ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Alternating electrical conductivity of polyaniline (1999)

Bianchi, R. F. ; Leal Ferreira, G. F.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 4602-4607

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The ac complex conductivity σ*(f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1–100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of σ*(f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.478341

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2

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Theoretical and experimental (113 K) electron-density study of lithium bis(tetramethylammonium) hexanitrocobaltate(III) (1996)

Bianchi, R. ; Gatti, C. ; Adovasio, V. ; [et al.]

Copenhagen : International Union of Crystallography (IUCr)

Acta crystallographica 52 (1996), S. 471-478

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ISSN: 1600-5740

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: This paper presents an analysis of the crystal structure and the charge density, ρ(r), for lithium bis(tetramethylammonium) hexanitrocobaltate(III) determined by the rigid pseudoatom model from accurate X-ray data measured at 113 K. This compound has also been investigated by an ab initio Hartree–Fock fully periodic approach. A comparison of the topological properties between the experimentally and theoretically derived density is also given. A notable agreement between experiment and theory is observed in the topological properties of the metal-ligand interaction and a close parallel between the orbital model description and the shape of the Laplacian distribution around the Co atom is outlined. The results confirm the typical 3d-electron distribution of octahedral CoIII complexes in a low-spin state and the presence of four C—H...O hydrogen bonds in the crystal structure. Important differences between experiment and theory remain for the Laplacian and the parallel curvature (λ3) values at the C—N and N—O bond critical points. The atomic charges derived from the Quantum Theory of Atoms in Molecules are remarkably close to the formal values.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0108768195016879

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3

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Experimental Electron-Density Study of 4-Cyanoimidazolium-5-olate at 120 K (1998)

Bianchi, R. ; Gervasio, G. ; Viscardi, G.

Copenhagen : International Union of Crystallography (IUCr)

Acta crystallographica 54 (1998), S. 66-72

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ISSN: 1600-5740

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: This paper presents an analysis of the electron density in 4-cyanoimidazolium-5-olate, determined by the rigid pseudoatom model from accurate X-ray data measured at 120 K. A comparison of the electrostatic potential between experiment and theory is given for the isolated molecule. The results confirm the typical mesoionic electron distribution of the title compound and the presence of three hydrogen bonds in the crystal structure. The atomic charges and molecular dipole moment derived from the ab initio Hartree–Fock method are close to those obtained from the multipole model, which includes the kappa radial parameters. Electrostatic energies are also calculated for hydrogen bonding and molecular stacking interactions.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0108768197009269

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4

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Local structure around Ce in the Nd $\mathsf{_{2-x}}$ Ce $\mathsf{_{x}}$ CuO $\mathsf{_{4\pm \delta}}$ superconductor probed by EXAFS (2004)

Ghigna, P. ; Spinolo, G. ; Santacroce, E. ; [et al.]

Springer

The European physical journal 41 (2004), S. 31-42

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ISSN: 1434-6036

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. The local structure around the Ce substitutional defects has been investigated by Ce and Nd K-edge EXAFS on Nd2-x Ce x CuO $_{4\pm \delta}$ samples with different dopant concentrations (x = 0.05, 0.10, 0.15 and 0.20) and oxygen amounts. The lattice distortion around the Ce $_{\rm Nd}^\bullet$ can be described as a shrinkage of the oxygen cuboid along the z crystallographic direction. Moreover, the CuO4 planes become corrugated. The lattice distortion is well localized and is largely independent of temperature and Ce and oxygen content. EXAFS measurements made at the Nd-K edge indicate that the local chemical environment of Nd is not distorted. The difference electron density maps, obtained from low temperature single crystal X-ray diffraction data, revealed three strong positive residuals which have been ascribed to cerium (at 0, 0, $z\cong 0.41$ ) and to two non equivalent oxygen apical positions O3 (at 0, 0, $z\cong 0.19$ ) and O4 (at 0, 0 $z\cong 0.24$ ). The electron population of O4 site, which is closer to cerium ( $d_{\rm Ce-O4} = 1.96$ Å), is 3-4 times the O3 one.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1140/epjb/e2004-00290-x

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5

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Morphogenesis in Helianthus Tuberosus: Genotypic Influence and Increased Totipotency in Previously Regenerated Plants (1999)

Bianchi, R. ; Fambrini, M. ; Pugliesi, C.

Springer

Biologia plantarum 42 (1999), S. 515-523

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ISSN: 1573-8264

Keywords: cellular determination ; competence ; somatic embryogenesis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Leaf tissues of 38 genotypes, derived from four accessions, of the hexaploid species Helianthus tuberosus (2n=6x=102) responded to growth regulators (BA, NAA) chiefly by forming callus, while aventitious organogenesis or somatic embryogenesis were induced occasionally. A remarkable regeneration frequency (about 30 %) was achieved only from leaves of genotype HTPI-15. Explants of many regenerated plants of HTPI-15 subjected to a second culture cycle in vitro displayed a high morphogenetic potential (regeneration frequency 〉 90 %). White globular structures were initiated on the adaxial surface of these leaves without a callus phase. Somatic embryogenesis was asynchronous and embryoids, of different developmental stage, were simultaneously detected on each explant. Although many embryos developed single or malformed cotyledons or germinated precocciously, without the differentiation of a complete root system, phenotypically normal plants were regenerated after rooting on regulator-free half-strength MS medium.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1002698511484

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6

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Influence of spinning velocity on mechanical and structural behavior of PET/nylon 6 fibers (1995)

Aslan, S. ; Laurienzo, P. ; Malinconico, M. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Journal of Applied Polymer Science 55 (1995), S. 57-67

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ISSN: 0021-8995

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Influence of spinning velocities on the mechanical and structural properties of polyethylene terephthalate (PET)/nylon 6 blend fibers have been reported. Fibers of PET/nylon 6 containing a small percentage of nylon (5% by weight) have been melt-spun at 3 different spinning velocities (2,900; 3,200; 3,600 m/min). The fibers have been characterized by thermal, morphological, structrual, and mechanical analysis. Various techniques such as SEM, DSC, X-ray diffraction, hot water shrinkage (HWS), viscosity, and birefringence have been used. SEM analysis revealed that in the blend, nylon 6 is well-dispersed as spheres in the PET matrix. The blend shows a marked decrease in the melt-flow index, which in turn leads to a beneficial effect on the rheological properties of the PET without negatively influencing its mechanical characteristics. This finding results in a saving on energetical requirements of the processing, as both temperature and pressure of spinning can be decreased. © 1995 John Wiley & Sons, Inc.

Additional Material: 14 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/app.1995.070550106

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7

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Structure-properties relationship in spun fibers of poly(ethylene terephthalate): Comparisons between samples obtained by terephthalic acid or dimethyl terephthalate processes (1997)

Russo, G. ; Parravicini, L. ; Auriemma, F. ; [et al.]

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 889-896

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ISSN: 0887-6266

Keywords: poly(ethylene terephtalate) ; terephthalic acid process ; dimethyl terephtalate process ; spun fibers ; structure-properties relationship ; orientation of amorphous phase ; Physics ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Some properties and structural aspects of fibers obtained by spinning, in a wide range of take-up speed (2,800-4,400 m/min), of commercial samples of PET, produced by dimethyl terephthalate (DMT) and the terephthalic acid (TPA) processes, are compared. For a same take-up speed, the considered fibers from TPA are spun at lower pack pressures and always show higher tenacity and lower ductility than fibers from DMT. X-ray diffraction, density, and birefringence measurements indicate that, for the fibers from the DMT process, an earlier crystallization occurs which prevents the progress of the orientation of the amorphous phase. The lower molecular orientation in the amorphous phase of the fibers from DMT, in turn, accounts for their lower tenacity. The earlier crystallization of the fibers from DMT would be related to their slightly higher melting temperatures and melt viscosities, which could be due to the lower amount of constitutional defects (diethylene glycol content) in the considered PET samples from DMT compared with those from TPA. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 889-896, 1997

Additional Material: 9 Ill.

Type of Medium: Electronic Resource

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8

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Wave-function optimization by least-squares fitting of the exact wave function sampled by quantum Monte Carlo (1996)

Bianchi, R. ; Bressanini, D. ; Cremaschi, P. ; [et al.]

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 57 (1996), S. 321-325

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ISSN: 0020-7608

Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The sampling of the exact solution of the Schrödinger equation by quantum Monte Carlo methods allows one to solve the problem of the optimization of linear and nonlinear parameters of a trial wave function by minimization of the distance to the exact wave function in Hilbert space even for those systems whose exact wave function is unknown. The overlap integrals between the basis functions and the exact wave function can be easily estimated within the quantum Monte Carlo formalism. Several observables of the helium atom ground state, computed both within the orbital approximation and by an explicitly correlated basis set, evidence the overall goodness of the wave function optimized according to this criterion. © 1996 John Wiley & Sons, Inc.

Additional Material: 3 Tab.

Type of Medium: Electronic Resource

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