12,837 research outputs found
Efficient randomized-adaptive designs
Response-adaptive randomization has recently attracted a lot of attention in
the literature. In this paper, we propose a new and simple family of
response-adaptive randomization procedures that attain the Cramer--Rao lower
bounds on the allocation variances for any allocation proportions, including
optimal allocation proportions. The allocation probability functions of
proposed procedures are discontinuous. The existing large sample theory for
adaptive designs relies on Taylor expansions of the allocation probability
functions, which do not apply to nondifferentiable cases. In the present paper,
we study stopping times of stochastic processes to establish the asymptotic
efficiency results. Furthermore, we demonstrate our proposal through examples,
simulations and a discussion on the relationship with earlier works, including
Efron's biased coin design.Comment: Published in at http://dx.doi.org/10.1214/08-AOS655 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Direct measurement of the magnetic field effects on carrier mobilities and recombination in tri-(8-hydroxyquinoline)-aluminum based light-emitting diodes
The magnetic field effects on the carrier mobilities and recombination in
tri-(8-hydroxyquinoline)-aluminum (Alq3) based light-emitting diodes have been
measured by the method of transient electroluminescence. It is confirmed that
the magnetic field has no effect on the electron and hole mobilities in Alq3
layers and can decrease the electron-hole recombination coefficient. The
results imply that the dominant mechanism for the magnetic field effects in
Alq3 based light-emitting diodes is the interconversion between singlet e-h
pairs and triplet e-h pairs modulated by the magnetic field when the driving
voltage is larger than the onset voltage of the electroluminescence.Comment: 14 pages, 4 figures,The revised version submitted to applied physics
letter
Facile Synthesis and Versatilities of Polyanthraquinoylamine Nanofibril Bundles with Self Stability and High Carbon Yield
A facile synthesis for nanosized conducting polymers with inherent self-stability and multi-functionalities is a main challenge. Here we simply synthesize intrinsically self-stabilized nanofibril bundles of poly(1-anthraquinoylamine) (PAQ) by a template-free method. The critical polymerization parameters were studied to significantly optimize the synthesis, size, properties, and functionalities of the resulted fine nanofibrils with a diameter of ca. 30 nm and length of ~6 μm. The PAQ obtained with ammonium persulfate possesses higher polymerization yield, purer composition, higher conductivity, better melting behaviour, higher thermostability, lower burning enthalpy, and slower degradation than that with other oxidants. Furthermore, the polymer nanofibrils exhibit high self-stability, powerful redispersibility, high purity, and clean surface because of a complete avoidance of the contamination from external stabilizer. The PAQ exhibits widely controllable conductivity moving across ten orders of magnitudes from 10^-9^ to 50 S/cm, photoluminescence, lead-ion adsorbability, very high thermostability in air and extremely high char yield in nitrogen at 1000˚C. These materials would be useful as advanced materials including photoluminescent materials, highly cost-effective carbon precursors, sorbents of toxic metal ions, and cost-efficient conductive nanocomposite with low percolation threshold
Transitions in the Standard Model Effective Field Theory
The anomalies observed in decays
have attracted much attention in recent years. In this paper, we study the
, , , , and decays, all
being mediated by the same quark-level transition, in the
Standard Model Effective Field Theory. The most relevant dimension-six
operators for these processes are , , ,
and in the Warsaw basis. Evolution of the corresponding Wilson
coefficients from the new physics scale ~TeV down to the
characteristic scale is performed at three-loop in QCD and
one-loop in EW/QED. It is found that, after taking into account the constraint
, a single
or
can still be used to resolve the
anomalies at , while a single
is already ruled out by the
measured at more than . By minimizing the
function constructed based on the current data on ,
, , , and , we obtain eleven most
trustworthy scenarios, each of which can provide a good explanation of the
anomalies at . To further discriminate these different
scenarios, we predict thirty-one observables associated with the processes
considered under each NP scenario. It is found that most of the scenarios can
be differentiated from each other by using these observables and their
correlations.Comment: 43 pages, 3 figures and 5 tables; references updated and more
discussions added, final version to be published in the journa
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