Perpendicular Temperature Gradient Research Articles

Numerical Simulation Study of the Effect of Liquid Depth on the Stability of Thermal Marangoni Convection in a Shallow Cavity

The effect of liquid depth on thermal Marangoni convection stability in a shallow cavity was investigated via three-dimensional (3D) numerical simulations. The liquid film in the cavity is silicone oil with a Prandtl number of 6.7. The cavity is subjected to perpendicular temperature gradients. The simulation results show that, for thinner films, a primary instability appears when the flow transits from a steady state to a 3D oscillatory pattern. In thicker films, a secondary instability appears when the flow changes from oscillatory to chaotic. The critical thermal Marangoni numbers (at which transitions occur) of thin films are higher than those of thicker films. The simulation results imply that the uniform steady flow behavior in thinner films can be utilized to a benefit in coating and thin film applications, while the chaotic flow behavior predicted in thicker films can be utilized to obtain better mixing in applications such as lubrication and mixing.

Y3Fe5O12 hybrid spin valves with appreciable spin Seebeck effect under perpendicular temperature gradient

Significant thermal voltage signals from spin Seebeck effect and conventional anomalous Nernst and anomalous Righi–Leduc effects have been recognized in the yttrium iron garnet Y3Fe5O12 (YIG)/Cu/NiFe/IrMn hybrid spin valves under a perpendicular temperature gradient. The spin transport characteristic parameters of the soft NiFe film can be quantitatively evaluated, including the spin diffusion length and spin Hall angle. The present results show the significance of the YIG hybrid spin valve structure in exploring various spin dependent phenomena.

Formation and homogenization of Si interconnects by non-equilibrium self-propagating exothermic reaction

Si chips have been interconnected by the self-propagating exothermic reactions using Al–Ni NanoFoil and Au80Sn20 solder layers. The instantaneous localized heat across the entire solder presents great potential for the integration of MEMS and optoelectronic components requiring minimal thermal effects. However, the extremely rapid heating and cooling (105−7 °C/s) in the reaction can cause non-equilibrium interfacial reactions and metastable solidification in the transient bonding region. Segregations and metastable phases different from equilibrium ones are inevitably formed in the Si interconnects. In this study, numerical predictions on the temperature profile of the bonding process and the microstructural characterizations by in-situ TEM/SEM were carried out to reveal the formation and homogenization of the reactive bonded structures. The convective mass transportation, directional solidification and inverse segregation due to the great perpendicular temperature gradient in the mushy reacting zone are confirmed to cause the formation of nano-sized metastable phases. Significant segregation of high-temperature phases (Au-enriched phases) was observed, likely due to the convective flow and the inverse segregation induced by volume contraction. These non-equilibrium phases can be homogenized towards the equilibrium status in subsequently accelerated aging, which was supported by the evident inter-diffusion, intermixing and subsequent growth.

Large Inverse Spin Hall Effect in Co-Pt Spin-Valve Heterostructures

Under a perpendicular temperature gradient, a heterostructure of ferromagnetic insulator plus normal metal yields a voltage via the inverse spin Hall effect (ISHE). When a $f\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ metal is used instead, though, it becomes tricky to evaluate the ISHE voltage. In systems with large spin-orbit interaction, the authors observe significantly enhanced ISHE signals, suggesting that exchange-bias structures can be effective for detecting spin currents. This study provides insight into engineering hybrid spintronic devices to generate, manipulate, and detect pure spin current.

Numerical Modeling of the Thermal Force for the Kinetic Test‐Ion Transport Simulation Based on the Fokker‐Planck Collision Operator

AbstractWe present an extended numerical model of the thermal force based on the Fokker‐Planck collision method. Our model is designed for the use of the test particle transport simulation in a fluid‐like magnetized background plasma. By a series of systematic test simulations performed in this study, we have confirmed that our model is able to correctly simulate the thermal force which is caused not only by parallel, but also by perpendicular temperature gradient with respect to the direction of magnetic field. Effective length of collision time step for numerical calculations has also been investigated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Convective instability in layered sloping warm-water aquifers

In a recent paper (McKibbin et al., 2011) some questions were posed about fluid and heat flows in a stratified groundwater aquifer with a small slope, subject to a perpendicular temperature gradient. The strength of shear flows in the direction of the maximum slope and the associated convected heat flux were quantified. This paper provides a method to quantify the stability of such flows and the shape and amplitude of convective rolls that may form when the critical Rayleigh number is exceeded. The associated issue of how the mean flow-path of a soluble species introduced into the aquifer is affected by the convective rolls, is also considered. The models formulated are for buoyancy-driven fluid flow in long, sloping warm-water aquifers with both smoothly- and discretely-layered structures.

Numerical modeling of the thermal force in a plasma for test-ion transport simulation based on a Monte Carlo Binary Collision Model (II) – Thermal forces due to temperature gradients parallel and perpendicular to the magnetic field

We have developed a numerical model of the thermal force for test-ion transport simulation in a magnetized background plasma, based on the Monte Carlo Binary Collision Model (BCM) [T. Takizuka, H. Abe, J. Comput. Phys. 25 (1977) 205]. The model is basically the same as presented in our previous paper [Y. Homma, A. Hatayama, J. Comput. Phys. 231 (2012) 3211–3227] for the case without magnetic field, but in the present paper, a more extended form of a distorted Maxwellian distribution is employed for the velocity distribution of background plasma ions to simulate the thermal force caused by parallel and perpendicular (with respect to the direction of magnetic field) temperature gradients. The model consists mainly of two steps: (i) choosing a background plasma ion velocity from a distorted Maxwellian distribution, and (ii) calculating a Coulomb collision between a test particle and the above chosen ion by using the BCM. In addition, equations of motion for charged test particle in the magnetic field are calculated by Buneman–Boris Algorithm.A series of test simulations has been done in a simple geometry with different temperature gradients and different strengths of magnetic field. Numerical results of the thermal force due to parallel and perpendicular temperature gradients agree well with the theoretical prediction for all test cases. Especially, it has been confirmed that the model reproduces the temperature screening effect of test particles (i.e. guiding center drift of test particle caused by the thermal force of perpendicular temperature gradient).

Extrinsic spin Nernst effect in two-dimensional electron systems

The spin accumulation due to the spin current induced by the perpendicular temperature gradient (the spin Nernst effect) is studied in a two-dimensional electron system (2DES) with spin-orbit interaction by employing the Boltzmann equation. The considered 2DES is confined within a symmetric quantum well with $\ensuremath{\delta}$ doping at the center of the well. A symmetry consideration leads to the spin-orbit interaction which is diagonal in the spin component perpendicular to the 2DES. As origins of the spin current, the skew scattering and the side jump are considered at each impurity on the center plane of the well. It is shown that, for repulsive impurity potentials, the spin-Nernst coefficient changes its sign at the impurity density where contributions from the skew scattering and the side jump cancel each other out. This is in contrast to the spin Hall effect in which the sign change of the coefficient occurs for attractive impurity potentials.

Thermal artifact on the spin Seebeck effect in metallic thin films deposited on MgO substrates

Spin Seebeck effect (SSE) was investigated in Heusler compound Co2MnSi (CMS) and ferromagnetic binary alloy Ni80Fe20 (Py) thin films deposited on MgO substrates at different ambient temperatures, T = 30 K to 295 K, by maintaining a finite temperature gradient along the film plane. Low temperature enhancement of voltage signal and a peak around T = 70 K were detected in a Pt wire placed on the higher temperature end of CMS (or Py) film. It has been found that the low temperature enhancement was dominated by a thermal artifact, which was generated by the anomalous Nernst effect with an additional perpendicular temperature gradient across the film plane. The remarkable mismatch between thermal conductivities of MgO and CMS (or Py) at low temperatures is considered to give rise to the perpendicular temperature gradient causing the thermal artifact. We showed that consideration of thermal conductivity matching between thin film and substrate is essential for performing experiments of SSE correctly; moreover, the observation of SSE could be realized only when minimization of the thermal artifact is possible.

CONVECTION AND HEAT TRANSFER IN LAYERED SLOPING,WARM-WATER AQUIFERS

What convective flow is induced if a geologically-tratified groundwater aquifer is subject to a vertical temperature gradient? How strong is the flow? What is the nett heat transfer? Is the flow stable? How does the convection affect the subsequent species distribution if a pollutant finds its way into the aquifer? This paper begins to address such questions. Quantitative models for buoyancy-driven fluid flow in long, sloping warm-water aquifers with both smoothly- and discretely-layered structures are formulated. The steady-state profiles are calculated for the temperature and for the fluid specific volume flux (Darcy velocity) parallel to the boundaries in a sloping system subjected to a perpendicular temperature gradient, at low Rayleigh numbers. The conducted and advected heat fluxes are compared and it is shown that the system acts somewhat like a heat pipe. The maximum possible ratio of naturally advected-to-conducted heat transfer is determined, together with the corresponding permeability and thermal conductivity profiles.

Establishment of experimental conditions for the rapid detection of mutations in the von Hippel-Lindau gene by parallel temperature gradient gel electrophoresis.

Renal cell carcinoma (RCC) is the most common adult kidney neoplasm and is present in approximately 3% of all adult malignancies. Mutations of the von Hippel-Lindau (VHL) gene had been found in 55-70% of sporadic RCC and appear to be a critical event in the pathogenesis of clear-cell RCC. Several screening procedures for the detection of mutations in the VHL gene such as single-strand conformation polymorphism analysis, Southern blot and polymerase chain reaction (PCR)-employing methods had been used. Recently, the perpendicular temperature gradient gel electrophoresis (TGGE) was successfully applied to detect genetic alterations in the VHL gene. Here, the experimental conditions for parallel TGGE were established. The results on eleven samples with mutations in different exons demonstrate that parallel TGGE can be used as a simple and rapid method to detect mutations in the VHL gene. Several samples can be run at the same time, making parallel TGGE ideal for the screening of a large number of samples.

Characterization of imidazole as a DNA denaturant by using TGGE of PCR products from a random pool of DNA.

Perpendicular temperature gradient gel electrophoresis (TGGE) profiles were analyzed for PCR products from a random pool of DNA [60 nts random region flanked by two primer (20 nts) sites]. Besides a normal transition profile of a homoduplex, unique mobility transition profiles of two kinds of heteroduplex with a big internal loop were observed, representing the successive helix-coil transitions of the DNAs. As the appearance of the heteroduplex band is an estimator of the complexity of a random pool, it will be applicable to monitor the extent of the selection process in the in vitro selection method. When imidazole was added to the electrophoretic buffer, the transition pattern shifted to the low temperature side. At a concentration of 1 M, imidazole lowered the melting temperature (Tm) of DNA by 13+/-2 degrees C for all the three chain separation transitions observed. Thus imidazole is a stronger denaturant than urea, at least at dilute concentration. Dependence of Tm on concentration of imidazole and the mobility change suggested that imidazole binds to nucleotide in the single-stranded state.

Second stable regime of nonlocal mixed slab-toroidal anisotropic ion-temperature-gradient-driven mode

Nonlocal effects on the mixed slab-toroidal ion-temperature-gradient-driven (ITG) instability are investigated with analytical and numerical approaches. Although it is more complex than the local analysis, the nonlocal analysis also leads to the same conclusion that a second stable regime exists at large values of the perpendicular temperature gradient. From a strictly theoretical point of view, this result provides a possible stabilization scheme for the ITG instability.

The trapped ion ITG mode with anisotropic eta i and collisions

The ion temperature gradient (ITG) driven instability is investigated for a plasma with trapped ions and collisions. For the toroidal branch, the perpendicular temperature gradient is needed for the stability in contrast to the slab branch. The threshold value of the temperature gradient is higher with trapped ions and is further increased by electron and ion collisions. A theoretical model is used to explain the experimental results for a hybrid trapped ion ITG mode in the Columbia linear machine

The ion temperature gradient instability in a linear machine

It is shown that anisotropy in the ion temperature gradient has a substantial effect on the ion temperature gradient driven mode. A gradient in the parallel temperature is needed for an instability to occur and a gradient in the perpendicular temperature gradient further enhances the instability indirectly as long as the frequency of the mode is near ion resonance. The physical reason for this important role difference is presented. The Columbia Linear Machine (CLM) [Phys. Rev. Lett. 57, 1729 (1986)] is being redesigned to produce and identify the ion temperature gradient driven ηi mode. Using the expected parameters, detailed predictions of the mode characteristics in the CLM have been developed. These include growth rate and real frequency as a function of the azimuthal number m, the drive parameter ηi ≡d(ln Ti)/d(ln n), and the parallel wavenumber k∥. Strong multimode instabilities are expected. Because the ion parallel and perpendicular ion temperature gradients are expected to differ significantly, the roles of ηi∥ and ηi⊥ are differentiated, and this difference is exploited for a stabilization scheme of the mode. Since all gradients are significantly variable over the expected radial wavelength of the mode, a nonlocal radial differential equation has been derived. With some approximations, this can be reduced to a Weber-type equation, which has been solved.