2,555 research outputs found
A native promoter–gene fusion created by CRISPR/Cas9-mediated genomic deletion offers a transgene-free method to drive oil accumulation in leaves
Achieving gain-of-function phenotypes without inserting foreign DNA is an important challenge for plant biotechnologists. Here we show that a gene can be brought under the control of a promoter from an upstream gene by deleting the intervening genomic sequence using dual-guide CRISPR/Cas9. We fuse the promoter of a non-essential photosynthesis-related gene to DIACYLGLYCEROL ACYLTRANSFERASE 2 (DGAT2) in the lipase-deficient sugar-dependent 1 mutant of Arabidopsis thaliana to drive ectopic oil accumulation in leaves. DGAT2 expression is enhanced more than twenty-fold and the triacylglycerol content increases by around thirty-fold. This deletion strategy offers a transgene-free route to engineering traits that rely on transcriptional gain-of-function, such as producing high lipid forage to increase the productivity and sustainability of ruminant farming
Microlensing of Circumstellar Disks
We investigate the microlensing effects on a source star surrounded by a
circumstellar disk, as a function of wavelength. The microlensing light curve
of the system encodes the geometry and surface brightness profile of the disk.
In the mid- and far-infrared, the emission of the system is dominated by the
thermal emission from the cold dusty disk. For a system located at the Galactic
center, we find typical magnifications to be of order 10-20% or higher,
depending on the disk surface brightness profile, and the event lasts over one
year. At around 20 microns, where the emission for the star and the disk are
comparable, the difference in the emission areas results in a chromatic
microlensing event. Finally, in the near-infrared and visible, where the
emission of the star dominates, the fraction of star light directly reflected
by the disk slightly modifies the light curve of the system which is no longer
that of a point source. In each case, the corresponding light curve can be used
to probe some of the disk properties. A fraction of 0.1% to 1% optical
microlensing events are expected to be associated with circumstellar disk
systems. We show that the lensing signal of the disk can be detected with
sparse follow-up observations of the next generation space telescopes. While
direct imaging studies of circumstellar disks are limited to the solar
neighborhood, this microlensing technique can probe very distant disk systems
living in various environments and has the potential to reveal a larger
diversity of circumstellar disks.Comment: 9 pages, 7 figures. Accepted for publication in Ap
[OI] disk emission in the Taurus star forming region
The structure of protoplanetary disks is thought to be linked to the
temperature and chemistry of their dust and gas. Whether the disk is flat or
flaring depends on the amount of radiation that it absorbs at a given radius,
and on the efficiency with which this is converted into thermal energy. The
understanding of these heating and cooling processes is crucial to provide a
reliable disk structure for the interpretation of dust continuum emission and
gas line fluxes. Especially in the upper layers of the disk, where gas and dust
are thermally decoupled, the infrared line emission is strictly related to the
gas heating/cooling processes. We aim to study the thermal properties of the
disk in the oxygen line emission region, and to investigate the relative
importance of X-ray (1-120 Angstrom) and far-UV radiation (FUV, 912-2070
Angstrom) for the heating balance there. We use [OI] 63 micron line fluxes
observed in a sample of protoplanetary disks of the Taurus/Auriga star forming
region and compare it to the model predictions presented in our previous work.
The data were obtained with the PACS instrument on board the Herschel Space
Observatory as part of the Herschel Open Time Key Program GASPS (GAS in
Protoplanetary diskS), published in Howard et al. (2013). Our theoretical grid
of disk models can reproduce the [OI] absolute fluxes and predict a correlation
between [OI] and the sum Lx+Lfuv. The data show no correlation between the [OI]
line flux and the X-ray luminosity, the FUV luminosity or their sum. The data
show that the FUV or X-ray radiation has no notable impact on the region where
the [OI] line is formed. This is in contrast with what is predicted from our
models. Possible explanations are that the disks in Taurus are less flaring
than the hydrostatic models predict, and/or that other disk structure aspects
that were left unchanged in our models are important. ..abridged..Comment: 9 pages, accepted for publication in A&
Confinement effects on glass forming liquids probed by DMA
Many molecular glass forming liquids show a shift of the glass transition T-g
to lower temperatures when the liquid is confined into mesoporous host
matrices. Two contrary explanations for this effect are given in literature:
First, confinement induced acceleration of the dynamics of the molecules leads
to an effective downshift of T-g increasing with decreasing pore size. Second,
due to thermal mismatch between the liquid and the surrounding host matrix,
negative pressure develops inside the pores with decreasing temperature, which
also shifts T-g to lower temperatures. Here we present dynamic mechanical
analysis measurements of the glass forming liquid salol in Vycor and Gelsil
with pore sizes of d=2.6, 5.0 and 7.5 nm. The dynamic complex elastic
susceptibility data can be consistently described with the assumption of two
relaxation processes inside the pores: A surface induced slowed down relaxation
due to interaction with rough pore interfaces and a second relaxation within
the core of the pores. This core relaxation time is reduced with decreasing
pore size d, leading to a downshift of T-g proportional to 1/d in perfect
agreement with recent differential scanning calorimetry (DSC) measurements.
Thermal expansion measurements of empty and salol filled mesoporous samples
revealed that the contribution of negative pressure to the downshift of T-g is
small (<30%) and the main effect is due to the suppression of dynamically
correlated regions of size xi when the pore size xi approaches
Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory
Context. Debris discs are thought to be formed through the collisional
grinding of planetesimals, and can be considered as the outcome of planet
formation. Understanding the properties of gas and dust in debris discs can
help us to comprehend the architecture of extrasolar planetary systems.
Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have
provided a valuable dataset for the study of debris discs gas and dust
composition. This paper is part of a series of papers devoted to the study of
Herschel PACS observations of young stellar associations.
Aims. This work aims at studying the properties of discs in the Beta Pictoris
Moving Group (BPMG) through far-IR PACS observations of dust and gas.
Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100
and 160 microns of 19 BPMG members, together with spectroscopic observations of
four of them. Spectroscopic observations were centred at 63.18 microns and 157
microns, aiming to detect [OI] and [CII] emission. We incorporated the new
far-IR observations in the SED of BPMG members and fitted modified blackbody
models to better characterise the dust content.
Results. We have detected far-IR excess emission toward nine BPMG members,
including the first detection of an IR excess toward HD 29391.The star HD
172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding
the short list of debris discs with a gas detection. No debris disc in BPMG is
detected in both [OI] and [CII]. The discs show dust temperatures in the range
55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii
from blackbody models in the range 3 to 82 AU. All the objects with a gas
detection are early spectral type stars with a hot dust component.Comment: 12 pages, 7 figures, 6 table
Sub-percent constraints on cosmological temperature evolution
The redshift dependence of the cosmic microwave background temperature is one of the key cosmological observables. In the standard cosmological model one has T (z) = T0(1 + z), where T0 is the present-day temperature. Deviations from this behavior would imply the presence of new physics. Here we discuss how the combination of all currently available direct and indirect measurements of T (z) constrains the common phenomenological parametrization T (z) = T0(1 + z)^(1−β) , and obtain the first sub-percent constraint on the temperature growth index 1 − β. Specifically, we find β = (7.6 ± 8.0) × 10^(−3) at the 68.3% confidence level
Randomized Clinical Trial of Azithromycin vs. Erythromycin for the Treatment of Chlamydia Cervicitis in Pregnancy
Objective: The purpose of this study was to prospectively test the null hypothesis that there is no
difference in the clinical effectiveness of azithromycin and erythromycin for the treatment of chlamydia
cervicitis in pregnancy
Growth, Structure and Properties of BiFeO3-BiCrO3 Films obtained by Dual Cross Beam PLD
The properties of epitaxial Bi2FeCrO6 thin films, recently synthesized by
pulsed laser deposition, have partially confirmed the theoretical predictions
(i.e. a magnetic moment of 2 muB per formula unit and a polarization of ~80
microC/cm2 at 0K). The existence of magnetic ordering at room temperature for
this material is an unexpected but very promising result that needs to be
further investigated. Since magnetism is assumed to arise from the exchange
interaction between the Fe and Cr cations, the magnetic behaviour is strongly
dependent on both their ordering and the distance between them. We present here
the successful synthesis of epitaxial Bi2FexCryO6 (BFCO x/y) films grown on
SrTiO3 substrates using dual crossed beam pulsed laser deposition. The crystal
structure of the films has different types of (111)-oriented superstructures
depending on the deposition conditions. The multiferroic character of BFCO
(x/y) films is proven by the presence of both ferroelectric and magnetic
hysteresis at room temperature. The oxidation state of Fe and Cr ions in the
films is shown to be 3+ only and the difference in macroscopic magnetization
with Fe/Cr ratio composition could only be due to ordering of the Cr3+ and Fe3+
cations therefore to the modification of the exchange interaction between them.Comment: Manuscript accepted for publication in IEEE-UFF
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