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Constitutive Modelling of Composites with Elastomer Matrix and Fibres with Significant Bending Stiffness
Fedorova, Svitlana ; Kotoul, Michal (referee) ; Menzel, Andreas (referee) ; Burša, Jiří (advisor)
Constitutive modelling of fibre reinforced solids is the focus of this work. To account for the resulting anisotropy of material, the corresponding strain energy function contains additional terms. Thus, tensile stiffness in the fibre direction is characterised by additional strain invariant and respective material constant. In this way deformation in the fibre direction is penalised. Following this logic, the model investigated in this work includes the term that penalises change in curvature in the fibre direction. The model is based on the large strain anisotropic formulation involving couple stresses, also referred to as “polar elasticity for fibre reinforced solids”. The need of such formulation arises when the size effect becomes significant. Mechanical tests are carried out to confirm the limits of applicability of the classical elasticity for constitutive description of composites with thick fibres. Classical unimaterial models fail to take into account the size affect of fibres and their bending stiffness contribution. The specific simplified model is chosen, which involves new kinematic quantities related to fibre curvature and the corresponding material stiffness parameters. In particular, additional constant k3 (associated with the fibre bending stiffness) is considered. Within the small strains framework, k3 is analytically linked to the geometric and material properties of the composite and can serve as a parameter augmenting the integral stiffness of the whole plate. The numerical tests using the updated finite element code for couple stress theory confirm the relevance of this approach. An analytical study is also carried out, extending the existing solution by Farhat and Soldatos for the fibre-reinforced plate, by including additional extra moduli into constitutive description. Solution for a pure bending problem is extended analytically for couple stress theory. Size effect of fibres is observed analytically. Verification of the new constitutive model and the updated code is carried out using new exact solution for the anisotropic couple stress continuum with the incompressibility constraint. Perfect agreement is achieved for small strain case. Large strain problem is considered by finite element method only qualitatively. Three cases of kinematic constraints on transversely isotropic material are considered in the last section: incompressibility, inextensibility and the double constraint case. They are compared with a general material formulation in which the independent elastic constants are manipulated in order to converge the solution to the “constraint” formulation solution. The problem of a thick plate under sinusoidal load is used as a test problem. The inclusion of couple stresses and additional bending stiffness constant is considered as well. The scheme of determination of the additional constant d31 is suggested by using mechanical tests combined with the analytical procedure.
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Social ties at work and effort choice: experimental evidence from Tanzania
Chegere, M. ; Falco, P. ; Menzel, Andreas
Many firms hire workers via social networks. Whether workers who are socially connected to their employers exert more effort on the job is an unsettled debate. We address this question through a novel experiment with small-business owners in Tanzania. Participants are paired with a worker who conducts a real-effort task, and receive a payoff that depends on the worker’s effort. Some business owners are randomly paired with workers they are socially connected with, while others are paired with strangers. With a design that is sufficiently powered to detect economically meaningful effects, we find that being socially connected to one’s employer does not affect workers’ effort.\n
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Effects of one school meal program on mothers' labor supply: Evidence from China
Liu, Sijia ; Menzel, Andreas (advisor) ; Ochsner, Christian (referee)
Female labor force participation is associated with welfare improvement for mothers and also contributes to the welfare for the next generation. I exploit China's school meal program to estimate its effects on the mother's labor supply using a difference-in-differences (DID) strategy. I find that mothers can work longer when children are exposed to a school lunch program, but this program does not change mother's employment status (work or not work). Thus, it increases mother's labor force participation on the intensive but not the extensive margin. Specifically, the program significantly increases their working hours per week by 9%-13%. This paper may help to inform policy and can help the government formulate reasonable policies to promote female labor participation rates. Keywords School meal program Mother's labor supply
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Revisiting Treatment Effects with Causal Forests
Bakirov, Aslan ; Zacchia, Paolo (advisor) ; Menzel, Andreas (referee)
Revisiting Treatment Effects with Causal Forests Aslan Bakirov Abstract This thesis focuses on the application of Causal Forests, a prominent causal machine learning algorithm, to estimate heterogeneous treatment effects in complex socio-economic phenomenon. Causal Forests leverage the capabilities of random forests to partition the high-dimensional covariate space and identify subgroups where the effect of an intervention remains constant. This approach is particularly valuable when dealing with heterogeneous causal effects, where a uniform measure of gains for all is an unrealistic assumption. Unlike traditional manual methods that are susceptible to p-hacking, the algorithm objectively uncovers nuanced treatment effect variations through data-driven analysis. The thesis demonstrates the algorithm's potential in exploring causal effects and providing valuable policy insights. An empirical illustration showcases the modeling of a complex socio-economic phenomenon, such as the gender wage gap, and leverages Causal Forests to extract policy learning from the identified heterogeneity. The study highlights the algorithm's contribution to credible and robust causal inference, bridging the gap between traditional decomposition methods and data-informed heterogeneity analysis. Keywords: Causal machine learning,...
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The Impact of Floods on Maternal and Newborn Healthcare in Pakistan
Kotarja, Angjelina ; Menzel, Andreas (advisor) ; Zacchia, Paolo (referee)
Floods can occur unexpectedly and affect certain groups more than others. I use a difference-in- difference method to identify the causal impact of the 2010 Pakistan flood on maternal and newborn health care utilization. To estimate the likelihood of health care utilization, I use Pakistan Demographic and Health Surveys data two years before and one year after the event, combined with the georeferenced data on the flood among studied years. Through logistic regressions, I determine whether flood-affected communities significantly predicted the differences in the utilization of health care services. Results show that the odds ratio of attending the required number of antenatal visits and postnatal checks was lower in flooded areas than in non-flooded areas. Similarly, the child's size at birth was reported as less than average in the exposed districts. Therefore, medical protection should be enhanced for vulnerable groups, and extra effort should be considered to ensure access to maternal health care services to protect pregnant women's livelihoods in similar disaster settings. Key Words: Difference-In-Difference, Flood, Maternal, Newborn, Pakistan
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Russia Versus Breast Cancer: Examination of the "White Rose" Charity Project
Kosenkova, Vlada ; Menzel, Andreas (advisor) ; Korovkin, Vasily (referee)
According to the World Cancer Research Fund International (2022), breast cancer is the most common cancer worldwide. Therefore, many countries have aimed to implement healthcare programs to decrease mortality rates associated with this type of cancer. Moreover, some part of these programs aims to decrease the burden on government budgets connected to medical expenses. In this thesis, I investigate the effects of the White Rose charity project implemented in Russia to raise awareness about breast cancer among women. I evaluate the influence of the project on health outcomes, including breast cancer mortality rates, the probability to die within a year after the diagnosis, and the share of primary stages of cancer among new diagnoses. I construct a novel dataset using official reports on the oncological situation on the regional level. Using the event study approach, I find intermediate effects that are more pronounced at the longer horizon. In addition, I notice a rise in the number of new breast cancer diagnoses, which might be an indicator of the effectiveness of the program. Because there are no prior studies of this program, the results of my research might be of interest to policymakers in Russia and other developing countries with similar economic structures. Keywords: Health Economics, Breast...
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Labor Market Effects of the Working Family Tax Credit on Single Mothers in the UK
Sinani, Sofiana ; Menzel, Andreas (advisor) ; Žigić, Krešimir (referee)
The Labor Market Effects of the Working Family Tax Credit on Single Mothers in the UK. Sofiana Sinani August 2022 Bibliographic note SINANI, Sofiana. The Labor Market Effects of the Working Family Tax Credit on Single Mothers in the UK. Prague 2022. Master thesis. Center for Economic Research and Graduate Education - Economics Institute, A joint workplace of Charles University and the Economics Institute of the Czech Academy of Sciences. Thesis supervisor: Andreas Menzel, Ph.D. Abstract The Working Family Tax Credit (WFTC) was introduced in the UK in 1999. This policy provided fi- nancial incentives for work to low-income parents with children (primarily single mothers). The parents received full credit if they worked 16 hours/week and the credit decreases with more hours of work. The credit increased marginally when the parent worked 30 hours/week to stimulate full-time work. The WFTC unambiguously made work attractive; however, the effect on labor hours for parents employed in pre-WFTC is unclear. In this thesis, I investigate the effect of the WFTC on single mothers' paid labor hours. I apply the quantile difference-in-difference approach and estimate the quantile treatment effects. This approach allows me to find the effect of the WFTC given the single mothers' paid labor hours in pre-WFTC. My results...
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Essays in Applied Economics
Travova, Ekaterina ; Menzel, Andreas (advisor) ; Cingl, Lubomír (referee) ; Ananyev, Maxim (referee)
The first chapter investigates the use of high-powered incentives for civil servants in the public sector by analyzing possible manipulations of drugs seized by Russian police. First, using a bunching estimator, I document a significant excess mass of heroin cases above the punishment threshold. Next, combining the bunching with an event study framework, I study the incentives for police officers to manipulate, and find evidence consistent with the motivation arising from officers' performance evaluations. Further negative consequences of inappropriate incentives are inequality in the enforcement of law and prolonged sentences for offenders. The second chapter investigates the influence of the Orthodox Church network in Post- Soviet Russia on individual political preferences and election results. I use the numbers of monks and nuns from Orthodox monasteries operated in the Russian Empire before the Revolution as historical religious markers to construct a Bartik-style instrument (1991). I find that a denser Church network increases the average local approval rating for the current president and the share of votes cast for the government candidate in presiden- tial elections. Further analysis of mechanisms shows that, today, the extending Church network is increasingly less able to attract people to attend...
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The different economic effects of the Covid-19 crisis on women and men in the Czech Republic
Menzel, Andreas ; Miotto, Martina
Women are very likely economically and socially affected harder by the Covid-19 crisis for at least three reasons. They are disproportionally employed in sectors affected harder by Covid-19 related lock-downs (tourism, hospitality, retail, services). They are likely to shoulder more of the additional child-care needs due to the closing of schools and child-care facilities. They are more likely to be victims of domestic violence, with many indicators pointing towards an increase in domestic violence due to the lock-down.
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Menstrual health, worker productivity and well-being among female Bangladeshi garment workers
Czura, K. ; Menzel, Andreas ; Miotto, Martina
We conducted a randomised controlled trial (RCT) on a sample of 1,000 female garment workers in three factories in Bangladesh, offering access to free sanitary pads at work to 500 of the workers. We cross-randomised participation in information sessions for hygienic menstrual health care implemented by an experienced local NGO, and we vary the salience of commonly perceived taboos in the pad collection process. We find effects of the free pads and information sessions on self-reported pad use, but not of the taboo variations. We find effects on absenteeism and adherence to traditional restrictive and health-adverse taboos surrounding menstruation, but not on worker turnover or self-reported well-being at work.
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