Nano-indentation study of dislocation evolution in GaN-based laser diodes.

The slip systems and motion behavior of dislocations induced by nano-indentation technique in GaN-based LDs were investigated. Dislocations with burgers vector of b = 1/3 <11 2 ¯ 3> were introduced on either {11 2 ¯ 2} <11 2 ¯ 3>, or {1 1 ¯ 01} <11 2 ¯ 3> pyramidal slip systems in the upper p-GaN layer. Besides, {0001} <11 2 ¯ 0> basal slip system was also activated. The AlGaN/InGaN multi-layers in device can provide mismatch stresses to prevent dislocations from slipping through. It was observed that the density of dislocations induced by the indenter significantly decreased from the upper to the lower regions of the multi-layers. The a + c dislocations on pyramidal slip planes were mostly blocked by the strained layers.

Insights into the Profile of the Human Expiratory Microbiota and Its Associations with Indoor Microbiotas.

Microorganisms residing in the human respiratory tract can be exhaled, and they constitute a part of environmental microbiotas. However, the expiratory microbiota community and its associations with environmental microbiotas remain poorly understood. Here, expiratory bacteria and fungi and the corresponding microbiotas from the living environments were characterized by DNA amplicon sequencing of residents' exhaled breath condensate (EBC) and environmental samples collected from 14 residences in Nanjing, China. The microbiotas of EBC samples, with a substantial heterogeneity, were found to be as diverse as those of skin, floor dust, and airborne microbiotas. Model fitting results demonstrated the role of stochastic processes in the assembly of the expiratory microbiota. Using a fast expectation-maximization algorithm, microbial community analysis revealed that expiratory microbiotas were differentially associated with other types of microbiotas in a type-dependent and residence-specific manner. Importantly, the expiratory bacteria showed a composition similarity with airborne bacteria in the bathroom and kitchen environments with an average of 12.60%, while the expiratory fungi showed a 53.99% composition similarity with the floor dust fungi. These differential patterns indicate different relationships between expiratory microbiotas and the airborne microbiotas and floor dust microbiotas. The results here illustrated for the first time the associations between expiratory microbiotas and indoor microbiotas, showing a potential microbial exchange between the respiratory tract and indoor environment. Thus, improved hygiene and ventilation practices can be implemented to optimize the indoor microbial exposome, especially in indoor bathrooms and kitchens.

Transmission electron microscopy sample preparation method for micrometer-sized powder particles using focused ion beam.

A TEM sample preparation technique for micrometer-sized powder particles in the 1-10 µm size range is proposed, using a focused ion beam (FIB) system. It is useful for characterizing elemental distributions across an entire cross-section of a particle. It is a simple and universal method without using any embedding agent, enabling the powder particles with different size, shape or orientation to be easily selected based on the SEM observations. The suitable particle is covered with Pt coating layers through an ion-beam-assisted deposition. The Pt coating layers provide sufficient support for the TEM lamella. A small piece of tungsten needle is used as a support under the particle by taking a series of operations using a micromanipulator. The particle can be precisely thinned by the ion beam to be suitable for both TEM observation and EDX elemental mapping. This novel technique reduces the TEM sample preparation time to a few hours, allowing much higher efficiency compared to complicated and time-consuming embedding methods.

Abundance and composition of airborne archaea during springtime mixed dust and haze periods in Beijing, China.

Archaea have an important role in the elemental biogeochemical cycle and human health. However, characteristics of airborne archaea affected by anthropogenic and natural processes are unclear. In this study, we investigated the abundance, structures, influencing factors and assembly processes of the archaeal communities in the air samples collected from Beijing in springtime using quantitative polymerase chain reaction (qPCR), high-throughput sequencing technology and statistical analysis. The concentrations of airborne archaea ranged from 101 to 103 copies m-3 (455 ± 211 copies m-3), accounting for 0.67% of the total prokaryote (sum of archaea and bacteria). An increase in airborne archaea was seen when the air quality shifted from clean to slightly polluted conditions. Sandstorm dust imported a large number of archaea to the local atmosphere. Euryarchaeota, Thaumarchaeota and Crenarchaeota were the dominant phyla, revealing the primary role of soil in releasing archaea to the ambient environment. Dispersal-related neutral processes play an important role in shaping the structure of airborne archaeal assembly. Of all phyla, methanogenic Euryarchaeota were most abundant in the air parcels come from the south of Beijing. Air masses from the west of Beijing, which brought sandstorm to Beijing, carried large amounts of ammonia oxidizing archaea Nitrososphaera. The results demonstrate the importance of air mass sources and local weather conditions in shaping the local airborne archaea community.

Indoor air filtration could lead to increased airborne endotoxin levels.

Stand-alone portable air purifiers (APs) have become an increasingly popular method of controlling individual inhalation exposure. Exposure to bacterial endotoxins has a causative role in respiratory inhalation health. Here, we studied the changes in endotoxin levels in indoor air before and after purification by a portable AP equipped with HEPA (high-efficiency particulate air) filters. An increase in endotoxins was observed when a previously used AP was turned on to clean the air. Replacing the HEPA filters in the AP helped to mitigate the increase in endotoxins of larger sizes but not endotoxins of smaller sizes. Consequently, the use of APs could lead to increased endotoxin deposition in airways, especially in the alveolar region. The endotoxin concentrations on the HEPA filters were well correlated with the free DNA concentrations on the HEPA filters. This correlation indicates that the disrupted bacteria, which released free DNA, could also release endotoxins, thus making HEPA filters a source of indoor airborne endotoxins. Our results illustrate a potential endotoxin inhalation risk associated with HEPA-APs as an air cleaning strategy and highlight the importance of composition-specific air cleaning while reducing the particle number/mass.

Characteristics of biological particulate matters at urban and rural sites in the North China Plain.

Depending on their concentrations, sizes, and types, particulate matters of biological origins (bioPM) significantly affect human health. However, for different air environments, they are not well characterized and can vary considerably. As an example, we investigated the bioPM differences at an urban (Beijing) site and a rural (Wangdu) site in the North China Plain (NCP) using an online monitoring instrument, an ultraviolet aerodynamic particle sizer (UV-APS), the limulus amebocyte lysate (LAL) assay, and a high-throughput sequencing method. Generally, lower concentrations of viable bioPM (hourly mean: 1.3 × 103 ±â€¯1.6 × 103 m-3) and endotoxin (0.66 ±â€¯0.16 EU/m3) in Beijing were observed compared to viable bioPM (0.79 × 105 ±â€¯1.4 × 105 m-3) and endotoxin (15.1 ±â€¯23.96 EU/m3) at the Wangdu site. The percentage of viable bioPM number concentration in the total PM was 3.1% in Beijing and 6.4% in Wangdu. Approximately 80% of viable bioPM was found to be in the range from 1 to 2.5 µm. Nevertheless, the size distribution patterns for viable bioPM at the Beijing and Wangdu sites differed and were affected by PM pollution, leading to distinct lung deposition profiles. Moreover, the distinct diurnal variations in viable bioPM on clean days were dimmed by the PM pollution at both sites. Distinct bacterial community structures were found in the air from the Beijing and Wangdu sites. The bacterial community in urban Beijing was dominated by genus Lactococcus (49.5%) and Pseudomonas (15.1%), while the rural Wangdu site was dominated by Enterococcus (65%) and Paenibacillus (10%). Human-derived genera, including Myroides, Streptococcus, Propionibacterium, Dietzia, Helcococcus, and Facklamia, were higher in Beijing, suggesting bacterial emission from humans in the urban air environment. Our results show that different air harbors different biological species, and people residing in different environments thus could have very different biological particle exposure.

Culturability, metabolic activity and composition of ambient bacterial aerosols in a surrogate lung fluid.

Interactions of particulate matter (PM) and respiratory tract play a crucial role in PM-related respiratory diseases. The majority of the work focuses on the oxidative stress induced by reactions between PM-borne redox-active components and lung lining fluid (LLF). The effects of PM-borne biological components are largely unknown. Of all PM-borne biologicals, bacteria, as living microorganisms, are closely related with inflammatory immune responses. However, its inhalation risk is usually determined without considering the respiratory physiological conditions. In this study, a surrogate lung fluid (SLF) with four typical antioxidants was applied to characterize the ambient bacteria, including concentrations of total bacteria/viable bacteria/culturable bacteria, metabolic activity, bacteria-derived endotoxin, as well as the community structure. Comparing to those determined by SLF, we find that use of PBS leads to an underestimation of the bacterial culturability and metabolic activity. No effect was seen regarding the number of total bacteria and viable bacteria (with intact membrane). Population structure change was seen for bacteria cultured from SLF-collected samples, when compared to that from PBS. Spore-forming bacteria, e.g., genus Bacillus, were found to be easily recovered with SLF. This implies that use of PBS could underestimate the bacteria inhalation risk, especially those bacterial endospores. Our work highlights the necessity to consider the respiratory airway environment when evaluating microbial inhalation risk.

Reduced graphene oxide/Mn3O4 nanohybrid for high-rate pseduocapacitive electrodes.

Nanostructure Mn3O4 is a promising pseudocapacitive electrode material due to its low cost, environmental compatibility, and intrinsically high capacity. However, the poor electrical conductivity and low accessible active sites limit its performance. We report that one-dimensional (1D) nanoscale Mn3O4 has been coupled with reduced graphene oxide (RGO) to fabricate RGO/Mn3O4 nanohybrid (MORGO) as a pseudocapacitive electrode material with high capacitance. The selective reduction of graphene oxide (GO) in Mn3O4/graphene oxide (MOGO) to reduced graphene oxide (RGO) while sustaining the unchanged oxidation state of manganese is the key to obtain MORGO. Specific surface area of MORGO is 14 times higher than pure Mn3O4, and the charge transfer resistance decreases 3.2 times. These enhanced properties lead to excellent specific capacitance of 538 F g-1 at the current density of 0.1 A g-1, and of 472 F g-1 at 10 A g-1 in 1 M Na2SO4 aqueous electrolyte. The capacitance retained 89% after 2000 cycles, demonstrating its excellent long-term cycling stability.

Nitric oxide releasing materials triggered by near-infrared excitation through tissue filters.

Novel materials for the phototherapeutic release of the bioregulator nitric oxide (nitrogen monoxide) are described. Also reported is a method for scanning these materials with a focused NIR beam to induce photouncaging while minimizing damage from local heating. The new materials consist of poly(dimethylsiloxane) composites with near-infrared-to-visible upconverting nanoparticles (UCNPs) that are cast into a biocompatible polymer disk (PD). These PDs are then impregnated with the photochemical nitric oxide precursor Roussin's black salt (RBS) to give UCNP_RBS_PD devices that generate NO when irradiated with 980 nm light. When the UCNP_RBS_PD composites were irradiated with NIR light through filters composed of porcine tissue, physiologically relevant NO concentrations were released, thus demonstrating the potential of such devices for minimally invasive phototherapeutic applications.

Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters.

We report the controlled growth of highly ordered and well aligned one-dimensional tellurium nanostructure arrays via a one-step catalyst-free physical vapor deposition method. The density, size and fine structures of tellurium nanowires are systematically studied and optimized. Field emission measurement was performed to display notable dependence on nanostructure morphologies. The ordered nanowire array based field emitter has a turn-on field as low as 3.27 V µm(-1) and a higher field enhancement factor of 3270. Our finding offers the possibility of controlling the growth of tellurium nanowire arrays and opens up new means for their potential applications in electronic devices and displays.

Hydrothermal synthesis, structural characteristics, and enhanced photocatalysis of SnO(2)/alpha-Fe(2)O(3) semiconductor nanoheterostructures.

Branched SnO(2)/alpha-Fe(2)O(3) semiconductor nanoheterostructures (SNHs) of high purity were synthesized by a low-cost and environmentally friendly hydrothermal strategy, through crystallographic-oriented epitaxial growth of the SnO(2) nanorods onto the alpha-Fe(2)O(3) nanospindles and nanocubes, respectively. It was demonstrated that the SnO(2) nanorods would change their preferential growth direction on the varied alpha-Fe(2)O(3) precursors with distinct crystallographic surface, driven by decrease in the distortion energy induced by lattice mismatch at the interfaces. All of the prepared SNHs were of high purity, ascribing to the successful preinhibition of the SnO(2) homonucleation in the reaction system. Significantly, some of the SnO(2)/alpha-Fe(2)O(3) SNHs exhibited excellent visible light or UV photocatalytic abilities, remarkably superior to their alpha-Fe(2)O(3) precursors, mainly owing to the effective electron-hole separation at the SnO(2)/alpha-Fe(2)O(3) interfaces.

Enhanced photoluminescence of Eu(3+) induced by energy transfer from In(2)O(3) nano-crystals embedded in glassy matrix.

Eu(3+)-doped transparent glass ceramics containing In(2)O(3) nano-crystals were prepared by melt quenching and subsequent heating. X-ray diffraction analysis, transmission electron microscope observation, and photoluminescence excitation spectra demonstrated that In(2)O(3) nano-particles sized 3-6 nm homogenously distributed among the glass matrix. Under excitation of these nano-particles, Eu(3+) luminescence was found greatly enhanced due to the energy transfer from the oxygen-vacancy-related defects of In(2)O(3) to Eu(3+) ions. The Eu(3+) content dependent energy transfer efficiency was evaluated, and the value reached 67% for 1 mol% Eu(3+) doped glass ceramics. Low temperature emission spectra demonstrated that the Eu(3+) ions of the glass ceramic locate mainly in the glass matrix.