24,147 research outputs found
A pseudo empirical likelihood approach for stratified samples with nonresponse
Nonresponse is common in surveys. When the response probability of a survey
variable depends on through an observed auxiliary categorical variable
(i.e., the response probability of is conditionally independent of
given ), a simple method often used in practice is to use categories as
imputation cells and construct estimators by imputing nonrespondents or
reweighting respondents within each imputation cell. This simple method,
however, is inefficient when some categories have small sizes and ad hoc
methods are often applied to collapse small imputation cells. Assuming a
parametric model on the conditional probability of given and a
nonparametric model on the distribution of , we develop a pseudo empirical
likelihood method to provide more efficient survey estimators. Our method
avoids any ad hoc collapsing small categories, since reweighting or
imputation is done across categories. Asymptotic distributions for
estimators of population means based on the pseudo empirical likelihood method
are derived. For variance estimation, we consider a bootstrap procedure and its
consistency is established. Some simulation results are provided to assess the
finite sample performance of the proposed estimators.Comment: Published in at http://dx.doi.org/10.1214/07-AOS578 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
B-12(SCN)(12)(-): An Ultrastable Weakly Coordinating Dianion
Stable dianions that are weakly coordinating with metal ions are not common. In this work, we show that the thiocyanate SCN- anion, known for its detoxification property of cyanide CN- and antidegradation property of perovskite solar cell materials, can also be used to produce a new set of weakly coordinating B-12(SCN)(12)(-) dianion complexes which are potential candidates for the anionic part inside the electrolytes of metal-ion, especially the magnesium-ion-based, batteries
Robust quantum repeater with atomic ensembles and single-photon sources
We present a quantum repeater protocol using atomic ensembles, linear optics
and single-photon sources. Two local 'polarization' entangled states of atomic
ensembles and are generated by absorbing a single photon emitted by an
on-demand single-photon sources, based on which high-fidelity local
entanglement between four ensembles can be established efficiently through
Bell-state measurement. Entanglement in basic links and entanglement connection
between links are carried out by the use of two-photon interference. In
addition to being robust against phase fluctuations in the quantum channels,
this scheme may speed up quantum communication with higher fidelity by about 2
orders of magnitude for 1280 km compared with the partial read (PR) protocol
(Sangouard {\it et al.}, Phys. Rev. A {\bf77}, 062301 (2008)) which may
generate entanglement most quickly among the previous schemes with the same
ingredients.Comment: 5 pages 4 figure
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