Significant Shear Forces Research Articles

Wear Mechanics of the Female Locust Digging Valves: The “Good Enough” Principle

AbstractAdult female desert locusts (Schistocerca gregaria) dig underground to lay their eggs, ensuring optimal conditions for successful hatching. Digging is performed using the two pairs of oviposition valves at the tip of the female's abdomen. These valves are subjected to considerable shear forces during the repeated digging cycles, potentially leading to wear over time. The resilience of the valves is investigated by analyzing the relationship between digging experience and valve damage and wear throughout the female locust's life. The findings reveal the ability of the valves to withstand the significant shear forces encountered during digging. Despite this resilience, however, perceptible limitations in the valves’ mechanical durability against wear are observed. Toward the end of the female locust's life, the valves show substantial signs of wear, indicating effective performance but with limited longevity, i.e., a designated life span that enables successful oviposition for ca. four oviposition cycles. A comparison of the valve material with that of the animals’ mandibles, which are used continuously throughout their life and show remarkable wear‐resistance, further highlights the evolutionary adaptation of the valve materials to their specific function, suggesting a trade‐off between energetic investment and the sufficient, or “good‐enough”, performance that is required for survival.

Investigation of the wind loads and flow patterns of a high-rise building under twisted wind flows based on LES

The twisted wind effect has attracted increasing attention among scholars due to its significant influence on the wind loads and wind induced responses of high-rise buildings. Nowadays, it is still challenging to simulate twisted wind flows (TWFs) with larger wind twist angles (WTAs) in the wind tunnel test. Compared to wind tunnel test limitations, the large eddy simulation (LES) offers an effective tool to simulate a broader WTA range. Several state-of-the-art numerical studies have generated TWFs that rely on multiple velocity inflow boundary (MVIB), but it results in vast computational domains and substantial abnormal pressure fluctuations. This paper proposes a single velocity inflow boundary (SVIB) method for modeling TWFs, which can significantly reduce the computational domain size without losing accuracy. Based on the SVIB method, we simulate TWFs with four WTAs (i.e., 0°, 25°, 35°, 45°) and conduct a comprehensive analysis of the influence of WTA and wind direction angle on both the wind load characteristics of and the flow patterns around a high-rise building. The results show that the TWFs will twist the vortex topology and trajectory, and the maximum extreme local resultant force coefficient under 35TWF is larger than that under SWF by around 10 %. The positive and negative wind pressures can simultaneously occur on a special surface at large WTAs (e.g., 35°, 45°), which may impose significant shear forces on the intermediate layers. The wind veering effect enhances the contribution of vortex shedding to the longitudinal fluctuating wind loads and the influence of incoming turbulence on lateral fluctuating wind loads. This study contributes to providing a more effective LES method to simulate TWFs with large WTAs and to reveal the effect of large WTA on the wind load characteristics of high-rise buildings under TWFs and the underlying flow mechanism, which is beneficial to the future wind-resistant design of skyscrapers.

Numerical Study of Tangential Traction Mechanism between Pattern Blocks of Agricultural Radial Tires and Soft Soil.

With the increasing requirements of agricultural machinery, the study of the contact relationship between the tire-soil interface and the improvement of traction efficiency has gradually become a main concern. In this study, the pattern on the agricultural tire was simplified into single-pitch pattern blocks. The pattern blocks were made of rubber material that was highly resistant to abrasion and bending. The experiment was carried out by pressing the three types of patterned block construction into the soil and the pure sliding under the soil. The simulation used the Coupled Eulerian-Lagrangian Method (CEL) to verify the experimental results. We found that the herringbone pattern block was subjected to the highest stress for the same depth of downward pressure. The horizontal force generated by the pure sliding was also the highest. The results showed that the numerically simulated and experimentally measured data exhibited similar trends and average values. In addition, the increase in the contact area between the tire and the soil reduced the compaction and sinking of the soil. The herringbone pattern structure not only had a large contact area but also produced the most significant shear force on the soil. Thus, it may generate greater traction in actual operations.

Medial Locking Plate Can Increase the Fixation Stability of Vertical Femoral Neck Fracture in Young Adults?

Introduction: Vertical femoral neck fractures in young adults are usually caused by high-energy trauma. These injuries are difficult to stabilize due to significant shear forces acting on the fracture site. Their treatment is challenging and with high risks of complications, such as fixation failure, malunion, nonunion, and avascular necrosis of the femoral head. Material and Methods: It compared the biomechanical stability provided by 3 different fixation methods: (1) dynamic hip screw with derotation screw, (2) cannulated screws with a conventional medial bone plate, and (3) cannulated screws with a locked medial bone plate. These fixation structures were applied on fourth-generation medium-sized synthetic bones, with a 17 pound per cubic foot cellular foam core and cervico-diaphyseal angle of 120 degrees were used. The comparison was performed through biomechanical tests under cyclic loading followed by an ultimate load. The interfragmentary movement at the fracture site was the main variable for the cyclical phase. Results: The biomechanical comparison showed no statistical differences (P > 0.05) in stiffness, micromovement level, and mechanical resistance among the fixation techniques evaluated. Discussion: To stabilize the vertical femoral neck fracture in young patients, the use of a medial bone plate associated with cannulated screws on a “tie-rod” assembly is an option that supports the mechanical demand until the fracture healing. The locked medial plate did not provide an advantage compared with the conventional bone plate.

Theoretical modeling for predicting the shear strength of partially-encased composite members with multiple transverse stiffeners

Partially encased composite (PEC) members are frequently used as girders in heavily-loaded or long-span structures. In PEC members, the steel web is encased in web concrete between the top and bottom flanges. When PEC members are used in continuous beam spans, the intermediate support area is subjected to significant shear force and negative bending, which is more critical than the span center. As a result, accurate prediction of shear strength is crucial for structural safety in practical design. Unlike traditional concrete or steel beams, PEC beams have multiple shear transfer mechanisms consisting of concrete, steel flanges, axial steel web, and transverse stiffeners (if necessary), and it is essential to investigate the shear contributions of the different mechanisms and how they work together as a composite structure. To solve this problem, this paper presents a novel shear strength model, in which the global shear strength is composed of two main components: the composite truss (steel flanges, web concrete, and transverse stiffeners) and the axial steel web, and these two components are unified by strain compatibility to show the composite action. Then, the proposed model is compared with existing shear equations using 25 existing specimens in the literature, and the results indicate that the proposed model can predict the shear strength of PEC beams with sufficient accuracy. Finally, the paper presents a simplified design method after validating the shear contributions of different anti-shear mechanisms, and the simplified method can facilitate practical design in engineering practices.

Kinetics of size change in air bubble and fat globule during ice cream freezing process

AbstractUsing a batch‐type freezer, this study investigated the influence of agitation speed on the time course change in the size of air bubbles and fat globules to establish kinetics of those during freezing. Higher agitation is advantageous not only for mixing enhancement but also for preventing local freezing and undesirable solidification, according to the results of flow visualization and time‐course change in the Reynolds number during freezing. Air bubbles and fat globule size were measured using samples obtained during freezing. For each agitations speed, the time‐course change in air bubble size was clearly different. Because of significant shear force, a smooth reduction in air bubble size was observed at a relatively high agitation speed. However, at the later stage of freezing, the increased collision frequency of the bubbles induced an undesirable increase in size. Aggregation of fat globules occurred immediately after the aqueous phase begin to be frozen. In addition, a greater agitation speed improved fat destabilization and hence increased the degree of aggregation (DA) as measured by the fat globule size distribution. At all agitation speeds, a decrease in DA was observed after a temporary increase in DA. This decrease can be explained by the breakup of the aggregates. At higher agitation speed, more serious decrease in DA was found. It was found that agitation speed significantly affects the kinetics of air bubbles and fat globules during freezing.Practical ApplicationsAfter freezing, air bubbles and fat globules size are important factors in determining ice cream quality. Nevertheless, no time‐course change in size has been constructed from the perspective of kinetics. To the best of our knowledge, this is the first study to investigate the effects of agitation speed on the time‐course change in air bubbles and fat globules size. The kinetics of air bubbles and fat globules are important in determining process parameters such as freezing time and agitation speed in the process design of freezers for ice cream manufacturing. Although this study was conducted using a bath‐type freezer, the kinetics of size change can be applied to process design with a continuous‐type freezer.

Punching tests on edge slab-column connections with refined measurements

Due to the significant shear forces developing around columns and the potential brittle failure associated, the punching capacity of flat slabs is the main concern at ultimate limit state. An effective way to understand the behaviour of slab-column connections has typically been by testing isolated specimens in the laboratory. While there exist many slab-column connection types in actual slabs, most research efforts have focused on the punching resistance at internal columns. Specifically, edge connections appear largely underrepresented in the literature when the number of existing tests is compared to their importance in typical building floor configurations. Furthermore, the favourable effect of slab continuity is generally neglected in this type of tests. This paper presents the results of an experimental campaign on two edge slab-column connections: one had no shear reinforcement, while the other had a large amount of shear reinforcement to evaluate maximum punching. A novel test setup was conceived to apply representative boundary conditions of actual continuous slabs, introducing moment continuity perpendicularly to the slab free edge. Refined measurement techniques were extensively used, monitoring the visible slab faces using Digital Image Correlation, and instrumenting the flexural and shear reinforcement with distributed fibre-optic sensors. The failure of the slab-column connection without shear reinforcement was triggered in the region of shear stress concentrations and propagated around the column thereafter. Well-anchored vertical legs of flexural reinforcement at the free face induced a smeared-like shear crack pattern. In the shear-reinforced slab-column connection, an initial crushing of the concrete at the column front corners was followed by the formation of a local yield line along the slab axis. In addition to the enhancement of the resistance and rotation capacity, the shear studs also served for increasing the moment redistribution capacity of the system. The experimental results are compared to different codes of practice, showing that improvements are needed to better assess the resistance of edge columns.

Synergistic Effects of Aqueous Phase Viscoelasticity and Reduced Interfacial Tension on Nonwetting Phase Displacement Efficiency: An In Situ Experimental Investigation.

This study uses in situ experimental investigation techniques to probe the synergistic effects of aqueous phase viscoelasticity and reduced interfacial tension on nonwetting phase displacement efficiency in natural porous media. Specifically, it examines the efficacy of viscoelastic surfactant (VES) solutions in enhancing oil recovery and investigates the pore-scale displacement mechanisms and VES-oil interactions. To this end, we first performed an extensive rheological characterization to select two VES solutions from multiple CTAB/NaNO3 (CTN) and Cocobetaine/SDS/NaCl (CSN) mixtures. The selected aqueous solutions were then used in unsteady-state imbibition experiments conducted on miniature, water-wet Prairie Shell carbonate core samples. The experiments were performed utilizing a high-pressure, high-temperature two-phase core-flooding apparatus integrated with a high-resolution X-ray imaging system to acquire pore-scale fluid occupancy maps during the displacements. The results indicate that the injection of the selected CSN and CTN solutions into the carbonate samples under capillary-dominated flow regimes boosts the oil recovery by 12 and 2%, respectively, compared to those of the base waterflood. The VES solutions lowered the oil-water interfacial tension and exerted significant shear forces at the entrance of pores. The shear forces could exceed the threshold surface free energy required to deform oil globules, and consequently, large oil clusters were fragmented into smaller blobs and eventually produced from the pore space. The higher oil recovery by CSN flooding was attributed to its stronger viscoelastic properties. The VES injection under the viscous-dominated flow regime intensified the frequency of oil globule fragmentation. As a result, residual oil saturation values were sharply reduced in the rock samples from 44 to 55% during the capillary-dominated flows to approximately 8%. The above-mentioned observations were also verified using morphological analysis of residual oil clusters. The impacts of VES flooding on the pore-scale oil configuration and the fragmentation of large oil clusters were particularly evident at higher VES flow rates.

Modular, Portable, Automatically, Rapidly, Sensitive, and Selectively Essence Sensor System

The ESSENCE platform is an electrochemical sensor system that utilizes non-planar porous microelectrode microfluidic chips with a fully programmable fluidic/sample system to be a “portable, automatic, rapid, sensitive, and selective” for different emerging contaminants and liquid biopsy. The system is designed with non-planar porous microelectrode interfaces, containing different functional capturing probes for specific sensing tasks. From our previous report, this 3D non-planar structure has advantages such as increased flow’s convective fluxes and disrupts diffusive processes like the electric double layer (EDL). The porous electrode structure utilized the packing material’s higher Zeta potential than the bare glass surface, resulting in the EDL length will be significantly smaller than the clear channel. Due to a smaller EDL length, the relaxation frequency will increase, which shifts the EIS signal to a higher frequency range (1kHz to 100MHz) and results in a fast response with a higher signal-to-noise ratio in Electrochemical Impedance Spectroscopy (EIS) measurements. From the perspective of electric field penetration, the top-down electric direction covers all the packing sensing areas, providing a generally higher electronic signal response than the traditional planar electrode system, leading to a higher signal-to-noise ratio. A second feature from the perspective of microfluidics is the significant fluidic shear force generated due to flow through the porous electrode surface. This higher shear force on the surface can unbind most false-positive signals generated by non-specific binding, such as physical adhesive or biofouling. These unique benefits provide physical enhancements of sensitivity and selectivity without manipulating the chemical material in the system. Earlier we showed that our detection of the biomolecules like DNA (fM sensitivity, which can distinguish against a mismatched DNA), proteins (breast cancer biomarker p53, fM sensitivity, which can distinguish it against another breast cancer biomarker HER2), PFOS (Perfluorooctanesulfonate, 0.5 ng) under the traditional desktop Electrochemical Impedance Spectroscopy (EIS) analyzer in the total process of hourly. In this talk, we have further developed our previous ESSENCE platform to a modular, automatic, and portable, one-stop instrument for clinicians to screen for infectious diseases, liquid biopsy, and toxin detection to detect emerging pathogens while significantly reducing false positives and false negatives, but also decreasing our detecting process to 15 mins in much more hazard background conditions to meet the criteria of POC. Second, A small (15 cm x 17cm) USB programable fluidic/oscilloscope base with a 15 minutes total detecting protocol is applied to our ESSENCE system for a fast Point-of-care (POC) diagnostic. This portable ESSENCE platform can respond to the measurable EIS signals from the oscilloscope with 25 ul samples size (DNA and HER2 proteins in undiluted artificial Urine) with a fully automatic process at the uM to pM regions in 15 minutes. Each ESSENCE chip is also significantly cheaper than the ELISA; the chip costs about $20 (for an academic lab) and can be reused. Figure 1

Can Liposomes Survive Inkjet Printing? The Effect of Jetting on Key Liposome Attributes for Drug Delivery Applications

PurposeInkjet printing has the potential to enable novel personalized and tailored drug therapies based on liposome and lipid nanoparticles. However, due to the significant shear force exerted on the jetted fluids, its suitability for shear-sensitive materials such as liposomes, has not been verified. We have conducted a proof-of-concept study to examine whether the particle concentration and size distribution of placebo liposomes are affected by common inkjet/dispensing technologies.MethodsWe have subjected three types of liposome-containing fluids (“inks”) to two different commercial dispensing/jetting technologies, which are relevant to most drug printing approaches. The liposome jetting processes were observed in real-time using strobographic imaging techniques. The phospholipid concentrations and particle size distributions were determined before and after jetting via enzymatic colorimetric and dynamic light scattering methods, respectively.ResultsOur results have shown that the jetting dynamics of the liposome inks are well predicted by the established inkjet printing regime map based on their physical properties and the jetting conditions. Importantly, although significant shear forces were confirmed during jetting, the liposome concentrations and particle size distributions in the collected samples remain largely unaffected.ConclusionThese findings, we believe, provide the essential proof-of-concept to encourage further development in this highly topical research area.

Aerospace Technology Improves Fermentation Potential of Microorganisms.

It is highly possible to obtain high-quality microbial products in appreciable amounts, as aerospace technology is advancing continuously. Genome-wide genetic variations in microorganisms can be triggered by space microgravity and radiation. Mutation rate is high, mutant range is wide, and final mutant character is stable. Therefore, space microorganism breeding is growing to be a new and promising area in microbial science and has greatly propelled the development of fermentation technology. Numerous studies have discovered the following improvements of fermentation potential in microorganisms after exposure to space: (1) reduction in fermentation cycle and increase in growth rate; (2) improvement of mixed fermentation species; (3) increase in bacterial conjugation efficiency and motility; (4) improvement of the bioactivity of various key enzymes and product quality; (5) enhancement of multiple adverse stress resistance; (6) improvement of fermentation metabolites, flavor, appearance, and stability. Aerospace fermentation technology predominantly contributes to bioprocessing in a microgravity environment. Unlike terrestrial fermentation, aerospace fermentation keeps cells suspended in the fluid medium without significant shear forces. Space radiation and microgravity have physical, chemical, and biological effects on mutant microorganisms by causing alternation in fluid dynamics and genome, transcriptome, proteome, and metabolome levels.

Medial Locking Plate Can Increase the Fixation Stability of Vertical Femoral Neck Fracture in Young Adults?

Vertical femoral neck fractures in young adults are usually caused by a high-energy trauma. These injuries are difficult to stabilize due to significant shear forces acting on the fracture site. Their treatment is challenging and has a high risk of complications, such as fixation failure, malunion, nonunion and avascular necrosis of the femoral head. In recent years, several studies have focused on the use of direct reduction of vertical femoral neck fractures in young adult patients. This technique allows for anatomical reduction as well as the placement of an intra-articular implant to avoid shear forces at the fracture site. The aim of this study was to evaluate, based on in vitro experimental tests, the biomechanical stability provided by three different fixation methods: (i) dynamic hip screw with derotation screw, (ii) cannulated screws with a conventional medial bone plate and (iii) cannulated screws with a locked medial bone plate. For the biomechanical tests, these techniques were applied to reduce the vertical osteotomy performed on synthetic bones for later verification of the mechanical behavior under axial cyclic loading and destructive axial loading. There were no statistical differences in stiffness, micromovement displacement and mechanical strength during the biomechanical comparison of the fixation methods. Therefore, we conclude that the use of a conventional medial bone plate associated with cannulated screws, with a transverse trochanteric screw, supports the mechanical demand while the fracture is healing and this option can be used to stabilize vertical femoral neck fractures in young patients.

A scaling relationship between power and shear for Bernoulli pads at equilibrium

Bernoulli pads can create a significant normal force on an object without contact. The radial outflow which creates this force also imposes a significant shear force on the object. Better understanding this shear force can improve pad designs in order to mitigate material deformation and damage, or allow the pads to be used as shear-based cleaning implements. Here, we use computational fluid dynamics to explore the parameter space and show a power-law relationship between the fluid power at the pad inlet and the maximum shear stress. These simulations are validated by a particle tracking velocimetry experiment. A relationship between the maximum shear stress and the inlet Reynolds number is provided, and some implications of the observed scaling relationships are explored.

Insight into acute heat stress on meat qualities of rainbow trout (Oncorhynchus mykiss) during short-time transportation

The objective was to investigate the changes of meat qualities of rainbow trout (Oncorhynchus mykiss) under acute heat stress (T2) during short-time transportation. The antioxidative enzymes, energy substances of metabolism of trout meat were monitored, and the related biological pathway were clarified. Samples without transportation (Control), transported with temperature control (T1), and transported with 30 mg L−1 ascorbic acid (T3) were comparatively studied. The results showed that CAT, SOD and T-AOC activities and T-GSH content of transported fish muscle significantly declined (p < 0.05), especially in T2 group. Significant higher LD, MetMb%, pH, shear force and expressible moisture, lower muscle glycogen and L⁎value were obtained in the transported fish (p < 0.05), and the color and shear force did not recover after 24 h chilling storage. The result of transcriptomic sequences indicated that acute heat stress during transportation changed the meat qualities by inhibiting favored amino acid biosynthesis, while the addition of ascorbic acid reduced the activity intensity and energy demand to relieve acute heat stress.

Effect of synthetic bone replacement material of different size on shear stress resistance within impacted native and thermodisinfected cancellous bone: an in vitro femoral impaction bone grafting model

Antibiotic carrier particles of variable size might influence mechanic properties within impacted thermodisinfected and native cancellous bone different. Herafill®G containing calciumsulfate and calciumcarbonate provides high local concentrations of gentamicin being important for revision surgery in infected joint replacements. Native and thermodisinfected cancellous bone derived from 6 to 7 months old piglets was used for in vitro impaction bone grafting and supplemented each with Herafill®G granules of two different sizes. Micromovement of implants related to shear force was measured in 29 specimens distributed in 6 groups. Thermodisinfected cancellous bone revealed a significant higher shear force resistance than native bone with a mean difference of 423.8 mdeg/Nm (p < 0.001) ranging within 95% confidence interval from 181.5 to 666.0 mdeg/Nm. Adding small granules to thermodisinfected bone did not reduce shear force resistance significantly since adding large granules to native bone improved it by 344.0 mdeg/Nm (p < 0.003). Shear force resistance was found higher at the distal region of the implant compared to a proximal point of measurement throughout all specimens. Less impaction impulses were necessary for thermodisinfected bone. Thermodisinfected cancellous bone might achieve a higher degree of impaction compared with native bone resulting in increased resistance against shear force since impaction was found increased distally. Supplementation of thermodisinfected bone with small granules of Herafill®G might be considered for application of local antibiotics. Large granules appeared more beneficial for supplementation of native bone. Heterogeneity of bone graft and technical aspects of the impaction procedure have to be considered regarding the reproducibility of femoral impaction bone grafting.

Effects of Perfusion Pressures on Podocyte Loss in the Isolated Perfused Mouse Kidney.

Podocytes are lost in most glomerular diseases, leading to glomerulosclerosis and progressive kidney disease. It is generally assumed, that podocytes are exposed to the filtration flow and thus to significant shear forces driving their detachment from the glomerular basement membrane (GBM). In this context, foot process effacement has been proposed as potential adaptive response to increase adhesion of podocytes to the GBM. We have tested these hypotheses using optical clearing and high-resolution 3-dimensional morphometric analysis in the isolated perfused murine kidney. We investigated the dynamics of podocyte detachment at different perfusion pressures (50, 300 and more than 450 mmHg) in healthy young or old mice (20 vs. 71 weeks of age), or mice injected with anti-GBM serum to induce global foot process effacement. Results show that healthy podocytes in young mice are tightly attached onto the GBM and even supramaximal pressures did not cause significant detachment. Compared to young mice, in aged mice and mice with anti-GBM nephritis and foot process effacement, gradual progressive loss of podocytes had occurred already before perfusion. High perfusion pressures resulted in a relatively minor additional loss of podocytes in aged mice. In mice with anti-GBM nephritis significant additional podocyte loss occurred at this early time point when increasing perfusion pressures to 300 mmHg or higher. This work provides the first experimental evidence that podocytes are extraordinarily resistant to acutely increased perfusion pressures in an ex vivo isolated kidney perfusion model. Only in glomerular disease, significant numbers of injured podocytes detached following acute increases in perfusion pressure.

Rheological investigation of clay-stabilized oil-in-water Pickering emulsions for potential reservoir applications

Particle-stabilized Pickering emulsions are attracting increasing interest in oil and gas industries due to their unique rheological properties and stability. In this work, the rheological behavior of Na-montmorillonite stabilized oil-in-water (O/W) Pickering emulsions was studied under various salinities, pHs, clay concentrations and oil volume fractions. Results suggested that the Na-montmorillonite particles form a three dimensional network in water by different particle-particle interactions under specific salinity and pH values. The emulsion rheology can be explained by such clay interactions. The clay stabilized emulsion exhibits shear thinning behavior. At moderate salinities (around 0.25–5 wt% NaCl), the emulsion possesses a high viscosity of up to 100 mPa s at a shear rate of 7 s−1. Evidence suggests that a strong three dimensional clay network which connects the oil droplets is formed. The clay-droplet network possesses enough strength to withstand significant shear force, giving the emulsion a high bulk viscosity. Both too low and too high a salinity is unfavorable for maintaining a high emulsion viscosity. The gradual breakdown of the clay network with increasing shear rate accounts for the shear thinning behavior of the emulsion. The emulsion viscosity decreases with increasing pH as the clay-droplet network is more likely to form in an acidic environment. A two dimensional diagram summarizing the impact of salinity and pH on emulsion viscosity was generated. Emulsion viscosity also increases with clay concentration, but not always increases with oil volume fraction at a fixed clay concentration. The clay-stabilized emulsion shows significant elastic behavior. The clay network formed under a range of salinities and pHs is resilient to breakdown and has the ability to reform during strain, thus giving the emulsion a high elastic modulus. Our work shows that a clay-stabilized O/W emulsion system can possess high viscosity, shear thinning rheology and elasticity at high salinities and different pH of 3.3, 4.7, 6, 8, 9.5 and 11. These properties make the emulsion a potential candidate for various reservoir applications.

Performance optimization of a novel passive T-shaped micromixer with deformable baffles

Micromixers are critical components within microfluidic fluid handling and analysis systems. When it comes to micromixing of biological samples, the hydrodynamical forces acting on biological specimens are of great importance besides mixing quality. Although adding rigid obstacles to the microchannels has shown to improve the mixing performance, they create a considerable pressure drop and impose a significant shear force on biological specimens. To address these problems, deformable baffles have been introduced here as a novel tuning tool for controlling the mixing characteristics. To optimize the device performance (maximizing the mixing performance and minimizing the pressure loss), two optimization algorithms have been employed to find out the suitable baffle geometry and material property. The Taguchi method was proposed as a fast and cost-effective approach for single-objective optimization of the mixing index or the pressure drop, and the Pareto optimality concept was introduced for parallel optimization of the mixing efficiency and the pressure loss. The results show that replacing the rigid with deformable baffles significantly reduces the pressure drop (by approximately 50%), causing a significant reduction in the shear stress on biological samples while a small reduction on the mixing efficiency (10 to 15%) was observed.

An unusual presentation of morel- lavallee lesion in the arm: a case report

&lt;p class="abstract"&gt;Morel-lavallee lesions (MLL) are post traumatic closed internal de-gloving injury with abrupt separation of skin and subcutaneous tissue from the underlying fascia. The shearing force damages the blood vessels and lymphatics, resulting in collection of the serosanguinous fluid and necrotized fat. Early diagnosis and management minimize complications like infections or extensive skin necrosis. MLLs commonly described in pelvic and lower extremity trauma, and there are limited reports in other locations. A 28-year-old male presented with pain and swelling over the left elbow for 6 days with multiple deep bruises over the skin extending from mid arm to proximal forearm. Ultrasound of the arm revealed a large encapsulated collection consistent with MLL. An open debridement with excision of all necrotic skin and necrotic tissue was performed followed by skin grafting. Intra-operative cultures were negative and pathology was consistent with MLL. Morel-lavallee lesions should always be considered as early diagnosis of previous trauma regardless the location. The key to recognize this injury depends on suspicious mechanism involving significant shear forces. Aggressive surgical debridement remains the key to prevent significant morbidity and mortality.&lt;/p&gt;

A novel way to dynamize a spatial frame and optimize fracture healing

BackgroundFracture site motion creates mechanical strains on the healing tissues which influences bone formation. Axial micro-motion maximizes dilatational strains, whereas shearing motions maximize deviatoric strains on the healing tissues. Dilatational strains optimize bone healing, deviatoric strains retard bone healing. Dynamization of external fixation using either an Ilizarov or Spatial Frame platform is used to increase loading on the limb which increases the mechanical stress and strain on the tissues to improve healing. The scientific literature does not address how dynamization of the spatial frame effects fracture site motion. The purpose of this study is to assess the effect of modified shoulder bolts incorporated into a spatial frame during dynamic loading. MethodsFive identical two-ring spatial frame constructed were mounted on Sawbones tibias with an osteotomy performed distal to the tibial tubercle. Sinusoidal load was applied at a rate of 0.25 Hz. Axial force and displacement, in addition to motion of the proximal and distal tibia segments were recorded. Eight constructs were tested: 1) All struts of the Spatial Frame rigid, 2) Strut #1 loose, 3) Struts #1 and #3 loose, 4) Struts #1, #3 and #5 loose, 5) All struts loose, 6) All struts rigid with dynamization bolts on the proximal end, 7) All struts rigid with dynamization bolts on alternating sides, 8) Threaded rods between the rings with two millimeters of dynamization. ResultsNo difference in vertical displacement was observed between the Ilizarov and all struts locked. No significant difference in shear values between all struts locked and modified shoulder bolt struts was observed. Increase in vertical movement with the modified shoulder bolts was an average of 1.83 mm. Significant shear forces at the fracture site were observed with unlocking single or multiple struts of the spatial frame. ConclusionModified shoulder bolts can be used for spatial frame dynamization without increasing shear motion.