Synthesis of (+)-laurencin via ring expansion of a C-glycoside derivative

Laurencin was efficiently synthesized from a C-glycoside derivative based on ring expansion of the oxane part of the starting compound into an eight-membered cyclic ether via a ring-cleavage/ring-closing olefin metathesis process, stereoselective introduction of a bromo group at C4, and convergent construction of the side-chain part using a lithiated enyne unit.     

Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface

The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.     

Pressure dependence of laser oscillation and superfluorescent emission from an optically pumped CF4 laser

Experiments on pressure dependence of a CF₄ laser have been carried out to elucidate dynamic characteristics of CF₄ molecules pumped by CO₂ lasers. The results are followed by a model calculation which characterizes collisional quenching of the energy levels related to the stimulated emission. The enhancement of the laser output induced by buffer-gas addition, which was found under specific conditions, is discussed in relation to the competition between laser and superfluorescent emissions.     

Improved activity of Fe---Cu catalysts by physical mixing with zeolites for the hydrogenation of carbon dioxide

The hydrogenation of carbon dioxide was catalyzed at 250°C over Fe---Cu/zeolite composite catalysts. Physical mixing of zeolites with Na-rich Fe---Cu Fischer-Tropsch catalysts drastically enhanced the activity. Branched and heavier hydrocarbons were obtained over such modified composite catalysts. It is proposed that sodium migrated from the surface of the metal catalyst to the zeolite via the solid-state reaction. It was illustrated that a solid-state reaction between physically-mixed catalysts is an attractive route to modification of the zeolites and to the preparation of bifunctional catalysts possessing both acidic and hydrogenation functions.     

Cleavage of hydrazine N-N bonds by RuMo3S4 cubane-type clusters

The mixed-metal cubane-type clusters [(Cp*Mo)3(mu3-S)4RuH2(PR3)][PF(6)] [Cp* = eta5-C5Me5; R = Ph (2), Cy (5)] were effective for the N-N bond cleavage of hydrazine and phenylhydrazine via a disproportionation reaction. The ammonia cluster [(C*Mo)3(mu3-S)4Ru(NH3)(PPh3)][PF6] (3) and/or the unprecedented double-cubane-type cluster with bridging nitrogenous ligands [{(Cp*Mo)3(mu3-S)4Ru}2(mu2-NH2)(mu2-NHNH2)][PF6]2 (4) were isolated from the reaction mixtures, and their structures were determined by X-ray diffraction studies.     

Chemical and enzymatic synthesis of neoglycolipids in the presence of cyclodextrins

The efficiency of cyclodextrins (CDs), α-CD, β-CD and γ-CD, for the blotting of hydrophobic substrates to water-soluble polymers and for the synthesis of neoglycolipids using glycosyltransferase is described. CDs did not disturb HPLC purification and did not bring lather. These merits are superior to surfactants commonly used in such a case. The utility of CDs as a novel and efficient supporting material for enzymatic glycosylation is also discussed.     

Info-gap robust design with load and model uncertainties

This paper develops a new structural design concept which incorporates uncertainties in both the load and the structural model parameters. Info-gap models of uncertainty are used to represent uncertainty in the power spectral density of the load and in parameters of the vibration model of the structure. It is demonstrated that any design which optimizes functional performance will also minimize the robustness to uncertainty. Since uncertainties are prevalent in many applications, this paper argues that it is necessary to satisfy critical performance requirements (rather than to optimize performance), and to maximize the robustness to uncertainty. The design implications of this robust-satisficing approach are demonstrated with several heuristic structural design examples. It is shown that design preferences depend upon performance requirements: preferences between designs can be reversed when performance requirements change. Also, we show that the info-gap robustness function provides an attractive tool for adjudicating between conflicting objectives in multi-criteria design.     

The Grothendieck group of a quantum projective space bundle

We compute the Grothendieck group of non-commutative analogues of projective space bundles. Our results specialize to give the Grothendieck groups of non-commutative analogues of projective spaces, and specialize to recover the Grothendieck group of a usual projective space bundle over a regular noetherian separated scheme. As an application, we develop an intersection theory for quantum ruled surfaces. S. P. Smith was supported by NSF grants DMS 9701578 and 0070560 Received: March 2006     

Nonequilibrium spin Hall accumulation in ballistic semiconductor nanostructures

We demonstrate that the flow of a longitudinal unpolarized current through a ballistic two-dimensional electron gas with Rashba spin-orbit coupling will induce a nonequilibrium spin accumulation which has opposite signs for the two lateral edges and is, therefore, the principal observable signature of the spin Hall effect in two-probe semiconductor nanostructures. The magnitude of its out-of-plane component is gradually diminished by static disorder, while it can be enhanced by an in-plane transverse magnetic field. Moreover, our prediction of the longitudinal component of the spin Hall accumulation, which is insensitive to the reversal of the bias voltage, offers direct evidence to differentiate experimentally between the extrinsic, intrinsic, and mesoscopic spin Hall mechanisms.