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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Environmental geology 40 (2000), S. 223-233 
    ISSN: 1432-0495
    Keywords: Keywords Coastal aquifers ; Seawater intrusion ; Leaky aquifer system ; Numerical modeling ; Numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A leaky aquifer system occurs in the coastal plain near Beihai, China. Seawater intrusion into the confined aquifer took place along the northern coast. Chloride concentrations at some observation wells increased steadily from 1988 and were at their peak in 1993. A quasi-three-dimensional element model has been developed to simulate the spatial and temporal evolution of hydraulic heads and chloride concentrations of the groundwater near the northern coast. The simulation model was based on the transition zone approach, which requires simultaneous solution of the governing water flow and solute transport equations. An irregular grid of a quadrangle was used to discretize the flow domain. Various aquifer parameters were verified with the numerical model in order to obtain satisfactory matches between computed values and observed data from an investigation. Three pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and chloride concentrations in groundwater in the study area. Results show that seawater intrusion would worsen in the confined aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area and to moderate pumpage rates from water supply wells far from the seashore, may limit seawater intrusion significantly and is considered attractive in the area.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 7445-7457 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In this paper we investigate the kinetic foundation of extended irreversible thermodynamics via the moment method. First we consider the construct of the 1-particle distribution function f in terms of its moments by maximizing the entropy density function. We then project f from its L2 space onto the local thermodynamic variables z=(z1,...,zN) in the thermodynamic base space B(circumflex)N. Thus instead of the Boltzmann equation we consider a set of evolution equations of z in B(circumflex)N. Second, we formulate the laws of thermodynamics governing the variable z in B(circumflex)N. These laws exhibit an intrinsic geometric structure of thermodynamics in the setting of contact geometry. Finally, as an illustration, we discuss the evolution equations for the bulk pressure Pb, heat flux Q, and the symmetric traceless tensor π(two down arrows) corresponding to the viscous and heat conduction irreversible processes. These equations can be formulated as an abstract inhomogeneous hyperbolic evolution equation. By employing the C0 semigroup technique, we discuss the solution of the evolution equation and its asymptotic behavior. We show that thermodynamic stability condition of the system implies asymptotic dynamical stability of the solution and vice versa. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9617-9623 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report density functional theory calculations, using pseudopotentials with a plane wave basis, of methyl adsorbed on the MoO3(010) surface at 0.5 and 1.0 ML coverages. The MoO3 surface is modeled by a one-layer slab. Methyl is adsorbed most strongly over the terminal oxygen, where methoxy is formed. Over the bridging oxygens, qualitatively different results are obtained depending on the coverage of methyl. At 0.5 ML, methoxy is formed over the bridging oxygens, with an associated relaxation of the surface caused by a repulsion between the methyl and the terminal oxygen. For the 1.0 ML coverage, methyl is not stable and decomposes. Over the asymmetric bridging oxygen, methyl reacts to form formaldehyde and hydroxyl, while over the symmetric bridging oxygen a formyl species and water are produced. The hydroxyl and water are formed via hydrogen transfer to a terminal oxygen. The bonding and reaction of methyl over the various oxygen species are analyzed and discussed using charge density difference plots as well as the crystal orbital overlap projection (COOP). For the 0.5 ML methyl coverage, this analysis shows that the tilting of the terminal oxygen bond weakens this bond slightly. For the 1.0 ML methyl coverage, the COOP plots indicate that the decomposition of methyl over the bridging oxygens is not as stable as methyl over the terminal oxygen because the presence of the carbon fragments affects the electronic structure, and causes a weakening of the Mo–terminal oxygen bond. These results are discussed in the context of partial oxidation reactions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 439-442 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Atom probe field ion microscopy was employed to investigate the distribution of Al in a nanocrystalline Fe88Zr7B3Al2 soft magnet with optimal magnetic performance. The atom probe concentration depth profiles show that the Al atoms preferentially partition into the residual amorphous phase, and the partitioning factor of Al is approximately five times larger in the amorphous phase than in the bcc Fe phase. Based on the experimental results, the beneficial effect of the addition of Al on the soft magnetic properties is attributed to the change of the inherent magnetostriction constant of the residual amorphous phase induced by Al partitioning. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6928-6930 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Atom probe field ion microscopy was employed to investigate the distribution of the alloying elements in a nanocrystalline Fe76.5Nd8Co8B6Nb1.5 (at. %) alloy consisting of soft magnetic α-Fe and hard magnetic Nd2Fe14B. It was found that Co atoms prefer to partition into Nd2Fe14B phase. The partitioning factor of Co in the hard magnetic phase is approximately 2 with respect to the soft magnetic phase, α-Fe. Atom probe concentration and integrated depth profiles showed that the Nb atoms segregate at the interfaces between the soft and the hard magnetic phases. Based on the atom probe results, the beneficial effects of Nb and Co on the microstructure and the hard magnetic properties of the nanocomposite are discussed. © 2000 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 76 (2000), S. 967-969 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.5−xNi10Mx (M=Ag, Pd, Au, or Pt; x=5 and 10 at %) alloys. The volume fraction (Vf) of the I phase is about 85% for the 5% M alloy and nearly 100% for the 10% M alloy. The I phase changes to Zr2Cu+Zr2Ni+Zr2Al3 in a fully annealed state. Compressive fracture strength (σc,f) and fracture elongation (εc,f) of the 10% Pd cylinder with a diameter of 2 mm are respectively 1640 MPa and 2.2% for the glassy phase and increase to 1830 MPa and 3.1% for the I phase. The increase in σc,f is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in εc,f results from the localization effect of deformation into the glassy layer. The precipitation of the I phase implies that the glassy alloys include randomly oriented I configurations. The present work shows promise for the new class of high-strength nanoquasicrystalline materials. © 2000 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 77 (2000), S. 4298-4300 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is proposed to measure the plastic deformation of thin metallic films on Si substrates induced by thermal cycling. The cross-sectional profiles of pattern-grown square Al films with a thickness of ∼250 nm and a size of ∼6 μm×6 μm were measured before and after thermal cycling by employing an atomic force microscope. With the assistance of statistical analysis, the change in the size and shape of the thin films were determined. Based on theoretical considerations, the thermal cycling deformation of thin films is attributed to creep and plasticity effects, accommodated by diffusion-controlled interfacial sliding. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1437-7780
    Keywords: Key words Cefpiramide ; Cephalosporin ; Clinical strains ; MIC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The in-vitro antibacterial activity of cefpiramide was compared with those of 15 other broad-spectrum cephalosporins. A total of 440 clinical strains of bacteria, including 9 bacterial species, were isolated from our hospital in 1998. The minimum inhibitory concentrations (MICs) of cefpiramide and five other antibiotics were determined for each species, using the agar-dilution method. The MIC of cefpiramide for Escherichia coli and Klebsiella pneumoniae was higher than those of three other third-generation cephalosporins, (ie, cefoperazone, ceftazidime, and ceftriaxone). Fifty-one percent (26/51) of Enterobacter cloacae isolates were resistant to cefpiramide. Cefoperazone/sulbactam and cefepime had greater activity against E. cloacae (resistance, 3.9% and 19.6%, respectively) than cefpiramide. Cefpiramide was more active against Pseudomonas aeruginosa (resistance rates, 12%) than cefoperazone, ceftazidime, ceftriaxone, aztreonam, and cefepime. Cefpiramide-resistant P. aeruginosa strains were resistant to ceftazidime, but 27% of ceftazidime-resistant strains were susceptible to cefpiramide; 15.3% of cefpiramide-resistant S. maltophilia strains were also susceptible to ceftazidime, but 50% of ceftazidime-resistant strains were still susceptible to cefpiramide. Cefoperazone/sulbactam was the most active agent against Acinetobacter baumannii, showing a resistance rate of 2%. Ampicillin/sulbactam, ceftazidime, and cefpiramide were the second most active agents, and about 50% of the tested strains were susceptible to these three antibiotics. Cefpiramide had an activity comparable to that of all tested β-lactams against oxacillin-susceptible Staphylococcus aureus (MIC90, 2 μg/ml). Against Streptococcus pneumoniae and Haemophilus influenzae, cefpiramide had good activity, with an MIC90 concentration at which 90% of the strain was inhibited of 1 μg/ml and 0.5 μg/ml, respectively. These results indicated that cefpiramide was more active against glucose non-fermenting bacteria than against Enterobacteriaceae, and was very active against oxacillin-susceptible Staphylo-coccus aureus, S. pneumoniae, and H. influenzae. Thus, cefpiramide may be a good choice of drug for the treatment of patients with infections with glucose non-fermenting bacteria and community acquired infections.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1437-7780
    Keywords: Key words Meropenem ; β-Lactams ; Clinical isolated strains ; MIC (E-test)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In 1999, a surveillance study was initiated in a hospital in Beijing to monitor the potency and spectrum of five extended-spectrum β-lactam antimicrobial agents (meropenem, imipenem, cefepime, ceftazidime, and cefoperazone/sulbactam) tested against 554 strains of bacteria. Five groups of organisms were tested by the E-test method, with results validated by concurrent quality control strain analysis. Results were tabulated, and 100% of quality assurance tests (16/16 tests) were within ranges recommended by the National Committee for Clinical Laboratory Standards. Of the five β-lactam drugs tested, meropenem and imipenem were the most active against all isolates tested. Overall, the rank order of activity of the five agents was: meropenem (94.6% susceptible) 〉 imipenem (90.1%) 〉 cefepime (77.6%), cefoperazone/sulbactam (77.5%), ceftazidime (76.6%). Ninety-five percent of Enterobacter were to meropenem, while 82% were susceptible to imipenem. Meropenem was more active than imipenem against Pseudomonas aeruginosa. The minimum inhibitory concentration (MIC) of meropenem was eightfold lower than that of imipenem. Meropenem had excellent activity against Haemophilus influenzae, Streptococcus pneumoniae, and oxacillin-susceptible staphylococci.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International archives of occupational and environmental health 73 (2000), S. 570-574 
    ISSN: 1432-1246
    Keywords: Key words Toluene diisocyanate ; Sampling efficiency ; Closed-face cassette ; Open-face cassette
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objectives: A modified closed-face cassette was developed for sampling and derivatizing airborne toluene diisocyanate (TDI). Methods: The cassette was assembled as a regular two-piece cassette sampler except that the whole inner surface of the sampler was loaded with coated filters to ensure that all of the aspirated TDI react with 1-(2-pyridyl) piperazine (1-2pp). Results: A test atmosphere study showed that the sampling efficiencies were 89.4% and 94.3% for 2,4-TDI and 2,6-TDI. One-third of the 2,4-TDI and 2,6-TDI mass was constantly collected on the top and middle-rim filters. A polyurethane (PU)-manufacturing plant study revealed an average of 35% and 33% of both isomer masses collected on the top and middle-rim filters. The 2,4-TDI collection of the closed-face cassette sampling was 21% higher than that of open-face sampling. Furthermore, consistent isomeric compositions of airborne 2,4-/2,6- TDI obtained from both types of samplers validated the use of the modified cassette sampler. Conclusions: The closed-face cassette sampler is capable of a higher collection of airborne TDI and the technique involved is as simple and feasible as that of the open-face sampler.
    Type of Medium: Electronic Resource
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