bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multilamellar vesicles in a commercial surfactant system
Authors: Liaw M. S. , Mackley M. R. , Bridgwater J. , Moggridge G. D. , Bayly A. E. 
Published: April 2004

AbstractThe manufacture of concentrated detergent granules in the detergent industry can be achieved by the incorporation of surfactant pastes, such as linear alkylbenzene sulfonate paste (LAS)—a lamellar liquid crystalline material (surfactant concentration of ca. 78 wt. %). LAS paste was processed at 25°C and 60°C, in both the absence and presence of sodium disilicate (Na2O:2SiO2) additive, and the effect on the formation of shear‐induced multilamellar vesicle (MLV) microstructures was studied. Our results suggest that LAS pastes of high hardness and stiffness are always associated with MLV microstructures and vice versa—these are known as “structured” pastes in industry, and also appear nonadhesive. MLVs are able to form from “pure” LAS at 25°C, although, at 60°C, sodium disilicate is necessary. With increased processing time, the size of the MLVs decreases and becomes more uniform—pastes are also increasingly hard and stiff. When stored, “structured” pastes eventually revert back to being soft and sticky, reflecting the metastable nature of the MLVs.
Gas turbulence modulation in a two‐fluid model for gas–solid flows
Authors: Zhang Yonghao , Reese Jason M. 
Published: April 2004

AbstractRecent rapid progress in the theoretical and experimental study of turbulence modulation has led to greater understanding of the physics of particle–gas turbulence interactions. A new two‐fluid model incorporating these advances for relatively dilute gas–solid flows containing high‐inertia particles is established. The effect of aerodynamic forces upon the particulate stresses is considered in this kinetic theory‐based model, and the influence of the particles on the turbulent gas is addressed: the work associated with drag forces contributes to the gas turbulent energy, and the space occupied by particles restricts the turbulent length scale. The interparticle length scale, which is usually ignored, has been incorporated into a new model for determining the turbulent length scale. This model also considers the transport effect on the turbulent length scale. Simulation results for fully developed steady flows in vertical pipes are compared with a wide range of published experimental data and, generally, good agreement is shown. This comprehensive and validated model accounts for many of the interphase interactions that have been shown to be important.
Optimal design of batch‐storage network with recycle streams
Authors: Yi Gyeongbeom , Reklaitis Gintaras V. 
Published: April 2004

AbstractAn effective methodology is reported for determining the optimal capacity (lot size) of batch processing and storage networks which include material recycle or reprocessing streams. It is assumed that any given storage unit can store one material type which can be purchased from suppliers, internally produced, and internally consumed and/or sold to customers. It is further assumed that a storage unit is connected to all processing stages that use or produce the material to which that storage unit is dedicated. Each processing stage transforms a set of feedstock materials or intermediates into a set of products with constant conversion factors. The objective for optimization is to minimize the total cost composed of raw material procurement, setup, and inventory holding costs, as well as the capital costs of processing stages and storage units. A novel production and inventory analysis formulation, the PSW model, provides useful expressions for the upper/lower bounds and average level of the storage inventory holdup. The expressions for the Kuhn‐Tucker conditions of the optimization problem can be reduced to two subproblems. The first yields analytical solutions for determining batch sizes, while the second is a separable concave minimization network flow subproblem whose solution yields the average material flow rates through the networks. For the special case in which the number of storage units is equal to the number of process stages and raw materials storage units, a complete analytical solution for average flow rates can be derived.
Process variations and the transient behavior of extruders
Authors: Mudalamane Rajath , Bigio David I. 
Published: April 2004

AbstractTo explain output fluctuation problems in extrusion, a transient model of material flow through an extruder is developed and used to study the transmission of external disturbances through the extruder. This model can be implemented for any extrusion geometry for which a pressure‐throughput model exists. Simulation results show that every extrusion process has a characteristic critical frequency. All disturbance frequencies above this critical value are damped out and the lower frequency components are transmitted through the process with little amplitude attenuation. These low frequency disturbances are of most concern since they are not damped by the extrusion process. Extrusion screw configurations are designed to satisfy steady‐state performance requirements, and nonsteady‐state performance is rarely considered. The findings indicate that a two pronged approach would be required combining screw design (passive control) to handle higher frequencies and closed‐loop control (active control) to detect and remove lower frequency disturbances.
Diagnostic tool to detect electrode flooding in proton‐exchange‐membrane fuel cells
Authors: He Wensheng , Lin Guangyu , Van Nguyen Trung 
Published: April 2004

AbstractAn electrode flooding monitoring device designed for PEM fuel cells with interdigitated flow distributors was proposed and tested. The pressure drop between the inlet and outlet channels can be used as a diagnostic signal to monitor the liquid water content in the porous electrodes, because of the strong dependence of the gas permeability of the porous electrodes on liquid water content. It can be used with no modification to existing fuel‐cell assembly to give real‐time flooding information in the electrode backing layers during operation. The device has been employed to investigate the correlation between the fuel‐cell performance and the liquid water saturation level in the backing layers, the effects of various operating parameters, and the dynamics and hysteresis behavior of liquid water in the backing layers. The results provide, for the first time, direct evidence to show that inadequate water removal causes liquid water build up in the cathode, which in excessive amounts can severely reduce the performance of a PEM fuel cell. It was observed that more than 30 min. were needed for a PEM fuel cell to reach a new steady state when subjected to current‐density changes, and this was attributed to the slow liquid water transport process. The results confirmed that increasing air flow rate or cell temperature increased the liquid water removal rate from the backing layers. The hysteresis behavior of fuel‐cell performance was related to the water imbibition and drainage cycles in the electrode backing layers and was attributed to the difference in the water removal rate by capillary force and the difference in membrane conductivity.
Influence of n‐paraffin composition on the aging of wax‐oil gel deposits
Authors: Paso K. G. , Fogler H. Scott 
Published: April 2004

AbstractAn excess Gibbs free energy model is applied to investigate the influence of n‐paraffin composition on the aging behavior of wax‐oil gel deposits known to form in subsea petroleum transport pipelines. The aging of wax‐oil gels occurs by a counterdiffusion process where wax molecules with carbon numbers greater than a critical carbon number (CCN) diffuse into the gel matrix, and vice versa. Model crude oils were formulated to exhibit varying decreasing exponential distributions of n‐paraffin components in the range n‐C9 to n‐C53. Deposition experiments were conducted using a laboratory cold finger apparatus simulating the cold wall of a subsea pipeline. Gas chromatography analysis of gel deposit compositions yielded experimental CCN values. A solid‐liquid‐phase equilibrium model, employing a modified version of UNIQUAC to compute solid‐phase component activity coefficients, was able to successfully predict the critical carbon number for a variety of model oil n‐paraffin compositions.
Thermodynamic isotope effect in partial oxidation of methane to syngas
Authors: Hu Yun Hang , Feeley Jennifer S. 
Published: April 2004

AbstractThermodynamic deuterium substitution effects on reactant conversion and product selectivity were investigated by computer simulation for the stoichiometric partial oxidation of methane. Methane conversion shows a normal deuterium isotope effect, whereas CO selectivity shows an inverse deuterium isotope effect. H2 selectivity exhibits a large normal deuterium effect. Moreover, deuterium isotope effects are dependent on reaction temperatures and pressures. When reaction pressure is very low, such as 0.001 MPa, all thermodynamic deuterium isotope effects are negligible at 650°C or above. Three criteria, based on the deuterium‐isotope effects, were proposed to determine whether a partial oxidation reaction of methane is kinetically controlled without accurately measured reaction temperatures.
Jenseits thermodynamischer Acidität: der Komplex‐induzierte Näherungseffekt (CIPE) bei Deprotonierungen
Authors: Whisler Marna C. , MacNeil Stephen , Snieckus Victor , Beak Peter 
Published: April 2004

AbstractDas Konzept des Komplex‐induzierten Näherungseffekts (complex induced proximity effect, CIPE) bei Deprotonierungen ist hilfreich bei der Aufklärung von Mechanismen in der Carbanionenchemie und bei der Planung organischer Synthesen. Im vorliegenden Aufsatz werden die Konsequenzen der Komplexierung von Organolithiumbasen an funktionellen Gruppen der Substrate vor dem Protonenübertragungsschritt diskutiert. Dabei zeigt sich, dass die experimentellen Daten aus kinetischen Messungen und Isotopenmarkierungsexperimenten ebenso wie die Ergebnisse von Rechnungen in vielen Fällen auf einen Prälithiierungskomplex als Reaktionsintermediat hinweisen. Einige Beispiele aus der Naturstoffsynthese verdeutlichen, wie mithilfe dieses Konzepts Zwischenstufen gezielt regio‐ oder stereoselektiv erhalten werden können. Von besonderem Interesse sind dabei Funktionalisierungen an Positionen, die von der koordinierenden Gruppe vermeintlich weit entfernt sind.
Properties of thermoplastic composites based on wheat‐straw lignocellulosic fillers
Authors: Le Digabel F. , Boquillon N. , Dole P. , Monties B. , Averous L. 
Published: April 2004

AbstractLignocellulosic fractions from wheat straw were used as natural fillers in composites of a polyolefin (a copolymer of polyethylene and polypropylene) and a biodegradable polyester [poly(butylene adipate‐co‐terephthalate)]. The mechanical properties of these injected composites were investigated with tensile and impact testing. A reinforcing effect of wheat‐straw residues was found for both types of composites. Compared with the polyester‐based composites, the polyolefin composites were more brittle. The addition of compatibilizing agents (γ‐methacryloxypropyltrimethoxysilane, maleic anhydride modified polypropylene, and stearic acid) did not improve the properties of the polyolefin composites. The surface properties were studied with contact‐angle measurements, and poor interfacial adhesion was found between the hydrophilic lignocellulosic filler and the hydrophobic polyolefin matrix. Thermal characterization revealed the formation of low intermolecular bonds between the polyester matrix and the lignocellulosic filler, in agreement with the surface tensions results and scanning electron microscopy observations. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 428–436, 2004
New oligomer‐bound antioxidants in natural rubber/polybutadiene rubber and natural rubber/styrene–butadiene rubber blends
Authors: Sulekha P. B. , Joseph R. , Manjooran K. B. 
Published: April 2004

AbstractNew paraphenylene diamine antioxidants were prepared. The efficiency and permanence of these oligomer‐bound paraphenylene diamines were compared with those of conventional amine‐type antioxidants in elastomer blends such as natural rubber/styrene–butadiene rubber and natural rubber/polybutadiene rubber. These oligomer‐bound antioxidants showed improved aging resistance and ozone resistance in comparison with the blends containing conventional antioxidants. The liquid oligomer‐bound paraphenylene diamine could replace the plasticizer required for compounding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 437–443, 2004
Silicate layer exfoliation in polyolefin/clay nanocomposites based on maleic anhydride modified polyolefins and organophilic clay
Authors: Hasegawa Naoki , Usuki Arimitsu 
Published: April 2004

AbstractSilicate layer exfoliation processes in maleic anhydride (MA) modified polyolefins were studied by using X‐ray diffraction measurements, scanning electron microscopy, and transmission electron microscopy observations. Modified polyolefins grafted with 0.09–4.5 wt % MA groups intercalate into the organophilic clay galleries modified with stearyl ammonium ions. Molten MA‐modified polypropylene continuously intercalates into the galleries and the silicate layers exfoliate spontaneously without shear. However, the silicate layers maintain arranging parallel together, although the interlayer spacing expands over 10 nm. By adding shear, the silicate layers homogeneously disperse into MA‐modified polypropylene matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 464–470, 2004
Enantioselective Fluorescence Sensing of Amino Acids by Modified Cyclodextrins: Role of the Cavity and Sensing Mechanism
Authors: Pagliari Sara , Corradini Roberto , Galaverna Gianni , Sforza Stefano , Dossena Arnaldo , Montalti Marco , Prodi Luca , Zaccheroni Nelsi , Marchelli Rosangela 
Published: April 2004

AbstractTwo selectors based on modified cyclodextrins containing a metal binding site and a dansyl fluorophore—6‐deoxy‐6‐N‐(Nα‐[(5‐dimethylamino‐1‐naphthalenesulfonyl)aminoethyl]phenylalanylamino‐β‐cyclodextrin—containing D‐Phe (3) and L‐Phe (4) moieties were synthesized. The conformations of the two selectors were studied by circular dichroism, two‐dimensional NMR spectroscopy and time‐resolved fluorescence spectroscopy. Cyclodextrin 4 was found to have a predominant conformation in which the dansyl group is self‐included in the cyclodextrin cavity, while 3 showed a larger proportion of the conformation with the dansyl group outside the cavity. As a consequence, the two cyclodextrins were found to bind copper(II) with different affinities, as revealed by fluorescence quenching in competitive binding measurements. Addition of D‐ or L‐amino acids induced increases in fluorescence intensity, which were dependent on the amino acid used and in some cases on its absolute configuration. The cyclodextrin 4 was found to be more enantioselective than 3, suggesting that the self‐inclusion in the cyclodextrin cavity strongly increases the chiral discrimination ability of the copper(II) complex. Accordingly, a linear fluorescent ligand Nα‐[(5‐dimethylamino‐1‐naphthalenesulfonyl)aminoethyl]‐N1‐propyl‐phenylalaninamide, which has the same binding site and absolute configuration as 4, showed very low chiral discrimination ability. The enantioselectivity in fluorescence response was found to be due to the formation of diastereomeric ternary complexes, which were detected by ESI‐MS and by circular dichroism. Time‐resolved fluorescence studies showed that the fluorescence of the dansyl group was completely quenched in the ternary complexes formed, and that the residual fluorescence was due to uncomplexed ligand.
Total Synthesis and Biological Evaluation of the Protein Phosphatase 2A Inhibitor Cytostatin and Analogues
Authors: Bialy Laurent , Waldmann Herbert 
Published: April 2004

AbstractThe total synthesis of the natural product cytostatin is described which inhibits protein phosphatase 2A. Cytostatin has anti‐metastatic properties and induces apoptosis. On the basis of this synthesis the relative and absolute configuration of cytostatin could be assigned. Key structural elements of cytostatin are an α,β‐unsaturated lactone group and a side chain embodying a phosphate and a rather unstable (Z,Z,E)‐triene subunit. In addition, the natural product carries six stereocenters. For the construction of the stereocenters reagent‐controlled transformations were used in order to ensure maximum stereochemical flexibility. The Evans syn‐aldol reaction was chosen to establish the stereochemistry at C‐4, C‐5, C‐9 and C‐10; C‐6 was introduced by means of the Evans asymmetric alkylation. In all cases the same chiral auxiliary was employed as stereodirecting group. The stereocenter at C‐11 was established by an asymmetric reduction using CBS‐oxazaborolidine. Temporary protection of the phosphate group was achieved best by using the base‐labile 9‐fluorenylmethyl group, which could be cleanly cleaved by an excess of triethylamine; this reaction yielded analytically pure phosphates after a simple aqueous work‐up. The (Z,Z,E)‐triene embodied in cytostatin was synthesized by means of a Stille coupling as key transformation. The synthesis sequence established in this way readily gave access to a series of analogues with simplified structure. Initial biological testing of these analogues proved that the α,β‐unsaturated lactone, the C‐11‐hydroxy group and a fully deprotected phosphate moiety at C‐9 are essential for the PP2A‐inhibitory activity of cytostatin. The rather unstable triene moiety in the side chain can be replaced by other lipophilic residues with only moderate decrease of biological activity. Other phosphatases, that is, PP1, VHR, PTP1B, CD45, were not inhibited by cytostatin or any of the analogues, demonstrating the high selectivity of this compound. These findings will be useful for the design and synthesis of cytostatin‐derived chemical tools for the study of biological processes influenced by PP2A.
Reaction of a Terminal Phosphinidene Complex with Azulenes: η1‐Complexes, CH Bond Insertions, and 1,4‐Adducts
Authors: Bulo Rosa E. , Ehlers Andreas W. , de Kanter Frans J. J. , Schakel Marius , Lutz Martin , Spek Anthony L. , Lammertsma Koop , Wang Bing 
Published: April 2004

AbstractReaction of an in situ generated phosphinidene complex [PhPW(CO)5] with the aromatic azulene and guaiazulene leads to unexpected 1,4‐adducts of the seven‐membered ring and to CH bond insertion of the five‐membered ring. A DFT analysis suggests that the reaction is initiated by formation of a η1‐complex between the phosphinidene and the five‐membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn‐ and anti‐1,2‐adducts. These undergo pericyclic 1,7‐sigmatropic rearrangements with remarkably low barriers to give 1,4‐adducts, with an inverted configuration at the phosphorus center. An X‐ray crystal structure is presented for one of the 1,4‐adducts of guaiazulene. The other two η1‐complexes insert with modest barriers into a CH bond of the five‐membered ring.
Stability of small‐amplitude shock profiles of symmetric hyperbolic‐parabolic systems
Authors: Mascia C. , Zumbrun K. 
Published: April 2004

AbstractCombining pointwise Green's function bounds obtained in a companion paper [36] with earlier, spectral stability results obtained in [16], we establish nonlinear orbital stability of small‐amplitude Lax‐type viscous shock profiles for the class of dissipative symmetric hyperbolic‐parabolic systems identified by Kawashima [20], notably including compressible Navier‐Stokes equations and the equations of magnetohydrodynamics, obtaining sharp rates of decay in Lp with respect to small L1 ∩ H3 perturbations, 2 ≤ p ≤ ∞. Our analysis extends and somewhat refines the approach introduced in [35] to treat stability of relaxation profiles. © 2004 Wiley Periodicals, Inc.
Chromium(III) Ion Selective Electrode Based on Oxalic Acid Bis(Cyclohexylidene Hydrazide)
Authors: Gholivand Mohammad Bagher , Raheedayat Firozeh 
Published: April 2004

AbstractA poly(vinyl chloride) membrane sensor based on oxalic acid bis (cyclohexylidene hydrazide) as membrane carrier was prepared and investigated as a Cr(III)‐selective electrode. The electrode reveals a Nernstian behavior (slope 19.8±0.4 mV decade−1) over a wide Cr(III) ion concentration range 1.0×10−7–1.0×10−2 mol dm−3 with a very low limit of detection (i.e., down to 6.3×10−8 mol dm−3). The potentiometric response of the sensor is independent of the pH of the test solution in the pH range 1.7–6.5. The electrode possesses advantage of very fast response, relatively long lifetime and especially good selectivity to wide variety of other cations. The sensor was used as an indicator electrode, in the potentiometric titration of chromium ion and in the determination of Cr(III) in waste water and alloy samples.
[Cu(L)](NO3)2 (L=4,7‐Bis(3‐aminopropyl)‐1‐thia‐4,7‐diazacyclononane) as a Suitable Ionophore for Construction of Thiocyanate‐Selective Electrodes and Their Use in Determination of Urinary and Salivary Thiocyanate Concentration
Authors: Shamsipur Mojtaba , Poursaberi Tahereh , Rezapour Morteza , Ganjali Mohammad Reza , Mousavi Mir Fazlollah , Lippolis Vito , Montesu Danilea Rita 
Published: April 2004

AbstractThe construction, performance characteristics, and application of polymeric membrane (PME) and coated graphite (CGE) thiocyanate‐selective electrodes are reported. The electrodes were prepared by incorporating the complex [Cu(L)](NO3)2 (L=4,7‐bis(3‐aminopropyl)‐1‐thia‐4,7‐diazacyclononane) into a plasiticized poly(vinyl chloride) membrane. The influence of membrane composition, pH of test solution, and foreign ions were investigated. The electrodes reveal Nernstian behavior over a wide SCN− ion concentration range (1.0×10−6–1.0×10−1 M for PME and 5.0×10−7–1.0×10−2 M for CGE) and show fast dynamic response times of 15 s and lower. The proposed sensors show high selectivity towards thiocyanate over several common organic and inorganic anions. They were successfully applied to the direct determination of thiocyanate in urine and saliva of smokers and nonsmokers, and as an indicator electrode in titration of Ag+ ions with thiocyanate.
Miniaturized Reference Electrodes. II. Use in Corrosive, Biological, and Organic Media
Authors: Ciobanu Madalina , Wilburn Jeremy P. , Lowy Daniel A. 
Published: April 2004

AbstractIn a recent paper [9] we reported the manufacturing and performance of miniaturized reference electrodes (MREs) with low sensitivity to chloride ions and pH. Here, we demonstrate the wide range applicability of a MRE based on an Ag/Ag2S internal reference element (IRE), imbedded in a photopolymerized hydrogel of improved composition, which contains the supporting electrolyte. Exchange current density, temperature coefficient, impedance value, and the voltammetric and potentiometric use of the Ag/Ag2S‐based MRE are discussed relative to the previously reported Ag/AgSCN, Ag/Ag3PO4, and Ag/AgCl‐based MREs. No special or extensive conditioning is required when moving these MREs from aqueous supporting electrolyte to an organic solution or from one organic medium to another, and the equilibration time in a new medium is very rapid (<6 min). The new Ag/Ag2S MRE has a highly stable potential in various media, including aqueous solutions (salt buffers and 20 wt.% H2SO4), biological samples (bovine serum albumin), mixed aqueous‐organic, and organic supporting electrolytes (methanol, ethanol, acetonitrile, propylene carbonate, methylene chloride, and DMSO). This is particularly advantageous when in the course of the electrochemical analysis an organic solution is being added to an aqueous supporting electrolyte. Such MREs are suitable for analyses of μL sample volumes and for use in protein‐containing media.