A model for crack formation during active solid pyrolysis of a char-forming solid: crack patterns; surface area generation; volatile mass efflux

A model is developed for the formation and propagation of cracks in a material sample that is heated at its top surface, pyrolyses, and then thermally degrades to form char. In this work the sample is heated uniformly over its entire top surface by a hypothetical flame (a heat source). The pyrolysis mechanism is described by a one-step overall reaction that is dependent nonlinearly on the temperature (Arrhenius form). Stresses develop in response to the thermal degradation of the material by means of a shrinkage strain caused by local mass loss during pyrolysis. When the principal stress exceeds a prescribed threshold value, the material forms a local crack. Cracks are found to generally originate at the surface in response to heating, but occasionally they form in the bulk, away from ever-changing material boundaries. The resulting cracks evolve and form patterns whose characteristics are described. Quantities examined in detail are: the crack spacing in the pyrolysis zone; the crack length evolution; the formation and nature of crack loops which are defined as individual cracks that have joined to form loops that are disconnected from the remaining material; the formation of enhanced pyrolysis area; and the impact of all of the former quantities on mass flux. It is determined that the mass flux from the sample can be greatly enhanced over its nominal (non-cracking) counterpart. The mass efflux profile qualitatively resembles those observed in Cone Calorimeter tests.     

Theranostic Iron@Gold Core–Shell Nanoparticles for Simultaneous Hyperthermia‐Chemotherapy upon Photo‐Stimulation

The challenges of nanoparticles, such as size‐dependent toxicity, nonbiocompatibility, or inability to undergo functionalization for drug conjugation, limit their biomedical application in more than one domain. Oval‐shaped iron@gold core–shell (oFe@Au) magnetic nanoparticles are engineered and their applications in magnetic resonance imaging (MRI), optical coherence tomography (OCT), and controlled drug release, are explored via photo stimulation‐generated hyperthermia. The oFe@Au nanoparticles have a size of 42.57 ± 5.99 nm and consist of 10.76 and 89.24 atomic % of Fe and Au, respectively. Upon photo‐stimulation for 10 and 15 minutes, the levels of cancer cell death induced by methotrexate‐conjugated oFe@Au nanoparticles are sixfold and fourfold higher, respectively, than oFe@Au nanoparticles alone. MRI and OCT confirm the application of these nanoparticles as a contrast agent. Finally, results of in vivo experiments reveal that the temperature is elevated by 13.2 °C, when oFe@Au nanoparticles are irradiated with a 167 mW cm^?2 808 nm laser, which results in a significant reduction in tumor volume and scab formation after 7 days, followed by complete disappearance after 14 days. The ability of these nanoparticles to generate heat upon photo‐stimulation also opens new doors for studying hyperthermia‐mediated controlled drug release for cancer therapy. Applications include biomedical engineering, cancer therapy, and theranostics fields.     

A variational approach of the rank function

In the same spirit as the one of the paper (Hiriart-Urruty and Malick in J. Optim. Theory Appl. 153(3):551–577, 2012) on positive semidefinite matrices, we survey several useful properties of the rank function (of a matrix) and add some new ones. Since the so-called rank minimization problems are the subject of intense studies, we adopt the viewpoint of variational analysis, that is the one considering all the properties useful for optimizing, approximating or regularizing the rank function.     

Complete set of periodic solutions of a discontinuous recurrence equation

A nonlinear three-term recurrence relation arising from seeking the steady states of a cellular neural network with bang‐bang control is studied. We show that each solution is periodic and its prime period can be determined by three of its consecutive terms. By means of this periodicity property, we may then solve the steady state problem which to our knowledge is not solved by other means.     

Templated synthesis of electroactive periodic mesoporous organosilica bridged with oligoaniline

The synthesis and characterization of novel electroactive periodic mesoporous organosilica (PMO) are reported. The silsesquioxane precursor, N,N'-bis(4'-(3-triethoxysilylpropylureido)phenyl)-1,4-quinonene-diimine (TSUPQD), was prepared from the emeraldine base of amino-capped aniline trimer (EBAT) using a one-step coupling reaction and was used as an organic silicon source in the co-condensation with tetraethyl orthosilicate (TEOS) in proper ratios. By means of a hydrothermal sol-gel approach with the cationic surfactant cetyltrimethyl-ammonium bromide (CTAB) as the structure-directing template and acetone as the co-solvent for the dissolution of TSUPQD, a series of novel MCM-41 type siliceous materials (TSU-PMOs) were successfully prepared under mild alkaline conditions. The resultant mesoporous organosilica were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry, X-ray diffraction, nitrogen sorption, and transmission electron microscopy (TEM) and showed that this series of TSU-PMOs exhibited hexagonally patterned mesostructures with pore diameters of 2.1-2.8 nm. Although the structural regularity and pore parameters gradually deteriorated with increasing loading of organic bridges, the electrochemical behavior of TSU-PMOs monitored by cyclic voltammetry demonstrated greater electroactivities for samples with higher concentration of the incorporated TSU units.     

Fabrication of CdS Nanorods in PVP Fiber Matrices by Electrospinning

Summary: A controlled fabrication of rod‐like nanostructures of cadmium sulfide (CdS) incorporated into polymer fiber matrices has been developed by an electrospinning method. Here, poly(vinyl pyrrolidone) (PVP) was used as a polymer capping reagent, utilizing the interactions of cadmium ions with the carbonyl groups in the PVP molecules. The formation of CdS nanorods inside the PVP was carried out via the reaction of Cd²⁺ with H₂S. SEM images showed that the electrospun films of PVP/CdS are composed of fibers with a diameter between 100 and 900 nm. TEM proved that most of the CdS nanorods are incorporated in the PVP fibrous film. The diameter of the rod is about 50 nm and the length is from 100 to 300 nm.

TEM image of the CdS nanorods formed in the PVP fibrous film.     

Impact of an indium oxide/indium-tin oxide mixed structure for GaN-based light-emitting diodes

An interesting GaN-based light emitting diode (LED) using a 50 nm indium oxide (In₂O₃)/250 nm indium-tin oxide (ITO) mixed structure to replace the commonly used ITO (250 nm) current spreading layer is fabricated and studied. Use of the In₂O₃ layer could reduce the contact resistance of p-GaN in LEDs. In addition, this highly-resistive In₂O₃ layer, below the ITO layer could improve the current spreading performance. Experimentally, at room temperature, using this mixed structure, the luminous and EL intensities are enhanced by 17.7 and 17.1%, respectively.     

Electrospray ionization tandem mass spectrometric characteristics and fragmentation mechanisms of distamycin analogues

The electrospray ionization tandem mass spectrometric (ESI-MS/MS) characteristics and fragmentation mechanisms of eight distamycin analogues containing N-methylpyrrole and N-methylimidazole were investigated. The members of two isomeric groups of distamycin analogues with the same elemental composition can be distinguished by MS/MS spectra of protonated molecules and of significant fragment ions.     

On the sign of the n-p mass difference in gauge models

We examine the sign of the n-p mass difference in some gauge models based on the SU(2) × U(1) × U(1) or SU(2)_L × SU(2)_R × U(1) group, and show that a few specific elements of the neutral-vector-meson mass matrix can determine the sign of Δm|_n?p. We also present an SU(2) × U(1) × U(1) model which can give the correct Δm|_n?p.