Enhanced Photoelectrochemistry in CdS/Au Nanoparticle Bilayers

Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation.     

A single-chip digitally calibrated 5.15-5.825-GHz 0.18-/spl mu/m CMOS transceiver for 802.11a wireless LAN

The drive for cost reduction has led to the use of CMOS technology in the implementation of highly integrated radios. This paper presents a single-chip 5-GHz fully integrated direct conversion transceiver for IEEE 802.11a WLAN systems, manufactured in 0.18-/spl mu/m CMOS. The IC features an innovative system architecture which takes advantage of the computing resources of the digital companion chip in order to eliminate I/Q mismatch and achieve accurately matched baseband filters. The integrated voltage-controlled oscillator and synthesizer achieve an integrated phase noise of less than 0.8/spl deg/ rms. The receiver has an overall noise figure of 5.2 dB and achieves sensitivity of -75 dBm at 54-Mb/s operation, both referred to the IC input. The transmit error vector magnitude is -33 dB at -5-dBm output power from the integrated power-amplifier driver amplifier. The transceiver occupies an area of 18.5 mm/sup 2/.     

Thermal conductivity of doped PbTe-based solid solutions with off-center impurities

The coefficients of thermopower and electrical and thermal conductivity in the PbTe_0.8Se_0.1 S _0.1 solid solution with electron concentration (4.6–54) × 10¹⁸ cm^?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb_1?x Sn_xTe_1?x Se_x alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L₀ numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L₀ = 0.75 is obtained for a lightly doped sample at ～130 K.     

Adaptive MAP error concealment for dispersively packetized wavelet-coded images

In this paper, we present an adaptive maximum a posteriori (MAP) error concealment algorithm for dispersively packetized wavelet-coded images. We model the subbands of a wavelet-coded image as Markov random fields, and use the edge characteristics in a particular subband, and regularity properties of subband/wavelet samples across scales, to adapt the potential functions locally. The resulting adaptive MAP estimation gives PSNR advantages of up to 0.7 dB compared to the competing algorithms. The advantage is most evident near the edges, which helps improve the visual quality of the reconstructed images.     

Discrete Chaos-I: Theory

We propose a definition of the discrete Lyapunov exponent for an arbitrary permutation of a finite lattice. For discrete-time dynamical systems, it measures the local (between neighboring points) average spreading of the system. We justify our definition by proving that, for large classes of chaotic maps, the corresponding discrete Lyapunov exponent approaches the largest Lyapunov exponent of a chaotic map when M/spl rarr//spl infin/, where M is the cardinality of the discrete phase space. In analogy with continuous systems, we say the system has discrete chaos if its discrete Lyapunov exponent tends to a positive number, when M/spl rarr//spl infin/. We present several examples to illustrate the concepts being introduced.     

Performance of decorrelating receivers in multipath Rician fading channels

This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver.     

Electrical and photoelectric properties of electrochemically fabricated SnO2/Cd0.4Zn0.6S/CdTe solar cells

Solar cells based on SnO₂/Cd_0.4Zn_0.6S/CdTe heterostructures are fabricated by electrochemical deposition, and the dependences of their electrical and photoelectric properties on the thermal annealing conditions are studied. It is shown that thermal annealing reduces the tunnel currents by almost two orders of magnitude. The best conditions of thermal annealing are determined (t = 300°C and τ = 9 min). These conditions provide the highest photosensitivity of the heterostructures under study (I _sc ≈ 21.2 mA/cm², U _oc ≈ 813 mV, and η = 14.7%).     

Towards intelligent dressing

The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability.     

Radiative lifetimes of electrons and holes in a thin semiconductor layer

Radiative lifetimes of nondegenerate electrons and holes distributed uniformly in a semiconductor layer either deposited on a substrate or bounded by two dielectric media are calculated. The obtained expression takes into account the radiation reabsorbtion and interference effects and determines the dependences of the radiative lifetimes on the refractive indices of the external media and on the layer thickness.