Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.     

Virtual queuing at airport security lanes

Airports continuously seek opportunities to reduce the security costs without negatively affecting passenger satisfaction. In this paper, we investigate the possibilities of implementing virtual queuing at airport security lanes, by offering some passengers a time window during which they can arrive to enter a priority queue. This process could result in a smoother distribution of arriving passengers, such that the required security personnel (costs) can be decreased. While this concept has received attention in a number of settings, such as theme parks, virtual queuing at airports bears an additional level of complexity related to the flight schedules, i.e., passengers can only be transferred forward in time to a limited extent, which we denote by the transfer time limit. We conducted a major simulation study in collaboration with a large international airport in Western Europe to determine the potential impact of virtual queuing and find that nearly one million Euro can be saved on security personnel cost without negatively impacting the passenger waiting time.     

Structural and optical properties of SrCu2O2 films deposited on sapphire substrates by pulsed laser deposition

We deposited SrCu₂O₂ (SCO) films on sapphire (Al₂O₃) (0 0 0 1) substrates by pulsed laser deposition. The crystallographic orientation of the SCO thin film showed clear dependence on the growth temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed that the film deposited at 400 °C was mainly oriented in the SCO [2 0 0] direction, whereas when the growth temperature was increased to 600 °C, the SCO film showed a dominant orientation of SCO [1 1 2]. The SCO film deposited at 500 °C was obvious polycrystalline, showing multi peaks from (2 0 0), (1 1 2), and (2 1 1) diffraction in the XRD spectrum. The SCO film deposited at 600 °C showed a band gap energy of 3.3 eV and transparency up to 80% around 500 nm. The photoluminescence (PL) spectra of the SCO films grown at 500 °C and 600 °C mainly showed blue-green emission, which was attributed to the intra-band transition of the isolated Cu⁺ and Cu⁺–Cu⁺ pairs according to the temperature dependent-PL analysis.     

Detection of a new SRS‐promoting phonon mode and cross‐cascaded χ(3)‐nonlinear lasing in single crystals of calcite (trigonal CaCO3)

For calcite (CaCO₃), one of the pioneer crystals in nonlinear optics, new results of stimulated Raman scattering (SRS) spectroscopy are presented. Among them are the discovery of a new SRS‐promoting vibration mode with ω_SRS2 ≈︁ 282 cm^‐1 and its participation, together with the main SRS mode ω_SRS1 ≈︁ 1086.5 cm^‐1, in cross‐cascaded (χ⁽³⁾ ↔ χ⁽³⁾) nonlinear‐lasing generation, as well as the observation of efficient self‐upconversion via cascaded parametric four‐wave processes of one‐micron Stokes and anti‐Stokes χ⁽³⁾‐lasing into the UV‐region of third harmonic generation. The investigations show that calcite is able to generate a χ⁽³⁾‐lasing comb of more than two octaves bandwidth. The article also gives a brief review on the discovery and study of the SRS‐effect in natural crystals (minerals), which have expanded our ability to study the photon‐phonon nonlinear‐laser interactions in crystalline materials. A short summary of information about χ⁽³⁾‐lasing properties of the triangular planar structure units in SRS‐active crystals is included.     

Thermoelastic-numerical hybrid analysis of holes and cracks in composites

An effective thermoelastic-numerical hybrid method is demonstrated for obtaining stress information on, and adjacent to, geometric discontinuities in orthotropic composites. This includes determining stress intensity factors. The technique involves evaluating the stress functions from measured thermoelastic data around the external boundary of a subregion containing the geometric discontinuity of interest. Knowing the stress functions, stresses throughout the subregion surrounding the geometric discontinuity, and stress intensity factors, are available.     

Homotopy algorithm for symmetric eigenvalue problems

Summary The homotopy method can be used to solve eigenvalue-eigenvector problems. The purpose of this paper is to report the numerical experience of the homotopy method of computing eigenpairs for real symmetric tridiagonal matrices together with a couple of new theoretical results. In practice, it is rerely of any interest to compute all the eigenvalues. The homotopy method, having the order preserving property, can provide any specific eigenvalue without calculating any other eigenvalues. Besides this advantage, we note that the homotopy algorithm is to a large degree a parallel algorithm. Numerical experimentation shows that the homotopy method can be very efficient especially for graded matrices.Research was supported in part by NSF under Grant DMS-8701349     

Analysis of cell gap-dependent driving voltage in a fringe field-driven homogeneously aligned nematic liquid crystal display

We have studied cell gap-dependent driving voltage characteristics in a homogeneously aligned nematic liquid crystal (LC) cell driven by a fringe electric field, termed the fringe field switching (FFS) mode. The results show that for the FFS mode using a LC with positive dielectric anisotropy, the operating voltage decreases as the cell gap decreases, whereas it increases with a decreasing cell gap when using a LC with negative dielectric anisotropy. The difference between LCs is explained by simulation and experiment.     

Proteomic analysis of Helicobacter pylori cellular proteins fractionated by ammonium sulfate precipitation

Among 1590 ORFs in the Helicobacter pylori genome, >250 have been identified as authentic genes by proteomic analysis. Low-abundance proteins need to be enriched to a minimal amount for MALDI-TOF analysis and salt precipitation has generally been used for protein enrichment. Here, a whole-cell extract of H. pylori strain 26695 was subjected to protein fractionation with stepwise concentrations of ammonium sulfate and the proteins were displayed by 2-DE. The protein spots were quantified using PDQUEST software and identified by peptide fingerprinting. The 2-DE profiles and intensities of individual protein spots differed among the protein fractions. Out of the 98 identified proteins, 61 were found in the stepwise ammonium sulfate fractions but not in the whole-cell extract. Out of these, 37 proteins, including KdsA, were found exclusively in a single fraction. In contrast, GroEL, UreA, UreB, TrxA, NapA, and FldA were ubiquitously present in all fractions. Iron-containing proteins such as NapA, SodB, CeuE, and Pfr were found predominantly in the 100% saturated ammonium sulfate precipitate. Additionally, 29 proteins were newly identified in this study. These data will facilitate the preparation of significant H. pylori proteins, as well as provide information about low-abundance proteins.     

Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum

A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 μg mL⁻¹ of BSA-DA and 1/7500 dilution of anti-DA antibody. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0 × 10⁻⁹ M (0.19 μg L⁻¹) and five orders (3.2 × 10⁻⁸ M to 3.2 × 10⁻³ M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient (R² = 0.9947): Abs. (in serum) = 0.6128 × Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.