199 research outputs found
Assessment of creep and rupture behavior of 2.25Cr-1Mo steel – A strain-based approach and its limitation
Increasing demand of 2.25Cr-1Mo steel, among different grades of low alloy Cr-Mo steels, in power plants and petrochemical industries is mainly because of its high creep resistance. Application of a strain based approach for a reliable assessment of creep and rupture behavior is thus of great importance. Creep data were generated under different microstructural conditions in the laboratory and collected from literature as well. The influence of thermal ageing and pre-strain on the shape of creep curves has been studied. Analysis of data revealed that irrespective of initial microstructures, thermal ageing increases the tendency to soften but not the pre-strain. Softening due to carbide coarsening thus appears to be the dominant mechanism of creep. Based on this, a strain based approach for creep life assessment was developed. A fairly accurate prediction of creep life up to 5% creep is achieved using eight materials constants extracted from the creep curves of steel having similar initial microstructure. The limitation and reliability of the approach used to assess creep behavior of service-exposed steels have been discussed
Probabilistic creep life assessment of austenitic stainless steel
Experimental investigations on the creep behaviour of engineering materials are frequently conducted for the purposes of design, development and service life prediction. However, tests on a single specimen yield a definite value for each material parameter. But when a number of specimens are tested, the parameter values randomly fluctuate from specimen to specimen. The scatter observed in creep deformation and failure data is of considerable technological importance because it greatly complicates the task of making accurate deformation and lifetime estimates for high temperature components. Repeat data on austenitic stainless steel provided a unique opportunity to identify stochastic creep properties and to use this information to build a probabilistic creep damage assessment for this alloy
SHORT COMMUNICATION: Reduction of Spirometric Lung Function Tests in Habitually Smoking Healthy Young Adults: Its Correlation with Pack Years
Background: Adolescent smoking and the subsequent health problems are a major concern today. However there are very few studies done on spirometric lung functions and its relation with pack years in young adult habitual smokers who are apparently healthy. Aims and Objectives: The present study is undertaken to assess the change in lung functions in apparently healthy young adult habitual smokers compared to their age matched controls. Materials and Methods: A random sample of apparently healthy young adult habitual smokers (n=40) and nonsmokers (n=40) between age group17-35 years with history suggesting of pack years of 2-10 years were selected from students & employees of B.L.D.E.Us Sri B.M. Patil Medical College,Hospital & Research Centre Bijapur (Karnataka), India. Spirometric lung functions recorded were forced expiratory volume in one second (FEV1), FEV1%, Peak expiratory flow rate (PEFR) and Maximal expiratory pressure (MEP). Results: The results suggested that inapparently healthy habitual smokers there was significant decrease in FEV1 (L) (-13.34%, p<0.001), FEV1 % (-10.76%, p<0.001), PEFR (-45.26%, p<0.0001) and MEP (-35.51%, p<0.0001) compared to nonsmokers and decrease in FEV1 was negatively correlated withpack years in smokers (r2=0.063, p=0.001). Reduced lung functions and negative correlation to pack years may be attributed todecreased airway diameter & reflex broncho- constriction in response to inhaled smoke particles. Conclusions: In conclusion young adulthabitual smokers who were apparently healthy are more prone for respiratory dysfunction than their nonsmoker counterparts. FEV1 reduction in relation to pack years acts as an important determinant for detecting lung dysfunction in the early stage of the disease. As the risk of having smoking related diseases depends mainly on number of pack years, it is suggested that quitting smoking earliest helps to get greatest health benefits in apparently healthy young adult habitual smokers
Bacteriological study of surgical site infections in a tertiary care hospital at Miraj, Maharashtra state, India
Background: Surgical site infections (SSI) are one of the common post-operative complications. Apart from bacterial contamination of wound, various patient and environment related factors play role in development and outcome of SSI. The present study is undertaken to study the frequency of SSI with reference to factors contributing to it and the antimicrobial susceptibility pattern of the causative organisms.Methods: This single-observer, cross-sectional, complete-enumeration prospective study was carried out over a period of one year. 196 pus samples from cases of surgical site infections were processed for gram staining, culture, biochemical identification tests and antimicrobial susceptibility testing. Methicillin-Resistant Staphylococcus aureus (MRSA) strains were detected by using oxacillin and cefoxitin disk diffusion and minimum inhibitory concentration (MIC) of oxacillin was tested by broth dilution technique.Results: The overall frequency of SSI was 6.17%. Most common isolates were Staphylococcus aureus, coagulase negative Staphylococci (CONS), E. coli and Pseudomonas aeruginosa. The frequency of MRSA was 8.6%. The maximum frequency was among patients operated on emergency basis in surgical department.Conclusions: The most important determinants for SSI were emergency surgery and presence of co-morbid conditions. The frequency of occurrence was age-dependent, with maximum rate of SSI in males and females in the third and sixth decades of life, respectively
Navigating the Web of Misinformation: A Framework for Misinformation Domain Detection Using Browser Traffic
The proliferation of misinformation and propaganda is a global challenge,
with profound effects during major crises such as the COVID-19 pandemic and the
Russian invasion of Ukraine. Understanding the spread of misinformation and its
social impacts requires identifying the news sources spreading false
information. While machine learning (ML) techniques have been proposed to
address this issue, ML models have failed to provide an efficient
implementation scenario that yields useful results. In prior research, the
precision of deployment in real traffic deteriorates significantly,
experiencing a decrement up to ten times compared to the results derived from
benchmark data sets. Our research addresses this gap by proposing a graph-based
approach to capture navigational patterns and generate traffic-based features
which are used to train a classification model. These navigational and
traffic-based features result in classifiers that present outstanding
performance when evaluated against real traffic. Moreover, we also propose
graph-based filtering techniques to filter out models to be classified by our
framework. These filtering techniques increase the signal-to-noise ratio of the
models to be classified, greatly reducing false positives and the computational
cost of deploying the model. Our proposed framework for the detection of
misinformation domains achieves a precision of 0.78 when evaluated in real
traffic. This outcome represents an improvement factor of over ten times over
those achieved in previous studies
Common fixed points of maps on fuzzy metric spaces
Following Grabiec's approach to fuzzy contraction principle, the purpose of this note is to obtain common fixed point theorems for asymptotically commuting maps on fuzzy metric spaces
Modelling Extracellular Matrix and Cellular Contributions to Whole Muscle Mechanics
Skeletal muscle tissue has a highly complex and heterogeneous structure comprising several physical length scales. In the simplest model of muscle tissue, it can be represented as a one dimensional nonlinear spring in the direction of muscle fibres. However, at the finest level, muscle tissue includes a complex network of collagen fibres, actin and myosin proteins, and other cellular materials. This study shall derive an intermediate physical model which encapsulates the major contributions of the muscle components to the elastic response apart from activation-related along-fibre responses. The micro-mechanical factors in skeletal muscle tissue (eg. connective tissue, fluid, and fibres) can be homogenized into one material aggregate that will capture the behaviour of the combination of material components. In order to do this, the corresponding volume fractions for each type of material need to be determined by comparing the stress-strain relationship for a volume containing each material. This results in a model that accounts for the micro-mechanical features found in muscle and can therefore be used to analyze effects of neuro-muscular diseases such as cerebral palsy or muscular dystrophies. The purpose of this study is to construct a model of muscle tissue that, through choosing the correct material parameters based on experimental data, will accurately capture the mechanical behaviour of whole muscle. This model is then used to look at the impacts of the bulk modulus and material parameters on muscle deformation and strain energy-density distributions
Uncertainty in Damage Assessment and Remaining Life Prediction of Engineering Materials Used In Petrochemical Industry
In this paper creep damage assessment of about 11 years’ service exposed HP-40 grade of steel used in
hydrogen reformer of a petrochemical industry has been carried out in terms of a discontinuous Markov process.
Experimentally determined conventional creep data under identical testing condition were used in the present
investigation. Scatter and damage accumulation due to creep deformation were evaluated through microstructural
assessment using light optical microscope and scanning electron microscope. Quantification of creep damage was
made from replicated creep data in terms of two damage parameters A and A*. Statistical analysis of void area
fraction has been carried out extensively for the both top and bottom portions of the reformer tube at 870 o C in the
stress range of 52-68 MPa. In addition, the proposed probabilistic model has been compared with the Kachanav’s
Continuum Damage Mechanics (CDM) model. Both the approaches displayed quantitative experimental support. A residual life of > 10 years is estimated at 870 degree C / operating stress. For 55 years’ service exposed Catalytic Cold Cracking (CCU) reactor vessel and Feed Processing Unit (FPU) distillation column materials of a petrochemical industry remnant life assessment studies were estimated by incorporating the uncertainty involved in calculation of
LMP (Larson Miller Parameter) values and from extrapolation of stress vs. LMP plot. Variability of normalized creep
damage for reactor and column materials is well approximated with the aid of Weibull distribution. As expected, it
is observed that the distributions shift towards the higher range of damage with increase in service exposure time
The Contributions of Extracellular Matrix and Sarcomere Properties to Passive Muscle Stiffness in Cerebral Palsy
Cerebral palsy results from an upper motor neuron lesion and significantly affects skeletal muscle stiffness. The increased stiffness that occurs is partly a result of changes in the microstructural components of muscle. In particular, alterations in extracellular matrix, sarcomere length, fibre diameter, and fat content have been reported; however, experimental studies have shown wide variability in the degree of alteration. Many studies have reported changes in the extracellular matrix, while others have reported no differences. A consistent finding is increased sarcomere length in cerebral palsy affected muscle. Often many components are altered simultaneously, making it difficult to determine the individual effects on muscle stiffness. In this study, we use a three dimensional modelling approach to isolate individual effects of microstructural alterations typically occurring due to cerebral palsy on whole muscle behaviour; in particular, the effects of extracellular matrix volume fraction, stiffness, and sarcomere length. Causation between the changes to the microstructure and the overall muscle response is difficult to determine experimentally, since components of muscle cannot be manipulated individually; however, utilising a modelling approach allows greater control over each factor. We find that extracellular matrix volume fraction has the largest effect on whole muscle stiffness and mitigates effects from sarcomere length
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