14,580 research outputs found
The Latin Leaflet, Number 29
Polymer electrolytes represent the ultimate in terms of desirable properties of energy storage/conversion devices, as they can offer an all-solid-state construction, a wide variety of shapes and sizes, light-weight, low costs, high energy density and safety.
Here we present our recent results concerning a novel strategy for preparing efficient polymer membranes which are successfully demonstrated as suitable electrolytes for several energy conversion and storage devices (i.e., Li- and Na-based batteries and DSSCs). Highly ionic conducting polymer electrolytes containing PEO-based functionalities and different components (e.g., Li/Na salts, RTILs, natural biosourced and cellulosic fillers) are successfully prepared via a rapid process and, directly or subsequently, cross-linked via UV irradiation (patent pending, PCT/IT2014/000008). All the prepared materials are thoroughly characterised in terms of their physical, chemical and morphological properties and tested for their electrochemical performances and durability. The UV-curing process on such materials led to the production of elastic and resistant amorphous macromolecular networks. Noticeably increased ionic conductivities are registered (10-3 S cm-1 at RT), along with very stable interfacial and storage stability and wide electrochemical stability windows. The different lab-scale solid-state devices show remarkable performances even at ambient temperature, at the level of those using liquid electrolytes, respect to which demonstrate much greater durability and safety.
The obtained findings demonstrate a new, easy and low cost approach to fabricate and tailor-make polymer electrolytes with highly promising prospects for the next generation of advanced flexible energy production and storage devices
Oblivion: Mitigating Privacy Leaks by Controlling the Discoverability of Online Information
Search engines are the prevalently used tools to collect information about
individuals on the Internet. Search results typically comprise a variety of
sources that contain personal information -- either intentionally released by
the person herself, or unintentionally leaked or published by third parties,
often with detrimental effects on the individual's privacy. To grant
individuals the ability to regain control over their disseminated personal
information, the European Court of Justice recently ruled that EU citizens have
a right to be forgotten in the sense that indexing systems, must offer them
technical means to request removal of links from search results that point to
sources violating their data protection rights. As of now, these technical
means consist of a web form that requires a user to manually identify all
relevant links upfront and to insert them into the web form, followed by a
manual evaluation by employees of the indexing system to assess if the request
is eligible and lawful.
We propose a universal framework Oblivion to support the automation of the
right to be forgotten in a scalable, provable and privacy-preserving manner.
First, Oblivion enables a user to automatically find and tag her disseminated
personal information using natural language processing and image recognition
techniques and file a request in a privacy-preserving manner. Second, Oblivion
provides indexing systems with an automated and provable eligibility mechanism,
asserting that the author of a request is indeed affected by an online
resource. The automated ligibility proof ensures censorship-resistance so that
only legitimately affected individuals can request the removal of corresponding
links from search results. We have conducted comprehensive evaluations, showing
that Oblivion is capable of handling 278 removal requests per second, and is
hence suitable for large-scale deployment
Cluster-based feedback control of turbulent post-stall separated flows
We propose a novel model-free self-learning cluster-based control strategy
for general nonlinear feedback flow control technique, benchmarked for
high-fidelity simulations of post-stall separated flows over an airfoil. The
present approach partitions the flow trajectories (force measurements) into
clusters, which correspond to characteristic coarse-grained phases in a
low-dimensional feature space. A feedback control law is then sought for each
cluster state through iterative evaluation and downhill simplex search to
minimize power consumption in flight. Unsupervised clustering of the flow
trajectories for in-situ learning and optimization of coarse-grained control
laws are implemented in an automated manner as key enablers. Re-routing the
flow trajectories, the optimized control laws shift the cluster populations to
the aerodynamically favorable states. Utilizing limited number of sensor
measurements for both clustering and optimization, these feedback laws were
determined in only iterations. The objective of the present work is not
necessarily to suppress flow separation but to minimize the desired cost
function to achieve enhanced aerodynamic performance. The present control
approach is applied to the control of two and three-dimensional separated flows
over a NACA 0012 airfoil with large-eddy simulations at an angle of attack of
, Reynolds number and free-stream Mach number . The optimized control laws effectively minimize the flight power
consumption enabling the flows to reach a low-drag state. The present work aims
to address the challenges associated with adaptive feedback control design for
turbulent separated flows at moderate Reynolds number.Comment: 32 pages, 18 figure
Carrier multiplication yields in PbS and PbSe nanocrystals measured by transient photoluminescence
We report here an assessment of carrier multiplication (CM) yields in PbSe
and PbS nanocrystals (NCs) by a quantitative analysis of biexciton and exciton
dynamics in transient photoluminescence decays. Interest in CM, the generation
of more than one electron and hole in a semiconductor after absorption of one
photon, has renewed in recent years because of reports suggesting greatly
increased efficiencies in nanocrystalline materials compared to the bulk form,
in which CM was otherwise too weak to be of consequence in photovoltaic energy
conversion devices. In our PbSe and PbS NC samples, however, we estimate using
transient photoluminescence that at most 0.25 additional e-h pairs are
generated per photon even at energies hv > 5Eg, instead of the much higher
values reported in the literature. We argue by comparing NC CM estimates and
reported bulk values on an absolute energy basis, which we justify as
appropriate on physical grounds, that the data reported thus far are
inconclusive with respect to the importance of nanoscale-specific phenomena in
the CM process.Comment: 10 pages, 7 figure
Enzymatic production of fructose fatty acid ester using lipases from C. antarctica and porcine pancreatic
The aim of this work was to produce fructose fatty acid ester by enzymatic esterification of a fatty
acid (oleic acid or linoleic acid) with fructose, using lipases (CALB) from Candida antarctica type B
and porcine pancreas. The esterification reaction was conducted at 150 rpm and 40 °C during 72
hours. Equimolar (0.5 mmol) amounts of fructose and fatty acid were mixed with 0.6 ml of
ethanol and sodium sulfate anhydrous (0.1 g) was added for the adsorption of the water
generated during the reaction. In all experiments, 22.5 mg of lipase were used. A control
experiment was performed using the same conditions except for the addition of lipase. Samples
were analyzed by thin layer chromatography (TLC), using silica gel plates. The plates were placed
in an iodine chamber to develop fatty acid and sugar ester spots. According to the literature an Rf
of 0.5 is expected for the fructose fatty acid ester using chloroform/ hexane (1:1, v/ v) as eluting
solvent. Four different reaction schemes were studied in this work namely, sample 1 (oleic acid,
fructose, C. antarctica lipase, sodium sulfate and ethanol), sample 2 (oleic acid, fructose, porcine
pancreatic lipase, sodium sulfate and ethanol), sample 3 (linoleic acid, fructose, C. antarctica
lipase, sodium sulfate and ethanol) and sample 4 (linoleic acid, fructose, porcine pancreatic
lipase, sodium sulfate and ethanol). From the TLC assays, the formation of fructose ester was
observed for samples 1, 2 and 3. Additionally, the yield of esterification was determined by
calculating the amount of residual fatty acid in the reaction mixture, which was determined using
a volumetric method, as described elsewhere. Esterification yields of 74.3, 41.4, 63.5 and 11.2 %
(v/ v) were determined for samples 1 to 4, respectively. Therefore, it was possible to conclude
that the lipase obtained from C. antarctica had a better performance than the one obtained from
porcine pancreas. Furthermore, the reaction schemes that used oleic acid conducted to higher
yields of fructose ester production. These results point out that the enzymatic production of
fructose esters is worthwhile and suggest the need for further research
Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals
We have studied the reflectivity of CMOS-compatible three-dimensional silicon
inverse woodpile photonic crystals at near-infrared frequencies.
Polarization-resolved reflectivity spectra were obtained from two orthogonal
crystal surfaces corresponding to 1.88 pi sr solid angle. The spectra reveal
broad peaks with high reflectivity up to 67 % that are independent of the
spatial position on the crystals. The spectrally overlapping reflectivity peaks
for all directions and polarizations form the signature of a broad photonic
band gap with a relative bandwidth up to 16 %. This signature is supported with
stopgaps in plane wave bandstructure calculations and with the frequency region
of the expected band gap.Comment: 9 pages, 5 figure
Isotropic representation of noncommutative 2D harmonic oscillator
We show that 2D noncommutative harmonic oscillator has an isotropic
representation in terms of commutative coordinates. The noncommutativity in the
new mode, induces energy level splitting, and is equivalent to an external
magnetic field effect. The equivalence of the spectra of the isotropic and
anisotropic representation is traced back to the existence of SU(2) invariance
of the noncommutative model.Comment: 15 pages, RevTex4, no figures; article format, improved version of
the previous paper; new references and aknowledgements adde
The Fundamental Surface of Quad Lenses
In a quadruply imaged lens system the angular distribution of images around
the lens center is completely described by three relative angles. We show
empirically that in the 3D space of these angles, spanning 180 x 180 x 90
degrees, quads from simple two-fold symmetric lenses of arbitrary radial
density profile and arbitrary radially dependent ellipticity or external shear
define a nearly invariant 2D surface. We give a fitting formula for the surface
using SIS+elliptical lensing potential. Various circularly symmetric mass
distributions with shear up to 0.4 deviate from it by typically, rms~0.1 deg,
while elliptical mass distributions with ellipticity of up 0.4 deviate from it
by rms~1.5 deg. The existence of a near invariant surface gives a new insight
into the lensing theory and provides a framework for studying quads. It also
allows one to gain information about the lens mass distribution from the image
positions alone, without any recourse to mass modeling. As an illustration, we
show that about 3/4 of observed galaxy-lens quads do not belong to this surface
within observational error, and so require additional external shear or
substructure to be modeled adequately.Comment: 24 pages, 9 figures, accepted to MNRA
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