From local to global control

In this paper the authors study the problem of the existence of multiple local operating points in control systems. In particular, they consider a method of going from local to global control, i.e. given a number of local, linearized systems, from which global system do they come, and, can global controllers be determined in this case

Access Control Synthesis for Physical Spaces

Access-control requirements for physical spaces, like office buildings and airports, are best formulated from a global viewpoint in terms of system-wide requirements. For example, "there is an authorized path to exit the building from every room." In contrast, individual access-control components, such as doors and turnstiles, can only enforce local policies, specifying when the component may open. In practice, the gap between the system-wide, global requirements and the many local policies is bridged manually, which is tedious, error-prone, and scales poorly. We propose a framework to automatically synthesize local access control policies from a set of global requirements for physical spaces. Our framework consists of an expressive language to specify both global requirements and physical spaces, and an algorithm for synthesizing local, attribute-based policies from the global specification. We empirically demonstrate the framework's effectiveness on three substantial case studies. The studies demonstrate that access control synthesis is practical even for complex physical spaces, such as airports, with many interrelated security requirements

Leaderless Swarm Formation Control: From Global Specifications to Local Control Laws

This paper introduces a distributed leaderless swarm formation control framework to address the problem of collectively driving a swarm of robots to track a time-varying formation. The swarm's formation is captured by the trajectory of an abstract shape that circumscribes the convex hull of robots' positions and is independent of the number of robots and their ordering in the swarm. For each robot in the swarm, given global specifications in terms of the trajectory of the abstract shape parameters, the proposed framework synthesizes a control law that steers the swarm to track the desired formation using the information available at the robot's local neighbors. For this purpose, we generate a suitable local reference trajectory that the robot controller tracks by solving the input-output linearization problem. Here, we select the swarm output to be the parameters of the abstract shape. For this purpose, we design a dynamic average consensus estimator to estimate the abstract shape parameters. The abstract shape parameters are used as the swarm state feedback to generate a suitable robot trajectory. We demonstrate the effectiveness and robustness of the proposed control framework by providing the simulation of coordinated collective navigation of a group of car-like robots in the presence of robots and communication link failures

Malaria control. generating evidence from local to global level

In addition of the provision of effective treatment to each case, malaria control is heavily relying on vector control with either insecticide treated mosquito nets (ITNs) or indoor residual spraying (IRS). The effectiveness of ITNs in controlling malaria in many different settings has already been comprehensively documented. On the other hand, while IRS has a long and distinguished history in malaria control, its health effects have never been properly quantified. The present thesis aimed at generating malaria control knowledge on local and global level. On a local level, new insights into the malaria burden in South-East PNG were generated. The work was carried out within an oil palm plantation, which allowed exploring options for malaria control, together with the management of the company. On a global level, this thesis aimed to quantify the effectiveness of IRS in reducing ill-health from malaria through a Cochrane review and to compare IRS to ITNs. Local level – malaria in Papua New Guinea To get an overview on malaria epidemiology within the Higaturu Oil Palms plantation (HOP) in Oro Province in PNG, different observational study approaches were used. In 2006, we carried out a cross-sectional study within six company villages, which included the determination of parasite rates by conventional microscopy, interviews and haemoglobin measurements. Passive surveillance data were collected from the 13 company aid posts for the years 2005 and 2006. Before the start of this study, malaria diagnosis was relying on clinical symptoms only. Since malaria symptoms are unspecific, we introduced rapid diagnostic tests (RDTs) in all aid posts. Finally, entomological data were collected by human landing catches. Prevalence of malaria was high, with more than a third of the participants (33.5%, 95% confidence interval (CI): 30.1-37.0) found with a malaria positive blood slide. Overall, prevalence was highest in the age group 5-9 years (40.3%, 95% CI 0.32-0.49). More than half of the infections were caused by Plasmodium falciparum (59.5%), followed by P. vivax with 37.6% and P. malariae (6.6%). Haemoglobin levels were low, with a mean of 11.0 g/dl (95% CI 10.8-11.1) for men and 10.4 g/dl (95% CI 10.3-10.5) for women. Plasmodium falciparum infections were significantly associated with anaemia (Hb < 10 g/dl). At the aid posts, all malaria cases in 2005 and January-March 2006 were diagnosed by symptoms only, while from April 2006 onwards most cases were tested by rapid diagnostic tests. Between 2005 and 2006, 22,023 malaria cases were diagnosed at the aid posts and malaria accounted for 30-40% of all clinical cases. Of the malaria cases, 13-20% were HOP employees. On average, an employee sick with malaria was absent for 1.8 days, resulting in a total of 9,313 workdays lost between 2005 and 2006. Sleeping outside of the house did not increase the risk for a malaria infection, neither did getting up before 7am. Anopheles punctulatus was the main vector founding the area. Malaria was found to be a major health burden in the Higaturu Oil Palm plantation, posing a high risk to company staff and their relatives, including expatriates and other non-immune workers. Reducing the malaria risk is a highly recommended investment for the company. Global level The health effects of IRS were summarized and quantified in the frame of a Cochrane review. Studies considered for the review had to be either Randomized Controlled Trials (RCTs), Controlled Before-and After studies (CBA), or Interrupted Time Series (ITS). They had to include children and adults living in malarious areas and be carried out with one of the World Health Organization (WHO) recommended insecticides. There was a great paucity of high-quality evidence. Only six out of 132 identified studies met the inclusion criteria (four RCTs, one CBA and one ITS) and not all key malariological outcomes were addressed within these studies. Also, the geographic spread of the included studies was limited. For stable malaria settings, malaria incidence was significantly reduced in children aged one to five years (RR 0.86, 95% CI 0.77 to 0.95), while no difference was seen for children older than five years. For malaria prevalence no difference was seen between the IRS and the control group. With regard to anaemia, the haemoglobin levels were significantly lower in the control group than in the IRS group (WMD 0.61 g/dl; 95% CI IRS group 9.99 to 10.02; 95% CI no IRS group: 9.38 to 9.40). When comparing IRS to ITNs, IRS showed a better protective effect in reducing malaria incidence for children aged one to five years (RR 0.88, 95% CI 0.78 to 0.98). No difference was seen for children older than five years. Prevalence rates were found to be equal within the IRS and ITN groups. No difference in haemoglobin levels was found (WMD 0.01; 95% CI IRS: 9.99 to 10.02; 95% CI ITN: 9.99 to 10.01). In regard to unstable malaria settings IRS was shown to significantly reduce the incidence rate of malaria infections with a protective efficacy ranging from 24% to 86%. IRS also significantly reduced the incidence of malaria when looking separately at P.falciparum and P. vivax (P.falciparum: RR 0.07, 95% CI 0.02 to 0.39; P. vivax: RR 0.21, CI 95% 0.10 to 0.55). Different results were seen when assessing the impact of IRS on malaria prevalence. No effect of IRS in reducing malaria prevalence was found in India. In children aged five to fifteen in Pakistan, IRS reduced the risk of getting infected with P. falciparum as well as with P.vivax - by 90% and 68%. Conflicting results were seen comparing IRS to ITNs against malaria incidence, with one study showing a better protection with ITNs (RR 1.55, 95% CI 1.49 to 1.60) and one study detecting no difference between the two interventions. Unfortunately, the aim of the review (to quantify the health effects of IRS) could not be achieved. A major conclusion of this work is the urgent need for high-quality evidence from two or three-arm RCTs. Ideally such trials should have one IRS arm, one ITN arm and an arm combining both interventions at high coverage. A control arm should not be planned for ethical reasons. This evidence will be crucial to support the long-term aim of malaria elimination/eradication

Divided attention, selective attention and drawing: Processing preferences in Williams syndrome are dependent on the task administered

The visuo-spatial abilities of individuals with Williams syndrome (WS) have consistently been shown to be generally weak. These poor visuo-spatial abilities have been ascribed to a local processing bias by some [30] and conversely, to a global processing bias by others [24]. In this study, two identification versions and one drawing version of the Navon hierarchical processing task, a non-verbal task, were employed to investigate this apparent contradiction. The two identification tasks were administered to 21 individuals with WS, 21 typically developing individuals, matched by non-verbal ability, and 21 adult participants matched to the WS group by mean chronological age. The third, drawing task was administered to the WS group and the TD controls only. It was hypothesised that the WS group would show differential processing biases depending on the type of processing the task was measuring. Results from two identification versions of the Navon task measuring divided and selective attention showed that the WS group experienced equal interference from global to local as from local to global levels, and did not show an advantage of one level over another. This pattern of performance was broadly comparable to that of the control groups. The third task, a drawing version of the Navon task, revealed that individuals with WS were significantly better at drawing the local form in comparison to the global figure, whereas the typically developing control group did not show a bias towards either level. In summary, this study demonstrates that individuals with WS do not have a local or a global processing bias when asked to identify stimuli, but do show a local bias in their drawing abilities. This contrast may explain the apparently contrasting findings from previous studies

A Comparison of LPV Gain Scheduling and Control Contraction Metrics for Nonlinear Control

Gain-scheduled control based on linear parameter-varying (LPV) models derived from local linearizations is a widespread nonlinear technique for tracking time-varying setpoints. Recently, a nonlinear control scheme based on Control Contraction Metrics (CCMs) has been developed to track arbitrary admissible trajectories. This paper presents a comparison study of these two approaches. We show that the CCM based approach is an extended gain-scheduled control scheme which achieves global reference-independent stability and performance through an exact control realization which integrates a series of local LPV controllers on a particular path between the current and reference states.Comment: IFAC LPVS 201

Think Globally, Act Locally? Stock vs Flow Regulation of a Fossil Fuel

Regulation of environmental externalities like global warming from the burning of fossil fuels (e.g., coal and oil) is often done by capping both emission flows and stocks. For example, the European Union and states in the Northeastern United States have introduced caps on flows of carbon emissions while the stated goal of the Intergovernmental Panel on Climate Change (IPCC) which provides the science behind the current global climate negotiations is to stabilize the atmospheric stock of carbon. Flow regulation is often local or regional in nature, while stock regulation is global. How do these multiple pollution control efforts interact when a nonrenewable resource creates pollution? In this paper we show that local and global pollution control efforts, if uncoordinated, may exacerbate environmental externalities. For example, a stricter cap on emission flows may actually increase the global pollution stock and hasten the date when the global pollution cap is reached.

Non-local control in the conduction coefficients: well posedness and convergence to the local limit

We consider a problem of optimal distribution of conductivities in a system governed by a non-local diffusion law. The problem stems from applications in optimal design and more specifically topology optimization. We propose a novel parametrization of non-local material properties. With this parametrization the non-local diffusion law in the limit of vanishing non-local interaction horizons converges to the famous and ubiquitously used generalized Laplacian with SIMP (Solid Isotropic Material with Penalization) material model. The optimal control problem for the limiting local model is typically ill-posed and does not attain its infimum without additional regularization. Surprisingly, its non-local counterpart attains its global minima in many practical situations, as we demonstrate in this work. In spite of this qualitatively different behaviour, we are able to partially characterize the relationship between the non-local and the local optimal control problems. We also complement our theoretical findings with numerical examples, which illustrate the viability of our approach to optimal design practitioners