Impact of environmental conditions on the marine natural product bryostatin 1

Marine Natural Products (MNPs), such as bryostatin 1, are exposed to a range of physical and chemical conditions through the life cycle of the host organism. These include exposure to sunlight, oxidizing and reducing agents, cation binding, and adsorption to reactive metal oxide surfaces. Using Fourier Transform-Ion Cyclotron Resonance (FT-ICR), Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS), UV/Vis absorbance spectroscopy, and molecular modeling, we studied the impact of UV light, TiO2, I2, and reaction with FeCl3 on the structure of bryostatin 1. Our results demonstrate that natural conditions transform bryostatin to a number of structures, including one with a molar mass of 806 Da, which we have previously identified in the sediment collected from the Gulf of Mexico. To date, at least 20 different structures of bryostatin have been reported in the literature. This work suggests that these variations may be products of the chemical environment in which the bryozoa Bugula neritina resides and are not the result of genetic variations within Bugula.     

Electrical and mechanical properties of hot-pressed versus sintered LiTi2(PO4)3

The electrical and mechanical properties of hot-pressed versus sintered LiTi₂(PO₄)₃ were investigated. The hot-pressed LiTi₂(PO₄)₃ had a higher density and larger average grain size than the sintered material. As a result of these microstructural differences the hot-pressed material exhibited a higher total ionic conductivity and lower hardness. The electronic conductivity of both materials was the same and increased by a factor of about 10⁷ when the hot-pressed and sintered materials were heated under a reducing atmosphere.     

Development of a two-phase xenon dark matter detector

The current status of the development study focused on building a novel two-phase xenon detector for dark matter search is described. Discrimination of the radioactive background is based on particle identification that comes from the analysis of the scintillation-to-ionization ratio. Electroluminescence (proportional scintillation) is used for “amplification” of the ionization signal.     

Manifold preprocessing for laser‐induced breakdown spectroscopy under Mars conditions

Laser‐induced breakdown spectroscopy (LIBS) is currently being used onboard the Mars Science Laboratory rover Curiosity to predict elemental abundances in dust, rocks, and soils using a partial least squares regression model developed by the ChemCam team. Accuracy of that model is constrained by the number of samples needed in the calibration, which grows exponentially with the dimensionality of the data, a phenomenon known as the curse of dimensionality. LIBS data are very high dimensional, and the number of ground‐truth samples (i.e., standards) recorded with the ChemCam before departing for Mars was small compared with the dimensionality, so strategies to optimize prediction accuracy are needed. In this study, we first use an existing machine learning algorithm, locally linear embedding (LLE), to combat the curse of dimensionality by embedding the data into a low‐dimensional manifold subspace before regressing. LLE constructs its embedding by maintaining local neighborhood distances and discarding large global geodesic distances between samples, in an attempt to preserve the underlying geometric structure of the data. We also introduce a novel supervised version, LLE for regression (LLER), which takes into account the known chemical composition of the training data when embedding. LLER is shown to outperform traditional LLE when predicting most major elements. We show the effectiveness of both algorithms using three different LIBS datasets recorded under Mars‐like conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Gradient elution in counter-current chromatography: a new layout for an old path

Gradient elution in CCC is a powerful tool, which needs further systematic development to become robust and easy to use. The first attempt to build a correlation between gradient elution profile and distribution ratio (K(D)) values for model mixtures containing typical representatives of pharmaceutical compounds is presented in this paper. The three step estimation of the solvent system composition of a heptane-ethyl acetate-methanol-water (HEMWat) series is described. The estimation is based on simple measurements of initial and final stationary phase retention for gradient elution run, calculating gradient distribution ratio and correlating it with static K(D) against HEMWat number.     

A visualization study of fluid-structure interaction between a circular cylinder and a channel bed

Flow visualization was used to study the fluid-structure interaction between a circular cylinder and a shallow turbulent open channel flow. The Reynolds number ranged from Re _D = 1500–4400 based on the cylinder diameter, and from Re _H =7,800?27,600 based on the channel hydraulic radius. The cylinder was mounted vertically on the channel bed and the flow depth-to-cylinder-diameter ratio was varied fromd/D=7.0?11.7. Tests were carried out over smooth and rough beds, with the rough beds being either permeable or impermeable. The study showed that the horseshoe vortex forming at the cylinder-bed junction affects many of the flow structures, including the mode of vortex shedding, the shear layer dynamics, the vortex formation length, and the width of the near-wake region. The influence of the horseshoe vortex can be recognized throughout the depth of flow; however, its influence decreases with an increase in distance from the channel bed. It was also possible to discern that the bed roughness resulted in a change to the above interaction and the permeability of the bed resulted in additional changes.     

Do columnar defects produce bulk pinning?

From magneto-optical imaging performed on heavy-ion-irradiated YBa(2)Cu(3)O(7-delta) single crystals, it is found that at fields and temperatures where strong single vortex pinning by individual irradiation-induced amorphous columnar defects is to be expected, vortex motion is limited by the nucleation of vortex kinks at the specimen surface. In the material bulk, vortex motion occurs through (easy) kink sliding. Depinning in the bulk determines the screening current only at fields comparable to or larger than the matching field, at which the majority of vortices is not trapped by an ion track.     

Two circular cylinders in cross-flow: A review

Pairs of circular cylinders immersed in a steady cross-flow are encountered in many engineering applications. The cylinders may be arranged in tandem, side-by-side, or staggered configurations. Wake and proximity interference effects, which are determined primarily by the longitudinal and transverse spacing between the cylinders, and also by the Reynolds number, have a strong influence on the flow patterns, aerodynamic forces, vortex shedding, and other parameters. This paper reviews the current understanding of the flow around two “infinite” circular cylinders of equal diameter immersed in a steady cross-flow, with a focus on the near-wake flow patterns, Reynolds number effects, intermediate wake structure and behaviour, and the general trends in the measurements of the aerodynamic force coefficients and Strouhal numbers. A primary focus is on the key experimental and numerical studies that have appeared since the last major review of this subject more than 20 years ago.