Towards Future Low Exposure Mobile Cellular Networks

Explosive growth of different type of wireless networks in the last decade has raised an issue of influence of electromagnetic fields originating from radio frequencies to human health. Thus, more and more researchers working on the solutions for the next generation wireless communication systems now have in mind the necessity of keeping the level of radiated power on the minimum level necessary for achieving the required performances. In this paper we analyze solutions for human exposure reduction in dual-hop Orthogonal Frequency Division Multiplexing (OFDM) based decode-and-forward (DF) relay systems, as this type of relay system is adopted for LTE-Advanced networks, also denoted as 4G. In our approach we seek for the solutions that keep the certain performance metric, i.e. system capacity in this analysis, on the same level like in baseline OFDM DF relay system, but attain exposure reduction from relay station (R) on downlink (DL). In one of the considered solutions, R station, having more than one antenna for DL communication, implements transmit antenna selection (TAS) on subcarrier basis, jointly with ordered subcarrier mapping (SCM). TAS solution assumes that on each subcarrier position, the transmit antenna having the best subcarrier channel transfer function is chosen. Ordered SCM is a technique where subcarriers from the first hop are mapped to corresponding subcarriers on the second hop in accordance to their instantaneous signal-to noise ratios. It is proven to be a mapping scheme that maximizes the achievable capacity in OFDM based DF relay systems, enabling bit error rate improvement at the same time. Besides this solution, we analyze the level of human exposure reduction in the cases where only SCM technique is implemented at R, as well as where only TAS is implemented. We have developed a simulation model for assessing the level of human exposure to EMF, with included real-case simulation parameters given in LTE-Advanced relay reference scenario. In this way, we have obtained and analyzed data on the level of human exposure reduction attained with the proposed solutions in indoor and outdoor environment, and for the different positions of end-users relative to R station.     

Extreme dry weather intervals of the growing season in Bačka,Yugoslavia

A method of describing and analyzing the stochastic process of droughts, which are defined here as the upper extremes of intervals of no rainfall, is recommended. All important components of extreme dry weather intervals such as their duration, time of occurrence, their total number in a given time interval [0, t], the longest drought duration in a given time interval [0, t], and time T(t) of occurrence of the longest drought are taken into consideration. Application of the method is performed using the records of nine meteorological stations in Baka, Yugoslavia and a good agreement is found between the theoretical and empirical distribution functions for all analyzed components of the process. On the basis of the performed computations, a set of maps showing the contours of extreme dry weather intervals, having return periods from 2, 5... up to 100 years, related to the growing season (1 April –30 September), for the region of Baka in Yugoslavia is obtained. If the period of exploitation of an irrigation system is 60 years, then it could be expected to appear as 20 dry weather intervals having 3 year return periods. The duration of dry weather intervals is given on the set of maps. The obtained results give a prognosis of an average state of droughts during long time intervals (60, 100, 200... years).     

Human-and-Humanoid Postures Under External Disturbances: Modeling,Simulation, and Robustness. Part 1: Modeling

It is a well-known fact that the growth of technology has radically changed our approach to biosciences and medicine. What is interesting is that in the last decade we have witnessed a reverse influence—a trend towards “biologically inspired” solutions to technical problems. This leads to a true symbiosis between bio and technical sciences. A good example is the intersection and overlapping of three distinct fields: sports, medicine, and robotics. This paper intends to apply sophisticated methods developed for mathematical modeling of humanoid robots in real human motions, particularly in posture stabilization and selection of appropriate postures for different situation in sports and every day life. A general simulation system is realized: following a deductive principle, the algorithm considers particular human/humanoid motions (like those occurring in different sports) as being just special cases of a general motion and impact theory. Simulation includes the interaction with the environment. Simulating a human/humanoid dynamics in a given task, all relevant characteristics could be found: trajectories, velocities and accelerations, loads of joints, power requirements, energy consumption, contact forces including ground reactions, impact effects, etc. Simulation is used in solving a problem that is important for both humans and humanoid robots, namely, the behavior of a posture (keeping stability or collapsing) when subject to different disturbances. Although “posture” is mainly a static term, maintaining its balance in the presence of disturbances is a truly dynamic problem. Typical postures from every day life and sports are considered, such as: upright standing, squat (and partial squat), and three karate postures. Two sorts of disturbances are applied to eventually, compromise the posture: external impulse and permanent external force. This paper does not aim to suggest some new control strategy but to develop the dynamic model and simulation algorithm, and apply them to compare the robustness of different postures to external disturbances.     

Results of a simple intercomparison of natural radioactivity measurements using a 'blue concrete' sample

A simple intercomparison of natural radioactivity and radon emanation factor measurements co-ordinated by the Medical Physics Department of the University of Cantabria UC, Spain, has been carried out during 1998 in the framework of the EU Concerted Action ERRICCA (European Research into Radon in Construction Concerted Action). All the measurements have been made on a 'blue concrete' sample kindly donated by Dr G. Akerblom from the Swedish Radiation Protection Institute. In addition to UC, two other participant laboratories, STUK from Finland and ZVD from the Republic of Slovenia, have contributed to the development of the intercomparison exercise. Considering the uncertainties of the measurements, a good agreement between the results obtained by the three participating laboratories has been ascertained. However, in accordance with experimental results obtained by other authors, data reported by UC show a significant decrease of the radon emanation factor as moisture content of the sample decreases below 5% (per weight).     

Robustness of the near infrared spectroscopy method determined using univariate and multivariate approach

The robustness assessment is a part of a method validation protocol, during which several characteristics of an analytical method are also evaluated (e.g. accuracy, repeatability, reproducibility, linearity, intermediate precision, measurement uncertainty) in order to assess its fitness for purpose. The purpose of robustness assessment of the near infrared spectroscopy method (NIRS) is to indicate which factor significantly influence the obtained results, as well as to point to the potential problems that might occur in the routine application of the method. The assessment of robustness of the NIRS method included variation of certain operational and environmental factors at three level (−1, 0, 1) by applying univariate (one-variable-at-a-time, OVAT) and multivariate (multivariate-at-a-time, MVAT) approach to the experimental design. Operational and environmental factors that were varied included the number of subsamples to be measured in the NIRS measurement (1), environmental temperature (2), sample temperature (3), environmental air humidity (4), instrument voltage (5) and lamp aging (6). Regardless the applied experimental design, external factors with significant influence on obtained NIRS results were indicated, as well as pointed the potential problems that might occur in the routine application of the method. In order to avoid them, every effort should be made to stabilize instrument and sample temperature and to standardize the homogeneity and number of subsamples to be measured in NIRS measurement. Moreover, the obtained results highlighted the necessity that the NIRS instruments should work through a voltage regulator.     

Simple route for the preparation of graphene/poly(styrene‐b‐butadiene‐b‐styrene) nanocomposite films with enhanced electrical conductivity and hydrophobicity

This paper reports a simple route for the preparation of graphene/poly(styrene‐b‐butadiene‐b‐styrene) (SBS) nanocomposite films employing a vacuum filtration method. Graphene is exfoliated well by an electrochemical procedure and homogeneously dispersed in the polymer matrix. The prepared nanocomposite films were characterized by XRD, Fourier transform IR (FTIR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, AFM and SEM. Morphological studies showed that graphene formed a smooth coating over the surface of SBS. The increase in graphene concentration induces the wrinkling of graphene sheets at the composite surface which causes a further increase in surface roughness. The FTIR, Raman and XPS spectra of graphene/SBS nanocomposite films indicate the strong interactions between graphene and the polymer matrix. According to the XRD patterns, introducing SBS into graphene did not modify the graphene structure additionally, i.e. the crystal lattice parameters do not depend on SBS content in graphene/SBS nanocomposite films. The graphene/SBS nanocomposite films also exhibited better hydrophobicity due to the increased surface roughness and lower sheet resistivity (reduced 10 times) compared to exfoliated graphene. © 2018 Society of Chemical Industry     

Comparative investigations of hydrotreating catalysts in laboratory and process conditions

Hydrotreating procedures have exceptional place in modern oil refineries as the most effective way to improve oil products quality. The variation of process parameters by laboratory reactor simulation using different crudes and catalysts is a useful and economic tool for the optimisation of these processes in practice. There are presented comparative investigations of commercial industrial hydrotreating catalysts and various feeds as a support for real refinery practice.