The morphology of supraglacial lake ogives

Supraglacial lakes on grounded regions of the Greenland and Antarctic ice sheets sometimes produce ‘lake ogives’ or banded structures that sweep downstream from the lakes. UsingSupraglacial lakes on grounded regions of the Greenland and Antarctic ice sheets sometimes produce ‘lake ogives’ or banded structures that sweep downstream from the lakes. Using a variety of remote-sensing data, we demonstrate that lake ogives originate from supraglacial lakes that form each year in the same bedrock-fixed location near the equilibrium-line altitude. As the ice flows underneath one of these lakes, an ‘image’ of the lake is imprinted on the ice surface both by summer- season ablation and by superimposed ice (lake ice) formation. Ogives associated with a lake are sequenced in time, with the downstream ogives being the oldest, and with spatial separation equal to the local annual ice displacement. In addition, lake ogives can have decimeter- to meter-scale topographic relief, much like wave ogives that form below icefalls on alpine glaciers. Our observations highlight the fact that lake ogives, and other related surface features, are a consequence of hydrological processes in a bedrock-fixed reference frame. These features should arise naturally from physically based thermodynamic models of supraglacial water transport, and thus they may serve as fiducial features that help to test the performance of such models.Research conducted at the University of Chicago was supported by several US National Science Foundation (NSF) grants, including ARC-0907834, ANT-0944248 and ANT-0944193. We thank Dorian S. Abbot for helpful discussions and review of earlier manuscripts. This work began as a result of NSF-supported summer research internships awarded in 2010 to Pablo S. Wooley (Bowdoin College) and Julia E. Vidonish (University of Chicago). We thank S.G. Warren for informative discussions about the brightening of lake bottom surfaces. We also thank Roman J. Motyka for helpful discussions and the use of SPOT5 products. SPOT data products used in this study were provided by the SPOT5 stereoscopic survey of Polar Ice: Reference Images and Topographies (SPIRIT) during the fourth International Polar Year (2007–09). We acknowledge W.T. Colgan for helpful criticism of the ideas presented in this paper, and review of earlier versions of the manuscript. We acknowledge the use of data and/or data products from CReSIS generated with support from NSF grant ANT- 0424589 and NASA grant NNX10AT68G. Ed Waddington, Derrick Lampkin and and two anonymous referees provided comments that significantly improved the manuscript. We dedicate this manuscript to the memory of Keith Echelmeyer, who first described lake ogives and considerably enriched the science of glaciology throughout his life.Ye

The Potential of Iron Chelators of the Pyridoxal Isonicotinoyl Hydrazone Class as Effective Antiproliferative Agents III: The Effect of the Ligands on Molecular Targets Involved in Proliferation

AbstractWe have identified specific iron (Fe) chelators of the pyridoxal isonicotinoyl hydrazone (PIH) class that are far more effective ligands than desferrioxamine (DFO; Richardson et al, Blood 86:4295, 1995; Richardson and Milnes, Blood 89:3025, 1997). In the present study, we have compared the effect of DFO and one of the most active chelators (2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone; 311) on molecular targets involved in proliferation. This was performed to further understand the mechanisms involved in the antitumor activity of Fe chelators. Ligand 311 was far more active than DFO at increasing Fe release from SK-N-MC neuroepithelioma and BE-2 neuroblastoma cells and preventing Fe uptake from transferrin. Like DFO, 311 increased the RNA-binding activity of the iron-regulatory proteins (IRPs). However, despite the far greater Fe chelation efficacy of 311 compared with DFO, a similar increase in IRP-RNA binding activity occurred after 2 to 4 hours of incubation with either chelator, and the binding activity was not inhibited by cycloheximide. These results suggest that, irrespective of the Fe chelation efficacy of a ligand, an increase IRP-RNA binding activity occurred via a time-dependent step that did not require protein synthesis. Further studies examined the effect of 311 and DFO on the expression of p53-transactivated genes that are crucial for cell cycle control and DNA repair, namely WAF1,GADD45, and mdm-2. Incubation of 3 different cell lines with DFO or 311 caused a pronounced concentration- and time-dependent increase in the expression of WAF1 and GADD45 mRNA, but not mdm-2 mRNA. In accordance with the distinct differences in Fe chelation efficacy and antiproliferative activity of DFO and 311, much higher concentrations of DFO (150 μmol/L) than 311 (2.5 to 5 μmol/L) were required to markedly increase GADD45 and WAF1 mRNA levels. The increase in GADD45 and WAF1 mRNA expression was seen only after 20 hours of incubation with the chelators and was reversible after removal of the ligands. In contrast to the chelators, the Fe(III) complexes of DFO and 311 had no effect on increasing GADD45 and WAF1 mRNA levels, suggesting that Fe chelation was required. Finally, the increase in GADD45 and WAF1 mRNAs appeared to occur by a p53-independent pathway in SK-N-MC and K562 cells, because these cell lines lack functional p53. Our results suggest that GADD45 and WAF1 may play important roles in the cell cycle arrest observed after exposure to these chelators.</jats:p

The Potential of Iron Chelators of the Pyridoxal Isonicotinoyl Hydrazone Class as Effective Antiproliferative Agents III: The Effect of the Ligands on Molecular Targets Involved in Proliferation

We have identified specific iron (Fe) chelators of the pyridoxal isonicotinoyl hydrazone (PIH) class that are far more effective ligands than desferrioxamine (DFO; Richardson et al, Blood 86:4295, 1995; Richardson and Milnes, Blood 89:3025, 1997). In the present study, we have compared the effect of DFO and one of the most active chelators (2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone; 311) on molecular targets involved in proliferation. This was performed to further understand the mechanisms involved in the antitumor activity of Fe chelators. Ligand 311 was far more active than DFO at increasing Fe release from SK-N-MC neuroepithelioma and BE-2 neuroblastoma cells and preventing Fe uptake from transferrin. Like DFO, 311 increased the RNA-binding activity of the iron-regulatory proteins (IRPs). However, despite the far greater Fe chelation efficacy of 311 compared with DFO, a similar increase in IRP-RNA binding activity occurred after 2 to 4 hours of incubation with either chelator, and the binding activity was not inhibited by cycloheximide. These results suggest that, irrespective of the Fe chelation efficacy of a ligand, an increase IRP-RNA binding activity occurred via a time-dependent step that did not require protein synthesis. Further studies examined the effect of 311 and DFO on the expression of p53-transactivated genes that are crucial for cell cycle control and DNA repair, namely WAF1,GADD45, and mdm-2. Incubation of 3 different cell lines with DFO or 311 caused a pronounced concentration- and time-dependent increase in the expression of WAF1 and GADD45 mRNA, but not mdm-2 mRNA. In accordance with the distinct differences in Fe chelation efficacy and antiproliferative activity of DFO and 311, much higher concentrations of DFO (150 μmol/L) than 311 (2.5 to 5 μmol/L) were required to markedly increase GADD45 and WAF1 mRNA levels. The increase in GADD45 and WAF1 mRNA expression was seen only after 20 hours of incubation with the chelators and was reversible after removal of the ligands. In contrast to the chelators, the Fe(III) complexes of DFO and 311 had no effect on increasing GADD45 and WAF1 mRNA levels, suggesting that Fe chelation was required. Finally, the increase in GADD45 and WAF1 mRNAs appeared to occur by a p53-independent pathway in SK-N-MC and K562 cells, because these cell lines lack functional p53. Our results suggest that GADD45 and WAF1 may play important roles in the cell cycle arrest observed after exposure to these chelators.</jats:p

Oil price fluctuations and the Nigerian economy

The single most important issue confronting a growing number of world economies today is the price of oil and its attendant consequences on economic output. Several studies have taken the approach of Hamilton (1983) in investigating the effect of oil price shocks on levels of gross domestic product. The focus of this paper is primarily on the relationship between oil price changes and economic development via industrial production. A vector auto regression model is employed on some macroeconomic variables from 1980 through 2004. The results indicate that oil price changes affect real exchange rates, which, in turn, affect industrial production. However, this indirect effect of oil prices on industrial production is not statistically significant. Therefore, the implication of the results presented in this paper is that an increase in oil prices does not lead to an increase in industrial production in Nigeria. Copyright 2005 Organization of the Petroleum Exporting Countries.

Issues in Modeling Repeat Leisure Consumption: Markov Modeling Examples

Models should be used to facilitate understanding structure in data. This article is about using models that are adequate approximations to reality if models are used. A theory and research context for Markov modeling is given for repeat holiday travel and the examination of destination loyalty. A simple Markov model based on the literature and an expanded state space Markov model based on repeat travel related concepts in the literature are presented. Analysis of travel to Turkey from the UK and to the USA from Australia, Japan and the UK confirms Oppermann's (1998a) claim that simple Markov models result in a poor approximation to reality. It is shown that expanded state space models can accommodate realism. Models producing hypothetical behavior or behavior that mirrors reality are discussed both generally and regarding repeat travel, specifically. Application of the ideas and methods presented to leisure research on matters other than travel is discussed