摘要:

SummaryX‐ray detection by energy‐dispersive spectrometry in the analytical electron microscope (AEM) is often limited by low collected X‐ray intensity (P), modest peak‐to‐background (P/B) ratios, and limitations on total counting time (τ) due to specimen drift and contamination. A new AEM has been designed with maximization ofP, P/B, and τ as the primary considerations. Maximization ofPhas been accomplished by employing a field‐emission electron gun, X‐ray detectors with high collection angles, high‐speed beam blanking to allow only one photon into the detector at a time, and simultaneous collection from two detectors.P/Bhas been maximized by reducing extraneous background signals generated at the specimen holder, the polepieces and the detector collimator. The maximum practical τ has been increased by reducing specimen contamination and employing electronic drift correction. Performance improvements have been measured using the NIST standard Cr thin film. The 0·3 steradian solid angle of X‐ray collection is the highest value available. The beam blanking scheme for X‐ray detection provides 3–4 times greater throughput of X‐rays at high count rates into a recorded spectrum than normal systems employing pulsepileup rejection circuits. Simultaneous X‐ray collection from two detectors allows the highest X‐ray intensity yet recorded to be collected from the NIST Cr thin film. The measuredP/Bof 6300 is the highest level recorded for an AEM. In addition to collected X‐ray intensity (cps/nA) and P/B measured on the standard Cr film, the product of these can be used as a figure‐of‐merit to evaluate instruments. Estimated minimum mass fraction (MMF) for Cr measured on the standard NIST Cr thin film is also proposed as a figure‐of‐merit for comparing X‐ray detection in AEMs. Determinations here of the MMF of Cr detectable show at least a thre

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03503.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryA method involving cryostat sectioning (10 μm thickness) and freeze‐drying is presented for the preparation of plant tissue for microanalytical studies. The method is well suited for semi‐quantitative imaging by secondary ion mass spectrometry (SIMS) and offers significant advantages over bulk freeze‐dried or freeze‐substitution preparations. Segments of corn or soybean root (5 mm) are quench‐frozen, embedded externally, sectioned in a cryostat (10 μm), pressed onto ultrapure Si and slowly freeze‐dried. Images of these sections with secondary electron microscopy and SIMS indicated good morphological preservation. It was possible to section tissues of a wide developmental range, as well as roots varying sixfold in diameter. SIMS images are presented which demonstrate the ability to detect and localize nutrient tracers, such as Rb+, following brief exposures (10 min) to the intact plant. Likewise, a toxic metal (Al) was localized in root tissue after brief exposure (<1 day) of the intact plant root to micromolar external concentrations. Elemental redistribution during processing was minimal, as demonstrated most explicitly by the lack of movement of loosely bound Ca from the outer cell walls into the adjacent embedding material. Preservation of compositional differences between cellular content and cell wall was supported by a semi‐quantitative treatment

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03504.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryIn the process of vitrifying aqueous suspensions for cryotransmission electron microscopy, water is solidified without crystallization. Vitrification can be achieved by rapidly plunging an aqueous thin film into a liquid cryogen. The preparation of aqueous thin films prior to vitrification must be performed in an environmental cabinet at controlled temperature and humidity in order to prevent evaporation and temperature‐induced phase changes in the thin film. The device described here incorporates several important features which make the apparatus simpler and more convenient to use than similar devices described in the literature. One of these features includes the use of a totally enclosed environmental cabinet in which the grid, sample, micropipette and absorbent paper are equilibrated before thin‐film preparation. Other features include a cryogen dewar on a swing arm for easy refilling, a guillotine shutter which is used to trigger the plunger electrically and a semiautomatic system which facilitates rapid transfer of the vitrified specimen from liquid propane to liquid nitrogen for storage and reduces handling of the specimen. To demonstrate the utility of the device, results showing the influence of temperature on the morphology of phospholipid vesicles are presented. A commercial cryotransfer apparatus (which is used for transportation of the vitrified specimen to the electron microscope cold‐stage) has been modified to reduce the possibility of reversion of the vitreous phase to the crystalline ice p

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03505.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryAn atomic force microscope (AFM) specifically designed for cytological and histological studies and able to operate on the same scale of the highest optical magnification is described. The AFM is a non‐invasive instrument; it operates on samples which do not require any kind of treatment and it can produce information that supplements and completes the information given by traditional microscopical methods. The apparatus has been used to image fixed human chromosomes and to investigate the action of trypsin during the staining for banding. First results showed that banding patterns very similar to G‐banding pre‐exist to staining and to trypsin treatment in human metaphase chromosomes, and that the trypsin treatment induces a structural collapse in the chromatin. The instrument was also used on thin sections of plant tissue and gave promising results. Experience confirmed that AFM is a suitable tool for this kind of investigation, and proved the importance of developing AFM microscopes specifically designed for routine use in cytology and histology, conceived for non‐specialize

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03506.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryMicroscope slides were coated with a layer of gelatin, the thickness of the gelatin increasing linearly along the long axis. The bacterial suspension is applied to the dried gelatin and covered by a coverslip. The medium is absorbed by the gelatin and thus the cells applied against the coverslip. By this method, cultures of concentrations below 108cells/ml provide statistically relevant numbers for observation without prior concentration steps. It is easier to apply than the existing methods for the observation of bacterial nucleoids by phase contrast imaging. Because the cells are maintained in growing conditions the method is useful for the vital fluorescence DAPI‐staining of various bacterial species and for observations of plasmolysis and its reversal at different physiological conditions and extracellular osmolalities. The previously generally assumed view that the plasmolytic changes of the cell morphology are immediate upon the hyperosmotic shock and are rapidly repaired when the cell is able to metabolize actively was confirmed; this is in contrast to some recent claim

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03507.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryOptical fibres bent in two mutually perpendicular planes have proven useful for randomizing illumination in light microscopes. These optical scramblers can increase the resolution and/or contrast obtained with several modes of light microscopy. Here, computer simulations are used to investigate several parameters affecting light randomization in curved optical fibres in order to further the theoretical basis for scrambler design. Light passing through 90° bends of optical fibre of varying radii of curvature was modelled by ray tracing in two dimensions, and scrambling mechanisms were observed. The effects of varying the position and angle of entry of light on the phase and direction of propagation of the emergent light were determined. It was found that (a) thorough scrambling does not necessarily require high numerical aperture (NA) entry of light into the fibre, (b) considerable order persists after a single 90° bend of an idealized fibre and (c) a higher degree of scrambling (at the cost of transmission efficiency) is achieved in more tightly curved fibres. The pathlength variations introduced by scrambling proved smaller than typical laser coherence lengths, requiring temporal scrambling (vibrating the fibre

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03508.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThree‐dimensional (3‐D) cell morphology is important for the understanding of cell function and can by quantified in terms of volume and surface area. Differential interference contrast (DIC, or Nomarski) imaging can enable cell edges to be clearly visualized in unstained tissue due to the slight difference in refractive index between aqueous media and cytoplasm. DIC is affected in only one direction ‐ the direction of the optical shear. A 1‐D edge detector was used in that direction with a scale length equal to that of an in‐focus edge to highlight cell boundaries. By comparison with the signal from the edge detector on an out‐of‐focus slice, the in‐focus slices could be segmented and, after noise suppression, cell outlines obtained. A voxel paradigm was used to calculate cell volume and differential geometry was used for surface area estimation. We applied this approach to obtain 3‐D dimensional information by optical sectioning of mot

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03509.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryA measure of texture, the nuclear diffuseness, was formulated for use in biological classification, and specifically to characterize quantitatively chromatin texture. Nuclear diffuseness corresponds to the amount of local intensity variation in the digitized image of a nuclear profile. As a setting in which to test the efficacy of nuclear diffuseness as a diagnostic tool, the identification of parathyroid adenoma and carcinoma was considered. Digitized images of sections of parathyroid chief cell nuclei were obtained from 16 biopsies, and the nuclear diffuseness, as well as other morphometric descriptors, were computed. With just the average nuclear diffuseness and average nuclear profile area, jackknife (leave‐one‐out) classification using an artificial neural network was able to diagnose correctly and unambiguously the condition (normal, parathyroid adenoma, or parathyroid carcinoma) in 15 of 16 cases. In one case, the neural network assigned a higher weight to the correct diagnosis, but was unable to distinguish between normal and adenoma conclusiv

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03510.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe purpose of this study is to estimate the transport coefficients (diffusion, permeability) of polymer composites from two‐dimensional images of these media (polyethylene/polyamide alloys) obtained by the scanning electron microscope. The main characteristics of the media investigated are a wide morphological variability (nodular and lamellar media) and transport properties that are very different according to the phase. The computation tools used must accordingly have a wide range of validity. The idea of the proposed algorithm is to calculate the distance from an edge of the image, with a modified distance according to the phase crossed. The results obtained are compared with those obtained by finite difference integration of Fick's laws, and with permeability measurements of hydrocarbons in the material

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1994.tb03511.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY