Search results for "FFR"
showing 10 items of 1798 documents
Tunable and reconfigurable microwave filter by use of a Bragg-grating-based acousto-optic superlattice modulator
2005
We present an all-optical novel configuration for implementing multitap transversal filters by use of a broadband source sliced by fiber Bragg grating arrays generated by propagating an acoustic wave along a strong uniform fiber Bragg grating. The tunability and reconfigurability of the microwave filter are demonstrated.
Neutron diffraction studies of the molecular compound [Co 2(bta)]n (H4bta =1,2,4,5-benzenetetracarboxylic acid): In the quest of canted ferromagnetism
2013
The exchange mechanism and magnetic structure of the organic-inorganic layered molecule-based magnet [Co2(bta)]n (1) (H 4bta =1,2,4,5-benzenetetracarboxylic acid) have been investigated through variable-temperature magnetic susceptibility measurements and supported with a series of neutron diffraction experiments. Cryomagnetic studies have shown an antiferromagnetic ordering at a transition temperature of 16 K that is followed by the appearance of a weak ferromagnetism below 11 K. The weak antiferromagnetic interlayer interaction plays an important role in this system in spite of the long interlayer separation. A ferromagnetic ordering is induced by applied magnetic fields greater than 1800…
Compact, cost-effective and field-portable microscope prototype based on MISHELF microscopy
2016
AbstractWe report on a reduced cost, portable and compact prototype design of lensless holographic microscope with an illumination/detection scheme based on wavelength multiplexing, working with single hologram acquisition and using a fast convergence algorithm for image processing. All together, MISHELF (initials coming from Multi-Illumination Single-Holographic-Exposure Lensless Fresnel) microscopy allows the recording of three Fresnel domain diffraction patterns in a single camera snap-shot incoming from illuminating the sample with three coherent lights at once. Previous implementations have proposed an illumination/detection procedure based on a tuned (illumination wavelengths centered…
Local structure of A-atom in ABO3 perovskites studies by RMC-EXAFS
2020
The measurements of Sr K-edge XAFS were performed under the approval of Proposal No. 97G042 of Photon Factory (KEK) and partially supported by the Research Grants of Hirosaki University. This work was supported by Bruce Ravel providing data for BTO. Boby Joseph acknowledges IISc Bangalore and ICTP Trieste for financial support through the award of the IISc-ICTP fellowship.
Syntheses and Structural Study of Novel Tetranuclear Bis(phenoxido)‐Bridged Cu II Metal–Organic Macrocycles
2012
Six new tetranuclear copper(II) complexes were prepared exploiting novel ditopic alkylenediamine-N,N,N′,N′-tetraphenolate ligands. The geometrical parameters of the compounds can be varied by introducing different solvents of crystallization into the lattice. The structures of all six complexes were determined from single-crystal X-ray diffraction analyses and the magnetic properties of the complexes were estimated by computational DFT calculations. The relationship between the magnetic exchange coupling constant (J) and the Cu–O–Cu angle (θ) in these bis(phenoxido)-bridged complexes was investigated and a magnetostructural correlation was established between J and the θ angle. All studied …
Commentaires sur la communication de Clément Lémelin : "l'offre d'éducation : coûts, productivité et efficacité"
1984
International audience
Synthetic Pathways for New Tubular Transition Metal Hydroxo- and Fluoro-Selenites: Crystal Structures ofM12(X)2(SeO3)8(OH)6(M=Co2+,Ni2+;X= OH−)
1996
The dumortierite-family structuresM12X2(SeO3)8(OH)6(M= Co2+and Ni2+;X= OH−and F−) have been synthesized. The crystal structures of the hydroxo-derivatives have been refined from X?ray powder diffraction data in the space groupP63mc(Z= 1) witha= 12.887(3) A andc= 4.981(4) A (M= Co2+,X= OH−or F−) anda= 12.704(5) A andc= 4.925(6) A (M= Ni2+,X= OH−or F−). Application of the Partial Charge Transference Model allows the understanding of the selenite derivatives crystal chemistry.
Strategies for structure solution and refinement of small organic molecules from electron diffraction data and limitations of the simulation approach
1999
In recent years, a series of non-linear optically active bis(benzylidene) ketones have been synthesized and investigated by electron crystallography. In most cases, structure refinement was possible by combining electron diffraction analysis and quantum-mechanical calculations with maximum-entropy methods. However, when the torsional angles between the phenyl rings and the C=C double bonds are strongly affected by the crystal field, this method fails because packing-energy calculations are not sufficiently sensitive. This problem can be solved by refining the approximate model with SHELXL, if the data set is sufficiently accurate and the model close to the correct structure. Here it is show…
Structure determination to calculate nonlinear optical coefficients in a class of organic material
1999
A class of molecules with intramolecular two-dimensional charge transfer upon excitation has been synthesized. It is expected that these materials should be prospective candidates for nonlinear optical (NLO) applications such as second harmonic (SHG) generation. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by x-ray methods, is a time-consuming and sometimes impossible ta…
ChemInform Abstract: Electron Crystallography and Organic Materials with Non-Linear Optical Properties
2010
Results of electron microscopic studies of crystal structures of a number of bis-benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non-linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main-chain NLO-active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO-coefficients, relating quantum-chemically calculated molecular first hyperpolarizability components to …