Interface control and photovoltaic properties of n-type silicon/metal junction by organic dye

The electronic parameters and photovoltaic properties of the Au/methylene blue/n-Si diodes were investigated by current-voltage and capacitance-conductance-frequency techniques. The diode exhibits a non-ideal behavior due the series resistance, organic layer and oxide layer. The barrier height (1.04 eV) of the Au/methylene blue/n-Si is higher than that of Au/n-Si Schottky diode (0.83 eV) due to an excess barrier formed by organic layer. The interface state density of the diode was determined using a conductance technique and was found to be 3.25 × 10¹² eV⁻¹ cm⁻². The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.23 V and short-circuit current I_sc of 20.8 μA under 100 mW/cm². It is evaluated that Au/methylene blue/n-Si is an organic-on-inorganic photodiode with the obtained electronic parameters and methylene blue organic dye controls the interface and electrical properties of conventional metal/n-type silicon junction.     

Controlling of electronic parameters of GaAs Schottky diode by poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic interlayer

The electronic properties of metal-organic semiconductor-inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current-voltage and capacitance-voltage methods. The Au/PEDOT/n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/n-GaAs/In (0.85 eV) and Au/n-GaAs/In Schottky diodes. The decrease in barrier height of Au/n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol).     

Fiber Quality Evaluation of Pakistan’s Locally Developed Cotton Varieties for Yarn Manufacturing

This paper discusses relation between fiber quality parameters and yarn quality, presenting results of the quality assessment of Pakistan’s five popular cotton varieties. Abadgar-901 was found to have highest effective length followed by Tarzen-1 when compared to other fibers studied and the Sattari showed the least effective length. Whereas, Tarzen-1 showed highest tenacity, Sindh-1 was second to that, yet Nayab-78 showed the least strength of the studied cotton fibers. Further, it was also found that except Nayab-78, all the other cotton varieties were found to have fineness value of premium cotton standards, however, Nayab proved to be a coarse fiber, Sindh-1 was finest fiber of them all. Moreover, Sattari was found to be the whitest in color when measured for CIE and Berger whiteness index, Nayab-78 followed it just after and the Abadgar proved to be the least white compared to the studied cotton varieties.     

Microsatellite instability in gynecological sarcomas and in hMSH2 mutant uterine sarcoma cell lines defective in mismatch repair activity

We have examined a panel of gynecological sarcomas for microsatellite instability. The genomic DNA from 11 of 44 sarcomas contained somatic alterations in the lengths of one or more di-, tri-, tetra-, or pentanucleotide microsatellite sequence markers, and 6 of these cases had alterations in two or more markers. In addition, di-, tri-, and tetranucleotide microsatellites were found to be highly unstable in single cell clones of two cell lines derived from a uterine mixed mesodermal tumor. Since such instability is characteristic of cells defective in postreplication mismatch repair, we examined mismatch repair activity in extracts made from these lines. Both extracts were repair deficient, while an extract of another gynecological sarcoma cell line not exhibiting microsatellite instability was repair proficient. The repair deficiency was complemented by a colon tumor cell extract that was defective in the hMLH1 protein but not by an extract defective in hMSH2 protein. This suggested that the defect in the uterine sarcoma line could be in hMSH2. Subsequent analysis of the gene revealed a 2-bp deletion in exon 14, leading to premature truncation of the hMSH2 protein at codon 796 and no detectable wild-type gene present. These data suggest that the microsatellite instability observed in these cell lines, and possibly in a significant number of gynecological sarcomas, is due to defective postreplication mismatch repair. There was no apparent correlation with microsatellite instability and clinical outcome.     

Mutation of MSH3 in endometrial cancer and evidence for its functional role in heteroduplex repair

Many human tumours have length alterations in repetitive sequence elements. Although this microsatellite instability has been attributed to mutations in four DNA mismatch repair genes in hereditary nonpolyposis colorectal cancer (HNPCC) kindreds, many sporadic tumours exhibit instability but no detectable mutations in these genes. It is therefore of interest to identify other genes that contribute to this instability. In yeast, mutations in several genes, including RTH and MSH3, cause microsatellite instability. Thus, we screened 16 endometrial carcinomas with microsatellite instability for alterations in FEN1 (the human homolog of RTH) and in MSH3 (refs 12-14). Although we found no FEN1 mutations, a frameshift mutation in MSH3 was observed in an endometrial carcinoma and in an endometrial carcinoma cell line. Extracts of the cell line were deficient in repair of DNA substrates containing mismatches or extra nucleotides. Introducing chromosome 5, encoding the MSH3 gene, into the mutant cell line increased the stability of some but not all microsatellites. Extracts of these cells repaired certain substrates containing extra nucleotides, but were deficient in repair of those containing mismatches or other extra nucleotides. A subsequent search revealed a second gene mutation in HHUA cells, a missense mutation in the MSH6 gene. Together the data suggest that the MSH3 gene encodes a product that functions in repair of some but not all pre-mutational intermediates, its mutation in tumours can result in genomic instability and, as in yeast, MSH3 and MSH6 are partially redundant for mismatch repair.     

Correction of hypermutability, N-methyl-N'-nitro-N-nitrosoguanidine resistance, and defective DNA mismatch repair by introducing chromosome 2 into human tumor cells with mutations in MSH2 and MSH6

The human DNA mismatch repair genes hMSH2 and hMSH6 encode the proteins that, together, bind to mismatches to initiate repair of replication errors. Human tumor cells containing mutations in these genes have strongly elevated mutation rates in selectable genes and at microsatellite loci, although mutations in these genes cause somewhat different mutator phenotypes. These cells are also resistant to killing by certain drugs and are defective in mismatch repair. Because the elevated mutation rates in these cells may lead to mutations in additional genes that are causally related to the other defects, here we attempt to establish a cause-effect relationship between the hMSH2 and hMSH6 gene mutations and the observed phenotypes. The endometrial tumor cell line HEC59 contains mutations in both alleles of hMSH2. The colon tumor cell line HCT15 contains mutations in hMSH6 and also has a sequence change in a conserved region of the coding sequence for DNA polymerase delta, a replicative DNA polymerase. We introduced human chromosome 2 containing the wild-type hMSH2 and hMSH6 genes into HEC59 and HCT15 cells. Introduction of chromosome 2 to HEC59 cells restored microsatellite stability, sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine treatment, and mismatch repair activity. Transfer of chromosome 2 to HCT15 cells also reduced the mutation rate at the HPRT locus and restored sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine treatment and mismatch repair activity. The results demonstrate that the observed defects are causally related to mutations in genes on chromosome 2, probably hMSH2 or hMSH6, but are not related to sequence changes in other genes, including the gene encoding DNA polymerase delta.     

Wavelet based robust sub-band features for phoneme recognition

Wavelet transform has been found to be an effective tool for the time-frequency analysis of non-stationary and quasi-stationary signals. Recent years have seen wavelet transform being used for feature extraction in speech recognition applications. In the paper a sub-band feature extraction technique based on an admissible wavelet transform is proposed and the features are modified to make them robust to additive white Gaussian noise. The performance of this system is compared with the conventional mel frequency cepstral coefficients (MFCC) under various signal to noise ratios. The recognition performance based on the eight sub-band features is found to be superior under the noisy conditions compared with MFCC features.     

Thermal diffusivity of liquids determined by flash heating of a three-layered cell

An investigation of the applicability of the flash heating of a three-layered cell for determining the thermal diffusivity of a central liquid layer at temperatures between its melting and boiling points is described. Two different cell designs were developed. In one, the outside layers were brazed to a ring-shaped central spacer; in the other, bolted flanges held the outside layers against a central spacer. Test units were fabricated from type 304 stainless steel. Thermal diffusivity results for water obtained with two brazed cells and one bolted cell were all within ±1% of standard reference values. Results obtained with a high temperature salt (Hitec) with two brazed cells were within ±2.5% of each other over the temperature range of 149–427°C. In contrast, bolted cell measurements were inconsistent.     

Gravity and configurational energy induced microstructural changes in liquid phase sintering

Liquid phase sintered materials consist of interconnected crystalline grains in a homogeneous matrix phase that forms the liquid at high temperatures. The dihedral angle, grain size, and volume fraction of solid determine the energy of the system. Energy minimization is possible by the separation of phases due to density differences. This explains why some materials exhibit settling or distortion due to gravity during liquid phase sintering. Experiments performed with W-Ni-Fe heavy alloys are used to measure the microstructural changesvs position that occur in liquid phase sintering under normal gravity. The experimentally observed segregation is less than the calculated equilibrium seg-regation due to the retarding effect from the rigid solid skeleton formed during sintering. These re-sults improve our understanding of microstructure, mechanical properties, component shape, and dimensional stability benefits that may be realized from low gravity sintering. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermo-dynamic Data Committee and the Material Processing Committee.     

Comparative response of mixed cultures of bacteria and virus to ozonation

The ozone disinfection studies were performed using five cultures of organisms: i.e. a yeast Candida parapsilosis. an acid-fast organism Mycobacterium fortuitum, Salmonella typhimurium, Escherichia coli and poliovirus to determine their relative resistance to ozone in a given completely mixed continuous flow system. Studies were conducted in both clean aqueous system and secondary wastewater effluent. Their resistance to ozone in both cases was observed in the following order: M. fortuitum > poliovirus type 1 Mahoney strain >C. parapsilosis > E. coli > S. typhinturium.