A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Reducing Encoder Bit-Rate Variation in MPEG Video

A shortcoming of current video transmission using the MPEG standard is that its encoder produces a variable bit rate (VBR). Due to this, the encoder output has to be buffered and released over the network at a constant rate. This buffering of the encoder output introduces an additional delay between the encoding and decoding phases of the video transmission. To remedy this problem, we present a strategy to distribute the load produced by the encoder as evenly as possible, i.e., try to have a constant bit rate (CBR). This is done by treating the slices in each frame separately while compressing them and then mixing the different kinds of slices that are sent over the network. The resulting load variation is much more uniform, reducing the buffering delay and making future bandwidth requirement estimates more accurate.This material is based upon work supported in part by the National Science Foundation under Award No. IRI-9526004, by the Texas Advanced Research Program under Grant No. 3652270, and by a grant from the University of Houston Institute of Space Systems Operations. Rajat Agarwal is now with Lucent Technologies. This paper is an extended version of a shorter paper presented at IEEE ICMCS 1999.Albert Mo Kim Cheng received the B.A. with Highest Honors in Computer Science at age 19, graduating Phi Beta Kappa, the M.S. in Computer Science with a minor in Electrical Engineering at age 21, and the Ph.D. in Computer Science at age 25, all from The University of Texas at Austin, where he held a GTE Foundation Doctoral Fellowship. Dr. Cheng is currently a tenured Associate Professor in the Department of Computer Science at the University of Houston, where he is the founding Director of the Real-Time Systems Laboratory. He has served as a technical consultant for several organizations, including IBM, and was also a visiting faculty in the Departments of Computer Science at Rice University (2000) and at the City University of Hong Kong (1995).He is the author/co-author of over seventy refereed publications in IEEE Transactions on Software Engineering, IEEE Transactions on Knowledge and Data Engineering, Real-Time Systems Symposium, Real-Time and Embedded Technology and Applications Symposium, and other leading conferences. One of his recent work presents a timing analysis of the NASA X-38 Space Station Crew Return Vehicle Avionics, which contains a fault-tolerant distributed system.Dr. Cheng has received numerous awards, including the National Science Foundation Research Initiation Award (now known as the NSF CAREER award). He has been invited to present seminars and tutorials at over 30 conferences, and has given invited seminars/keynotes at over 20 universities and organizations, most recently at ICEIS, Ecole Superieure de l Ouest (ESEO), Angers, France, April 2003. His next invited keynote speech will be at the 1st Intl. Conf. on Informatics in Control, Automation and Robotics (ICINCO), Setubal, Portugal, August 2004.He is an Associate Editor of the IEEE Transactions on Software Engineering (1998-2003), a Guest Co-Editor of two IEEE TSE Special Issues on Software and Performance (Nov. and Dec. 2000), an Associate Editor of the International Journal of Computer and Information Science, the work-in-progress program chair of the 2001 IEEE-CS Real-Time Technology and Applications Symposium, the work-in-progress session chair of the 2003 IEEE-CS Real-Time Systems Symposium, and the invited special panel chair for the software engineering for multimedia session at the 1999 IEEE-CS International Conference on Multimedia Computing Systems (ICMCS). Currently, he is a member of the program committees of RTSS, RTAS, ICEIS, ICECCS, RTAS, LCN, COMPSAC, ICCCN, AIA, DBA, PDCN, SE, and ICINCO. Dr. Cheng is an Honorary Member of the Institute for Systems and Technologies of Information, Control and Communication (INSTICC). He is a Senior Member of the IEEE.Dr. Cheng is the author of several book chapters on E-commerce/Enterprise Information Systems, and an article entitled Embedded OS, in the upcoming Encyclopedia of Computer Science and Engineering (John Wiley & Sons). He is the author of the new senior/graduate-level textbook entitled Real-Time Systems: Scheduling, Analysis, and Verification (John Wiley & Sons). cheng@cs.uh.eduRajat Agarwal received the M.S. in Computer Science from the University of Houston. He is currently a Member of the Technical Staff at Lucent Technologies. His research interest is in real-time multimedia systems.     

Hybrid Turbo FEC/ARQ Systems and Distributed Space-Time Coding for Cooperative Transmission

Cooperative transmission can be seen as a “virtual” MIMO system, where the multiple transmit antennas are in fact implemented distributed by the antennas both at the source and the relay terminal. Depending on the system design, diversity/multiplexing gains are achievable. This design involves the definition of the type of retransmission (incremental redundancy, repetition coding), the design of the distributed space-time codes, the error correcting scheme, the operation of the relay (decode & forward or amplify & forward) and the number of antennas at each terminal. Proposed schemes are evaluated in different conditions in combination with forward error correcting codes (FEC), both for linear and near-optimum (sphere decoder) receivers, for its possible implementation in downlink high speed packet services of cellular networks. Results show the benefits of coded cooperation over direct transmission in terms of increased throughput. It is shown that multiplexing gains are observed even if the mobile station features a single antenna, provided that cell wide reuse of the relay radio resource is possible.     

Discontinuous Sturm–Liouville Problems with Eigenparameter-Dependent Boundary and Transmissions Conditions

The purpose of this paper is to study a Sturm–Liouville problem with discontinuities in the case when an eigenparameter appears not only in the differential equation but it also appears in both the boundary and transmission conditions. We suggest a new approach for the definition of a suitable Hilbert space and a symmetric linear operator defined in this space in such a way that the considered problem can be interpreted as the eigenvalue problem of this operator and for construction and approximation of a fundamental solution. We apply these results to find asymptotic formulas of eigenvalues and corresponding eigenfunctions. Mathematics Subject Classification (2000) 34L20.This work was supported by the Research Fund of Gaziosmanpasa University under grand no:2004/01.     

The preparation and characterization of strained-layer superlattices in the GaAs + GaP System

The technique of metal organic chemical vapor deposi-tion has been used to prepare strained-layer superlattices in the GaAs + GaP system. The superlattices consist of alternating layers of GaP and GaAs_xP_1?x for x = 0.2 to 1.0, which vary in thickness from 30 to 400 Å. The layers were grown by the decomposition of trlmethylgallium and various mixtures of ASH₃ and PH₃ in H₂ at 800δC. The thickness and uniformity of the layers were determined by optical and transmission electron microscopy and x-ray diffraction. The composition of the layers was determined from x-ray diffraction. A new analysis has been developed to determine the layer strain as well as the composition of thick layers (～ 300 Å). Transmission electron microscopy has been used to yield direct evidence that strained-layer superlattices can be used to remove the misfit dislocations generated during the epitaxial growth of a GaAs_xP_1-x alloy on a lattice mismatched GaP substrate. These results are in agreement with the previous work of Matthews and Blakeslee. Optical absorption, photocurrent spectroscopy and photoluminescence have been used to deter-mine the band gap energy as well as the energies for other optical transitions. The values are in excellent agreement with the values predicted by tight binding and effective mass calculations.     

Effect of gaunt factor correction in soft x-ray plasma diagnostics

The effect of Gaunt factor correction on temperature estimation over a range 100 to 1500 eV had been studied. Greene’s analytical expression for the quantum mechanical Gaunt factor averaged over Maxwellian distribution is used. Transmission ratios are calculated with and without Gaunt factor for various combinations of beryllium foils, taking into account x-ray emission due to free-free transitions. A significant difference (≳ 15%) is observed between the temperatures estimated from classical and quantum mechanical curves, above 600 eV. Selection of foil combinations useful for estimating higher temperatures is also discussed.     

Improvements in Carrier-to-Noise-Ratio (CNR) of Lightwave Amplitude Modulated Vestigial-Sideband (AM-VSB) Transmission Systems by the Use of Optical Isolators

In lightwave community antena television (CATV) systems as well as other optical fiber communication networks, a transmitted optical signal is known to be degraded by an intensity noise produced within the fiber due to the interference between the signal and doubly reflected light. We report on the improvements to the signal degradation due to the double Rayleigh backscattering by inserting optical isolators in the trunk lines of the systems. A carrier-to-noise ratio (CNR) has been calculated as a function of the number and the insertion loss of the isolators. The calculated results indicate that there is an optimum number of isolators, and if the insertion loss is less than 0.3 dB, the CNR degradation can be restored by more than 60%. To test the calculated results, we conducted experiments for the specific case of employing one isolator, and obtained good agreements between the two.     

板状非线性介质表面耦合波的反射和透射

本文详细分析了平面波激励非线性介质后介质的非线性极化、麦克斯专方程及其解、广义的反射和透射定律；导出了板状非线性介质表面任意阶耦合波的反射场和透射场；对介质满足相位匹配和泵浦波正入射下的场进行了深入的讨论；给了非线性介质表面的布儒斯特角。     

Metalorganic vapor phase epitaxial growth and structural characterization of GaAs/InP heterostructures

Highly mismatched GaAs epitaxial layers with thickness ranging from 15 nm to 7 μm have been grown on InP substrates by atomospheric pressure metalorganic vapor phase epitaxy. Layers thinner than 30 nm exhibited 3-D growth mechanism; in the thicker layers, the islands coalesced and then the growth followed the layer by layer mechanism. The elastic strain and the extended defects have been studied by high resolution x-ray diffraction and transmission electron microscopy, respectively. The common observation of planar defects, misfit, and threading dislocations in the layers has been confirmed. The results on the elastic strain release have been discussed on the basis of the equilibrium theory.