Martin Wahlen

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The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling. During the last four transitions from glacial to interglacial conditions, over which such abrupt warmings occur, ice records indicate that the CO2 concentration of the atmosphere increased by(More)
A high–resolution record of the atmospheric CO2 concentration from 60 to 20 thousand years before present (kyr BP) based on measurements on the ice core of Taylor Dome, Antarctica is presented. This record shows four distinct peaks of 20 parts per million by volume (ppmv) on a millennial time scale. Good correlation of the CO2 record with temperature(More)
The biogeochemical cycling of nitrous oxide plays an important role in greenhouse forcing and ozone regulation. Laboratory studies of N2O:N2 mixtures irradiated between 193-207 nm reveal a significant enrichment of the residual heavy nitrous oxide isotopomers. The isotopic signatures resulting from photolysis are well modeled by an irreversible Rayleigh(More)
Bacillus subtilis cell wall-bound protein CWBP33 is encoded by lytE, a gene expressed during the exponential growth phase. Sequence analysis of LytE, a 33-kDa protein, reveals two domains. The N-terminal domain contains a threefold-repeated motif common to several peptidoglycan binding proteins, while the C-terminal domain, probably carrying the catalytic(More)
We show conditional lower bounds for well-studied &num;P-hard problems: The number of satisfying assignments of a 2-CNF formula with <i>n</i> variables cannot be computed in time exp(<i>o</i>(<i>n</i>)), and the same is true for computing the number of all independent sets in an <i>n</i>-vertex graph. The permanent of an <i>n</i>&#215; <i>n</i> matrix(More)
Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric(More)
We consider the “minor” and “homeomorphic” analogues of the maximum clique problem, i.e., the problems of determining the largest h such that the input graph (on n vertices) has a minor isomorphic to Kh or a subgraph homeomorphic to Kh, respectively, as well as the problem of finding the corresponding subgraphs. We term them as the maximum clique minor(More)
The stable isotope ratios of atmospheric CO(2) ((18)O/(16)O and (13)C/(12)C) have been monitored since 1977 to improve our understanding of the global carbon cycle, because biosphere-atmosphere exchange fluxes affect the different atomic masses in a measurable way. Interpreting the (18)O/(16)O variability has proved difficult, however, because oxygen(More)