108,947 research outputs found
Measurement of the 4Pi-confocal point spread function proves 75 nm axial resolution
No full textIn a 4Pi-confocal microscope the specimen is illuminated and observed coherently from above and below such that the numerical aperture is increased [S. W Hell, European Patent Application 91121368.4 (filed 1990, published 1992), S. W Hell and E. H. K. Stelzer, J. Opt. Soc. Am. A 9, 2159 (1992)]. The point spread functions of 4Pi-confocal and confocal microscopes were measured. Our measurements prove a three- to seven-fold increase of axial resolution, thus opening the prospect for a powerful three-dimensional imaging technique with an axial resolution down to 75 nm
Von Eisbären, Atomeisbrechern und Langstreckenflügen – die Bedeutung der "Roten Arktis" in Russland
No full textLogo der Kaffeekette Sever (dt.: Norden). – Foto: Agnes Stelzer Durch die Klimaerwärmung ist sie wieder in unser Blickfeld gerückt – die Arktis. Während den Polargebieten in Westeuropa nur aus aktuellem Anlass größere Beachtung geschenkt wird, sind sie in Russland ein wichtiger Bestandteil der Selbstidentifikation und des Nationalbewusstseins, selbst in den südlicheren Regionen des größten Landes der Welt. Auch wenn die Arktis schon immer einen Teil der russischen Geschichte darstellte, ist h..
Fundamental improvement of resolution with a 4Pi-confocal fluorescence microscope using two-photon excitation
No full textA new type of confocal fluorescence microscope with an unprecedented resolution is proposed. Calculations demonstrate that an axial resolution on the order of 100 nm can be achieved in a confocal microscope with enlarged aperture when two-photon excitation is applied. This axial resolution is up to four times higher than that of a confocal fluorescence microscope. The proposed microscope yields the highest point resolution ever achieved in far-field light microscopy
Properties of a 4Pi-confocal fluorescence microscope
No full textIn a 4Pi confocal fluorescence microscope two opposing microscope objective lenses were used to illuminate a fluorescent object from both sides and to collect the fluorescence emissions on both sides. Constructive interference of either the illumination wave fronts in the common focus or the detection wave fronts in the common detector pinhole resulted in an axial resolution approximately four times higher than that in a confocal fluorescence microscope. A precise 4Pi confocal fluorescence microscope that uses simultaneous illumination was built. The full width at half-maximum of the depth discrimination was determined experimentally to be approximately 110 nm when lenses with a numerical aperture of 1.4, an excitation of 633 nm, and detection of approximately 725 nm were used
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Aberrations in confocal fluorescence microscopy induced by mismatches in refractive index
No full textThe effect of refractive-index mismatch, as encountered in the observation of biological specimens, on the image acquisition process in confocal fluorescence microscopy is investigated theoretically. The analysis takes the vectorial properties of light into account and is valid for high numerical apertures. Quantitative predictions on the decrease of resolution, intensity drop and shift of focus are given for practical situations. When observing with a numerical aperture of 1.3 (oil immersion) and an excitation wavelength of 514 nm the centre of the focus shifts 1.7 mum per 10 mum of axial displacement in an aqueous medium, thus yielding an image that is scaled by a factor of 1.2 in the axial direction. Furthermore, it can be expected that for a fluorescent plane 20 mum deep inside an aqueous medium the peak intensity is 40% less than for a plane which is 10 mum deep. In addition, the axial resolution is decreased by a factor of 1.4. The theory was experimentally verified for test samples with different refractive indices
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