Additional Internal Degrees Of Freedom Research Articles

Schemes of momentum/reaction wheels unloading by mechanical restructuring and gearbox for spacecraft

A new principle and linked schemes of reaction/momentum wheels unloading are proposed and constructed. This principle is based on the instantaneous restructuring and changing the mechanical system itself, when additional internal degrees of freedom become available. These releasing additional degrees of freedom correspond to additional rotors, which take “after unfreezing” their own opportunity to rotate. At the connection of additional “unfrozen” rotors to the main wheels by gear type, these rotors become involved in the rotation with opposite direction relatively to the main wheels rotation, and it instantaneously provides nulling the relative angular momentum. Then electric motors of additional rotors and wheels can start the process of the rotational energy recovery, which decelerates and unloads angular velocities of all rotors and wheels. The proposed principle of releasing additional degrees of freedom and reconfiguring internal mechanical multi-rotor subsystem allow to immediately change values and directions of the relative angular momentum. This changeable multi-rotor subsystem represents the multifunctional attitude control system, which can be figuratively called as a “gearbox”. As a part of the gearbox a special mechanical device is proposed, which represents a “gravitational damper” to unloading the total absolute angular momentum of spacecraft with the help of external gravitational torques.

Influence of Charge Lipid Head Group Structures on Electric Double Layer Properties.

In this study we derived a model for a multicomponent lipid monolayer in contact with an aqueous solution by means of a generalized classical density functional theory and Monte Carlo simulations. Some of the important biological lipid systems were studied as monolayers composed of head groups with different shapes and charge distributions. Starting from the free energy of the system, which includes the electrostatic interactions, additional internal degrees of freedom are included as positional and orientational entropic contributions to the free energy functional. The calculus of variation was used to derive Euler–Lagrange equations, which were solved numerically by the finite element method. The theory and Monte Carlo simulations predict that there are mainly two distinct regions of the electric double layer: (1) the interfacial region, with thickness less than or equal to the length of the fully stretched conformation of the lipid head group, and (2) the outside region, which follows the usual screening of the interface. In the interfacial region, the electric double layer is strongly perturbed, and electrostatic profiles and ion distributions have functionality distinct to classical mean-field theories. Based purely on Coulomb interactions, the theory suggests that the dominant effect on the lipid head group conformation is from the charge density of the interface and the structured lipid mole fraction in the monolayer, rather than the salt concentration in the system.

High-Resolution "Magic"-Field Spectroscopy on Trapped Polyatomic Molecules.

Rapid progress in cooling and trapping of molecules has enabled first experiments on high-resolution spectroscopy of trapped diatomic molecules, promising unprecedented precision. Extending this work to polyatomic molecules provides unique opportunities due to more complex geometries and additional internal degrees of freedom. Here, this is achieved by combining a homogeneous-field microstructured electric trap, rotational transitions with minimal Stark broadening at a"magic" offset electric field, and optoelectrical Sisyphus cooling of molecules to the low millikelvin temperature regime. We thereby reduce Stark broadening on the J=5←4 (K=3) transition of formaldehyde at 364GHz to well below 1kHz, observe Doppler-limited linewidths down to 3.8kHz, and determine the magic-field line position with an uncertainty below 100Hz. Our approach opens a multitude of possibilities for investigating diverse polyatomic molecule species.

Pi pulses in a ferromagnet: Simulations for yttrium iron garnet

Using a many spin micromagnetic simulation tool that directly integrates the Landau-Lifshitz equation, we demonstrate that by applying an r.f. pulse, generally referred to as a Pi pulse, it is possible to near-perfectly reverse the direction of the magnetization in a ferromagnet, provided that the sample is sufficiently small and the angular dependence of the precession frequency is continuously matched using an appropriately “chirped” r.f. pulse of the proper length. Simulations are carried out for “prolate” uniaxially symmetric cylindrical samples in the presence of dipole and exchange interactions. Such reversals can be performed in the presence of a static external magnetic field or, importantly, at zero field under the sample’s own internal demagnetization field. However, the ability to perform near-perfect Pi or two-Pi rotations is lost for samples above certain dimensions for which additional internal degrees of freedom are excited, particularly at higher static fields. In such larger samples the magnetization may still be reversed by utilizing damping, provided it can be rotated past a critical angle.

Spin Ruijsenaars–Schneider Models from Reduction

Spin Ruijsenaars–Schneider model introduced by Krichever and Zabrodin is a generalisation of a finite-dimensional integrable system due to Ruijsenaars and Schneider, where particles carry additional internal degrees of freedom. We review how a Hamiltonian structure of the spin model with the hyperbolic potential can be obtained by means of Poisson reduction applied to a specially chosen Poisson manifold.

The introduction and the influence of semi-rigid connections in framed structures subjected to fire

This paper describes a recent development in a finite element software dedicated to the modeling of structures in fire which deals with the way connections are simulated in global structure analyses. This development allows modeling semi-rigid, temperature-dependent connections between beam-type finite elements. It relies on the definition of additional internal degrees of freedom in the elements. The objective is to enable efficient analysis of the influence of semi-rigid connections on the global structural response and on the demands for these connections. The theory and implementation are described in a geometrically non-linear software with large displacements. Then, a 3D frame structure is analyzed as a case study. The analyses show that structural capacity and failure mode depend on the degree of rotational restraint at the beam-column connections and at the base of the columns. The maximum fire resistance is obtained for an intermediate degree of restraint between beams and columns, while higher restraints lead to an unfavorable sway failure mode. The case study illustrates the capabilities introduced by the new development, and demonstrates that the effects of the connections on global response is complex, justifying the need for practical numerical methods for design and parametric analyses of structures in fire.

Control and Stability Evaluation of the Bipedal Walking Robot AnyWalker

In the laboratory of robotics and mechatronics of the Kuban State University, a walking non-anthropomorphic robot has been developed, capable of overcoming obstacles exceeding the size of the robot. The robot has additional internal degrees of freedom, responsible for the compensation of deflections (the dynamic stabilization system). The article presents the results of the calculation of the stability zones in the frontal plane of the robot with and without a stabilization system.

Development of robotic mobile platform with the universal chassis system

The problem of stabilizing the position of mobile devices is extremely relevant at the modern level of technology development. This includes the problem of stabilizing aircraft and stabilizing the pitching of ships. In the laboratory of robotics and mechatronics of the Kuban State University, a robot is developed. The robot has additional internal degrees of freedom, responsible for compensating for deflections - the dynamic stabilization system.

Improved Sensing with a Single Qubit.

We consider quantum metrology with arbitrary prior knowledge of the parameter. We demonstrate that a single sensing two-level system can act as a virtual multilevel system that offers increased sensitivity in a Bayesian single-shot metrology scenario, and that allows one to estimate (arbitrary) large parameter values by avoiding phase wraps. This is achieved by making use of additional degrees of freedom or auxiliary systems not participating in the sensing process. The joint system is manipulated by intermediate control operations in such a way that an effective Hamiltonian, with an arbitrary spectrum, is generated that mimics the spectrum of a multisystem interacting with the field. We show how to use additional internal degrees of freedom of a single trapped ion to achieve a high-sensitivity magnetic field sensor for fields with arbitrary prior knowledge.

A smart displacement based (SDB) beam element with distributed plasticity

The standard displacement based inelastic beam element suffers of approximations related to the inability of the cubic polynomial interpolation functions to properly describe the displacement response of the beam when exhibiting inelastic behaviour. The increase of the number of finite elements, or the use of higher order functions with additional internal degrees of freedom, are common remedies suggested to improve the approximation leading to an unavoidable reduction of the computational efficiency. Alternatively, it has been shown that the development of force based finite elements, based on the adoption of exact force shape functions, lead to more accurate results, although requiring different and more complicated iterative solution strategies. Within this scenario, this paper proposes a new inelastic beam element, within the context of the displacement based approach, based on variable displacement shape functions, whose analytic expressions are related to the plastic deformation evolution in the beam element. The adaptive generalised displacement shape are obtained by identifying, at each step, an equivalent tangent beam, characterised by abrupt variations of flexural stiffness, as a suitable representation of the current inelastic state of the beam. The presented approach leads to the formulation of a Smart Displacement Based (SDB) beam element whose accuracy appears to be comparable to those obtained through a force based approach but requiring a reduced implementation effort and a more straightforward approach. The term ‘smart’ aims at emphasizing the ability of the element to upgrade the displacement field according to the current inelastic state.

Problem-dependent cubic linked interpolation for Mindlin plate four-node quadrilateral finite elements

We employ the so-called problem-dependent linked interpolation concept to develop two cubic 4-node quadrilateral plate finite elements with 12 external degrees of freedom that pass the constant bending patch test for arbitrary node positions of which the second element has five additional internal degrees of freedom to get polynomial completeness of the cubic form. The new elements are compared to the existing linked-interpolation quadratic and nine-node cubic elements presented by the author earlier and to the other elements from literature that use the cubic linked interpolation by testing them on several benchmark examples.

An optical spectroscopic study on two-dimensional group-VI transition metal dichalcogenides.

The ultimate goal of making atomically thin electronic devices stimulates intensive research on layered materials, in particular the group-VI transition metal dichalcogenides (TMDs). Atomically thin group-VI TMD crystals with a 2H stacking order emerging as a family of intrinsic 2-dimensional (2D) semiconductors with a sizeable bandgap in the visible and near infrared range satisfy numerous requirements for ultimate electronics and optoelectronics. In addition, the characteristic inversion symmetry breaking presented in monolayer TMDs leads to non-zero but contrasting Berry curvatures and orbit magnetic moments at K/K' valleys located at the corners of the first Brillouin zone. These features provide an opportunity to manipulate electrons' additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDs a promising candidate for the conceptual valleytronics. Besides, the strong spin-orbit interactions and the subsequent spin-valley coupling demonstrated in atomically thin group-VI TMDs open up potential routes towards quantum manipulation. In this tutorial review, we highlight recent advances in the optical study on electronic structures, vibrational properties, excitonic effects, valley dependent optical selection rules, and the interplay of valley, spin, and layer degrees of freedoms in this class of atomic 2D semiconductors including MoS2, MoSe2, WS2, and WSe2.

NSQUID arrays as conveyers of quantum information

We have considered the quantum dynamics of an array of nSQUIDs—two-junction SQUIDs with negative mutual inductance between their two arms. Effective dual-rail structure of the array creates additional internal degree of freedom for the fluxons in the array, which can be used to encode and transport quantum information. Physically, this degree of freedom is represented by electromagnetic excitations localized on the fluxon. We have calculated the spatial profile and frequency spectrum of these excitations. Their dynamics can be reduced to two quantum states, so that each fluxon moving through the array carries with it a qubit of information. Coherence properties of such a propagating qubit in the nSQUID array are characterized by the dynamic suppression of the low-frequency decoherence due to the motion-induced spreading of the noise spectral density to a larger frequency interval.

Light-induced conical intersections in polyatomic molecules: General theory, strategies of exploitation, and application

When the carrier frequency of a laser pulse fits to the energy difference between two electronic states of a molecule, the potential energy surfaces of these states dressed by the field become energetically close and the states can couple strongly to each other. Recently, it has been predicted that for diatomic molecules these surfaces may exhibit a conical intersection induced by the laser light in the space of the nuclear internal and external coordinates. Here, we report a general theory of the light-induced conical intersections emerging in polyatomic molecules where additional internal degrees of freedom are involved in the dynamics. Freely rotating and also fixed-in-space arbitrary polyatomic molecules exposed to differently polarized optical laser pulses of resonant carrier frequency are considered. Detailed analysis of the theory shows how the light-induced conical intersections can be controlled by molecular orientation and by the carrier frequency, polarization, strength, and duration of the laser pulse. This opens the possibility to also control the ensuing non-adiabatic dynamics. Different strategies of exploitation of the light-induced conical intersections are proposed. The present theory is exemplified by utilizing the light-induced conical intersections to control photodissociation of the second electronically excited state S2 of the fixed-in-space cis-methyl nitrite CH3ONO.

Minimalistic model for navigation of mobile robots around obstacles based on complex-number calculus and inspired by human navigation behavior

It has recently been shown that the strategies and rules used by human agents to approach a goal position while avoiding collision with an obstacle can be used to construct a model for robot navigation. The robot navigation model thus obtained involves position variables for robot position and additional internal degrees of freedom. In the present work, we eliminate these internal degrees of freedom by means of a standard method of synergetics (theory of self-organization) while still making sure that the mobile robot will approach the goal position. In doing so, we arrive at a minimalistic navigation model that (i) is motivated by human navigation behavior, (ii) benefits from computational simplicity, (iii) can be re-formulated by means of complex number calculus, and (iv) allows to determine two-dimensional flow fields in analogy to hydrodynamic two-dimensional flows by means of computer simulations. We present the implementation of the navigation algorithm in terms of a complex-valued Euler forward scheme and exploit the simulation scheme to predict how the time to reach the goal position depends on some key parameters of the minimalistic robot navigation model.

Rounding of a first-order quantum phase transition to a strong-coupling critical point

We investigate the effects of quenched disorder on first-order quantum phase transitions on the example of the $N$-color quantum Ashkin-Teller model. By means of a strong-disorder renormalization group, we demonstrate that quenched disorder rounds the first-order quantum phase transition to a continuous one for both weak and strong coupling between the colors. In the strong-coupling case, we find a distinct type of infinite-randomness critical point characterized by additional internal degrees of freedom. We investigate its critical properties in detail and find stronger thermodynamic singularities than in the random transverse field Ising chain. We also discuss the implications for higher spatial dimensions as well as unusual aspects of our renormalization-group scheme.

Investigation the complex dynamic evolvement mechanism of particle cluster and surface integrity in the chemical mechanical planarization

The surface planarization in the chemical mechanical planarization is mainly realized by the mechanical effect which depends on the micro-tribology behavior of nanoparticles. The material removal rate is decreased and micro-scratch is generated in the wafer surface due to the agglomeration of particles. The slurry particles hold definite energy level and microstructure which makes the classical materials processing theory unable to give reasonable explanation about this process. Large-scale classical molecular dynamic simulation of interaction among nanoparticles and solid surface has been carried out to investigate the evolvement mechanism of particle cluster and surface planarization. It is showed that the particle aggregation behavior is a size-dependent process because of the high ratio of surface atoms to bulk atoms which leads to the active reactivity and catalytic activity of nanoparticles. The substrate materials (nanoparticle) become transforming from low-energy stable system to high-energy unstable system after the two-body collision which is favorable for aggregation process. There exists obvious geometry boundary between the particle elements in the large aggregates and only the dendritic aggregates formed. The larger particles have definite microstructure and additional internal degree of freedom which can be used to take up, store, and transfer energy, thus lower the activity of chemical reaction which weaken the particle aggregation process.

Isospin of topological defects in Dirac systems

We study the Dirac quasiparticles in $d$-dimensional lattice systems of electrons in the presence of domain walls ($d=1$), vortices ($d=2$), or hedgehogs ($d=3$) of superconducting and/or insulating, order parameters, which appear as mass terms in the Dirac equation. Such topological defects have been known to carry non-trivial quantum numbers such as charge and spin. Here we discuss their additional internal degree of freedom: irrespectively of the dimensionality of space and the nature of orders that support the defect, an extra mass-order-parameter is found to emerge in their core. Six linearly independent local orders, which close two mutually commuting three-dimensional Clifford algebras are proven to be in general possible. We show how the particle-hole symmetry restricts the defects to always carry the quantum numbers of a single effective isospin-1/2, quite independently of the values of their electric charge or true spin. Examples of this new degree of freedom in graphene and on surfaces of topological insulators are discussed.

Feedback control of a redundant wheeled snake mechanism using transverse functions SO(4)

The Transverse Function (TF) approach is applied to the control of a nonholonomic three-segments/snake-like wheeled mechanism, similar to the planar low-dimensional version of Hirose's Active Cord Mechanism (ACM) previously studied by the authors with the same control approach, but with two additional internal degrees of freedom (d.o.f.) whose actuation yields more flexible and efficient control solutions. From a theoretical point of view, these complementary d.o.f. modify the Control Lie Algebra of the system so that only first-order Lie brackets of the control vector fields are needed to satisfy the Lie Algebra Rank Condition (LARC). The fact that four independent (angular velocity) control inputs are used also implies for this system the existence of Transverse Functions (TF) defined on the six-dimensional special orthogonal group(4). Several examples of mechanisms whose control involve TF defined on(3) have been pointed out in the past. Beyond the specific control problem addressed here, a motivation for the present study is to illustrate for the first time how functions defined on the larger set(4) can be determined and used for the control of a physical system. This study is complemented with recalls concerning the parametrization of(4) by pairs of isoclinic quaternions and with the derivation of complementary differential calculus relations associated with this parametrization.

Enhanced passive targeted energy transfer in strongly nonlinear mechanical oscillators

Single-degree-of-freedom (SDOF) nonlinear energy sinks (NESs) can efficiently mitigate broadband disturbances applied to primary linear systems by means of passive targeted energy transfer (TET), but for a rather limited range of energies. We demonstrate that the TET can be significantly enhanced for broad range of energies by introducing additional internal degrees of freedom to the NES in a highly asymmetric fashion. Numerical simulations demonstrate that the enhanced performance is due to a positive synergistic effect of the internal degrees of freedom of the proposed NES with highly asymmetric stiffnesses.