Numerical simulations and surrogate-based optimization of cavitation performance for an aviation fuel pump

We used computational modeling to investigate the cavitation performance of an aviation fuel pump, and optimize structural parameters using the surrogate-based method. In the numerical simulation, a rotation-curvature correction was adapted to the k-ε turbulence model, and a four-component surrogate fuel was selected to reproduce the physical properties of the China RP-3 kerosene. Then the performance of the aviation fuel pump was predicted. In the optimization, based on the series of the numerical results, Surrogate-based analysis and optimization (SBAO) was used to optimize the structural parameters of the fuel pump (the variation of the outlet blade angle for the inducer △β _b1 and the variation of the inlet blade angle for the impeller △β _b2). The results show that the prediction of cavitation performance agrees well with the experimental data. The results show that cavitation areas are mainly distributed in the inlet of the inducer. The volume of cavities grows with the decreasing NPSHa. The head of the fuel pump has a sudden head-drop when NPSHa ≤ 5.64 m. Furthermore, the surrogate-based approach is available in structural optimization of the fuel pump. The cavitation performance of the optimized pump improved about 22 % with a little drop of head coefficient when △β _b1 = 4.33° and △β _b2 = 3.24°. The numerical approach employed in this paper can accurately predict the cavitating flow of the high rotating speed fuel pump and the surrogate-based method is available in the structural optimization for a better cavitation performance.

     

Discretized Markov chain in damage assessment using Rainflow cycle with effects of mean stress on an automobile crankshaft

We studied the effect of mean stress correction factor using the Rainflow counting technique to assess the fatigue damage of an automobile crankshaft under service loading by considering the stochastic process of the Markov chain. The failure of the crankshaft will cause serious damage to the engine and also to other connecting subcomponents. The service loading is computationally generated from the Discrete Markov chain model and the fatigue cycle is counted using the Rainflow counting technique with the consideration of the local minima and maxima load. To quantify the fatigue damage, the strain-life curve using the fatigue mean stresses was used to model the fatigue failure of the material used in for the crankshaft at N _f = 10 ⁶ . The fatigue mean stresses were used to estimate the effects of the mean stress on the fatigue strength of the component under service loading condition. Statistical verification with the boundary condition of the 90% confidence level was performed to observe the difference between the stochastic algorithms when compared towards the fatigue life behavior of the ductile cast iron material. We concluded that for the practical application, the proposed stochastic model provides a highly accurate assessment of fatigue damage prediction for improving the safety and controlling the risk factors in terms of structural health monitoring.     

Electron beam radiation damage to organic inclusions in vitreous,cubic, and hexagonal ice

Frozen hydrated specimens of various latex spheres were used as well-defined systems for the study of electron beam radiation damage to organic inclusions in vitreous, cubic and hexagonal ice. We found that radiolysis of organic material is modified by the presence of ice and that radiolysis in vitreous ice is different from that in crystalline ice. The pattern of damage depends also on the nature of the irradiated polymer, e.g., damage to poly(vinylchloride) is quite different from damage to polyacrylates, although in both polymers the main radiolytic process is chain scission. Some polymers such as polyacrylates were found to be much more stable in vitreous ice than in crystalline ice. The experimental results indicate that free radicals formed at the ice–organic matter interface play an important role in the radiolysis process which affects both the ice and embedded organic particles. Ice may play also a physical role in the process by limiting the diffusion of free radicals away from the interface. Although net mass loss is not much affected by ice, massive structural changes including repolymerization take place in its presence.     

The secondary fluorescence correction for X-ray microanalysis in the analytical electron microscope

A general formulation for the secondary fluorescence correction is presented. It is intended to give an intuitive appreciation for the various factors that influence the magnitude of the secondary fluorescence correction, the specimen geometry in particular, and to serve as a starting point for the derivation of quantitative correction formulae. This formulation is primarily intended for the X-ray microanalysis of electron-transparent specimens in the analytical electron microscope (AEM). The fluoresced intensity, I^Y_X, is expressed relative to the primary intensity of the fluorescing element, I_Y, rather than to that of the fluoresced element, I_X, as has been customary for microanalysis. The importance of this choice of I_Y as a reference intensity for the electron-transparent specimens examined in the AEM is discussed. The various factors entering the secondary fluorescence correction are grouped into three factors, representing the dependencies of the correction on specimen composition, X-ray fluorescence probability and specimen geometry. In principle, an additional factor should be appended to account for the difference in detection efficiencies of the fluoresced and fluorescing X-rays; however, this factor is shown to be within a few per cent of unity for practical applications of the secondary fluorescence correction. The absorption of secondary X-rays leaving the specimen en route to the detector is also accounted for through a single parameter. In the limit that the absorption of secondary X-rays is negligible, the geometric factor has the simple physical interpretation as the fractional solid angle subtended by the fluoresced volume from the perspective of the analysed volume. Studies of secondary fluorescence in the published literature are compared with this physical interpretation. It is shown to be qualitatively consistent with Reed's expression for secondary fluorescence in the electron probe microanalyser and with the specimen-thickness dependence of the Nockolds expression for the parallel-sided thin foil. This interpretation is also used to show that the ‘sec α’ dependence on specimen tilt in the latter expression is erroneous and should be omitted. The extent to which extrapolation methods can be used to correct for secondary fluorescence is also discussed. The notion that extrapolation methods, by themselves, can be used to correct for secondary fluorescence is refuted. However, extrapolation methods greatly facilitate secondary fluorescence correction for wedge-shaped specimens when used in conjunction with correction formulae.     

A single crystal of YALO3: Ce3+ as a fast scintillator in SEM

A new single-crystal scintillator intended for applications in a scanning electron microscope (SEM) is presented. It is a single-crystal disc of yttrium aluminium perovskite activated by trivalent cerium free of traces of Fe ions. The single crystals of YAlO₃: Ce³⁺ (YAP: Ce³⁺) were prepared by the Czochralski method in a reducing atmosphere of Ar and H₂ with an excess amount of Y³⁺ ions. Effective methods of purification and purity control of the raw material are described. The highest achievable concentration of Ce³⁺ ions in as grown crystals amounted to 0.3 wt%, concentration in the melt was 8–9 times higher. The best properties were found with samples of the maximum possible concentration of Ce³⁺. Compared with the previous aluminate Y₃ Al₅ O₁₂: Ce³⁺ (YAG: Ce³⁺) these samples showed higher efficiency, a shorter decay time of luminescence (40 ns) and an emission band in a more advantageous spectral region (378 nm). Because of high resistance to radiation damage, high chemical resistance and applicability to ultra-high vacuum it is also suitable for detection of other kinds of ionizing radiation.     

Electron microscopy of frozen biological suspensions

The methodology for preparing specimens in the frozen, hydrated state has been assessed using crystals and T4 bacteriophages. The methods have also been demonstrated with lambda bacteriophages, purple membrane of Halobacterium halobium and fibres of DNA. For particles dispersed in an aqueous environment, it is shown that optimum structural preservation is obtained from a thin, quench-frozen film with the bulk aqueous medium in the vitreous state. Crystallization of the bulk water may result in solute segregation and expulsion of the specimen from the film. Contrast measurements can be used to follow directly the state of hydration of a specimen during transition from the fully hydrated to the freeze-dried state and permit direct measurement of the water content of the specimen. By changing the concentration and composition of the aqueous medium the contrast of particles in a vitreous film can be controlled and any state of negative, positive or zero contrast may be obtained. At 100 K, frozen-hydrated, freeze-dried or sugar embedded crystals can withstand a three- to four-fold increase in electron exposure for the same damage when compared with similar sugar-embedded or freeze-dried samples at room temperature.     

Electron beam damage of behenic acid films

The rate of fading of electron diffraction patterns of behenic acid monolayer crystals as well as multilayer crystals was measured at 100 kV at room temperature to investigate the dependence of beam damage on specimen thickness. The diffracted intensities for monolayers and double layers decreased nearly exponentially with electron exposure; however, the intensities for multilayers were unchanged during initial electron exposures, often increased temporarily and then decreased with electron exposure. The critical dose, D_e, defined as the dose at which the diffracted intensity falls to 1/e of its initial value, was 1.0 electrons/Ų for the monolayers, 1.8 electrons/Ų for the double layers and more for multilayers. These results lead to the conclusion that D_e for behenic acid increases nearly linearly with specimen thickness in the range of about 25–100 Å for dose rate of 0.1–2 electrons/Ų min.     

Low voltage scanning electron microscopy

The scanning electron microscope (SEM) is usually operated with a beam voltage, V₀, in the range of 10–30 kV, even though many early workers had suggested the use of lower voltages to increase topographic contrast and to reduce specimen charging and beam damage. The chief reason for this contradiction is poor instrumental performance when V₀=1–3 kV, The problems include low source brightness, greater defocusing due to chromatic aberration greater sensitivity to stray fields, and difficulty in collecting the secondary electron signal. Responding to the needs of the semiconductor industry, which uses low V₀ to reduce beam damage, considerable efforts have been made to overcome these problems. The resulting equipment has greatly improved performance at low kV and substantially removes the practical deterrents to operation in this mode. This paper reviews the advantages of low voltage operation, recent progress in instrumentation and describes a prototype instrument designed and built for optimum performance at 1 kV. Other limitations to high resolution topographic imaging such as surface contamination, the de-localized nature of the inelastic scattering event and radiation damage are also discussed.     

Calculation and comparison of the backscattering factor R for characteristic x-ray emission

The backscattering factor R for characteristic radiation, which is a part of the atomic number correction commonly used in electron probe microanalysis, is calculated keeping mathematical simplifications at a minimum. The results are compared with the values calculated by means of three other often used expressions for the backscattering factor. It is shown that our results generally are similar to the ones of Duncumb and Reed and of Pouchou and Pichoir, but differ significantly from the ones of Love et al., whose expression seems not to be applicable if the overvoltage is higher than ～50.     

Microscopy and microanalysis of crystalline glazes

Crystalline glazes on ceramic plates produced commercially in the U.K. and on ceramic pots produced commercially in Taiwan and Spain have been examined by X‐ray diffraction, conventional and polarized light microscopy, and scanning electron microscopy in order to identify the crystalline phases present in the glazes and to ascertain through X‐ray microanalysis the partitioning behaviour of the transition metal ions used to colour the glazes and the crystals within them. In each case examined, the macroscopic two‐dimensional spherulites within the glazes clearly seen by the naked eye were found to consist of large numbers of radially orientated acicular crystals each 5 µm or less in width embedded within the silica‐rich glaze. Energy dispersive X‐ray microanalysis and X‐ray diffraction of these crystals identified these crystals as willemite, α‐Zn₂SiO₄. The strong [001] texture of these crystals within the glaze evident from the X‐ray diffraction patterns was consistent with polarized light microscopy observations of the willemite crystals. In addition to willemite, small iron‐doped gahnite (ZnAl₂O₄) crystals were found in a honey‐coloured crystalline glaze and acicular rutile (TiO₂) crystals were found in the Portmeirion Pottery plates examined. Transition metal ions with a preference for tetrahedral coordination were observed to substitute for Zn²⁺ ions in willemite and to partition preferentially to the willemite crystals, whereas ions preferring octahedral coordination preferred to remain in the glaze.     

Study of surface roughness effects in elastohydrodynamic lubrication of rolling line contacts using a deterministic model

A sinusoidal surface roughness model is adopted for the analysis of the effects of roughness amplitude and wavelength on pressure profile, film shape, minimum film thickness and coefficient of friction in a steady state EHL line contact. The influence coefficients used for the evaluation of surface displacements are calculated by utilizing a numerical method based on Fast Fourier Transform. Significant reduction is observed in the minimum film thickness due to surface roughness. Such reduction is quantified by roughness correction factor, C_R, and a relationship between C_R and non-dimensional surface roughness amplitude A is derived as: C_R=1−0.7823A^0.8213. This equation may prove to be of interest from designer's viewpoint. The friction coefficient is found to increase appreciably with increasing amplitude and decreasing wavelength of surface roughness.     

On the methodology of the thyroid epithelial cell thickness determination

The average thickness of the thyroid epithelial cells may be determined either directly or indirectly. By the direct or caliper method, this thickness is overestimated as a result of which its empirical value must be divided by a correction factor K_d. By the indirect method, on the other hand, the thickness of the thyroid gland epithelium is calculated as the ratio of the double volume density of the epithelium to the sum of the inner and the outer surface density of the epithelium; in this case the sought for thickness value is underestimated and must consequently be multiplied by a factor K_i. Both correction factors are algebraically defined. Their values are calculated and graphically represented as a function of the thyroid activation index (the ratio between the volume density of the epithelium and the colloid) for the range from 0·1 to 100. The validity of the theoretical interpretation of the discrepancy between the values obtained for the average thickness of the thyroid epithelium by the direct and the corresponding values obtained by the indirect method, is empirically tested. It is shown that by the introduction of appropriate correction factors the difference between the results obtained by each method can be reduced. These improved direct and indirect methods for determining the wall thickness of a hollow sphere seem to lend themselves to being used in the stereological analysis of other biological, perhaps even non-biological materials of similar structure.     

Structural changes in electron-irradiated paraffin crystals at < 15K and their relevance to lattice imaging experiments

The process of electron beam irradiation of orthorhombic monolamellar microcrystals of the n-paraffin n-tetratetracontane cooled < 15K is monitored by changes in the crystal structure to give a much clearer view of the beam damage process than is afforded by plots of diffraction intensity variation. The observed structural change in the chains, observed in the projection down the chain axes as an increasingly circular cross-section, is consistent with previous structural analyses of structural damage in an orthogonal view and also other observations of conformational flexibility of long chains induced by trans-vinylene groups. Nevertheless, within the 2.5 Å resolution available for direct lattice images (reported elsewhere), there is virtually no detectable structural change at the 10 e A^-2 electron dose used for these exposures.     

Multichannel wide‐field microscopic FRET imaging based on simultaneous spectral unmixing of excitation and emission spectra

Simultaneous spectral unmixing of excitation and emission spectra (ExEm unmixing) has inherent ability resolving spectral crosstalks, two key issues of quantitative fluorescence resonance energy transfer (FRET) measurement, of both the excitation and emission spectra between donor and acceptor without additional corrections. We here set up a filter‐based multichannel wide‐field microscope for ExEm unmixing‐based FRET imaging (m‐ExEm‐spFRET) containing a constant system correction factor (f_sc) for a stable system. We performed m‐ExEm‐spFRET with four‐ and two‐wavelength excitation respectively on our system to quantitatively image single living cells expressing FRET tandem constructs, and obtained accurate FRET efficiency (E) and concentration ratio of acceptor to donor (R_C). We also performed m‐ExEm‐spFRET imaging for single living cells coexpressing CFP‐Bax and YFP‐Bax, and found that the E values were about 0 for control cells and about 28% for staurosporin‐treated cells when R_C were larger than 1, indicating that staurosporin induced significant oligomerisation.     

Baseline correction of AFM force curves in the force–time representation

This note reports on the proper correction of force data acquired with an atomic force microscope (AFM). The force–time representation is hereby used to obtain the correction factors for the overall offset and slope for a single force–time curve, as the initial force, F₀ = F(t₀), and the rate of change in the force per unit of time, dF/dt, respectively. The report shows that a complete set of force data, including the approach, delay and retraction regions, can be simultaneously corrected in the force–time representation by subtracting the line CL_t = F₀ + dF/dt·t to the experimental data. The method described here outperforms the one commonly employed in the correction of AFM force curves and highlights the convenience of using the force–time representation for force data processing wherein the artifactual behavior can be expressed as a single, differentiable function of time.     

Diffraction patterns of artificial two-dimensional crystals synthesized in situ in an environmental scanning transmission electron microscope

In this study, we demonstrated the use of electron‐beam‐induced deposition for synthesis of artificial two‐dimensional crystals with an in situ scanning transmission electron microscope. The structures were deposited from W(CO)₆ in an environmental scanning transmission electron microscope on a 30‐nm‐thick Si₃N₄ substrate. We present clear electron beam diffraction patterns taken from those structures. The distance between the diffraction peaks corresponded to the dot spacing in the self‐made surface crystal. We propose using these arrays of dots as anchor points for making artificial crystals for diffraction analysis of weakly scattering or beam‐sensitive molecules such as proteins.     

Computer-controlled spot-scan imaging of crotoxin complex crystals with 400 keV electrons at near-atomic resolution.

400 keV electrons yield a better relative image contrast than 100 keV electrons for a beam-sensitive organic crystal when spot-scan imaging is used [J. Brink and W. Chiu, J. Microscopy 161 (1991) 279]. A FORTRAN 77 program has been written to operate the spot-scan imaging system on a computer workstation under the VMS operating system which is interfaced serially to the JEOL4000 electron microscope. We demonstrate the application of this implementation by imaging crotoxin complex crystals embedded in either vitreous ice or glucose to 2.5 A resolution. The intensity strength of the structure factors of this protein crystal are different at low (> 10 A) resolution but similar at high resolution (< 10 A) for the two embedding media as expected from their scattering contrast difference. Based on our experience as judged from the electron diffraction patterns of highly tilted crystals, flat crystals embedded in glucose can be readily obtained. Furthermore, our spot-scan imaging system also has the option of correcting the focus gradient that is present in images of tilted specimens.     

STM and AFM investigations of high-Tc superconductors

We have studied the (001) surface of single crystal YBa₂Cu₃O_7-x high-T_c superconductors using scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) at room temperature at ambient pressure. Both methods show flat terraces with steps which are multiples of the c-axis lattice constant (of 1·17 nm) high. Our results show that the bulk crystal structure extends to the surface and that the crystals were formed by island growth. Only occasionally tunnelling was possible with sample bias voltages below +1·0 V. We interpret the observed voltage dependence and the difficulty to get good STM images to be due to the presence of a less-conducting surface layer. Auger spectroscopy indicates that carbon is present at the surface, which is probably related to a contamination layer.     

The characterization of the damage introduced during Micro-erosion of MgO single crystals

The plastic damage introduced in MgO single crystals by bombardment with A1₂O₃ microspheres (0.3, 10, 20 and 27 μm diam.) has been studied using optical, transmission and scanning electron microscopy. Most of the damage is in the form of dislocation dipoles (two closely spaced dislocations of opposite sign) which lie on {110} slip planes. The dislocation density increases with the increase in the energy of the impinging particles. Using stereo-microscopy the damage has been shown to be uniformly distributed in thin foils. Studies done on indentations produced by a sharp pin show a very high density of single dislocations.     

Tunnelling spectroscopy of high-temperature superconductors

We measured samples of La_1·85Sr_0·15CuO_4-y and YBa₂Cu₃O_7-y with a UHV low-temperature scanning tunnelling microscope using tips made out of tungsten, aluminium and indium. The samples are either sintered pellets, single crystals, or thin films. A wide variety of I-V curves were obtained ranging from nearly ideal S-I-N and S-I-S characteristics, to strongly asymmetric and multiple-peaked characteristics. The best data are obtained with thin film samples and indium tips. Large values of 2δ/kT_c (～ 11) are observed in most cases. We discuss possible explanations for these large values. New data are presented obtained with thin films of Y-Ba-Cu-O made by e-beam evaporation in our laboratory. A system of loadlocks is used to ensure that these films are never exposed to the atmosphere.