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  • 1
    Electronic Resource
    Electronic Resource
    Mechanical Behavior of MoSi2 Reinforced–Si3N4Matrix Composites (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanical behavior of MoSi2 reinforced–Si3N4 matrix composites was investigated as a function of MoSi2 phase content, MoSi2 phase size, and amount of MgO densification aid for the Si3N4 phase. Coarse-phase MoSi2-Si3N4 composites exhibited higher room-temperature fracture toughness than fine-phase composites, reaching values 〉8 MP·am1/2. Composite fracture toughness levels increased at elevated temperature. Fine-phase composites were stronger and more creep resistant than coarse phase composites. Room-temperature strengths 〉1000 MPa and impression creep rates of ∼10−8 s−1 at 1200°C were observed. Increased MgO levels generally were deleterious to MoSi2-Si3N4 mechanical properties. Internal stresses due to MoSi2 and Si3N4 thermal expansion coefficient mismatch appeared to contribute to fracture toughening in MoSi2-Si3N4 composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03234.x
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  • 2
    Electronic Resource
    Electronic Resource
    Thermal Oxidation Kinetics of MoSi2-Based Powders (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation process of MoSi2 is very complex, and controversial results have been reported, especially for the early-stage oxidation before the formation of passive SiO2 film. Most oxidation studies have been carried out on bulk consolidated samples, and the early stage of oxidation has not been studied. In this investigation, very fine MoSi2 powder with an average particle size of 1.6 μm was used. Such a fine particle size makes it easier to study the early stages of oxidation since a significant portion of the powder is oxidized before the formation of passive SiO2 film. The oxidation kinetics of commercial MoSi2-SiC and MoSi2-Si3N4 powder mixtures were also studied for comparison. Weight changes were measured at discrete time intervals at 500° to 1100°C in 0.14 atm of oxygen. X-ray diffraction was used to identify the phases formed during oxidation. Our results show the formation of MoO3 phase and an associated weight gain at low temperatures (500° and 600°C). At temperatures higher than 900°C, Mo5Si3 phase formed first and was subsequently oxidized to solid SiO2 and volatile MoO3, resulting in an initial weight gain followed by subsequent weight loss. A model based on the assumption that oxidation kinetics of both MoSi2 and Mo5Si3 are proportional to their fractions in the system describes the experimental data well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02156.x
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  • 3
    Electronic Resource
    Electronic Resource
    Attenuated multi–mutated herpes simplex virus–1 for the treatment of malignant gliomas (1995)
    [s.l.] : Nature Publishing Group
    Nature medicine 1 (1995), S. 938-943 
    Details
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] We have created a double mutant of the herpes simplex virus (HSV) type 1 (termed G207) with favourable properties for treating human malignant brain tumours: replication–competence in glioblastoma cells (and other dividing cells), attenuated neurovirulence, temperature sensitivity, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nm0995-938
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  • 4
    Electronic Resource
    Electronic Resource
    Bite-force estimation for Tyrannosaurus rex from tooth-marked bones (1996)
    [s.l.] : Nature Publishing Group
    Nature 382 (1996), S. 706-708 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A recently unearthed Triceratops sp. pelvis from the Hell Creek Formation of Montana (USA) bears dozens of large bite marks (Fig. I)8. Casts of some of the deeper punctures show that an adult T. rex produced the marks using its longer anterior caniniform teeth8. The bitten bones are predominantly ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/382706a0
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  • 5
    Electronic Resource
    Electronic Resource
    A method for isolating and culturing vascular smooth muscle cells from porcine cerebral arteries (1996)
    Springer
    Methods in cell science 18 (1996), S. 41-46 
    Details
    ISSN: 1573-0603
    Keywords: Brain ; Artery ; Cultured smooth muscle cells ; cGMP ; cAMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cerebral blood vessels have unique properties when compared to most peripheral vascular beds. One such property is that large cerebral vessels are involved in the regulation of cerebral vascular resistance. Studying smooth muscle cells isolated from these vessels will determine how phenotypic properties of these cells contribute to unique cerebrovascular function. Therefore we developed a method of culturing smooth muscle cells from explants of cerebral arteries of porcine brains obtained, gratis, from a local slaughter house. Cells isolated and cultured by the methods described herein were of smooth muscle origin as indicated by histochemical staining for smooth muscle α-actin. Further, we examined the response of the cultured cells to agonists which activate the cGMP dependent vasodilator system by stimulating soluble guanylyl cyclase (nitroglycerin and sodium nitroprusside) or particulate guanylyl cyclase (C-type natriuretic peptide). Also, forskolin activation of adenylyl cyclase was examined. These agents stimulated an increase in intracellular cGMP and cAMP in a manner that was reproducible in every cell isolation (20 brains) and which remained unchanged through nine passages. Additionally, the cells could be frozen, thawed and replated without loss of responsiveness to these agents. The protocol reported here provides a method for culturing cerebral artery smooth muscle cells that is inexpensive, relatively simple, and which yields cells that can be utilized through multiple passages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123522
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  • 6
    Electronic Resource
    Electronic Resource
    Spatial scale influence on longterm temporal patterns of a semi-arid grassland (1996)
    Springer
    Landscape ecology 11 (1996), S. 107-113 
    Details
    ISSN: 1572-9761
    Keywords: scaling ; temporal patterns ; equilibrium ; stability ; succession ; predictability ; variability ; grassland ; savannah ; chaos ; ecological scale ; vegetation dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Longterm (45 years) temporal data were used to assess the influence of spatial scale on temporal patterns of a semi-arid west Texas grassland. Temporal basal area dynamics of common curlymesquite (Hilaria belangeri (Steud.) Nash) collected from permanent plots within two areas that were released from disturbance (longterm overgrazing and drought), were evaluated at two spatial scales (quadrat, site). Wiens (1989) proposed hypotheses to characterize the influence of scale on variability, predictability, and equilibrium. These hypotheses were tested for this grassland and temporal patterns observed were different for each spatial scale. The large scale (site) was characterized by low variation between units, high variation within units, high potential predictability, and possible movement toward a fluctuating but relatively stable or equilibrial state. At the small scale (quadrat), variation between units was high, predictability low, and there was no indication of movement toward a stable state; chaotic behavior may be expressed at this scale although the length of the temporal record may not be sufficient to evaluate this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02093742
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  • 7
    Electronic Resource
    Electronic Resource
    Chronic effects of oil spill on soil properties and microflora of a rainforest ecosystem in Nigeria (1996)
    Springer
    Water, air & soil pollution 86 (1996), S. 1-11 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Soil and microbiological properties of a tropical rain forest soil were evaluated 17 years after oil spillage to access the chronic effects of, and interrelationship between population of petroleum hydrocarbon utilizing and nitrifying microorganisms. The spatial distribution of petroleum hydrocarbons (oil), the nutrient status and the abundance of heterotrophic microbes along soil transect lines in the contaminated zones served as the index for corroborating the results. The pH status of soil in the contaminated (Heavy impact — HI, and moderate inpact — MI) zones varied from acidic, that is 4.0 to near neutral PH, that is 6.0. The C content of soils decreased from 3.6% at the HI zones to 2.84% at the MI zones. Total N in the HI and MI zones differed by a factor of 0.10%. Available P was higher at the MI than HI zone, while CEC decreased from a combined mean of 6.48 at the HI zones to 4.46 at the MI zones. Although residual oil content was higher in the HI zones than MI zone, the soil nutrient status within these two zones did not vary significantly (P=0.05). However, soil microbes responded differently. For instance, petroleum hydrocarbon utilizers correlated positively with the distribution of oil in the environment. But, not the nitrifying microorganisms. Aerobic nitrifiers were abundant at the HI than MI zones, while anaerobic nitrifiers were higher at the MI than HI zones. With the presence of petroleum hydrocarbon utilizers anf nitrifying microbes. It is possible to enhance the degradation of oil in the 17 yr old spillage by adopting bioremediation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279142
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  • 8
    Electronic Resource
    Electronic Resource
    Implantable hollow fiber bioreactor as a potential treatment for hypercholesterolemia: Characterization of the catalytic unit (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 48 (1995), S. 36-41 
    Details
    ISSN: 0006-3592
    Keywords: hollow fiber ; bioreactor ; immobilized enzymes ; porosity ; phospholipase A2 ; low densitylipoprotein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Previous studies have shown that the modification of low density lipoprotein (LDL) by the enzyme phospholipase A2(PLA2)results in a reduction of cholesterol levels in the plasma of hypercholesterolemic rabbits, due to accelerated clearance of the modified LDL. In the current study, we established techniques and optimized the ratio of enzyme to support for the immobilization of PLA2 on a polymeric support. Hollow fiber bioreactors made from polytetrafluoroethylene (PTFE) polymers were used to encapsulate immobilized PLA2. This design was adopted to eliminate hemolysis of red blood cells by the enzyme. Characterization of the resulting immobilized enzyme in terms of its activity, Michaelis-Menten kinetic constants, and the variation of its activity with incubation time is presented. The enzyme activity was not significantly altered upon incubation at 37°C in lipoprotein-deficient serum (LPDS), over the course of 2 months. The Michaelis-Menten kinetics constants are KM = 8.9 mM, Vmax = 6434.2 for the free enzyme and KappM = 16.7 mM, Vappmax = 619.7 for the immobilized enzyme. These data suggest that a system based on immobilized PLA2 in conjunction with hollow fiber bioreactors (HFBs) may be a good candidate for lowering LDL levels in plasma. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260480107
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  • 9
    Electronic Resource
    Electronic Resource
    The influence of soil depth on plant species response to grazing within a semi-arid savanna (1998)
    Springer
    Plant ecology 138 (1998), S. 89-96 
    Details
    ISSN: 1573-5052
    Keywords: Ecology ; Functional groups ; Diversity ; Herbivory ; Heterogeneity ; Patch dynamics ; Pattern ; Plant-animal interaction ; Rangelands ; Redundancy ; Scale ; Shifting mosaic ; Succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Grassland patches within a semi-arid savanna were evaluated over 45-years for (1) local temporal dynamics of basal area for five dominant grass species within long-term heavily grazed and ungrazed treatments, (2) the influence of soil depth (resource availability) on vegetation dynamics, and (3) the applicability of community-level grazing response groups over fine-scale patterns of soil heterogeneity. Temporal patterns in species composition and basal area were dependent upon soil depth. In the heavy grazed treatment, Hilaria belangeri dominated deep soils while Erioneuron pilosum and Bouteloua trifida were restricted to shallow soils. In the ungrazed treatment, removal of grazing resulted in successional changes that were significantly different across soil depths. After 45 years without grazing, Eriochloa sericea was most abundant on deep soils while Bouteloua curtipendula was more abundant on intermediate and shallow soils. Community-level functional groups that are based on grazing were not appropriate when multiple pattern-driving variables were considered across multiple scales indicating that functional groups should only be applied to certain processes at specific scales. Within the ungrazed treatments, variable soil depths have resulted in a shifting mosaic in time and space where early- and late-successional species co-exist continuously but spatially separated within the community. In the heavily grazed treatment, species are somewhat spatially arranged by soil depths, but much of the inherent heterogeneity is eliminated and species composition is dominated by the three grazing-resistant short-grasses. Broad scale successional changes may appear linear and predictable while at finer scales, the same changes may be described as non-linear and dependent upon soil depth resulting in thresholds that are partially explained by weather patterns, seed bank limitations and competitive inhibitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009704723526
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation and properties of radioactive rhenium glass microspheres intended for in vivo radioembolization therapy (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 617-625 
    Details
    ISSN: 0021-9304
    Keywords: liver tumor treatment ; glass microspheres ; Re-186 ; Re-188 ; rhenium radioisotopes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Rhenium glass microspheres composed of metallic rhenium particles dispersed within a magnesium alumino borate glass matrix were produced by sintering ReO2 powder and glass frit at 1050°C. The in vitro chemical durability of radioactive and nonradioactive microspheres was determined from chemical corrosion tests on microspheres immersed in phosphate-buffered saline (PBS) solution at 37°C. The dosimetric properties of these microspheres also were calculated. The rhenium glass microspheres are chemically durable in body fluids and release 〈 1.2% of radioactive rhenium after being immersed in PBS solution for 32 days at 37°C. Therapeutic radioactive rhenium activities can be obtained in 〈 10 h by neutron activation of these microspheres in a thermal neutron flux of 8 × 1013 cm-2s-1. A 50 mg injection of radioactive rhenium glass microspheres containing 3.7 GBq of 186Re and 8.5 GBq of 188Re could deliver a 100 Gy dose to a cancerous liver while limiting the total body dose from rhenium dissolution in vivo to approximately 1 mGy. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 617-625, 1998.
    Additional Material: 6 Ill.
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