Applications of electron paramagnetic resonance to studies of defects in insulators and semiconductors

Electron paramagnetic resonance (EPR) which is the absorption of electromagnetic waves in the microwave frequency domain has been used for many years to study magnetic dipoles in crystals subjected to magnetic fields. These magnetic dipoles arise from electrons in the material whose intrinsic spin is exposed due to processes such as doping with transition metal ions, doping with ions whose spin is not locked up with chemical bonding and irradiation with bond breaking energy. The sensitivity of the EPR technique depends on such experimental parameters as, incident microwave power, size of the sample, quality of the microwave cavity, number of paramagnetic spins participating in the absorption, width of the EPR resonance line, temperature of the sample and relaxation time of the spin system to the lattice. The experimental spectrum is described by parameters which by the application of basic quantum mechanics can be related to properties of the wave function of the electron spin in the crystal environment such as bonding directions to neighboring ions in the crystal lattice. Some examples of this analysis will be presented to show how EPR is used in the study of defects in Si and SiO₂.     

Australian SKA Pathfinder: A High-Dynamic Range Wide-Field of View Survey Telescope

The Australia SKA Pathfinder (ASKAP) is a new telescope under development as a world-class high-dynamic-range wide-field-of-view survey instrument. It will utilize focal plane phased array feeds on the 36 12-m antennas that will compose the array. The large amounts of data present a huge computing challenge, and ASKAP will store data products in an archive after near real-time pipeline processing. This powerful instrument will be deployed at a new radio-quiet observatory, the Murchison Radio-astronomy Observatory in the midwest region of Western Australia, to enable sensitive surveys of the entire sky to address some of the big questions in contemporary physics. As a pathfinder for the SKA, ASKAP will demonstrate field of view enhancement and computing/processing technology as well as the operation of a large-scale radio array in a remote and radio-quiet region of Australia.     

Landsat-5 bumper-mode geometric correction

The Landsat-5 Thematic Mapper (TM) scan mirror was switched from its primary operating mode to a backup mode in early 2002 in order to overcome internal synchronization problems arising from long-term wear of the scan mirror mechanism. The backup bumper mode of operation removes the constraints on scan start and stop angles enforced in the primary scan angle monitor operating mode, requiring additional geometric calibration effort to monitor the active scan angles. It also eliminates scan timing telemetry used to correct the TM scan geometry. These differences require changes to the geometric correction algorithms used to process TM data. A mathematical model of the scan mirror's behavior when operating in bumper mode was developed. This model includes a set of key timing parameters that characterize the time-varying behavior of the scan mirror bumpers. To simplify the implementation of the bumper-mode model, the bumper timing parameters were recast in terms of the calibration and telemetry data items used to process normal TM imagery. The resulting geometric performance, evaluated over 18 months of bumper-mode operations, though slightly reduced from that achievable in the primary operating mode, is still within the Landsat specifications when the data are processed with the most up-to-date calibration parameters.     

A Test Methodology for High Performance MCMs

Satellite and avionics applications represent an ideal application for the tremendous performance, cost, space, andreliability benefits of MCMs. These advantages are only realized,however, if accompanied by an efficient test strategy whichverifies defect-free fabrication. This paper describes a methodology developed to test high performance VLSI CMOS ICs thathave been mounted onto a multi-chip silicon substrate. A teststrategy, which addresses testing from the wafer level through tothe populated substrate, is detailed. This strategy uses acombination of LSSD, AC LSSD-On-Chip Self Test, Deterministic Delay Fault Testing, and Design for Partitionability to ensure high testquality at a reasonable cost. The methodology is then contrastedto alternative approaches.     

Efficiency of plasticization of PVC by higher-order di-alkyl phthalates and survey of mathematical models for prediction of polymer/diluent blend Tg's

Presently, a suitable theory to predict the T_g vs. composition relationship for a given polymer-plasticizer blend, based on detailed molecular structure and molecular energitics considerations, is not available. In particular, the plasticizer efficiency parameter, k, which is uniquely defined at low-to-moderate diluent concentrations, and is an essential variable in the Mauritz-Storey theory of the diffusion of large molecules in amorphous polymers in the rubbery state, must always be determined by experiment. In this work, k was determined by DSC for PVC that was plasticized over a range of concentrations with a number of higher branched and linear di-alkyl phthalates. The results will be used in our plasticizer diffusion theory as well as provide guidance in the future development of a general mathematical model for predicting k. It was seen that k decreased with increasing molecular weight for both the linear and branched phthalates. For a given molecular weight, the branched phthalates have higher k values than the linear structures. These results have been rationalized in terms of the additional free volume created by the inefficiency of packing polymer chains about these large penetrant molecules. The DSC scans also implied an increasing degree of microstructural heterogeneity with increasing plasticizer concentration. Finally, relationships between plasticizer diffusion coefficient in the rubbery state and the plasticized T_g were established for low-to-moderate diluent concentration for three of the plasticizers studied by utilizing experimental diffusion data from our earlier work on these systems.     

Activity of Fluorine‐Containing Analogues of WC‐9 and Structurally Related Analogues against Two Intracellular Parasites: Trypanosoma cruzi and Toxoplasma gondii

Two obligate intracellular parasites, Trypanosoma cruzi, the agent of Chagas disease, and Toxoplasma gondii, an agent of toxoplasmosis, upregulate the mevalonate pathway of their host cells upon infection, which suggests that this host pathway could be a potential drug target. In this work, a number of compounds structurally related to WC‐9 (4‐phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, were designed, synthesized, and evaluated for their effect on T. cruzi and T. gondii growth in tissue culture cells. Two fluorine‐containing derivatives, the 3‐(3‐fluorophenoxy)‐ and 3‐(4‐fluorophenoxy)phenoxyethyl thiocyanates, exhibited half‐maximal effective concentration (EC₅₀) values of 1.6 and 4.9 μm , respectively, against tachyzoites of T. gondii, whereas they showed similar potency to WC‐9 against intracellular T. cruzi (EC₅₀ values of 5.4 and 5.7 μm , respectively). In addition, 2‐[3‐ (phenoxy)phenoxyethylthio]ethyl‐1,1‐bisphosphonate, which is a hybrid inhibitor containing 3‐phenoxyphenoxy and bisphosphonate groups, has activity against T. gondii proliferation at sub‐micromolar levels (EC₅₀=0.7 μm ), which suggests a combined inhibitory effect of the two functional groups.     

Carbonaceous nanomaterials for the enhancement of TiO2 photocatalysis

Semiconductor photocatalysis has important applications such as achieving sustainable energy generation and treating environmental pollution. TiO₂ has been the most widely-researched photocatalyst, but suffers from low efficiency and narrow light response range. Combining TiO₂ with carbonaceous nanomaterials is being increasingly investigated as a means to increase photocatalytic activity, and demonstrations of enhancement are plentiful. This review surveys the literature and highlights recent progress in the development of nanocarbon-TiO₂ photocatalysts, covering activated carbon, carbon doping, carbon nanotubes, [60]-fullerenes, graphene, thin layer carbon coating, nanometric carbon black and more recently developed morphologies. Mechanisms of enhancement, synthesis routes and future applications are summarised and discussed. New insight and enhanced photocatalytic activity may be provided by novel nanocarbon-TiO₂ systems. Ongoing challenges and possible new directions are outlined.     

Indirect field-oriented control of an induction motor in thefield-weakening region

A self-organized field-oriented induction machine controller that addresses problems encountered in the field-weakening region is presented. The field-oriented controller (FOC) is based on model reference adaptive principles but relies on samples of the state of the machine to determine control inputs. The proposed controller is compared with other approaches to field-weakening operation, and the advantages and limitations of each are discussed. Experimental results are presented for the classical and the self-organized approaches to field-weakening operation