Current reversals in a rocking ratchet: dynamical vs symmetry-breaking mechanisms

Directed transport in ratchets is determined by symmetry-breaking in a system out of equilibrium. A hallmark of rocking ratchets is current reversals: an increase in the rocking force changes the direction of the current. In this work for a bi-harmonically driven spatially symmetric rocking ratchet we show that a class of current reversal is precisely determined by symmetry-breaking, thus creating a link between dynamical and symmetry-breaking mechanisms

Current reversals in a rocking ratchet: the frequency domain

Motivated by recent work [D. Cubero et al., Phys. Rev. E 82, 041116 (2010)], we examine the mechanisms which determine current reversals in rocking ratchets as observed by varying the frequency of the drive. We found that a class of these current reversals in the frequency domain are precisely determined by dissipation-induced symmetry breaking. Our experimental and theoretical work thus extends and generalizes the previously identified relationship between dynamical and symmetry-breaking mechanisms in the generation of current reversals

Exploring the limits of magnetic field focusing: Simple planar geometries

© 2020 The Authors This work explores the possibility to arbitrarily shape in space low-frequency magnetic fields using a recently introduced synthesization technique (Choi et al., 2016). We investigate the ability to focus a magnetic field on a two-dimensional region using magnetic field sources distributed on a parallel plane. In agreement with the recent work, arbitrarily tight focusing is demonstrated possible. However, our results indicate that this comes at the cost of exponentially large power requirements and also leads to exponentially large fields in the region between the source and target planes. This imposes strict limitations on the application of the technique. In addition, we also demonstrate that arbitrary steering of the magnetic field focus within the target region is possible, without any additional cost in terms of power requirement. In exploring the potential for magnetic field synthesis, our findings highlight limits to be considered for practical applications, as well as promising capabilities not identified before

Rectifying fluctuations in an optical lattice

We have realized a Brownian motor by using cold atoms in a dissipative optical lattice as a model system. In our experiment the optical potential is spatially symmetric and the time-symmetry of the system is broken by applying appropriate zero-mean ac forces. We identify a regime of rectification of forces and a regime of rectification of fluctuations, the latter corresponding to the realization of a Brownian motor

Vibrational mechanics in an optical lattice: controlling transport via potential renormalization

We demonstrate theoretically and experimentally the phenomenon of vibrational resonance in a periodic potential, using cold atoms in an optical lattice as a model system. A high-frequency (HF) drive, with frequency much larger than any characteristic frequency of the system, is applied by phase-modulating one of the lattice beams. We show that the HF drive leads to the renormalization of the potential. We used transport measurements as a probe of the potential renormalization. The very same experiments also demonstrate that transport can be controlled by the HF drive via potential renormalization.Comment: Phys. Rev. Lett., in pres

Phase-control of directed diffusion in a symmetric optical lattice

We demonstrate the phenomenon of directed diffusion in a symmetric periodic potential. This has been realized with cold atoms in a one-dimensional dissipative optical lattice. The stochastic process of optical pumping leads to a diffusive dynamics of the atoms through the periodic structure, while a zero-mean force which breaks the temporal symmetry of the system is applied by phase-modulating one of the lattice beams. The atoms are set into directed motion as a result of the breaking of the temporal symmetry of the system

Whole-genome sequencing and genetic analysis reveal novel stress responses to individual constituents of essential oils in Escherichia coli

Food preservation by the use of essential oils (EOs) is being extensively studied because of the antimicrobial properties of their individual constituents (ICs). Three resistant mutants (termed CAR, CIT, and LIM) of Escherichia coli MG1655 were selected by subculturing with the ICs carvacrol, citral, and (+)-limonene oxide, respectively. These derivative strains showed increased MIC values of ICs and concomitantly enhanced resistance to various antibiotics (ampicillin, trimethoprim, chloramphenicol, tetracycline, kanamycin, novobiocin, norfloxacin, cephalexin, and nalidixic acid) compared to those for the parental strain (wild type [WT]). Whole-genome sequencing (WGS) of these hyperresistant strains permitted the identification of single nucleotide polymorphisms (SNPs) and deletions in comparison to the WT. In order to analyze the contribution of these mutations to the increased antimicrobial resistance detected in hyperresistant strains, derivative strains were constructed by allelic reversion. A role of the SoxR D137Y missense mutation in CAR was confirmed by growth in the presence of some ICs and antibiotics and by its tolerance to ICs but not to lethal heat treatments. In CIT, increased resistance relied on contributions by several detected SNPs, resulting in a frameshift in MarR and an in-frame GyrB ¿G157 mutation. Finally, both the insertion resulting in an AcrR frameshift and large chromosomal deletions found in LIM were correlated with the hyperresistant phenotype of this strain. The nature of the obtained mutants suggests intriguing links to cellular defense mechanisms previously implicated in antibiotic resistance

Aetiology, Risk Factors, and Biomarkers in Systemic Sclerosis with Interstitial Lung Disease

Systemic sclerosis (SSc) is a complex, multi-organ, autoimmune disease. Lung fibrosis occurs in ~80% of patients with SSc; 25-30% develop progressive interstitial lung disease (ILD). The pathogenesis of fibrosis in SSc associated ILD (SSc-ILD) involves cellular injury, activation/differentiation of mesenchymal cells and morphological/biological changes in epithelial/endothelial cells. Risk factors for progressive SSc-ILD include older age, male sex, lung involvement on baseline high-resolution computed tomography, reduced diffusing capacity for carbon monoxide and reduced forced vital capacity. SSc-ILD is characterized by genetic risk architecture distinct from that associated with idiopathic pulmonary fibrosis (IPF). Presence of anti-Scl-70 antibodies and absence of anti-centromere antibodies indicate increased likelihood of progressive ILD. Elevated levels of serum Krebs von den Lungen-6 (KL6) and CRP are associated with SSc-ILD severity, although whether KL6 independently predicts SSc-ILD progression remains controversial. A promising prognostic indicator is serum chemokine (C-C motif) ligand 18. SSc-ILD shares similarities with IPF, although clear differences exist. Histologically, a non-specific interstitial pneumonia pattern is commonly observed in SSc-ILD, whereas IPF is defined by usual interstitial pneumonia. The course of SSc-ILD is variable, ranging from minor, stable disease to a progressive course, while all IPF patients experience progression of disease. Although appropriately treated SSc-ILD patients have better chances of stabilization and survival, a relentlessly progressive course, akin to IPF, is seen in a minority. Better understanding of cellular and molecular pathogenesis, genetic risk and distinctive features of SSc-ILD, and identification of robust prognostic biomarkers are needed for optimal disease management. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Features of Magneto-Optical Resonances in an Elliptically Polarized Traveling Light Wave

The parameters of nonlinear absorption magneto-optical resonances in the Hanle configuration have been studied as functions of the ellipticity of a traveling light wave. It has been found that these parameters (amplitude, width, and amplitude-to-width ratio) depend strongly on the polarization of the light wave. In particular, the resonance amplitude can increase by more than an order of magnitude when the polarization changes from linear to optimal elliptic. It has been shown that this effect is associated with the Doppler frequency shift for atoms in a gas. The theoretical results have been corroborated in experiments in Rb vapor.Comment: 5 page