Single-electron tunneling depressing synapse for cellular neural networks

In this paper, a cellular neural network with depressing synapses for contrast-invariant pattern classification and synchrony detection is presented, starting from the impulse model of the single-electron tunneling junction. The results of the impulse model and the network are simulated using simulation program with integrated circuit emphasis (SPICE). It is demonstrated that depressing synapses should be an important candidate of robust systems since they exhibit a rapid depression of excitatory postsynaptic potentials for successive presynaptic spikes.

Fabrication and optical optimization of spot-size converters with strong cladding layers

A silicon-on-insulator (SOI) optical fiber-to-waveguide spot-size converter (SSC) overlaid with specially treated silica is investigated for integrated optical circuits. Unlike the conventional process of simply depositing the hot silica on silicon waveguides, two successive layers of silicon dioxide were grown on etched SSC structures by PECVD (plasma-enhanced chemical vapor deposition). The two layers have 0.8% index contrast and supply stronger cladding for an incident light beam. Additionally, this process is able to reduce the effective refractive index of the input mode to less than 1.47 (extremely close to that of the fiber), substantially weakening the unwanted back reflection. Exploiting this technology, it was demonstrated that the SSC showed a theoretical low mode mismatch loss of 1.23 dB for a TE-like mode and has an experimental coupling efficiency of 66%.

Laterally confined modes in wet-etched, metal-coated, quantum-dot-inserted pillar microcavities

We report the fabrication and the measurement of microcavities whose optical eigenmodes were discrete and were well predicted by using the model of the photonic dot with perfectly reflected sidewalls. These microcavities were consisted of the semiconductor pillar fabricated by the simple wet-etched process and successive metal coating. Angle-resolved photoluminescence spectra demonstrate the characteristic emission of the corresponding eigenmodes, as its pattern revealed by varying both polar (0) and azimuthal (45) angles. It is shown that the metal-coated sidewalls can provide an efficient way to suppress the emission due to the leaking modes in these pillar microcavities.

Structural and optical properties of InAs/In0.52Al0.48As self-assembled quantum wires on InP(001)

Six-stacked InAs/In0.52Al0.48As self-assembled quantum wires (QWRs) on InP(001) by molecular-beam epitaxy (MBE) have been studied by high-resolution transmission electron microscopy (HRTEM) and polarized PL measurements. We obtained the chemical lattice fringe (CLF) image of InAs self-assembled QWRs embedded in the In0.52Al0.48As matrix by the interference between the (002)-diffracted beam and the transmitted beam in the image plane of the objective lens. The results show that the InAs QWRs were bounded by (113), (001) and (114) facets. Both the size and strain distribution in QWRs were determined. It was found that with the growth of successive periods, the height and height fluctuation of InAs QWRs decreased from the bottom period to the upper one. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs. (c) 2005 Elsevier B.V. All rights reserved.

Geometrical learning, descriptive geometry, and biomimetic pattern recognition

Studies on learning problems from geometry perspective have attracted an ever increasing attention in machine learning, leaded by achievements on information geometry. This paper proposes a different geometrical learning from the perspective of high-dimensional descriptive geometry. Geometrical properties of high-dimensional structures underlying a set of samples are learned via successive projections from the higher dimension to the lower dimension until two-dimensional Euclidean plane, under guidance of the established properties and theorems in high-dimensional descriptive geometry. Specifically, we introduce a hyper sausage like geometry shape for learning samples and provides a geometrical learning algorithm for specifying the hyper sausage shapes, which is then applied to biomimetic pattern recognition. Experimental results are presented to show that the proposed approach outperforms three types of support vector machines with either a three degree polynomial kernel or a radial basis function kernel, especially in the cases of high-dimensional samples of a finite size. (c) 2005 Elsevier B.V. All rights reserved.

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi4Ti3O12 (BTO) and Bi3.25In0.75Ti3O12 (BTO:In) thin films were prepared on fused quartz and LaNiO3/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E-0, the dispersion energy E-d, the average interband oscillator wavelength lambda(0), the average oscillator strength S-0, the refractive index dispersion parameter (E-0/S-0), the chemical bonding quantity beta, and the long wavelength refractive index n(infinity) were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity beta decreases in the BTO and BTO:In films compared with those of bulk. (C) 2007 Published by Elsevier B.V.

Evolution of InAs/GaAs(001) islands during the two- to three-dimensional growth mode transition in molecular-beam epitaxy

A detailed observation was made using atomic force microscopy on the two- to three-dimensional (2D-3D) growth mode transition in the molecular-beam epitaxy of InAs/GaAs(001). The evolution of the 3D InAs islands during the 2D-3D mode transition was divided into two successive phases. The first phase may be explained in terms of a critical phenomenon of the second-order phase transition.

Measurement of chirp parameter and modulation index of a semiconductor laser based on optical spectrum analysis

A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods.

A differential recursive scheme for suppression of Peak to average power ratio for OFDM

A differential recursive scheme for suppression of Peak to average power ratio (PAPR) for Orthogonal frequency division multiplexing (OFDM) signal is proposed in this thesis. The pseudo-randomized modulating vector for the subcarrier series is differentially phase-encoded between successive components in frequency domain first, and recursion manipulates several samples of Inverse fast Fourier transformation (IFFT) output in time domain. Theoretical analysis and experimental result exhibit advantage of differential recursive scheme over direct output scheme in PAPR suppression. And the overall block diagram of the scheme is also given.

Accurate mode analysis of ultraviolet-written channel waveguides

The transfer matrix method combined with the effective index method is adopted to model the silica-based channel waveguide patterned by UV writing. The effective indexes of the graded index channel waveguides with different dimension are calculated. The maximal error of the effective index is less than 3 x 10(-5). By this method, the number of the guided mode and the dimension range to guide certain modes can be obtained easily. Finally, the dimension range to guide a single mode is presented. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8-12 mu m infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers. (C) 1999 Elsevier Science B.V. All rights reserved.

Characterization of high-speed optoelectronics devices based optical and electrical spectra analyses - art. no. 68380Q

In this paper, we presents the characterization technique of high-speed optoelectronics devices based electrical and optical spectra, which is as important access to the devices performance as the prevalent vector network analyzer (VNA) sweeping method. The measurement of additional modulation of laser and frequency response of photodetector from electrical spectra, and the estimation of the modulation indexes and the chirp parameters of directly modulated lasers based on optical spectra analysis, are given as examples.

Mode analysis of the UV-written channel waveguide - art. no. 60340J

The effective index method (EIM) was adopted to model the channel waveguide patterned by the UV in photosensitive silica film. The effective indexes of the different dimension symmetrical and asymmetrical channel waveguides were calculated, and the resource of the error of the method was pointed out. At last, the dimension rang to propagate single mode was presented.

BIODIESEL PRODUCTION FROM DIFFERENT FEEDSTOCKS IN PILOT SCALE SYSTEM

In this study, the preparations of biodiesel from three different feedstocks, including rapeseed oil, high acidified Chinese wood oil and trap grease, were carried out in a pilot scale of 200 t yr(-1) biodiesel production system. The optimum operating conditions for transesterification of rapeseed oil in plug flow reactor were found to be as follows: the catalyst dosage is 1.2 wt%; the retention time is about 17 min; the bed temperature is 65 degrees C; the oil/methanol ratio is 1:6; the content of methyl ester is 96.33% under these conditions. A kind of ion exchange resin, a solid acid catalyst, filled in the fixed bed reactor was used as the esterification catalyst for the pretreating of high acidified oil. The acid value of Chinese wood oil could be reduced from 7 to 0.8 mg KOH.g(-1) after 88 min, the optimum operating conditions were obtained as follow: molar ratio of methanol to oil is about 6:1, the temperature of the fixed bed, 65 degrees C and the retention time, about 88 min. Also a kind of acidified oil, namely trap grease, with the acid value being 114 mg KOH.g(-1) could be equally converted to a good biodiesel product through this system. Generally, the refined biodiesel product generated through this system could meet China #0 Biodiesel Standard, as well as Germany Biodiesel Standard for most indexes. It indicates that the designed process in this system has a good adaptability for different kinds of oil.

Establishment and characterization of dual-species biofilms formed between a 3,5-dinitrobenzoic-degrading strain and bacteria with high biofilm-forming capabilities

In this study, the possibility of establishing a dual-species biofilm from a bacterium with a high biofilm-forming capability and a 3,5-dinitrobenzoic acid (3,5-DNBA)-degrading bacterium, Comamonas testosteroni A3, was investigated. Our results showed that the combinations of strain A3 with each of five strains with a high biofilm-forming capability (Pseudomonas sp. M8, Pseudomonas putida M9, Bacillus cereus M19, Pseudomonas plecoglossicida M21 and Aeromonas hydrophila M22) presented different levels of enhancement regarding biofilm-forming capability. Among these culture combinations, the 24-h dual-species biofilms established by C. testosteroni A3 with P. putida M9 and A. hydrophila M22 showed the strongest resistance to 3,5-DNBA shock loading, as demonstrated by six successive replacements with DMM2 synthetic wastewater. The degradation rates of 3,5-DNBA by these two culture combinations reached 63.3-91.6% and 70.7-89.4%, respectively, within 6 h of every replacement. Using the gfp-tagged strain M22 and confocal laser scanning microscopy, the immobilization of A3 cells in the dual-species biofilm was confirmed. We thus demonstrated that, during wastewater treatment processes, it is possible to immobilize degrader bacteria with bacteria with a high biofilm-forming capability and to enable them to develop into the mixed microbial flora. This may be a simple and economical method that represents a novel strategy for effective bioaugmentation.