221,650 research outputs found
Disorder in Extra-Large Pore Zeolite ITQ-33 Revealed by Single Crystal XRD
No full textThe single crystal of the extra-large pore zeolite, ITQ-33, was obtained and used to explore its crystal structure details. The ITQ-33 structure was found to be disordered with the columnar periodic building unit, explaining the morphology changes upon the different Si/Ge ratio, and the formation of the hierarchical structure from assembling of ITQ-33 nanofibers.Chemistry, MultidisciplinaryCrystallographyMaterials Science, MultidisciplinarySCI(E)EI0ARTICLE104168-41711
A High-Resolution Crystal Structure that Reveals Molecular Details of Target Recognition by the Calcium-Dependent Lipopeptide Antibiotic Laspartomycin C
No full textThe calcium-dependent antibiotics (CDAs) are an important emerging class of antibiotics. The crystal structure of the CDA laspartomycin C in complex with calcium and the ligand geranyl-phosphate at a resolution of 1.28 Å is reported. This is the first crystal structure of a CDA bound to its bacterial target. The structure is also the first to be reported for an antibiotic that binds the essential bacterial phospholipid undecaprenyl phosphate (C55-P). These structural insights are of great value in the design of antibiotics capable of exploiting this unique bacterial target
Impact of calcium on struvite crystal size, shape and purity.
No full textStruvite precipitation occurs spontaneously in wastewater treatment plants under conditions that are influenced by many factors including concentration of , and ions, pH, temperature and mixing energy. These parameters are often difficult to control and as a result struvite generates problems of scale deposits in areas such as pipes and recirculation pumps. At the same time, struvite is considered as a potentially marketable product as an alternative fertiliser. For those two reasons, it has become important to study the principles of struvite precipitation, and to assess the parameters controlling struvite crystallisation. In the present work the influence of ions on the precipitation of struvite was investigated in aqueous solution containing , and ions in a molar ratio 1:2:2 at room temperature and constant pH. Different laboratory experiments have been used to assess the effects of Ca2+ ions on size, shape, and purity of the crystals formed. Tools used include particle size analysis, X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDS). The experimental results showed that the presence of calcium in the media can affect significantly struvite crystal growth, and the characteristics of the crystal produced
Thin-film photonic crystal LEDs with enhanced directionality
No full textThe use of photonic crystals for light extraction from light-emitting diodes (LEDs)
gives the possibility to shape the farfield emission pattern. This is of particular interest
for étendue-limited LED applications that require a more directional farfield than state-
of-the-art Lambertian emitters. However, the application of a photonic crystal in a LED
results in directional emission only if the photonic crystal and the distribution of guided
modes in the LED are tuned correctly. In this thesis, red- and blue-emitting thin-film
PhC-LEDs in the AlGaInP and InGaN material systems were modelled, designed,
fabricated and characterized. The first experimental results show that light extraction
with photonic crystals from AlGaInP thin-film LEDs several microns thick is neither
directional nor more efficient than state-of-the-art LEDs with a rough surface structure.
Directional light extraction for AlGaInP PhC-LEDs is for the first time demonstrated in
much thinner devices where the photonic crystal light extraction of guided modes is
combined with the resonant-cavity effect. In an attempt to approach the ideal PhC-LED,
strong photonic crystal farfield shaping is demonstrated in InGaN thin-film LEDs of
sub-micron thickness. Analysis of their spectral farfields unexpectedly shows that high
order diffraction contributes significantly to the light extraction efficiency if the mode
absorption is sufficiently low. It is also demonstrated that directional photonic crystal
light extraction is possible in InGaN thin-film LEDs several microns thick. The
directionality stems from the modulation of the spontaneous emission caused by the
proximity of the active region to the bottom mirror. Two new concepts for enhanced
light extraction and high directionality are presented: Photonic crystals with two
dominating lattice constants are found to outperform conventional photonic crystal
LEDs. An alternative approach is the dielectric PhC-LED - FDTD simulations show
that the high extraction efficiency of LEDs with surface roughness is combined with the
higher directionality of photonic crystal light extraction
On the Crystal Structure of Azafullerene (C 59 N) 2
No full textSynchrotron X-ray powder diffraction data of the nitrogen-substituted fullerene solid with stoichiometry C59N point to a monoclinic crystal structure comprising dimeric molecular, (C59N)(2), units
Towards novel C–N materials
No full textTwo modifications of the novel guanidinium dicyanamide have been obtained by means of ion-exchange reaction in aqueous or methanolic solution. The hygroscopic compounds were characterized by solution state NMR, mass spectrometry and vibrational spectroscopy. The crystal structures of the polymorphs were elucidated by means of single-crystal X-ray diffraction at 200 K {β-[C(NH2)3][N(CN)2]: Pna21, Z=8, a=1373.1(3), b=495.5(1), c=1802.9(4) pm, U=1226.7(4)×106 pm3; α-[C(NH2)3][N(CN)2]: P21/c, Z=8, a=1924.9(4), b=496.0(1), c=1372.4(3) pm, β=110.46(3)°, U=1227.5(4)×106 pm3} and were found to be largely equivalent in terms of the overall assembly of the molecular ions. Thermodynamic and kinetic aspects of the temperature behaviour of the polymorphs, which is characterized by a succession of thermal events in the temperature region between 240 and 440 K, were assessed by means of temperature-dependent X-ray powder diffraction and thermal analysis. Due to the chemical composition of the novel dicyanamide (C3N6H6), which is formally identical with that of melamine C3N3(NH2)3, and its thermal reactivity, which is represented by the facile conversion into melamine around 400 K, guanidinium dicyanamide may be ideally suited as a molecular precursor for chemical approaches toward highly condensed graphitic carbon nitride materials
Hanging the harp on the willow tree: music and national identity in postcolonial Ireland
No full textAn inquiry into how music served as a nation building tool in the early decades of the Irish Free State.M.A.Includes bibliographical referencesby Crystal N. Galyea
Nogo Receptor crystal structures with a native disulfide pattern suggest a novel mode of self-interaction
No full textThe Nogo Receptor (NgR) is a glycophosphatidylinositol-anchored cell-surface protein and is a receptor for three myelin-associated inhibitors of regeneration: myelin-associated glycoprotein, Nogo66 and oligodendrocyte myelin glycoprotein. In combination with different co-receptors, NgR mediates signalling that reduces neuronal plasticity. The available structures of the NgR ligand-binding leucine-rich repeat (LRR) domain have an artificial disulfide pattern owing to truncated C-terminal construct boundaries. NgR has previously been shown to self-associate via its LRR domain, but the structural basis of this interaction remains elusive. Here, crystal structures of the NgR LRR with a longer C-terminal segment and a native disulfide pattern are presented. An additional C-terminal loop proximal to the C-terminal LRR cap is stabilized by two newly formed disulfide bonds, but is otherwise mostly unstructured in the absence of any stabilizing interactions. NgR crystallized in six unique crystal forms, three of which share a crystal-packing interface. NgR crystal-packing interfaces from all eight unique crystal forms are compared in order to explore how NgR could self-interact on the neuronal plasma membrane
A monohydrate pseudopolymorph of 3,4-dihydroxybenzophenone and the role of water in the crystal assembly of benzophenones
No full textDuring a polymorphism screening of hydroxybenzophenone derivatives, a monohydrate pseudopolymorph of (3,4-dihydroxyphenyl)(phenyl)methanone, C(13)H(10)O(3)center dot H(2)O, (I), was obtained. Structural relationships and the role of water in crystal assembly were established on the basis of the known anhydrous form [Cox, Kechagias & Kelly (2008). Acta Cryst. B64, 206-216]. The crystal packing of (I) is stabilized by classical intermolecular O-H...O hydrogen bonds, generating a three-dimensional network.FAPEMIGCNPqFAPESPCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)FINEPCT-INFRAPIBIC/CNPq/UNIFAL-M
Fast algorithms for liquid crystal modelling
No full textWe review different modeling and computational methods to determine the Q-tensor representation of the director field alignment in the absence of defects. Under this condition it is possible to represent the reorientation dynamics of the director field as the motion of the Q-tensor over an invariant manifold. This new representation allows us to develop very accurate codes for the alignment that are orders of magnitude faster than an equivalent full Q-tensor code. We illustrate this principle by discussing the case of a pure liquid crystal with or without flow and the case of a liquid crystal doped with fixed metallic nano-inclusions
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