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61.
Chin CL Wehrli FW Hwang SN Jaggard DL Hackney DB Wehrli SW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,160(1):20-25
It is well known that one-dimensional (1D) q-space imaging allows retrieval of structural information at cellular resolution. Here we demonstrate by simulation that boundary morphology of structured materials can be derived from 2D q-space mapping. Based on a finite-difference model for restricted diffusion, 2D q-space maps obtained from water diffusion inside apertures at various levels of asperity were simulated. The results indicate that the observed ring patterns (diffraction minima) reveal the boundary profiles of the apertures but become blurred in the case of significant variation in aperture size. For uniform size distribution of apertures, a quantitative measure of surface roughness can be established by means of spatial autocorrelation analysis. The results suggest that 2D q-space imaging may allow probing of the boundary morphology of structured materials and possibly biological cells. 相似文献
62.
N-tert-Butylimidozirconocene (Cp2Zr=Nt-Bu) and its analogue (ebthi)Zr=NAr (ebthi = ethylenebis(tetrahydroindenyl), Ar = 2,6-dimethylphenyl) undergo overall cycloaddition reactions at ambient temperature with epoxides that lack accessible beta-hydrogens. The process results in addition of the Zr=N bond to an epoxide C-O bond, leading to azazirconacyclopentanes. The regio- and stereochemistry of the products implicate a stepwise mechanism, with the intermediacy of zwitterions having substantial carbocation character at the substituted carbon of the ring-opened epoxide-derived fragment. The azametallacycles undergo facile cleavage to beta-amino alcohols upon addition of mild acid. 相似文献
63.
Reddick WE Russell JM Glass JO Xiong X Mulhern RK Langston JW Merchant TE Kun LE Gajjar A 《Magnetic resonance imaging》2000,18(7):787-793
Medulloblastoma is the most common malignant brain tumor in children, and approximately seventy percent of average-risk patients will achieve long-term survival. Craniospinal irradiation (CSI), combined with chemotherapy and surgery, is currently the mainstay of treatment but places children who survive at risk for serious neurocognitive sequelae. These sequelae are intensified with a younger age at treatment, greater elapsed time following treatment, and an increased radiation dose. Many newer treatment approaches have attempted to address this problem by reducing the dose of the CSI component of radiation therapy while maintaining the current survival rates. This study evaluates longitudinal MR imaging during therapy to assess the impact of the two CSI doses (conventional [36 Gy] and reduced [23.4 Gy]) on normal appearing white matter volumes (NAWMV) evaluated in a single index slice. Twenty-six children and young adults at least three years of age enrolled on an institutional protocol for newly diagnosed, previously untreated primary medulloblastoma had at least four MR examinations over a minimum nine month period following CSI. These serial volumes were evaluated as a function of time since CSI in three analyses: 1) all subjects, 2) subjects stratified by age at CSI, and 3) subjects stratified by CSI dose. The first analysis demonstrated that medulloblastoma patients treated with CSI have a significant loss of NAWMV in contradistiction to normally expected maturation. Stratifying the patients by age at CSI found no significant differences in the rate of NAWMV loss. The final analysis stratified the patients by CSI dose and revealed that the rate of NAWMV loss was 23% slower in children receiving reduced-dose. Serial quantitative MR measures of NAWMV may provide a neuroanatomical substrate for assessing functional impact of CSI on normal brain function following treatment for medulloblastoma. 相似文献
64.
The synthesis of an air‐stable series of Pd0 complexes with unsymmetric bidentate N‐pyridine N‐heterocyclic carbene ligands has been described. The carbenes were generated by synthesis of the silver(I) complexes from the imidazolium salts, followed by transmetallation of the C‐N ligands to obtain the target electron‐rich zerovalent palladium compounds. The bidentate coordination behaviour of the ligands was confirmed by 1H, 13C NMR and X‐ray spectroscopy. The complexes are active precatalysts for the selective transfer semihydrogenation of alkynes to Z‐alkenes, with selectivities up to 99%. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
65.
66.
Declan Williams Suzanne Ackloo Peihong Zhu Peter Bowden Kenneth R. Evans Christina L. Addison Chris Lock John G. Marshall 《Analytical and bioanalytical chemistry》2010,396(3):1223-1247
The endogenous peptides of human serum may have regulatory functions, have been associated with physiological states, and
their modifications may reveal some mechanisms of disease. In order to correlate levels of specific peptides with disease
alongside internal standards, the polypeptides must first be reliably extracted and identified. Endogenous blood peptides
can be effectively enriched by precipitation of the serum with organic solvents followed by selective extraction of peptides
using aqueous solutions modified with organic solvents. Polypeptides on filter paper were assayed with Coomasie brilliant
blue binding. The polypeptides were resolved by detergent tricine polyacrylamide electrophoresis and visualized by diamine
silver staining. Peptides in the extracts were collected by C18 and analyzed by matrix-assisted laser desorption/ionization
and liquid chromatography–electrospray ionization–tandem mass spectrometry (MS/MS) quadrupole time-of-flight MS/MS. Peptides
were resolved as multiple isotopic peaks in MS mode with mass deviation of 0.1 Da or less and similar accuracy for fragments.
The sensitivity of MS and MS/MS analysis was estimated to be in the picomolar range or less. The peptide composition of the
extracts was dependent on solvent formulation. Multiple peptides from apolipoproteins, complement proteins, coagulation factors,
and many others were identified by X!Tandem with high mass accuracy of peptide ions and fragments from collision-induced dissociation.
Many previously unreported posttranslational modifications of peptides including phosphorylations, oxidations, glycosylations,
and others were detected with high mass accuracy and may be of clinical importance. About 4,630 redundant peptides were identified
with 99% confidence separately, and together some 1,251 distinct proteins were identified with 99% confidence or greater using
the Paragon algorithm. 相似文献
67.
Jarrod J. M. Amoore Dr. Suzanne M. Neville Dr. Boujemaa Moubaraki Dr. Simon S. Iremonger Dr. Keith S. Murray Prof. Jean‐François Létard Dr. Cameron J. Kepert Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(6):1973-1982
We previously reported the dinuclear material [FeII2(ddpp)2(NCS)4] ? 4 CH2Cl2 ( 1? 4 CH2Cl2; ddpp=2,5‐di(2′,2′′‐dipyridylamino)pyridine) and its partially desolvated analogue ( 1? CH2Cl2), which undergo two‐ and one‐step spin‐crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one‐ or two‐step spin transition can be specifically targeted. The chloroform clathrate 1? 4 CHCl3 undergoes a relatively abrupt one‐step SCO, in which the two equivalent FeII sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1? 4 CHCl3 to form 1? 3 CHCl3 and 1? CHCl3 occurs through single‐crystal‐to‐single‐crystal processes (monoclinic C2/c to P21/n to P21/n) in which the two equivalent FeII sites become inequivalent sites within the dinuclear molecule of each phase. Both 1? 3 CHCl3 and 1? CHCl3 undergo one‐step spin transitions, with the former having a significantly higher SCO temperature than 1? 4 CHCl3 and the latter, and each has a broader SCO transition than 1? 4 CHCl3, attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials through reversibly resolvating the partially desolvated material with chloroform to produce the original one‐step SCO, or with dichloromethane to produce a two‐step SCO reminiscent of that seen for 1? 4 CH2Cl2. Furthermore, we investigate the light‐induced excited spin state trapping (LIESST) effect on 1? 4 CH2Cl2 and 1? CH2Cl2 and observe partial LIESST activity for the former and no activity for the latter. 相似文献
68.
We study numerically the formation of long-lived transient shear bands during shear startup within two models of soft glasses (a simple fluidity model and an adapted "soft glassy rheology" model). The degree and duration of banding depends strongly on the applied shear rate, and on sample age before shearing. In both models the ultimate steady flow state is homogeneous at all shear rates, consistent with the underlying constitutive curve being monotonic. However, particularly in the soft glassy rheology case, the transient bands can be extremely long lived. The banding instability is neither "purely viscous" nor "purely elastic" in origin, but is closely associated with stress overshoot in startup flow. 相似文献
69.
Fielding SM 《Physical review letters》2011,107(25):258301
We study the linear instability with respect to necking of a filament of polymeric fluid undergoing uniaxial extension. Contrary to the widely discussed Considère criterion, we find the onset of instability to relate closely to the onset of downward curvature in the time (and so strain) evolution of the zz component of the molecular strain, for extension along the z axis. In establishing this result numerically across five of the most widely used models of polymer rheology, and by analytical calculation, we argue it to apply generically. Particularly emphasized is the importance of polymer chain stretching in partially mitigating necking. We comment finally on the relationship between necking and the shape of the underlying steady state constitutive curve for homogeneous extension. 相似文献
70.