The fermionic hanbury brown and twiss experiment

A Hanbury Brown and Twiss experiment for a beam of electrons has been realized in a two-dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter to partition the incident beam into transmitted and reflected partial beams. In the nonequilibrium case the fluctuations in the partial beams are shown to be fully anticorrelated, demonstrating that fermions exclude each other. In equilibrium, the cross-correlation of current fluctuations at two different contacts is also found to be negative and nonzero, provided that a direct transmission exists between the contacts.     

Buddenbrockia is a cnidarian worm

A major evolutionary divide occurs in the animal kingdom between the so-called radially symmetric animals, which includes the cnidarians, and the bilaterally symmetric animals, which includes all worm phyla. Buddenbrockia plumatellae is an active, muscular, parasitic worm that belongs to the phylum Myxozoa, a group of morphologically simplified microscopic endoparasites that has proved difficult to place phylogenetically. Phylogenetic analyses of multiple protein-coding genes demonstrate that Buddenbrockia is a cnidarian. This active muscular worm increases the known diversity in cnidarian body plans and demonstrates that a muscular, wormlike form can evolve in the absence of overt bilateral symmetry.     

Was there really an Archean phosphate crisis?

During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted.     

Undergraduate Origins of American Scientists

An analysis of the college attendance or college choice for four high-aptitude, high-school senior samples suggests that the differential institutional productivity of scientists and scholars is a function of the differential college attendance, paternal vocational motivations, and their implied correlates among high-aptitude students. This formulation appears to be more probable for males than for females. The institutional productivity hypothesis proposed in previous studies is not supported by the present evidence (14).     

Influenza virus effects on cell membrane proteins

During infection by influenza virus, viral proteins become firmly attached to (or part of) host cell plasma membrane, nuclear membranes, mitochondrial, and microsomal membranes. Purified virus particles contain less than I percent host cell protein. Virus envelope proteins completely replace host membrane proteins in those discrete spots on the plasma membrane from which progeny virions bud out.     

Evidence for life on Earth more than 3850 million years ago

A recent study by Mojzsis et al., (Nature 384, 55, 1996) found evidence of life in rocks in Greenland estimated by new isotopic data to be more than 3800 million years old. The author examines this study in relation to studies conducted on rocks between 3250 and 3800 million years old and presents reasons to agree and disagree with the interpretation of data.     

Carbon monoxide measurements in the troposphere

During the second flight of the space shuttle, the measurement of air pollution from satellites (MAPS) experiment in the OSTA-1 payload acquired approximately 35 hours of radiometric measurements of the carbon monoxide mixing ratio in the middle troposphere, upper troposphere, and lower stratosphere. A gas filter radiometer operating in the 4.67-micrometer band was used to acquire the data over the region from 38 degrees N to 38 degrees S during both daytime and nighttime. The performance of the measurement system was excellent. The data reduced to date indicate the presence of significant gradients in the middle tropospheric carbon monoxide mixing ratio with both latitude and longitude over the North Atlantic, the Mediterranean Sea, and the Middle East. On the basis of comparisons with directly measured values, the accuracy of the measurements is approximately 15 percent. Comparisons of data taken on successive orbits over the same geographic region indicate that the repeatability of the measurements is approximately 5 percent.