A biomechanical model for the morphogenesis of regular echinoid tests

Paleobiology ◽  
1986 ◽  
Vol 12 (2) ◽  
pp. 143-160 ◽  
Author(s):  
Jacob Dafni
Keyword(s):  
Biomechanical Model ◽  
Bilateral Symmetry ◽  
Mechanical Effect ◽  
Mechanical Activity ◽  
Early Ontogenetic Stage ◽  
Phylogenetic Level ◽  
Sandy Habitat ◽  
Genetic Aberration ◽  
Oval Cross Section ◽  
Biomechanical Constraints

Experiments were conducted to test the hypothesis that biomechanical constraints determine the morphology of regular echinoids. Hard-bottom-dwellingTripneustes gratilla elatensiswere transferred to an artifical sandy habitat to evaluate whether the change in substrate affects their height to diameter ratio (H/D). Within 1–2 months their H/D ratio increased significantly. This change was shown to be reversible to some extent. Surgical damage to the ambulacral system of one ray caused inactivation of tubefeet and atrophy of injured ambulacra. Test shape was also affected: the damaged ray was lower, and the nondamaged ambulacra deflected toward the treated one, producing bilateral symmetry as in recorded cases of teratology. Study ofT. g. elatensistetramers showed that while “perfect” tetramery was apparently associated with genetic aberration, “imperfect” tetramery results from mechanical injury at an early ontogenetic stage. Micromorphological study shows that in the longitudinal sutures, normally under tension, long and slender trabeculae develop, associated with long and well-aligned collagenous sutural fibers, while the latitudinal trabeculae and fibers are short and less organized. A mechanical effect is suggested by the oval cross-section of the fiber-anchoring trabeculae. Further, echinoid plates interact like soap bubbles, whereas the entire test behaves like a balloon, fastened to the substrate by the ambulacral tubefeet. All these observations support earlier hypotheses on the biomechanical control of echinoid test growth. A model is proposed in which the expansion of the inner mass, counteracted by the mechanical activity of the ambulacral tubefeet, mesenterial threads, and lantern muscles, affects sutural growth, thus controlling echinoid morphogenesis.A morphometric survey among regular echinoids reveals an inverse relationship between ambulacral width and relative ambital height. Although both increase of ambulacral width and lowering of ambitus-line are evolutionary trends, it is suggested that they are a response to a mechanical effect. H/D ratio was not related to ambulacral width on the phylogenetic level. It is therefore suggested that the latter correlation is ontogenetically controlled. Aspects of irregular echonoid evolution, such as bilateral symmetry, flattening, and formation of the ambulacral petaloid, also are explained by this model.

scholarly journals Optimal use of limb mechanics distributes control during bimanual tasks

2018 ◽  
Vol 119 (3) ◽  
pp. 921-932 ◽  
Author(s):  
David Córdova Bulens ◽  
Frédéric Crevecoeur ◽  
Jean-Louis Thonnard ◽  
Philippe Lefèvre
Keyword(s):  
Nervous System ◽  
Feedback Control ◽  
Biomechanical Model ◽  
Movement Planning ◽  
Optimal Feedback Control ◽  
Joint Configuration ◽  
Bimanual Task ◽  
Target Force ◽  
Biomechanical Constraints ◽  
Bimanual Tasks

Bimanual tasks involve the coordination of both arms, which often offers redundancy in the ways a task can be completed. The distribution of control across limbs is often considered from the perspective of handedness. In this context, although there are differences across dominant and nondominant arms during reaching control ( Sainburg 2002 ), previous studies have shown that the brain tends to favor the dominant arm when performing bimanual tasks ( Salimpour and Shadmehr 2014 ). However, biomechanical factors known to influence planning and control in unimanual tasks may also generate limb asymmetries in force generation, but their influence on bimanual control has remained unexplored. We investigated this issue in a series of experiments in which participants were instructed to generate a 20-N force with both arms, with or without perturbation of the target force during the trial. We modeled the task in the framework of optimal feedback control of a two-link model with six human-like muscles groups. The biomechanical model predicted a differential contribution of each arm dependent on the orientation of the target force and joint configuration that was quantitatively matched by the participants’ behavior, regardless of handedness. Responses to visual perturbations were strongly influenced by the perturbation direction, such that online corrections also reflected an optimal use of limb biomechanics. These results show that the nervous system takes biomechanical constraints into account when optimizing the distribution of forces generated across limbs during both movement planning and feedback control of a bimanual task. NEW & NOTEWORTHY Here, we studied a bimanual force production task to examine the effects of biomechanical constraints on the distribution of control across limbs. Our findings show that the central nervous system optimizes the distribution of force across the two arms according to the joint configuration of the upper limbs. We further show that the underlying mechanisms influence both movement planning and online corrective responses to sudden changes in the target force.

scholarly journals Detection of Ventricular Fibrillation Based on Ballistocardiography by Constructing an Effective Feature Set

Sensors ◽  
2021 ◽  
Vol 21 (10) ◽  
pp. 3524
Author(s):  
Rongru Wan ◽  
Yanqi Huang ◽  
Xiaomei Wu
Keyword(s):  
Ventricular Fibrillation ◽  
Cross Validation ◽  
Rhythmic Activity ◽  
Detection Algorithm ◽  
Motion Artifacts ◽  
Cardiac Monitoring ◽  
Mechanical Activity ◽  
Time Frequency ◽  
S Transform ◽  
Fatal Arrhythmia

Ventricular fibrillation (VF) is a type of fatal arrhythmia that can cause sudden death within minutes. The study of a VF detection algorithm has important clinical significance. This study aimed to develop an algorithm for the automatic detection of VF based on the acquisition of cardiac mechanical activity-related signals, namely ballistocardiography (BCG), by non-contact sensors. BCG signals, including VF, sinus rhythm, and motion artifacts, were collected through electric defibrillation experiments in pigs. Through autocorrelation and S transform, the time-frequency graph with obvious information of cardiac rhythmic activity was obtained, and a feature set of 13 elements was constructed for each 7 s segment after statistical analysis and hierarchical clustering. Then, the random forest classifier was used to classify VF and non-VF, and two paradigms of intra-patient and inter-patient were used to evaluate the performance. The results showed that the sensitivity and specificity were 0.965 and 0.958 under 10-fold cross-validation, and they were 0.947 and 0.946 under leave-one-subject-out cross-validation. In conclusion, the proposed algorithm combining feature extraction and machine learning can effectively detect VF in BCG, laying a foundation for the development of long-term self-cardiac monitoring at home and a VF real-time detection and alarm system.

scholarly journals Estimation of Human Center of Mass Position through the Inertial Sensors-Based Methods in Postural Tasks: An Accuracy Evaluation

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 601 ◽  
Author(s):  
Marco Germanotta ◽  
Ilaria Mileti ◽  
Ilaria Conforti ◽  
Zaccaria Del Prete ◽  
Irene Aprile ◽  
...  
Keyword(s):  
Inertial Sensors ◽  
Center Of Mass ◽  
Correlation Coefficients ◽  
Biomechanical Model ◽  
Lower Limbs ◽  
Accuracy Evaluation ◽  
Postural Tasks ◽  
Single Sensor ◽  
Using Data ◽  
Displacement Based

The estimation of the body’s center of mass (CoM) trajectory is typically obtained using force platforms, or optoelectronic systems (OS), bounding the assessment inside a laboratory setting. The use of magneto-inertial measurement units (MIMUs) allows for more ecological evaluations, and previous studies proposed methods based on either a single sensor or a sensors’ network. In this study, we compared the accuracy of two methods based on MIMUs. Body CoM was estimated during six postural tasks performed by 15 healthy subjects, using data collected by a single sensor on the pelvis (Strapdown Integration Method, SDI), and seven sensors on the pelvis and lower limbs (Biomechanical Model, BM). The accuracy of the two methods was compared in terms of RMSE and estimation of posturographic parameters, using an OS as reference. The RMSE of the SDI was lower in tasks with little or no oscillations, while the BM outperformed in tasks with greater CoM displacement. Moreover, higher correlation coefficients were obtained between the posturographic parameters obtained with the BM and the OS. Our findings showed that the estimation of CoM displacement based on MIMU was reasonably accurate, and the use of the inertial sensors network methods should be preferred to estimate the kinematic parameters.

Epithelioid Sarcoma Arising in a Long-Term Survivor of an Atypical Teratoid/Rhabdoid Tumor in a Patient With Rhabdoid Tumor Predisposition Syndrome

2021 ◽  
pp. 109352662098649
Author(s):  
Tiffany G Baker ◽  
Michael J Lyons ◽  
Lee Leddy ◽  
David M Parham ◽  
Cynthia T Welsh
Keyword(s):  
Epithelioid Sarcoma ◽  
Rhabdoid Tumor ◽  
Malignant Rhabdoid Tumor ◽  
Atypical Teratoid Rhabdoid Tumor ◽  
Diagnostic Challenge ◽  
Patient Demographics ◽  
Immunohistochemical Markers ◽  
Genetic Aberration ◽  
Atypical Teratoid ◽  
Rhabdoid Tumors

Rhabdoid tumor predisposition syndrome (RTPS) is defined as the presence of a SMARCB1 or SMARCA4 genetic aberration in a patient with malignant rhabdoid tumor. Patients with RTPS are more likely to present with synchronous or metachronous rhabdoid tumors. Based on the current state of rhabdoid tumor taxonomy, these diagnoses are based largely on patient demographics, anatomic location of disease, and immunohistochemistry, despite their nearly identical histologic and immunohistochemical profiles. Thus, the true distinction between such tumors remains a diagnostic challenge. Central nervous system atypical teratoid/rhabdoid tumor (AT/RT) is a rare, aggressive, primarily pediatric malignancy with variable histologic features and a well documented association with loss of SMARCB1 expression. Epithelioid sarcoma (ES) is a rare soft tissue tumor arising in patients of all ages and characteristically staining for both mesenchymal and epithelial immunohistochemical markers while usually demonstrating loss of SMARCB1 expression. To our knowledge we herein present the first documented case of a patient with RTPS who presented with metachronous AT/RT and ES.

Stability as a constraint in sagittal plane human force exertion modeling

1998 ◽  
Vol 1 (1) ◽  
pp. 23-39
Author(s):  
Carter J. Kerk ◽  
Don B. Chaffin ◽  
W. Monroe Keyserling
Keyword(s):  
Muscle Strength ◽  
Ankle Joint ◽  
Coefficient Of Friction ◽  
Sagittal Plane ◽  
Biomechanical Model ◽  
Whole Body ◽  
The Stability ◽  
Joint Center ◽  
Static Conditions ◽  
Stability Limits

The stability constraints of a two-dimensional static human force exertion capability model (2DHFEC) were evaluated with subjects of varying anthropometry and strength capabilities performing manual exertions. The biomechanical model comprehensively estimated human force exertion capability under sagittally symmetric static conditions using constraints from three classes: stability, joint muscle strength, and coefficient of friction. Experimental results showed the concept of stability must be considered with joint muscle strength capability and coefficient of friction in predicting hand force exertion capability. Information was gained concerning foot modeling parameters as they affect whole-body stability. Findings indicated that stability limits should be placed approximately 37 % the ankle joint center to the posterior-most point of the foot and 130 % the distance from the ankle joint center to the maximal medial protuberance (the ball of the foot). 2DHFEC provided improvements over existing models, especially where horizontal push/pull forces create balance concerns.

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