Understanding Actuation Mechanisms of Conjugated Polymer Actuators: Ion Transport

This dissertation explored ion transport in conjugated polymers. Study in this dissertation focused on following subjects: 1. Driving mechanisms (migration and diffusion) for ion transport. 2. Correlation among ions, charge, and volume change. 3. Effects of experimental situations (voltage, swelling of polymers, film thickness, ion barrier thickness, electrolyte, and temperature) on ion transport. 4. Developing a physics-based model and conducting numerical simulations for ion transport in conjugated polymers. The research results of this dissertation were summarized mainly in 3 articles and presented in Chapter 3, Chapter 4, and Chapter 5 respectively. Chapter 3 reported preliminary experimental and modeling results of cation ingress in PPy(DBS). Cation ingress in the polymer was displayed through phase front propagations that were formed by electrochromism. Migration was found to dominate ion ingress evidenced by a linear relationship between phase front velocity and reduction potentials. Chapter 4 is a full-scale experimental study of ion transport in PPy(DBS). Besides phase front propagation velocity and broadening, current data and actuation strains of PPy(DBS) were also collected. Comparisons among these data gave more insights of cation transport in PPy(DBS). Diffusion of ions in PPy(DBS) was found to be non-Fickian diffusion, which has not been included in models in the literature. Cation egress was found to be independent with applied potentials, suggesting a diffusion controlled process, while cation ingress was found to be dominated by migration. This difference between cation ingress and cation egress has not been realized before this dissertation. The effect of polymer swelling on cation ingress was characterized for the first time, which suggested an exponential relationship between ion mobility and ion concentration. Chapter 5 reported more advanced theoretical modeling and simulation results. Nernst-Planck-Poisson's equations were used to model hole transport, ion transport, and potential profiles in conjugated polymers. The model was able to explore ion transport with various experimental situations including changing of voltage, ion diffusivity, hole mobility, Einstein relation, electrolyte concentration, and film geometry. The model successfully predicted both ion ingress and ion egress features for PPy(DBS). Predictions of anion transport conjugated polymers such as PPy(ClO4) were also reported

Microstructure-based numerical simulation of themechanical properties and fracture of a Ti-Al3Ti core-shell structured particulate reinforced A356 composite

A microstructure-based numerical simulation is performed to understand themechanical properties and fracture of a Ti-Al3Ti core-shell structured particulate reinforced A356 composite ((Ti-Al3Ti)cs/A356). A series of twodimensional (2D) representative volume element (RVE) models are generated automatically by embedding Ti- Al3Ti core-shell structured particulates in an A356 matrix. Microstructure-based 2D RVE of monolithic Al3Ti particulate reinforced A356 composite (Al3Tip/A356) is also simulated for comparison. The ductile fracture of both Ti core and A356 matrix aswell as the brittle fracture of the Al3Ti shell are considered. The simulation confirms that the high elongation of the (Ti-Al3Ti)cs/A356 composite is attributed to the uniform distribution of the overall ductile globular reinforcing particulates, which prevent a premature failure effectively by reducing local stress concentration both on and inside the core-shell structured particulates. The surrounding ductile phases of the Al3Ti shell blunt the crack tips effectively and, therefore, restricting the propagation of the cracks in a nominal strain range of 2.2%–6.1%. For both (Ti-Al3Ti)cs/A356 and Al3Tip/A356 composites, the simulation results are in good agreement with microstructural observations during an in-situ tensile test in a scanning electron microscope

Millimeter-VLBI Observations of Low-luminosity Active Galactic Nuclei with Source-frequency Phase Referencing

We report millimeter-VLBI results of low-luminosity active galactic nuclei (M84 and M87) up to 88 GHz with source-frequency phase-referencing observations. We detected the weak VLBI core and obtained the first image of M84 at 88 GHz. The derived brightness temperature of the M84 core was about 7.2 × 109 K, which could serve as a lower limit because the core down to 30 Schwarzschild radii was still unresolved in our 88 GHz observations. We successfully determined the core shifts of M87 at 22-44 GHz and 44-88 GHz through the source-frequency phase-referencing technique. The jet apex of M87 could be deduced at ~46 μas upstream of the 43 GHz core from core-shift measurements. The estimated magnetic field strength of the 88 GHz core of M87 is 4.8 ± 2.4 G, which is at the same magnitude of 1-30 G near the event horizon probed by the Event Horizon Telescope

Multi-frequency VLBI Observations of the M 84 Inner Jet/Counterjet

Observational studies of inner-most regions of the edge-on jets in nearby active galactic nuclei (AGN) are crucial to understand their kinematics and morphology. For the inner jet of the nearby low luminosity AGN in M 84, we present new high-sensitivity observations with very long baseline interferometry since 2019, as well as archival Very Long Baseline Array observations in 2014. We find that the compact core in M 84 has an inverted-to-flat spectrum from 1.5 to 88 GHz. Based on the turnover frequency of $4.2\pm 0.2$ GHz in the spectrum, we estimated a magnetic field strength of 1-10mG and an electron number density of $\sim 10^5 cm^{-3}$ in the core region. Three inner jet components within $\sim 3$ mas from the core are identified and traced in the images at 22 GHz, whose apparent speeds are 0.11 c, 0.27 c, and 0.32 c, respectively. We calculate the viewing angle of $\sim58$ degree for the inner jet based on the proper motion and the flux ratio of jet-to-counterjet. A propagating sinusoidal model with a wavelength of $\sim 3.4$ mas is used to fit the helical morphology of the jet extended to 20 mas ($\sim 2.2\times 10^4$ Schwarzschild Radii).Comment: 9 pages, 5 figures, accepted by the Ap

Detection of a ~ 0.1c radio knot in M81* associated with a moderate X-ray flare

Through very long baseline interferometry observations of one of the closest low-luminosity active galactic nuclei M81* at multifrequencies of 8.8, 22 and 44GHz, a bright discrete knot with an unusual low apparent speed $\sim$0.1c was detected. Combining with the contemporary monitoring of X-rays data at 2-10keV, it indicates that a moderate X-ray flare happened when the knot launched from the core region. Three possible origins of the knot are proposed to explain our observational results. They are an episodic jet ejection, a low-speed shock wave, and a possible secondary black hole in a binary system, respectively. Future intensive multiwavelength monitoring can help to understand the discrete knot as well as the central black hole better

BMI, reproductive factors, and breast cancer molecular subtypes: A case-control study and meta-analysis

BACKGROUND: The effects of body mass index (BMI) and reproductive factors may vary among breast cancer molecular subtypes, evidence of which is lacking in East Asia. METHODS: From 2002 to 2010, 1256 breast cancer patients and 1416 healthy women were recruited. Anthropometric and reproductive factors were collected from medical charts. Breast cancer subtype was defined by ER, PR, and HER2 status. Polytomous logistic regression was used to evaluate associations between risk factors and breast cancer subtypes, with subgroup analysis by menopausal status. A meta-analysis of relevant published studies in East Asia was also performed. RESULTS: In our case-control study, late menarche was negatively associated with luminal tumor risk (Ptrend = 0.03). Higher BMI was associated with risk of both luminal and triple-negative tumors (Ptrend<0.001). Late age at first live birth was associated with a 1.41- to 2.08-fold increased risk of all subtypes, while late menopause increased risk by 2.62-5.56 times. Heterogeneity of these associations was not detected for different menopausal statuses. The meta-analysis revealed a positive dose-response relationship between BMI and risk of both luminal and ER-PR- subtypes (Ptrend<0.05). Early menarche and nulliparity increased luminal tumor risk by 1.39 and 1.26 times, respectively. Non-breastfeeding also increased the risk of all subtypes. CONCLUSIONS: For East Asian women, overweight, late menopause, and lack of breastfeeding appear to increase risk of both luminal and ER-PR- tumors. Early menarche and nulliparity mainly impacted luminal tumor risk. These associations were not impacted by menopausal status

Bacterial diversity in Arctic marine sediment determined by culture-dependent and -independent approaches

Bacterial diversity in surface sediment from the Arctic Ocean was investigated by culture-dependent and -independent approaches. Conventional culture-dependent techniques revealed 11 strains based on their distinct morphological characteristics on marine Zobell 2216E agar plates. Phylogenetic analysis showed that these isolates belonged to three major lineages of the Bacteria, γ-proteobacteria, Bacteroidetes and Actinobacteria, and that they included 10 genera. Most isolates were psychrotrophic, and NaCl was not necessary for their growth. Furthermore, they exhibited activity of at least one extracellular hydrolytic enzyme at 4°C and had various abilities to assimilate carbon sources. A total of 67 phylotypes were detected among 142 clones based on the 16S rRNA library of the total community DNA and grouped into nine major lineages of bacteria. Phylotypes affiliated with γ-, δ- and ε-proteobacteria accounted for 36.7%, 21.8% and 16.9% of the total clones, respectively. The rest of the clones belonged to Bacteroidetes, α-proteobacteria, Actinobacteria, Fusobacteria, Nitrospirae and an unclassified group

Phylogenetic analysis and in vitro culture of mosses from the Antarctic Fildes Peninsula

Molecular genetic techniques have proven very useful for initial analysis of the extent of genetic variation and dispersal in several Antarctic moss species. In the present study, the small subunit ribosomal RNA (SSU rDNA) and internal transcribed spacers of the nuclear ribosomal DNA (ITS rDNA) were sequenced in nine individuals of different mosses from the Fildes Peninsula of Antarctica. Sequence alignment showed that the extreme environment tended to increase the genetic diversity of Antarctic mosses. In addition, in our phylogenetic analysis, one previously unidentified Antarctic moss species was characterized by comparison with SSU and ITS rDNA sequences of known moss species. Moreover, the optimal culture medium and conditions for surface explant sterilization and protonemata induction in tissue culture of Pohlia nutans were investigated. The successful establishment of a tissue culture protocol together with the phylogenetic analysis of Antarctic mosses will provide technological support to establish an effective resource regeneration method for discovering new functional genes and gaining novel insights into the mechanisms of stress acclimation