Demo Abstract: R.A.V.E.N. – Remote Autonomous Vehicle Explorer Network

Unmanned aerial vehicles (UAVs) have recently become a viable platform for surveillance and exploration tasks. Several commercial quadrotor aircraft have been successfully used as surveillance equipment with groups such as United States and Canadian police forces, and additional applications for this technology could include exploration of ra-dioactive/hazmat environments, naval search and rescue, or surveying a building on fire, to name a few. Despite the agility and speed of the quadrotor platform, current systems lack the redundancy and collaboration of a multi-unit team; current implementations of quadrotor UAV flocks require expensive equipment, limiting the system to operation within range of external sensors. We propose a system for intelligently controlling multiple quadrotor UAVs using a combination of on-board vision tracking and wireless communication of attitude measurements. The proposed system uses a lead, human-controlled quadrotor and one or more quadro-tors that track and follow the lead unit autonomously. The forthcoming system aims to improve the execution time required to complete missions and increase both breadth of search and platform effectiveness

Cooperative Flight Guidance of Autonomous Unmanned Aerial Vehicles

As robotic platforms and unmanned aerial vehicles (UAVs) increase in sophistication and complexity, the ability to determine the spatial orientation and placement of the platform in real time (localization) becomes an important issue. Detecting and extracting locations of objects, barriers, and openings is required to ensure the overall effectiveness of the device. Current methods to achieve localization for UAVs require expensive external equipment and limit the overall applicable range of the platform. The system described herein incorporates leader-follower unmanned aerial vehicles using vision processing, radio-frequency data transmission, and additional sensors to achieve flocking behavior. This system targets search and rescue environments, employing controls, vision processing, and embedded systems to allow for easy deployment of multiple quadrotor UAVs while requiring the control of only one. The system demonstrates a relative localization scheme for UAVs in a leader-follower configuration, allowing for predictive maneuvers including path following and estimation of the lead UAV in situations of limited or no line-of-sight

Influence of the Cation on the Reaction Mechanism of Sodium Uptake and Release in Bivalent Transition Metal Thiophosphate Anodes: A Case Study of Fe2_2P2_2S6_6

The layered active material Fe$_2$P$_2$S$_6$ was examined as anode material in sodium-ion batteries (SIBs) and compared to previously investigated Ni$_2$P$_2$S$_6$. A reversible specific capacity of 540 mAh g$^{−1}$ was achieved after 250 cycles, depicting similar electrochemical performance as observed for Ni$_2$P$_2$S$_6$. The rate capability and long-term behavior of these two materials are also very similar. Another objective was to elucidate the reaction mechanism during discharging and charging by applying several techniques such as X-ray diffraction, pair distribution function analysis as well as X-ray absorption and solid state NMR spectroscopy. The results clearly demonstrate that the majority of Fe$^{2+}$ is reduced to elemental Fe during the uptake of 5 Na/f.u., while an amorphous intermediate is generated, which was identified as Na$_4$P$_2$S$_6$ by solid state NMR spectroscopy. Completely discharging against a Na metal counter electrode leads to the formation of nanocrystalline Na$_2$S and indications of the formation of polymeric phosphorus were found. In sum, the Na uptake reaction process observed for Fe$_2$P$_2$S$_6$ coincides with the previously unraveled reaction pathway of Ni$_2$P$_2$S$_6$. We therefore conclude that a universal reaction takes places for bivalent transition metal thiophosphate (M$_2$P$_2$S$_6$) electrodes in SIBs

Probing the Effect of Titanium Substitution on the Sodium Storage in Na₃Ni₂BiO₆ Honeycomb-Type Structure

Na$_{3}$Ni$_{2}$BiO$_{6}$ with Honeycomb structure suffers from poor cycle stability when applied as cathode material for sodium-ion batteries. Herein, the strategy to improve the stability is to substitute Ni and Bi with inactive Ti. Monoclinic Na$_{3}$Ni$_{2-x}$Bi$_{1-y}$Ti$_{x+y}$O$_{6}$ powders with different Ti content were successfully synthesized via sol gel method, and 0.3 mol of Ti was determined as a maximum concentration to obtain a phase-pure compound. A solid-solution in the system of O3-NaNi$_{0.5}$Ti$_{0.5}$O$_{2}$ and O3-Na$_{3}$Ni$_{2}$BiO$_{6}$ is obtained when this critical concentration is not exceeded. The capacity of the first desodiation process at 0.1 C of Na$_{3}$Ni$_{2}$BiO$_{6}$ (~93 mAh g$^{-1}$) decreases with the increasing Ti concentration to ~77 mAh g$^{-1}$ for Na$_{3}$Ni$_{2}$Bi$_{0.9}$Ti$_{0.1}$O$_{6}$ and to ~82 mAh g$^{-1}$ for Na$_{3}$Ni$_{Zahl0.9}$Bi$_{0.8}$Ti$_{0.3}$O$_{6}$, respectively. After 100 cycles at 1 C, a better electrochemical kinetics is obtained for the Ti-containing structures, where a fast diffusion effect of Na$^{+}$-ions is more pronounced. As a result of in operando synchrotron radiation diffraction, during the first sodiation (O1-P3-O’3-O3) the O’3 phase, which is formed in the Na$_{3}$Ni$_{2}$BiO$_{6}$ is fully or partly replaced by P’3 phase in the Ti substituted compounds. This leads to an improvement in the kinetics of the electrochemical process. The pathway through prismatic sites of Na$^{+}$-ions in the P’3 phase seems to be more favourable than through octahedral sites of O’3 phase. Additionally, at high potential, a partial suppression of the reversible phase transition P3-O1-P3 is revealed

Use of Learned Dictionaries in Tomographic Reconstruction

We study the use and impact of a dictionary in a tomographic reconstruction setup. First, we build two different dictionaries: one using a set of bases functions (Discrete Cosine Transform), and the other that is learned using patches extracted from training images, similar to the image that we would like to reconstruct. We use K-SVD as the learning algorithm. These dictionaries being local, we convert them to global dictionaries, ready to be applied on whole images, by generating all possible shifts of each atom across the image. During the reconstruction, we minimize the reconstruction error by performing a gradient descent on the image representation in the dictionary space. Our experiments show promising results, allowing to eliminate standard artifacts in the tomographic reconstruction, and to reduce the number of measurements required for the inversion. However, the quality of the results depends on the convergence of the learning process, and on the parameters of the dictionaries (number of atoms, convergence criterion, atom size, etc.). The exact influence of each of these remains to be studied

In situ neutron diffraction for analysing complex coarse-grained functional materials

Complex functional materials play a crucial role in a broad range of energy-related applications and in general for materials science. Revealing the structural mechanisms is challenging due to highly correlated coexisting phases and microstructures, especially for in situ or operando investigations. Since the grain sizes influence the properties, these microstructural features further complicate investigations at synchrotrons due to the limitations of illuminated sample volumes. In this study, it is demonstrated that such complex functional materials with highly correlated coexisting phases can be investigated under in situ conditions with neutron diffraction. For large grain sizes, these experiments are valuable methods to reveal the structural mechanisms. For an example of in situ experiments on barium titanate with an applied electric field, details of the electric-field-induced phase transformation depending on grain size and frequency are revealed. The results uncover the strain mechanisms in barium titanate and elucidate the complex interplay of stresses in relation to grain sizes as well as domain-wall densities and mobilities

Illuminating milling mechanochemistry by tandem real-time fluorescence emission and Raman spectroscopy monitoring

In pursuit of accessible and interpretable methods for direct and real-time observation of mechanochemical reactions, we demonstrate a tandem spectroscopic method for monitoring of ball-milling transformations combining fluorescence emission and Raman spectroscopy, accompanied by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) modelling of solid-state fluorescence spectra. This proof-of-principle report presents this readily accessible dual-spectroscopy technique as capable of observing changes to the supramolecular structure of the model pharmaceutical system indometacin during mechanochemical polymorph transformation and cocrystallisation. The observed time-resolved in situ spectroscopic and kinetic data are supported by ex situ X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements. The application of first principles (ab initio) calculations enabled the elucidation of how changes in crystalline environment, that result from mechanochemical reactions, affect vibrational and electronic excited states of molecules. The herein explored interpretation of both real-time and ex situ spectroscopic data through ab initio calculations provides an entry into developing a detailed mechanistic understanding of mechanochemical milling processes and highlights the challenges of using real-time spectroscopy

Garnet to hydrogarnet: effect of post synthesis treatment on cation substituted LLZO solid electrolyte and its effect on Li ion conductivity

We investigated why commercial Li$_7$La$_3$Zr$_2$O$_{12}$ (LLZO) with Nb- and Ta substitution shows very low mobility on a local scale, as observed with temperature-dependent NMR techniques, compared to Al and W substituted samples, although impedance spectroscopy on sintered pellets suggests something else: conductivity values do not show a strong dependence on the type of substituting cation. We observed that mechanical treatment of these materials causes a symmetry reduction from garnet to hydrogarnet structure. To understand the impact of this lower symmetric structure in detail and its effect on the Li ion conductivity, neutron powder diffraction and $^6$Li NMR were utilized. Despite the finding that, in some materials, disorder can be beneficial with respect to ionic conductivity, pulsed-field gradient NMR measurements of the long-range transport indicate a higher Li$^+$ diffusion barrier in the lower symmetric hydrogarnet structure. The symmetry reduction can be reversed back to the higher symmetric garnet structure by annealing at 1100 °C. This unintended phase transition and thus a reduction in conductivity is crucial for the processing of LLZO materials in the fabrication of all-solid state batteries