Chemical vapor sensing properties of graphene based on geometrical evaluation

Graphene is a promising candidate for chemical vapor sensing. We prepared graphene sheets from highly oriented pyrolytic graphite through mechanical cleavage in order to investigate their responses to NH₃ and NO₂ as electron donors and acceptors, respectively. We investigated how the geometric characteristics of graphene, such as length-to-width (L/w) ratio and number of layers, affect chemical sensing properties at room temperature and ambient atmosphere. In this study, the L/w ratio of an individual graphene sheet, which is related to graphene conductivity, dominated the NH₃ sensing characteristics, while the number of graphene layers had no significant effect. We also studied the effects of various thermal treatments on graphene sensitivity and recovery time in an ambient atmosphere. This study confirms the effects of geometry, operation temperature and gas concentration on the NH₃ and NO₂ sensing performances of graphene.     

Mn-doped activated carbon aerogel as electrode material for pseudo-capacitive supercapacitor: Effect of activation agent

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and a series of activated carbon aerogels (ACA-X, X = H₃PO₄, K₂CO₃, KOH, and ZnCl₂) were then prepared by a chemical activation using different activation agent (X represented an activation agent). Specific capacitances of activated carbon aerogels were measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Among the samples prepared, ACA-K₂CO₃ showed the highest specific capacitance (152 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudo-capacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogels (Mn/ACA-X) by an incipient wetness impregnation method. Capacitance measurements revealed that Mn/ACA-K₂CO₃ showed the highest specific capacitance (189 F/g). The enhanced capacitance of Mn/ACA-K₂CO₃ was attributed to the fine pore structure and outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

Fence probe measurement of flow reversal in separating turbulent boundary layers

A small fence probe was evaluated for measurements in the time-dependent flow reversal region of the transition from boundary layer to separated flow. For moderate and high Reynolds numbers, the fence probe is demonstrated to be a usable tool for the measurement of the reverse flow associated with separation. Although the present probe pressure transducer system was limited to approximately 200?Hz, pulses of positive and negative shear stress were readily detected. At or near the location of zero surface shear stress, the measurements were limited by the signal-to-noise ratio. For the separated flow investigated, a marked reduction in the pressure gradient occurred when the fence probe indicated approximately 20?% reversal for the higher Reynolds numbers. The reversal increased to 24?% for the lower Reynolds numbers. The measurements indicate that flow reversal alone may not be adequate to identify the degree of separation. Upstream of turbulent boundary layer (intermittent) separation, the duration of the reversed shear stress was found to be very short (0.002?C0.007?s), suggesting a local, small-scale, impulse-type separation. At and beyond the location of intermittent separation, the shear stress reversal duration was an order of magnitude longer. Estimates of the maximum and minimum surface shear stress in the separation region were also obtained with the fence probe.     

Investigation of p-type behavior in Ag-doped ZnO thin films by E-beam evaporation

Ag-doped ZnO (ZnO:Ag) thin films were grown on glass substrates by E-beam evaporation technique. The structural, electrical and optical properties of the films were investigated as a function of annealing temperature. The films were subjected to post annealing at different temperatures in the range of 350-650 °C in an air ambient. All the as grown and annealed films at temperature of 350 °C showed p-type conduction. The films lost p-type conduction after post annealing treatment temperature of above 350 °C, suggesting a narrow post annealing temperature window for the fabrication of p-type ZnO:Ag films. ZnO:Ag film annealed at 350 °C revealed lowest resistivity of 7.25 × 10⁻² Ω cm with hole concentration and mobility of 5.09 × 10¹⁹ cm⁻³ and 1.69 cm²/V s, respectively. Observation of a free-to-neutral-acceptor (e,A^o) and donor-acceptor-pair (DAP) emissions in the low temperature photoluminescence measurement confirms p-type conduction in the ZnO:Ag films.     

Effect of grain-boundary flux pinning in MgB2 with columnar structure

We studied the flux pinning properties by grain boundaries in MgB₂ films prepared by using a hybrid physical chemical vapor deposition method on the c-axis oriented sapphire substrates. All the films we report here had the columnar grains with the growth direction perpendicular to the substrates and the grain sizes in the range of a few hundred nanometers. At very low magnetic fields, no discernable grain-boundary (GB) pinning effect was observed in all measuring temperatures, but above those fields, the effect of GB flux pinning was observed as enhanced critical current densities (J_cs) and reduced resistances when an external magnetic field (B) was aligned parallel to the c-axis. We interpret the B dependence of J_c in the terms of flux line lattice shear inside the columnar grains activated by dislocations of Frank–Read source while the flux lines pinned by GB act as anchors for dislocations. Magnetic field dependence of flux pinning force density for B parallel to the c-axis was reasonably explained by the above model.     

cis‐Dinitrito(1,4,8,11‐tetra­aza­cyclo­tetra­decane‐κ4N)­chromium(III) nitrite

In the title compound, [Cr(ONO)₂(cyclam)]NO₂ (cyclam is 1,4,8,11‐tetra­aza­cyclo­tetra­decane, C₁₀H₂₄N₂), the complex cation is located on a twofold symmetry axis. The central Cr atom has a distorted octahedral coordination, involving two Cr—O bonds, with the monodentate nitrite O atoms adopting a cis configuration, and four Cr—N bonds. The mean Cr—N and Cr—O distances are 2.0895 (14) and 1.9698 (14) Å.     

High transparent thermal curable hybrid polycarbonate films prepared by the sol–gel method

Polycarbonate/epoxy/silica hybrid films were prepared by curing an epoxy reaction via in situ sol–gel process. The influence of the synthetic conditions, such as the ratio of different epoxy reagents and the contents of [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane on the physical and optical properties of these hybrid films were investigated in details. The coefficient of thermal expansion, surface roughness, and light transmittance at a wavelength range from 250 to 800 nm were measured. These excellent overall performances make it a promising photonic packaging material.     

Psychological and Antibacterial Effects of Footbath Using the Lindera umbellata Essential Oil

Lindera umbellata (Lu) essential oil primarily contains linalool and has relaxation properties. We investigated the psychological and antibacterial effects of footbath with Lu essential oil. The participants included 20 women without medical history and received two intervention plans: footbath without any essential oil and footbath using Lu essential oil. Next, questionnaires regarding impressions and mood states were provided for them to answer. In addition, their autonomic nervous system activity was measured, and the aerobic viable of count on the feet was determined. The high-frequency value reflecting the parasympathetic nervous system activity significantly increased after footbath using Lu essential oil. In the questionnaire about the mood states, the subscale scores of tension–anxiety, depression, fatigue, and confusion after intervention were lower than those before intervention regardless of the use of the essential oil. Conversely, the anger–hostility score decreased only in the group using Lu essential oil. Furthermore, the decrease in aerobic viable count after intervention was not significantly different between the two groups. Footbath using Lu essential oil increased the parasympathetic nervous system activity and relieved anger. Taken together, we suggest that footbath using Lu essential oil has a relaxation effect.     

Optimization of the sonication extraction method of Hibiscus tiliaceus L. flowers

The influence of several experimental parameters on the ultrasonic extraction of Hibiscus tiliaceus L. flowers were investigated: extraction time, solvent polarity, sample amount, solvent volume and sample particle size. It was concluded that the most influential variables were extraction time and solvent polarity. The optimized procedure employed 5 g of ground flowers, 150 mL of methanol and 140 min of extraction. The extracts were fractionated using preparative silica columns and the resulting fractions were analyzed by GC/MS. Some saturated hydrocarbons, fatty acids, fatty acid methyl esters, phytosterols, and vitamin E were identified in the plant extracts.     

Manipulation of Supramolecular Columnar Structures of H-Bonded Donor-Acceptor Units through Geometrical Nanoconfinement

Ambipolar organic semiconductors are considered promising for organic electronics because of their interesting electric properties. Many hurdles remain yet to be overcome before they can be used for practical applications, especially because their orientation is hard to control. We demonstrate a method to control the orientation of columnar structures based on a hydrogen (H)-bonded donor-acceptor complex between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acid, using physicochemical nanoconfinement. The molecular configuration and supramolecular columnar assemblies in a one-dimensional porous anodic aluminium oxide (AAO) film were dramatically modulated by controlling the pore-size and by chemical modification of the inner surface of the porous AAO film. In situ experiments using grazing-incidence X-ray diffraction (GIXRD) were carried out to investigate the structural evolution produced at the nanometer scale by varying physicochemical conditions. The resulting highly ordered nanostructures may open a new pathway to effectively control the alignment of liquid crystal ambipolar semiconductors.