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排序方式: 共有100条查询结果,搜索用时 46 毫秒
61.
MacKay Cameron; McKee Sean; Mulholland Anthony J. 《IMA Journal of Applied Mathematics》2006,71(5):670-691
** Email: ajm{at}maths.strath.ac.uk Particle dispersion from a high chimney is considered and anexpression for the subsequent concentration of the particulatedeposited on the ground is derived. We consider the generalcase wherein the effects of both diffusion and convection onthe steady state ground concentration of particulate are incorporated.Two key parameters emerge from this analysis: the ratio of diffusionto convection and the nondimensionalised surface mass transferrate. We also solve the inverse problem of recovering thesetwo parameters given the boundary concentration profile andprovide an estimate of the concentration flux above the chimneystack. 相似文献
62.
Jacqueline C.S. WooD.Bruce MacKay 《Tetrahedron letters》2003,44(14):2881-2883
We have devised a novel strategy for the total synthesis of the manzacidins. Our approach utilizes an isothiourea iodocyclization strategy to directly form the heterocyclic core, and in the process induce stereoselectivity at the quaternary center. We have found that cyclization can be achieved using an isothiourea as the nucleophilic partner. Cyclization proceeds smoothly using IBr at low temperature, affording an advanced intermediate along our proposed route to manzacidin A in 92% yield. We have demonstrated the scope of the reaction by preparing several cyclic isothioureas, including an intermediate on our proposed route for the synthesis of manzacidin D. 相似文献
63.
It is proved that the polaronic and bipolaronic structures found in the adiabatic Holstein model at large electron-phonon coupling by Aubry, Abramovici, and Raimbault survive under connection of the electrons to a low-temperature heat bath, uniformly in the size of the system. Bounds are computed for one-dimensional nearest neighbor chains, and some sample solutions are continued numerically. 相似文献
64.
A 48-echo pulse sequence with five different echo-spacing combinations was examined to determine how one can most effectively measure the T2 relaxation characteristics of cerebral tissue containing a long T2 component. For each scan, the first 32 echoes had an echo spacing of 10 ms, while the spacing for Echoes 33-48 (DeltaTE2) was 10, 20, 30, 40 or 50 ms. In an in vivo study using 10 normal volunteers, it was found that the resolution of T2 distribution peaks for both myelin water (approximately 20 ms) and intracellular/extracellular (IE) water (approximately 80 ms) improved as DeltaTE2 increased. The geometric mean T2 values of the main peak agreed within the error for all DeltaTE2 values. A phantom study simulated T2 relaxation distributions that are expected in the brains of patients with demyelinating diseases. For phantoms in which the T2 values of the IE and lesion (200-500 ms) water compartments were separated by at least a factor of 3, each compartment in the distribution was better resolved when DeltaTE2=40 or 50 ms. On the basis of these results, we recommend the use of extended DeltaTE2 values for imaging patients with lesions, without the risk of losing valuable short T2 information. 相似文献
65.
Cheran LE Cheung S Al Chawaf A Ellis JS Belsham DD MacKay WA Lovejoy D Thompson M 《The Analyst》2007,132(3):242-255
Kelvin and acoustic fields of high-frequency have been employed in the non-invasive investigation of immortalized hypothalamic neurons, in order to assess their response to different concentrations of specific drugs, toxins, a stress-reducing hormone and neurotrophic factors. In an analytical systems biology approach, this work constitutes a first study of living neuron cultures by scanning Kelvin nanoprobe (SKN) and thickness shear mode (TSM) acoustic wave techniques. N-38 hypothalamic mouse neurons were immobilized on the gold electrode of 9 MHz TSM acoustic wave devices and gold-coated slides for study by SKN. The neurons were exposed to the neurochemicals betaseron, forskolin, TCAP, and cerebrolysin. Signals were collected with the TSM in real-time mode, and with the SKN in scanning and real-time modes, as the drugs were applied at biologically significant concentrations. With the TSM, for all drugs, some frequency and resistance shifts were in the same direction, contrary to normal functioning for this type of instrument. Possible mechanisms are presented to explain this behaviour. An oscillatory signal with periodicity of approximately 2 min was observed for some neuron-coated surfaces, where the amplitude of these oscillations was altered upon application of certain neurotrophic factors. These two new techniques present novel and non-invasive electrodeless methods for detecting changes at the cellular level caused by a variety of neuroactive compounds, without killing or destroying the neurons. 相似文献
66.
Yihsuan S. Tsai Alexander Scherl Jason L. Shaw C. Logan MacKay Scott A. Shaffer Patrick R. R. Langridge-Smith David R. Goodlett 《Journal of the American Society for Mass Spectrometry》2009,20(11):2154-2166
We present a precursor ion independent top-down algorithm (PIITA) for use in automated assignment of protein identifications
from tandem mass spectra of whole proteins. To acquire the data, we utilize data-dependent acquisition to select protein precursor
ions eluting from a C4-based HPLC column for collision induced dissociation in the linear ion trap of an LTQ-Orbitrap mass
spectrometer. Gas-phase fractionation is used to increase the number of acquired tandem mass spectra, all of which are recorded
in the Orbitrap mass analyzer. To identify proteins, the PIITA algorithm compares deconvoluted, deisotoped, observed tandem
mass spectra to all possible theoretical tandem mass spectra for each protein in a genomic sequence database without regard
for measured parent ion mass. Only after a protein is identified, is any difference in measured and theoretical precursor
mass used to identify and locate post-translation modifications. We demonstrate the application of PIITA to data generated
via our wet-lab approach on a Salmonella typhimurium outer membrane extract and compare these results to bottom-up analysis. From these data, we identify 154 proteins by top-down
analysis, 73 of which were not identified in a parallel bottom-up analysis. We also identify 201 unique isoforms of these
154 proteins at a false discovery rate (FDR) of <1%. 相似文献
67.
We generalise the classical Transition by Breaking of Analyticity for the class of Frenkel–Kontorova models studied by Aubry
and others to non-zero Planck’s constant and temperature. This analysis is based on the study of a renormalization operator
for the case of irrational mean spacing using Feynman’s functional integral approach. We show how existing classical results
extend to the quantum regime. In particular we extend MacKay’s renormalization approach for the classical statistical mechanics
to deduce scaling of low frequency effects and quantum effects. Our approach extends the phenomenon of hierarchical melting
studied by Vallet, Schilling and Aubry to the quantum regime 相似文献
68.
Over the last twenty years the treatment of cancer with protons and light nuclei such as carbon ions has moved from being the preserve of research laboratories into widespread clinical use. A number of choices now exist for the creation and delivery of these particles, key amongst these being the adoption of pencil beam scanning using a rotating gantry; attention is now being given to what technologies will enable cheaper and more effective treatment in the future. In this article the physics and engineering used in these hadron therapy facilities is presented, and the research areas likely to lead to substantive improvements. The wider use of superconducting magnets is an emerging trend, whilst further ahead novel high-gradient acceleration techniques may enable much smaller treatment systems. Imaging techniques to improve the accuracy of treatment plans must also be developed hand-in-hand with future sources of particles, a notable example of which is proton computed tomography. 相似文献
69.
Ranjbar VH Lee SY Huang H Luccio AU MacKay WW Ptitsyn V Roser T Tepikian S 《Physical review letters》2003,91(3):034801
Higher-order and coupled snake resonances were observed during the 2002 polarized proton run in RHIC. Strong depolarization was observed when the fractional part of the vertical betatron tune approached 1/4, and when the fractional part of the horizontal tune approached 3/14. Because of the closed orbit error, each snake resonance splits into two. From the width of the observed snake resonances, we can derive the strength of the imperfection spin resonance. Our results appear consistent with the measured closed orbit error. 相似文献
70.
Vedejs E Daugulis O Harper LA MacKay JA Powell DR 《The Journal of organic chemistry》2003,68(13):5020-5027
The synthesis and evaluation of chiral phosphines 11, 15a, 19a, 24a, and 28a as nucleophilic catalysts for anhydride activation and kinetic resolution of alcohols is described. The relative reactivity follows the order 11a > 11b > 15a > 1 in the monocyclic series, and 24a > 19a > 28ain the bicyclic series, with an overall rate advantage of ca. 2 orders of magnitude for the bicyclic phospholanes over the monocyclic analogues. The increased reactivity of the bicyclic phospholanes for the acylation of alcohols is attributed to conformational effects and ground-state destabilization in a highly associative mechanism. Kinetic resolution data demonstrate promising enantioselectivities for 24a. 相似文献