Design of Energy Absorbing Metamaterials Using Stochastic Soft-Wall Billiards

Physical principles for designing cellwise artificial materials with energy-absorbing/harvesting and wave guiding properties are discussed in the present work. We analyzed the evolution of waves in a one-dimensional lattice of 3D massive potential wells with light particles inside. The potential wells were coupled with elastic springs and represented soft-wall versions of the so-called stochastic billiards. A billiard could switch from repelling to the stadium type as the parameter of shape changed its sign from positive to negative. We found that certain shapes of the potential wells/containers provided a one-directional trend of the energy flow from the chain of containers into the chaotically moving light inclusions by increasing their total kinetic energy. As a result, propagating waves became trapped by giving rise to standing waves with chaotic mode shapes with decaying amplitudes.

A Single-Node Classifier Implementation on Chua Oscillator within a Physical Reservoir Computing Framework

The study lies in the field of physical reservoir computing and aims to develop a classifier using Fisher Iris dataset for benchmark tasks. Single Chua chaotic oscillator acts as a physical reservoir. The study was performed using computer simulation. The features of Iris flowers are represented as the consequence of short pulses at a constant level of a control parameter, which is fed to the oscillator, changing its dynamics. During the classification of flowers, the oscillator works without being reset, so each pulse on the input changes the phase trajectory and makes it unique for each Iris flower. Finally, the estimation of the symmetry of an attractor makes it possible to connect each species of Iris with the properties of the attractor. The resulting architecture of the classifier includes a single-node externally-driven Chua oscillator with time-delayed input. The classifier shows two mistakes in classifying the dataset with 75 samples working in chaotic mode.

Suppression of chaotic vibrations in nonlinear systems by the example of a mechanical tachometer

A method for controlling dynamic chaos is proposed by introducing state feedback and changing the spectrum of Lyapunov characteristic parameters of a closed system to achieve the desired result - the transition from chaotic mode to regular motion. The solution of this problem is considered on the example of stabilization of a mechanical tachometer. The parameters of the controller in the feed-back circuit are determined by the method of modal con-trol synthesis.

Digital analysis of a speckle pattern of chaotic mode composition and restoration of a regular intensity pattern after a multimode fiber

A process of mode matching in a chaotic speckle pattern without a reference beam responsible for the formation of a holographic grating was studied experimentally and theoretically. Our approach was based on measuring the amplitudes and phases of the Hermite-Gauss (HG) and Laguerre-Gauss (LG) modes in a speckle pattern formed by the radiation of a multimode gradient fiber. The speckle pattern was formed in a hologram of a spatial light modulator using a multimode gradient fiber model while taking into account the mode and polarization dispersion, as well as random phase jumps of each eigenmode. We managed to match 210 modes of the speckle pattern and restore not only the original pattern, but also each structured LG mode and the entire chain of HG eigenmodes.

Hybrid Regimes’ Response to the COVID-19 Pandemic: “The First Wave” Evidence from Ukraine and Georgia

Hybrid regimes have been largely overlooked in the scholarly discussion on the effectiveness of halting the new COVID-19 virus, not least due to the lack of conceptual clarity, as such regimes are considered as the halfway or “grey area” on the authoritarianism-to-democracy path. Hence, the present paper aims to contribute to the pool of research on the internal dynamics of hybridity through exploring the responses towards the pandemic by two stable post-Soviet hybrid regimes, namely Georgia and Ukraine. The “most similar systems” comparative research design allows us to demonstrate that the two countries’ different crisis management and communication strategies explain Georgia’s relative success in halting the virus spread in comparison to Ukraine throughout the first wave. The application of Henry Hale’s “single-pyramid” and “competitive pyramid” models of patronal politics highlights the lack of competitiveness in the formal and informal governance processes in Georgia’s case, as opposed to the chaotic mode of decision-making as well as plurality of informal actors in Ukraine’s case.

Regularities in the spectrum of chaotic p-modes in rapidly rotating stars

Context. Interpreting the oscillations of massive and intermediate mass stars remains a challenging task. In fast rotators, the oscillation spectrum of p-modes is a superposition of sub-spectra which corresponds to different types of modes, among which island modes and chaotic modes are expected to be the most visible. This paper is focused on chaotic modes, which have not been thoroughly studied before. Aims. We study the properties of high frequency chaotic p-modes in a polytropic model. Unexpected peaks appear in the frequency autocorrelations of the spectra. Our goal is to find a physical interpretation for these peaks and also to provide an overview of the mode properties. Methods. We used the 2D oscillation code “TOP” to produce the modes and acoustic ray simulations to explore the wave properties in the asymptotic regime. Using the tools developed in the field of quantum chaos (or wave chaos), we derived an expression for the frequency autocorrelation involving the travel time of acoustic rays. Results. Chaotic mode spectra were previously thought to be irregular, that is, described only through their statistical properties. Our analysis shows the existence, in chaotic mode spectra, of a pseudo large separation. This means that chaotic modes are organized in series, such that the modes in each series follow a nearly regular frequency spacing. The pseudo large separation of chaotic modes is very close to the large separation of island modes. Its value is related to the sound speed averaged over the meridional plane of the star. In addition to the pseudo large separation, other correlations appear in the numerically calculated spectra. We explain their origin by the trapping of acoustic rays near the stable islands.

Narrating Chaos: Theresa Hak Kyung Cha’s "DICTEE" and Korean American Fragmentary Writings

In The Wounded Storyteller: Body, Illness, and Ethics, sociologist Arthur Frank uses narratology to typologize the stories people tell about illness. Next to teleological stories of survival, which “reassure the listener that however bad things look, a happy ending is possible”, Frank discusses “the chaos narrative” in which “events are told as the storyteller experiences life: without sequence or discernible causality” 97. While the storytellers discussed by Frank mostly suffer from physical ailments and traumas, I would argue that the chaotic mode of telling also characterizes texts that explore other kinds of traumas, including those related to displacement and shaming experienced by several generations of Koreans and Americans of Korean descent. Drawing on affect studies, I analyze Theresa Hak Kyung Cha’s DICTEE 1982 alongside two essays, by Grace M. Cho and Hosu Kim published in The Affective Turn: Theorizing the Social 2007, all of which use the collage form to challenge the expectation that “in life as in story, one event [leads] to another” Frank 97. The speech act is foregrounded in all three texts; it is de-naturalized, deformed, shown as a recitation of prescribed language, and repeatedly interrupted. Nonetheless, as Frank suggests, “the physical act becomes the ethical act” because “to tell one’s life is to assume responsibility for that life.” It also allows others to “begin to speak through that story” xx–xxi.

Active EMI Reduction Using Chaotic Modulation in a Buck Converter with Relaxed Output LC Filter

DC-DC buck converters are widely used in portable applications because of their high power efficiency. However, their inherent fast switching releases electromagnetic emissions, making them prominent sources of electromagnetic interference (EMI). This paper proposes a voltage-controlled buck converter that reduces EMI by using a chaotic pulse-width modulation (PWM) technique based on a chaotic triangular ramp generator. The chaotic triangular ramp generator is constructed from a simple on-chip chaotic circuit linked with a symmetrically triangular ramp circuit. The proposed converter can thus operate in the chaotic mode reducing the EMI without requiring any EMI filters. Additionally, using the triangular ramp signal can relax the requirement for a large LC output filter in chaotic mode. The effectiveness of the proposed scheme was experimentally verified with a chaotic triangular ramp generator embedded in a voltage-mode controller buck converter using a 0.18 µm Complementary Metal Oxide Semiconductor (CMOS) process. The measurement results from a prototype showed that the EMI improvement from the proposed scheme is approximately 14.53 dB at the fundamental switching frequency with respect to the standard fixed-frequency PWM reference case.