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Resistance Change (resistance + change)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Preparation of Nanogapped Gold Nanoparticle Array for DNA Detection

ELECTROANALYSIS, Issue 4 2008
Shiho Tokonami
Abstract A novel DNA detection technique using a gold nanoparticle array film electrode has been reported here. The gold nanoparticles molecularly linked with binder molecule (1,10-decanedithiol) were separated 1.3,nm from each other, and the DNA conductivity change from single to double strand was measured by monitoring a voltage drop across the particles, between which a probe of a 12-mer oligonucleotide was immobilized. In adding a complementary oligonucleotide on the nanoparticle film chip, an immediate decrease in the film resistance (ca. 1.4 ,) due to a hybridization event occurred in a reproducible manner with this simple setup. In the paper, we have an interest in the primary sensing properties; effect of the film resistance on the sensor response, dependence of the resistance change on the DNA concentration, and the performance of the system for DNA detection including single nucleotide polymorphisms were described. [source]

Pressure Effect on the Homogeneity of Spark Plasma-Sintered Tungsten Carbide Powder

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
Salvatore Grasso
A combined experimental/numerical methodology was developed to aid full densification of pure ultrafine tungsten carbide powder by means of Spark Plasma Sintering (SPS) operating in Current Control mode. Applied pressure ranged from 5 to 80 MPa while the current intensity was set and held constant at 1400 A. The developed SPS model used a moving-mesh technique to account for the electrothermal contact resistance change during both shrinkage and punch sliding follow-up. The pressure dependence on the electrothermal contact resistance was also taken into account by the model. The experimental and numerical results showed the effects of pressure on grain growth, residual porosity, and hardness observed along the sample radius. Upon increasing sintering pressure, complete densification was obtained by reducing the peak temperature measured at the die surface. By combining experimental and modeling results, a direct correlation between compact microstructure homogeneity and sintering parameters (i.e., temperature and applied pressure) was established. [source]

Titanium dioxide thin films deposited by the sol-gel technique starting from titanium oxy-acetyl acetonate: gas sensing and photocatalyst applications

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2010
A. Maldonado
Abstract Titanium dioxide (TiO2) thin films were deposited onto sodocalcic glass plates by the sol-gel technique, starting from a non-alkoxide route, namely, titanium oxy-acetyl acetonate as Ti precursor. Film thickness effect on both the gas sensing and photocatalytic degradation performance was studied. The as-deposited films were annealed in air at 400 °C. All the X-ray spectra of the films show a very broad-peak centered in a 2, angle around 30°. In the case of the thinnest films the surface morphology is uniform and very smooth, whereas for the thickest films the corresponding surface is covered by grains with a rod-like shape with a length on the order of 140 nm. The films were tested both for two straightforward applications: ultraviolet assisted-degradation of methylene blue dissolved in water, at different times, as well as gas sensor in a controlled propane (C3H8) atmosphere. As the film thickness increases, the degradation of methylene blue (MB) also increases. The thickest TiO2 thin films after being exposed by 5 hours to the catalytic degradation, promoted by ultraviolet illumination, showed a final MB solution degradation in the order of 48%. This reult can be associated with the increase in the effective exposed area of the TiO2 thin films. On the other hand, the exposition of the films to a controlled propane atmosphere produced a significant change in the surface electrical resistance of the films at operating temperatures of 200 °C and above. In fact, in the case of the thickest TiO2 films, a dramatic electrical resistance change of non-exposed and propane exposed , 560 to 0.7 M, ,, was registered. The results show that TiO2 films deposited by an economical deposition technique, as is the case of the sol-gel technique, could have an important potential in industrial applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electrically conductive sensors for liquids based on ternary immiscible polymer blends containing polyaniline

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2004
H. Cooper
Abstract Electrically conductive blends, containing two immiscible polymers (ethylene vinyl acetate, EVA-19, and copolyamide 6/6.9, CoPA) and polyaniline (PANI), were produced by melt processing. These blends showed a preferred localization of PANI in the CoPA phase, thus enhancing the formation of continuous conducting networks. Electrically conductive PANI-containing filaments produced by a capillary rheometer process at various shear rate levels were studied as sensing materials for a homologous series of alcohols (methanol, ethanol and 1-propanol). All filaments showed a decreasing resistance upon exposure to these solvents. Filaments exposed to methanol, liquid or vapor, exhibited the highest resistance decrease. This behavior was related to the highest polarity of methanol, compared with ethanol and 1-propanol. The filaments' rate of production significantly affects the relative resistance change upon exposure to the various alcohols and their reproducibility. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Simultaneous measurement of resistance and viscoelastic responses of carbon black-filled high-density polyethylene subjected to dynamic torsion

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008
Jianfeng Zhou
Abstract The conduction and viscoelastic responses to temperature are measured simultaneously for carbon black (CB) filled high-density polyethylene (HDPE) subjected to dynamic torsion. PTC/NTC transition was correlated with the loss tangent peak and the quasi modulus plateau, which was ascribed to the filler network. The bond-bending model of elastic percolation networks was used to reveal the structural mechanisms for the cyclic resistance changes at different temperatures. The resistance changes at lower temperatures depended on the deformation of the polymer matrix, while the changes in melting state were mainly attributed to the rearrangement of the CB network. A simple scaling law is derived to relate resistance and dynamic storage modulus in the melting region. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Socioeconomic status and hemodynamic recovery from mental stress

PSYCHOPHYSIOLOGY, Issue 2 2003
Andrew Steptoe
Abstract We assessed the changes in cardiac index and total peripheral resistance underlying blood pressure reactions and recovery from acute mental stress, in relation to socioeconomic status. A sample of 200 men and women aged 47,59 years was divided on the basis of occupation into higher, intermediate, and lower socioeconomic status groups. Blood pressure was monitored using the Portapres, and hemodynamic measures were derived by Modelflow processing of the arterial pressure waveform. Blood pressure increases during two stressful behavioral tasks were sustained by increases in cardiac index and total peripheral resistance. During the 45-min posttask recovery period, cardiac index fell below baseline levels, whereas peripheral resistance remained elevated. Peripheral resistance changes during recovery varied with socioeconomic status and blood pressure stress reactivity, with particularly high levels in reactive low status participants. Results are consistent with the hypothesis that disturbances of stress-related autonomic processes are relevant to the social gradient in cardiovascular disease risk. [source]