Parameter identification of a nonlinear model: replicating the motion response of an autonomous underwater vehicle for dynamic environments

Nonlinear Dynamics - This study presents a system identification algorithm to determine the linear and nonlinear parameters of an autonomous underwater vehicle (AUV) motion response prediction...     

Molecular Sieving of Acetylene from Ethylene in a Rigid Ultra-microporous Metal Organic Framework.

Rigid molecular sieving materials are the ideal candidates for gas separation (e. g., C₂H₂/C₂H₄) due to their ultrahigh adsorption selectivity and the absence of gas co-adsorption. However, the absolute molecular sieving effect for C₂H₂/C₂H₄ separation has rarely been realized because of their similar physicochemical properties. Herein, we demonstrate the absolute molecular sieving of C₂H₂ from C₂H₄ by a rigid ultra-microporous metal-organic framework ( F−PYMO−Cu ) with 1D regular channels (pore size of ca. 3.4 Å). F−PYMO−Cu exhibited moderate acetylene uptake (35.5 cm³/cm³), but very low ethylene uptake (0.55 cm³/cm³) at 298 K and 1 bar, yielding the second highest C₂H₂/C₂H₄ uptake ratio of 63.6 up to now. One-step C₂H₄ production from a binary mixture of C₂H₂/C₂H₄ and a ternary mixture of C₂H₂/CO₂/C₂H₄ at 298 K was achieved and verified by dynamic breakthrough experiments. Coupled with excellent thermal and water stability, F−PYMO−Cu could be a promising candidate for industrial C₂ separation tasks.     

Stability‐indicating HPLC assay for lysine–proline–valine (KPV) in aqueous solutions and skin homogenates

A simple, sensitive and stability‐indicating high‐performance liquid chromatographic (HPLC) assay method was developed and validated for a bioactive peptide, lysine–proline–valine (KPV) in aqueous solutions and skin homogenates. Chromatographic separation was achieved on a reversed phase Phenomenex C₁₈ column (4.6 × 250 mm, packed with 5 µm silica particles) with a gradient mobile phase consisting of 0.1% trifluoroacetic acid (TFA) in water (A) and 0.1% TFA in acetonitrile (B). The proposed HPLC method was validated with respect to accuracy, precision, linearity, repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The calibration curve was linear with a correlation coefficient (r) of 0.9999. Relative standard deviation values of accuracy and precision experiments were <2. The LOD and LOQ of KPV were 0.01 and 0.25 µg/mL, respectively. Under stress conditions (acid, alkali and hydrogen peroxide) KPV yielded lys–pro–diketopiperazine as major degradation product, which was identified by flow injection MS analysis. The developed HPLC method was found to be efficient in separating the active peptide from its degradation products generated under various stress conditions. Also, the validated method was able to separate KPV from other peaks arising from endogenous components of the skin homogenate. Copyright © 2014 John Wiley & Sons, Ltd.     

Steepest-edge simplex algorithms for linear programming

We present several new steepest-edge simplex algorithms for solving linear programming problems, including variants of both the primal and the dual simplex method. These algorithms differ depending upon the space in which the problem is viewed as residing, and include variants in which this space varies dynamically. We present computational results comparing steepest-edge simplex algorithms and approximate versions of them against simplex algorithms that use standard pivoting rules on truly large-scale realworld linear programs with as many as tens of thousands of rows and columns. These results demonstrate unambiguously the superiority of steepest-edge pivot selection criteria to other pivot selection criteria in the simplex method.The research of this author was supported in part by NSF Grants DMS 85-12277, DMS 91-0619 and CDR 84-21402.     

Comparison of exact and mean beam length results for a radiating hydrogen plasma

The purpose of this work is to investigate the accuracy of the mean beam length technique in high-temperature radiative heat transfer, combined with other modes of heat transfer. In order to study the validity of the mean beam length method, Nusselt numbers are presented for fully developed channel flow of a radiating nonisothermal hydrogen plasma. Black isothermal boundaries are considered. Numerical results obtained from the exact integrodifferential equation have been obtained previously for this problem. Linearized radiation and local thermodynamic equilibrium are assumed.The results show that the Nusselt numbers obtained by using the geometric mean beam length are in close agreement with results obtained by using the mean beam length. Therefore the complicated calculations needed to obtain the mean beam length are unnecessary.A comparison of the results obtained in the present work with previously reported work shows that the mean beam length technique is a better approximation to the exact solution than the optically-thick, or nongray differential approximation solutions.     

Optical recording using hydrogen phthalocyanine thin films

Vacuum sublimed thin films of the blue dye hydrogen phthalocyanine (H₂Pc) were incorporated into various optical recording structures. The dye was shown to be thermally, hydrolytically, and oxidatively stable. In all cases, the writing mechanisms are dependent on the sublimation of H₂Pc. Several recording structures which take advantage of the sublimation property of H₂Pc are demonstrated, including pit forming and bubble forming media. These H₂Pc-based optical recording structures show very high optical contrast and low writing threshold energies. In addition, very thin films (50–75Å) of H₂Pc were incorporated into a tellurium-based medium, which significantly enhanced the writing contrast observed in that medium.     

Ultrafast spectral hole burning reveals the distinct chromophores in eumelanin and their common photoresponse

Eumelanin, the brown-black pigment found in organisms from bacteria to humans, dissipates solar energy and prevents photochemical damage. While the structure of eumelanin is unclear, it is thought to consist of an extremely heterogeneous collection of chromophores that absorb from the UV to the infrared, additively producing its remarkably broad absorption spectrum. However, the chromophores responsible for absorption by eumelanin and their excited state decay pathways remain highly uncertain. Using femtosecond broadband transient absorption spectroscopy, we address the excited state behavior of chromophore subsets that make up a synthetic eumelanin, DOPA melanin, and probe the heterogeneity of its chromophores. Tuning the excitation light over more than an octave from the UV to the visible and probing with the broadest spectral window used to study any form of melanin to date enable the detection of spectral holes with a linewidth of 0.6 eV that track the excitation wavelength. Transient spectral hole burning is a manifestation of extreme chemical heterogeneity, yet exciting these diverse chromophores unexpectedly produces a common photoinduced absorption spectrum and similar kinetics. This common photoresponse is assigned to the ultrafast formation of immobile charge transfer excitons that decay locally and that are formed among graphene-like chromophores in less than 200 fs. Raman spectroscopy reveals that chromophore heterogeneity in DOPA melanin arises from different sized domains of sp²-hybridized carbon and nitrogen atoms. Furthermore, we identify for the first time striking parallels between the excited state dynamics of eumelanin and disordered carbon nanomaterials, suggesting that they share common structural attributes.

Seeing the colors in black: ultrafast transient hole burning spectroscopy reveals the absorption properties of discrete chromophores and their interactions in the skin pigment eumelanin.     

Direct observation of the evolving metal–support interaction of individual cobalt nanoparticles at the titania and silica interface

Understanding the metal–support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced properties. Spatially resolved soft X-ray absorption spectroscopy (XAS) in combination with Atomic Force Microscopy (AFM) and Scanning Helium Ion-Milling Microscopy (SHIM) has been applied to visualise and characterise the behaviour of individual cobalt nanoparticles (CoNPs) supported on two-dimensional substrates (SiO_xSi(100) (x < 2) and rutile TiO₂(110)) after undergoing reduction–oxidation–reduction (ROR). The behaviour of the Co species is observed to be strongly dependent on the type of support. For SiO_xSi a weaker MSI between Co and the support allows a complete reduction of CoNPs although they migrate and agglomerate. In contrast, a stronger MSI of CoNPs on TiO₂ leads to only a partial reduction under H₂ at 773 K (as observed from Co L₃-edge XAS data) due to enhanced TiO₂ binding of surface-exposed cobalt. SHIM data revealed that the interaction of the CoNPs is so strong on TiO₂, that they are seen to spread at and below the surface and even to migrate up to ∼40 nm away. These results allow us to better understand deactivation phenomena and additionally demonstrate a new understanding concerning the nature of the MSI for Co/TiO₂ and suggest that there is scope for careful control of the post-synthetic thermal treatment for the tuning of this interaction and ultimately the catalytic performance.

Understanding the metal–support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced properties.