Solution-Based Synthesis of Submicrometer ZrB2 and ZrB2–TaB2

Zirconium diboride and a zirconium diboride/tantalum diboride mixture were synthesized by solution-based processing. Zirconium n -propoxide was refluxed with 2,4-pentanedione to form zirconium diketonate. This compound hydrolyzed in a controllable fashion to form a zirconia precursor. Boria and carbon precursors were formed via solution additions of phenol–formaldehyde and boric acid, respectively. Tantalum oxide precursors were formed similarly as zirconia precursors, in which tantalum ethoxide was used. Solutions were concentrated, dried, pyrolyzed (800°–1100°C, 2 h, flowing argon), and exposed to carbothermal reduction heat treatments (1150°–1800°C, 2 h, flowing argon). Spherical particles of 200–600 nm for pure ZrB₂ and ZrB₂–TaB₂ mixtures were formed.     

Characterization of surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

High-performance 0.3-μm-gate-length surface-undoped In_0.52 Al_0.48As/In_0.53Ga_0.47As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g_m/g₀ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-×150-μm-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB±1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures     

Allelochemicals in soil from no-tillage versus conventional-tillage wheat (Triticum aestivum) fields

Putative allelochemicals found in the soil of no-tillage and conventional-tillage wheat plots near Stillwater, Oklahoma, were obtained by a mild alkaline aqueous extraction procedure, bioassayed to determine their biological activity, purified, and analyzed with a capillary gas chromatography-mass spectrometry-data analysis system. The most significant inhibition was found in bioassays of extracts from soil collected immediately after harvest in June, July, and August. No-tillage soils produced significant inhibition during the rest of the year also. Mass spectrometry showed fatty acids as the most abundant compounds. However, when bioassayed authentic samples of the five free fatty acids showed no significant biological activity toward wheat.Journal Article No. 5650 of the Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma 74078.     

Laser-fabrication for solid-state electronics

Three fabrication procedures used in laser processing are described, and the characteristics that make ultraviolet laser sources useful in these techniques are examined. The use of UV lasers for VLSI metallization, ultrashallow doping, in-situ processing, and electronic packaging is discussed. Writing with a tightly focused beam is also considered, for both repair and fabrication purposes     

Digital passband filtering of megabaud transmitted data stream

A digital filter architecture for spectral shaping of a transmitted QAM signal is described. The technique requires that a binary representation for a finite sequence of multilevel symbols be interpreted as an address to memory that stores a pre-emphasised output that uniquely defines the desired transmitted transfer function. Design of a 6-34 Mbaud 16-QAM filter is illustrated.<>     

Silicon carbide PiN and merged PiN Schottky power diode models implemented in the Saber circuit simulator

Dynamic electrothermal circuit simulator models are developed for silicon carbide power diodes. The models accurately describe the temperature dependence of on-state characteristics and reverse-recovery switching waveforms. The models are verified for the temperature dependence of the on-state characteristics, and the di/dt, dv/dt, and temperature dependence of the reverse-recovery characteristics. The model results are presented for 1500 V SiC Merged PiN Schottky (MPS) diodes, 600 V Schottky diodes, and 5000 V SiC PiN diodes. The devices studied have current ratings from 0.25 A to 5 A and have different lifetimes resulting in different switching energy versus on-state voltage trade-offs. The devices are characterized using a previously reported test system specifically designed to emulate a wide range of application conditions by independently controlling the applied diode voltage, forward diode current, di/dt, and dv/dt at turn-off. A behavioral model of the test system is implemented to simulate and validate the models. The models are validated for a wide range of application conditions for which the diode could be used.     

A quantitative comparison of three Bode straight-line phaseapproximations for second-order, underdamped systems

Bode straight-line approximations are an extremely useful tool in the study of system frequency response. These approximations give good insight into the frequency variation of the amplitude and the phase of a system response without the use of computer simulation or complex calculations. Three Bode straight-line approximations to the phase of second-order, underdamped systems are subjected to quantitative error analysis. The magnitude of the maximum phase error and root-mean-square phase error are computed for each phase approximation as a function of the system damping coefficient. The results of the analysis indicates superiority of the little-known decade-fraction phase approximation technique     

In Search of a Common Core: A Content Analysis of Interventions to Promote Forgiveness.

This article reviews published methods for promoting forgiveness for a broad range of clinical issues. The review revealed a consensus among applied researchers regarding several broad types of interventions to promote forgiveness, namely, (a) defining forgiveness, (b) helping clients remember the hurt, (c) building empathy in clients for the perpetrator, (d) helping clients acknowledge their own past offenses, and (e) encouraging commitment to forgive the offender. Roughly half of the studies also prescribed interventions to help clients overcome unforgiveness (e.g., bitterness, vengefulness) without explicitly promoting forgiveness. Speculations about how to use forgiveness interventions in sensitive and client-supportive ways are advanced on the basis of the findings. (PsycINFO Database Record (c) 2011 APA, all rights reserved)