bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peri‐epithelial origin of prostanoids in the human colon
Authors: McCarn Kate , Yursik Brenna , Halim Sharif , Roche James K. 
Published: December 2002

AbstractThe biology of prostanoids in the normal human colon is only beginning to be understood. We used in situ and in vitro techniques to define the lineage, number, per cell enzyme content, and epithelial functional effect of prostaglandin‐generating cells, identified by the presence of cyclooxygenase 1 (COX 1). Immunohistochemical results were quantitated densitometrically, and cell surface staining in situ was verified by flow cytometry of isolated cells and by Western blotting. Three populations of COX 1+ mucosal cells were identified, based on their morphology and local distribution in human mucosa; these were in the intra‐epithelial, crypt apical, and lamina propria regions, with each containing a similar amount of COX 1 protein on a per cell basis. The most numerous were COX 1+ mononuclear cells in the lamina propria, identified as CD3+ T lymphocytes, both in situ and ex vivo. In toto, 21% of lamina propria mononuclear cells were COX 1+, and over 50% of these cells were CD3+ T cells. Findings were similar in the colon with mild‐moderate inflammation due to ulcerative colitis. Using established surface markers, intra‐epithelial and crypt apical COX 1+ cells were non‐lymphoid CD45+ leukocytes; neither IgA (B‐lymphocytes) nor α‐smooth muscle actin (myelofibroblasts) was co‐expressed on these COX 1+ cells. Examining the effect of a major product of COX 1 in an in vitro system of human colonic epithelial monolayers, prostaglandin E2 (PGE2) in low concentration (10−6 M) enhanced epithelial barrier function and partially protected epithelia from the barrier‐disruptive consequences of a pro‐inflammatory cytokine, IFN‐γ. We conclude that the human colon contains three tiers of cell types for local synthesis of prostanoids, distinguishable by their location, morphology, and cell lineage. Further, maintenance of the barrier function of colonic epithelium may be added to other cell functions in mucosa regulated, in part, by prostanoids. © 2002 Wiley‐Liss, Inc.
Compound specific plant amino acid δ15N values differ with functional plant strategies in temperate grassland
Authors: Bol Roland , Ostle Nick J. , Petzke Klaus J. 
Published: December 2002

AbstractThe distribution and natural abundance isotopic (δ15N) content of whole tissue and individual amino acids in plants in a temperate grassland were determined using ion chromatography (IC), continuous flow‐isotope ratio mass spectrometry (CF‐IRMS), and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). The results showed that the selected plants (Lolium perenne, Juncus effusus, and Brachythecium rutabulum) differed in their amino acid content and distribution from the parent grassland soil. Bulk and individual amino acid δ15N isotope signatures were different between the plants, which concurred with their functional strategy in relation to the relative acquisition of available N sources. The individual amino acid δ15N values of histidine and phenylalanine could be used to differentiate between the three plant species.
Soil nutrient supply and biomass production in a mixed forest on a skeleton‐rich soil and an adjacent beech forest
Authors: Hölscher Dirk , Hertel Dietrich , Koenies Horst 
Published: December 2002

AbstractIn the natural forest communities of Central Europe, beech (Fagus sylvatica L.) predominates in the tree layer over a wide range of soil conditions. An exception with respect to the dominance of beech are skeleton‐rich soils such as screes where up to 10 broad‐leaved trees co‐exist. In such a Tilia‐Fagus‐Fraxinus‐Acer‐Ulmus forest and an adjacent mono‐specific beech forest we compared (1) soil nutrient pools and net nitrogen mineralization rates, (2) leaf nutrient levels, and (3) leaf litter production and stem increment rates in order to evaluate the relationship between soil conditions and tree species composition. In the mixed forest only a small quantity of fine earth was present (35 g l—1) which was distributed in patches between basalt stones; whereas a significantly higher (P < 0.05) soil quantity (182 g l—1) was found in the beech forest. In the soil patches of the mixed forest C and N concentrations and also concentrations of exchangeable nutrients (K, Ca, Mg) were significantly higher than in the beech forest. Net N mineralization rates on soil dry weight basis in the mixed forest exceeded those in the beech forest by a factor of 2.6. Due to differences in fine earth and stone contents, the volume related soil K pool and the N mineralization rate were lower in the mixed forest (52 kg N ha—1 yr—1, 0—10 cm depth) than in the beech forest (105 kg N ha—1 yr—1). The leaf N and K concentrations of the beech trees did not differ significantly between the stands, which suggests that plant nutrition was not impaired. In the mixed forest leaf litter fall (11 %) and the increment rate of stem basal area (52 %) were lower than in the beech forest. Thus, compared with the adjacent beech forest, the mixed forest stand was characterized by a low volume of patchy distributed nutrient‐rich soil, a lower volume related K pool and N mineralization rate, and low rates of stem increment. Together with other factors such as water availability these patterns may contribute to an explanation of the diverse tree species composition on Central European screes.
Contribution of dissolved organic nitrogen to N leaching from four German agricultural soils
Authors: Siemens Jan , Kaupenjohann Martin 
Published: December 2002

AbstractDissolved organic nitrogen (DON) substantially contributes to N leaching from forest ecosystems. However, little is known about the role of DON for N leaching from agricultural soils. Therefore, the aim of our study was to quantify the contribution of DON to total N leaching from four agricultural soils. Concentrations and fluxes of DON and mineral N were monitored at two cropped sites (Plaggic Anthrosols) and two fallow plots (Plaggic Anthrosol and Gleyic Podzol) from November 1999 till May 2001 by means of glass suction plates. The experimental sites were located near the city of Münster, NW Germany. Median DON concentrations in 90 cm depth were 2.3 mg l—1 and 2.0 mg l—1 at the cropped sites and 1.6 mg l—1 and 1.3 mg l—1 at the fallow sites. There was only a slight (Anthrosols) or no (Gleyic Podzol) decrease in median DON concentrations with increasing depth. Total N seepage was between 19 kg N ha—1 yr—1 and 46 kg N ha—1 yr—1 at the fallow sites and 16—159 kg N ha—1 yr—1 at the cropped sites. For the fallow plots, DON seepage contributed 10—21 % to the total N flux (4—5 kg DON ha—1 yr—1), at the cropped sites DON seepage was 6—21 % of the total N flux (6—10 kg DON ha—1 yr—1). Thus, even in highly fertilized agricultural soils, DON is a considerable N carrier in seepage that should be considered in detailed soil N budgets.
Discriminating factors of the spatial variability of soil quality parameters at landscape‐scale
Authors: Emmerling Christoph , Udelhoven Thomas 
Published: December 2002

AbstractThe aim of the study was to evaluate the spatial variability pattern of some soil quality parameters at landscape‐scale, particularly soil microbial biomass‐C (Cmic) and ‐N (Nmic), and soil microbial activity (respiration) as well as soil organic carbon (Corg), and hot water extractable carbon (Chwe) by multivariate analyses of variance and canonical discriminant analyses (CDA). The study area was the Trier region, Rhineland‐Palatinate, which is characterized by a wide range of soil types developed from various parent materials. Additionally, the investigated fields differed in soil management intensity (conventional, integrated, organic farming) and crops grown. Within the whole study area CDA revealed a separation into three sub‐areas. Within the sub‐areas the soil quality parameters were significantly influenced by the soil management systems and the crops grown. Despite the spatial variability and the relationship to soil management, the contents of Cmic could be predicted by stepwise multiple linear regression models, both for arable and grassland soils. The explained variance for the regression models were 72 % for arable soils and 63 % for grassland soils, respectively. Regression models for predicting Nmic and microbial activity revealed an explained variance between 30 and 58 %.
The suitability of pde‐solvers in rhizosphere modeling, exemplified by three mechanistic rhizosphere models
Authors: Schnepf Andrea , Schrefl Thomas , Wenzel Walter W. 
Published: December 2002

AbstractMechanistic rhizosphere models are mathematical models that calculate the uptake of solutes (e.g. nutrients such as P or K) in a plant root and/or the concentration profiles of ions or microorganisms across the rhizosphere. They consist of partial differential equations (pde's) and their associated initial and boundary conditions, and often require numerical solutions due to non‐linearity. The suitability of the pde‐solver FlexPDE for rhizosphere modeling was evaluated by reproducing the outputs of three original rhizosphere models and comparing the results with the original model outputs. The models considered were NST 3.0 (Syring and Claassen, 1996), Kirk (1999), and Newman and Watson (1977). From visual comparison, the curves as produced by the original model and FlexPDE match very well. All calculated R2s (coefficients of determination) were equal to 1 with a rounding precision of three decimal places. Rescaling the time, using an upwind scheme in the presence of convection terms and controlling the relative error with the FlexPDE function errlimit were helpful in finding the most accurate numerical solution. These results showed that FlexPDE is a valuable tool in rhizosphere modeling.
Simplified procedure for steady‐state root nutrient uptake with linearized Michaelis‐Menten kinetics
Authors: Gräfe Jan , Kuchenbuch Rolf O. 
Published: December 2002

AbstractA mechanistic description of nutrient depletion of the soil volume around a root involves the solution of a cylindrical diffusion‐convection type differential equation with a non‐linear influx condition at the root surface and a no‐transfer or competition condition centred between two roots. As conventional numerical and analytical solution methods are complex and inflexible, approximations such as the steady‐state method are invaluable in this area. Because of its simplicity, the steady‐state approach to nutrient uptake by root systems is well suited to large plant simulation models. Here, we present an approximation of the Michaelis‐Menten function specifically for this approach, which is frequently used to quantify influx kinetics. When this linearization is used in uptake calculations along with the steady‐state method, no iterations per time step are required and analytical solutions for total nutrient uptake of non‐growing root systems can be found. A simulation study with an exact transient solution showed that the uncertainties with the steady‐state approach were greater than those caused by the described approximation scheme. Despite this, because of its adaptability and simplicity, the steady‐state approach is attractive for the representation of the tremendous heterogeneity of root‐soil systems.
Potassium efficiency mechanisms of wheat, barley, and sugar beet grown on a K fixing soil under controlled conditions
Authors: El Dessougi Hanadi , Claassen Norbert , Steingrobe Bernd 
Published: December 2002

AbstractPlant species differ in their potassium (K) efficiency, but the mechanisms are not clearly documented and understood. Therefore, K efficiency of spring wheat, spring barley, and sugar beet was studied under controlled conditions on a K fixing sandy clay loam. The effect of four K concentrations in soil solution ranging from low (5 and 20 μM K) to high (2.65 and 10 mM K) on plant growth and K uptake was investigated at 3 harvest dates (14, 21, and 31 days after sowing). The following parameters were determined: shoot dry matter (DM), K concentration in shoot dry matter, root length (RL), root length/shoot weight ratio (RSR), shoot growth rate/average root length ratio (GRs/aRL), K influx, and soil solution K concentrations. Wheat proved to have a higher agronomic K efficiency than barley and sugar beet, indicated by a greater relative yield under K‐deficient conditions. As compared to both cereals, sugar beet was characterized by higher K concentrations in the shoot dry matter, only 30—50 % of the root length, 15—30 % of the RSR and a 3 to 6 times higher GRs/aRL. This means that the shoot of sugar beet had a 3 to 6 times higher K demand per unit root length. Even at low K concentrations in the soil solution, sugar beet had a 7 to 10 times higher K influx than the cereals, indicating that sugar beet was more effective in removing low available soil K. Wheat and barley were characterized by slow shoot growth, low internal K requirement, i.e. high K utilization efficiency, and high RSR, resulting in a low K demand per unit root length. At low soil K concentrations, both cereals increased K influx with age, an indication of adaptation to K deficiency. The mechanism of this adaptation merits closer investigation. Model calculations were performed to estimate the K concentration difference between the bulk soil and the root surface (ΔCL) needed to drive the measured K influx. For the two cereals, the calculated ΔCL was smaller than the K concentration in the soil solution, but for sugar beet, ΔCL was up to seven times higher. This indicates that sugar beet was able to mobilize K in the rhizosphere, but the mechanisms responsible for this mobilization remain to be studied.
Identification of very long chain fatty acids by atmospheric pressure chemical ionization liquid chromatography‐mass spectroscopy from green alga Chlorella kessleri
Authors: Rězanka Tomáš 
Published: December 2002

AbstractA method is described for the enrichment of very long chain fatty acids (VLCFAs) from total fatty acids of heterotrophically cultivated green freshwater alga Chlorella kessleri and their identification as picolinyl esters by means of liquid chromatography‐mass spectrometry with atmospheric pressure chemical ionization (LC‐MS with APCI). The method is based on the use of preparative reversed phase HPLC of hundred‐milligram amounts and their subsequent identification by microbore APCI LC‐MS. A combination of these two techniques was used to identify unusual VLCFAs up to C47, both saturated and monounsaturated, with two positional isomers (ω‐9 and ω‐26).
Method development for the separation of steroids by capillary electrochromatography
Authors: Jiskra Jan , Claessens Henk A. , Cramers Carel A. 
Published: December 2002

AbstractA rapid capillary electrochromatography (CEC) method was developed to separate five structurally related steroid compounds from the production line of steroid hormones. The separation was performed on a Hypersil C8 MOS and Unimicro C18 stationary phases using acetonitrile (ACN), methanol (MeOH), and tetrahydrofuran (THF) as organic modifiers and tris(hydroxymethyl)aminomethane (Tris) as buffer additive. The Hypersil C8 MOS stationary phase performed best together with ACN as organic modifier and Tris buffer. The method was extensively tested for ruggedness with respect to sensitivity to temperature, ACN composition, pH change, concentration of Tris buffer, injected plug length, and run‐to‐run and day‐to‐day repeatability. The minimal detectable concentration and amount were investigated for quantification purposes. The developed CEC method was shown to be fast, rugged, and well suited for quantification of the steroids under study.
On.column pre‐concentration of alcohol dehydrogenase in capillary electrophoresis
Authors: Leung Shee‐Ann , de Mello Andrew J. 
Published: December 2002

AbstractThe analysis of alcohol dehydrogenase (ADH) at low concentration using capillary electrophoresis is described. Several simple and effective ways to improve detection limits and sensitivity are investigated. These include large volume sample stacking, head column field amplified sample stacking, and sweeping. Results indicate that by using a combination of head‐column field amplified sample stacking and sweeping, fluorescently labelled alcohol dehydrogenase can be pre‐concentrated online by dissolving samples in water or other low conductivity matrices, and injecting into a high conductivity micellar buffer. The abrupt changes in conductivity cause narrowing of the analyte length and thus enhance the detection sensitivity. Combination of this approach with laser induced fluorescence detection yields a limit of detection of 5×10–13 M. Both qualitative and quantitative aspects of this method are investigated.
Characterization of chromatographic supports for the analysis of basic compounds
Authors: Stella Cinzia , Seuret Patrick , Rudaz Serge , Carrupt Pierre‐Alain , Gauvrit Jean‐Yves , Lanteri Pierre , Veuthey Jean‐Luc 
Published: December 2002

AbstractReversed‐phase liquid chromatography (RP‐HPLC) has become a powerful and widely employed technique for the analysis of a great variety of substances and, in particular, of basic compounds. These compounds are present in various areas. In pharmacy, 80% of drugs are estimated to possess a basic function. Basic compounds can strongly interact with free silanol groups on the surface of the silica particles. These ion exchange interactions produce peak tailing which affects resolution, sensitivity, and reproducibility. For these reasons, many new stationary phases have been designed to reduce access to silanol groups. The main problem facing the analyst is to effectively select the best column for a particular type of separation. In order to characterize and evaluate the properties of these packings, several tests are proposed in the literature, which can be divided into two main categories: general tests and particular tests. In this work, a particular test was developed for the characterization of base deactivated RP‐HPLC stationary phases. For this purpose, a set of 14 basic test substances was selected and five different chromatographic supports were tested with three isocratic mobile phases. Furthermore, in order to undertake a complete characterization of these supports, batch and column reproducibility were also studied. Principal Component Analysis was applied to evaluate both the performance of the test compounds and of the stationary phases.
Shear controlled morphology of rubber/organoclay nanocomposites and dynamic mechanical analysis
Authors: Schön Frank , Thomann Ralf , Gronski Wolfram 
Published: December 2002

AbstractStyrene butadiene rubber/layered silicate composites were prepared using clays modified with alkyl ammonium salts of different structure. The influence of modifier structure and compounding conditions on the extent of exfoliation/intercalation of the silicates was investigated by electron microscopy and dynamic mechanical analysis. With increasing exfoliation the glass transition temperature is lowered and the stability of the filler network is enhanced.
Results coming from homogeneous and supported metallocene catalysts in the homo‐ and copolymerization of olefins
Authors: Quijada Raúl , Retuert Jaime , Guevara Juan L. , Rojas René , Valle Marcela , Saavedra Pilar , Palza Humberto , Galland Griselda B. 
Published: December 2002

AbstractEthylene, propylene and α‐olefins were homo‐ and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind)2ZrCl2 (I), Me2Si(Ind)2ZrCl2 (II), Et(2‐Me‐Ind)2ZrCl2 (III), Ph2C(Flu)(Cp)ZrCl2 (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol‐gel preparation technique. The homo‐ and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.
The strange case of the “oscillating” catalysts
Authors: Busico Vincenzo , Cipullo Roberta , Kretschmer Winfried , Talarico Giovanni , Vacatello Michele , Van Axel Castelli Valeria 
Published: December 2002

AbstractThe field of stereoselective propene polymerization has been dramatically innovated by the discovery of homogeneous metallocene‐based catalysts with well‐defined and tunable molecular structure. Of all, “oscillating” metallocenes are probably the most ingenious and challenging example of catalyst design. Their catalytic species were built to “flip‐flop” between a chiral and an achiral conformation, at a rate intermediate between those of monomer insertion and chain transfer. The result of this molecular switching would be a polypropylene with an isotactic/atactic stereoblock structure, performing as a thermoplastic elastomer. This essay discusses how the real polymerization mechanism differs from what the catalyst inventors had in mind, but also how ‐ through fortunate circumstances ‐their optimism has been rewarded.
Porous crosslinked spherical resins for diversified applications: packing materials for size exclusion chromatography
Authors: Coutinho Fernanda M.B. , Neves Márcia A.F.S. , Dias Marcos L. 
Published: December 2002

AbstractImprovements in the synthesis of porous polymers for different applications have been carried out in our laboratory. Beads of poly(styrene‐co‐divinylbenzene) with morphology adequate to the application at hand were prepared. Packing materials for size exclusion chromatography (SEC) weve prepared by single‐step swelling and polymerization (SSWP) and by modified suspension polymerization (MSP). High values of exclusion limit (106 and 8.0x106) were attained for SEC columns packed with poly(styrene‐co‐divinylbenzene) synthesized using high proportions of polystyrene, as porogen agent and divinylbenzene. The maximum values of exclusion limits were attained for SEC columns packed with beads prepared by SSWP method.
Conductive polymer blends: preparation, properties and applications
Authors: De Paoli Marco‐A. , Gazotti Wilson A. 
Published: December 2002

AbstractThis article presents a brief review concerning the production of conductive polymer blends and composites which combine conducting and insulating polymers. Different strategies for preparing these mixtures are examined, with emphasis on several properties of the final mixtures, such as: electronic conductivity, mechanical behaviour and thermal stability. The advantages of using blends in some technological applications instead of pure conducting polymers are discussed.
Gain and noise performances of an L‐band EDFA utilizing a ring laser cavity with fiber Bragg grating
Authors: Harun S. W. , Tamchek N. , Ahmad H. 
Published: December 2002

AbstractThe performances of gain and noise figure of an L‐band EDFA utilizing a ring laser cavity is demonstrated. It uses a fiber Bragg grating (FBG), arranged to propagate in opposition to the amplifier signal by a pair of circulators, to provide laser feedback. A flat‐gain spectrum with less than 1.1‐dB variation between 1568 nm and 1604 nm was observed with the laser wavelength at 1560 nm. A gain‐clamping effect was also observed with this configuration, which provided a constant gain for all tested input signal powers from −40 dBm to 0 dBm. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 1–2, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10652