339,798 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
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
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
Biological monitoring occupational exposures to styrene and styrene-(7,8)-oxide
No full textThis study investigated the capability of some urinary and haematic biomarkers to discriminate among different levels of occupational exposure to styrene (Sty) and styrene-(7,8)-oxide (StyOX) and evaluated the influence of smoking habit and genetic polymorphism of metabolic enzymes GSTM1 and GSTT1 on these biomarkers. With this aim, we recruited workers of the reinforced plastic industry (n=8), of the paint and dye industry (n=13), and a group of controls (n=22). Median personal exposure to airborne Sty and StyOX in the different working activities was 14.8, 3.1 and 0.3 mg/m3, and 126, 13 and <5 μg/m3, respectively, as evaluated by repeated measurements. These chemicals were strictly correlated with each other (Pearson r = 0.826), the ratio between Sty and StyOX being about 1000:5. Personal exposure was significantly higher in exposed workers than in controls and, among workers, in subjects of the reinforced plastic industry. Urinary biomarkers, namely unchanged styrene (StyU), mandelic acid (MA), phenylglyoxylic acid (PGA), phenylglycine (PHG), 4-vinylphenol (4-VP), and mercapturic acids (M1 and M2) were higher in end- than in pre-shift samples and significantly correlated with both airborne Sty and StyOX. The best correlations were observed between end-shift MA or MA + PGA and airborne Sty (r = 0.890 or 0.886, respectively). The excretion of mercapturic acids was 6-fold higher in subjects with GSTM1 active genotype in comparison with those with null genotype. Cysteinyl albumin and hemglobin adducts of StyOX could not distinguish the different exposure categories investigated. In conclusion, in both reinforced plastic and paint and dye industry there was co-exposure to airborne Sty and StyOX. Among the different biomarkers urinary MA and PGA and their sum showed the best capability to discriminate different exposures and are recommended for Sty exposure assessment starting from a level of 1 mg/m3
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.
GRAM: A True Null Model for Relative Binding Affinity Predictions
No full textRelative binding affinity prediction is a critical component in computer aided drug design. Significant amount of effort has been dedicated to developing rapid and reliable in silico methods. However, robust assessment of their performance is still a complicated issue, as it requires a performance measure applicable in the prospective setting and more importantly a true null model that defines the expected performance of random in an objective manner. Although many performance metrics, such as correlation coefficient (r2), mean unsigned error (MUE), and room mean square error (RMSE), are frequently used in the literature, a true and non-trivial null model has yet been identified. To address this problem, here we introduce an interval estimate as an additional measure, namely prediction interval (PI), which can be estimated from the error distribution of the predictions. The benefits of using the interval estimate are 1) it provides the uncertainty range in the predicted activities, which is important in prospective applications; 2) a true null model with well-defined PI can be established. We provide one such example termed Gaussian Random Affinity Model (GRAM), which is based on the empirical observation that the affinity change in a typical lead optimization effort has the tendency to distribute normally N (0, s). Having an analytically defined PI that only depends on the variation in the activities, GRAM should in principle allow us to compare the performance of relative binding affinity prediction methods in a standard way, ultimately critical to measuring the progress made in algorithm development.<br /
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
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