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Folding of a single polymer chain and phase transition

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Chinese Science Bulletin 2009年第11期54卷 1908-1911页

作者： DING yanwei zhang GuangZhao Hefei National Laboratory for Physical Sciences at the Microscale Department of Chemical Physics University of Science andTechnology of China Hefei 230026 China

Using an ultra-sensitive differential scanning calorimetry (US-DSC), we have investigated the folding and aggregation behaviors of poly(N-isopropylacrylamide) (PNIPAM) chains in dilute and semidilute solutions. In the heating process, the intrachain folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases with decreasing concentra-tion. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an ex-tremely dilute solution, PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration to zero, we have obtained the phase transition tempera-ture (TS) and enthalpy change (△HS) of the single chain folding. △HS is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single chain fold-ing can not be taken to be a macroscopic phase transition.

关键词：高分子链相变温度折叠法 PNIPAM 异丙基丙烯酰胺聚集行为差示扫描量热加热过程

Impact of typhoon Lekima(2019)on material transport in Laizhou Bay using Lagrangian coherent structures

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Journal of Oceanology and Limnology 2022年第3期40卷 922-933页

作者： Qi LOU Zhengyan LI yanwei zhang Yilei FENG Xueqing zhang College of Oceanic and Atmospheric Sciences Ocean University of ChinaQingdao 266100China Key Laboratory of Marine Science and Numerical Modeling Ministry of Natural Resources(MNR)Qingdao 266061China

Typhoon has an impact on an estuary and coastal ***,the present research lacks the detailed description of material transport processes during typhoon passage,such as the transport channels and barriers in the course of material transport and material accumulation area,***,Lagrangian coherent structures(a method developed for describing the transport structure of fluids in recent years)was introduced to investigate and predict the floating material and debris transport process in the Laizhou Bay,Bohai Sea,during typhoon Lekima in *** show that the Lagrangian coherent structure could well explain the complex flow phenomena in the *** the typhoon,the general direction of floating material transport in the Laizhou Bay was *** was a channel for material transport in the northwest and south of the bay,and there are transportation obstacles in the northeast-southwest direction in the middle of the ***,the typhoon might worsen the water *** results provide references for precise countermeasures to control the formulation of pollution in the Laizhou Bay.

关键词： material transport typhoon Lagrangian coherent structures Laizhou Bay

Records of the tsunami induced by the 2010 Chilean earthquake from Xiaoqushan seafloor observatory in the East China Sea

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Chinese Science Bulletin 2011年第27期56卷 2957-2965页

作者： zhang yanwei FAN DaiDu XU HuiPing State Key Laboratory of Marine Geology Tongji University Shanghai 200092 China

Sea-level variation can be induced by periodic tides, stochastic wind, air pressure, and swell. Larger sea-level variation has the potential to cause coastal disasters. In this paper, real-time continuous data obtained by the Xiaoqushan seafloor observatory in the East China Sea were analyzed employing frequency power spectral and tidal harmonic methods to extract the major components and periodicities of sea-level change. The sea-level anomaly (sla) was calculated by subtracting the tidal components from the observed sea level data. In the study period, the correlation between sla and the local north-south wind speed was high with a correlation coefficient of 0.65 at the 95% confidence level. The local wind-induced sea-level anomaly (sla wind ) was therefore computed through linear fitting. Although sla wind is one of the main components of sla, the residual sea-level anomaly (sla residual ) obtained by subtracting sla wind from sla is not zero, suggesting that there are other factors besides wind. Detailed analysis of the sea-level data at the time of the 8.8-magnitude Chilean earthquake on February 27, 2010 showed a peak sla residual value of 0.48 m at around 15:00 on February 28, which was highly coincident with the tsunami arrival time forecast by the Pacific Tsunami Warning Center. The peak sla residual event is therefore linked with the tsunami induced by the 2010 Chilean earthquake. This is the first time that a tsunami has been detected using real-time continuous data recorded by a seafloor observatory in the sea off China. Such observations are expected to improve tsunami forecast models and promote the development of a tsunami warning system and a seafloor observatory network in the East China Sea.

关键词：海啸预警系统海底观测站中国东海天文台地震智利海平面变化 SLA

Seasonal variability of tides in the deep northern South China Sea

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Science China Earth Sciences 2019年第4期62卷 671-683页

作者： Jiuqiang ZHAO yanwei zhang Zhifei LIU Yulong ZHAO Meng WANG State Key Laboratory of Marine Geology Tongji University

Tides are the major energy source for ocean mixing, regulating the variation of oceanic circulation and sediment transport in the deep sea. Here twenty months of high-resolution current profiles, which were observed via a mooring system at a water depth of 2100 m in the northern South China Sea(SCS), are used to investigate seasonal variability in deep-sea *** analysis shows that tides in this region are dominated by diurnal tide, and both diurnal and semidiurnal tide are vertical mode-1 dominant. Baroclinic diurnal tidal current exhibits pronounced seasonal variability, showing its kinetic energy was the strongest in summer, and the maximum depth-averaged value was up to 86.7 cm^2 s^(-2), which was about 1.5 times of that in winter and twice that in spring and autumn. In contrast, baroclinic semidiurnal tide displays no evident seasonal variability. Such seasonal variability in baroclinic tide was mainly modulated by the barotropic forcing from the Luzon Strait. On the other hand,two anticyclonic eddies and one cyclonic eddy, which originated off southwestern Taiwan in winter, crossed the mooring *** cyclonic eddy had weak impact on current velocity in the deep sea, but the two deep-reaching anticyclonic eddies enhanced the current velocity through the full-water column by inducing strong subinertial flows. Consequently, the kinetic energy of tides was strengthened and the incoherent variance of baroclinic diurnal tide increased in winter, which contributed ～85% of the variability in diurnal tide. Meanwhile, the velocity of baroclinic diurnal tide was reduced in winter, which was attributed to the weakened stratification induced by the passage of anticyclonic eddies in the deep sea. The seasonal variability of tides in the deep northern SCS can provide a dynamic mechanism for interpreting sediment transport processes in the deep sea on different time scales.

关键词： Tides Seasonal variability Subinertial current Mesoscale eddy Deep northern South China Sea

Temporal and spatial evolution of a deep-reaching anticyclonic eddy in the South China Sea

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Science China Earth Sciences 2019年第6期62卷 1002-1023页

作者： Meng WANG yanwei zhang Zhifei LIU Yulong ZHAO Jianru LI State Key Laboratory of Marine Geology Tongji University

The temporal and spatial evolution of a deep-reaching anticyclonic eddy(AE) is studied using a combination of satellite measurements, moored observations and ocean model reanalysis data in the South China Sea(SCS). Three evolutionary stages in eddy's lifecycle are identified from changes in eddy dynamical characteristics estimated from satellite altimetry: birth(22 days), growth(64 days), and decay(47 days). Similar patterns are also distinguished from dynamic signals in ***, flows reversal and upwelling of cold water below 1500 m were captured by the in-situ records when this energetic,highly nonlinear and long-lived(over 19 weeks) AE passed by our mooring position. Its detailed vertical structure is examined through temperature anomalies, vertical shear of horizontal velocities, and horizontal streamlines estimated from ocean model reanalysis data. Results from the model reveal a mesoscale AE with first-mode baroclinic structure: a bowl-shaped anticyclonic flow in the upper ocean connected to a slant-cylinder cyclonic flow at depth, with a transition layer at depths between 400 and 700 m. It is in good agreement with moored observations but showing a shallower transition depth, suggesting a slight deficiency in the model due to limited deep-sea observations. Last, we estimate eddy heat transport at different depths and stages along the AE's path based on the model data. The result reveals that pronounced heat fluxes occur during growth stage(depths 700–1500 m).Dynamical characteristics suggest that the vertical structure and temporal evolution of the eddy play significant roles in basinscale movement and heat transferring. Considering that mesoscale eddies are ubiquitous in the SCS, our results support a recently-proposed mechanism, whereby upper ocean flows produce changes in the deep-sea circulation, potentially influencing boundary l

关键词： Deep-reaching mesoscale eddy Evolution HYCOM The South China Sea

Oxygen-vacancy-anchoring Ni_(x)O_(y) loading towards efficient hydrogen evolution via photo-thermal coupling reaction

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Journal of Energy Chemistry 2021年第10期30卷 77-87,I0003页

作者： Qiliang Wu Zheng Li Xuhan zhang Chenyu Xu Mingjiang Ni Kefa Cen yanwei zhang State Key Laboratory of Clean Energy Utilization Zhejiang UniversityHangzhou 310027ZhejiangChina Department of Chemical and Materials Engineering University of AlbertaEdmonton ABT6G 1H9Canada

Oxygen vacancy(Vo)is a significant component in defect *** present work reports the anchoring effects of initial Vo for further loading modifications and the reducing capacity of photoinduced Vo for pure water ***,we propose Ni-loaded Cu-doped TiO_(2)(NCT)materials by successive doping and *** continuously added Ni ions should accumulate around the Vos and gradually grow into complete nickel oxide crystals,achieving a higher average valence state of the Ni *** crystals can be detected on a 0.5%NCT sample,while the structure of Ni_(2)O_(3) has been confirmed with a higher nickel mass ***,the introduction of nickel oxide effectively improves the photochemical and electrochemical performance by the interface charge separation,finally reaching an H2 yield of 30.6 pmol/g-cat on 0.5%NCT for Vo-based photo-thermal coupling reaction,which consists of Vo generation in photo and Vo consumption in thermal *** situ infrared spectroscopy further indicated that the presence of high valence state nickel oxide hindered the H2 formation but effectively promoted the conventional oxidizing reaction,with an H2 yield of 20.6 mmol/g-cat in a methanol-water reaction on the 2.0%NCT *** summary,Vo controls the morphological structure of Ni loading and produces diverse effects for reactions with dissimilar mechanisms,which provides a novel way to design modifications for promoting various chemical reactions.

关键词： Oxygen vacancy Nickel oxide Water splitting Photo-thermal coupling reaction DFT calculation

Pitfalls of acid leaching method for determining organic and inorganic carbon contents in marine sediments

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Acta Oceanologica Sinica 2020年第8期39卷 96-102页

作者： Chen Ling Zhifei Liu Jingwen zhang Yulong Zhao yanwei zhang Adrian RFernandez State Key Laboratory of Marine Geology Tongji UniversityShanghai 200092China

Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments.

关键词： marine sediments organic carbon inorganic carbon acid leaching method limitation

Self-supporting hierarchically micro/nano-porous Ni_(3)P-Co_(2)P-based film with high hydrophilicity for efficient hydrogen production

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Journal of Materials Science & Technology 2021年第6期65卷 118-125页

作者： Xiangtao Yu Xiangyu Ren yanwei zhang zhangfu Yuan Zhuyin Sui Mingyong Wang Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083China School of Chemistry&Chemical Engineering Yantai UniversityYantai 264005China State Key Laboratory of Advanced Metallurgy University of Science and Technology BeijingBeijing 100083China

Designing efficient and stable non-precious metal HER(hydrogen evolution reaction)electrocatalysts with high large current density adaptability is significant for industrial application of hydrogen production by water ***,a facile strategy was developed to construct a multi-phase Ni3 P-Co_(2)P-(Ni-Co)film with self-supporting hierarchically micro/nano-porous structure by using bubble template method electrodeposition of self-supporting micro-porous Ni Co P film,oxygen-free annealing for phase separation producing Ni_(3)P-Ni-Co_(2)P-Co structure,and acid etching for constructing surface nano-porous *** effective active sites for HER was significantly increased due to the hierarchically micro/nano-porous structure,which not only enlarged the surface roughness,but enhanced the bubble detachment by improving the ***,the HER electrolysis durability was improved benefiting from the Ni_(3)P-Co_(2)P phases with high corrosion resistance(especially in acid solution)and the self-supporting film structure without ***,the Ni Co P-OA-AE film exhibited high HER catalytic performance,which delivered a current density of 10 m A cm^(-2)at a low overpotential of 42.9 and 39.7 m V in 1 M KOH and 0.5 M H_(2)SO_(4),*** also possessed high long-term electrolysis durability,and the cell voltage of water electrolysis using self-supporting porous Ni Co P-OA-AE||Ir O_(2)-Ta_(2)O_(5) electrolyzer at 500 m A cm^(-2)for 250 h in 0.5 M H_(2)SO_(4 )is only 2.9 V.

关键词： Self-supporting Micro/nano-porous film High hydrophilicity Bubble detachment High HER(hydrogen evolution reaction) catalytic performance

Observations of marine snow and fecal pellets in a sediment trap mooring in the northern South China Sea

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Acta Oceanologica Sinica 2020年第3期39卷 141-147页

作者： Meng Gao Baoqi Huang Zhifei Liu Yulong Zhao yanwei zhang School of Earth and Space Sciences Peking UniversityBeijing 100871China State Key Laboratory of Marine Geology Tongji UniversityShanghai 200092China

Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern South China Sea(20.05°N, 117.42°E) at a water depth of 2 100 m and equipped with two sediment traps deployed at 500 m and 1 950 m. Samples were collected at 18-day intervals, and 20 samples were obtained at both depths from May 2014 to May 2015. Large amounts of fecal matter and marine snow were collected in the lower trap. The fluxes of marine snow and fecal pellets exhibited a fluctuating decrease between May 2014 and early August 2014 and then stabilized at a relatively low level. Scanning electron microscopy observations revealed that the main components of the marine snow and fecal pellets were diatoms, coccolithophores, radiolarians, and other debris, all of which are planktons mostly produced in photic zone. Used in conjunction with the particle collection range estimates from the lower trap and data on ocean surface chlorophyll, these marine snow and fecal pellets were related to the lateral transport of deep water and not vertical migrations from overlying water column. Moreover, the source area might be southwest of Taiwan.

关键词： northern South China Sea sediment trap marine snow fecal pellets