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Author

G Ramachandran

Bio: G Ramachandran is an academic researcher. The author has contributed to research in topics: Crystal. The author has an hindex of 1, co-authored 1 publications receiving 100 citations.
Topics: Crystal

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01 Jan 1963

100 citations


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Journal ArticleDOI
TL;DR: The use of the Fourier, variance and related methods in general requires that the diffraction lines are well resolved and it is thus restricted to materials with high symmetry or which exhibit a high degree of preferred orientation as discussed by the authors.
Abstract: In the 1960s the Fourier and variance methods superseded the use of the FWHM and integral breadth in detailed studies of microcrystalline properties. Provided that due allowance is made in the analysis for systematic errors, particularly the effects of truncation of diffraction line profiles at a finite range, these remain the best methods for characterising crystallite size and shape, microstrains and other imperfections in cases where accuracy is important. However, the application of the Fourier, variance and related methods in general requires that the diffraction lines are well resolved and it is thus restricted to materials with high symmetry or which exhibit a high degree of preferred orientation. Most materials, on the other hand, including many of technological importance, have complex patterns with severe overlapping of peaks. The introduction of pattern-decomposition methods, whereby a suitable model is fitted to the total diffraction pattern to give profile parameters for individual lines, means that microcrystalline properties can now be studied for any crystalline material or mixture of substances. The use of the FWHM and integral breadth has been given a new lease of life; though the information is less detailed than is given by the Fourier and variance methods and systematic errors are in general greater, self-consistent estimates of crystallite size and microstrains are obtained.

161 citations

Journal ArticleDOI
TL;DR: In this article, the authors review the history, theory, measurement technique and experimental results on gyrotropic phenomena including optical rotation (optical activity), electrogyration, the Faraday effect and magneto-electrogyration in transparent crystals, including examples of structural phase transitions.
Abstract: Here, we review the history, theory, measurement technique and experimental results on gyrotropic phenomena including optical rotation (optical activity), electrogyration, the Faraday effect and magneto-electrogyration in transparent crystals, including examples of structural phase transitions. Relations to the absolute structure are discussed and model calculations are performed on the basis of electronic polarizability and crystal structure.

116 citations

Journal ArticleDOI
TL;DR: In this paper, a semiorganic nonlinear optical material has been grown from solution by slow evaporation at ambient temperature and the solubility of GSN has been determined in water.

111 citations

Journal ArticleDOI
TL;DR: A singlecrystal neutron diffraction study of the structure of potassium oxalate monohydrate has been made as mentioned in this paper, which consists of oxalates ions hydrogen bonded by the water molecules into infinite linear chains which are held together by electrostatic interactions with the potassium ions.
Abstract: A single‐crystal neutron‐diffraction study of the structure of potassium oxalate monohydrate has been made. The structure consists of oxalate ions hydrogen bonded by the water molecules into infinite linear chains which are held together by electrostatic interactions with the potassium ions. The oxalate ion is planar, and the H–O–H angle of the water molecule is 107.9°±4.3°. The O–H distance is 0.963±0.029 A in a hydrogen bond of length 2.744±0.017 A, and the O–H···O angle is 169.1°±2.6°. The coordination of the water molecule is unusual with the two hydrogen atoms and two potassium ions lying almost in a plane around the water oxygen atom. A classification of the hydrogen‐bonded water molecules in hydrates with respect to their lone‐pair coordination reveals that K2C2O4·H2O may be the only reported structure of the type in which neither of the lone pairs of the hydrogen‐bonded water molecule is specifically directed despite the availability of metal ions in the structure.

93 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a new mathematical algorithm and software for computed tomographic (CT) reconstruction based on refraction contrast, which provides information on the deflection of the x-ray beam when penetrating through the object.
Abstract: Computed tomographic (CT) reconstruction technique is widely used in many fields of research. Commonly the CT-reconstruction is based on the x-ray absorption contrast. However, recently, methods for generating other x-ray contrasts have been developed. One of them is the refraction contrast which provides information on the deflection of the x-ray beam when penetrating through the object. This contrast has certain advantages and allows us to observe details invisible in the absorption images. Thus, CT based on the refraction contrast must have the same advantages. However, it requires a new mathematical algorithm and software. This letter is dedicated to the solution of the problem including theoretical consideration on the mathematical model which is the basis for the computer modeling and experimental realization of the technique. Actual experimental results together with the reconstructed images are presented and described.

80 citations