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Shear stress

A Benditz, S Auer, J F Spörrer, S Wolkerstorfer, J Grifka, F Suess, S Dendorfer
INTRODUCTION: The number of spinal fusion surgeries is steadily increasing and biomechanical consequences are still in debate. The aim of this study is to provide biomechanical insights into the sagittal balance of the spine and to compare spinal load before and after spinal fusion. METHOD: The joint reaction forces of 52 patients were analyzed in proximo-distal and antero-posterior direction from the levels T12-L1 to L5-S1 using musculoskeletal simulations. RESULTS: In 104 simulations, pre-surgical forces were equal to post-surgical...
January 19, 2018: European Spine Journal
Alexandra Lauric, James E Hippelheuser, Adel M Malek
BACKGROUND: Subtracted 3-D rotational angiography (3DRA) and cone-beam computed tomography angiography (CBCT-A) are often used in assessing cerebral aneurysm shape and haemodynamic profile. We sought to evaluate the effect of imaging modality, reconstruction parameters, and kernel selection on patient-derived aneurysm morphology and computational fluid dynamic (CFD) analysis to assess its potential contribution to inter-study variability. METHODS: Four patients (five aneurysms) underwent concurrent 3DRA followed by high-resolution CBCT-A...
January 19, 2018: Journal of Neurointerventional Surgery
K S Jayaprakash, A K Sen
We report the continuous splitting of aqueous droplets at the interface between two co-flowing immiscible oil streams in a microchannel. The aqueous droplets initially present in a primary continuous stream (CP1) migrate into a secondary continuous stream (CP2) when the ratio of the non-inertial lift force to the interfacial tension force exceeds a critical value (K. S. Jayaprakash, U. Banerjee and A. K. Sen, Langmuir, 2016, 32, 2136-2143). Here, experiments were performed to understand the droplet splitting phenomenon and demonstrate the splitting of droplets encapsulating microbeads and cells...
January 19, 2018: Soft Matter
Yan Feng, Wei Lin, M S Murillo
Transport properties of two-dimensional (2D) strongly coupled dusty plasmas have been investigated in detail, but never for viscosity with a strong perpendicular magnetic field; here, we examine this scenario using Langevin dynamics simulations of 2D liquids with a binary Yukawa interparticle interaction. The shear viscosity η of 2D liquid dusty plasma is estimated from the simulation data using the Green-Kubo relation, which is the integration of the shear stress autocorrelation function. It is found that, when a perpendicular magnetic field is applied, the shear viscosity of 2D liquid dusty plasma is modified substantially...
November 2017: Physical Review. E
Nikolai V Priezjev, Maxim A Makeev
Molecular dynamics simulations are carried out to investigate mechanical properties and porous structure of binary glasses subjected to steady shear. The model vitreous systems were prepared via thermal quench at constant volume to a temperature well below the glass transition. The quiescent samples are characterized by a relatively narrow pore size distribution whose mean size is larger at lower glass densities. We find that in the linear regime of deformation, the shear modulus is a strong function of porosity, and the individual pores become slightly stretched while their structural topology remains unaffected...
November 2017: Physical Review. E
Anaël Lemaître
After constructing a formalism to analyze spatial stress correlations in two-dimensional equilibrated liquids, we show that the sole conjunction of mechanical balance and material isotropy demands all anisotropic components of the inherent state (IS) stress autocorrelation matrix to decay at long range as 1/r^{2} in the large system size limit. Furthermore, analyzing numerical simulation data for an equilibrated supercooled liquid, we bring evidence that, in finite-sized periodic systems, the autocorrelations of pressure and shear stresses present uniform backgrounds of amplitudes proportional to the inverse cell area...
November 2017: Physical Review. E
Mathijs F J Vermeulen, Anwesha Bose, Cornelis Storm, Wouter G Ellenbroek
Disordered spring networks that are undercoordinated may abruptly rigidify when sufficient strain is applied. Since the deformation in response to applied strain does not change the generic quantifiers of network architecture, the number of nodes and the number of bonds between them, this rigidity transition must have a geometric origin. Naive, degree-of-freedom-based mechanical analyses such as the Maxwell-Calladine count or the pebble game algorithm overlook such geometric rigidity transitions and offer no means of predicting or characterizing them...
November 2017: Physical Review. E
Hisao Hayakawa, Satoshi Takada, Vicente Garzó
The Enskog kinetic theory for moderately dense gas-solid suspensions under simple shear flow is considered as a model to analyze the rheological properties of the system. The influence of the environmental fluid on solid particles is modeled via a viscous drag force plus a stochastic Langevin-like term. The Enskog equation is solved by means of two independent but complementary routes: (i) Grad's moment method and (ii) event-driven Langevin simulation of hard spheres. Both approaches clearly show that the flow curve (stress-strain rate relation) depends significantly on the volume fraction of the solid particles...
October 2017: Physical Review. E
Keng-Lin Lee, Fu-Ling Yang
We propose a constitutive model to describe the nonlocality, hysteresis, and several flow features of dry granular materials. Taking the well-known inertial number I as a measure of sheared-induced local fluidization, we derive a relaxation model for I according to the evolution of microstructure during avalanche and dissipation processes. The model yields a nonmonotonic flow law for a homogeneous flow, accounting for hysteretic solid-fluid transition and intermittency in quasistatic flows. For an inhomogeneous flow, the model predicts a generalized Bagnold shear stress revealing the interplay of two microscopic nonlocal mechanisms: collisions among correlated structures and the diffusion of fluidization within the structures...
December 2017: Physical Review. E
Oleg Schilling, Nicholas J Mueschke
Data from a 1152×760×1280 direct numerical simulation [N. J. Mueschke and O. Schilling, Phys. Fluids 21, 014106 (2009)PHFLE61070-663110.1063/1.3064120] of a Rayleigh-Taylor mixing layer modeled after a small-Atwood-number water-channel experiment is used to investigate the validity of gradient diffusion and similarity closures a priori. The budgets of the mean flow, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate transport equations across the mixing layer were previously analyzed [O...
December 2017: Physical Review. E
L Amarsid, J-Y Delenne, P Mutabaruka, Y Monerie, F Perales, F Radjai
By means of extensive coupled molecular dynamics-lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments...
July 2017: Physical Review. E
Bruno Chareyre
The effective stress model of Khamseh et al., Phys. Rev. E 92, 022201 (2015)PLEEE81539-375510.1103/PhysRevE.92.022201 is in semiquantitative agreement with the shear stress in simulated steady state flow of a wet granular material. Nonetheless, the predictions are increasingly biased at low normal pressure. The approximation of the capillary stress by a spherical tensor in this model is a sufficient cause of the prediction errors, as shown in this Comment. The re-examination reveals an excellent agreement between the data and the effective stress expression formerly introduced for similar systems, further validating a yet unexplained empirical result...
July 2017: Physical Review. E
Saeed Khamseh, Jean-Noël Roux, François Chevoir
In his Comment on our paper [Phys. Rev. E 92, 022201 (2015)10.1103/PhysRevE.92.022201], Chareyre criticizes, as inaccurate, the simple approach we adopted to explain the strong enhancement of the quasistatic shear strength of the material caused by capillary cohesion. He also observes that a similar form of the "effective stress" approach, accounting for the capillary shear stress, which we neglected, results in a quantitatively correct prediction of this yield stress. We agree with these remarks, which we deem quite relevant and valuable...
July 2017: Physical Review. E
Meng Fan, Kai Zhang, Jan Schroers, Mark D Shattuck, Corey S O'Hern
Amorphous materials such as metallic, polymeric, and colloidal glasses exhibit complex preparation-dependent mechanical response to applied shear. In particular, glassy solids yield, with a mechanical response that transitions from elastic to plastic, with increasing shear strain. We perform numerical simulations to investigate the mechanical response of binary Lennard-Jones glasses undergoing athermal, quasistatic pure shear as a function of the cooling rate R used to prepare them. The ensemble-averaged stress versus strain curve 〈σ(γ)〉 resembles the spatial average in the large size limit, which appears smooth and displays a putative elastic regime at small strains, a yielding-related peak in stress at intermediate strain, and a plastic flow regime at large strains...
September 2017: Physical Review. E
Jie Lin, Wen Zheng
The yielding transition of amorphous solids is a phase transition with a special type of universality. Critical exponents and scaling relations have been defined and proposed near the yield stress. We show here that, even in the initial stage of shear far below the yield stress, the stress-strain curve of amorphous solids also shows critical scaling with universal exponents. The key point is to remove the elastic part of the strain, and the shear stress exhibits a sublinear scaling with the plastic strain. We show how this critical scaling is related to the finite size effect of the minimum strain to trigger the first plastic avalanche after a quench...
September 2017: Physical Review. E
Zhaosheng Yu, Zhaowu Lin, Xueming Shao, Lian-Ping Wang
A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84%, and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10...
September 2017: Physical Review. E
Xiaokun Yang, Shawn P Coleman, Jerry Lasalvia, William A Goddard, Qi An
The roles of grain boundaries (GB) in mechanical properties have been examined extensively for metals and alloys; however, for covalent solids their roles in deformation response to applied stress are much less established. We consider here the unusual ceramic, boron carbide (B4C), which is very hard and lightweight but exhibits brittle impact behavior. We used quantum mechanics (QM) simulations to determine the mechanical response in the atomistic structures at GBs under pure shear and also with biaxial shear deformation that mimics indentation stress conditions...
January 18, 2018: ACS Applied Materials & Interfaces
Sehoon Jeong, Sunja Kim, John Buonocore, Jaewon Park, C Jane Welsh, Jianrong Li, Arum Han
OBJECTIVE: The blood-brain barrier (BBB) poses a unique challenge to the development of therapeutics against neurological disorders due to its impermeabi-lity to most of the chemical compounds. Most in vitro BBB models have limitations in mimicking in vivo conditions and functions. Here, we show a co-culture microfluidic BBB-on-a-chip that provides interactions between neurovascular endothelial cells and neuronal cells across a porous polycarbonate membrane, which better mimics the in vivo conditions, as well as allows in vivo level shear stress to be applied...
February 2018: IEEE Transactions on Bio-medical Engineering
Johan Petrini, Margareta Ring, Anders Franco-Cereceda, Kenneth Caidahl, Maria J Eriksson
BACKGROUND AND AIMS: Intima-media thickness is a marker for atherosclerosis but is also influenced by shear stress and flow. We evaluated the relation between intima-media thickness of the descending aorta (AoIMT) and the common carotid artery (CIMT) in patients with and without severe aortic valve disease (sAVD). METHODS: A total of 310 patients (233 with sAVD, 77 without) were examined with regard to AoIMT and CIMT using transesophageal echocardiography and carotid ultrasound, respectively, before valvular and/or aortic surgery...
January 17, 2018: Clinical Physiology and Functional Imaging
Seung Min Chung, Jung Hyun Oh, Jun Sung Moon, Yu Kyung Kim, Ji Sung Yoon, Kyu Chang Won, Hyoung Woo Lee
Critical shear stress (CSS, mPa) is an index of red blood cell (RBC) aggregability, defined as the minimal shear stress required to disperse RBC aggregates. This study aimed to investigate the association between CSS and the risk of diabetic kidney disease (DKD). A total of 421 (mean age, 58.1 ± 11.5 years; male, 250) individuals with T2DM were enrolled and divided into three groups according to CSS level. CSS was measured using a transient microfluidic technique. DKD was defined as a glomerular filtration rate (GFR) <60 ml/min/1...
January 17, 2018: Scientific Reports
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