MMPP models for multimedia traffic

The paper presents a study on the use of Markov‐Modulated Poisson Processes (MMPP's) for characterizing multimedia traffic with short‐term and long‐term correlation. The applicability of the 2‐state MMPP and a refined moment‐based parameter‐matching technique to model an arbitrary ATM traffic stream in evaluating its queueing performance are examined by simulation. Following a discussion on the limitation of the 2‐state MMPP model, a model using a superposition of N homogeneous 2‐state MMPP to characterize bursty multimedia traffic is presented. The proposed model requires only five parameters which can be estimated from the samples of the traffic counting process by using a pdf‐based matching technique. The introduced pdf‐based parameter‐matching procedure uses the probability density function of the arrival rate and the IDC curve of the traffic samples. An approximation for the probability of loss in MMPP/D/1 queues is also obtained. The versatility and accuracy of the proposed model to characterize bursty multimedia traffic are shown by several case studies and test results. This revised version was published online in June 2006 with corrections to the Cover Date.     

Novel thermally stable poly(ether imide ester)s from 2,6‐bis (4‐aminophenoxy) pyridine

2,6‐Bis (4‐aminophenoxy) pyridine was prepared via reaction of 4‐aminophenol with 2,6‐dichloropyridine in the presence of potassium carbonate in N‐methyl‐2‐pyrrolidone (NMP). This pyridine‐based ether diamine was reacted with two moles of trimellitic anhydride to synthesize related diimide‐diacid (DIDA). A high temperature solution polycondensation reaction of DIDA with different diols in the presence of triethylamine hydrochloride in dichlorobenzene resulted in different poly(ether imide ester)s. The monomer and polymers were fully characterized, and the physical and thermal properties of the polymers were studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 570–576, 2005     

Relevance of peat-draining rivers for the riverine input of dissolved iron into the ocean

Peat bogs have the ability to produce strong chelate ligands (humic and fulvic acids) which enhance the weathering rates of iron-silicate minerals and greatly increase the solubility of the essential trace metal iron in river water. Fluvial networks link peat bogs with the ocean, and thus terrestrial-derived fulvic-iron complexes fuel the ocean's biological productivity and biological carbon pump, but understanding this role is constrained by inconsistent observations regarding the behaviour of riverine iron in the estuarine mixing zone, where precipitation reactions remove iron from the water column. We applied a characterization of the colloidal iron carriers in peatland-draining rivers in North Scotland, using field-flow fractionation (FFF), in combination with end-member mixing experiments of river water sampled near the river mouth and coastal seawater using a ⁵⁹Fe radiotracer method. According to our results, the investigated river contributed “truly dissolved” Fe concentrations of about 3300 nmol L^− 1 to the ocean which is nearly two orders of magnitude higher than the dissolved iron contribution of the “average world” river (∼ 40 nmol L^− 1). Thus we conclude that peatland-draining rivers are important sources of dissolved iron to the ocean margins. We propose highly electrostatic and sterical stabilized iron-organic matter complexes in the size range of < 2 kDa to be responsible for iron transport across the estuarine mixing zone.     

Modified chitosan as a polymeric nanoreactor for fabrication of pure ZnO nano particles

ZnO nanoparticles have been prepared successfully by hydrogel decomposition method (HDM). Synthesized ZnO nanoparticles were characterized by X‐ray diffraction (XRD), fourier transforms infrared spectroscopy (FTIR), and transition electron microscopy (TEM) techniques. Narrow distribution of sizes with a 20–30 nm diameter and regular distribution of ZnO nanoparticles are attributed to the application of poly(acrylic acid‐co‐acrylamide) grafted chitosan hydrogel as coating agent. The results show that the polymer thermal decomposition technique is a perfect method for the synthesis of ZnO nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of ethane on the performance of commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes in CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation applications

Impurities such as hydrogen sulfide, water vapor and heavy hydrocarbons in natural gas have considerable effects on the membrane performance. Small amounts of condensable and polymer soluble components in the feed gas cause swelling or plasticization of glassy membranes, leading to a reduction in membrane selectivity. In the present research the influence of ethane was investigated on the permeance and selectivity of two commercially available hollow fiber membranes, namely Cardo-type polyimide and PPO hollow fibers for CO₂/CH₄ separations. It was concluded that the gas mixture permeation rate was increased in the presence of C₂H₆. However, the CO₂/CH₄ separation factors remained almost the same in the presence and absence of the C₂H₆.     

Polyoxometalate–molybdenylacetylacetonate hybrid complex: A reusable and efficient catalyst for oxidation of alkenes with tert-butylhydroperoxide

The hybrid complex consist of molybdenylacetylacetonate complex covalently linked to a lacunary Keggin-type polyoxometalate, K₈[SiW₁₁O₃₉] (POM), was synthesized and characterized by elemental analysis, SEM, XRD, diffuse reflectance UV–Vis and FT-IR spectroscopic methods. The hybrid complex, [MoO₂(acac)–POM] (1), was used for alkene epoxidation with tert-BuOOH in 1,2-dichloroethane as solvent. The complex (1) can catalyze epoxidation of various olefins including non-activated terminal olefins. The effect of reaction parameters such as oxidant, solvent, and temperature on the epoxidation of cyclooctene was also investigated. This heterogeneous catalyst was reused several times in the oxidation of cyclooctene.     

Parasitic compensation in CCI-based circuits for reduced power consumption

In this paper, the compensation advantage of the first-generation current conveyor (CCI) over the second-generation current conveyor (CCII) in tunable circuits is shown. For this purpose, a new floating frequency dependent negative resistor (FDNR) simulator using three CCIs is presented and employed in a third-order high-pass filter. The compensation feature of the CCI is shown for the proposed high-pass filter. As a second example, the presented compensation method is tested in a second-order band-pass filter constructed with two CCIs. Applying the proposed compensation technique, the CCI-based circuits can operate in lower biasing currents, which result in lower power consumption.     

Simultaneous minimization of total tardiness and waiting time variance on a single machine by genetic algorithms

This paper considers a single machine scheduling problem, with the objective of minimizing a linear combination of total tardiness and waiting time variance in which the idle time is not allowed. Minimizing total tardiness is always regarded as one of the most significant performance criteria in practical systems to avoid penalty costs of tardiness, and waiting time variance is an important criterion in establishing quality of service (QoS) in many systems. Each of these criteria is known to be non-deterministic polynomial-time hard (NP-hard); therefore, the linear combination of them is NP-hard too. For this problem, we developed a genetic algorithm (GA) by applying its general structure that further improves the initial population, utilizing some of heuristic algorithms. The GA is shown experimentally to perform well by testing on various instances.     

A new link function in GLM-based control charts to improve monitoring of two-stage processes with Poisson response

In this paper, a new procedure is developed to monitor a two-stage process with a second stage Poisson quality characteristic. In the proposed method, log and square root link functions are first combined to introduce a new link function that establishes a relationship between the Poisson variable of the second stage and the quality characteristic of the first stage. Then, the standardized residual statistic, which is independent of the quality characteristic in the previous stage and follows approximately standardized normal distribution, is computed based on the proposed link function. Then, Shewhart and exponentially weighted moving average (EWMA) cause-selecting charts are utilized to monitor standardized residuals. Finally, two examples and a case study with a Poisson response variable are investigated, and the performance of the charts is evaluated by using average run length (ARL) criterion in comparison with the best literature method.     

A High Throughput Configurable SDR Detector for Multi-user MIMO Wireless Systems

Spatial division multiplexing (SDM) in MIMO technology significantly increases the spectral efficiency, and hence capacity, of a wireless communication system: it is a core component of the next generation wireless systems, e.g. WiMAX, 3GPP LTE and other OFDM-based communication schemes. Moreover, spatial division multiple access (SDMA) is one of the widely used techniques for sharing the wireless medium between different mobile devices. Sphere detection is a prominent method of simplifying the detection complexity in both SDM and SDMA systems while maintaining BER performance comparable with the optimum maximum-likelihood (ML) detection. On the other hand, with different standards supporting different system parameters, it is crucial for both base station and handset devices to be configurable and seamlessly switch between different modes without the need for separate dedicated hardware units. This challenge emphasizes the need for SDR designs that target the handset devices. In this paper, we propose the architecture and FPGA realization of a configurable sort-free sphere detector, Flex-Sphere, that supports 4, 16, 64-QAM modulations as well as a combination of 2, 3 and 4 antenna/user configuration for handsets. The detector provides a data rate of up to 857.1 Mbps that fits well within the requirements of any of the next generation wireless standards. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed.