8,538 research outputs found
Physicochemical properties and leaching behavior of eight U.S. long-grain rice cultivars as related to rice texture
There are many long-grain rice cultivars produced commercially in the U.S.; however, little work has been done on correlating the structure and physicochemical properties of starch with their texture. The physicochemical properties, leaching behavior, and texture attributes of eight longgrain rice cultivars were studied. Differences were observed in the approximate composition of kernels, including crude protein (6.6-9.3%), crude lipid (0.18-0.51%), and apparent amylose content (25.5-30.9%). These cultivars also differed slightly in thermal properties, such as onset temperature (73.7° to 77.4°C) and peak temperature (78.8° to 81.9°C). Although they showed a similar pasting temperature, their peak viscosities ranged from 680 to 982 Brabender units. The amount and the molecular size distribution of the leached starch molecules varied greatly among the samples. The leached amylose, instead of the apparent amylose, was suggested to play an important role in cooked rice texture
Functional single index models for longitudinal data
A new single-index model that reflects the time-dynamic effects of the single
index is proposed for longitudinal and functional response data, possibly
measured with errors, for both longitudinal and time-invariant covariates. With
appropriate initial estimates of the parametric index, the proposed estimator
is shown to be -consistent and asymptotically normally distributed.
We also address the nonparametric estimation of regression functions and
provide estimates with optimal convergence rates. One advantage of the new
approach is that the same bandwidth is used to estimate both the nonparametric
mean function and the parameter in the index. The finite-sample performance for
the proposed procedure is studied numerically.Comment: Published in at http://dx.doi.org/10.1214/10-AOS845 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Unsteady forces on an accelerating plate and application to hovering insect flight
The aerodynamic forces on a flat plate accelerating from rest at fixed incidence in two-dimensional power-law flow are studied analytically and numerically. An inviscid approximation is made in which separation at the two plate edges is modelled by growing spiral vortex sheets, whose evolution is determined by the Birkhoff–Rott equation. A solution based on a similarity expansion is developed, valid when the scale of the separated vortex is much smaller than the plate dimension. The leading order is given by the well-known similarity growth of a vortex sheet from a semi-infinite flat plate, while equations at the second order describe the asymmetric sweeping effect of that component of the free-stream parallel to the plate. Owing to subtle cancellation, the unsteady vortex force exerted on the plate during the starting motion is independent of the sweeping effect and is determined by the similarity solution, to the order calculated. This gives a mechanism for dynamic stall based on a combination of unsteady vortex lift and pure added mass; the incidence angle for maximum vortex lift is independent of the acceleration profile. Circulation on the flat plate makes no direct contribution. Both lift and drag force predictions from the unsteady inviscid theory are compared with those obtained from numerical solutions of the two-dimensional unsteady Navier–Stokes equations for an ellipse of high aspect ratio, and with predictions of Wagner's classical theory. There is good agreement with numerical results at high incidence and moderate Reynolds number. The force per unit span predicted by the vortex theory is evaluated for parameters typical of insect wings and is found to be in reasonable agreement with numerical simulations. Estimates for the shed circulation and the size of the start-up vortices are also obtained. The significance of this flow as a mechanism for insect hovering flight is discussed
Modeling left-truncated and right-censored survival data with longitudinal covariates
There is a surge in medical follow-up studies that include longitudinal
covariates in the modeling of survival data. So far, the focus has been largely
on right-censored survival data. We consider survival data that are subject to
both left truncation and right censoring. Left truncation is well known to
produce biased sample. The sampling bias issue has been resolved in the
literature for the case which involves baseline or time-varying covariates that
are observable. The problem remains open, however, for the important case where
longitudinal covariates are present in survival models. A joint likelihood
approach has been shown in the literature to provide an effective way to
overcome those difficulties for right-censored data, but this approach faces
substantial additional challenges in the presence of left truncation. Here we
thus propose an alternative likelihood to overcome these difficulties and show
that the regression coefficient in the survival component can be estimated
unbiasedly and efficiently. Issues about the bias for the longitudinal
component are discussed. The new approach is illustrated numerically through
simulations and data from a multi-center AIDS cohort study.Comment: Published in at http://dx.doi.org/10.1214/12-AOS996 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Covariate adjusted functional principal components analysis for longitudinal data
Classical multivariate principal component analysis has been extended to
functional data and termed functional principal component analysis (FPCA). Most
existing FPCA approaches do not accommodate covariate information, and it is
the goal of this paper to develop two methods that do. In the first approach,
both the mean and covariance functions depend on the covariate and time
scale while in the second approach only the mean function depends on the
covariate . Both new approaches accommodate additional measurement errors
and functional data sampled at regular time grids as well as sparse
longitudinal data sampled at irregular time grids. The first approach to fully
adjust both the mean and covariance functions adapts more to the data but is
computationally more intensive than the approach to adjust the covariate
effects on the mean function only. We develop general asymptotic theory for
both approaches and compare their performance numerically through simulation
studies and a data set.Comment: Published in at http://dx.doi.org/10.1214/09-AOS742 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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