A novel double‐image Fizeau system for accurate investigation of anisotropic polymer fibres

This paper introduces a double‐image multiple‐beam Fizeau fringes system. The introduced system can dynamically determine the variations of the refractive indices for both parallel and perpendicular polarization simultaneously. This is achieved by the simultaneous capturing of two multiple‐beam interference patterns during the mechanical processing of isotactic polypropylene fibre. This parallel determination of the refractive indices of both polarization directions allowed us to determine the full‐field distribution of the stress vector, S . To accomplish this, a mathematical model was deduced to calculate the components of the stress vector, S , i.e. parallel stress component, S₁, and perpendicular stress component, S₂. Double‐image Fizeau fringes system and the deduced mathematical model were used to investigate the variation of the refractive index and stress components of the fibre during the stretching process and propagation of necked regions.     

Characterisation of lattice damage formation in tantalum irradiated at variable temperatures

The formation of radiation‐induced dislocation loops and voids in tantalum at 180(2), 345(3) and 590(5)°C was assessed by 3MeV proton irradiation experiments and subsequent damage characterisation using transmission electron microscopy. Voids formed at 345(3)°C and were arranged into a body centred cubic lattice at a damage level of 0.55 dpa. The low vacancy mobility at 180(2)°C impedes enough vacancy clustering and therefore the formation of voids visible by TEM. At 590(5)°C the Burgers vector of the interstitial‐type dislocation loops is a<100>, instead of the a/2 <111> Burgers vector characteristic of the loops at 180(2) and 345(3)°C. The lower mobility of a<100> loops hinders the formation of voids at 590(5)°C up to a damage level of 0.55 dpa.     

Quantitative image analysis of finite porous media

Software for the reconstruction of branch-node charts from serial sections is tested with a simple cubic lattice, and is applied to determine the genus per unit volume (specific genus) of a Berea sandstone sample from seventy-eight serial sections. The genus is found analytically for the cubic lattice as a function of depth, cross-section and volume. These results enable us to draw conclusions about the relative importance of depth and cross-section and provide useful information on how to treat finite sample data to obtain the specific genus of an infinite homogeneous porous medium. It is shown that it is more important to have a deep sample (many serial sections) than a sample of large cross-section. For samples which are too small in the direction of sectioning, the genus and the rate of change of genus with volume are too low because some of the large loops are not completed within the sample boundaries. For the Berea sample, this ‘shallow-sample depth’ is about 2·2 grain diameters (forty-five serial sections). Only data points at depths in excess of this value are used in determining the genus per unit volume. The slope of the genus versus volume curve is the better predictor of the genus per unit volume of the unbounded medium, of which the sample is a small part, than the value of genus/volume of the sample. For samples of finite cross-section, the G_min and G_max versus volume curves are divergent and they only become essentially parallel when the dimensions in the plane of sectioning are large multiples of the grain size. It is shown that it is reasonable to assume that the arithmetic mean slope found for a small cross-sectional area is a good estimate of the common slope that would be attained at high cross-sectional areas. Therefore, samples of small cross-section can be used, resulting in a reduction in the amount of data to be processed and an enhancement of the resolution of small features. The Berea sample data, beyond the ‘shallow-sample’ region, show the same qualitative features as predicted analytically for the cubic lattice. The ratio of the slopes of the G_max and G_min curves is 1·22 and the genus per unit volume from the mean slope is 52·6 × 10^?8 μm^?3.     

Optimising tolerance allocation for mechanical components correlated by selective assembly

Selective assembly can enlarge the tolerances of mechanical components for easier manufacturing. However, the non-independent dimensions of correlated components make it difficult to optimise tolerance allocation for an assembly. This paper proposes a solution for this constrained optimisation problem consisting of tolerances and non-independent dimensions as design variables. The approach is to develop a simplified algorithm applying a Lagrange multiplier method to evaluate the optimal tolerances efficiently. The solution is shown to be a global optimum at the given correlation coefficients. The correlation coefficients are key elements in determining the optimal solution, which is demonstrated in the given examples. The results are helpful in designing tolerances for selective assembly.Notation A _j coefficient matrix off _j - B _i coefficient of cost function - C total manufacturing cost function - C _i manufacturing cost function forx _i - F _j thejth dimensional constraint function - f _j thejth quadratic constraint function - f quadratic constraint vector - H _j thejth Hessian matrix - J _kj element ofn×m Jacobian matrix - L Lagrangian - m number of assembly dimensions - n number of component dimensions - p number of equality dimensional constraints - T tolerance vector of component dimensions [mm] or [°] - tolerance ofx _i [mm] or [°] - tolerance ofZ _j [mm] or [°] - x component dimension vector - x midpoint vector - x _i component dimension [mm] or [°] - x _i midpoint ofx _i [mm] or [°] - Z _j assembly dimension [mm] or [°] - _j confidence coefficient forZ _j - _i confidence coefficient forx _i> - _j given design value ofZ _j [mm] or [°] - Lagrange multiplier vector - _j thejth Lagrange multiplier - * Lagrange multiplier vector at the optimum solution - correlation coefficient forx _i andx _k - _x standard deviation vector - _x ^* standard deviation vector at the optimum solution - _x ⁰ candidate point satisfying the constraintsf( _x ^* )=0 - standard deviation ofx _i      

Trace analyses from LACBED patterns

Trace analysis is of major interest in transmission electron microscopy since the identification of the (h k l) indices of lattice planes or the [uvw] indices of lattice directions is required for the complete analysis of crystal defects (stacking faults, dislocations, etc). It is usually carried out from observations of micrographs and corresponding selected area electron diffraction patterns. The main difficulty comes from the rotation occurring between the image and the diffraction pattern. Therefore, the method requires a careful calibration of this rotation. The LACBED patterns have a unique property: they display information connected both with the direct and the reprocal lattices. The shadow image of the illuminated area of the specimen (direct lattice) is superimposed with the LACBED pattern composed of Bragg lines (reciprocal lattice). Since this shadow image is not rotated (or rotated by 180 degrees C) with respect to the diffraction pattern, LACBED patterns can be conveniently used to identify planes and directions. Several experimental methods are described. Most of them require observation of Bragg lines which are parallel or perpendicular to the trace of the analysed plane or direction.     

A method for determining void arrangements in inverse opals

The periodic arrangement of voids in ceramic materials templated by colloidal crystal arrays (inverse opals) has been analysed by transmission electron microscopy. Individual particles consisting of an approximately spherical array of at least 100 voids were tilted through 90° along a single axis within the transmission electron microscope. The bright‐field images of these particles at high‐symmetry points, their diffractograms calculated by fast Fourier transforms, and the transmission electron microscope goniometer angles were compared with model face‐centred cubic, body‐centred cubic, hexagonal close‐packed, and simple cubic lattices in real and reciprocal space. The spatial periodicities were calculated for two‐dimensional projections. The systematic absences in these diffractograms differed from those found in diffraction patterns from three‐dimensional objects. The experimental data matched only the model face‐centred cubic lattice, so it was concluded that the packing of the voids (and, thus, the polymer spheres that composed the original colloidal crystals) was face‐centred cubic. In face‐centred cubic structures, the stacking‐fault displacementvector is . No stacking faults were observed when viewingthe inverse opal structure along the orthogonal <110>‐type directions, eliminating the possibility of a random hexagonally close‐packed structure for the particles observed. This technique complements synchrotron X‐ray scattering work on colloidal crystals by allowing both real‐space and reciprocal‐space analysis to be carried out on a smaller cross‐sectional area.     

Radiation characteristics of getter materials in the region of a phase transformation

The results of studies of the radiation characteristics of samples of titanium and alloys thereof in the region of their polymorphous transformation and the temperature dependence of the emissivity in the β phase are presented. The calorimetric method of electron heating in high vacuum was used. It is shown that changes in the integral hemispherical emissivity ɛ _th for titanium iodide and industrial-grade titanium related to the transformation of a hexagonal close-packed lattice into a body-centered cubic lattice have different characters. Original Russian Text ? B.A. Shur, V.E. Peletskii, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 1, pp. 162–167.     

Interlaminar stresses of a rectangular laminated plate with simply supported edges subject to free vibration

The interlaminar stresses in a laminated rectangular orthotropic plate with four sides simply supported edges during free vibration was determined by using the integration method involving the dynamic inertia terms and displacements. The approximate stresses solutions are obtained under the effect of frequencies of vibration for four-layer symmetric cross-ply laminates with the ply configurations [0°/90°]_s and [90°/0°]_s, angle-ply laminates with the ply configuration [45°/−45°]_s. Numerical results show that the natural frequency has significant effects on the dominant interlaminar stresses in the stacking sequences [0°/90°]_s, [90°/0°]_s and [45°/−45°]_s.     

Towards automated diffraction tomography: part I--data acquisition

The ultimate aim of electron diffraction data collection for structure analysis is to sample the reciprocal space as accurately as possible to obtain a high-quality data set for crystal structure determination. Besides a more precise lattice parameter determination, fine sampling is expected to deliver superior data on reflection intensities, which is crucial for subsequent structure analysis. Traditionally, three-dimensional (3D) diffraction data are collected by manually tilting a crystal around a selected crystallographic axis and recording a set of diffraction patterns (a tilt series) at various crystallographic zones. In a second step, diffraction data from these zones are combined into a 3D data set and analyzed to yield the desired structure information. Data collection can also be performed automatically, with the recent advances in tomography acquisition providing a suitable basis. An experimental software module has been developed for the Tecnai microscope for such an automated diffraction pattern collection while tilting around the goniometer axis. The module combines STEM imaging with diffraction pattern acquisition in nanodiffraction mode. It allows automated recording of diffraction tilt series from nanoparticles with a size down to 5nm.     

On the calculation of the phase shift of superconducting fluxons: from the isolated to the lattice case

The numerical problems associated to the calculation of the phase shift due to a flux line lattice (FLL) in a thin superconducting specimen are presented and discussed. In order to be able to adequately treat the periodic case, the Fourier transform of the phase shift due to a flux tube is needed. This result is obtained by means of a new approach, where the phase shift is calculated from the beginning in the reciprocal space, treating separately each Fourier coefficient of the magnetic vector potential. The equivalence with the old approach is demonstrated and the utility of the new formulation for calculating the phase shift of closely packed FLL shown.     

Lattice parameters from direct-space images at two tilts

Lattices in three dimensions are oft studied from the "reciprocal space" perspective of diffraction. Today, the full lattice of a crystal can often be inferred from direct-space information about three sets of non-parallel lattice planes. Such data can come from electron-phase (or less easily Z contrast images) taken at two tilts, provided that one image shows two non-parallel lattice periodicities, and the other shows a periodicity not coplanar with the first two. We outline here protocols for measuring the 3D parameters of cubic lattice types in this way. For randomly oriented nano-crystals with cell side greater than twice the continuous transfer limit, orthogonal +/-15 degrees and +/-10 degrees tilt ranges might allow one to measure 3D parameters of all such lattice types in a specimen from only two well-chosen images. The strategy is illustrated by measuring the lattice parameters of a 10nm WC(1-x) crystal in a plasma-enhanced chemical-vapor deposited thin film.     

Interfacial heat transfer coefficient between metal and die during high pressure die casting process of aluminum alloy

The present work focused on the determination of the interfacial heat transfer coefficient (IHTC) between metal and die during the high pressure die casting (HPDC) process. Experiments were carried out on an aluminum alloy, ADC12Z, using “step shape” casting—so-called because of its shape. The IHTC was successfully determined by solving one of the inverse heat problems using the nonlinear estimation method first used by Beck. The calculation results indicated that the IHTC immediately increased after liquid metal was brought into the cavity by the plunger and decreased as the solidification process of the liquid metal proceeded. The liquid metal eventually solidified completely, a condition when the IHTC tended to be stable. Casting thickness played an important role in affecting the IHTC between the metal and die not only in terms of its value but also in terms of its change tendency. Also, under the test conditions, different change tendencies of the metal solid fraction were found between castings with different thicknesses and the die. __________ Translated from Acta Metallurgica Sinica, 2007, 43(1): 103–106 [ 译自: 金属学报]     

Signal to noise enhancement in dark field electron micrographs of vasopressin: filtering of arrays of images in reciprocal space

A technique for filtering arrays of images of dispersed molecules is presented which takes advantage of the crystallographic properties of regular arrays and the rapidity of optical treatment. A filter in reciprocal space consisting of perforations in a square or rectangular lattice, as determined by the image arrangement, reduces noise and averages the images simultaneously by transmitting only regularly recurring image structure. The filter is universal for all image contents and introduces no additional biases. The signal to noise improvement approaches √N for N independent images of the same molecule in the same configuration. The procedure, which is simple, rapid and inexpensive, is demonstrated with the aid of dark field electron micrographs of the protein vasopressin and combined with iodination of that molecule to elucidate its structure.     

A finite element analysis of rigid-plastic deformation of the flange in a deep-drawing process based on a fourth-degree yield function

A general formulation for finite element analyses of very large rigid-plastic deformation is given by introducing a local system of convected co-ordinates into each element and taking the rotation of the principal axes of orthotropy of the material into consideration with respect to the two cases: (1) the case where the equivalent strain-rate is given by a function of strain-rate components and (2) the case where is defined by the formula , where σ_ij are stress components and gs is the equivalent stress. example, large deformation of the flange region in a deep-drawing process of a circular orthotropic metal sheet is analyzed on the basis of the conventional quadratic yield function and a fourth-degree one. The result shows that the effect of the axis rotation suppresses the ear-development to a certain extent, that any explicit expression of in terms of is not necessarily required for calculation and the definition suffices for the purpose, that the fourth-degree yield function gives us the shape of the deformed flange in good agreement with the experiment in contrast with the quadratic one which gives a too excessive ear-development, and so forth.     

Resonance Rayleigh Scattering of K2Zn3[Fe(CN)6]2 Nanoparticles and its Application for the Determination of Vitamin C

Abstract

In Britton-Robinson buffer medium, (pH 4.43), potassium ferricyanide (K₃[Fe(CN)₆]) could react with vitamin C (VC) to produce potassium ferrocyanide (K₄[Fe(CN)₆]), which further reacted with Zn²⁺ to form potassium zinc hexacyanoferate K₂Zn₃[Fe(CN)₆]₂ nanoparticles. The shapes and diameters of the K₂Zn₃[Fe(CN)₆]₂ nanoparticles have been observed with transmission electron microscopy, which showed the shapes of these nanoparticles was cubic and their average sizes were about 50 nm in the presence of 2.0 × 10^?5 mol L^?1 VC. The characteristics of resonance Rayleigh scattering (RRS) spectra of this reaction have been studied. The optimum reaction condition for the determination of VC has been investigated. It was found that the RRS intensity of the system at the RRS peak of 363.4 nm was proportional to the VC concentration in the range of 4.0?80.0 µmol L^?1, and the detection limit (3σ) for VC was 0.075 µmol L^?1. A novel and simple RRS method for the determination of VC based on the formation of K₂Zn₃[Fe(CN)₆]₂ nanoparticles has been established.     

Some single zone scavenging models for two-stroke engines

The paper proposes a simplified version of the various multi-zone models which have been proposed for diesel engines to represent the pure air, mixing and residual zones of the real process, with or without short circuiting. [Benson, Int. J. Mech. Sci.19, (1977); Baudequin and Rochelle, Proc. Instn Mech. Engrs.194, (1980); Chen and Wallace, SAE paper 871657 (1987).]These models use flow coefficients defining the division of the air-flow entering, and of the outflow leaving, the cylinder between the various zones. The choice of these coefficients is rendered more difficult by the absence of direct experimental evidence.The present model in which the cylinder contents are represented by a single zone uses two coefficients which directly define the nature of the scavenging process.

1. (a) The fraction x of the initial cylinder contents subject to displacement scavenging during phase 1, and

2. (b) the short circuiting fraction y of the entering air during the mixing dominated phase 2.

Single zone representation of the cylinder contents is made possible by the use of a residual filter during phase 1 and an air filter during phase 2, the former allowing pure residuals, and the latter pure air, to be exhausted while the cylinder gases are undergoing a pure mixing process.The model is applied to typical scavenging situations for uniflow, cross flow and loop scavenged diesel engines, both for the idealized isobaric, isochoric case and for the ‘real’ engine using a full cycle simulation program.     

An electron diffraction study of paramylon storage granules from Euglena gracilis

Paramylon storage granules from Euglena gracilis were characterized by electron diffraction techniques using electrons of various accelerating voltages: 2 MV for the thick granules and 100 kV for the thinner ones. Intact granules gave well resolved, characteristic (1→3)-β-d glucan fibre diffraction diagrams with the glucan molecular orientation parallel to the longer axis of the granule. Hydrated electron diffraction patterns with better resolution were obtained from thinner granules by examination at low temperatures of quench-frozen specimens. In this case, the pattern indexed on an hexagonal system with a = b= 1·55 + 0·01 nm and c (fibre axis) = 1·86 ± 0·01 nm. Sections of embedded granules provided single crystal-like electron diffraction patterns corresponding to various sections of the reciprocal lattice of (1→3)-β-d glucan (including the hko section). Finally, by scanning electron microscopy, it was shown that the granules swell on contact with water and take up a characteristic ribbed, pumpkin-like shape.     

Structural analyses of Nd-doped CeO2 thin films deposited by pulsed laser deposition

CeO₂ thin films doped with neodymium oxides for application to gas sensors have been elaborated by the pulsed laser deposition technique. The films were deposited on orientated Si (100) substrates with variable deposition times (t = 90, 180 and 360 s) and molar fractions of Nd₂O₃ (0, 6.5, 15, 21.5 and 27 at.%). The resulting Nd–CeO₂ thin films were characterized by means of X‐ray diffraction analysis, scanning electron microscopy and transmission electron microscopy equipped with EDS (Energy Dispersive Spectrometer) microanalysis. From X‐ray diffraction analyses, it is clearly established that the texture is modified by Nd additions. The preferred (111) orientations of the CeO₂ crystals change into the (200) orientation. The morphology of the CeO₂ grains changes from triangles, for pure CeO₂ thin films, to spherical grains for Nd‐doped films. In addition, cell parameter analyses from X‐ray diffraction data show that a partial chemical substitution of Ce by Nd should occur in the face‐centred cubic lattice of ceria: this should give rise to Ce_1‐xNd_xO_2?z phases with oxygen non‐stoichiometry.     

Lubricant thickness effects on friction between Pd(100) surfaces

Friction measurements have been made between pairs of Pd(100) surfaces prepared in vacuum with adsorbed n-octane films ranging in thickness from 0 to 20 monolayers on each surface. These measurements have been made at lattice misorientation angles of 0° and 45°. Both sets of measurements reveal friction anisotropy at all except the highest n-octane coverages. The friction coefficient drops with increasing n-octane coverage until it reaches a limiting value of _s 0.4. The static friction coefficient reveals a different dependence on n-octane coverage than has been observed for alcohols. The friction coefficient decreases more slowly with increasing n-octane coverage than for increasing alcohol coverage.