Mode Spacing Research Articles

Gray space and default mode network-amygdala connectivity.

Aspects of the built environment relate to health factors and equity in living conditions, and may contribute to racial, ethnic, or economic health disparities. For example, urbanicity is linked with negative factors including exposure to gray space (e.g., impervious surfaces such as concrete, streets, or rooftops). While there is existing research on access to green space and urbanicity on some mental health and cognitive outcomes, there is limited research on the presence of gray space linked with cognitive functioning in youth. The goal of this study was to investigate the link between gray space and amygdala-default mode network (DMN) connectivity. This study used data from the ABCD Study. Participants (n = 10,144; age M = 119.11 months, female = 47.62%) underwent resting-state fMRI acquisition at baseline. Impervious surfaces (gray space) were measured via the Child Opportunity Index (COI). To examine the relationship between presence of gray space and -amygdala-DMN (left/right) connectivity, we employed linear mixed effects models. Correlations were run between amygdala-DMN connectivity and internalizing and externalizing symptoms. Finally, post hoc sensitivity analyses were run to assess the impact of race. More gray space, adjusting for age, sex, and neighborhood-level variables, was significantly associated with increased left amygdala-DMN connectivity (p = 0.0001). This association remained significant after sensitivity analyses for race were completed (p = 0.01). No significant correlations were observed between amygdala-DMN and internalizing or externalizing symptoms. Findings suggest gray space was linked with increased left amygdala-DMN connectivity, circuits that have been implicated in affective processing, emotion regulation, and psychopathology. Thus gray space may be related to alterations in connectivity that may enhance risk for emotion dysregulation. Future investigation of these relationships is needed, as neuroimaging findings may represent early dysregulation not yet observed in the behavioral analyses at this age (i.e., the present study did not find significant relationships with parent-reported behavioral outcomes). These findings can help to inform future public policy on improving lived and built environments.

Efficiency-boosted semiconductor optical amplifiers via mode-division multiplexing

Semiconductor optical amplifiers (SOAs) are a fundamental building block for many photonic systems. However, their power inefficiency has been setting back operational cost reduction, circuit miniaturization, and the realization of more complex photonic functions such as large-scale switches and optical phased arrays. In this work, we demonstrate significant gain and efficiency enhancement using an extra degree of freedom of light—the mode space. This is done without changing the SOA’s material design, and therefore high versatility and compatibility can be obtained. Light is multiplexed in different guided modes and reinjected into the same gain section twice without introducing resonance, doubling the interaction length in a broadband manner. Up to 87% higher gain and 300% higher wall-plug efficiency are obtained in a double-pass SOA compared to a conventional single-pass SOA, at the same operating current, in the wavelength range of 1560–1580 nm.

Fragment-based structural exploration and chemico-biological interaction study of HDAC3 inhibitors through non-linear pattern recognition, chemical space, and binding mode of interaction analysis

HDAC3 is an emerging target for the identification and discovery of novel drug candidates against several disease conditions including cancer. Here, a fragment-based non-linear machine learning (ML) method along with chemical space exploration followed by a structure-based binding mode of interaction analysis study was carried out on some HDAC3 inhibitors to obtain the key structural features modulating HDAC3 inhibition. Both the ML and chemical space analysis identified several physicochemical and structural properties namely lipophilicity, polar and relative polar surface area, arylcarboxamide moiety, bulky fused aromatic group, n-alkyl, and cinnamoyl moieties, the higher number of oxygen atoms, π-electrons for the substituted tetrahydrofuronaphthodioxolone moiety favorable for higher HDAC3 inhibition. Moreover, hydrogen bond forming capabilities, the length and substitution position of the linker moiety, the importance of phenyl ring in the linker motif, the contribution of heterocyclic cap moieties for effective inhibitor binding at the HDAC3 catalytic site that correspondingly affects the HDAC3 inhibitory potency. Again, macrocyclic ring structure and cyclohexyl cap moiety are responsible for lower HDAC3 inhibition. The MD simulation study of selected compounds explained strong binding patterns at the HDAC3 active site as evidenced by the lower RMSD and RMSF values. Nevertheless, it also explained the importance of the crucial structural fragments derived from the fragment-based analysis during ligand-enzyme interactions. Therefore, the outcomes of this current structural analysis will be a useful tool for fragment-based drug discovery of effective HDAC3 inhibitors for clinical therapeutics in the future. Communicated by Ramaswamy H. Sarma

Research on stabilization of the frequency of a single longitude mode optical fiber laser

An optical fiber laser that can continuously emit high stable single frequency laser is researched. The resonant cavity of the optical fiber laser is a compound ring resonator which is made with double sub ring resonant cavities sharing almost the same optical path. By employing erbium-doped fiber as the gain medium of the resonant cavity, the light of gain spectrum of the resonant cavity is obtained by using a fiber Bragg grating (FBG) to reflect the light of one of the fringes transmitting through a Fabry-Perot etalon (F-P1) which is inserted into the resonant cavity to filter the fluorescence emitted from the erbium-doped fiber pumped with a 980 nm laser. When the longitudinal mode spacing of the resonant cavity is adjusted to be corresponding to the linewidth of the gain spectrum, single frequency laser will oscillate. One of the transmitting frequencies of another Fabry-Perot etalon (F-P2) which is placed outside the resonant cavity is used as the basis of the laser’s frequency. Part of the fiber resonant cavity is wound on a PZT tube which is actuated by the output voltage of an electronic compensating circuit to adjust the resonant cavity length and thus the laser’s frequency will be stabilized at the transmitting frequency of F-P2 that is used as the basis. The stability of the frequency of the optical fiber laser can be higher than 10−8.

Verification of the Mode Decomposition Technique for Closely Distributed Modal Systems in the State Space Domain.

This study aims to propose and validate the state space mode decomposition technique for precise mode separation of non-classical damping systems and closely distributed modal systems. To assess the reliability and applicability of this technique, a 40-story building with a tuned mass damper is investigated, and acceleration responses measured by the building's health monitoring system are used for the verification of the technique. The mode separation results reveal that the separated modal power spectrum becomes distorted at neighboring natural frequency ranges when the performance index only considers the concentration of power spectral energy at the target natural frequency. However, by introducing an augmented performance index that includes a constraint condition to account for distortion, more accurate mode decomposition can be achieved.

Data-driven modal analysis of nonlinear quantities in turbulent plasmas using multi-field singular value decomposition

Nonlinear dynamics in the two-dimensional multi-component plasma turbulence described by the Hasegawa–Wakatani equation is investigated by using a data-driven modal analysis with the singular value decomposition (SVD). The conventional SVD is extended to ‘multi-field SVD’ which can decompose multiple turbulence fields simultaneously by a single set of orthonormal basis functions without imposing a priori scale separations. Then, in addition to the mode amplitude labeled by the singular value, the information on the phase relations in the nonlinear quantities such as a transport flux or a triad energy transfer is extracted in the mode space. Through applications to the two-dimensional plasma turbulence, it is revealed that the multi-field SVD can extract the dominant spatial structures for the turbulent transport and the nonlinear energy transfer, preserving the multi-scale nature of the original turbulent fields. It is also demonstrated that one can reduce the dimensionality or information using the multi-field SVD through comparisons with the conventional Fourier decomposition.

Modeless Raman fiber laser

The discrete multi-longitudinal mode structure and temporal periodic fluctuation are the intrinsic features of conventional lasers. However, longitudinal mode spacing limits the maximum resolution in high-resolution laser sensing systems. In addition, temporal periodic fluctuation reduces the security of secure communication and deteriorates the randomness in fast physical random bit generation. Therefore, it still remains an open challenge to realize a laser source without discrete longitudinal mode and temporal periodic fluctuation. Here, a modeless Raman fiber laser (RFL) with high efficiency was demonstrated. The output cavity mirror adopts a fiber Bragg grating with ultralow reflectance of −27dB. Due to the modulation instability, the discrete multi-longitudinal modes in the RFL gradually broaden with the increase of intracavity Stokes wave power and eventually fully overlap. At high power levels, the RFL no longer has discrete longitudinal modes like a conventional laser but generates a quasi-continuous spectrum. Benefiting from the modeless nature, the RFL can achieve extremely low relative intensity noise, favorable temporal stability, and rather low coherence. Modeless RFLs are expected to be ushered as ideal light sources into secure communication, optical sensing, and optical imaging.

Exploring nanofibrous networks with x-ray photon correlation spectroscopy through a digital twin.

We demonstrate a framework of interpreting data from x-ray photon correlation spectroscopy experiments with the aid of numerical simulations to describe nanoscale dynamics in soft matter. This is exemplified with the transport of passive tracer gold nanoparticles in networks of charge-stabilized cellulose nanofibers. The main structure of dynamic modes in reciprocal space could be replicated with a simulated system of confined Brownian motion, a digital twin, allowing for a direct measurement of important effective material properties describing the local environment of the tracers.

Lattice modes of periodic origami tessellations with voids

Elastic modes of origami lattices are of scientific value in the context of metamaterial applications. Miura-ori is a well-studied origami pattern, especially in engineering. A deeper understanding of spatially homogeneous deformations can be useful to homogenization-based material characterization. Miura-ori with rigid parallelogram panels deforms exclusively through crease-folding as a single degree of freedom (DOF) system. Substituting parallelograms with rigid triangular panels introduces two additional DOFs per vertex and could admit a rich space of lattice deformations. In this paper, we investigate the lattice modes of rigid triangulated Miura-ori (RTM) with enclosed voided regions within the tessellations. We use two widely adopted approaches — the bar and hinge framework (BHF) and a folding-angle framework (FAF), that are typically used for the analysis of origami lattices. Unlike the 2D RTM lattice without voids, we find that for the origami lattices with voids, the compatibility constraints based on the crease folding-angles alone are insufficient to capture the admissible deformation modes. Additional loop-closure constraints, based on Denavit–Hartenberg analysis of spatial linkages, must be imposed on creases around each enclosed void. We observe that the homogeneous modes with accumulation of deformations across the lattice are exclusive to the space of Bloch-wave modes within the FAF approach and are not straightforwardly obtained using BHF approach of modeling origami lattices. The 2D RTM lattices with voids, irrespective of the size and aspect ratio of enclosed voids, are found to exhibit exactly six such exclusive FAF modes which can be further characterized using intuitively defined relations between crease angle perturbations.

Controllable Optical Features of Multiple‐Layered Axial Heterostructure Nanorods for Multicolor Polariton Nanolasers

AbstractThe optical features of multiple‐layered axial heterostructures composed of III‐nitride semiconductors (GaN, InGaN, and AlGaN) are investigated to realize tunable nanolasers. The optical confinement effects develop exciton‐polariton in nanorods, leading to polariton lasing with distinctive dispersion. The lasing characteristics in the heterostructure are similar to those in the homostructure, although the carrier transfer between layers influences the optical gain. The energy‐dependent property of polariton changes the mode spacing of lasing peaks. The alloyed systems of InGaN can tune the color of lasing in the visible region, while the lasing of AlGaN is also achievable in the optimized configuration. The polarization of lasing indicates the predominant contribution of the fundamental transverse mode. Therefore, in the multiple‐layered heterostructure, controllable triple‐color lasing using the feature of polariton, modulation of band gap energy, and the amplification process of the waveguide is demonstrated for the first time, with the tunable color over a wide range of the visible region. Multicolor polariton nanolasers offer a promising path to diverse nanophotonic devices with controllable optical characteristics.

Multi-muscle synergies in preparation for gait initiation in Parkinson’s disease

ObjectiveWe investigated changes in indices of muscle synergies prior to gait initiation and the effects of gaze shift in patients with Parkinson’s disease (PD). A long-term objective of the study is to develop a method for quantitative assessment of gait-initiation problems in PD. MethodsPD patients without clinical signs of postural instability and two control groups (age-matched and young) performed a gait initiation task in a self-paced manner, with and without a quick prior gaze shift produced by turning the head. Muscle groups with parallel scaling of activation levels (muscle modes) were identified as factors in the muscle activation space. Synergy index stabilizing center of pressure trajectory in the anterior-posterior and medio-lateral directions (indices of stability) was quantified in the muscle mode space. A drop in the synergy index in preparation to gait initiation (anticipatory synergy adjustment, ASA) was quantified. ResultsCompared to the control groups, PD patients showed significantly smaller synergy indices and ASA for both directions of the center of pressure shift. Both PD and age-matched controls, but not younger controls, showed detrimental effects of the prior gaze shift on the ASA indices. ConclusionsPD patients without clinically significant posture or gait disorders show impaired stability of the center of pressure and its diminished adjustment during gait initiation. SignificanceThe indices of stability and ASA may be useful to monitor pre-clinical gait disorders, and lower ASA may be relevant to emergence of freezing of gait in PD.

Retracted: Construction and Analysis of Urban Cultural Plane Space Mode considering Particle Swarm Cultural Scientific Computing Algorithm

Retracted: Construction and Analysis of Urban Cultural Plane Space Mode considering Particle Swarm Cultural Scientific Computing Algorithm

Tunable frequency comb from echo-enabled harmonic generation free electron laser

We propose a novel scheme for the generation of a tunable soft x-ray frequency comb in a seeded free-electron laser (FEL) via the chirped pulse beating technology. Our research shows that harnessing the chirped pulse laser to imprint a submillimeter-scale energy modulation in the phase space of the relativistic electron beam together with the process of echo-enabled effect, multichromatic output soft x-ray radiation with a series of longitudinal modes can be amplified in an echo-enabled harmonic generation (EEHG) free electron laser, which finally forms a comb-liked shape in the frequency spectrum with the mode spacing frequency at terahertz (THz) band. Based on the theoretical and numerical analyses of the modulation process, the electron beam maintains a nanometer-scale microstructures due to the echo effect, while the beam obtains an energy modulation at submillimeter-scale from the chirped pulse beating laser. This leads to a series of longitudinal modes in the downstream radiator. Three-dimension time-dependent simulation results show that a frequency comb with a central wavelength of 8.9 nm can be generated directly with the help of chirped beating laser. The frequency spacing between the frequency lines on the radiation spectrum can be tuned easily by changing the parameters of chirped beating laser.

Multi-type dynamic load identification algorithm in continuous system: A numerical and experimental study based on SSM-Newmark-β

Dynamic load identification based on structural responses is an important problem in the field of engineering and plays an important role in the condition assessment of mechanical structures. Current popular load identification methods such as the state-space method (SSM) and the Green's kernel function method (GKFM) are implemented on discrete systems with outstanding performance, but when dealing with complex continuous systems, there are some limitations such as low efficiency and inaccuracy. In this paper, a continuous system load identification algorithm based on SSM and Newmark-β is proposed for the first time. Using modal coordinate transformation and modal truncation methods, the number of infinite vibration differential equations of a continuous system in physical space are converted to a finite number of vibration differential equations in modal space, where the modal truncation order and the optimal layout of the sensors are combined by modal strain energy. The Newmark-β method in modal space is derived and thus combined with SSM to obtain a load identification model Y=HF called SSM-Newmark-β method, which reduces the size of the transfer matrix H. The solution time of the proposed algorithm is 0.38 s for continuous systems, which is rather shorter than that for discrete systems. Furthermore, the simulations show that it has better accuracy and noise immunity than SSM and GKFM in the identification of sinusoidal load, impact load, and random load. The effect of time step is also discussed which reveals that the larger time step has less effect on the proposed algorithm. An experimental study is carried out on a cantilever beam system. The result verifies that the SSM-Newmark-β algorithm has better accuracy in load identification for the continuous system. This research provides a new sight for the real-time identification of dynamic loads for complex structures.

Stability and mutual coherence of Raman combs in high-Q silica microresonators

We investigated the stability and mutual coherence of a Raman microcomb in a silica microrod resonator by monitoring the output power and longitudinal mode spacings. The results indicate that we can obtain a stable Raman comb formation without the need for four-wave mixing processes. The use of a Raman comb will open the possibility of simplifying the setup because it will relax the phase matching condition usually required for microresonator frequency comb generation. Although there are some restrictions in regard to using a Raman comb for applications due to the coexistence of the comb components in different mode families, a proof-of-concept demonstration shows that it is sufficiently stable and robust for applications such as optical communications.

Schrödinger Dynamics and Berry Phase of Undulatory Locomotion.

Spectral mode representations play an essential role in various areas of physics, from quantum mechanics to fluid turbulence, but they are not yet extensively used to characterize and describe the behavioral dynamics of living systems. Here, we show that mode-based linear models inferred from experimental live-imaging data can provide an accurate low-dimensional description of undulatory locomotion in worms, centipedes, robots, and snakes. By incorporating physical symmetries and known biological constraints into the dynamical model, we find that the shape dynamics are generically governed by Schrödinger equations in mode space. The eigenstates of the effective biophysical Hamiltonians and their adiabatic variations enable the efficient classification and differentiation of locomotion behaviors in natural, simulated, and robotic organisms using Grassmann distances and Berry phases. While our analysis focuses on a widely studied class of biophysical locomotion phenomena, the underlying approach generalizes to other physical or living systems that permit a mode representation subject to geometric shape constraints.

Digital coding metasurface for Multi-Beam and Multi-Mode OAM in Full-Space

A digital coding metasurface is proposed to generate multi-beam and multi-mode orbital angular momentum (OAM) wave in the full space. The 3-bit coding elements are designed for multifunctional integrated digital coding metasurface (MIDCMS) based on the propagation phase theory. The variable-sized phase-shift scheme is applied on metal structures to realize different functionalities in linearly polarized (LP) incidence. Furthermore, the phase distribution of MIDCMS is determined by the pattern convolution theorem. The transmitted and reflected wavefronts are manipulated simultaneously through MIDCMS. As a proof of concept, a metasurface device was fabricated and measured for the four-beam OAM with +1 mode in transmission space and the four-beam OAM with −1 mode in reflection space. Both experimental results and simulated values verify that the proposed MIDCMS can effectively realize the full-space multi-beam multi-mode OAM generation and improve the capacity of information channels, which has potential applications for comprehensive implementations in the future wireless communication systems.

Experimental study on the spatial structures of filament during ELM crash in ELMy H-mode discharge on EAST

A high-speed vacuum ultraviolet imaging (VUVI) system with both high temporal and spatial resolutions in the Experimental Advanced Superconducting Tokamak has been developed for the study of the edge/pedestal plasma. Edge localized mode (ELM)-induced filamentary structures have been successfully visualized by the VUVI system during the ELMy high confinement mode (H-mode) discharges. The poloidal mode spacing and the pitch angle are employed to quantitatively characterize the spatial structure of the observed filamentary structures in the imaging data. The poloidal mode spacing of the filamentary structure is found to be proportional to the plasma current. The dominant toroidal mode number decreases as the plasma current ramps up. In addition, the temporal evolution of the pitch angle during an ELM crash was quantitatively investigated. No significant change in the pitch angle is observed during an ELM crash. The dominant toroidal mode number gradually decreases in the rise phase and increases in the decay phase in one ELM crash, respectively.

Metasurface based symmetry transformation for single-shot angular momentum detection within a large mode space

The spin angular momentum (SAM) and orbital angular momentum (OAM) are unique properties of vortex beams and widely used in optical communication and sensing, wherein unambiguous detection of them is of significance. However, the existing methodologies mostly require complicated optical setups, bulky devices, multiple measurements and suffer from limited detection range and ability. Here, we propose a novel angular momentum (AM) detection mechanism that based on optical symmetry transformation for single-shot AM detection within a large mode space. We first give a detailed theoretical derivation and then carry numerical verification. Subsequently, an ultra-compact metasurface is designed so that an OAM mode high up to 150 orders can be determined with a single-shot measurement. Finally, a spin-decoupled metasurface combining the propagation and geometric phase is constructed, which allows simultaneous discrimination of SAM and OAM. Our proposed method may be promising for a wide range of applications in AM measurements and polarization singularity detection.

Dynamic Footprints of the Specific Artificial Spin Ice Microstate on Its Spin Waves

We present a micromagnetic investigation of the spin dynamics at remanence (zero applied field) in a periodic square artificial spin ice (ASI) prepared four different microstates (i.e., with zero, two or four magnetic charges at the vertex). The ASI elements consist of permalloy elliptical dots with a fixed long axis, and a variable width and interdot separation. For each vertex configuration, we compute the equilibrium ground state at zero applied field by relaxing a previously set magnetic configuration (microstate). After the excitation of such ground state, we perform a Fourier analysis obtaining frequency spectra and space phase profiles. We discuss the behavior of the spectra in changing the system’s microstate and geometry, with reference to the spin mode space profiles, magnetization configuration, and effective internal field. Our results draw a correlation between ASI macrospin orientation at vertex and a few important dynamic properties like a phase-shift in the mode profiles or the frequency gap between the edge and fundamental modes. We suggest a few specific experiments to validate of our predictions, as well as applications in the field of interferometric magnonic devices. We believe that our results can help, from the fabrication stage, in tailoring the appropriate ASI geometry for specific application purposes.