An Inexpensive Digital Integrator for Gas Chromatography

SUMMARY

An inexpensive gas chromatographic integrator with digital readout is described. The device is precise to ±1 count and shows linear response to within ±2%. It is directly compatible with flame ionization detectors and is easily adapted to thermal conductivity detectors.     

Substrate properties affect the mass loss rate in collodion at liquid helium temperature

A previous measurement showed that mass loss from collodion supported by thin carbon films was linear with electron exposure at liquid helium temperature. No other organic solid had shown a linear loss of mass at any temperature. When measurements of collodion were done using titanium supports, the loss of mass proceeded exponentially with exposure at liquid helium temperature. This result suggested that the differing electrical conductivities of these substrates might be the cause of the different mass loss effects. Carbon films, which are typically used at ambient temperatures, have much lower electrical conductivity at very low temperature than titanium films. This suggested that specimen preparation materials and techniques used routinely for room temperature studies may need to be modified when microscopy is done using superconducting objective lenses. For both substrates, the rate of mass loss is slowest at liquid helium temperature.     

Compositional disordering and the formation of semi-insulating layers in AlAs-GaAs superlattices by MeV oxygen implantation

Data are presented demonstrating the use of MeV oxygen ion implantation and subsequent annealing procedures to induce compositional disordering and to create a semiinsulating region simultaneously within an AlAs-GaAs superlattice. High dose oxygen implantation yields a compositionally disordered region 3500? wide centered 1.25 μm below the surface of the superlattice, as determined by secondary ion mass spectrometry (SIMS) analysis. More extensive disordering of the superlattice occurs at lower implantation temperatures. Current-voltage measurements indicate the formation of a semiinsulating layer which is thermally stable to at least 850° C. The semi-insulating properties of the implanted superlattice are assigned to the disorder-enhanced formation of Al-O pairs and the substitutional introduction of deep level states.     

Ion beam mixing characteristics of MOCVD grown InGaAs/GaAs superlattices

The ion beam mixing behavior of InGaAs/GaAs strained layer superlattice structures grown by metalorganic chemical vapor deposition was studied using secondary ion mass spectroscopy and Rutherford backscattering channeling. The fluence dependence of intermixing by MeV Kr⁺ irradiation has been investigated. Significant intermixing occurs for fluences much lower than for similar intermixing in other superlattice systems (i.e. ALAs/GaAs). The intermixing exhibits no temperature dependence for fluences of 2 x 10¹⁵ to 5 x 10¹⁵ cm⁻² which sharply contrasts with the behavior of the AlAs/GaAs superlattice system which shows a strong temperature dependence, including a miscibility gap, in the temperature range 523 to 973K. Samples irradiated at 573K retain a high degree of crystallinity when compared to lower temperature irradiations indicating that the InGaAs/GaAs superlattice can be disordered and still retain crystallinity.     

Phosphorus oxynitride: a thermally stable fire retardant additive for polyamide 6 and poly(butylene terephthalate)

The combustion performance of polyamide 6 (PA 6) and poly(butylene terephthalate) (PBT), both fire retarded by phosphorus oxynitride (PON), was studied by oxygen index (OI) and Underwriters Laboratory UL94 tests. It was shown that either PON alone or in combination with different co-additives is efficient in PA 6 and much less active in PBT. Thermogravimetric experiments provided evidence that PON promotes charring in both PA 6 and PBT. The mechanism of the char formation from PA 6 and PBT in the presence of PON was discussed on the basis of IR studies of solid residues produced in the thermal decomposition. The effective fire retardant action of PON in PA 6 is related to the interaction with the polymer to produce char, whereas the less effective activity of PON in PBT is related to the unfavorable acceleration of the evolution of combustible aliphatic fragments.     

Effect of leaf and spike morphological traits on the relationship between spectral reflectance indices and yield in wheat

While certain spectral reflectance indices have been shown to be sensitive to the expression of a range of performance-related traits in crops, knowledge of the potentially confounding effects associated with plant anatomy could help improve their application in phenotyping. Morphological traits (leaf and spike wax content, leaf and spike orientation, and awns on spikes) were studied in 20 contrasting advanced wheat lines to determine their influence on spectral indices and in their association with grain yield under well-irrigated conditions. Canopy reflectance (400–1100 nm) was determined at heading and grain filling during two growing seasons and three vegetation indices (VIs; red normalized difference vegetation index (RNDVI), green normalized difference vegetation index (GNDVI), and simple ratio (SR)), and five water indices (WIs; one simple WI and four normalized WIs (NWI-1, NWI-2, NWI-3, and NWI-4)) were calculated. The major reflectance fluctuations caused by the differences in leaf and spike morphology mainly occurred in the infrared region (700–1100 nm) and little variation in the visible region (400–700 nm). The NWI-3 ((R₉₇₀ – R₈₈₀)/(R₉₇₀ + R₈₈₀)) consistently showed a stronger association with yield than the RNDVI by using uncorrected canopy reflectance (original raw data) and data adjusted by scattering and smoothing. When canopy reflectance was corrected by a scattering method, the NWI-3 and a modified RNDVI with 958 nm showed the strongest correlations with grain yield by grouping lines for waxy leaves and spikes, curved leaves, and erect and awnless spikes. The results showed that the relationship between the spectral indices and grain yield can be improved (higher correlations) by correcting canopy reflectance for confounding effects associated with differences in leaf and spike morphology.     

Characterization of endothelial cell amino acid transport systems involved in the actions of nitric oxide synthase inhibitors

N omega-Substituted analogues of L-arginine have proven useful as specific inhibitors of nitric oxide formation in various biological systems. In the present study we describe the characteristics of amino acid transporters that mediate uptake of N omega-methyl-L-arginine (L-NMA) and N omega-nitro-L-arginine (L-NNA) into cultured porcine aortic endothelial cells. The transport of L-[14C]NMA showed biphasic kinetics, with Km values of 4 and 368 microM, and was inhibited by L-arginine, L-homoarginine, L-lysine, and L-ornithine but not by L-leucine or L-isoleucine. Similar transport kinetics (Km values of 6 and 609 microM) and substrate specificities were obtained for L-[3H]arginine uptake, indicating that L-arginine and L-NMA are transported by the same system. In contrast to L-arginine and L-NMA transport, uptake of L-[3H]NNA was monophasic (Km = 617 microM) and was inhibited by L-leucine and L-isoleucine but not by L-arginine, L-homoarginine, L-NMA, L-lysine, or L-ornithine. Uptake studies with L-[3H]leucine revealed that the transport of this amino acid occurred in a manner very similar to that of L-[3H]NNA transport, suggesting that the uptake of both compounds may be mediated by the same system. In additional experiments, we determined the effects of L-NMA and L-NNA on the A23187-induced accumulation of intracellular cGMP, to establish to what extent these transport systems are involved in the actions of nitric oxide synthase inhibitors. L-Lysine and L-ornithine, which both inhibited L-NMA uptake, increased the IC50 of L-NMA from 7.8 microM to 57 microM but did not reduce the inhibitory effects of L-NNA. In the presence of L-leucine or L-isoleucine, however, which both inhibited L-NNA uptake, the IC50 of L-NNA was increased from 1.2 microM to 37 microM but the inhibitory actions of L-NMA remained unaffected. These data demonstrate that the endothelial transport systems for L-arginine and L-leucine mediate the biological effects of L-NMA and L-NNA, respectively.