Temporal bone preservation in a 2600-year-old Egyptian mummy

Perforated eardrums in the preserved temporal bones of a mummified Egyptian male in otherwise normal middle ears offer new evidence of acute otitis media and probable defective hearing among ancient Egyptians.     

Generation of spatially coherent light at extreme ultraviolet wavelengths

We present spatial coherence measurements of extreme ultraviolet (EUV) light generated through the process of high-harmonic up-conversion of a femtosecond laser. With a phase-matched hollow-fiber geometry, the generated beam was found to exhibit essentially full spatial coherence. The coherence of this laser-like EUV source was shown by recording Gabor holograms of small objects. This work demonstrates the capability to perform EUV holography with a tabletop experimental setup. Such an EUV source, with low divergence and high spatial coherence, can be used for experiments involving high-precision metrology, inspection of optical components for EUV lithography, and microscopy and holography with nanometer resolution. Furthermore, the short time duration of the EUV radiation (a few femtoseconds) will enable EUV microscopy and holography to be performed with ultrahigh time resolution.     

Outgassing behavior and composition of comet C/1999 S4 (LINEAR) during its disruption

The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelengths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small icy debris (相似文献   

Structural basis of type II topoisomerase inhibition by the anticancer drug etoposide

Type II topoisomerases (TOP2s) resolve the topological problems of DNA by transiently cleaving both strands of a DNA duplex to form a cleavage complex through which another DNA segment can be transported. Several widely prescribed anticancer drugs increase the population of TOP2 cleavage complex, which leads to TOP2-mediated chromosome DNA breakage and death of cancer cells. We present the crystal structure of a large fragment of human TOP2β complexed to DNA and to the anticancer drug etoposide to reveal structural details of drug-induced stabilization of a cleavage complex. The interplay between the protein, the DNA, and the drug explains the structure-activity relations of etoposide derivatives and the molecular basis of drug-resistant mutations. The analysis of protein-drug interactions provides information applicable for developing an isoform-specific TOP2-targeting strategy.     

Tandem regions of yeast DNA topoisomerase II share homology with different subunits of bacterial gyrase

The nucleotide sequence for the Saccharomyces cerevisiae gene TOP2, which encodes DNA topoisomerase II, was compared with the sequence for bacterial DNA gyrase. The amino and carboxyl terminal halves of the single-subunit yeast enzyme showed homologies with the B and A subunits of bacterial gyrase, respectively, at corresponding positions along the polypeptide chains. Although the two enzymes differ in both quaternary structure and activity, the homology between the two proteins indicates mechanistic as well as structural similarities, and a probable evolutionary relationship.     

Carbon-14 in methane sources and in atmospheric methane: the contribution from fossil carbon

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 (14)GH(4) seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 +/- 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 +/- 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH(4) concentrations, and delta(13)C in CH(4) indicate that 21 +/- 3% of atmospheric CH(4) was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of (14)CH(4).     

The involvement of the anterior cingulate cortex in remote contextual fear memory

Although the molecular, cellular, and systems mechanisms required for initial memory processing have been intensively investigated, those underlying permanent memory storage remain elusive. We present neuroanatomical, pharmacological, and genetic results demonstrating that the anterior cingulate cortex plays a critical role in remote memory for contextual fear conditioning. Imaging of activity-dependent genes shows that the anterior cingulate is activated by remote memory and that this activation is impaired by a null alpha-CaMKII mutation that blocks remote memory. Accordingly, reversible inactivation of this structure in normal mice disrupts remote memory without affecting recent memory.     

Shocks in ion sputtering sharpen steep surface features

We report a regime of ion beam sputtering that occurs for sufficiently steep slopes. High slopes propagate over large distances without dissipating the steepest features. Both the propagation velocity and the dynamically selected slope are universal, independent of the details of the initial shape of the surface. The resulting behavior can be understood as the propagation of a shock front that self-selects a stable slope, as has been previously observed in thin-film fluid flows. Experiments confirm predictions of the theory. An important implication of the propagative behavior at high surface slopes is that a pattern can be fabricated at a large length scale and, through uniform ion irradiation, reduced to a smaller length scale while preserving, or even sharpening, the sharpest features.