M. Menaka

Intercomparison of gamma scattering, gammatography, and radiography techniques for mild steel nonuniform corrosion detection

This paper focuses on the mild steel (MS) corrosion detection and intercomparison of results obtained by gamma scattering, gammatography, and radiography techniques. The gamma scattering non-destructive evaluation (NDE) method utilizes scattered gamma radiation for the detection of corrosion, and the scattering experimental setup is an indigenously designed automated personal computer (PC) controlled scanning system consisting of computerized numerical control (CNC) controlled six-axis source detector system and four-axis job positioning system. The system has been successfully used to quantify the magnitude of corrosion and the thickness profile of a MS plate with nonuniform corrosion, and the results are correlated with those obtained from the conventional gammatography and radiography imaging measurements. A simple and straightforward reconstruction algorithm to reconstruct the densities of the objects under investigation and an unambiguous interpretation of the signal as a function of material density at any point of the thick object being inspected is described. In this simple and straightforward method the density of the target need not be known and only the knowledge of the target materials mass attenuation coefficients (composition) for the incident and scattered energies is enough to reconstruct the density of the each voxel of the specimen being studied. The Monte Carlo (MC) numerical simulation of the phenomena is done using the Monte Carlo N-Particle Transport Code (MCNP) and the quantitative estimates of the values of signal-to-noise ratio for different percentages of MS corrosion derived from these simulations are presented and the spectra are compared with the experimental data. The gammatography experiments are carried out using the same PC controlled scanning system in a narrow beam, good geometry setup, and the thickness loss is estimated from the measured transmitted intensity. Radiography of the MS plates is carried out using 160 kV x-ray machine. The digitized radiographs with a resolution of 50 μm are processed for the detection of corrosion damage in five different locations. The thickness losses due to the corrosion of the MS plate obtained by gamma scattering method are compared with those values obtained by gammatography and radiography techniques. The percentage thickness loss estimated at different positions of the corroded MS plate varies from 17.78 to 27.0, from 18.9 to 24.28, and from 18.9 to 24.28 by gamma scattering, gammatography, and radiography techniques, respectively. Overall, these results are consistent and in line with each other.

Changes of skin temperature of parts of the body and serum asymmetric dimethylarginine (ADMA) in type-2 diabetes mellitus Indian patients

In India, number of people with type 2 Diabetes Mellitus (DM) would be 87 million by the year 2030. DM disturbs autonomic regulation of skin micro-circulation, and causes decrease in resting blood flows through the skin. The skin blood flow has a major effect on its temperature. The aim of the study was to evaluate changes of skin temperature of all parts of the body and serum asymmetric dimethylarginine, ADMA (μmol/L) in type-2 DM Indian patients. Group-I: Normal (n=17; M/F: 10/15, mean±SD= 43.2±9.4 years); Group-II: Type-2 DM without cardiovascular (CV) complications (n=15; M/F: 10/7, mean±SD= 46.3 ± 14.0 years); Thermograms of all parts of the body were acquired using a non-contact infrared (IR) thermography camera (ThermaCAM T400, FLIR Systems, Sweden). Blood parameters and thyroid hormone were measured biochemically. Indian diabetic risk score (IDRS) was calculated for each subject. In type-2 DM patients without CV group (n=15), there was a statistically significant (p=0.01) negative correlations between HbA<inf>1c</inf> and skin temperature of eye and nose (r= −0.57 and r= −0.55 respectively). ADMA was correlated significantly (p=0.01) with HbA<inf>1c</inf> (r=0.65) and estimated average glucose, eAG (r=0.63). In normal subjects, mean minimum and maximum values of skin temperatures were observed at posterior side of sole (26.89°C) and ear (36.85°C) respectively. In type-2 DM without CV, mean values of skin temperature in different parts of the body from head to toe were lesser than those values in control group; but this decreases were statistically significant in nose (32.66 Vs 33.99°C, p=0.024) as well as in tibia (32.78 Vs 33.13°C, p=0.036) regions.

Estimation of blood glucose by non-invasive infrared thermography for diagnosis of type 2 diabetes: an alternative for blood sample extraction.

The present study aims to estimate and validate the glycated haemoglobin (HbA(1c)) using non-contact infrared thermography. The diagnostic threshold was set as (HbA(1c)≥48 mmol/mol). The optimal regression model [r=0.643, p=0.000] was achieved from the significant variables correlating with the HbA(1c) and the validation was performed against the bio-chemical assay to indicate the sensitivity, specificity, positive predictive value, negative predictive value and with an accuracy of [90%, 55%, 65%, 85% and 72%] respectively. The non-invasive core body temperature measurement at the inner canthi of eye [r=-0.462, p<0.01] indicated negative correlation with HbA(1c), that signifies the early metabolic changes. In type 2 diabetes, the core body temperature decreases with a decrease in the body metabolism. Thereby, a truly non-invasive infrared thermography could be used for obtaining the accurate HbA(1c) with no blood sample extraction; further, it could be used as the preferred diagnostic tool for type 2 diabetes.

Defect Depth Quantification Using Pulsed Thermography

Pulsed Thermography is an advanced NDE technique which is becoming popular due to fast inspection rate, non contact nature and it gives full field image. Pulsed Thermography is successfully applied for defect detection, defect depth estimation, coating thickness evaluation and delamination detection in coatings but it is limited for evaluation of subsurface defects (of the order of few mm). In this paper we discuss the application of Pulsed Thermography for defect quantification and effect of defect size on it in AISI 316 grade SS which are important structural materials used in nuclear and other industries. Log First Derivative method is considered for defect depth quantification and the results are compared with Finite Difference Modeling carried out using ThermoCalc 6L software.