Translational Slip Research Articles

Spondilolysthesis L5-S1: An Original Article

Objectives: To assess the clinical, functional and radiological outcome of Posterior Lumbar Interbody Fusion (PLIF) by Banana cage with bone graft. Material and Methods: This retrospective analytical study was carried out in unit of Orthopaedic surgery department from January 2010 to December 2020. We did PLIF by Banana cage with bone graft for High-grade Lumbar Spondylolisthesis at L5-S1. The follow up period ranges from 1 year to 2 years (average 18 months). Within these follow up period we have assessed the patients clinically, functionally and radiologically. All patients were assessed by Visual Analogue Score (VAS), Oswestry Disability Index (ODI), Waddell Disability Index (WDI), Spino-pelvic parameters, Modified Macnab’s Criteria to find out overall outcome and Hackenberge ctriteria for radiological fusion. Results and Conclusions: Total 40 patients were included among them 16were male and 24 were female. The average age of the patients was 52.45±10.1 years. Maximum (60.0%) patients were housewife followed by 20.0%, 10.0%, 10% were day laborer, farmer and service holder respectively. Average pelvic tilt was 26.05±6.27° preoperatively and 24.10±6.26° at the final follow-up, average PI was 66.07±7.39° preoperatively and 61.19±7.08° at the final follow-up. Preoperative lumbar lordosis was 45.55±6.71° with postoperatively 37.29±6.19°at final follow-up. VAS score and ODI scales were improved significantly from preoperative 6.90±6.16 and 57.60±15.66, respectively, to postoperatively and final follow-up 2.0±0.8 and 7.60±2.40, respectively. Pre-operative Translation ratio, slip angle and disc height ratio were 21.96±10.25, -18.87±8.28, 11.03±4.36 respectively and postoperatively 13.17±6.57, -18.44±7.12, 19.60±3.36 respectively. Fusion was achieved in 36 cases (90%), 3 cases (7.5%) were fragmented and pseudoarthrosis showed only 1 case (2.5%). Most of the study population according to post operative clinical outcome showed excellent outcome (95%), 1 (2.5%) case had good and 1 (2.5%) case had fair outcome. Conclusion: It can be concluded that, Posterior Lumbar Interbody Fusion (PLIF) by Banana cage with bone graft can be a very good option for the treatment of High-grade Lumbar Spondylolisthesis at L5-S1 levels.

A Switched Adaptive Controller for Robotic Gripping of Novel Objects With Minimal Force

We present the design and implementation of an algorithm, equipped with a switched adaptive controller, for grasping unknown objects using a robot gripper. A Lyapunov-based analysis demonstrates that the switching controller is indeed asymptotically stable with both the translational and rotational slip velocities converging to the origin. Experimental results using a novel sensorized gripper prototype and objects of different sizes, shapes, and weights show that the proposed algorithm not only ensures the prevention of slippage of the grasped objects, but is also able to apply the minimal force needed to safely grasp these objects without causing excessive deformation.

A closed form solution for the internal stability of landfills considering spatial variability of the input seismic motion

The scope of this paper is to develop a calculation method of a closed form solution for the internal stability of the landfill considering spatial variability of the input seismic motion based on log-spiral combined sliding surface. A calculation method for multi-point seismic load of the log-spiral combined sliding surface landfill was proposed, which used to establish the multi-point seismic stability calculation model of the log-spiral combined sliding surface landfill. The calculation results for a typically shaped landfill of this method showed a lower result comparing with the method considering pseudo-static seismic action and translational slip surface. Thus, the coupling effect of the internal sliding of the landfill and multi-point seismic action should not be ignored in the seismic design of landfills.

214. MRI proxies for segmental instability in degenerative lumbar spondylolisthesis patients

<h3>BACKGROUND CONTEXT</h3> Lumbar degenerative spondylolisthesis (LDS) has a heterogeneous nature. Some patients have a dynamic component of segmental instability associated with LDS which complicates the surgical treatment. The radiological diagnosis of instability has been based on dynamic radiographs. But studies have shown that magnetic resonance imaging (MRI) can show signs of instability. These MRI proxies (MRIPs) for instability involves disc height, facet joint angle and effusion. <h3>PURPOSE</h3> To investigate whether findings on MRI can be proxies for segmental instability in patients with degenerative lumbar spinal stenosis (LSS) and/or LDS. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> Patients with LSS or LDS at L4/L5 scheduled for decompressive surgery with or without fusion from 2010 to 2017, with preoperative standing lateral spine radiographs and supine lumbar MRI and enrolled in Danish national spine surgical database, DaneSpine, 2-year follow-up. <h3>OUTCOME MEASURES</h3> Radiograph: sagittal translation (slip, mm). MRIPs for instability: sagittal translation (slip, mm), facet joint angle (FJA, degree), facet joint effusion (mm), disc height index (DHI, %) and presence of vacuum phenomena. <h3>METHODS</h3> Instability was defined as slip of > 3 mm on standing lateral radiographs. Patients were divided into two groups based on presence of instability. Slips >3mm were considered unstable and slips 3 mm on radiograph as the dependent variable and MRIPs for instability as independent variables. <h3>RESULTS</h3> A total of 232 patients in the cohort divided into two groups: 47 in the stable group and 185 in the unstable group. The two groups were comparable with regard to baseline patient-reported outcome measures (PROMs). Cut points for MRIPs for instability: bilateral FJA = 46°(AUC: 0.644, 95 % CI: [0.566 – 0.722]); bilateral facet effusion = 1.5mm (AUC: 0.601, 95 % CI: [0.536 – 0.666]) and DHI = 13 % (AUC: 0.613, 95 % CI: [0.537 – 0.689]). Logistic regression showed statistically significant association with > 3mm slip on MRI (OR: 221.5; SE: 201.0; 95% CI [37.4 – 1311.5]; p<0.001), bilateral FJA = 46°(OR: 5.6; SE: 3.0; 95% CI [1.9 – 16.1]; p=0.002), bilateral facet effusion = 1.5 mm (OR: 4.5; SE: 2.5; 95% CI [1.5 – 13.7]; p=0.009) and DHI = 13 % (OR: 9.1; SE: 7.5; 95% CI [1.8 – 46.0]; p=0.007). ROC curve with an AUC 0.951. In the absence of slip on MRI logistic regression showed statistically significant association between instability on radiograph and the remaining MRIPs: bilateral FJA = 46°(OR: 3.1; SE: 1.4; 95% CI [1.3 – 7.3]; p=0.008), facet effusion = 1.5 mm(OR: 2.4; SE: 0.9; 95% CI [1.2 – 4.9]; p=0.017) and DHI = 13 % (OR: 12.7; SE: 13.1; 95% CI [1.7 – 96.1]; p=0.014). ROC curve with AUC 0.757. <h3>CONCLUSIONS</h3> Presence of MRIPs for instability defined as >3 mm slip on MRI, bilateral FJA = 46°, bilateral facet effusion = 1.5 mm and DHI = 13% showed statistically significant association with instability and excellent ability to predict instability on standing radiograph at L4/L5 in LSS and LDS patients. Even in the absence of slip on MRI the MRIPs had a good ability to discriminate presence of instability. Further studies will determine whether presences of MRIPs makes radiographs obsolete at diagnosing segmental instability. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Clinical, Functional and Radiological Outcome of Posterior Lumbar Interbody Fusion by Banana Cage with Bone Graft for the Treatment of High-grade Lumbar Spondylolisthesis at L5-S1

Objectives: To assess the clinical, functional and radiological outcome of posterior lumbar interbody fusion (PLIF) by Banana cage with bone graft. Material and Methods: This retrospective analytical study was carried out in spine unit of Orthopaedic surgery department of BSMMU, and other private hospital in Dhaka from January 2010 to December 2020. We did PLIF by Banana cage with bone graft for High-grade Lumbar Spondylolisthesis at L5-S1. The follow-up period ranges from 1- 2 years (average 18 months. All patients were assessed by VAS, ODI, WDI, Spino-pelvic parameters, Modified Macnab’s Criteria to find out overall outcome and Hackenberge ctriteria for radiological fusion. Results: Total 40 patients were included among 16 were male and 24 were female. The average age of the patients was 52.45±10.1 years. 60.0% patients were housewife ,20.0%, 10.0%, 10% were day laborer, farmer and service holder respectively. Average pelvic tilt was 26.05±6.27° preoperatively and 24.10±6.26° at the final follow-up, average PI was 66.07±7.39° preoperatively and 61.19±7.08° at the final follow-up. Preoperative lumbar lordosis was 45.55± 6.71° &amp; at final follow-up 37.29±6.19°. VAS score and ODI scales were improved significantly from preoperative 6.90 ± 6.16 and 57.60±15.66 to at final follow-up 2.0±0.8 and 7.60±2.40. Pre-operative Translation ratio, slip angle and disc height ratio were 21.96±10.25, -18.87±8.28, 11.03±4.36 and at postoperatively 13.17±6.57, -18.44±7.12, 19.60±3.36. Fusion was achieved in 36 cases (90%), 3 cases (7.5%) were fragmented and pseudoarthrosis showed only 1 case (2.5%). Post-operative clinical outcome showed excellent outcome (95%), 1 (2.5%) case had good and 1 (2.5%) case had fair outcome. Conclusion: It can be concluded that, PLIF by Banana cage with bone graft is a very good option for the treatment of High-grade Lumbar Spondylolisthesis at L5-S1 levels. Keywords: Posterior Lumbar Interbody Fusion, High-grade Spondylolisthesis, Visual Analogue Score, Oswestry Disability Index, Waddell disability index, Hackenberge criteria, Pelvic parameters.

A novel anatomo-physiologic high-grade spondylolisthesis model to evaluate L5 nerve stretch injury after spondylolisthesis reduction

L5 nerve palsy is a well-known complication following reduction of high-grade spondylolisthesis. While several mechanisms for its occurrence have been proposed, the hypothesis of L5 nerve root strain or displacement secondary to mechanical reduction remains poorly studied. The aim of this cadaveric study is to determine changes in morphologic parameters of the L5 nerve root during simulated intraoperative reduction of high-grade spondylolisthesis. A standard posterior approach to the lumbosacral junction was performed in eight fresh-frozen cadavers with lumbosacral or lumbopelvic screw fixation. Wide decompressions of the spinal canal and L5 nerve roots with complete facetectomies were accomplished with full exposure of the L5 nerve roots. A 100% translational slip was provoked by release of the iliolumbar ligaments and cutting the disc with the attached anterior longitudinal ligament. To evaluate the path of the L5 nerves during reduction maneuvers, metal bars were inserted bilaterally at the inferomedial aspects of the L5 pedicle at a distance of 10 mm from the midpoint of the L5 pedicle screws. There was no measurable change in length of the L5 nerve roots after 50% and 100% reduction of spondylolisthesis. Mechanical strain or displacement during reduction is an unlikely cause of L5 nerve root injury. Further anatomical or physiological studies are necessary to explore alternative mechanisms of L5 nerve palsy in the setting of high-grade spondylolisthesis correction, and surgeons should favor extensive surgical decompression of the L5 nerve roots when feasible.

Effect of rotational slip on the physical parameter in a micropolar fluid flow past a stretching sheet

Micropolar fluid flow studied in this paper is influenced by microstructural slip. The flow is directed by a scheme of Partial Differential Equalities. These Partial Differential Equalities are then converted to nonlinear set of Ordinary Differential Equalities via boundary layer conversions. MATLAB bvp4c built in code is taken into account to resolve the leading set of ODEs, along with the initial-boundary settings. Hydro dynamical and thermal boundary layer outlines are considered and deliberated and the results are confirmed by linking with available literature in the classical case. Microstructural slip effects are shown on the Nusselt number and skin-friction coefficient. This model can better predict the effects and characteristics of rotational slip. Specifically, it is predicted from the tabular and graphical results that the rotational slip affects the boundary layer thickness when second-order translational slip disappears. It is important to mention that augmenting the standards of Prandtl number and radiation constraint declines the fluid temperature in the nonappearance and existence of microstructural slip. Moreover, increasing the values of magnetic parameter enhances the fluid temperature in presence as well as in absence of microstructural slip.

Centrifuge modelling of the use of discretely spaced energy pile row to reinforce unsaturated silt

Discretely spaced reinforced concrete (RC) energy pile rows have been proposed to be installed at the mid-height of soil slopes. Although the pile row can provide mechanical reinforcement to slopes, the piles can also potentially be used to (a) intercept solar energy from roadways for heat storage in the ground to mitigate extremely high carriageway temperatures and (b) to extract shallow geothermal energy for road surface de-icing. In this study, a series of centrifuge model tests was conducted to evaluate the shearing behaviour of unsaturated silt with and without reinforcement by conventional piles and energy piles. Three-dimensional finite-element coupled water–vapour–heat transport analysis was also performed to understand further the effects of pile heating on the responses of temperature and pore-water pressure of the soil. The measured and computed results revealed that the primary effect of pile heating was an increase in soil hydraulic conductivity due to the heat-induced reduction in water viscosity. The heated soil had enhanced water flow and hence developed higher suction. When subjected to translational slip, the silt reinforced by a row of closely spaced RC energy piles exhibited a more ductile shearing response and a lower peak shear resistance, compared to that reinforced by conventional piles. The peak bending moments mobilised in the energy piles in the stable stratum were also smaller. At larger shear displacements, however, the shear resistance converged to a similar value, regardless of the suction and temperature. These findings suggest that piles modified with additional energy transfer functionality can continue to act as reinforcement, potentially preventing soil from a sudden brittle failure, without attracting additional flexural stresses onto the piles.

Factors Affecting Slip Reduction in Oblique Lumbar Interbody Fusion With Posterior Fixation for Degenerative Spondylolisthesis.

Study Design:Retrospective case seriesObjectives:Reduction of translational/angular slip is a favorable radiological result in spinal fusion for degenerative spondylolisthesis, although its clinical significance remains controversial. Few studies have investigated slip reduction and associated factors in oblique lumbar interbody fusion (OLIF) for degenerative spondylolisthesis.Methods:This study involved a retrospective analysis of 56 operated levels of 52 consecutive patients who underwent OLIF for degenerative spondylolisthesis and had more than 1-year of regular follow-up. Translational/angular slip, anterior/posterior disc height, and spinopelvic parameters were measured preoperatively, postoperatively at 6-weeks, and at the last follow-up. Demographic, radiological, and surgical parameters were analyzed to determine factors associated with the amount of slip reduction.Result:The mean follow-up duration was 30.4 ± 12.9 months (range, 12 to 61). The mean decrease in translational slip was 5.7 ± 2.1 mm (13.6 ± 5.5%) and the mean increase in angular slip was 7.9 ± 7.1° at the last follow-up (both P < 0.001). The amount of slip reduction was greater in female sex, age < 65 years, use of a 12° cage, cage position from the anterior disc margin of < 7 mm, and cases with posterior decompression (laminectomy with inferior facetectomy).Conclusions:OLIF showed satisfactory translational/angular slip reduction in degenerative spondylolisthesis. Surgical techniques for optimal reduction include the use of a large angle cage, anterior cage placement, and resection of the inferior facet.

On Behavioral Response of Microstructural Slip on the Development of Magnetohydrodynamic Micropolar Boundary Layer Flow

In this paper, the concept of microstructural slip is introduced in the flow of micropolar fluids pertinent to model various physical situations. The flow is modeled by a set of PDEs which are transformed to a nonlinear system of ODEs by employing boundary layer transformations. The system of governing equations is implemented using MATLAB bvp4c function along with the initial-boundary conditions. The code is validated by comparing the computed results in the limiting case with the available literature. Influence of microstructural slip on the skin friction coefficient and Nusselt number along with hydrodynamic and thermal boundary layer profiles is studied and discussed. It is found that, in the presence of microstructural slip, the microrotational velocity boundary layer thickness decreases up to a maximum of 37.5% in its value, in comparison to the case where there is no microstructural slip effect. The results predict that, in the presence of first-order translational slip, the microrotations have shown counterrotational phenomena in comparison to the case where there is no translational slip effect. Moreover, second-order translational slip results in declining the microrotational velocity and associated layer thickness.

A tactile sensor for simultaneous measurements of 6-axis force/torque and the coefficient of static friction

We propose a new design for a tactile sensor that simultaneously measures 6-axis force/torque and the coefficient of static friction, which will enable robotic fingers to handle a slippery object while preventing both translational and rotational slips. The sensor consists of internal and external substrates, internal and external elastomers and normal/shear stress sensor chips. The sensor chips are arranged on the substrates and embedded in the elastomers to measure the deformation of the elastomers. The coefficient of static friction is estimated from the normal and spread deformations of the external elastomer. The 6-axis force/torque values are estimated from the normal, shear and torsional deformations of the internal elastomer. We evaluated the sensor responses when the sensor came into contact with various objects with different coefficients of static friction. We confirmed that the coefficient of static friction and the 6-axis force/torque changes were able to be estimated from the sensor outputs.

ПЕТРОЛОГИЯ КЫЗЫР-БУРЛЮКСКОГО МАФИТ-УЛЬТРАМАФИТОВОГО МАССИВА (СЕВЕРО-ВОСТОК ЗАПАДНОГО САЯНА)

Актуальность исследования. В Западном Саяне установлены многочисленные интрузивные мафит-ультрамафитовые тела. Их формационная принадлежность и металлогеническая специализация до настоящего времени остаются до конца не выясненными и постоянно привлекают внимание как производственных, так и научных организаций, в связи с их металлогенической специализацией на хром, никель, медь, благородные металлы. Для выяснения их формационной принадлежности нами получены оригинальные результаты петрологического исследования мафит-ультрамафитового Кызыр-Бурлюкского массива, которые позволяют выявить условия его формирования, последующего преобразования в процессе длительной эволюции на уровнях верхней мантии–земная кора. Объекты: мафит-ультрамафитовый Кызыр-Бурлюкский массив. Он расположен в северо-восточной части Западного Саяна и, совместно с Калнинским и Эргакским массивами, является составной частью потенциально хромитоносных массивов Амыльского рудного района. Методы. Петрографическое изучение ультрамафитов проводилось на поляризационном микроскопе AxioScope-40 Carl Zeiss. Диагностика химического состава силикатных и рудных минералов выполнена методом рентгеноспектрального микроанализа с применением электронного сканирующего микроскопа Tescan Vega II LMU, оборудованного энергодисперсионным Oxford INCA Energy 350 и волнодисперсионным Oxford INCA Wave 700 спектрометрами. Результаты. Согласно проведенному петрологическому исследованию Кызыр-Бурлюкский массив представлен главным образом предельно деплетированными дунитами, сформировавшимися в верхней мантии, на уровнях которой они претерпели интенсивные высокотемпературные пластические деформации внутрикристаллическим трансляционным скольжением при подчиненной роли синтектонической рекристаллизации. В коровых условиях, под воздействием более поздних габброидных интрузивов, дуниты подвергались высокотемпературному метасоматозому с образованием пород верлитклинопироксенитовой ассоциации.

Size-dependent velocity distributions and temperatures of metal clusters in a helium carrier gas

Combining a laser vaporization cluster source, a velocity scan system, and a time-of-flight mass spectrometer, we measured velocity distributions of few-atom cobalt clusters (${\text{Co}}_{n}, n=6--60$) suspended in a helium carrier gas and expanded into vacuum. The velocity distributions provide information about the cluster size dependence of the translational temperature, flow velocity, and velocity slip with respect to the helium carrier gas. The system of clusters in a carrier gas is found to violate the equipartition theorem. Although the clusters in the expansion do not thermalize with the helium gas, they do experience significant, size-dependent internal cooling. While expanding into vacuum, the clusters collide, at least a couple of hundred times, superelastically with the carrier gas, thereby transferring internal vibrational energy into self-acceleration and increasing the flow velocity of the gas as a whole. It is also demonstrated that the proposed velocity distribution measurements can be used to test whether a source produces thermalized clusters.

Multi-year, three-dimensional landslide surface deformation from repeat lidar and response to precipitation: Mill Gulch earthflow, California

Slow-moving landslides are often the dominant process that shapes hillslopes and delivers sediment to channels in weak lithologies. Understanding what controls their velocities is therefore essential for deciphering their role in landscape evolution and estimating hazards. In this study, we used four sequential airborne lidar data sets to derive the three-dimensional (3D), 1-m spatial resolution surface velocity field of the Mill Gulch earthflow, northern California, for three periods of time spanning a decade. Phase correlation, an image processing technique, applied to the precisely aligned lidar digital elevation models confidently resolved horizontal velocities from 0.2 to 5 m year−1. The velocity field defined three distinct kinematic zones of the landslide with different sensitivities to precipitation, such that the head moved slowly at 0.3–0.5 m year−1, the transport zone moved fastest at 2–5 m year−1, and a forked toe moved intermittently at 0–4 m year−1. Inverting the 3D surface velocity field to infer landslide thickness suggested that the head was underlain by a 6-m-deep, concave-up slip surface, while the transport zone likely had a 1–2.5-m-deep translational slip surface. We hypothesized that velocity in the head was least sensitive to changing precipitation because of its greater inferred depth, which likely dampened the amplitude of pore pressure fluctuations. A lack of major head scarp retrogressions also may have contributed to the relatively steady velocity in the head, while buttressing and debuttressing interactions between the landslide’s toes and the creek running in Mill Gulch may have contributed to the more dramatic changes in velocity in the transport zone and toes. Although predicting landslide velocity from precipitation data alone may therefore be challenging, producing detailed 3D deformation fields from repeat topographic data can be an important tool for deciphering interactions between internal controls, such as changes to landslide geometry, and external controls, such as climate, on landslide motion.

Study on the Instability Mechanism and Grouting Reinforcement Repair of Large‐Scale Underground Stopes

The environmental conditions due to unreasonable mining in underground stopes, the slurry diffusion mechanism in the grouting reinforcement of a stope within its influence, the causes of large‐scale instability collapse, and the catastrophic stope process are analyzed, and limit upper line analysis theory and numerical analysis methods are comprehensively adopted, revealing the continuous catastrophic collapse mode of large‐scale underground stopes. The method of determining the stope instability collapse boundary and the slip surface within the range based on the theory of the maximum shear strain increment is proposed, and the diffusion radius and range of the grouting slurry during the reinforcement process, which considers the multifield coupling factors, are obtained. The results show that the U‐shaped hidden danger area formed after the collapse of the large‐scale underground stope. The influence range reaches six adjacent stopes, which are symmetrically distributed around the collapse; the mining instability is manifested as a catastrophic chain process of stress change, energy accumulation, state change, and instability collapse. The damage mode of instability collapse is a combination method of wedge collapse, circular arc rotation, triangular translation, and strip slip. According to the multiphysics coupling numerical calculation, the diffusion radius of the grouting slurry is 12 m, exhibiting an elliptical distribution. The research results can be used to comprehensively control the underground mining environment, thus effectively solving the safety problems faced by tunnel or roadway excavations above the goaf.

In vivo changes in adjacent segment kinematics after lumbar decompression and fusion

The pathogenesis of lumbar adjacent segment disease is thought to be secondary to altered biomechanics resulting from fusion. Direct in vivo evidence for altered biomechanics following lumbar fusion is lacking. This study’s aim was to describe in vivo kinematics of the superior adjacent segment relative to the fused segment before and after lumbar fusion. This study analyzed seven patients with symptomatic lumbar degenerative spondylolisthesis (5 M, 2F; age 65 ± 5.1 years) using a biplane radiographic imaging system. Each subject performed two to three trials of continuous flexion of their torso according to established protocols. Synchronized biplane radiographs were acquired at 20 images per second one month before and six months after single-level fusion at L4-L5 or L5-S1, or two-level fusion at L3-L5 or L4-S1. A previously validated volumetric model-based tracking process was used to track the position and orientation of vertebrae in the radiographic images. Intervertebral flexion/extension and AP translation (slip) at the superior adjacent segment were calculated over the entire dynamic flexion activity. Skin-mounted surface markers were tracked using conventional motion analysis and used to determine torso flexion. Change in adjacent segment kinematics after fusion was determined at corresponding angles of dynamic torso flexion. Changes in adjacent segment motion varied across patients, however, all patients maintained or increased the amount of adjacent segment slip or intervertebral flexion/extension. No patients demonstrated both decreased adjacent segment slip and decreased rotation. This study suggests that short-term changes in kinematics at the superior adjacent segment after lumbar fusion appear to be patient-specific.

Particle tracking in ideal faulted blocks using 3D co-ordinate geometry

This article performs particle (/material point) tracking for ideal brittle faults with translational and rotational slip components. The fault planes are considered to be planar and step-like in separate cases. In the latter case the hangingwall block is considered to behave ductilely. For a specific choice of the three Cartesian co-ordinate axes, dip-slip fault will change two out of the three ordinates of any point in the faulted block that moves. A strike slip faulting can change one out of the three ordinates. On the other hand, whatever be the orientation of the orthogonal co-ordinate axes, an oblique slip fault of any dip amount and a purely rotational fault with dip ≠ 0, 90° alter all the three ordinates, except the pivot point in the latter case. As expected, oblique-slip faulting modifies the co-ordinates of the shifted material points depending on both (i) the pitch of stretching lineation, and (ii) the dip of the fault plane.

Simultaneous Prevention of Rotational and Translational Slip for a Humanoid Robot

Slip often occurs in humanoid robot walking, especially when the robot walks on a low friction floor or walks fast. Unexpected slip may cause the robot to fall and then sustain damage. In real environments, rotational and translational slip phenomena can happen during biped walking. Previous studies have mainly focused on solving these problems independently. In this paper, we propose strategies for simultaneous rotational and translational slip prevention based on a three mass model, which takes into account the effect of the swing leg. The rotational slip is prevented through a bionic walking pattern generator which mimics the yaw moment compensation mechanism of a human. The translational slip is eliminated through a novel reaction force ratio reduction control with the compensation of CoM (center of mass) acceleration. The effectiveness of the presented strategies is validated by simulations and experiments with an actual humanoid robot.

ISSLS PRIZE IN BIOENGINEERING SCIENCE 2018: dynamic imaging of degenerative spondylolisthesis reveals mid-range dynamic lumbar instability not evident on static clinical radiographs.

Degenerative spondylolisthesis (DS) in the setting of symptomatic lumbar spinal stenosis is commonly treated with spinal fusion in addition to decompression with laminectomy. However, recent studies have shown similar clinical outcomes after decompression alone, suggesting that a subset of DS patients may not require spinal fusion. Identification of dynamic instability could prove useful for predicting which patients are at higher risk of post-laminectomy destabilization necessitating fusion. The goal of this study was to determine if static clinical radiographs adequately characterize dynamic instability in patients with lumbar degenerative spondylolisthesis (DS) and to compare the rotational and translational kinematics in vivo during continuous dynamic flexion activity in DS versus asymptomatic age-matched controls. Seven patients with symptomatic single level lumbar DS (6M, 1 F; 66±5.0years) and seven age-matched asymptomatic controls (5M, 2 F age 63.9±6.4years) underwent biplane radiographic imaging during continuous torso flexion. A volumetric model-based tracking system was used to track each vertebra in the radiographic images using subject-specific 3D bone models from high-resolution computed tomography (CT). In vivo continuous dynamic sagittal rotation (flexion/extension) and AP translation (slip) were calculated and compared to clinical measures of intervertebral flexion/extension and AP translation obtained from standard lateral flexion/extension radiographs. Static clinical radiographs underestimate the degree of AP translation seen on dynamic in vivo imaging (1.0 vs 3.1mm; p=0.03). DS patients demonstrated three primary motion patterns compared to a single kinematic pattern in asymptomatic controls when analyzing continuous dynamic in vivo imaging. 3/7 (42%) of patients with DS demonstrated aberrant mid-range motion. Continuous in vivo dynamic imaging in DS reveals a spectrum of aberrant motion with significantly greater kinematic heterogeneity than previously realized that is not readily seen on current clinical imaging. Level V data These slides can be retrieved under Electronic Supplementary Material.

The lift on a small sphere in a linear shear flow near the interface of two immiscible fluids

AbstractAnalytical expressions have been derived which predict, to lowest order, the inertial lift and the lateral migration velocity of a rigid sphere translating and rotating in a linear shear flow field near the flat interface of two immiscible fluids. This asymptotic analysis is primarily based on the assumption that the two Reynolds numbers defined by the gap width between the interface and the sphere, the shear rate and the translational slip velocity with which the spherical particle moves parallel to the interface are small. Furthermore, the radius of the sphere is assumed to be small compared to the gap width. To leading order in this creeping flow regime, the linear Stokes equations are obtained and a symmetry argument can be used to show that the Stokes solution does not predict any lift force. The transverse force experienced by the sphere and its migration velocity are due to the small but finite inertial terms in the Navier‐Stokes equations, which can be studied by perturbation techniques. By applying a Green's function approach and matched asymptotic methods, which also incorporate the effects of the outer Oseen‐like flow regime, the three components comprising the lift velocity have been calculated in closed form: the one induced by the shear rate only, the purely slip induced one and the one due to the interaction of the slip velocity with the shear flow field. The thus obtained expressions for the case of two immiscible fluids with arbitrary density and viscosity ratios extend the results that already exist in the literature for other flow configurations, such as an unbounded shear flow field [1] or a wall‐bounded one, where the wall lies either within the leading order Stokes region [2] or in the outer Oseen region [3]. (© 2017 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)