Boston University

About: Boston University is a education organization based out in Boston, Massachusetts, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 48688 authors who have published 119622 publications receiving 6276020 citations. The organization is also known as: BU & Boston U.

Subduction factory 1. Theoretical mineralogy, densities, seismic wave speeds, and H 2 O contents

Abstract: [1] We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for mid-ocean ridge basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (<1.3 wt % H2O), and the uppermost mantle ranges from unhydrated to � 20% serpentinized (� 2.4 wt % H2O). Anhydrous eclogite cannot be distinguished from harzburgite on the basis of wave speeds, but its � 6% greater density may render it detectable through gravity measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60–80% hydration. INDEX TERMS: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 3660 Mineralogy and Petrology: Metamorphic petrology; 3919 Mineral Physics: Equations of state; 5199 Physical Properties of Rocks: General or miscellaneous; 8123 Tectonophysics: Dynamics, seismotectonics; KEYWORDS: subduction, seismic velocities, mineral physics, H2O

Sequence features and chromatin structure around the genomic regions bound by 119 human transcription factors.

Abstract: Chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) has become the dominant technique for mapping transcription factor (TF) binding regions genome-wide. We performed an integrative analysis centered around 457 ChIP-seq data sets on 119 human TFs generated by the ENCODE Consortium. We identified highly enriched sequence motifs in most data sets, revealing new motifs and validating known ones. The motif sites (TF binding sites) are highly conserved evolutionarily and show distinct footprints upon DNase I digestion. We frequently detected secondary motifs in addition to the canonical motifs of the TFs, indicating tethered binding and cobinding between multiple TFs. We observed significant position and orientation preferences between many cobinding TFs. Genes specifically expressed in a cell line are often associated with a greater occurrence of nearby TF binding in that cell line. We observed cell-line-specific secondary motifs that mediate the binding of the histone deacetylase HDAC2 and the enhancer-binding protein EP300. TF binding sites are located in GC-rich, nucleosome-depleted, and DNase I sensitive regions, flanked by well-positioned nucleosomes, and many of these features show cell type specificity. The GC-richness may be beneficial for regulating TF binding because, when unoccupied by a TF, these regions are occupied by nucleosomes in vivo. We present the results of our analysis in a TF-centric web repository Factorbook (http://factorbook.org) and will continually update this repository as more ENCODE data are generated.

Organization of growing random networks

Abstract: The organizational development of growing random networks is investigated. These growing networks are built by adding nodes successively, and linking each to an earlier node of degree k with an attachment probability ${A}_{k}.$ When ${A}_{k}$ grows more slowly than linearly with k, the number of nodes with k links, ${N}_{k}(t),$ decays faster than a power law in k, while for ${A}_{k}$ growing faster than linearly in k, a single node emerges which connects to nearly all other nodes. When ${A}_{k}$ is asymptotically linear, ${N}_{k}(t)\ensuremath{\sim}{\mathrm{tk}}^{\ensuremath{-}\ensuremath{ u}},$ with $\ensuremath{ u}$ dependent on details of the attachment probability, but in the range $2l\ensuremath{ u}l\ensuremath{\infty}.$ The combined age and degree distribution of nodes shows that old nodes typically have a large degree. There is also a significant correlation in the degrees of neighboring nodes, so that nodes of similar degree are more likely to be connected. The size distributions of the in and out components of the network with respect to a given node---namely, its ``descendants'' and ``ancestors''---are also determined. The in component exhibits a robust ${s}^{\ensuremath{-}2}$ power-law tail, where s is the component size. The out component has a typical size of order $\mathrm{ln}t,$ and it provides basic insights into the genealogy of the network.

Mitochondrial DNA deletions are abundant and cause functional impairment in aged human substantia nigra neurons

Abstract: Using a novel single-molecule PCR approach to quantify the total burden of mitochondrial DNA (mtDNA) molecules with deletions, we show that a high proportion of individual pigmented neurons in the aged human substantia nigra contain very high levels of mtDNA deletions. Molecules with deletions are largely clonal within each neuron; that is, they originate from a single deleted mtDNA molecule that has expanded clonally. The fraction of mtDNA deletions is significantly higher in cytochrome c oxidase (COX)-deficient neurons than in COX-positive neurons, suggesting that mtDNA deletions may be directly responsible for impaired cellular respiration.

Echocardiographic criteria for left ventricular hypertrophy: the Framingham heart study

Abstract: Of 6,148 original cohort and offspring subjects of the Framingham Heart Study who underwent routine evaluation, a healthy group of 347 men (aged 42 ± 12 years) and 517 women (aged 43 ± 12 years) was identified to develop echocardiographic criteria for left ventricular (LV) hypertrophy. Healthy subjects were defined as normotensive, receiving no cardiac or antihypertensive medications, nonobese and free of cardiopulmonary disease. Echocardiographic criteria (in accordance with the American Society of Echocardiography convention) for LV hypertrophy, based on mean plus 2 standard deviations for LV mass, LV mass corrected for body surface area and LV mass corrected for height in this healthy sample are, respectively: 294 g, 150 g/m2 and 163 g/m In men and 198 g, 120 g/m2 and 121 g/m in women. Criteria based on LV mass/height result in higher prevalence rates of LV hypertrophy than LV mass/body surface area while still correctIng for body size. The prevalence of LV hypertrophy in the entire study population (using LV mass/height criteria) is 16% in men and 19% in women. Until outcome guided criteria for LV hypertrophy are developed, application of sex-specific criteria based on a healthy population distribution of LV mass offer the best approach to echocardiographic diagnosis of LV hypertrophy.