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This study presents the experimental results of the flow characteristics, such as the flow adjustment, velocity profiles, mixing layer, and the momentum exchange, in the partially vegetated channel with homogeneous and heterogeneous layouts. Three cases are considered, including two homogeneous canopies with uniform sparse and dense vegetation patches respectively, and a heterogeneous canopy consisting of alternating patches of both densities. Results show that heterogeneous canopy requires a longer adjustment distance to reach the quasi-equilibrium region, compared with the homogenous canopy of the same density. In heterogeneous canopy flow, the mixing layer width and the momentum thickness fluctuates with the alternation of vegetation density. The increased values for these two parameters compared to those values for the homogeneous canopies indicate that the greater resistance and momentum loss occur for the heterogeneous layout. A wavy region of the enhanced in-plane turbulence kinetic energy (TKE) is observed in the heterogeneous canopy, suggesting a comparatively more chaotic flow condition, whereas the contours of in-plane TKE are smooth in homogeneous canopies. The presence of the coherent structures in heterogeneous canopy is identified by spectral analysis and the quasi-periodic fluctuations of velocities. The Reynolds stress associated with the coherent structures is found to be the dominator of the contribution to the total Reynolds stress. The comparison between the homogenous canopies of different density is also conducted. These results will be of practical importance for the design of vegetation layouts in water ecological restoration projects and for river management.

Secondary growth of the woody tree stem is governed by meristematic cell division and differentiation in the vascular cambium. Multiple hormonal signals and endogenous developmental programs regulate vascular cambium activity. Brassinosteroids (BRs) significantly promote secondary stem growth and wood formation in poplar trees. However, the underlying regulatory mechanisms of BRs within the vascular tissue remain unclear. Genetic and anatomical approaches were used here to elucidate the role of PagDET2, the rate-limiting enzyme for BRs biosynthesis, in regulating secondary vascular cambium activity in Populus. This study showed that the elevated endogenous castasterone (CS) levels in tree stems through overexpressing PagDET2 could enhance cambium meristem cell activity and xylem (XY) differentiation to promote secondary stem growth. RNA-seq analysis revealed that genes involved in BRs response, vascular cambium cell division, XY differentiation, and secondary cell wall synthesis were up-regulated.

The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river. So far, few studies have been conducted to investigate the suspended sediment transport capacity in the vegetated sediment-laden flow. In this study, a new formula is derived to predict the sediment transport capacity in a vegetated flow by considering the absolute value of the energy loss between the sediment-laden flow and the clear water flow. Finally, the formula is expressed in a practical form by using the logarithmic matching method.

ABA triblock copolymer nanoparticles of poly(2-hydroxypropyl methacrylate)-block-polystyrene-block-poly(2-hydroxypropyl methacrylate) (PHPMA-b-PS-b-PHPMA) with a hydrophobic core of the polystyrene (PS) block and a hydrophilic corona of the poly(2-hydroxypropyl methacrylate) (PHPMA) block were synthesized by dispersion RAFT polymerization. It is found that the particle diameter of the PHPMA-b-PS-b-PHPMA nanoparticles increases with the chain extension of the PS block and decreases with the increasing degree of polymerization (DP) of the PHPMA block. In comparison with the poly(2-hydroxypropyl methacrylate)-block-polystyrene (PHPMA-b-PS) diblock copolymer nanoparticles with a similar chemical composition, the PHPMA-b-PS-b-PHPMA nanoparticles have a larger diameter, and the chain density of the PHPMA chains tethered to the PS core is higher. It is found that the PHPMA-b-PS-b-PHPMA nanoparticles can decrease the n-hexane/water interfacial tension more than the PHPMA-b-PS nanoparticles and may act as an efficient emulsifier.

Parylene C (PC) films have been widely used in many fields, such as metal anti-corrosion, electronic packaging, etc. However, the relatively poor mechanical properties and the deteriorated water barrier performance due to the easy fracture under external stress have restricted their application. It is a relatively simple and good method to maintain the water vapor barrier and enhance the mechanical properties of PC film by covering a flexible coating on its surface. In this work, a new polyurethane acrylate (PUA) coating was prepared and coated on the PC film by ultraviolet curing technology to form the PC/PUA composite film. The results showed that the PUA coatings could improve the water vapor barrier and mechanical properties of the PC film simultaneously. The water vapor transmittance rate was reduced from 1.1791 g·(m−2·day−1) of the original PC film to 0.5636 g·(m−2·day−1) of the PC/PUA composite film. The elongation at break and the impact energy were increased to 48.36% and 41.67%, respectively, which would widen the application of PC films in the fields of flexible electronics or smart wear.

In this work, nanopalladium catalysts supported on the surface of reduced graphene oxide (rGO/Pd) with different palladium loadings have been prepared by one-step reduction in aqueous phase. They were mixed with 1,4-bis(phenylethynyl)benzene (DEB) to form rGO/Pd-DEB composites according to a mass ratio of 1:3. It was shown that nanopalladium particles with particle size of about 2–6 nm were disperse uniformly on the surface of rGO when the Pd loadings were in the range of 3.97–10.60 wt%. The maximum hydrogen uptake capacity of rGO/Pd-DEB composites at 25 °C determined according to PCT method was about 182.5 ml/g after reacted with hydrogen for about 20 h, which was some lower than that of the common Pd/C-DEB pallet getter (216 ml/g) but significantly higher than alkynyl modified polyvinyl alcohol supported palladium hydrogen absorbing materials (0.32 ml/g), indicating that rGO/Pd could be used in solid phase catalytic hydrogenation due to the high dispersion of palladium nanoparticles and the physical proximity of rGO/Pd catalyst with DEB organic molecules. This provides a good potential technical way for perparing the moldable carbon aerogel hydrogen absorption materials.

This study presents results from laboratory experiments to investigate the wake structure in the lee side of a scaled three-bladed horizontal axis tidal stream turbine with a mono-pile support structure. Experiments are conducted for a range of approaching flow velocity and installation height of rotor. Analysis of the results shows that bed shear stress increases with the increase of approaching velocity and decrease of installation height within 2D (D is the diameter of the rotor) downstream of the rotor. The flow field within 2D downstream of the rotor is greatly influenced by the presence of nacelle and mono-pile. Low stream-wise flow velocity and large turbulence intensity level is detected along the flume center right behind the nacelle and mono-pile from 1D to 2D downstream of the rotor. Stream-wise velocity at the blade tip height lower than the nacelle increases sharply from 1D to 2D and gradually grows afterwards. Correspondingly, the turbulence intensity decreases quickly from 1D to 2D and slowly afterwards. Large bed shear stress is measured from 1D to 2D, which is closely related to turbulence induced by the mono-pile. It is also found that the presence of the mono-pile might make the flow field more ‘disc-shaped’.

Hydrogen isotope behavior in tungsten coated on reduced activation ferritic/martensitic (RAFM) steels such as China low activation martensitic (CLAM) steel has attracted more attention in the fusio...

This study experimentally investigated the impacts of rough and porous (RP) bed and sedimentation processes on the coherent structures, turbulence intermittency, and anisotropy of saline and turbidity currents. The results reveal that the local current concentration responds immediately (saline current) or languidly (turbidity current) to turbulence bursting events. Inside the dense current, the turbulent momentum fluxes in the streamwise ([Formula: see text]) and vertical ([Formula: see text]) directions transfer downstream and downward, which favor the sweep events. Inside the ambient water, [Formula: see text] and [Formula: see text] transfer upstream and upward, contributing to the formation of ejection events. At the current–ambient water interface, [Formula: see text] and [Formula: see text] do not tend to transfer in particular directions resulting in almost equal quantities of sweep and ejection events. The Gram–Charlier series expansion is strictly applicable to probability density functions (PDFs) of the sweep and ejection events but not suitable ideally for PDFs of the outward and inward interaction events. The primary anisotropy invariant map (AIM) of gravity currents starts from the two-component plain strain limit (near the bed). It is followed by the three-dimensional isotropy (inside the dense current and ambient water) and the axisymmetric contraction limit (current–ambient water interface). Finally, it ends in two-dimensional isotropy (near the free surface). This AIM is sensitive to the RP boundary and the sedimentation processes. Along the streamwise direction, the RP boundary causes alternations between the anisotropic and isotropic turbulence, but the arranged pattern of the rough units determines the period of this alternation.

Solutions for dam-break flow mainly developed for rectangular channels are not applicable to prediction of the propagation of the dam-break wave in frictional triangular channels. This stud...

Waves and currents coexist widely in the ocean, and the interaction of waves and currents plays an important role in the instability of submarine pipelines. So far, most studies have concentrated on discussing the dynamic reaction within the seabed around a pipeline under pure wave action, monotypic sediment, and an exposed or fully buried condition. In this study, the effect of current characteristics (e.g., current velocity and propagation direction) and backfilling conditions (e.g., backfill depth and sand property) on the dynamic response around the submarine pipeline is investigated by conducting laboratory experiments. Pipeline was buried in the excavated trench using three types of sand with the median size of 0.150 mm, 0.300 mm and 0.045 mm, respectively. Five relative backfilled depths, with the ratios of backfill depth over the pipeline diameter being 0, 1/2, 1, 3/2 and 2, were tested. The excess pore pressure was measured simultaneously by using the pore pressure sensors installed around the pipeline surface and beneath the pipeline. Results show that both the pore pressure amplitude and its descent rate gradually decrease with an increasing backfill depth, which decreases the soil liquefaction potential. Under the co-current actions, the decrease rate of the pore pressure along the vertical direction increases with an increasing current velocity. However, the increased current velocity leads to a decrease of the attenuation rate under the counter-current actions compared with the pure wave actions, and the counter-current effect on the pore pressure within the seabed is greater than the co-current. The results indicate that the dynamic response around the pipeline in coarse sand is close to that without the backfill scenario, even if the backfill depth reaches up to two times that of the pipeline diameter. It is found that the larger the median particle size of backfill sand, the smaller the impact on pore pressure within the seabed beneath the pipeline.

The instability of soil slopes is directly related to the shear parameters of the soil material and groundwater, which usually causes some uncertainty. In this study, a novel method, the e...

We report high-performance star brush block copolymer electrolytes (SBBCEs) composed of 2-arm star polymer of [poly[poly(ethylene glycol) methyl ether acrylate]-b-polystyrene]2. The physically cros...

Aquatic vegetation can significantly affect flow structure, sediment transport, bed scour and water quality in rivers, lakes, reservoirs and open channels. In this study, the lattice Boltzmann method is applied for performing the two dimensional numerical simulation of the flow structure in a flume with rigid vegetation. A multi-relaxation time model is applied to improve the stability of the numerical scheme for flow with high Reynolds number. The vegetation induced drag force is added in lattice Boltzmann equation model with the algorithm of multi-relaxation time in order to improve the simulation accuracy. Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments. Analysis of the simulated and experimentally measured flow field shows that the numerical simulation can satisfactorily reproduce the laboratory experiments, indicating that the proposed lattice Boltzmann model has high accuracy for simulating flow-vegetation interaction in open channel.

Due to the randomness and variability of parameters, reliability analysis of rock slopes generally contains multiple failure modes. This reliability problem cannot be effectively treated by traditional methods, such as limit equilibrium method (LEM) and finite element method (FEM). A numerical method for performing reliability analysis of rock slope is proposed by combining the plastic limit analysis theory, rigid finite element discretization, mathematical programming theory and Monte Carlo method. The rock slope is discretized into rock blocks and interfaces using rigid finite elements to establish static admissible stress fields and kinematically admissible velocity fields for the rock slope. Additionally, stochastic programming models for performing reliability analysis of rock slopes are established according to the lower and upper bound theorems by setting the shear strength parameters of the interfaces to random variables. A numerical solution strategy is then proposed for stochastic programming models based on the Monte Carlo method at the same time. Finally, an estimation method for the failure probability of element is proposed based on the velocity fields. The proposed method is validated, and it has high precision and efficiency.

A depth-averaged two-dimensional (2D) numerical model was developed to investigate hydrodynamics in estuaries. The Qiantang estuary is taken as a demonstrative case study. The Qiantang estuary is famous for its macro tide during the spring tide and the Qiantang bore, which poses a challenging task for accurate simulation. In this study, the model was setup to simulate the tidal elevations and the tidal velocity field in the Qiantang estuary. A mesh sensitivity analysis was carried out to optimise the mesh arrangement to achieve computational efficiency while retaining computational accuracy. The simulation results showed that, in general, the numerical simulation agreed well with the field observations, indicating that the developed 2D model can be applied to calculate hydrodynamics in a macro tidal estuary. Some deviation between the simulation and measurements at some locations exists and this discrepancy is analysed and discussed.

Laboratory experiments are presented to investigate the effect of different piggyback pipeline configurations on the morphology of local scour under wave conditions. Scour depth and width around the pipelines under regular and irregular waves are measured and analyzed for a range of pipeline and wave conditions; such as the spacing between two pipes (G), gap between the main pipe and seabed (e), pipe diameter (D), wave height (H) and period (T). Experimental results reveal that both the scour depth and width around piggyback pipeline is much larger than those around single pipe under the same wave conditions. Scour depth increases with the increase of the Keulegan-Carpenter (KC) number and decreases with increase of G and e. When e exceeds 0.5D, scour depth tends to approach 0. When spacing G is greater than 0.4D, the destabilization from small pipe to large one is greatly reduced, resulting in scour depth around piggyback pipeline being close to that around single pipe. Similar to scour depth, scour width broadens with the increase of KC number increasing and decreases with the increase of G. Experiments also show that the effect of e on scour depth is greater than that of G under the same test conditions, while their impact on scour width is opposite. Furthermore, scour width under irregular waves is extended slightly compared with regular wave for otherwise the identical conditions.

This paper presents the results of laboratory experiments and numerical simulations to investigate the effect of different piggyback pipeline configuration on the morphology of local seabed scour subject to steady currents. Piggyback pipeline configuration investigated includes the commonly used piggyback pipeline, namely a small pipe attached on the top of large pipe and new form of piggyback pipeline proposed in this study in which a small pipe is attached to the large pipe on the upstream and downstream side, respectively. Pressure gradient, drag coefficient, lift coefficient and scour extent around pipelines are measured and analyzed for a range of pipelines and current conditions. Results show that the vortex strength downstream of the commonly used piggyback pipeline is larger than that for a single as well as the new piggyback pipeline under the same condition. This new type piggyback pipeline can effectively reduce the depth and width of the scour hole. In particular, when the ratio of the small pipe diameter over the large pipe diameter is greater than 0.3, little scour under this new type piggyback pipeline occurs for the test conditions. The bed topography downstream of the pipe has also been altered to favor the backfill.

Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structural materials for a fusion reactor. In this paper, the hydrogen diffusion behavior of two types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been studied by electrochemical technique over the temperature range of 293–323 K. Before hydrogen permeation, both sides of the CLAM and CLF-1 steels were coated with a thin layer of uniform and dense palladium (Pd) membrane by electro-plating method. The results showed that the diffusion coefficients of hydrogen through CLAM and CLF-1 steels were submitted to the relationships of D(cm2/s) = 3.04 × 10−6exp[-4.72(kJ⋅mol-1)/RT] and D(cm2/s) = 1.82 × 10-5exp[-10.07(kJ⋅mol-1)/RT], which were far higher than that of some other austenitic stainless steels, such as 316 S.S. This indicates that if the RAFM steels as the structural material for fusion reactor are free from hydrogen environment, the hydrogen isotopes will escape from them quickly under low temperatures, which is conducive to keeping the mechanical properties of RAFMs.

Calculation of the hydraulic coupling in the single penstock multi-machine (SPMM) is one of the main obstacles for control design of the hydro turbine governor. In order to resolve this problem, a multi-machine differential equation model suitable for control design and stability analysis is established in this study. First, the multi-machine differential equation with the hydraulic coupling model is then established to facilitate building the joint model of the hydro turbine with the hydraulic system and the generator considering the hydraulic-mechanic-electric coupling. Second, the dynamic head in the common penstock satisfying the superposition principle is revealed. This means that the dynamic head in the common penstock can be calculated by using the state variables of the branch pipe. Third, simulation reveals that the differential item in the hydraulic coupling is the main factor affecting the computational convergence. As such, the approximate method ignoring the differential item in the hydraulic coupling is proposed to solve the problem of computational convergence of the SPMM. Finally, the classical method of characteristic (MOC) is employed to verify the proposed model. The results show that the proposed model has higher accuracy and is easy to connect with the non-linear model of the generator.

A new thermoresponsive polymer of poly(N-acetoxylethyl acrylamide) (PNAEAA) exhibiting a lower critical solution temperature in neutral water around 50 °C is synthesized by solution RAFT polymerization. In RAFT polymerization, the molecular weight of PNAEAA increases linearly with monomer conversion and Đ keeps at low values, confirming a controllable synthesis of PNAEAA. PNAEAA undergoes a reversible and sharp phase transition with almost no hysteresis at the phase transition temperature (PTT). The parameters, e.g., polymer concentration, degree of polymerization (DP), pH, salts, urea and phenol, affecting the PTT of PNAEAA are studied. Results demonstrate that the thermoresponsive phase transition of PNAEAA is different from its isomer of poly(N-acryloylglycine ethyl ester) (PNAGEE) and the popular poly(N-isopropylacrylamide) (PNIPAM). Due to the different PTTs of PNAEAA and PNIPAM, a doubly thermoresponsive block copolymer of poly(N-isopropyl acrylamide)-block-poly(N-acetoxylethyl acrylamide) (PNIPAM-b-PNAEAA) showing two PTTs is also synthesized. The thermoresponsive PNAEAA enriches the category of thermoresponsive polymers and is believed to have promising applications.

Seabed instability around a pipeline is one of the primary concerns in offshore pipeline projects. To date, most studies focus on investigating the wave/current-induced response within a porous seabed around either a fully buried pipeline or a thoroughly exposed one. In this study, unlike previous investigations, a series of comprehensive laboratory experiments are carried out in a wave flume to investigate the wave-induced pore pressures around a partially embedded pipeline in a trench layer. Measurements show that the presence of the partially buried pipeline can significantly affect the excess pore pressure in a partially backfilled trench layer, which deviates considerably from that predicted by the theoretical approach. The morphology of the trench layer accompanied with the backfill sediments, especially the deeper trench and thicker backfill (i.e., b ≥ 1 D , e ≥ 0.5 D ), provides a certain degree of resistance to seabed instability. The amplitude of excess pore pressure around the trench layer roughly exhibits a left-right asymmetric distribution along the periphery of the pipeline, and decays sharply from the upper layer of the trench to the lower region. Deeper trench depth and thicker buried layer significantly weaken the pore-water pressures in the whole trench area, thus sheltering and protecting the submarine pipeline against the transient seabed liquefaction.

In the past six years or so, great progress has been made in the preparation of multicompartment block copolymer nanoparticles (MBCNs) via the traditional solution self-assembly or the recently emerging polymerization-induced self-assembly (PISA). Herein, we review the recent advances in the synthesis/preparation of MBCNs under dilute (solution self-assembly) or concentrated (PISA) conditions, with special emphasis on PISA.

The thermoresponsive ionic liquid diblock copolymer of poly[1-(4-vinylbenzyl)-3-methylimidazolium tetrafluoroborate]-block-poly(N-isopropylacrylamide) (P[VBMI][BF4]-b-PNIPAM) containing a hydrophilic poly(ionic liquid) block of P[VBMI][BF4] is prepared by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization. This P[VBMI][BF4]-b-PNIPAM exhibits an abnormal thermoresponsive phase transition at a temperature above the phase transition temperature (PTT) of the PNIPAM block. For P[VBMI][BF4]-b-PNIPAM including a short P[VBMI][BF4] block, its aqueous solution becomes turbid at a temperature above the PTT of the thermoresponsive PNIPAM block, whereas for P[VBMI][BF4]-b-PNIPAM containing a relatively long P[VBMI][BF4] block even in the case of a relatively long PNIPAM block, the aqueous solution remains transparent at a temperature far above the PTT of the PNIPAM block, although a soluble-to-insoluble phase transition of the PINIPAM block is confirmed by dynamic light scattering (DLS) analysis and variable temperature 1H NMR analysis. The reason that P[VBMI][BF4]-b-PNIPAM exhibits an abnormal thermoresponse is discussed and ascribed to the highly hydrophilic and charged poly(ionic liquid) block of P[VBMI][BF4] leading to the formation of small-sized micelles at a temperature above the PTT.

Estuarine and coastal regions are heavily populated and well-developed areas [...]

Horizontal-axis tidal turbines (HATTs) have an acknowledged potential to extract a considerable amount of clean renewable energy from ocean tides. Among these, bidirectional HATTs (BHATTs) with bidirectional hydrofoils are thought to have higher economy than general HATTs. To improve the BHATTs, this study systemically investigated the influence of swept blades on the performance and hydrodynamics of the BHATT. A three-dimensional (3D) numerical model based on OpenFOAM was adopted to simulate a full-scale BHATT. The numerical framework was validated using two well-known experiments, and the mesh convergence was taken into consideration. The results indicate that the forward and backward swept blades have a limited impact on the performance and hydrodynamics of the BHATT. The upstream swept blade leads to a 4.3% decrease in the load on the rotor at design tip speed ratio (TSR) with a 2.0% decrease in the power. The BHATT with a downstream swept blade can produce 3.2% more energy at TSR = 6. Moreover, the swept blades have the opposite effect on the power of the BHATT at TSR = 6 and TSR = 9.

Based on the method of characteristics, in this study an analytical solution for one-dimensional shallow-water equations is developed to simulate the instantaneous dam-break flows propagati...

There has been little study on the microscopic bubble entrainment and diffusion process on high-speed self-aerated flows, although the problem under investigation is theoretically important...

The existing analytical solutions of dam-break flow do not consider simultaneously the effects of wet downstream bottom and bed slope on the dam-break wave propagation. In this study, a new...