Kinking nonlinear elastic solids: theory and experiments

Recently it was postulated that most, if not all, plastically anisotropic solids can be classified as kinking nonlinear elastic (KNE) solids because their response to stress is nonlinear and fully reversible. Furthermore it was proposed that the large mechanical hysteresis observed was due to the fully reversible growth and shrinkage of incipient kink bands (IKBs). IKBs, the precursors of regular kink bands, are comprised of parallel dislocation loops, confined to two dimensions that remain extended if a load is applied and disappear if the load is removed.The stress-strain curves of KNE solids can be described by 4 parameters: stress, nonlinear strain, stored nonlinear energy and dissipated energy per unit volume per cycle. In this dissertation an IKB-based microscale model is proposed to relate the four parameters. Remarkable agreement between model and experiment is achieved. The model is so powerful that a decent picture of the size, densities and distribution of the dislocations that nucleate during the reversible loops emerges. Most important, the critical resolved shear stress of the IKB dislocations is obtainable from a simple compression experiment on a polycrystalline solid.The model was tested on select MAX phases (Ti3SiC2, Ti2AlC and some of their solids solutions) and the hexagonal metals (Ti, Mg, Co). All the experimental results, and some literature results, were shown to agree quite well with theoretical prediction. The model not only quantifies mechanical damping but also elucidates the nature of microyielding in a variety of solids, including the hexagonal metals. The nature of damping and microyielding in hexagonal metals were to date not fully understood or misunderstood for a long time.The phenomenological Preisach-Mayergoyz model was also applied to KNE solids. From the model, the stress distributions needed to nucleate and grow the hysteretic elements – viz. the IKBs - was determined. Once determined, this distribution can then be used to predict the response of these materials to any stress history.Based on this work there is little doubt that incipient kink bands constitute one of the last pieces in the deformation-of-solids puzzle, without which much of their early deformation cannot be understood.Ph.D., Materials Science and Engineering -- Drexel University, 200

Solution structure of a Plasmodium falciparum AMA-1/MSP 1 chimeric protein vaccine candidate (PfCP-2.9) for malaria

Background: The Plasmodium falciparum chimeric protein PfCP-2.9 is a promising asexual-stage malaria vaccine evaluated in clinical trials. This chimeric protein consists of two cysteine-rich domains: domain III of the apical membrane antigen 1 (AMA-1 [III]) and the C-terminal region of the merozoite surface protein 1 (MSP1-19). It has been reported that the fusion of these two antigens enhanced their immunogenicity and antibody-mediated inhibition of parasite growth in vitro. Methods: The N-15-labeled and C-13/N-15-labeled PfCP-2.9 was produced in Pichia pastoris for nuclear magnetic resonance (NMR) structure analysis. The chemical shift assignments of PfCP-2.9 were compared with those previously reported for the individual domains (i.e., PfAMA-1(III) or PfMSP 1-19). The two-dimensional spectra and transverse relaxation rates (R-2) of the PfMSP1-19 alone were compared with that of the PfCP-2.9. Results: Confident backbone assignments were obtained for 122 out of 241 residues of PfCP-2.9. The assigned residues in PfCP-2.9 were very similar to those previously reported for the individual domains. The conformation of the PfMSP1-19 in different constructs is essentially the same. Comparison of transverse relaxation rates (R-2) strongly suggests no weak interaction between the domains. Conclusions: These data indicate that the fusion of AMA-1(III) and MSP1-19 as chimeric protein did not change their structures, supporting the use of the chimeric protein as a potential malaria vaccine.Infectious DiseasesParasitologyTropical MedicineSCI(E)5ARTICLEnull

Dendritic Polyglycerol-Conjugated Gold Nanostars for Metabolism Inhibition and Targeted Photothermal Therapy in Breast Cancer Stem Cells

Breast cancer stem cells (CSCs) are believed to be responsible for tumor initiation, invasion, metastasis, and recurrence, which lead to treatment failure. Thus, developing effective CSC-targeted therapeutic strategies is crucial for enhancing therapeutic efficacy. In this work, GNSs-dPG-3BP, TPP, and HA nanocomposite particles are developed by simultaneously conjugating hexokinase 2 (HK2) inhibitor 3-bromopyruvate (3BP), mitochondrial targeting molecule triphenyl phosphonium (TPP), and CSCs targeting agent hyaluronic acid (HA) onto gold nanostars-dendritic polyglycerol (GNSs-dPG) nanoplatforms for efficient eradication of CSCs. The nanocomposite particles possess good biocompatibility and exhibit superior mitochondrial-bound HK2 binding ability via 3BP to inhibit metabolism, and further induce cellular apoptosis by releasing the cytochrome c. Therefore, it enhanced the therapeutic efficacy of CSCs-specific targeted photothermal therapy (PTT), and achieved a synergistic effect for the eradication of breast CSCs. After administration of the synergistic treatment, the self-renewal of breast CSCs and the stemness gene expression are suppressed, CSC-driven mammosphere formation is diminished, the in vivo tumor growth is effectively inhibited, and CSCs are eradicated. Altogether, GNSs-dPG-3BP, TPP, and HA nanocomposite particles have been developed, which will provide a novel strategy for precise and highly efficient targeted eradication of CSCs

Preparation and Photocatalytic Performance of Ti 3

Ti3C2/TiO2/CuO nanocomposites were synthesized via the decomposition of a mixture of Ti3C2 (a novel two-dimensional carbide) and cupric nitrate under an argon atmosphere. The morphology and structures of the obtained samples were characterized. X-ray diffraction and energy dispersive spectrometer analysis indicate that the sample is composed of Ti3C2, anatase-TiO2, and CuO. Scanning electron microscopy images show that CuO and TiO2 nanoparticles were evenly distributed on the surface of Ti3C2. The particles size increased with an increase in the cupric nitrate content. Photocatalytic degradation of methyl orange shows that the Ti3C2/TiO2/CuO nanocomposite has good photocatalytic degradation efficiency. A possible photocatalytic mechanism of the Ti3C2/TiO2/CuO nanocomposites was proposed. The data indicated that CuO and Ti3C2 effectively promote the separation of photoelectrons from vacancies

The vital role of hole-carriers for superconductivity in pressurized black phosphorus

The influence of carrier type on superconductivity has been an important issue for understanding both conventional and unconventional superconductors [1-7]. For elements that superconduct, it is known that hole-carriers govern the superconductivity for transition and main group metals [8-10]. The role of hole-carriers in elements that are not normally conducting but can be converted to superconductors, however, remains unclear due to the lack of experimental data. Here we report the first in-situ high pressure Hall effect measurements on single crystal black phosphorus, measured up to ~ 50 GPa, and find a correlation between the Hall coefficient and the superconducting transition temperature (TC). Our results reveal that hole-carriers play a vital role in developing superconductivity and enhancing TC. Importantly, we also find a Lifshitz transition in the high-pressure cubic phase at ~17.2GPa, which uncovers the origin of a puzzling valley in the superconducting TC-pressure phase diagram. These results offer insight into the role of hole-carriers in developing superconductivity in simple semiconducting solids under pressure.Comment: 9 pages anf 3 figure