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  • 1995-1999  (3)
  • 1985-1989  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2503-2505 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general method applicable to interacting fine-particle systems in the mean-field approximation is developed. When the external applied field is decreased, interaction and disorder give rise to a rotation of the integration domain that must be considered for the determination of the average values. This model provides useful expressions for obtaining the magnetic easy axis distribution, and reproducing the results of the preceding noninteracting theories when interaction between particles is not taken into account. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6079
    Keywords: 34.50H ; 79.20N ; 61.14F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present detailed double differential distributions of electrons emitted downstream when 100 and 170 keV protons interact with thin carbon, gold and aluminuum foils and compare them to those obtained with protons and neutral hydrogen projectiles interacting with helium gas. The distributions obtained with the gas target show, besides the well known convoy electron peak produced by capture or loss of electrons into the continuum of the emerging ion, a narrow ridge that is aligned with the beam direction. This ridge, which is attributed to electrons moving in the two Coulomb center potential saddle determined by the target and projectile ions, also appears in the ion-solid electron distributions. A typical solid state effect consists in the appearance of two strong lateral humps which are explained as due to diffraction of the ridge electrons in the three dimensional lattice of the polycrystalline foil material. Contrarily the diffraction of convoy electrons is impeded by their strong correlation to the moving ions. In the case of the Aluminuun target the observed diffraction is typical for Al2O3. This indicates that the observed electrons originate from a thin polycrystalline oxyde layer close to the downstream surface of emission.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6079
    Keywords: 34.50.Hc ; 73.30.+y ; 79.20.Rf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a coaxial cylindric electron spectrometer and an electrostatic ion energy analyzer in tandem, a direct measurement of the difference of the energy of convoy peak electron and the electron equivalent ion energy of protons emerging from the downstream surface of C, Au and Al foils is performed in the proton energy range from 60 to 250 keV. This measurement is made possible using the accepted evidence that for a gas target these energies are equal. It is found that also for the beam foil convoy peak electrons, within an experimental average uncertainty of about ±0.1 eV, there is no difference between these energies. If one accepts that the origin of convoy electrons is from inside the solid, the conclusion is that no retardation by the solid surface potential barrier, which is of the order of a few eV, is observed. This is attributed to the strong electron-ion Coulomb interaction which almost completely overshadows the force exerted on the electron by the field of the surface barrier.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-6079
    Keywords: 34.50.H ; 79.20.N ; 61.14.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this note we correct previous evidence, according to which a structure, found in double-differential electron distributions induced by ion beam-foil interaction, could be interpreted in terms of Bragg diffraction. We now attribute this structure to a distortion of the electric field of our spectrometer and present distributions taken with a new equipment in which this distortion is eliminated.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0789
    Keywords: Key words Mesquite ; Carbon dioxide production ; Nitrogen mineralization ; Microbial biomass carbon ; Nitrous oxide production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In the central highlands of Mexico, the vegetation is dominated by mesquite (Prosopis spp.), a leguminous tree or shrub. An experiment was carried out to investigate how cultivating the land and the disappearance of the natural ecosystem affected the biological functioning of the soil. Soil was sampled from under the canopy of isolated (MESQ treatment) and densely growing mesquite trees (DENS treatment), from the surrounding soil not covered by the canopies of the trees (BARE treatment) and from adjacent land cultivated with maize (ARABLE treatment). Soil was characterized and then incubated aerobically for 39 days at 22±1  °C and CO2, N2O production, microbial biomass C and inorganic N concentrations were monitored. The organic C content was 2.3 times and 1.1 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while microbial biomass C was 3.5 times and 1.3 times greater. The microbial biomass activity as expressed by CO2 production was 5.9 times and 3.9 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while N mineralization, as witnessed by the increase in NO3 – concentrations, was 3.4 times and 1.7 times greater. No significant amounts of N2O were produced in any of the treatments. It was found that cultivating land characterized by the presence of mesquite changed its characteristics profoundly, and even soil not covered by tree canopies had higher microbial biomass C, and C and N mineralization than soil cultivated with maize and beans.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the experimental setup at Centro Atómico Bariloche for the measurement of doubly differential electron distributions, in energy and angle of emission, induced by atomic collisions. We present detailed information about the performance of the equipment including a discussion of instrumental effects that could have affected the measured spectra. © 1996 American Institute of Physics.
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