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Borderline Cases (borderline + case)
Selected AbstractsStrong Evidence for an Unprecedented Borderline Case of Dissociation and Cycloaddition in Open-Shell 1,3-Dipole Chemistry: Transient Nitrilium Phosphane-Ylide Complex Radical CationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2009Holger Helten Abstract The reaction of 3-ferrocenyl-substituted 2H -azaphosphirene complexes 1a,c in the presence of substoichiometric amounts of ferrocenium hexafluorophosphate yields 3,5-diferrocenyl-substituted 2H -1,4,2-diazaphosphole complexes 3a,c and difluoro(organo)phosphane complexes 4a,c. The reaction of 1a,c and [FcH]PF6 with cyanoferrocene yields 3a,c in a straightforward way. The molecular structures of 3a,c were unambiguously identified by multinuclear NMR spectroscopic experiments, mass spectrometry, and single-crystal X-ray diffraction studies. DFT calculations on model complexes 1d,m and 3d,m reveal a close similarity of Mo and W complexes (vs. Cr) and a strong influence of the ferrocenyl substituent on the geometry, spin, and charge distribution of reactive intermediates and the reaction course. Strong support for the assumption of a dissociation,cycloaddition reaction sequence leading to 3 and thus a surprising "cannibalistic" reaction was obtained.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Triple-Bond Covalent RadiiCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2005Pekka Pyykkö Prof. Abstract A system of additive covalent radii is proposed for ,2,,4 triple bonds involving elements from Be to E,112 (eka-mercury). Borderline cases with weak multiple bonding are included. Only the elements in Group 1, the elements Zn,Hg in Group 12 and Ne in Group 18 are then totally excluded. Gaps are left at late actinides and some lanthanides. The standard deviation for the 324 included data points is 3.2 pm. Alkuaineille Be,(E,112) on määrätty ,2,,4 -kolmoissidoksille luonteenomaiset kovalenttiset säteet, rajatapaukset mukaan lukien. Vain ryhmän,1 alkuaineet, ryhmän,12 alkuaineet Zn,Hg, ryhmän,18 Ne sekä osa lantanoideista ja myöhemmät aktinoidit on tällöin kokonaan jätetty tarkastelun ulkopuolelle. Aineisto käsittää 324 pistettä ja tulosten standardipoikkeama on 3.2 pm.Abstract in German:Ein System additiver kovalenter Radien für ,2,,4Dreifachbindungen fast aller Elemente von Be bis E,112 (Eka-Quecksilber) wird vorgestellt. Grenzfälle mit schwachen Mehrfachbindungen wurden mit einbezogen. Die Elemente in Gruppe,1, Zn,Hg in Gruppe,12, Ne, die meisten Lantanide und einige Actinide wurden wegen mangelnder Daten nicht berücksichtigt. Die Standardabweichung für die 324 verwendeten Datenpunkte beträgt 3.2 pm. [source] Electron Fluctuation in Pericyclic and Pseudopericyclic ReactionsCHEMPHYSCHEM, Issue 1 2006Eduard Matito Borderline cases: Differentiating between pericyclic and pseudopericyclic reactions is controversial. The authors analyze the electron distribution of the transition state of some known and some controversial reactions by means of the electron localization function (ELF) to elucidate their mechanism (see figure). This analysis provides a definitive criterion to distinguish between both electrocyclic processes. [source] Imperfection Sensitivity or Insensitivity of Zero-stiffness Postbuckling , that is the QuestionPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Xin Jia Zero-stiffness postbuckling of a structure is characterized by a secondary load-displacement path along which the load remains constant. In sensitivity analysis of the (initial) postbuckling path it is usually considered as a borderline case between imperfection sensitivity and imperfection insensitivity. However, it is unclear whether zero-stiffness postbuckling as such is imperfection sensitive or insensitive. In this paper, Koiter's initial postbuckling analysis is used as a tool for sensitivity analysis. Distinction between two kinds of imperfections is made on the basis of the behavior of the equilibrium path of the imperfect structure. New definitions of imperfection insensitivity of the postbuckling behavior are provided according to the classification of imperfections. A structure with two degrees of freedom with a zero-stiffness postbuckling path is studied, considering four different imperfections. The results from this example show that zero-stiffness postbuckling is a case of transition from imperfection sensitivity to imperfection insensitivity for imperfections of the first kind and that it is imperfection insensitive for imperfections of the second kind. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Density Functional Theory Study on the Electrocyclization of 1,2,4,6-Heptatetraene Analogues: Converting a Pericyclic to a Pseudopericyclic ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005Enrique M. Cabaleiro-Lago Prof. Dr. Abstract A comprehensive B3LYP/6-31+G* study on the electrocyclization of 1,2,4,6-heptatetraene analogues was conducted. Starting from the cyclization of (2Z)-2,4,5-hexatrienal, a pericyclic disrotatory process favored by the assistance of a electron lone pair, we incorporated small modifications in its molecular structure to obtain a truly pseudopericyclic process. To this purpose electronegative atoms (fluorine and nitrogen) were added to give a more electrophilic character on the carbon atom which is attacked by the electron lone pair of the oxygen atom. The complete pathway for each reaction was determined, and changes in magnetic properties were monitored with a view to estimating the aromatization associated with each process. This information, together with the energetic and structural results, allowed us to classify the reactions as pseudopericyclic or pericyclic. Among all studied reactions only one was a truly pseudopericyclic process and another was a borderline case. The features of this unequivocally pseudopericyclic case were analyzed in depth. Se ha llevado a cabo un exhaustivo estudio B3LYP/6-31+G* de la electrociclación de análogos del 1,2,4,6-heptatetraeno. Partiendo de la ciclación del (2Z)-2,4,5-hexatrienal, un proceso pericíclico disrotatorio favorecido por la ayuda de un par electrónico solitario, hemos incorporado pequeñas modificaciones en su estructura molecular con el fin de obtener un proceso verdaderamente pseudopericíclico. Con este propósito se añadieron átomos electronegativos (flúor y oxígeno) para conseguir un mayor carácter electrofílico en el átomo de carbono que es atacado por el par electrónico solitario del átomo de oxígeno. Se han determinado los caminos de reacción completos y se ha observado la variación de las propiedades magnéticas con el fin de estimar la aromatización asociada a cada proceso. Esta información, junto con los resultados energéticos y estructurales, nos han permitido clasificar las reacciones como pseudopericíclicas o pericíclicas. De todas las reacciones estudiadas sólo una resultó ser realmente pseudopericíclica y otra resultó ser un caso límite. Las características de este caso inequívocamente pseudopericíclico han sido analizadas en profundidad. [source] Long-term reliability and observer comparisons in the radiographic diagnosis of periapical diseaseINTERNATIONAL ENDODONTIC JOURNAL, Issue 2 2002O. Molven Abstract Aim The aim of this study was to evaluate and compare the long-term diagnostic consistency of two examiners, an endodontist and a radiologist, and to make comparisons with findings recorded by an observer with more recent scientific and clinical experience in endodontics. Methodology Three groups, each consisting of 20 full mouth series of intraoral radiographs, with 79, 93 and 85 endodontically-treated roots, respectively, were successively evaluated for periapical disease. Evaluations were at first performed separately by the three observers. Disagreement and difficult, borderline cases were subjected to joint evaluation. Intra- and interexaminer comparisons were made. For two of the observers the observations were compared with findings recorded several years before for the same cases in the same radiographs. Results The intra- and interobserver long-term reliability of the two original examiners resulted in 83% overall agreement, the kappa values were 0.54, 0.57 and 0.53. Comparisons between all three observers disclosed 82%, 85% and 86% agreement and kappa values 0.55, 0.58 and 0.60. The joint evaluations and decisions did not indicate a dominating influence from any of the observers. Conclusions The long-term reliability of the two original observers was judged as being satisfactory. All three observers judged the overall disease status of the material in the same way. The joint discussions of selected cases might reduce observer variation to an acceptable level, avoid a number of false recordings and increase the reliability and validity of the findings. [source] Development of a decision support system for diagnosis and grading of brain tumours using in vivo magnetic resonance single voxel spectraNMR IN BIOMEDICINE, Issue 4 2006Anne R. Tate Abstract A computer-based decision support system to assist radiologists in diagnosing and grading brain tumours has been developed by the multi-centre INTERPRET project. Spectra from a database of 1H single-voxel spectra of different types of brain tumours, acquired in vivo from 334 patients at four different centres, are clustered according to their pathology, using automated pattern recognition techniques and the results are presented as a two-dimensional scatterplot using an intuitive graphical user interface (GUI). Formal quality control procedures were performed to standardize the performance of the instruments and check each spectrum, and teams of expert neuroradiologists, neurosurgeons, neurologists and neuropathologists clinically validated each case. The prototype decision support system (DSS) successfully classified 89% of the cases in an independent test set of 91 cases of the most frequent tumour types (meningiomas, low-grade gliomas and high-grade malignant tumours,glioblastomas and metastases). It also helps to resolve diagnostic difficulty in borderline cases. When the prototype was tested by radiologists and other clinicians it was favourably received. Results of the preliminary clinical analysis of the added value of using the DSS for brain tumour diagnosis with MRS showed a small but significant improvement over MRI used alone. In the comparison of individual pathologies, PNETs were significantly better diagnosed with the DSS than with MRI alone. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effect of smoking on seminal plasma ascorbic acid in infertile and fertile malesANDROLOGIA, Issue 6 2006T. Mostafa Summary This work aimed to assess the relationship of seminal ascorbic acid levels with smoking in infertile males. One hundred and seventy men were divided into four groups: nonobstructive azoospermia [NOA: smokers (n = 20), nonsmokers (n = 20)]; oligoasthenozoospermia [smokers (n = 30), nonsmokers (n = 20)]; asthenozoospermia [smokers (n = 20), nonsmokers (n = 20)] and normozoospermic fertile men [smokers (n = 20), nonsmokers (n = 20)]. The patients underwent medical history, clinical examination, conventional semen analysis and estimation of ascorbic acid in the seminal plasma calorimetrically. There was a significant decrease in the mean seminal plasma ascorbic acid levels in smokers versus nonsmokers in all groups (mean ± SD; 6.03 ± 2.18 versus 6.62 ± 1.29, 7.81 ± 1.98 versus 9.44 ± 2.15, 8.09 ± 1.98 versus 9.95 ± 2.03, 11.32 ± 2.15 versus 12.98 ± 12.19 mg dl,1 respectively). Fertile subjects, smokers or not, demonstrated significant higher seminal ascorbic acid levels than any infertile group. Seminal plasma ascorbic acid in smokers and nonsmokers was correlated significantly with sperm concentration (r = 0.59, 0.60, P < 0.001), sperm motility (r = 0.65, 0.55, P < 0.001) and negatively with sperm abnormal forms per cent (r = ,0.53, ,0.50, P < 0.001). Nonsignificant correlations were elicited with semen volume (r = 0.2, 0.09) or liquefaction time (r = 0.03, 0.06). It is concluded that seminal plasma ascorbic acid decreased significantly in smokers and infertile men versus nonsmokers and fertile men, and is significantly correlated with the main sperm parameters: count, motility and normal morphology. Also, cigarette smoking is associated with reduced semen main parameters that could worsen the male fertilizing potential, especially in borderline cases. [source] | |||||||||||||