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  • 1
    Electronic Resource
    Electronic Resource
    Field strength and dose dependence of contrast enhancement by gadolinium-based MR contrast agents (1999)
    Springer
    European radiology 9 (1999), S. 998-1004 
    Details
    ISSN: 1432-1084
    Keywords: Key words: MR imaging ; Contrast agents ; MR field strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The relaxivities r1 and r2 of magnetic resonance contrast agents and the T1 relaxation time values of tissues are strongly field dependent. We present quantitative data and simulations of different gadolinium-based extracellular fluid contrast agents and the modulation of their contrast enhancement by the magnetic field to be able to answer the following questions: How are the dose and field dependences of their contrast enhancement? Is there an interrelationship between dose and field dependence? Should one increase or decrease doses at specific fields? Nuclear magnetic relaxation dispersion data were acquired for the following contrast agents: gadopentetate dimeglumine, gadoterate meglumine, gadodiamide injection, and gadoteridol injection, as well as for several normal and pathological human tissue samples. The magnetic field range stretched from 0.0002 to 4.7 T, including the entire clinical imaging range. The data acquired were then fitted with the appropriate theoretical models. The combination of the diamagnetic relaxation rates (R1 = 1/T1 and R2 = 1/T2) of tissues with the respective paramagnetic contributions of the contrast agents allowed the prediction of image contrast at any magnetic field. The results revealed a nearly identical field and dose-dependent increase of contrast enhancement induced by these contrast agents within a certain dose range. The target tissue concentration (TTC) was an important though nonlinear factor for enhancement. The currently recommended dose of 0.1 mmol/kg body weight seems to be a compromise close to the lower limits of diagnostically sufficient contrast enhancement for clinical imaging at all field strengths. At low field contrast enhancement might be insufficient. Adjustment of dose or concentration, or a new class of contrast agents with optimized relaxivity, would be a valuable contribution to a better diagnostic yield of contrast enhancement at all fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003300050781
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  • 2
    Electronic Resource
    Electronic Resource
    Fabrication and dc, microwave characteristics of submicron Schottky-collector AlAs/In0.53Ga0.47As/InP resonant tunneling diodes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4819-4821 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the fabrication and dc, microwave characteristics of 0.1 μm, Schottky-collector resonant tunnel diodes (SRTDs) in the AlAs/In0.53Ga0.47As/InP material system. Devices with contact areas as small as 0.05 μm2 have been fabricated using electron beam lithography with an interrupted footprint T-gate process. SRTD's fabricated with 1.4 nm AlAs barriers exhibited a 5×105 A/cm2 peak current density at 0.95 V and a −19 mS/μm2 peak negative conductance. The devices incorporate fully depleted P-doped cap layers to suppress surface leakage currents. From the measured dc and microwave characteristics, a maximum frequency of oscillation fmax=2.2 THz is estimated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359405
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  • 3
    Electronic Resource
    Electronic Resource
    Heterogeneity and the voluntary provision of public goods (1999)
    Springer
    Experimental economics 2 (1999), S. 5-30 
    Details
    ISSN: 1573-6938
    Keywords: public goods ; voluntary provision ; heterogeneous agents ; H41 ; C92
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract We investigate the effects of heterogeneity and incomplete information on aggregate contributions to a public good using the voluntary contribution mechanism. The non-linear laboratory environment has three-person groups as partners under varying conditions of information and communication. Bergstrom, Blum and Varian predict that increasing heterogeneity will have no effect on aggregate contributions in a no-communication environment. Ledyard conjectures a positive effect of incomplete information, a negative effect of heterogeneity, and a positive interaction of heterogeneity and incomplete information. We find that incomplete information has a small but significantnegative effect. Heterogeneity has apositive effect on aggregate contributions, but its effects interact unexpectedly with communication. In a no-communication environment, heterogeneity in two dimensions (endowment and preferences) increases contributions substantially while heterogeneity in a single dimension (endowment or preferences) has little effect. In the communication environment we find the reverse. We also find a positive interaction between heterogeneity and incomplete information. Thus we reject the Bergstrom, Blume and Varian invariance result and provide mixed evidence on Ledyard's conjectures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669132
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  • 4
    Electronic Resource
    Electronic Resource
    Heterogeneity and the Voluntary Provision of Public Goods (1999)
    Springer
    Experimental economics 2 (1999), S. 5-30 
    Details
    ISSN: 1573-6938
    Keywords: public goods ; voluntary provision ; heterogeneous agents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract We investigate the effects of heterogeneity and incomplete information on aggregate contributions to a public good using the voluntary contribution mechanism. The non-linear laboratory environment has three-person groups as partners under varying conditions of information and communication. Bergstrom, Blum and Varian predict that increasing heterogeneity will have no effect on aggregate contributions in a no-communication environment. Ledyard conjectures a positive effect of incomplete information, a negative effect of heterogeneity, and a positive interaction of heterogeneity and incomplete information. We find that incomplete information has a small but significant negative effect. Heterogeneity has a positive effect on aggregate contributions, but its effects interact unexpectedly with communication. In a no-communication environment, heterogeneity in two dimensions (endowment and preferences) increases contributions substantially while heterogeneity in a single dimension (endowment or preferences) has little effect. In the communication environment we find the reverse. We also find a positive interaction between heterogeneity and incomplete information. Thus we reject the Bergstrom, Blume and Varian invariance result and provide mixed evidence on Ledyard's conjectures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009984414401
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Flame pyrolysis – a preparation route for ultrafine pure γ-Fe2O3 powders and the control of their particle size and properties (1997)
    Springer
    Journal of materials science 32 (1997), S. 1083-1092 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Highly dispersed γ-Fe2O3 powders with particle sizes down to 5 nm were directly synthesized by combustion of solutions of iron pentacarbonyl or iron(III) acetylacetonate in toluene in an oxyhydrogen flame. The particle size as well as other properties of the obtained powders can be controlled simply by varying the iron concentration in the starting solutions. Phase composition, morphological and magnetic properties of the powders were studied. The reasons for the formation of γ-Fe2O3 are discussed by means of structure–chemical/kinetic considerations. The materials are interesting as recording materials, or ferrofluids, or for colour imaging and bioprocessing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018598927041
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between structure and rheological properties in the melt of polymers containing spherical inclusions (1995)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 301-308 
    Details
    ISSN: 1042-7147
    Keywords: polymer blends ; melt rheology ; crosslinked rubber ; structured latex ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1995.220060508
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