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Railroad turnouts are an essential element of the track infrastructure that facilitates the movement of trains between adjacent or diverging tracks. Turnout frogs are subjected to high wheel impact forces due to the inherent need for a discontinuity in their geometry. To develop an optimised frog geometry to minimise wheel impacts, a parametric study was designed and executed that considered three critical design parameters: point (i.e. nose) slope, relative height difference between wing and point, and longitudinal wing slope. Four hundred wheel profiles were extracted from a dataset of one million revenue service wheel profiles based on a wheel classification methodology previously developed. Wheel impact was quantified for each frog geometry case based on wheel transfer distribution and vertical wheel trajectory which were analysed using a developed Python algorithm. A total of 30 unique geometries were evaluated, including the existing standard design geometry for a N.A. heavy point conformal frog. Results demonstrated that each parameter affects different locations along the frog and total impact is most affected by point slope. Lastly, an optimised frog geometry was selected that ensures well-distributed wheel transfer locations preventing the concentration of damage, and results in low total impact at the transfer point. [ABSTRACT FROM AUTHOR]

The structure and growth of a series of Lu-doped germanium clusters, LuGen q (n = 2–14, q = 0, −1) have been investigated by previous photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The ground states of the anionic LuGen – clusters obtained from DFT calculations are verified by comparing simulated PES with experimental results. The simulated PES for smaller clusters LuGen – (n ≤ 6) display relatively simple spectral patterns, suggesting high symmetry structures. It is observed that the pentagonal bipyramid shape is the basic framework for the nascent growth process of LuGen – (n = 2–8). The structures of LuGen – (n = 2–13) clusters are all exohedral structures with the Lu atom adsorbed at the surface of the bare Gen – clusters, while LuGe14– is the smallest endohedral Lu-doped germanium cluster with the Lu atom completely fallen into the germanium frame. It is found that the LuGen – clusters with even n are more stable than those with odd n and in the LuGen clusters there is an opposite trend. Especially, the LuGen q (n = 9, 12, q = 0, −1) clusters are extremely stable compared to other size clusters. HOMO–LUMO gap shows that the chemical stability of bare Gen – (n = 2–14) clusters are stronger than that of LuGen q (n = 2–14, q = 0, −1) clusters owing to the doping of a Lu atom. [ABSTRACT FROM AUTHOR]

This paper presents the geometry and material distribution influence on energy absorption systems and failure mode of glass epoxy tubes and carbon epoxy tubes in order to improve the structural performances. Experiments were carried out on different types of composite tubes subjected to axial compression load. After collecting the results of the crushing and drawing the load–displacement curve, the initial failure load, maximum crushing load and average load were found. From these parameters, the crashworthiness parameters were calculated. The comparison results between the parameters showed that the best structure of the glass epoxy tubes was the circular tube with eight layers, where produced the highest specific energy absorption at a value of 21.23 kJ/kg. [ABSTRACT FROM AUTHOR]

The paper deals with the optimisation of the geometry of screw machines, focussing on the wrap angle of the rotors. The Pi-theorem is used to identify independent thermodynamic and geometric factors for the optimisation of dry running twin screw compressors with uniform and dual lead rotors. Dual lead rotors possess two segments with different rotor leads, which can be selected to optimise the progression of chamber volume, clearance size and outlet area. Energy efficiency of the compressors is determined using a multi-chamber model simulation in which fluids are treated as ideal gases. The wrap angles of the rotors are optimised for a given set of characteristic numbers using the Nelder–Mead algorithm. Optimisation results reveal that the optimal geometry mainly depends on the circumferential Mach number and isentropic exponent of the fluid since these influence discharge throttling and the pressure progression due to volumetric compression. The results point out that dual lead compressors are most beneficial for fluids with low speed of sound and low isentropic exponent. [ABSTRACT FROM AUTHOR]

The combination of Additive Manufacturing (AM) and Hot Isostatic Pressing (HIP) offers great potential for industrial applications. Skilfully connecting AM and HIP creates a manufacturing process that unites the advantages of the two approaches. We demonstrate a production route for composite components by combining AM and HIP: a HIP capsule made of corrosion resistant steel is additively manufactured using Powder Bed Fusion with Laser Beam (LPBF). Before LPBF, the distortion and shrinkage of the capsule due to HIP is compensated by optimising the capsule's geometry using Finite Element (FE) simulation of the HIP process. The capsule is filled with steel powder and manufactured by a conventional powder HIP. After HIP, the capsule remains as an outer layer on the component, so that a functional net-shape composite component is produced. Subsequent investigations show that a complex extruder screw segment can be successfully produced with a geometrical deviation smaller than 1.5%. [ABSTRACT FROM AUTHOR]

Repeated computations on the same molecular system, but with different geometries, are often performed in quantum chemistry, for instance, in ab-initio molecular dynamics simulations or geometry optimisations. While many efficient strategies exist to provide a good guess for the self-consistent field procedure, little is known on how to efficiently exploit the abundance of information generated during the many computations. In this article, we present a strategy to provide an accurate initial guess for the density matrix, expanded in a set of localised basis functions, within the self-consistent field iterations for parametrised Hartree–Fock problems where the nuclear coordinates are changed along with a few user-specified collective variables, such as the molecule's normal modes. Our approach is based on an offline-stage where the Hartree–Fock eigenvalue problem is solved for some particular parameter values and an online-stage where the initial guess is computed very efficiently for any new parameter value. The method allows nonlinear approximations of density matrices, which belong to a non-linear manifold that is isomorphic to the Grassmann manifold, by mapping such a manifold onto the tangent space. Numerical tests on different amino acids show promising initial results. [ABSTRACT FROM AUTHOR]

The aim of the present study was a numerical investigation of the efficiency of the combustion process of a novel concept burner under different operating conditions. The design of the burner was a part of the development process of a complete SOFC based system and a challenging combination of technical requirements to be fulfilled. A Computational Fluid Dynamics model of a non-premixed burner was used to simulate combustion of exhaust gases from the anode region of Solid Oxide Fuel Cell stacks. The species concentrations of the exhaust gases were compared with experimental data and a satisfactory agreement of the conversion of hydrocarbons was obtained. This validates the numerical methodology and also proves applicability of the developed approach that quantitatively characterized the interaction between the exhaust gases and burner geometry for proper combustion modelling. Thus, the proposed CFD approach can be safely used for further numerical optimisation of the burner design.

The bidentate complex of glycylglycine with Mo(VI) ion in aqueous acidic solution was synthesised and characterised theoretically and experimentally. A theoretical study on the molecular geometry of dioxo-molybdenum(VI) complex with glycylglycine was done by using Density functional theory with B3LYP/6-31G(d,p) and pseudo-potential LANL2DZ for Mo atom. The natural bond orbital and frontier molecular orbital analyses were used for investigation of the electronic properties and chemical reactivity of the title compound. The experimental infrared spectrum was compared with calculated and complete vibrational assignment was provided. The oxidation of cyclohexene by tertbutyl hydroperoxide in the presence of dioxo-molybdenum(VI) complex with glycylglycine was studied. [ABSTRACT FROM AUTHOR]

Fluid Phase Resonance (FPR) mixers are investigated by means of Computational Fluid Dynamics (CFD) and Laser Doppler Anemometry (LDA). In FPR mixers, a pipe is immersed centrally into a liquid contained in a vessel. Two air cushions are produced above the liquid outside and inside the pipe. The latter is periodically pressurised so that the liquid in the central pipe and the vessel is oscillating, providing good flow conditions for mixing. Starting with a basic geometry, further configurations are developed and simulated with CFD to optimise the mixing quality. Results for two simulations are validated by LDA. Comparing velocity, turbulent kinetic energy, mixing quality, mixing time, and Newton number, the influence of geometry and oscillation frequency is investigated. The mixers are compared to standard stirred vessels by Newton numbers. It is found that FPR mixers can be as efficient as propeller stirrers. [ABSTRACT FROM AUTHOR]

In the present study, we have determined the crystal structure of 4-chloroanilinium hydrogen malonate, which displays strong O–H⋯O and N–H⋯O intermolecular contacts by generatingring motif leads to the formation of supramolecular self-assembly. The resultant experimental structure of the compound was optimised geometrically at ground state by Density Functional Theory and Hatree–Fock methods using 6-311++G(d,p) basis set. The vibrational spectrum of the title compound was measured using FTIR analysis and compared with theoretically computed IR frequencies. Molecular electrostatic potential mapping was carried out to understand the electrophilic and nucleophilic reactivities of the title compound. Frontier molecular orbital analysis was studied using Highest energy Occupied Molecular Orbital and Lowest energy Unoccupied Molecular Orbital theories to reveal the electron transitional property of the molecule. Thermodynamic functions such as entropy (S), enthalpy (H) and heat capacity (H) were evaluated in the temperature range from 10 to 500 K at global energy minima. Hirshfeld surface analysis and its associated 2-D fingerplot were visualised to investigate the whole molecular contacts of the compound. [ABSTRACT FROM AUTHOR]

A grid-connected integrated system incorporating cascade hydropower, solar/photovoltaic, and wind power requires a hydraulic turbine to operate frequently under off-design conditions, resulting in a series of instability issues, such as pressure fluctuations. In this study, a new draft tube shape optimisation methodology of introducing an inclined conical diffuser for a Francis turbine was proposed to eliminate vortex rope and mitigate the associated pressure fluctuations. Four different inclination angles in the range of 0°–16.8° were considered to investigate the effectiveness of the modified draft tube. The results demonstrated that the maximum pressure fluctuation amplitude within the draft tube was 1.64% times the equivalent pressure under the rated water head for the modified draft tube, showing an 18.4% reduction compared with that of the traditional case. In addition, an overall index of P degree was proposed to quantitatively measure the mitigating impact of this type of modified draft tube on the pressure fluctuations. When the inclination angle is 16.8°, the P degree on the downstream and upstream sides decreases by 34.1% and 23.1%, respectively, when compared to the traditional draft tube. Based on a comprehensive comparison of the vortex rope, instantaneous axial velocity, and pressure distribution, the mitigating mechanism of the modified draft tube was further explored. Finally, further optimisation direction was pointed out by means of entropy production theory. • A new draft tube with inclined conical diffuser is proposed. • Different inclination angles are investigated to alleviate flow instabilities. • The maximum pressure fluctuation amplitude of modified draft tube is reduced by 18.4%. • P degree is proposed to reflect the relative intensity of pressure fluctuation. [ABSTRACT FROM AUTHOR]

Thiirene and thiirane have been chosen as model molecules representative of products present in crude oil to study the key steps in hydrotreating. The hydrotreating which can be desulfurization, deoxygenation or denitrogenation is the treatment of oil crude products under hydrogen pressure in presence of catalysts. This process leads to hydrogenolysis of carbon-heteroatom bond accompanied by heteroatom elimination. The catalytic site used is based on molybdenum disulfide (MoS2), which is considered as active phase in the commercial catalysts containing molybdenum atoms. Two steps characterise the desulfurization process: the adsorption and the carbon-sulfur bond cleavage. The thiirene geometry has been destroyed through the cleavage of one of the carbon-sulfur bonds. The calculation results showed that the desulfurization of the thiirene and thiirane do follow a heterolytic process. At the end of process, the reaction pathways are the same with an activation energy which was higher for thiirane than for thiirene. These results confirmed the same catalytic site and molecules obtained in previous works in the EHT method.

Recently, we have suggested an approximate state-specific multi-reference coupled-cluster (SS-MRCC) singles, doubles and triples method based on the CCSDT-1a+d approximation applied to the single-reference CC approach, in which the contribution of the connected triple excitations is iteratively treated. The method, abbreviated as SS-MRCCSDT-1a+d is intruder-free and fully size-extensive. It has been employed for geometry optimisations of various systems possessing quasi-degeneracy of varying degrees (like N2H2and O3) by invoking numerical gradient scheme. The method is also applied to CH2and square cyclobutadiene in their excited states. For all systems under study, the computed values are in good accordance withstate-of-the-arttheoretical estimates indicating that the method might be a promising candidate for an accurate treatment of geometrical parameters of states plagued by electronic degeneracy in a computationally tractable manner. [ABSTRACT FROM PUBLISHER]

High-pressure induced structural transition from zircon-type phase into scheelite-type phase in YVO 4 is studied using ab initio calculations. Several structures with compressed volumes are evaluated, where for every considered volume the c/a ratio and atomic positions are optimised. The transition pressure and transition volume change are calculated. The reports on YVO 4 electronic structure and electronic band gap behaviour are followed by results of X-ray photoemission spectra XPS calculations. Most of our theoretical predictions are compared with experimental results taken from literature. [ABSTRACT FROM AUTHOR]

Complexes of Tb(III) with the biscoumarin derivative 3,3′-[(4-hydroxyphenyl)methyl]bis-(4-hydroxy- 2H -chromen-2-one) are synthesized by using a solution of tetraethylammonium hydroxide, [(C 2 H 5 ) 4 N]OH, in water as deprotonating base. Elemental analysis, IR- and fluorescence spectroscopy are used to characterize the samples obtained. The complexes have good fluorescent properties and show the characteristic emission bands of the Tb(III) ion. The triplet state of the mono-deprotonated ligand H 2 L − was determined. The optimised geometries of the ligand and the complexes were obtained by means of molecular modelling with first principles (DFT) methods. [ABSTRACT FROM AUTHOR]

The energy consumption of a building and its internal conditions are intimately related to its shape. There have been various attempts to use computer-based optimisation within a thermal simulation environment to produce designs with minimal energy consumption. Most of these studies have looked at optimising parameters such as U-values and glazing ratios, but a small number have looked into the form of the building, but in a way that does not naturally fit with the human-led design process. In this paper, the first practical methodology for optimising complex building facades and internal layouts is presented. The method allows for a free exploration of new, non-preconceived, design solutions in a way that complements the natural design process. The method has been tested on a design with eight facades. The rapid convergence of glazing ratios for all runs indicates their significance in the energy performance of a building. The solutions display a high degree of variability of floor shape without a compromise in performance, which indicates that human judgment can still be used as a filter even within an optimising framework. Typical solutions produced by the method show an annual total energy demand of 56 kWh/m, 51% lower than typical for the region in which the building was sited. [ABSTRACT FROM AUTHOR]

The Fock-space multi-reference coupled cluster method is used for the geometry optimisation of the low-lying excited states of the molecules. Molecular geometries of the carbon monohydride cation (CH)+, water (H2O), ozone (O3) and formaldehyde (HCHO) in their low-lying excited states are optimised. Excited state gradients are calculated using finite field multi-reference coupled cluster method. We compare our results with other theoretical and/or experimental results, wherever available. [ABSTRACT FROM PUBLISHER]

Abstract: This paper extends the work presented in a previous publication (Hansford, 2011 , subsequently referred to as Paper 1) to optimise the performance of a simple reflection-mode X-ray diffraction instrument with respect to the geometrical configuration. Both papers focus on the maximisation or minimisation of quantifiable characteristics of the X-ray beam incident on the sample in order to optimise the peak heights and widths in the resulting diffractogram. The reason for this approach is mathematical tractability, and its success relies on the relationship between the incident beam characteristics and the diffractogram properties. Part of Paper 1 was devoted to the minimisation of the equatorial divergence angle of the X-ray beam, while keeping the total X-ray flux constant, in order to minimise the diffractogram peak widths. While equatorial divergence and peak widths are certainly linked, their relationship is complex and depends quite significantly on other geometric parameters. An alternative optimisation approach is taken in this paper, focusing on the maximisation of the X-ray flux and minimisation of the incident beam axial divergence, while equatorial divergence is kept constant to ensure at least reasonable resolution. The rationale for this approach is that the incident beam flux and the axial divergence angle are more directly linked to diffractogram peak heights and peak asymmetry, respectively. Families of candidate geometric solutions result from this approach which is regarded as advantageous because there is no unique optimised solution and it allows the parameter space to be fully explored. [Copyright &y& Elsevier]

Abstract: An experimental and numerical investigation of the optimum ejector geometry for a small-capacity R744 heat pump was performed. Different ejector configurations were examined, including various lengths and diameters of the mixer and various angles of divergence for the diffuser. Based on a simplified, one-dimensional ejector model, an optimisation of the ejector geometry was performed. Based on both the numerical simulation and experimental work, the ejector efficiency proved to be notably dependent on the mixer length and the diameter, as well as on the diffuser divergence angle. The maximum increase in the coefficient of performance (COP) was 8% over a system with a conventional expansion valve. [Copyright &y& Elsevier]

A very simple quantum chemical model is proposed to simulate the effect of external forces acting on a single molecule. It involves optimising the geometry of a molecule with an external force applied to selected nuclei. This approach is used to investigate conformational transitions of the pyranose ring, which have been the subject of several atomic force microscopy (AFM) experiments, and to generate a number of previously unknown isomers of azobenzene. [ABSTRACT FROM AUTHOR]

Abstract: For four azodiazaphenanthrenes 1–4 and three acylaminodiazaphenanthrenes 5–7 the geometry was optimised and their effective charge and dipole moment values were calculated using DFT B3-LYP/3-21G method. For 5–7 the results have been compared with those obtained by AM1 method. The UV experimental values of 1–4 are presented. With the use of DFT B3-LYP/6-31G∗∗ optimised geometry the simulation of UV spectra of 5–7 by AM1 and ZINDO/S methods was made and correlations with experimental UV values have been performed. [Copyright &y& Elsevier]

We implement a flexible Z -matrix approach in the density functional theory (DFT) periodic boundary conditions code, SIESTA. This allows a mixture of Z -matrix and Cartesian coordinates to be used for geometry specification and optimisation. In addition, geometry constraints in the form of fixed coordinates and fixed linear relationships between coordinates can be specified. A Z -matrix approach in condensed phase calculations can be advantageous, for example in studying molecular adsorption onto a surface, both in terms of flexibility and efficiency. We demonstrate our implementation for the case of thiol adsorption on the Au(111) surface. [ABSTRACT FROM AUTHOR]

Abstract: A geometry optimisation of the perovskite and hexagonal phases of BaTiO3 has been conducted using Density Functional Theory (DFT) within the Local Density Approximation (LDA) and Generalised Gradient Approximation (GGA) schemes. The LDA was found to give lattice parameters closer to experiment than the GGA. A study of oxygen vacancies in the hexagonal phase has been performed and the results suggest an O(1) type (face sharing) vacancy is more stable than an O(2) type (corner sharing) vacancy in the octahedral structure. In addition, the effect of different Ru doping concentrations on the structure and stability of the hexagonal phase has been investigated. [Copyright &y& Elsevier]

The use of the molecular mechanics AMBER force field (FF) to predict product profiles for the hydroxylation of the monoterpenes 1R-camphor, 1S-camphor, 1R-norcamphor, 1S-norcamphor and camphane by the enzyme cytochrome P450cam from the soil bacterium Pseudomanas putida was investigated. Predictions were carried out by applying multiple substrate (starting) orientations in the enzyme pocket in two procedures; a procedure based on molecular dynamics (MD) and a procedure based on short MD simulations followed by geometry optimisations. The latter (GO) procedure is faster and enabled the use of more monoterpene starting orientations. Monoterpene orientations were transformed into product profiles by applying both energetic and geometrical criteria appropriate for the (monoterpene) hydrogen abstraction reaction. Good predictions compared to experimental data were obtained for most compounds in both the MD and GO procedures. Prior to the product profile calculations, the FF was calibrated by reproducing the experimental data for the binding energy of 1R-camphor and 1S-camphor to P450cam and the energy of vaporisation of water. Focus of the calibration was on the value for the scaling factor for the electrostatic interactions. [ABSTRACT FROM AUTHOR]

The addition of elemental sulphur to the 10-vertex nido dicarborane [6,9-C2B8H10]2−(2) engenders the new 11-vertex species [1,6,7-C2SB8H11]− (2), which has been structurally characterised using the ab initio/GIAO/NMR method and by deductions made from observations on its reaction chemistry. These combined studies revealed 2 to adopt a structure that is formally derived from the hypothetical parent [closo-B13H13]2− anion by removal of two adjacent six-coordinate and five-coordinate vertices. Since the GIAO calculations of 11B and 13C chemical shifts, employing the RMP2/6-31G* geometry, showed an excellent agreement with the experimental findings, in particular those for δ(11B) and δ(13C) that were computed at the GIAO-RMP2/II′ level, the RMP2/6-31G* parameters can be deemed a good representation of the molecular structure of 2 in solution. The other possible structural alternatives of 2 could be ruled out on the basis of geometrical, energetic, and NMR criteria. [Copyright &y& Elsevier]

The electrical component under analysis does not fulfil the mechanical performance required by the standard (a minimum force of 400 gf during the extraction of a 3.8 mm diameter pin after the introduction of a 5.1 mm pin). A numerical study using the finite element method was developed to understand the limited response of the component and to study the effect of changing material and geometry. Experimental tests were performed to obtain the elastic–plastic behaviour of the material and friction coefficient. The poor performance was explained by the exaggerated plastic deformation. The best solution was found to be the use of a new material (extra-hard brass) since the geometrical changes allowed have a limited effect. [Copyright &y& Elsevier]

Deuterium isotope effects on 15N, 13C and 1H chemical shifts have been measured in the protonated forms of DMAN, 4-bromo, 4-picryl, 4-nitro and 2- and 2,7-chloro derivatives. Structures have been geometry optimised using BPW91/6-31(d)G density functional theory (DFT) methods and show good correspondence to experimental X-ray data. 15N, 13C and 1H chemical shifts are calculated using GIAO/DFT methods. Chemical shifts for the two tautomers are calculated. Equilibrium constants are determined from 1J(N,H) coupling constants. A comparison of 1J(N,H) and 1J(N,D) couplings for the non-symmetrical derivatives show that upon deuteriation the equilibrium is shifted towards the dominant form. The experimental deuterium isotope effect on chemical shifts of DMANH+ shows only small values despite the apparently strong intramolecular hydrogen bonds as judged from primary isotope effects. The counter ion has little effect on the one-bond isotope effect. Secondary isotope effects on 15N and 13C chemical shifts for the non-symmetrical derivatives are divided into intrinsic and equilibrium contributions. The one-bond deuterium intrinsic isotope effect on 15N chemical shifts is close to 0.3 ppm and is related to charge delocalisation and the close proximity of the positive charge. The equilibrium contributions to the isotope effects at the nitrogens and at carbons are seen to increase throughout the series in parallel with the increase of the equilibrium constant. For 1H resonances only equilibrium contributions are found at the aromatic hydrogens. An important feature in the analysis of the protonated DMANs is the multi-isotope effect approach. [Copyright &y& Elsevier]

This paper describes the use of molecular mechanics to model the geometry of the sodium complex of a calix[4]arene tetraester, in the 1,3-alternate conformation 1. Partial charges were assigned to the calixarene on the basis of semi-empirical (AM1, PM3, MNDO, INDO, CNDO and ZINDO) calculations and the binding of the sodium ion to the calixarene was modelled using molecular mechanics. Agreement between the optimised and X-ray structures of the complex was very good. The effect of placing the cation in different starting positions on the energy-minimised geometry of the complex is described. [ABSTRACT FROM AUTHOR]