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Atomically precise synthesis of three-dimensional boron–nitrogen (BN)-based helical structures constitutes an undeveloped field with challenges in synthetic chemistry. Herein, we synthesized and comprehensively characterized a new class of helical molecular carbons, named benzo-extended [n]heli(aminoborane)s ([n]HABs), in which the helical structures consisted of n= 8 and n= 10 ortho-condensed conjugated rings with alternating BN atoms at the inner rims. X-ray crystallographic analysis, photophysical studies, and density functional theory calculations revealed the unique characteristics of this novel [n]HABsystem. Owing to the high enantiomerization energy barriers, the optical resolution of [8]HABand [10]HABwas achieved with chiral high-performance liquid chromatography. The isolated enantiomers of [10]HABexhibited record absorption and luminescence dissymmetry factors (|gabs|=0.061; |glum|=0.048), and boosted CPL brightness up to 292 M–1cm–1, surpassing most helicene derivatives, demonstrating that the introduction of BN atoms into the inner positions of helicenes can increase both the |gabs| and |glum| values.

Ice surfaces are closely relevant to many physical and chemical properties, such as melting, freezing, friction, gas uptake and atmospheric reaction1–8. Despite extensive experimental and theoretical investigations9–17, the exact atomic structures of ice interfaces remain elusive owing to the vulnerable hydrogen-bonding network and the complicated premelting process. Here we realize atomic-resolution imaging of the basal (0001) surface structure of hexagonal water ice (ice Ih) by using qPlus-based cryogenic atomic force microscopy with a carbon monoxide-functionalized tip. We find that the crystalline ice-Ih surface consists of mixed Ih- and cubic (Ic)-stacking nanodomains, forming 19×19periodic superstructures. Density functional theory reveals that this reconstructed surface is stabilized over the ideal ice surface mainly by minimizing the electrostatic repulsion between dangling OH bonds. Moreover, we observe that the ice surface gradually becomes disordered with increasing temperature (above 120 Kelvin), indicating the onset of the premelting process. The surface premelting occurs from the defective boundaries between the Ih and Ic domains and can be promoted by the formation of a planar local structure. These results put an end to the longstanding debate on ice surface structures and shed light on the molecular origin of ice premelting, which may lead to a paradigm shift in the understanding of ice physics and chemistry.

Community detection is an important method to analyze the characteristics and structure of community networks, which can excavate the potential links between nodes and further discover subgroups from complex networks. However, most of the existing methods only unilaterally consider the direct link topology without comprehensively considering the internal and external characteristics of the community as well as the result itself, which fails to maximize the access to the network information, thus affecting the effectiveness of community detection. To compensate for this deficiency, we propose a new community detection method based on multi-constraint non-negative matrix factorization, named orthogonal regular sparse constraint non-negative matrix factorization (ORSNMF). Based on the network topology, the ORSNMF algorithm models the differences of the outside of the community, the similarities of the nodes inside the community, and the sparseness of the community membership matrices at the same time, which together guides the iterative learning process to better reflect the underlying information and inherent attributes of the community structure in order to improve the correct rate of dividing subgroups. An algorithm with convergence guarantee is also proposed to solve the model, and finally a large number of comparative experiments are conducted, and the results show that the algorithm has good results.

Tuning the electronic properties of polymers is of great importance in designing highly efficient organic solar cells. Noncovalent intramolecular interactions have been often used for conformational control to enhance the planarity of polymers or molecules, which may reduce band gaps and promote charge transfer. However, it is not known if noncovalent interactions may alter the electronic properties of conjugated polymers through some mechanism other than the conformational control. Here, we studied the effects of various noncovalent interactions, including sulfur–nitrogen, sulfur–oxygen, sulfur–fluorine, oxygen–nitrogen, oxygen–fluorine, and nitrogen–fluorine, on the electronic properties of polymers with planar geometry using unconstrained and constrained density functional theory. We found that the sulfur–nitrogen intramolecular interaction may reduce the band gaps of polymers and enhance the charge transfer more obviously than other noncovalent interactions. Our findings are also consistent with the experimental data. For the first time, our study shows that the sulfur–nitrogen noncovalent interaction may further affect the electronic structure of coplanar conjugated polymers, which cannot be only explained by the enhancement of molecular planarity. Our work suggests a new mechanism to manipulate the electronic properties of polymers to design high-performance small-molecule-polymer and all-polymer solar cells.

Most current research on the trajectory planning of the autonomous lane change focuses on high-speed scenarios and assumes that the states of the surrounding vehicles keep stable during the lane change. The methods based on geometric-curve are mostly used for trajectory planning. In this paper, considering the inevitable development of the autonomous driving, the surrounding vehicles are assumed to be driven by human drivers, while the ego vehicles are able to autonomously change lanes. Representative local lane-change scenarios are then designed and analyzed in detail aiming at medium- and low-speed lane-change conditions. Additionally, in contrast with most research, dynamic trajectory planning which considers the possible state variations of the surrounding vehicles and the driver characteristics is studied and described by a fifth-order polynomial function. The safety and comfort of the dynamic trajectory planning are validated through simulation. Moreover, the elastic soft constraint of the safety domain is designed, whereby the sensitivity of the studied dynamic trajectory planning system is reduced under the premise of ensuring safety. The effectiveness of the elastic soft constraint in terms of improving comfort during the lane change is verified through simulation. The availability of the dynamic trajectory planning system with the elastic soft constraint is demonstrated with the addition of trajectory tracking based on model predictive control, showing its potential in practical applications.

Hexagonal boron nitride (hBN) encapsulation has been widely used in the electronic applications of two-dimensional (2D) materials to improve device performance by protecting 2D materials against contamination and degradation. It is often assumed that hBN layers as a dielectric would not affect the electronic structure of encapsulated 2D materials. Here, we studied few-layer MoS2encapsulated in hBN flakes using a combination of theoretical and experimental Raman spectroscopy. We found that after the encapsulation the out-of-plane, A1g, mode is upshifted, whereas the in-plane, E2g1, mode is downshifted. The measured downshift of the E2g1mode does not decrease with increasing the thickness of MoS2, which can be attributed to tensile strains in bilayer and trilayer MoS2caused by the typical experimental process of the hBN encapsulation. We estimated the strain magnitude and found that the induced strain may cause the K–Qcrossover in the conduction band of few-layer MoS2, so greatly modifying its electronic properties as an n-type semiconductor. Our study suggests that the hBN encapsulation should be used with caution, as it may affect the electronic properties of encapsulated few-layer 2D materials.

A 37-year-old man complained of a refractory posterior malleolar ulceration on his left ankle. He was diagnosed with Werner syndrome according to the progeroid clinical features and genetic testing. To approach the ulceration, a free flow-through right anterolateral thigh perforator flap with anterolateral thigh cutaneous nerve was harvested. One year later, he was readmitted due to a new ulceration on his right ankle. We harvested the left anterolateral thigh perforator flap with anterolateral thigh cutaneous nerve to reconstruct the defect. After one more year of follow-up, there was no recurrence of ulcers, and the sensation of the flap recovered partially after 6 months. We conclude that free flow-through anterolateral thigh perforator flap is a feasible choice for the repair of foot ulcers in Werner syndrome.

Mechanical stimuli can modify the energy landscape of chemical reactions and enable reaction pathways, offering a synthetic strategy that complements conventional chemistry. These mechanochemical mechanisms have been studied extensively in one-dimensional polymers under tensile stress using ring-opening and reorganization, polymer unzipping and disulfide reduction as model reactions. In these systems, the pulling force stretches chemical bonds, initiating the reaction. Additionally, it has been shown that forces orthogonal to the chemical bonds can alter the rate of bond dissociation. However, these bond activation mechanisms have not been possible under isotropic, compressive stress (that is, hydrostatic pressure). Here we show that mechanochemistry through isotropic compression is possible by molecularly engineering structures that can translate macroscopic isotropic stress into molecular-level anisotropic strain. We engineer molecules with mechanically heterogeneous components—a compressible (‘soft’) mechanophore and incompressible (‘hard’) ligands. In these ‘molecular anvils’, isotropic stress leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. Conversely, rigid ligands in steric contact impede relative motion, blocking reactivity. We combine experiments and computations to demonstrate hydrostatic-pressure-driven redox reactions in metal–organic chalcogenides that incorporate molecular elements that have heterogeneous compressibility, in which bending of bond angles or shearing of adjacent chains activates the metal–chalcogen bonds, leading to the formation of the elemental metal. These results reveal an unexplored reaction mechanism and suggest possible strategies for high-specificity mechanosynthesis.

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To develop a bionic maneuverable propulsion system to be applied in a small underwater vehicle, a new conceptual design of the bionic propulsion is applied to the traditional underwater glider. The numerical simulation focuses on the autonomous underwater glider (AUG)'s flapping propulsion at by solving the incompressible viscous Navier-Stokes equations coupled with the immersed boundary method. The systematic analysis of the effect of different motion parameters on the propulsive efficiency of the AUG is carried out, including the hydrofoil's heaving amplitude, the pitching amplitude, the phase lag between heaving and pitching and the flapping frequency. The results obtained in this study can provide some physical insights into the propulsive mechanisms in the flapping -based locomotion.

To develop a bionic maneuverable propulsion system to be applied in a small underwater vehicle, a new conceptual design of the bionic propulsion is applied to the traditional underwater glider. The numerical simulation focuses on the autonomous under-water glider (AUG)’s flapping propulsion at Re= 200 by solving the incompressible viscous Navier-Stokes equations coupled with the immersed boundary method. The systematic analysis of the effect of different motion parameters on the propulsive efficiency of the AUG is carried out, including the hydrofoil’s heaving amplitude, the pitching amplitude, the phase lag between heaving and pitching and the flapping frequency. The results obtained in this study can provide some physical insights into the propulsive mechanisms in the flapping -based locomotion.

Droplet migration in plane Poiseuille flow is numerically investigated with a dissipative particle dynamics method. The single droplet deformation in the channel flow is first studied to verify the current method and the physical model. The effect of the viscosity ratio between the droplet and the solvent and the effect of the confinement are systematically investigated. The droplet is in an off-centerline equilibrium position with a specific selection of the parameters. A large viscosity ratio makes the droplet locate in a near-wall equilibrium position, and a large capillary number makes the droplet migrate to the near-centerline region of the channel. For the droplet migration at the same Capillary number, there is a critical width of the channel, which is less than twice of the droplet diameter, and the droplet will only migrate to the channel centerline if the width is less than this critical value.

Droplet migration in plane Poiseuille flow is numerically investigated with a dissipative particle dynamics method. The single droplet deformation in the channel flow is first studied to verify the current method and the physical model. The effect of the viscosity ratio between the droplet and the solvent and the effect of the confinement are systematically investigated. The droplet is in an off-centerline equilibrium position with a specific selection of the parameters. A large viscosity ratio makes the droplet locate in a near-wall equilibrium position, and a large capillary number makes the droplet migrate to the near-centerline region of the channel. For the droplet migration at the same Capillary number, there is a critical width of the channel, which is less than twice of the droplet diameter, and the droplet will only migrate to the channel centerline if the width is less than this critical value.

Reservoirs have been widely constructed all over the world in recent years to alleviate the shortage of water resources. Nevertheless, the assessment method of water quality and its trophic status needs to be developed. In this study, water quality parameters of a newly constructed shallow reservoir were regularly monitored for a period of two years, which is used as a major drinking water source of Shanghai, China. Furthermore, the trophic state indices of the reservoir were investigated based on literature and evaluated with the two-year field data. The results indicated that the studied reservoir is reaching the mesotrophic–eutrophic boundary, where further nutrient enrichment could cause water quality degradation; total phosphorus is the limiting nutrient for algal growth in the studied reservoir. Results of the study can help operators understand change and status of water quality of the reservoir and provide valuable data demonstrating variation of water quality indicators and trophic characteristics in shallow reservoirs or lakes.

Acrylonitrile (AN) and itaconic acid (IA) were used to synthesize UHMWPAN by aqueous suspension method with 2,2’-azobisisobutyronitrile (AIBN) as the initiator and polyvinylalcohol (PVA) as the disperser at different temperatures (55°C~75°C) for different timings (1.0h~3.0h). The usage amounts of AN, IA, AIBN and PVA were also technical polymerization parameters used to obtain the optimal polymerization process. We found that the conversion and the viscosity average molecular weight both achieved the optimum levels when the conditions were as follows: the total monomer concentration (21wt%), the monomer ratio (AN: IA=98:2), the usage amount of the initiator (AIBN, 0.01wt%), the usage amount of the disperser (PVA, 0.1wt%), the polymerization temperature (70°C) and the polymerization time (2h).

Objective.To establish whether there is a relationship between serum magnesium (Mg) concentration and radiographic knee osteoarthritis (OA).Methods.There were 2855 subjects in this cross-sectional study. Serum Mg concentration was measured using the chemiluminescence method. Radiographic OA of the knee was defined as changes consistent with Kellgren-Lawrence (K-L) grade 2 on at least 1 side. Mg concentration was classified into 1 of 4 quartiles: ≤ 0.87, 0.88–0.91, 0.92–0.96, or ≥ 0.97 mmol/l. Multivariable logistic analysis was used to test the association between serum Mg and radiographic knee OA after adjustment for potentially confounding factors. The OR with 95% CI for the association between radiographic knee OA and serum Mg concentration were calculated for each quartile. The quartile with the lowest value was regarded as the reference category.Results.Significant association between serum Mg concentration and radiographic knee OA was observed in the model after adjustment for age, sex, and body mass index, as well as in the multivariable model. The multivariable-adjusted OR (95% CI) for radiographic knee OA in the second, third, and fourth serum Mg concentration quartiles were 0.90 (95% CI 0.71–1.13), 0.92 (95% CI 0.73–1.16), and 0.72 (95% CI 0.57–0.92), respectively, compared with the lowest (first) quartile. A clear trend (p for trend was 0.01) was observed. The relative odds of radiographic knee OA was decreased by 0.72 times in the fourth serum Mg quartile compared with the lowest quartile.Conclusion.Serum Mg concentration may have an inverse relationship with radiographic OA of the knee.

By using a new kind of single-beam normalized photo-acoustic tomography spectroscopy (PAS-CT) technology with non-damage detection, the photo-acoustic tomography spectroscopy and optical absorption properties of green and yellow leaves of Bauhinia blakeana were studied. The results show that: the photo-acoustic tomography spectroscopy of Bauhinia blakeana leaves could be obtained from different chopping frequency and different sample positions, and photosynthetic pigment content of their leaves is closely related to their photosynthetic intensity. The more photosynthetic pigment content the leaves of Bauhinia blakeana contain, the bigger optical absorption coefficient and the higher photosynthetic efficiency they have. The photosynthetic pigment content of the green leaves of Bauhinia blakeana is higher than that of the yellow ones. As a result, the photosynthesis of green leaves is better than that of the yellow ones. According to the results of our research, the photosynthetic efficiency of Bauhinia blakeana could be improved and its growth time could be effectively controlled to enhance the growth of Bauhinia blakeana. Furthermore, it could play an important role on the development of forestry, and meet the need of forest for 6 billion people. The research showed high science value to the study and applications of the photosynthesis of plants.

By using a new kind of single-beam normalized photo-acoustic tomography spectroscopy (PAS-CT) technology with non-damage detection, the photo-acoustic tomography spectroscopy, optical absorption properties and photosynthetic pigment content of the green and yellow leaves of Osmanthus fragrans were studied. The results show that: photo-acoustic tomography spectroscopy could be obtained from different chopping frequency and different sample position. The more photosynthetic pigment content the leaves of Osmanthus fragrans contains, the bigger optical absorption coefficient and the higher photosynthetic efficiency they have. In the research, we could find that the photosynthetic pigment content of the green leaves of Osmanthus fragrans is higher than that of the yellow ones. As a result, the optical absorption coefficient and the photosynthetic efficiency of the green ones are higher than the yellow ones. The photo-acoustic tomography spectroscopy technology could be a kind of non-damage detection to confirm the growth of trees.

The effects of ultra high molecular weight Polyacrylonitrile (UHMW-PAN) on the rheological behavior of PAN/DMSO solution have been investigated using a cone-plate rheometer in this work. The rheological behavior was characterized by steady shear and oscillation test It is observed from the measurements that, the rheological behavior of the polymer mixture of UHMW-PAN and AMW-PAN makes a difference to the AMW-PAN solution due to macromolecular entanglements, the viscosities of the solutions decreased with the rising of shear rate, shear viscosity rise with the increase of the molecular weight of the UHMW-PAN. For dynamic experiments, a steady increase of both and with the increase of oscillation frequency and molecular weight of UHMW-PAN was seen for all samples. The and increase with the decrease of the temperature or with the increase of the contents of the UHMW-PAN.

The water environment of swimming fish in nature is always complex which includes various vortices and fluctuations. In order to study the interaction between the fish and its surrounding complex flow, the physical model with a D-section cylinder placed at the front of a flapping foil is employed. The D-section cylinder is used to produce vortices to contact with the foil as well as the vortices shed from the foil. According to the experimental work of Gopalkrishnan et al., there are three interaction modes between vortices shed from the cylinder and the flapping foil, which are expanding wake, destructive interaction and constructive interaction. Here in this article, three of those typical cases are picked up to reproduce the vortices interaction modes with the modified immersed boundary methods and their hydrodynamic performances are studied further. Results show that, for expanding wake mode and destructive interaction mode, the incoming vortices contact with the foil strongly, inducing relative low pressure domains at the leading-edge of the foil and enlarging the thrust of foils. For constructive mode, the foil slalom between the shed vortices from the D-section cylinder do not contact with them obviously and the foil’s thrust is only enlarged a little.

Although the melting of ice is an everyday process, important issues remain unclear particularly on the nanoscale. Indeed despite extensive studies into ice melting and premelting, little is known about the relationship between (pre)melting and crystal size and morphology, with, for example, the melting temperature of ice nanocrystals being unclear. Here we report extensive long-time force-field-based molecular dynamics studies of the melting of hexagonal ice nanocrystals in the ca. 2 to 8 nm size range. We show that premelting is initiated at the corners of the crystals, then the edges between facets, and then the flat surfaces; that is, the melting temperature is related to the degree of coordination. A strong size dependence of the melting temperature is observed, with the combination of small particle size and premelting leading nanosized ice crystals to have liquid-like surfaces as low as about 130 K below the bulk ice melting temperature. These results will be of relevance in understanding the size dependence of ice crystal morphology and the surface reactivity of ice particles under atmospheric conditions.

This paper studies the oscillation behavior of a flexible plate in the wake of a D-section cylinder. The interaction between the flexible body and its surrounding vortices is investigated. A modified immersed boundary method is used to solve the motion of fluid, integrated with a linearized Euler-Bernoulli beam model to govern the motion of the flexible plate. Results show that, when the distance between cylinder and plate is small, the surface of the plate is surrounded by vortices layers and the plate oscillates periodically, with amplitude similar to the cylinder movement. However, if the distance becomes large, we find that the vortices are shed from the D-cylinder in front of the plate, and the incoming vortices make the plate oscillate with large amplitude at the beginning and then slant laterally. Also, the amplitude becomes smaller compared to the case of the small distance.

This paper studies the oscillation behavior of a flexible plate in the wake of a D-section cylinder. The interaction between the flexible body and its surrounding vortices is investigated. A modified immersed boundary method is used to solve the motion of fluid, integrated with a linearized Euler-Bernoulli beam model to govern the motion of the flexible plate. Results show that, when the distance between cylinder and plate is small, the surface of the plate is surrounded by vortices layers and the plate oscillates periodically, with amplitude similar to the cylinder movement. However, if the distance becomes large, we find that the vortices are shed from the D-cylinder in front of the plate, and the incoming vortices make the plate oscillate with large amplitude at the beginning and then slant laterally. Also, the amplitude becomes smaller compared to the case of the small distance.

An immersed-boundary method is used to investigate the flapping wings with different aspect ratios ranging from 1 to 5. The numerical results on wake structures and the performance of the propulsion are given. Unlike the case of the two-dimensional flapping foil, the wing-tip vortices appear for the flow past a three-dimensional flapping wing, which makes the wake vortex structures much different. The results show that the leading edge vortex merges into the trailing edge vortex, connects with the wing tip vortices and then sheds from the wing. A vortex ring forms in the wake, and exhibits different patterns for different foil aspect ratios. Analysis of hydrodynamic performances shows that both thrust coefficient and efficiency of the flapping wing increase with increasing aspect ratio.

Porous carbon microspheres with good morphology, high yield, and controllable particle size were prepared from phenolic resin. The particle size and pore structure of the carbon microspheres were mainly inherited from their precursors, resol microspheres, which were made through curing emulsified resol in water at 120°C under saturated pressure. The average particle size and specific surface area of the porous carbon microspheres was related to the concentration of resol and polyvinyl alcohol along with the heating program. The carbonization yield to 700°C was 55 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 798–803, 2006

Reversible addition–fragmentation chain transfer polymerization has been successfully applied to polymerize acrylonitrile with dibenzyl trithiocarbonate as the chain‐transfer agent. The key to success is ascribed to the improvement of the interchange frequency between dormant and active species through the reduction of the activation energy for the fragmentation of the intermediate. The influence of several experimental parameters, such as the molar ratio of the chain‐transfer agent to the initiator [azobis(isobutyronitrile)], the molar ratio of the monomer to the chain‐transfer agent, and the monomer concentration, on the polymerization kinetics and the molecular weight as well as the polydispersity has been investigated in detail. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and 1H NMR analyses have confirmed the chain‐end functionality of the resultant polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 490–498, 2006

A series of titanium complexes Cp*TiCl((OCH(R)CH2)2NAr) (Cp* = C5Me5, R = H, Ar = Phenyl (2a); R = H, Ar = 2,6‐dimethylphenyl (2b); R = Me, Ar = Phenyl (2c)) was prepared by the reaction of corresponding N,N‐diethoxylaniline derivatives, with Cp*TiCl3 in the presence of excessive triethylamine. All the titanium complexes display higher catalytic activities towards the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as a cocatalyst, and produce higher molecular weight polystyrenes with higher syndiotacticity and melting temperature than their mother complex Cp*TiCl3. The catalyst activities and polymer yields as well as polymer properties are considerably affected by the steric and electronic effect of the tridentate ligands. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1562–1568, 2005

Because of its atomic resolution, scanning tunnel microscopy (STM) was applied to the study of the surface topography, in air, of rayon-based carbon fibers (RCF) that were not previously studied. By a variety of larger scales, RCF exhibits some rugosities with “peaks” and “valleys.” The surfaces are characterized by stripe-form crystallite stackings with the diameter of about 10 nm aligned at an angle between 45 and 60° to the fiber axis. A graphitelike structure was first observed on the surface of RCF examined at an atomic resolution scale. Distances between two adjacent carbon atoms of RCF and that between the closest centers of hexagonal carbon rings were estimated. It was also concluded that the hexagonal structure of RCF is deformed graphene (graphitelike) compared with that of highly oriented pyrolytic graphite. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 754–758, 2003

The structure and properties of lyocell and viscose rayon fibers are compared in this paper. SAXS results show that the rayon precursor has a higher ratio of larger microvoids, WAXD curves show that both fibers have a monoclinic crystalline structure, but lyocell fibers have higher crystallinity and a larger crystal size. The morphology of lyocell and rayon, observed by scanning electron microscopy (SEM), is the same with an average diameter of 10.6 μm, but different distributions. A Gaussian statistical analysis indicates that the single-strand strength of lyocell fibers is twice as high as for rayon precursors, which have a wider strength distribution. Similar TGA curves show the same pyrolysis mechanism, and based on this, lyocell fibers are proposed as high performance carbon fiber precursors. Lyocell fibers are successfully carbonized under conditions identical to those for manufacturing rayon-based carbon fibers. The two kinds of carbon fibers are compared by SEM and a Weibull statistical analysis.

Using a microscope-television-video camera system, the diffusion coefficients of blend acrylic polymer dopes in the coagulation of a wet spinning process are determined in both dimethylformamide and aqueous NaSCN solvent systems, along with the effects of various dispersing polymers and their composition and content (blend ratio) on the diffusion coefficients. The relationship between the diffusion coefficients and the microporous structure is discussed.

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