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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 137-144 
    ISSN: 1476-5535
    Schlagwort(e): Composting ; Explosives ; Propellants ; Thermophilic ; Mesophilic ; Bioremediation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Composting was investigated as a bioremediation technology for clean-up of sediments contaminated with explosives and propellants. Two field demonstrations were conducted, the first using 2,4,6-trinitrotoluene (TNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and N-methyl-N,2,4,6-tetranitroaniline (tetryl) contaminated sediment, and the second using nitrocellulose (NC) contaminated soil. Tests were conducted in thermophilic and mesophilic aerated static piles. Extractable TNT was reduced from 11840 mg/kg to 3 mg/kg, and NC from 13090 mg/kg to 16 mg/kg under thermophilic conditions. Under mesophilic conditions, TNT was reduced from 11 190 mg/kg to 50 mg/kg. The thermophilic and mesophilic half-lives were 11.9 and 21.9 days for TNT, 17.3 and 30.1 days for RDX, and 22.8 and 42.0 days for HMX, respectively. Known nitroaromatic transformation products increased in concentration over the first several weeks of the test period, but decreased to low concentrations thereafter.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1476-5535
    Schlagwort(e): Fructo-oligosaccharide ; 1-Kestose ; Glycoprotein ; Fructosyl-transferring activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Two extracellular β-fructofuranosidases (E-1 andE-2) fromAureobasidium sp. ATCC 20524, producing 1-kestose (1F-β-fructofuranosyl-sucrose) from sucrose, were purified to homogeneity. Molecular weights of the enzymes were estimated to be about 304000 (E-1) and 315000 (E-2) Da by gel filtration. The enzymes contained 33% (w/w) (E-1) and 27% (w/w) (E-2) carbohydrate. TheK m values for sucrose ofE-1 andE-2 andE-2 were 0.34 and 0.28 M, respectively. were 0.34 and 0.28 M, respectively. The enzymatic profiles of these enzymes were almost identical to intracellular enzymesP-1 andP-2 except for the differences in carbohydrate content andK m values ofE-2 andP-2.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 149-161 
    ISSN: 1476-5535
    Schlagwort(e): Toxin ; Secondary plant metabolite ; Allelochemical ; Insecticide ; Mycotoxin ; Endocytobiont
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Many species of insects cultivate, inoculate, or contain symbiotic fungi. Insects feed on plant materials that contain plant-produced defensive toxins, or are exposed to insecticides or other pesticides when they become economically important pests. Therefore, it is likely that the symbiotic fungi are also exposed to these toxins and may actually contribute to detoxification of these compounds. Fungi associated with bark beetles, ambrosia beetles, termites, leaf-cutting ants, long-horned beetles, wood wasps, and drug store beetles can variously metabolize/detoxify tannins, lignins, terpenes, esters, chlorinated hydrocarbons, and other toxins. The fungi (Attamyces) cultivated by the ants and the yeast (Symbiotaphrina) contained in the cigarette beetle gut appear to have broad-spectrum detoxifying abilities. The present limiting factor for using many of these fungi for large scale detoxification of, for example, contaminated soils or agricultural commodities is their slow growth rate, but conventional strain selection techniques or biotechnological approaches should overcome this problem.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 163-172 
    ISSN: 1476-5535
    Schlagwort(e): Biosensors ; Process control ; Enzyme thermistor ; Immunoassay ; Bio-field effect transistor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary A short review about the biosensor research activities for bioprocess monitoring in the F.R.G. after its reunification is given. The principles of biosensor applications are presented. In situ sensors and sensors based on the principles of flow injection analysis are studied. Some applications of a four-channel enzyme thermistor, bio-field effect transistors, and immunoanalysis systems for real process monitoring are presented.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 1476-5535
    Schlagwort(e): Vibrio vulnificus ; Oyster ; Monoclonal antibody ; Most probable number ; Enzyme immunoassay
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Oysters, suspended particulate matter (SPM), sediment and seawater samples were collected from West Galveston Bay, Texas over a 16-month period and analyzed for the presence ofVibrio vulnificus, a naturally-occurring human marine pathogen. Detection and enumeration ofV. vulnificus was performed using a species-specific monoclonal antibody (mAb FRBT37) in an enzyme immunoassay (EIA)-most probable number (MPN) procedure capable of detecting as few as 2000 target organisms.V. vulnificus was not detected in seawater, oyster or SPM samples during the cold weather months, but was detected at low levels in several sediment samples during this time period. Increased levels of the organism were first observed in early spring in the sediment, and then in SPM and oysters. The major increase inV. vulnificus occurred only after the seawater temperature had increased above 20°C and the winter-spring rainfall had lowered the salinity below 16‰. The highestV. vulnificus levels at each site were associated with suspended particulate matter. These results are consistent with the hypothesis that (1)V. vulnificus over-winters in a floc zone present at the sediment-water interface, (2) is resuspended into the water column in early spring following changes in climatic conditions, (3) colonizes the surfaces of zooplankton which are also blooming during early spring and (4) are ingested by oysters during their normal feeding process.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 235-238 
    ISSN: 1476-5535
    Schlagwort(e): Biodegradation ; Pseudomonas putida ; Immobilization ; Sodium cyanide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Pseudomonas putida, isolated from contaminated industrial wastewaters and soil sites, was found to utilize sodium cyanide (NaCN) as a sole source of carbon and nitrogen. Cells, immobilized in calcium alginate beads (1–2 mm diameter) were aerated in air-uplift-type fluidized batch bioreactor containing 100–400 ppm of NaCN. Degradation of NaCN was monitored for 168 h by analyzing gaseous and dissolved ammonia (NH3), CO2, pH and optical density. The results indicated that the alginate-immobilized cells ofP. putida were able to degrade NaCN into NH3 and CO2 in a time-dependent manner.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 229-234 
    ISSN: 1476-5535
    Schlagwort(e): Heat shock protein (HSP) ; Yeast ; Saccharomyces ; Viability ; Thermotolerance ; Ethanol tolerance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Heat shock and ethanol stress of brewing yeast strains resulted in the induction of a set of proteins referred to as heat shock proteins (HSPs). At least six strongly induced HSPs were identified in a lager brewing strain and four HSPs in an ale brewing strain. Four of these HSPs with molecular masses of approximately 70, 38, 26 and 23 kDa were also identified in two laboratory strains ofSaccharomyces cerevisiae. The appearance of HSPs correlated with increased survival of strains at elevated temperatures and high concentrations of ethanol. These results suggest that HSPs may play a role in the ethanol and thermotolerance of yeasts. The properties of these proteins and membrane fatty acids in relation to heat and ethanol shock are being investigated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 239-245 
    ISSN: 1476-5535
    Schlagwort(e): Novel polysaccharide ; Bacillus licheniformis ; Raffia venifera ; d-Glucose ; d-Mannose ; d-Xylose
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary A polysaccharide producing strain ofBacillus licheniformis was isolated from exudate of raffia palm,Raffia vinifera. The optimum conditions for growth and polysaccharide production have been investigated and established. No appreciable polysaccharide was formed on glucose. It grew best in Czapek-Dox media with sucrose as the carbon source. The polysaccharide has been characterized as a heteropolymer containingd-glucose,d-mannose andd-xylose.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 269-269 
    ISSN: 1476-5535
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 251-255 
    ISSN: 1476-5535
    Schlagwort(e): β-Fructofuranosidase ; Deglycosylation ; Aureobasidium ; Enzymatic stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Most of the carbohydrate moiety of β-fructofuranosidaseP-1 fromAureobasidium sp. ATCC 20524 was removed by endo-β-N-acetylglucosaminidase F. A subunit of 94000 Da was observed in SDS-PAGE after deglycosylation. TheK m value for sucrose was not changed by deglycosylation but the stability at pH 4–5 and 50°C was decreased. The deglycosylated enzyme was more sensitive to proteases such as pronase E and subtilisin than the native enzyme. It is considered that the carbohydrate moiety of β-fructofuranosidaseP-1 contributes to the stability of the enzyme but is not essential in its catalytic function.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 37-43 
    ISSN: 1476-5535
    Schlagwort(e): Linear alkylbenzene sulfonate ; Biodegradation ; Plasmid ; Detergent ; Gene probe
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Linear alkylbenzene sulfonate (LAS) is a widely used anionic surfactant. Although approximately 1 million metric tons of LAS are produced annually, relatively little is known about the bacteria or the genetic factors that control LAS degradation in the environment. The objectives of this research were to: i) compare bacterial populations in wastewater and pristine pond systems; ii) determine the frequency of plasmids in bacteria from these sites; and iii) compare the frequency of DNA sequences coding for aromatic catabolism in isolates from these two sites. Plate counts indicated that exposure to wastewater resulted in higher levels of both heterotrophic bacteria and bacteria capable of growing on LAS containing medium (LAS/YEPG). In addition to higher numbers, a higher proportion of heterotrophs from the wastewater system were capable of growth on LAS/YEPG medium. Thus, the high levels of LAS in the wastewater system apparently selected fro organisms that were able to tolerate and/or degrade, it. Mineralization of14C-ring labelled LAS in any habitat related to the presence of organisms that grew on LAS/YEPG. Although may of these isolates could carry out primary degradation, no isolate, could mineralize14C-ring LAS in pure culture. A higher incidence of plasmids was found in bacteria from the wastewater pond and among bacteria that grew on LAS containing medium. However, the presence of plasmid, DNA did not necessarily confer the ability to degrade LAS nor was the ability to degrade LAS dependent on the presence of a plasmid. The incidence of selected genotypes for aromatic catabolism was similar among isolates on LAS/YEPG at both sites, suggesting that LAS ring degradation may be present in other populations or encoded by alternative sequences. In conclusion, LAS mineralization is mediated by a consortium and the evidence that initial attack of LAS is plasmid mediated is inconclusive.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 103-107 
    ISSN: 1476-5535
    Schlagwort(e): Fatty acid bioconversion ; hydroxy octadecenoic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Previously, we reported the discovery of a new compound, 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) which was produced from oleic acid by a new bacterial isolate PR3 [6,7]. The reaction is unique in that it involves a hydroxylation at two positions and a rearrangement of the double bond of the substrate molecule. Now, we have isolated another compound from the reaction mixture determined by GC/MS to be 10-hydroxy-8-octadecenoic acid (HOD). NMR and IR data indicate that the unsaturation is probablycis. The optimum pH and temperature for the production of HOD by strain PR3 were 6.5 and 30°C, about the same as those for DOD. However, the amount of HOD detected remained small throughout an 48-h reaction period during which the amount of DOD increased sharply. At 48 h of reaction, the ratio between HOD∶DOD was 1∶10. HOD may be an intermediate in the biosynthesis of DOD from oleic acid.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 109-113 
    ISSN: 1476-5535
    Schlagwort(e): Candida blankii ; Biomass ; d-Xylose ; l-Arabinose ; Acetate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary All fourCandida blankii isolates evaluated for growth in simulated bagasse hemicellulose hydrolysate utilized the sugars and acetic acid completely. The utilization ofd-xylose,l-arabinose and acetic acid were delayed by the presence ofd-glucose, but after glucose depletion the other carbon sources were utilized simultaneously. The maximum specific growth rate of 0.36 h−1 and cell yield of 0.47 g cells/g carbon source assimilate compared with published results obtained withC. utilis. C. blankii appeared superior toC. utilis for biomass production from hemicellulose hydrolysate in that it utilizedl-arabinose and was capable of growth at higher temperatures.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 115-119 
    ISSN: 1476-5535
    Schlagwort(e): Mycolytic enzymes ; Trichoderma viride ; Protoplasts ; Cochliobolus lunatus ; Fermentation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Microorganism useful for the induction of enzymes lytic towards walls of filamentous fungusCochliobolus lunatus were studies. Production of specificTrichoderma viride mycolytic enzymes was studied in a laboratory fermentor. The product with high chitinase and relatively low protease activity gave better yields ofC. lunatus protoplasts than commercial Novozym 234.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 121-125 
    ISSN: 1476-5535
    Schlagwort(e): Trichoderma viride ; Cellulase production ; Optimized production medium and parameters
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary A 25-l scale protocol is devised for the optimal secretion and recovery of fungal cellulase. Using a selected higher yieldingTrichoderma viride SMC strain, a protocol consisted of: a) an optimized production medium rich in microcrystalline cellulose (MCC), fortified with 1% (w/v) ammonium sulphate, 0.5% (w/v) soybean flour, 0.1% (v/v) Tween-80 and other trace nutrients; b) optimized physical parameters of production, such as an inoculum containing a homogeneous suspension of 6×107 conidia per 1,28±1°C, pH 4.0±0.5, 300±20 rpm, 11000±1000 l/h aeration, and 170–220 h duration; c) optimal recovery through a filter press (450 l/h rate of filtration) followed by precipitation with 2.5–3.0 volumes of acetone (15°C and basket centrifugation (27°C, 1700 rpm)); and d) vacuum drying (35°C, 4–6 h). This afforded 70% recovery of cellulase in the form of white fluffy powder containing 20000±2000 carboxy methyl cellulase and 1000±50 units filter paperase per g activities, with raw material cost of US$ 8–10 per million carboxy methyl cellulase units. During storage for 18 months at 4°C, ambient temperature and 37°C, the cellulase preparation was found to retain 100, 75 and 60% of its initial activity, respectively.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 131-135 
    ISSN: 1476-5535
    Schlagwort(e): Cheese ; Starters ; Production ; Alignate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Calcium alginate beads containingLactococcus lactis cells were used for three batch fermentations of milk or a commercially available growth medium (Gold Complete, Nordica) with the aim of producing concentrated cultures. Repeated fermentations did not significantly increase bead CFU counts which were between 3.3–7.8×1010 CFU/g. During the second and third fermentations, which lasted 6 h each, the bead populations decreased if the incubation was extended over 2 h. There was cell release from the beads. Fermentation media and fermentation time all had an effect on free cell counts, but none of these factors statistically interacted. Free cell counts were higher at the end of fermentations 2 and 3 than in the first fermentation and approximately 50% of the population was in the free state. Free cell counts were higher when the beads were incubated in Gold complete than in milk. Although the total bacterial population of a standard free cell fermentation was always higher than those having immobilized cells, immobilized cell technology did enable the production of dense cultures.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 247-250 
    ISSN: 1476-5535
    Schlagwort(e): Fructosyl-transferring enzyme ; 1-Kestose ; Fructo-oligosaccharide ; Continuous production
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary β-Fructofuranosidase P-1 fromAureobasidium sp. ATCC 20524, which produces a fructo-oligosaccharide (1-kestose) from sucrose, was immobilized covalently onto alkylamine porous silica with glutaraldehyde at high efficiency (44.4%). Optimum pore diameter of porous silica for immobilization of the enzyme was 91.7 nm. The enzymatic profiles of immobilized enzyme were almost identical to the native one except its stabilities to temperature and metal ions were improved. 1-Kestose was produced continuously and selectively from 40% (w/v) sucrose at fast flow rates by a column packed with the immobilized enzyme for up to 26 days, and the effluent concentration of 1-kestose remained in the range 113–135 mg ml−1.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 257-260 
    ISSN: 1476-5535
    Schlagwort(e): Polysaccharide ; Fructan ; Gum ; Fermentation ; Bacillus polymyxa ; Sweetener
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Bacillus polymyxa (NRRL-18475) produced a levan-type fructan (B, 2→6 fructofuranoside) when grown on sucrose, sugarcane juice, and sugarbeet molasses. The organism converted about 46% of the fructose moiety of sucrose to levan when grown on sucrose medium, however, the yields of levan from sugarcane juice and beet molasses were much less than sucrose solution. Such sugarcane juice and beet molasses can be made a good substrate for levan production by various modifications. Adding peptone to sugarcane juice or passing beet molasses through a column of gel filtration media improved levan yield to a level almost comparable to that obtained from sucrose.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 11-17 
    ISSN: 1476-5535
    Schlagwort(e): Eicosapentaenoic acid ; Mortierella elongata ; Omega-3 fatty acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary WhenMortierella elongata NRRL 5513 was cultured in shake flasks at 25°C, mycelial growth reached a stationary phase at 48 h but maximum eicosapentaenoic acid (EPA) production was observed at 6 days. When incubated at 11°C, EPA production also continued to rise during the stationary phase of growth, reaching a maximum after 10 days. An initial culture pH of 6.1 was found to be optimum for EPA production. The effect of temperature on EPA production was dependent on medium constituents. In glucose and linseed oil supplemented media, optimum temperature for EPA production was 11 and 15°C respectively. A maximum EPA yield of 0.61 g/l was obtained in linseed oil (2%), yeast extract (0.5%) supplemented basal medium. Maximum EPA content as a percentage of lipids (15.12%) was observed when the latter medium was supplemented with 0.25% urea.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 1-9 
    ISSN: 1476-5535
    Schlagwort(e): Recombinant culture ; Dissolved oxygen ; Biomass ; Plasmid content
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Four recombinant strains ofEscherichia coli were examined for the effects of the dissolved oxygen level on the level of biomass, the plasmid content, and the level of recombinant protein at the stationary phase of batch growth. Strains JM101/pYEJ001, and TB-1/pYEJ001 (encoding chloramphenicol acetyltransferase), and strain TB-1/p1034, and TB-1/pUC19 (encoding β-galactosidase) were grown at the constant dissolved oxygen levels of 0, 50, and 100% air saturation, as well as in the absence of dissolved, oxygen control. The biomass of all strains under constant aerobic conditions was 12–36 times higher than that under anaerobic conditions, but was the same as or slightly higher than that without dissolved oxygen control. The plasmid content in all strains under anaerobic conditions was 2.9–11.7 times higher than that under aerobic conditions. The optimal dissolved oxygen concentration for the specific activity of recombinant proteins was dependent upon the strain. In no strain were constant aerobic conditions optimal. However, because of the effect on biomass, controlled aerobic conditions were optimal for the volumetric activity of recombinant protein in all but one strain.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 19-25 
    ISSN: 1476-5535
    Schlagwort(e): Schizophyllum commune ; Sclerotium glucanicum ; Branched β-1,3-glucan ; Fan-impeller ; Oxygen limitation ; Process design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Glucan formation ofSchizophyllum commune andSclerotium glucanicum were investigated. Process data obtained during batch cultivation are presented. Glucan release can be improved by oxygen limitation. Thus, growth and glucan release are influenced by oxygen in opposite ways. Possible pathways of this oxygen-dependent regulation are discussed. A draft-tube/propeller system, rushtonturbine-, fan- and helicon-ribbon-impeller as well as a fundaspi and intermig agitator were tested. The 4-bladed fan impeller withd *=0.64 yielded the best results, since effective bulk mixing is much more important than bubble break up (micromixing) with regard to this system. Fed-batch cultivation always resulted in higher rates of glucan formation than the batch process.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 27-36 
    ISSN: 1476-5535
    Schlagwort(e): Genetically engineered microorganisms ; Bovine somatotropin ; Survival ; River
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary The fate in water ofEscherichia coli K-12 strain LBB269, both plasmid-free and carrying the recombinant plasmid pBGH1, was studied.E. coli K-12 strain LBB269 (pBGH1) is a nalidixic acid resistant derivative of W3110G (pBGH1), the microorganism used by Monsanto Company for the commercial production of bovine somatotropin. Water samples were obtained from the Missouri River and from the Monsanto Life Sciences Research Center aqueous waste basin. Strains LBB269 and LBB269 (pBGH1) were grown in fermentation vessel under bovine somatotropin (BST) production conditions, and inoculated into the water samples. The inoculated water samples were incubated, at 26°C, and the number of viableE. coli cells was determined as a function of time. In sterile water from both sources, the two strains remained, at a constant level for at least 28 days; LBB269 (pBGH1) remained at a constant level in sterile water for at least 300 days. In non-sterile water from both sources, the two strains declined from an initial concentration of about 3.0×106 cells per ml to less than 10 cells per ml in 147 h. The study conditions did not adversely affect the populations of indigenous microorganisms. The selective loss of strains LBB269 and LBB269 (pBGH1) demonstrates that theseE. coli strains do not survive in environmental sources of water. In addition, it was observed that the presence of pBGH1 had essentially no effect on the disappearance of strain LBB269 from either source of water.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 23
    ISSN: 1476-5535
    Schlagwort(e): Protein kinase C (PKC) ; Phorbol ester ; Methylpendolmycin ; Pendolmycin ; Actinomycete
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary During the course of screening for inhibitors of phorbol ester binding to protein kinase C, several actinomycete cultures were discovered that produce active metabolites. HPLC coupled to photodiode array and LC/MS techniques were applied to broth extracts to identify the presence of indolactams belonging to the teleocidin family. Various members of this family were rapidly identified from crude broth extracts using a combination of these spectroanalytical procedures. An analytical HPLC system was developed to optimize separation of teleocidin, A and B analogues directly from ethyl acetate extracts of whole broth cultures. This technique allowed us to identify a novel homologue of pendolmycin and demonstrated the utility of photodiode array HPLC coupled with LC/MS as an intial analytical tool in the analyses of these secondary metabolites produced by soil microorganisms.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 53-61 
    ISSN: 1476-5535
    Schlagwort(e): Bioremediation ; Biotransformation ; Cytochrome P-450 ; Metabolism ; PAHs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary The polycyclic aromatic hydrocarbons (PAHs) are a group of hazardous environmental pollutants, many of which are acutely toxic, mutagenic, or carcinogenic. A diverse group of fungi, includingAspergillus ochraceus, Cunninghamella elegans, Phanerochaete chrysosporium, Saccharomyces cerevisiae, andSyncephalastrum racemosum, have the ability to oxidize PAHs. The PAHs anthracene, benz[a]anthracene, benzo[a]pyrene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene, as well as several methyl-, nitro-, and fluoro-substituted PAHs, are metabolized by one or more of these fungi. Unsubstituted PAHs are oxidized initially to arene oxides,trans-dihydrodiols, phenols, quinones, and tetralones. Phenols andtrans-dihydrodiols may be further metabolized, and thus detoxified, by conjugation with sulfate, glucuronic acid, glucose, or xylose. Although dihydrodiol epoxides and other mutagenic and carcinogenic compounds have been detected as minor fungal metabolites of a few PAHs, most transformations performed by fungi reduce the mutagenicity and thus detoxify the PAHs.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 25
    ISSN: 1476-5535
    Schlagwort(e): α-Amylase ; Histidine ; Chemical modification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary The α-amylase ofBacillus caldovelox is inactivated by diethyl pyrocarbonate at pH 6.6 and 20°C by a monomolecular reaction with a second-order rate constant of 41.7 M−1·min−1. The rate of inactivation increases with decreasing pH, suggesting participation of an amino acid residue with a pK a of 6.6. The increase in absorbance at 240 nm, unchanged absorbance at 280 nm and reactivation in the presence of hydroxylamine suggest the participation of a histidine residue. Statistical analyses of inactivation suggest that only one histidine residue is essential for activity. Substrate afforded complete protection against inactivation, indicating the involvement of the histidine residue at the active site of the enzyme.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 26
    ISSN: 1476-5535
    Schlagwort(e): Secretion ; Periplasmic pre-S2 antigen ; Recombinant protein ; Experimental design ; Methylotrophic yeast
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary A central composite design (CCD) was used to evaluate, for the purpose of future process optimization, the influence of pH, yeast extract and ammonium chloride concentrations on the proportion of periplasmic hepatitisB pre-S2 antigen in the recombinant yeastHansenula polymorpha. Each factor was tested at five levels, and a second order polynomial model for the proportion of periplasmic antigen was fitted to the treatment combinations. pH showed the greatest effect: the proportion of periplasmic antigen was greatly increased at the higher pH levels. At the higher pH levels used, the proportion of periplasmic antigen was enhanced by a high concentration of ammonium chloride. Additional experiments have confirmed both the validity of the selected model and the optimal conditions found. A significant correlation was found between the proportion of periplasmic antigen and the total yield of antigen. These results indicated that is should be possible to modulate the distribution of the pre-S2 antigen between the periplasm and the cytoplasm of the yeast.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 91-96 
    ISSN: 1476-5535
    Schlagwort(e): Antimicrobial activity ; 2-Arylthio-N-alkylmaleimide ; Antibacterial activity ; Antifungal activity ; Minimum inhibitory concentration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary A variety of 2-arylthio-N-alkylmaleimides were prepared, and their antimicrobial activities were examined. Almost all of these compounds exhibited antibacterial activity against Gram-positive bacteria such asBacillus subtilis andStaphylococcus aureus. Some compounds such as 2-(halogeno-phenyl)-thio-N-methylmaleimides (4, 5, 6, 8 and 10) and 2-(2-carbamoylphenyl)thio-N-methylmaleimide(35) exhibited antibacterial activity againstEscherichia coli. All compounds tested were inactive againstPseudomonas aeruginosa except 2-(2-carbamoylphenyl)thio-N-methylmaleimide(35) which was marginally active. Activities against Gram-positive bacteria were not due to the effect of the substituent on the benzene ring, except in the instances 2-carboxy, 2-carbomethoxy, 2-amino groups and alkyl chains, however, activities against Gram-negative bacteria were due to phenylthio and the alkyl substituents. Some of 2-arylthio-N-alkylmaleimides were examined for their antifungal activities using eight strains of fungi, and they showed activity against these.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 73-90 
    ISSN: 1476-5535
    Schlagwort(e): β-Lactam antibiotics ; Penicillin ; Cephalosporin ; Cephamycin ; Biosynthetic gene clusters ; Control of expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary In the last decade numerous genes involved in the biosynthesis of antibiotics, pigments, herbicides and other secondary metabolites have been cloned. The genes involved in the biosynthesis of penicillin, cephalosporin and cephamycins are organized in clusters as occurs also with the biosynthetic genes of other antibiotics and secondary metabolites (see review by Martín and Liras [65]). We have cloned genes involved in the biosynthesis of β-lactam antibiotics from five different β-lactam producing organisms both eucaryotic (Penicillium chrysogenum, Cephalosporium acremonium (syn.Acremonium chrysogenum) Aspergillus nidulans) and procaryotic (Nocardia lactamdurans, Streptomyces clavuligerus). InP. chrysogenum andA. nidulans the organization of thepcbAB,pcbC andpenDE genes for ACV synthetase, IPN synthase and IPN acyltransferase showed a similar arrangement. InA. chrysogenum two different clusters of genes have been cloned. The cluster of early genes encodes ACV synthetase and IPN synthase, whereas the cluster of late genes encodes deacetoxycephalosporin C synthetase/hydroxylase and deacetylcephalosporin C acetyltransferase. InN. lactamdurans andS. clavuligerus a cluster of early cephamycin genes has been fully characterized. It includes thelat (for lysine-6-aminotransferase),pcbAB (for ACV synthase) andpcbC (for IPN synthase) genes. Pathway-specific regulatory genes which act in a positive (or negative) form are associated with clusters of genes involved in antibiotic biosynthesis. In addition, widely acting positive regulatory elements exert a pleiotropic control on secondary metabolism and differentiation of antibiotic producing microorganisms. The application of recombinant DNA techniques will contribute significantly to the improvement of fermentation organisms.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 97-101 
    ISSN: 1476-5535
    Schlagwort(e): Stereospecific degradation of 2,3-dichloro-1-propanol ; Pseudomonas sp. ; Microbial resolution ; (S)-2,3-Dichloro-1-propanol
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Pseudomonas sp. OS-K-29 assimilated (R)-2,3-dichloro-1-propanol preferentially as the sole source of carbon. Isolation of optically pure (S)-2,3-dichloro-1-propanol with 100% enantiomer excess (e.e.) from the racemate was done based on this bacterial assimilation using immobilized-cells of OS-K-29 with calcium-alginate. The overall examination of the reactor involved 19 batches for 50 days without loss of its activity. Highly pure (R)-epichlorohydrin with 99.5% e.e. was prepared from the (S)-2,3-dichloro-1-propanol with treatment of aqueous NaOH. This new method is simple and useful for manufacturing optically active (S)-2,3-dichloro-1-propanol and (R)-epichlorohydrin.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 127-130 
    ISSN: 1476-5535
    Schlagwort(e): Repression ; Derepression ; Transport ; Saccharomyces ; Glucose ; Maltose
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Growth of yeast cells on glucose resulted in complete inactivation of maltose transport and repression of the high affinity glucose transport system. When the cells were grown on maltose or subjected to substrate starvation, an increase in glucose and maltose transport was observed in both brewing and non-brewing yeast strains. The concentration of glucose employed in the growth medium was also observed to affect sugar transport activity. The higher the glucose concentration, the more pronounced the repressive effect. In addition, the time of growth of yeast on glucose or maltose also intermining the rate of sugar transport. These results are consistent with the repressive effect of glucose on the high affinity glucose and maltose transport systems.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 173-179 
    ISSN: 1476-5535
    Schlagwort(e): Monascus ; Water-soluble pigments ; Semi-synthesis ; Amino acids ; Natural food color
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary New water-soluble red pigments were produced byMonascus sp. in a chemically defined fermentation medium containing glutamate as nitrogen source. They were isolated and characterized as glutamate derivatives of the well-known orangeMonascus pigments (monascorubrin and rubropunctatin). The new pigments have several advantages over the known redMonascus pigments (rubropunctamine and monascorubramine) including very high water-solubility, higher absorption coefficient, and greater resistance to decoloration by light. Adding glutamate, glycine or leucine to a resting-cell system led to the formation of specific water-soluble red pigments corresponding to the exogenous amino acid. The water-soluble red pigments produced by resting-cells have retention times identical to those of the corresponding red derivatives made chemically from the orange pigments in methanol-phosphate buffer at pH 7. The hydrophobicities of the amino acid sources correspond to the HPLC retention times of the red pigments derived from them.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 193-199 
    ISSN: 1476-5535
    Schlagwort(e): Acetogenesis ; Biomarkers ; Cluster analysis ; Fermentation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary An anaerobic phase-separation biomass reactor was established on cellulose with the hydrolysis and fermentation steps occurring in the first stage, and acetogenesis and methanogenesis in the second stage. Based upon lipid biomarker analysis, eubacterial and eukaryotic cells accounted for approximately 6% of the volatile solids of the first stage and 17% of the second, while methanogens were approximately 1% of the volatile solids in the first stage and 9% of the second. Clustering the polar lipid fatty acids into groups based upon their distributions between the two stages of the reactor clarified the differences in community structure caused by phase-separated operation. Although inoculated from the same source, the two stages maintained very different microbial communities. Signature fatty acids known as indicators of unbalanced growth in eubacteria were significantly higher in the first stage of the reactor.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 201-211 
    ISSN: 1476-5535
    Schlagwort(e): Solanum tuberosum ; Dry-rot ; Rishitin ; Lubimin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Gibberella pulicaris (Fusarium sambucinum) is a major cause of dry-rot of stored potatoes (Solanum tuberosum) worldwide. The ability of field strains ofG. pulicaris to cause dry-rot is correlated with their ability to detoxify sesquiterpene phytoalexins produced by potato. All highly virulent field strains can detoxify the sesquiterpenes rishitin and lubimin. Meiotic recombinational analysis indicates that rishitin detoxification can be controlled at two or more loci. High virulence has been associated with one of these loci, designatedRiml. Detoxification of rishitin and lubimin comprises a complex pattern of reactions involving epoxidation, dehydrogenation, and cyclization. To date, seven lubimin metabolites and one rishitin metabolite have been characterized. Genes for rishitin and lubimin detoxification are being cloned fromG. pulicaris in order to more rigorously analyze the role and regulation of sesquiterpene metabolism in potato dry-rot. Our results indirectly support a role for sesquiterpene phytoalexins in resistance of potato tubers to dry-rot and may enhance research on alternative control strategies for this economically important potato disease.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 181-191 
    ISSN: 1476-5535
    Schlagwort(e): Pentachlorophenol ; Lignin-degrading fungi ; White-rot fungi ; Phanerochaete chrysosporium ; Phanerochaete sordida
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary The lignin-degrading fungiPhanerochaete chrysosporium, P. sordida, Trametes hirsuta, andCeriporiopsis subvermispora were evaluated for their ability to decrease the concentration of pentachlorophenol (PCP) and to cause dry weight loss in PCP-treated wood. Hardwood and softwood materials from PCP-treated ammunition boxes that were chipped to pass a 3.8-cm screen were used. All four fungi caused significant weight losses and decreases in the PCP concentration. The largest PCP decrease (84% in 4 weeks) was caused byT. hirsuta, and the smallest decrease was caused byC. subvermispora (37% in 4 weeks). After 4 weeks, the fate of spiked14C[PCP] in softwood chips inoculated withT. hirsuta was as follows: 27% was mineralized, 42.5% was non-extractable and bound to the chips, 23.5% was associated with fungal hyphae, and 6% was organic-extractable. Decreases of PCP byP. chrysosporium andP. sordida averaged 59% and 57%, respectively. PCP decreases caused byPhanerochaete spp. were not significantly affected by wood type or sterilization and were primarily due to methylation of PCP that resulted in accumulation of pentachloroanisole. Softwood weight losses caused byT. hirsuta, P. chrysosporium andC. subvermispora were respectively, 24, 6.5, and 17%, after 4 weeks. These weight losses are comparable to reported weight losses by these organisms in non-treated softwood. Nutrient supplementation significantly increased weight loss but not percentage decrease of PCP. The results of this research demonstrate the potential for using lignin-degrading fungi to destroy PCP-treated wood.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 213-218 
    ISSN: 1476-5535
    Schlagwort(e): Industrial waste ; Copper removal ; Bioleaching ; Fe medium ; Thiobacillus ferrooxidans
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Copper contained in a solid industrial waste produced in a silicone manufacturing process was leached with spent iron medium from aThiobacillus ferrooxidans culture. Most effective leaching was observed in a continuously fed, dual reactor system. Spent iron medium was generated by growingT. ferrooxidans in 0.9 K iron medium at pH 1.5 in the first reactor, and was transferred to a second reactor in which it leached the copper from the waste. Leaching was effective at a pulp density of the waste material as high as 20%. In experiments run at a pulp density of 2.5%, the spent iron medium was most efficient in leaching copper when it was first diluted 100-fold with a mineral salts solution at pH 1.5. Removal of the copper from the waste appeared to involve its displacement by acid, dissolved mineral salts, and ferric iron. Potentials for practical application of this process are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 9 (1992), S. 225-227 
    ISSN: 1476-5535
    Schlagwort(e): Pluronic F-127 ; Coal solubilization ; Polyol
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Summary Microbial coal solubilization and the extraction of solubilized coal products were carried out in media amended with polyol (Pluronic F-127), an agent which gels above 18°C but reverts to a liquid state at low temperature (4°C). The solubilized coal products, the unsolubilized coal particles and the mycelial mat were separated effectively by centrifugation at 4°C. The amount of coal solubilization was 30–50% higher in polyol-amended media than in agar media regardless of the microorganism. On the other hand, the amount of coal solubilization in polyol-amended control media was less compared to agar-amended control media.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 1-2 
    ISSN: 1436-3259
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 5-25 
    ISSN: 1436-3259
    Schlagwort(e): Solute transport ; Heterogeneity ; Dispersion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract Macrodispersion is spreading of a substance induced by spatial variations in local advective velocity at field scales. Consider the case that the steady-state seepage velocity and the local dispersion coefficients in a heterogeneous formation may be modeled as periodic in all directions in an unbounded domain. The equations satisfied by the first two spatial moments of the concentration are derived for the case of a conservative non-reacting solute. It is shown that the moments can be calculated from the solution of well-defined deterministic boundary value problems. Then, it is described how the rate of increase of the first two moments can be calculated at large times using a Taylor-Aris analysis as generalized by Brenner. It is demonstrated that the second-order tensor of macrodispersion (or effective dispersion) can be computed through the solution of steady-state boundary-value problems followed by the determination of volume averages. The analysis is based solely on volume averaging and is not limited by the assumption that the fluctuations are small. The large-time results are valid when the system is in a form of equilibrium in which a tagged particle samples all locations in an appropriately defined “phase space” with equal probability.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 89-101 
    ISSN: 1436-3259
    Schlagwort(e): Detention storage ; Pollution control ; Non-point pollutant runoff
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A simple expression is presented on the capability of storage-treatment systems to reduce non-point pollutant runoff load to natural waters. Their efficiency depends on the capacities of the facilities and probabilistic properties of runoff, such as interval, duration, volume, and concentration of runoff events. Assuming the compound Poisson process for runoff time series, the exact expressions of the ratio of treated load in terms of storage and treatment capacities are theoretically derived on the neighbourhoods of all boundaries of the domain on which the problem is defined. Then, an approximate expression over the whole domain is presented, of which the value and the first-order derivative coincide with those of the exact derived expressions near the boundaries. Accuracy is checked by Monte Carlo simulations.
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 55-68 
    ISSN: 1436-3259
    Schlagwort(e): Drought severity ; Drought duration ; Renewal-reward process
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract This research study focused on the hypothesis that extreme drought and high streamflow events come from different independent populations with different probability distributions which need to be studied separately, rather than considering the streamflow population as a whole. The inability of traditional streamflow generator models to consistently reproduce the frequency of occurrence of severe droughts observed in the historical record has been questioned by many researchers. Our study focused on the development of astochastic event generator model which would be capable of doing so. This was accomplished in a two-step process by first generating the drought event, and then deriving the streamflows which comprised that event. The model considered for this analysis was an alternating renewal-reward procedure that cycles between eventon andoff times, and is representative of drought or high streamflow event duration. The reward gained while the event ison oroff represents drought severity or high streamflow surplus. Geometric and gamma distributions were considered for drought duration and deficit respectively. Model validation was performed using calculated required capacities from the sequent peak algorithm.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 103-121 
    ISSN: 1436-3259
    Schlagwort(e): Probabilistic model ; Sensitivity ; Contaminant transport
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract A reliability approach is used to develop a probabilistic model of two-dimensional non-reactive and reactive contaminant transport in porous media. The reliability approach provides two important quantitative results: an estimate of the probability that contaminant concentration is exceeded at some location and time, and measures of the sensitivity of the probabilistic outcome to likely changes in the uncertain variables. The method requires that each uncertain variable be assigned at least a mean and variance; in this work we also incorporate and investigate the influence of marginal probability distributions. Uncertain variables includex andy components of average groundwater flow velocity,x andy components of dispersivity, diffusion coefficient, distribution coefficient, porosity and bulk density. The objective is to examine the relative importance of each uncertain variable, the marginal distribution assigned to each variable, and possible correlation between the variables. Results utilizing a two-dimensional analytical solution indicate that the probabilistic outcome is generally very sensitive to likely changes in the uncertain flow velocity. Uncertainty associated with dispersivity and diffusion coefficient is often not a significant issue with respect to the probabilistic analysis; therefore, dispersivity and diffusion coefficient can often be treated for practical analysis as deterministic constants. The probabilistic outcome is sensitive to the uncertainty of the reaction terms for early times in the flow event. At later times, when source contaminants are released at constant rate throughout the study period, the probabilistic outcome may not be sensitive to changes in the reaction terms. These results, although limited at present by assumptions and conceptual restrictions inherent to the closed-form analytical solution, provide insight into the critical issues to consider in a probabilistic analysis of contaminant transport. Such information concerning the most important uncertain parameters can be used to guide field and laboratory investigations.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 191-207 
    ISSN: 1436-3259
    Schlagwort(e): Hydrodynamic dispersion ; Fokker-Planck equation ; backward equation ; boundary layer ; complex potential function ; fraction of contaminated particles that enter a well
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 255-269 
    ISSN: 1436-3259
    Schlagwort(e): Emprical Orthogonal Functions ; interpolating runoff ; kriging
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The method of Empirical Orthogonal Functions (EOF method) is combined with an objective interpolation technique, kriging, to generate runoff series at ungauged locations. In a case study the results are compared to series interpolated by a combination of EOF analysis and regression using catchment characteristics as independent variables. The results are also compared to linear weighting of an existing runoff series, a commonly used method for spatial interpolation. The influence of altitude on the runoff is studied comparing kriging based on 2 and 3 coordinates. The study showed that the capacity of EOF analysis combined with kriging is as good as the traditionally used linear weighting. The results, when altitude is included in the kriging, are improved.
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  • 44
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    Stochastic environmental research and risk assessment 6 (1992), S. 270-288 
    ISSN: 1436-3259
    Schlagwort(e): Periodicities ; hydraulic cycle ; spectral methods
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract Periodicites in hydrologic data are frequently estimated and studied. In some cases the periodic components are subtracted from the data to obtain the stochastic components. In other cases the physical reasons for the occurrence of these periodicities are investigated. Apart from the annual cycle in the hydrologic data, periods corresponding to the 11 year sunspot cycle, the Hale cycle and others have been detected. The conclusions from most of these studies depend on the reliability and robustness of the methods used to detect these periodicities. Several spectral analysis methods have been proposed to investigate periodicities in time series data. Several of these have been compared to each other. The methods by Siddiqui and Wang and by Damsleth and Spjotvoll, which are stepwise procedures of spectrum estimation, have not been evaluated. Two of the methods of spectral analysis proposed by Siddiqui and Wang and by Damsleth and Spjotvoll are investigated in this study by using generated and observed data. Siddiqui and Wang's method is found to be superior to the Damsleth and Spjotvoll's method.
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  • 45
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    Stochastic environmental research and risk assessment 6 (1992), S. 289-303 
    ISSN: 1436-3259
    Schlagwort(e): Stream flow series ; shot-noise model ; sadolle-point approximation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract In this paper we consider the shot-noise model of streamflow series. We show how design discharge can be obtained by the stochastic intensity of thinned Poisson processes describing the peaks over a threshold. The main result concerns the stationary distribution of peaks. We derive an explicit expression for this limit distribution in terms of its Laplace transform. Approximation formulas are developed making use of the saddle point method for the asymptotic evaluation of contour integrals and the Post-Widder formula for inversion of Laplace transforms. We illustrate this methods on the case of Gamma-distributed shots. The stationary peak distribution is used to approximate the maximum value distribution for larger time intervals.
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  • 46
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    Mathematical programming 53 (1992), S. 63-78 
    ISSN: 1436-4646
    Schlagwort(e): Quadratic assignment problem ; relaxation ; lower bounds ; eigenvalue decomposition ; steepest ascent
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We investigate new bounding strategies based on different relaxations of the quadratic assignment problem. In particular, we improve the lower bound found by using an eigenvalue decomposition of the quadratic part and by solving a linear program for the linear part. The improvement is accomplished by applying a steepest ascent algorithm to the sum of the two bounds.
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  • 47
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    Mathematical programming 54 (1992), S. 127-153 
    ISSN: 1436-4646
    Schlagwort(e): Local minimization ; knapsack ; indefinite ; quadratic knapsack ; complexity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider the complexity of finding a local minimum for the nonconvex Quadratic Knapsack Problem. Global minimization for this example of quadratic programming is NP-hard. Moré and Vavasis have investigated the complexity of local minimization for the strictly concave case of QKP; here we extend their algorithm to the general indefinite case. Our main result is an algorithm that computes a local minimum in O(n(logn)2) steps. Our approach involves eliminating all but one of the convex variables through parametrization, yielding a nondifferentiable problem. We use a technique from computational geometry to address the nondifferentiable problem.
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  • 48
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    Mathematical programming 54 (1992), S. 155-176 
    ISSN: 1436-4646
    Schlagwort(e): Barrier function methods ; interior penalty methods ; minimax algorithms ; engineering design ; nondifferentiable optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract This paper presents an algorithm based on barrier functions for solving semi-infinite minimax problems which arise in an engineering design setting. The algorithm bears a resemblance to some of the current interior penalty function methods used to solve constrained minimization problems. Global convergence is proven, and numerical results are reported which show that the algorithm is exceptionally robust, and that its performance is comparable, while its structure is simpler than that of current first-order minimax algorithms.
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  • 49
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    Mathematical programming 54 (1992), S. 223-232 
    ISSN: 1436-4646
    Schlagwort(e): Global optimization ; Lipschitz functions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract This paper presents a best and worst case analysis of convergence rates for a deterministic global optimization algorithm. Superlinear convergence is proved for Lipschitz functions which are convex in the direction of the global maximum (concave in the direction of the global minimum). Computer results are given, which confirm the theoretical convergence rates.
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  • 50
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    Mathematical programming 54 (1992), S. 177-222 
    ISSN: 1436-4646
    Schlagwort(e): Nonlinear rescaling ; modified barrier functions ; multipliers method ; simultaneous solution ; dual problems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract The nonlinear rescaling principle employs monotone and sufficiently smooth functions to transform the constraints and/or the objective function into an equivalent problem, the classical Lagrangian which has important properties on the primal and the dual spaces. The application of the nonlinear rescaling principle to constrained optimization problems leads to a class of modified barrier functions (MBF's) and MBF Methods (MBFM's). Being classical Lagrangians (CL's) for an equivalent problem, the MBF's combine the best properties of the CL's and classical barrier functions (CBF's) but at the same time are free of their most essential deficiencies. Due to the excellent MBF properties, new characteristics of the dual pair convex programming problems have been found and the duality theory for nonconvex constrained optimization has been developed. The MBFM have up to a superlinear rate of convergence and are to the classical barrier functions (CBF's) method as the Multipliers Method for Augmented Lagrangians is to the Classical Penalty Function Method. Based on the dual theory associated with MBF, the method for the simultaneous solution of the dual pair convex programming problems with up to quadratic rates of convergence have been developed. The application of the MBF to linear (LP) and quadratic (QP) programming leads to a new type of multipliers methods which have a much better rate of convergence under lower computational complexity at each step as compared to the CBF methods. The numerical realization of the MBFM leads to the Newton Modified Barrier Method (NMBM). The excellent MBF properties allow us to discover that for any nondegenerate constrained optimization problem, there exists a “hot” start, from which the NMBM has a better rate of convergence, a better complexity bound, and is more stable than the interior point methods, which are based on the classical barrier functions.
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  • 51
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    Mathematical programming 54 (1992), S. 251-265 
    ISSN: 1436-4646
    Schlagwort(e): Linear programming ; Karmarkar's algorithm ; potential function ; standard form ; modified method ; rank-one updates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider partial updating in Ye's affine potential reduction algorithm for linear programming. We show that using a Goldstein—Armijo rule to safeguard a linesearch of the potential function during primal steps is sufficient to control the number of updates. We also generalize the dual step construction to apply with partial updating. The result is the first O(n 3 L) algorithm for linear programming whose steps are not constrained by the need to remain approximately centered. The fact that the algorithm has a rigorous “primal-only” initialization actually reduces the complexity to less than O(m 1.5 n 1.5 L).
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  • 52
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    Mathematical programming 54 (1992), S. 233-249 
    ISSN: 1436-4646
    Schlagwort(e): Hit and run methods ; redundancy ; linear inequalities ; coupon collector's problem
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract The hit and run methods are probabilistic algorithms that can be used to detect necessary (nonredundant) constraints in systems of linear constraints. These methods construct random sequences of lines that pass through the feasible region. These lines intersect the boundary of the region at twohit-points, each identifying a necessary constraint. In order to study the statistical performance of such methods it is assumed that the probabilities of hitting particular constraints are the same for every iteration. An indication of the best case performance of these methods can be determined by minimizing, with respect to the hit probabilities, the expected value of the number of iterations required to detect all necessary constraints. We give a set of isolated strong local minimizers and prove that for two, three and four necessary constraints the set of local minimizers is the complete set of global minimizers. We conjecture that this is also the case for any number of necessary constraints. The results in this paper also apply to sampling problems (e.g., balls from an urn) and to the coupon collector's problem.
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  • 53
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    Mathematical programming 54 (1992), S. 267-279 
    ISSN: 1436-4646
    Schlagwort(e): Linear complementarity ; P-matrix ; interior point ; potential function ; linear programming ; quadratic programming
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract The linear complementarity problem (LCP) can be viewed as the problem of minimizingx T y subject toy=Mx+q andx, y⩾0. We are interested in finding a point withx T y 〈ε for a givenε 〉 0. The algorithm proceeds by iteratively reducing the potential function $$f(x,y) = \rho \ln x^T y - \Sigma \ln x_j y_j ,$$ where, for example,ρ=2n. The direction of movement in the original space can be viewed as follows. First, apply alinear scaling transformation to make the coordinates of the current point all equal to 1. Take a gradient step in the transformed space using the gradient of the transformed potential function, where the step size is either predetermined by the algorithm or decided by line search to minimize the value of the potential. Finally, map the point back to the original space. A bound on the worst-case performance of the algorithm depends on the parameterλ *=λ*(M, ε), which is defined as the minimum of the smallest eigenvalue of a matrix of the form $$(I + Y^{ - 1} MX)(I + M^T Y^{ - 2} MX)^{ - 1} (I + XM^T Y^{ - 1} )$$ whereX andY vary over the nonnegative diagonal matrices such thate T XYe ⩾ε andX jj Y jj⩽n 2. IfM is a P-matrix,λ * is positive and the algorithm solves the problem in polynomial time in terms of the input size, |log ε|, and 1/λ *. It is also shown that whenM is positive semi-definite, the choice ofρ = 2n+ $$\sqrt {2n} $$ yields a polynomial-time algorithm. This covers the convex quadratic minimization problem.
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  • 54
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    Mathematical programming 54 (1992), S. 281-294 
    ISSN: 1436-4646
    Schlagwort(e): Linear complementarity problem ; Lemke's algorithm ; matroid intersection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider the problem of finding a maximum-weight complementary basis of anm × 2m matrix. The problem arises naturally, for example, when a complementary set of columns is proposed as an initial basis for a “warm start” of Lemke's algorithm, but the set of columns is rank-deficient. We show that the problem is a special case of the problem of finding a maximum-weight common base of two matroids. Furthermore, we show how to efficiently implement an algorithm for the general problem in the present context. Finally, we give computational results demonstrating the practicality of our algorithm in a typical application.
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  • 55
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    Mathematical programming 54 (1992), S. 295-305 
    ISSN: 1436-4646
    Schlagwort(e): Interior-point method ; linear programming ; Karmarkar's method ; polynomial-time algorithm ; logarithmic barrier function ; path-following method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We present a path-following algorithm for the linear programming problem with a surprisingly simple and elegant proof of its polynomial behaviour. This is done both for the problem in standard form and for its dual problem. We also discuss some implementation strategies.
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  • 56
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    Mathematical programming 54 (1992), S. 335-351 
    ISSN: 1436-4646
    Schlagwort(e): Adjacency ; convex game ; extreme point ; monotone path ; path length ; polymatroid ; submodular function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract This paper establishes bounds on the length of certain strictly monotone paths, relative to a given linear objective function, on a polymatroid or on the base of a polymatroid. Specialized bounds are given for a strict polymatroid and for a matroid polyhedron. Bounds on the diameter are included.
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  • 57
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    Mathematical programming 54 (1992), S. 307-333 
    ISSN: 1436-4646
    Schlagwort(e): Value convergence ; reachability ; solution set convergence ; tie-breaking ; stopping rule ; infinite horizon optimization ; production planning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider the problem of approximating an optimal solution to a separable, doubly infinite mathematical program (P) with lower staircase structure by solutions to the programs (P(N)) obtained by truncating after the firstN variables andN constraints of (P). Viewing the surplus vector variable associated with theNth constraint as a state, and assuming that all feasible states are eventually reachable from any feasible state, we show that the efficient set of all solutions optimal to all possible feasible surplus states for (P(N)) converges to the set of optimal solutions to (P). A tie-breaking algorithm which selects a nearest-point efficient solution for (P(N)) is shown (for convex programs) to converge to an optimal solution to (P). A stopping rule is provided for discovering a value ofN sufficiently large to guarantee any prespecified level of accuracy. The theory is illustrated by an application to production planning.
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  • 58
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    Mathematical programming 54 (1992), S. 353-367 
    ISSN: 1436-4646
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider the formulation of non-preemptive single machine scheduling problems using time-indexed variables. This approach leads to very large models, but gives better lower bounds than other mixed integer programming formulations. We derive a variety of valid inequalities, and show the role of constraint aggregation and the knapsack problem with generalised upper bound constraints as a way of generating such inequalities. A cutting plane/branch-and-bound algorithm based on these inequalities has been implemented. Computational experience on small problems with 20/30 jobs and various constraints and objective functions is presented.
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  • 59
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    Mathematical programming 55 (1992), S. 81-98 
    ISSN: 1436-4646
    Schlagwort(e): Quasiconvex function ; saddle point theorem ; duality ; Lagrangians
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract In this paper we show how saddle point theorems for a quasiconvex—quasiconcave function can be derived from duality theory. A symmetric duality framework that provides the machinery for deriving saddle point theorems is presented. Generating the theorems,via the framework, provides a deeper understanding of assumptions employed in existing theorems which do not utilize duality theory.
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  • 60
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    Mathematical programming 55 (1992), S. 1-15 
    ISSN: 1436-4646
    Schlagwort(e): Linear programming ; interior-point method ; projective algorithm ; combining phase I–phase II
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract Anstreicher has proposed a variant of Karmarkar's projective algorithm that handles standard-form linear programming problems nicely. We suggest modifications to his method that we suspect will lead to better search directions and a more useful algorithm. Much of the analysis depends on a two-constraint linear programming problem that is a relaxation of the scaled original problem.
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  • 61
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    Mathematical programming 55 (1992), S. 183-191 
    ISSN: 1436-4646
    Schlagwort(e): Chinese Postman problem ; integral LP duality ; integral packing ; plane integral multicommodity flows ; T-cuts
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract LetG = (V, E) be a graph and letw be a weight functionw:E →Z +. Let $$T \subseteq V$$ be an even subset of the vertices ofG. AT-cut is an edge-cutset of the graph which dividesT into two odd sets. AT-join is a minimal subset of edges that meets everyT-cut (a generalization of solutions to the Chinese Postman problem). The main theorem of this paper gives a tight upper bound on the difference between the minimum weightT-join and the maximum weight integral packing ofT-cuts. This difference is called the (T-join) integral duality gap. Letτ w be the minimum weight of aT-join, and letv w be the maximum weight of an integral packing ofT-cuts. IfF is a non-empty minimum weightT-join, andn F is the number of components ofF, then we prove thatτ w —v w ≤n F −1. This result unifies and generalizes Fulkerson's result for |T|=2 and Seymour's result for |T|= 4. For a certain integral multicommodity flow problem in the plane, which was recently proved to be NP-complete, the above result gives a solution such that for every commodity the flow is less than the demand by at most one unit.
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  • 62
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    Mathematical programming 56 (1992), S. 121-160 
    ISSN: 1436-4646
    Schlagwort(e): Max-cut problem ; cone ; polytope ; facet ; lifting ; hypermetric inequality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We study facets of the cut coneC n , i.e., the cone of dimension 1/2n(n − 1) generated by the cuts of the complete graph onn vertices. Actually, the study of the facets of the cut cone is equivalent in some sense to the study of the facets of the cut polytope. We present several operations on facets and, in particular, a “lifting” procedure for constructing facets ofC n+1 from given facets of the lower dimensional coneC n . After reviewing hypermetric valid inequalities, we describe the new class of cycle inequalities and prove the facet property for several subclasses. The new class of parachute facets is developed and other known facets and valid inequalities are presented.
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  • 63
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    Mathematical programming 56 (1992), S. 161-188 
    ISSN: 1436-4646
    Schlagwort(e): Cone ; polytope ; facet ; antiweb ; cut ; hypermetric inequality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We study new classes of facets for the cut coneC n generated by the cuts of the complete graph onn vertices. This cone can also be interpreted as the cone of all semi-metrics onn points that are isometricallyl 1-embeddable and, in fact, the study of the facets of the cut polytope is in some sense equivalent to the study of the facets ofC n . These new facets belong to the class of clique-web inequalities which generalize the hypermetric and cycle inequalities as well as the bicycle odd wheel inequalities.
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  • 64
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    Mathematical programming 56 (1992), S. 223-232 
    ISSN: 1436-4646
    Schlagwort(e): Convexity ; pseudoconvexity ; affine subspace ; potential function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract Second order conditions for the (pseudo-) convexity of a function restricted to an affine subspace are obtained by extending those already known for functions on ℝ n . These results are then used to analyse the (pseudo-) convexity of potential functions of the type introduced by Karmarkar.
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  • 65
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    Mathematical programming 56 (1992), S. 189-222 
    ISSN: 1436-4646
    Schlagwort(e): 65H10 ; 65K05 ; 65K10 ; Linearℓ 1 estimation ; linear programming ; interior-point algorithm ; simplex method ; least absolute value regression ; affine scaling method ; Karmarkar
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract Recently, various interior point algorithms related to the Karmarkar algorithm have been developed for linear programming. In this paper, we first show how this “interior point” philosophy can be adapted to the linear ℓ1 problem (in which there are no feasibility constraints) to yield a globally and linearly convergent algorithm. We then show that the linear algorithm can be modified to provide aglobally and ultimatelyquadratically convergent algorithm. This modified algorithm appears to be significantly more efficient in practise than a more straightforward interior point approach via a linear programming formulation: we present numerical results to support this claim.
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  • 66
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    Mathematical programming 56 (1992), S. 233-243 
    ISSN: 1436-4646
    Schlagwort(e): Convex programming problems ; exact penalty functions ; ε-solutions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract In this paper, we presentε-optimality criteria for convex programming problems associated with exact penalty functions. Several authors have given various criteria under the assumption that such convex problems and the associated dual problems can be solved. We assume the solvability of neither the convex problem nor the dual problem. To derive our criteria, we estimate the size of the penalty parameter in terms of anε-solution for the dual problem.
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  • 67
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    Mathematical programming 56 (1992), S. 245-284 
    ISSN: 1436-4646
    Schlagwort(e): Combinatorial optimization ; integer programming ; Karmarkar's method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We describe a cutting plane algorithm for solving combinatorial optimization problems. The primal projective standard-form variant of Karmarkar's algorithm for linear programming is applied to the duals of a sequence of linear programming relaxations of the combinatorial optimization problem.
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  • 68
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    Mathematical programming 56 (1992), S. 337-341 
    ISSN: 1436-4646
    Schlagwort(e): 90C25 ; 65K05 ; Lagrange dualization ; existence theorems ; numerical aspects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract In this note partially separable convex programs are dualized in such a way that, under certain assumptions, unconstrained concave duals arise. A return formula is given by which the solution of the primal is directly computed if a solution of the dual is known. Further, the solvability of both the primal and the dual is shown to depend essentially on the behaviour of the lower dimensional programs for determining the Fenchel conjugates.
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  • 69
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    Mathematical programming 56 (1992), S. 321-335 
    ISSN: 1436-4646
    Schlagwort(e): Network flow problems ; interior point method ; negative circuit method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract For solving minimum cost flow problems, we develop a combinatorial interior point method based on a variant of the algorithm of Karmarkar, described in Gonzaga [3, 4]. Gonzaga proposes search directions generated by projecting certain directions onto the nullspace ofA. By the special combinatorial structure of networks any projection onto the nullspace ofA can be interpreted as a flow in the incremental graph ofG. In particular, to evaluate the new search direction, it is sufficient to choose a negative circuit subject to costs on the arcs depending on the current solution. That approach results in an O(mn 2 L) algorithm wherem denotes the number of vertices,n denotes the number of arcs, andL denotes the total length of the input data.
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  • 70
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    Mathematical programming 56 (1992), S. 301-319 
    ISSN: 1436-4646
    Schlagwort(e): Linear program ; affine-scaling ; ergodic convergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract The affine-scaling algorithm, first proposed by Dikin, is presently enjoying great popularity as a potentially effective means of solving linear programs. An outstanding question about this algorithm concerns its convergence in the presence of degeneracy. In this paper, we give new convergence results for this algorithm that do not require any non-degeneracy assumption on the problem. In particular, we show that if the stepsize choice of either Dikin or Barnes or Vanderbei, et al. is used, then the algorithm generates iterates that converge at least linearly with a convergence ratio of $$1 - \beta /\sqrt n $$ , wheren is the number of variables andβ ∈ (0,1] is a certain stepsize ratio. For one particular stepsize choice which is an extension of that of Barnes, we show that the cost of the limit point is within O(β/(1−β)) of the optimal cost and, forβ sufficiently small (roughly, proportional to how close the cost of the nonoptimal vertices are to the optimal cost), is exactly optimal. We prove the latter result by using an unusual proof technique, that of analyzing the ergodic convergence of the corresponding dual vectors. For the special case of network flow problems with integer data, we show that it suffices to takeβ = 1/(6mC), wherem is the number of constraints andC is the sum of the cost coefficients, to attain exact optimality.
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  • 71
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    Mathematical programming 56 (1992), S. 343-360 
    ISSN: 1436-4646
    Schlagwort(e): Multiextremal optimization ; adaptive partition strategies ; necessary and sufficient convergence conditions ; examples
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract Following the presentation of a general partition algorithm scheme for seeking the globally best solution in multiextremal optimization problems, necessary and sufficient convergence conditions are formulated, in terms of respectively implied or postulated properties of the partition operator. The convergence results obtained are pertinent to a number of deterministic algorithms in global optimization, permitting their diverse modifications and generalizations.
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  • 72
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    Mathematical programming 56 (1992), S. 361-364 
    ISSN: 1436-4646
    Schlagwort(e): Affine scaling ; semi-infinite linear programming ; free variables
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We consider an extension of the affine scaling algorithm for linear programming problems with free variables to problems having infinitely many constraints, and explore the relationship between this algorithm and the finite affine scaling method applied to a discretization of the problem.
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  • 73
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    Mathematical programming 57 (1992), S. 215-238 
    ISSN: 1436-4646
    Schlagwort(e): Inductive inference ; Boolean function synthesis ; satisfiability ; artificial intelligence ; integer programming ; interior point method ; Riemannian geometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract In this paper we describe an interior point mathematical programming approach to inductive inference. We list several versions of this problem and study in detail the formulation based on hidden Boolean logic. We consider the problem of identifying a hidden Boolean functionℱ:{0, 1} n → {0, 1} using outputs obtained by applying a limited number of random inputs to the hidden function. Given this input—output sample, we give a method to synthesize a Boolean function that describes the sample. We pose the Boolean Function Synthesis Problem as a particular type of Satisfiability Problem. The Satisfiability Problem is translated into an integer programming feasibility problem, that is solved with an interior point algorithm for integer programming. A similar integer programming implementation has been used in a previous study to solve randomly generated instances of the Satisfiability Problem. In this paper we introduce a new variant of this algorithm, where the Riemannian metric used for defining the search region is dynamically modified. Computational results on 8-, 16- and 32-input, 1-output functions are presented. Our implementation successfully identified the majority of hidden functions in the experiment.
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  • 74
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    Mathematical programming 57 (1992), S. 279-311 
    ISSN: 1436-4646
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We considerε-approximation schemes for indefinite quadratic programming. We argue that such an approximation can be found in polynomial time for fixedε andt, wheret denotes the number of negative eigenvalues of the quadratic term. Our algorithm is polynomial in 1/ε for fixedt, and exponential int for fixedε. We next look at the special case of knapsack problems, showing that a more efficient (polynomial int) approximation algorithm exists.
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  • 75
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    Mathematical programming 57 (1992), S. 239-257 
    ISSN: 1436-4646
    Schlagwort(e): Complexity of algorithms ; convergence analysis ; interior point algorithms ; Newton's methods
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We present a theoretical result on a path-following algorithm for convex programs. The algorithm employs a nonsmooth Newton subroutine. It starts from a near center of a restricted constraint set, performs a partial nonsmooth Newton step in each iteration, and converges to a point whose cost is withinε accuracy of the optimal cost in $$O(\sqrt m \left| {\ln \varepsilon } \right|)$$ iterations, wherem is the number of constraints in the problem. Unlike other interior point methods, the analyzed algorithm only requires a first-order Lipschitzian condition and a generalized Hessian similarity condition on the objective and constraint functions. Therefore, our result indicates the theoretical feasibility of applying interior point methods to certainC 1-optimization problems instead ofC 2-problems. Since the complexity bound is unchanged compared with similar algorithms forC 2-convex programming, the result shows that the smoothness of functions may not be a factor affecting the complexity of interior point methods.
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  • 76
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    Mathematical programming 57 (1992), S. 337-339 
    ISSN: 1436-4646
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
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  • 77
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    Mathematical programming 57 (1992), S. 325-335 
    ISSN: 1436-4646
    Schlagwort(e): Strict complementarity ; interior point algorithms ; linear programming ; optimal face
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract It has been shown [8] that numerous interior-point algorithms for linear programming (LP) generate solution sequences that converge to strict complementarity solutions, or interior solutions on the optimal face. In this note we further establish a theoretical base for Gay's test (Gay, 1989) to identify the optimal face, and develop a new termination procedure to obtain an exact solution on the optimal face. We also report some numerical results for solving a set of LP test problems, each of which has a highly degenerate and unbounded optimal face.
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  • 78
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    Mathematical programming 57 (1992), S. 313-324 
    ISSN: 1436-4646
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract We discuss the average case complexity of global optimization problems. By the average complexity, we roughly mean the amount of work needed to solve the problem with the expected error not exceeding a preassigned error demand. The expectation is taken with respect to a probability measure on a classF of objective functions. Since the distribution of the maximum, max x f (x), is known only for a few nontrivial probability measures, the average case complexity of optimization is still unknown. Although only preliminary results are available, they indicate that on the average, optimization is not as hard as in the worst case setting. In particular, there are instances, where global optimization is intractable in the worst case, whereas it is tractable on the average. We stress, that the power of the average case approach is proven by exhibiting upper bounds on the average complexity, since the actual complexity is not known even for relatively simple instances of global optimization problems. Thus, we do not know how much easier global optimization becomes when the average case approach is utilized.
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  • 79
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    Computing 47 (1992), S. 323-336 
    ISSN: 1436-5057
    Schlagwort(e): 26C10 ; 26C15 ; 65H05 ; Multiplicity ; Zero identification ; Global optimination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir zeigen, daß man mit Hilfe gewisser Integrale die Anzahl der Nullstellen einer gegebenen Vielfachheit für eine Funktion einer Veränderlichen in einem beliebigen Intervall bestimmen kann. Das Vorgeben wird durch typische Beispiele erläutert.
    Notizen: Abstract It is shown that certain simple integrals determine the number of zeros with a certain multiplicity of a function of one variable in an arbitrary interval. Several typical numerical examples are given.
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  • 80
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    Computing 47 (1992), S. 337-353 
    ISSN: 1436-5057
    Schlagwort(e): 65G10 ; 65F05 ; Interval iteration ; linear interval systems ; standard simplices
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In der Literatur werden eine Reihe effizienter Algorithmen beschrieben zur Berechnung garantierter Einschließungen der Lösung numerischer Standardprobleme [3,4,8,11,12,13]. Die Einschließungen werden in Form von Mengen gegeben. In [12, 13] wird diese Menge mit Hilfe einer affinen Transformation berechnet, die stoppt, wenn eine nichtleere kompakte Menge in sich selbst abgebildet wird. Für Punkteingabedaten wurde gezeigt, daß diese Iteration genau dann stoppt, wenn die Iterationsmatrix konvergent ist [13]. In der vorliegenden Arbeit werden notwendige und hinreichende Stop-Bedingungen angegeben für Intervalleingabedaten und Intervalloperationen im reellen und im komplexen. Stoppen heißt hierbei, daß der Algorithmus aus [12] für Intervallgleichungssysteme eine Einschließung liefert. Ein Algorithmus von Neumaier wird diskutiert, und es wird ein Hybrid-Algorithmus vorgeschlagen, der die Vorteile Neumaiers und unseres Algorithmus kombiniert. Unter Benutzung einer Arbeit von Jansson [6, 7] wird eine interessante geometrische Interpretation von Einschließungsalgorithmen gegeben. Es wird gezeigt, daß die Einschließungsalgorithmen in bestimmtem Sinne optimal sind. für eine andere Klasse von Mengen, für Standardsimplexe, geben wir einige interessante Beispiele.
    Notizen: Abstract In the literature efficient algorithms have been described for calculating guaranteed inclusions for the solution of a number of standard numerical problems [3,4,8,11,12,13]. The inclusions are given by means of a set containing the solution. In [12,13] this set is calculated using an affine iteration which is stopped when a nonempty and compact set is mapped into itself. For exactly given input data (point data) it has been shown that this iteration stops if and only if the iteration matrix is convergent (cf. [13]). In this paper we give a necessary and sufficient stopping criterion for the above mentioned iteration for interval input data and interval operations. Stopping is equivalent to the fact that the algorithm presented in [12] for solving interval linear systems computes an inclusion of the solution. An algorithm given by Neumaier is discussed and an algorithm is proposed combining the advantages of our algorithm and a modification of Neumaier's. The combined algorithm yields tight bounds for input intervals of small and large diameter. Using a paper by Jansson [6,7] we give a quite different geometrical interpretation of inclusion methods. It can be shown that our inclusion methods are optimal in a specified geometrical sense. For another class of sets, for standard simplices, we give some interesting examples.
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  • 81
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    Computing 48 (1992), S. 177-189 
    ISSN: 1436-5057
    Schlagwort(e): Primary 65D30 ; Secondary 44A15 ; Strongly singular integrals ; finite-part integrals ; numerical approximation ; quadrature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In dieser Arbeit beschäftigen wir uns mit der numerischen Auswertung von singulären Integralen im Sinne von Hadamard mit Hilfe von einfachen Integrationsmethoden. Die entsprechenden Fehlerabschätzungen sowie Beispielrechnungen werden angegeben. Weiterhin wird die Optimalität der betrachteten Integrationsmethoden untersucht.
    Notizen: Abstract In this paper we deal with the numerical calculation of singular integrals in the sense of Hadamard by simple integration methods. Error estimates and numerical examples are given. The optimality of the quadrature rules will be examined.
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  • 82
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    Computing 48 (1992), S. 203-212 
    ISSN: 1436-5057
    Schlagwort(e): 68U05 ; Euclidean shortest path ; polyhedral obstacles ; computation geometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Es wird folgendes Problem untersucht: Gegeben sei eine Menge von einfachen Polyedern und zwei Punkte außerhalb dieser Polyeder; gesucht ist ein fast-optimaler Polygonzug der die beiden Punkte verbindet und dessen Durchschnitt mit allen Polyedern leer ist. Zur Lösung dieses Problems wird ein Algorithmus angegeben, durch den eine Menge von zulässigen Polygonzügen generiert werden kann. Ausgehend von dieser Menge wird mittels einer auf der ψ-Transformation basierenden Optimierungsprozedur ein fast-optimaler Polygonzug bestimmt.
    Notizen: Abstract The problem can be stated as follows: Given a set of simple polyhedra and two points belonging to the exterior domain of the given polyhedra, determine a near-optimal polygonal line connecting the two points so that the intersection of this polygonal line and the given polyhedra is an empty set. To solve this problem an algorithm is formed for generation of a set of admissible polygonal lines. On the basis of this set, using the optimisation procedure based on ψ-transform, a near-optimal polygonal line is determined.
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  • 83
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    Computing 48 (1992), S. 319-336 
    ISSN: 1436-5057
    Schlagwort(e): Global optimization ; interval arithmetic ; inclusion function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Vorgestellt wird eine Methode zum Auffinden aller globalen Minimierer einer reellwertigen Zielfunktion mehrerer Veränderlicher. Dabei wird ein problemorientierter Zahlentyp verwendet: der Bereich der reellen kompakten Intervalle. Der Wertebereich der Zielfunktion über einem rechteckigen Gebiet wird durch natürliche Intervallerweiterung einer geeigneten Modellfunktion abgeschätzt. Es wird ein Algorithmus zur Interpolation und Approximation in mehrdimensionalen Räumen entwickelt. Diese Optimierungsmethode kann auf herkömmliche, das heißt mit reeller Arithmetik programmierte, Funktionen erfolgreich angewendet werden.
    Notizen: Abstract A method for finding all global minimizers of a real-valued objective function of several variables is presented. For this purpose a problem-oriented type of number is used: the set of real compact intervals. The range of the objective function over a rectangular set is estimated by natural interval extension of a suitable modelling function. An algorithm for interpolation and approximation in multidimensional spaces is developed. This optimization method can be applied successfully to conventionally, e.g. with real arithmetic, programmed functions.
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  • 84
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    Computing 48 (1992), S. 373-380 
    ISSN: 1436-5057
    Schlagwort(e): 65D05 ; 65N20 ; Blending function ; shape preserving interpolation ; Poisson equation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Zur Bestimmung einer Anfangsnäherung für die Lösung eines Poisson-Problems wird eine Blending-Funktions-Technik mit einem eindimensionalen Interpolationsschema vorgeschlagen. Diese Näherung verbindet die exakte Wiedergabe der Randbedingungen mit der Interpolation irgendwoher bekannter Werte im Inneren. Bilineare Blending-Funktionen und ein gestalterhaltendes Interpolationsschema werden für numerische Testrechnungen verwendet.
    Notizen: Abstract A blending function technique with a monovariate interpolating scheme is proposed to provide an initial approximation to the solution of the Poisson problem. Such an approximation combines the interpolatory properties of exact matching of boundary conditions with some interior values of the solution, somehow known. The bilinear blending functions and a shape-preserving interpolation scheme are used in the numerical tests.
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  • 85
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    Computing 49 (1992), S. 11-23 
    ISSN: 1436-5057
    Schlagwort(e): 65M55 ; 65Y05 (primary) ; 65M60 (secondary) ; Domain decomposition ; parallel time stepping ; parabolic problems ; transputer system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Implementierung von Lösungs-methoden für parabolische Probleme erfordert eine ausreichende Balance zwischen der parallelen Effizienz voll-expliziter Schemata und der Notwendigkeit von Stabilität und Genauigkeit, welche einen gewissen Grad an Implizitheit bedingt. Als ein Kompromiß wird ein Gebietszerlegungsverfahren vorgeschlagen, welches lokal implizit ist auf leicht überlappenden Teilgebieten, die lokalen Randdaten aber durch einen einfachen expliziten Prozeß fortpflanzt. Die Analyse dieses Algorithmus zeigt, daß er zufriedenstellende Stabilitäts- und Approximationseigenschaften besitzt und effektiv parallelisiert werden kann. Diese theoretischen Resultate werden bestätigt durch numerische Tests auf einem Transputer-System.
    Notizen: Abstract In the parallel implementation of solution methods for parabolic problems one has to find a proper balance between the parallel efficiency of a fully explicit scheme and the need for stability and accuracy which requires some degree of implicitness. As a compromise a domain splitting scheme is proposed which is locally implicit on slightly overlapping subdomains but propagates the corresponding boundary data by a simple explicit process. The analysis of this algorithm shows that it has satisfactory stability and approximation properties and can be effectively parallelized. These theoretical results are confirmed by numerical tests on a transputer system.
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  • 86
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    Computing 49 (1992), S. 87-94 
    ISSN: 1436-5057
    Schlagwort(e): 65H10 ; 65G10 ; Nonlinear equations ; nondifferentiable operator ; quasi-Newton method ; convergence theorems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In der vorliegenden Arbeit wird die Konvergenz gewisser Quasi-Newton-Verfahren zur Lösung von nichtlinearen GleichungenAx+g(x)=0 aufD⊄R n untersucht, wobeiA eine (n×n)-Matrix undg ein nichtdifferenzierbarer, aber Lip-schitz-stetiger Operator ist. Mittels intervallanalytischer Techniken wird ein neuer Konvergenzsatz für die Verfahren hergeleitet.
    Notizen: Abstract In this paper, we study the convergence of some quasi-Newton methods for solving nonlinear equationAx+g(x)=0 in a domainD⊄R n , whereA is ann×n matrix andg is a nondifferentiable but Lipschitz continuous operator. By interval analysis, we give a new convergence theorem of the methods.
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  • 87
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    Computing 49 (1992), S. 129-137 
    ISSN: 1436-5057
    Schlagwort(e): 41A15 ; 65D05 ; Interpolation ; bivariate splines ; flows
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir entwickeln hinreichende Bedingungen, die garantieren, daß eine Punktmenge eindeutige Lagrange-Interpolation mit quadratischen Splines auf einer Typ 2—Triangulierung erlaubt. Die Interpolationseigenschaft dieser Mengen wird gezeigt, indem ein bivariates Problem auf eine endliche Folge univariater Probleme reduziert wird.
    Notizen: Abstract We give sufficient conditions which guarantee that a set of points admits unique Lagrange interpolation by quadratic splines on a four-directional mesh. The poisedness of these sets will be proved by reducing one bivariate problem to a finite sequence of univariate problems.
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  • 88
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    Computing 49 (1992), S. 151-158 
    ISSN: 1436-5057
    Schlagwort(e): 90B35 ; 90C27 ; Scheduling ; identical parallel machines ; set-up time ; heuristics ; worst-case analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir untersuchen ein preemptives Scheduling Problem mitm Maschinen undn Prozessen. Jedesmal wenn eine Maschine mit dem Abarbeiten eines neuen Prozesses beginnt, ist eine zusätzliche Set-up Zeit notwendig. Das Ziel ist es, ein Schedul zu finden, das alle Prozesse möglichst früh vollendet. Fürm≥2 Maschinen ist dieses Problem NP-vollständig. Für den Fall von prozeßabhängigen Set-up Zeiten haben Monma und Potts eine polynomiale Heuristik entwickelt, deren Worst Case Ratio gegen 5/3 geht, wenn die Anzahl der Maschinen gegen unendlich strebt. Wir untersuchen den Fall mit konstanten Set-up Zeiten. Wir konstruieren einen polynomialen Approximations Algorithmus mit Worst Case Ratio 7/6 fürm=2 und Worst Case Ratio 3/2–1/2m fürm≥3. Außerdem geben wir ein fully polynomial time approximation scheme für zwei Maschinen an.
    Notizen: Abstract We investigate the problem of preemptively schedulingn jobs onm parallel machines. Whenever there is a switch from processing a job to processing another job on some machine, a set-up time is necessary. The objective is to find a schedule which minimizes the maximum completion time. Form≥2 machines, this problem obviously is NP-complete. For the case of job-dependent set-up times, Monma and Potts derived a polynomial time heuristic whose worst case ratio tends to 5/3 as the number of machines tends to infinity. In this paper, we examine the case of constant (job- and machine-independent) set-up times. We present a polynomial time approximation algorithm with worst case ratio 7/6 form=2 machines and worst case ratio at most 3/2–1/2m form≥3 machines. Moreover, for the casem=2 we construct a fully polynomial time approximation scheme.
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  • 89
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    Computing 49 (1992), S. 213-237 
    ISSN: 1436-5057
    Schlagwort(e): 35Q35 ; 35R35 ; 76A05 ; Bingham fluids ; cool water slurries
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wir betrachten die quasistationäre, laminare, achsensymmetrische Strömung vom Bingham-Typus unter der Annahme, daß die Fließspannung mit einer zur inneren Dissipationsleistung proportionalen Rate zunimmt. Ein derartiges Verhalten ist in Kohle-Wasser-Gemischen beobachtet worden. Viele unterschiedliche Fälle können auftreten (einschließlich des Auftretens einer starren Schale am Rand der Rohrleitung); sie werden sowohl theoretisch als auch numerisch analysiert.
    Notizen: Abstract We consider a quasi steady laminar axisymmetric flow of Bingham type under the assumption that the yield stress increases at a rate proportional to the internal power dissipation. Such a behaviour has been observed in coal-water slurries. Many different cases can occur (including the appearance of a rigid shell at the boundary of the pipeline), which are analyzed both theoretically and numerically.
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  • 90
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    Computing 49 (1992), S. 303-314 
    ISSN: 1436-5057
    Schlagwort(e): 65L05 ; 65L07 ; Stability theory ; high-index DAEs ; parametric perturbations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Es ist bekannt, daß Algebrodifferentialgleichungen von höherem Index sehr empfindlich gegenüber Parameteränderungen sein können [1, p. 31]. Ebenso ist aus der Theorie der singulär gestörten Probleme bekannt, daß auch die Stabilitätseigenschaften bei derartigen Störungen sich ändern können. In diesem Aufsatz zeigen wir, daß beliebig kleine, glatte Störungen Instabilitäten dadurch verursachen können, daß die verallgemeinerten Eigenwerte des zugehörigen Matrizenbüschels beiz=∞ zu großen positiven Eigenwerte verfälscht werden. Das Problem wird dadurch umso instabiler je kleiner die Störung des Ausgangsproblems ist, ganz im Gegensatz zu der Situation bei expliziten DGLn. Auf diese Weise können einige Probleme von höherem Index als ein stabiler Grenzfall von benachbarten hoch instabilen Problemen, gewöhnlich von niedrigerem Index, angesehen werden.
    Notizen: Abstract It is well-known that linear time-varying high-index DAEs can be very sensitive to parametric perturbations, [1, p. 31]. Stability is also affected, as is known from singular perturbation theory. In this note, we show that arbitrarily small and smooth perturbations can cause dramatic instabilities by introducing “small” perturbations of the matrix pencil's generalized eigenvalues atz=∞, leading to large positive finite eigenvalues. The smaller the perturbation, the larger is the instability of the perturbed problem, in contrast to the ODE case. Some high-index problems can thus be considered as marginally stable, with neighboring problems (usually of lower index) exhibiting severe instabilities.
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  • 91
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    Computing 49 (1992), S. 265-278 
    ISSN: 1436-5057
    Schlagwort(e): 65N30 ; 73E25 ; Key words ; Continuous casting ; strand mechanics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Das Ausbauchen der Strangschale von Brammen kann die Stahlqualität erheblich herabsetzen. Wir präsentieren ein numerisches Verfahren zur Berechnung der Deformationen und der Spannungen in einer Bramme unter Verwendung einer gemischten Eulersch-Lagrangeschen Beschreibungsweise. Wegen der extremen Nichtlinearität des Werkstoffgesetzes sind Einbettungstechniken erforderlich, um Konvergenz zu erzielen.
    Notizen: Abstract Bulging of continuously cast slabs can reduce the steel quality quite heavily. We present a numerical method for the calculation of the deformations and the stresses in a slab using a formulation of the governing equations in mixed Eulerian-Lagrangian coordinates. Due to the extreme nonlinearity of the material law, imbedding techniques are necessary to achieve convergence.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Computing 48 (1992), S. 275-289 
    ISSN: 1436-5057
    Schlagwort(e): 65D07 ; 53A04 ; Computer aided geometric design ; nonuniform rational B-spline curve ; B-spline curve ; Bézier curve ; envelope ; uniqueness
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Eine nicht gleichförmige rationale B-Spline-Kurve kann durch die Einhüllende einer Gruppe von rationalen B-Spline-Kurven niederer Ordnung erzeugt werden, und diese Einhüllende ist eindeutig. Auf diese Weise kann eine rationale B-Spline-Kurve direkt geometrisch definiert werden.
    Notizen: Abstract Nonuniform rational B-spline curves may be recursively generated by the envelope of a family of low order rational B-spline curves, and this envelope is unique. Thus rational B-spline curves can be directly defined in a geometric way.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Computing 48 (1992), S. 303-317 
    ISSN: 1436-5057
    Schlagwort(e): 65K05 ; 65K10 ; Unconstrained optimization ; trust region ; curvilinear path ; nonmonotone ; convergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Es wird ein allgemeines nichtmonotones Konfidenzbereichs-Verfahren mit krummlinigem Pfad für die unrestringierte Optimierung vorgeschlagen. Obwohl bei diesem Verfahren die Folge der Werte der Objecktfunktion nicht monoton zu sein braucht, werden Konvergenzeigenschaften bewiesen, die denen der gängigen Verfahren dieser Art entsprechen. An Hand einiger numerischer Beispiele wird die Über-legenheit des nichtmonotonen Verfahrens bezüglich der Zahl der Gradienten- und der Funktions-auswertungen gezeigt.
    Notizen: Abstract A general nonmonotone trust region method with curvilinear path for unconstrained optimization problem is presented. Although this method allows the sequence of the objective function values to be nonmonotone, convergence properties similar to those for the usual trust region methods with curvilinear path are proved under certain conditions. Some numerical results are reported which show the superiority of the nonmonotone trust region method with respect to the numbers of gradient evaluations and function evaluations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Computing 48 (1992), S. 381-385 
    ISSN: 1436-5057
    Schlagwort(e): 65J ; Projections ; Convex sets
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Zur Bestimmung des Durchschnitts von endlich vielen abgeschlossenen Ronversen Mengen in einem Hilbertraum wird ein nichtlinearer Algorithmus vom SOR-Typ vorgeschlagen.
    Notizen: Abstract A nonlinear SOR-type algorithm is established to find the intersection of a finite number of closed convex sets in a Hilbert space.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Computing 49 (1992), S. 25-44 
    ISSN: 1436-5057
    Schlagwort(e): 35J25 ; 35J65 ; 65N15 ; 65G10 ; Elliptic boundary value problem ; nonlinear boundary value problem ; numerical existence proof ; explicit bounds ; enclosure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Gegeben sei ein elliptisches Randwertproblem der Form −ΔU+F(x, U, U x )=0 auf Ω,B[U]=0 auf ϖΩ, mit einer NichtlinearitätF, die einer quadratischen Wachstumsbedingung bezüglich des GradientenU x genügt, und mit einem linearen RandoperatorB von gemischtem Typ. Es wird eine numerische Methode vorgestellt, mit deren Hilfe sich die Existenz einer Lösung innerhalb einer “kleinen”H 1,4(Ω)-Umgebung einer Näherungslösung ω∈H 2(Ω), die die Randbedingung erfüllt, nachweisen läßt, sofern die Defektnorm ∥−Δω +F(·, ω, ω x )∥2 hinreichend klein ist und ferner die Linearisierung des gegebenen Problems in ω auf einen invertierbaren OperatorL führt. Die wesentlichen Hilfsmittel sind explizite Sobolevsche Einbettungen und Eigenwertschranken fürL oderL*L. Jegliche Monotonie- und Inverspositivitätsbedingungen werden vermieden.
    Notizen: Abstract For elliptic boundary value problems of the form −ΔU+F(x, U, U x )=0 on Ω,B[U]=0 on ϖΩ, with a nonlinearityF growing at most quadratically with respect to the gradientU x and with a mixed-type linear boundary opeatorB, a numerical method is presented which can be used to prove the existence of a solution within a “close”H 1,4(Ω)-neighborhood of some approximate solution ω∈H 2(Ω) satisfying the boundary condition, provided that the defect-norm ∥−Δω +F(·, ω, ω x )∥2 is sufficiently small and, moreover, the linearization of the given problem at ω leads to an invertible operatorL. The main tools are explicit Sobolev imbeddings and eigenvalue bounds forL or forL*L. All kinds of monotonicity or inverse-positivity assumptions are avoided.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Computing 49 (1992), S. 117-127 
    ISSN: 1436-5057
    Schlagwort(e): 34A05 ; Differential equations ; hypergeometric equations ; special functions ; symbolic computation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Um ihre Lösungen durch spezielle Funktionen auszudrücken, wird ein Verfahren beschrieben, womit man unter Benutzung von Faktorisierungstechniken entscheiden kann, ob eine lineare Differentialgleichung zweiter Ordnung mit polynomialen Koeffizienten durch eine rationale Variablentransformation auf die hypergeometrische oder die konfluente hypergeometrische Gleichung gebracht werden kann. Im ersten Fall muß für den Zählergrad des Bruchs, der die Variablentransformation bestimmt, eine obere Schranke vorgegeben werden.
    Notizen: Abstract So as to explore the possibilities of representing its solutions in terms of special functions, and using factorization techniques, a process is defined to decide whether a second order linear differential equation with polynomial coefficients can be brought to the hypergeometric or the confluent hypergeometric equation by a rational change of variable. In the first case, an upper bound has to be provided for the degree of the numerator of the rational function which defines the change of variable.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Computing 49 (1992), S. i 
    ISSN: 1436-5057
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Computing 49 (1992), S. 201-212 
    ISSN: 1436-5057
    Schlagwort(e): 65D15 ; 90C25 ; 90C50 ; Key words ; Polynomial approximation ; semi-inifinte programming ; cutting plane method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Lastdauerlinien spielen eine wichtige Rolle in der Planungspraxis der elektrischen Energiesysteme. In der Arbeit betrachten wir das Problem der Approximation einer Lastdauerlinie durch ein Polynom unter Monotonie und einigen anderen Nebendedingungen. Es wird gezeigt, daß die Verfahren der semi-infiniten Programmierung zur Lösung dieses Problems anwendbar sind. Eine konvergente innere-äußere Methode und ein endlicher ε-optimaler Algorithmus werden vorgeschlagen.
    Notizen: Abstract Load duration curves play an important role in the planning practice of electric power systems. In the paper, we consider the problem of approximating a load duration curve by a polynomial under monotonicity and some other constraints. We show that semi-infinite programming techniques can be applied for solving this problem. A convergent inner-outer method and a finite ε-optimal algorithm is proposed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Meteorology and atmospheric physics 47 (1992), S. 107-115 
    ISSN: 1436-5065
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geographie , Physik
    Notizen: Summary A number of cut-off processes are investigated, with the Alpine region in most cases lying at the margins of these upper lows. Our aim was to determine whether the thermal front parameter (TFP) can be used to objectively define the areas of bad weather from analysis charts and prognostic charts. An attempt is made to formulate two synoptic “guidelines”, for the eastern Alpine region, on front-sides and northern margins of upper lows, into objective synoptic rules.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Meteorology and atmospheric physics 47 (1992), S. 127-144 
    ISSN: 1436-5065
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geographie , Physik
    Notizen: Summary This study examined ECMWF operational analyses of the outflow layer of two tropical cyclones (Allen, 1980; Elena, 1985) during their passage across the Atlantic and Caribbean. Wind fields and related derived quantities were compared to those from objective analyses of specialized data sets. Errors in center position and storm motion from the ECMWF analyses were also evaluated. Analyses of wind and angular momentum flux in 1985, subsequent to upgrading of the operational model, were superior to those from 1980. High-resolution, uninitialized analyses from 1985, however, provided no advantages over lower resolution, initialized analyses for the same time period. For all ECMWF analyses, azimuthally averaged (mean) tangential velocity, and thus mean vorticity, were well represented. Mean radial velocity and mean divergence were poorly represented. Problems with the latter arose primarily due to underestimation of outflow, especially in the 1980 analyses. Azimuthaleddy fluxes of angular momentum in the ECMWF analyses quantitatively differed from but qualitatively resembled, the control analyses. Vorticity maxima at 850 mb in the operational analyses most accurately defined the center position of the storms, with a mean error less than or equal to one grid point. In contrast, surface pressure minima failed to provide reliable estimates. Over open ocean and at early stages of storms, analysis quality was uneven, with occasional large position errors and widely varying locations of vorticity maxima in the vertical. Nevertheless, in regions surrounded by even a few rawinsondes, such as the Caribbean or Gulf of Mexico, ECMWF analyses contained sufficient information to allow individual case studies of the tropical cyclone environment. In the same regions, estimates of the eddy flux convergence of angular momentum were found to be accurate enough to aid in operational hurricane intensity prediction. Enhancements in resolution and model initialization at ECMWF since 1985 should further improve operational analyses of the tropical cyclone environment.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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