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High-efficiency narrow-band luminescent materials have attracted intense interest, resulting in their great colorimetric purity. This has led to a variety of high-tech applications in high-definition displays, spectral analysis, and biomedicine. In this study, a rigid pyrene core was employed as the molecular backbone, and four narrow-band pyrene-based blue emitters were synthesized using various synthetic methods (such as Lewis-acid catalyzed cyclization domino reactions, Pd-catalyzed coupling reactions like Suzuki-Miyaura and Sonogashira). Due to the steric effect of the hydroxy group at the 2-position, the target compounds exhibit deep blue emission (<429 nm, CIEy < 0.08) with full width at half-maximum (FWHM) less than 33 nm both in solution and when solidified. The experimental and theoretical results indicated that the substituents at the 1- and 3-positions afford a large dihedral angle with the pyrene core, and the molecular motion is almost fixed by multiple intra- and intermolecular hydrogen bonding interactions in the crystallized state, leading to a suppression of the vibrational relaxation of the molecular structure. Moreover, we observed that the suppression of the vibrational relaxation in the molecular structures and the construction of rigid conjugated structures can help develop narrow-band organic light-emitting materials.

Materials with tunable stiffness responsive to stimuli are useful in a wide range of fields, such as soft robotics, reconfigurable structures and biomedical engineering. People have been pursuing stiffness variable materials for larger Young’s modulus change and faster response rate. However, the broad transition temperature range of stiffness variable polymers means that excessive energy consumption is needed to heat and trigger the softening. And limited smart microelectronic devices were developed based on stiffness variable polymers.We developed a series of stiffness variable polymers with narrow transition temperature range, high moduli change ratio. The transition temperature can be tuned to body temperature range, which provides opportunities to build thermal-responsive, mechanically adaptive devices to be used on skin or in tissue. We also demonstrated the materials used as functional actuation materials. In Chapter 1 and Chapter 2, we discussed the basics of stiffness variable materials. And we formulated a series of stiffness variable polymers with transition temperatures covering 30 ℃ to 43 ℃, the Young’s moduli of which can drop three to four orders of magnitude. The polymers’ thermal and mechanical properties were characterized and discussed. Because the transition can be triggered by body temperature, they can be used for thermal-responsive, mechanically adaptive neural interfaces, which are rigid before implantation and become soft after implantation. In Chapter 3, based on these polymers, the application as neural interfaces were explored. Intracortical probes were fabricated on the softening polymer showing great promise to provide tissue-like contact and reduce the micromotion around the tip. Based on the same polymer, we designed a multimodal neural probe that can simultaneously sense serotonin signal and electrophysiological signal. In vitro and ex vivo characterization of the neural probe were performed. In Chapter 4, the softening polymer was u

Materials with tunable stiffness responsive to stimuli are useful in a wide range of fields, such as soft robotics, reconfigurable structures and biomedical engineering. People have been pursuing stiffness variable materials for larger Young’s modulus change and faster response rate. However, the broad transition temperature range of stiffness variable polymers means that excessive energy consumption is needed to heat and trigger the softening. And limited smart microelectronic devices were developed based on stiffness variable polymers.We developed a series of stiffness variable polymers with narrow transition temperature range, high moduli change ratio. The transition temperature can be tuned to body temperature range, which provides opportunities to build thermal-responsive, mechanically adaptive devices to be used on skin or in tissue. We also demonstrated the materials used as functional actuation materials. In Chapter 1 and Chapter 2, we discussed the basics of stiffness variable materials. And we formulated a series of stiffness variable polymers with transition temperatures covering 30 ℃ to 43 ℃, the Young’s moduli of which can drop three to four orders of magnitude. The polymers’ thermal and mechanical properties were characterized and discussed. Because the transition can be triggered by body temperature, they can be used for thermal-responsive, mechanically adaptive neural interfaces, which are rigid before implantation and become soft after implantation. In Chapter 3, based on these polymers, the application as neural interfaces were explored. Intracortical probes were fabricated on the softening polymer showing great promise to provide tissue-like contact and reduce the micromotion around the tip. Based on the same polymer, we designed a multimodal neural probe that can simultaneously sense serotonin signal and electrophysiological signal. In vitro and ex vivo characterization of the neural probe were performed. In Chapter 4, the softening polymer was u

Dielectric elastomer actuators (DEAs) feature large, reversible in-plane deformation, and stacked DEA layers are used to produce large strokes in the thickness dimension. We introduce an electrophoretic process to concentrate boron nitride nanosheet dispersion in a dielectric elastomer precursor solution onto a designated electrode surface. The resulting unimorph nanocomposite dielectric elastomer (UNDE) has a seamless bilayer structure with 13 times of modulus difference. The UNDE can be actuated to large bending curvatures, with enhanced breakdown field strength and durability as compared to conventional nanocomposite dielectric elastomer. Multiple UNDE units can be formed in a simple electrophoretic concentration process using patterned electrode areas. A disc-shaped actuator comprising six UNDE units outputs large bidirectional stroke up to 10 Hz. This actuator is used to demonstrate a high-speed lens motor capable of varying the focal length of a two-lens system by 40 times.

Dielectric elastomer actuators (DEAs) feature large, reversible in-plane deformation, and stacked DEA layers are used to produce large strokes in the thickness dimension. We introduce an electrophoretic process to concentrate boron nitride nanosheet dispersion in a dielectric elastomer precursor solution onto a designated electrode surface. The resulting unimorph nanocomposite dielectric elastomer (UNDE) has a seamless bilayer structure with 13 times of modulus difference. The UNDE can be actuated to large bending curvatures, with enhanced breakdown field strength and durability as compared to conventional nanocomposite dielectric elastomer. Multiple UNDE units can be formed in a simple electrophoretic concentration process using patterned electrode areas. A disc-shaped actuator comprising six UNDE units outputs large bidirectional stroke up to 10 Hz. This actuator is used to demonstrate a high-speed lens motor capable of varying the focal length of a two-lens system by 40 times.

This thesis investigated the influence of neurobiological mechanisms in economic and financial risk taking, and their possible roles in understanding market stability. The evidences about risk preferences, trading behaviours and physiological responses, which were found in our laboratory and field experiments, supported a feedback theory. Our physiological responses under certain circumstances may exaggerate the emotions of exuberance and pessimism during market boom and bust times, reducing our abilities to engage in rational decisions.

Multicellular eukaryotes produce small RNA molecules (approximately 21-24 nucleotides) of two general types, microRNA (miRNA) and short interfering RNA (siRNA). They collectively function as sequence-specific guides to silence or regulate genes, transposons, and viruses and to modify chromatin and genome structure. Formation or activity of small RNAs requires factors belonging to gene families that encode DICER (or DICER-LIKE [DCL]) and ARGONAUTE proteins and, in the case of some siRNAs, RNA-dependent RNA polymerase (RDR) proteins. Unlike many animals, plants encode multiple DCL and RDR proteins. Using a series of insertion mutants of Arabidopsis thaliana, unique functions for three DCL proteins in miRNA (DCL1), endogenous siRNA (DCL3), and viral siRNA (DCL2) biogenesis were identified. One RDR protein (RDR2) was required for all endogenous siRNAs analyzed. The loss of endogenous siRNA in dcl3 and rdr2 mutants was associated with loss of heterochromatic marks and increased transcript accumulation at some loci. Defects in siRNA-generation activity in response to turnip crinkle virus in dcl2 mutant plants correlated with increased virus susceptibility. We conclude that proliferation and diversification of DCL and RDR genes during evolution of plants contributed to specialization of small RNA-directed pathways for development, chromatin structure, and defense.

Multicellular eukaryotes produce small RNA molecules (approximately 21-24 nucleotides) of two general types, microRNA (miRNA) and short interfering RNA (siRNA). They collectively function as sequence-specific guides to silence or regulate genes, transposons, and viruses and to modify chromatin and genome structure. Formation or activity of small RNAs requires factors belonging to gene families that encode DICER (or DICER-LIKE [DCL]) and ARGONAUTE proteins and, in the case of some siRNAs, RNA-dependent RNA polymerase (RDR) proteins. Unlike many animals, plants encode multiple DCL and RDR proteins. Using a series of insertion mutants of Arabidopsis thaliana, unique functions for three DCL proteins in miRNA (DCL1), endogenous siRNA (DCL3), and viral siRNA (DCL2) biogenesis were identified. One RDR protein (RDR2) was required for all endogenous siRNAs analyzed. The loss of endogenous siRNA in dcl3 and rdr2 mutants was associated with loss of heterochromatic marks and increased transcript accumulation at some loci. Defects in siRNA-generation activity in response to turnip crinkle virus in dcl2 mutant plants correlated with increased virus susceptibility. We conclude that proliferation and diversification of DCL and RDR genes during evolution of plants contributed to specialization of small RNA-directed pathways for development, chromatin structure, and defense.