82 research outputs found
Toward homochiral protocells in noncatalytic peptide systems
The activation-polymerization-epimerization-depolymerization (APED) model of
Plasson et al. has recently been proposed as a mechanism for the evolution of
homochirality on prebiotic Earth. The dynamics of the APED model in
two-dimensional spatially-extended systems is investigated for various
realistic reaction parameters. It is found that the APED system allows for the
formation of isolated homochiral proto-domains surrounded by a racemate. A
diffusive slowdown of the APED network such as induced through tidal motion or
evaporating pools and lagoons leads to the stabilization of homochiral bounded
structures as expected in the first self-assembled protocells.Comment: 10 pages, 5 figure
Academic research groups: evaluation of their quality and quality of their evaluation
In recent years, evaluation of the quality of academic research has become an
increasingly important and influential business. It determines, often to a
large extent, the amount of research funding flowing into universities and
similar institutes from governmental agencies and it impacts upon academic
careers. Policy makers are becoming increasingly reliant upon, and influenced
by, the outcomes of such evaluations. In response, university managers are
increasingly attracted to simple indicators as guides to the dynamics of the
positions of their various institutions in league tables. However, these league
tables are frequently drawn up by inexpert bodies such as newspapers and
magazines, using rather arbitrary measures and criteria. Terms such as
"critical mass' and "metrics" are often bandied about without proper
understanding of what they actually mean. Rather than accepting the rise and
fall of universities, departments and individuals on a turbulent sea of
arbitrary measures, we suggest it is incumbent upon the scientific community
itself to clarify their nature. Here we report on recent attempts to do that by
properly defining critical mass and showing how group size influences research
quality. We also examine currently predominant metrics and show that these fail
as reliable indicators of group research quality.Comment: Presented at the International Conference on Computer Simulation in
Physics and Beyond in Moscow, 2015. The Proceedings will appear in Journal of
Physics: Conference Series (JPCS
Nonlinearity and Topology
The interplay of nonlinearity and topology results in many novel and emergent
properties across a number of physical systems such as chiral magnets, nematic
liquid crystals, Bose-Einstein condensates, photonics, high energy physics,
etc. It also results in a wide variety of topological defects such as solitons,
vortices, skyrmions, merons, hopfions, monopoles to name just a few.
Interaction among and collision of these nontrivial defects itself is a topic
of great interest. Curvature and underlying geometry also affect the shape,
interaction and behavior of these defects. Such properties can be studied using
techniques such as, e.g. the Bogomolnyi decomposition. Some applications of
this interplay, e.g. in nonreciprocal photonics as well as topological
materials such as Dirac and Weyl semimetals, are also elucidated
Melting a Hubbard dimer: benchmarks of 'ALDA' for quantum thermodynamics
The competition between evolution time, interaction strength, and temperature
challenges our understanding of many-body quantum systems out-of-equilibrium.
Here we consider a benchmark system, the Hubbard dimer, which allows us to
explore all the relevant regimes and calculate exactly the related average
quantum work. At difference with previous studies, we focus on the effect of
increasing temperature, and show how this can turn competition between
many-body interactions and driving field into synergy. We then turn to use
recently proposed protocols inspired by density functional theory to explore if
these effects could be reproduced by using simple approximations. We find that,
up to and including intermediate temperatures, a method which borrows from
ground-state adiabatic local density approximation improves dramatically the
estimate for the average quantum work, including, in the adiabatic regime, when
correlations are strong. However at high temperature and at least when based on
the pseudo-LDA, this method fails to capture the counterintuitive qualitative
dependence of the quantum work with interaction strength, albeit getting the
quantitative estimates relatively close to the exact results
Descartáveis urbanos: discutindo a complexidade da população de rua e o desafio para políticas de saúde
Clinically applicable deep learning for diagnosis and referral in retinal disease
The volume and complexity of diagnostic imaging is increasing at a pace faster than the availability of human expertise to interpret it. Artificial intelligence has shown great promise in classifying two-dimensional photographs of some common diseases and typically relies on databases of millions of annotated images. Until now, the challenge of reaching the performance of expert clinicians in a real-world clinical pathway with three-dimensional diagnostic scans has remained unsolved. Here, we apply a novel deep learning architecture to a clinically heterogeneous set of three-dimensional optical coherence tomography scans from patients referred to a major eye hospital. We demonstrate performance in making a referral recommendation that reaches or exceeds that of experts on a range of sight-threatening retinal diseases after training on only 14,884 scans. Moreover, we demonstrate that the tissue segmentations produced by our architecture act as a device-independent representation; referral accuracy is maintained when using tissue segmentations from a different type of device. Our work removes previous barriers to wider clinical use without prohibitive training data requirements across multiple pathologies in a real-world setting
An Evaluation Schema for the Ethical Use of Autonomous Robotic Systems in Security Applications
The opportunity of energy storage in magnetic field by combining flywheel and ultracapacitor tools
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