ショウトツ フンリュウ ニヨル コウオンメン ノ キュウソク レイキャクチュウ ノ ヒテイジョウ デンネツ トクセイ

Transient heat transfer has been investigated experimentally with a subcooled water jet during quenching of hot cylindrical blocks made of copper, brass and steel for initial surface temperatures from 250 to 600 oC. The jet velocity was from 3 to 15 m/s and jet subcooling was from 5 to 80 K with a jet diameter of 2 mm. When the jet first struck the hot surface, the visible leading edge of the moving liquid (wetting front) became stagnant for a certain period of time in the small impinged region and splashed out from that region before wetting the entire surface. This wetting delay may be described as resident time which is a strong function of block material and jet subcooling and also a function of block initial temperature and jet velocity. New correlations for the resident time and the surface temperature at resident time at wetting front position have been proposed in this study which agree well with the experimental data. During the movement of the wetting front, the surface temperature at the wetting front drops to 120-200 oC and the surface heat flux reaches its maximum value due to forced convection nucleation boiling. The maximum heat flux is a strong function of the position on the hot surface, jet velocity, block material properties and jet subcooling. A new correlation for maximum heat flux is also proposed. When the resident time is short, the rate of movement of the maximum heat flux position increases with the increase of jet velocity and subcooling and decreases with the increase of block initial temperature. These trends are opposite for long resident time. During the movement of the wetting front over the hot surface, a darker moving vigorous boiling region is observed at the leading area of moving liquid. The width of this vigorous boiling region is described as the ‘boiling width’. Boiling width affects the heat flux estimation and distribution in jet impingement quenching. Boiling width increases with radial position. Higher conductivity of the test section material results in the higher v

Use of Infrared Piezobirefringence for Observation of Dislocations in Semiconductors With Cubic Symmetry.

The use of infrared piezobirefringence for characterization of defects in cubic semiconductor materials is investigated in this work. Under stress, these normally isotropic materials become birefringent. The stress can result from an applied external load or from defects present in the material. Defects can be generated in the material during its growth and/or processing. As a first step towards defect characterization, the case of diametrically loaded discs of semiconductor materials was simulated. This was done to obtain a better understanding of the simulation algorithm prior to its subsequent use in dislocation characterization. A dark-field plane polariscope was constructed using a He-Ne laser tuned to 1.15 $\mu$m wavelength as the light source. The computer simulated images matched well with the experimentally observed ones on diametrically loaded discs of silicon and gallium arsenide. The behavior of the stress-optic coefficient C was also investigated, which has been treated as a constant by other investigators in earlier works. In this work, it was found that for (100) oriented Si and GaAs discs under diametrical compression, the stress-optic coefficient C is a strong function of position for a given load, and also changes with the direction of the applied load with respect to the principal crystal axes. However, no such dependence was found for (111) oriented Si and GaAs discs under diametrical compression, as expected from the crystal symmetry. The values of C for (100) oriented Si disc under diametrical compression ranged from 2.0 $\times$ 10\sp{-12} cm\sp2/dyne to 3.0 $\times$ 10\sp{-12} cm\sp2/dyne and for (100) oriented GaAs disc under diametrical compression ranged from 0.8 $\times$ 10\sp{-12} cm\sp2/dyne to 2.6 $\times$ 10\sp{-12} cm\sp2/dyne for the cases investigated. The corresponding figures for (111) oriented Si and GaAs discs under diametrical compression are 2.33 $\times$ 10\sp{-12} cm\sp2/dyne and 1.94 $\times$ 10\sp{-12} cm\sp2/dyne respectively. Next, an accurate algorithm was developed for the simulation of the images of dislocations as a function of the sample orientation, the orientation of the dislocation line with respect to the principal crystal axes, the orientation of the Burger vector with respect to the dislocation line, and the polarization angle of the incident light. An image data bank has been created for different dislocations. This data bank can be utilized to obtain an accurate characterization of the image of a dislocation by comparing the experimentally obtained images with the simulated ones. In this work, images of the dislocations were observed experimentally and were matched with the simulated images. This approach provides a fast, non-destructive alternative technique for defect characterization in semiconductor materials

Thermal Stability Criteria of a Generic Quantum Black Hole

Thermodynamics of black holes were studied by Hawking, Bekenstein et al., considering black holes as classical spacetimes possessing a singular region hidden behind an event horizon. In this chapter, in contrast, we treat black hole from the perspective of a generic theory of quantum gravity, using certain assumptions which are consistent with loop quantum gravity (LQG). Using these assumptions and basic tenets of equilibrium statistical mechanics, we have derived criteria for thermal stability of black holes in any spacetime dimension with arbitrary number of charges (‘hairs’), irrespective of whether classical or quantum. The derivation of these thermal stability criteria makes no explicit use of classical spacetime geometry at all. The only assumption is that the mass of the black hole is a function of its horizon area and all the ‘hairs’ (i.e. charge, angular momentum, any other types of hairs). We get a series of inequalities between derivatives of the mass function with respect to the area and other ‘hairs’ as the thermal stability criteria. These criteria are then tested in detail against various types of black holes in various dimensions. This permits us to predict the region of the parameter space of a given black hole in which it may be stable under Hawking radiation

Greedy Selection of Materialized Views

Greedy based approach for view selection at each step selects a beneficial view that fits within the space available for view materialization. Most of these approaches are focused around the HRU algorithm, which uses a multidimensional lattice framework to determine a good set of views to materialize. The HRU algorithm exhibits high run time complexity as the number of possible views is exponential with respect to the number of dimensions. The PGA algorithm provides a scalable solution to this problem by selecting views for materialization in polynomial time relative to the number of dimensions. This paper compares the HRU and the PGA algorithm. It was experimentally deduced that the PGA algorithm, in comparison with the HRU algorithm, achieves an improved execution time with lowered memory and CPU usages. The HRU algorithm has an edge over the PGA algorithm on the quality of the views selected for materialization

Contact angle hysteresis can modulate the Newtonian rod climbing effect

The present work investigates the role of contact angle hysteresis at the liquid-liquid-solid interface (LLS) on the rod climbing effect of two immiscible Newtonian liquids using experimental and numerical approaches. Experiments revealed that the final steady state contact angle, $\theta_{w}$ at the LLS interface varies with the rod rotation speed, $\omega$. For the present system, $\theta_{w}$ changes from $\sim$69$^{\circ}$ to $\sim$83$^{\circ}$ when the state of the rod is changed from static condition to rotating at 3.3 Hz. With further increase in $\omega$, the $\theta_{w}$ exceeds 90$^{\circ}$ which cannot be observed experimentally. It is inferred from the simulations that the input value of $\theta_{w}$ saturates and attains a constant value of $\sim$120$^{\circ}$ for $\omega>$ 5 Hz. Using numerical simulations, we demonstrate that this contact angle hysteresis must be considered for the correct prediction of the Newtonian rod climbing effect. Using the appropriate values of the contact angle in the boundary condition, an excellent quantitative match between the experiments and simulations is obtained in terms of: the climbing height, the threshold rod rotation speed for onset of climbing, and the shape of liquid-liquid interface. This resolves the discrepancy between the experiments and simulations in the existing literature where a constant value of the contact angle has been used for all speeds of rod rotation