958 research outputs found
New global stability estimates for monochromatic inverse acoustic scattering
We give new global stability estimates for monochromatic inverse acoustic
scattering. These estimates essentially improve estimates of [P. Hahner, T.
Hohage, SIAM J. Math. Anal., 33(3), 2001, 670-685] and can be considered as a
solution of an open problem formulated in the aforementioned work
Infrared Observations of the Candidate LBV 1806-20 & Nearby Cluster Stars
We report near-infrared photometry, spectroscopy, and speckle imaging of the
hot, luminous star we identify as candidate LBV 1806-20. We also present
photometry and spectroscopy of 3 nearby stars, which are members of the same
star cluster containing LBV 1806-20 and SGR 1806-20. The spectroscopy and
photometry show that LBV 1806-20 is similar in many respects to the luminous
``Pistol Star'', albeit with some important differences. They also provide
estimates of the effective temperature and reddening of LBV 1806-20, and
confirm distance estimates, leading to a best estimate for the luminosity of
this star of . The nearby cluster stars have
spectral types and inferred absolute magnitudes which confirm the distance (and
thus luminosity) estimate for LBV 1806-20. If we drop kinematic measurements of
the distance ( kpc), we have a lower limit on the distance
of kpc, and on the luminosity of , based on
the cluster stars. If we drop both the kinematic and cluster star indicators
for distance, an ammonia absorption feature sets yet another lower limit to the
distance of kpc, with a corresponding luminosity estimate of for the candidate LBV 1806-20. Furthermore, based on very high
angular-resolution speckle images, we determine that LBV 1806-20 is not a
cluster of stars, but is rather a single star or binary system. Simple
arguments based on the Eddington luminosity lead to an estimate of the total
mass of LBV 1806-20 (single or binary) exceeding . We discuss
the possible uncertainties in these results, and their implications for the
star formation history of this cluster.Comment: 36 pages, including 8 figures (Figures 1 and 7 in JPG format due to
space); Accepted for publication in Ap
Soil respiration in a northeastern US temperate forest: a 22âyear synthesis
To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and interâannual variations in soil respiration (Rs), we analyzed more than 100,000 individual measurements of soil respiration from 23 studies conducted over 22 years at the Harvard Forest in Petersham, Massachusetts, USA. We also used 24 siteâyears of eddyâcovariance measurements from two Harvard Forest sites to examine the relationship between soil and ecosystem respiration (Re).
Rs was highly variable at all spatial (respiration collar to forest stand) and temporal (minutes to years) scales of measurement. The response of Rs to experimental manipulations mimicking aspects of global change or aimed at partitioning Rs into component fluxes ranged from â70% to +52%. The response appears to arise from variations in substrate availability induced by changes in the size of soil C pools and of belowground C fluxes or in environmental conditions. In some cases (e.g., logging, warming), the effect of experimental manipulations on Rs was transient, but in other cases the time series were not long enough to rule out longâterm changes in respiration rates. Interâannual variations in weather and phenology induced variation among annual Rs estimates of a magnitude similar to that of other drivers of global change (i.e., invasive insects, forest management practices, N deposition). At both eddyâcovariance sites, aboveground respiration dominated Re early in the growing season, whereas belowground respiration dominated later. Unusual aboveground respiration patternsâhigh apparent rates of respiration during winter and very low rates in midâtoâlate summerâat the Environmental Measurement Site suggest either bias in Rs and Re estimates caused by differences in the spatial scale of processes influencing fluxes, or that additional research on the hardâtoâmeasure fluxes (e.g., wintertime Rs, unaccounted losses of CO2 from eddy covariance sites), daytime and nighttime canopy respiration and its impacts on estimates of Re, and independent measurements of flux partitioning (e.g., aboveground plant respiration, isotopic partitioning) may yield insight into the unusually high and low fluxes. Overall, however, this dataârich analysis identifies important seasonal and experimental variations in Rs and Re and in the partitioning of Re aboveâ vs. belowground
Soil respiration in a northeastern US temperate forest: a 22âyear synthesis
To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and interâannual variations in soil respiration (Rs), we analyzed more than 100,000 individual measurements of soil respiration from 23 studies conducted over 22 years at the Harvard Forest in Petersham, Massachusetts, USA. We also used 24 siteâyears of eddyâcovariance measurements from two Harvard Forest sites to examine the relationship between soil and ecosystem respiration (Re).
Rs was highly variable at all spatial (respiration collar to forest stand) and temporal (minutes to years) scales of measurement. The response of Rs to experimental manipulations mimicking aspects of global change or aimed at partitioning Rs into component fluxes ranged from â70% to +52%. The response appears to arise from variations in substrate availability induced by changes in the size of soil C pools and of belowground C fluxes or in environmental conditions. In some cases (e.g., logging, warming), the effect of experimental manipulations on Rs was transient, but in other cases the time series were not long enough to rule out longâterm changes in respiration rates. Interâannual variations in weather and phenology induced variation among annual Rs estimates of a magnitude similar to that of other drivers of global change (i.e., invasive insects, forest management practices, N deposition). At both eddyâcovariance sites, aboveground respiration dominated Re early in the growing season, whereas belowground respiration dominated later. Unusual aboveground respiration patternsâhigh apparent rates of respiration during winter and very low rates in midâtoâlate summerâat the Environmental Measurement Site suggest either bias in Rs and Re estimates caused by differences in the spatial scale of processes influencing fluxes, or that additional research on the hardâtoâmeasure fluxes (e.g., wintertime Rs, unaccounted losses of CO2 from eddy covariance sites), daytime and nighttime canopy respiration and its impacts on estimates of Re, and independent measurements of flux partitioning (e.g., aboveground plant respiration, isotopic partitioning) may yield insight into the unusually high and low fluxes. Overall, however, this dataârich analysis identifies important seasonal and experimental variations in Rs and Re and in the partitioning of Re aboveâ vs. belowground
Formulas and equations for finding scattering data from the Dirichlet-to-Neumann map with nonzero background potential
For the Schrodinger equation at fixed energy with a potential supported in a
bounded domain we give formulas and equations for finding scattering data from
the Dirichlet-to-Neumann map with nonzero background potential. For the case of
zero background potential these results were obtained in [R.G.Novikov,
Multidimensional inverse spectral problem for the equation
-\Delta\psi+(v(x)-Eu(x))\psi=0, Funkt. Anal. i Ego Prilozhen 22(4), pp.11-22,
(1988)]
HL-1 cells express an inwardly rectifying K+ current activated via muscarinic receptors comparable to that in mouse atrial myocytes
An inwardly rectifying K^+ current is present in atrial cardiac myocytes that is activated by acetylcholine (I_{KACh}). Physiologically, activation of the current in the SA node is important in slowing the heart rate with increased parasympathetic tone. It is a paradigm for the direct regulation of signaling effectors by the GÎČÎł G-protein subunit. Many questions have been addressed in heterologous expression systems with less focus on the behaviour in native myocytes partly because of the technical difficulties in undertaking comparable studies in native cells. In this study, we characterise a potassium current in the atrial-derived cell line HL-1. Using an electrophysiological approach, we compare the characteristics of the potassium current with those in native atrial cells and in a HEK cell line expressing the cloned Kir3.1/3.4 channel. The potassium current recorded in HL-1 is inwardly rectifying and activated by the muscarinic agonist carbachol. Carbachol-activated currents were inhibited by pertussis toxin and tertiapin-Q. The basal current was time-dependently increased when GTP was substituted in the patch-clamp pipette by the non-hydrolysable analogue GTPÎłS. We compared the kinetics of current modulation in HL-1 with those of freshly isolated atrial mouse cardiomyocytes. The current activation and deactivation kinetics in HL-1 cells are comparable to those measured in atrial cardiomyocytes. Using immunofluorescence, we found GIRK4 at the membrane in HL-1 cells. Real-time RT-PCR confirms the presence of mRNA for the main G-protein subunits, as well as for M2 muscarinic and A1 adenosine receptors. The data suggest HL-1 cells are a good model to study IKAch
Delayed diagnosis and recovery of fulminant immune checkpoint inhibitor-associated myocarditis on VA-ECMO support
[Figure: see text
Plasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array
We characterize the plasma flows generated during the ablation stage of an
over-massed exploding planar wire array, fielded on the COBRA pulsed-power
facility (1 MA peak current, 250 ns rise time). The planar wire array is
designed to provide a driving magnetic field (80-100 T) and current per wire
distribution (about 60 kA), similar to that in a 10 MA cylindrical exploding
wire array fielded on the Z machine. Over-massing the arrays enables continuous
plasma ablation over the duration of the experiment. The requirement to
over-mass on the Z machine necessitates wires with diameters of 75-100 m,
which are thicker than wires usually fielded on wire array experiments. To test
ablation with thicker wires, we perform a parametric study by varying the
initial wire diameter between 33-100 m. The largest wire diameter (100
m) array exhibits early closure of the AK gap, while the gap remains open
during the duration of the experiment for wire diameters between 33-75 m.
Laser plasma interferometry and time-gated XUV imaging are used to probe the
plasma flows ablating from the wires. The plasma flows from the wires converge
to generate a pinch, which appears as a fast-moving (
kms) column of increased plasma density ( cm) and strong XUV emission. Finally, we compare the results
with three-dimensional resistive-magnetohydrodynamic (MHD) simulations
performed using the code GORGON, the results of which reproduce the dynamics of
the experiment reasonably well.Comment: 14 pages; 14 figure
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