Satellite image compression by concurrent representations of wavelet blocks

This paper proposes a complete compression and coding scheme for on-board satellite applications considering the main on-board constraints: low computational power and easy bit rate control. The proposed coding scheme improves the performance of the current Consultative Committee for Space Data Systems (CCSDS) recommendation for a low additional complexity. We consider post-transforms in the wavelet domain, select the best representation for each block of wavelet coefficients, and encode it into an embedded bit stream. After applying a classical wavelet transform of the image, several concurrent representations of blocks of wavelet coefficients are generated. The best representations are then selected according to a rate-distortion criterion. Finally, a specific bit-plane encoder derived from the CCSDS recommendation produces an embedded bit stream ensuring the easy rate control required. In this article, both the post-transforms and the best representation selection have been adapted to the low complexity constraint, and the CCSDS coder has been modified to compress post-transformed representations.     

Remote‐Controlled Hydrogel Depots for Time‐Scheduled Vaccination

Remote‐controlled drug depots represent a highly valuable tool for the timely controlled administration of pharmaceuticals in a patient compliant manner. Here, the first pharmacologically controlled material that allows for the scheduled induction of a medical response in mice is described. To this aim, a novel, humanized biohybrid material that releases its cargo in response to a small‐molecule stimulus licensed for human use is developed. The functionality of the material in mice is demonstrated by the remote‐controlled delivery of a vaccine against the oncogenic human papillomavirus type 16. It is shown that the biohybrid depot‐mediated immunoprotection is equivalent to the classical multi‐injection‐based vaccination. These results indicate that this material can be used as a universal remote‐controlled vehicle for the patient‐compliant delivery of vaccines and pharmaceuticals.     

Hydrogen‐Bonded Organic Semiconductors as Stable Photoelectrocatalysts for Efficient Hydrogen Peroxide Photosynthesis

Research on semiconductor photocatalysts for the conversion of solar energy into chemical fuels has been at the forefront of renewable energy technologies. Water splitting to produce H₂ and CO₂ reduction to hydrocarbons are the two prominent approaches. A lesser‐known process, the conversion of solar energy into the versatile high‐energy product H₂O₂ via reduction of O₂ has been proposed as an alternative concept. Semiconductor photoelectrodes for the direct photosynthesis of H₂O₂ from O₂ have not been applied up to now. Photoelectrocatalytic oxygen reduction to peroxides in aqueous electrolytes by hydrogen‐bonded organic semiconductor is observed photoelectrodes. These materials have been found to be remarkably stable operating in a photoelectrochemical cell converting light into H₂O₂ under constant illumination for at least several days, functioning in a pH range from 1 to 12. This is the first report of a semiconductor photoelectrode for H₂O₂ production, with catalytic performance exceeding prior reports on photocatalysts by one to two orders of magnitude in terms of peroxide yield/catalyst amount/time. The combination of a strongly reducing conduction band energy level with stability in aqueous electrolytes opens new avenues for this widely available materials class in the field of photo(electro) catalysis.     

Microfluidics structures for probing the dynamic behaviour of filamentous fungi

Although filamentous fungi live in physically and chemically complex natural environments that require optimal survival strategies, both at colony and individual cell level, their growth dynamics are usually studied on homogenous media. This study proposes a new research methodology based on the purposeful design, fabrication and operation of microfluidics structures to examine the temporal and spatial responses of filamentous fungi. Two model fungal strains, the wild type of Neurospora crassa – a commonly used model organisms – and the ro-1 mutant strain of this species impaired in hyphal growth and morphology, have been chosen to demonstrate the potential of this new methodology. Time-lapse observations of both species show that filamentous fungi respond rapidly to the physically microstructured environment without any detectable temporal or spatial adjustment period. Despite their genetic differences, and consequently different growth behaviour, both strains present efficient space-search strategies enabling them to solve the microsized networks successfully and in similar periods, thus demonstrating that the space-searching algorithms are robust and mutation-independent. Additionally, the use of the proposed methodology could put in evidence new biological mechanisms responsible for the apical extension of filamentous fungi, beyond the classical theory based on the central role of Spitzenkörper.     

Dynamic properties of AlGaAs vertical cavity surface emitting lasers with active region based on submonolayer InAs insertions

It has been shown that the use of submonolayer InAs insertions as an active region of AlGaAs vertical cavity surface emitting lasers make it possible to attain resonant frequencies as high as 17 GHz. In this case, single-mode devices with a smaller diameter of the current aperture make it possible to attain higher frequencies at lower current densities than those of multimode devices with a larger aperture diameter. The maximum error-free data transmission rate in the direct modulation mode in NRZ format is 20 Gb/s and is limited by the parasitic cutoff frequency. The high resonant frequency suggests that further optimization of the device design, directed to decreasing the electrical capacitance and resistances, the data transmission rate in lasers based on submonolayer insertions can be increased to 40 Gb/s.     

Laser-Empowered Random Metasurfaces for White Light Printed Image Multiplexing

Printed image multiplexing based on the design of metasurfaces has attracted much interest in the past decade. Optical switching between different images displayed directly on the metasurface is performed by altering the parameters of the incident light such as polarization, wavelength, or incidence angle. When using white light, only two-image multiplexing is implemented with polarization switching. Such metasurfaces are made of nanostructures perfectly controlled individually, which provide high-resolution pixels but small images and involve long fabrication processes. Here, it is demonstrated that laser processing of nanocomposites offers a versatile low-cost, high-speed method with large area processing capabilities for controlling the statistical properties of random metasurfaces, allowing up to three-image multiplexing under white light illumination. By independently controlling absorption and interference effects, colors in reflection and transmission can be varied independently yielding two-image multiplexing under white light. Using anisotropy of plasmonic nanoparticles, a third image can be multiplexed and revealed through polarization changes. The design strategy, the fundamental properties, and the versatility of implementation of these laser-empowered random metasurfaces are discussed. The technique, applied on flexible substrate, can find applications in information encryption or functional switchable optical devices, and offers many advantages for visual security and anticounterfeiting.     

Improving satellite services with cooperative communications

This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright © 2011 John Wiley & Sons, Ltd.