2,334 research outputs found
Modern Vertical Deformation above the Sumatran Subduction Zone: Paleogeodetic Insights from Coral Microatolls
Coral microatolls from the coast and outer-arc islands of Western Sumatra retain a stratigraphic and morphologic record of relative sea-level change, which is due in large part to vertical tectonic deformation above the Sumatran subduction zone. Low water levels, whose fluctuations produce measurable changes in coral morphology, limit the upward growth of the microatolls. Annual rings, derived from seasonal variations in coral density, serve as an internal chronometer of coral growth. The microatolls act as natural long-term tide gauges, recording sea-level variations on time scales of decades. Field observations and stratigraphic analysis of seven microatolls, five from the outer-arc islands and two from the mainland coast, indicate that the Mentawai Islands have been submerging at rates of 4–10 mm/yr over the last four or five decades, while the mainland has remained relatively stable. The presence of fossil microatolls up to several thousand years old in the intertidal zone indicates that little permanent vertical deformation has occurred over that time. Thus, most of the strain accumulated in the past few decades represents interseismic deformation that is recovered during earthquakes. Elastic dislocation models using these submergence data suggest that elastic strain is being accumulated in the interseismic period and that the subduction zone in this region is fully coupled
The core collapse supernova rate in the sdss-ii supernova survey
The Sloan Digital Sky Survey II Supernova Survey (SDSS-II SN), though designed as a type Ia supernova search for cosmology, also discovered a large sample of core collapse supernovae (CCSN). I use the SDSS-II SN data to measure the volumetric CCSN rate in the redshift range (0.03 \u3c z \u3c 0.09), finding a volume-averaged rate of 0.98±0.18 ×10⊃−4⊃h⊂70⊂⊃3⊃yr⊃−1⊃Mpc⊃−3⊃. The CCSN luminosity function is also extracted from the data, and its implications on the cosmic star formation history are considered
Submergence and uplift associated with the giant 1833 Sumatran subduction earthquake: Evidence from coral microatolls
The giant Sumatran subduction earthquake of 1833 appears as a large emergence event in fossil coral microatolls on the reefs of Sumatra's outer-arc ridge. Stratigraphic analysis of these and living microatolls nearby allow us to estimate that 1833 emergence increased trenchward from about 1 to 2 m. This pattern and magnitude of uplift are consistent with about 13 m of slip on the subduction interface and suggest a magnitude (M_w) of 8.8–9.2 for the earthquake. The fossil microatolls also record rapid submergence in the decades prior to the earthquake, with rates increasing trenchward from 5 to 11 mm/yr. Living microatolls show similar rates and a similar pattern. The fossil microatolls also record at least two less extensive emergence events in the decades prior to 1833. These observations show that coral microatolls can be useful paleoseismic and paleogeodetic instruments in convergent tectonic environments
Density functional theory embedding for correlated wavefunctions: Improved methods for open-shell systems and transition metal complexes
Density functional theory (DFT) embedding provides a formally exact framework
for interfacing correlated wave-function theory (WFT) methods with lower-level
descriptions of electronic structure. Here, we report techniques to improve the
accuracy and stability of WFT-in-DFT embedding calculations. In particular, we
develop spin-dependent embedding potentials in both restricted and unrestricted
orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and
we develop an orbital-occupation-freezing technique to improve the convergence
of optimized effective potential (OEP) calculations that arise in the
evaluation of the embedding potential. The new techniques are demonstrated in
applications to the van-der-Waals-bound ethylene-propylene dimer and to the
hexaaquairon(II) transition-metal cation. Calculation of the dissociation curve
for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces
full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating
errors in the dispersion interactions due to conventional exchange-correlation
(XC) functionals while simultaneously avoiding errors due to subsystem
partitioning across covalent bonds. Application of WFT-in-DFT embedding to the
calculation of the low-spin/high-spin splitting energy in the hexaaquairon(II)
cation reveals that the majority of the dependence on the DFT XC functional can
be eliminated by treating only the single transition-metal atom at the WFT
level; furthermore, these calculations demonstrate the substantial effects of
open-shell contributions to the embedding potential, and they suggest that
restricted open-shell WFT-in-DFT embedding provides better accuracy than
unrestricted open-shell WFT-in-DFT embedding due to the removal of spin
contamination.Comment: 11 pages, 5 figures, 2 table
The Spindle Assembly Checkpoint
During mitosis and meiosis, the spindle assembly checkpoint acts to maintain genome stability by delaying cell division until accurate chromosome segregation can be guaranteed. Accuracy requires that chromosomes become correctly attached to the microtubule spindle apparatus via their kinetochores. When not correctly attached to the spindle, kinetochores activate the spindle assembly checkpoint network, which in turn blocks cell cycle progression. Once all kinetochores become stably attached to the spindle, the checkpoint is inactivated, which alleviates the cell cycle block and thus allows chromosome segregation and cell division to proceed. Here we review recent progress in our understanding of how the checkpoint signal is generated, how it blocks cell cycle progression and how it is extinguished
Abstracts and Citations
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138936/1/head13152.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138936/2/head13152_am.pd
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