Wave Analogs Research Articles

Gravitational wave analogs in spin nematics and cold atoms

Large-scale gravitational phenomena are famously difficult to observe, making parallels in condensed matter physics a valuable resource. Here we show how spin nematic phases, found in magnets and cold atoms, can provide an analog to linearized gravity. In particular, we show that the Goldstone modes of these systems are massless spin-2 bosons, in one-to-one correspondence with quantized gravitational waves in flat spacetime. We identify a spin-1 model supporting these excitations and, using simulation, outline a procedure for their observation in a 23Na spinor condensate. Published by the American Physical Society 2024

Weyl points and topological surface states in a three-dimensional sandwich-type elastic lattice

Following the realization of Weyl semimetals in quantum electronic materials, classical wave analogues of Weyl materials have also been theorized and experimentally demonstrated in photonics and acoustics. Weyl points in elastic systems, however, have been a much more recent discovery. In this study, we report on the design of an elastic fully-continuum three-dimensional material that, while offering structural and load-bearing functionalities, is also capable of Weyl degeneracies and surface topologically-protected modes in a way completely analogous to its quantum mechanical counterpart. The topological characteristics of the lattice are obtained by ab initio numerical calculations without employing any further simplifications. The results clearly characterize the topological structure of the Weyl points and are in full agreement with the expectations of surface topological modes. Finally, full field numerical simulations are used to confirm the existence of surface states and to illustrate their extreme robustness towards lattice disorder and defects.

Photonic amorphous topological insulator

The current understanding of topological insulators and their classical wave analogs, such as photonic topological insulators, is mainly based on topological band theory. However, standard band theory does not apply to amorphous phases of matter, which are formed by non-crystalline lattices with no long-range positional order but only short-range order, exhibiting unique phenomena such as the glass-to-liquid transition. Here, we experimentally investigate amorphous variants of a Chern number-based photonic topological insulator. By tuning the disorder strength in the lattice, we demonstrate that photonic topological edge states can persist into the amorphous regime prior to the glass-to-liquid transition. After the transition to a liquid-like lattice configuration, the signatures of topological edge states disappear. This interplay between topology and short-range order in amorphous lattices paves the way for new classes of non-crystalline topological photonic bandgap materials.

Wave Analogs of Media Based on Phase Locked Loops

Introduction. At present, phase locked loops (PLLs) are widely used: from optimal signal detection and frequency synthesis to automatic control of phase distribution in phased scanned arrays. One of the simplest structures is a multi-stage (chain) PLL, which may contain a specially selected multi-connected control circuit. Such cascaded PLLs have wide application in solving a number of tasks of the theory of optimal estimates, multi-position phase telegraphy, in synchronizing of many tunable generators while preserving specified phase relations between their oscillations, etc. PLLs are actively used in radio physics both in analog and digital versions. One of the promising directions for collective PLLs development is the study of ensembles of neuromorphic networks based on PLL. Aim. To obtain wave analogues characterizing the collective PLL not as a discrete network, but as a continuous (distributed) media. Materials and methods. An unidirectional model (without mutual control circuits) of the cascade structure of the PLL. Results. Wave analogues of cascade-coupled phase synchronization systems that do not contain mutual control circuits were found. A solution of equations of wave analogues was found. A proof of validity of the obtained approximate solution in comparison with the exact one was presented. Conclusion. It was shown that by selecting a filter in a control circuit of each single-circuit circuit with different transmission coefficients, it is possible to obtain various types of continuous media or wave analogues of chain structures based on phase synchronization systems.

Edge modes of scattering chains with aperiodic order.

We study the scattering resonances of one-dimensional deterministic aperiodic chains of electric dipoles using the vectorial Green's matrix method, which accounts for both short- and long-range electromagnetic interactions in open scattering systems. We discover the existence of edge-localized scattering states within fractal energy gaps with characteristic topological band structures. Notably, we report and characterize edge-localized modes in the classical wave analogues of the Su-Schrieffer-Heeger (SSH) dimer model, quasiperiodic Harper and Fibonacci crystals, as well as in more complex Thue-Morse aperiodic systems. Our study demonstrates that topological edge-modes with characteristic power-law envelope appear in open aperiodic systems and coexist with traditional exponentially localized ones. Our results extend the concept of topological states to the scattering resonances of complex open systems with aperiodic order, thus providing an important step towards the predictive design of topological optical metamaterials and devices beyond tight-binding models.

DIFFRACTION ANTENNAS. A RIDGED DIELECTRIC WAVEGIDE

The paper is focused on discussion of the basic electrodynamic characteristics of ridged dielectric waveguides. These characteristics are necessary to be taken into account when constructing effectively operating linear diffraction antennas of the millimeter wavelength range that are the antennas implementing wave analogs of the Smith-Purcell phenomenon in the process electromagnetic wave radiation.

Enhanced Persistence of Equatorial Waves via Convergence Coupling in the Stochastic Multicloud Model

Abstract Recent observational and theoretical studies show a systematic relationship between tropical moist convection and measures related to large-scale convergence. It has been suggested that cloud fields in the column stochastic multicloud model compare better with observations when using predictors related to convergence rather than moist energetics (e.g., CAPE) as per Peters et al. Here, this work is extended to a fully prognostic multicloud model. A nonlocal convergence-coupled formulation of the stochastic multicloud model is implemented without wind-dependent surface heat fluxes. In a series of idealized Walker cell simulations, this convergence coupling enhances the persistence of Kelvin wave analogs in dry regions of the domain while leaving the dynamics in moist regions largely unaltered. This effect is robust for changes in the amplitude of the imposed sea surface temperature (SST) gradient. In essence, this method provides a soft convergence coupling that allows for increased interaction between cumulus convection and the large-scale circulation but does not suffer from the deleterious wave–conditional instability of the second kind (CISK) behavior of the Kuo-type moisture-convergence closures.

Fractional curve flows and solitonic hierarchies in gravity and geometric mechanics

Methods from the geometry of nonholonomic manifolds and Lagrange–Finsler spaces are applied in fractional calculus with Caputo derivatives and for elaborating models of fractional gravity and fractional Lagrange mechanics. The geometric data for such models are encoded into (fractional) bi–Hamiltonian structures and associated solitonic hierarchies. The constructions yield horizontal/vertical pairs of fractional vector sine–Gordon equations and fractional vector mKdV equations when the hierarchies for corresponding curve fractional flows are described in explicit forms by fractional wave maps and analogs of Schrödinger maps.

Modeling of open quantum dots and wave billiards using imaginary potentials for the source and the sink

A heuristic model for particle states and current flow in open ballistic two-dimensional (2D) quantum dots/wave billiards is proposed. The model makes use of complex potentials first introduced in phenomenological nuclear inelastic scattering theory (the optical model). Here we assume that external input and output leads connecting the system to the source and the drain regions may be represented by complex potentials. In this way, a current may be set up between the two ‘pseudo-leads’. Probability densities and current flows for an open quantum dot are analyzed here numerically and the results are compared with the microwave measurements used to emulate the system. The model is of conceptual as well as practical interest. In addition to quantum billiards, it may be used as a tool per se to analyze transport in classical wave analogues, such as microwave resonators, acoustic resonators, effects of leakage on such systems, etc.

Top-down processes during auditory phoneme categorization in dyslexia: A PET study

While persistence of subtle phonological deficits in dyslexic adults is well documented, deficit of categorical perception of phonemes has received little attention so far. We studied learning of phoneme categorization during an activation H(2)O(15) PET experiment in 14 dyslexic adults and 16 normal readers with similar age, handedness and performance IQ. Dyslexic subjects exhibited typical, marked impairments in reading and phoneme awareness tasks. During the PET experiment, subjects performed a discrimination task involving sine wave analogues of speech first presented as pairs of electronic sounds and, after debriefing, as syllables /ba/ and /da/. Discrimination performance and brain activation were compared between the acoustic mode and the speech mode of the task which involved physically identical stimuli; signal changes in the speech mode relative to the acoustic mode revealed the neural counterparts of phonological top-down processes that are engaged after debriefing. Although dyslexic subjects showed good abilities to learn discriminating speech sounds, their performance remained lower than those of normal readers on the discrimination task over the whole experiment. Activation observed in the speech mode in normal readers showed a strongly left-lateralized pattern involving the superior temporal, inferior parietal and inferior lateral frontal cortex. Frontal and parietal subparts of these left-sided regions were significantly more activated in the control group than in the dyslexic group. Activations in the right frontal cortex were larger in the dyslexic group than in the control group for both speech and acoustic modes relative to rest. Dyslexic subjects showed an unexpected large deactivation in the medial occipital cortex for the acoustic mode that may reflect increased effortful attention to auditory stimuli.

The inhibition of stuttering via the presentation of natural speech and sinusoidal speech analogs

Sensory signals containing speech or gestural (articulatory) information (e.g., choral speech) have repeatedly been found to be highly effective inhibitors of stuttering. Sine wave analogs of speech consist of a trio of changing pure tones representative of formant frequencies. They are otherwise devoid of traditional speech cues, yet have proven to evoke consistent linguistic percepts in listeners. Thus, we investigated the potency of sinusoidal speech for inhibiting stuttering. Ten adults who stutter read while listening to (a) forward-flowing natural speech; (b) forward-flowing sinusoid analogs of natural speech; (c) reversed natural speech; (d) reversed sinusoid analogs of natural speech; and (e) a continuous 1000 Hz pure tone. The levels of stuttering inhibition achieved using the sinusoidal stimuli were potent and not significantly different from those achieved using natural speech (∼50% in forward conditions and ∼25% in the reversed conditions), suggesting that the patterns of undulating pure tones are sufficient to endow sinusoidal sentences with ‘quasi-gestural’ qualities. These data highlight the sensitivity of a specialized ‘phonetic module’ for extracting gestural information from sensory stimuli. Stuttering inhibition is thought to occur when perceived gestural information facilitates fluent productions via the engagement of mirror neurons (e.g., in Broca's area), which appear to play a crucial role in our ability to perceive and produce speech.

Role of experience in eliciting perceptual overshoot with sine waves

Previous studies in vowel perception have demonstrated perceptual overshoot (PO) with vowels in CVC contexts. The first experiment investigated the elicitation of PO with speech and nonspeech signals. Boundary estimates were obtained for four continua: (1) steady-state synthetic vowels; (2) synthetic vowel transitions in /wV/ context; (3) sine wave analogs mimicking the steady-state vowels; and (4) sine wave analogs mimicking the transition continuum. Results replicated the findings of previous studies by demonstrating PO with synthetic vowels; however, PO was not elicited with the sine wave analogs. This led to a second experiment, where the role of training on the elicitation of PO with sine wave analogs was investigated. Subjects from the first experiment were divided into two groups. One group was trained to categorize the steady-state sine wave analogs based on their synthetic vowel boundary. Training occurred over 3–6 1-h sessions until subjects achieved 90%-correct identification. The control group received no training. Post-training boundary estimates were obtained for the four original continua from both groups. The results indicated that PO was now elicited with the sine wave analogs for the trained group, but not for the control group. Further implications of these findings will be discussed.

Nonlinear and quantum atom optics.

Coherent matter waves in the form of Bose-Einstein condensates have led to the development of nonlinear and quantum atom optics - the de Broglie wave analogues of nonlinear and quantum optics with light. In nonlinear atom optics, four-wave mixing of matter waves and mixing of combinations of light and matter waves have been observed; such progress culminated in the demonstration of phase-coherent matter-wave amplification. Solitons represent another active area in nonlinear atom optics: these non-dispersing propagating modes of the equation that governs Bose-Einstein condensates have been created experimentally, and observed subsequently to break up into vortices. Quantum atom optics is concerned with the statistical properties and correlations of matter-wave fields. A first step in this area is the measurement of reduced number fluctuations in a Bose-Einstein condensate partitioned into a series of optical potential wells.

On the computation of a wave field in a multilayer medium

In this paper, theoretical seismograms of waves propagating in a medium comprising four layers that rest on a half-space are presented. The seismograms are computed by the method of summation of kinematic and dynamic wave analogs. On the basis of these computations, some conclusions concerning the behavior of the wave field at large distances are drawn. Bibliography: 5 titles.

Low temperature physics without a cryostat: laser cooling and trapping of atoms

In recent years, there has been significant interest in the laser manipulation of neutral atoms, and specifically in the use of light fields to manipulate not only the internal but also the external coordinates of an atom. Among the most dramatic results of this work have been the production of dense ultra-cold samples of trapped neutral atoms. These samples have been used to expand the horizons of fundamental physics and have made possible significant advancements in metrology. Furthermore, the ability to manipulate atomic motion with light has helped to create entirely new fields of research such as atom optics where matter wave analogues of light wave systems are investigated and optical where light is used to create a periodic array of atoms similar to crystals.

Must sine wave analogs be perceived as implicit speech to be perceived categorically?

Sawusch and Gagnon [J. Exp. Psychol., HPP 21, 635–652 (1995)] obtained categorical responses to /la/–/ra/ sine wave analogs when listeners who heard the stimuli as nonspeech were frequently reminded of F3’s range or extremes. This result contrasts with responses to sine wave /la/–/ra/ obtained by Best et al. [Percept. Psychophys. 45, 237–250 (1989)] and responses to sine wave /wa/–/ja/ obtained by Johnson and Ralston [Phonetica 51, 195–209 (1994)]. Only those listeners who heard the analogs as (distorted) speech responded categorically. Instead of comparing speech and nonspeech listeners, the experiments tried to create an implicit expectation that sine wave analogs are (distorted) speech by playing listeners speech first. Listeners identified and discriminated members of sine wave /la/–/ra/ after identifying and discriminating either members of the original /la/–/ra/ speech continuum or of the same sine wave continuum. Other groups of listeners heard speech or sine wave /wa/–/ja/ before the sine wave /la/–/ra/; their performance allows us to separate acoustic from type similarity. If after hearing speech, listeners hear the analogs as implicit speech, they should perceive them more categorically than listeners who hear analogs first. Results show instead that listeners responses are as strongly categorical to the sine wave /la/–/ra/ in the second phase after all preceding stimulus types, even though the analogs are not heard as speech. Categorical perception thus does not depend on an implicit speech percept, nor are frequent reminders required to elicit it to sine wave analogs. [Work supported by NIH.]

Speech Perception Deficits in Poor Readers: Auditory Processing or Phonological Coding?

Poor readers are inferior to normal-reading peers in aspects of speech perception. Two hypotheses have been proposed to account for their deficits: (i) a speech-specific failure in phonological representation and (ii) a general deficit in auditory “temporal processing,” such that they cannot easily perceive the rapid spectral changes of formant transitions at the onset of stop-vowel syllables. To test these hypotheses, two groups of second-grade children (20 “good readers,” 20 “poor readers”), matched for age and intelligence, were selected to differ significantly on a /ba/–/da/ temporal order judgment (TOJ) task, said to be diagnostic of a temporal processing deficit. Three experiments then showed that the groups did not differ in: (i) TOJ when /ba/ and /da/ were paired with more easily discriminated syllables (/ba/–/sa/, /da/–/∳a/); (ii) discriminating nonspeech sine wave analogs of the second and third formants of /ba/ and /da/; (iii) sensitivity to brief transitional cues varying along a synthetic speech continuum. Thus, poor readers’ difficulties with /ba/–/da/ reflected perceptual confusion between phonetically similar, though phonologically contrastive, syllables rather than difficulty in perceiving rapid spectral changes. The results are consistent with a speech-specific, not a general auditory, deficit.

Sound-producing sources as objects of perception: Rate normalization and nonspeech perception

In a variety of experiments and paradigms, researchers have attempted to determine whether or not speech perception is specialized by comparing perception of speech syllables to perception of nonspeech analogs. While nonspeech analogs appear optimal as comparisons to speech because they are acoustically similar without being recognized as speechlike, it is argued that the comparison they offer is confounded and uninterpretable. Two experiments are designed to show that, in auditory perception generally where acoustic signals are causal consequences of mechanical events, perceptual experiences are of the mechanical events themselves, not of the acoustic signal. This has two consequences. One is that there is a confounding in comparisons of speech with sine wave analogs that, whereas the one perceived as speech also has a definite causal source, the other, perceived as nonspeech, has an indeterminate or ambiguous source. A second is that response patterns in classification tasks such as those used in the literature comparing speech to nonspeech will reflect properties of the perceived sound-producing event; they will not provide a clear window on auditory system processes used to recover event properties. Experiment 3 is designed to show that perception of many acoustic-signal-producing events can appear to be special by the logic of speech-sine wave comparisons--even events that cannot plausibly be supposed to involve a specialization.

Perception of sine wave analogs of stop consonant place information

Identification and discrimination procedures were used with nonspeech stimuli to investigate a possible auditory basis for categorical perception of place of articulation. One sinewave series consisted of linear frequency transitions (varying in onset frequency) followed by a steady-state portion. A second series was produced by combining each of the stimuli from the first series with a second tone (a rising initial transition followed by a steady state). The stimuli were modeled after the second and third formants of a stop consonant series varying in place of articulation. Subjects reliably sorted the one-tone-component series into three categories corresponding roughly to rising, flat, and falling transitions. The local maxima of subjects' discrimination functions fell near the labeling category boundaries. With the inclusion of the second tone, subjects reliably sorted the continuum into two, rather than three, categories. Further, a single discrimination maximum, located in the vicinity of the category boundary, was found for the two-component stimuli. The results suggest that auditory categories may underlie the perception of an analogous stop place series and that information is not extracted independently for each transition. Rather, the pattern of formant transitions seems to be the critical information that underlies the stop-place categories. [Work supported by NINCDS.]

Trading relations in nonspeech

Two acoustic features shown to be sufficient in specifying the distinction between intervocalic /b/ and /p/ are closure duration and the presence or absence of a low‐frequency voicing pulse during the closure interval. These features of the signal can be considered to exhibit a trading relation [B. Repp, Psych. Bull. 92, 81–110 (1982)] to the extent that a longer closure is required to perceive the consonant as voiceless when the pulse is present than when it is not. This study addressed the issue of whether a trading relation of the type found in speech can be demonstrated for nonspeech as well. Two types of square wave analogs, modeled after a speech series ranging from “rabid” to “rapid,” were constructed. One set of nonspeech stimuli contained frequency transitions into and out of the silent interval while frequency for the other nonspeech stimuli remained constant. Preliminary (AXB) identification results indicate that in the speech condition, the presence of the pulse affects a shift in the ID bound...