108 research outputs found
The Structural Colors of Photonic Glasses
The color of materials usually originates from a combination of wavelength-dependent absorption and scattering. Controlling the color without the use of absorbing dyes is of practical interest, not only because of undesired bleaching properties of dyes but also regarding minimization of environmental and health issues. Color control without dyes can be achieved by tuning the material's scattering properties in controlling size and spatial arrangement of scatterers. Herein, calibrated photonic glasses (PGs), which are isotropic materials made by random aggregation of nonabsorbing, monodisperse colloidal polystyrene spheres, are used to generate a wide spectral range of purely structural, angular-independent colors. Experimental reflectance spectra for different sized spheres compare well with a recent theoretical model, which establishes the latter as a tool for color mapping in PGs. It allows to determine the range of visible colors accessible in PGs as function of size, packing fraction, and refractive index of scatterers. It also predicts color saturation on top of the white reflectance as function of the sample's optical thickness. Blue, green, and red are obtained even with low index, while saturated green, cyan, yellow, and magenta can be reached in higher index PGs over several orders of magnitude of sample thickness.Deutsche Forschungsgemeinschaft. Grant Number: SFB1214
Swiss National Science Foundation. Grant Number: 200020M_162846
Alexander von Humboldt Foundatio
Testing bats in rehabilitation for SARS-CoV-2 before release into the wild
Several studies have suggested SARS-CoV-2 originated from a viral ancestor in bats, but whether transmission occurred directly or via an intermediary host to humans remains unknown. Concerns of spillover of SARS-CoV-2 into wild bat populations are hindering bat rehabilitation and conservation efforts in the United Kingdom and elsewhere. Current protocols state that animals cared for by individuals who have tested positive for SARS-CoV-2 cannot be released into the wild and must be isolated to reduce the risk of transmission to wild populations. Here, we propose a reverse transcription-quantitative polymerase chain reaction (RT-qPCR)-based protocol for detection of SARS-CoV-2 in bats, using fecal sampling. Bats from the United Kingdom were tested following suspected exposure to SARS-CoV-2 and tested negative for the virus. With current UK and international legislation, the identification of SARS-CoV-2 infection in wild animals is becoming increasingly important, and protocols such as the one developed here will help improve understanding and mitigation of SARS-CoV-2 in the future
Two-dimensional Vortices in Superconductors
Superconductors have two key characteristics. They expel magnetic field and
they conduct electrical current with zero resistance. However, both properties
are compromised in high magnetic fields which can penetrate the material and
create a mixed state of quantized vortices. The vortices move in response to an
electrical current dissipating energy which destroys the zero resistance
state\cite{And64}. One of the central problems for applications of high
temperature superconductivity is the stabilization of vortices to ensure zero
electrical resistance. We find that vortices in the anisotropic superconductor
BiSrCaCuO (Bi-2212) have a phase transition from
a liquid state, which is inherently unstable, to a two-dimensional vortex
solid. We show that at high field the transition temperature is independent of
magnetic field, as was predicted theoretically for the melting of an ideal
two-dimensional vortex lattice\cite{Fis80,Gla91}. Our results indicate that the
stable solid phase can be reached at any field as may be necessary for
applications involving superconducting magnets\cite{Has04,Sca04,COHMAG}. The
vortex solid is disordered, as suggested by previous studies at lower
fields\cite{Lee93,Cub93}. But its evolution with increasing magnetic field
displays unexpected threshold behavior that needs further investigation.Comment: 5 pages and 4 figures. submitted to Nature Physic
Localization of ultrasound in a three-dimensional elastic network
After exactly half a century of Anderson localization, the subject is more
alive than ever. Direct observation of Anderson localization of electrons was
always hampered by interactions and finite temperatures. Yet, many theoretical
breakthroughs were made, highlighted by finite-size scaling, the
self-consistent theory and the numerical solution of the Anderson tight-binding
model. Theoretical understanding is based on simplified models or
approximations and comparison with experiment is crucial. Despite a wealth of
new experimental data, with microwaves, light, ultrasound and cold atoms, many
questions remain, especially for three dimensions. Here we report the first
observation of sound localization in a random three-dimensional elastic
network. We study the time-dependent transmission below the mobility edge, and
report ``transverse localization'' in three dimensions, which has never been
observed previously with any wave. The data are well described by the
self-consistent theory of localization. The transmission reveals non-Gaussian
statistics, consistent with theoretical predictions.Comment: Final published version, 5 pages, 4 figure
Observations of suppression of static and dynamic disorder in Bi2.15Sr1.85CaCu2O8+d crystals by columnar defects
Muon spin rotation and small angle neutron scattering measurements have been carried out on Bi2.15Sr1.85CaCu2O8+delta single crystals irradiated with fast heavy ions. The data give substantial evidence that even below the matching field, the positions of the vortices, in a plane perpendicular to the tracks, are not random. Furthermore, the crossover to a glassy vortex arrangement, observed in the pristine material, is moved to higher fields. It is shown that the presence of the columnar defects also strongly suppresses the thermal fluctuations of the vortices in comparison with the pristine material.</p
Observations of suppression of static and dynamic disorder in Bi2.15Sr1.85CaCu2O8+d crystals by columnar defects
Muon spin rotation and small angle neutron scattering measurements have been carried out on Bi2.15Sr1.85CaCu2O8+delta single crystals irradiated with fast heavy ions. The data give substantial evidence that even below the matching field, the positions of the vortices, in a plane perpendicular to the tracks, are not random. Furthermore, the crossover to a glassy vortex arrangement, observed in the pristine material, is moved to higher fields. It is shown that the presence of the columnar defects also strongly suppresses the thermal fluctuations of the vortices in comparison with the pristine material.</p
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