crystal, unit cell

2009 ◽  
pp. 223-223
Keyword(s):  
Unit Cell ◽  
Crystal Unit Cell

Guest Orientation in Uniplanar-Axial Polymer Host Films and in Co-Crystal Unit-Cell, Determined by Angular Distributions of Polarized Guest Fluorescence

2008 ◽  
Vol 41 (23) ◽  
pp. 9156-9164 ◽  
Author(s):  
Hideyuki Itagaki ◽  
Tomohiro Sago ◽  
Miho Uematsu ◽  
Genki Yoshioka ◽  
Andrea Correa ◽  
...  
Keyword(s):  
Unit Cell ◽  
Angular Distributions ◽  
Crystal Unit Cell ◽  
Polymer Host

Single scattering approximations: the domains of validity for structural analysis of protein crystals by electron diffraction

1978 ◽  
Vol 36 (1) ◽  
pp. 186-187
Author(s):  
Robert M. Glaeser ◽  
Bing K. Jap ◽  
Ming Hslu Ho
Keyword(s):  
Electron Diffraction ◽  
Cell Size ◽  
Materials Science ◽  
Single Scattering ◽  
Crystallographic Analysis ◽  
Unit Cell ◽  
Protein Crystals ◽  
Scattering Effect ◽  
Unit Cell Size ◽  
Crystal Unit Cell

Single scattering approximations (the kinematic and the weak phase object approx- imation), because of their simplicity, are perhaps the most attractive formulations for structure analysis by electron diffraction. In these approximations, the diffracted wave function is linearly related to the object potential. The validities of these approximations are, however, limited to very thin crystals at low resolution. In materials science the failure of the single scattering approximations and the impor- tance of the dynamical scattering effect have been well accepted. In biological science, the large unit cell size and the low atomic number (e.g. protein crystals) have lead some to believe that the dynamical scattering effect is insignificant for crystallographic analysis. Contrary to this belief, the number of dynamically interacting beams increases with the crystal unit cell size. It is important to note here that the dynamical scattering effect depends on the values of the excitation errors and on the magnitudes of the Fourier coefficients of the crystal potential.

Seminvariant density decomposition and connectivity analysis and their application to very low resolution macromolecular phasing

1999 ◽  
Vol 55 (5) ◽  
pp. 916-925 ◽  
Author(s):  
V. Y. Lunin ◽  
N. L. Lunina ◽  
A. G. Urzhumtsev
Keyword(s):  
Electron Density ◽  
Finite Subgroup ◽  
Unit Cell ◽  
High Electron ◽  
Low Resolution ◽  
Fourier Synthesis ◽  
Compact Region ◽  
Crystal Unit Cell

A low-resolution Fourier synthesis is thought to show a molecule as a compact region of a high electron density. As a consequence, the number of such regions, chosen at a proper cut-off level, should be equal to the number of molecules in the unit cell. This hypothesis may be used as a basis for selection criteria in multisolution ab initio phasing procedures. However, when working with a small number of reflections, this hypothesis may break down. The suggested Fourier-synthesis decomposition explains some reasons for failure and provides a connectivity-based procedure for the determination of macromolecular position in the crystal unit cell and the phasing of several low-resolution reflections. The simplest decomposition consists in separating the reflections into two sets according to whether their phases do or do not depend on a permitted origin shift. It is shown that the partial Fourier syntheses corresponding to these subsets are simply a half-sum and a half-difference of the initial electron-density distribution with its shifted copy. Therefore, they display the true images overlapped with the shifted ones (or with shifted and additionally flipped copies for the latter synthesis). The paper generalizes the decomposition for the case of a finite subgroup of the group of permitted origin shifts and reveals the role of one-phase seminvariants.

scholarly journals Inulin isoforms differ by repeated additions of one crystal unit cell

2014 ◽  
Vol 103 ◽  
pp. 392-397 ◽  
Author(s):  
Peter D. Cooper ◽  
Thomas G. Barclay ◽  
Milena Ginic-Markovic ◽  
Andrea R. Gerson ◽  
Nikolai Petrovsky
Keyword(s):  
Unit Cell ◽  
Crystal Unit Cell

On one possibility of determining the atom position in the crystal unit cell

2013 ◽  
Vol 40 (4) ◽  
pp. 83-85
Author(s):  
P. N. Zhukova ◽  
T. H. Le ◽  
V. A. Nasonova ◽  
N. N. Nasonov ◽  
V. I. Sergienko
Keyword(s):  
Unit Cell ◽  
Crystal Unit Cell ◽  
Atom Position

Albertiniite, Fe2+(SO3)·3H2O, a new sulfite mineral species from the Monte Falò Pb-Zn mine, Coiromonte, Armeno Municipality, Verbano Cusio Ossola Province, Piedmont, Italy

2016 ◽  
Vol 80 (6) ◽  
pp. 985-994 ◽  
Author(s):  
P. Vignola ◽  
G. D. Gatta ◽  
N. Rotiroti ◽  
P. Gentile ◽  
F. Hatert ◽  
...  
Keyword(s):  
Structure Refinement ◽  
Unit Cell ◽  
Iron Sulfides ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Calculated Density ◽  
Cell Parameters ◽  
Quartz Veins ◽  
Crystal Unit Cell ◽  
Brittle Fractures

AbstractAlbertiniite, Fe2+(SO3)·3H2O, is a new Fe2+ sulfite trihydrate, related chemically to gravegliaite. It occurs at the Monte Falò Pb-Zn mine near Coiromonte, in the Armeno Municipality, Verbano–Cusio–Ossola Province, Italy. It is an intermediate product of oxidation between iron sulfides and sulfates, forming monoclinic, colourless to pale yellow, transparent crystals with a vitreous lustre. The mineral occurs associated with stolzite, pyromorphite, hinsdalite, plumbogummite, gibbsite, scheelite and jarosite on brittle fractures of quartz veins or chlorite-schist. Albertiniite is optically biaxial (+) with 2V(meas) ≈ 40° and 2V(calc) = 66°. The measured refractive indices, using sodium light (589 nm) are: α = 1.612(2)°, β = 1.618(2)° and γ = 1.632(2)°. The optical axis plane is parallel to the perfect {010} cleavage plane. It is non-fluorescent under shortwave (254 nm) or longwave (366 nm) ultraviolet light. The calculated density is 2.469 g cm–3 (from the crystal-structure refinement), or 2.458 g cm–3 (from the chemical analysis and the single-crystal unit-cell parameters). The empirical formula is (average of 16 spots and based on 3 anhydrous oxygen apfu) (Ca0.001Mg0.001Na0.003)∑1.061(S0.971O3)·2.84H2O, with the H2O content calculated by difference to 100 wt.%. Albertiniite is monoclinic, with space group P21/n. Its unit-cell parameters are: a = 6.633(1), b = 8.831(1), c = 8.773(1) Å, β = 96.106(8)° and V = 511.0(1) Å3, with Z = 4. The eight strongest measured lines in the powder X-ray diffraction pattern are [d in Å, (I/I0), (hkl)]: 4.072 (100) (1̄11), 3.539 (93) (1̄12), 5.533 (27) (1̄01), 6.167 (14) (011), 2.830 (14) (211), 4.998 (14) (101), 4.353 (12) (111) and 3.897 (12) (012). The mineral, which has been approved by the CNMNC, number IMA2015-004, is named albertiniite in honour of Claudio Albertini, an Italian mineral collector and expert in the systematic mineralogy of the Alps and pegmatites.

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