XWiki Mobile: architetture collaborative per device mobili

Studio di una interfaccia mobile web per la piattaforma XWiki.

Structured P2P Video Streaming and Collaborative Failure Detection

Il video streaming in peer-to-peer sta diventando sempre più popolare e utiliz- zato. Per tali applicazioni i criteri di misurazione delle performance sono: - startup delay: il tempo che intercorre tra la connessione e l’inizio della ripro- duzione dello stream (chiamato anche switching delay), - playback delay: il tempo che intercorre tra l’invio da parte della sorgente e la riproduzione dello stream da parte di un peer, - time lag: la differenza tra i playback delay di due diversi peer. Tuttavia, al giorno d’oggi i sistemi P2P per il video streaming sono interessati da considerevoli ritardi, sia nella fase di startup che in quella di riproduzione. Un recente studio su un famoso sistema P2P per lo streaming, ha mostrato che solitamente i ritardi variano tra i 10 e i 60 secondi. Gli autori hanno osservato anche che in alcuni casi i ritardi superano i 4 minuti! Si tratta quindi di gravi inconvenienti se si vuole assistere a eventi in diretta o se si vuole fruire di applicazioni interattive. Alcuni studi hanno mostrato che questi ritardi sono la conseguenza della natura non strutturata di molti sistemi P2P. Ogni stream viene suddiviso in blocchi che vengono scambiati tra i peer. A causa della diffusione non strutturata del contenuto, i peer devono continuamente scambiare informazioni con i loro vicini prima di poter inoltrare i blocchi ricevuti. Queste soluzioni sono estremamente re- sistenti ai cambiamenti della rete, ma comportano una perdita notevole in termini di prestazioni, rendendo complicato raggiungere l’obiettivo di un broadcast in realtime. In questo progetto abbiamo lavorato su un sistema P2P strutturato per il video streaming che ha mostrato di poter offrire ottimi risultati con ritardi molto vicini a quelli ottimali. In un sistema P2P strutturato ogni peer conosce esattamente quale blocchi inviare e a quali peer. Siccome il numero di peer che compongono il sistema potrebbe essere elevato, ogni peer dovrebbe operare possedendo solo una conoscenza limitata dello stato del sistema. Inoltre il sistema è in grado di gestire arrivi e partenze, anche raggruppati, richiedendo una riorganizzazione limitata della struttura. Infine, in questo progetto abbiamo progettato e implementato una soluzione personalizzata per rilevare e sostituire i peer non più in grado di cooperare. Anche per questo aspetto, l’obiettivo è stato quello di minimizzare il numero di informazioni scambiate tra peer.

Collaborative Change: Environmental Jolt, Network (Re)Design and Firm Performance

Motivated by the need to understand which are the underlying forces that trigger network evolution, we develop a multilevel theoretical and empirically testable model to examine the relationship between changes in the external environment and network change. We refer to network change as the dissolution or replacement of an interorganizational tie, adding also the case of the formation of new ties with new or preexisting partners. Previous research has paid scant attention to the organizational consequences of quantum change enveloping entire industries in favor of an emphasis on continuous change. To highlight radical change we introduce the concept of environmental jolt. The September 11 terrorist attacks provide us with a natural experiment to test our hypotheses on the antecedents and the consequences of network change. Since network change can be explained at multiple levels, we incorporate firm-level variables as moderators. The empirical setting is the global airline industry, which can be regarded as a constantly changing network of alliances. The study reveals that firms react to environmental jolts by forming homophilous ties and transitive triads as opposed to the non jolt periods. Moreover, we find that, all else being equal, firms that adopt a brokerage posture will have positive returns. However, we find that in the face of an environmental jolt brokerage relates negatively to firm performance. Furthermore, we find that the negative relationship between brokerage and performance during an environmental jolt is more significant for larger firms. Our findings suggest that jolts are an important predictor of network change, that they significantly affect operational returns and should be thus incorporated in studies of network dynamics.

Essays On CEO Compensation: New Evidence On The Managerial-Power Vs. Optimal Contracting Debate

This dissertation analyzes the effect of market analysts’ expectations of share prices (price targets) on executive compensation. It examines how well the estimated effects of price targets on compensation fit with two competing views on determining executive compensation: the arm’s length bargaining model, which assumes that a board seeks to maximize shareholders’ interests, and the managerial power model, which assumes that a board seeks to maximize managers’ compensation (Bebchuk et al. 2005). The first chapter documents the pattern of CEO pay from fiscal year 1996 to 2010. The second chapter analyzes the Institutional Broker Estimate System Detail History Price Target data file, which that reports analysts’ price targets for firms. I show that the number of price target announcements is positively associated with company share price’s volatility, that price targets are predictive of changes in the value of stocks, and that when analysts announce positive (negative) expectations of future stock price, share prices change in the same direction in the short run. The third chapter analyzes the effect of price targets on executive compensation. I find that analysts' price targets alter the composition of executive pay between cash-based compensation and stock-based compensation. When analysts forecast a rise (fall) in the share price for a firm, the compensation package tilts toward stock-based (cash-based) compensation. The substitution effect is stronger in companies that have weaker corporate governance. The fourth chapter explores the effect of the introduction of the Sarbanes-Oxley Act (SOX) in 2002 and its reinforcement in 2006 on the options granting process. I show that the introduction of SOX and its reinforcement eliminated the practice of backdating options but increased “spring-loading” of option grants around price targets announcements. Overall, the dissertation shows that price targets provide insights into the determinants of executive pay in favor of the managerial power model.

Studio ed integrazione di un sistema di collaborative filtering su piattaforma e-commerce business to consumer

I sistemi di raccomandazione sono una tipologia di sistemi di filtraggio delle informazioni che cercano di prevedere la valutazione o la preferenza che l'utente potrebbe dare ad un elemento. Sono diventati molto comuni in questi ultimi anni e sono utilizzati da una vasta gamma di applicazioni, le più popolari riguardano film, musica, notizie, libri, articoli di ricerca e tag di social networking. Tuttavia, ci sono anche sistemi di raccomandazione per i ristoranti, servizi finanziari, assicurazioni sulla vita e persone (siti di appuntamenti online, seguaci di Twitter). Questi sistemi, tuttora oggetto di studi, sono già applicati in un'ampia gamma di settori, come ad esempio le piattaforme di scoperta dei contenuti, utilizzate on-line per aiutare gli utenti nella ricerca di trasmissioni televisive; oppure i sistemi di supporto alle decisioni che utilizzano sistemi di raccomandazione avanzati, basati sull'apprendimento delle conoscenze, per aiutare i fruitori del servizio nella soluzioni di problemi complessi. Inoltre, i sistemi di raccomandazione sono una valida alternativa agli algoritmi di ricerca in quanto aiutano gli utenti a scoprire elementi che potrebbero non aver trovato da soli. Infatti, sono spesso implementati utilizzando motori di ricerca che indicizzano dati non tradizionali.

Prognosis of patients with HIV-1 infection starting antiretroviral therapy in sub-Saharan Africa: a collaborative analysis of scale-up programmes

Background Prognostic models have been developed for patients infected with HIV-1 who start combination antiretroviral therapy (ART) in high-income countries, but not for patients in sub-Saharan Africa. We developed two prognostic models to estimate the probability of death in patients starting ART in sub-Saharan Africa. Methods We analysed data for adult patients who started ART in four scale-up programmes in Côte d'Ivoire, South Africa, and Malawi from 2004 to 2007. Patients lost to follow-up in the first year were excluded. We used Weibull survival models to construct two prognostic models: one with CD4 cell count, clinical stage, bodyweight, age, and sex (CD4 count model); and one that replaced CD4 cell count with total lymphocyte count and severity of anaemia (total lymphocyte and haemoglobin model), because CD4 cell count is not routinely measured in many African ART programmes. Death from all causes in the first year of ART was the primary outcome. Findings 912 (8·2%) of 11 153 patients died in the first year of ART. 822 patients were lost to follow-up and not included in the main analysis; 10 331 patients were analysed. Mortality was strongly associated with high baseline CD4 cell count (≥200 cells per μL vs <25; adjusted hazard ratio 0·21, 95% CI 0·17–0·27), WHO clinical stage (stages III–IV vs I–II; 3·45, 2·43–4·90), bodyweight (≥60 kg vs <45 kg; 0·23, 0·18–0·30), and anaemia status (none vs severe: 0·27, 0·20–0·36). Other independent risk factors for mortality were low total lymphocyte count, advanced age, and male sex. Probability of death at 1 year ranged from 0·9% (95% CI 0·6–1·4) to 52·5% (43·8–61·7) with the CD4 model, and from 0·9% (0·5–1·4) to 59·6% (48·2–71·4) with the total lymphocyte and haemoglobin model. Both models accurately predict early mortality in patients starting ART in sub-Saharan Africa compared with observed data. Interpretation Prognostic models should be used to counsel patients, plan health services, and predict outcomes for patients with HIV-1 infection in sub-Saharan Africa.

Comparison of biological stability and metabolism of CCK2 receptor targeting peptides, a collaborative project under COST BM0607

Stability of radiolabelled cholecystokinin 2 (CCK2) receptor targeting peptides has been a major limitation in the use of such radiopharmaceuticals especially for targeted radionuclide therapy applications, e.g. for treatment of medullary thyroid carcinoma (MTC). The purpose of this study was to compare the in vitro stability of a series of peptides binding to the CCK2 receptor [selected as part of the COST Action on Targeted Radionuclide Therapy (BM0607)] and to identify major cleavage sites.

Comparison of the binding and internalization properties of 12 DOTA-coupled and ¹¹¹In-labelled CCK2/gastrin receptor binding peptides: a collaborative project under COST Action BM0607

Specific overexpression of cholecystokinin 2 (CCK2)/gastrin receptors has been demonstrated in several tumours of neuroendocrine origin. In some of these cancer types, such as medullary thyroid cancer (MTC), a sensitive diagnostic modality is still unavailable and therapeutic options for inoperable lesions are needed. Peptide receptor radionuclide therapy (PRRT) may be a viable therapeutic strategy in the management of these patients. Several CCK2R-targeted radiopharmaceuticals have been described in recent years. As part of the European Union COST Action BM0607 we studied the in vitro and in vivo characteristics of 12 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated CCK2R binding peptides. In the present study, we analysed binding and internalization characteristics. Stability, biodistribution and imaging studies have been performed in parallel by other centres involved in the project.

Tenofovir in second-line ART in Zambia and South Africa: collaborative analysis of cohort studies

Tenofovir (TDF) is increasingly used in second-line antiretroviral treatment (ART) in sub-Saharan Africa. We compared outcomes of second-line ART containing and not containing TDF in cohort studies from Zambia and the Republic of South Africa (RSA).

HIV treatment response and prognosis in Europe and North America in the first decade of highly active antiretroviral therapy: a collaborative analysis

BACKGROUND: Highly active antiretroviral therapy (HAART) for the treatment of HIV infection was introduced a decade ago. We aimed to examine trends in the characteristics of patients starting HAART in Europe and North America, and their treatment response and short-term prognosis. METHODS: We analysed data from 22,217 treatment-naive HIV-1-infected adults who had started HAART and were followed up in one of 12 cohort studies. The probability of reaching 500 or less HIV-1 RNA copies per mL by 6 months, and the change in CD4 cell counts, were analysed for patients starting HAART in 1995-96, 1997, 1998, 1999, 2000, 2001, and 2002-03. The primary endpoints were the hazard ratios for AIDS and for death from all causes in the first year of HAART, which were estimated using Cox regression. RESULTS: The proportion of heterosexually infected patients increased from 20% in 1995-96 to 47% in 2002-03, and the proportion of women from 16% to 32%. The median CD4 cell count when starting HAART increased from 170 cells per muL in 1995-96 to 269 cells per muL in 1998 but then decreased to around 200 cells per muL. In 1995-96, 58% achieved HIV-1 RNA of 500 copies per mL or less by 6 months compared with 83% in 2002-03. Compared with 1998, adjusted hazard ratios for AIDS were 1.07 (95% CI 0.84-1.36) in 1995-96 and 1.35 (1.06-1.71) in 2002-03. Corresponding figures for death were 0.87 (0.56-1.36) and 0.96 (0.61-1.51). INTERPRETATION: Virological response after starting HAART improved over calendar years, but such improvement has not translated into a decrease in mortality.

Rates of disease progression according to initial highly active antiretroviral therapy regimen: a collaborative analysis of 12 prospective cohort studies

BACKGROUND: No large clinical end-point trials have been conducted comparing regimens among human immunodeficiency virus type 1-positive persons starting antiretroviral therapy. We examined clinical progression according to initial regimen in the Antiretroviral Therapy Cohort Collaboration, which is based on 12 European and North American cohort studies. METHODS: We analyzed progression to death from any cause and to AIDS or death (AIDS/death), comparing efavirenz (EFV), nevirapine (NVP), nelfinavir, idinavir, ritonavir (RTV), RTV-boosted protease inhibitors (PIs), saquinavir, and abacavir. We also compared nucleoside reverse-transcriptase inhibitor pairs: zidovudine/lamivudine (AZT/3TC), stavudine (D4T)/3TC, D4T/didanosine (DDI), and others. RESULTS: A total of 17,666 treatment-naive patients, 55,622 person-years at risk, 1,617 new AIDS events, and 895 deaths were analyzed. Compared with EFV, the adjusted hazard ratio (HR) for AIDS/death was 1.28 (95% confidence interval [CI], 1.03-1.60) for NVP, 1.31 (95% CI, 1.01-1.71) for RTV, and 1.45 (95% CI, 1.15-1.81) for RTV-boosted PIs. For death, the adjusted HR for NVP was 1.65 (95% CI, 1.16-2.36). The adjusted HR for death for D4T/3TC was 1.35 (95% CI, 1.14-1.59), compared with AZT/3TC. CONCLUSIONS: Outcomes may vary across initial regimens. Results are observational and may have been affected by bias due to unmeasured or residual confounding. There is a need for large, randomized, clinical end-point trials.

Outcomes associated with drug-eluting and bare-metal stents: a collaborative network meta-analysis

Whether the two drug-eluting stents approved by the US Food and Drug Administration-a sirolimus-eluting stent and a paclitaxel-eluting stent-are associated with increased risks of death, myocardial infarction, or stent thrombosis compared with bare-metal stents is uncertain. Our aim was to compare the safety and effectiveness of these stents.