An experimental study of polymer electrolyte fuel cell operation at sub-freezing temperatures

The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society

Subfreezing operation of polymer electrolyte fuel cells: Ice formation and cell performance loss

In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid. © 2012 Elsevier Ltd. All rights reserved

Along-the-channel modeling and analysis of PEFCs at low stoichiometry: Development of a 1+2D model

Water management remains a key challenge in polymer-electrolyte fuel cells. In this work, a pseudo 3-D (1+2D) model is developed to account better for changes of water management along the channel, as well as verify the possibilities of using differential cells for data capture and translation to integral cell performance. An accurate 2-D membrane-electrode-assembly model is developed for differential cell modeling, which is combined with an along-the-channel stepping algorithm to account for down the channel changes in pressure, temperature, reactant concentration, and relative humidity. Variations in cell performance along the channel due to changes in operating conditions are characterized quantitatively and optimized, where drier feed conditions demonstratively require such an approach. Overall, the study identifies gaps between differential and integral cells including those related to flow velocity and highlights the need for better models to understand and link integral cell performance and water management

Investigation of optimization of attitude control systems, volume ii

Attitude control system optimization - computer programs, listings and subroutine

Investigation of optimization of attitude control systems, volume i

Optimization of attitude control systems by development of mathematical model and computer program for space vehicle simulatio

Unveiling mediastinal pathology: role of EUS guided fine needle aspiration in diagnosing mediastinal lesions

Background: Mediastinal lesion is the focus of investigation in diagnosis of infective, granulomatous or neoplastic pathology of respiratory system. Metastatic mediastinal node assessment is an integral part of oncological management. EUS provides access to sampling of mediastinal mass, sub-carinal and aorto-pulmonary nodes. This study aims to assess the clinical impact, diagnostic yield and safety of EUS guided FNA for mediastinal lesions.Methods: Retrospective analysis of prospectively collected data of 72 cases of mediastinal lesions between January 2014 and December 2017 was done. EUS-FNA was performed with a linear echoendoscope using a 22- or 25-gauge needle. Adequacy of cellularity was assessed by on site pathologist. Patient data (demographics, intervention and follow-up) were prospectively collected and introduced in a predefined computer database for later review.Results: EUS-FNA was performed from 57 lymph nodes and 15 mediastinal masses. Adequate samples were obtained in 67 of 72 patients (93.05%). All mediastinal masses were malignant and were identified in the 3rd, 5th and 6th decade of life. Of the 57 lymph nodes, 15 were malignant, 28 had granulomatous lymphadenitis of which 16 individuals became asymptomatic after anti tubercular therapy. Sample was inadequate in 5 circumstances. No major complications were encountered with the procedure in any of the individuals.Conclusions: EUS guided tissue diagnosis is a safe technique and our data supports the use of EUS-FNA in work-up of mediastinal lesions. It is minimally invasive, accurate and has easy access to mediastinum. It has significant impact on patient diagnosis, management and should be considered over other invasive techniques

Colorectal polyps and heterotrophic esophageal polyp of colon in a paediatric cohort in South India

Background: Clinical profile of polyps in paediatric cases are less in South India. Juvenile Polyps were the most common polyps in paediatric cases described in literature, presenting as LGI bleed. The aim of the study is to describe the clinical profile of colorectal polyps in paediatric population in a single tertiary care centre in South India.Methods: Paediatric cases between 0 and 16 years of age who underwent colonoscopy in our department from January 2002 to July 2018 were included from database. These cases were retrospectively analysed for presence of polyps, clinical presentation, indication for colonoscopy, histopathology of the resected polyps and other demographic details.  Incomplete procedures were excluded.Results: About 166 paediatric cases underwent colonoscopy in the study period. 21 cases (12.65%) had colorectal Polyps. 85.7% of the polyps were in recto sigmoid region. Most common histological type was Juvenile Polyp (51.6%). One infant had sessile polyp in descending colon which was reported as heterotrophic esophageal mucosa in histopathology. LGI bleed was the most common presentation in children with polyps (66.6%).Conclusions: The prevalence of polyps in our cohort was 12.65%. Solitary Juvenile Polyp was the most common polyp in children, with lower GI bleed as the most common presenting feature. Rare case of heterotrophic esophageal polyp was seen in descending colon

Image Features Based on Characteristic Curves and Local Binary Patterns for Automated HER2 Scoring

This paper presents novel feature descriptors and classification algorithms for the automated scoring of HER2 in Whole Slide Images (WSI) of breast cancer histology slides. Since a large amount of processing is involved in analyzing WSI images, the primary design goal has been to keep the computational complexity to the minimum possible level and to use simple, yet robust feature descriptors that can provide accurate classification of the slides. We propose two types of feature descriptors that encode important information about staining patterns and the percentage of staining present in ImmunoHistoChemistry (IHC)-stained slides. The first descriptor is called a characteristic curve, which is a smooth non-increasing curve that represents the variation of percentage of staining with saturation levels. The second new descriptor introduced in this paper is a local binary pattern (LBP) feature curve, which is also a non-increasing smooth curve that represents the local texture of the staining patterns. Both descriptors show excellent interclass variance and intraclass correlation and are suitable for the design of automatic HER2 classification algorithms. This paper gives the detailed theoretical aspects of the feature descriptors and also provides experimental results and a comparative analysis

Detection Methods for Lipopolysaccharides: Past and Present

Lipopolysaccharide (LPS) is the primary component of the outer membrane of Gram‐negativebacteria. LPS aids in protecting bacterial cells, and also defines the unique serogroups used to classify bacteria. Additionally, LPS is an endotoxin and the primary stimulator of innate immune cells in mammals, making it an ideal candidate for early detection of pathogens. However, the majority of methods for detection of LPS focus on detection of the endotoxic component of the molecule, lipid A. Since lipid A is largely conserved among bacterial species and serogroups, these detection approaches are highly nonspecific. Thus, the importance of identifying the O‐polysaccharide antigenic portion of LPS, which confers serogroup specificity, has received a great deal of attention in recent years. However, methods that are highly selective to the O‐antigens are typically less sensitive than those that target the endotoxin. Here we present a history and comparison of the sensitivity of these methods and their value for detecting bacteria in a variety of different sample types