On the effect of dispersion on nonlinear phase noise

The variance of nonlinear phase noise is analyzed by including the effect of intrachannel cross-phase modulation (IXPM)-induced nonlinear phase noise. Consistent with Ho and Wang [1] but in contrary to the conclusion of both Kumar [2] and Green et al. [3], the variance of nonlinear phase noise does not decrease much with the increase of chromatic dispersion. The results are consistent with a careful reexamination of both Kumar [2] and Green et al. [3].Comment: 3 pages, 1 figure, submitted to Optics Letter

Phase Statistics of Soliton

The characteristic function of soliton phase jitter is found analytically when the soliton is perturbed by amplifier noise. In additional to that from amplitude jitter, the nonlinear phase noise due to frequency and timing jitter is also analyzed. Because the nonlinear phase noise is not Gaussian distributed, the overall phase jitter is also non-Gaussian. For a fixed mean nonlinear phase shift, the contribution of nonlinear phase noise from frequency and timing jitter decreases with distance and signal-to-noise ratio.Comment: 8 pages, submitted to JOSA

Asymptotic Probability Density Function of Nonlinear Phase Noise

The asymptotic probability density function of nonlinear phase noise, often called the Gordon-Mollenauer effect, is derived analytically when the number of fiber spans is very large. The nonlinear phase noise is the summation of infinitely many independently distributed noncentral chi-square random variables with two degrees of freedom. The mean and standard deviation of those random variables are both proportional to the square of the reciprocal of all odd natural numbers. The nonlinear phase noise can also be accurately modeled as the summation of a noncentral chi-square random variable with two degrees of freedom and a Gaussian random variable.Comment: 13 pages, 3 figure

Non-Gaussian Statistics of the Soliton Timing Jitter due to Amplifier Noise

Based on the first-order perturbation theory of soliton, the Gordon-Haus timing jitter induced by amplifier noise is found to be non-Gaussian distributed. Compared with Gaussian distribution given by the linearized perturbation theory, both frequency and timing jitter have larger tail probability. The timing jitter has a larger discrepancy to Gaussian distribution than that of frequency jitter.Comment: 3 pages, 4 figures, submitted to Optics Letter

Maximum-Likelihood Detection of Soliton with Timing Jitter

Using the maximum-likelihood detector (MLD) of a soliton with timing jitter and noise, other than walk-out of the bit interval, timing jitter does not degrade the performance of MLD. When the MLD is simulated with important sampling method, even with a timing jitter standard deviation the same as the full-width-half-maximum (FWHM) of the soliton, the signal-to-noise (SNR) penalty is just about 0.2 dB. The MLD performs better than conventional scheme to lengthen the decision window with additive noise proportional to the window wide.Comment: 3 pages, 2 figures, submitted to Optics Letter

Reciprocity and Priority Allocation System for Organ Transplant: An Ethical Analysis

How to increase the supply of organs donations for transplant is a critical issue in healthcare. Although recently xenotransplantation has received much publicity, it may be years before this becomes clinically viable. The Reciprocity and Priority Allocation (RPA) System currently used in Israel and a few other countries may be a reasonable approach to increase organ donation in the foreseeable future. For this approach to be accepted by the public, a robust analysis on its ethical implications is needed. This paper applies two formal ethics frameworks to analyze the implication of the RPA system

Transient complete heart block following catheter ablation of a left lateral accessory pathway.

A 16-year-old female with symptomatic Wolff-Parkinson-White (WPW) syndrome underwent catheter ablation of a left-sided lateral accessory pathway. The accessory pathway was eliminated with the first ablation lesion; however, the patient immediately developed complete heart block (CHB). At first, complete heart block was thought to be due to ablation of left atrial extension of the AV node, and pacemaker therapy was considered. However, careful ECG analysis revealed that the development of CHB was in fact due to bump injury to the AV node during transseptal catheterization. Conservative management allowed resolution of AV nodal conduction without need for a permanent pacemaker

Two Dimensional Anti-de Sitter Space and Discrete Light Cone Quantization

We realize the two dimensional anti-de Sitter ($AdS_2$) space as a Kaluza-Klein reduction of the $AdS_3$ space in the framework of the discrete light cone quantization (DLCQ). Introducing DLCQ coordinates which interpolate the original (unboosted) coordinates and the light cone coordinates, we discuss that $AdS_2/CFT$ correspondence can be deduced from the $AdS_3/CFT$. In particular, we elaborate on the deformation of WZW model to obtain the boundary theory for the $AdS_2$ black hole. This enables us to derive the entropy of the $AdS_2$ black hole from that of the $AdS_3$ black hole.Comment: RevTeX, 11 pages, shorter version to appear in PL

Generalized Langevin models of molecular dynamics simulations with applications to ion channels

We present a new methodology, which combines molecular dynamics and stochastic dynamics, for modeling the permeation of ions across biological ion channels. Using molecular dynamics, a free energy profile is determined for the ion(s) in the channel, and the distribution of random and frictional forces is measured over discrete segments of the ion channel. The parameters thus determined are used in stochastic dynamics simulations based on the nonlinear generalized Langevin equation. We first provide the theoretical basis of this procedure, which we refer to as "distributional molecular dynamics," and detail the methods for estimating the parameters from molecular dynamics to be used in stochastic dynamics. We test the technique by applying it to study the dynamics of ion permeation across the gramicidin pore. Given the known difficulty in modeling the conduction of ions in gramicidin using classical molecular dynamics, there is a degree of uncertainty regarding the validity of the MD-derived potential of mean force (PMF) for gramicidin. Using our techniques and systematically changing the PMF, we are able to reverse engineer a modified PMF which gives a current-voltage curve closely matching experimental results.This work was supported by grants from the National Health and Medical Research Council of Australia. The calculations upon which this work is based were carried out using the SGI Altix cluster of the Australian National University Supercomputer Facility. NAMD was developed by the Theoretical and Computational Biophysics Group in the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign