ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02835.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The properties of existing semiconductors limit performance in a whole range of devices and leave many interesting potential applications (e.g. for lighting, power generation or air‐conditioning) possible in principle but technologically impracticable. Better properties, then, could be valuable. They could be obtained in two ways, by discovering new materials (a long‐range option apt for academic investigation) or by modifying existing materials either chemically (e.g. by forming solid solutions, perhaps of highly unconventional type) and/or physically (e.g. by low dimensional confinement effects). These options are reviewed and some of their implications explo

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02836.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The superior efficiency of systematic sampling at all levels in stereological studies is emphasized and various commonly used ways of implementing it are briefly described. Summarizing recent theoretical and experimental studies a set of very simple estimators of efficiency are presented and illustrated with a variety of biological examples. In particular, a nomogram for predicting the necessary number of points when performing point counting is provided. The very efficient and simple unbiased estimator of the volume of an arbitrary object based on Cavalieri's principle is dealt with in some detail. The efficiency of the systematic fractionating of an object is also illustrated.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02837.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Systems are described for the illumination and detection of light microscope images of fluorescence in living cells at low levels of excitation. The illumination system is based on the use of an acousto‐optic modulator to control the wavelength and power of the excitation beam. The detection system utilizes an image intensifier coupled with a television camera to acquire images at extremely low intensities. Both the illumination and detection systems have superior performance compared to existing device

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02838.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The possibility of focusing images by the autocorrelation function is explained. It can be shown that these techniques are less sensitive to disturbances by noise than others. Furthermore, focusing criteria derived from autocorrelation functions have different responses to image contrast.It has been shown that these focusing criteria can be determined using binary images and applying the laws of stochastic ergodic metrology. This leads to a large reduction in computing time.Moreover, an attempt was made to focus by means of binary images determined by simple segmentation. The experimental results show that such a focus criterion operates quite well. The criterion offers the advantage that brightness levels in the image can be chosen selectively for focusing.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02839.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A technique for measuring the extremely small (<2 nm) probe sizes generated in a field emission gun analytical electron microscope is described. The technique involves scanning the fine probe across the edge of small oriented MgO cubes. A mathematical description of the intensity profiles is developed and it is shown how this relates to various definitions of the probe size. The experimentally measured probe sizes are then combined in a consistent manner with both beam broadening calculations and experimental measurements. This approach results in the first self‐consistent definition of the spatial resolution of X‐ray microanalysis in thin fo

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02840.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Lattice parameter changes can be detected by the use of a previously established technique which is based upon computer simulation of HOLZ patterns. This simulation technique is then applied to two precipitation phenomena in Nimonic PE16. Firstly, the growth of gamma prime, γ, precipitates from a solid solution is monitored via the decrease in lattice parameter of the parent phase, and secondly the lattice parameter of coarsened, overaged γ is measured for precipitates sited both at grain boundaries and within grains. The variations thus detected between intergranular and intragranular precipitates are attributed to changes in the Ti/Al ratio due to preferential γ coarsening at the grain boundary. The very subtle compositional changes inferred (∼1 at. % Ti) would have been very difficult to establish by chemical analysis, but can be easily measured by convergent beam electron diffrac

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02841.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Extremely thin sections of unstained materials (beef liver catalase, double‐stranded calf thymus DNA, horse spleen ferritin and mammalian skeletal muscle), embedded in the water‐soluble melamine resin Nanoplast FB101, were studied by dark‐field electron microscopy and electron spectroscopic imaging.While ferritin molecules so recorded show 04 and 09 nm lattice fringes within the crystalline iron core, double‐stranded DNA shows a helical repeat with a spacing of 34 nm.The gain in resolution of structural detail reported here is probably due mainly to the reduced section thickness as compared to traditional thin‐sectioning techniques. As we reported earlier (Frösch&Westphal, 1984), melamine resins can be sectioned extremely thinly (<10 nm) and observed without a supporting film, making them especially suitable for dark‐field electro

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02842.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A method is presented for the infiltration and embedding of frozen micro‐organisms at a temperature of 190 K by Nanoplast MUV 116, a new UV‐polymerizable embedding medium for electron microscopy. The hardness achieved by UV irradiation in the cold is about 80% of the hardness needed for ultramicrotomy. Final hardening requires a post‐curing step at 333 K for 24 h.Applying this procedure to cyanobacteria, an improved ultrastructural preservation is demonstrated as compared to samples that were embedded in the water‐soluble medium Nanoplast FB 101 at ambient temperatures. Sections of materials treated in this way are suitable for histochemical techniques, such as Thiéry's silver staining method for

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02843.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A temperature controlled cell chamber is described which permits phase‐contrast and fluorescence microscopy of living cells. It is shown how the cellular uptake of fluorochromes can be investigated both photographically and photometrically. Some sample results are presented for the uptake of Evans Blu

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb02844.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY