Self‐Force in 1D Electrostatic Particle‐in‐Cell Codes for NonEquidistant Grids

Effects of non‐equidistant grids on momentum conservation is studied for simple test cases of an electrostatic 1D PIC code. The aim is to reduce the errors in energy and momentum conservation. Assuming an exact Poisson solver only numerical errors for the particle mover are analysed. For the standard electric field calculation using a central‐difference scheme, artificial electric fields at the particle position are generated in the case when the particle is situated next to a cell size change. This is sufficient to destroy momentum conservation. A modified electric field calculation scheme is derived to reduce this error. Independent of the calculation scheme additional fake forces in a two‐particle system are found which result in an error in the total kinetic energy of the system. This contribution is shown to be negligible for many particle systems. To test the accuracy of the two electric field calculation schemes numerical tests are done to compare with an equidistant grid set‐up. All tests show an improved momentum conservation and total kinetic energy for the modified calculation scheme of the electric field. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐Assembly of Drug–Drug Conjugates as Drug Self‐Delivery System for Tumor‐Specific pH‐Triggered Release

An acid‐labile doxorubicin dimer (D‐DOX) is designed as drug–drug conjugate for tumor intracellular pH‐triggered release, by conjugating doxorubicin (DOX) with adipic acid dihydrazide (ADH). The dimer‐based surfactants modified with polyethylene glycol (PEG), DOX‐ADH‐DOX‐PEG or are synthesized by mono‐PEGylation and bi‐PEGylation, respectively. Then the prodrug nanoparticles are fabricated with different drug contents via dialyzing the mixture solution of D‐DOX and the PEGylated surfactants in dimethyl sulfoxide (DMSO) with different mass ratios against water. It is found that the smaller prodrug nanoparticles (142–163 nm) could be obtained with the mono‐PEGylated surfactant, than those of 157–225 nm with the bi‐PEGylated surfactant. Furthermore, the mono‐PEGylated surfactant results in a higher drug content of 51% due to their lower PEG contents. All prodrug nanoparticles could release DOX completely within 36 h at pH 5.0, with the premature drug leakage of less than 10% at pH 7.4. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assays demonstrate the proposed drug self‐delivery system possessed an enhanced anticancer efficacy against HepG2 cells than the free DOX.     

Self‐Imaging Effect Based on Circular Airy Beams

The self‐imaging effect for a superposition of the fundamental circular Airy beams with successively changing radial displacements is investigated. In free space, this self‐imaging along a parabolic trajectory can persist before the focal point. In the linear index potentials with a gradient, the propagation trajectory of circular Airy–Talbot effect can follow some predefined trajectories determined by engineering the index gradient, and the self‐imaging extent can expand provided that each truncated constituent circular Airy beam maintains its form and continues to accelerate before dispersing strongly.     

Carbon Dots‐Cluster‐DOX Nanocomposites Fabricated by a Co‐Self‐Assembly Strategy for Tumor‐Targeted Bioimaging and Therapy

Carbon‐based nanomaterials could afford versatile potential applications in biomedical optical imaging and as nanoparticle drug carriers, owing to their promising optical and biocompatible capabilities. In this paper, it is first found that amphipathic cetylpyridinium chloride (CPC)‐stabilized oil‐soluble carbon dots (CDs) could self‐assemble into hydrophilic CDs clusters with hydrophobic core under ultrasound, in which CPC acts as carbon source, stabilizer, and phase transfer agent. Next, the size‐control (for size‐dependent passive tumor targeting) and doxorubicin (DOX) uploading of aqueous CDs clusters, and subsequent surface charge modification via overcoating with cRGD‐ and octylamine‐modified polyacrylic acid (cRGD‐PAA‐OA) (reversing their surface charges into negative and introducing active tumor‐targeting ability) are explored systematically. Based on this sequential administration mode, CDs‐cluster‐DOX/cRGD‐PAA‐OA nanocomposites exhibit selective human malignant glioma cell line (U87MG) tumor targeting. In in vitro drug release experiments, the nanocomposites could release DOX timely. Owning to the dual tumor targeting effects and seasonable drug release, CDs‐cluster‐DOX/cRGD‐PAA‐OA show remarkably tumor targetability and enhanced antitumor efficacy (and reduced adverse reaction), comparing to free DOX in animal models. These results indicate that fabricating nanocomposite via co‐self‐assembly strategy is efficient toward drug delivery system for tumor‐targeting theranostic.     

Self‐focusing of a cosh‐Gaussian laser beam in magnetized plasma under relativistic‐ponderomotive regime

The combined effect of relativistic and ponderomotive nonlinearities on the self‐focusing of an intense cosh‐Gaussian laser beam (CGLB) in magnetized plasma have been investigated. Higher‐order paraxial‐ray approximation has been used to set up the self‐focusing equations, where higher‐order terms in the expansion of the dielectric function and the eikonal are taken into account. The effects of various lasers and plasma parameters viz. laser intensity (a₀), decentred parameter (b), and magnetic field (ω_c) on the self‐focusing of CGLB have been explored. The results are compared with the Gaussian profile of laser beams and relativistic nonlinearity. Self‐focusing can be enhanced by optimizing and selecting the appropriate laser‐plasma parameters. It is observed that the focusing of CGLB is fast in a nonparaxial region in comparison with that of a Gaussian laser beam and in a paraxial region in magnetized plasma. In addition, strong self‐focusing of CGLB is observed at higher values of a₀, b, and ω_c. Numerical results show that CGLB can produce ultrahigh laser irradiance over distances much greater than the Rayleigh length, which can be used for various applications.     

Self‐Assembled Fluorescent and Antibacterial GHK‐Cu Nanoparticles for Wound Healing Applications

GHK‐Cu is demonstrated with the abilities to improve wound healing, accelerate anti‐inflammatory activity, and repair DNA damage. However, the instability of the GHK‐Cu in biological fluids is always a big challenge for its long‐term and efficient function at the target site. Therefore, the self‐assembled GHK‐Cu nanoparticles (GHK‐Cu NPs) are investigated in this work to solve the instability issue. The crystalline nanostructure within the GHK‐Cu nanoparticles offers them visible and near‐infrared fluorescent properties. With the excellent self‐assembly performance, the antibacterial properties of GHK‐Cu NPs are demonstrated using E. coli and S. aureus. The L929 dermal fibroblast cells are utilized to prove the good biocompatibility and enhanced wound healing applications of GHK‐Cu NPs. This study could pave the way for the design and elaboration of a new class of fluorescent peptides with various biological functions in biomedical applications.     

Self‐Propelled Micro/Nanoparticle Motors

The growing interest in the design and fabrication of novel autonomous micro‐ and nanoparticles is motivated by the vast advances in their motion efficiency and their further implementation in both biomedical and environmental fields. The present review covers the motion principle and fabrication procedures of synthetic and hybrid particle‐like micromotors reported to date to give a comprehensive view of the key design parameters and different approaches for optimal motor guidance. The applications of self‐propelled micro‐ and nanoparticles in different fields are classified accordingly to clarify not only the latest advances but also the current challenges and constraints in the field. This review aims to provide clues to develop more efficient and biocompatible autonomous microparticles in the future, with advanced multitasking and sensing capabilities while being able to perform cooperative work.     

Dust Self‐Organized Structures II. Solutions of Master Equations for Small Diffusion

Master equations for spherical dust structures are solved numerically using the asymptotic solutions at the center of the structures for the case of absence of external ionization and small diffusions. The structures are determined by a single parameter, the external plasma flux at the surface of the structure. The equilibrium states that are possible in a limited range of this parameter are investigated numerically. It is demonstrated that in the range of existence of equilibria the structures are changing their shapes and type of distributions inside the structures. For large external fluxes the ion and dust distributions can have peaks inside the structures while for low external fluxes the dust distribution has a single maximum at the structure center. The lower is the external flux supporting the structure the larger is its size. An increase of the external flux decreases the accumulation of dust and ions at the center. The total number of dust confined by the structure is larger for larger size structures. Estimates of dust crystallization inside structures are given. The role of diffusion is calculated by perturbations and is shown to be small in all structure regions except the structure edges. In the perturbation theory we use the exact expressions of the diffusion coefficients calculated previously numerically. The regions with dust density peaks inside the structures have been calculated with two order of magnitude larger precision that allows to resolve the structure parameter dependencies inside the peaks. It is shown that although in peaks the gradients of all parameters are increased the diffusion flux is still small and that the continuity and hydrodynamic approach are applicable within an accuracy about several %‐s (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐Organization of Anisotropic and Binary Colloids in Thermo‐Switchable 1D Microconfinement

Anisotropic and binary colloids self‐assemble into a variety of novel supracolloidal structures within the thermo‐switchable confinement of molecular microtubes, achieving structuring at multiple length scales and dimensionalities. The multistage self‐assembly strategy involving hard colloidal particles and a soft supramolecular template is generic for colloids with different geometries and materials as well as their binary mixtures. The colloidal architectures can be controlled by colloid shape, size, and concentration. Colloidal cubes align in chains with face‐to‐face arrangement, whereas rod‐like colloids predominantly self‐organize in end‐to‐end configurations with their long axis parallel with the long axis of the microtubes. The 1D microconfinement imposed on binary mixtures of anisotropic and isotropic colloids further increases the diversity of colloid‐in‐tube structures. In cube–sphere mixtures, cubes may act as additional confiners, locking in colloidal sphere chains, while a “colloidal Morse code” is generated where rods and spheres alternate in the case of rod–sphere mixtures. The versatile confined colloidal superstructures including their thermoresponsive assembly and disassembly are relevant for the development of stimulus–responsive materials where controlled release and encapsulation are desired.     

Polyurea Dendrimer‐Perylene Self‐Imprinted Nanoshells for Trace Explosive Detection

Polyurea dendrimer‐perylene nanoshells are found to accurately discriminate structurally closely related nitroaromatics. Both studied systems, PURE_G1‐PER₆ and PURE_G4‐PER₄₈ , present high sensitivity (detection limits between 5 × 10^?6 and 20 × 10^?6m ) and selectivity for 2,4,6‐trinitrotoluene (TNT) collected from a powdered military grenade and picric acid. The selectivity is highly dependent on the dendrimer generation. A conformationally restricted 3D arrangement in PURE_G4‐PER₄₈ , which is favored by shell π‐π stacking and core urea‐assisted hydrogen bonding, supports the formation of self‐imprinted channels with molecular recognition for picric acid and TNT in complex mixtures of nitroaromatics.     

Water‐Dispersible Silicon‐Quantum‐Dot‐Containing Micelles Self‐Assembled from an Amphiphilic Polymer

The dispersion of silicon quantum dots (Si QDs) in water has not been established as well as that in organic solvents. It is now demonstrated that the excellent dispersion of Si QDs in water with photoluminescence (PL) quantum yields (QYs) comparable to those for hydrophobic Si QDs can be realized by combining the processes of hydrosilylation and self‐assembly. Hydrogen‐passivated Si QDs are initially hydrosilylated with 1‐dodecence. The toluene solution of the resulting dodecyl‐passivated Si QDs is mixed with the water solution of the amphiphilic polymer of Pluronic F127 to form an emulsion. Dodecyl‐passivated Si QDs are encapsulated in the micelles self‐assembled from F127 in the emulsion. The size of the Si‐QD‐containing micelles may be tuned in the range from 10 to 100 nm. Although self‐assembly in the emulsion causes the PL QY of Si QDs to decrease, after a few days of storage in ambient conditions, Si QDs encapsulated in the water‐dispersible micelles exhibit recovered PL QYs of ≈24% at the PL wavelength of ≈680 nm. The intensity of the PL from Si QDs encapsulated in the water‐dispersible micelles is >90% of the original value after 60 min ultraviolet illumination, indicating excellent photostability.     

Self‐assembly of p‐tert‐butyl thiacalix[4]arenes and metal cations into nanoscale three‐dimensional particles

The shape of supramolecular aggregates based on stereoisomers of p‐tert‐butyl thiacalix[4]arenes functionalized with secondary, tertiary amide and hydrazide groups at the lower rim in cone, partial cone and 1,3‐alternate conformations with several metal cations were investigated by atomic force microscopy. The examined p‐tert‐butyl thiacalix[4]arenes form host–guest complexes; dimers, spherics ellipsoids and elongated nanoscale particles depending on the conformation of macrocycles, the nature of the binding centers and the nature of the metal cation. Only associates formed by p‐tert‐butyl thiacalix[4]arenes with morpholide groups at the lower rim in cone conformation with silver cations exhibited a higher antimicrobial activity. Copyright © 2012 John Wiley & Sons, Ltd.