Reciprocal Recommender System for Learners in Massive Open Online Courses (MOOCs)

Massive open online courses (MOOC) describe platforms where users with completely different backgrounds subscribe to various courses on offer. MOOC forums and discussion boards offer learners a medium to communicate with each other and maximize their learning outcomes. However, oftentimes learners are hesitant to approach each other for different reasons (being shy, don't know the right match, etc.). In this paper, we propose a reciprocal recommender system which matches learners who are mutually interested in, and likely to communicate with each other based on their profile attributes like age, location, gender, qualification, interests, etc. We test our algorithm on data sampled using the publicly available MITx-Harvardx dataset and demonstrate that both attribute importance and reciprocity play an important role in forming the final recommendation list of learners. Our approach provides promising results for such a system to be implemented within an actual MOOC.Comment: 10 pages, accepted as full paper @ ICWL 201

Graph-based Features for Automatic Online Abuse Detection

While online communities have become increasingly important over the years, the moderation of user-generated content is still performed mostly manually. Automating this task is an important step in reducing the financial cost associated with moderation, but the majority of automated approaches strictly based on message content are highly vulnerable to intentional obfuscation. In this paper, we discuss methods for extracting conversational networks based on raw multi-participant chat logs, and we study the contribution of graph features to a classification system that aims to determine if a given message is abusive. The conversational graph-based system yields unexpectedly high performance , with results comparable to those previously obtained with a content-based approach

Principles of Control for Decoherence-Free Subsystems

Decoherence-Free Subsystems (DFS) are a powerful means of protecting quantum information against noise with known symmetry properties. Although Hamiltonians theoretically exist that can implement a universal set of logic gates on DFS encoded qubits without ever leaving the protected subsystem, the natural Hamiltonians that are available in specific implementations do not necessarily have this property. Here we describe some of the principles that can be used in such cases to operate on encoded qubits without losing the protection offered by the DFS. In particular, we show how dynamical decoupling can be used to control decoherence during the unavoidable excursions outside of the DFS. By means of cumulant expansions, we show how the fidelity of quantum gates implemented by this method on a simple two-physical-qubit DFS depends on the correlation time of the noise responsible for decoherence. We further show by means of numerical simulations how our previously introduced "strongly modulating pulses" for NMR quantum information processing can permit high-fidelity operations on multiple DFS encoded qubits in practice, provided that the rate at which the system can be modulated is fast compared to the correlation time of the noise. The principles thereby illustrated are expected to be broadly applicable to many implementations of quantum information processors based on DFS encoded qubits.Comment: 12 pages, 7 figure

13CO(J=1−−0)^{13}CO(J = 1 -- 0) Depression in Luminous Starburst Mergers

It is known that the class of luminous starburst galaxies tends to have higher $R =^{12}CO(J=1--0)/^{13}CO(J=1--0)$ integrated line intensity ratios ($R>20$) than normal spiral galaxies ($R \sim 10$). Since most previous studies investigated only $R$, it remains uncertain whether the luminous starburst galaxies are overabundant in $^{12}$CO or underabundant in $^{13}$CO. Here we propose a new observational test to examine this problem. Our new test is to compare far-infrared luminosities [$L$(FIR)] with those of $^{12}$CO and $^{13}CO [L(^{12}CO)$ and $L(^{13}CO)$, respectively]. It is shown that there is a very tight correlation between $L(^{12}CO)$ and L(FIR), as found in many previous studies. However, we find that the $^{13}$CO luminosities of the high-R galaxies are lower by a factor of three on the average than those expected from the correlation for the remaining galaxies with ordinary $R$ values. Therefore, we conclude that the observed high $R$ values for the luminous starburst galaxies are attributed to their lower $^{13}$CO line intensities.Comment: 9 pages (aaspp4.sty), 3 postscript figures (embedded). Accepted for publication in Astrophysical Journal Letter

Magnetic Behavior in RRhX (R = rare earths; X=B, C) Compounds

We report on the magnetic behavior of RRhB (R = La, Ce, Pr, Nd, Gd, Tb and Tm) and RRhC (R = La, Ce, Pr and Gd) compounds crystallizing in the cubic perovskite type structure with space group Pm3m. The heat capacity data on Pauli-paramagnetic LaRhB and LaRhC indicate a high frequency vibrating motion of boron and carbon atoms in the unit cell. Ce is in -like nonmagnetic state in both the compounds. Pr compounds show a dominant crystal field effect with a nonmagnetic singlet ground state in PrRhB and a nonmagnetic quadrupolar doublet in PrRhC. Compounds with other rare earths order ferromagnetically at low temperatures except TmRhB in which the zero field evolution of magnetic interactions is relatively more complicated. The electrical resistivity of GdRhB decreases with increasing temperature in the paramagnetic state in the vicinity of T, which is rarely seen in ferromagnets. The behavior is discussed to be arising due to the short range spin fluctuation and a possible contribution from Fermi surface geometry.Comment: 14 Figs and a text fil

Shaping the formation of university-industry research collaborations: what type of proximity does really matter?

Research collaborations between universities and industry (U-I) are considered to be one important channel of potential localized knowledge spillovers (LKS). These collaborations favour both intended and unintended flows of knowledge and facilitate learning processes between partners from different organizations. Despite the copious literature on LKS, still little is known about the factors driving the formation of U-I research collaborations and, in particular, about the role that geographical proximity plays in the establishment of such relationships. Using collaborative research grants between universities and business firms awarded by the UK Engineering and Physical Sciences Research Council (EPSRC), in this article we disentangle some of the conditions under which different kinds of proximity contribute to the formation of U-I research collaborations, focusing in particular on clustering and technological complementarity among the firms participating in such partnerships

Information Horizons in Networks

We investigate and quantify the interplay between topology and ability to send specific signals in complex networks. We find that in a majority of investigated real-world networks the ability to communicate is favored by the network topology on small distances, but disfavored at larger distances. We further discuss how the ability to locate specific nodes can be improved if information associated to the overall traffic in the network is available.Comment: Submitted top PR

XMM-Newton Archival Study of the ULX Population in Nearby Galaxies

We present the results of an archival XMM-Newton study of the bright X-ray point sources (L_X > 10^38 erg/s) in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, searching for a soft-hard state dichotomy similar to that known for Galactic X-ray binaries and testing the specific predictions of the IMBH hypothesis. To this end, we searched for "low-state" objects, which we defined as objects within our sample which had a spectrum well fit by a simple absorbed power law, and "high-state" objects, which we defined as objects better fit by a combined blackbody and a power law. Assuming that ``low-state'' objects accrete at approximately 10% of the Eddington luminosity (Done & Gierlinski 2003) and that "high-state" objects accrete near the Eddington luminosity we further divided our sample of sources into low and high state ULX sources. We classify 16 sources as low-state ULXs and 26 objects as high-state ULXs. As in Galactic black hole systems, the spectral indices, Gamma, of the low-state objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures for the high state is 0.1-1 keV, with the most luminous systems tending toward the lowest temperatures. We therefore divide our high-state ULXs into candidate IMBHs (with blackbody temperatures of approximately 0.1 keV) and candidate stellar mass BHs (with blackbody temperatures of approximately 1.0 keV). A subset of the candidate stellar mass BHs have spectra that are well-fit by a Comptonization model, a property similar of Galactic BHs radiating in the "very-high" state near the Eddington limit.Comment: 54 pages, submitted to ApJ (March 2005), accepted (May 2006); changes to organization of pape