bluuebunny/crossref_metadata_2025 huggingface dataset:
Participation in Boys and Girls Clubs and relationships to youth outcomes
Authors: Anderson‐Butcher Dawn , Newsome W. Sean , Ferrari Theresa M.
Published: December 2002

Participation is a key issue in youth development organizations. In fact, research suggests that youths who attend the programs offered by these agencies will experience numerous benefits. One such youth development organization is the Boys and Girls Clubs of America (BGCA). Much of the research pertaining to the BGCA examines the importance of participation in structured prevention and educational programs such as Project SMART and Project Learn. The everyday Club participant, however, does not necessarily attend these structured programs. As such, the present study was designed to gain a better understanding of “typical” Club participation and how overall attendance at the Club is related to positive outcomes among youth. A total of 139 youths (aged 10 to 18 years old) participated in the study. Overall participation in the Club and age were both independently related to enhanced academic achievement, as well as increased substance use. Additionally, significant age and participation interaction effects point to the importance of Club participation at nullifying risks and problem behaviors associated with increasing age, particularly in relation to academic outcomes. Implications are discussed pertaining to program strategies that may serve as hooks or magnets that sustain youths' interest and continued involvement in BGCA activities and other youth development programs. © 2003 Wiley Periodicals, Inc.
Prevention of dog bites: Evaluation of a brief educational intervention program for preschool children
Authors: Wilson Fiona , Dwyer Fleur , Bennett Pauleen C.
Published: December 2002

Dog bites are an underestimated societal problem. Victims suffer injuries, both physical and emotional, that sometimes end in death, and the economic cost to the community is high. The most frequent victims are children, many of whom are bitten at home. Current interventions, primarily aimed at the control of dogs in public areas, appear unlikely to reduce the incidence of dog bites within this group. In this study, parents' beliefs about their children's behavior around familiar and strange dogs were investigated using a questionnaire. The impact of a brief educational dog safety program on 192 kindergarten children (M = 4.68 years of age) was then evaluated. The questionnaire data revealed that many children engage in unsafe behaviors around dogs, and that parents are largely unaware of the dangers associated with such behaviors. The dog safety program resulted in a significant increase in the ability of children to identify high risk situations for up to 4 weeks, with the benefits being even greater in those children whose parents were also given information regarding safe behaviors around dogs. © 2003 Wiley Periodicals, Inc.
Exploring “personal” and “shared” sense of community identity in Durham City, England
Authors: Puddifoot John E.
Published: December 2002

“Personal” and “shared” aspects of sense of community identity are explored in a an established community in Durham City, England. Durham City has a history of over 1,000 years of continuous settlement, and is generally viewed as a stable and relatively harmonious setting. In the study 102 residents responded to a Community Response Questionnaire based on Puddifoot's taxonomy of elements of sense of community. The findings suggest the existence of three underlying “personal” dimensions of Sense of Community Identity (SOCI), namely, “Sense of Personal Support,” “Sense of Personal Contentedness,” and “Personal Involvement,” and three “shared” dimensions of SOCI, namely, “Perceived Community Engagement,” “Perceived Neighborliness,” and “Perceived Settledness.” This article discusses these findings and the prospect of creating a measure for comparative analysis around these dimensions. © 2003 Wiley Periodicals, Inc.
Cyclin T: Three forms for different roles in physiological and pathological functions
Authors: De Luca Antonio , De Falco Maria , Baldi Alfonso , Paggi Marco G.
Published: December 2002

Cyclins are members of family of proteins involved in the cell cycle regulation. They are regulatory subunits of complexes with proteins called cyclin‐dependent kinases (CDKs). There are three forms of cyclin T: cyclin T1, cyclin T2a, and T2b. All cyclin T contain an N‐terminal “cyclin homology box,” the most conserved region among different members of the cyclin family that serves to bind CDK9. In addition to the N‐terminal cyclin domain, cyclin T contains a putative coiled‐coil motif, a His‐rich motif, and a C‐terminal PEST sequence. The CDK9/cyclin T complex is able to activate gene expression in a catalytic‐dependent manner, phosphorylating the carboxy‐terminal domain (CTD) of RNA polymerase II. In addition, only cyclin T1 supports interactions between Tat and TAR. The interaction of Tat with cyclin T1 alters the conformation of Tat to enhance the affinity and specificity of the Tat:TAR interaction. On the other hand, CDK9/cyclin T2 complexes are involved in the regulation of terminal differentiation in muscle cells. © 2002 Wiley‐Liss, Inc.
Analysis of hormone‐stimulated phosphatidylinositol synthesis
Authors: Monaco Marie E. , Moldover Nancy H. , Walden Paul D.
Published: December 2002

Agonist‐stimulated phosphoinositide turnover is accompanied by compensatory resynthesis of these lipids. Several lines of evidence suggest that resynthesis of phosphatidylinositol (PtdIns) involves phosphorylation of diacylglycerol (DG) (salvage pathway) rather than acylation of glycerol phosphate (de novo pathway), although a contribution from the de novo pathway has not been ruled out. To determine the relative contribution of the de novo and salvage pathways in stimulated PtdIns resynthesis, an inhibitor of de novo synthesis (Triacsin C) was incubated simultaneously with the hormone agonist. Results indicate that at early times (90 min), hormone‐stimulated PtdIns synthesis proceeds predominantly via the salvage pathway, although some de novo synthesis is also taking place. At later times (24 h), stimulated synthesis is solely via the de novo pathway. Increasing cellular DG content by either adding exogenous DG or treating cells with bacterial phospholipase C (bPLC) results in deacylation of the DG rather than phosphorylation; however, inhibition of this deacylation fails to stimulate phosphorylation by DG kinase (DGK), suggesting channeling of the DG substrate between PLC and DG kinase. Receptor activation is not required for activation of DGK, since treatment with a calcium ionophore induces the same Triacsin C‐insensitive PtdIns synthesis. Depletion of the polyphosphoinositide pools by treatment with wortmannin prevents both hormone and A23187‐induced polyphosphoinositide hydrolysis; however, A23187 is still able to induce hydrolysis of PtdIns and subsequent compensatory resynthesis. The inability of R59949 to inhibit either hormone‐induced or ionophore‐induced PtdIns resynthesis suggests that the α isoform is not involved; however, its possible that the channeling phenomenon prevents the inhibitor from gaining access to the diacylglycerol kinase enzyme. Further study will be required to determine which isoform catalyzes hormone‐induced resynthesis of PtdIns. © 2002 Wiley‐Liss, Inc.
Epidermal growth factor induces intracellular Ca2+ oscillations in microvascular endothelial cells
Authors: Moccia Francesco , Berra‐Romani Roberto , Tritto Simona , Signorelli Silvia , Taglietti Vanni , Tanzi Franco
Published: December 2002

An increase in intracellular Ca2+ concentration ([Ca2+]i) may play a role in the proliferative effect of several growth factors. In this study, the changes in [Ca2+]i elicited by epidermal growth factor (EGF) in rat cardiac microvascular endothelial cells (CMEC) have been investigated by using fura‐2 conventional and confocal microscopy. A large heterogeneity in the latency and in the pattern of the Ca2+ response was found at each dose of EGF (2.5–100 ng/ml), whereas some cells displayed a non‐oscillatory behavior and others exhibited a variable number of Ca2+ oscillations. On average, the fraction of responsive cells, the total number of oscillations and the duration of the Ca2+ signal were higher at around 10 ng/ml EGF, while there was no dose‐dependence in the lag time and in the amplitude of the [Ca2+]i increase. EGF‐induced Ca2+ spikes were abolished by the tyrosine kinase inhibitor genistein, but not by its inactive analogue daidzein, and by the phospholipase C blocker NCDC. Only 1–2 transients could be elicited in Ca2+‐free solution, while re‐addition of extracellular Ca2+ recovered the spiking activity. The oscillatory signal was prevented by the SERCA inhibitor thapsigargin and abolished by the calcium entry blockers Ni2+ and La3+. Moreover, EGF‐induced Ca2+ transients were abolished by the InsP3 receptor blocker caffeine, while ryanodine was without effect. Confocal imaging microscopy showed that the Ca2+ response to EGF was localized both in the cytoplasm and in the nucleus. We suggest that EGF‐induced [Ca2+]i increase may play a role in the proliferative action of EGF on endothelial cells. © 2002 Wiley‐Liss, Inc.
Potential role of apoptotic macrophages in pulmonary inflammation and fibrosis
Authors: Wang Liying , Antonini James M. , Rojanasakul Yon , Castranova Vincent , Scabilloni James F. , Mercer Robert R.
Published: December 2002

Induction of apoptosis has been associated with a variety of exposures which result in inflammatory and fibrotic lung disorders. Macrophages are key regulatory cells in the lung; however, the role of apoptotic macrophages in those pulmonary disorders is not well characterized. In the present investigation, apoptotic macrophages were instilled into the lungs of rats to study directly the pulmonary responses to apoptotic cells. The effects of apoptotic macrophages on lung inflammation and fibrosis, as well as associated protein expression of TNF‐α, TGF‐β, and matrix metalloproteinases (MMPs) were examined. Induction of macrophage apoptosis was carried out in vitro using a variety of known apoptosis inducers. Intratracheal administration of apoptotic macrophages (5 × 106 cells/rat) into the lung of rats caused an increase in pulmonary infiltration of macrophages and lung cell apoptosis 4 weeks after the treatment as indicated by terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labeling (TUNEL) assay. In contrast, pulmonary instillation of saline or normal control macrophages had no effect. Histological analysis of lung sections showed collagen deposition and fibrotic lesions after apoptotic cell treatment but not in control groups. Immunohistochemical studies revealed increased expression of TNF‐α, TGF‐β, MMP2, and MMP9 in the treatment group 4 weeks after the treatment. These results suggest a role for macrophage apoptosis in the initiation of these lung disorders. This study provides direct evidence that apoptotic macrophages can induce lung inflammation and fibrosis and that this induction may be associated with increased expression of TNF‐α, TGF‐β, MMP2, and MMP9. Published 2002 Wiley‐Liss, Inc.
Peri‐epithelial origin of prostanoids in the human colon
Authors: McCarn Kate , Yursik Brenna , Halim Sharif , Roche James K.
Published: December 2002

The 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

The 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

In 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

Dissolved 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

The 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

Mechanistic 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

A 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

Plant 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

A 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

A 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

The 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

Reversed‐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

Styrene 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

Ethylene, 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

The 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

Improvements 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

This 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

The 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
Intrinsic crosstalk analysis of a serial TDM FGB sensor array by using a tunable laser
Authors: Chan C. C. , Jin W. , Wang D. N. , Demokan M. S.
Published: December 2002

The effect of spectral shadowing and multiple reflections in a serial fiber Bragg grating (FBG)‐array are investigated. The wavelength detection errors for the distal FBG (reflectivity = 1%) in a 50‐FBG array are 18 pm and 12 pm for spectral shadowing and multiple reflections, respectively. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 2–4, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10653
Parallel‐plate waveguides with Kronig–Penney morphology as photonic band‐gap filters
Authors: Gómez Álvaro , Lakhtakia Akhlesh , Solano Miguel A. , Vegas Angel
Published: December 2002

Guided wave propagation in a parallel‐plate waveguide with Kronig–Penney morphology is analyzed. Modes in the photonic band‐gap (PBG) structure can be classified as either transverse electric or transverse magnetic with respect to the propagation direction. Above the modal cut‐off frequencies, band gaps exist where in propagation is forbidden. The locations and the widths of the band gaps depend on modal order, waveguide height, and the permittivity contrast and relative volumetric proportion of the two materials constituting the unit cell of the PBG structure. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 4–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10654
Numerical analysis of local interpolation error for 2D‐MLFMA
Authors: Ohnuki Shinichiro , Chew Weng Cho
Published: December 2002

The error control of local interpolation for a 2D MLFMA will be discussed. The way to select proper parameters is proposed in terms of both numerical accuracy and computational cost. Satisfying the conditions derived in this paper, error can be controlled at the same level as global interpolation, and the computational cost becomes less expensive than the global one. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 8–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10655
Analysis of ultra‐wide band signal propagation in an indoor environment
Authors: Schiavone Guy A. , Wahid Parveen , Palaniappan Ravi , Tracy Judd , Dere Troy
Published: December 2002

Ultra‐wide band signal propagation in an urban environment is measured and studied. The basic concept is to develop, transmit and receive an extremely short duration burst of radio frequency energy‐typically a few tens of pico seconds to a few nanoseconds in duration. The resultant waveforms are extremely broadband, so much so that it is often difficult to determine an actual RF center frequency—thus the term “carrier‐free” [1]. In this paper, the indoor propagation of UWB signals inside an office room is studied. A simulation model of this system is compared with the actual test results. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 13–15, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10656
Shaped‐beam pattern synthesis of equally and unequally spaced linear antenna arrays using a modified tabu search algorithm
Authors: Akdagli Ali , Guney Kerim
Published: December 2002

A flexible search technique based on a tabu search algorithm is presented for the shaped‐beam pattern synthesis of linear antenna arrays. To synthesize a desired pattern, element excitations and/or positions are optimally determined. Examples of cosecant, flat‐topped, and pencil beam patterns are given to illustrate the achievable performance. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 16–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10657
A simple approach to quasi‐TEM analysis of a planar multiconductor structure embedded in an elliptically stratified environment
Authors: Norgren Martin
Published: December 2002

The quasi‐TEM modes on a planar multiconductor transmission line embedded in an elliptically stratified cross section are considered. Electro‐ and magneto‐static problems are solved using separation of variables in elliptical coordinates. It is shown that asymptotic solutions for the radial dependences of the terms of the series can be used, under certain conditions, on the profiles of stratification. Results about the convergence and the usefulness of the asymptotic solution are presented. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 20–24, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10658
Wideband dielectric resonator antenna for mobile phones
Authors: Kivekäs Outi , Ollikainen Jani , Vainikainen Pertti
Published: December 2002

A novel small dual‐resonant dielectric resonator antenna is presented. The antenna has a simple structure, wide bandwidth, and high radiation efficiency. Its radiation pattern is suitable for cellular handset antenna applications. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 25–26, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10659
A proposed stacked microstrip antenna structure for bandwidth enhancement
Authors: Khodier Majid M. , Christodoulou Christos G.
Published: December 2002

A new stacked microstrip antenna structure that enhances the bandwidth without changing the resonance frequency is proposed and studied in this paper. The effect of the various antenna parameters on the bandwidth is investigated. The resulting antenna, using the proposed structure, has an ultra‐wide bandwidth of 35%, compared to 21.8% for the conventional stacked antenna structure. The proposed structure has little effect on the antenna's radiation characteristics. The analysis of the proposed structure is carried out using the FDTD method. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 26–28, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10660
Analysis of conical log‐periodic antennas
Authors: Hertel Thorsten W. , Smith Glenn S.
Published: December 2002

In this paper, a new log‐periodic antenna design is investigated using the finite‐difference time‐domain method. The two‐arm, conical log‐periodic antenna is linearly polarized and has uniform performance characteristics over a broad range of frequencies. It is shown that the shape of the antenna arms has a significant impact on the performance and the bandwidth of the antenna. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 28–32, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10661
Data reduction in the NF‐FF transformation with bi‐polar scanning
Authors: D'Agostino F. , Gennarelli C. , Riccio G. , Savarese C.
Published: December 2002

An efficient near‐field–far‐field transformation with bi‐polar scanning, which compensates for the effects of the measurement probe, is proposed in this paper. It is based on the theoretical results relevant to the nonredundant sampling representation of electromagnetic fields and, as a consequence, it requires a number of data—remarkably lower than that needed by the standard bi‐polar technique. Numerical examples assessing the accuracy and the stability of the far‐field reconstruction process are presented. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 32–36, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10662
A comparison of the performance of different tapers in continuous microstrip electromagnetic crystals
Authors: Erro M. J. , Laso M. A. G. , Lopetegi T. , Garde M. J. , Benito D. , Sorolla M.
Published: December 2002

The influence of the window shape in the frequency response of electromagnetic crystals (ECs), made by etching a sinusoidal continuous pattern of constant period and variable amplitude on the ground plane of a microstrip line, is studied in terms of rejection level, bandwidth, side‐lobe level, and stopband abruptness. A new parameter, the equivalent number of periods, is found to be a good estimate of the increase in length needed to maintain the rejection level and bandwidth of the uniform structure, while reducing the secondary lobes by applying a window. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 37–40, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10663
Planar monopole design considerations based on TLM estimation of current density
Authors: Evans J. A. , Ammann M. J.
Published: December 2002

It is shown that a section of the square planar monopole may be removed without significantly effecting antenna impedance or radiation performance. The proposed antenna forms a U‐shaped monopole and offers lower weight, wind resistance, and cost. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 40–42, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10664
A novel ultra‐wideband polarization‐agile antenna
Authors: Pal Ram , Sudhir H. , Bharath Jyothi M.
Published: December 2002

A state‐of‐the‐art multi‐octave band‐printed circuit log‐periodic antenna (LPA), which can characterize signal polarization accurately, has been designed and developed. A broadband compact‐size cylindrical cavity has been developed for the LPA. The feeding mechanism for the cavity‐backed structure was implemented using a Chebyshev‐tapered printed circuit balun. The antenna can be flush‐mounted with the platform surface and hence finds wide application in electronic warfare (EW) systems. The technique involved in the development of this antenna and its feeding mechanism along with the measurement results are presented. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 42–46, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10665
A low‐profile folded planar monopole antenna for wireless communication
Authors: Lin Shun‐Yun
Published: December 2002

This paper presents a novel design for a low‐profile planar monopole antenna. The proposed antenna is a rectangular planar monopole with folded end. Its total height is about 0.12 λ0 (the free‐space wavelength of the lowest operating frequency of the antenna), which is lower than other corresponding designs. In this study, a shorting plate is added to the edge of the rectangular plate to decrease the lower frequency for impedance matching. Furthermore, the offset center feeding is used to increase the upper frequency. Experimental results obtained from the constructed prototype show that the impedance bandwidth covers DCS (1720–1880 MHz), PCS (1850–1990 MHz), UMTS (1920–2170 MHz), and ISM (2400–2484 MHz, 5725–5852 MHz) bands. Moreover, the measured monopole‐like radiation patterns prove that the proposed antenna has omni‐directional radiation in the azimuthal plane. These performances suggest that the proposed antenna is suitable for application in wireless communication systems. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 46–48, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10666
A mutual impedance formula between patch antennas based on synthetic asymptote and variable separation
Authors: Sun Y. X. , Chow Y. L. , Fang D. G.
Published: December 2002

A formula for mutual impedance between patch antennas is constructed, based on the physics of the static near field and the radiation far field of the couplings. This leads to a synthetic asymptote form [1] of separated variables with center‐to‐center distancerand azimuth angle ϕ. Only 12 coefficients are to be determined by matching, using a full‐wave analysis with commercial software, such as IE3D. Our formula is complete with no restrictions on the detailed structures of patch, feed, and substrate. Numerical examples show that our formula is accurate. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 48–53, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10667
Improved perturbation analysis of a new omnidirectional circular rod antenna with multi dielectric gratings for millimeter‐wave application
Authors: Lin Kaihui , Xu Shanjia
Published: December 2002

The leakage characteristics of a new millimeter‐wave omnidirectional circular rod antenna with multi‐dielectric gratings are analyzed by an improved perturbation method. The analysis yields an expression for the leakage constant in a closed form so that the design procedure of the antenna becomes very convenient. It is found that under conditions of the same dimension of the antenna, the multi‐layer grating antenna has more radiation efficiency than that of the single one. Its accuracy has been verified with the exact solution based on the mode matching method. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 53–55, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10668