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121.
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123.
I. Soutar L. Swanson J. M. G. Cowie I. C. Barker N. J. Flint M. J. Conroy 《Macromolecular Symposia》1999,141(1):69-82
In this paper the use of two time-resolved luminescence techniques in the study of polymer behaviour is illustrated. Time-resolved anisotropy measurements, TRAMS, have been used to study macromolecular mobilities both in solution and bulk phases. The first use of TRAMS involving phosphorescent labels in the study of synthetic polymers is reported and the potential of the technique for future applications in polymer science is discussed. Time-resolved energy transfer has been used to study polymer compatibility and interdiffusion in blends of PS-PMMA. The data offer clear evidence of the fact that the local concentration of chain termini in phase-separated systems is enriched in the interphase regions compared to that in the two bulk phases of the blend. 相似文献
124.
Wavelet methods for image regularization offer a data-driven alternative to Gaussian smoothing in functional magnetic resonance (fMRI) analysis. Their impact has been limited by the difficulties in integrating regularization in the wavelet domain and inference in the image domain, precluding the probabilistic decision on which areas are activated by a task. Here we present an integrated framework for Bayesian estimation and regularization in wavelet space that allows the usual voxelwise hypothesis testing. This framework is flexible, being an adaptation to fMRI time series of a more general wavelet-based functional mixed-effect model. Through testing on a combination of simulated and real fMRI data, we show evidence of improved signal recovery, without compromising test accuracy in image space. 相似文献
125.
Joseph A Nielsen Pierre Lau Dragan Maric Jeffery L Barker Lynn D Hudson 《BMC neuroscience》2009,10(1):1-17
Background
While there is a general agreement that picture-plane inversion is more detrimental to face processing than to other seemingly complex visual objects, the origin of this effect is still largely debatable. Here, we address the question of whether face inversion reflects a quantitative or a qualitative change in processing mode by investigating the pattern of event-related potential (ERP) response changes with picture plane rotation of face and house pictures. Thorough analyses of topographical (Scalp Current Density maps, SCD) and dipole source modeling were also conducted.Results
We find that whilst stimulus orientation affected in a similar fashion participants' response latencies to make face and house decisions, only the ERPs in the N170 latency range were modulated by picture plane rotation of faces. The pattern of N170 amplitude and latency enhancement to misrotated faces displayed a curvilinear shape with an almost linear increase for rotations from 0° to 90° and a dip at 112.5° up to 180° rotations. A similar discontinuity function was also described for SCD occipito-temporal and temporal current foci with no topographic distribution changes, suggesting that upright and misrotated faces activated similar brain sources. This was confirmed by dipole source analyses showing the involvement of bilateral sources in the fusiform and middle occipital gyri, the activity of which was differentially affected by face rotation.Conclusion
Our N170 findings provide support for both the quantitative and qualitative accounts for face rotation effects. Although the qualitative explanation predicted the curvilinear shape of N170 modulations by face misrotations, topographical and source modeling findings suggest that the same brain regions, and thus the same mechanisms, are probably at work when processing upright and rotated faces. Taken collectively, our results indicate that the same processing mechanisms may be involved across the whole range of face orientations, but would operate in a non-linear fashion. Finally, the response tuning of the N170 to rotated faces extends previous reports and further demonstrates that face inversion affects perceptual analyses of faces, which is reflected within the time range of the N170 component. 相似文献126.
Richard Law Oliver Barker John J. Barker Thomas Hesterkamp Robert Godemann Ole Andersen Tara Fryatt Steve Courtney Dave Hallett Mark Whittaker 《Journal of computer-aided molecular design》2009,23(8):459-473
Fragment-based drug discovery (FBDD) represents a change in strategy from the screening of molecules with higher molecular
weights and physical properties more akin to fully drug-like compounds, to the screening of smaller, less complex molecules.
This is because it has been recognised that fragment hit molecules can be efficiently grown and optimised into leads, particularly
after the binding mode to the target protein has been first determined by 3D structural elucidation, e.g. by NMR or X-ray
crystallography. Several studies have shown that medicinal chemistry optimisation of an already drug-like hit or lead compound
can result in a final compound with too high molecular weight and lipophilicity. The evolution of a lower molecular weight
fragment hit therefore represents an attractive alternative approach to optimisation as it allows better control of compound
properties. Computational chemistry can play an important role both prior to a fragment screen, in producing a target focussed
fragment library, and post-screening in the evolution of a drug-like molecule from a fragment hit, both with and without the
available fragment-target co-complex structure. We will review many of the current developments in the area and illustrate
with some recent examples from successful FBDD discovery projects that we have conducted. 相似文献
127.
Chiral recognition and resolution of methanobenzazocines was investigated by HPLC using polysaccharide, Pirkle-type, native and derivatized β-cyclodextrin chiral stationary phases. Enantioseparation of phenyl substituted 2,6-methanobenzazocines was achieved with multiple chiral stationary phases throughout the classes described. Chiral resolution of the enantiomers of 1,5-methano-3-methyl-6-oxo-1,2,3,4,5,6-hexahydro-3-benzazocine was produced on both polysaccharide and Pirkle-type phases. In the case of 1,5-methano-3-methyl-6-phenyl-1,2,3,4,5,6-hexahydro-3-benzazocine only a dinitrophenyl substituted β-cyclodextrin produced a separation of enantiomers. 相似文献
128.
Experimental data for the photoisomerization of trans-stilbene (S(1)) in thermal bath gases at pressures up to 20 bar obtained previously by Meyer, Schroeder, and Troe (J. Phys. Chem. A 1999, 103, 10528-10539) are modeled by using a full collisional-reaction master equation that includes non-RRKM (Rice-Ramsperger-Kassel-Marcus) effects due to slow intramolecular vibrational energy redistribution (IVR). The slow IVR effects are modeled by incorporating the theoretical results obtained recently by Leitner et al. (J. Phys. Chem. A 2003, 107, 10706-10716), who used the local random matrix theory. The present results show that the experimental rate constants of Meyer et al. are described to within about a factor of 2 over much of the experimental pressure range. However, a number of assumptions and areas of disagreement will require further investigation. These include a discrepancy between the calculated and experimental thermal rate constants near zero pressure, a leveling off of the experimental rate constants that is not predicted by theory and which depends on the identity of the collider gas, the need to use rate constants for collision-induced IVR that are larger than the estimated total collision rate constants, and the choice of barrier-crossing frequency. Despite these unsettled issues, the theory of Leitner et al. shows great promise for accounting for possible non-RRKM effects in an important class of reactions. 相似文献
129.
Julio Garcia Michael Markl Susanne Schnell Bradley Allen Pegah Entezari Riti Mahadevia S. Chris Malaisrie Philippe Pibarot James Carr Alex J. Barker 《Magnetic resonance imaging》2014
Aims
The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method.Methods and Results
An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOAJSLD-2D and EOAJSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOACE) with the 2D PC-MRI velocity field and compared to the EOAJSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA = 0.78 cm2) and experimental measurement (EOAJSLD-4D = 0.78 ± 0.01 cm2) for peak velocities ranging from 0.9 to 3.7 m/s. In-vivo results showed good correlation and agreement between EOAJSLD-2D and EOACE (r = 0.91, p < 0.001; bias: − 0.01 ± 0.38 cm2; agreement limits: 0.75 to − 0.77 cm2), and between EOAJSLD-4D and EOACE (r = 0.95, p < 0.001; bias: − 0.09 ± 0.26 cm2; limits: 0.43 to − 0.62 cm2).Conclusion
This study demonstrates the feasibility of measuring EOAJSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOACE measurement variability. 相似文献130.
Leslie DC Li J Strachan BC Begley MR Finkler D Bazydlo LA Barker NS Haverstick DM Utz M Landers JP 《Journal of the American Chemical Society》2012,134(12):5689-5696
Combining DNA and superparamagnetic beads in a rotating magnetic field produces multiparticle aggregates that are visually striking, enabling label-free optical detection and quantification of DNA at levels in the picogram per microliter range. DNA in biological samples can be quantified directly by simple analysis of optical images of microfluidic wells placed on a magnetic stirrer without prior DNA purification. Aggregation results from DNA/bead interactions driven either by the presence of a chaotrope (a nonspecific trigger for aggregation) or by hybridization with oligonucleotides on functionalized beads (sequence-specific). This paper demonstrates quantification of DNA with sensitivity comparable to that of the best currently available fluorometric assays. The robustness and sensitivity of the method enable a wide range of applications, illustrated here by counting eukaryotic cells. Using widely available and inexpensive benchtop hardware, the approach provides a highly accessible low-tech microscale alternative to more expensive DNA detection and cell counting techniques. 相似文献