29 research outputs found
Static non-reciprocity in mechanical metamaterials
Reciprocity is a fundamental principle governing various physical systems,
which ensures that the transfer function between any two points in space is
identical, regardless of geometrical or material asymmetries. Breaking this
transmission symmetry offers enhanced control over signal transport, isolation
and source protection. So far, devices that break reciprocity have been mostly
considered in dynamic systems, for electromagnetic, acoustic and mechanical
wave propagation associated with spatio-temporal variations. Here we show that
it is possible to strongly break reciprocity in static systems, realizing
mechanical metamaterials that, by combining large nonlinearities with suitable
geometrical asymmetries, and possibly topological features, exhibit vastly
different output displacements under excitation from different sides, as well
as one-way displacement amplification. In addition to extending non-reciprocity
and isolation to statics, our work sheds new light on the understanding of
energy propagation in non-linear materials with asymmetric crystalline
structures and topological properties, opening avenues for energy absorption,
conversion and harvesting, soft robotics, prosthetics and optomechanics.Comment: 19 pages, 3 figures, Supplementary information (11 pages and 5
figures
Designing perturbative metamaterials from discrete models
Identifying material geometries that lead to metamaterials with desired functionalities presents a challenge for the field. Discrete, or reduced-order, models provide a concise description of complex phenomena, such as negative refraction, or topological surface states; therefore, the combination of geometric building blocks to replicate discrete models presenting the desired features represents a promising approach. However, there is no reliable way to solve such an inverse problem. Here, we introduce âperturbative metamaterialsâ, a class of metamaterials consisting of weakly interacting unit cells. The weak interaction allows us to associate each element of the discrete model with individual geometric features of the metamaterial, thereby enabling a systematic design process. We demonstrate our approach by designing two-dimensional elastic metamaterials that realize Veselago lenses, zero-dispersion bands and topological surface phonons. While our selected examples are within the mechanical domain, the same design principle can be applied to acoustic, thermal and photonic metamaterials composed of weakly interacting unit cells
Entanglement spectrum degeneracy and the Cardy formula in 1+1 dimensional conformal field theories
We investigate the effect of a global degeneracy in the distribution of the entanglement spectrum in conformal field theories in one spatial dimension. We relate the recently found universal expression for the entanglement Hamiltonian to the distribution of the entanglement spectrum. The main tool to establish this connection is the Cardy formula. It turns out that the Affleck-Ludwig non-integer degeneracy, appearing because of the boundary conditions induced at the entangling surface, can be directly read from the entanglement spectrum distribution. We also clarify the effect of the noninteger degeneracy on the spectrum of the partial transpose, which is the central object for quantifying the entanglement in mixed states. We show that the exact knowledge of the entanglement spectrum in some integrable spinchains provides strong analytical evidences corroborating our results
Topological sound in active-liquid metamaterials
Liquids composed of self-propelled particles have been experimentally
realized using molecular, colloidal, or macroscopic constituents. These active
liquids can flow spontaneously even in the absence of an external drive. Unlike
spontaneous active flow, the propagation of density waves in confined active
liquids is not well explored. Here, we exploit a mapping between density waves
on top of a chiral flow and electrons in a synthetic gauge field to lay out
design principles for artificial structures termed topological active
metamaterials. We design metamaterials that break time-reversal symmetry using
lattices composed of annular channels filled with a spontaneously flowing
active liquid. Such active metamaterials support topologically protected sound
modes that propagate unidirectionally, without backscattering, along either
sample edges or domain walls and despite overdamped particle dynamics. Our work
illustrates how parity-symmetry breaking in metamaterial structure combined
with microscopic irreversibility of active matter leads to novel
functionalities that cannot be achieved using only passive materials
A measure for spatial dependence in natural stochastic textures
Random textures differ from natural textures because they lack structure. Structure is a concept that is difficult to formalize, but we generally observe that it is associated with spatial dependence between adjacent pixels. Completely random textures, in fact, are characterized by independent pixels, while natural textures show some local dependence. In this paper, we propose a measure for such local dependence. The texture is scanned on a random walk path and the pixels values encountered are collected in form of a time-series. The statistical properties of the time-series are used to characterize the spatial dependence of the texture. We assume that the proposed measure can be used to help the model textures, to set the size of operating windows in texture synthesis algorithms, and to compute a simple indicator of texture scale. Moreover, we show how the measure can be linked to texture perception
Molecular and Functional Analyses of the Gene (eshA) Encoding the 52-Kilodalton Protein of Streptomyces coelicolor A3(2) Required for Antibiotic Production
Analysis of proteins recovered in the S100 precipitate fraction of Streptomyces griseus after ultracentrifugation led to the identification of a 52-kDa protein which is produced during the late growth phase. The gene (eshA) which codes for this protein was cloned from S. griseus, and then its homologue was cloned from Streptomyces coelicolor A3(2). The protein was deduced to be 471 amino acids in length. The protein EshA is characterized by a central region that shows homology to the eukaryotic-type cyclic nucleotide-binding domains. Significant homology was also found to MMPI in Mycobacterium leprae, a major antigenic protein to humans. The eshA gene mapped near the chromosome end and was not essential for viability, as demonstrated by gene disruption experiments, but its disruption resulted in the abolishment of an antibiotic (actinorhodin but not undecylprodigiosin) production. Aerial mycelium was produced as abundantly as by the parent strain. Expression analysis of the EshA protein by Western blotting revealed that EshA is present only in late-growth-phase cells. The eshA gene was transcribed just preceding intracellular accumulation of the EshA protein, as determined by S1 nuclease protection, indicating that EshA expression is regulated at the transcription level. The expression of EshA was unaffected by introduction of the relA mutation, which blocks ppGpp synthesis