Cloud Compute-and-Forward with Relay Cooperation

We study a cloud network with M distributed receiving antennas and L users, which transmit their messages towards a centralized decoder (CD), where M>=L. We consider that the cloud network applies the Compute-and-Forward (C&F) protocol, where L antennas/relays are selected to decode integer equations of the transmitted messages. In this work, we focus on the best relay selection and the optimization of the Physical-Layer Network Coding (PNC) at the relays, aiming at the throughput maximization of the network. Existing literature optimizes PNC with respect to the maximization of the minimum rate among users. The proposed strategy maximizes the sum rate of the users allowing nonsymmetric rates, while the optimal solution is explored with the aid of the Pareto frontier. The problem of relay selection is matched to a coalition formation game, where the relays and the CD cooperate in order to maximize their profit. Efficient coalition formation algorithms are proposed, which perform joint relay selection and PNC optimization. Simulation results show that a considerable improvement is achieved compared to existing results, both in terms of the network sum rate and the players' profits.Comment: Submitted to IEEE Transactions on Wireless Communication

Board Interlocks and Their Impact on Corporate Governance: The Indian Experience - Coping with Corporate Cholesterol

Board interlocks occur when a director of one organization sits on the board of directors of another organization. The causes and consequences of these interlocks have been much debated in the western literature but comparatively little is known about interlocks in Indian corporate boards. Board interlocks are essentially analogous to cholesterol. Both are facts of life. Like good cholesterol, there are aspects of interlocking directorates that are beneficial and there are others that are detrimental to the corporation and its stakeholders and their respective interests. In this study, we find that board interlocks are quite widespread in India. Taking a (numerically) small but nevertheless (in terms of market capitalization) an important slice of available corporate data, we observed that in 2010, ‘highly boarded’ directors (defined as those on the board of 5 or more listed NSE companies) who constitute just 6 percent of the overall pool of directors among NSE100 companies are associated with 486 NSE listed companies which account for a whopping 66 percent of the total market capitalization of all NSE listed companies. Interestingly, there appears to be a marked increase in market capitalization of these ‘highly boarded’ companies, which these ‘highly boarded’ directors are linked to over the last several years. For instance, for the 3 years from 2001 to 2003, the market capitalization of ‘highly boarded’ companies ranged between 33 percent to 43 percent; it moved up to peak of 70 percent in 2007 and was at 66 percent in 2010 (the latest year in the study period). The substantive rise in market capitalization of these ‘highly boarded’ companies has coincided with only a marginal increase (from 5% to 6%) in the proportion of ‘highly boarded’ directorships. These trends suggest that despite the well-intentioned regulatory reforms (a) the extent of over-boarding/interlocking among directors has not come down (there is actually a marginal increase) and (b) there appears to be increasing concentration of power among key individuals. Given the general view that concentration of power in a few individuals or entities is not desirable in the larger interests of society, it would appear that the observed trends in the concentration of power among a handful of the country’s corporate elite is a matter for substantive public policy concern. Finally, the regression analysis indicates a positive impact on Return on Assets (ROA) for ‘highly boarded’ directors signifying a negation of the agency centric conceptualization on the role of multiple directors. Instead, connectedness variables (Eigen vector) which proxy for the Resource dependency hypothesis are quite strongly supported. In a nutshell, from public policy perspective, the analysis potentially reflects the ‘bad cholesterol’ elements of multiple directorships in terms of a tiny segment of ‘highly boarded’ directors controlling a significant portion of the country’s economic prowess, whereas the positive influences on company performance provide some evidence of the ‘good cholesterol’.

The XMM-Newton Iron Line Profile of NGC 3783

We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV, with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV emission is the K-alpha line from near neutral Fe, whilst the 7.0 keV feature probably originates from a blend of the neutral Fe K-beta line and the H-like line of Fe at 6.97 keV. The relatively narrow velocity width of the K-alpha line (<5000 km/s), its lack of response to the continuum emission on short timescales and the detection of a neutral Compton reflection component are all consistent with a distant origin in Compton-thick matter such as the putative molecular torus. A strong absorption line from highly ionized iron (at 6.67 keV) is detected in the time-averaged iron line profile, whilst the depth of the feature appears to vary with time, being strongest when the continuum flux is higher. The iron absorption line probably arises from the highest ionization component of the known warm absorber in NGC 3783, with an ionization of logxi=3 and column density of 5x10^{22}cm{-2} and may originate from within 0.1pc of the nucleus. A weak red-wing to the iron K line profile is also detected below 6.4 keV. However when the effect of the highly ionized warm absorber on the underlying continuum is taken into account, the requirement for a relativistic iron line component from the inner disk is reduced.Comment: 34 pages, including 11 figures. Accepted for publication in Ap

Quenching of fluorescence of aromatic molecules by graphene due to electron transfer

Investigations on the fluorescence quenching of graphene have been carried out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester (PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II). Absorption and photoluminescence spectra of I and II recorded in mixture with increasing the concentrations of graphene showed no change in the former, but remarkable quenching of fluorescence. The property of graphene to quench fluorescence of these aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure