Convergence Theorems for Generalized Functional Sequences of Discrete-Time Normal Martingales

The Fock transform recently introduced by the authors in a previous paper is applied to investigate convergence of generalized functional sequences of a discrete-time normal martingale $M$. A necessary and sufficient condition in terms of the Fock transform is obtained for such a sequence to be strong convergent. A type of generalized martingales associated with $M$ are introduced and their convergence theorems are established. Some applications are also shown.Comment: 10 pages. arXiv admin note: text overlap with arXiv:1504.0500

Design of Power Combining Amplifiers for Mobile Communications

This work explores the application of various power amplifier design techniques for mobile communications. Several circuit configurations including class A amplifier, Doherty amplifier and power combining amplifier have been developed, which are to improve the performance of power amplifiers in terms of power added efficiency transmission power and bandwidth. In chapter 2, the cascode PA adopting tuning capacitor structure is proposed and implemented to enhance the efficiency. In chapter 3, a novel Doherty amplifier configuration using a 3-stage polyphase filter as power splitter is introduced. Moreover, the second harmonic cancellation function of balun combining PA is analysed and verified with experimental results in chapter 4. The fully integrated cascode class A amplifier adopts RC negative feedback, which is to enhance bandwidth and input/output matching. The integrated choke inductor compensating the parasitic capacitor of transistors has very low quality factor, which decreases the efficiency of the power amplifier. To reduce the inductance value of the choke inductor, a tuning capacitor is connected in parallel with the choke inductor. As a result, the inductor resistance is reduced as well, which diminishes the power consumption induced by the resistance of the choke inductor. This proposed PA configuration is validated by simulation results with the PAE improved by 3 % at the 1 dB compression point compared to the topology without tuning capacitor. The experimental results demonstrate a PA which delivers an output power of 21.3 dBm with PAE of 21 % at the 1 dB compression point. The Doherty amplifier with 2-way Wilkinson power splitter is integrated in a 0.9 mm×1.8 mm chip. The main and peak amplifier adopt cascode configuration to improve the stability of the Doherty amplifier. To minimize the chip size, the quarter wave transmission line in the topology is replaced by π-type lumped element equivalent network. To increase the operating bandwidth, the Doherty amplifier configuration using a 3-stage polyphase filter as power splitter is proposed. The topology consists of 3-stage RC polyphase filter, drive amplifiers, main amplifier, peak amplifier, and impedance inverter. By employing the polyphase filter, the quarter-wave transmission line at the input of the peak amplifier for compensating the phase shift of the impedance inverter is eliminated. According to the analysis of the polyphase filter prototype, the 3-stage polyphase filter is selected, and the component parameters are determined. The main amplifier and peak amplifier are using differential cascode configuration. The drive amplifier is to increase the power gain and provide proper impedance matching for the Doherty amplifier. The results demonstrate an outstanding broadband Doherty amplifier with a bandwidth of 1.8 GHz. The chip temperature rises dramatically due to the high power consumption of power amplifier. Consequently, the collector currents of the SiGe transistors are varying with the changing temperature, which deteriorates the PA performance. In the improved 3-stage PPF Doherty design, the bias voltages of the transistors in the first version 3-stage PPF Doherty amplifier are replaced by reference currents feeding through bias circuits. With current sources providing bias current to the transistors, the performance of the improved Doherty amplifier is enhanced. The power combining PAs are constructed on FR-4 PCB boards using discrete components. The single ended power amplifier in the power combining PA is built with high linearity HEMT transistor. The balun combining PA has an advantage of second harmonic cancellation, which is validated by both analysis and measurements. Moreover, power combining PAs with 2-way transmission line and lumped element Wilkinson power divider are designed. The transmission lines in these designs are analyzed using EM simulation tool and verified with testing structures on PCB boards

Kenaf bast for fiber reinforced polymer composites

Cellulosic fibers sized from the macro-scale to the nano-scale were prepared hierarchically from kenaf bast fibers using chemicals. The process began with a hermetical alkaline retting followed by a bleaching treatment. The bleached fibers were hydrolyzed using inorganic acid, from which microfibers and cellulose nanowhiskers (CNWs) were fabricated. Inorganic nanoparticle impregnation (INI) was used to treat the retted fibers for the improvement of the interfacial compatibility between the fiber and polypropylene (PP) matrix. The retted fibers and INI-treated fibers were used as reinforcement for the PP polymer composites. Film casting process was used to make CNW/PVA composites. The hermetical retting process used in this study produced fibers with high cellulose contents (81-92%) by removing the lignin and hemicelluloses. Higher retting temperature resulted in higher fiber surface hardness and elastic moduli. The tensile strengths and tensile moduli of the fibers decreased as the temperature increased. The SEM images showed the micropores in the cell wall structure for the fibers retted at over 130°C, providing the possibility to anchor nanoparticles into the cell wall. Surface morphology of the INI-treated fibers was examined with SEM, and showed that the CaCO3 nanoparticle crystals grew onto the fiber surface. Energy-dispersive X-ray spectroscopy (EDS) was used to verify the CaCO3 particle deposits on the fiber surface. As the size scale of the fibers decreased, the fiber crystallinity increased from 49.9% (retted fibers) to 83.9% (CNWs). About 23% á-cellulose in the raw kenaf bast fibers had been converted into CNWs. The retted fibers without INI treatment had poor compatibility with the polypropylene matrix. The INI treatment improved the compatibility between the fibers and the PP matrix, resulting in an improvement in kenaf fiber/PP composite tensile moduli and tensile strengths. The CNWs prepared from kenaf bast fiber gave excellent reinforcement for PVA composites. A nine percent increase of CNWs in the CNW/PVA composites yielded significant improvements in tensile strength and modulus of about 46% and 152%, respectively, compared with pure PVA

Yukawa Corrections to gamma gamma --> b\bar{b} in the Topcolor Assisted Technicolor Models

We study the Yukawa corrections to the gamma gamma --> b\bar{b} corss section in the topcolor assisted technicolor models at the photon-photon colliders. We find that, for the favorable parameters, the relative corrections from pseudo Goldstone bosons give out a 3.2%--5.9% decrement of the cross section from the tree level when \sqrt{s}=500 GeV, the contributions from new extended technicolor gauge bosons Z* and colored gauge bosons B are negligibly small, and the relative correction arising from new color-singlet heavy gauge boson Z' is less than -3.2%. Therefore, the total relative corrections are significantly larger than the corresponding corrections in the standard model, the general two Higgs doublet model and the minimal supersymmetric standard model. Since these corrections are obvious for the International Linear Colliders, the process gamma gamma --> b\bar{b} is really interesting in testing the standard model and searching for the signs of technicolor.Comment: 24 pages, 6 figures, version appeared in PR