NMR imaging of mass transport processes and catalytic reactions

NMR imaging and spectroscopy techniques are applied to study flow and filtration of liquids, gases and granular solids in various geometries and to the in situ studies of the interplay of mass transport and catalytic reactions in porous media. In particular, quantitative spatially resolved maps of flow velocities of liquids and gases in the channels of monoliths have been obtained. A comparative study of the filtration of water and propane through model porous media has revealed that the dispersion coefficients for water are dominated by the holdup effects even in a bed of nonporous glass beads. Similar experiments performed with the gravity driven flow of liquid-containing fine solid particles through a porous bed have yielded the distributions of particle velocities for various flow rates. The NMR imaging technique was employed to visualize the propagation of autocatalytic waves for the Belousov–Zhabotinsky reaction carried out in a model porous medium. It was demonstrated that the wave propagation velocity decreases as the wave crosses the boundary between the bulk liquid and the flooded bead pack. The images detected during the catalytic hydrogenation of -methylstyrene on a single catalyst pellet at elevated temperatures have revealed that the reaction and the accompanying phase transition alter the distribution of the liquid phase within the pellet.     

Near-field magneto-optical analysis in reflection mode SNOM

Observation of magnetic domains with in-plane magnetisations is demonstrated by scanning near-field optical microscopy (SNOM) in reflection mode. The longitudinal and transverse magneto-optical Kerr effects are employed as the contrast mechanisms; these are observed as either a change in the polarisation of the reflected light or reflectance, depending on magnetisation direction. SNOM images of Co and Ni thin films show magneto-optical contrast depending on polarisation of the incident and detected light. For the smooth cobalt thin films, the orientation for magnetic domains is estimated, based on the correlation between the contrasts in SNOM images obtained in different polarisation configurations and the directions of the magnetic vectors of the incident and reflected light. For the nickel films with pronounced topographic structures, the resulting near-field polarisation dependencies are more complicated, suggesting that the magneto-optical contrast in SNOM images are affected by the topographic cross-talk due to the depolarisation effects on surface topographic features.     

X-ray microscopy of plant cells by using LiF crystal as a detector

A lithium fluoride (LiF) crystal has been utilized as a new soft X-ray detector to image different biological samples at a high spatial resolution. This new type of image detector for X-ray microscopy has many interesting properties: high resolution (nanometer scale), permanent storage of images, the ability to clear the image and reuse the LiF crystal, and high contrast with greater dynamic range. Cells of the unicellular green algae Chlamydomonas dysosmos and Chlorella sorokiniana, and pollen grains of Olea europea have been used as biological materials for imaging. The biological samples were imaged on LiF crystals by using the soft X-ray contact microscopy and contact micro-radiography techniques. The laser plasma soft X-ray source was generated using a Nd:YAG/Glass laser focused on a solid target. The X-ray energy range for image acquisition was in the water-window spectral range for single shot contact microscopy of very thin biological samples (single cells) and around 1 keV for multishots microradiography. The main aim of this article is to highlight the possibility of using a LiF crystal as a detector for the biological imaging using soft X-ray radiation and to demonstrate its ability to visualize the microstructure within living cells.     

High-resolution water window X-ray imaging of in vivo cells and their products using LiF crystal detectors

High contrast imaging of in vivo Chlorella sorokiniana cells with submicron spatial resolution was obtained with a contact water window X-ray microscopy technique using a point-like, laser-plasma produced, water-window X-ray radiation source, and LiF crystals as detectors. This novel type of X-ray imaging detectors is based on photoluminescence of stable electronic point defects, characterized by high intrinsic resolution. The fluorescence images obtained on LiF crystals exposed in single-shot experiments demonstrate the high sensitivity and dynamic range of this new detector. The powerful performances of LiF crystals allowed us to detect the exudates of Chlorella cells in their living medium and their spatial distribution in situ, without any special sample preparation.     

Euromembrane 2000 highlights membrane-based water treatment technologies

The first instalment of our Euromembrane 2000 round-up, which was published in the January 2001 issue of Membrane Technology, looked at developments in liquid membranes and distillation. The conference also looked in detail at water treatment, and this article, the second in a series of three summaries covering the event that was held in Israel during September last year, considers the role which different types of membranes are now playing in this area.     

A new approach to solving problems of multi‐state system reliability optimization

Usually engineers try to achieve the required reliability level with minimal cost. The problem of total investment cost minimization, subject to reliability constraints, is well known as the reliability optimization problem. When applied to multi‐state systems (MSS), the system has many performance levels, and reliability is considered as a measure of the ability of the system to meet the demand (required performance). In this case, the outage effect will be essentially different for units with different performance rate. Therefore, the performance of system components, as well as the demand, should be taken into account. In this paper, we present a technique for solving a family of MSS reliability optimization problems, such as structure optimization, optimal expansion, maintenance optimization and optimal multistage modernization. This technique combines a universal generating function (UGF) method used for fast reliability estimation of MSS and a genetic algorithm (GA) used as an optimization engine. The UGF method provides the ability to estimate relatively quickly different MSS reliability indices for series‐parallel and bridge structures. It can be applied to MSS with different physical nature of system performance measure. The GA is a robust, universal optimization tool that uses only estimates of solution quality to determine the direction of search. Copyright © 2001 John Wiley & Sons, Ltd.     

A Simple DNAzyme-Based Fluorescent Assay for Klebsiella pneumoniae

Pathogenic bacteria pose a serious threat to public health, and the rapid and cost-effective detection of such bacteria remains a major challenge. Herein, we present a DNAzyme-based fluorescent paper sensor for Klebsiella pneumoniae. The DNAzyme was generated by an in vitro selection technique to cleave a fluorogenic DNA–RNA chimeric substrate in the presence of K. pneumoniae. The DNAzyme was printed on a paper substrate in a 96-well format to serve as mix-and-read fluorescent assay that exhibits a limit of detection (LOD) 10⁵ CFUs mL⁻¹. Evaluated with 20 strains of clinical bacterial isolates, the DNAzyme produced the desired fluorescence signal with the samples of K. pneumoniae, regardless of their source or drug resistance. The assay is simple to use, rapid, inexpensive, and avoids the complex procedures of sample preparation and equipment. We believe that this DNAzyme-based fluorescent assay has potential for practical applications to identify K. pneumoniae.     

Intracavity Laser Absorption Spectroscopy for flame diagnostics

Intracavity Laser Absorption Spectroscopy (ICLAS) is one of the most sensitive techniques in absorption spectroscopy. Application of this technique to combustion diagnostics offers many important advantages. Since ICLAS is an absorption-based method, it is not limited by the quenching and predissociation effects that compromise the sensitivity of Laser Induced Fluorescence (LIF), one of the most sensitive and widespread techniques applied in combustion diagnostics. For that reason, radicals that are subject to strong collisional quenching or predissociation, such as ¹CH₂ and HCO, can be measured by ICLAS with sensitivity much greater than that of LIF. For the same reason, ICLAS also possesses better sensitivity for NH and HNO. The present paper overviews the ICLAS measurements performed during the last decade in our laboratory and also presents recent results: first-time detection of the HSO radical in flames by ICLAS and application of Fiber Laser Intracavity Absorption Spectroscopy (FLICAS) based on Er-doped fiber laser for in-situ detection of ammonia and hydrogen cyanide in a low-pressure methane/air flame doped with a small amount of ammonia. Avenues for future research are discussed.     

Non‐covalently crosslinked hydrogels displaying a unique combination of water‐absorbing,elastic and adhesive properties

BACKGROUND: Stringent requirements must be satisfied by biomedical adhesives, including biocompatibility, adhesion, cohesiveness and processability. The ability to change mechanical properties in response to environmental changes may also be desirable. In the present work the water‐absorbing, adhesive and mechanical properties of blends based on hydrogen bonding complexes between poly(N‐vinyl pyrrolidone), poly(ethylene glycol) (PEG) and poly[(methacrylic acid)‐co‐(ethyl acrylate)] were investigated. These blends, consisting of pharmaceutical‐grade components, exhibit pH‐sensitive swelling and dissolution, along with rubber‐like elasticity and bioadhesion. RESULTS: Polymer blend films remained intact at pH = 5.6 but underwent dissolution at pH = 7.4, the difference being attributed to deprotonation of acidic side‐chains, with loss of hydrogen bonding and development of charge repulsion. Sol release was primarily due to PEG. Films swelled at low pH instead of dissolving, in a manner that was pH‐dependent but PEG‐independent. Films displayed elastic properties comparable to cured elastomers when mildly swollen, with modulus and ultimate strength decreasing with increasing PEG content. Dry films were nearly tack‐free, but became more adhesive with increasing water content, up to a point where the film dissolved. CONCLUSION: Due to their biocompatibility and dissolution/mechanical properties, the bioadhesive polymer blends investigated may be suitable for numerous biomedical applications. Copyright © 2008 Society of Chemical Industry