At the End of a Slippery Slope: A Pilot Study of Deceleration Mats for Snow Tubing

On-slope pilot testing of snow tubes was conducted at two ski areas in the United States to examine the effects of deceleration mats. Snow tube and rider kinematics were measured using an instrumented bodysuit and a GPS system worn by the rider. For each test, the riders descended a tubing run with minimal input and stopped in the run-out area. Snow tube and rider speeds when entering the run-out area were controlled to be approximately 9.5 m/s. Test trials were conducted with and without deceleration mats. Four deceleration mat conditions were tested, including two raised surface protuberances (ribs and projections) and two mat geometry parameters (flat and folded). The deceleration and effective coefficient of friction (COF) were determined for each trial. Data were recorded for 75 test trials with a mean (± standard deviation) speed entering the run-out area of 9.5 (±1.8) m/s. There were no significant differences in the deceleration or effective coefficient of friction between the surface protuberance conditions. The peak deceleration and effective COF for the folded mats (5.1 ± 1.6 m/s2 and 0.26 ± 0.14) was greater than for the flat (3.3 ± 0.8 m/s2 and 0.10 ± 0.07) and no mat (0.06 ± 0.3 m/s2 and 0.08 ± 0.03) conditions (all p < 0.05). Deceleration mats in run-out areas slow snow tube riders faster than without deceleration mats. Folding the deceleration mats produced greater deceleration but did not produce significantly different kinematics for the riders.

Nonprehensile Manipulation of Parts on a Horizontal Circularly Oscillating Platform with Dynamic Dry Friction Control

This paper presents a novel method for nonprehensile manipulation of parts on a circularly oscillating platform when the effective coefficient of dry friction between the part and the platform is being dynamically controlled. Theoretical and experimental analyses have been performed to validate the proposed method and to determine the control parameters that define the characteristics of the part’s motion. A mathematical model of the manipulation process with dynamic dry friction control was developed and solved. The modeling showed that by changing the phase shift between the function for dynamic dry friction control and the function defining the circular motion of the platform, the part can be moved in any direction as the angle of displacement can be controlled in a full range from 0 to 2π. The nature of the trajectory and the mean displacement velocity of the part mainly depend on the width of the rectangular function for dynamic dry friction control. To verify the theoretical findings, an experimental setup was developed, and experiments of manipulation were carried out. The experimental results qualitatively confirmed the theoretical findings. The presented analysis enriches the classical theories of nonprehensile manipulation on oscillating platforms, and the presented findings are relevant for mechatronics, robotics, mechanics, electronics, medical, and other industries.

Effective coefficient of diffusion and permeability of firn at Dome C and Lock In, Antarctica – Estimates over the 100–850 kg m⁻³ density range

Modeling air transport through the entire ice sheet column is needed to interpret climate archives. To this end, different regressions were proposed to estimate the effective coefficient of diffusion and permeability of firn. Such regressions are often valid for specific depth or porosity ranges and were little evaluated as data of these properties are scarce. To contribute with a new dataset, this study presents the effective coefficient of diffusion and the permeability at Dome C and Lock In, Antarctica, from the near-surface to the close-off (23 to 133 m depth). Also, microstructure is characterized based on density, specific surface area, closed porosity ratio, connectivity index and structural anisotropy through the correlation lengths. All properties were estimated based on pore-scale computations on 3D tomographic images of firn samples. Normalized diffusion coefficient ranges from 1.9 × 10−1 to 8.3 × 10−5 and permeability ranges from 1.2 × 10−9 to 1.1 × 10−12 m2, for densities between 565 and 888 kg m−3. No or little anisotropy is reported. Next, we investigate the relationship of the transport properties with density over the firn density range as well as over the entire density range encountered in ice sheets by including snow data. Classical analytical models and regressions from literature are evaluated. For firn (550–850 kg m−3), good agreements are found for permeability and diffusion coefficient with the regressions based on the open porosity of Freitag et al. (2002) and Adolph and Albert (2014), despite the rather different site conditions (Greenland). Over the entire 100–850 kg m−3 density range, permeability is accurately reproduced by the Carman-Kozeny and Self-Consistent (spherical bi-composite) model when expressed in terms of a rescaled porosity ϕres = (ϕ–ϕoff) / (1–ϕoff) to account for pore closure, with ϕoff the close-off porosity. For the normalized diffusion coefficient, none of the evaluated formulas were satisfactory so we propose a new regression based on the rescaled porosity that reads D/Dair = (ϕres)1.61.

Analysis of Sensitive Parameters Affecting Unlocking Force of Finger Lock in Landing Gear

The mechanical characteristics of the unlocking force of the landing gear finger lock were studied in this paper, the influence of its diameter, fingertip angle, wear, and other factors on the unlocking force in one complete working cycle was analyzed, and the sensitive parameters that affect the unlocking force were obtained. Firstly, the unlocking force and wear of finger lock were calculated theoretically, and the changing rule of the unlocking force and wear with each parameter was obtained. Then, the validity of the correlation coefficient and model was verified by experiment. Finally, combined with the effective coefficient obtained from the experiment, the Archard wear model was used to simulate the change rule of lock force. The results show that in one complete working cycle, the inner surface diameter is negatively related to the unlocking force, fingertip diameter has little effect on the unlocking force, fingertip angle is negatively related to the unlocking force, and wear is positively related to the unlocking force; friction coefficient and fingertip angle are high sensitive parameters that affect the unlocking force, which have obvious effect on the unlocking force. The inner surface diameter, fingertip diameter of finger lock, and wear are the low sensitive parameters that affect the unlocking force, and the influence on the unlocking force is weak.

Modeling of the vibroacoustic dynamic system “machined workpiece-slide” of turning center

Settlement dependences on determining the vibration characteristics of the machined workpieces, taking into account geometric, physical and mechanical characteristics and the force impact from the side of the cutting tool are established. In determining the dependences the effective coefficient of vibration energy losses was taken into account, providing the required value of which, is achieved by reducing vibration in the source due to the use of vibration-absorbing materials.

Cholinesterase from the Liver of Diodon hystrix for Detection of Metal Ions

The discharge of industrial effluents into nearby water bodies affects the inhabitants including living organisms. The presence of foreign materials such as heavy metals can be a threat to the ecosystem as they are enormously carcinogenic even though in minute concentration. Hence, an economical and time-efficient preliminary screening test is crucial to be developed for the detection of heavy metals, prior to employment of high technology instruments. In this study, cholinesterase (ChE) from Sabah porcupine fish, Diodon hystrix was purified to test for its potential as an alternative biosensor in detecting metal ions. Few enzymatic parameters including specificity of substrate, temperature and pH were applied to determine its optimal enzymatic activity. ChE enzyme was found to be more sensitive towards the presence of substrate, butyrylthiocholine iodide (BTC), in contrast to acetylthiocholine iodide (ATC) and propionylthiocholine iodide (PTC) with the effective coefficient at 7193, 3680.15 and 2965.26 Vmax/Km, respectively. Moreover, the extracted ChE enzyme showed the optimum activity at pH 9 of 0.1 M Tris-HCl and at 25°C to 30°C range of temperature. When subjected to heavy metals, ChE enzyme was significantly inhibited as the enzyme activity was reduced in the sequence of Hg > Ag > Cr > Cu > Cd > Pb ≥ Zn > As. As a conclusion, the partially purified ChE enzyme proved its sensitivity towards metal ion exposure and can be used as an alternative method in screening the level of contamination in the environment.

Impact of Horse Hoof Wall with Different Solid Surfaces

This study aimed to investigate the impact of a horse hoof wall on three solid surfaces: steel, concrete and asphalt. Impact experiments were conducted for different impact angles and different initial impact velocities. The effect of impact surfaces, impact angles and initial impact velocities on the coefficient of restitution and the effective coefficient of friction were tested using one-way ANOVA. Analytical and numerical modeling of the impact were developed. The impact interval was divided into two phases: compression and restitution. For compression, a contact force with a damping term was used. The restitution was characterized by an elastic contact force. The stiffness and damping coefficients of the contact force were estimated from the normal impacts. The simulated velocities after the oblique impacts were compared to the velocities in the in vitro investigation. The coefficient of restitution varied significantly on different surfaces. The effective coefficient of friction was lower on steel compared to concrete and asphalt. The model presented in this study can be applied to refine the impact simulation of the equine hoof during locomotion.