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101.
102.
Stephen D. Mayhew Bradley J. Macintosh Sharon G. Dirckx Gian Domenico Iannetti Richard G. Wise 《Magnetic resonance imaging》2010
We investigate the relationship between the temporal variation in the magnitude of occipital visual evoked potentials (VEPs) and of haemodynamic measures of brain activity obtained using both blood oxygenation level dependent (BOLD) and perfusion sensitive (ASL) functional magnetic resonance imaging (fMRI). Volunteers underwent a continuous BOLD fMRI scan and/or a continuous perfusion-sensitive (gradient and spin echo readout) ASL scan, during which 30 second blocks of contrast reversing visual stimuli (at 4 Hz) were interleaved with 30 second blocks of rest (visual fixation). Electroencephalography (EEG) and fMRI were simultaneously recorded and following EEG artefact cleaning, VEPs were averaged across the whole stimulation block (120 reversals, VEP120) and at a finer timescale (15 reversals, VEP15). Both BOLD and ASL time-series were linearly modelled to establish: (1) the mean response to visual stimulation, (2) transient responses at the start and end of each stimulation block, (3) the linear decrease between blocks, (4) the nonlinear between-block variation (covariation with VEP120), (5) the linear decrease within block and (6) the nonlinear variation within block (covariation with VEP15). 相似文献
103.
Rony Sharon 《Optics Communications》2010,283(20):4122-6351
A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time. 相似文献
104.
Ashbrook SE Whittle KR Lumpkin GR Farnan I 《The journal of physical chemistry. B》2006,110(21):10358-10364
The yttrium local environment in the series of pyrochlores Y2Ti2-xSnxO7 was studied using 89Y NMR. Oxides with the pyrochlore structure exhibit a range of interesting physical and chemical properties, resulting in many technological applications, including the encapsulation of lanthanide- and actinide-bearing radioactive waste. The use of the nonradioactive Y3+ cation provides a sensitive probe for any changes in the local structure and ordering with solid solution composition, through 89Y (I = 1/2) NMR. We confirm that a single pyrochlore phase is formed over the entire compositional range, with Y found only on the eight-coordinated A site. A significant (approximately 15 ppm) chemical shift is observed for each Sn substituted into the Y second neighbor coordination environment. The spectral signal intensities of the possible combinations of Sn/Ti neighbors match those predicted statistically assuming a random distribution of Sn4+/Ti4+ on the six-coordinated pyrochlore B site. 相似文献
105.
This research proposes a mortality model with an age shift to project future mortality using principal component analysis (PCA). Comparisons of the proposed PCA model with the well-known models—the Lee-Carter model, the age-period-cohort model (Renshaw and Haberman, 2006), and the Cairns, Blake, and Dowd model—employ empirical studies of mortality data from six countries, two each from Asia, Europe, and North America. The mortality data come from the human mortality database and span the period 1970-2005. The proposed PCA model produces smaller prediction errors for almost all illustrated countries in its mean absolute percentage error. To demonstrate longevity risk in annuity pricing, we use the proposed PCA model to project future mortality rates and analyze the underestimated ratio of annuity price for whole life annuity and deferred whole life annuity product respectively. The effect of model risk on annuity pricing is also investigated by comparing the results from the proposed PCA model with those from the LC model. The findings can benefit actuaries in their efforts to deal with longevity risk in pricing and valuation. 相似文献
106.
Mark McCartney Sharon Gibson 《International Journal of Mathematical Education in Science & Technology》2013,44(8):992-998
A model for car following on a closed loop is defined. The stability of the solutions of the model is investigated by considering the evolution of the roots of the corresponding characteristic equation in the complex plane. The solution provides a motivation for investigating the behaviour of the roots of a simple class of algebraic equation. 相似文献
107.
Jun Liu Lingchao Cai Wei Sun Rujin Cheng Nanxi Wang Ling Jin Sharon Rozovsky Ian B. Seiple Lei Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19015-19019
Small‐molecule crosslinkers are invaluable for probing biomolecular interactions and for crosslinking mass spectrometry. Existing chemical crosslinkers target only a small selection of amino acids, while conventional photo‐crosslinkers target almost all residues non‐specifically, complicating data analysis. Herein, we report photocaged quinone methide (PQM)‐based crosslinkers that target nine nucleophilic residues through Michael addition, including Gln, Arg, and Asn, which are inaccessible to existing chemical crosslinkers. PQM crosslinkers were used in vitro, in Escherichia coli, and in mammalian cells to crosslink dimeric proteins and endogenous membrane receptors. The heterobifunctional crosslinker NHQM could crosslink proteins to DNA, for which few crosslinkers exist. The photoactivatable reactivity of these crosslinkers and their ability to target multiple amino acids will enhance the use of chemical crosslinking for studies of protein–protein and protein–DNA networks and for structural biology. 相似文献
108.
We present a strategy for the development of electron-proton density functionals in multicomponent density functional theory, treating electrons and selected nuclei quantum mechanically without the Born-Oppenheimer approximation. An electron-proton functional is derived using an explicitly correlated electron-proton pair density. This functional provides accurate hydrogen nuclear densities, thereby enabling reliable calculations of molecular properties. This approach is potentially applicable to relatively large molecular systems with key hydrogen nuclei treated quantum mechanically. 相似文献
109.
Dr. Lidia A. Maslovskaya Dr. Andrei I. Savchenko Prof. Elizabeth H. Krenske Dr. Sharon Chow Tina Holt Dr. Victoria A. Gordon Dr. Paul W. Reddell Carly J. Pierce Prof. Peter G. Parsons Prof. Glen M. Boyle Prof. Andrei G. Kutateladze Prof. Craig M. Williams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(51):11862-11867
Structurally unique halimanes EBC-232 and EBC-323, isolated from the Australian rainforest plant Croton insularis, proved considerably difficult to elucidate. The two diastereomers, which consist an unusual oxo-6,7-spiro ring system fused to a dihydrofuran, were solved by unification and consultation of five in silico NMR elucidation and prediction methods [i.e., ACDLabs, olefin strain energy (OSE), DP4, DU8+ and TD DFT CD]. Structure elucidation challenges of this nature are prime test case examples for empowering future AI learning in structure elucidation. 相似文献
110.
This special issue of Ambix brings together eight new studies on Humphry Davy together with an appreciation of the life and work of David Knight, much of whose scholarship was devoted to understanding Davy. Taken together they provide a much richer and more nuanced account of aspects of Davy’s life, showing how he and his work fitted into the very complex and difficult social, cultural and political contexts of the opening decades of the nineteenth century. Taking as our starting point Thomas Carlyle’s 1829 critique of modern science, in this introduction we weld together the themes that emerge from these papers, many of which ground their results in the project to publish Davy’s Letters. This project has provided evidence that helps us critique the disciplinary boundaries that led to Davy becoming seen mostly as a chemist, while his friend Samuel Taylor Coleridge has generally been categorised as a poet. Such boundaries are now breaking down fruitfully as these essays all illustrate in their different ways. A consequence of the new understandings being produced, is that we need to consider anew what constitutes chemistry and chemists, how reputations and commemorations are constructed, the role of audiences (especially women) in developing knowledge and the use of language and literature, which, among other things, are key elements linking chemistry with other parts of society and culture. Davy provides an excellent location by which to address the historical issues involved, giving us an opportunity to balance carefully these and other components (such as human agency) in understanding how knowledge is constructed. 相似文献