A differential mechanical technique for tissue separation, based on the different physical resistance to grinding between mesophyll (M) and bundle sheath (BS) cells, was tested on dicotyledonous C4 plants A triplex canscens, A triplex halimus, Gomphrena globosa, Amaranthus retroflexus, Amaranthus caudatus and Portulaca oleracea. A metal sieve (35 mesh) was placed inside a mortar and pieces of leaves (0.5 cm2) were ground in an aqueous medium on the sieve to obtain a homogenate. The homogenate was at first collected below the sieve and was then filtered through six layers of muslin. Microscopic examination showed that the filtrate was enriched by the M cells and the residue was enriched by BS cells, few of which were broken. The BS cell fraction was then vigorously ground and filtered; this second filtrate was named the BS cell fraction and the first filtrate was named the M cell fraction. Ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) (RuBPC) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (PEPC) were assayed, and chlorophyll determinations and protein estimations were made on both fractions. As expected, PEPC showed higher activities in the M fractions; contrary to expectation RuBPC was present in M cell fractions in the six dicotyledonous C4 plants tested. The relative high RuBPC activities found in the M fraction could not be explained in terms of bundle sheath contamination.
Content-based composites are traditionally a commonly used material in civil engineering structures. The basic representative of this type of material is concrete, a quasi-brittle composite in which crack resistance can be achieved by the addition of fibres. The double-K fracture model can be used to calculate the fracture-mechanical parameter values of structural concrete with and without popypropylene fibres. This model combines the concept of cohesive forces acting on the crack length with a criterion based on the stress intensity factor, using a ‘softening function‘ to determine the cohesive part of fracture toughness. In this paper, authors determine the effect of the type of this softening function on the evaluation of fracture tests performed on sets of concrete specimens with and without polypropylene fibres. and Obsahuje seznam literatury
We consider a motion of spiral-shaped piecewise linear curves governed by a crystalline curvature flow with a driving force and a tip motion which is a simple model of a step motion of a crystal surface. We extend our previous result on global existence of a spiral-shaped solution to a linear crystalline motion for a power type nonlinear crystalline motion with a given rotating tip motion. We show that self-intersection of the solution curves never occurs and also show that facet extinction never occurs. Finally, we show that spiral-shaped solutions exist globally in time.