Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge

Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances, with observed changes in vent temperature. But these disturbances resulted from submarine volcanic activity; until now, there have been no observations of the response of a vent system to non-magmatic, tectonic events. Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4-11 days after the first earthquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days, extending along the entire ridge segment. Such a large, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and fluid, and the possible effect on vent biological communities.     

Methods for calculating the desorption rate of an isolated molecule from a surface: Water on MgO(0 0 1)

We present two types of Molecular Dynamics (MD) simulation for calculating the desorption rate of molecules from a surface. In the first, the molecules move freely between two surfaces, and the desorption rate is obtained either by counting the number of desorption events in a given time, or by looking at the average density of the molecules as a function of distance from the surface and then applying transition state theory (TST). In the second, the potential of mean force (PMF) for a molecule is determined as a function of distance from the surface and the desorption rate is obtained by means of TST. The methods are applied to water on the MgO(0 0 1) surface at low coverage. Classical potentials are used so that long simulations can be performed, to minimise statistical errors. The two sets of MD simulations agree well at high temperatures. The PMF method reproduces the 0 K adsorption energy of the molecule to within 5 meV, and finds that the well depth of the PMF is not linear with temperature. This implies the prefactor frequency f in the Polanyi-Wigner equation is a function of temperature, increasing at lower temperatures due to the reduction of the available configuration space associated with an adsorbed molecule compared with a free molecule.     

百麦外用中药制剂对小鼠乳腺增生的实验研究

目的:观察外用中药制剂对小鼠乳腺增生的预防作用并探讨其机理。方法:采用苯甲酸雌二醇腹腔注射造模,分对照组、模型组与预防组。模型组与预防组腹腔注射苯甲酸雌二醇,隔天1次,并且预防组小鼠乳房涂抹百麦外用中药制剂,每天1次,共30天;对照组小鼠腹腔注射生理盐水,隔天1次,共30 d。测定各组小鼠体重变化,乳晕及乳头直径变化,血清雌激素(E2)、孕激素(P)指标,并取小鼠第二对乳房组织病理切片检查。结果:预防组与模型组小鼠体重、乳晕及乳头直径比较均有显著性差异(P0.05);预防组与模型组比较,E2水平明显降低(P0.05),P水平明显升高(P0.05);预防组小鼠增生的乳腺小叶、腺泡数、腺泡腔直径、导管直径以及胞浆面积较模型组降低。结论:百麦外用中药制剂具有预防乳腺增生的作用,其机理可能是通过抑制血清雌二醇水平而实现。     

Dehn filling in relatively hyperbolic groups

We introduce a number of new tools for the study of relatively hyperbolic groups. First, given a relatively hyperbolic group G, we construct a nice combinatorial Gromov hyperbolic model space acted on properly by G, which reflects the relative hyperbolicity of G in many natural ways. Second, we construct two useful bicombings on this space. The first of these, preferred paths, is combinatorial in nature and allows us to define the second, a relatively hyperbolic version of a construction of Mineyev. As an application, we prove a group-theoretic analog of the Gromov-Thurston 2π Theorem in the context of relatively hyperbolic groups. The first author was supported in part by NSF Grant DMS-0504251. The second author was supported in part by an NSF Mathematical Sciences Post-doctoral Research Fellowship. Both authors thank the NSF for their support. Most of this work was done while both authors were Taussky-Todd Fellows at Caltech.     

Escape of DNA from mitochondria to the nucleus in Saccharomyces cerevisiae

The migration of genetic information from ancestral prokaryotic endosymbionts into eukaryotic nuclei is thought to have had an important role in the evolution of mitochondria and chloroplasts. Here we describe an assay for the detection of movement of DNA between mitochondria and the nucleus in yeast. Because recombinant plasmid DNA replicates after transformation into mitochondria of yeast strains lacking endogenous mitochondrial DNA we were able to propagate the nuclear genetic marker URA3 in mitochondria. As expected, the wild-type URA3 gene in mitochondria failed to complement the uracil auxotrophy (Ura-) caused by a nuclear ura3 mutation. But selection of Ura+ prototrophs from a Ura- strain carrying URA3 on a plasmid in its mitochondria enabled us to detect plasmid movement to the nucleus. Conversely, as the plasmid used also contained the mitochondrial gene COX2 required for respiratory growth, we were able to set up corresponding selections to detect migration of DNA from the nucleus to the mitochondria. Our results show that, in yeast, DNA escapes from mitochondria and appears in the nucleus at a surprisingly high frequency (approximately 2 x 10(-5) per cell per generation). But the rate at which DNA makes the journey in the opposite direction--nucleus to mitochondria--is apparently at least 100,000 times less.