Effect of silver nanoparticles on the standard soil arthropod Folsomia candida (Collembola) and the eukaryote model organism Saccharomyces cerevisiae

Additional file 2. Yeast colony formation

Prospects of a superradiant laser based on a thermal or guided beam of Sr-88

The prospects of superradiant lasing on the 7.5 kHz wide $^1$S$_0$-$^3$P$_1$ transition in $^{88}$Sr is explored by using numerical simulations of two systems based on realistic experimental numbers. One system uses the idea of demonstrating continuous superradiance in a simple, hot atom beam with high flux, and the other system is based on using ultra-cold atoms in a dipole guide. We find that the hot beam system achieves lasing above a flux of $2.5 \times 10^{12}$ atoms/s. It is capable of outputting hundreds of nW and suppressing cavity noise by a factor of 20-30. The second order Doppler shift causes a shift in the lasing frequency on the order of 500 Hz. For the cold atom beam we account for decoherence and thermal effects when using a repumping scheme for atoms confined in a dipole guide. We find that the output power is on the order of hundreds of pW, however the second order Doppler shift can be neglected, and cavity noise can be suppressed on the order of a factor 50-100. Additionally we show that both systems exhibit local insensitivity to fluctuations in atomic flux.Comment: 10 pages, 7 figure

Imaging and phase-locking of non-linear spin waves

Non-linear processes are a key feature in the emerging field of spin-wave based information processing and allow to convert uniform spin-wave excitations into propagating modes at different frequencies. Recently, the existence of non-linear magnons at half-integer multiples of the driving frequency has been predicted for Ni80Fe20 at low bias fields. However, it is an open question under which conditions such non-linear spin waves emerge coherently and how they may be used in device structures. Usually non-linear processes are explored in the small modulation regime and result in the well known three and four magnon scattering processes. Here we demonstrate and image a class of spin waves oscillating at half-integer harmonics that have only recently been proposed for the strong modulation regime. The direct imaging of these parametrically generated magnons in Ni80Fe20 elements allows to visualize their wave vectors. In addition, we demonstrate the presence of two degenerate phase states that may be selected by external phase-locking. These results open new possibilities for applications such as spin-wave sources, amplifiers and phase-encoded information processing with magnons

Voltage-programmable liquid optical interface

Recently, there has been intense interest in photonic devices based on microfluidics, including displays and refractive tunable microlenses and optical beamsteerers, that work using the principle of electrowetting. Here, we report a novel approach to optical devices in which static wrinkles are produced at the surface of a thin film of oil as a result of dielectrophoretic forces. We have demonstrated this voltage-programmable surface wrinkling effect in periodic devices with pitch lengths of between 20 and 240 µm and with response times of less than 40 µs. By a careful choice of oils, it is possible to optimize either for high-amplitude sinusoidal wrinkles at micrometre-scale pitches or more complex non-sinusoidal profiles with higher Fourier components at longer pitches. This opens up the possibility of developing rapidly responsive voltage-programmable, polarization-insensitive transmission and reflection diffraction devices and arbitrary surface profile optical devices

Faraday-shielded, DC Stark-free optical lattice clock

We demonstrate the absence of a DC Stark shift in an ytterbium optical lattice clock. Stray electric fields are suppressed through the introduction of an in-vacuum Faraday shield. Still, the effectiveness of the shielding must be experimentally assessed. Such diagnostics are accomplished by applying high voltage to six electrodes, which are grounded in normal operation to form part of the Faraday shield. Our measurements place a constraint on the DC Stark shift at the $10^{-20}$ level, in units of the clock frequency. Moreover, we discuss a potential source of error in strategies to precisely measure or cancel non-zero DC Stark shifts, attributed to field gradients coupled with the finite spatial extent of the lattice-trapped atoms. With this consideration, we find that Faraday shielding, complemented with experimental validation, provides both a practically appealing and effective solution to the problem of DC Stark shifts in optical lattice clocks.Comment: 5 pages + supplemental material; accepted to PR

Enzyme-powered hollow mesoporous Janus nanomotors

The development of synthetic nanomotors for technological applications in particular for life science and nanomedicine is a key focus of current basic research. However, it has been challenging to make active nanosystems based on biocompatible materials consuming nontoxic fuels for providing self-propulsion. Here, we fabricate self-propelled Janus nanomotors based on hollow mesoporous silica nanoparticles (HMSNPs), which are powered by biocatalytic reactions of three different enzymes: catalase, urease, and glucose oxidase (GOx). The active motion is characterized by a mean-square displacement (MSD) analysis of optical video recordings and confirmed by dynamic light scattering (DLS) measurements. We found that the apparent diffusion coefficient was enhanced by up to 83%. In addition, using optical tweezers, we directly measured a holding force of 64 ± 16 fN, which was necessary to counteract the effective self-propulsion force generated by a single nanomotor. The successful demonstration of biocompatible enzyme-powered active nanomotors using biologically benign fuels has a great potential for future biomedical applications

Phase separation transition in liquids and polymers induced by electric field gradients

Spatially uniform electric fields have been used to induce instabilities in liquids and polymers, and to orient and deform ordered phases of block-copolymers. Here we discuss the demixing phase transition occurring in liquid mixtures when they are subject to spatially nonuniform fields. Above the critical value of potential, a phase-separation transition occurs, and two coexisting phases appear separated by a sharp interface. Analytical and numerical composition profiles are given, and the interface location as a function of charge or voltage is found. The possible influence of demixing on the stability of suspensions and on inter-colloid interaction is discussed.Comment: 7 pages, 3 figures. Special issue of the J. Phys. Soc. Ja