Design and Synthesis of Thermal Contracting Polymer with Unique Eight-Membered Carbocycle Unit

It is uncommon for a solid substance to expand upon cooling and contract upon heating. In this work, we synthesized a carbocycle monomer that contains 1,2:5,6-dibenzocyclooctadiene (DBCOD) unit and the corresponding polymers with different amounts of DBCOD in the polymer main chain. The films produced from this DBCOD-based polymer showed reversible thermal contraction behavior with the negative thermal expansion (NTE) coefficient of -625 ppm/K (100-200 °C). Differential scanning calorimetry (DSC), variable-temperature nuclear magnetic resonance (VT-NMR), and density-functional theory (DFT) calculations indicated that the population of the chair conformer of DBCODs increased with the rise of temperature due to the conversion from twist-boat to chair conformer. This led to giant thermal contraction. Furthermore, the value of the NTE coefficient could be adjusted by the amount of DBCODs and their surrounding physical environment. This is the first demonstration of a linear polymer that exhibits reversible thermal contraction. The new monomer can be covalently incorporated into a variety of polymeric materials to construct negative thermal expansion or zero expansion materials for the specific applications

Ce–Nd separation by solid-phase micro-extraction and its application to high-precision 142Nd/144Nd measurements using TIMS in geological materials

In view of the low initial abundance of 146Sm, 142Nd anomalies are expected to be extremely small (less than 40 ppm), and their detection requires ultra-precise 142Nd/144Nd measurements. A rapid solid-phase micro-extraction (SPME) technique, using HEHEHP resin as sorbent, is established to completely separate Ce from rare earth element (REE) mixtures. This technique is applied to ultra-high-precision 142Nd/144Nd measurements in geological materials. In contrast to the traditional liquid–liquid micro-extraction (LLME) technique, the benefits of the SPME tandem column are high Nd recovery, low residual Ce (Ce/Nd 3.0. Thus, 142Ce interferences on 142Nd never exceed 1.3 ppm. Ultra-high-precision thermal ionization mass spectrometry analyses of silicate standards show that the internal precision of all runs are better than 4 ppm (2 RSE) for 142Nd/144Nd values. 142Nd/144Nd values for JNdi-1, JR-3, and BCR-2 have external precisions of ±4.8, ±4.4, and ±3.9 ppm (2 RSD), respectively. The external reproducibility is sufficient to distinguish and resolve 5 ppm anomalies in 142Nd/144Nd values

Tensile simulation of 6061 aluminum alloy

The quasi-static tensile simulation was carried out on the 6061 aluminum alloy round bar specimen, and the tensile specimen model was drawn. Three sets of simulation with uniaxial tensile velocity of 10 s-1, 15 s-1 and 20 s-1 were set at normal temperature, and the numerical simulation of the tensile process was carried out by using ABAQUS software. The experimental data were imported into the model, and the relevant parameters such as damage model were set. The derived simulation results are in good agreement with the experimental results, indicating that the established simulation model can simulate the uniaxial tensile behavior of 6061 aluminum alloy well

Single-step separation scheme and high-precision isotopic ratios analysis of Sr–Nd–Hf in silicate materials

Thermal ionization mass spectrometry and multiple-collector inductively coupled plasma mass spectrometry are considered to be “gold standards” for the determination of the isotope ratios of Sr–Nd and Hf in geological samples because of the extremely high precision and accuracy of these methods. However, the sample throughputs are hindered by time-consuming and tedious chemical procedures. Three-step ion exchange resin separation is traditionally employed to purify Sr–Nd–Hf from matrix elements. In this study, a one-step Sr–Nd–Hf separation scheme was developed to process geological samples. The separation scheme is based on the combined use of conventional AG50W-X12 cation-exchange resin and LN Spec extraction chromatographic material without any intervening evaporation step. The protocol not only prevents cross-contamination during operation using multiple-stage ion exchange resins but also significantly improves the efficiency of sample preparation. The stability of our chemical procedure was demonstrated by replicate measurements of 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios in six international reference materials of silicate rocks. The analytical results obtained for these standard rocks compare well with the published data. The external reproducibility (2 SD, n = 10) of a BCR-2 standard sample was ±0.000018 for 87Sr/86Sr, ±0.000010 for 143Nd/144Nd, and ±0.000014 for 176Hf/177Hf

Genetic factors related to the widespread dissemination of ST11 extensively drug-resistant carbapenemase-producing Klebsiella pneumoniae strains within hospital.

BackgroundCarbapenemase-producing Klebsiella pneumoniae (CP-Kp) poses distinct clinical challenges due to extensively drug resistant (XDR) phenotype, and sequence type (ST) 11 is the most dominant blaKPC-2-bearing CP-Kp clone in China. The purpose of this current retrospective study was to explore the genetic factors associated with the success of XDR CP-Kp ST11 strains circulated in the intensive care unit (ICU) of a Chinese tertiary hospital.MethodsSix ST11 XDR CP-Kp strains were identified between May and December 2014 and validated by minimum inhibitory concentration examination, polymerase chain reaction, and pyrosequencing. The six ST11 XDR CP-Kp, as well as three multi-drug resistant (MDR) and four susceptible strains, were sequenced using single-molecule real-time method. Comprehensively structural and functional analysis based on comparative genomics was performed to identify genomic characteristics of the XDR ST11 CP-Kp strains.ResultsWe found that ST11 XDR blaKPC-2-bearing CP-Kp strains isolated from inpatients spread in the ICU of the hospital. Functionally, genes associated with information storage and processing of the ST11 XDR CP-Kp strains were more abundant than those of MDR and susceptible strains, especially genes correlative with mobile genetic elements (MGEs) such as transposons and prophages. Structurally, eleven large-scale genetic regions taken for the unique genome in these ST11 XDR CP-Kp strains were identified as MGEs including transposons, integrons, prophages, genomic islands, and integrative and conjugative elements. Three of them were located on plasmids and eight on chromosomes; five of them were with antimicrobial resistance genes and eight with adaptation associated genes. Notably, a new blaKPC-2-bearing ΔΔTn1721-blaKPC-2 transposon, probably transposed and truncated from ΔTn1721-blaKPC-2 by IS903D and ISKpn8, was identified in all six ST11 XDR CP-Kp strains.ConclusionOur findings suggested that together with clonal spread, MGEs identified uniquely in the ST11 XDR CP-Kp strains might contribute to their formidable adaptability, which facilitated their widespread dissemination in hospital