Passive Stability Research Articles

Neuromuscular Control During Stair Descent and Artificial Tibial Translation After Acute ACL Rupture.

Background:Anterior cruciate ligament (ACL) rupture has direct effect on passive and active knee stability and, specifically, stretch-reflex excitability.Purpose/Hypothesis:The purpose of this study was to investigate neuromuscular activity in patients with an acute ACL deficit (ACL-D group) compared with a matched control group with an intact ACL (ACL-I group) during stair descent and artificially induced anterior tibial translation. It was hypothesized that neuromuscular control would be impaired in the ACL-D group.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Surface electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST) muscles was recorded bilaterally in 15 patients with ACL-D (mean, 13.8 days [range, 7-21 days] since injury) and 15 controls with ACL-I during stair descent and artificially induced anterior tibial translation. The movements of stair descent were divided into preactivity, weight acceptance, and push-off phases. Reflex activity during anterior tibial translation was split into preactivity and short, medium, and late latency responses. Walking on a treadmill was used for submaximal EMG normalization. Kruskal-Wallis test and post hoc analyses with Dunn-Bonferroni correction were used to compare normalized root mean square values for each muscle, limb, movement, and reflex phase between the ACL-D and ACL-I groups.Results:During the preactivity phase of stair descent, the hamstrings of the involved leg of the ACL-D group showed 33% to 51% less activity compared with the matched leg and contralateral leg of the ACL-I group (P < .05). During the weight acceptance and push-off phases, the VL revealed a significant reduction (approximately 40%) in the involved leg of the ACL-D group compared with the ACL-I group. At short latency, the BF and ST of the involved leg of the ACL-D group showed a significant increase in EMG activity compared with the uninvolved leg of the ACL-I group, by a factor of 2.2 to 4.6.Conclusion:In the acute phase after an ACL rupture, neuromuscular alterations were found mainly in the hamstrings of both limbs during stair descent and reflex activity. The potential role of prehabilitation needs to be further studied.

Corrosion behavior of severely plastically deformed Mg and Mg alloys

Magnesium (Mg) alloys have several advantages, such as low density, high specific strength and biocompatibility. However, they also suffer weak points, such as high corrosion, low formability and easy ignition, which makes their applications limited. Many studies have been conducted to overcome these disadvantages and further improve the advantages of Mg alloys. Severe plastic deformation (SPD) is one of the most important techniques and has great effects on the microstructure refinement of Mg alloys and improvements in their strength and formability. Several researchers have studied the corrosion behavior of SPD-processed Mg alloys in recent decades. However, these studies have reported some controversial effects of SPD on the corrosion of Mg alloys, which makes the research roadmap ambiguous. Therefore, it is important to review the literature related to the corrosion properties of Mg alloys prepared by SPD and understand the mechanisms controlling their corrosion behavior. Effective grain refinement by SPD improves the corrosion properties of pure Mg and Mg alloys, but control of the processing conditions is a key factor for achieving this goal because texture, dislocation density, size and morphology of secondary phase also importantly affects the corrosion properties of Mg alloys. Reduced grain size in the fine grain-size range can decrease the corrosion rate due to the increased barrier effect of grain boundaries against corrosion and the formation of a stable passivation layer on the surface of fine grains. Basal texture reduces the corrosion rate because basal planes with the highest atomic planar density are more corrosion resistant than other planes. Increased dislocation density after SPD deteriorates the corrosion resistance of the interior grains and thus proper annealing after SPD is important. The fine and uniform distribution of secondary phase particles during SPD is important to minimize the micro-galvanic corrosion effect and retain small grains during annealing treatment for removing dislocations.

A novel Ti42.5Zr42.5Nb5Ta10 multi-principal element alloy with excellent properties for biomedical applications

Body-centered cubic (BCC) Ti–Zr–Nb–Ta multi-principal element alloys (MPEAs) have drawn extensive research attention as orthopedic implant materials. In this work, a novel Ti42.5Zr42.5Nb5Ta10 multi-principal element alloy was developed for biomedical applications in terms of its microstructure, mechanical properties, wear performance, corrosion behavior, and in vitro biocompatibility. The Ti42.5Zr42.5Nb5Ta10 alloy after cold rolling followed by annealing at 880 °C (TZNT-880), possessed excellent mechanical properties combination, with a yield strength of 839.5 MPa, elongation at fracture of 22.6%, and Young's modulus of 63.2 GPa, superior to most of the currently existing biomedical BCC MPEAs. Meanwhile, TZNT-880 alloy exhibited higher wear resistance compared with commercial CP-Ti and Ti6Al4V, which is strongly related to its high H/E and H3/E2 values. Also, TZNT-880 alloy showed good corrosion resistance, as revealed by a nobler corrosion potential, lower corrosion current densities, and higher passivation stability, which is attributed to the formation of passivation films consisting of TiO2, ZrO2, Nb2O5, and Ta2O5. The in vitro biocompatibility tests demonstrated that the TiZrNbTa alloys can support cell adhesion and proliferation with high biocompatibility comparable to that of CP-Ti and Ti6Al4V, indicating their potential as a candidate for implant material.

Passive control and stability of the indoor temperature of a closed cavity based on the process of integrating phase change materials

Passive control and stability of the indoor temperature of a closed cavity based on the process of integrating phase change materials

Effect of the Trunk and Upper Limb Passive Stabilization on Hand Movements and Grip Strength Following Various Types of Strokes-An Observational Cohort Study.

Almost half of the patients surveyed report impaired function of the upper limbx and handx after stroke. The effect of the passive trunk and shoulder stabilization on the recovery of coordinated hand movement is unclear. This study examined whether passive stabilization of the trunk and shoulder could improve the functional state of the hands after various types of strokes. It is an observational prospective cohort study conducted at the Rehabilitation Clinic in two parallel groups of patients with four different types of strokes (hemorrhagic and ischemic of the brain, similar to the cerebellum). A total of 120 patients were analyzed. Patients were examined in various positions: sitting without a backrest with the upper limb adjacent to the body, supine with the upper limb perpendicular to the body, and supine with the arm stabilized in relation to the patient’s body. Hand Tutor devices and a hand dynamometer were used for the measurements. The frequency and maximum range of motion as well as the grip strength were measured in three different positions of the trunk and upper limb. Passive stabilization of the trunk and shoulder showed more statistically significant differences in Group II. In group II, both in patients after hemorrhagic stroke (wrist Hz p = 0.019; wrist ROM p = 0.005; Hz F5 p = 0.021; Hz F4 p = 0.016; Hz F3 p = 0.019; Hz F2 p = 0.021) and ischemic stroke (p = 0.001 for wrist Hz, wrist ROM, Hz F from 5 to F2; and ROM F1; ROM F3 p = 0.009; ROM F2 p = 0.010), and hemorrhagic cerebellum, improvement of parameters was observed. Stabilization of the upper limb and passive stabilization of the trunk improved the frequency and range of movements in the radiocarpal joint and in the fingers of patients after stroke, regardless of the type of stroke.

Levitation Characteristics of High-Temperature Superconducting Bulks of Different Orientations and Arrays

High-temperature superconducting (HTS) maglev has good application prospects due to its passive stability. There are a lot of researches on the levitation characteristics of a single HTS bulk in the applied magnetic field. However, the bulks are usually arranged in an array in practical applications. In addition, experiments proved that the levitation force and guidance force of the system with multiple bulks are not equal to their linear superposition. Therefore, it is interesting to further study the law of interaction between bulks quantitatively. In this paper, firstly, the method of how the bulk's inhomogeneities are described in the electromagnetic model is introduced. Secondly, the levitation and guidance force of bulks of different orientations and combinations are calculated using a three-dimensional (3D) simulation model considering the inhomogeneities. A Qualitative Rapid Analysis Method (QRAM) to predict the effect of the combinations is proposed. The accuracy of the prediction method has been verified for different working conditions. Finally, the effect of the shape of bulks on the levitation characteristics is investigated. The result shows a weak “aggregation advantage”. This paper provides some reference for the design and prediction of the levitation and guidance performance of the HTS maglev system with a combination of multiple HTS bulks.

A Full-Wave Generalized PEEC Model for Periodic Metallic Structure With Arbitrary Shape

In this work, a full-wave partial element equivalent circuit (PEEC) model for 2-D periodic metallic structures is proposed. The mixed potential integral equations (MPIEs) with periodic Green’s function (GF) are interpreted as loop equations following Kirchhoff’s voltage law (KVL) in a circuit domain. The impact of gauge freedom in the MPIE on the corresponding PEEC model is discussed. A tailored gauge function is introduced to form a generalized PEEC model for periodic structures, which demonstrates superior passivity and frequency stability. With the proposed PEEC model, lumped and active elements can be easily integrated with conducting bodies for field-circuit co-simulation. Through the distributed circuit including coupling elements, the PEEC model provides a clear physical insight into the electromagnetic behavior of the physical models for design and optimization. Three numerical examples, including frequency-selective surface (FSS), array antenna, and pixelwise meta-atom, are given to illustrate the accuracy and efficiency of the proposed PEEC model.

Walking in the Absence of Anterior Cruciate Ligament: The Role of the Quadriceps and Hamstrings

The actual need for surgical reconstruction of an injured anterior cruciate ligament (ACL) is still a matter of debate. The aim of this study was to quantify and analyze the knee kinematics and the ligament force redistribution resulting from the ACL sacrifice and the consequent effects of changing the quadriceps and hamstring activity during walking. A three-dimensional musculoskeletal model was used to simulate the behavior of the knee joint during the gait cycle, in different testing conditions: an ACL-deficient knee, an ACL-deficient knee with hamstrings inactivated and an ACL-deficient knee with quadriceps inactivated. Our results showed that in the ACL-deficient knee, the medial collateral ligament (MCL) was the main passive stabilizer of the anterior translation of the tibia. Furthermore, the compensation effects produced by the hamstrings and quadriceps in the ACL-deficient knee during walking were quantified and analyzed. In the case of ACL sacrifice, reducing the quadriceps activity would allow for relieving all ligaments in general, except for the posterior cruciate ligament, which required more consistent recruitment in the support phase. Meanwhile, hamstring activity was crucial not only to compensate for the absence of ACL in limiting the anterior tibial displacement but also to reduce the risk of MCL injury.

Analytic theory of ideal-MHD vertical displacements in tokamak plasmas

An analytic derivation of the relevant dispersion relation for vertical displacements in shaped tokamak plasmas is presented, valid for arbitrary values of the ellipticity parameter. The theory is developed within the framework of the reduced ideal-MHD model. A nearby, perfectly conducting wall can provide passive feedback stabilization of vertical displacements on the ideal-MHD timescale. The mechanism for passive stabilization relies on image currents induced on the metallic wall. However, if the plasma extends to the magnetic separatrix, where magnetic X-points are located, as in the case of a divertor tokamak configuration, perturbed axisymmetric currents carried by the plasma in the vicinity of the X-points are triggered. It is shown that these X-point currents can provide passive feedback stabilization, even in the absence of a nearby wall. X-point currents are excited due to the resonant nature of magnetic X-points with respect to toroidal axisymmetric perturbations. An intermediate case, where the plasma boundary is located just inside the magnetic separatrix, is also analyzed, providing additional insight into the stabilization mechanism.

Biomechanical considerations of the posterior surgical approach to the lumbar spine

Background contextThe effect of the posterior midline approach to the lumbar spine, relevance of inter- and supraspinous ligament (ISL&SSL) sparing, and potential of different wound closure techniques are largely unknown despite their common use. PurposeThe aim of this study was to quantify the effect of the posterior approach, ISL&SSL resection, and different suture techniques. Study DesignBiomechanical cadaveric study. MethodsFive fresh frozen human torsi were stabilized at the pelvis in the erect position. The torsi were passively loaded into the forward bending position and the sagittal angulation of the sacrum, L4 and T12 were measured after a level-wise posterior surgical approach from L5/S1 to T12/L1 and after a level-wise ISL&SSL dissection of the same sequence. The measurements were repeated after the surgical closure of the thoracolumbar fascia with and without suturing the fascia to the spinous processes. ResultsPassive spinal flexion was increased by 0.8±0.3° with every spinal level accessed by the posterior approach. With each additional ISL&SSL resection, a total increase of 1.6±0.4° was recorded. Suturing of the thoracolumbar fascia reduced this loss of resistance against lumbar flexion by 70%. If the ISL&SSL were resected, fascial closure reduced the lumbar flexion by 40% only. In both settings, suturing the fascia to the spinous processes did not result in a significantly different result (p=.523 and p=.730 respectively). ConclusionEach level accessed by a posterior midline approach is directly related to a loss of resistance against passive spinal flexion. Additional resection of ISL&SSL multiplies it by a factor of two. Clinical SignificanceThe surgical closure of the thoracolumbar fascia can reduce the above mentioned loss of resistance partially. Suturing the fascia to the spinal processes does not result in improved passive stability.

Cancellation of photothermally induced instability in an optical resonator

Optical systems are often subject to parametric instability caused by the delayed response of the optical field to the system dynamics. In some cases, parasitic photothermal effects aggravate the instability by adding new interaction dynamics. This may lead to the possible insurgence or amplification of parametric gain that can further destabilize the system. In this paper, we show that the photothermal properties of an optomechanical cavity can be modified to mitigate or even completely cancel optomechanical instability. By inverting the sign of the photothermal interaction to let it cooperate with radiation pressure, we achieve control of the system dynamics to be fully balanced around a stable equilibrium point. Our study provides a feedback solution for optical control and precise metrological applications, specifically in high-sensitivity resonating systems that are particularly susceptible to parasitic photothermal effects, such as our test case of a macroscopic optical levitation setup. This passive stabilization technique is beneficial for improving system performance limited by photothermal dynamics in broad areas of optics, optomechanics, photonics, and laser technologies.

Electrochemical corrosion behaviour of oxide dispersion strengthened iron aluminides in 3.5 wt % NaCl solution

Electrochemical corrosion and passivation characteristics of the oxide dispersion strengthened (ODS) Fe3Al–Ti and ODS Fe3Al–Ti–Zr alloys immersed for different exposure times of 1, 72, 120, 166 and 240 h in 3.5 wt % NaCl solution were studied using open-circuit potential, cyclic polarization and electrochemical impedance spectroscopy techniques. Both ODS Fe3Al–Ti and ODS Fe3Al–Ti–Zr alloys exhibit pitting corrosion under chloride ions exposure. In both alloys, corrosion rate decreased as immersion time increased and decreased beyond 72 h and similarly up to 240 h due to the formation of a passive layer that prevented further corrosion. ODS Fe3Al–Ti–Zr alloy exhibited more resistance to pitting corrosion for all exposure times than ODS Fe3Al–Ti alloy. Electrochemical impedance spectroscopy results indicated that the presence of Zr in ODS Fe3Al–Ti–Zr alloy improved the corrosion resistance, charge transfer resistance and its passive layer stability which can be attributed to the formation of a better protective passive layer as compared to ODS Fe3Al–Ti alloy. Even though the ODS Fe3Al–Ti–Zr alloy exhibited better passivation characteristics and corrosion resistance, the difference in electrochemical properties of the two alloys was marginal.

Robust Tipless Positioning Device for Near-Field Investigations: Press and Roll Scan (PROscan).

Scanning probe microscopes scan and manipulate a sharp tip in the immediate vicinity of a sample surface. The limited bandwidth of the feedback mechanism used for stabilizing the separation between the tip and the sample makes the fragile nanoscopic tip very susceptible to mechanical instabilities. We propose, demonstrate, and characterize an alternative device based on bulging a thin substrate against a second substrate and rolling them with respect to each other. We showcase the power of this method by placing gold nanoparticles and semiconductor quantum dots on the two opposite substrates and positioning them with nanometer precision to enhance the fluorescence intensity and emission rate. Furthermore, we exhibit the passive mechanical stability of the system over more than 1 h. Our design concept finds applications in a variety of other scientific and technological contexts, where nanoscopic features have to be positioned and kept near contact with each other.

Inhibition of Aluminum Corrosion with the Addition of the Tris(pentafluoroethyl)trifluorophosphate Anion to a Sulfonylamide-Based Ionic Liquid for Sodium-Ion Batteries

Ionic liquids (ILs) based on sulfonylamide-type anions have gained widespread utility as electrolytes for secondary batteries. Although sulfonylamide-based IL electrolytes are known to form a stable passivation layer that prevents Al corrosion, the Al electrode in the Na[FSA]-[C2C1im][FSA] ([FSA] = bis(fluorosulfonyl)amide and [C2C1im] = 1-ethyl-3-methylimidazolium) IL, is found to be afflicted by pitting corrosion at potentials above 4 V vs Na+/Na during electrochemical measurement at 90 °C. Therefore, this study investigates the suppressive effect of [FAP]− (FAP = tris(pentafluoroethyl)trifluorophosphate) on the Al corrosion behavior of the IL electrolyte. Here, the inhibited corrosion of the Al electrode is confirmed through a series of cyclic voltammetry measurements, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Charge-discharge tests performed using a Na3V2(PO4)2F3 positive electrode demonstrates that the addition of [FAP]– into the IL enhances cycling performance at the intermediate temperature of 90 °C.

Corrosion behavior of CoCrNiMoBC coatings obtained by laser cladding: Synergistic effects of composition and microstructure

In order to improve corrosion resistance of stainless steels, a CoCrNiMoBC coating was prepared by laser cladding. The microstructure, composition, and crystallographic orientation relationships of the coating were discussed. Electrochemical methods were used to evaluate its corrosion behavior. Results showed that the coating had remarkable resistance to chloride ion corrosion under strongly acidic conditions. The critical pitting temperature of the coating was higher than 80 °C in both neutral and acidic chloride ion environments. Immersion tests confirmed that pits did not expand significantly after 10 days immersion in 5 M HCl solution. The excellent corrosion resistance stemmed from a stable passivation film formed due to the synergistic effects of composition and microstructure.

Influence of positive pulse voltages on structure, mechanical, and corrosion inhibition characteristics of Si/DLC coatings

In this study, Si/DLC films were effectively deposited on 2024-Al alloy using a plasma-enhanced chemical vapor method at different pulse voltages. Scanning electron microscopy, X-ray diffraction spectroscopy, 2D optical profilometer, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the structure of the DLC coatings. The adhesion strength was performed using Scratch Tester. Further, the Nano Indenter G200 apparatus was used to measure the hardness and Young's modulus of coatings. The Ball-on-Disk Tester was used to measure the friction coefficient of the specimens. A Potentiostat/Galvanostat electrochemical workstation was used to examine the corrosion performance and passive stability of DLC coatings in 3.5 wt% NaCl solution. The findings demonstrated that the thickness of the coatings increased with increasing the pulse voltage to 1800 V, causing an improvement in mechanical properties and corrosion resistance. This is due to an increase in the amount of sp3 hybrid in the coating, which reduces the electrical conductivity of DLC and limits electron transfer and electrical charge exchange at the coating surface. However, the corrosion rate of the coatings increased when the pulse voltage increased to 2200 V.

Plasma sprayed graphene reinforced titanium nitride composite coating: An effective solution for mitigating the corrosion attack

Plasma sprayed graphene nanoplatelets (GNPs) reinforced titanium nitride (TiN) composite coating was found to be the best alternative for mitigating the corrosion attack. The coating reveals the presence of GNPs and it fills the voids and cracks, thus shrinking the inherent porosity in TiN coating. The porosity of composite coatings was reduced ~6 % just with the mere addition of 2 wt% of GNP (TiN-2GNPs). During electrochemical corrosion test, corrosion rates (CR) of TiN-1 wt% GNP (CR = 0.62 mpy) and TiN-2 wt% GNP (CR = 0.17 mpy) coatings were found ~5 and ~ 20 times lower, respectively than TiN (CR = 3.10 mpy) in 3.5 wt% NaCl electrolyte solution. This significant reduction in corrosion rate is attributed due to the densification of TiN matrix with addition of GNPs, creating the stable passivation between the electrolyte and the coating surface. Further, the detailed post-corrosion analysis disclosed the mitigation of corrosive salt through the composite coating and demonstrated the TiN-2GNP coating as an effective solution for corrosion attack.

Discovery of potent benzoxaborole inhibitors against SARS-CoV-2 main and dengue virus proteases

The RNA viruses SARS-CoV-2 and dengue pose a major threat to human health worldwide and their proteases (Mpro; NS2B/NS3) are considered as promising targets for drug development. We present the synthesis and biological evaluation of novel benzoxaborole inhibitors of these two proteases. The most active compound achieves single-digit micromolar activity against SARS-CoV-2 Mpro in a biochemical assay. The most active substance against dengue NS2B/NS3 protease has submicromolar activity in cells (EC50 0.54 μM) and inhibits DENV-2 replication in cell culture. Most benzoxaboroles had no relevant cytotoxicity or significant off-target inhibition. Furthermore, the class demonstrated passive membrane penetration and stability against the evaluated proteases. This compound class may contribute to the development of antiviral agents with activity against DENV or SARS-CoV-2.

Effect of the Tempering Process on the Corrosion Performance of Wire Arc Additively Manufactured 420 Martensitic Stainless Steel

With the aim of modifying the microstructure and improving the corrosion performance of a wire arc additive manufactured 420 martensitic stainless steel, heat treatment cycles consisting of austenitizing at 1,150°C followed by air cooling and subsequent tempering at different temperatures (300°C, 400°C, 500°C, and 600°C) were applied to the as-printed alloy. Microstructural analysis revealed that the austenitization and subsequent air-cooling treatment led to the removal of retained austenite and delta ferrite from the as-printed structure, while the tempering process resulted in the precipitation of a variety of carbide particles at different tempering temperatures. Electrochemical tests performed in an aerated 3.5 wt% NaCl solution showed that tempering at 400°C led to the highest corrosion resistance, while tempering at 500°C deteriorated the alloy’s resistance against localized corrosion. The most stable passive layer was found to form on the 400°C tempered sample due to the uniformity of Cr-concentration in the formed carbide precipitates and their surrounding matrix. However, Cr-rich carbide precipitates formed in the 500°C tempered sample were found to deteriorate the passive film stability throughout the immersion time in the electrolyte.

Sub-40 fs optical parametric oscillator beyond the gain bandwidth limit.

We report a compact and passively stable optical parametric oscillator for direct generation of sub-40 fs pulses, five times shorter than the 200 fs pump oscillator. By employing an intracavity all normal dispersion feedback fiber, we achieved low-noise and coherent broadening beyond the parametric gain bandwidth limitation. We demonstrate spectral coverage from 1.1 to 2.0 µm with excellent passive power and spectral stability below 0.1% rms and a footprint smaller than 14 × 14 cm2.