Quantitative prediction of ternary mixed gases based on an SnO2 sensor array and an SSA-BP neural network model.

This paper describes a tin oxide and copper doped tin oxide gas sensing material synthesized by a biological template method and simple hydrothermal reaction, which were used for the preparation of a gas sensor array. The sensor array is combined with the Sparrow Search Algorithm optimized BP neural network algorithm (SSA-BP) to predict and analyze the concentration of indoor toxic gases, including ammonia, xylene, and formaldehyde. Granular SnO2 was prepared by the biological template method and Cu/SnO2 doped with different copper ion concentrations was prepared by the hydrothermal method. The morphology of the synthesized nanomaterials was characterized by SEM, and the elemental composition and chemical state of the main elements were analyzed by XRD and XPS. The PL emission observed in the visible region is attributed to the defect level gap caused by oxygen. The optimal operating temperature, sensitivity, response/recovery time and the long-term stability of the sensor array have been studied. By combining the sensor array with the neural network algorithm in a simulated indoor environment at four humidity levels, the concentration information of the gas mixtures could be well predicted and the predicted concentration error was less than 0.84 ppm. Therefore, the sensor array prepared in this study combined with the SSA-BP algorithm achieved good results in predicting the concentrations of the three toxic mixtures.

Effect of Tempering Treatment on Microstructural Evolution and Mechanical Behavior of Heavy-Wall Heat Induction Seamless Bend Pipe.

In this paper, the microstructure and mechanical properties of heavy-wall seamless bend pipe after quenching at different tempering temperatures, including 550 °C, 600 °C, 650 °C, and 700 °C, were studied. Microstructure and dislocations observations were characterized by means of an optical microscope, a scanning electron microscope, a transmission electron microscope, and X-ray diffraction. As the tempering temperature increases, the dislocation density in the test steel gradually decreases, and the precipitation behavior of (Nb, V)(C, N) increases. The sample tempered at 650 °C exhibits a granular bainite structure with a dislocation cell structure and a large number of smaller precipitates. The yield platforms of tempered samples at 650 °C and 700 °C are attributed to the pinning effect of the Cottrell atmosphere on dislocations. The sample tempered at 650 °C not only presents the highest strength, but also the highest uniform elongation, which is attributed to the higher strain-hardening rate and instantaneous work-hardening index. This is closely related to the multiplication of dislocations, the interaction between dislocations and dislocations, and the interaction between dislocations and precipitates during plastic deformation of the 650 °C-tempered samples with low dislocation density, which delays the occurrence of necking.

Thermo-optic waveguide gate switch arrays based on direct UV-written highly fluorinated low-loss photopolymer.

Novel thermo-optic waveguide gate switch arrays were designed and fabricated based on the direct UV-written technique. Highly fluorinated low-loss photopolymers and organic-inorganic grafting materials were used as the waveguide core and cladding, respectively. The low absorption loss characteristics and excellent thermal stabilities of the core and cladding materials were obtained. The rectangular waveguides and arrayed electrode heaters have been theoretically designed and numerically simulated to realize single-mode transmission. The propagation loss of a 4-µm-wide straight waveguide was measured as 0.15 dB/cm. The insertion loss of the device was directly measured to be about 5.5 dB. The rise and fall times of the device applied 100 Hz square-wave voltage were obtained as 1.068 and 1.245 ms, respectively. The switching power was about 9.2 mW, and the extinction ratio was 17.8 dB. The low-loss integrated switch arrays are suitable for realizing large-scale photonic integrated circuits.

Pt/glassy carbon model catalysts prepared from PS-b-P2VP micellar templates.

Poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer was used as a micellar template to fabricate arrays of Pt nanoparticles on mica and glassy carbon (GC) supports. Polymer micellar deposition yields Pt nanoparticles with tunable particle size and surface number density on both mica and GC. After deposition of precursor-loaded micelles onto GC, oxygen plasma etching removes the polymer shell, followed by thermal treatment with H2 gas to reduce the Pt. Etching conditions were optimized to maximize removal of the polymer while minimizing damage to the GC. Arrays of Pt nanoparticles with controlled size and surface number density can be prepared on mica (for particle size characterization) and GC to make Pt/GC model catalysts. These model catalysts were characterized by tapping mode atomic force microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry to measure activity for oxidation of carbon monoxide or methanol. Cyclic voltammetry results demonstrate the existence of a correlation between Pt particle size and electrocatalytic properties including onset potential, tolerance of carbonaceous adsorbates, and intrinsic activity (based on active Pt area from CO stripping voltammetry). Results obtained with Pt/GC model catalysts duplicate prior results obtained with Pt/porous carbon catalysts therefore validating the synthesis approach and offering a new, tunable platform to study catalyst structure and other effects such as aging on proton exchange membrane fuel cell (PEMFC) reactions.

Pharmacokinetics, tissue distribution, metabolism, and excretion of depside salts from Salvia miltiorrhiza in rats.

Salviae miltiorrhiza, a traditional Chinese medical herb known as "Danshen," has been widely used in clinics to improve blood circulation, relieve blood stasis, and treat coronary heart disease. Depside salts from S. miltiorrhiza are a novel drug in which magnesium lithospermate B and its analogs are the active components. The pharmacokinetics, tissue distribution, metabolism, and excretion of three of the major components, lithospermic acid B, rosmarinic acid (RA), and lithospermic acid (LA), were studied by liquid chromatography-tandem mass spectrometry following intravenous administration in Sprague-Dawley rats. The elimination half-lives for LSB, RA, and LA were 1.04, 0.75, and 2.0 h, respectively, when 60 mg/kg S. miltiorrhiza depside salts were administrated. The areas under the curve for LSB, RA, and LA were 51.6, 6.6, and 25.2 mg . h/l, respectively, and the values decreased in the individual tissues in the following order: kidney > lung > liver > heart > spleen > brain for LSB; kidney > lung > heart > liver > spleen > brain for RA; and heart > lung > kidney > liver > spleen > brain for LA. After intravenous administration of 60 mg/kg S. miltiorrhiza depside salts, 86% of the LSB was excreted in the bile within 6 h. The main metabolites M1 and M2 were found in the serum. Overall, the results show that depside salts from S. miltiorrhiza are rapidly and widely distributed to tissues after intravenous administration in rats but that they are also rapidly cleared and excreted.

AFM characterization of dendrimer-stabilized platinum nanoparticles.

This work describes the use of atomic force microscopy (AFM) to measure the size of dendrimer-stabilized Pt nanoparticles (Pt DNs) deposited from aqueous solutions onto mica surfaces. Despite considerable previous work in this area, we do not fully understand the mechanisms by which PAMAM dendrimers template the formation of Pt DNs. In particular, Pt DN sizes measured by high-resolution transmission electron microscopy (HRTEM) are reported to be larger than expected if one assumes that each PAMAM molecule templates one spherical Pt nanoparticle. AFM provides a vertical height measurement that complements the lateral dimension measurement from HRTEM. We show that AFM height measurements can distinguish between "empty" PAMAM and Pt DNs. If the complexation of Pt precursor with PAMAM is prematurely terminated, AFM images and feature height distributions show evidence of arrested precipitation of Pt colloids. In contrast, sufficient Pt-PAMAM complexation time leads to AFM images and height distributions that have relatively narrow, normal distributions with mean values that increase with the nominal Pt:PAMAM ratio. The surface density of features in AFM images suggest that these Pt DNs reside on the mica surface as two-dimensional surface aggregates. These observations are consistent with an intradendrimer templating mechanism for Pt DNs. However, we cannot determine if the mechanism obeys a fixed loading law because we do not have definitive information about Pt DN shape. A second peak in the Pt DN height distribution appears when the Pt loading exceeds about 66% of PAMAM's theoretical capacity for Pt. Excluding these secondary particles, the dependence of mean feature height on the Pt:PAMAM ratio follows a power-law relationship. Also considering the magnitudes of the measured mean height values, the data suggest that Pt DNs exist as ramified, noncompact aggregates of Pt atoms interspersed within the PAMAM framework.

Dendrimer-mediated synthesis of platinum nanoparticles: new insights from dialysis and atomic force microscopy measurements.

In this work, we use AFM measurements in conjunction with dialysis experiments to study the synthesis mechanism and physical state of dendrimer-stabilized platinum nanoparticles. For characterizing particle size distributions by high resolution transmission electron microscopy and AFM, sample preparation by drop evaporation presumably minimizes the risk of sample bias that might be found in spin coating or dip-and-rinse methods. However, residual synthesis by-products (mainly salts) must be removed from solutions of dendrimer-stabilized metal nanoparticles prior to AFM imaging. Purification by dialysis is effective for this purpose. We discovered, by UV-visible spectrophotometry and atomic absorption (AA) spectroscopy, that dialysis using 'regular' cellulose dialysis tubing (12 000 Da cut-off) used in all previous work leads to substantial losses of poly(amidoamine) (PAMAM) dendrimer (G4OH), PAMAM-Pt(+2) complex, and PAMAM-stabilized Pt nanoparticles. Use of benzoylated dialysis tubing (1200 Da cut-off) shows no losses of G4OH or G4OH-Pt mixtures. We use AFM to see whether selective filtration during dialysis introduces sampling bias in the measurement of particle size distributions. We compare results (UV-visible spectra, AA results, and AFM-based particle size distributions) for a sample of G4OH-Pt(40) divided into two parts, one part dialysed with regular dialysis tubing and the other with benzoylated tubing. Exhaustive dialysis using benzoylated tubing may lead to the loss of colloidal Pt nanoparticles stabilized by adsorbed dendrimer, but not Pt nanoparticles encapsulated by the dendrimer. The comparisons also lead to new insights concerning the underlying synthesis mechanisms for PAMAM-stabilized Pt nanoparticles.

Electrophoretic analysis and purification of fluorescent single-walled carbon nanotube fragments.

Arc-synthesized single-walled carbon nanotubes have been purified through preparative electrophoresis in agarose gel and glass bead matrixes. Two major impurities were isolated: fluorescent carbon and short tubular carbon. Analysis of these two classes of impurities was done. The methods described may be readily extended to the separation of other water-soluble nanoparticles. The separated fluorescent carbon and short tubule carbon species promise to be interesting nanomaterials in their own right.

Platinum ion uptake by dendrimers: an NMR and AFM study.

The reaction of generation 2 and generation 4 poly(amidoamine) (PAMAM) dendrimers with K2PtCl2 was studied by several NMR methods. The time dependency of the Pt(II) complexation was followed with 195Pt NMR for both dendrimers and the equilibrium product was further characterized with (1)H NMR, and indirectly detected 13C NMR, in the case of the generation 2 dendrimer. After 2 days, a black precipitate of Pt(0) was observed, half the original 195Pt signal was lost, and approximately 20% of the initial Pt(II) was coordinated to the tertiary and secondary nitrogens of the generation 2 dendrimer. The uptake of Pt(II) by the generation 4 dendrimer was much slower, consistent with the steric crowding of the surface groups on the generation 4 dendrimer compared to the more open generation 2. After 10 days, 80% of the Pt(II) was deep within the generation 4 dendrimer; the remaining 20% was unreacted or bound near the surface nitrogens of a single dendrimer. The location and time course of the platinum ion uptake by the dendrimers provides valuable insight into the formation of Pt(0) nanoparticles made in the presence of dendrimers as stabilizers, visualized by atomic force microscopy.