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  • 1
    ISSN: 1432-1432
    Keywords: Key words: Hepatitis C virus — Synonymous substitutions — Functional constraints — Transition bias — Codon preference — RNA secondary structure — Evolutionary rate — Virus origins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Comparison of complete genome sequences for different variants of hepatitis C virus (HCV) reveals several different constraints on sequence change. Synonymous changes are suppressed in coding regions at both 5′ and 3′ ends of the genome. No evidence was found for the existence of alternative reading frames or for a lower mutation frequency in these regions. Instead, suppression may be due to constraints imposed by RNA secondary structures identified within the core and NS5b genes. Nonsynonymous substitutions are less frequent than synonymous ones except in the hypervariable region of E2 and, to a lesser extent, in E1, NS2, and NS5b. Transitions are more frequent than transversions, particularly at the third position of codons where the bias is 16:1. In addition, nucleotide substitutions may not occur symmetrically since there is a bias toward G or C at the third position of codons, while T ↔ C transitions were twice as frequent as A ↔ G transitions. These different biases do not affect the phylogenetic analysis of HCV variants but need to be taken into account in interpreting sequence change in longitudinal studies.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Climate dynamics 14 (1997), S. 45-53 
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  We investigate the behavior of the semiannual oscillation (SAO) in surface pressure and 500 hPa baroclinicity at high southern latitudes in a 1000-year GFDL coupled ocean-atmosphere GCM run. The model represents this feature but is shown to underestimate its amplitude and percentage of variance explained in the midlatitudes. South of 60 °S the simulation of the pressure oscillation, although somewhat too weak, is considerably better. Our analysis reveals significant interannual, decadal and centennial variability in the modeled SAO. While there is only a short historical record of observational data in the middle and high southern latitudes, existing studies suggest that the strength of the SAO does show significant variability on at least the first two of these time scales. Strong relationships between the semiannual cycles of surface pressure and baroclinicity are apparent in the model output, reinforcing the findings in earlier studies that the differing annual march of temperature between the midlatitudes and the Antarctic coast leads to a semiannual component in the baroclinicity and thence the surface pressure. We draw attention to extended periods when the model SAO is weak and strong, and have investigated the nature of the circulation during each period. The GFDL model results suggest that a significant proportion of the SAO variation was associated more with variations in the strength of the winter pressure maximum rather than the springtime minimum. The extent to which this and other aspects of the modeled longterm variability are related to actual atmospheric structure must await the availability of longer data records.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Potato research 40 (1997), S. 191-214 
    ISSN: 1871-4528
    Keywords: Solanum tuberosum L. ; propagation by sexual seed ; vegetative propagation ; socio-economic potential ; potatoes in the tropics ; breeding ; true potato seed (TPS)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The vast majority of cultivated potatoes are vegetatively propagated, outbred autotretraploids. Disease problems dominate the maintenance of vegetative stocks. There have been recent proposals to propagate the crop by sexual seed in order to evade some of those disease problems. Some success has been achieved but controlled crosses are necessary to avoid inbreeding depression and seed propagation is not as cheap or simple as had been hoped. The idea has evoked wide interest throughout the tropics and has had some (and increasing) practical impact on China, India and Vietnam. There is a strong tendency to use ‘tuberlets’ borne on crowded nursery plants rather than to grow true seedlings. Some seedling families have looked locally attractive but it is not always realised that to use them implies the abandonment of about half the genetic variation, a heavy price to pay for disease avoidance. There is emerging recognition that vegetative and seed propagation are complementary rather than competitive and that good breeding programmes will therefore serve both. This review concentrates upon genetic/plant breeding aspects of propagation by seed, a subject hitherto largely neglected in the literature.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4986
    Keywords: Glycoside ; synthesis ; cancer ; hexamethylmelamine ; methylol ; formaldehyde ; modelling ; deacetylation ; triazine ; N-hydroxymethyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The synthesis of analogues of the anti-tumour drug 2-[N-(hydroxymethyl)methylamino]-4,6-bis (dimethylamino)-1,3,5-triazine (HMPMM) in which the OH or a dimethylamino group is replaced by a carbohydrate has been explored. Triazinyl β-glycosides were readily prepared by reaction of sugars with trimethyl-triazinylammonium salts. These were made with one or two methylamino groups on the triazine for reaction with formaldehyde to give the cytotoxic NMeCH2OH group. However, reaction of the triazinyl glycosides with formaldehyde gave complex intractable mixtures. When the carbohydrate portion was changed to the fully protected 2,3,4,6-tetra-O-acetyl glucose a good yield of the 2-[N-(hydroxymethyl)methylamino]-4-(dimethylamino)-1,3,5-triazin-2-yl tetra-O-acetyl β-glucoside was obtained. However, de-acetylation using sodium methoxide also removed the N–CH2OH group. We are investigating protection of the base-sensitive N–CH2OH group as trialkylsilyl and benzyl ethers and are looking at de-acetylation methods that are more selective. We have prepared glycosides in which the sugar is joined through the oxygen of the NMeCH2OH group. Coupling of acetobromoglucose with HMPMM catalysed by silver salts was not successful. Although methyl and cyclohexyl derivatives of HMPMM may be produced in high yields by reaction of HMPMM with methyl and cyclohexyl alcohols under acidic catalysis, production of glycosides in this way gave poor yields. MNDO calculations on reactions of HMPMM helped us devise improved reaction conditions for the condensation of 2,3,4,6-tetra-O-acetyl glucose with HMPMM and its derivatives. The best procedure to generate one of the target glycosides is to react 2,3,4,6-tetra-O-acetyl glucose and formaldehyde with 2-methylamino- 4,6-bis(dimethylamino)-1,3,5-triazine. The β-glycoside product was de-acetylated using potassium carbonate in dry methanol. Abbreviations: HMM, hexamethylmelamine (2) or 2,4,6-tris(dimethylamino)-1,3,5-triazine; HMPMM, hydroxymethylpentamethylmelamine or 2-[N-(hydroxymethyl)-methylamino]-4,6-bis(dimethylamino)-1,3,5-triazine; PMM, Pentamethylmelamine or 2-methylamino-4,6-bis(dimethylamino)-1,3,5-triazine; TBMS, t-Butyldimethylsilyl; p-TSA, p-Toluenesulphonic acid
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-1561
    Keywords: Azadirachtin ; nimbin ; salannin ; antifeedant ; growth inhibition ; Azadirachta indica ; Spodoptera littoralis ; Locusta migratoria ; Schistocerca gregaria ; photooxidation ; photoisomerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Nimbin and salannin, major triterpenoids accompanying azadirachtin in extracts of neem (Azadirachta indica) seeds, were photooxidized by UV light in the presence of oxygen to more polar, unstable intermediates that rearranged on silica gel to two final products in which the furan ring had been oxidized to isomeric hydroxybutenolides. The isomeric hydroxybutenolides were also readily formed when a crude extract of triterpenoids from neem seeds was irradiated, and both isomers of salannin have been isolated from seeds. Photooxidation of nimbin and salannin proceeded much faster than that of azadirachtin. All photoproducts showed some biological activity againstSpodoptera littoralis, Locusta migratoria, andSchistocerca gregaria. Isonimbinolide was as potent as azadirachtin at inhibiting feeding in all three species, and it also inhibited the growth ofS. littoralis. Isosalanninolide showed potent antifeedant and growth inhibitory activity againstS. littoralis.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-0662
    Keywords: tropospheric ozone ; trends ; seasonal cycle ; carbon monoxide ; baseline monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Three independent methods have been used to sort the ozone, carbonmonoxide, and other radiatively important trace gases measured at Mace Head,Ireland, and thereby distinguish clean air masses transported over the NorthAtlantic from the more polluted air masses which have recently travelledfrom the European continent. Over the period April 1987–June 1995 theNorthern Hemisphere surface ozone baseline concentrations exhibited a meanconcentration of 34.8 ppb, with a small positive trend (+0.19 ppbyr-1), while the corresponding trend in air originating fromthe polluted European areas was negative (–0.39 ppbyr-1). Carbon monoxide measurements from March 1990 toDecember 1994 showed negative trends for both the unpolluted (–0.17ppb yr-1) and polluted data (–13.6 ppbyr-1). Overall the continent of Europe was shown to be a smallnet sink of 2.6 ppb for all occasions when European air was transported tothe North Atlantic.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-0662
    Keywords: O3 ; Ox ; boundary layer ; lower troposphere ; Europe ; distribution ; seasonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O3 concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO3 ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO3 values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O3 mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O3 levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O3 and Ox(= O3 + NO2)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied climatology 58 (1997), S. 197-210 
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary An Empirical Orthogonal Function (EOF) analysis has been applied to NOAA/NESDIS snow concentration data. The major modes of variability in January Northern Hemisphere snow concentration have been extracted and analysed. The analysis was completed separately over Eurasia and North America. Strong, coherent patterns were found for each of the first three EOFs that were analysed over both continents. Over Eurasia the first EOF showed much of Europe as well as western and central Asia in phase but eastern Asia of the opposite phase although the signal was somewhat weaker. North America had a very similar first EOF with a large positive anomaly centered over Montana reaching loadings of over 0.8. East of the Great Lakes, the anomaly changes sign, although again, its magnitude is much smaller. An EOF examination was also made of the anomalous 700 hPa geopotential height fields. These modes of variability were correlated with those of snow cover with the aim of investigating the mechanisms by which the surface boundary snow and the overlying circulation can interact. The stronger correlations were discussed and logical physical scenarios were presented for each. The results indicate that there was no common pattern whereby one medium was always forcing the other but rather a complex array of interactions where each medium could influence the other. To support the physical basis of the relationships being depicted by the EOF study, a case study of January 1981 was made. The presence of intercontinental relationships was also investigated and such relations were strongly suggested. It was proposed that the large scale organisation of the atmosphere between the two continents could go some way to explaining these links in snow variability.
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 1997-01-01
    Print ISSN: 0177-798X
    Electronic ISSN: 1434-4483
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
    Publication Date: 1997-12-16
    Print ISSN: 0930-7575
    Electronic ISSN: 1432-0894
    Topics: Geosciences , Physics
    Published by Springer
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