642 research outputs found
Thermo-Mechanical Structural Optimisation of a Chemical Propulsion Satellite Thruster Using Lattice Structures
Small satellite space thrusters are designed to provide force for short time periods.
ā¢ New generation of thrusters will be made with High Entropy Alloy (HEA) materials.
ā¢ Predicting damage initiation for this kind of metallic structure subjected to thermal shock is of fundamental importance.
ā¢ The preliminary thermal-stress analysis is mandatory in order to understand the complex failure mechanism of the space thruster.
ā¢ An optimisation analysis of the material distribution along the combustion chamber thickness can lead to an improvement of the thermal-stress response
Extreme Antimicrobial Peptide and Polymyxin B Resistance in the Genus Burkholderia
Cationic antimicrobial peptides and polymyxins are a group of naturally occurring antibiotics that can also possess immunomodulatory activities. They are considered a new source of antibiotics for treating infections by bacteria that are resistant to conventional antibiotics. Members of the genus Burkholderia, which includes various human pathogens, are inherently resistant to antimicrobial peptides. The resistance is several orders of magnitude higher than that of other Gram-negative bacteria such as Escherichia coli, Salmonella enterica, or Pseudomonas aeruginosa. This review summarizes our current understanding of antimicrobial peptide and polymyxin B resistance in the genus Burkholderia. These bacteria possess major and minor resistance mechanisms that will be described in detail. Recent studies have revealed that many other emerging Gram-negative opportunistic pathogens may also be inherently resistant to antimicrobial peptides and polymyxins and we propose that Burkholderia sp. are a model system to investigate the molecular basis of the resistance in extremely resistant bacteria. Understanding resistance in these types of bacteria will be important if antimicrobial peptides come to be used regularly for the treatment of infections by susceptible bacteria because this may lead to increased resistance in the species that are currently susceptible and may also open up new niches for opportunistic pathogens with high inherent resistance
Antimicrobial Heteroresistance: an Emerging Field in Need of Clarity
āHeteroresistanceā describes a phenomenon where subpopulations of seemingly isogenic bacteria exhibit a range of susceptibilities to a particular antibiotic. Unfortunately, a lack of standard methods to determine heteroresistance has led to inappropriate use of this term. Heteroresistance has been recognized since at least 1947 and occurs in Gram-positive and Gram-negative bacteria. Its clinical relevance may be considerable, since more resistant subpopulations may be selected during antimicrobial therapy. However, the use of nonstandard methods to define heteroresistance, which are costly and involve considerable labor and resources, precludes evaluating the clinical magnitude and severity of this phenomenon. We review the available literature on antibiotic heteroresistance and propose recommendations for definitions and determination criteria for heteroresistant bacteria. This will help in assessing the global clinical impact of heteroresistance and developing uniform guidelines for improved therapeutic outcomes
Learning to Segment from Scribbles using Multi-scale Adversarial Attention Gates
Large, fine-grained image segmentation datasets, annotated at pixel-level,
are difficult to obtain, particularly in medical imaging, where annotations
also require expert knowledge. Weakly-supervised learning can train models by
relying on weaker forms of annotation, such as scribbles. Here, we learn to
segment using scribble annotations in an adversarial game. With unpaired
segmentation masks, we train a multi-scale GAN to generate realistic
segmentation masks at multiple resolutions, while we use scribbles to learn
their correct position in the image. Central to the model's success is a novel
attention gating mechanism, which we condition with adversarial signals to act
as a shape prior, resulting in better object localization at multiple scales.
Subject to adversarial conditioning, the segmentor learns attention maps that
are semantic, suppress the noisy activations outside the objects, and reduce
the vanishing gradient problem in the deeper layers of the segmentor. We
evaluated our model on several medical (ACDC, LVSC, CHAOS) and non-medical
(PPSS) datasets, and we report performance levels matching those achieved by
models trained with fully annotated segmentation masks. We also demonstrate
extensions in a variety of settings: semi-supervised learning; combining
multiple scribble sources (a crowdsourcing scenario) and multi-task learning
(combining scribble and mask supervision). We release expert-made scribble
annotations for the ACDC dataset, and the code used for the experiments, at
https://vios-s.github.io/multiscale-adversarial-attention-gatesComment: Paper accepted for publication at: IEEE Transaction on Medical
Imaging - Project page:
https://vios-s.github.io/multiscale-adversarial-attention-gate
An automatic deep learning approach for coronary artery calcium segmentation
Coronary artery calcium (CAC) is a significant marker of atherosclerosis and
cardiovascular events. In this work we present a system for the automatic
quantification of calcium score in ECG-triggered non-contrast enhanced cardiac
computed tomography (CT) images. The proposed system uses a supervised deep
learning algorithm, i.e. convolutional neural network (CNN) for the
segmentation and classification of candidate lesions as coronary or not,
previously extracted in the region of the heart using a cardiac atlas. We
trained our network with 45 CT volumes; 18 volumes were used to validate the
model and 56 to test it. Individual lesions were detected with a sensitivity of
91.24%, a specificity of 95.37% and a positive predicted value (PPV) of 90.5%;
comparing calcium score obtained by the system and calcium score manually
evaluated by an expert operator, a Pearson coefficient of 0.983 was obtained. A
high agreement (Cohen's k = 0.879) between manual and automatic risk prediction
was also observed. These results demonstrated that convolutional neural
networks can be effectively applied for the automatic segmentation and
classification of coronary calcifications
Low cycle fatigue predictions of a space thruster built with a new refractory high entropy alloy
Directional thrusters are designed to provide force for short time periods.
ā¢ New generation of thrusters could be made using a High Entropy Alloy (HEA).
ā¢ Predicting fatigue damage initiation for this kind of metallic structure subjected to
cyclic loads is important.
ā¢ Design for fatigue resistance relies on empirical with high financial costs.
ā¢ Unified Mechanics Theory (UMT) will be used to predict fatigue damage initiation
of a material system without having experimental fatigue dat
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