scholarly journals C–O cleavage of aromatic oxygenates over ruthenium catalysts. A computational study of reactions at step sites

2015 ◽  
Vol 17 (23) ◽  
pp. 15324-15330 ◽  
Author(s):  
Cheng-chau Chiu ◽  
Alexander Genest ◽  
Armando Borgna ◽  
Notker Rösch
Keyword(s):  
Computational Study ◽  
Ruthenium Catalysts ◽  
Computational Results

C–O scissions of catecholate and phenolate on stepped Ru surfaces have accessible barriers. Computational results illustrate that benzene formation in the hydrodeoxygenation of aromatics over Ru occurs at step sites.

Computational Study of a Path-Based Algorithm and Its Variants for Static Traffic Assignment

1996 ◽  
Vol 1537 (1) ◽  
pp. 106-115 ◽  
Author(s):  
Carlos Sun ◽  
R. Jayakrishnan ◽  
Wei K. Tsai
Keyword(s):  
Line Search ◽  
Computational Study ◽  
Urban Traffic ◽  
Computer Memory ◽  
Traffic Networks ◽  
Computational Results ◽  
First Derivative ◽  
Line Search Techniques ◽  
Real Time Applications

Recent research has indicated that advances in computer memory have made the use of path-based algorithms in urban traffic networks a possibility. The path-based gradient projection (GP) offers significant benefits in computation times over the conventional Frank-Wolfe algorithm and may be especially suited for real-time applications. The computational results from applying GP to networks of up to 4,900 nodes, as well as the performance of different variants of GP, are discussed. Also discussed is the sensitivity of the results to parameters such as the number of destinations and the level of congestion. The variants of the basic GP algorithm examined are intended to further improve the per-iteration performance of the algorithm for larger networks. These variants include a GP version with a modified first derivative update and different versions that use line-search techniques, including a boundary stopping method. The results establish that GP indicates substantial benefits even for larger networks. The modifications, while they do improve the computation times per GP iteration, affect the convergence quality of the algorithm, indicating that the earlier GP algorithm is a better alternative for both large and small networks.

Experimental and Computational Study of Effects of Viscosity of the Filter Media in a Developed Particulate Trapping System

2018 ◽  
Vol 9 (5) ◽  
Author(s):  
Y. Liu
Keyword(s):  
Experimental Data ◽  
Management System ◽  
Experimental Validation ◽  
Computational Study ◽  
Cost Effective ◽  
Manufacturing Cost ◽  
Present System ◽  
Computational Results ◽  
Experimental Assessment ◽  
Good Agreement

A cost effective, portable particulate management system was developed, prototyped, and evaluated for further application and commercialization, which could remove and dispose particulate matter suspended in air efficiently and safely. A prototype of the present system was built for experimental assessment and validation. The experimental data showed that the developed particulate management system can effectively clean the air by capturing the particles inside it. Effects of viscosity of filter medium on the performance of the developed system were also discussed. The present system is very flexible, whose size and shape can be scaled and changed to be fit for different applications. Its manufacturing cost is less than $10. Based on the experimental validation results, it was found that the present system can be further developed, commercialized, and applied for a variety of industries. The experiments and experimental data were simulated and validated using computer fluent dynamics. A relatively good agreement was achieved between the experimental and computational results.

A Computational Study of In-Cylinder NOx Reduction Strategies for a Compression-Ignition Engine Fueled With Diesel/Hydrogen Mixtures

2015 ◽  
Author(s):  
Hassan A. Khairallah ◽  
Umit O. Koylu
Keyword(s):  
Chemical Kinetics ◽  
Alternative Fuels ◽  
Computational Study ◽  
Nox Reduction ◽  
Nox Emissions ◽  
Computational Results ◽  
Detailed Chemical Kinetics ◽  
Compression Ignition Engine ◽  
Performance And Emission ◽  
Main Challenge

Considerable efforts have been made to introduce alternative fuels for use in conventional diesel and gasoline engines. There is significant interest in adding hydrogen to a diesel engine to reduce emissions and improve efficiency. However, the main challenge associated with the use of hydrogen in diesel engines is high nitrogen oxide (NOX) emissions. In the present study, a reduced chemical kinetics mechanism, consisting of 52 reactions and 29 chemical species for n-heptane fuel combustion, was incorporated with detailed chemical kinetics consisting of 29 reactions for hydrogen as well as additional nitrogen oxidation. This reaction mechanism was coupled with 3-D advanced CFD software to investigate the performance and emission characteristics of a diesel-hydrogen dual-fuel engine. Computational results showed good agreements with the experimental results for brake thermal efficiency, CO2, CO, and NOX emissions. The model was then employed to examine the effects of exhaust gas recirculation (EGR) and N2 dilution on NOX emissions. The computational results quantified the reduction in NOX emissions with EGR and N2 dilution, and a more remarkable reduction was found with 30% N2 dilution. However, in terms of the N2 dilution, a general decreasing trend was observed for both NOX and CO2 emissions, while CO emissions increased. In relation to the EGR, the NOX emissions decreased while CO2 and CO emissions significantly increased. Additionally, the results showed that the indicated mean effective pressure (IMEP) and indicated power decreased as the N2 dilution increased. The same trend was observed for the EGR but the reduction was less compared to that of the N2 dilution.

REGIOSELECTIVITY INVESTIGATION FOR THE PYROLYSIS OF XANTHATES: A COMPUTATIONAL STUDY

2013 ◽  
Vol 12 (07) ◽  
pp. 1350064 ◽  
Author(s):  
PING WU ◽  
JOHNNY TRUONG ◽  
YONGSHUN HUANG ◽  
JIAXING LI
Keyword(s):  
Oxygen Atom ◽  
Computational Study ◽  
Transition States ◽  
Major Product ◽  
Membered Ring ◽  
Computational Results ◽  
Atomic Size ◽  
Rate Determining Step ◽  
Ring Transition State ◽  
Step Mechanism

MP2/6-31+G(d,p)//MP2/6-31G(d) method was employed to investigate the pyrolyses of O -sec-butyl S -methyl xanthate (Chugeav reaction) and S -sec-butyl O -methyl xanthate, which gave regioselective products of E-butene, Z-butene and 1-butene. Both procedures were found to have 13 possible pathways, of which nine pathways would generate the alkene products. For O -sec-butyl S -methyl xanthate, the computational results indicated that the most favorable three pathways corresponded to a two-step mechanism, with the rate-determining step to be a thion sulfur atom involved six-membered ring transition states. The calculated products distribution was consistent with the experimental observations. However, for S -sec-butyl O -methyl xanthate, thiol-participated four-membered ring transition states were found to be more energetically favored than the six-membered ring transition state to produce 1-butene, which can be attributed to a larger sulfur atomic size than an oxygen atom. As the calculation result, only trace amount of 1-butene could be obtained with a major product being E-butene and Z-butene as a minority.

Design and off-design behavior of a tandem rotor stage

2019 ◽  
Vol 234 (4) ◽  
pp. 927-942 ◽  
Author(s):  
Amit Kumar ◽  
AM Pradeep
Keyword(s):  
Flow Separation ◽  
Computational Study ◽  
Adverse Pressure Gradient ◽  
Computational Results ◽  
Suction Surface ◽  
Compressor Blades ◽  
Tip Leakage ◽  
To Come ◽  
And Performance ◽  
Parametric Analyses

With an ever-increasing focus on clean and sustainable energy for transport and power, aero-engine designers need to come up with engine designs that can meet the efficiency and thrust requirements. In this aspect, compressor/fan designers always aim at designs that can result in higher pressure ratios and maximum possible efficiency with a fewer number of stages. Compressor blades, which are designed for higher diffusion, have an inherent risk of flow separation. This, therefore, fixes the upper permissible limit in terms of diffusion. If the suction surface adverse pressure gradient can be efficiently managed to avoid flow separation, it would be possible to target higher diffusion factors. One such concept for achieving this is using tandem blading. In the present computational study, a conventional low-speed compressor stage performance is compared with a tandem stage. Both designs attempt similar levels of targeted diffusion. The computational results are simulated at the design and the off-design conditions. The computational results are validated with experimental data. A high percentage pitch and low axial overlap configuration are finalized for the design of the tandem rotor based on existing literature as well as initial parametric analyses. The study shows that it is possible to achieve higher diffusion for the tandem rotor in comparison to a single rotor. The behavior of the gap-nozzle, interaction of the tip leakage with the gap-nozzle, blockage due to the tip leakage vortex, performance of stator, and performance of both stages are discussed in detail in this paper.

scholarly journals Reinforced concrete ribbed slabs with wide-beam

2018 ◽  
Vol 11 (5) ◽  
pp. 966-996
Author(s):  
P. V. P. SACRAMENTO ◽  
M. S. PICANÇO ◽  
D. R. C. OLIVEIRA
Keyword(s):  
Shear Strength ◽  
Reinforced Concrete ◽  
Critical Point ◽  
Ultimate Load ◽  
Computational Study ◽  
Neutral Line ◽  
Computational Results ◽  
Test Results ◽  
Wide Beam ◽  
The Difference

Abstract Ribbed slabs have been widely used in buildings due to their many advantages, especially the decrease of concrete below the neutral line. This paper presents an experimental and computational study on ribbed slabs with wide-beam, two one-way slabs and two two-way slabs, with variable depths were tested to evaluate their resistance to punching and shear strength of slabs. Experimental and computational results showed that the wide-beam ribs connection is a critical point in the design of the slabs due to the difference in stiffness in the transition zone. Best results for the ultimate load estimates for ribs were provided by EC 2 (2004), while estimates of ACI 318 (2008) and NBR 6118 (2014) were respectively conservative and unsafe. Test results on slabs also revealed that the Brazilian alternative to analysis ribbed slabs as solid ones failed to give satisfactory results.

Experimental and Computational Study of Heat/Mass Transfer and Flow Structure for Four Dimple Shapes in a Square Internal Passage

2009 ◽  
Author(s):  
Fuguo Zhou ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Mass Transfer ◽  
Computational Study ◽  
Computational Results ◽  
Flow Conditions ◽  
Naphthalene Sublimation ◽  
Sublimation Method

Mass/heat transfer measurements are made using the naphthalene sublimation method in a square internal passage where one wall has a single dimple. Four types of dimple shapes are studied: square, triangular, circular and teardrop. Sherwood numbers are obtained both inside and around the dimples. Measurements are made at a Reynolds number of 21,000. In addition, computations are performed for the same dimple geometries, and with the same flow conditions as in the experiments. Flow patterns for the four dimples are identified, and heat transfer distributions for each dimple are obtained. Computational results are compared with the experimental data and show satisfactory agreement. Both experimental and numerical results suggest that the teardrop dimple has the highest heat /mass transfer among the four dimple shapes studied.

scholarly journals Structure of Cubic Lehman Matrices

10.37236/7947 ◽  
2019 ◽  
Vol 26 (3) ◽  
Author(s):  
Dillon Mayhew ◽  
Irene Pivotto ◽  
Gordon Royle
Keyword(s):  
Bipartite Graph ◽  
Adjacency Matrix ◽  
Computational Study ◽  
Computational Results ◽  
Alpha Omega ◽  
Regular Bipartite Graph

A pair $(A,B)$ of square $(0,1)$-matrices is called a Lehman pair if $AB^T=J+kI$ for some integer $k\in\{-1,1,2,3,\ldots\}$. In this case $A$ and $B$ are called Lehman matrices. This terminology arises because Lehman showed that the rows with the fewest ones in any non-degenerate minimally nonideal (mni) matrix $M$ form a square Lehman submatrix of $M$. Lehman matrices with $k=-1$ are essentially equivalent to partitionable graphs (also known as $(\alpha,\omega)$-graphs), so have been heavily studied as part of attempts to directly classify minimal imperfect graphs. In this paper, we view a Lehman matrix as the bipartite adjacency matrix of a regular bipartite graph, focusing in particular on the case where the graph is cubic. From this perspective, we identify two constructions that generate cubic Lehman graphs from smaller Lehman graphs. The most prolific of these constructions involves repeatedly replacing suitable pairs of edges with a particular $6$-vertex subgraph that we call a $3$-rung ladder segment. Two decades ago, Lütolf & Margot initiated a computational study of mni matrices and constructed a catalogue containing (among other things) a listing of all cubic Lehman matrices with $k =1$ of order up to $17 \times 17$.  We verify their catalogue (which has just one omission), and extend the computational results to $20 \times 20$ matrices. Of the $908$ cubic Lehman matrices (with $k=1$) of order up to $20 \times 20$, only two do not arise from our $3$-rung ladder construction. However these exceptions can be derived from our second construction, and so our two constructions cover all known cubic Lehman matrices with $k=1$.

COMPUTATIONAL STUDY OF UNIMOLECULAR DECOMPOSITION MECHANISM OF RDX EXPLOSIVE

2007 ◽  
Vol 06 (02) ◽  
pp. 341-351 ◽  
Author(s):  
MIN HSIEN LIU ◽  
GEN FA ZHENG
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Bond Breaking ◽  
Computational Results ◽  
Unimolecular Decomposition ◽  
Homolytic Cleavage ◽  
Trans Form ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Bonding Site

This study investigated the RDX (1,3,5-Trinitro-1,3,5-triazine) molecule to elucidate its possible decomposition species and the corresponding energies by performing the density-functional theory (DFT) calculations. Reasonable decomposition mechanisms are proposed based on the bond energy calculated using the differential overlap (INDO) program, which yields the weakest bonding site for reference and determines the site of easy cleavage. Computational results indicate that the activation energy of direct cis-form HONO elimination is lower than that of direct trans-form HONO elimination and that of a two-stage elimination of two forms of HONO ( N – N bond fission combined with C – H bond breaking) in the initial decomposition step, which are 213.9 kJ/mol and 93.8–101.8 kJ/mol, respectively. Two possible pathways are proposed; (1) N – N bond homolytic cleavage followed by elimination of cis-form HONO, and (2) N – N bond homolytic cleavage followed by elimination of trans-form HONO.

Experimental and Computational Study of Heat/Mass Transfer and Flow Structure for Four Dimple Shapes in a Square Internal Passage

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Sumanta Acharya ◽  
Fuguo Zhou
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Mass Transfer ◽  
Computational Study ◽  
Computational Results ◽  
Flow Conditions ◽  
Naphthalene Sublimation ◽  
Sublimation Method

Mass/heat transfer measurements are made using the naphthalene sublimation method in a square internal passage where one wall has a single dimple. Four types of dimple shapes are studied: square, triangular, circular, and teardrop. Sherwood numbers are obtained both inside and around the dimples. Measurements are made at a Reynolds number of 21,000. In addition, computations are performed for the same dimple geometries, and with the same flow conditions as in the experiments. Flow patterns for the four dimples are identified and heat transfer distributions for each dimple are obtained. The computational results are compared with the experimental data and show satisfactory agreement. Both the experimental and numerical results suggest that the teardrop dimple has the highest heat /mass transfer among the four dimple shapes studied.

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