bluuebunny/crossref_metadata_2025_split huggingface dataset:
4,15‐Diamino[2.2]paracyclophane as a Starting Material for Pseudo‐Geminally Substituted [2.2]Paracyclophanes
Authors: Shaieb Kamal El , Narayanan Vijay , Hopf Henning , Dix Ina , Fischer Axel , Jones Peter G. , Ernst Ludger , Ibrom Kerstin 
Published: May 2004

AbstractDiazotization of the title compound 3, followed by treatment of the formed bis(diazonium ion) with cuprous chloride, yields the pseudo‐geminal dichloride 1. Similarly, 3 is converted into the bis(azide) 5 when sodium azide is used as the trapping nucleophile. Hypochlorite oxidation of 3 furnishes the azo compound 4, the first multi‐bridged cyclophane with a bridge consisting only of heteroatoms. Reduction of 4 with zinc/acetic acid affords the substrate 3 again. Treatment of 4 with bromine/iron powder or iodine monochloride causes deazotization accompanied by halogen introduction in pseudo‐geminal position (i.e., formation of 2 and 6, respectively). Flash vacuum pyrolysis (450 °C, 0.01 Torr) of 4 produces the phenanthrene derivatives 13 and 14, while with tetracyanoethylene (TCNE) the azophane undergoes rapid cycloaddition at room temperature to give the [2+4] cycloadduct 16. The structures of 1, 2, 4−6, and 16 have been determined by X‐ray structural analysis. Molecular packing patterns are determined by weak hydrogen bonds; a common packing pattern for cyclophane derivatives is ascribed to C−H···π interactions. Full bandshape analyses of the bridge proton signals in the 1H NMR spectra of 1, 2, 6, and of the difluoro analogue 17 yielded the vicinal 1H,1H coupling constants. These reflect the 1:1 equilibrium between the two skew conformations of the bridges. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Highly π‐Facial Stereoselective Aldol Reaction of (S)‐Proline‐Derived Amide Enolate with Benzaldehydes
Authors: Adam Waldemar , Zhang Aimin 
Published: May 2004

AbstractThe asymmetric aldol reaction of the (S)‐proline‐derived bicyclic amide enolate 1 with benzaldehydes selectively affords the two diastereomeric aldol adducts (3S,3′R,8S)‐3a and (3S,3′S,8S)‐3a, of four possible diastereomers, in good yield. The high control of π‐facial stereoselectivity at the endocyclic C‐3 stereocenter is due to perfect shielding by the pseudo‐axial phenyl ring at the C‐1 position. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Two‐phase estimation of coverages with second‐phase corrections
Authors: Fattorini L. , Marcheselli M. , Pisani C. 
Published: May 2004

AbstractA two‐phase estimation of coverages of the k land categories partitioning a study area is considered. In the first phase a sample of N points is selected according to a spatial sampling design and the selected points are assigned to the k categories on the basis of satellite imagery or aerial photos. Simple random sampling, stratified sampling and systematic sampling of points are considered. The theoretical results suggest the use of stratified sampling as the best design‐based spatial strategy in the first phase. Subsequently, in the second phase, a sample of n < N points is selected using a finite population sampling design. Then the selected points are visited and correctly classified on the ground. To this purpose, a stratified sampling is considered in which the strata are determined by the aerial classification. The statistical properties of the resulting two‐phase estimator are derived and a conservative estimator of its variance–covariance matrix is proposed. The procedure is checked on the basis of a simulation study performed on some artificial populations. Copyright © 2004 John Wiley & Sons, Ltd.
Nonlinear estimation for PM2.5 transmission effects in Jefferson Co., Texas
Authors: Eun Kim Sung 
Published: May 2004

AbstractUrban air pollution consists of emission and transmission of air pollutants. In this article, we discuss a complex valued nonlinear regression model to characterize the effect of pollutant transmission by estimating the direction and velocity of the spatial propagation at a fixed sequence of time intervals. In case the pollutant is transmitted from a distant source during a certain time period, the monitoring stations in the local network detect the signal with time delays, which are nonlinearly related to the velocity and angle of approach or azimuth. An observed vector time series in the monitoring network is modeled as the sum of a lagged or delayed stochastic signal and a zero mean stationary noise vector. The Fourier transformation is applied to the model, and the maximum likelihood estimation of the transmission parameters under such a model is considered. Those estimates can be used to identify the possible sources of local pollutants and for better understanding of spatial distribution of pollutants. Data used in this study are based on hourly PM2.5 records from three monitoring stations in the Beaumont‐Port Arthur area in Texas for April to December 2002. The results indicate that during the months May, November and December, PM2.5 transmission were significant, with the dominant direction from the east. The velocity estimates during the period range from 4 to 20 km/h. During the summer season (June to October) the transmission effect was not very evident except for the first week of August and the first week of September. The model well detects both consistent and momentary transmissions. The parameter estimates and their standard errors are given for each week separately. Copyright © 2004 John Wiley & Sons, Ltd.
Survey of Protozoa and Metazoa populations in wastewater treatment plants by image analysis and discriminant analysis
Authors: Amaral A. L. , da Motta M. , Pons M. N. , Vivier H. , Roche N. , Mota M. , Ferreira E. C. 
Published: May 2004

AbstractThe biota present in the activated sludge of a wastewater treatment plant are mainly composed of bacteria, Protozoa and Metazoa. The Protozoa and Metazoa species are important micro‐organisms taking part in the ecosystem balance in wastewater treatment plants and are quite sensitive to physical, chemical and operational processes. Several authors have established relationships between the predominance of certain species or groups and some variables of the plant. Such analysis demands the identification and quantification of the different species, which requires skilled workers, specializing in zoology or protozoology, and is time‐consuming. To overcome those problems, semi‐automatic image analysis and discriminant analysis were carried out for the identification procedures. The overall results were very promising in terms of Protozoa and Metazoa group recognition and of survey of plant conditions. Copyright © 2004 John Wiley & Sons, Ltd.
Transient analysis of HVDC power transmission systems
Authors: Abdel‐Salam M. , Seddik H. 
Published: May 2004

AbstractThis paper describes a method for dynamic simulation of HVDC transmission systems based on transient circuit analysis during abnormal conditions. Such conditions include sudden drop or rise in the AC system voltage at the rectifier or inverter sides and short‐circuit faults on the DC link. The waveforms of the calculated DC current and terminal voltages of the DC link agreed reasonably with those reported before. The accuracy of the simulation method is also checked during normal operating conditions. For different short‐circuit faults on the DC link a conventional third‐order controller is proposed (for the first time) to reduce the DC current to its normal level in a more efficient way than the first‐order controller being used before. Copyright © 2004 John Wiley & Sons, Ltd.
Order of genetic events is critical determinant of aberrations in chromosome count and structure
Authors: Fauth Christine , O'Hare Michael J. , Lederer Gabi , Jat Parmjit S. , Speicher Michael R. 
Published: May 2004

AbstractA sequential acquisition of genetic events is critical in tumorigenesis. A key step is the attainment of infinite proliferative potential. Acquisition of this immortalization requires the activation of telomerase in addition to other activities, including inactivation of TP53 and the retinoblastoma family of tumor‐suppressor proteins. However, the importance of the order in which these genetic events occur has not been established. To address this question, we used a panel of normal mammary fibroblasts and endothelial cultures that were immortalized after transduction with the catalytic subunit of telomerase (hTERT) and a temperature‐sensitive mutant of the SV40 large‐tumor (tsLT) oncoprotein in different orders in early‐ and late‐passage stocks. These lines were maintained in continuous culture for up to 90 passages, equivalent to >300 population doublings (PDs) post‐explantation during 3 years of continuous propagation. We karyotyped the cultures at different passages. Cultures that received hTERT first followed by tsLT maintained a near‐diploid karyotype for more than 150 PDs. However, in late‐passage stocks (>200 PDs), metaphase cells were mostly aneuploid. In contrast, the reverse order of gene transduction resulted in a marked early aneuploidy and chromosomal instability, already visible after 50 PDs. These results suggest that the order of genetic mutations is a critical determinant of chromosome count and structural aberration events. © 2004 Wiley‐Liss, Inc.
Assessing the reliability of density functional methods in the conformational study of polypeptides: The treatment of intraresidue nonbonding interactions
Authors: Improta Roberto , Barone Vincenzo 
Published: May 2004

AbstractThe role of intraresidue interactions in determining the conformational behavior of polypeptides is analyzed by means of density functional and post‐Hartree–Fock computations on the alanine dipeptide analog and other model compounds. Our computations show that the accuracy of current density functionals is sufficient for H‐bond, electrostatic, inductive, and short‐range repulsive interactions, whereas medium‐range attractions between electron‐rich atoms and/or bonds are underestimated. This leads, in turn, to an underestimation of the stability of helical structures w.r.t. extended or folded conformers involving H‐bonds. Those results could pave the route for devising local ad hoc corrections able to significantly improve structural and dynamic predictions for polypeptides issuing from DFT computations. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1333–1341, 2004
In‐line mixing for production of citric acid byCandida lipolyticagrown onn‐paraffins
Authors: Crolla A , Kennedy KJ 
Published: May 2004

AbstractThis study reports on the effects of internal fermenter and external in‐line agitation and fed‐batch mode of operation on citric acid production fromCandida lipolyticausingn‐paraffin as the carbon source. An optimum range of fermenter agitation speeds in the range 800–1000 rpm corresponding to Reynolds numbers of 50433–62947 (based on initial batch conditions) seemed to give the best balance between substrate utilization for biomass growth and citric acid production. Proof of concept evidence is presented that indicates that an external in‐line agitator could be used in place of high speed internal agitation to increase citric acid production. However, more work is required to optimize the external agitator concept. Application of multiple fed‐batch feedings can be used to extend the batch fermentation and increase final citric acid concentrations and product yield. Experiments were conducted implementing a three‐cycle fed‐batch process which increased overall citric acid yields to 0.8–1.0 g citric acid g−1n‐paraffin, approximately 200% improvement from those found in the normal batch process. The three‐cycle fed‐batch mode of operation also increased the final citric acid concentration to 42 g dm−3from about 6 g dm−3for normal batch operation. Increased citric acid concentrations in three‐cycle fed‐batch mode was achieved at longer fermentation times. Copyright © 2004 Society of Chemical Industry
The specificity and the ability ofAspergillusferuloyl esterase to releasep‐coumaric acid from complex cell walls of oat hulls
Authors: Yu Peiqiang , McKinnon John J , Maenz David D , Racz Vern J , Christensen David A 
Published: May 2004

Abstractp‐Coumaric acid (4‐hydroxycinnamic) and ferulic acid (4‐hydroxy‐3‐methoxycinnamic), two major hydroxycinnamic acids found in the complex cell walls of oat hulls, act as cross‐linking agents between lignin and polysaccharides or between polysaccharides. As such, they are inhibitory to the biodegradation of cell walls by microorganisms. A previous study showed thatAspergillusferuloyl esterase withTrichodermaxylanase was able to break the ester linkage between ferulic acid and the attached sugar, releasing ferulic acid from the cell wall. The objective of this study was to investigate the specificity and the ability ofAspergillusferuloyl esterase to releasep‐coumaric acid from oat hulls. The results show there was no extensive release ofp‐coumaric acid in both the absence and presence ofTrichodermaxylanase byAspergillusferuloyl esterase. This indicates a specificity ofAspergillusferuloyl esterase, which is more active only on esters of certain hydroxycinnamic acids; in this case,Aspergillusferuloyl esterase will only sufficiently break the ester‐linked feruloyl group but not thep‐coumaroyl group in the complex cell walls of oat hulls. Copyright © 2004 Society of Chemical Industry
The effects of nitrate and nitrate‐supplemented leachate addition on methanogenesis from Municipal Solid Waste
Authors: El‐Mahrouki Iman Mohamed Lotfy , Watson‐Craik Irene Ann 
Published: May 2004

AbstractThe recirculation of nitrified leachate through landfill sites, followed by in situ denitrification, represents a novel and more sustainable approach for the removal of ammonia from leachate, prior to discharge. The effects of nitrate and leachate supplementation on methanogenesis in Municipal Solid Waste (MSW) were studied in batch cultures. The addition of a range of nitrate concentrations to MSW samples had an inhibitory effect on methanogenesis. The effects were dose‐dependent, such that recovery of methane production was recorded within 5 and 23 days with added 100 and 750 mg NO3 dm−3, respectively. Even after 24 days, no recovery was observed in cultures challenged with 1000 mg NO3 dm−3. The enumeration of denitrifying bacteria in a range of fresh, actively methanogenic and aged, well‐decomposed MSW confirmed the potential of MSW for rapid denitrification. Methanogenesis was not inhibited by the addition of leachate (20–100% strength) that contained high concentrations of VFAs. However, when the same leachate was supplemented with nitrate (250 mg NO3 dm−3), methanogenesis was inhibited by the addition of leachate concentrations ≥20%, which was attributed to inhibition of denitrification by VFAs. Propionate accumulated, confirming the importance of methanogenesis as an electron sink. With the removal of nitrate and the recovery of methanogenesis, net propionate concentrations decreased. Copyright © 2004 Society of Chemical Industry
Determination of fungicide residues in fruits by coupled‐column liquid chromatography
Authors: Zamora Tatiana , Hidalgo Carmen , López Francisco J. , Hernández Félix 
Published: May 2004

AbstractCoupled‐column liquid chromatography with fluorescence detection was applied to the determination of o‐phenylphenol and bitertanol residues in orange and banana fruits. After extraction with a mixture of acetone, dichloromethane‐petroleum ether, and ethyl acetate, an extract aliquot of 100 μL was injected directly without any additional clean‐up into the chromatographic system using two reversed phase C18 coupled columns. The LC‐LC approach allowed automated sample clean up of the vegetal extracts, leading to a simple and rapid analytical procedure, with limits of quantification between 0.01 and 0.05 mg kg–1. Recovery experiments performed on orange and banana samples fortified at different concentrations (0.01–4 mg kg–1) gave average recoveries between 70 and 113% with relative standard deviations lower than 15%. The procedure developed was finally applied to orange and banana samples from different geographical locations and the results were confirmed by GC‐MS.
Time‐resolved luminescence of terbium complexes with poly(2‐ and 4‐vinylpyridine N‐oxide)s in aqueous solution
Authors: Výprachticky Drahomír , Cimrová Věra , Okamoto Yoshi , Kotva Rudolf 
Published: May 2004

AbstractTerbium complexes with polymer ligands of poly(2‐ and 4‐vinylpyridine N‐oxide)s (P2VPNO, P4VPNO) in aqueous solution were prepared and characterized. Multi‐exponential decays of the 5D4 → 7F5 terbium transition at 545 nm of [P2VPNO‐Tb3+] and [P4VPNO‐Tb3+] complexes were measured. The non‐linearity of semi‐logarithmic plots of time‐resolved luminescence was more pronounced in [P4VPNO‐Tb3+] than in [P2VPNO‐Tb3+], being reduced by addition of salts such as sodium formate or acetate. We assume that multi‐exponential decays of Tb3+ in the complexes are caused by a back metal‐to‐ligand energy transfer via triplet state of N‐oxide polymer ligand. By carrying out separate experiments in water and deuterium oxide, the number of coordinated water molecules in the [P4VPNO‐Tb3+] complex was estimated as 4‐5, assuming that the Tb3+ aqua complex contains nine water molecules.
Physical properties and structure of thin conducting ion‐beam modified polymer films
Authors: Guenther Margarita , Gerlach Gerald , Suchaneck Gunnar , Schneider Dieter , Wolf Bodo , Deineka Alexander , Jastrabik Lubomir 
Published: May 2004

AbstractIn this work, a complex investigation of the film surface composition, chemical bonding, conductivity, optical properties, density, hardness and Young's modulus of ion‐beam‐modified polyimide films was carried out. It was shown that the partial destruction of chemical bonding under ion bombardment leads to the formation of graphite‐like, amorphous carbon islands, which increase the surface film conductivity by several orders of magnitude, from an insulating to a semiconducting region. Strong enhancements of both the conductivity and the optical absorption coefficient occur when the fraction of amorphous carbon clusters dispersed in a polyimide matrix reaches 40 %. The values of hardness, Young's modulus and density at high irradiation doses reach the values typical of a hydrogenated amorphous carbon.
Growth of organic n‐conductors on thin polymer films for use in organic field effect transistors
Authors: Michaelis W. , Kelting C. , Hirth A. , Wöhrle D. , Schlettwein D. 
Published: May 2004

AbstractThin films of different polymers ‐ poly(styrene) (PS), poly(methylmethacrylate) (PMMA), poly(vinylcarbazole) (PVCz), poly(vinylchloride) (PVC) and poly(vinylidene fluoride) (PVDF) ‐ were deposited by spin‐coating or by vapor deposition. On these polymers, thin films of (hexadecafluorophthalocyaninato)‐oxovanadium (F16PcVO) were prepared by physical vapor deposition. The growth of these films was monitored in situ by optical spectroscopy. The optical absorbance spectra were analyzed based on the coupling of transition dipoles to obtain information on the intermolecular arrangement of chromophores in the films. In all of these samples, the molecules are oriented with their molecular plane preferentially perpendicular to the substrate surface. This gives the desired overlap of the π‐systems for electric conductance parallel to the substrate. Differences in the interactions were detected when deposition temperatures below or above the glass transition temperature of a given polymer were compared. The morphology of the polymer films and the deposited semiconductors were investigated by atomic force microscopy and scanning electron microscopy. The influence of the chosen substrate on the film structure is determined. The optical and electric properties of the films could thereby be influenced and the applicability of such films as active layers in organic thin film transistors is discussed.
Quantum chemical study of oxidation processes in Cu‐phthalocyanine
Authors: Toman Petr , Nešpůrek Stanislav , Yakushi Kyuya 
Published: May 2004

AbstractQuantum chemical calculations reproduced quite well the experimental infrared spectra of CuPc and CuNO3Pc · HNO3. The agreement in the changes of line intensities during the oxidation supports the idea of ligand oxidation. This result is in agreement with the Mulliken population analysis.
Atmospheric aging of poly[methyl(phenyl)silanediyl] monitored by FTIR spectroscopy
Authors: Meszároš Oto , Schmidt Pavel , Pospíšil Jan , Nešpůrek Stanislav , Kelnar Ivan 
Published: May 2004

AbstractPoly[methyl(phenyl)silanediyl] films were irradiated in ATLAS Weather‐O‐Meter Ci 3000+ for ca 3 h. Changes in the region of siloxane, carbonyl, hydroxyl, and C‐H (aromatic) bands were monitored by FTIR. Main attention was paid to changes in siloxane formation, which could be reduced in the presence of phenolic UV absorber 1 and oxalanilide 3.
Hybrid organic‐inorganic coatings and films containing conducting polyaniline nanoparticles
Authors: Špírková Milena , Stejskal Jaroslav , Prokeš Jan 
Published: May 2004

AbstractHybrid organic‐inorganic coatings and free‐standing films made from [3‐(glycidyloxy)propyl]trimethoxysilane, amino‐terminated poly(oxypropylene) (Jeffamine D‐230), colloidal polyaniline nanoparticles and, in some cases, colloidal nanosilica were prepared and characterized. HCl or 4‐methylbenzene‐1‐sulfonic acid were used as catalysts for the sol‐gel process and pH tuning, water‐propan‐2‐ol mixture as a solvent. Electrical and mechanical properties and surface morphology of films were studied. The coatings were blue and non‐conducting, or green and conducting, depending on preparation conditions. They have a smoother surface than in‐situ polymerized polyaniline films.
Effect of a dipolar self‐assembly monolayer formation on indium‐tin oxide on the performance of single‐layer polymer‐based light‐emitting diodes
Authors: Morgado Jorge , Charas Ana , Barbagallo Nunzio , Alcácer Luis , Matos Manuel , Cacialli Franco 
Published: May 2004

AbstractWe report on the use of indium‐tin oxide surface modification, by grafting of highly polar p‐disubstituted benzenes, in the fabrication of light‐emitting diodes. The polar compounds possess COCl or SO2Cl grafting groups and CF3 or NO2 as highly electronegative groups, leading to the formation of a dipolar monolayer, which brings about an increase in ITO work function, thereby reducing the barrier for hole injection into luminescent polymers. We observe that the effect of this self‐assembled monolayer, in terms of light‐onset voltage, efficiency and luminance, is at least comparable to the use of a hole injection layer of doped poly[(3,4‐ethylenedioxy)thiophene] for LEDs using poly({2‐[(2‐ethylhexyl)oxy]‐5‐methoxy‐1,4‐phenylene}vinylene) (MEH‐PPV) and polyfluorene blends as active layers.
Coherent electronic transport through the single‐walled carbon nanotubes
Authors: Babiaczyk W. Iwo , Bułka Bogdan R. 
Published: May 2004

AbstractWe present the results for coherent electronic transport through the single walled carbon nanotubes. A large value of conductance is obtained for strong coupling to the electrodes, which is close to the ideal transmission of 4e2/h as in experiment. We also consider the system with ferromagnetic electrodes and analyze in detail conductance for separated channels in the coherent regime.
End‐functionalized π‐conjugated oligomeric materials for photoelectrical applications
Authors: Pavlík Martin , Pfleger Jiří , Jossifov Christo , Vohlídal Jiří 
Published: May 2004

AbstractSoluble poly(diphenylacetylene)s (PDA) capped with PhCO‐ groups (PDA‐C) and Ph2C= groups (PDA‐P) were prepared via McMurry reductive coupling of benzil and carbonyl‐olefin exchange reaction of tetraphenylethene and benzil, respectively. Fluoren‐9‐ylidene groups have been introduced into PDA by the McMurry coupling of PDA‐C with fluoren‐9‐one and via copolymerization of benzil and fluoren‐9‐one. The oligomers prepared are stable in air, soluble in a variety of solvents. They can be processed by casting to form good‐quality thin films suitable for measurements of electrical and optoelectrical properties.