Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution. Part II: An electrochemical quartz crystal microbalance study

Electropolymerization of phenol and mono-, di-, tri-, pentachlorophenols was studied using EQCM on a Pt electrode at 0.78 V (SHE) in 1 M NaOH solution containing 0.1 M of the corresponding phenol. The highest electropolymerization rate was found for ortho-substituted chlorophenols indicating a weak fouling of the electrode. Low electropolymerization rates for para-substituted chlorophenols suggest a low permeability of the polymer film, resulting in rapid electrode fouling. The EQCM data suggest that electropolymerization of chlorophenols occurs without Cl-elimination for the monomers with unsubstituted ortho and para positions. Dechlorination is most pronounced for electropolymerization of para-substituted isomers. The mechanism of electropolymerization of chlorophenols is discussed.     

Statistical Properties of Transition Amplitudes in Generic Systems

I review some recent results on the statistical properties of matrix elements of typical observables (transition amplitudes) in an eigenbasis of generic quantum Hamiltonian systems. The classical limit of an underlying system can be either integrable, or fully chaotic, or mixed with regular and irregular regions coexisting in phase space. In any case, the variance of transition amplitudes (the local average transition probability) as a function of energy and transition frequency can be calculated in terms of classical power spectra. The probability distribution of transition amplitudes in high energy (semiclassical) regime is derived by means of random matrix theory, whereas in low and intermediate energy (nonsemiclassical) regime the probability distribution of transition amplitudes exhibits universal exponential tails which still call for theoretical explanation.     

Ultrasonic air-coupled testing of square-shape CFRP composite rods by means of guided waves

In aerospace industry, one of the most important parts of gliders and motor-gliders is a lightweight longeron reinforcement made of carbon fibre reinforced plastics (CFRP) rods, known as Graphlite SM315 composite. During manufacturing, the rods as constructional elements are glued together in epoxy-filled matrix in order to build the arbitrary spar profile. The defects present in single rods such as breakage of fibres, multiple delaminations due to the lack of bonding between fibres and reduction in density affect essentially the strength and the fail-safety of the overall construction.The aim of the present work is to investigate the effects (transmission, reflection, scattering and mode conversion) of guided waves propagation along a square-shape CFRP rod in the case of contactless excitation/reception and interaction with region of multiple delaminations applying the numerical model and performing experiments.The square-shape CFRP composite rods possessing internal artificial delamination type defects have been investigated by numerical modelling and experiments employing the developed air-coupled technique (pitch-catch set-up) for cases of conventional transmission and advanced back-scattering configurations. Numerical predictions of guided wave interaction with a multiple delamination type defect in a CFRP composite rod have been made and the interaction mechanism explained. It is possible to conclude, that the actual sizes of the internal defects have been clearly detected using reception of the back-scattered waves over the edges of the defective regions only.     

Closed-loop control of hydraulic telescopic handler

Automatization is supposed to improve working conditions and safety in the construction industry, as it already did in manufacturing industries. This paper presents the development of a robotic control system for a commercially available hydraulic telescopic handler. The target application for the telescopic handler is semi-automated assembly of facade panels. The base handler was upgraded with two additional hydraulic axes, position sensors and closed-loop control system, while the original handler safety assurance mechanisms were preserved. The control approach is based on a PI controller with velocity feedforward and valve overlap compensation. The direct and inverse kinematic models of handler mechanism were developed to enable control of end-effector motion along a straight line in the Cartesian coordinate system. The motion performances were evaluated following the ISO 9283 standard with payload of 2000 kg. Results show the repeatability of positioning bellow 7.0 mm and the straight line tracking error smaller than 63 mm.     

Reduced decoder complexity and latency in pixel-domain Wyner–Ziv video coders

In some video coding applications, it is desirable to reduce the complexity of the video encoder at the expense of a more complex decoder. Wyner–Ziv (WZ) video coding is a new paradigm that aims to achieve this. To allocate a proper number of bits to each frame, most WZ video coding algorithms use a feedback channel, which allows the decoder to request additional bits when needed. However, due to these multiple bit requests, the complexity and the latency of WZ video decoders increase massively. To overcome these problems, in this paper we propose a rate allocation (RA) algorithm for pixel-domain WZ video coders. This algorithm estimates at the encoder the number of bits needed for the decoding of every frame while still keeping the encoder complexity low. Experimental results show that, by using our RA algorithm, the number of bit requests over the feedback channel—and hence, the decoder complexity and the latency—are significantly reduced. Meanwhile, a very near-to-optimal rate-distortion performance is maintained. This work has been partially supported by the Spanish Ministry of Education and Science and the European Commission (FEDER) under grant TEC2005-07751-C02-01. A. Pižurica is a postdoctoral research fellow of FWO, Flanders.     

A graded-gap detector of ionizing radiation

The current response of Al_xGa_1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick Al_xGa_1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of Al_xGa_1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap Al_xGa_1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×10³ V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.     

Mapping the Density of States Distribution of Organic Semiconductors by Employing Energy Resolved–Electrochemical Impedance Spectroscopy

Although the density of states (DOS) distribution of charge transporting states in an organic semiconductor is vital for device operation, its experimental assessment is not at all straightforward. In this work, the technique of energy resolved–electrochemical impedance spectroscopy (ER-EIS) is employed to determine the DOS distributions of valence (highest occupied molecular orbital (HOMO)) as well as electron (lowest unoccupied molecular orbital (LUMO)) states in several organic semiconductors in the form of neat and blended films. In all cases, the core of the inferred DOS distributions are Gaussians that sometimes carry low energy tails. A comparison of the HOMO and LUMO DOS of P3HT inferred from ER-EIS and photoemission (PE) or inverse PE (IPE) spectroscopy indicates that the PE/IPE spectra are by a factor of 2–3 broader than the ER-EIS spectra, implying that they overestimate the width of the distributions. A comparison of neat films of MeLPPP and SF-PDI₂ or PC(61)BM with corresponding blends reveals an increased width of the DOS in the blends. The results demonstrate that this technique does not only allow mapping the DOS distributions over five orders of magnitude and over a wide energy window of 7 eV, but can also delineate changes that occur upon blending.     

Time-independent,high electron mobility in thin PC61BM films: Relevance to organic photovoltaics

Ultrafast optical probing of electric field by means of electroabsorption combined with conventional photocurrent measurements was employed to investigate the drift and mobility dynamics of photo-generated charge carriers in the pristine PC₆₁BM film and in the blend with a merocyanine dye. Electrons passed a 40 nm thick PC₆₁BM film within a few picoseconds with time-independent and weakly dispersive mobility. The electron mobility is 1 cm²/(V s) at 1 MV/cm and an estimate of the zero-field mobility yields 5 ⋅ 10⁻² cm²/(V s). The initial electron mobility in the blend is of the order of 10⁻² cm²/(V s) and decreases rapidly. We conclude that electron motion in PC₆₁BM based organic bulk hetero-junction solar cells is limited by barriers between PC₆₁BM domains rather than by intrinsic PC₆₁BM properties.     

Transport of electrons in a GaAs quantum well in high electric fields

The rates of intrasubband and intersubband scattering of electrons by polar optical and intervalley phonons are determined in relation to the electron energy and width of a deep rectangular quantum well in GaAs. The Monte Carlo method was used to calculate the field dependences of the electron’s drift velocity in quantum wells with the width of 10, 20, and 30 nm. It is shown that the drift velocity in high electric fields in a quantum well vastly exceeds the maximum drift’s saturation velocity in the bulk material.     

BPC – A binary priority countdown protocol

In modern wireless ad hoc networks, with a high speed PHY, every collision means a significant loss of useful bandwidth. In the last few years different binary contention protocols have been introduced to address this problem. In this work we propose a novel binary contention protocol called binary priority countdown (BPC) protocol, whose goal is to reduce collisions as well as contention time. BPC uses a new priority countdown mechanism which exploits the efficiency of binary countdown, but the priority countdown process is not constrained to a single binary countdown round. This way, the priority space is not defined by the length of binary countdown round, like in other binary countdown protocols proposed in the literature, and arbitrary medium access priorities can be decremented through multiple binary countdown rounds if necessary. The ability of a new priority countdown mechanism to count down any priority number without changing the length of a binary countdown round, allows independent management of priority space. This “independence” of priority space introduces new optimization and adaptation possibilities. Collision memory effect is recognized and described. BPC protocol reveals connection between unary, binary and digit contention protocols. All three groups of protocols can now be seen as members of the same class of contention algorithms. Preliminary simulation results are shown.