Performance Analysis of a Discrete‐Time Two‐Phase Queueing System

This paper introduces the modeling and analysis of a discrete‐time, two‐phase queueing system for both exhaustive batch service and gated batch service. Packets arrive at the system according to a Bernoulli process and receive batch service in the first phase and individual services in the second phase. We derive the probability generating function (PGF) of the system size and show that it is decomposed into two PGFs, one of which is the PGF of the system size in the standard discrete‐time Geo/G/1 queue without vacations. We also present the PGF of the sojourn time. Based on these PGFs, we present useful performance measures, such as the mean number of packets in the system and the mean sojourn time of a packet.     

Performance of Differentially Detected DPSK Over Nonselective Rayleigh Fading Channels With Maximal Ratio Combining and Multiple Cochannel Interferers

In this paper, we investigate the performance of differentially detected differential phase-shift keying (DPSK) modulation with postdetection maximal ratio combining, in nonselective Rayleigh fading channels with multiple asynchronous cochannel interferers. The approach is based on an analytical technique we have presented earlier in the literature. Exact bit-error probability (BEP) results for binary DPSK and quaternary DPSK are derived. More specifically, we look into the effects of symbol-timing offsets between the interfering signals and the desired signal on the error performance. Our results show that when all the interfering signals are synchronous with the desired signal, the impairment caused by the cochannel interference to the desired user is maximum. On the other hand, when all the interfering signals are half-symbol-duration-delayed with respect to the desired user, they introduce the minimum impairment. Based on these findings, upper and lower bounds on the BEP are derived in simple closed form. Our explicit BEP results also show that the error probabilities of different transmitted symbols of the desired user are affected differently by the interfering signal     

Control of transient effects in distributed and lumped Ramanamplifiers

A robust control scheme for suppressing transients in both lumped and distributed Raman amplifiers is demonstrated. The control method uses only output power monitoring and holds gain fluctuations on surviving channels to <±0.06 dB in an experiment     

Controller optimization for minimum position error signals of harddisk drives

In order to reduce the position error signal (PES) and track misregistration (TMR) of disk drives, it is generally believed that the bandwidth of a disk drive servo system has to be increased. However, increase of the bandwidth is limited by available sampling frequency and mechanical resonances of a head-disk assembly. Hence, for a given servo-mechanical system, optimization of a servo controller is a crucial and economical way to get the best TMR performance. In this paper, optimization of a servo controller that yields minimum PES is presented. The equivalent position-mode disturbance is estimated by the error transfer function inversion method. The estimated disturbance is injected into the servo system to evaluate PES. The optimization process will select the best controller that minimizes PES under the specified constraints. It has been demonstrated that the minimization has been achieved by shaping the error transfer function rather than increase of the servo bandwidth, PES reduction has been confirmed by simulation and experiments     

Morphology Associated Positive Correlation between Carrier Mobility and Carrier Density in Highly Doped Donor–Acceptor Conjugated Polymers

Molecular doping in conjugated polymers (CPs) has recently received intensive attention for its potential to achieve high electrical conductivity in organic thermoelectric materials. In particular, it affects not only the carrier density n but also the carrier mobility µ because high degree of molecular doping changes the morphological properties. Herein, the effect of molecular doping in CP thin films on the pathways and mechanisms of charge transport is investigated, which govern the µ-n relationship. Two representative donor–acceptor type CPs with similar µ but different molecular assembly in an undoped state, that is poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)] (DPPDTT) and indacenodithiophene-co-benzothiadiazole (IDTBT), are prepared. Heavy doping with iron chloride (FeCl₃) induced DPPDTT with highly crystalline edge-on orientation to increase its µ up to 19.6 cm² V⁻¹ s⁻¹, whereas IDTBT with irregular intermolecular stacking showed little change in µ. It is revealed that this different µ-n relationship is highly attributed to the initial molecular ordering of CP films. The charge transport mechanism also becomes significantly different: both coherent and incoherent transports are observed in the doped DPPDTT, whereas incoherent transport is only found in the doped IDTBT. This study suggests guidelines for enhancing charge transport of CPs under doping in terms of structural disorder.     

Indicator Sensor Development and Fuel Cell Degradation Imaging

Although extensive research has been conducted, understanding the exact phenomena occurring during the operation of polymer electrolyte fuel cells (PEFCs) remains difficult. This research attempted to identify new reasons for the reduced performance of PEFC using an imaging technique. To begin with, H⁺ and OH⁻ indicator sensors, which display red, blue, and green values (RGB) using digital microscopes, are developed and attached to each electrode of a membrane electrode assembly to enable quantitative analysis of ion generation. The proposed reaction in the fuel cell can be confirmed, and various reactions occurring in the electrode can be examined using this approach. In particular, H⁺ is generated at the anode and cathode of the anion exchange membrane fuel cell, which is found to be a major cause of performance deterioration.     

Employing vertical dielectric layers to improve the operation performance of flash memory devices

A number of new device structures have been reported recently to improve the operation performance of flash memory. In this work, a novel flash device with a vertical dielectric layer in the depletion region is proposed through simulation approach. The simulation results show that the employment of a vertical dielectric layer in the depletion region can improve the operation performance of flash memory. The improvement can be attributed to a lower potential in the central region of device channel and the increase of the potential drop in the channel direction near drain junction. Thus, this proposed vertical dielectric layer increases the electrical field of the channel and thus the probability and the momentum of electron injection. The operation characteristics of the flash device with a vertical dielectric layer in the depletion region of source and drain are superior to those without. In addition, it is found that a vertical dielectric layer with lower dielectric constant can enhance the operation performance of flash device even more.     

High Performance Piezoelectric Microspeakers and Thin Speaker Array System

This paper reports on an improved piezoelectric microspeaker with a high sound pressure level of 90 dB, a total harmonic distortion of less than 15%, and coherence higher than 0.9. The fabricated Pb(Zr,Ti)O₃ (PZT) microspeakers have a thickness of only 1 mm including the speaker frame and an active area of 18 mm×20 mm. To achieve higher sound pressure and lower distortion, the PZT piezoelectric microspeaker has a well‐designed speaker frame and a piezoelectric diaphragm consisting of a tilted PZT membrane and silicone buffer layer. From the simulation and measurement results, we confirmed that the silicon buffer layer can lower the first resonant frequency, which enhances the microspeaker's sound pressure at a low frequency range and can also reduce useless distortion generated by the harmonics. The fabricated PZT piezoelectric microspeakers are implemented on a multichannel speaker array system for personal acoustical space generation. The output sound pressure at a 30 cm distance away from the center of the speaker line array is 15 dB higher than the sound pressure at the neighboring region 30 degrees from the vertical axis.     

An evaluation of the optical fiber beam as a force sensor

The present study reports the use of an intensity based plastic optical fiber (POF) as a force sensor. Different materials for beam, such as spring steel and mild steel, are used to evaluate the performance of the force sensor during macro-bending. The POF is surface bonded to a beam and subjected to force. The system relies on monitoring the light intensity, as the POF is subjected to transversal loading conditions. Experimentally obtained output of POF which could be measured with negligible hysteresis is compared with finite element analysis in the range between 0.0098 N to 19.613 N. The reproducibility of the sensor is observed in the limit of ±1%. The finding of this study highlights the potential use of POF sensors for various force sensing applications.