Construction Of Reference Frame Research Articles

Comparison of the kinematics, repeatability, and reproducibility of five different multi-segment foot models

BackgroundMulti-segment foot models (MFMs) for assessing three-dimensional segmental foot motions are calculated via various analytical methods. Although validation studies have already been conducted, we cannot compare their results because the experimental environments in previous studies were different from each other. This study aims to compare the kinematics, repeatability, and reproducibility of five MFMs in the same experimental conditions.MethodsEleven healthy males with a mean age of 26.5 years participated in this study. We created a merged 29-marker set including five MFMs: Oxford (OFM), modified Rizzoli (mRFM), DuPont (DFM), Milwaukee (MiFM), and modified Shriners Hospital for Children Greenville (mSHCG). Two operators applied the merged model to participants twice, and then we analysed two relative angles of three segments: shank-hindfoot (HF) and hindfoot-forefoot (FF). Coefficients of multiple correlation (CMC) and mean standard errors were used to assess repeatability and reproducibility, and statistical parametric mapping (SPM) of the t-value was employed to compare kinematics.ResultsHF varus/valgus of the MiFM and mSHCG models, which rotated the segment according to radiographic or goniometric measurements during the reference frame construction, were significantly more repeatable and reproducible, compared to other models. They showed significantly more dorsiflexed HF and plantarflexed FF due to their static offset angles. DFM and mSHCG showed a greater range of motion (ROM), and some models had significantly different FF points of peak angle.ConclusionsUnder the same conditions, rotating the segment according to the appropriate offset angle obtained from radiographic or goniometric measurement increased reliability, but all MFMs had clinically acceptable reliability compared to previous studies. Moreover, in some models, especially HF varus/valgus, there were differences in ROM and points of peak angle even with no statistical difference in SPM curves. Therefore, based on the results of this study, clinicians and researchers involved in the evaluation of foot and ankle dysfunction need an understanding of the specific features of each MFM to make accurate decisions.

A Local Reference Frame Construction Method Based on the Signed Surface Variation

A Local Reference Frame Construction Method Based on the Signed Surface Variation

Business Games como herramienta pedagógica para el desarrollo de habilidades en la toma de decisiones

Before the Second World War, the Industrial Engineer's work focused on studies of plant distribution, quality control, production and inventories. Currently, these professionals are also required to carry out economic activities. The paper presents a business simulation game model that serves as a pedagogical tool for the teaching-learning process in the decision-making area, in the Marketing, Productionand Finance disciplines. The research was carried out in four phases: data collection, reference frame construction, design construction, and testing. The theoretical and practical foundations were laid for future research, which improve the proposed model with the addition of Artificial Intelligence, Machine Learning and Deep Learning techniques, which optimize data processing and provide better support to the decision-making process.

An enhanced singular spectrum analysis method for constructing nonsecular model of GPS site movement

AbstractMany GPS time series contain offsets, sometimes nonsecular trends, and seasonal signals with time‐varying amplitudes due to several different types of geophysical phenomena. Therefore, the use of nonsecular models to depict the real geophysical movement of GPS sites is better than a linear model. In this study, an enhanced singular spectrum analysis (SSA) method for fitting GPS time series and predicting its coordinates is proposed. Simulation results show that the root‐mean‐square (RMS) of differences between the reconstructed and simulated signals is 1.7 mm; the RMS of the differences between the predicted coordinates and simulated signal is about 3 mm for the first half 1.5 years of testing period and decreases to 10 mm for the last half 1.5 years. Fitting results for three GPS time series are obtained using maximum likelihood estimation (MLE), which is used to fit the time series with a piecewise linear trend plus an annual/semiannual components, SSA, and state space model (SSM). Both SSA and SSM perform similarly and better than the MLE in extracting the nonsecular trend and annual/semiannual components from the GPS time series. The prediction results from SSA have higher coefficients with raw time series and lower power of annual/semiannual in their residuals than that from MLE for two case studies. The differences between the linear trend estimated by Plate Boundary Observatory and SSA nonsecular model for 16 GPS time series are all larger than 2 mm in up direction, which is not negligible for a high‐accuracy terrestrial reference frame construction.

Global coseismic deformations, GNSS time series analysis, and earthquake scaling laws

AbstractWe investigate how two decades of coseismic deformations affect time series of GPS station coordinates (Global Navigation Satellite System) and what constraints geodetic observations give on earthquake scaling laws. We developed a simple but rapid model for coseismic deformations, assuming different earthquake scaling relations, that we systematically applied on earthquakes with magnitude larger than 4. We found that coseismic displacements accumulated during the last two decades can be larger than 10 m locally and that the cumulative displacement is not only due to large earthquakes but also to the accumulation of many small motions induced by smaller earthquakes. Then, investigating a global network of GPS stations, we demonstrate that a systematic global modeling of coseismic deformations helps greatly to detect discontinuities in GPS coordinate time series, which are still today one of the major sources of error in terrestrial reference frame construction (e.g., the International Terrestrial Reference Frame). We show that numerous discontinuities induced by earthquakes are too small to be visually detected because of seasonal variations and GPS noise that disturb their identification. However, not taking these discontinuities into account has a large impact on the station velocity estimation, considering today's precision requirements. Finally, six groups of earthquake scaling laws were tested. Comparisons with our GPS time series analysis on dedicated earthquakes give insights on the consistency of these scaling laws with geodetic observations and Okada coseismic approach.

Reference Frames

After a short introduction on the definition and the construction of a reference frame, the presentation concentrates on the actual construction of the new IAU conventional reference frame. The 1991 IAU resolutions on reference systems is reviewed and the present state of the implementation of these resolutions is discussed. The IERS extragalactic reference frame is described and we show that it fulfills the IAU requirements. The Hipparcos catalogue will be linked to this frame before the end of this year. The state of advancement of this job is presented.