An efficient and operationally simple synthesis of the neodolestane diterpenoids (±)-heptemerone G and (±)-guanacastepene A is reported. The common tricyclic scaffold (±)-4 was prepared from 2-methylcyclopent-2-en-1-one via 23 isolated intermediates in 5.1% yield. The key features include a novel annulation sequence combining tandem conjugate addition, methylenation, and metathesis reaction and completely diastereoselective transformation of the azulene derivative 23 into rings AB building block 32. Stereochemistry of alkylation of both saturated trans-azulene enolate 38 and its α,β-unsaturated counterpart 48 was examined. Rather surprisingly, a different facial selectivity was recorded. Several synthetic methods were modified or developed, including an alternative methodology for the Wharton-type rearrangement, ketalization of epimerizable ketone under mild conditions, and efficient alkylation of a ketone via its kinetic enolate. 相似文献
We devise a protocol in which general nonclassical multipartite correlations produce a physically relevant effect, leading to the creation of bipartite entanglement. In particular, we show that the relative entropy of quantumness, which measures all nonclassical correlations among subsystems of a quantum system, is equivalent to and can be operationally interpreted as the minimum distillable entanglement generated between the system and local ancillae in our protocol. We emphasize the key role of state mixedness in maximizing nonclassicality: Mixed entangled states can be arbitrarily more nonclassical than separable and pure entangled states. 相似文献
A new model is presented of current transport in Metal Insulator Metal (MIM) structures by quantum mechanical tunnelling.
In addition to direct tunnelling through an insulating layer, tunnelling via defects present in the insulating layer plays
an important role. Examples of the influence of the material and thickness of the insulating layer, energy distribution of
traps, and metal work functions are also provided. 相似文献
TiO2 thick films deposited on macroporous reticulated Al2O3 foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO2 after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide® P25 coated Al2O3 foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller. 相似文献
We present results for the lowest order cross sections, calculated with the complete set of standard model Feynman diagrams,
of all possible detection channels of the associated production of the top quark pair and the light Higgs boson, which may
be used for determination of the top–Higgs Yukawa coupling at the future e+e− linear collider. We show that, for typical particle identification cuts, the background contributions are large. In particular,
the QCD background contributions are much bigger than could be expected when taking into account a possibly low virtuality
of exchanged gluons. Moreover, we include the initial state radiation effects and discuss the dependence of the cross sections
on the Higgs boson and top quark masses. 相似文献
The first total synthesis of (±)-heptemerone G, a diterpenoid metabolite of a submerged culture Coprinus heptemerus, and a new approach to an advanced intermediate for a synthesis of guanacastepene A are reported. 相似文献
The poor kinetics of hydrogen evolution and the irreversibility of the hydrogen discharge hamper the use of transition metal borohydrides as hydrogen storage materials, and the drawbacks of current synthetic methods obstruct the exploration of these systems. A wet‐chemistry approach, which is based on solvent‐mediated metathesis reactions of precursors containing bulky organic cations and weakly coordinating anions, leads to mixed‐metal borohydrides that contain only a small amount of “dead mass”. The applicability of this method is exemplified by Li[Zn2(BH4)5] and M[Zn(BH4)3] salts (M=Na, K), and its extension to other systems is discussed. 相似文献
This study is concerned with the investigation of the impact of heat flux on the fire hazard and the effective heat of combustion of sunflower seed hull pellets. Pellets produced by pressing common sunflower seed hulls (Helianthus annuus L.) were investigated. The samples were dried on water content of 0 mass% at a temperature of 103 ± 2 °C. The fire hazard and the heat of combustion have been determined via the cone calorimeter and by the testing procedure per ISO 5660-1:2015 at three heat fluxes (25, 35 and 50 kW m−2). The peak heat release rate increases with the increasing of the heat flux from 446 (at a heat flux of 25 kW m−2) to 601 kW m−2 (at a heat flux of 50 kW m−2). The carbon monoxide yield lies in the interval from 82.50 (at a heat flux of 25 kW m−2) to 154.15 g kg−1 (at a heat flux of 50 kW m−2). The effective heat of combustion decreases with the increasing of the heat flux from 15.84 (at a heat flux of 25 kW m−2) to 14.58 MJ kg−1 (at a heat flux of 50 kW m−2).