bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative bioactive compounds assessment and their relative contribution to the antioxidant capacity of commercial orange juices
Authors: Sánchez‐Moreno Concepción , Plaza Lucía , de Ancos Begoña , Cano M Pilar
Published: March 2003

Dietary recommendations for healthy eating include the consumption of fruit juices whose health effects are ascribed, in part, to carotenoids, phenolic compounds and vitamin C. These bioactive compounds have been implicated in the reduction of degenerative human diseases, mainly due to their antioxidant potential. Orange juice is characterized by substantial accumulation (apart from ascorbic acid) of flavonoids and carotenoids. Commercial orange juice is the main human dietary source of antioxidant compounds in developed countries. The qualitative and quantitative determination of carotenoid, flavonoid and vitamin C content of Spanish commercial orange juices was achieved by high‐performance liquid chromatography. The health‐related properties of bioactive compounds contained in orange juice are based on their antioxidant activity. The antioxidant capacity of these juices was assessed by 2,2‐diphenyl‐1‐picrylhydrazyl stable radical scavenging and was compared with a freshly squeezed orange juice. In addition, the relative contribution of the different bioactive compounds to the antioxidant activity of orange juices was calculated. Total vitamin C was found to be the major contributor to the antioxidant potential of the orange juices studied, followed by flavonoid and carotenoid compounds. Ascorbic acid, total vitamin C and β‐cryptoxanthin content correlated positively with the free‐radical scavenging parameters. No significant differences, in terms of antioxidant capacity, were found between commercial traditional pasteurized orange juices and freshly squeezed orange juice. Copyright © 2003 Society of Chemical Industry
Ammonium nitrate fertility levels influence flavour development in hydroponically grown ‘Granex 33’ onion
Authors: Coolong Timothy W , Randle William M
Published: March 2003

High levels of nitrogen (N) fertility have been shown to influence bulb flavour characteristics in onion (Allium cepa L). To test the effects of lower levels of N fertility on onion bulb flavour, ‘Granex 33’ onions were grown hydroponically in a greenhouse with varying solution N levels. Eleven levels were tested by increasing the concentration of NH4NO3 in solutions from 20 to 140 mg l−1 N. Mature plants were harvested and evaluated for plant leaf and bulb fresh weights (FWs), bulb soluble solids content (SSC), bulb total pyruvic acid, bulb total sulphur (S), and bulb sulphate (SO42−). To determine the effect of N on the flavour biosynthetic pathway of onion, total and individual S‐alk(en)yl cysteine sulphoxides and related peptide intermediates were also tested. Leaf and bulb FWs responded quadratically to N concentration, as did total bulb S. Bulb SO42− and SSC, though significantly influenced by N concentration, did not respond with a meaningful trend. Bulb pyruvic acid increased linearly with N level increases, as did (+)‐S‐propyl‐L‐cysteine sulphoxide. Total precursors, (+)‐S‐methyl‐L‐cysteine sulphoxide, and trans‐(+)‐S‐1‐propenyl‐L‐cysteine sulphoxide responded quadratically to N levels. At lower N levels, trans‐(+)‐S‐1‐propenyl‐L‐cysteine sulphoxide content was highest relative to the other precursors. However, at elevated N levels, (+)‐S‐methyl‐L‐cysteine sulphoxide accumulated in the highest concentrations. Peptide intermediates 2‐carboxypropyl glutathione and γ‐glutamyl propenyl cysteine sulphoxide responded linearly and quadratically respectively to increasing N fertility levels. Nitrogen fertility levels can influence flavour intensity and quality and should be considered when growing onions for flavour attributes. Copyright © 2003 Society of Chemical Industry
Fibre‐optic method for estimation of bovine fat quality
Authors: Irie M , Oka A , Iwaki F
Published: March 2003

Spectroscopy using remote surface, contact, insertion and transmission fibre‐optic probes and a sensor at wavelengths of 400 to 1100 nm was used for rapid estimation of the physio‐chemical characteristics of bovine fat. Surface reflectance of the adipose tissue was negatively correlated with the bovine fat colour score at many wavelengths and positively correlated with the contents of the polyunsaturated fatty acids at 400 to 650 nm (P < 0.05). Internal reflectance using an insertion probe at 445 to 1100 nm was positively correlated with melting point and negatively correlated with refractive index (P < 0.05). Internal reflectance using a contact probe tended to be related to saturated and monounsaturated fatty acid contents. Transmittance at almost all wavelengths was positively correlated with refractive index (P < 0.05). Internal reflectance of the intermuscular fat from 34 animals measured at a meat market was correlated (P < 0.01) with saturated fatty acid content (r = 0.72 at 650 nm) and with monounsaturated fatty acid content (r = −0.69 at 650 nm). These results indicated the possibility of using fibre‐optic measurements, requiring 1 s in bovine adipose tissue, to evaluate the quality of depot fat and that the various types of probe can be used to evaluate different physiochemical characteristics of fat. Copyright © 2003 Society of Chemical Industry
Evolution of available lysine and furosine contents in milk‐based infant formulas throughout the shelf‐life storage period
Authors: Ferrer Emilia , Alegría Amparo , Farré Rosaura , Abellán Pedro , Romero Fernando , Clemente Gonzalo
Published: March 2003

The evolution of the Maillard reaction (MR) by measuring the available lysine and furosine (FUR) contents in adapted and follow‐up powdered milk‐based infant formulas over the shelf‐life storage period, at 20 and 37 °C, was studied. Available lysine and FUR contents were determined by fluorimetry and high‐performance liquid chromatography respectively. Statistically significant differences were found between adapted and follow‐up infant formulas with respect to the available lysine and FUR contents. Available lysine contents decreased significantly throughout the storage time, and the contents at 37 °C were lower than at 20 °C. A statistically significant increase in FUR contents was observed during the storage period, with the contents being high at 37 °C than at 20 °C. A simple regression analysis between the available lysine and FUR contents during (a) the first year (b) the second year and (c) the two storage years was applied. The best correlations were obtained during the first year of storage. The results obtained show a clear MR evolution during the storage of infant formulas. Copyright © 2003 Society of Chemical Industry
Measurement of the parameters of the mass transfer kinetics in high performance liquid chromatography
Authors: Miyabe Kanji , Guiochon Georges
Published: March 2003

Fundamental studies of the mass transfer kinetics are as essential as those of the retention equilibrium for a detailed understanding of the characteristics and the mechanisms of chromatographic separations. The acquisition of a large amount of reliable experimental data and of meaningful results is necessary for any further progress of our knowledge of kinetics. The main goal of this review is to provide information on the methods used to perform accurate measurements and on the data analysis procedures used for deriving the kinetic parameters characterizing mass transfer in HPLC. First, the general characteristics of several methods of determination of some kinetic parameters are briefly reviewed. Secondly, we give detailed explanations of the experimental conditions of the pulse on a plateau method (i.e., elution chromatography on a plateau of finite concentration or pulse response method) and of the data analysis procedures based on moment analysis. Thirdly, we explain some important requirements for the acquisition of appropriate experimental data and discuss corrections to be applied when deriving several kinetic parameters. Fourthly, we discuss the accuracy of the kinetic parameters derived from the pulse on a plateau method and from moment analysis. Finally, some results concerning the mass transfer kinetics in RPLC systems are demonstrated as examples.
Characterization of HPLC packings
Authors: Neue Uwe D. , Van Tran Kim , Iraneta Pamela C. , Alden Bonnie A.
Published: March 2003

Several chromatographic test procedures are in use for the characterization of commercially available packings. The results of the test procedure used in our laboratory are updated and further refined. Two well‐defined physico‐chemical properties of packings can be derived from this test procedure, the hydrophobicity of a packing and the silanophilic activity at pH 7. In addition, our method is unique in its ability to differentiate between classical packings and packings with incorporated polar groups. We can also distinguish CN packings or fluorinated packings. Our database now includes over 100 commercially available packings. The ability of the test to cleanly discriminate between different classes of packings has been strengthened. Limited comparisons with other published tests are now possible as well, and the results of these comparisons are discussed.
Selection of suitable stationary phases and optimum conditions for their application in the separation of basic compounds by reversed‐phase HPLC
Authors: McCalley David V.
Published: March 2003

In this review, some aspects of the separation of basic compounds by HPLC are discussed with especial reference to work carried out by the author. Procedures for column evaluation are explained, together with the effect of mobile phase modifier, pH, temperature, nature of buffer, and sample overloading on the chromatography of basic compounds. Some evaluations of new column types, such as embedded polar group phases, monoliths, and hybrid inorganic/organic phases are presented.
Evaluation of column characteristics in RPLC using linear solvation energy relationships (LSERs)
Authors: Szepesy László
Published: March 2003

An overview is given of our studies on the use of linear solvation energy relationships (LSERs) for evaluation and comparison of RP‐HPLC columns. From among the columns investigated, 19 columns of different types, viz. 12 narrow‐pore, 7 wide‐pore silicas containing various ligands (C18, C8, C4, CN) and obtained from 7 manufacturers, were compared and evaluated. Retention factors of 32 solutes of widely differing chemical properties were measured and evaluated to determine the effect of stationary phase properties on the retention of various types of solutes. When the same mobile phase is used with the different columns, the regression coefficients determined by multivariate regression characterize the various stationary phases. The columns investigated were evaluated on the basis of the relative importance of the various types of interactions reflecting the various surface properties of the stationary phases. Since the selectivity of separation is more important than is absolute selectivity, we have investigated and compared the various selectivity terms, hydrophobic, polar, and specific selectivity, displayed by the various columns, for the separation of different types of compounds. As the selectivity of separation depends also on the type and composition of the mobile phase, the effect of mobile phase on the various selectivity terms was evaluated.
NMR investigations of stationary phases
Authors: Albert Klaus
Published: March 2003

An overview of the application of solid‐state and suspended‐state NMR spectroscopy for the characterization of stationary phases is given. Solid‐state 29Si NMR spectroscopy reveals valuable information about the variety and quantity of the surface species formed in the modification reaction. Solid‐state 13C NMR spectroscopy gives an insight into the dynamic properties of the immobilized ligands and ligand organization. With the help of 1H and 13C suspended‐state NMR spectroscopy, investigations can be performed in the presence of a mobile phase. Thus, the structural and dynamic properties of the stationary phase under real‐life chromatographic conditions can be derived from the NMR investigations. These findings can be directly correlated with the resulting chromatographic separation behaviour.
Design and characterization of novel stationary phases based on retention behavior studies with various aromatic compounds
Authors: Saito Yoshihiro , Ohta Hatsuichi , Jinno Kiyokatsu
Published: March 2003

Characterization of stationary phases by retention behavior studies with aromatic compounds is reviewed, focusing mainly on the authors' approach. Various aromatic compounds, such as polycyclic aromatic hydrocarbons (PAHs) and fullerenes, of different molecular shape and size were employed as the sample probes. For the systematic analysis of retention behavior, some spectroscopic techniques and theoretical calculations, such as energy minimized calculation of the phase structure, have also been employed to confirm the results from these retention studies. During these investigations, microcolumn chromatography was employed in order to evaluate small amounts of experimentally synthesized bonded phases. The design of several novel stationary phases, based on the molecular shape recognition concept, is also briefly reviewed along with the applications.
Characterization of liquid chromatographic chiral separation on chiral crown ether stationary phases
Authors: Hyun Myung Ho
Published: March 2003

Crown ether‐based chiral stationary phases (CSPs) have been known to be quite useful for the liquid chromatographic resolution of racemic compounds containing a primary amino group. Chiral separations on crown ether‐based CSPs are characterized by several factors. In this paper, the structural characteristics of five selected crown ether‐based CSPs, analyte characteristics and several factors characterizing chiral separations such as the mobile phase modifiers and the column temperature were reviewed. Among the various factors, the column temperature and the inorganic modifier in the mobile phase influence the chiral separations equally for the five selected crown ether‐based CSPs. In contrast, the effect of the organic and acidic modifier in the aqueous mobile phase on the chiral separations depends on the structural characteristics of CSPs.
The development of selective and biocompatible coatings for solid phase microextraction
Authors: Mullett Wayne M. , Pawliszyn Janusz
Published: March 2003

The development of solid phase microextraction (SPME) has seen huge growth since its conception as a new approach to sample preparation in the early 1990s. In comparison to existing technologies such as liquid‐liquid or solid phase extraction (LLE and SPE, respectively), the technique offers many advantages, including simplicity, speed, solventless extraction, and a convenient format. However, an important aspect in the future application and growth of SPME is the development of new extraction coatings. The objective of this review is to present an overview of the advances in coating development for solid phase microextraction (SPME). More specifically, this review will focus on the use of molecular recognition elements in SPME coatings to provide enhanced extraction selectivity and their applicability to the direct analysis of complex samples, such as biological fluids. The work will also include short overviews of emerging extraction phase technologies such as molecularly imprinted polymers (MIPs) and restricted access materials (RAM). The biocompatibility of RAMs has been combined with SPME and highlighted in several examples for more targeted and direct extraction possibilities in complex samples. The ability to perform direct and selective extraction of analytes from complex samples will extend SPME into the field of bioanalysis. Lastly, the future outlook for SPME and potential new applications for these fibers will be discussed.
Stationary phases for silver ion chromatography of lipids: Preparation and properties
Authors: Momchilova Svetlana , Nikolova‐Damyanova Boryana
Published: March 2003

Procedures for the preparation of stationary phases for several silver ion chromatographic techniques have been surveyed. Thin‐layer chromatography (TLC), conventional (normal pressure) column chromatography, solid phase extraction (SPE), high‐performance liquid chromatography (HPLC), and supercritical fluid chromatography (SFC) in silver ion mode have been considered. The utilization of these stationary phases for the analysis of fatty acids and triacylglycerols has been demonstrated.
Prediction of gradient retention from the linear solvent strength (LSS) model, quantitative structure‐retention relationships (QSRR), and artificial neural networks (ANN)
Authors: Kaliszan Roman , Ba̧czek Tomasz , Buciński Adam , Buszewski Bogusław , Sztupecka Małgorzata
Published: March 2003

The linear solvent strength (LSS) model combined with quantitative structure‐retention relationships (QSRR) and artificial neural network (ANN) analysis has been shown to permit approximate prediction of the gradient high‐performance liquid chromatography (HPLC) retention time for any analyte on a once‐characterized column. The approach applies well to the reversed‐phase HPLC mode with a methanol‐water (buffer) eluent of linearly changing composition. Its suitability was tested for a representative series of structurally diverse analytes. In this approach the determination of retention times, t R, in two gradient runs for a predesigned model series of 15 analytes is first needed. Next, model QSRR equations describing t R in terms of analyte structure are derived to characterize the HPLC systems of interest. To quantitatively characterize the structure of the analytes the following three structural descriptors from molecular modeling are employed: total dipole moment; electron excess charge of the most negatively charged atom; and water‐accessible molecular surface area. Using these data a general QSRR equation is derived which is valid for a given column/eluent system. Next, having the structural descriptors for any analyte to be chromatographed in such a characterized HPLC system, one employs the previously derived general QSRR equation to calculate the analyte's retention time. The expected gradient retention time for any gradient conditions can be calculated by means of appropriate LSS equations. Independent of the standard QSRR calculation procedure based on multiple regression analysis (MRA), predictions of gradient retention times were performed by means of artificial neural networks (ANN). It has been found that the predictive power of ANN is similar to that of MRA. The combined LSS/QSRR approach has been demonstrated to provide approximate, yet otherwise unattainable, a priori predictions of gradient retention of analytes based solely on their chemical formulae. That way a rational chemometric basis for a systematic optimization of chromatographic separations has been elaborated as an alternative to the trial‐and‐error method normally applied at present.
A new standard reference material for column evaluation in reversed‐phase liquid chromatography
Authors: Sander Lane C. , Wise Stephen A.
Published: March 2003

A new Standard Reference Material (SRM) for use in characterizing general aspects of liquid chromatographic column performance is described. SRM 870 Column Performance Test Mixture for Liquid Chromatography contains five components: uracil, toluene, ethylbenzene, quinizarin, and amitriptyline, and is intended to provide indications of column void volume, hydrophobicity, methylene selectivity, activity toward organic bases, and activity toward metal chelators. The test is performed under neutral, buffered conditions. The measurement of retention and peak asymmetry factors for the components facilitates column classification. It is anticipated that this material will be useful (1) in column selection during method development, (2) as a control material to monitor column performance over time, and (3) in quality control in column manufacturing.
Chromatographic classification and comparison of commercially available perfluorinated stationary phases for reversed‐phase liquid chromatography using Principal Component Analysis
Authors: Euerby Melvin R. , McKeown Alan P. , Petersson Patrik
Published: March 2003

A range of ten perfluorophenyl and perfluoroalkyl stationary phases has been evaluated using standard chromatographic tests and probes. Principal Component Analysis of the data has indicated that the phases can be divided into distinct groupings. Extending the dataset to include standard alkyl and phenyl phases provided further data interpretation to support the orthogonal selectivity claims made for perfluorinated phases. The analysis of a range of basic analytes showed an unusual extended retention of hydrophilic basic analytes with perfluorophases. Furthermore, a non‐linear relationship between the amount of organic modifier and the logarithm of the retention factor was observed, for the hydrophilic bases, which could not be modelled with LC prediction softwares. This was in sharp contrast to the alkyl and phenyl phases examined. Basic analyte retention on perfluoroalkyl phases could be modelled adequately for the lipophilic bases. Exploration of the retention mechanism of these perfluoro phases indicated that silanol interactions were important in retention and selectivity. Using a rapid, isocratic, high organic modifier methodology, it was possible to analyse a mixture containing a lipophilic steroid, hydrophilic base and an internal standard in < 4 minutes with a perfluorophenyl phase. This had previously only been achievable with an alkyl phase under gradient elution conditions.
Study on conical columns for semi‐preparative liquid chromatography
Authors: Jiping Ma , Yafeng Guan , Lingxin Chen
Published: March 2003

The dynamic flow profiles and column efficiencies in conically shaped semi‐preparative liquid chromatographic columns (inlet ID larger than outlet ID) with two different conical angles (7° and 15°) were studied. The dynamic flow profiles were studied by an on‐column visualization method. Conical columns were compared with cylindrical column of the same length and internal volume. The results showed that the flow profile of a sample band in the conical column of 7° (50 mm×17 mm → 11 mm ID) was parabolic in shape. The sample band migrated slower in the wall region than in the central region, as in the cylindrical column (50 mm×14 mm ID). However, the sample band in the conical column of 15° (50 mm×20 mm → 7 mm ID) migrated slower in the central region than in the wall region, resulting in a reverse parabolic flow profile, in contrast to that in cylindrical column. This indicated that a flat flow profile might be realized in a conical column with a conical angle between 7° and 15°. The conical column of 15° had the highest column efficiency among the three columns under the same conditions. Compared with the cylindrical column packed with identical packing material, the conical column of 15° had 22%–45% higher column efficiency and 11%–27% higher peak height.
Evaluation of HPLC columns: A study on surface homogeneity of chemically bonded stationary phases
Authors: Buszewski Bogusław , Krupczyńska Katarzyna , Gadzała‐Kopciuch Renata M. , Rychlicki Gerhard , Kaliszan Roman
Published: March 2003

The aim of the current work is to study the heterogeneity of the adsorbent surface on the basis of physicochemical investigations and chromatographic tests. A series of packing materials with octadecyl chains chemically bonded to a silica matrix were prepared for this purpose. The surface and structural properties of bare silica and silica‐based octadecyl phases were characterized by porosimetry, elemental analysis, 29Si CP/MAS NMR, etc. The most advanced characterization methods based on adsorption microcalorimetry (heat of wetting) measurements were employed to obtain information about the heterogeneity and topography of unmodified and modified silica gel. For the chromatographic study, these phases were evaluated on the basis of the retention data under non‐aqueous conditions. A test series of solutes with various chemical properties, such as pK a values, was used. It was found that heterogeneity of the packing surface results in low HPLC resolution. Use of a non‐aqueous mobile phase (n‐hexane) reduces analytical interference by eliminating hydrophobic interactions between alkyl ligands and the analyte.
Methacrylate monoliths prepared from various hydrophobic and hydrophilic monomers – Structural and chromatographic characteristics
Authors: Merhar Mojca , Podgornik Aleš , Barut Miloš , Žigon Majda , Štrancar Aleš
Published: March 2003

Methacrylate‐based monoliths are formed during radical copolymerization as a consequence of the precipitation of polymeric chains from the reaction mixture, which consists of monomers, initiator, and the porogenic solvents. The effect of various methacrylate monomers on the porous structure of the monolith was investigated. Although the chemical structure of the monomers significantly affects the size of the pores and the porosity, the mechanism of pore formation in the case of the precipitation during polymerization is preserved. The porous structure was further correlated with the specific surface area, pressure drop, and dynamic binding capacity of the monoliths studied.
Preparation and characterization of monolithic columns for capillary electrochromatography with weak electroosmotic flow
Authors: Zhang Lingyi , Ping Guichen , Zhang Lihua , Zhang Weibing , Zhang Yukui
Published: March 2003

Monolithic columns of capillary electrochromatography (CEC) with weak electroosmotic flow (EOF) have been prepared by in situ polymerization of butyl methacrylate and ethylene dimethacrylate, without any charged groups in the reaction mixture. The reproducibility of such columns has been proved good no matter whether they are prepared in the same batch or in different batches. In the case of BMA‐EDMA monoliths, besides the traditional ternary mixture – 1‐propanol, 1,4‐butanediol, and water, binary porogenic solvents with only alcohols have also been adopted. Compared with ternary porogenic solvents, the design with binary ones allows for fine control of the pore diameter and the formation of the specific surface of the monolithic polymers. The composition of porogenic reagents has also been shown to have an effect on EOF in the column systems. In addition, the Joule heat effect in such columns has been studied by varying the inner diameter of columns. Through the separation of acidic compounds, monolithic columns with low EOF have shown potential in the analysis of charged samples.
Nonlinear artificial boundary conditions with pointwise error estimates for the exterior three dimensional Navier–Stokes problem
Authors: Nazarov Sergej A. , Specovius–Neugebauer Maria
Published: April 2003

On a three–dimensional exterior domain Ω we consider the Dirichlet problem for the stationary Navier–Stokes system. We construct an approximation problem on the domain ΩR, which is the intersection of Ω with a sufficiently large ball, while we create nonlinear, but local artificial boundary conditions on the truncation boundary. We prove existence and uniqueness of the solutions to the approximating problem together with asymptotically precise pointwise error estimates as R tends to infinity.
Ordering in Stretched Bernoullian Copolymers
Authors: Litmanovich Arkady D. , Kudryavtsev Yaroslav V. , Kriksin Yury A. , Kononenko Oleg A.
Published: March 2003

A new approach is suggested to estimate the theoretical maximum capability to order for stretched Bernoullian copolymers AB, provided interchain AB contacts are unfavorable. A simple Monte Carlo procedure simulating the ordering of such copolymers via rotation of ring‐shaped chains reveals the capability to order even for quite long copolymer chains. The analytical probabilistic consideration is elaborated, which enables one to interpret the ordering via rotation in terms of a sliding of periodic Bernoullian chains. Using both the probabilistic analysis and Monte Carlo simulations it is shown that estimations of a capability to order given by the rotation procedure are also good for a sliding of true Bernoullian copolymers. Therefore, the simple Monte Carlo procedure seems suitable for estimating ordering in other classes of copolymers for which an analytical approach is more complicated. Such estimations might be useful for a consideration of various properties of irregular copolymers connected with their tendency to order.

Ordering by rotation of rings. As an example, an ordering for M = 10 000 chains of length N = 20 and composition p = 0.50 (p is the mole fraction of A units) is shown. See text.

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Ordering by rotation of rings. As an example, an ordering for M = 10 000 chains of length N = 20 and composition p = 0.50 (p is the mole fraction of A units) is shown. See text.
Molecular Weight Development during Simultaneous Chain Scission, Long‐Chain Branching and Crosslinking, 1
Authors: Tobita Hidetaka
Published: March 2003

A general matrix formula is proposed for the weight‐average molecular weights of the polymer systems formed through simultaneous scission, branching and crosslinking of N types of chains, assuming the chain connection statistics are Markovian. For the polymerization systems in which chains are generated consecutively, such as for free‐radical polymerization, the present theory can be applied by increasing the number of chain types N to infinity, by considering the chains formed at different times as different types of chains. The gel point determination reduces to the eigenvalue problem and the present theory extends the classical gelation theory to non‐random, history‐dependent reaction systems. From the mathematical point of view, this theory is capable of describing complex molecular build‐up processes through end‐linking, T‐ and H‐shaped chain connections, irrespective of reaction/reactor types used.

Schematic representation of the 0th generation segment and the connection to the 1st generation segments.

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Schematic representation of the 0th generation segment and the connection to the 1st generation segments.
Applikationsfelder organischer Funktionspolymere, Polymeraktoren und Polymertransistoren
Authors: Roth H.‐K. , Schrödner M.
Published: March 2003

Der Artikel gibt einen kurzen allgemeinen Überblick über zukünftige Hochtechnologieprodukte, in denen leitfähige Polymere und andere Polymere mit speziellen elektronischen Eigenschaften Anwendung finden werden oder bereits angewendet werden. Solche Produkte sind z. B. Polymeraktoren, organische Feldeffekttransistoren (OFET's) und integrierte Polymerschaltkreise, organische Leuchtdioden (OLED's), Polymersolarzellen bzw. Photovoltaikelemente, Membranen für Brennstoffzellen, Polymerbatterien sowie verschiedene Varianten von Polymersensoren.

Es wird kurz informiert über Strukturen und Eigenschaften von intrinsisch leitfähigen Polymeren und etwas detaillierter über elektro‐chemo‐mechanische Polymeraktoren und über polymere Feldeffekttransistoren.
High‐Tech‐Cellulose‐Funktionspolymere nach dem ALCERU®‐Verfahren
Authors: Meister F. , Vorbach D. , Niemz F. , Schulze T.
Published: March 2003

Cellulose gehört zu einem der ältesten Werkstoffe der Menschheit. Standen dabei die Nutzung als Konstruktionswerkstoff bzw. als Textilrohstoff im Vordergrund, so erweitert sich das Anwendungsprofil durch die Nutzung des ALCERU®‐Verfahrens zunehmend auch auf Funktionswerkstoffe.

Dabei gestattet die Verspinnung von Cellulose‐NMMNO‐Lösungen die Herstellung von Polster‐ und Filterwerkstoffen sowie von bioabbaubaren Feinstfolienbändchen mit exakten Formkörperquerschnitten. Nutzt man verschiedene Techniken zur Regenerierung lassen sich vielseitig verwendbare Cellulosefibride herstellen.

Ein großes Feld innovativer cellulosischer Funktionspolymere erschließt sich bei der Zugabe von funktionalen Additiven zur Celluloselösung. Beim Zusatz von keramischen Pulvern lassen sich so piezo‐elektrische Fasern oder aber auch Hochtemperaturfilterwerkstoffe generieren. Insbesondere PZT‐Grünfasern finden zunehmend Anwendung in sehr modernen Sensor‐ und Aktuatoranwendungen. Auf dem gleichen Weg erhält man durch die Zugabe von Leitfähigkeitsrußen elektrisch leitfähige Cellulosefasern, die gleichzeitig textil verarbeitet werden können. Durch den definierten Zusatz verschiedener Mengen an Ruß lassen sich Cellulosewerkstoffe mit genau an den Verwendungszweck angepaßten elektrischen Eigenschaften gewinnen. Schließlich erhält man durch die Variation der Verformungstechnik Celluloseperlen mit variablen Partikel‐ bzw. Porendurchmessern, die über ein attraktives Eigenschaftsspektrum für Anwendungen im Bereich der Blutwäsche sowie der affinitätschromatographischen Nutzung besitzen.
Möglichkeiten der Geruchsmessung und ‐minderung bei Naturfaserverbunden
Authors: Bledzki A. K. , Sperber V. E. , Wolff S.
Published: March 2003

Die kritische Einstellung der deutschen Öffentlichkeit zu Umweltfragen hat auch die Welt der Gerüche erfasst.

In den letzten Jahren haben die Bewertung und Verminderung von Gerüchen bei der Anwendung von Kunststoffen zunehmend an Bedeutung gewonnen. War es zunächst die Verpackungsbranche, die Produkte für Lebensmittelverpackungen olfaktometrisch untersuchte, so zeigt in den letzten Jahren die Automobilindustrie zunehmendes Interesse für Geruchsbestimmung und Messung, nicht zuletzt wegen des zunehmenden Einsatzes von naturfaserverstärkten Werkstoffen im Fahrzeuginnenraum.

Naturfaserverstärkte Kunststoffe haben neben Vorteilen gegenüber glas‐ und kohlefaserverstärkten Systemen (mechanisches Verhalten/Gewicht, ausgeglichene CO2‐Bilanz) auch Eigenschaften, die das Anwendungsspektrum einschränken können. Hierzu werden Emissionen und Geruchsentwicklung gezählt, die unter bestimmten Temperatur‐ und Feuchtigkeitsbedingungen auftreten können. Auch bei Verbundmaterialien stellt sich die Frage, welche Einzelkomponenten, Verfahrensschritte oder Kombinationen beider für einen bestimmten Geruch verantwortlich sind.

Der Weg zur Geruchsneutralität von Kunststoffen ist generell schwierig, da geeignete Herstellungsmethoden oder auch Zusätze nur in langen Versuchsketten ermittelt werden können und nach wie vor die menschliche Nase wichtiger als alle physikalischelektronischen Messverfahren ist.

Die Frage der Herkunft von Gerüchen und nach deren Bedeutung für Wohlbefinden und Gesundheit wird gestellt und zwingt nicht nur die Kunststoffindustrie zur Reaktion. Deshalb sind beide, Kunststoff‐ und Automobilindustrie, bemüht, auf die Tendenzen des Marktes zu reagieren, und es ist das Ziel der Autohersteller möglichst geruchsneutrale Neuwagen auszuliefern.
Modifizierung organischer Konstruktionswerkstoffe für technische Anwendungen
Authors: Heinemann K. , Meusel E. , Riedel B. , Müller W. , Strubl R. , Gottlöber R.‐P. , Seyfarth H.‐E. , Taeger E.
Published: March 2003

Berichtet wird über Experimente zur Synthese neuartiger reaktiver, thermotroper flüssig‐kristalliner Polymere (LCPs) sowie über Untersuchungen zum Einsatz dieser LCPs als Blendkomponente bei der Herstellung derart modifizierter Polyamid‐ und Polyesterfasern und deren Eigenschaften.

Diese reaktiven LCPs sind synthetisch leicht zugängliche Polyesterimidanhydride (PEIA), die sowohl seitenständige als auch endständige Anhydridgruppen besitzen. Die mittlere Zahl an Anhydridgruppen ist zwischen 4 und 18 variierbar. Es konten Produkte mit Molmassen von etwa 30 kg/mol bis hin zu 80 kg/mol erhalten werden.

Beim Mischen der Reaktiv‐LCPs mit Polyamid 6 [PA 6] oder Polyethylenterephthalat [PET] in einem Extruder unter Schmelzebedingungen reagieren beide Komponenten innerhalb weniger Minuten zu Pfropf‐Blockcopolymeren, an deren LCP‐Rückgratketten sich seiten‐ und endständige Polyamid‐ beziehungsweise Polyesterblöcke befinden. Diese schnell verlaufenden Modifizierungsreaktionen bilden die Basis für die industrielle Nutzanwendung in Form eines kontinuierlilch gestaltbaren “reactive blending‐spinning‐drawing”‐Prozesses.

Die auf diesem Wege im Sinne eines “reactive blending” synthetisierten Pfropf‐Blockcopolymeren sind zusammen mit dem jeweils adäquaten Matrixmaterial Polyamid 6 oder Polyester zu reckbaren Filamenten verarbeitbar. Nach Spinn‐ und Reckprozeduren unter geeigneten Bedingungen lassen sich in den erhaltenen Filamenten mit Molekülen des Basispolymers modifizierte lc‐PEIA‐Fibrillen mit Durchmessern von weniger als 500 nm nachweisen. Die angestrebte Mikrophasenverteilung der PA‐ beziehungsweise PET‐modifizierten lc‐PEIA‐Makromoleküle als verstärkungswirksame Systemkomponenten konnte erreicht werden. Zudem zeichnen sich die durch das “reactive blending” in‐situ entstehenden Pfropf‐Blockcopolymere auf Grund ihrer chemischen Ähnlichkeit zur Primärstruktur der jeweiligen Matrixmaterialien durch eine hohe thermodynamische Verträglichkeit aus, woraus ein relativ hoher Verstärkungseffekt resultiert.

Diese beiden Aspekte sowie die bei den Reckprozessen stattfindende Orientierung der lc‐PEIA‐Mikrophasen verursachen, obwohl Optimierungsversuche noch ausstehen, bemerkenswerte Steigerungen der Zugfestigkeiten sowie deutlich verbesserte Anfangsmoduli bei gleichzeitig erhöhter Reckfähigkeit der lc‐PEIA‐modifizierten Polyamid‐ und Polyesterfilamente. Diese Effekte lassen sich bereits mit PEIA‐Anteilen von weniger als 5 Masseprozent erreichen.
Propagation characteristics of transmission‐line transformers with different impedance variation patterns on substrates with very high dielectric constant
Authors: Carvalho M. C. R. , Conrado L. F. M. , Demenicis L. S. , Seixas D. L. A.
Published: March 2003

Transmission‐line transformers with different impedance variation patterns and printed on substrates with very high dielectric constant (εr = 80) are compared and the influence of the total length is studied. The propagation characteristics of the tapered lines were investigated using the finite‐element method. Dispersion effects and impedance variation with respect to the frequency have been taken into account in the analysis. The obtained results are in good agreement with theoretical predictions for ideal tapers, especially at low frequencies. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 174–177, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10859
Computation of Sommerfeld integrals using tanh transformation
Authors: Singh Surendra , Singh Ritu
Published: March 2003

A variable transformation is utilized in the computation of Sommerfeld integrals, which arise in the analysis of antennas radiating over a dielectric half‐space. The method involves a change of variable, which transforms the integrand into a rapidly converging one. Several numerical examples, which illustrate the effectiveness of the method, are presented and the results are compared with those reported in the literature. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 177–180, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10860
Coupled BORs scattering via an efficient MoM solution of CFIE
Authors: Bolli P. , Gentili G. G. , Nesti R. , Pelosi G.
Published: March 2003

In this work a numerical technique for an accurate modelling of the coupling among neighbouring bodies of revolution (BORs) is proposed. This problem is of high interest in modern applications, where clusters of feeds are being used more frequently in antenna systems to increase performances. The scattering problem, both for a stand‐alone body of revolution (BoR) and for coupled BoRs, has been solved using the combined field integral equation (CFIE) approach and the method of moments (MoM), with an efficient set of expansion functions whose validity is limited to BoR. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 180–183, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10861
Error control of the translation operator in 3D MLFMA
Authors: Hastriter Michael Larkin , Ohnuki Shinichiro , Chew Weng Cho
Published: March 2003

This paper presents an extension of a new approach to select the truncation number for translation operators in a 3D multilevel fast multipole algorithm (MLFMA). Although error is harder to control in 3D than in 2D problems, this recently developed new approach provides better error control in 3D problems over the excess bandwidth formula. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 184–188, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10862
High‐order finite‐element analysis of periodic absorbers
Authors: Lou Zheng , Jin Jian‐Ming
Published: March 2003

A high‐order vector finite‐element‐method (FEM) analysis of periodic absorbers is presented. By the virtue of the FEM, accurate modeling of complicated absorber structures is made possible. For a given accuracy, high‐order elements are used to reduce the number of unknowns and hence the computing time and memory consumption. The FEM is further combined with the asymptotic waveform evalaution (AWE) technique to produce fast‐frequency sweep. Both singly and doubly periodic absorbers are modeled and the accuracy of the method is demonstrated by comparisons with analytical solutions and published data. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 203–207, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10869
A dual‐band printed L‐shaped monopole for WLAN applications
Authors: Lin Yi‐Fang , Chen Horng‐Dean , Chen Hua‐Ming
Published: March 2003

A novel microstrip‐fed dual‐band L‐shaped monopole antenna has been developed for WLAN applications in the 2.4‐GHz and 5.2‐GHz bands. The antenna has a single L‐shaped radiator and is easy to construct. The obtained impedance bandwidth (1:1.5 VSWR) reaches 15.6% and 12.6% for the 2.4 and 5.2 GHz, respectively. Omnidirectional patterns, vertical null in the antenna patterns, and good efficiency of the two operating frequencies are given for the proposed antenna. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 214–216, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10873
Triple‐band triangular‐shaped meander monopole antenna with two coupled lines
Authors: Chen Horng‐Dean
Published: March 2003

A novel compact monopole antenna for triple‐band operation is proposed in this paper. The proposed antenna is designed to operate at 900, 1800, and 2450 MHz, and is realized by loading two coupled lines on a triangular‐shaped meander line. The longer coupled line controls the excitations of the first two resonant modes, and the shorter one controls the excitation of the third resonant mode. Good impedance bandwidth performance for the three bands is observed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 232–234, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10879
Reproducibility study of 3D geometrical reconstruction of the human carotid bifurcation from magnetic resonance images
Authors: Long Q. , Ariff B. , Zhao S.Z. , Thom S.A. , Hughes A.D. , Xu X.Y.
Published: March 2003

The combined magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) modeling approach is playing an increasingly important role in advancing our understanding of the relationship between hemodynamics and arterial disease. Nevertheless, such a modeling approach involves a number of uncertainties associated with various stages of the process. The present study is concerned with the reproducibility of geometry reconstruction, one of the most crucial steps in the modeling process. The reproducibility test was conducted on the right carotid bifurcation of eight normal human subjects, each of whom were scanned twice using the same MR protocol with an in‐plane resolution of 0.625 mm. Models constructed from different scans of the same subject were compared and assessed using four quantitative measures: centerline distance, cross‐sectional area, contour shape factors, and mean radius difference. The difference in the maximum carotid bulb area between the two scans was found to be <8.1% for all subjects. Shape factors (measuring the dissimilarity between two contours) of <10% were achieved in most of the common carotid arteries (CCAs) and internal carotid arteries (ICAs). The mean radius difference between the two scans was <0.4 mm for all subjects. Among the three vessels, the geometry of CCA was well reproduced by the reconstruction procedure in most of the cases, while the external carotid artery (ECA) showed the worst reproducibility. The impact of geometrical differences on CFD‐predicted flow patterns and wall shear stress (WSS) will be investigated and discussed in a separate paper. Magn Reson Med 49:665–674, 2003. © 2003 Wiley‐Liss, Inc.
In vivo oxygen detection using exogenous hemoglobin as a contrast agent in magnetic resonance microscopy
Authors: Sun Phillip Z. , Schoening Zachary B. , Jasanoff Alan
Published: March 2003

In this work we show that exogenous molecular hemoglobin (Hb) is an effective indicator of relative local oxygen tension in magnetic resonance (MR) microscopy studies in vivo. This approach is more sensitive than other MRI oximetry methods; it can be used at higher resolutions and in specimens with no blood oxygen level‐dependent (BOLD) effects. Using injection studies in flies, we show that Hb can permeate through relatively dense neural tissue, and that it is not obviously disruptive to physiology. Hb‐injected flies show large changes in signal intensity (40–50%) when external O2 levels are manipulated artificially from 0% to 21%. Oxygen‐dependent contrast changes produced by exogenous Hb are detected in T2‐weighted imaging experiments, and can be roughly calibrated if necessary. These studies demonstrate the feasibility of a contrast agent technique that may be useful for functional MRI (fMRI) studies of metabolism at tens of microns resolution. Magn Reson Med 49:609–614, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative tumor oxymetric images from 4D electron paramagnetic resonance imaging (EPRI): Methodology and comparison with blood oxygen level‐dependent (BOLD) MRI
Authors: Elas Martyna , Williams Benjamin B. , Parasca Adrian , Mailer Colin , Pelizzari Charles A. , Lewis Marta A. , River Jonathan N. , Karczmar Gregory S. , Barth Eugene D. , Halpern Howard J.
Published: March 2003

This work presents a methodology for obtaining quantitative oxygen concentration images in the tumor‐bearing legs of living C3H mice. The method uses high‐resolution electron paramagnetic resonance imaging (EPRI). Enabling aspects of the methodology include the use of injectable, narrow, single‐line triaryl methyl spin probes and an accurate model of overmodulated spectra. Both of these increase the signal‐to‐noise ratio (SNR), resulting in high resolution in space (1 mm)3 and oxygen concentrations (∼3 torr). Thresholding at 15% the maximum spectral amplitude gives leg/tumor shapes that reproduce those in photographs. The EPRI appears to give reasonable oxygen partial pressures, showing hypoxia (∼0–6 torr, 0–103 Pa) in many of the tumor voxels. EPRI was able to detect statistically significant changes in oxygen concentrations in the tumor with administration of carbogen, although the changes were not increased uniformly. As a demonstration of the method, EPRI was compared with nearly concurrent (same anesthesia) T/blood oxygen level‐dependent (BOLD) MRI. There was a good spatial correlation between EPRI and MRI. Homogeneous and heterogeneous T/BOLD MRI correlated well with the quantitative EPRI. This work demonstrates the potential for EPRI to display, at high spatial resolution, quantitative oxygen tension changes in the physiologic response to environmental changes. Magn Reson Med 49:682–691, 2003. © 2003 Wiley‐Liss, Inc.