bluuebunny/crossref_metadata_2025 huggingface dataset:
The microstructure of experimental SiC fibre‐reinforced yttrium magnesium aluminosilicate (SiCf‐YMAS) materials
Authors: VICENS J. , DOREAU F. , CHERMANT J. L.
Published: August 2011

Two experimental SiC fibre‐reinforced yttrium magnesium aluminosilicate (SiCf‐YMAS)‐type ceramic‐matrix composite (CMC) materials fabricated (i) by the glass process and (ii) by chemical precursor infiltration have been studied by light microscopy, transmission electron microscopy (TEM), high‐resolution electron microscopy (HREM) and energy‐dispersive X‐ray spectroscopy (EDS). The distribution of the fibres inside the composite as well as the average diameter of fibres have been determined by image analysis. The microstructure of the YMAS matrices has been characterized by TEM observations. YMAS matrices are formed of two main phases, cordierite and β‐yttrium silicate (Y2Si2O7). Two minor phases (mullite and spinel) have been found to crystallize inside the cordierite and the yttrium silicate crystals. Fibre‐matrix interfaces have been observed in HREM. A thin turbostratic carbon layer (20–30 nm) has been imaged in both composites at the fibre‐matrix interface. It crystallizes along the matrix interface and grows inside the fibre, forming a diffuse interphase. The carbon layer is believed to be the consequence of reaction between oxygen in the matrix and SiC nanocrystals of the Nicalon fibres.
Nanostructure of interlayers in different Nicalon fibre/glass matrix composites and their effect on mechanical properties
Authors: HÄHNEL A. , PIPPEL E. , WOLTERSDORF J.
Published: August 2011

Interlayer phenomena, revealed by high‐voltage electron microscopy (HVEM) and high‐resolution electron microscopy (HREM), are presented as they occur in various SiC(Nicalon) fibre‐reinforced Duran glass composites (differing in the specific sol‐gel supported production processes). Their dependence on the production parameters and their influence on the materials properties are discussed, taking into account the results of scanning electron microscope (SEM) in situ tensile tests.

Besides graphitic carbon, textured to a variable degree and influencing the tensile behaviour, oxycarbide formation is indicated.

A reactive matrix additive, such as, e.g. TiO2, resulted in a decrease in strength and a brittle behaviour, while the addition of ZrO2 markedly improves the mechanical properties.
Surface characteristics of Zirfon® composite ultrafiltration membranes
Authors: KUYPERS S. , GENNÉ I. , LEYSEN R.
Published: August 2011

This paper presents the first high‐resolution field emission scanning electron micrographs of the skin layers of a series of Zirfon® ultrafiltration membranes. The flux through these polymer‐based composite membranes is known to be proportional to the inorganic‐filler content. Image analysis of skin surface micrographs revealed the skin surface pore characteristics to be almost unchanged over a wide range of compositions. The inorganic filler was found to be present in the skin layer, where it modifies the polymer network and locally reduces the skin thickness. This latter effect might be able to account for the observed flux behaviour.
Microstructural investigation of colloidal silver embedded in glass
Authors: HOFMEISTER H. , DUBIEL M. , GOJ H. , THIEL S.
Published: August 2011

Nanoparticulate composites consisting of very small silver particles embedded in near‐surface regions of glass were obtained by sodium–silver ion exchange. Colloidal silver is formed by reduction of silver ions and aggregation of silver atoms in the glass matrix at elevated temperatures. Owing to absorption bands in the visible region, the silver particles cause a coloration of the glass that depends on their size and depth distribution. From high‐resolution electron microscopy imaging of lattice plane fringes of the silver particles, size‐dependent lattice contractions are deduced that are larger than those reported in the literature for supported particles not interacting with a matrix. This effect is the more pronounced the higher the annealing temperature is during the particle formation. The increased lattice contraction is attributed to compressive stresses that arise during the ion exchange process as well as during cooling after annealing.
Microstructure and fracture behaviour of particle‐reinforced metal–matrix composites
Authors: DERBY B.
Published: August 2011

The fracture behaviour of particle‐reinforced metal‐matrix composites is shown to be controlled by a period of damage nucleation and evolution prior to final failure. The nucleation of damage can be by reinforcement fracture or decohesion and the mode of damage is shown to be controlled by the size of the reinforcement and segregation of alloying elements from the matrix. The nucleation and growth of damage can be monitored by a number of techniques. Acoustic emission and tomography are used here and the results are found to be consistent with simple models of void growth.
Microstructure of a spray‐formed Al/SiC composite
Authors: VERMAUT P. , RUTERANA P.
Published: August 2011

The microstructure of an Al–6Cu–2Mn–0·45 Mg–1(Ag, Ti, V, Zr, Cr) alloy, reinforced with 13 vol.% SiC particles, made by spray deposition has been investigated by transmission electron microscopy, high‐resolution electron microscopy and electron diffraction X‐ray spectroscopy. Particular attention was focused on the influence of the reinforcement on the precipitation sequence. Instead of the expected

precipitation sequence due to the high Cu/Mg ratio, there is an additional σ precipitate which was previously observed in A1 alloys containing silicon. This precipitate becomes predominant at the T6 temper. The new precipitation sequence for this reinforced alloy is therefore

The precipitation of σ phase is believed to be due to the presence of SiC particles, and seems to be correlated with the occurrence of large Mn‐rich particles. Although expected, no S phase precipitation is found to occur in the matrix grains. At the matrix grain boundaries, small Al2Cu (θ) and Al2CuMg (S), as well as Mn‐rich precipitates are found. At the SiC particle surfaces, preferentially orientated Ag‐rich and Mg‐rich intermetallic precipitates are found. They can coexist with amorphous patches containing oxygen enclosed in an irregularly shaped Al2Cu (θ) phase remaining from large crystalline areas which did not go into solution.
X‐ray microtomographic studies of metal matrix composites using laboratory X‐ray sources
Authors: MUMMERY P. M. , DERBY B. , ANDERSON P. , DAVIS G. R. , ELLIOTT J. C.
Published: August 2011

X‐ray microtomography (XMT) is a non‐destructive technique that allows the internal structure of a material to be imaged by the spatial distribution of its linear X‐ray absorption coefficients. This paper demonstrates the use of XMT to investigate: (1) the distribution of TiB2 reinforcement in composites formed by powder processing; (2) the local void volume fraction as a function of position in highly deformed regions of failed tensile specimens of SiC‐reinforced material allowing a valid damage parameter to be defined at high strains; (3) absorption coefficients measured at different energies simultaneously using a multichannel analyser which can sometimes be used to separate linear absorption changes due to (a) density variations and (b) compositional variations in individual voxels; and (4) the use of sequential sections to provide a three‐dimensional representation of the failed specimens.
The use of a single fibre test technique to investigate interfacial phenomena in SiC/Ti3Al‐based composites
Authors: BRISSET F. , VASSEL A.
Published: August 2011

A study of the chemical compatibility of a Ti3 Al‐based alloy (Ti–24Al–10Nb, at.%) with two silicon carbide continuous fibres (SCS‐6, SM 1240) has been conducted. Owing to the difficulty in processing intermetallic matrix composites, this type of material has been simulated in the present work by sputtering a thin titanium aluminide layer onto fibres and heat treating at temperatures representative of fabrication conditions. The degradation of the fibre strength due to its interaction with the matrix was correlated with analytical studies of the fibre/matrix interface using a combination of SEM, TEM, EELS and a submicrometre ion probe.
Atomic force microscopy under liquid: A comparative study of three different AC mode operations
Authors: WONG T. M. H. , DESCOUTS P.
Published: August 2011

The image contrast mechanism of three newly proposed AC mode operations under liquid in three different frequency ranges is presented. They all rely on a strong repulsive force to damp the cantilever and the tip still ‘touches’ the sample surface. A direct comparison of the three different modes of operation with the conventional DC mode technique using the same gold sample under isopropanol was conducted. It was found that all the three AC modes exerted a much smaller lateral force than the DC mode although the normal loads were of the same order of magnitude. The suitability of such techniques in imaging physisorbed systems on hard substrates (such as soft biological samples) and the prospect of a true non‐contact repulsive mode operation are discussed.
Monitoring cutting forces with an instrumented histological microtome
Authors: WILLIS A. , VINCENT J. F. V.
Published: August 2011

A modification to the knife mounting of a histological microtome is described which can sense the load on the knife when a section is being cut. The performance of this microtome is described in general terms. The variation in force on the knife can be used to give information about the texture of the sample being cut.
The biological reality of the interlacunar network in the embryonic, cartilaginous, skeleton: A thiazine dye/absolute ethanol/LR White resin protocol for visualizing the network with minimal tissue shrinkage
Authors: LAWTON D. M. , OSWALDs W. B. , MCCLURE J.
Published: August 2011

Third toe phalanges of chicks aged 8–13 days in ovo and 7‐day post‐natal rat femoral growth plate were examined to determine whether the interlacunar network (IN), a structure with no lipoprotein membrane component or cytoplasmic organelles, is a genuine component of young growth cartilage. In chick phalanges dehydrated by 70% (v/v) ethanol and LR White resin, variable metachromatic staining of the interlacunar network by toluidine blue and red staining by picro‐Sirius red indicate the presence of glycosaminoglycans and collagen. The network in phalanges dehydrated by 80% (v/v) ethanol appears little different; however, the network is much less widely detectable in phalanges dehydrated by 90% (v/v) ethanol and, after dehydration by absolute ethanol, is almost completely undetectable. In contrast, when the young cartilage is permeated by a thiazine dye such as toluidine blue, using a solution of dye in the aldehyde fixative, the network is widely detectable, following dehydration by absolute ethanol, both in chick phalanges and in rat growth plate. Comparison of projected areas shows that the extent to which whole chick feet are found to have shrunk, by the time that they are photographed under LR White resin, is determined principally by the extent of dehydration, by 70% (v/v) or absolute ethanol; post‐shrinkage areas are 33% or 35% of areas measured in buffer for 70% (v/v) ethanol/LR White resin and 71% or 75% for absolute ethanol/LR White resin (the higher value in each is for the toluidine blue treatment). The network is thus present in radically shrunk tissue, but, significantly, is also fully represented in tissue shrunk by only a conventional margin and is therefore not produced as an artefact by exceptional tissue shrinkage as has been suggested.
Mechanism of image formation for thick biological specimens: exit wavefront reconstruction and electron energy‐loss spectroscopic imaging
Authors: HAN K. F. , SEDAT J. W. , AGARD D. A.
Published: August 2011

With increasing frequency, cellular organelles and nuclear structures are being investigated at high resolution using electron microscopic tomography of thick sections (0·3–1·0 μm). In order to reconstruct the structures in three dimensions accurately from the observed image intensities, it is essential to understand the relationship between the image intensity and the specimen mass density. The imaging of thick specimens is complicated by the large fraction of multiple scattering which gives rise to incoherent and partially coherent image components. Here we investigate the mechanism of image formation for thick biological specimens at 200 and 300 keV in order to resolve the coherent scattering component from the incoherent (multiple scattering) components.

Two techniques were used: electron energy‐loss spectroscopic imaging (ESI) and exit wavefront reconstruction using a through‐focus series. Although it is commonly assumed that image formation of thick specimens is dominated by amplitude (absorption) contrast, we have found that for conventionally stained biological specimens phase contrast contributes significantly, and that at resolutions better than ∼10 nm, superposed phase contrast dominates. It is shown that the decrease in coherent scattering with specimen thickness is directly related to the increase in multiple scattering. It is further shown that exit wavefront reconstruction can exclude the microscope aberrations as well as the multiple scattering component from the image formation. Since most of the inelastic scattering with these thick specimens is actually multiple inelastic scattering, it is demonstrated that exit wavefront reconstruction can act as a partial energy filter. By virtue of excluding the multiple scattering, the ‘restored’ images display enhanced contrast and resolution.

These findings have direct implications for the three‐dimensional reconstruction of thick biological specimens, where a simple direct relationship between image intensity and mass density was assumed, and the aberrations were left uncorrected.
V(Z) curve formation of solid spherical microparticles in scanning acoustic microscopy
Authors: MASLOV K. I. , ZININ P. V. , LOBKIS O. I. , KUNDU T.
Published: August 2011

Information about the properties of materials in acoustic microscopy can be obtained in the form of the V(Z) curves. The purpose of this paper is to present the theoretical and experimental study of the V(Z) curve formation for solid spheres. It is shown that an investigation of the position of different peaks in the V(Z) curves is useful to determine the size and acoustical properties of a spherical particle.
An ion microprobe study of the microchemistry of Ni‐base superalloy‐Al2O3 metal‐matrix composites
Authors: SONI K. K. , TSENG M. W. , WILLIAMS D. B. , CHABALA J. M. , LI JIANWEI , LEVI‐SETTI R. , BAMPTON C. C.
Published: August 2011

The chemical microstructure of Ni‐base superalloy/Al2O3 metal‐matrix composites (MMCs) has been studied by scanning ion microprobe microanalysis, using the secondary ion mass spectrometry (SIMS) technique. The MMCs were fabricated using the transient‐liquid‐phase bonding (TLP) process, with B‐doped superalloy powder as an interlayer. Boron was found to diffuse rapidly throughout the matrix to form boride phases, mostly at the grain boundaries in the matrix. These borides contain excess Cr (also Mo, Si, W) in comparison with the Ni alloy‐matrix, but are depleted in Ni (also in Al and Co). Carbides form at the grain boundaries as thin platelets and inside the grains as fine particles. Chemical reaction occurs between the sapphire fibre and the matrix; formation of NiAl2O4 spinel at the interface is suggested. This interface reaction layer is friable and parts of it peel off during consolidation to become inclusions in the matrix near the fibre/matrix interface.
Estimation of individual feature surface area with the vertical spatial grid
Authors: CRUZ‐ORIVE L. M. , HOWARD C. V.
Published: August 2011

The area of an individual bounded surface (e.g. the boundary of a properly sampled cell) can be estimated from an isotropic uniform random stack of parallel sections, or of non‐invasive planar scans, using the well‐known spatial grid. A standing problem was to estimate the area of an individual bounded surface with an arbitrary degree of accuracy from a vertical (i.e. not isotropic) stack of sections or scans. A new tool to do this, called the ‘vertical spatial grid’, is presented.
Computer‐assisted method for simultaneous three‐dimensional reconstruction of highly magnified nerve endings and low‐magnification contours of the spinal cord
Authors: LISS A. G.
Published: August 2011

Three‐dimensional reconstructions of biological structures can be obtained by the use of serial sections, tomography, confocal microscopy techniques and X‐ray crystallography. The earliest reconstructions were achieved manually, but semi‐automatic and automatic techniques are now available. Tissue studied by microscopy contains structures of greatly varying dimensions. When producing a three‐dimensional reconstruction of the contours of the spinal cord and its white and grey matter, greater magnification of the fine nerve endings may provide additional information. However, reconstruction at different magnifications of the structures of interest cannot be achieved automatically, but requires manual delineation of the structures. A method is described in which a commercial program was used to provide a wire‐frame reconstruction which had been drawn by hand. The data were processed further to obtain a realistic image which could be rotated to provide details of the three‐dimensional relationships of the spinal cord structures. This technique is useful when relationships and details are otherwise difficult to comprehend due to large size differences.
A system for aligning video‐recorded visual data and high‐quality multichannel recordings of simultaneously occurring signals
Authors: LUMSDON T. , DICKSON M. , GLADDEN M. H.
Published: August 2011

An electronic circuit is described which provides a unique number for each video frame, and which is superimposed on the frame as a 4‐digit light‐emitting diode display using a second camera and videomixer. The number is also encoded as a simple voltage waveform which is recorded separately together with electrical signals giving information about events related to, and coincident with, the visual data, for example nerve spike trains. Sophisticated computer analysis of signals can thus be related accurately to microscopical visual information processed by video analysis.
A low‐cost digitized microscope stage for linear measurements
Authors: ROHITHA B. H.
Published: August 2011

A low‐cost device for making fine, but repetitive linear measurements under the binocular microscope is described. Linear displacement is coupled on to digital callipers which read the measurements in numerical values. The accuracy of the measurements was such that their 95% confidence interval was within 0·01 mm when read through the apparatus. The data were assimilated on a computer and then transmitted into a PC for analysis.
The secondary fluorescence correction for X‐ray microanalysis in the analytical electron microscope
Authors: ANDERSON I. M. , BENTLEY J. , CARTER C. B.
Published: August 2011

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, IYX, is expressed relative to the primary intensity of the fluorescing element, IY, rather than to that of the fluoresced element, IX, as has been customary for microanalysis. The importance of this choice of IY 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.
Image contrast of dielectric specimens in transmission mode near‐field scanning optical microscopy: imaging properties and tip artefacts
Authors: VALASKOVIC G. A. , HOLTON M. , MORRISON G. H.
Published: August 2011

Near‐field scanning optical microscopy (NSOM) is a scanned probe technique utilizing a subwavelength‐sized light source for high‐resolution imaging of surfaces. Although NSOM has the potential to exploit and extend the experimental utility of the modern light microscope, the interpretation of image contrast is not straightforward. In near‐field microscopy the illumination intensity of the source (probe) is not a constant value, rather it is a function of the probe–sample electronic environment. A number of dielectric specimens have been studied by NSOM to elucidate the contrast role of specimen type, topography and crystallinity; a summary of metallic specimen observations is presented for comparative purposes. Near‐field image contrast is found to be a result of lateral changes in optical density and edge scattering for specimens with little sample topography. For surfaces with considerable topography the contributions of topographic (Z) axis contrast to lateral (X,Y) changes in optical density have been characterized. Selected near‐field probes have also been shown to exhibit a variety of unusual contrast artefacts. Thorough study of polarization contrast, optical edge (scattering) contrast, as well as molecular orientation in crystalline specimens, can be used to distinguish lateral contrast from topographic components. In a few cases Fourier filtering can be successfully applied to separate the topographic and lateral contrast components.
Viability assessment of bacteria in mixed populations using flow cytometry*
Authors: CARON G. NEBE‐VON , BADLEY R. A.
Published: August 2011

In microbiology cells are called viable when they can be shown to proliferate. Due to long lag phases and the cells' sensitivity to the conditions around them, this definition presents problems when investigating stressed or injured cells. Colony counts only show reproduction, whilst direct single‐cell investigation can divide the status of cells into four stages: (i) reproductive viable cells, (ii) vital cells, (iii) intact cells and (iv) dead cells.

Multicolour staining flow cytometry has been found to provide a powerful method for investigating these various states of viability. This is illustrated with examples with some emphasis on mixed bacterial populations.
Imaging small spinel particles in an NiO matrix
Authors: RASMUSSEN D. R. , SUMMERFELT S. R. , MCKERNAN S. , CARTER C. B.
Published: August 2011

The possibility of imaging NiFe2O4 spinel particles, with a dimension of only 1–3 nm, which are embedded in an NiO matrix has been examined. Computer image simulation studies based on the multislice method and complete, atomistic models of the particle–matrix structure have been performed. The effects of double diffraction in this geometry have been investigated, and the visibility of the particles determined for four different imaging modes: centred darkfield (CDF) imaging, high‐resolution structure imaging, ‘brightfield lattice (BFL) imaging’, and ‘darkfield lattice (DFL) imaging’. It is found that, if two complementary DFL images are obtained, the smallest particle will be detectable irrespective of its position within the foil. In the presence of an amorphous layer on the sample, however, the images at certain foil thicknesses may have insufficient contrast to be detectable above the background noise.
Past, present and future of electron holography
Authors: TONOMURA A.
Published: August 2011

Electron holography, originally devised for improving the resolution of electron microscopes, progressed significantly with the advent of the ‘coherent’ field‐emission electron beam. This permitted high‐resolution microscopy (Lichte, 1986), and opened up such new fields as high‐precision electron interferomentry. This paper briefly describes the developments in electron holography.
New parameters in iron‐free magnetic lens aberrations
Authors: ALAMIR A. S.
Published: August 2011

Current density and accelerating voltage are introduced as new parameters in the calculation of iron‐free lens aberrations. The results are presented in a manner particularly suited for the design of high‐performance magnetic lenses.
Studies on condenser‐objective lenses
Authors: ALAMIR A. S. A.
Published: August 2011

Scaling down the dimensions of a conventional magnetic objective lens to reduce aberrations is studied in detail. The values of other aberration coefficients for optimum lens size corresponding to desired minimum aberration are estimated. The possibility of using iron‐free condenser–objective lenses at high voltage is examined.
High‐order and multipole aberrations by aberration integral and direct ray‐tracing methods
Authors: MUNRO E. , ZHU X. , ROUSE J.
Published: August 2011

This paper describes methods for computing high‐order aberrations and multipole aberrations in electron optical systems. Two approaches are discussed – the first involves obtaining aberration integrals for the high‐order aberration coefficients, in terms of paraxial rays and axial field functions, while the second method uses direct ray‐tracing through fields computed accurately by finite element or finite difference methods. The methods are illustrated by several examples, including a wide‐angle focusing and deflection system with fifth‐order aberrations, a combined magnetic and electrostatic lens, a ‘supertip’ ion source, an electron mirror with negative spherical and chromatic aberration, and a chromatically corrected quadrupole lens.
Observation of lens aberrations for very high‐resolution electron microscopy. I. Theory
Authors: SAXTON W. O.
Published: August 2011

Least‐squares fitting methods are described, currently the most accurate known, for determining the imaging aberrations and other important parameters. The data required are either the image displacement or the image diffractogram shape (or both), as a function of injected beam tilt; the analysis is largely common to the two cases. Explicit solutions are given for some simple cases (e.g. coma‐free alignment on the basis of three images only) and some promising developments are considered; the relevant aberration theory is set out in detail. Experimental work reported in a companion paper has confirmed the presence of threefold astigmatism at significant levels, but has not shown any evidence of other higher order aberrations.
HREM structure characterization of interfaces in semiconducting multi‐layers using molecular‐dynamics‐supported image interpretation
Authors: SCHEERSCHMIDT K. , RUVIMOV S. , WERNER P. , HÖPNER A. , HEYDENREICH J.
Published: August 2011

Multi‐layer structures in binary systems, for example InAs/AlSb and AlSb/GaSb, as well as ternary InGaAs/AlGaAs quantum wells grown by molecular beam epitaxy (MBE) are investigated by high‐resolution electron miscroscopy (HREM). Interpretation of the micrographs requires methods of image analysis and the computer simulation of the HREM contrast. The relaxed atomic structure of the interfaces is modelled by molecular dynamics (MD) and energy minimization. The importance of strain relaxations to the image interpretation will be demonstrated and compared with the image spread and shift caused by the microscope aberrations. The possibility of revealing the compositional variations and the elastic deformations at the interfaces by HREM imaging under special defocus and sample thickness conditions will be discussed.
On the extinction coefficient in confocal polarization microscopy
Authors: WILSON T. , JUŠKAITIS R.
Published: August 2011

The extinction coefficient in conventional polarized light microscopes is non‐zero, even with perfect polars, solely because of the image formation process in these instruments. The imaging in confocal microscopes is different from conventional instruments and it is shown that in this case an infinite extinction coefficient results in the ideal case whereas a finite value is always to be expected with conventional instruments. Images of the same microelectronic specimen taken in both conventional and confocal polarized light microscopes are compared.
A simple and effective method for reducing wool for electron microscopy
Authors: GARLICK R. A. , ALLEN D. E.
Published: August 2011

A simple, yet effective, method for preparing wool for ultrastructural studies is described. Usually such procedures incorporate a reduction step to convert the disulphide bonds of keratin to thiol groups, which enhances subsequent staining. This reduction process generally involves exposing the wool fibres to severe chemical treatments, which may modify their ultrastructure. Additionally, many of the reagents employed are highly toxic and unpleasant to use. A method of reduction is reported that provides images of ultrastructure at least comparable to previous methods whilst exposing the wool fibres to much milder conditions. Tris(2‐carboxyethyl)phosphine has been used to reduce both bulk samples and ultrathin sections of wool, prior to staining with silver methenamine.
Improved staining procedures for photographic documentation of phenolic deposits in semithin sections of plant tissue
Authors: GUTMANN M.
Published: August 2011

Several modifications of the toluidine blue O and safranin O staining procedures and a differential staining method with safranin O/azure II are described. These modifications include prestaining oxidation with sodium hypochlorite and/or poststaining treatment with iodine/potassium iodide. Greatly enhanced contrast of phenolic vacuolar inclusions is achieved by prestaining oxidation. Additionally, poststaining treatment with iodine results in a characteristic colour change of all stained tissue constituents except phenolic vacuolar inclusions. In particular, cellulose walls and cytoplasm exhibit a marked shift in colour from violet to brown (toluidine blue O) or from red to orange (safranin O). It is concluded that the methods presented can be recommended for superior photographic documentation of vacuolar polyphenol deposition in semithin sections of glycol‐methacrylate‐embedded plant tissue.
A non‐invasive photographic modification for recording early vascular development in the chick
Authors: GILES J. J. , KAVANAGH H. J. , BANNIGAN J. G.
Published: August 2011

The chick embryo shell‐less culture technique allows continuous observation and access to the developing vessels of the area vasculosa (AV): hence, its value as an angiogenesis assay system. The main drawback of the method is that adequately contrasted photographs cannot be achieved without injection of a contrast medium which kills the embryo making further observation of the same specimen impossible. Furthermore, injection prior to 72 h incubation has a high failure rate. In an attempt to overcome these problems, we explored the possibility of using a high‐contrast photographic process. Embryos were explanted into shell‐less culture after 48 h incubation and photographed through a stereo microscope. After trials with different films we found that Kodalith ortho Type 3 (Kodak) and Technical Pan film (Kodak) produced images of the vasculature which were identical in contrast and detail to India‐ink‐injected specimens photographed with conventional film. In addition, excellent images could be recorded as early as 48 h of incubation.
In situ formation of composite microstructures
Authors: HANDWERKER C. A. , WALLACE J. S. , FOECKE T. J. , KATTNER U. R. , BLENDELL J. E.
Published: August 2011

Microstructural evolution in two in situ reinforced composite systems, one produced by partial reduction and the other by grain growth, has been examined over a range of size scales using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Metal‐ceramic matrix composites were formed by the partial reduction of Al2O3–Cr2O3 solid solutions to form Cr metal particles in an Al2O3–Cr2O3 matrix which had a lower Cr2O3 concentration. In a second system, grain growth of Si3N4 during liquid phase sintering produced large, whisker‐like grains in a fine‐grained Si3N4 matrix, bonded by an oxynitride phase. The mechanisms controlling microstructural evolution in these two systems were examined.
Surface rendering in electron tomography: A heuristic approach
Authors: TOSONI L. , LANZAVECCHIA S. , BELLON P. L.
Published: August 2011

The final result of an electron tomographic reconstruction, computed from several projections, is a 3‐D array of data which resides in the computer memory as a long string (from 323 to 2563) of numbers. It is vital to retrieve information relevant to biology from this vast amount of numbers, and to share it with the scientific community. This is done with the use of visualization processes that may represent the most time consuming task in a reconstruction. The present article describes a technique of surface rendering designed by the authors to represent structures characterized by the presence of a number of subunits and of features such as branching, holes and cavities. The software used produces a ‘structure’ (an array containing different types of variables, peculiar to the C programming language) that is able to exploit the resources of the graphic engines embedded in modern workstations and of graphic libraries. This structure can be used to produce visual presentations in the form of wireframe‐ and surface‐rendered models with shading determined by the Gouraud algorithm.
Atomic contrast transfer in annular darkfield images
Authors: TREACY M. M. J. , GIBSON J. M.
Published: August 2011

We examine some of the assumptions underlying the standard optical equation as used for modelling high‐resolution annular darkfield (Z‐contrast) images of thin specimens. The validity of the approximations (i) that scattering occurs as spherical waves (atoms are point potentials) and (ii) that the depth of focus is infinite is found to be resolution‐dependent.

The correction to the optical equation for non‐spherical wave scattering is found to be important when the probe size is of the order of 0·1 nm or smaller, and does not vanish in the ideal case of a large annular detector with no hole. Depth of focus becomes an important consideration at 100 kV for probes smaller than about 0·2 nm when the specimen thickness exceeds 10 nm. Both corrections can significantly degrade the effective point‐to‐point resolution of high‐resolution Z‐contrast images relative to that predicted by the standard optical equation.
Use of post mortem and in vitro tissue specimens for X‐ray microanalysis
Authors: HONGPAISAN J. , ROOMANS G. M.
Published: August 2011

Post mortem changes in the distribution of elements, as well as changes induced by dissection and incubation of tissue slices, were investigated by X‐ray microanalysis of brain tissue, liver, pancreas and submandibular gland. Dissection itself causes minor changes in the intracellular ionic concentrations, but even a brief exposure of dissected tissue slices to a physiological buffer causes an increase in intracellular Na and Cl and a decrease in intracellular K concentration. The effect is most marked in brain tissue and least marked in submandibular gland slices. Incubation in fluid resembling the extracellular compartment in its ion composition results in a further increase of Na and Cl in brain tissue (cortex and hippocampus) and liver; in pancreas and submandibular gland, on the other hand, a stable situation throughout 2h of incubation can be obtained. Incubation at lower temperature, and exchanging NaCl in the incubation medium for Na gluconate, has only relatively minor effects on the intracellular K/Na ratio. Exchanging the NaCl for K gluconate results in a high intracellular K/Na ratio throughout the incubation, but morphological evidence of tissue oedema was nevertheless observed. Physiological changes in intracellular ion content induced by cholinergic stimulation are similar in in vitro preparations as compared with stimulation in situ. The effect of dissection and brief incubation on the ionic composition of brain tissue is less pronounced 6h after death than in a living, anaesthetized animal, but this is largely due to the post mortem changes that already have taken place.
Quantitative imaging of green fluorescent protein in cultured cells: Comparison of microscopic techniques, use in fusion proteins and detection limits
Authors: NISWENDER K. D. , BLACKMAN S. M. , ROHDE L. , MAGNUSON M. A. , PISTON D. W.
Published: August 2011

To determine the application limits of green fluorescent protein (GFP) as a reporter gene or protein tag, we expressed GFP by itself and with fusion protein partners, and used three different imaging methods to identify GFP fluorescence. In conventional epifluorescence photomicroscopy, GFP expressed in cells could be distinguished as a bright green signal over a yellow‐green autofluorescence background. In quantitative fluorescence microscopy, however, the GFP signal is contaminated by cellular autofluorescence. Improved separation of GFP signal from HeLa cell autofluorescence was achieved by the combination of confocal scanning laser microscopy using 488‐nm excitation, a rapid cut‐on dichroic mirror and a narrow‐bandpass emission filter. Two‐photon excitation of GFP fluorescence at the equivalent of ≅ 390 nm provided better absorption than did 488‐nm excitation. This resulted in increased signal/background but also generated a different autofluorescence pattern and appeared to increase GFP photobleaching. Fluorescence spectra similar to those of GFP alone were observed when GFP was expressed as a fusion protein either with glutathione‐S‐transferase (GST) or with glucokinase. Furthermore, purified GST•GFP fusion protein displayed an extinction coefficient and quantum yield consistent with values previously reported for GFP alone. In HeLa cells, the cytoplasmic GFP concentration must be greater than ≅ 1 μM to allow quantifiable discrimination over autofluorescence. However, lower expression levels may be detectable if GFP is targeted to discrete subcellular compartments, such as the plasma membrane, organelles or nucleus.
New polarized light microscope with precision universal compensator
Authors: OLDENBOURG R. , MEI G.
Published: August 2011

A new type of polarized light microscope (‘new pol‐scope’) for fast and orientation‐independent measurement of birefringent fine structure has been developed. The design of the new pol‐scope incorporates a precision universal compensator made from two liquid crystal variable retarders. A video camera and digital image processing system provide fast measurements of specimen anisotropy (retardance magnitude and azimuth) at all points of the image forming the field of view. The images document fine structural and molecular organization within a thin optical section of the specimen. The sensitivity of the current instrument is 0·1 nm of specimen retardance, measured with data gathered in 0·43 s at all 640 × 480 image points. Examples of birefringence measurements in biological (microtubule arrays) and industrial (magneto‐optical disc substrate) specimens are presented.
Polarization contrast in photon scanning tunnelling microscopy combined with atomic force microscopy
Authors: PROPSTRA K. , VAN HULST N. F.
Published: August 2011

Photon scanning tunnelling microscopy combined with atomic force microscopy allows simultaneous acquisition and direct comparison of optical and topographical images, both with a lateral resolution of about 30 nm, far beyond the optical diffraction limit. The probe consists of a modified microfabricated silicon nitride tip mounted on a cantilever, commercially available for atomic force microscopy. The lateral resolution is further improved using ‘supertips’, by depositing a small needle on the silicon nitride tip. The combined microscopic technique is applied to thin films of indium tin oxide because of the small grain size and high surface flatness, providing high‐resolution optical contrast and limited far‐field scattering contribution. Polarization contrast is shown in experiments both changing the polarization of the incident and detected light. Approach curves, both measuring the optical signal and force interaction, show a difference in the optical coupling between p‐ and s‐polarized incident light. p‐Polarized light always provides optical contrast more correlated to topography than s‐polarized light, both for incident and detected light, in agreement with theoretical models.
Volume fraction measurement of dispersoids in a thin foil by parallel energy‐loss spectroscopy: development and assessment of the technique
Authors: BOTTON G. A. , L'ESPÉRANCE G. , GALLERNEAULT C. E. , BALL M. D.
Published: August 2011

A method to determine the volume fraction of a dispersoid phase based on measurements carried out on thin foils is presented. The method involves the reconstruction of the shape and volume, by electron energy‐loss spectroscopy thickness measurements, of the analysed foil and the determination of the volume of the dispersoids using more conventional electron microscopy imaging techniques. Hence the technique does not require the use of stereology theorems. The procedure to measure the total inelastic mean free path and the linearity of its measurement for thicknesses (t) relative to the mean free path (t/λ) up to t/λ ∼ 4 is described. A method allowing the conversion of one single experimental λ‐value to various collection conditions either graphically or by parameterization is also outlined.

Various imaging methods (CTEM, STEM and chemical mapping) were evaluated for their ability to retrieve the distribution of dispersoids and thus their volume. Artefacts of the technique and of the sample preparation method are also discussed. The possibility of applying such techniques using in‐column and post‐column imaging filters and the limitations of such methods are presented. Although the system has been applied to a relevant metallurgical system in the aluminium industry, it can be used for any other material provided that the values of the mean free path can be obtained.
Observations of changing fine structure in nanoscale EELS analysis of grain boundaries in stainless steels
Authors: YUAN J. , BROWN L. M. , WALMSLEY J. , FISHER S. B.
Published: August 2011

Increasingly sophisticated demands placed on metals in the modern world have stimulated the use of tailor‐designed multi‐component alloys in many applications. Solute segregation, whether due to thermodynamic or non‐equilibrium processes, can dramatically alter the alloy composition near the grain boundary leading to drastic (and often detrimental) change in the properties of the alloy. The solute segregation profile is often a nearly singular function centred at the boundary, leading to great difficulty in analysis. The traditional method of depth profiling using Auger electron spectroscopy can only examine fractured surfaces and, because of limited spatial resolution, yields laterally averaged information. Recent improvement in the efficiency of electron‐microscope‐based electron energy‐loss spectroscopy has allowed a new high‐resolution approach in analysing the chemical and electronic properties of buried interfaces on a nanometer scale, i.e. we can study the complicated details of the alloy boundary itself. As an example, we will present the result of a study on stainless‐steel alloys used in the U.K. nuclear industry. The effect of irradiation on the structure of the alloy boundary is investigated. The nanoscale change in the chemical state of the alloying element at the grain boundary is observed for the first time in situ. The result can be potentially utilized to predict the corrosion‐resistance of the stainless steels.
Two‐channel gastric pacing in patients with diabetic gastroparesis
Authors: Lin Zhiyue , Sarosiek Irene , Forster Jameson , Ross Robert A. , Chen Jiande D. Z. , McCallum Richard W.
Published: August 2011

Background  Our primary goals were to investigate the effects of two‐channel gastric pacing on gastric myoelectrical activity, and energy consumption with the secondary intent to monitor gastric emptying and symptoms in patients with severe diabetic gastroparesis.

Methods  Four pairs of temporary pacing wires were inserted on the serosa of the stomach at the time of laparotomy to place the Enterra™ System in 19 patients with severe gastroparesis not responding to standard medical therapies. Two of the pairs were for electrical stimulation and the other two for recording. Five days after surgery the optimal pacing parameters for the entrainment of gastric slow waves in each patient were identified by serosal recordings. Two‐channel gastric pacing was then initiated for 6 weeks using a newly developed external multi‐channel pulse generator. Electrogastrogram (EGG), Total Symptom Score (TSS), and a 4‐h gastric emptying test were assessed at baseline and after 6 weeks of active gastric pacing. Enterra™ device was turned OFF during the duration of this study.

Key Results  Two‐channel gastric pacing at 1.1 times the intrinsic frequency entrained gastric slow waves and normalized gastric dysrhythmia. After 6 weeks of gastric pacing, tachygastria was decreased from 15 ± 3 to 5 ± 1% in the fasting state and from 10 ± 2 to 5 ± 1% postprandially (P < 0.05), mean TSS was reduced from 21.3 ± 1.1 to 7.0 ± 1.5 (P < 0.05) and mean 4‐h gastric retention improved from 42 to 28% (P = 0.05).

Conclusions & Inferences  Two‐channel gastric pacing is a novel treatment approach which is able to normalize and enhance gastric slow wave activity as well as accelerate gastric emptying in patients with diabetic gastroparesis with a goal safety profile.