5,598 research outputs found
Secondary instability of electromagnetic ion-temperature-gradient modes for zonal flow generation
An analytical model for zonal flow generation by toroidal
ion-temperature-gradient (ITG) modes, including finite electromagnetic
effects, is derived. The derivation is based on a fluid model for ions and
electrons and takes into account both linear and nonlinear effects. The
influence of finite plasma on the zonal flow growth rate
() scaling is investigated for typical tokamak plasma parameters.
The results show the importance of the zonal flows close to marginal stability
where is obtained. In this region the parameter
increases with , indicating that the ITG
turbulence and associated transport would decrease with at a faster
rate than expected from a purely linear or quasi-linear analysis.Comment: RevTex 17 pages, 4 figures, submitted to Physics of Plasma
Effects of the Second Harmonic and Plasma Shaping on the Geodesic Acoustic Mode
The effects of second harmonics of the density and temperature perturbations
on the linear Geodesic Acoustic Mode (GAM) frequency and non-linear generation
of the GAM are investigated, using a fluid model. We show that the second
harmonics contribute to the frequency through the density gradient scale length
and the wave number of the GAM. In addition, the linear frequency of the GAM is
generally increased by coupling to the higher harmonic.Comment: 4 pages, 3 figures, 41st EPS Conference Berlin 201
Effects of the Second Harmonic on the GAM in Electron Scale Turbulence
The effects higher order harmonics have been self-consistently included in
the derivation of the electron branch of the electron Geodesic Acoustic Mode
(el-GAM) in an Electron-Temperature-Gradient (ETG) turbulence background. The
work is based on a two-fluid model including finite -effects while
retaining non-adiabatic ions. In solving the linear dispersion relation, it is
found that the due to the coupling to the mode the real frequency may be
significantly altered and yield higher values.Comment: 12 pages, 1 figure. Work presented at 15th EFTC 2013, September
23-26th, Oxford, Englan
High Frequency Geodesic Acoustic Modes in Electron Temperature Gradient Mode Turbulence
In this work the first demonstration of a high frequency branch of the
geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG)
modes is presented. The work is based on a fluid description of the ETG mode
retaining non-adiabatic ions and the dispersion relation for high frequency
GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for
ETG turbulence through the interaction with high frequency GAMs is found,
resulting in a significantly enhanced ETG turbulence saturation level compared
to the mixing length estimate.Comment: 14 pages, submitted to Physics of Plasma
High Frequency Geodesic Acoustic Modes in Electron Scale Turbulence
In this work the finite -effects of an electron branch of the geodesic
acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is
presented. The work is based on a fluid description of the ETG mode retaining
non-adiabatic ions and the dispersion relation for el-GAMs driven non-linearly
by ETG modes is derived. The ETG growth rate from the fluid model is compared
to the results found from gyrokinetic simulations with good agreement. A new
saturation mechanism for ETG turbulence through the interaction with el-GAMs is
found, resulting in a significantly enhanced ETG turbulence saturation level
compared to the mixing length estimate. It is shown that the el-GAM may be
stabilized by an increase in finite as well as by increasing
non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the
Maxwell stress.Comment: 15 pages, 4 figures. Presented at the IAEA conference 201
A moving control volume approach to computing hydrodynamic forces and torques on immersed bodies
We present a moving control volume (CV) approach to computing hydrodynamic
forces and torques on complex geometries. The method requires surface and
volumetric integrals over a simple and regular Cartesian box that moves with an
arbitrary velocity to enclose the body at all times. The moving box is aligned
with Cartesian grid faces, which makes the integral evaluation straightforward
in an immersed boundary (IB) framework. Discontinuous and noisy derivatives of
velocity and pressure at the fluid-structure interface are avoided and
far-field (smooth) velocity and pressure information is used. We re-visit the
approach to compute hydrodynamic forces and torques through force/torque
balance equation in a Lagrangian frame that some of us took in a prior work
(Bhalla et al., J Comp Phys, 2013). We prove the equivalence of the two
approaches for IB methods, thanks to the use of Peskin's delta functions. Both
approaches are able to suppress spurious force oscillations and are in
excellent agreement, as expected theoretically. Test cases ranging from Stokes
to high Reynolds number regimes are considered. We discuss regridding issues
for the moving CV method in an adaptive mesh refinement (AMR) context. The
proposed moving CV method is not limited to a specific IB method and can also
be used, for example, with embedded boundary methods
Prospective evaluation of electroencephalography, carotid artery stump pressure, and neurologic changes during 314 consecutive carotid endarterectomies performed in awake patients
ObjectiveThis study attempted to correlate neurologic changes in awake patients undergoing carotid endarterectomy (CEA) under cervical block anesthesia (CBA) with electroencephalography (EEG) and measurement of carotid artery stump pressure (SP).MethodsContinuous EEG and SP monitoring was measured prospectively in 314 consecutive patients undergoing CEA between April 1, 2003, and July 30, 2006, under CBA. Indications for CEA were asymptomatic 70% to 99% internal carotid artery stenosis in 242 (77.1%), transient ischemic attacks (including transient monocular blindness) in 45 (14.3%), and prior stroke in 27 (8.6%). Mean common carotid artery pressure before clamping, mean SP after carotid clamping, and intraarterial pressure were continuously monitored in all patients. An indwelling shunt was placed when neurologic events (contralateral motor weakness, aphasia, loss of consciousness, or seizures) occurred, regardless of SP or EEG changes.ResultsShunt placement was necessary because of neurologic changes in 10% (32/314) of all CEAs performed under CBA. Only 3 patients (1.4%) of 216 required shunt placement if SP was 50 mm Hg or more, vs 29 (29.6%) of 98 if SP was less than 50 mm Hg (P < .00001; sensitivity, 29.8%; specificity, 98.6%). In patients with SP of 40 mm Hg or more, 7 (2.6%) of 270 required shunt placement, vs 25 (56.8%) of 44 if SP was less than 40 mm Hg (P < .00001; sensitivity, 56.8%; specificity, 97.4%). Ischemic EEG changes were observed in 19 (59.4%) of 32 patients (false-negative rate, 40.6%) requiring shunt placement under CBA. Three patients had false-positive EEG results and did not require shunt placement (false-positive rate, 1.0%). The perioperative stroke/death rate was 4 (1.2%) in 314. All strokes occurred after surgery and were unrelated to cerebral ischemia or lack of shunt placement.ConclusionsTen percent of patients required a shunt placement during CEA under CBA. Shunt placement was necessary in 56.8% of patients with SP less than 40 mm Hg. EEG identified cerebral ischemia in only 59.4% of patients needing shunt placement, with a false-positive rate of 1.0% and a false-negative rate of 40.6%. Both SP and EEG as a guide to shunt placement have poor sensitivity. Intraoperative monitoring of the awake patients under regional anesthesia (CBA) is the most sensitive and specific method to identify patients requiring shunt placement
Falling Prices: Does This Cause Purchases to Be Delayed or Speed Up? Evidence From the Gasoline Market
When teaching macroeconomics, students intuitively know why macroeconomists stress the dangers of inflation, but question why economists will say deflation is worse. To explain macroeconomists will almost always point to Japan’s “Lost decade”, a spiral of declining economic activity intertwined with declining prices. Their claim is that the deflation was a principle driver for the deepening recession as declining prices could cause consumers not to purchase more (as the law of demand would normally expect) but rather less in anticipation of even lower prices to come. This paper looked at the empirical evidence from the energy sector, specifically gasoline sales during the 2013-2015 time period and verified that there is evidence that some US consumers did indeed delay purchases even if they ultimately bought more
Isolation of new racemic sugar (D/L galacturonic acid) from leaves of Paederia foetida Linn.
New racemic sugars (D/L galacturonic acid) were isolate from the leaves of Paederia foetida Linn by the column chromatography. Identification of these isolated compound achieved by TLC, 1H-NMR, 13C-NMR, FTIR and Mass spectral data
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