Search

Relating the in vitro mitochondrial effects of drug candidates to likely in vivo outcomes remains challenging. Better understanding of this relationship, alongside improved methods to assess mitochondrial dysfunction in vivo, would both guide safer drug candidate selection and better support discovery programmes targeting mitochondria for pharmacological intervention. The aim of this study was to profile the in vivo effects of a compound with suspected complex III electron transport chain (ETC) inhibitory activity (GSK932121A) at doses associated with clinical signs, and relate findings back to in vitro data with the same compound. Control liver mitochondria or HepG2 cells were treated in vitro with GSK932121A to assess mitochondrial effects on both calcium retention capacity (CRC) and oxygen consumption rate (OCR) respectively. The same assessments were then performed on liver mitochondria isolated from Crl:CD(SD) rats, 5 hours following intraperitoneal (IP) administration of GSK932121A. Lactate/pyruvate assessment, hepatic microscopy, blood gas analysis, glutathione profiling and transcriptomics were used to characterise the acute toxicity. In vivo, GSK932121A caused hypothermia, increased levels of hepatocellular oxidative stress and a metabolic shift in energy production, resulting in an increased lactate/pyruvate ratio, liver steatosis and glycogen depletion, together with gene expression changes indicative of a fasted state. As would be expected of an ETC inhibitor, GSK932121A reduced the CRC of liver mitochondria isolated from naive control animals and the OCR of HepG2 cells when treated directly in vitro. In contrast, mitochondria isolated from animals treated with GSK932121A in vivo unexpectedly showed an increase in CRC and basal OCR. Whilst seemingly contradictory, these differences likely reflect an adapted state in vivo resulting from the initial insult in combination with compensatory changes made by the tissue to maintain energy production. Only the initial, unconfounded, response is observable in vitro. These findings improve current understanding of the toxicological and molecular consequences of ETC inhibition. Furthermore, this work highlights key differences in the way that mitochondrial perturbation is manifest in vivo versus in vitro in terms of functional endpoints and helps guide endpoint selection for future studies with potential mitochondrial toxicants or drugs designed to modulate mitochondrial function for therapeutic benefit.

The carbon sequestration potential in coastal soils is linked to aboveground and belowground plant productivity and biomass, which in turn, is directly and indirectly influenced by nutrient input. We evaluated the influence of long-term and near-term nutrient input on aboveground and belowground carbon accumulation in seagrass beds, using a nutrient enrichment (nitrogen and phosphorus) experiment embedded within a naturally occurring, long-term gradient of phosphorus availability within Florida Bay (USA). We measured organic carbon stocks in soils and above- and belowground seagrass biomass after 17 months of experimental nutrient addition. At the nutrient-limited sites, phosphorus addition increased the carbon stock in aboveground seagrass biomass by more than 300 %; belowground seagrass carbon stock increased by 50–100 %. Soil carbon content slightly decreased ( ∼ 10 %) in response to phosphorus addition. There was a strong but non-linear relationship between soil carbon and Thalassia testudinum leaf nitrogen : phosphorus (N : P) or belowground seagrass carbon stock. When seagrass leaf N : P exceeded an approximate threshold of 75 : 1, or when belowground seagrass carbon stock was less than 100 g m−2, there was less than 3 % organic carbon in the sediment. Despite the marked difference in soil carbon between phosphorus-limited and phosphorus-replete areas of Florida Bay, all areas of the bay had relatively high soil carbon stocks near or above the global median of 1.8 % organic carbon. The relatively high carbon content in the soils indicates that seagrass beds have extremely high carbon storage potential, even in nutrient-limited areas with low biomass or productivity.

Borrichia frutescens (L.) DC., sea marigold, is a woody perennial shrub native to the Gulf and Atlantic coasts of North America and has potential as a landscape shrub or groundcover. This study assesses application rates of three commercially available plant growth regulators (PGRs) on B. frutescens during container production. In one experiment, plants were drenched with 0, 0.5, 1, 2, or 4 mg active ingredient (a.i.) pot−1 of uniconazole or 0, 5, 10, 20, or 40 mg a.i. pot−1 of paclobutrazol, and in a second experiment, plants were sprayed with solutions of either 0, 25, 50, 100, or 200 mg a.i. L−1 of uniconazole, 0, 50, 100, 200, or 400 mg a.i. L−1 of paclobutrazol, or 0, 2500, 5000, 10000, or 20000 mg a.i. L−1 of daminozide. Drench-applied paclobutrazol (40 mg a.i. pot−1) reduced shoot mass and root mass (52.9 and 48.5 %, respectively). Both paclobutrazol (40 mg a.i. pot−1) and uniconazole (2 mg a.i. pot−1) reduced leaf number by as much as 56.7 and 23.8 %, respectively. Height was reduced 54.9 % by paclobutrazol at 40 mg a.i. pot−1 and 34.9 % by uniconazole at 2 mg a.i. pot−1. Drench application of paclobutrazol and uniconazole reduced internode extension by 50.1 and 41.4 %, respectively. At the levels tested, daminozide, paclobutrazol, and uniconazole were generally ineffective at controlling growth when applied as a spray. Drench application of paclobutrazol or uniconazole can be used to control height during container production of B. frutescens, whereas spray application rates need to be tested at higher concentrations or multiple applications to achieve desired control.

Management of ecological disturbances requires an understanding of the time scale and dynamics of community responses to disturbance events. To characterize long-term seagrass bed responses to nutrient enrichment, we established six study sites in Florida Bay, USA. In 24 plots (0.25 m2) at each site, we regularly added nitrogen (N) and phosphorus (P) in a factorial design for 7 years. Five of the six sites exhibited strong P limitation. Over the first 2 years, P enrichment increased Thalassia testudinum cover in the three most P-limited sites. After 3 years, Halodule wrightii began to colonize many of the P-addition plots, but the degree of colonization was variable among sites, possibly due to differences in the supply of viable propagules. Thalassia increased its allocation to aboveground tissue in response to P enrichment; Halodule increased in total biomass but did not appear to change its aboveground: belowground tissue allocation. Nutrient enrichment did not cause macroalgal or epiphytic overgrowth of the seagrass. Nitrogen retention in the study plots was variable but relatively low, whereas phosphorus retention was very high, often exceeding 100% of the P added as fertilizer over the course of our experiments. Phosphorus retentions exceeding 100% may have been facilitated by increases in Thalassia aboveground biomass, which promoted the settlement of suspended particulate matter containing phosphorus. Our study demonstrated that low-intensity press disturbance events such as phosphorus enrichment can initiate a slow, ramped successional process that may alter community structure over many years.

A1N has been grown on 4H-SiC m-plane (1100) and a-plane (1120) substrates by RF-plasma-assisted molecular-beam epitaxy. Similarities and differences between the two growth orientations are discussed. High-quality A1N can be obtained in both orientations when grown in the metastable 4H-crystal structure. For both epilayer orientations Al-rich conditions were necessary to stabilize the 4H-polytype. 4H-A1N for both growth directions shows very narrow X-ray rocking curves widths less than 100 arcsec. a-plane 4H-A1N exhibited a much smoother morphology than m-plane 4H-A1N. On the other hand, reflection high-energy diffraction intensity oscillations in the initial growth stage were observed only for m-plane A1N.

Schematic showing the toxicological and adaptive effects of drug-induced respiratory chain inhibition in vivo; also highlighting unanticipated differences from observations made in vitro (in red)., Relating the in vitro mitochondrial effects of drug candidates to likely in vivo outcomes remains challenging. Better understanding of this relationship, alongside improved methods to assess mitochondrial dysfunction in vivo, would both guide safer drug candidate selection and better support discovery programmes targeting mitochondria for pharmacological intervention. The aim of this study was to profile the in vivo effects of a compound with suspected complex III electron transport chain (ETC) inhibitory activity (GSK932121A) at doses associated with clinical signs, and relate findings back to in vitro data with the same compound. Control liver mitochondria or HepG2 cells were treated in vitro with GSK932121A to assess mitochondrial effects on both calcium retention capacity (CRC) and oxygen consumption rate (OCR) respectively. The same assessments were then performed on liver mitochondria isolated from Crl:CD(SD) rats, 5 hours following intraperitoneal (IP) administration of GSK932121A. Lactate/pyruvate assessment, hepatic microscopy, blood gas analysis, glutathione profiling and transcriptomics were used to characterise the acute toxicity. In vivo, GSK932121A caused hypothermia, increased levels of hepatocellular oxidative stress and a metabolic shift in energy production, resulting in an increased lactate/pyruvate ratio, liver steatosis and glycogen depletion, together with gene expression changes indicative of a fasted state. As would be expected of an ETC inhibitor, GSK932121A reduced the CRC of liver mitochondria isolated from naive control animals and the OCR of HepG2 cells when treated directly in vitro. In contrast, mitochondria isolated from animals treated with GSK932121A in vivo unexpectedly showed an increase in CRC and basal OCR. Whilst seemingly contradictory, these differences likely reflect an adapted state in vivo resulting from the initial insult in combination with compensatory changes made by the tissue to maintain energy production. Only the initial, unconfounded, response is observable in vitro. These findings improve current understanding of the toxicological and molecular consequences of ETC inhibition. Furthermore, this work highlights key differences in the way that mitochondrial perturbation is manifest in vivo versus in vitro in terms of functional endpoints and helps guide endpoint selection for future studies with potential mitochondrial toxicants or drugs designed to modulate mitochondrial function for therapeutic benefit.

We evaluated how changes in nutrient supply altered the composition of epiphytic and benthic microalgal communities in a Thalassia testudinum (turtle grass) bed in Florida Bay. We established study plots at four sites in the bay and added nitrogen (N) and phosphorus (P) to the sediments in a factorial design. After 18, 24, and 30 months of fertilization we measured the pigment concentrations in the epiphytic and benthic microalgal assemblages using high performance liquid chromatography. Overall, the epiphytic assemblage was P-limited in the eastern portion of the bay, but each phototrophic group displayed unique spatial and temporal responses to N and P addition. Epiphytic chlorophyll a, an indicator of total microalgal load, and epiphytic fucoxanthin, an indicator of diatoms, increased in response to P addition at one eastern bay site, decreased at another eastern bay site, and were not affected by P or N addition at two western bay sites. Epiphytic zeaxanthin, an indicator of the cyanobacterial/coralline red algae complex, and epiphytic chlorophyll b, an indicator of green algae, generally increased in response to P addition at both eastern bay sites but did not respond to P or N addition in the western bay. Benthic chlorophyll a, chlorophyll b, fucoxanthin, and zeaxanthin showed complex responses to N and P addition in the eastern bay, suggesting that the benthic assemblage is limited by both N and P. Benthic assemblages in the western bay were variable over time and displayed few responses to N or P addition. The contrasting nutrient limitation patterns between the epiphytic and benthic communities in the eastern bay suggest that altering nutrient input to the bay, as might occur during Everglades restoration, can shift microalgal community structure, which may subsequently alter food web support for upper trophic levels.

The surface structure of ZrB2(0001) was investigated using coaxial impact-collision ion scattering spectroscopy (CAICISS). The ZrB2(0001) 1×1 surface was prepared by HF solution treatment and annealing in vacuum. It was directly evidenced that the ZrB2(0001) surface is terminated with a Zr layer. Moreover, we found that the interlayer spacing between the first Zr layer and the second B layer is expanded by 20% with regard to c-axis lattice constant. Since small amount of O atoms were detected after the cleaning, the incorporation of the residual O atoms into the subsurface region of the ZrB2(0001) surface is likely to be the origin of the large expansion.

ZrB 2 (0 0 0 1) crystals grown by the rf-floating zone technique were characterized by X-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and atomic force microscopy. These characteristics were investigated as a function of thermal cleaning temperature up to 1000 °C in vacuum for as-received substrates as well as substrates treated ex situ in HF aqueous solution. The HF treatment process removed the ZrO 2 native oxide layer present on as-received substrates and resulted in ZrB 2 (0 0 0 1) surfaces exhibiting long-range order. Upon annealing the HF-treated surface in high vacuum, two types of reconstructions were observed: an incommensurate reconstruction from 650 to 900 °C related to residual H 2 gas, and n × n reconstructions at 1000 °C, possibly related to oxygen.

Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7±0.2 eV) and for wurtzite GaN at (3.3±0.2 eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal.

Nitrogen-polar GaN was grown on lattice-matched ZrB2 substrates by a two-step rf-MBE process with conventional low-temperature GaN (LT-GaN) used as the nucleation layer. For nucleation in slightly Ga-rich conditions, a streaky RHEED pattern was maintained from the very beginning and persisted throughout subsequent high-temperature growth. However, despite the streaky RHEED pattern the initial nucleation was evidently not 2D as inferred from AFM and x-ray results. For nucleation in slightly N-rich conditions, spots appeared in the RHEED in the early stages of growth but a streak pattern was restored with high-temperature GaN growth. Tradeoffs were identified in optimizing the LT-GaN nucleation process. Slightly Ga-rich nucleation conditions offered the best x-ray characteristics with ω-scan FWHM values of 400-500 and 720-800 arcsec for the (0002) and (104) reflections, respectively. Short-length atomic steps (up to ∼200 nm) were present on the surfaces of such layers, but the morphology showed a sub-grain structure. Slightly N-rich nucleation conditions yielded remarkably smooth films surfaces (rms 0.5 nm over 10 µm2) with uninterrupted atomic steps up to several µm long, but inferior x-ray ω-scans (∼50% larger FWHM values). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Within the last few years indium nitride (InN) gained substantial interest due to its controversially discussed apparent band gap and its predicted highest maximum electron mobility among several III–V compounds, including Al(Ga)N and GaAs. The band gap of epitaxial InN has been recently reported to be around 0.7 eV rather than the previously accepted value of 1.9 eV obtained from polycrystalline films. Thus, InN could be a promising material for applications in infrared opto-electronics or high-speed electronics. However, the structural quality of the InN epilayers is still inferior to GaN and needs to be improved. Also, the role of many contaminants in InN and their effect on the epilayer's conductivity and/or luminescence properties is still under investigation. This work describes recent studies of InN growth by molecular beam epitaxy on sapphire (0 0 0 1) substrates. The effect of buffer layer variations including a prior substrate nitridation step is discussed. Structural properties (X-ray diffraction, AFM and TEM images) and chemical profiles (SIMS) will be correlated to Hall data and Photo-luminescence spectra. The role of oxygen and hydrogen as possible donors in InN will be discussed.

GaN:C epilayers were grown by plasma-assisted molecular beam epitaxy on metalorganic vapor phase epitaxy-GaN/sapphire templates using CCl 4 and CS 2 vapors as carbon doping sources. The resulting epilayers were characterized by secondary ion mass spectrometry, photoluminescence, and electrical resistivity among other techniques. Both sources were found to controllably introduce carbon in the concentration range 1×10 18 –3×10 19 cm −3 with insignificant contamination by other impurities. The CCl 4 source drastically reduced the effective Ga/N flux ratio due to a parasitic reaction, necessitating greatly increased Ga flux to maintain Ga-rich conditions. On the other hand GaN:C was successfully obtained with CS 2 with no parasitic reaction. For both sources an anomalous concentration dependence of the carbon incorporation behavior was observed, leading to reduced concentrations of electrically active C N acceptors for higher total doping levels.

A process to pattern Pd over-layers on reactive metal films was developed using ion milling through a tungsten trioxide mask patterned by photolithography and wet etching. The WO3 mask exhibited a low Ar+ sputter yield and, unlike conventional mask materials (SiO2, Si3N4), was easily etched in a mild alkaline solution. This procedure was applied to convert a 20-nm Pd cap over a 160-nm GdMg film to a Pd grid with ≈9-μm-diameter openings covering ≈40% of the surface. The Pd grid proved sufficient to catalyze the (de)hydriding reactions required to reversibly switch the GdMg film from reflecting to transparent. The maximum transmittance of the patterned Pd/GdMg hydride bi-layer was twice that of an otherwise identical sample with a continuous Pd cap, with similar hydriding kinetics.

Brown trout (Salmo trutta) were captured from a headwater stream contaminated with moth‐proofing agents. Synthetic pyrethroid residues within the tissues were obtained by ultrasonic extraction and examined by gas chromatography‐mass spectrometry operated in the negative ion chemical ionization mode (GC/NCI‐MS). Both permethrin and cyfluthrin had been bioaccumulated by the fish and the mean concentrations ( ± standard deviation) recorded were 2046 ( ± 203) μg kg‐1 and 25.4 ( ± 46.9) μg kg‐1 respectively. The concentrations of these pyrethroids are the highest recorded for freshwater fish captured from a natural ecosystem. At the time of sampling, permethrin could be detected within the stream water (0.034 μg l‐1) while cyfluthrin could not. A mean relative bioconcentration factor of approximately 60 000 was derived for the brown trout which was also greater than any previously determined for freshwater fish. The fish tissue extracts were also analyzed through use of an ELISA for permethrin. The ELISA repor...

The outcome of a 7-day pilot monitoring study on the anionic surfactant, LAS, at the Yorkshire Water Service's Owlwood activated sludge sewage treatment works (STW) is described. The average concentration of LAS found in daily flow related composites of raw sewage was 15.1 mg l−1 (range 11.8–18.2 mg l−1). The calculated per capita use of the surfactant at Owlwood of 4.5 g/d/person agrees closely with the predicted use of LAS in Western Europe (ca 4.0 g/d/p). Distinct diurnal variations in the raw sewage LAS concentrations were observed (3.7–31.8 mg l−1) and were apparent to a lesser degree in the treated effluent. The removal of the organic load (measured as BOD) and LAS at the works were both very high, 98 and 99.9% respectively. Hence, very low concentrations of LAS were discharged to the associated Sheffield Beck in the treated effluent (average daily composite of 10.4 μg l−1). Unexpectedly, the river upstream of the discharge was found to contribute a higher load of LAS to the river downstream than the Owlwood effluent. The average daily composite LAS concentration in the river below the mixing zone of the STW was 27 μg l−1 (range 9.4–47 μg l−1). The concentrations of LAS found on sediments in the immediate vicinity of the STW were very small (< 1 μg g−1). The implications of the study findings for the Standing Committee of Analysts (SCA) methodology used for the analysis of LAS and the design of further monitoring exercises on surfactants are discussed.

Gas chromatography-mass spectrometry operated in the negative chemical ionization mode (GC-NCI-MS) with selected-ion monitoring (SIM) showed both high sensitivity and excellent specificity for permethrin and cyfluthrin. The detection limit for both permethrin and cyfluthrin was 50 fg, whilst a linear response was observed from 50 fg to 80 pg. A sample extraction method using an ultrasonic bath was developed enabling simulataneous processing of multiple samples. Good percentage recoveries of both permethrin and cyfluthrin from spiked sediments were obtained (97.3 ± 4.8% and 93.9 ± 5.3%, respectively) and sample clean-up was avoided. These methods were also successfully applied to samples obtained from a contaminated ecosystem, the highest concentrations recorded in water and sediment samples were 0.048 μg l−1 and 305 μg kg−1, respectively.

A gas chromatographic/mass spectrometric method was developed for the simultaneous determination of five synthetic pyrethroid insecticides in soil, moss and fish tissue. These pyrethroids were extracted with hexane-dichloromethane by ultrasonication and cleaned up on Florisil (soil and moss) and mixed acid/base alumina (fish) columns prior to determination by gas chromatography/negative-ion chemical ionization mass spectrometry in selected ion monitoring mode. All the pyrethroids were analyzed simultaneously in a single run on a DB5-MS 15 m capillary column. Recoveries of the pyrethroids from the three matrices at fortification levels of 10, 50 and 100 μg/kg ranged from 80 to 117%. Four determinations were made at each concentration level for each matrix. The practical determination limit of the method was in the range 0.5 to 5 μg/kg depending on the compound. This method was also applied to samples obtained from a contaminated ecosystem.

Carbon-doped GaN layers grown by molecular-beam epitaxy are studied with photoluminescence and positron annihilation spectroscopy. Semi-insulating layers doped with >1018 cm−3 carbon show a strong luminescence band centered at ∼2.2 eV (yellow luminescence). The absolute intensity of the 2.2 eV band is compared with the gallium vacancy concentration determined by positron annihilation spectroscopy. The results indicate that a high concentration of gallium vacancies is not necessary for yellow luminescence and that there is in fact a causal relationship between carbon and the 2.2 eV band. Markedly different deep-level ionization energies are found for the high-temperature quenching of the 2.2 eV photoluminescence in carbon-doped and reference samples. We propose that while the model of Neugebauer and Van de Walle [Appl. Phys. Lett. 69, 503 (1996)] applies for GaN of low carbon concentration, a different yellow luminescence mechanism is involved when the interstitial carbon concentration is comparable to or ...

The synthetic pyrethroid permethrin has widespread use in agriculture and, as a result, is found in a variety of matrices. Chemical methods based on gas chromatography/mass spectrometry operated in...

Polyclonal antisera were produced in rabbits against two different synthetic immunogens, one of which incorporated 3‐phenoxybenzoic acid (PBA) while the other contained dichlorovinyl cyclopropane carboxylate (CPA). The immunogens were constructed such that the hapten was coupled to the carrier protein through a peptide bond to a six carbon spacing group (6‐amino hexanoic acid, 6‐AHA). Both the anti‐PBA and anti‐CPA antisera obtained were able to detect permethrin when used in an indirect competitive enzyme‐linked immunosorbent assay (IC‐ELISA) format. The detection limits typically obtained with both antisera were 10 mg l‐1with 50% inhibition of antibody binding (ho) at 100mg l‐1. Cross‐reactivity with the pyrethroids cyfluthrin, phenothrin and deltamethrin was observed for both antisera, the degree of which was related to the structural similarity of the compound to the immunizing hapten. Further development of the immunoassay for permethrin was examined through use of the anti‐PBA antiserum. Assay perfo...

Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

Gallium nitride epitaxial layers were grown on sapphire by molecular-beam epitaxy using nitridated gallium metal films as buffer layers. The mechanical properties of the buffer layers were investigated and correlated with their chemical composition as determined by synchrotron radiation photoelectron spectroscopy. Biaxial tension experiments were performed by bending the substrates in a pressure cell designed for simultaneous photoluminescence measurements. The shift of the excitonic luminescence peak was used to determine the stress induced in the main GaN epilayer. The fraction of stress transferred from substrate to main layer was as low as 27% for samples grown on nitridated metal buffer layers, compared to nearly 100% for samples on conventional low-temperature GaN buffer layers. The efficiency of stress relief increased in proportion to the fraction of metallic Ga in the nitridated metal buffer layers. These findings suggest GaN films containing residual metallic Ga may serve as compliant buffer layers for heteroepitaxy.

Wheat soilborne mosaic (WSBM) can significantly reduce wheat (L.) yields. The only feasible method for controlling this disease is to plant resistant cultivars; however, development of WSBM-resistant wheat can be difficult, because soil fertility, soil moisture, or other viruses cause symptoms that mimic or mask symptoms induced by the WSBM virus. Thus, the objective of this research was to develop a system that effectively identifies resistance to WSBM. Reactions to WSBM were determined for advanced breeder lines, single plants from advanced lines, and headrow progeny from advanced lines, using symptomatology and the enzyme-linked immunosorbent assay (ELISA) in growth chamber test and in the field. Results indicate that large numbers of plants or lines can be screened using the growth chamber test to eliminate susceptible entries. In addition to confirming results from the growth chamber test, the field test also detected lines segregating for disease reaction. Individual plants resistant to WSBM were identified from these segregating lines, using a combination of the growth chamber and field tests. Use of this system in breeding for resistance to WSBM reduces the possibility of misidentifying the reaction of wheat lines or plants to WSBM and facilitates the development of wheat resistant to this disease.

The optical switching properties of gadolinium–magnesium hydride have been demonstrated in a solid-state electrochromic device. With positive polarization of the hydride electrode, the visible reflectance approaches 35% with virtually zero transmission, while with negative polarization, the visible transmission exceeds 25% at 650 nm. The switching is reversible, with intermediate optical properties between the transparent and reflecting states.

The electrical and optical properties of carbon-related defects in GaN are studied. A series of samples with C concentrations varying from 5x10/sup 16/ to 1x10/sup 20/cm/sup -3/was characterized by SIMS, resistivity, photoluminescence, thermally simulated current, Raman scattering, and positron annihilation spectroscopy.

InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films.

Zirconium diboride (ZrB2) is a promising lattice-matched substrate for GaN-based materials. A key issue to realize high-quality heteroepitaxial growth is preparation of the substrate surface. The ZrB2 surface was studied by x-ray photoemission spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). XPS results indicated the presence of both ZrO2 and ZrB2 on the as-received substrate surface. Thermal cleaning at 1000°C in ultra-high vacuum, Ar+ ion sputtering, and wet chemical treatments were examined as surface preparation methods. After treatment with HF acid, the O peak intensity was much reduced. The combination of HF treatment and thermal cleaning resulted in sharp and intense RHEED from the ZrB2 surface. GaN grown on the surface by molecular-beam epitaxy exhibited intense photoluminescence, suggesting that this treatment is effective to obtain high-quality GaN on ZrB2 substrates.

Semi-insulating wurtzite GaN:C of high optical quality is obtained with CCl4or CS2 doping sources in plasma-assisted molecular-beam epitaxy in Ga-rich growth conditions. The highest resistivity (107Ω-cm) is found for [C] in the low 1018cm−3range. An increasing fraction of carbon appears to form electrically inactive pair defects for higher doping levels causing the concentration of uncompensated residual donors to be higher in films with [C] in the 1019cm−3range compared with [C] in the 1018cm−3range. Blue (2.9 eV) and yellow (2.2 eV) luminescence bands are associated with carbon-related defects, and additional support is provided for the association of the blue luminescence with the carbon-acceptor deactivating pair defect. Finally, the temperature dependence of the resistivity is described within the grain-boundary controlled transport model of Salzmanet al., Appl. Phys. Lett.76, 1431 (2000).

Metallic magnesium lanthanide thin films upon insertion of hydrogen transform to a highly transparent hydride phase. With a Pd overlayer, the transformation can be produced either by electrochemical insertion of hydrogen or by exposing the film to hydrogen gas. Unlike amorphous oxide electrochromics, the transformation is accompanied by a large change in visible reflectance (about 50%). The optical switching effect in these materials is investigated in terms of changes in the complex refractive index as determined by variable-angle spectroscopic ellipsometric and normal-incidence radiometric measurements over the solar spectrum. Furthermore the optical effect of converting the Pd cap-layer to Pd–H was determined. It is shown that the Pd layer limits the visible transmittance of the hydrided stack to about 35–40%. Whereas the extinction coefficient of the dehydrided LnMg-layers at 550 nm is between 2.2 and 3.1, it is as low as 10 −4 in the transparent state.

Recent developments in the photosensitivity of germania doped silica glass are reviewed. The cause and nature of the absorption band centered near 240 nm are discussed and possible structures for this defect are reported together with a summary of the proposed mechanisms for the UV index change. Experimental techniques for assessing the refractive index change are listed and this leads to a consideration of the effects of non-ideal grating formation. Mechanisms for enhancing the photosensitivity of fibers and germania doped silica films are assessed using a systematic study of the photosensitivity of fibers fabricated under the different techniques. Finally some of the possible applications for photosensitivity are briefly discussed.

InN thin films have been grown epitaxially on GaN-buffered sapphire substrates by molecular-beam epitaxy at 500°C. A high level of oxygen contamination in the growth chamber led to formation of In2O3 precipitates in the films. These precipitates were characterized in detail by transmission electron microscopy (TEM). The concentration of In2O3 was estimated to be less than 0.07vol% in the present samples of oxygen content ∼0.5at.%. Cross-sectional TEM investigations revealed that the precipitates adopt a preferred crystallographic orientation within the InN matrix, and show a characteristic diameter of ∼5nm with average distance of ∼500nm. These observations suggest the effective solubility of O in InN could be below 1at.% at 500°C.

Single-crystal GaN thin films have been deposited epitaxially on a HfN-buffered Si(111) substrates by molecular-beam epitaxy. The microstructural and compositional characteristics of the films were studied in detail by transmission electron microscopy (TEMs). Cross-sectional TEM investigations have revealed the crystallographic orientation relationship in different GaN∕HfN∕Si layers. GaN film polarity is studied by conventional TEM and convergent beam electron diffraction simulations, and the results show that the GaN film has a Ga polarity with relatively high density of inversion domains. Based on our observations, growth mechanisms related to the structural properties are discussed.

The dry matter and crude protein production of the perennial ryegrass varieties S24, S23, Premo, Houba, Barlenna, Melle and Sceempter Pasture at annual nitrogen application rates of 212, 425, 637 and 1062 kg ha−1 were studied for the years 1972–74 inclusive. The DM and CP response curves for the variety Melle were steeper than those for other varieties tested and levelled off at a higher N application rate. The results suggest that Melle is a variety with a genotype capahle of utilizing N more efficiently at higher rates than the other varieties tested.

The composition of the leachate from undisturbed monolith lysimeters cropped with white clover or meadow fescue or maintained bare was compared with that of the rain falling on them. No nitrogen fertilizer was applied only an initial dressing of phosphorus and potassium. The grass received much more nitrogen from the rain than it lost by leaching whereas the clover lost more than it received. Most of the leached nitrogen was NO3-N - 92 per cent on the bare soil and 90 per cent on the clover. About 27lb nitrogen per acre (30 kg/ha) per year was drained from the actively growing clover sward rising to about 117lb N/acre/year (131 kg/ha) when the clover died or was removed. Only 2.3lb/ac (2.5 kg/ha) was drained from the actively growing grass sward. It was estimated that the clover fixed at least 270lb N/ac/year (303 kg/ha/year. The rates of leaching of potassium from a grass sward was about 1.7lb/ac/year (1.9 kg/ha) and 0.8 lb (0.9 kg) phosphorus. The quantities were similar for clover. The grass received from the rain more phosphorus and potassium than was leached but only 60 per cent of the calcium and 13 per cent of the magnesium, similar results being obtained with white clover.

Samples of bracken were taken at fortnightly intervals from June to November at two centres. These were separated into leaf and stem and analysed.Larger samples were treated for the preparation of proteins and sugars by passing the bracken through a roller-mill, precipitating the protein with acid and concentrating the juice for sugars.Chemical composition. The main points in the analyses of the whole plants were as follows, all figures quoted being on a dry-matter basis:(1) The crude and true protein contents of young bracken in early June were high, 21 and 18%, but these fell rapidly to 10% in mid-July and finally to 3% in October.(2) The lignin content was high throughout, rising from almost 20% in young bracken to 34% in the nearly dead material.(3) The cellulose content followed the lignin content.(4) In July and August the bracken contained about 10% of total sugars. A rapid fall occurred in October, and the final samples contained very little sugars.

SUMMARYThe comparative effects of very heavy dressings of ammonium sulphate and urea on the growth of established plants of white clover (S100) have been studied in pot culture. Five applications each of 263 kg N/ha were applied over 9 months in 3 different ways (i) direct contact of the fertilizers with the leaves, (ii) only with the stolons or surface roots or (iii) applied 12·5 cm below the soil surface.The ammonium sulphate broadcast over the leaves reduced the growth of the clover whilst urea under the same conditions caused temporary damage with very little reduction in dry weight compared with the control. When the ammonium sulphate was applied to the soil surface or 12·5 cm below, there was appreciable reduction in dry weight but less than when the fertilizer was in contact with the leaves. Under the same conditions, urea did not reduce growth.The pH of the soil fell to about 4·6 with ammonium sulphate (control 6·1) but only slightly with urea.Root development was not affected by urea but greatly reduced with ammonium sulphate. With both fertilizers the root nodules were very pale in colour and few in number compared with the control.

Fugitive methane emissions from oil sands mining activities are a potentially important source of greenhouse gas emissions for which there are significant uncertainties and a lack of open data. This paper investigates the potential of a control-system approach to estimating fugitive methane emissions by analyzing releasable gas volumes in core samples extracted from undeveloped mine regions. Field experiments were performed by leveraging routine winter drilling activities that are a component of normal mine planning and development, and working in conjunction with an on-site drill crew using existing equipment. Core samples were extracted from two test holes, sealed at the surface, and transported for off-site lab analysis. Despite the challenges of the on-site sample collection and the limitations of the available drilling technology, notable quantities of residual methane (mean of 23.8 mgCH 4 /kg-core-sample (+41%/−35%) or 779 mgCH 4 /kg-bitumen (+69%/−34%) at 95% confidence) were measured in the collected core samples. If these factors are applied to the volumes of bitumen mined in Alberta in 2015, they imply fugitive methane emissions equivalent to 2.1 MtCO 2 e (as correlated with bitumen content) or 1.4 MtCO 2 e (as correlated with total mined material) evaluated on a 100-year time horizon. An additional ∼0.2 Mt of fugitive CO 2 emissions could also be expected. Although additional measurements at a larger number of locations are warranted to determine whether these emissions should be considered as additive to, or inclusive of, current estimates based on flux chamber measurements at the mine face, these first-of-their-kind results demonstrate an intriguing alternate method for quantifying fugitive emissions from oil sands mining and extraction.

A modified method for the determination of lignin in high-protein plant material has been developed. The main modification is the use of a single digestion with trypsin, rather than pepsin, this being preceded, instead of followed, by acid hydrolysis. The use of Gooch crucibles is recommended as alundum crucibles can be unreliable.

FOR crop production, soil should have a good crumb structure, the crumbs being highly adsorptive of water but stable when wetted. The ameliorative effect of certain microbial polysaccharides on soil structure has already been reported1, and it was of interest to see whether other constituents of micro-organisms have a similar effect.