The mismatch between World Bank actions and the decentralization of educational systems in LMICs

The World Bank’s (WB) growing emphasis on decentralizing educational systems has sparked widespread discussion in the literature. This study examines whether WB reforms are indeed associated with decentralizing educational systems in low- and middle-income countries (LMICs), as commonly assumed. Using unique, untapped country-level panel data on 30 LMICs from 1990 to 2019, I do not find a significant association between the WB’s actions and changes observed in educational systems. Employing the institutional logics perspective, I argue that the WB’s diffusion of “homogeneous” educational reforms may clash with “heterogeneous” socioeconomic, political, and cultural contexts, thus hindering the direct translation of reforms into tangible outcomes on the ground

Crack breathing mechanism in a cracked shaft subject to nontrivial mass unbalance

Rotating machinery is widely used in many industrial fields and is often damaged owing to the breathing of the fatigue crack. The fatigue crack opens and closes once per revolution during shaft rotation. The breathing of the fatigue crack reduces the stiffness of the shaft and hence alters its dynamic response. It changes the vibration characteristics of the shaft. Fatigue cracks are a common occurrence in large rotor systems and can cause catastrophic failure. Detecting faults in rotating machinery before failure is the best way to avoid damage. However, a generalised method of positively identifying a fatigue crack as the cause of anomalous vibrations is not yet available. Vibration diagnostics deliver insights into the mechanical ‘health’ of rotating machinery in real-time when the machine is running. However, studying the vibrations of naturally occurring fatigue cracks is difficult because shafts will often either fail before, or be taken out of service once, the crack is identified. Artificially introduced cracks do not exhibit behaviour identical to that of natural ones owing to the difficulty in cutting into a shaft and leaving a slot with close to zero radius at the crack tip. Therefore, considerable efforts have been devoted to numerically modelling cracked rotors and simulating their operating conditions so that the vibrations can be studied. Numerical modelling techniques are many and varied. In the present thesis, the literature on cracked rotor dynamics is reviewed. Of the crack modelling techniques reviewed, the second area moment method is identified as having potential for improvement. The second area moment method accounts for reduction in bending stiffness of a cracked rotor. Breathing of the fatigue crack is directly related to the second area moment at the crack location. It leads to changes in one of the shaft mechanical properties, stiffness. In a shaft with a crack, the shaft stiffness will change periodically at different rotational angles. Modelling the breathing of the fatigue crack is the key step to analyse the vibration response of a cracked shaft. This breathing phenomenon must be modelled accurately to detect the crack in a rotor. However, it is not yet fully understood how partial crack closure interacts with changes in shaft stiffness, and further, with key variables of the crack detection problem. Unfortunately, almost all existing models are not applicable near the shaft critical speed, because equations of motion developed under the assumption of rotor weight dominance are no longer suitable for analysis near the critical speed. Moreover, localised reduction in stiffness is directly related to crack depth, whereas global reduction in stiffness is directly related to the crack depth and crack location along the shaft. However, researchers opt to either ignore crack location or mitigate its effects. From the literature review, it is evident that accurate modelling, which considers the influence of the crack location and the effect of the unbalance force on the crack breathing behaviour of the fatigue crack to calculate the second area moment of inertia of a cracked shaft to form the stiffness matrix, is still absent. The first topic in this research work is developing a new unbalance model—effectual bending angle—to evaluate the crack breathing response and calculate the second area moment of inertia at any crack location along the shaft length. It is developed considering the effects of unbalance force, rotor weight, rotor physical and dimensional properties and a more realistic fixed-end boundary condition. It governs the opening and closing of a shaft crack that describes the proximity of the shaft bending direction (or shaft deformation direction) relative to the crack direction. The crack breathing behaviours have been studied for every possible crack location and shaft rotation angle. The presented model identifies unique crack breathing behaviours under the influence of unbalance force and rotor physical and dimensional properties, showing the strong dependence of the breathing mechanism on the crack location. Further, the newly developed model is used to obtain the second area moment of inertia of crack cross-section closed area at any crack location along the shaft length under the unbalance force effect about the centroid. The newly developed unbalance model results are validated through 3D FEM results. This thesis finds that this analytical unbalance model captures the main features of crack breathing and is in good agreement with the 3D FEM. However, the approach adopted in this study of using the existing balance model to identify the crack breathing behaviour and the second area moment of inertia needs to be improved. In this research work, a new method is developed to determine crack breathing, which is an improvement in terms of accuracy on adopted methods. The improvement is owing to the removal of two simplifying assumptions used by previous authors, namely, that the cracked shafts will only experience symmetrical bending and the neutral axis would lie perpendicular to the bending direction, that is, always be horizontal. Both assumptions are shown to be invalid on comparison with results from a three-dimensional finite element model. The newly developed method is then used to evaluate nonlinear crack breathing behaviour under different weight–unbalance force ratios at different crack locations by examining the percentage of opening of a crack. The breathing response predicted by the developed method is validated using the three-dimensional finite element model. The results of the algorithm show a significant improvement in accuracy when compared with data from the three-dimensional finite element model of cracked rotors. The mathematical modelling of calculating the cross-section properties, namely, the second area moment and centroid location, is also improved in this research work by considering neutral axis inclination, removing the assumption of collinearity between the bending moment and neutral axis at the crack location. The newly developed equations are used to evaluate the second area moment of inertia as a function of the crack locations and shaft’s angle of rotation about centroid axes. It is found to be highly dependent on crack location, similar to crack breathing behaviours. The work presented in this thesis demonstrates that a common assumption in the literature—that the effects of axial position of a crack can be neglected—is incorrect. The second topic of this research work is analysis of the crack breathing behaviour of an unbalance shaft with a more realistic transverse slant crack and elliptical crack at different crack locations along the shaft length. A three-dimensional finite element model consisting of a two-disk rotor with a crack is simulated with unbalance mass. The finite element model is simulated using Abaqus/standard. It is simulated considering the effects of unbalance force, rotor weight, rotor physical and dimensional properties and a more realistic fixed-end boundary condition. Crack breathing behaviours are visualised by the variation of the crack closed area and represented quantitatively by the percentage of the closing of the crack. Crack breathing behaviour is found to strongly depend on its axial position, angular position and depth ratios as well as unbalance force ratios and angular position of unbalance force. Compared with the balance shaft crack breathing behaviour, two different crack breathing regions along the shaft length are identified, where shaft stiffness is larger or smaller, depending on the unbalance force orientation, magnitude and crack location. However, four specific crack locations along the shaft length are identified where the crack remains fully closed or open or the same as in balance shaft crack breathing during shaft rotation under different loading conditions. The presented research results suggest that a more accurate prediction of the dynamic response of cracked rotors can be expected on considering the effects of unbalance force and individual rotor physical properties on crack breathing. The presented method and results of this research can be used to obtain the stiffness matrix of a cracked shaft element and then to study the vibration response of a cracked rotor where the rotor-weight-dominant assumption on crack breathing no longer holds

A NOVEL ESTIMATION METHOD BASED ON MAXIMUM LIKELIHOOD

The method of maximum likelihood (ML) is perhaps the most widely used statistical approach to estimate unknown parameters in a parametric setting. However, the required optimization of the likelihood function is rarely possible explicitly, and finding the estimators may be computationally challenging. On the other hand, maximum likelihood estimators are often simple to compute when the sample size is equal to one. Based on this observation, we propose a novel approach to estimation, where each individual observation in a random sample is used to derive an estimator of an unknown parameter using the ML principle. These individual estimators are then put together as a weighted average to produce the final estimator. The weights are chosen to be proportional to the likelihood function evaluated at the estimators based on each observation. It turns out that this method can be related to a Bayesian approach, where the prior distribution is data driven. In case of estimating a location parameter of a unimodal density, the prior distribution is the empirical distribution of the sample, and converges to the true distribution that generated the data as the sample size increases. We provide several examples illustrating the new method, and conduct simulation studies to assess the performance of the estimators. It turns out that this straightforward methodology produces consistent estimators, which seem to be comparable with those obtained by the ML method in large sample setting, and may actually outperform the latter when the sample size is small

Three Essays on Labor Supply Focusing on Entrepreneurship and Health Insurance

This dissertation consists of three essays analyzing policies that affect different aspects of labor supply. Economists are interested in many different aspects of labor supply decisions, such as whether to participate in the labor market, amount of work conditional on participation and career choice, among others. At the same time, a wide range of policies can impact labor supply such as: tax, immigration, healthcare, and unionization policies, among others. Analyzing policies using appropriate methodology may assist policymakers by presenting alternative solutions, trade-offs, and intended and unintended consequences of economic policies. While some of these issues have been explored extensively, others remain relatively unexplored. In this dissertation, I explore three such unexplored problems. First, I analyze the dynamic decision processes of entrepreneurs. Second, I explore the impact of the cost of health insurance on entrepreneurial activities. Third, I evaluate the effect of the availability of health insurance on workplace absenteeism.The first essay explores what induces individuals to become entrepreneurs creating jobs. Extant structural labor supply models used for ex-ante policy evaluations mostly exclude entrepreneurs. The first essay develops and estimates the first dynamic structural micro-econometric model explicitly accounting for the employer and non-employer entrepreneurs. In the model, individuals in each period choose to work as an employee, as one of the two entrepreneur types, or be non-employed. Different types of work experiences may affect earnings in the three careers in different ways. The model, estimated using German survey data, replicates key data patterns. This essay simulates how policy scenarios would affect individuals' choices to become employers and non-employers.The second essay explores whether the cost of health insurance affects entry into entrepreneurship. Entrepreneurship literature argues that a lack of access to health insurance is a potential barrier to become an entrepreneur (entrepreneurship lock), especially for individuals with a chronic health condition. Several papers have explored whether the guaranteed availability of health insurance brought about by the Affordable Care Act (ACA) of 2010 has increased the level of entrepreneurship, with conflicting results. However, the current literature focuses only on the availability of health insurance but not the cost of obtaining insurance. This essay explores whether the cost of health insurance rather than availability is a barrier to entrepreneurship. The results suggest that the probability of entry into self-employment is not sensitive to health insurance premiums.The third essay examines whether the expansion of health insurance coverage brought on by the Patient Protection and Affordable Care Act of 2010 (ACA), led to a decline in absenteeism among overweight and obese individuals. This essay uses data from the National Health Interview Survey (NHIS) to compare absenteeism among overweight and obese workers to absenteeism among normal-weight workers before and after the ACA. Results suggest that in the post-ACA period, the probability of being absent declined by about 1.3 (1.5) percentage points among obese (overweight) individuals. Disaggregated regressions suggest that the effect is significant among women but not among men. Furthermore, estimates (using a Tobit model) indicate that the obese (overweight) workers missed 0.32 (0.48) fewer days after the ACA. Again, the effect is concentrated among women. Results show that improved health outcomes led to reduced absenteeism. Results also show that there is no decline in absenteeism among elderly (age>=65) adults (who did not experience any increase in health insurance coverage as a result of the ACA), suggesting that the decline in absenteeism is indeed due to the expansion of health insurance coverage due to the ACA. Estimates of this essay imply that the ACA reduced the cost associated with absenteeism by about $350 million per year

Crack breathing behavior of unbalanced rotor system: A Quasi-static numerical analysis

Crack opening and closing during shaft rotation of a cracked rotor system have long been a focus of many previous studies. Previously published modeling work in the literature uses weight-governed crack breathing model for very large rotor systems. However, for lightweight or vertical or lightly damped rotors the opening and closing statuses of a crack are not always weight dominated as there is significant influence from dynamic loads. Further, the dependence of the breathing mechanism on the crack location has not been investigated yet. In this paper, the crack breathing behavior of an unbalanced shaft at the different crack location of a rotating shaft is investigated. A three-dimensional finite element model, consisting of a two-disk rotor with a transverse crack, is used. Finite element model is simulated using ABAQUS/Standard. Crack breathing behavior is found to strongly depend on its axial position, angular position, depth ratio, unbalanced force ratio and angular position. Two different crack breathing regions along the shaft length are identified, where unbalanced shaft stiffness may be larger or smaller than the balanced shaft, depending on the unbalance force orientation, magnitude and crack location. Further, four specific crack locations along the shaft length have been identified, where the crack remains fully closed or open or just behaves like in the balanced shaft. The results suggest that more accurate prediction of the dynamic response of cracked rotors can be expected when the effects of unbalance force and individual rotor physical properties on the crack breathing have been taken into account

Choice of Performance Measures and Performance of Textile Sector in Bangladesh

This study seeks out to establish the influence of quality as well as performance-based manufacturing strategy, diverse in performance measures, firm’s size, their interrelationship, and joint effects with the subjective measures on textile firm’s performance. Financial, objective, subjective, and non-financial measures have been taken into consideration. Bangladesh needs competitive strategies and measures to meet the challenges & opportunities for creating a sustainable position in the global market. Performance measures have been taken by the textile industries of Bangladesh to improve the performance. The influence of those measures is not always improving the performance as found in the earlier study. Responses from mid-level managers of 30 textile industries in Bangladesh have been taken into consideration using survey method using descriptive statistics, factor analysis, regression and correlation analysis. The result shows extensive use of measures and only subjective measures do not increase the performance of the industry, but customer-oriented measures, sustainability measures, manufacturing quality strategy with firm size increase the performance of the textile sectors. The study will open the scope of further exploration in the performance of the textile sector of Bangladesh. JEL Classification Code: G 2

A novel weighted likelihood estimation with empirical Bayes flavor

We propose a novel approach to estimation, where each individual observation in a random sample is used to derive an estimator of an unknown parameter using the maximum likelihood principle. These individual estimators are then combined as a weighted average to produce the final estimator. The weights are chosen to be proportional to the likelihood function evaluated at the estimators based on each observation. The method can be related to a Bayesian approach, where the prior distribution is data driven. In case of estimating a location parameter of a unimodal density, the prior distribution is the empirical distribution of the sample, and converges to the true distribution that generated the data as the sample size increases. We provide several examples illustrating the new method, argue for its consistency, and conduct simulation studies to assess the performance of the estimators. It turns out that this straightforward methodology produces consistent estimators, which seem to be comparable with those obtained by the maximum likelihood method

Relationship Between Health Insurance and Self-employment: A Systematic Review

This paper performs a systematic review on whether there is a relationship between health insurance and self-employment. There are three types of findings available regarding this issue in the entrepreneurship literature. First, health insurance clearly plays a vital role when individuals choose to become self-employed. Second, there is some evidence of the effect of health insurance on entrepreneurial choices for some individuals with some demographic characteristics, like married women, students, people with disabilities, etc. Third, the evidence of relationship between health insurance and entrepreneurial choices is anecdotal