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排序方式: 共有259条查询结果,搜索用时 265 毫秒
251.
Francis Bursa Luigi Del Debbio Liam Keegan Claudio Pica Thomas Pickup 《Physics letters. [Part B]》2011
We simulate SU(2) gauge theory with six massless fundamental Dirac fermions. We measure the running of the coupling and the mass in the Schrödinger Functional scheme. We observe very slow running of the coupling constant. We measure the mass anomalous dimension γ, and find it is between 0.135 and 1.03 in the range of couplings consistent with the existence of an IR fixed point. 相似文献
252.
Stone DA Tayi AS Goldberger JE Palmer LC Stupp SI 《Chemical communications (Cambridge, England)》2011,47(20):5702-5704
Symmetric oligothiophene derivatives containing hydrogen bond forming segments create self-supporting organogels consisting of self-assembled 1D nanostructures at low concentrations. Hydrogen bond formation and π-π stacking were both found to be crucial for the formation of conductive supramolecular networks of 1D nanostructures. 相似文献
253.
Smith DF Aizikov K Duursma MC Giskes F Spaanderman DJ McDonnell LA O'Connor PB Heeren RM 《Journal of the American Society for Mass Spectrometry》2011,22(1):130-137
We describe the construction and application of a new MALDI source for FT-ICR mass spectrometry imaging. The source includes a translational X-Y positioning stage with a 10×10 cm range of motion for analysis of large sample areas, a quadrupole for mass selection, and an external octopole ion trap with electrodes for the application of an axial potential gradient for controlled ion ejection. An off-line LC MALDI MS/MS run demonstrates the utility of the new source for data- and position-dependent experiments. A FT-ICR MS imaging experiment of a coronal rat brain section yields ~200 unique peaks from m/z 400-1100 with corresponding mass-selected images. Mass spectra from every pixel are internally calibrated with respect to polymer calibrants collected from an adjacent slide. 相似文献
254.
Switching light is one of the most fundamental functions of an optical circuit. As such, optical switches are a major research topic in photonics, and many types of switches have been realized. Most optical switches operate by imposing a phase shift between two sections of the device to direct light from one port to another, or to switch it on and off, the major constraint being that typical refractive index changes are very small. Conventional solutions address this issue by making long devices, thus increasing the footprint, or by using resonant enhancement, thus reducing the bandwidth. We present a slow-light-enhanced optical switch that is 36 times shorter than a conventional device for the same refractive index change and has a switching length of 5.2 microm. 相似文献
255.
Bog U Smith CL Lee MW Tomljenovic-Hanic S Grillet C Monat C O'Faolain L Karnutsch C Krauss TF McPhedran RC Eggleton BJ 《Optics letters》2008,33(19):2206-2208
We demonstrate postprocessed microfluidic double-heterostructure cavities in silicon-based photonic crystal slab waveguides. The cavity structure is realized by selective fluid infiltration of air holes using a glass microtip, resulting in a local change of the average refractive index of the photonic crystal. The microcavities are probed by evanescent coupling from a silica nanowire. An intrinsic quality factor of 57,000 has been derived from our measurements, representing what we believe to be the largest value observed in microfluidic photonic crystal cavities to date. 相似文献
256.
Ben W. Joynson Dr. Graham R. Cumming Dr. Liam T. Ball 《Angewandte Chemie (International ed. in English)》2023,62(31):e202305081
We demonstrate that arylchlorodiazirines serve as photo-activated halocarbene precursors for the selective one-carbon ring expansion of N-substituted pyrroles and indoles to the corresponding pyridinium and quinolinium salts. Preliminary investigations indicate that the same strategy also enables the conversion of N-substituted pyrazoles to pyrimidinium salts. The N-substituent of the substrate plays an essential role in: (1) increasing substrate scope by preventing product degradation, (2) enhancing yields by suppressing co-product inhibition, and (3) activating the azinium products towards subsequent synthetic manipulations. This latter point is illustrated by subjecting the quinolinium salts to four complementary partial reductions, which provide concise access to ring-expanded products with different degrees of increased C(sp3) character. Thermal analysis of the diazirines by differential scanning calorimetry (DSC) provides detailed insight into their energetic properties, and highlights the safety benefits of photolyzing—rather than thermolyzing—these reagents. 相似文献
257.
Skeletal editing involves making specific point-changes to the core of a molecule through the selective insertion, deletion or exchange of atoms. It thus represents a potentially powerful strategy for the step-economic modification of complex substrates and is a perfect complement to methods such as C−H functionalization that target the molecular periphery. Given their ubiquity in biologically active compounds, the ability to perform skeletal editing on – and therefore interconvert between – aromatic heterocycles is especially valuable. This review summarizes both recent and key historical examples of skeletal editing as applied to interconversion of aromatic rings; we anticipate that it will serve to highlight not only the innovative and enabling nature of current skeletal editing methods, but also the tremendous opportunities that still exist in the field. 相似文献
258.
Dr. Phillip M. Danby Andrew Jeong Dr. Lyann Sim Dr. Ryan P. Sweeney Jacob F. Wardman Ryan Karimi Dr. Andreas Geissner Dr. Liam J. Worrall Prof. Dr. Jolene. P. Reid Prof. Dr. Natalie C. J. Strynadka Prof. Dr. Stephen G. Withers 《Angewandte Chemie (International ed. in English)》2023,62(21):e202301258
Suitably configured allyl ethers of unsaturated cyclitols act as substrates of β-glycosidases, reacting via allylic cation transition states. Incorporation of halogens at the vinylic position of these carbasugars, along with an activated leaving group, generates potent inactivators of β-glycosidases. Enzymatic turnover of these halogenated cyclitols (F, Cl, Br) displayed a counter-intuitive trend wherein the most electronegative substituents yielded the most labile pseudo-glycosidic linkages. Structures of complexes with the Sulfolobus β-glucosidase revealed similar enzyme-ligand interactions to those seen in complexes with a 2-fluorosugar inhibitor, the lone exception being displacement of tyrosine 322 from the active site by the halogen. Mutation of Y322 to Y322F largely abolished glycosidase activity, consistent with lost interactions at O5, but minimally affected (7-fold) rates of carbasugar hydrolysis, yielding a more selective enzyme for unsaturated cyclitol ether hydrolysis. 相似文献