Efficient QoS support in a slotted multihop WDM metro ring

A novel distributed access protocol for a slotted wavelength-division-multiplexing (WDM) metro ring employing all-optical packet switching and supporting quality-of-service (QoS) classes is presented and analyzed. Since we assume that there are more nodes than available wavelengths in the network, we obtain a scalable multihop WDM ring as underlying network architecture. By dividing each channel into several time slots and further applying destination release and slot reuse, data packets can be efficiently transmitted and received in a statistically multiplexed manner. In our architecture, each node is equipped with one tunable transmitter and one fixed-tuned receiver. Furthermore, as we generally consider so-called a posteriori access strategies, different packet selection schemes are proposed and compared. An analytical model based on the semi-Markov process methodology is developed to quantify the performance of one of these schemes. As a key element of the protocol, an efficient QoS support access mechanism is proposed and its performance is evaluated. The new QoS control scheme adopts a frame-based slot reservation strategy including connection setup and termination, which only slightly increases the signaling and node processing overhead. Thus, an efficient hybrid protocol combining connectionless and connection-oriented packet transmissions is proposed     

Cubic GaN/AlGaN Schottky-barrier devices on 3C-SiC substrates

In this work, we focus on the fabrication of cubic GaN based Schottky-barrier devices (SBDs) and measured current voltage (I-V) characteristics and the critical field for electronic breakdown. Phase-pure cubic GaN and c-Al_xGa_1 − xN/GaN structures were grown by plasma assisted molecular beam epitaxy (MBE) on 200 μm thick free-standing 3C-SiC (1 0 0) substrates, which were produced by HOYA Advanced Semiconductor Technologies Co., Ltd. The thickness of the c-GaN and c-Al_0.3Ga_0.7N epilayers were about 600 and 30 nm, respectively. Ni/In Schottky contacts 300 μm in diameter were produced on c-GaN and c-Al_0.3Ga_0.7N/GaN structures by thermal evaporation using contact lithography. A clear rectifying behavior was measured in our SBDs and the I-V behavior was analyzed in detail, indicating the formation of a thin surface barrier at the Ni-GaN interface. Annealing of the Ni Schottky contacts in air at 200 °C reduces the leakage current by three orders of magnitude. The doping density dependence of breakdown voltages derived from the reverse breakdown voltage characteristics of c-GaN SBDs is investigated. The experimental values of breakdown voltage in c-GaN are in good agreement with theoretical values and show the same dependence on doping level as in hexagonal GaN. From our experimental data, we extrapolate a blocking voltage of 600 V in c-GaN films with a doping level N_D = 5 × 10¹⁵ cm⁻³.     

A model study of a conventional fixed bed tubular reactor with a catalyst layer on the inside tube wall

Mathematical simulation of a novel design of tubular reactor, supplied with a conventional fixed bed of catalyst and a catalyst layer on the inside tube wall, is carried out. The oxidation process of o-xylene to phthalic anhydride is investigated, using the kinetics of Calderbank and co-workers. In comparison with the conventional fixed bed reactor the new design displays several advantages, namely: higher productivity, better selectivity, relieved temperature regime, longer catalyst life, and shorter tubes.     

Interfacially compatibilized LDPE/POE blends reinforced with nanoclay: investigation of morphology,rheology and dynamic mechanical properties

Morphological, melt rheological and dynamic mechanical properties of low-density polyethylene (LDPE)/ethylene–octene copolymer (POE)/organo-montmorillonite (OMMT) nanocomposites, prepared via melt compounding were studied. The XRD traces indicated different levels of intercalated structures for the nanocomposites. Addition of a compatibilizer (PE-g-MA) improved the intercalation process. TEM results revealed existence of clay layers in both phases but they were mainly localized in the elastomeric POE phase. Addition of 5 wt% OMMT to the LDPE/POE blend led to reduction in the size of the elastomer particles confirmed by AFM. The complex viscosity and storage modulus showed little effect of the presence of the clay when no compatibilizer was added. As the extent of exfoliation increased with addition of compatibilizer, the linear viscoelastic behavior of the composites gradually changed specially at low-frequency regions. The interfacially compatibilized nanocomposites with 5 wt% OMMT had the highest melt viscosity and modulus among all the studied nanocomposites and blends. Also, this particular composition showed the best improvement in dynamic storage modulus. The results indicated that clay dispersion and interfacial adhesion, and consequently different properties of LDPE/POE/clay nanocomposites, are greatly affected by addition of compatibilizer.     

Effect of ash on maximum thickness of plastic layer of coals

A study of the effect of ash yield on the maximum thickness of the plastic layer (MTPL) of some coking coals (as measured by the Sapozhnikov plastometer) has revealed that with an increase in the former the latter in general decre?es. A rectilinear relation approximately exists between the ash percentage (dry basis) and log MTPL values of coals. For the samples studied, a multiple correlation incorporating the rank factor was found to be unnecessary. Higher Fe₂O₃ and SO₃ contents from the coal were found to be associated with higher MTPL values.     

Effects of environmental temperature and relative humidity on the rehydration of dried pistachios

In this study, the environmental air temperature and relative humidity effects were investigated through rehydration on the dried and roasted Siirt Pistachios (S_PS) and Antep pistachios (A_PS) with an experimental and computational approach. Therefore, an experimental apparatus was set-up in lab conditions. A series of experiments were conducted to evaluate the water activity and weight change as a function of the relative humidity and temperature of ambient air. The experimental results show that there is a combined effect of relative humidity and temperature on the increase in the weight change and water activity (a_w). The shell of pistachio is a good hygroscopic material despite its hard texture. The roasted pistachios are less prone to absorb moisture compared to the unroasted pistachios. Beside this experimental study, an intelligent modeling called “artificial neural network” model was used for prediction of the increase in the weight of different types of pistachios.     

Breitbandkommunikation

Ohne Zusammenfassung     

Über die Bereitung und die Zusammensetzung der spezifisch bulgarischen Käsesorten

European Food Research and Technology -     

Cobalt loaded organic acid modified kaolin clay for the enhanced catalytic activity of hydrogen release via hydrolysis of sodium borohydride

Inorganic acids such as hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄) are generally used in the acid modification of clays. Here, CoB catalyst was synthesized on the acetic acid-activated kaolin support material (CH₃COOH -kaolin- CoB) with an alternative approach. This prepared catalyst, firstly, was used to catalyze the hydrolysis of NaBH₄ (NaBH₄-HR). The structure of the raw kaolin, kaolin-CH₃COOH, and CH₃COOH-kaolin-CoB samples were characterized by X-ray diffraction spectroscopy (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), and nitrogen adsorption. At the same time, this catalyst performance was examined by Co loading, NaBH₄ concentration, NaOH concentration, temperature and reusability parameters. The end times of this hydrolysis reaction using raw kaolin-CoB and CH₃COOH-kaolin-CoB were found to be approximately 140 and 245 min, respectively. The maximum hydrogen generation rates (HGRs) obtained at temperatures 30 °C and 50 °C were 1533 and 3400 mL/min/g_catalyst, respectively. At the same time, the activation energy was found to be 49.41 kJ/mol.     

Schlüsseltechnologien künftiger Kommunikationsnetze

The goal of infrastructures of modern communication networks is a seamless operation in a heterogeneous environment of network technologies by using a high degree of network intelligence and integrated network management. The contribution describes the features of the key network technologies and addresses basic trends of their future evolution.