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  • 1
    Digitale Medien
    Digitale Medien
    A novel leupeptin-sensitive serine endopeptidase present in normal and malignant rat mammary tissues (1990)
    Springer
    Molecular and cellular biochemistry 94 (1990), S. 19-36 
    Details
    ISSN: 1573-4919
    Schlagwort(e): leupeptin ; endopeptidase ; trypsin-like ; proteinase ; malignant ; mammary
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary N-Methyl-N-nitrosourea (MNU)-induced rat mammary adenocarcinomas contain high levels of a novel leupeptin-sensitive serine endopeptidase. Its properties apparently differ from those of other similar endopeptidases reported to be present in various normal and malignant mammalian tissues. The same leupeptinsensitive serine endopeptidase was also detected in normal rat mammary tissues, but at levels approximately 20 times lower than those in MNU-induced mammary tumors. This enzyme, which is a trypsin-like serine endopeptidase, preferentially hydrolyzes various synthetic endopeptidase substrates at the carboxyl side of an arginyl residue. It has an apparent Mr of approximately 160,000 and a Stokes radius of 49\rA, as determined by gel filtration. Its isoelectric points range from 4.5 to 4.8, and it has a pH optimum of approximately 7.0. The enzyme is stable from pH 4.0 to 7.0, but is extremely unstable above pH 7.0. Besides leupeptin, its activity is inhibited by antipain, aprotinin, Nα-p-tosyl-L-lysine chloromethyl ketone and phenylmethylsulfonyl fluoride, but is not inhibited by soybean trypsin inhibitor. Many other potential inhibitors or activators such as 2-mercaptoethanol, p-hydroxymercuribenzoic acid and EDTA have no effect on its activity. The enzyme is adsorbed to p-aminobenzamidine agarose affinity beads at pH 6.5 and elutes at pH 4.0.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00223559
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  • 2
    Digitale Medien
    Digitale Medien
    Ultrashort light pulse generation under coherent interaction of a field with a medium (1992)
    Springer
    Journal of Russian laser research 13 (1992), S. 96-108 
    Details
    ISSN: 1573-8760
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We consider the dynamics of propagation and compression of ultrashort electromagnetic-wave pulses in a multicomponent two-level field, one component of which emits or absorbs light in a regime of coherent interaction of the radiation with the substance. We consider also the question of the dynamics of the field in planar superconducting structures (such as, e.g., layered high-temperature superconductors of the YBa2Cu3O7=x type). With Josephson tunneling of the electrons between the layers it becomes possible here to describe the field-induced current in a model using Bloch equations for particles with near-zero frequency of the transition between levels and with infinite relaxation times, i.e., to reduce the problem to that of the dynamics of a field coherently interacting with a two-level medium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01125507
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  • 3
    Digitale Medien
    Digitale Medien
    Sulfur dioxide and dimethyl sulfide in the central Pacific troposphere (1993)
    Springer
    Journal of atmospheric chemistry 17 (1993), S. 1-13 
    Details
    ISSN: 1573-0662
    Schlagwort(e): Sulfur dioxide ; dimethyl sulfide ; carbon disulfide ; Pacific troposphere ; volcanic impacts
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Boundary-layer and free-troposphere measurements of sulfur dioxide, dimethyl sulfide, and carbon disulfide were made during transits of the central and southern Pacific Ocean between Hawaii and Australia. Sulfur dioxide was generally less than 100 pptv and highly variable with no correlation with respect to geographic location or altitude. Dimethyl sulfide in the boundary layer had a concentration range of 〈10 to 200 pptv. Highest concentrations of DMS were in the equatorial region of the southern hemisphere although the concentrations were dependent on location and meteorological regime. In the region of the Fiji Islands several boundary layer samples had SO2, DMS, and CS2. In 1989, additional SO2 measurements were made between Hawaii and the equator and to the west of Hawaii downwind of the Kilauea volcano plumes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00699110
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  • 4
    Digitale Medien
    Digitale Medien
    The annual cycle of peroxides and ozone in marine air at Cape Grim, Tasmania (1996)
    Springer
    Journal of atmospheric chemistry 23 (1996), S. 221-252 
    Details
    ISSN: 1573-0662
    Schlagwort(e): photochemistry ; hydrogen peroxide ; ozone ; Cape Grim ; Tasmania
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of〉1.4 ppbv in summer (December) to 〈0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NOx ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00055155
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  • 5
    Digitale Medien
    Digitale Medien
    Processing of oxidised nitrogen compounds by passage through winter-time orographic cloud (1996)
    Springer
    Journal of atmospheric chemistry 24 (1996), S. 211-239 
    Details
    ISSN: 1573-0662
    Schlagwort(e): air pollution ; field study ; modelling ; atmospheric chemistry ; troposphere ; clouds ; nitrogen compounds ; NO x ; NO3 ; N2O5 ; NO3 - ; NO2 - ; HNO3 ; HNO2
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Four case studies are described, from a three-site field experiment in October/November 1991 using the Great Dun Fell flow-through reactor hill cap cloud in rural Northern England. Measurements of total odd-nitrogen nitrogen oxides (NO y ) made on either side of the hill, before and after the air flowed through the cloud, showed that 10 to 50% of the NO y , called NO z , was neither NO nor NO2. This NO z failed to exhibit a diurnal variation and was often higher after passage through cloud than before. No evidence of conversion of NO z to NO3 - in cloud was found. A simple box model of gas-phase chemistry in air before it reached the cloud, including scavenging of NO3 and N2O5 by aerosol of surface area proportional to the NO2 mixing ratio, shows that NO3 and N2O5 may build up in the boundary layer by night only if stable stratification insulates the air from emissions of NO. This may explain the lack of evidence for N2O5 forming NO3 - in cloud under well-mixed conditions in 1991, in contrast with observations under stably stratified conditions during previous experiments when evidence of N2O5 was found. Inside the cloud, some variations in the calculated total atmospheric loading of HNO2 and the cloud liquid water content were related to each other. Also, indications of conversion of NO x to NO z were found. To explain these observations, scavenging of NO x and HNO2 by cloud droplets and/or aqueous-phase oxidation of NO2 - by nitrate radicals are considered. When cloud acidity was being produced by aqueous-phase oxidation of NO x or SO2, NO3 - which had entered the cloud as aerosol particles was liberated as HNO3 vapour. When no aqueous-phase production of acidity was occurring, the reverse, conversion of scavenged HNO3 to particulate NO3 -, was observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00210284
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  • 6
    Digitale Medien
    Digitale Medien
    The effect of cattle grazing on soil physical and chemical properties in a silvopastoral system in the Peruvian Amazon (1998)
    Springer
    Agroforestry systems 40 (1998), S. 109-124 
    Details
    ISSN: 1572-9680
    Schlagwort(e): acid soils ; cover crop ; humid tropics ; peach palm ; Peru ; silvopastroal system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In a six-year-old peach palm (Bactris gasipaes) plantation, centrosema (Centrosema macrocarpum), a leguminous forage plant, was established as a cover crop which was eventually grazed. This experiment was designed to monitor probable changes in soil physical and chemical properties and measure peach palm fruit production and live-weight gain of cattle grazing this silvopastoral system. The experiment was installed on land that was previously cleared by a D7 bulldozer having a straight blade that mixed the thin layer of topsoil with the acid subsoil (20–40 cm) and severely compacted the soil. The results demonstrated that the centrosema cover crop reduced soil bulk density, increased water infiltration rates and reduced mechanical resistance. In general soil physical properties were improved with the use of Centrosema as forage and cover crop. Soil acidity and aluminum saturation decreased considerably, while potassium concentrations increased. Calcium and magnesium concentrations decreased over time as these minerals were stored in the pasture biomass, translocated to fresh peach palm fruits and/or exported to animals. A strong competition for nutrients was observed between the peach palm plants and Centrosema. The low production of peach palm fruits was in response to mechanized land clearing during initial establishment of the plantation, and also probably due to deficits of N, P, K, Ca and Mg in the soil instead of being a consequence to the presence of cattle. The average increase in live-weight gains of the cattle was at a rate of 445 g/animal/day during the four-years of the study. Such an increase is substantially greater than those registered in the area under traditional grazing systems used in the region.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006075114659
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  • 7
    Digitale Medien
    Digitale Medien
    Determination of part-per-trillion levels of atmospheric dimethyl sulfide by isotope dilution gas chromatography/mass spectrometry (1990)
    Springer
    Journal of atmospheric chemistry 11 (1990), S. 299-308 
    Details
    ISSN: 1573-0662
    Schlagwort(e): Dimethyl sulfide ; isotope dilution ; gas chromatography ; mass spectrometry ; troposphere
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Stable isotopic dilution was applied to the determination of dimethyl sulfide (DMS) in ambient air at the low part-per-trillion by volume (pptrv) levels. Perdeuterated DMS was used as an internal standard in the gas chromatography/mass spectrometry determination. The isotopically labelled internal standard provided insensitivity to possible losses of DMS in sampling and analysis. The lower limit of detection (LLD) was 1 pptrv with a sample acquisition time of 2 min.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00053779
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  • 8
    Digitale Medien
    Digitale Medien
    Determination of trace aqueous dimethylsulfoxide concentrations by isotope dilution gas chromatography/mass spectrometry: Application to rain and sea water (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 53-60 
    Details
    ISSN: 1573-0662
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract A method has been developed for determining trace quantities of dimethyl sulfoxide (DMSO) in aqueous solutions using isotope dilution gas chromatography/mass spectrometry. The method consisted of first reducing DMSO to dimethyl sulfide (DMS), followed by purge and trap preconcentration of DMS. The concentration of DMSO was determined from the signal ratio obtained for the parent ions of DMS and d6-DMS, and the known aqueous concentration of d6-DMSO. The precision of this method was determined to be ± 2.9 %, based on replicate DMSO determinations of a test solution prepared by adding isotopically unenriched (h6-DMSO) to distilled water. The detection limit was 0.010 nmoles/L for the sampling conditions used in this study. This method was applied to the determination of DMSO concentrations in both rain and sea water. The concentration of DMSO in rain was found to be in the range of 2–4 nmoles/L for samples collected at an inland location (Phila, PA) and 8–11 nmoles/L for samples collected at a coastal location (Lewes, DE). Determination of DMSO in sea water required special sample preparation steps to eliminate positive interferences. A depth profile of DMS, DMSO, and dimethyl sulfoniopropionate (DMSP) concentrations is reported for sea water collected off the coast of Ocean City, Md, in August, 1990
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00115222
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  • 9
    Digitale Medien
    Digitale Medien
    A time series for carbonyl sulfide in the northern hemisphere (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 527-534 
    Details
    ISSN: 1573-0662
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract The variation of OCS in the northern hemisphere for the period 1977–1991 was investigated by grouping all measurements made by our research group for that period. The data set contained 1066 measurements made in the northern hemisphere over a longitude range of 52 E to 155 W and a latitude range of 10 N to 85 N. About 50% of the measurements were made from aircraft. The overall data set had a mean of 512 parts per trillion by volume (pptv) and a standard deviation of 119 pptv. The data obtained from aircraft had a mean of 514 pptv and a standard deviation of 64 pptv. A study of the time series constructed from the data set and several subsets indicate that the change in global OCS with time is between −1.5 and 1.5 parts per trillion per year at the 95% confidence level. The data had no seasonal dependence within the precision of the data set.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00115256
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  • 10
    Digitale Medien
    Digitale Medien
    Grab sampling for the determination of sulfur dioxide and dimethyl sulfide in air by isotope dilution gas chromatography/mass spectrometry (1993)
    Springer
    Journal of atmospheric chemistry 16 (1993), S. 23-30 
    Details
    ISSN: 1573-0662
    Schlagwort(e): Dimethyl sulfide ; sulfur dioxide ; isotope dilution ; gas chromatography ; mass spectrometry ; grab sampling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO2 are used as internal standards. Spiked air samples are dried to a dew point of 〈−60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO2 and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO2 and 42% for DMS at concentrations from 5–15 pptv. Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00696621
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