Quantum transport in semiconductor quantum dot superlattices: electron-phonon resonances and polaron effects

Electron transport in periodic quantum dot arrays in the presence of interactions with phonons was investigated using the formalism of nonequilibrium Green's functions. The self-consistent Born approximation was used to model the self-energies. Its validity was checked by comparison with the results obtained by direct diagonalization of the Hamiltonian of interacting electrons and longitudinal optical phonons. The nature of charge transport at electron -- phonon resonances was investigated in detail and contributions from scattering and coherent tunnelling to the current were identified. It was found that at larger values of the structure period the main peak in the current -- field characteristics exhibits a doublet structure which was shown to be a transport signature of polaron effects. At smaller values of the period, electron -- phonon resonances cause multiple peaks in the characteristics. A phenomenological model for treatment of nonuniformities of a realistic quantum dot ensemble was also introduced to estimate the influence of nonuniformities on current -- field characteristics

NOx emissions from intermediate-temperature combustion of steel-industry by-product gases

Journal ArticleA study of NOx emissions from the combustion of coke-oven gas and blast-furnace gas (steel industry by-product gases) was undertaken using detailed kinetic modeling to elucidate the pathways for NOx formation. The study was performed at the intermediate temperatures (1200-1400K) and 1 atm, which represent conditions found in a commercial, ultra-low NOx burner. Simulation results indicated that nitric oxide is formed exclusively in the radical-rich flame zone under these conditions. The traditionally-accepted pathway of Fenimore 'prompt' NO formation, through methylidene and methylene attack on nitrogen molecules, was found to play no role under the conditions of our simulations. In light of this finding, kinetic pathways for NO formation were re-examined. It was found that, according to currently available kinetic parameters, the NO formation is controlled by the H + N 2 reaction. Recently published studies on this reaction, as well as on the rate for the products-set-corrected spin-conserved pathway for the CH + N2 reaction, agree with our finding that the H + N2 channel will be the dominant initiation reaction to NO formation from nitrogen molecule. The NOx emissions from our simulations were found to consist almost exclusively of nitric oxide

Leak Detection and Localization through Demand Components Calibration

Success in the application of any model-based methodology (e.g., design, control, supervision) highly depends on the availability of a well-calibrated model. The calibration of water distribution networks needs to be performed online due to the continuous evolution of demands. During the calibration process, background leakages or bursts can be unintentionally incorporated to the demand model and treated as a system evolution (change in demands). This work proposes a leak-detection and localization approach to be coupled with a calibration methodology that identifies geographically distributed parameters. The approach proposed consists in comparing the calibrated parameters with their historical values to assess if changes in these parameters are caused by a system evolution or by the effect of leakage. The geographical distribution allows unexpected behavior of the calibrated parameters (e.g., abrupt changes, trends, etc.) to be associated with a specific zone in the network. The performance of the methodology proposed is tested on a real water distribution network using synthetic data. Tested scenarios include leaks occurring at different locations and ranging from 2.5 to 13% of the total consumption. Leakage is represented as pressure-dependent demand simulated as emitter flows at the network nodes. Results show that even considering a low number of sensors, leaks with an effect on parameters higher than the parameters’ uncertainty can be correctly detected and located within 200 m.FP7 - ICT - 2012 - 318556 (EFFINET)European CommissionPolytechnic University of Cataloni

A Formal Analysis of a Business Contract Language

This paper presents a formal system for reasoning about violations of obligations in contracts. The system is based on the formalism for the representation of contrary-to-duty obligations. These are the obligations that take place when other obligations are violated as typically applied to penalties in contracts. The paper shows how this formalism can be mapped onto the key policy concepts of a contract specification language, called Business Contract Language (BCL), previously developed to express contract conditions for run time contract monitoring. The aim of this mapping is to establish a formal underpinning for this key subset of BCL

Distribution of Electric Currents in Solar Active Regions

There has been a long-lasting debate on the question of whether or not electric currents in solar active regions are neutralized. That is, whether or not the main (or direct) coronal currents connecting the active region polarities are surrounded by shielding (or return) currents of equal total value and opposite direction. Both theory and observations are not yet fully conclusive regarding this question, and numerical simulations have, surprisingly, barely been used to address it. Here we quantify the evolution of electric currents during the formation of a bipolar active region by considering a three-dimensional magnetohydrodynamic simulation of the emergence of a sub-photospheric, current-neutralized magnetic flux rope into the solar atmosphere. We find that a strong deviation from current neutralization develops simultaneously with the onset of significant flux emergence into the corona, accompanied by the development of substantial magnetic shear along the active region's polarity inversion line. After the region has formed and flux emergence has ceased, the strong magnetic fields in the region's center are connected solely by direct currents, and the total direct current is several times larger than the total return current. These results suggest that active regions, the main sources of coronal mass ejections and flares, are born with substantial net currents, in agreement with recent observations. Furthermore, they support eruption models that employ pre-eruption magnetic fields containing such currents.Comment: 6 pages, 5 figures, to appear in Astrophysical Journal Letter

Implementation of packet processing functions in high capacity internet routers.

Internet predstavlja jedan od najvažnijih temelja razvoja modernog društva i učestvuje u svim aspektima svakodnevnog života - poslovnom, socijalnom, zabavnom, edukativnom itd. Internet je postigao globalni uspeh zahvaljujući svojoj robusnosti i mogućnosti da povezuje različite tehnologije u jednu meñusobno povezanu mrežu. Osnovu arhitekture Interneta čine ruteri koji omogućavaju globalnu povezanost svih delova Internet mreže. Pošto ruteri čine osnovnu gradivnu jedinicu Interneta, performanse i mogućnosti rutera imaju ogroman uticaj na kvalitet rada Internet mreže. Broj Internet korisnika neprestano raste. Takoñe, razvijaju se i nove aplikacije i servisi koji zahtevaju sve veće protoke, usled čega se u Internet mreži instaliraju linkovi sve većih kapaciteta. Kao posledica, količina saobraćaja na Internetu neprestano raste, pa samim tim Internet ruteri postaju sve opterećeniji, naročito u jezgru Internet mreže gde je saobraćaj najintezivniji. Internet ruteri moraju neprestano da se usavršavaju i unapreñuju, da bi mogli veoma brzo obrañivati ogromne količine podataka. Dodatne otežavajuće okolnosti sa stanovišta obrade podataka u ruterima su potreba za uvoñenjem mehanizama kvaliteta servisa i multikast saobraćaj koji je sve popularniji. Mnogi istraživači i naučnici rade na unapreñivanju funkcionalnosti rutera i razvoju novih rešenja i algoritama koji treba da omoguće efikasniji rad rutera. Meñutim, velik problem u razvoju novih rešenja i unapreñenja postojećih funkcija je zatvorenost rutera komercijalnih proizvoñača pa samim tim razvijana rešenja se tipično ispituju zasebno bez potpune integracije sa svim funkcijama rutera. Ovakav način ispitivanja je nepotpun jer ne omogućava kompletan uvid u kvalitet rada novog rešenja u realnom okruženju. Da bi se izbegli navedeni problemi, razvojni tim pod vodstvom dr Aleksandre Smiljanić je u okviru projekta „Sistemska integracija Internet rutera“ podržanog od strane Ministarstva za Nauku i tehnološki razvoj Republike Srbije započeo razvoj prototipa Internet rutera. Konačni cilj projekta je bio razvoj komercijalnog proizvoda, meñutim, pored ovog cilja namera je bila i da se obezbedi otvorena platforma istraživačima i studentima na kojoj bi mogli da proučavaju internu strukturu i arhitekturu rutera i da razvijaju i testiraju nova rešenja u realnom okruženju.Internet is one of the most important parts of the modern society. It participates in all aspects of everyday’s life - business, social, entertainment, education etc. Internet achieved global success thanks to its robustness and internetworking between various technologies. Routers enable Internet’s global connectivity and thus represent the foundation of the Internet. As routers are the main components of the Internet, their performances and capabilities have great impact on Internet quality performances. The number of Internet users continuously grows. New applications and services that demand high throughput are constantly developed, and as consequence higher capacity links are installed. The Internet traffic continuously grows, so Internet routers are more and more loaded with traffic, especially in the Internet core, where Internet traffic is most intensive. Therefore, Internet routers must be always upgraded to support high speed processing of large amount of the Internet traffic. QoS mechanisms and multicast traffic represent additional difficulties in the future router development. Many researchers and scientists are involved in router development process that includes development of new solutions and algorithms that enable more efficient router performances. However, the main problem in the development process is the closed router architecture in routers of commercial companies, thus developed solutions are tested without complete integration with the rest of the router functions. This leads to incomplete development and testing. To avoid aforementioned problems, research team led by Aleksandra Smiljanić started Internet router prototype development in the project „System integration of the Internet router“ supported by the Serbian Ministry of Science. The main goal of the project was development of the commercial router. Also, very important goal was development of the open source platform for researchers and students that would be used for the education purposes, as well as the research purposes where new solutions could be tested in the real environment. Internet routers contain two planes - data plane and control plane. Data plane is implemented in hardware and is responsible for fast IP packet processing. Control plane is implemented in software and is responsible for communication with router’s environment (neighbor routers, administrators and etc.). In this PhD thesis IP packet processors are developed and implemented. IP packet processors represent the most important part of the data plane

Nauka i proces industrijalizacije u Srbiji

Predavanje na Inženjerskom forumu 4: Nacionalne tehnološke platforme Srbije. 160 godina industrije i fabrike za budućnost Srbije Beograd, Srpska akademija nauka i umetnosti, 5. decembar 2013

The Influence of Mechanical Deformation on Some Characteristics of Bipolar Semiconductor Devices

Rad je posvećen proučavanju elektronskih karakteristika germanijuma i silicijuma i bipolarnih poluprovodni čkih naprava podvrgnutih elastičnoj mehaničkoj deformaciji. Cilj prve dve glave ovog rada bio je da formuliše opštu teoriju pomoću koje bi se mogli razmatrati fenomeni prenosa naelektrisanja kod poluprovoclnika i problemi injekcije manjinskih nosilaca kod bipolarnih poluprovodničkih naprava, podvrgnutih deformaciji koja je nastala spoljašnjom primenom sile ili je poslediea mehaničkih napona uvedenih u toku tehnoloških procesa njihovog dobijanja. Pri formulaciji ove teorije korišćen je model deformacionog potencijala i Kroemerov dokaz egzistencije kvazielektričnih sila u nehomogenim poluprovodnicima. Tako razvijena teorija primenjena je u trećoj glavi, na proučavanje uticaja nehomogene deformacije na statičke karakteristike bipolarnih poluprovodničkih naprava. Posebna pažnja posvećena je smanjenju pojačanja tranzistora, pod uticajem lokalizovane, spolja primenjene deformacije i deformacije nastale pri difuziji visokih koncentracija primesa u emiteru. Pri razmatranju problema smanjenja pojačanja pod uticajem lokalizovane deformacije, bilo je potrebno da se pored teorije razvijene u prve dve glave razmotri i uticaj efekta „visoke injekcije“ u deformisanoj oblasti. Ovi uslovi nastaju pri dovoljno velikim kompresionim deformacijama, pošto su injektovane struje manjinskih nosilaca, eksponencijalno povezane sa mehaničkim naponima u toj oblasti. Ovde dato razmatranje, pretstavlja proširenje našeg ranije objavljenog rada, s tim što su pored naših eksperimentalnih rezultata za silicijumske tranzistore uključeni i novi eksperimentalni rezultati Sirkina i Feokistove koji pokazuju da se navedena teorija može sasvim dobro primeniti i na germanijumske i na silicijumske tranzistore. Osim tog, ovde je data teorija i eksperimentalni rezultati otkrivenog efekta povećanja probojnog napona kolektor-emiter usled primene lokalizovane deformacije na emiter planarnog tranzistora. Praktičan značaj proučavanja uticaja lokalizovane deformacije na pojačanje tranzistora sa uzemljenim emitorom povezan je sa činjenicom da je ovaj efekat najčešće korišćen pri konstrukciji pretvarača pritiska poznatih pod nazivom „Pitran“, poluprovodničkih mikrofona itd. Proučavanje uticaja mehaničkih napona nastalih u toku tehnoloških procesa izrade bipolarnih poluprovodničkih naprava na njihove karakteristike, inspirisano je ranije eksperimentalno ustanovljenom činjenicom da se pojačanje tranzistora sa uzemljenim emiterom smanjuje pri povećanju koncentracije primesa kojima se dopinguju emiter i baza. Ovaj efekat, kao i efekti anomalne difuzije bora i fosfora i silicijum predstavljaju ograničenje daljeg razvoja visokofrekventnih silicijumskih tranzistora, jer se pri njihovoj fabrikaciji, radi postizanja visokih graničnih frekvencija koriste visoke koncentracije primesa. Mada se razmatranje ovog efekta komplikuje činjenicom da je pri analizi potrebno koristiti nedovoljno razvijenu teoriju p-n spojeva, formiranih od degenerisanih poluprovodnika, i uračunati efekat politropije primesa, mi smo pokazali da se pomoću teorije razvijene u prve dve glave ovog rada, mogu kvalitativno, a u nekim slučajevima i kvantitativno objasniti navedeni efekti. Kraj treće glave posvećen je teoriji anomalnih ili kooperativnih efekata difuzije. Mi smatramo, da je teorija data u prvom delu ovog rada ovde našla jednu od najpotpunijih primen

Uloga nautičkog turizma u održivom razvoju Crne Gore

In the last quarter of the twentieth century, Montenegro, by virtue of tourism development, finally came up with an opportunity to valorize exceptional natural beauties and thus provide significant revenues for the national economy. However, although in that period, in the developed Mediterranean destinations and in America, nautical tourism, as one of the forms of tourism, recorded exceptional growth rates, in Montenegro, this segment of the tourist offer has begun to develop more seriously in the last ten years. Growth and development of nautical tourist offer in Montenegro is not the result of strategic planning activities, but the epilogue of individual initiatives of private investors, which calls into question the future sustainability of this process. Purpose of research – The purpose of research in the subject doctoral dissertation is firstly reflected in providing a comprehensive insight into the chronology of development and the state of nautical tourism as part of a complex economic phenomenon such as tourism in general. After describing the role of tourism in Montenegro, the research focuses on establishing a relationship between the development of nautical tourism and the previously established principles of sustainable development in Montenegro. The ultimate intention is to emphasize the importance of applying the principles of sustainability in all development stages of nautical tourism on the Montenegrin part of the Adriatic. Research design - Empirical research was carried out by processing and analyzing data from primary and secondary sources. Data obtained from secondary sources are the basis for establishing projections of future trends, while data from primary sources, collected by surveying 116 stakeholders in the period from 2012 to the end of 2017, were put into the function of testing the previously defined expectations. Research findings - After evaluating the role of tourism in general and nautical in particular, it was established that these activities are of strategic importance for the economy of Montenegro, and that they represent one of the foundations of future prosperity, only if they are realized in accordance with the principles of sustainable development. Significance of research - Since nautical tourism is relatively poorly explored in Montenegro, the significance of this research is reflected in a comprehensive analysis of this developmental phenomenon, on the basis of which appropriate conclusions were made, along with recommendations for future activities within the framework of reasonably observed sustainable parameters, on a specific tourist destination - Montenegrin coast