Nanocarriers for Biomedicine: From Lipid Formulations to Inorganic and Hybrid Nanoparticles

Encapsulation of cargoes in nanocontainers is widely used in different fields to solve the problems of their solubility, homogeneity, stability, protection from unwanted chemical and biological destructive effects, and functional activity improvement. This approach is of special importance in biomedicine, since this makes it possible to reduce the limitations of drug delivery related to the toxicity and side effects of therapeutics, their low bioavailability and biocompatibility. This review highlights current progress in the use of lipid systems to deliver active substances to the human body. Various lipid compositions modified with amphiphilic open-chain and macrocyclic compounds, peptide molecules and alternative target ligands are discussed. Liposome modification also evolves by creating new hybrid structures consisting of organic and inorganic parts. Such nanohybrid platforms include cerasomes, which are considered as alternative nanocarriers allowing to reduce inherent limitations of lipid nanoparticles. Compositions based on mesoporous silica are beginning to acquire no less relevance due to their unique features, such as advanced porous properties, well-proven drug delivery efficiency and their versatility for creating highly efficient nanomaterials. The types of silica nanoparticles, their efficacy in biomedical applications and hybrid inorganic-polymer platforms are the subject of discussion in this review, with current challenges emphasized.     

Plastic buckling with residual stresses—1. Postbifurcation behaviour

The influence of residual stresses on the bifurcation load and initial postbifurcation behaviour of elastic—plastic structures is studied. The applied load is supposed to be proportional to a monotonically increasing parameter and the 'perfect' version of the structure is assumed to display an 'abrupt' bifurcation, which takes place when the material is in the plastic range. A strain-hardening flow theory of plasticity for solids characterized by a smooth yield surface is employed as constitutive relation. Symmetric self-equilibrated residual stress distributions are onsidered and the analysis is based on Hill's incremental approach to bifurcation and on its extension into the initial postbifurcation range as developed by Hutchinson. The proposed method consists of an investigation of the effect of residual stresses on the lowest possible bifurcation load and on the first two terms of an asymptotically exact postbifurcation expansion. It is also possible to obtain estimates of the maximum load supported by structures containing residual stresses. An illustration of the theory is provided by two problems, namely a continuous spring model and an axially compressed cylindrical column. The analytical results are compared with fully numerical solutions.     

碳纤维增强卷边槽形钢柱的非线性性能和承载力

对碳纤维增强卷边槽形钢柱的试验结果、非线性性能的数值分析以及承载力进行研究。基于GBT的基础研究,涉及柱弹性抗弯性能的研究集中在下列方面:i)布的位置(腹板、翼缘、卷边);ii)碳纤维的方向(纵向、横向或倾斜)以便对加固效果(性能价格比)进行优化。对19个端固定的短、长卷边槽形钢柱的试验过程进行描述。采用碳纤维布对钢柱的不同部位(腹板、翼缘、卷边)进行加固,纤维的方向包括纵向和横向:因为研究的目标是评估碳纤维加固对柱的结构响应的影响,对未加固钢试件也进行了试验。基于壳有限单元模型并采用Abaqus规定,由包含非线性平衡路径(荷载与轴向压缩的比值)和极限强度(大部分与局部/屈曲失稳破坏机理相关)组成的试验结果被用于校准和验证几何及物理非线性数值分析。最后,根据试验和数值结果,对于受到局部/屈曲失稳影响的卷边槽形钢柱,得出碳纤维布加固的有效位置和纤维方向的相关结论。     

Joint QoE-based user association and efficient cell–carrier distribution for enabling fully hybrid spectrum sharing approach in 5G mmWave cellular networks

Densifying the network by adding more minicell towers or relays throughout a hot spot area while extensively reusing the available spectrum is an essential choice to improve QoS. Unfortunately, this approach can be prohibitively costly. One possible solution to reduce the capital and operating expenditure in such overdensified networks is the adoption of the spectrum-sharing approach. However, both approaches would complicate the interference phenomenon either among inter- or intraoperators, which may cause serious performance degradation. In this paper, a fully hybrid spectrum-sharing (FHSS) approach aided by an efficient cell–carrier distribution was proposed with consideration to the interference dilemma. Moreover, an adaptive hybrid QoE-based mmWave user association (mUA) scheme was presented to assign a typical user to the serving mmWave base station (mBS), which offers the highest achievable data rate. The proposed FHSS approach (with the presented QoE-based mUA) was compared with recent works and with both FHSS approach using the conventional max-SINR-based mUA, which assigns a typical user to the tagged mBS carrying the highest signal-to-interference-plus noise ratio and the baseline scenario (licensed spectrum access). In particular, three spectrum access methods (licensed, semipooled, and fully pooled) were integrated in a hybrid manner to engage improved data rates to users. Numerical results show that the joint cell–carrier distribution and FHSS approach with QoE-based mUA outperform both baselines FHSS with the max-SINR mUA scheme and the licensed spectrum access. Furthermore, results demonstrate the effectiveness of the proposed approach in terms of both operators’ independence and fairness.

     

Local/distortional mode interaction in cold-formed steel lipped channel beams

This paper reports a numerical investigation concerning the post-buckling behaviour of cold-formed steel lipped channel beams, subjected to uniform major axis bending, affected by local/distortional mode interaction – the results presented and discussed were obtained through shell finite element analyses performed using the code Abaqus. One analyses simply supported beams (locally/globally pinned and free to warp end sections) (i) with cross-section dimensions ensuring coincident local and distortional critical buckling moments and (ii) having critical-mode initial geometrical imperfections with different shapes and the same overall amplitude – local buckling is triggered either by the compressed flange (most common case) or by the web. The results reported consist of (i) elastic and elastic–plastic post-buckling equilibrium paths, (ii) curves and figures showing how the beam deformed configuration evolves along those paths and, for the elastic–plastic beams, (iii) figures making it possible to visualise (iii₁) the location and growth of plastic strains and (iii₂) the nature of the failure mechanisms detected.     

Flexural-Torsional Buckling of Cantilever Strip Beam-Columns with Linearly Varying Depth

In this paper, one investigates the elastic flexural-torsional buckling of linearly tapered cantilever strip beam-columns acted by axial and transversal point loads applied at the tip. For prismatic and wedge-shaped members, the governing differential equation is integrated in closed form by means of confluent hypergeometric functions. For general tapered members (0<(hmax?hmin)/hmax<1), the solution to the boundary value problem is obtained in the form of a Frobenius’ series, which is shown to converge in the interior of the domain and at the boundary if and only if 0<(hmax?hmin)/hmax<1/2. Therefore, for 1/2?(hmax?hmin)/hmax<1 the Frobenius’ series solution cannot be used to establish the characteristic equation for the cantilever beam-columns; the problem is then solved numerically by means of a collocation procedure. Some of the analytical solutions (buckling loads) were compared with the results of shell finite-element analyses and an excellent agreement was found in all cases, thus validating the mathematical model and confirming the correctness of the analytical results. The paper closes with a discussion on the convexity of the stability domain (in the load parameter space) and the accuracy of approximations based on Dunkerley-type theorems.     

On the local and global buckling behaviour of angle,T-section and cruciform thin-walled members

This paper reports the results of an investigation aimed at providing fresh insight on the mechanics underlying the local and global buckling behaviour of angle, T-section and cruciform thin-walled steel members (columns, beams and beam-columns). Due to the lack of primary warping resistance, members displaying these cross-section shapes possess a minute torsional stiffness and, therefore, are highly susceptible to buckling phenomena involving torsion – moreover, it is often hard to distinguish between torsion and local deformations. Almost all the numerical results presented are obtained by means of Generalised Beam Theory (GBT) analyses and, taking advantage of its unique modal features, it is possible to shed some new light on how to characterise and/or distinguish the local and global buckling modes of the above thin-walled members. Finally, some comments are made concerning the development of a rational and efficient (safe and economic) approach for their design.     

纳米材料在提高原油采收率中的研究进展

近年来,油田采油过程对驱油材料的性能提出了更高的要求,使用纳米材料是从微观角度提升驱油剂性能的重要方法。研究表明,对纳米材料进行改性处理,如表面接枝改性、构造核-壳分子结构等,以及将纳米材料与其他驱油材料(如聚合物、表面活性剂等)复配,可从降低油水界面张力、乳化原油降低原油粘度、改善岩石表面润湿性、稳定泡沫等方面推动原油流动,可见纳米材料在提高原油采收率方面具有重要意义。综述了近几年国内外纳米SiO₂、纳米TiO₂、纳米纤维素、聚合物纳米微球、纳米石墨烯等纳米材料在驱油材料中应用的研究进展,解析了其研发中的瓶颈问题及今后的研发方向,评述了各种纳米材料提高原油采收率、抗温、抗盐等性能,以期为相关研究提供借鉴。     

Post-buckling behaviour and strength of cold-formed steel lipped channel columns experiencing distortional/global interaction

This paper reports the results of a numerical investigation concerning the elastic and elastic–plastic post-buckling behaviour of cold-formed steel lipped channel columns affected by distortional/global (flexural–torsional) buckling mode interaction. The results presented and discussed were obtained by means of analyses performed using the finite element code Abaqus and adopting column discretisations into fine 4-node isoparametric shell element meshes. The columns analysed (i) are simply supported (locally/globally pinned end sections that may warp freely), (ii) have cross-section dimensions and lengths that ensure equal distortional and global (flexural–torsional) critical buckling loads, thus maximising the distortional/global mode interaction effects, and (iii) contain critical-mode initial geometrical imperfections exhibiting different configurations, all corresponding to linear combinations of the two “competing” critical buckling modes. After briefly addressing the lipped channel column “pure” distortional and global post-buckling behaviours, one presents and discusses in great detail a fair number of numerical results concerning the post-buckling behaviour and strength of similar columns experiencing strong distortional/global mode interaction effects. These results consist of (i) elastic (mostly) and elastic–plastic non-linear equilibrium paths, (ii) curves or figures providing the evolution of the deformed configurations of several columns (expressed as linear combination of their distortional and global components) and, for the elastic–plastic columns, (iii) figures enabling a clear visualisation of (iii₁) the location and growth of the plastic strains and (iii₂) the characteristics of the failure mechanisms more often detected in the course of this research work.