ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00318.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYA point‐projection microscope is described which uses an electric field of several volts per nanometre to generate ions from a layer of benzene condensed in high vacuum on to the apex of a cryogenically cooled field‐emitter tip. Clusters of ferritin (a spherical protein molecule) embedded in the layer, have been imaged by exposing their contours during controlled field‐desorption. Image contrast is high. A magnification of 2 times 105has been achieved at a spatial resolution estimated to be better than 3 nm. Three‐dimensional reconstructions of cluster morphology from a series of molecular contours are in qualitative agreement with transmission‐electron micrographs of the ferritin covered emitter apex. Reproducibility of the cluster contours, and TEM images of the apex before and after imaging suggest that the imaging procedure is nonde

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00319.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYEnergy dispersive X‐ray detectors are frequently attached to electron microscopes to enable microanalysis to be performed, but because such detectors accept X‐rays generated within an appreciable solid angle, the recorded spectra usually include some spurious contributions from the instrument. This paper describes instrumental modifications firstly to reduce and secondly to permit the subtraction of the residual extraneous contributions. The probable accuracy of this subtraction procedure is examined.Results are presented showing the effects of various instrumental modifications on spectra from thin specimens and demonstrate that by careful attention to experimental details it is possible to separate the spectrum due to the thin specimen alone from all other extraneous signals.Two test specimens and a number of test procedures for investigating the analytical performance of (scanning) transmission electron microscopes are presented.Sources of error and the method of their correction when the thin specimen Bremsstrahlung is used for quantitative analysis are discus

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYA system of cinemicrography has been developed in which a single microscope and 16 mm camera are multiplexed to produce a time‐lapse photographic record of many fields simultaneously. The field coordinates and focus are selected via a control console and entered into the memory of a dedicated microcomputer; they are then automatically recalled in sequence, thus permitting the photographing of additional fields in the interval between exposures of any given field. Sequential exposures of each field are isolated in separate sections of the film by means of a specially designed random‐access camera that is also controlled by the microcomputer. The need to unscramble frames is thereby avoided, and the developed film can be directly analy

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThe stereological practice of using integral test systems in the estimation of the fundamental stereological ratios is studied in the light of recent theoretical developments in sampling. The estimation of a ratio is based oncountsonly, obtained from two, in general different, test sets constituting the integral test system. The ordinary ratio‐of‐sums estimator based on counts from uniformly positioned integral test systems is compared with two estimators based on non‐uniform, weighted sampling. It is shown that the estimators based on weighted sampling are not, in general, unbiased. Furthermore, it is pointed out that the mean‐of‐ratios estimator based on replicated weighted sampling needs not have smaller MSE than the ordinary ratio‐of‐sums estimator based on replicated uniform sampling.The fact that the estimation is based on counts as opposed to complete 2‐d observations does not necessarily mean a reduction in information. For certain types of stereological ratios, the ordinary ratio‐of‐sums estimator based on complete observation is shown, counter to intuition, to belessaccurate than that based on simpl

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00322.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYAn apparatus for time‐lapse cinemicrography of living animal cellsin vitrois described. It has an increased information capacity in comparison with conventional types of equipment in that successful combination of the highest possible spatial resolution with phase contrast microscopy and an improved temporal resolution provided by flash light illumination has been achieved. The interval between exposures of 1/200 s approximately can be reduced to 1/4 s using a negative phase‐contrast objective of NA 1·3. Negative phase‐contrast also appeared to be the best technique for imaging of tiny cell surface structures. Thus the new apparatus is suitable for the study of the patterns of cell surface motilityin

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00323.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThe contribution of glutaraldehyde (GA) to the effective osmolarity of GA fixatives, the osmotic reactivity of the cells after fixation in GA, and also the duration of fixation in GA on cell volume, were investigated using cultured smooth muscle cells (SMC) and spiral aortic strips. Four fixation procedures were studied. We found that GA contributes to the total effective osmolarity of the fixatives, and that the type of buffers used for the fixatives can also affect the cell volume differently during GA fixation. After GA fixation, the cells were still osmotically reactive, regardless of the buffer types for making up the GA fixatives, so that the osmolarity of the wash buffer after GA fixation is important. However, OsO4eliminates osmotic responses, thus the osmolarity of OsO4fixative and wash buffer have negligible influence on the cell volume. Longer fixation time up to 4 h had no effect on the cell volume.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00324.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYAt present a model‐free, design‐based theory of unbiased estimation, and a model‐based one of linear unbiased estimation of minimum variance, are available for stereology. The main developments rest upon the nested scheme {section(quadrat)}, whence the raw data are expressible in terms of area, length and number. The main aim of this paper is to complete the available model‐based theory by introducing the step in which sections are analysed bypoint‐countingviacoherent test systems(CTSs). Using this development, the stereologist should be able to handle raw point and intersection counts optimally, in order to find the best estimator of a ratioRin a given specimen in a wide range of circumstances. The latter include, for instance, the use of different CTSs on different sections and of double CTSs on each section, as well as the case—(not uncommon in electron microscopy)—in which different sections from the same sample are observed at slightlydifferentmagnifications but analysed by quadrats (via automatic or semi‐automatic image analysers, for instance), or CTSs offixedsizes. The main conclusion pertaining to the latter case is that the estimators obtained viasection‐wisemagnification corrections are in general superior to those corrected via a global, average magnification.In order to illustrate the methodology, a synthetic numerical example, and a re

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00325.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThis paper shows that a means of accurately measuring beam current during microprobe analysis of inorganic fluid microdroplets is essential, since certain elements were sublimated from such specimens under easily achieved beam current densities, i.e. S at 1·8 nA/μm2, K at 2·5 nA/μm2, Na at 3·5 nA/μm2, P at 5·3 nA/μm2. In comparison, Cl was volatilized even under the mildest conditions used (0·35 nA/μm2), and Ca, Mg and Co were stable under the severest operating conditions (7·1 nA/μm2). Elements were less stable in large (3 μm diameter) droplets than in small (1 μm) droplets under identical irradiation conditions. The onset of volatilization is a direct function of the current delivered per unit area and not of the total integrated dose.The addition of 50 g/l of urea to the mixed‐salts (isoatomic) solution, or (a) the mounting of the droplets so that the carbon‐celloidin support film was interposed between them and the electron source, and (b) top‐coating the droplets with carbon, did not, in general, raise the threshold of volatilization of a given element, but did effectively retard the rate of loss at current densities above the volatilization threshold. A literature survey confirmed that similar losses can occur from biological tissue specimens, albeit at higher beam current densities.Finally, the possibility that local specimen heating during electron/specimen interaction is a cause of element loss during microprobe an

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00326.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYAddition of 0·05% OsO4to a conventional glutaraldehyde fixative for the first 10 min of fixation was found to improve greatly the preservation of ultrastructure in the eggs ofUrechis caupo.Several workers have since confirmed this result in other marine invertebrate tissues. Specific protocols and techniques are given. We believe that the OsO4rapidly renders the plasma membranes of cells freely permeable to glutaraldehyde, allowing faster penetration of this fixative. This method should be applicable to a wide variety of tissues that are difficult to fix

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb00327.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY