Nature of S ⋯· O interaction in short X –S ⋯· O contacts: charge density experimental studies and theoretical interpretation

1984 ◽  
pp. 191-196 ◽  
Author(s):  
Claudine Cohen-Addad ◽  
Mogens S. Lehmann ◽  
Pierre Becker ◽  
László Párkányi ◽  
Alajos Kálmán
Keyword(s):  
Charge Density ◽  
Experimental Studies ◽  
Theoretical Interpretation

Electron Density Studies of Molecular Crystals

1997 ◽  
Author(s):  
Philip Coppens
Keyword(s):  
Charge Density ◽  
Electron Scattering ◽  
Experimental Studies ◽  
Molecular Crystals ◽  
Chemical Environment ◽  
Light Atom ◽  
Core Electron ◽  
The Core ◽  
Core Electrons ◽  
Electron Donor And Acceptor

Small molecules consisting of light-, few-electron atoms were the first species beyond atoms to yield to quantum-mechanical methods. Similarly, crystals of small light-atom molecules have served as most useful test cases of charge density mapping. The small number of core electrons in first-row atoms enhances the relative contribution of valence electron scattering to the diffraction pattern. Early studies, done just after automated diffractometers became widely available, were concerned with molecular crystals such as uracil (Stewart and Jensen 1967), s-triazine (Coppens 1967), oxalic acid dihydrate (Coppens et al. 1969), decaborane (Dietrich and Scheringer 1978), fumaramic acid (Hirshfeld 1971), glycine (Almlof et al. 1973), and tetraphenylbutatriene (Berkovitch-Yellin and Leiserowitz 1976). While thermal motion is often pronounced in molecular crystals, advances in low-temperature data collection have done much to alleviate this disadvantage. In recent years, subliquid-nitrogen cooling techniques have been increasingly applied. Among the most interesting aspects of molecular crystals are the influence of intermolecular interactions on the electronic structure. Physically meaningful Coulombic parameters pertinent to a molecule in a condensed environment can be obtained from the diffraction analysis, and can be used in the modeling of macromolecules. The enhancement of the electrostatic moments relative to those of the isolated species has been noted in chapter 7. But, beyond these considerations, molecular crystals are important in their own right. For example, crystals of aromatic molecules substituted with π-electron donor and acceptor groups are among the most strongly nonlinear optical solids known, considerably exceeding the nonlinearity of inorganic crystals such as potassium titanyl phosphate (KTP); while mixed-valence organic components of low-dimensional solids can become superconducting at low temperatures. The relation between such properties of molecular crystals and their charge distribution provides a continuing impetus for further study. The suitability of light-atom crystals for charge density analysis can be understood in terms of the relative importance of core electron scattering. As the perturbation of the core electrons by the chemical environment is beyond the reach of practically all experimental studies, the frozen-core approximation is routinely used. It assumes the intensity of the core electron scattering to be invariable, while the valence scattering is affected by the chemical environment, as discussed in chapter 3.

Experimental Studies and Theoretical Interpretation of the Calorimetric Effects Accompanying Ion Adsorption at Oxide/Electrolyte Interfaces:  Application of Flow Adsorption Calorimetry†

Langmuir ◽  
1999 ◽  
Vol 15 (18) ◽  
pp. 5921-5931 ◽  
Author(s):  
Władysław Rudziński ◽  
Robert Charmas ◽  
Wojciech Piasecki ◽  
Alexander J. Groszek ◽  
Fabien Thomas ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Theoretical Interpretation ◽  
Ion Adsorption ◽  
Adsorption Calorimetry ◽  
Oxide Electrolyte

Theoretical and experimental studies of the charge density in urea

1984 ◽  
Vol 40 (4) ◽  
pp. 398-404 ◽  
Author(s):  
S. Swaminathan ◽  
B. M. Craven ◽  
M. A. Spackman ◽  
R. F. Stewart
Keyword(s):  
Charge Density ◽  
Experimental Studies

scholarly journals Visual search of illusory contours: Shape and orientation effects

Psihologija ◽  
2008 ◽  
Vol 41 (1) ◽  
pp. 53-67 ◽  
Author(s):  
Vasilije Gvozdenovic
Keyword(s):  
Visual Search ◽  
Visual Processing ◽  
Experimental Studies ◽  
The Other ◽  
Integration Theory ◽  
Theoretical Interpretation ◽  
Specific Class ◽  
Illusory Contours ◽  
Experimental Procedure ◽  
Feature Integration Theory

Illusory contours are specific class of visual stimuli that represent stimuli configurations perceived as integral irrespective of the fact that they are given in fragmented uncompleted wholes. Due to their specific features, illusory contours gained much attention in last decade representing prototype of stimuli used in investigations focused on binding problem. On the other side, investigations of illusory contours are related to problem of the level of their visual processing. Neurophysiologic studies show that processing of illusory contours proceed relatively early, on the V2 level, on the other hand most of experimental studies claim that illusory contours are perceived with engagement of visual attention, binding their elements to whole percept. This research is focused on two experiments in which visual search of illusory contours are based on shape and orientation. The main experimental procedure evolved the task proposed by Bravo and Nakayama where instead of detection, subjects were performing identification of one among two possible targets. In the first experiment subjects detected the presence of illusory square or illusory triangle, while in the second experiment subject were detecting two different orientations of illusory triangle. The results are interpreted in terms of visual search and feature integration theory. Beside the type of visual search task, search type proved to be dependent of specific features of illusory shapes which further complicate theoretical interpretation of the level of their perception.

scholarly journals Analysis of Theoretical Concepts for Interpretation the Result of the Experimental Studies of Free Groundwater Level Oscillation in Wells

2021 ◽  
Vol 6 (1) ◽  
pp. p123
Author(s):  
Mikhail M. Burakov
Keyword(s):  
Groundwater Level ◽  
Critical Analysis ◽  
Experimental Studies ◽  
Theoretical Interpretation ◽  
Free Oscillations ◽  
Piezometric Level ◽  
Consistent Theory ◽  
Theoretical Concepts ◽  
Level Oscillation ◽  
Number Of Publications

A number of publications present the results of an experimental study of free oscillations of groundwater piezometric level in wells with their eigenfrequencies. The oscillations were initiated by a pulsed impact on the aquifer through the well. Also in a number of publications a theoretical interpretation was proposed for the established phenomenon. However, the existing theoretical ideas about free oscillations of the groundwater level seem to be incorrect. In the present work, a critical analysis of these available theoretical concepts is performed. The analysis served as an impetus to the development of a consistent theory of relaxation filtration of groundwater.

Experimental studies of collisions of excited Li(4p) atoms with C2H4, C2H6, C3H8 and theoretical interpretation of the Li–C2H4 system

2009 ◽  
Vol 355 (2-3) ◽  
pp. 157-163 ◽  
Author(s):  
Natenael Semmineh ◽  
Solomon Bililign ◽  
Denis Hagebaum-Reignier ◽  
Gwang-Hi Jeung
Keyword(s):  
Experimental Studies ◽  
Theoretical Interpretation

3-D reconstruction and analysis of mammalian mitotic spindle structure

1992 ◽  
Vol 50 (1) ◽  
pp. 578-579
Author(s):  
Kent McDonald ◽  
David Mastronarde ◽  
Rubai Ding ◽  
Eileen O'Toole ◽  
J. Richard McIntosh
Keyword(s):  
Cross Sections ◽  
Mitotic Spindle ◽  
Experimental Studies ◽  
Video Camera ◽  
Three Dimensions ◽  
Mitotic Spindles ◽  
Black And White ◽  
Reconstruction Methods ◽  
Spindle Structure ◽  
Tissue Culture Line

Mammalian spindles are generally large and may contain over a thousand microtubules (MTs). For this reason they are difficult to reconstruct in three dimensions and many researchers have chosen to study the smaller and simpler spindles of lower eukaryotes. Nevertheless, the mammalian spindle is used for many experimental studies and it would be useful to know its detailed structure.We have been using serial cross sections and computer reconstruction methods to analyze MT distributions in mitotic spindles of PtK cells, a mammalian tissue culture line. Images from EM negatives are digtized on a light box by a Dage MTI video camera containing a black and white Saticon tube. The signal is digitized by a Parallax 1280 graphics device in a MicroVax III computer. Microtubules are digitized at a magnification such that each is 10-12 pixels in diameter.

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