441 research outputs found
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
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
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-
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
Multidrug Resistance-Associated Protein 2 Is Primarily Responsible for the Biliary Excretion of Fexofenadine in Mice
Previous studies implicated P-glycoprotein (P-gp) as the major transport protein responsible for the biliary excretion of fexofenadine (FEX). However, FEX biliary excretion was not impaired in P-gp- or Bcrp-knockout mice, and Mrp2-deficient rats. The present study tested the hypothesis that species differences exist in the transport protein primarily responsible for FEX biliary excretion between mice and rats. Livers from Mrp2-knockout (Mrp2KO) mice and Mrp2-deficient (TR−) rats were perfused in a single-pass manner with 0.5 μM FEX. GF120918 (10 μM) was employed to inhibit P-gp and Bcrp. The biliary excretion rate of FEX was decreased 85% in Mrp2KO relative to wild-type mice (18.4 ± 2.2 vs. 122 ± 34 pmol/min/g liver). In mice, more than 50% of FEX unbound intrinsic biliary clearance (CLbile, int = 3.0 ml/hr/g liver) could be attributed to Mrp2 (Mrp2-dependent CLbile, int ~ 1.7 ml/hr/g liver), with P-gp and Bcrp playing a minor role (P-gp- and Bcrp-dependent CLbile, int ~ 0.3 ml/hr/g liver). Approximately one-third of FEX CLbile, int was attributed to unidentified mechanisms in mice. In contrast to mice, FEX biliary excretion rate (245 ± 38 and 250 ± 25 pmol/min/g liver) and CLbile, int (9.72 ± 2.5 and 6.49 ± 0.68 ml/hr/g liver) were comparable between Mrp2-deficient (TR−) and control Wistar rats, respectively, suggesting that unidentified transport mechanism(s) can completely compensate for the loss of Mrp2 function in rats. Mrp2 clearly plays a major role in FEX biliary excretion in mice. In conclusion, remarkable species differences exist in FEX hepatobiliary transport mechanisms
Cooperation, Norms, and Revolutions: A Unified Game-Theoretical Approach
Cooperation is of utmost importance to society as a whole, but is often
challenged by individual self-interests. While game theory has studied this
problem extensively, there is little work on interactions within and across
groups with different preferences or beliefs. Yet, people from different social
or cultural backgrounds often meet and interact. This can yield conflict, since
behavior that is considered cooperative by one population might be perceived as
non-cooperative from the viewpoint of another.
To understand the dynamics and outcome of the competitive interactions within
and between groups, we study game-dynamical replicator equations for multiple
populations with incompatible interests and different power (be this due to
different population sizes, material resources, social capital, or other
factors). These equations allow us to address various important questions: For
example, can cooperation in the prisoner's dilemma be promoted, when two
interacting groups have different preferences? Under what conditions can costly
punishment, or other mechanisms, foster the evolution of norms? When does
cooperation fail, leading to antagonistic behavior, conflict, or even
revolutions? And what incentives are needed to reach peaceful agreements
between groups with conflicting interests?
Our detailed quantitative analysis reveals a large variety of interesting
results, which are relevant for society, law and economics, and have
implications for the evolution of language and culture as well
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