Comment on "Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 Ga"

Harrison et al. (Reports, 23 December 2005, p. 1947) proposed that plate tectonics and granites existed 4.5 billion years ago (Ga), within 70 million years of Earth's formation, based on geochemistry of >4.0 Ga detrital zircons from Australia. We highlight the large uncertainties of this claim and make the more moderate proposal that some crust formed by 4.4 Ga and oceans formed by 4.2 Ga.     

Causal reasoning in rats

Empirical research with nonhuman primates appears to support the view that causal reasoning is a key cognitive faculty that divides humans from animals. The claim is that animals approximate causal learning using associative processes. The present results cast doubt on that conclusion. Rats made causal inferences in a basic task that taps into core features of causal reasoning without requiring complex physical knowledge. They derived predictions of the outcomes of interventions after passive observational learning of different kinds of causal models. These competencies cannot be explained by current associative theories but are consistent with causal Bayes net theories.     

Enhancing access to the Bibliome: the TREC 2004 Genomics Track

Background

The goal of the TREC Genomics Track is to improve information retrieval in the area of genomics by creating test collections that will allow researchers to improve and better understand failures of their systems. The 2004 track included an ad hoc retrieval task, simulating use of a search engine to obtain documents about biomedical topics. This paper describes the Genomics Track of the Text Retrieval Conference (TREC) 2004, a forum for evaluation of IR research systems, where retrieval in the genomics domain has recently begun to be assessed.

Results

A total of 27 research groups submitted 47 different runs. The most effective runs, as measured by the primary evaluation measure of mean average precision (MAP), used a combination of domain-specific and general techniques. The best MAP obtained by any run was 0.4075. Techniques that expanded queries with gene name lists as well as words from related articles had the best efficacy. However, many runs performed more poorly than a simple baseline run, indicating that careful selection of system features is essential.

Conclusion

Various approaches to ad hoc retrieval provide a diversity of efficacy. The TREC Genomics Track and its test collection resources provide tools that allow improvement in information retrieval systems.

     

Identification of Molecular Markers Linked to a Pyrenophora teres Avirulence Gene

ABSTRACT Genetic control of avirulence in the net blotch pathogen, Pyrenophora teres, was investigated. To establish an appropriate study system, a collection of 10 net form (P. teres f. teres) and spot form (P. teres f. maculata) isolates were evaluated on a set of eight barley lines to identify two isolates with differential virulence on an individual host line. Two net form isolates, WRS 1906, exhibiting avirulence on the cv. Heartland, and WRS 1607, exhibiting high virulence, were mated and 67 progeny were isolated and phenotyped for reaction on Heartland. The population segregated in a 1:1 ratio, 34 avirulent to 33 virulent (chi(2) = 0.0, P = 1.0), indicating single gene control of WRS 1906 avirulence on Heartland. Bulked segregant analysis was used to identify six amplified fragment length polymorphism markers closely linked to the avirulence gene (Avr(Heartland)). This work provides evidence that the P. teres-barley pathosystem conforms to the gene-for-gene model and represents an initial step toward map-based cloning of this gene.     

Evolution of the earliest horses driven by climate change in the Paleocene-Eocene Thermal Maximum

Body size plays a critical role in mammalian ecology and physiology. Previous research has shown that many mammals became smaller during the Paleocene-Eocene Thermal Maximum (PETM), but the timing and magnitude of that change relative to climate change have been unclear. A high-resolution record of continental climate and equid body size change shows a directional size decrease of ~30% over the first ~130,000 years of the PETM, followed by a ~76% increase in the recovery phase of the PETM. These size changes are negatively correlated with temperature inferred from oxygen isotopes in mammal teeth and were probably driven by shifts in temperature and possibly high atmospheric CO(2) concentrations. These findings could be important for understanding mammalian evolutionary responses to future global warming.     

Voting power and target-based site prioritization

Indices for site prioritization are widely used to address the question: which sites are most important for conservation of biodiversity? We investigate the theoretical underpinnings of target-based prioritization, which measures sites’ contribution to achieving predetermined conservation targets. We show a strong connection between site prioritization and the mathematical theory of voting power. Current site prioritization indices are afflicted by well-known paradoxes of voting power: a site can have zero priority despite having non-zero habitat (the paradox of dummies) and discovery of habitat in a new site can raise the priority of existing sites (the paradox of new members). These paradoxes arise because of the razor’s edge nature of voting, and therefore we seek a new index that is not strictly based on voting. By negating such paradoxes, we develop a set of intuitive axioms that an index should obey. We introduce a simple new index, “fraction-of-spare,” that satisfies all the axioms. For single-species site prioritization, the fraction-of-spare(s) of a site s equals zero if s has no habitat for the species and one if s is essential for meeting the target area for the species. In-between those limits it is linearly interpolated, and equals area(s)/(total area - target). In an evaluation involving multi-year scheduling of site acquisitions for conservation of forest types in New South Wales under specified clearing rates, fraction-of-spare outperforms 58 existing prioritization indices. We also compute the optimal schedule of acquisitions for each of three evaluation measures (under the assumed clearing rates) using integer programming, which indicates that there is still potential for improvement in site prioritization for conservation scheduling.     

以色列花卉业迎来新时代

以色列花卉产业目前发展迅速。据估计,2005年以色列花卉的全部销售收入达3.4亿欧元,与2004年的3亿欧元相比,增长了13%。     

Detection and prediction of hydrolytic rancidity in milk by multiple regression analysis of short-chain free Fatty acids determined by solid phase microextraction gas chromatography and quantitative flavor intensity assessment

The objective was to establish a method for detecting and predicting hydrolytic rancidity in milk by correlating quantitative sensory data with individual short-chain free fatty acids (FFA) (C(4)-C(12)) in milk determined by solid phase microextraction and gas chromatography (SPME-GC). A FFA-based equation for determining rancid flavor intensities in milk was derived by stepwise regression analysis. A highly significant (p < 0.001) correlation coefficient (R (2)) of 0.84 indicated that rancidity scores were dependent on FFA obtained by SPME-GC and that a good proportion of the variation in the rancidity scores was explained by the model. When rancidity scores were predicted for 19 commercial milks, one sample was found to be distinctly rancid by the statistical model and by the trained sensory panel. The rest of the samples were found to be nonrancid by either method. Thus, the predicting power of the model was shown because there was 100% correct flavor classification for the samples tested.