36 research outputs found
Dynamic protein methylation in chromatin biology
Post-translational modification of chromatin is emerging as an increasingly important regulator of chromosomal processes. In particular, histone lysine and arginine methylation play important roles in regulating transcription, maintaining genomic integrity, and contributing to epigenetic memory. Recently, the use of new approaches to analyse histone methylation, the generation of genetic model systems, and the ability to interrogate genome wide histone modification profiles has aided in defining how histone methylation contributes to these processes. Here we focus on the recent advances in our understanding of the histone methylation system and examine how dynamic histone methylation contributes to normal cellular function in mammals
Atmospheric benzenoid emissions from plants rival those from fossil fuels
Despite the known biochemical production of a range of aromatic compounds by plants and the presence of benzenoids in floral scents, the emissions of only a few benzenoid compounds have been reported from the biosphere to the atmosphere. Here, using evidence from measurements at aircraft, ecosystem, tree, branch and leaf scales, with complementary isotopic labeling experiments, we show that vegetation (leaves, flowers, and phytoplankton) emits a wide variety of benzenoid compounds to the atmosphere at substantial rates. Controlled environment experiments show that plants are able to alter their metabolism to produce and release many benzenoids under stress conditions. The functions of these compounds remain unclear but may be related to chemical communication and protection against stress. We estimate the total global secondary organic aerosol potential from biogenic benzenoids to be similar to that from anthropogenic benzenoids (~10 Tg y-1), pointing to the importance of these natural emissions in atmospheric physics and chemistry
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Damage constraints in the design of high energy lasers for fusion applications
Airborne flux measurements of biogenic isoprene over California
The article of record as published may be located at http://dx.doi.org/10.5194/acp-14-10631-2014The Supplement related to this article is available online
at doi:10.5194/acp-14-10631-2014-supplement.Biogenic isoprene fluxes were measured onboard
the CIRPAS Twin Otter aircraft as part of the California Airborne
Biogenic volatile organic compound (BVOC) Emission
Research in Natural Ecosystem Transects (CABERNET)
campaign during June 2011. The airborne virtual disjunct
eddy covariance (AvDEC) approach used measurements
from a proton transfer reaction mass spectrometer
(PTR–MS) and a wind radome probe to directly determine
fluxes of isoprene over 7400 km of flight paths focusing on
areas of California predicted to have the largest emissions.
The fast Fourier transform (FFT) approach was used to calculate
fluxes of isoprene over long transects of more than
15 km, most commonly between 50 and 150 km. The continuous
wavelet transformation (CWT) approach was used
over the same transects to also calculate instantaneous isoprene
fluxes with localization of both frequency and time independent
of non-stationarities. Fluxes were generally measured
by flying consistently at 400m±50m (a.g.l.) altitude,
and extrapolated to the surface according to the determined
flux divergence determined in the racetrack-stacked profiles.
The wavelet-derived surface fluxes of isoprene averaged to
2 km spatial resolution showed good correspondence to basal
emission factor (BEF) land-cover data sets used to drive
BVOC emission models. The surface flux of isoprene was
close to zero over Central Valley crops and desert shrublands,
but was very high (up to 15 mgm−2 h−1) above oak
woodlands, with clear dependence of emissions on temperature
and oak density. Isoprene concentrations of up to 8 ppb
were observed at aircraft height on the hottest days and over
the dominant source regions
Airborne Flux Measurements of BVOCs above Californian Oak Forests: Experimental Investigation of Surface and Entrainment Fluxes, OH Densities, and Damköhler Numbers
The article of record as published may be located at http://dx.doi.org/10.1175/JAS-D-13-054.1Airborne flux measurements of isoprene were performed over the Californian oak belts surrounding the
Central Valley. The authors demonstrate for the first time 1) the feasibility of airborne eddy covariance
measurements of reactive biogenic volatile organic compounds; 2) the effect of chemistry on the vertical
transport of reactive species, such as isoprene; and 3) the applicability of wavelet analysis to estimate regional
fluxes of biogenic volatile organic compounds. These flux measurements demonstrate that instrumentation
operating at slower response times (e.g., 1–5 s) can still be used to determine eddy covariance fluxes in the
mixed layer above land, where typical length scales of 0.5–3km were observed. Flux divergence of isoprene
measured in the planetary boundary layer (PBL) is indicative of OH densities in the range of 4–7 3 106
molecules per cubic centimeter and allows extrapolation of airborne fluxes to the surface with Damk€ohler
numbers (ratio between the mixing time scale and the chemical time scale) in the range of 0.3–0.9. Most of the
isoprene is oxidized in the PBL with entrainment fluxes of about 10% compared to the corresponding surface
fluxes. Entrainment velocities of 1–10 cm s21 were measured. The authors present implications for parameterizing
PBL schemes of reactive species in regional and global models
Characterization of myocardial viability using MR and CT imaging
Cardiovascular magnetic resonance (MR) imaging is of proven clinical value for the noninvasive characterization of myocardial viability. Computed tomography (CT) is also being exploited for this indication. Examples of each of these imaging strategies for the assessment of myocardial viability will be provided in this review. Key MRI concepts and practical considerations such as customized MR imaging techniques and tailored imaging protocols dedicated to viability assessment are outlined with the primary focus on recent developments. Clinical applications of MR-based viability assessment are reviewed, ranging from rapid functional cine imaging to tissue characterization using T2-weighted imaging and T1-weighted late-contrast-enhanced imaging. Next, the merits and limitations of state-of-the-art CT imaging are surveyed, and their implications for viability assessment are considered. The final emphasis is on current trends and future directions in noninvasive viability assessment using MRI and CT
LASER/FIBER OPTIC BREAKDOWN OF A PULSE CHARGED 90% Ar-10% N2 GAS SWITCH
Precise laser initiation of the breakdown in a pulse charged gas switch is described. A novel feature is the transport of the 40 ns triggering laser pulse through a 1.5 m long 1 mm diameter optical fiber. Optimization of gas breakdown characteristics was necessary as a result of the limited power transported through the fiber. Low, nanosecond delay and jitter were achieved at reduced fields approaching 180 V/cm-Torr in the overvolted gas gap through the use of 90% argon/10% nitrogen gas mixtures. The influence of laser power, gas mixture, focal point location, pressure, time of laser insertion etc. on switch performance is presented