分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Poly[bis(phenoxyphosphazene)] (PBPP) and magnesium hydroxide (MH) are used as a flame retardant blend with low-density polyethylene (LDPE) for the nuclear cable. This study aims to investigate the effects of PBPP in MH-LDPE blend composites on flame retardance and electron beam irradiation. The structure, morphology, and properties of the blend composites irradiated by an electron beam to different absorbed doses were characterized. The results indicated that PBPP provides lubrication during processing. As the PBPP content in the blend increases the melt flow rate at 20 phr MH, meaning the material is easier to process. The higher the PBPP content, the higher the limiting-oxygen index. The elongation at the break of the PBPP containing composites (at 50 phr MH) was evidently higher than the non-PBPP ones at different absorbed doses by electron beam irradiation. The thermogravimetric analysis results indicated that the improved mechanical property, resulting from electron-beam irradiation, could be attributed to the consumption of PBPP.
分类: 地球科学 >> 空间物理学 提交时间: 2017-03-10
摘要: High-energy electron precipitation in the high latitude regions enhances the ionization of the atmosphere, and subsequently increases the atmospheric conductivities and the vertical electric field of the atmosphere near the ground as well. The high-energy electron flux (HEEF) data measured by the Feng-Yun III meteorological satellite are analyzed together with the data of near-surface atmospheric vertical electric field measured at the Russian Vostok Station. Three HEEF enhancements are identified and show that when the HEEF increases to a certain level, the local atmospheric vertical electric field near the ground can increase substantially than usual. The time of the response of the electric field to the HEEF enhancement is about 3.7 to 4 days (delay time).
分类: 地球科学 >> 空间物理学 提交时间: 2017-01-22
摘要: High-energy electron precipitation in the high latitude regions enhances the ionization of the atmosphere, and subsequently increases the atmospheric conductivities and the vertical electric field of the atmosphere near the ground as well. The High-Energy Electron Flux (HEEF) data measured by the Fengyun-3 meteorological satellite are analyzed together with the data of nearsurface atmospheric vertical electric field measured at the Russian Vostok Station. Three HEEF enhancements are identified and it is shown that when the HEEF increases to a certain level, the local atmospheric vertical electric field near the ground can increase substantially than usual. The response time of the electric field to HEEF enhancement is about 3.7 to 4 days.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-12
摘要: Rv0880 from the pathogen Mycobacterium tuberculosis is classified as a MarR family protein in the Pfam database. It consists of 143 amino acids and has an isoelectric point of 10.9. Crystals of Rv0880 belonged to space group P1, with unit-cell parameters a = 54.97, b = 69.60, c = 70.32 angstrom, alpha = 103.71, beta = 111.06, gamma = 105.83 degrees. The structure of the MarR family transcription regulator Rv0880 was solved at a resolution of 2.0 angstrom with an R-cryst and R-free of 21.2 and 24.9%, respectively. The dimeric structure resembles that of other MarR proteins, with each subunit comprising a winged helix-turn-helix domain connected to an alpha-helical dimerization domain.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: We describe the synthesis of bimetallic dendritic platinum decorated gold nanorods (AuNRs) by the spatial control of Pt growth over gold nanorods using a heterogeneous seed-mediated growth method. The amounts of the Au seed and Pt-precursor were changed to achieve a tunable volume fraction of Pt coverage on the Au NRs surface. Pt nanostructures were spatially separated from each other, which was highly favorable for promising optical and catalytic properties. The dendritic-Pt decorated AuNRs with variable Au/Pt ratios were exploited to study their surface plasmonic properties and catalytic activities. Interestingly, the Pt decorated AuNRs showed strong surface plasmon resonance (SPR) peak due to noncompact dendritic Pt shell in contrast to the conventional core–shell Au@Pt nanoparticles (NPs). Moreover, the longitudinal peak of the AuNRs was finely tuned from 820 to 950 nm (NIR region) by controlling the volume fraction of the Pt decoration over the AuNRs. The catalytic activity of the dendritic-Pt decorated AuNRs on the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) as reducing agent was studied and found to be superior to the activities compared to the monometallic Au NRs. Considering practical applications, dendritic-Pt decorated AuNRs nanostructures were immobilized successfully on the hydrophilic polyvinylidene difluoride (PVDF) film as an efficient reusable catalyst.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Lysine acetylation is an important post-translational modification and is known to regulate many eukaryotic cellular processes. Little, however, is known about acetylated proteins in prokaryotes. Here, using immunoblotting, mass spectrometry and mutagenesis studies, we investigate the acetylation dynamics of the DNA repair protein Ku and its relationship with the deacetylase protein Sir2 and the non-homologous end joining (NHEJ) pathway in Mycobacterium smegmatis. We report that acetylation of Ku increases with growth, while NHEJ activity decreases, providing support for the hypothesis that acetylation of Ku may be involved in the DNA damage response in bacteria. Ku has multiple lysine sites. Our results indicate that K29 is an important acetylation site and that deficiency of Sir2 or mutation of K29 affects the quantity of Ku and its acetylation dynamics. Our findings expand knowledge of acetylation targets in prokaryotes and indicate a new direction for further research on bacterial DNA repair mechanisms.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Quantitative investigation is conducted on the resistance sources of the components in the NiOeYSZ/ YSZ/GDC/LSCFeGDC solid oxide electrolysis cell (SOEC) stack at the H2O/H2 ratios of 70/30, 80/20 and 90/ 10 at 750 C. The results indicate that the cell resistance accounts for 76.3e66.7% of that of the stack repeating unit (SRU), the contact resistance (CR) between the air electrode current-collecting layer (AECCL) and the interconnect accounts for 23.6e27.0%, the CR between the hydrogen electrode current- collecting layer (HECCL) and the interconnect only accounts for 2.3e3.2%, and the resistance of the interconnect can be neglected. Duration test of the stack is conducted at 0.8 A cm 2 for 380 h, the cell resistance increase is found to be the major contribution of the SRU degradation (82.2% of the SRU degradation) while the air electrode CR increase and the hydrogen electrode CR increase are other two important factors.
提交时间: 2017-05-02
摘要: Development of self-healing polymers with spontaneous self-healing capability and good mechanical performance is highly desired and remains a great challenge. Here, mechanical robust and self-healable supramolecular hydrogels have been fabricated by using
提交时间: 2017-05-02
摘要: A simple strategy is provided to construct a novel pH- and sugar-induced shape memory hydrogel based on dynamic phenylboronic acid [PBA]-diol interactions formed by PBA-modified sodium alginate [Alg-PBA] and poly[vinyl alcohol] [PVA]. The dynamic PBA-diol
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A polymer-based visible and quantitative fluorometric assay for CO2 gas is constructed using branched polyethyleneimine (PEI) covalently modified with tetraphenylethylene (TPE). The sensing mechanism relies on the reaction of CO2 with alkylamines of PEI to induce the “solution-to-precipitation” phase transi- tion of the sensory polymer (TPE–PEI), thus resulting in strong aggregation-induced fluorescent emission of TPE–PEI. It works in a relatively environmental benign ethanol medium and avoids the use of toxic amine compounds with unpleasant odor. More importantly, this system is proved to be highly tolerant to possibly coexisting water, carbon monoxide, acid SO2 and H2 S gases as well as many common volatile organic compounds. These characteristics make the presently developed fluorescent chemosensor hold great potential for many real-world applications.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Bimetallic nanocatalysts often display enhanced physical and chemical properties compared to those of their monometallic counterparts. Herein, we introduce a simple method to fabricate an island like array of tiny Ag nanoparticles bounded on triangular Au nanoplates as the surface-enhanced Raman scattering (SERS) substrate. The surface morphology of the synthesized nanoparticles was characterized via field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). Rhodamine 6G (R6G) is used as a model analyte to evaluate the performance of the tiny Ag nanoparticle bounded triangular Au nanoplates as a SERS-active substrate and validate the SERS effect. The fabricated SERS substrate showed drastically enhanced intensity with a SERS enhancement factor as high as 107, which is enough to detect a single molecule, and excellent reproducibility (less than `5%) of the signal intensity. This is because of the island-like tiny Ag nanoparticle bounded triangular Au nanoplates and their large number of “hot spots”. This substrate could also be used for label-free immunoassays, biosensing, and nanoscale optical antennas and light sources.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Supertough biomimetic hydrogels have been fabricated through in situ synthesis and guided assembling of positively charged conjugated polymer belts by using a parent poly(2-acrylamido-2-methylpropanesulfonic acid)/poly- (acrylamide) double network (PAMPS/PAAm DN) gel template. The inter- penetrating structures of the poly(3,4-ethylenedioxythiophene) (PEDOT) belt mesh and PAMPS/PAAm host network have been confirmed by SEM, CLSM, and Raman spectroscopy. The presence of PEDOT belts improves the Young’s modulus, compressive strength, and toughness of the biomimetic (BM) hydrogels, in comparison to the parent DN gels. Cyclic tensile (300% strain) and compressive (even 90% strain) loadings demonstrate extraordinary fatigue resistance of these BM gels. Upon ten cycles, the compressive toughness remained about 1000 J m−2, which is comparable to that of articular cartilage. The internal fracture behavior and fatigue resistance of these biomimetic interpenetrating hydrogels are further investigated. These extremely tough and fatigue resistant BM hydrogels may find applications as promising substitutes for load-bearing tissues.
提交时间: 2017-05-02
摘要: High fidelity and regularity structures of nanoscale materials has opened up new opportunities for developing miniaturized devices. A simple yet robust approach of magnetic field assisted controlled evaporative self-assembly [CESA] is developed to achieve
分类: 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间: 2016-05-12
摘要: The biotin biosynthesis pathway is an attractive target for development of novel drugs against mycobacterial pathogens, however there are as yet no suitable inhibitors that target this pathway in mycobacteria. 7-Keto-8-aminopelargonic acid synthase (KAPA synthase, BioF) is the enzyme which catalyzes the first committed step of the biotin synthesis pathway, but both its structure and function in mycobacteria remain unresolved. Here we present the crystal structure of Mycobacterium smegmatis BioF (MsBioF). The structure reveals an incomplete dimer, and the active site organization is similar to, but distinct from Escherichia coli 8-amino-7-oxononanoate synthase (EcAONS), the E. coli homologue of BioF. To investigate the influence of structural characteristics on the function of MsBioF, we deleted bioF in M. smegmatis and confirmed that BioF is required for growth in the absence of exogenous biotin. Based on structural and mutagenesis studies, we confirmed that pyridoxal 5'-phosphate (PLP) binding site residues His129, Lys235 and His200 are essential for MsBioF activity in vivo and residue Glul 71 plays an important, but not essential role in MsBioF activity. The N-terminus (residues 1-37) is also essential for MsBioF activity in vivo. The structure and function of MsBioF reported here provides further insights for developing new anti-tuberculosis inhibitors aimed at the biotin synthesis pathway. (C) 2014 Elsevier Ltd. All rights reserved.
提交时间: 2017-05-02
摘要: This study demonstrates that uniform materials of reduced graphene oxide/polydopamine composite thin film can serve as a highly sensitive and ultrafast responsive actuator driven by water gradients absorption-induced in situ formation of bilayer structures in swelling difference along the lateral uniform thin film
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Poly(vinylidene fluoride) (PVDF) membranes have been widely applied to treat wastewater, however, the removal of toxic aromatic phenolic compounds remains a technical challenge due to the serious adsorption fouling and difficult degradation. Herein, we aimed to design a superhydrophilic PVDF membrane decorated with Au nanoparticles, which enhanced the rapid degradation of p-nitrophenol (4-NP). The superhydrophilic PVDF membrane with a micro/nano structured surface was decorated with Au nanoparticles via poly(dopamine) (PDA) as a spacer. The influences of membrane affinity (e.g. Hydrophilic Membrane (HM), micro/nano structured superhydrophilic membrane (MSiM), and micro/ nano structured superhydrophobic membrane (MSoM)) on PDA deposition and the subsequent Au decoration were comprehensively investigated. The synthesized Au nanoparticles were characterized using transmission electron microscopy (TEM) and UV-vis absorption spectra. The morphology and composition was evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static catalytic experiments demonstrated that MSiM degraded over 90% of 4-NP in 5 minutes with a kinetic reaction rate constant of 47.84 10 2 min 1 and high stability over 6 cycles. A membrane catalytic reactor (MCR) was designed to realize the continuous catalytic degradation of 4-NP with a kinetic reaction rate constant of 7 10 2 min 1.