490 research outputs found
On the computation of finite bottom-quark mass effects in Higgs boson production
We present analytic results for the partonic cross-sections contributing to
the top-bottom interference in Higgs production via gluon fusion at hadron
colliders at NLO accuracy in QCD. We develop a method of expansion in small
bottom-mass for master integrals and combine it with the usual infinite
top-mass effective theory. Our method of expansion admits a simple algorithmic
description and can be easily generalized to any small parameter. These results
for the integrated cross-sections will be needed in the computation of the
renormalization counter-terms entering the computation of finite bottom-quark
mass effects at NNLO.Comment: Updated affiliations and abstract, added reference, and corrected
minor typo
Emergence of active nematic behaviour in monolayers of isotropic cells
There is now growing evidence of the emergence and biological functionality
of liquid crystal features, including nematic order and topological defects, in
cellular tissues. However, how such features that intrinsically rely on
particle elongation, emerge in monolayers of cells with isotropic shapes is an
outstanding question. In this article we present a minimal model of cellular
monolayers based on cell deformation and force transmission at the cell-cell
interface that explains the formation of topological defects and captures the
flow-field and stress patterns around them. By including mechanical properties
at the individual cell level, we further show that the instability that drives
the formation of topological defects and leads to active turbulence, emerges
from a feedback between shape deformation and active driving. The model allows
us to suggest new explanations for experimental observations in tissue
mechanics, and to propose designs for future experiments
Active Inter-cellular Forces in Collective Cell Motility
The collective behaviour of confluent cell sheets is strongly influenced both
by polar forces, arising through cytoskeletal propulsion and by active
inter-cellular forces, which are mediated by interactions across cell-cell
junctions. We use a phase-field model to explore the interplay between these
two contributions and compare the dynamics of a cell sheet when the polarity of
the cells aligns to (i) their main axis of elongation, (ii) their velocity, and
(iii) when the polarity direction executes a persistent random walk.In all
three cases, we observe a sharp transition from a jammed state (where cell
rearrangements are strongly suppressed) to a liquid state (where the cells can
move freely relative to each other) when either the polar or the inter-cellular
forces are increased. In addition, for case (ii) only, we observe an additional
dynamical state, flocking (solid or liquid), where the majority of the cells
move in the same direction. The flocking state is seen for strong polar forces,
but is destroyed as the strength of the inter-cellular activity is increased.Comment: 15 pages,22 figure
Fluctuation-induced dynamics of nematic topological defects
Topological defects are increasingly being identified in various biological
systems, where their characteristic flow fields and stress patterns are
associated with continuous active stress generation by biological entities.
Here, using numerical simulations of continuum fluctuating nematohydrodynamics
we show that even in the absence of any specific form of active stresses
associated with self-propulsion, mesoscopic fluctuations in either
orientational alignment or hydrodynamics can independently result in flow
patterns around topological defects that resemble the ones observed in active
systems. Our simulations further show the possibility of extensile- and
contractile-like motion of fluctuation-induced positive half-integer
topological defects. Remarkably, isotropic stress fields also reproduce the
experimentally measured stress patterns around topological defects in
epithelia. Our findings further reveal that extensile- or contractile-like flow
and stress patterns around fluctuation-induced defects are governed by passive
elastic stresses and flow-aligning behavior of the nematics
Query-based Hard-Image Retrieval for Object Detection at Test Time
There is a longstanding interest in capturing the error behaviour of object
detectors by finding images where their performance is likely to be
unsatisfactory. In real-world applications such as autonomous driving, it is
also crucial to characterise potential failures beyond simple requirements of
detection performance. For example, a missed detection of a pedestrian close to
an ego vehicle will generally require closer inspection than a missed detection
of a car in the distance. The problem of predicting such potential failures at
test time has largely been overlooked in the literature and conventional
approaches based on detection uncertainty fall short in that they are agnostic
to such fine-grained characterisation of errors. In this work, we propose to
reformulate the problem of finding "hard" images as a query-based hard image
retrieval task, where queries are specific definitions of "hardness", and offer
a simple and intuitive method that can solve this task for a large family of
queries. Our method is entirely post-hoc, does not require ground-truth
annotations, is independent of the choice of a detector, and relies on an
efficient Monte Carlo estimation that uses a simple stochastic model in place
of the ground-truth. We show experimentally that it can be applied successfully
to a wide variety of queries for which it can reliably identify hard images for
a given detector without any labelled data. We provide results on ranking and
classification tasks using the widely used RetinaNet, Faster-RCNN, Mask-RCNN,
and Cascade Mask-RCNN object detectors. The code for this project is available
at https://github.com/fiveai/hardest
Osteoporosis case finding in the general practice: phalangeal radiographic absorptiometry with and without risk factors for osteoporosis to select postmenopausal women eligible for lumbar spine and hip densitometry
Mass screening for osteoporosis using DXA measurements at the spine and hip is presently not recommended by health authorities. Instead, risk factor questionnaires and peripheral bone measurements may facilitate the selection of women eligible for axial bone densitometry. The aim of this study was to validate a case finding strategy for postmenopausal women who would benefit most from subsequent DXA measurement by using phalangeal radiographic absorptiometry (RA) alone or in combination with risk factors in a general practice setting. The sensitivity and specificity of this strategy in detecting osteoporosis (T-score ≤2.5SD at the spine and/or the hip) were compared with those of the current reimbursement criteria for DXA measurements in Switzerland. Four hundred and twenty-three postmenopausal women with one or more risk factors for osteoporosis were recruited by 90 primary care physicians who also performed the phalangeal RA measurements. All women underwent subsequent DXA measurement of the spine and the hip at the Osteoporosis Policlinic of the University Hospital of Berne. They were allocated to one of two groups depending on whether they matched with the Swiss reimbursement conditions for DXA measurement or not. Logistic regression models were used to predict the likelihood of osteoporosis versus "no osteoporosis” and to derive ROC curves for the various strategies. Differences in the areas under the ROC curves (AUC) were tested for significance. In women lacking reimbursement criteria, RA achieved a significantly larger AUC (0.81; 95% CI 0.72-0.89) than the risk factors associated with patients' age, height and weight (0.71; 95% C.I. 0.62-0.80). Furthermore, in this study, RA provided a better sensitivity and specificity in identifying women with underlying osteoporosis than the currently accepted criteria for reimbursement of DXA measurement. In the Swiss environment, RA is a valid case finding tool for patients with risk factors for osteoporosis, especially for those who do not qualify for DXA reimbursemen
Stability of Etoposide Solutions in Disposable Infusion Devices for Day Hospital Cancer Practices
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