Transitional Segment Research Articles

Development of a new partially restrained energy dissipater: Experimental and numerical analyses

Energy dissipaters constructed in structures play an important fuse-type role in concentrating damage and protecting the primary structure. A stable hysteretic behavior, easy fabrication and a low cost are expected characteristics of high-performance energy dissipaters. Previously studied energy dissipaters have disadvantages such as difficult grouting, insufficiently hysteretic capacity and low material utilization. In this paper, a new partially restrained energy dissipater consisting of an inner core bar and an outer partially restraining tube was developed. The inner core bar is milled along the longitudinal direction of the core bar, avoiding the adverse effects of grouting and welding and improving the utilization of the material. Parametric studies on geometrical variables were performed to investigate the low-cycle fatigue behaviors and deformation patterns of the proposed partially restrained energy dissipaters. Test results showed that the partially restrained energy dissipaters demonstrated stable hysteretic performance, and no local or overall buckling was observed. Design guidelines concerning the prevention of torsion buckling, control of section expansion and avoidance of local failure of the transitional segment were developed. The buckling responses, contact conditions and plastic deformations were analyzed via validated numerical models.

Opening of Hess Deep Rift at the Galapagos Triple Junction

AbstractAt the Galapagos triple junction, the westward propagating Cocos‐Nazca (C‐N) Rift breaks into ~0.5 Ma crust accreted at the East Pacific Rise. Rifting transitions to full magmatic seafloor spreading in the wake of the propagating tip. The 25‐km‐long Hess Deep rift is the transitional segment from rifting to spreading. Intrarift ridge (IRR), located within Hess Deep rift, is interpreted as a detachment fault, which exhumes deep‐seated rocks to the seafloor. Although transitional segments must have occurred throughout the westward propagation of C‐N Rift, IRR is the only obvious detachment fault along the base of the Rift scarps in the last ~5 Ma of its propagation. IRR formation may be in response to a decrease in spreading rate (~40 to <20 mm/yr) and presumed lower melt supply, resulting from the formation of the Galapagos microplate ~1.4 Ma, which now controls the opening at the C‐N Rift tip.

Multistage Coupling of Laser-Wakefield Accelerators with Curved Plasma Channels.

Multistage coupling of laser-wakefield accelerators is essential to overcome laser energy depletion for high-energy applications such as TeV-level electron-positron colliders. Current staging schemes feed subsequent laser pulses into stages using plasma mirrors while controlling electron beam focusing with plasma lenses. Here a more compact and efficient scheme is proposed to realize the simultaneous coupling of the electron beam and the laser pulse into a second stage. A partly curved channel, integrating a straight acceleration stage with a curved transition segment, is used to guide a fresh laser pulse into a subsequent straight channel, while the electrons continue straight. This scheme benefits from a shorter coupling distance and continuous guiding of the electrons in plasma while suppressing transverse beam dispersion. Particle-in-cell simulations demonstrate that the electron beam from a previous stage can be efficiently injected into a subsequent stage for further acceleration while maintaining high capture efficiency, stability, and beam quality.

Paratrigeminal, Paraclival, Precavernous, or All of the Above? A Circumferential Anatomical Study of the C3-C4 Transitional Segment of the Internal Carotid Artery.

Although the term paraclival carotid pervades recent skull base literature, no clear consensus exists regarding boundaries or anatomical segments. To reconcile various internal carotid artery (ICA) nomenclatures for transcranial and endoscopic-endonasal perspectives, we reexamined the transition between lacerum (C3) and cavernous (C4) segments using a C1-C7 segments schema. In this cadaveric study, we obtained a 360°-circumferential view integrating histological, microsurgical, endoscopic, and neuroradiological analyses of this C3-C4 region and identified a distinct transitional segment. In 13 adult, silicone-injected, formalin-fixed cadaveric heads (26 sides), transcranial-extradural-subtemporal and endoscopic-endonasal CT-guided dissections were performed. A quadrilateral area was noted medial to Meckel's cave between cranial nerve VI, anterolateral and posterolateral borders of the lateral-paratrigeminal aspect of the precavernous ICA, and posterior longitudinal ligament. Endoscopically, a medial-paraclival aspect was defined. Anatomical correlations were made with histological and neuroradiological slides. We identified a distinct precavernous C3-C4 transitional segment. In 18 (69%) specimens, venous channels were absent at the quadrilateral area, on the paratrigeminal border of the precavernous ICA. A trigeminal membrane, seen consistently on the superior border of V2, defined the lateral aspect of the cavernous sinus floor. The medial aspect of the precavernous ICA corresponded with the paraclival ICA. Our study revealing the juncture of 2 complementary borders of the ICA, endoscopic endonasal (paraclival) and transcranial (paratrigeminal), reconciles various nomenclature. A precavernous segment may clarify controversies about the paraclival ICA and support the concept of a "safe door" for lesions involving Meckel's cave, cavernous sinus, and petrous apex.

A review of lumbosacral transitional vertebrae and associated vertebral numeration.

To review the current literature on methods of accurate numeration of vertebral segments in patients with Lumbosacral transitional vertebrae (LSTVs). LSTVs are a common congenital anomaly of the L5-S1 junction. While their clinical significance has been debated, unquestionable is the need for their identification prior to spinal surgery. We hypothesize that there are no reliable landmarks by which we can accurately number transitional vertebrae, and thus a full spinal radiograph is required. A Pubmed and EMBASE search using various combinations of specific key words including "LSTV", "lumbosacral transitional vertebrae", "count", "vertebral numbering", and "number" was performed. The gold standard for spinal segment numeration in patients with LSTV remains whole spine imaging and counting caudally, starting from C2. If whole spine imaging is not available, the use of the iliac crest tangent sign on coronal magnetic resonance imaging (MRI) has fairly reliable sensitivity and specificity (81 and 64-88%, respectively) for accurate numeration of LSTV. The role of paraspinal anatomic markers such as the right renal artery, superior mesenteric artery, aortic bifurcation, and conus medullaris, for identification of vertebral levels is unreliable and should not be used. A sagittal whole spine view should be added as a scout view when patients obtain lumbar MRI to standardize the vertebral numbering technique. To date, there has been no other method for accurate numeration of a transitional vertebral segment, other than counting caudally from C2. These slides can be retrieved under Electronic Supplementary Material.

Heterogeneous subduction structure within the Pacific plate beneath the Izu-Bonin arc

The Izu-Bonin subduction zone is a subduction system formed in early Eocene. The structure of the subduction zone becomes complicated with the evolution of the surrounding plate motion, and many aspects are still unkown or ambiguous. The geodynamic implications are further investigated in related to published seismic observations and geochemical characters of the Izu-Bonin subduction zone.As indicated by seismic tomography and epicentral distributions, the dip angle of the plate beneath the segment to the south of 29°–30°N (the southern Izu-Bonin) is much steeper than the northern one (the northern Izu-Bonin). Deep focus events in the southern segment extend to the depth of ∼600 km, whereas in the northern section deep events just terminate at 420–450 km. Particularly, tomographic images show an obvious boundary between the northern and southern Izu-Bonin at depths of 150–600 km neglected in the previous studies. The northern and southern segments are even separated by a wide range of low-velocity anomaly in P and S wave tomography at 380 km and 450 km depths. In this depth range, three events near 30°N are characterized by strike-slip mechanisms with slab parallel σ1 and horizontally north-south trending σ3, which differ with the typical down-dip compression mechanisms for neighboring events. These events could be attributed to an abrupt change of the morphology and movement of the slab in the transition segment between the northern and southern Izu-Bonin. Indicated by the focal mechanisms, the northern and southern Izu-Bonin exhibits an inhomogeneous stress field, which is closely related to age differences of the downgoing slab. Because of the reheating process, the thermal age of the Pacific plate entering the Izu-Bonin trench in the past 10 Ma, is only 60–90 ± 20 Ma, along with the younger plate subducting in the northern segment. The seismic anisotropy implies that mantle wedge flow orientation is between the motion direction of the Pacific plate and trench strike, which may be caused by the viscous coupling to the subducting plate and along-trench N-S shearing. The NE splitting direction oblique or perpendicular to the NW-NNW movement of the Pacific plate beneath the transition segment results from the “tearing” of the slab, which is also confirmed by the slab-related velocity anomalies, a sharp change in the dip angle of the Wadati-Benioff zone, the tectonic stress characteristics and along-arc variations of Sr-Nd-Pb isotope ratios in the transition segment.

Dynamic response of a historical armory building using the finite element model validated by the ambient vibration test

In this paper, the aim was to determine the nonlinear dynamic response of historical masonry armory buildings using a validated finite element model. Eight ambient vibration tests were conducted on the building, using three different measurement test setups to extract the dynamic characteristics using the Enhanced Frequency Domain Decomposition method. A finite element model was constructed in ANSYS and the dynamic characteristics were obtained numerically. It can be seen that there is a good correlation between the mode shapes, but there are differences in natural frequencies with maximum values of 10.1%, 7.4% and 13.4% for first the three modes. To determine the nonlinear dynamic response, the validated finite element model was analyzed using the Kocaeli earthquake motion. The Drucker–Prager criterion and Willam–Warnke surface were considered for the nonlinear material models. At the end of the analyses, maximum displacements, principal stresses and strains are given in detail using contour diagrams. It is evident that the displacements show an increasing trend from the base to the top point of the building. Stresses occurred on the corners, openings and transition segments. In addition, crack distribution diagrams were drawn up to illustrate the stress accumulation points.

The Termination Level of the Dural Sac Relevant to Caudal Epidural Block in Lumbosacral Transitional Vertebrae: A Comparison between Sacralization and Lumbarization Groups

Lumbosacral transitional vertebrae (LSTV) are a relatively common variant and have been considered as one of the reasons for back pain. It is not unusual for clinicians to encounter patients with LSTV who require caudal epidural block (CEB) for pain management. We investigated the termination level of the dural sac (DS) and anatomical features of the lumbosacral region relevant to CEB in patients with LSTV and compared these findings between sacralization and lumbarization groups. A retrospective evaluation. A university hospital with inpatient and outpatient LSTV cases presenting low back pain. Four hundred ninety-four LSTV patients were included and categorized into sacralization (n = 201) or lumbarization groups (n = 293). Magnetic resonance imaging (MRI) of all of the LSTV patients were reviewed to determine the level of DS termination, the shortest distance between the apex of the sacral hiatus and DS, and the presence and the caudal level of sacral perineural cysts. Each lumbosacral vertebra column was divided into 3 equal portions (upper, middle, and lower thirds). The MRI findings in both of the groups were compared and analyzed. The distribution frequency of the levels of DS termination demonstrated a significant difference between the 2 groups. The mean caudal DS level in the lumbarization group was significantly lower than the sacralization group (lower third of the S2 [131 {44.7%} of 293 patients] vs. lower third of the S1 [78 {38.8%} of 201 patients]). The DS terminated at the S3 in more than 19% of the lumbarization group, whereas in only one case of the sacralization group. Although the incidence of perineural cysts was not significantly different between the 2 groups, the mean level of caudal margin of perineural cysts in the lumbarization group was significantly lower than the sacralization group (middle third of the S3 [10 {35.7%} of 28 cases] vs. middle third of the S2 [11 {44%} of 25 cases]). This study reveals several limitations including the practical challenge of accurate enumeration of the transitional segment and the constraints on generalizability posed by the single-country study. When planning CEB for patients with LSTV, pre-procedural MRI to check the anatomical structures, including the level of DS termination and caudal margin of perineural cysts, would be of great use for lowering the risk of unexpected dural puncture during the procedure, especially in the lumbarization cases. Termination of the dural sac, dural sac termination, lumbosacral transitional vertebrae, transitional vertebra, caudal epidural block.

Time-Optimal Trajectory Planning for Delta Robot Based on Quintic Pythagorean-Hodograph Curves

In this paper, a time-optimal trajectory planning method based on quintic Pythagorean-Hodograph (PH) curves is proposed to realize the smooth and stable high-speed operation of the Delta parallel robot. The trajectory is determined by applying the quintic PH curves to the transition segments in the pick-and-place operation trajectory and the 3-4-5 polynomial motion law to the trajectory. The quintic PH curves are optimized to reduce the cycle time of the pick-and-place operation. In addition, a comparison between different trajectory planning methods has been implemented so as to observe the performance of the obtained results. The MATLAB simulation results reveal that compared with the trajectory planning based on vertical and horizontal motion superposition, the trajectory planning based on quintic PH curves is completed with a shorter motion cycle time and more stable motion performance, with the velocities, accelerations, and jerks in joint space bounded and continuous. Experiments carried out on the prototype also confirm that the trajectory planning based on quintic PH curves has a shorter cycle time, which is of great importance to high-speed operations of Delta parallel robots.

Choice of surgical procedures and control of surgical risks in chronic constipation

Surgery, as one of the methods for the treatment of chronic constipation, is the final choice after the failure of non-surgical treatment with its specific particularity. The history of surgical treatment of chronic constipation is complex and tortuous. How to select operation among many kinds of surgery, and control risk is difficult for clinician. The choice of surgical procedure depends mainly on the patient's conditions, the objective examination basis and the experience of physician teams. Based on the previous reports and the team's experience, this paper discusses the choice of surgical treatment for the following types of chronic constipation: (1) Slow transit constipation: subtotal colorectal resection plus ileorectal anastomosis or ascending colon rectum anastomosis is widely used at present in the domestic, and its efficacy is quite good. (2) Outlet obstructive constipation: surgical treatment needs to be cautious with no consensus, and surgeons must follow the advice of "minimally invasive first" principle. (3) Mixed constipation: there is no clear and unified surgical treatment, while Jinling surgery is a promising way of operation. (4) Adult Hirschsprung's disease: surgery is the only treatment, and removing the stenosis segment, transitional segment and obvious expansion segment is the basic principle, and preventive ileostomy at the same time is also recommended. (5) Adult idiopathic megacolon: subtotal colectomy with ileorectal anastomosis or ascending colon rectum anastomosis is highly recommended. (6) Hypoganglionosis: it is rare, and no consensus has been reached in surgical treatment. How to select the proper timing and mode of operation, and how to control the operation risk are the contents that clinicians must master. With the development of laparoscopic surgical technology, minimally invasive surgery is becoming the main direction of constipation treatment.

Neural network and GMM based feature mappings for consonant–vowel recognition in emotional environment

In this work, we propose a mapping function based feature transformation framework for developing consonant–vowel (CV) recognition system in the emotional environment. An effective way of conveying messages is by expressing emotions during human conversations. The characteristics of CV units differ from one emotion to other emotions. The performance of existing CV recognition systems is degraded in emotional environments. Therefore, we have proposed mapping functions based on artificial neural network and GMM models for increasing the accuracy of CV recognition in the emotional environment. The CV recognition system has been explored to transform emotional features to neutral features using proposed mapping functions at CV and phone levels to minimize mismatch between training and testing environments. Vowel onset and offset points have been used to identify vowel, consonant and transition segments. Transition segments are identified by considering initial 15% speech samples between vowel onset and offset points. The average performance of CV recognition system is increased significantly using feature mapping technique at phone level in three emotional environments (anger, happiness, and sadness).

The method of signal receiving in the artificial voice device

The further development of the model of artificial voice apparat, which based on analysis electromyographic signal from neck was made in the arcticle. The algorithm of analysis electromyographic signal of the superficial neck muscles for detections of transitional speech segment had been proposed. The mathematical models, which are the most accurately describe the electromyographic and voice signals were analyzed. Results of proposed algorithm were shown. Figs.: 2. Refs.: 11 titles.Keywords: artificial voice apparat; electromyographic signal; transitional speech segment.

Biomechanical effects of hybrid stabilization on the risk of proximal adjacent-segment degeneration following lumbar spinal fusion using an interspinous device or a pedicle screw-based dynamic fixator.

OBJECTIVE Pedicle screw-rod-based hybrid stabilization (PH) and interspinous device-based hybrid stabilization (IH) have been proposed to prevent adjacent-segment degeneration (ASD) and their effectiveness has been reported. However, a comparative study based on sound biomechanical proof has not yet been reported. The aim of this study was to compare the biomechanical effects of IH and PH on the transition and adjacent segments. METHODS A validated finite element model of the normal lumbosacral spine was used. Based on the normal model, a rigid fusion model was immobilized at the L4-5 level by a rigid fixator. The DIAM or NFlex model was added on the L3-4 segment of the fusion model to construct the IH and PH models, respectively. The developed models simulated 4 different loading directions using the hybrid loading protocol. RESULTS Compared with the intact case, fusion on L4-5 produced 18.8%, 9.3%, 11.7%, and 13.7% increments in motion at L3-4 under flexion, extension, lateral bending, and axial rotation, respectively. Additional instrumentation at L3-4 (transition segment) in hybrid models reduced motion changes at this level. The IH model showed 8.4%, -33.9%, 6.9%, and 2.0% change in motion at the segment, whereas the PH model showed -30.4%, -26.7%, -23.0%, and 12.9%. At L2-3 (adjacent segment), the PH model showed 14.3%, 3.4%, 15.0%, and 0.8% of motion increment compared with the motion in the IH model. Both hybrid models showed decreased intradiscal pressure (IDP) at the transition segment compared with the fusion model, but the pressure at L2-3 (adjacent segment) increased in all loading directions except under extension. CONCLUSIONS Both IH and PH models limited excessive motion and IDP at the transition segment compared with the fusion model. At the segment adjacent to the transition level, PH induced higher stress than IH model. Such differences may eventually influence the likelihood of ASD.

Improved characterization of multi-stage voltage dips based on the space phasor model

This paper proposes a method for characterizing voltage dips based on the space phasor model of the three phase-to-neutral voltages, instead of the individual voltages. This has several advantages. Using a K-means clustering algorithm, a multi-stage dip is separated into its individual event segments directly instead of first detecting the transition segments. The logistic regression algorithm fits the best single-segment characteristics to every individual segment, instead of extreme values being used for this, as in earlier methods. The method is validated by applying it to synthetic and measured dips. It can be generalized for application to both single- and multi-stage dips.

The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata

BackgroundSegmental composition and homologies of the head of stem-group Euarthropoda have been the foci of recent studies on arthropod origins. An emerging hypothesis suggests that upper-stem group euarthropods possessed a three-segmented head/brain, including an ocular segment (protocerebrum) followed by the deutocerebrum with associated antennae/raptorial limbs and the tritocerebrum, while in the lower stem, head structures of Radiodonta are wholly associated with the protocerebrum and its preceding part. However, this hypothesis is incompletely tested because detailed knowledge on the head components of radiodontans is patchy, and informative articulated specimens are lacking for many taxa. Amplectobelua symbrachiata is the most common radiodontan species in the Chengjiang biota (ca. 520 Ma), normally known as isolated frontal appendages. Here we present detailed descriptions of new articulated specimens that elucidate the morphology and function of its head structures, and discuss their implications for hypotheses about euarthropod cephalic organisation.ResultsIn addition to a central oval head shield, A. symbrachiata also bears a pair of P-elements connected by an elongated rod. The mouth consists of sets of smooth and tuberculate plates, in contrast to the typical radial oral cones of other radiodontans. Previously identified ‘palm-like teeth’ are located external to the mouth in the posterior head region, and are interpreted as segmental gnathobase-like structures (GLSs) associated with at least three reduced transitional flaps in a one (pair)-to-one (pair) pattern, consistent with an appendicular nature. Comparisons with other panarthropods show that GLSs are morphologically similar to the mandibles and other gnathobasic mouthparts of euarthropods, as well as to the jaws of onychophorans, indicating their functional integration into the feeding activities of A. symbrachiata.ConclusionsThe functional head of A. symbrachiata must include the reduced transitional segments (and their associated structures), which have been identified in several other radiodontans. This functional view supports the idea that the integration of segments (and associated appendages) into the head region, probably driven by feeding, occurred along the euarthropod stem-lineage. However, the number of reduced transitional segments varies between different groups and it remains uncertain whether GLSs represent proximal or distal parts of appendages. Our study is the first description of appendicular structures other than the frontal appendages in the functional head region of radiodontans, revealing novel feeding structures in the morphological transition from the lower- to the upper- stem-group of Euarthropoda.

Investigation of the expression of apoptosis-inducing factor-mediated apoptosis in Hirschsprung's disease.

One of the widely accepted hypotheses of Hirschsprung's disease (HD) is that the absence of ganglion cells in the distal part of the intestine is caused by the death of enteric neural crest-derived cells following migration. Although a caspase-dependent pathway has not yet been detected in the HD bowel, it is unclear whether a caspase-independent pathway contributes toward aganglionosis. In the current study, we observed highly condensed marginal heterochromatin in nuclei only in the transitional segment using electron microscopy and a high proportion of TUNEL-positive cells were observed in the transitional segment. Activation of caspase was not observed in any segments of the HD bowel upon characterization of the apoptotic pathway. Rather, real-time PCR results showed that apoptosis-inducing factor (AIF) and calpain-1 mRNAs were highly expressed in the transitional segment, whereas autophagy protein 5 (Atg5) was highly expressed in the narrow segment. Western blot results were consistent with mRNA levels, with increased AIF, calpain-1, and Atg5 expressions in the transitional segment compared with the dilated segment. Furthermore, correlation analysis indicated an inverse correlation between calpain-1 and Atg5 mRNA levels in both the narrow segment and the transitional segment. These results indicated that apoptosis occurs in the HD bowel. The detection of related genes indicates that the AIF-mediated apoptotic pathway may be responsible for the absence of ganglion cells in HD and calpain-1 may act as the regulatory switch between autophagy and apoptosis.

Grain size‐dependent strength of phyllosilicate‐rich gouges in the shallow crust: Insights from the SAFOD site

AbstractThe San Andreas Fault Observatory at Depth (SAFOD) drilling project directly sampled a transitional (between creeping and locked) segment of the San Andreas Fault at 2.7 km depth. At the site, changes in strain rate occur between periods of coseismic slip (>10−7 s−1) and interseismic creep (10−10 s−1) over decadal scales (~30 years). Microstructural observations of core retrieved from the SAFOD site show throughgoing fractures and gouge‐rich cores within the fractures, evidence of predominantly brittle deformation mechanisms. Within the gouge‐rich cores, strong phases show evidence of deformation by pressure solution once the grain size is reduced to a critical effective grain size. Models of pressure solution‐accommodated creep for quartz‐phyllosilicate mixtures indicate that viscous weakening of quartz occurs during the interseismic period once a critical effective grain size of 1 μm is achieved, consistent with microstructural observations. This causes pronounced weakening, as the strength of the mixture is then controlled by the frictional properties of the phyllosilicate phases. These results have pronounced implications for the internal deformation of fault zones in the shallow crust, where at low strain rates, deformation is accommodated by both viscous and brittle deformation mechanisms. As strain rates increase, the critical effective grain size for weakening decreases, localizing deformation into the finest‐grained gouges until deformation can no longer be accommodated by viscous processes and purely brittle failure occurs.

Down-regulation of fibronectin and the correlated expression of neuroligin in hirschsprung disease.

The goal of this study was to investigate the expression of fibronectin (FN) and the correlated abundance of neuroligins (NLs) in the enteric nervous system (ENS) and to find a novel diagnostic marker in the serum of Hirschsprung disease (HSCR) patients. The expression levels of FN, neuroligin-1 and neuroligin-2 were detected in 114 children with or without HSCR. The expression and localization of the NLs and FN were assessed morphologically by immunohistochemical staining. Western blot analysis and real-time fluorescence quantitative PCR (qPCR) were performed to examine the correlated expression of the NLs and FN in aganglionic, transitional, and normal ganglionic colon tissues. An enzyme-linked immunosorbent assay (ELISA) was performed to evaluate and compare serum FN levels between HSCR and non-HSCRand between long-type HSCR and short-type HSCR. These studies showed that both neuroligin-1 and neuroligin-2 were expressed at low levels in aganglionic segments and at intermediate levels in transitional segments compared to their high level of expression in normal tissue. In contrast, FN expression was negatively correlated, with expression in these three samples transitioning from highest to lowest. The serum FN level was higher in HSCR than in non-HSCR, but no significant difference between short-type HSCR and long-type HSCR was observed. FN affects the expression of both neuroligin-1 and neuroligin-2 in HSCR, which may lead to the hypoplasia of ganglion cells in the ENS. This correlation may play a key role in the pathogenesis, diagnosis, or classification of HSCR.

Magnetohydrodynamic flows tuning in a conduit with multiple channels under a magnetic field applied perpendicular to the plane of flow

In this study, three-dimensional liquid-metal magnetohydrodynamic flows in a conduit with multiple channels under a uniform magnetic field are numerically investigated. The geometry of the conduit is of a four-parallel-channels system including one inflow channel and three outflow channels. The liquid-metal flows into the inflow channel, then turns through in the transition segment, finally flows into three different outflow channels. This kind of channel system can induce counter flow and co-flow, which is rarely investigated before though the conceptual designs of duct flow in the blanket have suggested this type of flow. A structured grid system is chosen after a series of mesh independence tests in the present study. The axial velocity in the side layer near the first partitioning wall, located between the inflow channel and the first outflow channel, is the highest with the lowest electric potential formed therein. The pressure almost linearly decreases in the main flow direction, except in the transition segment. Moreover, the pressure gradient in the first outflow channel is the largest among the three outflow channels. The interdependency of the current, fluid velocity, pressure, electric potential is examined in order to describe the electromagnetic characteristics of the liquid-metal flows.

Is a gradual reduction of stiffness on top of posterior instrumentation possible with a suitable proximal implant? A biomechanical study

Background ContextProximal junctional kyphosis (PJK) is a challenging complication after rigid posterior instrumentation (RI) of the spine. Several risk factors have been described in literature so far, including the rigidity of the cranial aspect of the implant. PurposeThe aim of this biomechanical study was to compare different proximal implants designed to gradually reduce the stiffness between the instrumented and non-instrumented spine. Study Design/SettingThis is a biomechanical study. MethodsEight calf lumbar spines (L2–L6) underwent RI with a titanium pedicle screw rod construct at L4–L6. The proximal transition segment (L3–L4) was instrumented stepwise with different supplementary implants—spinal bands (SB), cerclage wires (CW), hybrid rods (HR), hinged pedicle screws (HPS), or lamina hooks (LH)—and compared with an all-pedicle screw construct (APS). The flexibility of each segment (L2–L6) was tested with pure moments of ±10.0 Nm in the native state and for each implant at L3–L4, and the segmental range of motion (ROM) was evaluated. ResultsOn flexion and extension, the native uninstrumented L3–L4 segment showed a mean ROM of 7.3°. The CW reduced the mean ROM to 42.5%, SB to 41.1%, HR to 13.7%, HPS to 12.3%, LH to 6.8%, and APS to 12.3%. On lateral bending, the native segment L3–L4 showed a mean ROM of 15°. The CW reduced the mean ROM to 58.0%, SB to 78.0%, HR to 6.7%, HPS to 6.7%, LH to 10.0%, and APS to 3.3%. On axial rotation, the uninstrumented L3–L4 segment showed a mean ROM of 2.7°. The CW reduced the mean ROM to 55.6%, SB to 77.8%, HR to 55.6%, HPS to 55.6%, LH to 29.6%, and APS to 37.0%. ConclusionsUsing CW or SB at the proximal transition segment of a long RI reduced rigidity by about 60% in relation to flexion and extension in that segment, whereas the other implants tested had a high degree of rigidity comparable with APS. Clinical randomized controlled trials are needed to elucidate whether this strategy might be effective for preventing PJK.