A review of selected methods of predicting base flow environment in supersonic flow

Methods of predicting base flow environment in supersonic flo

Reciprocity in Social Networks with Capacity Constraints

Directed links -- representing asymmetric social ties or interactions (e.g., "follower-followee") -- arise naturally in many social networks and other complex networks, giving rise to directed graphs (or digraphs) as basic topological models for these networks. Reciprocity, defined for a digraph as the percentage of edges with a reciprocal edge, is a key metric that has been used in the literature to compare different directed networks and provide "hints" about their structural properties: for example, are reciprocal edges generated randomly by chance or are there other processes driving their generation? In this paper we study the problem of maximizing achievable reciprocity for an ensemble of digraphs with the same prescribed in- and out-degree sequences. We show that the maximum reciprocity hinges crucially on the in- and out-degree sequences, which may be intuitively interpreted as constraints on some "social capacities" of nodes and impose fundamental limits on achievable reciprocity. We show that it is NP-complete to decide the achievability of a simple upper bound on maximum reciprocity, and provide conditions for achieving it. We demonstrate that many real networks exhibit reciprocities surprisingly close to the upper bound, which implies that users in these social networks are in a sense more "social" than suggested by the empirical reciprocity alone in that they are more willing to reciprocate, subject to their "social capacity" constraints. We find some surprising linear relationships between empirical reciprocity and the bound. We also show that a particular type of small network motifs that we call 3-paths are the major source of loss in reciprocity for real networks

Dynamics of Chainlike Molecules on Surfaces

We consider the diffusion and spreading of chainlike molecules on solid surfaces. We first show that the steep spherical cap shape density profiles, observed in some submonolayer experiments on spreading polymer films, imply that the collective diffusion coefficient $D_C(\theta)$ must be an increasing function of the surface coverage $\theta$ for small and intermediate coverages. Through simulations of a discrete model of interacting chainlike molecules, we demonstrate that this is caused by an entropy-induced repulsive interaction. Excellent agreement is found between experimental and numerically obtained density profiles in this case, demonstrating that steep submonolayer film edges naturally arise due to the diffusive properties of chainlike molecules. When the entropic repulsion dominates over interchain attractions, $D_C(\theta)$ first increases as a function of $\theta$ but then eventually approaches zero for $\theta \to 1$. The maximum value of $D_C(\theta)$ decreases for increasing attractive interactions, leading to density profiles that are in between spherical cap and Gaussian shapes. We also develop an analytic mean field approach to explain the diffusive behavior of chainlike molecules. The thermodynamic factor in $D_C(\theta)$ is evaluated using effective free energy arguments, and the chain mobility is calculated numerically using the recently developed dynamic mean field theory. Good agreement is obtained between theory and simulations.Comment: 16 pages, 13 Postscript figure

Testing the Effectiveness of Regulation and Competition on Cable Television Rates

Regulation of the cable television industry was marked by remarkable periods of deregulation, re-regulation, and re-deregulation during the 1980s and 1990s. Using FCC firm-level survey data spanning 1993 to 2001, we model and econometrically estimate the effect of regulation and competition on cable rates. Our calculations indicate that while regulation lowered rates for small system operators, it raised them for medium and large systems. Meanwhile, competition consistently decreased rates from 5.6 to 8.8 percent, with even larger declines during periods of regulation. Our results suggest that competition is more effective than regulation in containing cable prices.cable rates, regulation, competition

Testing the Effectiveness of Regulation and Competition on Cable Television Rates

Regulation of the cable television industry was marked by remarkable periods of deregulation, re-regulation, and re-deregulation during the 1980s and 1990s. Using FCC firm-level survey data spanning 1993 to 2001, we model and econometrically estimate the effect of regulation and competition on cable rates. Our calculations indicate that while regulation lowered rates for small system operators, it raised them for medium and large systems. Meanwhile, competition consistently decreased rates from 5.6 to 8.8 percent, with even larger declines during periods of regulation. Our results suggest that competition is more effective than regulation in containing cable prices.cable rates, regulation, competition

Quantum state transfer via the ferromagnetic chain in a spatially modulated field

We show that a perfect quantum state transmission can be realized through a spin chain possessing a commensurate structure of energy spectrum, which is matched with the corresponding parity. As an exposition of the mirror inversion symmetry discovered by Albanese et. al (quant-ph/0405029), the parity matched the commensurability of energy spectra help us to present the novel pre-engineered spin systems for quantum information transmission. Based on the these theoretical analysis, we propose a protocol of near-perfect quantum state transfer by using a ferromagnetic Heisenberg chain with uniform coupling constant, but an external parabolic magnetic field. The numerical results shows that the initial Gaussian wave packet in this system with optimal field distribution can be reshaped near-perfectly over a longer distance.Comment: 5 pages, 2 figure