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Abstract

Shear stress is one of the most critical parameters in hydraulic and coastal engineering, which is often measured indirectly. Since there is no instrument to measure this parameter directly and given that it is usually calculated by measuring other parameters such as velocity and pressure and using some equations, shear stress measurement is often accompanied with large measurement errors. In this study, a new technique and direct measurement using physical modeling in a hydraulic knife-edge flume and load cell were employed to measure the shear stress in a rectangular channel with rigid unsubmerged vegetation with Dv= 20, 25, and 32mm in

Q=25 and 30 Lit/S and y=10, 12, 17, and 20 cm. The results indicate that the shear stress and the dimensionless τ0τ ratio decrease in a constant flow discharge with increasing the flow depth. It was also shown that the shear stress would be enhanced with an increase

in vegetation diameter due to increasing vegetation density against flow. According to dimensionless ratios of τ0τ and Dvy in the graphs and considering the trend lines with appropriate correlation coefficients, some equations were presented to calculate the shear stress in the concerned range.

Experimental Tooling for Contact Stress Measurement in Bulk Metal Forming Processes

Knowledge of contact stresses in metal forming operations is essential not only for optimal die design, but also for theoretical and numerical analysis of the metal forming processes. Determination of contact stresses can be performed theoretically and experimentally. This paper presents a tool construction with built-in pin-load cells for experimental determination of contact stresses and friction coefficient at upsetting of prismatic specimen with cylindrical dies. This construction allows measurement of contact stresses in any point of the contact surface of specimen, due to adjustable location of pin-load cells. The adjustments are performed by turning cylindrical dies around its own axis in combination with the change of axial position of the specimen. Experimental determination of contact stresses in upsetting of Ck35 prismatic specimens using cylindrical tools was performed at the Laboratory for technology of plasticity, FTN Novi Sad.

Abstract

Resisted sprint training is believed to increase strength specific to sprinting. Therefore, the knowledge of force output in these tasks is essential. The aim of this study was to analyze the effect of sled towing (10%, 15% and 20% of body mass (Bm)) on sprint performance and force production during the acceleration phase. Twenty-three young experienced sprinters (17 men and 6 women; men = 17.9 ± 3.3 years, 1.79 ± 0.06 m and 69.4 ± 6.1 kg; women = 17.2 ± 1.7 years, 1.65 ± 0.04 m and 56.6 ± 2.3 kg) performed four 30 m sprints from a crouch start. Sprint times in 20 and 30 m sprint, peak force (Fpeak), a peak rate of force development (RFDpeak) and time to RFD (TRFD) in first step were recorded. Repeated-measures ANOVA showed significant increases (p ≤ 0.001) in sprint times (20 and 30 m sprint) for each resisted condition as compared to the unloaded condition. The RFDpeak increased significantly when a load increased (3129.4 ± 894.6 N·s−1, p ≤ 0.05 and 3892.4 ± 1377.9 N·s−1, p ≤ 0.01). Otherwise, no significant increases were found in Fpeak and TRFD. The RFD determines the force that can be generated in the early phase of muscle contraction, and it has been considered a factor that influences performance of force-velocity tasks. The use of a load up to 20% Bm might provide a training stimulus in young sprinters to improve the RFDpeak during the sprint start, and thus, early acceleration.

Abstract

This paper represents the development of a prototype robotic system for automatic bone drilling in orthopaedic surgery. A new design of the mechanical structure is proposed, answering the surgical requirements for the robot dimensions and weight to be as small as possible. The new structure design is based on idea of parallelism of the axis of the linear actuator and the axis of the rotary one. The control system is improved by using a new micro-controller. A new type of linear drive and a new force sensor (load cell) are built in, so that the quality characteristics of the “Orthopaedic bone Drilling Robot” (ODRO) are not only the same as previous its two versions, but becomes better.

An experimental setup is arranged and experiments are executed to test and to verify the robot quality features and functional capabilities.

Abstract

The main priorities in crop production are increasing the yield and decreasing the cost of production. Precision farming is the best practice to approach these goals. For real time measurement of sugar beet yield, a yield monitor was developed, and installed on the exterior side of the harvester’s chassis. The advantage of this arrangement over similar systems is the location of the load cell and system’s frame which prevents blockage by trash, mud or plant roots. For measurement of weight, one load cell on each side of the harvester chassis was used. Conveyor and ground speeds were measured using two proximity sensors. Because vibrations of the harvester can affect the output signals, it is necessary to find the main bandwidth associated with the weights moving on the conveyor. For this purpose, three different masses were placed on the moving conveyor and this bandwidth was determined using signal processing. Then, a suitable filter was designed and undesirable frequencies acting as noise were attenuated. After calibrating all the sensors, final evaluation of the system was performed in the field and the mean and standard deviation of error were 6.48% and 1.52, respectively. Although the error may seem to be somewhat high but the low of standard deviation indicates that there is a similar error in all tests. These negative errors indicate that the weight is systematically overestimated by the monitor. Thus, the error can be reduced by minor changes in conveyor shape or modified by software means. By software modification, the systematic error was alleviated. The median sugar beet yield was thus obtained to be 42.7 t/ha. Comparing this with the actual mean yield of 41.8 t/ha, it differs by only about 2%.

Abstract

Background: Cell seeding technique is a fundamental component of the tissue engineering construction. Effective cell seeding can not only shorten the construction time but also improve the final outcome of tissue engineered substitutes.

Objective: We improved the seeding efficiency of monolayer cells on the surface of biomaterials in tissue engineering. Cell sheet technology was applied to seed monolayer cell sheet instead of concentrated cell suspension, which was termed cell-sheet seeding.

Methods: Equal quantities of endothelial cells were seeded on the surface of equally sized acellular bovine pericardia by cell-sheet seeding and cell suspension seeding respectively. After culturing cell-seeded pericardia for 24 hours, the effects of these 2 cell seeding methods were evaluated and compared.

Results: As compared to cell suspension seeding, a larger quantity of loading cells, higher tissue-plasminogen activator (t-PA) and prostacyclin (PGI-2) content, and higher homogeneity of cells distribution on the surface of the pericardia was achieved with cell-sheet seeding. Furthermore, cell-sheet seeding did not affect metabolism or increase endothelial cells damage.

Conclusion: Cell-sheet seeding is an effective and time-saving method of seeding monolayer cells on the surface of biomaterials. This novel seeding method is particularly suitable for building tissue engineered substitutes with monolayered cells distribution and 2-dimensional structure.

Abstract

The purpose of the present investigation was to examine the association of a novel test of upper body isometric strength against a 1RM bench press measurement. Forty college age adults (n = 20 female, n = 20 male; age 22.8 ± 2.8 years; body height 171.6 ± 10.8 cm; body mass 73.5 ± 16.3 kg; body fat 23.1 ± 5.4%) volunteered for the present investigation. The participants reported to the lab on three occasions. The first visit included anthropometric measurements and familiarization with both the upper body isometric test and bench press exercise. The final visits were conducted in a randomized order, with one being a 1RM assessment on the bench press and the other consisting of three trials of the upper body isometric assessment. For the isometric test, participants were positioned in a “push-up” style position while tethered (stainless steel chain) to a load cell (high frequency) anchored to the ground. The peak isometric force was consistent across all three trials (ICC = 0.98) suggesting good reliability. Multiple regression analysis was completed with the predictors: peak isometric force, gender, against the outcome variable 1RM bench press. The analysis resulted in a significant model (r2 = 0.861, p≤0.001) with all predictor variables attaining significance in the model (p<0.05). Isometric peak strength had the greatest effect on the model (Beta = 5.19, p≤0.001). Results from this study suggest that the described isometric upper body strength assessment is likely a valid and reliable tool to determine strength. Further research is warranted to gather a larger pool of data in regard to this assessment.

Abstract

In this work, drying of tomato slices was studied in a laboratory scale batch dryer working at conditions specific for geographical locations with low ambient pressure and low relative humidity of air. Tomato is a perishable farm product with high moisture content. Despite their high value, tomatoes are subjected to wastage and spoilage during their seasonal period; to last longer after harvested, they need to be treated by drying. Drying is one of the most widely used methods of tomato preserving for a longer period of time. This study involves experimental work on tomatoes drying in a tray laboratory batch dryer with the dimensions of (490 × 330 × 310) mm, a load cell-force sensor (range: 0–5 kg), fan (speed: 0–2500 rpm), air flow sensor (0–150 l/min) and a temperature and humidity monitoring system. This study was aimed at the development of a suitable drying method for the production of dehydrated agricultural products under specific air properties and climate conditions such as low ambient pressure and low relative humidity. During the experiment, the average ambient pressure was 82 kPa, and the average relative humidity of air was 20 %. Drying characteristics of tomato slices were determined at three temperature levels, namely: 50 °C, 60 °C and 70 °C,and three air flow rates: 30 l/s, 40 l/s and 50 l/s, for each temperature level. In this study, the effect of temperature, air flow rate, and ambient conditions on the drying rate of tomato slices were studied. The results indicate that during the experiments, tomatoes were dried to the final moisture content of 32.2 % from 92 %. Drying time at 50 °C, 60 °C and 70°C, and air flow of 30 l/s was 17.80 h, 15.80 h, and 14.08 h, respectively. For the air flow rate of 40 l/s, the drying time was 15.0 h, 12.9 h and 11.7 h and for the air flow rate of 50 l/s, the drying time of tomato slices was 14.0 h, 11.6 h and 10.2 h, respectively.

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Lacalle, A. Celaya, A. Lamikiz and J. Albizuri. “Surface improvement of shafts by the deep ball-burnishing technique”, Surface & Coatings Technology, vol. 206, 2012, pp. 2817-2824. [9] F.J. Shiou and C.H. Chen. “Ultra-precision surface finish of NAK80 mould tool steel using sequential ball burnishing and ball polishing processes”, Journal of Materials Processing Technology, vol. 201, 2008, pp. 554-559. [10] F.J. Shiou and C.H. Chuang. “Precision surface finish of the mold steel PDS5 using an innovative ball burnishing tool embedded with a load cell”, Precision