Transport properties of copper-doped carbon aerogels

The magnetic susceptibility, conductivity, magnetoresistance (MR) and Hall effect of copper-doped carbon aerogels are measured and compared with corresponding results from the original carbon aerogels. The experimental results indicate that the temperature-dependent magnetic susceptibility of the copper-doped and of the original carbon aerogels is well fit by a Curie function at low temperatures. The copper-doped carbon aerogels show a higher susceptibility and spin concentration than the original carbon aerogel. After doping by copper, the materials exhibit a more linear current-voltage curve than the original carbon aerogel under the same measurement conditions. The electrical resistance of the copper-doped carbon aerogels is strikingly lower than that of the original carbon aerogels, and decreases with increasing copper content in the samples. The temperature-dependent resistivity ρ(T) of all of the copper-doped and original carbon aerogels can be fitted by an exp(T^−1/2) dependence for T<100 K. The copper-doped and pristine carbon aerogels follow a quadratic MR behavior Δρ/ρ=AB² in the magnetic field range B investigated (up to 5 T), except at very low temperatures (T<4 K).     

Transparent and Conductive Polyethylene Oxide Film by the Introduction of Individualized Single‐Walled Carbon Nanotubes

It is demonstrated that an optically transparent and electrically conductive polyethylene oxide (PEO) film is fabricated by the introduction of individualized single‐walled carbon nanotubes (SWNTs). The incorporated SWNTs in the PEO film sustain their intrinsic electronic and optical properties and, in addition, the intrinsic properties of the polymer matrix are retained. The individualized SWNTs with smaller diameter provide high transmittance as well as good electrical conductivity in PEO films.

     

Mixed-Ligand Complex Formation Equilibria of Vanadium(III) with 2,2′-Bipyridine and the Amino Acids Glycine, Proline, α-Alanine and β-Alanine Studied in 3.0 mol?dm?3 KCl at 25 °C

We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2??-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), ??-alanine (H??Ala), and ??-alanine (H??Ala) by means of electromotive forces measurements emf(H) using 3.0?mol?dm^?3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V₂O(Bipy)(B)]³⁺, [V₂O(Bipy)₂(B)₂]²⁺, [V(OH)(Bipy)(B)₂] and [V(OH)₂(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.     

Bismuth nanowires for potential applications in nanoscale electronics technology.

Nanowires of bismuth with diameters ranging from 10 to 200 nm and lengths of 50 microm have been synthesized by a pressure injection method. Nanostructural and chemical compositional studies using environmental and high resolution transmission electron microscopy with electron stimulated energy dispersive X-ray spectroscopy have revealed essentially single crystal nanowires. The high resolution studies have shown that the nanowires contain amorphous Bi-oxide layers of a few nanometers on the surface. In situ environmental high resolution transmission electron microscopy (environmental-HRTEM) studies at the atomic level, in controlled hydrogen and other reducing gas environments at high temperatures demonstrate that gas reduction can be successfully applied to remove th oxide nanolayers and to maintain the dimensional and structural uniformity of the nanowires, which is key to attaining low electrical contact resistance.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Effectiveness of universal pre-enrichment broth for recovery of Salmonella from selected dairy foods

The relative efficiencies of 2 Bacteriological Analytical Manual (BAM) pre-enrichments, lactose broth (LAC) and brilliant green water (BGW), were compared with Universal Pre-enrichment (UP) broth for the recovery of individual Salmonella serovars from instant nonfat dry milk (NFDM), dry whole milk (DWM), lactic casein (LC), and liquid whole milk (LWM). BGW was compared with UP broth for the analysis of NFDM and DWM but not with the other 2 matrixes. LAC was compared with UP broth for the analysis of LC and LWM. UP broth was made both from a commercial dehydrated preparation (UPC) and from individual ingredients (UPI). Bulk quantities of the selected dairy foods were inoculated with Salmonella serovars at levels intended to produce fractionally positive results, where at least half of the test portions analyzed, with one of the methods being evaluated, would be shown to be Salmonella-positive. For NFDM, in 6 of 9 experiments, with 2 different Salmonella serovars, BGW was significantly more productive than either UPI or UPC broth (p < 0.05). Salmonella was recovered from 118 of 180 test portions with BGW, from 25 of 180 test portions with UPC, and from 14 of 180 test portions with UPI. For DWM, in 2 of 4 experiments, with 2 different Salmonella serovars, BGW was significantly more productive than either UPI or UPC broth (p < 0.05). Salmonella was recovered from 67 of 80 test portions with BGW, from 36 of 80 test portions with UPC, and from 37 of 80 test portions with UPI. For LWM, in 9 of 9 experiments, with 3 different Salmonella serovars, there were no significant differences among the broths. Salmonella was recovered from 120 of 180 test portions with LAC, from 135 of 180 test portions with UPC, and from 129 of 180 test portions with UPI. For LC, in 5 of 7 experiments, with 2 different Salmonella serovars, both UPI and UPC broth were significantly more productive than LAC (p < 0.05). Salmonella was recovered from 42 of 140 test portions with LAC, from 114 of 140 test portions with UPC, and from 114 of 140 test portions with UPI. In addition, overall results showed that UPC and UPI broths were equivalent for the recovery of Salmonella from the foods tested, without regard to their performance in comparison with either LAC or BGW.