bluuebunny/crossref_metadata_2025 huggingface dataset:
Existence and convergence for quasi‐static evolution in brittle fracture
Authors: Francfort Gilles A. , Larsen Christopher J.
Published: August 2003

This paper investigates the mathematical well‐posedness of the variational model of quasi‐static growth for a brittle crack proposed by Francfort and Marigo in [15]. The starting point is a time discretized version of that evolution which results in a sequence of minimization problems of Mumford and Shah type functionals. The natural weak setting is that of special functions of bounded variation, and the main difficulty in showing existence of the time‐continuous quasi‐static growth is to pass to the limit as the time‐discretization step tends to 0. This is performed with the help of a jump transfer theorem which permits, under weak convergence assumptions for a sequence {un} of SBV‐functions to its BV‐limit u, to transfer the part of the jump set of any test field that lies in the jump set of u onto that of the converging sequence {un}. In particular, it is shown that the notion of minimizer of a Mumford and Shah type functional for its own jump set is stable under weak convergence assumptions. Furthermore, our analysis justifies numerical methods used for computing the time‐continuous quasi‐static evolution. © 2003 Wiley Periodicals, Inc.
Cover Picture: Freely Suspended Actin Cortex Models on Arrays of Microfabricated Pillars (ChemPhysChem 8/2003)
Authors: Roos Wouter H. , Roth Alexander , Konle Johannes , Presting Hartmut , Sackmann Erich , Spatz Joachim P.
Published: August 2003

The cover picture shows the first demonstration of a biomimetic model of the cellular actin cortex. The actin filamental network imaged as a fluorescent micrograph (orange) is suspended on top of an array of microfabricated silicon pillars, schematically drawn in light blue. The actin network is obtained by polymerising actin filaments from a template provided by gold‐capped pillars. Subsequently adding filamin as actin‐crosslinking protein causes the formation of the ordered network within minutes. Find out more in the article by Spatz and co‐workers on pages 872–877.
Considerations for the development of real‐time dynamic testing using servo‐hydraulic actuation
Authors: Zhao J. , French C. , Shield C. , Posbergh T.
Published: August 2003

This paper presents a study of the use of servo‐hydraulic systems in the implementation of real‐time large‐scale structural testing methods in force control such as effective force testing (EFT) and in displacement control such as real‐time pseudodynamic testing (RPsD). Mathematical models for both types of control systems are presented and used to investigate the influences of servo‐systems on the overall system performance. Parameters investigated include the overall system dynamics, nonlinearities of servo‐systems, actuator damping, system mass including piston mass, and system response delay. Results of both numerical simulations and experiments showed that many of the influences of the servo‐hydraulic system that significantly affect the real‐time dynamic tests can be properly compensated through control schemes identified in this paper. Copyright © 2003 John Wiley & Sons, Ltd.
Evaluation of nitric oxide scavenging activity of certain spices in vitro: A preliminary study
Authors: Baliga Manjeshwar Shrinath , Jagetia Ganesh Chandra , Rao Shaival Kamalaksha , Babu S Kiran
Published: August 2003

The plant extracts of some commonly used spices were examined for their possible regulatory effect on nitric oxide (NO) levels using sodium nitroprusside as a NO donor in vitro. Most of the extracts tested demonstrated direct scavenging of NO and exhibited significant activity and the potency of scavenging activity was in the following order: Foeniculum vulgare (aqueous) > Citrus limettiodes > Murraya koenigii (seed, aqueous) > Murraya koenigii (leaf, aqueous) > Curcuma aromatica (aqueous) > Murraya koenigii (leaf, dichloromethane:methanol) > Mentha arvensis (chloroform) > Mentha arvensis (aqueous) > Curcuma longa > Gingko biloba > Foeniculum vulgare (dichloromethane:methanol) > Zingiber officinale (aqueous) > Curcuma aromatica (ethanolic) > Murraya koenigii (seed, dichloromethane:methanol). All the evaluated extracts exhibited a dose‐dependent NO scavenging activity. The aqueous extract of Foeniculum vulgare showed a greatest NO scavenging effect of 79.75% at 62.5 μg/mL as compared to the positive control, Gingko biloba where 36.22% scavenging was observed at similar concentration. The present results suggest that these spices might be potent and novel therapeutic agents for scavenging of NO and the regulation of pathological conditions caused by excessive generation of NO and its oxidation product, peroxynitrite.
Improved use of SNP information to detect the role of genes
Authors: Jannot A.‐S. , Essioux L. , Reese M.G. , Clerget‐Darpoux F.
Published: August 2003

A topical question in genetic association studies is the optimal use of the information provided by genotyped single‐nucleotide polymorphisms (SNPs) in order to detect the role of a candidate gene in a multifactorial disease. We propose a strategy called “combination test” that tests the association between a quantitative trait and all possible phased combinations of various numbers of SNPs. We compare this strategy to two alternative strategies: the association test that considers each SNP separately, and a multilocus genotype‐based test that considers the phased combination of all SNPs together. To compare these three tests, a quantitative trait was simulated under different models of correspondence between phenotype and genotype, including the extreme case when two SNPs interact with no marginal effects of each SNP. The genotypes were taken from a sample of 290 independent individuals genotyped for three genes with various number of SNPs (from 5–8 SNPs). The results show that the “combination test” is the only one able to detect the association when the two SNPs involved in disease susceptibility interact with no marginal effects. Interestingly, even in the case of a single etiological SNP, the “combination test” performed well. We apply the three tests to Genetic Analysis Workshop 12 (Almasy et al. [2001] Genet. Edpidemiol. 21:332–338) simulated data, and show that although there was no interactions between the etiological SNPs, the “combination test” was preferable to the two other compared methods to detect the role of the candidate gene. Genet Epidemiol 25:158–167, 2003. © 2003 Wiley‐Liss, Inc.
Hierarchical fuzzy segmentation of brain MR images
Authors: Kwon M. J. , Han Y. J. , Shin I. H. , Park H. W.
Published: August 2003

In brain magnetic resonance (MR) images, image segmentation and 3D visualization are very useful tools for the diagnosis of abnormalities. Segmentation of white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) is the basic process for 3D visualization of brain MR images. Of the many algorithms, the fuzzy c‐means (FCM) technique has been widely used for segmentation of brain MR images. However, the FCM technique does not yield sufficient results under radio frequency (RF) nonuniformity. We propose a hierarchical FCM (HFCM), which provides good segmentation results under RF nonuniformity and does not require any parameter setting. We also generate Talairach templates of the brain that are deformed to 3D brain MR images. Using the deformed templates, only the cerebrum region is extracted from the 3D brain MR images. Then, the proposed HFCM partitions the cerebrum region into WM, GM, and CSF. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 115–125, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10035
Image reconstructions from two orthogonal projections
Authors: Wang Yuanmei , Heng Pheng Ann , Wahl Friedrich M.
Published: August 2003

A vector entropy optimization‐based neural network approach is presented to handle image reconstructions from two orthogonal projections. An accurate and parallel reconstruction is attained with this method allowing parallel implementation. This is an attempt to extract the image information from two projections. It is especially meaningful for clinical applications and three‐dimensional modeling of the coronary arteries. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 141–145, 2003; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/ima.10036
Cultural variation and the psychological contract
Authors: Thomas David C. , Au Kevin , Ravlin Elizabeth C.
Published: August 2003

Literature on the psychological contract has made significant contributions to our understanding of the exchange relationship between employees and their employer. However, the influence of cultural differences on perceptions of the employment relationship has largely been neglected. We propose both cognitive and motivational mechanisms through which the cultural profiles of individuals influence (a) formation of the psychological contract, (b) perceptions of violations of the psychological contract, and (c) responses to perceived violations. General mechanisms for the influence of culture on the psychological contract are followed by specific examples of the influence of individualism and collectivism. Copyright © 2003 John Wiley & Sons, Ltd.
Using southern oscillation index phases to forecast sugarcane yields: a case study for northeastern Australia
Authors: Everingham Y. L. , Muchow R. C. , Stone R. C. , Coomans D. H.
Published: August 2003

Climate is a key driver of sugarcane productivity. Advance knowledge of the likely climate and its impact on production could add value to production, harvest and marketing efforts. A climate forecast system that incorporates five patterns or phases of the southern oscillation index is used to assess whether an early indication of sugarcane yield anomalies in Australia can be produced. Results indicate that, for certain sugarcane growing regions, the climate forecast system offers better estimates of the direction of the anomaly when compared with no climate forecast system. Improved results of the direction of the yield anomaly can be obtained some 7 months prior to the commencement of harvest. This information can then be used by marketers to plan better the customer allocations, shipping schedules and storage requirements for the next season. Advance knowledge of the crop size can also assist industry decision makers in scheduling when the harvest season should commence. Further research is required to determine if other climatic indices, such as sea surface temperatures, can improve yield estimation. Consideration also needs to be given to determining whether the magnitude and the direction of the yield anomaly can be more accurately forecasted with varying lead times. Copyright © 2003 Royal Meteorological Society
Precipitation trends in Sri Lanka since the 1870s and relationships to El Niño–southern oscillation
Authors: Malmgren Björn A. , Hulugalla Ranatunge , Hayashi Yousay , Mikami Takehiko
Published: August 2003

The last 130 years of fluctuations in precipitation associated with the Southwest Monsoon (summer monsoon), Northeast Monsoon (winter monsoon), First Intermonsoon, and Second Intermonsoon seasons have been analysed at 15 climate stations in Sri Lanka. Analyses of trends in the interannual seasonal series indicated statistically significant temporal changes in Southwest‐Monsoon‐related precipitation at five of the stations, with three stations showing enhanced rainfall (total of 100 mm/month over the entire time interval) and two stations a decrease in rainfall with time (total of 150 mm/month). In addition, one station experienced a decrease of both First and Second Intermonsoon rainfall over time (total of 80 mm/month). The stations showing loss of rainfall are confined to higher elevation areas and those exhibiting enhanced rainfall are located in the lowlands in the southwestern sector of Sri Lanka. None of the stations show any significant change in Northeast Monsoon precipitation through time. Most of the stations are shown to have received significantly greater amounts of Second Intermonsoon precipitation during El Niño years. The Second Intermonsoon rainfall is, on average, 70 mm/month greater during El Niño years. However, a few stations show increased Southwest Monsoon precipitation (May to September) during La Niña years. Two stations along the eastern and northern coastal areas receive, on average, between 14 and 20 mm/month more Southwest Monsoon rainfall during La Niña years than during El Niño years. Copyright © 2003 Royal Meteorological Society
Analysis and regionalization of northern European winter precipitation based on its relationship with the North Atlantic oscillation
Authors: Uvo Cintia B.
Published: August 2003

The relationship between the North Atlantic oscillation (NAO) and winter temperature and precipitation over northern Europe has long been known. However, its strength is variable within this region. In this paper, an analysis of the regional variability of the influence of the NAO on winter precipitation in northern Europe is developed using empirical orthogonal function analysis, cluster analysis and simple correlation. Results show that precipitation in most of the region studied is affected by the NAO, although with varying intensity. The NAO strongly influences winter precipitation along the Norwegian coast, in northern Sweden and in southern Finland. It is evident that the region on the lee side of the Scandes (the mountain chain between Norway and Sweden) is protected from the effects of the moist western winds from the Atlantic that, in turn, are strongly related to the NAO. As a result, precipitation in this shielded area is mainly related to southeasterly winds. Copyright © 2003 Royal Meteorological Society
On measuring quality of a probabilistic commodity forecast for a system that incorporates seasonal climate forecasts
Authors: Potgieter A. B. , Everingham Y. L. , Hammer G. L.
Published: August 2003

Regional commodity forecasts are being used increasingly in agricultural industries to enhance their risk management and decision‐making processes. These commodity forecasts are probabilistic in nature and are often integrated with a seasonal climate forecast system. The climate forecast system is based on a subset of analogue years drawn from the full climatological distribution. In this study we sought to measure forecast quality for such an integrated system. We investigated the quality of a commodity (i.e. wheat and sugar) forecast based on a subset of analogue years in relation to a standard reference forecast based on the full climatological set. We derived three key dimensions of forecast quality for such probabilistic forecasts: reliability, distribution shift, and change in dispersion. A measure of reliability was required to ensure no bias in the forecast distribution. This was assessed via the slope of the reliability plot, which was derived from examination of probability levels of forecasts and associated frequencies of realizations. The other two dimensions related to changes in features of the forecast distribution relative to the reference distribution. The relationship of 13 published accuracy/skill measures to these dimensions of forecast quality was assessed using principal component analysis in case studies of commodity forecasting using seasonal climate forecasting for the wheat and sugar industries in Australia. There were two orthogonal dimensions of forecast quality: one associated with distribution shift relative to the reference distribution and the other associated with relative distribution dispersion. Although the conventional quality measures aligned with these dimensions, none measured both adequately. We conclude that a multi‐dimensional approach to assessment of forecast quality is required and that simple measures of reliability, distribution shift, and change in dispersion provide a means for such assessment. The analysis presented was also relevant to measuring quality of probabilistic seasonal climate forecasting systems. The importance of retaining a focus on the probabilistic nature of the forecast and avoiding simplifying, but erroneous, distortions was discussed in relation to applying this new forecast quality assessment paradigm to seasonal climate forecasts. Copyright © 2003 Royal Meteorological Society
Surface meshing using a geometric error estimate
Authors: Frey P. J. , Borouchaki H.
Published: August 2003

In this paper we discuss an a posteriori interpolation error estimate based on the Hessian of the surface and we propose a new geometric error estimate related to the local deformation of the surface. The new approach makes possible the construction of adapted geometric meshes for surfaces by specifying the element sizes (and directions) so as to bound the error below a user‐given threshold value. The surfaces considered here are Cartesian surfaces. An analytical example is provided so as to emphasize the potential of the approach. Copyright © 2003 John Wiley & Sons, Ltd.
Improving the quality of meshes for the simulation of semiconductor devices using Lepp‐based algorithms
Authors: Hitschfeld N. , Villablanca L. , Krause J. , Rivara M. C.
Published: August 2003

This paper discusses a new post‐process algorithm for generating valid Delaunay meshes for the Box‐method (finite‐volume method) as required in semiconductor device simulation. In such an application, the following requirements must be considered: (i) in critical zones of the device, edges aligned with the flow of the current (anisotropic meshes) are needed; (ii) boundary and interface triangles with obtuse angles opposite to the boundary/interfaces are forbidden; (iii) large obtuse angles in the interior of the device must be destroyed and (iv) interior vertices with high vertex‐edge connectivity should be avoided. By starting from a fine Delaunay mesh that satisfies condition (i), the algorithm produces a Delaunay mesh that fully satisfies condition (ii) and satisfies conditions (iii) and (iv) according to input tolerance parameters γ and c, where γ is a maximum angle tolerance value and c is a maximum vertex‐edge connectivity tolerance value. Both to destroy any target interior obtuse triangle t and any target high vertex‐edge connectivity, a Lepp–Delaunay algorithm is used. The elimination of obtuse angles opposite to the boundary and/or interfaces is done either by longest edge bisection or by the generation of isosceles triangles. The Lepp–Delaunay algorithm allows a natural improvement of the input mesh by inserting a few points in some existing edges of the current triangulation. Examples of the use of the algorithm over Delaunay constrained meshes generated by a normal offsetting approach will be shown. A comparison with an orthogonal refinement method followed by Voronoi point insertion is also included. Copyright © 2003 John Wiley & Sons, Ltd.
Domain decomposition approach for parallel unstructured mesh generation
Authors: Larwood B. G. , Weatherill N. P. , Hassan O. , Morgan K.
Published: August 2003

In this paper, a method to generate large unstructured meshes on parallel computers is demonstrated. Using the Message Passing Interface, a coarse‐grained parallel harness has been developed, that allows the use of sequential generators in a parallel environment. Meshes of over 500 million elements will be shown. Copyright © 2003 John Wiley & Sons, Ltd.
A new indirect anisotropic quadrilateral mesh generation scheme with enhanced local mesh smoothing procedures
Authors: Lee Y. K. , Lee C. K.
Published: August 2003

An enhanced version of indirect advancing front technique is proposed for the construction of full quadrilateral anisotropic meshes on 3D surfaces. The final quadrilateral mesh is constructed from a background triangular mesh and the merging procedure is carried out in the parametric space. The proposed method employed the systemic merging technique for the formation of quadrilaterals and the metric specifications for controlling the anisotropic characteristics of the elements. In order to generate well‐graded anisotropic quadrilaterals, the selection criteria of base segment for merging are carefully defined. Furthermore, in order to improve the shape quality of the final mesh, a set of new local smoothing algorithms for anisotropic quadrilateral mesh quality enhancement has been proposed and tested in this study. Numerical examples obtained indicate that the proposed enhanced local smoothing schemes can effectively improve the quality of the quadrilateral meshes produced and increase the robustness of the mesh generation scheme. Copyright © 2003 John Wiley & Sons, Ltd.
Multiple material marching cubes algorithm
Authors: Wu Ziji , Sullivan John M.
Published: August 2003

The accurate reconstruction of three‐dimensional (3D) boundary surfaces from two‐dimensional (2D) medical images is a crucial procedure in most applications of computational biomedical engineering. This paper addresses an innovative system that efficiently reconstructs accurate, multiple‐material, 3D surface meshes from 2D medical images. It is based on an enhanced marching cubes algorithm, the multi‐material marching cubes algorithm (M3C), which extracts boundary surfaces between different materials within one sweep of the image stack in an integrated manner. The continuity and integrity of the surfaces are ensured with this robust algorithm. Surface adjustment algorithms were also revised to adapt to the multiple‐material nature of the system. Copyright © 2003 John Wiley & Sons, Ltd.
New view on cerebellar cortical background activity in rat: simulation
Authors: Kalauzi A. , Ćulić M. , Martać Lj. , Grbić G. , S̆aponjić J. , Jovanović A. , Janković B. , Spasić S.
Published: August 2003

The aim of this study was to reveal the nature and meaning of interspike background activity (RBA) recorded in Prukinje cell layer of rat cerebellum. We compared Fourier amtplitude spectra of recorded, extracted and averaged simple spike(s)—SS and complex spike(s)—CS with the mean amplitude spectrum of the remaining interspike RBA. A much greater similarity of spectral characteristics was noticed between SS and RBA, than between CS and RBA. Then, we simulated background activity (SBA), by superimposing averaged SS with randomized amplitudes and time delays. There was a significant correlation (p<0.005) between linearly transformed simulated and recorded amplitude spectra. Mean amplitude spectra of SBA were positively correlated with the number of superimposed SS. We propose to use this fact as a qualitative indication about the direction of change in the mean activity of surrounding neuronal population.
The personal norm of reciprocity
Authors: Perugini Marco , Gallucci Marcello , Presaghi Fabio , Ercolani Anna Paola
Published: August 2003

Reciprocity is here considered as an internalized social norm, and a questionnaire to measure individual differences in the internalized norm of reciprocity is presented. The questionnaire, Personal Norm of Reciprocity (PNR), measures three aspects of reciprocity: positive reciprocity, negative reciprocity, and beliefs in reciprocity. The PNR has been developed and tested in two cultures, British and Italian, for a total of 951 participants. A cross‐cultural study provides evidence of good psychometric properties and generalizability of the PNR. Data provide evidence for criterion validity and show that positive and negative reciprocators behave in different ways as a function of the valence (positive or negative) of the other's past behaviour, the type of feasible reaction (reward versus punishment), and the fairness of their reaction. Copyright © 2002 John Wiley & Sons, Ltd.
General‐base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions
Authors: Buurma Niklaas J. , Blandamer Michael J. , Engberts Jan B. F. N.
Published: August 2003

The reactivity of 1‐benzoyl‐3‐phenyl‐1,2,4‐triazole (1a) was studied in the presence of a range of weak bases in aqueous solution. A change in mechanism is observed from general‐base catalysed hydrolysis to nucleophilic substitution and general‐base catalysed nucleophilic substitution. A slight tendency is also observed for the more hydrophobic general bases to show higher reactivity towards 1a. Aspartame is an effective nucleophile, possibly because nucleophilic substitution is subject to intramolecular general‐base catalysis. A general conclusion derived from the present results is that unexpected rate effects can only be rationalised provided that the detailed reaction mechanisms are well understood. Copyright © 2003 John Wiley & Sons, Ltd.
Reactivity of heterophospholes toward 1,3‐dipolar cycloaddition of diazo compounds—an FMO analysis
Authors: Jikyo Tamaki , Schatz Jürgen , Maas Gerhard
Published: August 2003

The molecular geometries and the frontier orbital energies of three diazo compounds [diazodiphenylmethane (2), the α‐silyl‐α‐diazoketone 3 and the isomeric 2‐siloxy‐1‐diazoalkene 4], 10 heterophospholes with a PC bond and two heterophospholes with a PN bond were obtained from DFT calculations at the B3LYP/6–311+G** level. The 1,3‐dipolar cycloaddition reactivity of diazo compounds 2–4 toward the heterophospholes is discussed on the basis of FMO theory. It is concluded that in most cases, the dominant frontier orbital interaction is between the HOMO(diazo) and the LUMO(heterophosphole), and that the reactivity should decrease in the order­2 >4 >3. The 1,2‐thiaphosphole 9 and 1,3‐azaphosphole 10 have HOMOs of high energy and, therefore, the HOMO(heterophosphole)–LUMO(diazo) interaction is also important. Among the different types of heterophos‐pholes considered here, the 2‐acyl‐1,2,3‐diazaphosphole 5, 3H‐1,2,3,4‐triazaphosphole 8, 1,2‐thiaphosphole 9 and 1,3,4‐thiazaphosphole 14 are predicted to have the highest dipolarophilic reactivities. These conclusions are in qualitative agreement with available experimental results. Copyright © 2003 John Wiley & Sons, Ltd.
N‐Isopropyl enols of carboxylic acid amides
Authors: Lei Yi Xiong , Casarini Daniele , Cerioni Giovanni , Rappoport Zvi
Published: August 2003

Eight N‐isopropyl compounds of the formal structure YY′CHCONHPr‐i (6), Y,Y′ = CO2Me, CO2CH2CF3, CN; YY′ = Meldrum′s acid residue; Y = CO2Me, Y′ = CO2CH2CF3, CN; Y = CO2CH2CF3, CO2CH(CF3)2, Y′ = CN, and the N‐t‐butyl derivative of Meldrum's acid were prepared and their structures were investigated in the solid state and in solution. The x‐ray diffraction data indicate that in the solid state the structure is that of the amide 6, when Y = Y′ = CO2Me, whereas when Y = CO2Me, Y′ = CN or YY′ = Meldrum′s acid residue the structure is that of the enol (5) YY′C=C(OH)NHPr‐i. The solid‐state 13C spectra indicate structure 6 when Y = CO2Me, Y′ = CO2R, R = Me, CH2CF3 and an enol structure for the other compounds studied. 1H, 13C and when available 19F NMR spectra showed that the enol/amide composition in solution is structure and solvent dependent, in analogy with the previously investigated N‐Ph analogs. The percentage of enol (and KEnol) decrease in the order of solvents CCl4 > CDCl3 > THF‐d8 > CD3CN > DMSO‐d6, DMF‐d7. For Y,Y′ the percentage of enol increases when the number of fluorine atoms in R of the CO2R increases, when CN replaces a CO2R group or for the cyclic Meldrum's acid derivative. Both E‐ and Z‐enols were observed when Y ≠ Y′, mostly at low temperature. The δ(OH) values increase with increased polarity of the medium and with increased strength of the hydrogen bonds in which they are involved. In THF‐d8 and DMF‐d7 the Z‐enol/E‐enol and the amide/enol ratios increase with increase in temperature. A main conclusion from the work is that the percentage of the enol increases, but not drastically, when the N‐substituent is changed from Ph to i‐Pr. Copyright © 2003 John Wiley & Sons, Ltd.
Generation of a cyclopentenyl cation labelled with a single deuterium at C‐4. Rate studies of the scrambling reaction
Authors: Brunelle Patrick , Sorensen Ted S. , Taeschler Christoph
Published: August 2003

The kinetics of the hydrogen scrambling reaction in the cyclopentenyl cation 1 were studied. The pure 4‐deutero derivative of 1 was prepared using superacid conditions and the activation energy ΔG‡ for the rearrangement of this label to the C‐1(3) position of 1 was determined using low‐temperature 2H NMR spectroscopy. In addition, the sequential rearrangement of the deuterium label from C‐4(5) → C‐1(3) → C‐2 was noted in a qualitative fashion. Based on a statistical analysis, the activation free energy ΔG‡ for a single hydrogen (deuterium) migration leading to the 4‐cyclopentenyl cation intermediate was determined to be 18.3 kcal mol−1 (−20.8 °C), in good agreement with the less direct determination provided by an earlier NMR line‐broadening and spin‐saturation transfer experiment. Copyright © 2003 John Wiley & Sons, Ltd.
NMR Spectroscopic and quantum chemical characterization of the (E )− and (Z )− isomers of the penta‐1,3‐dienyl‐2‐cation
Authors: Siehl Hans‐Ullrich , Müller Thomas , Gauss Jürgen
Published: August 2003

Dilute solutions of the (E )− and (Z )− isomers of pent‐1,3‐dienyl‐2‐cations (1) were obtained from reaction of 4‐chloro‐1,2‐pentadiene (2) with SbF5 in SO2ClF/SO2F2 at −135 °C using high‐vacuum co‐condensation techniques. The experimental NMR spectra of the mixture of the two isomers were compared with quantum chemical 13C NMR chemical shift calculations at HF‐SCF, MP2, CCSD and CCSD(T) levels using MP2/tzp geometries. Quantum chemical shift calculations were performed with a tzp basis (9s5p1d/5s3p1d) for carbon and a dz basis (4s/2s) for hydrogen using gauge‐including atomic orbitals (GIAOs). The HF‐SCF calculations deviate significantly for the positively charged carbon atoms of the allyl‐type resonance system showing up to 40 ppm too deshielded values compared with the experimentally observed chemical shifts. The HF‐SCF approach is therefore not sufficient in predicting satisfactorily the shielding tensors in this type of carbocation. Inclusion of electron correlation, however, allows an unequivocal assignment of the spectra of the Z‐ and E‐isomers. The mean deviation between experimental and calculated NMR chemical shifts at the CCSD(T) level is 1.8 and 2.0 ppm for (Z)‐ and (E)‐1, respectively. The dienyl cations (E/Z)‐1 are the smallest vinyl cations ever generated as persistent species in superacidic solutions and observed by 13C NMR spectroscopy. These carbocations were structurally fully characterized by advanced ab initio quantum chemical calculations of structure and NMR chemical shifts. Copyright © 2003 John Wiley & Sons, Ltd.
Structure‐Activity Relationships for the Toxicity of Substituted Poly‐hydroxylated Benzenes to Tetrahymena pyriformis: Influence of Free Radical Formation
Authors: Netzeva Tatiana I. , Aptula Aynur O. , Chaudary Shaqil H. , Duffy Judith C. , Wayne Schultz T. , Schüürmann Gerrit , Cronin Mark T. D.
Published: August 2003

The aim of this study was to develop quantitative structure‐activity relationships for the toxicity to Tetrahymena pyriformis of 30 substituted poly‐hydroxylated benzenes. Physico‐chemical descriptors for the expression of free radical formation, associated with the OH moiety on the aromatic ring, were calculated. These included one‐electron equilibrium constants that did and did not account for the oxidation of an OH‐group, homolytic bond dissociation energy (BDE), electronegativity (EN) and absolute hardness (AH), in addition to the distribution coefficient (log D) as a measure of hydrophobicity. The reactivity descriptors were calculated using the semi‐empirical AM1 Hamiltonian in the MOPAC molecular orbital software. Statistically significant two‐parameter QSARs for toxicity were obtained by combination of log D with either BDE or AH. The QSARs suggested that toxicity is associated with hydrophobicity and the probability of radical formation.
Coalescing times for IID random variables with applications to population biology
Authors: Adler Ilan , Ahn Hyun‐Soo , Karp Richard M. , Ross Sheldon M.
Published: August 2003

We consider a coalescing particle model where particles move in discrete time. At each time period, each remaining ball is independently put in one of n bins according to a probability distribution p = (p1, …, pn), and all balls put into the same bin merge into a single ball. Starting with k balls, we are interested in the properties of E[N(p, k)], the expected time until all balls merge into one. We derive both upper and lower bounds for E[N(p, k)], some asymptotic results, and show that P{N(p, k) > t}, and thus E[N(p, k)], is a Schur concave function of p. Applications to population biology are noted. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 155–166, 2003
Proof of a tiling conjecture of Komlós
Authors: Shokoufandeh Ali , Zhao Yi
Published: August 2003

A conjecture of Komlós states that for every graph H, there is a constant K such that if G is any n‐vertex graph of minimum degree at least (1 − (1/χcr(H)))n, where χcr(H) denotes the critical chromatic number of H, then G contains an H‐matching that covers all but at most K vertices of G. In this paper we prove that the conjecture holds for all sufficiently large values of n. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 180–205, 2003
The development of the concept of “matter”: A cross‐age study of how children classify materials
Authors: Krnel Dušan , Glažar Saša S. , Watson Rod
Published: August 2003

The development of the concept of matter was explored in children aged 3–13. Eighty four children were asked to classify four sets of objects and matter and to explain their classifications during interviews. Younger children tended to classify using a mixture of extensive properties (properties of objects) and intensive properties (properties of matter), whereas older children (above 9 years old) tended to use intensive properties most of the time. The effect of using sets of objects and matter with different characteristics was explored. The different sets of objects and matter consisted of ones made of different substances, of various shapes and particle size, and of different states of matter. The ways in which children classified were analyzed from a Piagetian perspective, which hypothesizes that the epigenesis of concepts takes place through children acting on the world. Through their actions children gradually develop more elaborated schema which enable them to distinguish between extensive and intensive properties and hence between object and matter. © 2003 Wiley Periodicals, Inc. Sci Ed 87:621–639, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10080
Investigating the relationship between refutational text and conceptual change
Authors: Palmer David H.
Published: August 2003

The aim of this study was to identify the type of conceptual change (assimilation or accommodation) that can be induced by a refutational text. Individual interviews were carried out with a stratified sample of eighty‐seven grade 9 students. Forty‐four percent of them were found to have a misconception about the concept of ecological role—they believed that some living things do not have a role in nature. These 36 students were asked to read either a text that refuted the misconception, or a control text that consisted of a didactic explanation of ecological role. They then participated in an immediate posttest and a delayed posttest. Surprisingly, both texts were able to induce accommodation in a large proportion of the students. Factors such as the high motivation of the students, encouragement of metacognition, age‐readiness of the students, and a relative lack of robustness of the misconception were considered to have greatly facilitated the conceptual change process. © 2003 Wiley Periodicals, Inc. Sci Ed 87:663–684, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.1056
Measuring student understanding of geological time
Authors: Dodick Jeff , Orion Nir
Published: August 2003

There have been few discoveries in geology more important than “deep time”—the understanding that the universe has existed for countless millennia, such that man's existence is confined to the last milliseconds of the metaphorical geological clock. The influence of deep time is felt in a variety of sciences including geology, cosmology, and evolutionary biology. Thus, any student that wants to master these subjects must have a good understanding of geological time. Despite its critical importance, there has been very little attention given to geological time by science education researchers. Of the work that has been done, much of it ignores the cognitive basis for students' understanding of geological time. This work addresses this gap by presenting a validation study for a new instrument—the GeoTAT (Geological Time Aptitude Test). Consisting of a series of open puzzles, the GeoTAT tested the subjects' ability to reconstruct and represent the transformation in time of a series of geological structures. Montagnero (1992, 1996) terms this ability “diachronic thinking.” This instrument was distributed to a population of 285 junior and senior high school students with no background in geology, as well as 58 high school students majoring in geology. A comparison of the high school (grades 11–12) geology and non‐geology majors indicated that the former group held a significant advantage over the latter in solving problems involving diachronic thinking. This relationship was especially strengthened by the second year of geological study (grade 12), with the key factor in this improvement being exposure to fieldwork. Fieldwork both improved the subjects' ability in understanding the 3‐D factors influencing temporal organization, as well as providing them with experience in learning about the types of evidence that are critical in reconstructing a transformational sequence. © 2003 Wiley Periodicals, Inc. Sci Ed 87:708–731, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.1057
Transient hydrops fetalis of the donor fetus in twin–twin transfusion syndrome after therapeutic amnioreduction
Authors: Morine M. , Maeda K. , Higashino K. , Miura N. , Kinoshita T. , Endo S. , Irahara M.
Published: August 2003

We present a case of twin–twin transfusion syndrome associated with transient hydrops fetalis observed in the donor after therapeutic amnioreduction at 22 weeks of gestation. After the amnioreduction, the bladder of the donor could be visualized and the donor subsequently began to make amniotic fluid, with spontaneous regression of hydrops fetalis. It is suspected that after therapeutic amnioreduction, intrauterine hemodynamic changes occurred and the donor developed transient hydrops fetalis due to volume overload. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Fetal cerebellar hemorrhage in a severely growth‐restricted fetus: natural history and differential diagnosis from Dandy–Walker malformation
Authors: Yüksel A. , Batukan C.
Published: August 2003

This is a report of an intracerebellar hemorrhage in a severely growth‐restricted fetus with pathological Doppler findings of the fetal and uteroplacental circulations. The diagnosis was made sonographically at 22 weeks of gestation and the natural course of the hemorrhage was followed. Interestingly, the final sonographic appearance of the posterior fossa was quite similar to that of the classic form of Dandy–Walker malformation: absence of the vermis and an enlarged fourth ventricle. However, careful sonographic examination showed that the enlargement of the fourth ventricle was actually caused by a porencephalic cystic lesion of the left cerebellar lobe. Pathological examination revealed complete absence of the vermis and cerebellar hypoplasia. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Introital and transvaginal ultrasound as the main tool in the assessment of urogenital and pelvic floor dysfunction: an imaging panel and practical approach
Authors: Tunn R. , Petri E.
Published: August 2003

This article reviews the different applications of ultrasound in benign urogynecological diseases. The findings presented here were obtained by introital and transvaginal ultrasound, both of which can be performed with the same equipment (5–7‐MHz sector transducer, emission angle of at least 90°; for introital sonography, the transducer is placed over the external urethral orifice with the transducer axis corresponding to the body axis). Female voiding dysfunction, including urge symptoms, recurrent urinary tract infections and urinary incontinence, may occur secondary to morphological and topographical changes of the urogenital organs. Findings such as urethral diverticula, periurethral masses, funneling of the urethra and distension cystoceles are identified by introital ultrasound. Transvaginal ultrasound enables the detection of pathologies of the bladder and uterus including its appendages. Ultrasound as part of the diagnostic work‐up of stress urinary incontinence and genitourinary prolapse allows for the morphological and dynamic assessment of the lower urinary tract. It is possible, for example, to classify sonographically identified changes of the endopelvic fascia as lateral (distraction cystocele, funneling of the urethra) and central (pulsation cystocele) defects as well as to determine the reactivity of the pelvic floor muscles. Ultrasound has replaced radiography in yielding information on the abnormal morphology of the urogenital organs, which should be taken into account in planning the treatment of urogynecological conditions. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Outcome of antenatally diagnosed intracranial hemorrhage: case series and review of the literature
Authors: Ghi T. , Simonazzi G. , Perolo A. , Savelli L. , Sandri F. , Bernardi B. , Santini D. , Bovicelli L. , Pilu G.
Published: August 2003

Objectives

Prenatal diagnosis of intracranial hemorrhage (ICH) has been widely reported. Hemorrhages may occur either within the cerebral ventricles, subdural space or infratentorial fossa. The aim of this study was to determine the sonographic criteria for the diagnosis of fetal ICH, the role of in utero magnetic resonance imaging (MRI) and the outcome of this condition.

Methods

The archives of our ultrasound laboratory and the literature were searched for all cases of antenatally diagnosed ICH. A grading system was used to classify the intraventricular lesions as suggested in postnatal sonographic studies.

Results

Adding our series of 16 fetuses to the 93 cases identified in the literature, a group of 109 fetal ICHs was obtained: 89 were intracerebral (79 intraventricular and 10 infratentorial) and 20 were subdural hemorrhages. Intraventricular lesions were mostly classified as severe (32 each for Grades III and IV). In 27 cases antenatal MRI was performed additionally to ultrasound and confirmed the sonographic findings. Of the entire group, 65 infants (59%) were reported to be alive 1 month after birth (51 intraventricular hemorrhages, three infratentorial hemorrhages, 11 subdural hematomas). At 12 months, of the 48 infants whose follow‐up was available, 25 or 52% were judged neurologically normal (17/36 or 47% among the intraventricular hemorrhages, 6/9 or 66% among the hematomas, and 2/3 or 66% among the infratentorial hemorrhages).

Conclusions

Fetal ICH may be accurately identified and categorized by antenatal sonography. The outcome is usually poor, especially for those fetuses affected by higher‐grade intraventricular hemorrhages. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Prenatal sonographic diagnosis of isolated agnathia: a case report
Authors: Yang S. H. , Seo Y. S. , Lee Y. S. , Choi S. J. , Kim Y. A. , Kim J. H.
Published: August 2003

Agnathia is a rare malformation characterized by the absence of the mandible, microstomia, aplasia or hypoplasia of the tongue, and low‐set or medially fused ears. It occurs alone or in combination with a variety of malformations such as holoprosencephaly. All previous cases of the prenatal diagnosis of agnathia have been accompanied with fatal anomalies. We report here the first case of isolated agnathia, which was diagnosed by prenatal sonography at 32 weeks of gestation. In this case, prenatal sonographic examination showed the severe defect of the chin, small opening of the mouth and severe polyhydramnios. There was no sonographic evidence of holoprosencephaly or anomalies in other organ systems. The diagnosis was confirmed postnatally. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
The pedicle artery sign based on sonography with color Doppler imaging can replace second‐stage tests in women with abnormal vaginal bleeding
Authors: Timmerman D. , Verguts J. , Konstantinovic M. L. , Moerman P. , Van Schoubroeck D. , Deprest J. , Van Huffel S.
Published: August 2003

Objective

Unenhanced transvaginal sonography is not accurate in the detection of endometrial polyps. Currently, second‐stage tests such as saline contrast sonohysterography and office hysteroscopy are used to diagnose endometrial lesions, but both have limitations and side effects. We proposed visualization of the pedicle artery on color Doppler imaging as a sign of polyps.

Methods

This was a prospective observational study involving 3099 consecutive patients referred for assessment of the endometrium and myometrium. The uterus was assessed in sagittal and coronal planes using color Doppler sonography. Patients with suspected endometrial pathology on sonography were noted and the volume of the focal lesion was calculated. Patients with a clearly visible pedicle artery reaching the central part of the endometrium were regarded as test‐positive. The gold standard was defined as the presence or absence of an endometrial polyp at hysterectomy, hysteroscopy and/or endometrial histology on dilatation and curettage within 1 year of sonography.

Results

Of the 3099 women, no gold standard was available in 2230. Only 28 of the 199 patients who were test‐positive did not have a gold standard. In the 869 patients in whom a gold standard was available, 182 had one or more endometrial polyps. The pedicle artery test had an apparent sensitivity for detection of endometrial polyps of 76.4%, specificity of 95.3%, positive predictive value (PPV) of 81.3%, and negative predictive value of 93.8%. When extending the test to the prediction of any focal intracavitary pathology the PPV was 94.2%.

Conclusions

The pedicle artery test has a very high PPV for intracavitary pathology. We expect that in the majority of patients with an endometrial polyp this test may replace more invasive established second‐stage tests, such as saline contrast sonohysterography and office hysteroscopy. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Ordering the Earth's magnetic field by geocentric magnetospheric equatorial coordinates: Lessons from HEOS
Authors: Dunlop Malcolm W. , Cargill Peter J.
Published: August 2003

HEOS high‐resolution magnetic field measurements have been recovered and are used here to complete and regenerate an early study of the Earth's cusp field geometry, first made by Hedgecock [1975]. We make use of a special coordinate transformation, introduced by Hedgecock and Thomas [1975], to merge data from cusp crossings corresponding to different dipole tilt angles. The coordinates correspond to a geocentric magnetospheric equatorial (GME) system which was defined originally to apply both to position and the magnetic field. The transformation can be extended to incorporate other magnetotail models, for example, and these and other modifications are being investigated. Low‐resolution summary data are merged over the whole mission from both HEOS‐1 and ‐2 to provide global coverage of the magnetospheric field. This is found to be well ordered in GME coordinates, which remove to a large degree the effect of the dipole orientation on field geometry. Use of the Tsyganenko [1989] field model (as well as recent magnetopause models), which was not available for the 1975 study, can assist in such an investigation and provides a baseline test of the ordering effect of GME.