scholarly journals FOX: A friendly tool to solve nonmolecular structures from powder diffraction

2005 ◽  
Vol 20 (4) ◽  
pp. 359-365 ◽  
Author(s):  
Radovan Černý ◽  
Vincent Favre-Nicolin
Keyword(s):  
Powder Diffraction ◽  
Structural Model ◽  
A Priori ◽  
Three Dimensional ◽  
Building Blocks ◽  
Global Optimization Algorithm ◽  
Structural Units ◽  
Coordination Polyhedra ◽  
Extended Solids ◽  
Framework Compounds

Structural characterization from powder diffraction of compounds not containing isolated molecules but three-dimensional infinite structure (alloys, intermetallics, framework compounds, extended solids) by direct space methods has been largely improved in the last 15 years. The success of the method depends very much on a proper modeling of the structure from building blocks. The modeling from larger building blocks improves the convergence of the global optimization algorithm by a factor of up to 10. However, care must be taken about the correctness of the building block, like its rigidity, deformation, bonding distances, and ligand identity. Dynamical occupancy correction implemented in the direct space program FOX has shown to be useful when merging excess atoms, and even larger building blocks like coordination polyhedra. It also allows joining smaller blocks into larger ones in the case when the connectivity was not a priori evident from the structural model. We will show in several examples of nonmolecular structures the effect of the modeling by correct structural units.

scholarly journals Na3Co2(As0.52P0.48)O4(As0.95P0.05)2O7

2013 ◽  
Vol 69 (12) ◽  
pp. i85-i86 ◽  
Author(s):  
Youssef Ben Smida ◽  
Abderrahmen Guesmi ◽  
Mohamed Faouzi Zid ◽  
Ahmed Driss
Keyword(s):  
Solid State ◽  
Solid State Reaction ◽  
Title Compound ◽  
General Position ◽  
Structural Model ◽  
Three Dimensional ◽  
The Other ◽  
Coordination Polyhedra ◽  
Bond Valence Sum ◽  
Full Occupancy

The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. It is isostructural with Na3Co2AsO4As2O7. The framework shows the presence of CoX22O12(X2 is statistically disordered with As0.95P0.05) units formed by sharing corners between Co1O6octahedra andX22O7groups. These units form layers perpendicular to [010]. Co2O6octahedra andX1O4(X1 = As0.54P0.46) tetrahedra form Co2X1O8chains parallel to [001]. Cohesion between layers and chains is ensured by theX22O7groups, giving rise to a three-dimensional framework with broad tunnels, running along thea- andc-axis directions, in which the Na+ions reside. The two Co2+cations, theX1 site and three of the seven O atoms lie on special positions, with site symmetries 2 andmfor the Co,mfor theX1, and 2 andm(× 2) for the O sites. One of two Na atoms is disordered over three special positions [occupancy ratios 0.877 (10):0.110 (13):0.066 (9)] and the other is in a general position with full occupancy. A comparison between structures such as K2CdP2O7, α-NaTiP2O7and K2MoO2P2O7is made. The proposed structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number.

scholarly journals The Polyvalent Gold Nanoparticle Conjugate—Materials Synthesis, Biodiagnostics, and Intracellular Gene Regulation

MRS Bulletin ◽  
2010 ◽  
Vol 35 (7) ◽  
pp. 532-539 ◽  
Author(s):  
Chad A. Mirkin
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Directed Assembly ◽  
Building Blocks ◽  
Nanometer Scale ◽  
Materials Synthesis ◽  
Plasmon Resonances ◽  
Detection Capabilities ◽  
Extended Materials ◽  
Potential Use

AbstractAdvances in nanoscale directed assembly strategies have enabled researchers to analogize atomic assembly via chemical reactions and nanoparticle assembly, creating a new nanoscale “periodic table.” We are just beginning to realize the nanoparticle equivalents of molecules and extended materials and are currently developing the ground rules for creating programmable nanometer-scale coordination environments. The ability to create a diverse set of nanoscale architectures from one class of nanoparticle building blocks would allow for the synthesis of designer materials, wherein the physical properties of a material could be predicted and controlled a priori. Our group has taken the first steps toward this goal and developed a means of creating tailorable assembly environments using DNA-nanoparticle conjugates. These nanobioconjugates combine the discrete plasmon resonances of gold nanoparticles with the synthetically controllable and highly selective recognition properties of DNA. Herein, we elucidate the beneficial properties of these materials in diagnostic, therapeutic, and detection capabilities and project their potential use as nanoscale assembly agents to realize complex three-dimensional nanostructures.

scholarly journals Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison

2016 ◽  
Vol 72 (8) ◽  
pp. 1159-1162 ◽  
Author(s):  
Alagappa Rammohan ◽  
James A. Kaduk
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Density Functional ◽  
Three Dimensional ◽  
Carboxylate Group ◽  
Powder Diffraction Data ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Graph Set

The crystal structure of anhydrous tripotassium citrate, [K3(C6H5O7)]n, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The three unique potassium cations are 6-, 8-, and 6-coordinate (all irregular). The [KOn] coordination polyhedra share edges and corners to form a three-dimensional framework, with channels running parallel to thecaxis. The only hydrogen bond is an intramolecular one involving the hydroxy group and the central carboxylate group, with graph-set motifS(5).

scholarly journals Crystal structure of trirubidium citrate from laboratory X-ray powder diffraction data and DFT comparison

2017 ◽  
Vol 73 (2) ◽  
pp. 250-253 ◽  
Author(s):  
Alagappa Rammohan ◽  
James A. Kaduk
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Density Functional ◽  
Three Dimensional ◽  
Powder Diffraction Data ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Methylene Groups ◽  
Graph Set

The crystal structure of trirubidium citrate, 3Rb+·C6H5O73−, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The two independent Rb+cations are seven- and eight-coordinate, with bond-valence sums of 0.99 and 0.92 valence units. The coordination polyhedra share edges and corners to form a three-dimensional framework. The only hydrogen bond is an intramolecular one between the hydroxy group and the central carboxylate, with graph setS(5). The hydrophobic methylene groups lie in pockets in the framework.

scholarly journals Structures of dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), from laboratory X-ray powder diffraction data and DFT calculations

2020 ◽  
Vol 76 (10) ◽  
pp. 1566-1571
Author(s):  
Andrew J. Cigler ◽  
James A. Kaduk
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Metal Ion ◽  
Density Functional ◽  
Three Dimensional ◽  
Hydroxyl Group ◽  
Powder Diffraction Data ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Carboxylate Oxygen

The crystal structures of the isostructural compounds dipotassium rubidium citrate monohydrate, K2RbC6H5O7(H2O), and potassium dirubidium citrate monohydrate, KRb2C6H5O7(H2O), have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The compounds are isostructural to K3C6H5O7(H2O) and Rb3C6H5O7(H2O), but exhibit different degrees of ordering of the K and Rb cations over the three metal-ion sites. The K and Rb site occupancies correlate well to both the bond-valence sums and the DFT energies of ordered cation systems. The MO6 and MO7 coordination polyhedra share edges to form a three-dimensional framework. The water molecule acts as a donor in two strong charge-assisted O—H...O hydrogen bonds to carboxylate groups. The hydroxyl group of the citrate anion forms an intramolecular hydrogen bond to one of the central carboxylate oxygen atoms.

A Reissner’s Mixed Variational Theorem Applied to Vibration Analysis of Multilayered Shell

1999 ◽  
Vol 66 (1) ◽  
pp. 69-78 ◽  
Author(s):  
E. Carrera
Keyword(s):  
Normal Stress ◽  
Structural Model ◽  
Dynamic Equilibrium ◽  
A Priori ◽  
Three Dimensional ◽  
Single Layer ◽  
Transverse Normal Stress ◽  
Variational Theorem ◽  
Reissner’S Mixed Variational Theorem ◽  
Static Conditions

A comprehensive model of anisotropic multilayered double curved shells fulfilling a priori the interlaminar continuity requirements for the transverse shear and transverse normal stress as well as the static conditions on the bounding surfaces of the shell is developed in this paper. To this end, Reissner’s mixed variational theorem is employed to derive the equations governing the dynamic equilibrium and compatibility of each layer, while the interlaminar continuity conditions are used to drive the equations at the multilayered level. No assumptions have been made concerning the terms of type thickness to radii shell ratio h/R. Classical displacement formulations and related equivalent single layer equations have been derived for comparison purposes. Comparison of frequency predictions based upon the presented structural model with a number of results spread throughout the specialized literature and obtained via other models reveals that this advanced model provides results in excellent agreement with the ones based on three-dimensional elasticity theory, and better as compared to the ones violating the interlaminar stress continuity requirements and/or transverse normal stress and related effects.

scholarly journals Spatial Agents for Geological Surface Modelling

2021 ◽  
Author(s):  
Eric A. de Kemp
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Building Blocks ◽  
Linear Interpolation ◽  
Sparse Data ◽  
Spatial Gradient ◽  
Orientation Data ◽  
Spatial Continuity ◽  
Gradient Information ◽  
Complex Geology

Abstract. Semi-autonomous software entities called spatial agents can be programmed to perform spatial and property interrogation functions, estimations and construction operations for simple graphical objects, that may be usable in building three-dimensional geological surfaces. These surfaces form the building blocks from which full topological models are built and may be useful in sparse data environments, where ancillary or a-priori information is available. Critical in developing natural domain models is the use of gradient information. Increasing the density of spatial gradient information (fabric dips, fold plunges, local or regional anisotropies) from geologic feature orientations (planar and linear) is key to more accurate geologic modelling, and core to the functions of spatial agents presented herein. This study, for the first time, examines the potential use of spatial agents to increase these types of gradient constraints in the context of the Loop 3D project (loop3d.org) in which new complementary methods are being developed for modelling complex geology for regional applications. The Spatial Agent codes presented may act to densify and supplement gradient and on contact control points used in LoopStructural (www.github.com/Loop3d/LoopStructural) and Map2Loop (https://doi.org/10.5281/zenodo.4288476). Spatial agents are used to represent common geological data constraints such as interface locations and gradient geometry, and simple but topologically consistent triangulated meshes. Spatial agents can potentially be used to develop surfaces that conform to reasonable geological patterns of interest, provided they are embedded with behaviors that are reflective of the knowledge of their geological environment. Initially this would involve detecting simple geological constraints; locations, trajectories and trends of geological interfaces. Local and global eigenvectors enable spatial continuity estimates which can reflect geological trends with rotational bias using a quaternion implementation. Spatial interpolation of structural geology orientation data with spatial agents employ a range of simple nearest neighbour to inverse distance weighted (IDW) and quaternion based spherical linear interpolation (SLERP) schemes. This simulation environment implemented in NetLogo is potentially useful for complex geology - sparse data environments where extension, projection and propagation functions are needed to create more realistic geological forms.

scholarly journals Lath Martensite Microstructure Modeling: A High-Resolution Crystal Plasticity Simulation Study

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 691
Author(s):  
Francisco-José Gallardo-Basile ◽  
Yannick Naunheim ◽  
Franz Roters ◽  
Martin Diehl
Keyword(s):  
High Resolution ◽  
Mechanical Behavior ◽  
Crystal Plasticity ◽  
Lath Martensite ◽  
Three Dimensional ◽  
Building Blocks ◽  
Quantitative Agreement ◽  
Carbon Steels ◽  
Plastic Behavior ◽  
Austenitic Phase

Lath martensite is a complex hierarchical compound structure that forms during rapid cooling of carbon steels from the austenitic phase. At the smallest, i.e., ‘single crystal’ scale, individual, elongated domains, form the elemental microstructural building blocks: the name-giving laths. Several laths of nearly identical crystallographic orientation are grouped together to blocks, in which–depending on the exact material characteristics–clearly distinguishable subblocks might be observed. Several blocks with the same habit plane together form a packet of which typically three to four together finally make up the former parent austenitic grain. Here, a fully parametrized approach is presented which converts an austenitic polycrystal representation into martensitic microstructures incorporating all these details. Two-dimensional (2D) and three-dimensional (3D) Representative Volume Elements (RVEs) are generated based on prior austenite microstructure reconstructed from a 2D experimental martensitic microstructure. The RVEs are used for high-resolution crystal plasticity simulations with a fast spectral method-based solver and a phenomenological constitutive description. The comparison of the results obtained from the 2D experimental microstructure and the 2D RVEs reveals a high quantitative agreement. The stress and strain distributions and their characteristics change significantly if 3D microstructures are used. Further simulations are conducted to systematically investigate the influence of microstructural parameters, such as lath aspect ratio, lath volume, subblock thickness, orientation scatter, and prior austenitic grain shape on the global and local mechanical behavior. These microstructural features happen to change the local mechanical behavior, whereas the average stress–strain response is not significantly altered. Correlations between the microstructure and the plastic behavior are established.

Applications of 3D printing in critical care medicine: A scoping review

2021 ◽  
pp. 0310057X2097665
Author(s):  
Natasha Abeysekera ◽  
Kirsty A Whitmore ◽  
Ashvini Abeysekera ◽  
George Pang ◽  
Kevin B Laupland
Keyword(s):  
Critical Care ◽  
Scoping Review ◽  
A Priori ◽  
Three Dimensional ◽  
Critical Care Medicine ◽  
Future Research ◽  
Care Practice ◽  
Three Dimensional Printing ◽  
Wide Range ◽  
Dimensional Printing

Although a wide range of medical applications for three-dimensional printing technology have been recognised, little has been described about its utility in critical care medicine. The aim of this review was to identify three-dimensional printing applications related to critical care practice. A scoping review of the literature was conducted via a systematic search of three databases. A priori specified themes included airway management, procedural support, and simulation and medical education. The search identified 1544 articles, of which 65 were included. Ranging across many applications, most were published since 2016 in non – critical care discipline-specific journals. Most studies related to the application of three-dimensional printed models of simulation and reported good fidelity; however, several studies reported that the models poorly represented human tissue characteristics. Randomised controlled trials found some models were equivalent to commercial airway-related skills trainers. Several studies relating to the use of three-dimensional printing model simulations for spinal and neuraxial procedures reported a high degree of realism, including ultrasonography applications three-dimensional printing technologies. This scoping review identified several novel applications for three-dimensional printing in critical care medicine. Three-dimensional printing technologies have been under-utilised in critical care and provide opportunities for future research.

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