Showing papers by "Yi Chen published in 1997"

Synthesis and characterization of porous chromia-pillared layered titanoniobate

Abstract: Oligomeric chromium(III)-intercalated titanoniobate has been prepared by the intercalation of propylamine into KTiNbO 5 followed by substitution of propylammonium for tetramethylammonium and finally refluxing with an aqueous solution of Cr(O 2 CMe) 3 . The first chromia-pillared layered titanoniobate was then obtained by calcination of oligomeric chromium(III)-intercalated titanoniobate at 400 °C in a flow of N 2 . Characterization of chromia-pillared titanoniobate revealed that the material has the porous layered structure with a Brunauer–Emmett–Teller surface area of 122.4 m 2 g -1 and an interlayer distance of 13.4 A as well as a narrow pore-size distribution in the range 30–46 A. The layered structure can be retained up to 500 °C. However, calcination of the oligomeric chromium(III)-intercalated titanoniobate in air at the same temperature led to a product with a low surface area and a small interlayer space. X-Ray photoelectron studies indicate the existence of different states of chromia in the products obtained in the different atmospheres. The IR spectra of the pyridine-adsorbed material and the ammonia temperature-programmed desorption profile demonstrate the presence of a large amount of acid sites with medium strength on the surface of the new chromia-pillared material. Isopropyl alcohol decomposition confirms the existence of only acid sites in the sample.

Chemically prepared Fe-B ultrafine amorphous alloy particles: influence of the way of mixing reactants

Abstract: Fe-B ultrafine amorphous alloy particles have been prepared by the addition of FeSO4 solutions into KBH4 solutions. The reaction was found to automatically maintain constant pH levels in a basic medium and produced Fe-B samples with higher boron content as compared to the reaction for the addition of KBH4 solutions into FeSO4 solutions. The latter reaction automatically maintained constant pH levels in an acidic medium. The mechanism of the overall reaction between FeSO4 and KBH4 in aqueous solution is composed of three simple independent reactions which are shown to be valid for both addition routes for the reaction. The concentration and addition rate of FeSO4 solutions were also found to significantly influence the boron content and properties of the produced Fe-B samples.

Logical Granulometric Filtering in the Signal—Union—Clutter Model

Abstract: A basic problem of binary morphological image filtering is to remove background clutter (noise) in order to reveal a desired target (signal) The present paper discusses the manner in which filtering can be achieved using morphological granulometric filters Logical granulometries are unions of intersections of reconstructive openings and these use shape elements to identify image components to be passed (in full), whereas others are deleted Assuming opening structuring elements are parameterized, the task is to find parameters that result in optimal filtering Optimization is achieved via the notion of granulometric sizing For situations where optimization is impractical or intractable, filter design can be achieved via adaptation Based upon correct or incorrect decisions as to whether or not to pass a component, the filter parameter vector is adapted during training in accordance with a protocol that adapts towards correct decisions The adaptation scheme yields a Markov chain in which the parameter space is the state space of the chain Convergence of the adaptation procedure is characterized by the stationary distribution of the parameter vector State-probability equations are derived via the Chapman-Kolmogorov equations and these are used to describe the steady-state distribution

Selective Oxidation of Toluene over Complex Fe–Mo Oxides in the Absence of Molecular Oxygen

Abstract: Fe–Mo catalysts prepared by a sol–gel method for selective oxidation of toluene are studied in the absence of molecular oxygen; a high benzaldehyde yield and high specific activity are achieved at an atomic ratio (Mo∶Fe) of about 1.0.

Digital measurement of gene expression in a cDNA microarray

Abstract: Gene expression can be quantitatively analyzed by hybridizing fluor-tagged mRNA to targets on a cDNA micro- array. Comparison of expression levels arising from co- hybridized samples is achieved by taking ratios of average expression levels for individual genes. The present paper concerns image processing to automatically segment digitized micro-arrays and measure median gene expression levees across cDNA target sites. The main difficulty arises from determination of the target site when signal intensity is low. Segmentation must be accomplished for target sites that can possess highly unstable geometry and consist of a relatively small number of pixels. Segmentation must also be computationally efficient. The present paper proposes a nonparametric statistical method that separates target site from local background using the Mann-Whitney test.

A novel selective oxidation catalyst: ultrafine complex molybdenum based oxide particles

Abstract: Publisher Summary Mo-based and V-based oxides have been widely used as selective oxidation catalysts and the studies on the structure and catalytic properties of these oxides have demonstrated that the nature of oxygen species in the oxides is one of the most important parameters, influencing catalytic selectivity. To increase the reactivity of lattice oxygen species and to improve the catalytic selectivity, great efforts have been made to modify the state of lattice oxygen species by adding some promoters to these oxides. It has been found that Bi, Fe, Sn, W, and rare earth oxides are the effective promoters of the molybdenum-based and vanadium-based oxide catalysts for selective oxidation of toluene to benzaldehyde. The ultrafine complex oxide particles are potentially new catalytic materials for selective oxidation reactions. It has been found that the reactivity of lattice oxygen ions can be improved by decreasing the oxide particle size to nano-scale and that the ultrafine oxide particles exhibit unique catalytic properties for selective oxidation. The interaction of Ce with Mo and its effect on the nature of active oxygen species in the complex oxides were studied by using temperature-programmed reduction (TPR) and laser Raman spectroscopy (LRS). The morphology of Mo–Ce oxide samples (Ce/Mo atomic ratio = 2/3) prepared by different methods are presented in this chapter. It can been seen that the particle size of Mo–Ce(sg) was in the range of 20-80 nm, while that of Mo–Ce(cp) was higher than 500nm. These results have shown that the Mo-Ce oxides prepared by the sol-gel method are actually the ultrafine oxide particles (

Scaling approach to the in-plane resistivity of single crystalline La1.85Sr0.15CuO4 as a function of temperature, magnetic field and its orientation

Abstract: Scaling approach to the in-plane resistivity in the mixed state of La 1.85 Sr 0.15 SrCuO 4 as a function of temperature ( T ), magnetic field ( H ), and angle (θ) between the field and the ab -planes is examined in terms of different models. It is firstly shown that the |sin θ| scaling by the two-dimensional (2-D) vortex pancake model is inappropriate to the present system. Although scaling approach to the data could be formallly performed according to the quasi-2-D model proposed by Tinkham, the anisotropy extracted from the scaling is decreased with temperature, which is contrary to the quasi-2-D prediction. Best scaling is obtained with the anisotropic three-dimensional (3-D) model. The temperature-independent anisotropy parameter ( γ ∼ 14.7) so obtained is consistent with the anistropic 3-D model for strongly coupled superconducting layers.

Synthesis of a New Solid Acid: Silica Pillared Lanthanum Niobate with a Supergallery.

Abstract: Stepwise intercalations of n-decylamine and oligosiloxanes followed by calcination at 823 K in air results in a thermostable supergallery layered lanthanum niobate; the new material shows an interlayer free spacing of 17.4 A along with a high Brunauer–Emmett–Teller surface area of 251 m 2 g - 1 ; the acidity of the new pillared material is markedly enhanced with respect to the original lanthanum niobate.

[Characteristics of lip-mouth region in smiling position from 80 adults with acceptable faces and individual normal occlusions].

Abstract: The Characteristics of Lip-mouth region including the soft and hard tissues in smiling position with frontal fixed position photographic computered analysis was studied. The examples were 80 adults (40 males and 40 females) with acceptable faces and individual normal occlusions. The age was between 17-25 years of age. The method adopting maximum smiling position to study the lip-mouth region is scientific, and the maximum smile line could be divided into three categories: low smile line-a-counted for 16.25% of the total samples; average smile line--68.75%; high smile line--15%.