Molecular insights into the complex mechanics of plant epidermal cell walls

Plants have evolved complex nanofibril-based cell walls to meet diverse biological and physical constraints. How strength and extensibility emerge from the nanoscale-to-mesoscale organization of growing cell walls has long been unresolved. We sought to clarify the mechanical roles of cellulose and matrix polysaccharides by developing a coarse-grained model based on polymer physics that recapitulates aspects of assembly and tensile mechanics of epidermal cell walls. Simple noncovalent binding interactions in the model generate bundled cellulose networks resembling that of primary cell walls and possessing stress-dependent elasticity, stiffening, and plasticity beyond a yield threshold. Plasticity originates from fibril-fibril sliding in aligned cellulose networks. This physical model provides quantitative insight into fundamental questions of plant mechanobiology and reveals design principles of biomaterials that combine stiffness with yielding and extensibility.

Evaluation of S2 alar and traditional S1 pedicle fixation for severe lumbar spondylolisthesis in different bone mineral densities: a finite element analysis

Purpose: Little is known about the biomechanical performance of L5-S2 alar internal fixation constructs after posterior lumbar interbody fusion. This study aimed to compare the biomechanical effect of L5-S1 internal fixation and L5-S2 alar internal fixation on severe lumbar spondylolisthesis. Methods: A normal male volunteer without a history of spinal disease was selected, lumbar CT data was collected. An intact L5-S2 three-dimensional finite element model was created by Mimics and Geomagic.Two kinds of fixation methods were reconstructed including (1) the L5-S1 screw fixation model and (2) the L5-S2 alar fixation model. The inverse repair was performed using Geomagic software, the internal fixation device was drawn using Creo software, and the model parameters were set and analyzed using ANSYS Workbench software. Results: The validity of the intact model shows that the ROM of the model is similar to that of a reported cadaveric study. The average stress of the L5-S2 alar internal fixation device was 86.9-111% higher(P＜0.001) than that of the L5-S1 fixation device when the bone of the S1 screw path reached the yield threshold. The maximal stress of the S1 screw in the L5-S2 alar fixation was significantly lower (P＜0.001) than it in the L5-S1 fixation when the stress exceeds the S1 bone yield threshold. When the S1 screw path bone yielded, the maximal deformation value of the S1 screw path was similar in both models (P>0.05), while the average deformation value of the S1 screw path in L5-S2 alar fixation was significantly higher (P＜0.01) than it in L5-S1 fixation. Conclusion: Extending fixation to the S2 wing can significantly improve internal fixation device stability and reduce the risk of intraoperative and postoperative fractures while avoiding injury to the sacroiliac joint, reducing the difficulty of surgery and the risk of injury to surrounding tissues. It is a reasonable plan for the treatment of moderate and severe lumbar spondylolisthesis with osteoporosis.

Investigation of the cavitational stability of an aluminum piston surface based on a three-dimensional model

The problem of determining the optimal material for manufacturing the surface of a movable element (piston) is considered, which has an increased resistance to cavitation failure, in order to justify the expediency of using structural materials for the manufacture of pistons in fuel automatics elements. On the basis of three-dimensional numerical modeling of the elasticity equations, the conditions under which a cavitation bubble collapse on the surface of a piston made of various structural materials can lead to irreversible deformations of the piston. The pressure acting on the piston determined from the model of nonspherical bubble collapse with the formation of a cumulative stream. The impact on the surface of the collapse of both a single bubble and a pair of bubbles located at different distances from each other is studied. Calculations showed that with special treatment the surface of the piston will become more resistant to erosion destruction. Deformations are localized near the region to which the force is applied, at a distance of the order of two bubble diameters. Cavitation destruction of the material is associated with the yield threshold and grain size, is independent of the Young's modulus and inversely proportional to the Poisson's ratio. The simultaneous collapse of two bubbles at a distance of the order of one or two sizes of the bubble increases the maximum pressure on the surface and, consequently, increases the probability of irreversible deformation of the surface.

Combining seasonal yield, silage dry matter yield, quality and persistency in an economic index to assist perennial ryegrass variety selection

SUMMARYA total economic merit index (Pasture Profit Index, PPI) for perennial ryegrass variety selection was developed to rank perennial ryegrass varieties (Lolium perenneL.) based on their economic potential for grass-based ruminant production systems. The key traits of importance identified were: spring, mid-season (April 11–August 10) and autumn dry matter (DM) yield, first and second cut silage DM yield, grass quality April to July (inclusive) and sward persistency. Variety persistency was quantified by determining the ground score (GS) change across years, which was associated with a yield threshold which triggered sward replacement. Each one-unit decline in GS was associated with a 1683 kg loss in DM yield. Data generated in the Irish recommended list trials for value for cultivation and use were analysed to quantify the relative performance of each variety for each of the aforementioned traits. A previously developed methodology to generate economic values was used with updated price assumptions to develop economic values, which were applied to the analysed performance data of individual varieties. These data were used to estimate the total economic merit of each variety. Thirty-nine varieties were ranked on total economic merit with the highest performing variety (Cv111) generating €213 per ha/year compared withCv201, which was the lowest ranking variety generating −€31 per ha/year. Use of the PPI provides information to end users in relation to the economic merit of one variety over another, facilitating a more informed decision-making process at farm level.

Development of streamflow drought severity–duration–frequency curves using the threshold level method

This study developed a streamflow drought severity–duration–frequency (SDF) curve that is analogous to the well-known depth–duration–frequency (DDF) curve used for rainfall. Severity was defined as the total water deficit volume to target threshold for a given drought duration. Furthermore, this study compared the SDF curves of four threshold level methods: fixed, monthly, daily, and desired yield for water use. The fixed threshold level in this study is the 70th percentile value (Q70) of the flow duration curve (FDC), which is compiled using all available daily streamflows. The monthly threshold level is the monthly varying Q70 values of the monthly FDC. The daily variable threshold is Q70 of the FDC that was obtained from the antecedent 365 daily streamflows. The desired-yield threshold that was determined by the central government consists of domestic, industrial, and agricultural water uses and environmental in-stream flow. As a result, the durations and severities from the desired-yield threshold level were completely different from those for the fixed, monthly and daily levels. In other words, the desired-yield threshold can identify streamflow droughts using the total water deficit to the hydrological and socioeconomic targets, whereas the fixed, monthly, and daily streamflow thresholds derive the deficiencies or anomalies from the average of the historical streamflow. Based on individual frequency analyses, the SDF curves for four thresholds were developed to quantify the relation among the severities, durations, and frequencies. The SDF curves from the fixed, daily, and monthly thresholds have comparatively short durations because the annual maximum durations vary from 30 to 96 days, whereas those from the desired-yield threshold have much longer durations of up to 270 days. For the additional analysis, the return-period–duration curve was also derived to quantify the extent of the drought duration. These curves can be an effective tool to identify streamflow droughts using severities, durations, and frequencies.

Linking stem diameter variations to sap flow, turgor and water potential in tomato

Water status plays an important role for fruit quality and quantity in tomato (Solanum lycopersicum L.). However, determination of the plant water status via measurements of sap flow (FH2O) or stem diameter (D) cannot be done unambiguously since these variables are influenced by other effectors than the water status. We performed a semi-seasonal and a diurnal analysis of the simultaneous response of FH2O and D to environmental conditions, which allowed us to distinguish different influences on ΔD such as plant age, fruit load and water status and to reveal close diurnal relationships between FH2O and ΔD. In addition, an analysis of the diurnal mechanistic link between both variables was done by applying a slightly modified version of a water flow and storage model for trees. Tomato stems, in contrast with trees, seemed to maintain growth while transpiring because a large difference between turgor pressure (Ψp) and the yield threshold (Γ) was maintained. Finally, the simultaneous response of D and FH2O on irrigation events showed a possibility to detect water shortages.

C2H4-Based Plasma-Assisted CD Shrink and Contact Patterning for RRAM Application

Critical dimension (CD) shrink and patterning of contact features via plasma etching were studied for typical resistive random access memory (RRAM) stacks. These consist of SiO2 and Si3N4 (total thickness of 65 80 nm) with NiO or pure Ni at the bottom. First, the contact patterning of RRAM stacks was investigated for 90 nm contacts. Thus, a standard high power contact etch recipe was shown to give rise to resist strip challenges due to the incorporation of sputtered Ni in the resist film. Therefore, a low-sputter-yield contact etch recipe based on a CF4/H2/Ar gas chemistry was introduced. The ion sputter efficiency of the recipe was estimated from a blanket SiO2 sputter-yield experiment in Ar plasma for the same recipe settings: this yielded values close to the Ni sputter-yield threshold. Second, plasma-assisted CD shrink was studied in combination with the newly developed patterning scheme to get the contact CD well below the initial 90-nm litho print size. It was shown that a low contact etch power regime could also provide a larger window for contact CD shrink using a C2H4-based chemistry: e.g. the demonstrated CD shrink from 90 nm down to sub-40 nm was shown to be extremely challenging in the case of a high power regime due to polymer instability enhanced with the resulting thickness increase. Perhaps, the relaxation of the polymer film stress, which was measured to be in the range of 1200-1500 MPa, is more easily triggered at higher power settings, which leads to polymer blistering. Finally, the optimization of the plasma-assisted CD shrink step in combination with the low-sputter-yield contact etch recipe was demonstrated to be able to provide CDs as small as 27 nm. The demonstrated approach shows that plasma-assisted CD shrink can provide a robust test vehicle for research programs that require the patterning of small features in the sub-40-nm CD range.