Artificial Oscillator Research Articles

Simultaneous control of intensity, phase, and polarization in real time under a weak oscillation theory

Manipulating polarization, phase, and amplitude simultaneously in real time is an ultimate pursuit of controlling light. Several types of controllable metasurfaces have been realized, but with either low transmission efficiencies or limited control over amplitude, polarization, and phase in real time. Here we present a weak oscillation theory dealing with a new, to the best of our knowledge, type of optical system consisting of many layers of artificial oscillators, with each layer weakly interacting with the external field. As an application of our theory, we demonstrate and simulate a graphene-based metasurface structure to show that the oscillator system could change the focal length by changing the bias voltages. The polarization state to focus can also be selected by the bias voltage. The weak oscillation theory provides a flexible method to control the intensity, phase, and polarization.

The reversible function switching of the circadian clock protein KaiA is encoded in its structure

BackgroundCircadian rhythms are important to the evolution of organisms and human health, and recent studies proved that post-translational circadian clocks widely exist in all phyla. The circadian clock of cyanobacteria is an important model system as the first verified circadian oscillator independent of transcriptional-/translational-level regulations. This circadian oscillator consists of three proteins, KaiA, KaiB, and KaiC, in which KaiA stimulates KaiC's phosphorylation but KaiB antagonizes KaiA. Despite of intense research on the molecular mechanism of this oscillator in the last decades, the regulation mechanism of KaiA's function remains unclear. MethodsIn this study, we combined computational tools and experimental assays to study the function switching of KaiA. We adopted different strategies to re-design KaiA protein to elucidate its function switch during the circadian oscillation. ResultsWe showed that KaiA's function switch is determined by its structural dynamics, and KaiB antagonizes KaiA by switching it from an active state to an inactive state with the help of KaiC. ConclusionsThe reversible function switching of KaiA is key to the KaiABC oscillator, and the switching could be regulated by the 3-D domain swapped homo-dimer conformation of KaiA, which provides the necessary structural flexibility. General significanceOur finding updated the current knowledge on the regulation of KaiA's function. This work would deepen our understanding of the KaiABC oscillator, and should be conceptually useful in the design of artificial biological oscillators.

Temperature dependence of the evolving oscillations along the electrocatalytic oxidation of methanol

Despite the constancy of all controllable experimental parameters, most natural and artificial oscillators are known to slowly evolve over time. In electrochemical systems, this spontaneous evolution has been ascribed to the surface deactivation that gently drives the system and acts a bifurcation parameter. We investigate the effect of temperature on the electro-oxidation of methanol on platinum, with focus on the potential oscillations and its spontaneous temporal evolution. The study was performed at comparable applied currents (normalized with respect to the oscillatory window) at nine temperatures between 10°C and 50°C, in acidic media, and oscillations were not observed at 50°C. The main results were discussed in connection with voltammetric data, which were deconvoluted into three regions according to the electrode potential. While the frequency of potential oscillations followed a regular Arrhenius-like dependence, the size of the oscillatory window was found to remain nearly unaffected by temperature. From the mechanistic point-of-view, these dependencies were attributed to the existence of more than one Langmuir–Hinshelwood (LH) step that consumes adsorbed oxygenated species. This fact was corroborated by voltammetric data. The relative magnitude of the activation energies of the LH processes were estimated as higher than that of the deactivation process, as previously suggested.

Stability analysis of an artificial biomolecular oscillator with non-cooperative regulatory interactions

ABSTRACTOscillators are essential to fuel autonomous behaviours in molecular systems. Artificial oscillators built with programmable biological molecules such as DNA and RNA are generally easy to build and tune, and can serve as timers for biological computation and regulation. We describe a new artificial nucleic acid biochemical reaction network, and we demonstrate its capacity to exhibit oscillatory solutions. This network can be built in vitro using nucleic acids and three bacteriophage enzymes, and has the potential to be implemented in cells. Numerical simulations suggest that oscillations occur in a realistic range of reaction rates and concentrations.

Task-Oriented Parameter Tuning Based on Priority Condition for Biologically Inspired Robot Application

This work gives a biologically inspired control scheme for controlling a robotic system. Novel adaptive behaviors are observed from humans or animals even in unexpected disturbances or environment changes. This is why they have neural oscillator networks in the spinal cord to yield rhythmic-motor primitives robustly under a changing task. Hence, this work focuses on rhythmic arm movements that can be accomplished in terms of employing a control approach based on an artificial neural oscillator model. The main challenge is to determine various parameters for applying a neural feedback to robotic systems with performing a desired behavior and self-maintaining the entrainment effect. Hence, this work proposes a task-oriented parameter tuning algorithm based on the simulated annealing (SA). This work also illustrates how to technically implement the proposed control scheme exploiting a virtual force and neural feedback. With parameters tuned, it is verified in simulations that a 3-DOF planar robotic arm traces a given trajectory precisely, adapting to uneven external disturbances.

Implementation of CPG-based locomotion controller on Minimule Robot

Creating effective locomotion for legged robots is a very challenging task especially in an unknown environment. Currently, most research works on locomotion control are focused on the trajectory based method. Here we are implementing a biologically inspired Central Pattern Generator(CPG) based controller for a quadruped Minimule robot. This local control system of quadruped animals is modelled through an artificial neural oscillator based structure. The robot was first modelled using MSC ADAMS and integrated with MATLAB for simulation. This paper deals with parameter modulation of the CPG network, the gait transition for the robot and environment adaptability through limit cycle stability. Various parameters for locomotion like frequency, velocity and gait can be obtained just by changing a single parameter, the duty factor. The CPG based Minimule robot can achieve both trot and walk gait by varying the phase relationship between the limbs and is stable due to the inherent property of CPG.

LTCC 의사 유전체 공진기를 이용한 초소형 전압제어발진기 설계

본 논문에서는 LTCC(Low Temperature Co-fired Ceramics) 공정을 이용하여 다층 구조의 의사 유전체 공진기를 설계하고, 이를 HMIC(Hybrid Microwave Integrated Circuit) 형태의 증폭기, 위상천이기와 함께 폐루프를 구성하여 초소형 전압 제어 의사 유전체 공진기 발진기(Vt-ADRO: Voltage-tuned Artificial Dielectric Resonator Oscillator)를 제작하였다. 의사 유전체 공진기는 주기적인 도체 패턴과 적층을 통해 기존의 유전체 공진기보다 소형의 크기를 갖는 공진기이다. 의사 유전체 공진기의 형상은 기본 도체 패턴 원판형을 갖고 이것을 적층하는 구조를 선정하였으며, 공진기의 물리적 치수 및 적층 수에 따른 공진 특성을 분석하였다. 소형의 크기로 제작하기 위하여 LTCC 기판의 상부에 의사 유전체 공진기를 내장하고, 하부에 증폭기, 위상천이기를 집적하였다. 제작된 의사 유전체 공진기 발진기는 <TEX>$13{\times}13{\times}3mm^3$</TEX>로 초소형이며, SMT(Surface Mount Technology) 형태를 갖는다. 설계된 발진기는 설계 주파수에서 개루프 발진 조건을 만족하였으며, 폐루프 측정 결과, 발진 주파수는 조정 전압 0~5 V에서 2.025~2.108 GHz, 위상 잡음은 100 kHz offset에서 <TEX>$-109{\pm}4$</TEX> dBc/Hz, 출력 전력은 <TEX>$6.8{\pm}0.2$</TEX> dBm을 보이며, PFTN(Power Frequency Tuning Normalized) FOM(Figure Of Merit)은 -30.88 dB를 보인다. In this paper, we present an ultra miniaturized voltage tuned oscillator, with HMIC-type amplifier and phase shifter, using LTCC artificial dielectric resonator. ADR which consists of periodic conductor patterns and stacked layers has a smaller size than a dielectric resonator. The design specification of ADR is obtained from the design goal of oscillator. The structure of the ADR with a stacked circular disk type is chosen. The resonance characteristic, physical dimension and stack number are analyzed. For miniaturization of ADRO, the ADR is internally implemented at the upper part of the LTCC substrate and the other circuits, which are amplifier and phase shifter are integrated at the bottom side respectively. The fabricated ADRO has ultra small size of <TEX>$13{\times}13{\times}3mm^3$</TEX> and is a SMT type. The designed ADRO satisfies the open-loop oscillation condition at the design frequency. As a results, the oscillation frequency range is 2.025~2.108 GHz at a tuning voltage of 0~5 V. The phase noise is <TEX>$-109{\pm}4$</TEX> dBc/Hz at 100 kHz offset frequency and the power is <TEX>$6.8{\pm}0.2$</TEX> dBm. The power frequency tuning normalized figure of merit is -30.88 dB.

An Artificial Muscle Ring Oscillator

Dielectric elastomer artificial muscles have great potential for the creation of novel pumps, motors, and circuitry. Control of these devices requires an oscillator, either as a driver or clock circuit, which is typically provided as part of bulky, rigid, and costly external electronics. Oscillator circuits based on piezo-resistive dielectric elastomer switch technology provide a way to embed oscillatory behavior into artificial muscle devices. Previous oscillator circuits were not digital, able to function without a spring mass system, able to self-start, or suitable for miniaturization. In this paper we present an artificial muscle ring oscillator that meets these needs. The oscillator can self-start, create a stable 1 Hz square wave output, and continue to function despite degradation of the switching elements. Additionally, the oscillator provides a platform against which the performance of different dielectric elastomer switch materials can be benchmarked.

Simple harmonic oscillator immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network

In heterogeneous wireless network environment, wireless local area network (WLAN) are usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network could occur frequently, with regard to vertical handoff performance, there is a critical need for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, propose an artificial simple harmonic oscillator immune algorithm-based vertical handoff decision scheme, and perform the simulation experiments to validate proposed solution. Experimental result shows that the proposed solution, compared with literature solutions, can not only balance the overall load among all networks but also increase the collective battery lifetime of mobile terminals, and has the advantage of good application value.

Timing molecular motion and production with a synthetic transcriptional clock

The realization of artificial biochemical reaction networks with unique functionality is one of the main challenges for the development of synthetic biology. Due to the reduced number of components, biochemical circuits constructed in vitro promise to be more amenable to systematic design and quantitative assessment than circuits embedded within living organisms. To make good on that promise, effective methods for composing subsystems into larger systems are needed. Here we used an artificial biochemical oscillator based on in vitro transcription and RNA degradation reactions to drive a variety of "load" processes such as the operation of a DNA-based nanomechanical device ("DNA tweezers") or the production of a functional RNA molecule (an aptamer for malachite green). We implemented several mechanisms for coupling the load processes to the oscillator circuit and compared them based on how much the load affected the frequency and amplitude of the core oscillator, and how much of the load was effectively driven. Based on heuristic insights and computational modeling, an "insulator circuit" was developed, which strongly reduced the detrimental influence of the load on the oscillator circuit. Understanding how to design effective insulation between biochemical subsystems will be critical for the synthesis of larger and more complex systems.

Dynamics of coupled repressilators: The role of mRNA kinetics and transcription cooperativity

Oscillatory regulatory networks have been discovered in many cellular pathways. An especially challenging area is studying dynamics of cellular oscillators interacting with one another in a population. Synchronization is only one of and the simplest outcome of such interaction. It is suggested that the outcome depends on the structure of the network. Phase-attractive (synchronizing) and phase-repulsive coupling structures were distinguished for regulatory oscillators. In this paper, we question this separation. We study an example of two interacting repressilators (artificial regulatory oscillators based on cyclic repression). We show that changing the cooperativity of transcription repression (Hill coefficient) and reaction timescales dramatically alter synchronization properties. The network becomes birhythmic-it chooses between the in-phase and antiphase synchronization. Thus, the type of synchronization is not characteristic for the network structure. However, we conclude that the specific scenario of emergence and stabilization of synchronous solutions is much more characteristic.

Dynamical properties of the repressilator model

Oscillatory regulatory networks have been discovered in many regulatory pathways. Due to their enormous complexity, it is necessary to study their dynamics by means of highly simplified models. These models have received particular value because artificial regulatory networks can be engineered experimentally. In this paper, we study dynamical properties of an artificial regulatory oscillator called repressilator. We have shown that oscillations arise from the existence of an absorbing toruslike region in the phase space of the model. This geometric structure requires monotonic repression at all promoters and the absence of any regulatory connections apart from a cyclic repression loop. We show that oscillations collapse as only weak extra connections are introduced if there is imbalance between the attended concentrations and those sufficient for saturation of the promoters. We found that a pair of diffusively coupled repressilators displays synchronization properties similar to those of relaxation oscillators if the regulatory connections in the cyclic repression loop are strong. Thus, the role of strengthening these connections can be viewed as introducing time scale separation among variables. This may explain controversial synchronization properties reported for repressilators in earlier studies.

Biologically Inspired Robotic Arm Control Using an Artificial Neural Oscillator

We address a neural-oscillator-based control scheme to achieve biologically inspired motion generation. In general, it is known that humans or animals exhibit novel adaptive behaviors regardless of their kinematic configurations against unexpected disturbances or environment changes. This is caused by the entrainment property of the neural oscillator which plays a key role to adapt their nervous system to the natural frequency of the interacted environments. Thus we focus on a self-adapting robot arm control to attain natural adaptive motions as a controller employing neural oscillators. To demonstrate the excellence of entrainment, we implement the proposed control scheme to a single pendulum coupled with the neural oscillator in simulation and experiment. Then this work shows the performance of the robot arm coupled to neural oscillators through various tasks that the arm traces a trajectory. With these, the real-time closed-loop system allowing sensory feedback of the neural oscillator for the entrainment property is proposed. In particular, we verify an impressive capability of biologically inspired self-adaptation behaviors that enables the robot arm to make adaptive motions corresponding to an unexpected environmental variety.

Tightly trapped acoustic phonons in photonic crystal fibres as highly nonlinear artificial Raman oscillators

Interactions between light and hypersonic waves can be enhanced by tight field confinement, as shown in periodically structured materials1, microcavities2, micromechanical resonators3 and photonic crystal fibres4,5,6 (PCFs). There are many examples of weak sound–light interactions, for example, guided acoustic-wave Brillouin scattering in conventional optical fibres7. This forward-scattering effect results from the interaction of core-guided light with acoustic resonances of the entire fibre cross-section, and is viewed as a noise source in quantum-optics experiments8. Here, we report the observation of strongly nonlinear forward scattering of laser light by gigahertz acoustic vibrations, tightly trapped together in the small core of a silica–air PCF. Bouncing to and fro across the core at close to 90∘ to the fibre axis, the acoustic waves form optical-phonon-like modes with a flat dispersion curve and a distinct cutoff frequency Ωa. This ensures automatic phase-matching to the guided optical mode so that, on pumping with a dual-frequency laser source tuned to Ωa, multiple optical side bands are generated, spaced by Ωa. The number of strong side bands in this Raman-like process increases with pump power. The results point to a new class of designable nonlinear optical device with applications in, for example, pulse synthesis, frequency comb generation for telecommunications and fibre laser mode-locking.

Resonant hopping of a robot controlled by an artificial neural oscillator

The bouncing gaits of terrestrial animals (hopping, running, trotting) can be modeled as a hybrid dynamic system, with spring-mass dynamics during stance and ballistic motion during the aerial phase. We used a simple hopping robot controlled by an artificial neural oscillator to test the ability of the neural oscillator to adaptively drive this hybrid dynamic system. The robot had a single joint, actuated by an artificial pneumatic muscle in series with a tendon spring. We examined how the oscillator-robot system responded to variation in two neural control parameters: descending neural drive and neuromuscular gain. We also tested the ability of the oscillator-robot system to adapt to variations in mechanical properties by changing the series and parallel spring stiffnesses. Across a 100-fold variation in both supraspinal gain and muscle gain, hopping frequency changed by less than 10%. The neural oscillator consistently drove the system at the resonant half-period for the stance phase, and adapted to a new resonant half-period when the muscle series and parallel stiffnesses were altered. Passive cycling of elastic energy in the tendon accounted for 70–79% of the mechanical work done during each hop cycle. Our results demonstrate that hopping dynamics were largely determined by the intrinsic properties of the mechanical system, not the specific choice of neural oscillator parameters. The findings provide the first evidence that an artificial neural oscillator will drive a hybrid dynamic system at partial resonance.

Resonant hopping of a robot controlled by an artificial neural oscillator

Resonant hopping of a robot controlled by an artificial neural oscillator

Semi‐empirical model for site effects on acceleration time histories at soft‐soil sites. Part 1: formulation and development

AbstractA criterion is developed for the simulation of realistic artificial ground motion histories at soft‐soil sites, corresponding to a detailed ground motion record at a reference firm‐ground site. A complex transfer function is defined as the Fourier transform of the ground acceleration time history at the soft‐soil site divided by the Fourier transform of the acceleration record at the firm‐ground site. Working with both the real and the imaginary components of the transfer function, and not only with its modulus, serves to keep the statistical information about the wave phases (and, therefore, about the time variation of amplitudes and frequencies) in the algorithm used to generate the artificial records. Samples of these transfer functions, associated with a given pair of soft‐soil and firm‐ground sites, are empirically determined from the corresponding pairs of simultaneous records. Each function included in a sample is represented as the superposition of the transfer functions of the responses of a number of oscillators. This formulation is intended to account for the contributions of trains of waves following different patterns in the vicinity of both sites. The properties of the oscillators play the role of parameters of the transfer functions. They vary from one seismic event to another. Part of the variation is systematic, and can be explained in terms of the influence of ground motion intensity on the effective values of stiffness and damping of the artificial oscillators. Another part has random nature; it reflects the random characteristics of the wave propagation patterns associated with the different events. The semi‐empirical model proposed recognizes both types of variation. The influence of intensity is estimated by means of a conventional one‐dimensional shear wave propagation model. This model is used to derive an intensity‐dependent modification of the values of the empirically determined model parameters in those cases when the firm‐ground earthquake intensity used to determine these parameters differs from that corresponding to the seismic event for which the simulated records are to be obtained. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Toward construction of a self-sustained clock-like expression system based on the mammalian circadian clock.

Despite recent advances in circadian biology, detailed understanding of how a biological pacemaker system is assembled, maintained, and regulated continues to be a significant challenge. We have assembled and characterized a first-generation, regulatable, self-sustained clock-like expression system based on key components of the mammalian circadian clock. The molecular setup of the clock-like oscillator was reduced to the core set of positive and negative elements common to all known circadian pacemakers. Sophisticated tetracycline-responsive multi-cistronic expression integrated with forefront lentiviral transduction tools enabled autoregulated reporter transgene expression in a human cell line. We characterized transgene expression kinetics of an artificial oscillator and showed that its expression profiles could be modulated by a serum shock and administration of regulating tetracycline antibiotics. Design of a generic mammalian clock-like expression system will offer novel opportunities to study circadian biology and may provide a unique tool for rhythmic expression of desired transgenes fostering advances in biopharmaceutical manufacturing, gene therapy, and tissue engineering.

Dynamics of a hybrid system of a brain neural network and an artificial nonlinear oscillator

In the brain, many functional modules interact with each other to execute complex information processing. Understanding the nature of these interactions is necessary for understanding how the brain functions. In this study, to mimic interacting modules in the brain, we constructed a hybrid system mutually coupling a hippocampal CA3 network as an actual brain module and a radial isochron clock (RIC) simulated by a personal computer as an artificial module. Return map analysis of the CA3-RIC system's dynamics showed the mutual entrainment and complex dynamics dependent on the coupling modes. The phase response curve of CA3 was modeled regarding the CA3 as a nonlinear oscillator. Using the phase response curves of CA3 and RIC, we reconstructed return maps of the hybrid system's dynamics. Although the reconstructed return maps almost agreed with the experimental data, there were deviations dependent on the coupling mode. In particular, we noted that the deviation was smaller under the bidirectional coupling conditions than during the one-way coupling from RIC to CA3. These results suggest that brain modules may flexibly change their dynamical properties through interaction with other modules.

Nonlinear dynamics of a hibrid consisting of a thin hippocampal slice and an artificial oscillator

Nonlinear dynamics of a hibrid consisting of a thin hippocampal slice and an artificial oscillator