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  • 1
    Electronic Resource
    Electronic Resource
    An integrated instrumentation for light-scattering and time-resolved fluorescence measurements (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2405-2410 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An integrated instrumentation which combines in the same system static and dynamic laser light scattering and time-resolved fluorescence spectroscopy is described. The two types of measurements can be performed simultaneously on the same sample contained in a thermostated cuvette. The light scattering allows measurements of molecular weights and hydrodynamic radii in the range of 20 A(ring) to a few micrometers. The overall time resolution of fluorescence measurements is around 50 ps. The system provides the simultaneous acquisition of the fluorescence decay curve, of the time integrated emission spectrum, and of two time-gated spectra. The light-scattering technique gives information on the global structure of the aggregates, while fluorescence measurements are sensitive to the local interactions of a fluorescence probe with the surroundings. The contemporary use of these two complementary techniques can be quite valuable mostly for biological samples for which stability and reproducibility with time can sometimes be a problem. As an example, combined measurements of the dimension of dimyristoylphosphatidylcholine vesicles around their temperature transition and of fluorescence lifetimes of the diphenylhexatriene probe incorporated in the vesicles is shown. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145638
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  • 2
    Electronic Resource
    Electronic Resource
    A modified Kjeldahl procedure for determining strongly fixed NH4+-N (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: This paper reports a procedure for determining the content of strongly fixed NH4+ in soil. The procedure consists of a Kjeldahl digestion followed by an acid attack of the residue with a 5 m HF:1 m HCl solution. Distillations after each of the two treatments recover different forms of NH4+. The procedure was tested on fine earth (〈 2 mm) and skeleton (〉 2 mm) fractions of two forest soils developed on sandstone parent material. In both soil fractions we evaluated three different forms of NH4+-N: (i) Kjeldahl, (ii) non-exchangeable and (iii) micaceous. The last is located in the interlayer of mica flakes larger than 50 μm that resist the Kjeldahl digestion and is considered strongly fixed. The total NH4+-N content of a soil is obtained by the summation of the Kjeldahl and the micaceous NH4+-N. In the soils under consideration, the micaceous form prevails in the skeleton because this fraction is richer in micas of sand size (〉 50 μm). Following the proposed procedure, we found that micas (muscovite and biotite) contain about 3000 mg kg–1 of NH4+-N in the interlayer. The presence of micaceous NH4+-N in soil is generally ignored because the skeleton is usually excluded from analyses, and the micas larger than 50 μm cannot be dissolved by the Kjeldahl treatments. The micaceous NH4+ is the least extractable form of NH4+-N, and we infer that it is the least available to plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1999.00248.x
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  • 3
    Electronic Resource
    Electronic Resource
    Release of Al by hydroxy-interlayered vermiculite and hydroxy-interlayered smectite during determination of cation exchange capacity in fine earth and rock fragments fractions (1997)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 48 (1997), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The fine earth (〈2 mm) and rock fragments (〉2 mm) fractions of two soils derived from Oligocene sandstone have been examined to assess the origin of the discrepancies between cation exchange capacity (CEC) and effective CEC (ECEC). The soils differ in terms of acidity: soil A is more acid than soil B. When the A samples are treated with BaCl2, the solution became sufficiently acid (pH 〈 4·5) to dissolve and to maintain Al in solution. From these samples more Al is released than base cations. Aluminium was continuously replenished even after 192 h, so that the ECEC was always larger than the CEC. Samples from soil B contain less H and Al ions, and the BaCl2 solution could not lower the pH below 5·0. In these samples little Al is released, and the base cations dominate the exchangeable pool of ions. This Al can be considered to be exchangeable, and a good agreement exists between the ECEC and the CEC. The source of non-exchangeable Al in the A samples is the OH-Al polymers of the hydroxy-interlayered vermiculite (HIV) and hydroxy-interlayered smectite (HIS) that tend to dissolve during the BaCl2 treatments. In the less acid B samples the Al polymers are not affected by BaCl2 treatment. Different results were obtained when the clays, extracted from an Na-dispersed suspension, were treated with BaCl2 solution. Because the clays are no longer acid, no H+ is released, and the OH-Al polymers are not dissolved. Therefore, the saturating ions play an important role in the dissolution of the OH-Al polymers and cause differences between the CEC and ECEC. We discount organic matter and specifically Al-organo complexes as a source of non-exchangeable Al. Both A and B soils contain very similar pyrophosphate-extractable Al, but show substantial differences in the amount of exchangeable Al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1997.tb00545.x
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  • 4
    Electronic Resource
    Electronic Resource
    Susceptibility and 89Y nuclear magnetic resonance in Y1−xCaxVO3 : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6624-6626 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Temperature-dependent (10–300 K) field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities, and 89Y NMR spectra and relaxation in Y1−xCaxVO3 with 0≤x≤0.9 are reported. In the paramagnetic phase (PA) of YVO3 and for T≥120 K the susceptibility χ is of antiferromagnetic (AF) type, with no field dependence. Around the Neel temperature T(1)N=113±1 K a field-dependent ferromagnetic behavior is observed under FC condition. Below T(2)N(approximately-equal-to)77 K (AF phase with AF interplane coupling) strong difference is present between FC and ZFC χ's. For T→T(1)+N the 89Y NMR line shows marked broadening and no measurable shift, consistent with a dominant dipolar contribution in the nucleus–electrons interaction. The 89Y relaxation rate T−11, related to the correlated spin dynamics of V3+ S(t), seems to indicate that the interplane ferromagnetic symmetry of the spin fluctuations is quenched in strong fields. The peculiar findings for χ and T1 could result from a field-dependent weak ferromagnetism of Dzyaloshinsky–Moriya character. In Y1−xCaxVO3, χ and T−11 decrease on increasing x, still preserving the qualitative behavior as for x=0. For x(approximately-equal-to)0.6 (Ca concentration which drives the transition to the metallic phase) the marks of the PA–AF transition are practically suppressed and behaviors characteristic of correlated metals are observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361904
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  • 5
    Electronic Resource
    Electronic Resource
    7Li nuclear magnetic resonance spectra and relaxation in Ni1−xLixO : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6621-6623 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 7Li nuclear magnetic resonance (NMR) spectra and relaxation rates in Ni1−xLixO, for 0.01≤x≤0.46 and for 20≤T≤550 K are presented. For x≤0.2 the antiferromagnetic (AF) phase typical of NiO is still observed. The Neel temperatures TN(x), the temperature dependence of the field at the Li site, and the role of the extra holes in driving the correlated spin dynamics of Ni2+ are derived. In particular, from 7Li relaxation rates W the hopping frequencies of the holes on the AF background and the energy gaps between itinerant and localized states are extracted. In the mixed regime (x≥0.3, LiNiO2 structure-type) in which partial ordering on alternate Li+ and Ni3+ layers occurs, 7Li NMR data display the features typical of disordered paramagnets, consistent with a picture of random distribution of Ni3+ (S=1/2), Ni2+ (S=1) and of spin vacancies Li+ (S=0). In particular, for x=0.46, on cooling, a paramagnetic-like divergence of the width and of the shift of the NMR line is observed while 7Li W's indicate slowing down of the spin fluctuations. The fluctuation frequency decreases in the MHz range below a freezing temperature Tf(approximately-equal-to)40 K. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361903
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence for crossover effects in the spin dynamics of the two-dimensional antiferromagnet Sr2CuO2Cl2 from 35Cl nuclear magnetic resonance : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5084-5086 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 35Cl nuclear magnetic resonance (NMR) and relaxation measurements have been performed in stacked Sr2CuO2Cl2 single crystals with Néel temperature TN=257 K for two crystal orientations with respect to the applied field: H(parallel)c and H⊥c. All the parameters of 35Cl NMR are found to exhibit a strong orientation dependence varying in temperature. In particular, the unconventional anisotropy and strong temperature dependence of the 35Cl nuclear spin–spin relaxation rate, T−12, are presented and discussed in terms of a crossover of the Cu2+ spin dynamics from Heisenberg to XY-like correlation for T→T+N. The onset of anisotropic broadening and shift of the 35Cl NMR line was observed well above TN, which is in agreement with the previous results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361581
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanism of suramin-induced deoligomerization of tumor necrosis factor .alpha. (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 6344-6350 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00019a012
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  • 8
    Electronic Resource
    Electronic Resource
    Spin dynamics in S=1/2 chains and ladders from NMR and susceptibility measurements in Sr14−xNaxCu24O41 : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6602-6604 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The authors report on NMR and susceptibility measurements in Sr14−xNaxCu24O41 for 0≤x≤2. The analysis of the susceptibility evidences that only a small fraction of Cu2+ spins are involved in the dimerization of Cu(1)O2 chains. The introduction of extra holes by Na+ doping is found to decrease the Cu(1)2+ uniform static susceptibility without affecting the amplitude of the dimerization gap. On the other hand, the amplitude of the spin gap in the Cu(2)2O3 two-leg-ladders and the resistivity are reduced by doping. The origin of the discrepancy in the amplitude of the gap estimated by means of nuclear spin-lattice relaxation and susceptibility measurements is briefly discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367744
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic properties and spin dynamics in hole-doped S=1 AF chain: 89Y NMR and susceptibility in Y2−xCaxBaNiO5 : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6605-6607 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hole-doping effects in Haldane chain have been studied by means of magnetic susceptibility and 89Y nuclear magnetic resonance in Y2−xCaxBaNiO5 for x=0, x=0.06 and x=0.18. In nominally pure YBNO detailed information on this prototype of Haldane systems is extracted. In the charge-doped compounds the 89Y relaxation rates indicate that holes induce low-energy excitations with an effective spectral density having a structure characterized by a narrow central peak. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367608
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  • 10
    Electronic Resource
    Electronic Resource
    An optical interferometer for gas bubble measurements (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3564-3566 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact and stable interferometer for the measurement of the radius of a gas bubble in a liquid is described. The system combines a very high sensitivity in radius change measurements (1 A(ring)) with a good determination of the absolute value of the radius itself. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147247
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