Photodetectors demystified

The author focuses on light detectors and their properties. A classification of detectors is given, and phototubes and photomultiplier-tubes are described. Just as the tubes were classified, so again a distinction can made between solid-state detectors that have an internal gain and detectors that have no internal gain. Detectors with internal gain are the photoconductive detectors, the avalanche photodiode, and the phototransistor; detectors without internal gain include the p-i-n and Schottky barrier photodiodes. A discussion on how to choose photodetectors for a given application is given. Applications of different photodetectors and future research are discussed     

Layered-Double-Hydroxide-Supported Pd(TPPTS)2Cl2: A New Heterogeneous Catalyst for Heck Arylation of Olefins

The Pd(TPPTS)₂Cl₂ (TPPTS: triphenylphosphine trisulfonate, sodium salt) complex is immobilized on layered double hydroxides by the ion-exchange method. This heterogeneous catalyst is successfully used in Heck arylation of olefins. The catalyst can be recycled several times with almost consistent activity.     

Development of process modeling methodology for flip chip on flex interconnections with non-conductive adhesives

This paper presents a comprehensive methodology to model the assembly process of flip chip on flex interconnections with non-conductive adhesives (NCAs). The methodology combines experimental techniques for material characterization, finite element modeling, and model validation. A non-conductive adhesive has been characterized using several techniques. A unique experimental technique has been developed to measure the cure shrinkage. A 2D axisymmetric finite element model is used for analysis of flip chip on flex package with the non-conductive adhesive (NCA), which takes into account assembly force, cure shrinkage, adhesive modulus buildup, removal of assembly force, and cooling down to room temperature. The relationship between the bump contact resistance and the bump pressure has been established through the development of a dedicated experimental setup, which uses a micro-force tester combined with a digital multimeter and a nano-voltmeter. The process modeling has been validated by comparing the predicted bump contact resistance value and the measured bump contact resistance value after assembly process. The approach developed in this paper can be used to provide guidelines with respect to adhesive material properties, assembly process parameters, and good reliability performances.     

Influence of alloying additives on the performance of commercial grade aluminium as galvanic anode in alkaline zincate solution for use in primary alkaline batteries

The self-corrosion of different grades of commercial aluminium such as 2S, 3S, 26S and 57S in 4 M NaOH containing 0.6 M ZnO has been determined by weight loss measurements. It is found that 26S and 57S aluminium exhibit negligible corrosion rates in the range 0.05–0.06 mg cm^–2 min^–1, which can be attributed to the formation of a zincate coating on the aluminium surface. The influence of zincating on the performance of binary and ternary alloys of 26S and 57S aluminium obtained by incorporating alloying elements such as zinc, indium, thallium, gallium and tin as galvanic anode in 4 M NaOH containing 0.6 M ZnO has been examined by studying self corrosion, steady state open circuit potential, galvanostatic polarization and anode efficiency. It is found that zincated ternary alloys of 26S and 57S aluminium containing zinc and indium can serve as good galvanic anodes in alkaline medium. AC impedance measurements and X-ray diffraction studies have been carried out to understand the nature of the film formed on the aluminium surface.     

Hysteresis parameter identification with limited experimental data

The Preisach operator and its variants have been successfully used in the modeling of hysteresis observed in ferromagnetic, magnetostrictive, and piezoelectric materials. However, in designing with these "smart" materials, one has to determine a density function for the Preisach operator by using the input-output behavior of the material at hand. In this paper, we describe a method for numerically determining an approximation of the density function when there is not enough experimental data to uniquely solve for the actual density function by Mayergoyz's method. We present theoretical justification for our method by establishing links to regularization methods for ill-posed problems. We also present numerical results where we estimate an approximate density function from data published in the literature for a magnetostrictive actuator and two electroactive polymers.     

An address-light, integrated MAC and routing protocol for wireless sensor networks

We propose an address-light, integrated MAC and routing protocol (abbreviated AIMRP) for wireless sensor networks (WSNs). Due to the broad spectrum of WSN applications, there is a need for protocol solutions optimized for specific application classes. AIMRP is proposed for WSNs deployed for detecting rare events which require prompt detection and response. AIMRP organizes the network into concentric tiers around the sink(s), and routes event reports by forwarding them from one tier to another, in the direction of (one of) the sink(s). AIMRP is address-light in that it does not employ unique per-node addressing, and integrated since the MAC control packets are also responsible for finding the next-hop node to relay the data, via an anycast query. For reducing the energy expenditure due to idle-listening, AIMRP provides a power-saving algorithm which requires absolutely no synchronization or information exchange. We evaluate AIMRP through analysis and simulations, and compare it with another MAC protocol proposed for WSNs, S-MAC. AIMRP outperforms S-MAC for event-detection applications, in terms of total average power consumption, while satisfying identical sensor-to-sink latency constraints.     

Soil moisture retrieval from AMSR-E

The Advanced Microwave Scanning Radiometer (AMSR-E) on the Earth Observing System (EOS) Aqua satellite was launched on May 4, 2002. The AMSR-E instrument provides a potentially improved soil moisture sensing capability over previous spaceborne radiometers such as the Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager due to its combination of low frequency and higher spatial resolution (approximately 60 km at 6.9 GHz). The AMSR-E soil moisture retrieval approach and its implementation are described in this paper. A postlaunch validation program is in progress that will provide evaluations of the retrieved soil moisture and enable improved hydrologic applications of the data. Key aspects of the validation program include assessments of the effects on retrieved soil moisture of variability in vegetation water content, surface temperature, and spatial heterogeneity. Examples of AMSR-E brightness temperature observations over land are shown from the first few months of instrument operation, indicating general features of global vegetation and soil moisture variability. The AMSR-E sensor calibration and extent of radio frequency interference are currently being assessed, to be followed by quantitative assessments of the soil moisture retrievals.     

A study of HF field strength variation in India and its prediction

Measured field strength data pertaining to several HF broadcast transmissions monitored in India during 1987-90 has been analysed to study solar activity, local time and seasonal variations in the field-strength. Values tend to saturate at high solar activity levels when sunspot numbers are beyond 120. Variations in field strength have also been studied with varying ratios of operational frequency to maximum usable frequency (f_op/MUF) and equivalent vertical frequency of the links. Based on this study a prediction method for HF field strength has been suggested for India. Comparison of values estimated using this technique has been made with actual measured field strength values for different HF transmissions for different months. This method is to be particularly suitable for field operators     

Selectivity dependence on the alloying element of carbon supported Pt-alloy catalysts in the hydrogenation of phenol

Single step vapour phase hydrogenation of phenol over Pt-M/C (M = Cr, V and Zr) alloy catalysts was investigated at atmospheric pressure and 200°C. The alloying element shows a significant effect on the product selectivities. While Pt-Cr/C and Pt-V/C catalysts are highly selective for hydrogenation of phenol to cyclohexanone, the Pt-Zr/C catalysts are predominantly selective to cyclohexanol.