A robust imputation method for missing responses and covariates in sample selection models

Sample selection arises when the outcome of interest is partially observed in a study. Although sophisticated statistical methods in the parametric and non-parametric framework have been proposed to solve this problem, it is yet unclear how to deal with selectively missing covariate data using simple multiple imputation techniques, especially in the absence of exclusion restrictions and deviation from normality. Motivated by the 2003-2004 NHANES data, where previous authors have studied the effect of socio-economic status on blood pressure with missing data on income variable, we proposed the use of a robust imputation technique based on the selection-t sample selection model. The imputation method, which is developed within the frequentist framework, is compared with competing alternatives in a simulation study. The results indicate that the robust alternative is not susceptible to the absence of exclusion restriction- a property inherited from the parent selection-t model- and performs better than models based on the normal assumption even when the data is generated from the normal distribution. Applications to missing outcome and covariate data further corroborate the robustness properties of the pro-posed method. We implemented the proposed approach within the MICE environment in R Statistical Software

The Impact of Online Learning as Emerging Technology on Parents: Case Study of Parents of Primary School Children in Nairobi, Kenya.

Kenya, as a nation has a stable schooling system based on synchronous classroom learning. The advent of the COVID 19 pandemic has led to the sudden shift in paradigm to remote schooling learning systems. Several studies have been carried out on remote schooling systems and the impact of parent’s involvement in children’s remote school, but none has been sighted on its impact on parents. The objective of this study was to determine the impact of the sudden paradigm shift on parents of remote schooling pupils in Kenya during this pandemic. A descriptive survey design was utilized. Primary data was collected by online questionnaires and secondary data from past studied. The analysis was done with a statistical application. It was found out that, remote schooling may be easily accepted by many Kenyan parents with 39.8% of parents indicating that they will recommend remote schooling having indicated some benefits derived from it and 24.8% indicating that they will not. It was therefore recommended that the national government should address factors that may hinder effective remote learning, thus encouraging parental involvement and support. It was also recommended that the government and education practitioners should officially develop and implement standards and curriculum for the implementation of remote learning in Kenya in preparation for future pandemics. Keywords: remote schooling, remote learning, descriptive survey desig

Design and implementation of robust decentralized control laws for the ACES structure at Marshall Space Flight Center

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line-of-sight accuracy. In order for these concepts to become operational it is imperative that the benefits of active vibration control be practically demonstrated in ground based experiments. The results of the experiment successfully demonstrate active vibration control for a flexible structure. The testbed is the Active Control Technique Evaluation for Spacecraft (ACES) structure at NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues

Predictive performance of penalized beta regression model for continuous bounded outcomes

Prediction models for continuous bounded outcomes are often developed by fitting ordinary least-square regression. However, predicted values from such method may lie outside the range of the outcome as it is bounded within a fixed range, with nonlinear expectation due to the ceiling and floor effects of the bounds. Thus, regular regression models such as normal linear or nonlinear models, are inadequate for prediction purposes for bounded response variable and the use of distributions that can model different shapes are essential. Beta regression, apart from modeling different shapes and constraining predictions to an admissible range, has been shown to be superior to alternative methods for data fitting but not for prediction purposes. We take data structures into account and compared various penalized beta regression method on predictive accuracy for bounded outcome variables using optimism corrected measures. Contrary to results obtained under many regression contexts, the classical maximum likelihood method produced good predictive accuracy in terms of R2 and RMSE. The ridge penalized beta regression performed better in terms of g-index, which is a measure of performance of the methods in external data sets. We restricted attention to prespecified models throughout and as such variable selection methods are not evaluated

High performance, accelerometer-based control of the Mini-MAST structure at Langley Research Center

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optimal Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off

Improving Delivery of Construction Projects in Ghana's Cities: A Lean Construction Approach

The construction industry plays a vital role in the physical and socio-economic development of cities. However, poor execution and frequent breakdown of construction works such as roads and houses obstruct the overall development of cities since most social and economic activities depend of these projects. This paper sought to assess the extent to which lean construction principles are utilised in construction activities in Ghana’s cities and ways that these principles can be applied effectively to improve the delivery of construction works. The study concentrated in Accra, Kumasi and Sekondi-Takoradi cities whilst officials from the Metro Works Departments of the selected cities and various construction professionals constituted the target population. Questionnaire was the research instrument employed and Spearman Rank Correlation Coefficient Test was used to analyse the results. It was revealed that various lean construction principles such as value, value stream, flow, pull and perfection are poorly implemented with each of these principles having less than 50 percent rate of application. Barriers such as long lead time, poor procurement system and contracts, cultural and human factors, political influence, and lack of financial and management commitment were found to be responsible for that. To successfully apply the lean construction principles and enhance the sustainability of construction projects, measures such as benchmarking, process mapping, last planner procedures and continuous training of workers in the construction industry have been recommended

Electrolyte disorders in a young female following short-term omeprazole therapy

A 29 years old female presented to us in the metabolic clinic of the University of Port Harcourt Teaching Hospital (UPTH) on account of a week history of easy fatigability, weakness, and lower extremity muscle cramps associated with numbness and tingling sensation in the peri-oral area, fingers and toes. Two weeks prior to the onset of her presenting symptoms, she had visited a local pharmaceutical shop on account of a distressing epigastric discomfort and was subsequently placed on daily oral omeprazole 20mg daily for a month by a pharmacist. She had been on the omeprazole medication for two weeks before her present symptoms manifested. Her past medical history was not suggestive of hypoparathyroidism nor pancreatitis. She was married with three children and has an uneventful family, social and obstetric histories. On examination, she was a healthy well-oriented young female with positive Trousseau’s, Chvostek’s and epigastric tenderness signs. Further Laboratory evaluation revealed she had low plasma magnesium, low plasma albumin-corrected calcium, and low serum parathyroid hormone levels, while other laboratory parameters were essentially normal. A diagnosis of omeprazole-induced electrolyte disorders (hypomagnesaemia and hypocalcaemia) associated with hypoparathyroidism was made following the review of her clinical examination and laboratory findings. She was subsequently managed with oral magnesium supplements following the withdrawal of the omeprazole medication (replaced with oral ranitidine), monitored weekly, and full recovery was achieved after three weeks

Stronger at Depth: Jamming Grippers as Deep Sea Sampling Tools

In this work we experimentally demonstrate (a) that the holding strength of universal jamming grippers increases as a function of the jamming pressure to greater than three atmospheres, and (b) that jamming grippers can be used for deep sea grasping tasks in ambient pressures exceeding one hundred atmospheres, where such high jamming pressures can be readily achieved. Laboratory experiments in a pressurized, water filled test cell are used to measure the holding force of a \u27universal\u27 style jamming gripper as a function of the pressure difference between internal membrane pressure and ambient pressure. Experiments at sea are used to demonstrate that jamming grippers can be installed on, and operated from, remotely operated vehicles (ROVs) at depths in excess of 1200m. In both experiments, the jamming gripper consists of a latex balloon filled with a mixture of fresh water and ~200 micron glass beads, which are cheaply available in large quantities as sand blasting media. The use of a liquid, rather than gas, as the fluid media allows operation of the gripper with a closed loop fluid system; jamming pressure is controlled with an electrically driven water hydraulic cylinder in the lab, and with an oil hydraulic driven large-bore water hydraulic cylinder at sea

Aplicación de Muestreo basado en Modelos de Control Predictivo a un Vehículo Autónomo Subacuático

Unmanned Underwater Vehicles (UUVs) can be utilized to perform difficult tasks in cluttered environments such as harbor and port protection. However, since UUVs have nonlinear and highly coupled dynamics, motion planning and control can be difficult when completing complex tasks. Introducing models into the motion planning process can produce paths the vehicle can feasibly traverse. As a result, Sampling-Based Model Predictive Control (SBMPC) is proposed to simultaneously generate control inputs and system trajectories for an autonomous underwater vehicle (AUV). The algorithm combines the benefits of sampling-based motion planning with model predictive control (MPC) while avoiding some of the major pitfalls facing both traditional sampling-based planning algorithms and traditional MPC. The method is based on sampling (i.e., discretizing) the input space at each sample period and implementing a goal-directed optimization (e.g., A*) in place of standard numerical optimization. This formulation of MPC readily applies to nonlinear systems and avoids the local minima which can cause a vehicle to become immobilized behind obstacles. The SBMPC algorithm is applied to an AUV in a 2D cluttered environment and an AUV in a common local minima problem. The algorithm is then used on a full kinematic model to demonstrate the benefits.Los UUVs pueden ser utilizados para realizar tareas difíciles en ambientes atiborrados de reflexiones de onda tales como muelles y puertos. Sin embargo, dado que los UUVs tienen dinámicas áltamente acopladas y no lineales, la programación de movimiento y el control pueden ser complicados cuando son realizadas tareas complejas. Introducir modelos en el proceso de programación del movimiento puede producir patrones que el vehículo puede cruzar de manera viable. Como resultado, el modelo de control predictivo basado en muestreo (SBMPC, por sus siglas en inglés) es propuesto para generar simultáneamente entradas de control y trayectorias de sistema para un vehículo autónomo sumergible. El algoritmo combina los beneficios de la planeación de movimiento con el control predictivo de modelo (MPC), mientras que evita algunos de los mayores obstáculos que enfrentan tanto los algoritmos basados en muestreo como el tradicional MPC. El método está basado en el muestreo (es decir, discretización) del espacio de entrada en cada período de muestreo e implementación de una optimización dirigida a objetivos (por ejemplo, A*) en lugar de la optimización numérica estándar. Esta formulación del MPC aplica fácilmente a los sistemas no lineales y evita el mínimo local, el cual puede ocasionar que un vehículo quede inmóvil detrás de los obstáculos. El algoritmo SBMPC se aplica a un UAV en un ambiente cargado de reflexiones de onda y a un UAV en un problema de mínimo común local. El algoritmo es luego usado en un modelo cinemático completo para demostrar los beneficios de aplicar restricciones y un modelo en programación de movimiento