44,307 research outputs found
The appearance, motion, and disappearance of three-dimensional magnetic null points
No full textN.A.M. acknowledges support from NASA grants NNX11AB61G, NNX12AB25G, and NNX15AF43G; NASA contract NNM07AB07C; and NSF SHINE grants AGS-1156076 and AGS-1358342 to SAO. C.E.P. acknowledges support from the St Andrews 2013 STFC Consolidated grant.While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the magnetic field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or convergence of the null-null pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating null-null pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating null-null pair. The motion of separators cannot be described using solely local parameters because the identification of a particular field line as a separator may change as a result of non-ideal behavior elsewhere along the field line.Peer reviewe
Estimation in threshold autoregressive models with a stationary and a unit root regime
No full textThis paper treats estimation in a class of new nonlinear threshold autoregressive models with both a stationary and a unit root regime. Existing literature on nonstationary threshold models have basically focused on models where the nonstationarity can be removed by differencing and/or where the threshold variable is stationary. This is not the case for the process we consider, and nonstandard estimation problems are the result. This paper proposes a parameter estimation method for such nonlinear threshold autoregressive models using the theory of null recurrent Markov chains. Under certain assumptions, we show that the ordinary least squares (OLS) estimators of the parameters involved are asymptotically consistent. Furthermore, it can be shown that the OLS estimator of the coefficient parameter involved in the stationary regime can still be asymptotically normal while the OLS estimator of the coefficient parameter involved in the nonstationary regime has a nonstandard asymptotic distribution. In the limit, the rate of convergence in the stationary regime is asymptotically proportional to n-1/4, whereas it is n-1 in the nonstationary regime. The proposed theory and estimation method are illustrated by both simulated data and a real data example.Autoregressive process; null-recurrent process; semiparametric model; threshold time series; unit root structure.
Chen Chen, 42nd Annual ODU Literary Festival
No full textChen Chen is the author of When I Grow Up I Want to Be a List of Further Possibilities (BOA Editions, 2017), which was long-listed for the National Book Award and won the Thom Gunn Award, among other honors. Bloodaxe Books published a UK edition in June. He is also the author of four chapbooks, most recently You MUST Use the Word Smoothie (Sundress Publications, 2019) and Gesundheit! (in collaboration with Sam Herschel Wein and forthcoming from Glass Poetry Press, fall 2019). His work appears in many publications, including Poem-a-Day, The Massachusetts Review, The Best American Poetry, and The Best American Nonrequired Reading. He has received a Pushcart Prize and fellowships from Kundiman and the National Endowment for the Arts. He holds an MFA from Syracuse University and a PhD from Texas Tech University. He teaches at Brandeis University as the Jacob Ziskind Poet-in-Residence and co-runs the journal, Underblong. He lives in Waltham, Massachusetts, with his partner, Jeff Gilbert, and their pug, Mr. Rupert Gile
Supporting data used in the paper: Xi Chen, 2020, The LMARS based shallow-water dynamical core on generic gnomonic cubed-sphere geometry
No full text# Simulation results of the unstaggered shallow water model
This repository contains the supporting data used in the paper: Xi Chen, 2020, The LMARS based shallow‐water dynamical core on generic gnomonic cubed‐sphere geometry, DOI: 10.1029/2020MS002280
Organization of the repository:
The tar archive with this data submission has a:
doc directory contains a README.md with information regarding naming conventions to label the model configurations for a shallow water test simulation. Additional information can also be found in README.md. Table 4 in the paper provides additional details.
The data directory contains the supporting data files (NetCDF format).Disclaimer: "This was prepared by Xi Chen under award NA18OAR4320123 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration, or the U.S. Department of Commerce.
Semiparametric Regression Estimation in Null Recurrent Nonlinear Time Series
No full textEstimation theory in a nonstationary environment has been very popular in recent years. Existing studies focus on nonstationarity in parametric linear, parametric nonlinear and nonparametric nonlinear models. In this paper, we consider a partially linear model and propose to estimate both alpha and g semiparametrically. We then show that the proposed estimator of alpha is still asymptotically normal with the same rate as for the case of stationary time series. We also establish the asymptotic normality for the nonparametric estimator of the function g and the uniform consistency of the nonparametric estimator. The simulated example is given to show that our theory and method work well in practice.asymptotic normality; beta-null recurrent Markov chain; consistency; kernel estimator; partially linear model
Artimpaza brevilineata Tian & Chen, 2012 in Tian, Chen & Li 2012
No full textArtimpaza brevilineata Tian & Chen, 2012 in Tian, Chen & Li, 2012: 43, figs. 1–9. (Figs. 28a, b) Type locality: China, Yunnan, Pu’er City, Yutang. Gender: female. Date collected: 2011.V.25 (2010.V.25, in the original description, is incorrect). Collector: Li-Chao TIAN & Gui-Qiang HUANG. Paratypes: 1 female, China, Yunnan, Lincang City, 1980.VI.1, Fen LIU leg. Remarks: In the original description, the type locality is “ Yunnan, Jinghong” while it is “ Yunnan, Yutang” according to the label. “Yutang” is actually in Pu’er, not Jinghong. The first author described the type locality by mistake. In the original description, the collector was only listed as Li-Chao TIAN, which was a mistake.Published as part of Li, Zhu & Chen, Li, 2020, Primary types of longhorned beetles (Coleoptera, Cerambycidae, Vesperidae and Disteniidae) of Southwest University (SWU), pp. 25-46 in Zootaxa 4718 (1) on page 33, DOI: 10.11646/zootaxa.4718.1.2, http://zenodo.org/record/360220
Optimization Of Off-Null Ellipsometry For Air/Solid Interfaces
No full textThe optimization of off-null ellipsometry is described with emphasis on the improvement of sample thickness sensitivity. Optimal conditions are dependent on azimuth angle settings of the polarizer, compensator, and analyzer in a polarizer-compensator-sample-analyzer ellipsometer arrangement. Numerical simulation utilized offers an approach to present the dependence of the sensitivity on the azimuth angle settings, from which optimal settings corresponding to the best sensitivity are derived. For a series of samples of SiO2 layer (thickness in the range of 1.8-6.5 nm) on silicon substrate, the theory analysis proves that sensitivity at the optimal settings is increased 20 times compared to that at null settings used in most works, and the relationship between intensity and thickness is simplified as a linear type instead of the original nonlinear type, with the relative error reduced to similar to 1/100 at the optimal settings. Furthermore the discussion has been extended toward other factors affecting the sensitivity of the practical system, such as the linear dynamic range of the detector, the signal-to-noise ratio and the intensity from the light source, etc. Experimental results from the investigation Of SiO2 layer on silicon substrate are chosen to verify the optimization. (c) 2007 Optical Society of America
Author contributions
No full textPlease browse the "Files" tag to access the appendix specifying the author - Chen Hsi Tsai's contributions to the seven papers included in the thesis
Ying Chen\u27s Impressions of Summer
No full textChapbook of narrative/personal poems by Ying Chen originally published by Finishing Line Press in 2013. Translated from the French by Peter Schulman, ODU Professor of French and International Studies.https://digitalcommons.odu.edu/worldlanguages_books/1016/thumbnail.jp
PsdR-expressing strain exhibits LasR-null-like phenotypes.
No full text(A-C) PsdR-expressing strain produces metabolites to the levels similar to the LasR-null mutant. (A) Pyocyanin production (OD695/OD600 values) in shown strains. (B) Elastase production (OD495/OD600 values) in these strains. (C) The relative concentrations of hydrogen cyanide in shown strains. A one-way ANOVA with Bonferroni posttest was used for statistical analysis (n.s., not significant). (TIF)</p
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