 0.1%, 0.15%, 0.33%, 0.85% and 2.7%. For the first time the photon fraction at EeV energies is constrained at the sub-percent level. The improved limits are below the flux of diffuse photons predicted by some astrophysical scenarios for cosmogenic photon production. The new results rule-out the early top-down models - in which ultra-high energy cosmic rays are produced by, e.g., the decay of super-massive particles - and challenge the most recent super-heavy dark matter models.

Plasma-wall interaction studies within the EUROfusion consortium: progress on plasma-facing components development and qualification

Abstract: The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a suc ...

Structure of nanoscale-pitch helical phases: blue phase and twist-bend nematic phase resolved by resonant soft X-ray scattering.

Abstract: Periodic structures of phases with orientational order of molecules but homogenous electron density distribution: a short pitch cholesteric phase, blue phase and twist-bend nematic phase, were probed by resonant soft X-ray scattering (RSoXS) at the carbon K-edge. The theoretical model shows that in the case of a simple heliconical nematic structure, two resonant signals corresponding to the full and half pitch band should be present, while only the full pitch band is observed experimentally. This suggests that the twist-bend nematic phase has a complex structure with a double-helix built of two interlocked, shifted helices. We confirm that the helical pitch in the twist-bend nematic phase is in a 10 nm range for both the chiral and achiral materials. We also show that the symmetry of the blue phase can be unambiguously determined through a resonant enhancement of the X-ray diffraction signals, by including polarization effects, which are found to be an important indicator in phase structure determination.

Improved electron–hole separation and migration in anatase TiO2 nanorod/reduced graphene oxide composites and their influence on photocatalytic performance

Abstract: The as-synthesized TiO2 nanorods a-TNR (amorphous TiO2 layer covering the crystalline anatase TiO2 core) and TNR (fully crystalline anatase TiO2) were decorated with reduced graphene oxide (rGO) to synthesize two series of TiO2 + rGO composites with different nominal loadings of GO (from 4 to 20 wt%). The structural, surface and electronic properties of the obtained TiO2 + rGO composites were analyzed and correlated to their performance in the photocatalytic oxidation of aqueous bisphenol A solution. X-ray photoelectron spectroscopy (XPS) analyses revealed that charge separation in TiO2 + rGO composites is improved due to the perfect matching of TiO2 and rGO valence band maxima (VBM). Cyclic voltammetry (CV) experiments revealed that the peak-to-peak separations (ΔEp) are the lowest and the oxidation current densities are the highest for composites with a nominal 10 wt% GO content, meaning that it is much easier for the charge carriers to percolate through the solid, resulting in improved charge migration. Due to the high charge carrier mobility in rGO and perfect VBM matching between TiO2 and rGO, the electron–hole recombination in composites was suppressed, resulting in more electrons and holes being able to participate in the photocatalytic reaction. rGO amounts above 10 wt% decreased the photocatalytic activity; thus, it is critical to optimize its amount in the TiO2 + rGO composites for achieving the highest photocatalytic activity. BPA degradation rates correlated completely with the results of the CV measurements, which directly evidenced improved charge separation and migration as the crucial parameters governing photocatalysis.

Leptoquark mechanism of neutrino masses within the grand unification framework

Abstract: We demonstrate the viability of the one-loop neutrino mass mechanism within the framework of grand unification when the loop particles comprise scalar leptoquarks (LQs) and quarks of the matching electric charge. This mechanism can be implemented in both supersymmetric and non-supersymmetric models and requires the presence of at least one LQ pair. The appropriate pairs for the neutrino mass generation via the up-type and down-type quark loops are $$S_3$$ – $$R_2$$ and $$S_{1,\,3}$$ – $$\tilde{R}_2$$ , respectively. We consider two distinct regimes for the LQ masses in our analysis. The first regime calls for very heavy LQs in the loop. It can be naturally realized with the $$S_{1,\,3}$$ – $$\tilde{R}_2$$ scenarios when the LQ masses are roughly between $$10^{12}$$ and $$5 \times 10^{13}$$ GeV. These lower and upper bounds originate from experimental limits on partial proton decay lifetimes and perturbativity constraints, respectively. Second regime corresponds to the collider accessible LQs in the neutrino mass loop. That option is viable for the $$S_3$$ – $$\tilde{R}_2$$ scenario in the models of unification that we discuss. If one furthermore assumes the presence of the type II see-saw mechanism there is an additional contribution from the $$S_3$$ – $$R_2$$ scenario that needs to be taken into account beside the type II see-saw contribution itself. We provide a complete list of renormalizable operators that yield necessary mixing of all aforementioned LQ pairs using the language of SU(5). We furthermore discuss several possible embeddings of this mechanism in SU(5) and SO(10) gauge groups.

Superior Performance of Microporous Aluminophosphate with LTA Topology in Solar-Energy Storage and Heat Reallocation

Abstract: Hydrophilic porous materials are recognized as very promising materials for water-sorption-based energy storage and transformation. In this study, a porous, zeolite-like aluminophosphate with LTA (Linde Type A) topology is inspected as an energy-storage material. The study is motivated by the material's high predicted pore volume. According to sorption and calorimetric tests, the aluminophosphate outperforms all other zeolite-like and metal-organic porous materials tested so far. It adsorbs water in an extremely narrow relative-pressure interval (0.10 < p/p0 < 0.15) and exhibits superior water uptake (0.42 g g−1) and energy-storage capacity (527 kW h m−3). It also shows remarkable cycling stability; after 40 cycles of adsorption/desorption its capacity drops by less than 2%. Desorption temperature for this material, which is one of crucial parameters in applications, is lower from desorption temperatures of other tested materials by 10–15 °C. Furthermore, its heat-pump performance is very high, allowing efficient cooling in demanding conditions (with cooling power up to 350 kW h m−3 even at 30 °C temperature difference between evaporator and environment). On the microscopic scale, sorption mechanism in AlPO4-LTA is elucidated by X-ray diffraction, nuclear magnetic resonance measurements, and first-principles calculations. In this aluminophosphate, energy is stored predominately in hydrogen-bonded network of water molecules within the pores.