Flexural buckling behaviour and residual strengths of stainless steel CHS columns after exposure to fire

The flexural buckling behaviour and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were studied, based on a thorough experimental and numerical modelling programme, and reported in this paper. The experimental programme was performed on three series of specimens, and each series contained five geometrically identical specimens, with one unheated and the other four heated to different levels of elevated temperatures (namely 300 °C, 600 °C, 800 °C and 1000 °C). The detailed heating, soaking and cooling processes, material testing and pin-ended column tests were described, with the derived key experimental results fully presented. The testing programme was supplemented by a numerical modelling programme, including a validation study where finite element models were developed and validated against the test results, and a parametric study where the validated finite element models were employed to derive further numerical results over an extended range of cross-section dimensions and member lengths. Due to the absence of existing design codes for stainless steel structures after exposure to fire, the codified design provisions for stainless steel CHS columns at ambient temperature, as established in the Europe, America and Australia/New Zealand, were assessed for their applicability to stainless steel CHS columns after exposure to fire, based on the obtained test and numerical data. The assessment results generally revealed that the design buckling curve, as adopted in the European code, and the tangent modulus method, as employed in the American specification, lead to unsafe and scattered design flexural buckling strengths for stainless steel CHS columns after exposure to fire, while the explicit approach, as used in the Australian/New Zealand standard, yields a high level of accuracy and consistency in predicting the post-fire flexural buckling strengths of stainless steel CHS columns

Y Chromosomes of 40% Chinese Are Descendants of Three Neolithic Super-grandfathers

Demographic change of human populations is one of the central questions for delving into the past of human beings. To identify major population expansions related to male lineages, we sequenced 78 East Asian Y chromosomes at 3.9 Mbp of the non-recombining region (NRY), discovered >4,000 new SNPs, and identified many new clades. The relative divergence dates can be estimated much more precisely using molecular clock. We found that all the Paleolithic divergences were binary; however, three strong star-like Neolithic expansions at ~6 kya (thousand years ago) (assuming a constant substitution rate of 1e-9/bp/year) indicates that ~40% of modern Chinese are patrilineal descendants of only three super-grandfathers at that time. This observation suggests that the main patrilineal expansion in China occurred in the Neolithic Era and might be related to the development of agriculture.Comment: 29 pages of article text including 1 article figure, 9 pages of SI text, and 2 SI figures. 5 SI tables are in a separate ancillary fil

Stable Hydrazone-Linked Covalent Organic Frameworks Containing O,N,O'-Chelating Sites for Fe(III) Detection in Water.

Two stable crystalline hydrazone-linked covalent organic frameworks (COFs) (Bth-Dha and Bth-Dma) containing functional O,N,O'-chelating sites have been designed and successfully synthesized by the Schiff-base condensation reactions between benzene-1,3,5-tricarbohydrazide (Bth) and 2,5-dihydroxyterephthalaldehyde (Dha) or 2,5-dimethoxyterephthal-aldehyde (Dma), respectively. Bth-Dma exhibits strong fluorescence in the solid state and in an aqueous dispersion, while no fluorescence can be observed for Bth-Dha. Interestingly, the as-synthesized Bth-Dma can be used as a turn-off fluorescence sensor for the Fe(III) ion in aqueous solution with outstanding selectivity and sensitivity. The recognition process can be attributed to the coordination interaction between Fe(III) ion and the O,N,O'-chelating sites in the pore wall of Bth-Dma COF, as verified by X-ray photoelectron spectroscopy and 1H NMR spectroscopy. To the best of our knowledge, this is the first report on the rational design of luminescent COF with predesigned O,N,O'-chelating sites as a fluorescence sensor for highly selective and sensitive metal ion detection. This work may pave the way for designing luminescent COF sensors with functional binding sites for detecting specific metal ions

From transients to permanent residents: the existence of obligate aerobic microorganisms in the goat rumen

The rumen serves as a complex ecosystem, harboring diverse microbial communities that play crucial ecological roles. Because previous studies have predominantly focused on anaerobic microorganisms, limited attention has been given to aerobic microorganisms in the goat rumen. This study aims to explore the diversity of aerobic microorganisms in the rumen and understand their niche and ecological roles. Rumen fluid samples were collected from 6 goats at different time points post-morning feeding. pH, NH3-N, and volatile fatty acid (TVFA) concentrations were measured, while In vitro cultivation of aerobic microorganisms was performed using PDA medium. Internal Transcribed Spacer (ITS) and 16S sequencing unveiled microbial diversity within the rumen fluid samples. Evidence of obligate aerobic microorganisms in the goat rumen suggests their potential contribution to ecological functionalities. Significantly, certain aerobic microorganisms exhibited correlations with TVFA levels, implying their involvement in TVFA metabolism. This study provides evidence of the existence and potential ecological roles of obligate aerobic microorganisms in the goat rumen. The findings underscore the significance of comprehensively deciphering goat rumen microbial communities and their interactions, with aerobes regarded as permanent residents rather than transients. These insights form a solid foundation for advancing our understanding of the intricate interplay between goat and their aerobic microorganisms in the rumen

Desorption Electrospray Ionization Mass Spectrometry for Monitoring the Kinetics of Baeyer-Villiger Solid-State Organic Reactions

Desorption electrospray ionization mass spectrometry (DESI-MS) has been used for monitoring solid-state organic reaction in ambient air, specifically the Baeyer-Villiger (BV) type reaction involving the oxidation of ketones (benzophenone or deoxybenzoin) by m-chloroperbenzoic acid (m-CPBA) in solid-state. The DESI mass spectra obtained at regular intervals during the BV reaction processes are featured, with the amount of ester products increasing as those of ketone reactants decrease. Quantitative analyses of relative intensities of the product, made to quantify the reaction degree of typical solid-state organic reaction (SSOR), show a precision with RSDs of around 5% to 12%, though the RSDs for direct analysis of intensities of the reactant or the product in the solid-state are obviously larger. The kinetics of the Baeyer-Villiger type reactions in solid-state are shown to be dramatically different, in reaction rate, kinetic curve, as well as concentration dependence, from those of the same reactions taking place in solution.NSFC,20525103,20721001 National Basic Research Program of China (973 Program)2007CB81530

Structural and Functional Characterization of Mature Forms of Metalloprotease E495 from Arctic Sea-Ice Bacterium Pseudoalteromonas sp. SM495

E495 is the most abundant protease secreted by the Arctic sea-ice bacterium Pseudoalteromonas sp. SM495. As a thermolysin family metalloprotease, E495 was found to have multiple active forms in the culture of strain SM495. E495-M (containing only the catalytic domain) and E495-M-C1 (containing the catalytic domain and one PPC domain) were two stable mature forms, and E495-M-C1-C2 (containing the catalytic domain and two PPC domains) might be an intermediate. Compared to E495-M, E495-M-C1 had similar affinity and catalytic efficiency to oligopeptides, but higher affinity and catalytic efficiency to proteins. The PPC domains from E495 were expressed as GST-fused proteins. Both of the recombinant PPC domains were shown to have binding ability to proteins C-phycocyanin and casein, and domain PPC1 had higher affinity to C-phycocyanin than domain PPC2. These results indicated that the domain PPC1 in E495-M-C1 could be helpful in binding protein substrate, and therefore, improving the catalytic efficiency. Site-directed mutagenesis on the PPC domains showed that the conserved polar and aromatic residues, D26, D28, Y30, Y/W65, in the PPC domains played key roles in protein binding. Our study may shed light on the mechanism of organic nitrogen degradation in the Arctic sea ice