Highly permeable monolithic columns have been prepared directly within capillaries of various internal diameters by the in situ polymerization of high purity divinylbenzene, characterized, and used as novel stationary phases for gas‐solid chromatography. The chromatographic properties of these columns are demonstrated by the efficient separation of mixtures of volatile organic compounds as well as their aqueous solutions. 相似文献
The design of hydrogen storage materials is one of the principal challenges that must be met before the development of a hydrogen economy. While hydrogen has a large specific energy, its volumetric energy density is so low as to require development of materials that can store and release it when needed. While much of the research on hydrogen storage focuses on metal hydrides, these materials are currently limited by slow kinetics and energy inefficiency. Nanostructured materials with high surface areas are actively being developed as another option. These materials avoid some of the kinetic and thermodynamic drawbacks of metal hydrides and other reactive methods of storing hydrogen. In this work, progress towards hydrogen storage with nanoporous materials in general and porous organic polymers in particular is critically reviewed. Mechanisms of formation for crosslinked polymers, hypercrosslinked polymers, polymers of intrinsic microporosity, and covalent organic frameworks are discussed. Strategies for controlling hydrogen storage capacity and adsorption enthalpy via manipulation of surface area, pore size, and pore volume are discussed in detail.
Summary
Highly branched aliphatic molecules have been used for the first time as tethers in the preparation of polymeric chiral stationary
phases. Attachment of a specifically designed chiral selector to organic porous polymer beads through a branched linker substantially
increases the enantioselectivity compared to that of the equivalent separation medium with a traditional linear tether.
Received: 31 March 1998/Revised version: 27 May 1998/Accepted: 27 May 1998 相似文献
An application of remotely detected magnetic resonance imaging is demonstrated for the characterization of flow and the detection of fast, small molecule separations within hypercrosslinked polymer monoliths. The hyper-cross-linked monoliths exhibited excellent ruggedness, with a transit time relative standard deviation of less than 2.1%, even after more than 300 column volumes were pumped through at high pressure and flow. Magnetic resonance imaging enabled high-resolution intensity and velocity-encoded images of mobile phase flow through the monolith. The images confirm that the presence of a polymer monolith within the capillary disrupts the parabolic laminar flow profile that is characteristic of mobile phase flow within an open tube. As a result, the mobile phase and analytes are equally distributed in the radial direction throughout the monolith. Also, in-line monitoring of chromatographic separations of small molecules at high flow rates is shown. The coupling of monolithic chromatography columns and NMR provides both real-time peak detection and chemical shift information for small aromatic molecules. These experiments demonstrate the unique power of magnetic resonance, both direct and remote, in studying chromatographic processes. 相似文献
Ion beam methods for modification of nanohardness of surface nanolayers of the titanium alloy Ti6AI4V were applied. After deposition of carbon nanolayers by electron beam evaporation, the ion implantation of nitrogen into samples was carried out. The chemical composition of the modified surface area was investigated by AES (auger electron spectroscopy). The nanohardness of resulted ion beam modified surface nanolayers were investigated by nanoindentation testing. The measured concentration profiles indicate the atomic mixing of carbon into the substrate. It was found that the modified samples had a markedly higher nanohardness than the unmodified samples. The increased nanohardness is attributed to the newly created phases in the surface area. 相似文献
ABSTRACTThis paper presents a numerical investigation of three direct architectures and three indirect architectures for identifying a plant operating in closed loop. Motivated by adaptive control of systems with nonminimum-phase (NMP) zeros and taking advantage of the fact that zeros are not moved by feedback, the performance metric is the accuracy of the estimates of the NMP zeros of the plant. Assuming known plant order, single-input, single-output, infinite-impulse-response models are constructed in the presence of process and sensor noise. Least squares provides the baseline estimation technique, and prediction error methods are used to account for correlation between the model input and noise. The goal is to compare the accuracy of the NMP-zero estimates obtained from each method and for each architecture. 相似文献
Summary
Two different families of peptidomimetics have been synthesized and used as chiral selectors for enantioselective chromatography.
The functionalization of compounds with multiple nitrogen atoms allows their use in the preparation of chiral stationary phases
(CSPs), with acrylic or styril comonomers, in both bead and monolithic formats. Some of these separation media, having the
appropriate morphological properties for their use in chromatographic columns, were able to efficiently discriminate enantiomers
of aminoacid derivatives and pharmaceuticals such as Oxazepam.
Received: 24 September 2001/Revised version: 2 January 2002/ Accepted: 21 January 2002 相似文献