68,647 research outputs found
Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations
The nonlinear dynamics of collisionless reconnecting modes is investigated,
in the framework of a three-dimensional gyrofluid model. This is the relevant
regime of high-temperature plasmas, where reconnection is made possible by
electron inertia and has higher growth rates than resistive reconnection. The
presence of a strong guide field is assumed, in a background slab model, with
Dirichlet boundary conditions in the direction of nonuniformity. Values of ion
sound gyro-radius and electron collisionless skin depth much smaller than the
current layer width are considered. Strong acceleration of growth is found at
the onset to nonlinearity, while at all times the energy functional is well
conserved. Nonlinear growth rates more than one order of magnitude higher than
linear growth rates are observed when entering into the small- regime
SCF E3 Ligase Substrates Switch from CAN-D to Can-ubiquitylate
Liu et al. (2018) report a mathematical model predicting how the cellular repertoire of SCF E3 ligases is assembled by âadaptive exchange on demand,â with the limited pool of CUL1 scanning the vast sea of F-box proteins for those with substrates demanding ubiquitylation
Correlation length scalings in fusion edge plasma turbulence computations
The effect of changes in plasma parameters, that are characteristic near or
at an L-H transition in fusion edge plasmas, on fluctuation correlation lengths
are analysed by means of drift-Alfven turbulence computations. Scalings by
density gradient length, collisionality, plasma beta, and by an imposed shear
flow are considered. It is found that strongly sheared flows lead to the
appearence of long-range correlations in electrostatic potential fluctuations
parallel and perpendicular to the magnetic field.Comment: Submitted to "Plasma Physics and Controlled Fusion
Nonlinear gyrofluid computation of edge localised ideal ballooning modes
Three dimensional electromagnetic gyrofluid simulations of the ideal
ballooning mode blowout scenario for tokamak edge localized modes (ELMs) are
presented. Special emphasis is placed on energetic diagnosis, examining changes
in the growth rate in the linear, overshoot, and decay phases. The saturation
process is energy transfer to self generated edge turbulence which exhibits an
ion temperature gradient (ITG) mode structure. Convergence in the decay phase
is found only if the spectrum reaches the ion gyroradius. The equilibrium is a
self consistent background whose evolution is taken into account. Approximately
two thirds of the total energy in the edge layer is liberated in the blowout.
Parameter dependence with respect to plasma pressure and the ion gyroradius is
studied. Despite the violent nature of the short-lived process, the transition
to nonlinearity is very similar to that found in generic tokamak edge
turbulence.Comment: The following article has been submitted to Physics of Plasmas. After
it is published, it will be found at http://pop.aip.org
The Lanczos algorithm with selective orthogonalization
A new stable and efficient implementation of the Lanczos algorithm is presented. The algorithm is a powerful method for finding a few eigenvalues and eigenvectors at one or both ends of the spectrum of a symmetric matrix A. The algorithm is particularly effective if A is large and sparse in that the only way in which A enters the calculation is through a subroutine which computes Av for any vector v. Thus the user is free to take advantage of any sparsity structure in A and A need not even be represented as a matrix et al
Innovative Opportunities for Elementary and Middle School Teachers to Maintain Currency in Mathematics and Science: A Community College-School System Partnership
Since 1992 the Manassas Campus of Northern Virginia Community College â in response to requests from local school systems â has developed four innovative methods of assisting elementary, secondary and middle school teachers to enhance their content knowledge in science and mathematics, as well as integrate curriculum units for classroom presentation. These methods are based on the assumptions that: - While teachers at this level have fundamental understanding of math and science, if they wish to incorporate new concepts or technologies from these fields, graduate level content courses are generally beyond their background level. - Community College faculty can often provide a bridge that connects advanced content in science and mathematics with the applications that can be adapted to elementary/middle school curriculum. - Presenting content to a mixed audience of teachers from K-8 allows teachers to see how content can be adapted to grade levels above and below. - Content delivery methods must be interactive and must be responsive to the multiple demands on these teachersâ time. This requires flexibility in scheduling and course requirements
Multinomial selection index
Comparison of multivariate statistical analysis techniques for multinomial selection indice
A short, cylindrical antenna as a diagnostic probe for measuring collision frequencies in a collision-dominated, non-Maxwellian plasma
Effects of particle collisions on antiresonant characteristics of cylindrical antennas used in electron plasma temperature and density measurement
SIMULATING OZONE EFFECTS ON FOREST PRODUCTIVITY: INTERACTIONS AMONG LEAFâ, CANOPYâ, AND STANDâLEVEL PROCESSES
Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leafâlevel ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with standâ and canopyâlevel factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients.
The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high waterâholding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3â22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Withinâcanopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest.
Sensitivity analyses indicate a tradeâoff between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed
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