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991.
Two powerful strategies: rapid construction of allylic alkynoates via cyclopropenium ion chemistry and mild, palladium-catalyzed decarboxylative coupling were employed in a concise, 5-steps synthesis of the natural product rooperol. The overall approach allows the preparation of rooperol analogs in as few as 3 steps. 相似文献
992.
Consumers and governments are pressuring firms to strike a balance between profitability and sustainability. However, this balance can only be maintained in the long run if the firm can take a holistic approach to sustain the financial flow (profit), resource flow (planet) and development flow (people) for the entire ecosystem comprising poor producers in emerging/developing markets, global supply chain partners, consumers in developed countries, and the planet. By considering the flows associated with different entities within the ecosystem, we classify and summarize recent Operations Research/Management Science (OR/MS) research developments. Also, we identify several gaps for future research in this important area. 相似文献
993.
We describe a method for determining the minimal length of elements in the generalized Thompson’s groups F(p). We compute the length of an element by constructing a tree pair diagram for the element, classifying the nodes of the tree
and summing associated weights from the pairs of node classifications. We use this method to effectively find minimal length
representatives of an element.
相似文献
994.
One of the key performance measures in queueing systems is the decay rate of the steady-state tail probabilities of the queue
lengths. It is known that if a corresponding fluid model is stable and the stochastic primitives have finite moments, then
the queue lengths also have finite moments, so that the tail probability ℙ(⋅>s) decays faster than s
−n
for any n. It is natural to conjecture that the decay rate is in fact exponential. 相似文献
995.
Li D Parkin S Wang G Yee GT Clérac R Wernsdorfer W Holmes SM 《Journal of the American Chemical Society》2006,128(13):4214-4215
The synthesis and structural and magnetic characterization of an S = 6 cyanide-bridged octanuclear FeIII4NiII4 (1) complex is described. Ac susceptibility and mu-SQUID measurements suggest that fast magnetization relaxation is present in zero-field due to quantum tunneling of the ground spin state (QTM) while application of small magnetic fields induces slow relaxation of the magnetization. 相似文献
996.
Hinds S Taft BJ Levina L Sukhovatkin V Dooley CJ Roy MD MacNeil DD Sargent EH Kelley SO 《Journal of the American Chemical Society》2006,128(1):64-65
We engineer colloidal quantum dot nanocrystals through the choice of biomolecular ligands responsible for nanoparticle nucleation, growth, stabilization, and passivation. We systematically vary the presence of, and thereby elucidate the role of, phosphate groups and a multiplicity of functionalities on the mononucleotides used as ligands. The results provide the basis for synthesis of nanoparticles using precisely controlled synthetic oligonucleotide sequences. 相似文献
997.
998.
Treatment of [NEt4][(pzTp)Fe(III)(CN)3] (1) with Ni(II)(OTf)2 (OTf = trifluoromethanesulfonate) and 1,5,8,12-tetraazadodecane (L) affords {[(pzTp)Fe(III)(CN)3]2[Ni(II)L]} x 1/2MeOH (2), while 2,2'-bipyridine (bipy) affords {[(pzTp)Fe(III)(CN)3]2[Ni(II)(bipy)2]} x 2 H2O (3). Magnetic measurements indicate that 2 and 3 have S = 2 ground states and that 3 exhibits slow relaxation of the magnetization above 2 K. 相似文献
999.
The combination of HgF2 and 2-aminoethanethiol (AET, with some AET.HCl present) yielded a cyclic tetranuclear thiolate, [Hg4Cl4(SCH2CH2NH2)4] (1), with alternating Hg and S atoms. The Cl from the reaction mixture led to the formation of Hg-Cl bonds with no Hg-F in the final product. In contrast, a similar reaction with HgBr2 yielded a nonanuclear cluster, [Hg9Br15(SCH2CH2NH3)15]3+ (2), and the disulfide salt {[HgBr4][(NH3CH2CH2S-)2]} (3). Despite similar reactions, the AET groups in 2 are protonated compared to the nonprotonated amine groups in 1, which allows the ligand to chelate the Hg atom in the latter compound. The reaction with HgI2 yielded a cyclic tetranuclear compound, [Hg4I6(SCH2CH2NH2)2(SCH2CH2NH3)2](H2O/EtOH) (4), containing protonated and nonprotonated AET groups. Compound 4 at room temperature irreversibly rearranges to [Hg4I4(SCH2CH2NH2)4] (5), which is isostructural to 1. A systematic pathway for the formation of 1 along with the intramolecular conversion of 4 to 5 is proposed. These compounds demonstrate that very diverse Hg-S compounds form under similar reaction conditions. 相似文献
1000.
Sheehan SM Meloni G Parsons BF Wehres N Neumark DM 《The Journal of chemical physics》2006,124(6):64303
Anion photoelectron spectra of Ga(2)N(-) were measured at photodetachment wavelengths of 416 nm(2.978 eV), 355 nm(3.493 eV), and 266 nm(4.661 eV). Both field-free time-of-flight and velocity-map imaging methods were used to collect the data. The field-free time-of-flight data provided better resolution of the features, while the velocity-map-imaging data provided more accurate anisotropy parameters for the peaks. Transitions from the ground electronic state of the anion to two electronic states of the neutral were observed and analyzed with the aid of electronic structure calculations and Franck-Condon simulations. The ground-state band was assigned to a transition between linear ground states of Ga(2)N(-)(X (1)Sigma(g) (+)) and Ga(2)N(X (2)Sigma(u) (+)), yielding the electron affinity of Ga(2)N, 2.506+/-0.008 eV. Vibrationally resolved features in the ground-state band were assigned to symmetric and antisymmetric stretch modes of Ga(2)N, with the latter allowed by vibronic coupling to an excited electronic state. The energy of the observed excited neutral state agrees with that calculated for the A (2)Pi(u) state, but the congested nature of this band in the photoelectron spectrum is more consistent with a transition to a bent neutral state. 相似文献