558 research outputs found
Motional diminishing of optical activity: a novel method for studying molecular dynamics in liquids and plastic crystals
Molecular dynamics calculations and optical spectroscopy measurements of
weakly active infrared modes are reported. The results are qualitatively
understood in terms of the "motional diminishing" of IR lines, a process
analogous to the motional narrowing of a nuclear magnetic resonance (NMR)
signal. In molecular solids or liquids where the appropriate intramolecular
resonances are observable, motional diminishing can be used to study the
fluctuations of the intermolecular interactions having time scales of 1psec to
100psec.Comment: RevTeX in LaTeX file, 12 preprint pages, 4 ps figures included. Also
available from http://insti.physics.sunysb.edu/~mmartin/pubs.html Accepted
for publication in Chem. Phys. Let
Model for monitoring of a charge qubit using a radio-frequency quantum point contact including experimental imperfections
The extension of quantum trajectory theory to incorporate realistic
imperfections in the measurement of solid-state qubits is important for quantum
computation, particularly for the purposes of state preparation and
error-correction as well as for readout of computations. Previously this has
been achieved for low-frequency (dc) weak measurements. In this paper we extend
realistic quantum trajectory theory to include radio frequency (rf) weak
measurements where a low-transparency quantum point contact (QPC), coupled to a
charge qubit, is used to damp a classical oscillator circuit. The resulting
realistic quantum trajectory equation must be solved numerically. We present an
analytical result for the limit of large dissipation within the oscillator
(relative to the QPC), where the oscillator slaves to the qubit. The rf+dc mode
of operation is considered. Here the QPC is biased (dc) as well as subjected to
a small-amplitude sinusoidal carrier signal (rf). The rf+dc QPC is shown to be
a low-efficiency charge-qubit detector, that may nevertheless be higher than
the dc-QPC (which is subject to 1/f noise).Comment: 12 pages, 2 colour figures. v3 is published version (minor changes
since v2
A counterexample to well-posedness of entropy solutions to the compressible Euler system
We deal with entropy solutions to the Cauchy problem for the isentropic
compressible Euler equations in the space-periodic case. In more than one space
dimension, the methods developed by De Lellis-Sz\'ekelyhidi enable us to show
failure of uniqueness on a finite time-interval for entropy solutions starting
from any continuously differentiable initial density and suitably constructed
bounded initial linear momenta.Comment: 29 page
Learning To Pay Attention To Mistakes
In convolutional neural network based medical image segmentation, the
periphery of foreground regions representing malignant tissues may be
disproportionately assigned as belonging to the background class of healthy
tissues
\cite{attenUnet}\cite{AttenUnet2018}\cite{InterSeg}\cite{UnetFrontNeuro}\cite{LearnActiveContour}.
This leads to high false negative detection rates. In this paper, we propose a
novel attention mechanism to directly address such high false negative rates,
called Paying Attention to Mistakes. Our attention mechanism steers the models
towards false positive identification, which counters the existing bias towards
false negatives. The proposed mechanism has two complementary implementations:
(a) "explicit" steering of the model to attend to a larger Effective Receptive
Field on the foreground areas; (b) "implicit" steering towards false positives,
by attending to a smaller Effective Receptive Field on the background areas. We
validated our methods on three tasks: 1) binary dense prediction between
vehicles and the background using CityScapes; 2) Enhanced Tumour Core
segmentation with multi-modal MRI scans in BRATS2018; 3) segmenting stroke
lesions using ultrasound images in ISLES2018. We compared our methods with
state-of-the-art attention mechanisms in medical imaging, including
self-attention, spatial-attention and spatial-channel mixed attention. Across
all of the three different tasks, our models consistently outperform the
baseline models in Intersection over Union (IoU) and/or Hausdorff Distance
(HD). For instance, in the second task, the "explicit" implementation of our
mechanism reduces the HD of the best baseline by more than , whilst
improving the IoU by more than . We believe our proposed attention
mechanism can benefit a wide range of medical and computer vision tasks, which
suffer from over-detection of background.Comment: Accepted at BMVC 202
Comparison and aggregation of event sequences across ten cohorts to describe the consensus biomarker evolution in Alzheimer's disease
BACKGROUND: Previous models of Alzheimer's disease (AD) progression were primarily hypothetical or based on data originating from single cohort studies. However, cohort datasets are subject to specific inclusion and exclusion criteria that influence the signals observed in their collected data. Furthermore, each study measures only a subset of AD-relevant variables. To gain a comprehensive understanding of AD progression, the heterogeneity and robustness of estimated progression patterns must be understood, and complementary information contained in cohort datasets be leveraged. METHODS: We compared ten event-based models that we fit to ten independent AD cohort datasets. Additionally, we designed and applied a novel rank aggregation algorithm that combines partially overlapping, individual event sequences into a meta-sequence containing the complementary information from each cohort. RESULTS: We observed overall consistency across the ten event-based model sequences (average pairwise Kendall's tau correlation coefficient of 0.69 ± 0.28), despite variance in the positioning of mainly imaging variables. The changes described in the aggregated meta-sequence are broadly consistent with the current understanding of AD progression, starting with cerebrospinal fluid amyloid beta, followed by tauopathy, memory impairment, FDG-PET, and ultimately brain deterioration and impairment of visual memory. CONCLUSION: Overall, the event-based models demonstrated similar and robust disease cascades across independent AD cohorts. Aggregation of data-driven results can combine complementary strengths and information of patient-level datasets. Accordingly, the derived meta-sequence draws a more complete picture of AD pathology compared to models relying on single cohorts
Targeted Screening for Alzheimer's Disease Clinical Trials Using Data-Driven Disease Progression Models
Heterogeneity in Alzheimer's disease progression contributes to the ongoing failure to demonstrate efficacy of putative disease-modifying therapeutics that have been trialed over the past two decades. Any treatment effect present in a subgroup of trial participants (responders) can be diluted by non-responders who ideally should have been screened out of the trial. How to identify (screen-in) the most likely potential responders is an important question that is still without an answer. Here, we pilot a computational screening tool that leverages recent advances in data-driven disease progression modeling to improve stratification. This aims to increase the sensitivity to treatment effect by screening out non-responders, which will ultimately reduce the size, duration, and cost of a clinical trial. We demonstrate the concept of such a computational screening tool by retrospectively analyzing a completed double-blind clinical trial of donepezil in people with amnestic mild cognitive impairment (clinicaltrials.gov: NCT00000173), identifying a data-driven subgroup having more severe cognitive impairment who showed clearer treatment response than observed for the full cohort
Scanning Quantum Decoherence Microscopy
The use of qubits as sensitive magnetometers has been studied theoretically
and recent demonstrated experimentally. In this paper we propose a
generalisation of this concept, where a scanning two-state quantum system is
used to probe the subtle effects of decoherence (as well as its surrounding
electromagnetic environment). Mapping both the Hamiltonian and decoherence
properties of a qubit simultaneously, provides a unique image of the magnetic
(or electric) field properties at the nanoscale. The resulting images are
sensitive to the temporal as well as spatial variation in the fields created by
the sample. As an example we theoretically study two applications of this
technology; one from condensed matter physics, the other biophysics. The
individual components required to realise the simplest version of this device
(characterisation and measurement of qubits, nanoscale positioning) have
already been demonstrated experimentally.Comment: 11 pages, 5 low quality (but arXiv friendly) image
Thermodynamically Stable One-Component Metallic Quasicrystals
Classical density-functional theory is employed to study finite-temperature
trends in the relative stabilities of one-component quasicrystals interacting
via effective metallic pair potentials derived from pseudopotential theory.
Comparing the free energies of several periodic crystals and rational
approximant models of quasicrystals over a range of pseudopotential parameters,
thermodynamically stable quasicrystals are predicted for parameters approaching
the limits of mechanical stability of the crystalline structures. The results
support and significantly extend conclusions of previous ground-state
lattice-sum studies.Comment: REVTeX, 13 pages + 2 figures, to appear, Europhys. Let
Disease Knowledge Transfer across Neurodegenerative Diseases
We introduce Disease Knowledge Transfer (DKT), a novel technique for
transferring biomarker information between related neurodegenerative diseases.
DKT infers robust multimodal biomarker trajectories in rare neurodegenerative
diseases even when only limited, unimodal data is available, by transferring
information from larger multimodal datasets from common neurodegenerative
diseases. DKT is a joint-disease generative model of biomarker progressions,
which exploits biomarker relationships that are shared across diseases. Our
proposed method allows, for the first time, the estimation of plausible,
multimodal biomarker trajectories in Posterior Cortical Atrophy (PCA), a rare
neurodegenerative disease where only unimodal MRI data is available. For this
we train DKT on a combined dataset containing subjects with two distinct
diseases and sizes of data available: 1) a larger, multimodal typical AD (tAD)
dataset from the TADPOLE Challenge, and 2) a smaller unimodal Posterior
Cortical Atrophy (PCA) dataset from the Dementia Research Centre (DRC), for
which only a limited number of Magnetic Resonance Imaging (MRI) scans are
available. Although validation is challenging due to lack of data in PCA, we
validate DKT on synthetic data and two patient datasets (TADPOLE and PCA
cohorts), showing it can estimate the ground truth parameters in the simulation
and predict unseen biomarkers on the two patient datasets. While we
demonstrated DKT on Alzheimer's variants, we note DKT is generalisable to other
forms of related neurodegenerative diseases. Source code for DKT is available
online: https://github.com/mrazvan22/dkt.Comment: accepted at MICCAI 2019, 13 pages, 5 figures, 2 table
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