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Kong, Felix Honglim - One of the best experts on this subject based on the ideXlab platform.
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Phase-Indexed Iterative Learning Control for Bipedal Dynamic Walking
Faculty of Engineering and Information Technologies School of Aerospace Mechanical and Mechatronic Engineering, 2019Co-Authors: Kong, Felix HonglimAbstract:Iterative Learning Control is a control strategy to improve performance over repeated attempts at a certain task. By recording the signals generated from the previous attempt, a feedforward control signal can be generated to improve performance in the next attempt. The use of information from the previous iteration means that ILC is a feedback controller in the iteration domain. As with any feedback controller, there is the possibility of divergence, or instability, resulting in unbounded control signals. For nonlinear systems, convergence criteria for ILC systems are known for several specific cases, including the popular noncausal adjoint- and Newton-step update laws. In this thesis we develop a more general framework for certifying the convergence of nonlinear, noncausal ILC systems which includes, but is not limited to, the aforementioned specific cases. We do so using contraction theory, resulting in a convex convergence certificate, which is amenable to numerical computation. The other major topic in this thesis is the application of ILC to dynamic walking robots. Dynamic walking robots have the potential for versatile, efficient, and lifelike locomotion, but are often difficult to control, due to underactuation and undermodelling. ILC is known to be robust to undermodelling; however, ILC cannot be applied directly to dynamic walking robots, due to underactuation. We propose a variant of ILC suitable for dynamic walking robots that uses a phase Variable as an Index Variable instead of using time. ``Phase-Indexing'' ILC allows better control of dynamic walking robots, including learning to perform more prescribed motions more accurately, and in a more energy efficient way. Hardware experiments on a 2 degree of freedom compass-gait walking robot and simulation results on the compass-gait and 5-link dynamic walking robot verify the efficacy of the proposed method
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Phase-Indexed Iterative Learning Control for Bipedal Dynamic Walking
The Australian Centre for Field Robotics, 2019Co-Authors: Kong, Felix HonglimAbstract:Iterative Learning Control is a control strategy to improve performance over repeated attempts at a certain task. By recording the signals generated from the previous attempt, a feedforward control signal can be generated to improve performance in the next attempt. The use of information from the previous iteration means that ILC is a feedback controller in the iteration domain. As with any feedback controller, there is the possibility of divergence, or instability, resulting in unbounded control signals. For nonlinear systems, convergence criteria for ILC systems are known for several specific cases, including the popular noncausal adjoint- and Newton-step update laws. In this thesis we develop a more general framework for certifying the convergence of nonlinear, noncausal ILC systems which includes, but is not limited to, the aforementioned specific cases. We do so using contraction theory, resulting in a convex convergence certificate, which is amenable to numerical computation. The other major topic in this thesis is the application of ILC to dynamic walking robots. Dynamic walking robots have the potential for versatile, efficient, and lifelike locomotion, but are often difficult to control, due to underactuation and undermodelling. ILC is known to be robust to undermodelling; however, ILC cannot be applied directly to dynamic walking robots, due to underactuation. We propose a variant of ILC suitable for dynamic walking robots that uses a phase Variable as an Index Variable instead of using time. ``Phase-Indexing'' ILC allows better control of dynamic walking robots, including learning to perform more prescribed motions more accurately, and in a more energy efficient way. Hardware experiments on a 2 degree of freedom compass-gait walking robot and simulation results on the compass-gait and 5-link dynamic walking robot verify the efficacy of the proposed method.Access is restricted to staff and students of the University of Sydney . UniKey credentials are required. Non university access may be obtained by visiting the University of Sydney Library
Sayaka Nakamura - One of the best experts on this subject based on the ideXlab platform.
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Title: Reciprocity in the Formation of Intergenerational Coresidence Reciprocity in the Formation of Intergenerational Coresidence
2020Co-Authors: Meliyanni Johar, Shiko Maruyama, Sayaka NakamuraAbstract:Abstract Children play a key role in supporting elderly parents, and the literature has consistently found reciprocity whereby parents compensate their children for providing care and attention. To understand how the mode of compensation is related to the characteristics of parents and children, we studied the determinants of transitions to parent-child coresidence in Japan. The results conformed to the hypothesis that the mode of reciprocity depends on the costs and benefits of coresidence for each family member. Parental assets and care needs were associated with coresidence. Additionally, transitions to coresidence with married parents were characterized by young, unmarried children and the presence of parental housing assets, whereas transitions to coresidence with widowed mothers were characterized by mothers' non-housing assets. Keywords: transition analysis, latent class model, informal care, parent-child coresidence, aged care. JEL codes: I10, J14. 2 In aging societies, care and attention provided by adult children remains an important source of support in old age. Although the demand for aged care in general is growing at an unprecedented rate, in the early 2000s, approximately 80% of the hours of care were provided informally, with children providing 41% of all informal care in the US, 43% in the UK, and 60% in Japan Non-monetary time-related services may be another channel of transfers; in particular, parents can reward children by providing childcare for grandchildren (Kim 2004; To advance the literature, we explored how the mode of compensation is related to the characteristics of parents and children. To our knowledge, no study has examined the conditions for intergenerational coresidence for elderly parents in different health and economic situations or examined how widowhood and parental health alter the reciprocal nature of intergenerational coresidence. Detailed knowledge about the nature of reciprocity between elderly parents and adult children could have considerable policy implications in relation to public support for frail or disabled elderly parents and their families. To better understand how the mode of compensation is related to the characteristics of elderly parents and their children, we investigated the determinants of parent-child coresidence in Japan. We focused on intergenerational coresidence -a comprehensive form of hands-on care and support for elderly parents with a long-term commitment (Konrad et al. 2002; Kureishi and Wakabayashi 2009; Pezzin and Schone 1999; we investigated the determinants of the transition to coresidence by elderly Japanese parents and their children, building on demographic and sociological studies that focus on transitions in the living arrangements of the elderly (Brandon 2012; Brown et al. 2002; Dostie and Léger 2005; Our definition of "the transition to coresidence" included all three possible cases: children moving in with parents, parents moving in with children, and both children and parents moving to begin living together. We did not distinguish among them because in 2 Approximately 18% and 14% were cared for primarily by a coresident child and a coresident child's spouse, respectively, whereas 25% were cared for primarily by a coresident spouse. Our main findings are as follows. First, our results are consistent with the widely documented reciprocity in intergenerational coresidence. On the one hand, the transition to coresidence is often associated with parents' health deterioration and the loss of a spouse, confirming that coresidence is motivated by parental care needs. On the other hand, our estimates underscore the relevance of the costs and benefits of coresidence to children. On average, coresidence is more likely to start when a child is young and unmarried, lives nearby, and has small children and when a parent owns a house and possesses assets other than the house. Second, families engage in two distinct modes of reciprocity. The majority of families tend to start coresidence that involves young unmarried children and married parents. In this type of family, the main mode of intergenerational compensation 7 appears to be housing assets. The other type of family tends to start coresidence that involves a widowed parent, typically a widowed mother. This type of family has a higher tendency to start coresidence, and the primary mode of transfer is non-house wealth. For the parents of this group, wealth accumulation is important for safeguarding old age support. Overall, our results are consistent with the hypothesis that the mode of reciprocity depends on the costs and benefits of coresidence to each family member. Data The data were derived from the NUJLSOA, a nationally representative survey of Japanese aged 65 and over. The survey was designed primarily to investigate the health status of the Japanese elderly and changes in health status over time and to provide data for each wave so that it remained representative of the population in each wave. In the first wave, the sample response rate was 74.6%, and the data set had 4,997 respondents. Wave 2 consisted of 4,623 observations. Of 4,997 respondents in Wave 1, 327 (6.5%) died by the next wave, 946 (18.9%) were lost, and 3,724 (74.5%) were interviewed again in Wave 2. Added to Wave 2 were 899 observations in the additional cohorts. The attrition rate became slightly higher in later waves due to the older sample. Waves 3 and 4 had 4,507 and 3,414 respondents, respectively. 4 For details of the NUJLSOA, see http://www.usc.edu/dept/gero/CBPH/nujlsoa/. 8 [ From the states "living alone" and "spouse only," the most common transitional change 5 The coresidence rate in Japan is also declining in the longer term. [ The NUJLSOA asked elderly parents who began coresidence with a child within the previous two years the reasons for the coresidence, which is the main focus of this study. The question had multiple-choice responses, and parents could indicate more than one reason. The results reported in Specifically, compared to fathers, mothers were less likely to answer "It's what I want" and "To financially support my child," but they were more likely to answer "Being with my child supports me mentally" and "My spouse passed away." Second, 10 [ Our population of interest was elderly individuals aged 65 years and older with at least one surviving child. We used three comparison periods : 1999/2001, 2001/2003, and 2003/2006. Our population consisted of elderly parents who completed two consecutive surveys and had at least one surviving child in both surveys. 6 The definition of a child included biological, step-, and adopted children, but not childrenin-law. This was because we did not have information on widowed children-in-law unless they lived with their parents-in-law and because the parental relationship with children-in-law is different in many aspects from the relationship with one's own children (Hanaoka and Norton 2008). Furthermore, because our focus was on the transition to coresidence, we required that an elderly parent did not live with any child or child-in-law in the base year. We also restricted the sample to elderly parents who had no surviving parent throughout the period to avoid the complications of elderly parents who were also in the position of being a "child." In addition, a few elderly parents who lived with someone other than a spouse, such as siblings, grandchildren (but not children), and other relatives, were excluded. We also excluded observations of those in a hospital or jail at any time during the period or those in a nursing home during the base year. Nursing homes are growing in Japan as in other developed countries, but 6 Hence, people who died before the second interview were not included in our analysis. This exclusion is a potential source of selection bias, particularly given that 11 the number of users in our data period was small. In our data, we observed the transition to a nursing home for less than 0.5% of elderly parents between two consecutive surveys. Those with critical missing values or inconsistent answers and those labeled by interviewers as "unreliable" respondents were also excluded. We conducted the analysis at two levels, the child level and the family level, as explained in the next section. For the family-level model, imposing the above restrictions led to a final sample of 3,513 elderly parent periods. In the child-level model, the sample was expanded due to multiple-child families. For example, a family with three children would have one observation in the family-level model in a given period and three observations in the child-level model. The final sample size was 9,140 parent-period-child observations based on 2,841 family-period observations. The number of family-period observations in the child-level analysis was smaller than that in the family-level analysis because detailed information about every child was sometimes not available, and a small number of parents coresided with multiple children. We verified that our findings were robust with respect to this sample restriction. [ Our dependent Variable was a binary Variable for the transition of an elderly parent to coresidence between consecutive surveys. In the child-level analysis, C_CoresNext was a binary Variable for starting coresidence by the next period with a particular child. In the family-level analysis, CoresNext was a binary Variable for starting coresidence by the next period with at least one child in the family. Two sets of Variables, parent and child characteristics, were used in the following analysis and are defined in [ The parent characteristics included shock, health status, and socio-economic Variables. The shock Variables were dummy Variables constructed to capture major negative events and health deterioration between two consecutive waves. These Variables included the loss of a spouse, adverse health shocks in physical ability and in the ability to perform the activities of daily life (ADL), and deterioration in spousal ability to care for others. All explanatory Variables except the shock Variables were defined in terms of the base years. For parental health measures in the base year, we considered the ability to perform a series of activities. We constructed two indices, one for physical ability and another for the ability to perform ADL. Each Index was constructed as an average of values between 0 and 10 that were assigned to individual tasks based on the level of difficulty. Each Index was valued at 0 if all tasks could be performed without difficulty 7 This figure may be biased if the re-contact rate was significantly lower for those who moved. However, even using our most conservative estimates, the vast majority of parents (75-80%) who started coresidence did not move and accommodated children. 13 and at 10 if none of them was possible. 8 We also included an Index Variable for subjective health. Although mental health and cognitive impairments were also likely determinants of coresidence, it was difficult to incorporate them because our data were self-reported. Individuals with severe impairments in mental health or cognitive ability were likely omitted from our sample because it would have been difficult for them to participate in the survey and because we excluded individuals reported as "unreliable" by the interviewers. Nevertheless, the effects of mental health and cognitive ability were captured to some degree by our measures of ADL and subjective health (Dodge et al. 2005; Pinquart 2001 ). All health Variables were defined such that they took smaller values when the parent was healthier and physically stronger. [ Parental demographic and economic characteristics may have affected coresidence because these characteristics indicate the degree of economic independence and support available from non-child sources. They may also have reflected the resources available to children. With regard to demographics, one of the most relevant Variables was the presence of a spouse. Of the sampled elderly parents, 74.3% lived 8 Physical activities used to construct the Index included (1) walking 200 or 300 meters; (2) climbing 10 stairs without resting; (3) standing for two hours; (4) continuing to sit for two hours; (5) squatting and kneeling; (6) raising hands above head; (7) extending arms out in front; (8) grasping with fingers or using fingers easily; and (9) lifting a heavy load of 10 kg. ADL included (1) taking a bath/shower; (2) dressing; (3) eating; (4) standing up from a bed or chair and sitting down; (5) walking around the house; (6) going outside; and (7) going to the bathroom. 14 with a spouse, and 5.4% of these married parents lost a spouse by the following wave In Japanese tradition, the eldest son's family is the main family that succeeds the family headship and is responsible for the family's continuation. According to the format of the survey question, this eldest-son dummy Variable was defined as whether the parent, or the spouse if the parent was a mother, was an eldest son. For economic Variables, we included the current working status, the primary career occupation, and wealth. Given the limited information on wealth from the NUJLSOA, we used a dummy Variable of house ownership. For those who owned a house, we estimated the value of the house using information on the land area of the house owned by the parent. 9 Regarding other asset components, we constructed a dummy Variable that indicated the possession of substantial non-house assets because the limited information did not allow us to compute an accurate wealth value. This Variable covered real estate assets other than the 9 Because this land area information was available for Wave 2 and after, the land area The NUJLSOA provided child information regardless of whether a child lived with the parent. We included children's age, family structure, years of education, geographical proximity to parents (whether living in the same municipality), health, and coresidence status with parents-in-law. average, all shocks were observed more frequently for parents who started coresidence. These parents also tended to be older and have less education. In addition, Empirical Strategy We conducted two econometric analyses. First, we estimated a conditional logit model at the child level utilizing the characteristic Variables of each child. Second, we conducted a family-level analysis to study the coresidence decision of families. In particular, we estimated a finite mixture binary logit model to incorporate unobserved family heterogeneity and to address potential bias from irregular time intervals and attrition over time. Although we do not report the results here, a standard binary logit model without finite mixture components was also estimated at the family level, and the results were consistent with the other models. Conditional Logit Model New coresidence begins when a family reaches the decision to coreside according to latent family bargaining or an authoritative family member. To analyze this coresidence transition at the parent-child level, we denoted the transition to coresidence of parent i and child k between two observation periods by an indicator function, , where N was the total number of families in the sample and i K was the number of children, which varied by family. Each child represented an alternative to the parent. The parent could also choose to live independently of children ("outside option"). The size of the choice set for family i, therefore, was Assume that ik y is generated by the latent construct, * ik y , specified as where ik X is a vector that includes (1) family i 's characteristics that are constant across children within a family, such as the parent's age and family wealth, and The logit model arises when ik ε is assumed to follow a type I extreme value distribution independently, conditional on ik X . The probability that child k in family i begins coresidence is given by Notice that (2) is conditional on sibling size, i K . In other words, we assumed that sibling size was given, and we abstracted away from a family's fertility decision. Although it is possible that parents make fertility decisions expecting a child to provide future informal care, we expected that bias due to such behavior was less of an issue because we focused on the transition to coresidence. Finite Mixture Binary Logit Model (Family Level) Next, we studied the transition to coresidence at the family level. In this analysis, the child information was aggregated to the family level (e.g., the children's average age and years of education). Although the above conditional logit model at the child level provided useful insights on the characteristics of individual children that influence the transition to coresidence, the family-level analysis had several advantages over the child-level analysis. First, the restriction on the substitution pattern among alternatives 18 imposed in the child-level logit model was no longer necessary in the family-level analysis. This restrictive property, known as the Independence of Irrelevant Alternatives (IIA), may not be appropriate given the interdependency of siblings' location decisions (Maruyama and Johar 2013). Second, we could include elderly parents who started to live with more than one child in the family-level analysis. Third, families in which detailed information regarding individual children was missing were included in the family-level analysis. For these reasons, the estimation of the family-level model provided an opportunity to examine the robustness of our results. Instead of a standard binary logit model at the family level, we estimated a Heckman and Singer (1984)-type finite mixture logit model for the following two reasons. First, by non-parametrically incorporating unobservable family-level heterogeneity, this model allowed us to gain insights into the heterogeneity of families without imposing a priori sub-grouping. Second, the model reduced potential bias due to unobserved heterogeneity, which may occur even when unobserved heterogeneity is not correlated with any regressors. This potential bias is due to the sample selection that arises from attrition. Consider families with unobserved lower tendencies of coresidence. In our framework, all families lived independently of children in the base year, and families with a low tendency to coreside appeared in the data more often in later periods than did families with higher coresidence tendencies because the latter were more likely to begin coresidence and thus drop out of the sample in earlier periods. In a fairly general setting, the neglect of such unobserved heterogeneity may lead to an 19 underestimation of the coefficients (Cameron and Trivedi 2005, pp. 617-618). 10 By explicitly incorporating the unobserved heterogeneity, the finite mixture model alleviated selection bias. Let an indicator Variable, , denote the transition to coresidence between wave years t and t+1 by parent i with any of his/her children (hence, the child subscript k is dropped). Recall that the NUJLSOA surveys were conducted in 1999, 2001, 2003, and 2006, with a longer interval between the last two waves. To adjust for the higher probability of new coresidence when survey intervals are longer, let I t denote the number of years between the current and the next waves. Denoting the one-year transition probability under a binary logistic distribution by , the individual likelihood function can be written as The first square bracket term represents the probability that coresidence begins in any year between the two waves. Note that if I t equals 1, this likelihood becomes the likelihood of a standard logit model with annual panel data. The estimates of β are interpreted as the effect of the covariates on the one-year transition probability. We now introduce a two-component mixture into the likelihood function. We assume two unobserved types, or latent classes of families, across which β may vary. For simplicity of presentation, assume that the types affect only the intercept term, such 10 The use of random and fixed effects models is the standard approach to overcome this bias. This approach, however, is not feasible in our framework because it requires the removal of a large number of observations that appear only once. . Introducing heterogeneity in other coefficient terms is a straightforward extension. 11 Results Conditional Logit: Full Sample Analysis The conditional logit results for the entire sample are shown in the first column of [ 12 This house effect may capture the physical disadvantages of rental properties over owned houses for beginning coresidence, such as restrictions on renovation and a low availability of rental properties in Japan that can accommodate large, multigenerational families. 13 The HouseFamily dummy indicated that the house was owned by a family member, but not by the parent or the spouse. Coresidence was more likely with this type of house than with a parent-owned house. Upon closer examination of the NUJLSOA, it was found that the majority of these houses, approximately 60%, were owned by a 12 Rented properties did not include assisted-living facilities because individuals living in these facilities were not included in our sample. 13 Another explanation for the low propensity of coresidence of those who lived in rented properties is attrition bias because these parents were more likely to move when they started coresidence with children. Because the re-contact rate was lower for those who mov
Álvarez Oquendo, Lina María - One of the best experts on this subject based on the ideXlab platform.
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Efecto de la información contable y de mercado sobre los precios de las acciones después de la adopción de las Normas Internacionales de Información Financiera en Colombia
'Wiley', 2021Co-Authors: Álvarez Oquendo, Lina MaríaAbstract:Este artículo examina el impacto de la aplicación de los Estándares Internacionales de Información Financiera (NIIF) en la calidad contable de la información de las empresas en la economía colombiana, respecto a su marco normativo local (COLGAAP); usando una muestra de 15 compañías que cotizan en Bolsa de Valores y durante los periodos 2010-2019. Se analiza la calidad contable desde 7 Variables independientes: El EBITDA, los Activos Totales, el Patrimonio, la Eficiencia, el ROE, el ROA y el índice bursátil COLCAP. Los hallazgos sugieren un mejoramiento de la calidad contable, evidenciado a través de varios factores: primero, una mejoría sustancial en la revelación de los Activos; segundo, la adopción de las NIIF mejora el reconocimiento de los ingresos y costos operativos, y esto se refleja en el aumento de la calidad del EBITDA; tercero, un mayor poder explicativo del patrimonio dado el enfoque al valor razonable de las normas internacionales; cuarto, las NIIF tuvieron un impacto mayor en las empresas con mayor capitalización bursátil lo que se vio reflejado en la significancia de la Variable Índice (COLCAP).This article examines the impact of the application of the International Financial Information Standards (IFRS) on the accounting quality of the information of companies in the Colombian economy, with respect to its local regulatory framework (COLGAAP); Using a sample of 15 companies listed on the Stock Exchange and during the periods 2010-2019. The accounting quality is analyzed from 7 independent Variables: EBITDA, Total Assets, Equity, Efficiency, ROE, ROA and the COLCAP stock Index. The findings suggest an improvement in accounting quality, evidenced by several factors: first, a substantial improvement in the disclosure of Assets; second, the adoption of IFRS improves the recognition of operating income and costs, and this is reflected in the increase in the quality of EBITDA; third, a greater explanatory power of equity given the approach to fair value of international standards; Fourth, IFRS had a greater impact on companies with the highest market capitalization, which was reflected in the significance of the Index Variable (COLCAP).Magíster en FinanzasMaestrí
Alias Radam - One of the best experts on this subject based on the ideXlab platform.
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some new estimates of shadow economy for 80 countries using pooled mean group estimator
International Journal of Business and Society, 2017Co-Authors: Yanling Tan, Muzafar Shah Habibullah, Shivee Ranjanee Kaliappan, Alias RadamAbstract:The purpose of this study is to estimates the size of the shadow economy for 80 countries from nine regions spanning the period 1975-2012 based on Tanzi-type currency demand approach (CDA). This study contributes to the literature in three distinct ways. First, we augment CDA regression with a macroeconomic uncertainty Index (MUI). Second, the construction of the uncertainty Index is based on the dynamic factor model (DFM). Third, the pooled mean group (PMG) estimator allows in capturing the heterogeneity across countries in the short-run dynamics but imposing restrictions in the long-run parameters. The results confirm the existence of the longrun equilibrium relationship among the Variables examined. All coefficients show expected signs along with statistical significance. More importantly, the macroeconomic uncertainty Index Variable show positive relationship, suggesting that public tend to hold more currency in an uncertain macroeconomic environment. In addition, we observe that developing regions (ranging from 19.9% to 37.3%) exhibit relatively large size of the shadow economy. On the contrary, developed regions have a considerable smaller estimate (ranging from 13.7% to 19.0%) of the size of shadow economy. On average, the world estimate of the shadow economy as a percentage of GDP is about 23.1%. Keywords: Shadow Economy; Currency Demand; Macroeconomic Uncertainty; Pooled Mean Group.
Anis Amalina - One of the best experts on this subject based on the ideXlab platform.
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Some new estimates of shadow economy for 80 countries using pooled mean group estimator
International Journal of Business and Society Universiti Malaysia Sarawak, 2017Co-Authors: Anis AmalinaAbstract:The purpose of this study is to estimates the size of the shadow economy for 80 countries from nine regions spanning the period 1975-2012 based on Tanzi-type currency demand approach (CDA). This study contributes to the literature in three distinct ways. First, we augment CDA regression with a macroeconomic uncertainty Index (MUI). Second, the construction of the uncertainty Index is based on the dynamic factor model (DFM). Third, the pooled mean group (PMG) estimator allows in capturing the heterogeneity across countries in the short-run dynamics but imposing restrictions in the long-run parameters. The results confirm the existence of the longrun equilibrium relationship among the Variables examined. All coefficients show expected signs along with statistical significance. More importantly, the macroeconomic uncertainty Index Variable show positive relationship, suggesting that public tend to hold more currency in an uncertain macroeconomic environment. In addition, we observe that developing regions (ranging from 19.9% to 37.3%) exhibit relatively large size of the shadow economy. On the contrary, developed regions have a considerable smaller estimate (ranging from 13.7% to 19.0%) of the size of shadow economy. On average, the world estimate of the shadow economy as a percentage of GDP is about 23.1%
