Systematic Topology Analysis and Generation Using Degree Correlations

We present a new, systematic approach for analyzing network topologies. We first introduce the dK-series of probability distributions specifying all degree correlations within d-sized subgraphs of a given graph G. Increasing values of d capture progressively more properties of G at the cost of more complex representation of the probability distribution. Using this series, we can quantitatively measure the distance between two graphs and construct random graphs that accurately reproduce virtually all metrics proposed in the literature. The nature of the dK-series implies that it will also capture any future metrics that may be proposed. Using our approach, we construct graphs for d=0,1,2,3 and demonstrate that these graphs reproduce, with increasing accuracy, important properties of measured and modeled Internet topologies. We find that the d=2 case is sufficient for most practical purposes, while d=3 essentially reconstructs the Internet AS- and router-level topologies exactly. We hope that a systematic method to analyze and synthesize topologies offers a significant improvement to the set of tools available to network topology and protocol researchers.Comment: Final versio

The appearance of a compact jet in the soft-intermediate state of 4U 1543-47

Recent advancements in the understanding of jet-disc coupling in black hole candidate X-ray binaries (BHXBs) have provided close links between radio jet emission and X-ray spectral and variability behaviour. In 'soft' X-ray states the jets are suppressed, but the current picture lacks an understanding of the X-ray features associated with the quenching or recovering of these jets. Here we show that a brief, ~4 day infrared (IR) brightening during a predominantly soft X-ray state of the BHXB 4U 1543-47 is contemporaneous with a strong X-ray Type B quasi-periodic oscillation (QPO), a slight spectral hardening and an increase in the rms variability, indicating an excursion to the soft-intermediate state (SIMS). This IR 'flare' has a spectral index consistent with optically thin synchrotron emission and most likely originates from the steady, compact jet. This core jet emitting in the IR is usually only associated with the hard state, and its appearance during the SIMS places the 'jet line' between the SIMS and the soft state in the hardness-intensity diagram for this source. IR emission is produced in a small region of the jets close to where they are launched (~ 0.1 light-seconds), and the timescale of the IR flare in 4U 1543-47 is far too long to be caused by a single, discrete ejection. We also present a summary of the evolution of the jet and X-ray spectral/variability properties throughout the whole outburst, constraining the jet contribution to the X-ray flux during the decay.Comment: Accepted to MNRAS. 11 pages, 6 figure

Molecular epidemiology of hepatitis C virus genotypes in Bushehr province, Iran

Background and Objectives: Molecular epidemiology of hepatitis C virus (HCV) is very important for the treatment of hepatitis C infection. The aim of this study was to determine the distribution of HCV genotypes in Bushehr province (South West of Iran). Materials and Methods: A total of 100 patients who were detected as positive for HCV antibody (by using ELISA method and RIBA test) referred to Arya Virology Laboratory between 2007-2009 in order to molecular diagnosis and furthermore virus genotyping. After detection of HCV, RNA genotyping of virus was done by using genotype specific primers. Results: Genotype 1a was found in 49% of the patients and genotype 3a was found in 40% of the patients and 1b in 5% of patients, while the genotype of the virus could not be identified in 5% of the patients. Finally, in 1% of patients coinfection due to 1a-3a genotypes was identified. Conclusion: The dominant genotype of HCV in Bushehr province, Iran, was determined as 1a.with acute hepatitis C ultimately develop chronic infection1. Only a minority of cases of acute HCV recover completely, with spontaneous virus eradication. In most cases the acute infection progresses to chronicity. Chronic HCV infection is defined as an infection that persists for more than 6 months, with or without clinical manifestations of hepatic or extrahepatic disease. Chronic type of this infection can cause cirrhosis, liver failure, and liver cancer. HCV infection is a global health problem and it is estimated that 200 million people of the world population are infected5. The global spread of chronic HCV infection coincided with the widespread use of transfused blood and blood products and with the expansion of intravenous drug use but decreased prior to the wide implementation of anti-HCV screening6. There are at least six major genotypes designated by Arabic numerals and more than 50 subtypes of HCV identified by lower case letters. The different genotypes have different geographic distributions1,4. Genotype determination of HCV is one of the most important factors in order to prediction of the viral persistency, pathogenicity and resistancy to antivirals7. The success and the treatment period of interferon and ribavirin seems to be related to the genotype of virus8. Furthermore, HCV genotyping is a useful tool to determine its molecular epidemiology, as they are indicative of transmission route of infection9,10. There is no published data about the distribution of HCV genotypes from Bushehr province (South West of Iran). Prevalence of HCV genotypes in Bushehr is an issue that is not sufficiently investigated and there is a need, therefore, to study this in detail

Hyperbolic Geometry of Complex Networks

We develop a geometric framework to study the structure and function of complex networks. We assume that hyperbolic geometry underlies these networks, and we show that with this assumption, heterogeneous degree distributions and strong clustering in complex networks emerge naturally as simple reflections of the negative curvature and metric property of the underlying hyperbolic geometry. Conversely, we show that if a network has some metric structure, and if the network degree distribution is heterogeneous, then the network has an effective hyperbolic geometry underneath. We then establish a mapping between our geometric framework and statistical mechanics of complex networks. This mapping interprets edges in a network as non-interacting fermions whose energies are hyperbolic distances between nodes, while the auxiliary fields coupled to edges are linear functions of these energies or distances. The geometric network ensemble subsumes the standard configuration model and classical random graphs as two limiting cases with degenerate geometric structures. Finally, we show that targeted transport processes without global topology knowledge, made possible by our geometric framework, are maximally efficient, according to all efficiency measures, in networks with strongest heterogeneity and clustering, and that this efficiency is remarkably robust with respect to even catastrophic disturbances and damages to the network structure

Self-organized Emergence of Navigability on Small-World Networks

This paper mainly investigates why small-world networks are navigable and how to navigate small-world networks. We find that the navigability can naturally emerge from self-organization in the absence of prior knowledge about underlying reference frames of networks. Through a process of information exchange and accumulation on networks, a hidden metric space for navigation on networks is constructed. Navigation based on distances between vertices in the hidden metric space can efficiently deliver messages on small-world networks, in which long range connections play an important role. Numerical simulations further suggest that high cluster coefficient and low diameter are both necessary for navigability. These interesting results provide profound insights into scalable routing on the Internet due to its distributed and localized requirements.Comment: 3 figure

tert-Butyl 6-benzoyl-5-hydr­oxy-2-oxo-2H-chromene-4-carboxyl­ate

In the title compound, C21H18O6, a previously unknown coumarin derivative, the benzoyl substitutent makes a dihedral angle of 53.80 (16)° with the plane of the coumarin rings. An intramolecular O—H⋯O hydrogen bond is observed

(E)-Dimethyl 2-(6-benzoyl-7-hydr­oxy-4-methoxy­carbonyl-2-oxo-2H-chromen-8-yl)but-2-enedioate

The mol­ecule of the title compound, C24H18O10, a previously unknown coumarin derivative, contains methoxy­carbonyl, 2-butenedioate and benzoyl groups aligned at angles of 28.04 (2), 76.89 (3) and 42.48 (13)°, respectively, to the plane of the coumarin ring system. Intra­molecular O—H⋯O hydrogen bonding between hydr­oxy and carbonyl groups and weak inter­molecular C—H⋯O hydrogen bonding is present in the crystal structure. The two carbon atoms and attached H atom of the ethylene bond are disordered over two positions, with site occupancy factors of ca 0.9 and 0.1

Producing gold nanoparticles from loaded activated carbon and its separation with carbon fiber film formation at the oil/water interface in the acetone- water-sodium chloride system

Abstract Due to the wide spread applications of gold in medicine, electronic computational industries, catalysts, and its special application in biological researches and more over by attention to high cost and complicated production of gold nanoparticles (AuNPs) and in the other hand, the importance of substituting the environmental pollutants such as cyanide compounds in most commonly processes of gold recovery from ores and concentrates, finding a simple, economic and environmental way to achieve AuNPs has to be considered. Because of its large surface area, activated carbon (AC) is used in extracting gold. In this research work a new way has been mentioned for production and separation of AuNPs from loaded AC. By heating loaded AC in the air at 300 for 30 min, gold metal nanoparticles were produced on the surfaces of AC with reducing the gold cyanide complex. The detachment of the AuNPs from AC surfaces was done by two ways: 1. Abrasion of AC by NaCl 2. Using ultrasound; the separation of the detached AuNPs from AC granules abraded by NaCl was done based on the difference between AC and gold density and using water and oil mixture. Effect of abrasion time, salt to carbon weight ratio and prewashed loaded AC conditions on the amount of gold recovered from loaded AC was evaluated in abrasion method. In a novel approach, separation of carbon from gold-containing aqueous solution was done by addition of acetone in mixture and forming carbon microfibers film at the oil/water interface. Acid washing was done to remove impurities after separating carbon from gold-containing solution. As a result, relatively pure AuNPs were obtained after acid washing