1,080 research outputs found
Thermal conductance and thermoelectric figure of merit of C-based single-molecule junctions: electrons, phonons, and photons
Motivated by recent experiments, we present here an ab initio study of the
impact of the phonon transport on the thermal conductance and thermoelectric
figure of merit of C-based single-molecule junctions. To be precise, we
combine density functional theory with nonequilibrium Green's function
techniques to compute these two quantities in junctions with either a C
monomer or a C dimer connected to gold electrodes, taking into account
the contributions of both electrons and phonons. Our results show that for
C monomer junctions phonon transport plays a minor role in the thermal
conductance and, in turn, in the figure of merit, which can reach relatively
high values on the order of 0.1, depending on the contact geometry. At the
contrary, phonons completely dominate the thermal conductance in C dimer
junctions and strongly reduce the figure of merit as compared to monomer
junctions. Thus, claims that by stacking C molecules one could achieve
high thermoelectric performance, which have been made without considering the
phonon contribution, are not justified. Moreover, we analyze the relevance of
near-field thermal radiation for the figure of merit of these junctions within
the framework of fluctuational electrodynamics. We conclude that photon
tunneling can be another detrimental factor for the thermoelectric performance,
which has been overlooked so far in the field of molecular electronics. Our
study illustrates the crucial roles that phonon transport and photon tunneling
can play when critically assessing the performance of molecular junctions as
potential nanoscale thermoelectric devices
Experimental Characterization and Micromechanical Modeling of Woven Carbon/Copper Composites
The results of an extensive experimental characterization and a preliminary analytical modeling effort for the elastoplastic mechanical behavior of 8-harness satin weave carbon/copper (C/Cu) composites are presented. Previous experimental and modeling investigations of woven composites are discussed, as is the evolution of, and motivation for, the continuing research on C/Cu composites. Experimental results of monotonic and cyclic tension, compression, and Iosipescu shear tests, and combined tension-compression tests, are presented. With regard to the test results, emphasis is placed on the effect of strain gauge size and placement, the effect of alloying the copper matrix to improve fiber-matrix bonding, yield surface characterization, and failure mechanisms. The analytical methodology used in this investigation consists of an extension of the three-dimensional generalized method of cells (GMC-3D) micromechanics model, developed by Aboudi (1994), to include inhomogeneity and plasticity effects on the subcell level. The extension of the model allows prediction of the elastoplastic mechanical response of woven composites, as represented by a true repeating unit cell for the woven composite. The model is used to examine the effects of refining the representative geometry of the composite, altering the composite overall fiber volume fraction, changing the size and placement of the strain gauge with respect to the composite's reinforcement weave, and including porosity within the infiltrated fiber yarns on the in-plane elastoplastic tensile, compressive, and shear response of 8-harness satin C/Cu. The model predictions are also compared with the appropriate monotonic experimental results
Pharmacology: The Pharmacodynamics of Nutrients and Nutrient Interactions in Biological Functions
World Ocean Review 2013 : Living with the ocean : 2. The Future of Fish - The Fisheries of the Future
Noise2Recon: Enabling Joint MRI Reconstruction and Denoising with Semi-Supervised and Self-Supervised Learning
Deep learning (DL) has shown promise for faster, high quality accelerated MRI
reconstruction. However, supervised DL methods depend on extensive amounts of
fully-sampled (labeled) data and are sensitive to out-of-distribution (OOD)
shifts, particularly low signal-to-noise ratio (SNR) acquisitions. To alleviate
this challenge, we propose Noise2Recon, a model-agnostic, consistency training
method for joint MRI reconstruction and denoising that can use both
fully-sampled (labeled) and undersampled (unlabeled) scans in semi-supervised
and self-supervised settings. With limited or no labeled training data,
Noise2Recon outperforms compressed sensing and deep learning baselines,
including supervised networks, augmentation-based training, fine-tuned
denoisers, and self-supervised methods, and matches performance of supervised
models, which were trained with 14x more fully-sampled scans. Noise2Recon also
outperforms all baselines, including state-of-the-art fine-tuning and
augmentation techniques, among low-SNR scans and when generalizing to other OOD
factors, such as changes in acceleration factors and different datasets.
Augmentation extent and loss weighting hyperparameters had negligible impact on
Noise2Recon compared to supervised methods, which may indicate increased
training stability. Our code is available at https://github.com/ad12/meddlr
A Double-Layered Timber Plate Shell - Computational Methods for Assembly, Prefabrication, and Structural Design
This paper presents a new lightweight construction system for doubly-curved shells, built from two interconnected layers of structural wood veneer plates. The system uses integral through-tenon joints for a fast, precise, and simple assembly, allowing for the construction of a series of differently shaped shells without a costly mould or support structure. Instead, inclined joints cut with a 5-axis CNC milling machine embed the correct location and angle between plates into the shape of the parts. This constrains the relative motions between joined parts to one assembly path. To take advantage of the benefits of such connectors, the constrained assembly paths must be considered in the fundamental design of the system, allowing for the insertion of each plate. This imposes additional constraints in the segmentation process of doubly-curved shells. In order to meet the requirements and resolve the multi-constraint system, we use a global, non-linear optimisation approach. Developed as a close collaboration between architects, computer scientists and structural engineers, the paper includes an experimental analysis of the influence of parametric modifications in the shape of connectors on their load-bearing performance
VORTEX: Physics-Driven Data Augmentations Using Consistency Training for Robust Accelerated MRI Reconstruction
Deep neural networks have enabled improved image quality and fast inference
times for various inverse problems, including accelerated magnetic resonance
imaging (MRI) reconstruction. However, such models require a large number of
fully-sampled ground truth datasets, which are difficult to curate, and are
sensitive to distribution drifts. In this work, we propose applying
physics-driven data augmentations for consistency training that leverage our
domain knowledge of the forward MRI data acquisition process and MRI physics to
achieve improved label efficiency and robustness to clinically-relevant
distribution drifts. Our approach, termed VORTEX, (1) demonstrates strong
improvements over supervised baselines with and without data augmentation in
robustness to signal-to-noise ratio change and motion corruption in
data-limited regimes; (2) considerably outperforms state-of-the-art purely
image-based data augmentation techniques and self-supervised reconstruction
methods on both in-distribution and out-of-distribution data; and (3) enables
composing heterogeneous image-based and physics-driven data augmentations. Our
code is available at https://github.com/ad12/meddlr.Comment: Accepted to MIDL 202
Diagnostic Image Quality Assessment and Classification in Medical Imaging: Opportunities and Challenges
Magnetic Resonance Imaging (MRI) suffers from several artifacts, the most
common of which are motion artifacts. These artifacts often yield images that
are of non-diagnostic quality. To detect such artifacts, images are
prospectively evaluated by experts for their diagnostic quality, which
necessitates patient-revisits and rescans whenever non-diagnostic quality scans
are encountered. This motivates the need to develop an automated framework
capable of accessing medical image quality and detecting diagnostic and
non-diagnostic images. In this paper, we explore several convolutional neural
network-based frameworks for medical image quality assessment and investigate
several challenges therein.Comment: 4 pages, 8 Figures, Conference Submissio
Determinants of patient-reported functional mobility in people with Parkinson's disease: A systematic review.
peer reviewed[en] BACKGROUND: Information on determinants of patient-reported functional mobility is lacking but would inform the planning of healthcare, resources and strategies to promote functional mobility in people with Parkinson's disease (PD).
RESEARCH QUESTION: To identify the determinants of patient-reported functional mobility of people with PD.
METHODS: Eligible: Randomized Controlled Trials, cohort, case-control, or cross-sectional analyses in people PD without date or setting restrictions, published in English, German, or French. Excluded: instruments with under 50 % of items measuring mobility. On August 9th 2023 we last searched Medline, CINAHL and PsychInfo. We assessed risk of bias using the mixed-methods appraisal tool. Results were synthesized by tabulating the determinants by outcomes and study designs.
RESULTS: Eleven studies published 2012-2023 were included (most in Swedish outpatient settings). Samples ranged from 9 to 255 participants. Follow-up varied from 1.5 to 36 months with attrition of 15-42 %. Heterogenic study designs complicated results synthesis. However, determinants related to environment seem to associate the strongest with patient-reported functional mobility, although determinants related to body structures and functions were most investigated. We identified disease duration, the ability to drive, caregiving, sex, age, cognitive impairment, postural instability and social participation as determinants of patient-reported functional mobility.
DISCUSSION: Methodological quality of the studies was limited. No study reported an a priori power calculation. Three studies controlled for confounders. The included studies lack representativeness of the population of people living with PD. Standardized sets of outcomes could enable more systematic research synthesis.
CONCLUSIONS: Future research should focus on activities, participation and environmental factors and improve methodological quality
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