Detection of microfracture processes in composite laminates by thermo-acoustic emission

The damage process in composite laminates subjected to cryogenic cooling was monitored employing a thermo-acoustic emission (AE) technique. The thermo-AE signals processed with a short-time Fourier transform could be classified into three different types which were correlated with individual microfracture processes. In the initial stage of cryogenic cooling, very strong AE signals with low and high frequency bands were dominantly detected showing that large cracks accompanying fiber breakages were developed mainly. With an increase in the cooling time, weak emissions with low frequency bands became prevalent indicating the propagation of microfractures in the matrix and/or fiber-matrix interface. Similar types of AE signals, however, having weak amplitudes, were also observed for the cryogenically-treated specimens during thermal heating and cooling load cycles. Thus, analysis of thermo-AE behavior through the thermal load cycle led to the nondestructive evaluation for the cryogenic damage of composites.     

A partially insulated field-effect transistor (PiFET) as a candidate for scaled transistors

Highly manufacturable partially insulated field-effect transistors (PiFETs) were fabricated by using Si-SiGe epitaxial growth and selective SiGe etch process. Owing to these technologies, pseudo-silicon-on-insulator (SOI) structures, partially insulating oxide (PiOX) under source/drain (PUSD) and PiOX under channel (PUC), could be easily realized with excellent structural and process advantages. We are demonstrating their preliminary characteristics and properties. Especially, in the PUSD PiFET, junction capacitance, leakage current, and DIBL in bulk devices could be reduced and the floating body problem in SOI devices was also cleared without any area penalty. Thus, this PiFET structure can be a promising candidate for the future DRAM cell transistor.     

Reaction of TiO2-Al-C in the Combustion Synthesis of TiC-Al2O3 Composite

Reaction mechanisms and the thermal structure in the reaction zone during the combustion of TiO₂, Al, and C to form TiC-Al₂O₃ composite were studied. The reaction between each component was studied and the combustion wave structure and real-time temperature profile were analyzed. Titanium aluminide species, present in the aluminothermic reduction of TiO₂, did not occur in the presence of C, because of the high thermodynamic stability of TiC. The activation energies of the exothermic reaction in the 3TiO₂-4Al-3C system were determined by DSC analysis. This suggests that the combustion reaction is mainly controlled by carbon diffusion through solid TiC. The combustion wave was observed to propagate in an unstable mode. The temperature profiles in the reaction zone were of the sawtooth type and the products were of layered structure.     

Excitation mechanisms of multiple Er3+ sites in Er-implanted GaN

Site-selective photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies carried out at 6K on the ∼1540 nm ⁴I_13/2→⁴I_15/2 emissions of Er³⁺ in Er-implanted GaN have revealed the existence of four different Er³⁺ sites and associated PL spectra in this semiconductor. Three of these four sites are excited by below-gap, impurity- or defect-related absorption bands, with subsequent nonradiative energy transfer to the Er³⁺ 4f electrons; a fourth site is excited by direct Er³⁺ 4f shell absorption. PLE spectra obtained by selectively detecting Er³⁺ PL from each of the three sites pumped by broad below-gap absorption bands are compared with the PLE spectra of broad PL bands attributed to implantation damage-induced defects in the Er-implanted GaN. This comparison enables us to distinguish broad-band, below-gap optical excitation processes for Er³⁺ emission that are attributable to (1) absorption due to implantation damage-induced defects; (2) absorption due to defects or impurities characteristic of the as-grown GaN film; and (3) an Er-specific absorption band just below the band gap which may involve the formation of an Er-related isoelectronic trap. The two sites excited by impurity-or defect-related absorption bands are also strongly pumped by above-gap excitation, while the sites pumped by the Er-related trap and direct 4f shell absorption are not. This observation indicates that excitation of Er³⁺ luminescence in crystalline semiconductor hosts by either optical or electrical injection of electron-hole pairs is dominated by trap-mediated carrier capture and energy transfer processes. These trap-mediated processes may also control the thermal quenching of Er³⁺ emission in semiconductors.     

Testing Hypotheses Regarding the Causes of Comorbidity: Examining the Underlying Deficits of Comorbid Disorders.

The authors examined the validity of a method commonly used to test alternative hypotheses regarding the causes of comorbidity: the examination of underlying deficits of comorbid disorders. The authors simulated data in which the true causes of comorbidity were known, then compared the patterns of underlying deficits of the comorbid disorders found in the simulated data with the predicted results. The method of examining the underlying deficits of comorbid disorders could distinguish between several comorbidity models, including those that could not be distinguished well using other methods. The ability to distinguish the correct model decreased as the sample size and the correlation between the underlying deficits and the symptom scores decreased, suggesting that the issue of power should be considered carefully. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bit-error probability for maximum-likelihood decoding of linearblock codes and related soft-decision decoding methods

In this correspondence, the bit-error probability P_b for maximum-likelihood decoding of binary linear block codes is investigated. The contribution P_b(j) of each information bit j to P_b is considered and an upper bound on P_b(j) is derived. For randomly generated codes, it is shown that the conventional approximation at high SNR P_b≈(d_H/N).P_s, where P_s represents the block error probability, holds for systematic encoding only. Also systematic encoding provides the minimum P_b when the inverse mapping corresponding to the generator matrix of the code is used to retrieve the information sequence. The bit-error performances corresponding to other generator matrix forms are also evaluated. Although derived for codes with a generator matrix randomly generated, these results are shown to provide good approximations for codes used in practice. Finally, for soft-decision decoding methods which require a generator matrix with a particular structure such as trellis decoding, multistage decoding, or algebraic-based soft-decision decoding, equivalent schemes that reduce the bit-error probability are discussed. Although the gains achieved at practical bit-error rates are only a fraction of a decibel, they remain meaningful as they are of the same orders as the error performance differences between optimum and suboptimum decodings. Most importantly, these gains are free as they are achieved with no or little additional circuitry which is transparent to the conventional implementation     

A study on autobalancing of a casing oscillator using feedback control

The casing oscillator used for basic construction of buildings, factories, and bridges is a construction machine which rotates and rolls the casing to insert it into the ground. It is very important that the casing is retained at a perpendicular position to sea level regardless of the slope of ground. In this paper, we present a new casing oscillator that does need not to be level to the ground for the casing insertion to work. The kinematic analysis for work space of a casing oscillator is presented and carried out with autobalancing of the casing oscillator using feedback control.     

An 18-mW 2.5-GHz/900-MHz BiCMOS dual frequency synthesizer with<10-Hz RF carrier resolution

A 2.5-GHz/900-MHz dual fractional-N/integer-N frequency synthesizer is implemented in 0.35-μm 25-GHz BiCMOS. A ΔΣ fractional-N synthesizer is employed for RF channels to have agile switching, low in-band noise, and fine frequency resolution. Implementing two synthesizers with an on-chip ΔΣ modulator in a small package is challenging since the modulator induces substantial digital noise. In this work, several design aspects regarding noise coupling are considered. The fractional-N synthesizer offers less than 10-Hz frequency resolution having the in-band noise contribution of -88 dBc/Hz for 2.47-GHz output frequency and -98 dBc/Hz for 1.15-GHz output frequency, both measured at 20-kHz offset frequency. The prototype dual synthesizer consumes 18 mW with 2.6-V supply     

Channel-forming activity of immunoaffinity-purified connexin32 in single phospholipid membranes

Connexin32, a member of the family of proteins that forms gap junction channels between cells, was immunoaffinity-purified from rat liver using a monoclonal antibody, under nondenaturing conditions and reconstituted into unilamellar phospholipid liposomes and bilayers. Gel-filtration studies indicate that the connexin32 is purified predominantly in structures of a size consistent with that of single hemichannels and too small to be junctional channels (dimers of hemichannels). Purified connexin formed channels permeable to sucrose and to Lucifer Yellow. The permeability was reversibly reduced by acidic pH and unaffected by several agents that modulate coupling between cells. Modeling of the distribution of the permeability in the liposomes indicates that it is mediated by connexin structures that distribute among the liposomes as single hemichannels. Bilayer recordings of the purified connexin show high conductance channels with asymmetric voltage sensitivity. The results show that immunopurified connexin32 can form channels, in single phospholipid membranes, that have permeability similar to that of gap junction channels and thus can be utilized in studies of permeability and its regulation to investigate its role in normal physiological function, development, and disease.