53,022 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
Linear Operator Inequality and Null Controllability with Vanishing Energy for Unbounded Control Systems
No full textWe consider a linear boundary or point control system on a Hilbert space which is null controllable at some time . To every initial state we associate the minimal ``energy'' needed to transfer to in a time (``energy'' of a control being the square of its norm). Clearly, it decreases with the control time . We shall prove that, under suitable spectral properties of the linear system operator, the minimal energy converges to for $ T\to+\infty
Hanlin Zhang Lightning Talk
No full textHanlin Zhang presents his research related to a practicum he performed with Business Intelligence at Facilities & Services, UIUC.Open Restriction set for Item 99148 on 2017-05-05T16:33:23Z with date null by [email protected] by Daniel Mills ([email protected]) on 2017-05-05T16:38:22Z
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Previous issue date: 2017-04-07Ope
Size distortions of tests of the null hypothesis of stationarity: Evidence and implications for applied work
No full textIt is common in applied econometrics to test the null hypothesis of a level-stationary process against the alternative of a unit root process. We show that the use of conventional asymptotic critical values for the stationarity tests of Kwiatkowski et al. (1992) and Leybourne and McCabe (1994) may cause extreme size distortions, if the model under the null hypothesis is highly persistent. The existence of such size distortions has not been recognized in the previous literature. We illustrate the practical importance of these distortions for the problem of testing for long-run purchasing power parity under the recent float. Size distortions of tests of the unit root null hypothesis may be overcome by the use of finite-sample or bootstrap critical values. We show that such corrections are not possible for tests of the null hypothesis of stationarity. Our results suggest that the common practice of viewing tests of stationarity as complementary to tests of the unit root null will tend to result in contradictions or in spurious acceptances of the unit root hypothesis. We conclude that tests of the null hypothesis of stationarity cannot be recommended for applied work unless the sample size is very large. --I(0) null hypothesis,finite-sample critical values,size,Monte Carlo simulation
†Chuchinolepididae Zhang 1978
No full textFamily †Chuchinolepididae Zhang 1978, spelling in prevailing recent practice †Chuchinolepidae Zhang 1978a: 296 (family) † Chuchinolepis Zhang 1978 [family name also seen as †Chuchinolepididae; author also seen as Chang] †Qujinolepidae Zhang 1978b: 173 (family) † Qujinolepis Zhang 1978 [family name sometimes seen as † Qujinolepididae] †Procondylolepidae Zhang 1984: 82 (family) † Procondylolepis Zhang 1984Published as part of Laan, Richard Van Der, 2018, Family-group names of fossil fishes, pp. 1-167 in European Journal of Taxonomy 466 on page 27, DOI: 10.5852/ejt.2018.466, http://zenodo.org/record/555755
Comparison of Evolutionary Optimization Algorithms for FM-TV Broadcasting Antenna Array Null Filling
No full textBroadcasting antenna array null filling is a very
challenging problem for antenna design optimization. This paper
compares five antenna design optimization algorithms (Differential
Evolution, Particle Swarm, Taguchi, Invasive Weed, Adaptive
Invasive Weed) as solutions to the antenna array null filling
problem. The algorithms compared are evolutionary algorithms
which use mechanisms inspired by biological evolution, such as
reproduction, mutation, recombination, and selection. The focus of
the comparison is given to the algorithm with the best results,
nevertheless, it becomes obvious that the algorithm which produces
the best fitness (Invasive Weed Optimization) requires very
substantial computational resources due to its random search
nature
Uniform Consistency for Nonparametric Estimators in Null Recurrent Time Series
No full textThis paper establishes a suite of uniform consistency results for nonparametric kernel density and regression estimators when the time series regressors concerned are nonstationary null-recurrent Markov chains. Under suitable conditions, certain rates of convergence are also obtained for the proposed estimators. Our results can be viewed as an extension of some well-known uniform consistency results for the stationary time series case to the nonstationary time series case.β-null recurrent Markov chain, nonparametric estimation, rate of convergence, uniform consistency
An enhanced author name dataset for PubMed/MEDLINE
No full text<p>The incompleteness of author names is a well-known issue in the MEDLINE database. It was since 2002, the full author name has been systematically indexed in MEDLINE. Although many full author names have been added to MEDLINE, we still found a significant number of abbreviated names in papers published after 2002.</p>
<p>Here we built an enhanced author name dataset for MEDLINE, called EAN, achieved by linking the whole PubMed to other large literature databases and conducting a large-scale name comparison and restoration with obtained multi-sources author names. Our evaluation shows that more than 90% of author names in EAN are complete as compared to the ratio of ~60% in MEDLINE.</p>
An enhanced author name dataset for PubMed/MEDLINE
No full text<p>The incompleteness of author names is a well-known issue in the MEDLINE database. It was since 2002, the full author name has been systematically indexed in MEDLINE. Although many full author names have been added to MEDLINE, we still found a significant number of abbreviated names in papers published after 2002.</p>
<p>Here we built an enhanced author name dataset for MEDLINE, called EAN, achieved by linking the whole PubMed to other large literature databases and conducting a large-scale name comparison and restoration with obtained multi-sources author names. Our evaluation shows that more than 90% of author names in EAN are complete as compared to the ratio of ~60% in MEDLINE.</p>
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