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Normal Strain (normal + strain)
Selected AbstractsAbortive translation caused by peptidyl-tRNA drop-off at NGG codons in the early coding region of mRNAFEBS JOURNAL, Issue 20 2005Ernesto I. Gonzalez De Valdivia In Escherichia coli the codons CGG, AGG, UGG or GGG (NGG codons) but not GGN or GNG (where N is non-G) are associated with low expression of a reporter gene, if located at positions +2 to +5. Induction of a lacZ reporter gene with any one of the NGG codons at position +2 to +5 does not influence growth of a normal strain, but growth of a strain with a defective peptidyl-tRNA hydrolase (Pth) enzyme is inhibited. The same codons, if placed at position +7, did not give this effect. Other codons, such as CGU and AGA, at location +2 to +5, did not give any growth inhibition of either the wild-type or the mutant strain. The inhibitory effect on the pth mutant strain by NGG codons at location +5 was suppressed by overexpression of the Pth enzyme from a plasmid. However, the overexpression of cognate tRNAs for AGG or GGG did not rescue from the growth inhibition associated with these codons early in the induced model gene. The data suggest that the NGG codons trigger peptidyl-tRNA drop-off if located at early coding positions in mRNA, thereby strongly reducing gene expression. This does not happen if these codons are located further down in the mRNA at position +7, or later. [source] Inelastic constitutive properties and shear localization in Tennessee marbleINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2001D. J. Holcomb Abstract The inelastic response of Tennessee marble is modelled by an elastic plastic constitutive relation that includes pressure dependence of yield, strain-softening and inelastic volume strain (dilatancy). Data from 12 axisymmetric compression tests at confining pressures from 0 to 100 MPa are used to determine the dependence of the yield function and plastic potential, which are different, on the first and second stress invariants and the accumulated inelastic shear strain. Because the data requires that the strain at peak stress depends on the mean stress, the locus of peak stresses is neither a yield surface nor a failure envelope, as is often assumed. Based on the constitutive model and Rudnicki and Rice criterion, localization is not predicted to occur in axisymmetric compression although faulting is observed in the tests. The discrepancy is likely due to the overly stiff response of a smooth yield surface model to abrupt changes in the pattern of straining. The constitutive model determined from the axisymmetric compression data describes well the variation of the in-plane stress observed in a plane strain experiment. The out-of-plane stress is not modelled well, apparently because the inelastic normal strain in this direction is overpredicted. In plane strain, localization is predicted to occur close to peak stress, in good agreement with the experiment. Observation of localization on the rising portion of the stress,strain curve in plane strain does not, however, indicate prepeak localization. Because of the rapid increase of mean stress in plane strain, the stress,strain curve can be rising while the shear stress versus shear strain curve at constant mean stress is falling (negative hardening modulus). Copyright © 2001 John Wiley & Sons, Ltd. [source] Use of the tangent derivative boundary integral equations for the efficient computation of stresses and error indicatorsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2002K. H. Muci-Küchler Abstract In this work, a new global reanalysis technique for the efficient computation of stresses and error indicators in two-dimensional elastostatic problems is presented. In the context of the boundary element method, the global reanalysis technique can be viewed as a post-processing activity that is carried out once an analysis using Lagrangian elements has been performed. To do the reanalysis, the functional representation for the displacements is changed from Lagrangian to Hermite, introducing the nodal values of the tangential derivatives of those quantities as additional degrees of freedom. Next, assuming that the nodal values of the displacements and the tractions remain practically unchanged from the ones obtained in the analysis using Lagrangian elements, the tangent derivative boundary integral equations are collocated at each functional node in order to determine the additional degrees of freedom that were introduced. Under this scheme, a second system of equations is generated and, once it is solved, the nodal values of the tangential derivatives of the displacements are obtained. This approach gives more accurate results for the stresses at the nodes since it avoids the need to differentiate the shape functions in order to obtain the normal strain in the tangential direction. When compared with the use of Hermite elements, the global reanalysis technique has the attraction that the user does not have to give as input data the additional information required by this type of elements. Another important feature of the proposed approach is that an efficient error indicator for the values of the stresses can also be obtained comparing the values for the stresses obtained through the use of Lagrangian elements and the global reanalysis technique. Copyright © 2001 John Wiley & Sons, Ltd. [source] Genetic and hormonal control of melanization in reddish,brown and albino mutants in the desert locust Schistocerca gregariaPHYSIOLOGICAL ENTOMOLOGY, Issue 1 2010KOUTARO MAENO The genetic and hormonal control of body colouration is investigated using two recessive genetic mutant strains, the reddish,brown (RB) mutant and an albino mutant, as well as a normal (pigmented) strain of the desert locust Schistocerca gregaria. The colour patterns of the RB nymphs are similar to those of a normal strain, although the intensity of the melanization is weaker in the former. Reciprocal crosses between the RB and albino mutants produce only normal phenotypes in the F1 generation. In the F2 generation, the normal, RB and albino phenotypes appear in a ratio of 9 : 3 : 4, indicating that two Mendelian units might determine the appearance of dark body colour and the intensity of melanization, respectively. In other words, at least two steps of regulation might be involved in the expression of body colour. Injections of [His7]-corazonin, a neuropeptide inducing dark colour in this locust, fail to induce dark colour in albino nymphs but show a dose-dependent darkening in RB nymphs in the range, 10 pmol to 1 nmol. Some RB nymphs become indistinguishable from normal individuals after injection of the peptide. Implantation of corpora cardiaca (CC) taken from RB mutants into other RB individuals induces darkening in the latter and CC from RB, albino and normal strains have similar dark colour-inducing activity when implanted into albino Locusta migratoria. These results suggest the possibility that the RB mutant gene regulates the intensity of melanization, possibly through controlling the pathway of pigment biosynthesis associated with [His7]-corazonin. [source] Masticatory stress and the mechanics of "wishboning" in colobine jawsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009David J. Daegling Abstract Cercopithecoid monkeys experience relatively high strains along the lingual aspect of the mandibular symphysis because of lateral transverse bending of the mandibular corpora ("wishboning") during mastication. Hylander (Am J Phys Anthropol 64 (1984) 1,46; Am Zool 25 (1985) 315,330) demonstrated that the distribution of strains arising from wishboning loads is comprehensible with reference to the mechanics of curved beams. Theory of curved beams suggests that lingual tensile strains are some multiple of labial compressive strains, yet limitations of experimental methods and uncertainty in estimating parameters needed for theoretical calculations have confounded attempts to characterize the magnitude of this disparity of normal strains. We evaluate the theoretical disparity of normal strains in wishboning in comparison to in vitro strains collected under controlled loads for a sample of mandibles representing two colobine species (N = 6). These data suggest that in colobine monkeys, maximum normal lingual strains should be at least twice maximum labial strains. In addition, we reexamine the distribution of symphyseal stress under an assumption of asymmetric bending, a general approach for calculation of stress appropriate for members that lack a plane of symmetry and are bent along an axis that is not coincident with the member's principal axes. Under asymmetric bending in colobine mandibles, the effect of symphyseal inclination on lingual strain is mitigating at the superior transverse torus and exacerbating at the inferior transverse torus. Relative compliance of colobine mandibular bone further supports the hypothesis that the structural and material properties of the colobine mandibular symphysis do not represent a morphological strategy for minimizing masticatory strain. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||