Electrochemical reduction of tert-butyl chloride—Computational study

In this work kinetics of the electrochemical reduction of the tert-butyl chloride molecule are studied. The two-dimensional potential surface E(x, y) was obtained from the Hamiltonian model used earlier [1] to study quantum effects on the reaction rate of the same reaction. In series of molecular dynamics simulations two different models, isotropic (γ_x = γ_y) and anisotropic (γ_x > γ_y), of the friction parameters for the solvent (γ_x) and for the C-Cl bond (γ_y) were considered. An influence of several factors, such as an overpotential, a solvent friction coefficient and a temperature, on the rate constants k obtained with the two models are presented and compared to the results obtained for the non-adiabatic mechanism. It is shown, that the anisotropic model predicts generally much smaller rates when compared to those calculated with the isotropic model and also with the non-adiabatic model. On the curves k(γ_x) the turnover region is very well defined for relatively low frictions in the isotropic case, while for the anisotropic case it is shifted towards much higher γ_x values. In all simulations the saddle point avoidance phenomenon was observed and its extent for different models and reaction conditions is discussed. Transfer coefficients α obtained for adiabatic and non-adiabatic reaction mechanisms as a function of the overpotential and temperature are also presented.     

Effects of channel modification on microstructure and mechanical properties of C/SiC composites prepared by LA-CVI process

Carbon fiber reinforced SiC matrix composites (C/SiC) with four different deposition channel sizes were fabricated via a novel laser-assisted chemical vapor infiltration (LA-CVI) method. Effects of infiltration channel sizes on microstructure and mechanical properties of C/SiC composites were investigated. The results showed that increasing the size of channels could expand infiltration passages and densification bands, which was consistent with theoretical calculations. Due to the presence of channels, the flexural strength of C/SiC composite increased by 14.47% when the channel diameter was 0.3?mm, compared to C/SiC composites prepared via conventional CVI process. Characteristics of matrix cracking and crack propagation on fracture surface were analyzed by using scanning electron microscopy. LA-CVI C/SiC composites displayed significantly improved damage-tolerant fracture behavior. Thus, findings of this work demonstrate that LA-CVI fabricated C/SiC composites are promising for a wide range of applications, particularly for enclosed-structure and thick-section C/SiC composites.     

Holistic Analysis of the Tribological Interfaces of an Axial Piston Pump – Focusing on the Pump Efficiency

Research work performed on an axial piston pump is shown in a holistic manner, analyzing each lubricating interface by linking their gap height and temperature behavior to the overall pump efficiency. The temperature field and dynamic fluid film height were measured in two of the three lubricating interfaces. This is the first time that the temperature fields and gap heights were simultaneously measured in two of the main three interfaces of an axial piston machine. For a deeper analysis of the measurement data, all gaps were simulated with a numerical tool which takes solid body deformation due to temperature and pressure loads into account. This unique combination of both extensive measurement data and sophisticated simulation resulted in novel trends that clarify the complex phenomena occurring in these hydrostatic fluid films.     

A Unified Approach for Physical and Geometric Modeling for Graphics and Animation

We present a unified approach for geometric and physical modeling using implicit functions, for application to graphics and animation. This method extends previously proposed techniques, and allows the standard finite element method to be directly combined with geometric modeling, resulting in quick calculation of an object's mass and stiffness matrices, and its vibration modes and frequencies. Because the approach is based on an implicitfunction representation, it allows very fast collision detection and characterization. Examples of complex physical and geometric modeling are presented.     

A theoretical study of activated nanostructured materials for hydrogen storage

The adsorption of molecular hydrogen on activated nanostruture materials is studied through computational simulations based on the pseudopotential density functional method. The hydrogen sorption energy and its diffusion through chemically activated pores in the materials are particularly investigated. It is found that the sorption energy of hydrogen reaches as high as about 29 kJ/mol at activated sites and can be controlled by modifying the structure and chemistry of the pores. The equilibrium pressure of hydrogen adsorption is also presented as a function of temperature by including the temperature and pressure dependence of hydrogen entropy. The desorption temperature is estimated to be close to 270 K for optimized activated nanostructures. This study demonstrates a pathway of materials search based on computational simulations for proper media that can hold hydrogen at ambient conditions through physisorption.     

Density evolution in formation of swift heavy ion tracks in insulators

Swift heavy ion irradiation leaves a latent ion track around the ion path in many materials. Here we report computational molecular dynamics (MD) simulation results on track formation in several insulating materials, quartz, amorphous silica (a-SiO₂), zinc oxide and diamond, concentrating especially in mass transport leading to density variations in the track volume during the initial stages of track formation. These details are largely unobservable in experiments due to the picosecond timescale and very local nature, and also in many computational models of track formation. Earlier a low-density core - high-density shell fine structure has been observed in latent tracks in amorphous silica, and here we study if other materials than silica show similar behavior. The results highlight the dynamical nature of track formation, that includes competing effects of heat and mass transport, rapid quenching of the heated area and recrystallization.     

Large eddy simulations of 45° and 60° inclined dense jets with bottom impact

In the present study, we performed a numerical study with the Large Eddy Simulations (LES) approach to simulate inclined dense jets with 45° and 60° inclinations in a stagnant ambient, including the bottom impact and subsequent spreading on the wall boundary. The objective was to evaluate the performance of LES on the predictions of both the kinematic and mixing behavior of the inclined dense jet with bottom boundary in the near field region. The Dynamic Smagorinsky sub-grid model was adopted with near-wall modeling for the bottom boundary. The results showed that LES can reasonably predict the jet trajectory with the present mesh scheme, including the locations of the return point and impact point at the boundary. The localized concentration build-up at the impact point reported by Abessi and Roberts (2015) was also reproduced. The impact dilution was however underestimated by ∼20% in general corresponding to the grid resolution adopted in the present study, which demonstrated the challenge to simulate accurately the dynamics of the mixing behaviour as well as the wall interaction processes. The spreading layer was examined to the end of the near field region as defined by Roberts et al. (1997). The profiles of the mean concentration and concentration fluctuation along the spreading layer were found to be similar to previous experimental results with self-similar behaviour. The dilution was however also under-predicted within the spreading layer.     

Theoretical model for the external quantum efficiency of organic light-emitting diodes and its experimental validation

An optical energy loss mechanism including the surface plasmon polariton (SPP) loss, wave guide (WG) mode and substrate mode in organic light-emitting diodes (OLEDs) is introduced based on CPS theory. The theoretical calculations of both the out-coupling efficiency (OCE) and the external quantum efficiency (EQE) of OLEDs are proposed. MATLAB tools are applied to simulate the optical model and provide the results of the two efficiencies. It is demonstrated that, the OCE and the EQE in a green phosphorescence OLED with optimized device structure can reach up to 20% and 27%, respectively (intrinsic quantum efficiency q = 90% assumed). The simulation results based on the theoretical model are further validated experimentally.     

First universal pharmacophore model for hERG1 K+ channel activators: acthER

The intra-cavitary drug blockade of hERG1 channel has been extensively studied, both experimentally and theoretically. Structurally diverse ligands inadvertently block the hERG1 K⁺ channel currents lead to drug induced Long QT Syndrome (LQTS). Accordingly, designing either hERG1 channel openers or current activators, with the potential to target other binding pockets of the channel, has been introduced as a viable approach in modern anti-arrhythmia drug development. However, reports and investigations on the molecular mechanisms underlying activators binding to the hERG1 channel remain sparse and the overall molecular design principles are largely unknown. Most of the hERG1 activators were discovered during mandatory screening for hERG1 blockade. To fill this apparent deficit, the first universal pharmacophore model for hERG1 K⁺ channel activators was developed using PHASE. 3D structures of 18 hERG1 K⁺ channel activators and their corresponding measured binding affinity values were used in the development of pharmacophore models. These compounds spanned a range of structurally different chemotypes with moderate variation in binding affinity. A five sites AAHRR (A, hydrogen-bond accepting, H, hydrophobic, R, aromatic) pharmacophore model has shown reasonable high statistical results compared to the other developed more than 1000 hypotheses. This model was used to construct steric and electrostatic contour maps. The predictive power of the model was tested with 3 external test set compounds as true unknowns. Finally, the pharmacophore model was combined with the previously developed receptor-based model of hERG1 K⁺ channel to develop and screen novel activators. The results are quite striking and it suggests a greater future role for pharmacophore modeling and virtual drug screening simulations in deciphering complex patterns of molecular mechanisms of hERG1 channel openers at the target sites. The developed model is available upon request and it may serve as basis for the synthesis of novel therapeutic hERG1 activators.     

Extraordinary Macroscale Wear Resistance of One Atom Thick Graphene Layer

During the last few years, graphene's unusual friction and wear properties have been demonstrated at nano to micro scales but its industrial tribological potential has not been fully realized. The macroscopic wear resistance of one atom thick graphene coating is reported by subjecting it to pin‐on‐disc type wear testing against most commonly used steel against steel tribo‐pair. It is shown that when tested in hydrogen, a single layer of graphene on steel can last for 6400 sliding cycles, while few‐layer graphene (3–4 layers) lasts for 47 000 cycles. Furthermore, these graphene layers are shown to completely cease wear despite the severe sliding conditions including high contact pressures (≈0.5 GPa) observed typically in macroscale wear tests. The computational simulations show that the extraordinary wear performance originates from hydrogen passivation of the dangling bonds in a ruptured graphene, leading to significant stability and longer lifetime of the graphene protection layer. Also, the electronic properties of these graphene sheets are theoretically evaluated and the improved wear resistance is demonstrated to preserve the electronic properties of graphene and to have significant potential for flexible electronics. The findings demonstrate that tuning the atomistic scale chemical interactions holds the promise of realizing extraordinary tribological properties of monolayer graphene coatings.