Accurate analysis of MMI devices with two-dimensional confinement

The accurate analysis of multimode interference (MMI) devices with two-dimensional (2-D) confinement has been demonstrated by using the least squares boundary residual (LSBR) method. Accurate modal propagation constants and spatial field profiles in the MMI section are obtained by using the vector H-field based finite element method. The accurate calculation of the excited modal coefficients is achieved by using the LSBR, which satisfies the continuity of the transverse field components more rigorously than using simple overlap integrals     

Cyclobutanones as markers for irradiated samples of Brie and Camembert cheese

The feasibility of applying a chemical method based on the formation of 2-alkylcyclobutanone to samples of irradiated soft cheese (Brie and Camembert) was investigated. Significant quantities of 2-dodecylcyclobutanone (DCB) and 2-tetradecylcyclobutanone (TCB) were detected in both types of irradiated cheese and are proposed as qualitative markers. Other members of the cyclobutanone family (decyl- and tetradecenyl-) are also thought to be present but could not be substantiated due to a lack of authentic standards. These compounds were absent from the unirradiated samples. Results also show a significant linear relationship between the irradiation dose (1 to 8 kGy) and the amount of DCB and TCB detected in the cheese.     

Finite-element modeling of one- and two-dimensional MQWsemiconductor optical waveguides

A finite-element characterization of optical waveguides incorporating multiple-quantum-well (MQW) structures is presented. Optical modeling of a planar MQW region is tested to verify that the quantum-well region can be replaced by a homogeneous region with a suitable effective index. Optical modeling of a semiconductor laser incorporating MQW regions with two-transverse-dimensional confinement is then used to identify the range of single-lateral-mode operation. The effective index, the power fraction in the active region, and the spot size dependence on the total optical power for the case of a self-defocusing MQW region are also presented     

Robust and precision motion control system of linear-motor direct drive for high-speed X-Y table positioning mechanism

In this paper, design and implementation of an H/sub /spl infin//-based precision motion control system is presented for a high-speed linear-motor direct-drive X-Y table positioning mechanism in semiconductor wire-bonding applications. The system works with a cascaded robust feedback control, which has an inner loop velocity controller and an outer loop position controller, and an autotuning feedforward compensator. The design aim is to achieve high and consistent tracking performance even in the presence of considerable resonance uncertainties and external disturbances. Toward this aim the velocity controller is designed using H/sub /spl infin// optimization technique, based on reduced-order modeling that considers three significant resonance modes and neglects all other resonance modes having an insignificant amplitude and/or too high frequency. These neglected modes and variations of the three resonance modes from machine to machine (due to manufacturing tolerance) and/or with different operating conditions are taken care of by appropriate additive uncertainty representation in the design phase. The resulting system is validated and implemented with a profile motion of a maximum acceleration of 5.2 g (1g=9.81 m/s/sup 2/) on mass-produced wire bonding machines.     

A load-aware energy-efficient and throughput-maximized asynchronous duty cycle MAC for wireless sensor networks

Being a pivotal resource, conservation of energy has been considered as the most striking issue in the wireless sensor network research. Several works have been performed in the last years to devise duty cycle based MAC protocols which optimize energy conservation emphasizing low traffic load scenario. In contrast, considering the high traffic situation, another research trend has been continuing to optimize both energy efficiency and channel utilization employing rate and congestion control at the MAC layer. In this paper, we propose A Load-aware Energy-efficient and Throughput-maximized Asynchronous Duty Cycle MAC (LET-MAC) protocol for wireless sensor networks to provide an integrated solution at the MAC layer considering both the low-and high-traffic scenario. Through extensive simulation using ns-2, we have evaluated the performance of LET-MAC. LET-MAC achieves significant energy conservation during low traffic load (i.e., no event), compared to the prior asynchronous protocol, RI-MAC, as well as attains optimal throughput through maximizing the channel utilization and maintains lower delay in regard to the CSMA/CA-like protocol during a high volume of traffic (i.e., when an event occurs).     

New look on relay selection strategies for full-duplex multiple-relay NOMA over Nakagami-m fading channels

Wireless Networks - By removing the orthogonal use of radio-resources, non-orthogonal multiple access (NOMA) has been introduced to improve the spectral efficiency of fifth generation (5G) and...     

High capacity cable's role in once and future grids

High temperature superconducting (HTS) cables cooled to 77 K are starting to be tested and could soon be carrying a lot more current through the same old underground city pipes. If superconducting transmission cables can be made to work compatibly with other emerging high-temperature superconducting technologies then it may be possible to layout grids in innovative ways and to position generators closer to customers without having to step voltage up and down. Conventional underground cables normally incorporate fluid, such that the use of liquid-nitrogen coolant in superconducting cables is not such a departure as it might at first seem. The main immediate challenge in developing superconducting cables is to acquire operational experience. Only by working with live-networks and with the users of network equipment will it be possible to evaluate compatibility with existing components, system reliability, maintenance and total system costs. Two basic types of superconducting cable designs are emerging. In one the HTS conductor is enclosed in a cryogenic environment, which in turn is covered by conventional room temperature dielectric. In the other, a cryogenic-dielectric design, two concentric HTS conductors are used transmit electricity. These designs are discussed as are superconducting tapes for 77 K operation, cooling and insulation, joints and terminations, and testing parameters     

Improvement of form accuracy in hybrid machining of microstructures

Micromachining is gaining popularity due to recent advancements in Micro Electro Mechanical Systems. Using conventional micromachining, it is relatively difficult to produce moving components in the order of microns. In this study, an attempt is made to fabricate microstructures using a combination of turning and electrodischarge machining (EDM). Several sets of experiments have been performed to study the characteristics of the hybrid machining process. From the experiments, it has been observed that a higher form of accuracy could be obtained by integrating the on-machine fabrication of the tool and by subsequently using the same tool for EDM. The main cause of the form error is due to the deflection of the shaft during turning. Hence, an attempt is made to observe the deflection of the shaft using a deflection sensor. The influence of micro-EDM parameters such as feed rate, discharge circuits, and gap control parameters on material removal rate and tool wear is also discussed in this study.     

Interference coordination for LTE-Advanced and FM broadcasting interoperability

The surest way to guarantee that multiple wireless systems can concurrently exist harmlessly, when operating in the same or adjacent channel, is by analyzing spectrum overlapping. This paper proposes a more accurate model to evaluate the interference power from co-channel and adjacent channel of orthogonal frequency division multiplexing-based long term evolution-advanced (LTE-Advanced) towards broadcasting frequency modulation systems at 800?MHz. Power spectral density overlapping factor is employed, and closed form of the interference power loss is derived. Numerical results demonstrate that the proposed method evaluates more exact interference power than the advanced minimum coupling loss (A-MCL) method, where the co-channel and adjacent channel interference powers are reduced by 1.3 and 3?dB, correspondingly, compared to that obtained using the A-MCL method. This decreases the minimum separation distance between the two systems, which can eventually lead to efficient radio spectrum resources utilization.     

Performance evaluation of endrills

This paper evaluates the performance of a relatively new type of drill called an endrill which is a cross between a drill and an endmill. Investigations into the effects of its cutting conditions on the drilling forces, surface finish, drill wear and hole oversize were carried out. It was found that endrills produced better quality holes than conventional twist drills, better surface finish and less oversize of the holes. Hence, with proper feed, speed and flow rate of the pressurized flushing coolant, a good finish of about R_a = 1 μm can be attained without reaming. Thus, the productivity of finished holes can be remarkably improved. Compared to twist drills, lower torque and thrust were observed which yielded improved tool life and reduced power consumption. No “walking phenomenon” was observed when this kind of drill was used and the amount of hole oversize was found to average about 0.7% of the drill diameter as compared to 1.6% when twist drills were used. Finally, general equations for the drill torque and thrust were derived from the experimental results.