Security and Privacy in Online Social Networks

The explosive growth of Online Social Networks (OSNs) over the past few years has redefined the way people interact with existing friends and especially make new friends. OSNs have also become a great new marketplace for trade among the users. However, the associated privacy risks make users vulnerable to severe privacy threats. In this dissertation, we design protocols for private distributed social proximity matching and a private distributed auction based marketplace framework for OSNs. In particular, an OSN user looks for matching profile attributes when trying to broaden his/her social circle. However, revealing private attributes is a potential privacy threat. Distributed private profile matching in OSNs mainly involves using cryptographic tools to compute profile attributes matching privately such that no participating user knows more than the common profile attributes. In this work, we define a new asymmetric distributed social proximity measure between two users in an OSN by taking into account the weighted profile attributes (communities) of the users and that of their friends’. For users with different privacy requirements, we design three private proximity matching protocols with increasing privacy levels. Our protocol with highest privacy level ensures that each user’s proximity threshold is satisfied before revealing any matching information. The use of e-commerce has exploded in the last decade along with the associated security and privacy risks. Frequent security breaches in the e-commerce service providers’ centralized servers compromise consumers’ sensitive private and financial information. Besides, a consumer’s purchase history stored in those servers can be used to reconstruct the consumer’s profile and for a variety of other privacy intrusive purposes like directed marketing. To this end, we propose a secure and private distributed auction framework called SPA, based on decentralized online social networks (DOSNs) for the first time in the literature. The participants in SPA require no trust among each other, trade anonymously, and the security and privacy of the auction is guaranteed. The efficiency, in terms of communication and computation, of proposed private auction protocol is at least an order of magnitude better than existing distributed private auction protocols and is suitable for marketplace with large number of participants

Ambient processed (110) preferred MAPbI3thin films for highly efficient perovskite solar cells

Organic-inorganic hybrid perovskites have attracted intensive attention due to their exceptional optoelectronic properties. With a massive leap of efficiency from 3.8% to 25.2% in a decade, perovskite solar cells (PSCs) have been considered the most promising next-generation photovoltaic technology. Recently, the methylamine (MA)-gas-mediated approach has been widely studied for preparing precursor solutions to deposit large scale perovskite thin films for PSCs. In this article, high-quality MAPbI3films were spin-coated using a MA-gas-mediated perovskite precursor. The deposited MAPbI3films showed larger crystal grains, lower surface roughness, and a preferred (110) crystal orientation compared to the films deposited by the Lewis adduct method. Planar PSC devices fabricated using the MA-gas-mediated precursor showed a high efficiency of 19.28% and a higher average efficiency than the devices fabricated by the Lewis adduct method

Democratic Middle Ground in Nepal: A Perspective from the North American Nepali Diaspora

The call of our time is to safeguard the accomplishments of the 1990 Peoples Movement, to restore sovereignty to the people, and to work towards the middle ground to resolve the nation\u27s core problems. History teaches us that recognizing, adopting and adhering to the middle path takes much vision and courage. The natural instinct is to stick to one\u27s own interpretation of the world (usually based on narrow self-interest) and to shun ideas and individuals that require a moderation of one\u27s views. However, success in politics and statecraft, more so than in any other area of human affairs, is hinged to the middle ground in a way that ultimately requires friend and foe to migrate sufficiently towards each other so that the peoples\u27 business can move forward and flourish. We urge all political forces in Nepal to recognize that great achievements in the affairs of nations come about when leaders practice the art of compromise. There is no dishonor for Nepal\u27s monarch and political leaders if they follow the path of the likes of Gandhi, Nehru and Mandela.\u2

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum