Synthesis and properties of donor acceptor molecular dyads

PhD ThesisThis thesis is concerned with the design, preparation and structural characterisation of several molecular dyads. The molecular dyads were synthesized for the study of energy/electron/charge transfer processes to advance our understanding of artificial photosynthesis. We were hoping to enhance our ability in mimicking natural photosynthesis through our discoveries. Chapter 1 introduces the field of artificial photosynthesis. The working principles and the highest efficiency dye sensitized solar cells (DSSCs) to date are highlighted. Molecular units working as photo-active switches for fabrication of light-driven molecular scale machines are emphasized. Finally, previous work on the acridinium-, naphthalimde-, viologen- and 1,1'-bi-2-naphthol-based derivatives are reviewed. Chapter 2 is the experimental section, it describes the techniques used for characterisation, and details of synthetic procedures used to obtain molecular dyads discussed in chapters 3 to 6. Chapter 3 discusses the synthesis and properties of expanded acridinium dyads, and their application as sensitizers for DSSCs. Coupling of N,N-dimethylaniline and an expanded acridinium unit afforded a purple dyad, DMA. The charge transfer property of DMA was studied by solvent polarity dependent UV-Visible absorption spectroscopy. The fluorescence of DMA was almost totally quenched by the charge transfer state. The quenching of fluorescence was also found in BODAC, which couples a bodipy unit with the expanded acridinium unit through an acetylene bridge. No long-lived species were found from a transient absorption study of DMA and a decay model was proposed to explain the relaxation process. We demonstrated for the first time that acridinium based dyads can be used as sensitizers for DSSCs by testing results of two dyads on p-and/ or n-type semiconductors. Chapter 4 demonstrates the synthesis of donor-acceptor systems based on naphthalimide and phthalimide derivatives for a solid state charge transfer fluorescence study. The fluorescence images of the dyads were obtained through confocal microscopy. UV-Vis absorption spectra also revealed their charge transfer properties. X-ray crystal structures of several compounds were obtained. The existence of two polymorphs of one dyad enabled us to compare their solid state fluorescence properties more closely. The polymorphs displayed different properties such as colours, melting points and the emission lifetimes. Chapter 5 concerns the synthesis of a disulfide-strapped methyl viologen derivative DSV, which can work as a molecular switch. The viologen derivative is capable of storing up to four electrons as revealed by reversible reduction peaks for a cyclic voltammogram. DSV is one of the easiest to reduce viologen derivatives to date. Molecular orbital calculations were used to model the “spring opening” of the disulfide-strapped six membered ring. Chapter 6 continues our further work into bridging units for donor acceptor assemblies and focuses on the synthesis of 1,1'-bi-2-naphthol based molecular dyads. The length of alkyl chain to link the diol group was varied to control the conformation of the chiral bridges. The aim was to study chirality effects on energy/electron transfer processes. Different synthetic routes were tried to achieve the target molecular dyads. Primary photophysical properties and results on attaching the dyad to fullerene are presented

Hierarchical Attention Network for Visually-aware Food Recommendation

Food recommender systems play an important role in assisting users to identify the desired food to eat. Deciding what food to eat is a complex and multi-faceted process, which is influenced by many factors such as the ingredients, appearance of the recipe, the user's personal preference on food, and various contexts like what had been eaten in the past meals. In this work, we formulate the food recommendation problem as predicting user preference on recipes based on three key factors that determine a user's choice on food, namely, 1) the user's (and other users') history; 2) the ingredients of a recipe; and 3) the descriptive image of a recipe. To address this challenging problem, we develop a dedicated neural network based solution Hierarchical Attention based Food Recommendation (HAFR) which is capable of: 1) capturing the collaborative filtering effect like what similar users tend to eat; 2) inferring a user's preference at the ingredient level; and 3) learning user preference from the recipe's visual images. To evaluate our proposed method, we construct a large-scale dataset consisting of millions of ratings from AllRecipes.com. Extensive experiments show that our method outperforms several competing recommender solutions like Factorization Machine and Visual Bayesian Personalized Ranking with an average improvement of 12%, offering promising results in predicting user preference for food. Codes and dataset will be released upon acceptance

Research on Degree Program Construction Platform Scheme Based on Data Fusion Thinking

The article analyzes the existing system for evaluating the construction of degree programs, sorts out the requirements for various work tasks such as application, assessment, evaluation, and inspection, and extracts various data information related to the direction, teachers, students, teaching and research, process, quality, and other aspects of degree program construction. On this basis, a degree program construction platform scheme was designed using data fusion thinking, taking into account all relevant work related to degree program construction, and unifying the management of data related to degree program construction. This has a positive promoting effect on the long-term construction and efficient management of degree programs, and is also a beneficial attempt to modernize the governance system and governance capabilities of the degree programs

A Brief Review and Perspective on the Functional Biodegradable Films for Food Packaging

High-performance, environmentally-friendly biodegradable packaging as substitutes for conventional plastics becomes severe demand to nowadays economy and society. As an aliphatic aromatic copolyester PBAT is recognized as the preferred alternative to traditional plastics. However, the relatively high cost and weak properties obstacles the widespread adoption of PBAT. Modification pertaining to improve the properties, lower the cost, and include the functional additives of PBAT is a continuous effort to meet the needs of food accessibility, antibacterial properties, oxygen resistance, high mechanical strength, stable size, low moisture absorption, and various gas permeability for commercial competitiveness

Flash Flood Simulation Using Geomorphic Unit Hydrograph Method: Case Study Of Headwater Catchment Of Xiapu River Basin, China

The flash flood refers to flood produced by heavy local rainfalls and often occurs in mountainous areas. It is characterized by a quick rise of water level causing a great threat to the lives of those exposed. Many countries and regions face the threat of flash floods. However, some traditional hydrological models can hardly simulate the flash flood process well due to the lack of hydrological data and the insufficient understanding of complicated runoff mechanism in mountainous and hilly areas. According to this condition, a new hydrological model based on the framework of Xinanjiang model, widely used in humid and semi-humid regions in China, is presented to simulate flash flood. The highlight of new model is using the geomorphic unit hydrograph (GUH) method to simulate the overland flow process. This method has clear physical concept and can easily provide unit hydrographs of various time intervals only based on DEM data. This feature makes the method extremely valuable in ungauged catchment. The new presented hydrological model is used in the headwater catchment of Xiapu River basin and the results demonstrate that the computed data generally agrees well with the measured data and it can be treated as a useful tool for flash flood hazard assessment in mountainous catchment

Identification and Analysis of Intermediate Size Noncoding RNAs in the Human Fetal Brain

The involvement of noncoding RNAs (ncRNAs) in the development of the human brain remains largely unknown. Applying a cloning strategy for detection of intermediate size (50–500 nt) ncRNAs (is-ncRNAs) we have identified 82 novel transcripts in human fetal brain tissue. Most of the novel is-ncRNAs are not well conserved in vertebrates, and several transcripts were only found in primates. Northern blot and microarray analysis indicated considerable variation in expression across human fetal brain development stages and fetal tissues for both novel and known is-ncRNAs. Expression of several of the novel is-ncRNAs was conspicuously absent in one or two brain cancer cell lines, and transient overexpression of some transcripts in cancer cells significantly inhibited cell proliferation. Overall, our results suggest that is-ncRNAs play important roles in the development and tumorigenesis of human brain

Extremal permutations in routing cycles

Let G be a graph whose vertices are labeled 1, ... , n, and pi be a permutation on [n] := {1, 2, ... , n}. A pebble p(i) that is initially placed at the vertex i has destination pi(i) for each i is an element of [n]. At each step, we choose a matching and swap the two pebbles on each of the edges. Let rt(G, pi), the routing number for pi, be the minimum number of steps necessary for the pebbles to reach their destinations. Li, Lu and Yang proved that rt(C-n, pi) = 5, if rt(C-n, pi) = n-1, then pi = 23 ... n1 or its inverse. By a computer search, they showed that the conjecture holds for n \u3c 8. We prove in this paper that the conjecture holds for all even n \u3e= 6

The three-dimensional simulation of vortex on the bottom of a particle in gas-liquid two- phase flow

The sophisticated industrial applications demand deep knowledge of local flow hydrodynamics on a particle surface in fixed bed reactors in order to improve process efficiency, particularly micro- (or particle-) scale of gas-liquid two-phase flow, which the study of vortex on the bottom of a particle is much more meaningful. The three-dimensional numerical simulations of gas-liquid two phase flow passing a spherical particle were investigated using Computational Fluid Dynamics (CFD) methodology with the volume of fluid (VOF) method. The effects of gas velocity, liquid velocity, liquid-solid contact angle, surface tension coefficient, and liquid viscosity on the interface status of fluid flow were presented in this paper. The simulation conditions were particle diameters of 10mm, water and air as liquid and gas respectively, droplet size 4mm, and an atmospheric pressure. Results show that the droplet movement and gas streamlines are greatly dependent on the air flow conditions and the liquid physical conditions. To better observe the flow field around the liquid droplet, the 3D plot is drawn for the contact angle of 50° with the gas velocity of 1.0m/s at the time instant of 0.015s as shown in Figure 1. Vortices are produced on the bottom of a particle known as Von Kármán vortex street, which have the opposite direction of rotation and the double row arrangement vortex. In addition, vortices are found to be more obvious and farer from the particle at higher gas and/or liquid velocities, and the droplet moves faster with the increasing gas velocity (0.2m/s-2.0m/s) and liquid velocity (0.24m/s-0.465m/s). Moreover, the generated vortices can be clearly observed at downstream of particle, and the droplet shape varies with the flow time. Vortex radius changes from 0.5mm to 2.5mm with the time going at the gas velocity 0.5m/s and liquid velocity 0.24m/s. The liquid-solid contact angle between 40° and 80° mainly affects particle surface wettability, which results in the different droplet shape and flow gas streamlines. At the beginning, the shape of the droplet is spherical and thereafter it changes to appropriate shape according to the surface properties and the contact angle. When the liquid-solid contact angle is 50°, vortex is comparatively density which radius is only 0.5mm initially, and then changes to 3.5mm approximately with an increase of the flow time. Meanwhile, the surface tension can affect the contractile properties and the gas streamline Please click Additional Files below to see the full abstract

Study of Effects of Equity Incentive in Gem Listed Company

Based on the analysis of Chinese gem listed company equity incentive the implementation of the status quo, on the basis of choosing the gem in 2011, in 2012 the implementation of equity incentive plan of the 55 of listed companies and the matching with the implementation of equity incentive of 55 transverse comparison of listed companies, found that the gem listed company equity incentive can improve the company’s performance. Selected by August 31, 2013, 114 published the draft of the equity incentive of the gem listed companies as samples, using linear regression analysis, found that the validity of equity incentive, incentive, stock option incentive model and company performance there is no significant correlation. Key words: Gem; The listed company; Equity incentive; The company’s performanc