Analytical chemistry

A room-temperature titania-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination

Abstract: described is a room-temperature hydrogen sensor comprised of a TiO2-nanotube array able to recover substantially from sensor poisoning through ultraviolet (UV) photocatalytic oxidation of the contaminating agent; in this case, various grades of motor oil. The TiO2 nanotubes comprising the sensor are a mixture of both anatase and rutile phases, having nominal dimensions of 22-nm inner diameter, 13.5-nm wall thickness, and 400-nm length, coated with a 10-nm-thick noncontinuous palladium layer. At 24°C, in response to 1000 ppm of hydrogen, the sensors show a fully reversible change in electrical resistance of approximately 175,000%. Cyclic voltammograms using a 1 N KOH electrolyte under 170 mW/cm2 UV illumination show, for both a clean and an oil-contaminated sensor, anodic current densities of approximately 28 mA/cm2 at 2.5 V. The open circuit oxidation potential shows a shift from 0.5 V to –0.97 V upon UV illumination.

A room-temperature titania-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination, Mor, Gopal K., Carvalho Maria A., Varghese Ooman K., Pishko Michael V., and Grimes Craig A. , Journal of Materials Research, 02/2004, Volume 19, Issue 2, p.628?634, (2004)

Masses of Ar-32 and Ar-33 for Fundamental Tests

Masses of the short-lived radionuclides 32Ar (T1/2=98   ms) and 33Ar (T1/2=173   ms) have been determined with the Penning trap mass spectrometer ISOLTRAP. Relative uncertainties of 6.0×10-8 (δm=1.8   keV) and 1.4×10-8 (δm=0.44   keV), respectively, have been achieved. At present, these new mass data serve as the most stringent test of the quadratic form of the isobaric-multiplet mass equation. Furthermore, the improved accuracy for the mass of 32Ar will allow for a better constraint on scalar contributions to the weak interaction. New mass values have also been measured for 44Ar and 45Ar, and a 20σ deviation for 44Ar from the literature value was found and interpreted.

Masses of Ar-32 and Ar-33 for Fundamental Tests, Blaum, K., Audi G., Beck D., Bollen G., Herfurth F., Kellerbauer A., Kluge H. - J., Sauvan E., and Schwarz S. , Phys. Rev. Lett., 12/2003, Volume 91, Number 26, p.260801, (2003)

Scientists create fifth form of carbon

Scientists create fifth form of carbon

Magnetic carbon 'nanofoam' could find medical applications.

Researchers have created a new form of carbon: a spongy solid that is extremely lightweight and, unusually, attracted to magnets. The foam could one day help treat cancer and enhance brain scans, say the inventors.

Scientists create fifth form of carbon, Giles, Jim , news@nature, 3/2004, (2004)

Probable observation of a supersolid helium phase

Abstract: When liquid 4He is cooled below 2.176 K, it undergoes a phase transition—Bose–Einstein condensation—and becomes a super- fluid with zero viscosity. Once in such a state, it can flow without dissipation even through pores of atomic dimensions. Although it is intuitive to associate superflow only with the liquid phase, it has been proposed theoretically that superflow can also occur in the solid phase of 4He. Owing to quantum mechanical fluctuations, delocalized vacancies and defects are expected to be present in crystalline solid 4He, even in the limit of zero temperature. These zero-point vacancies can in principle allow the appearance of superfluidity in the solid. However, in spite of many attempts, such a 'supersolid' phase has yet to be observed in bulk solid 4He. Here we report torsional oscillator measurements on solid helium confined in a porous medium, a configuration that is likely to be more heavily populated with vacancies than bulk helium. We find an abrupt drop in the rotational inertia5 of the confined solid below a certain critical temperature. The most likely interpretation of the inertia drop is entry into the supersolid phase. If confirmed, our results show that all three states of matter—gas, liquid and solid—can undergo Bose–Einstein condensation.

Probable observation of a supersolid helium phase, Kim, E., and Chan M. H. W. , Nature, 1/2004, Volume 427, Issue 6971, p.225 - 227, (2004)

Argon isotope mass measurements

A physicsweb.org article states that an international team working at the ISOLTRAP mass spectrometer at CERN has determined the masses of two isotopes of argon (32Ar and 33Ar) with the highest precision ever. This is important if you want "to place constraints on aspects of the weak interaction that are not included in the Standard Model".1

Carbonate minerals on Mars

A NASA press release indicates that NASA's Spirit, the first of two Mars Exploration Rovers on the surface within Mars' Gusev crater, has identified carbonate minerals "in the rover's first survey of the site with its infrared sensing instrument, called the miniature thermal emission spectrometer or Mini-TES. Carbonates form in the presence of water, but it's too early to tell whether the amounts detected come from interaction with water vapor in Mars' atmosphere or are evidence of a watery local environment in the past, scientists emphasized."

"We came looking for carbonates. We have them. We're going to chase them," said Dr. Phil Christensen of Arizona State University, Tempe, leader of the Mini-TES team. Previous infrared readings from Mars orbit have revealed a low concentration of carbonates distributed globally. Christensen has interpreted that as the result of dust interaction with atmospheric water. First indications are that the carbonate concentration near Spirit may be higher than the Mars global average.

After the rover drives off its lander platform, infrared measurements it takes as it explores the area may allow scientists to judge whether the water indicated by the nearby carbonates was in the air or in a suspected ancient lake. http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040109a/graph-carb...

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