Showing papers on "Temperature gradient published in 1974"
TL;DR: In this article, a theoretical model was developed to explain the variation in cellular or dendritic tip temperatures with velocity and temperature gradient, and it was shown that the undercooling can be considered to arise as a result of build up of average solute concentration ahead of the growth front depending mainly on the imposed temperature gradient.
421 citations
TL;DR: In this article, the steady motion of water in an enclosed rectangular cavity with differentially heated vertical end walls was studied experimentally, and the results were compared with the findings of parts 1 and 2.
Abstract: The steady motion of water in an enclosed rectangular cavity with differentially heated vertical end walls was studied experimentally, and the results are compared with the findings of parts 1 and 2. The depth-to-length ratios of the cavities were 102 and 1·9 × 102, and the Rayleigh number was allowed to vary sufficiently to enable a study to be made of the transition from a flow driven by the vertical wall boundary layers to one sustained by a longitudinal temperature gradient in the central sections of the cavity.
141 citations
TL;DR: In this paper, the stability of convection in a horizontal porous layer subjected to horizontal as well as vertical temperature gradients is investigated, and the preferred mode of disturbance is stationary, being longitudinal rolls, i.e. rolls having axes aligned in the direction of the basic flow.
73 citations
TL;DR: In this article, the microwave brightness of heterogeneous materials is decreased by internal scattering, and the effect depends upon the dominance of scattering over absorption, volume scattering tends to mask a temperature gradient, and darkening is slightly greater for V- than for H-polarized radiation.
Abstract: The microwave brightness of heterogeneous materials is decreased by internal scattering. This study, based upon radiative transfer theory, shows that for low loss media darkening can be many tens of degrees, that the effect is greater for materials of lower dielectric constant, that darkening depends upon the dominance of scattering over absorption, that volume scattering tends to mask a temperature gradient, that darkening is slightly greater for V- than for H-polarized radiation, and that darkening increases slightly with view angle. For isotropic scattering, the analysis yields the brightness temperature as a function of the scattering albedo, the complex dielectric constant, thermal temperature, and the temperature gradient.
64 citations
TL;DR: In this paper, the authors measured the heat flux and temperature gradient in a layer of saline solution stably stratified by Soret diffusion and heated from below and observed the onset of convection by the growth of very small oscillations which eventually trigger finite amplitude convection.
Abstract: Measurements of the heat flux and temperature gradient in a layer of saline solution stably stratified by Soret diffusion and heated from below exhibit the onset of convection by the growth of very small oscillations which eventually trigger finite amplitude convection. The critical Rayleigh numbers and periods of oscillation are consistent with published theoretical calculations. Several non-linear modes are observed, even for the same heat flux, near the point of onset.
55 citations
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12 Nov 1974TL;DR: In this article, a cold, electrical gradient, terminal section for a superconductor cable for alternating current power transmission for making an electrical connection between room-temperature components and a cable that is operating in the superconducting mode and is carrying electrical power.
Abstract: Cold, electrical gradient, terminal section for a superconductor cable for alternating current power transmission for making an electrical connection between room-temperature components and a cable that is operating in the superconducting mode and is carrying electrical power. In one embodiment, this invention has a cold electrical gradient section in series with a separate thermal gradient section, the former having an electrical stress cone of increasing diameter filled with a flowing, pressurized, gaseous, He, cryogenic coolant, which acts as an electrical insulator and longitudinally separates spaced-apart, solid, oppositively tapered, electrical insulators axially arranged between co-axial, cylindrical superconductors forming composite structures in a containment for the cryogenic coolant for providing control of the electrical field intensity and current density in a cold electrical gradient terminal section that is in series with a thermal gradient section having a room temperature portion containing high pressure seals. The cable may be rigid or flexible.
53 citations
TL;DR: In this article, a solution of the solute diffusion equation for an infinite paraboloidal dendrite, moving in a fixed temperature gradient, was obtained for a dilute binary alloy.
47 citations
TL;DR: In this paper, the distribution of wind, temperature, ozone, and turbulence within a multiple structured frontal zone-jet stream system was described using a combination of direct horizontal measurements by meteorologically-instrumented research aircraft and conventional aerological soundings.
Abstract: The distribution of wind, temperature, ozone, and turbulence within a multiple structured frontal zone-jet stream system is described using a combination of direct horizontal measurements by meteorologically-instrumented research aircraft and conventional aerological soundings. Results document the spatial continuity of these zones and associated intrusions of ozone-rich stratospheric air. Aircraft turbulence measurements show the zones with strong vertical wind shear and near-critical values of Richardson number are preferred regions of CAT encounter. Diagnostic calculations of the terms of the gradient thermal wind equation illustrate the importance of the sign and magnitude of the air trajectory curvature and its vertical derivative in maintaining regions of strong vertical wind shear and small Richardson number in the presence of weak horizontal thermal gradient.
45 citations
TL;DR: In this paper, the authors calculate the gradient threshold for planar and homeotropic configurations by solving the exact two-dimensional problem taking into account the boundary conditions, where the value and the sign of gradient threshold depend on the initial liquid crystal configuration.
45 citations
TL;DR: In this article, a rotary graphite crucible in a vertical furnace was used to grow GaAs and (GaAl)As from Ga solution, using a Rotary Graphite Crucible (RGC).
44 citations
TL;DR: In this paper, it was shown that the thermal stability of aligned, fibrous, eutectic composites may often be greatly decreased if a temperature gradient perpendicular to the fibre axes is present.
Abstract: It is shown that the thermal stability of aligned, fibrous, eutectic composites may often be greatly decreased if a temperature gradient perpendicular to the fibre axes is present. An analogous effect is predicted for aligned, lamellar composites in a temperature gradient perpendicular to the direction of the growth of the alloy. Since the above thermal configurations are those existing in a typical turbine blade, the present study indicates that the isothermal stability of an eutectic composite, at present used for selecting possible turbine-blade materials, may often be largely irrelevant.
TL;DR: In this article, a theoretical and experimental study of the thermal properties of a well aligned nematic liquid crystal in a vertical temperature gradient is presented, where the authors show that due to the long time constant of the relaxation of the liquid crystal and the anisotropy of the heat conductivity, the value of the temperature gradient threshold for convective instabilities is strongly modified.
Abstract: We present a theoretical and experimental study of the thermal properties of a well aligned nematic Liquid Crystal in a vertical temperature gradient. Due to the long time constant of the relaxation of the director and to the anisotropy of the heat conductivity, the value of the temperature gradient threshold for convective instabilities is strongly modified as compared to the isotropic case. Experiments on planar MBBA films show a drastic reduction of the threshold. A detailed description of the shape and temperature distribution of the convective rolls is given.
TL;DR: In this paper, an analysis of the behavior of the hydrodynamic modes in a horizontal fluid layer subject to a downward-directed temperature gradient which, when reaching a critical value, drives the system into convective instability is presented.
Abstract: An analysis is presented of the behavior of the hydrodynamic modes in a horizontal fluid layer subject to a downward-directed temperature gradient which, when reaching a critical value, drives the system into convective instability. It is found that the combination of this thermal constraint and gravity gives rise to a coupling between the heat-diffusion mode and the transverse mode (curl curl v→)z, with v→, the velocity field, and the z axis pointing in the vertical direction. As a result of this mode coupling, which is absent in a fluid at equilibrium, the damping factor of one of the coupled modes goes to zero when the temperature gradient increases to its critical value. On the basis of this mode analysis, the spectral distribution of the light scattered by the nonequilibrium fluid is then computed. The main features of the light-scattering spectrum consist of the appearance of an additional central component and the respective narrowing and broadening of the spectral components corresponding to the coupled modes as the instability critical point is approached. © 1974 The American Physical Society.
TL;DR: In this article, the average heat transfer coefficient of a horizontal heated square plate facing downward in air was studied with three different edge conditions: vertical surfaces extending up from the plate edge cooled to ambient temperature, vertical surfaces keeping at the plate temperature, and adiabatic horizontal extensions next to the outer edge of the plate.
TL;DR: In this paper, the thermal stability of aligned, fibrous Al-Al3Ni eutectic when subjected to a temperature gradient of approx. 5 K/mm perpendicular to the fibre axes was investigated.
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TL;DR: In this paper, a semiconductor diode comprises a first body of semiconductor material having a selected resistivity and a first type conductivity, and a region of second type conductivities and selected resistivities.
Abstract: A semiconductor diode comprises a first body of semiconductor material having a selected resistivity and a first type conductivity and a region of second type conductivity and a selected resistivity. The second body consists of recrystallized semiconductor material or a layer thereof having solid solubility of a dopant therein and has the same crystallographic structure as the first body. The second region is formed by a temperature gradient zone melting process embodying the migration of a metal-enriched melt of semiconductor material through the second body of semiconductor material which initially has a axial crystallographic orientation.
TL;DR: In this paper, a simple equation is presented to describe the interdendritic spacing for dendritic growth from a super-heated alloy melt, which is then rationalized for a simple conceptual extreme: steady-state unidirectional growing from a liquid under a constant, positive, temperature gradient.
TL;DR: In this paper, the force on a spherical aerosol particle in a gas which sustains a temperature gradient is analyzed with a method previously applied to thermal transpiration and planar radiometric force.
Abstract: With a method previously applied to thermal transpiration and planar radiometric force, the force on a spherical aerosol particle in a gas which sustains a temperature gradient is analyzed. Expressions for thermal force and thermal velocity span all values of the particle Knudsen number and show the effect of imperfect accommodation. The results are compared with other theories and with experimental data.
TL;DR: In this paper, an investigation of the thermal stability of the aligned Pb-Ag eutectic composite with a temperature gradient of 4 K mm −1 imposed perpendicular to the growth direction in the temperature range of 525 to 554K was made.
TL;DR: In this article, the relation between temperature gradient and the liquid/solid interface profile of Czochralski grown Al2O3 and YAG crystals is described, and four types of interface profiles were found.
Abstract: The relation between temperature gradient and the liquid/solid interface profile of Czochralski grown Al2O3 and YAG crystals is described. Lowering the radial component as well as increasing the axial component of temperature gradient during crystal growth causes the convex or pointed interface to be flattened. In the range of magnitudes both of the components of temperature gradient used, four types of interface profiles were found. An alteration of the interface profile which causes local increase of the growth rate can be accompanied by cell formation. The volume of the portion of the growing crystal submerged in the melt is directly proportional to the optical transmissivity of the crystal and inversely proportional to the optical transmissivity of the melt.
TL;DR: In this paper, the spatial spectrum of ocean temperature fluctuations at six different depths between 500 and 2500 m was estimated using a depth-stable, self-propelled instrument carrier, where temperature samples were taken at 0.2 m intervals over a track typically 10 km long, corresponding to a spectral bandwidth of 1-2500 cycles per kilometer (cpkm).
Abstract: Estimates of the spatial spectrum of ocean temperature fluctuations at six different depths between 500 and 2500 m are presented. Measurements were made with a depth-stable, self-propelled instrument carrier. Temperature samples were taken at 0.2 m intervals over a track typically 10 km long, corresponding to a spectral bandwidth of 1–2500 cycles per kilometer (cpkm). The observed spectrum falls into three distinct bands; these are tentatively identified with the effects of internal waves (W), fine-scale layering (L), and turbulent mixing (T). Each band has a characteristic wavenumber dependence which is invariant with depth. The intensity in each band scales with depth in characteristic fashion. Depth scaling over the range of interest accords with the empirical formula N2∝dT/dz∝ exp[−(Z−500)/λ], where the stability frequency and mean vertical temperature gradient are equivalent variables, and λ=750 m is the observed local scale height. Then the spectrum in band T is PT=Ak−1, where the intensity...
TL;DR: In this article, the stability of ion acoustic waves propagating in a magnetized plasma containing an electron temperature gradient is investigated, and the dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature-gradient drift velocities.
Abstract: The stability of ion acoustic waves propagating in a magnetized plasma containing an electron temperature gradient is investigated. The dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature gradient drift velocities. Earlier predictions, based on analytic calculations for small temperature ratios and drift velocities, are confirmed and some new results are presented. In particular, it is shown that a temperature gradient is a more effective destabilizing agent than a simple drift between ions and electrons. Dispersion plots and neutral stability curves are given.
TL;DR: In this article, a two-phase bicrystal model was developed for growing macroscopic two phase brass brass, and the results can be explained on the basis of diffusion and solid-state transformations.
01 Aug 1974
TL;DR: In this article, the stability of ion acoustic waves propagating in a magnetized plasma contabin and QD electron temperature gradient is investigated, and the dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature-gradient drift velocities.
Abstract: The stability of ion acoustic waves propagating in a magnetized plasma contabin& QD electron temperature gradient is investigated. The dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature gradient drift velocities. Earlier pre- dictions, based on analytic calculations for small temperature ratios and drift velocities, are con- firmed and some new results are presented. In particular, it is shown that a temperature gradient is a more effective destabilizing agent than a simple drift between ions and electrons. Dispersion plots and neutral stability curves are given.
TL;DR: In this article, the authors investigated the thermomagnetic pressure difference for polyatomic gas at room temperature and the connections of this effect with the thermomic torque (Scott effect) are discussed.
TL;DR: In this paper, the authors proposed that the application of an external temperature gradient to a semiconductor can lead to the amplification of the acoustic wave, and they showed that the effect of external temperature gradients can be independent of the semiconductor properties.
Abstract: We propose that the application of an external temperature gradient to a semiconductor can lead to the amplification of the acoustic wave.
TL;DR: In this paper, the entrance problem of convective magnetohydrodynamic channel flow between two parallel plates subjected simultaneously to an axial temperature gradient and a pressure gradient is investigated numerically, and the solutions match to the fully developed solutions after a certain entrance length.
TL;DR: In this article, it was shown that the kinetic coefficient for solidification at the ice-droplet interfaces was ⪕4.1×10-2mm s-1K-1 if growth occurs uniformly, or 9.3 mm s − 1K-2 if growth requires screw dislocations.