2,844 research outputs found
Could cancer drugs provide ammunition against aging?
Recent advances in our understanding of the molecular and cellular signaling pathways that drive aging have revealed several genetic and environmental manipulations that can increase lifespan across different species. Research on the underlying biology of aging has not only revealed it to be a biologically malleable process but has also paved the way for the development of pharmacological interventions that could increase lifespan and delay the onset and/or progression of age-related disease
Regional geochemical variations in a metamorphosed black shale: a reconnaissance study of the Silurian Smalls Falls Formation, Maine, USA
A reconnaissance geochemical study of 21 samples of sulphidic black phyllite and schist from the Silurian Smalls Falls Formation in Maine was undertaken in order to evaluate compositional changes during regional metamorphism. These samples represent variably metamorphosed black shale. Analyzed samples come from the chlorite zone in northern Maine and the biotite, garnet, and staurolite-andalusite zones in west-central Maine. Strata of the Smalls Falls Formation are distinctive in containing abundant pyrite and/or pyrrhotite (total S = 1.2–9.7 wt%), but only minor organic matter or graphite (TOC = 0.43–1.85 wt%); TOC/S ratios are uniformly low (average = 0.37 ± 0.22). Median enrichment factors were calculated for each element by normalizing the concentration to Ti in each sample to the Ti-normalized median composition of global black shale. In the chlorite zone, moderate to large decreases in enrichment factors (-23.1 to -49.8%) are evident for V, Cr, Cu, Ni, Zn, Pb, Sb, and U, attributed here to various factors during sedimentation plus variable element mobility during diagenesis. With increasing metamorphic grade (biotite through staurolite-andalusite zones), systematic small to extreme decreases (-14.5 to -99.0%) were found for Ba, Sb, Au, and U, together with less-systematic moderate to large decreases (-35.4 to -61.1%) for V and As. Molybdenum shows an extreme decrease (-94.7%) from the garnet to staurolite-andalusite zones. Excluding Ba, these results are interpreted to mainly reflect mobility of trace elements during pyrite recrystallization, and during the metamorphic transformations of organic matter to graphite and of pyrite to pyrrhotite. Moderate to large increases for Rb (+28.1 to +61.5%) and Th (+39.1 to +47.3%) from the biotite to staurolite-andalusite zones likely record the introduction of alkalis and mass loss, respectively, during metamorphism. Three samples from one site in the garnet zone differ in having anomalously high Fe/Al and low La/Yb ratios, attributed here to epigenetic formation of pyrite and related leaching of light rare earth elements during syn-metamorphic, channelized fluid flow.Geologic and geochemical data indicate that strata of the Smalls Falls Formation were deposited during an interval of anoxia on the northwestern flank of the Central Maine Basin, for which detrital sources included an evolved continental arc. Onset of anoxia coincided with deposition of the Mayflower Hill Formation of the Vassalboro Group, on the basin’s southeastern flank, related to emergence of the Brunswick subduction complex. We suggest that this emergence played a role in promoting both lateral and vertical circulation changes, nutrient loading, and deoxygenation through subsequent basin closure that culminated with Acadian deformation and metamorphism. Based on the relatively high contents of total sulphur present in our Smalls Falls samples, sediments in the Black Sea represent the only known plausible candidate among those in modern suboxic to euxinic basins
Unintended Consequences Of Equal Employment Opportunity: Unequal Parties In The Selection Process?
There arevarious regulations that are intended to promote equal employment opportunityand avoid illegal discrimination in the employment process. These regulationsdetermine what information employers may seek, and require that informationsought be job-related or it is illegal to seek such information as age, maritalstatus, or religion. Information that is not a bona fide occupationalqualification (BFOQ) is usually out of bounds as employers gather informationto determine the suitability of applicants for employment. Since one of thebedrock laws affecting the employment relationship is the “at will” doctrinethat assumes both employer and applicant come together as equal partners in theformation of the employment contract, this paper raises the issues aboutwhether such regulations unintentionally leave the employer at an informationdisadvantage by negating the concept of equality assumed by the “at will”doctrine. Some suggestions for practical ways of reducing the identifiedemployer information disadvantages are provided
A2: Smalls Falls Revisted: A Journey Through a Paleozoic Sedimentary Basin
Guidebook for field trips in Western Maine and Northern New Hampshire: New England Intercollegiate Geological Conference, p. 35-60
Lattice thermal conductivity of disordered NiPd and NiPt alloys
Numerical calculations of lattice thermal conductivity are reported for the
binary alloys NiPd and NiPt. The present work is a continuation of an earlier
paper by us [PRB, 72, 214207 (2005)]which had developed a theoretical framework
for the calculation of configuration-averaged lattice thermal conductivity and
thermal diffusivity in disordered alloys. The formulation was based on the
augmented space theorem combined with a scattering diagram technique. In this
paper we shall show dependence of the lattice thermal conductivity on a series
of variables like phonon frequency, temperature and alloy composition. The
temperature dependence of and its realtion to the measured thermal
conductivity is discussed. The concentration dependence of appears to
justify the notion of a minimum thermal conductivity as discussed by Kittel,
Slack and others. We also study the frequency and composition dependence of the
thermal diffusivity averaged over modes. A numerical estimate of this quantity
gives an idea about the location of mobility edge and the fraction of states in
the frequency spectrum which is delocalized.Comment: 23 pages, 18 figure
Thermoelectric transport in strained Si and Si/Ge heterostructures
The anisotropic thermoelectric transport properties of bulk silicon strained
in [111]-direction were studied by detailed first-principles calculations
focussing on a possible enhancement of the power factor. Electron as well as
hole doping were examined in a broad doping and temperature range. At low
temperature and low doping an enhancement of the power factor was obtained for
compressive and tensile strain in the electron-doped case and for compressive
strain in the hole-doped case. For the thermoelectrically more important high
temperature and high doping regime a slight enhancement of the power factor was
only found under small compressive strain with the power factor overall being
robust against applied strain. To extend our findings the anisotropic
thermoelectric transport of an [111]-oriented Si/Ge superlattice was
investigated. Here, the cross-plane power factor under hole-doping was
drastically suppressed due to quantum-well effects, while under electron-doping
an enhanced power factor was found. With that, we state a figure of merit of
ZT and ZT at T=\unit[300]{K} and T=\unit[900]{K} for the
electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in
terms of band structure features
Glass-Like Heat Conduction in High-Mobility Crystalline Semiconductors
The thermal conductivity of polycrystalline semiconductors with type-I
clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr
and/or Eu) exhibit lattice thermal conductivities typical of amorphous
materials. Remarkably, this behavior occurs in spite of the well-defined
crystalline structure and relatively high electron mobility (). The dynamics of dopant ions and their interaction with the
polyhedral cages of the structure are a likely source of the strong phonon
scattering.Comment: 4 pages, 3 postscript figures, to be published, Phys. Rev. Let
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