1,249 research outputs found
Small Fermi energy, zero point fluctuations and nonadiabaticity in MgB
Small Fermi energy effects are induced in MgB by the low hole doping in
the bands which are characterized by a Fermi energy eV. We show that, due to the particularly strong deformation
potential relative to the phonon mode, lattice fluctuations are
reflected in strong fluctuations in the electronic band structure. Quantum
fluctuations associated to the zero-point lattice motion are responsible for an
uncertainty of the Fermi energy of the order of the Fermi energy itself,
leading to the breakdown of the adiabatic principle underlying the
Born-Oppenheimer approximation in MgB even if , where are the characteristic phonon
frequencies. This amounts to a new nonadiabatic regime, which could be relevant
to other unconventional superconductors.Comment: to appear on Physical Review
Linear response separation of a solid into atomic constituents: Li, Al, and their evolution under pressure
We present the first realization of the generalized pseudoatom concept
introduced by Ball, and adopt the name enatom to minimize confusion. This
enatom, which consists of a unique decomposition of the total charge density
(or potential) of any solid into a sum of overlapping atomiclike contributions
that move rigidly with the nuclei to first order, is calculated using
(numerical) linear response methods, and is analyzed for both fcc Li and Al at
pressures of 0, 35, and 50 GPa. These two simple fcc metals (Li is fcc and a
good superconductor in the 20-40 GPa range) show different physical behaviors
under pressure, which reflects the increasing covalency in Li and the lack of
it in Al. The nonrigid (deformation) parts of the enatom charge and potential
have opposite signs in Li and Al; they become larger under pressure only in Li.
These results establish a method of construction of the enatom, whose potential
can be used to obtain a real-space understanding of the vibrational properties
and electron-phonon interaction in solids.Comment: 13 pages, 9 figures, 1 table, V2: fixed problem with Fig. 7, V3:
minor correction
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
In medio stat victus: Labor Demand Effects of an Increase in the Retirement Age
After falling for four decades, statutory retirement ages are increasing in most OECD countries. The labor market adjustment to these reforms has not yet been thoroughly investigated by the literature. We draw on a major pension reform that took place in Italy in December 2011 that increased the retirement age by up to six years for some categories of workers. We have access to a unique dataset validated by the Italian social security administration (INPS), which identifies in each private firm, based on an administrative exam of eligibility conditions, how many workers were locked in by the sudden increase in the retirement age, and for how long. We find that firms mostly affected by the lock in are those that were downsizing even before the policy shock. The increase in the retirement age seems to displace more middle-aged workers than young workers. Furthermore, there is not a one-to-one increase in the number of older workers in the firms where some workers were locked in by the reform. We provide tentative explanations for these results, based on the interaction between retirement, employment protection legislation and liquidity constraints of firms
How to guide the selection of patients for trimodality therapy: The case for tumor immune and stromal signature
The Redevelopment of The Heritage of Social Housing in Italy: Survey and Assessment Instruments. The Case Study of Pilastro Neighborhood in Bologna
Abstract The increasing importance of social housing in order to deal with the emergency caused by the pressing demand, places in the foreground the need to redevelop the existing public housing heritage. The paper proposes the deepening of one case study, the Pilastro neighborhood, a significant example of social housing high density settlement, situated in the outskirts of Bologna in order to brought out the technical, functional and social factors, on which the level of quality of the settlement and the phenomena of social uneasiness depend. It also highlighted some factors that may pose a resistance to the measures of improvement
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 energy–related 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 study’s 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
buildings’ 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
Study of temperature dependent atomic correlations in MgB
We have studied the evolution with temperature of the local as well as the
average crystal structure of MgB using the real-space atomic pair
distribution function (PDF) measured by high resolution neutron powder
diffraction. We have investigated the correlations of the B-B and B-Mg nearest
neighbor pair motion by comparing, in the wide temperature range from T=10 K up
to T=600 K, the mean-square displacements (MSD) of single atoms with the
mean-square relative displacements (MSRD) obtained from the PDF peak
linewidths. The results show that the single atom B and Mg vibrations are
mostly decoupled from each other, with a small predominance of positive (in
phase) correlation factor for both the B-B and B-Mg pairs. The small positive
correlation is almost temperature independent, in contrast with our theoretical
calculations; this can be a direct consequence of the strong decay processes of
the anharmonic phonons
Single 20meV boson mode in KFe2As2 detected by point-contact spectroscopy
We report an experimental and theoretical investigation of the electron-boson
interaction in KFe2As2 by point-contact (PC) spectroscopy, model, and ab-initio
LDA-based calculations for the standard electron-phonon Eliashberg function.
The PC spectrum viz. the second derivative of the I - V characteristic of
representative PC exhibits a pronounced maximum at about 20meV and surprisingly
a featureless behavior at lower and higher energies. We discuss phonon and
non-phonon (excitonic) mechanisms for the origin of this peak. Analysis of the
underlying source of this peak may be important for the understanding of
serious puzzles of superconductivity in this type of compounds.Comment: 10 pages, 6 figs., to be published in PR
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