The transition from the annular to the slug flow regime in two-phase flow

Experiments were conducted to determine the transition from annular to semiannular flow regimes for two-phase, gas-liquid upflow in vertical tubes. The influencesof liquid flow rate, tube diameter, liquid viscosity, surface tension, and density ratio were tested. The transition location, giving the least gas flow which will support annular flow, is correlated for low liquid flows. The effects of surface tension and liquid viscosity are small for tubes of 0.5" and greater diameter. For large liquid flows the transition occurs at constant quality. Over the range of variables tested, the void fraction at transition lies between 80% and 90%. The criterion of transition is the appearance of liquid plugs which intermittently bridge across the tube. The pressure drop and volume void fraction at transition are reported but not correlated. Recommendations for extension of the experimental results to untested conditions are presented.Sponsored by The Atomic Energy Commission DS

Linear Chains of Styrene and Methyl-Styrene Molecules and their Heterojunctions on Silicon: Theory and Experiment

We report on the synthesis, STM imaging and theoretical studies of the structure, electronic structure and transport properties of linear chains of styrene and methyl-styrene molecules and their heterojunctions on hydrogen-terminated dimerized silicon (001) surfaces. The theory presented here accounts for the essential features of the experimental STM data including the nature of the corrugation observed along the molecular chains and the pronounced changes in the contrast between the styrene and methyl-styrene parts of the molecular chains that are observed as the applied bias is varied. The observed evolution with applied bias of the STM profiles near the ends of the molecular chains is also explained. Calculations are also presented of electron transport along styrene linear chains adsorbed on the silicon surface at energies in the vicinity of the molecular HOMO and LUMO levels. For short styrene chains this lateral transport is found to be due primarily to direct electron transmission from molecule to molecule rather than through the silicon substrate, especially in the molecular LUMO band. Differences between the calculated position-dependences of the STM current around a junction of styrene and methyl-styrene molecular chains under positive and negative tip bias are related to the nature of lateral electron transmission along the molecular chains and to the formation in the LUMO band of an electronic state localized around the heterojunction.Comment: 17 pages plus 11 figures. To appear in Physical Review

Central Arctic Caribou and Petroleum Development: Distributional, Nutritional, and Reproductive Implications

We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23000 in 1992, declined to 18 000 by 1995, and again increased to 27 000 by 2000. Net calf production was consistent with changes in herd size. In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within 4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for eastern females (e.g., 1988–94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd. Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable natural environment.On a procédé à une synthèse des résultats de travaux de recherche coopérative concernant les effets de l’exploitation pétrolière sur le caribou (Rangifer tarandus granti) formant la harde du centre de l’Arctique (HCA). La population de celle-ci est passée de 6000 têtes en 1978 à 23 000 en 1992, puis a diminué à 18 000 en 1995 pour augmenter de nouveau à 27 000 en 2000. La production nette des veaux allait de pair avec les changements dans la taille de la harde. Dans la zone de développement de Kuparuk (KDA), située à l’ouest de Prudhoe Bay, l’abondance des caribous qui mettaient bas était inférieure à celle prévue dans une bande de 4 km de part et d’autre des routes, et elle déclinait de façon exponentielle avec la densité routière. Avec une augmentation des infrastructures, on assistait à un déplacement du vêlage à forte densité de la KDA vers des zones de l’intérieur ayant une biomasse de fourrage moins importante. Durant juillet et au début d’août, il était assez rare que les caribous réussissent à traverser les corridors routiers/pipeliniers dans la KDA, surtout lorsqu’ils formaient de vastes agrégations harcelées par les insectes; l’abondance de même que les déplacements des femelles étaient en outre moindres au sein du complexe pétrolier de Prudhoe Bay qu’à d’autres endroits situés le long du rivage arctique. Il est possible que les femelles qui étaient exposées à l’exploitation pétrolière à l’ouest de la rivière Sagavanirktok aient consommé moins de fourrage au cours de la période de vêlage et que, durant la saison des insectes au milieu de l’été, elles aient connu une balance énergétique inférieure à celle des femelles vivant sans perturbations à l’est de la rivière. Les conséquences probables étaient un état corporel de qualité inférieure au moment de l’accouplement, et des taux de parturition plus faibles pour les femelles situées à l’ouest que pour celles situées à l’est (p. ex., de 1988 à 1994: 64 % c. 83 % de parturientes respectivement: p = 0,003), faisant ainsi baisser la productivité de la harde. Les évaluations des effets cumulatifs de l’exploitation pétrolière sur le caribou doivent intégrer les interactions complexes avec un environnement naturel variable

Does Revlon Matter? A Empirical and Theoretical Study

We empirically examine whether and how the doctrine of enhanced judicial scrutiny that emerged from Revlon and its progeny actually affects M&A transactions. Combining hand-coding and machine-learning techniques, we assemble data from the proxy statements of publicly announced mergers between 2003 and 2017 into a dataset of 1,913 unique transactions. Of these, 1,167 transactions were subject to the Revlon standard, and 553 were not. After subjecting this sample to empirical analysis, our results show that Revlon does indeed matter for companies incorporated in Delaware. We find that in Delaware, Revlon deals are more intensely negotiated, involve more bidders, and result in higher transaction premiums than non-Revlon deals. However, these results do not hold for target companies incorporated in other jurisdictions that have adopted the Revlon doctrine. Our results shed light on the implications of the current state of uncertainty surrounding Revlon and provide some direction for courts going forward. We theorize that Revlon is a monitoring standard whose effectiveness depends upon the judiciary’s credible commitment to intervene in biased transactions. The precise contours of the doctrine are unimportant as long as the judiciary retains a substantive avenue for intervention. Recent Delaware decisions in C&J and Corwin have been criticized for overly restricting Revlon, but we suggest that such concerns are overstated so long as Delaware judges continue to monitor the substance of transactions. Thus, in applying these decisions, Delaware judges should focus not on procedural aspects but the substantive component of transactions, which Revlon initially sought to regulate

XO-2b: a hot Jupiter with a variable host star that potentially affects its measured transit depth

The transiting hot Jupiter XO-2b is an ideal target for multi-object photometry and spectroscopy as it has a relatively bright ($V$-mag = 11.25) K0V host star (XO-2N) and a large planet-to-star contrast ratio (R$_{p}$/R$_{s}\approx0.015$). It also has a nearby (31.21") binary stellar companion (XO-2S) of nearly the same brightness ($V$-mag = 11.20) and spectral type (G9V), allowing for the characterization and removal of shared systematic errors (e.g., airmass brightness variations). We have therefore conducted a multiyear (2012--2015) study of XO-2b with the University of Arizona's 61" (1.55~m) Kuiper Telescope and Mont4k CCD in the Bessel U and Harris B photometric passbands to measure its Rayleigh scattering slope to place upper limits on the pressure-dependent radius at, e.g., 10~bar. Such measurements are needed to constrain its derived molecular abundances from primary transit observations. We have also been monitoring XO-2N since the 2013--2014 winter season with Tennessee State University's Celestron-14 (0.36~m) automated imaging telescope to investigate stellar variability, which could affect XO-2b's transit depth. Our observations indicate that XO-2N is variable, potentially due to {cool star} spots, {with a peak-to-peak amplitude of $0.0049 \pm 0.0007$~R-mag and a period of $29.89 \pm 0.16$~days for the 2013--2014 observing season and a peak-to-peak amplitude of $0.0035 \pm 0.0007$~R-mag and $27.34 \pm 0.21$~day period for the 2014--2015 observing season. Because of} the likely influence of XO-2N's variability on the derivation of XO-2b's transit depth, we cannot bin multiple nights of data to decrease our uncertainties, preventing us from constraining its gas abundances. This study demonstrates that long-term monitoring programs of exoplanet host stars are crucial for understanding host star variability.Comment: published in ApJ, 9 pages, 11 figures, 3 tables; updated figures with more ground-based monitoring, added more citations to previous work

Las Vegas metropolitan area social survey 2010 highlights

UNLV sociologists conducted the Las Vegas Metropolitan Area Social Survey (LVMASS) to identify the socio-spatial distribution of attitudes and attributes relevant to urban sustainability in the Las Vegas Valley. The project goal is to understand how Las Vegas residents think about urban sustainability issues across three dimensions: 1) natural environment; 2) community and quality of life; 3) economy

A multimerizing transcription factor of sea urchin embryos capable of looping DNA

SpGCF1 is a recently cloned sea urchin transcription factor that recognizes target sites in several different sea urchin genes. We find that in gel-shift experiments this factor is able to multimerize. A quantitative simulation of the gel-shift results suggests that SpGCF1 molecules that are bound to DNA target sites may also bind to one another, thus associating several DNA probe molecules. SpGCF1 might therefore be able to loop DNA molecules bearing its target sites at distant locations. We demonstrate this prediction by electron microscopy, and using the well-characterized cis-regulatory domain of the CyIIIa cytoskeletal actin gene, we show that the loop conformations predicted from the known SpGCF1 target site locations are actually formed in vitro. We speculate that the multimerization of this factor in vivo may function to bring distant regions of extended regulatory domains into immediate proximity so that they can interact with one another