From colloidal CdSe quantum dots to microscale optically anisotropic supercrystals through bottom-up self-assembly

This is the author accepted manuscript. The final version is available on open access from Royal Society of Chemistry via the DOI in this recordThe development of fabrication techniques for novel nanostructured materials is one of the key tasks of modern materials science. One pathway to successfully complete this task is the bottom-up assembly of colloidal nanoparticles into ordered superstructures, possessing both the properties of individual nanoparticles and further novel properties resulting from their interactions. However, nanoparticle self-assembly depends on a variety of parameters, which makes the precise control of this process a complicated problem. Here, the time course of quantum dot (QD) self-assembly into ordered superstructures has been analyzed, along with the evolution of their morphological and optical properties. QD self-assembly occurs through two distinct stages (homo- and hetero-geneous), leading to the formation of supercrystals with a layered morphology. Analysis of the optical properties throughout the superstructures’ growth has shown that the absorption and photoluminescence (PL) bands are blue shifted, retaining almost the same PL lifetimes as in the initial QD solution. The supercrystals formed possess a further unique optical property caused by their layered morphology; namely, a four-fold symmetry characterized by strong birefringence. Such supercrystals may be used for the fabrication of microscale optical paths with high extinction coefficients and specific polarization properties for novel optoelectronic devices.This study was supported by the Ministry of Education and Science of the Russian Federation through the grant No. 14.584.21.0032 (ID RFMEFI58417X0032), the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom via the EPSRC Centre for Doctoral Training in Electromagnetic Metamaterials (Grant No. EP/L015331/1) and via EP/N035569/1, and the Royal Society via International Exchange Grant No. 2016/R1

Fatou flowers and parabolic curves

In this survey we collect the main results known up to now (July 2015) regarding possible generalizations to several complex variables of the classical Leau-Fatou flower theorem about holomorphic parabolic dynamics

Understanding the Origins of Bacterial Resistance to Aminoglycosides through Molecular Dynamics Mutational Study of the Ribosomal A-Site

Paromomycin is an aminoglycosidic antibiotic that targets the RNA of the bacterial small ribosomal subunit. It binds in the A-site, which is one of the three tRNA binding sites, and affects translational fidelity by stabilizing two adenines (A1492 and A1493) in the flipped-out state. Experiments have shown that various mutations in the A-site result in bacterial resistance to aminoglycosides. In this study, we performed multiple molecular dynamics simulations of the mutated A-site RNA fragment in explicit solvent to analyze changes in the physicochemical features of the A-site that were introduced by substitutions of specific bases. The simulations were conducted for free RNA and in complex with paromomycin. We found that the specific mutations affect the shape and dynamics of the binding cleft as well as significantly alter its electrostatic properties. The most pronounced changes were observed in the U1406C∶U1495A mutant, where important hydrogen bonds between the RNA and paromomycin were disrupted. The present study aims to clarify the underlying physicochemical mechanisms of bacterial resistance to aminoglycosides due to target mutations

Evidence for Divergent Evolution of Growth Temperature Preference in Sympatric Saccharomyces Species

The genus Saccharomyces currently includes eight species in addition to the model yeast Saccharomyces cerevisiae, most of which can be consistently isolated from tree bark and soil. We recently found sympatric pairs of Saccharomyces species, composed of one cryotolerant and one thermotolerant species in oak bark samples of various geographic origins. In order to contribute to explain the occurrence in sympatry of Saccharomyces species, we screened Saccharomyces genomic data for protein divergence that might be correlated to distinct growth temperature preferences of the species, using the dN/dS ratio as a measure of protein evolution rates and pair-wise species comparisons. In addition to proteins previously implicated in growth at suboptimal temperatures, we found that glycolytic enzymes were among the proteins exhibiting higher than expected divergence when one cryotolerant and one thermotolerant species are compared. By measuring glycolytic fluxes and glycolytic enzymatic activities in different species and at different temperatures, we subsequently show that the unusual divergence of glycolytic genes may be related to divergent evolution of the glycolytic pathway aligning its performance to the growth temperature profiles of the different species. In general, our results support the view that growth temperature preference is a trait that may have undergone divergent selection in the course of ecological speciation in Saccharomyces

Changes to the Fossil Record of Insects through Fifteen Years of Discovery

The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well

Directional Optical Sorting of Silicon Nanoparticles

© 2017 American Chemical Society. Optical manipulation of nanoparticles is a topic of great practical importance, with applications in surface science, colloidal chemistry, microfluidics, biochemistry, and medicine. One of the major highlights of this topic is particle sorting, which serves to create monodisperse systems remotely and to separate particles of different composition and size. Here, we analyze optical forces acting on spherical silicon nanoparticles that exhibit high-quality Mie resonances and demonstrate the potential of optical sorting methods for these systems. In particular, we propose multidirectional static sorting of nanoparticles using noncollinear beams with different wavelengths, which results in all-optical separation into an angular spectrum of sizes. We also validate the proposed methods by considering the operation in the presence of Brownian motion and in the evanescent wave configuration

Nonlinear symmetry breaking in symmetric oligomers

A novel type of nonlinear symmetry breaking in symmetric plasmonic oligomers is reported. By monitoring the strength of the second-harmonic signal while changing the polarization angle of the pump, we observe nonlinear symmetry breaking as a large variation in the generated nonlinear signal. Importantly, the strongly anisotropic nonlinear response is produced by a symmetric structure with isotropic linear response when rotating polarization. We provide theoretical analysis to describe and characterize this effect. Our finding opens new avenues to reveal and characterize the symmetry of nanoscale structures and molecules and also to remotely monitor variations of near-field patterns produced by symmetric nanostructure