Stability radii for positive linear time-invariant systems on time scales

We deal with dynamic equations on time scales, where we characterize the positivity of a system. Uniform exponential stability of a system is determined by the spectrum of its matrix. We investigate the corresponding stability radii with respect to structured perturbations and show that, for positive systems, the complex and the real stability radius coincide.     

Improvements in modeling and evaluation of electrical power systemreliability

This paper describes updates in an electrical reliability modeling process, first described in a 1993 paper for the Petroleum and Chemical Industry Committee of the IEEE Industry Applications Society. The paper also describes an additional new method for evaluating power system design options. The electrical reliability model has been expanded with more extensive component failure and repair values. Additional modeling techniques have been developed for evaluating typical electrical systems found in petroleum and chemical facilities. The reliability calculation results, based on the actual modeling of many refineries in the US, are described. The paper also describes a new method which was developed to evaluate and compare power system designs, based on the resulting composite reliability values and other factors, including recovery from faults, availability for maintenance, safety and cost. This new method provides an analytical approach to optimize the power system design to the plant operation and maintenance requirements     

Influence of strain rate and crystallographic orientation on dynamic recrystallization of pure Zn during room-temperature compression

This work investigates the strain rate dependence of dynamic recrystallization behaviour of high-purity zinc in room temperature compression under strain rates of 10-4 s-1,10-2 s-1 and 0.5 s-1.Results from electron backscatter diffraction provide insight into the deformation and dynamic recrystallization mech-anisms operative.Continuous dynamic recrystallization,twin-induced dynamic recrystallization,and discontinuous dynamic recrystallization are all active under compressive deformation at room temper-ature.Due to the high stacking fault energy of Zn,continuous dynamic recrystallization is the dominant mechanism while discontinuous dynamic recrystallization only operates in the early stages of compres-sion at 10-4 S-1.Dynamic recrystallization kinetics are enhanced at higher strain rates(10-2 s-1 and 0.5 s-1)due to an increased contribution from twin-induced dynamic recrystallization.The present study reveals that the controlling mechanisms for continuous dynamic recrystallization are basalslip and 2nd order pyramidalslip activity.Because the activation of slip systems is mainly deter-mined by crystallographic orientation,continuous dynamic recrystallization behaviour varies with grain orientation according to their propensity for basal and 2nd order pyramidal slip.     

Scattering effect of SiO2 particles on correlated color temperature uniformity of multi-chip white light LEDs

This study proposes the addition of SiO₂ scattering particles into the phosphor layer of a multi-chip white light LED (MCW-LED) for enhancing its performance. It is demonstrated by computer simulations that SiO₂ particles can bring significant effects on the correlated color temperature (CCT) uniformity and luminous flux. Through the simulation experiments, it was found that the MCW-LED with hybrid SiO₂ structure with SiO₂ particle size around 1 μm can achieve higher color uniformity than other package structures. We investigated the influence of SiO₂ (quartz) concentration on the CCT and the output flux of the MCW-LED with CCTs 7000, 7700, and 8500 K, respectively. Compared to an LED package without SiO₂, SiO₂ packages can shrink the CCT deviation about 48%. In this study, it was demonstrated that the inclusion of about 5–10% SiO₂ can produce an MCW-LED with higher CCT uniformity and optimal lumen output.     

OFDM Scheme for Data Transmission Over Inductive Channels

Although OFDM has become a widely used method for transmitting digital data on multicarrier frequencies in wideband digital communication, this scheme has barely been used for near field inductive communication. Therefore, in this paper, OFDM is applied to three inductive communication systems including two, three and four node systems in order to transmit data over inductive channels. Furthermore, the channel responses for these three circuits are analysed in details to clarify the accurate inductive channels for data transmission that were defined alternatively in other papers. Besides, the effects of second neighbour interaction on inductive systems are also included in this work. More importantly, the OFDM scheme has been simulated in MATLAB and implemented in MATLAB SIMULINK in order to verify the method in either theory or practice. The BER versus SNR performances obtained by simulation and implementation are compared with the theoretical results to verify the data transmission errors.     

Micro-structuring of glass with features less than 100 μm by electrochemical discharge machining

Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 μm in size, such as Ø 60 μm micro-holes, a 10 μm-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.     

Jute fibre/epoxy composites: Surface properties and interfacial adhesion

Jute fibres were surface treated in order to enhance the interfacial interaction between jute natural fibres and an epoxy matrix. The fibres are exposed to alkali treatment in combination with organosilane coupling agents and aqueous epoxy dispersions. The surface topography and surface energy influenced by the treatments were characterized. Single fibre pull-out tests combined with SEM and AFM characterization of the fracture surfaces were used to identify the interfacial strengths and to reveal the mechanisms of failure.     

Microstructure and abrasive wear in silicon nitride ceramics

It is well known that abrasive wear resistance is not strictly a materials property, but also depends upon the specific conditions of the wear environment. Nonetheless, characteristics of the ceramic microstructure do influence its hardness and fracture toughness and must, therefore, play an active role in determining how a ceramic will respond to the specific stress states imposed upon it by the wear environment. In this study, the ways in which composition and microstructure influence the abrasive wear behavior of six commercially-produced silicon nitride based ceramics are examined. Results indicate that microstructural parameters, such as matrix grain size and orientation, porosity, and grain boundary microstructure, and thermal expansion mismatch stresses created as the result of second phase formation, influence the wear rate through their effect on wear sheet formation and subsurface fracture. It is also noted that the potential impact of these variables on the wear rate may not be reflected in conventional fracture toughness measurements.