Shape-programmed 3D printed swimming microtori for the transport of passive and active agents.

Through billions of years of evolution, microorganisms mastered unique swimming behaviors to thrive in complex fluid environments. Limitations in nanofabrication have thus far hindered the ability to design and program synthetic swimmers with the same abilities. Here we encode multi-behavioral responses in microscopic self-propelled tori using nanoscale 3D printing. We show experimentally and theoretically that the tori continuously transition between two primary swimming modes in response to a magnetic field. The tori also manipulated and transported other artificial swimmers, bimetallic nanorods, as well as passive colloidal particles. In the first behavioral mode, the tori accumulated and transported nanorods; in the second mode, nanorods aligned along the tori's self-generated streamlines. Our results indicate that such shape-programmed microswimmers have a potential to manipulate biological active matter, e.g. bacteria or cells.

Real-Time Observation of Carbon Oxidation by Driven Motion of Catalytic Ceria Nanoparticles within Low Pressure Oxygen.

Carbon particulate matter (PM) is an undesirable aerosol pollutant formed from combustors such as power plants, refineries, and engines. The most common and effective method of mitigating PM emission is the capture of particulates using a filter, before particles are released into the atmosphere. In order to develop and improve advanced filtering materials, a better understanding is required of their chemical and mechanical behavior. We report on a novel phenomenon on the mobility and oxidation behavior of catalytic iron doped ceria nanoparticles in contact with mobile carbon black nanoparticles. The process is recorded by real time imaging within an environmental transmission electron microscope. In contrast to observations in previous studies, the separated ceria nanoparticles are found to actively move on the substrate and consume the connecting carbon particles one-by-one. The velocity of particle motion is correlated to the reaction temperature and oxygen pressure, both determining the reaction rate. Modeling using the Density Functional Theory suggests this motion is driven by the chemical bonding between the surface oxygen of the catalyst and the graphite layers of carbon black, initiated through the Van der Waals force between two types of nanoparticles.

Development of an improved data analysis approach for combined laser extinction and two-angle elastic light scattering diagnostics of soot aggregates.

An improved data analysis approach has been developed for the combined laser extinction and two-angle elastic light scattering diagnostics to relate the various measured optical cross sections to soot aggregate properties. The performance of the proposed approach is assessed using the comprehensive dataset of Santoro ethylene-air co-flow diffusion flame. Compared to previously reported studies, the proposed approach can be applied to a wider range of soot sources by removing the assumption made to the scattering regime or moment ratio of aggregate size distribution. The proposed approach also considers the contribution of scattering to extinction in determining the soot volume fraction, and this contribution is shown to increase as soot aggregate size becomes larger. The sensitivity of the calculation to the assumed parameters of the approach is examined and discussed. The mean radius of gyration of soot aggregates and the ratio of scattering intensities at the two measurement angles are shown to be independent of soot refractive index and are therefore recommended for soot model validation purposes.

Optical absorption measurements of hydrogen chloride at high temperature and high concentration in the presence of water using a tunable diode laser system for application in pyrohydrolysis non-ferrous industrial process control.

A tunable diode laser (TDL) was used to measure hydrogen chloride (HCl) spectra at 5747 cm(-1) (1.74 µm) and temperatures of 25-950 °C in a quartz cell. The purpose was to evaluate the capability of monitoring HCl concentration under pyrohydrolysis conditions using a near-infrared (NIR) laser. These conditions are characterized by 20-40% HCl, 2-40% H2O, and the presence of metal chloride vapors at temperatures of 600-1000 °C. Spectral peak area measurements of HCl-N2 mixtures at atmospheric pressure and a path length of 8.1 cm showed linear absorption behavior between concentrations of 5-95% and temperatures of 25-950 °C. Results from the addition of 2-40% water (H2O) indicate that the HCl peak area relationships are not affected for temperatures of 350-950 °C. Evaporating NiCl2 within the cell did not show spectral interference effects with HCl between 650 and 850 °C. The results from this work indicate that a near-infrared optical sensor is capable of measuring high HCl concentrations at high temperatures in the presence of high H2O content during pyrohydrolysis process conditions.

Molecular characterization of organic content of soot along the centerline of a coflow diffusion flame.

High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (λ = 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200-600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initial mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen abstraction-carbon addition mechanism currently considered in fundamental models of soot formation.

In situ optical absorption mercury continuous emission monitor.

This paper reports the development of an in situ continuous emission monitor (CEM) for measuring elemental mercury (Hg(0)) concentration in the exhaust stream of coal-fired power plants. The instrument is based on the ultraviolet atomic absorption of a mercury lamp emission line by elemental mercury and a light-emitting diode (LED) background correction system. This approach allows an in situ measurement since the absorption of other species such as SO(2) can be removed to monitor the Hg(0) contribution only. Proof of concept was established through a laboratory-based investigation, and a limit of detection, [Hg(0)](min), of 2 microg/m(3) was measured for a 1-min averaged sample and an absorption path length of 49 cm. [Hg(0)](min) is anticipated to be better than 0.2 microg/m(3) across a 7 m diameter stack. Finally, the apparatus was field-tested in a 230 MW coal-fired power plant. The operability of the measurement in real conditions was demonstrated, leading to the first Hg(0) concentration values recorded by the in situ CEM. Comparison with an accepted standard method is required for validation.

In situ combustion measurements of CO, H2O, and temperature with a 1.58-microm diode laser and two-tone frequency modulation.

An optical near-infrared process sensor for electric are furnace pollution control and energy efficiency is proposed. A near-IR tunable diode laser has performed simultaneous in situ measurements of CO (1,577.96 nm), H2O (1,577.8 and 1,578.1 nm), and temperature in the exhaust gas region above a laboratory burner fueled with methane and propane. The applicable range of conditions tested is representative of those found in a commercial electric arc furnace and includes temperatures from 1,250 to 1,750 K, CO concentrations from 0 to 10%, and H20 concentrations from 3 to 27%. Two-tone frequency modulation was used to increase the detection sensitivity. An analysis of the method's accuracy has been conducted with 209 calibration and 105 unique test burner setpoints. Based on the standard deviation of differences between optical predictions and independently measured values, the minimum accuracy of the technique has been estimated as 36 K for temperature, 0.5% for CO, and 3% for H2O for all 105 test data points. This accuracy is sufficient for electric arc furnace control. The sensor's ability to nonintrusively measure CO and temperature in real time will allow for improved process control in this application.