Creep Modelling of Rootstock during Holding in Watermelon Grafting

The fragile structure of a rootstock predisposes the stem to mechanical damage during grafting. Thus, it is necessary to take into account the rootstock’s rheological properties under mechanical compression when designing a clamping mechanism. This study focused on cucurbit, a typical rootstock for watermelon grafting. Firstly, we adopted a four-element Burgers model to analyze viscoelastic behavior and deformation characteristics of the rootstock, then conducted creep tests to obtain the parameters of the viscoelastic model. Next, we developed a model for the rootstock during holding based on viscoelastic parameters, loading force and contact time. Moreover, we evaluated the effect of various loading forces and test velocities on creep deformation to reveal the least damage on the rootstock. Results showed that the influence of loading force on the creep deformation was greater than test velocity. Finally, the holding test indicated that the clamping mechanism with silicone rubber can effectively prevent the damage to the stem. Specifically, the loading force should be controlled below 4 N to reduce the associated damage. Taken together, our findings provide a theoretical basis for analyzing the holding damage mechanism during watermelon grafting.

Juvenile Chinook salmon use of sandbar willows in a large-scale, simulated riparian floodplain: microhabitat and energetics

Outmigrating, juvenile Chinook salmon Oncorhynchus tshawytscha, with access to floodplains (e.g., Yolo Bypass California, USA), grow faster than those restricted to the main channel of the Sacramento River. How these young salmon might use rooted, vegetative structure (e.g., to decrease energy expenditures) while holding positions in flowing water on floodplains and flooded riparian zones is unknown. We conducted daytime experiments in a large (24.4 m long) flume containing a planted area (9.76 m × 1.22 m) of sandbar willows, Salix interior. Flume water was maintained at 1.5 m depth and 16 °C over a 15–90 cm s−1 test velocity range. Fish were videoed using 19 cameras to determine positional behavior, including their depth, use of vegetation, and tail-beat (body-undulation) frequencies (TBFs). These TBFs were replicated with similarly-sized salmon in a calibrated, Brett-type swimming respirometer, where oxygen consumption rates were measured. Using these laboratory measurements, we estimated their swimming velocities and energetic costs associated with occupying sandbar willow habitats in the flume. As flume velocities increased and the leafy canopies of the willows were bent over from the flow, salmon occupied deeper water, among the thick stems of the willows, and maintained their positions. Even at the highest (90 cm s−1) nominal flume velocities, their estimated swimming velocities were only 35.6 cm s−1, within the bottom 15 cm of the water column. This resulted in unchanged energetic costs, compared with those estimated at lower nominal water velocities. The use of vegetated (e.g., with sandbar willow common to the riparian zone) floodplains, rather than non-vegetated ones, can potentially provide energy-saving, growth-promoting daytime habitat for migrating juvenile salmonids during river-flow periods that include floodplain inundation.

CHANGES IN THE FLEXOR AND EXTENSOR MUSCLES AT DIFFERENT SPEEDS

ABSTRACT Introduction: Centrifugal strength is an important element for strength quality. Developing muscle centrifugal strength can effectively increase the stability of lower limbs and reduce the risk of injury. Objective: To explore the characteristics of contractile force of flexor ahods in strength training and rehabilitation training, and the extensor muscles of the knee joint in athletes with different speeds of centripetal force. Methods: The knee joint muscle group of 8 first-level male high jumpers and 8 second-level male high jumpers were tested by isokinetic centrifugal contraction; the angular test velocity was 60 °/s, 120 °/s, 240 °/s, and the indexes included peak torque, relative peak torque (peak torque/body weight), and the peak torque flexural extension ratio. Results: With the centrifugal contraction of the knee joint muscle group (P < 0.05), the second-level high jumpers should increase the ability of the knee flexor muscle group of the take-off leg. In the case of constant velocity centrifugal contraction (P < 0.01), taking off time must be reduced, that is, taking off speed must be accelerated. Conclusions: The difference in the knee joint muscle isokinetic test results is one of the reasons for the difference in knee joint flexor and extensor muscle contractility under the different speed forces of high jumpers. Level of evidence II; Therapeutic studies - investigation of treatment results.

Behaviour of Soft Clayey Soil Improved by Fly Ash and Geogrid under Cyclic Loading

The effect of Cyclic loading on the foundation behaviour of many engineering structures presents more important and related to many problems in geotechnical engineering, Especially when construction on soft ground area which represent one of the major concerns in geotechnical engineering. This paper is conducted to investigate the influence of using several improving techniques as (fly ash, Geo-grid, fly ash and Geo-grid) on the behavior of soft clayey soil subjected to cyclic loading. A total of twenty four models have been tested which consists of a wide domain of boundary conditions, such as untreated model, Geo-grid reinforced models, fly ash treated models and models treated with fly ash incorporated with Geo-grid were conducted by varying parameters such as, footing elevations, test velocity and number of geogrid layers. The analysis demonstrates that the settlement behaviour of footing resting on treated models with fly ash and two Geo-grid layers perform better than other improving techniques. Also observed there was an increase in settlement, which corresponds to the increase in test velocity from 6 to 9 mm/sec. Furthermore, it was conducted that the more depth of footing the soil settlement decreases. In general, when other factors remaining constant, the bearing capacity of soil goes on increasing when the depth increased.

Effect of Confluence Ratio Change on Hydrodynamic Character in Reservoir Area

Major factors that affect hydrodynamic character include confluence ratio, junction angle, bed discordance and channel gradient. In reservoir area, the river confluence is also affected by change of water level results from impoundment. Focused on asymmetrical confluence with 90° junction angle in reservoir area and based on model test, velocity distribution, location and range of reverse flow zone under different confluence ratios and water levels were investigated. The results show that flow velocity always declined along the channel after convergence. When confluence ratio increased, velocity decline rate accelerated, tributary flow diffused more fiercely at the conflux section, reverse flow zone enlarged. As the water level rising up, overall flow field velocity was weakened, the degree of tributary deflection increased. The velocity declined much slower in high water level.

The Study of LEFP Based on One Part of Semicircle Liner

In order to obtain the forming and the velocity of LEFP(Linear Explosively Formed Penetrators) based on one part of semicircle liner, the X-ray radiography and test velocity technology are used to obtain the forming and velocity of LEFP. In this paper, an analytical approach to describe the two-dimensional liner motion of LSCs is addressed firstly at a detonation-point. The relationship of LEFP flight distance can approximate a linear equation to estimate the distance of LEFP before contacting target. Experimental results showed that the shape of LEFP likes a scimitar according to gray image, and LEFP can close around linear explosive charge length axis direction.

Mechanical properties of some granular agricultural materials used in silo design

The aim of this research was to provide values for different material properties considered in either traditional or more recent numerical silo design methods. Different samples of granular agricultural materials commonly stored in silos were tested. Common geotechnical devices have been used in order to make the replications easier. Based on these experiments it was determined that the different material properties were not affected by the test velocity, except in the case of Poisson ratio. From a practical point of view, the test velocity correlates well with the sliding velocity of grain during discharge. The values obtained for material properties considered in traditional silo design methods were similar to those reported by other authors. No significant differences were observed in the results obtained when using either the square shear box or the circular shear cell. The same conclusion was reached when comparing the results from direct shear tests with preconsolidated and unconsolidated samples. This means that simplified devices and procedures can be used in agricultural grains against other products. Finally, a table with the recommended values for the different parameters determined for each sample tested was provided in this work.