bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of several lanthanide trichloride hydrates on the melting behavior and spherulitic superstructure of poly(ethylene oxide)
Authors: Tang Jianguo , Lee Cynthia K. S. , Belfiore Laurence A.
Published: August 2003

Binary mixtures of poly(ethylene oxide) (PEO) with the trichloride hydrates of lanthanum, cerium, europium, terbium, and ytterbium have been studied with calorimetry, polarized optical microscopy, and infrared spectroscopy. Melting‐point depression of the PEO‐rich phase occurs in all cases. At sufficiently high concentrations of the low molecular weight lanthanide complex, crystallization of the polymer is absent. The lighter lanthanides with larger ionic radii, such as lanthanum and cerium, are more effective in suppressing PEO crystallization from solution or the molten state because they are more oxophilic. The spherulitic superstructure of PEO disappears at rather low concentrations of the lanthanide salts, between 2 and 8 mol % Ln3+. Lanthanum and terbium are most efficient at disrupting the formation of PEO spherulites, and europium is least efficient. Infrared spectroscopy identifies twisting and wagging vibrational absorptions of CH2 groups in the polymer that are sensitive to the morphologies of these mixtures. Modifications of the PEO infrared absorbances in the presence of these five lanthanide salts correlate more closely with the presence or absence of major PEO melting, not the formation of a spherulitic superstructure. The phase behavior is rather simple, with no evidence of eutectic solidification upon cooling from the molten state. Multiple melting endotherms are observed in the differential scanning calorimetry heating traces of binary mixtures containing 8 mol % Yb3+ and between 10 and 20 mol % Eu3+, but the concentration dependence of these first‐order endothermic transitions is not characteristic of eutectic phase behavior. The presence of trivalent cations, such as Eu3+ or Yb3+, in these complexes perturbs the crystallization kinetics of PEO upon cooling from the molten state, as well as the melting behavior upon heating. Ion–dipole or electrostatic interactions between the lanthanide cation and the ether oxygen of PEO might alter the surface free energy at the periphery of the crystalline lamellae and perturb the chain‐folding characteristics of PEO. Consequently, coupling between the amorphous matrix and the PEO crystallites is strengthened, and this provides stability for the existence of multiple‐chain‐folded crystals composed of rather thin lamellae that could be responsible for multiple melting behavior. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2200–2213, 2003
Specific reversible melting of polyethylene
Authors: Androsch R. , Wunderlich B.
Published: August 2003

The specific reversibility of the crystallization and melting of linear and branched polyethylene has been determined as function of temperature by temperature‐modulated differential scanning calorimetry. The specific reversibility of crystallization and melting is defined as the ratio of the reversible enthalpy to the total enthalpy of the transition, both measured at the same temperature. This definition emphasizes a close connection between the reversible and irreversible parts of the transition. As one would expect, the crystal‐to‐melt transition of a given portion of a sample can only be reversible at a temperature close to its own temperature of irreversible melting. Reversible melting is absent at temperatures far from irreversible melting, and this is usually seen by experimentation as its zero‐entropy production melting temperature. The reversible change in the fold length, in contrast, is observed far from the melting temperature of the crystal involved. The specific reversibility of the crystallization and melting of polyethylene crystals may exceed 50% outside the temperature range of the main crystallization and melting. The specific reversibility seems rather independent of the branch concentration, and this points to similar mechanisms of the reversible transition in linear polyethylene of high crystallinity and in branched polyethylene of low crystallinity. The reversible transition is due to a local equilibrium at the crystal surface and is, therefore, largely independent of the overall morphology of the sample. In this study, a model is developed that is based on partial molecular melting, which avoids the need of molecular nucleation and permits, therefore, reversible melting as seen for small molecules in the presence of crystal nuclei. It provides an explanation of the rather large number of the crystals that may participate in reversible melting and allows a connection to the fully reversible crystallization of paraffins and the fully irreversible crystallization of extended‐chain crystals of high crystallinity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2157–2173, 2003
Impact of average free‐volume element size on transport in stereoisomers of polynorbornene. I. Properties at 35 °C
Authors: Wilks Broderick R. , Chung Won J. , Ludovice Peter J. , Rezac Mary R. , Meakin Pavla , Hill Anita J.
Published: August 2003

This article demonstrates that transport of gases through glassy polymers is significantly influenced not only by the absolute amount but also by the distribution of free volume. Two stereoisomers of polynorbornene with nearly equivalent total free volume, but markedly different average free‐volume sizes, were evaluated. The free‐volume element size was probed with positron annihilation lifetime spectroscopy, wide‐angle X‐ray scattering, gas sorption, and molecular modeling. The permeation, sorption, and diffusion of light gases were measured in each stereoisomer at 35 °C. All analytical techniques indicated that one isomer (labeled as Architecture II) had a larger average free‐volume element size but fewer elements. This isomer also had a very slightly higher bulk density (1.000 vs 0.992 g/cm3 for the other stereoisomer). Architecture II also had gas sorption and diffusion coefficients that were two to three times those of the less dense counterpart. These differences have been attributed to differences in the free‐volume element size available within the polymer matrix. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2185–2199, 2003
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

The 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

Laser 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

We 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

The 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

Picknpoints 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

Let 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

Mental 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

This 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

This 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

Objectives

Treatment 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.

Methods

We 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.

Results

We 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.

Conclusion

Growth 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

Objective

To detect fetal movements during non‐stressed cardiotocography to evaluate the validity of the Hewlett‐Packard Doppler ultrasound actograph in detecting fetal movements.

Methods

This 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.

Results

The 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.

Conclusions

Use 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

Persistent 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

An 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

Objective

To examine the detection rate of chromosomal abnormalities using a combination of nuchal translucency (NT) and maternal age in a United States population.

Methods

A 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.

Results

Chromosomal 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.

Conclusion

A 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

Objective

To determine the number of ultrasound examinations necessary for training sonographers to examine accurately the fetal nasal bone at 11–14 weeks' gestation.

Methods

Fifteen 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.

Results

In 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.

Conclusion

The 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

Objective

To evaluate the examination and measurement of fetal nasal bone at 10–14 weeks of gestation.

Methods

The 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.

Results

The 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).

Conclusions

The 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.
Peri‐ and intraventricular cerebral sonography in second‐ and third‐trimester high‐risk fetuses: a comparison with neonatal ultrasound and relation to neurological development
Authors: van Gelder‐Hasker M. R. , van Wezel‐Meijler G. , de Groot L. , van Geijn H. P. , de Vries J. I. P.
Published: August 2003

Objectives

To determine whether periventricular leukomalacia (PVL) and peri‐ and intraventricular hemorrhages can be detected in fetuses at risk for preterm birth and to establish the clinical significance of this finding.

Methods

Prenatal cerebral sonography was performed in 26 fetuses at risk for uteroplacental insufficiency on the day of inclusion into the study and weekly until delivery. Neonatal cerebral ultrasound examination was performed within 24 h of birth and biweekly until discharge. The infants underwent standardized neurological examinations.

Results

During 30 observations, 21/26 fetuses presented in a cephalic position. Successful visualization in the coronal and sagittal planes was significantly correlated with that of a control population (r = 0.615; 95% CI, 0.390–0.771). In 20/21 fetuses at least one observation was adequate for analysis. Eleven cerebral abnormalities were found in nine fetuses, periventricular echodensities in four, intraventricular hemorrhage in two, and localized thalamic densities in five. In six of these infants ultrasound abnormalities persisted after birth. Neurological follow‐up at 24 months demonstrated abnormalities in three infants, two infants were normal and one was lost to follow‐up. The three infants with normal ultrasound results after birth had a normal follow‐up. Five infants with normal antenatal ultrasound results showed ultrasound abnormalities during the neonatal period; four of them developed PVL Grade 1 and one developed PVL Grade 2. The follow‐up of two of these infants was normal, two died and one developed spastic tetraplegia. Abnormal antenatal brain sonography was significantly correlated with gestational age at birth (r = 0.487; P = 0.029).

Conclusion

Peri‐ and intraventricular echodensities can be detected reliably before birth in fetuses at high risk for uteroplacental insufficiency. When abnormalities persist, there is a high risk for an adverse outcome. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Intra‐ and interoperator variability in fetal nasal bone assessment at 11–14 weeks of gestation
Authors: Senat M. V. , Bernard J. P. , Boulvain M. , Ville Y.
Published: August 2003

Objectives

Examination of the fetal nasal bones by ultrasound between 11 and 14 weeks of gestation has been proposed as an additional tool in the detection of trisomy 21 in a high‐risk population. However the variability in the identification of fetal nasal bones by ultrasound has not yet been investigated. The aim of this study was to assess the intraobserver and interobserver reproducibility of fetal nasal bone identification by ultrasound between 11 and 14 weeks of gestation.

Methods

A total of 1040 consecutive ultrasound examinations were performed at 11–14 weeks of gestation for nuchal translucency (NT) measurement and nasal bone identification by ultrasound. A total of 657 consecutive video‐loops were assessed by three experienced operators. Each operator assigned cases to one of three categories, namely present, uncertain or absent nasal bones, and the results were compared between operators. To assess the intraoperator variability each operator reviewed 100 randomly selected videos out of the 657 loops and again used the same classification. Results were compared by pairwise unweighted and weighted Kappa index to evaluate the inter‐ and intraoperator variability.

Results

Among the 1040 fetuses, there were 51 (4.9%) with an NT measurement above the 95th centile. Nasal bones were identified by ultrasound in 948, not seen in eight and impossible to assess in 84 fetuses. Four fetuses had trisomy 21 including three with absent nasal bones and increased NT and one with present nasal bones and normal NT. The Kappa and weighted Kappa values for interoperator variability between the three operators were between 0.26 and 0.37 and 0.33 and 0.44, respectively. The Kappa and weighted Kappa values for intraoperator variability were between 0.35 and 0.48 and 0.43 and 0.55, respectively.

Conclusion

The assessment of fetal nasal bones is only fairly reproducible. Although the performance of the test in fetuses at high risk for trisomy 21 has been reported to be good, its implementation as an additional screening technique in the general population must be accompanied by teaching and quality control programs. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Conjoined twins in a triplet pregnancy: early prenatal diagnosis with three‐dimensional ultrasound and review of the literature
Authors: Sepulveda W. , Munoz H. , Alcalde J. L.
Published: August 2003

We report two cases of conjoined twins complicating a triplet pregnancy diagnosed by two‐dimensional ultrasound in the first trimester and evaluated further by three‐dimensional ultrasound. A review of the literature over the last 30 years revealed 11 other cases diagnosed prenatally by ultrasound. Overall, three (23%) of these 13 pregnancies were achieved by assisted reproductive techniques and 10 (77%) were diagnosed before 18 weeks. Four women opted for termination of the whole pregnancy and three were managed expectantly, with two delivering before 32 weeks. Two monochorionic pregnancies underwent selective feticide with intrauterine demise of the non‐conjoined fetus in both cases. All four dichorionic pregnancies undergoing selective termination or spontaneous embryo reduction to singleton in the first trimester resulted in term delivery of the non‐conjoined fetus. The rare condition of conjoined twins in a triplet pregnancy poses a significant obstetric challenge from both diagnostic and management points of view. Accurate determination of chorionicity in these cases plays a critical role in determining management and outcome. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Delta‐NT or NT MoM: which is the most appropriate method for calculating accurate patient‐specific risks for trisomy 21 in the first trimester?
Authors: Spencer K. , Bindra R. , Nix A. B. J. , Heath V. , Nicolaides K. H.
Published: August 2003

Objective

To assess whether in screening for trisomy 21 by nuchal translucency (NT) the delta or the multiples of the median (MoM) approach is the most appropriate method for calculating accurate individual patient‐specific risks.

Methods

Data on fetal NT and crown–rump length from 128 030 unaffected and 428 trisomy 21 pregnancies, measured by sonographers who had obtained The Fetal Medicine Foundation Certificate of Competence in the 11–14‐Week Scan, were used. We examined first, if the distribution of NT MoM and log10(NT MoM) was Gaussian; second, if the standard deviation of the distributions did not change with gestation; and third, if the median MoM in the affected population was a constant proportion of the median for unaffected pregnancies. All of these features are required to underpin the MoM approach. NT distributions and those of delta‐NT were also analyzed. A non‐parametric kernel density method was then used to assess the validity of both methods. Errors in the estimation of individual patient‐specific risks using the MoM approach were assessed.

Results

In the unaffected pregnancies, the distributions of NT MoM and log10(NT MoM) were not Gaussian and the standard deviation of log10(NT MoM) decreased with gestation. In the trisomy 21 pregnancies, the median NT MoM decreased significantly with gestation, whereas the median delta‐NT did not change with gestation. The non‐parametric density approach showed that contours of constant likelihood ratio were parallel to the gestational age‐dependent median NT values, thus supporting the delta‐NT approach. The NT MoM approach resulted in women being given an overestimate of risk for trisomy at 11 weeks and a considerable underestimate of risk at 13 weeks.

Conclusion

In the calculation of risk for trisomy 21 by NT the NT MoM approach is inaccurate and inappropriate because the underlying assumptions are not valid. In contrast, the delta‐NT approach gives accurate estimates of risks. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Is there a relationship between estimated fetal weight and umbilical artery Doppler impedance indices?
Authors: Owen P. , Murphy J. , Farrell T.
Published: August 2003

Objective

To establish whether there is a relationship between estimated fetal weight (EFW) and umbilical artery Doppler waveform impedance indices in the third trimester.

Methods

The pulsatility index (PI) and S/D (systolic/diastolic) ratio were obtained together with the EFW from 274 low‐risk pregnancies. Measurements were made at fortnightly intervals from 30 weeks' gestation until delivery. A relationship between the two impedance indices and EFW was sought at gestational age ranges of 30–32, 33–35, 36–38 and 39–41 weeks.

Results

There were 918 pairs of PI (with S/D) and EFW available for analysis. The mean of the impedance indices decreased with advancing gestational age as expected. There was no clinically relevant correlation between impedance indices and EFW within any of the gestational age ranges.

Conclusion

Impedance indices from the umbilical artery Doppler waveform decrease with advancing gestational age due, at least partially, to expansion of the placental vascular tree. Within narrow gestational age ranges in the third trimester, there is no meaningful correlation between fetal weight and impedance indices. It is therefore not necessary to adjust umbilical artery Doppler impedance indices to account for fetal size. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Doppler sonography for predicting fetal anemia caused by massive fetomaternal hemorrhage
Authors: Sueters M. , Arabin B. , Oepkes D.
Published: August 2003

Fetomaternal hemorrhage (FMH) can cause severe anemia in the fetus. Untreated, this may cause hydrops or even fetal death. However, correct diagnosis of FMH followed by blood transfusion can prevent these life‐threatening consequences. We describe two cases in which fetal anemia was suspected because of maternal reporting of decreased or absent fetal movements, the detection of a sinusoidal heart rate pattern and increased blood flow velocities of the middle cerebral artery and umbilical vein. Together with the Betke–Kleihauer test showing fetal cells in the maternal circulation, this led to the correct diagnosis of severe fetal anemia caused by FMH. A Cesarean section was performed within a few hours. Both neonates were severely anemic and received immediate blood transfusions. They are currently alive and well. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Reference leaks for sniffer leak detectors
Authors: Jitschin W.
Published: August 2003

Bei der Dichtheitsprüfung und Lecksuche mit Prüfgas muss die ordnungsgemäße Funktion und die Empfindlichkeit des benutzten Gerätes mittels zertifizierter Prüflecks überwacht werden. Beim sogenannten Schnüffelbetrieb wird das zu testende Bauteil mit dem Prüfgas unter Überdruck gesetzt, so dass bei Vorhandensein eines Lecks das Prüfgas nach Atmosphäre ausströmt. Das atmosphärische Gas wird vom benutzten Gerät angesaugt und auf den Gehalt an Prüfgas untersucht. Zur Überwachung der Gerätefunktion gibt es kommerzielle Prüflecks für verschiedene Gase, die einen definierten Leckagestrom liefern. Aufbau und Eigenschaften eines derartigen kommerziellen Prüflecks werden beschrieben. Das Prüfleck besitzt einen internen Gasvorrat und eine Kapillare als Leckelement. Da der Eingangsdruck der Kapillare mittels eines Druckreglers konstant gehalten wird, bleibt der Leckagestrom über mehrere Jahre konstant, auch wenn der Druck im Gasvorrat allmählich abnimmt. Die Kalibrierung des Leckagestroms mittels Volumenstrommessung wird detailliert diskutiert. Die Messung des Volumenstroms kann mit einem Flüssigkeitstropfen in einer Messkapillare oder mit einem Verdrängerkolben in einer Dosierspritze erfolgen.
Applications of surface technology in space
Authors: Luther Wolfgang
Published: August 2003

Immer anspruchsvollere Missionen zur wissenschaftlichen Erkundung des Weltraums und die zunehmende Nutzung satellitengestützter Dienstleistungen in den Bereichen Telekommunikation, Navigation und Erdbeobachtung erfordern in Zukunft die Entwicklung effizienterer, kostengünstigerer und widerstandsfähigerer Raumfahrttechniken und ‐systeme. Eine vom Deutschen Zentrum für Luft‐ und Raumfahrt (DLR e.V.) in Auftrag gegebene Untersuchung des VDI‐Technologiezentrums in Düsseldorf zeigt, dass die Nanotechnologie, insbesondere im Bereich der Oberflächentechnik, signifikante Lösungsbeiträge und technologische Durchbrüche für die Entwicklung zukünftiger Raumfahrtsysteme liefern könnte. Anwendungsbeispiele in den Bereichen reibungs‐ und verschleißmindernde Schichten, thermische Schutzschichten, Magnetoelektronik, Röntgenastronomie und Dünnschichtechnologien für Raumfahrtstrukturen werden vorgestellt.
Developments and trends in the coating industry
Authors: Wijngaard Jan H. , Schütze Andreas
Published: August 2003

Die technische Entwicklung von PVD‐Beschichtungen eröffnete in den letzten Jahrzehnten einen breiten Markt mit weiter großen Wachstumsraten. Neben dem traditionellen Markt für Werkzeuge in der Zerspanung stehen zunehmend Märkte wie das Stanzen und Umformen sowie Großserienbeschichtungen von Bauteilen im Mittelpunkt des Interesses. Nach Jahren starken Wachstums mit gesteigertem Wettbewerbsdruck gilt es nun das Produktportfolio sowie die Produktivität an die strategische Ausrichtung des jeweiligen Unternehmens anzupassen.
Superhard amorphous carbon films
Authors: Schultrich Bernd
Published: August 2003

Kohlenstoffschichten zeichnen sich durch die mit ihnen erreichbaren besonderen Eigenschaften und durch ihre strukturelle Vielfalt aus. Amorphe Kohlenstoffschichten mit überwiegend tetragonaler Bindung (ta‐C‐Schichten) haben durch die Kombination von extremer Härte und geringer Adhäsionsneigung ein hohes Anwendungspotential als tribologische Schutzschichten. Mit den gepulsten Vakuumbogenverfahren stehen industriell einsetzbare Technologien zur Abscheidung derartiger Schichten zur Verfügung.
Distributional analysis of boundary value problems in half‐spaces – exemplified by Melan's problem of elastostatics
Authors: Kirchner G.
Published: August 2003

Using a result on the ${\cal C}^\infty$‐dependence (with respect to a distinguished variable) of solutions to partially hypoelliptic operators, we present a definition for Green's function which allows to prove a representation theorem. Afterwards we discuss the construction of a Green's matrix for Melan's problem of elastostatics using the reflection principle and single layer potentials. This involves the solution of convolution equations as well as the explicit computation of convolutions. In this special case also the question of uniqueness is investigated.
The linear stability of a viscoelastic jet (liquid cylinder) surrounded by another viscoelastic fluid
Authors: Brunn P.O. , Ryssel E.
Published: August 2003

The linear stability of a viscoelastic liquid thread surrounded by another viscoelastic liquid is studied. If in the undisturbed state there is no relative motion between the two liquids the results hold without requiring any rheological modeling of the liquids. The complex viscosity, or equivalently the complex modulus will govern the stability behaviour. If in the undisturbed state there is a relative motion (say of velocity u), then model fluids are required and the present analysis will be the model‐free u → 0 limit of such studies.
On the lack of analytic solutions of the Van der Pol oscillator
Authors: Panayotounakos D.E. , Panayotounakou N.D. , Vakakis A.F.
Published: August 2003

In this work it is shown that by a series of transformations the classical Van der Pol oscillator can be exactly reduced to Abel's equations of the second kind. The absence of exact analytic solutions in terms of known (tabulated) functions of the reduced equations leads to the conclusion that there are no exact solutions of the Van der Pol oscillator in terms of known (tabulated) functions. In the limits or small or large values of the parameter ϵ the reduced equations are amenable to asymptotic analysis. For the case of large values of the parameter (relaxation oscillations) an analytic solution to the problem is provided that is exact up to O(ϵ‐2).
Finite difference methods for multi time scale differential algebraic equations
Authors: Pulch R.
Published: August 2003

In radio frequency applications, electronic circuits include oscillatory signals with widely separated time scales. Thus transient analysis demands a large amount of computation. A multidimensional signal model yields an alternative approach. This strategy causes savings in computation time and memory, if the arising partial differential algebraic equation (PDAE) is solved efficiently. For this purpose, we construct a specific finite difference method, which is based on the information transport in the PDAE system. Test results confirm that both PDAE model and corresponding finite difference technique are suitable for simulating driven oscillators.
Steady two‐dimensional asymmetric stagnation point flow of a micropolar fluid
Authors: Lok Y.Y. , Amin N. , Pop I.
Published: August 2003

Numerical solutions are presented for the steady two‐dimensional boundary‐layer flow of a micropolar fluid near an asymmetric plane stagnation point. The transformed non‐similar boundary‐layer equations are solved numerically using an implicit finite‐difference method known as Keller‐box method. Numerical results are given for the reduced velocity and microrotation profiles, as well as for the reduced skin friction coefficient when the material parameter K takes the value K = 0 (Newtonian fluid), 0.5, 1, 1.5, 2, 2.5, and 3. Important features of these flow characteristics are shown on graphs and in tables. Comparisons with existing solutions for both symmetric and asymmetric stagnation point flow cases are given and it is shown that these results are in very good agreement. Discussion of the flow characteristics is also made.
New results for the normal shock in inviscid flow at a curved surface
Authors: Zierep J.
Published: August 2003

The well known problem of a normal shock in inviscid flow at a curved wall is discussed again. Behind the shock we have in general a singularity for the gradients of velocity and pressure. This singularity is discussed on the one hand for the full Euler equations with shock equations and on the other hand for the Small Disturbance Transonic equations. Some misunderstandings and open questions in the past are corrected and answered. The solutions are of interest for similar problems in Gasdynamics and for adaption of the local grids for CFD‐methods.
Semicontinuity of multifunctions and a stochastic fluid oscillator
Authors: Fritsch H.
Published: August 2003

In this paper on stochastic differential inclusions with set‐valued drift, we will consider the possible existence of strong solutions in the case of a kind of lower semicontinuous multifunctions as well as of upper semicontinuous ones. The dispersion matrix conditions are weakened in the classical way. To show existence results for such inclusions, we will use a locally Lipschitzean approximation of lower semicontinuous multifunctions. A set‐valued stochastic system with an upper semicontinuous drift will be used to describe the motion of a fluid oscillator with small random perturbations.