Variation Of Moment Research Articles

Trajectory deflection of noncircular cross-section projectile penetrating into metal targets

To analyze the trajectory deflection of a noncircular cross-section projectile penetrating into multiple metal targets, numerical simulations with different impact velocities, projectile tip height and charge geometry are conducted. The simulation model is established using the finite element software LS-DYNA and verified based on the experiment carried out by a single-stage light gas gun. The results show that the impact velocity significantly affects the trajectory deflection of noncircular cross-section projectile. Although the deflections may be different in direction, the magnitudes exhibit decreasing trends with the increasing impact velocity. Besides, the trajectory varies from downward deflection to upward deflection with the increase of projectile tip height, and changes significantly with the tip height ranging from 0.8mm to 1.1mm. Further, as the geometry profile of projectile remains unchanged, the ones with noncircular charge exhibit better ballistic stability as compared with the circular charge projectile. This is mainly related to the variation in projectile mass instead of the variation in moment of inertia.

Action Path and Mechanism of Segment Joints in the Failure History of Shield Tunnel Lining

Focusing on the failure history of single-ring segmental lining structure, the action path and mechanism of segment joint on the segment bending moment was investigated in this study. The explicit equations of segment bending moment increment difference and segment bending moment diffusion coefficient were derived, and the causes of segment bending moment state variation in high load level were studied. In the failure history of segmental tunnel lining, the bending moment variation was mainly controlled by the bending moment increment difference per unit time (IND). IND was mainly controlled by the relative stiffness ratio of segment joints and their derivative. The action path of segment joints on segment internal force can be divided into: 1) the opening and yielding of segment joints, 2) the attenuation of rotational stiffness of segment joints, 3) the change of relative stiffness ratio and its derivative, 4) the IND value of non-zero, and 5) the drastic change of segment bending moment state. Furthermore, the rotation stiffness of the segment joint attenuated, and then the acceleration variation of segment bending moment was caused by segment joint effects because IND was not equal to 0, i.e., the segment bending moment increased or decreased sharply.

Attenuation in hydroelastic response of floating-elastic-plate by porous membrane in two-layer fluid with bottom undulation

The prime intention of this article is to study the effects of bottom undulation and a porous membrane barrier on the hydroelastic response of an elastic plate floating in a two-layer fluid with changing bottom topography assuming the small amplitude waves and potential flow theory. Finite and semi-infinite plates coupled with porous membrane barriers are considered in this study. As a mathematical technique, the eigenfunction expansion method along with an approximation method mild-slope are adopted for the uniform bottom and variable bottom topographies, respectively. In the variable bottom topography, a system of differential equations is solved. By using matching and jump conditions, the solution is expressed as a linear algebraic system, from which the unknown constants of interest are computed. The effects of fluid density ratio, water depth ratio, bottom topography, and porous membrane on the bending moment, shear force, and deflection of the elastic plate are studied. It is found that when the density ratio becomes closer to one, the bending moments and shear forces acting on the elastic plates tend to diminish. The variations in the bending moments, shear forces, and plate deflection with respect to changing density ratios are found to be in opposite trends caused by surface and interfacial waves, respectively. With higher tension and a less porous membrane, the bending moment, shear forces, and pate deflection are reduced. Concave-up bottoms reflect more surface wave energy, whereas concave-down bottoms reflect more interfacial wave energy. The observations made in this article may help in analyzing the response of very-large floating structures in the presence of an undulating seabed.

Conditions for Graviton Emission in the Recombination of a Delocalized Mass

In a known gedanken experiment, a delocalized mass is recombined while the gravitational field sourced by it is probed by another (distant) particle; in it, this is used to explore a possible tension between complementarity and causality in case the gravitational field entangles with the superposed locations, a proposed resolution being graviton emission from quadrupole moments. Here, we focus on the delocalized particle (forgetting about the probe and the gedanken experiment) and explore the conditions (in terms of mass, separation, and recombination time) for graviton emission. Through this, we find that the variations of quadrupole moments in the recombination are generically greatly enhanced if the field is entangled compared to if it is sourced instead by the energy momentum expectation value on the delocalized state (moment variation ∼md2 in the latter case, with m mass, d separation). In addition, we obtain the (upper) limit recombination time for graviton emission growing as m in place of the naive expectation m. In this, the Planck mass acts as threshold mass (huge, for delocalized objects): no graviton emission is possible below it, however fast the recombination occurs. If this is compared with the decay times foreseen in the collapse models of Diósi and Penrose (in their basic form), one finds that no (quadrupole) graviton emission from recombination is possible in them. Indeed, right when m becomes large enough to allow for emission, it also becomes too large for the superposition to survive collapse long enough to recombine.

Spin-orbit coupling effects in the spectroscopy and predissociation of the low-lying states of germanium monobromide

In this work, the electronic structure of GeBr is investigated by high-level multireference configuration interaction (MRCI) method plus Davidson correction (+Q). To improve the accuracy of the computations, the core-valence (CV) electrons correlations, and spin-orbit coupling (SOC) effect are considered. The potential energy curves (PECs) of 23 low-lying states correlated with the lowest three dissociation limits are obtained, as well as those of 45 Ω states originated from the 23 low-lying states. The spectroscopic constants of low-lying states are obtained, which are in agreement with the available experiments. The abrupt variations of dipole moments (DMs) are attributed to the change of the electronic configurations in the avoided crossing regions. Based on the computed PECs of the electronic states and SO matrix elements, the predissociation pathway of the vibrational levels of 4Σ− and 2Π(Ⅲ) sates are discussed. Finally, the transition dipole moments (TDMs), Franck-Condon factors (FCFs), and radiative lifetimes of A2Σ+-X2Π, 2Π(Ⅲ)-X2Π, 1/2(Ⅱ)-X2Π1/2, 1/2(Ⅲ)-X2Π1/2, X2Π3/2-X2Π1/2, and 3/2(Ⅱ)-X2Π1/2 transitions are estimated.

Safety range in bridge areas based on the influence of cross flow on ship navigation

The obstructive effect of bridge piers on water flow forms a cross flow, which threatens the navigation of ships. The objective of this study is to contribute to the quantitative study of navigation safety in restricted waters. For this purpose, a hydrodynamic numerical simulation that takes into account ship motion characteristics is combined with navigation safety analysis. Firstly, the cross flow characteristics around tandem double circular piers and their influence on ships are revealed, and the yaw moment is employed to verify the influence. Then, the influence of cross flow on ship navigation is quantified by analyzing the turbulent width under different bridge pier spacings and Reynolds numbers. Finally, the safety range of ship navigation in bridge areas is partitioned. The results demonstrate that when the ship-pier spacing ratio is between 0 and 2.5, there are obvious peak points of the ship's yaw moment near the pier. When the ratio is between 2.5 and 3.0, there is only a negative peak point at the pier body, and the peak value is reduced by 43%, resulting in decreased risk; The qualitative trend of turbulent width is consistent under both single-pier and two-pier conditions. With an increase in Reynolds number, the cross flow velocity in the recirculation region is greater, the stable period of the turbulent width is shorter, and the variation is more noticeable at the downstream pier body; The critical ship-pier spacing ratio for partitioning the high-risk range and the low-risk range is 2.5, and the variation of the ship's yaw moment is consistent with the partition of the safety range by the turbulent width. The research results provide a reference for refined early warning of navigation management.

The mechanism of pyroelectricity in polar material hemimorphite

It is known that a crystal structure and symmetry determine the physical properties of materials. Lattice distortion can strongly affect the symmetry of the crystal structure. Polar materials show changes in polarization with temporal fluctuations of temperature due to the asymmetry. As a polar crystal, hemimorphite shows excellent pyroelectric properties. However, to date, there are a few studies on its intrinsic physical properties, and the mechanism of its pyroelectricity remains unclear. In this paper, single-crystal x-ray diffraction measurement was carried out to obtain the atomic positions at 100–400 K. Furthermore, the electric dipole moments of [ZnO4] and [SiO4] polyhedrons along a, b, and c axes have been calculated. The calculated pyroelectric coefficient derived from the intrinsic electric dipole moment was compared with the experimental measurement. The results indicate that the pyroelectric coefficients of hemimorphite at different temperatures mainly come from the variation of the electric dipole moment of [ZnO4] and [SiO4] polyhedrons along the c axis. The electric dipole moment changes as a function of temperature from 100 to 400 K, which is induced by the random lattice distortion. It is found that pyroelectricity is strongly correlated with the random lattice distortion. The establishment of the relationship between lattice distortion and pyroelectricity helps us to regulate the specific electrical parameters of the material, which may lead to future work in energy harvesting and further properties.

Nonlinear Optical Responses of Photoswitchable Donor–Acceptor Stenhouse Adducts

This work combines hyper-Rayleigh scattering (HRS) experiments performed in the NIR range (1.30 and 1.60 μm) and quantum chemical calculations to provide a comprehensive description of the second harmonic generation (SHG) responses of donor-acceptor Stenhouse adducts (DASAs). Representative derivatives of the three generations of DASAs, which differ by the nature of their electron-donating and withdrawing moieties and also include clickable species, have been synthesized and their photoswitching behavior fully characterized. The HRS measurements allow us to establish relationships between the magnitude of the SHG response of open forms and the nature of the donor and acceptor groups. The largest SHG responses are obtained for derivatives incorporating either a barbituric acid or an indanedione acceptor unit, while N-methylaniline appears as the most efficient donor group. The calculations support well the experimental data and show that high hyperpolarizabilities are associated to low excitation energies and large extent of the photoinduced intramolecular charge transfer, which enhances the dipole moment variation between the ground and first dipole-allowed electronic excited state. In addition, a complete investigation of the photoswitching kinetics of DASAs in chloroform solution shows important differences, highlighting in particular the role of the donor group on the photoswitching efficiency.

Mechanical model and characteristics of deep-water drilling riser-wellhead system under internal solitary waves

Internal solitary waves with a huge amount of energy easily trigger the large dynamic responses of riser-wellhead system and threaten its structural safety. However, previous studies have only focused on the dynamic response of the riser under internal solitary waves. The riser may experience excessive traction from the platform, especially from the mooring platform, in response to the arrival of internal solitary waves. The bottom of the riser connects to the wellhead system, which in turn exerts a reaction force on the riser. To address this problem, a coupled dynamic model of deep-water drilling mooring platform-riser-wellhead system under internal solitary waves is developed in this paper. A dynamic response analysis method based on the fourth-order Runge-Kutta method and finite element method is also proposed for the mooring platform-riser-wellhead system. A dynamical solver for the coupled system is then developed using MATLAB. The dynamic response characteristics of the riser-wellhead system under internal solitary waves are calculated. Results show that the displacement and bending moment of the system initially increases and then decreases along with the propagation of internal solitary waves, and finally reach equilibrium position. The displacement and bending moment reach their peak before the trough of internal solitary waves passes through the riser-wellhead system. The dynamic responses of the riser-wellhead system under the influence of internal solitary wave loads are much larger than those without the effect of internal solitary wave loads. The riser system experiences shearing loads at the interface of internal solitary waves, which trigger a step-like bending moment variation. The bending moment of the conductor under the mudline is greatly increased by the internal solitary waves.

Reduction of wave load on monopile-supported offshore wind turbine by a gear-type plate

This study investigates the wave diffraction problem of a vertical cylinder with a gear-type plate by using the linear wave theory and the method of eigenfunction expansion. The present model is demonstrated to be accurate, through a comparison with the numerical results of the boundary element method. The horizontal wave force acting on the cylinder can be reduced considerably by the gear-type plate. Meanwhile, the variation in bending moment at the bottom of the cylinder depends on the wave conditions and geometry parameters. A low value of the ratio between water depth and cylinder radius (d/r0) can result in an increase in the bending moment on the cylinder, rather than a decrease, due to the additional loads exerted by the gear-type plate. The bending moment on the cylinder can be reduced significantly by the gear-type plate as d/r0 increases. Within d/r0∈[4,10] of the present monopile-supported wind turbines, the wave loads on the monopile foundation can be reduced significantly by the proposed gear-type plate. Compared with a ring-type plate, a gear-type plate exhibits superior reduction effects over an equal plate area. The loads on the structures are insensitive to the wave exposure angle when the teeth number increases beyond three.

Spacecraft attitude maneuver planning with multi–sensor pointing constraints using improved RRT–star algorithm

During the spacecraft attitude maneuvers for the observation of mission targets, multiple instruments may face different pointing constraints, and they are rarely considered by the current attitude maneuver planning methods. In this case, this paper proposes an improved rapidly–exploring random trees star (RRT*) algorithm to obtain discrete quaternion path nodes while satisfying the pointing constraints of multiple sensors. Next, the temporal properties of these path nodes are defined by a trapezoidal path planning method, and bounded constraints on the angular velocity and control moment during the attitude maneuver are introduced. Then, the continuous quaternion curves through the discrete quaternion path nodes are calculated by a segmented cubic spline interpolation function. Finally, the angular velocity and control moment are calculated through the inverse dynamics. The simulation results verify the feasibility of the method. It can satisfy complex constraints and obtain the attitude optimization path, and alleviate the large control moment variations in the start and stop phases of the rest–to–rest maneuver.

Temperature Variation of Gilbert Damping Constant in 3d Transition Metals from First Principles

A theoretical investigation of temperature-dependent Gilbert damping is presented. We evaluate the Gilbert damping constant α (and the corresponding Landau frequency λ) at a finite temperature for hcp-Co, fcc-Ni, and Cu-doped fcc-Ni from first principles by combining the torque correlation model and the disordered local moment scheme, in which the finite-temperature effect is included as the transverse spin fluctuation. The calculated λ has, from the viewpoint of the material dependence, well reproduced the experimental results, but quantitatively, these values are more underestimated than the experimental values. A comparison with the lifetime approximation results reveals that a change in the electronic structure due to the spin fluctuation affects λ for Co and Ni but not for Fe. On the basis of the variation of the local magnetic moment of Co and Ni at finite temperature, we conclude that these differences in λ are due to the difference in the degree of itinerancy of spins.

Theoretical study on the propagation of high impact energy in the rotor with local plastic deformation after blade off

A theoretical model of an elastic supported rotor system under impact by blade off is established based on d'Alembert principle. The gyroscopic moment of the blade-disk with asymmetrical inertia is considered in the dynamic model. The formation criterion of the plastic hinge in the cylinder rotor are derived and applied in the dynamic model to consider the local plastic deformation of the rotor with large deformation. This model extends the impact model of non-rotating beam with rigid support to the rotating beam and can describe the main mechanical properties of the rotor with blade off. The influence of the main factors, such as sudden unbalance, gyroscopic moment, geometric dimensions and concentrated mass, on the propagation of the impact energy in the rotor are analyzed. The gyroscopic moment can suppress the wave propagation characteristics of the impact energy in a rotating beam, resulting in an overall bending deformation, compared with the wave propagation characteristics of the impact energy in the non-rotating beam. Larger local concentrated mass can reduce the effect of impact, and increasing the cross-section size can significantly improve the plastic limit bending moment of the rotor. The variation of the bending moment in the low-pressure rotor is mainly determined by gyroscopic moment and bending deformation. Due to the constraint of the 1# and 2# pivots, the strain energy generated by fan blade off is mainly distributed in the shaft segment in front of the 2# pivot. Therefore, the impact resistance of this shaft segment should be improved to fulfill the safety design requirement of fan blade off failure.

Thermo-mechanical characteristics of laterally loaded energy piles under multiple heating-cooling cycles in mountain area

In this paper, model tests of energy piles used in mountain area under asymmetry filed condition with and without an external lateral load under multiple heating-cooling cycles were conducted. The asymmetry of the soil will produce asymmetric temperature field and stress field in mountain area. The variation of pile top displacement, horizontal soil pressure, and pile bending moment due to cyclic temperature load were measured and analyzed. The results showed that the pile top horizontal displacement with an external lateral load decreased when the energy pile was heated and increased when it was cooled. However, the variation trends of pile top horizontal displacement with and without an external lateral load showed a significant difference. When the pile subjected to an external load was heated, the soil pressure at the upper part behind the pile would increase and that at the lower part would decrease, and the change was opposite during cooling. The bending moment would be changed by the thermal load, and it increased during heating with an external lateral load, while the variation of bending moment was not obvious during cooling.

The influence of body segment estimation methods on body segment inertia parameters and joint moments in javelin throwing

Calculated intersegmental moments are commonly used in analyzing throwing movements. The inverse dynamics (ID) results can vary due to the chosen set of body segment inertia parameters (BSIP). A multitude of methods to determine BSIP sets are available. The purpose of this study was to clarify the influence of different estimation methods on the BSIPs and the respective impact on the ID results in javelin throwing. Movement kinematics were recorded for ten male javelin throwers. Six different methods were used to estimate BSIP sets for the upper extremities of each thrower. Subsequently, ID results were obtained for each thrower and BSIP set. Results show variations between 8% and 120% between the BSIP sets, and maximum intersegmental moments varied between 6% and 21%, respectively. Joint-specific variations of intersegmental moments were observed as well as movement-specific variations within a joint related to the different BSIP sets. Furthermore, the influence of BSIP sets appears to be subject-specific as well, with observed variations between 9% and 18% – some athletes are better represented by the chosen methods than others. Hence, our study results suggest that the method to determine BSIP sets needs to be carefully chosen for calculating joint kinetics in throwing movements.

Numerical Investigations of Progressive Collapse Behaviour of Multi-Storey Reinforced Concrete Frames

This paper presents numerical simulations of multi-storey reinforced concrete frames under progressive collapse scenarios. Reinforced concrete frames with different storeys are modelled using DIANA. The load resistance and failure mode of frames are obtained from the numerical simulation. Variations in axial force and bending moment at the beam end are also determined and analysed to shed light on the force transfer mechanism. Numerical results show that the single-storey frame can develop compressive arch action at the initial loading stage and subsequent catenary action at large deformations. However, in multi-storey frames, only the first-storey beam develops compressive arch action and catenary action, whereas beams in other storeys show rather limited axial compression force. Based on numerical results, a design method is proposed for multi-storey frames to resist progressive collapse. Comparisons between numerical results and design methods suggest that the design method can evaluate the progressive collapse resistance of multi-storey frames with good accuracy.

Periodicities and Plasma Density Structure of Jupiter's Dawnside Magnetosphere

AbstractAbility to quantify variations in magnetic field topology and density within Jupiter's magnetosphere is an important step in understanding the overall structure and dynamics. The Juno spacecraft has provided a rich data set in the dawnside magnetosphere. The recent Grid Agnostic MHD for Extended Research Applications (GAMERA) global simulation study by Zhang et al. (2021, https://doi.org/10.1126/sciadv.abd1204) showed a highly structured plasmadisc with closed magnetic field lines mapped between the outer dawn‐tail flank and the high‐latitude polar region. To test these model predictions, we examined Juno's magnetic field data and electron/energetic particle data to categorize portions of orbits 1–15 into one of three regions based on plasma confinement: the flux pileup region, the intermediate region, and the plasmadisc region. For each region we examined periodicities from magnetic field fluctuations and particle density fluctuations on the 1–10 hr time scale. Periodicities on this time scale could relate to internal (e.g., plasmadisc structure) or external processes (e.g., Kelvin‐Helmholtz vortices). Similar analysis was performed on the GAMERA simulation with the data split into two regions, an outer (150 > R > 60) region and an inner (R < 60) region. Finally, using published density moments from Huscher et al. (2021, https://doi.org/10.1029/2021JA029446), we compared the relative density variations of the Juno moments and the GAMERA simulation to further understand the overall structure and dynamics of the plasmadisc. The agreement between data and simulation supports the existence of such a highly structured plasmadisc.

The Chemical Enrichment of the Milky Way Disk Evaluated Using Conditional Abundances

Chemical abundances of Milky Way disk stars are empirical tracers of its enrichment history. However, they capture joint-information that is valuable to disentangle. In this work, we quantify how individual abundances evolve across the present-day Galactic radius, at fixed supernovae contribution ([Fe/H], [Mg/Fe]). We use 18,135 Apache Point Observatory Galactic Evolution Experiment Data Release 17 red clump stars and 7943 GALactic Archaeology with HERMES Data Release 3 main-sequence stars to compare the abundance distributions conditioned on ([Fe/H], [Mg/Fe]) across 3–13 kpc and 6.5–9.5 kpc, respectively. We examine 15 elements: C, N, Al, K (light), O, Si, S, Ca, (α), Mn, Ni, Cr, Cu, (iron-peak) Ce, Ba (s-process) and Eu (r-process). We find that the conditional neutron-capture and light elements most significantly trace variations in the disk’s enrichment history, with absolute conditional radial gradients ≤0.03 dex kpc−1. The other elements studied have absolute conditional gradients ≲0.01 dex kpc−1. We uncover structured conditional abundance variations with [Fe/H] for the low-α, but not the high-α , sequence. The average scatter between the mean conditional abundances at different radii is σ intrinsic ≈ 0.02 dex (Ce, Eu, Ba σ intrinsic > 0.05 dex). These results serve as a measure of the magnitude via which different elements trace Galactic radial enrichment history once fiducial supernovae correlations are accounted for. Furthermore, we uncover subtle systematic variations in moments of the conditional abundance distributions and bimodal differences in [Al/Fe]. These suggest a nonuniform enrichment of each chemical cell, and will presumably constrain chemical evolution models of the Galaxy.

Highly sensitive and selective sensing-performance of 2D Co-decorated phthalocyanine toward NH3, SO2, H2S and CO molecules

Developing excellent sensing-materials for detecting and monitoring toxic gases in the air is significant for environmental monitoring and industrial emission evaluation. Herein, the first-principles calculations were employed to systematically investigate the adsorption characteristics of twelve different gas molecules (NH3, NO, NO2, SO2, H2S, CO, CO2, CH4, H2O, H2, O2, N2) on the two-dimensional phthalocyanine (Pc) and Co decorated phthalocyanine (CoPc), the electronic properties of various adsorption systems and their sensing-mechanism were also elucidated. The results show that the toxic NH3, NO, NO2, SO2, H2S are chemically adsorbed on the pristine Pc surface, whereas the poor sensitivity of Pc monolayer makes it not suitable to be a sensing-material. By contrast, the CoPc monolayer exhibits the appropriate adsorption strength toward the six poisonous gases (NH3, NO, NO2, SO2, H2S, CO), which is detailedly explained by the analysis of charge transfer, charge density difference and density of states. Moreover, the CoPc monolayer possesses high selectivity to those six gases even if it is in a humid environment. The CoPc monolayer also has excellent sensitivity for those toxic gases due to the obvious variations of bandgap, magnetic moment or work function. Additionally, the recovery time of NH3, SO2, H2S and CO is estimated to be about 3.91 min, 0.02 s, 24.19 ns and 226.38 ns at room temperature, respectively. Consequently, the CoPc monolayer based gas sensor has a great potential application for the NH3, SO2, H2S and CO detection.

Boron migration during amorphous to crystalline transformation in CoFeB/MgO multilayers: A reflectivity study

Migration of boron in CoFeB/MgO multilayer during amorphous to crystalline transformation in CoFeB has been studied using Polarized Neutron Reflectivity (PNR) and anomalous Soft X-ray Reflectivity (SXR). PNR gives information about the possible redistribution of B in the multilayer during thermal annealing, as well as about the variation in the average magnetic moment. Sensitivity of the soft X-ray reflectivity to the movement of boron is enhanced by doing a series of measurements with X-ray energy spanning across the K absorption edge of B. Both the PNR and anomalous SXR results clearly suggest that upon thermal annealing, boron prefers to move away from the MgO/CoFeB interfaces, and forms a layer of boride in the middle of the magnetic layer. These results are important in view of the existing ambiguity regarding the role of boron in CoFeB/MgO based magnetic tunnel junctions.