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1.
ACS Appl Mater Interfaces ; 12(1): 609-618, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31799826

RESUMO

Cobalt-salen-based porous ionic polymers, which are composed of cobalt and halogen anions decorated on the framework, effectively catalyze the CO2 cycloaddition reaction of epoxides to cyclic carbonates under ambient conditions. The cooperative effect of bifunctional active sites of cobalt as the Lewis acidic site and the halogen anion as the nucleophile responds to the high catalytic performance. Moreover, density functional theory results indicate that the cobalt valence state and the corresponding coordination group influence the rate-determining step of the CO2 cycloaddition reaction and the nucleophilicity of halogen anions.

2.
Artigo em Inglês | MEDLINE | ID: mdl-31718019

RESUMO

BACKGROUND: School physical activity (PA) policy, physical education curriculum, teacher training, knowledge of physical fitness, and parental support are among the key issues underlying the declining trend of physical fitness in children and adolescents. The Chinese CHAMPS was a multi-faceted intervention program to maximize the opportunities for moderate and vigorous physical activity (MVPA), and increase physical fitness in middle school students. The purpose of the study was to test whether the levels of modification in school physical education policy and curriculum incrementally influenced the changes in cardiorespiratory fitness and other physical fitness outcomes. METHODS: This 8-month study was a clustered randomized controlled trial using a 2 × 2 factorial design. The participants were 680 7th grade students (mean age = 12.66 years) enrolled in 12 middle schools that were randomly assigned to one of four treatment conditions: school physical education intervention (SPE), afterschool program intervention (ASP), SPE+ASP, and control. Targeted behaviors of the Chinese CHAMPS were the student's sedentary behavior and MVPA. The study outcomes were assessed by a test battery of physical fitness at the baseline and posttest. Sedentary behavior and MVPA were measured in randomly selected students using observations and accelerometry. RESULTS: The terms contrasting the pooled effect of SPE, ASP, and SPE+ASP vs. Control, the pooled effect of SPE and SPE+ASP vs. ASP only, and the effect of SPE+ASP vs. ASP on CRF and other physical fitness outcomes were all significant after adjusting for covariates, supporting the study hypothesis. Process evaluation demonstrated high fidelity of the intervention in the targeted students' behaviors. CONCLUSIONS: Chinese CHAMPS demonstrated the impact of varying the amount of MVPA and vigorous physical activity (VPA) on the physical fitness in middle school students in support of the need to increase the opportunity for PA in schools and to introduce high-intensity exercises in school-based PA programs. Modification of school policy, quality of physical education curriculum, and teacher training were important moderators of the improvement in physical fitness. (Trial registration: ChiCTR-IOR-14005388, the Childhood Health; Activity and Motor Performance Study.).

3.
Sensors (Basel) ; 19(19)2019 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-31546704

RESUMO

Three-dimensional (3D) object detection is an important research in 3D computer vision with significant applications in many fields, such as automatic driving, robotics, and human-computer interaction. However, the low precision is an urgent problem in the field of 3D object detection. To solve it, we present a framework for 3D object detection in point cloud. To be specific, a designed Backbone Network is used to make fusion of low-level features and high-level features, which makes full use of various information advantages. Moreover, the two-dimensional (2D) Generalized Intersection over Union is extended to 3D use as part of the loss function in our framework. Empirical experiments of Car, Cyclist, and Pedestrian detection have been conducted respectively on the KITTI benchmark. Experimental results with average precision (AP) have shown the effectiveness of the proposed network.

4.
Comput Assist Surg (Abingdon) ; : 1-7, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30938210

RESUMO

Stereoscopic display based on Virtual Reality (VR) can facilitate doctors to observe the 3 D virtual anatomical models with the depth cues, assist them in intuitively investigating the spatial relationship between different anatomical structures without mental imagination. However, there is few input device can be used in controlling the virtual anatomical models in the sterile operating room. This paper presents a cost-effective VR application system for demonstration of 3 D virtual anatomical models with non-contact interaction and stereo display. The system is integrated with hand gesture interaction and voice interaction to achieve non-contact interaction. Hand gesture interaction is implemented based on a Leap Motion controller mounted on the Oculus Rift DK2. Voice is converted into operation using Bing Speech for English language and Aitalk for Chinese language, respectively. A local relationship database is designed to record the anatomical terminologies to speech recognition engine to query these uncommon words. The hierarchical nature of these terminologies is also recorded in a tree structure. In the experiments, ten participants were asked to perform the evaluation on the proposed system. The results show that our system is more efficient than traditional interactive manner and verify the feasibility and practicability in the sterile operating room.

5.
Int J Biol Macromol ; 129: 564-570, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30707998

RESUMO

Lignin, one of the most abundant natural polymers, has been successfully used as an effective lubricant additive with high value. The chemical structure of lignin is very diverse and strongly affected by both the source of lignin (i.e. plant species) and the lignin extraction process. In this work, a series of lignin from different biomass sources (hard or soft wood) and extraction process (organosolv with or without acid catalyst) has been successfully incorporated into poly(ethylene glycol) (PEG) and fortified lubricating properties were achieved. The effects of different lignin on the rheological, thermal and tribological properties of the lignin/EG lubricants were systematically investigated by different characterization techniques. Lignin in PEG significantly improves the lubricating property, where a wear reduction of 93.8% was observed. The thermal and lubrication properties of the PEG lubricants filled with different kinds of lignin are tightly related to the synergistic state of hydrogen bonding and molecular weight distribution. Lignin with broader molecular weight distribution and higher hydroxyl content shows better adhesion on metal surfaces and strengthened lubricating film, which could be used as the efficient lubricating additives. This work provides a criterion for selecting appropriate lignin as the efficient lubricant additive and accelerates the application of lignin.


Assuntos
Lignina/química , Lubrificantes/química , Polietilenoglicóis/química , Ligações de Hidrogênio , Peso Molecular , Viscosidade
6.
Comput Assist Surg (Abingdon) ; 24(sup1): 131-136, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-30741020

RESUMO

Stereoscopic display based on Virtual Reality (VR) can facilitate clinicians observing 3 D anatomical models with the depth cue which lets them understand the spatial relationship between different anatomical structures intuitively. However, there are few input devices available in the sterile field of the operating room for controlling 3 D anatomical models. This paper presents a cost-effective VR application for stereo display of 3 D anatomical models with non-contact interaction. The system is integrated with hand gesture interaction and voice interaction to achieve non-contact interaction. Hand gesture interaction is based on Leap Motion. Voice interaction is implemented based on Bing Speech for English language and Aitalk for Chinese language. A local database is designed to record the anatomical terminologies organized in a tree structure, and provided to the speech recognition engine for querying these uncommon words. Ten participants were asked to practice the proposed system and compare it with the common interactive manners. The results show that our system is more efficient than the common interactive manner and prove the feasibility and practicability of the proposed system used in the sterile field.

7.
ACS Appl Mater Interfaces ; 10(33): 28166-28175, 2018 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-30036034

RESUMO

Covalent bonding is widely adopted in graphene oxide (GO) membrane to improve structural integrity and restrict swelling, while it comes with a price of enlarged d-spacing and sacrifices membrane selectivity. This work offers a facile strategy to break the trade-off between membrane stability and selectivity. Specifically, graphene oxide (GO)/reduced graphene oxide (rGO) hybrid membranes were fabricated by a controlled pre-cross-linking method. With this method, restricted swelling by cross-linking and reduced d-spacing by GO reduction can be achieved simultaneously by controlling reaction time. Membranes were prepared on porous alumina support by vacuum filtration method. Two different d-spacing values (∼12.0 and ∼7.5 Å) were found in the hybrid membrane, representing the layer structures of expanded GO interspacing with inserted cross-linker and reduced layer spacing after GO reduction. The presence of such mixed layer structures enables restricted swelling, excellent mechanical strength, and unique separation property. The hybrid membrane shows excellent permselective H2/CO2 separation with a separation factor of 22.93 ± 1.57 and H2 permeance of 2.46 ± 0.01× 10-8 mol m-2 s-1 Pa-1. In desalination test with 3.5 wt % sea salt solution, the hybrid membrane shows high ion (Na+, K+, Mg2+, Cl-, and SO42-) rejection rate of above 99%, as well as excellent durability.

8.
Molecules ; 23(3)2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-29495559

RESUMO

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants.


Assuntos
Etilenoglicol/química , Lignina/química , Lubrificantes/química , Madeira/química , Biomassa , Peso Molecular , Solventes , Espectroscopia de Infravermelho com Transformada de Fourier , Viscosidade
9.
Sensors (Basel) ; 18(1)2018 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-29324708

RESUMO

Golay complementary waveforms can, in theory, yield radar returns of high range resolution with essentially zero sidelobes. In practice, when deployed conventionally, while high signal-to-noise ratios can be achieved for static target detection, significant range sidelobes are generated by target returns of nonzero Doppler causing unreliable detection. We consider signal processing techniques using Golay complementary waveforms to improve radar detection performance in scenarios involving multiple nonzero Doppler targets. A signal processing procedure based on an existing, so called, Binomial Design algorithm that alters the transmission order of Golay complementary waveforms and weights the returns is proposed in an attempt to achieve an enhanced illumination performance. The procedure applies one of three proposed waveform transmission ordering algorithms, followed by a pointwise nonlinear processor combining the outputs of the Binomial Design algorithm and one of the ordering algorithms. The computational complexity of the Binomial Design algorithm and the three ordering algorithms are compared, and a statistical analysis of the performance of the pointwise nonlinear processing is given. Estimation of the areas in the Delay-Doppler map occupied by significant range sidelobes for given targets are also discussed. Numerical simulations for the comparison of the performances of the Binomial Design algorithm and the three ordering algorithms are presented for both fixed and randomized target locations. The simulation results demonstrate that the proposed signal processing procedure has a better detection performance in terms of lower sidelobes and higher Doppler resolution in the presence of multiple nonzero Doppler targets compared to existing methods.

10.
Nanoscale ; 10(4): 1695-1703, 2018 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-29308501

RESUMO

The polymer/filler interface is usually considered as a thermal barrier in composites due to the mismatch of the phonon frequency across the interface. How the interface plays its role in thermal conduction has not yet been fully understood. In this work, scanning thermal microscopy is used to map the probe current across the composite interface and force-displacement curves are obtained to assess the polymer stiffness. The microscale stiffness-thermal conduction relationship is investigated at the composite interface in three representative cases: a single aggregated particle domain, two neighboring particle domains and two parallelly aligned particle chains. In the studied poly(vinyl alcohol) (PVA)/Fe3O4 composites, it is revealed that the interface property dominates the thermal conduction behavior rather than particle percolation. The long range order of polymer chains surrounding the particle domains is responsible for the enhanced crystallinity and thermal conductivity of the composites. With magnetic alignment of Fe3O4 particles, PVA crystallinity and thermal conductivity can be further enhanced. The macroscopic thermal conductivity measurement is highly consistent with the microscale observation. Specifically, with only 2.3 vol% loading of Fe3O4 in PVA, the thermal conductivity can be increased by 56% to 0.42 W m-1 K-1. By the magnetic alignment of the particles at the same loading, 133% enhancement of thermal conductivity (∼0.63 W m-1 K-1) can be achieved. This work presents an experimental study on the exploration of the interface property-thermal conductivity relationship in differently structured micro-domains and reveals the positive role of the composite interface in thermal conduction.

12.
Colloids Surf B Biointerfaces ; 159: 108-117, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-28780457

RESUMO

The TiO2 nanotube pattern with features down to 20nm (TN20) is highly and efficiently resistant to fibrinogen and S. aureus attachment. The ability of TN20 to resist biofouling adsorption, is due to low biofouling-surface adhesion force that determines the initial biofouling attachment, as well as the low friction coefficient that enables a complete removal of biofouling from a low-adhesive 'repelling' TN20 substrate under fluid flow. By grafting PEG molecules onto TN20, a significantly higher S. aureus cells attachment was observed, because of the stronger adhesion forces originated from the deformation of the soft PEG coatings. The complete interaction of S. aureus on structure-free dense TiO2 (DT), yields larger contact area and thus higher adhesion force than on any other TiO2 surfaces, resulting in a high coverage of bacteria. The existing high friction coefficient of S. aureus on TN80 (TiO2 with 80nm nanotubular size) and TN80-P (PEG-modified TN80), due to the much greater surface roughness, would contribute to the immobilization of biofouling on the surface under fluid flow, even though the two surfaces exhibit low adhesion forces. The analysis of adhesion and friction forces manipulated by TiO2 nanotubular topography and posted PEG patterns, advances our understanding of the mechanisms by which nanotopography patterned surfaces reduce biofouling attachment.


Assuntos
Polietilenoglicóis/química , Titânio/química , Bactérias/efeitos dos fármacos , Incrustação Biológica , Microscopia de Força Atômica , Nanotubos/química , Propriedades de Superfície , Titânio/farmacologia
13.
Med Phys ; 44(10): 5143-5152, 2017 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-28675445

RESUMO

PURPOSE: To investigate the feasibility of a 3D imaging system utilizing a 155 Eu source and pixelated cadmium-zinc-telluride (CZT) detector for applications in adaptive radiotherapy. Specifically, to compare the reconstructed stopping power ratio (SPR) values of a head phantom obtained with the proposed imaging technique with theoretical SPR values. METHOD: A Geant4 Monte Carlo simulation was performed with the novel imaging system. The simulation was repeated with a typical 120 kV X-ray tube spectrum while maintaining all other parameters. Dual energy 155 Eu source cone beam computed tomography (CBCT) images were reconstructed with an iterative projection algorithm known as total variation superiorization with diagonally relaxed orthogonal projections (TVS-DROP). Single energy 120 kV source CBCT images were also reconstructed with TVS-DROP. Reconstructed images were converted to SPR with stoichiometric calibration techniques based on ICRU 44 tissues. Quantitative accuracy of reconstructed attenuation coefficient images as well as SPR images were compared. RESULTS: Images generated by gamma emissions of 155 Eu showed superior contrast resolution to those generated by the 120 kV spectrum. Quantitatively, all reconstructed images correlated with reference attenuation coefficients of the head phantom within 1 standard deviation. Images generated with the 155 Eu source showed a smaller standard deviation of pixel values. Use of a dual energy conversion into SPR resulted in superior SPR accuracy with the 155 Eu source. CONCLUSION: 155 Eu was found to display desirable qualities when used as a source for dual energy CBCT. Further work is required to demonstrate whether the simulation results presented here can be translated into an experimental prototype.


Assuntos
Tomografia Computadorizada de Feixe Cônico , Európio , Método de Monte Carlo , Terapia com Prótons , Radioisótopos , Cádmio , Imagens de Fantasmas , Dosagem Radioterapêutica , Telúrio , Zinco
14.
Phys Chem Chem Phys ; 19(29): 19468-19477, 2017 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-28718482

RESUMO

The debate regarding the possible molecular origins of the Mullins effect has been ongoing since its discovery. Molecular dynamics (MD) simulations were carried out to elucidate the underlying mechanism of the Mullins effect. For the first time, the key characteristics associated with the Mullins effect, including (a) the majority of stress softening occurring in the first stretch, (b) continuous softening with stress increase, (c) a permanent set, and (d) recovery with heat treatment, are captured by molecular modeling. It is discovered that the irreversible disentanglement of polymer chains is physically sufficient to interpret these key characteristics, providing molecular evidence for this long-controversial issue. Our results also reveal that filled polymers exhibit three distinct regimes, i.e., the polymer matrix, the interface, and the filler. When subjected to external strain, the polymer matrix suffers from excess deformation, indicating strong heterogeneity within the filled polymer, which offers molecular insight for the formulation of physics-based constitutive relations for filled polymers.

15.
J Phys Chem B ; 121(22): 5669-5678, 2017 06 08.
Artigo em Inglês | MEDLINE | ID: mdl-28525712

RESUMO

Synthetic additives are widely used in lubricants nowadays to upgrade lubrication properties. The potential of integrating sustainable components in modern lubricants has rarely been studied yet. In this work, two sustainable resources lignin and gelatin have been synergistically incorporated into ethylene glycol (EG), and their tribological properties were systematically investigated. The abundant hydrogen bonding sites in lignin and gelatin as well as their interchain interaction via hydrogen bonding play the dominating roles in tuning the physicochemical properties of the mixture and improving lubricating properties. Moreover, the synergistic combination of lignin and gelatin induces charge separation of gelatin that enables its preferable adsorption on the friction surface through electrostatic force and forms a robust lubrication layer. This layer will be strengthened by lignin through the interpolymer chain hydrogen bonding. At an optimized lignin:gelatin mass ratio of 1:1 and 19 wt % loading of each in EG, the friction coefficient can be greatly stabilized and the wear loss was reduced by 89% compared to pure EG. This work presents a unique synergistic phenomenon between gelatin and lignin, where hydrogen bonding and change separation are revealed as the key factor that bridges the individual components and improves overall lubricating properties.

16.
J Environ Manage ; 196: 168-177, 2017 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-28284939

RESUMO

Hierarchically porous carbon adsorbents were successfully fabricated from different biomass resources (softwood, hardwood, bamboo and cotton) by a facile two-step process, i.e. carbonization in nitrogen and thermal oxidation in air. Without involving any toxic/corrosive chemicals, large surface area of up to 890 m2/g was achieved, which is comparable to commercial activated carbon. The porous carbons with various surface area and pore size were used as adsorbents to investigate the pore size dependent adsorption phenomenon. Based on the density functional theory, effective (E-SSA) and ineffective surface area (InE-SSA) was calculated considering the geometry of used probing adsorbate. It was demonstrated that the adsorption capacity strongly depends on E-SSA instead of total surface area. Moreover, a regression model was developed to quantify the adsorption capacities contributed from E-SSA and InE-SSA, respectively. The applicability of this model has been verified by satisfactory prediction results on porous carbons prepared in this work as well as commercial activated carbon. Revealing the pore size dependent adsorption behavior in these biomass derived porous carbon adsorbents will help to design more effective materials (either from biomass or other carbon resources) targeting to specific adsorption applications.


Assuntos
Carbono , Adsorção , Biomassa , Econazol/análogos & derivados , Porosidade
17.
ACS Appl Mater Interfaces ; 9(13): 12138-12145, 2017 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-28318228

RESUMO

In this work, poly(vinyl alcohol) (PVA)/amino acid (AA) composites were prepared by a self-organized crystallization process. Five different AAs (cysteine, aspartic acid, glutamic acid, ornithine, and lysine) were selected based on their similar functional groups but different molecular structures. The different PVA-AA interactions in the five PVA/AA composites lead to two crystal patterns, i.e., continuous network (cysteine and lysine) and discrete particles (glutamic acid, ornithine, and aspartic acid). Scanning thermal microscopy is then applied to map the distribution of thermal conduction in these composites. It is found that the interface surrounding the crystals plays a dominating role in phonon transport where the polymer chains are greatly restrained by the interfacial confinement effect. Continuous crystal network builds up a continuous interface that facilitates phonon transfer while phonon scattering occurs in discrete crystalline structures. Significantly improved thermal conductivity of ∼0.7 W/m·K is observed in PVA/cysteine composite with AA loading of 8.4 wt %, which corresponds to a 170% enhancement as compared to pure PVA. The strong PVA-AA molecular interaction and self-organized crystal structure are considered the major reasons for the unique interface property and superior thermal conductivity.

18.
J Colloid Interface Sci ; 498: 47-54, 2017 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-28319840

RESUMO

Two different heteroelement-rich molecules have been successfully grafted on graphene oxide (GO) sheets which were then used as lubricant additives in bio-ionic liquid. The grafting was processed with reactions between GO sheets and synthesized heteroelement-rich molecules (Imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, respectively). The modified GO (m-GO) was added into [Choline][Proline] ([CH][P]) bio-ionic liquid, and has been demonstrated effective additive in promoting lubrication. Different characterization techniques have been utilized to study the reaction between GO and the two modifiers. The effect of molecular structure of the modifiers on the rheological and tribological properties of m-GO/[CH][P] lubricants was systematically investigated. Both theoretical calculation and experimental results demonstrated that the introduced heteroelement-rich groups are beneficial to increase the robustness of lubrication film by intensified hydrogen bonding and enhance the lubricant/friction surface adhesion by increased polarity of the m-GO. As a result, the interfacial lubrication could be significantly improved by these newly developed m-GO/[CH][P] lubricants.

19.
Sensors (Basel) ; 18(1)2017 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-29295566

RESUMO

We propose an alternative waveform scheme built on mutually-orthogonal complementary sets for a distributed multistatic radar. Our analysis and simulation show a reduced frequency band requirement for signal separation between antennas with centralized signal processing using the same carrier frequency. While the scheme can tolerate fluctuations of carrier frequencies and phases, range sidelobes arise when carrier frequencies between antennas are significantly different.

20.
ACS Appl Mater Interfaces ; 8(42): 29080-29087, 2016 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-27696810

RESUMO

Phonon transfer is greatly scattered in traditional polymer composites due to the unpaired phonon frequency at the polymer/filler interface. A key innovation of this work is to build continuous crystal network by self-organization and utilize it as "thermal highway" that circumvents the long-existing interfacial thermal barrier issue in traditional composites. By tuning the molecular diffusion rate of dicarboxylic acids (oxalic acid, malonic acid, and succinic acid), different crystal structures including skeletal, dendrite, diffusion-limited aggregates, and spherulite were synthesized in PVA film. These continuous crystal structures benefit the efficient phonon transfer in the composites with minimized interfacial scattering and lead to a significant thermal conductivity enhancement of up to 180% compared to that of pure polymer. Moreover, the transparent feature of these composite films provides additional benefits in display applications. The post heat treatment effect on the thermal conductivity of the composite films shows a time-dependent behavior. These uniquely structured polymer/crystal composites are expected to generate significant impacts in thermal management applications.

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