Density Evolution for Asymmetric Memoryless Channels

Density evolution is one of the most powerful analytical tools for low-density parity-check (LDPC) codes and graph codes with message passing decoding algorithms. With channel symmetry as one of its fundamental assumptions, density evolution (DE) has been widely and successfully applied to different channels, including binary erasure channels, binary symmetric channels, binary additive white Gaussian noise channels, etc. This paper generalizes density evolution for non-symmetric memoryless channels, which in turn broadens the applications to general memoryless channels, e.g. z-channels, composite white Gaussian noise channels, etc. The central theorem underpinning this generalization is the convergence to perfect projection for any fixed size supporting tree. A new iterative formula of the same complexity is then presented and the necessary theorems for the performance concentration theorems are developed. Several properties of the new density evolution method are explored, including stability results for general asymmetric memoryless channels. Simulations, code optimizations, and possible new applications suggested by this new density evolution method are also provided. This result is also used to prove the typicality of linear LDPC codes among the coset code ensemble when the minimum check node degree is sufficiently large. It is shown that the convergence to perfect projection is essential to the belief propagation algorithm even when only symmetric channels are considered. Hence the proof of the convergence to perfect projection serves also as a completion of the theory of classical density evolution for symmetric memoryless channels.Comment: To appear in the IEEE Transactions on Information Theor

J0041+3224: a new double-double radio galaxy

We report the discovery of a double-double radio galaxy (DDRG), J0041+3224, with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency observations with the Very Large Array (VLA). The inner and outer doubles are aligned within about 4 deg and are reasonably collinear with the parent optical galaxy. The outer double has a steeper radio spectrum compared with the inner one. Using an estimated redshift of 0.45, the projected linear sizes of the outer and inner doubles are 969 and 171 kpc respectively. The time scale of interruption of jet activity has been estimated to be about 20 Myr, similar to other known DDRGs. We have compiled a sample of known DDRGs, and have re-examined the inverse correlation between the ratio of the luminosities of the outer to the inner double and the size of the inner double, l_{in}. Unlike the other DDRGs with l_{in} larger than about 50 kpc, the inner double of J0041+3224 is marginally more luminous than the outer one. The two DDRGs with l_{in} less than about a few kpc have a more luminous inner double than the outer one, possibly due to a higher efficiency of conversion of beam energy as the jets propagate through the dense interstellar medium. We have examined the symmetry parameters and find that the inner doubles appear to be more asymmetric in both its armlength and flux density ratios compared with the outer doubles, although they appear marginally more collinear with the core than the outer double. We discuss briefly possible implications of these trends.Comment: Accepted for publication in MNRAS, 9 pages, 10 figure

Inhomogeneous vortex-state-driven enhancement of superconductivity in nanoengineered ferromagnet-superconductor heterostructures

Thin film heterostructures provide a powerful means to study the antagonism between superconductivity (SC) and ferromagnetism (FM). One interesting issue in FM-SC hybrids which defies the notion of antagonistic orders is the observation of magnetic field induced superconductivity (FIS). Here we show that in systems where the FM domains/islands produce spatial inhomogeneities of the SC order parameter, the FIS can derive significant contribution from different mobilities of the magnetic flux identified by two distinct critical states in the inhomogeneous superconductor. Our experiments on nanoengineered bilayers of ferromagnetic CoPt and superconducting NbN where CoPt/NbN islands are separated by a granular NbN, lend support to this alternative explanation of FIS in certain class of FM-SC hybrids.Comment: 5 figure

Histological correlation of nasal mass: a five year retrospective and prospective study

Background:The presence of mass in the nose may seem to be a simple problem; however it raises several issues about the differential diagnosis. The aim of this study is to evaluate the histological profile of nasal masses in the environment.Methods:This is a retrospective and prospective study of nasal masses during a period of five years of patients presenting to the clinician in our hospital.Results:A total of 90 patients were analysed age ranging from 3 to 80 years. Majority of patients were in the second decade. Sex wise distribution showed a male to female ratio of 2.2:1. The main presenting symptom was nasal obstruction seen in 53.30% patients, while proptosis was seen only in malignant lesion. Among a total of 90 lesions in the nasal cavity 81.1% were benign, 15.5 % were malignant and 3.3% were inadequate sample The commonest non neoplastic lesion was nasal polyp which comprised about 83.33% followed by rhinoscleroma, while the commonest benign neoplastic lesion was papilloma and comprised about 42.10% and squamous cell carcinoma was the most common malignant neoplastic lesion in the nasal cavity and comprised about 42.85%. Most patients with benign lesion were in the second decade. Malignant lesions occurred mainly after fifth decade, while inadequacy of sample was seen in the second decade.  Conclusion: Males are more commonly affected then females. Nasal obstruction is the commonest symptom Simple inflammatory nasal polyp is still the commonest histological pattern seen while papilloma being the most common benign lesion and squamous cell carcinoma the most common malignant lesion.

On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources

The interpretation of the observed relation between median angular sizes (θm) of extragalactic radio sources and flux density at 408 MHz has been examined. The predicted θm-S relations based on well-observed strong sources in parent samples selected at 178 and 1400 MHz, and existing models of the evolving radio luminosity function can be made to fit the observed relation only by invoking cosmological evolution in linear sizes even for the q0 = 0 universe. Predictions based on a parent sample at 2.7 GHz are shown to overestimate the contribution of steep-spectrum, compact (SSC) sources in low-frequency samples unless the downward curvature in the spectra of such sources is taken into account. When approximate corrections are made for this effect, predictions based on the 2.7 GHz parent sample cannot obviate the need for linear size evolution as claimed in the literature

Metallicity Evolution of Damped Lyman-Alpha Galaxies

We have reanalyzed the existing data on Zinc abundances in damped Ly-alpha (DLA) absorbers to investigate whether their mean metallicity evolves with time. Most models of cosmic chemical evolution predict that the mass- weighted mean interstellar metallicity of galaxies should rise with time from a low value ~ 1/30 solar at z ~ 3 to a nearly solar value at z ~ 0. However, several previous analyses have suggested that there is little or no evolution in the global metallicity of DLAs. We have used a variety of statistical techniques to quantify the global metallicity-redshift relation and its uncertainties, taking into account both measurement and sampling errors. Three new features of our analysis are: (a) an unbinned N(H I)-weighted nonlinear chi-square fit to an exponential relation; (b) survival analysis to treat the large number of limits in the existing data; and (c) a comparison of the data with several models of cosmic chemical evolution based on an unbinned N(H I)-weighted chi-square. We find that a wider range of evolutionary rates is allowed by the present data than claimed in previous studies. The slope of the exponential fit to the N(H I)-weighted mean Zn metallicity vs. redshift relation is -0.20 plus minus 0.11 counting limits as detections and -0.27 plus minus 0.12 counting limits as zeros. Similar results are also obtained if the data are binned in redshift, and if survival analysis is used. These slopes are marginally consistent with no evolution, but are also consistent with the rates predicted by several models of cosmic chemical evolution. Finally, we outline some future measurements necessary to improve the statistics of the global metallicity-redshift relation.Comment: 25 pages, 1 figure, accepted for publication in the Astrophysical Journa

Mechanisms of rolling contact spalling

The results of a study aimed at analyzing the mechanical material interactions responsible for rolling contact spalling of the 440 C steel, high pressure oxygen turbopump bearings are presented. A coupled temperature displacement finite element analysis of the effects of friction heating under the contact is presented. The contact is modelled as a stationary, heat generating, 2 dimensional indent in an elastic perfectly plastic half-space with heat fluxes up to 8.6 x 10000 KW/m sq comparable to those generated in the bearing. Local temperatures in excess of 1000 C are treated. The calculations reveal high levels of residual tension after the contact is unloaded and cools. Efforts to promote Mode 2/Mode 3 fatigue crack growth under cyclic torsion in hardened 440 C steel are described. Spalls produced on 440 C steel by a 3 ball/rod rolling contact testing machine were studied with scanning microscopy. The shapes of the cyclic, stress strain hysteresis loops displayed by hardened 440 C steel in cyclic torsion at room temperature are defined for the plastic strain amplitudes encountered in rolling/sliding contact. Results of these analyses are discussed in detail

Assessment of drug-drug interactions in the prescription of elderly patients on cardiovascular drugs

Background: Cardiovascular disease is one of the major causes of mortality and morbidity in a developing country like India. These patient’s prescription contains multiple drugs to reduce the mortality and morbidity and they also contain drugs for treatment of co morbidities leading to polypharmacy. The main objective of the study was to identify the pattern of drug- drug interaction (DDI) in patients on cardiovascular drugs with various co existing morbidities.Methods: This study was conducted in the Department of General Medicine of a tertiary care center. Prescription of 200 patients were analysed for demographic details like gender, age, comorbidities and drugs prescribed. DDI were assessed using Micromedex software.Results: In this study, conducted on the prescription of 200 elderly patients, 13 (66%) prescription had 408 DDI, of which 158 (39%) were major, 246 (60%) were moderate and 1 (0.02%) was contraindicated and 3 (0.007%) were minor.Conclusions: It can be concluded from the present study that the risk of DDI increases with the increase in number of drugs in the prescription and there is increase in number of drugs in the prescription with the increase in number of co morbidities. The antiplatelet and anticoagulant group of drugs were responsible for majority of DDI, followed by antihypertensives and hypoglycaemic agents. Most of these DDI could be avoided with slight modification in the dosage regimen based on the pharmacokinetics and pharmacodynamics of the drug