On the adiabatic temperature gradient in the earth's shell ob adiabaticheskom gradiente temperatur v obolochke zemli
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Zharov, V. N.↗
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Hot Pot Contoured Temperature Gradient Map
Temperature gradient contours derived from Oski temperature gradient hole program and from earlier published information.
15 GEOTHERMAL ENERGY↗
Viscous effects on the Rayleigh-Taylor instability with background temperature gradient
Here we studied the growth rate of the compressible Rayleigh-Taylor instability in the presence of a background temperature gradient, Θ, using a normal mode analysis. The effect of Θ variation is examined for three interface types corresponding to the combinations of the viscous properties of the fluids (inviscid-inviscid, viscous-viscous, and viscous-inviscid) at different Atwood numbers, At, and when at least one of the fluids' viscosity is non-zero, as a function of the Grashof number. For the general case, the resulting ordinary differential equations are solved numerically; however, dispersion relations for the growth rate are presented for several limiting cases. An analytical solution is found for the inviscid-inviscid interface and the corresponding dispersion equation for the growth rate is obtained in the limit of large Θ. For the viscous-inviscid case, a dispersion relation is derived in the incompressible limit and Θ=0. Compared to Θ=0 case, the role of Θ<0 (hotter light fluid) is destabilizing and becomes stabilizing when Θ>0 (colder light fluid). The most pronounced effect of Θ ≠ 0 is found at low At and/or at large perturbation wavelengths relative to the domain size for all interface types. On the other hand, at small perturbation wavelengths relative to the domain size, the growth rate for the Θ<0 case exceeds the infinite domain incompressible constant density result. The results are applied to two practical examples, using sets of parameters relevant to Inertial Confinement Fusion coasting stage and solar corona plumes. The role of viscosity on the growth rate reduction is discussed together with highlighting the range of wavenumbers most affected by viscosity. The viscous effects further increase in the presence of background temperature gradient, when the viscosity is temperature dependent.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Temperature gradients and clear-air turbulence probabilities
In order to forecast clear-air turbulence (CAT) in jet aircraft flights, a study was conducted in which the data from a special-purpose instrument aboard a Boeing 747 jet airliner were compared with satellite-derived radiance gradients, conventional temperature gradients from analyzed maps, and temperature gradients obtained from a total air temperature sensor on the plane. The advantage of making use of satellite-derived data is that they are available worldwide without the need for radiosonde observations, which are scarce in many parts of the world. Major conclusions are that CAT probabilities are significantly higher over mountains than flat terrain, and that satellite radiance gradients appear to discriminate between CAT and no CAT better than conventional temperature gradients over flat lands, whereas the reverse is true over mountains, the differences between the two techniques being not large over mountains.
Bender, M. A.↗
Development of core ion temperature gradients and edge sheared flows in a helicon plasma device investigated by laser induced fluorescence measurements
We report experimental observation of ion heating and subsequent development of a prominent ion temperature gradient in the core of a linear magnetized plasma device, and the controlled shear de-correlation experiment. Simultaneously, we also observe the development of strong sheared flows at the edge of the device. Both the ion temperature and the azimuthal velocity profiles are quite flat at low magnetic fields. As the magnetic field is increased, the core ion temperature increases, producing centrally peaked ion temperature profiles and therefore strong radial gradients in the ion temperature. Similarly, we observe the development of large azimuthal flows at the edge, with increasing magnetic field, leading to strong radially sheared plasma flows. The ion velocities and temperatures are derived from laser induced fluorescence measurements of Doppler resolved velocity distribution functions of argon ions. These features are consistent with the previous observations of simultaneously existing radially separated multiple plasma instabilities that exhibit complex plasma dynamics in a very simple plasma system. The ion temperature gradients in the core and the radially sheared azimuthal velocities at the edge point to mechanisms that can drive the multiple plasma instabilities, that were reported earlier.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The study of the transition regime between slab and mixed slab-toroidal electron temperature gradient modes in a basic experiment
Electron temperature gradient (ETG) modes are suspected sources of anomalous electron thermal transport in magnetically confined plasmas as in tokamaks. Prior work in the Columbia Linear Machine (CLM) has been able to produce and identify slab ETG modes in a slab geometry [Wei et al., Phys. Plasmas 17, 042108 (2010)]. Now by modifying CLM to introduce curvature to the confining axial magnetic field, we have excited mixed slab-toroidal modes. Linear theory predicts a transition between slab and toroidal ETG modes when (k{sub ∥}R{sub c})/(k{sub y}ρ) ∼1 [J. Kim and W. Horton, Phys. Fluids B 3, 1167 (1991)]. We observe changes in the mode amplitude for levels of curvature R{sub c}{sup −1}≪(k{sub ∥,slab})/(k{sub ⊥}ρ) , which may be explained by reductions in k{sub ∥} in the transition from slab to mixed slab-toroidal modes, as also predicted by theory. We present mode amplitude scaling as a function of magnetic field curvature. Over the range of curvature available in CLM experimentally we find a modest increase in saturated ETG potential fluctuations (∼1.5×), and a substantial increase in the power density of individual mode peaks (∼4–5×)
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Microwave Heating-Induced Temperature Gradients in Liquid–Liquid Biphasic Systems
Microwaves (MWs) can enable the electrification and intensification of chemical manufacturing. They have been applied to various unit separations, such as drying, distillation, and extraction, entailing gas–liquid and solid–liquid systems. However, a limited quantitative understanding of MW-heated liquid–liquid biphasic systems related to extraction exists. This work measures the temporal and spatial temperature difference between an aqueous and an organic phase in batch and continuous microfluidic modes. We demonstrate permanent temperature differences between phases over 35 °C and spatiotemporal periodic and quasiperiodic oscillations modulated by the flow patterns. The temperature differences are primarily driven by the faster absorption rate of MW irradiation by the aqueous phase versus the slower heat transfer from the aqueous phase to the organic phase. These are amplified by low specific interfacial area and modifications of the electromagnetic field. We employ a multiphysics model to predict the temperature difference in a batch system. The model is in good agreement with the experiments. We demonstrate a strong effect of input power, dielectric properties of organic solvents, the volume of solvents, and the volume ratio between phases on the temperature difference. A simple analytical model describes the temperature difference and provides design principles. Furthermore, the combined approach offers new insights into the design and optimization of the MW-heated biphasic systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Sound beam manipulation based on temperature gradients
Previous research with temperature gradients has shown the feasibility of controlling airborne sound propagation. Here, we present a temperature gradients based airborne sound manipulation schemes: a cylindrical acoustic omnidirectional absorber (AOA). The proposed AOA has high absorption performance which can almost completely absorb the incident wave. Geometric acoustics is used to obtain the refractive index distributions with different radii, which is then utilized to deduce the desired temperature gradients. Since resonant units are not applied in the scheme, its working bandwidth is expected to be broadband. The scheme is temperature-tuned and easy to realize, which is of potential interest to fields such as noise control or acoustic cloaking.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Gradient-driven flux-tube simulations of ion temperature gradient turbulence close to the non-linear threshold
It is shown that Ion Temperature Gradient turbulence close to the threshold exhibits a long time behaviour, with smaller heat fluxes at later times. This reduction is connected with the slow growth of long wave length zonal flows, and consequently, the numerical dissipation on these flows must be sufficiently small. Close to the nonlinear threshold for turbulence generation, a relatively small dissipation can maintain a turbulent state with a sizeable heat flux, through the damping of the zonal flow. Lowering the dissipation causes the turbulence, for temperature gradients close to the threshold, to be subdued. The heat flux then does not go smoothly to zero when the threshold is approached from above. Rather, a finite minimum heat flux is obtained below which no fully developed turbulent state exists. The threshold value of the temperature gradient length at which this finite heat flux is obtained is up to 30% larger compared with the threshold value obtained by extrapolating the heat flux to zero, and the cyclone base case is found to be nonlinearly stable. Transport is subdued when a fully developed staircase structure in the E × B shearing rate forms. Just above the threshold, an incomplete staircase develops, and transport is mediated by avalanche structures which propagate through the marginally stable regions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A novel high-temperature MAS probe with optimized temperature gradient across sample rotor for in-situ monitoring of high-temperature high-pressure chemical reactions
We present a novel nuclear magnetic resonance (NMR) probe design focused on optimizing the temperature gradient across the sample for high temperature magic angle spinning (MAS) experiments using standard rotors. Computational flow dynamics (CFD) simulations were used to assess and optimize the temperature gradient across the sample under MAS conditions. The chemical shift and linewidth of 207 Pb direct polarization in lead nitrate were used to calibrate the sample temperature and temperature gradient, respectively. A temperature gradient of less than 3 °C across the sample was obtained by heating bearing gas flows and adjusting its temperature and flow rate during variable temperature (VT) experiments. A maximum temperature of 350 °C was achieved in this probe using a Varian 5 mm MAS rotor with standard Vespel drive tips and end caps. Time-resolved 13 C and 1 H MAS NMR experiments were performed at 325 °C and 60 bar to monitor an in-situ mixed phase reverse water gas shift reaction, industrial synthesis of CH 3 OH from a mixture of CO 2 and H 2 with a Cu/ZnO/Al 2 O 3 catalyst, demonstrating the first in-situ NMR monitoring of a chemical system at temperatures higher than 250 °C in a pressurized environment. Lastly, the combination of this high-temperature probe and high-pressure rotors will allow for in-situ NMR studies of a great variety of chemical reactions that are inaccessible to conventional NMR setup.
47 OTHER INSTRUMENTATION↗
Coronal temperatures and temperature gradients from OSO-7 spectroheliograms
Temperatures and temperature gradients for the outer corona are obtained from brightness gradients of EUV lines that were measured with the spectroheliograph on OSO-7. Brightness gradients show considerable deviations from isothermal model calculations that include collisional excitation and photoexcitation. A negative temperature gradient that gives both positive and negative ion-abundance gradients appears to be able to account for the discrepancy. For the 284-A of Fe XV, perhaps the strongest line from the outer corona, measurements during 1972 appear to be consistent with a temperature near 2.3 million K near the equator at about 1.3 solar radii from the solar center and with temperature-gradient values near -0.7 that extend from as low as 1.2 to about 1.8 solar radii. Temperatures from strong lines of Fe XIV and Fe XVI indicate that variations of about 200,000 K exist along lines of sight where emission is appreciable. There appears to be some agreement between these results and temperature measurements from ion abundances in the solar wind and the Doppler width of the 5303-A line.
Nakada, M. P.↗
Effect of Temperature Gradient on Thick Film Selective Emitter Emittance
A temperature gradient across a thick (greater than or equal to .1 mm) film selective emitter will produce a significant reduction in the spectral emittance from the no temperature gradient case. Thick film selective emitters of rare earth doped host materials such as yttrium-aluminum-garnet (YAG) are examples where temperature gradient effects are important. In this paper a model is developed for the spectral emittance assuming a linear temperature gradient across the film. Results of the model indicate that temperature gradients will result in reductions the order of 20% or more in the spectral emittance.
Chubb, Donald L.↗
Microturbulence in edge of a tokamak plasma with medium density and steep temperature gradient
Gyrokinetic simulations of electrostatic micro-turbulence have been carried out for transport barriers (TBs) in tokamak plasmas. It is found that the ion temperature gradient (ITG) mode is dominant in the pedestal with medium density gradient and steep temperature gradient. The mode width shrinks with increase of the ratio of the density and temperature gradients, which is in good agreement with the analytic theory. Unstable mode with herringbone-like structure is excited in the simulation annulus. The simulation results also indicate that multiple ITG modes are induced by a high temperature gradient. Radial electric field shear decreases the mode growth rate while increases the real frequency. Lastly, the generation of the GAM and its interaction with the turbulence are also observed in the nonlinear simulation.
tokamak↗
Organic-matter decomposition along a temperature gradient in a forested headwater stream
Here, we used a natural temperature gradient in Walker Branch, a spring-fed forested stream in eastern Tennessee, USA, to examine the influence of temperature on organic-matter decomposition. These upstream sites are warmer than downstream sites in winter and are cooler than downstream sites in summer. We used a cotton-strip assay to examine breakdown of a substrate of uniform quality (95% cellulose) along the temperature gradient monthly for 2 y and litter bags to examine the interactive effects of leaf-litter quality (labile red maple [Acer rubrum] and tulip poplar [Liriodendron tulipifera], and less labile white oak [Quercus alba]), invertebrates, and temperature on breakdown rates along the downstream temperature gradient for 90 d in winter. Cotton-strip tensile loss and leaf-litter breakdown rates were highly variable. Tensile-loss rates likely were driven by a combination of daily and diel temperature, discharge, streamwater nutrients that varied seasonally and spatially along the temperature gradient. Leaf litter breakdown rates tended to be faster in warmer upstream sites (red maple = 0.0452/d, tulip poplar = 0.0376/d, white oak = 0.0142/d) and slower in cooler downstream sites (red maple = 0.0312/d, tulip poplar = 0.0236/d, white oak = 0.0107/d), and breakdown rates were positively correlated with total invertebrate density. Furthermore, temperature sensitivity of decomposition was similar among the 3 litter types. These results highlight the high degree of spatial and temporal heterogeneity that can exist for ecosystem processes and their drivers. Quantifying this heterogeneity is important when scaling functional metrics to stream and watershed scales and for understanding how organic-matter processing will respond to the warmer streamwater temperatures expected as a result of global climate change.
59 BASIC BIOLOGICAL SCIENCES↗
Demonstrating the Temperature Gradient Impact on Grain Growth in UO2 Using the Phase Field Method
Grain boundaries (GBs) are driven to migrate up a temperature gradient. In this work, we use a phase field (PF) model to investigate the impact of temperature gradients on normal grain growth. GB motion in 2D UO2 polycrystals is predicted under increasing temperature gradients. We find that the temperature gradient does not significantly impact the average grain growth behavior, because the curvature driving force is dominant. However, it does cause significant local migration of the individual grains. In addition, the change in the GB mobility due to the temperature gradient results in larger grains in the hot portion of the polycrystal.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
A STUDY OF SOLAR PHOTOSPHERIC TEMPERATURE GRADIENT VARIATION USING LIMB DARKENING MEASUREMENTS
The variation in area of quiet magnetic network measured over the sunspot cycle should modulate the spatially averaged photospheric temperature gradient, since temperature declines with optical depth more gradually in magnetic flux tube atmospheres. Yet, limb darkening measurements show no dependence upon activity level, even at an rms precision of 0.04%. We study the sensitivity of limb darkening to changes in area filling factor using a 3D MHD model of the magnetized photosphere. The limb darkening change expected from the measured 11-year area variation lies below the level of measured limb darkening variations, for a reasonable range of magnetic flux in quiet network and internetwork regions. So the remarkably constant limb darkening observed over the solar activity cycle is not inconsistent with the measured 11-year change in area of quiet magnetic network. Our findings offer an independent constraint on photospheric temperature gradient changes reported from measurements of the solar spectral irradiance from the Spectral Irradiance Monitor, and recently, from wavelength-differential spectrophotometry using the Solar Optical Telescope aboard the HINODE spacecraft.
79 ASTRONOMY AND ASTROPHYSICS↗