BER Performance of IM/DD FSO System with OOK using APD Receiver

In this paper, the performance of intensity-modulated with direct detection (IM/DD) free space optical (FSO) system using the on-off keying (OOK) and avalanche photodiode (APD) receiver is observed. The gamma-gamma model is used to describe the effect of atmospheric turbulence since it provides good agreement in the wide range of atmospheric conditions. In addition, the same FSO system with equal gain combining applied at the reception is analyzed. After theoretical derivation of the expression for the bit error rate (BER), the numerical integration with previously specified relative calculation error is performed. Numerical results are presented and confirmed by Monte Carlo simulations. The effects of the FSO link and receiver parameters on the BER performance are discussed. The results illustrate that the optimal APD gain in the minimum BER sense depends considerably on the link distance, atmospheric turbulence strength and receiver temperature. In addition, the value of this optimal gain is slightly different in the case of spatial diversity application compared with single channel reception

TESLINI IZUMI U FIZICI I NJEGOV INŽINJERSKI DUH

The article describes Tesla’s inventions in physics. Tesla’s engineering spirit is compared to M. Faraday’s and A. A. Michelson’s spirit of discovery in electromagnetism. Tesla’s unfinished investigative journey, from great experiments in electrical technology and radio technology to the physical theories he derived from them, are examined historically and scientifically. Several discoveries and individual experiments are described that were significant in the subsequent development of accelerator technology, as well as Tesla’s monopole antenna for high power and long-range electromagnetic waves, in which the principle of Tesla’s transformer is applied. Within the framework of classical electromagnetic theory, calculations and modern analysis of the system for the study of Tesla’s model of the long-distance wireless transmission of electromagnetic energy or information are presented, demonstrating the scientific basis for Tesla’s ideas. The coverage of Tesla’s inventions and contributions in the physics and electrical engineering curricula at the University of Zagreb is reviewed, especially in textbooks and other works by Ivan Supek, Vatroslav Lopašić and Tomo Bosanac. An interpretation is offered of Tesla’s interest in Goethe’s poetry, which provided an impetus for his inventions and desire for knowledge.U članku se opisuju Teslini izumi u fizici i njegov inženjerski duh, uz usporedbu s otkrivačkim duhom u elektromagnetizmu M. Faradaya i A. A. Michelsona. Promišlja se, povijesno-znanstvenom metodom, Teslin nedovršeni istraživački put od velikih pokusa u elektrotehnici i radiotehnici do fizikalne teorije koja bi se na njima zasnivala. Opisana su neka otkrića i pojedini pokusi koji su važni za kasniji razvoj akceleratorske tehnologije te Teslina unipol-antena elektromagnetskih valova velikih snaga i dosega u kojima se koristi princip Teslinog transformatora. U okviru klasične elektromagnetske teorije izvedeni su proračuni i moderna analiza sklopa za istraživanja Teslinog modela bežičnog prijenosa elektromagnetske energije ili informacije na daljinu, dokazujući znanstvenu utemeljenost tih Teslinih zamisli. Dan je osvrt i na zastupljenost Tesle i njegovih izuma i doprinosa u nastavi fizike i elektrotehnike na Sveučilištu u Zagrebu, napose u udžbenicima i radovima Ivana Supeka, Vatroslava Lopašića i Tome Bosanca. Na kraju se protumačio Teslin interes za Goetheovom poezijom, što je stalno poticalo Teslinu težnju za izumima i spoznajom

Phase transition of interacting disordered bosons in one dimension

Interacting bosons generically form a superfluid state. In the presence of disorder it can get converted into a compressible Bose glass state. Here we study such transition in one dimension at moderate interaction using bosonization and renormalization group techniques. We derive the two-loop scaling equations and discuss the phase diagram. We find that the correlation functions at the transition are characterized by universal exponents in a finite region around the fixed point.Comment: five pages and two pages and one figur

The Effect of Randomness on the Mott State

We reinvestigate the competition between the Mott and the Anderson insulator state in a one-dimensional disordered fermionic system by a combination of instanton and renormalization group methods. Tracing back both the compressibility and the ac-conductivity to a vanishing kink energy of the electronic displacement field we do not find any indication for the existence of an intermediate (Mott glass) phase.Comment: 4 page

Transnationalism of Еuropean christian democracy in 20th century

Хришћанска демократија представља један од најзначајнијих идеолошких праваца у Западној Европи, који је од друштвено-политичког покрета и конфесионалних партија, прерастао у водеће европске демократске партије настале након Другог светског рата. Демохришћански лидери који су изразито били посвећени начелима хришћанске демократије, покренули су процес европских интеграција који је резултирао стварањем Европске уније. Демохришћанске идеје федерализма, социјалне тржишне привреде, социјалне правде и принципа супсидијарности обликовале су процес европских интеграција, постајући кључно обележје наднационалне европске политике. Демохришћанска идеја је свој извор имала у римокатоличкој социјалној мисли и принципима универзалности и персонализма који су током времена задобијали нови идеолошки оквир који је, поред хришћанских вредности, био прожет демократским и секуларним принципима утканим у политичка начела хришћанске демократије. Рад настоји да покаже да је демохришћанско политичко деловање посебно добило на значају транснационалним удруживањем демохришћана, које је почело да се развија још од двадесетих година XX века. Разлози за демохришћански транснационализам леже како у демохришћанском схватању друштва које надилази оквире нације и државе, тако и у политичким околностима које су упућивале на удруживање и заједничко деловање демократских политичких снага на простору Западне Европе. Демохришћански транснационализам подразумевао је транснационални простор који се огледао у стварању европског партијског система и развоју политичког програма ЕУ. Европска народна партија као кровна конструкција свих демохришћана у Европи била је прва европска политичка партија, али и најјача посланичка група у Европском парламенту, чије је деловање директно утицало на саму институционалну и политичку архитектуру Европске уније. Допринос хришћанске демократије и њених лидера у процесу изградње ЕУ, као и демохришћански вредносни оквир, уз све идеолошке и политичке промене, главни су истраживачки циљ за којим трага овај рад. Такође, у раду се разматрају демохришћански принципи који су постали саставни део европског законодавства, као и конкретни примери и фазе транснационалног демохришћанског ангажмана који је био гарант наставка процеса европских интеграција, упркос политичким кризама које су претиле да тај процес зауставеChristian Democracy is one among the most significant ideological directions in Western Europe, which had evolved from a socio-political movement and confessional political parties into the leading European democratic parties that emerged after World War II. Manifestly committed to the principles of Christian democracy, Christian Democrat leaders had initiated the European integration process which has resulted in the creation of the European Union. Christian Democrat ideas of federalism, social market economy, social justice, and the subsidiarity principle, were the ones to shape the process of European integration, thus becoming a hallmark feature of European supra-national policy. The Christian Democrat idea was inspired by the Roman Catholic social thought, and by the principles of universality and personalism; over time, these have appropriated a new ideological framework which, in addition to core Christian values, became infused with democratic and secular principles embedded into political tenets of Christian democracy. This thesis seeks to demonstrate that the significance of Christian democratic political engagement has been particularly fuelled by transnational associating of Christian Democrats that has begun in 1920s. The reasons of Christian Democrat transnationalism are to be found both in the Christian Democrat concept of a society that transcends the limits of nation and state, and in the political background that gave rise to the allying and joint operation of democratic political forces in Western Europe. Christian Democrat transnationalism implied a transnational space, which reflected in the creation of the European party system and the development of the EU’s political programme. The European People’s Party, as an umbrella of all Christian Democrats in Europe, was the first European political party and also the largest parliamentary group in the European Parliament, whose activities have directly impacted the European Union’s institutional and political architectures. The contribution invested by Christian Democracy and its leaders to the development of EU, as well as the Christian Democrat values framework together with its ideological and political modifications, are the core researching objectives being sought by this thesis. Further, the thesis examines Christian Democrat principles which became incorporated into European legislation, and includes specific examples and stages of Christian Democrat’s transnational operation which was the guarantor of the continuing European integrations, regardless of the political crises threatening to halt this proces

The maximal energy of classes of integral circulant graphs

The energy of a graph is the sum of the moduli of the eigenvalues of its adjacency matrix. We study the energy of integral circulant graphs, also called gcd graphs, which can be characterized by their vertex count $n$ and a set $\cal D$ of divisors of $n$ in such a way that they have vertex set $\mathbb{Z}_n$ and edge set ${{a,b}: a,b\in\mathbb{Z}_n, \gcd(a-b,n)\in {\cal D}}$. For a fixed prime power $n=p^s$ and a fixed divisor set size $|{\cal D}| =r$, we analyze the maximal energy among all matching integral circulant graphs. Let $p^{a_1} < p^{a_2} < ... < p^{a_r}$ be the elements of ${\cal D}$. It turns out that the differences $d_i=a_{i+1}-a_{i}$ between the exponents of an energy maximal divisor set must satisfy certain balance conditions: (i) either all $d_i$ equal $q:=\frac{s-1}{r-1}$, or at most the two differences $[q]$ and $[q+1]$ may occur; %(for a certain $d$ depending on $r$ and $s$) (ii) there are rules governing the sequence $d_1,...,d_{r-1}$ of consecutive differences. For particular choices of $s$ and $r$ these conditions already guarantee maximal energy and its value can be computed explicitly.Comment: Discrete Applied Mathematics (2012

Supplementary material for the article: Jevtić, S.; Stefanović, A.; Stanković, D. M.; Pergal, M. V.; Ivanović, A. T.; Jokić, A.; Petković, B. B. Boron-Doped Diamond Electrode — A Prestigious Unmodified Carbon Electrode for Simple and Fast Determination of Bentazone in River Water Samples. Diamond and Related Materials 2018, 81, 133–137. https://doi.org/10.1016/j.diamond.2017.12.009

Supplementary material for: [https://doi.org/10.1016/j.diamond.2017.12.009]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2081]Related to accepted version: [http://cherry.chem.bg.ac.rs/handle/123456789/3177

Supplementary material for the article: Jevtić, S.; Stefanović, A.; Stanković, D. M.; Pergal, M. V.; Ivanović, A. T.; Jokić, A.; Petković, B. B. Boron-Doped Diamond Electrode — A Prestigious Unmodified Carbon Electrode for Simple and Fast Determination of Bentazone in River Water Samples. Diamond and Related Materials 2018, 81, 133–137. https://doi.org/10.1016/j.diamond.2017.12.009

Supplementary material for: [https://doi.org/10.1016/j.diamond.2017.12.009]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2081]Related to accepted version: [http://cherry.chem.bg.ac.rs/handle/123456789/3177