Energy-efficient video streaming over Bluetooth using rateless coding

Energy-efficient error control for IEEE 802.15.1 (Bluetooth) video communication is proposed. The scheme is based on block-oriented incremental redundancy provided by rateless coding and receiver feedback. Results are presented for time-sensitive video streaming applications under a Markovian channel model. When the proposed algorithm is compared to variations of Bluetooth forward error control, there are improvements of around 3 dB in received video quality and of over 10% in energy efficiency.     

A 2.5-Gb/s 15-mW clock recovery circuit

This paper describes the design of a 2.5-Gb/s 15-mW clock recovery circuit based on the quadricorrelator architecture. Employing both phase and frequency detection, the circuit combines high-speed operations such as differentiation, full-wave rectification, and mixing in one stage to lower the power dissipation. In addition, a two-stage voltage-controlled oscillator is utilized that incorporates both phase shift elements to provide a wide tuning range and isolation techniques to suppress the feedthrough due to input data transitions. Fabricated in a 20-GHz 1-μm BiCMOS technology, the circuit exhibits an rms jitter of 9.5 ps and a capture range of 300 MHz     

Statistical analysis of fiber-optic CDMA communication systems. I. Device modeling

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs).     

Chain “stationary” insertion mechanism and production of isotactic polypropylene with C 1 symmetric catalyst systems

In this contribution, the stereochemistry of propylene insertion/propagation reactions with a variety of C ₁ symmetric metallocene catalysts, containing bridged cyclopentadienyl-fluorenyl ligand for the preparation of highly stereoregular polypropylene is presented. The impact of the distal substitutent’s size and composition and changes that the catalytic sites undergo upon such substitution is elaborated. A comprehensive mechanism is proposed to explain the resulting catalytic changes that bring about the irreversible C _s/C ₁ site transformation and tactic behavior inversion. Furthermore the cyclopentadienyl’s combined distal/proximal and fluorenyl’s frontal substituent effects on molecular weight, regio-, and stereoregularity of the final polymers are discussed. Finally, stereoselectivities of C ₂ and C ₁ symmetric catalyst systems are compared. It is shown that current high performance C ₁ symmetric catalyst systems with central site chirality can be isotactic selective as well or even better in certain aspects than the C ₂ symmetric bridged bisindenyl-based metallocene catalysts. The text was submitted by the authors in English.     

A 6 GHz 68 mW BiCMOS phase-locked loop

The design of a 6 GHz fully monolithic phase-locked loop fabricated in a 1 μm, 20 GHz BiCMOS technology is described. The circuit incorporates a voltage-controlled oscillator that senses and combines the transitions in a ring oscillator to achieve a period equal to two ECL gate delays. A mixer topology is also used that exhibits full symmetry with respect to its inputs and operates with supply voltages as low as 1.5 V. Dissipating 60 mW from a 2 V supply, the circuit has a tracking range of 300 MHz, an rms jitter of 3.1 ps, and phase noise of -75 dBc/Hz at 1 kHz offset     

A 200-MHz 15-mW BiCMOS sample-and-hold amplifier with 3 V supply

A sample-and-hold amplifier designed for the front end of high-speed low-power analog-to-digital converters employs a BiCMOS sampling switch and a low-voltage amplifier to achieve a sampling rate of 200 MHz while allowing input/output voltage swings of 1.5 V with a 3-V supply. The circuit also incorporates a cancellation technique to relax the trade-off between the hold-mode feedthrough and the sampling speed. Fabricated in a 20-GHz 1-μm BiCMOS technology, an experimental prototype exhibits a harmonic distortion of -65 dB with a 10-MHz analog input and occupies an area of 220×150 μm². The measured feedthrough is -52 dB for a 50-MHz analog input and the droop rate is 40 μV/ns     

Metallocene–methylaluminoxane catalyst for olefin polymerization. II. Bis-η5-(neomenthyl cyclopentadienyl)zirconium dichloride

Bis(neomenthyl cyclopentadienyl)zirconium dichloride/methyl aluminoxane (η⁵-(NMCp)₂ZrCl₂/MAO) catalyst has been investigated for ethylene polymerization. About 51% of the Zr forms active sites more or less instantaneously according to quenching with tritiated methanol. There is an initial drop of rate of polymerization, R_p, of about 30% which remains constant thereafter. The catalytic activity increases monotonically with temperature; it is proportional to [MAO]^1.75 at a constant [Zr] = 1.5 μM and proportional to [Zr]^?1.2 at a constant [MAO] = 64.5 mM. At very large [MAO]/[Zr], the catalyst has extremely high activity; κ_p = 5 × 10³ (Ms)^?1 at 50°C. There is also facile chain transfer to aluminum, κ = 0.14 s^?1 at 50°C. Both κ_p and κ are about 30 times greater than the corresponding rate constants for MgCl₂ supported TiCl₃ catalysts. The TiCl₃/MgCl₂ and (NMCp)₂/MAO catalysts have nearly the same activation energy for propagation (ca. 7 kcal/mol^?1). The higher activity of the latter is due to its larger preexponential factor in κ_p. The dependence of catalytic activity on the [MAO]/[Zr] ratio may be explained by rapid association-dissociation equilibria of MAO involving acid-base and/or electron deficient bridge complexation.     

Investigation of hydrogen and methane adsorption/separation on silicon nanotubes: a hierarchical multiscale method from quantum mechanics to molecular simulation

A combination of ab initio quantum mechanical (QM) calculations and canonical Monte Carlo (CMC) simulations are employed to investigate possible usage of single-walled silicon nanotubes (SWSiNTs) as a novel media for hydrogen and methane adsorption as well as their separation from each other. By fitting the force field, a Morse potential model is selected as an efficient potential to describe the binding energies between both hydrogen-SiNTs and methane-SiNTs obtained from ab initio calculations. Then CMC simulations are performed to evaluate the adsorption and separation behaviors of H₂ and CH₄ on the three different sizes of SiNTs including (5, 5), (7, 7), and (9, 9) SiNTs at ambient temperatures and pressures from 1 up to 10 MPa. As a comparison, the adsorption and separation of H₂ and CH₄ on the (8, 8) CNTs which are isodiameter with (5, 5) SiNTs are also simulated. Results are indicative of remarkable enhancement of H₂ and CH₄ adsorption capacity on the SiNTs compared to the CNTs, which arise from stronger van der Waals (VDW) attractions. In the case of methane adsorption on SiNTs, the stored volumetric energy exceeds the goal of the US Freedom CAR Partnership by 2010, which can not be achieved by methane compression at such low pressures. Moreover, simulation results indicate that SiNTs preferentially adsorb methane relative to hydrogen in their equimolar mixture, which results in efficient separation of these gases from each other at 293 K.     

A new characteristic approach for incompressible thermo‐flow in Cartesian and non‐Cartesian grids

A virtual‐characteristic approach is developed for thermo‐flow with finite‐volume methodology in which a multidimensional characteristic (MC) scheme is applied along with artificial compressibility. To obtain compatibility equations and pseudo‐characteristics, energy equation is taken into account in the MC scheme. With this inherent upwinding of convective fluxes, no artificial viscosity is required even at high Reynolds numbers. Another remarkable advantage of the MC scheme lies in its faster convergence rate with respect to the averaging scheme that is found to exhibit substantial delays in convergence. As benchmarks, forced and mixed convections in a cavity and in flow over cylinder and between parallel plates are examined for a wide range of Reynolds, Grashof, and Prandtl numbers. The MC and averaging schemes are applied for simulation purposes. Results show the better performance of the MC scheme in forced and mixed convections. Results confirm the robustness of the MC scheme in terms of accuracy and convergence. Copyright © 2015 John Wiley & Sons, Ltd.