6,540 research outputs found
Spectral theorem for the Lindblad equation for quadratic open fermionic systems
The spectral theorem is proven for the quantum dynamics of quadratic open
systems of n fermions described by the Lindblad equation. Invariant eigenspaces
of the many-body Liouvillean dynamics and their largest Jordan blocks are
explicitly constructed for all eigenvalues. For eigenvalue zero we describe an
algebraic procedure for constructing (possibly higher dimensional) spaces of
(degenerate) non-equilibrium steady states.Comment: 19 pages, no figure
Asymptotic Entanglement and Lindblad Dynamics: a Perturbative Approach
We consider an open bipartite quantum system with dissipative Lindblad type
dynamics. In order to study the entanglement of the stationary states, we
develop a perturbative approach and apply it to the physically significant case
when a purely dissipative perturbation is added to the unperturbed generator
which by itself would produce reversible unitary dynamics.Comment: 15 page
Permalloy-based carbon nanotube spin-valve
In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy,
forms contacts to carbon nanotubes (CNTs) that meet the requirements for the
injection and detection of spin-polarized currents in carbon-based spintronic
devices. We establish the material quality and magnetization properties of Py
strips in the shape of suitable electrical contacts and find a sharp
magnetization switching tunable by geometry in the anisotropic
magnetoresistance (AMR) of a single strip at cryogenic temperatures. In
addition, we show that Py contacts couple strongly to CNTs, comparable to Pd
contacts, thereby forming CNT quantum dots at low temperatures. These results
form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance
switchings in the tunneling magnetoresistance, which directly correspond to the
magnetization reversals in the individual contacts observed in AMR experiments.Comment: 3 page
Temporal and spatial distributions of delphinid species in Massachusetts Bay (USA) using passive acoustics from ocean gliders
© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Silva, T. L., Mooney, T. A., Sayigh, L. S., & Baumgartner, M. F. Temporal and spatial distributions of delphinid species in Massachusetts Bay (USA) using passive acoustics from ocean gliders. Marine Ecology Progress Series, 631, (2019): 1-17, doi:10.3354/meps13180.Knowledge about marine mammal habitat use is necessary for informing ecosystem-based management and mitigating human impacts. Massachusetts Bay is an important marine mammal foraging area in the Gulf of Maine and an area of substantial human activity, but delphinid habitat use is poorly understood. The goals of this work were to (1) document temporal and spatial occurrence of delphinid species in Massachusetts Bay using passive acoustic monitoring from ocean gliders and (2) explore the potential influences of environmental conditions on delphinid distributions. Gliders were deployed in late fall and early winter of 2014 and 2015-2016 and were equipped with a digital acoustic recorder and conductivity-temperature-depth instrument. Gliders surveyed an area of approximately 1000 km2. Delphinid whistles were detected on 93 of 128 (73%) deployment days. Animals were detected more often at night. Presence was consistent over 2 years, although detection rates showed annual and monthly variability. Spatial distribution differed between years, but most detections occurred close to Stellwagen Bank. Visual assessment of spectrograms suggests the presence of 2 species, Atlantic white-sided dolphins and common dolphins. The reoccurrence of 2 probable signature whistles over several weeks and consecutive winter seasons suggests prolonged occupancy during winter and possible annual site fidelity. These data show a consistent and frequent presence of delphinids near a known marine mammal foraging area (Stellwagen Bank) during late fall and winter and are a first step towards understanding both how odontocetes influence the Massachusetts Bay/Gulf of Maine ecosystem and how they may be impacted by human activities.We gratefully acknowledge the NOAA Northeast Fisheries Science Center, Stellwagen Bank National Marine Sanctuary, The Nature Conservancy, Massachusetts Division of Marine Fisheries, and the University of Massachusetts Dartmouth for their collaboration and support for this project. We thank Susan Parks, Julie Oswald, Sofie Van Parijs, and Danielle Cholewiak for helpful discussionsand sharing acoustic recordings for species comparisons. We are grateful to Ben Hodges for critical assistance with preparing, deploying, and recovering gliders. Thanks to Michael Thompson for assistance with spatial analysis
and Dave Wiley for support and insights into the Stellwagen Bank ecosystem. The WHOI Marine Mammal Center provided
additional funding for this work. Funding support for T.L.S. was provided by the NOAA Dr. Nancy Foster Scholarship. Finally, we thank the 3 anonymous re viewers for their comments and suggestions that improved this manuscript
MR image reconstruction using deep density priors
Algorithms for Magnetic Resonance (MR) image reconstruction from undersampled
measurements exploit prior information to compensate for missing k-space data.
Deep learning (DL) provides a powerful framework for extracting such
information from existing image datasets, through learning, and then using it
for reconstruction. Leveraging this, recent methods employed DL to learn
mappings from undersampled to fully sampled images using paired datasets,
including undersampled and corresponding fully sampled images, integrating
prior knowledge implicitly. In this article, we propose an alternative approach
that learns the probability distribution of fully sampled MR images using
unsupervised DL, specifically Variational Autoencoders (VAE), and use this as
an explicit prior term in reconstruction, completely decoupling the encoding
operation from the prior. The resulting reconstruction algorithm enjoys a
powerful image prior to compensate for missing k-space data without requiring
paired datasets for training nor being prone to associated sensitivities, such
as deviations in undersampling patterns used in training and test time or coil
settings. We evaluated the proposed method with T1 weighted images from a
publicly available dataset, multi-coil complex images acquired from healthy
volunteers (N=8) and images with white matter lesions. The proposed algorithm,
using the VAE prior, produced visually high quality reconstructions and
achieved low RMSE values, outperforming most of the alternative methods on the
same dataset. On multi-coil complex data, the algorithm yielded accurate
magnitude and phase reconstruction results. In the experiments on images with
white matter lesions, the method faithfully reconstructed the lesions.
Keywords: Reconstruction, MRI, prior probability, machine learning, deep
learning, unsupervised learning, density estimationComment: Published in IEEE TMI. Main text and supplementary material, 19 pages
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Visual Feature Attribution using Wasserstein GANs
Attributing the pixels of an input image to a certain category is an
important and well-studied problem in computer vision, with applications
ranging from weakly supervised localisation to understanding hidden effects in
the data. In recent years, approaches based on interpreting a previously
trained neural network classifier have become the de facto state-of-the-art and
are commonly used on medical as well as natural image datasets. In this paper,
we discuss a limitation of these approaches which may lead to only a subset of
the category specific features being detected. To address this problem we
develop a novel feature attribution technique based on Wasserstein Generative
Adversarial Networks (WGAN), which does not suffer from this limitation. We
show that our proposed method performs substantially better than the
state-of-the-art for visual attribution on a synthetic dataset and on real 3D
neuroimaging data from patients with mild cognitive impairment (MCI) and
Alzheimer's disease (AD). For AD patients the method produces compellingly
realistic disease effect maps which are very close to the observed effects.Comment: Accepted to CVPR 201
BAC-FISH assays delineate complex chromosomal rearrangements in a case of post-Chernobyl childhood thyroid cancer
Structural chromosome aberrations are known hallmarks of many solid tumors. In the papillary form of thyroid
cancer (PTC), for example, activation of the receptor tyrosine kinase (RTK) genes, RET and neurotrophic tyrosine kinase
receptor type I (NTRK1) by intra- and interchromosomal rearrangements has been suggested as a cause of the disease. However,
many phenotypically similar tumors do not carry an activated RET or NTRK-1 gene or express abnormal ret or NTRK-
1 transcripts. Thus, we hypothesize that other cellular RTK-type genes are aberrantly expressed in these tumors. Using fluorescence
in situ hybridization-based methods, we are studying karyotype changes in a relatively rare subgroup of PTCs,
i.e., tumors that arose in children following the 1986 nuclear accident in Chernobyl, Ukraine. Here, we report our technical
developments and progress in deciphering complex chromosome aberrations in case S48TK, an aggressively growing PTC
cell line, which shows an unusual high number of unbalanced translocations
Investor protection through model case procedures – implementing collective goals and individual rights under the 2012 Amendment of the German Capital Markets Model Case Act (KapMuG)
The German Capital Markets Model Case Act (KapMuG) and its amendment of 2012 highlight some fundamentals of collective redress in civil law countries at the example of model case procedures in the field of investor protection. That is why a survey of the ongoing activities of the European Union in the area of collective redress and of its repercussions on the member state level forms a suitable basis for the following analysis of the 2012 amendment of the KapMuG. It clearly brings into focus a shift from sector-specific regulation with an emphasis on the cross-border aspect of protecting consumers towards a “coherent approach” strengthening the enforcement of EU law. As a result, regulatory policy and collective redress are two sides of the same coin today. With respect to the KapMuG such a development brings about some tension between its aim to aggregate small individual claims as efficiently as possible and the dominant role of individual procedural rights in German civil procedure. This conflict can be illustrated by some specific rules of the KapMuG: its scope of application, the three-tier procedure of a model case procedure, the newly introduced notification of claims and the new opt-out settlement under the amended §§ 17-19
A generalized baleen whale call detection and classification system
Author Posting. © Acoustical Society of America, 2011. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 129 (2011): 2889-2902, doi:10.1121/1.3562166.Passive acoustic monitoring allows the assessment of marine mammal occurrence and distribution at greater temporal and spatial scales than is now possible with traditional visual surveys. However, the large volume of acoustic data and the lengthy and laborious task of manually analyzing these data have hindered broad application of this technique. To overcome these limitations, a generalized automated detection and classification system (DCS) was developed to efficiently and accurately identify low-frequency baleen whale calls. The DCS (1) accounts for persistent narrowband and transient broadband noise, (2) characterizes temporal variation of dominant call frequencies via pitch-tracking, and (3) classifies calls based on attributes of the resulting pitch tracks using quadratic discriminant function analysis (QDFA). Automated detections of sei whale (Balaenoptera borealis) downsweep calls and North Atlantic right whale (Eubalaena glacialis) upcalls were evaluated using recordings collected in the southwestern Gulf of Maine during the spring seasons of 2006 and 2007. The accuracy of the DCS was similar to that of a human analyst: variability in differences between the DCS and an analyst was similar to that between independent analysts, and temporal variability in call rates was similar among the DCS and several analysts.Funding for the fieldwork was provided by the
NOAA NEFSC, WHOI Ocean Life Institute, and the WHOI
John E. and Anne W. Sawyer Endowed Fund. Development
of the detection and classification system was supported by a
grant from the Office of Naval Research
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