Alkylating esters VIII. The action of the isomers of dimethylmyleran on spermatogenesis

Zusammenfassung Als Antifertilitätsmittel haben dasmeso-Isomer und die (±)-Isomere von Dimethylmyleran eine synergistische Wirkung auf die Spermatogenese von Ratten. Bei Mäusen und Wachteln hat ein 50% iges Gemisch der Isomere eine niedrigere Toxizität als die einzelnen Isomere, was bei höherer Dosis des Gemisches zu längerdauernder Sterilität führt.     

Identification of comet Hyakutake's extremely long ion tail from magnetic field signatures

Observations of the varying orientations of comet tails led to the suggestion of the existence of the solar wind--a continuous outflow of ionized material from the Sun. It is now well established that gas from comets is ionized by several processes and joins the solar wind, forming an ion (plasma) tail that points away from the Sun. The plasma environments of three comets have been measured in situ, but only in the upstream direction or less than 8,000 km downstream of the nucleus. Here we report a fortuitous crossing by a spacecraft of the plasma tail of comet Hyakutake (C/1996 B2), at a distance of more than 3.8 astronomical units (550 million kilometres) from its nucleus. This surpasses the tail length of 2 AU determined for the Great March Comet of 1843 (C/1843 D1). Our measurements reveal that, at this distance, the tail of comet Hyakutake was a structured entity at least 7 million kilometres in diameter.     

Seismic considerations for spent nuclear fuel storage in dry casks

o aid the United States’ Nuclear Regulatory Commission, Sandia National Laboratories (SNL) was contracted to investigate the seismic behavior of typical dry cask storage systems. Parametric evaluations characterized the sensitivity of calculated cask response characteristics to input parameters. The parametric evaluation investigated two generic cask design (cylindrical and rectangular), three different foundation types (soft soil, hard soil, and rock), and three different cask to pad coefficients of friction (0.2, 0.55, 0.8) for earthquakes with peak ground accelerations of 0.25g, 0.6g, 1.0g and 1.25g. A total of 1 165 analyses were completed, with regression analyses being performed on the resulting cask response data to determine relationships relating the mean (and 16 % and 84 % confidence intervals on the mean) to peak ground acceleration, peak ground velocity, and pseudo-spectral acceleration at 1 Hz and 5 % damping. In general, the cylindrical casks experienced significantly larger responses in comparison to the rectangular cask. The cylindrical cask experienced larger top of cask displacements, larger cask rotations (rocking), and more occurrences of cask toppling (the rectangular cask never toppled over). The cylindrical cask was also susceptible to rolling once rocking had been initiated, a behavior not observed in the rectangular cask. Cask response was not overly sensitive to foundation type, but was significantly dependent on the response spectrum employed.     

A large discontinuity in the mid-twentieth century in observed global-mean surface temperature

Data sets used to monitor the Earth's climate indicate that the surface of the Earth warmed from approximately 1910 to 1940, cooled slightly from approximately 1940 to 1970, and then warmed markedly from approximately 1970 onward. The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors, such as atmosphere-ocean interactions and anthropogenic emissions of sulphate aerosols. Here we call attention to a previously overlooked discontinuity in the record at 1945, which is a prominent feature of the cooling trend in the mid-twentieth century. The discontinuity is evident in published versions of the global-mean temperature time series, but stands out more clearly after the data are filtered for the effects of internal climate variability. We argue that the abrupt temperature drop of approximately 0.3 degrees C in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record. Corrections for the discontinuity are expected to alter the character of mid-twentieth century temperature variability but not estimates of the century-long trend in global-mean temperatures.     

DNA sequence of human chromosome 17 and analysis of rearrangement in the human lineage

Chromosome 17 is unusual among the human chromosomes in many respects. It is the largest human autosome with orthology to only a single mouse chromosome, mapping entirely to the distal half of mouse chromosome 11. Chromosome 17 is rich in protein-coding genes, having the second highest gene density in the genome. It is also enriched in segmental duplications, ranking third in density among the autosomes. Here we report a finished sequence for human chromosome 17, as well as a structural comparison with the finished sequence for mouse chromosome 11, the first finished mouse chromosome. Comparison of the orthologous regions reveals striking differences. In contrast to the typical pattern seen in mammalian evolution, the human sequence has undergone extensive intrachromosomal rearrangement, whereas the mouse sequence has been remarkably stable. Moreover, although the human sequence has a high density of segmental duplication, the mouse sequence has a very low density. Notably, these segmental duplications correspond closely to the sites of structural rearrangement, demonstrating a link between duplication and rearrangement. Examination of the main classes of duplicated segments provides insight into the dynamics underlying expansion of chromosome-specific, low-copy repeats in the human genome.     

A quantitative protein interaction network for the ErbB receptors using protein microarrays

Although epidermal growth factor receptor (EGFR; also called ErbB1) and its relatives initiate one of the most well-studied signalling networks, there is not yet a genome-wide view of even the earliest step in this pathway: recruitment of proteins to the activated receptors. Here we use protein microarrays comprising virtually every Src homology 2 (SH2) and phosphotyrosine binding (PTB) domain encoded in the human genome to measure the equilibrium dissociation constant of each domain for 61 peptides representing physiological sites of tyrosine phosphorylation on the four ErbB receptors. This involved 77,592 independent biochemical measurements and provided a quantitative protein interaction network that reveals many new interactions, including ones that fall outside of our current view of domain selectivity. By slicing through the network at different affinity thresholds, we found surprising differences between the receptors. Most notably, EGFR and ErbB2 become markedly more promiscuous as the threshold is lowered, whereas ErbB3 does not. Because EGFR and ErbB2 are overexpressed in many human cancers, our results suggest that the extent to which promiscuity changes with protein concentration may contribute to the oncogenic potential of receptor tyrosine kinases, and perhaps other signalling proteins as well.     

Global distribution and conservation of rare and threatened vertebrates

Global conservation strategies commonly assume that different taxonomic groups show congruent geographical patterns of diversity, and that the distribution of extinction-prone species in one group can therefore act as a surrogate for vulnerable species in other groups when conservation decisions are being made. The validity of these assumptions remains unclear, however, because previous tests have been limited in both geographical and taxonomic extent. Here we use a database on the global distribution of 19,349 living bird, mammal and amphibian species to show that, although the distribution of overall species richness is very similar among these groups, congruence in the distribution of rare and threatened species is markedly lower. Congruence is especially low among the very rarest species. Cross-taxon congruence is also highly scale dependent, being particularly low at the finer spatial resolutions relevant to real protected areas. 'Hotspots' of rarity and threat are therefore largely non-overlapping across groups, as are areas chosen to maximize species complementarity. Overall, our results indicate that 'silver-bullet' conservation strategies alone will not deliver efficient conservation solutions. Instead, priority areas for biodiversity conservation must be based on high-resolution data from multiple taxa.