Ce travail explore l'utilisation de l'effet magnéto-optique pour étudier la dynamique de spin des électrons de conduction dans les semi-conducteurs non magnétiques lorsqu'ils sont pompés avec des photons polarisés circulairement. En général, les moments magnétiques hors-équilibre induits optiquement dans les semi-conducteurs non magnétiques sont plus petits que ceux des matériaux magnétiques. L'effet magnéto-optique en principe offre une sensibilité suffisante pour détecter ces faibles moments magnétiques via une mesure de rotation Faraday dans la limite de bruit de photons. Nous avons comparés trois méthodes de détection: les polariseurs partiellement croisés, l’interféromètre de Sagnac et le pont optique. L'interféromètre de Sagnac se révèle fonctionnellement équivalent aux polariseurs partiellement croisés, avec une sensibilité diminuée par la perte de photons à chacun des séparateurs de faisceaux nécessairement présents dans cette configuration expérimentale. Par contre, il a été démontré précédemment que les interféromètres de Sagnac permettent de faire la distinction entre les rotations dites réciproques et non réciproques, et cette thèse propose de nouvelles géométries de Sagnac pour distinguer les rotations en fonction de leurs symétries en temps et en parité. La technique du pont optique présente les meilleures performances. Elle permet une mesure de l'angle de rotation de Faraday limitée par le bruit de photons, même avec des puissances lumineuses importantes reçues par les détecteurs, ce qui permet d'obtenir la meilleure figure de mérite possible. Dans les expériences conduites sur des matériaux magnétiques, un bruit de quelques nrad/√Hz a été mesuré pour une puissance de sonde de 10 mW. Une série de mesures de rotation Faraday pompe-sonde à température ambiante a été réalisée sur GaAs pompé optiquement. Les plus grands signaux sont obtenus lorsque le moment magnétique généré et détecté est maximisé en focalisant fortement les faisceaux pompe et sonde et en choisissant une longueur d'onde de la sonde accordée à une résonance optique dans la structure électronique. Les mesures en champ magnétique transversal montrent un champ Hanle de 0.43 T, à partir duquel on déduit la durée de vie de spin de 88 ps. / This work explores the use of the magneto-optical Kerr effect to study conduction electron spin dynamics in non-magnetic semiconductors when pumped with circularly polarized photons. Typically, non-equilibrium, optically-induced magnetic moments in non-magnetic semiconductors are orders of magnitude smaller than those of magnetized materials, including both magnetic and non-magnetic materials in an external magnetic field. The magneto-optical Kerr effect in principal offers sufficient sensitivity to detect such small magnetic moment via a measurement of the Faraday rotation angle of a probe beam in the photon shot noise limit. Three detection configurations have been experimentally compared: partially crossed polarizers, a Sagnac interferometer and an optical bridge. The Sagnac interferometer is shown to be functionally equivalent to partially crossed polarizers, although its sensitivity is compromised by lost photons at each of the obligatory beam splitters present in such a geometry. On the other hand, it has previously been shown that Sagnac interferometers can distinguish between so-called reciprocal and non-reciprocal rotations, and this thesis proposes novel Sagnac geometries to distinguish rotations according to their time and parity symmetries. The optical bridge technique allows for a photon-shot noise limited measurement of the Faraday rotation angle, even with large photon intensities on the detectors, thereby yielding the best possible figure-of-merit. In demonstrations on magnetic materials, a noise floor of a few nrad//√Hz was measured for a probe power of 10 mW. A series of room-temperature, pump-probe Faraday rotation measurements is performed on optically pumped GaAs to compare and contrast this method with standard polarized photo-luminescence techniques. The largest signals are found when the locally probed moment is maximized by strongly focusing the pump and probe beams, and by choosing a probe wavelength tuned to an optical resonance in the electronic structure. Measurements in transverse magnetic field show a Hanle field of 0.43 T, from which the spin lifetime of 88 ps is deduced.

No description available.

<p><p><p>This thesis has focused on specific aspects of the law concerning the 2nd paragraph of The Care of Young Persons Act (1990:52), LVU. The purpose of this study was to examine the provision <em>other circumstance in the home </em>from a legal perspective; how is the provision defined in the law? A second purpose was to reveal any discrepancy between the intention of the legislation of the already mentioned provision and how this provision was interpreted and applied in practice. This study was jurisprudential and based on both traditional juristic method and sociological methods with qualitative interviews with social workers and text analysis of a case from The County Administrative Court. The gathered information was analysed using a method of discourse analysis. The theoretical framework for this thesis was social constructionism based upon the work of Berger and Luckmann. The conclusion of this study was that the provision <em>other circumstance in the home </em>is connected to the role of the mother though this is not noticed through the legislation. Another conclusion was that the practice considers the legal demand to anticipate as unattainable. The interpretation and application of the provision made by the practice, compared with the intention of the legislation, was representing both an expand and restriction of the provision.</p></p></p>

In light of Sweden ratifying the United Nations Convention on the rights of the child, Swedish law supports the right for children to express their opinions and have their voice heard in situations concerning them. The aim of this study was to gain a deeper understanding of young people’s participation, by investigating how young people’s opinions and attitudes are taken into account in decision making concerning the lack of care shown in 2§ The Compulsory Care of Young Persons Act (1990:52). To explore this subject, this study was based on the textual analysis of 16 court cases from the administrative court from the year 2016, concerning young people aged between 15-18 years old. We found that young people’s opinions and attitudes are generally taken into account in the process of compulsory care. Our results indicate that young people’s opinions and attitudes are taken into account to a higher extent in the whole legal process when the decision of the administrative court corresponds with the young person’s opinion and attitude. In cases where the court’s decision did not correspond with the young person’s opinion and attitude, the opinions and attitudes of children were taken into account to a lesser degree. Our analysis has shown, according to the Ladder of Participation, that all young people can be seen as participators in the process of compulsory care. However, children’s participation is a complex phenomenon and additional research is needed to unpack this subject further.

Made available in DSpace on 2016-04-29T14:27:19Z (GMT). No. of bitstreams: 1 Luciano dos Santos.pdf: 1159889 bytes, checksum: fb68a3bb20601f633debd31cdc4c675b (MD5) Previous issue date: 2011-08-15 / The National Conference of Bishops of Brazil, by means of Documents 43 and 52, inspires the ecclesial communities and guides their celebrations. It encourages communities to celebrate the Paschal Mystery of Christ that involves their lives, to celebrate the Passover of Christ along with the congregation Passover, through the Sunday Celebration of God´s Word conducted by laypeople. However, it is often noticed that there is a separation among personal, social life and religion, affecting the way communities celebrate, where people's lives are not tied to the liturgy and the latter, in turn, is not tied to people´s lives The believer´s life and the history of the humanity are not understood as Passover connected to the Passover of Jesus. Therefore, by analyzing documents 43 and 52 of the Brazilian Bishops and some elements of the liturgical tradition, as well as in the Church General Magisterium about life in the celebration, the aim of this paper is to highlight elements that encourage the integration between life and liturgy, especially regarding the Sunday Celebration of God´s Word. Such search will also verify that the liturgy celebrates the Passover happening in people's lives and history without making use of its authenticity and that the Sunday Celebration of God‟s Word authenticity resides in celebrating life as a Paschal process, as a passage from death to life, thanks to the liberating intervention of God. This paper also intends to state that the relation between liturgy and life helps the People of God, who participate in the celebrations, to existentially penetrate in the Mystery, manifesting it later on in their own lives‟ conducts / The National Conference of Bishops of Brazil, by means of Documents 43 and 52, inspires the ecclesial communities and guides their celebrations. It encourages communities to celebrate the Paschal Mystery of Christ that involves their lives, to celebrate the Passover of Christ along with the congregation Passover, through the Sunday Celebration of God´s Word conducted by laypeople. However, it is often noticed that there is a separation among personal, social life and religion, affecting the way communities celebrate, where people's lives are not tied to the liturgy and the latter, in turn, is not tied to people´s lives The believer´s life and the history of the humanity are not understood as Passover connected to the Passover of Jesus. Therefore, by analyzing documents 43 and 52 of the Brazilian Bishops and some elements of the liturgical tradition, as well as in the Church General Magisterium about life in the celebration, the aim of this paper is to highlight elements that encourage the integration between life and liturgy, especially regarding the Sunday Celebration of God´s Word. Such search will also verify that the liturgy celebrates the Passover happening in people's lives and history without making use of its authenticity and that the Sunday Celebration of God‟s Word authenticity resides in celebrating life as a Paschal process, as a passage from death to life, thanks to the liberating intervention of God. This paper also intends to state that the relation between liturgy and life helps the People of God, who participate in the celebrations, to existentially penetrate in the Mystery, manifesting it later on in their own lives‟ conducts / A Conferência Nacional dos Bispos do Brasil, por meio dos Documentos 43 e 52, anima as comunidades eclesiais e orienta suas celebrações. Incentiva as comunidades a celebrar o Mistério Pascal de Cristo que envolve as suas vidas, a celebrar a Páscoa dos fiéis na Páscoa de Cristo, através da Celebração Dominical da Palavra de Deus presidida por leigos e leigas. Porém, nota-se com frequência que há uma separação entre a vida pessoal, social e a religião, afetando o modo de celebrar de nossas comunidades, onde a vida das pessoas não incide na liturgia e esta, por sua vez, não incide na vida das pessoas. A vida do fiel e a história da humanidade não são compreendidos como Páscoa na Páscoa de Jesus. Por isso, ao analisar os Documentos 43 e 52 da CNBB e alguns elementos da tradição litúrgica e do magistério geral da Igreja sobre a vida na celebração, pretende-se destacar elementos que incentivem a integração entre vida e liturgia, especialmente no que diz respeito à Celebração Dominical da Palavra de Deus. Buscar-se-á, também, verificar que a liturgia celebra a Páscoa acontecendo na vida das pessoas e na história sem que seja instrumentalizada em sua autenticidade e que a própria autenticidade da Celebração Dominical da Palavra de Deus está em celebrar a vida como um processo pascal, como uma passagem da morte para vida, graças à libertadora intervenção de Deus. Deseja-se, ainda, apresentar que a relação entre liturgia e vida auxilia o povo de Deus, que participa das celebrações, a penetrar existencialmente no Mistério, manifestando-o depois na própria conduta de vida

This thesis has focused on specific aspects of the law concerning the 2nd paragraph of The Care of Young Persons Act (1990:52), LVU. The purpose of this study was to examine the provision other circumstance in the home from a legal perspective; how is the provision defined in the law? A second purpose was to reveal any discrepancy between the intention of the legislation of the already mentioned provision and how this provision was interpreted and applied in practice. This study was jurisprudential and based on both traditional juristic method and sociological methods with qualitative interviews with social workers and text analysis of a case from The County Administrative Court. The gathered information was analysed using a method of discourse analysis. The theoretical framework for this thesis was social constructionism based upon the work of Berger and Luckmann. The conclusion of this study was that the provision other circumstance in the home is connected to the role of the mother though this is not noticed through the legislation. Another conclusion was that the practice considers the legal demand to anticipate as unattainable. The interpretation and application of the provision made by the practice, compared with the intention of the legislation, was representing both an expand and restriction of the provision.

Den 1 juli 2013 meddelade Högsta förvaltningsdomstolen (HFD) beslut i ett mål gällande kvittningsrätten för kapitalvinster och kapitalförluster på delägarrätter. Frågan som be-handlades i målet var om aktiebolaget hade rätt att kvitta sina kapitalförluster mot kapital-vinsterna som uppkommit i den utländska delägarbeskattade juridiska personen. HFD beslutade att neka aktiebolaget möjligheten till kvittning på grund av att lagstöd saknades. Denna bedömning väcker frågor, då aktiebolag som väljer att placera delägarrätter i del-ägarbeskattade juridiska personer får en mindre utsträckt kvittningsrätt vid jämförelse om delägarrätterna hade placerats direkt i aktiebolaget. Vid närmare granskning av kvittnings-möjligheterna kan det konstateras att även kvittningsrätten för kapitalförluster (inte bara kapitalvinster) på delägarrätter i delägarbeskattade juridiska personer är begränsade, vid jämförelse om motsvarande kapitalförluster hade uppkommit direkt i aktiebolaget. Be-gränsningarna för kapitalförlusterna på delägarrätter i delägarbeskattade juridiska perso-ner innebär att kapitalförlusten ska kvoteras till 70 % innan kvittning kan ske, vilket inte är ett krav om kapitalförlusten hade uppkommit direkt i aktiebolaget. Vidare finns varken en sparanderegel eller en koncernkvittningsregel att tillgå i 48 kap. 27 § IL, vilket finns om kapitalförlusten hade uppkommit direkt i aktiebolaget enligt 48 kap. 26 § IL. Frågan som uppkommer är hur dessa begränsningar står i förhållande till den skatterätts-liga neutralitetsprincipen, där den skattskyldiges val ska styras i minsta möjliga utsträck-ning av skattesystemet. Avsteg från denna princip kan göras i syfte att motverka oönskad skatteplanering. Av en samlad bedömning anser skribenterna att samtliga begränsningar av kvittningsrätten för delägarrätter ägda via delägarbeskattade juridiska personer är oför-enliga med neutralitetsprincipen. Detta grundar skribenterna på att aktiebolag som väljer att placera delägarrätter via delägarbeskattade juridiska personer missgynnas ur ett skatte-mässigt perspektiv, vid jämförelse om delägarrätterna hade placerats direkt i aktiebolaget. iii En av de motiveringar som har anförts av lagstiftaren har varit att motverka oönskad skatteplanering. Denna motivering anser skribenterna inte vara hållbar för att rättfärdiga dessa begränsningar. Reglerna borde därmed ändras så att kvittningsmöjligheten på delä-garrätter ägda via delägarbeskattade juridiska personer blir lika omfattande som om delä-garrätterna hade ägts direkt av aktiebolaget. Den framtida existensen av kvittningsrätten på delägarrätter har diskuterats av lagstiftaren och det återstår att se ifall den kommer att avskaffas eller inte. / July 1, 2013, the Supreme Administrative Court (SAC) announced a decision in a case concerning the right to set off of capital gains and losses on securities. The question that was raised in the case was whether the Swedish company had the right to set off their capital losses against capital gains arisen in the foreign part-owner taxable legal person. SAC decided to deny the company the right to set off due to lack of legal support. This decision raises questions, because companies that chooses to place securities in part-owner taxable legal persons gets less extended rights to set off, in comparison to if the securities had been placed directly in the Swedish company. By a closer examination of the possibilities to set off, it can be concluded that the right to set off of capital losses (not just capital gains) on securities in part-owner taxable legal persons are limited, in comparison to if the corresponding capital losses incurred directly in the Swedish com-pany. The limitations of capital losses on securities in part-owner taxable legal persons means that the capital losses should be subject to a quota of 70 % before set off can occur, which is not a requirement when capital losses incurred directly in the Swedish company. Furthermore, there is neither a carry forward rule nor an intra-group set off rule in Chap-ter 48. 27 § Swedish Income Tax Act (SITA), which exists if the capital losses incurred directly in the company according to Chapter 48. 26 § SITA. The question that arises is how these limitations stand in relation to the principle of neutrality where the taxpayer's choices should be controlled as little as possible by the legal tax system. Derogations from this principle can be made in order to coun-teract undesirable tax planning. By an overall assessment the writers consider that all limitations to set off of secu-rities owned via part-owner taxable legal persons are incompatible with the principle v of neutrality. The reason for this opinion is that a company who chooses to place securities via part-owner taxable legal persons is affected adversely from a tax per-spective in comparison to if the securities were owned directly by the Swedish com-pany itself. According to the writers, there is no sustainable justification for these limitations. The rules should therefore be amended so that the set off possibilities on securities owned via part-owner taxable legal persons should be as extensive as if the securities were owned directly by the Swedish company. The future existence of the set-off right on securities has been discussed by the legislature and the future will tell if it will be abolished or not.

The aim of the diploma thesis is to propose a modification of the road I / 52 between the junction with the D1 motorway and Rajhrad on the D52 motorway in a way that a continuous highway can be created without the need to create an alternative route over the southern tangent in route Wien-Prague and D2 and also to design routes for transport which cannot enter the highway. The other aim is to define the problem elements and create a variant solution.

[pt] Do impulso ao mergulho numa paisagem submersa, este almanaque propõe uma reflexão sobre surdez e escuta. A escrita conduz o pensamento através da observação de imagens submarinas, seguindo um percurso que cruza fronteiras; entre o lúdico e os dados científicos, a teoria e a intuição, a certeza e incerteza, humano e bicho, natural artificial. Num caminho que deseja chegar ao abismo, para conhecer seus monstros e sua pluralidade. / [en] From impulse to diving in a submerged landscape, this almanac proposes a reflection on deafness and listening. Writing leads thought through the observation of under-water images, following a route that crosses borders; between ludic and scientific data, theory and intuition, certainty and uncertainty, human and animal, natural and artificial. In a path that wants to reach the abyss, to know its monsters and plurality.

Η τεράστια ανάπτυξη του Παγκόσμιου Ιστού τις τελευταίες δεκαετίες έχει αναδείξει την αναζήτηση πληροφοριών ως ένα από τα πιο σημαντικά ζητήματα στον τομέα της έρευνας στις Τεχνολογίες της Πληροφορικής. Σήμερα, οι σύγχρονες μηχανές αναζήτησης απαντούν αρκετά ικανοποιητικά στα ερωτήματα των χρηστών, αλλά τα κορυφαία αποτελέσματα που επιστρέφονται δεν είναι πάντα σχετικά με τα δεδομένα που αναζητά ο χρήστης. Ως εκ τούτου, οι μηχανές αναζήτησης καταβάλλουν σημαντικές προσπάθειες για να κατατάξουν τα πιο σχετικά αποτελέσματα του ερωτήματος ως προς τον χρήστη στα κορυφαία αποτελέσματα της λίστας κατάταξης των αποτελεσμάτων. Η διατριβή αυτή ασχολείται κυρίως με το παραπάνω πρόβλημα, δηλαδή την κατάταξη στις υψηλότερες θέσεις των πιο σχετικών αποτελεσμάτων ως προς τον χρήστη (ειδικά για ερωτήματα που οι όροι τους έχουν πολλαπλές σημασίες). Στο πλαίσιο της παρούσας έρευνας κατασκευάστηκαν αλγόριθμοι και τεχνικές που βασίζονται στην τεχνική της σχετικής ανατροφοδότησης (relevance feedback) για την βελτίωση των αποτελεσμάτων που επιστρέφονται από μια μηχανή αναζήτησης. Βασική πηγή της ανατροφοδότησης ήταν τα αποτελέσματα που επιλέγουν οι χρήστες κατά την διαδικασία πλοήγησης. Ο χρήστης επεκτείνει την αρχική πληροφορία αναζήτησης (λέξεις κλειδιά) με νέα πληροφορία που προέρχεται από τα αποτελέσματα που διαλέγει. Έχοντας ένα νέο σύνολο πληροφορίας που αφορά τις προτιμήσεις του χρήστη, συγκρίνεται η σημασιολογική πληροφορία του συνόλου αυτού με τα υπόλοιπα αποτελέσματα (αυτά που επιστράφηκαν πριν επιλέξει το συγκεκριμένο αποτέλεσμα) και μεταβάλλεται η σειρά των αποτελεσμάτων προωθώντας και προτείνοντας τα αποτελέσματα που είναι πιο σχετικά με το νέο σύνολο πληροφορίας. Ένα άλλο πρόβλημα που πρέπει να αντιμετωπιστεί κατά την υποβολή ερωτημάτων από τους χρήστες σε μια μηχανή αναζήτησης είναι ότι τα ερωτήματα που υποβάλλονται στις μηχανές αναζήτησης είναι συνήθως μικρά σε αριθμό λέξεων και αμφίσημα. Συνεπώς, πρέπει να υπάρχουν τρόποι αποσαφήνισης των διαφορετικών εννοιών των όρων αναζήτησης και εύρεσης της έννοιας που ενδιαφέρει τον χρήστη. Η αποσαφήνιση των όρων αναζήτησης είναι μια διαδικασία που έχει μελετηθεί στην βιβλιογραφία με αρκετούς διαφορετικούς τρόπους. Στην διατριβή μου προτείνω νέες στρατηγικές αποσαφήνισης των εννοιών των όρων αναζήτησης των μηχανών αναζήτησης και εξερευνάται η αποδοτικότητά τους στις μηχανές αναζήτησης. Η καινοτομία τους έγκειται στη χρήση του Page-Rank σαν ενδείκτη της σημαντικότητας μιας έννοιας για έναν όρο του ερωτήματος. Επίσης είναι ευρέως γνωστό ότι ο Παγκόσμιος Ιστός περιέχει έγγραφα με την ίδια πληροφορία και έγγραφα με σχεδόν ίδια πληροφορία. Παρά τις προσπάθειες των μηχανών αναζήτησης με αλγόριθμους εύρεσης των κειμένων που περιέχουν επικαλυπτόμενη πληροφορία, ακόμα υπάρχουν περιπτώσεις που τα κείμενα που ανακτώνται από μια μηχανή αναζήτησης περιέχουν επαναλαμβανόμενη πληροφορία. Στην διατριβή αυτή παρουσιάζονται αποδοτικές τεχνικές εύρεσης και περικοπής της επικαλυπτόμενης πληροφορίας από τα αποτελέσματα των μηχανών αναζήτησης χρησιμοποιώντας τις σημασιολογικές πληροφορίες των αποτελεσμάτων των μηχανών αναζήτησης. Συγκεκριμένα αναγνωρίζονται τα αποτελέσματα που περιέχουν την ίδια πληροφορία και απομακρύνονται, ενώ ταυτόχρονα τα αποτελέσματα που περιέχουν επικαλυπτόμενη πληροφορία συγχωνεύονται σε νέα κείμενα(SuperTexts) που περιέχουν την πληροφορία των αρχικών αποτελεσμάτων χωρίς να υπάρχει επαναλαμβανόμενη πληροφορία. Ένας άλλος τρόπος βελτίωσης της αναζήτησης είναι ο σχολιασμός των κειμένων αναζήτησης έτσι ώστε να περιγράφεται καλύτερα η πληροφορία τους. Ο σχολιασμός κειμένων(text annotation) είναι μια τεχνική η οποία αντιστοιχίζει στις λέξεις του κειμένου επιπλέον πληροφορίες όπως η έννοια που αντιστοιχίζεται σε κάθε λέξη με βάση το εννοιολογικό περιεχόμενο του κειμένου. Η προσθήκη επιπλέον σημασιολογικών πληροφοριών σε ένα κείμενο βοηθάει τις μηχανές αναζήτησης να αναζητήσουν καλύτερα τις πληροφορίες που ενδιαφέρουν τους χρήστες και τους χρήστες να βρουν πιο εύκολα τις πληροφορίες που αναζητούν. Στην διατριβή αυτή αναλύονται αποδοτικές τεχνικές αυτόματου σχολιασμού κειμένων από τις οντότητες που περιέχονται στην Wikipedia, μια διαδικασία που αναφέρεται στην βιβλιογραφία ως Wikification. Με τον τρόπο αυτό οι χρήστες μπορούν να εξερευνήσουν επιπλέον πληροφορίες για τις οντότητες που περιέχονται στο κείμενο που τους επιστρέφεται. Ένα άλλο τμήμα της διατριβής αυτής προσπαθεί να εκμεταλλευτεί την σημασιολογία των αποτελεσμάτων των μηχανών αναζήτησης χρησιμοποιώντας εργαλεία του Σημασιολογικού Ιστού. Ο στόχος του Σημασιολογικού Ιστού (Semantic Web) είναι να κάνει τους πόρους του Ιστού κατανοητούς και στους ανθρώπους και στις μηχανές. Ο Σημασιολογικός Ιστός στα πρώτα βήματά του λειτουργούσε σαν μια αναλυτική περιγραφή του σώματος των έγγραφων του Ιστού. Η ανάπτυξη εργαλείων για την αναζήτηση σε Σημασιολογικό Ιστό είναι ακόμα σε πρώιμο στάδιο. Οι σημερινές τεχνικές αναζήτησης δεν έχουν προσαρμοστεί στην δεικτοδότηση και στην ανάκτηση σημασιολογικής πληροφορίας εκτός από μερικές εξαιρέσεις. Στην έρευνά μας έχουν δημιουργηθεί αποδοτικές τεχνικές και εργαλεία χρήσης του Παγκόσμιου Ιστού. Συγκεκριμένα έχει κατασκευαστεί αλγόριθμος μετατροπής ενός κειμένου σε οντολογία ενσωματώνοντας την σημασιολογική και συντακτική του πληροφορία έτσι ώστε να επιστρέφονται στους χρήστες απαντήσεις σε ερωτήσεις φυσικής γλώσσας. Επίσης στην διατριβή αυτή αναλύονται τεχνικές φιλτραρίσματος XML εγγράφων χρησιμοποιώντας σημασιολογικές πληροφορίες. Συγκεκριμένα παρουσιάζεται ένα αποδοτικό κατανεμημένο σύστημα σημασιολογικού φιλτραρίσματος XML εγγράφων που δίνει καλύτερα αποτελέσματα από τις υπάρχουσες προσεγγίσεις. Τέλος, στα πλαίσια αυτής της διδακτορικής διατριβής γίνεται επιπλέον έρευνα για την βελτίωση της απόδοσης των μηχανών αναζήτησης από μια διαφορετική οπτική γωνία. Στην κατεύθυνση αυτή παρουσιάζονται τεχνικές περικοπής ανεστραμμένων λιστών ανεστραμμένων αρχείων. Επίσης επιτυγχάνεται ένας συνδυασμός των προτεινόμενων τεχνικών με υπάρχουσες τεχνικές συμπίεσης ανεστραμμένων αρχείων πράγμα που οδηγεί σε καλύτερα αποτελέσματα συμπίεσης από τα ήδη υπάρχοντα. / The tremendous growth of the Web in the recent decades has made the searching for information as one of the most important issues in research in Computer Technologies. Today, modern search engines respond quite well to the user queries, but the results are not always relative to the data the user is looking for. Therefore, search engines are making significant efforts to rank the most relevant query results to the user in the top results of the ranking list. This work mainly deals with this problem, the ranking of the relevant results to the user in the top of the ranking list even when the queries contain multiple meanings. In the context of this research, algorithms and techniques were constructed based on the technique of relevance feedback which improves the results returned by a search engine. Main source of feedback are the results which the users selects during the navigation process. The user extends the original information (search keywords) with new information derived from the results that chooses. Having a new set of information concerning to the user's preferences, the relevancy of this information is compared with the other results (those returned before choosing this effect) and change the order of the results by promoting and suggesting the results that are more relevant to the new set of information. Another problem that must be addressed when the users submit queries to the search engines is that the queries are usually small in number of words and ambiguous. Therefore, there must be ways to disambiguate the different concepts/senses and ways to find the concept/sense that interests the user. Disambiguation of the search terms is a process that has been studied in the literature in several different ways. This work proposes new strategies to disambiguate the senses/concepts of the search terms and explore their efficiency in search engines. Their innovation is the use of PageRank as an indicator of the importance of a sense/concept for a query term. Another technique that exploits semantics in our work is the use of text annotation. The use of text annotation is a technique that assigns to the words of the text extra information such as the meaning assigned to each word based on the semantic content of the text. Assigning additional semantic information in a text helps users and search engines to seek or describe better the text information. In my thesis, techniques for improving the automatic annotation of small texts with entities from Wikipedia are presented, a process that referred in the literature as Wikification. It is widely known that the Web contain documents with the same information and documents with almost identical information. Despite the efforts of the search engine’s algorithms to find the results that contain repeated information; there are still cases where the results retrieved by a search engine contain repeated information. In this work effective techniques are presented that find and cut the repeated information from the results of the search engines. Specifically, the results that contain the same information are removed, and the results that contain repeated information are merged into new texts (SuperTexts) that contain the information of the initial results without the repeated information. Another part of this work tries to exploit the semantic information of search engine’s results using tools of the Semantic Web. The goal of the Semantic Web is to make the resources of the Web understandable to humans and machines. The Semantic Web in their first steps functioned as a detailed description of the body of the Web documents. The development of tools for querying Semantic Web is still in its infancy. The current search techniques are not adapted to the indexing and retrieval of semantic information with a few exceptions. In our research we have created efficient techniques and tools for using the Semantic Web. Specifically an algorithm was constructed that converts to ontology the search engine’s results integrating semantic and syntactic information in order to answer natural language questions. Also this paper contains XML filtering techniques that use semantic information. Specifically, an efficient distributed system is proposed for the semantic filtering of XML documents that gives better results than the existing approaches. Finally as part of this thesis is additional research that improves the performance of the search engines from a different angle. It is presented a technique for cutting the inverted lists of the inverted files. Specifically a combination of the proposed technique with existing compression techniques is achieved, leading to better compression results than the existing ones.