Search results for "magic"
showing 10 items of 160 documents
Precise measurement of 1H 90° pulse in solid-state NMR spectroscopy for complex and heterogeneous molecular systems
2007
The 90 degrees pulse calibration is essential in NMR spectroscopy to prevent artefacts in the liquid state or to enhance cross-polarization efficiency in the solid state. We verified pulse-angle (PA) errors due to circuit impedances in solid-state NMR and suggested a possible solution to prevent the inconvenience of PA errors. The classic pulse sequences used to calibrate (1)H 90 degrees pulse lengths by direct detection of protons or by cross-polarization were modified in order to replace single (1)H pulses with (1)H pulse trains. Pulse trains were found to decrease the effect of PA imperfections in the calibration of basic pulses (i.e. 90 degrees and 180 degrees ) for a number of organic …
Quantification and classification of high-resolution magic angle spinning data for brain tumor diagnosis.
2007
The goal of this work is to propose a complete protocol (preprocessing, processing and classification) for classifying brain tumors with proton high-resolution magic-angle spinning ((1)H HR-MAS) data. The different steps of the procedure are detailed and discussed. Feature extraction techniques such as peak integration, including also the automated quantitation method AQSES, were combined with linear (LDA) and non-linear (least-squares support vector machine or LS-SVM) classifiers. Classification accuracy was assessed using a stratified random sampling scheme. The results suggest that LS-SVM performs better than LDA while AQSES performs better than the standard peak integration feature extr…
Wellbeing, resilience, and coping: Are there differences between healthy older adults, adults with mild cognitive impairment, and adults with Alzheim…
2018
The changes that occur with cognitive impairment and Alzheimer's disease could affect psychological aspects unrelated to memory. The purpose of this study is to compare 32 healthy older adults, 31 amnestic mild cognitively impaired (aMCI) adults, and 32 patients diagnosed with Alzheimer's disease (AD), in order to determine whether there are differences in their psychological wellbeing, resilience, and coping strategies. Unifactorial MANOVAS and ANOVAS were performed to analyze the between-group differences. The results reveal that the AD group showed lower levels of resilience and orientation toward problem-solving and greater use of religious strategies. In addition, they had significantl…
Evolutionary Hysteresis and Ratchets in the Evolution of Periodical Cicadas
2019
It has been previously hypothesized that the perfectly synchronized mass emergence of periodical cicadas (Magicicada spp.) evolved as a result of a switch from size-based to age-based emergence. In the former case, cicada nymphs emerge immediately (at the first opportunity) on reaching maturity, whereas in the latter case, nymphs wait in order to emerge at a specific age. Here we use an individual-based model to simulate the cicada life cycle and to study the evolution of periodicity. We find that if age-based emergence evolves in a constant abiotic environment, it typically results in a population that is protoperiodic, and synchronous emergence of the whole population is not achieved. How…
Can a magic recipe foster university spin-off creation?
2015
This study examines factors that explain the creation of university spin-offs. The study focuses on mechanisms that technology transfer offices (TTOs) and universities employ to foster spin-offs. These mechanisms include technology transfer activities that support spin-offs, normative frameworks, support infrastructures (i.e., business incubators and science parks), and TTO staff's specialist technical skills. The analysis also differentiates between public and private universities. Spin-offs belong to one or more of the following groups: spin-offs with support from the university's TTO, spin-offs operating under a license agreement, and spin-offs in which the TTO or university holds equity…
Synthesis and Characterization of SiC/MC/C Ceramics (M = Ti, Zr, Hf) Starting from Totally Non-oxidic Precursors
2002
The reaction of poly(dimethylsilane) (PDMS) and poly(dimethylcarbosilane) (PCS) with bis(cyclopentadienyl)M dichloride Cp2MCl2 (M ) Ti, Zr, Hf) complexes has been used as a new route to obtain ceramic materials based on SiC-containing M. The reaction is completed at a relatively low temperature, 900 °C, yielding the corresponding amorphous SiC/MC ceramics which have been characterized by means of 29 Si MAS NMR. These amorphous materials have been treated at higher temperatures, 1350 °C, under a purified argon atmosphere, yielding partially crystallized products which have been studied by X-ray powder diffraction and 29 Si MAS NMR. The effect of the composition of the mixture of precursors is
H3PW12O40 supported on mesoporous MCM-41 and Al-MCM-41 materials: preparation and characterisation
2011
MCM-41 and Al–MCM-41 has been synthesized using cetyl-trimethylammonium bromide (CTAB) surfactant as template and adding the silica precursor to aqueous solutions containing CTAB. The obtained solids were calcined at 600 °C for 4 h. HPW heteropolyacid supported on the mesoporous were prepared using the incipient wetness method. The characterization of materials was performed by X-ray diffraction, Transmission Electron Microscopy, N2 adsorption, 29Si Cross Polarization–Magic Angle Spinning and 27Al MAS NMR. Results showed that the hexagonal structure is obtained in both cases. The Aluminium species are located inside an extra-framework. The impregnation reduces the surface area of the mesopo…
Low-temperature Ti-containing 3:2 and 2:1 mullite nanocrystals from single-phase gels
2007
Abstract TiO 2 -containig single-phase gels with (Al 2 O 3 + TiO 2 )/(SiO 2 ) molar ratios 3/2 and 2/1 were prepared by gelling mixtures of aluminium nitrate, tetraethylorthosilicate and titanium isopropoxide. Gels were fast heated at several temperatures up to 1100 °C. Dried and heated gels were characterized by differential thermal analysis (DTA), magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray powder diffraction (XRD), and scanning and transmission electron microscopies (SEM and TEM). Coupled DTA and XRD results of gels fast heated at 900 °C showed the crystallisation of two mullites as well as a small amount of alumina-silica spinel. 27 Al NMR spectra showed the format…
Gram-scale selective synthesis of WO3−x nanorods and (NH4)xWO3 ammonium tungsten bronzes with tunable plasmonic properties
2021
Localized surface plasmon resonance properties in unconventional materials like metal oxides or chalcogenide semiconductors have been studied for use in signal detection and analysis in biomedicine and photocatalysis. We devised a selective synthesis of the tungsten oxides WO3-x and (NH4)xWO3 with tunable plasmonic properties. We selectively synthesized WO3-x nanorods with different aspect ratios and hexagonal tungsten bronzes (NH4)xWO3 as truncated nanocubes starting from ammonium metatungstate (NH4)6H2W12O40·xH2O. Both particles form from the same nuclei at temperatures >200 °C; monomer concentration and surfactant ratio are essential variables for phase selection. (NH4)xWO3 was the prefe…
Influence of Whole-Body Dynamics on 15N PISEMA NMR Spectra of Membrane Proteins: A Theoretical Analysis
2009
AbstractMembrane proteins and peptides exhibit a preferred orientation in the lipid bilayer while fluctuating in an anisotropic manner. Both the orientation and the dynamics have direct functional implications, but motions are usually not accessible, and structural descriptions are generally static. Using simulated data, we analyze systematically the impact of whole-body motions on the peptide orientations calculated from two-dimensional polarization inversion spin exchange at the magic angle (PISEMA) NMR. Fluctuations are found to have a significant effect on the observed spectra. Nevertheless, wheel-like patterns are still preserved, and it is possible to determine the average peptide til…