1,680,415 research outputs found
Null Subjects in Northeast English
No full textThis paper presents data and analysis relating to null subjects in spoken colloquial English.
While English is not a „pro-drop? language (i.e. subjects must usually be overt), a corpus of
speech collected on Tyneside and Wearside in 2007 shows that null subjects are permitted in
finite clauses in certain contexts. This paper analyses these examples and follow-up
questionnaires, and compares the data with the other types of null subject described in the
literature (pro-drop, topic-drop, early null subjects, aphasics? null subjects and „diary-drop?),
ultimately concluding that the colloquial English phenomenon is most closely related to diary-
drop
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
Frataxin null mutants of arabidopsis are embryo lethals
No full textFrataxin is a nuclear encoded protein targeted to the mitochondrial matrix. In humans, frataxin deficiency
is associated with Friedreich’s ataxia, a neurodegenerative and cardiac disorder characterized by
accumulation of iron in the mitochondria and a diminished activity of various mitochondrial proteins,
including aconitase. Yeast cells lacking frataxin show a complex respiratory deficient phenotype,
defective in the maturation of mitochondrial Fe/S enzymes, hypersensitivity to oxidative stress, instability
of mtDNA and defects in heme biosynthesis. It has been proposed that frataxin has ferroxidase activity
and iron storage properties which may protect the mitochondria from iron toxicity, and that it also acts as
a chaperone to donate iron to the proteins involved in the two major pathways of iron utilization, Fe/S
cluster assembly and heme synthesis. Recently, an Arabidopsis gene (AtFH) highly similar to the human
frataxin gene and possessing a mitochondrial targeting sequence has been described (Busi et al. 2004):
AtFH is able to complement a yeast frataxin null mutant and in the plant is mainly expressed in flowers.
We identified in the Salk collection two T-DNA insertions in the AtFH gene and characterized genetically
the two mutants. Upon selfing heterozygous plants, we cannot recover in the progeny homozygote null
seeds while homozygous wt and heterozygous seeds were in a ratio 1: 2 (as observed after PCR analysis).
The ratio was consistent with lethality of the homozygous null genotypes during embryogenesis.
Accordingly we analyze the pattern of embryo development in siliques segregating homozygous null
embryos: an early arrest at the 8-16 cells stage was consistently observed
Publication Bias Against Null Results
No full textStudies suggest a bias against the publication of null (p > .05) results. Instead of significance, we advocate reporting effect sizes and confidence intervals, and using replication studies. If statistical tests are used, power tests should accompany them.publication, bias, null results
MHD wave propagation in the neighbourhood of a two-dimensional null point
No full textThe nature of fast magnetoacoustic and Alfvén waves is investigated in a zero β plasma. This gives an indication of wave propagation in the low β solar corona. It is found that for a two-dimensional null point, the fast wave is attracted to that point and the front of the wave slows down as it approaches the null point, causing the current density to accumulate there and rise rapidly. Ohmic dissipation will extract the energy in the wave at this point. This illustrates that null points play an important role in the rapid dissipation of fast magnetoacoustic waves and suggests the location where wave heating will occur in the corona. The Alfvén wave behaves in a different manner in that the wave energy is dissipated along the separatrices. For Alfvén waves that are decoupled from fast waves, the value of the plasma β is unimportant. However, the phenomenon of dissipating the majority of the wave energy at a specific place is a feature of both wave types
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.
Current sheet formation and nonideal behavior at three-dimensional magnetic null points
No full textThe nature of the evolution of the magnetic field, and of current sheet formation, at three-dimensional (3D) magnetic null points is investigated. A kinematic example is presented that demonstrates that for certain evolutions of a 3D null (specifically those for which the ratios of the null point eigenvalues are time-dependent), there is no possible choice of boundary conditions that renders the evolution of the field at the null ideal. Resistive magnetohydrodynamics simulations are described that demonstrate that such evolutions are generic. A 3D null is subjected to boundary driving by shearing motions, and it is shown that a current sheet localized at the null is formed. The qualitative and quantitative properties of the current sheet are discussed. Accompanying the sheet development is the growth of a localized parallel electric field, one of the signatures of magnetic reconnection. Finally, the relevance of the results to a recent theory of turbulent reconnection is discussed
A Panel Test of Purchasing Power Parity Under the Null of Stationarity
No full textPurchasing Power Parity (PPP) is tested using a sample of real exchange rate data for
twelve European countries. Acknowledging that Augmented Dickey Fuller tests have
low power, we apply a Panel test that considers the null of stationarity and corrects for
serial dependence using a non-parametric kernel based method
Author Guidelines
No full textReproduction Rights Universitas Scientiarum is licensed under Creative Commons: Attribution - Noncommercial - No derivative works, 2.5 of Colombia. Consequently, it can be electronically reproduced, distributed and publically communicated, provided the authors and the Pontificia Universidad Javeriana are acknowledged. Commercial use of this work is not permitted. Modifications to the original work, and distribution of modified copies are prohibited. Upon acceptance of the article, the author will send the journal’s Office a printed and signed license of economic rights transfer, which authorizes its reproduction in Universitas Scientiarum (the license can be downloaded from the journal website; http://revistas.javeriana.edu.co/scientarium/web; http://revistas.javeriana.edu.co/scientarium/ojs). Such permission will infer the author’s acceptance of the article’s dissemination not only on paper but also in electronic media, that is, in websites and in national and international bibliographic databases. The magazine accepts pre-print articles, previously uploaded to e-print servers (OAI - such as arxiv.org)
Null and overt subject biases in Spanish and Italian: a cross-linguistic comparison
No full textOver the last twenty years a great deal of linguistic research has investigated how anaphoric expressions retrieve their antecedents in the discourse showing that a variety of pragmatic factors together with grammatical and cognitive constraints contribute in determining the distribution of different types of expressions. A particularly interesting case for the study of such phenomena is that of Null Subjec
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