85 research outputs found
Development of functionalized mesoporous inorganic-organic sorbents for removal of phenols and mercury ions from water, 2007
No full textPeriodic mesoporous organosilicates (PMOs), containing bridging organic groups, such as phenylene- or ethylene-, and pendant groups such as imidazole- or thiol-, were synthesized by the hydrolysis and co-condensation of alkoxysilyl precursors, bis(triethoxysilyl)ethane (BTSE) or bis(triethoxysilyl)benzene (BTSB) under basic conditions. Cetyltrimethylammonium chloride was used to increase the porosity and surface areas of these materials via the surfactant template approach. Further functionalization was achieved by co-condensation with trialkoxyorganosilanes, including 3-mercaptopropyltrimethoxysilane or -(3-triethoxysilylpropyl)-4,5- dihydroimidazole. Structural characterization of these materials was carried out by nitrogen gas sorption, X-ray diffraction, TEM, TGA, NMR, EDS and elemental analysis. The adsorption of phenolic compounds (phenol, 4-nitrophenol, 4-chlorophenol, 4- methylphenol, 2,4-dinitrophenol, 2,4-dichlorophenol, 2,4-dimethylphenol) and mercury (II) were investigated by batch testing. The material containing imidazole group exhibited a high affinity for 2,4-dinitrophenol. The capacities of the materials are: BTSE-IM (83.7 mg/g), BTSB-IM (53.8 mg/g) and MCM-IM (118.5 mg/g). The sorption of 24-DNP on BTSE-IM and BTSB-IM closely follow the Langmuir adsorption model. This means the sorption occurred on homogeneous surface as on a monolayer. The sorption of 24-DNP on MCM-IM, and 24-DCP, 24-DMP, 24-DNP on BTSE are more suitable to the Freundlich adsorption model. That means these sorptions are non-ideal and multi-layered on heterogeneous surface. The adsorption test for mercury (II) indicated that the materials containing -SH functional group showed better affinity for bonding mercury (II) than the materials containing the -IM group. These materials would be highly effective for removal of mercury (II)
Transgenic Improvement for Biotic Resistance of Crops
No full textBiotic constraints, including pathogenic fungi, viruses and bacteria, herbivory insects, as well as parasitic nematodes, cause significant yield loss and quality deterioration of crops. The effect of conventional management of these biotic constraints is limited. The advances in transgenic technologies provide a direct and directional approach to improve crops for biotic resistance. More than a hundred transgenic events and hundreds of cultivars resistant to herbivory insects, pathogenic viruses, and fungi have been developed by the heterologous expression of exogenous genes and RNAi, authorized for cultivation and market, and resulted in a significant reduction in yield loss and quality deterioration. However, the exploration of transgenic improvement for resistance to bacteria and nematodes by overexpression of endogenous genes and RNAi remains at the testing stage. Recent advances in RNAi and CRISPR/Cas technologies open up possibilities to improve the resistance of crops to pathogenic bacteria and plant parasitic nematodes, as well as other biotic constraints
Mechanical behavior of the joints between carbon/carbon composites and Li2O–Al2O3–SiO2 glass ceramics with YAS interlayer at high temperature
No full textReconstruction of the East Asian monsoon variability since the mid-Holocene from the Pearl River estuary, southern China
No full textThe principal aim of this thesis is to reconstruct East Asian Monsoon (EAM) variability during the mid-Holocene, developing a relatively new proxy of bulk organic carbon isotopic signature (δ13C). C/N ratios and trace elements are also employed to conduct a multi-proxy case study from the Pearl River estuary, southern China. Sources of sediments within an estuary include river-derived terrestrial/freshwater input, in situ brackish-water suspended sediment and tide-derived marine input. This study assumes the three proxies can help differentiate sources of sediments relating to monsoon-driven freshwater flux and help reconstruct monsoonal precipitation history during the mid-Holocene when the sea level was relatively stable.
To achieve the aims of this thesis a range of modern samples were collected from terrestrial areas, including plants and soil samples, through to estuarine areas, including seasonal estuarine suspended organic matter (SOM) and surface sediment. Results suggest that bulk organic δ13C and C/N ratios can successfully identify sources of the organic component of the estuarine sediment, and thus can be used to infer relative changes in monsoon-driven freshwater flux to the estuary. For example, more negative δ13C values reflect a greater level of contribution of freshwater organic carbon, i.e. stronger monsoonal freshwater discharge. Results also show that a combination of selected metals, such as the terrigenous metals (Fe, Mn, Co and As), can be useful for indicating sediment sources and sedimentary environment.
Analysis of an estuarine core (UV1) shows that freshwater discharge from the Pearl River catchment gradually declined from 6400 to 2000 cal. years BP, suggesting a gradual weakening of summer monsoon precipitation, responding to the weakening insolation controlled by the orbital-driven precession cycle. Superimposed on this are wet/dry intervals, ranging from centennial- to millennial- scale, driven by solar activity. Changes in ENSO and high-latitude cooling events might be responsible for dry/wet events at centennial- to decadal- scale, identified during the mid-Holocene. This study also suggests that the coupling of thermal and moist conditions of the EAM might only have become stable after 4500 cal. yr BP. A sudden shift in the geochemical signature indicates agricultural activity in the Pearl River delta intensified from 2000 cal. yr BP
Wavelike interfacial design and mechanical behaviour of joint between Si-SiC coated carbon/carbon composites and Li2O-Al2O3-SiO2 glass ceramics
No full textThree strategies of transgenic manipulation for crop improvement
No full textHeterologous expression of exogenous genes, overexpression of endogenous genes, and suppressed expression of undesirable genes are the three strategies of transgenic manipulation for crop improvement. Up to 2020, most (227) of the singular transgenic events (265) of crops approved for commercial release worldwide have been developed by the first strategy. Thirty-eight of them have been transformed by synthetic sequences transcribing antisense or double-stranded RNAs and three by mutated copies for suppressed expression of undesirable genes (the third strategy). By the first and the third strategies, hundreds of transgenic events and thousands of varieties with significant improvement of resistance to herbicides and pesticides, as well as nutritional quality, have been developed and approved for commercial release. Their application has significantly decreased the use of synthetic pesticides and the cost of crop production and increased the yield of crops and the benefits to farmers. However, almost all the events overexpressing endogenous genes remain at the testing stage, except one for fertility restoration and another for pyramiding herbicide tolerance. The novel functions conferred by the heterologously expressing exogenous genes under the control of constitutive promoters are usually absent in the recipient crops themselves or perform in different pathways. However, the endogenous proteins encoded by the overexpressing endogenous genes are regulated in complex networks with functionally redundant and replaceable pathways and are difficult to confer the desirable phenotypes significantly. It is concluded that heterologous expression of exogenous genes and suppressed expression by RNA interference and clustered regularly interspaced short palindromic repeats-cas (CRISPR/Cas) of undesirable genes are superior to the overexpression of endogenous genes for transgenic improvement of crops
The complete mitochondrial genome of natural hybridization of Anser albifrons and Anser fabalisthe (Anser albifrons × Anser fabalis)
No full textHybridization between birds in wild nature is an interesting phenomenon in the wild, but not common in waterfowl in the wild. In this study, we report the complete mtDNA of the natural hybridization bird between Anser albifrons and Anser fabalis. The complete mtDNA of the hybridization is 16,740 bp in length, contains the typical set of 37 genes, including 13 PCGs, two rRNAs, 22 tRNAs, and a 1177 bp CR. In the 13 PCGs, ATG is generally as the start codon, TAA is the most frequent stop codon, one of three, TAA, TAG, and T-, commonly observed. All tRNAs can be folded into canonical cloverleaf secondary structures except for tRNASer (AGY) and tRNALeu (CUN) missing the “DHU” arm. The new mtDNA sequence contains 12S rRNA and 16S rRNA of rRNAs, separated with tRNAval. The CR is 1177 bp in length, located between tRNAGlu and tRNAPhe. Our phylogenetic trees suggest the hybridization has a close genetic relationship among Anser species
Constructing self-healing ZrSi2-MoSi2 coating for C/C composites with enhanced oxidation protective ability
No full textCoexistence of T-cell lymphoblastic lymphoma and acute myeloid leukemia mimicking acute lymphocytic leukemia
No full text- …
