Use of spread spectrum time domain reflectometry to estimate state of health of power converters

pre-printA new online measurement and analysis method has been presented in this paper to identify the state of health of power converter circuits. Using spread spectrum time domain reflectometry (SSTDR), impedance in the various current paths inside the converter as well as any fault can be identified without interrupting the circuit's normal operation. Multiple sets of test data have been generated while the SSTDR process is applied to each of the components i.e. the power MOSFETs, the dc bus capacitor and the load. These obtained test data are analyzed to show how these test results are consistent with the impedances in various current paths. An impedance matrix was formed for a non-aged converter and a corresponding matrix using SSTDR data was formed as well. The matrices could be formed for any power converter, and the impedance matrix for the non-aged converter could be considered as a "Reference matrix" for comparison purpose. By comparing these two matrices, the variation in path impedances due to aging could be determined. This research aims to identify the measurable quantities to characterize the aging process, their origins of these quantities and propose convenient methods to measure them

Characterization of aging process in power converters using spread spectrum time domain reflectometry

pre-printThis paper aims to find a new technique to predict the state of health of power converters by characterizing the most vulnerable components in the converter without affecting the normal circuit operation. Spread spectrum time domain reflectometry (SSTDR) can detect most of the aged components inside the converter while the converter is operational. Semiconductor switches and electrolytic capacitors are the two most sensitive components in power converter circuits, and this paper demonstrated how SSTDR can be used to determine the degradation of these components. Multiple sets of test data have been generated while the SSTDR process is applied to the power MOSFETs, IGBTs connected in a chopper circuit and to the aluminum electrolytic capacitors connected in an RC circuit. Analysis is done on these obtained test data to show how the SSTDR generated data are consistent with the aging of power MOSFETs, IGBTs and electrolytic capacitors

Quantifying device degradation in live power converters using SSTDR assisted impedance Matrix

pre-printA noninterfering measurement technique designed around spread spectrum time domain reflectometry (SSTDR) has been proposed in this paper to identify the level of aging associated with power semiconductor switches inside a live converter circuit. Power MOSFETs are one of the most age-sensitive components in power converter circuits, and this paper demonstrates how SSTDR can be used to determine the characteristic degradation of the switching MOSFETs used in various power converters. An SSTDR technique was applied to determine the aging in power MOSFETs, while they remained energized in live circuits. In addition, SSTDR was applied to various test nodes of an H-bridge ac-ac converter, and multiple impedance matrices were created based on the measured reflections. An error minimization technique has been developed to locate and determine the origin and amount of aging in this circuit, and this technique provides key information about the level of aging associated to the components of interest. By conducting component level failure analysis, the overall reliability of an H-bridge ac-ac converter has been derived and incorporated in this paper

Comparative outcome of socket shield method and conventional immediate implant implantation with immediate temporization- a 10 years follow-up

Background: Dental implants are now regarded as an effective treatment option for replacing missing teeth. The objective was to evaluate the socket shield approach with immediate temporization to the conventional instantaneous implant with immediate temporization utilizing the parameters of horizontal and vertical dimensional bone loss, crestal bone thickness (CBT) and pink esthetic score (PES). Methods: This prospective study was carried out at Banasree Dental and German Dental implant surgery centers from December 2010 to December 2020 where 74 patients who had non-restorable maxillary teeth in the esthetic region were conducted and evaluated for implant settlement. The allocated individuals were divided into two groups immediate implant with socket shield group (study group, n=22) and the conventional immediate implant placement group (control group, n=52). SPSS version 21.0 was used to analyze all of the data. Results: Mean value of crestal bone thickness (CBT) at the pre-operative time was 1.31±0.2 in both groups but at the 6 months follow-up time it was 1.2±0.22 and 1.07±0.21, at the 24 months follow-up time it was 1.13±0.24 and 0.99±0.20 and at the 60 months follow-up time in was 1.05±0.27 and 0.79±0.15 and at the 120 months follow-up time it was 1.03±0.29 and 0.69±0.17 in the study and control group respectively. In the study group, the mean value of pink esthetic score was 11.45±1.6 at 6 months follow-up time, 12±0.89 at 24 months, 12.5±0.87 at the 60 months and 12.5±0.86 at the 120 months follow-up time whereas in the control group, it was 11±1.32, 10±1.52, 8.9±1.63 and 7.5±1.55, respectively. Conclusions: The SST group revealed minimal reduction in CBT, horizontal and vertical bone loss and a superior PES compared to conventional immediate implant

INVESTIGATION OF THE BULK, SURFACE AND TRANSFER PROPERTIES OF CHLORINE BLEACHED DENIM APPAREL AT DIFFERENT CONDITION

Oxidizing bleaching agent (calcium hypochlorite or bleaching powder) is widely used in the apparel washing plant as a color removing and cost effective finishing chemical. As the faded denim or old look denim is preferred by the today’s youth it has become a crucial issue for the technologists to modify denim apparel to fulfill the demand of existing trend. Calcium hypochlorite (Ca(OCl)Cl) fades the denim effectively but a significant changes are happened in the properties of the denim apparel. The main objective of this paper was to investigate the changes of bulk, surface and transfer properties of denim apparel after the chlorine bleach action at varying length of washing time (10,15 and 30 min) with fixed concentration and temperature (50°C). These properties are related to the performance of the end product. 100% cotton indigo dyed 2/1 twill denim apparel was treated with 5gm/l (Ca(OCl)Cl). To determine the end use performance of the modified denim the changes of tensile strength, stiffness, dimensional stability (bulk properties), hand roughness, rubbing fastness (surface properties), air permeability, water repellency (transfer properties) of the modified denim apparel were evaluated. It has been monitored from the experimental data that the bulk properties play down but the surface properties have a noticeable improvement after the chlorine bleach action. It is also noticed that washing time has a significant effect on air permeability of the treated denim apparel

INVESTIGATION OF THE BULK, SURFACE AND TRANSFER PROPERTIES OF CHLORINE BLEACHED DENIM APPAREL AT DIFFERENT CONDITION

Oxidizing bleaching agent (calcium hypochlorite or bleaching powder) is widely used in the apparel washing plant as a color removing and cost effective finishing chemical. As the faded denim or old look denim is preferred by the today’s youth it has become a crucial issue for the technologists to modify denim apparel to fulfill the demand of existing trend. Calcium hypochlorite (Ca(OCl)Cl) fades the denim effectively but a significant changes are happened in the properties of the denim apparel. The main objective of this paper was to investigate the changes of bulk, surface and transfer properties of denim apparel after the chlorine bleach action at varying length of washing time (10,15 and 30 min) with fixed concentration and temperature (50°C). These properties are related to the performance of the end product. 100% cotton indigo dyed 2/1 twill denim apparel was treated with 5gm/l (Ca(OCl)Cl). To determine the end use performance of the modified denim the changes of tensile strength, stiffness, dimensional stability (bulk properties), hand roughness, rubbing fastness (surface properties), air permeability, water repellency (transfer properties) of the modified denim apparel were evaluated. It has been monitored from the experimental data that the bulk properties play down but the surface properties have a noticeable improvement after the chlorine bleach action. It is also noticed that washing time has a significant effect on air permeability of the treated denim apparel

The relationship between conversion factors and health: evidence from the ready-made garment workers in Bangladesh

This study examined the association between health condition and conversion factors(i.e. environmental, individual and social) among workers in the ready-made garment(RMG) industry in Bangladesh. It used data gathered from a cross-sectional survey of 775 RMG workers in the Dhaka and Narayanganj districts. Using multiple logistic regression, the study found that: (i) achieving good health among RMG workers is hindered by various factors including high job-related demands, high noise levels,workplace crowding, heavy workloads, and low level of educational attainment; (ii)job-related rewards and marital status have contributed to achieving good health; (iii)health condition of workers is worse for women than for men; and (iv) poor health condition was more prevalent among the oldest age group than in the lowest age category. The main contributions of this research are: (i) this study develops a comprehensive framework to determine the factors affecting the health condition of manufacturing workers in general, and RMG workers in particular; and (ii) this study examines the effects of both psychosocial and physical working conditions on the health of RMG workers

Classroom interaction in ESL classrooms: a comparative study between group work and individual work

This dissertation is submitted in partial fulfillment of the requirements for the degree of Masters of Arts in English, 2009Cataloged from PDF version of dissertation.Includes bibliographical references (page 43 - 44).Rabeya Nasrin KhanM.A. in Englis

Response of morphological and biochemical traits of maize genotypes under waterlogging stress

Maize (Zea mays L.) is one of the most important cereal crops cultivated around the world. Waterlogging stress is a major production constraint of maize production in rain-fed agricultural systems. The main objective of this experiment was to investigate the effect of continuous waterlogging on morphological and biochemical traits of maize genotypes at the vegetative stage. Ten maize genotypes were treated under no waterlogging (control) and continuous waterlogging of five centimeters depth for 10 days. The treatments were applied to the plants at their 45 days of age. Visual leaf injury scores from Leaf 4 (youngest leaf is the reference point) to Leaf 7 separated tolerant and susceptible genotypes. Waterlogging stress significantly reduced the total number of live leaves and chlorophyll content in leaf tissues in susceptible genotypes. The anatomical study revealed that tolerant maize genotypes produce a large number of aerenchyma cells under waterlogging stress compared to susceptible genotypes. The enzymatic activities of ascorbate peroxidase (APX) and peroxidase (POD) exhibited a greater increase in tolerant genotypes than susceptible genotypes whereas the contents of reactive oxygen species (H2O2) greatly increased in susceptible genotypes than tolerant genotypes under waterlogging stress compared to control. Principal component 2 (PC2) indicated that increasing plant height in the genotypes BHM-14, BHM-13 and BHM-9 was associated with waterlogging tolerance. The findings of this experiment will add value to maize breeding to screen out maize genotypes for waterlogging stress tolerance

3D LIDAR Human Skeleton Estimation for Long Range Identification

This research project is the continuation of an effort by the Vision Lab to understand human gait and motion using special-purpose imaging sensors and novel computer vision algorithms. The project began using a Motion Capture (MoCap) system which measures 3D human skeleton information in real-time by attaching markers to a human subject and viewing the human motion with a set of cameras at different angles. We developed an algorithm to determine the gender of a subject wearing these sensors. The current phase of this project extends this work using a state-of-the-art flash Lidar sensor. This sensor scans the surface of objects and gives a 3D depth map of the object in real-time. We developed a computer vision system that can estimate a human skeleton from Lidar data, which resembles the MoCap data format. Using these computed 3D skeletons we can perform human identification. The poster outlines the current Lidar-based algorithm using a flow chart to explain the input and output for each component of the system and how each data modality is used to build the final skeleton. The poster compares performance for our human identification with other methods for human- identification using 3D sensors. Finally, future work using infrared sensing is discussed.https://digitalcommons.odu.edu/gradposters2021_engineering/1003/thumbnail.jp