Still image coding based on vector quantization and fractalapproximation

In this paper, we propose a coding algorithm for still images using vector quantization (VQ) and fractal approximation, in which low-frequency components of an input image are approximated by VQ, and its residual is coded by fractal mapping. The conventional fractal coding algorithms indirectly used the gray patterns of an original image with contraction mapping, whereas the proposed fractal coding method employs an approximated and then decimated image as a domain pool and uses its gray patterns. Thus, the proposed algorithm utilizes fractal approximation without the constraint of contraction mapping. For approximation of an original image, we employ the discrete cosine transform (DCT) rather than conventional polynomial-based transforms. In addition, for variable blocksize segmentation, we use the fractal dimension of a block that represents the roughness of the gray surface of a region. Computer simulations with several test images show that the proposed method shows better performance than the conventional fractal coding methods for encoding still pictures.     

A 44-GHz monolithic waveguide plane-wave amplifier with improvedunit cell design [using pHEMTs]

A 44-GHz monolithic waveguide plane-wave amplifier (PWA) with improved unit cell design is presented in this paper. The unit cell is a two-stage direct-coupled design and satisfies size, bistability, and stability requirements of the waveguide PWA. The ultra-compact unit cell had a cell size of 0.8 mm², and showed a small-signal gain of 8 dB and an output power of 15 dBm at 44 GHz with a corresponding dc-to-RF efficiency of 10%. A monolithic waveguide PWA using these unit cells showed a “flange-to-flange” gain of 5 dB, an output power of 0.3 W, and an efficiency of 2% at 44 GHz     

Rooster testicular germ cells and epididymal sperm contain P450 aromatase

We recently found that cytochrome P450 aromatase (P450arom) is present in germ cells of the mammalian testis and is capable of converting androgens to estrogens in the male reproductive tract. The objective of the present study was to determine whether testicular germ cells and epididymal sperm of an avian species are also capable of synthesizing estrogen. P450arom was localized in the rooster testis and epididymal region by immunocytochemistry, using an antiserum generated against purified human placental cytochrome P450arom. Immunostaining was present in pachytene spermatocytes, round spermatids, elongated spermatids, flagella of late spermatids, and sperm in the epididymal region. A positive reaction was also found in nonciliated cells of the epididymal region. However, the absence of mRNA for P450arom in the epididymal region indicated that the immunoreactive protein present in the epididymal region is not synthesized in this region. The immunoreactive P450arom found in epididymal sperm was shown to be active through use of a 3H2O assay. On the basis of these data, we conclude that rooster testicular germ cells and epididymal sperm are sites for the synthesis of estrogen, a potential regulator or modulator of germinal epithelium in the testis and the epithelium of the epididymal region of the avian species.     

A physics-based GaAs PHEMT noise model for low drain bias operation using characteristic potential method

A new physics-based noise model of a GaAs PHEMT is developed using the characteristic potential method (CPM). The model calculates the intrinsic noise current sources using CPM. Combined with the extrinsic noise parameters extracted from the measured S-parameters, the model reproduces four noise parameters of the device accurately under low drain bias voltages without using any fitting parameters. The model is verified with a 0.2-/spl mu/m GaAs PHEMT and shows excellent agreement with the measurements for all the noise parameters up to a drain voltage of 1 V Also, the proposed method allows the simulation of the microscopic noise distribution and thus allows one to obtain a physical understanding of noise mechanisms inside the device.     

Breakdown probabilities for thin heterostructure avalanche photodiodes

The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified.     

A One‐Kilobit PQR‐CMOS Smart Pixel Array

The photonic quantum ring (PQR) laser is a three dimensional whispering gallery (WG) mode laser and has anomalous quantum wire properties, such as microampere to nanoampere range threshold currents and √T‐dependent thermal red shifts. We observed uniform bottom emissions from a 1‐kb smart pixel chip of a 32×32 InGaAs PQR laser array flip‐chip bonded to a 0.35 µm CMOS‐based PQR laser driver. The PQR‐CMOS smart pixel array, now operating at 30 MHz, will be improved to the GHz frequency range through device and circuit optimization.     

Estimation of Aeroelastic Parameters of Bridge Decks Using Neural Networks

A new method of estimating flutter derivatives using artificial neural networks is proposed. Unlike other computational fluid dynamics based numerical analyses, the proposed method estimates flutter derivatives utilizing previously measured experimental data. One of the advantages of the neural networks approach is that they can approximate a function of many dimensions. An efficient method has been developed to quantify the geometry of deck sections for neural network input. The output of the neural network is flutter derivatives. The flutter derivatives estimation network, which has been trained by the proposed methodology, is tested both for training sets and novel testing sets. The network shows reasonable performance for the novel sets, as well as outstanding performance for the training sets. Two variations of the proposed network are also presented, along with their estimation capability. The paper shows the potential of applying neural networks to wind force approximations.     

Strength and fracture toughness of nano and micron-silica particles bidispersed epoxy composites: evaluated by fragility parameter

In this study, we discuss the composition effect of 240 nm and 1.56 μm-silica particles on strength and fracture toughness by examining two parameters, fragility and glass transition temperature, that were derived from the thermo-viscoelasticity measurements. Experimental results showed that the composites had a lower fragility with higher strength and fracture toughness as the content of nanoparticles was increased regardless of glass transition temperature. The improvement in mechanical properties from adding nanoparticles was definitely explained by the fragility represented the heterogeneity in polymer matrix, and this was related to the interaction between particles and matrix. The fragility was found to be an effective parameter for evaluating strength and fracture toughness of epoxy composite containing a bidispersion of nano and micron-silica particles.