Analytical Surface Research Articles

Predictive Modeling of Surface Roughness in Grinding

Surface quality of the machined component is one of the most important criteria for the assessment of grinding process. The importance of the surface finish of a product depends upon its functional requirements. Since surface finish is governed by many factors, its experimental determination is laborious and time consuming. So the establishment of a model for the reliable prediction of surface roughness is still a key issue for grinding. In this study, a new analytical surface roughness model is developed on the basis of stochastic nature of the grinding process, governed mainly by the random geometry and the random distribution of cutting edges on the wheel surface having random grain protrusion heights. A simple relationship between the surface roughness and the chip thickness was obtained, which was validated by the experimental results of AISI 4340 steel in surface grinding.

Partially umbilic singularities of hypersurfaces of [formula omitted

This paper establishes the geometric structure of the lines of principal curvature of a hypersurface immersed in R4 in a neighborhood of the set S of its principal curvature singularities, consisting of the points at which at least two principal curvatures are equal. Under generic conditions defined by appropriate transversality hypotheses it is proved that S is the union of regular smooth curves S12 and S23, consisting of partially umbilic points, where only two principal curvatures coincide. This curve is partitioned into regular arcs consisting of points of Darbouxian types D1, D2, D3, with common boundary at isolated semi-Darbouxian transition points of types D12 and D23. The stratified structure of the partially umbilic separatrix surfaces, consisting of the boundary of the set of points through which the principal lines approach S, established in this work, extends to hypersurfaces in R4 the results of Darboux in [1] for umbilic points on analytic surfaces in R3, reformulated by Gutierrez and Sotomayor in [8], to describe the umbilic separatrix structures of the umbilic types D1, D2, D3, and further developed by Garcia, Gutierrez and Sotomayor in [6], for their D12 and D23 generic bifurcations. This work complements results of Garcia [5] on the structure of principal curvature lines around the generic partially umbilic points of hypersurfaces in R4.

Many-body effects on the structures and stability of Ba²⁺Xe(n) (n = 1-39, 54) clusters.

The structures and relative stabilities of mixed Ba(2+)Xe(n) (n = 1-39, 54) clusters have been theoretically studied using basin-hopping global optimization. Analytical potential energy surfaces were constructed from ab initio or experimental data, assuming either purely additive interactions or including many-body polarization effects and the mutual contribution of self-consistent induced dipoles. For both models the stable structures are characterized by the barium cation being coated by a shell of xenon atoms, as expected from simple energetic arguments. Icosahedral packing is dominantly found, the exceptional stability of the icosahedral motif at n = 12 being further manifested at the size n = 32 where the basic icosahedron is surrounded by a dodecahedral cage, and at n = 54 where the transition to multilayer Mackay icosahedra has occurred. Interactions between induced dipoles generally tend to decrease the Xe-Xe binding, leading to different solvation patterns at small sizes but also favoring polyicosahedral growth. Besides attenuating relative energetic stability, many-body effects affect the structures by expanding the clusters by a few percents and allowing them to deform more.

Immobilized nickel hexacyanoferrate on activated carbons for efficient attenuation of radio toxic Cs(I) from aqueous solutions

The aim of this study is to immobilize nickel hexacyanoferrate onto the large surface of activated carbons (ACs) precursor to rice hulls and areca nut waste materials. These nickel hexacyanoferrate immobilized materials are then assessed in the effective attenuation of radio logically important cesium ions from aqueous solutions. The solid samples are characterized by the XRD analytical method and surface morphology is obtained from the SEM images. The batch reactor experiments show that an increase in sorptive pH (2.0–10.0) apparently not affecting the high percent uptake of Cs(I). Equilibrium modeling studies suggest that the data are reasonably and relatively fitted well to the Langmuir adsorption isotherm. Kinetic studies show that sorption process is fairly rapid and the kinetic data are fitted well to the pseudo-second order rate model. Increasing the background electrolyte concentration from 0.001 to 0.1mol/L NaCl causes insignificant decrease in Cs(I) removal which infers the higher selectivity of these materials for Cs(I) from aqueous solutions. Further, the column reactor operations enable to obtain the breakthrough data which are then fitted to the Thomas non-linear equation as to obtain the loading capacity of column for Cs(I). The results show that the modified materials show potential applicability in the attenuation of radio toxic cesium from aqueous solution.

A Parametric Computational Fluid Dynamics Analysis of the Valve Pocket Losses in Reciprocating Compressors

The reduction of pressure losses is one of the most important challenges for the efficiency increase of a reciprocating compressor. Since the absorbed power is strongly affected by the losses through pocket valves and cylinder ducts, an accurate prediction of these losses is essential. The use of computational fluid dynamics (CFD) simulation has shown great potential for the study of the entire reciprocating compressor, but is still limited by high computational costs. Recently, the authors have presented a simplified CFD approach: the actual valve geometry is replaced with an equivalent porous region, which has significantly increased the speed of calculation while ensuring accuracy as well. Based on this approach, a new methodology for the evaluation of pocket valve losses is presented. A set of CFD simulations using a parameterized geometry of the pocket valve was performed to evaluate the relationship between the losses of the pocket and its geometrical features. An analytical response surface (RS) was defined using the values of the geometrical dimensions as inputs and the pocket flow coefficient as output. Finally, the response surface was validated through a set of test cases performed on different geometries with the actual valve and the results have shown good predictability of the tool.

Quasiclassical trajectory study of the effect of antisymmetric stretch mode excitation on the O(³P) + CH₄(ν₃ = 1) → OH + CH₃ reaction on an analytical potential energy surface. Comparison with experiment.

Motivated by a recent crossed-beam experiment on the title reaction reported by Pan and Liu [J. Chem. Phys. 140, 191101 (2014)], a detailed dynamics study was performed at three collision energies using quasiclassical trajectory (QCT) calculations based on a full-dimensional potential energy surface recently developed by our group (PES-2014). Although theory/experiment agreement is not yet quantitative, in general the theoretical results reproduce the experimental evidence: the vibrational branching ratio of OH(v = 1)/OH(v = 0) is ~0.8/0.2, excitation of the antisymmetric CH stretching mode in methane increases reactivity by factor 2.28-1.50, although an equivalent amount as translational energy is more efficient in promoting the reaction and, finally, product angular distribution shifts from backward in the CH4(ν = 0) ground-state to sideways when the antisymmetric CH stretching mode is excited. These results give confidence to the PES-2014 surface, depend on the quantization procedure used, are comparable with recent QCT calculations or improve previous theoretical studies using a different surface, and demonstrate the utility of the theory/experiment collaboration.

A DUAL-STAGE SAMPLING BASED ARTIFICIAL NEURAL NETWORK RESPONSE SURFACE METHODOLOGY AND ITS APPLICATION TO TUBULAR PERMANENT-MAGNET LINEAR SYNCHRONOUS MOTOR

A dual-stage sampling (DSS) is proposed to reduce training samples of artificial neural network for establishing the analytical response surface model. The procedure of the DSS-based artificial neural network response surface (ANNRS) methodology is divided into two stages. At the rough stage, new sample is generated in the entire space by maximizing the minimum distance to existed samples. Then at the refine stage, new sample is produced in the same way, but is limited in the partial space between two samples with larger gradient and larger distance. And the efficiency of the DSS method is proved by a test function. Considering design variables about slot width and depth, permanent magnet (PM) width and height, and end tooth width, tubular permanent-magnet linear synchronous motor (TPMLSM) modeling problem is represented, whose thrust and ripple are calculated time-consumingly by finite element analysis. Then, The DSS-based ANNRS is applied to establish the TPMLSM model in good accuracy with fewer samples, lower consumption.

Theoretical Analysis about Off-Axis Parabolic Surface Machining under Two Different Accurate Spiral Tool Paths

Off-axis aspheric surface is an indispensable optical device for the high precision measurement and manufacturing equipment, and the tool path generation is a very important factor for the manufacturing to obtain the surface with high precision form and nanometric surface finish. In this paper, the systemic description of tool path generation method about the off-axis parabolic surface with ultra-precision single point diamond turning is processed. Two effective methods of generating the accurate spiral tool path are proposed and compared. The proposed methods are mainly based on mathematical calculation directly from analytic surfaces, including the general process of tool path generation, cutting-tool compensation and avoiding tool interference. This work can provide the theoretical basis of choosing the cutting tool path for off-axis parabolic surface and can improve the efficiency and precision of machine. Finally, some cutting simulations are implemented to prove the proposed methods.

A molecular dynamics simulation of hydrogen atoms collisions on an H-preadsorbed silica surface

The interaction of hydrogen atoms and molecules with a silica surface is relevant for many research and technological areas. Here, the dynamics of hydrogen atoms colliding with an H-preadsorbed β-cristobalite (0 0 1) surface has been studied using a semiclassical collisional method in conjunction with a recently developed analytical potential energy surface based on density functional theory (DFT) calculations. The atomic recombination probability via an Eley–Rideal (E–R) mechanism, as well as the probabilities for other competitive surface processes, have been determined in a broad range of collision energies (0.04–3.0 eV) for off-normal (θv = 45°) and normal (θv = 0°) incidence and for two different surface temperatures (TS = 300 and 1000 K). H2,gas molecules form in roto-vibrational excited levels while the energy transferred to the solid surface is below 10% for all simulated conditions. Finally, the global atomic recombination coefficient (γE–R) and vibrational state resolved recombination coefficients (γ(v)) were calculated and compared with the available experimental values. The calculated collisional data are of interest in chemical kinetics studies and fluid dynamics simulations of silica surface processes in H-based low-temperature, low-pressure plasmas.

Numerical Study on the Influence of Crystallographic Texture and Grain Shape on the Yield Surface of Textured Aluminum Sheet Material

The paper investigates by numerical modeling the effects of crystallographic texture and grain shape on the shape of the yield surface of aluminum sheet material at small strains. Different representative volume elements (RVEs) of the material are considered. Plane stress state is assumed in the sheet. A rate-dependent model of crystal plasticity (CP) is used in combination with either the full-constraint (FC) Taylor model or the finite element method (FEM) to compute the volume averaged stress of the material. The effect of different crystallographic textures observed in aluminum alloys on the shape of the yield surface is firstly investigated. An analytical yield function is used to generate yield surfaces for the different crystallographic textures. The deviation between the stress states at yielding computed by FC-Taylor model and the analytical yield surface is used to evaluate the capability of the yield function to fit the anisotropic yield surfaces representing different strong crystallographic textures. Two different shapes of the grains are introduced in the RVEs of CP-FEM in order to study the effect of the grain morphology. Small effects of grain shape are found at small strain compared with the marked influence of crystallographic texture.

Full-dimensional diabatic potential energy surfaces including dissociation: The 2E″ state of NO3

A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the (2)E″ state of the NO3 radical. An accurate potential energy surface for the NO₃⁻ anion ground state is developed as well. Both surfaces are based on high-level ab initio calculations. The model consists of a diabatic potential matrix, which is expanded to higher order in terms of symmetry polynomials of symmetry coordinates. The choice of coordinates is key for the accuracy of the obtained potential energy surfaces and is discussed in detail. A second central aspect is the generation of reference data to fit the expansion coefficients of the model for which a stochastic approach is proposed. A third ingredient is a new and simple scheme to handle problematic regions of the potential energy surfaces, resulting from the massive undersampling by the reference data unavoidable for high-dimensional problems. The final analytical diabatic surfaces are used to compute the lowest vibrational levels of NO₃⁻ and the photo-electron detachment spectrum of NO₃⁻ leading to the neutral radical in the (2)E″ state by full dimensional multi-surface wave-packet propagation for NO3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces.

Identification of Knowledge Gaps Regarding Healthcare Workers' Exposure to Antineoplastic Drugs: Review of Literature, North America versus Europe.

We have been examining the issue of healthcare workers' exposure to antineoplastic drugs for nearly a decade and have observed that there appears to be more publications on the subject matter originating from Europe than from North America. The concern is that findings from Europe may not be generalizable to North America because of differences in handling practices, regulatory requirements, and training. Our objective was to perform a literature review to confirm our observation and, in turn, identify gaps in knowledge that warrants addressing in North America. Using select keywords, we searched for publications in PubMed and Web of Science. All papers were initially classified according to the originating continent and then categorized into one or more subject categories (analytical methods, biological monitoring, occupational exposure, surface contamination, and probability of risk/exposure). Our review identified 16 papers originating from North America and 55 papers from Europe with surface contamination being the subject matter most often studied overall. Based on our results, we are of the opinion that North American researchers need to further conduct dermal and/or urinary drug contamination studies as well as assess the exposure risk faced by healthcare workers who handle antineoplastic drugs. Trends in exposure levels should also be explored.

Free surface intake vortices: scale effects due to surface tension and viscosity

ABSTRACTEngineers frequently use physical scale models of hydropower intakes to assess and minimize the occurrence of harmful free surface vortices. The impact of surface tension, viscosity and turbulence on the scaling behaviour of the vortices is examined here using an analytical free surface vortex model developed from measurements in a laboratory-scale hydropower intake. First, the effect of surface tension on the free surface depression is computed using a finite-difference model over a wide range of depression scales and shapes. The impact and scaling behaviour of surface tension are found to be qualitatively different depending on whether the depression is dimple- or funnel-shaped. The influence of viscosity on scaling predicted by the analytical vortex model contradicts trends recorded by previous authors, which suggests that additional processes such as turbulent diffusion may play a significant role at larger scales. Scale effects due to the interplay of viscosity and turbulence require further investigation, whereas those due to surface tension are fairly easily quantified and predicted.

Twistor construction of asymptotically hyperbolic Einstein–Weyl spaces

Starting from a real analytic conformal Cartan connection on a real analytic surface S, we construct a complex surface T containing a family of pairs of projective lines. Using the structure on S we also construct a complex 3-space Z, such that Z is a twistor space of a self-dual conformal 4-fold and T is a quotient of Z by a holomorphic local C× action. We prove that T is a minitwistor space of an asymptotically hyperbolic Einstein–Weyl space with S as an asymptotic boundary.

Integrable perturbed magnetic fields in toroidal geometry: An exact analytical flux surface label for large aspect ratio

An analytical description of magnetic islands is presented for the typical case of a single perturbation mode introduced to tokamak plasma equilibrium in the large aspect ratio approximation. Following the Hamiltonian structure directly in terms of toroidal coordinates, the well known integrability of this system is exploited, laying out a precise and practical way for determining the island topology features, as required in various applications, through an analytical and exact flux surface label.

Design, Development and Evaluation of a New Mechanism for Sugarcane Metering Device Using Analytical Hierarchy Method and Response Surface Methodology

The application of machines to agricultural production has been one of the most significant developments in the agricultural world. Among the machines contributing to higher yield in current farming are planting machines. Sugarcane planting needs precision metering device operated under best combination of performance parameters. Though sugarcane planting is a labour intensive operation and is done manually in many countries. A new mechanism of sugarcane metering device, designed and modeled with Catia software, was fabricated. Main components of this machine were inclined surface, fixed tooth, metering device and its tooth. Effect of metering device tooth length and speed of sugarcane billet metering device were studied in order to find the best combination for improving distance uniformity and filling of metering device cells by reduction in the amount of billets used for planting. Analytical hierarchy process used to select the best combination for desired distance uniformity between planted billets and filling of metering device cells. The 2 cm tooth length and 0.75 m/s forward speed for metering device was the best suited combination for sugarcane billet metering device and consistency ratio computed lower than 0.1 that indicated acceptable results.

Twistor holomorphic affine surfaces and projective invariants

We study affine immersions with twistor lifts. Using a decomposition of a connection, we obtain several projective invariants for such affine immersions. In particular, affine immersions with holomorphic twistor lifts are considered. We can show the property that an affine immersion has holomorphic twistor lifts is invariant under projective transformations and characterize immersions with holomorphic twistor lifts by vanishing of some of projective invariants. In the case of compact affine surfaces with holomorphic twistor lifts, we see a quantization phenomenon for one of the projective invariants which we obtain. Moreover, we prove that a real analytic twistor holomorphic affine surface with the symmetric Ricci tensor with respect to both complex structures is totally geodesic or totally umbilic.

Quasi-classical trajectory study of the vibrational and translational effects on the O((3)P) + CD4 reaction.

The effects of vibrational excitation and translational energy, connected to mode selectivity and Polanyi's rules, are important issues in dynamics studies. To analyze these effects on the O((3)P) + CD4 reaction, an exhaustive dynamics study was performed using quasi-classical trajectory calculations on a full-dimensional analytical potential energy surface. The independent excitation of the C-D symmetric or asymmetric stretch modes leads to reactions with similar reaction cross sections and product scattering distributions, mode selectivity being discarded. Finally, translational energy raises the reactivity more effectively than an equal amount of energy in vibration, thus indicating that for this "central barrier" reaction it is not clear how to apply the venerable Polanyi's rules. The strong coupling between vibrational modes is responsible for this behavior, which seems to be the general tendency in polyatomic systems.

Theoretical kinetics study of the O(³P) + CH₄/CD₄ hydrogen abstraction reaction: the role of anharmonicity, recrossing effects, and quantum mechanical tunneling.

Using a recently developed full-dimensional accurate analytical potential energy surface [Gonzalez-Lavado, E., Corchado, J. C., and Espinosa-Garcia, J. J. Chem. Phys. 2014, 140, 064310], we investigate the thermal rate coefficients of the O((3)P) + CH4/CD4 reactions with ring polymer molecular dynamics (RPMD) and with variational transition-state theory with multidimensional tunneling corrections (VTST/MT). The results of the present calculations are compared with available experimental data for a wide temperature range 200-2500 K. In the classical high-temperature limit, the RPMD results match perfectly the experimental data, whereas VTST results are smaller by a factor of 2. We suggest that this discrepancy is due to the harmonic approximation used in the present VTST calculations, which leads to an overestimation of the variational effects. At low temperatures the tunneling plays an important role, which is captured by both methods, although they both overestimate the experimental values. The analysis of the kinetic isotope effects shows a discrepancy between both approaches, with the VTST values smaller by a factor about 2 at very low temperatures. Unfortunately, no experimental results are available to shed any light on this comparison, which keeps it as an open question.

Constructing polyatomic potential energy surfaces by interpolating diabatic Hamiltonian matrices with demonstration on green fluorescent protein chromophore

Simulating molecular dynamics directly on quantum chemically obtained potential energy surfaces is generally time consuming. The cost becomes overwhelming especially when excited state dynamics is aimed with multiple electronic states. The interpolated potential has been suggested as a remedy for the cost issue in various simulation settings ranging from fast gas phase reactions of small molecules to relatively slow condensed phase dynamics with complex surrounding. Here, we present a scheme for interpolating multiple electronic surfaces of a relatively large molecule, with an intention of applying it to studying nonadiabatic behaviors. The scheme starts with adiabatic potential information and its diabatic transformation, both of which can be readily obtained, in principle, with quantum chemical calculations. The adiabatic energies and their derivatives on each interpolation center are combined with the derivative coupling vectors to generate the corresponding diabatic Hamiltonian and its derivatives, and they are subsequently adopted in producing a globally defined diabatic Hamiltonian function. As a demonstration, we employ the scheme to build an interpolated Hamiltonian of a relatively large chromophore, para-hydroxybenzylidene imidazolinone, in reference to its all-atom analytical surface model. We show that the interpolation is indeed reliable enough to reproduce important features of the reference surface model, such as its adiabatic energies and derivative couplings. In addition, nonadiabatic surface hopping simulations with interpolation yield population transfer dynamics that is well in accord with the result generated with the reference analytic surface. With these, we conclude by suggesting that the interpolation of diabatic Hamiltonians will be applicable for studying nonadiabatic behaviors of sizeable molecules.