Dynamics of relaxor ferroelectrics

We study a dynamic model of relaxor ferroelectrics based on the spherical random-bond---random-field model and the Langevin equations of motion. The solution to these equations is obtained in the long-time limit where the system reaches an equilibrium state in the presence of random local electric fields. The complex dynamic linear and third-order nonlinear susceptibilities $\chi_1(\omega)$ and $\chi_3(\omega)$, respectively, are calculated as functions of frequency and temperature. In analogy with the static case, the dynamic model predicts a narrow frequency dependent peak in $\chi_3(T,\omega)$, which mimics a transition into a glass-like state.Comment: 15 pages, Revtex plus 5 eps figure

High-Temperature Dielectric Response of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3: Does Burns Temperature Exist in Ferroelectric Relaxors?

It has been considered that polar nanoregions in relaxors form at Burns temperature Td approx 600 K. High-temperature dielectric investigations of Pb(Mg1/3Nb2/3)O3 (PMN) and 0.7PMN-0.3PbTiO3 reveal, however, that the dielectric dispersion around 600 K appears due to the surface-layer contributions. The intrinsic response, analyzed in terms of the universal scaling, imply much higher Td or formation of polar nanoregions in a broad temperature range, while high dielectric constants manifest that polar order exists already at the highest measured temperatures of 800 K. The obtained critical exponents indicate critical behavior associated with universality classes typically found in spin glasses

Feasibility study of the brewing process using the ANSI/ISA – 88 standard

V magistrski nalogi je prikazana študija izvedljivosti vodenja procesa varjenja piva po standardu ANSI/ISA-88. Celotna rešitev je na nivoju vodenja izvedena po standardu ANSI/ISA – 88, in sicer v programskem okolju Siemens TIA Portal. Siemens TIA Portal je namenjen programiranju logičnih krmilnikov in vmesnikov človek-stroj. Standard ANSI/ISA – 88 je razvit tako za namene vodenja procesa kot tudi načrtovalno filozofijo pri načrtovanju procesa. Standard skozi filozofijo načrtovanja vodenja predvideva uporabo stanj in ukazov. Ukazi po standardu ANSI/ISA – 88 predpisujejo pogoj za prehod procesa iz stanja obratovanja v enega od stanj, ki so predpisani po tem, ko je ukaz izpolnjen. V prvem delu naloge so razložene osnove standarda ANSI/ISA – 88 na primeru procesa varjenja piva, ter procesni, fizični in postopkovni modeli. Predstavljene so povezave med modeli, stanja ter osnovni ukazi za vodenje procesa po standardu ANSI/ISA-88. Grafično so predstavljene povezave med stanji in ukazi. Vsak od ukazov ima pogoje za proženje, prav tako pa ima tudi vsako od stanj pogoj, da je aktivno. Stanja in ukazi so detajlno obrazloženi v prvem delu. Predstavljen je tudi osnovni postopek proizvodnje piva, ki sestoji iz šestih osnovnih procesov. V drugem delu naloge je predstavljena študija izvedljivosti vodenja procesa varjenja piva. V študiji sem izvedel vodenje, ki zajema uporabo ukazov in stanj kot jih narekuje standard ANSI/ISA – 88, na PLK-ju. Študija zajema vseh šest osnovnih procesov, ki so potrebni za proizvodnjo piva. Izvedena je tudi vizualizacija nadzornega sistema vsakega izmed segmentov in vizualizacija fazne logike - PLI-ja. Vizualizacija je združena v tri sklope in zajema vizualizacijo vseh šestih osnovnih procesov, vmesnik PLI pa prikazuje stanje vsakega procesa.The thesis presents a feasibility study of process control in beer production according to ANSI/ISA – 88 standard. The complete solution in terms of process control is implemented in Siemens TIA Portal software, which is intended for programing programmable logic controllers and human machine interfaces. The standard was developed in order to provide a consistent set of standards and terminology for batch control and design philosophy. The philosophy of the standard proposes a control design based on actions and states. The actions define a transition condition for crossing from one state to another. The first part of the thesis presents the basics of the ANSI/ISA – 88 standard on the example of a brewing process, where process models, physical models, procedural models, and the relations between the models, commands and states are explained. Each command has a requirement for triggering. Similarly, also the states have a requirement for transition into other states. The first part also includes an explanation of the brewing process, which consists of six basic processes. The second part of the thesis includes a feasibility study of the brewing process control using the ANSI/ISA – 88 standard. Process control is designed and developed in Siemens TIA Portal according to the ANSI/ISA – 88 standard philosophies on the PLC control level. The study includes implementation of all six basic processes of beer production. The second part also shows the designed solution on the HMI level with PLI visualization and control visualization of each process part. The visualization is divided to three main parts, which include all basic process on the visualization level and the visualization of the PLI of each process

USING THE MULTIPATH TCP PROTOCOL IN A HYBRID ACCESS NETWORK

Protokol za krmiljenje prenosa (TCP) je eden najbolj uporabljenih protokolov transportnega sloja. Pri uporabi sodobnih komunikacijskih naprav, ki imajo več omrežnih vmesnikov, pa se pokaže njegova omejenost. Vzpostavljena seja TCP se prekine, ko končna naprava zamenja omrežno povezljivost z enega vmesnika na drugega. Poleg tega pri napravah z več omrežnimi vmesniki nimamo možnosti, da bi znotraj ene seje izkoristili kapacitete obeh prenosnih poti. Namen naloge je predstaviti protokol Multipath TCP (MPTCP) in njegovo uporabo v hibridnem dostopovnem omrežju. Na začetku sem na kratko opisal zgodovino protokola TCP ter pojasnil vzroke za njegovo evolucijo, ki jo predstavlja protokol multipath TCP. Sledi podrobnejša analiza delovanja protokola in razlogi za njegovo vpeljavo. Multipath TCP je odprtokoden in možno ga je implementirati v Linux jedro. Navedel sem nekaj primerov, kjer ga že uporabljajo v komercialne namene. Predvsem me je zanimala izvedba hibridnega dostopa do interneta, kjer hkrati uporabimo širokopasovni dostop prek fiksnega omrežja digitalne naročniške zanke in mobilnega omrežja dolgoročne evolucije (LTE). Predstavil sem prednosti in slabosti take rešitve in jo podrobneje preveril v petem poglavju. V ta namen sem izvedel testno postavitev, kjer sem v jedro Linux operacijskega sistema implementiral MPTCP ter postavil vzpostavil dodaten proxy strežnik. Generiral sem internetni promet in spremljal, kako se ustvari več hkratnih povezav ter kako se porazdeli promet. Naknadno sem preveril, kaj se zgodi ob morebitnem izpadu ene povezave in kako dodatna omrežna povezava poveča prenosne hitrosti. Z meritvami sem določil spodnjo mejo jakosti signala LTE, da ne prihaja do prevelikega nihanja, ter predlagal uporabo zunanjih anten za stabilnejše delovanje. Opisal sem ovire, ki so se pojavile pri testiranju, in na koncu predstavil nekaj možnosti potencialne komercialne uporabe. Izkazalo se je, da je hibridni dostop zelo primerna rešitev za internetne ponudnike, ki želijo izboljšati svoje storitve predvsem na območjih s slabšimi internetnimi povezavami.Transmission control protocol (TCP) is one of the most used protocols on the transport layer of ISO/OSI model. When using devices with multiple network interfaces we encounter its limits. Established TCP session fails when end device changes network connection from one interface to another. Moreover, these devices do not have the ability to transfer data over both interfaces at the same time to increase throughput. The objective of this thesis is to introduce the protocol Multipath TCP (MPTCP) and its usage in hybrid access network. First I described a TCP protocol and how it came to the idea of upgrading it to multipath TCP. I analyzed the principles of how it works and where or why it could be useful. Multipath TCP is an open-source protocol and it is possible to implement it into Linux kernel. There are already some innovative products that use it on the field. The main focus was the usage of MPTCP in hybrid access, where we used fixed broadband network and mobile network of long term evolution (LTE). In the fifth chapter I introduced benefits and drawbacks of this solution. Proof of concept was made with the implementation of MPTCP in the Linux kernel and setting up a proxy server. I generated internet traffic and observed the creation of subflows and usage of multiple network interfaces. MPTCP offers backup in case of failure of one network interface. Observation of hand-over was made with various Linux tools. With field measurements of LTE signal I evaluated what is the lowest signal strength that guarantees stable connection and proposed usage of external antennas. Challenges during testing were middleboxes that do not support MPTCP. In conclusion, hybrid access with multipath TCP is a very suitable solution for internet service providers that would like to offer advanced services in rural areas