Coherent absorption and enhanced photoluminescence in thin layers of nanorods

We demonstrate a large light absorptance (80%) in a nanometric layer of quantum dots in rods (QRs) with a thickness of 23 nm. This behavior is explained in terms of the coherent absorption by interference of the light incident at a certain angle onto the very thin QR layer. We exploit this coherent light absorption to enhance the photoluminescent emission from the QRs. Up to a seven- and fivefold enhancement of the photoluminescence is observed for p- and s-polarized incident light, respectively.Comment: Physical Review B 201

Memory-induced Excitability in Optical Cavities

Neurons and other excitable systems can release energy suddenly given a small stimulus. Excitability has recently drawn increasing interest in optics, as it is key to realize all-optical artificial neurons enabling speed-of-light information processing. However, the realization of all-optical excitable units and networks remains challenging. Here we demonstrate how laser-driven optical cavities with memory in their nonlinear response can sustain excitability beyond the constraints of memoryless systems. First we demonstrate different classes of excitability and spiking, and their control in a single cavity with memory. This single-cavity excitability is limited to a narrow range of memory times commensurate with the linear dissipation time. To overcome this limitation, we explore coupled cavities with memory. We demonstrate that this system can exhibit excitability for arbitrarily long memory times, even when the inter-cavity coupling rate is smaller than the dissipation rate. Our coupled-cavity system also sustains spike trains -- a hallmark of neurons -- that spontaneously break mirror symmetry. Our predictions can be readily tested in thermo-optical cavities, where thermal dynamics effectively give memory to the nonlinear optical response. The huge separation between thermal and optical time scales in such cavities is promising for the realization of artificial neurons that can self-organize to the edge of a phase transition, like many biological systems do

Tailoring dispersion and eigenfield profiles of plasmonic surface lattice resonances

We investigate the radiative coupling between localized surface plasmon resonances (LSPRs) and Rayleigh anomalies (RAs) in periodic arrays of metallic nanorods with varying dimensions but equal lattice constants. The dimensions of the nanorods determine the energy and line width of the LSPR and, thus, enable tailoring of the mixed LSPR RA states: surface lattice resonances (SLRs). We present variable angle light extinction experimental spectra for five arrays with different nanorod width and explain our results with numerical simulations. The numerical simulations are done for driven and undriven systems, with the latter revealing the SLR eigenmode properties for the first time. We provide a plane wave model that interprets the near- and far-fields of these eigenmodes, describing the intricate behavior of confinement and radiative loss versus in-plane momentum. The SLR line width, band gap associated with the coupled modes, and field extension into the surrounding dielectric are tunable via the dimensions of the nanorods

MicroRNA and tasiRNA diversity in mature pollen of Arabidopsis thaliana

<p>Abstract</p> <p>Background</p> <p>New generation sequencing technology has allowed investigation of the small RNA populations of flowering plants at great depth. However, little is known about small RNAs in their reproductive cells, especially in post-meiotic cells of the gametophyte generation. Pollen - the male gametophyte - is the specialised haploid structure that generates and delivers the sperm cells to the female gametes at fertilisation. Whether development and differentiation of the male gametophyte depends on the action of microRNAs and trans-acting siRNAs guiding changes in gene expression is largely unknown. Here we have used 454 sequencing to survey the various small RNA populations present in mature pollen of <it>Arabidopsis thaliana</it>.</p> <p>Results</p> <p>In this study we detected the presence of 33 different microRNA families in mature pollen and validated the expression levels of 17 selected miRNAs by Q-RT-PCR. The majority of the selected miRNAs showed pollen-enriched expression compared with leaves. Furthermore, we report for the first time the presence of trans-acting siRNAs in pollen. In addition to describing new patterns of expression for known small RNAs in each of these classes, we identified 7 putative novel microRNAs. One of these, ath-MIR2939, targets a pollen-specific F-box transcript and we demonstrate cleavage of its target mRNA in mature pollen.</p> <p>Conclusions</p> <p>Despite the apparent simplicity of the male gametophyte, comprising just two different cell types, pollen not only utilises many miRNAs and trans-acting siRNAs expressed in the somatic tissues but also expresses novel miRNAs.</p

Shape Transition of Nanostructures created on Si(100) surfaces after MeV Implantation

We have studied the modification in the Surface morphology of the Si(100) surfaces after 1.5 MeV Sb implantation. Scanning Probe Microscopy has been utilized to investigate the ion implanted surfaces. We observe the formation of nano-sized defect features on the Si surfaces for various fluences. These nanostructures are elliptical in shape and inflate in sizefor higher fluences. Furthermore, these nanostructures undergo a shape transition from an elliptical shape to a circular-like at a high fluence. We will also discuss the modification in surface roughness as a function of Sb fluence.Comment: 9 pages, 4 figure

Divide and rule: Frontinus and Roman land-surveying

This paper aims to cast new light on one of our main sources for ancient science, Sextus Julius Frontinus; to cast new light on the science of the Graeco-Roman period; and to contribute ancient materials to present discussions on the relations between power and knowledge, and/or science and empire