Slow spin relaxation of Rb atoms confined in glass cells filled with dense 4He gas at 1.85 K

At temperatures below 2.1 K, long-lived gaseous Rb atoms in glass cells have been generated with a simple method: irradiating the cells, containing 4He gas and Rb metal, with a cw laser. The obtained atomic Rb density ( approximately 10(8) cm(-3)) decreases with a 1/e time constant of about 10 s at 1.85 K. We have performed optical pumping of the Rb atoms and measured the longitudinal electronic spin relaxation time at 1.85 K as well. For processes (such as Rb-He collisions) which do not remove the atomic Rb from the vapor, this relaxation time is found to be about 60+/-15 s.     

Effect of tea polyphenols on glucan synthesis by glucosyltransferase from Streptococcus mutans

In the course of our studies on the development of anti-plaque agents for prevention of dental caries, we investigated effects of some of tea preparations and their individual components on the glucan synthesis catalyzed by glucosyltransferase (GTF) from Streptococcus mutans. Extracts of green tea and black tea, and polyphenol mixtures showed appreciable inhibition in the synthesis of insoluble glucan. Among the components isolated from tea infusions, theaflavin and its mono- and digallates had potent inhibitory activities at concentrations of 1-10 mM against GTF. (+)-Catechin, (-)-epicatechin and their enantiomers had moderate inhibitory activities at these concentrations, while galloyl esters of (-)-epicatechin, (-)-epigallocatechin and (-)-gallocatechin had increased inhibitory activities.     

Synthesis and structural revision of marine eicosanoid agardhilactone

Synthesis of the marine eicosanoid agardhilactone has been achieved. The relative and absolute configuration of agardhilactone was successfully determined.     

Measurement of the wrong-sign decays D0 --> K+ pi- pi0 and D0 --> K+ pi- pi+ pi-, and search for CP violation

Using 281 fb-1 of data from the Belle experiment recorded at or near the (4S) resonance, we have measured the rates of the "wrong-sign" decays D0 --> K+ pi- pi0 and D0 --> K+ pi- pi+ pi- relative to those of the Cabibbo-favored decays D0 --> K- pi+ pi0 and D0 --> K- pi+ pi+ pi-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D0 mixing; the latter has not yet been observed. We obtain R(WS)(K pi pi0) = [0.229 +/- 0.015(stat)(+0.013)(-0.009)(syst)]% and R(WS)(K3pi) = [0.320 +/- 0.018(stat)(+0.018)(0.013)(syst)]%. The CP asymmetries are measured to be -0.006 +/- 0.053 and -0.018 +/- 0.044 for the K+ pi- pi0 and K+ pi- pi+ pi- final states, respectively.     

Remarkable reactivities of the xanthone ketyl radical in the excited state compared with that in the ground state

The properties and reactivities of the xanthone (Xn) ketyl radical (XnH*) in the doublet excited state (XnH*(D1)) were examined by using two-color two-laser flash photolysis. The absorption and fluorescence of XnH*(D1) were observed for the first time. Several factors governing the deactivation processes of XnH*(D1) such as interaction and reaction with solvent molecules were discussed. The remarkable change of reactivity of XnH*(D1) compared with that in the ground state (XnH*(D0)) was indicated from the experimental results. The rapid halogen abstraction of XnH*(D1) from some halogen donors such as carbon tetrachloride (CCl4) was found to occur. The halogen abstraction occurred more efficiently in the polar solvents than in the nonpolar solvents. It is suggested that the polar solvents promote the spin distribution of XnH*(D1) of the phenyl ring favorable to the halogen abstraction.     

Delayed feedback control based on the act-and-wait concept

This paper proposes a delayed feedback control (DFC) based on the act-and-wait concept, which reduces the dynamics of DFC systems to that of discrete-time systems. Based on this concept, a delayed feedback controller is designed for a prototype two-dimensional oscillator using a simple systematic procedure. This control has two advantages: the feedback delay time can be large and it can obtain deadbeat behavior. A numerical example using a double-scroll circuit model demonstrates these theoretical results.     

Post-synthesis dispersion of metal nanoparticles by poly(amidoamine) dendrimers: size-selective inclusion, water solubilization, and improved catalytic performance

Intermetallic Pt(3)Ti nanoparticles are solubilized in water by using a generation-five, hydroxyl-terminated, poly(amidoamine) dendrimer, G5OH, as a post-synthesis surfactant. Pt(3)Ti nanoparticles, encapsulated in G5OH and dispersed over the electrode surface, exhibited a superior catalytic activity toward the electro-reduction reaction of oxygen compared to as-prepared, highly agglomerated nanoparticles.     

Artabotryols A – E,New Lanostane Triterpenes from the Seeds of Artabotrys odoratissimus

Six new lanostane triterpenes, artabotryols A, B, C1, C2, D, and E ( 1, 2, 3a, 3b, 4 , and 5 , resp.) have been isolated from the seeds of Artabotrys odoratissimus (Annonaceae). Their structures have been established as (3α,22S,25R)‐3‐hydroxy‐22,26‐epoxylanost‐8‐en‐26‐one ( 1 ), (3α,22S,25R)‐22,26‐epoxylanost‐8‐ene‐3,26‐diol ( 2 ), (3α,22S,25R,26R)‐26‐methoxy‐22,26‐epoxylanost‐8‐en‐3‐ol ( 3a ), (3α,22S,25R, 26S)‐26‐methoxy‐22,26‐epoxylanost‐8‐en‐3‐ol ( 3b ), (3α,22S,25R)‐3,22‐dihydroxylanost‐8‐en‐26‐oic acid ( 4 ) and (3α,7α,11α,22S,25R)‐3,7,11‐trihydroxy‐22,26‐epoxylanost‐8‐en‐26‐one ( 5 ) by spectroscopic studies and chemical correlations.     

Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in ⁶He and ⁶Be were investigated by using the ⁶Li(⁷Li, ⁷Be)⁶He reaction at 455 MeV and ⁶Li(³He, t)⁶Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at E _x =18.0±1.0 MeV in ⁶He and into ³He + ³He from one at E _x =18.0±1.2 MeV in ⁶Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for ⁶He and ⁶Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around E _x =18 MeV in ⁶He and ⁶Be.