2,628 research outputs found
On cross-validated estimation of skew normal model
Skew normal model suffers from inferential drawbacks, namely singular Fisher
information in the vicinity of symmetry and diverging of maximum likelihood
estimation. To address the above drawbacks, Azzalini and Arellano-Valle (2013)
introduced maximum penalised likelihood estimation (MPLE) by subtracting a
penalty function from the log-likelihood function with a pre-specified penalty
coefficient. Here, we propose a cross-validated MPLE to improve its performance
when the underlying model is close to symmetry. We develop a theory for MPLE,
where an asymptotic rate for the cross-validated penalty coefficient is
derived. We further show that the proposed cross-validated MPLE is
asymptotically efficient under certain conditions. In simulation studies and a
real data application, we demonstrate that the proposed estimator can
outperform the conventional MPLE when the model is close to symmetry
Dirac operators with torsion, spectral Einstein functionals and the noncommutative residue
Recently Dabrowski etc. \cite{DL} obtained the metric and Einstein
functionals by two vector fields and Laplace-type operators over vector
bundles, giving an interesting example of the spinor connection and square of
the Dirac operator. Pfffle and Stephan \cite{PS1} considered
orthogonal connections with arbitrary torsion on compact Riemannian manifolds
and computed the spectral action. Motivated by the spectral functionals and
Dirac operators with torsion, we give some new spectral functionals which is
the extension of spectral functionals to the noncommutative realm with torsion,
and we relate them to the noncommutative residue for manifolds with boundary.
Our method of producing these spectral functionals is the noncommutative
residue and Dirac operators with torsion.Comment: arXiv admin note: substantial text overlap with arXiv:1303.3713. text
overlap with arXiv:2307.15921. text overlap with arXiv:2308.0000
Using chitosan as a thickener for electrospinning dilute PVA solutions to improve fibre uniformity
Chitosan was added to PVA aqueous solutions as a thickener to improve the electrospinning process. The presence of a small amount of chitosan considerably improved the uniformity of as-spun nanofibres. This improvement is attributed to its significant effect on the solution viscosity and conductivity, with only a slight impact on the surface tension. The concentration of the PVA required to produce bead-free and uniform nanofibres was reduced with the increase in chitosan concentration. The chitosan thickener suppressed the jet break-up and facilitated the jet stretching so that fine and uniform fibres could be electrospun even from a dilute PVA solution.<br /
Functional applications of electrospun nanofibers
With the rapid development of nanoscience and nanotechnology over the last two decades, great progress has been made not only in preparation and characterization of nanomaterials, but also in their functional applications. As an important one-dimensional nanomaterial, nanofibers have extremely high specific surface area because of their small diameters, and nanofiber membranes are highly porous with excellent pore interconnectivity. These unique characteristics plus the functionalities from the polymers themselves impart nanofibers with many desirable properties for advanced applications
Nanofibrous p-n junction and its rectifying characteristics
Randomly oriented tin oxide (SnO2) nanofibers and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/polyvinylpyrrolidone (PEDOT:PSS/PVP) nanofibers were prepared by a two-step electrospinning technique to form a layered fibrous mat. The current-voltagemeasurement revealed that the fibrousmat had an obvious diode-rectifying characteristic. The thickness of the nanofiber layers was found to have a considerable influence on the device resistance and rectifying performance. Such an interesting rectifying property was attributed to the formation of a ??-?? junction between the fibrous SnO2 and PEDOT:PSS/PVP layers. This is the first report that a rectifying junction can be formed between two layers of electrospun nanofiber mats, and the resulting nanofibrous diode rectifier may find applications in sensors, energy harvest, and electronic textiles
Superhydrophobic nanofibre membranes : effects of particulate coating on hydrophobicity and surface properties
Superhydrophobic electrospun polyacrylonitrile nanofibre membranes have been prepared by surface coating of silica nanoparticles and fluorinated alkyl silane. The coated membranes were characterised by scanning electron microscopy, water contact angle, thermogravimetry analysis, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. It was shown that the loading of nanoparticle on the nanofibre membrane was controlled by the particle concentration in the coating solution, which played a critical role in the formation of superhydrophobic surface. Increased particle loading led to higher surface roughness and WCA. The nanoparticle coating had little influence on the porosity of the nanofibre membranes. However, overloading of the particles would affect the specific surface area of the nanofibre membrane
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