Optimization along families of periodic and quasiperiodic orbits in dynamical systems with delay

This is the final version. Available on open access from Springer Verlag via the DOI in this recordThis paper generalizes a previously-conceived, continuation-based optimization technique for scalar objective functions on constraint manifolds to cases of periodic and quasiperiodic solutions of delay-differential equations. A Lagrange formalism is used to construct adjoint conditions that are linear and homogenous in the unknown Lagrange multipliers. As a consequence, it is shown how critical points on the constraint manifold can be found through several stages of continuation along a sequence of connected one-dimensional manifolds of solutions to increasing subsets of the necessary optimality conditions. Due to the presence of delayed and advanced arguments in the original and adjoint differential equations, care must be taken to determine the degree of smoothness of the Lagrange multipliers with respect to time. Such considerations naturally lead to a formulation in terms of multi-segment boundary-value problems (BVPs), including the possibility that the number of segments may change, or that their order may permute, during continuation. The methodology is illustrated using the software package coco on periodic orbits of both linear and nonlinear delay-differential equations, keeping in mind that closed-form solutions are not typically available even in the linear case. Finally, we demonstrate optimization on a family of quasiperiodic invariant tori in an example unfolding of a Hopf bifurcation with delay and parametric forcing. The quasiperiodic case is a further original contribution to the literature on optimization constrained by partial differential BVPs.Engineering and Physical Sciences Research Council (EPSRC)European Union Horizon 202

Equity in maternal health services use in Bangladesh: an analysis of social gradients, demographic and structural determinants, and major policy changes

Equity in health services use is related to utilizing equal treatment for equal health needs, irrespective of socio-economic status. Inequity in maternal health services in low- and middle-income countries has become a central public health policy and research issue in recent years to achieve universal health coverage by 2030. The dissertation’s main objective was to examine how equity in maternal health services evolved in Bangladesh and to assess the roles of the facility readiness and the national health program on equity. In the first paper of the dissertation, we assessed if the socioeconomic equity improved more in high facility readiness districts than in the rest of the country by using data from three rounds of household sample surveys linked to health facility surveys during 2001‒2016. Our analyses documented impressive improvement in the overall use of maternal health services, but the increase was not uniform for all the population groups. Though there has been a modest but significant reduction in the inequity in antenatal care and treatment for complications, both the services are still used disproportionately more by women from higher wealth quintiles. On the other hand, the inequity in facility delivery significantly increased by 135% during the study period. The nonpoor-poor gap in the high facility readiness districts increased faster than the low readiness districts, resulting in a more inequitable distribution of facility delivery. The second paper of the dissertation estimated the impact of sector-wide approach (SWAp) for the health sector in Bangladesh on equitable coverage of skilled birth attendance (SBA) using a novel, data-driven impact evaluation technique known as synthetic control analysis (SCA). We used data from a series of nationally representative surveys such as the Demographic and Health Survey (DHS) and the Multiple Indicator Cluster Survey (MICS), and widely accepted and used global sources such as the World Bank and the World Health Organization for Bangladesh and 16 potential control countries covering 1990–2017. The SCA optimization process selected three countries (Zimbabwe, Dominican Republic, and Haiti) to construct the synthetic control for Bangladesh (i.e., ‘Synthetic Bangladesh’) and resulted in a reasonable fitting for pre-SWAp trends for inequity in SBA use between Bangladesh and Synthetic Bangladesh. The inference procedures involving placebo test and bootstrap confidence intervals indicated a robust, statistically significant causal effect of the health SWAp on increasing SBA inequity in Bangladesh. To our knowledge, this is the first systematic investigation of the role of facility readiness on maternal health equity and statistical impact evaluation of health SWAp in Bangladesh. The empirical evidence and policy measures presented here provide a way forward to provide equitable care for safe delivery services. The policymakers and the program managers need to ensure the readiness of essential maternal health services at all levels in the health sector to provide equitable maternity care in Bangladesh.Doctor of Philosoph

Exploring the effects of health shocks on antipoverty interventions : experience of poor beneficiary households in Bangladesh

How and whether health shocks impact poverty reduction interventions remains a largely unexplored topic to which not much attention has been paid. This study explored whether and how health shocks affect anti-poverty interventions targeted to extremely poor households using data from 8 focus group discussions and 12 case studies. Those in extremely poor households mostly experienced episodes of chronic disease that incurred greater health-care costs, largely financed by the out-of-pocket payment system. The majority of those from poor households met health-care costs by selling their means of livelihood, borrowing cash, and marketing physical assets. This study argues that livelihood support alone is likely to be insufficient to reduce poverty. Health needs, subsequently, should be prioritized while designing an anti-poverty program

Resource Allocation in Uplink NOMA-IoT Networks: A Reinforcement-Learning Approach

Non-orthogonal multiple access (NOMA) exploits the potential of the power domain to enhance the connectivity for the Internet of Things (IoT). Due to time-varying communication channels, dynamic user clustering is a promising method to increase the throughput of NOMA-IoT networks. This paper develops an intelligent resource allocation scheme for uplink NOMA-IoT communications. To maximise the average performance of sum rates, this work designs an efficient optimization approach based on two reinforcement learning algorithms, namely deep reinforcement learning (DRL) and SARSA-learning. For light traffic, SARSA-learning is used to explore the safest resource allocation policy with low cost. For heavy traffic, DRL is used to handle traffic-introduced huge variables. With the aid of the considered approach, this work addresses two main problems of fair resource allocation in NOMA techniques: 1) allocating users dynamically and 2) balancing resource blocks and network traffic. We analytically demonstrate that the rate of convergence is inversely proportional to network sizes. Numerical results show that: 1) Compared with the optimal benchmark scheme, the proposed DRL and SARSA-learning algorithms have lower complexity with acceptable accuracy and 2) NOMA-enabled IoT networks outperform the conventional orthogonal multiple access based IoT networks in terms of system throughput

Nalidixic acid screening test in detection of decreased fluoroquinolone susceptibility in salmonella typhi isolated from blood

OBJECTIVE: To determine the validity of nalidixic acid screening test in the detection of high MICs of fluoroquinolone against Salmonella(S.) typhi isolated from blood and correlate zone diameters of ofloxacin with that of MIC value for nalidixic acid sensitive and resistant strains. DESIGN: Cross-sectional analytical study. PLACE AND DURATION OF STUDY: Clinical Microbiology Laboratory of the Aga Khan Hospital, Karachi from January 2002 to December 2003.METHODS: Two hundred S. typhi isolates from blood were included for nalidixic acid screening and ofloxacin susceptibility. Antibiotic susceptibilities for both the antibiotics were obtained by disc diffusion method whereas MICs were determined by standard agar dilution method as recommended by NCCLS guidelines. Sensitivity, specificity and correlation between both antimicrobial susceptibility methods were calculated and results expressed as scattergrams.RESULTS: The results broadly classify S. typhi isolates into nalidixic acid resistant strains with no zone of inhibition around 30 mug nalidixic acid disc and nalidixic acid sensitive strains with mean zone of inhibition of 24.9 mm. All S. typhi isolates with ofloxacin MIC of capital ZHE, Cyrillic 0.125 microg/ml were found to be nalidixic acid resistant (MIC capital ZHE, Cyrillic32 microg/ml) whereas the isolates with ofloxacin MIC 0.06 microg/ml were nalidixic acid sensitive (MIC 8 microg/ml). Screening for nalidixic acid resistance was found to be 100% sensitive and 97% specific in identifying S. typhi strains with reduced susceptibility to fluoroquinolone (MIC capital ZHE, Cyrillic 0.125 microg/ml).CONCLUSION: Nalidixic acid resistance as a screening method is proved to be significant in identifying S. typhi isolates with reduced susceptibility to fluoroquinolones. It is also suggested that inhibition zone of 25 mm around 5 microg ofloxacin disc is appropriate as a selection criterion to detect S. typhi isolates with reduced susceptibility to fluoroquinolones

Reducing Inequity in Urban Health: Have the Intra-urban Differentials in Reproductive Health Service Utilization and Child Nutritional Outcome Narrowed in Bangladesh?

Bangladesh is undergoing a rapid urbanization process. About one-third of the population of major cities in the country live in slums, which are areas that exhibit pronounced concentrations of factors that negatively affect health and nutrition. People living in slums face greater challenge to improve their health than other parts of the country, which fuels the growing intra-urban health inequities. Two rounds of the Bangladesh Urban Health Survey (UHS), conducted in 2013 and 2006, were designed to examine the reproductive health status and service utilization between slum and non-slum residents. We applied an adaptation of the difference-indifferences (DID) model to pooled data from the 2006 and 2013 UHS rounds to examine changes over time in intra-urban differences between slums and non-slums in key health outcomes and service utilization and to identify the factors associated with the reduction in intraurban gaps. In terms of change in intra-urban differentials during 2006–2013, DID regression analysis estimated that the gap between slums and non-slums for skilled birth attendant (SBA) during delivery significantly decreased. DID regression analysis also estimated that the gap between slums and non-slums for use of modern contraceptives among currently married women also narrowed significantly, and the gap reversed in favor of slums. However, the DID estimates indicate a small but not statistically significant reduction in the gap between slums and non-slums for child nutritional status. Results from extended DID regression model indicate that availability of community health workers in urban areas appears to have played a significant role in reducing the gap in SBA. The urban population in Bangladesh is expected to grow rapidly in the coming decades. Wide disparities between urban slums and non-slums can potentially push country performance off track during the post-2015 era, unless the specific health needs of the expanding slum communities are addressed. To our knowledge, this is the first systematic explanation and quantification of the role of various factors for improving intra-urban health equity in Bangladesh using nationally representative data. The findings provide a strong rationale for continuing and expanding community-based reproductive health services in urban areas by the NGOs with a focus on slum populations

Lithium-Ion Supercapacitor Using Vertically-Aligned Carbon Nanotubes From Direct Growth Technique, And Its Electrochemical Characteristics

This paper reports the fabrication of a lithium ion supercapacitor from vertically-aligned carbon nanotubes (VACNTs) directly grown on a conductive substrate (SUS 310S alloy), using alcohol catalytic chemical vapour deposition technique. CNTs direct growth technique on an electrically conducting foil simplifies the electrode assembly, thus reducing the fabrication process, because the foil can directly act as a current collector. With the VACNT direct growth technique, the supercapacitor electrode was easily prepared and assembled with a non-aqueous 1 M LiPF6 electrolyte. Experimental results show that CNTs (multi-walled type structures of good quality) were perpendicularly grown to the substrate. This device demonstrates a specific capacitance of up to 101 F g-1 (at a scan rate of 1 mVs-1), and a high-rate capability, up to a scan rate of 1000 mVs-1. The VACNT electrode electrochemical performance was also measured by galvanostatic charge-discharge and electrochemical impedance spectroscopy. The effect of free standing CNTs direct growth on the current collector makes insulating binder material unnecessary, thus producing better ion accessibilities to its surface. This also contributes to the good and reliable electrochemical supercapacitor performance

Matter collineations of Spacetime Homogeneous G\"odel-type Metrics

The spacetime homogeneous G\"odel-type spacetimes which have four classes of metrics are studied according to their matter collineations. The obtained results are compared with Killing vectors and Ricci collineations. It is found that these spacetimes have infinite number of matter collineations in degenerate case, i.e. det$(T_{ab}) = 0$, and do not admit proper matter collineations in non-degenerate case, i.e. det$(T_{ab}) \ne 0$. The degenerate case has the new constraints on the parameters $m$ and $w$ which characterize the causality features of the G\"odel-type spacetimes.Comment: 12 pages, LaTex, no figures, Class. Quantum.Grav.20 (2003) 216