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Selected AbstractsA new interpretation of the female genitalia in Macrocyclops albidus (Copepoda, Cyclopidae)ACTA ZOOLOGICA, Issue 1 2003D. Defaye Abstract The female genital structures of Macrocyclops albidus (Cyclopidae, Eucyclopinae) were studied using light and electron microscopy. The results confirm that the exterior genital area shows only a copulatory pore, located anteromedially on the ventral face of the genital double-somite, and paired gonopores (not directly visible), situated laterally under the P6 plates. An internal seminal receptacle, composed of several parts, is connected to the gonopores by ventro-lateral cuticular extensions or seminal ducts. The lateral site of communication shows a complex set of connections between the seminal receptacle and the oviducts (via the egg-laying ducts). The structure until now designated as ,transverse ducts', visible by transparency on the ventral face, is in fact constituted of internal cuticular thickenings resulting of the fusion of the 6th thoracic somite and the 1st abdominal somite forming the genital double-somite and appearing externally as a part of the suture line; the term ,suture cord' is proposed to designate it. The functioning of the system is explained. [source] Electronic Structure of Linearly Coordinated EQ Complexes of the Type [(N3N)W(EQ)] [N3N = N(CH2CH2NSiMe3)3; E = P, As, Sb, Bi; Q = O, S, Se, Te]: A DFT StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2007Gábor Balázs Abstract Density functional theory (DFT) calculations were carried out on the terminal EQ complexes [(N3N)W(EQ)] {N3N = N(CH2CH2NSiMe3)3; E = P, As, Sb, Bi; Q = O, S, Se Te} to clarify the bonding situation within the linear Nax,W,E,Q core. This unusual structural motif gives rise to a bonding arrangement in which the ,-electron density is delocalised over the three atoms of the W,E,Q unit. Fragment calculations and natural bond order (NBO) data indicated that the ,-bonding component of the Nax,W,E,Q unit comprises two occupied , orbitals, while the , component of bonding comprises two sets of degenerate , orbitals. In general, the , orbitals of the Nax,W,E,Q core are higher in energy compared to the , orbitals. The phosphorus monoxide (EQ = PO) complexes provide an exception to this rule, with the 1, orbitals of the W,P,O core lower in energy than the , orbitals. Generally, as the atomic number of either the pnicogen (E) or chalcogen (Q) atom increases the extent of ,-orbital delocalisation decreases, whereas the ,-orbital delocalisation increases. Fractional bond orders and Wiberg bond indices were used to establish whether localisation of the ,-electron density gives rise to a W,E or an E,Q double or triple bond. Both methods indicate a W,E as well as an E,Q double bond. The ionic nature of the complexes were analysed by inspection of the Hirschfeld charge distribution which shows only a moderate ionic character. Exceptions are the pnicogen monoxide complexes, which are more ionic. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Low-Loss Microwave Dielectrics in the Spinel-Structured (Mg1,xNix)Al2O4 Solid SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Cheng-Liang Huang Solid solutions of (Mg1,xNix)Al2O4 (x=0,1) have been prepared using the solid-state reaction method and their dielectric properties were measured at microwave frequencies. Formation of single-phase spinel-structured solid solutions was confirmed by X-ray diffraction analysis throughout the entire compositional range, and the measured lattice parameters varied linearly from 8.0810 Å at x=0 (MgAl2O4) to 8.0445 Å at x=1 (NiAl2O4) leading to a linear decrease in the unit cell volume from 527.71 to 520.59 Å3. The ionic polarizability obtained, however, increased with the increase of x to a maximum at x=0.25 and decreased thereafter. It shows only a small variance in the ,r with Ni substitution for Mg and a maximum ,r of 8.21 was achieved for (Mg0.75Ni0.25)Al2O4 in response to the highest ionic polarizability and relative density. However, the Q×f value can be significantly promoted up to a maximum value of 130 000 GHz (measured at 15.4 GHz) at x=0.25. In addition, substitution of Mg by Ni also helps to decline the ,f value from ,65 ppm/°C at x=0 to ,53.5 ppm/°C at x=0.25. [source] Assessment in the context of uncertainty: how many members are needed on the panel of reference of a script concordance test?MEDICAL EDUCATION, Issue 3 2005R Gagnon Purpose, The script concordance test (SCT) assesses clinical reasoning in the context of uncertainty. Because there is no single correct answer, scoring is based on a comparison of answers provided by examinees with those provided by members of a panel of reference made up of experienced practitioners. This study aims to determine how many members are needed on the panel to obtain reliable scores to compare against the scores of examinees. Methods, A group of 80 residents were tested on 73 items (Cronbach's ,: 0.76). A total of 38 family doctors made up the pool of experienced practitioners, from which 1000 random panels of reference of increasing sizes (5, 10, 15, 20, 25 and 30) were generated with a resampling procedure. Residents' scores were computed for each panel sample. Units of analysis were means of residents' score, test reliability coefficient and correlation coefficient between scores obtained with a given panel of reference versus the scores obtained with the full panel of 38. Statistics were averaged across the 1000 samples for each panel size for the mean and test reliability computations, and across 100 samples for the correlation computation. Results, For sample variability, there was a 3-fold increase in standard deviation of means between a sample panel size of 5 (SD = 1.57) and a panel size of 30 (SD = 0.50). For reliability, there was a large difference in precision between a panel size of 5 (0.62) and a panel size of 10 (0.70). When the panel size was over 20, the gain became negligible (0.74 for 20 and 0.76 for 38). For correlation, the mean correlation coefficient values were 0.90 with 5 panel members, 0.95 with 10 members and 0.98 with 20 members. Conclusion, Any number over 10 is associated with acceptable reliability and good correlation between the samples versus the full panel of 38. For high stake examinations, using a panel of 20 members is recommended. Recruiting more than 20 panel members shows only a marginal benefit in terms of psychometric properties. [source] Microscopic diagnostics of DNA molecules on mono-crystalline diamondPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2007Bohuslav Rezek Abstract Detailed data about deoxyribonucleic acid (DNA) attachment, arrangement, density and functionality on mono-crystalline diamond surfaces are obtained by direct measurements in electrolytic solutions using fluorescence microscopy and atomic force microscopy in various regimes (oscillating, contact, phase, and surface potential imaging) and by fitting the data into a microscopic geometrical model of DNA. DNA is immobilized on undoped and boron-doped diamonds with hydrogen and oxygen surface terminations which were functionalized by aminodecene and nitrofenyl linker molecules. The data show that, except photochemically processed oxidized diamond surfaces, the DNA molecules are covalently linked to diamond in a 65,92 Å thin and highly dense layers (6 × 1012 molecules/cm2) with sub-nanometer intermolecular spacing and a strong tilt of 31° with respect to the surface. Ordering of these DNA layers shows only a weak (<10%) response to a change of buffer salinity in the range of 1,300 mM. The data are discussed with view to biosensor applications. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Deciphering interactions of the aminoglycoside phosphotransferase(3,)-IIIa with its ligandsBIOPOLYMERS, Issue 9 2009Lingzhi Wu Abstract Aminoglycoside phosphotransferase(3,)-IIIa (APH) is the enzyme with broadest substrate range among the phosphotransferases that cause resistance to aminoglycoside antibiotics. In this study, the thermodynamic characterization of interactions of APH with its ligands are done by determining dissociation constants of enzyme,substrate complexes using electron paramagnetic resonance and fluorescence spectroscopy. Metal binding studies showed that three divalent cations bind to the apo-enzyme with low affinity. In the presence of AMPPCP, binding of the divalent cations occurs with 7-to-37-fold higher affinity to three additional sites dependent on the presence and absence of different aminoglycosides. Surprisingly, when both ligands, AMPPCP and aminoglycoside, are present, the number of high affinity metal binding sites is reduced to two with a 2-fold increase in binding affinity. The presence of divalent cations, with or without aminoglycoside present, shows only a small effect (<3-fold) on binding affinity of the nucleotide to the enzyme. The presence of metal,nucleotide, but not nucleotide alone, increases the binding affinity of aminoglycosides to APH. Replacement of magnesium (II) with manganese (II) lowered the catalytic rates significantly while affecting the substrate selectivity of the enzyme such that the aminoglycosides with 2,-NH2 become better substrates (higher Vmax) than those with 2,-OH. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 801,809, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||