3,852 research outputs found
Short-term effects of COâ-induced low pH exposure on target gene expression in Platynereis dumerilii
Objective: Increasing atmospheric COâ concentration are causing changes to the seawater carbonate chemistry, lowering the pH and we study potential impacts of these changes at the molecular level in a non-calcifying, marine polychaete species Platynereis dumerilii. Methods: we investigate the relative expression of carbonic anhydrase (CA), Na+/H+ exchangers (NHE), and calmodulin (CaM) genes from P. dumerilii under acidified seawater conditions (pH 7.8) induced by COâ using qPCR. Results: mRNA expression of CA in the COâ-induced worms was significantly up-regulated at low pH conditions (pH 7.8, 1h), suggesting changes in acid-base balance. In contrast, the expression of NHE and CaM showed no significant change. In addition, we compare these results to a previous study using inorganic acid (HCl)-induced pH changes. Conclusions: results suggest that carbonate chemistry has an impact on gene expression that differs from pH-associated change. To our knowledge, this is the first study that compares low pH exposure experiments using HCl and COâ as the inducing agents
Measurement of the drift field in the ARGONTUBE LAr TPC with 266~nm pulsed laser beams
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift
field generated in-situ by a Greinacher voltage multiplier circuit. We present
results on the measurement of the drift-field distribution inside ARGONTUBE
using straight ionization tracks generated by an intense UV laser beam. Our
analysis is based on a simplified model of the charging of a multi-stage
Greinacher circuit to describe the voltages on the field cage rings
Focused Fluid Flow along the Nootka Fault Zone and Continental slope, ExplorerâJuan de Fuca Plate Boundary
Key Points:
- Fluid flow is focused along Nootka Fault traces resulting in shallow bright spots
- Two seafloor mounds are the result of basaltic intrusions in the Nootka Fault zone
- Gas hydrates occur at the Nootka Slope and are imaged seismically as bottom-
simulating reflectors suggesting a regional heat-flow of ~80 mW/m2 along the slope
Abstract
Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from > 20 years of investigations to demonstrate the nature of fluidâflow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to nearâseafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100 â 300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show oppositeâtoâseafloor reflection polarity, and are associated with frequencyâreduction and velocity pushâdown indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonâconformable high amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottomâvideo observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios < 500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate related bottomâsimulating reflectors are widespread and occur at depths indicating heatâflow values of 80 â 90 mW/m2
A method to suppress dielectric breakdowns in liquid argon ionization detectors for cathode to ground distances of several millimeters
We present a method to reach electric field intensity as high as 400 kV/cm in
liquid argon for cathode-ground distances of several millimeters. This can be
achieved by suppressing field emission from the cathode, overcoming limitations
that we reported earlier
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment
We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation
functions characterizing the polymer segmental motion in polymer electrolytes
PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of
the salt on the polymer dynamics, we compare results for different ether oxygen
to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions,
we find nonexponential correlation functions, which can be described by a
Kohlrausch function. The mean correlation times show quantitatively that an
increase of the salt concentration results in a strong slowing down of the
segmental motion. Consistently, for the high 6:1 salt concentration, a high
apparent activation energy E_a=4.1eV characterizes the temperature dependence
of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV
are observed for moderate salt contents. The correlation functions are most
nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for
higher and lower salt concentrations. A similar dependence of the correlation
functions on the evolution time in the presence and in the absence of ions
indicates that addition of salt hardly affects the reorientational mechanism.
For all compositions, mean jump angles of about 15 degree characterize the
segmental reorientation. In addition, comparison of results from 2H and 7Li NMR
stimulated-echo experiments suggests a coupling of ion and polymer dynamics in
15:1 PPO-LiClO4.Comment: 14 pages, 12 figure
On the Electric Breakdown in Liquid Argon at Centimeter Scale
We present a study on the dependence of electric breakdown discharge
properties on electrode geometry and the breakdown field in liquid argon near
its boiling point. The measurements were performed with a spherical cathode and
a planar anode at distances ranging from 0.1 mm to 10.0 mm. A detailed study of
the time evolution of the breakdown volt-ampere characteristics was performed
for the first time. It revealed a slow streamer development phase in the
discharge. The results of a spectroscopic study of the visible light emission
of the breakdowns complement the measurements. The light emission from the
initial phase of the discharge is attributed to electro-luminescence of liquid
argon following a current of drifting electrons. These results contribute to
set benchmarks for breakdown-safe design of ionization detectors, such as
Liquid Argon Time Projection Chambers (LAr TPC).Comment: Minor revision according to editor report. 17 pages, 15 figures, 2
tables. Turboencabulato
First Demonstration of a Pixelated Charge Readout for Single-Phase Liquid Argon Time Projection Chambers
Liquid Argon Time Projection Chambers (LArTPCs) have been selected for the
future long-baseline Deep Underground Neutrino Experiment (DUNE). To allow
LArTPCs to operate in the high-multiplicity near detector environment of DUNE,
a new charge readout technology is required. Traditional charge readout
technologies introduce intrinsic ambiguities, combined with a slow detector
response, these ambiguities have limited the performance of LArTPCs, until now.
Here, we present a novel pixelated charge readout that enables the full 3D
tracking capabilities of LArTPCs. We characterise the signal to noise ratio of
charge readout chain, to be about 14, and demonstrate track reconstruction on
3D space points produced by the pixel readout. This pixelated charge readout
makes LArTPCs a viable option for the DUNE near detector complex.Comment: 13 pages, 9 figure
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