Anomalous propulsion regime in axonemal-propelled cargoes

Bio-actuated micro-swimmers provide a platform to understand physical principles related to the motion of micro-organisms at low Reynolds numbers. Here, we used isolated and demembranated flagella from green algae Chlamydomonas reinhardtii as an ATP-fueled bio-actuator for propulsion of micron-sized beads. Chlamydomonas flagella have an asymmetric waveform, which can be accurately described as a superposition of a static component corresponding to an arc-shaped intrinsic curvature, a mode describing the global oscillations of the axonemal curvature, and a main base- to-tip traveling wave component. By decomposing experimental beat patterns in Fourier modes, and applying resistive force theory, we performed numerical simulations and obtained analytical approximations for the mean rotational and translational velocities of a flagellum-propelled bead. Our analysis reveals the existence of a counter- intuitive anomalous propulsion regime where the speed of the flagellum-driven cargo increases with increasing the cargo size. Further, it demonstrates that in addition to the intrinsic curvature and even harmonics, asymmetric bead-flagellum attachment also contributes in the rotational velocity of the micro-swimmer. This turning mechanism induced by sideways cargo attachment has potential applications in fabrication of bio- actuated medical micro-robots in the subject of targeted drug delivery and synthetic micro-swimmers.

Combined Structural and Voltage Control of Giant Nonlinearities in Semiconductor Superlattices

Recent studies have predicted a strong increase in high harmonic emission in unbiased semiconductor superlattices due to asymmetric current flow. In parallel, an external static bias has led to orders of magnitude control of high harmonics. Here, we study how this control can affect the operation of superlattice multipliers in a range of input frequencies and powers delivered by commercially available GHz sources. We show that the strongly nonlinear behavior can lead to a very complex scenario. Furthermore, it is natural to ask what happens when we combine both asymmetry and voltage control effects. This question is answered by the simulations presented in this study. The efficiency of high-order even harmonics is increased by the combined effects. Furthermore, the development of ‘petals’ in high-order emission is shown to be more easily achieved, opening the possibility to very interesting fundamental physics studies and more efficient devices for the GHz–THz range.

Enhanced XUV harmonics generation from diatomic gases using two orthogonally polarized laser fields

Enhanced high repetition rate coherent extreme ultraviolet (XUV) harmonics represent efficient probe of electron dynamics in atoms, molecules and solids. In this work, we used orthogonally-polarized two-color laser field to generate strong even and odd high order harmonics from molecular gas targets. The dynamics of odd and even harmonics from O2, and N2 gases were investigated by employing single- and two-color laser fields using the fundamental radiation and second harmonic of 1030 nm, 37 fs, 50 kHz pulses. The relative efficiencies of harmonics were analyzed as a function of the thickness of the barium borate crystal used for second harmonic generation. Defocusing-assisted phase matching conditions were achieved in N2 gas for different groups of XUV harmonics.

Toward constraining Saturn's rotation rate by interior modeling

<p>The rotation rate of the outer planet Saturn is not well constrained by classical measurements of periodic signals [1]. Recent and diverse approaches using a broad spectrum of Cassini and other observational data related to shape, winds, and oscillations are converging toward a value about 6 to 7 minutes faster than the Voyager rotation period.<br>Here we present our method of using zonal wind data and the even harmonics J<sub>2</sub> to J<sub>10</sub> measured during the Cassini Grand Finale tour [2] to infer the deep rotation rate of Saturn. We assume differential rotation on cylinders and generate adiabatic density profiles that match the low-order J<sub>2</sub> and J<sub>4</sub><br>values. Theory of Figures to 7th order is applied to estimate the differences in the high-order moments J<sub>6 </sub>to J<sub>10</sub> that may result from the winds and the assumed reference rotation rate. Presented results are preliminary as the method is under construction [3].</p><p>[1] Fortney, Helled, Nettelmann et al, in: 'Saturn in the 21st century', Cambridge U Press (2018)<br>[2] Iess, Militzer, Kaspi, Science 364:2965 (2019)<br>[3] Nettelmann, AGU Fall Meeting, P066-0007 (2020)</p><p> </p>

Reexamining Different Factors of the Resonance-Enhanced High-Order Harmonic Generation in Atomic and Nanoparticle Laser-Induced Tin Plasmas

We reexamine the resonance enhancement of a single harmonic emission during the propagation of ultrafast pulses through atomic and nanoparticle tin-containing laser-induced plasma (LIP). We compare the single atomic Sn and Sn nanoparticle plasmas to demonstrate a distinction in the enhancement factor of the single harmonic in the case of fixed and tunable near-infrared pulses. The analysis of the dynamics of Sn LIP shows the range of optimal delays between heating and driving pulses (130–180 ns), at which the maximal harmonic yield can be achieved. The enhancements of the 17th and 18th harmonics of 806 nm pulses were analyzed in the case of single-color and two-color pumps of LIP, showing up to a 12-fold enhancement of even harmonics in the two-color pump case. We show the enhancement of a single harmonic in the vicinity of the 4d105s25p2P3/2→4d95s25p2 transitions of Sn II ions and demonstrate how this process depends on the constituency of the plasma components at different conditions of target ablation. The application of tunable (1280–1440 nm) radiation allows for demonstrating the variations of single harmonic enhancement using a two-color pump of Sn-containing LIP.

Effects of a Perpendicularly Applied Magnetic Field on Harmonically Driven Quasi-two-dimensional Electron Gas: the Static Macrostates Symmetry Breaking and Generation of Even Harmonics in System Output

In this paper, we consider activation processes in a nonlinear metastable system based on a quasi-two-dimensional superlattice and study the dynamics of such a system, which is externally driven by a harmonic force in regimes of controlled instabilities. The spontaneous transverse electric field is considered as an order parameter and the forced violations of the order parameter are considered as a response of a system to periodic driving. The internal control parameters are the longitudinal applied electric field, the sample temperature and the magnetic field which is orthogonal to the superlattice plane. We investigate the cooperative effects of self-organization and high harmonic forcing in such a system from the viewpoint of catastrophe theory It is shown through numerical simulations that the additional magnetic field breaks the static macrostates symmetry and leads to generation of even harmonics; it also allows the control of the intensity of particular harmonics. The intensity of even harmonics demonstrates resonant-type nonmonotonic dependence on control parameters with the maxima at points close to critical points of the synergetic potential.

Mathematical Model for the Harmonic Analysis of Electric Arc Currents and Voltages in an Electric Arc Furnace

This paper analyzes how the relative effective total odd and even current and voltage harmonics of an electric arc in a furnace correlate with the thermal time constant of the arc, with the valve effect, and with the asymmetrical operation. The furnace circuit model was used to theorize upon the effectiveness of using even harmonics data to diagnose the charge melting stage during initial melting; and odd harmonics to analyze the late stages. The results of mathematical modeling helped draw guidelines for the design of the charge melting diagnosis unit to be part of the electrical parameters control system; the unit design depends on the furnace type. The results could be of use in research of better control algorithms for electric arc furnaces and lade furnaces with a focus on reducing the energy costs of producing molten steel.