Beating Phase Research Articles

Coherent high-power terahertz vortex generation with tunable orbital angular momentum based on transverse phase mask shaping

Abstract Terahertz (THz) radiation has become a significant tool in cutting-edge research due to its superior properties. THz vortices with tunable orbital angular momentum (OAM) are particularly attractive to the scientific community due to their well-defined discrete azimuthal phase around the propagation axis. However, the generation of high-power THz radiation with OAM remains a challenge for most existing technologies. In this paper, a new method for generating coherent high-power THz vortices with tunable OAM and frequency is proposed by combining frequency beating and transverse phase mask shaping techniques. Theoretical analyses and numerical simulations indicate that this method can generate coherent THz vortices with peak powers in the tens of megawatts and tunable topological charge numbers.

Coherence enhancement between incoherent lasers based on passive phase compensation

AbstractCoherent light beams play an important role in the development of opto‐electronic microwave and terahertz technologies, serving as a source for generating RF carrier signals with very high quality. The authors explore in this work an approach to enhance the coherence between two incoherent lasers so as to provide coherent light beams, and proof‐of‐concept demonstrates a terahertz signal generation with low phase noise. Based on the proposed passive phase compensation technique, the phase noise between two independent lasers can be well suppressed and the carrier to noise ratio in the terahertz regime remains high. In the experiment, the beating phase noise between two independent lasers is reduced from −60.68 dBc/Hz@10kHz to −90.05 dBc/Hz@10kHz at about 280 GHz, which is promisingly applicable in the terahertz photonics community.

A Fast and Easy Method to Co-extract DNA and RNA from an Environmental Microbial Sample.

We herein propose a fast and easy DNA and RNA co-extraction method for environmental microbial samples. It combines bead beating and phenol-chloroform phase separation followed by the separation and purification of DNA and RNA using the Qiagen AllPrep DNA/RNA mini kit. With a handling time of ~3 h, our method simultaneously extracted high-quality DNA (peak size >10-15‍ ‍kb) and RNA (RNA integrity number >6) from lake bacterioplankton filtered samples. The method is also applicable to low-biomass samples (expected DNA or RNA yield <50‍ ‍ng) and eukaryotic microbial samples, providing an easy option for more versatile eco-genomic applications.

Long-Time Phase Correlations Reveal Regulation of Beating Cardiomyocytes.

Spontaneous contractions of cardiomyocytes are driven by calcium oscillations due to the activity of ionic calcium channels and pumps. The beating phase is related to the time-dependent deviation of the oscillations from their average frequency, due to noise and the resulting cellular response. Here, we demonstrate experimentally that, in addition to the short-time (1-2Hz), beat-to-beat variability, there are long-time correlations (tens of minutes) in the beating phase dynamics of isolated cardiomyocytes. Our theoretical model relates these long-time correlations to cellular regulation that restores the frequency to its average, homeostatic value in response to stochastic perturbations.

An Experimental Study on the Fish Body Flapping Patterns by Using a Biomimetic Robot Fish

This letter presents an experimental study on how different body flapping patterns affect the performances of fish cruising. First, a biomimetic robot fish is designed and built as the experimental platform, which mimics the skeleton structure and the muscle arrangement of real fish. Moreover, an improved Central Pattern Generator (CPG) is developed to generate different patterns, which are characterized by four control parameters: (1) the amplitude, (2) the frequency, (3) the time ratio between the beating phase and half cycle, (4) the shape parameter. Then, a number of experiments are conducted to investigate the thrust, the recoil, the cruising speed and the swimming efficiency. Based on the experimental results, following conclusions can be drawn: (1) Fish cruising follows the traveling wave model proposed in Lighthill's Elongated Body Theory. This model offers a balance among the thrust, the recoil and the swimming speed, which results in a high efficiency. (2) The time asymmetry of the body flapping patterns reduces the thrust. (3) The triangular pattern offers the smallest recoil and the cambering sinusoidal pattern gives the largest thrust. These findings provide better understandings on how fish swims and can be used as guidelines for designing the body flapping patterns for robot fish.

Statistical design of in silico experiments for the robustness analysis of electrophysiologic response simulators

To assess the risk of Torsade de Pointes, the CiPA initiative has proposed to test in silico models able to reconstruct electrophysiologic responses and analyze mechanistic causes of specific toxicological events such as TdP. One example of such simulators is the O’Hara Rudy’s model, used herein as a benchmark model. Such in silico models are composed of a large number of biological parameters. Their values are never fully known and they are generally estimated with a substantial uncertainty. So, what happens if the values of some parameters are wrong? Can we still trust the simulated responses? In this application context, our objective is to firstly identify the critical modeling parameters. To reduce the computation time, we propose a statistical approach suited to the screening of model parameters. Our approach relies on a Placket-Burman design of numerical assays. 79 models parameters have been tested and only 80 numerical experiments were carried out. The action potential response was split up into five phases and three statistics (duration, AUC and amplitude) were computed for each phase. Accordingly, 15 response variables were analyzed. A Pareto analysis is finally used to rank the most critical parameters. Results show that all the tested modeling factors have the same order of effect on the global response. In other terms, no parameter can be neglected. Two parameters appear as more critical than the other ones: the stimulus current and the initial temperature of the cell. The effects of all the parameters on each of the five beating phase are also estimated and ranked. This study analyzes the sensitivity of the simulated potential action response with respect to uncertainty on 79 modeling parameters. All of them have significant effects on at least one part of the response, which emphasizes the relevance to accurately estimate them to trust simulations. As a consequence, another crucial question is worth asking and deals with the model identifiability, i.e. the possibility to learn the true values of the model parameters after obtaining an infinite (theoretical identifiability) or a finite (practical identifiability) number of in vitro observations.

Non-Linear Model for Mechanical Entrainment of Cardiomyocytes

Recent experiment by the group of Tzlil (Nitsan et al., Nat. Phys. 2016) have shown that nearby cardiac cells seeded (∼ 100 micrometers apart) on an elastic gel, synchronize their beating phase and frequency even without direct contact. By introducing an inert probe that induced periodic elastic deformations in the substrate, the experiments showed that one can pace beating cardiac cells that are relatively far from the probe. The time required to pace the cell was on the order of ∼ 15 min, and the cell maintained the new beating frequency for as long as ∼ 1 hr after the probe was removed. These long time scales are in complete contrast to the very short time scales (∼ 1 sec) that characterize relaxation after electrical stimulation is removed. We construct a simple, analytical model based on the works of Julicher and Duke (Duke et al., PNAS, 2000), and treat the deterministic dynamics of beating. The model predicts spontaneous, entrained beating (with the probe frequency) and “bursting” (short periods of entrainment to the probe separated by quiescence) of paced cells, and how these depend on the probe amplitude and frequency, in agreement with experiment (Nitsan et al., Nat. Phys. 2016). We further consider the interesting effects of small noise on the non-linear oscillator model of the beating cell, and show how it affects the coherence of beating. Finally, we predict the dependence of time required for a cell to transition from spontaneous to entrained beating once the probe is applied as well as its dependence on the probe amplitude. We account for the origin of the much longer time scale (minutes) required to entrain spontaneously beating cells by considering biological adaptation (which delays the response of the cell to the external signal).

Design of hair-like appendages and comparative analysis on their coordination toward steady and efficient swimming

The locomotion of water beetles has been widely studied in biology owing to their remarkable swimming skills. Inspired by the oar-like legs of water beetles, designing a robot that swims under the principle of drag-powered propulsion can lead to highly agile mobility. But its motion can easily be discontinuous and jerky due to backward motions (i.e. retraction) of the legs. Here we proposed novel hair-like appendages and consider their coordination to achieve steady and efficient swimming on the water surface. First of all, we propose several design schemes and fabrication methods of the hair-like appendages, which can passively adjust their projected area while obtaining enough thrust. The coordination between the two pairs of legs, as with water beetles in nature, were also investigated to achieve steady swimming without backward movement by varying the beating frequency and phase of the legs. To verify the functionality of the hair-like appendages and their coordinations, six different types of appendages were fabricated, and two robots (one with a single pair of legs and the other with two pairs of legs) were built. Locomotion of the robots was extensively compared through experiments, and it was found that steady swimming was achieved by properly coordinating the two pairs of legs without sacrificing their speed. Also, owing to the lower velocity fluctuation during swimming, it was shown that using two pairs of legs was more energy efficient than the robot with single pair of legs.

Elastic interactions synchronize beating in cardiomyocytes.

Motivated by recent experimental results, we study theoretically the synchronization of the beating phase and frequency of two nearby cardiomyocyte cells. Each cell is represented as an oscillating force dipole in an infinite, viscoelastic medium and the propagation of the elastic signal within the medium is predicted. We examine the steady-state beating of two nearby cells, and show that elastic interactions result in forces that synchronize the phase and frequency of beating in a manner that depends on their mutual orientation. The theory predicts both in-phase and anti-phase steady-state beating depending on the relative cell orientations, as well as how synchronized beating varies with substrate elasticity and the inter-cell distance. These results suggest how mechanics plays a role in cardiac efficiency, and may be relevant for the design of cardiomyocyte based micro devices and other biomedical applications.

Externally driven global Alfvén eigenmodes applied for effective mass number measurement on TCABR

The excitation and detection of Global Alfvén Eigenmodes on TCABR for diagnostic purposes are presented. The modes can be excited with one or two in-vessel antennae, with up to 15 A of current in each, in the frequency range from 2 to 4 MHz. This scheme allows the estimation of the effective mass number at the plasma center, which value is affected by impurity concentration in the core. An amplifier based on MOSFETs is used to excite the waves driven by low power, in order to not change the basic plasma parameters. The variation of the GAE with density is verified and the location of the mode resonance at the plasma center is confirmed by the sawtooth beating, so that the correspondingly beating phase inversion improves the precision on the resonant condition determination. The toroidal parity of the modes N = 1,2 is determined by use of two opposite located antennae with different phase of the RF current. Knowledge of toroidal mode number is important as it identifies GAE location and defines the estimated effective mass value. The estimated value for Aeff is ∼1.4–1.5, corresponding to 5–7% of carbon impurity concentration. The measured value of Aeff is used to estimate Zeff, which is compared to older TCA experiments and the value obtained by the Spitzer conductivity.

Anomalous beating phase of the oscillating interlayer magnetoresistance in layered metals

We analyze the beating behavior of the magnetic quantum oscillations in a layered metal under the conditions when the cyclotron energy $\hbar \omega_c $ is comparable to the interlayer transfer energy $t$. We find that the positions of the beats in the interlayer resistance are considerably shifted from those in the magnetization oscillations, and predict that the shift is determined by the ratio $\hbar \omega_c/t$. A comparative study of the Shubnikov-de Haas and de Haas-van Alphen effects in the quasi-two-dimensional organic metal $\beta $-(BEDT-TTF)$_2$IBr$_2$ appears to be consistent with the theoretical prediction.

Conversion of beating mode inChlamydomonas flagella induced by electric stimulation

Electric stimulation of a single Chlamydomonas cell by means of a suction electrode induced a temporary conversion of flagellar waveform from an asymmetric forward mode to a symmetric reverse mode. The reverse mode continued for about 0.5 seconds, after which the forward mode was resumed. Anodic stimulation (current passing outward through the membrane outside the suction pipette) was more effective in inducing the flagellar response than cathodic stimulation. No flagellar response was induced in the absence of free Ca2+ or in the presence of calcium channel inhibitors, pimozide (5 microM) and diltyazem (0.3 mM). These findings indicate that the flagellar response by membrane depolarization followed by a Ca2+ influx through voltage-dependent calcium channels. This experimental system allowed us to quantitatively analyze the behavior of flagella during the waveform conversion. The flagellar bending pattern quickly changed from the forward mode to the reverse mode and, thereafter, gradually resumed the forward mode through two discrete phases: changes during reverse mode beating (phase I) and a distinct transitional phase (phase II). Recovery in curvature and sliding velocity of principal bends occurred mostly in phase I. Almost all of the recovery of reverse bends, returning the curvature to the low values characteristic of asymmetric forward mode beating, occurred in phase II. Beat frequency recovered through both phases. Phase II was often interrupted by a temporary stoppage of beating. These findings indicate that the bending pattern is converted through multiple steps that are controlled by Ca2+.