bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeation measurements in ethylene‐1‐hexene, ethylene‐1‐octene, and ethylene‐1‐dodecene copolymers synthesized with metallocene catalysts
Authors: Laguna M. F. , Cerrada M. L. , Benavente R. , Pérez E. , Quijada R. 
Published: August 2003

AbstractThe permeation behavior of different ethylene‐1‐hexene, ethylene‐1‐octene, and ethylene‐1‐dodecene copolymers synthesized with metallocene catalysts has been analyzed. These copolymers cover a wide range of comonomer contents, so their crystallinities display rather considerable variations. The results for the permeability to oxygen of the different ethylene copolymers show that the main factor influencing the permeability is the noncrystalline fraction, although some influence of the kind of comonomer may also be present, which may be explained by the fact that when the alkyl branch of the α‐olefin is longer, there is an increase in the free volume in the amorphous and interfacial regions, causing slightly higher values of the permeability coefficient. From the results with different gases, it follows that, in general, an increase in the size of the penetrant (as expressed by its kinetic diameter or critical molar volume) leads to an increase in the solubility and a decrease in the diffusion coefficient. A wide range of permeability values is covered by these ethylene copolymers, depending basically on the crystallinity of the sample, but the permselectivity of CO2 with respect to oxygen (and probably between other pairs of gases) does not differ very much among the different copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2174–2184, 2003
Raman spectroscopic investigation of the phase behavior and phase transitions in a poly(methyl methacrylate)‐carbon dioxide system
Authors: Takahashi Masayoshi , Yamamoto Yoshitaka , Nawaby A. Victoria , Handa Y. Paul 
Published: August 2003

AbstractLaser Raman spectroscopy, in conjunction with an optical high‐pressure cell, was used to investigate the poly(methyl methacrylate)‐carbon dioxide system. The Raman shifts associated with carbon dioxide molecules in the gas phase and those dissolved in the polymer were used to derive sorption kinetics of carbon dioxide and the carbon dioxide‐induced phase changes in the polymer. Measurements were made in the temperature and pressure ranges in which this system is known to exhibit retrograde vitrification behavior. The Raman results on the sorption kinetics and on the onset of plasticization were in agreement with those obtained by gravimetric and calorimetric techniques, respectively. This technique provides a versatile and rapid way of characterizing polymer‐gas systems and information that so far has been obtainable only through painstaking and time‐consuming techniques. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2214–2217, 2003
Randomly coloring graphs with lower bounds on girth and maximum degree
Authors: Dyer Martin , Frieze Alan 
Published: August 2003

AbstractWe consider the problem of generating a randomq‐coloring of a graphG= (V,E). We consider the simple Glauber Dynamics chain. We show that if the maximum degree Δ >c1lnnand the girthg>c2ln Δ (n= |V|) for sufficiently largec1,c2, then this chain mixes rapidly providedq/Δ > β, where β ≈ 1.763 is the root of β =e1/β. For this class of graphs, this beats the 11Δ/6 bound of VigodaE. Vigoda, Improved bounds for sampling colorings, Proc 40th Annu IEEE Symp Foundations of Computer Science, 1999, pp. 51–59for general graphs. We extend the result to random graphs. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 167–179, 2003
The computational complexity of two‐state spin systems
Authors: Goldberg Leslie Ann , Jerrum Mark , Paterson Mike 
Published: August 2003

AbstractThe subject of this article is spin‐systems as studied in statistical physics. We focus on the case of two spins. This case encompasses models of physical interest, such as the classical Ising model (ferromagnetic or antiferromagnetic, with or without an applied magnetic field) and the hard‐core gas model. There are three degrees of freedom, corresponding to our parameters β, γ, and μ. Informally, β represents the weights of edges joining pairs of “spin blue” sites, γ represents the weight of edges joining pairs of “spin green” sites, and μ represents the weight of “spin green” sites. We study the complexity of (approximately) computing the partition function in terms of these parameters. We pay special attention to the symmetric case μ = 1. Exact computation of the partition function Z is NP‐hard except in the trivial case βγ = 1, so we concentrate on the issue of whether Z can be computed within small relative error in polynomial time. We show that there is a fully polynomial randomised approximation scheme (FPRAS) for the partition function in the “ferromagnetic” region βγ ≥ 1, but (unless RP = NP) there is no FPRAS in the “antiferromagnetic” region corresponding to the square defined by 0 < β < 1 and 0 < γ < 1. Neither of these “natural” regions—neither the hyperbola nor the square—marks the boundary between tractable and intractable. In one direction, we provide an FPRAS for the partition function within a region which extends well away from the hyperbola. In the other direction, we exhibit two tiny, symmetric, intractable regions extending beyond the antiferromagnetic region. We also extend our results to the asymmetric case μ ≠ 1. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 133–154, 2003
On smallest triangles
Authors: Grimmett Geoffrey , Janson Svante 
Published: August 2003

AbstractPicknpoints independently at random in ℝ2, according to a prescribed probability measure μ, and let Δ≤ Δ≤ … be the areas of the () triangles thus formed, in nondecreasing order. If μ is absolutely continuous with respect to Lebesgue measure, then, under weak conditions, the set {n3Δ:i≥ 1} converges asn→ ∞ to a Poisson process with a constant intensity κ(μ). This result, and related conclusions, are proved using standard arguments of Poisson approximation, and may be extended to functionals more general than the area of a triangle. It is proved in addition that if μ is the uniform probability measure on the regionS, then κ(μ) ≤ 2/|S|, where |S| denotes the area ofS. Equality holds in that κ(μ) = 2/|S| ifSis convex, and essentially only then. This work generalizes and extends considerably the conclusions of a recent paper of Jiang, Li, and Vitányi. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 206–223, 2003
Perfect matchings in random uniform hypergraphs
Authors: Kim Jeong Han 
Published: August 2003

AbstractLet ℋ︁k(n, p) be the random k‐uniform hypergraph on V = [n] with edge probability p. Motivated by a theorem of Erdős and Rényi 7 regarding when a random graph G(n, p) = ℋ︁2(n, p) has a perfect matching, the following conjecture may be raised. (See J. Schmidt and E. Shamir 16 for a weaker version.) Conjecture. Let k|n for fixed k ≥ 3, and the expected degree d(n, p) = p(). Then

(Erdős and Rényi 7 proved this for G(n, p).) Assuming d(n, p)/n1/2 → ∞, Schmidt and Shamir 16 were able to prove that ℋ︁k(n, p) contains a perfect matching with probability 1 − o(1). Frieze and Janson 8 showed that a weaker condition d(n, p)/n1/3 → ∞ was enough. In this paper, we further weaken the condition to

A condition for a similar problem about a perfect triangle packing of G(n, p) is also obtained. A perfect triangle packing of a graph is a collection of vertex disjoint triangles whose union is the entire vertex set. Improving a condition p ≥ cn−2/3+1/15 of Krivelevich 12, it is shown that if 3|n and p ≫ n−2/3+1/18, then

© 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 111–132, 2003
Learners' mental models of metallic bonding: A cross‐age study
Authors: Coll Richard K. , Treagust David F. 
Published: August 2003

AbstractMental models of metallic bonding held by learners from three academic levels, secondary school (year 12), undergraduate, and postgraduate, were probed using semistructured interviews including the use of Interviews‐About‐Events focus cards depicting metallic properties and cards containing depictions of models from curriculum material. The learners in this study hold realist views about the bonding and structure for metallic substances and prefer the sea of electrons model. However, the undergraduate and postgraduate learners commonly utilized concepts from other models, such as the molecular orbital theory, to supplement their descriptions of their mental models. In addition, they were more critical of depicted models and held views of the continuous nature of metallic lattices that were more in accord with the scientific view. Few of the learners were able to describe the bonding in alloys, and although learners across all three academic levels offered reasonable explanations for the conductivity of metals, they were unable to explain malleability. It is recommended that it may be prudent to postpone the teaching of highly abstract mental models until later in an undergraduate degree program, since exposure to complex and abstract models is more appropriate for learners who wish to continue their studies in chemistry. © 2003 Wiley Periodicals, Inc. Sci Ed 87:685–707, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10059
Mediating mental models of metals: Acknowledging the priority of the learner's prior learning
Authors: Taber Keith S. 
Published: August 2003

AbstractThis paper describes the conceptualizations, or mental models, of the nature of the bonding and structure of metals of a group of U.K. college students. It is suggested that these mental models may be understood in terms of the students' prior learning about covalent and ionic bonding, and the prevalence of a common alternative conceptual framework for chemical bonding labeled “the octet framework.” This study illustrates the prominence of prior learning in channeling the interpretation of subsequent teaching, and highlights the significance of the decisions made by curriculum planners, textbook authors, and teachers on the order of presenting subject content, the degree of simplification of scientific models, and the selection and presentation of metaphors. © 2003 Wiley Periodicals, Inc. Sci Ed 87:732–758, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10079
Learning the electric field concept as oriented research activity
Authors: Furió C. , Guisasola J. , Almudí J. M. , Ceberio M. 
Published: August 2003

AbstractThis work is grounded in a constructivistic conception of the learning of science, more particularly on the model known as teaching–learning as oriented research. In accordance with this theoretical basis we have developed an empirical research project to investigate the teaching of electrostatics in high schools. The designs developed have enabled us to assess the learning achieved by the students from conceptual, procedural, and attitudinal stances. According to our findings we can say that the materials developed and the way we have worked with them have contributed to more significant learning and favored a more positive attitude toward the subject. © 2003 Wiley Periodicals, Inc. Sci Ed 87:640–662, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10100
Pelvic ultrasound evaluation in patients with Turner syndrome during treatment with growth hormone
Authors: Sampaolo P. , Calcaterra V. , Klersy C. , Alfei A. , De Leonardis C. , Maino M. , Larizza D. 
Published: August 2003

AbstractObjectivesTreatment with growth hormone (GH), alone or in combination with oxandrolone, is used in patients affected by Turner syndrome to improve growth velocity and adult height. Since GH interacts with gonadotropins in the stimulation of the human ovary, the aim of our study was to evaluate the possible effects of GH administration on uterine and ovarian characteristics.MethodsWe performed pelvic ultrasound assessment in 29 patients with Turner syndrome aged 7.5–16.6 years (19 with 45,X karyotype; 10 with variant karyotypes) before and during treatment with GH alone. Uterine volume and ovarian size and morphology were compared to those of 23 age‐matched girls with Turner syndrome not treated with GH. Both patients and controls were divided into prepubertal and pubertal groups. Cross‐sectional and longitudinal studies (before and every 6 months during GH treatment for 2 years) were performed.ResultsWe observed a significantly higher uterine anteroposterior diameter and volume in younger (≤ 11 years) GH‐treated Turner syndrome girls than in those who were untreated. Also visualization and heterogeneous echopattern of the ovaries were significantly more frequent in treated than in untreated Turner syndrome patients, particularly before the age of 11 years. The longitudinal study showed a significant increase in uterine volume, more related to treatment than to age. Spontaneous breast development and menarche were found more frequently in GH‐treated Turner syndrome girls.ConclusionGrowth hormone therapy can have a co‐gonadotropin role in patients with Turner syndrome. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Validity of the Hewlett‐Packard actograph in detecting fetal movements
Authors: de Wit A. C. , Nijhuis J. G. 
Published: August 2003

AbstractObjectiveTo detect fetal movements during non‐stressed cardiotocography to evaluate the validity of the Hewlett‐Packard Doppler ultrasound actograph in detecting fetal movements.MethodsThis was a prospective, observational study. Thirty healthy pregnant women were divided into two gestational age groups (Group I, 31 + 0 to 34 + 0 weeks, n = 15; Group II, 37 + 0 to 40 + 0 weeks, n = 15). A Hewlett‐Packard M‐1350‐A actocardiograph was used to make recordings of 45 min for each woman. Fetal movements were also detected sonographically by an observer and they were recorded independently by the pregnant woman. Ninety consecutive 30‐s periods were analyzed to study agreement between the three techniques.ResultsThe mean total agreement for fetal activity plus quiescence between ultrasound and the actograph was 63.7% for Group I, and 72.2% for Group II. In cases of fetal activity only, these values were 45.8% and 47.6%, respectively. Total agreements between ultrasound and the pregnant woman were 74.0% and 79.0%, respectively, for Groups I and II. Cohen's kappa values for total agreement between ultrasound and actograph were 0.31 (95% CI, 0.27–0.36), indicating ‘fair’ agreement in Group I, and 0.43 (95% CI, 0.38–0.47), indicating ‘moderate’ agreement in Group II.ConclusionsUse of the Hewlett‐Packard actograph may offer some additional information during routine cardiotocography. However, our results were disappointing; the technique appears not to be suitable for detailed recordings of fetal behavior, and may even be misleading when difficult cardiotocographic patterns have to be interpreted. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Myometrial trophoblastic implant as a complication of surgically induced first‐trimester termination of pregnancy
Authors: Pascual M. A. , Tresserra F. , Dexeus D. , Grases P. J. , Dexeus S. 
Published: August 2003

AbstractPersistent trophoblastic tissue has been described in the abdominal cavity after surgical treatment of tubal ectopic pregnancy. More infrequently the cause of the ectopic trophoblast is linked to uterine perforation due to surgically induced termination of pregnancy (TOP). Ultrasonographic images may suggest an ectopic pregnancy. A case of myometrial trophoblastic tissue implantation following surgically induced first‐trimester TOP is described. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Pelvic echinococcus mimicking multicystic ovary
Authors: Tampakoudis P. , Assimakopoulos E. , Zafrakas M. , Tzevelekis P. , Kostopoulou E. , Bontis J. 
Published: August 2003

AbstractAn unusual case of pelvic echinococcus cyst is presented, appearing initially on transvaginal ultrasound as a pelvic mass mimicking a multicystic ovary. A similar mass in the liver raised preoperatively the suspicion of echinococcosis, making an open surgical procedure preferable to laparoscopy. Diagnosis was confirmed pathologically after removal of the cyst. Though their location in the pelvis is rare, echinococcal cysts should be considered in the differential diagnosis of pelvic masses, especially in patients from endemic areas. Evaluation of previous medical history and current symptoms, together with the ultrasonographic findings, is important for correct diagnosis and appropriate management. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
First‐trimester screening for aneuploidy with fetal nuchal translucency in a United States population
Authors: Chasen S. T. , Sharma G. , Kalish R. B. , Chervenak F. A. 
Published: August 2003

AbstractObjectiveTo examine the detection rate of chromosomal abnormalities using a combination of nuchal translucency (NT) and maternal age in a United States population.MethodsA total of 2131 pregnancies with 2339 fetuses underwent NT screening from April 2000 to April 2002 in our ultrasound unit. Nuchal translucency was measured from 11 to 14 weeks' gestation. Fetal crown–rump length (CRL) was also measured. The risk for trisomy 21 was calculated from a combination of maternal age and fetal NT with the use of software provided by The Fetal Medicine Foundation (FMF). Sensitivity and false‐positive rates were calculated for different risk cut‐offs.ResultsChromosomal defects were diagnosed in 32 cases, including 12 cases of trisomy 21 and 10 cases of trisomy 18. The estimated risk based on maternal age and fetal NT was 1 in 300 or greater in 195 (8.3%) cases and these included 10/12 (83.3%) pregnancies with trisomy 21 and 9/10 (90.0%) pregnancies with trisomy 18.ConclusionA combination of maternal age and fetal NT provides an effective method of screening for chromosomal defects. Using ultrasound techniques and risk algorithms from The FMF, the performance of the test in an American population is similar to that described in international populations. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Learning curve for sonographic examination of the fetal nasal bone at 11–14 weeks
Authors: Cicero S. , Dezerega V. , Andrade E. , Scheier M. , Nicolaides K. H. 
Published: August 2003

AbstractObjectiveTo determine the number of ultrasound examinations necessary for training sonographers to examine accurately the fetal nasal bone at 11–14 weeks' gestation.MethodsFifteen sonographers with experience in measuring nuchal translucency were asked to examine the nasal bone during the routine 11–14‐week scan. The supervising doctor recorded if the sonographer succeeded in obtaining the correct image. Each sonographer performed a total of 140 examinations, and the data were analyzed in seven groups of 20 examinations. In a second study, two sonographers with extensive experience in examining the nasal bone examined independently 100 consecutive patients at a median fetal crown–rump length of 65 (45–84) mm and median gestational age of 12 (11–14) weeks and recorded whether the nasal bone was absent or present.ResultsIn the first group of 20 examinations, there was failure to obtain the correct image of the fetal profile in 1–5 (median, 4) cases. In the subsequent three groups, there was failure to obtain the correct image in 0–3 (median, 1) cases. In the fifth and sixth groups failure occurred in 0–2 (median, 0) cases and in the seventh group all sonographers obtained successful images of the fetal profile in all cases. One sonographer obtained successful images of all cases after the first 40 scans, four after the first 60 scans, six after the first 80 and two each after the first 100 and 120 scans. In the second study, there was agreement between the two sonographers that the nasal bone was absent in two and present in 98 of the 100 consecutive patients examined.ConclusionThe minimum number of scans required for an experienced sonographer to become competent in examining the fetal nasal bone is on average 80, with a range of 40–120. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Examination of fetal nasal bone and repeatability of measurement in early pregnancy
Authors: Kanellopoulos V. , Katsetos C. , Economides D. L. 
Published: August 2003

AbstractObjectiveTo evaluate the examination and measurement of fetal nasal bone at 10–14 weeks of gestation.MethodsThe study included 501 fetuses in 496 consecutive pregnant women attending for the routine first‐trimester ultrasound examination. The presence or absence of the fetal nasal bone was determined in the mid‐sagittal plane and the length was measured by one of four examiners (measurement A; n = 501). A second measurement was taken by the same examiner (B, n = 300) and a different examiner repeated the measurement (C, n = 200) whenever possible. Measurements were made to the nearest 0.1 mm. The duration of one hundred consecutive examinations was recorded, as was that of another 100 consecutive routine first‐trimester examinations without measuring the nasal bone.ResultsThe median nasal bone length was 1.6 (0.8–2.4) mm, the median gestational age was 12 (10–14) weeks and the median crown–rump length (CRL) was 63 (32–90) mm. The fetal profile was examined in all 501 cases and the fetal nasal bone was present in all but one case (99.8%). No transvaginal scans were needed for the examination of nasal bone only. The average time for the sonographic examination (8.3 min) was not significantly different from the average time for first‐trimester scans in which the fetal nasal bone was not measured (8.0 min). The fetal nasal bone length increased from 1.1 mm at a CRL of 35 mm to 2.1 mm at a CRL of 90 mm (nasal bone = 0.016 × CRL + 0.619, P < 0.001, r = 0.655). The repeatability coefficient for intraobserver measurements was 0.080 mm and the coefficient for interobserver measurements was similar (0.083 mm).ConclusionsThe nasal bone can be detected from 10 weeks of gestation onwards. Consistent visualization and repeatable measurement of fetal nasal bone can be performed by an experienced sonographer in the first trimester without extending the length of time required for scanning or introducing the need for transvaginal sonography. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.