Usporedba električkih nadomjesnih shema ljudskog zuba korištenih za mjerenje duljine korijenskog kanala

An accurate determination of the root canal length, which is the most critical procedure in the endodontic treatment of a tooth, is commonly performed nowadays by electronic apex locators which are based on electrical impedance measurements. In this paper tooth impedances were measured in vitro on extracted tooth in alginate material using HP 4284A LCR meter and a specially designed stalk with a micrometer for precise file positioning. In order to develop a more accurate measurement procedure human tooth was modeled by electrical equivalent circuit. Four new equivalent circuits comprising of resistors, capacitors and constant-phase elements were proposed in this paper and compared with four previously suggested circuits. Elements of equivalent circuits were determined by complex nonlinear least squares fitting using LEVM software. Different quality factors were defined to describe the fit quality of a certain equivalent circuit at each file position. The overall fitting efficiency in the region of file positions of interest was calculated as well. A detailed discussion was given on equivalent circuit parameters that can be used to measure the root canal length. Upon these results the most appropriate equivalent circuit was selected and a new measurement procedure was proposed.Točno određivanje duljine korijenskog kanala zuba, što je najkritičniji postupak u endodontskom tretmanu, se uobičajeno danas provodi elektroničkim detektorima apeksa koji se temelje na mjerenju električne impedancije. U ovoj studiji su impedancije zuba izmjerene in vitro na izvađenom zubu uronjenom u alginat. Korišten je HP 4284A LCR metar i posebno izrađeni stalak s mikrometrom za precizno pozicioniranje endodontskog instrumenta u kanalu. U svrhu razvoja točnije mjerne metode ljudski je zub modeliran električkom nadomjesnom shemom. Četiri nove nadomjesne sheme sastavljene od otpora, kapaciteta i elemenata s konstantnom fazom su predložene u ovom radu i uspoređene s četiri ranije predložene nadomjesne sheme. Elementi nadomjesnih shema su izračunati metodom kompleksnih nelinearnih najmanjih kvadrata korištenjem programa LEVM. Definirano je više faktora kvalitete kako bi se usporedilo svojstvo nadomjesnih shema da modeliraju izmjerenu impedanciju na pojedinim položajima endodontskog instrumenta u kanalu. Izračunati su i faktori kojima se uspoređuje sveukupna efikasnost nadomjesne sheme. Detaljno su objašnjeni parametri nadomjesnih shema koji se mogu koristiti za mjerenje duljine korijenskog kanala. Temeljem dobivenih rezultata odabrana je najpogodnija nadomjesna shema te je predložen novi mjerni postupak

Usporedba električkih nadomjesnih shema ljudskog zuba korištenih za mjerenje duljine korijenskog kanala

An accurate determination of the root canal length, which is the most critical procedure in the endodontic treatment of a tooth, is commonly performed nowadays by electronic apex locators which are based on electrical impedance measurements. In this paper tooth impedances were measured in vitro on extracted tooth in alginate material using HP 4284A LCR meter and a specially designed stalk with a micrometer for precise file positioning. In order to develop a more accurate measurement procedure human tooth was modeled by electrical equivalent circuit. Four new equivalent circuits comprising of resistors, capacitors and constant-phase elements were proposed in this paper and compared with four previously suggested circuits. Elements of equivalent circuits were determined by complex nonlinear least squares fitting using LEVM software. Different quality factors were defined to describe the fit quality of a certain equivalent circuit at each file position. The overall fitting efficiency in the region of file positions of interest was calculated as well. A detailed discussion was given on equivalent circuit parameters that can be used to measure the root canal length. Upon these results the most appropriate equivalent circuit was selected and a new measurement procedure was proposed.Točno određivanje duljine korijenskog kanala zuba, što je najkritičniji postupak u endodontskom tretmanu, se uobičajeno danas provodi elektroničkim detektorima apeksa koji se temelje na mjerenju električne impedancije. U ovoj studiji su impedancije zuba izmjerene in vitro na izvađenom zubu uronjenom u alginat. Korišten je HP 4284A LCR metar i posebno izrađeni stalak s mikrometrom za precizno pozicioniranje endodontskog instrumenta u kanalu. U svrhu razvoja točnije mjerne metode ljudski je zub modeliran električkom nadomjesnom shemom. Četiri nove nadomjesne sheme sastavljene od otpora, kapaciteta i elemenata s konstantnom fazom su predložene u ovom radu i uspoređene s četiri ranije predložene nadomjesne sheme. Elementi nadomjesnih shema su izračunati metodom kompleksnih nelinearnih najmanjih kvadrata korištenjem programa LEVM. Definirano je više faktora kvalitete kako bi se usporedilo svojstvo nadomjesnih shema da modeliraju izmjerenu impedanciju na pojedinim položajima endodontskog instrumenta u kanalu. Izračunati su i faktori kojima se uspoređuje sveukupna efikasnost nadomjesne sheme. Detaljno su objašnjeni parametri nadomjesnih shema koji se mogu koristiti za mjerenje duljine korijenskog kanala. Temeljem dobivenih rezultata odabrana je najpogodnija nadomjesna shema te je predložen novi mjerni postupak

Analysis of Power Losses in Constrained Cycloid Drive

The aim of this paper is to present a theoretical model for efficiency evaluation of a simple cycloid drive train with one degree of freedom (DOF) or constrained cycloid drive. In order to evaluate the efficiency, it is necessary to find the losses generated in the simple cycloid drive, where only losses depending on the load were considered. Expressions for determining speed ratios, efficiency, velocities and forces acting inside the cycloid drive are presented. These expressions are implemented in the theoretical model, where the places where the losses occur are defined. A computer program was created to facilitate analysis and obtain loss values based on different input data. Only load-dependent losses were considered in the theoretical model and computer program. In order to verify the theoretical model, experimental measurements were performed. A physical model of the simple cycloid drive train was created and analyzed on the test bench. The results for "S1" operating mode, i.e. when shaft 2 is stopped, show a mean value of the efficiency of 63.49%, for experimental measurements, while the mean value for theoretical analysis is 65.25%. For the operating mode "S2", i.e. with shaft 1 stopped, the mean value of the experimental measurements of the efficiency is 60.9%, while the theoretical mean value is 62.82%

Geschlechts-/Gendergebundene Unterschiede bei Online-Sexaktivitäten und ihre Folgen

Sadašnja istraživanja, premda ograničena broja, upućuju na osobitu raširenost on-line seksualnih aktivnosti (OSA) među mlađim, obrazovanijim i profesionalno dokazanim generacijama. Uz to studije sugeriraju spolnu/rodnu specifičnost OSA. Kako bismo saznali u kojoj su mjeri rezultati inozemnih studija primjenjivi na razumijevanje situacije u Hrvatskoj, potkraj 2004. godine proveli smo prvo domaće on-line istraživanje OSA. Analize pokazuju da se muškarci i žene razlikuju prema količini vremena provedenog u OSA, omjeru između komunikacijskih i konzumacijskih OSA, uspješnosti ostvarivanja fizičkih susreta s on-line poznanicima, netočnom prikazivanju vlastita izgleda i učestalosti intimnih problema (ne i problema u društvenom funkcioniranju) izazvanih OSA. U nekoliko važnih detalja naši se rezultati razlikuju od onih dobivenih u istraživanjima provedenim u SAD-u i Švedskoj. Bez obzira na metodološka ograničenja studije, u zaključku naglašavamo potrebu nastavka praćenja fenomenologije internetske seksualnosti zbog potpunijega razumijevanja suvremenih promjena u seksualnim značenjima i obrascima interakcije.Current studies, although low in number, point to high prevalence of online sexual activities (OSA) among the younger, educated and professionally accomplished generations. Also, the existing body of research indicates a pattern of gender differences in OSA. In order to find out whether these findings are applicable to Croatia, in 2004 we carried out the first online survey on OSA. The analyses show that men and women differ in several important dimensions: in the amount of time spent in OSA, in the ratio between communicational and consummative motives for OSA, in the relative success of offline contacts, in lying about one\u27s appearance, and in the prevalence of intimate (but not professional) problems caused by OSA. In several important details, our findings do not corroborate the results of two US and a Swedish study. In conclusion, the authors emphasize the need for continuing research on the phenomenology of Internet sexuality. In spite of the methodological shortcomings and limitations typical of online surveys, such studies can provide better understanding of the contemporary, increasingly technologically mediated, sexual meanings, interactions and exchanges.Obwohl die Zahl einschlägiger Untersuchungen begrenzt ist, zeigen diese, dass Online-Sexaktivitäten (OSA) besonders in der Generation junger, beruflich realisierter Menschen mit höherem Bildungsgrad verbreitet sind. Die vorliegenden Studien suggerieren außerdem das Bestehen geschlechts-/ gendergebundener Spezifika von OSA. Um herauszufinden, inwiefern die Ergebnisse ausländischer Studien für ein Verständis der in Kroatien herrschenden Verhältnisse verwendbar sind, haben die Autoren Ende 2004 die erste kroatische Online-Umfrage zur Untersuchung von OSA und möglichen relevanten Folgen durchgeführt. Männer und Frauen unterscheiden sich hinsichtlich der mit OSA verbrachten Zeit; unterschiedlich sind auch das Verhältnis zwischen kommunikationsbeschränkten und "konsumierten" OSA, die Erfolgsrate physischer Kontakte mit Online- Bekanntschaften, die (von der Wirklichkeit abweichende) Beschreibung des eigenen Aussehens, die Häufigkeit intimer Probleme als einer Folge von OSA (nicht gemeint sind Probleme mit dem allgemeinen Funktionieren in der Gesellschaft). Die kroatischen Umfrageergebnisse weichen von den in den USA und in Schweden gewonnenen Resultaten in einigen wesentlichen Punkten ab. Ungeachtet der methodologischen Einschränkungen der Studie wird schlussfolgernd die Notwendigkeit betont, die Phänomenologie von Online-Sexaktivitäten auch in Zukunft mitzuverfolgen, um die aktuellen Wandel bezüglich des sexuellen Hintergrunds und der unterschiedlichen Muster menschlichen Interagierens besser verstehen zu können

Electrical model of a tooth for the root canal length measurement

Ovaj rad se bavi problematikom električnih svojstava i modela zuba te metode određivanja duljine korijenskoga kanala elektroničkim endometrom tijekom endodontskog postupka. Također su razmotrene mjerne elektrode korištene pri ispitivanju vitaliteta zubne pulpe. Uspoređeni su fizički in vitro modeli zuba u fiziološkoj otopini te u alginatu za uzimanje zubnog odlijevka te je zaključeno da u interesnom frekvencijskom području model na alginatu daje električki bolje performanse u odnosu na dostupna mjerenja in vivo. Metodom konačnih elemenata je razvijen trodimenzionalni električni model zuba kao alternativa in vitro mjerenju. Model sadrži frekvencijsku ovisnost dielektričnih svojstava tkiva prema Cole-Cole modelu te model dvosloja na površini mjerne elektrode. Paramteri modela dentina i dvosloja su izmjereni u ovom radu. Impedancija zuba je predstavljena električnim nadomjesnim shemama. Deset shema je predloženo u ovom radu te uspoređeno sa shemama drugih autora. Optimalnom se pokazala shema predložena u ovom radu. Komentirano je fizikalno značenje pojedinih elemenata, kao i mogućnost uporabe pri mjerenju duljine korijenskoga kanala. Ispitan je utjecaj pojedinih parametara modela (položaj igle, specifična voodljivost dentina, sredstvo u kanalu) s konačnim elementima na elemente odabrane nadomjesne sheme. Korištenjem odabrane nadomjesne sheme postignuto je značajno razdvajanje utjecaja električnog dvosloja na pojedine elemente sheme te djelomično razdvajanje utjecaja dentina, što omogućuje smanjenje pogreške mjerenja duljine korijenskoga kanala.The root canal length is measured during the endodontic treatment in order to determine the working length i.e. the length of the root canal instrumentation. When the dental pulp is infected, it should be completely removed from the root canal. If inflamed tissue remains in the canal or the cleaning is carried too deep damaging the surrounding tissue, unnecessary complications may occur. Therefore, the success of whole endodontic treatment is directly dependent on the accuracy of determining the position of the apex. The root canal length may be measured using radiographs. However, the accuracy of such measurements is limited because the projection of the curved and overlapped canals on the film does not always indicate the actual canal length. Therefore, after preliminary radiographs, an electronic apex locator or endometer is commonly used to determine the working length. They work on the principle of electrical impedance measurement between the active electrode inside the root canal (an endodontic file) and a neutral electrode placed at the oral mucosa. The first endometers have used direct current to measure the resistance between the electrodes, which proved to be unreliable because of the polarization potential at the metal to electrode interface. Therefore, present devices instead of measuring resistance measure the impedance at one or more frequencies. Based on that measurement the position of endodontic instrument inside the root canal is determined and indicated. It was found that the presence of conductive fluids that are commonly used during the endodontic treatment may influence the apex locator accuracy as well as the other parameters like the root canal width, morphology of the root, the possible lateral canals or perforation. The problem with verification of radiographic and electronic methods of determining the root canal length in vivo is that the actual position of the active electrode in the canal can be verified (by optical microscope) only when the tooth is extracted. Therefore, comparison of different electronic apex locators is usually performed in vitro on a physical model or by comparing results with the radiograph. The in vitro physical model usually consists of an extracted and prepared tooth immersed in to a conductive medium. Several of these in vitro models exist, and they are used arbitrary and non-critically. Therefore their electrical behavior is evaluated and compared in this study. There are plenty of papers that concentrate at endometer accuracy verification, however there are only a few that focus on the electrical properties of root canal. In these papers the total impedance in the measurement circuit is presented by a simple electrical equivalent circuit containing of two or three elements like resistors and capacitors. It is shown that these circuits can describe the impedance in narrow frequency band only. In order to achieve reasonable agreement in a wider frequency range, the elements needs to be frequency dependent, making them useless for root canal length determination purposes. Therefore, more complex equivalent circuits with up to five elements including a constant phase element is developed. When the number of free circuit elements rises, especially if they are a constant phase elements, the complexity of parameter estimation rises as well. Circuit element estimates became dependant not only on desired impedance spectrum, but on each other as well. Local convergence minima in the iterative estimation procedure occur. In this thesis the parameter estimation procedure for given equivalent circuits is defined and the circuits are compared according to the fit quality and parameter utilization efficiency. Physical representation of individual equivalent circuit elements are discussed based on witch a new measurement procedure is proposed

Accuracy of low-cost GPS receivers with and without differential corrections

U radu je dan pregled današnjih sustava satelitske navigacije. Izneseno je trenutno stanje GPS sustava i planovi njegova razvoja. Izdvojene su posebnosti vezane uz GPS, a koje se odnose na teritorij Republike Hrvatske. Detaljno je opisana interna građa i princip rada niskobudžetnog softverskog GPS prijamnika počevši od njegove antene, sklopovlja za prilagodbu i uzorkovanje RF signala, sve do postupaka akvizicije i praćenja digitaliziranog signala te uporabe navigacijskih podataka i izračuna krajnjeg položaja. Rad softverskog GPS prijamnika simuliran je u MATLAB-u te su promotrena interna stanja pojedinih dijelova prijamnika uz realan ulazni signal. Razmotreni su danas korišteni principi poboljšanja sustava u smislu točnosti i proširenja usluge. Razvijena je sklopovska i programska podrška potrebna za terensko vrednovanje Lassen LP i Lassen iQ GPS modula proizvođača Trimble i GM862-GPS modula proizvođača Telit. Ispitan je utjecaj postavki prijamnika na njegovu točnost. Uspoređene su točnosti pojedinih prijamnika u različitim uvjetima rada: stacionarno mjerenje uz dobar prijem signala, stacionarno mjerenje u urbanoj sredini, gradska vožnja i vožnja otvorenom cestom. Ispitan je utjecaj komercijalnih diferencijskih korekcija i diferencijskog mjerenja pomoću para nekorigiranih prijamnika za svaki od spomenutih uvjeta rada. Razmotren je utjecaj izmjene konstelacije. Uočena je sporo promjenjiva komponenta pogreške položaja i ispitana mogućnost njenog usrednjavanja.This thesis presents an overview of the Global Navigation Satellite Systems (GNSS). Current GPS state and modernization plans were given. Specificity of the GPS on Croatian territory was described. Internal architecture and operating principles of a low-cost software-based GPS receiver was elaborated in detail, with the emphasis on a GPS antenna, an RF front-end, signal acquisition and tracking, navigation data and position solution. A software-based GPS receiver was simulated in MATLAB. Receiver subsystems were evaluated using real-world signals. An overview of the current operating principles of GPS augmentation was given. A hardware and software platforms were developed for the evaluation of Trimble Lassen LP and Lassen iQ GPS modules and Telit GM862-GPS modules. Influence of receiver parameters on position accuracy was evaluated. Position accuracy of used receivers was compared in various environments: statitionary and moving measurement with the clear view to the sky and in the urban environment with the obscured sky view. Influence of commercial differential corrections and differential measurement using a pair of uncorrected receivers was evaluated. Influence of the constellation-switch on a measured position was demonstrated. Slow-changing mean position drift was illustrated and an averaging time considered

Electrical model of a tooth for the root canal length measurement

Ovaj rad se bavi problematikom električnih svojstava i modela zuba te metode određivanja duljine korijenskoga kanala elektroničkim endometrom tijekom endodontskog postupka. Također su razmotrene mjerne elektrode korištene pri ispitivanju vitaliteta zubne pulpe. Uspoređeni su fizički in vitro modeli zuba u fiziološkoj otopini te u alginatu za uzimanje zubnog odlijevka te je zaključeno da u interesnom frekvencijskom području model na alginatu daje električki bolje performanse u odnosu na dostupna mjerenja in vivo. Metodom konačnih elemenata je razvijen trodimenzionalni električni model zuba kao alternativa in vitro mjerenju. Model sadrži frekvencijsku ovisnost dielektričnih svojstava tkiva prema Cole-Cole modelu te model dvosloja na površini mjerne elektrode. Paramteri modela dentina i dvosloja su izmjereni u ovom radu. Impedancija zuba je predstavljena električnim nadomjesnim shemama. Deset shema je predloženo u ovom radu te uspoređeno sa shemama drugih autora. Optimalnom se pokazala shema predložena u ovom radu. Komentirano je fizikalno značenje pojedinih elemenata, kao i mogućnost uporabe pri mjerenju duljine korijenskoga kanala. Ispitan je utjecaj pojedinih parametara modela (položaj igle, specifična voodljivost dentina, sredstvo u kanalu) s konačnim elementima na elemente odabrane nadomjesne sheme. Korištenjem odabrane nadomjesne sheme postignuto je značajno razdvajanje utjecaja električnog dvosloja na pojedine elemente sheme te djelomično razdvajanje utjecaja dentina, što omogućuje smanjenje pogreške mjerenja duljine korijenskoga kanala.The root canal length is measured during the endodontic treatment in order to determine the working length i.e. the length of the root canal instrumentation. When the dental pulp is infected, it should be completely removed from the root canal. If inflamed tissue remains in the canal or the cleaning is carried too deep damaging the surrounding tissue, unnecessary complications may occur. Therefore, the success of whole endodontic treatment is directly dependent on the accuracy of determining the position of the apex. The root canal length may be measured using radiographs. However, the accuracy of such measurements is limited because the projection of the curved and overlapped canals on the film does not always indicate the actual canal length. Therefore, after preliminary radiographs, an electronic apex locator or endometer is commonly used to determine the working length. They work on the principle of electrical impedance measurement between the active electrode inside the root canal (an endodontic file) and a neutral electrode placed at the oral mucosa. The first endometers have used direct current to measure the resistance between the electrodes, which proved to be unreliable because of the polarization potential at the metal to electrode interface. Therefore, present devices instead of measuring resistance measure the impedance at one or more frequencies. Based on that measurement the position of endodontic instrument inside the root canal is determined and indicated. It was found that the presence of conductive fluids that are commonly used during the endodontic treatment may influence the apex locator accuracy as well as the other parameters like the root canal width, morphology of the root, the possible lateral canals or perforation. The problem with verification of radiographic and electronic methods of determining the root canal length in vivo is that the actual position of the active electrode in the canal can be verified (by optical microscope) only when the tooth is extracted. Therefore, comparison of different electronic apex locators is usually performed in vitro on a physical model or by comparing results with the radiograph. The in vitro physical model usually consists of an extracted and prepared tooth immersed in to a conductive medium. Several of these in vitro models exist, and they are used arbitrary and non-critically. Therefore their electrical behavior is evaluated and compared in this study. There are plenty of papers that concentrate at endometer accuracy verification, however there are only a few that focus on the electrical properties of root canal. In these papers the total impedance in the measurement circuit is presented by a simple electrical equivalent circuit containing of two or three elements like resistors and capacitors. It is shown that these circuits can describe the impedance in narrow frequency band only. In order to achieve reasonable agreement in a wider frequency range, the elements needs to be frequency dependent, making them useless for root canal length determination purposes. Therefore, more complex equivalent circuits with up to five elements including a constant phase element is developed. When the number of free circuit elements rises, especially if they are a constant phase elements, the complexity of parameter estimation rises as well. Circuit element estimates became dependant not only on desired impedance spectrum, but on each other as well. Local convergence minima in the iterative estimation procedure occur. In this thesis the parameter estimation procedure for given equivalent circuits is defined and the circuits are compared according to the fit quality and parameter utilization efficiency. Physical representation of individual equivalent circuit elements are discussed based on witch a new measurement procedure is proposed

Electrical model of a tooth for the root canal length measurement

Ovaj rad se bavi problematikom električnih svojstava i modela zuba te metode određivanja duljine korijenskoga kanala elektroničkim endometrom tijekom endodontskog postupka. Također su razmotrene mjerne elektrode korištene pri ispitivanju vitaliteta zubne pulpe. Uspoređeni su fizički in vitro modeli zuba u fiziološkoj otopini te u alginatu za uzimanje zubnog odlijevka te je zaključeno da u interesnom frekvencijskom području model na alginatu daje električki bolje performanse u odnosu na dostupna mjerenja in vivo. Metodom konačnih elemenata je razvijen trodimenzionalni električni model zuba kao alternativa in vitro mjerenju. Model sadrži frekvencijsku ovisnost dielektričnih svojstava tkiva prema Cole-Cole modelu te model dvosloja na površini mjerne elektrode. Paramteri modela dentina i dvosloja su izmjereni u ovom radu. Impedancija zuba je predstavljena električnim nadomjesnim shemama. Deset shema je predloženo u ovom radu te uspoređeno sa shemama drugih autora. Optimalnom se pokazala shema predložena u ovom radu. Komentirano je fizikalno značenje pojedinih elemenata, kao i mogućnost uporabe pri mjerenju duljine korijenskoga kanala. Ispitan je utjecaj pojedinih parametara modela (položaj igle, specifična voodljivost dentina, sredstvo u kanalu) s konačnim elementima na elemente odabrane nadomjesne sheme. Korištenjem odabrane nadomjesne sheme postignuto je značajno razdvajanje utjecaja električnog dvosloja na pojedine elemente sheme te djelomično razdvajanje utjecaja dentina, što omogućuje smanjenje pogreške mjerenja duljine korijenskoga kanala.The root canal length is measured during the endodontic treatment in order to determine the working length i.e. the length of the root canal instrumentation. When the dental pulp is infected, it should be completely removed from the root canal. If inflamed tissue remains in the canal or the cleaning is carried too deep damaging the surrounding tissue, unnecessary complications may occur. Therefore, the success of whole endodontic treatment is directly dependent on the accuracy of determining the position of the apex. The root canal length may be measured using radiographs. However, the accuracy of such measurements is limited because the projection of the curved and overlapped canals on the film does not always indicate the actual canal length. Therefore, after preliminary radiographs, an electronic apex locator or endometer is commonly used to determine the working length. They work on the principle of electrical impedance measurement between the active electrode inside the root canal (an endodontic file) and a neutral electrode placed at the oral mucosa. The first endometers have used direct current to measure the resistance between the electrodes, which proved to be unreliable because of the polarization potential at the metal to electrode interface. Therefore, present devices instead of measuring resistance measure the impedance at one or more frequencies. Based on that measurement the position of endodontic instrument inside the root canal is determined and indicated. It was found that the presence of conductive fluids that are commonly used during the endodontic treatment may influence the apex locator accuracy as well as the other parameters like the root canal width, morphology of the root, the possible lateral canals or perforation. The problem with verification of radiographic and electronic methods of determining the root canal length in vivo is that the actual position of the active electrode in the canal can be verified (by optical microscope) only when the tooth is extracted. Therefore, comparison of different electronic apex locators is usually performed in vitro on a physical model or by comparing results with the radiograph. The in vitro physical model usually consists of an extracted and prepared tooth immersed in to a conductive medium. Several of these in vitro models exist, and they are used arbitrary and non-critically. Therefore their electrical behavior is evaluated and compared in this study. There are plenty of papers that concentrate at endometer accuracy verification, however there are only a few that focus on the electrical properties of root canal. In these papers the total impedance in the measurement circuit is presented by a simple electrical equivalent circuit containing of two or three elements like resistors and capacitors. It is shown that these circuits can describe the impedance in narrow frequency band only. In order to achieve reasonable agreement in a wider frequency range, the elements needs to be frequency dependent, making them useless for root canal length determination purposes. Therefore, more complex equivalent circuits with up to five elements including a constant phase element is developed. When the number of free circuit elements rises, especially if they are a constant phase elements, the complexity of parameter estimation rises as well. Circuit element estimates became dependant not only on desired impedance spectrum, but on each other as well. Local convergence minima in the iterative estimation procedure occur. In this thesis the parameter estimation procedure for given equivalent circuits is defined and the circuits are compared according to the fit quality and parameter utilization efficiency. Physical representation of individual equivalent circuit elements are discussed based on witch a new measurement procedure is proposed

Accuracy of low-cost GPS receivers with and without differential corrections

U radu je dan pregled današnjih sustava satelitske navigacije. Izneseno je trenutno stanje GPS sustava i planovi njegova razvoja. Izdvojene su posebnosti vezane uz GPS, a koje se odnose na teritorij Republike Hrvatske. Detaljno je opisana interna građa i princip rada niskobudžetnog softverskog GPS prijamnika počevši od njegove antene, sklopovlja za prilagodbu i uzorkovanje RF signala, sve do postupaka akvizicije i praćenja digitaliziranog signala te uporabe navigacijskih podataka i izračuna krajnjeg položaja. Rad softverskog GPS prijamnika simuliran je u MATLAB-u te su promotrena interna stanja pojedinih dijelova prijamnika uz realan ulazni signal. Razmotreni su danas korišteni principi poboljšanja sustava u smislu točnosti i proširenja usluge. Razvijena je sklopovska i programska podrška potrebna za terensko vrednovanje Lassen LP i Lassen iQ GPS modula proizvođača Trimble i GM862-GPS modula proizvođača Telit. Ispitan je utjecaj postavki prijamnika na njegovu točnost. Uspoređene su točnosti pojedinih prijamnika u različitim uvjetima rada: stacionarno mjerenje uz dobar prijem signala, stacionarno mjerenje u urbanoj sredini, gradska vožnja i vožnja otvorenom cestom. Ispitan je utjecaj komercijalnih diferencijskih korekcija i diferencijskog mjerenja pomoću para nekorigiranih prijamnika za svaki od spomenutih uvjeta rada. Razmotren je utjecaj izmjene konstelacije. Uočena je sporo promjenjiva komponenta pogreške položaja i ispitana mogućnost njenog usrednjavanja.This thesis presents an overview of the Global Navigation Satellite Systems (GNSS). Current GPS state and modernization plans were given. Specificity of the GPS on Croatian territory was described. Internal architecture and operating principles of a low-cost software-based GPS receiver was elaborated in detail, with the emphasis on a GPS antenna, an RF front-end, signal acquisition and tracking, navigation data and position solution. A software-based GPS receiver was simulated in MATLAB. Receiver subsystems were evaluated using real-world signals. An overview of the current operating principles of GPS augmentation was given. A hardware and software platforms were developed for the evaluation of Trimble Lassen LP and Lassen iQ GPS modules and Telit GM862-GPS modules. Influence of receiver parameters on position accuracy was evaluated. Position accuracy of used receivers was compared in various environments: statitionary and moving measurement with the clear view to the sky and in the urban environment with the obscured sky view. Influence of commercial differential corrections and differential measurement using a pair of uncorrected receivers was evaluated. Influence of the constellation-switch on a measured position was demonstrated. Slow-changing mean position drift was illustrated and an averaging time considered

Accuracy of low-cost GPS receivers with and without differential corrections

U radu je dan pregled današnjih sustava satelitske navigacije. Izneseno je trenutno stanje GPS sustava i planovi njegova razvoja. Izdvojene su posebnosti vezane uz GPS, a koje se odnose na teritorij Republike Hrvatske. Detaljno je opisana interna građa i princip rada niskobudžetnog softverskog GPS prijamnika počevši od njegove antene, sklopovlja za prilagodbu i uzorkovanje RF signala, sve do postupaka akvizicije i praćenja digitaliziranog signala te uporabe navigacijskih podataka i izračuna krajnjeg položaja. Rad softverskog GPS prijamnika simuliran je u MATLAB-u te su promotrena interna stanja pojedinih dijelova prijamnika uz realan ulazni signal. Razmotreni su danas korišteni principi poboljšanja sustava u smislu točnosti i proširenja usluge. Razvijena je sklopovska i programska podrška potrebna za terensko vrednovanje Lassen LP i Lassen iQ GPS modula proizvođača Trimble i GM862-GPS modula proizvođača Telit. Ispitan je utjecaj postavki prijamnika na njegovu točnost. Uspoređene su točnosti pojedinih prijamnika u različitim uvjetima rada: stacionarno mjerenje uz dobar prijem signala, stacionarno mjerenje u urbanoj sredini, gradska vožnja i vožnja otvorenom cestom. Ispitan je utjecaj komercijalnih diferencijskih korekcija i diferencijskog mjerenja pomoću para nekorigiranih prijamnika za svaki od spomenutih uvjeta rada. Razmotren je utjecaj izmjene konstelacije. Uočena je sporo promjenjiva komponenta pogreške položaja i ispitana mogućnost njenog usrednjavanja.This thesis presents an overview of the Global Navigation Satellite Systems (GNSS). Current GPS state and modernization plans were given. Specificity of the GPS on Croatian territory was described. Internal architecture and operating principles of a low-cost software-based GPS receiver was elaborated in detail, with the emphasis on a GPS antenna, an RF front-end, signal acquisition and tracking, navigation data and position solution. A software-based GPS receiver was simulated in MATLAB. Receiver subsystems were evaluated using real-world signals. An overview of the current operating principles of GPS augmentation was given. A hardware and software platforms were developed for the evaluation of Trimble Lassen LP and Lassen iQ GPS modules and Telit GM862-GPS modules. Influence of receiver parameters on position accuracy was evaluated. Position accuracy of used receivers was compared in various environments: statitionary and moving measurement with the clear view to the sky and in the urban environment with the obscured sky view. Influence of commercial differential corrections and differential measurement using a pair of uncorrected receivers was evaluated. Influence of the constellation-switch on a measured position was demonstrated. Slow-changing mean position drift was illustrated and an averaging time considered