bluuebunny/crossref_metadata_2025_split huggingface dataset:
Drug screening: Actual status, pitfalls and suggestions for improvement/Drogenscreening: Gegenwärtiger Stand, Fehlermöglichkeiten und Verbesserungsvorschläge
Authors: Külpmann Wolf R. 
Published: August 2004

Abstract

Abstract Immunoassays for drug screening are often regarded as procedures which are easily performed and interpreted. But in fact, many aspects have to be considered to obtain a meaningful result. Among these are sampling, specificity and sensitivity of assays, and quality assessment. Although the mechanised procedures yield quantitative results, there are good reasons to generally report qualitative findings. The mechanised procedures allow the adjustment of the cut-off concentration to the clinical setting, e.g. in the case of acute intoxication, chronic abuse or drug withdrawal, an important advantage as compared to test strips. Procedures for the detection of amphetamines, barbiturates, benzodiazepines or opiates are hampered by the fact that the analytical signal is in principle not related to the pharmacological effect of the contributing drug. A proposal for adjusting the analytical response to the pharmacodynamic action of a compound is presented, as well as a list of drugs for which immunoassays are required. This may give guidance to manufacturers for improving and developing assays. Procedures for individual compounds should in general specifically detect the pertinent metabolite in urine as a proof of drug uptake. Hydrolysis is mandatory in case of poor cross-reactivity of the antibody with the excreted conjugates.
Therapeutisches Drug Monitoring von Antidepressiva und Antipsychotika/Therapeutic monitoring of antidepressant and antipsychotic drugs
Authors: Hiemke Christoph 
Published: August 2004

Abstract

Abstract Studies have shown the beneficial effects of Therapeutic Drug Monitoring (TDM) for some antidepressant (tricyclic antidepressants) and antipsychotic drugs (e.g. haloperidol or clozapine). For these drugs, TDM should be used as standard care. Moreover, TDM is useful for a number of specific indications such as control of compliance, drug-drug interactions, comorbidity, nonresponse, or unexpected side effects. In practice, blood should be taken under steady state conditions and analytical methods should be sufficiently sensitive (lower limit of quantification about 5 to 50 ng/ml) and precise (day-to-day variabilities below 20%). Chromatographic methods are suitable, whereas immunoassays for antidepressants and radioreceptor assays for antipsychotics have insufficient reliability. TDM results should be reported with inclusion of a qualified comment as soon as possible after blood withdrawal. The clinical decision must consider not only blood levels but also time under drug therapy, clinical improvement and side effects. Some studies have shown an economical impact of TDM. The potential beneficial effects of TDM in anti-psychotic and anti-depressive drug therapy are not adequately utilized, since psychiatrists order these tests too rarely.
Extraction and separation of Am(III) and Sr(II) by N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA)
Authors: Suzuki H. , Sasaki Y. , Sugo Y. , Apichaibukol A. , Kimura T. 
Published: August 2004

Summary
By using an extractant, N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA), extraction and separation of Sr(II) from Am(III) were investigated for the partitioning of high level liquid waste (HLLW). Both metal ions, accompanied with the counter anion, NO3
-, and HNO3 without dissociation, were extracted by TODGA. We used two distinct methods for the separation of Am(III) and Sr(II). A mixture of TODGA and monoamide reduced the distribution ratio D of Sr(II) compared to that without monoamide, whereas D(Am) was still high value under the identical condition. After extraction of Am(III) by TODGA and monoamide, Sr(II) remaining in HLLW can be extracted by using enough concentration of TODGA at the next step. In the other method, Sr(II) was coextracted with Am(III) by TODGA. It was observed that D(Sr) decreased with an increase of HNO3 from 3 M to 6 M HNO3 at the same TODGA concentration, while D(Am) increased until 6 M HNO3. By using 6 M HNO3, Am(III) and Sr(II) were separated after coextraction.
Monitoring of metallurgical process plants by using biplots
Authors: Aldrich C. , Gardner S. , Le Roux N. J. 
Published: August 2004

AbstractAlthough principal component analysis has been applied widely for monitoring plant performance in a broad range of industrial processes, the use of accompanying biplots has not received similar attention. Moreover, principal component analysis is a linear technique that tends to break down when processes exhibit significant nonlinear behavior. In this paper biplot methodology is introduced. This methodology allows for projecting high‐dimensional data to a low‐dimensional subspace that can be visualized by a human operator. It provides management with sophisticated tools, highly graphical in nature, to extract information regarding variation in process variables, correlations among these variables, as well as class separation, taking into account the multidimensional character of the data. Biplot methodology can also be applied to data sets exhibiting nonlinear behavior. As is shown by way of two case studies, operating regions can be quantitatively explored by superimposing alpha bags on biplots, which facilitates the automatic detection and visualization of process disturbances. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2167–2186, 2004
Comparison of micromixing models for CFD simulation of nanoparticle formation
Authors: Wang Liguang , Fox Rodney O. 
Published: August 2004

AbstractReactive precipitation is an important research topic in chemical engineering because of its numerous industrial applications in the formation of nanoparticles. Recently, computational fluid dynamics (CFD) has been successfully coupled with micromixing models and probability density function (PDF) methods to predict the effect of mixing on the particle size distribution. The micromixing model is generally based on the presumed PDF method. The objective of this work is to compare multienvironment‐presumed PDFs and a recently proposed direct‐quadrature‐method‐of‐moments‐interaction‐by‐exchange‐with‐the‐mean (DQMOM‐IEM) micromixing model with transported PDF predictions for the simulation of reactive precipitation, including simultaneous mixing‐limited reaction, nucleation, and growth in a plug‐flow reactor. DQMOM is applied to calculate the turbulent spurious dissipation rate for the multienvironment micromixing models. The results show that the DQMOM‐IEM model agrees well with the transported PDF simulations, even when the number of nodes used in DQMOM is small (such as 2–4). Given the computational efficiency of the DQMOM‐IEM model relative to transported PDF methods, this model offers great promise as a practical CFD tool for simulating plant‐scale reactors. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2217–2232, 2004
Closed‐loop behavior of nonlinear model predictive control
Authors: Tenny Matthew J. , Rawlings James B. , Wright Stephen J. 
Published: August 2004

AbstractModel predictive control (MPC) relies on real‐time optimization to determine open‐loop control profiles and state estimates given process measurements. When the underlying process model is nonlinear, the MPC system exhibits unique behavior not seen in linear MPC. Some of the characteristics are highlighted of nonlinear models in the context of closed‐loop performance. The effects are examined of disturbance models on closed‐loop performance and necessary conditions are shown for how and where steady states of the closed‐loop system may be found. These conditions are demonstrated on a simple example to show that the input disturbance model can lead to failure of the control system, and that linear MPC is inadequate for controlling this class of systems. Additionally, due to nonconvexity, the optimization problems solved in nonlinear MPC may have local optima. These local minima may lead to undesirable performance, particularly in the state estimator. The existence is studied of these optima in the regulator and estimator and their potential effects are examined on the performance of the closed‐loop system. To avoid unwanted local minima, the use is advocated of constraints in the estimator and regulator formulations and it is shown how a shorter prediction horizon in the regulator leads to better control profiles for some nonlinear models. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2142–2154, 2004
Modeling ethane oxy‐dehydrogenation over monolithic combustion catalysts
Authors: Caputo Francesco Donsfi Tiziana , Russo Gennaro , Di Benedetto Almerinda , Pirone Raffaele 
Published: August 2004

AbstractA numerical approach is used to investigate the role of a combustion catalyst in the oxidative dehydrogenation of ethane at short contact times for ethylene production. A two‐dimensional (2‐D) model, with mass and energy equations coupled with the Navier‐Stokes equations, is applied to show that an oxidation catalyst can beneficially affect the formation of ethylene, by optimizing the sacrifice of ethane for producing heat with a larger selectivity to CO2 than a purely homogeneous process. Simulations also showed that for exceedingly high catalyst activity hot spots are formed on the catalyst walls, as the characteristic times of heat production become comparable with those of heat transfer. This may result into the formation of byproducts that reduce ethylene selectivity. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2233–2245, 2004
Helical flows and chaotic mixing in curved micro channels
Authors: Jiang F. , Drese K. S. , Hardt S. , Küpper M. , Schönfeld F. 
Published: August 2004

AbstractThe mixing due to helical flows in curved micro channels is investigated. A new chaotic mixing mechanism is presented relying on alternately switching between different flow patterns exhibiting four Dean vortices. Flow patterns and interfacial stretching factors are numerically computed for various Dean numbers. For experimental studies a prototype of a chaotic mixer with curved channels was fabricated. The experimental evaluation of the mixing performance corroborates the numerical prediction: the mixing performance found for Dean numbers above 140 is qualitatively different from that at lower Dean numbers; the periodic switching between different vortex patterns leads to efficient mixing, manifesting itself in an exponential growth of interfacial area. In addition to the studies on mixing, residence‐time distributions in the mixing channel are computed numerically. These investigations indicate that due to mass‐transfer enhancement originating from the transversal redistribution of matter in the chaotic flow, hydrodynamic dispersion is substantially reduced relative to a straight channel. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2297–2305, 2004
Temperature control of heterogeneous reactive distillation
Authors: Huang Shih‐Ger , Kuo Chien‐Lin , Hung Shih‐Bo , Chen Yi‐Wei , Yu Cheng‐Ching 
Published: August 2004

AbstractIn this work, we explore the temperature control of heterogeneous reactive distillation. By heterogeneous reactive distillation, we mean a two‐liquid phase exists in the reflux drum and a decanter is used to separate the aqueous product from the organic reflux. Process characteristics of n‐butyl propionate are explored and a systematic procedure is proposed for the design of butyl propionate reactive distillation. The control structure design procedure consists of the following steps: (1) setting the control objective, (2) selection of manipulated variables, (3) determination of temperature‐control trays, (4) finding controller settings for regulatory control, and (5) providing feedforward compensation for production rate variation. Because specifications on the bottoms product have to be met and stoichiometric balance has to be maintained, we have a 2 × 2 control problem with two obvious inputs: reboiler duty and feed ratio. The reactive distillation exhibits unique temperature sensitivities and the nonsquare relative gain successfully identifies temperature‐control trays, which results in an almost one‐way decoupled system. Therefore, decentralized PI controllers are used at the regulatory level. As a result of the unique feature of a kinetically controlled distillation column, maintaining constant tray temperatures does not imply the same quality specification. Feedforward temperature compensation is necessary to maintain the desired product composition. The proposed design procedure is further extended to butyl acetate reactive distillation, where a similar process behavior is observed, and good control performance can be achieved using simple temperature control. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2203–2216, 2004
The social and discursive construction of computing skills
Authors: Talja Sanna 
Published: August 2004

AbstractIn this article a social constructionist approach to information technology (IT) literacy is introduced. This approach contributes to the literature on IT literacy by introducing the concept of IT self as a description of the momentary, context‐dependent, and multilayered nature of interpretations of IT competencies. In the research literature, IT literacy is often defined as sets of basic skills to be learned, and competencies to be demonstrated. In line with this approach, research on IT competencies conventionally develops models for explaining user acceptance, and for measuring computer‐related attitudes and skills. The assumption is that computer‐related attitudes and self‐efficacy impact IT adoption and success in computer use. Computer self‐efficacy measures are, however, often based on self‐assessments that measure interpretations of skills rather than performance in practice. An analysis of empirical interview data in which academic researchers discuss their relationships with computers and IT competence shows how a self‐assessment such as “computer anxiety” presented in one discussion context can in another discussion context be consigned to the past in favor of a different and more positive version. Here it is argued that descriptions of IT competencies and computer‐related attitudes are dialogic social constructs and closely tied with more general implicit understandings of the nature of technical artifacts and technical knowledge. These implicit theories and assumptions are rarely taken under scrutiny in discussions of IT literacy yet they have profound implications for the aims and methods in teaching computer skills.
Stem cells as probabilistic self‐producing entities
Authors: Ramalho‐Santos Miguel 
Published: August 2004

AbstractStem cells have the capacity both to self‐renew and to give rise to differentiated progeny, and are vital to the organization of multicellular organisms. Stem cells raise a number of fundamental questions regarding lineage restriction and cellular differentiation, and they hold enormous promise for cell‐based therapies. Here I propose a theoretical framework for stem cell biology based on the concepts of autopoiesis (self‐production) and complementarity. I argue that stem cells are pivotal in the self‐production of the organism and that we need complementary approaches to understand their probabilistic behavior. I discuss how this framework generates testable hypotheses regarding stem‐cell functions. BioEssays 26:1013‐1016, 2004. © 2004 Wiley Periodicals, Inc.
Bile ducts as a source of pancreatic β cells
Authors: Burke Zoë D. , Shen Chia‐Ning , Tosh David 
Published: August 2004

AbstractIn recent years, there have been a number of well‐documented examples demonstrating that one cell type can be converted to another. Two such examples are the appearance of ectopic pancreas in the liver and formation of hepatic tissue in the pancreas. The conversion of liver to pancreas raises the intriguing possibility of generating insulin‐producing β cells for therapeutic transplantation into diabetics. There is now a striking addition to the growing list of pancreatic conversions: the formation of pancreatic tissue in the developing biliary system.1 BioEssays 26:932–937, 2004. © 2004 Wiley Periodicals, Inc.
Adding to the ends: what makes telomerase processive and how important is it?
Authors: Lue Neal F. 
Published: August 2004

AbstractTelomerase is a cellular reverse transcriptase responsible for telomere maintenance in most organisms. It does so by adding telomere repeats onto pre‐existing ends using an integral RNA component as template. Compared to “prototypical” reverse transcriptases, telomerase is unique in being able to repetitively copy a short templating RNA segment, thus adding multiple copies of the repeat to the DNA substrate following a single binding event. This uniquely processive property hints at the intricate conformational alterations that the enzyme must choreograph during its reaction cycles. Recent studies have identified distinct structural elements within both the RNA and protein components of telomerase that modulate enzyme processivity. Pharmacological and genetic analysis suggest that telomerase processivity is a significant determinant of telomere length. Because telomere maintenance and the lack thereof have been linked to tumor progression and aging, further investigation of telomerase processivity may lead to novel medical intervention strategies. BioEssays 26:955–962, 2004. © 2004 Wiley Periodicals, Inc.
Superconductivity in Copper, Silver, and Gold Compounds
Authors: Larsson Sven 
Published: August 2004

AbstractHigh‐temperature superconductivity exists in layered, square‐planar cuprates, but is almost absent in most other CuII compounds and in most AgII and AuII compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III (“negative‐U compounds”). The two‐electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.
Facile Access to Redox‐Active C2‐Bridged Complexes with Half‐Sandwich Manganese End Groups
Authors: Kheradmandan Sohrab , Venkatesan Koushik , Blacque Olivier , Schmalle Helmut W. , Berke Heinz 
Published: August 2004

AbstractThe dinuclear mixed‐valent complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)]+[(η2‐MeC5H4)3Mn]− [1]+[2]− (dmpe=1,2‐bis(dimethylphosphanyl)ethane) was prepared by the reaction of [Mn(MeC5H4)2] with dmpe and Me3SnCCSnMe3. The reactions of [1]+[2]− with K[PF6] and Na[BPh4] yielded the corresponding anion metathesis products [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6] ([1][PF6]) and [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][BPh4] ([1][BPh4]). These mixed‐valent species can be reduced to the neutral form by reaction with Na/Hg. The obtained complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)] (1) displays a triplet/singlet spin equilibrium in solution and in the solid state, which was additionally studied by DFT calculations. The diamagnetic dicationic species [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6]2 ([1][PF6]2) was obtained by oxidizing the mixed‐valent complex [1][PF6] with one equivalent of [Fe(C5H5)2][PF6]. Both redox processes are fully reversible. The dinuclear compounds were characterized by NMR, IR, UV‐visible, and Raman spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X‐ray diffraction studies were performed on [1][2], [1][PF6], [1][BPh4], and [1][PF6]2.
Boron–Diindomethene (BDI) Dyes and Their Tetrahydrobicyclo Precursors—en Route to a New Class of Highly Emissive Fluorophores for the Red Spectral Range
Authors: Shen Zhen , Röhr Holger , Rurack Knut , Uno Hidemitsu , Spieles Monika , Schulz Burkhard , Reck Günter , Ono Noboru 
Published: August 2004

AbstractThe X‐ray crystallographic, optical spectroscopic, and electrochemical properties of a newly synthesized class of boron–diindomethene (BDI) dyes and their tetrahydrobicyclo precursors (bc‐BDP) are presented. The BDI chromophore was designed to show intensive absorption and strong fluorescence in an applicationary advantageous spectral range. Its modular architecture permits fusion of a second subunit, for example, a receptor moiety to the dye's core to yield directly linked yet perpendicularly prearranged composite systems. The synthesis was developed to allow facile tuning of the chromophore platform and to thus adjust its redox properties. X‐ray analysis revealed a pronounced planarity of the chromophore in the case of the BDIs, which led to a remarkable close packing in the crystal of the simplest derivative. On the other hand, deviation from planarity was found for the diester‐substituted bc‐BDP benzocrown that exhibits a “butterfly”‐like conformation in the crystal. Both families of dyes show charge‐ or electron‐transfer‐type fluorescence‐quenching characteristics in polar solvents when equipped with a strong donor in the meso‐position of the core. These processes can be utilized for signaling purposes if an appropriate receptor is introduced. Further modification of the chromophore can invoke such a guest‐responsive intramolecular quenching process, also for receptor groups of low electron density, for example, benzocrowns. In addition to the design of various prototype molecules, a promising fluoroionophore for Na+ was obtained that absorbs and emits in the 650 nm region and shows a strong fluorescence enhancement upon analyte binding. Furthermore, investigation of the remarkable solvatokinetic fluorescence properties of the “butterfly”‐like bc‐BDP derivatives suggested that a second intrinsic nonradiative deactivation channel can play a role in the photophysics of boron–dipyrromethene dyes.
Revealing the Configuration and Crystal Packing of Organic Compounds by Solid‐State NMR Spectroscopy: Methoxycarbonylurea, a Case Study
Authors: Macholl Sven , Börner Frank , Buntkowsky Gerd 
Published: August 2004

AbstractThe molecular configuration and intermolecular arrangement of polycrystalline methoxycarbonylurea (MCU) has been studied by a combination of chemical editing, rotational echo double resonance (REDOR) spectroscopy and ab initio calculations. From the multispin ISnREDOR experiments several dipolar couplings were determined and converted into distance constraints. Intra‐ and intermolecular dipolar couplings were distinguished by isotope dilution. The configuration of the MCU molecule can be determined from three torsion anglesΨ1,Ψ2, andΨ3. Ab initio calculations showed that these angles are either 0° or 180° (ZorE). From the REDOR experiments, theEconfiguration was found forΨ1andΨ2and theZconfiguration forΨ3. Thus the configuration of MCU in the solid state was determined to beEEZ. Distance constraints for the intermolecular arrangement of MCU were obtained by performing REDOR experiments on13C15N2MCU with different degrees of isotope dilution and on a cocrystallized 1:1 mixture of13C(urea) MCU and15N(amide) MCU. By combining these distance constraints with molecular modeling, three different possible packing motifs for MCU molecules were found. The molecules in these motifs are arranged as linear chains with methoxy groups at the borders of the chains. All the intermolecular hydrogen bond donors and acceptors in the interior of the chain are saturated.