Atomic-Scale Mapping of Impurities in Partially Reduced Hollow TiO2 Nanowires

The incorporation of impurities during the chemical synthesis of nanomaterials is usually uncontrolled and rarely reported because of the formidable challenge in measuring trace amounts of often light elements with sub-nanometer spatial resolution. And yet, these foreign elements (introduced by doping, for example) influence functional properties. We demonstrate how the hydrothermal growth and a partial reduction reaction on hollow TiO₂ nanowires leads to the introduction of parts per millions of boron, sodium, and nitrogen. This doping explains the presence of oxygen vacancies and reduced Ti states at the surface, which enhance the functional properties of TiO₂. Our results were obtained on model metal oxide nanomaterials and they shed light on a general process that leads to the uncontrolled incorporation of trace impurities in TiO₂, thereby, having a strong effect on applications in energy-harvesting.     

Rheological properties of suspensions of polyethylene-coated aluminum nanoparticles

Ultrafine aluminum powder was identified as very promising fuels for novel energetic materials formulations. However, the large specific surface area of this powder facilitates its oxidation and greatly reduces its shelf life. Therefore, different coating processes were proposed to solve this problem. The rheology of viscous suspensions of nanoparticles still remains poorly understood and the effect of the coating of such particles on the flow behavior is even more difficult to assess. We have studied the rheology of ultrafine aluminum suspensions in three low molecular weight polymers of different viscosities: a hydroxy-terminated polybutadiene, a polypropylene glycol, and a polysiloxane. The nanosize aluminum powder was previously coated by a thin layer of high-density polyethylene using an in situ polymerization process. The rheological characterization of the suspensions was conducted by the means of steady and oscillatory shear flow measurements for noncoated and coated particles. The effect of the coating process on the rheology of the suspensions is discussed in terms of the interactions between the particles and the suspending fluids.     

Noise reduction efforts for the ALS infrared beamlines

The quality of infrared microscopy and spectroscopy data collected at synchrotron based sources is strongly dependent on signal-to-noise. We have successfully identified and suppressed several noise sources affecting beamlines 1.4.2, 1.4.3, and 1.4.4 at the advanced light source (ALS), resulting in a significant increase in the quality of FTIR spectra obtained. In this paper, we present our methods of noise source analysis, the negative effect of noise on the infrared beam quality, and the techniques used to reduce the noise. These include reducing the phase noise in the storage ring radio-frequency (RF) system, installing an active mirror feedback system, analyzing and changing physical mounts to better isolate portions of the beamline optics from low-frequency environmental noise, and modifying the input signals to the main ALS RF system. We also discuss the relationship between electron beam energy oscillations at a point of dispersion and infrared beamline noise.     

Multiscale NMR investigations of two anatomically contrasted genotypes of sorghum under watered conditions and during drought stress

Today, in the presence of global warming, understanding how plants respond to drought stress is essential to meet the challenge of developing new cultivars and new irrigation strategies, consistent with the maintenance of crop productivity. In this context, the study of the relation between plants and water is of central interest for modeling their responses to biotic and abiotic constraints. Paradoxically, there are very few direct and noninvasive methods to quantify and measure the level and the flow of water in plants. The present work aims to develop a noninvasive methodology for living plant based on nuclear magnetic resonance (NMR) at low magnetic field and imaging (MRI) to tackle the issue of water quantity in plants. For this purpose, a portable NMR device measuring the signal level at 8 mT was built. This instrument addresses specific challenges such as miniaturization, accessibility, and overheating in order to maintain the plant intact of time over long period. Time dependence of the water content in sorghum plants is reported under abiotic stress as well as the fraction of transpirable soil water and the photosynthesis activity through the leaves. At high magnetic field (9.4 T), T2 maps were acquired on the same sorghum plants at two time points. The combination of these approaches allows us to identify ecophysiological biomarkers of drought stress. One particular interesting result concerns the spatial distribution of water in two anatomically contrasted sorghum genotypes.     

Chemistry Platform for the Ultrafast Continuous Synthesis of High-Quality III–V Quantum Dots

A chemistry platform for the fast continuous synthesis of III–V quantum dots is demonstrated. III-nitride QDs are prepared by using short residence times (less than 30 s) in a one-step continuous process with supercritical solvents. GaN QDs prepared via this route exhibit strong UV photoluminescence with a structuring of the emission signal at low temperature (5 K), confirming their high quality. An example of metal site substitution is given with the synthesis of In_xGa_1-xN solid solution. A continuous bandgap shift towards lower energies is demonstrated when increasing the indium content with strong photoluminescence signals from UV to visible. The chemistry platform proposed could be easily extrapolated to binary and ternary III phosphides or arsenides with the homologous V source.     

On maximizing the profit of a satellite launcher: Selecting and scheduling tasks with time windows and setups

At regular times, a satellite launcher company has to plan the use of its launcher to get the maximum profit. In a more formal way, the problem consists of selecting and scheduling a subset of unit-length jobs constrained by capacitated time slots so that the overall cost is a minimum. The data associated with each job are its weight, its time-window and its expected gain when it is performed. With each time slot are associated a setup cost and a capacity. The setup cost of a time slot is due when this time-slot is used to perform at least one job. Moreover the total weight of all jobs scheduled within a time slot is at most the time slot capacity. We first show that the general problem is hard and provide some easy special cases. We then propose a first dynamic-programming polynomial-time algorithm for the special case with unit weights. A second and more efficient dynamic programming algorithm is also provided for the special case of unit weights and agreeable time windows. This last algorithm is finally improved for the special case of equal gains.     

Low-Flammable Parahydrogen-Polarized MRI Contrast Agents

Many MRI contrast agents formed with the parahydrogen-induced polarization (PHIP) technique exhibit biocompatible profiles. In the context of respiratory imaging with inhalable molecular contrast agents, the development of nonflammable contrast agents would nonetheless be highly beneficial for the biomedical translation of this sensitive, high-throughput and affordable hyperpolarization technique. To this end, we assess the hydrogenation kinetics, the polarization levels and the lifetimes of PHIP hyperpolarized products (acids, ethers and esters) at various degrees of fluorine substitution. The results highlight important trends as a function of molecular structure that are instrumental for the design of new, safe contrast agents for in vivo imaging applications of the PHIP technique, with an emphasis on the highly volatile group of ethers used as inhalable anesthetics.