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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of applied electrochemistry 26 (1996), S. 1037-1043 
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Mechanically polished zirconium electrodes were potentiodynamically polarized in phosphate buffer solutions of various pH values and in 0.5 lvl NaOH. The results show that the shape of the I-E curves is independent of the solution pH. At relatively low scan rates, oxygen gas evolution was observed. The oxide film thickness was calculated from the values of the charge consumed in the anodic process assuming 100% current efficiency for oxide formation below oxygen evolution (lower values for the current efficiency are assumed for potentials above oxygen evolution). Capacitance measurements, together with the calculated oxide thickness, were used to estimate values for the dielectric constant of the oxide. Two different values of the dielectric constant were obtained for the oxides formed in the range of potential below and above oxygen evolution. Also, higher dielectric constant values were obtained with increasing solution pH. Anion incorporation was assumed to increase the conductivity of the oxide films and, hence, decrease the dielectric constant. A two-layer structure is proposed for the anodically formed oxide on zirconium in aqueous solutions; an anion-free layer near the metal and an outer layer containing the incorporated anions.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 127 (1996), S. 455-459 
    ISSN: 1434-4475
    Keywords: Herpes simplex virus ; Human immunodeficiency virus ; Isocytidines ; N2-alkyl-5-methyl ; Nucleosides ; convergent synthesis of ; 2-Thiouridine ; 5,S2-dimethyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung N2-substituierte 5-Methylisocytidin-Derivate wurden ausgehend von S2-Methyl-2-thiothymidin entweder durch direkte Substitution der Methylthiogruppe durch eine Aminogruppe und anschließende Kondensation mit 1,2,3,5-tetra-O-Acetyl-β-D-ribofuranose zum acetylierten Nucleosid oder umgekehrt durch Synthese eines acetylierten 5,S2-Dimethyl-2-thiouridins und nachfolgende Behandlung mit dem entsprechenden Amin hergestellt.
    Notes: Summary N2-Substituted 5-methylisocytidine derivatives were synthesized from S2-methyl-2-thiothymine either by direct substitution of the methylthio group by an amino group and subsequent condensation with 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose to give the acetylated nucleoside or by the opposite sequence first preparing an acetylated 5,S2-dimethyl-2-thiouridine followed by treatment with the appropriate amine.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The international journal of advanced manufacturing technology 12 (1996), S. 255-265 
    ISSN: 1433-3015
    Keywords: Abrasive waterjet technology ; Erosion ; Machining processes ; Material cutting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abrasive waterjet cutting operates by the impingement of a high-velocity abrasive-laden waterjet against the workpiece. The jet is formed by mixing abrasive particles with high-velocity water in mixing tubes and is forced through a tiny sapphire orifice. The accelerated jet exiting the nozzle travels at more than twice the speed of sound and cuts as it passes through the workpiece. This cutting process is being developed as a net-shape and near-net-shape machining process for cutting many metals and hard-to-machine materials. The narrow kerf produced by the stream results in neither delimitation nor stresses along the cutting path. This new technology offers significant advantages over traditional processes for its ability to cut through most sections of dense or hard materials without the need for secondary machining, to produce contours, and to be integrated into computer-controlled systems. The abrasive waterjet cutting process involves a large number of process and material parameters which are related to the waterjet, the abrasive particles, and workpiece material. Those parameters are expected to effect the material removal rates and the depth of cut. The purpose of the present work is to propose a model which is capable of predicting the maximum depth of cut for different types of materials using different process parameters. A comparison of the results of the proposed model and the models reported in the literature is introduced along with a discussion of the limitations of those models.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-4475
    Keywords: Nucleosides, convergent synthesis of ; Nucleosides, 2′,3′-dideoxy-3′-fluoro ; Nucleosides, 2′,3′-dideoxy-3′-amino ; 2-Methylthiopyridin-4(1H)-one nucleosides ; Human immunodeficiency virus ; Herpes simplex virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Methyl-2,3-didesoxy-3-fluoro-5-O-(4-phenylbenzoyl)-β-D-erythro-pentofuranosid (3) und 1,5-di-O-Acetyl-2,3-didesoxy-3-phthalimido-β-D-erythro-pentofuranose (12) wurden in Gegenwart von Trimethylsilyltriflat als Katalysator mit den silylierten 2-Methylthiopyridin-4(1H)-onen2a, b zu den entsprechenden Nucleosiden5–6 und13 kondensiert. Bei diesen Reaktionen tritt als Nebenreaktion eine Öffnung der endocyclischen C-O — Bindung auf, sodaß auch die acyclischen Nucleoside4a, b gebildet werden. Die 3′-Fluoronucleoside wurden mit NH3/MeOH entschützt, die 3′-Phthalimidonucleoside mit Methylamin in Ethanol. Letztere Reaktion resultierte in eine gleichzeitigen Substitution der Pyrimidineinheit unter Austausch der Methylthiogruppe. Das 2-Methylthioanalogon zu 3′-Desoxy-3′-fluorthymidin zeigt mäßige Aktivität gegen HIV-1.
    Notes: Summary Methyl 2,3-dideoxy-3-fluoro-5-O-(4-phenylbenzoyl)-β-D-erythro-pentofuranoside (3) as well as 1,5-di-O-acetyl-2,3-dideoxy-3-phthalimodo-β-D-erythro-pentofuranose (12) were condensed with silylated 2-methylthiopyridin-4(1H)-ones2a, b in the presence of trimethylsilyl triflate as a catalyst to produce the corresponding nucleosides5, 6, 13. In these reactions, an endocyclic cleavage of C-O in3 took place; therefore, acyclic nucleosides4a, b were also formed. All 3′-fluoro nucleosides were deprotected with NH3/MeOH; the 3′-phthalimido nucleosides were deprotected with methylamine in ethanol. The latter method resulted in a concomitant substitution reaction in the pyrimidine moiety with replacement of the methylthio group. The 2-methylthio analogue of 3′-deoxy-3′-fluorothylmidine showed moderate activity against HIV-1.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0630
    Keywords: 78.20.-e ; 81.15.-z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Solid solutions of ZnSe x Te1−x (0. 1 ≤x ≤ 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe x Te1−x (0.1 ≤x ≤ 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10−4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe x Te1−x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE g andE g +Δ so The variations in bothE g andE g +Δ so, withx indicate that ZnSe x Te1−x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0630
    Keywords: PACS: 78.20. ; e; 81.15. ; z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Solid solutions of ZnSe x Te 1-x (0.1≤x≤1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fraction x following Vegard’s law: a(x)=6.165−0.485x. Thin films of ZnSe x Te 1-x (0.1≤x≤1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10-4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe x Te 1-x polycrystalline films of different compositions have two direct transitions with corresponding energy gaps E g and E g+ΔSO The variations in both E g and E g+ΔSO with x indicate that ZnSe x Te 1-x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0789
    Keywords: Atrazine ; Microbial biomass ; Herbicide degradation ; Basal respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory incubation experiment was set up to determine the effects of atrazine herbicide on the size and activity of the soil microbial biomass. This experiment was of a factorial design (0, 5, and 50 μg g−1 soil of non-labelled atrazine and 6.6×103 Bq g−1 soil of 14C-labelled atrazine) x (0, 20, and 100 μg g−1 soil of urea-N) x (pasture or arable soil with a previous history of atrazine application). Microbial biomass, measured by substrate-induced respiration and the fumigation-incubation method, basal respiration, incorporation of 14C into the microbial biomass, degradation of atrazine, and 14C remaining in soil were monitored over 81 days. The amount of microbial biomass was unaffected by atrazine although atrazine caused a significant enhancement of CO2 release in the non-fumigated controls. Generally, the amounts of atrazine incorporated into the microbial biomass were negligible, indicating that microbial incorporation of C from atrazine is not an important mechanism of herbicide breakdown. Depending on the type of soil and the rate of atrazine application, 18–65% of atrazine was degraded by the end of the experiment. Although the pasture soil had twice the amount of microbial biomass as the arable soil, and the addition of urea approximately doubled the microbial biomass, this did not significantly enhance the degradation of atrazine. This suggests that degradation of atrazine is largely independent of the size of the microbial biomass and suggests that other factors (e.g., solubility, chemical hydrolysis) regulate atrazine breakdown. A separate experiment conducted to determine total amounts of 14C-labelled atrazine converted into CO2 by pasture and arable soils showed that less than 25% of the added 14C-labelled atrazine was oxidised to 14CO2 during a 15-week period. The rate of degradation was significantly greater in the arable soil at 24%, compared to 18% in the pasture soil. This indicates that soil microbes with previous exposure to atrazine can degrade the applied atrazine at a faster rate.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1572-8943
    Keywords: HgS ; Sb2S3 ; thermophysical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The specific heat (C p), thermal conductivity (λ), thermal diffusivity (a), and electrical conductivity (σ) were measured for polycrystalline HgS and Sb2S3 in the temperature range 300–600 K. The measurements were performed with an experimental apparatus based on a socalled flash method. The results showed that the mechanism of heat transfer is mainly due to phonons, whereas the contribution of electrons and bipolars is very small indeed. The energy gap of the samples was also calculated.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-1561
    Keywords: Allelopathy ; bioassay ; Carduus nutans L. ; comparative approach ; correlative evidence ; forage plant ; grassland ; phytometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Various allelopathy bioassays were used to evaluate the allelopathic potential of 10 grassland forage species against a common test (phytometer) species,Carduus nutans L. Aqueous extracts did not influenceC. nutans germination, although radicle elongation was often severely inhibited.C. nutans was strongly affected by shoot, but not root, leachates. Decomposing ground tissue had mixed effects, and often stimulated shoot production ofC. nutans. Calculation ofR 2 (coefficient of determination) values between these results, and the results of previous experiments investigating the effects of the same 10 species onC. nutans emergence and development in field plots and glasshouse competition experiments frequently revealed strong, statistically significant relationships. Our results therefore provide correlative evidence for the importance of allelopathy in field conditions.
    Type of Medium: Electronic Resource
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