899,922 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
Interpreting null findings from trials of alcohol brief interventions
No full textThe effectiveness of alcohol brief intervention (ABI) has been established by a succession of meta-analyses but, because the effects of ABI are small, null findings from randomized controlled trials are often reported and can sometimes lead to skepticism regarding the benefits of ABI in routine practice. This article first explains why null findings are likely to occur under null hypothesis significance testing (NHST) due to the phenomenon known as ‘the dance of the p-values’. A number of misconceptions about null findings are then described, using as an example the way in which the results of the primary care arm of a recent cluster randomized trial of ABI in England (the SIPS project) have been misunderstood. These misinterpretations include the fallacy of ‘proving the null hypothesis’ that lack of a significant difference between the means of sample groups can be taken as evidence of no difference between their population means, and the possible effects of this and related misunderstandings of the SIPS findings are examined. The mistaken inference that reductions in alcohol consumption seen in control groups from baseline to follow-up are evidence of real effects of control group procedures is then discussed and other possible reasons for such reductions, including regression to the mean, research participation effects, historical trends, and assessment reactivity, are described. From the standpoint of scientific progress, the chief problem about null findings under the conventional NHST approach is that it is not possible to distinguish ‘evidence of absence’ from ‘absence of evidence’. By contrast, under a Bayesian approach, such a distinction is possible and it is explained how this approach could classify ABIs in particular settings or among particular populations as either truly ineffective or as of unknown effectiveness, thus accelerating progress in the field of ABI research
EPP revisited: evidence from null subject languages*
No full textThe present paper examines the correlation between the pro-drop parameter and rich verbal morphology. With evidence from Greek, Old French (OF) and Brazilian Portuguese (BP), it is shown that null subjects are not licensed only in languages that have rich verbal morphology (e.g. Greek), but also in languages in which the verb may lack some agreement properties (e.g. OF and BP). Moreover, it is argued that the licensing of null subjects is triggered not only for syntactic but also for discourse reasons. Based on evidence from the aforementioned languages the featural requirement represented by the EPP is revisited; EPP simply encodes a P(honological)-feature
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
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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.
Sources of prey availability data alter interpretation of outputs from prey choice null networks.
No full textNull models provide a valuable baseline against which fundamental ecological hypotheses can be tested and foraging choices that cannot be explained by neutral processes or sampling biases can be highlighted. In this way, null models can advance our understanding beyond simplistic dietary descriptions to identify drivers of interactions. This method, however, requires estimates of resource availability, which are generally imperfect representations of highly dynamic systems. Optimising method selection is crucial for study design, but the precise effects of different resource availability data on the efficacy of null models are poorly understood.
Using spider–prey networks as a model, we used prey abundance (suction sample) and activity density (sticky trap) data, and combinations of the two, to simulate null networks. We compared null diet composition, network properties (e.g., connectance and nestedness) and deviations of simulations from metabarcoding-based spider dietary data to ascertain how different prey availability data alter ecological interpretation.
Different sampling methods produced different null networks and inferred distinct prey selectivity. Null models based on prey abundance and combined frequency-of-occurrence data generated null diet compositions, which more closely resembled the diet composition determined by metabarcoding. Null models based on prey abundance, activity density and proportionally combined data generated null network properties most like the networks constructed via dietary metabarcoding.
We show that survey method choice impacts all aspects of null network analyses, the precise effects varying between methods but ultimately altering ecological interpretation by increasing disparity in network properties or trophic niches between null and directly constructed networks. Merging datasets can generate more complete prey availability data but is not a panacea because it introduces different biases. The choice of method should reflect the research hypotheses and study system being investigated. Ultimately, survey methods should emulate the foraging mode of the focal predator as closely as possible, informed by the known ecology, natural history and behaviour of the predator
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
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