7,197 research outputs found
Ultrafast fluorescent decay induced by metal-mediated dipole-dipole interaction in two-dimensional molecular aggregates
Two-dimensional molecular aggregate (2DMA), a thin sheet of strongly
interacting dipole molecules self-assembled at close distance on an ordered
lattice, is a fascinating fluorescent material. It is distinctively different
from the single or colloidal dye molecules or quantum dots in most previous
research. In this paper, we verify for the first time that when a 2DMA is
placed at a nanometric distance from a metallic substrate, the strong and
coherent interaction between the dipoles inside the 2DMA dominates its
fluorescent decay at picosecond timescale. Our streak-camera lifetime
measurement and interacting lattice-dipole calculation reveal that the
metal-mediated dipole-dipole interaction shortens the fluorescent lifetime to
about one half and increases the energy dissipation rate by ten times than
expected from the noninteracting single-dipole picture. Our finding can enrich
our understanding of nanoscale energy transfer in molecular excitonic systems
and may designate a new direction for developing fast and efficient
optoelectronic devices.Comment: 9 pages, 6 figure
PtSi Clustering In Silicon Probed by Transport Spectroscopy
Metal silicides formed by means of thermal annealing processes are employed
as contact materials in microelectronics. Control of the structure of
silicide/silicon interfaces becomes a critical issue when the device
characteristic size is reduced below a few tens of nanometers. Here we report
on silicide clustering occurring within the channel of PtSi/Si/PtSi Schottky
barrier transistors. This phenomenon is investigated through atomistic
simulations and low-temperature resonant tunneling spectroscopy. Our results
provide evidence for the segregation of a PtSi cluster with a diameter of a few
nanometers from the silicide contact. The cluster acts as metallic quantum dot
giving rise to distinct signatures of quantum transport through its discrete
energy states
Hidden Ferronematic Order in Underdoped Cuprates
We study a model for low doped cuprates where holes aggregate into oriented
stripe segments which have a vortex and an antivortex fixed to the extremes. We
argue that due to the interaction between segments a state with macroscopic
polarization is stabilized, which we call a ferronematic. This state can be
characterized as a charge nematic which, due to the net polarization, breaks
inversion symmetry and also exhibits an incommensurate spin modulation. Our
calculation can reproduce the doping dependent spin structure factor of
lanthanum cuprates in excellent agreement with experiment and allows to
rationalize experiments in which the incommensurability has an order
parameter-like temperature dependence.Comment: 5 pages, 4 figure
Neural network-based retrieval from software reuse repositories
A significant hurdle confronts the software reuser attempting to select candidate components from a software repository - discriminating between those components without resorting to inspection of the implementation(s). We outline an approach to this problem based upon neural networks which avoids requiring the repository administrators to define a conceptual closeness graph for the classification vocabulary
The role of aggregates in the thermal stability of Mg-PSZ refractories for vacuum induction melting
Mg-PSZ refractories used as vacuum induction melting crucibles are particle-reinforced composites with aggregate and matrix phases comprising fused zirconia. Three commercial varieties were cycled eight times to service temperatures and their microstructural and thermomechanical evolution investigated, with focus placed on the aggregate populations.
Two refractories, with large aggregates of similar size, were found to retain stiffness after cycling but in the refractory containing aggregates with high stabiliser levels, reaction between the stabiliser and Al and Si impurities produced secondary phases. Volume changes accompanying formation of these phases, and subsequent thermal expansion mismatches, led to aggregate break-up with consequent reductions in refractory toughness and strength. Secondary phases developed only rarely in the aggregates (with lower levels of stabiliser) of the second refractory. These aggregates remained intact and the refractory retained its toughness and strength. A third refractory contained small, unstabilised aggregates in a stabilised matrix and the strain mismatches that ensued during polymorphic transformation damaged microstructural interfaces. Refractory stiffness halved within eight cycles and toughness and strength were lost. All three refractories displayed R-curve behaviour and quasi-stable fracture curves were observed during bend tests.
The study shows that when using fused zirconia aggregates to design refractories, engineers need to i) limit stabiliser concentrations - a difference of just ±1 wt% Mg (in the presence of impurity elements) may determine whether secondary phase formation occurs and ii) eliminate alumina and silica impurities when possible through substitution of zircon sand with baddeleyite as the source for fused zirconia.Open Acces
Agent-based Social Psychology: from Neurocognitive Processes to Social Data
Moral Foundation Theory states that groups of different observers may rely on
partially dissimilar sets of moral foundations, thereby reaching different
moral valuations. The use of functional imaging techniques has revealed a
spectrum of cognitive styles with respect to the differential handling of novel
or corroborating information that is correlated to political affiliation. Here
we characterize the collective behavior of an agent-based model whose inter
individual interactions due to information exchange in the form of opinions are
in qualitative agreement with experimental neuroscience data. The main
conclusion derived connects the existence of diversity in the cognitive
strategies and statistics of the sets of moral foundations and suggests that
this connection arises from interactions between agents. Thus a simple
interacting agent model, whose interactions are in accord with empirical data
on conformity and learning processes, presents statistical signatures
consistent with moral judgment patterns of conservatives and liberals as
obtained by survey studies of social psychology.Comment: 11 pages, 4 figures, 2 C codes, to appear in Advances in Complex
System
Phase Stability and Thermoelectric Properties of the Mineral FeS2: An Ab Initio Study
First principles calculations were carried out to study the phase stability
and thermoelectric properties of the naturally occurring marcasite phase of
FeS at ambient condition as well as under pressure. Two distinct density
functional approaches has been used to investigate the above mentioned
properties. The plane wave pseudopotential approach was used to study the phase
stability and structural, elastic, and vibrational properties. The full
potential linear augment plane wave method has been used to study the
electronic structure and thermoelectric properties. From the total energy
calculations, it is clearly seen that marcasite FeS is stable at ambient
conditions, and it undergoes a first order phase transition to pyrite FeS
at around 3.7 GPa with a volume collapse of about 3. The calculated ground
state properties such as lattice parameters, bond lengths and bulk modulus of
marcasite FeS agree quite well with the experiment. Apart from the above
studies, phonon dispersion curves unambiguously indicate that marcasite phase
is stable under ambient conditions. Further, we do not observe any phonon
softening across the marcasite to pyrite transition and the possible reason
driving the transition is also analyzed in the present study, which has not
been attempted earlier. In addition, we have also calculated the electronic
structure and thermoelectric properties of the both marcasite and pyrite
FeS. We find a high thermopower for both the phases, especially with p-type
doping, which enables us to predict that FeS might find promising
applications as good thermoelectric materials.Comment: 10 Figure
Using neural networks in software repositories
The first topic is an exploration of the use of neural network techniques to improve the effectiveness of retrieval in software repositories. The second topic relates to a series of experiments conducted to evaluate the feasibility of using adaptive neural networks as a means of deriving (or more specifically, learning) measures on software. Taken together, these two efforts illuminate a very promising mechanism supporting software infrastructures - one based upon a flexible and responsive technology
Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs
Mantle plumes are thought to play a key role in transferring heat from the core\u2013mantle
boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging
on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate
hotspots, large igneous provinces and hence considerable dynamic topography. However, the
active role of mantle plumes on subducting slabs remains poorly understood. Here we show
that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern
Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau.
Our findings are based on comparisons between 3D anisotropic tomography images and 3D
petrological-thermo-mechanical models, which self-consistently explain several unique
features of the Fiji\u2013Tonga region. We identify four possible slip systems of bridgmanite in the
lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab
(VSH4VSV) with thermo-mechanical calculations
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