6,406 research outputs found
Migration and Final Location of Hot Super Earths in the Presence of Gas Giants
Based on the conventional sequential-accretion paradigm, we have proposed
that, during the migration of first-born gas giants outside the orbits of
planetary embryos, super Earth planets will form inside the 2:1 resonance
location by sweeping of mean motion resonances (Zhou et al. 2005). In this
paper, we study the subsequent evolution of a super Earth (m_1) under the
effects of tidal dissipation and perturbation from a first-born gas giant (m_2)
in an outside orbit. Secular perturbation and mean motion resonances
(especially 2:1 and 5:2 resonances) between m_1 and m_2 excite the eccentricity
of m_1, which causes the migration of m_1 and results in a hot super Earth. The
calculated final location of the hot super Earth is independent of the tidal
energy dissipation factor Q'. The study of migration history of a Hot Super
Earth is useful to reveal its Q' value and to predict its final location in the
presence of one or more hot gas giants. When this investigation is applied to
the GJ876 system, it correctly reproduces the observed location of GJ876d
around 0.02AU.Comment: 7 pages, 4 figure
Mitochondrial metagenomics: letting the genes out of the bottle
‘Mitochondrial metagenomics’ (MMG) is a methodology for shotgun sequencing of total DNA from specimen mixtures and subsequent bioinformatic extraction of mitochondrial sequences. The approach can be applied to phylogenetic analysis of taxonomically selected taxa, as an economical alternative to mitogenome sequencing from individual species, or to environmental samples of mixed specimens, such as from mass trapping of invertebrates. The routine generation of mitochondrial genome sequences has great potential both for systematics and community phylogenetics. Mapping of reads from low-coverage shotgun sequencing of environmental samples also makes it possible to obtain data on spatial and temporal turnover in whole-community phylogenetic and species composition, even in complex ecosystems where species-level taxonomy and biodiversity patterns are poorly known. In addition, read mapping can produce information on species biomass, and potentially allows quantification of within-species genetic variation. The success of MMG relies on the formation of numerous mitochondrial genome contigs, achievable with standard genome assemblers, but various challenges for the efficiency of assembly remain, particularly in the face of variable relative species abundance and intra-specific genetic variation. Nevertheless, several studies have demonstrated the power of mitogenomes from MMG for accurate phylogenetic placement, evolutionary analysis of species traits, biodiversity discovery and the establishment of species distribution patterns; it offers a promising avenue for unifying the ecological and evolutionary understanding of species diversity
Shot noise detection in hBN-based tunnel junctions
High quality Au/hBN/Au tunnel devices are fabricated using transferred
atomically thin hexagonal boron nitride as the tunneling barrier. All tunnel
junctions show tunneling resistance on the order of several
k/m. Ohmic I-V curves at small bias with no signs of
resonances indicate the sparsity of defects. Tunneling current shot noise is
measured in these devices, and the excess shot noise shows consistency with
theoretical expectations. These results show that atomically thin hBN is an
excellent tunnel barrier, especially for the study of shot noise properties,
and this can enable the study of tunneling density of states and shot noise
spectroscopy in more complex systems.Comment: 20 pages, 4 figure
Euclidean Path Integral, D0-Branes and Schwarzschild Black Holes in Matrix Theory
The partition function in Matrix theory is constructed by Euclidean path
integral method. The D0-branes, which move around in the finite region with a
typical size of Schwarzschild radius, are chosen as the background. The mass
and entropy of the system obtained from the partition function contain the
parameters of the background. After averaging the mass and entropy over the
parameters, we find that they match the properties of 11D Schwarzschild black
holes. The period \b of Euclidean time can be identified with the reciprocal
of the boosted Hawking temperature. The entropy is shown to be proportional
to the number of Matrix theory partons, which is a consequence of the
D0-brane background.Comment: 15 pages, Late
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