Residual Compression Research Articles

Characterization and in vivo study of decellularized aortic scaffolds using closed sonication system

ABSTRACTExtracellular matrix (ECM) based bioscaffolds prepared by decellularization has increasingly emerged in tissue engineering application because it has structural, biochemical, and biomechanical cues that have dramatic effects upon cell behaviors. Therefore, we developed a closed sonication decellularization system to prepare ideal bioscaffolds with minimal adverse effects on the ECM. The decellularization was achieved at 170 kHz of ultrasound frequency in 0.1% and 2% Sodium Dodecyl Sulphate (SDS) solution for 10 hours. The immersion treatment as control was performed to compare the decellularization efficiency with our system. Cell removal and ECM structure were determined by histological staining and biochemical assay. Biomechanical properties were investigated by the indentation testing to test the stiffness, a residual force and compression of bioscaffolds. Additionally, in vivo implantation was performed in rat to investigate host tissue response. Compared to native tissues, histological staining and biochemical assay confirm the absence of cellularity with preservation of ECM structure. Moreover, sonication treatment has not affected the stiffness [N/mm] and a residual force [N] of the aortic scaffolds except for compression [%] which 2% SDS significantly decreased compared to native tissues showing higher SDS has a detrimental effect on ECM structure. Finally, minimal inflammatory response was observed after 1 and 5 weeks of implantation. This study reported that the novelty of our developed closed sonication system to prepare ideal bioscaffolds for tissue engineering applications.

Comparison of the middle-term follow-up results between anterior decompression with fusion and posterior open-door laminoplasty for treatment of multi-level cervical spondylotic myelopathy

Objective To compare the medium-term clinical and radiologic outcomes between anterior decompression with fusion (ADF) and posterior open-door laminoplasty (LAMP) in the treatment of multi-level cervical spondylotic myelopathy (MCSM). Methods Data of 121 patients meeting to inclusion criteria from October 2011 to February 2016 were retrospectively analyzed. All the patients were treated with ADF (ADF group, n=57) or LAMP (LAMP group, n=64) for MCSM. There were 39 males and 18 females in ADF group, aged from 35 to 77 years, with an average age of 58.8±10.1 years. And there were 64 cases in LAMP group, including 48 males and 16 females, aged from 28 to 82 years, with an average of 60.6±12.2 years. The operation time and blood loss were recorded. The clinical efficacy was evaluated by Japanese Orthopaedic Association Scores (JOA), improvement rate and visual analogue scale (VAS) before operation, 1, 3, 6, 12 and 24 months after operation and at the latest follow-up. At the same time, sagittal alignment of the C2-C7 lordotic angle and range of motion (ROM) in flexion and extension on plain X-rays was measured. Residual anterior compression to the spinal cord (ACS) in LAMP group on MRI was investigated. The incidence of complications such as axial symptoms and C5 nerve root paralysis were recorded. Results The average follow-up period was 25.6±3.8 months in ADF group and 27.3±4.1 months in LAMP group. Demographics were similar between the two groups. The mean JOA scores in ADF group increased from preoperative 8.25±2.33 to 14.62±3.15 at the latest follow-up, with an average recovery rate of 72.81%±11.32%. The mean JOA scores in LAMP group increased from preoperative 8.84±3.65 to 12.97±4.32 at the latest follow-up, with an average recovery rate of 66.54%±14.75%. The difference between two groups was statistically significant. Both of the VAS scores in the two groups decreased significantly at 1 month after the surgery, but the difference between the ADF group (1.92±0.75) and the LAMP group (2.78±0.68) was statistically significant (t=2.364, P=0.021). There was no significant difference in VAS score between the two groups at 3 months after operation. Cervical lordosis of ADF group increased from 15.3°±7.6° to 19.2°±5.7°, while that of LAMP group decreased from 16.8°±8.3° to 13.6°±4.3°. There was significant difference in cervical curvature between the two groups at the latest follow-up. Both two groups exhibited decreased cervical ROM, 15.2°±3.6° and 18.1°±4.1°, respectively, and the difference between two groups was statistically significant (t=3.392, P=0.000) . At the latest follow-up, the incidence of complication was 35.1% in ADF group and 20.3% in LAMP group, and the difference between two groups has no statistically significant. The LAMP group was divided into two subgroups: (1) ACS(+)(n=11) comprising patients who had ACS after surgery, and (2) ACS(-) (n=53) comprising patients without ACS. At the latest follow-up, the average JOA score of patients with anterior residual compression of spinal cord was 10.85±5.46, while the average JOA score of patients without anterior residual compression of spinal cord was 14.18±4.52. The recovery rate differed significantly between the ACS(+) and ACS(-) groups, 40.52%±9.76% and 70.38%±10.52%, respectively. Also at the latest follow-up, the cervical curvature, ROM and ROM loss angle were 10.2°±7.3°, 15.6°±6.7° and 11.8°±8.3° in the group with anterior residual compression of spinal cord, respectively. The groups without anterior residual compression of spinal cord were 15.8°±6.5°, 20.4°±10.2° and 8.8°±6.8°, respectively. Conclusion Both ADF and LAMP groups provided good outcomes at 2-year time-point whereas ADF could achieve more satisfactory outcomes and better sagittal alignment at the middle-term. ADF can remove the compression directly, maintain the curvature of cervical vertebra effectively and restore the nerve function well. The clinical outcomes after LAMP could be influenced by ACS, due to the reduction of cervical curvature and the decrease of cervical range of motion. Key words: Cervical vertebrae; Spinal cord compression; Spinal fusion

Ossified Posterior Longitudinal Ligament Existing at an Intervertebral Level Limits Compensatory Mechanism of Cervical Lordosis after Muscle-Preserving Selective Laminectomy.

Introduction As C7 slope increases, lordotic change of C2-C7 angle compensates for adjustments in cervical sagittal balance. However, ossification of the posterior longitudinal ligament (OPLL) may affect the compensatory mechanism of the cervical spine. This study aims to evaluate the impact of OPLL on cervical lordotic compensation after muscle-preserving selective laminectomy (SL). Methods This study involved 235 patients with cervical spondylotic myelopathy (CSM) and OPLL who underwent ≥ 3 consecutive levels of SL. OPLL was classified into continuous, segmental, mixed, or localized type on the basis of the criteria previously reported. In this study, based on the motion preservation at the intervertebral level, patients were divided into CSM (n = 114), OPLL segmental type (OPLL-S; n = 44), and other types of OPLL (OPLL-O; i.e., continuous, mixed, and localized; n = 77). The cervical sagittal alignment, degree of spinal cord decompression, and surgical outcomes were compared among the three groups. Results The OPLL-O group had a larger postoperative C7 slope (p = 0.020), larger pre- (p = 0.021) and postoperative (p = 0.001) C2-C7 sagittal vertical axis, and greater pre- (p = 0.034) and postoperative (p = 0.002) C7 slope minus C2-C7 angle. Narrower postoperative spinal cord clearance (PSCC) from OPLL (p < 0.001) and more residual spinal cord compression (p < 0.001) were observed in the OPLL-O group. Correlation between postoperative C7 slope minus C2-C7 angle and PSCC was detected (r = −0.238, p < 0.001). The recovery rate of the Japanese Orthopedic Association score was slightly lower in the OPLL-O group (p < 0.001), and it was correlated with postoperative residual spinal cord compression (r = −0.305, p < 0.001). Conclusions OPLL-O limits cervical lordotic compensation, resulting in cervical sagittal balance mismatch. It affects the degree of spinal cord decompression, which might be related to surgical outcome.

Relationship between residual flexural strength and compression strength in steel-fiber reinforced concrete within the new Eurocode 2 regulatory framework

Annex L of the next Eurocode 2 establishes a classification of the steel-fiber reinforced concrete (SFRC) by means of classes of residual flexural strength for two values of crack mouth opening displacement, 0.5 mm and 2.5 mm. Nevertheless, this indexing does not completely describe the resistance behavior of the SFRC since it does not include the residual compression strength of the material, defined as the stress resisted when the deformation is three times that reached under the maximum load [Hormigón y Acero 69:S1 (2018) 75–80], the value of which is not negligible when steel fiber is included in the concrete. The principal objective of this research consists of determining the relationship that exists between compressive and flexural residual strengths by applying the Response Surface Methodology (RSM) as an instrument of analysis. It has been performed on a combination of experimental data collected in two databases, one with compression tests and the other with flexural tests, with 484 and 197 pieces of data respectively. The classification of SFRC could be completed when the value of residual compression strength corresponding to each class of concrete given by the RSM analysis is included, thereby completely characterizing the material for the practical effects of analysis and structural design. In addition, the RSM analysis provides numerous insights on the relations of the residual strengths with the parameters of the base concrete and the fiber. The paper also provides a new cylinder/cube conversion formula based in the results of Viso, Carmona and Ruiz [Cement and Concrete Research 38 (2008) 386–395] and in the Bažant’s size-effect law, which can be used for cubes of any edge length and of any strength grade.

Effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon fiber composites

The effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon fiber composites were systematically investigated by comparing the mass loss, morphologies, dynamic mechanical properties, and chemical structures of aged and non-aged specimens. The relationships between dent depth, damage area, residual compression strength, and impact energy were also discussed in detail. The obtained results showed that the non-aged composite featured good fiber-resin bonding, whereas hygrothermal and thermal aging led to fiber-matrix interface damage. For thermally aged samples, dent depth rapidly increased with impact energy above the inflection point, and the corresponding amplitude was greater than those observed for non-aged and hygrothermally aged specimens. Notably, hygrothermal and thermal aging did not affect the impact-induced damage morphology and the after-impact compression failure mode. At a constant impact energy, the damage area of thermally aged samples exceeded those of non-aged and hygrothermally aged ones; moreover, thermal aging exhibited greater influence on residual compressive strength than hygrothermal aging. Finally, whereas hygrothermal aging reduced the glass transition temperature (Tg) and did not induce the formation of new materials or the occurrence of chemical reactions, thermal aging resulted in increased Tg and was accompanied by the concomitant occurrence of oxidation reactions.

RedSync: Reducing synchronization bandwidth for distributed deep learning training system

Data parallelism has become a dominant method to scale Deep Neural Network (DNN) training across multiple nodes. Since the bandwidth requirement of synchronizing the gradients of the local model can be a bottleneck for large-scale distributed training, compressing communication traffic has gained widespread attention recently. Among several recent proposed compression algorithms, Residual Gradient Compression (RGC) is one of the most successful approaches—it can significantly compress the transmitting message size (0.1% of the gradient size) of each node and still achieve correct accuracy and the same convergence speed. However, the literature on compressing deep networks focuses almost exclusively on achieving good theoretical compression rate, while the efficiency of RGC in real implementation has been less investigated. In this paper, we develop an RGC method that is able to reduce the end-to-end training time on real-world multi-GPU systems. Our proposed RGC system design called RedSync, introduces a set of optimizations to reduce communication bandwidth while introducing limited overhead. We examine the performance of RedSync on two different multiple GPU platforms, including 128 GPUs of a supercomputer and an 8-GPU server. Our test cases include image classification on Cifar10 and ImageNet, and language modeling tasks on Penn Treebank and Wiki2 datasets. For DNNs featured with high communication to computation ratio, which has long been considered with poor scalability, RedSync shows significant performance improvement.

Testing, numerical modelling and design of S690 high strength steel welded I-section stub columns

This paper describes a comprehensive testing and numerical simulation investigation into the material properties, membrane residual stresses and compression capacities of S690 high strength steel welded I-section stub columns. The testing programme was performed on eight welded I-sections fabricated from 5 mm thick S700MC high strength steel hot-rolled plates by means of gas metal arc welding, and included material tensile coupon tests, membrane residual stress measurements, initial local geometric imperfection measurements, and sixteen concentrically loaded stub column tests. A membrane residual stress distribution model for S690 high strength steel welded I-sections was firstly proposed, based on the experimentally measured results. In conjunction with the structural testing, a numerical modelling study was carried out, in which finite element models were initially developed and validated against the experimental results, and afterwards employed to conduct parametric studies, aiming at generating further structural performance data over a broader range of cross-section sizes. The obtained experimental and numerical data were used to evaluate the accuracy of the slenderness limits (for classifications of plate elements and cross-sections) and design rules for S690 high strength steel welded I-section stub columns, as set out in the European, American and Australian standards. The results of the evaluation revealed that the codified slenderness limits are accurate for the plate element and cross-section classifications of S690 welded I-sections in compression, and the established local buckling design provisions in the considered three codes result in precise and consistent cross-section compression resistance predictions for both non-slender and slender S690 welded I-section stub columns.

Development of a technology for the surface strengthening of barrel channels in the large-caliber artillery guns

High temperatures and exposure to the chemical effect of powder gases that accompany artillery salvos actively destroy the surface layer of a barrel channel material. This disrupts the geometry of a barrel channel, thereby reducing the accuracy of an artillery gun aimed firing. We have proposed a technology of surface plastic deformation of the channel inner surface for strengthening the barrels of large caliber artillery and tank guns. The strengthening implies the cold-work hardening of a barrel channel metal with spherical deforming bodies that are mounted onto a massive cylindrical reinforcer. During machining, the reinforcer is driven into a rolling motion over the treated inner surface of a barrel channel and moves along the geometrical center of the machined gun’s barrel. As a result of such a hardening treatment, the residual compression stresses form in the thickness of a barrel channel material, thereby improving its surface microhardness. That contributes to an increase in the resistance of a barrel channel material against its burn-out and wear during artillery salvos.The reinforcing equipment for the implementation of such a treatment includes a reinforcer in the form of a cylinder with deforming bodies, an electric motor of the drive, and a mechanism to transfer the torque from the motor shaft to the reinforcer. During strengthening treatment, the set-up moves along a gun barrel channel, cold-working its material. The ensured hardening thickness is 0.15‒0.20 mm.The hardened surface layer of a gun barrel material, due to the heightened microhardness, firmly opposes the formation of operational microcracks within it. The compression stresses, formed in the thickness of a barrel channel metal, resist the temperature propagation of microcracks. Owing to this, the resistance of the hardened barrel metal against operational destruction increases, thereby improving the reliability and durability of costly artillery armament.

Effects of long-term loading on fire-damaged reinforced-concrete stub columns

The effect of long-term loading on fire-damaged reinforced-concrete (RC) stub columns was experimentally investigated. RC stub columns were axially loaded and heated to predetermined temperatures. After the specimens were cooled to ambient temperature, long-term loading was applied and kept constant for 98 d and 192 d and axial deformations due to the creep effect were recorded. The specimens were then compressed to failure. The residual compressive strength and residual compression stiffness were analysed to assess the effect of long-term loading on the post-fire mechanical behaviour of the specimens. It was found that long-term loading had a significant effect on the residual mechanical behaviour of fire-damaged RC stub columns. The fire-damaged specimens resulted in obviously increased creep during the loading period. Based on the model given in ACI 209R-92 and existing experimental data on fire-damaged concrete obtained previously by the authors, a fire-induced creep modification factor is proposed to predict the creep of fire-damaged concrete under long-term loading. It is recommended that the effect of creep should be taken into consideration in assessing fire-damaged RC columns.

Development of a traumatic cervical dislocation spinal cord injury model with residual compression in the rat

BackgroundPreclinical spinal cord injury models do not represent the wide range of biomechanical factors seen in human injuries, such as spinal level, injury mechanism, velocity of spinal cord impact, and residual compression. These factors may be responsible for differences observed between experimental and clinical study results, especially related to the controversial issue of timing of surgical decompression. New methodSomatosensory Evoked Potentials were used to: a) characterize residual compression depths in a dislocation model, and b) evaluate the physiological effect of whether or not the spinal cord was decompressed following the initial injury, prior to the application of residual compression. Modifications to vertebral clamps and the development of a novel surgical frame allowed us to conduct surgical and injury procedures in a controlled manner without the risk of additional damage to the spinal cord. Behavioural outcomes were evaluated following varying dislocation displacements, in addition to the survivability of 4 h of residual compression following a traumatic injury. ResultsResidual compression immediately following the initial dislocation demonstrated significantly different electrophysiological response compared to when the residual compression was delayed. Comparison with existing methodThere are currently no other residual compression models that utilize a dislocation injury mechanism. Many residual compression studies have demonstrated the effectiveness of early decompression, however the compression of the spinal cord is often not representative of clinical traumatic injuries. Preclinical studies typically model residual compression using a sustained force through quasi-static application, when human injuries often occur at high velocities, followed by a sustained displacement occlusion of the spinal canal. ConclusionsThis study has validated several novel procedural approaches and injury parameters, and provided critical details to implement in the development of a traumatic cervical dislocation SCI model with residual compression.

Low-velocity impact damage research on CFRPs with Kevlar-fiber toughening

This paper provides a comprehensive understanding of the influence mechanism of short fiber toughening on low-velocity impact resistance of carbon fiber reinforced polymer composite laminates (CFRPs). Three kinds of layup laminates with and without short Kevlar-fiber toughening were designed and experimental tests were conducted using a drop-weight impact machine. After the low-velocity impact test, ultrasonic C-scan and industrial computed tomography (ICT) were utilized to comprehensively reveal the internal damage, including damage area and damage distribution. Based on the energy absorption and the impact dynamic responses, mechanical behaviors of CFRPs were analyzed in detail. Furthermore, the residual compression strength and failure strain of CFRPs with and without short Kevlar-fiber toughening were tested. It was observed that damage resistance of toughened laminates at lower impact energy did not show obvious advantages, but the compression-after-impact (CAI) strengths and the failure strain values improved under all energy levels with short Kevlar-fiber toughening. Three-dimensional distribution of internal damage and electron microscope analysis, together with fracture toughness analysis, were employed to explain the experimental findings and relevant mechanisms.

MAGNETIC-PULSE PRESSING OF ELECTRICAL CONNECTIONS FOR STRANDED WIRES

Purpose. The research of the process peculiarities of magnetic- pulse fitting of electric stranded conductor joints, made of different materials, using couplings. Evaluation of loading optimal parameters, providing high operational reliability of electric connecting units. Methodology. In order to carry out simulation and research of the process of magnetic-pulse fitting of electric stranded conductor joints CRUG24 software package was used, which was developed to estimate impact interaction. Handling the problem was carried out numerically using finite differences. Metallographic study of collected cross-sectional cuts was performed with the use of optical microscope МЕТАМ ЛВ-71, equipped with digital-still camera, connected to the computer, which used image analysis system IMEGE Expert Pro3. The electrical tests of wire joints were carried out using the thermal bench from exposure to two factors: heating with rated current and expansion by operating load. Results. It was ascertained that magnetic-pulse pressing of electric joints was followed by partial self-purification and bedding component contacting surfaces of electric joints. Oxides and contaminating impurities were expelled into small localized zones between wires, between a wire and a coupling, which resulted in the contact of juvenile surfaces. Upon mutual deformation and displacement of metal wire surface capacity size and coupling tight mechanical contact was created, which provided minimal transient resistivity. The existence of residual compression stress provides the longstanding high-quality electric contact in joints. While using magnetic-pulse pressing of electric joints, due to high speed of deformation and impact of great inertial forces, deformation containment of connected components takes place in the zone of load action. The wires in contact with each other and with couplings generate faceting, but coupling sidewall hardly has any thinning. Filled density of cross-section is approximately 100 %. This fact provides a high degree of sealing capacity of joints, which to a wide extent prevents the oxidation of contacting surfaces and the rise of transient resistivity of electric joints in the operational process. As a result of processing of the results of thermal and electrical tests it was ascertained that pressed joint factors of defectiveness with all types of wires according to thermal impact and resistivity, are significantly lower than unity. Practical value. Magnetic-pulse pressing of unattended joints in electric stranded monometallic, bimetallic and composite conductors provides high operational reliability of connecting units and it may be used while mounting overhead system of railways, transmission lines and fitting connecting components of electrical transport electric circuits.

Quantitative study of the effect of atlas posterior arch resection on cervical posterior decompression

Objective To quantitatively compare the effect of preservation or removal of atlas posterior arch on cervical posterior decompression, so as to provide a basis for reasonable selection of upper cervical spine decompression range and determination of surgical indications for atlas posterior arch resection. Methods The data of 45 patients with posterior decompression of upper cervical spine were retrospectively analyzed. According to the decompression range, the patients were divided into C2-C7 group and C1-C7 group. There were 25 cases in the C2-C7 group, 19 males and 6 females, with an average age of 56.3 years (40-71 years), 4 cases of cervical spondylotic myelopathy and 21 cases of ossification of the posterior longitudinal ligament of cervical spine. All of the 25 patients underwent open-door laminoplasty: 20 cases with hinge side anchoring procedure and 5 cases with preservation of the unilateral posterior muscular-ligament complex procedure (titanium cable procedure). There were 20 cases in C1-C7 group, 12 males and 8 females, with an average age of 58.4 years (44-75 years). All of the 20 cases underwent atlas posterior arch resection as well as C2-C7 open-door laminoplasty, including anchoring procedure in 1 case, titanium miniplate procedure in 4 cases, and titanium cable procedure in 15 cases. Standardized vertebral-cord distance (SVCD) at each level from atlas to level C6,7 was measured on T2-weighted images of MR on the mid-sagittal plane in the neutral position performed 3-12 months postoperatively at each individual level. As the main outcomes, the SVCD values obtained at the same level of the two groups were compared between the two groups. Shapiro-Wilk normality test was performed on the SVCD values at C1,2 and C2 levels of two groups. The area under the normal distribution curve of SVCDs was used to calculate the corresponding residual compression rate with different magnitude of compression mass to further discover the difference of the decompression effect between the two groups. Results The SVCD obtained at the level of the anterior arch of atlas (C1), the junction of odontoid process and axis (C1,2) and the middle part of axis body (C2) in the C2-C7 group was 9.91±1.34 mm, 8.35±1.27 mm, and 8.22 ±1.43 mm, respectively. The SVCD at the same levels was 11.02±1.60 mm, 9.72±1.24 mm, and 9.12±1.11 mm, respectively. SVCDs differed significantly in the above range between the two groups. However, from level C2,3 to C6,7, there was no significant difference in SVCDs between the two groups. The JOA score of group C2-C7 was 11.8±2.7 preoperatively and increased significantly to 14.7±1.8 at 12 months postoperatively(t=-7.006, P<0.001) with a recovery rate of 57.0%±32.2%. The JOA score of group C1-C7 was 11.7±2.8 preoperatively and increased significantly to 14.2±2.3 at 12 months postoperatively(t=-6.177, P<0.001) with a recovery rate of 51.9%±32.1%. Conclusion Atlas posterior arch resection can significantly increase the decompression effect of posterior cervical surgery from the anterior arch of atlas to the middle part of axis body, but it would not increase the decompression effect at level C2,3 or below. When the magnitude of the ventral compression factor exceeds the decompression limit (8.5 mm) available with C2-C7 decompression in the range from atlas to the middle of the axis body, extending the decompression range by atlas posterior arch resection is an effective means to achieve adequate decompression. Key words: Cervical atlas; Axis; Ossification of posterior longitudinal ligament; Spinal cord compression; Decompression, surgical

A Theoretical and Numerical Analysis of the Worst-Case Size of Reduced Ordered Binary Decision Diagrams

Binary Decision Diagrams (BDDs) and in particular ROBDDs (Reduced Ordered BDDs) are a common data structure for manipulating Boolean expressions, integrated circuit design, type inferencers, model checkers, and many other applications. Although the ROBDD is a lightweight data structure to implement, the behavior, in terms of memory allocation, may not be obvious to the program architect. We explore experimentally, numerically, and theoretically the typical and worst-case ROBDD sizes in terms of number of nodes and residual compression ratios, as compared to unreduced BDDs. While our theoretical results are not surprising, as they are in keeping with previously known results, we believe our method contributes to the current body of research by our experimental and statistical treatment of ROBDD sizes. In addition, we provide an algorithm to calculate the worst-case size. Finally, we present an algorithm for constructing a worst-case ROBDD of a given number of variables. Our approach may be useful to projects deciding whether the ROBDD is the appropriate data structure to use, and in building worst-case examples to test their code.

The low-velocity impact and post-impact properties of ultra-high-molecular-weight polyethylene fiber weft plain knitted structural composites

This study investigated the impact and post-impact behavior of different layer weft plain knitted composite materials based on modified ultra-high-molecular-weight polyethylene/epoxy composites. The modified ultra-high-molecular-weight polyethylene weft plain knitted composites with 8, 12, 16 layers were prepared by vacuum-assisted resin transfer molding process and then subjected to impact and post-impact compression test. The impact properties were analyzed using the contact force–deflection and energy–time curves, and the post-impact compression was analyzed using the compression strength–strain curves. It can be obtained that the maximum contact force, absorbed energy, and residual compression strength after impact of the 16-layer specimen are 81.40%, 74.18%, and 73.25% more than those in the 8-layer specimen. respectively. According to the ultrasonic C-scan tests for the impact samples, the 16-layer specimen had the least damage area after the impact test, and the 8-layer composites damage area was 117.45% more than the 16-layer specimen.

Structure–property relationships of hydrothermally treated western hemlock

Western hemlock (Tsuga heterophylla), mostly found in west coast of North America, is a highly underutilized and low-value timber species, partially because of the presence of wet pockets, which makes wood processing challenging, especially when drying and sawing. The present work studies the modification of western hemlock using a hydrothermal process, which induced significant changes in the chemical structure and physical characteristics of the wood. The treatment caused the degradation of hemicellulose and reduced the quantity of adsorbed water and free hydroxyl groups. As a result, the wood became less hygroscopic and exhibited improved dimensional and thermal stability with a darker and more attractive color. The hydrothermally-induced variations in the wood structure also influenced its mechanical properties. Flexural bending tests revealed that the specific modulus of rupture and specific maximum load decreased after treatment, while the specific modulus of elasticity increased. In addition, the hydrothermal process was successful in eliminating case hardening, which is typically caused by residual compression stress during conventional kiln drying of wood. These results reveal that hydrothermal treatment is a promising method to expand utilization and develop value-added wood products using low quality wood, such as western hemlock.

Post-operative nerve injuries after cervical spine surgery.

Although relatively rare, post-operative nerve injuries may occur after cervical spine procedures. The most common post-operative neural disorder is C5 nerve palsy. The risk factors for C5 nerve palsy are male gender, OPLL, and posterior cervical approaches. It generally presents with deltoid and/or biceps weakness, and may present immediately or several days after surgery. Treatment is generally conservative due to transient duration of symptoms, but evaluation of residual compression at C4-5 is essential. PTS (Parsonage-Turner syndrome) is an idiopathic plexopathy generally presenting with severe neuropathic pain in the shoulder, neck, and arms, followed by neurological deficits involving the upper brachial plexus. The deficits typically present in a delayed fashion after the onset of pain. Once residual nerve compression is ruled out, initial treatment is based on pain control and physical therapy. Post-operative C8-T1 nerve palsies occur with weakness of the five intrinsic muscles of the hand innervated by the medial nerve, with sensory symptoms in the territory innervated by the ulnar nerve (ulnar two digits of the hand), and also the medial forearm. The risk factors for C8-T1 nerve injuries after surgery are C7 pedicle subtraction osteotomies and posterior fixation of the cervico-thoracic junction, especially in patients with preoperative C7-T1 stenosis. A wide foraminal decompression at C7-T1 region is necessary to minimize risk of this complication. Finally, Horner's syndrome can occur post-operatively, especially after anterolateral approaches to the middle and lower levels of the cervical spine. It is characterized by ipsilateral papillary miosis, facial anhydrosis, and ptosis secondary to injury of the cervical sympathetic nerves. Avoid using the cautery on the lateral border of the longus colli muscle, where the sympathetic chain lies and place the retractors properly underneath the muscle to decrease the chance of sympathetic injuries. It can also occur from iatrogenic compression or injury to the T1 nerve root, as the sympathetic chain gets some of its fibers from that level. Understanding the most common potential nerve injuries after cervical spine procedures is helpful in prevention, early diagnosis, and appropriate management.

Examination of low‐velocity impact and mechanical properties after impact of fiber‐reinforced prepreg composites

Fiber‐reinforced prepreg composites are considered to be the most promising materials for aerospace applications. However, these composites are susceptible to impact during in‐service phases. The impact can cause various types of damage, such as matrix cracks, delamination and fiber breakage, thereby considerably decreasing their mechanical properties. In this study, a series of experiments were carried out to investigate the LVI characteristics. The impact damage characteristics of the fiber‐reinforced prepreg composites were examined; the influencing factors and rules of impact damage were investigated; and the damage process and failure mechanism were revealed. X‐ray 3D computed tomography was employed to examine the internal damaged state of the fiber‐reinforced prepreg composites. An experimental study was carried out to investigate their compression after impact performance. The results indicated that impact energy mainly affects damage failure. With increasing impact energy, the impact contact time decreases, while the impact force fluctuation increases. The damage zone was spherical, and the damaged area increased with energy. The impact damage led to the sharp decrease in the remaining compressive strength and stiffness of the material, and the residual compression strength and stiffness were decreased to 62.25 and 76.6%, respectively. POLYM. COMPOS., 40:2154–2164, 2019. © 2018 Society of Plastics Engineers

Micro-Magnetic and Microstructural Characterization of Wear Progress on Case-Hardened 16MnCr5 Gear Wheels.

The evaluation of wear progress of gear tooth flanks made of 16MnCr5 was performed using non-destructive micro-magnetic testing, specifically Barkhausen noise (BN) and incremental permeability (IP). Based on the physical interaction of the microstructure with the magnetic field, the micro-magnetic characterization allowed the analysis of changes of microstructure caused by wear, including phase transformation and development of residual stresses. Due to wide parameter variation and application of bandpass filter frequencies of micro-magnetic signals, it was possible to indicate and separate the main damage mechanisms considering the wear development. It could be shown that the maximum amplitude of BN correlates directly with the profile form deviation and increases with the progress of wear. Surface investigations via optical and scanning electron microscopy indicated strong surface fatigue wear with micro-pitting and micro-cracks, evident in cross-section after 3 × 105 cycles. The result of fatigue on the surface layer was the decrease of residual compression stresses, which was indicated by means of coercivity by BN-analysis. The different topographies of the surfaces, characterized via confocal white light microscopy, were also reflected in maximum BN-amplitude. Using complementary microscopic characterization in the cross-section, a strong correlation between micro-magnetic parameters and microstructure was confirmed and wear progress was characterized in dependence of depth under the wear surface. The phase transformation of retained austenite into martensite according to wear development, measured by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) was also detected by micro-magnetic testing by IP-analysis.

Characterizations of macroscopic deformation and particle crushing of crushed gangue particle material under cyclic loading: In solid backfilling coal mining

In solid backfilling coal mining (SBCM), the deformation resistance of crushed gangue particle material (CGPM) is critical for controlling overburden strata movement and ground surface subsidence. In engineering practice, CGPM is generally circularly compacted first by the compaction machine to reduce its compressibility. However, a systematic approach to guide the compaction practices does not appear to be available. This study implemented an experimental approach to investigate the macroscopic deformation and particle crushing characteristics of CGPM during constant amplitude cyclic loading (CACL) and continuously loading again after CACL (CL-CACL). At the same time, the influence mechanism of particle crushing on macroscopic deformation of CGPM was also revealed. The results show that the residual compression ratio increased with the cyclic loading times in CACL experiments, but in CL-CACL experiments, the final compression ratio decreased with the cyclic loading times that the samples have borne before, which indicates that cyclic loading can significantly improve the deformation resistance of CGPM. It is also shown that the crushing ratio (Bg) increased with the cyclic loading times in CACL experiments. However, it was opposite in CL-CACL experiments. There existed a piecewise linear relationship between the residual compression ratio and the crushing ratio, which indicates the particle crushing is a key factor to leads macroscopic deformation of CGPM. The research can reveal the influence mechanism of particle crushing on macroscopic deformation of CGPM and provide a systematic approach to guide the compaction engineering practices in SBCM.