ANALYSIS AND PROCESSING OF LMF－COSTAS STEPPED FREQUENCY RADAR SIGNAL

Linear Modulated Frequency (LMF) Costas Stepped Frequency Radar (SFR) signal is introduced. Its ambiguity function is derived and analyzed in detail and its feasibility is validated in theory. The scheme of the proposed signal processing is also presented. The results of theoretic analysis and simulation show that, by using the proposed signal and increasing the bandwidth of the total stepped frequency, the ambiguity sidelobe is well suppressed and the range-velocity coupling in the stepped frequency radar is also greatly weakened.     

ACCELERATION AMBIGUITY FUNCTION OF RADAR SIGNALS AND ITS APPLICATION

High acceleration of radar targets is analyzed using Acceleration Ambiguity Function(AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.     

Thermo-oxidative degradation of some polymer couples containing HNBR

Summary In this paper thermal behavior of some HNBR blends with CPE, PVC, CR and NBR at three temperatures, 150, 170 and 190°C is presented. Changes in characteristic IR bands, gel fraction, and chlorine content were assessed. Some mechanistic differences between the studied systems, regarding the involvement the depletion of chlorine and modification in gel content, were pointed out. Cyclization of nitrile structure was also observed by means of 2240 cm⁻¹ band ascribed to >C=NH. Kinetic considerations are presented. Received: 3 June 2002/Revised version: 14 November 2002/ Accepted 20 November 2002 Correspondence to Traian Zaharescu     

Rare-earth-enabled universal solders for microelectromechanical systems and optical packaging

In packaging of microelectromechanical systems (MEMS), optical, and electronic devices, there is a need to directly bond a wide variety of inorganic materials, such as oxides, nitrides, and semiconductors. Such applications involve hermetic-sealing components, three-dimensional MEMS assembly components as well as active semiconductor or optical components, dielectric layers, diffusion barriers, waveguides, and heat sinks. These materials are known to be very difficult to wet and bond with low melting-point solders. New Sn-Ag- or Au-Sn-based universal solders doped with a small amount of rare-earth (RE) elements have been developed, which now allow direct and powerful bonding onto the surfaces of various MEMS, optical, or electronic device materials. The microstructure, interface properties, and mechanical behavior of the bonds as well as the potential packaging applications of these new solder materials for MEMS and optical fiber devices are described. Various packaging-related structural, thermal, or electrical issues in MEMS are also discussed.     

Influence of fretting on the fatigue strength at the vise clamp-specimen interface

Fretting fatigue is one of the most important phenomena for inducing a significant reduction of fatigue strength and consequently, leading to unexpected failure accidents of the engineering structures even at very low stresses. In the present study, both plain and fretting fatigue tests with zero mean stress were carried out on two different types of steel, low-carbon steel and martensitic stainless steel, by means of a reversed bending fatigue testing machine. The drop in the fatigue strengths through fretting at vise clamp-specimen interface were significant for both tested steels. The fretting processes produced a reduction in fatigue strength of about 27% for low-carbon steel and 16% for martensitic stainless steel.     

Co-evolution as a computational and cognitive model of design

Co-evolutionary design has been developed as a computational model that assumes two parallel search spaces: the problem space and the solution space. The design process iteratively searches each space using the other space as the basis for a fitness function when evaluating the alternatives. Co-evolutionary design can also be developed as a cognitive model of design by characterizing the way in which designers iteratively search for a design solution, making revisions to the problem specification. This paper presents the computational model of co-evolutionary design and then describes a protocol study of human designers looking for evidence of co-evolution of problem specifications and design solutions. The study shows that co-evolutionary design is a good cognitive model of design and highlights the similarities and differences between the computational model and the cognitive model. The results show that the two kinds of co-evolutionary design complement each other, having strengths in different aspects of the design process. Electronic Publication     

Microstructure and thermal behavior of Sn-Zn-Ag solders

The microstructure and thermal behavior of the Sn-Zn-Ag solder were investigated for 8.73–9% Zn and 0–3.0% Ag. The scanning electron microscopy (SEM) analysis shows the Ag-Zn compound when the solder contains 0.1% Ag. X-ray diffraction (XRD) analysis results indicate that Ag₅Zn₈ and AgZn₃ become prominent when the Ag content is 0.3% and above. Meanwhile, the Zn-rich phase is refined, and the Zn orientations gradually diminish upon increase in Ag content. The morphology of the Ag-Zn compound varies from nodular to dendrite structure when the Ag content increases. The growth of the Ag-Zn compounds is accompanied by the diminishing of the eutectic structure of the Sn-9Zn solder. Differential scanning calorimetry (DSC) investigation reveals that the solidus temperature of these solders exists at around 198°C. A single, sharp exothermic peak was found for the solders with Ag content less than 0.5%. Liquidus temperatures were identified with the DSC analysis to vary from 206°C to 215°C when the Ag content ranges from 1.0% to 3.0%     

A physically based approach to granular media mechanics: grain-scale experiments,initial results and implications to numerical modeling

It is generally appreciated that the mechanical behavior of granular media depends fundamentally on the interaction of the constituent particles, and that the validity of numerical models of granular media would be greatly improved with knowledge of the grain-scale mechanics. However, most supporting experimental work has been conducted on highly idealized materials, and a limited amount of information exists on grain-scale force–displacement relationships for naturally occurring materials. To address this shortcoming, we are conducting a program that integrates laboratory experiments on grains of naturally occurring aggregate with the discrete element modeling method, with the goal of relating the grain-scale physical and mechanical properties of granular media to bulk behavior. The paper describes the equipment and methods that have been developed to conduct close-loop controlled, grain-scale experiments under monotonic and cyclic loading conditions, and presents results from an initial set of experiments on unbonded grains. The implications of the grain-scale results to the discrete element model are discussed. Discussions center on the applicability of a physically based approach to the mechanics of granular media in general. In light of future exploration missions and the resulting need to predict the mechanical properties of lunar and planetary regoliths, the paper examines the potential usefulness of our physically based approach to the problem of predicting the behavior of the types of materials found in those environments.     

New intramolecular effect observed for polyesters: An anomeric effect

A series of polyesters was prepared to evaluate hydrolytic stability as a function of cyclohexyl dibasic acid content. The three cyclohexyl dibasic acids: 1,2; 1,3; and 1,4 were formulated into polyesters with two glycols. The proportion of cis and trans isomers was evaluated via ¹H NMR. The hydrolytic stability of short chain polyesters was evaluated in an acetone/water mixture which solubilized the polyesters to mimic oligoester behavior within a thermosetting polyester coating environment. The rate of hydrolysis was monitored by acid titration and corroborated by GPC. Surprisingly, 1,2-cylohexyl diacid-based polyesters were robust, and 1,3-cyclohexyl diacid-based polyesters were the most susceptible to hydrolysis. Evidently, a 1,2-anchimeric effect for cyclohexyl dibasic acid polyesters was not an important consideration, while the 1,3-cyclohexyl ester interaction was. Consequently, an anomeric effect was proposed. Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.