Restrictive Constraints Research Articles

On the Application of Machine Learning to the Design of UAV-Based 5G Radio Access Networks

A groundbreaking design of radio access networks (RANs) is needed to fulfill 5G traffic requirements. To this aim, a cost-effective and flexible strategy consists of complementing terrestrial RANs with unmanned aerial vehicles (UAVs). However, several problems must be solved in order to effectively deploy such UAV-based RANs (U-RANs). Indeed, due to the high complexity and heterogeneity of these networks, model-based design approaches, often relying on restrictive assumptions and constraints, exhibit severe limitation in real-world scenarios. Moreover, design of a set of appropriate protocols for such U-RANs is a highly sophisticated task. In this context, machine learning (ML) emerges as a useful tool to obtain practical and effective solutions. In this paper, we discuss why, how, and which types of ML methods are useful for designing U-RANs, by focusing in particular on supervised and reinforcement learning strategies.

Unifying Gaussian dynamic term structure models from a Heath–Jarrow–Morton perspective

In this paper, we show that most existing Gaussian dynamic term structure models (GDTSMs) can be nested as special cases under a unified Heath–Jarrow–Morton (HJM)-based framework of GDTSM construction. Our study provides not only a systematic way to examine the commonality of many seemingly distinct GDTSMs, but also a novel and convenient approach to constructing GDTSMs that are otherwise unavailable or intractable under the traditional approach. In our empirical study using the Euro area forward rates, we conduct a specification analysis based on this novel approach. The analysis reveals that the traditional models impose restrictive constraints limiting their flexibility in capturing key features of the correlations and volatilities of the forward rates.

Spatial Scheduling of Informative Meetings for Multi-Agent Persistent Coverage

In this work, we develop a novel decentralized coordination algorithm for a team of autonomous unmanned aerial vehicles (UAVs) to surveil an aggressive forest wildfire. For dangerous environmental processes that occur over very large areas, like forest wildfires, multi-agent systems cannot rely on long-range communication networks. Therefore, our framework is formulated for very restrictive communication constraints: UAVs are only able to communicate when they are physically close to each other. To accommodate this constraint, the UAVs schedule a time and place to meet in the future to guarantee that they will be able to meet up again and share their belief of the wildfire state. In contrast with prior work, we allow for a discrete time, discrete space Markov model with a large state space as well as restrictive communication constraints. We demonstrate the effectiveness of our approach using simulations of a wildfire model that has $10^{298}$ total states.

Stability Guarantees for Translational Thrust-Propelled Vehicles Dynamics Through NMPC Designs

We propose two different nonlinear model predictive control (NMPC) schemes (with and without terminal cost and constraints) for stabilizing the translational dynamics of thrust-propelled vehicles. Both approaches make use of an elaborated nonlinear feedback linearization controller and its associated ellipsoidal invariant set under restrictive input constraints, hence guaranteeing the closed-loop asymptotic stability. The terminal constraint set of the corresponding NMPC design is easy to tune due to its clear formulation expressed directly in terms of the tuning variables, while for the NMPC scheme without terminal constraint, the design allows to stabilize the system with a significantly shorter prediction horizon in comparison with the existing method in the literature. Simulation and experimental tests over a nano-drone platform validate the proposed approaches.

The dynamical history of the evaporating or disrupted ice giant planet around white dwarf WD J0914+1914

ABSTRACT Robust evidence of an ice giant planet shedding its atmosphere around the white dwarf WD J0914+1914 represents a milestone in exoplanetary science, allowing us to finally supplement our knowledge of white dwarf metal pollution, debris discs, and minor planets with the presence of a major planet. Here, we discuss the possible dynamical origins of this planet, WD J0914+1914 b. The very young cooling age of the host white dwarf (13 Myr) combined with the currently estimated planet–star separation of about 0.07 au imposes particularly intriguing and restrictive coupled constraints on its current orbit and its tidal dissipation characteristics. The planet must have been scattered from a distance of at least a few au to its current location, requiring the current or former presence of at least one more major planet in the system in the absence of a hidden binary companion. We show that WD J0914+1914 b could not have subsequently shrunk its orbit through chaotic f-mode tidal excitation (characteristic of such highly eccentric orbits) unless the planet was or is highly inflated and possibly had partially thermally self-disrupted from mode-based energy release. We also demonstrate that if the planet is currently assumed to reside on a near-circular orbit at 0.07 au, then non-chaotic equilibrium tides impose unrealistic values for the planet’s tidal quality factor. We conclude that WD J0914+1914 b either (i) actually resides interior to 0.07 au, (ii) resembles a disrupted ‘Super-Puff’ whose remains reside on a circular orbit, or (iii) resembles a larger or denser ice giant on a currently eccentric orbit. Distinguishing these three possibilities strongly motivates follow-up observations.

A Web-Based Communication Platform to Improve Home Care Services in Norway (DigiHelse): Pilot Study.

BackgroundHome care service in Norway is struggling to meet the increasing demand for health care under restricted budget constraints, although one-fourth of municipal budgets are dedicated to health services. The integration of Web-based technology in at-home care is expected to enhance communication and patient involvement, increase efficiency and reduce cost. DigiHelse is a Web-based platform designed to reinforce home care service in Norway and is currently undergoing a development process to meet the predefined needs of the country’s municipalities. Some of the main features of the platform are digital messages between residents and the home care service, highlighting information on planned and completed visits, the opportunity to cancel visits, and notifications for completed visits.ObjectiveThis study aimed to test the usability and economic feasibility of adopting DigiHelse in four districts in Oslo by applying registry and behavioral data collected throughout a one-year pilot study. Early health technology assessment was used to estimate the potential future value of DigiHelse, including the predictive value of behavior data.MethodsOutcome measures identified by stakeholder insights and scenario drafting in the project’s concept phase were used to assess potential socioeconomic benefits. Aggregated data were collected to assess changes in health consumption at baseline, and then 15 and 52 weeks after DigiHelse was implemented. The present value calculation was updated with data from four intervention groups and one control group. A quasi-experimental difference-in-difference design was applied to estimate the causal effect. Descriptive behavioral data from the digital platform was applied to assess the usability of the platform.ResultsOver the total study period (52 weeks), rates increased for all outcome estimates: the number of visits (rate ratio=1.04; P=.10), unnecessary trips (rate ratio=1.37; P=.26), and phone calls (rate ratio=1.24; P=.08). A significant gap was found between the estimated value of DigiHelse in the concept phase and after the one-year pilot. In the present pilot assessment, costs are expected to exceed potential savings by €67 million (US $75 million) over ten years, as compared to the corresponding concept estimates of a potential gain of €172.6 million (US $193.6 million). Interestingly, behavioral data from the digital platform revealed that only 3.55% (121/3405) of recipients actively used the platform after one year.ConclusionsBehavioral data provides a valuable source for assessing usability. In this pilot study, the low adoption rate may, at least in part, explain the inability of DigiHelse to perform as expected. This study points to an early assessment of behavioral data as an opportunity to identify inefficiencies and direct digital development. For DigiHelse, insight into why the recipients in Oslo have not made greater use of the Web-based platform seems to be the next step in ensuring the right improvement measures for the home care service.

RMPC for Uncertain Nonlinear Systems With Non-Additive Dynamic Disturbances and Noisy Measurements

In this paper, we present a robust, model-predictive control scheme for the general class of uncertain and constrained discrete-time nonlinear systems subject to noisy measurements. The relationships between the system's dynamics, uncertainties, disturbances and the measurement noise are nonlinear and not necessarily additive. In particular, the disturbance is the output of an uncertain system with an unknown input. This study serves the threefold ultimate objective of ensuring robust satisfaction of the state constraints, recursive feasibility and stability. To satisfy state constraints, the proposed algorithms adopt a constraints tightening approach using the restricted constraint sets computed online. Several bounds on the prediction level and rate are derived and the size of the terminal region is maximized using polytopic linear differential inclusions (PLDI). An explicit bound on the maximum allowable disturbance for recursive feasibility is also derived based on optimization of the one-step ahead controllable set to the terminal region. The disturbance and uncertainties are non-vanishing and therefore only Input-to-state practical stability (ISpS) can be ensured. A simulation example demonstrates the efficacy of the mathematical framework and algorithms developed in this work.

Braginskii viscosity on an unstructured, moving mesh accelerated with super-time-stepping

ABSTRACT We present a method for efficiently modelling Braginskii viscosity on an unstructured, moving mesh. Braginskii viscosity, i.e. anisotropic transport of momentum with respect to the direction of the magnetic field, is thought to be of prime importance for studies of the weakly collisional plasma that comprises the intracluster medium (ICM) of galaxy clusters. Here, anisotropic transport of heat and momentum has been shown to have profound consequences for the stability properties of the ICM. Our new method for modelling Braginskii viscosity has been implemented in the moving mesh code arepo. We present a number of examples that serve to test the implementation and illustrate the modified dynamics found when including Braginskii viscosity in simulations. These include (but are not limited to) damping of fast magnetosonic waves, interruption of linearly polarized Alfvén waves by the firehose instability, and the inhibition of the Kelvin–Helmholtz instability by Braginskii viscosity. An explicit update of Braginskii viscosity is associated with a severe time-step constraint that scales with (Δx)2, where Δx is the grid size. In our implementation, this restrictive time-step constraint is alleviated by employing second-order accurate Runge–Kutta–Legendre super-time-stepping. We envision including Braginskii viscosity in future large-scale simulations of Kelvin–Helmholtz unstable cold fronts in cluster mergers and AGN-generated bubbles in central cluster regions.

Physiological and perceptual responses to exercise according to locus of symptom limitation in COPD

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease, with pulmonary and extra-pulmonary factors contributing to exercise intolerance. The primary self-reported exercise-limiting symptom may reflect the primary pathophysiological factor contributing to exercise intolerance. We compared physiological and perceptual responses at the symptom-limited peak of incremental cardiopulmonary cycle exercise testing between people with COPD reporting breathlessness (B, n = 34), leg discomfort (LD, n = 16), or a combination of B and LD (BOTH, n = 42) as their main exercise-limiting symptom(s). Despite similarly impaired health status, symptomology and peak exercise capacity, the B group had greater restrictive constraints on tidal volume expansion at end-exercise and was more likely to report unpleasant qualities of exertional breathlessness than LD and BOTH groups. In conclusion, reporting breathlessness as the primary exercise-limiting symptom indicated the presence of distinct lung pathophysiology and symptom perception during exercise in people with COPD.

Space–time residual distribution on moving meshes

This article investigates the potential for an r-adaptation algorithm to improve the efficiency of space–time residual distribution schemes in the approximation of time-dependent hyperbolic conservation laws, e.g. scalar advection, shallow water flows, on unstructured, triangular meshes. In this adaptive framework the connectivity of the mesh, and hence the number of degrees of freedom, remain fixed, but the mesh nodes are continually “relocated” as the flow evolves so that features of interest remain resolved as they move within the domain.Adaptive strategies of this type are well suited to the space–time residual distribution framework because, when the discrete representation is allowed to be discontinuous in time, these algorithms can be designed to be positive (and hence stable) for any choice of time-step, even on the distorted space–time prisms which arise from moving the nodes of an unstructured triangular mesh. Consequently, a local increase in mesh resolution does not impose a more restrictive stability constraint on the time-step, which can instead be chosen according to accuracy requirements. The order of accuracy of the fixed-mesh scheme is retained on the moving mesh in the majority of applications tested.Space–time schemes of this type are analogous to conservative ALE formulations and automatically satisfy a discrete geometric conservation law, so moving the mesh does not artificially change the flow volume for pure conservation laws. For shallow water flows over variable bed topography, the so-called C-property (retention of hydrostatic balance between flux and source terms, required to maintain the steady state of still, flat, water) can also be satisfied by considering the mass balance equation in terms of free surface level instead of water depth, even when the mesh is moved.The r-adaptation is applied within each time-step by interleaving the iterations of the nonlinear solver with updates to mesh node positions. The node movement is driven by a monitor function based on weighted approximations of the scaled gradient and Laplacian of the local solution and regularised by a smoothing iteration. Numerical results are shown in two dimensions for both scalar advection and for shallow water flow over a variable bed which show that, even for this simple implementation of the mesh movement, reductions in cpu times of up to 60% can be attained without increasing the error.

Conditions of technological absorption in cocoa production units of the south of Bahia

Cocoa production in the south of Bahia represents a segment and region that does not benefit from the national agricultural technological development and, consequently, coexists with poverty and low productivity due to the limited technological input applied to the crop. This configuration implies the need for technological absorption in this agricultural environment, which requires a thorough diagnosis and analysis of the conditions that interfere in this process. Therefore, the present study proposed the identification and construction of an analytical-conceptual model of the factors that interfere in the technological absorption of cocoa producers in the south of Bahia. The model was applied to the producers in the form of a quantitative survey in order to identify their perceptions regarding the constraints, followed by a statistical verification of possible interferences of location and the size of the production units on these perceptions. The results indicated that the investigated producers, although favorable to technological absorption, perceived the existence of restrictive constraints on technological absorption. Moreover, for some constraints, the location and size of the production units influenced the producers' perceptions. Finally, the study contributes to the research of factors conditioning the technological absorption in agricultural segments and regions at the margin of technological development and serves as a methodological basis for studies in other agricultural environments with similar technological characteristics.Keywords: agriculture; public policies; regional development.TRINDADE, Lucas Xavier; PEREIRA, João Pedro de Castro Nunes. Condicionantes à absorção tecnológica em unidades agrícolas de produção de cacau do sul da Bahia. Estudos Sociedade e Agricultura, v. 27, n. 3, p. 617-644, out. 2019.Submitted in May 2019.Accepted in August 2019.

Semiglobal Finite-Time Trajectory Tracking Realization for Disturbed Nonlinear Systems via Higher-Order Sliding Modes

This paper investigates an alternative nonrecursive finite-time trajectory tracking control methodology for a class of nonlinear systems in the presence of general mismatched disturbances. By integrating a finite-time disturbance feedforward decoupling process via higher-order sliding modes, it is shown that, a novel nonrecursive design framework resulting a simpler controller expression and easier gain tuning mechanism is presented. A new feature is that a quasi-linear inherent nonsmooth control law could be constructed straightforwardly from the system information, which is essentially detached from the determination of a series of virtual controllers. Moreover, by proposing a less ambitious semiglobal tracking control objective, the synthesis procedure can be achieved without restrictive nonlinear growth constraints. Explicit stability analysis is given to ensure the theoretical justification. A numerical example and an application to the speed regulation of permanent magnet synchronous motor are provided to illustrate the simplicity and effectiveness of the proposed nonrecursive control design approach.

Performers First: Gift Exchange and Digital Access to Live Folk Music Archives

Archives commonly hold full, unedited, and unpublished recordings of live musical performances, particularly those archives that focus their collecting on local communities. Much of this content resides on deteriorating magnetic tape with highly restrictive intellectual property constraints that threaten its digital future. This article explores a possible resolution of this dilemma of preservation and access by giving preference to the perspectives and prerogatives of the musical artists represented on live folk music recordings. The article characterizes The Ark in Ann Arbor and the at-risk recordings made at this nationally recognized coffeehouse between 1969 and 1980 in the context of the late-era folk revival scene in the United States and the challenges that copyright restrictions pose for making digitized copies available to contemporary audiences. The authors present and discuss the findings of innovative memory triggering interviews with folk music performers that point toward a way to extend into the realm of digital surrogates a philosophy of the gift exchange cycle. The article argues that archives could embrace asynchronous digital streaming as an extension of the well-established folk process that is so central to the intimacy of the coffeehouse and sidestep if not completely mitigate the barriers imposed by today's intellectual property framework.

The new era of software reuse

The new era of software reuse

Personality disorder co-morbidity in primary care 'Improving Access to Psychological Therapy' services: A qualitative study exploring professionals' perspectives of working with this patient group.

A high prevalence of people present to 'Improving Access to Psychological Therapies' (IAPT) in England with common mental health disorders and co-morbid personality disorder. This group have suboptimal treatment outcomes in IAPT. Whilst new short-term treatment approaches are advocated, no solutions or guidance have been provided. This qualitative study explored IAPT health-care professional (N=28) perspectives of working with people who present to IAPT with co-morbid personality disorder. Individual semi-structured interviews were digitally recorded, transcribed verbatim and analysed using a framework analysis approach. Results identified a lack of skills and confidence in working with this patient group, restrictive service constraints and a treatment gap between the interface of primary and secondary services. Insight into acceptable adaptions to practice are identified that have transferable utility to a wider international audience who can identify people outside of specialist mental health services with common mental health disorders and co-morbid personality disorder traits. © 2019 John Wiley & Sons, Ltd.

Robust Model Predictive Control of Linear Systems With Predictable Disturbance With Application to Multiobjective Adaptive Cruise Control

This paper presents a novel robust model predictive control (RMPC) concept for linear time-invariant systems with a predictable additive disturbance and linear constraints on the state and the input. Major properties of the approach are that: 1) available knowledge of the disturbance is considered in the optimization and 2) the robustness and the performance are addressed separately. As a result, the control performance is optimized while a less conservative condition on constraint satisfaction and recursive feasibility compared to the existing RMPC schemes is obtained. Traditionally, the Lyapunov function is chosen as the optimum of the objective function which must usually be quadratic in terms of the state and the input and contain a terminal cost term. These standard assumptions for the stability may restrict the flexibility of the optimization problem formulation and, thus, limit the applicability of the related RMPC strategies. To overcome this limitation, this paper proposes an explicit Lyapunov function and ensures the input-to-state stability (ISS) with a quadratic constraint, allowing to use any arbitrary convex objective function. To evaluate the novel RMPC concept, a multiobjective adaptive cruise control (ACC) is proposed and a simulation study using measured velocity profiles for the leading vehicle on a highway is presented. In the evaluation, a less restrictive constraint tightening and a larger terminal constraint set compared to the classical RMPC policies could be found and multiple objectives including driving comfort, energy efficiency, stability, and robust recursive fulfillment of safety, velocity, and further physical constraints could be achieved with the novel RMPC concept.

The effect of boundary and loading conditions on patient classification using finite element predicted risk of fracture

BackgroundOsteoporotic proximal femoral fractures associated to falls are a major health burden in the ageing society. Recently, bone strength estimated by finite element models emerged as a feasible alternative to areal bone mineral density as a predictor of fracture risk. However, previous studies showed that the accuracy of patients' classification under their risk of fracture using finite element strength when simulating posterolateral falls is only marginally better than that of areal bone mineral density. Patients tend to fall in various directions: since the predicted strength is sensitive to the fall direction, a prediction based on certain fall directions might not be fully representative of the physical event. Hence, side fall boundary conditions may not be completely representing the physical event. MethodsThe effect of different side fall boundary and loading conditions on a retrospective cohort of 98 postmenopausal women was evaluated to test models' ability to discriminate fracture and control cases. Three different boundary conditions (Linear, Multi-point constraints and Contact model) were investigated under various anterolateral and posterolateral falls. FindingsThe stratification power estimated by the area under the receiver operating characteristic curve was highest for Contact model (0.82), followed by Multi-point constraints and Linear models with 0.80. Both Contact and MPC models predicted high strains in various locations of the proximal femur including the greater trochanter, which has rarely reported previously. InterpretationA full range of fall directions and less restrictive displacement constraints can improve the finite element strength ability to classify patients under their risk of fracture.

Optimum Balancing of the Four-Bar Linkage Using Fully Cartesian Coordinates

This article presents the design optimization of the four-bar linkage for the reduction of the Shaking Force and the Shaking Moment. It is followed a novel procedure based on fully Cartesian Coordinates (Natural Coordinates) and the use of counterweights. These counterweights with as little restrictive constraints on their geometric parameters as possible. No particular counterweight shape in advance is assumed. The analytical equations for the linear momentum and for the angular momentum are obtained, resulting in equations expressed in terms on the mass and the coordinates of the center of mass of the counterweights. These expressions are then used to obtain the Shaking Force and the Shaking Moment of the system in a very direct way. To solve the inverse dynamics problem the inversion of the transpose of the Jacobian matrix, associated to the kinematic constraints, is not required. The links’ masses are restricted only by imposing positive mass values. As a novelty, the most influencing optimization variables are identified using a global sensitivity analysis method, leading to a reduction on the number of optimization variables. The minimization is done using Evolutionary Computation. The results obtained are validated by simulations, and compared to those presented in previous representative works.

Constrained Pseudorandom Functions for Turing Machines Revisited: How to Achieve Verifiability and Key Delegation

Constrained pseudorandom functions (CPRF) are an enriched variant of traditional pseudorandom functions (PRF)—a fundamental tool of modern cryptography. A CPRF enables a master PRF key holder to issue constrained keys corresponding to specific constraint predicates over the input domain. A constrained key can be used to evaluate the PRF on inputs accepted by the associated constraint predicate, while the PRF outputs on the rest of the inputs still remain computationally indistinguishable from uniformly random values. A constrained verifiable pseudorandom function (CVPRF) enhances a CPRF by adding a non-interactive public verification mechanism for checking the correctness of PRF evaluations. On the other hand, a delegatable constrained pseudorandom function (DCPRF) augments a CPRF with the ability to empower constrained key holders to delegate further constrained keys that allow PRF evaluations on inputs accepted by more restricted constraint predicates compared to ones embedded in their own constrained keys. Until recently, all the proposed constructions of CPRFs and their extensions (i) either could handle constraint predicates representable as circuits or (ii) were based on risky knowledge-type assumptions. In EUROCRYPT 2016, Deshpande et al. presented a CPRF supporting constraint predicates realizable by Turing machines (TM) based on indistinguishability obfuscation and injective pseudorandom generators. Their construction was claimed to be selectively secure. The first contribution of this paper is demonstrating that their claim is not valid. In fact, their CPRF construction can actually be proven secure not in the selective model, rather in a significantly weaker one where the adversary is completely static. We then modify their construction with innovative techniques so as to make the resulting CPRF selectively secure. Towards our goal, we suitably redesign the security proof as well. Most significantly, our modification does not involve any additional heavy duty cryptographic tool. Next, employing only standard public key encryption, we extend our improved CPRF construction to present the first ever CVPRF and DCPRF constructions that can handle constraints expressible as TMs.

Design and Experimental Assessment of an Active Fault-Tolerant LPV Vertical Dynamics Controller

This article addresses the design of an active fault-tolerant full-vehicle semi-active suspension controller by linear parameter-varying (LPV) control methods. The restrictive force constraints of the semi-active damper are modeled by saturation indicator parameters and treated as scheduling parameters in the LPV design. The synthesized LPV controller is subsequently augmented by a damper force reconfiguration exploring the weak input redundancy provided by four dampers in a full-vehicle application. In this way, the controller compensates for damper forces lost in the case of saturation or failure by the remaining dampers. The performance of the proposed LPV controller is validated by experiments on a four-post test-rig. The results show the improved tradeoff between ride comfort and road-holding of the full-vehicle LPV controller compared with a quarter-vehicle LPV controller and a Skyhook-Groundhook controller.