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991.
Marro KI Lee D Shankland EG Mathis CM Hayes CE Amara CE Kushmerick MJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,195(1):67-75
The limited bandwidths of volume selective RF pulses in localized in vivo MRS experiments introduce spatial artifacts that complicate spectral quantification of J-coupled metabolites. These effects are commonly referred to as a spatial interference or "four compartment" artifacts and are more pronounced at higher field strengths. The main focus of this study is to develop a generalized approach to numerical simulations that combines full density matrix calculations with 3D localization to investigate the spatial artifacts and to provide accurate prior knowledge for spectral fitting. Full density matrix calculations with 3D localization using experimental pulses were carried out for PRESS (TE=20, 70 ms), STEAM (TE=20, 70 ms) and LASER (TE=70 ms) pulse sequences and compared to non-localized simulations and to phantom solution data at 4 T. Additional simulations at 1.5 and 7 T were carried out for STEAM and PRESS (TE=20 ms). Four brain metabolites that represented a range from weak to strong J-coupling networks were included in the simulations (lactate, N-acetylaspartate, glutamate and myo-inositol). For longer TE, full 3D localization was necessary to achieve agreement between the simulations and phantom solution spectra for the majority of cases in all pulse sequence simulations. For short echo time (TE=20 ms), ideal pulses without localizing gradients gave results that were in agreement with phantom results at 4 T for STEAM, but not for PRESS (TE=20). Numerical simulations that incorporate volume localization using experimental RF pulses are shown to be a powerful tool for generation of accurate metabolic basis sets for spectral fitting and for optimization of experimental parameters. 相似文献
992.
Alexandre Tamion Frédéric Ott Pierre-Emmanuel Berche Etienne Talbot Catherine Bordel Didier Blavette 《Journal of magnetism and magnetic materials》2008
An experimental and numerical study of the magnetization in (Fe 3 nm/Dy 2 nm) multilayers is presented. The samples were thermally evaporated under ultra-high vacuum at two different substrate temperatures, 320 and 570 K. In order to get the magnetization depth profile of these transition metal/rare earth (TM/RE) multilayers, a fine investigation of the structural, chemical, and magnetic properties was carried out. The samples were studied by X-ray reflectivity (XRR), high resolution transmission electron microscopy (HRTEM), conversion electron Mössbauer spectrometry (CEMS), SQUID magnetometry and polarized neutron reflectivity (PNR). Magnetization profiles were obtained by Monte Carlo simulations to support the PNR fits. The key role of the crystalline structure is emphasized by magnetic depth profile measurements performed using polarized neutron reflectometry. The antiparallel configuration of Fe and Dy layers’ magnetizations was evidenced, as well as the perpendicular magnetic anisotropy (PMA), especially in the case of the sample prepared at 570 K. 相似文献
993.
The amount of acoustic information that native and non-native listeners need for syllable identification was investigated by comparing the performance of monolingual English speakers and native Spanish speakers with either an earlier or a later age of immersion in an English-speaking environment. Duration-preserved silent-center syllables retaining 10, 20, 30, or 40 ms of the consonant-vowel and vowel-consonant transitions were created for the target vowels /i, I, eI, epsilon, ae/ and /a/, spoken by two males in /bVb/ context. Duration-neutral syllables were created by editing the silent portion to equate the duration of all vowels. Listeners identified the syllables in a six-alternative forced-choice task. The earlier learners identified the whole-word and 40 ms duration-preserved syllables as accurately as the monolingual listeners, but identified the silent-center syllables significantly less accurately overall. Only the monolingual listener group identified syllables significantly more accurately in the duration-preserved than in the duration-neutral condition, suggesting that the non-native listeners were unable to recover from the syllable disruption sufficiently to access the duration cues in the silent-center syllables. This effect was most pronounced for the later learners, who also showed the most vowel confusions and the greatest decrease in performance from the whole word to the 40 ms transition condition. 相似文献
994.
Michèle S. Titcombe Michael J. Ward & Mary Catherine Kropinski 《Studies in Applied Mathematics》2000,105(2):165-190
Low Reynolds number fluid flow past a cylindrical body of arbitrary shape in an unbounded, two-dimensional domain is a singular perturbation problem involving an infinite logarithmic expansion in the small parameter ε, representing the Reynolds number. We apply a hybrid asymptotic–numerical method to compute the drag coefficient, C D and lift coefficient C L to within all logarithmic terms. The hybrid method solution involves a matrix M , depending only on the shape of the body, which we compute using a boundary integral method. We illustrate the hybrid method results on an elliptic object and on a more complicated profile. 相似文献
995.
Jeffrey K. S. Wan Marilena Radoiu Ivan Kalatchev M. Catherine Depew 《Research on Chemical Intermediates》2000,26(9):931-939
Since the granting of our first US patent on microwave induced catalytic decomposition of PCBs some 18 years ago, microwave
technology has slowly begun to attract some industrial attention in the last few years. There was no doubt that microwaves
had been applied to facilitate the conventional bleaching process of wood pulps in the past but with little or no success.
The myth that microwaves can be regarded and manipulated as a rapid heat source probably caused most of the failures of unsuccessful
microwave applications. It is therefore necessary to understand the real potential of microwaves as an energy source and to
identify the many critical electromagnetic properties of the load (chemical systems), before a final choice of a proper microwave
system be designed and installed. In this preliminary report, we demonstrate the real potential of pulsed microwave radiation
for non-alkaline bleaching of mechanical pulps. Typically, very high consistency TMP up to 93% can be treated by pulsed microwave
in the order of 90 seconds with an average increase of 20 to 25 points in brightness. 相似文献
996.
Catherine E. Housecroft Dorn M. Nixon Arnold L. Rheingold 《Journal of Cluster Science》2001,12(1):89-98
The pentaruthenium boride cluster [Ru5(CO)15B]- has been prepared from [Ru6(CO)17B]- but is unstable. The Ru5(CO)15B-core can be stabilized in the form of [Ru5(CO)15BAuPR3] (R=Ph or o-tolyl). Addition of [(Ph3PAu)3O][BF4] to [Ru5(CO)15B]- gives the trigold derivative [Ru5(CO)14B(AuPPh3)3] which possesses an novel core structure. 相似文献
997.
T-z. Peng Qiong Cheng Catherine F. Yang 《Analytical and bioanalytical chemistry》2001,370(8):1082-1086
The adsorptive properties and electrochemical behavior of ketoconazole, an oral anti-fungal agent, are demonstrated at a glassy carbon electrode. The adsorption of the compound obeys the Frumkin isotherm with an interaction factor (α) of 0.985 and adsorptive coefficient (β) of 1.98 × 106 L mol–1. The Gibbs energy of adsorption (ΔG) is –3.59 × 104 J mol–1 at 25?°C. A very sensitive electroanalytical method has been developed for determination of the drug with a detection limit of 4.0 × 10–11 mol L–1. Relationships between stripping current and concentration of ketoconazole were linear in the range 10–6–10–10 mol L–1 with different preconcentration periods. The method has been used to measure the ketoconazole content of tablets. 相似文献
998.
Catherine Greenhill 《Linear and Multilinear Algebra》1999,46(3):213-244
We describe a polynomial-time algorithm for recognising the exterior square of a matrix. The approach involves manipulation of the equations which relate the entries of a matrix and the entries of its exterior square. Conditions are given which are necessary and sufficient for two matrices to have the same exterior square. The definition of the exterior square of a matrix, and the algorithm used to recognise one, are both easily extended to matrix groups. 相似文献
999.
Raquel Gutirrez-Climente Margaux Clavi Jrmie Gouyon Giang Ngo Yoann Ladner Pascal Etienne Pascal Dumy Pierre Martineau Martine Pugnire Catherine Perrin Gilles Subra Ahmad Mehdi 《Molecules (Basel, Switzerland)》2021,26(19)
Ordered mesoporous materials and their modification with multiple functional groups are of wide scientific interest for many applications involving interaction with biological systems and biomolecules (e.g., catalysis, separation, sensor design, nano-science or drug delivery). In particular, the immobilization of enzymes onto solid supports is highly attractive for industry and synthetic chemistry, as it allows the development of stable and cheap biocatalysts. In this context, we developed novel silylated amino acid derivatives (Si-AA-NH2) that have been immobilized onto SBA-15 materials in biocompatible conditions avoiding the use of toxic catalyst, solvents or reagents. The resulting amino acid-functionalized materials (SBA-15@AA) were characterized by XRD, TGA, EA, Zeta potential, nitrogen sorption and FT-IR. Differences of the physical properties (e.g., charges) were observed while the structural ones remained unchanged. The adsorption of the enzyme lysozyme (Lyz) onto the resulting functionalized SBA-15@AA materials was evaluated at different pHs. The presence of different functional groups compared with bare SBA-15 showed better adsorption results, for example, 79.6 nmol of Lyz adsorbed per m2 of SBA-15@Tyr compared with the 44.9 nmol/m2 of the bare SBA-15. 相似文献
1000.
The Human Melanocyte as a Particular Target for UVA Radiation and an Endpoint for Photoprotection Assessment 总被引:2,自引:0,他引:2
Laurent Marrot Jean-Philippe Belaidi Jean-Roch Meunier Philippe Perez Catherine Agapakis-Causse 《Photochemistry and photobiology》1999,69(6):686-693
The induction of DNA breaks by UVA (320-400 nm) in the nucleus of normal human melanocytes in culture was investigated using single cell gel electrophoresis, also called the comet assay. Endogenous pigment and/or melanin-related molecules were found to enhance DNA breakage: comets were more intense in melanocytes than in fibroblasts, in cells with high melanin content or after stimulation of melanogenesis by supplying tyrosine in the culture medium. After UVA doses where strong comets were observed, neither cytotoxicity nor stimulation of tyrosinase activity were detected. However, the accumulation of p53 protein suggested that cells reacted to genotoxic stress under these experimental conditions. The same approach was used to compare two sunscreens with identical sun protection factors but different UVA protection factors. The results presented in this paper suggest that human melanocytes may be used as a target cell to evidence broadspectrum photoprotection. Moreover, these data appear to be helpful in getting a better understanding of the role of sunlight in the initiating steps of melanocyte transformation. 相似文献