Interneti võimalused ja ohud: noorte online-praktikate mõju nende subjektiivsele heaolule

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Teismelised on ühed kõige aktiivsemad internetikasutajad ja internet moodustab loomuliku osa nende igapäevaelust. Kuna internet on siiski suhteliselt uus meedium, mille kasutust ei raamista väga kindlad normid, kuid mille noored on väga kiirelt ja aktiivselt omaks võtnud, ärgitab see küsima, millist mõju internetikasutus noortele avaldab – kas positiivset või negatiivset. Heaolu kontseptsioonist lähtudes on doktoritöös vaatluse all nii internetikasutuse positiivsed kui ka negatiivsed küljed ning nende mõju noorte elukvaliteedile. Viimane aspekt on eriti oluline, kuna teismeiga on üks olulisemaid arenguperioode. Doktoritöös olid vaatluse all noorte online-praktikad – ühelt poolt blogimine kui positiivne ja teiselt poolt ülemäärane internetikasutus kui problemaatiline praktika – ning see, kuidas ja missugustel tingimustel need suurendavad või vähendavad noore heaolu. Nii meediumi valikut kui kasutust kujundavad laiemad kontekstuaalsed tegurid nagu vanus, sugu ja sotsiaalne keskkond (näiteks suhted pere ja eakaaslastega) ning ühiskondlikud tingimused (kultuuriline tasand), milles inimene elab, aga ka meediumi enda või selle rakenduste omadused. Seega võib järeldada, et just kontekst loob ja määrab internetikasutuse võimalikud positiivsed või negatiivsed tulemid. Internetikasutusel võivad olla erinevad tagajärjed. Näiteks avaldavad noored blogides enamasti tõele vastavat sisu, millega nad kujundavad enda identiteeti ja hoiavad sotsiaalseid suhteid, või mis pakub võimalust pälvida tunnustust eakaaslaste hulgas. Samas jagavad noored blogis enda kohta intiimset infot, millel võivad olla negatiivsed tagajärjed. Ülemäärane internetikasutus on seotud nii psühholoogiliste probleemide, internetis veedetava aja kui ka noore digitaalsete oskustega ja sellega, mida ta online-keskkonnas teeb. Ülemäärane internetikasutus võib olla ühelt poolt toimetulekustrateegia, saamaks üle negatiivsetest emotsioonidest, kuna just noortele ekspertkasutajatele pakub internet mitmesuguseid võimalusi meelelahutuseks ja tujutõstmiseks. Teiselt poolt võib see toimetulekumehhanism avaldada pikemas perspektiivis noore heaolule negatiivset mõju.Teenagers have become the most prominent users of the Internet as they effortlessly incorporate the medium into their everyday lives. Due to the newness of the medium, only partially settled norms surrounding usage, and intensity with which the online space was adopted by the youth, much attention has been paid to dwell upon whether the usage of the Internet by the young people brings along positive or negative outcomes. The concept of well-being is used in the thesis to simultaneously look both at the positive and negative aspects of Internet use and to ask how these phenomena are related to young people’s quality of life. The latter question is especially important as adolescence is the formative period in young people’s development. The thesis looked at online practices – blogging as a positive side, and excessive Internet use as a problematic one – and how and in what condition they increase or decrease the well-being of the young. The findings suggest that both media choice and usage, as well as the well-being of the young Internet users, are framed by larger contextual factors – age and gender of the user; social environment (e.g. family and peer influence) and societal (cultural level) conditions individuals live in; and the structural characteristics of the medium or its applications. Hence, the thesis suggests that it is the context which creates and defines the positivity and negativity of certain outcomes of Internet usage. For instance, adolescent bloggers primarily stay truthful to their offline selves in their blogs, and hence the practice could be seen as a mechanism for maintaining one’s identity and social contacts, but also as an opportunity to seek prestige and competence among the peer group. At the same time, revealing intimate details about one’s life in a blog can also lead to possible negative consequences. Excessive Internet use among the young is related to psychological distress and the time spent online but also to one’s digital skills and the activities one engages in online. Hence, on the one hand, excessive Internet use may be a coping strategy, especially for more expert young users of the medium, as it offers a wide range of opportunities for mood management and entertainment; on the other hand, it may have negative outcomes on one’s well-being in the long run

Mixing time of a kinetically constrained spin model on trees: power law scaling at criticality

On the rooted k-ary tree we consider a 0-1 kinetically constrained spin model in which the occupancy variable at each node is re-sampled with rate one from the Bernoulli(p) measure iff all its children are empty. For this process the following picture was conjectured to hold. As long as p is below the percolation threshold pc = 1/k the process is ergodic with a finite relaxation time while, for p > pc, the process on the infinite tree is no longer ergodic and the relaxation time on a finite regular sub-tree becomes exponentially large in the depth of the tree. At the critical point p = pc the process on the infinite tree is still ergodic but with an infinite relaxation time. Moreover, on finite sub-trees, the relaxation time grows polynomially in the depth of the tree. The conjecture was recently proved by the second and forth author except at crit- icality. Here we analyse the critical and quasi-critical case and prove for the relevant time scales: (i) power law behaviour in the depth of the tree at p = pc and (ii) power law scaling in (pc − p)−1 when p approaches pc from below. Our results, which are very close to those obtained recently for the Ising model at the spin glass critical point, represent the first rigorous analysis of a kinetically constrained model at criticality

Probabilistic Reasoning across the Causal Hierarchy

We propose a formalization of the three-tier causal hierarchy of association, intervention, and counterfactuals as a series of probabilistic logical languages. Our languages are of strictly increasing expressivity, the first capable of expressing quantitative probabilistic reasoning -- including conditional independence and Bayesian inference -- the second encoding do-calculus reasoning for causal effects, and the third capturing a fully expressive do-calculus for arbitrary counterfactual queries. We give a corresponding series of finitary axiomatizations complete over both structural causal models and probabilistic programs, and show that satisfiability and validity for each language are decidable in polynomial space.Comment: AAAI-2

The density of planar sets avoiding unit distances

By improving upon previous estimates on a problem posed by L. Moser, we prove a conjecture of Erd\H{o}s that the density of any measurable planar set avoiding unit distances cannot exceed $1/4$. Our argument implies the upper bound of $0.2470$.Comment: 24 pages, 6 figures. Final version, to appear in Mathematical Programmin

Improved inclusion-exclusion identities via closure operators

Let (A_v)_v ∈ V be a finite family of sets. We establish an improved inclusion-exclusion identity for each closure operator on the power set of V having the unique base property. The result generalizes three improvements of the inclusion-exclusion principle as well as Whitney's broken circuit theorem on the chromatic polynomial of a graph