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  • 1
    Electronic Resource
    Electronic Resource
    Flow development of xanthan solutions in capillary rheometers (1992)
    Springer
    Rheologica acta 31 (1992), S. 83-93 
    Details
    ISSN: 1435-1528
    Keywords: Capillary rheometer ; xanthan solutions ; Bagley correction ; slip development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Flow experiments through capillaries with 0.2% xanthan in aqueous solution and 0.1 N NaCl brine were carried out to study the influence of the molecular conformation on the flow development at relatively low shear rates, from 20s−1 to 400s−1. Capillaries with a wide range of length-to-diameter ratios, L/D = 4.5 to 1015 were used. The apparent viscosity as a function of L/D at a constant shear rate shows a continuous decrement of the viscosity as L/D increases, until an asymptotic value is reached. The decrement in the apparent viscosity is partially explained in terms of slip. It was found that slip is a function of L/D as well as shear stress, i.e., slip develops during flow, thus inducing spatial anisotropy in the fluid until a stable state is reached. However, the substantial difference in apparent viscosity between short capillaries and capillaries longer than 300 D may be attributed to dominant elongational flow due to the contraction in the small capillaries and slip in long capillaries. The flow in a sufficiently long capillary can be divided in four regions rather than three, as is usually assumed. In the first region, which corresponds to the entry, elongational and shear flow coexist and elongational flow dominant. In the second region, end effects and slip development are coupled. In the third region the flow is fully developed and end effects are negligible. However, the fluid shows physical characteristics different from those of the fluid at rest, as a consequence of prior slip development. The fourth zone is the exit region in which the velocity rearranges due to the change of boundary conditions. The length of each region depends on the conformation of the macromolecules and shear rate. In addition, it was found that the stiffness of xanthan increases with the increase of the ionic strength. Finally, a performance of Bagley's analysis in the whole range of L/D studied showed that the use of the Bagley correction is not a reliable way to correct for end effects when the flow is not fully developed and/or in the presence of slip.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396470
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  • 2
    Electronic Resource
    Electronic Resource
    Biologia deMeteorus rubens (Hym.: Braconidae), parasitoide primario deAgrotis ipsilon (Lep.: Noctuidae) (1992)
    Springer
    BioControl 37 (1992), S. 301-309 
    Details
    ISSN: 1573-8248
    Keywords: Meteorus rubens ; Agrotis ipsilon ; Agrotis puta ; Noctuidae ; gama de hospedantes ; estadios adecuados ; estadios preferidos ; Meteorus rubens ; Agrotis ipsilon ; Agrotis puta ; host range ; host instar preference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Summary The development of the braconidMeteorus rubens (Nees) was studied under laboratory conditions in the noctuids speciesAgrotis ipsilon (Hufnagel),A. puta (Hübner)A. segetum (Denis & Schiffermüller),Peridroma saucia (Hübner),Spodoptera littoralis (Boisduval) andAutographa gamma (L.). The only suitable hosts wereAgrotis ipsilon andA. puta. InA. ipsilon, this braconid parasitized and completed development in the 3rd, 4th, 5th and 6th instars, showing a strong preference for the two later instars. The number of adult females that parasitized hosts, the percentage of parasitized larvae and the number of parasitoids which emerged per host were directly related to host age at parasitization. In host larvae parasitized at third instar, the time required for the development ofM. rubens was significantly longer than for the three later instars. However, the age of the host at parasitization did not significantly effect adult longevity.
    Notes: Resumen El desarrollo del bracónidoMeteorus rubens (Nees) se estudió en condiciones de laboratorio sobre las especies de noctuidosAgrotis ipsilon (Hufnagel),A. puta (Hübner),A. segetum (Denis & Schiffermüller),Peridroma saucia (Hübner),Spodoptera littoralis (Boisduval) yAutographa gamma (L.). Las larvas deA. ipsilon yA. puta fueron las únicas adecuadas para el desarrollo del parasitoide. EnA. ipsilon este bracónido parasitó y completó su desarrollo en el tercero, cuarto, quinto y sexto estadios larvarios, mostrando preferencia por los dos últimos estadios. El número de hembras que parasitan, el porcentaje de larvas parasitadas y el número de parasitoides emergidos por hospedante estuvo en relación directa con la edad del hospedante en el momento de la parasitación. En las larvas parasitadas en el tercer estadio el tiempo de desarrollo del parasitoide fue significativamente mayor que en los otros tres estadios. Sin embargo, el estadio en que fueron parasitadas las larvas no influyó en la longevidad de los adultos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02372431
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