Πολυοξομεταλλικές ενώσεις του βολφραμίου και του μολυβδαινίου ως στρώματα μεταφοράς φορτίων σε οργανικές διόδους εκπομπής φωτός

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Μικροσυστήματα και Νανοδιατάξεις

A Taxonomy of Privacy-Preserving Record Linkage Techniques

The process of identifying which records in two or more databases correspond to the same entity is an important aspect of data quality activities such as data pre-processing and data integration. Known as record linkage, data matching or entity resolution, this process has attracted interest from researchers in fields such as databases and data warehousing, data mining, information systems, and machine learning. Record linkage has various challenges, including scalability to large databases, accurate matching and classification, and privacy and confidentiality. The latter challenge arises because commonly personal identifying data, such as names, addresses and dates of birth of individuals, are used in the linkage process. When databases are linked across organizations, the issue of how to protect the privacy and confidentiality of such sensitive information is crucial to successful application of record linkage. In this paper we present an overview of techniques that allow the linking of databases between organizations while at the same time preserving the privacy of these data. Known as 'privacy-preserving record linkage' (PPRL), various such techniques have been developed. We present a taxonomy of PPRL techniques to characterize these techniques along 15 dimensions, and conduct a survey of PPRL techniques. We then highlight shortcomings of current techniques and discuss avenues for future research

An Efficient Two-Party Protocol for Approximate Matching in Private Record Linkage

The task of linking multiple databases with the aim to identify records that refer to the same entity is occurring increasingly in many application areas. If unique identifiers for the entities are not available in all the databases to be linked, techniques that calculate approximate similarities between records must be used for the identification of matching pairs of records. Often, the records to be linked contain personal information such as names and addresses. In many applications, the exchange of attribute values that contain such personal details between organisations is not allowed due to privacy concerns. The linking of records between databases without revealing the actual attribute values in these records is the research problem known as 'privacy-preserving record linkage' (PPRL).While various approaches have been proposed to deal with privacy within the record linkage process, a viable solution that is well applicable to real-world conditions needs to address the major aspect of scalability of linking very large databases while preserving security and linkage quality. We propose a novel two-party protocol for PPRL that addresses scalability, security and quality/ accuracy. The protocol is based on (1) the use of reference values that are available to both database owners, and allows them to individually calculate the similarities between their attribute values and the reference values; and (2) the binning of these calculated similarity values to allow their secure exchange between the two database owners. Experiments on a real-world database with nearly two million records yield linkage results that have a linear scalability to large databases and high linkage accuracy, allowing for approximate matching in the privacy-preserving context. Since the protocol has a low computational burden and allows quality approximate matching while still preserving the privacy of the databases that are matched, the protocol can be useful for many real-world applications requiring PPRL

Σύνδεση της παραγώγου συνάρτησης με τη μονοτονία της ξεκινώντας από διαισθητικές προσεγγίσεις.

Η σύνδεση του προσήμου της παραγώγου μιας συνάρτησης με τη μονοτονία της είναι ένα από τα βασικά θέματα ενός μαθήματος εισαγωγικού λογισμού. Διακρίνουμε δύο βασικούς τρόπους προσέγγισης. Ο πρώτος έχει αποκλειστικά διαισθητικό χαρακτήρα και αφορά τη χρήση ψηφιακών εργαλείων και οπτικών αναπαραστάσεων. Ο δεύτερος αφορά την προηγούμενη εισαγωγή του θεωρήματος μέσης τιμής και τη χρήση του για να δοθούν απλές αποδείξεις των σχετικών αποτελεσμάτων. Σε επίπεδο δευτεροβάθμιας εκπαίδευσης, η Ελλάδα είναι μια από τις λίγες χώρες που ακολουθεί το δεύτερο τρόπο. Υποστηρίζουμε ότι η επιλογή αυτή έχει δημιουργήσει δυσκολίες στους μαθητές και έχει ενισχύσει τη διαδικαστική μάθηση. Προτείνουμε μια νέα προσέγγιση που αφορά την εισαγωγή μιας μαθηματικής πρότασης (Simplified Racetrack Principle) που βρίσκεται πιο κοντά στις διασθήσεις των μαθητών. Οι μαθητές μπορούν να ανακαλύψουν την αρχή αυτή δουλεύοντας σε ένα πλαίσιο σχετικό με τη φυσική και στη συνέχεια να τη χρησιμοποιήσουν για να κατασκευάσουν τις μαθηματικές αποδείξεις που αιτιολογούν τη σύνδεση μονοτονίας και παραγώγου. Η νέα προσέγγιση συνδυάζει τον απαραίτητο στη δευτεροβάθμια εκπαίδευση διαισθητικό χαρακτήρα με την κατασκευή τυπικών συλλογισμών στο αντικείμενο του λογισμού. Σχεδιάσαμε και υλοποιήσαμε μια διδακτική παρέμβαση με ομάδες μαθητών δύο λυκείων που ακολουθεί τη νέα προσέγγιση και αναλύσαμε τα αποτελέσματα της χρησιμοποιώντας το μοντέλο επιστημικών δράσεων RBC της θεωρίας AiC.The connection of the sign of the derivative of a function with its monotonicity is one of the key topics of introductory calculus. We distinguish two main approaches. The first has an exclusively intuitive character and makes use of digital tools and visual representations. The second involves the introduction of the mean value theorem and its use to give simple proofs of the relevant results. At the level of secondary education, Greece is one of the few countries that follow the second approach. We argue that this choice has created diculties for students and has enhanced pro- cedural learning. We propose a new approach that involves the introduction of a mathematical principle (Simplified Racetrack Principle) which is closer to students’ intuitions. Students can discover this principle by working in a context related to physics and then use it to construct mathematical proofs justifying the connection between monotonicity and derivative. The new approach combines intuition (neces- sary in secondary education) with formal reasoning in the domain of calculus. We designed and implemented a didactic intervention with groups of students from two high schools that follows the new approach. Our analysis of the results uses the RBC model of scientific actions proposed by AiC