1,098 research outputs found
A novel route to Pt-Bi2O3 composite thin films and their application in photo-reduction of water
A novel homoleptic bismuth(III) β-diketonate (dibenzoylmethane – dbm) complex [Bi(dbm)3]2 has been used as a precursor to thin films of crystalline β-Bi2O3, and hexachloroplatinic acid (H2PtCl6·6H2O) has been demonstrated as a suitable precursor for deposition of platinum nanoparticles, both deposited via aerosol-assisted chemical vapour deposition (AACVD). Thin films of Pt–Bi2O3 were co-deposited from a mixture of [Bi(dbm)3]2 and H2PtCl6·6H2O; the introduction of Pt particles into β-Bi2O3 causes hydrogen to be evolved during photolysis of water over the composite material, a property not found for Pt particles or β-Bi2O3 alone
Periodic orbit bifurcations and scattering time delay fluctuations
We study fluctuations of the Wigner time delay for open (scattering) systems
which exhibit mixed dynamics in the classical limit. It is shown that in the
semiclassical limit the time delay fluctuations have a distribution that
differs markedly from those which describe fully chaotic (or strongly
disordered) systems: their moments have a power law dependence on a
semiclassical parameter, with exponents that are rational fractions. These
exponents are obtained from bifurcating periodic orbits trapped in the system.
They are universal in situations where sufficiently long orbits contribute. We
illustrate the influence of bifurcations on the time delay numerically using an
open quantum map.Comment: 9 pages, 3 figures, contribution to QMC200
BASiCS: Bayesian Analysis of Single-Cell Sequencing Data
Single-cell mRNA sequencing can uncover novel cell-to-cell heterogeneity in gene expression levels in seemingly homogeneous populations of cells. However, these experiments are prone to high levels of unexplained technical noise, creating new challenges for identifying genes that show genuine heterogeneous expression within the population of cells under study. BASiCS (Bayesian Analysis of Single-Cell Sequencing data) is an integrated Bayesian hierarchical model where: (i) cell-specific normalisation constants are estimated as part of the model parameters, (ii) technical variability is quantified based on spike-in genes that are artificially introduced to each analysed cell's lysate and (iii) the total variability of the expression counts is decomposed into technical and biological components. BASiCS also provides an intuitive detection criterion for highly (or lowly) variable genes within the population of cells under study. This is formalised by means of tail posterior probabilities associated to high (or low) biological cell-to-cell variance contributions, quantities that can be easily interpreted by users. We demonstrate our method using gene expression measurements from mouse Embryonic Stem Cells. Cross-validation and meaningful enrichment of gene ontology categories within genes classified as highly (or lowly) variable supports the efficacy of our approach
Enhancement of quantum dot peak-spacing fluctuations in the fractional q uantum Hall regime
The fluctuations in the spacing of the tunneling resonances through a quantum
dot have been studied in the quantum Hall regime. Using the fact that the
ground-state of the system is described very well by the Laughlin wavefunction,
we were able to determine accurately, via classical Monte Carlo calculations,
the amplitude and distribution of the peak-spacing fluctuations.
Our results clearly demonstrate a big enhancement of the fluctuations as the
importance of the electronic correlations increases, namely as the density
decreases and filling factor becomes smaller.
We also find that the distribution of the fluctuations approaches a Gaussian
with increasing density of random potentials.Comment: 6 pages, 3 figures all in gzipped tarred fil
Session-Based Role Programming for the Design of Advanced Telephony Applications
International audienceStimulated by new protocols like SIP, telephony applications are rapidly evolving to o er and combine a variety of communications forms including presence status, instant messaging and videoconferencing. This situation changes and complicates significantly the programming of telephony applications that consist now of distributed entities involved into multiple heterogeneous, stateful and long-running interactions. This paper proposes an approach to support the development of SIP-based telephony applications based on general programming language. Our approach combines the concepts of Actor, Session and Role. Role is the part an actor takes in a session and we consider a session as a collaboration between roles. By using these concepts, we are able to break the complexity of SIP entities programming and provide flexibility for defi ning new ones. Our approach is implemented as a coding framework above JAIN-SIP
Measuring the Lyapunov exponent using quantum mechanics
We study the time evolution of two wave packets prepared at the same initial
state, but evolving under slightly different Hamiltonians. For chaotic systems,
we determine the circumstances that lead to an exponential decay with time of
the wave packet overlap function. We show that for sufficiently weak
perturbations, the exponential decay follows a Fermi golden rule, while by
making the difference between the two Hamiltonians larger, the characteristic
exponential decay time becomes the Lyapunov exponent of the classical system.
We illustrate our theoretical findings by investigating numerically the overlap
decay function of a two-dimensional dynamical system.Comment: 9 pages, 6 figure
On the semiclassical theory for universal transmission fluctuations in chaotic systems: the importance of unitarity
The standard semiclassical calculation of transmission correlation functions
for chaotic systems is severely influenced by unitarity problems. We show that
unitarity alone imposes a set of relationships between cross sections
correlation functions which go beyond the diagonal approximation. When these
relationships are properly used to supplement the semiclassical scheme we
obtain transmission correlation functions in full agreement with the exact
statistical theory and the experiment. Our approach also provides a novel
prediction for the transmission correlations in the case where time reversal
symmetry is present
Sensitivity of codispersion to noise and error in ecological and environmental data
Codispersion analysis is a new statistical method developed to assess spatial
covariation between two spatial processes that may not be isotropic or
stationary. Its application to anisotropic ecological datasets have provided
new insights into mechanisms underlying observed patterns of species
distributions and the relationship between individual species and underlying
environmental gradients. However, the performance of the codispersion
coefficient when there is noise or measurement error ("contamination") in the
data has been addressed only theoretically. Here, we use Monte Carlo
simulations and real datasets to investigate the sensitivity of codispersion to
four types of contamination commonly seen in many real-world environmental and
ecological studies. Three of these involved examining codispersion of a spatial
dataset with a contaminated version of itself. The fourth examined differences
in codisperson between plants and soil conditions, where the estimates of soil
characteristics were based on complete or thinned datasets. In all cases, we
found that estimates of codispersion were robust when contamination, such as
data thinning, was relatively low (<15\%), but were sensitive to larger
percentages of contamination. We also present a useful method for imputing
missing spatial data and discuss several aspects of the codispersion
coefficient when applied to noisy data to gain more insight about the
performance of codispersion in practice.Comment: 20 pages, 14 figure
Lyapunov exponent of the random frequency oscillator: cumulant expansion approach
We consider a one-dimensional harmonic oscillator with a random frequency,
focusing on both the standard and the generalized Lyapunov exponents,
and respectively. We discuss the numerical difficulties that
arise in the numerical calculation of in the case of strong
intermittency. When the frequency corresponds to a Ornstein-Uhlenbeck process,
we compute analytically by using a cumulant expansion including
up to the fourth order. Connections with the problem of finding an analytical
estimate for the largest Lyapunov exponent of a many-body system with smooth
interactions are discussed.Comment: 6 pages, 4 figures, to appear in J. Phys. Conf. Series - LAWNP0
- …