Institut Mihajlo Pupin

This paper is devoted to the permanence of the concept of Zero-Moment Point, widely-known by the acronym ZMP. Thirty-five years have elapsed since its implicit presentation (actually before being named ZMP) to the scientific community and thirty-three years since it was explicitly introduced and clearly elaborated, initially in the leading journals published in English. Its first practical demonstration took place in Japan in 1984, at Waseda University, Laboratory of Ichiro Kato, in the first dynamically balanced robot WL-10RD of the robotic family WABOT. The paper gives an in-depth discussion of source results concerning ZMP, paying particular attention to some delicate issues that may lead to confusion if this method is applied in a mechanistic manner onto irregular cases of artificial gait, i.e. in the case of loss of dynamic balance of a humanoid robot. After a short survey of the history of the origin of ZMP a very detailed elaboration of ZMP notion is given, with a special review concerning "boundary cases" when the ZMP is close to the edge of the support polygon and "fictious cases" when the ZMP should be outside the support polygon. In addition, the difference between ZMP and the center of pressure is pointed out. Finally, some unresolved or insufficiently treated phenomena that may yield a significant improvement in robot performance are considered.

The connection between the dynamics of an object and the algorithmic level has been modified in this paper, based on two-level control. The central modification consists in introducing feedbacks, that is, a system of regulators at the level of the formed typed of gait only. Such a modification originates from the assumption that a very narrow class of gait types needs to be taken into account when generating the gait. In the paper the gait has been formed on the basis of a fixed program having a kinematic-dynamic character. The kinematic part concerns the kinematic programnmed connections for activating the lower extremities, while the dynamic part exposes appropriate changes in the characteristic coordinates of the compensation system. Such a connection with a minimum number of coordinates extends the possibility of solving the problem of equilibrium in motion for one type of gait without any particular algorithm that would take into account the motion coordinates and form out of them a stable motion at a higher algebraic level.

The stability of legged machines in locomotion is considered. The general machine has a rigid body to which legs are attached. Locomotion is performed on level smooth surfaces.

Cursive script word recognition is the problem of transforming a word from the iconic form of cursive writing to its symbolic form. Several component processes of a recognition system for isolated offline cursive script words are described. A word image is transformed through a hierarchy of representation levels: points, contours, features, letters, and words. A unique feature representation is generated bottom-up from the image using statistical dependences between letters and features. Ratings for partially formed words are computed using a stack algorithm and a lexicon represented as a trie. Several novel techniques for low- and intermediate-level processing for cursive script are described, including heuristics for reference line finding, letter segmentation based on detecting local minima along the lower contour and areas with low vertical profiles, simultaneous encoding of contours and their topological relationships, extracting features, and finding shape-oriented events. Experiments demonstrating the performance of the system are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The potential antifungal effects of Thymus vulgaris L., Thymus tosevii L., Mentha spicata L., and Mentha piperita L. (Labiatae) essential oils and their components against 17 micromycetal food poisoning, plant, animal and human pathogens are presented. The essential oils were obtained by hydrodestillation of dried plant material. Their composition was determined by GC-MS. Identification of individual constituents was made by comparison with analytical standards, and by computer matching mass spectral data with those of the Wiley/NBS Library of Mass Spectra. MIC's and MFC's of the oils and their components were determined by dilution assays. Thymol (48.9%) and p-cymene (19.0%) were the main components of T. vulgaris, while carvacrol (12.8%), a-terpinyl acetate (12.3%), cis-myrtanol (11.2%) and thymol (10.4%) were dominant in T. tosevii. Both Thymus species showed very strong antifungal activities. In M. piperita oil menthol (37.4%), menthyl acetate (17.4%) and menthone (12.7%) were the main components, whereas those of M. spicata oil were carvone (69.5%) and menthone (21.9%). Mentha sp. showed strong antifungal activities, however lower than Thymus sp. The commercial fungicide, bifonazole, used as a control, had much lower antifungal activity than the oils and components investigated. It is concluded that essential oils of Thymus and Mentha species possess great antifungal potential and could be used as natural preservatives and fungicides.

This paper presents an overview of defense related applications of wireless sensor networks (WSNs). The operational context of modern military engagement has diversified into four scenarios, which set requirements and constraints upon applications of WSNs. The sensor types and their capabilities determine and constrain the application of WSNs. We classify military applications of WSNs according to operation scenarios and sensor types, and describe key classes. We also discuss research and engineering issues for future generations of military WSN applications.

This paper summarizes the report prepared by an IEEE PES Task Force. Resilience is a fairly new technical concept for power systems, and it is important to precisely delineate this concept for actual applications. As a critical infrastructure, power systems have to be prepared to survive rare but extreme incidents (natural catastrophes, extreme weather events, physical/cyber-attacks, equipment failure cascades, etc.) to guarantee power supply to the electricity-dependent economy and society. Thus, resilience needs to be integrated into planning and operational assessment to design and operate adequately resilient power systems. Quantification of resilience as a key performance indicator is important, together with costs and reliability. Quantification can analyze existing power systems and identify resilience improvements in future power systems. Given that a 100% resilient system is not economic (or even technically achievable), the degree of resilience should be transparent and comprehensible. Several gaps are identified to indicate further needs for research and development.

Integral control of large-scale systems implies application of control and information exchange via communication networks in which random delays may exist. The design of such systems rely on conservative sufficient stability tests for systems with random, time-varying delays. In this report, necessary and sufficient conditions are found for zero-state mean-square exponential stability of the considered class of control systems. Numerical tests for zero-state stability are outlined and illustrated by a simple example. Finally, the results are also demonstrated on specific hardware, multiprocessor real-time control network which has been recently developed.

A review of the basic approaches to the artificial hand design is given. The importance of new ideas in this field using progress in automatic control theory is stressed. The most importemt feature of the new hand is the two level control. The movements of the hand can be controlled by signals produced by man as well as by external stimuli. For this purpose simple pressure sensitive transducers are placed in the hand to provide the control signals for reflexive-type movements. An adaptive control circuit is present for automatic weight adjustment. All these features are incorporated into the hand using simple and standard servocomponents. Use of appropriate feedback loops eliminates the need for complicated mechanical parts.

Future smart healthcare systems - often referred to as Internet of Medical Things (IoMT) - will combine a plethora of wireless devices and applications that use wireless communication technologies to enable the exchange of healthcare data. Smart healthcare requires sufficient bandwidth, reliable and secure communication links, energy-efficient operations, and Quality of Service (QoS) support. The integration of Internet of Things (IoT) solutions into healthcare systems can significantly increase intelligence, flexibility, and interoperability. This work provides an extensive survey on emerging IoT communication standards and technologies suitable for smart healthcare applications. A particular emphasis has been given to low-power wireless technologies as a key enabler for energy-efficient IoT-based healthcare systems. Major challenges in privacy and security are also discussed. A particular attention is devoted to crowdsourcing/crowdsensing, envisaged as tools for the rapid collection of massive quantities of medical data. Finally, open research challenges and future perspectives of IoMT are presented.

The solution to the inverse manipulation problem for redundant manipulators has mostly been considered from a geometric-kinematic standpoint. A procedure for the inverse problem solution using the dynamic model of the manipulator and its actuators is developed. Nominal trajectories in the space of joint coordinates are generated so as to be optimal with respect to total energy consumption of the actuators (hydraulic or electric). The treatment of constraints on joint coordinates and rates is also involved in the procedure. The algorithm is illustrated by two industrial robots.

This paper describes, in a polemical way, the possible ways for synthesis of artificial gait, taking into account its application in the rehabilitation of severely disabled paraplegics. The essential relation between the hierarchical control concept of artificial legged locomotion systems and human beings has been treated. The method of prescribed synergy has been described in detail. This method, in the author's opinion, renders wide possibilities in solving delicate problems in the synthesis and control of artificial anthropomorphic gait. The possibility of applying the gait-logic description in the synthesis of finite automata and the possibility of driving system hybridization in the rehabilitation of persons with muscular insufficiency have also been considered.

Specific intrusion detection systems (IDSs) are needed to secure modern supervisory control and data acquisition (SCADA) systems due to their architecture, stringent real-time requirements, network traffic features and specific application layer protocols. This article aims to contribute to assess the state-of-the-art, identify the open issues and provide an insight for future study areas. To achieve these objectives, we start from the factors that impact the design of dedicated intrusion detection systems in SCADA networks and focus on network-based IDS solutions. We propose a structured evaluation methodology that encompasses detection techniques, protected protocols, implementation tools, test environments and IDS performance. Special attention is focused on assessing implementation maturity as well as the applicability of each surveyed solution in the Future Internet environment. Based on that, we provide a brief description and evaluation of 26 selected research papers, published in the period 2015-2019. Results of our analysis indicate considerable progress regarding the development of machine learning-based detection methods, implementation platforms, and to some extent, sophisticated testbeds. We also identify research gaps and conclude the analysis with a list of the most important directions for further research.

Summary This paper deals with floor acceleration spectra, which are used for the seismic design and assessment of acceleration‐sensitive equipment installed in buildings. In design codes and in practice, not enough attention has been paid to the seismic resistance of such equipment. An ‘accurate’ determination of floor spectra requires a complex and quite demanding dynamic response history analysis. The purpose of the study presented in this paper is the development of a direct method for the determination of floor acceleration spectra, which enables their generation directly from the design spectrum of the structure, by taking into account the structure's dynamic properties. The method is also applicable to inelastic structures, which can greatly improve the economic aspects of equipment design. A parametric study of floor acceleration spectra for elastic and inelastic single‐degree‐of‐freedom (SDOF) and multiple‐degree‐of‐freedom structures was conducted by using (non)linear response history analysis. The equipment was modelled as an elastic single‐degree‐of‐freedom system. The proposed method was validated by comparing the results obtained with the more accurate results obtained in a parametric study. Due to its simplicity, the method is an appropriate tool for practice. In the case of inelastic structural behaviour, the method should be used in combination with the N2 method, or another appropriate method for simplified nonlinear structural analysis. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Manipulation robots belong to a class of complex, nonlinear dynamic systems. In addition, they are subjected to the constraints resulting from work-space obstacles, kinematical and physical characteristics of the mechanism itself and the actuators. Therefore, the application of optimal control theory (in energy or time optimization) leads to substantial practical difficulties, so that significant simplifications are usually performed, either in model complexity or by neglecting the existing constraints. In this paper the problem of obtaining such an optimization method, which would take into account the complete system dynamics and all the constraints is considered. The only method found to be suitable for such a complex optimization should be based on dynamic programming. In this paper an algorithm for determining optimal velocity distribution for a given manipulator tip trajectory is elaborated in detail. Practical application of the developed procedure is in off-line calculation of nominal input generalized forces (programmed control) of a nonredundant manipulator, by which the minimum of consumed energy is ensured. This is specially important for high speed motions as well as handling of heavy loads.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new technique for estimation of the instantaneous frequency based on simultaneous sampling of three-phase voltage signals is presented. The structure consists of two decoupled modules: the first is for adaptive filtering of input signals, and the second is for frequency estimation. A suitable and robust algorithm for frequency estimation is obtained. This technique provides better performance, compared with the technique based on a single-phase signal in relation to waveforms with noise. The technique is particularly important when asymmetric sags generate zero voltage in one of the three phases. In addition, it allows the measurement of the instantaneous frequency value of real signals for single- or three-phase systems. To demonstrate the performance of the developed algorithm, computer-simulated data records and calibrator-generated signals are processed. The proposed algorithm has been put to test with distorted three-phase voltage signals. </para>

Supply chain management is a discipline dealing with organization, coordination, and optimization of relations within supply chains. Complexity and dynamics of supply chains are not always proportional to their reliability, and supply chain risk management becomes a very important tool in minimizing risk and uncertainties caused by, or impacting on, logistics-related activities or resources in the supply chain. Because risk modeling presents a very important segment of risk management, the paper includes a description of the main characteristics of supply chains and a model for risk assessment based on the Analytic Hierarchy Process (AHP) and Fuzzy Analytic Hierarchy Process (FAHP) methods. The main intention of the research presented here is to propose approaches based on application of the AHP and FAHP methods which are used as a tool for ranking supply chain risk categories, determining its share in total risk, and as a method for the supply chain risk assessment. The proposed approach is based on the experience and the knowledge of experts from insurance companies which are professionally engaged in the process of risk assessment, and possibility of its application is tested on a numerical example.

One of basic characteristics of the regular bipedal walk of humanoid robots is the maintenance of their dynamic balance during the walk, whereby a decisive role is played by the unpowered degrees of freedom arising at the foot–ground contact. Hence, the role of the Zero-Moment Point (ZMP) as an indicator of dynamic balance is indispensable. This paper gives a detailed discussion of some basic theoretical assumptions related to the ZMP in the light of imprecise, and even incorrect, interpretations that have recently appeared, and which have led to some erroneous conclusions. Examples are given to show some erroneous basic attitudes and the genesis of some of them is indicated. It is also pointed out that in the domain of bipedal walk there are still notions that are not clearly defined and their meanings differentiated in some related branches of science and engineering. One of the examples is dynamic balance and stability, which are often used interchangeably.

Vibrating membranes are the cornerstone of acoustic technology, forming the backbone of modern loudspeakers and microphones. Acoustic performance of condenser microphone is derived mainly from the membrane's size and achievable static tension. The widely studied and available nickel has been the one of dominant membrane material for several decades. In this paper we introduce multilayer graphene as membrane material for a condenser microphone. The graphene device outperforms a high end commercial nickel-based microphone over a significant part of the acoustic spectrum, with a larger than 10 dB enhancement of sensitivity. Our experimental results are supported with numerical simulations, which show that a 300 layer thick graphene membrane under maximum tension would offer excellent extension of the frequency range, up to 1 MHz, with similar sensitivity as commercial condenser microphones.

The AC-DC transfer differences of thermal converters due to thermoelectric effects in the heater circuit are directly measured with a fast reversed DC to an uncertainty of a few parts in 10/sup 7/. This new and independent method allows former theoretical methods for evaluating thermoelectric effects in thermal converters to be checked.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>