bluuebunny/crossref_metadata_2025 huggingface dataset:
Elongational rheology of LLDPE / LDPE blends
Authors: Ajji A. , Sammut P. , Huneault M. A.
Published: April 2003

The objective of this study is to investigate the effect of low density polyethylene (LDPE) content in linear low density polyethylene (LLDPE) on the crystallinity and strain hardening of LDPE / LLDPE blends. Three different linear low density polyethylenes (LL‐1, LL‐2 and LL‐3) and low density polyethylenes (LD‐1, LD‐2 and LD‐3) were investigated. Eight blends of LL‐1 with 10, 20, 30 and 70 wt % of LD‐1 and LD‐3, respectively, were prepared using a single screw extruder. The elongational behavior of the blends and their constituents were measured at 150°C using an RME rheometer. For the blends of LL‐1 with LD‐1, the low shear rate viscosity indicated a synergistic effect over the whole range of concentrations, whereas for the blends of LL‐1 with LD‐3, a different behavior was observed. For the elongational viscosity behavior, no significant differences were observed for the strain hardening of the 10–30% LDPE blends. Thermal analysis indicated that at concentrations up to 20%, LDPE does not significantly affect the melting and crystallization temperatures of LLDPE blends. In conclusion, the crystallinity and rheological results indicate that 10–20% LDPE is sufficient to provide improved strain hardening in LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3070–3077, 2003
Comparison between the effects of alcohols and diols on polymethyl‐methacrylate and polyacrylamide with positron annihilation lifetime and electric conductivity measurements
Authors: Gomaa E. , Mazzroua A. , Mohamed M.
Published: April 2003

Comparison between the effect of alcohols and diols on poly(methylmethacrylate) (PMMA) and polyacrylamide (PAA) was investigated by positron annihilation lifetime (PAL) spectroscopy and electric conductivity measurements. The samples were prepared by adding alcohols, such as ethanol (E), isopropyl alcohol (P), and butyl alcohol (B), and diols, such as ethanediol (E1,2), isoproponendiol (P1,2), and butanediol (B1,2, B1,3, B1,4). The o‐Ps lifetime values (τ3) of PMMA–alcohol or PMMA–diol composites are shorter than the τ3 value of the virgin PMMA, whereas the τ3 values of PAA–alcohol or PPA–diol composites fluctuate above and blow the corresponding value of virgin PAA. On the other hand, a significant increased was observed in the o‐Ps intensities (I3) of both PMMA and PAA composites with added alcohols and diols compared with pure PMMA and PAA. The electric conductivity (σ) also increased for both PMMA and PAA composites with added alcohols and diols compared with the virgin PMMA or PAA polymer. A correlation was found between positron annihilation lifetime parameters and electric conductivity of PAA composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3078–3083, 2003
H2O2 as a modifier of phenol–formaldehyde resin used in the production of particleboards
Authors: Czarnecki Rafał , Łȩcka Janina
Published: April 2003

The purpose of the research was to study the influence of H2O2 on the properties of fluid phenolic (PF) resin, the curing process, the cured resin structure, and the properties of the particleboards produced with its use. The influence of added H2O2 on resin usability at 20°C, on the gel time of the modified PF resin in the temperature range 110–140°C, and on the activation energy of the curing process were studied. Also, the structure of the cured resin was examined by Fourier transform infrared spectroscopy. Finally, the properties of the obtained particleboards were determined. The results indicate that the H2O2 modification leads to greater reactivity of the phenolic resin and increases the mechanical properties of particleboards. In contrast, there is no significant influence of H2O2 on the water resistance of the particleboards. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3084–3092, 2003
Study on PET/PP microfibrillar composites. I. Morphological development in melt extrusion
Authors: Lin X. D. , Cheung W. L.
Published: April 2003

Poly(ethylene terephthalate)/polypropylene (PET/PP) blends of different compositions were extruded through a 2‐mm capillary die using a corotating twin‐screw extruder. The extrudates were cryogenically fractured and examined using scanning electron microscopy. The viscosity ratio of the constituent polymers alone was found not suitable for explaining the polymer blend morphology. At a PET concentration of 20%, the extrudate consists of three regions: The skin layer, about 10 μm thick, has a lower concentration of the dispersed PET phase than that of the overall concentration. The intermediate region, about 400 μm thick, has profuse PET fibers and some small PET particles. The central region, approximately 800 μm in diameter, contains mainly PET particles that are generally bigger. A low barrel temperature, low die temperature, and fast cooling rate helped to retain the fibers near the extrudate skin. Meanwhile, variation of the barrel temperature, die temperature, and cooling media did not affect the PET particle‐size distribution significantly in the central region of the extrudate. A high screw speed and a high postextrusion drawing speed were very effective in producing fibers in the extrudates through elongation of the particles. At a PET concentration of 30%, coalescence of the PET phase was prevalent, leading to the formation of PET platelets near the extrudate skin and irregular PET networks in the central region of the extrudate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3100–3109, 2003
Surface characteristics of hydrosilylated polypropylene
Authors: Long J. , Tzoganakis C. , Chen P.
Published: April 2003

Polypropylene containing terminal unsaturation was modified with a hydride‐terminated polydimethylsiloxane (PDMS) at three different temperatures through a catalytic hydrosilylation reaction in the melt phase. A comprehensive study on the surface characteristics of hydrosilylated polypropylene (SiPP) was conducted by combining macroscopic thermodynamics, microstructure, and chemical composition measurements. Axisymmetric drop shape analysis–profile (ADSA‐P) was used to characterize the surface wettability. The morphology, roughness, and heterogeneity of the surfaces were investigated by the lateral‐force mode of atomic force microscopy (LFM). X‐ray photoelectron spectroscopy (XPS) was used to quantify the surface chemical composition. LFM images showed that all sample surfaces were rough and heterogeneous on a micrometer scale. XPS analysis showed that the surfaces investigated were complicated in composition and that various oxides existed on the surfaces. The surface wettability was well correlated to the surface microstructure and composition. The surfaces investigated were modeled based on the microstructure observed, and a new scheme was developed to calculate surface free energy and adhesion work. For SiPPs, the lower the reaction temperature, the more PDMS incorporation was observed, the smaller the surface free energy and the work of adhesion, the more hydrophobic the surface, and the lower the permeability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3117–3131, 2003
Foam extrusion of high density polyethylene/wood‐flour composites using chemical foaming agents
Authors: Li Qingxiu , Matuana Laurent M.
Published: April 2003

A one‐way analysis of variance and thermal analysis were performed in this study to examine the influences of the contents, types (exothermic vs. endothermic), and forms (pure vs. masterbatch) of chemical foaming agents (CFAs), as well as the use of coupling agents, on the density reduction (or void fraction) and cell morphology of extrusion‐foamed neat high density polyethylene (HDPE) and HDPE/wood‐flour composites. The CFA types and forms did not affect the void fractions of both the neat HDPE and HDPE/wood‐flour composites. However, a gas containment limit was observed for neat HDPE foams whereas the average cell size achieved in the HDPE/wood‐flour composite foams remained insensitive to the CFA contents, irrespective of the foaming agent types. The experimental results indicated that the use of coupling agent in the formulation was required to achieve HDPE/wood‐flour composite foams with high void fraction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3139–3150, 2003
Chemical modification of controlled‐pore silica with N‐propylsalicylaldimine
Authors: Abou‐El‐Sherbini Khaled , Kenawy I. M. M. , Issa R. M.
Published: April 2003

Two controlled‐pore silica phases were prepared with a sol–gel precursor from a sodium silicate solution. N‐Propylsalicylaldimine was immobilized on these silica species to be used as chelating ion exchangers (IE11 and IE2). The monomer phase was also prepared for comparison. The N‐propylsalicylaldimine moiety was detected by Fourier transform infrared and ultraviolet in both the ion exchangers and the monomer phases. 1H‐NMR and mass spectrometry of the monomer also confirmed the structure. The capacity (C) of the ion exchangers was dependent on the porosity of the ion exchanger (CIE11 = 0.36 mmol of Cu/g and CIE2 = 0.026 mmol of Cu/g). The uptake behavior of IE11 toward some metal ions was studied, and log distribution coefficient (kd) was within the range of 2.19–5.16. Also, thermogravimetric and differential thermogravimetric analysis data were used to study the kinetics of the thermal decomposition process of IE11. Some thermodynamic parameters for the ion exchanger were calculated by the application of the rate theory of the first‐order reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3159–3167, 2003
A new type synthetic filter material for biofilter: Poly(vinyl alcohol)/peat composite bead
Authors: Chan Wu‐Chung , Lu Ming‐Cun
Published: April 2003

In this study, a new type of poly(vinyl alcohol) (PVA)/peat composite bead was prepared and was proved suitable as a filter material in the biofiltration process. The composite bead is a porous spherical particle and has a diameter of 2.4–6.0 mm and a density of 0.69 kg/cm3. It contains 3.25 mg N/g dry solid and 2.91 mg P/g dry solid. The equilibrium moisture content of the composite bead for adsorption and holding experiments is 50.5 and 66.8% by wet basis, respectively. The initial compression strength of the composite bead is 0.32 kg/cm2. It has higher moisture holding capacity and compression strength than pig manure compost filter material. The adsorption behavior of ethyl acetate and composite bead follows the Freundlich adsorption isotherm. The composite bead has buffer capacity and could keep the filter bed at pH = 6.9–7.2 during operating. The percentage of removed ethyl acetate was 99% for up to 33 days as the composite bead adsorbed nutrients. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3248–3255, 2003
Steady viscoelastic diffusion
Authors: Vrentas J. S. , Vrentas C. M.
Published: April 2003

A viscoelastic constitutive equation is derived for the diffusion flux of an infinitely dilute solute diffusing in a polymeric fluid under steady flow conditions. It is shown that the mass transfer rate of gas into an ideal polymer jet increases with increasing elasticity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3256–3263, 2003
Enhanced corrosion protection coatings prepared from soluble electronically conductive polypyrrole‐clay nanocomposite materials
Authors: Yeh Jui‐Ming , Chin Chih‐Ping , Chang Susan
Published: April 2003

A series of electronically conductive nanocomposite materials that consisted of soluble polypyrrole (PPY) and layered montmorillonite (MMT) clay platelets were prepared by effectively dispersing the inorganic nanolayers of MMT clay in organic PPY matrix via an in situ oxidative polymerization with dodecylbenzene sulfonic acid (DBSA) as dopant. Organic pyrrole monomers were first intercalated into the interlayer regions of organophilic clay hosts and followed by a one‐step oxidative polymerization. The as‐synthesized electronically conductive polypyrrole–clay nanocomposite (PCN) materials were then characterized by Fourier transformation infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD), and transmission electron microscopy (TEM). PCNs in the form of coatings with low clay loading (e.g., 1.0 wt %) on cold‐rolled steel (CRS) were found to exhibit much better in corrosion protection over those of pristine PPY based on a series of electrochemical measurements including corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. Effects of the material composition on the thermal stability, optical properties, and electrical conductivity of pristine PPY along with PCN materials, in the form of fine powder, powder‐pressed pellet, and solution, were also studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), UV‐visible absorption spectra, and four‐point probe technique, respectively. The viscosity of PPY existed in PCN materials and pristine PPY were determined by viscometric analysis with m‐cresol as solvent. The heterogeneous nucleating effect of MMT clay platelets in PPY matrix was studied by wide‐angle powder XRD. The corresponding morphological images of the nucleating behavior of clay platelets in PPY matrix were investigated by scanning electron microscopy (SEM). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3264–3272, 2003
PET microfiber prepared by carbon dioxide laser heating
Authors: Suzuki Akihiro , Mochizuki Noriaki
Published: April 2003

In preliminary experiments to optimize the condition of a laser heating, zone drawing for poly(ethylene terephthalate) (PET) fiber, a microfiber was prepared by a continuous‐wave carbon dioxide (CW CO2) laser heating. CW CO2 laser heating was carried out at an extremely low applied tension (σa) at a higher laser power density (PD) as compared to the optimum condition for the laser heating, zone drawing of PET fiber reported previously. The microfibers were obtained by CO2 laser heating carried out at a PD of 15.8 W cm−2 and under a σa of 0.66 MPa or lower. The diameter of the fiber decreased with a decreasing σa and increasing PD. The smaller the diameter, the higher was its birefringence. The smallest diameter fiber obtained at σa = 0.17 MPa at PD = 21 W cm−2 had a diameter of 4.5 μm and a birefringence of 0.112, and its draw ratio estimated from the diameter reached 3086 fold. Such a high draw ratio was not previously attained by any drawing method. In a wide‐angle X‐ray diffraction photograph of the smallest diameter fiber, indistinct reflections due to oriented crystallites were observed. An SEM micrograph of the smallest diameter fiber showed a smooth surface without any crack and was uniform in diameter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3297–3283, 2003
Polyimide bonded magnets: Processing and properties
Authors: Yudin V. E. , Otaigbe J. U. , Bui Tho X. , Svetlichnyi V. M.
Published: April 2003

We report a new method of polyimide synthesis based on the interaction of dianhydrides with acylated diamines for preparing a melt processable mixture of prepolymer and rare earth magnetic alloy particles in the form of 75–100 μm particles. This mixture can be easily converted to useful thermoplastic polyimide bonded magnets by heating at 300°C. It is shown that the prepolymer based on 1,3‐bis(3,4‐dicarboxyphenoxy)benzene dianhydride and the diacetyl derivative of 2,2‐bis(4‐(4‐aminophenoxy)phenyl)sulfone diamine after removing less than 5% by weight of the volatile components can be melted at 220–240°C to give a fluid with a viscosity of 10–20 Pas. This low viscosity of the prepolymer facilitates blending it with magnetic particles at relatively high volume fractions (up to 85 vol %) that are not possible using conventional methods. The resulting polyimide‐bonded magnets exhibit excellent thermal stability and a high storage modulus of 10 GPa at 400°C. Magnetic property measurements showed a ≥10% increase in energy products over that of typical commercial bonded magnet materials such as the ones containing thermoplastic poly(phenylene sulfide) or polyamide matrices. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3151–3158, 2003
Improved Repeated Confidence Bounds in Trials with a Maximal Goal
Authors: Brannath W. , König F. , Bauer P.
Published: April 2003

Repeated confidence intervals can be computed at every interim analysis of a flexible group sequential design without the need to stop the trial with a pre‐planned stopping rule. Often, however, there is a maximal goal such that the trial is surely stopped if this goal is reached. This induces a maximal stopping rule, and repeated confidence intervals are strictly conservative, when adhering to it. A modification is proposed which uniformly improves the one sided repeated confidence interval in such a situation. It preserves the monitoring character, and leads to uniformly smaller intervals, when reaching the maximal goal at an interim analysis. The modification is worked out for two stage designs and is indicated for multi‐stage trials. The extent of the improvement is quantified for two simple scenarios.
A comparison of the Dodo, EST, and ATI factors among comorbid stimulant‐dependent, depressed patients
Authors: Beutler Larry E. , Moleiro Carla , Malik Mary , Mark Harwood T. , Romanelli Robert , Gallagher‐Thompson Dolores , Thompson Larry
Published: April 2003

Describes pilot findings from a treatment development study aimed at improving treatment for comorbid depressed and chemically‐dependent patients. A comparison of standard RCT analyses with Hierarchical Multiple Regression (HLM) procedures revealed the latter to be more sensitive to the relative effects of patient, treatment, and patient–treatment matching variables among a small sample of (N = 40) depressed, stimulant‐abusing patients. Participants were randomly assigned to one of three treatments, a standard Cognitive Therapy for Drug Abuse (CT), a contrasting Cognitive‐Narrative Therapy (NT), and a Prescriptive Therapy (PT), the latter of which selectively applied procedures from both of the other two treatments following an Aptitude × Treatment Interaction (ATI) model. The results supported a multiple factor view of psychotherapy effects, including the hypothesis that patient, treatment, relationship, and patient‐therapy matching variables add independent power to the prediction of treatment outcome, especially during follow‐up. ATI effect sizes were stronger than those associated with specific treatments. Copyright © 2003 John Wiley & Sons, Ltd.
Recall of threat and submissiveness in childhood: development of a new scale and its relationship with depression, social comparison and shame
Authors: Gilbert P. , Cheung M. S‐P. , Grandfield T. , Campey F. , Irons C.
Published: April 2003

Research on the link between recall of early parenting and psychopathology has focused on recall of parental behaviours such as neglect, rejection, low warmth and overprotection. This study investigates recall of the personal feelings of perceived threat and subordination in childhood. A short, new self‐report scale was developed, called the Early Life Experiences Scale (ELES) and given to 225 undergraduate students. Analysis revealed three factors: a factor for threat, a factor related to submissiveness and a factor related to feeling (un)valued. All participants completed measures of recall of parental behaviour and depression; 119 also completed a shame scale, and 106 completed a social comparison scale. Both the recall of parental behaviour measure and the ELES correlated significantly with depression, social comparison and shame. However, a standard multiple regression analysis found that only the submissive factor of the ELES predicted depression. Copyright © 2003 John Wiley & Sons, Ltd.
Biopolymer albumin for diagnosis and in drug delivery
Authors: Patil Gayathri V.
Published: April 2003

This article reviews the developmental stages and strategies used to assess the biomedical utility of biopolymer albumin from the 1970s to early 2002. The basic method and mechanism(s) of preparation of albumin microspheres and subsequent modifications made to overcome the drawbacks of earlier approaches and the need for further developments are discussed, as are the processing parameters and the level of various ingredients affecting the physicochemical properties of the albumin microspheres. Different equations proposed by various investigators to modulate in vitro release kinetics are reviewed. The microscopic structural and surface properties, the chemical modification of the biopolymer (e.g., cationization, tagging with amino acids and sugar moieties) for tissue specificity or to influence the release profile and biodegradation are discussed. An array of potential diagnostic applications and the use of albumin microspheres as a drug delivery system are reviewed. Drug Dev. Res. 58:219–247, 2003.© 2003 Wiley‐Liss, Inc.
Simultaneous detection of S‐adenosylmethionine and S‐adenosylhomocysteine in mouse and rat tissues by capillary electrophoresis
Authors: Uthus Eric O.
Published: April 2003

A capillary electrophoresis method for the determination of S‐adenosylmethionine (SAM) and S‐adenosylhomocysteine (SAH) in rat liver and kidney and mouse liver is described. The method can also be used to determine SAM in whole blood. The method provides rapid (approximately 16 min sample to sample) resolution of both compounds in perchloric extracts of tissues. Separation was performed by using an uncoated 50 μm ID capillary with 60 cm total length (50 cm to the detector window). Samples were separated at 22.5 kV and the separation running buffer was 200 mM glycine pH 1.8 (with HCl). The method compares favorably to HPLC methods (r 2 = 0.994 for SAM, r 2 = 0.998 for SAH) and has a mass detection limit of about 10 fmol for both SAM and SAH at a signal‐to‐noise ratio of 3. The method is linear over ranges of 1–100 μM SAM and 1–250 μM SAH. This method can be used to determine tissue concentrations of SAM and SAH, two metabolites that can provide insight into many biological processes.
Predicting heats of combustion of polymers using an empirical approach
Authors: Hshieh Fu‐Yu , Hirsch David B. , Beeson Harold D.
Published: April 2003

The heats of combustion of 75 pure organic polymers with various chemical classes were used to develop empirical equations for predicting the gross and net heats of combustion of organic polymers. The equations were developed using atomic contribution and multiple linear regression methods. The gross and net heats of combustion per unit weight can be obtained by dividing the gross and net heats of combustion per mole by the molecular weight of the monomer. The average absolute % error for the predictions is 3.9%. In addition, two previously developed empirical equations, which predict the heats of combustion of organosilicon compounds, were used to predict the heats of combustion of silicone polymers. Copyright © 2003 John Wiley & Sons, Ltd.
Finite volume/mixed finite element analysis of pollutant transport and bioremediation in heterogeneous saturated aquifers
Authors: Gallo Claudio , Manzini Gianmarco
Published: April 2003

The adoption of a suitable pumping–injecting well network and the human enhancement of the activity of soil bacteria, whose metabolism contributes to degrade and transform many pollutants in non‐toxic substances, may be crucial in the process of remediation of contaminated soils. Organic contaminant transport in a subsurface aquifer and its biological degradation kinetics is numerically addressed by using a four contaminant species model. A numerical approach is proposed, that is based on a cell‐centre finite volume method for the system of advection–dispersion equations of contaminants with a mixed‐hybrid finite element method for the solution of a single‐phase Darcy's equation. The effectiveness of the method and its accuracy in retaining the main physical properties of the continuous mathematical model is illustrated by simulating the time evolution of contaminant concentrations in a set of realistic scenarios. Copyright © 2003 John Wiley & Sons, Ltd.
A novel fully‐implicit finite volume method applied to the lid‐driven cavity problem—Part II: Linear stability analysis
Authors: Sahin Mehmet , Owens Robert G.
Published: April 2003

A novel finite volume method, described in Part I of this paper (Sahin and Owens, Int. J. Numer. Meth. Fluids 2003; 42:57–77), is applied in the linear stability analysis of a lid‐driven cavity flow in a square enclosure. A combination of Arnoldi's method and extrapolation to zero mesh size allows us to determine the first critical Reynolds number at which Hopf bifurcation takes place. The extreme sensitivity of the predicted critical Reynolds number to the accuracy of the method and to the treatment of the singularity points is noted. Results are compared with those in the literature and are in very good agreement. Copyright © 2003 John Wiley & Sons, Ltd.
Distribution and partition of trace metals in the Amazon basin
Authors: Seyler Patrick T. , Boaventura Geraldo R.
Published: April 2003

The distribution of trace metals (V, Cr, Mn, Co, Cu, Zn, As, Rb, Sr, Mo, Cd, Sb, Cs, Ba, U) was investigated in surface waters and associated particulates in the Amazon mainstream (Solimões and Amazon rivers). Dissolved V, Cu, As, Sr, Ba, U correlate with major ions and appear to be predominantly derived from soluble rocks occurring in the Amazon upper basin. These elements appear conservative in waters and are progressively diluted by less‐concentrated waters coming from the lowland and shield areas. A monthly time series obtained at the Óbidos gauging station shows that temporal variability of trace element concentrations reflects the source, remobilization and/or biological processes occurring in the channel or in the surrounding floodplain lakes. The trace element concentrations in the particulate matter show a clear relationship with the location of the samples. V, Co, Cr, Mn, Sr, Cs and Ba concentrations are higher in the Solimões and the Rio Negro is enriched in Fe, Al and Zn. In the Rio Solimões, V, Cr, Mn, Co, Ni, Zn, Cs and Pb are almost entirely carried by the river particulate matter; Cu, Rb, Sr, Ba and U are transported mainly by the suspended particles, but a dissolved phase contributes to the transport. In the Rio Negro, the proportion of elements transported by the dissolved phase is higher for the whole set of elements. The implications of these results allow us to compute the fluxes from the Amazon River to the Atlantic Ocean. Copyright © 2003 John Wiley & Sons, Ltd.
Rare earth elements in the Amazon basin
Authors: Gerard M. , Seyler P. , Benedetti M. F. , Alves V. P. , Boaventura G. R. , Sondag F.
Published: April 2003

The rare earth element (REE) concentrations of the dissolved and particulate fractions and bed sediment between Manaus and Santarém in the Amazon River, and in some major tributaries, were evaluated. A very important zone in the Amazon basin, the ‘encontro das aguas’ area where the Rio Solimões and the Rio Negro meet, was especially sampled. Different size fractions were isolated by ultrafiltration. Water samples were collected at different stages of the mixing. Three groups of waters are distinguished: group I has a low pH (<5·5) and is represented by the Negro basin rivers; group II has alkalinity less than 0·2 meq l−1 and is represented by the Rios Tapajós and Trombetas; group III has high alkalinity (>0·2 meq l−1) and higher pH (>6·5) and is represented by the Madeira basin rivers, the Solimões and the Amazon. The highest dissolved REE concentration is in the Rio Negro and the lowest in the Rio Tapajós (dissolved REEs vary by more than a factor of ten). The solubility of REEs is pH dependent: in river waters with a pH < 6 the Ce concentration is twice that of La, whereas in rivers with a higher pH the concentrations of Ce and La are similar. Dissolved REE concentrations are positively correlated with the dissolved organic carbon. Correlations between Fe, Al, and La suggest that La is associated with Al (Fe)‐rich organic matter and/or related to dissolved Fe‐rich inorganic material. Dissolved REEs normalized to North American shale composite show an enrichment in intermediate/heavy REEs (from Eu to Er), except for the shields rivers (such as Rio Negro and Rio Trombetas). Both of them are depleted in heavy REEs and show a relative Ce enrichment. In contrast, for the Andeans rivers (such as Rio Solimões), light REEs are slightly depleted and a negative Ce relative anomaly occurs. The pattern of the Amazon River at Óbidos confirms the major influence of the Rios Negro and Solimões with REE fractionation. For the Rio Negro, 60 to 70% of REEs are concentrated in the particulate fraction (>0·2 µm), 20 to 30% are in the colloidal fraction (0·2 µm to 5000 Da) and less than 10% are in solution (<5000 Da). For the Solimões the distribution is different. More than 95% of REEs are in the particulate fraction. In the mixing area, the colloidal fraction is enriched in heavy REEs. Copyright © 2003 John Wiley & Sons, Ltd.
Characteristics of organic matter in the mixing zone of the Rio Negro and Rio Solimões of the Amazon River
Authors: Moreira‐Turcq Patricia F. , Seyler Patrick , Guyot Jean Loup , Etcheber Henri
Published: April 2003

The nature and distribution of organic matter in the mixing zone of black (Rio Negro) and white (Rio Solimões) waters in the Amazon River was studied to understand the processes responsible for its transport and distribution. Water samples from 13 stations, including Rio Negro, Rio Solimões and Rio Madeira and ten stations downstream of the confluence with the Amazon, were collected during a low‐water period. Particulate organic matter (POM; >0·7 µm) and dissolved organic matter (DOM; <0·7 µm) were quantified by analysing elemental carbon and nitrogen and by high‐temperature catalytic oxidation, and characterized by infrared spectrometry and fluorescence microscopy. We also performed adsorption experiments with DOM and alumina particles to determine the adsorption abilities and the nature of the most reactive DOM. Adsorption was estimated by measuring the amount of dissolved organic carbon (DOC) lost during the experiments. We found a significant difference between the measured and theoretical fluxes of the two end members in DOC (−52%), particulate organic carbon (−32%), and particulate organic nitrogen (−59%). This suggests that organic matter is not conservative at the confluence of the two rivers. Among processes affecting POM and DOM during the mixing of the two rivers, adsorption may be one of the principal mechanisms by which the dissolved fraction is removed. Adsorption experiments showed that up to ca 40% of DOC can be removed by adsorption reactions. Furthermore, dissolved organic nitrogen was preferentially adsorbed onto alumina surfaces, which may be important for the fractionation of organic matter in the Amazon river system and seems to be related to the origin and freshness of the DOM. Copyright © 2003 John Wiley & Sons, Ltd.
Transport, distribution and speciation of mercury in the Amazon River at the confluence of black and white waters of the Negro and Solimões Rivers
Authors: Maurice‐Bourgoin Laurence , Quemerais Bernadette , Moreira‐Turcq Patricia , Seyler Patrick
Published: April 2003

This study describes the transport and speciation of mercury (Hg) and the associated role of organic matter in these processes at the confluence of the Negro (‘black waters’) and Solimões (‘white waters’) Rivers, which form the Amazon River. The Negro has the highest total Hg content (11·6 to 18·2 ng l−1) due to the extreme particulate Hg concentrations (2074 ng g−1 at the surface), 10 to 20 times higher than those measured in other Amazon tributaries. The total organic carbon (TOC) consists primarily of dissolved organic carbon, which corresponds to 89% and 66% of the TOC in the Negro and Solimões Rivers respectively, and is mainly composed of humic substances, carriers for most of the metal ions transported in rivers. At the confluence of the Negro and Solimões Rivers, the total Hg concentrations decrease markedly. An isotopic mass balance showed that the complete mixing of the two rivers was achieved 25 km downstream of the confluence. At 60 km downstream of the confluence, the flux of Hg decreases to 73 kg day−1, which represents a net losses of 5 kg day−1 and 15 kg day−1 of dissolved Hg and particulate Hg respectively, assuming that the discharge was constant during the sampling survey and without significant lateral input. Moreover, the Hg losses are correlated with the total suspended matter concentrations, which vary throughout the mixing zone, and also with the particulate and dissolved organic carbon distribution. We suggest that the dissolved loss occurs during the flocculation of organic matter within the zone of rapidly changing physical and chemical conditions downstream of the confluence, and that the particulate loss is by the deposition of particles along the mixing zone favoured by decreasing stream velocities during the sampling survey. Adsorption processes of Hg on dissolved organic matter seem to be responsible for the decrease of dissolved Hg concentrations in the mixing zone. Copyright © 2003 John Wiley & Sons, Ltd.
Inland variability of carbon–nitrogen concentrations and δ13C in Amazon floodplain (várzea) vegetation and sediment
Authors: Martinelli Luiz A. , Victoria Reynaldo L. , de Camargo Plinio B. , Piccolo Marisa de Cassia , Mertes Leal , Richey Jeffrey E. , Devol Allan H. , Forsberg Bruce R.
Published: April 2003

We analysed carbon, nitrogen and δ13C values in sediment sampled in the Amazon floodplains. The surface sediment samples were collected along inland transects divided according to their vegetation cover: (a) forest, where the dominant vegetation was inundation forests; (b) grass, where the dominant vegetation was grasses, mainly from Echnochloa polystachya; (c) mixed, where the vegetation changed from grasses near the river bank to forest inland. The average sediment carbon and nitrogen concentrations were significantly higher in forest samples (C = 0·99%, N = 0·12%) than in grass samples (C = 0·84%, N = 0·10%). The average sediment δ13C was significantly heavier in grass (−26·7‰ ) than in forest samples (−28·6‰ ), reflecting the isotopically heavier C4 grasses carbon. In the forest and mixed transects inland, increases in the carbon and nitrogen concentrations were observed. At approximately 50 to 60 m from the riverbank, the concentration of carbon and nitrogen became similar to the river particulate organic carbon (POC) concentration, which is the primary floodplain sediment source. We hypothesized that this trend is caused by the deposition of carbon‐ and nitrogen‐depleted sand‐size particles in the first few metres of the floodplain, whereas the more enriched silt–clay particles are preferentially deposited far inland. In contrast to inland trends, no significant downriver trend was observed in the carbon and nitrogen concentrations. However, a downriver δ13C increase was observed for sediment in grass‐covered areas. Based on δ13C values in different várzea environments, we estimated the relative contribution of riverine POC and vegetation material present in the várzea sediments under different vegetation covers. For forest sediment samples we estimated that 60% of the carbon was derived from the riverine POC and the forests provided the remaining 40%. For open areas covered with grasses we estimated that only 10% was derived from these plants, and 90% was derived from riverine POC. Copyright © 2003 John Wiley & Sons, Ltd.
Nitrogen fixation and denitrification in a floodplain forest near Manaus, Brazil
Authors: Kreibich Heidi , Kern Jürgen
Published: April 2003

The Amazon floodplain (várzea) is seasonally affected by water level fluctuations of the Solimões/Amazon River. The drastic environmental changes that occur also include microbiological processes, such as nitrogen (N2) fixation and denitrification. Both processes were measured in the soil by the acetylene reduction assay and the acetylene block method in a várzea forest on Ilha de Marchantaria, Central Amazonia, Brazil. In the surface soil horizon (0–5 cm), N2fixation was highest during the exposed period (0·04–0·26 nmolN h−1g−1dry weight (dw)). In contrast, denitrification varied from 0 to 1·40 nmolN h−1g−1dw, with high rates during the submerged and the transition periods. No significant difference between locations with legume trees, with non‐legume trees and without trees could be observed. N2fixation rates of incubations (litter down to 450 cm depth) for samples collected during the exposed period ranged from 0 to 0·11 nmolN h−1g−1dw, with highest rates in the surface soil horizon (0–5 cm). Denitrification ranged from 0 to 0·05 nmolN h−1g−1dw, with the highest rate at 250–300 cm depth, which was just below the water table. The maximum N2fixation rate (0·89 nmolN h−1g−1dw) and denitrification rate (0·09 nmolN h−1g−1dw) occurred in the litter layer. On average, at least three times as much N is lost from the surface soil horizon via denitrification than is gained by N2fixation annually, but the rates are strongly influenced by the flood pulse. Copyright © 2003 John Wiley & Sons, Ltd.
Biogenic gas production from major Amazon reservoirs, Brazil
Authors: Rosa Luiz Pinguelli , Dos Santos Marco Aurelio , Matvienko Bohdan , Sikar Elisabeth , Lourenço Ronaldo Sérgio M. , Menezes Carlos Frederico
Published: April 2003

Methane (CH4) and carbon dioxide (CO2) emissions from Brazilian reservoirs were assessed. Point measurements were made during 1998 and 1999 (using inverted funnels for bubbles and air and water concentration gradients for diffusion) in the 559 km2 Samuel reservoir, which was initially flooded in 1988, and the 2430 km2 Tucuruí reservoir, which was flooded in 1984, and the data were evaluated with respect to historical measurements in other Brazilian reservoirs. Bubble emissions of CH4 were higher in Samuel (ranging from 2 to 70 mgCH4 m−2 day−1) than in Tucuruí (ranging from 0·5 to 30 mgCH4 m−2 day−1), with the highest values occurring the shallowest regions in each reservoir. CH4 from diffusion for the Tucuruí reservoir ranged from 5 to 30 mgCH4 m−2 day−1, which is lower than that for the Samuel reservoir, which ranged from 10 to 80 mgCH4 m−2 day−1. The smaller emissions in Tucuruí compared with Samuel are attributed to a larger depletion in the source organic material that was present when the reservoir was filled. The CO2 concentration was similar for each reservoir, and ranged from 1000 to 10 000 mgCO2 m−2 day−1. Copyright © 2003 John Wiley & Sons, Ltd.
Does inequality cause conflict?
Authors: Cramer Christopher
Published: April 2003

This paper suggests that economic inequality is important to explaining civil conflict, but that the links are not as direct as is often supposed. It is important to focus on the variety of ways in which inequalities are managed by societies, and the significance of varying kinds of inequality. It is also important to understand the transmission mechanisms that enable a relatively peaceable durable inequality to turn into a violent conflict. These considerations, together with the poor quality of the available inequality data, should make us more cautious about the conclusions reached by cross‐country empirical studies into the causes of conflict which ascribe a strong predictive power to measures of inequality. Copyright © 2003 John Wiley & Sons, Ltd.
Buying peace or fuelling war: the role of corruption in armed conflicts
Authors: Le Billon Philippe
Published: April 2003

Although corruption may have a corrosive effect on economies and rule‐based institutions, it also forms part of the fabric of social and political relationships. This endogenous character means that conflict may be engendered more by changes in the pattern of corruption than by the existence of corruption itself. Such changes, frequently associated with domestic or external shocks, can lead to armed conflict as increasingly violent forms of competitive corruption between factions ‘fuel war’ by rewarding belligerents. Controversially, ‘buying‐off’ belligerents can facilitate a transition to peace; but ‘sticks’ such as economic sanctions, rather than ‘carrots’, have dominated international conflict resolution instruments. While ‘buying peace’ can present a short‐term solution, the key challenge for peace‐building initiatives and fiscal reforms is to shift individual incentives and rewards away from the competition for immediate corrupt gains. This may be facilitated by placing public revenues under international supervision during peace processes. Copyright © 2003 John Wiley & Sons, Ltd.
Clans, cliques and captured states: rethinking ‘transition’ in Central and Eastern Europe and the former Soviet Union
Authors: Wedel Janine R.
Published: April 2003

An understanding of informal systems and of the ways in which they can shape political, economic and social institutions and processes is important in fashioning both systemic change and post‐conflict reconstruction strategies. In its absence attempts at reform are unlikely to have the intended effects. This paper distinguishes between the partially appropriated state and the clan‐state. The two models fall along a continuum—from substantial appropriation of the state and use of politics by private actors to sweeping appropriation and a near wholesale intertwining of state resources and politics. Both models are characterized by the negotiable status of informal groups, entities and institutions situated between state and private. Both may result in an expanded state sphere marked by ambiguity of status and responsibility. Copyright © 2003 John Wiley & Sons, Ltd.
The political economy of Zimbabwe's descent into conflict
Authors: Addison Tony , Laakso Liisa
Published: April 2003

The last two years have seen intensifying political violence in Zimbabwe. Could Zimbabwe slide further into political and economic turmoil? Or are there sufficient checks and balances in the social system to halt decline? The paper argues that the failed economic stabilization of the 1990s led to increased support for the opposition movement, especially among the middle‐class and trade unionists who were hit by high inflation. The veterans of the liberation war and peasants—who are the power base of the ruling party both ideologically and as voters—also became increasingly disgruntled as they had received very little after independence while the leadership had enriched itself. The government was able buy the loyalty of the war veterans and to use them to intimidate the opposition, although it does not have full control over their actions. The paper concludes that democratic forces within civil society can play an important role in conflict prevention and resolution by building bridges between the different dissatisfied groups. Copyright © 2003 John Wiley & Sons, Ltd.
Building institutions in post‐conflict African economies
Authors: Aron Janine
Published: April 2003

Institutions are altered by conflict, depending on the scale, duration and type of conflict. At one extreme, formal political, social and economic institutions may be completely destroyed (e.g. Somalia), while the importance and type of informal institutions may be changed. This survey addresses some of the current issues in the design and implementation of institution‐building and reform in sub‐Saharan Africa, and highlights the particular difficulties faced by post‐conflict countries. However, research on practical policy interventions toward institution‐building is still at an early stage. Copyright © 2003 John Wiley & Sons, Ltd.
Regional dimensions of conflict and peace‐building in contemporary Africa
Authors: Shaw Timothy M.
Published: April 2003

Africa's conflicts are diverse in their causes and consequences, and they are increasingly interrelated as well as regional in character. Their economic and non‐state features are undeniable, leading to some promising possibilities in terms of diplomacy, involving think tanks and NGOs in addition to formal institutions, both on and off the continent, such as the ‘Kimberley Process’ around ‘blood’ diamonds. Development corridors and trans‐frontier peace‐parks may also constitute innovative ways to moderate and contain conflict. As so often, changeable African cases challenge established assumptions, analyses and policies, such as those around civil society and governance as well as regional and security studies. Copyright © 2003 John Wiley & Sons, Ltd.
Organization‐internal transfer of knowledge and the role of motivation: a qualitative case study
Authors: Kalling Thomas
Published: April 2003

This paper reports a case study of a knowledge transfer programme in a manufacturing MNC, and suggests that firm‐internal knowledge transfer programmes are exercises requiring a great deal of recipient motivation. In contrast to existing theory, which has a tendency to address the role of cognitive factors such as tacitness, causal ambiguity and absorptive capacity, this paper suggests that motivation needs to be in place first. In the studied case, differences in local perceptions of transfer ventures, aspiration and strategic ambitions, internal competition, the view on the nature of knowledge and local communication seem to explain success and failure in transfer ventures. If motivation is not in place ‘naturally’, it can be managed in different ways, including local and corporate management control routines as well as organization structure. Consequently, we argue that knowledge transfer theory should not presume that organizational units are interested in the knowledge transferred, or that knowledge is always ‘good’. Knowledge is contextual, meaning it fits certain operations and strategies better, even in instances where intra‐organizational units are homogeneous. Hence motivation is central to transfer success. Copyright © 2003 John Wiley & Sons, Ltd.
Valuing of firms' prior knowledge: a measure of knowledge distance
Authors: Liyanage Shantha , Barnard Ross
Published: April 2003

Knowledge, especially scientific and technological knowledge, grows according to knowledge trajectories and guideposts that make up the prior knowledge of an organization. We argue that these knowledge structures and their specific components lead to successful innovation. A firm's prior knowledge facilitates the absorption of new knowledge, thereby renewing a firm's systematic search, transfer and acquisition of knowledge and capabilities. In particular, the exponential growth in biotechnology is characterized by the convergence of disparate scientific and technological knowledge resources. This paper examines the shift from protein‐based to DNA‐based diagnostic technologies as an example, to quantify the value of a firm's prior knowledge using relative values of knowledge distance. The distance between core prior knowledge and the rate of transition from one knowledge system to another has been identified as a proxy for the value a firm's prior knowledge. The overall ‘difficulty of transition’ from one technology paradigm to another is discussed. We argue this transition is possible when the knowledge distance is minimal and the transition process has a correspondingly high value of absorptive capacities. Our findings show knowledge distance is a determinant of the feasibility, continuity and capture of scientific and technological knowledge. Copyright © 2003 John Wiley & Sons, Ltd.
Chain propagation rate constants for gas‐phase polymerization of propene and 1‐butene with Ziegler‐Natta catalysts
Authors: Oliva Leone , Di Serio Martino , Peduto Nicolangelo , Santacesaria Elio
Published: April 2003

13C NMR analysis of propene/1‐butene block copolymers obtained by gas‐phase polymerization with Ziegler‐Natta catalysts allows the determination of the propagation rate constants for the homopolymerization of the two monomers. They are very similar for the Solvay type catalyst δ‐TiCl3/AlMe3 and the supported catalyst TiCl4/MgCl2/phthalate/AlMe3. The constant of propene polymerization is three times higher than that of 1‐butene polymerization. The high value of the constant found for propene polymerization is in agreement with the literature value determined by the stopped flow polymerization method.