This review covers peer-reviewed publications about free time of school-aged children and youth in Croatia, published since 1990. We briefly present these publications and extract their common points. Based on that, we suggest possible addition to leisure time activities of school-aged children and youth.

. In mine detection within the humanitarian demining probing is a reliable technique, but accompanying with a relatively high level of risk and large duration. The adding of ultrasonic sensor to hand probe was demonstrated to overcome insufficiencies of traditional hand probing. The ultrasonic sensor should not screen the hand probing based on a physical contact between the hand probe and a buried object. In this paper we evaluate novel proposal for realisation of the relevant parts of ultrasonic sensor which maximally follow requirements for hand probe geometry

The article discusses the interplay between the enterpriseness and higher education. Current attitudes toward enterpriseness of the Croatian undergraduate students of mechanical engineering were collected partially with a questionnaire. The attitudes are analysed and their alignment with the general technology trends discussed.

Communication among humans is one of crucial human activities.Yet, its importance is not accompanied with the accurate and precise formal measure.Two starting points of this article are: (i) treating the communication among humans as a means to convene diverse individual and collective stimuli and needs; (ii) partitioning human environment into available, well-characterised communication modes, most of which makes possible mediated communication.Based on these starting points, a generic model of human communication between individuals and their environment is formulated and discussed.It is argued that there is a definite relation between the utilised communication modes and intensity of convened matter.

Hovering unmanned aerial vehicles, or drones, can function as distant platforms for mounted sensors, as signal transceivers or for other purposes. However, they must be tethered, the tether functioning as a power cable which connects a tethered drone with a ground power unit. In this article we developed a concept in which a power cable is of modular structure, consisting of mutually identical modules. Each module has motorised propellers and is capable of preserving itself in a given, hovering position. We formulate an equation for current that, for a given set of parameters, make possible hovering of a drone with such a modular cable. The developed concept does not show significant improvement in maximal height of a drone thereby obtained. Causes of that are extracted from a set of assumptions defining the concept.

Remote visual testing of infrastructure, power plants and other important constructions is regularly conducted. It is regularly a crucial way of collecting data about the surface conditions and overall functionality of the tested objects. It includes a large number of technical, environmental and economic parameters, because of what researchers and experts constantly try to optimise it. The use of unmanned aerial vehicles (popularly known as drones) is a novel, currently rather undeveloped approach to conducting the remote visual testing. In this paper we present and develop a concept of a smart configuration for remote visual testing. It is innovative in that it includes a manipulator mounted onto an unmanned aerial vehicle of rotocopter type. Presence of a manipulator makes possible considerably augmented scope of remote visual testing, in comparison with other approaches. Prerequisites for, as well as consequences of such an innovation are analysed and mutually compared.

Aerial load transport by Unmanned Aerial Vehicles (UAVs) can be performed either using a single UAV or using a group of cooperative UAVs. The latter option is assumed more reliable, yet more demanding regarding the control and required power, than the former one. This article theoretically evaluates power consumption for aerial load transport by the use of two UAVs and compares it with the power consumption in case of a single UAV. In all treated cases, we assume a stationary level flight. For the stated comparison the theoretical model for aerial load transport by two identical UAVs is formulated. Generic flight characteristics and UAVs characteristics are prescribed, and corresponding solutions of the model evaluated. Independent parameters of the model are masses of the UAVs and the load, as well as flight velocity. Variables in the model are vertical and horizontal distances between the UAVs. The emphasis is put on the available instantaneous power and sensitivity to occasional wind gusts. We extract intervals of the model parameters for which each of the two UAVs is less loaded than a UAV which solitary carries a load. The sensitivity to wind gusts is lesser in configurations in which one UAV carries most of the load while the other provides the additionally needed instantaneous power.

The paper discusses the capabilities of industrial computed tomography (CT) in the field of dimensional measurement of products with close tolerances. Computed tomography is a method that allows inspection and measurements of both reachable and unreachable characteristics which makes it very desirable and interesting for application in wide range of industries. In order to evaluate the quality of measurement results obtained by industrial CT, two objects with the same geometry, and made from different materials, were measured. Results obtained with CT were compared with the results obtained by coordinate measuring machine, which were considered to be reference values, and deviations between the results have been analysed. Measurements were repeated five times under repeatability conditions. Repeatability is expressed quantitatively in terms of the dispersion characteristics of the results. Statistical analysis showed that in majority of cases, there were no statistically significant differences between measurement results of equal characteristics obtained at different materials. Obtained deviations in the research could be explained by the fact that the measurements were performed at the industrial CT for general applications. Much better results can be achieved by using a metrology CT device.

Background: Interdisciplinary scientific areas regularly develop unique methodologies, yet utilise the conventional communication modes to disseminate results of their researches. Objectives: This paper analyses whether a novel, interdisciplinary communication mode can be found in a gradually developing interdisciplinary journal. Methods/Approach: The content of the journal was categorised based on the characteristics attributed to the published papers. Statistical tests were performed to check for the overlapping categories. Results: A number of indicators, related to papers or to their authors, are introduced and quantified. Conclusions: Methodology utilised and data collected serve, on the one hand, as a referent set for treating the content of other interdisciplinary or disciplinary scientific journals, and, on the other hand, as a set for comparison and extraction of universalities or specificities of the journals. Fluctuations accompanying a gradual rise of the considered journal content prevent a definite answer to the question whether there are some emerging interdisciplinary communication novelties.

Simulation modelling is applied onto a market dynamics of a company conducting two qualitatively different services and has a bounded total daily volume. The model contains qualitatively and in a simplified form the characteristics of the dynamics of a general service providing company. The company applies a single strategy how to influence, thus minimise, the number of agents who wait for a given service. The strategy is realised by changing the relative proportion of the daily conducted services. Rather small modification of priority level between the two services influences considerably both the number and the type of end users who wait for a particular service. The model enables the researchers to test different strategies how to control the number of end users who wait for services, by proper changes in priority level of services conducted. The fact important for practitioners is that partial optimisation is achieved through slight difference in priorities between the services.

Quality level, achieved by a service-providing company, has complex dynamics. It is demanding to optimise the company's performances in a realistic, non-characterised environment. This article contributes to stated optimisation by formulating the agent-based model for performance of a service-providing company. A set of elements and relations representing a structure of such a company is described and explained. In addition, some elements occurring in realistic situations are not included in the model and their absence is explained. Parameters of the model are divided into two groups. First group consists of parameters describing interactions between the company and its environment and second group of the parameters describing internal interactions among the company's elements. Interactions are represented using time-dependent information entropy. Quality of the company's performances is related to values of accompanying information entropies. Relatively simple agent-based model makes possible reliable representations of a variety of observed functions of service companies.

Background: Embedded systems are a ubiquitous part of modern civilisation. Trends point to further intensification of their use. In this article we discuss long-term implications of that process, from the point of view of systems science. Objectives: On a general level, we relate embedded systems to a general class of objects and argue about their role in human life. On a somewhat more specific level, we consider in more details the development of unmanned aerial vehicles. Methods/Approach: In order to achieve the set objectives, we conducted inductive theoretical considerations and presented the results in this section. Results: The hierarchy of notions relating human civilization to environment is established, and embedded systems are positioned within it. Conclusions: Broadening and intensification of the use of embedded systems is a gradual process, heavily intertwined with societal changes. The case study of the development of the unmanned aerial vehicles reveals the potentials of the concept of embedded systems, also in the area of human resources management.

In this paper, a high-precision algorithm for parameter identification of nonlinear multivariable dynamic systems is proposed. The proposed computational approach is based on the following assumptions: a) system is nonlinearly parameterized by a vector of unknown system parameters; b) only partial measurement of system state is available; c) there are no state observers; d) initial conditions are unknown except for measurable system states. The identification problem is formulated as a continuous dynamic optimization problem which is discretized by higher-order Adams method and numerically solved by a backward-in-time recurrent algorithm which is similar to the backpropagation-through-time (BPTT) algorithm. The proposed algorithm is especially effective for identification of homogenous spatially distributed nonlinear systems what is demonstrated on the parameter identification of a multi-degree-of-freedom torsional system with nonlinearly parameterized elastic forces, unknown initial velocities and positions measurement only.

In this paper, a robust output tracking controller for the quadrotor helicopter is proposed. The proposed controller requires the measurement of only four state variables: positions in the inertial coordinate frame and the yaw angle. Also, the controller is robust with respect to the unmodelled dynamics and provides rejections of all external force and torque disturbances. The effectiveness of the proposed controller is tested on a simulation example of a quadrotor tracking under the influence of wind which is modelled as unmatched external force disturbances in the horizontal plane.

The absolute temperature T has a recognized physical meaning in equilibrium thermodynamics. The scale realized by the closely related Lagrange coefficient "b" usually figures as an auxiliary scale. In this article, the scale spanned by "b"is a proper intensive thermal quantity for equilibrium and, suitably generalized, for stationary non-equilibrium state description. The coefficient "b" measures a relative deviation of a system state from the state of uniform distribution function. The cause of deviation is coupling to environment, which is realized as a net energy transfer and which ceases in the "b" = 0 state. A canonical ensemble of two level atoms coupled to electromagnetic quasi-continuum is considered as an example. The proposed and the usual interpretations of "b" are applied to stationary states of the same system, in which case the notion of the generalized absolute temperature is introduced. The generalized absolute temperature is a measure of a deviation of a system state from a state of infinitely intense external influence.

Citations to published scientific articles are regularly collected and processed, bringing about the impact factor and a large number of other bibliometric indicators. We interpret the set of citations collected during fixed period as a characteristic statistical distribution of citations, argue about its properties and conjecture what statistical measures represent reliably such distributions. In that way we try to contribute to determining precisely the scope and level of suitability of impact factor if accompanied with a small set of additional indicators, all derived solely from the distribution function.

Group of young researchers in higher education institutions in general perform demandable tasks with relatively high contribution to institutions' and societies' innovation production. In order to analyse in more details interaction among young researchers and diverse institutions in society, we aim toward developing the numerical simulation, agent-based model. This article presents foundations of the model, preliminary results of its simulation along with perspectives of its further development and improvements.