一种快速响应电场敏感多孔水凝胶的合成及其性能研究

以4-乙酰基丙烯酰乙酸乙酯(AAEA)、2-丙烯酰胺基-2-甲基-1-丙磺酸(AMPS)为单体,不同分子量的聚乙二醇(PEG)为成孔剂,通过自由基溶液聚合法,合成了新型多孔快速响应电场敏感性水凝胶.结果表明,成孔剂PEG被洗脱后在凝胶内部形成了互相贯穿的孔洞结构,孔径在30～120μm之间.以PEG6000为成孔剂致孔后的多孔凝胶溶胀速率和消溶胀速率最快,在去离子水中30s达到溶胀平衡,在0.1mol/L的NaCl溶液中40min达到消溶胀平衡;电场作用下凝胶的消溶胀速度大大加快,12min内即可达到平衡.凝胶中AMPS含量的增多会加快凝胶在电场中的响应速度;而高温下,随着AAEA含量的增加,凝胶内部疏水基团增多并收缩产生大量的疏水微区,限制了凝胶内部水分的持续排出,因此n(AAEA)∶n(AMPS)=3∶1的凝胶4min内即可排出表面水分达到消溶胀平衡,可保水率却高达75%.同时,增大电解液的pH值、浓度以及提高电解电压,均会加快凝胶的消溶胀行为.     

A fast directional algorithm for high-frequency electromagnetic scattering

This paper is concerned with the fast solution of high-frequency electromagnetic scattering problems using the boundary integral formulation. We extend the O(N log N) directional multilevel algorithm previously proposed for the acoustic scattering case to the vector electromagnetic case. We also detail how to incorporate the curl operator of the magnetic field integral equation into the algorithm. When combined with a standard iterative method, this results in an almost linear complexity solver for the combined field integral equations. In addition, the butterfly algorithm is utilized to compute the far field pattern and radar cross section with O(N log N) complexity.     

A non-dimensional approach to diffraction phenomena in the Fresnel approximation

The paper presents a theoretical and numerical study of the diffraction problem approached in the Fresnel approximation. The problem was formulated by a non-dimensional approach, which implies the definition of two non-dimensional quantities: F and ζ. In particular the parameter F is the well-known Fresnel number, whose value was usually used to classify diffraction regime. In analyzing the numerical approach some limitations imposed by the discretization arise; in particular these limitations constrain the level of sampling to be used for the diffracting field by requiring more and more elements when the diffraction conditions become more severe — i.e. increasing the dimension of the diffracting aperture and/or decreasing the distance of the plane where the diffracted field is observed.     

Effect of surface nanocrystallization induced by fast multiple rotation rolling on hardness and corrosion behavior of 316L stainless steel

A nanostructured layer was fabricated by using fast multiple rotation rolling (FMRR) on the surface of 316L stainless steel. The microstructure in the surface was characterized by transmission electron microscopy and X-ray diffraction. The effects of FMRR on the microhardness, surface roughness and corrosion behavior of the stainless steel were investigated by microhardness measurements, surface roughness measurements, potentiodynamic polarization curves and pitting corrosion tests. The surface morphologies of pitting corrosion specimens were characterized by scanning electron microscopy. The results show that FMRR can cause surface nanocrystallization with the grain size ranges from 6 to 24 nm in the top surface layer of the sample. The microhardness of FMRR specimen in the top surface layer remarkably increases from 190 to 530 HV. However, the surface roughness slightly rises after FMRR treatment. The potentiodynamic polarization curves and pitting corrosion tests indicated that the FMRR treated 316L stainless steel with a surface nanocrystallized layer reduced the corrosion resistance in a 3.5% NaCl solution and enhanced the pitting corrosion rate in a FeCl₃ solution. Possible reasons leading to the decrease in corrosion resistance were discussed.     

A fast dual proximal gradient algorithm for convex minimization and applications

We consider the convex composite problem of minimizing the sum of a strongly convex function and a general extended valued convex function. We present a dual-based proximal gradient scheme for solving this problem. We show that although the rate of convergence of the dual objective function sequence converges to the optimal value with the rate O(1/k²)$O(1/k^2)$, the rate of convergence of the primal sequence is of the order O(1/k)$O(1/k)$.     

Simulating bistable biochemical systems by means of reactive multiparticle collision dynamics

Based on a reactive multiple particle collision method, we construct a mesoscopic dynamics model to simulate chemical system. The validity of the reactive multiple particle collision method under various conditions in a double-feedback bi-stable chemical system is studied. Then, we extend it to simulate diffusion-limited reactions with fast reaction rate in cellular environment. Using the improved method, we observe bi-stable behavior with randomly distributed reactants and spatial domain separation of opposite phases. The particle-based mesoscopic method is computationally efficient, although hydrodynamic interactions and fluctuation are both properly accounted for. Stochastic effects shown to play dominant roles in biochemical dynamics are also considered. The improved method could be used to explore a variety of reactions with disparate scale of reaction rates.     

Determination of Protein Levels in Nigerian Grains Using 14 MeV Neutron Activation Analysis

Fast (14 MeV) neutrons have been successfully used in investigating the protein content of different food grains (Soya Beans, Sorghum, Maize and Beans) locally grown and consumed in Nigeria. Protein was estimated via nitrogen using the ¹⁴N(n, 2n)¹³N reaction. Quantification of nitrogen was achieved through a γ-γ coincidence counting of 511 keV positron emissions from the decaying ¹³N. The implication of the use of the emitted annihilation positrons, the interference introduced in the analytical energy spectra from other activated target nuclides present in the sample, as well as possible proton “knock on” reactions anticipated from cellulose in grain matrix were assessed, and their contributions to the 511 keV gamma energy resolved. For comparative purposes, replicates of samples analyzed through Fast Neutron Activation Analysis (FNAA) were investigated using the Kjeldahl method. The samples were carried through the Kjeldahl process of pre-digestion (with appropriate catalysts), digestion and titration. The results obtained through the Kjeldahl process were found to be in good agreement with those obtained using FNAA although slightly lower. Protein content (%) of Nigerian grains analyzed varied from a low 8.75 ± 2.96 for sorghum to 35.93 ± 0.31 for soya beans.     

Investigation of the effect of electron cyclotron heating on runaway generation in the KSTAR tokamak

Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges.     

Improved algorithm about NSFOT

For the purpose of further saving computing time, an improved algorithm about NSFOT is provided in this paper. That is, by introducing the simple operations such as preprocessing or after-processing, Haar and Walsh transforms are performed conveniently on the multiprocessor. As a result, one large size problem is divided into several small size sub-problems, load on every processor not only decreases greatly but also gets so uniform that much time is saved. Both the theoretical analysis and experimental results demonstrate the effectiveness of the proposed approach.