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991.
Turner PJ Harris R Kamal S Hayden ME Broun DM Morgan DC Hosseini A Dosanjh P Mullins GK Preston JS Liang R Bonn DA Hardy WN 《Physical review letters》2003,90(23):237005
There has long been a discrepancy between microwave conductivity measurements in high temperature superconductors and the conductivity spectrum expected in the simplest models for impurity scattering in a d-wave superconductor. Here we present a new type of broadband measurement of microwave surface resistance that finally shows some of the spectral features expected for a d(x2-y2) pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency range in highly ordered crystals of YBa2Cu3O6.50 and YBa2Cu3O6.99. 相似文献
992.
We describe how twist could play an essential role in stabilizing 20 nm diameter sickle hemoglobin fibers. Our theory successfully reproduces the observed variation of helical pitch length with fiber diameter. With no remaining adjustable parameters it also yields a prediction for the torsional rigidity of sickle hemoglobin fibers that is in good agreement with experiment and hence retains the striking feature that such fibers can be highly mechanically anisotropic, even with a ratio of bending to torsional rigidity of about 50. We discuss how our study might be relevant to the development of treatment strategies. 相似文献
993.
Shell cross-linked nanoparticles (SCKs) constitute a unique class of materials with amphiphilic core-shell morphology; SCKs are characterised by their structural integrity and available functionality to attach receptor-recognising or receptor-specific ligands on the shell surface and, therefore, hold great potential in drug delivery applications; in an attempt to develop novel, cancer cell specific delivery vehicles, folate receptor targeted SCKs have been prepared. 相似文献
994.
995.
X-Ray data for two N-acyloxy-N-alkoxyamides, a class of direct-acting mutagens, indicate extreme pyramidalisation at the amide nitrogen in keeping with spectroscopic and theoretically determined properties of amides with bisoxosubstitution at nitrogen. The combined electronegativity of two oxygens leads to average angles at nitrogen of 107.8 and 108.1 degrees and [chiN] of 66 degrees and 65 degrees. The sp3 nature of nitrogen results in negligible amide resonance as evidenced by long N-C(O) bonds, high IR carbonyl stretch frequencies, carbonyl 13C NMR data and very low amide isomerisation barriers. In addition, conformations in the solid state support a strong n(O)-sigma*(NOAc), anomeric interaction as predicted by molecular orbital theory. HF/6-31G* calculations on formamide, N-methoxyformamide and N-formyloxy-N-methoxyformamide support these findings. 相似文献
996.
[reaction: see text] A three-step synthesis of cyclohexane-1,3-dione (CHD) resin 6 on polystyrene resin is described. Resin 6 was used to prepare an amide library of high purity by microwave-assisted serial "capture and release" and can be recycled for this purpose. High-loading CHD resin 10 was also shown to scavenge allyl cations in solution. 相似文献
997.
Wander A Schedin F Steadman P Norris A McGrath R Turner TS Thornton G Harrison NM 《Physical review letters》2001,86(17):3811-3814
The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001;)-O surfaces is 4.0 J/m(2) comparable to 2.32 J/m(2) for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications. 相似文献
998.
High-frequency plasma discharges are often sustained by collisionless heating of electrons; the nature of these mechanisms is a central problem in the theory of such discharges. In capacitive discharges, collisionless heating occurs near boundaries, and is usually attributed to inelastic collisions of electrons with oscillating plasma sheaths, regarded as moving rigid barriers. We show that, when current conservation is required, such heating necessarily vanishes, and we conclude that this model of the heating process is not correct. We develop an alternative view that associates the heating with acoustic disturbances in the electron fluid. An analytic model, based on moments of the Vlasov equation, gives results in good agreement with particle-in-cell simulations. In terms of individual particle dynamics, this acoustic heating may be interpreted as a transit-time effect. 相似文献
999.
I. R. Turner 《The Journal of the Operational Research Society》1981,32(9):747-753
The organisation and philosophy of the ‘Area Service’ of the National Coal Board's Operational Research Executive is described, with special reference to factors which assist the Executive's O.R. scientists to develop good working relationships with managers. 相似文献
1000.