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Three-dimensional printing is becoming increasingly popular because of its extensive applicability. However, printing materials remain limited. To determine the mechanical properties of polylactic acid (PLA) and copper powder-filled polylactic acid (PLA-Cu) materials subjected to static and dynamic loading, stress–strain curves were obtained under the conditions of different strain rates using a universal material testing machine and a separated Hopkinson pressure bar experimental device. Scanning electron microscopy (SEM) was used to analyze the micro-morphology of the quasi-static compression fracture and dynamic impact sections. The results revealed that the yield stress and elastic modulus of the two materials increased with increasing strain rate. When the strain rate reached a critical point of 0.033 s−1, the rate of crack propagation in the PLA samples increased, resulting in the material undergoing a change from ductile to brittle. The strength of the material subjected to dynamic loading was significantly higher than that subjected to quasi-static loading. The SEM image of the PLA-Cu material revealed that copper powder was evenly distributed throughout the 3D-printed sample and that stress initially began to concentrate at the defect site corresponding to the interface between the copper powder and PLA matrix; this resulted in comparatively lower toughness. This finding was consistent with the photographs captured via high-speed photography, which confirmed that the destruction of the specimen was accompanied by an explosive crushing process. Additionally, a Zhu–Wang–Tang constitutive model was used to fit the experimental results and establish a viscoelastic constitutive model of the material. By comparing the dynamic stress–strain curve to the theoretically predicted curve, we found that the established constitutive model could predict the mechanical properties of the PLA-Cu material with reasonable accuracy when the strain was below 7%.

In this paper, the effect of manufacturing methods on the compressive properties of Cu-PTFE (polytetrafluoroethylene) composites was investigated. Two types of specimens were prepared through different manufacturing methods (extrusion forming and hot-press sintering). The specimens were tested using an electrohydraulic press and split-Hopkinson pressure bars for quasi-static loading and dynamic impact, respectively. The specific fracture processes were recorded by using a high-speed camera, and the failure microstructures of the specimens were analysed by SEM. According to the results, hot-press sintered specimens have consistently higher strength and toughness under dynamic compression than the extruded specimens, while the mechanical properties of hot-press sintered specimens are inferior to those of extruded specimens under quasi-static compression. The failure of extruded specimens is primarily caused by the elastic mismatch between the PTFE matrix and Cu particles, as well as the polymerisation of plastic pores, which leads to particle pullout. However, the cracks in the hot-press sintered specimens were caused by the shear deformation and interface sliding of the PTFE matrix, which led to matrix tearing.

The relation between the structural properties of the network and its dynamics is a central question in the analysis of dynamical networks. It is especially relevant for complex networks found in real-world applications. This work presents mathematically rigorous analysis of coupled dynamical systems on power law graphs. Specifically, we study large systems of coupled Kuramoto phase oscillators. In the limit as the size of the network tends to infinity, we derive analytically tractable mean field partial differential equation for the probability density function describing the state of the coupled system. The mean field limit is used to establish an explicit formula for the synchronization threshold for coupled phase oscillators with randomly distributed intrinsic frequencies. Furthermore, we study stable spatial patterns generated by the Kuramoto model with repulsive coupling. In particular, we identify a family of stable steady-state solutions having multiple regions with distinct statistical properties. We call these solutions contrast states. Like chimera states, contrast states exhibit coexisting regions of highly localized (coherent) behavior and highly irregular (incoherent) distribution of phases. We provide a detailed mathematical analysis of contrast states in the KM using the Ott–Antonsen ansatz. The analysis of synchronization and contrast states provides new insights into the role of power law connectivity in shaping dynamics of coupled dynamical systems. In particular, we show that despite sparse connectivity, power law networks possess remarkable synchronizability: the synchronization threshold can be made arbitrarily low by varying the parameter of the power law distribution.

The immediate killing effect of atmospheric-pressure plasma (APP) has been frequently investigated, but its sustained killing activity is poorly understood. The goal of the present study is to evaluate both the immediate and sustained killing effects of APP on Enterococcus faecalis. The APP jet was evaluated by optical emission spectroscopy (OES) and laser-induced fluorescence spectroscopy (LIF). Hydroxyapatite (HA) discs coated with bovine dermal type I collagen were used as substrates for bacterial growth. After the formation of E. faecalis biofilms on the HA discs for seven days or three weeks, the samples were treated with (A) 2 ml of saline, (B) APP, or (C) 2 ml of 2% chlorhexidine digluconate (CHX) for 5 min. The treated samples were then cultured for three or seven days, after which they were examined by scanning electron microscopy and confocal laser scanning microscopy. The OES results showed that typical reactive oxygen and nitrogen species were included in the full spectrum. The fitted curve indicated that the rotation temperature of N2 was close to room temperature. The LIF results showed that the maximal O and OH intensities occurred at 5 mm from the nozzle. For both the seven-day and three-week biofilms, the CHX and APP treatments had significant sterilization results (P < 0.05) compared to the saline group in terms of immediate and sustained killing effects. APP demonstrated excellent potential for use as an alternative approach for the treatment of periapical diseases.

Nearly monodispersed silica core−poly(N-vinylcarbazole) shell (SiO2@PVK) microspheres of 226, 235, and 244 nm in average diameters were first synthesized by surface-initiated distillation-precipitation polymerization of N-vinylcarbazole, in the presence of divinylbenzene, from the 197 nm silica template microspheres prepared by the sol−gel reaction of tetraethyl orthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPS). The SiO2@PVK−PNIPAM core−shell hairy microspheres (PNIPAM = poly(N-isopropylacrylamide)) were subsequently prepared by grafting the PNIPAM chains (Mn = 11 600 g/mol, polydispersity index =1.32), prepared a priori by reversible addition−fragmentation chain transfer (RAFT) polymerization, to the SiO2@PVK microspheres via the thiol−ene click chemistry. The grafting density of PNIPAM brushes on the SiO2@PVK microspheres was about 0.1 chains/nm2. Hairy hollow microspheres with a fluorescent and cross-linked PVK shell and temperature-responsive PNIPAM brushes were finally obtained, a...

A new type of double hydrophilic block copolymer, poly(ethylene oxide) (PEO)-block-poly(glycerol monoacrylate) (PGA) have been synthesized via atom transfer radical polymerization of solketal acrylate (SA) using PEO-Br as macro-initiator, and subsequent hydrolysis of the acetal-protecting group in 1N HCl solution in THF. The polymerization is of a "living" nature and the copolymers with controlled molecular weight and narrow polydispersity (M(w)/M(n) = 1.01-1.03) were obtained. The complete hydrolysis of the acetal-protecting group was verified by IR and NMR spectroscopies. A hydrophobic fluorescent compound, 1-pyrenecarboxaldehyde, was used as a model drug, which was covalently bound to the PEO-b-PGA block copolymer via a pH-sensitive acetal linkage. The kinetics of the pyrene release was studied in THF/aqueous buffers at pH 5.0 (close to pH in endosomes) and 7.4 (pH of blood plasma) by fluorescent spectroscopy. The pyrene was released much faster at pH 5.0 than that at pH 7.4. The micelle behavior in solutions at pH 5.0 and 7.4 was studied by dynamic light scattering. All results show that this double hydrophilic PEO-b-PGA is a promising candidate for potential application as drug carrier for those carbonyl-containing hydrophobic drugs.

Novel amphiphilic block copolymers, poly(ethylene oxide)- b -poly( p -nitrophenyl methacrylate) (PEO- b -PNPMA) with controlled molecular weights and narrow molecular weight distribution were successively synthesized by ATRP of NPMA using PEO–Br as initiator. Self-assembling of the diblock copolymer PEO 113 - b -PNPMA 28 in the different solvent mixtures yielded various morphologies of star micelle-like aggregates, such as spheres, vesicles, cauliflower-like aggregates and rod-like aggregates, which are determined by the nature of the common solvents and the selective solvents. Thus the critical selective solvent contents and the solvent contents in PNPMA-rich phase were measured, and they have the following order: ethanol > methanol > water, and THF > CH 3 NO 2 > DMSO. The probable self-assembling mechanism is discussed. This method is convenient for preparation of multiple morphological star micelle-like aggregates in solution, especially from the amphiphilic block copolymers with relatively longer block shell.

We prove a sufficient condition for synchronization for coupled one-dimensional maps and estimate the size of the window of parameters where synchronization takes place. It is shown that coupled systems on graphs with positive eigenvalues (EVs) of the normalized graph Laplacian concentrated around 1 are more amenable for synchronization. In the light of this condition, we review spectral properties of Cayley, quasirandom, power-law graphs, and expanders and relate them to synchronization of the corresponding networks. The analysis of synchronization on these graphs is illustrated with numerical experiments. The results of this paper highlight the advantages of random connectivity for synchronization of coupled chaotic dynamical systems., Comment: Keywords: synchronization, chaos, Cayley graph, quasirandom graph, power-law graph, expander

Hexa-armed star block copolymers, s-[poly(l-lactide)-b-poly(styrene-co-N-acryloxysuccinimide)]6 (s-[PLLA-b-poly(St-co-NAS)]6) with triphenylene core have been successively prepared by the combination of ring-opening polymerization and atom transfer radical copolymerization, and they were used in the self-assembly in tetrahydrofuran, and the micelles with triphenylene core and PLLA as inner layer as well as poly(St-co-NAS) as shell were formed. After shell was cross-linked, PLLA was hydrolyzed in aqueous NaOH solution, the hollow spheres were formed. The structures, molecular weight and polydispersity index of the polymers were characterized by their 1H NMR and FT-IR spectra, as well as GPC. Their morphologies were studied by TEM. The influence factors on the formation of various morphologies are under investigation.

The Kuramoto model (KM) of coupled phase oscillators on complete, Paley, and Erdos-Renyi (ER) graphs is analyzed in this work. As quasirandom graphs, the complete, Paley, and ER graphs share many structural properties. For instance, they exhibit the same asymptotics of the edge distributions, homomorphism densities, graph spectra, and have constant graph limits. Nonetheless, we show that the asymptotic behavior of solutions in the KM on these graphs can be qualitatively different. Specifically, we identify twisted states, steady state solutions of the KM on complete and Paley graphs, which are stable for one family of graphs but not for the other. On the other hand, we show that the solutions of the IVPs for the KM on complete and random graphs remain close on finite time intervals, provided they start from close initial conditions and the graphs are sufficiently large. Therefore, the results of this paper elucidate the relation between the network structure and dynamics in coupled nonlinear dynamical systems. Furthermore, we present new results on synchronization and stability of twisted states for the KM on Cayley and random graphs., Journal of Nonlinear Science, 2015