bluuebunny/crossref_metadata_2025 huggingface dataset:
Bridge response with tractor‐trailer vehicle loading
Authors: Mulcahy N. Lex
Published: March 2007

A method for the calculation of dynamic response and loading of single span multigirder bridges due to vehicle loads is described. The analysis takes account of vehicle acceleration or braking, road surface roughness and eccentric placement of the vehicle on the bridge. The analysis is presented for a three‐axle tractor‐trailer vehicle and the bridge is modelled as an orthotropic plate using higher order finite strips.

As an example application, the loadings produced with braking of the three‐axle vehicle and a nominally equivalent two‐axle vehicle on a bridge were computed. Previous theoretical studies of bridge loading with vehicle braking had employed a two‐axle idealization of a three‐axle vehicle. The results of the present study show that this approximation is not valid for braking studies as the behaviour of the two vehicle models is significantly different. The loadings produced by a three‐axle vehicle are generally less severe than those due to an ‘equivalent’ two‐axle vehicle.
Decoupling approximation to the evaluation of earthquake‐induced plastic slip in earth dams
Authors: Lin Jeen‐Shang , Whitman Robert V.
Published: March 2007

Newmark's sliding block analysis for evaluating earthquake‐induced permanent displacements of earth dams and slopes did not consider the effects of elastic dynamic response. Makdisi and Seed extended the analysis to include such effects, using the simpfying assumption that the computation of dynamic response and plastic slip can be decoupled. This paper examines the error introduced by this assumption, using three idealized lumped‐mass models for a dam. Both sinusoidal and synthetic earthquake motions are employed. When the predominant frequency of the input motion lies in the proximity of the fundamental frequency of the dam, the slip based upon the decoupling assumption exceeds the exact value. This error decreases as the threshold acceleration required to initiate slip and the damping in the soil increase. For practical application, the error should seldom exceed 20 per cent.
On the application of the mode‐acceleration method to structural engineering problems
Authors: Cornwell R. E. , Craig R. R. , Johnson C. P.
Published: March 2007

Mode‐superposition has been extensively used in computing the dynamic response of complex structures. Two versions of mode‐superposition, namely the mode‐displacement method and the mode‐acceleration method, have been employed. The present paper summarizes the results of a systematic study comparing the accuracy of the mode‐displacement and mode‐acceleration methods when applied to structures with various levels of damping or various excitation frequencies. The paper also discusses several details concerning the implementation of the mode‐acceleration method.
Acanthodian remains from the Middle‐Late Permian of Brazil
Authors: Mutter Raoul J. , Richter Martha
Published: March 2007

Acanthodian fishes have been recorded from Silurian through to Permian rocks. Bone beds in the Teresina Formation of the Passa Dois Group (Paraná Basin) in São Gabriel, State of Rio Grande do Sul (southern Brazil) have yielded acanthodian scales and fin spine fragments and are preserved in association with shark and lower actinopterygian fish scales and teeth and possible shark fin spines. All fish remains are disarticulated and preservation is often fragmentary. However, there is no geological or palaeontological evidence that the materials in these bone beds, of Middle‐Late Permian age, could have been re‐worked from older strata. We therefore interpret these bone beds and the acanthodian remains as the youngest known record of acanthodians worldwide. The presence of acanthodians in the Passa Dois Group enhances the significance of the Middle‐Upper Permian rocks of the Paraná Basin in South America in interregional correlation, and may contribute to the discussion of the allegedly global mass extinction event at the end of the Palaeozoic era. Copyright © 2007 John Wiley & Sons, Ltd.
Chemiluminescent determination of leukocyte alkaline phosphatase: an advantageous alternative to the cytochemical assay
Authors: Kanegae Marília P.P. , Ximenes Valdecir F. , Falcão Roberto P. , Colturato Virgílio A.R. , de Mattos Éderson R. , Brunetti Iguatemy L. , da Fonseca Luiz Marcos
Published: March 2007

The determination of leukocyte alkaline phosphatase (LAP) is used as an aid to diagnose many diseases in the laboratory. For example, it can be used to distinguish chronic myeloid leukemia (CML) from other myeloproliferative disorders (particularly myelofibrosis and polycythemia) and leukemoid reactions (LR). Traditionally, this test is performed with the use of subjective cytochemical assays that assign a score to the level of LAP. Here we present a nonsubjective, quantitative, sensitive, and inexpensive chemiluminescent technique that determines LAP based on the commercial reagent Immulite® (AMPPD). To validate this methodology, intact leukocytes obtained from 32 healthy subjects, nine CML patients, and nine LR patients were submitted to the optimized protocol. By measuring the light emission elicited by four concentrations of neutrophils, we were able to estimate the activity of LAP per cell (the slope of the curve obtained by linear regression). A high linear correlation was found between the chemiluminescent result (slope) and the cytochemical score. The slope for healthy individuals ranged between 0.61 and 8.49 (10–5 mV.s/cell), with a median of 2.04 (10–5 mV.s/cell). These results were statistically different from those of CML patients (range=0.07–1.75, median=0.79) and LR patients (range= 3.84–47.24, median=9.58; P<0.05). J. Clin. Lab. Anal. 21:91–96, 2007. © 2007 Wiley‐Liss, Inc.
A modification of the kinetic determination of pancuronium bromide based on its inhibitory effect on cholinesterase
Authors: Stankov‐Jovanovic V.P. , Nikolic‐Mandic S.D. , Mandic Lj.M. , Mitic V.D.
Published: March 2007

A modification of the existing spectrophotometric kinetic method for the determination of pancuronium bromide (PCBr), based on pooled human serum cholinesterase (ChE, EC 3.1.1.8 acylcholine acylhydrolase) inhibition, was developed. Butyrylthiocholine iodide (concentration 1.667 mmol/L) was used as substrate and determination was performed at pH 7.6. Essential basic kinetic parameters were also determined: Michaelis‐Menten's constant KM=0.33 mmol/L, maximal reaction rate Vmax=42.29 µmol/L min, inhibition constant KI=0.34 µmol/L, and IC50=0.235 µmol/L. Linear dependence between the reaction rate and the inhibitor concentration exists in PCBr concentration range 8.29–265.28 nmol/L, which corresponds to the real sample concentrations from 0.166 to 5.306 µmol/L. The method detection limit was established to be 1.86 nmol/L and the quantification limit was 6.18 nmol/L. Precision of the method was tested for three pancuronium concentrations (16.58, 99.48, and 198.96 nmol/L). The relative standard deviation (RSD) was in the range 0.78–5.13%. Accuracy was examined by the standard addition method. The influence of substances usually present in serum and urine on the reaction rate was determined. The method developed was applied for PCBr determination in spiked serum and urine samples and in the urine taken during surgery. The method was proven to have good sensitivity, accuracy, and precision and can be considered suitable for clinical practice. J. Clin. Lab. Anal. 21:124–131, 2007. © 2007 Wiley‐Liss, Inc.
Puromycin insensitive leucyl‐specific aminopeptidase (PILSAP) affects RhoA activation in endothelial cells
Authors: Suzuki Takahiro , Abe Mayumi , Miyashita Hiroki , Kobayashi Toshimitsu , Sato Yasufumi
Published: March 2007

Puromycin insensitive leucyl‐specific aminopeptidase (PILSAP) expressed in endothelial cells (ECs) plays an important role in angiogenesis due to its involvement in migration, proliferation and network formation. Here we examined the biological function of PILSAP with respect to EC morphogenesis and the related intracellular signaling for this process. When mouse endothelial MSS31 cells were cultured, a dominant negative PILSAP mutant converted cell shape to disk‐like morphology, blocked stress fiber formation, and augmented membrane ruffling in random directions. These phenotypic changes led us to test whether PILSAP affected activities of Rho family small G‐proteins. Abrogation of PILSAP enzymatic activity or its expression attenuated RhoA but not Rac1 activation during cell adhesion. This attenuation of RhoA activation was also evident when G‐protein coupled receptors such as proteinase‐activated receptor or lysophosphatidic acid receptor were activated in ECs. These results indicate that PILSAP affects RhoA activation and that influences the proper function of ECs. J. Cell. Physiol. 211: 708–715, 2007. © 2007 Wiley‐Liss, Inc.
cDNA‐AFLP analysis of differential gene expression in human hepatoma cells (HepG2) upon dengue virus infection
Authors: Ekkapongpisit Maneerat , Wannatung Tirawat , Susantad Tharinee , Triwitayakorn Kanokporn , Smith Duncan R.
Published: March 2007

In infectious diseases, the disease pathogenesis is the outcome of the interaction between the genome of the host and the genome of the pathogen. Despite the wide distribution of dengue infections in the world, and the large number of annual infections, few studies have investigated how the dengue genome alters the global transcriptional profile of the host cell. To investigate alterations in the liver cell transcriptome in response to dengue virus infection, liver cells (HepG2) were infected with dengue serotype 2 at MOI 5 and at 3 days post‐infection RNA extracted and analyzed by cDNA‐AFLP in parallel with mock‐infected cells. From 73 primer combinations over 5,000 transcription‐derived fragments (TDFs) were observed, of which approximately 10% were regulated differentially in response to infection. Sixty‐five TDFs were subsequently cloned and sequenced and 27 unique gene transcripts identified. Semi‐quantitative reverse transcription (RT)‐PCR was used to validate the expression of 12 of these genes and 10 transcripts (CK2, KIAA509, HSP70, AK3L, NIPA, PHIP, RiboS4, JEM‐1, MALT1, and HSI12044) were confirmed to be differentially regulated, with four transcripts (HSP70, NIPA, RiboS4, and JEM‐1) showing a greater than twofold regulation. These results suggest that the expression of a large number of genes is altered in response to dengue virus infection of liver cells, and that cDNA‐AFLP is a useful tool for obtaining information on both characterized and as yet uncharacterized transcripts whose expression is altered during the infection process. J. Med. Virol. 79:552–561, 2007. © 2007 Wiley‐Liss, Inc.
Molecular epidemiology of hepatitis A virus in a group of Portuguese citizens living in Lisbon area
Authors: Rodrigues L. , Pista A. , Oliveira A. , Água‐Doce I. , Manita C. , Paixão M.T.
Published: March 2007

Hepatitis A virus (HAV) is the most important cause of acute infectious hepatitis worldwide. In Portugal, due to improvements in sanitation epidemic outbreaks of HAV infection have become less frequent. This report is the first, to our knowledge that characterized HAV in Portugal. For the detection and molecular characterization of HAV cases in a group of Portuguese individuals in the Lisbon area, 31 serum samples were tested: 8 from symptomatic children from an acute hepatitis A outbreak in a Roma (Gipsies) community (2004–2005), and 22 from patients with acute HAV from sporadic cases (2005–2006). A sample of CSF involved in a case of meningitis was also included. IgM anti‐HAV detection and nested reverse transcription (RT‐PCR), with primers located at the VP1‐P2a region, was undertaken to detect HAV genome. In positive samples, molecular characterization was followed by phylogenetic analysis. All samples (n = 31) were positive for IgM anti‐HAV. HAV RNA was found in 96.7% of cases. All isolates were classified as genotype I: 22 belonged to sub‐genotype IA (73.3%), and 8 to sub‐genotype IB (26.7%). All strains obtained from an acute HAV outbreak had sub‐genotype IA, in which seven isolates (87.5%) had identical sequences. In HAV sporadic cases sub‐genotypes IA and IB were identified, and this may reflect the co‐circulation of these two sub‐genotypes in Portugal. Molecular epidemiology of HAV infection in this group of Portuguese appears to be similar to other European countries. HAV phylogenetic studies can provide important information for the design of appropriate public health measures. J. Med. Virol. 79:483–487, 2007. © 2007 Wiley‐Liss, Inc.
Utilizing self‐prepared ELISA plates for a cross‐population study of different anti‐HBe IgG subclass profiles
Authors: Wang Lina , Tsai Tzu‐Hsin , Huang Chien‐Fu , Ho Mei‐Shang , Lin Ding‐Bang , Ho Yung‐Chyuan , Lin Shih‐Shen , Wei James Cheng‐Chung , Chou Ming‐Chih , Yang Chi‐Chiang
Published: March 2007

Fourteen serum samples obtained from hepatitis B virus (HBV) chronic carriers and patients recovered from hepatitis B infection were used with four sodium dodecyl sulfate‐treated enzyme‐linked immunosorbent assay (ELISA) plates available commercially, and one self‐prepared HBcAg analog for evaluation of anti‐HBe subclass pattern absorbance. The self‐prepared plates had the best performance and were thus used for samples obtained from 104 (60 male and 44 female) HBV chronic carriers and 439 (247 male and 192 female) recovered individuals. Tests for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also carried out in 21 of the subjects (>25 IU/ml). Statistical comparison of these patients with elevated ALT/AST levels with other ALT/AST‐normal chronic carriers revealed no significant differences in the anti‐HBe OD, although the mean optical density (OD) of patients with elevated ALT/AST levels was higher. The results suggest that the anti‐HBe IgG subclass profiles in the chronic carriers did not change with inflammation of the liver, and were independent of sex and age. In contrast to previous anti‐HBc findings, the distribution pattern of anti‐HBe subclasses in HBV chronic carriers was IgG1 > IgG4 > IgG3 while in the recovered individuals it was IgG1 > IgG3 > IgG4, for both males and females. Subclasses IgG1 and IgG2 were the most and least prevalent isotypes, respectively, in both study groups. The results of the study suggest that induction of IgG1 and/or IgG3 antibodies is important for effective virus neutralization, while IgG2 antibodies are of limited importance. Significantly higher OD values for anti‐HBe IgG4 were observed when comparing samples from the chronic carriers and recovered individuals, which may reflect the effects of persistence. Further, in contrast to previous anti‐HBs results, the concentrations of total IgG and IgG1 were higher in the samples from chronic carriers relative to those from recovered individuals. J. Med. Virol. 79:495–502, 2007. © 2007 Wiley‐Liss, Inc.
Cell specific internal translation efficiency of Epstein–Barr virus present in solid organ transplant patients
Authors: Isaksson Åsa , Berggren Malin , Ekeland‐Sjöberg Kerstin , Samuelsson Tore , Ricksten Anne
Published: March 2007

The U leader exon in the 5′ untranslated region of the Epstein–Barr virus nuclear antigen 1 (EBNA1) gene contains an internal ribosome entry site, the EBNA internal ribosome entry segment (IRES), which promotes cap‐independent translation and increases the expression level of the EBNA1 protein. It was previously reported that immunosuppressed organ transplanted patients showed an alternatively spliced EBNA1 transcript, excluding the EBNA IRES element. To further investigate the function of the EBNA IRES, sequence analysis of the EBNA IRES mRNA was performed in samples from seven organ transplant patients. Two nucleotide changes, G → A at position 67531 and C → U at position 67585 were found in the EBNA IRES mRNA, relative to the corresponding genomic Epstein–Barr virus (EBV) sequence in all patients. Moreover, the patient derived EBNA IRES mRNA was shown to differ from the IRES mRNA derived from the cell line B95.8 at position 67531 and from the cell lines Rael and P3HR1 at positions 67531 and 67585. cDNA from the various EBNA IRES sequences were cloned into bicistronic vectors, respectively, and used in transient transfection experiments in six human cell lines. The patient specific sequence significantly decreased the IRES activity in T‐cells, while the base changes had no significant impact on the activity in B‐ or in epithelial cells. The genetic mechanisms behind EBV‐associated diseases are complex, involving gene regulation by alternative promoters, alternative splicing, and translational control. The nucleotide changes in the patient specific EBNA IRES transcript and its influence on the translational activity, might illustrate new strategies utilised by the EBV to adapt to the immune control in patients with EBV associated diseases. J. Med. Virol. 79:573–581, 2007. © 2007 Wiley‐Liss, Inc.
Telomerase activity, hTERT expression, and phosphorylation are downregulated in CD4+T lymphocytes infected with human immunodeficiency virus type 1 (HIV‐1)
Authors: Franzese Ornella , Adamo Riccardo , Pollicita Michela , Comandini Alessandro , Laudisi Anastasia , Perno Carlo Federico , Aquaro Stefano , Bonmassar Enzo
Published: March 2007

Human immunodeficiency virus type 1 (HIV‐1) infection is characterized by a progressive decrease of CD4+T cells accompanied by other immune dysfunctions. Telomerase is transiently activated in lymphocytes during activation and is able to compensate for the progressive telomeric loss that occurs at each cell division, contributing to ensure the telomere length necessary for multiple proliferative events. The effect of HIV‐1 infection on telomerase activity and on the expression of some of the factors involved in its regulation in CD4+T cells was investigated. Telomerase was found to be downregulated in both nuclear and cytoplasmic compartments, together with an impairment of human telomerase reverse transcriptase (hTERT) expression and of the cell machinery involved in hTERT phosporylation. J. Med. Virol. 79:639–646, 2007. © 2007 Wiley‐Liss, Inc.
Human caliciviruses in symptomatic and asymptomatic infections in children in Vellore, South India
Authors: Monica Bindhu , Ramani Sasirekha , Banerjee Indrani , Primrose Beryl , Iturriza‐Gomara Miren , Gallimore Christopher I. , Brown David W. , M Fathima , Moses Prabhakar D. , Gray James J. , Kang Gagandeep
Published: March 2007

Pediatric gastroenteritis is a major cause of childhood morbidity and mortality worldwide, especially in developing countries. It has been increasingly recognised that human caliciviruses (HuCV), comprising noroviruses (NoV), and sapoviruses (SaV), are important in both outbreak and non‐outbreak settings. This study aimed to characterise caliciviruses detected in the faeces of hospitalized children and children in the community in India. This study examined 350 faecal samples from children presenting to the hospital with acute gastroenteritis and 673 samples collected from children in the community, 500 from children with diarrhea, and 173 samples from children without diarrhea. Strain characterisation was performed by reverse transcription‐polymerase chain reaction (RT‐PCR) and partial sequencing of the gene encoding the RNA‐dependent RNA polymerase (RdRp) and/or a region spanning the open reading frames (ORFs) 1 and 2 (ORF1/ORF2) junction. A total of 68 of 350 specimens (19.4%) from hospitalized children were positive, and SaV and NoV accounted for 5.1 and 15.1% of the infections, respectively. Mixed infections of HuCVs with other enteric pathogens were seen in 9.4% of the total children tested. Sixty‐eight out of 673 (10.1%) samples collected from children in the community were positive for caliciviruses, and SaV and NoV accounted for 3.4 and 6.6% of the infections. In the community cohort 55/500 (11%) and 13/173 (7.5%) were from symptomatic and asymptomatic children, respectively, and SaVs accounted for 17/500 (3.4%) and NoVs for 38/500 (7.6%) of the symptomatic infections. This is the first report of genotyping of circulating caliciviruses in both hospital and community in India and has increased the evidence for the role of these viruses in pediatric gastroenteritis in India. J. Med. Virol. 79:544–551, 2007. © 2007 Wiley‐Liss, Inc.
Insulin and insulin‐like growth factor type‐I up‐regulate the vanilloid receptor‐1 (TRPV1) in stably TRPV1‐expressing SH‐SY5Y neuroblastoma cells
Authors: Lilja Johanna , Laulund Frida , Forsby Anna
Published: March 2007

The capsaicin receptor, transient receptor potential, vanilloid type 1 (TRPV1), is a Ca2+‐permeable ion channel activated by noxious stimuli eliciting pain. Several reports have shown modulation of TRPV1 activity and expression by neuronal growth factors. Here, we study the long‐term effects on TRPV1 expression mediated by insulin‐like growth factor type‐I (IGF‐I) and insulin in a stably TRPV1‐expressing SH‐SY5Y neuroblastoma cell line. We show that, after 72 hr of 10 nM IGF‐I or insulin exposure, the TRPV1 protein level was up‐regulated 2.5‐ and 2‐fold, respectively. By blocking phosphatidylinositol‐3‐kinase [PI(3)K] or mitogen‐activated protein kinase (MAPK) signaling, we concluded that the increase in total TRPV1 protein content induced by IGF‐I was controlled by PI(3)K signaling, whereas insulin seemed to regulate TRPV1 protein expression via both PI(3)K and MAPK pathways. Inhibiting protein kinase C (PKC) blocked the effects of both IGF‐I and insulin. Furthermore, the concentrations causing a 50% Ca2+ increase (EC50) after insulin and IGF‐I treatments were significantly lowered compared with untreated cells. We conclude that IGF‐I and insulin enhance TRPV1 protein expression and activity, and impaired pain sensation might result from distorted TRPV1 regulation in the peripheral nervous system. © 2007 Wiley‐Liss, Inc.
BH3‐only proteins Bid and BimEL are differentially involved in neuronal dysfunction in mouse models of Huntington's disease
Authors: García‐Martínez Juan M. , Pérez‐Navarro Esther , Xifró Xavier , Canals Josep M. , Díaz‐Hernández Miguel , Trioulier Yael , Brouillet Emmanuel , Lucas José J. , Alberch Jordi
Published: March 2007

Apoptosis, a cell death mechanism regulated by Bcl‐2 family members, has been proposed as one of the mechanisms leading to neuronal loss in Huntington's disease (HD). Here we examined the regulation of Bcl‐2 family proteins in three different mouse models of HD with exon 1 mutant huntingtin: the R6/1, the R6/1:BDNF+/−, and the Tet/HD94 in which the huntingtin transgene is controlled by the tetracycline‐inducible system. Our results disclosed an increase in the levels of the BH3‐only proteins Bid and BimEL in the striatum of HD mouse models that was different depending on the stage of the disease. At 16 weeks of age, Bid was similarly enhanced in the striatum of R6/1 and R6/1:BDNF+/− mice, whereas BimEL protein levels were enhanced only in R6/1:BDNF+/− mice. In contrast, at later stages of the disease, both genotypes displayed increased levels of Bid and BimEL proteins. Furthermore, Bax, Bak, Bad, Bcl‐2, and Bcl‐xL proteins were not modified in any of the points analyzed. We next explored the potential reversibility of this phenomenon by analyzing conditional Tet/HD94 mice. Constitutive expression of the transgene resulted in increased levels of Bid and BimEL proteins, and only the Bid protein returned to wild‐type levels 5 months after mutant huntingtin shutdown. In conclusion, our results show that enhanced Bid protein levels represent an early mechanism linked to the continuous expression of mutant huntingtin that, together with enhanced BimEL, may be a reporter of the progress and severity of neuronal dysfunction. © 2007 Wiley‐Liss, Inc.
Serum albumin improves recovery from spinal cord injury
Authors: Cain Lisa D. , Nie Linghui , Hughes Michael G. , Johnson Kathia , Echetebu Clement , Xu Guo‐Ying , Hulsebosch Claire E. , McAdoo David J.
Published: March 2007

A neuroprotective factor is shown to be present in mammalian serum. This factor is identified by Western blotting to be serum albumin. The serum factor and albumin both protected cultured spinal cord neurons against the toxicity of glutamate. The inability of K252a, a blocker of the high affinity tyrosine kinase receptor for members of the nerve growth factor family, to block the neuroprotective effect of the serum factor established that the serum factor is not a member of the nerve growth factor family. Post‐injury injection of albumin intravenously or into the site of injury immediately after injury both improved significantly locomotor function according to Basso‐Beattie‐Bresnahan assessment and spontaneous locomotor activity recorded with a photobeam activity system. Albumin has multiple mechanisms whereby it may be neuroprotective, and it is a potentially useful agent for treating neurotraumas. © 2007 Wiley‐Liss, Inc.
An increase in S‐glutathionylated proteins in the Alzheimer's disease inferior parietal lobule, a proteomics approach
Authors: Newman Shelley F. , Sultana Rukhsana , Perluigi Marzia , Coccia Rafella , Cai Jian , Pierce William M. , Klein Jon B. , Turner Delano M. , Butterfield D. Allan
Published: March 2007

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by neurofibrillary tangles, senile plaques, and loss of synapses. Many studies support the notion that oxidative stress plays an important role in AD pathogenesis. Previous studies from our laboratory employed redox proteomics to identify oxidatively modified proteins in the AD inferior parietal lobule (IPL) and hippocampus. The proteins were consistent with biochemical or pathological alterations in AD and have been central to further investigations of the disease. The present study focused on the identification of specific targets of protein S‐glutathionylation in AD and control IPL by using a redox proteomics approach. For AD IPL, we identified deoxyhemoglobin, α‐crystallin B, glyceraldehyde phosphate dehydrogenase (GAPDH), and α‐enolase as significantly S‐glutathionylated relative to these brain proteins in control IPL. GAPDH and α‐enolase were also shown to have reduced activity in the AD IPL. This study demonstrates that specific proteins are sensitive to S‐glutathionylation, which most likely is due to their sensitivity to cysteine oxidation initiated by the increase in oxidative stress in the AD brain. © 2007 Wiley‐Liss, Inc.
Late Quaternary river development in the southwest Chad Basin: OSL dating of sediment from the Komadugu palaeofloodplain (northeast Nigeria)
Authors: Gumnior Maren , Preusser Frank
Published: March 2007

The Komadugu river system is the major Nigerian tributary to Lake Chad. Its large alluvial complex represents an important archive of the late Quaternary environmental history of the Chad Basin. Modern floodplains are incised into an older fluvial terrace that extends over 5000 km2. Evidence from satellite images suggests that the ancient river system was dammed up by the Bama Beach Ridge during high stands of mega Lake Chad. This caused the formation of extensive wetlands with a chaotic network of relic channels. The first set of luminescence ages presented here fits well into the previously established environmental history of the Chad Basin. Both the early and mid‐Holocene pluvial periods as well as a final relatively humid period during the late Holocene are reflected by point bar to overbank deposits or channel fills. The onset of the Holocene was characterised by erosion of older dune fields as indicated by grain‐size distributions of the alluvium. Satellite images and sedimentological observations show that the floodplain was dominated by meandering channels shifted by frequent avulsion, reflecting a high variability in precipitation and discharge patterns at the beginning and end of Holocene humid periods. Copyright © 2007 John Wiley & Sons, Ltd.
Conduction and excitability properties of peripheral nerves in end‐stage liver disease
Authors: Ng Karl , Lin Cindy S.‐Y. , Murray Nicholas M.F. , Burroughs Andrew K. , Bostock Hugh
Published: March 2007

The pathophysiology of hepatic neuropathy is poorly understood, but membrane depolarization due to a toxic inhibition of oxidative metabolism has been proposed. We investigated the relationship between nerve excitability properties, nerve dysfunction, and liver function in 11 pretransplant patients, the majority of whom were oligo‐ or asymptomatic for peripheral neuropathy. Abnormalities were detected on clinical examination (6), large‐fiber nerve conduction (4), and thermal quantitative sensory testing (10). Small‐fiber involvement was characterized by elevation of warm more than cold detection thresholds. Autonomic dysfunction was less frequent (4). Nerve excitability parameters in both upper and lower limbs provided evidence of membrane depolarization compared with controls, even in those patients without a history of alcohol abuse. No clear correlation was found between neurophysiological indices and scores of hepatic reserve or various blood parameters including ammonia level. Although chronic membrane depolarization may be involved, the degree of depolarization in large fibers was small, and its role in the pathophysiology of neuropathy uncertain. Muscle Nerve, 2007
Formation and characterization of polymersomes made by a solvent injection method
Authors: Yildiz M. E. , Prud'homme R. K. , Robb I. , Adamson D. H.
Published: March 2007

In this article a solvent injection method is described for vesicle formation using poly(butadiene)‐ b‐poly(acrylic acid) diblock copolymers as the amphiphilic molecules. Vesicles composed of polymer bilayers are commonly referred to as polymersomes. Solvent injection is shown to be a rapid method for polymersome formation suitable to make large volumes of polymersome solution. The method can be manipulated to obtain a wide range of vesicle sizes depending on the polymer concentration and preparation conditions. Polymersome solutions in this study are characterized using dynamic light scattering (DLS), fluorescent microscopy, and electron microscopy. Polymersome sizes range from tens of nanometers to several microns. The membrane thickness of smaller polymersomes is found to lie between 14–20 nm. Larger polymersomes are found to have somewhat thicker membranes. The procedure involves the addition of polymers dissolved in an organic solvent to a stirred aqueous solution. The formation of polymersomes by this method is proposed to be governed by the limited mutual solubility of the two solvents and the simultaneous diffusion of solvent and water out of and in to initially formed organic solvent droplets. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of the separation of Coulomb centers on the activation energy in electronic hopping transport: A reinterpretation in poly‐N‐vinylcarbazole
Authors: Santos S. , Caraballo D.
Published: March 2007

The effect of the separation of Coulomb centers in the activation energy for the electronic hopping transport of noncrystalline organic materials was studied. The theoretical analysis was carried out in absence of an applied electric field, using a simple one‐dimensional model of two centers separated by a distance R. It was found that the height of the potential well is reduced by an amount e2/4πεε0R due to the overlapping of the Coulomb centers. This reduction defines an effective activation energy given by (ΔE)0 − e2/4πεε0R, where (ΔE)0 is the height of the nonperturbed potential well. As an experimental application of this result, current–voltage characteristic in poly‐N‐vinylcarbazole at different temperatures was obtained, from which the conductivity at zero electric field was estimated by extrapolation to zero field in Poole‐Frenkel plots. The correspondent activation energy was estimated from Arrhenius plots in the order of 0.65 eV. Because the carriers transport in this polymer occurs by hopping between the molecules of carbazole whose mean separation is in the order of 6.5 × 10−10 m, the height of the nonperturbed Coulomb barrier of a single hopping site in this material would be really estimated in 1.18 eV. POLYM. ENG. SCI., 47:545–550, 2007. © 2007 Society of Plastics Engineers.
Modeling the vulcanization reaction of silicone rubber
Authors: Lopez L.M. , Cosgrove A.B. , Hernandez‐Ortiz J.P. , Osswald T.A.
Published: March 2007

Characterization of the vulcanization process of silicone rubber was achieved through the modeling of dynamic DSC tests. The Kissinger equation and the Kamal‐Sourour model were used to determine kinetic parameters that fit the experimental data. The technique allows for the determination of the activation energy through Kissinger's model, which is then used to mathematically determine the other five parameters for the Kamal‐Sourour model. This novel technique finds a physically meaningful activation energy. The method generates a single set of parameters that accurately models all scanning rates tested (1, 2.5, 5, and 10 K/min). Five formulations of liquid silicone rubber as well as one solid silicone rubber were tested and modeled. For each material, the models generated fitting parameters that were in agreement with the dynamic DSC scans. The models were used to compare the processing of the liquid and solid silicone rubber. The characterization of both materials demonstrates the lower processing time, temperatures, and energy consumption when processing liquid silicone rubber, as compared to processing of hard silicone rubber. POLYM. ENG. SCI., 47:675–683, 2007. © 2007 Society of Plastics Engineers.
Rubber‐toughened polypropylene/acrylonitrile‐co‐butadiene‐co‐styrene blends: Morphology and mechanical properties
Authors: Šlouf Miroslav , Kolařík Jan , Kotek Jiří
Published: March 2007

The RTPP/ABS (rubber toughened polypropylene/poly (acrylonitrile‐co‐butadiene‐co‐styrene) blends, both noncompatibilized and compatibilized with polypropylene‐g‐polystyrene, were prepared by melt mixing in a Brabender Plasti‐Corder. As the torque ratio of RTPP and ABS was about 2, phase cocontinuity in the blends was achieved at ABS volume fractions around 0.16, which was evidenced by both microscopic analysis and mechanical testing. A new microscopic and image analysis technique was introduced, whose combination provides two semiquantitative parameters: structure roughness and structure cocontinuity. The latter parameter is closely associated with the predictive scheme based on the equivalent box model and percolation theory, which was used in this study. The predicted mechanical properties were confronted with the experimental data for tensile modulus, yield strength, and tensile impact strength. While the modulus of noncompatibilized blends is reasonably fitted by the model, the compatibilizer accounts for a positive deviation attributed to a strong interaction between the compatibilizer and the matrix. The yield strength of noncompatibilized blends indicates poor interfacial adhesion, which is so enhanced by the compatibilizer that no phase debonding occurs before yielding. Tensile impact strength, in contrast to modulus and yield strength, passes through a deep minimum for both types of blends; two tentative explanations of this detrimental behavior were suggested. POLYM. ENG. SCI., 47:582–592, 2007. © 2007 Society of Plastics Engineers.
Wear of poly (methyl methacrylate) against a metallic surface in dry conditions
Authors: Geringer Jean , Forest Bernard , Combrade Pierre
Published: March 2007

Wear of Poly (methyl methacrylate), PMMA, against a metallic surface, AISI 316L stainless steel (SS) has been investigated in dry conditions. These materials have been used to simulate the degradation of the contact, femoral stem‐bone cement in the field of hip prosthesis. First of all, no significant wear was observed on the 316L SS. PMMA wear has been quantified: the energy wear coefficient, slope of the line, and wear volume according to the cumulated dissipated energy, don't depend on the normal load, FN. This energy analysis allows predicting the PMMA wear depth. According to the comparison between the measured dissipated energy and the energy breaking polymer chains, mechanical dissipated energy is used essentially to transform third body structure and to expel it from the contact between the two materials. Moreover, the experimental results have highlighted the stick‐slip phenomenon. Lastly, Attenuated Total Reflectance‐Fourier Transform InfraRed and Reflection Absorption‐Fourier Transform InfraRed have shown that PMMA debris configuration and conformation have changed after wear against 316L SS. The driving force of these changes seems to be the acid–base interactions between PMMA and hydroxyl groups of the SS surface. POLYM. ENG. SCI., 47:633–648, 2007. © 2007 Society of Plastics Engineers.
Computer simulation of reactive extrusion processes for free radical polymerization
Authors: Jia Yuxi , Zhang Guofang , Wu Lili , Sun Sheng , Zhao Guoqun , An Lijia
Published: March 2007

The reactive extrusion for polymerization is an integrated polymer processing technology. A new semi‐implicit iterative algorithm was proposed to deal with the complicated relationships among the chemical reaction, the macromolecular structure and the chemorheological property. Then the numerical computation expressions of the average molecular weight, the monomer conversion, and the initiator concentration were deduced, and the computer simulation of the reactive extrusion process for free radical polymerization was carried out, on basis of which reactive processing conditions can be optimized. POLYM. ENG. SCI., 47:667–674, 2007. © 2007 Society of Plastics Engineers.
An applicable electrospinning process for fabricating a mechanically improved nanofiber mat
Authors: Kim Geun Hyung , Han Houkseop , Park Jong Ha , Kim Wan Doo
Published: March 2007

Engineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape‐ability to form a variety of shapes and sizes. In this study, we produced design‐based poly (ε‐carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x‐y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric‐field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x‐y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.
Highly Conjugated Organic Polymers as Heterogeneous Catalysts. I. Introduction and Literature Survey
Authors: Cooper David R. , Law Adrian M. G. , Tighe Brian J.
Published: March 2007

The use of highly conjugated organic polymers as heterogeneous catalysts is reviewed as part of a series of papers relating to their use in reactions involving oxides of nitrogen. The polymers which have been examined and the types of catalysed reaction so far recorded are described.

In general the structural features, including extensive conjugation, which are considered important for catalytic activity and selectivity, are also responsible for their high thermal stability. The presence of hetero‐atoms, a high stable concentration of delocalised electrons and semiconductivity, have each been proposed as primary requisites for catalytic activity.
Gel permeation chromatographic evaluation of ethyl cellulose extrudates exhibiting “Sharkskin effect”
Authors: Brookshaw Alan P. , Hillman Donald E. , Paul John I.
Published: March 2007

Gel permeation chromatography has been utilised to investigate the molecular weight distribution of samples of ethyl cellulose which have exhibited extrusion defects corresponding to the phenomenon known as “sharkskin effect”. The results have indicated that a narrow molecular weight distribution is largely responsible for these defects. The effect of processing the polymer was to cause a fall in the number average molecular weight MN and weight average molecular weight MW although the distribution (MW/MN) did not change significantly. An improvement in the appearance of reprocessed material was attributed to an increase in the homogeneity of the sample, rather than an increase in the molecular weight distribution. Processing parameters could be altered to improve the finish of the extrudate, e.g. an increase in die temperature and a reduction in extrusion rate, but this is non‐viable on a production basis.

Anomalous gel permeation chromatography results obtained using methylene chloride as solvent have been attributed to association due to residual hydroxyl groups in the ethyl cellulose.
High frequency mechanical properties of a polymer–surfactant filler system
Authors: Jones Ian H. , West George H.
Published: March 2007

The high frequency mechanical properties have been determined of ammonium perchlorate‐polyisobutane mixtures to which surfactants of various kinds have been added. A model has been suggested for the structure of the surfactant layer formed at the interface based on packing density and chain mobility as the controlling factors.
Dispersion polymerisation in organic media
Authors: Barrett Keith E. J.
Published: March 2007

The development of a technique for the direct preparation of polymer dispersions of controlled particle size in organic media is described. This method of dispersion polymerisation involves the polymerisation of a monomer dissolved in an organic liquid to produce insoluble polymer dispersed in the continuous phase. An amphipathic graft or block copolymer is used as the dispersant. The general features of the process, including the method used for stabilising the polymer dispersions and the mode of particle formation and growth, are reviewed.
Particulate reinforcement of polyacrylate elastomers. I. Introduction and Preparation of Materials
Authors: Blackley David C. , Sheikh Majid W.
Published: March 2007

The series of papers, of which this is the first, aims to demonstrate the importance of chemical reactions between filler particles and elastomer matrix in determining the physical properties of filled elastomers. A model system comprising small glass beads as the filler and crosslinked polyethylacrylate as the elastomer has been used. The beads themselves are inert towards the matrix during polymerisation, but the reactivity of the surfaces of the beads can be varied by suitable treatments. This paper describes techniques for fractionating the beads to give narrow particle‐size distribution, for preparing unfilled and filled elastomer sheets, and for preparing composites in which an elastomer sheet is polymerised in contact with a glass plate which may or may not have been previously subjected to surface treatment.
Polyester‐polyether block copolymers. I. Wide‐angle X‐ray diffraction studies of poly(hexamethylene terephthalate)/poly(oxytetramethylene) and related block polymers
Authors: Ghaffar Abdul , Goodman Isaac , Hall Ivan H.
Published: March 2007

The crystallisation and orientation of the individual structural components of poly(hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been studied by wide‐angle X‐ray diffraction. The crystallisation behaviour in the unstretched state is determined by the proportions and molecular weights of the polyether blocks. For copolymers containing less than 60 wt% of polyether of m. w. ≯ 2000, only the polyester segments crystallise spontaneously, but with polyether m. w > 2000 two crystalline phases are formed. Similar behaviour was found in block polymers from other readily crystallising polyesters, but with non‐crystallising polyesters the polyether segments crystallised spontaneously.

Moderate tensile deformation of the block copolymers from polyether of m. w. 2000 leads to the stress‐reversible highly oriented crystallisation of the polyether whilst the polyester remains undeformed. At higher extensions, irreversible orientation of the polyester segments occurs. The observations suggest that the polyester and polyether segments form discrete regions since otherwise homogeneous crystallisation should occur.
Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C
Authors: Monteiro Michael J. , Guliashvili Tamaz , Percec Virgil
Published: March 2007

A mechanistic comparison of the ATRP and SET‐LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer‐sphere single‐electron transfer process responsible for the SET‐LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner‐sphere electron‐transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET‐LRP, the Cu(II)X2/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET‐LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET‐LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X2/L and, subsequently, to change the polymerization mechanism from ATRP to SET‐LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.
Build‐up of carboxylic acids in polyethylene and their relation to off‐flavor and carbonyl index
Authors: Strandberg Clara , Albertsson Ann‐Christine
Published: March 2007

Oxidation of polyethylene (PE) gives a mixture of degradation products. Carboxylic acids are among the major ones. They are believed to cause off‐flavor in food and beverage packaging. Our previous research has shown that identification and use of indicator products gives earlier detection of oxidation in plastic materials. In the present study, the relation between off‐flavor in water extracts of PE and each of the carboxylic acids in the homologous series from propanoic to nonanoic acid were investigated. Also, a comparison between carbonyl index in solid PE and each of the carboxylic acids in the homologous series from propanoic to decanoic acid were examined. The amount of the carboxylic acids was assessed by head‐space solid‐phase microextraction (HS‐SPME) and gas chromatography–mass spectroscopy (GC‐MS). It was found that the amount of butanoic and hexanoic acid correlated well with the rated off‐flavor intensities in the water extracts. This confirmed earlier results on a linkage between these two carboxylic acids and highly rated off‐flavor intensities. Moreover, a relation between the build‐up of propanoic acid in the solid PE and carbonyl index was found. Hence, propanoic acid could be used as an indicator product for earlier oxidation detection in these PE materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1848–1859, 2007