Multiple passive element enriched photoacoustic computed tomography

Recently, we presented a method using laser-induced ultrasound from an external absorber (passive element) to image the ultrasound transmission parameters of an object under photoacoustic tomographic investigation. The method suffers from long measurement times due to the requirement for a large number of views and consequently physical projections around the object. Here we propose and validate an approach that permits a multitude of views to be obtained within a limited projection scenario. The approach uses a plurality of spatially distributed external absorbers in the path of the light, that results in multiple laser-induced ultrasound sources to interrogate the object from a number of angles. This reduces the required number of rotation angles or physical projections around the object, permitting a considerable reduction in imaging time without significant degradation in image quality. The approach brings the concept of hybrid imaging of ultrasound transmission parameters together with photoacoustic imaging, into the realm of practical application.     

Asymptotic Behavior of Predator-Prey Systems Perturbed by White Noise

In this paper, we develop the results in Rudnicki (Stoch. Process. Appl. 108:93–107, 2003) to a stochastic predator-prey system where the random factor acts on the coefficients of environment. We show that there exists the density functions of the solutions and then, study the asymptotic behavior of these densities. It is proved that the densities either converges in L ¹ to an invariant density or converges weakly to a singular measure on the boundary.     

Thermal degradation and flammability behavior of polypropylene/clay/carbon nanotube composite systems

This paper reports on the testing and development of a polypropylene (PP) nanocomposite systems with improved flame retardancy. The work utilizes the unique properties of sepiolite nanoclay (Sep) in combination with carbon nanotubes (CNTs) in order to develop an optimized ternary nanocomposite system. Thermogravimetric analysis (TGA) showed significant improvements to the residual char towards the later stages of the thermal ramp. The pyrolysis combustion flow calorimeter (PCFC) was employed to screen the various PP composites with respect to their potential flammability performance. The heat release capacity, which is an indicator of a materials fire hazard, did not show any reduction with the addition of nanofillers using the apparatus standard testing procedure. However, this changed by switching to a lower burn within the PCFC's furnace; this diverted oxygen to the pyrolysing sample. Using the results gained from TGA and the PCFC, the optimized ternary nanocomposite system (10 wt.% Sep + 2 wt.% CNT) was compounded on a larger scale and tested in the cone calorimeter. This showed a significant reduction of 82% in peak heat release rate in comparison to unfilled PP. Comparisons were also made between the testing of these samples in the PCFC and cone calorimeter. The main objectives were to develop a flame‐retardant PP nanocomposite ternary system as well as assessing the PCFC with traditional techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of lipid-polymer hybrid nanoparticles with pH-triggered poly(ethylene glycol) shedding

Novel lipid-polymer hybrid nanoparticles are designed with a poly(ethylene glycol) (PEG) coating that is shed in response to a low pH trigger. This allows the nanoparticles to be stable during systemic circulation and at neutral pH, but destabilize and fuse with lipid membranes in acidic environments. The hybrid nanoparticles consist of a poly(lactic-co-glycolic acid) core with a lipid and lipid-PEG monolayer shell. To make the hybrid nanoparticles pH sensitive, a lipid-(succinate)-mPEG conjugate is synthesized to provide a hydrolyzable PEG stealth layer that is shed off the particle surface at low pH. The pH-sensitivity of the nanoparticles is tunable using the molar concentration of the lipid-(succinate)-mPEG incorporated in the lipid shell of the particles. Possible uses of these pH-sensitive nanoparticles include aggregating in acidic tumor microenvironments, escaping acidified endosomes, or aggregating in deep lung tissue for improved inhalation administration.     

Direct Detection of Pharmaceuticals and Personal Care Products from Aqueous Samples with Thermally-Assisted Desorption Electrospray Ionization Mass Spectrometry

An ambient mass spectrometric method based on desorption electrospray ionization (DESI) has been developed to allow rapid, direct analysis of contaminated water samples, and the technique was evaluated through analysis of a wide array of pharmaceutical and personal care product (PPCP) contaminants. Incorporating direct infusion of aqueous sample and thermal assistance into the source design has allowed low ppt detection limits for the target analytes in drinking water matrices. With this methodology, mass spectral information can be collected in less than 1 min, consuming ~100 μL of total sample. Quantitative ability was also demonstrated without the use of an internal standard, yielding decent linearity and reproducibility. Initial results suggest that this source configuration is resistant to carryover effects and robust towards multi-component samples. The rapid, continuous analysis afforded by this method offers advantages in terms of sample analysis time and throughput over traditional hyphenated mass spectrometric techniques.     

Sharpness of the Phase Transition and Exponential Decay of the Subcritical Cluster Size for Percolation on Quasi-Transitive Graphs

We study homogeneous, independent percolation on general quasi-transitive graphs. We prove that in the disorder regime where all clusters are finite almost surely, in fact the expectation of the cluster size is finite. This extends a well-known theorem by Menshikov and Aizenman & Barsky to all quasi-transitive graphs. Moreover we deduce that in this disorder regime the cluster size distribution decays exponentially, extending a result of Aizenman & Newman. Our results apply to both edge and site percolation, as well as long range (edge) percolation. The proof is based on a modification of the Aizenman & Barsky method.     

H2O2水热合成双峰介孔硅MCM-48球

在温和的条件下,通过H₂O₂水热处理预合成的MCM-48,得到了有序的双峰介孔硅MCM-48球． 结果表明H₂O₂对于同时去除有机模板剂及形成双峰介孔硅MCM-48球具有重要的作用．采用XRD、TEM、FT-IR和N₂吸附-解吸等方法对双峰介孔MCM-48材料进行了表征,对双峰介孔MCM-48的形成机理也进行了探讨．     

A new multifunctional initiator system for the living cationic polymerization of vinyl ethers

Combination of hexa(chloromethyl)melamine (HCMM) and zinc chloride was found to be a multifunctional initiator system for the living cationic polymerization of isobutyl vinyl ether. HCMM was synthesized by reaction of hexa(methoxymethyl)melamine and boron trichloride. Characterization of the polymers by means of GPC and ¹H NMR showed that initiation was rapid and quantitative and that the initiator is hexafunctional, leading to six‐armed star‐shaped polymers.