Analytical 3D Research Articles

S-PROCESSING IN AGB STARS REVISITED. II. ENHANCED 13C PRODUCTION THROUGH MHD-INDUCED MIXING

ABSTRACT Slow neutron captures are responsible for the production of about 50% of elements heavier than iron, mainly occurring during the asymptotic giant branch phase of low-mass stars (1 ≲ M/M ⊙ ≲ 3), where the main neutron source is the 13C(α, n)16O reaction. This last reaction is activated from locally produced 13C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt to describe a physical mechanism for the formation of the 13C reservoir, studying the mass circulation induced by magnetic buoyancy without adding new free parameters to those already involved in stellar modeling. Our approach represents the application to the stellar layers relevant for s-processing of recent exact analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but is extended over a large fractional mass of the He-layers, thus producing 13C reservoirs of several 10−3 M ⊙. The ensuing 13C-enriched zone has an almost flat profile, while only a limited production of 14N occurs. In order to verify the effects of our new findings we show how the abundances of the main s-component nuclei can be accounted for in solar proportions and how our large 13C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

Tracing the manganese ore accumulations in Sinai Peninsula, Egypt, using magnetic method

In this study, an ideal area known for manganese ore accumulations in Sinai Peninsula has been investigated in detail using geological, laboratory analyses and magnetic tools. The main target is to establish a relationship between the ore accumulations, geology and the subsurface faults (shear structures) which are extending to deeper depths in the basement rocks of the study area and then use it as key for the un-explored areas in the Sinai Peninsula. To achieve this target, a detailed land magnetic survey has conducted to the selected area and later extended to include the whole peninsula. The geological data have obtained from the drilled wells and Egyptian Geological Survey and Mining Authority of Egypt. The geological investigations are including studying the surface geology and interpretation the well logging data to trace the ore mineral distributions along the different depths in the peninsula. The magnetic data has processed using a series of techniques, namely, second vertical gradient, 3D analytical signal, trend analyses, Euler deconvolution, Werner deconvolution and 3D modeling techniques. Also, the Curie depth method has applied along more than 31 grids forming the magnetic map of Sinai Peninsula to study the behavior of geothermal solutions and their effects in the host country rocks and their relationship to the existing ore accumulations. Furthermore, more than 300 rock samples have collected from different sites covering Sinai Peninsula area. These samples were subjected to laboratory measurements of the magnetic susceptibility. The results show that the Curie magnetic depth confirms that these shear structures at the intersection points are extended to deep depths which make as a pass way for the hydrothermal solutions into the host rocks which are probably forming the ore accumulations. The ore mineral accumulations appear to be confined to the carbonate rocks and to the shear zones intersections of the structures which are trending NW–SE and NE–SW directions. The depth to these accumulations was found to be ranging between 300 m at the southern parts to more than 3 km at the northern parts of the Sinai Peninsula. The measured magnetic susceptibility values range between 0.4 SI and 1.8 SI. Five new areas namely; Sharm El Sheikh, Wadi Zaghrah, SW Taba, Libni and Maghara can be prospected in the Sinai Peninsula have the similar conditions which are existing at Abu Zneima known mine area.

Propagation of a fundamental laser mode and its numerical simulation by the angular spectrum technique

This research aims to make a comparison between the analytical and numerical methods of simulation of the Gaussian beam propagation in free space. This comparison brings evaluation of the accuracy and applicability limitations of the angular spectrum diffraction algorithm. In this approach, planar harmonic waves are assumed as basic components of a propagating wave, so the algorithm combines the angular spectrum technique and the 2D fast Fourier transformation procedures. It means a quite different approach than the well-established Huygens–Sommerfeld one, based on spherical waves. The Gaussian beam is a rare case of the exact analytical 3D solution of a specific wave diffraction problem, in paraxial scalar approximation. Gaussian beam form has been chosen here as an evaluation reference. It allows to avoid comparisons between two numerical procedures, both of which may suffer from imperfections. In this comparison, the respective 2D cross-sections of calculated 3D complex valued wave fields distributions are presented. Also values of specific Gaussian beam parameters like full phase and Gouy phase shift and wave-front curvature radius are presented. The comparison between that form and the results of the angular spectrum algorithm brings information about the performance quality of that algorithm.

Propagation of a fundamental laser mode and its numerical simulation by the angular spectrum technique

This research aims to make a comparison between the analytical and numerical methods of simulation of the Gaussian beam propagation in free space. This comparison brings evaluation of the accuracy and applicability limitations of the angular spectrum diffraction algorithm. In this approach, planar harmonic waves are assumed as basic components of a propagating wave, so the algorithm combines the angular spectrum technique and the 2D fast Fourier transformation procedures. It means a quite different approach than the well-established Huygens–Fresnel–Rayleigh–Sommerfeld one, based on spherical waves. The Gaussian beam is a rare case of the exact analytical 3D solution of a specific wave diffraction problem, in paraxial scalar approximation. Gaussian beam form has been chosen here as an evaluation reference. It allows to avoid comparisons between two numerical procedures, both of which may suffer from imperfections. In this comparison, the respective 2D cross-sections of calculated 3D complex valued wave fields distributions are presented. Also values of specific Gaussian beam parameters like full phase and Gouy phase shift and wave-front curvature radius are presented. The comparison between that form and the results of the angular spectrum algorithm brings information about the performance quality of that algorithm.

Evaluation of the optimal turbine pressure drop ratio for a solar chimney power plant

The optimal turbine pressure drop ratio fopt for a solar chimney power plant (SCPP) is investigated using an analytical approach and 3D numerical simulations. Results indicate that the solar radiation and ambient temperature have obvious influences to the optimal turbine pressure drop ratio fopt and an improved performance of the SCPP system leads to a high fopt. The performance comparison between the cases with different collector shapes, a circular collector and a square collector with the same area, is conducted for the first time. It is found that the m-th power law assumption can also be applied to the SCPP system with a square collector; the values of fopt for the cases with a square collector are close to those for the cases with a circular collector. A fitting equation with variables of solar radiation and ambient temperature is obtained using the simulation results of the Spanish prototype; the results reveal that the fopt of the Spanish prototype ranges from 0.90 to 0.94 under normal climate conditions. This paper provides an approach to the preliminary estimation of plant performance, and reference data for an optimal pressure drop through solar chimney turbines.

Analytical model of Europa’s O2 exosphere

The origin of the exosphere of Europa is its water ice surface. The existing exosphere models, assuming either a collisionless environment (simple Monte Carlo techniques) or a kinetic approach (Direct Monte Carlo Method) both predict that the major constituent of the exosphere is molecular oxygen. Specifically, O2 is generated at the surface through radiolysis and chemical interactions of the water dissociation products. The non-escaping O2 molecules circulate around the moon impacting the surface several times, due to their long lifetime and due to their non- sticking, suffering thermalization to the surface temperature after each impact. In fact, the HST observations of the O emission lines proved the presence of an asymmetric atomic Oxygen distribution, related to a thin asymmetric molecular Oxygen atmosphere. The existing Monte Carlo models are not easily applicable as input of simulations devoted to the study of the plasma interactions with the moon. On the other hand, the simple exponential density profiles cannot well depict the higher temperature/higher altitudes component originating by radiolysis. It would thus be important to have a suitable and user-friendly model able to describe the major exospheric characteristics to use as a tool.This study presents an analytical 3D model that is able to describe the molecular Oxygen exosphere by reproducing the two-component profiles and the asymmetries due to diverse configurations among Europa, Jupiter and the Sun. This model is obtained by a non-linear fit procedure of the EGEON Monte Carlo model (Plainaki et al. 2013) to a Chamberlain density profile. Different parameters of the model are able to describe various exosphere properties thus allowing a detailed investigation of the exospheric characteristics. As an example a discussion on the exospheric temperatures in different configurations and space regions is given.

A Comparative Analysis of a Si/SiGe Heterojunction-Bipolar Transistors: APT, STEM-EDX and ToF-SIMS

Due to the complexity of characterising compound semiconductors, including dopant distribution, multiple characterisation techniques are needed. Traditionally time-of-flight secondary ion mass spectroscopy (SIMS) has been the tool of choice for chemical profiling of semiconductor systems. Although it affords a lower limit of detection, it is constrained by a low lateral resolution, making large test zones necessary (several hundred microns). More recently, energy dispersive X-ray scanning transmission electron microscopy (STEM-EDX) allows local specimen preparation and can generate 2D concentration maps. But due to low sensitivity it cannot quantify light elements (i.e. boron). Because of size effects, large test zones are not always representative of the local chemistry in the device and a complete picture is therefore unavailable. Atom probe tomography (APT) is an analytical 3D microscopy technique which maps the position of atoms in a material allowing composition measurements of a small selected volume. With a sub-nanometre spatial resolution, analysis of localised structures is possible and all elements are detected with the same probability. Initially dedicated to metals, semiconductor applications have escalated in recent years [1].

Will oscillating wave surge converters survive tsunamis?

With an increasing emphasis on renewable energy resources, wave power technology is becoming one of the realistic solutions. However, the 2011 tsunami in Japan was a harsh reminder of the ferocity of the ocean. It is known that tsunamis are nearly undetectable in the open ocean but as the wave approaches the shore its energy is compressed, creating large destructive waves. The question posed here is whether an oscillating wave surge converter (OWSC) could withstand the force of an incoming tsunami. Several tools are used to provide an answer: an analytical 3D model developed within the framework of linear theory, a numerical model based on the non-linear shallow water equations and empirical formulas. Numerical results show that run-up and draw-down can be amplified under some circumstances, leading to an OWSC lying on dry ground!

A comparison of 1D analytical model and 3D Finite Element Analysis with experiments for a Rosen-type piezoelectric transformer

This article is dedicated to the study of Piezoelectric Transformers (PTs), which offer promising solutions to the increasing need for integrated power electronics modules within autonomous systems. The advantages offered by such transformers include: immunity to electromagnetic disturbances; ease of miniaturisation for example, using conventional micro fabrication processes; and enhanced performance in terms of voltage gain and power efficiency. Central to the adequate description of such transformers is the need for complex analytical modeling tools, especially if one is attempting to include combined contributions due to (i) mechanical phenomena owing to the different propagation modes which differ at the primary and secondary sides of the PT; and (ii) electrical phenomena such as the voltage gain and power efficiency, which depend on the electrical load.The present work demonstrates an original one-dimensional (1D) analytical model, dedicated to a Rosen-type PT and simulation results are successively compared against that of a three-dimensional (3D) Finite Element Analysis (COMSOL Multiphysics software) and experimental results. The Rosen-type PT studied here is based on a single layer soft PZT (P191) with corresponding dimensions 18mm×3mm×1.5mm, which operated at the second harmonic of 176kHz. Detailed simulational and experimental results show that the presented 1D model predicts experimental measurements to within less than 10% error of the voltage gain at the second and third resonance frequency modes. Adjustment of the analytical model parameters is found to decrease errors relative to experimental voltage gain to within 1%, whilst a 2.5% error on the output admittance magnitude at the second resonance mode were obtained. Relying on the unique assumption of one-dimensionality, the present analytical model appears as a useful tool for Rosen-type PT design and behavior understanding.

An analytical 3D model for short-channel effects in undoped FinFETs

An analytical and scalable model for the threshold voltage in FinFETs has been developed by solving the 3-D Poisson equation using appropriate techniques. The model is also based on a physical anal...

Investigation of 3D SPECT Reconstruction with Multi-energy Photon Emitters

Parallel projection based Single Emission Computed Tomography is a widely used nuclear imaging technique. Non-homogeneous attenuation medium and the distance dependent spacial resolution (DDSR) of the parallel imaging cause serious artefacts during image reconstruction. Both effects are dependent on the energy of gamma photons used for imaging. In this paper an efficient parallel reconstruction algorithm is introduced that is executed on the Graphics Processing Unit. The aim of the presented study was to investigate the possibilities of reconstruction techniques when multi-energy photon emitters are used. An analytical 3D projector with attenuation and detector response modelling was used to generate projection sets for Gallium-67 isotope studies. Data were reconstructed from one photopeak only using the corresponding attenuation map. The projection data sets were added together and reconstructed using average attenuation and DDSR compensation values as well as simulating every photopeak individually. The third combined reconstruction technique was using every projection set as separate measurement. In this study we showed that all three strategies result in similar image quality, however the average attenuation correction method is computationally less demanding.

A New Approach for Determining Joint Stiffness of Bolted Joints

Joint member stiffness in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. Thus, the accurate determination of the stiffness is of extreme importance to predict the behavior of bolted assemblies. In this paper, An analytical 3D axisymmetric model of bolted joints is proposed to obtain the joint stiffness of Bolted Joints. Considering many different analytical models have been proposed to calculate the joint stiffness, the expression based force equilibrium can be a easy way to choose the best expression for the joint stiffness as a judgment criteria.

Gaussian uncertainty in homogenization of rubber–carbon black nanocomposites

The objective of this work is Gaussian uncertainty in material parameters of the rubber–carbon black particle reinforced nano-composite in the framework of determination of its effective elastic parameters. The analytical 3D micro-mechanical model is contrasted here with the Finite Element Method one realized with the use of the system ABAQUS® and its tetrahedral finite elements C3D4. They discretize cubic Representative Volume Element (RVE) with a centrally located spherical carbon black particle, whose deformation energies accumulated during the uniaxial and biaxial uniform tension are computed. The polynomial-based Response Function Method allows to determine analytical functions relating effective elasticity tensor with Young moduli and Poisson ratios of this composite original components via the Weighted Least Squares Method; this is done in the symbolic environment of MAPLE. These functions serve for the initial sensitivity analysis, where we detect Poisson ratio of the rubber matrix as the crucial design parameter and its Young modulus as having secondary importance, while particle Young modulus and Poisson ratio are totally irrelevant. Next, the most influential parameters are randomized according to the Gaussian distribution and are employed in the dual probabilistic scheme – by using the stochastic perturbation and, independently, semi-analytical techniques to determine up to the fourth order probabilistic characteristics of the effective tensor components. Deterministic and probabilistic hypersensitivity of the effective constitutive tensor, expected according to the rubber matrix presence, is confirmed in all computational experiments. Such a probabilistic energy-related FEM approach will allow for future applications of more advanced constitutive models for the carbon black nano-composites, for the RVEs of larger sizes – containing large agglomerations of these particles and for the imperfect interfaces simulation.

On the solution of exterior plane problems by the boundary element method: A physical point of view

The paper is devoted to the solution of Laplace equation by the boundary element method. The coupling between a finite element solution inside a bounded domain and a boundary integral formulation for an exterior infinite domain can be performed by producing a stiffness or matrix. It is shown in a first step that the use of classical Green's functions for plane domains can lead to impedance matrices which are not satisfying, being singular or not positive-definite. Avoiding the degenerate scale problem is classically overcome by adding to Green's function a constant which is large compared to the size of the domain. However, it is shown that this constant affects the solution of exterior problems in the case of non-null resultant of the normal gradient at the boundary. It becomes therefore important to define this constant related to a characteristic length introduced into Green's function. Using a 'slender body theory allows to show that for long cylindrical domains with a given cross section, the characteristic length is shown as being asymptotically equal to the length of the cylindrical domain. Comparing numerical or analytical 3D and 2D solutions on circular cylindrical domains confirms this result for circular cylinders.

Characterization of Fluid Film Produced by an Atomization-Based Cutting Fluid Spray System During Machining

The atomization-based cutting fluid (ACF) spray system has recently been proposed as a cooling and lubrication solution for machining hard to machine materials (e.g., titanium alloys). On the tool rake face, the ACF spray system forms a thin film from cutting fluid that penetrates into the tool–chip interface to improve tool life. The objective of this work is to characterize this thin fluid film in terms of thickness and velocity for a set of ACF spray parameters. ACF spray experiments are performed by varying impingement angle to observe the nature of the spreading film and to determine the film thickness at different locations after impingement of the droplets. It is observed that the film spreads radially outward producing three fluid film development zones (i.e., impingement, steady, and unsteady). The steady zone is found to be between 3 and 7 mm from the focus (impingement point) of the ACF spray for the set of parameters investigated. An analytical 3D thin fluid film model for the ACF spray system has also been developed based on the Navier–Stokes equations for mass and momentum. The model requires a unique treatment of the cross-film velocity profile, droplet impingement, and pressure distributions, as well as a strong gas–liquid shear interaction. The thickness profiles predicted by the analytical film model have been validated. Moreover, the model predictions of film velocity and chip flow characteristics during a titanium turning experiment reveal that the fluid film can easily penetrate into the entire tool–chip interface with the use of the ACF spray system.

The Wooden Roof of <i>Banesa e Skendulate</i> in Gjirokastra, Albania: The Role of the Diagnostic Test Campaign in the Structural Safety Evaluation

Banesa e Skendulate is part of the historical center of the museum-city of Gjirokastra (Albanian UNESCO World Heritage), an unique and well-preserved example of Albanian urban vernacular architecture influenced by the ottoman architectural style, situated in a strategic position in the valley of the Drino. Banesa e Skendulate represents not only the typical compositional characteristics of this architecture but also a culture and a lifestyle deeply rooted in its own traditions. As its known, historic roofings are load-bearing structures made of timber according to an empirical and intuitive design, without structural engineering theory support, and Banesa e Skendulates roof is a clear example of the posts and beams system and shows the ability of the local craftsmen to deal with the support of heavy stone roofing. In the following paragraphs, will be presented the non-destructive diagnostic testing performed on the wooden structure of the roofing together with a detailed geometric and technological survey in order to recognize the structural system, its behavior and pathology and then process the analytical 3D model. Furthermore, the paper deals with the problem arose as consequence of the interpretation of the results obtained by the diagnostic tests, concerning the determination of the classes of resistance attached to ancient structural wooden elements that, for obvious reasons, cannot be classified according to the strength classes defined by the regulations for new timber constructions. Applying the reference strength values classified for the new timber elements to the historic ones, can cause a heavy penalty in terms of structural safety verification of the roof; that is why the role of the diagnostic test campaign should guide the reinforcement project applying reference values determined on the real conditions of the wooden elements.

Determination of the friction coefficient as a function of sliding speed and normal pressure for steel C45 and steel 40HM

This paper presents a method of determining the coefficient of friction as a function of sliding speed and normal pressure for different friction pairs of materials used in friction dampers. A schematic of the experimental setup is shown and the course of the experiment is described. An analytical relation describing the influence of sliding speed and normal pressure on the friction coefficient for C45 and 40HM steel was derived. Then on the basis of the analytical relation 3D numerical models were created. Computations using the Abaqus/Standard software package were performed.

Analytical solution for free vibration analysis of composite plates with layer-wise displacement assumptions

This paper presents an analytical closed form solution for free vibration analysis of multilayered plates by using a layer-wise displacement assumption based on Carrera’s Unified Formulation. A wide range of boundary conditions are analysed by using a Levy type solution. By using such a solution, the number of the differential equations of motion depends on the number of plies. This means that for plates with different number of plies the equations of motion need to be re-derived and re-solved. In this paper, a procedure has been devised to overcame this problem and the equation of motions can be automatically obtained and solved to obtain natural frequencies and mode shapes for plates with any number of layers. This procedure has been called “L-matrix method”. The novel solutions have been validated by analytical 3D and 2D Navier type solutions for plates simply supported at all edges. A comparison of the results with 2D and 3D NASTRAN finite element models is also carried out showing the superiority of the analytical solution. Furthermore, benchmark solutions have been obtained for plates with different boundary conditions. The presented Levy type solution can be easily extended to static, buckling and response analysis.

Fatigue behavior of [0n/90n]s composite cantilever beam under tip impulse loading

Vibration induced fatigue analysis of cross-ply [0n/90n]s cantilever beam under tip impulse loading is presented. As a first step, vibration induced stress for the given tip impulse loading was evaluated using modal analysis. Viscous damping model was used for evaluating the stress state as a function of time. The stress-time history was converted into block loading consisting of many sub-blocks. The block loading consisted of four sub-blocks and a total of 135 numbers of cycles. The block loading was repeated after certain time duration. Further, fatigue analysis was performed based on the block loading condition evaluated. Fatigue failure initiation was examined using S–N curve based approach, residual strength approach as well as failure function approach. Number of blocks to failure initiation and the location of failure were obtained. Analysis of cross-ply [0n/90n]s cantilever beam under tip static loading was also conducted for comparison. Studies are also presented using 3D finite element analysis (FEA). Number of blocks required to cause fatigue failure initiation under tip impulse loading was found to be 332 and 331 using the analytical method and 3D FEA, respectively for the geometry of the beam, material properties and loading condition considered.

Levitation force analysis of medium and low speed maglev vehicles

The rule of levitation force variation with different structure and electromagnetic parameters provides a basis for electromagnet design of electromagnetic suspension (EMS) medium and low speed maglev vehicles. In order to acquire accurate calculation results of levitation force, different calculation methods, including analytical method, 2D FEM (finite element method), and 3D FEM, are applied to investigate the impact of various structural parameters, such as excitation current, air gap, lateral offset, and pole width, on levitation force. The analytical analysis is based on the classic mathematical model of levitation force between electromagnet and rail and performed with MATLAB. In the 2D and 3D FEMs, the numerical calculation of the levitation force is conducted with Ansoft by taking the magnetic saturation into account. In addition, the longitudinal end effect on the levitation force calculation is considered in the 3D FEM. The results show that the 3D FEM is the most accurate among the above three methods for calculating the levitation force, and the analytical method can only work for small current and/or large air gap conditions. A lateraloffset between vehicle and rail will reduce the levitation force; the levitation force descends sharply once the lateral offset exceeds the threshold, i.e., 8% of the pole width for U-shaped electromagnets. The maximum lift-to-weight ratio emerges when the pole width ratio of F type rail to electromagnet is 6:7. This may offer a reference for EMS maglev vehicle design and application.