Extra Stress Research Articles

On the macroscopic modelling of dilute emulsions under flow

A new macroscopic model describing the rheology and microstructure of dilute emulsions with droplet morphology is developed based on an internal contravariant conformation tensor variable which is physically identified with the deformed ellipsoidal geometry of the dispersed phase. The model is consistent with existing first-order capillary number,$O(Ca)$, theory describing the microstructure as well as$O(Ca^{2})$theory describing the emulsion-contributed extra stress. These asymptotic solutions are also used to determine all of the model parameters, making it the only macroscopic emulsion model that is consistent with all available asymptotic theories in the limit of small$Ca$. The governing equations are obtained from the Poisson and dissipation brackets, as developed for an incompressible fluid system endowed with an internal contravariant second-order tensor, subject to the imposition of the constraint of a unit determinant. First proposed by Maffettone & Minale (J. Non-Newtonian Fluid Mech., vol. 78, 1998, pp. 227–241), this constraint physically corresponds to conservation of the volume of the dispersed phase in the emulsion. The Hamiltonian of the emulsion is expressed through the surface energy of the dispersed phase, in addition to the kinetic energy, following previous work by Grmelaet al.(J. Non-Newtonian Fluid Mech., vol. 212, 2014, pp. 1–12), but employing a more accurate evaluation of the surface area in terms of the internal contravariant conformation tensor. Structural predictions of the ellipsoid droplet morphology obtained with the new model are compared with classic experiments by Torzaet al.(J. Colloid Interface Sci., vol. 38, 1972, pp. 395–411), showing good agreement.

Balancing of Peak Currents Between Paralleled SiC MOSFETs by Drive-Source Resistors and Coupled Power-Source Inductors

The peak currents between two paralleled SiC MOSFETs could differ significantly due to the mismatch in threshold voltages $V_{{\rm{th}}}$ . The method described herein employs passive compensation (drive-source resistors and coupled power-source inductors) to balance the peak currents using one gate driver, no sensors, and no feedback—without increasing total switching loss when equivalent gate-drive resistance $(R_{g} + 0.5R_{k})$ is kept constant. This solution works for both polarities of $V_{{\rm{th}}}$ mismatch and forces balancing from the first current peak. The extra voltage stress from this solution is mitigated by negative coupling. The passive components (resistance, self-inductance, and mutual inductance) are determined by an equation involving the magnitude of $V_{{\rm{th}}}$ mismatch, current rise time, and unbalance percentage. The influence of other parasitic inductances on current sharing is analyzed. The robustness of this passive balancing method is experimentally verified by a prototype with a significant amount of parasitic inductances. Test results show that the difference of peak currents can be reduced from 15% to 3% without changing the switching loss and voltage stress.

Transient computations using the natural stress formulation for solving sharp corner flows

In this short communication, we analyse the potential of the natural stress formulation (NSF) (i.e. aligning the stress basis along streamlines) for computing planar flows of an Oldroyd-B fluid around sharp corners. This is the first attempt to combine the NSF into a numerical strategy for solving a transient fluid flow problem considering the momentum equation in Navier–Stokes form (the elastic stress entering as a source term) and using the constitutive equations for natural stress variables. Preliminary results of the NSF are motivating in the sense that accuracy of the numerical solution for the extra stress tensor is improved near to the sharp corner. Comparison studies among the NSF and the Cartesian stress formulation (CSF) (i.e. using a fixed Cartesian stress basis) are conducted in a typical benchmark viscoelastic fluid flow involving a sharp corner: the 4 : 1 contraction. The CSF needs a mesh approximately 10 times smaller to capture similar near singularity results to the NSF.

Dietary Restriction Ameliorates Age-Related Increase in DNA Damage, Senescence and Inflammation in Mouse Adipose Tissuey

Ageing is associated with redistribution of fat around the body and saturation of visceral adipose depots. Likewise, the presence of excess fat in obesity or during ageing places extra stress on visceral depots, resulting in chronic inflammation and increased senescence. This process can contribute to the establishment of the metabolic syndrome and accelerated ageing. Dietary restriction (DR) is known to alleviate physiological signs of inflammation, ageing and senescence in various tissues including adipose tissue.ObjectivesOur pilot study aimed to analyse senescence and inflammation parameters in mouse visceral fat tissue during ageing and by short term, late-onset dietary restriction as a nutritional intervention.Design, measurementsIn this study we used visceral adipose tissue from mice between 5 and 30 months of age and analysed markers of senescence (adipocyte size, γH2A.X, p16, p21) and inflammation (e.g. IL-6, TNFα, IL-1β, macrophage infiltration) using immuno-staining, as well as qPCR for gene expression analysis. Fat tissues from 3 mice per group were analysed.ResultsWe found that the amount of γH2A.X foci as well as the expression of senescence and inflammation markers increased during ageing but decreased with short term DR. In contrast, the increase in amounts of single or aggregated macrophages in fat depots occurred only at higher ages. Surprisingly, we also found that adipocyte size as well as some senescence parameters decreased at very high age (30 months).ConclusionsOur results demonstrate increased senescence and inflammation during ageing in mouse visceral fat while DR was able to ameliorate several of these parameters as well as increased adipocyte size at 17.5 months of age. This highlights the health benefits of a decreased nutritional intake over a relatively short period of time at middle age.

Family of Soft-Switching Bidirectional Converters With Extended ZVS Range

This paper proposes a family of soft-switching bidirectional converters. In many applications, the bidirectional converters operate over a wide range of duty cycle and load variations. In the proposed converters, in order to extend the zero-voltage switching operation range, two supplemental voltage sources utilizing passive components are implemented in the auxiliary circuit. By using this method, the soft-switching features are ensured for an extensive range of the converter duty cycles. This is achieved independent of the output power value or the converter operation mode, and so, soft switching is ensured within the entire converter operating region. In these converters, all semiconductors components are soft switched, and the auxiliary circuit does not contribute to the complexity of the control circuit. Also, no extra voltage stress exists on the main switches and the voltage stress on the auxiliary switches is lower than the main switches voltage stress. In this paper, the proposed bidirectional buck/boost converter is analyzed and to confirm the feasibility of the proposed method, experimental results of a 150-W prototype converter are presented.

XEN implant and UC3 ‐ what I learned from my first 20 cases

SummaryStarting with new glaucoma techniques gives a beginning surgeon some extra stress. In this session, we will go into more detail how to perform those techniques and to select the right patient for the right technique. We will elaborate more how to avoid pitfalls and how to handle complications intra‐ and postoperatively.

Modified dynamic stress concentration factor for twin tunnels using a novel approach of FEM-scattering

The frequent failure of newly built tunnels under earthquake loading has led to a broader range of research into assessing the effect of seismic waves on tunnels. Numerous researchers have worked on twin tunnels and the effect of wave scattering due to vibration of harmonic waves to date. As for the near-field wave scattering and range of the recording of the acceleration of the ground during an earthquake. However, little research has been conducted on a comprehensive scale. This study attempted to examine the scattering in Si-o-seh Pol Bridge, a monument in Isfahan city, using the Hankel’s function of the first and second kinds for near-field earthquakes (Northridge, Tabas and Kobe). All of scattering analysis were done through FESCAM code that designed and developed in MATLAB software as a toolbox by authors of this paper. The historic bridge of Si-o-seh Pol Bridge and its neighboring twin tunnels for subway were selected as a case study. The first kind of Hankel’s function was considered as a supplementary parameter to the seismic analysis using finite element method procedure. The amount of dynamic scattering of twin tunnels subjected seismic loads considered as extra strain and stress around tunnels using Hankel’s function results. The results between two cases with and without considering scattering waves of tunnels show that the mean horizontal displacement and the mean vertical displacement of Si-o-seh Pol Bridge can be increased about 28.8% and 30.11% respectively. The results of statistical analysis with Mann-Whitney test show that there is no significant difference between the seismic performance of Si-o-seh Pol Bridge with and without consideration of the scattering effect of the tunnels (P-Value=0.6>0.05). However, the results of this study versus the past studies reflect the fact that horizontal and vertical displacements when involving the tunnel are 34.10% increase and −48.51% decline, respectively. This means that the twin tunnels are effective in displacement of the adjacent monument from the engineering perspective.

CuInS2/ZnS Quantum Dots Conjugating Gd(III) Chelates for Near-Infrared Fluorescence and Magnetic Resonance Bimodal Imaging.

A bimodal contrast nanoagent was developed by chelating gadolinium ions to 2-[bis[2-[carboxymethyl-[2-oxo-2-(2-sulfanylethyl-amino)ethyl]amino]ethyl]amino]acetic acid (DTDTPA)-modified CuInS2/ZnS quantum dots (QDs). The longitudinal relaxivity (r1) of the resulted QDs@DTDTPA-Gd nanoparticles (NPs) was calculated to be 9.91 mM-1 s-1, which was 2.5 times as high as that of clinically approved Gd-DTPA (3.9 mM-1 s-1). In addition, the in vivo imaging experiments showed that QDs@DTDTPA-Gd NPs could enhance both near-infrared fluorescence and T1-weighted magnetic resonance (MR) imaging of tumor tissue through passive targeting accumulation. Moreover, the high colloidal and fluorescence stabilities and good biocompatibility indicate that QDs@DTDTPA-Gd NPs have a great potential for use as an efficient nanoagent to integrate the extremely high sensitivity of fluorescence imaging to the high resolution of MR imaging. Integration of bimodal detectability in the same agent of QDs@DTDTPA-Gd NPs can avoid extra stress on the blood clearance mechanisms as the administration of multiple dose of agents.

English

A novel ‘dilution tube method’ (DTM) which is a modification of the ‘dilution method’ (DM) is hereby described for the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). This new DTM uses only broth medium in tubes and the required antibiotic. MIC and MBC for Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus were determined in tubes by double diluting (or higher dilutions), broths containing gentamicin concentrations that inhibit bacterial growth, and incubating at 37°C for 18 to 24 h. The tube for MIC showed growth and appeared turbid after incubation while that for MBC remained clear. The results obtained using DTM agrees completely with those obtained with DM. The advantages of this novel DTM include the elimination of extra stress, time and costs associated with preparing and inoculating agar medium as done in DM. Key words: Antibiotics, minimum inhibitory concentration, minimum bactericidal concentration, dilution tube method, dilution method.

A highly efficient ZVT–ZCT PWM boost converter with direct power transfer

In this paper, a high-efficiency ZVT–ZCT PWM boost converter with direct power transfer is proposed. In the proposed converter, the main switch turns on with zero voltage transition and turns off with zero current transition. The main diode turns on with zero voltage switching and turns off with zero current switching. All of the other semiconductors in the converter turn on and off with soft switching. There is no extra current or voltage stress on the main semiconductors. The most important feature of the proposed converter is that it has direct power transfer. So, the efficiency of converter can be increased. Also, it has features as low cost, simple structure and easy control. In this study, detailed theoretical analysis of the proposed converter is made by operation intervals. A prototype with 500 W output power and 100 kHz switching frequency is realized in laboratory. It is shown that the experimental results are compatible with theoretical analysis. The efficiency of the proposed converter is 98.9% at nominal power.

Two novel p38 MAPKs identified from Epinephelus coioides and their expression pattern in response to Cryptocaryon irritans infection

P38 mitogen-activated protein kinases (MAPKs) are one of the most important central regulatory proteins response to extra environmental stresses. In this study, two novel p38 MAPKs, Ec-P38γ and Ec-P38δ, were identified from Epinephelus coioides, an economically important cultured fish in China and Southeast Asian counties. Both of Ec-p38γ and Ec-p38δ sequences contain a serine/threonine protein kinase (S_TKc) domain and a highly conserved Thr-Gly-Tyr (TGY) motif. Analysis of phylogenetic relationships illustrated that p38 amino acid sequences were conserved between different species indicating that the functions may be similar. The four subtypes of p38 (α, β, γ, and δ) mRNA can be detected in all thirteen tissues examined, but the expression level is different in these tissues. The expression patterns of the four Ec-p38 subtypes in E. coioides were also detected response to Cryptocaryon irritans infection, one of the most important protozoan pathogens of marine fish. The expression of four p38 subtypes was up-regulated in the tissues examined, with the highest expressions of Ec-p38α (5.2 times) and Ec-p38δ (4.2 times) occurring in the skin, while Ec-p38β (24.8 times) and γ (16.6 times) occurred in the spleen. There was no significantly correlation between the expression of Ec-p38γ/Ec-p38δ and the expression of nuclear factor kappaB (NF-kB). The results indicated the sequences and the characters of Ec-p38γ and Ec-p38δ were conserved, the p38 subtypes showed tissue-specific expression patterns in healthy grouper, and their expressions were significantly up-regulated post C. irritans infection, suggesting these p38 MAPKs may play important roles in these tissues during pathogen-caused inflammation.

Numerical analysis of the mechanical behavior of ZTAp/Fe composites

Composites are complex and inhomogeneous. Various factors of microstructure will affect their mechanical behaviors. Based on a systematic numerical analysis, we present a coupling effect of the volume fraction of reinforced particles and the particle-matrix interface properties on the mechanical properties of ZTAp/Fe composites. We find that for yield limit and peak stress, the particle-matrix interface properties show a dominant impact while for the critical strain the particle volume fraction is the main factor. A combined effect of the particle volume fraction and the interface properties is found on the elastic modulus. The von Mises stress distributions are investigated and the results show that the particles clustered in the direction perpendicular to tensile load have larger debonding potential. In addition, the probability of particle cracking and the number of interface debonding are investigated to analyze the damage mechanism of the composites. We find that strong bonded interface can withstand more extra stress and protect the particle from cracking. The interface debonding rate becomes smooth after some critical value as the strain increases continuously due to a steady crack propagation after crack initiation along the interface line. This paper provides a guidance towards the design of advanced ceramic particle reinforced metal matrix composite materials.

A partition-of-unity based three-node triangular element with continuous nodal stress using radial-polynomial basis functions

A partition-of-unity (PU) based “FE-Meshfree” three-node triangular element (Trig3-RPIM) was recently developed for linear elastic problems. This Trig3-RPIM element employs hybrid shape functions that combine the shape functions of three-node triangular element (Trig3) and radial-polynomial basis functions for the purpose of synergizing the merits of both finite element method and meshfree method. Although Trig3-RPIM element is capable of obtaining higher accuracy and convergence rate than the Trig3 element and four-node iso-parametric quadrilateral element without adding extra nodes or degrees of freedom (DOFs), the nodal stress field through Trig3-RPIM element is not continuous and extra stress smooth operations are still needed in the post processing stage. To further improve the property of Trig3-RPIM element, a new PU-based triangular element with continuous nodal stress, called Trig3-RPIMcns, is developed. Numerical examples including several linear, free vibration and forced vibration test problems, have confirmed the correctness and feasibility of the proposed Trig3-RPIMcns element.

Lagrangian Mesh Model with Regridding for Planar Poiseuille Flow

AbstractMany biological settings involve complex fluids that have non-Newtonian mechanical responses that arise from suspended microstructures. In contrast, Newtonian fluids are liquids or mixtures of a simple molecular structure that exhibit a linear relationship between the shear stress and the rate of deformation. In modeling complex fluids, the extra stress from the non-Newtonian contribution must be included in the governing equations.In this study we compare Lagrangian mesh and Oldroyd-B formulations of fluid-structure interaction in an immersed boundary framework. The start-up phase of planar Poiseuille flow between two parallel plates is used as a test case for the fluid models. For Newtonian and Oldroyd-B fluids there exist analytical solutions which are used in the comparison of simulation and theoretical results. The Lagrangian mesh results are compared with Oldroyd-B using comparable parameters. A regridding algorithm is introduced for the Lagrangian mesh model. We show that the Lagrangian mesh model simulations with regridding produce results in close agreement with the Oldfoyd-B model.

Flow-resistive Inspiratory Muscle Training Improves Running Time To Exhaustion With Thoracic Load Carriage

Exercise while carrying an external load upon the thoracic cavity imposes extra stress on the cardiopulmonary and limb locomotor systems. This in turn, negatively impacts exercise tolerance and performance, as well as pulmonary and respiratory muscle function. Thoracic load carriage exercise (LC) has been shown to induce global respiratory muscle fatigue as assessed by volitional mouth pressures, with a concomitant impairment in running time-trial performance. Inspiratory muscle training (IMT) has been shown to improve performance in a running time-trial with thoracic LC. However, in many occupational and recreational activities that require thoracic LC, the capacity to sustain prolonged exercise may be of equal or greater importance than performance in a time-trial. PURPOSE: To determine the efficacy of 6 weeks of flow-resistive IMT on running time to exhaustion with thoracic LC; and to determine whether 6 weeks of flow-resistive IMT moderates diaphragmatic fatigue that may occur following a thoracic LC running time to exhaustion test. METHODS: Twelve recreationally active males completed two runs to exhaustion (Tlim) at a fixed speed eliciting 70 % of V˙O2max while carrying a 10 kg backpack. Visits were completed at baseline and after 6 weeks of either IMT or placebo-IMT. Exercise metabolic and ventilatory measures were recorded and diaphragm strength was measured using bilateral phrenic nerve stimulation in conjunction with esophageal balloon-tipped catheters to measure intrathoracic pressures. Twitch transdiaphragmatic pressure amplitude was recorded pre-exercise and immediately post-exercise in both trials. Maximal volitional mouth pressures (PImax) were recorded at baseline and post-IMT. RESULTS: 6 weeks of IMT significantly improved Tlim (p = 0.029, %Δ +29.3 ± 6.4 % IMT, -8.8 ± 11.1 %), but did not alter the change in diaphragm strength following a run to exhaustion (p > 0.05). The %Δ in PImax from pre- to post-training was significantly correlated with the %Δ in Tlim from pre- to post-training (p = 0.031, r = 0.622). No changes were observed in minute ventilation or breathing mechanics (all p > 0.05). CONCLUSIONS: IMT improves exercise tolerance with thoracic LC, but does not attenuate the severity of diaphragmatic fatigue following a running time to exhaustion test.

Multilayer Mg–Stainless Steel Sheets, Twinning and Texture Evolution

In the present study, different combinations of multilayer sheets were prepared from 1 and 2 mm Mg AZ31 along with 0.25, 0.5, and 1 mm 304 L stainless steel. The texture and microstructure of the elongated samples (20 and 30 pct strain) were studied. It was found that the transversal stress plays an important role in both texture evolution and twinning in these composites. The obtained pole figures revealed an axial texture tilt with increasing steel layer volume fraction (Vf). It was found that this is a direct effect of transverse stress, which becomes more significant upon reducing Mg Vf. This extra stress component tilts the basal planes away from the original normal direction in monolithic samples. Moreover, our results indicate that with decreasing Mg Vf, twinning activity was increased in the 20 pct deformed samples but reduced in the samples with 30 pct elongation. It is known that at high strains where sufficient transverse stress is generated, the activity of prismatic slip is significantly enhanced, which promotes the motion of dislocations and reduces the necessity of twinning. With decreasing Mg Vf, stronger transversal stress is generated and Mg reaches the critical threshold of prismatic activity at lower strains.

Soft switched SVPWM controlled PRDCL inverter

In this study, soft switched space vector PWM controlled parallel-resonant DC link (PRDCL) inverter is proposed for fuel cells (FC) applications. The proposed circuit is applied to an induction motor to evaluate the converter system. Application and simulation results are compared and the results are both compatible. It is observed that all the semiconductor switches in the circuit are turned on and off nearly zero voltage switching (ZVS) or zero current switching (ZCS). There are no additional extra voltage stress on the main switch. The semiconductor switching losses are obtained with considering the module temperature variation. The proposed soft switched SVPWM controlled PRDCL inverter has 95.3% efficiency at full load.

Technologies and application of pipeline centerline and bending strain of In-line inspection based on inertial navigation

Inertial mapping unit (IMU) in-line inspection (ILI) has become routine practice for long-distance buried transport pipelines of oil and gas. It is capable of measuring the pipeline centerline position coordinates and locating the pipeline anomalies, features and fittings to help the oil company manage it. The IMU inspection data also can be used to compute the pipeline bending strain and assess the potential deviation from the original position where endures the extra stress. This paper introduces the main principle, measurement and data processing for IMU ILI. As a key point of calculation for centerline and bending strain, the identification and optimization of the signal are also discussed. At the end of this paper, the developments of IMU ILI are presented. The IMU ILI becomes an important and effective method for pipeline integrity management and safe operation of buried oil and gas pipelines.

Effect of Pr addition on properties and Sn whisker growth of Sn–0.3Ag–0.7Cu low-Ag solder for electronic packaging

In this study, trace amount of rare earth Pr was added into Sn–0.3Ag–0.7Cu low-Ag solder to enhance properties of solders. Experimental results indicated that optimal amount of Pr addition (~0.06 wt%) can improve properties of wettability, shear force and ductility of Sn–0.3Ag–0.7Cu low-Ag solder. This is because that solder with optimal Pr addition not only had a refined microstructure but also owned a regular and thin interfacial IMC layer after soldering on Cu substrate. Meanwhile, we have explained the change of morphology and thickness of interfacial IMC layer after Pr addition based on Kim and Tu’s kinetic model of interfacial IMC growth. However, it was found excessive Pr addition led to the formation of PrSn3 phase, which was easy to be oxidized and became a great deterioration on the properties referred above. Besides, the fracture mode of solder joint also gradually changed from ductile fracture to cleavage fracture. Moreover, this oxidized PrSn3 became the birthplace of Sn whisker since it provided abundant supply of Sn sources and compressive stress for Sn whisker growth. By the in-situ observation of Sn whisker growth in 0.5 wt% Pr-doped solder joint, we obtained that the incubation period of Sn whisker is very short and its growth rate may have a great decrease with time extending. Besides, it was found after 1 day at room temperature, spindly and rod-like Sn whiskers also grew in 0.5 wt% Pr-doped solder joint besides dot-shaped Sn whisker that grew in 0.5 wt% Pr-doped solder matrix. We suggest this may be related with the extra compressive stress provided by interfacial IMC layer growth in 0.5 wt% Pr-doped solder joint.

Modeling of complex fluids using micro-macro approach with transient network dynamics

In this work, the micro-macro approach is used to simulate the flow of dilute polymer solutions by means of a kinetic model coupled with the dynamics of a transient network. The transient network modeling is based on the original formulation, in which the kinetics of microstates describes the complexity of interactions among the macromolecules suspended in a Newtonian solvent (Rincon et al, J Non-Newton Fluid 131:64–77, 2005). The average concentration of microstates, at a given time, defines a variable maximum segment length (variable extensibility) of the molecular FENE model. The non-Newtonian contribution to the extra stress tensor is computed according to the Brownian configuration-fields method. Comparisons with the Oldroyd-B model validates its limiting behavior. Numerical results show the influence of the solvent to total viscosity ratio and shear rate, on the transient and steady rheological phenomena of complex fluids with microstates.