87 research outputs found
Energy-based shape regulation of soft robots with unactuated dynamics dominated by elasticity
No full textThis paper proposes a model-based control design approach for a broad class of soft robots, having their elastic field dominating gravity in the unactuated coordinates. To this end, we consider finite-dimensional dynamic models obtained from approximations of the system's energy. Then, we propose a general control architecture that can stabilize soft robots based on potential energy shaping. We discuss three specializations of this general architecture: a PD with mixed feedback-feedforward gravity compensation, a PD with feedforward compensation, and a saturated version of the latter. We provide a physical interpretation of the controllers, and we illustrate their applicability through simulations.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Learning & Autonomous ControlTeam Azita Dabir
On the Role of Coupled Damping and Gyroscopic Forces in the Stability and Performance of Mechanical Systems
Get PDFDamping injection is a well-studied tool in nonlinear control theory to stabilize and shape the transient of mechanical systems. Interestingly, the injection of coupled damping yielding gyroscopic forces has received far less attention. This letter aims to fill this gap for gyroscopic forces that couple actuated and unactuated coordinates. First, we establish sufficient conditions for the stability of the closed loop. Then, we provide analytic results proving that injecting coupled damping may improve the closed-loop performance. We illustrate the results via the stabilization of three mechanical systems.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Learning & Autonomous ControlTeam Azita Dabir
Have transport costs contributed to the relative decline of sub-Saharan African exports? Some preliminary empirical evidence
Get PDFFrom the mid-1950s to 1990, sub-Saharan Africa's share of global exports fell from 3.1 to under 1.2 percent, a decline that implies associated export earning losses of about $65 billion annually. Previous studies show that foreign trade barriers do not account for this poor performance. Indeed, African exports enjoy OECD tariff preferences. In the sub-Saharan African countries, too high a proportion of foreign exchange earnings is paying for Africa's high export transport costs. The authors demonstrate that relatively high transportation costs - especially for processed products - often place African exporters at a serious competitive disadvantage. African countries must use a far larger share of their foreign exchange earnings to pay for international transport services than other developing countries do - and the relative importance of those payments has been increasing. Why are Africa's transport costs so high? Ill-advised policies on the part of some African governments seem to have played a role, as their cargo reservation policies produced high"rents"for lines that have been shielded from the effects of competition. The failure to maintain or improve port and transport infrastructure has also played a role.Rural Roads&Transport,Economic Theory&Research,Transport and Trade Logistics,Common Carriers Industry,Environmental Economics&Policies,Transport and Trade Logistics,Common Carriers Industry,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Environmental Economics&Policies,Economic Theory&Research
Type 1 diabetes and hyperthyroidism in a family with celiac disease after exposure to gluten: a rare case report
No full textAbstract Background Celiac disease (CD) is an autoimmune disorder related to the gluten and can be also associated with some other endocrine disorders such as type 1 diabetes and thyroid disease. Gluten exposure in CD may have especial role in developing other auto immune disorder. Case presentation We reported two familial cases with celiac disease who were on a gluten free diet (GFD) and hyperthyroidism and type 1 diabetes were appeared following a regular diet. Their autoimmune disorders were ameliorated after avoidance of dietary gluten. Conclusions These cases highlighted the role of gluten exposure in developing other autoimmune disorders associated with CD, especially in young patients whom they are not cooperative to keep GFD. We recommended to evaluate the organ specific antibodies for risk assessment in these patients
Incident indicators for freeway traffic flow models
Get PDFDeveloped in this paper is a traffic flow model parametrised to describe abnormal traffic behaviour. In large traffic networks, the immediate detection and categorisation of traffic incidents/accidents is of capital importance to avoid breakdowns, further accidents. First, this claims for traffic flow models capable to capture abnormal traffic condition like accidents. Second, by means of proper real-time estimation technique, observing accident related parameters, one may even categorize the severity of accidents. Hence, in this paper, we suggest to modify the nominal Aw-Rascle (AR) traffic model by a proper incident related parametrisation. The proposed Incident Traffic Flow (ITF) model is defined by introducing the incident parameters modifying the anticipation and the dynamic speed relaxation terms in the speed equation of the AR model. These modifications are proven to have physical meaning. Furthermore, the characteristic properties of the ITF model is discussed in the paper. A multi stage numerical scheme is suggested to discretise in space and time the resulting non-homogeneous system of PDEs. The resulting systems of ODE is then combined with receding horizon estimation methods to reconstruct the incident parameters. Finally, the viability of the suggested incident parametrisation is validated in a simulation environment.Team Azita Dabir
Public sector debt, fiscal deficits, and economic adjustment : a comparative study of six EMENA countries
Get PDFThe authors analyzed the experience of six countries (Algeria, Morocco, Pakistan, Portugal, Turkey, and Yugoslavia) and compared it with the experiences of Latin American countries. They conclude that some countries successfully absorbed the external shock of the 1980s by: (a) minimizing the effects of the external shock by combining external and domestic debt strategies; (b) adjusting their fiscal deficits; (c) experiencing a positive external shock; and (d) fostering growth by stimulating export growth and developing domestic financial markets. No single country fully implemented this strategy; those most successful in doing so were Morocco, Portugal, and Turkey. Their experience contrasts with that of some Latin American countries that experienced a similar external shock but failed to undertake fiscal adjustment and financed most of their deficit through money finance - thus experiencing high inflation levels and overburdening their private sector. In some respects, Yugoslavia had the same experience.Environmental Economics&Policies,Economic Theory&Research,Strategic Debt Management,Economic Stabilization,Public Sector Economics&Finance
Bi-level model predictive control for metro networks: Integration of timetables, passenger flows, and train speed profiles
No full textThis paper deals with the train scheduling problem for metro networks taking into account time-dependent passenger origin–destination demands and train speed profiles. The aim is to adjust train schedules online according to time-dependent passenger demands so that passenger satisfaction and operational costs are jointly optimized. An extended passenger absorption model that explicitly includes time-dependent passenger origin–destination demands is developed, where the term “absorption” refers to passengers boarding trains. Then, the passenger absorption model is extended to a bi-level framework, where passenger demands and rolling stock availability are considered at the higher level, and detailed timetables and train speed profiles are included at the lower level. A bi-level model predictive control (MPC) approach is developed for the integrated problem. The optimization problems of both levels of the bi-level MPC approach can be converted into mixed-integer linear programming (MILP) problems, which enables us to solve them with existing MILP solvers. We then show that the recursive feasibility of both the higher-level and the lower-level optimization problems can be guaranteed. In this way, we can achieve real-time train scheduling for the metro system. Numerical experiments, based on real-life data from the Beijing metro network, illustrate the effectiveness of the extended passenger absorption model and the proposed bi-level MPC approach.Team Bart De SchutterTeam Azita DabiriDelft Center for Systems and Contro
Timetable Scheduling for Passenger-Centric Urban Rail Networks: Model Predictive Control based on a Novel Absorption Model
No full textTimetable scheduling plays a key role in daily operations of urban rail transit systems, as it determines the quality of service provided to passengers. In order to develop efficient timetable scheduling methods, it is necessary to develop a proper model to integrate timetable-related and passenger-related factors in urban rail network efficiently. In this paper, a novel passenger absorption model for passenger- centric urban rail networks is established. The model explicitly integrates time-varying passenger origin-destination demands and the departure frequency of each line for real-time timetable scheduling. Then, a model predictive control (MPC) method for the timetable scheduling problem is proposed based on the developed model. The resulting MPC optimization problem can be formulated as a mixed-integer programming (MILP) problem, which can be solved efficiently by using the existing MILP solvers. The effectiveness of the absorption model and the corresponding MILP-based MPC approach is illustrated through the case study based on two Beijing subway lines. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Bart De SchutterTeam Azita DabiriDelft Center for Systems and Contro
Prevalence of osteoporosis and osteopenia in men and premenopausal women with celiac disease: a systematic review
No full textAbstract Background Celiac disease (CD) is known as a reason of metabolic osteopathy. Progression of non-invasive methods such as bone densitometry has shown that an important ratio of CD cases is faced with impaired bone mass and such cases are prone to bone fractures. Variety of low bone mineral density in CD is probably because of ignored confounding factors such as age, menopause, and drug. The aim of our study was to systematically review the osteoporosis and osteopenia incidences among premenopausal females and males with CD. Methods This systematic review was done based on preferred reporting items for systematic reviews (PRISMA) guidelines. PubMed and Scopus and Cochran databases were searched according to the relevant medical subject headings (MeSH) of CD and bone mineral density until 2018. Prevalence of osteopenia and osteoporosis were used as effect size for meta-analysis. Cochrane Q (p < 0.05) and I2 index were presented to reveal the heterogeneity. Results 54 eligible full text reviews were included and nineteen selected for data extraction. Eleven articles didn’t have our inclusion criteria and had ignored confounding factors like age and menopause, and we excluded; data extraction was done in eight studies. A total of 563 premenopausal women and men who were from, UK, Brazil, India, Hungary, and Poland were included. The pooled prevalence of osteoporosis was 14.4% [95%CI: 9–20.5%] (Cochrane Q = 7.889, p = 0.96, I2 = 49.29%), and osteopenia was 39.6% [31.1–48.8%] (Cochrane Q = 14.24, p = 0.07, I2 = 71.92%), respectively. Conclusion Our findings suggest that bone loss is more prevalent in celiac disease and can be associated with increased risk of fracture. However, but results are pooled prevalence and we need more case –control studies with more sample size and consideration of confounding factors
Towards establishing an automated selection framework for underwater image enhancement methods
No full textThe majority of computer vision architectures are developed based on the assumption of the availability of good quality data. However, this is a particularly hard requirement to achieve in underwater conditions. To address this limitation, plenty of underwater image enhancement methods have received considerable attention during the last decades, but due to the lack of a commonly accepted framework to systematically evaluate them and to determine the likely optimal one for a given image, their adoption in practice is hindered, since it is not clear which one can achieve the best results. In this paper, we propose a standardized selection framework to evaluate the quality of an underwater image and to estimate the most suitable image enhancement technique based on its impact on the image classification performance.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Bart De SchutterTeam Azita DabiriDelft Center for Systems and Contro
- …
