Experiments and FE-analysis of 2-D root-soil contact problems based on node-to-segment approach

Accurate predictions of the mechanical response of root-soil systems are required for assessing and reducing the risk of landslides, surface erosions, and lodging. The present paper proposes the use of the node-to-segment (NTS) approach with the finite element method for predicting contact phenomena between roots and soils, such as collision, sliding, and separation. To obtain reliable predictions for the deformation of such geometrically complex problems, a stabilizing algorithm within the NTS approach is proposed and implemented here. The proposed algorithm prevents the well-known non-uniqueness problem of the pairing algorithm in the NTS approach, which has been an obstacle to applying the approach to root-soil systems. The current method is employed for two numerical examples. The first is an example of validation, in which pullout experiments are re-analyzed to examine the applicability of the method to a geometrically simple root-soil contact problem. It is shown that the current method provides a reasonable prediction of the pullout response, and that both the friction and the cohesion can also be accurately estimated with it. The second is an example of a realistic problem, in which a 2-D lodging experiment, analogous to pile-loading problems, is conducted and simulated to demonstrate the accuracy and applicability of the NTS approach in plant-scale problems with complex root geometries. The relationship between the displacement and the reaction force of the simulation is consistent with that of the experiment, and it enables the visualization of the stress contour and deformation of the rhizosphere.     

Functional Characterization of the GH10 and GH11 Xylanases from Streptomyces olivaceoviridis E-86 Provide Insights into the Advantage of GH11 Xylanase in Catalyzing Biomass Degradation

We functionally characterized the GH10 xylanase (SoXyn10A) and the GH11 xylanase (SoXyn11B) derived from the actinomycete Streptomyces olivaceoviridis E-86. Each enzyme exhibited differences in the produced reducing power upon degradation of xylan substrates. SoXyn10A produced higher reducing power than SoXyn11B. Gel filtration of the hydrolysates generated by both enzymes revealed that the original substrate was completely decomposed. Enzyme mixtures of SoXyn10A and SoXyn11B produced the same level of reducing power as SoXyn10A alone. These observations were in good agreement with the composition of the hydrolysis products. The hydrolysis products derived from the incubation of soluble birchwood xylan with a mixture of SoXyn10A and SoXyn11B produced the same products as SoXyn10A alone with similar compositions. Furthermore, the addition of SoXyn10A following SoXyn11B-mediated digestion of xylan produced the same products as SoXyn10A alone with similar compositions. Thus, it was hypothesized that SoXyn10A could degrade xylans to a smaller size than SoXyn11B. In contrast to the soluble xylans as the substrate, the produced reducing power generated by both enzymes was not significantly different when pretreated milled bagasses were used as substrates. Quantification of the pentose content in the milled bagasse residues after the enzyme digestions revealed that SoXyn11B hydrolyzed xylans in pretreated milled bagasses much more efficiently than SoXyn10A. These data suggested that the GH10 xylanases can degrade soluble xylans smaller than the GH11 xylanases. However, the GH11 xylanases may be more efficient at catalyzing xylan degradation in natural environments (e.g. biomass) where xylans interact with celluloses and lignins.     

Characterization of mechanical stress distributions in a cross section of cucumber fruits: bisector reference line represents tissue anatomy

This study sought to statistically analyze the difference of planar stress distribution in a cross section of cucumber cultivars. The method dealt with statistically comparable data, incorporating both the stress magnitude and their positional information, and was developed to reduce complexity without losing anatomical information. Utilizing the trigonal symmetry of cross‐sectioned cucumbers, a reference line bisecting the cross section was introduced on the rupture frame for referencing the relative locations of stress‐sensing points to the underlying anatomical tissue distribution. The stress–location curves on the reference line statistically differed among the cultivars, especially at the center of the cross section. The corresponding tissue for the center of the curve was the seed cavity, so the cultivar differences arise from mainly the mechanical differences in this tissue. The stress–strain analysis of definite tissues revealed flesh stiffness to exceed the seed cavity stiffness, but both differed from the average stiffness of the whole cross section in all cultivars. Copyright © 2004 Society of Chemical Industry     

Bioactivity of Zirconia-Toughened Glass-Ceramics

Bioactivity of zirconia-toughened glass-ceramic composites was evaluated by their surface reaction in simulated body fluid and the bonding strength to living bone. The composite containing 30 vol% zirconia showed high bioactivity, whereas that containing 50 vol% zirconia, extremely low. TEM observation indicated that Ca in the glass-ceramic particles reacted with the zirconia during sintering. It was found that the decrease in Ca in the particles degraded the bioactivity of the composite. In this study, the optimum composition was determined for high-strength and bioactive ceramic.     

Synthesis of zeolite L crystals with different shapes

Zeolite L crystals were synthesized hydrothermally from aqueous mixtures of potassium hydroxide, metallic aluminum, and colloidal silica. The influence of hydrothermal conditions and the addition of triethanolamine (N(C₂H₄OH)₃; H₃tea) upon the formation and shape of the resulting zeolite L crystals was examined. When the mixtures of KOH:Al:SiO₂:H₂O = 2.2 or 2.5:1.0:4.5:80 were hydrothermally treated at 130 or 175 °C, the zeolite L crystals had a columnar shape. Decrease in the added amount of KOH facilitated crystal growth in the axial direction, whereas a decrease in hydrothermal temperature inhibited it. For the synthesis using H₃tea, a silica-rich starting composition of KOH:Al:SiO₂:H₂O:H₃tea = 10:1.0:15:250:x and a hydrothermal temperature of 120 °C was used. When no H₃tea was added, the obtained zeolite L crystals had an indistinct shape. H₃tea addition at x = 2 led to the formation of zeolite L crystals with a well-defined, clam-like shape. The formation of the well-defined shape is due to the coordination of H₃tea to aluminate ions. The starting composition has some influence on the formation of the clam-like shape. The zeolite L crystal morphologies obtained in this study ranged from stick-like shapes to clam-like ones. The length-to-diameter ratios ranged from 0.2 to 5.8.