Dominant Transfer Mechanism Research Articles

Turbulent characteristics of momentum flux in the marine atmospheric boundary layer of North Bay of Bengal

We use a 16-month-long, 20 Hz wind data from a mooring deployed in the Bay of Bengal (BoB) to study the characteristics of turbulent wind stress (u′w′)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime})$$\\end{document} events in the marine atmospheric boundary layer (MABL). Quadrant analysis of the motion-corrected u′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}$$\\end{document} and w′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${w}{\\prime}$$\\end{document} suggests that sweep and ejections, representing downward stress transfer into the ocean, dominate the u′w′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime}$$\\end{document} (~ 140%). In comparison, outward and inward interactions representing an upward stress transfer into the atmosphere provide the counter-contribution (~ 40%). We found a wind speed (ws) dependency on stress transfer for ws > 3 m/s, while for low ws, the swell-dominated ocean state modulates the u′w′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime}$$\\end{document} with a significant reverse stress transfer into the atmosphere, especially during intermonsoon periods. It is found that for weak winds (ws\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ws$$\\end{document}< 3 m/s), the number of turbulent events (N) is less, but they frequently repeat with more considerable flux per event (f^)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widehat{f})$$\\end{document}, with outward and inward interactions (sweeps and ejections) dominating during intermonsoon periods (monsoon periods). For medium to strong winds, sweeps and ejections dominate u′w′.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime}.$$\\end{document} Ejections are found to be the most efficient method of stress transfer in the BoB, contributing 80% of u′w′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime}$$\\end{document}, compared to sweeps contributing ~ 60% and interaction processes contributing ~ − 20% each to the u′w′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${u}{\\prime}{w}{\\prime}$$\\end{document}. Though the duration of sweep events is larger than ejections and with comparable flux energy per event (f^\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widehat{f}$$\\end{document}), the larger number N of ejection events makes it the dominant stress transfer mechanism in the Bay in all seasons.

Experimental investigation of the compressive and shear resistance of laminated steel-reinforced glass beams

This paper presents an experimental investigation into the compressive and shear resistance of triple-layered laminated steel-reinforced glass beams. Two types of tests are performed: (a) local compressive tests (force over a support) and (b) bending tests (force close to a support). In total, six local compressive tests and eight bending tests are performed. Overall, beams with a shear span-to-effective depth ratio (a/d) approximately equal to 0, 0.63, and 1.0 are tested. Two different types of flexural reinforcement are used separately: solid (S) and hollow (H) reinforcement. The behaviour of the outer glass panes, and top and bottom reinforcement is monitored using strain gauges and Digital Image Correlation (DIC). The test results are elaborated in terms of load-displacement curves, the evolution of strains and crack patterns. Three failure modes are observed: yielding of the reinforcement (PF), crushing of glass (CF), and rupture of the reinforcement (RR). Shear failure occurred due to the crushing of glass in the compressed diagonal strut in the shear span. It was found that the shear resistance increases with a smaller shear span-to-effective depth ratio and stronger reinforcement. The dominant shear transfer mechanism was the direct strut action. It was found that the post-fracture capacity had a relatively constant value for all the tests with a slight increase for smaller a/d. The actual tensile strains in the bottom reinforcement measured by DIC are compared with the calculated strains based on the curvature of uncracked and cracked cross-sections, assuming plane section behaviour. It was observed that the actual strains are systematically larger than the calculated ones because, in reality, the section does not remain plane. After the appearance of the first crack, the beams essentially behave like strut-and-tie systems, where the strut is the diagonally compressed laminated glass and the tie is the bottom reinforcement.

Low-temperature radiation damage studies in single-walled carbon nanotube bundles by hopping conductance

The paper shows the results of studying radiation defects in single-walled carbon nanotube bundles at low temperatures. The data were obtained in a unique experiment that inseparably combines 1 MeV electron irradiation at a temperature of ∼10 K and electrical conductivity measurements over a wide temperature range of 5–300 K. The experiment allowed us to reveal and separate the influence of stable and unstable radiation defects on the electrical properties of SWCNTs. It is shown that the 2D Mott variable range hopping conduction regime exhibits resistance to electron irradiation. The hopping conductivity is the dominant charge transfer mechanism in the temperature range of 5–50 K in both the pristine and irradiated SWCNT samples. It was found that the parameters of hopping transport demonstrate high sensitivity to the introduction and annealing of radiation defects. The low-temperature electron irradiation revealed the possibility of the emergence of an additional conduction channel in the irradiated SWCNTs. This channel demonstrates thermally activated behavior with a low activation energy of ∼0.5 meV at temperatures of 5–50 K. The obtained data indicate that unstable radiation defects create conditions for the possibility of impurity band conduction in SWCNT bundles.

Electrical and Photoelectric Properties of Organic-Inorganic Heterojunctions PEDOT:PSS/n-CdTe

PEDOT: PSS thin films are widely used as transparent coatings in flexible semiconductor devices including solar cells. However, they are not widely used as transparent coatings in combination with crystal substrates. This work shows the possibility of using PEDOT:PSS thin films as a frontal transparent conducting layer in hybrid organic-inorganic Schottky type heterojunctions of the PEDOT:PSS/n‑CdTe, which were prepared by deposition of PEDOT:PSS thin films (using the spin-coating method) on crystalline cadmium telluride substrates. The current-voltage (in a wide temperature range) and capacitance-voltage (at room temperature) characteristics of heterojunctions were measurement and analyzed. It has been established that PEDOT:PSS/n-CdTe heterojunctions have good diode properties with a high rectification ratio RR≈105, a potential barrier height φ0 = 0.95 eV, and series Rs = 91 Ohm and shunt Rsh = 5.7 × 107 Ohm resistances. Analysis of the forward branches of the I–V characteristics of heterojunctions showed that the dominant charge transfer mechanisms are determined by the processes of radiative recombination at low biases (3kT/e &lt;V &lt;0.3 V) and tunneling through a thin depleted layer at high biases (0.3 V &lt;V &lt;0.6 V). Capacity-voltage characteristics are plotted in the Mott-Schottky coordinate, taking into account the influence of series resistance, measured at a frequency of 1 MHz. Used the C-V characteristic was determined the value of the built-in potential Vc = 1.32 V (it correlates well with the cutoff voltage determined from the current-voltage characteristics) and the concentration of uncompensated donors in the n-CdTe substrate ND-NA = 8.79 × 1014 cm-3. Although the photoelectric parameters of unoptimized PEDOT:PSS/n-CdTe heterojunctions are low, their photodiode characteristics (Detectivity D*&gt; 1013 Jones) are very promising for further detailed analysis and improvement. The proposed concept of a hybrid organic-inorganic heterojunction also has potential for use in inexpensive γ- and X-ray detectors.

Bacterial Concentrations and Water Turbulence Influence the Importance of Conjugation Versus Phage-Mediated Antibiotic Resistance Gene Transfer in Suspended Growth Systems.

Despite the abundance of phage-borne antibiotic resistance genes (ARGs) in the environment, the frequency of ARG propagation via phage-mediated transduction (relative to via conjugation) is poorly understood. We investigated the influence of bacterial concentration and water turbulence level [quantified as Reynold's number (Re)] in suspended growth systems on the frequency of ARG transfer by two mechanisms: delivery by a lysogenic phage (phage λ carrying gentamycin-resistance gene, genR) and conjugation mediated by the self-transmissible plasmid RP4. Using Escherichia coli (E. coli) as the recipient, phage delivery had a comparable frequency (1.2 ± 0.9 × 10-6) to that of conjugation (1.1 ± 0.9 × 10-6) in suspensions with low cell concentration (104 CFU/mL) and moderate turbulence (Re = 5 × 104). Turbulence affected cell (or phage)-to-cell contact rates and detachment (due to shear force), and thus, it affected the relative importance of conjugation versus phage delivery. At 107 CFU/mL, no significant difference was observed between the frequencies of ARG transfer by the two mechanisms under quiescent water conditions (2.8 ± 0.3 × 10-5 for conjugation vs 2.2 ± 0.5 × 10-5 for phage delivery, p = 0.19) or when Re reached 5 × 105 (3.4 ± 1.5 × 10-5 for conjugation vs 2.9 ± 1.0 × 10-5 for phage delivery, p = 0.52). Transcriptomic analysis of genes related to conjugation and phage delivery and simulation of cell (or phage)-to-cell collisions at different Re values corroborate that the importance of phage delivery relative to conjugation increases under either quiescent or turbulent conditions. This finding challenges the prevailing view that conjugation is the dominant ARG transfer mechanism and underscores the need to consider and mitigate potential ARG dissemination via transduction.

Enhanced output performance of ZnO thin film triboelectric nanogenerators by leveraging surface limited ga doping and insulting bulk

Although triboelectric nanogenerator (TENG) has been developed as a new green energy source, the dominant charge transfer mechanism regarding surface chemistry has not been fully uncovered yet, especially in semiconductor materials. Semiconductor materials are technically important not only capable of tuning total carrier concentrations available for charge transfer in TENG, but corresponding optoelectronic properties for applications into tribo-tronics. However, doping renders one serious drawback as tribo-charges tend to leak and cannot be held in place for energy output. In order to prevent carriers from leaking while maintain the characteristics of tunable carrier concentrations in semiconductors, a two-layer structure of Ga-doped ZnO/undoped-ZnO is proposed by a two-step growth methodology. A ZnO thin film was first grown by magnetron sputter followed by Ga doping restricted to a shallow surface region by thermal diffusion treatment in the second step. The results support that surface work function difference between two materials in electrification under the well preservation of tribo-charges retention governs the charge transfer capability responsible for output performance of TENGs, where the output voltage and current of the ZnO film doped with 0.93 at% Ga can be drastically enhanced by 16 and 13 times, respectively. However, β-Ga2O3 forms on the surface when Ga concentration is higher than 0.93 at%. Nevertheless, the even larger work function of β-Ga2O3 than Ga-doped ZnO does not lead to larger output performance, implying that work function difference is not the prime factor but carrier concentration in the conduction band needs to be considered for the performance of TENGs. This work demonstrated a viable method to modify the work function of ZnO only confined to the surface through doping without disturbing the bulk, optimizing the device structure for TENGs based on semiconductor.

Development of the Hydrus-1D freezing module and its application in simulating the coupled movement of water, vapor, and heat

In cold regions, freeze-thaw cycles play a critical role in many engineering and agricultural applications and cause soil water flow and heat transport studies to be much more complicated due to phase changes involved. A fully coupled numerical module for simulating the simultaneous movement of water, vapor, and heat during freezing-thawing periods was developed and incorporated in the Hydrus-1D software in this study. To avoid numerical instabilities caused by a sudden increase in the apparent heat capacity during a phase change, a new approach based on the available energy concept was adopted to adjust soil temperature when the freezing temperature is reached. The proposed freezing module's performance was then validated using experimental data collected at three field sites with typical seasonal freezing/thawing processes. Results showed that the model could efficiently obtain a convergent solution and that simulated soil moisture and temperature variations captured the observed data well. Driven by soil matric potential and temperature gradients, both liquid water and water vapor flowed towards the freezing front. The isothermal liquid flux was the most significant component of overall flow in most soil depths except in the frozen layer, where it decreased by 1–5 orders of magnitude from values before freezing. Instead, the thermal vapor flux was the dominant moisture transfer mechanism in the frozen layer and contributed about 10% to the ice formation. These results indicate that the model, which considers the coupled movement of water, vapor, and heat, can better describe the physical mechanisms of the hydrological cycle in the vadose zone during the freezing-thawing periods.

Solvent-free dynamic nuclear polarization enhancements in organically modified mesoporous silica.

High-field dynamic nuclear polarization is a powerful tool for the structural characterization of species on the surface of porous materials or nanoparticles. For these studies the main source of polarization are radical-containing solutions which are added by post-synthesis impregnation of the sample. Although this strategy is very efficient for a wide variety of materials, the presence of the solvent may influence the chemistry of functional species of interest. Here we address the development of a comprehensive strategy for solvent-free DNP enhanced NMR characterization of functional (target) species on the surface of mesoporous silica (SBA-15). The strategy includes the partial functionalization of the silica surface with Carboxy-Proxyl nitroxide radicals and target Fmoc-Glycine functional groups. As a proof of principle, we have observed for the first time DNP signal enhancements, using the solvent-free approach, for 13C{1H} CPMAS signals corresponding to organic functionalities on the silica surface. DNP enhancements of up to 3.4 were observed for 13C{1H} CPMAS, corresponding to an experimental time save of about 12 times. This observation opens the possibility for the DNP-NMR study of surface functional groups without the need of a solvent, allowing, for example, the characterization of catalytic reactions occurring on the surface of mesoporous systems of interest. For 29Si with direct polarization NMR, up to 8-fold DNP enhancements were obtained. This 29Si signal enhancement is considerably higher than the obtained with similar approaches reported in literature. Finally, from DNP enhancement profiles we conclude that cross-effect is probably the dominant polarization transfer mechanism.

Transfer mechanisms in semiconductor hybrids with colloidal core/shell quantum dots on ZnSe substrates

Hybrid systems consisting of colloidal CdS/ZnS core/shell quantum dots on ZnSe semiconductor substrates have been studied by continuous-wave and nanosecond time-resolved photoluminescence. On the basis of kinetic calculations, we studied the interplay between the possible transfer processes in these hybrids. The considered transfer mechanisms were resonance energy transfer, photon reabsorption, electron and hole tunneling. Depending on the size of the CdS cores the dominating transfer mechanism is changing. Carrier tunneling was found only for quantum dots in direct contact to the substrate. For large quantum dots a hole tunneling was found, whereas in case of small dots the fast electron tunneling is decisive. Eventually, we were able to determine the conduction band offset between CdS and ZnSe to 0.56 eV at 10 K.

Plasma induced vibrational excitation of CH4—a window to its mode selective processing

Vibrational excitation of methane is believed to promote chemistry and improve product selectivity, compared to thermal conversion methods. We report on unique direct measurements of vibrational–rotational non-equilibrium in methane plasma. The non-equilibrium is sustained for 50 μs, after which the gas temperature equilibrates with the vibrational temperature at around 900 K. The plasma is generated by applying 200 μs, 30 Hz pulses of microwave radiation to methane at 25 mBar. We demonstrate that in microwave discharges, power transfer to vibrational modes of CH4 is the dominant power transfer mechanism, which leads to creation of a vibrational–translational (VT) non-equilibrium. VT relaxation is determined to be the dominant translational heating mechanism in the discharge. However, the high electron temperature at breakdown also leads to strong electronic excitation which may be responsible for some of the heating. Furthermore, we find that the CH4 vibrational levels are in equilibrium with each other due to fast intra-polyad relaxation (VV), and therefore bending vibrational modes population density is greatly in excess of stretching vibrational modes. The window of opportunity to exploit this non-equilibrium is limited by the VT relaxation timescale, which is approximately 50 μs in our experiment.

On the material-dependent charge transfer mechanism of the contact electrification

Abstract Although contact electrification (CE) has been discovered for more than 2600 years, its dominant charge transfer mechanism by either electrons or materials/ions continues to elude the scientific community. Here, the material-dependent CE mechanism with a model established through the extracted potential barrier height W is demonstrated via the contact-separation mode triboelectric nanogenerator as the tool. The results indicate the W in metal/polymer pairs is mainly determined by the polymer rather than the metal, implying the electron transfer dominant mechanism. On the contrary, the W extracted in CE of polymer/polymer pairs may be related to multiple material surfaces and/or other factors such as chemical reactions, indicating the possible co-existence of both electron transfer and material transfer mechanisms. This material-dependent charge transfer mechanism may give a potential answer to the millennium debate on the CE, which is essential for controlling the surface charge level upon requirements of applications.

Laboratory Characterization of The Load Transfer-Crack Width Relation for Innovative Short Concrete Slabs Pavements

Aggregate interlock is the dominant load transfer mechanism in non-dowelled Jointed Plain Concrete Pavements, as the innovative short concrete slabs. Although the Load Transfer Efficiency of this pavement innovation is based on that mechanism, the structural design methods do not relate the Load Transfer Efficiency by aggregate interlock with its direct cause, which is the Crack Width under the joints. The objective of the present article is to characterise in the laboratory the Load Transfer Efficiency−Crack Width relation for innovative short slabs Jointed Plain Concrete Pavements. Additionally, as an alternative to large-scale laboratory tests to study the Load Transfer Efficiency, a practical test on a reduced scale is proposed. The results confirmed that short slabs Jointed Plain Concrete Pavements with high-quality aggregates are able to provide adequate Load Transfer Efficiency (above 70%) without dowels bars. Based on the laboratory results, complemented with previous field data, a Load Transfer Efficiency−Crack Width curve is proposed and made available for structural design methods of short slabs Jointed Plain Concrete Pavements. Finally, the laboratory test on a reduced scale is useful to develop specific Load Transfer Efficiency−Crack Width relations using standard equipment available in traditional concrete laboratories.

One‐pot synthesis of two‐dimensional porphyrin‐based polymer and derived N‐doped porous carbon as efficient oxygen reduction catalysts

This work describes the synthesis and functions of a two-dimensional porous polymer based on porphyrin. Upon condensation, coordination and treatment with high temperature, porphyrin-based porous carbon nanosheets were obtained with the high specific surface area of 466 m2 g−1. Benefiting from its high surface area, co-doping with iron/nitrogen and hierarchical porous structure, the optimised example exhibits excellent electrochemical performance for the oxygen reduction reaction under alkaline conditions with a low half-wave potential of 0.73 V (lower than 0.78 V for Pt/C), a dominant four-electron transfer mechanism (n = 3.97 at 0.64 V) and a high diffusion limiting current density of 5.27 mA cm−2.

Low-Cost and Highly Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction: Environment-Friendly Three-Dimensional B, N Co-doped Graphene Aerogels

Nitrogen (N) and boron (B) co-doped graphene materials have been certified as promising catalyst for oxygen reduction reaction (ORR), since the dual doping of foreign atoms could induce a unique electronic structure in graphene and create a synergistic coupling effect between heteroatoms. However, previously reported B, N co-doped graphene materials suffered from shortcomings such as needing highly toxic precursors or high cost or complex preparation procedures. Herein, one highly efficient metal-free ORR catalyst, three-dimensional graphene aerogels (GAs) co-doped with B and N using economical and environmentally friendly melamine and boric acid as heteroatom precursors, was prepared through a one-step hydrothermal method. The as-prepared microporous B, N co-doped GAs showed excellent electrochemical catalytic performances for ORR under alkaline condition (0.1 M KOH) with a much more positive onset potential (0.994 V vs. RHE) than most of the existing B, N co-doped ones, a dominant four-electron transfer mechanism (n = 3.73 at 0.6 V), as well as excellent stability.

One-step electrochemical strategy for in-situ synthesis of S,N-codoped graphene as metal-free catalyst for oxygen reduction reaction

A simple and economic method was developed for synthesizing efficient S,N-codoped graphene based catalyst for oxygen reduction reaction via a one-step electrochemical exfoliation of graphite rod in melamine and (NH4)2SO4 mixture solution. On one hand, melamine and (NH4)2SO4 co-worked as electrolyte to enhance the exfoliation efficiency of graphite into graphene nanosheets. On the other hand, they also provided nitrogen and sulphur sources for in-situ codoping of the as-prepared graphene. As evidenced, the N and S elements are distributed uniformly throughout the graphene nanosheets which possessed larger interlayer spacing, more lattice disorder and higher defect density. Accordingly, the obtained SNG shows efficient ORR catalytic activity with an onset potential of 0.88 V and a dominant four-electron transfer mechanism (n = 3.98 at 0.5 V), long-time durability and excellent methanol tolerance, which are comparable or superior to those of commercial Pt/C catalysts.

The role of redox hopping in metal-organic framework electrocatalysis.

The dominant charge transfer mechanism in a vast number of metal-organic frameworks (MOFs) is that of redox hopping, a process best explained through the motion of electrons via self-exchange reactions between redox centers coupled to the motion of counter-balancing ions. Mechanistic studies of redox hopping transport in MOFs reveal characteristics that recall pioneering studies in linear redox polymers. When MOFs are employed as electrocatalysts, consideration must be given to both the catalytic properties - turn-over frequency (TOF) and energetic requirements (overpotential, TON) - and the charge transport properties - rate of charge hopping, measured via an apparent diffusion coefficient (Dapp). Herein, we provide a mathematical framework to provide constraints to MOF catalyst development by relating Dapp, TOF, and film thickness in the context of providing 10 mA cm-2 of catalytic current. Lastly with the mechanistic studies discussed as a foundation, design rules for future MOF electrocatalysts are provided and the challenges to the community to optimize MOF charge transport are laid out.

Evaluation of dominant momentum transfer mechanisms across a part of the city of Abu Dhabi

Quantifying and understanding momentum transfer close to and above buildings within a city, and the mixing and transport within the Urban Canopy Layer (UCL) are important to tackle problems such as air pollution, the heat island effect and other transport phenomena. The correct temporal and spatial averaging of the Navier-Stokes equations give rise to three new terms that constitute the fluid’s shear stress. The two most significant are the turbulent stress and the dispersive stress. Their relative importance has been studied in the literature but, as Manes, et al. [1] point out, analysing only the value of these stresses might be misleading for assessing the dominant momentum transfer mechanisms involved. The derivate of the turbulent and dispersive stresses dictate the Navier-Stokes equations and thus, these should be studied. Furthermore, the flow’s turbulent characteristics and the turbulent stress inside the urban canopy and right above it, have been extensively studied in field campaigns, laboratory experiments and numerical simulations, although most of these studies make use of arrays of cuboids as proxies for buildings. Numerical simulation of real cities, rather than arrays of cuboids, involve much greater model complexity and computation time. A 3D steady-state Reynolds Averaged Navier-Stokes equations (RANS) simulation is conducted to derive and evaluate the dominant transfer mechanisms across a real city – Abu Dhabi.

Comparative Study of the Magnetic Field Dependent Signal Enhancement in Solid-State Dynamic Nuclear Polarization Experiments

A detailed study of the magnetic field dependent signal enhancement in solid-state dynamic nuclear polarization (DNP) experiments is presented for a specific sample consisting of AMUPol dissolved in the nonionic surfactant C10E6. C10E6 displays a superposition of “direct” and “indirect channel” resonances in 13C MAS DNP NMR spectra. The shapes of the DNP enhancement profiles are essentially identical for the 1H MAS, 1H → 13C CP MAS, and 13C MAS indirect channel signals, which confirms that the same polarization transfer process from electron to proton is responsible for the obtained enhancements of these experiments. The shape of the DNP enhancement profiles of 1H and of 13C direct channel resonances reveals that the cross effect is the dominant polarization transfer mechanism for the studied sample. The magnitudes of the 13C MAS DNP enhancement profiles for 1H → 13C CP MAS, direct and indirect channel signals were found to be not uniform. For 1H → 13C CP MAS and the indirect channel signals, this observa...

Knowledge transfer: an information theory perspective

Personalization and codification are two dominant knowledge transfer (KT) mechanisms found in organizations and organizational networks. This paper proposes a theoretical model of KT that explains organizations’ choice of KT mechanisms in terms of the tacitness of knowledge being shared and the corresponding information content. Shannon’s entropy, an information theoretical concept, has been used to define the constructs of tacitness and information content and explain their influence on the choice of the corresponding KT mechanisms. Contributions of the paper include (a) use of information content as a predictor of the choice of KT mechanisms, (b) development of an expression for tacitness, and an intuitive explanation of the tacit-explicit continuum, (c) characterization of product variety in terms of information content, and (d) development of a KT theoretical model that can be operationalized for predicting the choice of KT mechanisms in real-life situations.

Hollow-structured conjugated porous polymer derived Iron/Nitrogen-codoped hierarchical porous carbons as highly efficient electrocatalysts

Iron and nitrogen (Fe/N) co-doped porous carbons have already shown great potential as electrocatalysts for oxygen reduction reaction in alkaline media. However, it still remains a great challenge to finely integrate a hierarchical porous structure and Fe/N co-doping effect into one material at the same time. In this work, a rational design toward Fe/N-codoped hierarchical porous carbon spheres was developed by the formation of an iron-porphyrin-containing conjugated microporous polymer sphere with hollow structure (HCMP) through a silica sphere template directed condensation of pyrrole and 1,4-phthalaldehyde, then etched with NaOH, and treated with FeCl2. The resulting HCMP-Fe polymer was readily converted to a series of Fe/N co-doped hierarchical porous carbons (HPC-Fe/N-X, X=700–900) upon pyrolysis at different temperatures and etching treatment. These porous carbons exhibit the high specific surface areas up to 518m2g−1 and the contents of N and Fe up to 3.28at.% and 0.85wt.%, respectively. Benefiting from the high surface area, Fe/N co-doping character, HPC-Fe/N-700 exhibited excellent electrochemical catalytic performance for oxygen reduction reaction under alkaline condition (0.1M KOH) with a low half-wave potential (0.84V), a dominant four-electron transfer mechanism (n=3.89 at 0.65V), as well as a high diffusion limiting current density (JL=5.19mAcm−2), comparable to those porous carbon-based ORR catalysts with excellent electrochemical performance.