Harmonic-loaded microwave power amplifiers: Nonlinear design procedure

A nonlinear design procedure for microwave power amplifiers is presented. The methodology makes use of a complete nonlinear model for the active device and an exact nonlinear analysis method. Suitable harmonic loading conditions for efficient power performance are imposed simultaneously and consistently with the analysis. The procedure is much faster than conventional repeated nonlinear analyses. © 1995 John Wiley & Sons, Inc.     

The effect of reactive monomers and functional polymers on the mechanical properties of an unsaturated polyester resin

A general-purpose unsaturated polyester resin with 2:1 mol ratio of styrene to polyester unsaturation was modified with three vinyl monomers and two hydroxyl terminated polybutadienes. Tensile, flexural, and puncture impact properties were examined. The three acrylate monomers were tetraethylene glycol dimethylacrylate, 1,3 butylene glycol dimethacrylate, and trimethylpropane trimethylacrylate with weight percents of 2.5, 5, 15, and 30. Two hydroxyl terminated polybutadienes with slightly different contents of hydroxyl functionality were also employed in the weight percents of 2.5, 5.0, and 10.0. Results showed that an increase in the number of crosslinks and crosslink density resulted in a deterioration in the mechanical properties. The addition of an immiscible polybutadiene polymer to the polyester resin also showed a decrease in the mechanical performance of the resulting thermoset materials.     

Trade openness and regional development in a developing country

This paper examines how economic openness influences regional development in a developing country, with the Philippines as a case study. It first looks at the disparities in economic and social indicators across the country's 14 regions and over time. Metro Manila continues to tower over the national economic landscape, although economic dispersal especially in adjacent regions appears to be expanding. The paper then analyzes the determinants of regional development, using five-year panel data. Trade openness appears to be beneficial to regional economic growth and, via growth, poverty reduction. However, it cannot by itself be expected to bring about more balanced regional development. The authors thank Emma Fan, Jesus Felipe, Rana Hasan, and participants in the conference on the Impacts of Globalization on Urban Development, Bellagio, Lake Como, Italy, 19–23 August 2002, for their helpful comments.     

Thermal effects in polytetrafluoroethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for polytetrafluroethylene (PTFE, Teflon) in the reference temperature range from 294° to 381°K and in the pressure range from 13.8 to 200 MN/m². The thermal effects were found to be higher at the reference temperature approximating the transition temperatures of 19° and 30°C than at higher reference temperature. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (?T/?P = αT/ρC_p). A curvefitting analysis showed that the empirical curve, (?T/?P) = ab(ΔP)^b?1, described the experimental thermoelastic coefficients obtained from the experiments. The fact that no agreement was found between the predicted and the experimental coefficients is due to the physical changes in PTFE at the transition temperatures. The relationship between the thermal effects and the chain molecular motion is discussed by including dynamic mechanical analysis and differential scanning calorimetry DSC measurements for the PTFE samples.     

Résolution d’un problème d’affectation à l’aide d’une procédure de réarrangement

The problem of allocating a certain number of resources and working out their time schedule to flow a given traffic in a minimum time (under certain constraints) is considered. Unlike other algorithms, which work out the solution from rather long manipulations of the matrix traffic, we use a simple assignement heuristic and solve the very few conflicts through a fast and easy rearranging process. This technique allows a dynamic adjustment to an evolution of the traffic matrix.     

A frequency-domain approach to interconnect crosstalk simulation and minimization

A frequency-domain approach to efficiently simulate and minimize the crosstalk between high speed interconnects is proposed in this paper. Several methods for modeling coupled microstrip transmission lines are discussed. Several possible simulation strategies are also considered. A straightforward yet rigorous frequency-domain approach is followed. This approach can be used for linearly and non-linearly terminated microstrip coupled lines, since it exploits the harmonic balance technique. A typical example of microstrip interconnects is simulated and the results are compared with those obtained in previous work by other authors using time-domain methods. The simulation method proposed in this work yields good accuracy. A crosstalk minimization problem is formulated and solved following the method proposed.     

The Relationship between Chemical Flexibility and Nanoscale Charge Collection in Hybrid Halide Perovskites

Hybrid organometal halide perovskites are known for their excellent optoelectronic functionality as well as their wide‐ranging chemical flexibility. The composition of hybrid perovskite devices has trended toward increasing complexity as fine‐tuned properties are pursued, including multielement mixing on the constituents A and B and halide sites. However, this tunability presents potential challenges for charge extraction in functional devices. Poor consistency and repeatability between devices may arise due to variations in composition and microstructure. Within a single device, spatial heterogeneity in composition and phase segregation may limit the device from achieving its performance potential. This review details how the nanoscale elemental distribution and charge collection in hybrid perovskite materials evolve as chemical complexity increases, highlighting recent results using nondestructive operando synchrotron‐based X‐ray nanoprobe techniques. The results reveal a strong link between local chemistry and charge collection that must be controlled to develop robust, high‐performance hybrid perovskite materials for optoelectronic devices.     

Thioethyl‐Porphyrazine/Nanocarbon Hybrids for Photoinduced Electron Transfer

A novel pyrene‐substituted thioethyl‐porphyrazine ( PzPy ) and the formation of supramolecular assembly with nanocarbons demonstrating photoinduced electron transfer ability are designed. As revealed by spectroscopic and electrochemical studies, PzPy displays wide spectral absorption in the visible range, charge separation upon photoexcitation, as well as bandgap and highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) energy values, matching the key requirements of organic optoelectronic. Moreover, the presence of a pyrene moiety promotes attractive interactions with π‐conjugated systems. In particular, theoretical calculations show that in the PzPy the HOMO and LUMO are localized on different positions of the molecule, i.e., the HOMO on the pyrene moiety and the LUMO on the macrocycle. Therefore, HOMO–LUMO excitation gives rise to a charge separation, preventing excitons recombination. Two kinds of noncovalent hybrid composites are prepared by mixing the PzPy with single‐wall carbon nanotubes (SWNTs) and graphene nanoflakes (GNFs), respectively, and used for photocurrent generation through charge transfer processes between PzPy and nanocarbons. Photoconduction experiments show photocurrent generation upon visible light irradiation of both PzPy /SWNT and PzPy /GNF composites (0.78 and 0.71 mA W^?1 at 500 nm, respectively), demonstrating their suitability for optoelectronic applications and light harvesting systems.     

Robust auto tool change for industrial robots using visual servoing

This work presents an automated solution for tool changing in industrial robots using visual servoing and sliding mode control. The robustness of the proposed method is due to the control law of the visual servoing, which uses the information acquired by a vision system to close a feedback control loop. Furthermore, sliding mode control is simultaneously used in a prioritised level to satisfy the constraints typically present in a robot system: joint range limits, maximum joint speeds and allowed workspace. Thus, the global control accurately places the tool in the warehouse, but satisfying the robot constraints. The feasibility and effectiveness of the proposed approach is substantiated by simulation results for a complex 3D case study. Moreover, real experimentation with a 6R industrial manipulator is also presented to demonstrate the applicability of the method for tool changing.     

Heavy Moving Averages and Their Application in Econometric Forecasting

This paper presents the heavy ordered weighted moving average (HOWMA) operator. It is an aggregation operator that uses the main characteristics of two well-known techniques: the heavy ordered weighted averaging (OWA) and the moving averages. Therefore, this operator provides a parameterized family of aggregation operators from the minimum to the total operator and includes the OWA operator as a special case. It uses a heavy weighting vector in the moving average formulation and it represents the information available and the knowledge of the decision maker about the future scenarios of the phenomenon, according to his attitudinal character. Some of the main properties of this operator are studied, including a wide range of families of HOWMA operators such as the heavy moving average and heavy weighted moving average operators. The HOWMA operator is also extended using generalized and quasi-arithmetic means. An example concerning the foreign exchange rate between US dollars and Mexican pesos is also presented.