A mobile user may voluntarily disconnect itself from the web server to save battery life and also to avoid the high communication price. To allow web pages to be updated while the mobile user is disconnected from the web server, updates can be staged in the mobile unit and propagated back to the web server upon reconnection. In this thesis, we investigate methods for supporting disconnected write operations and develop a performance model which helps identify the optimal length of the disconnection period under which the cost of update propagation is minimized. We validate the analytic model with simulation in the thesis. We also show how the result can be applied to real-time web applications with a deadline requirement to propagate updates of web pages. The analysis result is particularly applicable to web applications which allow wireless mobile users to modify web contents while on the go. The algorithms that we have developed can be generally applied to other data items such as files and databases. / Master of Science

Collocations are groups of words which are co-occurring more often than appearing separately. They also include phrases that give a new meaning to a group of unrelated words. This thesis is aimed to find collocations in large data and to create a database that allows their retrieval. The Pointwise Mutual Information, a value based on word frequency, is computed for finding the collocations. Words with the highest value of PMI are considered candidates for good collocations. Chosen collocations are stored in a database in a format that allows searching with Apache Lucene. A part of the thesis is to create a Web user interface as a quick and easy way to search collocations. If this service is fast enough and the collocations are good, translators will be able to use it for finding proper equivalents in the target language. Students of a foreign language will also be able to use it to extend their vocabulary. Such database will be created independently in several languages including Czech and English. Powered by TCPDF (www.tcpdf.org)

Made available in DSpace on 2016-04-04T18:31:39Z (GMT). No. of bitstreams: 1 Deivis Fernandes Pirani.pdf: 1504986 bytes, checksum: e4989c06d3fc9c76df085862e18609d0 (MD5) Previous issue date: 2014-02-07 / This paper shows a field-trial investigation comparing the use of IPv4 and IPv6 protocols on web pages access considering the real user perspective and the transition period from IPv4 to IPv6. To perform this study, it was developed a testbed in which three adressing configurations of Internet Protocol, IPv4, IPv6, and Duas Stack (IPv4+IPv6), were used to access the top 100 world most visited web pages with an IPv6 enabled address. In addiction, several software tools were developed, that enabled more than 600 simultaneous accesses between IPv4, IPv6 and Dual Stack, to each of these pages. Those accesses were performed every hour during the period of a month, enabling to obtain more than 20 GB of information on the web access. Results showed that lower loading times obtained by IPv6 and Dual Stack are related to the partial acquisition of the content. In fact, for IPv6, the number of web pages with faster loading times goes from 57 to 20% when the average number of bytes obtained by IPv6 and the IPv4 is similar. For Dual Stack the number goes from 25 to 5% given the same conditions. It was also noted that 18 of the 100 pages which were considered, no content would be presented to the user in more than 50% of the performed accesses. Regarding the preference for IPv6 instead of IPv4, on Dual Stack it was observed that 90% of the acquired content for 27 of 100 web pages was made by IPv6. / Este trabalho apresenta um estudo de campo, comparativo, sobre a utiliza??o dos protocolos IPv4 e IPv6 no acesso a p?ginas web. Foi considerada a perspectiva de um usu?rio real deste tipo de servi?o, no atual per?odo de transi??o do IPv4 para o IPv6. Para que tal estudo pudesse ser realizado, foi desenvolvido um arranjo no qual tr?s configura??es de endere?amento do Protocolo de Internet, IPv4, IPv6 e Pilha Dupla (IPv4+IPv6), foram utilizadas nos acessos ?s 100 p?ginas web, com suporte ao I v6, mundialmente mais visitadas. Al?m disso, foram desenvolvidas uma s?rie de shell scripts que possibilitaram mais de 600 acessos simult?neos do IPv4, IPv6 e Pilha Dupla, a cada uma dessas p?ginas. Tais acessos foram executados de hora em hora, durante o per?odo de um m?s, possibilitando a obten??o de mais de 20 GB de informa??es relativas ao acesso web. Os resultados do estudo mostraram que os tempos de carregamento menores obtidos pelo IPv6 e pela Pilha Dupla, est?o relacionados com a aquisi??o parcial do conte?do. De fato, para o IPv6, o n?mero de p?ginas web com tempos de carregamento menores diminui de 57 para 20% quando a m?dia do n?mero de bytes obtidos pelo IPv6 e pelo IPv4 ? similar. Para a Pilha Dupla, dadas as mesmas condi??es, o n?mero diminui de 25 para 5%. Tamb?m foi observado que para 18 das 100 p?ginas web consideradas, nenhum conte?do foi apresentado ao usu?rio em mais de 50% dos acessos efetuados. Com rela??o ? prefer?ncia pelo IPv6 ao IPv4, na Pilha Dupla, observou-se que 90% da aquisi??o do conte?do, de 27 das 100 p?ginas web, ocorreu pelo IPv6.

Η διατριβή εισάγει μια νέα ανοιχτή αρχιτεκτονική για επικοινωνία ιατρικών απεικονιστικών εξετάσεων, η οποία παρουσιάζεται μέσω ενός νέου PACS-ιστού που εστιάζει στην τηλεακτινολογία. Η προτεινόμενη αρχιτεκτονική είναι βασισμένη στις αρχές της επέκτασης ιστού του DICOM που είναι η υπηρεσία/πρωτόκολλο WADO (Πρόσβαση μέσω Ιστού σε Επίμονα Στοιχεία Εξέτασης DICOM). Η αρχιτεκτονική ενσωματώνει υπηρεσίες DICOM και κοινές υπηρεσίες Διαδικτύου (βασισμένες στον ιστό, στο FTP, και στο ηλεκτρονικό ταχυδρομείο). Η διατριβή επίσης επεκτείνει την δυνατότητα πρόσβασης της WADO σε ολόκληρη την ιεραρχία DICOM (Ασθενής, Διαγνωστική Εξέταση, Σειρά Εξέτασης και Στοιχείο Εξέτασης). Η επέκταση της WADO καλείται WADA (Πρόσβαση μέσω Ιστού σε Συστήματα Αρχειοθέτησης DICOM). Σε αντιδιαστολή με τη WADO, η WADA περιλαμβάνει ένα πρόσθετο εσωτερικό μηχανισμό αναζήτησης και υποστηρίζει την υποβολή ιατρικής διάγνωσης. Το σύνολο των προτεινόμενων υπηρεσιών υποστηρίζει την εκτεταμένη πρόσβαση και είναι ενσωματωμένο σε μια δομή τριών επιπέδων (πελάτη, εξυπηρετητή και δεδομένων) που εξασφαλίζει ευελιξία πρόσβασης, κινητικότητα χρηστών και ενισχυμένη ασφάλεια δεδομένων. Η πλευρά των εξυπηρετητών της αρχιτεκτονικής παρέχει διεπαφές των υπηρεσιών μέσω ιστού και διασφαλισμένο χώρο προσωρινής αποθήκευσης που καλείται Περιοχές Χρηστών. Η παρούσα διατριβή μελετά επίσης υποδομή υπολογιστικού πλέγματος για την αρχιτεκτονική του PACS-ιστού και ένα συνεργατικό σχήμα μεταξύ PACS και RIS για ολοκληρωμένη διαχείριση απεικονιστικών εξετάσεων μέσω ιστού. Η προτεινόμενη αρχιτεκτονική υλοποιήθηκε πιλοτικά κυρίως με τεχνολογίες βασισμένες σε Java και προϊόντα συμβατά με πρότυπα. Η υλοποιημένη αρχιτεκτονική αξιολογήθηκε από μηχανικούς σε συνεργασία με ιατρούς. / The dissertation introduces a new open architecture for medical imaging communication illustrating a novel web Picture Archiving and Communication System (PACS), which focuses on teleradiology. The proposed architecture is based on the concept of the web extension of Digital Imaging and Communication in Medicine (DICOM) that is the Web Access to DICOM Persistent Objects (WADO) protocol/service. The architecture integrates DICOM services and common Internet services (based on web, FTP, and e-mail). The dissertation also extends WADO access capability to the whole DICOM hierarchy (Patient, Study, Series and Object). The extended WADO is called Web Access to DICOM Archives (WADA). WADA, as opposed to WADO, includes an extra internal query mechanism and support of medical reports submission. The whole of the proposed services support the extended access and are integrated into a three-tier structure (client, server and data tiers) which ensures flexibility in access, user mobility and enhanced data security. The server site of the architecture provides service interfaces through web and invulnerable space for temporary storage, called as User Domains. This dissertation also studies a computing grid infrastructure for the web PACS architecture and a cooperative scheme between PACS and Radiology Information System (RIS) for integrated administration of imaging examinations through web. The proposed architecture is pilot implemented using mainly Java-based technologies and standard-compliant products. Τhe implemented architecture is evaluated by engineers in collaboration with doctors.