Simulation and Fabrication of SAW-Based Gas Sensor with Modified Surface State of Active Layer and Electrode Orientation for Enhanced H<Subscript>2</Subscript> Gas Sensing

The design, analysis, optimization, and fabrication of layered and nanostructure-based surface acoustic wave (SAW) gas sensors are presented. A lithium niobate and zinc oxide (ZnO) nano multilayer structure is proposed to enhance the sensitivity of the SAW-based gas sensor. Different materials are considered for the intermediate layer in the design for optimization purposes. The sensitivity of the sensor could be improved due to increased active surface area obtained by varying the aspect ratio of the nanorods, the thickness of the intermediate layer, and the gap between the electrodes. The total displacement and frequency shift of the device were significantly improved. Overall, the mechanically engineered surface-based (nanorod) SAW gas sensor offered better sensing response than the layered SAW gas sensor in terms of sensitivity performance.     

A review of some issues and identification of some barriers in the implementation of FMS

Global competition, advancements in technology and ever changing customers’ demand have made the manufacturing companies to realize the importance of flexible manufacturing systems (FMS). These organizations are looking at FMS as a viable alternative to enhance their competitive edge. But, implementation of this universally accepted and challenging technology is not an easy task. A large number of articles have been reviewed and it is found that the existing literature lacks in providing a clear picture about the implementation of FMS. In this paper, work of various researchers has been studied and it is found that it is really a very difficult task for any organization to transform into FMS on the basis of existing research results. A wide gap exists between the proposed approaches/algorithms for the design of different components of FMS and the real-life complexities. Besides describing the gap in various issues related to FMS, some barriers, which inhibit the adaptation and implementation of FMS, have also been identified in this paper.     

Analysis of water absorbency into knitted spacer structures

The absorbency properties of knitted structures are very important in designing garments that both remove liquid sweat from the skin and provide tactile and sensorial comfort to the wearer. Water absorbency by knitted spacer structures was experimentally investigated using a gravimetric absorbency tester to record absorbency rate, total absorbency and time taken to saturate the structure. The geometry of spacer structures was analysed and a model created to define the capillary characteristic in the spacer yarn. Absorbency into the spacer structures was modelled using the fabric parameters, the capillary radius and the properties of water. Experimental and theoretical results were compared to validate the models.     

Undoped AlGaN/GaN HEMTs for microwave power amplification

Undoped AlGaN/GaN structures are used to fabricate high electron mobility transistors (HEMTs). Using the strong spontaneous and piezoelectric polarization inherent in this crystal structure a two-dimensional electron gas (2DEG) is induced. Three-dimensional (3-D) nonlinear thermal simulations are made to determine the temperature rise from heat dissipation in various geometries. Epitaxial growth by MBE and OMVPE are described, reaching electron mobilities of 1500 and 1700 cm ²/Ns, respectively, For electron sheet density near 1×10¹³/cm², Device fabrication is described, including surface passivation used to sharply reduce the problematic current slump (dc to rf dispersion) in these HEMTs. The frequency response, reaching an intrinsic f_t of 106 GHz for 0.15 μm gates, and drain-source breakdown voltage dependence on gate length are presented. Small periphery devices on sapphire substrates have normalized microwave output power of ~4 W/mm, while large periphery devices have ~2 W/mm, both thermally limited. Performance, without and with Si₃N₄ passivation are presented. On SiC substrates, large periphery devices have electrical limits of 4 W/mm, due in part to the limited development of the substrates     

Some extended semaphore primitives

Summary This paper presents a proposal for synchronizing primitives obtained as an extension of Dijkstra's P, V primitives. The extended primitives are shown to be complete: they can represent any desired interaction between processes without the use of conditionals. The usefulness of these primitives is illustrated by presenting simple solutions to a series of coordination problems of increasing complexity. Two selected problems are used to illustrate disadvantages of existing synchronizing mechanisms. The extended primitives shift some of the burden from the programmer to the system since they are easier to use but more difficult to implement. However, even though each primitive operation may take longer to execute (as compared to the simple P, V primitives) the total system overhead can be substantially less especially for complex coordination problems. The paper presents a straightforward but efficient implementation of the extended primitives.This work was supported in part by the U.S. Atomic Energy Commision under contract AT(11-1 3288) and in part by the Joint Services Electronics Program under contract AFOSR F4620-76-C-0089