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The origin and limit of asymmetric transmission in chiral resonators
Get PDFWe observe that the asymmetric transmission (AT) through photonic systems with a resonant chiral response is strongly related to the far-field properties of eigenmodes of the system. This understanding can be used to predict the AT for any resonant system from its complex eigenmodes. We find that the resonant chiral phenomenon of AT is related to, and is bounded by, the nonresonant scattering properties of the system. Using the principle of reciprocity, we determine a fundamental limit to the maximum AT possible for a single mode in any chiral resonator. We propose and follow a design route for a highly chiral dielectric photonic crystal structure that reaches this fundamental limit for AT
Information-theoretic analysis of the directional influence between cellular processes
Get PDFInferring the directionality of interactions between cellular processes is a major challenge in systems biology. Time-lagged correlations allow to discriminate between alternative models, but they still rely on assumed underlying interactions. Here, we use the transfer entropy (TE), an information-theoretic quantity that quantifies the directional influence between fluctuating variables in a model-free way. We present a theoretical approach to compute the transfer entropy, even when the noise has an extrinsic component or in the presence of feedback. We re-analyze the experimental data from Kiviet et al. (2014) where fluctuations in gene expression of metabolic enzymes and growth rate have been measured in single cells of E. coli. We confirm the formerly detected modes between growth and gene expression, while prescribing more stringent conditions on the structure of noise sources. We furthermore point out practical requirements in terms of length of time series and sampling time which must be satisfied in order to infer optimally transfer entropy from times series of fluctuations
Halide Perovskite 3D Photonic Crystals for Distributed Feedback Lasers
Get PDFHalide perovskites are under intense investigation for light harvesting applications in solar cells. Their outstanding optoelectronic properties such as long charge carrier diffusion lengths, high absorption coefficients, and defect tolerance also triggered interest in laser and LED applications. Here, we report on the lasing properties of 3D distributed feedback halide perovskite nanostructures prepared via an all-solution process. A colloidal crystal templating approach was developed to precisely control the hybrid halide perovskite structure on the nanoscale. The prepared CH3NH3PbBr3 thin films with inverse opal morphology show narrow lasing emissions with a full width half maximum as low as 0.15 nm and good long term stability under pulsed laser excitation above the lasing threshold of 1.6 mJ cm-2 in ambient atmosphere. Furthermore, lasing emission was also observed for CH3NH3PbI3 inverse opals under excitation with a focused laser beam. Unlike other protocols for the fabrication of distributed feedback perovskite lasers, control of the nanostructure of hybrid halide perovskites is achieved without the use of expensive and elaborate lithography techniques or high temperatures. Therefore, the presented protocol opens a route to the low cost fabrication of hybrid halide perovskite lasers
Visualizing near-field coupling in terahertz dolmens
Get PDFStrong interactions between resonant structures in the near-field occur at length scales shorter than the wavelength, and can be exploited for modifying the propagation of electromagnetic radiation. Dolmen-like structures, formed by a rod supporting a dipolar (bright) resonance and two orthogonal rods with a quadrupolar (dark) resonance at the same frequency, represent a geometry of significant interest for near-field electromagnetic coupling. These structures demonstrate electromagnetically induced transparency (EIT) through coupling between these resonances, concurrently providing a sharp spectral selectivity in transmission and large group velocity reduction. We use near-field terahertz scanning microscopy to map the electric fields in the vicinity of a metallic dolmen in both amplitude and phase. In this way, we directly measure the interaction between bright and dark modes in the time-domain, revealing the physics resulting in EIT. We experimentally demonstrate the hybridization of bright and dark modes accompanying the near-field coupling, as well as the excitation of the dark mode at the frequency of the far-field transparency
Biochemical Machines for the Interconversion of Mutual Information and Work
Get PDFWe propose a physically realizable information-driven device consisting of an enzyme in a chemical bath, interacting with pairs of molecules prepared in correlated states. These correlations persist without direct interaction and thus store free energy equal to the mutual information. The enzyme can harness this free energy, and that stored in the individual molecular states, to do chemical work. Alternatively, the enzyme can use the chemical driving to create mutual information. A modified system can function without external intervention, approaching biological systems more closely.
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Canalization of C. elegans Vulva Induction against Anatomical Variability
Get PDFIt is not understood how development occurs with astounding reproducibility despite variability on the cellular level. We show how a feedback mechanism involving cell signaling and migration generates an invariant cell fate pattern in C.elegans vulva development, even though anatomical variability causes strong initial variation in cell fate induction
Photochemical conversion of tin-oxo cage compounds studied using hard x-ray photoelectron spectroscopy
Get PDFMolecular inorganic materials are currently considered photoresists for extreme ultraviolet lithography (EUVL). Their high EUV absorption cross section and small building block size potentially allow high sensitivity and resolution as well as low line-edge roughness. The photochemical reaction mechanisms that allow these kinds of materials to function as photoresists, however, are still poorly understood. We discuss photochemical reactions upon deep UV (DUV) irradiation of a model negative-tone EUV photoresist material, namely the well-defined molecular tin-oxo cage compound [(SnBu)12O14(OH)6](OH)2, which is spin-coated to thin layers of 20 nm. The core electronic structures (Sn 3d, O 1s, and C 1s) of unexposed and DUV exposed films were then investigated using synchrotron radiation-based hard x-ray photoelectron spectroscopy. Different chemical oxidation states and concentrations of atoms and atom types in the unexposed and exposed films were found. We observed that the exposure in a nitrogen atmosphere prevented the oxidation but still led to carbon loss, albeit with a smaller conversion. Finally, a mechanistic hypothesis for the basic DUV photoreactions in molecular tin-oxo cages is proposed
Communication: Slow proton-charge diffusion in nanoconfined water
Get PDFWe investigate proton-charge mobility in nanoscopic water droplets with tuneable size. We find that the diffusion of confined proton charges causes a dielectric relaxation process with a maximumloss frequency determined by the diffusion constant. In volumes less than similar to 5 nm in diameter, proton-charge diffusion slows down significantly with decreasing size: for diameters < 1 nm, the diffusion constant is about 100 times smaller than in bulk water. The low mobility probably results from the more rigid hydrogen-bond network of nanoconfined water, since proton-charge mobility in water relies on collective hydrogen-bond rearrangements
Visual Understanding of Light Absorption and Waveguiding in Standing Nanowires with 3D Fluorescence Confocal Microscopy
Get PDFSemiconductor nanowires are promising building blocks for nextgeneration photonics. Indirect proofs of large absorption cross sections have been reported in nanostructures with subwavelength diameters, an effect that is even more prominent in vertically standing nanowires. In this work we provide a three-dimensional map of the light around vertical GaAs nanowires standing on a substrate by using fluorescence confocal microscopy, where the strong long-range disruption of the light path along the nanowire is illustrated. We find that the actual long-distance perturbation is much larger in size than calculated extinction cross sections. While the size of the perturbation remains similar, the intensity of the interaction changes dramatically over the visible spectrum. Numerical simulations allow us to distinguish the effects of scattering and absorption in the nanowire leading to these phenomena. This work provides a visual understanding of light absorption in semiconductor nanowire structures, which is of high interest for solar energy conversion applications