1,537 research outputs found
Effects of magnetism and doping on the electron-phonon coupling in BaFeAs
We calculate the effect of local magnetic moments on the electron-phonon
coupling in BaFeAs using the density functional perturbation
theory. We show that the magnetism enhances the total electron-phonon coupling
by , up to , still not enough to explain the
high critical temperature, but strong enough to have a non-negligible effect on
superconductivity, for instance, by frustrating the coupling with spin
fluctuations and inducing order parameter nodes. The enhancement comes mostly
from a renormalization of the electron-phonon matrix elements. We also
investigate, in the rigid band approximation, the effect of doping, and find
that versus doping does not mirror the behavior of the density of
states; while the latter decreases upon electron doping, the former does not,
and even increases slightly.Comment: 4 pages, 3 figure
Electrons and phonons in the ternary alloy CaAlSi} as a function of composition
We report a detailed first-principles study of the structural, electronic and
vibrational properties of the superconducting C phase of the ternary
alloy CaAlSi, both in the experimental range ,
for which the alloy has been synthesised, and in the theoretical limits of high
aluminium and high silicon concentration. Our results indicate that, in the
experimental range, the dependence of the electronic bands on composition is
well described by a rigid-band model, which breaks down outside this range.
Such a breakdown, in the (theoretical) limit of high aluminium concentration,
is connected to the appearance of vibrational instabilities, and results in
important differences between CaAl and MgB. Unlike MgB, the
interlayer band and the out-of-plane phonons play a major role on the stability
and superconductivity of CaAlSi and related C intermetallic compounds
Experimental tests to recover the photovoltaic power by battery system
The uncertainty and variability of the Renewable Energy Sources (RES) power plants within the power grid is an open issue. The
present study focuses on the use of batteries to overcome the limitations associated with the photovoltaic inverter operation,
trying to maximize the global energy produced. A set of switches, was placed between a few photovoltaic modules and a
commercial inverter, capable to change configuration of the plant dynamically. Such system stores the power that the inverter is
not able to let into the grid inside batteries. At the base of this optimization, there is the achievement of two main configurations
in which the batteries and the photovoltaic modules are electrically connected in an appropriate manner as a function of inverter
efficiency and thus solar radiation. A control board and the relative program, to change the configuration, was designed and
implemented, based on the value of the measured radiation, current, batteries voltage, and calculated inverter efficiency. Finally
from the cost and impact analysis we can say that, today the technology of lithium batteries, for this application, is still too
expensive in comparison with lead-acid batteries
Energy Gaps and Kohn Anomalies in Elemental Superconductors
The momentum and temperature dependence of the lifetimes of acoustic phonons
in the elemental superconductors Pb and Nb was determined by resonant spin-echo
spectroscopy with neutrons. In both elements, the superconducting energy gap
extracted from these measurements was found to converge with sharp anomalies
originating from Fermi-surface nesting (Kohn anomalies) at low temperatures.
The results indicate electron many-body correlations beyond the standard
theoretical framework for conventional superconductivity. A possible mechanism
is the interplay between superconductivity and spin- or charge-density-wave
fluctuations, which may induce dynamical nesting of the Fermi surface
Reversibility and Durability as Potential Indicators for Circular Building Technologies
According to the Circularity Gap Report 2020, a mere 8.6% of the global economy was circular in 2019. The Global Status Report 2018 declares that building construction and operations accounted for 36% of global final energy use and 39% of energyârelated carbon dioxide (CO2) emissions. The Paris Agreement demands that the building and construction sector decarbonizes globally by 2050. This requires strategies that minimize the environmental impact of buildings and practices extending the lifecycle of their constituents within a circular resource flow. To ensure that effective measures are applied, a suitable method is needed to assess compliance in materials, processes, and design strategies within circular economy principles. The studyâs assumption is that synthetic and reliable indicators for that purpose could be based on reversibility and durability features. The paper provides an overview of building design issues within the circular economy perspective, highlighting the difficulty in finding circular technologies which are suitable to enhance
buildingsâ service life while closing material loops. The results identify reversibility and durability as potential indicators for assessing circular building technologies. The next research stage aims to further develop the rating of circularity requirements for both building technologies and entire buildings
Effects of PAHs and dioxins on the earthworm Eisenia andrei: a multivariate approach for biomarker interpretation.
In this study, a battery of biomarkers was utilised to evaluate the stress syndrome induced in the earthworm Eisenia andrei by exposure to environmentally realistic concentrations of benzo[a]pyrene (B[a]P) and 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) in OECD soil. The set of tests was then employed to assess the toxicity of field soils contaminated with organic xenobiotic compounds (such as PAHs, dioxins and PCBs). Biomarker responses (comprising biomarkers of stress and of genotoxicity) varied depending on chemicals, dose and time of exposure; and among the different polluted field soils. The results highlighted an impairment of immune and metabolic functions and genotoxic damage in worms exposed also to lower bioavailable concentrations of toxic chemicals. Multivariate analysis of biomarker data showed that all different contaminated soils had a detrimental effect on the earthworms; control animals being clearly separated from the treated ones. A separation between temporal and concentration factors were also evident for B[a]P and TCDD treatments; and field contaminated soils were further differentiated reflecting a diverse contamination. Multivariate analysis also demonstrated that lysosomal membrane stability can be considered as a predictive tool of the adverse effects on worm health status provoked by increasing bioavailable concentrations of toxic chemicals
A combined experimental and computational study of the pressure dependence of the vibrational spectrum of solid picene C_22H_14
We present high-quality optical data and density functional perturbation
theory calculations for the vibrational spectrum of solid picene
(CH) under pressure up to 8 GPa. First-principles calculations
reproduce with a remarkable accuracy the pressure effects on both frequency and
intensities of the phonon peaks experimentally observed . Through a detailed
analysis of the phonon eigenvectors, We use the projection on molecular
eigenmodes to unambiguously fit the experimental spectra, resolving complicated
spectral structures, in a system with hundreds of phonon modes. With these
projections, we can also quantify the loss of molecular character under
pressure. Our results indicate that picene, despite a \sim 20 % compression of
the unit cell, remains substantially a molecular solid up to 8 GPa, with phonon
modes displaying a smooth and uniform hardening with pressure. The Grueneisen
parameter of the 1380 cm^{-1} a_1 Raman peak () is much lower
than the effective value () due to K doping. This is an
indication that the phonon softening in K doped samples is mainly due to charge
transfer and electron-phonon coupling.Comment: Replaced with final version (PRB
The challenge of unravelling magnetic properties in LaFeAsO
First principles calculations of magnetic and, to a lesser extent, electronic
properties of the novel LaFeAsO-based superconductors show substantial apparent
controversy, as opposed to most weakly or strongly correlated materials. Not
only do different reports disagree about quantitative values, there is also a
schism in terms of interpreting the basic physics of the magnetic interactions
in this system. In this paper, we present a systematic analysis using four
different first principles methods and show that while there is an unusual
sensitivity to computational details, well-converged full-potential
all-electron results are fully consistent among themselves. What makes results
so sensitive and the system so different from simple local magnetic moments
interacting via basic superexchange mechanisms is the itinerant character of
the calculated magnetic ground state, where very soft magnetic moments and
long-range interactions are characterized by a particular structure in the
reciprocal (as opposed to real) space. Therefore, unravelling the magnetic
interactions in their full richness remains a challenging, but utterly
important task
A miniaturized in vitro 3D model to assess the neuroprotective effect of mesenchymal stromal cell secretome on neuroblastoma cells exposed to oxidative stress
Mode of action of Cr(VI) in immunocytes of earthworms: Implications for animal health
Chromium (Cr) is one of the major and most detrimental pollutant, widely present in the environment as a result of several anthropogenic activities. In mammalian cells, Cr(VI) is known to enhance reactive oxygen species (ROS) production and to cause toxic and genotoxic effects. Less commonly investigated are the effects and mode of action of this contaminant in invertebrates, particularly in soil organisms. In this work, earthworms of the species Eisenia andrei were exposed for 1 and 3 days to various sublethal concentrations of Cr(VI) (2, 15, 30 ”g mLâ1) using the paper contact toxicity test. In amoeboid leukocytes we investigated intracellular ROS and lipoperoxide production, oxidative DNA damage, and the effects on different cell functions. The analysis of the results shows that Cr(VI) triggered severe adverse reactions; the first events were an increase of intracellular ROS levels, generating in the cells oxidative stress conditions leading to membrane lipid peroxidation and oxidative DNA damage. Lysosomes showed relevant changes such as a strong membrane destabilization, which was accompanied by an increased catabolism of cytoplasmic proteins and accumulation of lipofuscin. With an increase in the dose and/or time of exposure, the physiological status of intracellular organelles (such as lysosomes, nucleus and mitochondria) showed further impairment and amoebocyte immune functions were adversely affected, as shown by the decrease of the phagocytic activity. By mapping the responses of the different parameters evaluated, diagnostic of (oxidative) stress events, against lysosomal membrane stability, a âhealth statusâ indicator (able to describe the stress syndrome from its early phase to pathology), we have shown that this biomarker is suitable as a prognostic test for health of earthworms. This is viewed as a crucial step toward the derivation of explanatory frameworks for prediction of pollutant impact on animal health
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