154,631 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
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
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
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
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
Asymptotic null distributions of stationarity and nonstationarity
No full textThe purpose of this paper is to investigate the asymptotic null distribution of stationarity and nonstationarity tests when the distribution of the error term belongs to the normal domain of attraction of a stable law in any finite sample but the error term is an i.i.d. process with finite variance as T " 1. This local-to-finite variance setup is helpful to highlight the behavior of test statistics under the null hypothesis in the borderline or near borderline cases between finite and infinite variance and to assess the robustness of these test statistics to small departures from the standard finite variance context. From an empirical point of view, our analysis can be useful in settings where the (non)-existence of the (second) moments is not clear-cut, such as, for example, in the analysis of financial time series. A Monte Carlo simulation study is performed to improve our understanding of the practical implications of the limi theory we develop. The main purpose of the simulation experiment is to assess the size distortion of the unit root and stationarity tests under investigation.Stable distributions, unit root tests, stationarity tests, asymptotic distributions,local-to-finite variance, size distortion
T cells facilitate Brugia malayi development in TCRalpha(null) mice.
No full textThe host-parasite interactions of Brugia malayi in mice are complex and multifactorial. In order to study the role of T cells in early B. malayi development, we infected TCRalpha(null) mice, which retain a population of CD4+ TCRbeta+ cells and TCRbeta(null) mice, which lack all TCRalphabeta(+) T cells. TCRalpha(null) mice were permissive to L4 larval and adult worm development but TCRbeta(null) mice were not. Depletion of the CD4(+) T cells in the former abrogated the permissive phenotype. It appears that the CD4(+) TCRbeta(+) T cells that have been described in TCRalpha(null) mice may facilitate early B. malayi development. These data are similar to our earlier demonstration of the role of NK cells in facilitating worm growth in SCID mice. Copyright 1999 Academic Press
Null spherical t-designs
No full textThe survey paper [2] of Eiichi Bannai and Etsuko Bannai provided an overview of the study of spherical designs and algebraic combinarotics. In the survey paper the authors focused on the study of good finite subsets of the unit sphere in n-dimension, n{u100000}1 and that part of their problem is to define what good finite subsets should mean. However, up to today, no definite answer is known and it is unrealistic to expect a single good answer. A possible point of view that one could take is to de ne a good subset of the unit sphere to be the one that globally approximates the whole sphere using only a finite number of point. A reasonable definition to what it means for a finite subset to approximate the sphere was given by Delsarte-Goethals-Seidel in 1966 as follows: a finite subset X on n{u100000}1 is called a spherical t-design on n{u100000}1, if for any polynomial f(x) = f(x1 x2 : : : xn) of degree at most t, the value of the integral of f(x) on n{u100000}1 (divided by the volume of n{u100000}1) is just the average value of f(x) on the finite set X that is, 1 j n{u100000}1j Z x2 n{u100000}1 f(x)d (x) = 1 jX j X x2X f(x) where is a Lesbegue measure on n{u100000}1: In
In one of the talks on Algebraic Combinatorics at Shanghai Jiao Tong University on May 2012, Eiichi Bannai defined the notion of a null spherical t-design on the unit sphere in n-dimension. For any non-negative integers n t such that n \u3e 1 and t 0 a pair (X !) is a null spherical t-design on n{u100000}1 if X is a finite subset of n{u100000}1 and ! is a non-zero weight function on X that satisfies X x2X !(x)f(x) = 0 for any homogeneous harmonic polynomial f(x) in n variables of degree at most t: This definition generalizes the notion of the usual spherical t-designs on the unit sphere by allowing non-zero weights.
In this study, properties of null spherical t-designs similar to properties of spherical t-designs are presented. Construction of null spherical designs is also provided using known spherical designs. Null spherical designs are also described using the Gegenbauer polynomials and characteristic matrices. Bounds on the number of points in a null spherical design are determined. In particular, we conjecture that the minimum number of points in a null spherical t-design on n{u100000}1 is 2(t + 1)
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.
Phosphoinositide-dependent kinase 1 controls migration and malignant transformation but not cell growth and proliferation in PTEN-null lymphocytes
No full textIn normal T cell progenitors, phosphoinositide-dependent kinase l (PDK1)-mediated phosphorylation and activation of protein kinase B (PKB) is essential for the phosphorylation and inactivation of Foxo family transcription factors, and also controls T cell growth and proliferation. The current study has characterized the role of PDK1 in the pathology caused by deletion of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN). PDK1 is shown to be essential for lymphomagenesis caused by deletion of PTEN in T cell progenitors. However, PTEN deletion bypasses the normal PDK1-controlled signaling pathways that determine thymocyte growth and proliferation. PDK1 does have important functions in PTEN-null thymocytes, notably to control the PKB-Foxo signaling axis and to direct the repertoire of adhesion and chemokine receptors expressed by PTEN-null T cells. The results thus provide two novel insights concerning pathological signaling caused by PTEN loss in lymphocytes. First, PTEN deletion bypasses the normal PDK1-controlled metabolic checkpoints that determine cell growth and proliferation. Second, PDK1 determines the cohort of chemokine and adhesion receptors expressed by PTEN-null cells, thereby controlling their migratory capacity.</p
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