BURNOUT HEAT FLUXES FOR LOW-PRESSURE WATER IN NATURAL CIRCULATION

Twenty-nine experimental determinations of burn-out heat flux were made with water flowing by natural circulaion through electrically heated vertical tubes with and without internal twisted tapes and through rectangular cross sections of three aspect ratios. Heated lengths varied from 10 to 33 in., system pressure at the testsection flow exit from 14.7 to 26.3 psia, inlet subcooling from 36 to 170 deg F, and burn-out heat flux from 13,000 to 218,500 Btu/hr/sq ft. Tests were made with both unrestricted and restricted return flow paths. Three correlations were developed for predicting natural-circulation burn-out heat fluxes for such conditions. Two are useful for rapid estimation but the third involves a more fundamental assessment of the coolant mass velocity at burn-out by a graphical matching of the heat flux that a given flow rate can sustain to the heat flux that will produce that flow rate. For all the data, this approach gave average and maximum deviations of 15 and 38%, respectively. It was found that use of a slip ratio of unity is adequate for burnout prediction, and the reasons for this are discussed in detail. The small burn-out penalty incurred by a substantial restriction of return flow path, experimentally observed, is in complete accord with the theoretical model. (auth

The development of reading tests for use in a regularly spelled language.

Data are presented on the development of tests of reading skill in rural Tanzanian primary school pupils. Instruction in these schools is in Kiswahili, a regularly spelt language. Using a translation of a standard reading test, children could read aloud all words once they had learnt sound-letter correspondences, regardless of comprehension. In addition, children can appear to pass traditional comprehension tasks by decoding only some of the words. Three graded tests were developed which allow testing of children who either have only some letter knowledge, can read single words, or are proficient readers. The tests require children to both decode and understand the reading material in order to achieve high scores. The tests correlated well with scores on other educational achievement tests, and showed age and school grade differences. It is suggested that these tests are useful measures of reading development in a regularly spelt language. Adaptation to English and validation against standardised instruments is planned

HFIR HEAT-TRANSFER STUDIES OF TURBULENT WATER FLOW IN THIN RECTANGULAR CHANNELS

In support of the High Flux Isotope Reactor program, experimental determinations were made of friction factors, burnout heat fluxes, and average and local nonboiling heattransfer coefficients for forced-convection flow of water through this aluminum and nickel rectangular channels under the following conditions: heat flux = 0.1 x 10/sup 6/ to 7.4 x 10/sup 6/ Btu/hr - ft/sup 2/, velocity = 10 to 85 fps, Reynolds number = 9,000 to 270,000, pressure = 1 to 39 atmospheres absolute, flow gap = 0.043 to 0.057 in., and heated length = 12 and 18 in. A few tests were made to ascertain the effect of an axially oriented cylindrical spacer strip on surface temperature distribution and burnout heat flux. The results of these studies, are in reasonably good agreement with accepted ccrrelations. The friction factors are in satisfactory agreement with the Moody chart for the relative roughness of the test sections used, the burnout heat fluxes are well reproduced by the Soviet Zenkevich-Subbotin correlation, and the local and average heat-transfer coefficients are slightly larger than values predicted by the Hausen and Sieder-Tate equations. Miscellaneous experimental and analytical HFIR heat-transfer studies are included. (auth

Burnout Heat Fluxes for Low-Pressure Water in Natural Circulation

Twenty-nine experimental determinations of burn-out heat flux were made with water flowing by natural circulaion through electrically heated vertical tubes with and without internal twisted tapes and through rectangular cross sections of three aspect ratios. Heated lengths varied from 10 to 33 in., system pressure at the testsection flow exit from 14.7 to 26.3 psia, inlet subcooling from 36 to 170 deg F, and burn-out heat flux from 13,000 to 218,500 Btu/hr/sq ft. Tests were made with both unrestricted and restricted return flow paths. Three correlations were developed for predicting natural-circulation burn-out heat fluxes for such conditions. Two are useful for rapid estimation but the third involves a more fundamental assessment of the coolant mass velocity at burn-out by a graphical matching of the heat flux that a given flow rate can sustain to the heat flux that will produce that flow rate. For all the data, this approach gave average and maximum deviations of 15 and 38%, respectively. It was found that use of a slip ratio of unity is adequate for burnout prediction, and the reasons for this are discussed in detail. The small burn-out penalty incurred by a substantial restriction of return flow path, experimentally observed, is in complete accord with the theoretical model. (auth

Attacking Group Protocols by Refuting Incorrect Inductive Conjectures

Automated tools for finding attacks on flawed security protocols often fail to deal adequately with group protocols. This is because the abstractions made to improve performance on fixed 2 or 3 party protocols either preclude the modelling of group protocols all together, or permit modelling only in a fixed scenario, which can prevent attacks from being discovered. This paper describes Coral, a tool for finding counterexamples to incorrect inductive conjectures, which we have used to model protocols for both group key agreement and group key management, without any restrictions on the scenario. We will show how we used Coral to discover 6 previously unknown attacks on 3 group protocols

Adaptive Optics Imaging of QSOs with Double-Peaked Narrow Lines: Are they Dual AGNs?

Active galaxies hosting two accreting and merging super-massive black holes (SMBHs) -- dual Active Galactic Nuclei (AGN) -- are predicted by many current and popular models of black hole-galaxy co-evolution. We present here the results of a program that has identified a set of probable dual AGN candidates based on near Infra-red (NIR) Laser Guide-Star Adaptive Optics (LGS AO) imaging with the Keck II telescope. These candidates are selected from a complete sample of radio-quiet Quasi-stellar Objects (QSOs) drawn from the Sloan Digital Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the twelve AGNs imaged, we find six with double galaxy structure, of which four are in galaxy mergers. We measure the ionization of the two velocity components in the narrow AGN lines to test the hypothesis that both velocity components come from an active nucleus. The combination of a well-defined parent sample and high-quality imaging allows us to place constraints on the fraction of SDSS QSOs that host dual accreting black holes separated on kiloparsec (kpc) scales: ~0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during a typical merger and find a value that is much lower than estimates that arise from QSO space densities and galaxy merger statistics. We discuss possible reasons for this difference. Finally, we compare the SMBH mass distributions of single and dual AGN and find little difference between the two within the limited statistics of our program, hinting that most SMBH growth happens in the later stages of a merger process.Comment: 9 pages, 4 figures, 1 table; accepted to the Astrophysical Journa