The well-known problem about the meeting of two bodies starting from two different points and moving along their line is extended by the general case when the bodies move in a plane at a non-zero ...angle to the given line. The task is solved graphically, analytically and using GeoGebra. This approach makes it possible to use IT technologies close to students in both standard and distance education.
Five decades of radioglaciology — CORRIGENDUM Schroeder, Dustin M.; Bingham, Robert G.; Blankenship, Donald D. ...
Annals of glaciology,
09/2021, Letnik:
62, Številka:
85-86
Journal Article
Probability kinematics is a leading paradigm in probabilistic belief change. It is based on the idea that conditional beliefs should be independent from changes of their antecedents' probabilities. ...In this paper, we propose a re-interpretation of this paradigm for Spohn's ranking functions which we call Generalized Ranking Kinematics as a new principle for iterated belief revision of ranking functions by sets of conditional beliefs with respect to their specific subcontext. By taking into account semantical independencies, we can reduce the complexity of the revision task to local contexts. We show that global belief revision can be set up from revisions on the local contexts via a merging operator. Furthermore, we formalize a variant of the Ramsey-Test based on the idea of local contexts which connects conditional and prepositional revision in a straightforward way. We extend the belief change methodology of c-revisions to strategic c-revisions which will serve as a proof of concept. Keywords Iterated belief revision * Kinematics * Spohn's ranking functions * Jeffrey's rule Mathematics Subject Classification (2010) 68T30 Knowledge representation
Category:
Basic Sciences/Biologics; Hindfoot
Introduction/Purpose:
Progressive collapsing foot deformity (PCFD) is a complex 3-dimensional pathology with a wide variety of surgical treatments. ...Regardless of technique, operative management of PCFD aims to restore normal foot architecture with attention to avoid the consequences of under- or over-correction. However, current methods of evaluating PCFD correction rely on static measurements, which do not assess dynamic function of the foot. Recent advances in robotic technology allow for the dynamic assessment of surgical correction of PCFD. This study sought to assess the effects of 2 osteotomies for PCFD, the medializing calcaneal osteotomy (MCO) and lateral column lengthening (LCL), on kinematics and plantar pressure during simulated gait. We hypothesized that the combination of LCL and MCO would restore joint kinematics and plantar pressure values to normal levels.
Methods:
Twelve cadaveric mid-tibia specimens (mean age 73 years, 8 female) were loaded on a 6-degree of freedom robotic gait simulator. Ground reaction forces and muscle forces were optimized utilizing an established iterative process. An 8-camera motion capture system was utilized to calculate joint kinematics using reflective markers attached by k-wires into bone. Plantar pressures were recorded using a pedography mat attached to the force platform. Testing was performed first in the native intact state, and again after creation of the flatfoot model. After flatfoot testing, surgical reconstruction and testing were performed in stages with MCO, and LCL with sequential 6mm and 8mm grafts. Bias-corrected bootstrapped 95% confidence intervals were calculated from the repeated measures difference between normal, flatfoot, post-MCO, post-MCO and post-reconstructive conditions. Center of plantar pressure excursion index (CPEI) was calculated and compared between conditions using a repeated measures ANOVA with Tukey post hoc analysis.
Results:
Overall, surgical correction restored kinematics to normal levels (Figure). MCO alone resulted in statistically significant improvement in subtalar eversion in the first 20% of stance, and post-MCO subtalar kinematics were statistically similar to normal. LCL (either 6mm and 8mm) alone did not significantly correct talonavicular abduction after PCFD. However, in conjunction with MCO, LCL was able to significantly correct talonavicular kinematics throughout the majority of stance phase, with kinematics statistically similar to normal levels. Each surgical step (LCL 6mm, LCL 8mm, MCO) resulted in sequential lateralization of the center of plantar pressure. At the culmination of surgical reconstruction (MCO + LCL), plantar pressure was significantly corrected compared to PCFD (P<0.0001). After surgical reconstruction, CPEI was slightly increased (lateralized) in comparison to normal, but was not significantly different from the normal state.
Conclusion:
The findings from this study support our hypothesis that surgical reconstruction of PCFD via MCO and LCL restores normal level walking kinematics. While the isolated effect of MCO and LCL resulted in significant changes in subtalar and talonavicular kinematics, the synergistic effect of combining MCO and LCL were most effective in restoring normal kinematics. However, lateralization of plantar pressure after combining MCO and LCL compared to the normal condition indicates the potential for overload of the lateral column, as described previously. Therefore, surgeons should be cautious in increasing osteotomy size at the lateral column to avoid overload.
Based on an observation from a previous work, the authors use the degree of passive freedom of a mechanism with roller follower to propose a new type of mechanism. In the new mechanism, the roller is ...replaced by a jointed element that forms two contacts with the cam. The obtaining of the cam profile is the main disadvantage of the cam mechanisms but in the present work, by using a cam formed by two connected discs, it is aimed to be avoided. The method is illustrated by designing the mechanism in CAD software followed by the simulation of its movement. To optimize the movement of the final element, the equivalent mechanism with lower pairs is used which has the advantage that the lengths of the elements are constant. The kinematics of the final element is particularly sensitive to the variation of the dimensions of the mechanism, fact illustrated by an example.
Las lesiones de transeúntes relacionadas al uso de teléfono celular han aumentado en relación con el total de accidentes peatonales. El objetivo de este estudio fue comparar variables cinemáticas y ...electromiográficas de ambas extremidades inferiores al enfrentar un obstáculo, con (CC) y sin (SC) el uso de celular. Diez mujeres jóvenes fueron evaluadas, las cuales caminaron y enfrentaron un obstáculo CC y SC. Con un modelo biomecánico 3D se evaluó la cinemática de extremidad inferior (plano sagital de cadera, rodilla, tobillo, junto al “toe clearance”). Al mismo tiempo se registró la actividad electromiográfica (EMG) de los siguientes músculos: tibial anterior (TA), gastrocnemio medial (GM), recto anterior (RA) y bíceps femoral (BF). Se calculó la amplitud EMG promedio de cada músculo, y el porcentaje de coactivación muscular entre: TA-GM y RA-BF. Se analizó la estrategia de ambas piernas, considerando un primer (P1) y segundo paso (P2) al cruzar el obstáculo, comparando entre una marcha CC vs CS. Según los resultados, la marcha CC incrementa el toe clearance, flexión de cadera, y la amplitud del GM, observado tanto en P1 como P2 al cruzar el obstáculo. Adicionalmente, el P2 reveló un incremento en la flexión de rodilla y tobillo. Por otro lado, la amplitud del TA y coactivación muscular entre TA-GM también aumentó CC en el P2. En conclusión, las variables cinemáticas y electromiográficas en las extremidades inferiores se modifican al cruzar un obstáculo CC. Estos hallazgos podrían indicar una estrategia protectora durante la tarea dual evaluada, minimizar el riesgo de caída.
Abstract. Pedestrian injuries related to the use of cell phone have increased in relation to the total number of pedestrian accidents. The aim of this study was to compare kinematic and electromyographic variables in both lower limbs at facing an obstacle, with (WC) and without (WoC) the use of a cell phone. Ten young women were evaluated, while walking and facing an obstacle WC and WoC. A 3D biomechanical model was used to evaluate the lower limb kinematics (hip, knee, ankle in the sagittal plane, together with “toe clearance”). At the same time, the electromyographic (EMG) activity was registered in the following muscles: tibialis anterior (TA), gastrocnemius medialis (GM), rectus femoris (RF) and biceps femoris (BF). The mean EMG amplitude of each muscle and the muscular coactivation percentage between: TA-GM and RA-BF were calculated. The strategy for both lower limbs considering the first (P1) and the second step (P2) were analyzed when crossing the obstacle, comparing between gait WC vs WoC. According to results, the gait WC increase the toe clearance, hip flexion, and the GM amplitude, observed both in P1 as P2 when the person crossed the obstacle. Furthermore, the P2 revealed an increase in the knee and ankle flexion. On the other hand, the TA amplitude and the muscular coactivation between TA-GM also increased WC in the P2. In conclusion, the kinematic and electromyographic variables in the lower limbs are modified when crossing an obstacle WC. These findings could indicate a protective strategy during the dual-task evaluated, minimizing the risk of falling.
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