Normal Air Environment Research Articles

High-Performance pH Sensor Electrodes Based on a Hexagonal Pt Nanoparticle Array-Coated Nanoporous Alumina Membrane.

Porous anodic alumina membranes coated with Pt nanoparticles (PAAM/Pt) have been employed as pH sensor electrodes for H+ ion detection. The PAAM was designed using a two-step anodization process. Pt nanoparticles were then sputtered onto the membrane at different deposition times. The membrane’s morphological, chemical, and optical characteristics were carefully assessed following the fabrication stage using a variety of analytical techniques. The potential of the PAAM/Pt sensor electrode was investigated by measuring the potential using a simple potentiometric method. The effects of depositing Pt nanoparticles for 3–7 min on sensor electrode sensitivity were examined. The optimal potentiometric Nernstian response slope for the PAAM/Pt sensor electrode with 5 min Pt sputter coating is 56.31 mV/decade in the pH range of 3.0 to 10 at 293 K. Additionally, the PAAM/Pt sensor electrode’s stability and selectivity in various ions solutions were examined. The sensor electrode had a lifetime of more than six weeks and was kept in a normal air environment.

Influence of low vacuum condition on mechanical performance and microstructure of hardened cement paste at early age

• The mechanical performance of early-age paste after low vacuum exposure is evaluated. • The influence of low vacuum on phase composition and pore structure is analyzed. • The evolution of the mechanical performance of paste is explained from the perspective of multi-scale pore structure. To explore the influence of low vacuum on the mechanical performance and microstructure of cement-based materials at early age, the mechanical properties, phase composition and multi-scale pore structure of 7d-aged hardened cement pastes exposed to low vacuum and normal air environment were studied, and the relation between mechanical performance and microstructure was analyzed. The results show that low vacuum can significantly retard the strength growth of paste at early age, and lead to the decline of strength with exposure time increasing. Moreover, the mechanical performance of cement pastes in low vacuum condition was generally weaker than that under normal air environment. Furthermore, the number of gel pores decreased, while the most probable aperture and total porosity increased after low vacuum exposure, and more micron-scale macropores and millimeter-scale defects appeared. The multi-scale variation of pore structure is the dominating reason for the delayed development and degradation of mechanical performance under low vacuum environment. In addition, the phase composition of cement pastes did not change during low vacuum exposure, and the strength of pastes was highly correlated with the total amount of some key hydration products (e.g. C-S-H gel, ettringite, calcite et al.).

Chloride maximum phenomenon near the surface of cement paste induced by moisture evaporation and carbonation

Abundant studies of cyclic wetting–drying of concrete have suggested a “maximum phenomenon” by which chloride concentrations first increase with depth to a local maximum and then decrease at greater depths. This phenomenon may arise primarily because of carbonation, but may also be exacerbated by cyclic capillary suction and moisture evaporation during wetting–drying cycles. This paper investigates the mechanism responsible for the maximum phenomenon under conditions that exclude cyclic capillary suction. The results show that different chloride maxima form near the surface of all specimens under conditions of either accelerated carbonation or carbonation in normal air environment. A large amount of bound chloride is released when carbonation causes decomposition of Friedel’s salt and C–S–H gel, and the decrease in water content significantly increases the chloride concentration in the pore solution near the specimen surface. The resulting chloride concentration gradient drives free chloride diffusion from the surface to the interior, thereby reducing the actual chloride content near the exposed surface. More severe carbonation conditions increase the severity of the maximum phenomenon.

Sensing of low concentration of ammonia at room temperature by decorated multi-walled carbon nanotube: fabrication and characteristics

A chemical sensor based on multi-walled carbon nanotube (MWCNT) decorated with densely populated thiol-capped gold nanoparticles (AuNPs) with sizes smaller than 3 nm for sensing low concentrations of ammonia gas is reported. The functionalized MWCNTs, subsequently decorated with AuNPs following an easy fabrication route were exposed to NH3 gas at the room temperature and the electrical resistance of the sensor changed upon exposure. The sensor also partially recovered the initial state after sensing in the normal air environment (without any dry air or N2 gas purge). The gold nanoparticles decoration is found to enhance the sensitivity and selectivity of MWCNT towards NH3 gas under ambient conditions with a reduced response and recovery time. The material was structurally characterized by Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. Thermal stability of the sensor till 574 °C was demonstrated by TGA analysis. This papers describes how thiol-capped AuNPs are uniformly decorated on the outer walls of the MWCNTs with a separation of 2–3 nm making use of the ionic nature of Au and how this uniform distribution of AuNPs increases the active sites for absorption of NH3 gas molecules leading to sensing its low concentrations.

Sensorial and chemical changes in buffalo milk Kheer Mohan during storage

Kheer Mohan is an energy dense popular sweet of eastern Rajasthan. Similar to other traditional Indian dairy products, this product also has the problem of short shelf life. It has maximum shelf life of six days at room temperature. Present investigation was undertaken to check the suitability of different packaging methods viz. normal, vacuum and nitrogen packaging using nylon films for shelf life enhancement as well as to monitor changes in sensory attributes, pH, free fatty acid (FFA) content and microbial counts during its storage at 30±1 0 C. For storage period and packaging conditions, significant (p<0.01) difference in overall acceptability scores was observed. Packaging conditions and storage period had highly significant (p<0.01) decreasing effect on pH value during storage. Storage period showed highly significant (p<0.01) increasing effect on FFA values, whereas packaging condition had non-significant effect on the same. Both packaging and storage period had highly significant (p<0.01) increasing effect on SPC of Kheer Mohan. Vacuum packaging of Kheer Mohan samples was not feasible as it not only altered the shape of product but also made sugar syrup to squeeze out from the samples. Packaging of Kheer Mohan samples in nitrogen environment resulted in minimum 1.5 times increase in product shelf life (9 days) as compared to the product packed in normal air environment (6 days) at 30±1 0 C storage temperature.

Synthesis and luminescence characteristics of DHLA-capped PbSe quantum dots with biocompatibility

In this work, we report a facile aqueous route to prepare PbSe QDs with strong photoluminescent and near-infrared (NIR) emission using dihydrolipoic acid (DHLA) as the capping ligands. It was found that the synthesis parameters including the molar ratio of DHLA/Pb, the pH value and the reaction time have considerable influence on photoluminescent intensity (PL) of the PbSe QDs. The as-synthesized DHLA-capped PbSe QDs were characterized by high-resolution transmission electron microscopy (HRTEM), energy-dispersive analysis of X-ray (EDX) and X-ray diffraction (XRD), the results indicated that the QDs were about 8.0±0.2nm in size and had good monodisperse and a rock salt crystalline structure. Also, there was DHLA on the surface of QDs, which was confirmed by Fourier transform infrared (FT-IR) spectrometry. The PbSe QDs exhibited optimal PL intensity when Pb:Se:DHLA=1:0.6:1 in weak alkaline aqueous. The as-synthesized QDs kept highly PL intensities when stored in the dark in normal air environment during the period of 60days. In addition, the biocompatibility of these QDs was measured by hemolytic test, which indicated that DHLA-stabilized QDs are biocompatible. It is important for QDs as biomarkers in biological detection and diagnosis.

Active suppression of air refractive index fluctuation using a Fabry–Perot cavity and a piezoelectric volume actuator

Air refractive index fluctuation (Δn(air)) is one of the largest uncertainty sources in precision interferometry systems that require a resolution of nanometer order or less. We introduce a method for the active suppression of Δn(air) inside a normal air-environment chamber using a Fabry-Perot cavity and a piezoelectric volume actuator. The temporal air refractive index (n(air)) at a local point is maintained constant with an expanded uncertainty of ~4.2 × 10(-9) (k = 2), a sufficiently low uncertainty for precise measurements unaffected by Δn(air) to be made inside a chamber.

Oxygenation prevents sudden death in seizure-prone mice.

Sudden unexpected death in epilepsy (SUDEP) is a significant health problem for some with epilepsy, but no preventive therapy has been developed for high-risk patients. Sudden death in mice, after sound-induced (audiogenic) seizures, can model the seizure-associated respiratory arrest that contributes to SUDEP in some humans and may be useful for evaluating potential SUDEP therapies. This study evaluated the effects of oxygenation on sudden fatal audiogenic seizures (AGSs) in three mouse strains, DBA/2J (D2), B6SAS, and primed C57BL/6J (B6) that differ in genetic background and seizure etiology (idiopathic or acquired). The incidence of fatal AGSs was measured in (a) a normal air environment; (b), an oxygen-rich environment; (c) a normal air environment 24 h after a nonfatal AGS; (d) an oxygen-rich environment 24 h after a nonfatal AGS; and (e) a normal air environment 60 s after exposure to an oxygen-rich environment. Sudden, fatal AGS occurred in 100%, 100%, and 58% of the D2, B6SAS, and primed-B6 mice, respectively, in the air environment. Oxygenation completely prevented fatal AGSs in each strain, but had no effect on seizure incidence or severity. Furthermore, the protective effect of oxygenation against fatal seizures occurred only when the mice were in an oxygen-rich environment. These findings indicate that oxygenation prevents sudden death in seizure-prone mice and suggest that oxygenation may protect some seizure-prone humans at risk for SUDEP.

A SiC-reinforced aluminum alloy by rapid pressureless infiltration in uncontrolled atmospheres

A SiC-aluminum composite was fabricated by infiltrating Al-Si alloy pressurelessly into a carbon-containing SiC preform in a normal air environment. The infiltration is rapid, less than 10 min for a 10 mm thick section, and the obtained composite was near-net-shape. The microstructure and mechanical properties of the composite are reported.

Atomic force microscope measurements of nucleosome cores assembled along defined DNA sequences.

We have found that the atomic force microscope (AFM) can be used to image the "beads-on-a-string" chromatin structure in a normal air environment following adsorption onto a cover glass substrate. Individual nucleosome cores and linker DNA could be resolved clearly along chromatin fibers that were reconstituted using histone octamers and a tandemly repeated 208-bp nucleosome positioning DNA sequence (208-18). AFM measurements showed that the compaction of the 3780-bp DNA by different loadings of histone octamers was consistent with 146 bp of DNA wrapped 1.75 turns about the histone octamer to form the 11-nm nucleosome core. Precise internucleosome core spacing measurements could be performed along the chromatin fiber axis. In other experiments, AFM images of chromatin reconstituted using closed circular DNA showed highly tangled beaded fibers, as expected. These images and measurements demonstrate that AFM can provide useful high-resolution structural information about chromatin that can be used to complement other more established techniques such as electron microscopy.

Photoreceptor redox state monitored in vivo by transmission and fluorescence microspectrophotometry in blowfly compound eyes

The transmission and fluorescence of the compound eye of living, intact blowflies Calliphora erythrocephala, mutant chalky, were studied microspectrophotometrically. Transmission spectra were recorded under four conditions. The fly was either in the normal air environment or in a nitrogen atmosphere, and in both cases the investigated eye was adapted to red and blue light, respectively. The absorbance difference spectra obtained from the two chromatic adapted conditions showed the clear characteristics of the main visual pigment; the difference spectra for the air and the N 2 case were virtually identical. The absorbance difference spectrum obtained from the air vs N 2 case was very similar to the redox difference spectrum of the pigments in the mitochondrial chain. The redox difference spectra obtained for the two photosteady states were essentially the same. The fluorescence emission spectra induced by UV and blue excitation were measured with the fly in air and in a nitrogen atmosphere, respectively. The UV-induced blue emission increased under hypoxia, whereas the blue-induced green emission dropped. The changes are typical for a reduction of mitochondrial NADH and flavoproteins, respectively. The transmission and fluorescence measurements corroborate each other and demonstrate mitochondrial activity in photoreceptors in vivo and non-invasively.

Hyperoxia: effects on the vascularization of the developing central nervous system.

Litters of experimental and control hamsters were killed on postnatal days 3, 4, 7, 14, 21, and 28 following 7 days of exposure to 85% oxygen at normabaric pressure. Using analysis of variance (ANOVA), light microscopy quantitation of the number of blood vessel profiles per unit area in the region of the frontal cerebral cortex demonstrated that the combined effect of treatment and age on the animals produced a highly statistically significant difference (p less than 0.001) in the numbers of blood vessel profiles. The statistically separated treatment effect was also found to be significant (P less than 0.05). The data are summarized in Table 1. Ultrastructural analysis of animals exposed to oxygen only, i.e., killed without being returned to the normal air environment, demonstrated severe signs of vaso-obliteration. Animals which were returned to a normal atmosphere following 7 days in oxygen showed a progressive decrease in the signs of vaso-obliteration. This present study demonstrated the marked similarity between the effects of hyperoxia on he CNS and on the neuro-retina.