The Effects of Altering the Center of Pressure in Standing Subjects Exposed to Foot-Transmitted Vibration on an Optimized Lumped-Parameter Model of the Foot

Many workers are exposed to foot-transmitted vibration, which can lead to the development of vibration-induced white foot: a debilitating condition with neurological, vascular and osteoarticular symptoms. To design effective prevention mechanisms (i.e., boots and insoles) for isolating workers from vibration exposure, continued model development of the foot’s biodynamic response in different positions is necessary. This study uses a previously developed model of the foot–ankle system (FAS) to investigates how altering the center of pressure (COP) location can change the biodynamic response of the FAS to standing vibration exposure. Formerly published experimental responses for apparent mass and transmissibility at five anatomical locations in three COP positions were used to optimize the model. Differences occurred with the Kelvin–Voigt elements used to represent the soft tissues of the foot sole: at the heel, the distal head of the metatarsals and distal phalanges. The stiffness increased wherever the COP was concentrated (i.e., forward over the toes or backward over the heel). The variability of the model parameters was always greatest when the COP was concentrated in the heel. This suggests future FAS models need to more clearly address how the soft tissue of the plantar fat pad is modelled.

Uncertainty of factor Z in gravimetric volume measurement

<p class="Abstract">In the gravimetric volume measurement method, the factor <em>Z</em> is generally used to facilitate an easy conversion from the apparent mass obtained using a balance to the liquid volume. The uncertainty of the measurement used for the liquid volume can be divided into two specific contributions: one from the components related to the mass measurements and one from those related to the mass-to-volume conversion. However, some ISO standards and calibration guides have suggested that the uncertainty due to the factor <em>Z</em> is generally neglected in the uncertainty calculation pertaining to gravimetric volume measurement. This paper describes the combined effects of the density of the water, the density of the reference weights, and the air buoyancy on the uncertainty of factor <em>Z</em> in terms of how they subsequently affect the uncertainty of the measurement results.</p>

Development and analysis of a novel biomechanical model for seated occupants

Seated occupants may experience discomfort or meet with injuries if the vertical vibration frequency lies in the range of 4–20 Hz. To examine the effect of vibration on seated occupants, it is necessary to develop a biomechanical model that can precisely predict the biodynamic responses (seat to head transmissibility, driving point mechanical impedance, and apparent mass) of a real human. In the past, none of the studies segregated the human body mass into bones and muscles mass that have distinct mechanical properties. In this article, the work is carried out in four steps: first, development of a novel 8- dofs biomechanical model by considering both bone and muscle masses; second, development of all the feasible configurations of 8- dofs model followed by identification and optimization of model parameters with firefly algorithm (FA); third, calibration of all the feasible models as per the standards of biodynamics and selection of best four models; and fourth, comparison of biodynamic responses of best four models with experimental responses and past developed models. The goodness of fit of a seat to head transmissibility, driving point mechanical impedance, and apparent mass for the best model is obtained 0.986, 0.976, and 0.956, respectively.

Magnetic Janssen effect

A pile of grains, even when at rest in a silo, can display fascinating properties. One of the most celebrated is the Janssen effect, named after the pioneering engineer who explained the pressure saturation at the bottom of a container filled with corn. This surprising behavior arises because of frictional interactions between the grains through a disordered network of contacts, and the vessel lateral walls, which partially support the weight of the column, decreasing its apparent mass. Here, we demonstrate control over frictional interactions using ferromagnetic grains and an external magnetic field. We show that the anisotropic pairwise interactions between magnetized grains result in a radial force along the walls, whose amplitude and direction is fully determined by the applied magnetic field. Such magnetic Janssen effect allows for the fine tuning of the granular column apparent mass. Our findings pave the way towards the design of functional jammed materials in confined geometries, via a further control of both their static and dynamic properties.

Renal lobar dysmorphism: a potential mimic of renal malignancy

A renal pseudotumour is any apparent renal mass that simulates a tumour on radiological imaging but is composed of normal tissue. Renal pseudotumours may be inflammatory, vascular, postsurgical or congenital. We report a case of renal lobar dysmorphism (RLD) of the kidney, a congenital renal pseudotumour. A 45-year-old man presented with scrotal swelling. Testicular ultrasound showed an epididymal cyst. Renal ultrasound showed a right solid renal apparent mass of 2.4 cm in diameter. Triphasic renal CT showed this was consistent with RLD. Intravenous urography confirmed a central calyx within the dysmorphic lobe. RLD is a rare congenital normal anatomical variant, which can appear as a renal pseudotumour. No further investigation or intervention is necessary. We present the radiological findings of RLD and review the literature.

Avoiding chaos in granular dampers

Granular dampers are passive devices used to attenuate mechanical vibrations. The most common configuration consists in an enclosure, partiallyfilled with particles, attached to the vibrating structure that needs to be damped. The energy is dissipated due to inelastic collisions and friction between the grains and between the grains and the inner walls of the container as the structure vibrates. As a result of the collisions, the mechanical response of the system often results in chaotic motion even if the driving is harmonic. Despite the vibration attenuation achieved, this chaotic response may render the granular damper unsuitable for a range of applications. In this work, we showcase two simple modifications of the enclosure design that are able to mitigate the chaotic response of the granular damper. To this end we use Discrete Element Method simulations of: (a) a granular damper with a conical base, and (b) a granular damper with obstaclesfixed inside the enclosure. We compare results against a standardflat-base enclosure damper. The basic mechanical response of the dampers is characterized by measuring the apparent mass and the loss factor. The suppression of the chaotic response is assessed qualitatively via the phase space diagram.

Biodynamic Responses to Whole-Body Vibration Training: A Systematic Review

In recent years, whole-body vibration (WBV) training has received an increasing interest in the sports and medical fields. However, there has been inconsistency among several studies regarding the effect of WBV training on the human body, which is partly due to the lack of the existence of guidelines for using WBV training machines. To understand the effect of WBV training on the human body and build the needed regulations, it is essential first to understand the biodynamic responses to vibration which represent how vibration is transmitted to and through the human body. The purpose of this study is to systematically review previous studies that measured biodynamic responses when using WBV training machines to highlight inconsistencies in their results and provide possible reasons for them. An extensive literature search was performed on the SCOPUS database to obtain relevant studies. One hundred and fifty-six potentially relevant studies were obtained but after further screening, 23 papers from 2007 to 2020 met inclusion criteria and were included in the study. The papers were analysed with respect to acceleration, transmissibility, interface force, and apparent mass during different vibration settings, body posture, age, and sex. Results and conflicts among studies were highlighted and possible explanations for the inconsistency were provided.