bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melt rheology of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites during capillary extrusion
Authors: Liang Ji‐Zhao 
Published: December 2002

AbstractThe melt flow properties during capillary extrusion of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites were measured by using a Rosand rheometer to identify the effects of the filler content and operation conditions on the rheological behaviour of the sample melts. The experiments were conducted under the following test conditions: temperature varied from 220 to 240 °C and shear rate ranged from 10 to 104 s−1. The filler volume fractions were 0, 10, 20, 30, 40 and 50%. The results showed that the shear flow did not strictly obey the power law under the test conditions, and that the entry pressure drop (ΔPen) and the extension stress (σe) in entry flow increased nonlinearly, while the melt shear viscosity (ηs) and extension viscosity (ηe) decreased with increasing the wall shear stress (τw) at constant test temperature. The dependence of the melt shear viscosity on the test temperature was approximately consistent with the Arrhenius expression at fixed τw. When τw was constant, ηs and ηe increased while ΔPen and σe decreased with the addition of the filler volume fraction.© 2002 Society of Chemical Industry
X‐ray photoelectron spectroscopic study of silk fibroin surface
Authors: Shao Jianzhong , Liu Jinqiang , Zheng Jinhuan , Carr C M 
Published: December 2002

AbstractX‐ray photoelectron spectroscopy (XPS) has been used to probe the nature of silk fibroin surface, in particular the tyrosine content and sulfur species on the surface. The iodine labelling treatment of silk, followed by XPS surface analysis, reveals that silk fibroin has a tyrosine‐enriched surface, and that there are sulfur‐containing amino acids present on the surface, mainly occurring in the S6+ component. UV/ozone treatment modifies/removes the surface tyrosine‐ and sulfur‐containing species.© 2002 Society of Chemical Industry
Polymerisation of ethylene catalysed by mono‐imine‐2,6‐diacetylpyridine iron/methylaluminoxane (MAO) catalyst system: effect of the ligand on polymer microstructure
Authors: Fernandes Susete , Bellabarba Ronan M , Ribeiro Alejandro F G , Gomes Pedro T , Ascenso José R , Mano João F , Dias Alberto R , Marques Maria M 
Published: December 2002

AbstractThe complex, {1‐{6‐[(2,6‐diisopropylphenyl)‐ethaneimidoyl]‐2‐pyridinyl}‐1‐ethanone}iron(II) dichloride (2), has been synthesised and characterised. Treatment of complex 2 with methylaluminoxane resulted in a very active catalytic system for the preparation of polyethylene (PE). The system shows activities in the order of magnitude 107 g (PE) mol−1(Fe) h−1 bar−1. Characterisation by 13C NMR indicated that branched PE was obtained and that experimental conditions affect polymer microstructure. PE produced contained six to eight branches per 100 carbons.© 2002 Society of Chemical Industry
Effect of isotacticity distribution on crystallization kinetics of polypropylene
Authors: Lu Hongbin , Qiao Jinliang , Yang Yuliang 
Published: December 2002

AbstractThe crystallization kinetics of isotactic polypropylene (iPP) depends not only on the undercooling but also on its microstructure characteristics. In this paper the effect of isotacticity distribution on the isothermal kinetics of iPPs in the crystallization regime III was examined by differential scanning calorimetry. The microstructure features of two commercial film grade iPPs were characterized with temperature rising elution fractionation and size exclusion chromatography. The results indicated that, although the overall isotacticities and molecular weights of two iPPs were similar, their isothermal crystallization kinetics displayed marked differences due to the disparity in isotacticity distributions. With increasing molecular weight of components containing crystallizable units, the isothermal crystallization rate exhibited a higher temperature dependence. When the isotactic defects in polypropylene chains increase with the molecular weight of components, both the fold surface free energy σe and the work of chain folding q decreases, in spite of the higher molecular weight.© 2002 Society of Chemical Industry
Kinetic and thermodynamic studies of depolymerisation of poly(ethylene terephthalate) by saponification reaction
Authors: Mishra S , Zope V S , Goje A S 
Published: December 2002

AbstractDepolymerisation reaction of polyester waste was carried out by a saponification reaction. Yields of depolymerised products were up to 85% for a 2.5‐h reaction time. Products obtained were characterized by chemical as well as instrumental analysis such as mp (sublimation), acid value and FTIR spectra. The valued obtained for terephthalic acid (TPA) agreed with those for the pure substance. Chemical kinetics of this reaction shows that it is a first‐order reaction with respect to poly(ethylene terephthalate) (PET) concentration with a velocity constant of the order of 10−2 min−1. In the light of the Yashioka modified shrinking core model, a simultaneous fragmentation and depolymerisation model was proposed for the kinetics of hydrolysis of PET. The modified model is based on change in acid value of the product obtained, which is directly related to the change in surface area of particle. The energy of activation and the Arrhenius constant (frequency factor) obtained by Arrhenius plot were 59.71 kJ g−1 and 8.325 × 106 min−1 respectively.© 2002 Society of Chemical Industry
Poly(hydroxyethyl methacrylate‐co‐glycidyl methacrylate) reactive membrane utilised for cholesterol oxidase immobilisation
Authors: Akgöl Sinan , Bayramoğlu Gülay , Kacar Yasemin , Denizli Adil , Arıca M Yakup 
Published: December 2002

AbstractPoly(2‐hydroxyethyl methacrylate‐co‐glycidyl methacrylate) p(HEMA–GMA) membrane was prepared by UV‐initiated photopolymerisation of 2‐hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the presence of an initiator, azobisisobutyronitrile (AIBN). Cholesterol oxidase was immobilised directly on the membrane by forming covalent bonds between its amino groups and the epoxide groups of the membrane. An average of 53 µg of enzyme was immobilised per cm2of membrane, and the bound enzyme retained about 67% of its initial activity. Immobilisation improved the pH stability of the enzyme as well as its temperature stability. The optimum temperature was 5 °C higher than that of the free enzyme and was significantly broader. The thermal inactivation rate constants for free and immobilised preparations at 70 °C were calculated aski (free)1.06 × 10−1min−1andki (imm)2.68 × 10−2min−1, respectively. The immobilised enzyme activity was found to be quite stable in the repeated experiments.© 2002 Society of Chemical Industry
Relaxation peak broadening and polymer chain dynamics in aramid‐fiber‐reinforced nylon‐66 microcomposites
Authors: Ryabov Ya. E. , Nuriel H. , Marom G. , Feldman Yu. 
Published: December 2002

AbstractThe relationship between the parameter of symmetric broadening of the glass‐transition relaxation process and the structure of aramid‐fiber‐reinforced nylon‐66 microcomposites is investigated in this article. The approach is based on a previously derived model that sets a quantitative interrelation between the Cole–Cole parameter α, the relaxation time, and the fractal dimension of a mobile polymer segment. The microcomposite, the dielectric response of which reflects the transcrystallinity effects, indeed exhibits significantly different values, such as higher Kirkwood correlation factor and α exponent values, in comparison with the control materials, and this indicates its different crystalline morphology and perhaps lower order in the amorphous phase. However, at this stage, it is still difficult to establish a quantitative relationship with the polymer chain dynamics. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 217–223, 2003
Predictors of well‐structured and ill‐structured problem solving in an astronomy simulation
Authors: Shin Namsoo , Jonassen David H. , McGee Steven 
Published: December 2002

AbstractThis study compared the problem‐solving skills required for solving well‐structured problems and ill‐structured problems in the context of an open‐ended, multimedia problem‐solving environment in astronomy. Two sets of open‐ended questions assessed students' abilities for solving well‐structured and ill‐structured problems. Generalized, rubric scoring systems were developed for assessing problem‐solving skills. Instruments were also developed and administered to assess cognitive and affective predictors of problem‐solving performance. By regressing the scores on the cognitive and affective predictors onto students' scores on the well‐structured and ill‐structured problems, we concluded that solving well‐structured and ill‐structured problems require different component skills. Domain knowledge and justification skills were significant predictors of well‐structured problem‐solving scores, whereas ill‐structured problem‐solving scores were significantly predicted by domain knowledge, justification skills, science attitudes, and regulation of cognition. Implications for problem solving in science education are presented. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 6–33, 2003
LIN-39/Hox triggers cell division and represses EFF-1/fusogen-dependent vulval cell fusion
Authors: Shemer Gidi , Podbilewicz Benjamin 
Published: December 2002

General mechanisms by which Hox genes establish cell fates are known. However, a few Hox effectors mediating cell behaviors have been identified. Here we found the first effector of LIN-39/HoxD4/Dfd inCaenorhabditis elegans. In specific vulval precursor cells (VPCs), LIN-39 represses early and late expression of EFF-1, a membrane protein essential for cell fusion. Repression of eff-1 is also achieved by the activity of CEH-20/Exd/Pbx, a known cofactor of Hox proteins. Unfused VPCs in lin-39(−);eff-1(−) double mutants fail to divide but migrate, executing vulval fates. Thus,lin-39 is essential for inhibition of EFF-1-dependent cell fusion and stimulation of cell proliferation during vulva formation.Supplemental material is available at http://www.genesdev.org.
Transcriptional Profile of theEscherichia coliResponse to the Antimicrobial Insect Peptide Cecropin A
Authors: Hong Robert W. , Shchepetov Mikhail , Weiser Jeffrey N. , Axelsen Paul H. 
Published: December 2002

ABSTRACTCationic antimicrobial peptides are believed to exert their primary activities on anionic bacterial cell membranes; however, this model does not adequately account for several important structure-activity relationships. These relationships are likely to be influenced by the bacterial response to peptide challenge. In order to characterize the genomic aspect of this response, transcription profiles were examined forEscherichia coliisolates treated with sublethal and lethal concentrations of the cationic antimicrobial peptide cecropin A. Transcript levels for 26 genes changed significantly following treatment with sublethal peptide concentrations, and half of the transcripts corresponded to protein products with unknown function. The pattern of response is distinct from that following treatment with lethal concentrations and is also distinct from the bacterial response to nutritional, thermal, osmotic, or oxidative stress. These results demonstrate that cecropin A induces a genomic response inE. coliapart from any lethal effects on the membrane and suggest that a complete understanding of its mechanism of action may require a detailed examination of this response.
Antimicrobial Susceptibilities of
Campylobacter
Strains Isolated from Finnish Subjects Infected Domestically or from Those Infected Abroad
Authors: Rautelin Hilpi , Vierikko Antti , Hänninen Marja-Liisa , Vaara Martti 
Published: December 2002

ABSTRACT

The in vitro susceptibilities of 678
Campylobacter jejuni
and
Campylobacter coli
strains isolated from stool samples of the same number of Finnish subjects were studied. A total of 523 patients, representing inhabitants from throughout Finland, had not traveled abroad within the 2 weeks prior to becoming ill, whereas 155 persons had presumably acquired their infections abroad. The antimicrobial agents studied were erythromycin, ciprofloxacin, levofloxacin, trovafloxacin, and moxifloxacin. The MICs of these antimicrobial agents were determined by the agar dilution method. The growth of all domestic isolates was inhibited by erythromycin at concentrations of 4 μg/ml, and for these isolates the fluoroquinolone MICs at which 90% of isolates are inhibited (MIC
90
s) ranged from 0.06 to 0.5 μg/ml. For the foreign isolates, the erythromycin MIC
90
was still low (4 μg/ml), but their susceptibilities to fluoroquinolones were clearly reduced (MIC
90
s, 8 to 64 μg/ml). Of the four different fluoroquinolones studied, ciprofloxacin was the least active (MIC
90
, 64 μg/ml).
Structure-Activity Relationships for Inhibition of Cysteine Protease Activity and Development of
Plasmodium falciparum
by Peptidyl Vinyl Sulfones
Authors: Shenai Bhaskar R. , Lee Belinda J. , Alvarez-Hernandez Alejandro , Chong Pek Y. , Emal Cory D. , Neitz R. Jeffrey , Roush William R. , Rosenthal Philip J. 
Published: December 2002

ABSTRACT

The
Plasmodium falciparum
cysteine proteases falcipain-2 and falcipain-3 appear to be required for hemoglobin hydrolysis by intraerythrocytic malaria parasites. Previous studies showed that peptidyl vinyl sulfone inhibitors of falcipain-2 blocked the development of
P. falciparum
in culture and exerted antimalarial effects in vivo. We now report the structure-activity relationships for inhibition of falcipain-2, falcipain-3, and parasite development by 39 new vinyl sulfone, vinyl sulfonate ester, and vinyl sulfonamide cysteine protease inhibitors. Levels of inhibition of falcipain-2 and falcipain-3 were generally similar, and many potent compounds were identified. Optimal antimalarial compounds, which inhibited
P. falciparum
development at low nanomolar concentrations, were phenyl vinyl sulfones, vinyl sulfonate esters, and vinyl sulfonamides with P
2
leucine moieties. Our results identify independent structural correlates of falcipain inhibition and antiparasitic activity and suggest that peptidyl vinyl sulfones have promise as antimalarial agents.
In Vitro Susceptibilities to and Bactericidal Activities of Garenoxacin (BMS-284756) and Other Antimicrobial Agents against Human Mycoplasmas and Ureaplasmas
Authors: Waites Ken B. , Crabb Donna M. , Bing Xue , Duffy Lynn B. 
Published: December 2002

ABSTRACT

The in vitro susceptibilities to garenoxacin (BMS-284756), an investigational des-fluoroquinolone, and eight other agents were determined for 63
Mycoplasma pneumoniae
, 45
Mycoplasma hominis
, 15
Mycoplasma fermentans
, and 68
Ureaplasma
sp. isolates. Garenoxacin was the most active quinolone, inhibiting all isolates at ≤1 μg/ml. The garenoxacin MIC at which 90% of isolates are inhibited (MIC
90
s; ≤0.008 μg/ml) was at least 4-fold less than those of moxifloxacin and clindamycin, 8-fold less than that of sparfloxacin, and 64-fold less than those of levofloxacin and ciprofloxacin for
M. pneumoniae
. For
M. hominis
, the garenoxacin MIC
90
(≤0.008 μg/ml) was 4-fold less than those of clindamycin and moxifloxacin, 8-fold less than that of sparfloxacin, and 64-fold less than those of levofloxacin and ciprofloxacin. All 15
M. fermentans
isolates were inhibited by garenoxacin at concentrations ≤0.008 μg/ml, making it the most active drug tested against this organism. For
Ureaplasma
spp., the garenoxacin MIC
90
(0.25 μg/ml) was equivalent to those of moxifloxacin and doxycycline, 4-fold less than those of levofloxacin and sparfloxacin, 8-fold less than that of azithromycin, and 32-fold less than that of ciprofloxacin. Garenoxacin and the other fluoroquinolones tested were demonstrated to have bactericidal activities against
M. pneumoniae
and
M. hominis
by measurement of minimal bactericidal activities and by time-kill studies. Further study of garenoxacin is required, as it has great potential for use in the treatment of infections due to mycoplasmas and ureaplasmas.
The Proton Channel Is the Minimal Structure of ATP Synthase Necessary and Sufficient for Microcin H47 Antibiotic Action
Authors: Rodríguez Eliana , Laviña Magela 
Published: December 2002

ABSTRACT

It had been previously determined that the presence of F
o
F
1
ATP synthase was required for microcin H47 antibiotic action. In this work, microcin-resistant
atp
mutants were genetically analyzed. Their mutations, originated by Tn
5
insertion, in all cases were found to affect determinants for the F
o
portion of ATP synthase. To discern if microcin action required the presence of the entire complex or if the F
o
proton channel would suffice, recombinant plasmids carrying different segments of the
atp
operon were constructed and introduced into an
atp
deletion strain. The phenotypic analysis of the strains thus obtained clearly indicated that the presence of the F
o
proton channel was absolutely required for microcin H47 action, while the F
1
catalytic portion was found to be dispensable. Furthermore, when any of the three components of the proton channel was missing, total resistance to the antibiotic ensued. Complementation analysis between
atp
::Tn
5
chromosomal mutations and recombinant
atp
plasmid constructions further supported the idea that the proton channel would be the minimal structure of the ATP synthase complex needed for microcin H47 antibiotic action.
Discrepancies between Protease Inhibitor Concentrations and Viral Load in Reservoirs and Sanctuary Sites in Human Immunodeficiency Virus-Infected Patients
Authors: Solas Caroline , Lafeuillade Alain , Halfon Philippe , Chadapaud Stéphane , Hittinger Gilles , Lacarelle Bruno 
Published: December 2002

ABSTRACT
The variable penetration of antiretroviral drugs into sanctuary sites may contribute to the differential evolution of human immunodeficiency virus (HIV) and the emergence of drug resistance. We evaluated the penetration of indinavir, nelfinavir, and lopinavir-ritonavir (lopinavir/r) in the central nervous system, genital tract, and lymphoid tissue and assessed the correlation with residual viral replication. Plasma, cerebrospinal fluid (CSF), semen, and lymph node biopsy samples were collected from 41 HIV-infected patients on stable highly active antiretroviral therapy regimens to determine drug concentrations and HIV RNA levels. When HIV RNA was detectable, sequencing of the reverse transcriptase and protease genes was performed. Ratios of the concentration in semen/concentration in plasma were 1.9 for indinavir, 0.08 for nelfinavir, and 0.07 for lopinavir. Only indinavir was detectable in CSF, with a concentration in CSF/concentration in plasma ratio of 0.17. Differential penetration into lymphoid tissue was observed, with concentration in lymph node tissue/concentration in plasma ratios of 2.07, 0.58, and 0.21 for indinavir, nelfinavir, and lopinavir, respectively. HIV RNA levels were <50 copies/ml in all CSF samples of patients in whom HIV RNA was not detectable in plasma. HIV RNA was detectable in the semen of three patients (two patients receiving nelfinavir and one patient receiving lopinavir/r), and its detection was associated with multiple resistance mutations, while the viral load in plasma was undetectable. HIV RNA was detectable in all lymph node tissue samples. Differential drug penetration was observed among the three protease inhibitors in the sanctuary sites, but there was no correlation between drug levels and HIV RNA levels, suggesting that multiple factors are involved in the persistence of viral reservoirs. Further studies are required to clarify the role and clinical relevance of drug penetration in sanctuaries in terms of long-term efficacy and drug resistance.
Synergistic Activity of the N-Terminal Peptide of Human Lactoferrin and Fluconazole against
Candida
Species
Authors: Lupetti Antonella , Paulusma-Annema Akke , Welling Mick M. , Dogterom-Ballering Heleen , Brouwer Carlo P. J. M. , Senesi Sonia , van Dissel Jaap T. , Nibbering Peter H. 
Published: December 2002

ABSTRACT

In light of the need for new antifungal regimens, we report that at noncandidacidal concentrations, the lactoferrin-derived peptide hLF(1-11), which is highly active against fluconazole-resistant
Candida albicans
, acts synergistically with fluconazole against this yeast and a fluconazole-sensitive
C. albicans
strain as well as
C. glabrata
,
C. krusei
,
C. parapsilosis
, and
C. tropicalis
. When these yeasts were exposed to hLF(1-11) for 5 min and then incubated with fluconazole, they were killed effectively, while no candidacidal activity was observed when they were incubated first with fluconazole and then exposed to the peptide, indicating that the candidacidal activity is initiated by the peptide while fluconazole is only required during the effector phase. Investigations of the effect of azide, which inhibits mitochondrial respiration, on the activity of combinations of hLF(1-11) and fluconazole against fluconazole-resistant
C. albicans
revealed that it inhibits this activity, even when added during the effector phase only. As expected, azide inhibited the accumulation of rhodamine 123 in mitochondria and the production and release of ATP by
C. albicans
that occurred upon exposure to the combination of hLF(1-11) and fluconazole. Accordingly, oxidized ATP (oATP), an antagonist of ATP receptors, completely blocked the candidacidal activity of the hLF(1-11)-fluconazole combination, whereas oATP did not block the activity when its presence was restricted to the effector phase. The candidacidal activity of combinations of hLF(1-11) and fluconazole, which is initiated by the peptide through the involvement of energized mitochondria, renders fluconazole-resistant
C. albicans
sensitive to this azole.
Topoisomerase Targeting with and Resistance to Gemifloxacin in
Staphylococcus aureus
Authors: Ince Dilek , Zhang Xiamei , Silver L. Christine , Hooper David C. 
Published: December 2002

ABSTRACT

Gemifloxacin, a novel quinolone with potent activity against
Staphylococcus aureus
, was 8- to 16-fold more active against wild-type
S. aureus
than ciprofloxacin. The two- to fourfold increase in the MIC of gemifloxacin in genetically defined
grlBA
mutants and the twofold increase in a single
gyrA
mutant, supported by the low frequency of selection of resistant mutants at twice the MIC (7.4 × 10
−11
to 1.1 × 10
−10
), suggested similar targeting of the two enzymes by gemifloxacin. Dual mutations in both gyrase and topoisomerase IV caused a 64- to 128-fold increase in the MIC of gemifloxacin, similar to that seen with ciprofloxacin. Gemifloxacin also had similar activity in vitro against topoisomerase IV and gyrase purified from
S. aureus
(50% inhibitory concentrations of 0.25 and 0.31 μg/ml, respectively). This activity was 10- to 20-fold higher than that of ciprofloxacin for topoisomerase IV and 33-fold higher than that for gyrase. In contrast to the in vitro findings, only topoisomerase IV mutants were selected in first-step mutants. Overexpression of the NorA efflux pump had a minimal effect on resistance to gemifloxacin, and a mutation in the promoter region of the gene for NorA was selected only in the sixth step of serial selection of mutants. Our data show that although gemifloxacin targets purified topoisomerase IV and gyrase similarly in vitro, topoisomerase IV is the preferred target in the bacteria. Selection of novel resistance mutations in
grlA
requires further expansion of quinolone-resistance-determining regions, and their study may provide increased insight into enzyme-quinolone interactions.