Showing papers by "Leibniz University of Hanover published in 1990"

Stick-slip vibrations and chaos

Abstract: Stick-slip vibrations are self-sustained oscillations induced by dry friction. They occur in engineering systems as well as in our everyday life, e.g. the sound of bowed instruments results from stick—slip vibrations of the strings. Two discrete and two continuous models of stick-slip systems have been investigated in this paper, which exhibit rich bifurcational and chaotic behaviour. Results from numerical simulations and experimental observations could be obtained. In the latter case, chaos has to be distinguished from noise in the measurements. This requires special analysis methods like the reconstruction of a pseudo-state space from a time series and the calculation of the so-called correlation integral.

A general procedure for the direct computation of turning and bifurcation points

Abstract: We address the formulation and numerical implementation of general purpose algorithme suitable for the direct computation of stability points in non linear solid mechanics. The effectiveness of the resulting algorithm is illustrated by numerical simulation that include bifurcation and loss of stability in elastoplasticity, non linear rods and non linear three dimensional shells

Effect of intraarterial versus intravenous cisplatin in addition to systemic doxorubicin, high-dose methotrexate, and ifosfamide on histologic tumor response in osteosarcoma (study COSS-86).

Abstract: In osteosarcoma, intraarterial (IA) administration of systemic treatment has been advocated to improve local tumor response preparing for, or even obviating, definitive surgery. Because data from the literature did not unequivocally support the local superiority of IA infusion, a comparative study was started in 1986. Preoperative chemotherapy consisted of 45 mg/m2 of doxorubicin on days 1 and 2; 12 g/m2 of high-dose methotrexate on days 15 and 22; and 3 g/m2 of ifosfamide on days 29, 30, 50, and 51 followed on days 31 and 52 by intravenous (IV) versus IA tourniquet infusion of cisplatin (DDP). A strict randomization of patients was not feasible. A balanced distribution of risk factors was strived for by stratifying and allocating the appropriate patients centrally. The infusion time was prolonged from 1 to 5 hours in the IV group, and the DDP dose was reduced from 150 to 120 mg/m2 in both arms when intolerable ototoxicity became apparent. A multivariate analysis was performed to exclude a bias on the response rates from risk factor distribution and from modifications of DDP infusion time and dosage. The overall fraction of histologic good responders (greater than 90% necrosis) was not found to be different after IA versus IV treatment (34/50 [68%] vs. 41/59 [69%]). Intraarterial instead of IV use of DDP within an aggressive systemic treatment does not seem to improve the local tumor response.

Intravenous Therapy with High Doses of Ranitidine and Omeprazole in Critically Ill Patients with Bleeding Peptic Ulcerations of the Upper Intestinal Tract: An Open Randomized Controlled Trial

Abstract: Thirty-nine critically ill patients with actively bleeding peptic ulcerations – Forrest lb – in the stomach or duodenum were randomly allocated to intravenous therapy with 400 mg ranitidine per day or

Therapy with garlic: results of a placebo-controlled, double-blind study.

Abstract: A double-blind study of 40 hypercholesterolaemic out-patients was carried out over a period of four months to examine the effects of a garlic powder preparation*. The drug group received 900 mg garlic powder per day, equivalent to 2,700 mg of fresh garlic. During the therapy, the drug group showed significantly lower total cholesterol, triglycerides and blood pressure than those of the placebo group. In addition, results of a self-evaluation questionnaire indicated that patients in the drug group had a greater feeling of 'well-being'.

Larval development of Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) from Greece as influenced by different host plants under laboratory conditions.

Abstract: The pine processionary caterpillar Thaumetopoea pityocampa is one of the pine defoliators of high economic importance, especially in forests of the Mediterranean. Various species of Pinus serve as food plants to this polyphagous forest pest. To observe the effects of different pines on the development and mortality, newly hatched larvae from egg batches collected at Kassandra/Greece were treated with 13 different species of pines and with one species of larch. Pinus mugo Turra was taken as the standard host plant and the effects shown by the caterpillars feeding on other pine needles were compared with those feeding on P. mugo. The pine twigs used for the current study were made available by “Berggarten” of Hannover. Caterpillars fed with the needles of P. strobus L., P. parviflora S. & Z., P. cembra L., P. wallichiana Jacks and Larix kaempferi (Lamb.) Carr. showed a delayed larval development. Moreover, a 100 % mortality could be observed within the first instar in the larvae feeding on P. parviflora and within the second instar in those feeding on P. strobus and L. kaempferi. The larvae fed with P. cembra needles could live till third instar. Though some of the mature larvae fed on P. wallichiana (= P. excelsa Wall.) migrated into the soil (larval mortality 96.7 %), none of the pupae could survive. The difference in the mean pupal weight could not be statistically verified in pupae of those caterpillars which had fed on P. contorta Dough, P. nigra Arm, and P. leucodermis Ant., although the larval mortality was recorded to be 11.7 %, 43.3 % and 33.3 %, respectively. The mean pupal weight of other groups ranged from weakly to highly significant level. Zusammenfassung Larvalentwicklung von Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) aus Griechenland auf verschiedenen Wirtspflanzen unter Laborbedingungen Vom Kiefernprozessionsspinner Thaumetopoea pityocampa (Den. & Schiff.) werden in der Mittelmeerregion verschiedene Pinus-Arten befallen. Um zu prufen, ob auch Pinien, die auserhalb des mediterranen Bereiches wachsen, als Wirtspflanzen fur die polyphagen Raupen dieses Insektes in Frage kommen, wurden frisch geschlupfte Raupen zu jeweils 20 Tieren auf Zweige von 13 verschiedenen Pinus-Arten und einer Larchen-Art verteilt und ihr Frasverhalten, Nestbau, ihre Entwicklungsgeschwindigkeit sowie Mortalitatsrate registriert. Die Gelege, aus denen die Raupen schlupften, stammten von der Halbinsel Kassandra in Nordost-Griechenland. Als Standardwirt diente Pinus mugo Turra, mit der das Frasverhalten auf den anderen Arten verglichen wurde. Alle Testpflanzen stammten aus dem Berggarten von Hannover. Raupen, die an Nadeln von P. strobus L., P. parviflora S. & Z., P. cembra L., P. wallichiana Jacks. und Larix kaempferi (Lamb.) Carr. gefressen hatten, zeigten eine verzogerte Larvalentwicklung. Eine 100 %ige Mortalitat des ersten Stadiums wurde bei Raupen gefunden, die auf P. parviflora frasen und des zweiten Stadiums bei solchen, die Nadeln von P. strobus aund L. kaempferi befressen hatten. Auf P. cembra erreichten die Raupen das dritte Stadium. Nach 96,7 %iger Mortalitat wanderten einige Larven des funften und letzten Stadiums, die auf P. wallichiana (= P. excelsa Wall.) gefressen hatten zur Verpuppung in die Erde, jedoch uberlebte keine der Puppen. Unterschiede im mittleren Puppengewicht von Tieren, die auf P. contorta Dough, P. nigra Arn. und P. leucodermis Ant. gefressen hatten, liesen sich statistisch nicht absichern. Die Larvenmortalitat betrug auf diesen Pinus-Arten 11,7%, 43,3% bzw. 33,3%. Das mittlere Puppengewicht der anderen Versuchstiergruppen unterschied sich von den P. mugo-Tieren schwach bis hoch signifikant.

Effect of pH and nitrogen source on aluminium tolerance of rye ( Secale cereale L.) and yellow lupin ( Lupinus luteus L.)

Abstract: Soluble aluminium (Al) is a major factor limiting plant growth in acid mineral soils. Aluminium concentrations in soil solutions are mainly determined by soil pH. However, pH also affects the ratio between activities of protons and cationic Al species and the equilibrium between mono-and polynuclear hydroxy-Al species. The phytotoxicity of these species is not yet clear. The objective of the present study was to clarify the role of minor changes of pH in the rhizosphere on Al phytotoxicity in two Al-tolerant plant species by direct control of the pH in the nutrient solution (4.1, 4.3, 4.5) and in addition by varying the pH in the root apoplast using either nitrate or ammonium as N source. The plants were grown in solution culture at constant external pH. Whereas the Al-sensitive plant species barley and horse bean were damaged at very low Al supplies (1.85 μM and 9.3 μM respectively), 222 μM had to be applied to rye and yellw lupin for a comparable inhibition of root elongation. Yellow lupin was initially severely inhibited in root growth by Al, but then gradually recovered from this ‘Al shock’ within 3 days. In contrast to lupin, rye was hardly affected by Al initially, and it took about 16 h until maximum inhibition of root elongation. In the presence of nitrate, raising the pH from 4.1 to 4.5 aggravated root-growth depression by Al in rye and lupin. Whereas rye roots were severely damaged by ammonium especially at low pH, lupin was rather indifferent to the N source. Aluminium toxicity was less severe in presence of ammonium compared to nitrate N. This effect was less clear with rye at lower pH, because of it's higher proton sensitivity compared to lupin. Less Al injury at lower pH and in presence of ammonium was related to lower Al concentrations in the 1 cm root tips. The results are compatible with data showing high phytotoxicity of mononuclear and polynuclear hydroxy-Al species. However, they could also be interpreted in the light of proton amelioration of Al toxicity owing to competition for Al-sensitive binding sites in the root apoplast.

A total synthesis of racemic and optically active terrein (trans-4,5-dihydroxy-3-[(E)-1-propenyl]-2-cyclopenten-1-one).

Abstract: Two routes to terrein (1), employing a novel ring contraction of 6-alkoxy-2,3-dihydro-6H-pyran-3-ones (5, 13) are described. Separation into enantiomers was carried out by classical resolution via diastereomeric camphanic acid ester intermediates (14, 15). A new method for cleavage of the 2-(trimethylsilyl)ethyl protecting group in the presence of acid and base sensitive functionality is reported.

The impact of innovation centres on small technology-based firms: The example of the federal republic of Germany

Abstract: Small and medium-sized enterprises have not only in the Federal Republic of Germany been the source of several strategies of economic development and innovation policy for some time. The majority of these measures aims at revealing the potential strength of small and medium-sized enterprises in the innovation process by eliminating particular bottlenecks in the development and other problems of these enterprises which large enterprises do not have. Since 1983, the instrument of innovation centres for a specific promotion of a part of the small and medium-sized enterprises, namely, the new technology-based firms, has been applied also in the Federal Republic. This article investigates to what extent the meanwhile nearly 70 innovation centres could have a positive influence on the development of technology-based small firms. The empirical basis of the analysis consists of data collected in 31 innovation centres and 177 of the enterprises located there.

Mechanical impedance increases aluminium tolerance of soybean (Glycine max) roots

Abstract: The effect of aluminium (Al) on root elongation was studied in solution culture and sand culture. Compared to solution culture, in sand culture a ten times higher Al supply was necessary to inhibit root elongation to a comparable degree. This was due to a much lower Al uptake into the 5 mm root tips in sand culture. Fe concentrations in root tips were also lower in sand culture. Ca concentrations were higher and less depressed by Al, whereas Mg and K concentrations were not affected by the culture substrate. Regressions of Al concentrations in root tips versus inhibition of root elongation by Al revealed root damage at lower Al concentrations in sand culture. The effect of culture substrate on Al tolerance was independent of N source and could also be shown in flowing solution culture with and without sand. The results indicate that mechanical impedance in sand culture decreased Al uptake. This may be due to enhanced exudation of organic complexors thus reducing activites of monomeric Al species.

Solid state fermentation : physical and nutritional factors influencing gibberellic acid production

Abstract: The production of gibberellic acid (GA3) was found to be influenced by physical and nutritional factors. The nutritional factors studied were the urea nitrogen and MgSO4 concentrations, whereas the physical factors were moisture content, autoclaving time, inoculum ratio and moist medium to culture flask volume ratio. The yield of GA3 was improved 2.9 times by judicious selection of these parameters. Thus, the increase in GA3 yield in the wheat bran medium reduces the expense on medium and further leads to reduction of the overall cost of production.

Correlation Field Splitting in a Two‐Dimensional Phase: CO2 Adsorbed on the NaCl(100) Cleavage Plane

Abstract: L'adsorption de CO 2 sur NaCl (100) dans des conditions d'ultravide pour des temperatures comprises entre 73 et 95 o K est etudiee par spectrometrie IR a transformee de Fourier

Control of Thaumetopoea pityocampa (Den. & Schiff.) by extracts of Melia azedarach L. (Meliaceae)1

Abstract: The effects of methanolic extract of Melia azedarach L. drupes on all the larval instars of Thaumetopoea pityocampa were studied under laboratory conditions. The caterpillars were let to feed on the twigs of Pinus mugo sprayed with different concentrations (1, 5 and 10%) of Melia extract. A clear antifeedant effect could be seen with the increasing concentrations of the extract. The animals lost their weights. They neither clustered in the group nor spun the nest. Not only 5 and 10% but 1% Melia extract was also effective to get a 100% mortality. The young stage larvae treated with this extract acquired higher mortality in shorter duration than the mature ones. On the basis of the laboratory study, field trials in a pine forest in Greece were undertaken. Interestingly enough, the results found here were more or less similar to those observed in the lab: Mortality rose higher, as decided by the increasing concentrations. It could often be observed that at higher concentrations the caterpillars did not come out of the nests. Though the nests and the branches on the periphery of the nests were sprayed with this extract, the parasites of Thaumetopoea larvae still showed their activities. Zusammenfassung Bekampfung von Thaumetopoea pityocampa (Den. & Schiff.) mit Extrakten von Melia azedarach L. (Meliaceae) Die Wirkung methanolischer Extrakte aus Fruchten von Melia azedarach auf die Raupen des Kiefernprozessionsspinners wurde untersucht. Im Labor wurden Experimente mit allen Stadien durchgefuhrt. Die Larven wurden dazu auf kleinen Zweigen von Pinus mugo gehalten, die mit verschiedenen Konzentrationen eines Melia-Extraktes (1, 5 und 10%) bespruht waren. In Abhangigkeit von der ansteigenden Konzentration konnte eine deutliche frasabschreckende Wirkung beobachtet werden. Die Tiere verloren nachfolgend an Gewicht, vereinzelten sich und bauten kein Nest mehr. Bei allen Konzentrationen wurde nach einer gewissen Zeit 100%ige Mortalitat erreicht. Jungere Stadien, die mit diesem Extrakt behandelt wurden, erreichten hohe Mortalitat in kurzerer Zeit als die alteren Larven. Auf der Grundlage dieser Laborexperimente wurden Freilandversuche in einem Kiefernforst in Griechenland unternommen. Die Ergebnisse waren denen im Labor recht ahnlich: Die Mortalitat bzw. Anzahl der geschadigten Tiere stieg in Abhangigkeit von der eingesetzten Extraktkonzentration stark an. Bei hohen Konzentrationen verliesen die Raupen ihre Nester in vielen Fallen nicht mehr. Interessanterweise zeigten die Parasitoiden der Thaumetopoea-Raupen weiterhin ungehindert ihre Aktivitaten, obwohl die Nester und die umliegenden Zweige mit Melia-Extrakt bespruht waren.

Pure enantiomers from retro-diels-alder processes

Abstract: Diastereoselective and regioselective transformations of cycloadducts to enantiomerically pure cyclopentadienes are reported Retro-Diels-Alder processes finally give rise to pure enantiomers in high yield

Radial gas diffusion from roots of rice ( Oryza sativa L.) and Kallar grass ( Leptochloa fusca L. Kunth), and effects of inoculation with Azospirillum brasilense Cd

Abstract: Cortical root air space (aerenchyma) helps rice and Kallar grass to survive flooding conditions. The dependence of the oxygen concentration in the rhizosphere on the root aerenchyma volume, the plant age,-species and plant respiration is described. Additionally diffusional effects of different types of gases are evaluated. Inoculation of the rhizosphere with the micro-aerobically N2-fixing microorganismAzospirillum brasilense Cd brought about an increased oxygen concentration in the rhizosphere by the factor 3.3 for rice and 5.3 for Kallar grass. This effect is thought to be due to enhanced root cell wall permeability probably caused by IAA-like phytohormones released by the bacteria.

Isolation and growth of a bacterium able to degrade nitrilotriacetic acid under denitrifying conditions.

Abstract: A Gram-negative bacterium was isolated from river sediment which was able to grow with nitrilotriacetic acid as a combined carbon, nitrogen and energy source in the absence of molecular oxygen using nitrate as the terminal electron acceptor. Batch growth parameters and mass balances are reported for growth under both aerobic and denitrifying conditions.