3,495 research outputs found
Special Issue about Competing Risks and Multi-State Models
There is a clear growing interest, at least in the statistical literature, in competing risks and multi-state models. With the rising interest in competing risks and multi-state models a number of software packages have been developed for the analysis of such models. The present special issue of the Journal of Statistical Software introduces a selection of R packages devoted to competing risks and multi-state models. This introduction to the special issue contains some background and highlights the contents of the contributions.
In search of an observational quantum signature of the primordial perturbations in slow-roll and ultra slow-roll inflation
In the standard inflationary paradigm, cosmological density perturbations are
generated as quantum fluctuations in the early Universe, but then undergo a
quantum-to-classical transition. A key role in this transition is played by
squeezing of the quantum state, which is a result of the strong suppression of
the decaying mode component of the perturbations. Motivated by ever improving
measurements of the cosmological perturbations, we ask whether there are
scenarios where this decaying mode is nevertheless still observable in the late
Universe, ideally leading to a ``smoking gun'' signature of the quantum nature
of the perturbations. We address this question by evolving the quantum state of
the perturbations from inflation into the post-inflationary Universe. After
recovering the standard result that in slow-roll (SR) inflation the decaying
mode is indeed hopelessly suppressed by the time the perturbations are observed
(by orders of magnitude), we turn to ultra slow-roll (USR)
inflation, a scenario in which the usual decaying mode actually grows on
super-horizon scales. Despite this drastic difference in the behavior of the
mode functions, we find also in USR that the late-Universe decaying mode
amplitude is dramatically suppressed, in fact by the same orders of
magnitude. We finally explain that this large suppression is a general result
that holds beyond the SR and USR scenarios considered and follows from a
modified version of Heisenberg's uncertainty principle and the observed
amplitude of the primordial power spectrum. The classical behavior of the
perturbations is thus closely related to the classical behavior of macroscopic
objects drawing an analogy with the position of a massive particle, the
curvature perturbations today have an enormous effective mass of order , making them highly classical.Comment: 27 pages, 7 figures. Comments welcom
Opportunities and constraints for improved vegetable production technology in tropical Asia
A description of the characteristics of vegetable production in tropical Asia is presented. The description is followed by a discussion of the opportunities and constraints of improved non-seed vegetable production technologies. Sowing of seeds and seedling emergence, transplant production, irrigation, mulching, fertiliser use, crop protection and weed control methods, protected cultivation and harvest date planning are discussed in relation to their use and impact. Conditions for successful introduction of new technologies and the role of outside actors are discussed. It is argued that in order to increase the success of adoption of improved technologies, farmers and public and private institutions should work together. With increasing prosperity, the demand for vegetables, especially in the expanding urban areas, will increase, leading to the intensification of production and higher profitability. With better profitability, the application of mulch, drip irrigation, fertigation and protected cultivation will become more common. With increasing production, harvest date planning as related to year-round city market demand, will become essential to improve profitability. It is recommended that, next to the development and introduction of improved production technologies, research and extension on vegetables in tropical Asia, should also focus on methods to improve harvest date planning and year-round suppl
To Bin or Not To Bin: Decorrelating the Cosmic Equation of State
The physics behind the acceleration of the cosmic expansion can be elucidated
through comparison of the predictions of dark energy equations of state to
observational data. In seeking to optimize this, we investigate the advantages
and disadvantages of using principal component analysis, uncorrelated
bandpowers, and the equation of state within redshift bins. We demonstrate that
no one technique is a panacea, with tension between clear physical
interpretation from localization and from decorrelated errors, as well as model
dependence and form dependence. Specific lessons include the critical role of
proper treatment of the high redshift expansion history and the lack of a
unique, well defined signal-to-noise or figure of merit.Comment: 26 pages, 28 figure
Efficient estimation of Banach parameters in semiparametric models
Consider a semiparametric model with a Euclidean parameter and an
infinite-dimensional parameter, to be called a Banach parameter. Assume: (a)
There exists an efficient estimator of the Euclidean parameter. (b) When the
value of the Euclidean parameter is known, there exists an estimator of the
Banach parameter, which depends on this value and is efficient within this
restricted model. Substituting the efficient estimator of the Euclidean
parameter for the value of this parameter in the estimator of the Banach
parameter, one obtains an efficient estimator of the Banach parameter for the
full semiparametric model with the Euclidean parameter unknown. This hereditary
property of efficiency completes estimation in semiparametric models in which
the Euclidean parameter has been estimated efficiently. Typically, estimation
of both the Euclidean and the Banach parameter is necessary in order to
describe the random phenomenon under study to a sufficient extent. Since
efficient estimators are asymptotically linear, the above substitution method
is a particular case of substituting asymptotically linear estimators of a
Euclidean parameter into estimators that are asymptotically linear themselves
and that depend on this Euclidean parameter. This more general substitution
case is studied for its own sake as well, and a hereditary property for
asymptotic linearity is proved.Comment: Published at http://dx.doi.org/10.1214/009053604000000913 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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