1,721,186 research outputs found
Relazione del lavoro commissionato dalla ditta Jasper, svolto sui campioni di acido ialuronico in presenza di arginina : metodi utilizzati e risultati ottenuti
No full textMOBILITY, MICROSTRUCTURE AND MRI. DTI WITHOUT A DTI BLACK BOX: THE ART OF MAKING DO.
No full textBecause of its non invasive nature, NMR is a unique tool for studying the
microstrusture of biological and material samples. This is usually done by monitoring
the diffusion coefficients and relaxation times, whose behavior is related to the
translational and rotational random molecular motion of the system components. These
parameters report on motion on very different time scales, thus providing structural
information at a microscopic scale well beyond the usual image resolution. However,
while relaxation-weighted images are relatively straightforward to record and analyze,
the study of diffusion through MRI calls for an higher level of complexity from both a
theoretical and instrumental point of view and it is nowadays well established in the
form of diffusion tensor imaging (DTI), a technique introduced by Basser et al. in 1994
[1]. Although software modules exist that alleviate the tedious task of setting all the
parameters for the DTI sequence in newer instruments or medical scanners, our old
spectrometer - a 4.7 Tesla Bruker AM WB equipped with a PFG drive unit for
microimaging - did not offer the "turnkey” DT-MRI Bruker acquisition interface. We
got round this by implementing a DTI acquisition module and analyzing the raw data
with an open source DTI reconstruction software [2]. Our experience led us to elaborate
some of the theoretical and methodological basic concepts of DTI, summarized in the
following steps: i) Theoretical basis and assumptions of the equations that lead to the
true and apparent calculation of the diffusion coefficient(s) [3]; ii) Acquisition scheme:
a diffusion-weighted preparation module based on stimulated echo (STEAM) to provide
long diffusion times with minimal T2 relaxation [4] prior to and independent of the
imaging scheme; iii) DTI scheme: the amount of diffusion weighting and at least six not
collinear PFG orientations (icosahedral geometry) to estimate the six independent
elements of the symmetric diffusion tensor; iv) the corrections for cross-terms
interactions [5]; v) reduction of eddy currents that generate image artifacts; vi) diffusion
tensor reconstruction from DTI raw data, providing information on sample
microstructure and architecture for each voxel: mean diffusivity; anisotropy indices and
fiber orientation mapping; vii) Phantoms to test and validate the whole procedure:
isotropic (water, BSA) and anisotropic (fibers and celery) at different anisotropy degre
Magnetic Resonance Imaging of molecular transport in living Morning Glory stems.
Full text linkMRI was applied to investigate the transport pathways in Morning Glory plant stems. The study was carried out on living plants without affecting their integrity. The architecture of a dicotyledonous plant was deeply characterized: the root system structure and the vascular bundle location were identified, the presence of central voids caused by cell maturation and loss were observed in the stem. Molecular transport components were recognized, by observing the concentration profile of a tracer, which changed with time after its absorption by the plant roots. MRI analysis revealed the presence of an axial transport as the progress of the tracer front through the vascular bundles and a radial molecular transport from the vascular bundles toward the surface of the stem. As a result, the tracer molecular transport formed the parabolic tracer front (PTF). A model was built up through the analysis of the PTF that consisted of an axial front at the peak position and a radial front at the width of the parabolic tail. PTF analysis revealed differences between the tracer transport velocities in the axial and the radial directions in the plant stem. The model revealed that the width of the parabolic tail reflected the magnitudes of diffusion and permeation of the tracer in the plant stem
Nuclear Magnetic Resonance of 129Xe and 1H as a probe for the characterization of void space in human myoglobin isoforms in solution
No full textSolid state and microscopy NMR study of the chemical constituents of Afzelia Cuanzensis seeds
No full textMulti-echo, chemical shift selective, and 3D NMR imaging at microscopy resolution, and CP MAS 13C NMR spectroscopy have been applied to the chemistry study of oil in oil-rich seeds of Afzelia cuanzensis, a tropical plant belonging to the Leguminosae taxum Caesalpinoideae or Caesalpinaceae
Detection and clustering of light charged particles via system identification techniques
No full text1H and 13C NMR study of some polychlorobuta‐1,3‐diene derivatives
No full textBecause of the upsurge of interest in polychlorobuta-1,3-diene derivatives as uncommon contaminants
in underground water, seven congeners, the three pentachloro- and four tetrachloro- [(Z)- and (E)-1,1,3,4-
tetrachloro-, 1,1,4,4-tetrachloro- and (Z,Z)-1,2,3,4-tetrachloro]buta-1,3-dienes, were synthesized and their 1H and
13C NMR chemical shifts, nJ(1H,1H) and nJ(13C,1H) coupling constants were measured. The 13C NMR spectra
were recorded in perdeuteroacetone with and without proton decoupling. In addition, to assign the 13C NMR
spectrum of 1,1,2,4,4-pentachlorobuta-1,3-diene, a 2D-INADEQUATE 13C experiment was performed. The present
results were compared with literature data on organochlorine compounds and possible conformations are discussed
NMR and chemical studies of the morphologically different parts of the olive fruit (Olea europea Linn)
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