Background
This study identified the risk factors for severe acute respiratory syndrome coronavirus 2 infection among household contacts of index patients and determined the incubation period (IP), ...serial interval, and estimates of secondary infection rate in Kerala, India.
Methods
We conducted a cohort study in three districts of Kerala among the inhabitants of households of reverse transcriptase polymerase chain reaction‐positive coronavirus disease 2019 patients between January and July 2021. About 147 index patients and 362 household contacts were followed up for 28 days to determine reverse transcriptase polymerase chain reaction positivity and the presence of total antibodies against SARS‐CoV‐2 on days 1, 7, 14, and 28.
Results
The mean IP, serial interval, and generation time were 1.6, 3, and 3.9 days, respectively. The secondary infection rate at 14 days was 43.0%. According to multivariable regression analysis persons who worked outside the home were protected (adjusted odds ratio aOR, 0.45; 95% confidence interval CI, 0.24–0.85), whereas those who had kissed the coronavirus disease 2019‐positive patients during illness were more than twice at risk of infection (aOR, 2.23; 95% CI, 1.01–5.2) than those who had not kissed the patients. Sharing a toilet with the index patient increased the risk by more than twice (aOR, 2.5; 95% CI, 1.42–4.64) than not sharing a toilet. However, the contacts who reported using masks (aOR, 2.5; 95% CI, 1.4–4.4) were at a higher risk of infection in household settings.
Conclusions
Household settings have a high secondary infection rate and the changing transmissibility dynamics such as IP, serial interval should be considered in the prevention and control of SARS‐CoV‐2.
Background: The human cornea is the most densely innervated tissue, and the corneal sensitivity is a measure of its function and an indicator of the integrity of the protective mechanism. Corneal ...sensitivity plays a vital role in the protection and maintenance of corneal health and is known to vary with race, age, region, climate, environment, and the time of the day. The study was aimed to quantify and establish the range of corneal sensations in different age groups in an Indian population using the Cochet-Bonnet Esthesiometer (CBE). Materials and Methods: This was a cross-sectional study done at a tertiary care center in South India, between January and April 2018. One hundred and fifty patients (30 patients stratified by age into five groups) were enrolled after informed consent. The corneal sensations were measured using CBE by a single examiner in a specified period of a day over five regions and the data analyzed. Results: The average measured corneal sensitivity was 58.36 (21-30 years), 57.96 (31-40 years), 56.43 (41-50 years), 56.40 (51-60 years), and 54.84 (>60 years) mm, respectively. The frequency of having maximal measurable sensations (60 mm) in all the tested regions dropped with increasing age from 46.67% to 16.67%. All regions showed a sensitivity drop with an increase in age, the maximum in the nasal quadrant and the least drop in the central region. No statistically significant difference in the corneal sensitivity was found between the genders. Conclusions: An inverse linear correlation between the corneal sensitivity and age was evident. The central and the superior regions are the most and least sensitive regions of the cornea, respectively, in our study population. The varied pattern of change in corneal sensations in different populations highlights the importance of establishing normal ranges of corneal sensitivity in patients from different ethnic and geographical backgrounds.
Sensorless Direct Torque Control (DTC) is a powerful control scheme for high performance control of induction motor (IM) drives, which provides very quick dynamic response with simple structure and a ...decoupled control of torque and flux. The performance of the DTC drive depends greatly on the accuracy of the estimated flux components, torque and speed, using monitored stator voltages and currents. Low speed estimation is a great challenge because of the presence of transient offset, drift and domination of ohmic voltage drop.Extended Kalman filter (EKF) is a non linear adaptive filter which performs the process of finding the best estimate from the noisy data based on state space techniques and recursive algorithm. This paper mainly focuses on the accurate estimation of speed ranging from very low speed to rated speed using the equation of motion. A new state space model of the IM is developed for estimation in EKF, with load torque as an input variable and not as an estimated quantity which is the case in most previous studies. The developed algorithm is validated using MATLAB-Simulink platform for speeds ranging from low speed to rated speed at rated torque and at various torque conditions. An exhaustive analysis is carried out to validate the performance of DTC Induction motor drive especially at the low speeds. The results are promising for accurate estimation of speed ranging from low speed to rated speed using EKF.
Low speed estimation in DTC IMD is not accurate due to the presence of transient offset, drift and domination of ohmic voltage drop in the measured stator voltages and currents used for estimating ...the stator flux required for accurate estimation of speed. EKF is a nonlinear, recursive adaptive algorithm capable of estimating speed ranging from very low speed to rated speed using equation of motion from noisy measured currents and voltages based on state space technique. In the previous work a new state space model of IM was developed for estimation in EKF by feeding load torque profile as an input variable instead of estimating it by considering load torque as constant, validated using MATLAB-Simulink software. In this paper real time validation of the EKF controller with load profile fed as input for speed estimation in DTC IMD is carried out using OPAL-RT simulator and real time results validates the simulation results and proves the effectives of the new EKF for low speed estimation in DTC IMD
This paper presents a closed loop Model Reference Adaptive system (MRAS) observer with artificial intelligent Nuero fuzzy controller (NFC) as the adaptation technique to mitigate the low speed ...estimation issues and to improvise the performance of the Sensorless Direct Torque Controlled (DTC) Induction Motor Drives (IMD). Rotor flux MRAS and reactive power MRAS with NFC is explored and detailed analysis is carried out for low speed estimation. Comparative analysis between rotor flux MRAS and reactive power MRAS with PI as well as NFC as adaptive controller is performed and results are presented in this paper. The comparative analysis among these four speed estimation methods shows that reactive power MRAS with NFC as adaptation mechanism shows reduced speed estimation error and actual speed error at steady state operating conditions when the drive is subjected to low speed operation. Simulation carried out using MATLAB-Simulink software to validate the performance of the drive especially at low speeds with rated and variable load conditions.
This paper presents an active LC clamped dv/dt filter to mitigate the over voltages appearing across the motor terminals. The over voltages at motor terminal is due to voltage reflection effect of ...long motor cable connected between high frequency PWM inverter having high dv/dt switching waveforms and ac motor drives. The voltage reflection due to fast switching transients can be reduced by increasing the rise time and fall time of inverter output voltage pulses. The most commonly available mitigating technique is a passive dv/dt filter between inverter and cable. Since, size, cost and losses of passive LC dv/dt filter is more, an active dv/dt filtering technique is used to reduce over voltage at motor terminals. Active LC clamp filtering technique used here consists of a small LC filter designed for a single motor cable length which can be used for any lengths of cable up to 1000m only by changing the active control of the PWM pulses to achieve the desired voltage slope during voltage transition period. The basic principle of active dv/dt filer used here is to charge and discharge the capacitor in the filter with modified PWM pulses to increase the rise time and fall time of output voltage pulses without any extra devices to handle the transient response of the LC filter. Detailed investigation is carried out by simulation using MATLAB-Simulink software with active control of common LC clamp dv/dt filter suitable for various cable lengths ranging from 100 m to 1000 m. Comparative analysis is done with active dv/dt filter designed with a common LC clamp filter and active LC clamp dv/dt filter designed for various cable lengths and also with diode clamped passive dv/dt filter. The results proves the effectiveness of the active common LC dv/dt filter to mitigate the over voltages at motor terminal for cable lengths up to 1000m.
Whereas a large number of empirical studies have been devoted to analyzing determinants of environmental compliance (EC) by firms, less attention has been paid to EC by public water systems (PWS). To ...address this gap in the literature, this article uses data on compliance with maximum contaminant levels (MCL) under the Safe Drinking Water Act for 971 PWS in Arizona and identifies the characteristics of PWS that are associated with violation of MCL standards. Three main findings emerge from the analysis. First, larger PWS are more likely to violate MCL standards than smaller PWS. Second, publicly owned PWS have slightly higher probability of violating MCL standards than privately owned systems. Finally, PWS serving residential areas are more likely to violate MCL standards, as opposed to PWS serving school districts or office buildings. The results suggest that for ensuring safe water for people, effectiveness of monitoring policy, and an efficient utilization of resources, the environmental agencies may focus their monitoring and enforcement efforts on these water systems.(JEL K32, Q53)
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