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     

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     

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).     

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.     

Optical Properties of K<Subscript>2</Subscript>O-Li<Subscript>2</Subscript>O-WO<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glasses: Evidence of Mixed Alkali Effect

Glass with compositions xK₂O-(30 ? x)Li₂O-10WO₃-60B₂O₃ for 0 ≤ x ≤ 30 mol.% have been prepared using the normal melt quenching technique. The optical reflection and absorption spectra were recorded at room temperature in the wavelength range 300–800 nm. From the absorption edge studies, the values of the optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple Di-Domenico model.     

Human action recognition employing negative space features

We proposed a region based method to recognize human actions from video sequences. Unlike other region based methods, it works with the surrounding regions of the human silhouette termed as negative space. This paper further extends the idea of negative space to cope with the changes in viewpoints. It also addresses the problem of long shadows which is one of the major challenges of human action recognition. Some systems attempt suppressing shadows during the segmentation process but our system takes input of segmented binary images of which the shadow is not suppressed. This makes our system less dependent on segmentation process. Further, this approach can complement the positive space (silhouette) based methods to boost recognition. The system consists of a hierarchical processing: histogram analysis on segmented input image, followed by motion and shape feature extraction, pose sequence analysis by employing Dynamic Time Warping and at last classification by Nearest Neighbor classifier. We evaluated our system by most commonly used datasets and achieved higher accuracy than the state of the arts methods. Our system can also retrieve video sequences from queries of human action sequences.     

Collision avoidance slot allocation scheme for multi-cluster wireless sensor networks

This paper introduces a collision avoidance slot allocation scheme for Time Division Multiple Access (TDMA) based Medium Access Control (MAC) in multi-cluster wireless sensor networks. TDMA MAC protocols have built-in active-sleep duty cycle that can be leveraged for limiting idle listening. Also, they can overcome the overhearing problem, thus have better energy efficiency. Enabling concurrent intra-cluster communications using a single radio channel is a key issue in TDMA MAC protocols. Using orthogonal frequency channels or different Code Division Multiple Access codes for different adjacent clusters can solve the problem at the expense of cost. In this paper, we propose a new distributed slot allocation protocol called  Coordinated   Time   Slot   Allocation (CTSA) that can reduce collisions significantly using a single radio channel. We use simulations to study the effects of different system parameters on the performance of our proposed protocol. Simulation results show that applying CTSA over clustering protocols can significantly reduce collisions. It also shows fast convergence for our proposed CTSA protocol. In this paper we apply our CTSA scheme to the Low Energy Adaptive Clustering Hierarchy protocol which forms the basis for many cluster based routing protocols. CTSA is also compared with the SRSA algorithm proposed by Wu and Biswas (Wirel Netw 13(5):691–703, 2007) by means of simulation.     

Multibit Σ–∆ PWM Digital Controller IC for DC–DC Converters Operating at Switching Frequencies Beyond 10 MHz

An integrated digital controller for dc-dc switch-mode power supplies (SMPS) used in portable applications is introduced. The controller has very low power consumption, fast dynamic response, and can operate at programmable constant switching frequencies exceeding 10 MHz. To achieve these characteristics, three novel functional blocks, a digital pulse-width modulator based on second-order sigma-delta concept (Sigma-Delta DPWM), dual-clocking mode compensator, and nonlinear analog-to-digital converter are combined. In steady state, to minimize power consumption, the controller is clocked at a frequency lower than SMPS switching frequency. During transients the clock rate is increased to the switching frequency improving transient response. The controller integrated circuit (IC) is fabricated in a standard 0.18-mum process and tested with a 750-mW buck converter prototype. Experimental results show the controller current consumption of 55 muA/MHz and verify closed-loop operation at programmable switching frequencies up to 12.3 MHz. Simulation results indicating that this architecture can potentially support operation at switching frequencies beyond 100 MHz are also presented.     

Assessment of triboelectricity in colossal-surface-area-lanthanum oxide nanocrystals synthesized via low-temperature hydrothermal process

Journal of Materials Science: Materials in Electronics - Triboelectric nanogenerators (TENGs) have marked their applications in various fields, most importantly, in medical devices. The electrical...