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  • 1
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dynamics of fungal and bacterial potential physiological activities during leaf, branch, and bark litter decomposition along a gap size gradient in a subtropical forest was determined using substrate-induced respiration (SIR) with antibiotics selective for fungi and bacteria, respectively. A gap size gradient (1) was under closed canopy; (2) had small gaps with a diameter (≤5m); (3) had small to intermediate gaps (5–15 m diameter); (4) had intermediate to large gaps (15–30 m diameter); and (5) had large gaps (≥30 m diameter). Litter decomposition was studied using a litter bag technique. Fungi had higher SIR than bacteria for each type of litter in any size class of gaps. Gaps 1, 2, and 3 had higher fungal and bacterial SIRs than gaps 4 and 5. Moreover, decomposing leaf litter exhibited higher fungal and bacterial SIRs than branch, and branch higher than bark. Simple correlation analysis indicated that fungal SIR was a reliable index of decomposition rates. Fungal SIR was significantly and positively correlated with soil moisture, whereas bacterial SIR was not significantly correlated with soil moisture. The relationships among microclimatic factors, fungal and bacterial physiological activities, and rates of plant litter decomposition suggest that, in subtropical ecosystems, fungal community activities were strongly and directly regulated by the environmental heterogeneity within gaps, and an important regulator of rates of plant litter decomposition rates.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 83 (1999), S. 535-556 
    ISSN: 0945-3245
    Keywords: Mathematics Subject Classification (1991):G65F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary. We describe a new iterative method for the solution of large, very ill-conditioned linear systems of equations that arise when discretizing linear ill-posed problems. The right-hand side vector represents the given data and is assumed to be contaminated by measurement errors. Our method applies a filter function of the form $\varphi_\beta(t):=1-\exp(-\beta t^2)$ with the purpose of reducing the influence of the errors in the right-hand side vector on the computed approximate solution of the linear system. Here $\beta$ is a regularization parameter. The iterative method is derived by expanding $\varphi_\beta(t)$ in terms of Chebyshev polynomials. The method requires only little computer memory and is well suited for the solution of large-scale problems. We also show how a value of $\beta$ and an associated approximate solution that satisfies the Morozov discrepancy principle can be computed efficiently. An application to image restoration illustrates the performance of the method.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food processing and preservation 23 (1999), S. 0 
    ISSN: 1745-4549
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cranberry juice was treated either by high voltage pulsed electric field (PEF) at 20 kV/cm and 40 kV/cm for 50 and 150°s, or by thermal treatment at 90C for 90s. Higher field strength and longer treatment time reduced more viable microbial cells. the overall volatile profile of the juice was not affected by PEF treatment but it was affected by thermal treatment. No Significant difference in color was observed between the control and PEF treated samples. the application of 40kV/cm for 150 1ts resulted in no growth of molds and yeasts during storage at 22 and 4C, and no growth of aerobic bacteria during storage at 4C. PEF is an alternative process to thermal pasteurization for cranberry juice.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food process engineering 20 (1997), S. 0 
    ISSN: 1745-4530
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Microbial inactivation kinetic models are needed to predict treatment dosage in food pasteurization processes. In this study, we determined inactivation kinetic models of Salmonella dublin in skim milk with a co-field flow high voltage pulsed electric field (PEF) treatment system. Electric field strength of 15–40 kV/cm, treatment time of 12–127 μs, medium temperatures of 10–50C were tested. A new inactivation kinetic model that combines the effect of treatment time to electric field strength or medium temperature was developed.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied extended x-ray absorption fine structure (EXAFS) spectroscopy to study the cation distribution in a series of spin-sprayed NiZn-ferrite films, Ni0.15ZnyFe2.85−yO4 (y=0.16, 0.23, 0.40, 0.60). The Ni, Zn, and Fe EXAFS were collected from each sample and analyzed to Fourier transforms. Samples of Ni-ferrite, Zn-ferrite, and magnetite were similarly studied as empirical standards. These standards, together with EXAFS data generated from the theoretical EXAFS FEFF codes, allowed the correlation of features in the Fourier transforms with specific lattice sites in the spinel unit cell. We find that the Ni ions reside mostly on the octahedral (B) sites whereas the Zn ions are predominantly on the tetrahedral (A) sites. The Fe ions reside on both A and B sites in a ratio determined by the ratio of Zn/Fe. The addition of Zn displaces a larger fraction of Fe cations onto the B sites serving to increase the net magnetization. The fraction of A site Ni ions is measured to increase peaking at ≈25% for y=0.6. At higher Zn concentrations (y≥0.5) the lattice experiences local distortions around the Zn sites causing a decrease in the superexchange resulting in a decrease in the net magnetization. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2054-2056 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a large electrostrictive strain in electron irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer at a composition with 65 mol % vinylidene fluoride, which also exhibits a large ratio of strain to applied field (∼275 pm/V). The strain response is nearly independent of the external driving condition (unipolar or bipolar field) and does not change with temperature in about 20 °C temperature range near room temperature. Moreover, near room temperature, the material can reach a relatively high quasistatic longitudinal electromechanical coupling factor k33∼0.33. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1048-1050 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrostrictive coefficients of prototype cubic phase of PbMg1/3Nb2/3O3 are studied using a high-resolution neutron powder diffraction experiment. The key idea of the approach is to "eliminate" from the material the inhomogeneity related to the presence of the double-phase mixture "polar regions/nonpolar matrix," and to study two structurally homogeneous states: prototype cubic at temperatures above 600 K and rhombohedral ferroelectric at temperatures below 220 K. The obtained value of volumetric electrostrictive coefficient, Qh=(8.3±1.0)×10−2 ×(m4/C2), is consistent with those of other perovskite ferroelectrics with a prototype cubic phase. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 407-409 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polymer optical fibers have received much attention in recent years as they can replace silica glass fibers in local area nets in the future. A neodymium ion (Nd3+)-doped poly(methyl methacrylate) (PMMA) fiber has been made from Nd3+ containing PMMA as a core and silica resin as claddings. Fluorescence of the fiber results from the transition of 4G5/2 to 4I9/2 in a three energy level system. Amplified spontaneous emission (ASE) at 575 nm has also been observed and the critical power at a pump wavelength of 514.5 nm for the onset of ASE has been found to be 85 mW. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3181-3187 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The aging characteristics of the electrostrictive lead magnesium niobate–lead titanate [(1−x)PMN–xPT] under dc bias field were investigated. It was observed that the amount of aging increases with the PT content for the compositions investigated (x≤0.3). For a fixed composition, the aging rate rises with temperature. It was shown that the aging follows a stretched exponential time law, which is typical for the time-dependent behavior in polar glass and random field systems. In PMN–PT, the dielectric constant shows a much weaker aging than the piezoelectric coefficient, reflecting the importance of the stress coupling of the defect field to the micropolar region during the aging since the polar vector of the microregions can have both 180° and non-180° reorientations while only the non-180° reorientation contributes to the observed piezoelectric effect. Experimental results also reveal that the defect field developed during the aging in these materials under dc bias field is quite different from those in normal ferroelectrics and in Mn-doped PMN and 0.9 PMN–0.1PT. The direction of the defect electric field is opposite to the direction of the original dc bias field, indicating that the defect field is the result of a direct coupling to the external bias field rather than induced by the polar domains. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3754-3761 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The piezoelectric shear strain S5 of several commercial lead zirconate titanate (PZT) piezoceramics was evaluated under the nonresonant condition in a sinusoidal ac-field E1(t) applied perpendicular to the poling direction. Results obtained on donor doped (soft PZT) and acceptor doped (hard PZT) ceramics are compared. At fields sufficiently below the limiting field Elim necessary to electrically depole the sample, we find a linear, nonhysteretic relationship between S5 and the polarization P1. In soft PZT ceramics, the effective piezoelectric shear coefficient d15=S5/E1 shows a pronounced ac-field dependence which was fitted according to d15(E1)=dlin[1+(dnlE1)α] with α(approximate)1.2. The results indicate that irreversible motion of non-180° walls causes the nonlinearity of PZT and the contribution of 180° walls to the linear and nonlinear coefficients is negligible. The analysis of the relationship between linear and nonlinear coefficients obtained at different ceramic systems suggests that there exists another extrinsic contribution to the permittivity in PZT which may not be attributed to domain wall motion but may be responsible to the dielectric dispersion at microwave frequencies. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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