Rare-earth–activated glass ceramics for use as solar-cell down-converter layers

The efficiency of a solar cell can be increased by using photon management to make better use of the solar spectrum. In particular the downconversion process which permits us to obtain two low-energy (980 nm) photons from one high-energy photon. In particular we present a system consisting of a 70 SiO2-30 HfO2 glass ceramic waveguide co-doped with Tb3+ and Yb3+ ions. We present the assesment of the energy transfer efficiency from an excited Tb3+ ion to two Yb3+ ions in its vicinity

Information-theoretic measures as a generic approach to human-robot interaction : Application in CORBYS project

Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for third-party components of this work must be honored. For all other uses, contact the Owner/AuthorThe objective of the CORBYS project is to design and implement a robot control architecture that allows the integration of high-level cognitive control modules, such as a semantically-driven self-awareness module and a cognitive framework for anticipation of, and synergy with, human behaviour based on biologically-inspired information-theoretic principles. CORBYS aims to provide a generic control architecture to benefit a wide range of applications where robots work in synergy with humans, ranging from mobile robots such as robotic followers to gait rehabilitation robots. The behaviour of the two demonstrators, used for validating this architecture, will each be driven by a combination of task specific algorithms and generic cognitive algorithms. In this paper we focus on the generic algorithms based on information theoryFinal Accepted Versio

Counting addressing method: Command addressable element and extinguishing module

The specific requirements that appear in addressable fire detection and alarm systems and the shortcomings of the existing addressing methods were discussed. A new method of addressing of detectors was proposed. The basic principles of addressing and responding of a called element are stated. Extinguishing module is specific subsystem in classic fire detection and alarm systems. Appearing of addressable fire detection and alarm systems didn't caused essential change in the concept of extinguishing module because of long calling period of such systems. Addressable fire security system based on counting addressing method reaches high calling rates and enables integrating of the extinguishing module in addressable system. Solutions for command addressable element and integrated extinguishing module are given in this paper. The counting addressing method was developed for specific requirements in fire detection and alarm systems, yet its speed and reliability justifies its use in the acquisition of data on slowly variable parameters under industrial conditions.

Interdependence of fundamental and applied research in material science

Development of materials with desirable properties essentially depends on realization of interdependence: natural science ⇔ technical sciences. Taking this into account, in order to develop of new advanced materials it is essential to determine principles that characterize this interdependency. Therefore, in this article the principles of fundamental research and the importance of obtained results are considered and implemented in the field of technical realizations

Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy

The magnetization processes in binary magnetic/nonmagnetic amorphous alloy Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied with the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained with the superparamagnetic behaviour of the single domain magnetic clusters inside the nonmagnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found out that magnetic clusters occupy the characteristic volume from 25 up to 200 nm3 . The validity of the superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long range magnetic ordering. This work throws more light on magnetic behaviour of other amorphous alloys, too

Methodology of incereasing reamening working life parts of ventilation mills

Последњих година спроводе се значајна истраживања, која се односе на продужење животног века радних делова термоенергетских постројења. Опрема у термоелектранама је изложена дуготрајном дејству високих температура и притисака, хабању и цикличном оптерећењу. У наведеним условима експлоатације различити узроци могу довести до оштећења, појединих компонената као што је хабање радних делова вентилационог млина. Последице су смањење производног капацитета и вентилационог дејства млина у односу на пројектовану вредност, као и чести застоји због замене делова, што значајно утиче на продуктивност, економичност и енергетску ефикасност термоелектране. Уколико се констатује оштећење компоненте, које може довести до поремећаја у раду постројења, у пракси постоје три могућности: да се она остави у погону уз редовну и чешћу контролу, да се изврши ревитализација компоненте или да се замени потпуно новом компонентом. Одлука се доноси на основу техничких, технолошких и економских критеријума у зависности од могућности набавке новог дела, цене замене или ревитализације, могућности заустављања постројења и аспеката сигурности и заштите околине. У овиру ове докторске тезе пажња је усмерена на анализу радних услова и израду процедуре за продужење радног века делова вентилационог млина у Термоелектрани Костолац Б, поступцима наваривања и метализације. Тачније, предмет ових истраживања ће бити да се на основу техничко – технолошке анализе рада и стања компоненти вентилационог млина, које су доминантно изложене абразивном и ерозивном хабању, изврши избор радног дела, у овом случају усисних плоча, као и карактеризација основног материјала. Први део дисертације је усмерен и на примену савремених метода нумеричке симулације вишефазног струјања у вентилационом млину у циљу детаљније анализе услова хабања (проблема) везаних за појаву абразије и ерозије изабране компоненте. На овај начин, применом софтверског пакета ANSYSFLUENT 12, добиће се детаљнији приказ мултифазног струјања и брзине мешавине која омогућује да се на основу интензитета и смера брзине, прецизније одреде критичне зоне у којима ће се појавити оштећења елемената вентилационог млина. Ове зоне се по правилу налазе у оним деловима млина, у којима је због смера и брзине струјања као и удела чврстих честица смеше (угаљ, минералне материје, песак) највеће хабање истих...In recent years implemented significant research, concerning the extension of the life of the working parts of a thermal energy plant. Equipment in thermal power plants exposed to long-term effect of high temperatures and pressure, abrasion and load cycle counting. In these circumstances the exploitation of different causes can lead to damages, the individual components such as the wear and tear of working parts of an air mill. The consequences of the reduction in production capacity and air operations of the mill compared to the projected value, as well as frequent delays due to the replacement of parts, which significantly affects the productivity, profitability and energy efficiency of thermal power plants. If is detected damage to components, which can lead to disturbances in the plant, in practice there are three possibilities: that it be left in the drive with a regular and frequent control, to carry out a revitalization component or to replace entirely new component. The decision is made on the basis of technical, technological and economic criteria, depending on the possibilities for acquiring new works, replacement rates or revitalization, the possibilities of stopping the plant and aspects of safety and environmental protection. As part of this doctoral thes is in focus on the analysis of working conditions and create procedures for the extension of the service life of parts of the ventilation mill in thermal power plant Kostolac B, surfacing and metallization processes. More specifically, the subject of this research will be that based on the technical - technological analysis of the work and the state of the components of the ventilation mills, which are predominantly exposed to abrasive and erosive wear, make the selection of the working part, in this case the suction plate and the characterization of the base material. The first part of the dissertation will focus on the use of modern methods of numerical simulation of multiphase flow in ventilation mill for the purpose of detailed analysis of problems related to the occurrence of abrasion and erosion of the selected component. In this way, using the software package ANSYS FLUENT 12, will get a more detailed view of multiphase flow and speed of the mixture that enables that based on the intensity and direction of speed, precisely identify critical areas in which will appear the breakdown of the ventilation mill. These zones are typically located in those parts of the mill, which is due to the direction of flow velocity and content of solid particles mixtures (coal, minerals, sand) maximum wear them...

On the influence of spike shape at supersonic flow past blunt bodies

Da bi se eliminsala pojava jakog udarnog talasa pri nadzvučnom opstrujavanju projektila, koja zanačajno povećava otpor pri letu krozvazduh, na njegov vrh montira se igla. U radu se daju rezultati eksperimentalnog istraživanja uticaja oblika igle na aerodinamičke koeficijente (uzgona, otpora, momenta propinjanja, kao i položaj centra pritiska) pri nadzvučnom opstrujavanju tela zaobljenog vrha. Eksperiment je izveden u aereotunelu, za jednu vrednost Mahovog i Rejnoldsovog broja, kao i za jednu vrednost napadnog ugla α = 2o. Za telo bez igle, kao i za telo sa četiri različita modela igle merene su aerodinamičke sile i momenti. U radu su predloženi kriterijumi za procenu uticaja igle zasnovani isključivo na rezultataima dobijrenim vizualizacijom strujanja. Igla najboljih karakteristika, od ispitanih konfiguracija, izabrana na osnovu izmerenih aerodinamičkih koeficijenata, uklapa se u ove kvalitativne kriterijume.In order to eliminate the appearance of a strong shock wave at a supersonic flight of a missile, which considerably increases the drag during its flight through the air, a spike is mounted on its nose. Presented paper offers the results of an experimental analysis of the influence of the spike's shape on the aerodynamic coefficients (drag, lift and pitching moment coefficient, as well as the location of the center of pressure) at supersonic flow past blunt-nosed body. The experiment was carried out in a wind tunnel, for one value of Mach and Reynolds numbers, and for one value of the angles of attack, α = 2o. For the body without spike, and with four different spike shapes, the aerodynamic forces and moment were measured. Using only the photos obtained by Schlieren visualization of the flow, the paper proposes a criterion of estimating the aerodynamic effect of the spike shape. The best spike shape from the experimental set of spikes, selected by the measurement of the aerodynamic coefficients, coincided with this qualitative criterion

On the influence of spike shape at supersonic flow past blunt bodies

Da bi se eliminsala pojava jakog udarnog talasa pri nadzvučnom opstrujavanju projektila, koja zanačajno povećava otpor pri letu krozvazduh, na njegov vrh montira se igla. U radu se daju rezultati eksperimentalnog istraživanja uticaja oblika igle na aerodinamičke koeficijente (uzgona, otpora, momenta propinjanja, kao i položaj centra pritiska) pri nadzvučnom opstrujavanju tela zaobljenog vrha. Eksperiment je izveden u aereotunelu, za jednu vrednost Mahovog i Rejnoldsovog broja, kao i za jednu vrednost napadnog ugla α = 2o. Za telo bez igle, kao i za telo sa četiri različita modela igle merene su aerodinamičke sile i momenti. U radu su predloženi kriterijumi za procenu uticaja igle zasnovani isključivo na rezultataima dobijrenim vizualizacijom strujanja. Igla najboljih karakteristika, od ispitanih konfiguracija, izabrana na osnovu izmerenih aerodinamičkih koeficijenata, uklapa se u ove kvalitativne kriterijume.In order to eliminate the appearance of a strong shock wave at a supersonic flight of a missile, which considerably increases the drag during its flight through the air, a spike is mounted on its nose. Presented paper offers the results of an experimental analysis of the influence of the spike's shape on the aerodynamic coefficients (drag, lift and pitching moment coefficient, as well as the location of the center of pressure) at supersonic flow past blunt-nosed body. The experiment was carried out in a wind tunnel, for one value of Mach and Reynolds numbers, and for one value of the angles of attack, α = 2o. For the body without spike, and with four different spike shapes, the aerodynamic forces and moment were measured. Using only the photos obtained by Schlieren visualization of the flow, the paper proposes a criterion of estimating the aerodynamic effect of the spike shape. The best spike shape from the experimental set of spikes, selected by the measurement of the aerodynamic coefficients, coincided with this qualitative criterion