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Step-up photophobic responses of the unicellular alga Haematococcus pluvialis and their interpretation in terms of photoreceptive apparatus characteristics
No full textThis paper reports a systematic study of the step-up photophobic responses exhibited by the unicellular alga Haematococcus pluvialis when stimulated unidirectionally or bidirectionally. The stimulus-response curves, obtained at four different wavelengths, are interpreted in terms of the structure of the photoreceptive apparatus. In addition, an indirect method to obtain information about the stigma and photoreceptor(s) is reported. This method is based on the interpolation of experimental with simulated data. Our results confirm the widely accepted view that the photoreceptors are located in the stigma region, and suggest the presence of two photoreceptors
Longitudinal patterns similar to G-banding in untreated human chromosomes: evidence from atomic force microscopy
No full textThe structure of human metaphase chromosomes, fixed according to standard procedures for optical microscopy but not treated for banding, was examined by atomic force microscopy (AFM). The images show that chromosomes display a banding pattern very similar to G-banding, detected by the AFM as a variation in the thickness of chromatin. This similarity allows the identification of individual chromosomes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Atomic force microscope imaging of chromosome structure during G-banding treatments
No full textSurface topography of human chromosomes was examined by atomic force microscopy during treatments for G-banding. Trypsin treatment resulted in a structural modification in the chromatin. Subsequent Giemsa staining caused a general swelling of the chromosomal surface that was greater in the areas of G-band positive regions. By means of a quantitative evaluation method we showed that the G-banding process produces a 10-fold enhancement of a pre-existing pattern of chromatin between G-band positive and G-band negative regions on mitotic chromosomes
TRANSIENT PHOTORESPONSES OF A PHOTOTACTIC MICROORGANISM, HAEMATOCOCCUS-PLUVIALIS, REVEALED BY LIGHT-SCATTERING
No full textMicroscopia a forza atomica:un'esperienza nello studio della struttura dei cromosomi umani
No full textAn atomic force microscope for cytological and histological investigations
No full textAn 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-specialized users
A geometrical pattern similar to G-banding pre-exist to staining in human chromosomes: evidence by atomic force microscope
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