摘要:

SUMMARYWhen attempting to estimate stereological parameters starting from measurements in a limited domain, the question has to be addressed of how large the domain size must be in order to ensure representative measurements. To answer that question, the concept of ‘integral range’ is introduced. It allows a comparison between the scale of the phenomenon under study and the scale of observation. The integral range can be assessed using curves of dispersion variance, which can also yield empirical laws of change of sc

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03099.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYWithin the concept of point processes, a review is presented of quantities which can be used in studies of three‐dimensional (3‐D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3‐D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3‐D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitabl

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03100.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYA thermophysical model is established to analyse the influence of pre‐cooling of a biological specimen in the cold gas layer associated with spray‐freezing techniques. The basic principles governing the process of pre‐cooling are provided. It is concluded that pre‐cooling is one of the major limiting steps in attaining an overall ultra‐rapid cooling rate. Pre‐cooling has a substantial influence on the nature of the final frozen specimens. In order completely to avoid crystallization before entry into the liquid cryogen and maximize the overall cooling rate of the specimen, precautions should be taken to control the height of the gaseous layer and the size of the specimen. The probability of the specimen being frozen in the cold gaseous layer is reduced by increasing the entry speed. The effectiveness, however, becomes less marked at speeds greater than 10 m/s. In order to minimize the risk of misinterpreting the measured cooling rate, it is necessary to specify the pre‐cooling conditions. The pre‐cooling effect is much more evident in liquid helium than in cryogens such as propane, ethane, Freo

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03101.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYIn order to determine if cryosectioning involves ‘fracturing’ or ‘cutting’ we examined the surfaces obtained in cryosectioning by a metal‐replicating procedure commonly used in freeze‐fracture microscopy. Platinum‐carbon replicas were made of the surfaces of both the sections and the complementary surfaces of the sample stubs from which the sections were cut. When samples of frozen red cells were sectioned at −120°C with large knife advancements (1 μm), the chips produced did not resemble sections. Membrane fracture faces, produced by splitting of the lipid bilayer, were found in electron micrographs of replicas of the sample stubs. This demonstrates that a cryomicrotome can be used to produce large intact replicas. When dull knives were used with small knife advancements, both smooth and fractured regions were found. The sections produced with dull knives had a snowflake appearance in the light microscope. When sharp knives were used with small advancements (0·1 μm), replicas of the surfaces were free of fracture faces and the sections had a cellophane‐like appearance in the light microscope. Therefore, in cryosectioning a different process other than ‘fracturing’ is responsible. This ‘cutting’ process may be micromelting of a superficial layer by the mechanism of melting‐point depression from the pressure exerted

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03102.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYThe structure of protein A‐coated colloidal gold particles, and of macrophage cell‐surface receptors conjugated with immunogold particles, was studied using an ultrahigh‐resolution scanning electron microscope. Protein A, when conjugated with 15‐nm gold, formed a coat completely surrounding the particle. Particles conjugated with both protein A and immunoglobulin G (IgG) were similar, but with additional protrusions formed by the IgG. IgG molecules directly bound to gold were resolved sometimes as complexes of three units, sometimes as more filamentous, V‐shaped structures.On the cell surface of a macrophage reacted with a monoclonal antibody to Mac‐1 antigen (the murine C3bi receptor) followed by protein A‐gold, gold particles were seen to be linked via the IgG to the receptor, visualized as a

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03103.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYWhen specimens are observed by soft X‐ray microscopy, they always absorb many photons, causing radiation damage at the imaged site. The problems of radiation damage were studied in view of the principle of image formation; absorption contrast, scattering (holography), or phase contrast. In all cases, photons with a wavelength of 1–10 nm interact with the specimen mainly through the photoelectric effect followed by the transfer of energy to the imaging site either directly (absorption imaging) or indirectly (holography or phase contrast). This absorbed energy will cause structural changes to the imaging site. From a review of the literature the absorbed dose is estimated to be as high as 107Gy when the expected resolution of the specimen (1–10 thick) is 10 nm. This dose is far in excess of the amount required for cells to be able to survive when live mammalian cells are exposed. The levels of radiation effects were extrapolated to the estimated absorbed dose from the reported values for cell survival, chromosome aberrations, and DNA strand breaks with respect to observations on mammalian chromosomes. The extrapolated results show that some damage will occur in every 10 times 10‐nm (expected resolution) size unit. Although these studies focused only on the effects on mammalian chromosomes, the present results are more or less common phenomena in the observation of biological specimens. Hence, the results suggest that dynamic observations will be difficult. On the other hand, a time‐scale study of the effects of radiation on structural integrity suggests that single‐shot imaging with short‐pulsed (probably shorter than a few milliseconds) X‐rays may be appropriate for the observation of intact live biological specimens in the hydrated condition, before they ha

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03104.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYThe atom probe can be used to characterize fine‐scale microstructures. The results presented in this and a subsequent paper attempt to develop a methodology for interpreting information concerning 3‐D structures from the sequence of ions detected in the atom probe. Probability theory (Bernoulli trials and Markov processes) is used to build appropriate mathematical descriptions of different types of microstruct

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03105.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYMathematical descriptions of typical microsctructures which are observed in the atom probe are constructed from the theory of Markov chains. Short‐range ordering and clustering, overlapping and non‐overlapping particles and spinodal decomposition can all be modelled using this formalism. The models are used to calculate the important autocorrelation funct

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03106.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYDue to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03107.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARYSections cut dry for the X‐ray microanalysis of diffusible elements were fixed to adhesive‐coated single fine‐bar grids. The drawbacks of folding grids normally used for this purpose can thus largely be av

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1991.tb03108.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY