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61.
Spectral analysis of multichannel MRS data 总被引:2,自引:0,他引:2
Sandgren N Stoica P Frigo FJ Selén Y 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,175(1):79-91
The use of phased-array receive coils is a well-known technique to improve the image quality in magnetic resonance imaging studies of, e.g., the human brain. It is common to incorporate proton (1H) magnetic resonance spectroscopy (MRS) experiments in these studies to quantify key metabolites in a region of interest. Detecting metabolites in vivo is often difficult, requiring extensive scans to achieve signal-to-noise ratios (SNR) that provide suitable diagnostic results. Combining the MR absorption spectra obtained from several receive coils is one possible approach to increase the SNR. Previous literature does not give a clear overview of the wide range of possible approaches that can be used to combine MRS data from multiple detector coils. In this paper, we consider the multicoil MRS approach and introduce several signal processing tools to address the problem from different nonparametric, semiparametric, and parametric perspectives, depending on the amount of available prior knowledge about the data. We present a numerical study of these tools using both simulated 1H MRS data and experimental MRS data acquired from a 3T MR scanner. 相似文献
62.
Petre Birza 《Journal of Molecular Spectroscopy》2005,229(2):276-282
The rotationally resolved electronic spectrum of a vibrational band in the transition of the cumulene carbon chain C3H2 was measured in the 625 nm region in a supersonic discharge using cw cavity ring down spectroscopy. The rotational structure was analysed using a conventional Hamiltonian for an asymmetric top molecule, and the constants A′, B′, and C′ in the upper state were determined. The observed band is assigned to a combination of a1 and b2 vibrations with the frequency around 2000 cm−1. The geometries in the 1A1, 1A2, 1B1 states and the intersection point between the latter two were obtained using ab initio calculations. The effective structure in the measured vibrational level of the 1A2 state was inferred from the determined constants. 相似文献
63.
64.
Anca Paun Irina Zarafu Miron T. Caproiu Constantin Draghici Maria Maganu Ani I. Cotar Mariana C. Chifiriuc Petre Ionita 《Comptes Rendus Chimie》2013,16(7):665-671
Starting from benzocaine, a well-known anaesthetic, ten derivatives were synthesized and characterized by UV–vis, IR, NMR, and elemental analysis. Most of the compounds contain residues with recognized biological activity, like nicotinic acid (vitamin B3 or PP), biotin (vitamin B7 or H), lipoic acid (thioctic acid), adamantine, as well as other residues of crown-ether type, benzofurazane, naphtylurea, di- and tri-nitrobenzene, and a nitroxide radical. The biological evaluation of the obtained compounds included hydrophobicity (lipophobicity) assay, total antioxidant and microbiological activity tests. 相似文献
65.
Simona Somacescu Viorica Parvulescu Jose Maria Calderon-Moreno Soong-Hyuck Suh Petre Osiceanu Bao-Lian Su 《Journal of nanoparticle research》2012,14(6):1-17
The design of cell-based bioreactors for inorganic particles formation requires both a better understanding of the underlying processes and the identification of most suitable organisms. With this purpose, the process of Au3+ incorporation, intracellular reduction, and Au0 nanoparticle release in the culture medium was compared for four photosynthetic microorganisms, Klebsormidium flaccidum and Cosmarium impressulum green algae, Euglena gracilis euglenoid and Anabaena flos-aquae cyanobacteria. At low gold content, the two green algae show maintained photosynthetic activity and recovered particles (ca. 10?nm in size) are similar to internal colloids, indicating a full biological control over the whole process. In similar conditions, the euglenoid exhibits a rapid loss of biological activity, due to the absence of protective extracellular polysaccharide, but could grow again after an adaptation period. This results in a larger particle size dispersity but larger reduction yield. The cyanobacteria undergo rapid cell death, due to their prokaryotic nature, leading to high gold incorporation rate but poor control over released particle size. Similar observations can be made after addition of a larger gold salt concentration when all organisms rapidly die, suggesting that part of the process is not under biological control anymore but also involves extracellular chemical reactions. Overall, fruitful information on the whole biocrystallogenesis process is gained and most suitable species for further bioreactor design can be identified, i.e., green algae with external coating. 相似文献
66.
67.
Petre Makreski Tom
e Run
evski Gligor Jovanovski 《Journal of Raman spectroscopy : JRS》2011,42(1):72-77
The characterization and spectra–structure correlations of grossular and uvarovite garnets by Raman and infrared (IR) spectroscopy were carried out. Attention was focused on the explanation of the spectral differences between both minerals from structural and compositional points of view because they are isomorphous and share the general chemical formula [Ca3Y2(SiO4)3; Y = Al (grossular) and Cr (uvarovite)]. It was established that the prominent spectral differences are mainly due to the presence of various Y3+ cations and the possibility for their interchange. It was found that the substitution of Al3+ with Cr3+ promotes blue shifting of the high‐energy Raman bands (SiO4 stretchings) and red shifting of the corresponding IR bands. This peculiar observation is explained by the introduction of two different effects that promote band shifting in opposite directions—the effect of different cation crystal field stabilization energies versus the effect of different cation masses and radii. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
68.
Take σ to be a continuous semiflow on the locally compact metric space Θ, and let {A(θ)}θ∈Θ be a family of (possibly unbounded) densely defined closed operators on the Banach space X. 相似文献
69.
Petre?Birtea Ioan?Ca?uEmail author Tudor?S.?Ratiu Murat?Turhan 《Journal of Nonlinear Science》2012,22(2):187-212
The stability for all generic equilibria of the Lie–Poisson dynamics of the
\mathfrakso(4)\mathfrak{so}(4) rigid body dynamics is completely determined. It is shown that for the generalized rigid body certain Cartan subalgebras
(called of coordinate type) of
\mathfrakso(n)\mathfrak{so}(n) are equilibrium points for the rigid body dynamics. In the case of
\mathfrakso(4)\mathfrak{so}(4) there are three coordinate type Cartan subalgebras whose intersection with a regular adjoint orbit gives three Weyl group
orbits of equilibria. These coordinate type Cartan subalgebras are the analogues of the three axes of equilibria for the classical
rigid body in
\mathfrakso(3)\mathfrak{so}(3). In addition to these coordinate type Cartan equilibria there are others that come in curves. 相似文献
70.
Br?ndu?a-Alina Petre Martina Ulrich Mihaela Stumbaum Bogdan Bernevic Adrian Moise Gerd D?ring Michael Przybylski 《Journal of the American Society for Mass Spectrometry》2012,23(11):1831-1840
Tyrosine nitration in proteins occurs under physiologic conditions and is increased at disease conditions associated with oxidative stress, such as inflammation and Alzheimer??s disease. Identification and quantification of tyrosine-nitrations are crucial for understanding nitration mechanism(s) and their functional consequences. Mass spectrometry (MS) is best suited to identify nitration sites, but is hampered by low stabilities and modification levels and possible structural changes induced by nitration. In this insight, we discuss methods for identifying and quantifying nitration sites by proteolytic affinity extraction using nitrotyrosine (NT)-specific antibodies, in combination with electrospray-MS. The efficiency of this approach is illustrated by identification of specific nitration sites in two proteins in eosinophil granules from several biological samples, eosinophil-cationic protein (ECP) and eosinophil-derived neurotoxin (EDN). Affinity extraction combined with Edman sequencing enabled the quantification of nitration levels, which were found to be 8?% and 15?% for ECP and EDN, respectively. Structure modeling utilizing available crystal structures and affinity studies using synthetic NT-peptides suggest a tyrosine nitration sequence motif comprising positively charged residues in the vicinity of the NT- residue, located at specific surface- accessible sites of the protein structure. Affinities of Tyr-nitrated peptides from ECP and EDN to NT-antibodies, determined by online bioaffinity- MS, provided nanomolar KD values. In contrast, false-positive identifications of nitrations were obtained in proteins from cystic fibrosis patients upon using NT-specific antibodies, and were shown to be hydroxy-tyrosine modifications. These results demonstrate affinity- mass spectrometry approaches to be essential for unequivocal identification of biological tyrosine nitrations. 相似文献