Active Queue Management Exploiting the Rate Information in TCP-IP Networks

In this paper, we propose a new mechanism called explicit rate notification (ERN) to be used in end-to-end communications. The ERN scheme encodes in the header of transmission control protocol (TCP) packets information about the sending rate and the round trip time (RTT) of the flows. This new available information to the intermediate nodes (routers) is used to improve fairness, increase utilization, decrease the number of drops, and minimize queueing delays. Thus, it induces a better management of the queue. A comparison of our scheme with preexistent schemes, like the explicit congestion notification scheme, shows the effectiveness of the proposed mechanism.      

Chemical modification of poly(vinyl chloroformate) and of its copolymers using phase transfer catalysis

The chemical modification of poly(vinyl chloroformate) and of its copolymers with compounds containing labile hydrogen atoms like amines, phenols, alcohols and 2-oxazolidone as well as with potassium cyanide and potassium fluoride has been investigated. Phase transfer catalysis conditions lead to soluble modified polymers with good substitution yields.     

Comparative Study of Streamers＇ Characteristics in Different Seed Based Insulating Oils under Lightning Impulse Voltages

This paper is aimed at the streamers in natural esters （vegetable oils） in point--plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are investigated. Six untreated commercial oils extracted from grape seeds, sunflower and rape seeds, corn, rice and sesame that could constitute potential liquids for high voltage applications are tested. A naphthenic mineral oil is also tested for comparison. It＇s shown that the streamers are filamentary for both polarities. For a given voltage, the stopping lengths （Lf） of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf-are very close in all tested oils. The streamers＇ velocities are in the same range for all vegetable oils and they vary between 0.4 km/s and 1.2 km/s for positive polarity and 0.2 km/s and 0.8 km/s for negative polarity.     

PBDDs/Fs and PCDDs/Fs in the raw and clean flue gas during steady state and transient operation of a municipal waste combustor

Concentrations of polybrominated dibenzo-p-dioxins, and -dibenzofurans (PBDDs/Fs) and polychlorinated dibenzo-p-dioxins, and -dibenzofurans (PCDDs/Fs), were determined in the pre- and post-air pollution control system (APCS) flue gas of a municipal waste combustor (MWC). Operational transients of the combustor were found to considerably increase levels of PBDDs/Fs and PCDDs/Fs compared to steady state operation, both for the raw and clean flue gas; ΣPBDDs/Fs increased from 72.7 to 700 pg dscm(-1) in the raw, pre-APCS gas and from 1.45 to 9.53 pg dscm(-1) in the post-APCS flue gas; ΣPCDDs/Fs increased from 240 to 960 ng dscm(-1) in the pre-APCS flue gas, and from 1.52 to 16.0 ng dscm(-1) in the post-APCS flue gas. The homologue profile of PBDDs/Fs and PCDDs/Fs in the raw flue gas (steady state and transients) was dominated by hexa- and octa-isomers, while the clean flue gas homologue profile was enriched with tetra- and penta-isomers. The efficiency of the APCS for PBDD/F and PCDD/F removal was estimated as 98.5% and 98.7%, respectively. The cumulative TEQ(PCDD/F+PBDD/F) from the stack was dominated by PCDD/F: the TEQ of PBDD/F contributed less than 0.1% to total cumulative toxic equivalency of MWC stack emissions.     

Weibull statistics in electrical aging of polyesterimide under AC voltage

This article is aimed at the investigation of electrical aging of polyesterimide under AC voltage using Weibull statistical analysis. It's shown that the time to breakdown characteristic (V–t) of polyesterimide includes two zones (segments of straight line). The first zone characterizes a statistical dispersion of the intrinsic defects of material. The second zone expresses the real aging of polymer. The variation of the slope of lifetime curve is attributed to the change in the degradation mechanism. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Transient two-dimensional model of heat and mass transfer in a PEM fuel cell membrane

In the present work, a numerical study of heat and mass transfer within the membrane of a proton exchange membrane fuel cell is presented. The electrolyte membrane is considered an isotropic porous medium and ideal insulator for electrons and reactants. The adopted model in this study is based on the assumption of single-phase and multi-spices flow, supposed two-dimensional and unsteady. For the water transport, the major considered forces are; the convective force, resulting from the pressure gradient, the osmotic force, due to the concentration gradient and the electric force caused by the proton migration from the anode to the cathode. Based on a one-dimensional model, found in the literature, a transient two-dimensional one was proposed. The set of governing equations, written in velocity–pressure formulation, is solved by the implicit finite difference method. An alternating Direct Implicit scheme was used for the calculation. The numerical resolution gives the time- and space-dependent temperature and water concentration. The main focus lies on the influence of different cases of boundary conditions on water concentration and heat transfer variation with the intention of testing the reliability of the proposed computational fluid dynamic (CFD) code.     

Synergetic association of grafted PLA and functionalized graphene on the properties of the designed nanocomposites

The synergetic association of poly(lactic acid) grafted with maleic anhydride (MA-g-PLA) containing 0.44 wt% of maleic anhydride and epoxy-functionalized graphene (GFe) on the properties of the designed nanocomposites was studied. Rheological, mechanical and barrier properties of PLA nanocomposites were studied using different content of epoxy-functionalized graphene and MA-g-PLA compatibilizer. The PLA/MA-g-PLA/GFe nanocomposites prepared by melt blending, containing 5 wt% of MA-g-PLA, yield a maximum in storage modulus G′ and a rheological plateau at low frequencies, with a content of epoxy-functionalized graphene comprised between 4 and 7 wt%. This phenomenon was ascribed to a pseudo-solid behavior resulting from the high degree of epoxy-functionalized graphene exfoliation due to strong interfacial interactions with PLA and epoxy-functionalized graphene. The better mechanical and barrier performances were obtained with PLA/GFe containing 10 wt% of epoxy-functionalized graphene and 5 wt% of MA-g-PLA compatibilizer. The variation of the percentage of compatibilizer showed that 5 wt% of maleated PLA was sufficient to improve the thermal, rheological, mechanical and barrier properties of the PLA nanocomposite containing 7 wt% of epoxy-functionalized graphene.     

Exploitation of an insulated air chamber as a glazed cover of a conventional solar still

The countries of North Africa suffer from a serious problem that affects a large number of people. The trouble is the provisioning of drinking water. Several techniques are used but solar distillation; which seems to be an appropriate, economical, and easy solution. Conventional solar distiller is used in the Saharan areas but the yield of this device is low, that's why there are several studies that are focused on improving this distiller. The technique of double glazing gives an increase in the efficiency of a solar collector; hence, the idea of using the same technique in a conventional solar distiller. Two covers of glasses separated by 1 cm, isolated from the four sides was put on a distiller of dimensions 0.5 × 0.5 m. The results show that this technique minimizes the distiller's yield by 56.52% when compared with the conventional solar distiller.