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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 62 (2000), S. 429-450 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Bioconvection occurs as the result of the collective behaviour of many microorganisms swimming in a fluid and is realized as patterns similar to those of thermal convection which occur when a layer of fluid is heated from below. We consider the phenomenon of pattern formation due to gyrotaxis, an orientation mechanism which results from the balance of gravitational and viscous torques acting on bottom-heavy micro-organisms. The continuum model of Pedley et al. (1988, J. Fluid. Mech. 195, 223–237) is used to describe the suspension. The system is governed by the Navier-Stokes equations for an incompressible fluid coupled with a micro-organism conservation equation. These equations are solved numerically using a conservative finite-difference scheme. To examine the dependence of the horizontal pattern wavelengths on the parameters, we consider two-dimensional solutions in a wide chamber using rigid side walls. The wavelengths of the numerical computations are in good agreement with the experimental observations and we provide the first computational examples of the commonly seen ‘bottom-standing’ plumes.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 49 (1988), S. 175-179 
    ISSN: 1570-7458
    Keywords: mosquito repellents ; di-ethyl toluamide ; permethrin ; pyrethrins ; soap ; mosquito coils ; vaporizing mats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Comparisons were made with human subjects of repellency of free flying Anopheles gambiae using soaps containing deet and permethrin or permethrin alone. The reduction in biting did not differ statistically significantly between these two forms of repellent soap. Some mosquitoes which touched the permethrin soap layer without biting died within the next day. The soap with deet was compared with the same amount of deet in a commercially available stick or as a liquid. Only in the latter form did the repellent show resistance to being washed off by cold water. Electrically heated vaporizing mats containing bio-allethrin were shown to be more effective than smouldering coils containing natural pyrethrins, in that there was more complete prevention of biting, and more rapid knock-down and kill. Operation of the vaporizing mat caused deposition of insecticide on the room surfaces.
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  • 3
    ISSN: 1432-1041
    Keywords: Aedes aegypti ; Mosquito bite ; Homeopathic after-bite gel ; erythema ; immunological response ; phytotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract A randomised, placebo controlled clinical trial was conducted to examine the efficacy of a homeopathic after-bite gel in the symptomatic relief of mosquito bites. Sixty eight healthy volunteers were bitten under laboratory conditions by Aedes aegypti mosquitoes at three spots, on the ventral aspect of the forearm. One bite was treated with the homeopathic after-bite gel, another bite with a placebo gel which was identical in appearance and smell to the homeopathic after-bite gel, and the third bite remained untreated. Immediately after the bites and 1, 3, 6, 26 and 31 hours post-bite, the length and width of the erythema were measured with a calliper, and photographs were taken of the bite sites from which the size of the erythema was subsequently determined. This was followed by assessment of the extent of itching with a verbal analogue scale, and finally treatment took place. For each spot the total erythema was calculated as the area under the plotted curve of the erythema at different time points (mm2*h) and the total sum of the itch scores was determined. For the bites treated with the homeopathic after-bite gel the median total erythema was 10.500 mm2*h. For the spots treated with the placebo gel and the untreated spots the median total erythema was 12.900 mm2*h and 13.300 mm2*h, respectively. The difference between the spots treated with the homeopathic after-bite gel and the untreated spots came close to significance (two-tailed P=0.06), which was not the case for the difference between the spots treated with the homeopathic after-bite gel and the spots treated with placebo gel (P=0.13). After pooling the data of a very similar previous pilot study and the present study (n total=83), the homeopathic after-bite gel was significantly superior to no treatment (two-tailed P=0.003) as well as to placebo gel (two-tailed P=0.03). Comparing itching after the three treatments, no significant differences could be demonstrated. The extent of itching was positively correlated with the area of the erythema (r=0.63). Treatment of mosquito bites with the homeopathic after-bite gel will reduce the erythema compared to no treatment. Comparison with the placebo gel suggests it is the plant extracts which are the active components of this gel.
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  • 4
    ISSN: 1573-1561
    Keywords: Neotyphodium ; Acremonium ; ergot alkaloids ; diallel cross ; heritability ; fescue toxicosis ; endophyte ; tall fescue ; mutualism ; symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Ergot alkaloids in endophyte-infected (E+) tall fescue (Festuca arundinacea) are responsible for livestock toxicosis. The host plant is capable of modifying the extent to which endophyte produces ergot alkaloids, possibly via endophyte nutrition by the host. Endophytes vary in alkaloid production. Maintaining the E+ tall fescue is essential for plant survival. Therefore, crop scientists are interested in reducing alkaloid concentration of E+ tall fescue. The objectives of this study were to determine maternal and paternal effects as an estimate of plant and endophyte genotype interactions for ergot alkaloid phenotype and the heritability of the ergot alkaloid trait in divergently selected E+ tall fescue populations. Diallel crosses were conducted among four tall fescue genotypes that varied in alkaloid concentration. Five of six crosses had progeny means less than the parental means when genotypes with lowest alkaloid were the female parents. Four of six crosses had progeny means similar to the parental means of crosses when high alkaloid genotypes were the female parents. Large ranges in progeny suggest an interaction between endophyte and plant affects alkaloid phenotype. In a second experiment, a tall fescue population was screened for alkaloid concentration. Low- and high-alkaloid plants were selected and poly-crossed within each class. Mean alkaloid concentrations of the high- and low-alkaloid progeny were higher or lower than the parental population. The trait was highly heritable and alkaloid concentration was reduced by 86% in the low-alkaloid population after two generations of selection.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 36 (1998), S. 269-298 
    ISSN: 1432-1416
    Keywords: Key words: Suspensions ; Fokker-Planck Equation ; Dipolar particles ; Orientation distributions ; Bioconvection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract.  Analytic approximations are obtained to solutions of the steady Fokker-Planck equation describing the probability density functions for the orientation of dipolar particles in a steady, low-Reynolds-number shear flow and a uniform external field. Exact computer algebra is used to solve the equation in terms of a truncated spherical harmonic expansion. It is demonstrated that very low orders of approximation are required for spheres but that spheroids introduce resolution problems in certain flow regimes. Moments of the orientation probability density function are derived and applications to swimming cells in bioconvection are discussed. A separate asymptotic expansion is performed for the case in which spherical particles are in a flow with high vorticity, and the results are compared with the truncated spherical harmonic expansion. Agreement between the two methods is excellent.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 38 (1999), S. 135-168 
    ISSN: 1432-1416
    Keywords: Key words: Bioconvection patterns ; Swimming micro-organisms ; Gyrotaxis ; Travelling waves ; Fokker ; Planck equation ; Amplitude equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract.  The non-linear structure of deep, stochastic, gyrotactic bioconvection is explored. A linear analysis is reviewed and a weakly non-linear analysis justifies its application by revealing the supercritical nature of the bifurcation. An asymptotic expansion is used to derive systems of partial differential equations for long plume structures which vary slowly with depth. Steady state and travelling wave solutions are found for the first order system of partial differential equations and the second order system is manipulated to calculate the speed of vertically travelling pulses. Implications of the results and possibilities of experimental validation are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pharmacy world & science 18 (1996), S. 35-41 
    ISSN: 1573-739X
    Keywords: Aedes oegypti ; Clinical trials ; Echinacea angustifolia ; Erythema ; Homeopathy ; Insect bites and stings ; Ledum palustre ; Pruritus ; Urtico urens L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Objective: This study was conducted to examine the efficacy of Prrrikweg® gel, a homeopathic after-bite gel, in relleving the effects of mosquito bites, in particular itching and erythema. Design: A double-blind, randomized, placebo-controlled clinical trial. Setting: London School of Hygiene and Tropical Medicine. Subjects: 100 healthy volunteers. Methods: All subjects were bitten under laboratory conditions by Aedes aegypti mosquitoes at one spot on the ventral aspect of the left forearm and another on a corresponding position on the right forearm. One spot was treated with the homeopathic after-bite gel and the other with a placebo gel. Main outcome measures: Itching was assessed on a 5-point discrete rating scale at 0, 0.5, 1, 26.5, and 48 h post-bite to compare the itch-relieving efficacy of the two treatments. Erythema development was assessed by photographing the bite sites, measuring length and width of the erythema with at baseline (T0) to the mean erythema surface at 0.5, 1, 26.5, and 48 h post-bite (Tmean) for the two treatments. Results: Testing erythema development by comparing the ratio T0/Tmean, after-bite gel and the ratio T0/Tmean, placebo gel gave a two-tailed p=0.098 (95% Cl,−0.031–0.361) in favour of the after-bite gel. There was not a statistically significant difference between the itch relief provided by the two treatments (two-tailed p=0.424; 95% Cl,−0.541–0.191). The correlation between itching and erythema was significant (r=0.46; p〈0.001). Conclusions: There are strong indications that the homeopathic after-bite gel reduces erythema development following mosquito bites. The homeopathic mother tinctures of Echinacea angustifolia DC., Ledum palustre L, Urtica urens L. as well as the Hamamelis extract in this gel, whether alone or in combination, are the biologically active ingredients. The homeopathic after-bite gel was not demonstrated to relieve itching, however, based on the correlation between erythema and itching, an effect on itching is not inconceivable.
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  • 8
    ISSN: 1573-1561
    Keywords: Tall fescue ; fescue toxicosis ; endophyte ; alkaloids ; peramine ; ergovaline ; Acremonium coenophialum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Peramine and ergovaline have ecological and economical significance because they possess insect and/or mammalian toxicity properties. The relationship between these endophytically derived alkaloids in tall fescue (Festuca arundinacea Schreb.) is unknown. Seasonal and plant tissue effects on the concentration of peramine and ergovaline was investigated in field and greenhouse experiments. The relationship between the alkaloids and the regulatory effects of endophyte and plant on their content were investigated among progeny of reciprocal crosses between high- and low-ergovaline and peramine plant-endophyte combinations. Variation in peramine concentration ranged from 750 to 1742 µg/kg in greenhouse-grown plants, and there was no seasonal trend in peramine content. There was a correlation (r=0.69) between peramine and ergovaline content among leaf tissues of field-grown plants, but there was no correlation between the alkaloids in the culm (r=0.20) or panicle (r=0.17) tissues. Mean leaf ergovaline concentration of progeny derived from the low-ergovaline parent (163 µg/kg) was less than the midparent value (228 µg/kg), but mean of progeny from the high-ergovaline parent was not different from the mid-parent value. Ranges within each progeny set were approximately double their mean. Mean leaf peramine concentrations of the progeny sets were similar to the mid-parent value (3354 µg/kg) but ranges were from 1716 to 8753 µg/kg. There was no correlation between leaf peramine and ergovaline (r=0.01). These data suggest that endophytically produced alkaloids are independently regulated and are controlled by both plant and endophyte genotype.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 23 (1997), S. 2721-2736 
    ISSN: 1573-1561
    Keywords: Neotyphodium ; Acremonium ; ergot alkaloids ; mutualism ; antagonism ; fescue toxicosis ; tall fescue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Livestock grazing endophyte-infected tall fescue (Festuca arundinacea Schreb.) pastures often suffer from ergot poisoning. The endophyte,Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin, comb. nov., also provides drought-tolerant, insect-resistant, and disease-resistant qualities to the plant. Therefore, producers are faced with a biological dilemma of risking loss of pasture by using endophyte-free tall fescue pasture or animal losses with endophyte-infected tall fescue pasture. One potential solution is to breed endophyte-infected tall fescue with lower levels of alkaloids. However, breeding could select for plants that are antagonistic to the endophyte, resulting in reduced plant vigor as a consequence of disruption of the mutualistic association between the organisms. The objectives of this study were to determine the relationship between plant mass and endophyte mycelial proteins versus ergot alkaloid concentration. To examine the endophyte effect on mycelial mass, tissue culture regenerants from tall fescue genotype PDN2 were infected with endophyte isolates EDN11, EDN12, and EDN2 to eliminate confounding effects of multiple plant genotypes. Crosses with PDN11 as the maternal parent and plant genotypes DN2, DN12, and DN15 as paternal parents were used to produce a population of different plant genotypes, all containing the same endophyte. Fungal mycelial protein was extracted from lyophilized tall fescue leaf sheath tissue and immunochemically quantified with monoclonal antibodies specific toN. coenophialum proteins. Ergot alkaloid concentration was also immunochemically measured. Quantities of mycelial protein and ergot alkaloids were calculated by regressing experimental values against standards of each. There was no correlation between herbage mass and alkaloid concentration or fungal protein quantity and alkaloid concentration when different fungal isolates were inserted into the same plant genotype. Coefficients of determination (r 2) were low (0.31 and 0.17) between leaf sheath and leaf blade alkaloid concentrations and endophyte protein when different plant genotypes contained the same endophyte isolate. Likewise,r 2 values were low between leaf sheath and leaf blade alkaloid concentrations and herbage mass. These data suggest that little or no antagonism occurred to the endophyte among plants low in alkaloid concentration.
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  • 10
    ISSN: 1435-0653
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin comb. Nov. in tall fescue (Festuca arundinacea Schreb.) seed and plant tissue would be beneficial for tall fescue breeding and seed lot analysis. This experiment was conducted to determine the accuracy, reliability, and reproducibility of the Phytoscreen Neotyphodium immunoblot detection kit (Agrinostics Ltd. Co, Watkinsville, GA). Tissue immunoblot was compared with histological staining followed by microscopic analysis on tall fescue tillers from a greenhouse grow-out test, field grown spaced plants, established field paddocks, and different tall fescue seed lots. Endophyte-infected and endophyte-free tall fescue populations were evaluated by both methods. Results obtained by both methods were similar regardless of the infection level of the population, type of tissue assayed, or the technician that conducted the assay. The immunoblot detection kit was accurate and reliable and readily accommodated large numbers of samples.
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