135 research outputs found
Microwave-Assisted Treatment of Waste Wood Biomass with Deep Eutectic Solvents
Abstract.
The increasing depletion of fossil feeds and the environmental concerns linked to the use of
traditional energy sources have stimulated both academic and industrial worlds in exploiting new
sustainable and renewable suppliers of raw materials [1]. In this framework, lignocellulosic biomass
can play an important role, acting as the starting material of a biorefinery leading to biofuels,
chemicals, and other value-added products, commonly obtained from petroleum. Recently,
numerous protocols for processing lignocellulosic biomass of selected plants have been reported.
However, developing an environment-friendly method is still a big goal. This challenge becomes
more interesting if lignocellulosic biomass coming from wood wastes could be efficiently treated.
Deep eutectic solvents (DESs) are new sustainable and cheap reaction media, combining the
features of ionic liquids and organic solvents. They are made by association of hydrogen-bond
donors and hydrogen-bond acceptors, and they can promote the hydrolysis of lignocellulosic bonds
[2]. Herein, we report on the microwave-assisted treatment of waste wood flours with DESs formed
by choline chloride and oxalic acid to get a cellulosic residue separated from lignin degradation
products, identified by NMR spectroscopy. The insoluble deposit was characterized by SEM, TGA,
DSC, FTIR-ATR and 13C CP/MAS NMR techniques and could be available for further uses such as
nanocellulose production.
[1] Haldar D., Purkait M.K. Chemosphere 2021, 128523.
[2] Liu S., Zhang Q., Gou S., Zhang L., Wang Z. Carbohydr. Polym. 2021, 251, 11701
Multiple Andreev reflections in a quantum dot coupled to superconducting leads: Effect of spin-orbit coupling
We study the out of equilibrium current through a multilevel quantum dot contacted to two superconducting leads and in the presence of Rashba and Dresselhaus spin-orbit couplings, in the regime of strong dot-lead coupling. The multiple Andreev reflection (MAR) subgap peaks in the current-voltage characteristics are found to be modified (but not suppressed) by the spin-orbit interaction in a way that it strongly depends on the shape of the dot confining potential. In a perfectly isotropic dot the MAR peaks are enhanced when the strength αR and αD of Rashba and Dresselhaus terms are equal. When the anisotropy of the dot confining potential increases, the dependence of the subgap structure on the spin-orbit angle decreases. Furthermore, when an in-plane magnetic field is applied to a strongly anisotropic dot, the peaks of the nonlinear conductance oscillate as a function of the magnetic-field angle and the location of the maxima and minima allows for a straightforward read-out of the spin-orbit angle $theta
Revealing the electronic structure of a carbon nanotube carrying a supercurrent
Carbon nanotubes (CNTs) are not intrinsically superconducting but they can
carry a supercurrent when connected to superconducting electrodes. This
supercurrent is mainly transmitted by discrete entangled electron-hole states
confined to the nanotube, called Andreev Bound States (ABS). These states are a
key concept in mesoscopic superconductivity as they provide a universal
description of Josephson-like effects in quantum-coherent nanostructures (e.g.
molecules, nanowires, magnetic or normal metallic layers) connected to
superconducting leads. We report here the first tunneling spectroscopy of
individually resolved ABS, in a nanotube-superconductor device. Analyzing the
evolution of the ABS spectrum with a gate voltage, we show that the ABS arise
from the discrete electronic levels of the molecule and that they reveal
detailed information about the energies of these levels, their relative spin
orientation and the coupling to the leads. Such measurements hence constitute a
powerful new spectroscopic technique capable of elucidating the electronic
structure of CNT-based devices, including those with well-coupled leads. This
is relevant for conventional applications (e.g. superconducting or normal
transistors, SQUIDs) and quantum information processing (e.g. entangled
electron pairs generation, ABS-based qubits). Finally, our device is a new type
of dc-measurable SQUID
Observation of Umklapp processes in non-crystalline materials
Umklapp processes are known to exist in cristalline materials, where they
control important properties such as thermal conductivity, heat capacity and
electrical conductivity. In this work we report the provocative observation of
Umklapp processes in a non-periodical system, namely liquid Lithium. The lack
of a well defined periodicity seems then not to prevent the existence of these
scattering processes mechanisms provided that the local order of the systems
i.e. the maxima of the static structure factor supply the equivalent of a
reciprocal lattice vector in the case of cristalline materials.Comment: 13 pages P
The energy center initiative at politecnico di torino: practical experiences on energy efficiency measures in the municipality of torino
Urban districts should evolve towards a more sustainable infrastructure and greener energy carriers. The utmost challenge is the smart integration and control, within the existing infrastructure, of new information and energy technologies (such as sensors, appliances, electric and thermal power and storage devices) that are able to provide multi-services based on multi-actors and multi and interchangeable energy carriers. In recent years, the Municipality of Torino represents an experimental scenario, in which practical experiences in the below-areas have taken place through a number of projects: 1. energy efficiency in building; 2. smart energy grids management and smart metering; 3. biowaste-to-energy: mixed urban/industrial waste management with enhanced energy recovery from biogas. This work provides an overview and update on the most interesting initiatives of smart energy management in the urban context of Torino, with an analysis and quantification of the advantages gained in terms of energy and environmental efficiency
Critical temperature of non-interacting Bose gases on disordered lattices
For a non-interacting Bose gas on a lattice we compute the shift of the
critical temperature for condensation when random-bond and onsite disorder are
present. We evidence that the shift depends on the space dimensionality D and
the filling fraction f. For D -> infinity (infinite-range model), using results
from the theory of random matrices, we show that the shift of the critical
temperature is negative, depends on f, and vanishes only for large f. The
connections with analogous results obtained for the spherical model are
discussed. For D=3 we find that, for large f, the critical temperature Tc is
enhanced by disorder and that the relative shift does not sensibly depend on f;
at variance, for small f, Tc decreases in agreement with the results obtained
for a Bose gas in the continuum. We also provide numerical estimates for the
shift of the critical temperature due to disorder induced on a non-interacting
Bose gas by a bichromatic incommensurate potential.Comment: 18 pages, 8 figures; Fig. 8 improved adding results for another value
of q (q=830/1076
Quantum-critical pairing with varying exponents
We analyse the onset temperature T_p for the pairing in cuprate
superconductors at small doping, when tendency towards antiferromagnetism is
strong. We consider the model of Moon and Sachdev (MS), which assumes that
electron and hole pockets survive in a paramagnetic phase. Within this model,
the pairing between fermions is mediated by a gauge boson, whose propagator
remains massless in a paramagnet. We relate the MS model to a generic
\gamma-model of quantum-critical pairing with the pairing kernel \lambda
(\Omega) \propto 1/\Omega^{\gamma}. We show that, over some range of
parameters, the MS model is equivalent to the \gamma-model with \gamma =1/3
(\lambda (\Omega) \propto \Omega^{-1/3}). We find, however, that the parameter
range where this analogy works is bounded on both ends. At larger deviations
from a magnetic phase, the MS model becomes equivalent to the \gamma-model with
varying \gamma >1/3, whose value depends on the distance to a magnetic
transition and approaches \gamma =1 deep in a paramagnetic phase. Very near the
transition, the MS model becomes equivalent to the \gamma-model with varying
\gamma <1/3. Right at the magnetic QCP, the MS model is equivalent to the
\gamma-model with \gamma =0+ (\lambda (\Omega) \propto \log \Omega), which is
the model for color superconductivity. Using this analogy, we verified the
formula for T_c derived for color superconductivity.Comment: 10 pages, 8 figures, submitted to JLTP for a focused issue on Quantum
Phase Transition
The evolution of vibrational excitations in glassy systems
The equations of the mode-coupling theory (MCT) for ideal liquid-glass
transitions are used for a discussion of the evolution of the
density-fluctuation spectra of glass-forming systems for frequencies within the
dynamical window between the band of high-frequency motion and the band of
low-frequency-structural-relaxation processes. It is shown that the strong
interaction between density fluctuations with microscopic wave length and the
arrested glass structure causes an anomalous-oscillation peak, which exhibits
the properties of the so-called boson peak. It produces an elastic modulus
which governs the hybridization of density fluctuations of mesoscopic wave
length with the boson-peak oscillations. This leads to the existence of
high-frequency sound with properties as found by X-ray-scattering spectroscopy
of glasses and glassy liquids. The results of the theory are demonstrated for a
model of the hard-sphere system. It is also derived that certain schematic MCT
models, whose spectra for the stiff-glass states can be expressed by elementary
formulas, provide reasonable approximations for the solutions of the general
MCT equations.Comment: 50 pages, 17 postscript files including 18 figures, to be published
in Phys. Rev.
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Landau Levels and Edge States in Graphene with Strong Spin-Orbit Coupling
We investigate the electronic properties of graphene in a magnetic and a strain-induced pseudo-magnetic field in the presence of strong spin-orbit interactions (SOI). For a homogeneous field we provide analytical results for the Landau level eigenstates for arbitrary intrinsic and Rashba SOI, including also the effect of a Zeeman field. We then study the edge states in a semi-infinite geometry in the absence of the Rashba term. We find that, for a critical value of the magnetic field, a quantum phase transition occurs, which separates two phases both with spin-filtered helical edge states but with opposite direction of the spin current. Finally,we discuss magnetic waveguides with inhomogeneous field profiles that allow for chiral snake orbits. Such waveguides are practically immune to disorder-induced backscattering, and the SOI provides non-trivial spin texture to these modes
Static and Dynamic Properties of a Viscous Silica Melt Molecular Dynamics Computer Simulations
We present the results of a large scale molecular dynamics computer
simulation in which we investigated the static and dynamic properties of a
silica melt in the temperature range in which the viscosity of the system
changes from O(10^-2) Poise to O(10^2) Poise. We show that even at temperatures
as high as 4000 K the structure of this system is very similar to the random
tetrahedral network found in silica at lower temperatures. The temperature
dependence of the concentration of the defects in this network shows an
Arrhenius law. From the partial structure factors we calculate the neutron
scattering function and find that it agrees very well with experimental neutron
scattering data. At low temperatures the temperature dependence of the
diffusion constants shows an Arrhenius law with activation energies which
are in very good agreement with the experimental values. With increasing
temperature we find that this dependence shows a cross-over to one which can be
described well by a power-law, D\propto (T-T_c)^gamma. The critical temperature
T_c is 3330 K and the exponent gamma is close to 2.1. Since we find a similar
cross-over in the viscosity we have evidence that the relaxation dynamics of
the system changes from a flow-like motion of the particles, as described by
the ideal version of mode-coupling theory, to a hopping like motion. We show
that such a change of the transport mechanism is also observed in the product
of the diffusion constant and the life time of a Si-O bond, or the space and
time dependence of the van Hove correlation functions.Comment: 30 pages of Latex, 14 figure
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