3,479 research outputs found
Pathwise convergence of the Euler scheme for rough and stochastic differential equations
The convergence of the first order Euler scheme and an approximative variant
thereof, along with convergence rates, are established for rough differential
equations driven by c\`adl\`ag paths satisfying a suitable criterion, namely
the so-called Property (RIE), along time discretizations with vanishing mesh
size. This property is then verified for almost all sample paths of Brownian
motion, It\^o processes, L\'evy processes and general c\`adl\`ag
semimartingales, as well as the driving signals of both mixed and rough
stochastic differential equations, relative to various time discretizations.
Consequently, we obtain pathwise convergence in p-variation of the
Euler--Maruyama scheme for stochastic differential equations driven by these
processes.Comment: 43 page
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Observed and simulated precipitation responses in wet and dry regions 1850–2100
Global warming is expected to enhance fluxes of fresh water between the surface and atmosphere, causing wet regions to become wetter and dry regions drier, with serious implications for water resource management. Defining the wet and dry regions as the upper 30% and lower 70% of the precipitation totals across the tropics (30° S–30° N) each month we combine observations and climate model simulations to understand changes in the wet and dry regions over the period 1850–2100. Observed decreases in precipitation over dry tropical land (1950–2010) are also simulated by coupled atmosphere–ocean climate models (−0.3%/decade) with trends projected to continue into the 21st century. Discrepancies between observations and simulations over wet land regions since 1950 exist, relating to decadal fluctuations in El Niño southern oscillation, the timing of which is not represented by the coupled simulations. When atmosphere-only simulations are instead driven by observed sea surface temperature they are able to adequately represent this variability over land. Global distributions of precipitation trends are dominated by spatial changes in atmospheric circulation. However, the tendency for already wet regions to become wetter (precipitation increases with warming by 3% K−1 over wet tropical oceans) and the driest regions drier (precipitation decreases of −2% K−1 over dry tropical land regions) emerges over the 21st century in response to the substantial surface warming
Document Filtering for Long-tail Entities
Filtering relevant documents with respect to entities is an essential task in
the context of knowledge base construction and maintenance. It entails
processing a time-ordered stream of documents that might be relevant to an
entity in order to select only those that contain vital information.
State-of-the-art approaches to document filtering for popular entities are
entity-dependent: they rely on and are also trained on the specifics of
differentiating features for each specific entity. Moreover, these approaches
tend to use so-called extrinsic information such as Wikipedia page views and
related entities which is typically only available only for popular head
entities. Entity-dependent approaches based on such signals are therefore
ill-suited as filtering methods for long-tail entities. In this paper we
propose a document filtering method for long-tail entities that is
entity-independent and thus also generalizes to unseen or rarely seen entities.
It is based on intrinsic features, i.e., features that are derived from the
documents in which the entities are mentioned. We propose a set of features
that capture informativeness, entity-saliency, and timeliness. In particular,
we introduce features based on entity aspect similarities, relation patterns,
and temporal expressions and combine these with standard features for document
filtering. Experiments following the TREC KBA 2014 setup on a publicly
available dataset show that our model is able to improve the filtering
performance for long-tail entities over several baselines. Results of applying
the model to unseen entities are promising, indicating that the model is able
to learn the general characteristics of a vital document. The overall
performance across all entities---i.e., not just long-tail entities---improves
upon the state-of-the-art without depending on any entity-specific training
data.Comment: CIKM2016, Proceedings of the 25th ACM International Conference on
Information and Knowledge Management. 201
Highly controlled, reproducible measurements of aerosol emissions from combustion of a common African biofuel source
Particulate emissions from biomass burning can both alter the atmosphere's radiative
balance and cause significant harm to human health. However, due to the large
effect on emissions caused by even small alterations to the way in which
a fuel burns, it is difficult to study particulate production of biomass
combustion mechanistically and in a repeatable manner. In order to address
this gap, in this study, small wood samples sourced from Côte D'Ivoire in
West Africa were burned in a highly controlled laboratory environment. The
shape and mass of samples, available airflow and surrounding thermal
environment were carefully regulated. Organic aerosol and refractory black
carbon emissions were measured in real time using an Aerosol Mass
Spectrometer and a Single Particle Soot Photometer, respectively. This
methodology produced remarkably repeatable results, allowing aerosol
emissions to be mapped directly onto different phases of combustion.
Emissions from pyrolysis were visible as a distinct phase before flaming was
established. After flaming combustion was initiated, a black-carbon-dominant
flame was observed during which very little organic aerosol was produced,
followed by a period that was dominated by organic-carbon-producing
smouldering combustion, despite the presence of residual flaming. During
pyrolysis and smouldering, the two phases producing organic aerosol, distinct
mass spectral signatures that correspond to previously reported variations in
biofuel emissions measured in the atmosphere are found. Organic aerosol
emission factors averaged over an entire combustion event were found to be
representative of the time spent in the pyrolysis and smouldering phases,
rather than reflecting a coupling between emissions and the mass loss of the
sample. Further exploration of aerosol yields from similarly carefully
controlled fires and a careful comparison with data from macroscopic fires
and real-world emissions will help to deliver greater constraints on the
variability of particulate emissions in atmospheric systems
Development and application of an indirect enzyme-linked immunosorbent assay using recombinant truncated Cap protein for the diagnosis of porcine circovirus-like virus P1
Tight-binding study of the influence of the strain on the electronic properties of InAs/GaAs quantum dots
We present an atomistic investigation of the influence of strain on the
electronic properties of quantum dots (QD's) within the empirical tight-binding (ETB) model with interactions up to 2nd nearest neighbors
and spin-orbit coupling. Results for the model system of capped pyramid-shaped
InAs QD's in GaAs, with supercells containing atoms are presented and
compared with previous empirical pseudopotential results. The good agreement
shows that ETB is a reliable alternative for an atomistic treatment. The strain
is incorporated through the atomistic valence force field model. The ETB
treatment allows for the effects of bond length and bond angle deviations from
the ideal InAs and GaAs zincblende structure to be selectively removed from the
electronic-structure calculation, giving quantitative information on the
importance of strain effects on the bound state energies and on the physical
origin of the spatial elongation of the wave functions. Effects of dot-dot
coupling have also been examined to determine the relative weight of both
strain field and wave function overlap.Comment: 22 pages, 7 figures, submitted to Phys. Rev. B (in press) In the
latest version, added Figs. 3 and 4, modified Fig. 5, Tables I and II,.and
added new reference
Mapping the unconventional orbital texture in topological crystalline insulators
The newly discovered topological crystalline insulators (TCIs) harbor a
complex band structure involving multiple Dirac cones. These materials are
potentially highly tunable by external electric field, temperature or strain
and could find future applications in field-effect transistors, photodetectors,
and nano-mechanical systems. Theoretically, it has been predicted that
different Dirac cones, offset in energy and momentum-space, might harbor vastly
different orbital character, a unique property which if experimentally
realized, would present an ideal platform for accomplishing new spintronic
devices. However, the orbital texture of the Dirac cones, which is of immense
importance in determining a variety of materials properties, still remains
elusive in TCIs. Here, we unveil the orbital texture in a prototypical TCI
PbSnSe. By using Fourier-transform (FT) scanning tunneling
spectroscopy (STS) we measure the interference patterns produced by the
scattering of surface state electrons. We discover that the intensity and
energy dependences of FTs show distinct characteristics, which can directly be
attributed to orbital effects. Our experiments reveal the complex band topology
involving two Lifshitz transitions and establish the orbital nature of the
Dirac bands in this new class of topological materials, which could provide a
different pathway towards future quantum applications
Strongly Correlated Quantum Fluids: Ultracold Quantum Gases, Quantum Chromodynamic Plasmas, and Holographic Duality
Strongly correlated quantum fluids are phases of matter that are
intrinsically quantum mechanical, and that do not have a simple description in
terms of weakly interacting quasi-particles. Two systems that have recently
attracted a great deal of interest are the quark-gluon plasma, a plasma of
strongly interacting quarks and gluons produced in relativistic heavy ion
collisions, and ultracold atomic Fermi gases, very dilute clouds of atomic
gases confined in optical or magnetic traps. These systems differ by more than
20 orders of magnitude in temperature, but they were shown to exhibit very
similar hydrodynamic flow. In particular, both fluids exhibit a robustly low
shear viscosity to entropy density ratio which is characteristic of quantum
fluids described by holographic duality, a mapping from strongly correlated
quantum field theories to weakly curved higher dimensional classical gravity.
This review explores the connection between these fields, and it also serves as
an introduction to the Focus Issue of New Journal of Physics on Strongly
Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas. The
presentation is made accessible to the general physics reader and includes
discussions of the latest research developments in all three areas.Comment: 138 pages, 25 figures, review associated with New Journal of Physics
special issue "Focus on Strongly Correlated Quantum Fluids: from Ultracold
Quantum Gases to QCD Plasmas"
(http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Strongly%20Correlated%20Quantum%20Fluids%20-%20from%20Ultracold%20Quantum%20Gases%20to%20QCD%20Plasmas
Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors
In the first three years since the discovery of Fe-based high Tc
superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed
light on three important questions. First, STM has demonstrated the complexity
of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle
interference (QPI) imaging and low temperature spectroscopy have shown that the
pairing order parameter varies from nodal to nodeless s\pm within a single
family, FeTe1-xSex. Second, STM has imaged C4 -> C2 symmetry breaking in the
electronic states of both parent and superconducting materials. As a local
probe, STM is in a strong position to understand the interactions between these
broken symmetry states and superconductivity. Finally, STM has been used to
image the vortex state, giving insights into the technical problem of vortex
pinning, and the fundamental problem of the competing states introduced when
superconductivity is locally quenched by a magnetic field. Here we give a
pedagogical introduction to STM and QPI imaging, discuss the specific
challenges associated with extracting bulk properties from the study of
surfaces, and report on progress made in understanding Fe-based superconductors
using STM techniques.Comment: 36 pages, 23 figures, 229 reference
Castor bean organelle genome sequencing and worldwide genetic diversity analysis
Castor bean is an important oil-producing plant in the Euphorbiaceae family. Its high-quality oil contains up to 90% of the unusual fatty acid ricinoleate, which has many industrial and medical applications. Castor bean seeds also contain ricin, a highly toxic Type 2 ribosome-inactivating protein, which has gained relevance in recent years due to biosafety concerns. In order to gain knowledge on global genetic diversity in castor bean and to ultimately help the development of breeding and forensic tools, we carried out an extensive chloroplast sequence diversity analysis. Taking advantage of the recently published genome sequence of castor bean, we assembled the chloroplast and mitochondrion genomes extracting selected reads from the available whole genome shotgun reads. Using the chloroplast reference genome we used the methylation filtration technique to readily obtain draft genome sequences of 7 geographically and genetically diverse castor bean accessions. These sequence data were used to identify single nucleotide polymorphism markers and phylogenetic analysis resulted in the identification of two major clades that were not apparent in previous population genetic studies using genetic markers derived from nuclear DNA. Two distinct sub-clades could be defined within each major clade and large-scale genotyping of castor bean populations worldwide confirmed previously observed low levels of genetic diversity and showed a broad geographic distribution of each sub-clade
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