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Methane (CH4) is a strong greenhouse gas known to have perturbed global climate in the past, especially when released in large quantities over short time periods from continental or marine sources. It is therefore crucial to understand and, if possible, quantify the individual and combined response of these variable methane sources to natural climate variability. However, past changes in the stability of greenhouse gas reservoirs remain uncertain and poorly constrained by geological evidence. Here, we present a record from the Congo fan of a highly specific bacteriohopanepolyol (BHP) biomarker for aerobic methane oxidation (AMO), 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), that identifies discrete periods of increased AMO as far back as 1.2 Ma. Fluctuations in the concentration of aminopentol, and other 35-aminoBHPs, follow a pattern that correlates with late Quaternary glacial-interglacial climate cycles, with highest concentrations during warm periods. We discuss possible sources of aminopentol, and the methane consumed by the precursor methanotrophs, within the context of the Congo River setting, including supply of methane oxidation markers from terrestrial watersheds and/or marine sources (gas hydrate and/or deep subsurface gas reservoir). Compound-specific carbon isotope values of -30 per mil to -40 per mil for BHPs in ODP 1075 and strong similarities between the BHP signature of the core and surface sediments from the Congo estuary and floodplain wetlands from the interior of the Congo River Basin, support a methanotrophic and likely terrigenous origin of the 35-aminoBHPs found in the fan sediments. This new evidence supports a causal connection between marine sediment BHP records of tropical deep sea fans and wetland settings in the feeding river catchments, and thus tropical continental hydrology. Further research is needed to better constrain the different sources and pathways of methane emission. However, this study identifies the large potential of aminoBHPs, in particular aminopentol, to trace and, once better calibrated and understood, quantify past methane sources and fluxes from terrestrial and potentially also marine sources.

We empirically study the information-persuasion trade-off in advertising using data on the information content of advertisements, which we measure with the number of information cues in ads. We propose a simple theoretical framework to motivate an ordered probit model of information content. We find that stronger vertical differentiation is positively associated with the delivery of more product information in a brand’s advertisements: brands with higher levels of quality include more information cues. Next, comparative advertisements contain significantly more product information than self-promotional advertisements. Finally, brands with higher market shares and brands competing against strong generic substitutes have less information content.

The title complex, [Ni ( C 3 H 6 O 2 N ) 2 ( H 2 O ) 2 ] ⋅ 2 H 2 O , has been prepared from nickel(II) chloride in aqueous solution by adding L-alanine and potassium hydroxide. It has been crystallized from aqueous solution, and its structure was determined by X-ray structure analysis. The nickel(II) ion adopts distorted octahedral coordination geometry with two bidentate L-alanine molecules and two water molecules. The complex is neutral and dihydrated. The crystal structure shows the hydrogen bonding between water and amide hydrogens within the lattice, and each fragment of the complex contains two water molecules as hydrated water. The L-alaninato ligand skeleton of the compound adopts the most stable trans-III configuration in the solid state. The alternating two five-membered chelate rings are in the stable gauche conformation.

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb ii and Nb iii and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture elements. Methods. We used the time-resolved laser-induced fluorescence technique to measure radiative lifetimes in Nb ii. Branching fractions were measured from spectra recorded using Fourier transform spectroscopy. The radiative lifetimes and the branching fractions were combined yielding transition probabilities. In addition, we calculated lifetimes and transition probablities in Nb ii and Nb iii using a relativistic Hartree-Fock method that includes core polarization. Abundances of the sun and five metal-poor stars were derived using synthetic spectra calculated with the MOOG code, including hyperfine broadening of the lines. Results. We present laboratory measurements of 17 radiative lifetimes in Nb ii. By combining these lifetimes with branching fractions for lines depopulating the levels, we derive the transition probabilities of 107 Nb ii lines from 4d35p configuration in the wavelength region 2240−4700 Å. For the first time, we present theoretical transition probabilities of 76 Nb III transitions with wavelengths in the range 1430−3140 Å. The derived solar photospheric niobium abundance log = 1.44 ± 0.06 is in agreement with the meteoritic value. The stellar Nb/Eu abundance ratio determined for five metal-poor stars confirms that the r-process is a dominant production method for the n-capture elements in these stars.

Given a multivariate real (or complex) polynomial $p$ and a domain $cal D$, we would like to decide whether an algorithm exists to evaluate $p(x)$ accurately for all $x in {cal D}$ using rounded real (or complex) arithmetic. Here ``accurately'' means with relative error less than 1, i.e., with some correct leading digits. The answer depends on the model of rounded arithmetic: We assume that for any arithmetic operator $op(a,b)$, for example $a+b$ or $a cdot b$, its computed value is $op(a,b) cdot (1 + delta)$, where $| delta |$ is bounded by some constant $epsilon$ where $0 < epsilon ll 1$, but $delta$ is otherwise arbitrary. This model is the traditional one used to analyze the accuracy of floating point algorithms. Our ultimate goal is to establish a decision procedure that, for any $p$ and $cal D$, either exhibits an accurate algorithm or proves that none exists. In contrast to the case where numbers are stored and manipulated as finite bit strings (e.g., as floating point numbers or rational numbers) we show that some polynomials $p$ are impossible to evaluate accurately. The existence of an accurate algorithm will depend not just on $p$ and $cal D$, but on which arithmetic operators and constants are available to the algorithm and whether branching is permitted in the algorithm. Toward this goal, we present necessary conditions on $p$ for it to be accurately evaluable on open real or complex domains ${cal D}$. We also give sufficient conditions, and describe progress toward a complete decision procedure. We do present a complete decision procedure for homogeneous polynomials $p$ with integer coefficients, ${cal D} = C^n$, using only arithmetic operations $+$, $-$ and $cdot$.

Vague impact criteria are a blessing in disguise. Researchers who push against criteria that allow considerable autonomy are foolish and should learn from overseas contemporaries that a clearer definition of impact requirements is not dissimiliar from a tightening of the noose, write J. Britt Holbrook and Robert Frodeman.

The geochemical measurements within the long-lived, crustose coralline red alga Clathromorphum compactum in calibration experiments, and the environmental conditions selected for the controlled laboratory aquaria.

We investigate the power of voting among diverse, randomized software agents. With teams of computer Go agents in mind, we develop a novel theoretical model of two-stage noisy voting that builds on recent work in machine learning. This model allows us to reason about a collection of agents with different biases (determined by the first-stage noise models), which, furthermore, apply randomized algorithms to evaluate alternatives and produce votes (captured by the second-stage noise models). We analytically demonstrate that a uniform team, consisting of multiple instances of any single agent, must make a significant number of mistakes, whereas a diverse team converges to perfection as the number of agents grows. Our experiments, which pit teams of computer Go agents against strong agents, provide evidence for the effectiveness of voting when agents are diverse.