Core Solution Research Articles

Fabrication of Ta2O5 Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method

In this study, we investigate the effect of oxide dispersion strengthening on mechanical properties by dispersion of nano-sized Ta2O5 particles in Mo-Si-B alloy. A Mo-Si-B core-shell powder consisting of two intermetallic compounds of Mo5SiB2 and Mo3Si as the core and nano-sized Mo solid solution surrounding intermetallic compounds was fabricated by chemical vapor transport. And Mo-Si-B core-shell powder with uniformly dispersed nano-sized Ta2O5 particles on the surface of a Mo solid solution shell was produced by a wet blending process with TaCl5 solution and heat treatment. Then, pressureless sintering was performed at 1400°C for 3 h under a H2 atmosphere. The hardness and fracture toughness of the Ta2O5-dispersed Mo-Si-B alloy were measured using Vickers hardness and 3-point bending tests, respectively. The Vickers hardness and fracture toughness of the fabricated Mo-Si-B-Ta2O5 alloy were more improved than that of the Mo-Si-B alloy fabricated using core-shell powder with no addition of Ta2O5 particles (Mo-Si-B alloy: 353 Hv, 13.5 MPa·√m, Mo-Si-B-Ta2O5 alloy: 509 Hv, 15.1 MPa·√m).

Preparation of P3HB4HB/(Gelatin + PVA) Composite Scaffolds by Coaxial Electrospinning and Its Biocompatibility Evaluation.

This study was conducted to prepare coaxial electrospun scaffolds of P3HB4HB/(gelatin + PVA) with various concentration ratios with P3HB4HB as the core solution and gelatin + PVA mixture as the shell solution; the mass ratios of gelatin and PVA in each 10 mL shell mixture were 0.6 g : 0.2 g (Group A), 0.4 g : 0.4 g (Group B), and 0.2 g : 0.6 g (Group C). The results showed that the pore size, porosity, and cell proliferation rate of Group C were better than those of Groups A and B. The ascending order of the tensile strength and modulus of elasticity was Group A < Group B < Group C. The surface roughness was Group C > Group B > Group A. The osteogenic and chondrogenic-specific staining showed that Group C was stronger than Groups A and B. This study demonstrates that when the mass ratio of gelatin : PVA was 0.2 g : 0.6 g, a P3HB4HB/(gelatin + PVA) composite scaffold with a core-shell structure can be prepared, and the scaffold has good biocompatibility that it may be an ideal scaffold for tissue engineering.

Effect of the electrical conductivity of core solutions on the morphology and structure of core–shell CA-PCL/CS nanofibers

CA-PCL/CS nanofibers with controllable core to shell ratios were prepared by altering the electrical conductivities of core solutions.

Secure and Efficient Protocol for Route Optimization in PMIPv6-Based Smart Home IoT Networks

The communication in the Smart Home Internet of Things (SH-IoT) comprising various electronic devices and sensors is very sensitive and crucial. In addition, the key requirements of the SH-IoT include channel security, handover support, mobility management, and consistent data rates. Proxy mobile IPv6 (PMIPv6) is considered as one of the core solutions to handle extreme mobility; however, the default PMIPv6 cannot ensure performance enhancement in SH-IoT scenarios, i.e., Route Optimization (RO). The existing security protocols for PMIPv6 cannot support secure RO for smart home IoT services, where mobile nodes (MNs) communicate with home IoT devices not belonging to their domain. Motivated by this, a secure protocol is proposed, which uses trust between PMIPv6 domain and smart home to ensure security as well as performance over the path between MNs and home IoT devices. The proposed protocol includes steps for secure RO and handover management, where mutual authentication, key exchange, perfect forward secrecy, and privacy are supported. The correctness of the proposed protocol is formally analyzed using BAN-logic and Automated Validation of Internet Security Protocols and Applications (AVISPA). Furthermore, network simulations are conducted to evaluate the performance efficiency of the proposed protocol. The results show that the proposed approach is capable of providing secure transmission by resolving the RO problem in PMIPv6 along with the reduction in handover latency, end to end delay and packet loss, and enhancement in throughput and transmission rate even during the handover phase.

Nano Secondary Ion Mass Spectrometry Imaging of Dopamine Distribution Across Nanometer Vesicles.

We report an approach to spatially resolve the content across nanometer neuroendocrine vesicles in nerve-like cells by correlating super high-resolution mass spectrometry imaging, NanoSIMS, with transmission electron microscopy (TEM). Furthermore, intracellular electrochemical cytometry at nanotip electrodes is used to count the number of molecules in individual vesicles to compare to imaged amounts in vesicles. Correlation between the NanoSIMS and TEM provides nanometer resolution of the inner structure of these organelles. Moreover, correlation with electrochemical methods provides a means to quantify and relate vesicle neurotransmitter content and release, which is used to explain the slow transfer of dopamine between vesicular compartments. These nanoanalytical tools reveal that dopamine loading/unloading between vesicular compartments, dense core and halo solution, is a kinetically limited process. The combination of NanoSIMS and TEM has been used to show the distribution profile of newly synthesized dopamine across individual vesicles. Our findings suggest that the vesicle inner morphology might regulate the neurotransmitter release event during open and closed exocytosis from dense core vesicles with hours of equilibrium needed to move significant amounts of catecholamine from the protein dense core despite its nanometer size.

Energy-aware relay selection in cooperative wireless networks: An assignment game approach

In the future connected societies, everyone and everything will be inter-connected, under the umbrella of the Internet of Things, where tens to hundreds of devices will be serving every single citizen. However, connecting this massive number of energy-constrained devices pose a serious challenge on the wireless networking paradigm; energy efficiency still represents a major challenge within the design of the future generation of wireless networking (5G). In this paper, we address reducing energy consumption of energy-constrained wireless devices, through energy-aware cooperative relaying in future heterogeneous networks (HetNets). Using game theory concepts, we formulate the problem as an assignment game. In the first stage of the game, the optimal relay selection is formulated as a linear programming problem, whose solution assigns suitable relays to their perspective sources. In the final stage, the core solution is derived, which guarantees fair distribution of the payoff among players, to keep them satisfied and discourage them from quitting the coalition. Our solution also proposes a credit based system to reward cooperative players; hence possibly excluding selfish users from cooperative coalitions. The proposed relay selection algorithm is evaluated using extensive NS2 simulations. The simulation results show significant energy savings using cooperative relaying, reaching up to 22%, with extensive increase in battery lifetime.

High-order free vibration analysis of FGM sandwich plates with non-monotonically graded flexible core

Free vibration analysis of sandwich plates with non-monotonically graded flexible core is studied using a high-order sandwich panel theory. The non-monotonically graded flexible core is considered as two monotonically graded flexible core layers. In this high-order theory, the first-order shear deformation theory is used for the face sheets and a 3D-elasticity solution of weak core is employed for each single core layer. The laminated two-layered core is analyzed and formulated by the mixed layer-wise theory. Based on the continuity of the displacements and transverse stresses at the interfaces of the face sheets and the core, equations of motion are derived by Hamilton’s principle. The accuracy of the present approach is validated by comparing with the numerical results obtained from finite element method and good agreements are reached. Parametric study is also conducted to investigate the effect of distribution of functionally graded material properties, the monotonically graded core thickness ratio, and the thickness-to-side ratio on the vibration frequency.

Semipermeable Elastic Microcapsules for Gas Capture and Sensing.

Monodispersed microcapsules for gas capture and sensing were developed consisting of elastic semipermeable polymer shells of tunable size and thickness and pH-sensitive, gas selective liquid cores. The microcapsules were produced using glass capillary microfluidics and continuous on-the-fly photopolymerization. The inner fluid was 5-30 wt % K2CO3 solution with m-cresol purple, the middle fluid was a UV-curable liquid silicon rubber containing 0-2 wt % Dow Corning 749 fluid, and the outer fluid was aqueous solution containing 60-70 wt % glycerol and 0.5-2 wt % stabilizer (poly(vinyl alcohol), Tween 20, or Pluronic F-127). An analytical model was developed and validated for prediction of the morphology of the capsules under osmotic stress based on the shell properties and the osmolarity of the storage and core solutions. The minimum energy density and UV light irradiance needed to achieve complete shell polymerization were 2 J·cm(-2) and 13.8 mW·cm(-2), respectively. After UV exposure, the curing time for capsules containing 0.5 wt % Dow Corning 749 fluid in the middle phase was 30-40 min. The CO2 capture capacity of 30 wt % K2CO3 capsules was 1.6-2 mmol/g depending on the capsule size and shell thickness. A cavitation bubble was observed in the core when the internal water was abruptly removed by capillary suction, whereas a gradual evaporation of internal water led to buckling of the shell. The shell was characterized using TGA, DSC, and FTIR. The shell degradation temperature was 450-460 °C.

Fabrication of poly(glycerol sebacate) fibrous membranes by coaxial electrospinning: Influence of shell and core solutions

Although poly(glycerol sebacate) (PGS) has enjoyed great success in soft tissue engineering, it remains challenging to fabricate PGS fibers. In this study, coaxial electrospinning, in which polylactide (PLA) was used to confine and draw PGS prepolymer, was used to fabricate PGS fibrous membranes. Specifically, effects of adding poly(ethylene oxide) (PEO), which was removed prior to curing, in the shell were investigated. Transmission and scanning electron microscopy were used to confirm core–shell structure and morphology of fibers, respectively. Both the removal of PEO or PLA in the shell and the efficacy of PGS curing were verified by Fourier transform infrared spectroscopy and differential scanning calorimetry. Mechanical properties of the membranes with different shell and core contents were examined. We found that the addition of PEO to the shell reduced Young׳s modulus of the resulting cured membrane and increased its elongation at break significantly, the latter indicating better PGS curing. Moreover, with the addition of PEO, increasing PGS prepolymer concentration further increased the elongation at break and appeared to enhance the structural integrity of fibers; PGS fibrous membranes (with no PLA shell) were thus successfully fabricated after the removal of PLA. The Young׳s modulus of the PGS fibrous membrane was ~0.47MPa, which is similar to that of PGS solid sheets and some soft tissues. Finally, the cytocompatibility of the electrospun membranes was validated by Alamar blue and LDH assays.

Borch’s theorem, equal margins, and efficient allocation

The economic concept of margin guides or justifies the sharing of risks and resources. Broadly, by Borch’s theorem, competing claimants, ends or users ought see equal margins along any efficient allocation.However helpful this maxim, its application is often hampered, and occasionally misguided, by concerns with the differentiability of objectives—or with the interiority of solutions. Circumventing such concerns, this paper introduces a quite applicable, generalized notion, called essential margin.Presuming transferable or quasi-linear utility, the coincidence of such margins supports efficiency, competitive equilibria, and core solutions. The said coincidence also defines deductibles and prioritized claims, seen in finance and insurance.

Social-Aware Video Multicast Based on Device-to-Device Communications

To meet the explosive demand on delivering high-definition video steams over cellular networks, we design a So cial-aware video multi Cast (SoCast) system leveraging device-to-device (D2D) communications. One salient feature of SoCast is to stimulate effective cooperation among mobile users (clients), by making use of two types of important social ties, i.e., social trust and social reciprocity. By using SoCast, clients form groups to obtain missing packets from other clients and restore incomplete video frames, according to the unique video encoding structure. In return, the user perception of the mobile video quality can be substantially improved. Specifically, we first cast the problem of social ties based group formation among clients for cooperative video multicast as a coalitional game, and then devise a distributed algorithm to obtain the core solution (group formation) for the formulated coalitional game. Further, a resource allocation scheme is proposed for the base station to handle D2D radio resource requests from client groups. Extensive numerical studies using real video traces corroborate the significant gain using SoCast.

Coalitional stability in the location problem with single-dipped preferences: An application of the minimax theorem

This study considers a situation in which agents choose the location of a public facility from a street according to a given mechanism. Agents have single-dipped preferences over a set of feasible locations. We analyze coalitional behavior for any given mechanism for this situation. We identify a necessary and sufficient condition for a mechanism to possess a strong Nash equilibrium by applying the minimax theorem of von Neumann and Morgenstern (1944). We introduce a class of core solutions and show that these solutions are characterized by strong Nash implementability. As a byproduct of these results, we propose a simple mechanism that implements any core solution in strong Nash equilibria.

Endogenous interval games in oligopolies and the cores

In this article we study interval games in oligopolies following the γ-approach. First, we analyze their non-cooperative foundation and show that each coalition is associated with an endogenous real interval. Second, the Hurwicz criterion turns out to be a key concept to provide a necessary and sufficient condition for the non-emptiness of each of the induced core solution concepts: the interval and the standard γ-cores. The first condition permits to ascertain that even for linear and symmetric industries the interval γ-core is empty. Moreover, by means of the approximation technique of quadratic Bezier curves we prove that the second condition always holds, hence the standard γ-core is non-empty, under natural properties of profit and cost functions.

Designing highly structured polycaprolactone fibers using microfluidics

Microfibers are becoming increasingly important for biomedical applications such as regenerative medicine and tissue engineering. We have used a microfluidic approach to create polycaprolactone (PCL) microfibers in a controlled manner. Through the variations of the sheath fluid flow rate and PCL concentration in the core solution, the morphology of the microfibers and their cross-sections can be tuned. The microfibers were made using PCL concentrations of 2%, 5%, and 8% in the core fluid with a wide range of sheath-to-core flow rate ratios from 120:5µL/min to 10:5µL/min, respectively. The results revealed that the mechanical properties of the PCL microfibers made using microfluidic approach were significantly improved compared to the PCL microfibers made by other fiber fabrication methods. Additionally, it was demonstrated that by decreasing the flow rate ratio and increasing the PCL concentration, the size of the microfiber could be increased. Varying the sheath-to-core flow rate ratios from 40:5 to 10:5, the tensile stress at break, the tensile strain at break, and the Young׳s modulus were enhanced from 24.51MPa to 77.07MPa, 567% to 1420%, and 247.25MPa to 539.70MPa, respectively. The porosity and roughness of microfiber decreased when the PCL concentration increased from 2% to 8%, whereas changing the flow rate ratio did not have considerable impact on the microfiber roughness.

The morphology of Taylor cone influenced by different coaxial composite nozzle structures

Coaxial electrospinning is an effective method to produce core-shell nanofibers, which is associated closely with the morphological stability of Taylor cone. However, the nozzle structure mainly influences the formation of Taylor cone during the coaxial electrospinning procedure. In the present work, since the numerical simulation is a novel and convenience method in the theoretical research of the coaxial electrospinning, the influence of different coaxial composite nozzle structures on Taylor cone shape was studied by ANSYS finite element simulation method. Different coaxial composite nozzle structures — concave type, flush type and convex type, were designed in this work. 2D electric field model of the nozzle structures was simulated by utilizing ANSYS finite element analysis software. The simulation results indicated that electric field intensity distribution of concave type nozzle structure was more uniform than those of the other two types. Therefore, a more stable coaxial Taylor cone was formed in the tip of concave type nozzle structure. To verify the accuracy of the simulation results, core-shell nanofibers were spun by using different coaxial composite nozzle structures. In each experiment, PAN and PVP were employed to be the shell and core solution respectively. Besides that high-speed camera was employed to monitor the coaxial electrospinning procedure. The cross-section morphology of electrospun nanofibers was characterized by scanning electron microscope (SEM). The experimental results showed that when the concave type nozzle was used in the coaxial electrospinning process, Taylor Cone morphology was more stable than other type coaxial composite nozzle structures. The cross-section morphology of electrospun fibers observed by SEM revealed that the high stability in core-shell structure also occurred in coaxial electrospinning by using concave nozzle structure. Furthermore, the simulation and experimental results verified the concave type nozzle is the better nozzle structure for coaxial electrospinning to form stable coaxial Taylor cone.

Aqueous-Based Coaxial Electrospinning of Genetically Engineered Silk Elastin Core-Shell Nanofibers.

A nanofabrication method for the production of flexible core-shell structured silk elastin nanofibers is presented, based on an all-aqueous coaxial electrospinning process. In this process, silk fibroin (SF) and silk-elastin-like protein polymer (SELP), both in aqueous solution, with high and low viscosity, respectively, were used as the inner (core) and outer (shell) layers of the nanofibers. The electrospinnable SF core solution served as a spinning aid for the nonelectrospinnable SELP shell solution. Uniform nanofibers with average diameter from 301 ± 108 nm to 408 ± 150 nm were obtained through adjusting the processing parameters. The core-shell structures of the nanofibers were confirmed by fluorescence and electron microscopy. In order to modulate the mechanical properties and provide stability in water, the as-spun SF-SELP nanofiber mats were treated with methanol vapor to induce β-sheet physical crosslinks. FTIR confirmed the conversion of the secondary structure from a random coil to β-sheets after the methanol treatment. Tensile tests of SF-SELP core-shell structured nanofibers showed good flexibility with elongation at break of 5.20% ± 0.57%, compared with SF nanofibers with an elongation at break of 1.38% ± 0.22%. The SF-SELP core-shell structured nanofibers should provide useful options to explore in the field of biomaterials due to the improved flexibility of the fibrous mats and the presence of a dynamic SELP layer on the outer surface.

Electrospun pH-sensitive core–shell polymer nanocomposites fabricated using a tri-axial process

A modified tri-axial electrospinning process was developed for the generation of a new type of pH-sensitive polymer/lipid nanocomposite. The systems produced are able to promote both dissolution and permeation of a model poorly water-soluble drug. First, we show that it is possible to run a tri-axial process with only one of the three fluids being electrospinnable. Using an electrospinnable middle fluid of Eudragit S100 (ES100) with pure ethanol as the outer solvent and an unspinnable lecithin-diclofenac sodium (PL–DS) core solution, nanofibers with linear morphology and clear core/shell structures can be fabricated continuously and smoothly. X-ray diffraction proved that these nanofibers are structural nanocomposites with the drug present in an amorphous state. In vitro dissolution tests demonstrated that the formulations could preclude release in acidic conditions, and that the drug was released from the fibers in two successive steps at neutral pH. The first step is the dissolution of the shell ES100 and the conversion of the core PL–DS into sub-micron sized particles. This frees some DS into solution, and later the remaining DS is gradually released from the PL–DS particles through diffusion. Ex vivo permeation results showed that the composite nanofibers give a more than twofold uplift in the amount of DS passing through the colonic membrane as compared to pure DS; 74% of the transmitted drug was in the form of PL–DS particles. The new tri-axial electrospinning process developed in this work provides a platform to fabricate structural nanomaterials, and the core–shell polymer-PL nanocomposites we have produced have significant potential applications for oral colon-targeted drug delivery. Statement of SignificanceA modified tri-axial electrospinning is demonstrated to create a new type of core–shell pH-sensitive polymer/lipid nanocomposites, in which an electrospinnable middle fluid is exploited to support the un-spinnable outer and inner fluids. The structural nanocomposites are able to provide a colon-targeted sustained release and an enhanced permeation performance of diclofenac sodium. The developed tri-axial process can provide a platform for fabricating new structural nanomaterials with high quality. The strategy of a combined usage of polymeric excipients and phospholipid in a core–shell format should provide new possibilities of developing novel drug delivery systems for efficacious oral administration of poorly-water soluble drugs.

Preparation, Characterization, and Optimization of Folic Acid-Chitosan-Methotrexate Core-Shell Nanoparticles by Box-Behnken Design for Tumor-Targeted Drug Delivery.

The objective of this study was to investigate the combined influence of independent variables in the preparation of folic acid-chitosan-methotrexate nanoparticles (FA-Chi-MTX NPs). These NPs were designed and prepared for targeted drug delivery in tumor. The NPs of each batch were prepared by coaxial electrospray atomization method and evaluated for particle size (PS) and particle size distribution (PSD). The independent variables were selected to be concentration of FA-chitosan, ratio of shell solution flow rate to core solution flow rate, and applied voltage. The process design of experiments (DOE) was obtained with three factors in three levels by Design expert software. Box-Behnken design was used to select 15 batches of experiments randomly. The chemical structure of FA-chitosan was examined by FTIR. The NPs of each batch were collected separately, and morphologies of NPs were investigated by field emission scanning electron microscope (FE-SEM). The captured pictures of all batches were analyzed by ImageJ software. Mean PS and PSD were calculated for each batch. Polynomial equation was produced for each response. The FE-SEM results showed the mean diameter of the core-shell NPs was around 304nm, and nearly 30% of the produced NPs are in the desirable range. Optimum formulations were selected. The validation of DOE optimization results showed errors around 2.5 and 2.3% for PS and PSD, respectively. Moreover, the feasibility of using prepared NPs to target tumor extracellular pH was shown, as drug release was greater in the pH of endosome (acidic medium). Finally, our results proved that FA-Chi-MTX NPs were active against the human epithelial cervical cancer (HeLa) cells.

Fabrication of TiO2 micro-/nano-spheres embedded in nanofibers by coaxial electrospinning

A novel structure with TiO2 micro-/nano-spheres embedded in nanofibers was fabricated by coaxial electrospinning. The formation mechanism of the embedded structure and the effects of core flow rates on photocatalytic properties were investigated, and their photocatalytic properties were compared with the photocatalytic properties of nano-spheres and nanofibers. The micro-/nano-spheres were embedded in TiO2 nanofibers with different physical properties of core and shell spinning solutions. The specific surface area of the nanofibers improved to 23.852m2/g, and the degradation rate for methylene blue increased to 91.56%. The novel structure has large nanofiber gaps. We obtained a high specific surface area for the micro-/nano-spheres, which present a loose structure and are conducive for UV injection to improve photocatalytic efficiency.

Fabrication of polystyrene fibers with tunable co-axial hollow tubing structure for oil spill cleanup

Hollow tubing polystyrene (PS) fibers (HFs) with porous shell were successfully fabricated through co-axial electrospinning and selectively dissolving and removing polyvinyl pyrrolidone (PVP) core of the co-axial PS/PVP fibers using C2H5OH at room temperature. The size of co-axial hollow tubing structure (CHTS) and the thickness of shell can be controlled by varying the feed rate ratio of the core solution to the shell solution. The oil-sorption results show that the oil-sorption capacity increases with the increasing of the size of CHTS in the HFs, and the HFs have higher oil-sorption capacities than the porous PS fibers (PFs) without CHTS. It is noticeable that the diesel sorption capacity (66g/g) of the HFs is approximately 1.74 times as much as that (38g/g) of the PFs. The motor oil sorption capacity (147g/g) of the HFs is approximately 1.55 times as much as that (95g/g) of the PFs. It is suggested that the HFs have a better oil-sorption performance than the PFs, especially for the low viscosity oil, which is contributed to large CHTS and high porosity.