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11.
Quantum Zeno and anti-Zeno paradoxes 总被引:1,自引:0,他引:1
Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox).
We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure
change of state: an anti-Zeno paradox. 相似文献
12.
粉粒体两相流的电容层析成象测量 总被引:4,自引:0,他引:4
粉粒体系统中的固相浓度分布的在线测量是十分困难的问题.电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术.它不干扰流场,不受流动中颗粒浓度、加速度、不透明等因素的制约.本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策. 相似文献
13.
ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling
behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency
conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime. 相似文献
14.
Dr. Gourishetty Srikanth Dr. Anil Ravi Dr. Anusha Sebastian Jobi Joseph Prof. Monther A. Khanfar Prof. Mohammed I. El-Gamal Prof. Raed A. Al-Qawasmeh Prof. Ihsan A. Shehadi Scott McN. Sieburth Prof. Imad A. Abu-Yousef Prof. Amin F. Majdalawieh Prof. Taleb H. Al-Tel 《European journal of organic chemistry》2023,26(13):e202300080
The discovery of novel small molecules endowed with high 3D-content remains a powerful tool for interrogating underrepresented biological space. To this end, the pseudo-natural products (pseudo-NP) strategy has become one of the most important tools to deliver biologically significant chemical probes. In this article, we describe the development of a new class of pseudo-NP collection, through connecting tryptamines with a furanose derivative followed by subjecting the product from this operation to a ring distortion strategy that led to diastereoselective synthesis of camptothecin-like compounds. This process is driven by a cascade that unites Pictet–Spengler reaction with Michael addition reaction, followed by oxidative-ring enlargement and subsequent transannular aldol cyclization delivering camptothecin-like architectures. The obtained diastereoselectivity was verified using density functional theory (DFT) calculations. 相似文献
15.
Silanediol peptidomimetics are demonstrated to inhibit a serine protease. Asymmetric synthesis of the inhibitor was accomplished using Brown hydroboration and CBS reduction of an acylsilane intermediate. The silanediol product was found to inhibit the serine protease chymotrypsin with a K(i) of 107 nM. Inhibition of the enzyme may involve exchange of a silane hydroxyl with the active site serine nucleophile, contrasting with previous silanediol protease inhibitors. 相似文献
16.
DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements
have been reported for the Co1.1−x
Zn
x
Ge0.1Fe1.2O1 spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic
ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained
under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important
role of magnetic anisotropy (due to the presence of Co2+ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed. 相似文献
17.
Lee YG McGee KF Chen J Rucando D Sieburth SM 《The Journal of organic chemistry》2000,65(20):6676-6681
Intramolecular photocycloaddition of 2-pyridones connected through a four-carbon tether (6-[4-(1,2-dihydro-1-methyl-2-oxo-3-pyridinyl)-4-[[(1,1-dimethylethyl)++ +dimethylsilyl]oxy]butyl]-4-methoxy-1,3-dimethyl-2(1H)-pyridinone) yields a single tetracyclic product with four new stereogenic centers. The diastereoselectivity of this [4 + 4] reaction is fully controlled by a stereogenic carbon of the tether. Treatment of the photoproduct with osmium tetraoxide transforms the alkene to a diol and the enol ether to an alpha-hydroxy ketone, with stereocontrol dictated by nearby lactams that block one face of each alkene. Allylmagnesium bromide addition to the ketone also yields a single diastereomer, but unexpectedly this product results from approach of the nucleophile to the most-hindered face of the ketone. Study of this reaction in a model system has found the allylic nucleophile to be unique, with nonallylic reagents approaching along the expected, least-hindered path. This contrasteric addition likely results from coordination of the allylic nucleophile to the nearby amide. The amide can therefore act either as a steric shield or as a directing group. The three steps of photocycloaddition, cis-hydroxylation, and nucleophilic addition constructs both quaternary carbons of the cyclooctane and four of the five stereogenic centers found in the eight-membered ring of Taxol. 相似文献
18.
Four-carbon-tethered pyridones undergo photocycloaddition to give exclusively trans-[4 + 4] products. The presence of a tether alcohol engenders a solvent-dependent diastereoselectivity for the cycloaddition by intramolecular hydrogen bonding to the adjacent pyridone. Following cycloaddition, the alcohol can deliver a carbonyl group to the proximal, hindered amide nitrogen, leading to a very facile amide hydrolysis. 相似文献
19.
Paul A. Wender Scott McN. Sieburth Joseph J. Petraitis Sunil K. Singh 《Tetrahedron》1981,37(23):3967-3975
Treatment of 1,2-(E,E)-di(1-buta-1,3-dienyl)cyclohexanol (21) with potassium hydride in tetrahydrofuran at room temperature resulted in the facile formation of a 14-membered ring dienolate which on kinetic protonation provided cyclotetradeca-3,5,7-trien-1-one. This novel rearrangement which provides the basis for an efficient, eight unit ring expansion method was also observed when 5,8-dimethyl-5-hydroxy-1,3,7,9-decapentaene (28), the acyclic analogue of 21, was treated with potassium hydride in tetrahydrofuran. Methodology for the preparation of 21 and 28 including the preparation of 1-lithio-1,3-butadiene is also described. 相似文献
20.
[Structure: see text] Transannular ring closure of a pyridone-furan [4+4] photoadduct has been evaluated in a model system. A combination of nitrogen substitution and an isopropyl group gave full control of the four new stereogenic centers. Chlorination transformed the 1,5-cyclooctadiene to a [4.2.0] ring system instead of to the expected [3.3.0] ring system. Changing an alkene to an enone suppressed this pathway and led to a new rearrangement, converting the 5-8-5 ring system to a 6-7-5 system. 相似文献