Exploring demographic information in social media for product recommendation

In many e-commerce Web sites, product recommendation is essential to improve user experience and boost sales. Most existing product recommender systems rely on historical transaction records or Web-site-browsing history of consumers in order to accurately predict online users’ preferences for product recommendation. As such, they are constrained by limited information available on specific e-commerce Web sites. With the prolific use of social media platforms, it now becomes possible to extract product demographics from online product reviews and social networks built from microblogs. Moreover, users’ public profiles available on social media often reveal their demographic attributes such as age, gender, and education. In this paper, we propose to leverage the demographic information of both products and users extracted from social media for product recommendation. In specific, we frame recommendation as a learning to rank problem which takes as input the features derived from both product and user demographics. An ensemble method based on the gradient-boosting regression trees is extended to make it suitable for our recommendation task. We have conducted extensive experiments to obtain both quantitative and qualitative evaluation results. Moreover, we have also conducted a user study to gauge the performance of our proposed recommender system in a real-world deployment. All the results show that our system is more effective in generating recommendation results better matching users’ preferences than the competitive baselines

Γενικευμένη θεωρία ευθύγραμμης και καμπύλης δοκού με ισογεωμετρική ανάλυση

The present doctoral thesis is organized in seven chapters and two appendices. Each one of the chapters 2 to 6 consists of an introduction containing the necessary literature review of the corresponding problem, the statement of the problem, the numerical solution, a number of representative numerical examples and finally some concluding remarks. In the final chapter, the main conclusions drawn within the present doctoral thesis are summarized, while suggestions and goals for future research are proposed. In Chapter 2, the Analog Equation Method (AEM), a boundary element based method, is employed for the nonuniform torsional problem of bars of arbitrary constant cross section, considering a quadratic B-spline approximation for the fictitious loads of a substitute problem. In addition to this, refinement procedures have been employed in some of the numerical examples in order to investigate their efficiency in increasing accuracy. In Chapter 3, the AEM, a boundary element based method, is employed for the analysis of a homogenous beam element of arbitrary cross section (thin- or thick- walled) taking into account nonuniform warping and shear deformation effects (shear lag due to both flexure and torsion), considering B-splines for the approximation of the fictitious loads. The Isogeometric tools, either integrated in Finite Element Method (FEM) or AEM, are employed for the vibration analysis of this element, too. In Chapter 4, the static and dynamic generalized warping problem of horizontally curved beams of arbitrary cross section, loading and boundary conditions is presented. The proposed beam element possesses ten degrees of freedom (DOFs) per node in order to account for out-of-plane nonuniform warping due to both flexure and torsion (shear lag due to both flexure and torsion). In Chapter 5, the static and vibration analysis of straight or horizontally curved beams of arbitrary cross section, loading and boundary conditions including generalized cross sectional warping and distortional effects due to both flexure and torsion is presented. The aim of this Chapter is to propose a new formulation by enriching the beam’s kinematics both with out-of- and in-plane deformation modes and, thus, take into account both cross section’s warping and distortion in the final 1D analysis of curved members, towards developing GBT further for curved geometries while employing independent warping parameters, which are commonly used in Higher Order Beam Theories (HOBT). In Chapter 6, the beam formulations presented in Chapters 4 and 5 are employed together with design guidelines which specify the maximum spacing of intermediate diaphragms in order to prevent from excessive distortional effects in cross section’s plane. In Chapter 7, the main conclusions drawn in this doctoral thesis are summarized and the key features and novelties of the developed formulations are highlighted. Moreover, directions for further research are suggested.Στη διατριβή αυτή διερευνάται και επιλύεται σειρά προβλημάτων μέσω της ανάπτυξης εξελιγμένων προσομοιωμάτων ευθύγραμμης και καμπύλης δοκού. Πιο συγκεκριμένα, αντιμετωπίζονται τα προβλήματα ανομοιόμορφης στρέψης, γενικευμένης στρέβλωσης λόγω διάτμησης και στρέψης (μέσω των οποίων μελετάται το φαινόμενο της διατμητικής υστέρησης), διαστρέβλωσης (παραμόρφωση των διατομών της δοκού στο επίπεδό τους) καθώς και το πρόβλημα της δυναμικής ανάλυσης ευθύγραμμων και καμπύλων δοκών. Η αντιμετώπιση των προβλημάτων αυτών βασίζεται στη γενικευμένη διατύπωση καινοτόμων θεωριών δοκού (Generalized Beam Theories - GBT), με τις οποίες το πεδίο μετατοπίσεων και οι συνιστώσες των τανυστών παραμόρφωσης και τάσης διατυπώνονται ως γραμμικοί συνδυασμοί γινομένων μονοδιάστατων και διδιάστατων συναρτήσεων.Η αναλυτική λύση των μονοδιάστατων και διδιάστατων προβλημάτων συνοριακών και αρχικών-συνοριακών τιμών που μορφώνονται εν γένει δεν είναι εφικτή. Ως εκ τούτου, τα προβλήματα αυτά επιλύονται αριθμητικά εφαρμόζοντας τη Μέθοδο Συνοριακών Στοιχείων (Boundary Element Method - BEM), τη Μέθοδο Αναλογικής Εξίσωσης (Analog Equation Method - AEM), η οποία αποτελεί εξέλιξη της BEM, καθώς και τη Μέθοδο Πεπερασμένων Στοιχείων (Finite Element Method - FEM). Όσον αφορά στην επίλυση μονοδιάστατων προβλημάτων, οι αριθμητικές μέθοδοι που χρησιμοποιoύνται (AEM και FEM) συνδυάζονται με εργαλεία της Ισογεωμετρικής Ανάλυσης (Isogeometric Analysis - IGA) ώστε να επιτευχθεί μία προσέγγιση με χαμηλότερο υπολογιστικό κόστος καθώς και πιο διαδραστική μεταξύ ανάλυσης και γεωμετρίας που θα επιτυγχάνει πιο αξιόπιστα αποτελέσματα περιορίζοντας το σφάλμα που πηγάζει από την προσέγγιση της γεωμετρίας. Συγκεκριμένα, οι παραμετρικές καμπύλες B-splines και NURBS (Non-Uniform Rational B-Splines) που έχουν υιοθετήσει τα λογισμικά πακέτα μοντελοποίησης με υπολογιστή (Computer-Aided Design - CAD) εφαρμόζονται στην παρούσα διατριβή. Με βάση τις αναπτυχθείσες αναλυτικές και αριθμητικές διαδικασίες συντάσσονται καινοτόμα προγράμματα ηλεκτρονικού υπολογιστή για την ανάλυση τρισδιάστατων ευθύγραμμων και καμπυλόγραμμων ραβδωτών φορέων. Κάθε κύριο κεφάλαιο της διατριβής αποτελείται από την εισαγωγή, τη διατύπωση του προβλήματος, την αριθμητική επίλυση, αντιπροσωπευτικά αριθμητικά παραδείγματα και τα συμπεράσματα. Στην εισαγωγή κάθε κύριου κεφαλαίου περιέχεται η βιβλιογραφική επισκόπηση του ερευνητικού έργου (State of the Art) του αντίστοιχου εξεταζόμενου προβλήματος και παρουσιάζονται τα πρωτότυπα σχετικά στοιχεία της εργασίας. Τέλος, στο τελικό κεφάλαιο παρουσιάζονται τα συμπεράσματα και προτάσεις για μελλοντική έρευνα

Generalized vibration analysis of beams including warping effects by isogeometric methods

In this paper, the Isogeometric tools, either integrated in the Finite Element Method (FEM) or in a Boundary Element based Method (BEM) called Analog Equation Method (AEM), are employed for the vibration analysis of homogeneous beams of arbitrary cross section (thin- or thick- walled) taking into account nonuniform warping and shear deformation effects (shear lag due to both flexure and torsion). The beam is subjected to the combined action of arbitrarily distributed or concentrated axial and transverse loading, as well as to bending, twisting and warping moments. Its edges are subjected to the most general boundary conditions. By employing a distributed mass model system accounting for longitudinal, transverse, rotatory, torsional and warping inertia, ten boundary value problems with respect to the variable along the beam time-dependent 1-D kinematical components are formulated. The numerical solution or the spectrum analysis of the aforementioned problems is performed through IGA, FEM and AEM, leading to a system of second-order differential equations, which are quasi-static and solved for the free vibration case, formulating a generalized eigenvalue problem. Special cases of the generalized problem have also been studied in order to demonstrate the efficiency of AEM in reducing computational effort and improving accuracy, especially when combined to Isogeometric tools, such as NURBS and B-splines. </jats:p

Supplement versus Supplant: A case study of the effect of internet lottery sales on traditional lottery sales

In 2012, the first state lottery began to sell its product over the internet. The additional digital delivery method represents a new era for a product that has been in the market for over three decades. Permitting a potentially competing delivery method for the same product presents an opportunity to examine the impact internet lottery sales have on traditional lottery sales. The thesis builds on work that explored what motivates policy makers to approve innovative policy solutions, such as a new internet delivery method for lottery sales, and how that decision impacts the overall viability of the existing product. By analyzing sales, profits, and growth rates, I sought to determine if market cannibalization or revenue displacement occurred when the new delivery method was added. My findings show that state lotteries experienced sales growth prior to internet sales. Prior to internet sales, only one state experienced flat gross domestic product growth in the year preceding internet sales, while the five others analyzed experienced declining GDP growth. This suggests that poor economic indicators may have led decision makes to approve a new policy for a product that otherwise was growing to address fiscal stress. After internet sales were introduced, profits and in-person lottery sales at retail locations were higher than before internet sales. Total lottery sales grew in all states that permitted internet sales; however, not all states saw sales growth grow as fast as before internet sales. This suggests that internet lottery sales have a positive impact but might dilute what could have been higher sales growth rates.Master of ArtsLotteries date back to ancient times. They originated out of necessity for the primary reason we use them today - leaders need money to fund public works and programs. Often, voluntary taxes like lotteries are a more politically effective way to raise funds than mandatory taxes. Modern lotteries in the United States reemerged as a legitimate state funding source in the mid-1960s. In 2020, 45 states had lotteries. My findings show lotteries continue to see growth in sales, many to benefit public education. Yet some seek to innovate the method of delivery by allowing lottery purchases over the internet. When this is permitted, how does the ability to purchase lottery over the internet impact traditional lottery sales at retail store locations? This thesis analyzed sales data from the six states that permit internet sales to show that internet sales increased lottery profits, retail sales, and total sales. However, after implementing internet sales, two of the four states with at least three years of internet sales experienced sales growth that was slower than before internet sales were permitted. This may mean some revenue displacement occured when the additional delivery method was implemented. It is rational for lotteries to want to increase sales and respond to rising customer demands in this digital age. However, legislators who may be interested in growing lottery sales as a way to combat other fiscal stress should consider whether any cannibalization may occur by permitting additional lottery delivery methods