Temporally and Longitudinally Tailored Dynamic Space-Time Wave Packets

In general, space-time wave packets with correlations between transverse spatial fields and temporal frequency spectra can lead to unique spatiotemporal dynamics, thus enabling control of the instantaneous light properties. However, spatiotemporal dynamics generated in previous approaches manifest themselves at a given propagation distance yet not arbitrarily tailored longitudinally. Here, we propose and demonstrate a new versatile class of judiciously synthesized wave packets whose spatiotemporal evolution can be arbitrarily engineered to take place at various predesigned distances along the longitudinal propagation path. Spatiotemporal synthesis is achieved by introducing a 2-dimensional spectrum comprising both temporal and longitudinal wavenumbers associated with specific transverse Bessel-Gaussian fields. The resulting spectra are then employed to produce wave packets evolving in both time and axial distance - in full accord with the theoretical analysis. In this respect, various light degrees of freedom can be independently manipulated, such as intensity, polarization, and transverse spatial distribution (e.g., orbital angular momentum). Through a temporal-longitudinal frequency comb spectrum, we simulate the synthesis of the aforementioned wave packet properties, indicating a decrease in relative error compared to the desired phenomena as more spectral components are incorporated. Additionally, we experimentally demonstrate tailorable spatiotemporal fields carrying time- and longitudinal-varying orbital angular momentum, such that the local topological charge evolves every ~1 ps in the time domain and 10 cm axially. We believe that our space-time wave packets can significantly expand the exploration of spatiotemporal dynamics in the longitudinal dimension, and potentially enable novel applications in ultrafast microscopy, light-matter interactions, and nonlinear optics

In Vitro Assembly of Multiple DNA Fragments Using Successive Hybridization

Construction of recombinant DNA from multiple fragments is widely required in molecular biology, especially for synthetic biology purposes. Here we describe a new method, successive hybridization assembling (SHA) which can rapidly do this in a single reaction in vitro. In SHA, DNA fragments are prepared to overlap one after another, so after simple denaturation-renaturation treatment they hybridize in a successive manner and thereby assemble into a recombinant molecule. In contrast to traditional methods, SHA eliminates the need for restriction enzymes, DNA ligases and recombinases, and is sequence-independent. We first demonstrated its feasibility by constructing plasmids from 4, 6 and 8 fragments with high efficiencies, and then applied it to constructing a customized vector and two artificial pathways. As SHA is robust, easy to use and can tolerate repeat sequences, we expect it to be a powerful tool in synthetic biology

Market dynamics, innovation, and transition in China's solar photovoltaic (PV) industry: a critical review

China's photovoltaic (PV) industry has undergone dramatic development in recent years and is now the global market leader in terms of newly added capacity. However, market diffusion and adoption in China is not ideal. This paper examines the blocking and inducement mechanisms of China's PV industry development from the perspective of technological innovation. By incorporating a Technological Innovation System (TIS) approach, the analysis performed here complements the previous literature, which has not grounded itself in a theoretical framework. In addition, to determine the current market dynamics, we closely examine market concentration trends as well as the vertical and horizontal integration of upstream and downstream actors (74.8% and 36.3%). The results of applying the TIS framework reveal that poor connectivity in networks, unaligned competitive entities and a lack of market supervision obstruct the development of China's PV industry. Therefore, we maintain that inducement mechanisms are required to instigate learning-by-doing capacities, which may help overcome blocking mechanisms and offset functional innovation deficiencies. In addition, policy implications are proposed for promoting the development of the PV industry in China

Characterization of selenium containing proteins in the coral Acropora millepora

Selenium (Se) and Se-containing proteins are believed to be involved in many physiological processes. Recent studies have revealed complex repertoires of Se containing proteins in mammals, of which some (known as selenoproteins) contain selenocysteine (Sec; encoded by in-frame UGA codons) and others in which the selenium is bound (selenium binding proteins; SeBPs) without selenoproteins. There have been few studies to date on the selenium protein complements of non-Bilateria animals, and many of the non-Bilateria selenoprotein genes in the public sequence databases are mis-annotated. The main objective of the work described in this thesis was to describe the selenoprotein and selenium-binding protein repertoire of the coral Acropora millepora, a representative non-Bilateria animal and to investigate aspects of the expression of some of the corresponding genes. These studies should not only provide evolutionary insights into selenium biology, but also be relevant to the physiology of coral stress.\ud \ud To achieve these goals, phylogenetic tools were used to survey the repertoires of selenium-containing proteins in A. millepora and other model organisms, qPCR and immunohistochemistry employed to follow changes in the expression of genes encoding non-enzymatic selenium containing proteins under experimental manipulation, bioinformatics tools used to model the structure of proteins of interest, and chemical tools employed to analyze the Se binding ability of recombinant selenium binding protein towards the inorganic Se in vitro.\ud \ud The evolutionary studies summarized in Chapter 2 show that in the known invertebrates which have been studied their selenium components, the coral A. millepora has the most complex selenium repertoire (21 Sec-containing selenoproteins and 2 selenium binding proteins); other cnidarians also contain complex selenium repertoires. These results suggest that most of the known selenium components seen in bilaterian animals predate the bilaterian-cnidarian split. In Chapter 3 we report that the expression of several non-enzymatic selenium containing proteins in the coral A. millepora is highly up-regulated by oxidants, suggesting physiology roles for these selenium components in redox regulation.\ud \ud Studies in Chapter 4 and 5 focused on the A. millepora 56 kDa SeBPs (amSeBPs). Sequence analysis and structure modeling revealed that the conserved cysteine residues that are characteristic of these proteins, together with nearby motifs, cluster at the centre of the monomer protein models. The amSeBPs were ubiquitously expressed and markedly up-regulated at the planula and presettlement stages. Immunolocalisation experiments imply that the amSeBPs are enriched in adult A. millepora gastrodermal tissue that is adjacent to Symbiodinium. The in vitro selenite/amSeBP binding assays showed that the binding of inorganic selenium by amSeBP is dependent on the redox state. These studies imply that the positions of the redox sensitive cysteine residues and nearby motifs are critical for amSeBP function; these constraints presumably underlie the high level of sequence conservation of the 56 kDa SeBP sequences among animals, plants and even microorganisms.\ud \ud In summary, these results imply important roles for the selenium containing proteins that are abundant in A. millepora. Although some of these proteins have been systematically characterized and implicated in redox metabolism, the mechanistic details remain unclear. To date, functional studies have focused mainly on mammalian Se proteins. Functional analyses in non-Bilateria animals could shed some light on the significance of Se-proteins and selenium biology more broadly

Biotechnological Application of Cutinase: A Powerful Tool in Synthetic Biology

Cutinases (EC 3.1.1.74) are widely distributed in fungi, bacteria and plants with diversified structures and properties. Besides acting on the natural substrate cutin, cutinases are the first line of natural biocatalysts to hydrolyze artificial polyesters and toxic xenobiotics such as polyethylene terephthalate (PET), polycaprolactone (PCL), polylactic acid (PLA), polyhydroxybutyl succinate (PBS), phthalate and malathion esters. Moreover, cutinases can act as promising stereoselective catalysts in esterification and transesterification reactions and present better selectivities than lipases. These pioneering studies indicate that the biotechnological application of cutinase as a powerful tool in synthetic biology deserves further investigation, for both degradation and biosynthesis towards a broader range of ester bond-containing substrates. This review summarizes the classifications and properties of cutinases from different sources and insights into the structure–function relationship of different cutinases. It also highlights the uniqueness and advantages of representative cutinases in biodegradation and biosynthesis, and then prospects the future application of natural and engineered cutinases in synthetic biology

Metabolic engineering of Escherichia coli for the production of xylonate.

Xylonate is a valuable chemical for versatile applications. Although the chemical synthesis route and microbial conversion pathway were established decades ago, no commercial production of xylonate has been obtained so far. In this study, the industrially important microorganism Escherichia coli was engineered to produce xylonate from xylose. Through the coexpression of a xylose dehydrogenase (xdh) and a xylonolactonase (xylC) from Caulobacter crescentus, the recombinant strain could convert 1 g/L xylose to 0.84 g/L xylonate and 0.10 g/L xylonolactone after being induced for 12 h. Furthermore, the competitive pathway for xylose catabolism in E. coli was blocked by disrupting two genes (xylA and xylB) encoding xylose isomerase and xylulose kinase. Under fed-batch conditions, the finally engineered strain produced up to 27.3 g/L xylonate and 1.7 g/L xylonolactone from 30 g/L xylose, about 88% of the theoretical yield. These results suggest that the engineered E. coli strain has a promising perspective for large-scale production of xylonate