scholarly journals Subtle metastability of the layered magnetic topological insulator MnBi2Te4 from weak interactions

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Jinliang Ning ◽  
Yanglin Zhu ◽  
Jamin Kidd ◽  
Yingdong Guan ◽  
Yu Wang ◽  
...  
Keyword(s):  
Topological Insulator ◽  
Thermodynamic Stability ◽  
Degrees Of Freedom ◽  
Weak Interactions ◽  
Magnetic Coupling ◽  
Material Synthesis ◽  
Specific Heats ◽  
Emergent Phenomena ◽  
Quantum Materials ◽  
Computational Predictions

Abstract Layered quantum materials can host interesting properties, including magnetic and topological, for which enormous computational predictions have been done. Their thermodynamic stability is much less visited computationally, which however determines the existence of materials and can be used to guide experimental synthesis. MnBi2Te4 is one of such layered quantum materials that was predicted to be an intrinsic antiferromagnetic topological insulator, and later experimentally realized but in a thermodynamically metastable state. Here, using a combined first-principles-based approach that considers lattice, charge, and spin degrees of freedom, we investigate the metastability of MnBi2Te4 by calculating the Helmholtz free energy for the reaction Bi2Te3 + MnTe → MnBi2Te4. We identify a temperature range (~500–873 K) in which the compound is stable with respect to the competing binary phases, consistent with experimental observation. We validate the predictions by comparing the calculated specific heats contributed from different degrees of freedom with experimental results. Our findings indicate that the degrees of freedom responsible for the van der Waals interaction, lattice vibration, magnetic coupling, and nontrivial band topology in MnBi2Te4 not only enable emergent phenomena but also play a crucial role in determining its thermodynamic stability. This conclusion lays the foundation for the future computational material synthesis of novel layered systems.

A Magnetic Drive Actuator for Micro Electrical Discharge Machining

2012 ◽  
Vol 591-593 ◽  
pp. 303-306
Author(s):  
Xiao You Zhang ◽  
Akio Kifuji ◽  
Dong Jue He
Keyword(s):  
Electrical Discharge ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Electrical Discharge Machining ◽  
Magnetic Coupling ◽  
Magnetic Bearings ◽  
Coupling Mechanism ◽  
Micro Electrical Discharge Machining ◽  
Long Stroke ◽  
Magnetic Drive

Electrical discharge machining has the capability of machining all conductive materials regardless of hardness, and has the ability to deal with complex shapes. However, the speed and accuracy of conventional EDM are limited by probability and efficiency of the electrical discharges. This paper describes a three degrees of freedom (3-DOF) controlled, wide-bandwidth, high-precision, long-stroke magnetic drive actuator. The actuator can be attached to conventional electrical discharge machines to realize a high-speed and high-accuracy EDM. The actuator primarily consists of thrust and radial magnetic bearings, thrust and radial air bearings and a magnetic coupling mechanism. By using the thrust and radial magnetic bearings, the translational motions of the spindle can be controlled. The magnetic drive actuator possesses a positioning resolution of the order of micrometer, a bandwidth greater than 100Hz and a positioning stroke of 2mm.

HOLOGRAPHIC SPACETIME

2012 ◽  
Vol 21 (11) ◽  
pp. 1241004 ◽  
Author(s):  
TOM BANKS
Keyword(s):  
String Theory ◽  
Degrees Of Freedom ◽  
Good Description ◽  
De Sitter ◽  
Finite Radius ◽  
Full Field ◽  
Mass Scaling ◽  
Finite Dimensional ◽  
Emergent Phenomena ◽  
Holographic Screen

The theory of holographic spacetime (HST) generalizes both string theory and quantum field theory (QFT). It provides a geometric rationale for supersymmetry (SUSY) and a formalism in which super-Poincare invariance follows from Poincare invariance. HST unifies particles and black holes, realizing both as excitations of noncommutative geometrical variables on a holographic screen. Compact extra dimensions are interpreted as finite-dimensional unitary representations of super-algebras, and have no moduli. Full field theoretic Fock spaces, and continuous moduli are both emergent phenomena of super-Poincare invariant limits in which the number of holographic degrees of freedom goes to infinity. Finite radius de Sitter (dS) spaces have no moduli, and break SUSY with a gravitino mass scaling like Λ1/4. In regimes where the Covariant Entropy Bound is saturated, QFT is not a good description in HST, and inflation is such a regime. Following ideas of Jacobson, the gravitational and inflaton fields are emergent classical variables, describing the geometry of an underlying HST model, rather than "fields associated with a microscopic string theory". The phrase in quotes is meaningless in the HST formalism, except in asymptotically flat and AdS spacetimes, and some relatives of these.

Chaos and Quasi-Periodic Motions on the Homoclinic Surface of Nonlinear Hamiltonian Systems With Two Degrees of Freedom

2005 ◽  
Vol 1 (2) ◽  
pp. 135-142 ◽  
Author(s):  
Albert C. J. Luo
Keyword(s):  
Energy Spectrum ◽  
Hamiltonian System ◽  
Kinetic Energy ◽  
Degrees Of Freedom ◽  
Weak Interactions ◽  
Kam Theorem ◽  
Periodic Motions ◽  
Chaotic Motions ◽  
Nonlinear Hamiltonian System ◽  
Two Degree Of Freedom

The numerical prediction of chaos and quasi-periodic motion on the homoclinic surface of a two-degree-of-freedom (2-DOF) nonlinear Hamiltonian system is presented through the energy spectrum method. For weak interactions, the analytical conditions for chaotic motion in such a Hamiltonian system are presented through the incremental energy approach. The Poincaré mapping surfaces of chaotic motions for this specific nonlinear Hamiltonian system are illustrated. The chaotic and quasi-periodic motions on the phase planes, displacement subspace (or potential domains), and the velocity subspace (or kinetic energy domains) are illustrated for a better understanding of motion behaviors on the homoclinic surface. Through this investigation, it is observed that the chaotic and quasi-periodic motions almost fill on the homoclinic surface of the 2-DOF nonlinear Hamiltonian system. The resonant-periodic motions for such a system are theoretically countable but numerically inaccessible. Such conclusions are similar to the ones in the KAM theorem even though the KAM theorem is based on the small perturbation.

scholarly journals Coherent Phonon Disruption and Lock-In During a Photoinduced Charge-Density-Wave Phase Transition

2021 ◽  
Author(s):  
Spencer A. Reisbick ◽  
Yichao Zhang ◽  
Jialiang Chen ◽  
Paige Engen ◽  
David Flannigan
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Degrees Of Freedom ◽  
Structural Phase ◽  
Density Wave ◽  
Optical Excitation ◽  
Partial Coherence ◽  
Periodic Lattice ◽  
Coherent Phonon ◽  
Quantum Materials

Ultrafast manipulation of phases and phase domains in quantum materials is a key approach to unraveling and harnessing interwoven effects of charge and lattice degrees of freedom. In the intensely-studied charge-density-wave (CDW) material, 1<i>T</i>-TaS<sub>2</sub>, phonon coupling to periodic lattice distortions (PLDs) and atomically-incoherent picosecond structural phase transitions suggest transitional periods could exist for delayed onset of mode coherence. Here we find evidence for such a connection between displacively-excited coherent acoustic phonons and PLDs using 4D ultrafast electron microscopy. Following femtosecond optical excitation of an ultrathin crystal, a propagating hybridized mode is imaged emerging from linear defects within a 1-μm region. Partial coherence and low amplitudes during onset of the incommensurate phase convert to higher-amplitude, increasingly-coherent oscillations as phase-growth stabilizes. The hybrid mode consists of large out-of-plane distortions coupled to basal-plane bond oscillations propagating at anomalously high velocities. The strongly-correlated behaviors observed here represent a potential means to control phase behaviors in quantum materials using defect-engineered coherent-phonon seeding.

scholarly journals Computational and cellular studies reveal structural destabilization and degradation of MLH1 variants in Lynch syndrome

2019 ◽  
Author(s):  
Amanda B. Abildgaard ◽  
Amelie Stein ◽  
Sofie V. Nielsen ◽  
Katrine Schultz-Knudsen ◽  
Elena Papaleo ◽  
...  
Keyword(s):  
Lynch Syndrome ◽  
Thermodynamic Stability ◽  
Saturation Mutagenesis ◽  
Mutation Rates ◽  
Loss Of Function ◽  
Unknown Significance ◽  
Steady State Levels ◽  
Defective Mismatch Repair ◽  
Hereditary Cancer Predisposition ◽  
Computational Predictions

AbstractDefective mismatch repair leads to increased mutation rates, and germline loss-of-function variants in the repair component MLH1 cause the hereditary cancer predisposition disorder known as Lynch syndrome. Early diagnosis is important, but complicated by many variants being of unknown significance. Here we show that a majority of the disease-linked MLH1 variants we studied are present at reduced cellular levels. We show that destabilized MLH1 variants are targeted for chaperone-assisted proteasomal degradation, resulting also in degradation of co-factors PMS1 and PMS2.In silicosaturation mutagenesis and computational predictions of thermodynamic stability of MLH1 missense variants revealed a correlation between structural destabilization, reduced steady-state levels and loss-of-function. Thus, we suggest that loss of stability and cellular degradation is an important mechanism underlying manyMLH1variants in Lynch syndrome. Combined with analyses of conservation, the thermodynamic stability predictions separate disease-linked from benignMLH1variants, and therefore hold potential for Lynch syndrome diagnostics.

scholarly journals Probing light-driven quantum materials with ultrafast resonant inelastic X-ray scattering

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Matteo Mitrano ◽  
Yao Wang
Keyword(s):  
Degrees Of Freedom ◽  
Spectroscopic Method ◽  
Future Research ◽  
Time Resolved ◽  
X Ray ◽  
Ultrafast Optical ◽  
X Ray Scattering ◽  
Quantum Materials ◽  
Review State ◽  
Ray Scattering

Abstract Ultrafast optical pulses are an increasingly important tool for controlling quantum materials and triggering novel photo-induced phase transitions. Understanding these dynamic phenomena requires a probe sensitive to spin, charge, and orbital degrees of freedom. Time-resolved resonant inelastic X-ray scattering (trRIXS) is an emerging spectroscopic method, which responds to this need by providing unprecedented access to the finite-momentum fluctuation spectrum of photoexcited solids. In this Perspective, we briefly review state-of-the-art trRIXS experiments on condensed matter systems, as well as recent theoretical advances. We then describe future research opportunities in the context of light control of quantum matter.

Interruption performance design of variable freedom mechanism triggered by electro-mechanical-magnetic coupling

2016 ◽  
Vol 231 (18) ◽  
pp. 3330-3341 ◽  
Author(s):  
Jinghua Xu ◽  
Shuyou Zhang ◽  
Jianrong Tan ◽  
Sheng Hongsheng
Keyword(s):  
Degrees Of Freedom ◽  
Magnetic Coupling ◽  
Radiation Energy ◽  
Degree Of Freedom ◽  
Design Parameters ◽  
Coupling Mechanism ◽  
Variable Degree ◽  
Algebraic Equations ◽  
Tightening Force ◽  
Linear Algebraic Equations

Coupling mechanism plays an important role in transmitting, motivating and actuating mechanical functions. However, it is difficult to obtain the transient dynamics performance of mechanism with variable degree of freedom precisely. Therefore, an interruption performance design method of variable freedom mechanism triggered by electro-magneto-thermo coupling is put forward. The Euler-Lagrange partial differential equations of variable freedom mechanism are built using generalized coordinates. Degree of freedom reduction rules are proposed to merge transformation or rotation constraints and obtain the total degrees of freedom of variable freedom mechanism at each transient status. Bivariate interpolating is employed to determine the electro-mechanical-magnetic coupled Lorentz force. Dynamics performance is simulated by iteration of linear algebraic equations using implicit predictor-corrector integration method. The design parameters such as stiffness and pre-tightening force of trigger spring, permissible dimension deviations and hole-shaft fit tolerance are determined and improved using the sensitivity analysis of simulation results. The pneumatic mechanical endurance and thermal infrared temperature rise experiments are accomplished to determine the infrared radiation energy distribution and transient working status of components. It gives an auxiliary thermo-visual approach for transient performance design of coupling mechanism.

Modeling and analysis of a novel conical magnetic bearing for vernier-gimballing magnetically suspended flywheel

2013 ◽  
Vol 228 (13) ◽  
pp. 2416-2425 ◽  
Author(s):  
Jiancheng Fang ◽  
Chune Wang ◽  
Jiqiang Tang
Keyword(s):  
Permanent Magnet ◽  
Degrees Of Freedom ◽  
Magnetic Coupling ◽  
Magnetic Bearing ◽  
Modeling And Analysis ◽  
Control Moment ◽  
Novel Structure ◽  
Force Coupling ◽  
Conical Structure ◽  
The Mathematical Model

The vernier-gimballing magnetically suspended flywheel can generate control moment in radial directions by tilting the spinning rotor to rotate around the radial axes. In order to reduce the extra tilting torque caused by the uniform distribution of flux density and the magnetic coupling among different channels, a novel 3 degrees of freedom conical permanent-magnet-biased magnetic bearing is proposed in the paper. The axial and radial stators are both designed with the normal directions of the midst faces directing to the centroid of the rotor, so as to decrease the extra torque by shortening the length of torque arm. A novel structure of radial X and Y stator poles separated by nonmagnetic material is proposed, and the upper and lower conical stators are designed to be mirror structures with each other, so that the magnetic coupling can be reduced. The mathematical model of the proposed permanent-magnet-biased magnetic bearing is constructed by methods of equivalent magnetic circuit and finite element. Calculations and simulations are carried out on the suspension force, extra tilting torque, and force coupling. The results show that with the conical structure, the extra tilting torque can be decreased from 10.83 Nm to 0.11 Nm when the rotor tilts around X axis for 1°. The magnetic forces among X, Y, and Z directions are almost decoupled even when the rotor shifts in some direction. All the results prove that the novel permanent-magnet-biased magnetic bearing is suitable for application in vernier-gimballing magnetically suspended flywheel.

scholarly journals Advances in Reconfigurable Vectorial Thrusters for Adaptive Underwater Robots

2021 ◽  
Vol 9 (2) ◽  
pp. 170
Author(s):  
Henrique Fagundes Gasparoto ◽  
Olivier Chocron ◽  
Mohamed Benbouzid ◽  
Pablo Siqueira Meirelles
Keyword(s):  
Degrees Of Freedom ◽  
Autonomous Underwater Vehicles ◽  
Magnetic Coupling ◽  
Underwater Vehicles ◽  
Water Jet ◽  
Present Review ◽  
Underwater Robots ◽  
Enabling Technologies ◽  
New Generation ◽  
Water Tightness

Manoeuvrability is one of the essential keys in the development of improved autonomous underwater vehicles for challenging missions. In the last years, more researches were dedicated to the development of new hulls shapes and thrusters to assure more manoeuvrability. The present review explores various enabling technologies used to implement the vectorial thrusters (VT), based on water-jet or propellers. The proposals are analysed in terms of added degrees of freedom, mechanisms, number of necessary actuators, water-tightness, electromagnetomechanical complexity, feasibility, etc. The usage of magnetic coupling thrusters (conventional or reconfigurable) is analysed in details since they can assure the development of competitive full waterproof reconfigurable thrusters, which is a frictionless, flexible, safe, and low-maintenance solution. The current limitations (as for instance the use of non conductive hull) are discussed and ideas are proposed for the improvement of this new generation of underwater thrusters, as extending the magnetic coupling usage to obtain a fully contactless vector thrust transmission.

scholarly journals Coherent Phonon Disruption and Lock-In During a Photoinduced Charge-Density-Wave Phase Transition

2021 ◽  
Author(s):  
Spencer A. Reisbick ◽  
Yichao Zhang ◽  
Jialiang Chen ◽  
Paige Engen ◽  
David Flannigan
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Degrees Of Freedom ◽  
Transition Period ◽  
Density Wave ◽  
Domain Growth ◽  
Periodic Lattice ◽  
Coherent Phonon ◽  
Linear Defects ◽  
Quantum Materials

Ultrafast manipulation of phases and phase domains in quantum materials is a key approach to unraveling and harnessing interwoven effects of charge and lattice degrees of freedom. In the intensely-studied charge-density-wave (CDW) material, 1<i>T</i>-TaS<sub>2</sub>, static Rayleigh-phonon coupling to periodic lattice distortions (PLDs), as well as incommensurate (IC) domain growth and coarsening over the first 100 ps following femtosecond photoexcitation, suggests ultrafast, displacively-excited coherent acoustic phonons (CAPs) may strongly couple to PLDs. Here we find evidence for such coupling using 4D ultrafast electron microscopy (UEM). For ultrathin room-temperature crystals, photoinduced Bragg-peak dynamics spanning the first 75 ps are characterized by partial CAP coherence and localized low-amplitude <i>c</i>-axis dilations. These relatively weak, partially-coherent dynamics then give way to higher-amplitude, increasingly-coherent oscillations, the transition period of which is well-matched to timescales of photoinduced IC domain growth and stabilization from the nearly-commensurate (NC) phase. Diffraction experiments are correlated with nanoscale UEM imaging, where it is found that phonon wave trains emerge from nanoscale linear defects 100 ps after photoexcitation. The CAPs consist of coupled longitudinal and transverse character and propagate at an anomalously-high 4.6 nm/ps along wave vectors independent from NC-phase PLDs, instead being dictated by static defect orientation. Such behaviors illustrate a potential means to control phases in quantum materials using defect-engineered coherent-phonon seeding.<br>

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