László Nádai

Controllability of Quantum Bits from the von Neumann Architecture to Quantum Computing

In this paper we consider the (state) reachability and controllability problems of special two-level quantum systems, the so-called quantum bits via externally applied electro-magnetic field. The system is described by special a bilinear right-invariant model whose state varies on the Lie group of 2 x 2 special unitary matrices. We show that if two or more independent controls are used, then every state can be achieved in arbitrary time using finite energy. The mathematical construction is motivated by the demand of manipulating (or logically operating on) the state of quantum bits, and the results provide some insight into the feasibility of realizing given operations in quantum computers. The paper has a special actuality: both computer science and quantum mechanics are closely related to the famous Hungarian mathematician John von Neumann, and this year there is the 50 th Anniversary of his early and sorrowful death.

Adaptive controllability of the brusselator model with input coupling

For replacing Lyapunovs ingenious but complicated “2nd method” in designing adaptive controllers for nonlinear systems the use of “Robust Fixed Point Transformations (RFPT)” was extensively studied in the past few years mainly for “Classical Mechanical Systems (CMS)”. In spite of the strongly nonlinear coupling that is typical in the Euler-Lagrange equations of motion CMS are simple in the sense that their state variables (i.e. the generalized coordinates and their time-derivatives), driving force or torque components, as well as the tracking error signals are physically well interpreted both in the positive and the negative domains. Furthermore, the time-derivatives of the control forces do not occur in the equations of motion. Therefore simple PIDtype controllers with great feedback gains as well as RFPT-based adaptive ones of smaller feedback gains but of the aptitude for introducing strong nonlinear transient fluctuations after their switching on can successfully deal with such systems. In contrast to CMS “Chemical Systems (CS)”, besides their multiplication and power-type terms in the reaction equations also have further strong nonlinearities due to phenomenological restrictions. Neither negative concentrations, nor negative ingress rates of pure reagents can occur in the case of “Continuous Stirring Tank Reactors (CSTR)”. Such effects were recently investigated by assuming the ingress of very concentrated reagents in the control that do not considerably dilute the other reagents in the CTRS. In this paper the far reaching consequences of this mutual diluting effect are studied. It is shown that the RFPT-based adaptive controller still can be useful but the control strategy has to take far more complicated form.

Cost function-free optimization in inverse kinematics of open kinematic chains

The traditional ways of solving various tasks “optimally” in control technology and robotics normally are based on the minimization of some cost function (or functional). On the basis of function minimization various “generalized inverse matrices” can be introduced that have special significance in the inverse kinematic tasks of redundant manipulators, where the possible solutions are ambiguous—therefore various choices are available. The solution suggested here tackles the question of optimality by the geometric interpretation of the simple and computationally efficient Gram-Schmidt algorithm. The method is presented via simulations using a redundant arm structure.

Characterization of of urban traffic by using mobile phone traces

The current trend of urbanization involving changes within the activities in a city has created several problems. Addressing these problems requires reliable and detailed information regarding urban structure and related dynamics. This study uses mobile phone Call Detail Records (CDR) data collected from cellular towers in Györ, Hungary. First, our method began with the pre-processing of the telecom data. Then, experiments were carried out to understand the city dynamics through GIS visualization and statistical analysis. The visualizations provided a quantitative explanation of how the movement of cellular activity is useful in highlighting the flow of people in an urban infrastructure. This approach could complement and augment the efforts of traditional urban data collection methodologies, which are usually not readily available to urban planners and policy makers.

Analysis of Mobility Patterns during a Large Social Event

The cellular networks including the millions of mobile devices generate a huge volume (mobile phone call records) of data by which the movements of people could be sensed. In this paper, a method (based on mobile phone call records) applied to characterize the patterns of urban population during a big social event is underlined. The proposed method is also to show the regions in the city where the similar trend of mobility takes place. This paper demonstrates the applicability of the approach on the data provided by a Hungarian mobile network operator during a public demonstration event. The results obtained can be helpful in understanding the structure of the city in the sense of human mobility related to large-scale events.

Tackling complexity and missing information in adaptive control by fixed point transformation-based approach

Complexity is the most common feature of the practical tasks to be solved in control technology. Grasping only a little particular segment of reality, often referred to as “model building”, provides us with imprecise and incomplete models of certain subsystems that operate in dynamic interaction with their neglected environment. The classical method of Model Predictive Control (MPC) assumes that our models, though they are not perfect, at least well describe the most important features of the system under control, therefore these models can be used for controller design and the remaining errors can be treated as uncertainties and/or unknown external perturbations.

Modeling of commercial vehicles for vehicle dynamics control development

Commercial vehicle modeling strategies are presented in this paper. Models created are suitable for vehicle dynamics control development, computationally efficient, and well-structured. Important feature of the models is that they can easily support a huge number of possible vehicle variants with different geometrical and structural requirements. Model is built-up in a multi-body structure. This paper details the modeling of the vehicle frame and the suspension and gives brief insight into the tire modeling for which a brush-model approach is used. Finally, simulation results are presented.