55,599 research outputs found
Hypothesis testing of multiple inequalities: the method of constraint chaining
Econometric inequality hypotheses arise in diverse ways. Examples include concavity restrictions on technological and behavioural functions, monotonicity and dominance relations, one-sided constraints on conditional moments in GMM estimation, bounds on parameters which are only partially identified, and orderings of predictive performance measures for competing models. In this paper we set forth four key properties which tests of multiple inequality constraints should ideally satisfy. These are (1) (asymptotic) exactness, (2) (asymptotic)similarity on the boundary, (3) absence of nuisance parameters from the asymptotic null distribution of the test statistic, (4) low computational complexity and boostrapping cost. We observe that the predominant tests currently used in econometrics do not appear to enjoy all these properties simultaneously. We therefore ask the question : Does there exist any nontrivial test which, as a mathematical fact, satisfies the first three properties and, by any reasonable measure, satisfies the fourth ? Remarkably the answer is affirmative. The paper demonstrates this constructively. We introduce a method of test construction called chaining which begins by writing multiple inequalities as a single equality using zero-one indicator functions. We then smooth the indicator functions. The approximate equality thus obtained is the basis of a well-behaved test. This test may be considered as the baseline of a wider class of tests. A full asymptotic theory is provided for the baseline. Simulation results show that the finite-sample performance of the test matches the theory quite well
Testing hypotheses in the Birnbaum-Saunders distribution under type-II censored samples
The two-parameter Birnbaum-Saunders distribution has been used succesfully to
model fatigue failure times. Although censoring is typical in reliability and
survival studies, little work has been published on the analysis of censored
data for this distribution. In this paper, we address the issue of performing
testing inference on the two parameters of the Birnbaum-Saunders distribution
under type-II right censored samples. The likelihood ratio statistic and a
recently proposed statistic, the gradient statistic, provide a convenient
framework for statistical inference in such a case, since they do not require
to obtain, estimate or invert an information matrix, which is an advantage in
problems involving censored data. An extensive Monte Carlo simulation study is
carried out in order to investigate and compare the finite sample performance
of the likelihood ratio and the gradient tests. Our numerical results show
evidence that the gradient test should be preferred. Three empirical
applications are presented.Comment: Submitted for publicatio
Fretting wear of TiN PVD coating under variable relative humidity conditions – development of a “composite” wear law
Fretting is defined as a small oscillatory displacement between two contacting bodies. The
interface is damaged by debris generation and its ejection from the contact area. The
application of hard coatings is an established solution to protect against fretting wear. For this
study the TiN hard coating manufactured by a PVD method has been selected, and tested
against a polycrystalline alumina smooth ball. A fretting test programme has been carried out
at a frequency of 5 Hz, 100 N normal load, 100 μm displacement amplitude and at five values
of relative humidity: 10, 30, 50, 70 and 90% at a temperature of 296 K. The intensity of the
wear process is shown to be significantly dependent on the environmental conditions. A
dissipated energy approach has been employed in this study to quantify wear rates of the hard
coating. The approach predicts wear kinetics under constant medium relative humidity in a
stable manner. It has been shown that an increase of relative humidity promotes the formation
of hydrate structures at the interface and modifies the third body rheology. This phenomenon
has been characterised by the evolution of wear kinetics associated with a significant variation
of the corresponding energy wear coefficient. Hence, a ‘composite’ wear law, integrating the
energy wear coefficient as a function of relative humidity, is introduced. It permits a
prediction of wear under variable relative humidity conditions from 10 to 90% within a single
fretting test. The stability of this approach is demonstrated by comparing various variable
relative humidity sequences
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