Tellurium implantation in GaAs

Electron concentration and mobility profiles for Te implanted semi-insulating GaAs samples annealed with a reactively sputtered silicon nitride protective layer (or cap) have been measured as a function of the dose of implanted Te and the annealing temperature. Results of high dose implants into n-type epitaxial samples are essentially the same as those obtained using semi-insulating material from different suppliers. Samples in which Ga was implanted either before or after the implantation of Te exhibited essentially the same electron concentration and mobility profiles as those in which only Te was implanted. Attempts to introduce As vacancies by preannealing Te implanted samples without a cap at temperatures between 550 and 700°C also had no effect on the measured profiles. The use of an aluminum oxy-nitride cap resulted in about twice the doping efficiency and three times the maximum electron concentration than was obtained with a silicon nitride cap for doses of 1 × 10¹⁴ Te ions/cm².     

Stable carbon and oxygen isotopic analysis of atmospheric carbon monoxide using continuous-flow isotope ratio MS by isotope ratio monitoring of CO

We have developed a rapid and simple measurement system for both content and stable isotopic compositions (13C and 18O) of atmospheric CO, using continuous-flow isotope ratio mass spectrometry by simultaneously monitoring the CO+ ion currents at masses 28, 29, and 30. The analytical system consisted sequentially of a sample trapping port (liquid nitrogen temperature silica gel and molecular sieve 5A), a gas dryer, a CO purification column (molecular sieve 5A), a cryofocusing unit, and a final purification column using a GC capillary. Analytical precision of 0.2 per thousand for 13C and 0.4 per thousand for 18O can be realized for samples that contain as little as 300 pmol of CO within 40 min for one sample analysis. Analytical blanks associated with the method are less than 1 pmol. The extent of analytical error in delta13C due to mass-independent fractionation of oxygen in natural CO is estimated to be less than 0.3 per thousand. Based on this system, we report herein a kinetic isotopic effect during CO consumption in soil.     

XV. Yeast sequencing reports. Sequence analysis of a 9873 bp fragment of the left arm of yeast chromosome XV that contains the ARG8 and CDC33 genes,a putative riboflavin synthase beta chain gene,and four new open reading frames

The DNA sequence of a 9873 bp fragment located near the left telomere of chromosome XV has been determined. Sequence analysis reveals seven open reading frames. One is the ARG8 gene coding for N-acetylornithine aminotransferase. Another corresponds to CDC33, which codes for the initiation factor 4E or cap binding protein. The open reading frame AOE169 can be considered as the putative gene for the Saccharomyces cerevisiae riboflavin synthase beta chain, since its translation product shows strong homology with four prokaryotic riboflavin synthase beta chains. The nucleotide sequence reported here has been submitted to the EMBL data library under the Accession Number X84036.     

XV. Yeast sequencing reports. DNA sequence analysis of a 13 kbp fragment of the left arm of yeast chromosome XV containing seven new open reading frames

The sequence of a 13 kbp fragment located in the vicinity of the left telomere of chromosome XV (cosmid pEOA179) has been determined. Seven new open reading frames (ORFs) encoding polypeptides longer than 100 residues have been found (AOB629, AOA342, AOC231, AOE555, AOE236, AOA236 and AOE1045). Three of them show no identity with proteins deposited in the data banks. ORF AOB629 (629 amino acids) has some similarity with previously described ferric reductases from Saccharomyces cerevisiae and Schizosaccharomyces pombe. ORF AOA342 encodes a polypeptide reminiscent of dihydroflavonol-4-reductases from a number of plant species. AOE236 displays a high level of identity when compared with peroxisomal membrane proteins previously cloned from the methylotrophic yeast Candida boidinii. Finally, AOE1045 encodes a large protein (1045 residues) with some identity with a hypothetical 147 kDa protein identified during the sequencing of Caenorhabditis elegans chromosome 3. The complete nucleotide sequence of the 13 kbp fragment has been deposited at the EMBL data base (Accession Number Z48239).     

The low-affinity component of the glucose transport system in Saccharomyces cerevisiae is not due to passive diffusion

It has been claimed that the low-affinity component of glucose transport in Saccharomyces cerevisiae is due to passive diffusion of the sugar across the plasma membrane. We have investigated this possibility. For this purpose we have measured the permeability coefficient of hexoses in this organism. We have found that this coefficient is at least two to three orders of magnitude lower than required to account for the low-affinity component of glucose transport, and have concluded that this component is not due to passive diffusion.     

Announcement of coming events

Basic characteristics of ion beam lithography and its potential as a high resolution, high-speed lithography technique are described. The technique is thought to be one which allows delineation of fine patterns with a feature size less than 0.1 μm, rendering it increasingly important in micro- or nanometer devices.     

Classification of arid lands,including soil degradation and irrigated areas,based on vegetation and aridity indices

It is preferable to prepare internally consistent maps of arid regions on a global scale in order to understand the present conditions of arid regions, especially deserts and soil degradation areas. We attempted to delimit arid regions at a global scale by combining climate data, i.e. aridity index (AI), and vegetation data, i.e. vegetation index. The annual AI was estimated by the ratio of mean annual precipitation to mean annual potential evapotranspiration, using the Thornthwaite method. The long-term mean of yearly maximum normalized difference vegetation index (NDVI_ymx) was used as an indicator of the vegetation condition. Arid regions of the world were classified into four categories, namely A, severe deserts, where both aridity and vegetation indices are very small; G, semi-arid regions, where the vegetation index is proportionally related to the AI; I, irrigated areas and oases, where the vegetation is relatively abundant despite severe dryness; and S, soil degradation areas, where the vegetation is poor despite relatively humid conditions. The Sahel from Niger to Chad, the Sahel in Darfur, and the Ordos Plateau in China are within Category S. The standard deviation of NDVI_ymx is very small/large in severe deserts/semi-arid areas, respectively. Thus, the Sahara desert was clearly distinguished from the Sahel; the latter belongs to Category G and drought occurs frequently here. In Category S zones, the standard deviation of NDVI_ymx is relatively small compared with that within the Category G zone because the return rainfall does not seem to promptly restore productivity. Category S was divided into three subdivisions according to the degree of degradation, expressed by the ratio of the AI to vegetation index. Category G was also divided into four classes, according to degree of vegetation (or aridity). The distribution of Category S is comparable to the soil degradation areas mapped by Global Assessment of Human-Induced Soil Degradation (GLASOD) data. True deserts, where the standard deviation of NDVI_ymx is very small, were selected from the ‘severe desert’ group. Desert areas were classified as true deserts, severe deserts, grassland deserts (Category G), and soil degradation deserts (Category S).     

Removal of phenolic endocrine disruptors by Portulaca oleracea

Portulaca oleracea, a garden plant prevalent from spring to autumn in Japan, showed the ability to efficiently remove from water bisphenol A (BPA), which is well known as an endocrine disrupting compound (EDC) having estrogenic properties. In water culture, 50 muM BPA was almost completely removed within 24 h when the ratio of whole plant weight to the water volume was set up at 1 g to 25 ml. The estrogenic activity of the water decreased in parallel with the elimination of BPA. This plant also rapidly removed other EDCs having a phenol group including octylphenol (OP), nonylphenol (NP), 2,4-dichlorophenol (2,4-DCP) and 17beta-estradiol and, thereby, removed the endocrine disrupting activities. In addition, the ability of P. oleracea to remove BPA was not affected by BPA concentration (up to 250 microM), by cultivation in the dark, by temperatures ranging from 15 degrees C to 30 degrees C, or by pH ranging from 4 to 7. Moreover, the ability of P. oleracea to individually remove BPA, NP, and OP was the same as when they were all present. These results suggest that P. oleracea is a promising material for practical phytoremediation of landfill leachates and industrial wastewater contaminated with the tested EDCs.     

Microbeam line with 1.5 MeV helium ions and protons at Osaka

A microprobe for Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) measurements has been realized by focusing 1.5 MeV helium-ion or proton beams with a demagnification system consisting of piezo-driven objective slits and a magnetic quadrupole doublet. Minimum beam spot sizes of 1.3 × 2.2 μm² for helium ions and 2.2 × 4.0 μm² for protons have been achieved. The factors which may limit the minimum spot size are discussed using a Monte Carlo simulation procedure. Rutherford backscattering image mapping of 3-dimensional structures is demonstrated.