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Abstract

A room-temperature hydrogen gas (H2) sensor was successfully fabricated by dispersion of palladium nanoparticles (Pd NPs) on graphene sheets (GRs) (hereafter referred to as “Pd NPs/GRs”). GRs and Pd NPs were synthesized by chemical vapor deposition technique and by polyol process, respectively. A colloidal solution of Pd NPs with an average diameter of 11 nm was then dispersed onto the GRs by spin coating technique. The density of dispersed Pd NPs on GRs was controlled by varying the volume of the dispersed solution within the range of 50 – 150 μL. The fabricated Pd NPs/GRs sensors exhibited a high sensitivity for H2 gas with a concentration of 1500 – 6000 ppm at room temperature. Upon H2 exposure, the Pd NPs/GRs sensors showed an increase in electrical resistance, which could easily be measured. The relationship between sensor response and H2 concentration is in correspondence with the Langmuir adsorption model. The H2 detection limit is estimated to be 1 ppm. The results demonstrate that the Pd NPs/GRs sensor is an easily fabricated, but very effective means for room-temperature detection of H2at ppm level.

Abstract

Novel nonlinear optical semi-organic, potassium phthalate di lithium borate (KPDLiB) single crystals were successfully grown by the slow solvent evaporation technique. Good crystalline nature and an orthorhombic structure were confirmed by powder X-ray diffraction and single crystal X-ray diffraction studies. The functional groups of KPDLiB were identified using FT-IR spectrum recorded in the range of 4000 cm −1 to 450 cm−1. UV-Vis spectrum showed transmitting ability of the crystals in the entire visible region. The photoluminescence spectrum exhibited good fluorescence emission in a visible region at 384 nm, 416 nm and 578 nm. The second harmonic generation efficiency of the grown crystal was evaluated from Kurtz powder technique.

Abstract

Dilute nitride and antimony GaNAsSb alloy can be considered as an alloy formed by adding N and Sb atoms into the host material GaAs. Under this condition, its band gap energy depending on pressure can be divided into two regions. In the low pressure range, the band gap energy is due to two factors. One is the coupling interaction between the N level and the Γ conduction band minimum (CBM) of GaAs. The other one is the coupling interaction between the Sb level and the Γ valence band maximum (VBM) of GaAs. In the high pressure range, the band gap energy depends also on two factors. One is the coupling interaction between the N level and the X CBM of GaAs. The other one is the coupling interaction between the Sb level and the Γ VBM of GaAs. In addition, it has been found that the energy difference between the Γ CBM and the X CBM in GaNAsSb is larger than that in GaAs. It is due to two factors. One is the coupling interaction between the N level and the Γ CBM of GaAs. The other is the coupling interaction between the N level and the X CBM of GaAs.

Abstract

The structural, electronic and optical properties of (AlSb)m/(GaSb)n (m-n: 1-1, 2-2, 1-3 and 3-1) superlattices are investigated within the density functional theory (DFT) by using the last version of the first principles full potential linear muffin tin orbital method (FP-LMTO) as implemented in LmtART 7.0 code. The exchange and correlation potential is treated by the local density approximation (LDA) for the total energy calculations. Our calculations of the band structure show that the superlattices (n ≠ 1) have a direct band gap Γ-Γ. The optical constants, including the dielectric function ∈ (w), the refractive index n(w) and the reflectivity R(w) are calculated and discussed.

Buildings and Environment

Abstract

On Sunday, June 19, 2016, a Space Acceleration Measurement System triaxial sensor head flew on a suborbital flight aboard Blue Origin's New Shepard vehicle to collect precision vibratory accelerometry data. The Space Acceleration Measurement System (SAMS) sensor head was mounted inside of a Blue Origin single payload locker inside of the crew capsule. This paper describes the configuration, capture, and analysis of the SAMS data from this flight along with other, related flight log information provided by Blue Origin. Three overlapping periods during the flight were identified and characterized to provide future users of the platform with insight into options that may prove suitable for their research needs. Average accelerations in the Post-Separation Period were consistent with other low-g research platforms, while the shorter Microgravity Period in the middle of the flight showed ultra-quiet vibratory acceleration environments. Researchers can consider this microgravity quality versus time a tradeoff in their experimental designs.

Abstract

The Cosmic Ray Exposure Sequencing Science (CRESS) payload system was a proof of concept experiment to assess the genomic impact of space radiation on seeds. CRESS was designed as a secondary payload for the December 2016 high-altitude, long-duration south polar balloon flight carrying the Boron and Carbon Cosmic Rays in the Upper Stratosphere (BACCUS) experiment. Investigation of the biological effects of Galactic Cosmic Radiation (GCR), particularly those of ions with High-Z and Energy (HZE), was of interest due to the genomic damage this type of radiation inflicts. The biological effects of radiation above Antarctica (ANT) were studied using Arabidopsis thaliana seeds and compared to a simulation of GCR at Brookhaven National Laboratory (BNL) and to laboratory control seeds. The CRESS payload was broadly designed to 1U CubeSat specifications (10 cm × 10 cm × 10 cm, ≤1.33 kg), maintained 1 atm internal pressure, and carried an internal cargo of 580,000 seeds and twelve CR-39 Solid-State Nuclear Track Detectors (SSNTDs). Exposed BNL and ANT M0 seeds showed significantly reduced germination rates and elevated somatic mutation rates when compared to non-irradiated controls, with the BNL mutation rate also being higher than that of ANT. Genomic DNA from plants presenting distinct aberrant phenotypes was evaluated with whole-genome sequencing using PacBio SMRT technology, which revealed an array of structural genome variants in the M0 and M1 plants. This study was the first whole-genome characterization of space-irradiated seeds and demonstrated both the efficiency and efficacy of Antarctic long-duration balloons for the study of space radiation effects on eukaryote genomes.

Abstract

This work investigates the suitability of membrane aerated biological reactors (MABRs) for biological treatment of a space-based waste stream consisting of urine, hygiene/grey water, and humidity condensate within an overall water recycling system. Water represents a critical limiting factor for human habitation and travel within space; thus, water recycling systems are essential. Biological treatment of wastewater provides a more efficient sustainable means of stabilizing the waste stream within water recycling system architectures in comparison to current chemical stabilization processes that utilize harsh chemicals, which represent both a hazardous and an unsustainable approach. To assess the capabilities of MABRs for providing microgravity compatible biological treatment and verify long duration operation and integration with desalination processes, two full-scale MABR systems were challenged with various loading rates and operational scenarios during sustained operation for over 1 year. The MABRs were able to maintain 196 g-C/m3-d and 194 g-N/m3-d volumetric conversion rates. Additionally the systems were able to handle intermittent loading and recover rapidly from system hibernation periods of up to 27 days. Overall, the use of MABRs within a wastewater treatment system architecture provides several potential benefits including minimizing the use of toxic chemical pretreatment solutions and providing an effluent solution that is easier to desalinate and dewater.

Abstract

International Space Station crewmembers experience microgravity, resulting in musculoskeletal losses. It remains unclear how much mechanical loading during disuse is sufficient to mitigate disuse-induced bone loss. We examined 75 minutes of weight-bearing per day on disuse-induced bone loss during hindlimb unloading (HU). Female C57BL/6J mice, 17 weeks (n=10/group), were exposed to HU for 28 days or were ambulatory controls (CC). Half of the HU animals were continuously unloaded while the remainder were removed from tail suspension for ~75 min/day for cage activity weight-bearing (HU+WB). HU and HU+WB led to total body mass and bone mineral density loss. HU+WB mitigated HU-induced losses in total body fat and lean mass and, in the distal femur, prevented losses in μCT measures of cancellous bone volume and microarchitecture. These findings support the robust impact of short durations of normal loading on preventing or mitigating HU-induced bone loss.

Abstract

Thin liquid films on isothermal substrates, where the film is flat and parallel to the substrate, succumb to thermocapillary instabilities and rupture, forming local hot-spots. These long wavelength instabilities are specific to aspect ratios where the liquid film mean thickness is several orders of magnitude less than the substrate characteristic dimension. Absent stabilizing gravitational acceleration, the growth rate of thermocapillary instabilities is further intensified, driving the film to rupture even earlier.

Numerical simulations of zero gravity dynamics of Newtonian liquid films on a solid, horizontal, isothermal substrate were conducted. When the solid, isothermal substrate was replaced with a one-dimensionally porous substrate, was fully saturated with the same fluid as the liquid film, and was deep enough to accommodate all the liquid on it, we observed that destabilizing spatial modes were damped thereby preventing rupture and prolonging the film lifespan. This nonlinear evolution was visualized and quantified using recurrence plots.