| 1. |
- Tran, K. B., et al.
(författare)
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The global burden of cancer attributable to risk factors, 2010-19: a systematic analysis for the Global Burden of Disease Study 2019
- 2022
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Ingår i: Lancet. - 0140-6736. ; 400:10352, s. 563-591
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Tidskriftsartikel (refereegranskat)abstract
- Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.
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| 2. |
- Bryazka, D., et al.
(författare)
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Population-level risks of alcohol consumption by amount, geography, age, sex, and year: a systematic analysis for the Global Burden of Disease Study 2020
- 2022
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Ingår i: Lancet. - 0140-6736. ; 400:10347, s. 185-235
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Tidskriftsartikel (refereegranskat)abstract
- Background The health risks associated with moderate alcohol consumption continue to be debated. Small amounts of alcohol might lower the risk of some health outcomes but increase the risk of others, suggesting that the overall risk depends, in part, on background disease rates, which vary by region, age, sex, and year. Methods For this analysis, we constructed burden-weighted dose-response relative risk curves across 22 health outcomes to estimate the theoretical minimum risk exposure level (TMREL) and non-drinker equivalence (NDE), the consumption level at which the health risk is equivalent to that of a non-drinker, using disease rates from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2020 for 21 regions, including 204 countries and territories, by 5-year age group, sex, and year for individuals aged 15-95 years and older from 1990 to 2020. Based on the NDE, we quantified the population consuming harmful amounts of alcohol. Findings The burden-weighted relative risk curves for alcohol use varied by region and age. Among individuals aged 15-39 years in 2020, the TMREL varied between 0 (95% uncertainty interval 0-0) and 0.603 (0.400-1.00) standard drinks per day, and the NDE varied between 0.002 (0-0) and 1.75 (0.698-4.30) standard drinks per day. Among individuals aged 40 years and older, the burden-weighted relative risk curve was J-shaped for all regions, with a 2020 TMREL that ranged from 0.114 (0-0.403) to 1.87 (0.500-3.30) standard drinks per day and an NDE that ranged between 0.193 (0-0.900) and 6.94 (3.40-8.30) standard drinks per day. Among individuals consuming harmful amounts of alcohol in 2020, 59.1% (54.3-65.4) were aged 15-39 years and 76.9% (7.0-81.3) were male. Interpretation There is strong evidence to support recommendations on alcohol consumption varying by age and location. Stronger interventions, particularly those tailored towards younger individuals, are needed to reduce the substantial global health loss attributable to alcohol. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd.
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| 3. |
- Burstein, R., et al.
(författare)
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Mapping 123 million neonatal, infant and child deaths between 2000 and 2017
- 2019
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 574:7778, s. 353-358
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Tidskriftsartikel (refereegranskat)abstract
- Since 2000, many countries have achieved considerable success in improving child survival, but localized progress remains unclear. To inform efforts towards United Nations Sustainable Development Goal 3.2—to end preventable child deaths by 2030—we need consistently estimated data at the subnational level regarding child mortality rates and trends. Here we quantified, for the period 2000–2017, the subnational variation in mortality rates and number of deaths of neonates, infants and children under 5 years of age within 99 low- and middle-income countries using a geostatistical survival model. We estimated that 32% of children under 5 in these countries lived in districts that had attained rates of 25 or fewer child deaths per 1,000 live births by 2017, and that 58% of child deaths between 2000 and 2017 in these countries could have been averted in the absence of geographical inequality. This study enables the identification of high-mortality clusters, patterns of progress and geographical inequalities to inform appropriate investments and implementations that will help to improve the health of all populations. © 2019, The Author(s).
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| 4. |
- Sheena, B. S., et al.
(författare)
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Global, regional, and national burden of hepatitis B, 1990-2019: a systematic analysis for the Global Burden of Disease Study 2019
- 2022
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Ingår i: Lancet Gastroenterology & Hepatology. - : Elsevier BV. - 2468-1253. ; 7:9, s. 796-829
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Tidskriftsartikel (refereegranskat)abstract
- Background Combating viral hepatitis is part of the UN Sustainable Development Goals (SDGs), and WHO has put forth hepatitis B elimination targets in its Global Health Sector Strategy on Viral Hepatitis (WHO-GHSS) and Interim Guidance for Country Validation of Viral Hepatitis Elimination (WHO Interim Guidance). We estimated the global, regional, and national prevalence of hepatitis B virus (HBV), as well as mortality and disability-adjusted life-years (DALYs) due to HBV, as part of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. This included estimates for 194 WHO member states, for which we compared our estimates to WHO elimination targets. Methods The primary data sources were population-based serosurveys, claims and hospital discharges, cancer registries, vital registration systems, and published case series. We estimated chronic HBV infection and the burden of HBV-related diseases, defined as an aggregate of cirrhosis due to hepatitis B, liver cancer due to hepatitis B, and acute hepatitis B. We used DisMod-MR 2.1, a Bayesian mixed-effects meta-regression tool, to estimate the prevalence of chronic HBV infection, cirrhosis, and aetiological proportions of cirrhosis. We used mortality-to-incidence ratios modelled with spatiotemporal Gaussian process regression to estimate the incidence of liver cancer. We used the Cause of Death Ensemble modelling (CODEm) model, a tool that selects models and covariates on the basis of out-ofsample performance, to estimate mortality due to cirrhosis, liver cancer, and acute hepatitis B. Findings In 2019, the estimated global, all-age prevalence of chronic HBV infection was 4 center dot 1% (95% uncertainty interval [UI] 3 center dot 7 to 4 center dot 5), corresponding to 316 million (284 to 351) infected people. There was a 31 center dot 3% (29 center dot 0 to 33 center dot 9) decline in all-age prevalence between 1990 and 2019, with a more marked decline of 76 center dot 8% (76 center dot 2 to 77 center dot 5) in prevalence in children younger than 5 years. HBV-related diseases resulted in 555 000 global deaths (487 000 to 630 000) in 2019. The number of HBV-related deaths increased between 1990 and 2019 (by 5 center dot 9% [-5 center dot 6 to 19 center dot 2]) and between 2015 and 2019 (by 2 center dot 9% [-5 center dot 9 to 11 center dot 3]). By contrast, all-age and age-standardised death rates due to HBV-related diseases decreased during these periods. We compared estimates for 2019 in 194 WHO locations to WHO-GHSS 2020 targets, and found that four countries achieved a 10% reduction in deaths, 15 countries achieved a 30% reduction in new cases, and 147 countries achieved a 1% prevalence in children younger than 5 years. As of 2019, 68 of 194 countries had already achieved the 2030 target proposed in WHO Interim Guidance of an all-age HBV-related death rate of four per 100 000. Interpretation The prevalence of chronic HBV infection declined over time, particularly in children younger than 5 years, since the introduction of hepatitis B vaccination. HBV-related death rates also decreased, but HBV-related death counts increased as a result of population growth, ageing, and cohort effects. By 2019, many countries had met the interim seroprevalence target for children younger than 5 years, but few countries had met the WHO-GHSS interim targets for deaths and new cases. Progress according to all indicators must be accelerated to meet 2030 targets, and there are marked disparities in burden and progress across the world. HBV interventions, such as vaccination, testing, and treatment, must be strategically supported and scaled up to achieve elimination.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Menden, MP, et al.
(författare)
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Community assessment to advance computational prediction of cancer drug combinations in a pharmacogenomic screen
- 2019
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1, s. 2674-
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Tidskriftsartikel (refereegranskat)abstract
- The effectiveness of most cancer targeted therapies is short-lived. Tumors often develop resistance that might be overcome with drug combinations. However, the number of possible combinations is vast, necessitating data-driven approaches to find optimal patient-specific treatments. Here we report AstraZeneca’s large drug combination dataset, consisting of 11,576 experiments from 910 combinations across 85 molecularly characterized cancer cell lines, and results of a DREAM Challenge to evaluate computational strategies for predicting synergistic drug pairs and biomarkers. 160 teams participated to provide a comprehensive methodological development and benchmarking. Winning methods incorporate prior knowledge of drug-target interactions. Synergy is predicted with an accuracy matching biological replicates for >60% of combinations. However, 20% of drug combinations are poorly predicted by all methods. Genomic rationale for synergy predictions are identified, including ADAM17 inhibitor antagonism when combined with PIK3CB/D inhibition contrasting to synergy when combined with other PI3K-pathway inhibitors in PIK3CA mutant cells.
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| 9. |
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| 11. |
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| 13. |
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| 14. |
- Keshmiri, F., et al.
(författare)
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Contextualization and validation of the interprofessional collaborator assessment rubric (ICAR) through simulation : Pilot investigation.
- 2016
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Ingår i: Medical journal of the Islamic Republic of Iran. - : Iran University of Medical Sciences. - 1016-1430 .- 2251-6840. ; 30, s. 742-749
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND:Simulation can be used for educating, evaluating and assessing psychometric properties of an instrument. The aim of this study was to contextualize and assess the validity and reliability of the Interprofessional Collaborative Assessment tool (ICAR) in an Iranian context using simulation.METHODS:In this descriptive study, contextualization of the ICAR was assessed through several steps. Firstly, validity assessment was approved through expert panels and Delphi rounds. Secondly, reliability assessment was done by arranging a simulation video and assessing reproducibility, test-retest (ICC), internal consistency (Cronbach's Alpha) and inter-rater reliability (Kappa).The participants included 26 experts, 27 students and 6 staff of the Standardized Simulation Office of Teheran University of Medical Sciences.RESULTS:Contextualization and validity of the ICAR were approved in an Iranian context. The reliability of the tool was computed to be 0.71 according to Cronbach´s Alpha. The test-retest was calculated to be 0.76.CONCLUSION:The Iranian ICAR can be a useful tool for evaluating interprofessional collaborative competencies. The development of the instrument through a simulation scenario has been a positive prospect for researchers.
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| 15. |
- Tavakol, M, et al.
(författare)
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Diagnostic Approach to the Patients with Suspected Primary Immunodeficiency
- 2020
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Ingår i: Endocrine, metabolic & immune disorders drug targets. - : Bentham Science Publishers Ltd.. - 2212-3873 .- 1871-5303. ; 20:2, s. 157-171
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Tidskriftsartikel (refereegranskat)abstract
- Primary immunodeficiency diseases (PIDs) are a group of more than 350 disorders affecting distinct components of the innate and adaptive immune systems. In this review, the classic and advanced stepwise approach towards the diagnosis of PIDs are simplified and explained in detail.Results:Susceptibility to recurrent infections is the main hallmark of almost all PIDs. However, noninfectious complications attributable to immune dysregulation presenting with lymphoproliferative and/or autoimmune disorders are not uncommon. Moreover, PIDs could be associated with misleading presentations including allergic manifestations, enteropathies, and malignancies.Conclusion:Timely diagnosis is the most essential element in improving outcome and reducing the morbidity and mortality in PIDs. This wouldn’t be possible unless the physicians keep the diagnosis of PID in mind and be sufficiently aware of the approach to these patients.
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| 16. |
- Alinejad, M., et al.
(författare)
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Lignin-based polyurethanes : Opportunities for bio-based foams, elastomers, coatings and adhesives
- 2019
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a widerange of properties for various applications and market segments. Utilizing lignin as a polyol presentsan opportunity to incorporate a currently underutilized renewable aromatic polymer into theseproducts. In this work, we will review the current state of technology for utilizing lignin as a polyolreplacement in different polyurethane products. This will include a discussion of lignin structure,diversity, and modification during chemical pulping and cellulosic biofuels processes, approachesfor lignin extraction, recovery, fractionation, and modification/functionalization. We will discussthe potential of incorporation of lignins into polyurethane products that include rigid and flexiblefoams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating ligninin polyurethane formulations, potential solutions and approaches that have been taken to resolvethose issues.
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| 17. |
- Bagheri, Z., et al.
(författare)
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Cross-cultural measurement invariance of the Quality of Life Enjoyment and Satisfaction Questionnaire-Short form across ten countries: the application of Bayesian approximate measurement invariance
- 2022
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Ingår i: Bmc Psychology. - : Springer Science and Business Media LLC. - 2050-7283. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q-LES-Q-SF) is the most frequently used generic quality of life (QOL) measure in many countries and cultures worldwide. However, no single study has been carried out to investigate whether this questionnaire performs similarly across diverse cultures/countries. Accordingly, this study aimed to assess the cross-cultural measurement invariance of the Q-LES-Q-SF across ten different countries. Methods: The Q-LES-Q-SF was administrated to a sample of 2822 university students from ten countries: Bangladesh, Brazil, Croatia, India, Nepal, Poland, Serbia, Turkey, the United Arab Emirates, and Vietnam. The Bayesian approximate measurement invariance approach was used to assess the measurement invariance of the Q-LES-Q-SF. Results: Approximate measurement invariance did not hold across the countries for the Q-LES-Q-SF, with only two out of 14 items being non-invariant; namely items related to doing household and leisure time activities. Conclusions: Our findings did not support the cross-cultural measurement invariance of the Q-LES-Q-SF; thus, considerable caution is warranted when comparing QOL scores across different countries with this measure. Item rewording and adaptation along with calibrating non-invariant items may narrow these differences and help researchers to create an invariant questionnaire for reliable and valid QOL comparisons across different countries.
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| 18. |
- Morra, Pierluigi
(författare)
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Modelling and control of turbulent and transitional flows
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dynamics of fluid motion can accurately be described by the Navier– Stokes equations. Manipulating these equations to reduce their complexity but preserving their main characteristics has always been a key research activity in the field of fluid mechanics. Effort has been made to provide high-fidelity models for wall-bounded turbulent flows or reduced-order models for applications such as drag reduction, lift enhancement, or noise suppression. Model order reduction has also been employed for studying the dynamics of the Navier-Stokes equations. In this PhD thesis, the emphasis is on providing computationally inexpensive methods for industrial applications.Numerical simulations are performed to tackle model order reduction for flow control of transitional boundary-layer flows for drag reduction. It is assumed that localized wall sensors and actuators are available, and that only the time signals accessible in experiments are provided. Thus, a method to include unknown high-dimensional input disturbances in a reduced-order model of a transitional boundary-layer flow is presented. The method is applied for the design of an optimal controller for drag reduction through delay of transition. Moreover, the role of the actuator is discussed and a comparison between realistic actuators and actuators computed using optimization methods is presented. Here, the emphasis is on the effectiveness of the actuators for the studied flow control cases.Numerical simulations are also performed to tackle high-fidelity modeling in wall-bounded turbulent flows. The accuracy of the resolvent analysis in predicting the most energetic flow structures in a wall-bounded turbulent flow is quantified for different temporal frequencies. A direct comparison between the predictions from the resolvent analysis and the flow structures identified in DNS data is presented. Moreover, the beneficial effects attained with the inclusion of the Reynolds-stresses via an eddy-viscosity model are clarified for flows with friction Reynolds number up to 1007.
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| 19. |
- Yada, S., et al.
(författare)
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Droplet leaping governs microstructured surface wetting
- 2019
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 15:46, s. 9528-9536
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Tidskriftsartikel (refereegranskat)abstract
- Microstructured surfaces that control the direction of liquid transport are not only ubiquitous in nature, but they are also central to technological processes such as fog/water harvesting, oil-water separation, and surface lubrication. However, a fundamental understanding of the initial wetting dynamics of liquids spreading on such surfaces is lacking. Here, we show that three regimes govern microstructured surface wetting on short time scales: spread, stick, and contact line leaping. The latter involves establishing a new contact line downstream of the wetting front as the liquid leaps over specific sections of the solid surface. Experimental and numerical investigations reveal how different regimes emerge in different flow directions during wetting of periodic asymmetrically microstructured surfaces. These insights improve our understanding of rapid wetting in droplet impact, splashing, and wetting of vibrating surfaces and may contribute to advances in designing structured surfaces for the mentioned applications.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Bafekry, A., et al.
(författare)
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Van der Waals heterostructure of graphene and germanane: tuning the ohmic contact by electrostatic gating and mechanical strain
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:37, s. 21196-21206
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Tidskriftsartikel (refereegranskat)abstract
- Recent exciting developments in synthesis and properties study of the Germanane (GeH) monolayer have inspired us to investigate the structural and electronic properties of the van der Waals GeH/Graphene (Gr) heterostructure by the first-principle approach. The stability of the GeH/Gr heterostructure is verified by calculating the phonon dispersion curves as well as by thermodynamic binding energy calculations. According to the band structure calculation, the GeH/Gr interface is n-type Ohmic. The effects of different interlayer distances and strains between the layers and the applied electric field on the interface have been investigated to gain insight into the van der Waals heterostructure modifications. An interlayer distance of 2.11 angstrom and compressive strain of 6% alter the contact from Ohmic to Schottky status, while the electric field can tune the GeH/Gr contact as p- or n-type, Ohmic, or Schottky. The average electrostatic potential of GeH/Gr and the Bader charge analysis have been used to explain the results obtained. Our theoretical study could provide a promising approach for improving the electronic performance of GeH/Gr-based nano-rectifiers.
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| 25. |
- Bagheri, B., et al.
(författare)
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Comparsion study of different simulation codes for positive streamers
- 2017
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Ingår i: Proceedings of the International Conference on Phenomena in Ionized Gases (ICPIG).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For streamer simulations a range of computational models have been developed by various groups for various purposes. These models differ in dimensionality (2D, 3D), model type (particle, fluid or hybrid approach and further differentiation), their numerical implementation, type of grid and its refinement, and their spatial/temporal discretization. The aim of the present study is to benchmark the results of different simulation codes for axisymmetric single positive streamers in air at 1 bar and 300 K using a fluid model.
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| 26. |
- Bagheri, Mehdi, et al.
(författare)
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Evaluation of Rock Mass Modulus by Ramamurthy Equivalent Media - A Case Study of Masjed Soleyman Cavern
- 2006
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Ingår i: Proceedings of the International Symposium on Dams in the Societies of the 21st Century, ICOLD-SPANCOLD. ; , s. 731-735
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Konferensbidrag (refereegranskat)abstract
- In situ rock mass modulus is one of the most important parameters for designing the underground excavations. Rock Mass modulus can be determined by rock massclassification, equivalent media approach or by performing of in-situ tests. Ramamurthyequation has been applied to the numerical code, Flac, to evaluate rock mass modulussurrounding Masjed Soleyman Power House Cavern. The results have been compared to those obtained from back analysis and equations based on rock mass classification. This comparison indicates that the rock mass modulus obtained from Ramamurthyequations is more reliable than those obtained from equations based on rock massclassification. Another advantage of the Ramamurthy equivalent media is the possibility of distinguishing the variations of modulus due to the excavating. It is suggested that by helping of a numerical code and Ramamurthy equivalent media the variation of moduluscan be observed during different stages of excavation.
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| 27. |
- Bagheri, Shervin, et al.
(författare)
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Matrix-free methods for the stability and control of boundary layers
- 2009
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Ingår i: AIAA Journal. - : American Institute of Aeronautics and Astronautics (AIAA). - 0001-1452 .- 1533-385X. ; 47:5, s. 1057-1068
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents matrix-free methods for the stability analysis and control design of high-dimensional systems arising from the discretized linearized Navier-Stokes equations. The methods are applied to the two-dimensional spatially developing Blasius boundary-layer. A critical step in the process of systematically investigating stability properties and designing feedback controllers is solving very large eigenvalue problems by storing only velocity fields at different times instead of large matrices. For stability analysis, where the entire dynamics of perturbations in space and time is of interest, iterative and adjoint-based optimization techniques are employed to compute the global eigenmodes and the optimal initial conditions. The latter are the initial conditions yielding the largest possible energy growth over a finite time interval. The leading global eigenmodes take the shape of Tollmien-Schlichting wavepackets located far downstream in streamwise direction, whereas the leading optimal disturbances are tilted structures located far upstream in the boundary layer. For control design on the other hand, the input-output behavior of the system is of interest and the snapshot-method is employed to compute balanced modes that correctly capture this behavior. The inputs are external disturbances and wall actuation and the outputs are sensors that extract wall shear stress. A low-dimensional model that capture the input-output behavior is constructed by projection onto balanced modes. The reduced-order model is then used to design a feedback control strategy such that the growth of disturbances are damped as they propagate downstream.
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| 28. |
- Bagheri, Shervin, et al.
(författare)
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Transition delay using control theory
- 2011
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Ingår i: Philosophical Transactions. Series A. - : The Royal Society. - 1364-503X .- 1471-2962. ; 369:1940, s. 1365-1381
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Tidskriftsartikel (refereegranskat)abstract
- This review gives an account of recent research efforts to use feedback control for the delay of laminar-turbulent transition in wall-bounded shear flows. The emphasis is on reducing the growth of small-amplitude disturbances in the boundary layer using numerical simulations and a linear control approach. Starting with the application of classical control theory to two-dimensional perturbations developing in spatially invariant flows, flow control based on control theory has progressed towards more realistic three-dimensional, spatially inhomogeneous flow configurations with localized sensing/actuation. The development of low-dimensional models of the Navier-Stokes equations has played a key role in this progress. Moreover, shortcomings and future challenges, as well as recent experimental advances in this multi-disciplinary field, are discussed.
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| 29. |
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| 30. |
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| 31. |
- Bagheri, Zahra M., et al.
(författare)
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An autonomous robot inspired by insect neurophysiology pursues moving features in natural environments
- 2017
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Ingår i: Journal of Neural Engineering. - : IOP Publishing. - 1741-2560 .- 1741-2552. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- Objective. Many computer vision and robotic applications require the implementation of robust and efficient target-tracking algorithms on a moving platform. However, deployment of a real-time system is challenging, even with the computational power of modern hardware. Lightweight and low-powered flying insects, such as dragonflies, track prey or conspecifics within cluttered natural environments, illustrating an efficient biological solution to the target-tracking problem. Approach. We used our recent recordings from 'small target motion detector' neurons in the dragonfly brain to inspire the development of a closed-loop target detection and tracking algorithm. This model exploits facilitation, a slow build-up of response to targets which move along long, continuous trajectories, as seen in our electrophysiological data. To test performance in real-world conditions, we implemented this model on a robotic platform that uses active pursuit strategies based on insect behaviour. Main results. Our robot performs robustly in closed-loop pursuit of targets, despite a range of challenging conditions used in our experiments; low contrast targets, heavily cluttered environments and the presence of distracters. We show that the facilitation stage boosts responses to targets moving along continuous trajectories, improving contrast sensitivity and detection of small moving targets against textured backgrounds. Moreover, the temporal properties of facilitation play a useful role in handling vibration of the robotic platform. We also show that the adoption of feed-forward models which predict the sensory consequences of self-movement can significantly improve target detection during saccadic movements. Significance. Our results provide insight into the neuronal mechanisms that underlie biological target detection and selection (from a moving platform), as well as highlight the effectiveness of our bio-inspired algorithm in an artificial visual system.
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| 32. |
- Bagheri, Zahra M, et al.
(författare)
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Performance of an insect-inspired target tracker in natural conditions
- 2017
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Ingår i: Bioinspiration and Biomimetics. - : IOP Publishing. - 1748-3182 .- 1748-3190. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Robust and efficient target-tracking algorithms embedded on moving platforms, are a requirement for many computer vision and robotic applications. However, deployment of a real-time system is challenging, even with the computational power of modern hardware. As inspiration, we look to biological lightweight solutions-lightweight and low-powered flying insects. For example, dragonflies pursue prey and mates within cluttered, natural environments, deftly selecting their target amidst swarms. In our laboratory, we study the physiology and morphology of dragonfly 'small target motion detector' neurons likely to underlie this pursuit behaviour. Here we describe our insect-inspired tracking model derived from these data and compare its efficacy and efficiency with state-of-the-art engineering models. For model inputs, we use both publicly available video sequences, as well as our own task-specific dataset (small targets embedded within natural scenes). In the context of the tracking problem, we describe differences in object statistics within the video sequences. For the general dataset, our model often locks on to small components of larger objects, tracking these moving features. When input imagery includes small moving targets, for which our highly nonlinear filtering is matched, the robustness outperforms state-of-the-art trackers. In all scenarios, our insect-inspired tracker runs at least twice the speed of the comparison algorithms.
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| 33. |
- Bagheri, Zahra M, et al.
(författare)
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Properties of neuronal facilitation that improve target tracking in natural pursuit simulations.
- 2015
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5662 .- 1742-5689. ; 12:108
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Tidskriftsartikel (refereegranskat)abstract
- Although flying insects have limited visual acuity (approx. 1°) and relatively small brains, many species pursue tiny targets against cluttered backgrounds with high success. Our previous computational model, inspired by electrophysiological recordings from insect 'small target motion detector' (STMD) neurons, did not account for several key properties described from the biological system. These include the recent observations of response 'facilitation' (a slow build-up of response to targets that move on long, continuous trajectories) and 'selective attention', a competitive mechanism that selects one target from alternatives. Here, we present an elaborated STMD-inspired model, implemented in a closed loop target-tracking system that uses an active saccadic gaze fixation strategy inspired by insect pursuit. We test this system against heavily cluttered natural scenes. Inclusion of facilitation not only substantially improves success for even short-duration pursuits, but it also enhances the ability to 'attend' to one target in the presence of distracters. Our model predicts optimal facilitation parameters that are static in space and dynamic in time, changing with respect to the amount of background clutter and the intended purpose of the pursuit. Our results provide insights into insect neurophysiology and show the potential of this algorithm for implementation in artificial visual systems and robotic applications.
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| 34. |
- Bagheri, Zahra, et al.
(författare)
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Performance assessment of an insect-inspired target tracking model in background clutter
- 2014
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Ingår i: 2014 13th International Conference on Control Automation Robotics and Vision, ICARCV 2014. - 9781479951994 ; , s. 822-826
-
Konferensbidrag (refereegranskat)abstract
- Biological visual systems provide excellent examples of robust target detection and tracking mechanisms capable of performing in a wide range of environments. Consequently, they have been sources of inspiration for many artificial vision algorithms. However, testing the robustness of target detection and tracking algorithms is a challenging task due to the diversity of environments for applications of these algorithms. Correlation between image quality metrics and model performance is one way to deal with this problem. Previously we developed a target detection model inspired by physiology of insects and implemented it in a closed loop target tracking algorithm. In the current paper we vary the kinetics of a salience-enhancing element of our algorithm and test its effect on the robustness of our model against different natural images to find the relationship between model performance and background clutter.
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| 35. |
- Cossu, Carlo, et al.
(författare)
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Secondary threshold amplitudes for sinuous streak breakdown
- 2011
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 23:7, s. 074103-
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear stability of laminar sinuously bent streaks is studied for the plane Couette flow at Re = 500 in a nearly minimal box and for the Blasius boundary layer at Re(delta)(*)=700. The initial perturbations are nonlinearly saturated streamwise streaks of amplitude A(U) perturbed with sinuous perturbations of amplitude A(W). The local boundary of the basin of attraction of the linearly stable laminar flow is computed by bisection and projected in the A(U) - A(W) plane providing a well defined critical curve. Different streak transition scenarios are seen to correspond to different regions of the critical curve. The modal instability of the streaks is responsible for transition for A(U) = 25%-27% for the considered flows, where sinuous perturbations of amplitude below A(W) approximate to 1%-2% are sufficient to counteract the streak viscous dissipation and induce breakdown. The critical amplitude of the sinuous perturbations increases when the streamwise streak amplitude is decreased. With secondary perturbations amplitude A(W) approximate to 4%, breakdown is induced on stable streamwise streaks with A(U) approximate to 13%, following the secondary transient growth scenario first examined by Schoppa and Hussain [J. Fluid Mech. 453, 57 (2002)]. A cross-over, where the critical amplitude of the sinuous perturbation becomes larger than the amplitude of streamwise streaks, is observed for streaks of small amplitude A(U) < 5%-6%. In this case, the transition is induced by an initial transient amplification of streamwise vortices, forced by the decaying sinuous mode. This is followed by the growth of the streaks and final breakdown. The shape of the critical A(U) - A(W) curve is very similar for Couette and boundary layer flows and seems to be relatively insensitive to the nature of the edge states on the basin boundary. The shape of this critical curve indicates that the stability of streamwise streaks should always be assessed in terms of both the streak amplitude and the amplitude of spanwise velocity perturbations.
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| 36. |
- Dadfar, Reza, 1978-
(författare)
-
Active Control and Reduced-Order Modeling of Transition in Shear Flows
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis direct numerical simulation is used to investigate the possibilityto delay the transition from laminar to turbulent in boundary layer flows.Furthermore, modal analysis is used to reveal the coherent structures in highdimensional dynamical systems arising in the flow problems.Among different transition scenarios, the classical transition scenario isanalysed. In this scenario, the laminar-turbulent transition occurs when Tollmien-Schlichting waves are triggered inside the boundary layer and grow exponentiallyas they move downstream in the domain. The aim is to attenuate the amplitudeof these waves using active control strategy based on a row of spatiallylocalised sensors and actuators distributed near the wall inside the boundarylayer. To avoid the high dimensional system arises from discretisation of theNavier Stokes equation, a reduced order model (ROM) based on EigensystemRealisation Algorithm (ERA) is obtained and a linear controller is designed.A plasma actuator is modelled and implemented as an external forcing on theflow. To account for the limitation of the plasma actuators and to further reducethe complexity of the controller several control strategies are examinedand compared. The outcomes reveal successful performance in mitigating theenergy of the disturbances inside the boundary layer.To extract coherent features of the wind turbine wakes, modal decompositiontechnique is employed where a large scale dynamical system is reduced toa fewer number of degrees of freedom. Two decomposition techniques are employed:proper orthogonal decomposition and dynamic mode decomposition.In the former procedure, the flow is decomposed into a set of uncorrelated structureswhich are rank according to their energy. In the latter, the eigenvaluesand eigenvectors of the underlying approximate linear operator is computedwhere each mode is associated with a specific frequency and growth rate. Theresults revealed the structures which are dynamically significant to the onsetof instability in the wind turbine wakes.
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| 37. |
- Dadfar, Reza, et al.
(författare)
-
Centralised Versus Decentralised Active Control of Boundary Layer Instabilities
- 2014
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Ingår i: Flow Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1386-6184 .- 1573-1987. ; 93:4, s. 537-553
-
Tidskriftsartikel (refereegranskat)abstract
- We use linear control theory to construct an output feedback controller for the attenuation of small-amplitude three-dimensional Tollmien-Schlichting (TS) wavepackets in a flat-plate boundary layer. A three-dimensional viscous, incompressible flow developing on a zero-pressure gradient boundary layer in a low Reynolds number environment is analyzed using direct numerical simulations. In this configuration, we distribute evenly in the spanwise direction up to 72 localised objects near the wall (18 disturbances sources, 18 actuators, 18 estimation sensors and 18 objective sensors). In a fully three-dimensional configuration, the interconnection between inputs and outputs becomes quickly unfeasible when the number of actuators and sensors increases in the spanwise direction. The objective of this work is to understand how an efficient controller may be designed by connecting only a subset of the actuators to sensors, thereby reducing the complexity of the controller, without comprising the efficiency. If n and m are the number of sensor-actuator pairs for the whole system and for a single control unit, respectively, then in a decentralised strategy, the number of interconnections deceases mn compared to a centralized strategy, which has n (2) interconnections. We find that using a semi-decentralized approach - where small control units consisting of 3 estimation sensors connected to 3 actuators are replicated 6 times along the spanwise direction - results only in a 11 % reduction of control performance. We explain how "wide" in the spanwise direction a control unit should be for a satisfactory control performance. Moreover, the control unit should be designed to account for the perturbations that are coming from the lateral sides (crosstalk) of the estimation sensors. We have also found that the influence of crosstalk is not as essential as the spreading effect.
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| 38. |
- Fabbiane, Nicolò, 1986-, et al.
(författare)
-
Adaptive and model-based control theory applied to convectively unstable flows
- 2014
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Ingår i: Applied Mechanics Review. - : ASME International. - 0003-6900 .- 1088-8535 .- 2379-0407. ; 66:6, s. 060801-
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Forskningsöversikt (refereegranskat)abstract
- Research on active control for the delay of laminar-turbulent transition in boundary layers has made a significant progress in the last two decades, but the employed strategies have been many and dispersed. Using one framework, we review model-based techniques, such as linear-quadratic regulators, and model-free adaptive methods, such as least-mean square filters. The former are supported by a elegant and powerful theoretical basis, whereas the latter may provide a more practical approach in the presence of complex disturbance envi- ronments, that are difficult to model. We compare the methods with a particu- lar focus on efficiency, practicability and robustness to uncertainties. Each step is exemplified on the one-dimensional linearized Kuramoto-Sivashinsky equa- tion, that shows many similarities with the initial linear stages of the transition process of the flow over a flat plate. Also, the source code for the examples are provided.
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| 39. |
- Fabbiane, Nicolò, et al.
(författare)
-
Adaptive control of finite-amplitude 3D disturbances in 2D boundary-layer flows
- 2015
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Ingår i: 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. - : TSFP-9.
-
Konferensbidrag (refereegranskat)abstract
- Friction drag is reduced in a two-dimensional (2D) boundary-layer flow by delaying the laminar-to-turbulence transition. A localised forcing in the wall region is used to attenuate the growing 3D disturbances that eventually trigger the turbulent regime farther downstream. An adaptive filtered-X least-mean-squared (FXLMS) algorithm is used to process the information of the flow gathered from two rows of surface hot-wires sensors and compute the forcing, performed by a row of plasma actuators. LES simulations are used to evaluate and analyze the performance of the described control strategy: in particular, a study on the streamwise position of the sensor and an actual transition delay scenario are presented.
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| 40. |
- Fabbiane, Nicolo, et al.
(författare)
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Energy efficiency and performance limitations of linear adaptive control for transition delay
- 2017
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 810, s. 60-81
-
Tidskriftsartikel (refereegranskat)abstract
- A reactive control technique with localised actuators and sensors is used to delay the transition to turbulence in a flat-plate boundary-layer flow. Through extensive direct numerical simulations, it is shown that an adaptive technique, which computes the control law on-line, is able to significantly reduce skin-friction drag in the presence of random three-dimensional perturbation fields with linear and weakly nonlinear behaviour. An energy budget analysis is performed in order to assess the net energy saving capabilities of the linear control approach. When considering a model of the dielectric-barrier-discharge (DBD) plasma actuator, the energy spent to create appropriate actuation force inside the boundary layer is of the same order as the energy gained from reducing skin-friction drag. With a model of an ideal actuator a net energy gain of three orders of magnitude can be achieved by efficiently damping small-amplitude disturbances upstream. The energy analysis in this study thus provides an upper limit for what we can expect in terms of drag-reduction efficiency for linear control of transition as a means for drag reduction.
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| 41. |
- Fabbiane, Nicolo, et al.
(författare)
-
Energy efficiency and performance limitations of linear adaptive control for transition delay
-
Ingår i: Journal of Fluid Mechanics. - 0022-1120 .- 1469-7645.
-
Tidskriftsartikel (refereegranskat)abstract
- Reactive-control techniques have been longly investigated to control local flow instabilities in boundary-layer flows – Tollmien-Schlichting waves – that would eventually cause laminar-to-turbulence transition. Several studies have been published about the control of two-dimensional (2D) disturbances supposing a transition delay. In this study, a three-dimensional (3D) disturbance environment is considered in a 2D zero-pressure-gradient boundary-layer flow. A control- law based on a multi-input-multi-output (MIMO) filtered-x least-mean-squares (fxLMS) adaptive algorithm is introduced and its performances are analysed for increasing disturbance amplitude. Transition delay is achieved by the investigated control set-up; moreover, an energy budget is conducted in order to asses the net energy saving capabilities of the investigated control approach. Ideal as well as real actuators models are considered, focusing in particular on dielectric-barrier-discharge (DBD) plasma actuators. To our knowledge, this is the first time that drag-reduction and energy-saving capabilities are studied for reactive transition-delay techniques.
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| 42. |
- Fabbiane, Nicolo, et al.
(författare)
-
On the role of adaptivity for robust laminar flow control
- 2015
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 767, s. R1-R12
-
Tidskriftsartikel (refereegranskat)abstract
- In boundary layer flows, one may reduce skin friction drag by delaying the onset of laminar-to-turbulent transition via the attenuation of small-amplitude Tollmien Schlichting (TS) waves In this work, we use numerical simulations and experiments to compare the robustness of adaptive and model-based techniques for reducing the growth of two-dimensional TS disturbances. In numerical simulations, the optimal linear quadratic Gaussian (LQG) regulator shows the best performance under the conditions it was designed for However, it is found that the performance deteriorates linearly with the drift of the Reynolds number from its nominal value. As a result, an order-of-magnitude loss of performance is observed when applying the computation-based I.QG controller in wind-tunnel experiments In contrast, it is shown that the adaptive filtered-X least-mean-squares (FXLMS) algorithm is able to maintain an essentially constant performance for significant deviations of the nominal values of the disturbance amplitude and Reynolds number.
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| 43. |
- Fabbiane, Nicolò
(författare)
-
Transition delay in boundary-layer flows via reactive control
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transition delay in boundary-layer flows is achieved via reactive control of flow instabilities, i.e. Tollmien-Schlichting (TS) waves. Adaptive and model-based control techniques are investigated by means of direct numerical simulations (DNS) and experiments. The action of actuators localised in the wall region is prescribed based on localised measurement of the disturbance field; in particular, plasma actuators and surface hot-wire sensors are considered.Performances and limitations of this control approach are evaluated both for two-dimensional (2D) and three-dimensional (3D) disturbance scenarios. The focus is on the robustness properties of the investigated control techniques; it is highlighted that static model-based control, such as the linear-quadratic- Gaussian (LQG) regulator, is very sensitive to model-inaccuracies. The reason for this behaviour is found in the feed-forward nature of the adopted sensor/actuator scheme; hence, a second, downstream sensor is introduced and actively used to recover robustness via an adaptive filtered-x least-mean-squares (fxLMS) algorithm.Furthermore, the model of the flow required by the control algorithm is reduced to a time delay. This technique, called delayed-x least-mean-squares (dxLMS) algorithm, allows taking a step towards a self-tuning controller; by introducing a third sensor it is possible to compute on-line the suitable time-delay model with no previous knowledge of the controlled system. This self-tuning approach is successfully tested by in-flight experiments on a motor-glider.Lastly, the transition delay capabilities of the investigated control con- figuration are confirmed in a complex disturbance environment. The flow is perturbed with random localised disturbances inside the boundary layer and the laminar-to-turbulence transition is delayed via a multi-input-multi-output (MIMO) version of the fxLMS algorithm. A positive theoretical net-energy- saving is observed for disturbance amplitudes up to 2% of the free-stream velocity at the actuation location, reaching values around 1000 times the input power for the lower disturbance amplitudes that have been investigated.
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| 44. |
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| 45. |
- Ilak, Milos, et al.
(författare)
-
Bifurcation and stability analysis of a jet in cross-flow : onset of global instability at a low velocity ratio
- 2012
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 696, s. 94-121
-
Tidskriftsartikel (refereegranskat)abstract
- We study direct numerical simulations (DNS) of a jet in cross-flow at low values of the jet-to-cross-flow velocity ratio R. We observe that, as the ratio R increases, the flow evolves from simple periodic vortex shedding (a limit cycle) to more complicated quasi-periodic behaviour, before finally becoming turbulent, as seen in the simulation of Bagheri et al. (J. Fluid. Mech., vol. 624, 2009b, pp. 33-44). The value of R at which the first bifurcation occurs for our numerical set-up is found, and shedding of hairpin vortices characteristic of a shear layer instability is observed. We focus on this first bifurcation, and find that a global linear stability analysis predicts well the frequency and initial growth rate of the nonlinear DNS at the critical value of R and that good qualitative predictions about the dynamics can still be made at slightly higher values of R where multiple unstable eigenmodes are present. In addition, we compute the adjoint global eigenmodes, and find that the overlap of the direct and the adjoint eigenmode, also known as a 'wavemaker', provides evidence that the source of the first instability lies in the shear layer just downstream of the jet.
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| 46. |
- Ilak, Milos, et al.
(författare)
-
Model Reduction of the Nonlinear Complex Ginzburg-Landau Equation
- 2010
-
Ingår i: SIAM Journal on Applied Dynamical Systems. - : Society for Industrial & Applied Mathematics (SIAM). - 1536-0040. ; 9:4, s. 1284-1302
-
Tidskriftsartikel (refereegranskat)abstract
- Reduced-order models of the nonlinear complex Ginzburg-Landau (CGL) equation are computed using a nonlinear generalization of balanced truncation. The method involves Galerkin projection of the nonlinear dynamics onto modes determined by balanced truncation of a linearized system and is compared to a standard method using projection onto proper orthogonal decomposition (POD) modes computed from snapshots of nonlinear simulations. It is found that the nonlinear reduced-order models obtained using modes from linear balanced truncation capture very well the transient dynamics of the CGL equation and outperform POD models; i.e., a higher number of POD modes than linear balancing modes is typically necessary in order to capture the dynamics of the original system correctly. In addition, we find that the performance of POD models compares well to that of balanced truncation models when the degree of nonnormality in the system, in this case determined by the streamwise extent of a disturbance amplification region, is lower. Our findings therefore indicate that the superior performance of balanced truncation compared to POD/Galerkin models in capturing the input/output dynamics of linear systems extends to the case of a nonlinear system, both for the case of significant transient growth, which represents a basic model of boundary layer instabilities, and for a limit cycle case that represents a basic model of vortex shedding past a cylinder.
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| 47. |
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| 48. |
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| 49. |
- Rowley, Clarence, et al.
(författare)
-
Reduced-order models for flow control : balanced models and Koopman modes
- 2010
-
Ingår i: Seventh IUTAM Symposium on Laminar-Turbulent Transition. - Dordrecht : Springer Netherlands. ; , s. 43-50
-
Konferensbidrag (refereegranskat)abstract
- This paper addresses recent developments in model-reduction techniques applicable to fluid flows The main goal is to obtain low-order models tractable enough to be used for analysis and design of feedback laws for flow control, while retaining the essential physics. We first give a brief overview of several model reduction techniques. including Proper Orthogonal Decomposition [3], balanced truncation [8, 9], and the related Eigensystem Realization Algorithm [5, 6], and discuss strengths and weaknesses of each approach We then describe a new method for analyzing nonlinear flows based on spectral analysis of the Koopman operator a linear operator defined for any nonlinear dynamical system We show that, for an example of a Jet in crossflow, the resulting Koopman modes decouple the dynamics at different timescales more effectively than POD modes, and capture the relevant frequencies more accurately than lineal stability analysis
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| 50. |
- Rowley, Clarence W., et al.
(författare)
-
Spectral analysis of nonlinear flows
- 2009
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Ingår i: Journal of Fluid Mechanics. - 0022-1120 .- 1469-7645. ; 641, s. 115-127
-
Tidskriftsartikel (refereegranskat)abstract
- We present a technique for describing the global behaviour of complex nonlinear flows by decomposing the flow into modes determined from spectral analysis of the Koopman operator, an infinite-dimensional linear operator associated with the full nonlinear system. These modes, referred to as Koopman modes, are associated with a particular observable, and may be determined directly from data (either numerical or experimental) using a variant of a standard Arnoldi method. They have an associated temporal frequency and growth rate and may be viewed as a nonlinear generalization of global eigenmodes of a linearized system. They provide an alternative to proper orthogonal decomposition, and in the case of periodic data the Koopman modes reduce to a discrete temporal Fourier transform. The Arnoldi method used for computations is identical to the dynamic mode decomposition recently proposed by Schmid & Sesterhenn (Sixty-First Annual Meeting of the APS Division of Fluid Dynamics, 2008), so dynamic mode decomposition can be thought of as an algorithm for finding Koopman modes. We illustrate the method on an example of a jet in crossflow, and show that the method captures the dominant frequencies and elucidates the associated spatial structures.
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