Large Moment Research Articles

Defects Engineering Induced Ultrahigh Magnetization in Rare Earth Element Nd‐doped MoS2

AbstractVarious concentrations (0, 0.5, 1, and 5 at%) of Nd are doped into MoS2 single crystals via ion implantation. Experimental results reveal that Nd exists in the form of trivalent state when the doping concentration is below 5 at% and a variety of defects, such as sulfur and molybdenum vacancies, are formed in Nd‐doped MoS2. Compared to pure MoS2 that only shows diamagnetism, Nd doping successfully induces room‐temperature ferromagnetic ordering. Extremely high magnetization (1640 emu cm−3) is observed in 1 at% Nd‐doped MoS2. First‐principles density functional theory calculations suggest that the various structural defects, including substitutions, vacancies, interstitials, antisites, and their complexes, are magnetic possessing large spin moments. The defects coupled with Nd dopants ferromagnetically may form the bound magnetic polarons to induce ferromagnetic ordering. The work has demonstrated that through defects engineering and rare earth element doping, extremely high magnetization materials can be achieved in layered structured materials. On the other hand, though the experiment work is done by implanting MoS2 single crystals, theoretical calculations indicate that 2D MoS2 with bilayers or a few layers can also result in ultrahigh magnetization.

Kinematics observed during ACL injury are associated with large early peak knee abduction moments during a change of direction task in healthy adolescents.

Cluster analysis of knee abduction moment waveforms may be useful to examine biomechanical data. The aim of this study was to analyze if the knee abduction moment waveform of early peaks, consistent with anterior cruciate ligament injury mechanisms, was associated with foot‐trunk distance, knee kinematics, and heel strike landing posture, all of which have been observed during anterior cruciate ligament injuries. One hundred and seventy‐seven adolescent athletes performed cutting maneuvers, marker‐based motion capture collected kinetic and marker data and an 8‐segment musculoskeletal model was constructed. Knee abduction moment waveforms were clustered as either a large early peak, or not a large early peak using a two‐step process with Euclidean distances and the Ward‐d2 cluster method. Mediolateral distance between foot and trunk was associated with the large early peak waveform with an odds ratio (95% confidence interval) of 3.4 (2.7–4.4). Knee flexion angle at initial contact and knee flexion excursion had odds ratios of 1.9 (1.6–2.4) and 1.6 (1.3–2.0). Knee abduction excursions had an odds ratio of 1.8 (1.1–2.4) and 1.8 (1.4–2.4), respectively. Heel strike landings and anteroposterior distance between foot and trunk were not associated with the large early peak waveform with odds ratios of 1.2 (0.9–1.7) and 1.1 (0.8–1.3), respectively. The knee abduction moment waveform is associated with several kinematic variables observed during ACL injury. The results support intervention programs that can modify these kinematics and thus reduce early stance phase knee abduction moments.

Керування вектором тяги ракетного двигуна вдувом продуктів детонації в надзвукову частину сопла

For solving non-traditional problems of rocket flight control, in particular, for the conditions of impact of a nuclear explosion, non-traditional approaches to the organization of the thrust vector control of a rocket engine are required. Various schemes of gas-dynamic thrust vector control systems that counteract impact actions on the rocket were studied. It was found that the dynamic characteristics of traditional gas-dynamic thrust vector control systems do not allow one to solve the problem of counteracting impact actions on the rocket. Appropriate dynamic characteristics can provide a perturbation of the supersonic flow by injecting into the nozzle the detonation products with the main shock wave propagating in the supersonic flow. This way to perturb the supersonic flow in a rocket engine nozzle is investigated in this paper. In order to identify the principles of producing control forces and provide a perturbation of the supersonic flow by injecting into the nozzle the detonation products with the main shock wave propagating in the supersonic flow, a computer simulation of the nozzle flow was performed. The nozzle of the 11D25 engine developed by Yuzhnoye State Design Office and used in the third stage of the Cyclone-3 launch vehicle was taken as a basis. The thrust vector control scheme relies on the use of the main fuel component detonation. The evolution of the detonation wave in the supersonic flow of the combustion chamber nozzle was simulated numerically. According to the nature of the perturbation propagation in the nozzle, the lateral force from the perturbation has an alternating character with the perturbation stabilization in sign and magnitude when approaching the critical nozzle section. The value of the relative lateral force is sufficient for counteracting large disturbing moments of short duration. Thus, the force factors that can be used to control the rocket engine thrust vector are identified. Further research should focus on finding the optimal location of the detonation product injection in order to prevent mutual compensation of force factors.

Performance of sheet pile as a seismic retrofit for old piled abutment subjected to liquefaction-induced lateral spreading

Liquefaction-induced lateral spreading causes severe damage to the pile foundation of structures. Old structures that are not properly designed for liquefaction are more vulnerable to a strong earthquake. Many old piled abutments require a remedial measure against lateral spreading. This paper examines the responses of an old piled abutment subjected to liquefaction-induced lateral spreading and efficacy of the sheet pile reinforcement technique to mitigate the associated damage through dynamic centrifuge experiments. The experiment on the old piled abutment reveals that the abutment moves together with the spreading soil and shows a significant channel-ward movement without pinning effect. The large bending moments are found to take place around the pile head and the interface of the loose and the dense layer as expected. The installation of sheet pile in front of the abutment considerably reduces the channel-ward movement of the abutment thus mitigate the bending moment demand of the piles.

Damage analysis of the cut-off wall in a landslide dam based on centrifuge and numerical modeling

A concrete cut-off wall has been recently used in a landslide dam as an anti-seepage measure. Due to it is under a complex loading condition, the wall may undergo inelastic straining and have a potential of cracking. Several centrifuge model tests and numerical simulation are conducted to investigate the damage behavior of the cut-off wall. The numerical method of concurrently modelling small cracks in the cut-off wall and the overall landslide dam based on the finite element method (FEM)-Peridynamics (PD) multiscale coupling method is confirmed to be effective by the centrifuge model tests. The cut-off wall buried in a landslide dam bears a bending effect under lateral loadings in the absence of overlying fill. The lower part of the wall may have a potential to form cracks induced by large bending moments. The wall is in a tension-shear failure mode with an inclined crack. A parametric study demonstrates that properties of the wall and the soil have a significant effect on the damage behavior of the wall. Also, creep deformation of the dam body does not elongate the crack significantly, but it expands the width of the crack. The crack tends to stabilize over a period of time.

Design models for steel encased high-strength precast concrete piles under axial-flexural loads

The use of steel-encased precast concrete (SC) piles has risen rapidly for the construction of earthquake-resilient foundation systems for buildings in Japan and Southeast Asia. SC piles are used near the pile-pile cap connection owing to their increased ductility, and resistance against large bending moments and axial forces, compared to the other precast concrete piles. However, there are no official guidelines available for the design of SC piles in severe earthquakes, except for a proposed draft by the AIJ committee for the determination of bending capacities. In this work, a database of 79 tests on SC piles, all tested under axial-flexural loads, was created. The bending capacities obtained from these tests were used to verify the provisions of the proposed draft and the provisions for composite member design in AIJ, Eurocode 4 and, AISC. Furthermore, a distributed plasticity formulation was adopted to develop a non-linear static model, that takes into account the concrete confinement and local buckling of steel casing, for prediction of moment and drift capacities. The accuracy of the model was verified against various experiments, and the capability to reproduce the moment-drift relations was confirmed.

Bulk and element-specific magnetism of medium-entropy and high-entropy Cantor-Wu alloys

Magnetic Compton scattering, x-ray magnetic circular dichroism spectroscopy and bulk magnetometry measurements are performed on a set of medium (NiFeCo and NiFeCoCr) and high (NiFeCoCrPd and NiFeCoCrMn) entropy Cantor-Wu alloys. The bulk spin momentum densities determined by magnetic Compton scattering are remarkably isotropic, and this is a consequence of the smearing of the electronic structure by disorder scattering of the electron quasiparticles. Non-zero x-ray magnetic circular dichroism signals are observed for every element in every alloy indicating differences in the populations of the majority and minority spin states implying finite magnetic moments. When Cr is included in the solid solution, the Cr spin moment is unambiguously antiparallel to the total magnetic moment, while a vanishingly small magnetic moment is observed for Mn, despite calculations indicating a large moment. Some significant discrepancies are observed between the experimental bulk and surface magnetic moments. Despite the lack of quantitative agreement, the element specific surface magnetic moments seem to be qualitatively reasonable.

Vibration Feedforward Compensation for Magnetically Suspended Control and Sensitive Gyroscope with Spherical Rotor

Magnetically suspended control and sensitive gyroscope (MSCSG) with two capabilities including attitude control and attitude measurement is promising in meeting the requirements of novel spacecraft. When the momentum vector of a high-speed rotor suspended in five directions is tilted by Lorentz force-type magnetic bearing, the instantaneous large control moment is obtained. The spacecraft attitude can be sensed by a high-speed rotor without deflection interference torque. In this paper, a novel MSCSG with sphere rotor is presented, and its spherical structure and working principle are introduced. The magnetic bearing-rotor dynamic model is established based on Newton’s second law and the gyrokinetic equations. The generating mechanism of three interferences, including bearing dynamic reaction force, deflection torque, and centrifugal force, is analyzed. The feedforward compensation control against three interferences for MSCSG is adopted, and the loading sequence of three interferences is simulated. The optimal sequence of bearing dynamic reaction force, deflection torque, and centrifugal force is used. The radial and axial vibration displacement amplitudes are reduced from 20.8 μm and 31.7 μm to 9.4 μm and 14.9 μm, respectively. The experimental results are in good agreement with the simulation, which indicates the MSCSG rotor unbalance vibration is suppressed effectively by the feedforward compensation method.

First principles investigations of Fe3+ impurity and Fe3+ + V−Cd complex in strongly confined CdSe quantum dot

Solitary dopant or defect in a semiconductor is the basis of the emerging field of optoelectronics known as solotronics. It has been shown that the spin of a single magnetic ion impurity can be manipulated optically. Among the magnetic ions, Fe3+ has been proposed as a primary candidate for the design of quantum dots (QDs) for solotronics because of its zero nuclear spin in contrast to Mn2+ and larger magnetic moment compared to Fe2+. In this work, we performed density function theory calculations to determine optimal parameters for the colloidal synthesis of single FeCd3+over FeCd2+ in CdSe of 1 nm in radius. We also investigated Fe3+ plus Cd vacancy complex (FeCd3++VCd−). Transition energy level calculations show FeCd3+ to be a deep-level donor and VCd− to be a shallow acceptor. Charge difference plots show that the charge of the ionized electron is localized around FeCd3+. Tetrahedral symmetry is retained at the FeCd3+ site. The magnetic moment of Fe3+ is almost the same in the core and at the surface and is equal to ∼4.27 μB for passivated QD. The large moment can be manipulated for spin control in conjunction with unoccupied vacancy states of the triplet t2 level of the shallow VCd acceptor to create a hole spin current in a lithographically patterned surface.

Shear resistance of aluminum alloy extruded H-Section beams

A total of ten 6061-T6 aluminum alloy extruded H-section beams were tested under shear load. The primary design variables were the web slenderness, the shear aspect ratios and the end post conditions. A shear dominant failure mode was observed in specimens with the aspect ratio of 1.0 and a bending failure mode was observed in specimens with larger aspect ratios. Finite element models were developed and verified by the test results. Then a parametric study was carried out to generate an extensive numerical data pool on aluminum alloy H-section beams loaded in shear. The obtained test and numerical results with other available data were subsequently compared with the predictions according to Eurocode 9 and the Direct Strength Method (DSM) in AISI S100 and AS/NZS 4600. In general, the EC 9 provides more accurate results than the DSM formulae, but unsafe ultimate shear load predictions could also be obtained in cases of plastic shear buckling of the web and the relatively flexible flanges subjected to a fairly large moment. The DSM could provide considerably conservative predictions, because the rigidity of end posts and the effect of the stiffness of flanges on the interaction of bending and shear are not considered explicitly.

Searching for general binary inspirals with gravitational waves

We study whether binary black hole template banks can be used to search for the gravitational waves emitted by general binary coalescences. To recover binary signals from noisy data, matched-filtering techniques are typically required. This is especially true for low-mass systems, with total mass M ≲ 10 M⊙, which can inspiral in the LIGO and Virgo frequency bands for thousands of cycles. In this paper, we focus on the detectability of low-mass binary systems whose individual components can have large spin-induced quadrupole moments and small compactness. The quadrupole contributes to the phase evolution of the waveform whereas the compactness affects the merger frequency of the binary. We find that binary black hole templates (with dimensionless quadrupole κ=1) cannot be reliably used to search for objects with large quadrupoles (κ≳ 20) over a wide range of parameter space. This is especially true if the general object is highly spinning and has a larger mass than its binary companion. A binary that consists of objects with small compactness could merge in the LIGO and Virgo frequency bands, thereby reducing its accumulated signal-to-noise ratio during the inspiraling regime. Template banks which include these more general waveforms must therefore be constructed. These extended banks would allow us to realistically search for the existence of new astrophysical and beyond the Standard Model compact objects.

Structural investigation of the collapse of the 16‐story Plasco building due to fire

SummaryOn January 19, 2017, the 16‐story Plasco tower located in Tehran, the capital city of Iran, collapsed in several stages, due to a fire lasting 3.5 h. This paper presents the results of numerical investigations on how the structure behaved during that incident. In this regard, initially, a part of floor system including main truss girders, secondary truss beams, tie beams, and reinforced concrete slab is simulated to study its deformed shape and collapse modes. Then 2D and 3D models of the building are developed to evaluate the global behavior of the structure under fire. The results show that at elevated temperatures, deflection of the floor system, main trusses, and out‐of‐plane bending of the beam‐to‐column gusset plates become excessive, leading to partial collapse of floor, in the location of fire initiation. Also, 2D models show that thermal expansion and catenary action of heated truss induce large lateral displacement and bending moment in perimeter column that cause failure of this column at about 650°C. Finally, 3D models indicate that general collapse of the building is initiated by buckling of the external columns located in the southern perimeter of the building. This result is in good agreement with videos and photos showing actual collapse of the structure.

Wave and Wind Responses of a Very-Light FOWT with Guy-Wired-Supported Tower: Numerical and Experimental Studies

A floating offshore wind turbine (FOWT) concept with a guy-wire-supported tower was investigated to obtain motion results in waves considering its elastic model characteristics. The FOWT concept studied aims to reduce the construction costs by using a light-weight structure tensioned with guy wires and a downwind type. Wave tank experiments of an elastically similar segmented backbone model in the 1:60 scale were carried out to clarify the dynamic elastic response features of the structure. The experimental results were compared with numerical simulations obtained from NK-UTWind and WAMIT codes. The bending moment measured at the tower and pontoons had two peak values for different wave periods carried out. The short-wave period peak was due to sagging/hogging when the wavelength matched the floater length. The second peak was due to the large tower top acceleration, which caused a large bending moment at the tower base and pontoon to support the inertia force. The wind force was not significant to modify the FOWT response. The sensibility analysis in pontoons and tower rigidities confirmed the importance of the guy wires to support the inertia due to the waves and wind incidence. The new concept of a very-light FOWT with a guy-wire-supported tower may be an option for future FOWT developments.

Seismic behavior of a dolphin-type berth subjected to liquefaction induced lateral spreading: 1g large scale shake table testing and numerical simulations

The effects of liquefaction induced lateral spreading on the piles of a dolphin-type berth were investigated using 1 g large scale shake table testing accompanied by numerical simulations. For this purpose, various aspects of the response of the soil and the pile group to lateral spreading were considered. The results indicated that large bending moments were induced in the piles during lateral spreading and the downslope piles of the group received greater bending moments than the upslope one. The monotonic components of bending moments in the piles were reasonably predicted by the displacement based numerical approach using p-y springs when they were properly tuned for strength reduction in liquefied soil and the pile position in the group. A three dimensional hydro-mechanical finite element analysis was also undertaken in OpenSees which appropriately reproduced the physical model behavior. Lastly, a comprehensive parametric study on the verified finite element model revealed that the relative density of soil and the amplitude of base excitation can profoundly affect the induced bending moments in piles as well as the pile cap displacements while the effect of pile flexibility was comparably smaller in this regard.

Biomechanical evaluation of total ankle arthroplasty. Part II: Influence of loading and fixation design on tibial bone-implant interaction.

Finite element (FE) models to evaluate the burden placed on the interaction between total ankle arthroplasty (TAA) implants and the bone often rely on peak axial forces. However, the loading environment of the ankle is complex, and it is unclear whether peak axial forces represent a challenging scenario for the interaction between the implant and the bone. Our goal was to determine how the loads and the design of the fixation of the tibial component of TAA impact the interaction between the implant and the bone. To this end, we developed a framework that integrated robotic cadaveric simulations to determine the ankle kinematics, musculoskeletal models to determine the ankle joint loads, and FE models to evaluate the interaction between TAA and the bone. We compared the bone-implant micromotion and the risk of bone failure of three common fixation designs for the tibial component of TAA: spikes, a stem, and a keel. We found that the most critical conditions for the interaction between the implant and the bone were dependent on the specimen and the fixation design, but always involved submaximal forces and large moments. We also found that while the fixation design influenced the distribution and the peak value of bone-implant micromotion, the amount of bone at risk of failure was specimen dependent. To account for the most critical conditions for the interaction between the implant and the bone, our results support simulating multiple specimens under complex loading profiles that include multiaxial moments and span entire activity cycles.

Aggregated Hierarchical Sliding Mode Control for Vibration Suppression of an Excavator on an Elastic Foundation

Crawler excavators are important, utilitarian machines in construction industries. Special features of the chain and chassis allow them to operate and move on unstable ground. The shock motions of the links, which coincide with the changes of the forces impacting the foundation, create vibrations within the entire system. The highest level of vibrations appears when the boom moves, as it holds the robotic excavator's entire actuator with large mass and moment of inertia. These undesired fluctuations cause system instability, driver discomfort, reduced operating efficiency, and increased energy consumption. In this study, a hierarchical sliding mode control focusing on boom movement is designed based on the system dynamic model. This controller allows the boom to move precisely with a slight fluctuation angle of the main body, even while the other links are moving using a parameter estimator. Maintaining stable boom movements significantly simplifies arm and bucket control. The effectiveness of the entire work is investigated by numerical simulation and implementation results on a small-scale hydraulic excavator.

3D Numerical Analyses of Column-Supported Embankments: Failure Heights, Failure Modes, and Deformations

Design of column-supported embankments (CSE) requires the evaluation of global stability using the conventional limit equilibrium method (LEM). Yet, for CSEs using unreinforced concrete columns and load transferring geogrids, the failure mechanisms and corresponding soil-structure interactions are not well understood. There is increasing evidence pointing to large bending moments in columns and failure of columns in flexure, as opposed to a failure by shear as assumed in limit equilibrium analyses. In response to these design uncertainties, the failure height, failure mode, and deformations of eight column-supported embankment scenarios were investigated using three-dimensional (3D) numerical analyses. For the same embankment scenarios at failure height, factors of safety (FS) were then calculated using the two-dimensional (2D) LEM for investigating its applicability in evaluating global stability of CSEs. The 3D numerical analyses examined CSE stability for the limiting conditions at undrained end-of-construction and after long-term dissipation of excess pore water pressures. The numerical model included representations of flexural tensile failure in the concrete columns and tensile failure in the geosynthetic reinforcement. Scenarios consisted of a base case with typical concrete column design, five single-parameter variations using base case conditions, and two multiparameter variations using base case conditions. The undrained condition was the most critical, and two failure modes were found: (1) multisurface shearing in the embankment coupled with bending failure of columns and near-circular shear failure in the clay, and (2) multisurface shearing in the embankment coupled with bending failure of columns and shearing in the upper portion of the soft foundation clay. Both failure modes were accompanied by a rupture of the geosynthetic when included in the load transfer platform. Soil-column interactions were complex, and many columns failed in bending at lower embankment heights than those that produced collapse. The factors of safety calculated using the LEM were overstated. This is because the LEM assumes failure by shear, which has limited applicability for examining the complex mechanisms by which CSEs fail. The practical implication is that the LEM should not be used for evaluating global stability of this system type and, by extension, other system types in which soil-structure interactions result in failures controlled by mechanisms other than shear.

Minimizing corner cracking during the de-moulding process of industrial-size GFRP components: a case study

This article, through an industrial-level case study, presents workflows employed for decision-making to mitigate cracking of glass fibre reinforced polymer (GFRP) parts in tight radii corner locations, often resulting from displacement-controlled de-moulding processes. Namely, using process simulation to evaluate the cure cycle of the GFRP composite parts, it was possible to optimize the time of de-moulding and reduce the potential for part damage. It was observed that the most significant factors influencing the corner defect were boundary conditions of the part during de-moulding, the workshop temperature and part thickness. The poorest process design case was identified as hot workshop temperature, a laminate with thickness on the upper end of tolerances and a boundary condition where most sides are free, allowing for the development of larger moment forces at the tight corners. Further to this, a de-moulding time chart was developed to account for the changes in material properties as a function of temperature and material thickness, allowing for the in situ decision-making of technicians to reduce the occurrence of corner cracks.

On the composite design of wood branches leading to improved bending strength

Wooden branches are designed to carry large bending moments, and so are longer composite structures, e.g. rotor blades for wind turbines. Being a natural fibrous composite material, wood is made from relatively simple biopolymer building blocks. In this preliminary work, we describe the composition and structure of softwood branches, including 3D images from X-ray computed tomography. The main difference in branch structure compared with other wood tissues is the reaction wood formed on the compressive side in e.g. spruce and pine. A simple beam is used to show that maximum bending moment is multiplied several times solely from the reaction wood. This is noteworthy, since chemical composition of the reaction wood does not differ significantly from the rest of the wood. The tissue gradients in the branch resulting from variation in density, microfibrillar angle and cell geometry contribute to the strength improvements. In composite structures, sandwich design is used to improve the load carrying capacity. From a general perspective, also local features as found in wood, such as smooth gradients and controlled cellular structure, could be further explored to improve bending strength in engineered composite materials.

Strength analysis of large motor

Large motors are widely used in industrial production, mainly playing the role of load operation, equipment cooling and so on, and playing a vital role in the corresponding system, whose safety and reliability determine the stability of the entire industrial production. However, as the large motor is a rotating mechanism with a large volume, it will produce a large moment of inertia when it works at high speed. At this time, the structure between the rotor and bearing, the rotor itself, the rotor ventilation slot and other structures need to ensure a certain mechanical strength. This paper takes a 4500kW large motor as the research object, calculates the strength of rotor core and torsional strength by means of strength calculation, and analyzes the distribution of the internal stress field of the motor due to centrifugal force when it is running at high speed through finite element analysis, determines the location of stress concentration and calculates the strength requirements.