Absorbing boundary conditions for reaction-diffusion equations

We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reaction–diffusion equations.     

New measurement of the beta decay rate of the16N(0−)-16O(0+) transition

The beta decay rate of the¹⁶N(0^?; 120keV) →¹⁶O(0⁺, G.S.) transition has been remeasured. Our result (Λ _β =0.48±0.024 s^?1) is in excellent agreement with a previous measurement but strongly disagrees with another experimental value. The two agreeing results provide an experimental verification of the importance of meson exchange currents in 0⁺-0^? weak transitions. A value ofg _p/g _A～11–12 can be inferred from the correspondingΛ _μ rate.     

Measurement of the beta spectrum of the 0− (120 keV) state of16N

We have measured the beta spectrum of the 0^?(120 keV,t _1/2=5.25 μs) state of¹⁶N. The response function of our detector has been measured, parameterized and then fitted to known spectral shapes taken under conditions close to those in the actual experiment. Using this response function and subtracting a 56 μs half-life background due to neutron capture in the detector, the measured 0^? spectrum compares well with the allowed shape for the 0^?→0⁺ spectrum plus a small contribution from the allowed 0^?→1^? transition.     

The3He(γ,2p)n reaction for Eγ=80-170MeV

The cross section for the³He(γ, 2p) reaction has been measured in a complete kinematics experiment in the energy rangeE _γ=80–170 MeV, forθ _P1=θ _P2=90°. This configuration was selected in order to investigate the role of proton-proton final state interactions in the three-body breakup process. The measured proton spectra are seen to be consistent with a prediction using the Watson-Migdal formalism. The magnitude of the observed cross section clearly indicates an enhancement over phase space, presumably due to the strong proton-proton interaction in the final state. The experimental results agree, within their limited statistical accuracy, with a theoretical calculation which includes this effect.     

Photochemical properties of selected flavonol dyes: Effects on their separation using capillary electrophoresis

Flavonols are naturally occurring dyes that can be extracted from plants. Because of their antioxidant properties, they are thought to have health benefits. In this study, the photochemical degradation properties of selected flavonols were investigated. Dilute solutions of dyes were exposed to light from a broadband visible light source, and the rate of photodegradation was determined by measuring the decrease in fluorescence of the dyes with respect to time. At pH 9.24, the first-order rate constants for 10?µg?mL^?1 solutions of myricetin, quercetin, kaempferol, and morin were 0.468, 0.162, 0.108, and 0.126?s^?1, respectively. Interestingly, the stability of these historical dyes was also found to be greatly affected by pH. Awareness of the photochemical properties and stability of flavonol dyes is very important for capillary electrophoresis (CE) separations. Photodegradation of the flavonol dyes under the alkaline conditions (pH 9.2) used in CE can have a profound effect on the reproducibility of repeated separations. Even a modest decrease in pH (pH 8.5) greatly improved the stability of these dyes and enabled the successful separation of these flavonol dyes with minimal degradation over time.     

Measurement of CP-violating asymmetries in B0 decays to CP eigenstates

We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23x10(6) Upsilon(4S)-->BbarB decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events in which one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay time distributions in such events. The result is sin2beta = 0.34+/-0.20 (stat)+/-0.05 (syst).     

Dynamics of the NbCl5‐Catalyzed Cycloaddition of Propylene Oxide and CO2: Assessing the Dual Role of the Nucleophilic Co‐Catalysts

A mechanistic study on the synthesis of propylene carbonate (PC) from CO₂ and propylene oxide (PO) catalyzed by NbCl₅ and organic nucleophiles such as 4‐dimethylaminopyridine (DMAP) or tetra‐n‐butylammonium bromide (NBu₄Br) is reported. A combination of in situ spectroscopic techniques and kinetic studies has been used to provide detailed insight into the reaction mechanism, the formation of intermediates, and interactions between the reaction partners. The results of DFT calculations support the experimental observations and allow us to propose a mechanism for this reaction.