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Results for “effective diffusivity”
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Nonlinear Layer-by-Layer Films: Effects of Chain Diffusivity on Film Structure and Swelling
Here in this paper, we report on the role of molecular diffusivity in the formation of nonlinearly growing polyelectrolyte multilayers (nlPEMs). Electrostatically bound polyelectrolyte multilayers were assembled from poly(methacrylic acid) (PMAA) as a polyanion and quaternized poly(2-(dimethylamino)ethyl methacrylate) (QPC) as a polycation. Film growth as measured by ellipsometry was strongly dependent on the time allowed for each polymer deposition step, suggesting that the diffusivities of the components are crucial in controlling the rate of film growth. Uptake of polyelectrolytes within nlPEMs was relatively slow and occurred on time scales ranging from minutes to hours, depending on the film thickness. Spectroscopic ellipsometry measurements with nlPEM films exposed to aqueous solutions exhibited high (severalfold) degrees of film swelling and different swelling values for films exposed to QPC or PMAA solutions. FTIR spectroscopy showed that the average ionization of film-assembled PMAA increased upon binding of QPC and decreased upon binding of PMAA, in agreement with the charge regulation mechanism for weak polyelectrolytes. The use of neutron reflectometry (NR) enabled quantification of chain intermixing within the film, which was drastically enhanced when longer times were allowed for polyelectrolyte deposition. Diffusion coefficients of the polycation derived from the uptake rates of deuterated chains within hydrogenated films were of the order of 10 –14 cm 2 /s, i.e., 5–6 orders of magnitude smaller than those found for diffusion of free polymer chains in solution. Exchange of the polymer solutions to buffer inhibited film intermixing. Taken together, these results contribute to understanding the mechanism of the growth of nonlinear polyelectrolyte multilayers and demonstrate the possibility of controlling film intermixing, which is highly desirable for potential future applications.
Effect of a diffusion process on the stress concentration near a circular hole
System of differential equations that reflects interrelationships of deformation, diffusion, and thermoconductivity used to study stress concentration around holes in elastic body
Effects of phosphorus diffusions in epitaxial silicon layers.
Phosphorus diffusion into epitaxial silicon layers studied by electrical and structural characteristics of epitaxial diffused planar junctions
Diffusive and radiative effects on vaporization times of drops in film boiling.
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Chemical potential effects on neutrino diffusion in supernovae
The validity of imposing a zero chemical potential for neutrinos in hydrodynamic calculations of collapsing supernovae is investigated in the diffusion approximation of neutrino transport. A coupled system of equations is solved for neutrino and energy diffusion fluxes as well as lepton diffusion in a collapsing supernovae ambient medium, and the results indicate a substantial growth in the neutrino chemical potential for densities greater than 10 to the 12th power gm/cu cm. The rate of energy transport is shown to be significantly affected by increases in Fermi integrals and chemical-potential gradients accompanied by decreases in temperature, and the extent of neutrino particle/antiparticle reactions is found also to affect energy diffusion rates. It is concluded that the photon-like behavior usually assumed for neutrinos may be incorrect and that an extension of the Sn transport approximation to include lepton characteristics is necessary for a definitive answer to the question of neutrino transport in supernovae.
A preliminary study of the effects of vortex diffusers (winglets) on wing flutter
Some experimental flutter results are presented for a simple, flat-plate wing model and for the same wing model equipped with two different upper surface vortex diffusers over the Mach number range from about 0.70 to 0.95. Both vortex diffusers had the same planform, but one weighed about 0.3 percent of the basic wing weight, whereas the other weighed about 1.8 percent of the wing weight. The addition of the lighter vortex diffuser reduced the flutter dynamic pressure by about 3 percent; the heavier vortex diffuser reduced the flutter dynamic pressure by about 12 percent. The experimental flutter results are compared at a Mach number of 0.80 with analytical flutter results obtained by using doublet lattice and lifting surface (Kernel function) unsteady aerodynamic theories.
High-beta effects and anomalous diffusion in plasmas expanding into magnetic fields
A metallic laser-produced plasma is allowed to expand transversely into an applied magnetic field, under conditions where the typical ion cyclotron radius is much larger, and the electron cyclotron radius much smaller, than the experimental dimensions. A stationary background plasma may also be present. Initially, the flow energy density exceeds (B squared/8 times pi), where B is the ambient magnetic field. Magnetic coil probes, Langmuir probes, and microwave diagnostics are used to study the plasma-field interaction. Field compression at the leading edge and field exclusion within the expanding plasma are seen. The diagnostic measurements and comparison with a theoretical model demonstrate plasma turbulence and anomalously high diffusion of field into the expanding plasma.
Effect of diffusion-thermal processes on the high-latitude topside ionosphere
The extent to which diffusion-thermal heat flow affects H(+) temperatures in the high-latitude topside ionosphere is studied. Such a heat flow occurs whenever there are H(+)-O(+) relative drifts. From our study we have found that at high-latitudes, where H(+) flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H(+) temperatures by 500-600 K at altitudes above about 900 km.
Effects of interstage diffuser flow distortion on the performance of a 15.41-centimeter tip diameter axial power turbine
The performance of a variable-area stator, axial flow power turbine was determined in a cold-air component research rig for two inlet duct configurations. The two ducts were an interstage diffuser duct and an accelerated-flow inlet duct which produced stator inlet boundary layer flow blockages of 11 percent and 3 percent, respectively. Turbine blade total efficiency at design point was measured to be 5.3 percent greater with the accelerated-flow inlet duct installed due to the reduction in inlet blockage. Blade component measurements show that of this performance improvement, 35 percent occurred in the stator and 65 percent occurred in the rotor. Analysis of inlet duct internal flow using an Axisymmetric Diffuser Duct Code (ADD Code) were in substantial agreement with the test data.
Effects of interstage diffuser flow distortion on the performance of a 15.41-centimeter tip diameter axial power turbine
The performance of a variable-area stator, axial flow power turbine was determined in a cold-air component research rig for two inlet duct configurations. The two ducts were an interstage diffuser duct and an accelerated-flow inlet duct which produced stator inlet boundary layer flow blockages of 11 percent and 3 percent, respectively. Turbine blade total efficiency at design point was measured to be 5.3 percent greater with the accelerated-flow inlet duct installed due to the reduction in inlet blockage. Blade component measurements show that of this performance improvement, 35 percent occurred in the stator and 65 percent occurred in the rotor. Analysis of inlet duct internal flow using an Axisymmetric Diffuser Duct Code (ADD Code) were in substantial agreement with the test data.
Investigation of Effect of Increased Diffusion of Rotor-blade Suction-surface Velocity on Performance of Transonic Turbine
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An experimental investigation of the effects of several diffusers and diffuser-entrance-mixing-section combinations on the power requirements of a 4 1/2-inch by 4 1/2-inch slotted transonic wind tunnel
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Effects of Refractive Index and Diffuse or Specular Boundaries on a Radiating Isothermal Layer
Equilibrium temperatures of an absorbing-emitting layer were obtained for exposure to incident radiation and with the layer boundaries either specular or diffuse. For high refractive indices the surface condition can influence the radiative heat balance if the layer optical thickness is small. Hence for a spectrally varying absorption coefficient the layer temperature is affected if there is significant radiative energy in the spectral range with a small absorption coefficient. Similar behavior was obtained for transient radiative cooling of a layer where the results are affected by the initial temperature and hence the fraction of energy radiated in the short wavelength region where the absorption coefficient is small. The results are a layer without internal scattering. If internal scattering is significant, the radiation reaching the internal surface of a boundary is diffused and the effect of the two different surface conditions would become small.
Turbulent Diffusion and Its Effects on the Chemical Composition of Cloud Cores
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Comparison of the measured and analytical response profiles of 3.3. to 15.5 mu imaging system and the effect of detector diffusion
This paper provides an overview of the Tropospheric Emission Spectrometer (TES) and its mission, as part of NASA's Earth Observing System.
Seasonal variability in global eddy diffusion and the effect on neutral density
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