Search

Israel phosphate-bearing rock is shown to contain in addition to calcite another form of carbonate, which dissociates irreversibly below the dissociation temperature of calcite. The phenomenon can be explained on the assumption that the calcium oxide produced on dissociation of the second form becomes an integral part of the apatite lattice. It is therefore plausible to suggest that the second form is either finely dispersed throughout the apatite or itself constitutes part of the apatite lattice.

The following terminal, carbonyl-conjugated alkynes were reacted with N-bromosuccinimide (NBS) and N-iodosuccinimide (NIS) in MeOH/H2SO4 to give dibromo and diiodo acetals in the indicated yields: ...

The following terminal, carbonyl-conjugated alkynes were reacted with N-bromosuccinimide (NBS) and N-iodosuccinimide (NIS) in MeOH/H2SO4 to give dibromo and diiodo acetals in the indicated yields: ...

This paper deals with the field use of a multi-technique electrochemical corrosion monitoring system, to differentiate between general and localized corrosion activity in a water injection system. The technology was used to identify the corrosion mechanism that resulted in failures in the system, showing benefit over and above 'conventional' corrosion monitoring techniques (e.g. Linear Polarisation Resistance, LPR, and coupons) that had failed to identify the corrosion risk. Subsequent to identifying the type of corrosion in the system, the multi-technique approach aided the identification of a suitable corrosion inhibitor to mitigate the corrosion. The findings from the study have been confirmed by weight loss coupon data and 'conventional' monitoring techniques after implementation of a treatment program using the optimized corrosion inhibitor formulation.

Large scale digital integrated circuits containing over 6000 active devices (1 μm MESFETs and Schottky diodes) have recently been achieved in GaAs Schottky Diode FET Logic. The planar, ion implanted process used to fabricate these circuits results in very uniform device properties because of the excellent control of critical device interfaces. The present status of LSI GaAs ICs is reviewed, including a description of the performance of an 8×8 bit multiplier LSI circuit. VLSI circuit prospects and the applicability of new high speed GaAs active devices for VLSI application in GaAs are considered.

A sensitive search has been made in Drosophila melanogaster DNA for short repetitive sequences interspersed with single copy sequences. Five kinds of measurements all yield the conclusion that there are few short repetitive sequences in this genome: 1) Comparison of the kinetics of reassociation of short (360 nucleotide) and long (1,830 nucleotide) fragments of DNA; 2) reassociation kinetics of long fragments (2,200 nucleotide) with an excess of short (390 short nucleotide) fragments; 3) measurement of the size of S1 nuclease resistant reassociated repeated sequences; 4) measurement of the hyperchromicity of reassociated repetitive fragments as a function of length; 5) direct assay by kinetics of reassociation of the amount of single copy sequence present on 1,200 nucleotide long fragments which also contain repetitive sequences.

Structural relationships within a family of long repeated DNA sequences have been determined by molecular cloning of individual family members. About half of the family members are truncated at one end. There is a short, tandemly repeating region flanked by direct repeats associated with truncation. Recombination in a region near the tandemly repeating segment has apparently generated much of the diversity in this family.

Octopine has been detected in normal tobacco leaf and stem tissue, normal sunflower stem tissue, pinto bean leaves, and normal tobacco callus tissue in culture. Octopine was identified in extracts by means of electrophoresis and chromatography in several solvent systems. Tobacco and sunflower tumor lines induced by various strains of Agrobacterium tumefaciens were found to contain from 1 to 240 times as much octopine as the normal plant tissues examined. Several strains of A. tumefaciens produce undifferentiated tobacco tumors containing high levels of octopine, but produce undifferentiated sunflower tumors containing normal levels of octopine and high levels of arginine. Further, strain CGIC of A. tumefaciens produces in tobacco an undifferentiated tumor which contains high levels of octopine and a teratoma which contains normal levels of octopine. This evidence shows that there is no consistent relationship between the causative strain of A. tumefaciens and the octopine content of the resulting crown gall tumor.

The organization of repetitive and single copy DNA sequences in sea urchin DNA has been examined with the single strand specific nuclease S1 from Aspergillus. Conditions and levels of enzyme were established so that single strand DNA was effectively digested while reassociated divergent repetitive duplexes remained enzyme resistant. About 25% of sea urchin DNA reassociates with repetitive kinetics to form S1 resistant duplexes of two distinct size classes derived from long and short repetitive sequences in the sea urchin genome. Fragments 2,000 nucleotides long were reassociated to Cot 20 and subjected to controlled digestion with S1 nuclease. About half of the resistant duplexes (13% of the DNA) are short, with a mode size of about 300 nucleotide pairs. This class exhibits significant sequence divergence, and principally consists of repetitive sequences which were interspersed with single copy sequences. About one-third of the long duplexes (4% of the DNA) are reduced in size after extensive S1 nuclease digestion to about 300 nucleotide pairs. About two-thirds of the long resistant duplexes (8% of the DNA) remains long after extensive SI nuclease digestion. These long reassociated duplexes are precisely base paired. The short duplexes are imprecisely paired with a melting temperature about 9 degrees C below that of precisely paired duplexes of the same length. The relationship between length of repetitive duplex and precision of repetition is confirmed by an independent method and has been observed in the DNA of a number of species over a wide phylogenetic area.

Extensive studies with pea, tomato, and barley failed to confirm the evidence presented by previous investigators for integration or replication of exogenously applied bacterial DNA in these plants. Labeled DNA of buoyant density in CsCl intermediate between that of high density donor bacterial DNA and of plant DNA was never observed with axenic plants. Intermediate peaks, similar to those used as evidence for recombination by earlier investigators, were observed only when the plants were contaminated with bacteria. Plant DNA prepared by a published procedure [Ledoux, L. & Huart, R. (1969) J. Mol. Biol. 43, 243-262] was found to be contaminated with unidentified impurities. Such DNA was partially protected from the action of DNase and produced aberrant banding patterns in CsCl after shearing. Much of the published evidence for integration of foreign DNA in plants is based upon experiments with plant DNA prepared by this procedure. We conclude that contamination is the likely explanation for what has been interpreted as evidence for integration.

A discussion is presented of fabrication technologies for manufacturing GaAs devices. Advantages and drawbacks of heterojunction devices are outlined. Areas of concern in GaAs production lines are also examined. The discussion covers the depletion-mode metal-semiconductor field-effect transistor (D-MESFET), the enhancement-mode MESFET (E-MESFET), and the high-electron-mobility transistor (HEMT).

The electron spin resonance spectrum of Fremy's salt—17O, [(SO3)2N17O]K2—has been studied in aqueous solution. Twelve out of the expected 18 17O satellites were clearly resolved. The measured hyperfine coupling constant for 17O, aO, is 20.7±0.2 G. Variations in linewidth between the 17O satellites were observed and interpreted quantitatively in terms of relaxation by modulation of the anisotropic dipolar and g tensors. The relaxation rate is mainly determined by interactions involving the magnetic moment of 17O. The terms in the expression for the linewidth that depend on mN are small, except for a cross term EmNmO. Analysis of the results combined with a knowledge of the sign of the g‐tensor anisotropy allowed the determination of the signs of aN and aO, which are positive and negative, respectively.

The electron spin resonance spectrum of 17O labeled parabenzosemiquinone in aqueous ethanol solutions has been examined. The hyperfine splitting constant due to 17O, a0, was 9.02±0.02 G. The splitting constant has the same sign as Δg, the anisotropy of the g tensor, and since Δg is negative, the sign of a0 is also negative. Taking into account the fact that 17O has a negative gyromagnetic ratio, the sign found for a0 implies that the net spin polarization at the 17O nucleus is the same as that in the radical.Marked variations in linewidth occur between the different components of the 17O hyperfine structure due to modulation through molecular tumbling of the anisotropic dipolar and g‐tensor interactions. These variations are quantitatively accounted for by the general theory of ESR linewidths due to Freed and Fraenkel. Analysis of the spectrum gives | Δg | = 0.0029, and a correlation time for the tumbling of the molecule of 9.4×10−11 sec.

It is shown that in the decomposition of triethylaluminium and diethylaluminium halide by titanium chlorides no free ethyl radicals are liberated. Instead ethane is evolved through intramolecular abstraction of hydrogen by one ethyl group from a neighbouring ethyl group. The molecule then rearranges to give a C 4 H 9 AlCl radical which in conjunction with the titanium chloride appears to catalyse the polymerization of α-olefines.

The effects of ionizing radiation in large-geometry MOS structures were studied by use of internal photoemission techniques. Barrier heights at both the silicon-silicon dioxide and the silicon dioxide-metal (chromium and aluminum) interfaces were measured before and after irradiation in a Co60 gamma cell. It was determined that the measured barrier energy heights may be considerably reduced by radiation-induced oxide charge. The internal photoemission technique also provided significant information concerning the effects of impurities in the oxide and the related radiation hardness of the oxide layer. Oxide layers doped with chromium ions showed significant electron trapping at two discrete energy levels (3.4 and 3.8 eV). Samples exhibiting the 3.4 eV level showed great radiation hardness, while those with only the 3.8 eV peak were very radiation soft. The information obtained, using the internal photoemission technique, has provided considerable insight into the mechanisms and fabrication processes associated with radiation-hardened MOS devices.

The higher electron mobility in GaAs relative to silicon makes it possible to design an ultra‐high‐Speed charge‐coupled device. A buried‐channel Schottky barrier gate GaAs charge‐coupled device (CCD) is described which has been operated at up to 500 MHz clock frequency. The transit‐time‐limited upper clock frequency in this device is predicted to exceed 5 GHz.

The effects of ionizing radiation in large geometry MOS structures were studied by use of internal photoemission techniques. Barrier heights at both the silicon‐silicon dioxide and the silicon dioxide‐metal (chromium) interface were measured before and after irradiation in a Co60 gamma cell. It was determined that the measured barrier energy heights were considerably reduced by radiation‐induced oxide charge.

The superior electronic properties of GaAs, as compared with silicon, make possible the achievement of much higher performance levels in GaAs signal processing devices than have been demonstrated with silicon. Only recently, however, have advanced in GaAs materials and processing technology made possible the fabrication of such devices as sub-100 ps propagation delay, high density planar GaAs integrated circuits with LSI compatible power levels', and high transfer efficiency GaAs charge coupled devices' which should be capable of multi-gigahertz clocking rate operation. These high performance device technologies should have major impact on the high speed signal processing area, making possible, through their much higher speeds and lower power requirements, system approaches which could not be practically realized with existing silicon technology.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Part of the repeated deoxyribonucleic acid (DNA) in the chicken genome had a clustered organization. The following description of clustered repeated sequences is derived both from analysis of DNA segments cloned in lambda and from hybridization of individual cloned sequences to Southern blots of restricted total DNA. A cluster usually exceeds 20 kbp in length and consists principally, if not entirely, or repetitive DNA. Each cluster contains one cope of several different repeated sequences. The individual sequences occur several hundred times in the genome, but only once per cluster. Many of the clusters contain the same assortment of sequences but in scrambled order. In the genome, those repeated sequences that are elements of clusters occur mainly within the clustered context and are seldom, if ever, found as isolated elements flanked by nonrepeated DNA. These aspects of cluster organization suggest that the clustered sequences undergo limited rearrangement, maintaining the associations within clusters but allowing variability of sequence arrangement from cluster to cluster. The clusters that occupy the cloned DNA segments together represent at least 10% of the repetitive DNA of the chicken.

The superior electronic properties of GaAs, as compared with silicon, make possible the achievement of much higher performance levels in GaAs signal processing devices than have been demonstrated with silicon. Only recently, however, have advances in GaAs materials and processing technology made possible the fabrication of such devices as sub-100 ps propagation delay, high density planar GaAs in-tegrated circuits with large-scale integration (LSI) compatible power levels,1 and high transfer efficiency GaAs charge-coupled devices2 which should be capable of multi-gigahertz clocking rate operation. These high performance device technologies should have major impact on the high speed signal processing area, making possible, through their much higher speeds and lower power requirements, system approaches which could not be practically realized with existing silicon technology. In this paper the advantages of GaAs for high speed signal processing are reviewed and laboratory results obtained with high speed GaAs devices are reported.

An ultra high speed buried channel Schottky barrier gate GaAs CCD is described which has been operated up to a clock frequency of 500 MHz. The transit time limited upper clock frequency is predicted to exceed 5 GHz.

A GaAs CCD with high transfer efficiency is described and implications for high speed devices fabricated with this technology are described.

Labeled ribonucleic acid (RNA) complementary to Agrobacterium tumefaciens DNA and PS8 bacteriophage DNA (cRNA) were used in a systematic study of the sensitivity of cRNA/deoxyribonucleic acid (DNA)-filter hybridization for detection of small amounts of phage or bacterial DNA immobilized on filters. A. tumefaciens cRNA of specific activity 10 6 to 2 × 10 6 counts per min per μg reacted to a significant extent when the DNA-filter contained 1% A. tumefaciens DNA in a salmon DNA background, but 0.1% A. tumefaciens DNA was not detectable. PS8 phage cRNA of the same specific activity reacted to a significant extent when the DNA-filter contained as little as 0.01% PS8 DNA in a salmon DNA background. Both kinds of cRNA were found to bind to tobacco crown gall tumor DNA-filters. Similar reaction was found with control normal callus DNA-filters but not with tobacco seedling DNA-filters. The “hybrids” formed by cRNA with normal callus and tumor DNA-filters had low thermal stability. Attempts to purify the tumor and normal callus DNA prior to immobilization on the filter resulted in elimination of this spurious binding. No evidence was found for bacterial or phage DNA in crown gall tumor DNA.

In the chicken genome there are middle repetitive DNA sequences with a clustered organization. Each cluster is composed of members of different families of repeated DNA sequences and usually contains only one member of each family. Many clusters have the same assortment of repeated sequences but they are in scrambled order from cluster to cluster. These clusters usually exceed 20 × 103 bases in length and comprise at least 10% of the repeated DNA of the chicken. The repeated sequences that are cluster components are extensively methylated. Methylation was detected by comparing HpaII and MspI digests of total DNA, where the occurrence of the sequence C-m5C-G-G is indicated when HpaII (cleaves C-C-G-G) fragments are larger than those generated by MspI (cleaves C-m5C-G-G or C-C-G-G). In hybridization experiments with Southern (1975) blots of total DNA digested with either HpaII or MspI, the cloned probes representing clustered repeated sequences showed a dramatic difference in the lengths of restriction fragments detected in the two digests. Many of the sequences that comprise these clusters are methylated in most of their genomic occurrences. There are patterns of methylation that are reproduced faithfully from copy to copy. The overall distribution of methylation within clusters seems to be regional, with long methylated DNA segments interrupted by specific undermethylated regions.

A naturally occurring opal suppressor serine tRNA has been purified from chicken liver and used as a probe to isolate the corresponding gene from a library of chicken DNA in bacteriophage lambda. This minor tRNA is encoded by a single-copy gene that is not part of a tRNA gene cluster. DNA sequence analysis of the gene and its flanking DNA segments shows that the gene is encoded in an 87-base-pair segment without intervening sequences and specifies a tRNA that reads the termination codon UGA. This gene has additional nucleotides in the 5' internal promoter region but has a normal 3' internal promoter sequence and the usual termination signal.

A systematic study of the DNA-DNA-filter reaction is presented which measures its ability to detect small amounts of simple DNA (bacterial or bacteriophage) in model mixtures of DNA immobilized on filters. Saturation curves show qualitatively that significant binding occurs when there is 10% Agrobacterium tumefaciens DNA on the filter but not 1%. PS8 bacteriophage DNA is detectable at a level of 0.1%. True saturation is not attained in the bacterial DNA reaction : radioactivity bound represents only 3% of the theoretical saturation value. The bacteriophage DNA reactions attain 15-30% of the expected saturation value. When crown gall tumor DNA filters were tested for the presence of A. tumefaciens or PS8 bacteriophage DNA by saturation reactions, an apparently significant amount of binding was observed compared with usual background levels for heterologous DNA filters. However thermal dissociation profiles revealed that no well-matched duplexes were formed. Normal tobacco callus DNA filters exhibited the same type of binding of labeled DNA to a similar extent (50-100% as much as tumor DNA filters). Both types of DNA-filters bound Bacillus subtilis and bacteriophage T4 DNA as efficiently as A. tumefaciens and PS8 DNA. The high non-specific background binding of labeled DNA by filters containing DNA isolated from plant tissue culture materials is ascribed to low single strand molecular weight of the filterbound DNA. This study provides no evidence for foreign DNA in crown gall tumors, and raises objections to the interpretation of the data of earlier investigators (Quetier, F., Huguet, T. and Guille, E. (1969) Biochem, Biophys. Res, Commun. 34, 128-133 and Srivastava, B.I.S. (1970) Life Sci. 9, 889-892) who claimed to detect A. tumefaciens DNA in crown gall tumors by DNA-DNA-filter hybridization.

Long and short repetitive sequences of sea urchin DNA were prepared by reassociation of 2000 nucleotide long fragments to Cot 4 and digestion with the single strand specific nuclease S1. The S1 resistant duplexes were separated into long repetitive and short repetitive fractions on Agarose A50. The extent of shared sequences was studied by reassociating a labeled preparation of short repetitive DNA with an excess of unlabeled long repetitive DNA. Less than 10% of the long repetitive DNA preparation was able to reassociate with the short repetitive DNA. Thus the long and short repetitive elements appear to be principally independent sequence classes in sea urchin DNA. Precisely reassociating repetitive DNA was prepared by four successive steps of reassociation and thermal chromatography on hydroxyapatite. This fraction (3% of the genome) was reassociated by itself or with a great excess of total sea urchin DNA. The thermal stability of the products was identical in both cases (Tm=81 degrees C), indicating that precisely repeated sequences do not have many imprecise copies in sea urchin DNA.

The ac characterization of ultra high speed digital GaAs ICs in which the total input pad to output pad logic signal propagation delays are in the 100ps to 1000ps range for typical 'NISI to LSI functions represents a challenge well beyond the capabilities of present commercial IC testers. This paper reviews techniques developed at GigaBit Logic for the high speed evaluation of GaAs ICs, both for detailed engineering characterization of new product designs, and for the much more rapid, high volume production testing of commercial GaAs IC's.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The electronic properties of GaAs and their implications to device performance have been the subject of discussion for some time, and discrete devices such as diodes and f.e.t, with performance exceeding that which has been achieved in similar silicon devices, are commercially available. Recent advances in GaAs material and processing technologies have made possible the realisation of integrated devices with substantial complexity which have demonstrated greater speed and lower power dissipation than equivalent silicon devices. Digital integrated circuits with sub-100 ps propagation delay and power dissipation compatible with large scale integration have been demonstrated. In this paper, we describe a GaAs charge-coupled device which has demonstrated some of the attributes expected from GaAs devices of this type. This device has been operated at fcl = 500 MHz which is faster than any other ccd. Design considerations and application areas for this device are discussed.

A modified Sprengel pump is described with which permanent gases can be circulated at a rate of 100 ml. min-1 at any desired sub-atmospheric pressure. The pump can also be used for evacuation to better than 1 μtorr and for collection of gas samples of the order of 1 μmole.

This paper reports the use of atomic substitution techiques in some preliminary studies by neutron scattering spectroscopy of the microscopic transport properties of acetic acid and methanol. By making selective substitution of deuterium and fluorine for the hydrogens in the CH3 and OH groups of these molecules, the separate contributions to the quantized and diffusive motions of each have been analyzed. This is possible because the substitution of fluorine or deuterium for hydrogen in a particular group reduces the scattering cross-section of that group by at least an order of magnitude. The contributions of the group motions to the neutron scattering spectrum are then correspondingly reduced. In the inelastic scattering region of the spectrum we have been able to make vibrational assignments as a result. In the quasi-elastic region the intensity and angular dependence of the scattering show a marked dependency on the nature of the protons substituted. In this region the results have been analyzed by determining an effective molecular diffusion coefficient and by comparing this with values from bulk-phase studies. Particular attention has been devoted to the question of the extent to which intra-molecular hindered rotation contributes to the quasi-elastic scattering.