Different Degrees Of Freedom Research Articles

Data Exchange of Relay Transmission and Information Scheduling in Shared Networks

With the diversification of the kinds of wireless transmission service, the transmission rate and reliability of wireless communication have been demanded sharply. The shortage of resources of spectrum has become continuously prominent. These are bottlenecks to restrict the development of wireless communication. The current multi-antenna cooperative relay communication system can’t sense complex communication scenes agilely, and adjust the strategy of interference suppression according to the signal characteristics adaptively, and optimize the resource of the system dynamically. Moreover, the degree of freedom and transmission system reliability should have been further improved. Aiming at the above problems, this paper extracts the features of the combined signal from different degrees of freedom, considering the influence and effect of the distribution characteristics of the signal on its separability, and signal spatial structure to enhance the ability to adapt to complex environmental interference. It explores multiple interactive cooperative transmission scheduling to optimize the wireless resource dispatching and new network coding jointly, and get a unified multi antenna relay transmission processing standards and to improve the efficiency of information transmission. It carries out theoretical studies of interference coordination algorithms which can acquire higher forwarding efficiency at relay in the view of energy efficiency and spectral efficiency.

Optical absorption spectroscopy in hybrid systems of plasmons and excitons

Understanding the physics of light emitters in quantum nanostructures regarding scalability, geometry, structure of the system and coupling between different degrees of freedom is important as one can improve the design and further provide rigorous controls of quantum devices. The coupling between these degrees of freedom, in general, depends on the external field, the geometry of nano particles, and the experimental design. An effective model is proposed to describe the plasmon-exciton hybrid systems and its optical absorption spectra, which is studied in detail by exact diagonalization. Two different designs are discussed: a nano particle planet surrounded by quantum dot satellites and a quantum dot planet surrounded by nano particle satellites. In both setups, details of many quantum dots and nano particles are studied, and the spectra are discussed in detail regarding the energy of transition peaks and the weight distribution of allowed transition peaks. Also, different polarization of external fields is considered, which results in anisotropic couplings, and the absorption spectra clearly reveal the difference qualitatively. Finally, the system will undergo a phase transition in the presence of attractive interactions between excitons. Our work sheds light on the design of nano scale quantum systems to achieve photon emitter/resonator theory in plasmon-exciton hybrid systems.

A consistent kinetic model for a two-component mixture of polyatomic molecules

We consider a multi component gas mixture with translational and internal energy degrees of freedom assuming that the number of particles of each species remains constant. We will illustrate the derived model in the case of two species, but the model can be easily generalized to multiple species. The two species are allowed to have different degrees of freedom in internal energy and are modelled by a system of kinetic ES-BGK equations featuring two interaction terms to account for momentum and energy transfer between the species. We prove consistency of our model: conservation properties, positivity of the temperature, H-theorem and convergence to a global equilibrium in the form of a global Maxwell distribution. Thus, we are able to derive the usual macroscopic conservation laws. For numerical purposes we apply the Chu reduction to the developed model for polyatomic gases and give an application for a gas consisting of a mono atomic and a diatomic species.

Resource Management in Future Millimeter Wave Small-Cell Networks: Joint PHY-MAC Layer Design

The millimeter wave (mmWave) frequency band will become a key enabler for future wireless systems currently facing the explosive growth of data traffic and the sparsity of the traditional ultra-high frequency (UHF) band. Nevertheless, the challenges for mmWave communications lie in high propagation loss, sensitivity to blockage, high cost for equipping directional antennas, and so on. Furthermore, the traditional design for the UHF networks cannot be directly used for future mmWave networks, which needs to be reshaped from the perspectives of fundamental objectives, various constraints, and different degrees of freedom. This paper addresses the key functions and discusses the challenges for PHY layer and MAC layer design in mmWave small-cell networks, including mmWave antenna design, beamforming, initial access, radio resource allocation, power allocation, and so on. The novel resource management approach for the joint PHY-MAC layer design is proposed to find the trade-off among hardware cost of the mmWave antenna, beamforming overhead, and efficiency of the new resource block (RB) allocation in beam-frequency-time (B-T-F)-dimension. © 2013 IEEE.

Influence of stiffness gradient on friction between graphene layers

According to the molecular dynamics simulations and the mechanism of energy dissipation of nanofriction, we construct a model system with a flake sliding in commensurate configuration on a monolayer suspended graphene anchored on a bed of springs. The system is to analyze the contributions of different regions (T1-T7) of the graphene flake to friction force, with the substrate characterized by different stiffness gradients and midpoint stiffness.</br>The results indicate that the soft region of contact (T1) always contributes to the driving force, whereas the hard region (T7) leads to the biggest friction force on all column atoms of the flake. Moreover, as the support stiffness increases, when the stiffness gradient and the midpoint stiffness are equal to 1.34 nN/nm<sup>2</sup> and 12 nN/nm, respectively, the contribution ratio of T7 to the total friction increases from 33% to 47%, which is approximately 4-15 times greater than those of each column atoms in T3-T6. The results also indicate that the energy barrier decreases with the increase of support stiffness along the stiffness gradient direction of the substrate, which induces the resistance forces on the relative motion to decrease. Meanwhile, the amplitude of the thermal atomic fluctuation is higher in the softer region while lower in the harder one. This difference in amplitude leads to the considerable potential gradient that ultimately causes the driving force. Finally, for a given point at the end of the flake (T1 or T7), the intensity of the van der Waals potential field is mainly determined by the nearest substrate atoms at that point. Part of these nearest atoms lie inside the contact region while the others do not. Consequently, the thermal vibration of the atoms inside the contact region is different from that of the atoms outside the confinement. The different thermal vibrations induce the greater edge barriers. In addition, T1 lies in the soft edge region and T7 in the hard one. As a result, the normal deformations of these two regions are always different, and therefore they also generate the driving force.</br>At these points, the results reported here suggest that the friction force in each contact region is caused by the coupling of the energy barrier and the elastic deformation between the graphene surfaces. The former contribution, i.e.the energy barrier, includes the interfacial potential barrier in commensurate state which is against the sliding of the surfaces with respect to each other, and the potential gradient caused by the different vibration magnitudes of the substrate atoms against the different spring stiffness in the direction of stiffness gradient. The latter contribution, i.e. the elastic deformation, is the unbalanced edge energy barrier resulting from the asymmetrical deformation and the different degrees of freedom between the edge atoms of the slider and atoms inside and outside the contact area of the substrate. Results of this paper are expected to be able to provide theoretical guidance in considering the influence of stiffness gradient on friction between commensurate surfaces and in designing the nanodevices.

Magic v.3: An integrated software package for systematic structure-based coarse-graining

Molecular simulations of many phenomena related to biomolecular systems, soft matter and nanomaterials require consideration of length scales above 10 nm and time scales longer than 1μs, which necessitates the use of coarse-grained (low resolution) models, where each site of the model represents a group of atoms, and where the solvent is often omitted. Our software package MagiC is designed to perform systematic structure-based coarse-graining of molecular models, in which the effective pairwise potentials between coarse-grained sites of low-resolution molecular models are constructed to reproduce structural distribution functions obtained from modeling of systems in a high resolution (atomistic) description. The software takes as input atomistic trajectories generated by an external molecular dynamics package, and produce as an output interaction potentials for coarse-grained models which can be directly used in a coarse-grained simulations package. Here we present a major update (v.3) of the software with substantially improved functionality, compatibility with several major atomistic and coarse-grained simulations packages (GROMACS, LAMMPS, GALAMOST), analysis suite with graphical possibilities, diagnostics, documentation. We describe briefly the coarse-graining methodology, the structure of the software, describe users actions, and illustrate the whole process with two complex examples: cholesterol containing lipid bilayers and condensation of DNA caused by multivalent ions. Program summaryProgram Title: MagiCProgram Files doi:http://dx.doi.org/10.17632/9gnfxyshj8.1Licensing provisions: GPLv3Programming language: Fortran, PythonNature of problem: Systematic bottom-up multiscale modeling is a complex multi-stage process, in which results of simulations of a high-resolution (atomistic) model are used to construct a low resolution (coarse-grained) model, providing the same structural properties for the coarse-grained system as for the high-resolution system. Within the approach, structural properties of the high-resolution model are computed in terms of radial distribution functions and distributions of intramolecular degrees of freedom. Then the inverse problem is solved, in which the interaction potentials for the low-resolution model are determined which provide distribution functions coinciding with those obtained in the high-resolution simulations. The low-resolution model can be then used for simulations of the same system on larger length and time-scale.Solution method: The presented software package implements all stages of the systematic structure-based coarse-graining. It works as an integrated pipeline, giving the user ability to easily derive a coarse-grained model for a multicomponent complex molecular system and then use it for large-scale simulations. MagiC implements two approaches to solve the inverse problem: (i) the Inverse Monte Carlo method in which the inverse problem is solved using the Newton–Raphson method, with inversion of the Jacobian for the discretized relationship between interaction potentials and structural distribution functions; and (ii) the Iterative Boltzmann approach in which the inverse problem is solved using approximative relationships neglecting correlations between different degrees of freedom. The inverse solver includes also variational Inverse Monte Carlo approach when some of the coarse-grained potentials are fixed while others vary in order to fit the whole set of reference distribution functions.Additional comments: The MagiC main module can be also used for conventional Monte Carlo simulations of molecular systems described by tabulated pairwise potentials in the canonical ensemble.

Understanding the Enhancement of Surface Diffusivity by Dimerization.

Beyond dilute coverage, the collective diffusion of molecules might enhance material transport. We reveal an enhanced mobility of molecular dimers by separating two motions, diffusion and rotation, of CO dimers on elemental Ag(100) as well as on a dilute Cu alloy of Ag(100). From time-lapsed scanning tunneling microscopy movies recorded between 15 and 25K, we determine the activation energy of dimer diffusion on elemental Ag(100) to be, at (40±2) meV, considerably smaller than the one for monomer diffusion, at (72±1) meV. The alloyed Cu atoms reduce the dimer mobility facilitating to determine their rotational barrier separately to be (39±3) meV. Disentangling different degrees of freedom suggests that a rotational motion is at the origin of enhanced dimer diffusivity.

Articulating parametric resonance for an OWC spar buoy in regular and irregular waves

Wave energy devices are designed, and controlled, to be extremely responsive to incoming wave excitation, hence, maximising power absorption. Due to the consequent large motion excursions, highly nonlinear behaviour is likely to occur, especially in relation to variations in wetted surface. Moreover, nonlinearities may induce parametric instability, or activate internal mechanisms for exchanging energy between different degrees of freedom (DoFs), usually affecting the overall efficiency of the device. Consequently, single-DoF linear models may produce overly optimistic power production predictions, and neglect important dynamics of the system. One highly nonlinear phenomenon, potentially detrimental to power absorption for several wave energy converters, is parametric roll/pitch; due to parametric excitation, part of the energy flow is internally diverted, from the axis where the power take-off is installed, to a secondary axis, generating parasitic motion. This paper proposes a computationally efficient multi-DoF nonlinear model, which can effectively describe nonlinear behaviour, such as parametric pitch and roll, and their impact on motion prediction, power production assessment, and optimal control parameters.

Effects of Degrees of Motion Freedom on Free-Fall of A Sphere in Fluid

Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations (DNS). We mainly focus on the effects of different degrees-of-freedom (DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.

Anisotropic polarization-induced conductance at a ferroelectric-insulator interface.

Coupling between different degrees of freedom, that is, charge, spin, orbital and lattice, is responsible for emergent phenomena in complex oxide heterostrutures1,2. One example is the formation of a two-dimensional electron gas (2DEG) at the polar/non-polar LaAlO3/SrTiO3 (LAO/STO)3-7 interface. This is caused by the polar discontinuity and counteracts the electrostatic potential build-up across the LAO film3. The ferroelectric polarization at a ferroelectric/insulator interface can also give rise to a polar discontinuity8-10. Depending on the polarization orientation, either electrons or holes are transferred to the interface, to form either a 2DEG or two-dimensional hole gas (2DHG)11-13. While recent first-principles modelling predicts the formation of 2DEGs at the ferroelectric/insulator interfaces9,10,12-14, experimental evidence of a ferroelectrically induced interfacial 2DEG remains elusive. Here, we report the emergence of strongly anisotropic polarization-induced conductivity at a ferroelectric/insulator interface, which shows a strong dependence on the polarization orientation. By probing the local conductance and ferroelectric polarization over a cross-section of a BiFeO3-TbScO3 (BFO/TSO) (001) heterostructure, we demonstrate that this interface is conducting along the 109° domain stripes in BFO, whereas it is insulating in the direction perpendicular to these domain stripes. Electron energy-loss spectroscopy and theoretical modelling suggest that the anisotropy of the interfacial conduction is caused by an alternating polarization associated with the ferroelectric domains, producing either electron or hole doping of the BFO/TSO interface.

A parametric stability analysis of the offshore jacket launch: a case study in the Persian Gulf

The fixed jacket platforms are one of the commonly used offshore structures. The jacket launch process includes several steps which should be carefully analyzed to ensure a safe installation procedure. An important consideration for a successful construction is the design of the symmetric jacket frame to prevent the uncontrolled motions during the launch process. However, due to some unavoidable structural imperfections, which may occur during the barge shipment, the existence of some imperfection is inevitable. Therefore, the placement of buoyancy tanks is required to address this problem through the minimization of undesirable motions. In this paper, the effects and performance of the buoyancy tanks are studied by considering the significant parameters such as the jacket motions, velocity components, and the rocker arms. The effect of these variables has been studied on the rotation of jacket and its velocity during launching process. These studies have been discussed in types of jackets with and without buoyancy tanks. Moreover, different local parameters including the sea-water density, winch velocity, drag coefficient, and barge geometrical dimensions are considered as the other important factors of the launch process. As an important result of this research, in addition, it is observed that the buoyancy tanks did not have a major influence on the linear motions through the different degrees of freedom. It is worthy of note that not only the final yaw rotation of the jacket did not vary significantly, but also changes of launch variables did not show feasible effects on the center of gravity and buoyancy of the jacket.

Visualizing electronic structures of quantum materials by angle-resolved photoemission spectroscopy

Electronic structures are critical characteristics that determine the electrical, magnetic and optical properties of materials. With the capability of directly visualizing band dispersions and Fermi surfaces, angle-resolved photoemission spectroscopy (ARPES) has emerged as a powerful experimental tool to extract the electronic structures of materials and the coupling of these electronic structures to different degrees of freedom in crystal lattices. In the past three decades, advances in instrumentation and light sources have significantly improved the accuracy and efficiency of ARPES experiments. These advances have enabled the application of ARPES in novel material systems to aid our understanding of their physical properties and behaviours. In this Review, we give a brief introduction to the principles of ARPES and outline its applications in different material systems, with a focus on topological quantum materials and transition metal dichalcogenides.

Variational study of U(1) and SU(2) lattice gauge theories with Gaussian states in1+1dimensions

We introduce a method to investigate the static and dynamic properties of both Abelian and non-Abelian lattice gauge models in 1+1 dimensions. Specifically, we identify a set of transformations that disentangle different degrees of freedom, and apply a simple Gaussian variational ansatz to the resulting Hamiltonian. To demonstrate the suitability of the method, we analyze both static and dynamic aspects of string breaking for the U(1) and SU(2) gauge models. We benchmark our results against tensor network simulations and observe excellent agreement, although the number of variational parameters in the Gaussian ansatz is much smaller.

Automatic detection of degenerate planetary gear trains with different degree of freedoms

• A fully automatic algorithm to detect degenerate PGTs is proposed, based on our new graph model . • The algorithm is applicable for PGTs with any number of degree of freedoms. • The algorithm has been applied to a large number of PGTs, including the counterexamples found in literature. • The algorithm has some merits relative to the existing ones. • The algorithm is helpful for designing transmissions applied in engineering. Planetary gear trains (PGT) are widely used in transmissions of vehicles, pulley blocks, wrist watches, machine tool, robots, etc. The structural synthesis of PGTs is an effective way to create novel transmissions. In the synthesis process, one of the most important problems is to detect and eliminate degenerate PGTs. This paper proposes a fully automatic algorithm to resolve this key problem. Our previous graph representation of PGT is first introduced and the corresponding adjacency matrix is used as the numerical tool, based on which the fundamental circuits (f-circuit) of PGT can be easily determined. The present algorithm is executed by successively adding a single f-circuit to generate sub-graphs. The detection process has been automated by an interactive computer program. The algorithm is applicable for PGTs with any number of degree of freedoms (DOF). The algorithm has been applied to a large number of PGTs, including the counterexamples found in literature. Our results of all the tested PGTs are verified to be correct.

Robust Student’s <inline-formula> <tex-math notation="LaTeX">$t$ </tex-math> </inline-formula>-Based Cooperative Navigation for Autonomous Underwater Vehicles

A robust leader–slave cooperative navigation (CN) algorithm for autonomous underwater vehicles (AUVs) based on the Student’s $t$ extended Kalman filter (SEKF) is proposed. Compared with the conventional EKF based on a Gaussian distributed noise assumption, which has been widely used in the field of CN, the Student’s $t$ -based filtering algorithms show an improved robustness against outliers existing in the process and measurement noises. The utilization of the Student’s $t$ distribution can minimize the negative effect induced by the outliers existing in the underwater acoustic communication system and the cheap but unreliable dead reckoning sensors equipped on the slave AUVs. After a detailed derivation of the robust CN algorithm based on the SEKF, two approximation methods that are required in the Student’s $t$ -based filter are discussed and compared. Simulation results show the efficiency and superiority of the robust SEKF-based leader–slave CN algorithm as compared with the conventional EKF-based CN algorithm. The validity of the proposed CN algorithm is also evaluated on field trial data, and the performance of different degrees of freedom (DOF) values, which determine the tail behavior of the Student’s $t$ distribution is compared and analyzed, and then the link between the DOF value and the robust effect of the Student’s $t$ distribution is revealed, which will act as a guide when applying the Student’s $t$ -based filter in the field of CN.

Robust selection of the degrees of freedom in the Student’s t distribution through Multiple Model Adaptive Estimation

Abstract A robust Multiple Model Adaptive Estimation (MMAE) framework of parallel extended Student’s t filters (ESTFs) with different degrees of freedom (dof) is proposed. Compared with the conventional extended Kalman filter (EKF) based on a Gaussian distributed noise assumption, the Student’s t based filtering algorithms show a better robustness against outliers existing in process and measurement noises. In a Student’s t based filter, the dof which determines the tail behavior of the noise density plays a significant role in the performance of the filter. However, there is currently no appropriate selection criterion for the dof for the Student’s t based filters, because it is related to the properties of the outliers which are usually time-varying and unpredictable. In this paper, the extended Student’s t filtering algorithm is derived, and three typical dof values which represent extreme and intermediate heavy tailed distributed noise together with approximated Gaussian distributed noise are chosen. The state estimation is the weighted summation of all three extended Student’s t filters, and the effect of each dof value is automatically and dynamically adjusted via the MMAE framework. Simulation results show the efficiency and superiority of the proposed MMAE framework for the extended Student’s t filters as compared with the conventional EKF, conventional UKF, and the extended Student’s t filter and unscented Student’s t filter with a fixed dof value.

Real homotopy theory and supersymmetric quantum mechanics

In the context of studying string backgrounds, much work has been devoted to the question of how similar a general quantum field theory (specifically, a two-dimensional superconformal field theory) is to a sigma model. Put differently, one would like to know how well or poorly one can understand the physics of string backgrounds in terms of concepts of classical geometry. Much attention has also been given of late to the question of how geometry can be encoded in a microscopic physical description that makes no explicit reference to space and time. We revisit the first question and review both well-known and less well-known results about geometry and sigma models from the perspective of dimensional reduction to supersymmetric quantum mechanics. The consequences of arising as the dimensional reduction of a d-dimensional theory for the resulting quantum mechanics are explored. In this context, we reinterpret the minimal models of rational (more precisely, complex) homotopy theory as certain supersymmetric Fock spaces, with unusual actions of the supercharges. The data of the Massey products appear naturally as supersymmetric vacuum states that are entangled between different degrees of freedom. This connection between entanglement and geometry is, as far as we know, not well known to physicists. In addition, we take note of an intriguing numerical coincidence in the context of string compactification on hyper-Kähler eight-manifolds.

18-Qubit Entanglement with Six Photons' Three Degrees of Freedom.

Full control of multiple degrees of freedom of multiple particles represents a fundamental ability for quantum information processing. We experimentally demonstrate an 18-qubit Greenberger-Horne-Zeilinger entanglement by simultaneous exploiting three different degrees of freedom of six photons, including their paths, polarization, and orbital angular momentum. We develop high-stability interferometers for reversible quantum logic operations between the photons' different degrees of freedom with precision and efficiencies close to unity, enabling simultaneous readout of 2^{18}=262 144 outcome combinations of the 18-qubit state. A state fidelity of 0.708±0.016 is measured, confirming the genuine entanglement of all 18 qubits.

Certifying an Irreducible 1024-Dimensional Photonic State Using Refined Dimension Witnesses.

We report on a new class of dimension witnesses, based on quantum random access codes, which are a function of the recorded statistics and that have different bounds for all possible decompositions of a high-dimensional physical system. Thus, it certifies the dimension of the system and has the new distinct feature of identifying whether the high-dimensional system is decomposable in terms of lower dimensional subsystems. To demonstrate the practicability of this technique, we used it to experimentally certify the generation of an irreducible 1024-dimensional photonic quantum state. Therefore, certifying that the state is not multipartite or encoded using noncoupled different degrees of freedom of a single photon. Our protocol should find applications in a broad class of modern quantum information experiments addressing the generation of high-dimensional quantum systems, where quantum tomography may become intractable.

Intersectionality and emergence in time use analysis: possible pathways for gender research and work–family reconciliation policy in Italy

ABSTRACTTracking how time is shared between work and family has the potential to unearth implicit gender biases and empowerment processes as women mobilize hidden resources and become aware of their own agency and differences vis-à-vis social groups they belong to or are excluded from. Building upon a time use study of a sample of 100 women working within administrative agencies, firms and social coops within the Italian Mezzogiorno, I examine work–family reconciliation interfaces through the epistemological dimensions of intersectionality and reflexive emergence. I interpret time use findings intersectionally to identify those workers who are vulnerable to time poverty associated with different degrees of freedom and power. Through the lens of reflexive emergence, I seek to grasp the unpredictable, unique and oftentimes invisible empowerment situations women experience in balancing work responsibilities with family care. Intersectionality and reflexive emergence in time use analysis help design work–family reconciliation policies by targeting occupational measures and welfare provisions according to different beneficiaries’ needs in public agencies, private firms and non-profit work organizations.