DETERMINING THE GROUND REACTION FORCE EXPERIENCED IN BEACH RUNNING

INTRODUCTION: Running on a beach is a popular fitness activity, as well as a critical component in the professional sport of ironman. In this event, ironmen athletes run over terrain ranging from wet compacted sand to dry uncompacted sand, as their distance from the ocean surf line increases. The dynamic loading response of sand surfaces at the extremes of this range has been investigated recently by Barrett et al. using a force plate, and variables such as the peak impact force and the surface stiffness were calculated. In this study we demonstrate how the time response of the ground reaction force (GRF) experienced in beach running can be predicted from the measured plate reaction force, for either wet or dry sand surfaces. METHODS: The ground reaction force experienced in beach running can be measured directly using an accelerometer attached to the runner’s lower extremity. However it is often more convenient to sample the reaction force from a sandcovered force plate in a controlled environment. This idea motivated us to consider the resulting problem of determining the GRF indirectly using the measured plate force. In the measurement process, the instrument response of the force plate, which can be described in the linear regime by a transfer function, is convoluted with the GRF in the time domain. Thus in order to reconstruct the GRF we need to apply the reverse process: a deconvolution of the measured plate force using a known transfer function. The deconvolution is performed in the frequency domain. The transfer function corresponding to the force plate has to be determined a priori by „calibrating“ direct GRF measurements with plate force measurements. RESULTS: The reconstruction of the GRF allows us to estimate any physical quantity we are interested in, such as the time of delay between the moment of impact and the trigger of the plate force reaction, or the peak GRF. We have also determined that the frequency characteristics of the force plate transfer function depend on the impact mass, the impact energy and the effective depth of the sand, and have investigated the changes apparent in this parameter space. CONCLUSIONS: The transfer function approach presented in this study reconstructs the time response of the GRF experienced in beach running conditions, using plate force measurements. Thus, with the exception of calibration measurements, we can eliminate the need to attach an accelerometer to the runner when taking GRF measurements. REFERENCES: Barrett, R.S., Neal, R.J., Roberts, L.J. (1998). The Dynamic Loading Response of Surfaces Encountered in Beach Running. Journal of Science and Medicine in Sport 1, 3-13, 1998

Guide For Recommended Practices To Perform Crack Tip Opening Displacement Tests In High Strength Low Alloy Steels

Fracture mechanics approach is important for all mechanical and civil projects that might involve cracks in metallic materials, and especially for those using welding as a structural joining process. This methodology can enhance not only the design but also the service life of the structures being constructed. This paper includes detailed consideration of several practical issues related to the experimental procedures to assess the fracture toughness in high strength low alloy steels (HSLA) using the crack tip opening displacement (CTOD) parameter, specifically pipeline steels for oil and gas transportation. These considerations are important for engineers who are new in the field, or for those looking for guidelines performing different procedures during the experimentation, which usually are difficult to understand from the conventional standards. We discuss on topics including geometry selection, number of replicate tests, fatigue precracking, test procedure selection and realization, reports of results and other aspects.213290302Colciencias [512]PetrobrasLNNano/CNPE

Association Between Preexisting Versus Newly Identified Atrial Fibrillation and Outcomes of Patients With Acute Pulmonary Embolism

Background Atrial fibrillation (AF) may exist before or occur early in the course of pulmonary embolism (PE). We determined the PE outcomes based on the presence and timing of AF. Methods and Results Using the data from a multicenter PE registry, we identified 3 groups: (1) those with preexisting AF, (2) patients with new AF within 2 days from acute PE (incident AF), and (3) patients without AF. We assessed the 90-day and 1-year risk of mortality and stroke in patients with AF, compared with those without AF (reference group). Among 16 497 patients with PE, 792 had preexisting AF. These patients had increased odds of 90-day all-cause (odds ratio [OR], 2.81; 95% CI, 2.33-3.38) and PE-related mortality (OR, 2.38; 95% CI, 1.37-4.14) and increased 1-year hazard for ischemic stroke (hazard ratio, 5.48; 95% CI, 3.10-9.69) compared with those without AF. After multivariable adjustment, preexisting AF was associated with significantly increased odds of all-cause mortality (OR, 1.91; 95% CI, 1.57-2.32) but not PE-related mortality (OR, 1.50; 95% CI, 0.85-2.66). Among 16 497 patients with PE, 445 developed new incident AF within 2 days of acute PE. Incident AF was associated with increased odds of 90-day all-cause (OR, 2.28; 95% CI, 1.75-2.97) and PE-related (OR, 3.64; 95% CI, 2.01-6.59) mortality but not stroke. Findings were similar in multivariable analyses. Conclusions In patients with acute symptomatic PE, both preexisting AF and incident AF predict adverse clinical outcomes. The type of adverse outcomes may differ depending on the timing of AF onset.info:eu-repo/semantics/publishedVersio