Modelling PAH curvature in laminar premixed flames using a detailed population balance model

© 2016 The Combustion Institute A detailed population balance model, which includes the kinetic Monte Carlo-aromatic site (KMC-ARS) model for detailed polycyclic aromatic hydrocarbon (PAH) growth, is used to compute the Gauss curvature of PAHs in laminar premixed ethylene and benzene flames. Previous studies have found that capping of an embedded 5-member ring causes curvature in graphene edges. In this work, a capping process is added to the KMC-ARS model with the rate coefficient of the capping reaction taken from the work of You et al. (2011). We demonstrate that the Gauss–Bonnet theorem can be used to derive a correlation between the number of 5- and 6-member rings in a PAH and its Gauss curvature (or radius of curvature), independent of where the 5-member ring is embedded within the PAH structure. Numerical simulation yields satisfactory results when compared to the experimentally determined Gauss curvature reported in the literature. Computed and experimental fringe length distributions are also compared and the results suggest that PAHs smaller than the size required for inception are able to condense onto particles.This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its CREATE programme. Mr. Edward K. Y. Yapp was supported by the Gates Cambridge, Cambridge, UK. Prof. Markus Kraft was supported by the Weierstrass Institute for Applied Analysis and Stochastics, Berlin, Germany

A detailed particle model for polydisperse aggregate particles

The mathematical description of a new detailed particle model for polydisperse aggregate particles is presented. An aggregate particle is represented as a collection of overlapping spherical primary particles and the model resolves the composition, radius and position coordinates of each individual primary to form a detailed geometrical description of aggregate morphology. Particles transform under inception, coagulation, surface growth, sintering and coalescence processes. The new particle description is used to model the aerosol synthesis of titanium dioxide (TiO2) aggregates from titanium tetraisopropoxide (TTIP) precursor. TiO2 particles are formed through collision-limited inception and growth reactions of Ti(OH)4 from the gas-phase, produced from the thermal decomposition of TTIP. Coupling between the particle population balance and detailed gas-phase chemistry is achieved by operator splitting. A numerical study is performed by simulating a simple batch reactor test case to investigate the convergence behaviour of key functionals with respect to the maximum number of computational particles and splitting time step. Finally, a lab-scale hot wall reactor is simulated to demonstrate the advantages of a detailed geometrical description. Simulated particle size distributions were in reasonable agreement with experimental data. Further evaluation of the model and a parametric sensitivity study are recommended

Consequences of delayed maintenance of pavement networks

Pavement networks must preserve an acceptable level of service to sustain the economic, social, and environmental development of society. The preservation of pavements is only possible when timely maintenance actions are conducted on a regular basis. Delayed maintenance can cause significant impacts on the pavement network but a systematic procedure to quantify this impact is required. This paper describes the application of a framework to quantify the consequences of delayed maintenance of pavement networks. In this framework, a pavement preservation policy is defined, and performance objectives are established. Maintenance treatments and budget needs are identified based on the pavement condition. A case study is used to demonstrate the impact of delayed maintenance of three pavement networks at different conditions (Good, Fair, Poor) at the beginning of the analysis. A number of maintenance scenarios are analyzed for these pavement networks: all needs, do nothing, delayed maintenance treatments by 2 years, and budget-driven with limited funds for maintenance. The trends observed in the pavement network condition, total agency costs, backlog costs, and remaining life as a result of the analysis were similar for the three pavement networks, although the impact is higher for pavement networks in fair and poor condition. In a broader perspective, delayed maintenance may affect not only pavement condition, but also mobility, safety, transportation agency and user’s costs over time.Papers Presented at the 2018 37th Southern African Transport Conference 9-12 July 2018 Pretoria, South Africa. Theme "Towards a desired transport future: safe, sufficient and affordable"

Evaluation of a hospital-based integrated model of eye care for diabetic retinopathy assessment: A multimethod study

Objectives Diabetic eye disease is a leading cause of blindness but can be mitigated by regular eye assessment. A framework of issues, developed from the literature of barriers to eye assessment, was used to structure an examination of perceptions of a new model of care for diabetic retinopathy from the perspective of staff using the model, and health professionals referring patients to the new service. Design Multimethod: interviews and focus groups, and a separate survey. Setting A new clinic based on an integrated model of care was established at a hospital in outer metropolitan Sydney, Australia in 2017. Funded jointly by Centre for Eye Health (CFEH) and the hospital, the clinic was equipped and staffed by optometrists who work alongside the ophthalmologists in the existing hospital eye clinic. Participants Five (of seven) hospital staff working in the clinic (ophthalmologists and administrative officers) or referring to it from other departments (endocrinologists); nine optometrists from CFEH who developed or worked in the clinic; 10 community-based optometrists as potential referrers. Results The new clinic was considered to have addressed known barriers to eye assessment, including access, assistance for patients unable/unwilling to organise eye checks and efficient management of human resources. The clinic optimised known drivers of this model of care: providing clear scope of practice and protocols for shared care between optometrists and ophthalmologists, good communication between referrers and eye professionals and a collegial approach promoting interprofessional trust. Remaining areas of concern were few referrals from general practitioners, fewer referrals from hospital endocrinologists than expected and issues with stretched administrative capacity. There were also perceived mismatches between the priorities of hospital management and aims of the clinic. Conclusions The new model was considered to have addressed many of the barriers to assessment. While there remain issues with the model, there were also unexpected benefits

Functional assessment of gap junctions in monolayer and three-dimensional cultures of human tendon cells using fluorescence recovery after photobleaching

Gap junction-mediated intercellular communication influences a variety of cellular activities. In tendons, gap junctions modulate collagen production, are involved in strain-induced cell death, and are involved in the response to mechanical stimulation. The aim of the present study was to investigate gap junction-mediated intercellular communication in healthy human tendon-derived cells using fluorescence recovery after photobleaching (FRAP). The FRAP is a noninvasive technique that allows quantitative measurement of gap junction function in living cells. It is based on diffusion-dependent redistribution of a gap junction-permeable fluorescent dye. Using FRAP, we showed that human tenocytes form functional gap junctions in monolayer and three-dimensional (3-D) collagen I culture. Fluorescently labeled tenocytes following photobleaching rapidly reacquired the fluorescent dye from neighboring cells, while HeLa cells, which do not communicate by gap junctions, remained bleached. Furthermore, both 18 β-glycyrrhetinic acid and carbenoxolone, standard inhibitors of gap junction activity, impaired fluorescence recovery in tendon cells. In both monolayer and 3-D cultures, intercellular communication in isolated cells was significantly decreased when compared with cells forming many cell-to-cell contacts. In this study, we used FRAP as a tool to quantify and experimentally manipulate the function of gap junctions in human tenocytes in both two-dimensional (2-D) and 3-D cultures

The Polarization of Polycyclic Aromatic Hydrocarbons Curved by Pentagon Incorporation: The Role of the Flexoelectric Dipole

© 2017 American Chemical Society. Curvature in polyaromatic hydrocarbons (PAHs), due to pentagon inclusion, produces a dipole moment that contributes significantly to self-assembly processes and adsorption at the surface of carbon materials containing curved structures. This work presents electronic structure calculations of the dipole moment for 18 different curved PAH molecules for various numbers of pentagons and the total number of aromatic rings. A significant dipole moment was found that depends strongly on the number of aromatic rings (4-6.5 D for ring count 10-20). The main cause for the dipole is shown to be the π-electron flexoelectric effect. An atom-centered partial charge representation of the charge distribution in these molecules is insufficient to correctly describe their electrostatic potential; distributed multipoles were required instead

Assessing cellular efficacy of bromodomain inhibitors using fluorescence recovery after photobleaching

BACKGROUND: Acetylation of lysine residues in histone tails plays an important role in the regulation of gene transcription. Bromdomains are the readers of acetylated histone marks, and, consequently, bromodomain-containing proteins have a variety of chromatin-related functions. Moreover, they are increasingly being recognised as important mediators of a wide range of diseases. The first potent and selective bromodomain inhibitors are beginning to be described, but the diverse or unknown functions of bromodomain-containing proteins present challenges to systematically demonstrating cellular efficacy and selectivity for these inhibitors. Here we assess the viability of fluorescence recovery after photobleaching (FRAP) assays as a target agnostic method for the direct visualisation of an on-target effect of bromodomain inhibitors in living cells. RESULTS: Mutation of a conserved asparagine crucial for binding to acetylated lysines in the bromodomains of BRD3, BRD4 and TRIM24 all resulted in reduction of FRAP recovery times, indicating loss of or significantly reduced binding to acetylated chromatin, as did the addition of known inhibitors. Significant differences between wild type and bromodomain mutants for ATAD2, BAZ2A, BRD1, BRD7, GCN5L2, SMARCA2 and ZMYND11 required the addition of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) to amplify the binding contribution of the bromodomain. Under these conditions, known inhibitors decreased FRAP recovery times back to mutant control levels. Mutation of the bromodomain did not alter FRAP recovery times for full-length CREBBP, even in the presence of SAHA, indicating that other domains are primarily responsible for anchoring CREBBP to chromatin. However, FRAP assays with multimerised CREBBP bromodomains resulted in a good assay to assess the efficacy of bromodomain inhibitors to this target. The bromodomain and extraterminal protein inhibitor PFI-1 was inactive against other bromodomain targets, demonstrating the specificity of the method. CONCLUSIONS: Viable FRAP assays were established for 11 representative bromodomain-containing proteins that broadly cover the bromodomain phylogenetic tree. Addition of SAHA can overcome weak binding to chromatin, and the use of tandem bromodomain constructs can eliminate masking effects of other chromatin binding domains. Together, these results demonstrate that FRAP assays offer a potentially pan-bromodomain method for generating cell-based assays, allowing the testing of compounds with respect to cell permeability, on-target efficacy and selectivity

A moment projection method for population balance dynamics with a shrinkage term

A new method of moments for solving the population balance equation is developed and presented. The moment projection method (MPM) is numerically simple and easy to implement and attempts to address the challenge of particle shrinkage due to processes such as oxidation, evaporation or dissolution. It directly solves the moment transport equation for the moments and tracks the number of the smallest particles using the algorithm by Blumstein and Wheeler (1973) [41]. The performance of the new method is measured against the method of moments (MOM) and the hybrid method of moments (HMOM). The results suggest that MPM performs much better than MOM and HMOM where shrinkage is dominant. The new method predicts mean quantities which are almost as accurate as a high-precision stochastic method calculated using the established direct simulation algorithm (DSA).This research is supported by the National Research Foundation, Prime Minister's Office, Singapore under its CREATE programme

Modelling of soot formation in a diesel engine with the moment projection method

© 2017 The Author(s). In this work, the recently developed moment projection method (MPM) is coupled with the Stochastic Reactor Model engine code to simulate the formation of soot in a direct injection diesel engine. The simulations take into account convective heat transfer, turbulent mixing, and adopts a detailed chemical mechanism so that the concentrations of soot precursors can be predicted. The soot model considered in this work is based on integration and modification of existing sub-models for soot inception, coagulation, condensation, surface growth and oxidation. The soot moment equations are solved using MPM which has been proven to be accurate and robust. A single-cylinder research version of the Great Wall 4D20 diesel engine with exhaust gas recirculation is modelled for two test cases with different injection timings, injection pressures and fuel consumptions. Simulations are fast (on the order of minutes) and comparison of computed and experimental pressure and heat release rate are in excellent agreement. The amount of soot produced is in qualitative agreement with measurements of diesel smoke opacity.This research is supported by the National Research Foundation, Prime Minister’s office, Singapore under its CREATE programme

Extension of moment projection method to the fragmentation process

© 2017 Elsevier Inc. The method of moments is a simple but efficient method of solving the population balance equation which describes particle dynamics. Recently, the moment projection method (MPM) was proposed and validated for particle inception, coagulation, growth and, more importantly, shrinkage; here the method is extended to include the fragmentation process. The performance of MPM is tested for 13 different test cases for different fragmentation kernels, fragment distribution functions and initial conditions. Comparisons are made with the quadrature method of moments (QMOM), hybrid method of moments (HMOM) and a high-precision stochastic solution calculated using the established direct simulation algorithm (DSA) and advantages of MPM are drawn