Synthesis of Highly Luminescent SnO2 Nanocrystals: Analysis of their Defect‐Related Photoluminescence Using Polyoxometalates as Quenchers

Colloidal semiconductor nanocrystals (NCs), called quantum dots (QDs), have been intensively studied because of their excellent photoluminescence (PL) quantum yields. However, commercial QDs such as CdSe and InP contain toxic or expensive rare elements, limiting their sustainable use. This study focuses on nontoxic, stable, and cheap tin oxides, and synthesized luminescent SnO₂ NCs of ≈2 nm in size by a heating‐up method. Tin precursors and diols in a high‐boiling point solvent with oleylamine as the surfactant are heated at 240 °C. SnO₂ NCs show defect‐related photoluminescence at 400–460 nm by excitation at 370 nm, achieving a high quantum yield of more than 60%. The PL intensity is stable even when the NCs are stored in atmospheric air at room temperature for over 1 year. The defect‐related emissions of the SnO₂ NCs are studied using polyoxometalates (POMs) as the PL quencher. POMs efficiently quench the PL emissions by extracting excited electrons from the conduction band and shallow surface defects. The results reveal that PL emissions from SnO₂ NCs are associated with radiative charge recombination via shallow defect levels on the surface and in the bulk, demonstrating the effectiveness of the PL quenching technique using POMs in studying the PL emission mechanism in QDs.     

A dual–polarimetric approach to earthquake damage assessment

In this study, a novel physical approach is proposed to detect damages due to earthquakes using dual polarimetric (DP) coherent Synthetic Aperture Radar (SAR) imagery. An optimization method, aimed at enhancing scattering basis differences between measurements collected before and after the event, is designed exploiting Lagrange optimization of the difference between two polarimetric covariance matrices. A meaningful showcase is presented to demonstrate the soundness of the proposed approach that consists of processing Sentinel–1 C–band scenes related to 2016 Central Italy Earthquake. The proposed approach, which is contrasted with the conventional coherence based single– and dual–polarization approaches, results in the best sensitivity to damages.     

Multi-agent Rapidly-exploring Pseudo-random Tree

Real-time motion planning and control for groups of heterogeneous and under-actuated robots subject to disturbances and uncertainties in cluttered constrained environments is the key problem addressed in this paper. Here we present the Multi-agent Rapidly-exploring Pseudo-random Tree (MRPT), a novel technique based on a classical Probabilistic Road Map (PRM) algorithm for application in robot team cooperation. Our main contribution lies in the proposal of an extension of a probabilistic approach to be used as a deterministic planner in distributed complex multi-agent systems, keeping the main advantages of PRM strategies like simplicity, fast convergence, and probabilistic completeness. Our methodology is fully distributed, addressing missions with multi-robot teams represented by high nonlinear models and a great number of Degrees of Freedom (DoFs), endowing each agent with the ability of coordinating its own movement with other agents while avoiding collisions with obstacles. The inference of the entire team’s behavior at each time instant by each individual agent is the main improvement of our method. This scheme, which is behavioral in nature, also makes the system less susceptible to failures due to intensive traffic communication among robots. We evaluate the time complexity of our method and show its applicability in planning and executing search and rescue missions for a group of robots in S E3 outdoor scenarios and present both simulated and real-world results.     

The Effect of Aniline Hydrochloride Hydrotrope on the Phase Behavior of SDS/Water System

The aim of this work was to determine the detailed phase behavior of the sodium dodecyl sulfate/aniline hydrochloride/water system as a function of concentration of sodium dodecyl sulfate (SDS), aniline hydrochloride (AHC) to sodium dodecyl sulfate molar ratio (R = [AHC]/[SDS]) and temperature. Phase behavior information was obtained via polarizing microscopy, differential scanning calorimetry (DSC), cryo-scanning electron microscopy (Cryo-SEM) and oscillatory linear rheological measurements with good agreement among these techniques. It is well known that SDS in water forms spherical micelles at concentrations lower than 40 wt% and temperatures above its Krafft temperature (T _k = 16–21 °C). In this region, the SDS/water system exhibits Newtonian rheological behavior, which is characteristic of spherical micellar solutions. The addition of the hydrotrope, aniline hydrochloride, to SDS aqueous solutions produces a viscosity increase in this system as R augments, and a maximum of about five orders of magnitude was found at R = 0.47 for 5 wt% SDS at 20 °C. Moreover, the system shows a transition from viscous to strong viscoelastic behavior. These changes in the rheological behavior are produced by the transitions from sphere to rodlike micelles, which are induced by the hydrophobicity of AHC causing it to be absorbed into the core and the hydrophilic interface of the micelles, which screens the repulsions between the charged head groups.     

GC-MS and 13C NMR Investigation of Lead Zirconate Titanate Precursor Sols for Fiber Preparation

Different macroscopic properties of PZT fibers have been obtained when using acetic acid and methacrylic acid to modify the PZT precursor. In order to clarify the role of the acids the molecular structure of the acidified PZT precursors was investigated and compared by gas chromatography-mass spectrometry, Fourier transform infrared, ¹³C nuclear magnetic resonance (NMR) spectroscopy (solution and solid state ¹³C NMR) and the reason for obtaining long PZT fibers is discussed. The results indicate that when methacrylic acid was used, long gel and ceramic fibers have been obtained because strongly co-ordinating carboxylate groups of methacrylic acid were formed. Linear chains, like those of methacrylic acid propyl ester and methacrylic acetate, have been formed in the PZT precursor sols. In addition, after heat treatment the polymer decomposed quickly so that pure perovskite could be obtained at low temperature in the PZT fibers. When acetic acid was used short fibers were obtained. Acetic acid may act as chelate agent to form oxo acetate in the precursors; this oxo acetate nature also resulted in PZT fibers drawing. However, the longest gel and ceramic fibers have been prepared from precursors with methacrylic acid.