Some results of photospheric fine structure investigations at the Pulkovo observatory

2006 ◽  
pp. 259-260 ◽  
Author(s):  
V.N. Karpinsky
Keyword(s):  
Fine Structure ◽  
Pulkovo Observatory ◽  
Structure Investigations

Platymonas Impellucida Sp.Nov. From Puerto Rico

1967 ◽  
Vol 47 (3) ◽  
pp. 723-733 ◽  
Author(s):  
J. Mclachlan ◽  
M. Parke
Keyword(s):  
Puerto Rico ◽  
Fine Structure ◽  
Cell Division ◽  
Related Genus ◽  
Anatomical Features ◽  
Whole Cells ◽  
New Information ◽  
Electron Microscopes ◽  
Structure Investigations

The morphology and microanatomy of Platymonas impellucida sp.nov. have been investigated using light and electron microscopes and unusual stages of cell division studied. The anatomical features closely resemble those recently described for Platymonas convolutae (cf. Parke & Manton, 1967). As in that species the pyrenoid is penetrated from many directions by cytoplasmic canaliculi lined with the double plastid membrane but unlike that species a starch shell is not developed around the pyrenoid. In whole cells of P. impellucida therefore, it is extremely difficult, in most cases impossible, to detect the presence of the pyrenoid. This new information on the absence of a starch shell in a member of the Prasinophyceae is of importance since pyrenoid structure appears to be of major importance for taxonomic purposes. Apparent fusion stages have been shown to be a variation in vegetative division not previously encountered in the genus Platymonas.IntroductionRecent studies on members of the Prasinophyceae have assisted greatly in characterizing this class of green-pigmented algae although the limits are not as yet entirely defined. Fine-structure investigations have, in addition, elucidated certain features of generic significance. The genus Platymonas is now well described and can be unequivocally distinguished from Prasinocladus, a closely related genus. Previously these two genera were separated on the presence or absence of non-motile dendroid colonies, but such colonies are now known in both genera (Parke & Manton, 1967).The remaining significant diagnostic generic characteristic is the structure of the pyrenoid. In Platymonas the branched canaliculi invading the pyrenoid either from a direction facing the nucleus (Gibbs, 1962; Manton & Parke, 1965) or from many directions (Parke & Manton, 1967) contain cytoplasm rather than protrusions of the nucleus as in Prasinocladus (Parke & Manton, 1965).

Near-Edge X-ray Absorption Fine Structure Investigations of Order in Carbon Nanotube-Based Systems†

2005 ◽  
Vol 109 (17) ◽  
pp. 8489-8495 ◽  
Author(s):  
Sarbajit Banerjee ◽  
Tirandai Hemraj-Benny ◽  
Sharadha Sambasivan ◽  
Daniel A. Fischer ◽  
James A. Misewich ◽  
...  
Keyword(s):  
Fine Structure ◽  
Carbon Nanotube ◽  
X Ray ◽  
Absorption Fine ◽  
Structure Investigations ◽  
X Ray Absorption

New Opportunities to Study Defects by Soft X-Ray Absorption Fine Structure

2007 ◽  
Vol 131-133 ◽  
pp. 473-478
Author(s):  
Federico Boscherini ◽  
D. De Salvador ◽  
G. Bisognin ◽  
G. Ciatto
Keyword(s):  
Fine Structure ◽  
Local Structure ◽  
Light Elements ◽  
Semiconductor Physics ◽  
X Ray ◽  
Absorption Fine ◽  
Radiation Sources ◽  
Structure Investigations ◽  
X Ray Absorption ◽  
Semiconductor Properties

X-ray absorption fine structure can determine the local structure of most atoms in the periodic table. The great recent improvements in the performance of synchrotron radiation sources and techniques and advances in the simulations of the spectra have opened new opportunities, especially in the study of dilute systems in the soft X-ray range. In this contribution we will show some recent results that demonstrate how semiconductor physics may greatly benefit from such progress. In fact, doping or alloying of semiconductors with light elements, that have K absorption edges in the soft X-ray range, is widely employed to tune semiconductor properties. X-ray absorption fine structure investigations on such systems can give an important contribution towards the understanding and optimization of technological processes.

scholarly journals Extended-X-ray-absorption-fine-structure investigations of zinc in 5-aminolaevulinate dehydratase

1985 ◽  
Vol 230 (3) ◽  
pp. 625-633 ◽  
Author(s):  
S S Hasnain ◽  
E M Wardell ◽  
C D Garner ◽  
M Schlösser ◽  
D Beyersmann
Keyword(s):  
Fine Structure ◽  
Nitrogen Atom ◽  
Molecular Mass ◽  
Thiol Groups ◽  
Air Oxidation ◽  
X Ray ◽  
Absorption Fine ◽  
Catalytic Role ◽  
Structure Investigations ◽  
X Ray Absorption

The zinc co-ordination in 5-aminolaevulinate dehydratase (5-aminolaevulinate hydro-lyase, EC 4.2.1.24) was investigated by recording and interpreting the extended X-ray-absorption fine structure (e.x.a.f.s.) associated with the zinc K-edge. The enzyme has a molecular mass of 280 000 Da and consists of eight subunits of 35 000 Da each; the samples studied contained approx. 1 g-atom of zinc/mol of subunit. Four forms of the enzyme were investigated and details of the zinc environment were elucidated, as follows. In the native enzyme, zinc is considered to be co-ordinated to three sulphur atoms at 0.228(2)nm [2.28(2)A] and a lower-Z atom at 0.192(5)nm [1.92(5)A] (if nitrogen) or 0.189(5)nm [1.89(5)A] (if oxygen). Reaction of the enzyme with the inhibitor 2-bromo-3-(imidazol-5-yl)propionic acid produced significant changes in the e.x.a.f.s., the nature of which are consistent with co-ordination by about three sulphur atoms at 0.222(2)nm [2.22(2)A], a nitrogen atom at 0.193(5)nm [1.93(5)A] and a nitrogen atom from the inhibitor at 0.214(5)nm [2.14(5)A]. Inactivation of the enzyme by air-oxidation of essential thiol groups and binding of the substrate produce slight changes in the e.x.a.f.s. consistent with slight re-arrangement of ligands with additional lighter ligands (nitrogen or oxygen). These results, when combined with previous findings, are taken to indicate that zinc has a structural rather than a direct catalytic role in 5-aminolaevulinate dehydratase.

High spatial resolution extended energy loss fine structure investigations of silicon dioxide compounds

1995 ◽  
Vol 59 (1-4) ◽  
pp. 149-157 ◽  
Author(s):  
Zou Wei Yuan ◽  
Stefan Csillag ◽  
Mohammad A. Tafreshi ◽  
Christian Colliex
Keyword(s):  
Fine Structure ◽  
Energy Loss ◽  
Silicon Dioxide ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Structure Investigations
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