379 research outputs found
Programming with C++Â concepts
AbstractThis paper explores the definition, applications, and limitations of concepts and concept maps in C++, with a focus on library composition. We also compare and contrast concepts to adaptation mechanisms in other languages.Efficient, non-intrusive adaptation mechanisms are essential when adapting data structures to a library’s API. Development with reusable components is a widely practiced method of building software. Components vary in form, ranging from source code to non-modifiable binary libraries. The Concepts language features, slated to appear in the next version of C++, have been designed with such compositions in mind, promising an improved ability to create generic, non-intrusive, efficient, and identity-preserving adapters.We report on two cases of data structure adaptation between different libraries, and illustrate best practices and idioms. First, we adapt GUI widgets from several libraries, with differing APIs, for use with a generic layout engine. We further develop this example to describe the run-time concept idiom, extending the applicability of concepts to domains where run-time polymorphism is required. Second, we compose an image processing library and a graph algorithm library, by making use of a transparent adaptation layer, enabling the efficient application of graph algorithms to the image processing domain. We use the adaptation layer to realize a few key algorithms, and report little or no performance degradation
Charge Solitons in 1-D Arrays of Serially Coupled Josephson Junctions
We study a 1-D array of Josephson coupled superconducting grains with kinetic
inductance which dominates over the Josephson inductance. In this limit the
dynamics of excess Cooper pairs in the array is described in terms of charge
solitons, created by polarization of the grains. We analyze the dynamics of
these topological excitations, which are dual to the fluxons in a long
Josephson junction, using the continuum sine-Gordon model. We find that their
classical relativistic motion leads to saturation branches in the I-V
characteristic of the array. We then discuss the semi-classical quantization of
the charge soliton, and show that it is consistent with the large kinetic
inductance of the array. We study the dynamics of a quantum charge soliton in a
ring-shaped array biased by an external flux through its center. If the
dephasing length of the quantum charge soliton is larger than the circumference
of the array, quantum phenomena like persistent current and coherent current
oscillations are expected. As the characteristic width of the charge soliton is
of the order of 100 microns, it is a macroscopic quantum object. We discuss the
dephasing mechanisms which can suppress the quantum behaviour of the charge
soliton.Comment: 26 pages, LaTex, 7 Postscript figure
Activation of Central Melanocortin Pathways by Fenfluramlne
D-fenfluramine (d-FEN) was once widely prescribed and was among the most effective weight loss drugs, but was withdrawn from clinical use because of reports of cardiac complications in a subset of patients. Discerning the neurobiology underlying the anorexic action of d-FEN may facilitate the development of new drugs to prevent and treat obesity. Through a combination of functional neuroanatomy, feeding, and electrophysiology studies in rodents, we show that d-FEN-induced anorexia requires activation of central nervous system melanocortin pathways. These results provide a mechanistic explanation of d-FEN\u27s anorexic actions and indicate that drugs targeting these downstream melanocortin pathways may prove to be effective and more selective antiobesity treatments
The gravitational-wave background null hypothesis: Characterizing noise in millisecond pulsar arrival times with the Parkes Pulsar Timing Array
The noise in millisecond pulsar (MSP) timing data can include contributions
from observing instruments, the interstellar medium, the solar wind, solar
system ephemeris errors, and the pulsars themselves. The noise environment must
be accurately characterized in order to form the null hypothesis from which
signal models can be compared, including the signature induced by
nanohertz-frequency gravitational waves (GWs). Here we describe the noise
models developed for each of the MSPs in the Parkes Pulsar Timing Array (PPTA)
third data release, which have been used as the basis of a search for the
isotropic stochastic GW background. We model pulsar spin noise, dispersion
measure variations, scattering variations, events in the pulsar magnetospheres,
solar wind variability, and instrumental effects. We also search for new timing
model parameters and detected Shapiro delays in PSR~J06143329 and
PSR~J19025105. The noise and timing models are validated by testing the
normalized and whitened timing residuals for Gaussianity and residual
correlations with time. We demonstrate that the choice of noise models
significantly affects the inferred properties of a common-spectrum process.
Using our detailed models, the recovered common-spectrum noise in the PPTA is
consistent with a power law with a spectral index of , the value
predicted for a stochastic GW background from a population of supermassive
black hole binaries driven solely by GW emission.Comment: 18 pages, 10 figures. Accepted for publication in ApJ
Extremely high conductivity observed in the triple point topological metal MoP
Weyl and Dirac fermions have created much attention in condensed matter
physics and materials science. Recently, several additional distinct types of
fermions have been predicted. Here, we report ultra-high electrical
conductivity in MoP at low temperature, which has recently been established as
a triple point Fermion material. Here we show that the electrical resistivity
is 6 n-ohm cm at 2 K with a large mean free path of 11 microns. de Haas-van
Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to
noble metals with similar conductivity and number of carriers, the
magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the
momentum relaxing time of the electrons is found to be more than 15 times
larger than the quantum coherence time. This difference between the scattering
scales shows that momentum conserving scattering dominates in MoP at low
temperatures.Comment: Updated texts and supplementar
High-yield single-step catalytic growth of graphene nanostripes by plasma enhanced chemical vapor deposition
We report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power (≤60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m^2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >∼130:1) and typical widths from tens to hundreds of nanometers on various transition-metal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility ∼10^4 cm^2/V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios
High-yield single-step catalytic growth of graphene nanostripes by plasma enhanced chemical vapor deposition
We report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power (≤60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m^2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >∼130:1) and typical widths from tens to hundreds of nanometers on various transition-metal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility ∼10^4 cm^2/V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios
Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array
Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves
(GWs). A background of GWs modulates pulsar arrival times and manifests as a
stochastic process, common to all pulsars, with a signature spatial
correlation. Here we describe a search for an isotropic stochastic
gravitational-wave background (GWB) using observations of 30 millisecond
pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA),
which spans 18 years. Using current Bayesian inference techniques we recover
and characterize a common-spectrum noise process. Represented as a strain
spectrum , we measure and respectively (median and 68%
credible interval). For a spectral index of , corresponding to an
isotropic background of GWs radiated by inspiraling supermassive black hole
binaries, we recover an amplitude of .
However, we demonstrate that the apparent signal strength is time-dependent, as
the first half of our data set can be used to place an upper limit on that
is in tension with the inferred common-spectrum amplitude using the complete
data set. We search for spatial correlations in the observations by
hierarchically analyzing individual pulsar pairs, which also allows for
significance validation through randomizing pulsar positions on the sky. For a
process with , we measure spatial correlations consistent with a
GWB, with an estimated false-alarm probability of (approx.
). The long timing baselines of the PPTA and the access to southern
pulsars will continue to play an important role in the International Pulsar
Timing Array.Comment: 19 pages, 10 figures, Accepted for publication in ApJ
3DKL v1.0: creating the first 3D geological model of Kuala Lumpur
The objective of UN Sustainable Development Goal 11 is to make cities and human settlements inclusive, safe, resilient and sustainable. Geoscience can play a significant role in achieving targets within this goal by developing a better understanding of geological properties and processes within urban environments, and by ensuring that this understanding is integrated into urban development. A key step in this process will be enhancing awareness of urban geology among non-geoscience decision-makers, so that inherent subsurface risks and benefits are understood and accounted for during all phases of development. Three-dimensional geological models are an effective tool for geologists to communicate with stakeholders in government and industry during that process. They can also provide a framework to enable geological data and information to be integrated into Building and City Information Models, and thus facilitate more effective infrastructure and utility asset management. This paper describes the modelling workflow adopted by a consortium of geoscientists from government, industry and academia to deliver the first 3D geological model of Kuala Lumpur – 3DKL v1.0. The modelling workflow involved: digitising borehole logs from site investigation reports and storing them in a dedicated geospatially-enabled SQLite borehole database; viewing and interpreting that borehole data using QGIS software; generating multiple orthogonally oriented cross-section profiles across the modelled area using Groundhog Desktop software; and integrating the information derived from the interpreted boreholes, surface data and cross-section profiles to generate a 3D geological model in Leapfrog Geo software. 3DKL v1.0 has demonstrated proof-of-concept: we have developed a workflow, based largely on freely-available software, for transforming borehole information, previously captured in paper records, into a conceptual 3D model. The modelling process has also identified areas where geological knowledge and data need to be enhanced if 3DKL is to fulfil its potential to support more sustainable and resilient urban development in Kuala Lumpur
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