Developmental and molecular correlates of bovine preimplantation embryos

Expression of embryonic genes is altered in different culture conditions, which influence developmental potential both during preimplantation and fetal development. The objective of this study was to define the effects of culture conditions on: bovine embryonic development to blastocyst stage, blastocyst cell number, apoptosis and expression patterns of a panel of developmentally important genes. Bovine embryos were cultured in vitro in three culture media containing amino acids, namely potassium simplex optimization medium (KSOMaa), Charles Rosenkrans 1 (CR1aa) and synthetic oviductal fluid (SOFaa). Apoptosis in blastocysts was determined by TUNEL assay and expression profiles of developmentally important genes were assayed by real-time PCR. In vivo-produced bovine blastocysts were used as controls for experiments determining gene expression patterns. While the cleavage rates did not differ, embryos cultured in SOFaa had higher rates of development to blastocyst stage (P < 0.05). Mean cell numbers and percentages of apoptotic cells per blastocyst did not differ among the groups. Expression of the heat shock protein 70 (Hsp70) gene was significantly up-regulated in both CR1aa and KSOMaa when compared with SOFaa (P < 0.001). DNA methyltransferase 3a (Dnmt3a) expression was higher in embryos cultured in CR1aa than in those cultured in SOFaa (P < 0.001). Expression of interferon tau (IF-tau) and insulin-like growth factor II receptor (Igf-2r) genes was significantly up-regulated in KSOMaa when compared with CR1aa (P < 0.001). Gene expression did not differ between in vivo-derived blastocysts and their in vitro-derived counterparts. In conclusion, SOFaa supports higher development to blastocyst stage than KSOMaa and CR1aa, and the culture conditions influence gene expression.     

Comparison of acid and enzymatic hydrolysis of tobacco stalk xylan for preparation of xylooligosaccharides

Tobacco stalk (TS), a major agricultural waste in the Black Sea region of Turkey, was used for the production of xylooligosaccharides (XOs). It contains about 22 g/100 g xylan whose composition was determined as 93.5 g/100 g xylose, 6.54 g/100 g glucose and 11.2 g/100 g uronic acid after complete acid hydrolysis. XO production was performed by enzymatic and acid hydrolysis of xylan which was obtained by alkali extraction from tobacco stalk. In enzyme hydrolysis, xylan was hydrolyzed using a xylanase preparation and the effects of pH, temperature, hydrolysis period, substrate and enzyme concentrations on the xylooligosaccharide yield and degree of polymerization were investigated. For enzymatic hydrolysis under optimum conditions XO yield with respect to tobacco stalk xylan (TSX) was 8.2 g/100 g after 8 h and 11.4 g/100 g after 24 h reaction period. In the acid hydrolysis, sulfuric acid was used and the hydrolyzate contained different amount of oligosaccharides and monosaccharides. For acid hydrolysis under optimum conditions, XO yield with respect to TSX was 13.0 g/100 g. Enzymatically obtained oligosaccharides were purified via ultrafiltration by using 10 and 3 kDa membranes. After a two-step membrane processing, the permeate containing mostly oligosaccharides was obtained.     

Extraction of aminoglycoside antibiotics with reverse micelles

The reverse micelle system of sodium di-2-ethylhexyl phosphate was used to extract aminoglycoside antibiotics, neomycin and gentamicin. The aminoglycosides can be efficiently extracted into a reverse micelle solution, and the antibiotics extracted into the micelle phase can readily be recovered back to a divalent cation aqueous solution, such as Ca²⁺. The transfer efficiency, %E, is heavily dependent on pH and salt concentration in the aqueous feed solution. %E decreases drastically with pH in the pH range 8·5–11, and declines with increasing (NH₄)₂SO₄ concentration. A simple transfer mechanism was proposed which suggests that the antibiotic molecules were extracted into the inner water cores of reverse micelles through attractive electrostatic interaction during forward transfer. In backward transfer, the antibiotics loaded in the micelle phase are released back to an aqueous phase through breaking up of the reverse micelles by using divalent cation solutions. The model is supported by the results of dynamic light scattering and infra-red spectroscopy study.     

Optimizing the structural and photocatalytic performance of Ag-decorated ZnO/Zn(OH)2 nanoparticles for RhB degradation

In this study, as-prepared and Ag-decorated ZnO/Zn(OH)₂ composite nanoparticles (NPs) were obtained using the sol–gel technique. First, the effect of aging on the structural, optical, and morphological features was examined. Ag NPs can interact with the electronic structure of ZnO/Zn(OH)₂ NPs, resulting in changes in their energy levels. It was found that the composite NPs obtained after 6 h solution aging increased in full width at half maximum and good crystallinity of the structures from the X-ray diffraction (XRD) measurements. The Raman spectrum supports the experimental data obtained from XRD and Fourier transform infrared, a material containing a mixture of ZnO and Zn(OH)₂. From the morphological study, Ag NPs were successfully decorated on the ZnO/Zn(OH)₂ surface, and composite NPs did not change the morphological appearance of the structure. Second, the photocatalytic performance of the samples was investigated. In the experimental setting, ultra-violet A light was employed as the irradiation source, whereas rhodamine B (RhB) was used as the dyestuff. The photo-degradation of the RhB dyestuff on composite NPs was observed to be 98.5% and 92.5% for 6 and 2 h aged samples, respectively. On Ag NPs, the catalytic performance of the sample was increased up to 95% after 180 min.     

Surface crack problems in plates

The mode I crack problem in plates under membrane loading and bending is reconsidered. The purpose is to examine certain analytical features of the problem further and to provide some new results. The formulation and the results given by the classical and the Reissner plate theories for through and part-through cracks are compared. For surface cracks the three-dimensional finite element solution is used as the basis of comparison. The solution is obtained and results are given for the crack/contact problem in a plate with a through crack under pure bending and for the crack interaction problem. Also, a procedure is developed to treat the problem of subcritical crack growth and to trace the evolution of the propagating crack.

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Résumé On considère la propagation dynamique en conditions stable de deux fissures parallèles semi-infinies de Mode III, dans un corps quelconque à visco-élasticité linéaire et à caractéristiques infinie, homogène et isotrope.On suppose exister à l'extrémité de la fissure une zone de rupture de type Barenblatt et on tire une formulation pour la vitesse de relaxation de l'énergie, qui fournit des comparaisons immédiates avec le modèle correspondant pour une fissure simple.On illustre par des calculs numériques l'influence de la vitesse de la fissure, de la distance séparant les fissures et des propriétés du matériau sur la vitesse de relaxation de l'énergie, dans le cas d'un matériau à comportement parabolique, et dans le cas d'un matériau linéaire standard.Comme cas limites de l'analyse, on établit les résultats pour des problèmes élastiques et des problèmes visco-élastiques quasi-statiques.

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This work was supported by NSF under the Grant MSM-8613611 and by NASA-Langley under the Grant NAG-1-713.     

The elasticity problem for a thick-walled cylinder containing a circumferential crack

The elasticity problem for a long hollow circular cylinder containing an axisymmetric circumferential crack subjected to general nonaxisymmetric external loads is considered. The problem is formulated in terms of a system of singular integral equations with the Fourier coefficients of the derivative of the crack surface displacement as density functions. The stress intensity factors and the crack opening displacement are calculated for a cylinder under uniform tension, bending by end couples, and self-equilibrating residual stresses.     

A half plane and a strip with an arbitrarily located crack

The paper introduces a technique to deal with the problem of an elastic domain containing an arbitrarily oriented internal crack. The problem is formulated as a system of integral equations for a fictitious layer of body forces imbedded in the plane along a closed smooth curve encircling the original domain. The problems of a half plane with a crack in the neighborhood of its free boundary and of an infinite strip containing a symmetrically located internal crack with an arbitrary orientation are considered as examples. In each case the stress intensity factors are computed and are given as functions of the crack angle.     

Stress singularities in a two-material wedge

A method for the determination of stresses in a two-material wedge-shaped region is presented. The method is applicable for plane strain or plane stress problems and treats the general case where each region is a wedge of arbitrary angle. The results are obtained by the use of the Mellin transform and the theory of residues.The characteristic equation is investigated to determine the stress singularity resulting from certain combination of geometry and material properties. A formal solution is then presented for the case where the loading is in the form of a point dislocation along the interface. This solution is the Green's function for the more general mismatch problems and therefore has applications in solving other problems with compatible boundary conditions. The results obtained show that for small values of r the dominant effect is due to geometry and the secondary effect is caused by the choice of elastic constants of the materials.This work was supported by the National Science Foundation under Grant GK-11977, and the Bell Telephone Laboratories Doctoral Support Program.