Rapid, Precise, and High-Sensitivity Acquisition of Paleomagnetic and Rock-Magnetic Data: Development of a Low-Noise Automatic Sample Changing System for Superconducting Rock Magnetometers

Among Earth sciences, paleomagnetism is particularly linked to the statistics of large sample sets as a matter of historical development and logistical necessity. Because the geomagnetic field varies over timescales relevant to sedimentary deposition and igneous intrusion, while the fidelity of recorded magnetization is modulated by original properties of rock units and by alteration histories, "ideal" paleomagnetic results measure remanent magnetizations of hundreds of samples at dozens of progressive demagnetization levels, accompanied by tests of magnetic composition on representative sister specimens. We present an inexpensive, open source system for automating paleomagnetic and rock magnetic measurements. Using vacuum pick-and-place technology and a quartz-glass sample holder, the system can in one hour measure remanent magnetizations, as weak as a few pAm2, of ~30 specimens in two vertical orientations with measurement errors comparable to those of the best manual systems. The system reduces the number of manual manipulations required per specimen ~8 fold

Electronic structure and magnetism in X_xW_{1-x}O_3 (X=Nb,V,Re) from supercell calculations

Some doped semiconductors have recently been shown to display superconductivity or weak ferromagnetism. Here we investigate the electronic structure and conditions for magnetism in a supercells of cubic XW_{26}O_{81}, where X=Nb,V and Re. The undoped material is an insulator, and although the slightly doped material is a metal, it is far from the Stoner criterion of magnetism. The conditions of a localized density-of-states which varies rapidly with the energy, resemble those of doped hexaborides. The virtual crystal approximation is used to vary the doping level. A small moment appears if the Fermi energy coincides with a large derivative of the DOS.Comment: 5 pages, 5 figures, to appear in JMM

A dynamic Archean sulfur cycle

Many aspects of the Earth’s early sulfur cycle, from the origin of mass anomalous fractionations to the scale and degree of biological involvement, remain poorly understood. We have been studying the nature of multiple sulfur isotope (^(32)S, ^(33)S, and ^(34)S) signals using a novel combination of scanning high-resolution low-temperature superconductivity SQUID microscopy and secondary ion mass spectrometry (SIMS) techniques in a suite of samples from distal slope and basinal environments adjacent to a major Late Archean-age (~2.6-2.52 Ga) carbonate platform. Coupled with petrography, these techniques allow us to interrogate, at the same microscopic scale, the complex history of mineralization in samples containing diverse sulfide-bearing mineral components. Because of a general lack of Archean sulfate minerals, we focused our analyses on early diagenetic pyrite nodules, precipitated in surface sediments. This allows us to assay fractionations by controlling for isotope mass balance

Optical coherence microscopy for the evaluation of a tissue-engineered artificial cornea

A transparent artificial cornea derived from biological material is the ultimate goal of corneal research. Attempts at artificial corneal constructs produced from synthetic polymers have proved unsuccessful due to lack of biocompatibility and ability to integrate into the tissue. We have designed a corneal model derived from collagenous biological materials that has several advantages: it has low antigenicity and therefore small chance of eliciting an immune reaction, it can be broken down by the body’s own cells and gradually replaced over time by natural materials, and it may contain signaling information for native cells, thereby inducing normal phenotype and behavior. In addition, a transparent corneal model has the potential to be used for testing of novel ophthalmic drugs or gene therapy approaches, eliminating the need for animal testing. We have used an optical coherence microscope (OCM) to evaluate both the structure of our tissue constructs over time in culture and the optical properties of the tissue itself. This imaging technique promises to be an important diagnostic tool in our efforts to understand the influence of mechanical forces, cell phenotype, and soluble factors on the transparency of corneal tissue. From the 26th Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society [September 01-05, 2004, San Francisco, CA] IEEE Engn Med & Biol Soc, Whitaker Fdn, Cyberonics, NIH, NIBIB, NIDOCD, NINDS ISBN: 0-7803-8439-

Geology and geochronology of the Tana Basin, Ethiopia: LIP volcanism, super eruptions and Eocene–Oligocene environmental change

New geological and geochronological data define four episodes of volcanism for the Lake Tana region in the northern Ethiopian portion of the Afro–Arabian Large Igneous Province (LIP): pre-31 Ma flood basalt that yielded a single 40Ar/39Ar age of 34.05±0.54/0.56 Ma; thick and extensive felsic ignimbrites and rhyolites (minimum volume of 2–3×103 km3) erupted between 31.108±0.020/0.041 Ma and 30.844±0.027/0.046 Ma (U–Pb CA-ID-TIMS zircon ages); mafic volcanism bracketed by 40Ar/39Ar ages of 28.90±0.12/0.14 Ma and 23.75±0.02/0.04 Ma; and localised scoraceous basalt with an 40Ar/39Ar age of 0.033±0.005/0.005 Ma. The felsic volcanism was the product of super eruptions that created a 60–80 km diameter caldera marked by km-scale caldera-collapse fault blocks and a steep-sided basin filled with a minimum of 180 m of sediment and the present-day Lake Tana. These new data enable mapping, with a finer resolution than previously possible, Afro–Arabian LIP volcanism onto the timeline of the Eocene–Oligocene transition and show that neither the mafic nor silicic volcanism coincides directly with perturbations in the geochemical records that span that transition. Our results reinforce the view that it is not the development of a LIP alone but its rate of effusion that contributes to inducing global-scale environmental change

Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe2

IrTe2, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. This transition is characterized by the formation of Ir-Ir bonds along the b-axis. We found that the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the appearance of a structural critical point in the T = 0 limit at xc = 0.035. Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at Tc = 3.1 K is induced by the bond breaking in a narrow range of x > xc in Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved in the emergence of superconductivity.Comment: 10 pages, 4 figure

A single atom detector integrated on an atom chip: fabrication, characterization and application

We describe a robust and reliable fluorescence detector for single atoms that is fully integrated into an atom chip. The detector allows spectrally and spatially selective detection of atoms, reaching a single atom detection efficiency of 66%. It consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multi-mode fiber to collect the fluorescence. The fibers are mounted in lithographically defined holding structures on the atom chip. Neutral 87Rb atoms propagating freely in a magnetic guide are detected and the noise of their fluorescence emission is analyzed. The variance of the photon distribution allows to determine the number of detected photons / atom and from there the atom detection efficiency. The second order intensity correlation function of the fluorescence shows near-perfect photon anti-bunching and signs of damped Rabi-oscillations. With simple improvements one can boost the detection efficiency to > 95%.Comment: 24 pages, 11 figure