Performance analysis of the IEEE 802.16e sleep mode for correlated downlink traffic

In this paper, we evaluate the performance of the IEEE 802.16e sleep mode mechanism in wireless access networks. This mechanism reduces the energy consumption of a mobile station (MS) by allowing it to turn off its radio interface (sleep mode) when there is no traffic present at its serving base station (BS). After a sleep period expires, the MS briefly checks the BS for data packets and switches off for the duration of another sleep period if none are available. Specifically for IEEE 802.16e, each additional sleep period doubles in length, up to a certain maximum. Clearly, the sleep mode mechanism can extend the battery life of the MS considerably, but also increases the delay at the BS buffer. For the performance analysis, we use a discrete-time queueing model with general service times and multiple server vacations. The vacations represent the sleep periods and have a length depending on the number of preceding vacations. Unlike previous studies, we take the (short-range) traffic correlation into account by assuming a D-BMAP arrival process, i.e. the distribution of the number of packet arrivals per slot is modulated by the transitions in a Markov chain with N background states. As results, we obtain the distribution of the number of packets in the queue at various sets of time epochs, the distribution of the packet delay and the antenna activity rate. We apply these results to the IEEE 802.16e sleep mode mechanism with correlated downlink traffic. By means of some examples, we show the influence of both the configuration parameters and the traffic correlation on the delay and the energy consumption.     

An analytic study of a scalable video buffer

In this contribution, we investigate the performance of the output buffer of an ‘on-demand’ video streaming server. The server maintains a local database of stored video clips and movies which can be streamed to the users upon request. We assume that the stored video is encoded in a scalable way, which means that the data streams contain a base layer ensuring a minimum of guaranteed quality and a stack of additional enhancement layers progressively improving the quality of the video. For the purpose of performance analysis, we assume that a video stream is split up in logical units called frames. Every frame consists of a number of packets, each containing information of one layer only. When the output buffer gets congested, one may choose to drop the transmission of some of the layers in a frame, thus reducing the frame transmission time and expediting the restoration of the buffer size to normal levels. A discrete-time finite capacity queueing model with buffer size dependent transmission times is proposed. Using a probability generating function approach, we focus on the characteristics of idle and busy periods. We obtain performance measures such as the frame loss ratio and the average frame transmission time. The latter measure relates to the quality of the video stream. We conclude with some numerical examples, including a realistic case study.     

Externality of risk and crash severity at roundabouts

The severity of 1491 crashes on 148 roundabouts in Flanders-Belgium was examined in order to investigate which factors might explain the severity of crashes or injuries and to relate these factors to the existing knowledge about contributing factors for injury severity in traffic. Logistic regression and hierarchical binomial logistic regression techniques were used.A clear externality of risk appeared to be present in the sense that vulnerable road user groups (pedestrians, bicyclists, moped riders and motorcyclists) are more severely affected than others. Fatalities or serious injuries in multiple-vehicle crashes for drivers of four-wheel vehicles are much rarer.Injury severity increases with higher age. Crashes at night and crashes outside built-up areas are more severe. Single-vehicle crashes seem to have more severe outcomes than multiple-vehicle crashes. However, systematic differences in the reporting rate of crashes are likely to exist and may have affected the stated results. Correlations with important, but unobserved variables like the impact speeds in the crashes might exist as well and could provide an alternative explanation for some results.     

Stimulus Generalization in Two Associative Learning Processes.

Recent studies involving nonlinear discrimination problems suggest that stimuli in human associative learning are represented configurally with nairow generalization, such that presentation of stimuli that are even slightly dissimilar to stored configurations weakly activate these configurations. The authors note that another well-known set of findings in human associative learning, cue-interaction phenomena, suggest relatively broad generalization. Three experiments show that current models of human associative learning, which try to model both nonlinear discrimination and cue interaction as the result of 1 process, fail because they cannot simultaneously account for narrow and broad generalization. Results suggest that human associative learning involves (a) an exemplar-based process with configural stimulus representation and narrow generalization and (b) an adaptive learning process characterized by broad generalization and cue interaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the stability of almost parallel boundary layer flows

The spatial stability of a two-dimensional boundary-layer flow along a flat plate, including its non-parallel character, is determined by means of a multiple scale approximation. This leads to inhomogeneous Orr-Sommerfeld equations for the corrections due to the non-parallel effect. These equations have been solved by the method of order reduction. A neutral curves of total amplifications have been calculated based on the kinetic energy of the disturbance. The non-parallel effect decreasesthe stability.     

Static solvent contact angle measurements, surface free energy and wettability determination of various self-assembled monolayers on silicon dioxide

In many fields and applications, a good knowledge of the wetting behaviour of solvents on a surface is crucial. Self-assembled monolayers (SAMs) have enabled improved control over surface properties, while more recent fields such as organic electronics gave rise to new applications and requirements regarding solvent-substrate interactions. However, most reported wettability studies are limited to practically less relevant solvents such as water, diiodomethane or hexadecane. Herein we report static contact angle measurements of various, typical SAM-modified surfaces, characterizing these surfaces' wettabilities over a wide range of practically relevant solvents. Surface energies, both the polar and the disperse component, of these SAM-modified surfaces are extracted with various methods from the contact angle data. Reliable methods for surface energy extraction, such as the Owens-Wendt-Rabel-Kaelble method and the method after Wu, yield values which could be expected from the chemical structure and nature of the self-assembled molecules and which correspond well to the few reported literature values. We also determined wetting envelopes for the various surfaces which allow easy prediction of the surfaces' wettability for a certain solvent and which ensure relevance for current and future solvents.     

Listeria monocytogenes repellence by enzymatically modified PES surfaces

The effect of enzyme‐catalyzed modification of poly(ethersulfone) (PES) on the adhesion and biofilm formation of two Listeria monocytogenes strains is evaluated under static and dynamic flow conditions. PES has been modified with gallic acid, ferulic acid and 4‐hydroxybenzoic acid. The surfaces modified with any of these compounds show up to 70% reduced adhesion of L. monocytogenes under static conditions and up to 95% under dynamic flow conditions compared with unmodified surfaces. Also, under static conditions the formation of biofilms is reduced by ～70%. These results indicate that the brush structures that are formed by the polymers on the PES surface directly influence the ability of microorganisms to interact with the surface, thereby reducing attachment and biofilm formation of L. monocytogenes. Based on these results, it is expected that enzyme‐catalyzed surface modification is a promising tool to reduce microbial adhesion and biofilm formation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41576.     

An evaluation of the impact of SG1 disproportionation and the addition of styrene in NMP of methyl methacrylate

A kinetic modeling study is presented for batch nitroxide mediated polymerization (NMP) of methyl methacrylate (MMA; nitroxide: N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] (SG1)). Arrhenius parameters for SG1 disproportionation (A = 1.4 10⁷ L mol^?1 s^?1; E_a = 23 kJ mol^?1) are reported, based on homopolymerization data accounting for unavoidable temperature variations with increasing time, that is, nonisothermicity. For low targeted chain lengths (TCLs ≤ 300), this nonisothermicity is also relevant for NMP of MMA with a small amount of styrene. Parameter tuning to copolymerization data confirms a penultimate monomer unit effect for activation (s_a2 = k_a12/k_a22=6.7; 363 K; 1: MMA; 2: styrene). To obtain, for a broad TCL range (up to 800), a dispersity well below 1.3 an initial styrene mass fraction of ca. 10% is required. An interpretation of the comonomer incorporation is performed by calculating the fractions of activation‐growth‐deactivation cycles with a given amount of monomer units and the copolymer composition distribution. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2545–2559, 2018     

Polyamide nanofiber membranes functionalized with zinc phthalocyanines

Electrospinning is an efficient method for the production of polyamide nanofiber membranes that are suitable for water filtration. Previous studies have shown that nanofiber membranes have high clean water permeability. The pathogen removal efficiency can be improved by functionalization with (organic) biocides. However, these membranes, like other membranes, are vulnerable to fouling which reduces the filtration efficiency. Therefore the present article investigates the potential of zinc phthalocyanines, which can produce singlet oxygen in the presence of visible light, as a functionalizing agent. The polyamide nanofiber membranes were functionalized with phthalocyanines using both a pre‐functionalizing and post‐functionalizing method. Only the post‐functionalization method shows to result in nanofiber membranes capable of producing singlet oxygen. After 30 min 45% of 1,2‐diphenylisobenzofuran (DPBF), used as an oxygen quencher, was removed by reaction with singlet oxygen. This resulted in a removal rate of 0.33 mol DBPF mol^?1Zn min^?1. During short term leaching tests, phthalocyanines could not be detected. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40486.