Field-Induced Phase Fractionation in Multiphase Polymer Flow Systems: A Review

The paper reviews the kinetics and morphology of the various phase-segregation processes that may be encountered in multiphase polymer flow systems. A primary aim of this review has been to investigate how certain processing variables influence the polymer structure and the degree of phase segregation in various geometries of interest. A pronounced distinction is made between the terms “diffusion” and “field-induced segregation.” The former is conventionally regarded as the mass transfer resulting from Brownian motion and, in any case, is a randomizing process. The latter, on the other hand, implies “flow” of matter subject to a “driving potential.” As opposed to diffusion in the classical sense, field-driven transport may be affected against the concentration gradient. It is seen that the application of an appropriate lateral field generates transversal migration of suspended material or additive and, in certain cases, the segment domains in the “matrix” polymer. In particular, the potential of shear fields to generate locally segregated flow structures, which might be preserved during the fabrication procedure, has been assessed. It has been shown that with an expression for the lateral “drift” velocity, the time and space evolution of the cross-flow concentration profile may be obtained from the continuity relation. Even though one finds a surprisingly large variety of driving forces available for segregation transport, the efficacy of highly specific processes lies in the novel application of boundary conditions. Convection promoted shear transport has been cited as a relevant example with an initial condition which specifies a cross-flow velocity component in an existing shear field. Other promising configurations include the sequential flow in two-phase flow and rheological segregation. The investigation reveals that migratory transport in polymer processing channels has the potential to generate localized changes in the polymer morphology and structure, apart from affecting phase redistribution of additive species (both solid and liquid systems) on a more global scale. Experimental evidence obtained on the phase fractionation in polydispersed low-density polyethylene (LDPE) and thermosetting polyurethane (PU) clearly demonstrates the phenomenon.     

Preparation and properties of bisphenol A polyetherketoneketone based phthalonitrile resins

A promising high temperature phthalonitrile (PN) resin composed of a polyetherketoneketone (PEKK) core bridged by two bisphenol A linkers and end capped with PN groups is presented. This PEKK-PN resin was characterized via differential scanning calorimetry, thermogravimetric analysis, proton nuclear magnetic resonance spectroscopy, scanning electron microscopy, dynamic mechanical analysis, attenuated total reflection Fourier transform infrared, and rheometry. The PEKK-PN resin was evaluated with two different compositions containing 1) 70:30 PEKK-PN to bisphenol A PN (n = 0) and 2) pure PEKK-PN. The 70:30 PEKK-PN resin was mixed with bis[4-(3-aminophenoxy)phenyl]sulfone and exhibited a melt viscosity of 271 cP, much lower than the 657 cP viscosity of the pure PEKK-PN mixture. Void-free PEKK-PN polymers were easily prepared by degassing and curing up to 380°C, resulting in fully crosslinked networks exhibiting thermal stability above 500°C and a 75% char yield. Additionally, the cured PEKK-PN polymer samples displayed good mechanical integrity retaining 50% stiffness at 300°C. This combination of properties suggests these new PEKK-PN resins are excellent materials for high temperature thermosets in composite applications.     

Ferritinophagy and α-Synuclein: Pharmacological Targeting of Autophagy to Restore Iron Regulation in Parkinson’s Disease

A major hallmark of Parkinson’s disease (PD) is the fatal destruction of dopaminergic neurons within the substantia nigra pars compacta. This event is preceded by the formation of Lewy bodies, which are cytoplasmic inclusions composed of α-synuclein protein aggregates. A triad contribution of α-synuclein aggregation, iron accumulation, and mitochondrial dysfunction plague nigral neurons, yet the events underlying iron accumulation are poorly understood. Elevated intracellular iron concentrations up-regulate ferritin expression, an iron storage protein that provides cytoprotection against redox stress. The lysosomal degradation pathway, autophagy, can release iron from ferritin stores to facilitate its trafficking in a process termed ferritinophagy. Aggregated α-synuclein inhibits SNARE protein complexes and destabilizes microtubules to halt vesicular trafficking systems, including that of autophagy effectively. The scope of this review is to describe the physiological and pathological relationship between iron regulation and α-synuclein, providing a detailed understanding of iron metabolism within nigral neurons. The underlying mechanisms of autophagy and ferritinophagy are explored in the context of PD, identifying potential therapeutic targets for future investigation.     

Hydrothermally treated chitosan spontaneously forms water-soluble spherical particles stable at a wide pH range

The authors report the spontaneous formation of water-soluble chitosan-tartaric acid (CS-TA) spherical particles. Particles are formed by heating chitosan in the presence of tartaric acid under hydrothermal conditions. Tartaric acid serves as an ionic cross-linker, a depolymerizing agent, and a particle stabilizer in aqueous phase. The CS-TA particles exhibit superior colloidal stability at a wide pH range due to their surface charge tunability, which is due to the colocalization of surface hydroxyl, amine, and carboxyl groups. At physiological pH condition, particles have zwitterionic structure as determined by the zeta potential measurements. Still, CS-TA maintains colloidal stability at neutral pH due to the abundance of surface hydroxyl groups. As a proof-of-concept study, the CS-TA particles were labeled with a model insoluble cargo (fluorescein isothiocyanate [FITC]) to demonstrate their capacity for solubilizing hydrophobic drugs. The CS-TA/FITC conjugates were found to remain well dispersed at neutral pH, while maintaining FITC fluorescence properties.     

Finite element simulation and experimental investigation of thermal tensioning during welding of DP600 steel

The locally introduced heating and cooling cycle of welding generates residual stresses and distortion. Costly post-weld heat treatments are required in order to reduce welding residual stresses and distortion. Thermal tensioning is one of the more promising in-process techniques to control welding distortion and can be classified into transient thermal tensioning (TTT) and side heating (SH). In thermal tensioning additional heat sources are applied during welding. If the additional heaters are close to the weld centre line and influence the thermal field of the weld, the process is called TTT. If there is no interference to the thermal field of the weld, the process is called SH. In this work, the SH during welding of 2?mm thick DP600 steels has been extensively investigated using numerical and experimental approaches. The thermal and mechanical fields during conventional welding and SH were examined by means of finite element models, and validated by comparison with experimental observation of temperature, distortion and residual stresses. The microstructure was investigated experimentally.     

Multiscale, Multiphysics Numerical Modeling of Fusion Welding with Experimental Characterization and Validation

Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.     

Transcriptional Modulation of the Hippo Signaling Pathway by Drugs Used to Treat Bipolar Disorder and Schizophrenia

Recent reports suggest a link between positive regulation of the Hippo pathway with bipolar disorder (BD), and the Hippo pathway is known to interact with multiple other signaling pathways previously associated with BD and other psychiatric disorders. In this study, neuronal-like NT2 cells were treated with amisulpride (10 µM), aripiprazole (0.1 µM), clozapine (10 µM), lamotrigine (50 µM), lithium (2.5 mM), quetiapine (50 µM), risperidone (0.1 µM), valproate (0.5 mM), or vehicle control for 24 h. Genome-wide mRNA expression was quantified and analyzed using gene set enrichment analysis (GSEA), with genes belonging to Hippo, Wnt, Notch, TGF- β, and Hedgehog retrieved from the KEGG database. Five of the eight drugs downregulated the genes of the Hippo pathway and modulated several genes involved in the interacting pathways. We speculate that the regulation of these genes, especially by aripiprazole, clozapine, and quetiapine, results in a reduction of MAPK and NFκB pro-inflammatory signaling through modulation of Hippo, Wnt, and TGF-β pathways. We also employed connectivity map analysis to identify compounds that act on these pathways in a similar manner to the known psychiatric drugs. Thirty-six compounds were identified. The presence of antidepressants and antipsychotics validates our approach and reveals possible new targets for drug repurposing.     

Microwave plasma chemical vapor deposition of nano-structured Sn/C composite thin-film anodes for Li-ion batteries

A novel synthesis method of thin-film composite Sn/C anodes for lithium batteries is reported. Thin layers of graphitic carbon decorated with uniformly distributed Sn nanoparticles were synthesized from a solid organic precursor Sn(IV) tert-butoxide by a one-step microwave plasma chemical vapor deposition (MPCVD). The thin-film Sn/C electrodes were electrochemically tested in lithium half cells and produced a reversible capacity of 423 and 297 mAh g⁻¹ at C/25 and 5C discharge rates, respectively. A long-term cycling of the Sn/C nanocomposite anodes showed 40% capacity loss after 500 cycles at 1C rate.     

Online Testing of MEMS Based on Encoded Stimulus Superposition

This article presents a technique that enables online testing of sensors through the superposition of the test stimulus onto the measurand. Perturbations due to the surrounding environment can very often introduce fluctuations in the test output creating a major concern for this type of sensor testing. In this paper, a signal processing technique is proposed where the test stimulus is encoded by a pseudo-random sequence in order to reduce the test output fluctuations. The trade-off between the level of rejection of a perturbation and the overall test time is studied. In the case of the MEMS accelerometer considered in this paper, it is theoretically demonstrated that the rejection is more than 20 dB for a test time of 2.55 s. Furthermore, excessively strong perturbations can be monitored so that the test status is updated only if the accuracy of the test signal permits so. The technique has been implemented on a demonstration board and validated on a vibration platform.