Soft-lubrication interactions between a rigid sphere and an elastic wall

The motion of an object within a viscous fluid and in the vicinity of a soft surface induces a hydrodynamic stress field that deforms the latter, thus modifying the boundary conditions of the flow. This results in elastohydrodynamic interactions experienced by the particle. Here, we derive a soft-lubrication model, in order to compute all the forces and torque applied on a rigid sphere that is free to translate and rotate near an elastic wall. We focus on the limit of small deformations of the surface with respect to the fluid-gap thickness, and perform a perturbation analysis in dimensionless compliance. The response is computed in the framework of linear elasticity, for planar elastic substrates in the limiting cases of thick and thin layers. The EHD forces are also obtained analytically using the Lorentz reciprocal theorem.

Characterising Penetrometer Tip Contact during Concrete Condition Assessment

Concrete condition assessing penetrometers need to be able to distinguish between making contact with a hard (concrete) surface as opposed to a semi-solid (corroded concrete) surface. If a hard surface is mistaken for a soft surface, concrete corrosion may be over-estimated, with the potential for triggering unnecessary remediation works. Unfortunately, the variably-angled surface of a concrete pipe can cause the tip of a force-sensing tactile penetrometer to slip and thus to make this mistake. We investigated whether different shaped tips of a cylindrical penetrometer were better than others at maintaining contact with concrete and not slipping. We designed a range of simple symmetric tip shapes, controlled by a single superellipse parameter. We performed a finite element analysis of these parametric models in SolidWorks before machining in stainless steel. We tested our penetrometer tips on a concrete paver cut to four angles at 20∘ increments. The results indicate that penetrometers with a squircle-shaped steel tip (a=b=1,n=4) have the least slip, in the context of concrete condition assessment.

The Estimation of Seismic Site Amplification of Bukittinggi City, West Sumatera, Indonesia

Bukittinggi city area is exposed substantial risk of both, close to seismic source line and site amplification due to soft surface sediment / soil layer. The Great Sumateran Fault (GSF) which is crossing this area, notorious as a very active seismic source. Its responsible to some major earthquake in the vicinity of the fault line. Generally, Bukittinggi area is covered by volcanic product as pumiceous tuff. We applied combined array and single station microtremor measurement to characterize near surface sediment in this area. Based on analysis microtremor single station and array using spatial autocorrelation (SPAC) method, weathered surface layer thickness is in the range of 0-108 m with shear wave velocity in the range of 62-190 m/s, while the fresh pumiceous tuff is in the range of 375-629 m/s. The estimation of site amplification in this area which is indicated by mean amplification is in the range of 1-1.95. The high amplification zone is occupies the northernmost area and some area locally in the southern part of Bukittinggi city.

Rola pszczół i wosku pszczelego w tworzeniu głagolickich liter

The article shows what role the writing instruments, in particular wax tablets, used by St. Cyril the Philosopher, could play in shaping the material form of Glagolitic writing. In this research approach, writing is treated not only as a system of abstract signs, but also as their factual figure formed by a tool on a writing material. In the case of the Glagolitic alphabet, its creation was therefore both a mental and physical process involving objects such as wax tablets. The ease of engraving the shapes of new letters on a soft surface and the possibility of repeatedly erasing them allowed Cyril to experiment with their forms without consuming valuable parchment. Therefore, this process depended mainly on the material properties of the wax produced by honeybees, which was used to cover the wooden tablets designed for writing with a stylus. In this way, these insects participated in the creation of the material dimension of Slavic writing, on a par with people who took the stick from them, choosing the wax from the hives to further process it. This proves that Cyril did not force the Glagolitic letters formed in his mind onto passive material, but that beeshaped, writing wax affordances actively cooperated in this process.

Effects of Plyometric Training on Soft and Hard Surfaces for Improving Running Economy

The present study investigated the effects of plyometric jump training on hard and soft surfaces on running economy (RE), maximal oxygen uptake (VO2max), running performance and the rate of force development in orienteers. Nineteen orienteers (11 women and 8 men, body mass 61.1 ± 7.3 kg, age 21 ± 5.8 yrs) were randomly stratified based on sex, age, VO2max and RE to plyometric jumping training (8 sessions over 4 weeks) on either a hard or a soft surface. RE, VO2max and running performance were assessed on a treadmill and outdoor on- and off-trail loops. Moreover, ground reaction forces and force development were assessed during a one leg drop-jump test. The training intervention led to an overall 2-7% improvement in treadmill and off-trail RE, independent of the jumping surface and running velocity assessed. These improvements were not explained by force development during drop jump tests, which remained unchanged following the intervention. The changes in time-trial performance were associated with changes in RE. Plyometric training improved RE with no difference between the hard or the soft training surface and improved RE was also independent of the running speed assessed. Furthermore, improved running performance was associated with changes in RE after the intervention.

The Effects of 8 Weeks TRX Exercises and Core Stability in the Stable Level on the Landing Pattern, the Stability of the Core Area and Balance of Girls Football Players

Background and Aims: This study aimed at the effects of 8 weeks TRX exercises and core stability exercises in the stable level on the landing pattern, the stability of the core area, and the balance of girls football players. Methods: Thirty athletes with trunk defects were screened by Tuck Jump test and selected as a statistical sample. Finally, assigned to two groups of 15 subjects at a stable level and varying level training. Both groups participated in pretest and post-test. Both groups training sessions for 8 weeks and three weeks each week on core stability training at both sustained (stable) and unstable (TRX). This study used the core stability practice protocol in the training section at a stable and unstable level. The static and dynamic balance were evaluated by BESS and Y tests, respectively. McGill’s endurance tests also evaluated the endurance of the core region. In addition, landing mechanics were assessed using the Landing Error Score System test. ANCOVA test was used to compare the differences between the research variables by two types of training. The stability of the core body was used in two groups of training (stable and TRX) and a t-test for correlating the changes within the group. Results: The results of the analysis of t-test showed that in the results of the stable training (P≤0.001) and TRX (P≤0.001) effect on score of the error of landing error, LESS, flexion 60 °, Sorensen, Right Plank, static balance and total dynamic balance score. In the post-test, there are significant differences between the two groups in the TRX and stable levels in LESS, Sorensen, static balance in the state stand on two legs on a soft surface and stand in the Tandem on a soft surface (P≤0.05). Conclusion: the results of this study showed that the use of core stability training at a stable and unstable level by helping to improve the landing jump activity, as well as improving muscular balance and endurance, can be eliminated by modifying some of the risk factors associated with an ACL injury to prevent Lower limb non-limiting injury in athletes with trunk defects.

Differences in equine spinal kinematics between straight line and circle in trot

Work on curved tracks, e.g. on circles, is commonplace within all forms of horse training. Horse movements in circles are naturally asymmetric, including the load distribution between inner and outer limbs. Within equestrian dressage the horse is expected to bend the back laterally to follow the circle, but this has never been studied scientifically. In the current study 12 horses were measured (optical motion capture, 100 Hz) trotting on left and right circles and on the straight without rider (soft surface). Data from markers placed along the spine indicated increased lateral bending to the inside (e.g. left bending on the left circle) of the thoracolumbar back (difference left circle vs. straight − 3.75°; right circle + 3.61°) and the neck (left − 5.23°; right + 4.80° vs. straight). Lateral bending ROM increased on the circle (+ 0.87° and + 0.62°). Individual variation in straight-circle differences was evident, but each horse was generally consistent over multiple trials. Differences in back movements between circle and straight were generally small and may or may not be visible, but accompanying changes in muscle activity and limb movements may add to the visual impression.

Electromagnetic Soft Surface (EMSS) Integrated MIMO Antennas With Reduced Mutual Coupling And Cross-Polarization Radiation

For closely spaced microstrip antenna elements, Mutual Coupling (MC) is an inevitable phenomenon which degrades antenna performances like gain, radiation pattern, return loss, radiation efficiency etc. Lot of works have been done on the reduction of MC and published the results in the open literatures. This paper presents an approach to suppress MC between two closely spaced microstrip radiators. This is achieved by inserting properly designed EMSS structure between the radiating elements. This EMSS acts as an electrical wall between two rectangular patches and reduces mutual coupling up to 50 dB at resonance frequency of 4.35 GHz. In this attempt, Cross Polarization (XP) reduction of 12.5dB has also been achieved with a gain 5.40dBi for the proposed antenna. The centre to centre spacing between the antenna elements is taken as 22.1mm (0.32λ).The proposed MIMO antenna system can be used for satellite communication and radar system.