12,334 research outputs found
A Partially Linear Framework for Massive Heterogeneous Data
We consider a partially linear framework for modelling massive heterogeneous
data. The major goal is to extract common features across all sub-populations
while exploring heterogeneity of each sub-population. In particular, we propose
an aggregation type estimator for the commonality parameter that possesses the
(non-asymptotic) minimax optimal bound and asymptotic distribution as if there
were no heterogeneity. This oracular result holds when the number of
sub-populations does not grow too fast. A plug-in estimator for the
heterogeneity parameter is further constructed, and shown to possess the
asymptotic distribution as if the commonality information were available. We
also test the heterogeneity among a large number of sub-populations. All the
above results require to regularize each sub-estimation as though it had the
entire sample size. Our general theory applies to the divide-and-conquer
approach that is often used to deal with massive homogeneous data. A technical
by-product of this paper is the statistical inferences for the general kernel
ridge regression. Thorough numerical results are also provided to back up our
theory.Comment: 40 pages main text + 40 pages suppl, To appear in Annals of
Statistic
Self-desiccation and self-desiccation shrinkage of silica fume-cement pastes
Self-desiccation is one common phenomenon of high-performance cementitious materials, which are
characterized by low water/binder (w/b) ratio and high mineral admixture incorporation. As a
consequence, large magnitude of self-desiccation shrinkage, a key factor which influences the
cracking behavior of concrete, develops rapidly in the cement matrix due to the internal relative
humidity (RH) decrease and capillary pressure induced by self-desiccation.
The objective of this study is to evaluate the behavior of self-desiccation and self-desiccation
shrinkage in silica fume (SF) blended cement pasts with low w/b ratio of 0.25. The self-desiccation
process was revealed by the measurement of internal RH of the sealed cement pastes with
conventional method of hygrometer. The shrinkage of the sealed cement pastes was measured by the
corrugated tube method, permitting measurements to start at early age.
Experimental results revealed that SF blending leads to a higher internal RH, indicating slower
self-desiccation process, compared with pure cement paste. Consequently, less self-desiccation
shrinkage was observed in SF blended cement pastes than that in pure cement paste
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