Computer analysis of random and channeled backscattering spectra

Three types of computer codes are described which simulate random and channeled backscattering spectra from: (1) multielemental, multilayered structures, (2) specimens with inhomogneously distributed impurities and (3) single crystals damaged by ion implantation. Both effects of energy fluctuation and isotopic shifts from each constituent element are taken into account in the simulation. The elemental compositions and layer thicknesses of multielemental, multilayered films and the damage distributions induced by ion implantation are determined by fitting the simulated spectrum to the corresponding experimental one. The effect of surface and interface roughness on the spectrum shape is also discussed.     

Resolution of small molecules by passage through an open capillary

When a solute passes through an open capillary, in which a laminar flow is established, different peak profiles can be obtained according to its diffusion property under a working condition, i.e., the radius and length of the capillary and the flow rate of the carrier solution. If a solute diffuses over the entire cross section of the capillary before it is eluted, a Gaussian-shaped diffusion peak appears, which has an apex at the travel time of the average flow. Insufficient solute diffusion, which is realized, e.g., by increasing flow rates or capillary radius, produces a new peak having an apex at the travel time of the maximum flow. This implies that two solutes can be resolved simply by passing through a capillary. However, our previous study indicated that the diffusion coefficients of two solutes should be at least one order different for their resolution based on this principle, suggesting that its applicability is highly restricted. In the present paper, this concept has been extended to the resolution between dissolved solutes that have similar intrinsic diffusion properties. The incorporation of molecular aggregates in the carrier makes a solute less diffusive according to the extent of their interaction and allows the resolution of a dissolved molecule from other ones differing in the affinity to the molecular aggregates. Several examples of peak resolution for phenols, aromatic hydrocarbons, and inorganic anions are shown and discussed on the basis of the modification of the diffusion natures due to their interactions with micelles or vesicles.     

In vivo pressure estimation using subharmonic contrast microbubble signals: proof of concept

Changes in ambient pressure affects the reflectivity of ultrasound contrast microbubbles leading to an excellent correlation between subharmonic signals and hydrostatic pressure. The aortas of two dogs were scanned with an experimental pulse-echo system to validate in vivo pressure estimation based on subharmonic microbubble signals. Results matched well with instantaneous pressure measurements (from 20-60 mmHg) obtained simultaneously with a pressure catheter (root mean square errors <27%).     

Anisotropy of styrene–butadiene rubber

Anisotropy of styrene–butadiene rubber (SBR) was investigated. The anisotropy of the copolymer varies linearly with the styrene content and the ultimate value coincides with that of polystyrene at elevated temperature. From these facts, the transverse configuration of the pendant phenyl group is estimated irrespective of the styrene content of SBR.     

Monitoring biofilm development in a microfluidic device using modified confocal reflection microscopy

The feasibility of a method to monitor biofilm development non-destructively in a microfluidic device was addressed. Here, we report that biofilm growth could be non-destructively monitored by an image analysis technique based on modification of confocal reflection microscopy.     

Synthesis of proton conductive membranes based on inorganic–organic hybrid structure bound with phosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol–gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. ¹³C and ²⁹Si NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si–O–Si linkages by sol–gel reaction. TG–DTA analysis revealed that these membranes were thermally stable up to 200 °C in dry O₂. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA = 1/6 revealed proton conductivities of 6.3 × 10⁻³ and 2.4 × 10⁻⁴ S cm⁻¹ at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 °C.     

BP神经网络权值初始值与收敛性问题研究

BP神经网络的收敛性问题是一直受到广泛关注的问题。本文针对BP网络在运算过程中陷入局部最小区，收敛速度慢的问题，从BP算法的原理出发，讨论了权值初始值对网络训练速度的强烈影响（仿真结果证明了这一点），并提出了解决方法。     

Thermal‐Insulation,Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

Foaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO₂. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.