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In the context of epidemic spreading over a network the problem of curing some nodes to curb the spreading under budget constraint is often discussed. While strategies exist for heterogeneous networks as scale-free networks (networks with a power-law degree distribution), there is no established link between the scale-free coefficient and the efficiency of the method. Thus, we first present a theoretical result linking the scale-free coefficient and the efficiency of the strategy of allocation in scale-free networks. Then, based on this we derive a new strategy for homogeneous networks as grid-like networks. To do so we use a scale-free abstraction of the network allowing to identify the most interesting zones to cure. Finally, we show that the link between scale-free coefficient and efficiency can also be observed within this version.

In this paper we investigate the problem of optimal games played over networks and focus our attention on the importance of the topology of communication between the agents. We consider a set of agents which are connected via a directed communication graph: each agent in the network has to optimize a local cost function which depends on the agent’s decision and on the decision taken by the set of its neighbors, giving rise to a Network Game. We show that, by condensing the strongly connected components of the control graph into super-nodes, it is possible to give a hierarchical interpretation to the Network Game. Then we apply the proposed architecture to the case of a large scale network which takes inspiration by traffic networks application.

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Conventionally the control of dry clutch's engagement during a standing start in AMT vehicles is assured by look-up tables whose values are carefully chosen to produce a smooth synchronisation at the expense of a long slipping time. This article proposes, instead, a two phase approach: a first open-loop look-up table phase aiming to reduce the slipping time and a second observer-based optimal control phase assuring the engagement comfort. Particular attention has been given to the details of the on-line implementation on a Clio AMT prototype. Experimental results show both a close match between the predicted and the actual trajectories and a high level of comfort.

After Pokémonviewing triggered an epidemic of seizures in Japan, many efforts have been made to design safety guidelines and systems to protect subjects with photosensitivity. The authors developed a new method based upon nonlinear diffusion techniques capable of filtering the epileptogenic content of a video sequence related to color without altering its spatial and luminance content.

The paper address the problem of designing lin-ear controllers for drive-by-wire steering vehicles. The main control design aim is to provide particular closed-loop properties such as: safety and ride confort. Since such criteria are subjective, they are replaced by mathematical specifications such as passivity and transparency, previously used in the context of tele-manipulation systems. Such a formulation leads to a multi-objective control problem for which we investigate potential solutions through linear matrix inequalities optimisation.

The endothelium releases dilating autacoids, such as nitric oxide (NO), prostaglandins, and endothelium-derived hyperpolarizing factor (EDHF). Different mechanisms of interaction between these autacoids have been identified and are briefly reviewed here. NO, which dilates resistance vessels via the second messenger cGMP, also amplifies the responses to vasodilators, which act by elevation of cAMP (e. g., prostaglandins), in a synergistic manner. This amplification is most likely due to a cGMP-dependent inhibition of the breakdown of cAMP. An interaction of these autacoids can not only be found in vascular smooth muscle cells but also in the endothelium. A closer look towards the site of production reveals that prostacyclin attenuates the release of NO, which is achieved by a decrease of the intracellular calcium levels in endothelial cells. This feedback mechanism leads to enhanced NO formation after inhibition of cyclooxygenase. While NO does not seem to modulate prostaglandin dynthesis, it has been shown recently in coronary arteries that NO attenuates the release of EDHF. Under conditions of compromised NO formation EDHF might act via this mechanism as a second line of defense. This could help in maintaining endothelium-dependent vasodilation unless an altered smooth muscle responsiveness generally reduces the efficacy of endothelial vasodilators (including EDHF). Convincing experimental evidence for such an impaired relaxation of smooth muscle has been presented recently following exposure to elevated oxLDL levels.

The human adenovirus 5 E1A region can immortalize primary cultures of baby rat kidney cells, but requires the presence of the E1B region for complete oncogenic transformation. One of the effects of the E1B region in the transformation process is the activation of E1A expression. We have investigated the mechanism of this stimulation of E1A expression using nuclear run‐on assays with nuclei from Ad5 E1A‐ and Ad5 E1‐transformed cells. It was found that E1B enhances E1A at the level of transcription‐initiation. This activation is mainly observed when the E1A and E1B regions are integrated simultaneously into the cellular genome and only minimally when these genes are integrated separately, strongly suggesting that a close physical linkage of these regions is essential for the observed effect.

The purpose of this note is to contribute to the understanding in how to design discontinuous controllers and to underline their intrinsic aspects and their main properties. The paper gives a sequential control construction based on invariant manifolds and presents several control design possibilities.

This paper presents a new estimation algorithm, which is essentially a modification of the weighted recursive least squares algorithm (W-RLS), for systems with bounded disturbances. Assuming the knowledge of a disturbance upper bound, the algorithm's derivation is performed the minimization of a cost function weighted by two factors : one is fixed by the user and exponentially weights the arrival information, the other is time-varying and data-dependent. The purpose of the latter is to ensure the algorithm stability faced with the bounded disturbances and to enhance the convergence rate, as much as permitted by the available data. The final algorithm has a very compact and simple form. It completely depends upon the significative information and it stops when the arrival data are redundant. After the algorithm derivation, the paper presents the convergence properties, analyses the algorithm behavior faced with time-varying systems and presents some simulations.

This paper presents an exponentially stable controller for a two-degree-of-freedom robot with nonholonomic constraints. Although this system is controllable, it has been shown to be non-stabilizable via smooth state feedback. In [6], a particular class of piecewise continuous controllers is proposed which exponentially stabilizes the robot about the origin. Here, this approach is extended to stabilize about an arbitrary position and orientation, and to follow a path which is composed of a sequence of straight lines and circle segments, i.e. shortest paths of bounded curvature in the plane. The velocity along the path is to be specified to any desired profile, and may for instance pass through or converge to zero.

Nonlinear systems without drift having less inputs than states have been shown not to be stabilizable by pure smooth state feedback, [4]. Examples of such systems are mecanical systems with nonholonomic constraints, i.e. mobile robots. carts, multifinger hands, etc. Asymptotic stabilization via time varying controllers have recently been proposed [14], [6], [12]. As indicated by [14], time-varying controllers seems to have the property of rather slow convergence rate, for the example studied in [14]) the time rate is at most 1/t. In this paper an other type of controller is investigated. Piecewise smooth feedback control is proposed as an alternative to the time-varying control. It is shown that convergence rate is improved and. in some examples, it is even exponential.

The problem of controlling a robot manipulator while the end effector is in contact with an environment of finite but unknown stiffness is considered in this paper. An exponentially stable control law is derived starting from a Slotine and Li position control algorithm. The original position trajectory is scaled so as to fulfill the force control objective. A passivity-based adaptive observer is designed to compute the time-varying scaling factor, which depends on the unknown stiffness constant of the environment. The paper is an extension of a previous work where the one-degree-of-freedom linear case is analyzed.

This paper presents a new approach for designing simple nonlinear robust controllers for underwater vehicles. The paper presents several in-water experiments performed on the VORTEX vehicle developed by IFREMER. We first introduce some general modeling considerations of underwater vehicles, then we present the VORTEX dynamic model and some of the special features of the VORTEX vehicle that are important for control. Among these, low sampling rates for sensor and actuator nonlinearities are considered. The main aim of this paper is to experimentally investigate the benefits of adding an easy-to-tune nonlinear control loop to the actual linear compensator in order to improve the stability and the disturbance rejection properties of the closed-loop system. The advantage of this method is two-fold. First the additional nonlinear loop does not modify the original linear (PID) regulator. Second the design of this additional loop does not rely on the system model and is simple to tune. The results presented in this paper were obtained using the VORTEX vehicle both in simulation and during real experiments; they demonstrate the advantages of using a PID with this nonlinear loop over a simple PID control.

The highly unstable c-myc mRNA has been shown to be stabilized in cells treated with protein synthesis inhibitors. We have studied this phenomenon in an effort to gain more insight into the degradation pathway of this mRNA. Our results indicate that the stabilization of c-myc mRNA in the absence of translation can be fully explained by the inhibition of translation-dependent poly(A) tail shortening. This view is based on the following observations. First, the normally rapid shortening of the c-myc poly(A) tail was slowed down by a translation block. Second, c-myc messengers which carry a short poly(A) tail, as a result of prolonged actinomycin D or 3'-deoxyadenosine treatment, were not stabilized by the inhibition of translation. We propose that c-myc mRNA degradation proceeds in at least two steps. The first step is the shortening of long poly(A) tails. This step requires ongoing translation and thus is responsible for the delay in mRNA degradation observed in the presence of protein synthesis inhibitors. The second step involves rapid degradation of the body of the mRNA, possibly preceded by the removal of the short remainder of the poly(A) tail. This last step is independent of translation.

In this paper, stabilizing controllers with exponential rates of convergence are proposed for different examples of nonholonomic systems. First, some examples of driftless kinematic systems, i.e. underwater vehicle and m-chains single generator systems are considered, followed by systems including drift. In particular we consider the case of mobile robots with cascade integrators.

This paper illustrates the application of model-based adaptive friction compensation schemes on a DC motor servomechanism. A dynamic friction model and the control structure previously studied were used as a basis for this study. Two adaptive globally stable mechanisms are introduced to deal with structured normal forces and temperature variations. Assuming that a nominal friction model is known adaptation is performed on the basis of only one parameter that captures friction variations. Experimental tracking results with the application of friction perturbations by means of a mechanical brake are presented, thus validating and comparing the two adaptive control schemes.

This note presents a new direct adaptive impedance controller for force /position task. We assume that the environment stiffness is unknown and we consider the one-degree of freedom (dof) case. One of the major consequence of this study is that a generalization of the time-varying impedance leads to integral force feedback. Experimental results on a 2-dof planar manipulator are reported.

This paper presents a nonlinear control law for a set of unconnected carts which are expected to move as a convoy-like vehicle. Applications of such control scheme can be found in highways where cars are desired to move at the same speed and to control the distance between them. Also in automated flexible factories where set of mobile robots are required to follow a leader mobile robot and also in public transports programs where personalized vehicles are assumed to move in a convoy-like configurations. The control law presented in this paper is based on a previous work on feedback design for a train-like vehicle (Canudas et al., 1994) consisting of connected carts.

This paper is concerned with the problem of regulating force and position for a robot manipulator whose end effector is in contact with a compliant environment. The end-effector position set point is suitably scaled in order to match the desired force set point along the normal direction, where the scaling factor is updated according to an adaptive mechanism. Global asymptotic stability is formally proved. Experimental results on an industrial robot with open control architecture are presented.

Ten human milk samples, collected from two towns, Uppsala and Sundsvall, in Sweden in 1994 were analysed for selected chlorinated pesticides (HCB, α-and γ-HCH, DDT, DDD and DDE) and PCB congeners (PCBs 28, 77,101, 105, 118, 126, 138, 153, 156, 158, 167, 169 and 180), PCDDs and PCDFs. The levels found in this study, including the toxic equivalent (TEQ) values, showed a slight downward trend between 1986 and 1994 and are somewhat lower than levels reported from other countries. The contribution of both the mono- and non-orthoPCBs, together with that of PCDD/Fs to the total TEQ values was assessed. Over 70% of the TCDD equivalents was derived from PCBs, PCB 126 being the major contributor. Other high PCB contributors were PCBs 156 and 118. The levels of HCB, α- and γ-HCH, and SDDT were generally higher in Uppsala than in Sundsvall. They were, however, over 50% lower in 1990 than in 1986 and have since changed little. For the PCDD/Fs the results show a marked decrease (ca 50%) in levels between 1986 and 1994. There is an indication that PCB 153 and PCB 126 may be good indicators for total PCB and TEQ levels respectively.

High precision measurements of the joint displacements are available on robot manipulators. By contrast, the velocity measurements obtained through tachometers are in many cases contaminated of noise. Its is therefore economically and technically interesting to investigate the possibility of accurately estimating the speed from indirect available measurements. This paper presents a new approach for estimating the state vector of a robot manipulator, using nonlinear sliding mode observers. Robot models with and without friction are analyzed. In both cases, convergence conditions for the observed state vector are given. The results are strongly based on the physical properties of the robot, such as energy conservation and the quadratic nature of the Coriolis and centripetal forces. These facts are also used to simplify the observer design.

This paper presents a method for simplifying the dynamic equations of a rigid robot manipulator. The idea consists in eliminating some of the components of the robot Hamiltonian on the base of a cost function which describes the total delivered energy for a particular trajectory. This leads to a nonlinear optimization problem where additional constraints are added in order to ensure that the simplified model verifies fundamental physical properties of mechanical systems. A study case shows that these simplifications leads to a substantial reduction of the computation burden without significantly affecting the performance of the closed-loop response.

This paper reviews friction phenomena and friction models of interest for automatic control. Particular emphasis is given to two recently developed dynamic friction models: the Bliman-Sorine model and the LuGre model. These models capture many frictional phenomena observed in laboratory experiments. The behaviours of the models in different situations are discussed in detail. Methods for friction compensation are presented and illustrated with results from practical experiments.

Abstract:  We studied whether a flow-independent increase of luminal wall shear stress (WSS) could dilate hamster arterioles in vivo and which endothelial mediators are potentially involved. To this end the plasma viscosity was elevated by exchanging blood for dextran-erythrocyte solution thereby augmenting WSS. Diameters of small and large arterioles as well as red blood cell velocities were measured before and after exchange of blood for solutions of identical haematocrit containing either high- (HMWD) or low-molecular weight dextran (LMWD). The potential role of endothelial autacoids was investigated by local application of the NO-synthase inhibitor N G-nitro-L-arginine (L-NNA), the inhibitor of cyclooxygenase, indomethacin (3 μM), or the K+-channel blocker, tetrabutylammonium (TBA, 0.1 mM) to assess the potential effects of EDHF. HMWD (n = 11 animals) increased plasma viscosity by 64 3% and dilated arterioles of all branching orders (A1–A4) significantly [by 24 3% (A1–A2) and 32 3% (A3–A4)]. This dilation compensated fully for the calculated initial increase of WSS. LMWD (n = 6) did not affect plasma viscosity or arteriolar diameters. Tissue treatment with L-NNA (30–300 μM, n = 12) substantially diminished the HMWD-induced dilation in small arterioles (A3–A4; to 13 3%; P<0.05) and virtually abolished it in large ones (A1–A2). Consequently, the calculated WSS increased significantly in these arterioles (by 31 5%). TBA combined with L-NNA (n = 4) did not reduce further the remaining dilation. Indomethacin (n = 6) had no effect on HMWD-induced dilation. We conclude that an increase of WSS induces a mainly NO-mediated arteriolar dilation. This dilation occurs in all arteriolar branching orders and is of sufficient magnitude to compensate for the initial WSS-increase. Thus, any elevations of WSS fulfil the requirement for a signal to change diameter along the arteriolar tree in a coordinated manner. The fully compensating dilation which we observed indicates that WSS is a controlled variable. It does, however, raise questions as to its role as a continuous endothelial stimulus.

The present work deals with the problem of minimizing the magnetic energy of the induction motor for steady-state operation under torque regulation. Aspects of efficiency improvement of this approach are analysed. Some control possibilities are presented, as well, followed by some simulated examples.

In this paper we present two continuous-time versions (with and without data normalization) of the Exponentially Weighted Recursive Least-squares Algorithm (EW-RLS) developped in [1]. These algorithms are suitable for identifying systems with bounded partially-known disturbances since they explicitly account for these disturbances and ensure parameter boundedness. The paper presents the derivation of these algorithms and the associated convergence issues.

In this paper is presented a control approach for a set of unconnected cars arranged in a platoon-like fashion using the “follow-the-leader” principle. The main goal of this work is the simultaneous longitudinal and lateral dynamic control of a platoon of cars. Application of a such control scheme would be useful in many nowadays public traffic transportation programs. This control is a dynamic extension of a previous work on nonlinear control for a convoy-like vehicle (Canudas and NDoudi-Likoho, 1994), applied to four-wheeled vehicles. The asymptotical convergence of the following cars towards the “leader’s” path is established and simulation results are presented.

This paper presents two different aspects concerning the control design laws for induction motors: (1) It derives state operating points (steady-state values for currents and fluxes)parameterized in terms of the desired motor torque, defining minimum energy operation conditions for the electrical motor. (2) It gives a state space feedback control design methodology based on Lyapunov analysis which renders the minimum energy operating points invariant. A PI-type control is here proposed. The PI-structure is introduced to deal with motor parameter uncertainties. Stability of this control schemes is studied.

This paper illustrates the application of a model‐based adaptive friction compensation on a DC motor servomechanism. The dynamic friction model and the control structure studied previously by the authors were used as a basis for this study. The paper first proposes a two‐step off‐line method to estimate the nominal static and dynamic parameters associated with the model. Then two adaptive globally stable mechanisms are introduced to deal with structured normal forces and temperature variations. Assuming that a nominal friction model is known and that the friction variations can be suitably structured, adaptation is performed on the basis of only one parameter. The paper presents experimental results validating the identification of the dynamic friction model and the adaptive control scheme. These results show that the adaptive loop improves over a fixed compensation scheme and over a PID controller without friction compensation. © 1997 by John Wiley & Sons, Ltd.

The E1 region of human adenovirus type 12 (Ad12 E1) represses the expression of major histocompatibility complex (MHC) class I genes in transformed primary rodent cells. Conflicting results have been reported as to whether this E1A-mediated repression occurs at a transcriptional or a posttranscriptional level. In the present study, we show that in Ad12 E1-transformed primary baby mouse kidney cells from transgenic mice harboring the human growth hormone gene under control of an H-2K promoter both the expression of the endogenous MHC class I genes and the expression of the transgene are repressed. This experiment, as well as nuclear run-on analyses performed with single-stranded probes, revealed that Ad12 E1A inhibits MHC class I gene expression by repressing its promoter.

n this paper we revisited the effect of dither signal in servo-drives with dynamic friction. In opposition to existing results based in memoryless friction models, the average effect of friction can be qualified in terms of amplitude and frequency of the dither signal. This results is obtained by a new proposed modification of singular perturbation theory that allow us to handle a special class of nonlinear systems which are not differentiable anywhere and does not satisfy the Tikhonov's condition. Experimental results showing the stick-slip extinction are also presented.

Application of adaptive control to a very flexible arm is considered in this paper. A different approach of adaptive control schemes is used. It consists in: (1) Estimating only the unknown and/or time varying arm parameters, namely payload mass, m, and Coulomb friction, Tf, by using recursive estimation techniques of continuous-time process parameters, and in (2) Designing a linear controller which compensates for Tfand tunes its parameters based on the estimate of m. Robustness in the estimation scheme is thus obtained by reducing the number of parameters to be estimated. Different control policies are discussed, and some simulation results are given.

This paper deals with the problem of improving the parameter identifiability properties of robot model. Through the exploitation of the upper-triangular structure of the information matrix, the estimation of the invariants (masses, inertias, etc). which usually requires at the most 11 n parameters for a robot manipulator with n degrees of freedom (DOF), can be performed link by link in a sequential manner by n algorithms of size niwhere Σ niis smaller than 11n. Optimization of the robot trajectories seeking to improve parameters identifiability can be simplified. A study case is presented of a 4-DOF robot used for nuclear maintenance having three co-linear axes. Instead of having a single-pass algorithm of dimension 12, the method yields a 4-passes estimation algorithm with a parameter vector dimension of 4, 4, 3 and 1 respectively for each pass. This method enhances the numerical algorithm conditioning and facilitates the selection of a high excited identification sequence improving the parameter identifiability.

Summary A detailed scheme of carboxylate formation and retention by plant tissues as a result of ion uptake and utilization is given.

The author of this report was assigned to investigate the mathematical aspects of meteorological ship routeing by Prof. Dr. R. Timman of the Delft University of Technology. The assignment was accomplished in 1968, resulting in a doctor’s thesis, entitled “Mathematical Treatment of Optimal Ocean Ship Routeing” [1]. This report describes the outlines of this dissertation. The first section contains the problem statement as well as some notational conventions. In order to avoid metric difficulties, the navigated region G is to be mapped conformally onto a plane, keeping the scale alteration as small as possible. Section 2 gives a curse treatment of the most important mappings that fit this purpose. In the 3rd section the minimal time problem is discussed as an application of Pontryagin’s optimal control theory. The concept of a timefront is introduced and some attention is given to possible structure complications of these fronts. Also modifications of the general theory, in the event that part of a trajectory should coincide with the boundary of the region G, are briefly mentioned. Section 4 cursely treats wave prediction methods and the determination of a ship’s behaviour in sea waves. In the 5th section the computer program to evaluate the least time track is described and the results of a practical application are exhibited. The consequences of data incertainties and the practical use of the treated method are briefly discussed. The two appendices contain mathematical treatments of the general minimal time problem and of the minimal time problem with co-ordinate restrictions.

An apparatus permitting to record the heart-beats of working persons is described. The input signal is obtained from a barrier layer photocell and a lamp at the ear-lobe. The signal is amplified by a differential amplifier with symmetrical input and feed-back.

A theory of light relations in plant canopies is presented which has potential applications in remote sensing and photosynthetic modeling of plant canopies. Predictions of the model are compared with field measurements of light reflection and transmission in a corn crop. Both reflection at the top of the canopy and transmission at the bottom are predicted within 1% of the measured values. Profiles connecting these upper and lower limits are equally well approximated. Variations in the predictions with altitude angle of the sun are confirmed by the observation of several investigators.

Injury to the anal sphincter during childbirth is accepted as a major risk factor for fecal incontinence in women. As many as 50% of women with such injury report fecal incontinence, due mainly to a persistently defective sphincter. Risk factors for anal sphincter injury during operative vaginal delivery were examined in a population-based observational study of 7478 Dutch women who had forceps delivery and 21,254 who delivered by vacuum extraction. Cases were taken from a validated Dutch national obstetrical database for the years 1994–1995. Partial sphincter injuries were included.

PURPOSE: The dexterity™ pneumo sleeve is designed to provide abdominal access for the surgeon's hand while preserving pneumoperitoneum during laparoscopy. The first experience using the dexterity™ pneumo sleeve in colorectal surgery is reported. METHODS: Four patients with diverticulitis and one with a dolichocolon had manually assisted laparoscopic sigmoid colectomy with the dexterity™ pneumo sleeve. RESULTS: Assistance of the left hand, introduced through the dexterity™ device proved to be extremely helpful in identifying the plane of dissection in one patient with a large diverticular mass and in another with a colovaginal fistula. Mean operative time was 109 minutes, blood loss was 80 ml, and length of incision was 7.5 cm. Flatus reoccurred at the second postoperative day, bowel movement occurred on the third day after surgery, and patients were discharged after 4.8 days. CONCLUSIONS: With the dexterity™ pneumo sleeve, the tactile sensation is regained, which makes laparoscopic-assisted colectomy safer and faster.