36,981 research outputs found
NaCl transport stimulates prostaglandin release in cultured renal epithelial (MDCK) cells
Prostaglandins (PGs) can modulate a variety of renal functions, including Na+ and Cl- reabsorption. However, it is not known if a direct interdependence exists between PG synthesis and transport activity. The present study was done to find out whether or not the rate of NaCl transport has an influence on PG synthesis in renal tubular cells. For our studies we used cultures of so-called high-resistance MDCK cells, which were originally derived from canine kidney. This cell type has a loop diuretic- and ouabain-sensitive NaCl transport that can be enhanced by activation of the adenylate cyclase (AC). In MDCK cell cultures we found that each state of increased NaCl transport during stimulation of AC by either epinephrine (10(-6) M), isoprenaline (10(-5) M), or forskolin (10(-5) M) was accompanied by a twofold increase in PG release. During inhibition of NaCl transport by furosemide (10(-4) M) or ouabain (2 X 10(-4) M), stimulation of AC failed to increase PGE2 release, whereas basal PG production was not inhibited by either furosemide or ouabain. Furthermore, PG formation during activation of AC was dependent on the concentration of extracellular Na+, whereas PG formation in the absence of activators of AC was independent of extracellular Na+. These results suggest that increased NaCl transport stimulates PG formation in cultures of high-resistance MDCK cells
Nonlinear resonance absorption in laser-cluster interaction
Rare gas or metal clusters are known to absorb laser energy very efficiently.
Upon cluster expansion the Mie plasma frequency may become equal to the laser
frequency. This linear resonance has been well studied both experimentally and
theoretically employing pump probe schemes. In this work we focus on the
few-cycle regime or the early stage of the cluster dynamics where linear
resonance is not met but nevertheless efficient absorption of laser energy
persists. By retrieving time-dependent oscillator frequencies from
particle-in-cell simulation results, we show that nonlinear resonance is the
dominant mechanism behind outer ionization and energy absorption in near
infrared laser-driven clusters.Comment: 4 pages, 4 figures, REVTeX, minor modifications according to referee
comments, accepted for publication in Phys. Rev. Let
Magnetic phase diagram of MnSi inferred from magnetization and ac susceptibility
We report simultaneous measurements of the magnetization and the ac
susceptibility across the magnetic phase diagram of single-crystal MnSi. In our
study we explore the importance of the excitation frequency, excitation
amplitude, sample shape, and crystallographic orientation. The susceptibility,
dM/dH, calculated from the magnetization, is dominated by pronounced maxima at
the transition from the helical to the conical and the conical to the skyrmion
lattice phase. The maxima in dM/dH are not tracked by the ac susceptibility,
which in addition varies sensitively with the excitation amplitude and
frequency at the transition from the conical to the skyrmion lattice phase. The
same differences between dM/dH and the ac susceptibility exist for Mn1-xFexSi
(x=0.04) and Fe1-xCoxSi (x=0.20). Taken together our study establishes
consistently for all major crystallographic directions the existence of a
single pocket of the skyrmion lattice phase in MnSi, suggestive of a universal
characteristic of all B20 transition metal compounds with helimagnetic order.Comment: 19 pages, 20 figure
Runtime Verification of Temporal Properties over Out-of-order Data Streams
We present a monitoring approach for verifying systems at runtime. Our
approach targets systems whose components communicate with the monitors over
unreliable channels, where messages can be delayed or lost. In contrast to
prior works, whose property specification languages are limited to
propositional temporal logics, our approach handles an extension of the
real-time logic MTL with freeze quantifiers for reasoning about data values. We
present its underlying theory based on a new three-valued semantics that is
well suited to soundly and completely reason online about event streams in the
presence of message delay or loss. We also evaluate our approach
experimentally. Our prototype implementation processes hundreds of events per
second in settings where messages are received out of order.Comment: long version of the CAV 2017 pape
Phase Transitions in a Two-Component Site-Bond Percolation Model
A method to treat a N-component percolation model as effective one component
model is presented by introducing a scaled control variable . In Monte
Carlo simulations on , , and simple cubic
lattices the percolation threshold in terms of is determined for N=2.
Phase transitions are reported in two limits for the bond existence
probabilities and . In the same limits, empirical formulas
for the percolation threshold as function of one
component-concentration, , are proposed. In the limit a new
site percolation threshold, , is reported.Comment: RevTeX, 5 pages, 5 eps-figure
Combination of a magnetic Feshbach resonance and an optical bound-to-bound transition
We use laser light near resonant with an optical bound-to-bound transition to
shift the magnetic field at which a Feshbach resonance occurs. We operate in a
regime of large detuning and large laser intensity. This reduces the
light-induced atom-loss rate by one order of magnitude compared to our previous
experiments [D.M. Bauer et al. Nature Phys. 5, 339 (2009)]. The experiments are
performed in an optical lattice and include high-resolution spectroscopy of
excited molecular states, reported here. In addition, we give a detailed
account of a theoretical model that describes our experimental data
Nonsequential Double Recombination in Intense Laser Fields
A second plateau in the harmonic spectra of laser-driven two-electron atoms
is observed both in the numerical solution of a low-dimensional model helium
atom and using an extended strong field approximation. It is shown that the
harmonics well beyond the usual cut-off are due to the simultaneous
recombination of the two electrons, which were emitted during different,
previous half-cycles. The new cut-off is explained in terms of classical
trajectories. Classical predictions and the time-frequency analysis of the ab
initio quantum results are in excellent agreement. The mechanism corresponds to
the inverse single photon double ionization process in the presence of a (low
frequency) laser field.Comment: 4 pages, RevTeX, v2 with an extended strong field approximation
treatment of the process; instead, v1 describes an attosecond control scheme
to enhance the proces
Determination of the optimal level for combining area and yield estimates
Several levels of obtaining both area and yield estimates of corn and soybeans in Iowa were considered: county, refined strata, refined/split strata, crop reporting district, and state. Using the CCEA model form and smoothed weather data, regression coefficients at each level were derived to compute yield and its variance. Variances were also computed with stratum level. The variance of the yield estimates was largest at the state and smallest at the county level for both crops. The refined strata had somewhat larger variances than those associated with the refined/split strata and CRD. For production estimates, the difference in standard deviations among levels was not large for corn, but for soybeans the standard deviation at the state level was more than 50% greater than for the other levels. The refined strata had the smallest standard deviations. The county level was not considered in evaluation of production estimates due to lack of county area variances
Mechanism of NaCl transport-stimulated prostaglandin formation in MDCK cells
Recently we have found that stimulation of NaCl transport in high-resistance MDCK cells enhances their prostaglandin formation. In the present study, we investigated the mechanisms by which prostaglandin formation could be linked to the ion transport in these cells. We found that stimulation of transport caused a transient stimulation of prostaglandin formation lasting 5-10 min. The rise in prostaglandin formation was paralleled by a rise of free intracellular arachidonic acid. Analysis of membrane lipids revealed that the rise of free arachidonic acid was paralleled by a loss of arachidonic acid from polyphosphoinositides. We failed to obtain indications for the stimulation of calcium-dependent phospholipase A2. However, we did obtain evidence that the incorporation of arachidonic acid into phospholipids was diminished during stimulation of ion transport, indicating a decreased rate of reesterification. Despite the fact that there was no significant fall in total cellular ATP on stimulation of ion transport, we found a high and transient rise of lactate production of the cells on stimulation of the ion transport indicating an alteration of the ADP/ATP ratio. Moreover, prostaglandin formation and lactate formation were linearly correlated in this situation. When glucose utilization was inhibited by mannoheptulose, the rise in lactate formation was abolished, whereas that of PG formation was unaltered, indicating that lactate formation and prostaglandin formation were not causally linked on stimulation of ion transport. Our results suggest that an increase in the rate of sodium chloride transport by MDCK cells stimulates formation by an inhibition of reesterification of free arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS
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