Characterization and surface-reactivity of nanocrystalline anatase in aqueous solutions

The chemical and electrostatic interactions at mineral-water interfaces are of fundamental importance in many geochemical, materials science, and technological processes; however, the effects of particle size at the nanoscale on these interactions are poorly known. Therefore, comprehensive experimental and characterization studies were completed, to begin to assess the effects of particle size on the surface reactivity and charging of metal-oxide nanoparticles in aqueous solutions. Commercially available crystalline anatase (TiO2) particles were characterized using neutron and X-ray small-angle scattering, electron microscopy, and laser diffraction techniques. The 4 nm primary nanoparticles were found to exist almost exclusively in a hierarchy of agglomerated structures. Potentiometric and electrophoretic mobility titrations were completed in NaCl media at ionic strengths from (0.005 to 0.3) mol/kg, and 25 degrees C, with these two experimental techniques matched as closely as the different procedures permitted. The pH of zero net proton charge (pHznpc, from potentiometric titration) and isoelectric point pH value (pHiep, from electrophoretic mobility titrations) were both in near perfect agreement (6.85 +/- 0.02). At high ionic strengths the apparent pHznpc value was offset slightly toward lower pH values, which suggests some specific adsorption of the Na+ electrolyte ions. Proton-induced surface charge curves of nanocrystalline anatase were very similar to those of larger rutile crystallites when expressed relative to their respective pHznpc values, indicating that the development of positive and negative surface charge away from the pHznpc for nanocrystalline anatase is similar to that of larger TiO2 crystallites.     

Applications of a time correlation function theory for the fifth-order Raman response function I: atomic liquids

Multidimensional spectroscopy has the ability to provide great insight into the complex dynamics and time-resolved structure of liquids. Theoretically describing these experiments requires calculating the nonlinear-response function, which is a combination of quantum-mechanical time correlation functions R5(t1,t2) was expressed with a two-time, computationally tractable, classical TCF. Writing the response function in terms of classical TCFs brings the full power of atomistically detailed molecular dynamics to the problem. In this paper, the new TCF theory is employed to calculate the fifth-order Raman response function for liquid xenon and investigate several of the polarization conditions for which experiments can be performed on an isotropic system. The theory is shown to reproduce line-shape characteristics predicted by earlier theoretical work.     

Fourth Order Linear Recurrences Satisfied by Wythoff Pairs

A result of Stolarsky is extended to show that there are infinitely many irreducible fourth order linear recurrences satisfied by sequences of pairs , where i is a natural number and is the golden ratio . It is also proved that the characteristic polynomial of every such recurrence factorizes non-trivially if is adjoined to the rationals.     

Approaches to identify, clone, and express symbiont bioactive metabolite genes

This review discusses approaches to identify, clone, and express bioactive metabolite genes from symbionts of marine invertebrates. Criteria for proving symbiotic origin of bioactive metabolites are presented, followed by a comprehensive, practically-oriented overview of techniques to be applied. The Bugula neritina/Endobugula sertula association is used as a primary example, but other symbioses are discussed. Thirty-six compounds are presented and 111 references are cited.     

Observation of completely destructive quantum interference between interacting resonances in molecular predissociation

A unique observation is presented of interacting predissociating resonances which exhibit completely destructive interference in a region between the resonances. The use of a double-resonance technique, in which single rotational levels of the b (1)Sigma(+)(g) state of O2, prepared by pumping the magnetic-dipole b <--X transition, are probed by (2+1) resonance-enhanced multiphoton-ionization spectroscopy, eliminates overlapping rotational structure and enables observation of the interference process. Using a diabatic coupled-channel model, the interacting resonances are shown to be derived from the d (1)Pi(g)(v = 3,J = 17) Rydberg and II (1)Delta(g)(v = 6,J = 17) valence states.     

Preparation of stable,camphor-derived,optically active allylic sulfoxides

(+)-Camphor has been stereospecifically converted in three steps into a single isoborneol allyl sulfoxide derivative, which upon heating to 145° is quantitatively converted into its sulfoxide epimer; the anions of these compounds undergo stereospecific conjugate addition to cyclopent-2-en-1-one.     

Selective generation of longitudinal microsonic waves in n-GaAs

Longitudinal acoustic waves have been amplified from the thermal background in {111} oriented n-type GaAs and have been studied by observing Brillouin scattering. The generating technique uses a tuned voltage-square-wave, which eliminates the amplification of off-axis transverse modes.