Rapid evolution of miniaturized, automatic, robotized, function-centered devices has redefined space technology, bringing closer the realization of most ambitious interplanetary missions and intense near-Earth space exploration. Small unmanned satellites and probes are now being launched in hundreds at a time, resurrecting a dream of satellite constellations, i.e., wide, all-covering networks of small satellites capable of forming universal multifunctional, intelligent platforms for global communication, navigation, ubiquitous data mining, Earth observation, and many other functions, which was once doomed by the extraordinary cost of such systems. The ingression of novel nanostructured materials provided a solid base that enabled the advancement of these affordable systems in aspects of power, instrumentation, and communication. However, absence of efficient and reliable thrust systems with the capacity to support precise maneuvering of small satellites and CubeSats over long periods of deployment remains a real stumbling block both for the deployment of large satellite systems and for further exploration of deep space using a new generation of spacecraft. The last few years have seen tremendous global efforts to develop various miniaturized space thrusters, with great success stories. Yet, there are critical challenges that still face the space technology. These have been outlined at an inaugural International Workshop on Micropropulsion and Cubesats, MPCS-2017, a joint effort between Plasma Sources and Application Centre/Space Propulsion Centre (Singapore) and the Micropropulsion and Nanotechnology Lab, the G. Washington University (USA) devoted to miniaturized space propulsion systems, and hosted by CNR-Nanotec—P.Las.M.I. lab in Bari, Italy. This focused review aims to highlight the most promising developments reported at MPCS-2017 by leading world-reputed experts in miniaturized space propulsion systems. Recent advances in several major types of small thrusters including Hall thrusters, ion engines, helicon, and vacuum arc devices are presented, and trends and perspectives are outlined.

As a vehicle reenters or travels through the atmosphere at hypersonic velocities, the shock-heated air surrounding the vehicle becomes weakly ionized. This plasma layer causes an important systems operation problem known as communications blackout or radio blackout. At sufficiently high plasma density, the plasma layer either reflects or attenuates radiowave communications to and from the vehicle. In this paper, we study the application of electric and magnetic fields to reduce the plasma density. Specifically, an E B crossed-field configuration is proposed. Both analytical and numerical results suggest that significant reduction of the plasma density is possible at large altitudes. For instance, plasma density reduction by a factor of 10 is predicted in the case of 81 km and a magnetic field of about 0.1 T. Theoretical results suggest that significant reduction of the plasma density is possible, enabling radio communication across the plasma layer. The benefit of the reduced plasma density in terms of electromagnetic wave absorption across the plasma layer is estimated.

During hypersonic reentry flight, the shock heated air generates a weakly ionized plasma layer. Because the weakly ionized plasma layer has a high plasma number density, it causes an important systems operation problem that is known as a communication, or radio, blackout. The radio blackout occurs when the plasma frequency of the plasma layer is higher than a radio wave frequency. In this case, the radio wave signals to and from the vehicle are reflected or attenuated so that the vehicle loses voice communication, data telemetry, and Global Positioning System navigation. The radio blackout problem can be solved by reducing the plasma number density of the plasma layer because the plasma frequency is mainly related to the plasma number density of the plasma layer. To reduce the plasma number density of the plasma layer, an electromagnetic E B layer approach is proposed. The proposed E B layer is analyzed by a two-dimensional model. It suggests that an E B layer can be used to allow transmission of the communication signals through the plasma layer. We also propose an alternative to reduce the plasma density, based on an electrostatic plasma sheath.

Light-matter interaction gives optical microscopes tremendous versatility compared with other imaging methods such as electron microscopes, scanning probe microscopes, or x-ray scattering where there are various limitations on sample preparation and where the methods are inapplicable to bioimaging with live cells. However, this comes at the expense of a limited resolution due to the diffraction limit. Here, we demonstrate a novel method utilizing elastic scattering from disordered nanoparticles to achieve subdiffraction limited imaging. The measured far-field speckle fields can be used to reconstruct the subwavelength details of the target by time reversal, which allows full-field dynamic super-resolution imaging. The fabrication of the scattering superlens is extremely simple and the method has no restrictions on the wavelength of light that is used. DOI: 10.1103/PhysRevLett.113.113901 PACS numbers: 42.25.Fx, 42.25.Kb, 42.40.-i Since the first experimental demonstration of the nearfield scanning optical microscope (NSOM) [1], various methods to probe the near fields have been proposed. The field of bioimaging has shown the largest number of new techniques due to the direct need to use visible wavelengths and observation in a nonvacuum environment. Although the currently developed methods are comprised of multiple unique ideas, the common goal of all super-resolution techniques is the effective delivery of the high spatial frequency components of the target object's angular spectrum, which are evanescent and are restricted to distances smaller than the wavelength of light from the object of interest.Here, we propose to use multiple scattering in turbid media to deliver the near-field wave vectors to the observable far field, which allows optical subdiffraction limited imaging using conventional optics. Similar to the hyperlens [2] or in structured illumination [3] where a specific nearfield mode corresponds to a corresponding far-field mode, multiple scattering induces the mixture and transfer between the far and near fields. Because elastic scattering is described by Maxwell's equations, which has time-reversal symmetry, multiple scattering of light exhibits time-reversal symmetry no matter how complicated and random each scattering event is. This property has allowed fascinating demonstrations such as the removal of inhomogeneity in the generation of photon echoes [4] or perfect absorption which is the opposite of lasing [5]. In imaging, multiple scattering and the principle of time reversal have been capitalized in reconstructing the incident field prior to multiple scattering [6][7][8]. In the microwave region, it has also been shown that scattering materials placed in the near field of a target object can scatter the near fields into propagating farfield components [9,10]. More recently, similar phenomena have been shown numerically in the optical region utilizing subwavelength coupled resonators [11] and subwavelength imaging has been demonstrated by using the combination of the memory effect and a hig...

Aqueous zinc ion batteries are receiving increasing attention for large-scale energy storage systems owing to their attractive features with respect to safety, cost, and scalability. Although vanadium oxides with various compositions have been demonstrated to store zinc ions reversibly, their limited cyclability especially at low current densities and their poor calendar life impede their widespread practical adoption. Herein, we reveal that the electrochemically inactive zinc pyrovanadate (ZVO) phase formed on the cathode surface is the main cause of the limited sustainability. Moreover, the formation of ZVO is closely related to the corrosion of the zinc metal counter electrode by perturbing the pH of the electrolyte. Thus, the dissolution of VO2(OH)2−, the source of the vanadium in the ZVO, is no longer prevented. The proposed amalgamated Zn anode improves the cyclability drastically by blocking the corrosion at the anode, verifying the importance of pH control and the interplay between both electrodes.