484 research outputs found
Magnetotunneling Between Two-dimensional Electron Gases in InAs-AlSb-GaSb Heterostructures
We have observed that the tunneling magnetoconductance between
two-dimensional (2D) electron gases formed at nominally identical InAs-AlSb
interfaces most often exhibits two sets of Shubnikov-de Haas oscillations with
almost the same frequency. This result is explained quantitatively with a model
of the conductance in which the 2D gases have different densities and can
tunnel between Landau levels with different quantum indices. When the epitaxial
growth conditions of the interfaces are optimized, the zero-bias
magnetoconductance shows a single set of oscillations, thus proving that the
asymmetry between the two electron gases can be eliminated.Comment: RevTeX format including 4 figures; submit for publicatio
A comprehensive set of transcript sequences of the heavy metal hyperaccumulator Noccaea caerulescens
Noccaea caerulescens is an extremophile plant species belonging to the Brassicaceae family. It has adapted to grow on soils containing high, normally toxic, concentrations of metals such as nickel, zinc, and cadmium. Next to being extremely tolerant to these metals, it is one of the few species known to hyperaccumulate these metals to extremely high concentrations in their aboveground biomass. In order to provide additional molecular resources for this model metal hyperaccumulator species to study and understand the mechanism of adaptation to heavy metal exposure, we aimed to provide a comprehensive database of transcript sequences for N. caerulescens. In this study, 23,830 transcript sequences (isotigs) with an average length of 1025 bp were determined for roots, shoots and inflorescences of N. caerulescens accession “Ganges” by Roche GS-FLEX 454 pyrosequencing. These isotigs were grouped into 20,378 isogroups, representing potential genes. This is a large expansion of the existing N. caerulescens transcriptome set consisting of 3705 unigenes. When translated and compared to a Brassicaceae proteome set, 22,232 (93.2%) of the N. caerulescens isotigs (corresponding to 19,191 isogroups) had a significant match and could be annotated accordingly. Of the remaining sequences, 98 isotigs resembled non-plant sequences and 1386 had no significant similarity to any sequence in the GenBank database. Among the annotated set there were many isotigs with similarity to metal homeostasis genes or genes for glucosinolate biosynthesis. Only for transcripts similar to Metallothionein3 (MT3), clear evidence for an additional copy was found. This comprehensive set of transcripts is expected to further contribute to the discovery of mechanisms used by N. caerulescens to adapt to heavy metal exposur
Vortex loop operators, M2-branes and holography
This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/ by/4.0/archiveprefix: arXiv primaryclass: hep-th reportnumber: HU-EP-08-43 slaccitation: %%CITATION = ARXIV:0810.4344;%%archiveprefix: arXiv primaryclass: hep-th reportnumber: HU-EP-08-43 slaccitation: %%CITATION = ARXIV:0810.4344;%
The Pseudo-Conformal Universe: Scale Invariance from Spontaneous Breaking of Conformal Symmetry
We present a novel theory of the very early universe which addresses the
traditional horizon and flatness problems of big bang cosmology and predicts a
scale invariant spectrum of perturbations. Unlike inflation, this scenario
requires no exponential accelerated expansion of space-time. Instead, the early
universe is described by a conformal field theory minimally coupled to gravity.
The conformal fields develop a time-dependent expectation value which breaks
the flat space so(4,2) conformal symmetry down to so(4,1), the symmetries of de
Sitter, giving perturbations a scale invariant spectrum. The solution is an
attractor, at least in the case of a single time-dependent field. Meanwhile,
the metric background remains approximately flat but slowly contracts, which
makes the universe increasingly flat, homogeneous and isotropic, akin to the
smoothing mechanism of ekpyrotic cosmology. Our scenario is very general,
requiring only a conformal field theory capable of developing the appropriate
time-dependent expectation values, and encompasses existing incarnations of
this idea, specifically the U(1) model of Rubakov and the Galileon Genesis
scenario. Its essential features depend only on the symmetry breaking pattern
and not on the details of the underlying lagrangian. It makes generic
observational predictions that make it potentially distinguishable from
standard inflation, in particular significant non-gaussianities and the absence
of primordial gravitational waves.Comment: 51 pages, 3 figures. v2 discussion and refs added, minus sign in
transformation laws fixed. Version appearing in JCA
Beyond genomic variation - comparison and functional annotation in three Brassica rapa genotypes: a turnip, a rapid cycling and a Chinese cabbage
Background - Brassica rapa is an economically important crop species. During its long breeding history, a large number of morphotypes have been generated, including leafy vegetables such as Chinese cabbage and pakchoi, turnip tuber crops and oil crops. Results - To investigate the genetic variation underlying this morphological variation, we re-sequenced, assembled and annotated the genomes of two B. rapa subspecies, turnip crops (turnip) and a rapid cycling. We then analysed the two resulting genomes together with the Chinese cabbage Chiifu reference genome to obtain an impression of the B. rapa pan-genome. The number of genes with protein-coding changes between the three genotypes was lower than that among different accessions of Arabidopsis thaliana, which can be explained by the smaller effective population size of B. rapa due to its domestication. Based on orthology to a number of non-brassica species, we estimated the date of divergence among the three B. rapa morphotypes at approximately 250,000 YA, far predating Brassica domestication (5,000-10,000 YA). Conclusions - By analysing genes unique to turnip we found evidence for copy number differences in peroxidases, pointing to a role for the phenylpropanoid biosynthesis pathway in the generation of morphological variation. The estimated date of divergence among three B. rapa morphotypes implies that prior to domestication there was already considerably divergence among B. rapa genotypes. Our study thus provides two new B. rapa reference genomes, delivers a set of computer tools to analyse the resulting pan-genome and uses these to shed light on genetic drivers behind the rich morphological variation found in B. rapa
Unconventional Cosmology
I review two cosmological paradigms which are alternative to the current
inflationary scenario. The first alternative is the "matter bounce", a
non-singular bouncing cosmology with a matter-dominated phase of contraction.
The second is an "emergent" scenario, which can be implemented in the context
of "string gas cosmology". I will compare these scenarios with the inflationary
one and demonstrate that all three lead to an approximately scale-invariant
spectrum of cosmological perturbations.Comment: 45 pages, 10 figures; invited lectures at the 6th Aegean Summer
School "Quantum Gravity and Quantum Cosmology", Chora, Naxos, Greece, Sept.
12 - 17 2012, to be publ. in the proceedings; these lecture notes form an
updated version of arXiv:1003.1745 and arXiv:1103.227
T-functions revisited: New criteria for bijectivity/transitivity
The paper presents new criteria for bijectivity/transitivity of T-functions
and fast knapsack-like algorithm of evaluation of a T-function. Our approach is
based on non-Archimedean ergodic theory: Both the criteria and algorithm use
van der Put series to represent 1-Lipschitz -adic functions and to study
measure-preservation/ergodicity of these
Prevalence and phylogenetic characterization of canine coronavirus from diseased pet dogs in Beijing, China
Holography of BPS surface operators
We study a class of dilatation invariant BPS surface operators in
4-dimensional N=4 Super Yang-Mills theory and their holographic duals in type
IIB string theory in AdS_5 x S^5. First we take an example of 1/4 BPS surface
operator and study it in detail from the holographic point of view. The gravity
dual of this surface operator is a D3-brane characterized by a holomorphic
submanifold. The supersymmetry and vacuum expectation value are checked in both
the gauge theory side and the gravity side. We also calculate the correlation
functions with the chiral primary operators in both sides and find good
agreement. Next we consider more general dilatation invariant BPS surface
operators. The gravity duals of those operators are proposed.Comment: 34 pages, 1 figure, added comments about path-integra
Giant Planet Formation and Migration
© 2018, The Author(s). Planets form in circumstellar discs around young stars. Starting with sub-micron sized dust particles, giant planet formation is all about growing 14 orders of magnitude in size. It has become increasingly clear over the past decades that during all stages of giant planet formation, the building blocks are extremely mobile and can change their semimajor axis by substantial amounts. In this chapter, we aim to give a basic overview of the physical processes thought to govern giant planet formation and migration, and to highlight possible links to water delivery.S.-J. Paardekooper is supported by a Royal Society University Research Fellowship. A. Johansen is supported by the Knut and Alice Wallenberg Foundation, the Swedish Research Council (grant 2014-5775) and the European Research Council (ERC Starting Grant 278675-PEBBLE2PLANET)
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