Direct observation of oxygen depletion and product formation during photocatalysis at a TiO2 surface using scanning electrochemical microscopy

Using scanning electrochemical microscopy (SECM) we have measured quantitatively the depletion of O2 during the photodegradation of 4-chlorophenol at supported TiO2 films for the first time and established the connection between Cl-formation and O2 depletion rates.     

A new strategy for the protection of deoxyguanosine during oligonucleotide synthesis

The protection of the 6-oxo group of deoxyguanosine with the 2-trimethylsilylethyl ($\text{2}$), phenylthioethyl ($\text{3}$), 4-nitrophenylthioethyl ($\text{4}$), 4-nintrophenethyl ($\text{5}$), and cyanoethyl ($\text{6}$) groups is described. Each protecting group is introduced in good yield and is cleaved under mild conditions. Compatibility with the various approaches to oligonucleotide synthesis is discussed.     

A study of the magnetic superexchange interactions in the solid-solution series CaxSr1−xRuO3 by ruthenium-99 Mo¨ssbauer spectroscopy

Ruthenium-99 Mo¨ssbauer spectroscopy has been used to examine magnetic superexchange interactions in the distorted perovskite solid-solutions Ca_xSr_1?xRuO₃ (x = 0.1, 0.2, 0.3, 0.4, and 0.5). The end members of this series also have a slightly distorted perovskite structure but CaRuO₃ is Curie-Weiss paramagnetic, with only a single-line Mo¨ssbauer spectrum, whereas SrRuO₃ is ferromagnetic and shows a broad well-resolved hyperfine pattern. For x ? 0.2 a substantial proportion of the ruthenium atoms experience a magnetic flux density (hyperfine magnetic field) close to 35T, but inward collapse of the spectrum suggests that an increasing proportion of ruthenium atoms experience smaller flux densities. For samples with x ? 0.3 there is an intense central “paramagnetic” component which increases rapidly with increasing x. The observed behaviour is incompatible with a conventional localized electron structure but can be interpreted satisfactorily on a collective electron model in which the average spin moment and hence the magnetic flux density at any given ruthenium atom is proportional to the strength of the exchange interactions with the six nearest-neighbour ruthenium atoms. The results imply that the greater electron-pair acceptor strength (Lewis acidity) of Ca²⁺ compared to Sr²⁺ results in a more effective competition with ruthenium for the oxygen anion orbitals involved in the superexchange interaction. It appears that, for a ruthenium to have a coupled spin-moment, it must have at least two exchange interactions through cube faces containing at least three strontium atoms. Possible origins of the reduced magnetic moment of SrRuO₃ are discussed and it is suggested that the latter probably stems from spin-canting rather than from partial overlap of spin-up and spin-down bands.     

A variant of the hypergraph removal lemma

Recent work of Gowers [T. Gowers, A new proof of Szemerédi's theorem, Geom. Funct. Anal. 11 (2001) 465-588] and Nagle, Rödl, Schacht, and Skokan [B. Nagle, V. Rödl, M. Schacht, The counting lemma for regular k-uniform hypergraphs, Random Structures Algorithms, in press; V. Rödl, J. Skokan, Regularity lemma for k-uniform hypergraphs, Random Structures Algorithms, in press; V. Rödl, J. Skokan, Applications of the regularity lemma for uniform hypergraphs, preprint] has established a hypergraph removal lemma, which in turn implies some results of Szemerédi [E. Szemerédi, On sets of integers containing no k elements in arithmetic progression, Acta Arith. 27 (1975) 299-345], and Furstenberg and Katznelson [H. Furstenberg, Y. Katznelson, An ergodic Szemerédi theorem for commuting transformations, J. Anal. Math. 34 (1978) 275-291] concerning one-dimensional and multidimensional arithmetic progressions, respectively. In this paper we shall give a self-contained proof of this hypergraph removal lemma. In fact we prove a slight strengthening of the result, which we will use in a subsequent paper [T. Tao, The Gaussian primes contain arbitrarily shaped constellations, preprint] to establish (among other things) infinitely many constellations of a prescribed shape in the Gaussian primes.     

Rapid Raman mapping of a fulgurite

A fulgurite is a naturally occurring glass formed when lightning hits sand, rock, or soil. The formation of fulgurites is accompanied by mineralogical and sometimes compositional changes, and may record information about the environment in which they were formed. A previous investigation using Raman point spectroscopy discovered the presence of anatase, a low-temperature polymorph of TiO₂, and polyaromatic hydrocarbons within a fulgurite. These findings indicate that there were regions within the sample that were not subjected to temperatures of 2,000 K or more that the matrix is reported to attain when struck by lightning. This paper seeks to expand the previous research by utilizing the capabilities of a new Raman spectroscopic technological development that enables rapid mapping. The entire surface area of a cross-sectioned fulgurite (∼40 mm × 23 mm) sample was mapped allowing several regions of polyaromatic hydrocarbons and anatase to be located. Furthermore, shocked quartz was found within the boundary regions of the fulgurite, and is proposed to have resulted from contact with vaporized material during the lightning strike. Shocked quartz is typically indicative of extraterrestrial impact, yet its discovery here suggests that its formation is not exclusive to the impact process.     

Current development in microfluidic immunosensing chip

This review accounts for the current development in microfluidic immunosensing chips. The basic knowledge of immunoassay in relation to its microfluidic material substrate, fluid handling and detection mode are briefly discussed. Here, we mainly focused on the surface modification, antibody immobilization, detection, signal enhancement and multiple analyte sensing. Some of the clinically important currently implemented on the microfluidic immunoassay chips are C-reactive protein (CRP), prostate specific antigen (PSA), ferritin, vascular endothelial growth factor (VEGF), myoglobin (Myo), cardiac troponin T (cTnT), cardiac troponin I (cTnI), and creatine kinase-cardiac muscle isoform (CK-MB). The emerging microfludic immunosensor technology may be a promising prospect that can propel the improvement of clinical and medical diagnosis.     

Scaling Limits of Wick Ordered KPZ Equation

Consider the KPZ equation [(u)\dot](t,x)=Du(t,x)+|?u(t,x)|²+W(t,x)\dot u(t,x)=\Delta u(t,x)+|\nabla u(t,x)|^2+W(t,x), x]Â^d, where W(t,x) is a space-time white noise. This paper investigates the question of whether, for some exponents h and z, k^{mh}u(k^z t, kx) converges in some sense as k?￥k\to\infty, and if so, what are the values of these exponents. The non-linear term in the KPZ equation is interpreted as a Wick product and the equation is solved in a suitable space of stochastic distributions. The main tools for establishing the scaling properties of the solution are those of white noise analysis, in particular, the Wiener chaos expansion. A notion of convergence in law in the sense of Wiener chaos is formulated and convergence in this sense of k^{mh}u(k^z t, kx) as kMX is established for various values of h and z depending on the dimension d.     

Effects of electrolytes on adsorbed polymer layers: poly(ethylene oxide)-silica system

The effects of various electrolytes on the adsorption of poly(ethylene oxide) onto silica have been studied. The salts were the chlorides of Na+, Mg2+, Ca2+, and La3+. The methods used were adsorption isotherms, found using a depletion method with phosphomolibdic acid, photon correlation spectroscopy, and solvent relaxation NMR. All the salts increased the particle-polymer affinity and adsorbed amount according to the adsorption isotherms, and a linear relationship was found between the initial slope of the isotherms and the ionic strength of the solution. Final adsorbed amounts were approximately 0.4-0.5 mg m(-2). The polymer layer thicknesses as found by PCS were of the same order as the radius of gyration of the polymer and increased with both the concentration and the valency of the salt due to increased adsorption. Solvent relaxation NMR showed that NaCl is too weak to have a noticeable effect on the polymer train layer, but the divalent salts clearly did increase both the strength of solvent binding close to the silica surface and the amount of PEO required to reach the maximum train density.