Beryllium

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Detection of formaldehyde using mid-infrared difference-frequency generation

3 (PPLN) is reported. Minimum detectable concentration of 30 ppb was achieved with a compact, portable room-temperature gas sensor configured for formaldehyde (H₂CO) detection. This sensitivity, coupled with high selectivity and long term stability, is sufficient for various environmental applications. Received: 29 September 1997     

Adsorption properties of CO on low-index Pt3Sn surfaces

The adsorption properties of CO on Pt₃Sn were investigated by utilizing quantum mechanical calculations. The (1 1 1), (1 1 0) and (0 0 1) surfaces of Pt₃Sn were generated with all possible bulk terminations, and on these terminations all types of active sites were determined. The adsorption energies and the geometries of the CO molecule at those sites were found. Those results were compared with the results obtained from the adsorption of CO on similar sites of Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) surfaces. The comparison reveals that adsorption of CO is stronger on Pt surfaces; this may be the reason why catalysts with Pt₃Sn phase do not suffer from CO posioning in experimental works. Aiming to understand the interactions between CO and the metal adsorption sites in detail, the local density of states (LDOS) profiles were produced for atop-Pt adsorption, both for the carbon end of CO for its adsorbed and free states, and for the Pt atom of the binding site. LDOS profiles of C of free and adsorbed CO and Pt for corresponding pure Pt surfaces, Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) were also obtained. The comparison of the LDOS profiles of Pt atoms of atop adsorption sites on the same faces of bare Pt₃Sn and Pt surfaces showed the effect of alloying with Sn on the electronic properties of Pt atoms. Comparison of LDOS profiles of the C end of CO in its free and atop adsorbed states on Pt₃Sn and LDOS of Pt on bare and CO adsorbed Pt₃Sn surface were used to clear out the electronic changes occurred on CO and Pt upon adsorption. The study showed that (i) inclusion of a Sn atom at the adsorption site structure causes dramatic decrease in stability which limits the number of possible CO adsorption sites on Pt₃Sn surface, (ii) the presence of Sn causes angles different from 180° for M-C-O orientation, (iii) the presence of Sn in the neighborhood of Pt on which CO is adsorbed causes superposition of the 5σ/1π derived-state peaks at the carbon end of CO and changes in adsorption energy of CO, (iv) Sn present beneath the adsorption site strengthens the CO adsorption, whereas neighboring Sn on the surface weakens it for all Pt₃Sn surfaces tested and (v) the most stable site for CO adsorption is the atop-Pt site of the mixed atom termination of Pt₃Sn(1 1 0).     

Dispersion of mass by two-dimensional homogeneous and incompressible Çinlar flows

We consider the dispersion of passive tracers in stationary, homogeneous and incompressible Çinlar flows on the plane. The associated velocity field is generated by the superposition of eddies of various size, arrival time and location which form a Poisson point process. Our focus is on the dispersion of a tracer cloud, which is measured through the variance of its centroid and the mean of the dispersion tensor. We also study single particle dispersion and particle pair separations in conjunction with dispersion. Monte Carlo simulations of all these measures first establish the relation of the dispersion to the parameters of the flow model. Second, the physical predictions on the behavior of these measures with respect to time as well as their relationship to each other are confirmed.     

Use of Magnetic Nanoparticles and a Microplate Reader with Fluorescence Detection to Detect C‐reactive Protein

Two approaches based on magnetic nanoparticles (MNPs) have been compared to analyze C‐reactive protein (CRP). Both the non‐eluted and eluted MNP‐1°Ab‐CRP‐2°Ab/FITC bioconjugates were measured by a microplate reader with fluorescence detection. The linear ranges for the non‐elution and elution methods were 10‐200 and 0.1‐2.0 μg/mL, respectively. The concentration limits of detection for the nonelution and elution methods were 2.91 and 0.04 μg/mL, respectively. The non‐ elution method gave better precision and recovery than the elution method, and also showed comparable results to that of ELISA assay. The non‐elution method is simple and only needs minute volumes of sample and buffer. There is no need to dissociate the fluorescence probes from the bioconjugates, and the fluorescence signals can be directly measured on the MNP‐1°Ab‐CRP‐2°Ab/FITC bioconjugates. Meanwhile, samples with high CRP concentrations are not necessarily to be diluted before analysis.     

Separation of Lipids on Human Very Low‐density Lipoproteins by Micellar Electrokinetic Chromatography

Liquid‐phase and solid‐phase extractions (SPE) in combination with a simple micellar electrokinetic chromatography (MEKC) method were used to investigate human very low‐density lipoprotein (VLDL) lipids for two healthy donors. At absorbance 200 nm, the effective mobilities and peak areas of the MEKC profiles showed good reproducibility and precisions. A major peak and several minor peaks appeared for the total lipids of native VLDL, but both the peak numbers and areas reduced for the in vitro oxidized VLDL. Two chloroform and two methanol fractions were obtained from SPE of VLDL total lipids. Significant differences were observed for the first methanol fraction between native and in vitro oxidized VLDL lipids. The first methanol fraction showed a major peak and several minor peaks for native VLDL, but both the peak numbers and areas reduced for oxidized VLDL. Oxidation of VLDL caused decomposition of lipids, and thus the reduction of peak numbers and areas.     

Design of Fe-MOF-bpdc deposited with cobalt oxide (CoOx) nanoparticles for enhanced visible-light-promoted water oxidation reaction

Research on Chemical Intermediates - This work spotlights the facile method to deposit cobalt oxide (CoOx) nanoparticles as a cocatalyst on Fe-MOF-bpdc to enhance its photocatalytic activity for...     

Velocity fields with power-law spectra for modeling turbulent flows

We consider a generalization of homogeneous and isotropic Çinlar velocity fields to capture power-law spectra. The random velocity field is non-Gaussian with a representation motivated by Lagrangian and Eulerian observations. A wide range of turbulent flows can be generated by varying the stochastic parameters of the model. The velocity field being a functional version of Poisson shot-noise is constructed as the superposition of eddies randomized through their types and arrival times. We introduce a dependence between the eddy types which are spatial parameters and the decay parameter which is temporal. As a result, long-range correlation in space and a power-law spectrum previously used with Ornstein–Uhlenbeck velocity fields are achieved. We show that a corresponding power-law form for the probability distribution of the eddy diameter is sufficient for this result. The parameters of the probability distribution are further specified in view of Kolmogorov theory of the inertial scales. In particular, ∣k∣^−5/3 scaling of the spectrum is obtained. In the diffusive limit, we show that the parameters governing the decay and the arrival rate, and the speed of rotation of an eddy increase while its diameter decreases. That is, the eddies arrive fast, decay fast, and rotate fast with a small radius for a Brownian limit.     

A new imputation method for incomplete binary data

In data analysis problems where the data are represented by vectors of real numbers, it is often the case that some of the data-points will have “missing values”, meaning that one or more of the entries of the vector that describes the data-point is not observed. In this paper, we propose a new approach to the imputation of missing binary values. The technique we introduce employs a “similarity measure” introduced by Anthony and Hammer (2006) [1]. We compare experimentally the performance of our technique with ones based on the usual Hamming distance measure and multiple imputation.     

Search for differences in oscillation parameters for atmospheric neutrinos and antineutrinos at Super-Kamiokande

We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande-I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best-fit antineutrino mixing is found to be at (Δm2,sin2 2θ)=(2.0×10(-3) eV2, 1.0) and is consistent with the overall Super-K measurement.