Showing papers on "Degrees of freedom published in 2020"
TL;DR: Recent developments of multiplexing and multifunctional metasurfaces, which enable concurrent tasks through a dramatic compact design, are reviewed and a detailed overview of polarization-controlled, wavelength- selective, angle-selective, and reconfigurable multiplexed/multifunctional meetasurfaced is provided.
Abstract: Metasurfaces are planar photonic elements composed of subwavelength nanostructures, which can deeply interact with light and exploit new degrees of freedom (DOF) to manipulate optical fields. In the past decade, metasurfaces have drawn great interest from the scientific community due to their profound potential to arbitrarily control light. Here, recent developments of multiplexing and multifunctional metasurfaces, which enable concurrent tasks through a dramatic compact design, are reviewed. The fundamental properties, design strategies, and applications of multiplexing and multifunctional metasurfaces are then discussed. First, recent progress on angular momentum multiplexing, including its behavior under different incident conditions, is considered. Second, a detailed overview of polarization-controlled, wavelength-selective, angle-selective, and reconfigurable multiplexing/multifunctional metasurfaces is provided. Then, the integrated and on-chip design of multifunctional metasurfaces is addressed. Finally, future directions and potential applications are presented.
147 citations
TL;DR: The requirements for multiplexed sources are studied, various approaches to multiplexing using different degrees of freedom are compared and higher single-photon probabilities are allowed.
Abstract: We review the rapid recent progress in single-photon sources based on multiplexing multiple probabilistic photon-creation events. Such multiplexing allows higher single-photon probabilities and lower contamination from higher-order photon states. We study the requirements for multiplexed sources and compare various approaches to multiplexing using different degrees of freedom.
93 citations
TL;DR: In this article, a personal perspective on metamterials with high degrees of freedom and dimensionality and their potential roles in enriching light-matter interaction in photonics and related fields is presented.
Abstract: Abstract In this brief opinionated article, I present a personal perspective on metamterials with high degrees of freedom and dimensionality and discuss their potential roles in enriching light–matter interaction in photonics and related fields.
84 citations
TL;DR: Unsupervised, semi-supervised and supervised machine learning methods to direct numerical simulations data of homogeneous isotropic turbulence, Rayleigh-Bénard convection, and the minimal flow unit of a turbulent channel flow are discussed.
Abstract: The physical complexity and the large number of degrees of freedom that can be resolved today by direct numerical simulations of turbulent flows, and by the most sophisticated experimental techniqu...
67 citations
TL;DR: A review of exceptional field theory as discussed by the authors is a generalisation of Kaluza-Klein theory that unifies the metric and p-form gauge field degrees of freedom of supergravity into a generalised or extende...
Abstract: This is a review of exceptional field theory: a generalisation of Kaluza–Klein theory that unifies the metric and p-form gauge field degrees of freedom of supergravity into a generalised or extende...
65 citations
TL;DR: In this article, the authors discuss aspects of non-perturbative unitarity in quantum field theory and show that the additional ghost degrees of freedom arising in truncations of an effective action at a finite order in derivatives could be fictitious degrees offreedom.
63 citations
TL;DR: A new method for two-dimensional (2-D) direction-of-arrival (DOA) estimation using two parallel nested arrays that exploits the difference coarray to increase the array aperture and degrees of freedom and can achieve parameter automatic pairing.
Abstract: In this letter, we propose a new method for two-dimensional (2-D) direction-of-arrival (DOA) estimation using two parallel nested arrays. In this method, an augmented covariance matrix is firstly constructed using the outputs of two parallel difference coarrays. Based on the augmented covariance matrix, the 2-D DOA estimation problem is then converted into two one-dimensional estimation problems. Finally, the azimuth and elevation angle estimates are derived using the estimated direction cosines. Unlike the traditional methods, our algorithm exploits the difference coarray to increase the array aperture and degrees of freedom. Moreover, it does not require any peak searching and can achieve parameter automatic pairing. Numerical simulations are conducted to verify the performance of the proposed method.
62 citations
17 Aug 2020
49 citations
TL;DR: In this article, a 4 degrees of freedom ship performance prediction model is used to compare wind-assisted ship propulsion technologies: the Flettner rotor, a wingsail and the DynaRig concept.
Abstract: A 4 degrees of freedom ship performance prediction model is used to compare wind-assisted ship propulsion technologies: the Flettner rotor, a wingsail and the DynaRig concept. An Aframax Oil Tanker...
46 citations
TL;DR: It is shown that non-resonant ratios of these time scales have maximal memory capacities and that networks that originate from a system with resonant delay-times and clock cycles fail to utilize all of their degrees of freedom, which causes the degradation of their performance.
37 citations
TL;DR: In this article, a review on the progress on the design of different nanostructured metasurfaces for lightwave manipulation, including by varying/fixing the dimensions and/or orientations of isotropic/anisotropic nanostructure, which can therefore provide various functionalities for different applications.
Abstract: Abstract The unusual electromagnetic responses of nanostructured metasurfaces endow them with an ability to manipulate the four fundamental properties (amplitude, phase, polarization, and frequency) of lightwave at the subwavelength scale. Based on this, in the past several years, a lot of innovative optical elements and devices, such as metagratings, metalens, metaholograms, printings, vortex beam generators, or even their combinations, have been proposed, which have greatly empowered the advanced research and applications of metasurfaces in many fields. Behind these achievements are scientists’ continuous exploration of new physics and degrees of freedom in nanostructured metasurface design. This review will focus on the progress on the design of different nanostructured metasurfaces for lightwave manipulation, including by varying/fixing the dimensions and/or orientations of isotropic/anisotropic nanostructures, which can therefore provide various functionalities for different applications. Exploiting the design degrees of freedom of optical metasurfaces provides great flexibility in the design of multifunctional and multiplexing devices, which can be applied in anticounterfeiting, information encoding and hiding, high-density optical storage, multichannel imaging and displays, sensing, optical communications, and many other related fields.
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TL;DR: In this article, the Euclidean wormhole spacetimes and their associated cosmological physics might be described within the context of AdS/CFT, and the authors point out that a holographic model for cosmology proposed recently in arXiv:1810.10601 can be understood as a specific example of this picture.
Abstract: Certain closed-universe big-bang/big-crunch cosmological spacetimes may be obtained by analytic continuation from asymptotically AdS Euclidean wormholes, as emphasized by Maldacena and Maoz. We investigate how these Euclidean wormhole spacetimes and their associated cosmological physics might be described within the context of AdS/CFT. We point out that a holographic model for cosmology proposed recently in arXiv:1810.10601 can be understood as a specific example of this picture. Based on this example, we suggest key features that should be present in more general examples of this approach to cosmology. The basic picture is that we start with two non-interacting copies of a Euclidean holographic CFT associated with the asymptotic regions of the Euclidean wormhole and couple these to auxiliary degrees of freedom such that the original theories interact strongly in the IR but softly in the UV. The partition function for the full theory with the auxiliary degrees of freedom can be viewed as a product of partition functions for the original theories averaged over an ensemble of possible sources. The Lorentzian cosmological spacetime is encoded in a wavefunction of the universe that lives in the Hilbert space of the auxiliary degrees of freedom.
TL;DR: A thermodynamics-based theoretical framework is presented to gauge the effectiveness of a given simplified representation by measuring its information content, and shows that these highly informative representations share common features that are intrinsically related to the biological properties of the proteins under examination, thereby establishing a bridge between protein structure, energetics, and function.
Abstract: In theoretical modeling of a physical system, a crucial step consists of the identification of those degrees of freedom that enable a synthetic yet informative representation of it. While in some c...
TL;DR: In this article, a skyrmion crystal has internal degrees of freedom in terms of vorticity and helicity, which gives rise to fascinating types of SKYMION phases (Neel, Bloch, and anti-skyrmions).
Abstract: A skyrmion crystal has internal degrees of freedom in terms of vorticity and helicity, which gives rise to fascinating types of skyrmion phases (Neel, Bloch, and anti-skyrmion). We show how the deg...
TL;DR: In this paper, double holography was used to study the Hawking radiation emitted by the eternal BTZ black hole in equilibrium with a thermal bath, but in the form of warped CFT$_2$ degrees of freedom.
Abstract: We use the notion of double holography to study Hawking radiation emitted by the eternal BTZ black hole in equilibrium with a thermal bath, but in the form of warped CFT$_2$ degrees of freedom. In agreement with the literature, we find entanglement islands and a phase transition in the entanglement surface, but our results differ significantly from work in AdS/CFT in three major ways: (1) the late-time entropy decreases in time, (2) island degrees of freedom exist at all times, and not just at late times, with the phase transition changing whether or not these degrees of freedom include the black hole interior, and (3) the physics involves a field-theoretic IR divergence, emerging when the boundary interval is too big relative to the black hole's inverse temperature. This behavior in the entropy appears to be consistent with the non-unitarity of holographic warped CFT$_2$ and demonstrates that the islands are not a phenomenon restricted to black hole information in unitary setups.
TL;DR: The molecular roughness difference is calculated by a numerical comparison of the molecular surfaces of both the atomistic and coarse-grained systems, and the acceleration factor of the seven test systems reach a very good linear correlation.
Abstract: Coarse-grained models include only the most important degrees of freedom to match certain target properties and thus reduce the computational costs. The dynamics of these models is usually accelera...
TL;DR: The exceptional field theory as mentioned in this paper is a generalisation of Kaluza-Klein theory that unifies the metric and $p$-form gauge field degrees of freedom of supergravity into a generalised or extended geometry, whose additional coordinates may be viewed as conjugate to brane winding modes.
Abstract: This is a review of exceptional field theory: a generalisation of Kaluza-Klein theory that unifies the metric and $p$-form gauge field degrees of freedom of supergravity into a generalised or extended geometry, whose additional coordinates may be viewed as conjugate to brane winding modes This unifies the maximal supergravities, treating their previously-hidden exceptional Lie symmetries as a fundamental geometric symmetry Duality orbits of solutions simplify into single objects, that in many cases have simple geometric interpretations, for instance as wave or monopole-type solutions It also provides a route to explore exotic or non-geometric aspects of M-theory, such as exotic branes, U-folds, and more novel sorts of non-Riemannian spaces
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TL;DR: In this paper, it was shown that there are boundary degrees of freedom residing at the horizon of a black hole and their symmetries and their interactions with gravitational waves are described.
Abstract: Horizons of black holes or cosmologies are peculiar loci of spacetime where interesting physical effects takes place, some of which are probed by recent (EHT and LIGO) and future experiments (ET and LISA). We discuss that there are boundary degrees of freedom residing at the horizon. We describe their symmetries and their interactions with gravitational waves. This fits into a larger picture of boundary plus bulk degrees of freedom and their interactions in gauge theories. Existence and dynamics of the near horizon degrees of freedom could be crucial to address fundamental questions and apparent paradoxes in black holes physics.
TL;DR: In this article, the dressed-metric approach is shown to violate general covariance by demonstrating that it cannot have an off-shell completion in which the correct infinitesimal relations of space-time hypersurface deformations are realized.
Abstract: The dressed-metric approach is shown to violate general covariance by demonstrating that it cannot have an off-shell completion in which the correct infinitesimal relations of space-time hypersurface deformations are realized. The main underlying reason---a separation of background degrees of freedom and modes of inhomogeneity that is incompatible with covariance---is shared with other approaches such as hybrid loop quantum cosmology.
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TL;DR: In this article, the authors use the dictionary between general field theories and strongly homotopy algebras to provide an algebraic formulation of the procedure of integrating out of degrees of freedom in terms of homhotopy transfer.
Abstract: We use the dictionary between general field theories and strongly homotopy algebras to provide an algebraic formulation of the procedure of integrating out of degrees of freedom in terms of homotopy transfer. This includes more general effective theories in which some massive modes are kept while other modes of a comparable mass scale are integrated out, as first explored by Sen in the context of closed string field theory. We treat $L_\infty$-algebras both in terms of a nilpotent coderivation and, on the dual space, in terms of a nilpotent derivation (corresponding to the BRST charge of the field theory) and provide explicit formulas for homotopy transfer. These are then shown to govern the integrating out of degrees of freedom at tree level, while the generalization to loop level will be explored in a sequel to this paper.
TL;DR: In this paper, the authors propose a multigroup confirm-and-confirm approach to measure invaraiance in psychological assessment and a fundamental prerequisite for meaningful comparisons across groups.
Abstract: . Measurement invaraiance is a key concept in psychological assessment and a fundamental prerequisite for meaningful comparisons across groups. In the prevalent approach, multigroup confirm...
TL;DR: An extension is proposed of the Shannon entropy-based structural complexity measure introduced by Krivovichev, taking into account the geometric coordinational degrees of freedom a crystal structure has, yielding an even more refined scheme of complexity measures which can be obtained from a crystalructure's description: the six C's of complexity.
Abstract: An extension is proposed of the Shannon entropy-based structural complexity measure introduced by Krivovichev, taking into account the geometric coordinational degrees of freedom a crystal structure has. This allows a discrimination to be made between crystal structures which share the same number of atoms in their reduced cells, yet differ in the number of their free parameters with respect to their fractional atomic coordinates. The strong additivity property of the Shannon entropy is used to shed light on the complexity measure of Krivovichev and how it gains complexity contributions due to single Wyckoff positions. Using the same property allows for combining the proposed coordinational complexity measure with Krivovichev's combinatorial one to give a unique quantitative descriptor of a crystal structure's configurational complexity. An additional contribution of chemical degrees of freedom is discussed, yielding an even more refined scheme of complexity measures which can be obtained from a crystal structure's description: the six C's of complexity.
TL;DR: A novel 3-UPU (P and U stand for prismatic and universal joints, respectively) parallel mechanism and its variant PM are proposed that have two rotational and one translational degrees of freedom (DOFs) without involving any parasitic motion.
Abstract:
In this paper, a novel 3-UPU (P and U stand for prismatic and universal joints, respectively) parallel mechanism (PM) and its variant PM are proposed. Both of them have two rotational and one translational (2R1T) degrees of freedom (DOFs) without involving any parasitic motion. Mobility analysis shows that the three constraint forces provided by three limbs of the mechanism are located on the same plane and the mobile platform can translate perpendicular to this plane and rotate around any axis on it. Analysis of the mechanism’s motion characteristics demonstrates that the mobile platform outputs either pure rotation or pure translation. Moreover, the rotational axis can be fixed during the rotation process, which means no parasitic motion is involved. The causes of the motion characteristics are analyzed by the combination of an overall Jacobian matrix, a statistical method, and a geometric method. The PMs only need to translate or rotate once to move from the initial configuration to the final configuration, which allows for easy control of speeds. The relationship between mechanism parameters and singularity is analyzed. A speed control method for the PMs is proposed and a prototype is designed and made. Experiments are conducted to verify the determined motion characteristics, the speed control method, and the singularity analysis.
TL;DR: Tools from nonlinear analysis are used to understand emergent oscillation modes of various robot configurations and connect them to overall locomotion using geometric mechanics and feedback control for robots that may not fully utilize all available inputs.
Abstract: Conventional approaches in prescribing controls for locomoting robots assume control over all input degrees of freedom (DOFs). Many robots, such as those with non-holonomic constraints, may not req...
TL;DR: In this paper, an efficient algorithm for determining the Hilbert series of an effective theory, which counts the number of operators with a specific field content, and a companion code called Eco (Efficient Counting of Operators) in Form.
TL;DR: In this paper, the authors considered the nonparametric regression problem with multivariate predictors and provided a characterization of the degrees of freedom and divergence for estimators of the estimators.
Abstract: –In this article, we consider the nonparametric regression problem with multivariate predictors. We provide a characterization of the degrees of freedom and divergence for estimators of the...
TL;DR: A method is developed for automatic generation of nonreactive intermolecular two-body potential energy surfaces (PESs) including intramonomer degrees of freedom, an extension of the autoPES method developed earlier, which assumes rigid monomers.
Abstract: A method is developed for automatic generation of nonreactive intermolecular two-body potential energy surfaces (PESs) including intramonomer degrees of freedom. This method, called flex-autoPES, i...
TL;DR: In this article, the authors proposed new massive gravity theories with 5 dynamical degrees of freedom, which evade uniqueness theorems regarding the form of the kinetic and potential terms by adopting the ''generalized massive gravity'' framework, where a global translation invariance is broken.
Abstract: We propose new massive gravity theories with 5 dynamical degrees of freedom. We evade uniqueness theorems regarding the form of the kinetic and potential terms by adopting the ``generalized massive gravity'' framework, where a global translation invariance is broken. By exploiting the rotation symmetry in the field space, we determine two novel classes of theories. The first one is an extension of generalized massive gravity with a nonminimal coupling. On the other hand, the second theory produces a mass term that is different from de Rham, Gabadadze, Tolley construction and trivially has 5 degrees of freedom. Both theories allows for stable cosmological solutions without infinite strong coupling, which are free of ghost and gradient instabilities.
TL;DR: The mobility analysis method of the mechanical network proposed in this study facilitates the solution of the constraint matrix rank and can be used as a reference for other mechanical networks constructed of single-loop linkages.
Abstract:
In this study, the mobility of the threefold-symmetric Bricard linkage and its network are analyzed using screw theory. First, the screw motion equation of the linkage is derived. By applying the modified Grübler–Kutzbach criterion, we deduce that the degree of freedom (DOF) of the linkage is equal to 1. Then, we analyze the mechanical network constructed of threefold-symmetric Bricard linkages and provide its topological constraint graph. Using graph theory and screw theory, the constraint matrix of the mechanical network is obtained. Then, we solve the matrix rank via linear column transformation. Results show that the DOF of the mechanical network is equal to 1. The mobility analysis method of the mechanical network proposed in this study facilitates the solution of the constraint matrix rank and can be used as a reference for other mechanical networks constructed of single-loop linkages.
TL;DR: This work showcases a method that can be used to effectively enhance the energy efficiency through motion design, using a detailed dynamic model of the UR5 serial robot arm, based on an optimization of the motion profile using a parametrized description of the end-effector orientation.
Abstract: This work proposes to exploit functional redundancy as a tool to enhance the energy efficiency of a robotic system. In a functionally redundant system, i.e., one in which the number of degrees of freedom required to complete the task is smaller than the number of available degrees of freedom, the motion of the extra degrees of freedom can be tailored to enhance a performance metric. This work showcases a method that can be used to effectively enhance the energy efficiency through motion design, using a detailed dynamic model of the UR5 serial robot arm. The method is based on an optimization of the motion profile, using a parametrized description of the end-effector orientation: the results showcase an increased efficiency that allows energy savings up to 20.8%, according to the energy consumption results according to the electro-mechanical dynamic model of the robot.