Il processo di Mining e la Blockchain

Bitcoin è un sistema di crittovaluta elettronica inventato da Satoshi Nakamoto nel 2008 ed esaminato nel suo articolo dal titolo ''Bitcoin: a peer-to-peer electronic cash sistem’’, in cui spiega come vengono risolti i problemi che insorgono in un sistema non regolamentato da una Banca centrale, bensì da un network di nodi peer-to-peer. Una delle maggiori difficoltà di questo nuovo sistema è la necessità di eliminare la fiducia verso terze parti durante una transazione: l’obiettivo è far sì che tutti siano d’accordo sull’ordine cronologico delle transazioni, in modo tale da evitare il problema del double-spending. Per fare ciò è necessario introdurre un algoritmo di consenso che permetta di mettere d’accordo i diversi nodi del network e di risolvere il cosiddetto ''Problema dei Generali Bizantini'': si supponga che due generali, dislocati in diverse aree geografiche debbano decidere come coordinare l’attacco di una città nemica potendo comunicare solo mediante messaggeri. Tra questi è altamente probabile che vi siano dei traditori che mandino messaggi che vanno contro la strategia dell’esercito. Il problema è portare avanti l’attacco in modo efficiente nonostante il rischio di tradimento: ciò è conosciuto come consenso decentralizzato. Nakamoto risolse questo problema grazie alla catena delle proof-of-work basata sulla potenza computazionale dei nodi. Il seguente elaborato di tesi mira ad analizzare i meccanismi alla base del sistema Bitcoin, focalizzandosi sull'aspetto crittografico. Nel primo capitolo si riportano le nozioni di crittografia che saranno alla base della Blockchain e delle crittovalute, cercando di dare le nozioni di base per comprendere il sistema crittografico sul quale si basano le transazioni, ossia l’elliptic Curve DSA. Si studiano poi le transazioni, la loro struttura e lo scambio di denaro basato sugli UTXO e si conclude analizzando la Blockchain ed il Mining, cioè il meccanismo grazie al quale le operazioni vengono validate

The Italian Helpdesk under the Regulation (EC) No. 1272/2008 (CLP): three-year activity and experience (2009-2011)

INTRODUCTION: The Regulation (EC) No. 1272/2008 on classification, labelling and packaging of substances and mixtures (CLP) sets further obligations for manufacturers, importers, distributors, downstream users of substances either on their own or in mixtures. According to the European mandate, each Member State has constituted its National Helpdesk to provide advice to the interested parties on their duties under this Regulation. In Italy, the contact point for questions has been established at the National Centre for Chemical Substances of the Istituto Superiore di Sanita. FUNCTIONS: The responders of the Italian CLP Helpdesk process the requests that have been submitted by the dedicated website. Applicants are asked to complete the form with all the required information. The Helpdesk staff also take part in the European network of CLP, REACH and ECHA Helpdesks together with the European Commission and other parties, that is the HelpNet. RESULTS: The present paper describes the results of the three-year activity of the Italian CLP Helpdesk (2009-2011)

Assessment of the Concurrent Validity of the Leadership Skills Inventory with Gifted Students and Their Teachers

60 students currently enrolled in state-approved public school programs for the gifted at Grades 6 and 7 were given the Leadership Skills Inventory. Four certified teachers of these students were asked to complete an inventory on each subject to assess its concurrent validity. On mean T scores of students and mean teachers' ratings of students t-tests showed no significant differences between the means of the students and ratings of two teachers who had several years of experience teaching gifted students and who had more experience with the inventory. It was concluded that the inventory should be used primarily as a self-rating instrument. </jats:p

Assessment of Criterion-Related Validity of the Leadership Skills Inventory

This study was designed to assess criterion-related validity of the Leadership Skills Inventory. The student subjects were 113 girls and boys (Grades 6–11) who had recently completed a 1-wk. Leadership Studies Program. Adult subjects were 55 community leaders who were chosen by a panel to represent arts, business, government, professions, and civic activities. Both groups completed the inventory. Mean self-rating for the children who had completed the training leadership was higher than mean self-rating of adults. Results are consistent with the criterion-related validity of the instrument. </jats:p

Personality Characteristics of Student Leaders

95 students were nominated by their schools to attend the Leadership Studies Program, a summer residential program for students in Grades 6 through 11. Students were administered the High School Personality Questionnaire to assess their personality characteristics and differences between boys and girls on any of the factors on the instrument. Girls were significantly higher than boys on Emotional Stability (Factor C), Dominance (Factor E), and on the secondary factor of Independence. </jats:p

Student Leaders and Social Performance as Measured by the Social Performance Survey Schedule

There is a paucity of research on the social skills of student leaders, although studies have been conducted on other groups of students and adults. In this study, the Social Performance Survey Schedule was administered to 114 student leaders in Grades 6 to 11. Consistent with previous research applying the survey on diverse populations, girls engaged in more positive social behaviors, fewer negative behaviors, and had higher over-all performance than boys. Suggestions for those who may have contact with such students were made. </jats:p

Social Performance of Gifted Students as Measured by the Social Performance Survey Schedule

Few studies have investigated the relative contributions of both positive and negative behaviors in the social performance of intellectually gifted students. In the present study, the Social Performance Survey Schedule was administered to 80 gifted subjects in a special program. To determine whether the observed differences between boys and girls were significant, analysis of variance with repeated measures was performed on the Schedule Total, Part A, and Part B means. Consistent with previous research on the schedule, girls engaged in a greater number of positive social behaviors, engaged in fewer negative behaviors, and generally had higher over-all performance than boys. Suggestions were made concerning the implications of the findings for those who may have contact with gifted children in clinical or educational settings. </jats:p

Correlations of Scores on Verbal and Nonverbal Measures of Intelligence for Intellectually Gifted Students

For 80 intellectually gifted students, intelligent quotients and percentiles from the WISC—R, Stanford-Binet, Standard Progressive Matrices, and the Culture-Fair Intelligence Test were correlated. Pearson correlations were larger among the nonverbal measures of intelligence than between the nonverbal and verbal measures. </jats:p