Phase Equilibria of Lattice Polymers from Histogram Reweighting Monte Carlo Simulations

Histogram-reweighting Monte Carlo simulations were used to obtain polymer / solvent phase diagrams for lattice homopolymers of chain lengths up to r=1000 monomers. The simulation technique was based on performing a series of grand canonical Monte Carlo calculations for a small number of state points and combining the results to obtain the phase behavior of a system over a range of temperatures and densities. Critical parameters were determined from mixed-field finite-size scaling concepts by matching the order parameter distribution near the critical point to the distribution for the three-dimensional Ising universality class. Calculations for the simple cubic lattice (coordination number z=6) and for a high coordination number version of the same lattice (z=26) were performed for chain lengths significantly longer than in previous simulation studies. The critical temperature was found to scale with chain length following the Flory-Huggins functional form. For the z=6 lattice, the extrapolated infinite chain length critical temperature is 3.70+-0.01, in excellent agreement with previous calculations of the temperature at which the osmotic second virial coefficient is zero and the mean end-to-end distance proportional to the number of bonds. This confirms that the three alternative definitions of the Theta-temperature are equivalent in the limit of long chains. The critical volume fraction scales with chain length with an exponent equal to 0.38+-0.01, in agreement with experimental data but in disagreement with polymer solution theories. The width of the coexistence curve prefactor was tentatively found to scale with chain length with an exponent of 0.20+-0.03 for z = 6 and 0.22+-0.03 for z = 26. These values are near the lower range of values obtained from experimental data.Comment: 23 pages, including 7 figure

Effective hadronic Lagrangian for charm mesons

An effective hadronic Lagrangian including the charm mesons is introduced to study their interactions in hadronic matter. Using coupling constants that are determined either empirically or by the SU(4) symmetry, we have evaluated the absorption cross sections of $J/\psi$ and the scattering cross sections of $D$ and $D^*$ by $\pi$ and $\rho$ mesons.Comment: 5 pages, 4 eps figures, presented at Strangeness 2000, Berkeley. Uses iopart.cl

Specular surface recovery from reflections of a planar pattern undergoing an unknown pure translation

LNCS v. 6493 entitled: Computer Vision – ACCV 2010: 10th Asian Conference on Computer Vision, Queenstown, New Zealand, November 8-12, 2010, Revised Selected Papers, Part 2This paper addresses the problem of specular surface recovery, and proposes a novel solution based on observing the reflections of a translating planar pattern. Previous works have demonstrated that a specular surface can be recovered from the reflections of two calibrated planar patterns. In this paper, however, only one reference planar pattern is assumed to have been calibrated against a fixed camera observing the specular surface. Instead of introducing and calibrating a second pattern, the reference pattern is allowed to undergo an unknown pure translation, and a closed form solution is derived for recovering such a motion. Unlike previous methods which estimate the shape by directly triangulating the visual rays and reflection rays, a novel method based on computing the projections of the visual rays on the translating pattern is introduced. This produces a depth range for each pixel which also provides a measure of the accuracy of the estimation. The proposed approach enables a simple auto-calibration of the translating pattern, and data redundancy resulting from the translating pattern can improve both the robustness and accuracy of the shape estimation. Experimental results on both synthetic and real data are presented to demonstrate the effectiveness of the proposed approach. © 2011 Springer-Verlag Berlin Heidelberg.postprintThe 10th Asian Conference on Computer Vision, Queenstown, New Zealand, 8-12 November 2010. In Lecture Notes in Computer Science, 2010, v. 6493, p. 137-14

Beyond Counting: New Perspectives on the Active IPv4 Address Space

In this study, we report on techniques and analyses that enable us to capture Internet-wide activity at individual IP address-level granularity by relying on server logs of a large commercial content delivery network (CDN) that serves close to 3 trillion HTTP requests on a daily basis. Across the whole of 2015, these logs recorded client activity involving 1.2 billion unique IPv4 addresses, the highest ever measured, in agreement with recent estimates. Monthly client IPv4 address counts showed constant growth for years prior, but since 2014, the IPv4 count has stagnated while IPv6 counts have grown. Thus, it seems we have entered an era marked by increased complexity, one in which the sole enumeration of active IPv4 addresses is of little use to characterize recent growth of the Internet as a whole. With this observation in mind, we consider new points of view in the study of global IPv4 address activity. Our analysis shows significant churn in active IPv4 addresses: the set of active IPv4 addresses varies by as much as 25% over the course of a year. Second, by looking across the active addresses in a prefix, we are able to identify and attribute activity patterns to network restructurings, user behaviors, and, in particular, various address assignment practices. Third, by combining spatio-temporal measures of address utilization with measures of traffic volume, and sampling-based estimates of relative host counts, we present novel perspectives on worldwide IPv4 address activity, including empirical observation of under-utilization in some areas, and complete utilization, or exhaustion, in others.Comment: in Proceedings of ACM IMC 201

X-ray Observations of Parsec-Scale Tails behind Two Middle-Aged Pulsars

Chandra and XMM-Newton resolved extremely long tails behind two middle-aged pulsars, J1509-5850 and J1740+1000. The tail of PSR J1509-5850 is discernible up to 5.6' from the pulsar (6.5 pc at a distance of 4 kpc), with a flux of 2*10^{-13} erg s^{-1} cm^{-2} in 0.5-8 keV. The tail spectrum fits an absorbed power-law (PL) model with the photon index of 2.3\pm0.2, corresponding to the 0.5-8 keV luminosity of 1*10^{33} ergs s^{-1}, for n_H= 2.1*10^{22} cm^{-2}. The tail of PSR J1740+1000 is firmly detected up to 5' (2 pc at a 1.4 kpc distance), with a flux of 6*10^{-14} ergs cm^{-2} s^{-1} in 0.4-10 keV. The PL fit yields photon index of 1.4-1.5 and n_H=1*10^{21} cm^{-2}. The large extent of the tails suggests that the bulk flow in the tails starts as mildly relativistic downstream of the termination shock, and then gradually decelerates. Within the observed extent of the J1509-5850 tail, the average flow speed exceeds 5,000 km s^{-1}, and the equipartition magnetic field is a few times 10^{-5} G. For the J1740+1000 tail, the equipartition field is a factor of a few lower. The harder spectrum of the J1740+1000 tail implies either less efficient cooling or a harder spectrum of injected electrons. For the high-latitude PSR J1740+1000, the orientation of the tail on the sky shows that the pulsar is moving toward the Galactic plane, which means that it was born from a halo-star progenitor. The comparison between the J1509 and J1740 tails and the X-ray tails of other pulsars shows that the X-ray radiation efficiency correlates poorly with the pulsar spin-down luminosity or age. The X-ray efficiencies of the ram-pressure confined pulsar wind nebulae (PWNe) are systematically higher than those of PWNe around slowly moving pulsars with similar spin-down parameters.Comment: 14 pages, 16 figures and 5 table

Achieving sub-diffraction imaging through bound surface states in negative-refracting photonic crystals at the near-infrared

We report the observation of imaging beyond the diffraction limit due to bound surface states in negative refraction photonic crystals. We achieve an effective negative index figure-of-merit [-Re(n)/Im(n)] of at least 380, ~125x improvement over recent efforts in the near-infrared, with a 0.4 THz bandwidth. Supported by numerical and theoretical analyses, the observed near-field resolution is 0.47 lambda, clearly smaller than the diffraction limit of 0.61 lambda. Importantly, we show this sub-diffraction imaging is due to the resonant excitation of surface slab modes, allowing refocusing of non-propagating evanescent waves

Decoupled UL/DL User Association in Wireless-Powered HetNets with Full-Duplex Small Cells

In this paper, we propose two downlink (DL)-uplink (UL) decoupled (DUDe) user association schemes in wireless-powered full-duplex (FD) heterogeneous networks (HetNets). We consider a two-tier HetNet comprising of half-duplex (HD) massive multi-antenna macrocell base stations (MBSs) and dual-antenna FD small cell base stations (SBSs) to support UL and DL transmissions of FD user equipments (UEs). Each FD UE is first associated to one MBS/SBS, based on the mean maximum received power (MMP) scheme or maximum received power (MRP) to harvest energy. During the consecutive data transmission phase, UEs choose to receive DL traffic from the same MBSs/SBSs as that associated with during energy harvesting phase, and send UL traffic through the same/another SBS. Leveraging tools from the stochastic geometry, we develop an analytical framework to analyze the average harvested energy and derive expressions for the UL and DL coverage probabilities of the proposed DUDe user association schemes. Our results show that there is an optimal value for the SBS density in the wireless-powered FD HetNets, at which both DL and UL coverage probabilities are maximized. Moreover, by applying MMPA and MRPA scheme, wireless-powered FD HetNets with DUDe achieves up to $138.78\%$ and $83.37\%$ energy efficiency gain over the FD HetNets with DL/UL coupled user association scheme and without wireless power transfer, respectively