Magnetic properties of the Old Crow tephra: Identification of a complex iron titanium oxide mineralogy

International audience[1] The mineralogy and grain-size distribution of the Fe-Ti oxide population of the Old Crow tephra bed, outcropping at the Halfway House loess deposit in central Alaska, are characterized through multiple low-and high-temperature magnetization experiments. The characterization is facilitated by heavy liquid separation of the bulk sample into a low-density ( 0.8 and may play an equally important role as magnetic indicator of titanomagnetite. Furthermore, we demonstrate the ability of low-temperature magnetism to locate a 1 mm thick tephra bed dispersed in loess over 10 cm depth, through the identification of very low concentrations of a titanohematite phase with y = 0.9. The potential for advancing regional correlation of sedimentary deposits through the identification of Fe-Ti oxides common to tephra beds by low-temperature magnetism is illustrated in this study. INDEX TERMS: 1540 Geomagnetism and Paleomagnetism: Rock and mineral magnetism; 1512 Geomagnetism and Paleomagnetism: Environmental magnetism; 1519 Geomagnetism and Paleomagnetism: Magnetic mineralogy and petrology; 8404 Volcanology: Ash deposits; 5109 Physical Properties of Rocks: Magnetic and electrical properties; KEYWORDS: low-temperature magnetism, frequency and amplitude dependence of AC susceptibility, ilmenite-hematite and magnetite-ulvospinel solid solution series, tephra, stratigraphic correlatio

A quantitative anharmonic analysis of the amide A band in α-helical poly( L -alanine)

Polarized ir spectra of oriented films of α-helical poly( l -alanine) (α-PLA) have been obtained as a function of residual solvent dichloroacetic acid (DCA). The amide A, B, II, and V regions exhibit multiple bands whose structure depends on the residual DCA content, and those associated with the α I -PLA structure have been identified. A calculation of the relevant cubic anharmonic force constants indicates that, contrary to previous assignments, the overtone of amide II(A) is in Fermi resonance with the NH stretch fundamental, whose unperturbed frequency we now find to be at 3314 cm −1 , significantly higher than the previously suggested 3279 cm −1 . The presence of a structure in addition to the standard α I -PLA is indicated by our analysis. © 1999 John Wiley & Sons, Inc. Biopoly 49: 195–207, 1999Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34322/1/1_ftp.pd

Current efficiency of alloy plating and the electrochemical equivalent of an alloy

Electrochemical equivalent is defined in the context of the calculation of the current density of electrodeposition of alloys. In order to calculate the current efficiency of the alloy deposition process, it is necessary to know the mass of the alloy expected to be deposited per Faraday of electricity when no other electrode reaction than the alloy deposition occurs at the electrode surface. Since alloys do not have a faxed composition, in other words, since alloys do not obey the law of definite properties, it is not possible to calculate theoretically the mass of the alloy deposited per Faraday. Thus there exists no fixed value for the electrochemical equivalent of an alloy. However, the current efficiency for an alloy deposition process can easily be calculated, without any need to know or define the electrochemical equivalent of an aUoy. An analysis of the alloy deposited can be obtained experimentally and the corresponding Faradays utilised can be calculated. The ratio of this quantity to the number of Faradays passed through the cell would give the current efficiency for the alloy deposition process. The above a..<;pects are dealt with in detail in the paper

Electrodiffusion and charge separation

It has also been realised quite early that there existed some inconsistencies in Planck’s theory of diffusion potentials, regarding the electroneutrality principle. Many workers have tried, to account for the inconsistencies, based on the charge separation over small intervals of time, distance and the variation of dielectric constant across the junction etc. However, in steady state, these theories adapt themselves, to give Planck’s result. It is proposed to discuss in this paper this problem from the definition of the ionic current and the Nernst-Planck flux equations. This leads to the conclusion that, with the assumptions made by Planck, one can only arrive at the equilibrium potential or the Nernst reversible potential, and cannot get with the given initial and boundary conditions any charge separation even in the nonsteady stat