A W-band monolithic downconverter

The design, fabrication, and evaluation of a fully integrated W-band monolithic downconverter based on InGaAs pseudomorphic HEMT technology are presented. The monolithic downconverter consists of a two-stage low-noise amplifier and a single-balanced mixer. The single-balanced mixer has been designed using the HEMT gate Schottky diodes inherent to the process. Measured results of the complete downconverter show conversion gain of 5.5 dB and a double-sideband noise figure of 6.7 dB at 94 GHz. Also presented is the downconverter performance characterized over the -35°C to +65°C temperature range. The downconverter design was a first pass success and has a high circuit yield     

Generalized hybrid-combined methods for the singularity problems of homogeneous elliptic equations

Combinations of the Ritz–Galerkin and finite element methods are applied to solving singularity problems of homogeneous, elliptic equations. The Ritz-Galerkin method is used in the subdomains where there exist singular points; and the finite element method is still used in the rest of the solution domains. More general coupling techniques than those of Reference 6 along the common boundary of subdomains are discussed. Numerical experiments using these kinds of coupling techniques are provided for the first time. It is interesting that the calculated results of Motz's problem have shown the simplified hybrid strategy in Reference 6 to be optimal for both error bounds and stability of numerical solutions, among all general coupling techniques.     

Performance analysis of the aluminum casting furnace

The casting furnace plays a central role in the production of aluminum. Its design and operation are complex and involve some 450 parameters. There is a need for a model to predict and analyze its performance. We propose a simplified model in which each main component of the furnace is treated as a 1-D heat conduction medium. Based on the equations of conservation of mass, energy, and chemical species, complemented by the equations of conduction and the Hottel’s formulation of radiative heat transfer, this dynamic model can simulate any sequence of operations such as loading, heating, stirring, skimming … that constitutes a batch, and can take into account other operational details such as the opening of doors. It is validated on a real furnace, then used to predict furnace performance in other modes of operation, and also to determine an optimal fuel flow that minimizes a chosen cost function.     

A new kind of combinations between the Ritz-Galerkin and finite element methods for singularity problems

The coupling techniques of simplified hybrid plus penalty functions are first presented for matching the Ritz-Galerkin method and thek(k>-1)-order Lagrange finite element methods to solve complicated problems of elliptic equations, homogeneous or nonhomogeneous, in particular with singularities or unbounded domains. Optimal convergence rates of numerical solutions have been proved in the Sobolev norms. Moreover, the theoretical results obtained in this paper have been verified by numerical experiments for the singular Motz problem.     

Heat transfer during the rewetting of hot horizontal channels

The heat transfer in the rewetting of hot horizontal channels is investigated. The physical model assumes an inclined rewetting front advancing at a uniform velocity. Precursory cooling in the dry region is considered. Three-dimensional energy equations are solved numerically by a finite difference method. Further, the axial and circumferential temperature distributions are predicted. The influence of various parameters on the rewetting velocity is analyzed, as are the variations of the different heat transfer mechanisms, convection to the fluid and conduction in the three-dimensions, as a function of time.     

Distributed Link Scheduling With Constant Overhead

This paper proposes a new class of simple, distributed algorithms for scheduling in multihop wireless networks under the primary interference model. The class is parameterized by integers k ges 1. We show that algorithm k of our class achieves k/(k + 2) of the capacity region, for every k ges 1. The algorithms have small and constant worst-case overheads. In particular, algorithm k generates a new schedule using a) time less than 4k + 2 round-trip times between neighboring nodes in the network and b) at most three control transmissions by any given node for any k. The control signals are explicitly specified and face the same interference effects as normal data transmissions. Our class of distributed wireless scheduling algorithms are the first ones guaranteed to achieve any fixed fraction of the capacity region while using small and constant overheads that do not scale with network size. The parameter k explicitly captures the tradeoff between control overhead and throughput performance and provides a tuning-knob protocol designers can use to harness this tradeoff in practice.     

Experimental and numerical studies of wingtip and downwash effects on horizontal tail

Journal of Mechanical Science and Technology - Studying wing downwash, which is caused by the wingtip effect, and its influence on horizontal tail is important for aircraft design. In this work,...