2,523 research outputs found
Properties of bio-based gum Arabic/clay aerogels
Lightweight bio-based aerogels from sustainable gum Arabic (GA) and sodium montmorillonite (Na+-MMT) clay were prepared by means of a simple freeze-drying process. GA/clay aerogels showed high porosity (87.9%–94.9%) of mainly open type and the mechanical properties were improved by the clay. When 40% of clay was added to pure GA, the specific modulus and the absorbed energy of resultant aerogels increased by 1.6 and 4.2 times respectively. On the other hand, the exponent value for modulus in the power-law model for cellular materials increased from 1.95 to 3.28 due to the more anisotropic structures induced by the presence of the clay. In terms of thermal stability and flame retardancy, clay content played a dominant role. With 50% of clay loading, the initial decomposition temperature increased by nearly 16 °C and the peak of heat release rate was 3-fold reduced.Peer ReviewedPostprint (author's final draft
The correlated insulators of magic angle twisted bilayer graphene at zero and one quantum of magnetic flux: a tight-binding study
Magic angle twisted bilayer graphene (MATBG) has become one of the prominent
topics in Condensed Matter during the last few years, however, fully atomistic
studies of the interacting physics are missing. In this work, we study the
correlated insulator states of MATBG in the setting of a tight-binding model,
under a perpendicular magnetic field of and T, corresponding to zero
and one quantum of magnetic flux per unit cell. At zero field and for dopings
of two holes () or two electrons () per unit cell, the Kramers
intervalley coherent (KIVC) order is the ground state at the Hartree-Fock
level, although it is stabilized by a different mechanism to that in continuum
model. At charge neutrality, the spin polarized state is competitive with the
KIVC due to the on-site Hubbard energy. We obtain a strongly electron-hole
asymmetric phase diagram with robust insulators for electron filling and metals
for negative filling. In the presence of magnetic flux, we predict an insulator
with Chern number for , a spin polarized state at charge
neutrality and competing insulators with Chern numbers and at
. The stability of the insulators is determined by the
screening environment, allowing for the possibility of observing a topological
phase transition.Comment: 14+11 pages, 13+6 figure
Recommended from our members
Subunit Composition of Neurotransmitter Receptors in the Immature and in the Epileptic Brain
Neuronal activity is critical for synaptogenesis and the development of neuronal networks. In the immature brain excitation predominates over inhibition facilitating the development of normal brain circuits, but also rendering it more susceptible to seizures. In this paper, we review the evolution of the subunit composition of neurotransmitter receptors during development, how it promotes excitation in the immature brain, and how this subunit composition of neurotransmission receptors may be also present in the epileptic brain. During normal brain development, excitatory glutamate receptors peak in function and gamma-aminobutiric acid (GABA) receptors are mainly excitatory rather than inhibitory. A growing body of evidence from animal models of epilepsy and status epilepticus has demonstrated that the brain exposed to repeated seizures presents a subunit composition of neurotransmitter receptors that mirrors that of the immature brain and promotes further seizures and epileptogenesis. Studies performed in samples from the epileptic human brain have also found a subunit composition pattern of neurotransmitter receptors similar to the one found in the immature brain. These findings provide a solid rationale for tailoring antiepileptic treatments to the specific subunit composition of neurotransmitter receptors and they provide potential targets for the development of antiepileptogenic treatments
Parallel Multi-Hypothesis Algorithm for Criticality Estimation in Traffic and Collision Avoidance
Due to the current developments towards autonomous driving and vehicle active
safety, there is an increasing necessity for algorithms that are able to
perform complex criticality predictions in real-time. Being able to process
multi-object traffic scenarios aids the implementation of a variety of
automotive applications such as driver assistance systems for collision
prevention and mitigation as well as fall-back systems for autonomous vehicles.
We present a fully model-based algorithm with a parallelizable architecture.
The proposed algorithm can evaluate the criticality of complex, multi-modal
(vehicles and pedestrians) traffic scenarios by simulating millions of
trajectory combinations and detecting collisions between objects. The algorithm
is able to estimate upcoming criticality at very early stages, demonstrating
its potential for vehicle safety-systems and autonomous driving applications.
An implementation on an embedded system in a test vehicle proves in a
prototypical manner the compatibility of the algorithm with the hardware
possibilities of modern cars. For a complex traffic scenario with 11 dynamic
objects, more than 86 million pose combinations are evaluated in 21 ms on the
GPU of a Drive PX~2
Toughened carbon fiber fabric-reinforced pCBT composites
Toughened carbon fiber-fabric reinforced polymerized
cyclic butylene terephthalate (pCBT) composites were
obtained by chemical modification of cyclic butylene
terephthalate (CBT) with small amounts of epoxy resin
and isocyanates as chain extenders. Homogeneous
CBT/epoxy and CBT/isocyanate blends were prepared
by melt blending the components in a lab-scale batch
mixer at low temperatures and high shear rate. Melt
blending was stopped before the ring-opening polymerization
of CBT could start. The modified CBT was
the starting material for carbon fiber fabric-reinforced
pCBT composites (fiber content at about 65 wt%)
which were prepared by ring-opening polymerization
during compression molding using a simple powder
prepreg method. Interlaminar shear strength, flexural
strength, and failure strain of the chemically modified
composites increased up to 60% with respect to
unmodified pCBT composites. Nevertheless, the flexural
moduli slightly decreased due to the toughening
effect of the chain extender on the pCBT matrix. Drop
weight impact tests revealed that the energy absorption
of the modified composites was relatively higher
as compared to unmodified pCBT composites.Peer ReviewedPostprint (author’s final draft
Crowdsourcing Dialect Characterization through Twitter
We perform a large-scale analysis of language diatopic variation using
geotagged microblogging datasets. By collecting all Twitter messages written in
Spanish over more than two years, we build a corpus from which a carefully
selected list of concepts allows us to characterize Spanish varieties on a
global scale. A cluster analysis proves the existence of well defined
macroregions sharing common lexical properties. Remarkably enough, we find that
Spanish language is split into two superdialects, namely, an urban speech used
across major American and Spanish citites and a diverse form that encompasses
rural areas and small towns. The latter can be further clustered into smaller
varieties with a stronger regional character.Comment: 10 pages, 5 figure
Predicting the energy output of wind farms based on weather data: important variables and their correlation
Pre-print available at: http://arxiv.org/abs/1109.1922Wind energy plays an increasing role in the supply of energy world wide. The energy output of a wind farm is highly dependent on the weather conditions present at its site. If the output can be predicted more accurately, energy suppliers can coordinate the collaborative production of different energy sources more efficiently to avoid costly overproduction. In this paper, we take a computer science perspective on energy prediction based on weather data and analyze the important parameters as well as their correlation on the energy output. To deal with the interaction of the different parameters, we use symbolic regression based on the genetic programming tool DataModeler. Our studies are carried out on publicly available weather and energy data for a wind farm in Australia. We report on the correlation of the different variables for the energy output. The model obtained for energy prediction gives a very reliable prediction of the energy output for newly supplied weather data. © 2012 Elsevier Ltd.Ekaterina Vladislavleva, Tobias Friedrich, Frank Neumann, Markus Wagne
Effect of the viscosity ratio on the PLA/PA10.10 bioblends morphology and mechanical properties
PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50wt.% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt.% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt.% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bio-blends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt.% and co-continuity was observed already at 44 wt.% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.Peer ReviewedPostprint (published version
PLA/PA bio-blends: induced morphology by extrusion
The effect of processing conditions on the final morphology of Poly(Lactic Acid) (PLA) with bio-based Polyamide 10.10 (PA) 70/30 blends is analyzed in this paper. Two types of PLA were used: Commercial (neat PLA) and a rheologically modified PLA (PLAREx), with higher melt elasticity produced by reactive extrusion. To evaluate the ability of in situ micro-fibrillation (µf) of PA phase during blend compounding by twin-screw extrusion, two processing parameters were varied: (i) Screw speed rotation (rpm); and (ii) take-up velocity, to induce a hot stretching with different Draw Ratios (DR). The potential ability of PA-µf in both bio-blends was evaluated by the viscosity (p) and elasticity (k’) ratios determined from the rheological tests of pristine polymers. When PLAREx was used, the requirements for PA-µf was fulfilled in the shear rate range observed at the extrusion die. Scanning electron microscopy (SEM) observations revealed that, unlike neat PLA, PLAREx promoted PA-µf without hot stretching and the aspect ratio increased as DR increased. For neat PLA-based blends, PA-µf was promoted during the hot stretching stage. DMTA analysis revealed that the use of PLAREx PLAREx resulted in a better mechanical performance in the rubbery region (T > Tg PLA-phase) due to the PA-µf morphology obtained.Peer ReviewedPostprint (published version
- …