Dynamic bandwidth allocation for quality-of-service over Ethernet PONs

Ethernet-based passive optical network (EPON) technology is being considered as a promising solution for next-generation broadband access networks due to the convergence of low-cost Ethernet equipment and low-cost fiber infrastructures. A major feature for this new architecture is the use of a shared transmission media between all users; hence, medium access control arbitration mechanisms are essential for the successful implementation of EPON: i.e., to ensure a contention-free transmission and provide end users with equal access to the shared media. We propose to use the multipoint control protocol defined by the IEEE 802.3ah task force to arbitrate the transmission of different users, and we present different dynamic bandwidth allocation (DBA) algorithms to allocate bandwidths effectively and fairly between end users. These DBA algorithms are also augmented to support differentiated services, a crucial requirement for a converged broadband access network with heterogeneous traffic. We show that queueing delays under strict bandwidth allocation algorithms result in an unexpected behavior for certain traffic classes, and we suggest the use of DBA with appropriate local queue management to alleviate this inappropriate behavior. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed protocols.     

SPECIALLY TAILORED TRANS FINITE-ELEMENT FORMULATIONS FOR HYPERBOLIC HEAT CONDUCTION INVOLVING NON-FOURIER EFFECTS

The phenomenon of hyperbolic heat conduction in contrast to the classical (parabolic) form of Fourier heat conduction involves thermal energy transport that propagates only at finite speeds as opposed to an infinite speed of thermal energy transport. To accommodate the finite speed of thermal wave propagation, a more precise form of heat flux law is involved, thereby modifying the heat flux originally postulated in the classical theory of heat conduction. As a consequence, for hyperbolic heat conduction problems, the thermal energy propagates with very sharp discontinuities at the wave front. The primary purpose of the present paper is to provide accurate solutions to a class of one-dimensional hyperbolic heat conduction problems involving non-Fourier effects that can precisely help understand the true response and furthermore can be used effectively for representative benchmark tests and for validating alternate schemes. As a consequence, the present paper purposely describes modeling/analysis formulations via specially tailored hybrid computations for accurately modeling the sharp discontinuities of the propagating thermal wave front. Comparative numerical test models are presented for various hyperbolic heat conduction models involving non-Fourier effects to demonstrate the present formulations.     

Nano and micro structural studies of thin films of ZnO

Zinc oxide thin films grown by sol–gel and RF sputtering methods have been characterized. The characterization techniques used involve ellipsometry, optical absorption, scanning tunneling microscopy, scanning and transmission electron microscopy. The films grown by sol–gel spin method which followed zinc acetate route exhibited a smoother texture than the films, which were deposited by using zinc nitrate route. The later type of films showed a dendritic character. Nano-structured fine grains of size ranging from 20 to 60 nm were observed with zinc nitrate precursor film. Individual grains show a sharp contrast with different facets and boundaries. Crystal planes and lattice parameters calculated by electron diffraction and X-ray diffraction are quite close and in agreement with the reported values in literature. Scanning tunneling microscopy has been used for measuring the average roughness of the surface and estimating the lattice constants. The STM studies of RF sputtered films, although showing a ZnO structure, exhibited a disturbed lattice. This was presumably due to the fact that after deposition the films were not annealed. Nanographs of 2D and 3D view of atomic positions of ZnO have been presented by using scanning tunneling microscopy.     

Preparation of thermal resistant gas barrier chitosan nanobiocomposites

Nanobiocomposites of chitosan/clay were prepared by solution method using CuSO₄/glycine chelate complex as the catalyst with variable percentage of clay loading. The chemical interaction of chitosan and clay was studied by Fourier transform infrared spectroscopy. The structure of chitosan and clay nanobiocomposites was investigated by X‐ray diffraction and high resolution transmission electron microscopy. From thermogravimetric analysis, it was found that chitosan/clay nanobiocomposites were more thermally stable as compared to pure chitosan. A substantial reduction in oxygen permeability was obtained from the gas permeameter with increase in clay concentrations by which the synthesized nanocomposites materials may be used for packaging applications. POLYM. COMPOS., 35:2324–2328, 2014. © 2014 Society of Plastics Engineers     

Development and Characterization of Inorganic-Organic (Si-O-Al) Hybrid Geopolymeric Precursors via Solid State Method

Silicon - In this study, an innovative one part, solution free concept applied for the development of hybrid inorganic–organic geopolymeric precursors having Si-O-Al networks at the precursor...     

Nitroarenes as Antitubercular Agents: Stereoelectronic Modulation to Mitigate Mutagenicity

Nitroarenes are less preferred in drug discovery due to their potential to be mutagenic. However, several nitroarenes were shown to be promising antitubercular agents with specific modes of action, namely, nitroimidazoles and benzothiazinones. The nitro group in these compounds is activated through different mechanisms, both enzymatic and non‐enzymatic, in mycobacteria prior to binding to the target of interest. From a whole‐cell screening program, we identified a novel lead nitrobenzothiazole (BT) series that acts by inhibition of decaprenylphosphoryl‐β‐d ‐ribose 2′‐epimerase (DprE1) of Mycobacterium tuberculosis (Mtb). The lead was found to be mutagenic to start with. Our efforts to mitigate mutagenicity resulted in the identification of 6‐methyl‐7‐nitro‐5‐(trifluoromethyl)‐1,3‐benzothiazoles (cBTs), a novel class of antitubercular agents that are non‐mutagenic and exhibit an improved safety profile. The methyl group ortho to the nitro group decreases the electron affinity of the series, and is hence responsible for the non‐mutagenic nature of these compounds. Additionally, the co‐crystal structure of cBT in complex with Mtb DprE1 established the mode of binding. This investigation led to a new non‐mutagenic antitubercular agent and demonstrates that the mutagenic nature of nitroarenes can be solved by modulation of stereoelectronic properties.     

Graph Theory Concepts in Frequency and Availability Analysis

Steady-state availability and failure frequency are two key indices in a repairable system. They are generally evaluated from Markov models with constant transition rates. Numerical solutions can be found for relatively large systems using computer programs. It is more difficult to obtain general equations for a specific system using transition rate symbols. The determination of these equations usually involves linear simultaneous equations, either directly or using Cramer's Rule. This paper describes a general purpose graphical approach for obtaining steady-state availability and frequency expressions from a flow graph based on the Markov model. A set of generalised formulae is developed and applied to several configurations. This technique avoids the need to use matrices for developing general purpose equations. Its direct approach is useful to practising engineers and students of reliability concepts.     

A Scalable and High Capacity All-Optical Packet Switch: Design,Analysis, and Control

In this paper, a modular and scalable all-optical packet switch (AOPS) is proposed. The range of its capacity can be easily scaled from gigabit per second to multi-terabits per second. Due to its broadcast-and-select property, the proposed AOPS is capable of performing a multicast function. By taking the advantage of wavelength division multiplexing (WDM), this architecture can provide the best network performance using a limited number of optical fiber delay lines as buffers. To perform the header replacement function, a novel all-optical header replacement unit (HRU) is introduced to be integrated with the switching function. The proposed HRU is shared by all the inputs which provides cost advantages. In addition, we present a generic control scheme for the proposed AOPS. To implement the function of the AOPS, two possible approaches, based on the design of wavelength conversion pools (WCPs), are presented and their cascadability performances are compared. Our simulations show that the proposed AOPS with an arrayed waveguide grating (AWG) based WCP provides better cascadability performance than the one with a star coupler based WCP. We conclude that, based on the status of current optical and electronic technologies, the proposed architecture is feasible to be implemented, and can be a good candidate for future packet switching solutions.     

The subunit structure of human macrophage migration inhibitory factor: evidence for a trimer

The subunit structure of human macrophage migration inhibitoryfactor (MIF) has been studied by preliminary X-ray analysisof wild-type and selenomethionine-MIF and dynamic light scattering.Crystal form I of MIF belongs to space group P2₁2₁2₁ and isgrown from 2 M ammonium sulfate at pH 8.5. A native data sethas been collected to 2.4 Å resolution. Self-rotationstudies and V_m values indicate that three molecules per asymmetricunit are present A data set to 2.8 Å resolution has beencollected for crystal form II, which belongs to space groupP3¹21 or P3²21 and grows from 2 M ammonium sulfate, 2% polyethyleneglycol (average molecular mass 400), 0.1 M HEPES, pH 7.5. Three,four, five or six monomers in the asymmetric unit are consistentwith V_m values for this crystal form. Analysis of crystal formII containing selenomethionine-MIF indicates nine selenium sitesare present per asymmetric unit. Dynamic light scattering ofMIF suggests that the major form of the protein in solutionis a trimer. The results of these studies are in contrast toprevious reports indicating that MIF is a monomer or dimer.The subunit arrangement of MIF is similar to that of tumor necrosisfactor and suggests that signal transduction might require trimerizationof receptor subunits.