Passive Portion Research Articles

Simulation of Uterus Active Contraction and Fetus Delivery in ls-dyna.

Vaginal childbirth is the final phase of pregnancy when one or more fetuses pass through the birth canal from the uterus, and it is a biomechanical process. The uterine active contraction, causing the pushing force on the fetus, plays a vital role in regulating the fetus delivery process. In this project, the active contraction behaviors of muscle tissue were first modeled and investigated. After that, a finite element method (FEM) model to simulate the uterine cyclic active contraction and delivery of a fetus was developed in ls-dyna. The active contraction was driven through contractile fibers modeled as one-dimensional truss elements, with the Hill material model governing their response. Fibers were assembled in the longitudinal, circumferential, and normal (transverse) directions to correspond to tissue microstructure, and they were divided into seven regions to represent the strong anisotropy of the fiber distribution and activity within the uterus. The passive portion of the uterine tissue was modeled with a Neo Hookean hyperelastic material model. Three active contraction cycles were modeled. The cyclic uterine active contraction behaviors were analyzed. Finally, the fetus delivery through the uterus was simulated. The model of the uterine active contraction presented in this paper modeled the contractile fibers in three-dimensions, considered the anisotropy of the fiber distribution, provided the uterine cyclic active contraction and propagation of the contraction waves, performed a large deformation, and caused the pushing effect on the fetus. This model will be combined with a model of pelvic structures so that a complete system simulating the second stage of the delivery process of a fetus can be established.

Simulation of the Childbirth Process in LS-DYNA.

Childbirth or labor, as the final phase of a pregnancy, is a biomechanical process that delivers the fetus from the uterus. It mainly involves two important biological structures in the mother, the uterus-generating the pushing force on the fetus-and the pelvis (bony pelvis and pelvic floor muscles)-resisting the movement of the fetus. The existing computational models developed in this field that simulate the childbirth process have focused on either the uterine expulsion force or the resistive structures of the pelvis, not both. An FEM model including both structures as a system was developed in this paper to simulate the fetus delivery process in LS-DYNA. Uterine active contraction was driven by contractile fiber elements using the Hill material model. The passive portion of the uterus and pelvic floor muscles were modeled with Neo Hookean and Mooney-Rivlin materials, respectively. The bony pelvis was modeled as a rigid body. The fetus was divided into three components: the head, neck, and body. Three uterine active contraction cycles were modeled. The model system was validated based on multiple outputs from the model, including the stress distribution within the uterus, the maximum Von Mises and principal stress on the pelvic floor muscles, the duration of the second stage of the labor, and the movement of the fetus. The developed model system can be applied to investigate the effects of pathomechanics related to labor, such as pelvic floor disorders and brachial plexus injury.

A Comprehensive and Unified Procedure for Symbolic Analysis of Analog Circuits

The objective here is to develop a uniform and comprehensive procedure for symbolic analysis of linear circuits using the Sum of the Tree Products (STP) of the circuit. We achieve this goal in two stages. In the first stage a circuit with active devices, such as VCCSs and I/O ports, is changed to a nullor circuit, i.e., to a circuit with only passive components and nullors. The nullor circuit is also partitioned into two parts, a passive circuit and an all-nullor circuit. It is shown that the magnitude of the STP, i.e., the determinant of the NAM, of the circuit is equal to the STP of the passive portion of the circuit, and the sign (0, 1, or −1) of the STP comes from its all-nullor part. Another significant development in this presentation is the replacement of the regular STP methodology with a rather new Admittance Method ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AM</i> ). It is shown that by doing this the entire two-graph theory for active circuits as well as the use of 2-tree procedures for I/O ports analysis are eliminated. It is these new developments that substantially simplifies the circuit analysis and makes it quite efficient for symbolic representation of transfer functions.

Phase‐field Fracture with Representative Crack Elements for Non‐linear Material Behaviour

AbstractThe mechanical energy potential of phase‐field fracture models is subdivided into a portion which (actively) drives the crack and a passive portion. This decompositions depends further on the crack state (opened, closed) in order to consider the re‐contact of the crack surfaces. The identification of the crack state and the decomposition is mostly approximated based on splits of the deformation or stress tensor. Stobel and Seelig [1], and Steinke and Kaliske [2] have shown unrealistic predictions for the crack kinematic for those models in quasi‐static and dynamic analyses. The approach proposed by these authors allows to predict the crack kinematic consistently. Nevertheless, this model is restricted to linear, isotropic elasticity and small deformations.In Storm et al. [3], the underlying concept is generalised. The crack kinematics is consistently obtained from a representative, discrete crack model and coupled to the phase‐field model by means of a variational homogenisation formulation. Thus, the crack driving force is a unique result of the framework of Representative Crack Elements. Analytical solutions for the mechanical problem of the representative crack element applied to linear, anisotropic elasticity and linear thermo‐elasticity at small deformations are presented there.In the current contribution to the method of phase‐field fracture, the framework for Representative Crack Elements is applied to non‐linear bulk materials. The iterative solution scheme for the representative crack element is presented and applied to elasticity with crack surface friction, visco‐elastic and elasto‐plastic materials.

Passive Appreciation in Divorce: A Quantitative Measure

ABSTRACT Breaking up is hard to do. High net worth marital estates often contain family businesses started or inherited by one or both spouses. The growth in the value of such business interests occurring during the marriage can consist of two components. It may be attributable to environmental factors (passive) or marital efforts and resources (active). Quantifying the passive contribution of economic environment changes during the marriage is a complex task. A substantial body of case law dealing with establishing causation and attributing impact has developed in the torts and class action practice areas. This paper presents this statistically sound, empirically tested, and peer reviewed methodology for estimating the passive (caused by/resulting from external forces) portion of appreciation for a business. This methodology can assist the forensic accountants in identifying pertinent causal factors and quantifying their impact (passive appreciation) on the value of a business during a marriage. Data Availability: Economic data used for the analysis in this paper were obtained from the FRED database maintained by the Federal Reserve Bank of St. Louis. This database is extensive and can be accessed at https://research.stlouisfed.org/. The dataset used for the illustrative analysis presented in this paper is found in Appendix C. JEL Classifications: C51; C52; J12; K36.

Passive Appreciation in Divorce A Quantitative Measure

Breaking up is hard to do. High net worth marital estates often contain family businesses started or inherited by one or both spouses. The growth in the value of such business interests occurring during the marriage can consist of two components. It may be attributable to environmental factors (passive) or marital efforts and resources (active). Quantifying the passive contribution of economic environment changes during the marriage is a complex task. A substantial body of case law dealing with establishing causation and attributing impact has developed in the torts and class action practice areas. This paper presents this statistically sound, empirically tested, and peer reviewed methodology for estimating the passive (caused by/resulting from external forces) portion of appreciation for a business. This methodology can assist the forensic accountants in identifying pertinent causal factors and quantifying their impact (passive appreciation) on the value of a business during a marriage.

Effect of Nonuniform Flexibility on Hydrodynamic Performance of Pitching Propulsors

Many aquatic animals propel themselves efficiently through the water by oscillating flexible fins. These fins are, however, not homogeneously flexible, but instead their flexural stiffness varies along their chord and span. Here, we develop a simple model of these functionally graded materials where the chordwise flexibility of the foil is modeled by one or two torsional springs along the chord line. The torsional spring structural model is then strongly coupled to a boundary element fluid model to simulate the fluid–structure interactions. We show that the effective flexibility of the combined fluid–structure system scales with the ratio of the added mass forces acting on the passive portion of the foil and the elastic forces defined by the torsional spring hinge. Importantly, by considering this new scaling of the effective flexibility, the propulsive performance is then detailed for a foil with a flexible hinge that is actively pitching about its leading edge. The scaling allows for the resonance frequency of the fluid–structure system and the bending pattern of the propulsor to be independently varied by altering the effective flexibility and the location of a single torsional spring along the chord, respectively. It is shown that increasing the flexion ratio, by moving the spring away from the leading edge, leads to enhanced propulsive efficiency, but compromises the thrust production. Proper combination of two flexible hinges, however, can result in a gain in both the thrust production and propulsive efficiency.

An Early History of Neuroglial Research: Personalities

Neuroscience, like most other divisions of natural philosophy, emerged in the Hellenistic world following the first experimental discoveries of the nerves connecting the brain with the body. The first fundamental doctrine on brain function highlighted the role for a specific substance, pneuma, which appeared as a substrate for brain function and, being transported through the hollow nerves, operated the peripheral organs. A paradigm shift occurred in 17th century when brain function was relocated to the grey matter. Beginning from the end of the 18th century, the existence of active and passive portions of the nervous tissue were postulated. The passive part of the nervous tissue has been further conceptualised by Rudolf Virchow, who introduced the notion of neuroglia as a connective tissue of the brain and the spinal cord. During the second half of the 19th century, the cellular architecture of the brain was been extensively studied, which led to an in-depth morphological characterisation of multiple cell types, including a detailed description of the neuroglia. Here, we present the views and discoveries of the main personalities of early neuroglial research.

Определение параметров движения границы раздела сред «газ – жидкость» в топливных баках космических ступеней ракет-носителей на пассивных участках полета

Определение параметров движения границы раздела сред «газ – жидкость» в топливных баках космических ступеней ракет-носителей на пассивных участках полета

Dynamic annealing in Ge studied by pulsed ion beams

The formation of radiation damage in Ge above room temperature is dominated by complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. Here, we study the dynamics of radiation defects in Ge in the temperature range of 100–160 °C under pulsed beam irradiation with 500 keV Ar ions when the total ion fluence is split into a train of equal square pulses. By varying the passive portion of the beam duty cycle, we measure a characteristic time constant of dynamic annealing, which rapidly decreases from ~8 to 0.3 ms with increasing temperature. By varying the active portion of the beam duty cycle, we measure an effective diffusion length of ~38 nm at 110 °C. Results reveal a major change in the dominant dynamic annealing process at a critical transition temperature of ~130 °C. The two dominant dynamic annealing processes have an order of magnitude different activation energies of 0.13 and 1.3 eV.

Radiation defect dynamics studied by pulsed ion beams

The formation of stable radiation damage in solids often proceeds via complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. Our current understanding of the underlying physics is still not sufficient for predicting radiation damage even for Si, which is arguably the simplest and most extensively studied material. The complexity of radiation damage is closely related to radiation defect dynamics. Here, we demonstrate how defect interaction dynamics can be studied by pulsed beam irradiation when the total ion fluence is split into a train of equal square pulses. By varying the passive portion of the beam duty cycle, we measure a characteristic time constant of dynamic annealing and, hence, the defect relaxation rate. Measurements of stable lattice disorder as a function of the active portion of the beam duty cycle give an effective defect diffusion length. We illustrate the pulsed beam method with examples for Si bombarded at 100°C with 500keV Ar ions.

Dynamics of the Formation of a Rotating Orbital Tether System with the Help of Electro-thruster

The dynamics of the process of forming the rotating orbital tether system, which is a bundle of two small satellites, is analyzed. The cases of transition deployed tether system in rotation by means of two electric jet engines located on the end bodies are considered. Engines together form a pair of forces required sign, the control program includes active and passive portions of the motion system. Satellites are material points whose masses are comparable in magnitude, and the tether is weightless. The control program is formed by a relatively simple model in the mobile orbital coordinate system in the case of inextensible tether. The elongation effect of the tether, which leads to its eventual sagging is analyzed by a more complete model in a fixed geocentric coordinate system.

A New Approach for Harmonic Distortion Minimization in Power Systems Supplying Nonlinear Loads

In view of many problems associated with harmonics pollution within industrial firms, the development of new passive and/or hybrid filtering techniques of higher quality, higher efficiency, and lower cost is a necessity for the forthcoming power quality age. This article suggests a hybrid passive filter, which consists of a certain combination of a shunt passive filter (SPF) with a series passive portion as a substitute to overcome the shortcomings of conventional shunt passive filtering techniques. Constrained optimization is used to find the optimal sizing of parameters of the hybrid passive filter in order to reduce both harmonic voltages and harmonic currents in the power system to an acceptable level, as well as to improve the load power factor. The optimal design of the hybrid passive filter and its feasibility are compared with those of the C-type passive filter and the conventional SPF by means of four study cases taken from existing publications. Several simulation results are shown in order to highlight the viability of the proposed filter.

Impact of flow rates and electrode specifications on degradations during repeated startups and shutdowns in polymer-electrolyte membrane fuel cells

Separate testing protocols for fuel cell startup (SU) and shutdown (SD) are developed to distinguish between the effects of SU and SD on performance degradation. The internal currents during SU and SD operation are measured in a segmented cell to evaluate the charge exchanged between the active (H2/Air) and passive (Air/Air) portions of the cell. Cells with different membrane-electrode assemblies (MEAs) are subjected to SU or SD sequences to evaluate the time evolution of spatially resolved decrease of performance and electrochemical active surface area (ECSA). We examine the influence of the cathode and anode Pt loading, and the type of carbon for cathode catalyst support.Both the CO2 emissions and the charges exchanged increase with the common residence time of air and hydrogen in the anode compartment. However, the evolved CO2 accounts for less than 25% of the total exchanged charge. Startups are consistently more damaging than the shutdowns, evidenced by more evolved CO2 and charge exchanged, severe ECSA decrease, and higher performance losses.

Differential segmental strain during active lengthening in a large biarticular thigh muscle during running

The iliotibialis lateralis pars postacetabularis (ILPO) is the largest muscle in the hindlimb of the guinea fowl and is thought to play an important role during the stance phase of running, both absorbing and producing work. Using sonomicrometry and electromyography, we examined whether the ILPO experiences differential strain between proximal, central and distal portions of the posterior fascicles. When the ILPO is being lengthened while active, the distal portion was found to lengthen significantly more than either the proximal or central portions of the muscle. Our data support the hypothesis that the distal segment lengthened farther and faster because it began activity at shorter sarcomere lengths on the ascending limb of the length-tension curve. Probably because of the self-stabilizing effects of operating on the ascending limb of the length-tension curve, all segments reached the end of lengthening and started shortening at the same sarcomere length. During shortening, this similarity in sarcomere length among the segments was maintained, as predicted from force-velocity effects, and shortening strain was similar in all segments. The differential active strain during active lengthening is thus ultimately determined by differences in strain during the passive portion of the cycle. The sarcomere lengths of all segments of the fascicles were similar at the end of active shortening, but after the passive portion of the cycle the distal segment was shorter. Differential strain in the segments during the passive portion of the cycle may be caused by differential joint excursions at the knee and hip acting on the ends of the muscle and being transmitted differentially by the passive visco-elastic properties of the muscle. Alternatively, the differential passive strain could be due to the action of active or passive muscles in the thigh that transmit force to the IPLO in shear. Based on basic sarcomere dynamics we predict that differential strain is more likely to occur in muscles undergoing active lengthening at the beginning of contraction than those undergoing only shortening.

In vivo porcine left atrial wall stress: Computational model

Most computational models of the heart have so far concentrated on the study of the left ventricle, mainly using simplified geometries. The same approach cannot be adopted to model the left atrium, whose irregular shape does not allow morphological simplifications. In addition, the deformation of the left atrium during the cardiac cycle strongly depends on the interaction with its surrounding structures. We present a procedure to generate a comprehensive computational model of the left atrium, including physiological loads (blood pressure), boundary conditions (pericardium, pulmonary veins and mitral valve annulus movement) and mechanical properties based on planar biaxial experiments. The model was able to accurately reproduce the in vivo dynamics of the left atrium during the passive portion of the cardiac cycle. A shift in time between the peak pressure and the maximum displacement of the mitral valve annulus allows the appendage to inflate and bend towards the ventricle before the pulling effect associated with the ventricle contraction takes place. The ventricular systole creates room for further expansion of the appendage, which gets in close contact with the pericardium. The temporal evolution of the volume in the atrial cavity as predicted by the finite element simulation matches the volume changes obtained from CT scans. The stress field computed at each time point shows remarkable spatial heterogeneity. In particular, high stress concentration occurs along the appendage rim and in the region surrounding the pulmonary veins.

Ontogeny of behaviour in larvae of marine demersal fishes

The development of behaviours that are relevant to larval dispersal of marine, demersal fishes is poorly understood. This review focuses on recent work that attempts to quantify the development of swimming, orientation, vertical distribution and sensory abilities. These behaviours are developed enough to influence dispersal outcomes during most of the pelagic larval stage. Larvae swim in the ocean at speeds similar to the currents found in many locations and at 3–15 body lengths per second (BL s−1), although, based on laboratory measurements, species from cold environments swim slower than those from warm environments. At least in warm-water species, larvae swim in an inertial hydrodynamic environment for most of their pelagic period. Unfed swimming endurance is >10 km from about 8–10 mm, and reaches more than 50 km before settlement in several species. Larval fishes are efficient swimmers. In most species, a large majority of larvae have orientated swimming in the ocean, but the precision of orientation does not improve with growth. Swimming direction of the larvae frequently changes ontogenetically. Vertical distribution changes ontogenetically in most species, and both ontogenetic ascents and descents are found. Development of schooling is poorly understood, but it may influence speed, orientation and vertical distribution. Sensory abilities (hearing, olfaction, vision) form early, are well developed and are able to detect cues relevant to orientation for most of the pelagic larval stage. All this indicates that the passive portion of the pelagic larval duration will be short, at least in most warm-water species, and that behaviour must be taken into account when considering dispersal, and in particular in dispersal models. Although quantitative information on the ontogeny of some behaviours is available for a relatively small number of species, more research in this field is required, especially on species from colder waters.

Resonant pumping in a multilayer impedance pump

This paper introduces the concept of multilayer impedance pump, a novel pumping mechanism inspired by the embryonic heart structure. The pump is a composite two-layer fluid-filled elastic tube featuring a thick gelatinous internal. Pumping is based on the impedance pumping mechanism. In an impedance pump, elastic waves are generated upon external periodic compressions of the elastic tube. These waves propagate along the tube’s walls, reflect at the tube’s extremities, and drive the flow in a preferential direction. The originality in the multilayer impedance pump design relies on the use of the thick internal gelatinous layer to amplify the elastic waves responsible for the pumping. As a consequence, only small excitations are needed to produce significant flow. This fully coupled fluid-structure interaction problem is solved for the flow and the structure using the finite element method over a relevant range of frequencies of excitation. Results show that the multilayer impedance pump is a complex system that exhibits a resonant response. Flow output and inner wall motion are maximal when the pump is actuated at the resonant frequency. The wave interaction mechanism present in an impedance pump is described here in details for the case of a multilayer impedance pump. Using energy balance for the passive portion of the elastic tube, we show that the elastic tube itself works as a pump and that at resonance maximum energy transmission between the elastic tube and the fluid occurs. Finally, the pump is especially suitable for many biomedical applications.

QUANTIFYING PASSIVE AND DRIVEN LARGE-SCALE EVOLUTIONARY TRENDS

Abstract.— I introduce a new statistical method, analysis of skewness, for quantifying large‐scale evolutionary trends as a combination of both passive and driven trends. My approach is based on the skewness of subclades within a parent clade. I partition the total skewness of the parent clade into three components: (1) skewness between subclades; (2) skewness within subclades; and (3) skewness due to changes in variance among subclades. The third component corresponds to a new type of passive trend, in which overall skewness of a parent clade is due to greater variability in subclades to the right of the mean. Using this partitioning, I decompose an observed trend into two components: a driven portion and a passive portion, thus quantifying the effect of small‐scale dynamics on large‐scale behavior of clades. Applications are given to Miocene‐Pliocene rodent size and Ordovician brachiopod muscle geometry.

Changes in lung function and tidal airflow patterns after increasing extrathoracic airway resistance

The aim of this study was to determine what changes occur in previously described tidal expiratory flow patterns when extrathoracic resistance is added. A total of 16 subjects with normal lung function and 15 patients with chronic COPD, were studied. The following measurements were made before and after the addition of an extrathoracic expiratory resistance (EER; 0.89 kPa/L s at a flow of 0.5 L/s) during uncoached tidal breathing: expiratory time (tE), frequency (f), expiratory time to maximum flow/total expiratory time (tPTEF/tE), tidal maximum expiratory flow (PEF(TIDAL)), and time constant of the respiratory system calculated from the passive portion of tidal expiration (trs(TIDAL)). Post peak profiles were categorized as convex, linear or concave and time for flow to fall to 80% and 20% of maximum (t80 and t20) were measured. Tidal indices tE, f and PEF(TIDAL), were similar in the two groups, but tPTEF/tE was greater and trs(TIDAL) was less in the normal subjects than in the COPD patients. Addition of EER in both groups caused PEF(TIDAL) to decrease and trs(TIDAL), t80 and the percentage of convex profiles to increase. tPTEF/tE increased in the COPD patients but was unchanged in the control group. After addition of EER during tidal breathing, expiratory flow in COPD patients resembled that seen in normal subjects.