Traffic management for connectionless services over ATM

This paper is concerned with the transport of connectionless traffic over ATM networks. Several architectures have been defined and standardized for this purpose, like LANE, CBDS, Classical IP or MPOA. However traffic management for resources optimization of these architectures remains mostly an open issue. One of the key problem there is to control – and dimension – the capacity of the required ATM virtual circuits. In [19,21], dynamic capacity allocation schemes have been defined for this purpose. They have shown great promise through simulation and analytical studies. In this paper, we analyze the behavior of a multiplexer with such dynamic capacity allocation schemes when fed by several bursty flows. EATA properties [5,18] are used to compute the loss probability seen by each individual multiplexed stream, extending the analytical analysis of [9]. The study gives insight into the usefulness of these schemes and highlights several interesting properties: namely, the reduction of inter‐dependency between multiplexed flows and the reduction of the average queue occupancy. Such properties allow a better multiplexing gain. The particular case of dynamic allocation schemes for TCP/IP is then discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetic Study of the Isomerization of Glucose into Fructose in the Presence of Anion‐modified Hydrotalcites

Isomerization of glucose to fructose was performed in a batch mode at 363 K in the presence of a commercial hydrotalcite catalyst, namely DHT‐4A2 from Kyowa, in its carbonate, hydroxide or mixed carbonate‐hydroxide form. Catalysts in their total or partial hydroxide form were found to be both more active and slightly more selective for fructose than in the carbonate form. However, in all cases, the high selectivity observed (≥90%) tends to drop relatively rapidly after 15% of glucose conversion. Nevertheless, in contrast to cation‐exchanged zeolites, no lixiviation phenomenon was observed. The recycled catalyst was as active as a fresh sample and the selectivity towards fructose was unchanged.     

Modified volume expansion method for measuring gas holdup

A simple, modified volume expansion method, or inclined tube method, is compared to the pressure difference method for determining gas holdup in an airlift bioreactor. The modified volume expansion method could be used for all pneumatic bioreactors where fluid fluctuation is vigorous and visual observation of the continuous phase rise is difficult. The overall gas holdup data measured using the inclined tube method are shown to be very close to overall gas holdup determined using a gamma ray density monitor system. However, the overall gas holdup measured by the pressure difference method is found to be significantly different. This difference is due to energy dissipation in the External Loop Airlift Bioreactor (ELAB) used in this study, which causes the pressure difference method to be incorrect.     

Physical simulation of land vehicles with obstacle avoidance and various terrain interactions

Programming the motions of an autonomous planetary robot moving in an hostile and hazardous environment is a complex task which requires both the construction of nominal motion plans and the anticipation as far as possible of the effects of the interactions existing between the vehicle and the terrain. In this paper we show how physical models and dynamic simulation tools can be used for amending and completing a nominal motion plan provided by a classical geometrical path planner. The purpose of our physical modeller-simulator is to anticipate the dynamic behaviour of the vehicle while executing the nominal motion plan. Then the obtained simulation results can be used to assess and optimize the nominal motion plan. In the first part, we outline the physical models that have been used for modelling the different types of vehicle, of terrain and of vehicle-surface interactions. Then we formulate the motion planning problem through the definition of two basic abstract constructions derived from physical model: the concept of generalized obstacle and the concept of physical target. We show with various examples how it is possible, when using this method, to solve the locomotion problem and the obstacle avoidance problem simultaneously and, furthermore, to provide the human operator with a true force feedback gestural control over the simulated robot.     

High Dielectric Breakdown Strength Nanoplatelet-Based Multilayer Thin Films

Dielectric materials that can withstand high voltages are of great interest due to the growing need for high-performance insulation systems in electronics. Polymer nanocomposites have gained popularity as electrical insulators due to their processability, high operating voltage, and tortuous paths for current flow created by the nanoparticles in the polymer matrix. The dielectric breakdown strength of a relatively thick multilayer thin film containing polyethylenimine (PEI) and vermiculite clay (VMT), thickened with tris(hydroxymethyl)aminomethane (tris), is evaluated as a function of bilayers (BL) deposited. The resulting nanobrick wall structure of this clay-based assembly is ideal for protective insulation. An 8 BL PEI+tris/VMT film achieves a dielectric breakdown strength of 245 kV mm⁻¹, with a thickness of 5 µm. With increasing bilayers, the breakdown strength gradually decreases, but 20 BL of PEI+tris/VMT achieves a breakdown voltage of 2.36 kV. This nanoplatelet-based system is the first “thick growing” layer-by-layer deposited film to be used as an insulating layer. Its unusually high breakdown strength can be useful for the protection of various high voltage electronics.     

Highly Tunable Syngas Product Ratios Enabled by Novel Nanoscale Hybrid Electrolytes Designed for Combined CO2 Capture and Electrochemical Conversion

Coupling renewable energy with the electrochemical conversion of CO₂ to chemicals and fuels has been proposed as a strategy to achieve a new circular carbon economy and help mitigate the effects of anthropogenic CO₂ emissions. Liquid-like Nanoparticle Organic Hybrid Materials (NOHMs) are composed of polymers tethered to nanoparticles and are previously explored as CO₂ capture materials and electrolyte additives. In this study, two types of aqueous NOHM-based electrolytes are prepared to explore the effect of CO₂ binding energy (i.e., chemisorption versus physisorption) on CO₂ electroreduction over a silver nanoparticle catalyst for syngas production. Poly(ethylenimine) (PEI) and Jeffamine M2070 (HPE) are ionically tethered to SiO₂ nanoparticles to form the amine-containing NOHM-I-PEI and ether-containing NOHM-I-HPE, respectively. At less negative cathode potentials, PEI and NOHM-I-PEI-based electrolytes produce CO at higher rates than 0.1 molal. KHCO₃ due to favorable catalyst-electrolyte interactions. Whereas at more negative potentials, H₂ production is favored because of the carbamate electrochemical inactivity. Conversely, HPE and NOHM-I-HPE-based electrolytes display poor CO₂ reduction performance at less negative potentials. At more negative potentials, their performance approached that of 0.1 molal. KHCO₃, highlighting how the polymer functional groups of NOHMs can be strategically selected to produce value-added products from CO₂ with highly tunable compositions.     

Structural characterization,energy transfer,and Judd–Ofelt analysis of pure and the Eu3+-doped Ca2LiMg2V3O12 phosphors

A novel vanadate host Ca₂LiMg₂V₃O₁₂ (CLMV) and the Eu³⁺-doped samples were synthesized via a solid-state reaction method. The phase formation and the morphological analysis were studied in detail. The Rietveld refinement result shows that the host belongs to cubic space group Ia-3d (230) with lattice parameter, a = 12.3948 Å, V = 1904.23 Å³, and Z = 8. The diffuse reflectance spectroscopy measurement estimated the bandgap of the host and the CLMV:0.05Eu³⁺ phosphors. The host exhibits a broad absorption band (peak at 345 nm) ranging from 240 to 380 nm, which is attributed to the charge transfer in the O²⁻–V⁵⁺ complex. Under near UV excitation (λ_exc = 345 nm), the host gives a broad emission band covering the visible region from 400 to 730 nm and the emission is in the bluish–green region of the CIE diagram. When the host is doped with the Eu³⁺ ions and excited at 345 nm, the emission spectrum depicts the superimposition of the characteristic emission bands (red emission) of the Eu³⁺ ions corresponding to the f–f transitions over the broad emission band of the host. The calculated color coordinates (9600 to 2280 K) demonstrated the color tuning ability of the phosphor as the dopant concentration is increased in the host. This is because the VO₄³⁻ group plays the sensitiser role and partially transfers energy with the Eu³⁺ ions. When the same set of phosphors were excited at the dominant characteristic excitation band (λ_exc = 394 nm) of the Eu³⁺, the characteristic emission bands of the Eu³⁺ in the orange–red region were observed. As the electric dipole transition of the Eu³⁺ was found to be dominant, the prepared phosphors possessed high color purity (CP). The energy transfer mechanism and the lifetime values were also presented. The temperature-dependent PL studies showed good thermal stability of the optimum sample. Various radiative transition properties were analyzed by the Judd–Ofelt theory. The photometric results reveal the color tuning ability and CP of the CLMV:xEu³⁺ phosphors.     

Development of al-doped MgMn2O4-based cathode materials for magnesium ion cells

Magnesium ion battery is an alternative for secondary battery instead of lithium ion battery due to its advantages of low cost, safety and environment friendly. Magnesium (Mg) is safer compared to lithium (Li) where it has high stability in contact of air and prevent the formation of dendrites during electrochemical cycling. The cathode materials of un-doped MgMn₂O₄ and Al-doped MgMn_2-xAl_xO₄, x = .01, .02, .03 were prepared using self-propagating combustion method with triethanolamine fuel as a reducing agent. All samples (powder form) were annealed at 700˚C in 6 h based on the thermogravimetric analysis results. The samples were been characterized using X ray diffraction, field emission electron microscopy, energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy to study structural and morphological properties of the samples. Electrochemical properties of linear sweep voltammetry, cyclic voltammetry, and charge-discharge capacity were performed in 1 M Magnesium Trifluoromethanesulfonate (MgTf₂) with ratio 1:1 of ethylene carbonate: dimethyl ether electrolyte. The discharge capacity of magnesium ion cells using Al-doped cathode material showed the improvement of 68% compared to the un-doped sample.     

Anomaly Detection and Classification in Streaming PMU Data in Smart Grids

The invention of Phasor Measurement Units (PMUs) produce synchronized phasor measurements with high resolution real time monitoring and control of power system in smart grids that make possible. PMUs are used in transmitting data to Phasor Data Concentrators (PDC) placed in control centers for monitoring purpose. A primary concern of system operators in control centers is maintaining safe and efficient operation of the power grid. This can be achieved by continuous monitoring of the PMU data that contains both normal and abnormal data. The normal data indicates the normal behavior of the grid whereas the abnormal data indicates fault or abnormal conditions in power grid. As a result, detecting anomalies/abnormal conditions in the fast flowing PMU data that reflects the status of the power system is critical. A novel methodology for detecting and categorizing abnormalities in streaming PMU data is presented in this paper. The proposed method consists of three modules namely, offline Gaussian Mixture Model (GMM), online GMM for identifying anomalies and clustering ensemble model for classifying the anomalies. The significant features of the proposed method are detecting anomalies while taking into account of multivariate nature of the PMU dataset, adapting to concept drift in the flowing PMU data without retraining the existing model unnecessarily and classifying the anomalies. The proposed model is implemented in Python and the testing results prove that the proposed model is well suited for detection and classification of anomalies on the fly.     

Encapsulation of Nanoparticle Organic Hybrid Materials within Electrospun Hydrophobic Polymer/Ceramic Fibers for Enhanced CO2 Capture

Liquid-like nanoparticle organic hybrid materials (NOHMs) consisting of a silica core with ionically grafted branched polyethyleneimine chains (referred to as NIPEI) are encapsulated within submicron-scale polyacrylonitrile (PAN)/polymer-derived-ceramic electrospun fibers. The addition of a room-temperature curable, liquid-phase organopolysilazane (OPSZ) ceramic precursor to the PAN/NOHM solution enhances the internal dispersion of NOHMs and forms a thin ceramic sheath layer on the fiber exterior, shielding the hydrophilic NIPEI to produce near-superhydrophobic non-woven fiber mats with contact angles exceeding 140°. 60:40 loadings of NOHMs to PAN/OPSZ can be reliably achieved with low OPSZ percentages required, and up to 4:1 NOHM:polymer loadings are possible before losing hydrophobicity. These fibers demonstrate up to ≈2 mmol CO₂ g⁻¹ fiber capture capacities in a pure CO₂ atmosphere through the nonwoven fibrous networks and the permeability of the OPSZ shell. The hybrid fibers additionally show enhanced capture kinetics under pure CO₂ and 400 ppm CO₂ conditions, indicating their promising application as a direct air capture platform.