Full Geometry Research Articles

Crystal chemistry rationale and ab initio investigation of ultra-hard dense rhombohedral carbon and boron nitride

Rhombohedral dense forms of carbon, rh-C2 (or hexagonal h-C6), and boron nitride, rh-BN (or hexagonal h-B3N3), are derived from rhombohedral 3R graphite based on original crystal chemistry scheme backed with full cell geometry optimization to minimal energy ground state computations within the quantum density functional theory. Considering throughout hexagonal settings featuring extended lattices, the calculation of the hexagonal set of elastic constants provide results of large bulk moduli with B0 (rh-C2) = 438 GPa close to that of diamond, and B0 (rh-BN) = 369 GPa close to that of cubic BN. The hardness assessment in the framework of three contemporary models enables both phases to be considered as ultra-hard. From the electronic band structures calculated in the hexagonal Brillouin zones, 3R graphite is a small-gap semiconductor, oppositely to rh-C2 that is characterized by a large band gap of 6 eV, and rh-BN is a large band gap insulator with Egap = 5 eV.

Technical note: GAMMORA, a free, open-source, and validated GATE-based model for Monte-Carlo simulations of the Varian TrueBeam.

Monte Carlo (MC) is the reference computation method for medical physics. In radiotherapy, MC computations are necessary for some issues (such as assessing figures of merit, double checks, and dose conversions). A tool based on GATE is proposed to easily create full MC simulations of the Varian TrueBeam STx. GAMMORA is a package that contains photon phase spaces as a pre-trained generative adversarial network (GAN) and the TrueBeam's full geometry. It allows users to easily create MC simulations for simple or complex radiotherapy plans such as VMAT. To validate the model, the characteristics of generated photons are first compared to those provided by Varian (IAEA format). Simulated data are also compared to measurements in water and heterogeneous media. Simulations of 8 SBRT plans are compared to measurements (in a phantom). Two examples of applications (a second check and interplay effect assessment) are presented. The simulated photons generated by the GAN have the same characteristics (energy, position, and direction) as the IAEA data. Computed dose distributions of simple cases (in water) and complex plans delivered in a phantom are compared to measurements, and the Gamma index (3%/3mm) was always superior to 98%. The feasibility of both clinical applications is shown. This model is now shared as a free and open-source tool that generates radiotherapy MC simulations. It has been validated and used for five years. Several applications can be envisaged for research and clinical purposes.

Supersymmetric black holes with spiky horizons

We use the recipe of [1] to find half-BPS near-horizon geometries in the t3 model of N = 2, D = 4 gauged supergravity, and explicitely construct some new examples. Among these are black holes with noncompact horizons, but also with spherical horizons that have conical singularities (spikes) at one of the two poles. A particular family of them is extended to the full black hole geometry. Applying a double-Wick rotation to the near-horizon region, we obtain solutions with NUT charge that asymptote to curved domain walls with AdS3 world volume. These new solutions may provide interesting testgrounds to address fundamental questions related to quantum gravity and holography.

Modelling topographic waves in a polar basin

This study is concerned with properties of freely propagating barotropic Rossby waves in a circular polar cap, a prototype model for the Arctic Ocean. The linearised shallow-water equations are used to derive an amplitude equation for the waves in which full spherical geometry is retained. Almost by definition, polar basin dynamics are confined to regions of limited latitudinal extent and this provides a natural small scale which can underpin a rational asymptotic analysis of the amplitude equation. The coefficients of this equation depend on the topography of the basin and, as a simple model of the Arctic basin, we assume that the basin interior is characterised by a constant depth, surrounded by a continental shelf-slope the depth of which has algebraic dependence on co-latitude. Isobaths are therefore a family of concentric circles with centre at the pole. On the shelf and slope regions the leading order amplitude equation is of straightforward Euler type. Asymptotic values of the wave frequencies are derived and these are compared to values computed directly from the full amplitude equation. It is shown that the analytic results are in very good accord with the numerical predictions. Further simulations show that the properties of the waves are not particularly sensitive to the precise details of the underlying topography; this is reassuring as it is difficult to faithfully represent the shelf topography using simple mathematical functions.

Tracking the Amide I and αCOO- Terminal ν(C=O) Raman Bands in a Family of l-Glutamic Acid-Containing Peptide Fragments: A Raman and DFT Study.

The E-hook of β-tubulin plays instrumental roles in cytoskeletal regulation and function. The last six C-terminal residues of the βII isotype, a peptide of amino acid sequence EGEDEA, extend from the microtubule surface and have eluded characterization with classic X-ray crystallographic techniques. The band position of the characteristic amide I vibration of small peptide fragments is heavily dependent on the length of the peptide chain, the extent of intramolecular hydrogen bonding, and the overall polarity of the fragment. The dependence of the E residue’s amide I ν(C=O) and the αCOO− terminal ν(C=O) bands on the neighboring side chain, the length of the peptide fragment, and the extent of intramolecular hydrogen bonding in the structure are investigated here via the EGEDEA peptide. The hexapeptide is broken down into fragments increasing in size from dipeptides to hexapeptides, including EG, ED, EA, EGE, EDE, DEA, EGED, EDEA, EGEDE, GEDEA, and, finally, EGEDEA, which are investigated with experimental Raman spectroscopy and density functional theory (DFT) computations to model the zwitterionic crystalline solids (in vacuo). The molecular geometries and Boltzmann sum of the simulated Raman spectra for a set of energetic minima corresponding to each peptide fragment are computed with full geometry optimizations and corresponding harmonic vibrational frequency computations at the B3LYP/6-311++G(2df,2pd) level of theory. In absence of the crystal structure, geometry sampling is performed to approximate solid phase behavior. Natural bond order (NBO) analyses are performed on each energetic minimum to quantify the magnitude of the intramolecular hydrogen bonds. The extent of the intramolecular charge transfer is dependent on the overall polarity of the fragment considered, with larger and more polar fragments exhibiting the greatest extent of intramolecular charge transfer. A steady blue shift arises when considering the amide I band position moving linearly from ED to EDE to EDEA to GEDEA and, finally, to EGEDEA. However, little variation is observed in the αCOO− ν(C=O) band position in this family of fragments.

Application of fracture mechanics for the characterization of poly(vinyl chloride) pipes. II. Evaluation of a ring‐type specimen for fracture mechanics testing

AbstractAn unplasticized poly(vinyl chloride) (U‐PVC) pipe sample used in infrastructure applications in Brazil (nominal diameter DN 100, outside diameter 110 mm) was evaluated according to different fracture mechanics methodologies, including essential work of fracture (EWF) and other fracture toughness parameters such as the stress intensity factor and plane strain energy release rate . This pipe sample was also tested for the quality of processing (degree of gelation) via differential scanning calorimetry (DSC) and tensile strength. The comparative evaluation of different specimen configurations—curved specimens in three‐point bending (CTPB) and full rings in tension (SNRT), in thicknesses varying from 5 to 30 mm, showed initial evidence of the suitability of ring‐type specimens for the evaluation of EWF and . Results also indicate that the full ring geometry, at least in the present experimental setup, presents some drawbacks probably due to the storage of large amounts of elastic energy throughout the test. This fact leads to relevant deviations in both load–displacement behavior and results for strain energy release rate (), and the results found here will guide future research using full and split rings in different loading modes and improved experimental setups. It was also confirmed that the value of , determined by a modified Charpy test, is independent of the type of specimen tested, as long as the test mode and specimen width are the same. Both the experimental value of and the estimated value for the plane strain stress intensity factor () showed excellent agreement with values reported for other U‐PVC compositions.

A basis set superposition error‐free second‐order perturbation theory from Hermitian chemical Hamiltonian approach self‐consistent field canonic orbitals

AbstractWe present an alternative perturbational approach free of basis set superposition error (BSSE) within the framework of the chemical Hamiltonian approach (CHA). The new formulation (CHA‐S‐MP2) is based on canonic (and orthogonal) CHA orbitals obtained from a hermitized CHA Fock operator. The final expression shows a considerable simplification of the method as compared to the previous CHA‐MP2 formalism. Numerical full geometry optimizations of water and hydrogen fluoride dimers and potential energy surfaces for helium and argon dimers for several basis sets are presented. The present method is compared to both the counterpoise and previous CHA‐MP2 BSSE correction schemes, showing a remarkable agreement between all three methods. However, the wrong behavior using the aug‐cc‐pVDZ basis set indicates that the present method is not as robust as the original non‐hermitian CHA‐MP2 formulation.

Direct numerical simulation of the two-dimensional speed bump flow at increasing Reynolds numbers

The Speed Bump flow model was designed by Boeing to provide a mildly three-dimensional flow with separation from a very smooth surface, strongly controlled by the turbulence. Experiments are conducted by several teams, as are simulations, over a range of Reynolds numbers. Direct Numerical Simulations (DNS) are not possible for the full 3D geometry of width L, leading several groups to conduct DNS over a two-dimensional geometry, in other words the cross-section of the full geometry, with periodic lateral conditions and a typical domain width of 0.04L. This does not allow precise comparisons with experiment, but code-to-code comparison is instructive. A shallow separation bubble is present, as intended. The domain width becomes marginal after reattachment, where the boundary layer is much thicker. The Reynolds number based on L has been 106, so far in the literature, which causes partial relaminarization and tends to defeat the purpose of testing turbulence models. Flow visualisation is clear on this. Here, we present results at the Reynolds number 106 and 1.4 × 106, and the higher value essentially eliminates relaminarization. Detailed results are shown, including studies of domain width, grid resolution, and numerical dissipation. The turbulence models give inaccurate results for skin friction, already in the intense favourable pressure gradient, which causes the formation of an internal boundary layer; the separation prediction on the other hand is reasonable. The wall curvature seems to play a role. The present results also provide trustworthy data to test Large-Eddy Simulation (LES), especially if using a Wall Model (WMLES). The comparisons will have a preliminary character until the results of the ongoing detailed experiments and of DNS at even higher Reynolds number and with a wider domain are available and carefully compared.

Minimal twist for the Standard Model in noncommutative geometry: The field content

Noncommutative geometry provides both a unified description of the Standard Model of particle physics together with Einstein-Hilbert action (in euclidean signature) and some tools to go beyond the Standard Model. In this paper, we extend to the full noncommutative geometry of the Standard Model the twist (in the sense of Connes-Moscovici) initially worked out for the electroweak sector and the free Dirac operator only. Namely, we apply the twist also to the strong interaction sector and the finite part of the Dirac operator. To do so, we are forced to take into account a violation of the twisted first-order condition. As a result, we still obtain the extra scalar field required to stabilise the electroweak vacuum and fit the Higgs mass, but it now has two chiral components. We also get the additive field of 1-forms already pointed out in the electroweak model, but with a richer structure. Finally, we obtain a pair of Higgs doublets, which are expected to combine into a single Higgs doublet in the action formula, as will be investigated in the second part of this work.

Numerical Homogenization of Multi-Layered Corrugated Cardboard with Creasing or Perforation.

The corrugated board packaging industry is increasingly using advanced numerical tools to design and estimate the load capacity of its products. This is why numerical analyses are becoming a common standard in this branch of manufacturing. Such trends cause either the use of advanced computational models that take into account the full 3D geometry of the flat and wavy layers of corrugated board, or the use of homogenization techniques to simplify the numerical model. The article presents theoretical considerations that extend the numerical homogenization technique already presented in our previous work. The proposed here homogenization procedure also takes into account the creasing and/or perforation of corrugated board (i.e., processes that undoubtedly weaken the stiffness and strength of the corrugated board locally). However, it is not always easy to estimate how exactly these processes affect the bending or torsional stiffness. What is known for sure is that the degradation of stiffness depends, among other things, on the type of cut, its shape, the depth of creasing as well as their position or direction in relation to the corrugation direction. The method proposed here can be successfully applied to model smeared degradation in a finite element or to define degraded interface stiffnesses on a crease line or a perforation line.

Simulations of ICRF heating of fusion oriented plasmas in plane-stratified and full toroidal geometry

We compare results from the fully toroidal TORIC–SSFPQL package (Brambilla and Bilato 2006 Nucl. Fusion 46 s387) and from the plane-stratified geometry solver FELICE (Brambilla 1989 Plasma Phys. Control. Fusion 31 723) to illustrate the advantages and the limitations of the two approaches for the simulations of Ion Cyclotron Radio Frequency heating of tokamak plasmas. We point out that some of the predictions of the plane-stratified models do not straightforwardly apply to the true toroidal configuration. This is the case, in particular, for the excitation of guided modes between the plasma surface and the vessel.

Crystal chemistry and ab initio prediction of ultrahard rhombohedral B2N2 and BC2N

New ultrahard rhombohedral B2N2 and BC2N – or hexagonal B6N6 and B3C6N3 – are derived from 3R graphite based on crystal chemistry rationale schematizing a mechanism for 2D → 3D transformation. Full unconstrained geometry optimizations leading to ground state energy structures and energy derived quantities as energy-volume equation of states (EOS) and the elastic constants were based on computations within the density functional theory (DFT) with generalized gradient approximation (GGA) for exchange-correlation (XC) effects. The new binary and ternary phases are characterized by tetrahedral stacking alike diamond, visualized with charge density representations, and illustrating ion characters. Atom averaged total energies are similar between cubic BN and rh-B2N2 on one hand, and larger stabilization of rhombohedral BC2N versus cubic and orthorhombic forms (in literature) assigned to favorable C–C and B–N bonding, on the other hand. The electronic band structures are characteristic of insulators with Egap ~5 eV. Both phases are characterized by large bulk and shear moduli and high hardness values.

3D Numerical Modeling of Pile embankment performance on Soft Soil

Embankments are often required in many civil engineering construction projects involving infrastructure development to elevate the ground level. Due to the limitation of land availability for infrastructure projects in many countries, a large number of projects are now being carried out on soft ground. However, embankment construction over soft ground is a challenging task due to several undesirable characteristics associated with soft soils such as local instability, inadequate bearing capacity and large settlements, which can occur over a long period of time. These problems can generally result in expensive remedial measures and long construction delays. The conventional soft ground improvement methods based on consolidation such as vertical drains and preloading are not suitable when projects have to be completed within a short period of time or the ground improvement has to be carried out in contaminated ground. In such situations, reinforced pile-supported embankments are increasingly used as an alternative construction method due to the shorter construction time required compared to consolidation based methods and due to the higher reliability of the method when the subsoil properties cannot be relied upon. . This paper presents a comprehensive numerical study carried out using the finite element method in order to investigate the performance of reinforced pile supported embankment. A detailed parametric study is presented inthree-dimensional conditions incorporating the full geometry of embankment system. The influence of pile embedded length, pile diameter, elastic modulus of piles, height of the embankment, construction rate of the embankment were investigated on the performance of the selected embankment.

Structural insight into locked nucleic acid based novel antisense modifications: A DFT calculations at monomer and MD simulations at oligomer level

In the present study, five novel LNA based antisense modifications have been proposed. A conformational search was carried out using TANGO, followed by geometry optimization using MOPAC. Based on their electronic energies the most stable conformation for each modification was identified. Further, DFT based full geometry optimization on the most stable conformations at the gas phase B3LYP/6-31G(d,p) using a Gaussian03 and single point energy calculations on the optimized structures at the solvent phase B3LYP/6-311G(d,p) level of theory were done to derive their quantum chemical descriptors using the Gaussian09. A comparison of global reactivity descriptors confirmed that the LNA based modifications were the most reactive. Base-pair stability was recorded by observing the binding energies and base-pairing conformations of modified GC base pairs at the B3LYP/6-311G(d,p) level of theory. Molecular dynamics simulations have been performed at the oligomer duplex level by incorporating individual modifications on 20-mer RNA-RNA duplexes using AMBER16. Free energy calculations of duplex structures suggested that incorporation of A2 modification into the RNA-RNA duplex increased the duplex binding affinity similar to LNA. Whereas, the A3 modification showed less binding compared to LNA but improved binding compared to MOE. This computational approach using quantum chemical methods may be very useful to propose better modifications than the existing ones before performing the experiments in the area of antisense technology.

Cad for Gears Part 1 Helical and Double Helical Gears.(Dept.M)

The aim of this paper is to construct a software containing a complete design procedure and detailed drawing for spur, helical and double helical gears. This software can be executed on all the IBM personal computers XT/AT or compatibles. The main elements of the design In this program are : input data, type end shape of gear tooth system (IS. US, BS and DIN), module, minimum number of teeth to avoid interference, tooth profile modification, centre distance, contact ratio, face width, helix angle, material, equations for bending strength (Lewis, modified Lewis and Buckingham) and surface durability, and load carrying capacity for bending strength and surface durability using ISO, AGMA and BS equations with constant or variable tooth load. Many equations and practical formulae are selected for making the gear construction integer gear, solid gear, gear with web, gear with web and holes, gear with arms, gear with Two walls and composite gear). With running the software. full specifications, geometry, kinematics, loads, stresses and detailed drawing of the gears are obtained according to the input data. Different examples are selected to show the variety of the Output data and the strength of the software. Also these runs show the sava in time and accuracy of the results.

Magnetization loss of no-insulation coil for an electrodynamic suspension system

A high-temperature superconducting no-insulation (NI) coil, with its self-protection property, high engineering current density and unique demagnetization property, becomes a potential candidate for an electrodynamic suspension (EDS) system. Compared with the applications in high field magnets, the NI coil used in the EDS system is considered as working in a dynamic state, the magnetization loss generated in the NI coil is essential for the design of a cryogenic system. This paper presents the study on AC magnetization loss of NI coils by both numerical and experimental methods. Firstly, a 3D finite element numerical model representing the full geometry of the NI coil is built to analyse the effect of field frequency, field magnitude, as well as the radial characteristic resistance. Then, systematic discussions are conducted to figure out the working mechanism of NI coils. Finally, a calibration-free method testing platform is installed to validate the numerical model, and a modified model is proposed to represent the non-uniform radial characteristic resistance caused by stress distribution. The conclusions of this paper will be used in the future optimization of NI coils and the cryogenic design of the EDS system.

Complex geometries in additive manufacturing: A new solution for lattice structure modeling and monitoring

The production of novel types of complex shapes is nowadays enabled by new manufacturing paradigms such as additive manufacturing, also known as 3D printing. The continuous increase of shape complexity imposes new challenges in terms of inspection, product qualification and process monitoring methodologies. Previously proposed methods for 2.5D free-form surfaces are no longer applicable in the presence of this kind of new full 3D geometries. This paper aims to tackle this challenge by presenting a statistical quality monitoring approach for structures that cannot be described in terms of parametric models. The goal consists of identifying out-of-control geometrical distortions by analyzing either local variations within the part or changes from part to part. The proposed approach involves an innovative solution for modeling the deviation between the nominal geometry (the originating 3D model) and the real geometry (measured via x-ray computed tomography) by slicing the shapes and estimating the deviation slice by slice. 3D deviation maps are then transformed into 1D deviation profiles enabling the use of a profile monitoring scheme for local defect detection. The feasibility and potential of this method are demonstrated by focusing on a category of complex shapes where an elemental geometry regularly repeats in space. These shapes are known as lattice structures, or metamaterials, and their trabecular shape is thought to provide innovative mechanical and functional performance. The performance of the proposed method is shown in real and simulated case studies.

Laser-driven ion acceleration from near-critical Gaussian plasma density profile

In this paper, we report on multiple phases of efficient laser-driven ion acceleration from near-critical density plasma of Gaussian density profile. Tracking of high-energy accelerated ions in multidimensional particle-in-cell simulations reveals the development of accelerating fields affecting the particles and the contribution of each acceleration phase to final ion energies. While the acceleration of ions occurs in a short time interval when a steep (infinite) density gradient is present, the accelerating field affecting the most energetic ions has unexpected local maxima about 50 fs after the moment when ultrashort (30 fs) laser pulse completely left the target with smooth density gradients. This field can be attributed to the apex of electron filament created behind the transmitted laser pulse. Full 3D simulation confirms the observations in 2D simulations in terms of ion acceleration mechanisms. However, it shows a substantial reduction of maximum achievable ion energies and a larger angular spread of accelerated ions compared with 2D approach, which demonstrates the necessity of using computationally demanding full 3D geometry for similar numerical studies.

Numerical study on the aerodynamics of an experimental wind turbine: Influence of nacelle and tower on the blades and near-wake

The nacelle and tower affect the flow through the rotor and near-wake of horizontal-axis wind turbines. For this reason, aerodynamic models of the full geometry of wind turbines are needed to gain insight to improve turbine designs. In this work, the unsteady flow around an experimental horizontal-axis wind turbine is studied using computational fluid dynamics simulations. The emphasis is put on the effects of the nacelle, tower and rotation of the blades on the induction region and near-wake. The simulations are performed using unsteady Reynolds-Averaged Navier-Stokes equations in conjunction with the shear-stress transport k-ω model. The sliding mesh method is employed to enable the rotation of the blades. The simulations were performed at the design tip speed ratio (λ=6.67) and two off-design conditions (λ = 4.17 and 10) to assess the general validity of the numerical model. The obtained results of global loads, force distribution on the blades and tower, velocity components and angle of attack are presented in detail. It is found that the tower has little effect on the rotor loads (circular pattern), but the blades have an important effect on the tower (three-leaved rose pattern). The force distribution reveals only significant fluctuations on the blades (r/R<0.75) at λ = 4.17, whereas the tower is affected in the zone exposed to the wake behind the rotor for all three wind speeds. Furthermore, the interaction between blades is evaluated in terms of velocity and angle of attack. The correspondence between the results for different rotor blade positions reveals the effect of the ground on the rotor is negligible. The Omega method is used to visualize the behaviour of the tip and root vortices, wake expansion, coherent structures and development of the near-wake. The numerical results presented here contribute to a deeper understanding of the unsteady flow around horizontal-axis wind turbines.

Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter

Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.