Health monitoring of civil infrastructures by subspace system identification method: an overview

Structural health monitoring (SHM) is the main contributor of the future's smart city to deal with the need for safety, lower maintenance costs, and reliable condition assessment of structures. Among the algorithms used for SHM to identify the system parameters of structures, subspace system identification (SSI) is a reliable method in the time-domain that takes advantages of using extended observability matrices. Considerable numbers of studies have specifically concentrated on practical applications of SSI in recent years. To the best of author's knowledge, no study has been undertaken to review and investigate the application of SSI in the monitoring of civil engineering structures. This paper aims to review studies that have used the SSI algorithm for the damage identification and modal analysis of structures. The fundamental focus is on data-driven and covariance-driven SSI algorithms. In this review, we consider the subspace algorithm to resolve the problem of a real-world application for SHM. With regard to performance, a comparison between SSI and other methods is provided in order to investigate its advantages and disadvantages. The applied methods of SHM in civil engineering structures are categorized into three classes, from simple one-dimensional (1D) to very complex structures, and the detectability of the SSI for different damage scenarios are reported. Finally, the available software incorporating SSI as their system identification technique are investigated

A comparative study of the data-driven stochastic subspace methods for health monitoring of structures: a bridge case study

Subspace system identification is a class of methods to estimate state-space model based on low rank characteristic of a system. State-space-based subspace system identification is the dominant subspace method for system identification in health monitoring of the civil structures. The weight matrices of canonical variate analysis (CVA), principle component (PC), and unweighted principle component (UPC), are used in stochastic subspace identification (SSI) to reduce the complexity and optimize the prediction in identification process. However, researches on evaluation and comparison of weight matrices' performance are very limited. This study provides a detailed analysis on the effect of different weight matrices on robustness, accuracy, and computation efficiency. Two case studies including a lumped mass system and the response dataset of the Alamosa Canyon Bridge are used in this study. The results demonstrated that UPC algorithm had better performance compared to two other algorithms. It can be concluded that though dimensionality reduction in PC and CVA lingered the computation time, it has yielded an improved modal identification in PC

Comparative analysis of different weight matrices in subspace system identification for structural health monitoring

Subspace System Identification (SSI) is considered as one of the most reliable tools for identification of system parameters. Performance of a SSI scheme is considerably affected by the structure of the associated identification algorithm. Weight matrix is a variable in SSI that is used to reduce the dimensionality of the state-space equation. Generally one of the weight matrices of Principle Component (PC), Unweighted Principle Component (UPC) and Canonical Variate Analysis (CVA) are used in the structure of a SSI algorithm. An increasing number of studies in the field of structural health monitoring are using SSI for damage identification. However, studies that evaluate the performance of the weight matrices particularly in association with accuracy, noise resistance, and time complexity properties are very limited. In this study, the accuracy, noise-robustness, and time-efficiency of the weight matrices are compared using different qualitative and quantitative metrics. Three evaluation metrics of pole analysis, fit values and elapsed time are used in the assessment process. A numerical model of a mass-spring-dashpot and operational data is used in this research paper. It is observed that the principal components obtained using PC algorithms are more robust against noise uncertainty and give more stable results for the pole distribution. Furthermore, higher estimation accuracy is achieved using UPC algorithm. CVA had the worst performance for pole analysis and time efficiency analysis. The superior performance of the UPC algorithm in the elapsed time is attributed to using unit weight matrices. The obtained results demonstrated that the process of reducing dimensionality in CVA and PC has not enhanced the time efficiency but yield an improved modal identification in PC

Improving ‘lipid productivity’ in microalgae by bilateral enhancement of biomass and lipid contents: A review

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Microalgae have received widespread interest owing to their potential in biofuel production. However, economical microalgal biomass production is conditioned by enhancing the lipid accumulation without decreasing growth rate or by increasing both simultaneously. While extensive investigation has been performed on promoting the economic feasibility of microalgal-based biofuel production that aims to increase the productivity of microalgae species, only a handful of them deal with increasing lipid productivity (based on lipid contents and growth rate) in the feedstock production process. The purpose of this review is to provide an overview of the recent advances and novel approaches in promoting lipid productivity (depends on biomass and lipid contents) in feedstock production from strain selection to after-harvesting stages. The current study comprises two parts. In the first part, bilateral improving biomass/lipid production will be investigated in upstream measures, including strain selection, genetic engineering, and cultivation stages. In the second part, the enhancement of lipid productivity will be discussed in the downstream measure included in the harvesting and after-harvesting stages. An integrated approach involving the strategies for increasing lipid productivity in up-and down-stream measures can be a breakthrough approach that would promote the commercialization of market-driven microalgae-derived biofuel production

Interventions based on PRECEDE-PROCEED for promoting safety behaviors in Primary school boys

Introduction & Objective: Pedestrian injuries are a significant source of morbidity, mortality and disability among children. Prevention of these injuries is thus a major priority for public health and requires a comprehensive approach and educational strategies. The purpose of this study was designing and evaluation of an educational program, based on the PRECEED-PROCEED model for improvement of safety behavior in primary school boys. Materials & Methods: This study is a field trial carried out in 6th areas of Tehran in 2007. Participants (n=88) were 10 – 11 year old who followed by items measuring the PRECEED-PROCEED model before and after two months of intervention. The collected data were analyzed with T test, X2 and pair T test using SPSS software. Results: After participating in educational program, significant improvements were found in knowledge, attitude, behavior, enabling and reinforcing factors of the components of PRECEEDPROCEED model. Conclusion: The findings suggest the beneficial effects of educational intervention based on the PRECEDE-PROCEED model on improving the safety behavior. It can be recommended that health education plan be used on educational models

Why Iranian married women use withdrawal instead of oral contraceptives? A qualitative study from Iran

<p>Abstract</p> <p>Background</p> <p>Withdrawal as a method of birth control is still used in Iran. The aim of this study was to explore married women's perspectives and attitudes on withdrawal use instead of oral contraceptive (OC) in Tehran, Iran.</p> <p>Methods</p> <p>This was a qualitative study. Participants were 50 married women, not currently pregnant, not desiring pregnancy and who had been using withdrawal for contraception. Face-to face interviews were conducted to collect data. Content analysis was performed to analyze the data.</p> <p>Results</p> <p>Four major themes were extracted from the interviews: advantages, disadvantages, barriers for OC use, and husband-related factors. Advantages of withdrawal use were identified as: easy to use, convenient, ease of access, natural. Even those participants who had experienced unwanted pregnancy while using withdrawal, relied on withdrawal as their contraceptive method. Disadvantages of OC included concerns about side effects. Barriers related to use of OC included the need for medical advice, vaginal examination and daily use. Husband-related factors included: the husband wanted to be the primary decision maker on the number of children and that he preferred withdrawal.</p> <p>Conclusion</p> <p>Health providers should address misunderstandings that exist about OC and highlight the non-contraceptive health benefits of OC to balance the information provided for women. We suggest that not only women but also their spouses be advised in family planning programs.</p

The impact of a sleep hygiene intervention on sleep habits in children with attention deficit/hyperactivity disorder

Background Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental disorders of childhood. Up to 50 of these children suffer from at least one comorbid sleep disorder. Considering the deleterious effects of sleep problems on all aspects of children's life, this study was designed to investigate the impact of a sleep hygiene intervention on sleep habits in children with ADHD and comorbid sleep disorders. Materials and Methods This randomized controlled trial, was conducted on 62 children aged 7 to13 years with diagnosis of ADHD and comorbid sleep disorders. Children's Sleep Habits Questionnaire (CSHQ) was completed by children's mothers and then the participants allocated randomly into experimental (n=28) and control (n=28) groups. Mothers of the children in experimental group received a sleep hygiene educational intervention which was delivered through a training session and a booklet followed by two telephone calls and educational text messages. Participants in the control group received usual clinical care. The post-test was performed two months after intervention. Results 56 children (case and control groups) completed the survey (mean age 8.62 � 1.57 years). Data analysis showed that, compared with control children, experimental children had a significant- reduction in mean scores of Bedtime resistance (P < 0.05), Sleep onset delay (P < 0.05), Sleep duration (P < 0.05), Sleep anxiety (P < 0.05), Daytime sleepiness (P < 0.05) and total score of CSHQ (P < 0.05), after controlling pre-test. Conclusion The sleep hygiene intervention improved sleep problems in a sample of children with ADHD by parent report. The findings of this study support the design, implementation and evaluation of educational programs on good sleep-hygiene practices for children and adolescents

Fourth generation biofuel from genetically modified algal biomass: Challenges and future directions.

Genetic engineering applications in the field of biofuel are rapidly expanding due to their potential to boost biomass productivity while lowering its cost and enhancing its quality. Recently, fourth-generation biofuel (FGB), which is biofuel obtained from genetically modified (GM) algae biomass, has gained considerable attention from academic and industrial communities. However, replacing fossil resources with FGB is still beset with many challenges. Most notably, technical aspects of genetic modification operations need to be more fully articulated and elaborated. However, relatively little attention has been paid to GM algal biomass. There is a limited number of reviews on the progress and challenges faced in the algal genetics of FGB. Therefore, the present review aims to fill this gap in the literature by recapitulating the findings of recent studies and achievements on safe and efficient genetic manipulation in the production of FGB. Then, the essential issues and parameters related to genome editing in algal strains are highlighted. Finally, the main challenges to FGB pertaining to the diffusion risk and regulatory frameworks are addressed. This review concluded that the technical and biosafety aspects of FGB, as well as the complexity and diversity of the related regulations, legitimacy concerns, and health and environmental risks, are among the most important challenges that require a strong commitment at the national/international levels to reach a global consensus