286,973 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
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
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
On the Symbols of Strictly m-Null Elementary Operators
No full textThis paper extends the previous work by the author on m-null pairs of operators in Hilbert space. If an elementary operator L has elementary symbols A and B that are p-null and q-null, respectively, then L is (p+q−1)-null. Here, we prove the converse under strictness conditions, modulo some nonzero multiplicative constant—if L is strictly (p+q−1)-null, then a scalar λ≠0 exists such that λA is strictly p-null and λ−1B is strictly q-null. Our constructive argument relies essentially on algebraic and combinatorial methods. Thus, the result obtained by Gu on m-isometries is recovered without resorting to spectral analysis. For several operator classes that generalize m-isometries and are subsumed by m-null operators, the result is new
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
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
Null Polynomials modulo m
No full textThis paper studies so-called "null polynomials modulo m", i.e., polynomials with integer coefficients that satisfy f(x)=0 (mod m) for any integer x. The study on null polynomials is helpful to reduce congruences of higher degrees modulo m and to enumerate equivalent polynomial functions modulo m, i.e., functions over Z_m={0, ..., m-1} generated by integer polynomials. The most well-known null polynomial is f(x)=x^p-x modulo a prime p. After pointing out that null polynomials modulo a composite can be studied by handling null polynomials modulo each prime power, this paper mainly focuses on null polynomials modulo p^d (d>=1). A typical monic null polynomial of the least degree modulo p^d is given for any value of d>=1, from which one can further enumerate all null polynomials modulo p^d. The most useful result obtained in this paper are Theorem 32 in Sec. 4.4 and its derivative -- Theorem 34 in Sec. 4.5. The results given in Sec. 4.3 form a basis of the induction proofs given in Sec. 4.4. However, if you do not care how the proofs in Sec. 4.4 were established, you can simply skip Sec. 4.3. Theorems 28 and 31 are very important for the proof of Theorem 32 and should be paid more attention. Note: After finishing this draft, we noticed that some results given in this paper have been covered in Kempner's papers [3,4]. Since we use a different way to obtain the results, this work can be considered as an independent and different proof. For a brief introduction to Kempner's proof, see the Appendix of this paper
Elementary Operators with m-Null Symbols
No full textMotivated by Botelho and Jamison’s seminal 2010 study on elementary operators that are m-isometries, in this paper, we introduce the concept of m-null pairs of operators and establish some structural properties and characterizations of the class of elementary operators whose symbols are m-null (so-called m-null elementary operators). It is shown that if the symbols of an elementary operator L are, in turn, a p-null elementary operator and a q-null elementary operator, then L is a (p+q−1)-null elementary operator. Some extant results on elementary m-isometries can be recovered from this renewed perspective, often providing added value
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.
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