600 research outputs found
Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
The Earth's Moon is thought to have formed by an impact between the Earth and
an impactor around 4.5 billion years ago. This impact could have been so
energetic that it could have mixed and homogenized the Earth's mantle. However,
this view appears to be inconsistent with geochemical studies that suggest that
the Earth's mantle was not mixed by the impact. Another plausible outcome is
that this energetic impact melted the whole mantle, but the extent of mantle
melting is not well understood even though it must have had a significant
effect on the subsequent evolution of the Earth's interior and atmosphere. To
understand the initial state of the Earth's mantle, we perform giant impact
simulations using smoothed particle hydrodynamics (SPH) for three different
models: (a) standard: a Mars-sized impactor hits the proto-Earth, (b)
fast-spinning Earth: a small impactor hits a rapidly rotating proto-Earth, and
(c) sub-Earths: two half Earth-sized planets collide. We use two types of
equations of state (MgSiO3 liquid and forsterite) to describe the Earth's
mantle. We find that the mantle remains unmixed in (a), but it may be mixed in
(b) and (c). The extent of mixing is most extensive in (c). Therefore, (a) is
most consistent and (c) may be least consistent with the preservation of the
mantle heterogeneity, while (b) may fall between. We determine that the Earth's
mantle becomes mostly molten by the impact in all of the models. The choice of
the equations of state does not affect these outcomes. Additionally, our
results indicate that entropy gains of the mantle materials by a giant impact
cannot be predicted well by the Rankine-Hugoniot equations. Moreover, we show
that the mantle can remain unmixed on a Moon-forming timescale if it does not
become mixed by the impact.Comment: Accepted for publication in EPS
Investigation of the Initial State of the Moon-Forming Disk: Bridging SPH Simulations and Hydrostatic Models
According to the standard giant impact hypothesis, the Moon formed from a
partially vaporized disk generated by a collision between the proto Earth and a
Mars sized impactor. The initial structure of the disk significantly affects
the Moon forming process, including the Moons mass, its accretion time scale,
and its isotopic similarity to Earth. The dynamics of the impact event
determines the initial structure of a nearly hydrostatic Moon forming disk.
However, the hydrostatic and hydrodynamic models have been studied separately
and their connection has not previously been well quantified. Here, we show the
extent to which the properties of the disk can be inferred from Smoothed
Particle Hydrodynamic (SPH) simulations. By using entropy, angular momentum and
mass distributions of the SPH outputs as approximately conserved quantities, we
compute the two dimensional disk structure. We investigate four different
models: (a) standard, the canonical giant impact model, (b) fast spinning
Earth, a collision between a fast spinning Earth and a small impactor, (c) sub
Earths, a collision between two objects with half Earths mass, and (d)
intermediate, a collision of two bodies whose mass ratio is 7:3. Our SPH
calculations show that the initial disk has approximately uniform entropy. The
disks of the fast spinning Earth and sub Earths cases are hotter and more
vaporized (80-90% vapor) than the standard case (20%). The intermediate case
falls between these values. In the highly vaporized cases, our procedure fails
to establish a unique surface density profile of the disk because the disk is
unstable according to the Rayleigh criterion. In these cases, we estimate
non-unique disk models by conserving global quantities. We also develop a semi
analytic model for the thermal structure of the disk, which requires only two
inputs: the average entropy and the surface density of the disk.Comment: Accepted for publication in Icaru
NcorpiN : A software for N-body integration in collisional and fragmenting systems
NcorpiN is a -body software developed for the time-efficient
integration of collisional and fragmenting systems of planetesimals or moonlets
orbiting a central mass. It features a fragmentation model, based on crater
scaling and ejecta models, able to realistically simulate a violent impact. The
user of NcorpiN can choose between four different built-in modules
to compute self-gravity and detect collisions. One of these makes use of a
mesh-based algorithm to treat mutual interactions in time.
Another module, much more efficient than the standard Barnes-Hut tree code, is
a tree-based algorithm called FalcON. It relies on fast
multipole expansion for gravity computation and we adapted it to collision
detection as well. Computation time is reduced by building the tree structure
using a three-dimensional Hilbert curve. For the same precision in mutual
gravity computation, NcorpiN is found to be up to 25 times faster
than the famous software REBOUND. NcorpiN is written entirely in
the C language and only needs a C compiler to run. A python add-on, that
requires only basic python libraries, produces animations of the simulations
from the output files. The name NcorpiN, reminding of a scorpion,
comes from the French -corps, meaning -body, and from the mathematical
notation , due to the running time of the software being almost
linear in the total number of moonlets. NcorpiN is designed
for the study of accreting or fragmenting disks of planetesimal or moonlets. It
detects collisions and computes mutual gravity faster than REBOUND, and unlike
other -body integrators, it can resolve a collision by fragmentation. The
fast multipole expansions are implemented up to order six to allow for a high
precision in mutual gravity computation.Comment: 29 pages, 6 figure
MicroRNAs from biology to future pharmacotherapy: Regulation of cytochrome P450s and nuclear receptors
金沢大学医薬保健研究域薬学系MicroRNAs (miRNAs) are a family of short, non-coding RNAs whose final product is a 22-nucleotide functional RNA molecule. They regulate the expression of target genes by binding to complementary regions of transcripts to repress their translation or promote mRNA degradation. Since miRNAs regulate every aspect of cellular function, their dysregulation is associated with a variety of diseases including cancer, diabetes, and cardiovascular diseases. Therefore, miRNAs are now considered new therapeutic targets. However, the roles of miRNAs in the metabolism of xenobiotics and endobiotics have only recently been revealed. This review describes the current knowledge on the regulation of cytochrome P450s and nuclear receptors by miRNAs, the physiological and clinical significance. The miRNA expression is readily altered by chemicals, carcinogens, drugs, hormones, stress, or diseases, and the dysregulation of specific miRNAs might lead to changes in the drug metabolism potency or pharmacokinetics as well as pathophysiological changes. In the field of pharmacogenomics, the evaluation of miRNA-related polymorphisms would provide useful information for personalized medicine. Utilizing miRNAs opens a new era in the fields of drug metabolism and pharmacokinetics as well as toxicology. © 2011 Elsevier Inc. All rights reserved
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