64,156 research outputs found
A strong constitutive ethylene-response phenotype conferred on Arabidopsis plants containing null mutations in the ethylene receptors ETR1 and ERS1
Background: The ethylene receptor family of Arabidopsis consists of five members, falling into two subfamilies. Subfamily 1 is composed of ETR1 and ERS1, and subfamily 2 is composed of ETR2, ERS2, and EIN4. Although mutations have been isolated in the genes encoding all five family members, the only previous insertion allele of ERS1 (ers1-2) is a partial loss-of-function mutation based on our analysis. The purpose of this study was to determine the extent of signaling mediated by subfamily-1 ethylene receptors through isolation and characterization of null mutations.
Results: We isolated new T-DNA insertion alleles of subfamily 1 members ERS1 and ETR1 (ers1-3 and etr1-9, respectively), both of which are null mutations based on molecular, biochemical, and genetic analyses. Single mutants show an ethylene response similar to wild type, although both mutants are slightly hypersensitive to ethylene. Double mutants of ers1-3 with etr1-9, as well as with the previously isolated etr1-7, display a constitutive ethylene-response phenotype more pronounced than that observed with any previously characterized combination of ethylene receptor mutations. Dark-grown etr1-9;ers1-3 and etr1-7;ers1-3 seedlings display a constitutive triple-response phenotype. Light-grown etr1-9;ers1-3 and etr1-7;ers1-3 plants are dwarfed, largely sterile, exhibit premature leaf senescence, and develop novel filamentous structures at the base of the flower. A reduced level of ethylene response was still uncovered in the double mutants, indicating that subfamily 2 receptors can independently contribute to signaling, with evidence suggesting that this is due to their interaction with the Raf-like kinase CTR1.
Conclusion: Our results are consistent with the ethylene receptors acting as redundant negative regulators of ethylene signaling, but with subfamily 1 receptors playing the predominant role. Loss of a single member of subfamily 1 is largely compensated for by the activity of the other member, but loss of both subfamily members results in a strong constitutive ethylene-response phenotype. The role of subfamily 1 members is greater than previously suspected and analysis of the double mutant null for both ETR1 and ERS1 uncovers novel roles for the receptors not previously characterized
Forward-backward asymmetry of photoemission in C excited by few-cycle laser pulses
We theoretically analyze angle-resolved photo-electron spectra (ARPES)
generated by the interaction of C with intense, short laser pulses. In
particular, we focus on the impact of the carrier-envelope phase (CEP) onto the
angular distribution. The electronic dynamics is described by time-dependent
density functional theory, and the ionic background of \csixty is
approximated by a particularly designed jellium model. Our results show a clear
dependence of the angular distributions onto the CEP for very short pulses
covering only very few laser cycles, which disappears for longer pulses. For
the specific laser parameters used in a recent experiments, a very good
agreement is obtained. Furthermore, the asymmetry is found to depend on the
energy of the emitted photoelectrons. The strong influence of the angular
asymmetry of electron emission onto the CEP and pulse duration suggests to use
this sensitivity as a means to analyze the structure of few-cycle laser pulses.Comment: 8 pages, 6 figure
The Effects of Halo Assembly Bias on Self-Calibration in Galaxy Cluster Surveys
Self-calibration techniques for analyzing galaxy cluster counts utilize the
abundance and the clustering amplitude of dark matter halos. These properties
simultaneously constrain cosmological parameters and the cluster
observable-mass relation. It was recently discovered that the clustering
amplitude of halos depends not only on the halo mass, but also on various
secondary variables, such as the halo formation time and the concentration;
these dependences are collectively termed assembly bias. Applying modified
Fisher matrix formalism, we explore whether these secondary variables have a
significant impact on the study of dark energy properties using the
self-calibration technique in current (SDSS) and the near future (DES, SPT, and
LSST) cluster surveys. The impact of the secondary dependence is determined by
(1) the scatter in the observable-mass relation and (2) the correlation between
observable and secondary variables. We find that for optical surveys, the
secondary dependence does not significantly influence an SDSS-like survey;
however, it may affect a DES-like survey (given the high scatter currently
expected from optical clusters) and an LSST-like survey (even for low scatter
values and low correlations). For an SZ survey such as SPT, the impact of
secondary dependence is insignificant if the scatter is 20% or lower but can be
enhanced by the potential high scatter values introduced by a highly correlated
background. Accurate modeling of the assembly bias is necessary for cluster
self-calibration in the era of precision cosmology.Comment: 13 pages, 5 figures, replaced to match published versio
Polariton Condensate Transistor Switch
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits
Confocal microscopic image sequence compression using vector quantization and 3D pyramids
The 3D pyramid compressor project at the University of Glasgow has developed a compressor for images obtained from CLSM device. The proposed method using a combination of image pyramid coder and vector quantization techniques has good performance at compressing confocal volume image data. An experiment was conducted on several kinds of CLSM data using the presented compressor compared to other well-known volume data compressors, such as MPEG-1. The results showed that the 3D pyramid compressor gave higher subjective and objective image quality of reconstructed images at the same compression ratio and presented more acceptable results when applying image processing filters on reconstructed images
A Sino-German 6cm polarisation survey of the Galactic plane IX. HII regions
Large-scale radio continuum surveys provide data to get insights into the
physical properties of radio sources. HII regions are prominent radio sources
produced by thermal emission of ionised gas around young massive stars. We
identify and analyse HII regions in the Sino-German 6cm polarisation survey of
the Galactic plane. Objects with flat radio continuum spectra together with
infrared and/or Halpha emission were identified as HII regions. For HII regions
with small apparent sizes, we cross-matched the 6cm small-diameter source
catalogue with the radio HII region catalogue compiled by Paladini and the
infrared HII region catalogue based on the WISE data. Extended HII regions were
identified by eye by overlaying the Paladini and the WISE HII regions onto the
6cm survey images for coincidences. The TT-plot method was employed for
spectral index verification. A total of 401 HII regions were identified and
their flux densities were determined with the Sino-German 6cm survey data. In
the surveyed area, 76 pairs of sources are found to be duplicated in the
Paladini HII region catalogue, mainly due to the non-distinction of previous
observations with different angular resolutions, and 78 objects in their
catalogue are misclassified as HII regions, being actually planetary nebulae,
supernova remnants or extragalactic sources that have steep spectra. More than
30 HII regions and HII region candidates from our 6cm survey data, especially
extended ones, do not have counterparts in the WISE HII region catalogue, of
which 9 are identified for the first time. Based on the newly derived radio
continuum spectra and the evidence of infrared emission, the previously
identified SNRs G11.1-1.0, G20.4+0.1 and G16.4-0.5 are believed to be HII
regions.Comment: version after some minor corrections and language editing, full Table
2 - 5 will appear in CDS, accepted for publication in A&
Strongly Enhanced Hole-Phonon Coupling in the Metallic State of the Dilute Two-Dimensional Hole Gas
We have studied the temperature dependent phonon emission rate () of a
strongly interacting (22) dilute 2D GaAs hole system using a standard
carrier heating technique. In the still poorly understood metallic state, we
observe that () changes from () to ()
above 100mK, indicating a crossover from screened piezoelectric(PZ) coupling to
screened deformation potential(DP) coupling for hole-phonon scattering.
Quantitative comparison with theory shows that the long range PZ coupling
between holes and phonons has the expected magnitude; however, in the metallic
state, the short range DP coupling between holes and phonons is {\it almost
twenty times stronger} than expected from theory. The density dependence of
() shows that it is {\it easier} to cool low density 2D holes in GaAs
than higher density 2D hole systems.Comment: To appear in Phys. Rev. Let
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