| 1. |
- Zhang, L. N., et al.
(författare)
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Triple helix of beta-D-glucan from Lentinus Edodes in 0.5 M NaCl aqueous solution characterized by light scattering
- 2001
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Ingår i: Polymer journal. - : Springer Science and Business Media LLC. - 0032-3896 .- 1349-0540. ; 33:4, s. 317-321
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Tidskriftsartikel (refereegranskat)abstract
- beta-(1 -->3)-D-glucan with (1 -->6) branching (L-FV-I) from Lentinus edodes in water was degraded into seven fractions of different molecular weights by ultrasonic irradiation. Weight-average molecular weight M,, radius of gyration (1/2)(5) and intrinsic viscosity [eta] of the beta -D-glucan and its fractions in 0.5 M NaCl aqueous solution and dimethylsulfoxide (DMSO) were studied by multi-angle laser light scattering (MALLS), GPC combined with MALLS, and viscometry. M, dependence of [eta] for the glucan in 0.5 M NaCl aqueous solution was represented approximately by [eta] =7.69 x 10(-6) M-w(1.32) (cm(3) g(-1)) at M-w from 1.87 X 10(5) to 1.20 X 10(6) at 25 degreesC. GPC chromatograms of the glucans in aqueous solution contained two peaks, a main peak corresponding to triple-stranded chains with molecular weight M-w,M-m, and small second peak corresponding to fragments of single chains with M-w,M-s (about 20 +/-5% content). Analysis of M-w,M-m and (1/2)(z,m) in term of the known theory for wormlike chains yielded 2180 +/- 100 nm(-1), 120 +/- 10 nm and 0.31 nm for molar mass per unit contour length M-L, persistence length q, and contour length h per main-chain glucose residue, respectively, which agree closely with theory data of triple-helical chains and reported parameters for triple-helix schizophyllan in 0.01 M NaOH aqueous solution. The ratios of M-w,M-m, in 0.5 M NaCl to M, in DMSO were calculated to be roughly 3. The predominant species of the glucan in 0.5 M NaCl aqueous solution exist as triple-helical chains with high rigidity, and in DMSO as single-flexible chains.
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| 2. |
- Zhang, Shi-Li, et al.
(författare)
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Differences between interfacial and surface molybdenum in the formation Of TiSi2
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:3, s. 1641-1646
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Tidskriftsartikel (refereegranskat)abstract
- Backscattering and diffraction results are presented for the effects of an interfacial or a surface Mo layer on the formation of Ti-silicides during solid-state interaction between Ti films and Si substrates. It is shown that the interfacial and surface Mo are fundamentally different in their involvement in the Ti-silicide formation. The interfacial Mo induces the formation of C40 (Mo,Ti)Si-2 at the interface adjacent to the Si substrate already after annealing at 550 degreesC, in agreement with our previous results. Hence, the desired C54 TiSi2 can grow directly on top of the C40 (Mo,Ti)Si-2 at relatively low temperatures as a result of the template effect. The surface Mo is, however, found in a metal-rich silicide presumably (Mo,Ti)(5)Si-3 at 550-600 degreesC, which eventually converts to (Mo,Ti)Si-2 upon annealing at higher temperatures. Underneath this metal-rich silicide lies a fully developed C49 TiSi2 layer. Consequently, the formation of C54 TiSi2 in the presence of surface Mo follows the usual path of the C49-C54 phase transition. This important difference in the participation of Mo in the silicide formation spreads doubts about the validity of using interfacial Mo versus surface Mo to study the dominant mechanism(s) responsible for the enhanced formation of C54 TiSi2.
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| 3. |
- Aberg, J, et al.
(författare)
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Electrical properties of the TiSi2-Si transition region in contacts : The influence of an interposed layer of Nb
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:5, s. 2380-2388
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Tidskriftsartikel (refereegranskat)abstract
- The influence of an interposed ultrathin Nb layer between Ti and Si on the silicide formation and the electrical contact between the silicide formed and the Si substrate is investigated. The presence of the Nb interlayer results in the formation of ternary alloy (Nb,Ti)Si-2 in the C40 crystallographic structure adjacent to the Si substrate. Depending on the nature of the Si substrates and/or the amount of the initial Nb, the interfacial C40 (Nb,Ti)Si-2 leads, in turn, to either epitaxial growth of a highly faulted metastable C40 TiSi2 or formation of the desired C54 TiSi2 at a lower temperature than needed for it to form in reference samples with Ti deposited directly on Si. On p-type substrates doped to various concentrations, the Nb also leads to a considerably lower specific contact resistivity than that obtained in the reference samples: a twofold to fourfold reduction in the contact resistivity is found using cross-bridge Kelvin structures in combination with two-dimensional numerical simulation. As C40 (Nb,Ti)Si-2 forms at the interface when an interfacial Nb is present, the interface characterized is likely to represent the one between (Nb,Ti)Si-2 and Si. For the reference samples, the interface studied is between TiSi2 and Si.
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| 4. |
- Biemont, E, et al.
(författare)
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Core-polarization effects and radiative lifetime measurements in PrIII
- 2001
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 64:2
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Tidskriftsartikel (refereegranskat)abstract
- New radiative lifetimes of eight levels in Pr III have been measured using the time-resolved laser-induced fluorescence method. A tunable frequency-doubled dye laser with 1-ns pulse duration was used to excite selectively doubly ionized praseodymium in a laser-produced plasma. The experimental results agree generally well with theoretical data, provided core-polarization effects are considered in the calculations in an adequate way.
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| 5. |
- Biemont, E, et al.
(författare)
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Experimental and theoretical energy levels, transition probabilities and radiative lifetimes in YbIII
- 2001
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 34:10, s. 1869-1876
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of the spectrum of Yb rn has been extended allowing us to establish 11 new energy level values. In addition, radiative lifetimes of two excited states of Yb III have been measured for the first time using time-resolved laser-induced fluorescence following two-photon excitation. The good agreement between experimental results and semi-empirical calculations performed with the relativistic Hartree-Fock method including core-polarization effects allows the determination of transition probabilities for 15 lines.
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| 6. |
- Biemont, E, et al.
(författare)
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Radiative lifetime measurements and transition probabilities of astrophysical interest in ErIII
- 2001
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 321:3, s. 481-486
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetimes of seven excited states of Er iii have been measured using time-resolved laser-induced fluorescence following two-photon excitation. Relativistic Hartree-Fock calculations taking core-polarization effects into account are found to be in excellent agreement with the experimental results. A large set of new calculated transition probabilities is presented for many transitions of astrophysical interest. These results will be useful for investigating the composition of chemically peculiar stars.
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| 7. |
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| 8. |
- d'Heurle, F. M., et al.
(författare)
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Formation of C54TiSi(2) : Effects of niobium additions on the apparent activation energy
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:12, s. 6409-6415
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Tidskriftsartikel (refereegranskat)abstract
- The formation of C54 TiSi2 using Ti-Nb alloys deposited on polycrystalline Si substrates was studied by means of in situ x-ray diffraction and resistance measurements during temperature ramping. Alloys with Nb contents ranging from 0 to 13.6 at. % were used. The formation temperature of C54 TiSi2 was reduced in the presence of Nb. However, the addition of Nb in Ti did not cause fundamental changes in the evolution of resistance versus temperature. This latter observation suggests that the mechanism for the formation of C54 TiSi2 remained the same in spite of the enhancement effect. For alloys with up to 8 at. % of Nb, the C49 TiSi2 phase formed first, as with pure Ti. When annealing the alloy with 13.6 at. % Nb, neither C49 TiSi2 nor C54 were found in the usual temperature ranges, instead, C40 (Nb,Ti)Si-2 was observed. This phase transformed to C54 (Nb,Ti)Si-2 above 950 degreesC. The apparent activation energy associated with the formation of C54 TiSi2 was obtained by annealing the samples at four different ramp rates from 3 to 27 K/s; it decreased continuously from 3.8 to 2.5 eV with increasing Nb content from 0 to 8 at. %. The apparent activation energy for the formation of C40 (Nb,Ti)Si-2 was found to be 2.6 eV. The possible physical meaning, or lack thereof, of the high activation energies derived from experimental measurements is extensively discussed. A qualitative model is proposed whereby nucleation would be rate controlling in pure TiSi2, and interface motion in samples with 8 at. % Nb.
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| 9. |
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| 10. |
- Ji, Xiaoyan, et al.
(författare)
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Determination of the activity coefficients of NaCl in the system NaCl-NH4Cl-H2O
- 2001
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Ingår i: Journal of Solution Chemistry. - 0095-9782 .- 1572-8927. ; 30, s. 463-473
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Tidskriftsartikel (refereegranskat)abstract
- Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl-NH4Cl-H2O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH4Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH4+ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg-1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.
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