分类: 材料科学 >> 纳米科学和纳米技术 提交时间: 2017-01-10
摘要: Spongy graphene paper with inside foldable corrugated structure is fabricated by electrothermal reduction of the oxygen-containing groups inside RGO paper. Reversible macroscopical length contraction of the spongy graphene paper with strain of 2.4% under 10V voltage is exhibited, mostly attributed to the deformation of corrugated structures.
分类: 化学 >> 核化学 提交时间: 2023-05-31
摘要: The rapid development of advanced techniques for selective and efficient U(VI) extraction from aqueous solutions is essential for addressing U(VI) environmental pollution and energy issues. Here, we share recent progress in U(VI) extraction from aqueous solutions, especially the most frequently applied techniques such as adsorption, catalysis (photocatalysis, piezocatalysis, and electrocatalysis), chemical deposition, and reduction by zero-valent metal particles. We attempt toelucidate the strategies and various mechanisms that contribute to the enhancement of selective U(VI) extraction. At the end of our review, we highlight the outlook, challenges, and prospects for the development of this field.
分类: 化学 >> 物理化学 提交时间: 2017-11-05 合作期刊: 《结构化学》
摘要: Alloys based on non-noble metals could be the next generation of high-performance catalysts for many chemical reactions. However, precisely composition controlled synthesis of non-noble alloys remains a significant challenge. In this work, we report a simple synthesis of Cu0.5Ni0.5 alloys without any component segregation. Its success relies on the use of Cu–Ni oxalate precursors, which are chelated in the proximity by oxalate ligands. One of the attractive features for the oxalate routes of catalyst preparation is that no classical support material is needed. The actual component ratios of the obtained Cu0.5Ni0.5 alloy are consistent with the initial ratio. Cu0.5Ni0.5 alloy shows a higher catalytic activity than pure Cu and Ni catalysts in the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) by sodium borohydride (NaBH4) in an aqueous solution, and the performance depends strongly on the strong interaction between Cu and Ni. The findings reported here are highly helpful to understand the relationship between the synergistic effects in alloys and their catalytic performance, and therefore could provide appropriate strategies to obtain desirable catalysts with improved activity in various catalytic applications.
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 oxygen-evolving center (OEC) in photosystem II catalyzes a water splitting reaction. Great efforts have already been made to artificially synthesize the OEC, in order to elucidate the structure-function relationship and the mechanism of the reaction. Now, a new synthetic model makes the best mimic yet of the OEC. This recent study opens up the possibility to study the mechanism of photosystem II and photosynthesis in general for applications in renewable energy and synthetic biology.
分类: 天文学 >> 天文仪器与技术 提交时间: 2025-04-24 合作期刊: 《Astronomical Techniques and Instruments》
摘要: A detector's nondestructive readout mode allows its pixels to be read multiple times during integration, enabling generation of a series of "up-the-ramp" images that continuously accumulate photons between successive frames. Because noise is correlated across these images, optimal stacking generally requires the images to be weighted unequally to achieve the best possible target signal-to-noise ratio (SNR). Objects in the sky present wildly varied brightness characteristics, and the counts in individual pixels of the same object can also span wide ranges. Therefore, a single set of weights cannot be optimal in all cases. To ensure that the stacked image is easily calibratable, we apply the same weight to all pixels within the same frame. In practice, results for high-SNR cases degraded only slightly when we used weights derived for low-SNR cases, whereas the low-SNR cases remained more sensitive to the weights. Therefore, we propose a quasi-optimal stacking method that maximizes the stacked SNR for the case where the RSN=1 per pixel in the last frame and use simulated data to demonstrate that this approach enhances the SNR more strongly than the equal-weight stacking and ramp fitting methods. Furthermore, we estimate the improvements in the limiting magnitudes for the China Space Station Telescope using the proposed method. When compared with the conventional readout mode, which is equivalent to selecting the last frame from the nondestructive readout, stacking 30 up-the-ramp images can improve the limiting magnitude by approximately 0.5 mag for the telescope's near-infrared observations, effectively reducing readout noise by approximately 62%.
分类: 地球科学 >> 地质学 提交时间: 2018-04-04 合作期刊: 《古脊椎动物学报》
摘要: Tooth reduction and loss was an important evolutionary process in Mesozoic birds. Analysis of evolutionary trends in the total mass of the dentition, a function of tooth size and tooth number, has the potential to shed light on the evolutionary pattern of tooth reduction and loss, and on the causes of this pattern. Because modern birds lack teeth, however, they cannot provide the basis for a model that would allow estimation of tooth masses in their Mesozoic counterparts. We selected the teeth of crocodilians as analogues of those in Mesozoic birds because the former are the closest living relatives of the latter, and the two groups are similar in tooth morphology, tooth implantation, and tooth replacement pattern. To estimate tooth masses in Mesozoic birds, we formulated four regression equations relating tooth mass to various linear dimensions, which were measured in 31 intact isolated teeth from eight individual crocodiles (Crocodylus siamensis). The results for Mesozoic birds show that dental mass as a proportion of body mass was negligible, at least from the perspective of flight performance, suggesting that selection pressure favoring body mass reduction was probably not the primary driver of tooth reduction or loss. Variations in dental mass among Mesozoic birds may reflect the different foods they ate, and the different types of feeding behavior they displayed.
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: The functionalization of multi-walled carbon nanotubes (MWCNTs) by ozone treatment has been sys- tematically investigated by using Raman spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), organic elemental anal- ysis (OEA) and Boehm titration. The results showed that the functionalization process occurred at defective sites (opened mouths, tube caps, debris, etc.) before opening caps and truncating walls, and finally the graphitic structure was deteriorated. The surface oxygen content first increased with the treatment time but kept at around 8.0 wt% after 5 h. The analysis of the distribution of oxygen-containing groups re- vealed that phenolic hydroxyl was gradually converted to carboxyl and lactone. The carboxyl was found to play a pivotal role to reduce the over-potentials when we used the functionalized MWCNTs as the cat- alyst for oxygen reduction reaction (ORR).
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Most materials can be easily corroded or ineffective in carbonaceous atmospheres at high temperatures in the reactor core of the high temperature gas-cooled reactor (HTGR). To solve the problem, a material performance test apparatus was built to provide reliable materials and technical support for relevant experiments of the HTGR. The apparatus uses a center high-purity graphite heater and surrounding thermal insulating layers made of carbon fiber felt to form a strong carbon reducing atmosphere inside the apparatus. Specially designed tungsten rhenium thermocouples which can endure high temperatures in carbonaceous atmospheres are used to control the temperature field. A typical experimental process was analyzed in the paper, which lasted 76 hours including seven stages. Experimental results showed the test apparatus could completely simulate the carbon reduction atmosphere and high temperature environment the same as that confronted in the real reactor and the performance of screened materials had been successfully tested and verified. Test temperature in the apparatus could be elevated up to 1600篊, which covered the whole temperature range of the normal operation and accident condition of HTGR and could fully meet the test requirements of materials used in the reactor.
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: 2017-11-02 合作期刊: 《热科学学报》
摘要: As one of the key units of space CCD camera, the temperature range and stability of CCD components affect the image's indexes. Reasonable thermal design and robust thermal control devices are needed. One kind of temperature control loop heat pipe (TCLHP) is designed, which highly meets the thermal control requirements of CCD components. In order to study the dynamic behaviors of heat and mass transfer of TCLHP, particularly in the orbital flight case, a transient numerical model is developed by using the well-established empirical correlations for flow models within three dimensional thermal modeling. The temperature control principle and details of mathematical model are presented. The model is used to study operating state, flow and heat characteristics based upon the analyses of variations of temperature, pressure and quality under different operating modes and external heat flux variations. The results indicate that TCLHP can satisfy the thermal control requirements of CCD components well, and always ensure good temperature stability and uniformity. By comparison between flight data and simulated results, it is found that the model is to be accurate to within 1 degrees C. The model can be better used for predicting and understanding the transient performance of TCLHP.
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The reduction stripping behavior of Pu(IV) from 30%TBP/OK with hydroxysemicarbazide (HSC) was investigated, and the separation efficiency of HSC and DMHAN-MMH for U/Pu partitioning in Purex process was compared. The results show that HSC can effectively realize the separation of Pu from U; using mixer-settlers to simulate U/Pu separation in 1B bank of PUREX, from 16-stage counter current extraction experiment (in which 6 stages for supplemental extraction, 10 stages for stripping) with flow rate ratio (1BF:1BX:1BS) =4:1:1 in 1B contactor, good result was achieved that the yields are both more than 99.99% for uranium and Pu, the separation factor of plutonium from uranium (SFPu/U) is 2.8�104, and separation factor of uranium from plutonium (SFU/Pu) is 5.9�104. As a stripping reductant, HSC can effectively achieve the separation of Pu from U and the separation effect is nearly the same with DMHAN-MMH, which contributed to replace enough the latter with HSC in the U/Pu separation in Advanced Purex Process Based on Organic Reagent (APOR) process.
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: This paper presents the mitigation effects of fission product reduction strategies that can be applied to severe accident management for CANDU6 plants. Strategy effects for 'control of the reactor building condition and 'reduction of the fission product release have been evaluated. The operations of a dousing spray system, local air cooler system, and containment filtered vent system are simulated as severe accident management strategies. The present analysis is mainly focused on determining an estimate of the fission products in the release and transport processes, i.e., (1) their release from the reactor core, (2) their distribution in a primary heat transport system, calandria vessel, molten corium, and reactor building, and (3) their release from the reactor building into the environment during a severe accident.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2018-03-30
摘要: Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORR). Here, we have designed novel reduced graphene oxides (rGO) supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole(Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V, a half-wave potential of 0.81 V in alkaline solutions, which is much better than that of the counterpart N-C and N-C/rGO catalysts, and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR perfomance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (Fe3O4, Fe4C) and Fe-Nx sites, as well as fast mass transfer and accessible active sites benefitting from the mesporous structure and high specific surface area. This work provides new insight for synthesis of a more promising non-platinum electrocatalyst for metal-air batteries and fuel-cell applications.
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-05-09
摘要: Perylene tetracarboxylic anhydride (PTCDA) was reacted with 6-aminocaproic acid to form the corresponding perylene bisimide (PBI). PBI was used as the foundation for oligomerisation of glycidol in a ring-opening reaction of glycidol leading to a hyper branched, water-soluble glycidol derivative of perylene (PBI-HPG). PBI-HPG was bound to the reduced graphene oxide via p–p stacking resulting in a compound termed PBI-HPG/RGO. The structure and morphology of PBI-HPG/RGO were investigated by infrared spectroscopy (FT-IR), wide angle X-ray diffractometry (WAXD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). PBI- HPG/RGO was blended at different loadings in order to improve the thermal and mechanical properties of epoxy composites. The maximum Tg of the epoxy composites was about 20 C and the decomposition temperature (Td) was 26 C higher than that of neat epoxy. The incorporation of PBI- HPG/RGO yields a material with an impact strength of 39.6 kJ m 2 and a tensile strength at 0.7 wt%. It increased by 50.8% and 62.3%, respectively, compared to the neat epoxy.
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: 2017-08-15
摘要: Great effort is made to maximize the surface area and expose active sites of a catalyst by distributing it over a suitable electronic conducting support. We present a design and eco-friendly construction of a two-dimensional Pt/SnO2/reduced-graphene-oxide (rGO) nanocomposite to study the strong metal-semiconductor-support interactions as candidate highly active and durable electrocatalyst. Distinctively, highly reactive SnOx nanoparticles (NPs) induced by laser ablation in liquids were used as a precursor to transform the graphene oxide (GO). Simultaneously, the initial amorphous-like SnOx further crystallized into SnO2 NPs, which were uniformly anchored onto rGO sheets. Afterward, the photo-excited electrons from semiconductor SnO2 were used as green reducing agents. Ultrafine Pt NPs with an average size of about 1–2 nm were in situ reduced and uniformly anchored on the surface of crystallized SnO2 NPs. Compared with the Pt/rGO catalysts without SnO2 modification, the prepared Pt/SnO2/rGO catalysts not only show larger electrochemical active surface area and higher catalytic activity toward methanol oxidation but also exhibit better tolerance toward CO and long-term cycle stability. The significantly enhanced electrochemical performance should be attributed to the uniformly dispersed Pt NPs with ultrafine size and the synergetic effect from the hybrid noble metal-semiconductor-carbon network components, which possess promising potential applications as electrocatalysts for methanol oxidation.
提交时间: 2017-05-02
摘要: As reported, the foaming of layered graphene films into porous graphene foams could improve their performance for absorbents, catalysis and supercapacitors. Herein, to emphasize the impact of porous structure on electromagnetic interference [EMI] shieldin
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: 2017-04-06
摘要: A series of La1-xBaxCoO3(x = 0, 0.1, 0.2, 0.3) perovskites were synthesized by the modified sol-gel method, and their activities for NO oxidation were investigated as well. The relevant structural characterizations of the prepared catalysts were conducted
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-03-30
摘要: A series of La1-xBaxCoO3(x = 0, 0.1, 0.2, 0.3) perovskites were synthesized by the modified sol-gel method, and their activities for NO oxidation were investigated as well. The relevant structural characterizations of the prepared catalysts were conducted
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-03-30
摘要: A series of La1-xBaxCoO3(x = 0, 0.1, 0.2, 0.3) perovskites were synthesized by the modified sol-gel method, and their activities for NO oxidation were investigated as well. The relevant structural characterizations of the prepared catalysts were conducted
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: 2017-04-06
摘要: A structure of hexadecyl trimethyl ammonium bromide (CTAB) micelle-assisted reduced graphene oxide-Ag nanoparticle (rGO-AgNP) hybrids is designed and fabricated for SERS detection of nonpolar polycyclic aromatic hydrocarbons (PAHs), in which CTAB micelles
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-16
摘要: We calculate the one-loop QCD corrections to t-->(t) over tilde(1)(0)(j) using the dimensional reduction scheme, including QCD and supersymmetric QCD corrections. The analytic expressions for the corrections to the decay width are given, which can easily be extended to t-->(+)(j)(b) over tilde(i). The numerical results show that the correction amounts to more than a 10% reduction in the partial width relative to the tree level result. We also compare the corrections in the no-mixing top squark case with those in the mixing top squark case.