Tension Distribution Research Articles

Modeling spatial distribution of oxygen in 3d culture of islet beta-cells.

Three-dimensional (3D) scaffold culture of pancreatic β-cell has been proven to be able to better mimic physiological conditions in the body. However, one critical issue with culturing pancreatic β-cells is that β-cells consume large amounts of oxygen, and hence insufficient oxygen supply in the culture leads to loss of β-cell mass and functions. This becomes more significant when cells are cultured in a 3D scaffold. In this study, in order to understand the effect of oxygen tension inside a cell-laden collagen culture on β-cell proliferation, a culture model with encapsulation of an oxygen-generator was established. The oxygen-generator was made by embedding hydrogen peroxide into nontoxic polydimethylsiloxane to avoid the toxicity of a chemical reaction in the β-cell culture. To examine the effectiveness of the oxygenation enabled 3D culture, the spatial-temporal distribution of oxygen tension inside a scaffold was evaluated by a mathematical modeling approach. Our simulation results indicated that an oxygenation-aided 3D culture would augment the oxygen supply required for the β-cells. Furthermore, we identified that cell seeding density and the capacity of the oxygenator are two critical parameters in the optimization of the culture. Notably, cell-laden scaffold cultures with an in situ oxygen supply significantly improved the β-cells' biological function. These β-cells possess high insulin secretion capacity. The results obtained in this work would provide valuable information for optimizing and encouraging functional β-cell cultures. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:221-228, 2017.

Effect of Static Deformation on Basic Flow Patterns in Thermocapillary-Driven Free Liquid Film

A series of terrestrial, parabolic-flight and on-orbit experiments on thermocapillary-driven flows in free liquid films are carried out. We focus on the basic flow patterns induced in the film formed in a rectangular hole by varying the film volume in order to make a comparison with the results of the fluid physics experiments under microgravity conditions conducted by one of the authors, Pettit, on the International Space Station. The free liquid film is formed in a rectangular hole of O(0.1 mm) in thickness under a designated temperature difference between the end walls. The temperature dependence of the surface tension results in a non-uniform surface tension distribution over the free surfaces. A liquid generally has a negative temperature coefficient of surface tension; i.e., the fluid over a free surface is driven from a higher-temperature region to a lower-temperature region. In the case of a thin free liquid film with two free surfaces, however, an unusual flow pattern is realized. That is, the fluid seems to be driven toward the heated region from a colder region. In order to understand the physical mechanism of this behavior in the free liquid film, a series of on-orbit and ground experiments were conducted. We indicate several flow patterns in the film and corresponding film profiles as well as the surface temperature distribution. We also try to illustrate the cross-sectional flow structures in the thin free liquid film with two free surfaces.

Impact of electrochemically active diaphragm on dehydration of finely dispersed precipitates

The article has proposed a new method of intensification of the dehydration of clayey dispersion based on the use of an electrochemically active diaphragm. Analyzed was impact of a carbon diaphragm on the distribution of the field tension in a cell and the electroosmotic transport of the liquid at different pH of the porous solution. Optimal conditions for dehydration of a model dispersion have been determined.

Computational Investigation of Transmural Differences in Left Ventricular Contractility.

Myocardial contractility of the left ventricle (LV) plays an essential role in maintaining normal pump function. A recent ex vivo experimental study showed that cardiomyocyte force generation varies across the three myocardial layers of the LV wall. However, the in vivo distribution of myocardial contractile force is still unclear. The current study was designed to investigate the in vivo transmural distribution of myocardial contractility using a noninvasive computational approach. For this purpose, four cases with different transmural distributions of maximum isometric tension (Tmax) and/or reference sarcomere length (lR) were tested with animal-specific finite element (FE) models, in combination with magnetic resonance imaging (MRI), pressure catheterization, and numerical optimization. Results of the current study showed that the best fit with in vivo MRI-derived deformation was obtained when Tmax assumed different values in the subendocardium, midmyocardium, and subepicardium with transmurally varying lR. These results are consistent with recent ex vivo experimental studies, which showed that the midmyocardium produces more contractile force than the other transmural layers. The systolic strain calculated from the best-fit FE model was in good agreement with MRI data. Therefore, the proposed noninvasive approach has the capability to predict the transmural distribution of myocardial contractility. Moreover, FE models with a nonuniform distribution of myocardial contractility could provide a better representation of LV function and be used to investigate the effects of transmural changes due to heart disease.

Seismic design and response of steel multi-tiered concentrically braced frames in Canada

This article investigates the seismic design and response of steel multi-tiered concentrically braced frames (MT-BFs) in which braces meet at columns between diaphragms. The seismic design provisions of CSA S16-14 are described and illustrated for three-tiered Type MD (moderately ductile) and five-tiered Type LD (limited ductile) braced frames. Analysis methods are proposed to evaluate the in-plane flexural demand on columns. The seismic response of the frames is examined through nonlinear response history analysis. As assumed in design, inelastic deformations tend to concentrate in one tier over the frame height, causing non-uniform drift demands and in-plane bending moments in the columns. CSA S16 provisions predicted well the frame in-plane flexural response and result in acceptable ductility demands on the braces. An extended seismic analysis and design approach that accounts for vertical distribution of brace tension yielding along the frame height is proposed for frames that exceed the limits prescribed in CSA S16.

TENSION OF GEOMORPHOLOGIC CONDITIONS IN THE MARGINAL MOUNTAIN BELTS OF THE PACIFIC RIM

The maps of naturally determined geomorphologic tension, scale 1:8 million, for the territory of the Russian Far East and the central fragment of the mountain system of the Andes (between 5°S – 19°S) were compiled. We are using the term “tension” to define predisposition of the territory for the development of catastrophic processes. Tension was evaluated in nominal scores accordingly to the regional level of generalization. Assessment was based on the analysis of seismicity, amount of precipitation, the depth of the relief dissection and the spectrum of the dominant geomorphologic processes. The value of geomorphologic tension in the Russian Far East region ranges from 3 to 16 conventional points: in the Western Okhotsk Sea coast area it was estimated at 7–10 points, in the Sakhalin – 10–12, in the Eastern Kamchatka – 13–15 and in separate Kuril Islands – 16 points. Thus, the study results confirmed the formerly stated supposition about the increase of nature-defined geomorphologic tension of the NW Pacific Ocean sector from the west to the east. The zone of maximum potential development of catastrophic processes in the SE sector of the Pacific Rim is situated at the western mega slope of the Peruvian Andes between 9°S and 13°30’S and in the band width of 100 km along the Pacific coast. The geomorphologic tension of this area reaches 15–16 points due to natural causes. The tension on the eastern mega slope of the Andes ranges from 9 to 12 points, except for some areas where it increases to 13–14; on the Altiplano it decreases to 6–10 points. An important feature of the study area is the asymmetric distribution of geomorphologic processes, so the geomorphologic tension, which significantly different at the oceanic and the inland (continental) slopes of the mountain chain. Comparison of data obtained for the two segments (NW and SE) of the Pacific Rim allows reaching a conclusion about the general regularities of the distribution of geomorphologic tension in the territory of marginal mountain belts around the Pacific Ocean with more confidence. The areas of potential catastrophic processes are located near the edge of the continent in either case.

Experimental and analytical analysis of reinforced concrete columns strengthened with CFRP

The technology of the Construction Industry is advancing constantly. Every year, new materials, equipment, and building techniques are introduced. In the specific case of reinforced and pre-stressed concrete structures, the innovations have contributed to the improvement of the properties of the concrete and the durability of the structures that incorporate this material. These advances are not restricted to the construction of new structures, however, and it is important to recognize the need to recuperate structural elements or increase their resistance, which has provided incentives for the improvement of techniques of structural reinforcement. In this context, the present study used a combined theoretical and experimental approach for the investigation of the effectiveness of the reinforcement of concrete columns by jacketing them with polymer mantles strengthened with carbon fibers. The analyses aimed to determine the effectiveness of the mantles in terms of the increase in resistance to axial compression and contribute to the understanding of the structural behavior of columns strengthened using this technique. To this end, centered axial compression tests were run on five short reinforced concrete columns, including one control column and four experimental columns with different reinforcement ratios. Numerical simulations were also run in the Abaqus software to determine the distribution of tensions inside the columns. The sum of the evidence was analyzed and it was verified that the strengthening used in the columns increased considerably their resistant capacities, thus the gain in this capacity was directly proportional to the value of the used strengthening rate—the column with the biggest strengthening rate bore a last load 42.8 % bigger than the one borne by the column of reference, with no strengthening. From these data, it was possible to obtain a simple predictive model of the increase in resistance capacity of columns strengthened with carbon fibers.

Destabilization of Emulsion Formed During Aqueous Extraction of Peanut Oil: Synergistic Effect of Tween 20 and pH

AbstractTo destabilize the emulsion formed during aqueous extraction processing (AEP) of peanuts, Tween and Span series surfactants (Tween 20, Tween 80, Span 20, and Span 80) were used alone or in combination to break the emulsion. Results indicate that only Tween surfactants had a pronounced demulsifying effect that was dependent on Tween concentration and system pH. When 1.2 wt% Tween 20 aqueous solution was used for oil extraction at pH 10.0, the highest free oil yield was achieved at 76.1 %, which was similar to the oil recovery of using proteases as a destabilization agent. The results obtained using a model emulsion system containing peanut oil and Tween 20/peanut protein isolates (PPI) showed that when Tween 20 and PPI coexisted in extraction medium at pH 10.0, the dynamic interfacial tension and droplet size distribution curves were very similar to those when Tween 20 was used alone, suggesting that Tween 20 dominated at the interface, instead of PPI. Destabilization of the model emulsions relied on three important factors: inclusion of Tween 20 at the initial mixing stage, high pH, and a gentle mixing speed. A synergistic destabilization mechanism of using Tween 20 at high pH during AEP was proposed. The discovery of Tween 20 as an effective demulsifier significantly contributes to the development of AEP of oilseeds.

Model identification and vision-based H∞ position control of 6-DoF cable-driven parallel robots

ABSTRACTThis paper presents methodologies for the identification and control of 6-degrees of freedom (6-DoF) cable-driven parallel robots (CDPRs). First a two-step identification methodology is proposed to accurately estimate the kinematic parameters independently and prior to the dynamic parameters of a physics-based model of CDPRs. Second, an original control scheme is developed, including a vision-based position controller tuned with the H∞ methodology and a cable tension distribution algorithm. The position is controlled in the operational space, making use of the end-effector pose measured by a motion-tracking system. A four-block H∞ design scheme with adjusted weighting filters ensures good trajectory tracking and disturbance rejection properties for the CDPR system, which is a nonlinear-coupled MIMO system with constrained states. The tension management algorithm generates control signals that maintain the cables under feasible tensions. The paper makes an extensive review of the available methods and presents an extension of one of them. The presented methodologies are evaluated by simulations and experimentally on a redundant 6-DoF INCA 6D CDPR with eight cables, equipped with a motion-tracking system.

Critical values of mechanical stress and strain during traumatic cervical spinal cord injury: Clinical study with the use of Finite Element Modelling

Study design: Prospective case-control study. Objective: Aim of the study was to assess critical values of mechanical stress and strain in the cervical spinal cord based on the Finite Element Method (FEM) simulations of specified clinical cases. Summary of background data: The knowledge about the values and distribution of tension and deformation, which are noted at the moment of traumatic spinal cord injury (tSCI) may enable determination of the range of primary and secondary injury. Methods: Total of 28 patients after cervical spine (C-spine) injury were enrolled, 14 with neurological symptoms of tSCI (study group, SG) and 14 neurologically intact (control group, CG). Both groups were age and sex matched. A three-dimensional (3D) numerical model of the cervical spinal cord containing dura and pia matter together with denticulate ligament was created. The variable boundary conditions were established individually for each case and allowed to reconstruct the moment of the injury in computer environment. Factors differentiating between SG and CG were tested with multiple logistic regression model. The predictors of ASIA scale outcomes were evaluated in the ordinal multinomial probit regression model. Results: There were no correlations between age, sex and the level of injury and the values of stress and strain. The results in longitudinal axis (z), in stress (OR-6.3; 95%CI 3.94-8.78; p < .033) and strain (OR-7.8; 95%CI 3.03-10.19; p < .046) were the risk factors of neurological deficits after tSCI. The cut off value for stress was 8.1 kPa (sensitivity-85.7%; specificity-78.6%; AUC-0.819, p < .001), and for strain 0.0117 (sensitivity-92.9%; specificity-72.5%; AUC-0.645, p < .001). Results in the longitudinal axis (z), in stress and strain correspond with grading in ASIA scale. One grade change in ASIA scale correlates with the decrease in z axis by 4.01 kPa and 0.012 in stress and strain respectively. Conclusions: The severity of damage of osseous and ligament structures of the spine, significantly influences the range of the mechanical stress applied to the spinal cord. Neural tissue of the spinal cord is the most resistant to the mechanical stimulus acting in sagittal direction, distraction appears to be the most destructive component of the injury phenomenon.

Magnetoelastic Effect-Based Transmissive Stress Detection for Steel Strips: Theory and Experiment

For the deficiencies of traditional stress detection methods for steel strips in industrial production, this paper proposes a non-contact stress detection scheme based on the magnetoelastic effect. The theoretical model of the transmission-type stress detection is established, in which the output voltage and the tested stress obey a linear relation. Then, a stress detection device is built for the experiment, and Q235 steel under uniaxial tension is tested as an example. The result shows that the output voltage rises linearly with the increase of the tensile stress, consistent with the theoretical prediction. To ensure the accuracy of the stress detection method in actual application, the temperature compensation, magnetic shielding and some other key technologies are investigated to reduce the interference of the external factors, such as environment temperature and surrounding magnetic field. The present research develops the theoretical and experimental foundations for the magnetic stress detection system, which can be used for online non-contact monitoring of strip flatness-related stress (tension distribution or longitudinal residual stress) in the steel strip rolling process, the quality evaluation of strip flatness after rolling, the life and safety assessment of metal construction and other industrial production links.

Experimental observation of the dislocation walls in heterostructures with two interfaces: Ge/Ge0.5Si0.5 10 nm/Si(001) as an example

High-resolution electron microscopy (HREM) at the atomic scale has been applied to study the edge dislocation redistribution between interfaces in Ge/Ge0.5Si0.5/Si(0 0 1) heterostructures. Our results provide a direct explanation that plastic relaxation of the GeSi buffer layer proceeds owing to motion of Lomer-type dislocation complexes consisting of a pair of complementary 60° dislocations with the ends of the {1 1 1} extra planes being located at a distance of ~2–12 interplanar spacings from each other. It is demonstrated that edge dislocations belonging to the upper and lower interfaces become arranged one under the other and dislocation walls are formed. The distributions of tension and compression in the [0 0 1] direction between two edge dislocations, obtained by processing the HREM image, testify to superposition of strain fields.

Theoretical and experimental investigation of deep drawing of tailor-welded IF steel blanks with non-uniform blank holder forces

Tailor-welded blank is one of the promising technologies in the application of lightweight materials for auto body parts manufacturing. The material discontinuity across the weld line results in an inhomogeneous deformation and weld line displacement. In this study, a two-dimensional analytical model is proposed to predict the tension distribution along the cross section. An energy method is used to calculate the restraining force due to bending, sliding, and unbending phenomena on the die and punch radii. To control the weld line movement, a blank holder force control strategy is proposed to achieve force equilibrium at the bottom of the part across the weld line. Finite element simulations are performed to study the effect of die and punch radii, friction coefficient, thickness ratio, and blank holder forces on the weld line displacement in strip drawing process. Under a uniform blank holder force, the weld line moves toward the thicker/stronger side implying a higher blank holder force is required for the thinner/weaker side. The results show that the weld line displacement can be controlled by an appropriate blank holder force adjustment. In order to control the weld line movement in square cup deep drawing, blank holder force on the thinner side is increased and its influences on the deformation process are investigated. Comparisons of material draw-in, weld line movement, and forming force show a good agreement between the theoretical, numerical, and experimental results.

Investigation on the probabilistic distribution of mooring line tension for fatigue damage assessment

This paper is to investigate the applicable probability density functions (PDFs) for the short- and long-term mooring line tension amplitudes to be used for accurately assessing the mooring line fatigue damage with the spectral method. Statistical characteristics of the mooring line tensions were investigated, in which kurtosis and skewness were computed and compared to validate the non-normality of the line tension response. Several PDFs, including Rayleigh, GEV, and Gamma distributions, are used to express the short-term statistical distribution of the mooring line tension amplitudes. Results indicate that the Gamma distribution can give much better fitting than the Rayleigh and GEV distributions. In order to identify the long-term distribution of the tension amplitudes, the Gamma distribution is modified by bringing in a location parameter. Compared with the generally used Weibull distribution, the modified Gamma distribution can characterize the long-term PDF of the tension amplitudes much better. Moreover, the modified Gamma distribution can give much more accurate assessment of the mooring line fatigue damage than the Weibull distribution.

Mathematical relationship between mean cable tensions and structural parameters of deployable reflectors

The main purpose of the paper is to investigate the effects of structural parameters of deployable reflectors on their mean cable tensions. The proportional relations between spatial and plane cable nets are firstly explored on the basis of projection principle. By the means of obtained proportional relations, the analytical expressions between the mean spatial cable tensions and structural parameters of deployable reflectors including aperture, subdivision number and focal length are then derived. In the following, a modified plane projection method is proposed for pretension design of offset reflectors. Finally, numerical simulations are taken to verify the analytical expressions, as well as the modified plane projection method. The results show that the mean spatial cable tensions are predicted accurately by the analytical expressions, and uniform tension distribution is obtained by the modified plane projection method. With the applications of the analytical expressions and the modified plane projection method, the cable tensions can be controlled more flexible and convenient in engineering applications.

Comments on “A Four-Layer Wound Closure Technique with Barbed Sutures for Stable Reset of the Inframammary Fold in Breast Augmentation”

It is a well-established fact that the inframammary fold (IMF) is an important anatomical landmark. With breast augmentation, it often needs to be repositioned and secured to its new position to avoid bottoming out deformity and scar displacement. Montemurro et al1 describe a suturing technique using long-lasting and resorbable barbed sutures to stabilize the IMF in the desired position. The barbed suture is used for closure of the first three deep layers whilst a common absorbable monofilament is used for the final epidermal layer to prevent the anchors from interfering with epidermal healing. Advantages of their technique over traditional suturing techniques include speed in execution and better tissue control, with even distribution of tension along the deep suture line and …

A microfluidic chip of multiple-channel array with various oxygen tensions for drug screening

Oxygen participates in numbers of cellular activities and behaviors in both normal and pathological tissues. In physiological microenvironment, oxygen tension is generally below 21 % and varies in different species, states and regions of organs. However, present studies of cellular behavior in vitro are performed in an ambient level, which is not conformity to the reality in vivo. In this study, a microfluidic device was developed to generate controllable oxygen tensions on a multiple-channel array chip for high-throughput drug screening. Controlling various concentrations of chemical reagents with confined flow rate, specific oxygen tensions can be established from 1.6 to 21 %, where the oxygen tension of each channel can be modulated in demand. When the concentrations of pyrogallol change from 100 to 700 μg/mL with the flow rate of 5 μL/min, oxygen tensions in cell chambers range from 12.5 to 3.87 %. Pyrogallol with the concentration of 0 μg/mL is used as the control group to obtain 20.9 % oxygen condition. The developed microfluidic chip was used to investigate the cytotoxicity of TPZ and cisplatin, and the results demonstrate different manners of two oxygen-sensitive anti-tumor drugs in oxygen-dependent cytotoxic responses. Due to its character, the microfluidic device is believed to establish any desired and measurable oxygen tension distribution for pharmacology development, which is promising to improve efficiency and reduce tedious operation for pharmaceutical studies.

Study on Spinning triangles in the common ring spinning and Super draft ring spinning systems

In the paper, one kind of super draft ring spinning frame with four drafting rollers and corresponding three drafting zones were introduced. The yarn qualities spun by the super draft ring spinning frame were analyzed by studying the shape of spinning triangles. Using the high speed camera system OLYMPUS i-speed3 and one kind of transparent front top roller, the spinning triangles were captured, and the geometry size of spinning triangle were measured. Then, according to the theoretical model of fiber tension in the spinning triangle, fiber tension distributions in the spinning triangles were presented by using Matlab software. Using the combed roving of 350 tex as raw material, three kinds of cotton yarns, 27.8 tex (21S), 18.2 tex (32S) and 14.6 tex (40S), were spun in the common ring spinning frame with three different suitable spindle speeds, travelers and twist factors. Using the combed roving of 350 tex and 500 tex as raw material, 14.6 tex cotton yarns were spun in the super draft ring spinning frame with three different drafting ratios at back zone. It is shown that with the increasing of spindle speed, a more asymmetric shape of spinning triangle would be produced, and lead to worsen yarn evenness. With the decreasing of traveler weight, the height and horizontal deviation of the spinning triangle is decreased, and may lead to better yarn evenness and less long hairiness. By taking suitable large yarn twist factors, the comprehensive qualities can be improved. Comparing with the common ring spinning, the spinning triangle is larger in the super draft ring spinning. That is, in the super draft ring spinning, the fibers in the strand in the front roller nip are more dispersed, and not benefit for yarn qualities. Therefore, the compact device was introduced into the super draft ring spinning, and the cotton pure yarns and blend yarns were spun, and the yarn qualities were measured and analyzed.

Quasi-stationary mechanics of elastic continua with bending stiffness wrapping on a pulley system

In many engineering applications elastic continua such as ropes and belts often are subject to bending when they pass over pulleys / sheaves. In this paper the quasi-stationary mechanics of a cable-pulley system is studied. The cable is modelled as a moving Euler- Bernoulli beam. The distribution of tension is non-uniform along its span and due to the bending stiffness the contact points at the pulley-beam boundaries are not unknown. The system is described by a set of nonlinear ordinary differential equations with undetermined boundary conditions. The resulting nonlinear Boundary Value Problem (BVP) with unknown boundaries is solved by converting the problem into the ‘standard’ form defined over a fixed interval. Numerical results obtained for a range of typical configurations with relevant boundary conditions applied demonstrate that due to the effects of bending stiffness the angels of wrap are reduced and the span tensions are increased.

The genesis of vertisols with gilgai microtopography: A review

Different hypotheses about the genesis of gilgai microtopography and corresponding soil complexes with clayey swelling soils are considered in this review. Their diversity is stipulated by specificities of the objects themselves and by the history of studies of the composition, properties, regimes, and landscape conditions of the areas with Vertisols in different countries. Most of the hypotheses about the genesis of Vertisols with the gilgai microtopography suggest that strong swelling–shrinking processes take place in these soils in the course of moistening–drying cycles; the origin of shear stress in the soils, its spatial patterns, and the particular ways of translocation of the soil material are discussed. At the early stage of Vertisol studies, a hypothesis about the leading role of the process of “self-swallowing” of the soils as a result of filling of open cracks with the material from the upper soil horizons was popular. However, numerous facts suggest that the intensity of this process is relatively low, so that it cannot play the major role in the gilgai formation and cyclic changes in the thickness and properties of the soil horizons in Vertisols. Another important mechanism is the uneven moistening and drying of the whole soil volume resulting in the irregular distribution of inner tensions in the soil with the development of shear stress and plastic deformation of the soil mass. The hypotheses suggested in the recent decades are based on the models of soil mechanics. A number of hypotheses consider possible alternation and duration of evolutionary stages of the development of Vertisols with the gilgai microtopography.