从电磁感应定律看负磁导率的产生过程

以左手材料中产生负磁导率的开口谐振环结构模型为例,从磁导率的定义出发,借助于电磁感应定律,推导了负磁导率的产生过程.     

考虑最大与最小孔隙半径比的相渗曲线计算模型

相对渗透率对指导油田开发具有十分重要的作用,分形理论的出现为计算相对渗透率曲线提供了一种新的方法,但已有求取相对渗透率曲线的分形模型都将最大与最小孔隙半径比视为无穷大进行简化计算,误差较大.因此建立了考虑最大与最小孔隙半径比求取油水相渗曲线的模型,并分析了最大与最小孔隙半径比对相渗曲线的影响,结果表明最大与最小孔隙半径比的增大对油相渗透率影响微弱,对水相渗透率影响巨大,且水相渗透率曲线随着最大最小半径比的增大渐向右移,两相区面积逐渐减小,当比值为无穷大时两相区面积为零.最后,结合F储层,验证了采用比值变化模型计算的相渗曲线与实验测得曲线误差甚微.说明该方法简单易行,精准度高,值得推广与应用.     

Evaluation of methoxy polyethylene glycol‐polylactide diblock copolymers as additive in hypromellose film coating

This paper deals with a new application of diblock methoxy polyethylene glycol‐polylactide block copolymers, a class of synthetic biomaterials largely studied in the pharmaceutical and biomedical fields owing to their favorable properties such as biocompatibility, biodegradability, low immunogenicity, and good mechanical properties. In this work, these materials were evaluated as additives for gastro‐soluble pharmaceutical coating aimed to reduce film stiffness and water permeability. Two copolymers with different polylactide chain lengths were synthesized and characterized in term of molecular weight and solid‐state properties. A series of free films with different hypromellose/copolymers ratio were prepared and characterized in terms of appearance, components miscibility, plasticity, and water vapor permeability. The obtained results demonstrate that copolymers effectively influence hypromellose film properties according to their concentration and molecular weight. Specifically, the addition of the copolymer with a molecular weight of 6.5 kDa in a ratio hypromellose:polymer 5:1, allowed to obtain films with good appearance, improved plasticization, and water permeability properties. For higher molecular weight, copolymer or different ratios was not possible to observe the improvement of all the properties at the same time. The results also make possible to define the critical features to improve in order to use block copolymers as additive in hypromellose film coating. The availability of new water‐soluble additives able to work as plasticizer and moisture sealer in polymeric films represents an important progress not only in the field of pharmaceutical coating but also in that of food coatings, as for example in the formulation of edible films. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamic Docking and Undocking Processes Addressing Selectively the Outside and Inside of Polymersomes

Increasing complexity and diversity of polymersomes and their compartments is a key issue for mimicking cellular functions and protocells. Thus, new challenges arise in terms of achieving tunable membrane permeability and combining it with control over the membrane diffusion process, and thus enabling a localized and dynamic control of functionality and docking possibilities within or on the surface of polymeric compartments. This study reports the concept of polymersomes with pH‐tunable membrane permeability for controlling sequential docking and undocking processes of small molecules and nanometer‐sized protein mimics selectively on the inside and outside of the polymersome membrane as a further step toward the design of intelligent multifunctional compartments for use in synthetic biology and as protocells. Host–guest interactions between adamantane and β‐cyclodextrin as well as noncovalent interactions between poly(ethylene glycol) tails and β‐cyclodextrin are used to achieve selective and dynamic functionalization of the inner and outer spheres of the polymersome membrane.     

Use of biopartitioning micellar chromatography and RP-HPLC for the determination of blood–brain barrier penetration of α-adrenergic/imidazoline receptor ligands,and QSPR analysis

For this study, 31 compounds, including 16 imidazoline/α-adrenergic receptor (IRs/α-ARs) ligands and 15 central nervous system (CNS) drugs, were characterized in terms of the retention factors (k) obtained using biopartitioning micellar and classical reversed phase chromatography (log k_BMC and log k_wRP, respectively). Based on the retention factor (log k_wRP) and slope of the linear curve (S) the isocratic parameter (φ₀) was calculated. Obtained retention factors were correlated with experimental log BB values for the group of examined compounds. High correlations were obtained between logarithm of biopartitioning micellar chromatography (BMC) retention factor and effective permeability (r(log k_BMC/log BB): 0.77), while for RP-HPLC system the correlations were lower (r(log k_wRP/log BB): 0.58; r(S/log BB): –0.50; r(φ₀/P_e): 0.61). Based on the log k_BMC retention data and calculated molecular parameters of the examined compounds, quantitative structure–permeability relationship (QSPR) models were developed using partial least squares, stepwise multiple linear regression, support vector machine and artificial neural network methodologies. A high degree of structural diversity of the analysed IRs/α-ARs ligands and CNS drugs provides wide applicability domain of the QSPR models for estimation of blood–brain barrier penetration of the related compounds.     

Laboratory Studies of Depressurization with a High Concentration of Surfactant in Low-Permeability Reservoirs

To solve the problem of high pressure of water injection in low permeability reservoirs, a high concentration of surfactant system was developed in this article. With the solubilization of oil in aqueous surfactant solution as a criterion, a formula was screened from anionic and nonionic-anionic surfactants, and the optimal depressurized system was obtained as follows, 13.3% surfactant HEX +2.23% n-propanol +4.47% n-butanol, the solubilization capability being up to 0.66 g/g. This system had good salt tolerance, and it exhibited water external microemulsion in the range of of 1 to 200 g/L NaCl. Core flooding results show that this high concentration of surfactant system formed water external microemulsion with the residual oil in the core, reducing the displacement pressure over 35%. Meanwhile, the effects of concentration and injection volume on depressurization were also investigated. It is indicated that a good depressurization effect was achieved after injecting 1 pore volume of the system with the salt concentration of 100 g/L.     

Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites

This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ^?) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the frequency range from 1 MHz to 3 GHz in a longitudinal magnetization field of up to 700 Ое and in the temperature interval from −20 °С to +150 °С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ^?. It is established that, at high frequencies, the μ^? of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ^? in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn-PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization.     

Vascular permeability in cancer and infection as related to macromolecular drug delivery, with emphasis on the EPR effect for tumor-selective drug targeting

Tumor and inflammation have many common features. One hallmark of both is enhanced vascular permeability, which is mediated by various factors including bradykinin, nitric oxide (NO), peroxynitrite, prostaglandins etc. A unique characteristic of tumors, however, is defective vascular anatomy. The enhanced vascular permeability in tumors is also distinctive in that extravasated macromolecules are not readily cleared. We utilized the enhanced permeability and retention (EPR) effect of tumors for tumor selective delivery of macromolecular drugs. Consequently, such drugs, nanoparticles or lipid particles, when injected intravenously, selectively accumulate in tumor tissues and remain there for long periods. The EPR effect of tumor tissue is frequently inhomogeneous and the heterogeneity of the EPR effect may reduce the tumor delivery of macromolecular drugs. Therefore, we developed methods to augment the EPR effect without inducing adverse effects for instance raising the systemic blood pressure by infusing angiotensin II during arterial injection of SMANCS/Lipiodol. This method was validated in clinical setting. Further, benefits of utilization of NO-releasing agent such as nitroglycerin or angiotensin-converting enzyme (ACE) inhibitors were demonstrated. The EPR effect is thus now widely accepted as the most basic mechanism for tumor-selective targeting of macromolecular drugs, or so-called nanomedicine.     

Tb0.3Dy0.7Fe2合金磁畴偏转研究

研究了Tb_0.3Dy_0.7Fe₂合金在压磁和磁 弹性效应中的磁畴偏转和磁导率特性. 基于Stoner-Wolhfarth 模型能量极小原理, 绘制了自由能与磁畴偏转角度的关系曲线, 研究了压应力和磁场载荷作用下磁畴角度的偏转特性, 计算分析了不同载荷作用下磁畴偏转的磁导率特性, 并与实验数据进行比较论证. 研究表明,应力和磁场的作用都将使磁畴方向[111]和[111]发生角度跃迁, 直观有效地解释了材料巨磁致伸缩效应的机理; 应力和磁场作用下磁畴的偏转将使材料磁导率呈减小趋势, 其中磁场能对磁导率的影响大于应力能, 这一现象在小载荷作用下尤为明显. 实验结果表明, 磁导率的计算数据与实验数据符合得较好, 验证了计算方法的正确性. 理论分析对Terfenol-D磁畴偏转模型的完善 和磁化过程中磁滞回线的绘制非常有意义.