Application of Solid-State NMR to Photoreaction Mechanism in Material Science

Solid-state nuclear magnetic resonance (NMR) has been frequently used in solving protein structures and material sciences. The benefits from solid-state NMR, such as Magic-Angle-Spinning, contribute a lot to improving the resolution of NMR spectrum, which is important in protein structure assignments. This thesis will bring another view of benefits from solid-state NMR. The photochemical reaction of materials can be clearly drawn by solid-state NMR during the photodimerization. Single-crystal NMR is another powerful tool for investigating the photochemical reaction, which has orientation dependence. The spin-lattice relaxation curve is also useful for determining the domain interactions and domain sizes. Characteristics of anthracene-9-carboxylic acid tert-butyl ester (9TBAE) during the photodimerization were investigated in chapter two. The objective is to prove the photoreaction will form a metastable intermediate crystal and this intermediate structure will have the ester sidegroups pointing inward prior to rotating to the lower energy outward-facing position. A newly designed single crystal goniometer probe was used for 13C CP NMR experiments of 9TBAE. The design details, benefits and performance of this home-built probe are presented in this chapter. This probe has the two axes adjustment system and Hall Effect sensor for sample tube orientation. The ester sidegroups rotation was determined by the change of quartet peaks based on 13C dipolar coupling. The photodimerization and T1 measurement of 9-methylanthracene (9-MA) by 13C solid-state NMR were investigated in chapter three. 1H T1 relaxation curves were obtained for both the monomer and the dimer. A series of Solid-state NMR spectra provide the process of photodimerization based on various UV exposure times. The spin diffusion rate between the monomer and the dimer is quite small from a global fitting of spin diffusion model. It will contribute to determine that the domain size is over 1000 nm, which indicates the formation of large dimer domains in our sample. The photochemical dynamics of crystals composed of 4-chlorocinnamic acid (4Cl-CA) was investigated in chapter four, whose photochemistry is dominated by an irreversible {2+2} photodimerization reaction. The 13C CPMAS solid-state NMR spectra showed the whole progress of photodimerization. While 4Cl-CA is probably not of practical interest as a photomechanical material, our results provide evidence that the photoinduced twisting of this class of photoreactive crystals is a general phenomenon. We discuss possible mechanisms for this size dependence, and propose a mechanism by which the mechanical response of photoreactive molecular crystals may be enhanced by reducing the crystal dimensions

Research on Constructing a Healing Environment for the Street Spaces of a High-Density City: Using Street Spaces in Macao’s Old City Area

It is commonly recognized that street spaces in high-density cities are able to cause negative impacts in terms of residents’ physical and mental health. This research intends to investigate and analyze how residents use street spaces in a high-density city in order to construct a healing environment for these street spaces. The research was conducted in Macao’s old town by using spatial syntax methods to define the research areas, and implemented on-site observations that evaluated the age of the residents in the space and the conditions of their usage of the space. The study collected data through expert grading and employed the Analytic Hierarchy Process to calculate the weight of each indicator in order to attain accurate and objective research outcomes. The evaluation results indicate that the current Macao street spaces are poor healing environments. By analyzing the effective factors for constructing a healing environment in these street spaces, so that residents can get more space for healing when they use it, the paper aims to provide a model example for those who are involved with city governance, planning and design

Classification of Ground-Based Cloud Images by Improved Combined Convolutional Network

Changes in clouds can affect the outpower of photovoltaics (PVs). Ground-based cloud images classification is an important prerequisite for PV power prediction. Due to the intra-class difference and inter-class similarity of cloud images, the classical convolutional network is obviously insufficient in distinguishing ability. In this paper, a classification method of ground-based cloud images by improved combined convolutional network is proposed. To solve the problem of sub-network overfitting caused by redundancy of pixel information, overlap pooling kernel is used to enhance the elimination effect of information redundancy in the pooling layer. A new channel attention module, ECA-WS (Efficient Channel Attention–Weight Sharing), is introduced to improve the network’s ability to express channel information. The decision fusion algorithm is employed to fuse the outputs of sub-networks with multi-scales. According to the number of cloud images in each category, different weights are applied to the fusion results, which solves the problem of network scale limitation and dataset imbalance. Experiments are carried out on the open MGCD dataset and the self-built NRELCD dataset. The results show that the proposed model has significantly improved the classification accuracy compared with the classical network and the latest algorithms

Deferoxamine produces nitric oxide under ferricyanide oxidation, blood incubation, and UV-irradiation.

Deferoxamine (DFO), an iron chelator, is used therapeutically for the removal of excess iron in multiple clinical conditions such as beta thalassemia and intracerebral hemorrhage. DFO is also used as an iron chelator and hypoxia-mimetic agent in in vivo and in vitro basic research. Here we unexpectedly discover DFO to be a nitric oxide (NO) precursor in experiments where it was intended to act as an iron chelator. Production of NO from aqueous solutions of DFO was directly observed by ozone-based chemiluminescence using a ferricyanide-based assay and was confirmed by electron paramagnetic resonance (EPR). DFO also produced NO following exposure to ultraviolet light, and its incubation with sheep adult and fetal blood resulted in considerable formation of iron nitrosyl hemoglobin, as confirmed by both visible spectroscopy and EPR. These results suggest that experiments using DFO can be confounded by concomitant production of NO, and offer new insight into some of DFOs unexplained clinical side effects such as hypotension

Mechanism of Photoinduced Bending and Twisting in Crystalline Microneedles and Microribbons Composed of 9‑Methylanthracene

The solid-state photodimerization of 9-methylanthracene is used as a model system to investigate how crystal morphology and reaction dynamics affect photomechanical deformations of single microcrystals. By varying the crystallization conditions, two different crystal shapes, microneedles and microribbons, are grown on a clean water surface. The microribbons twist under irradiation, while the microneedles bend. In both shapes, the maximum deformation occurs at roughly the midpoint of the reaction, while further dimerization causes the crystals return to their original shapes. Powder X-ray diffraction patterns establish that the needles and ribbons have the same crystal orientation and that the photoreaction proceeds in a crystal-to-crystal manner. NMR spin–lattice relaxation measurements are consistent with the rapid formation of large (>100 nm) dimer crystal domains. Simultaneous measurement of the needle bending and monomer fluorescence signal allows us to correlate the bending with the reaction progress. The behavior is qualitatively reproduced by a model in which the motion is driven by strain between spatially distinct reactant and product domains, also called heterometry. We consider several different mechanisms that could give rise to these spatially distinct domains. The ability to control the photoinduced crystal deformation by manipulating crystal shape and solid-state reaction kinetics suggests that photoreactive molecular crystals may be useful for generating well-defined motions on small length scales

Efficient Enhancement of Electron Transport and Collection Capability in PTB7:PC71BM-based Solar Cells Enabled by Sulforhodamine Cathode Interlayers

Efficient Enhancement of Electron Transport and Collection Capability in PTB7:PC71BM-based Solar Cells Enabled by Sulforhodamine Cathode Interlayer

Preparation and Characterization of Cattail-Derived Biochar and Its Application for Cadmium Removal

Biochars produced from aquatic plants have attracted increasing attention for the removal of heavy metals from the environment. Therefore, biochars derived from the roots (CBR), stems (CBS) and leaves (CBL) of cattail were investigated in this paper for their higher adsorption capacity, particularly for Cd(II). The adsorption characteristics and the leaching of alkali (soil) metals within biochars obtained from the different tissues of cattail were also discussed. The results showed that the specific surface area of cattail root biochar reached 15.758 m2 g−1. Langmuir, Freundlich and D-R isotherm equations were used to fit the experimental data, and the last equation revealed the best fitting result. The adsorption kinetics for Cd(II) removal were determined by using two different models. The experimental data for CBR and CBS were in good agreement with the pseudo second-order model, whereas the pseudo first-order model provided a better fit for CBL. The amount of leached K reached 73.214 mg g−1 in CBS (55.087 mg g−1 in CBL), which was almost an order of magnitude higher than those of Mg and Ca. The experimental data showed that the leached Mg and Ca metals in CBL had maximum levels of 6.543 and 10.339 mg g−1, respectively. The mechanism of Cd(II) sorption by the biochar is complex and probably involves a combination of mass transfer, ion exchange, and mineral precipitation through the macropores and micropores of the biochar in the sorption process

月球立方星姿态控制系统的初步设计与测试

CubeSats are miniature functional satellites. The increasing interest in CubeSats has uncovered the potential for planetary missions. Besides, CubeSats is an excellent educational platform. The preliminary attitude control system is designed and the corresponding hardware is built using commercial products for a lunar mission employing a CubeSat constellation to provide positioning service for landers/rovers on the far side of the moon. At the same time, the basic frame and necessary subsystems including the structure, power and on-board computer subsystems, and the attitude experiment platform are constructed. Based on the hardware platform, the control model is deeply understood through measuring damping coefficients by experiments. A PD control method is designed to control the attitude. The numerical and physical simulation results match well, and the CubeSat system achieves accurate attitude maneuver.</p