Glaciers and Polar Environment [Working Title]

2021 ◽  
Keyword(s):  
Polar Environment

scholarly journals Depositional Landforming Processes at the Snouts of Five Surging Glaciers in Vestspitsbergen (Abstract only)

1981 ◽  
Vol 2 ◽  
pp. 115-115 ◽  
Author(s):  
D. G. Croot
Keyword(s):  
Simple Model ◽  
Recent Work ◽  
Central Area ◽  
Morphological Features ◽  
Landscape Development ◽  
Maximum Extension ◽  
The Core ◽  
Polar Environment ◽  
Compressive Flow ◽  
Ice Leads

Recent work by Clapperton (1975) proposes that the rapid rates of advance experienced by glaciers which surge may lead to enhanced debris incorporation, increased compressive flow near the glacier snout at the point of maximum extension, and to the upward translation and vertical stacking of debris near the glacier snout and margin. Five glaciers in Spitsbergen (Battyebreen, Holmströmbreen, Lisbetbreen, Vonbreen, Elnabreen) display morphological features which are widely accepted as being diagnostic of surging glaciers.Results of detailed observations regarding the nature, distribution, melt-out, and reworking of englacial debris at Battyebreen are presented. Basally derived till is brought to the surface of the glacier in narrow lateral and terminal belts, no more than 100 m wide. Within this zone, (i.e. up-valley from the snout and towards the valley centre) the ice is debris-free with the exception of small amounts of en-glacial debris which form the core of lobate medial moraines. Differential ablation of debris-free and debris-rich ice leads to the production of a topographic basin within which melt-out and reworking processes occupy restricted locations, as follows. Immediately inside the encircling melt-out till, a zone of flow tills is found. Melt streams are located at the foot of, the flow till-mantled slope, producing narrow (150 m wide) outwash trains, which merge into deltas. The central area of the topographic basin is occupied by a supraglacial lake.Observations of the remaining four locations confirm that other glaciers in the vicinity, which display similar characteristics associated with surging, are developing a stagnant-ice zone of identical appearance. The pattern of processes observed at Battyebreen is thus repeated at each site.A simple model of depositional landscape development is proposed for surging valley glaciers in a sub-polar environment.

scholarly journals Iodination of insulin in aqueous and organic solvents

1969 ◽  
Vol 115 (1) ◽  
pp. 11-18 ◽  
Author(s):  
A. Massaglia ◽  
U. Rosa ◽  
G. Rialdi ◽  
C. A. Rossi
Keyword(s):  
Ethylene Glycol ◽  
Organic Solvents ◽  
Molecular Conformation ◽  
Aqueous Media ◽  
Native Structure ◽  
Experimental Conditions ◽  
Polar Environment ◽  
Polar Area ◽  
The Difference ◽  
A Chain

1. The iodination of insulin was studied under various experimental conditions in aqueous media and in some organic solvents, by measuring separately the uptake of iodine by the four tyrosyl groups and the relative amounts of monoiodotyrosine and di-iodotyrosine that are formed. In aqueous media from pH1 to pH9 the iodination occurs predominantly on the tyrosyl groups of the A chain. Some organic solvents increase the iodine uptake of the B-chain tyrosyl groups. Their efficacy in promoting iodination of Tyr-B-16 and Tyr-B-26 is in the order: ethylene glycol and propylene glycol≃methanol and ethanol>dioxan>8m-urea. 2. It is suggested that each of the four tyrosyl groups in insulin has a different environment: Tyr-A-14 is fully exposed to the solvent; Tyr-A-19 is sterically influenced by the environmental structure, possibly by the vicinity of a disulphide interchain bond; Tyr-B-16 is embedded into a non-polar area whose stability is virtually independent of the molecular conformation; Tyr-B-26 is probably in a situation similar to Tyr-B-16 with the difference that its non-polar environment depends on the preservation of the native structure.

Cognitive performance during long-term residence in a polar environment

2010 ◽  
Vol 30 (1) ◽  
pp. 129-132 ◽  
Author(s):  
F.U. John Paul ◽  
Manas K. Mandal ◽  
K. Ramachandran ◽  
M.R. Panwar
Keyword(s):  
Cognitive Performance ◽  
Polar Environment

Synthesis and Catalytic Applications of Chemically Grafted SiH-Functionalized Tripodal Ti-POSS Complexes in Crosslinked Hyperbranched Poly(siloxysilane)

2015 ◽  
Vol 68 (7) ◽  
pp. 1091 ◽  
Author(s):  
Emad H. Aish
Keyword(s):  
High Activity ◽  
Active Site ◽  
Polyhedral Oligomeric Silsesquioxane ◽  
Polar Environment ◽  
Hyperbranched Poly ◽  
Chemical Grafting ◽  
Synthesis Activity ◽  
Catalytic Applications ◽  
Oligomeric Silsesquioxane

This study investigated the synthesis, activity, epoxide selectivity, H2O2 efficiency, and recyclability of new heterogeneous alkene epoxidation catalysts prepared by chemical grafting of new SiH-functionalized tripodal Ti–polyhedral oligomeric silsesquioxane (Ti-POSS) complexes in hyperbranched poly(siloxysilane) via hydrosilation. Crosslinked hyperbranched poly(siloxysilane)-grafted [{(p-HSiMe2(CH2)2C6H4)(c-C6H11)6Si7O12}Ti(NMe2)] (11) and crosslinked hyperbranched poly(siloxysilane)-grafted [{(HSiMe2(CH2)3)(i-C4H9)6Si7O12}- Ti(NMe2)] (12) displayed high activity, epoxide selectivity (≥98 %), and H2O2 efficiency (≥97 %) in cyclohexene and 1-octene epoxidation with aqueous H2O2. Moreover, these catalysts were highly recyclable with retained activity and durability and proved to be truly heterogeneous. Using chemical grafting for the synthesis of 11 and 12 enhanced their recyclability and durability with retained activity. The high H2O2 efficiency can be attributed to the uniformly non-polar environment provided about Ti in 11 and 12 by the polymer; this results in low water concentrations and higher [alkene] : [H2O2] ratios at the Ti active site than in the rest of the solution. These effects enhance the epoxide selectivity and minimize leaching of titanium.

Discussion on the papers on life sciences

1977 ◽  
Vol 279 (963) ◽  
pp. 113-121
Keyword(s):  
Southern Ocean ◽  
Vascular Plants ◽  
Life Sciences ◽  
Oceanic Island ◽  
Maritime Antarctic ◽  
Polar Environment ◽  
The Antarctic

R . M. Laws Would Dr Holdgate amplify his brief comments on time as a factor? Can we expect these simple ecosystems to become more diverse and complex? M. W. Holdgate These ecosystems may be impoverished for two reasons: the harsh polar environment and the difficulties of colonizing the habitats available across the wide sea barriers of the Southern Ocean. I believe that the Antarctic does present some of the features of an oceanic island in this respect. Probably more species will succeed in invading habitats in the maritime Antarctic as time goes by, assuming that the climate does not deteriorate. Experimental introductions suggest that more vascular plants could probably live in the most favourable places if they could reach them, and I would expect the same to apply to invertebrates.

DNA and RNA enzymes with peroxidase activity — An investigation into the mechanism of action

2006 ◽  
Vol 84 (4) ◽  
pp. 613-619 ◽  
Author(s):  
Paola Travascio ◽  
Dipankar Sen ◽  
Andrew J Bennet
Keyword(s):  
Nucleic Acid ◽  
Hydrophobic Interactions ◽  
Basic Component ◽  
Axial Position ◽  
General Base ◽  
Dna And Rna ◽  
Polar Environment ◽  
Guanine Quadruplex ◽  
Acid Catalyzed ◽  
Catalyzed Reactions

A DNA–hemin complex (PS2.M–hemin), and its RNA counterpart (rPS2.M–hemin), have previously been reported, in the presence of nitrogenous buffers such as HEPES, to show enhanced peroxidative activity relative to both uncomplexed hemin and a control DNA–hemin complex (Chem. Biol. 5, 505, 1998). A kinetic analysis of these two hemin-utilizing nucleic acid enzymes provides key insights into the mechanisms for their catalyzed peroxidation reactions. First, control experiments indicate that charge on the added detergent, required for solubility reasons, has little effect on the efficiency of the nucleic-acid-catalyzed reactions. Second, the key functional impact of the two nucleic acid frameworks, either DNA or RNA, appears to be a reduction in the acidity of a water molecule coordinated to the iron atom of the hemin that is bound to the ribozyme and DNAzyme scaffolds. This effect could result from a polar environment and possibly hydrogen bond(s) at the axial position of the hemin, along with favourable hydrophobic interactions for the periphery of the porphyrin ring. Third, the basic component of the buffer enhances the activities; this likely results from a general-base-catalyzed process. Cumulatively, these data supply important clues as to how biopolymers other than a protein can complex with hemin to form productive peroxidase enzymes.Key words: ribozyme, DNAzyme, hemin, peroxidase, mechanism, guanine quadruplex.

Metabolic opportunists: feeding and temperature influence the rate and pattern of respiration in the high arctic woollybear caterpillar gynaephora groenlandica (Lymantriidae)

1999 ◽  
Vol 202 (1) ◽  
pp. 47-53 ◽  
Author(s):  
V.A. Bennett ◽  
O. Kukal ◽  
R.E. Lee
Keyword(s):  
Cold Adaptation ◽  
Freeze Tolerance ◽  
High Arctic ◽  
Temperature Influence ◽  
Temperature Changes ◽  
Respiration Rates ◽  
Polar Environment ◽  
Lepidopteran Larvae ◽  
Gynaephora Groenlandica ◽  
Metabolic Cold Adaptation

Arctic woollybear caterpillars, Gynaephora groenlandica, had the capacity to rapidly and dramatically increase respiration rates up to fourfold within 12–24 h of feeding and exhibited similar decreases in respiration of 60–85 % in as little as 12 h of starvation. At the peak of their feeding season, the respiration rates of caterpillars also increased significantly with temperature from 0.5 to 22 degreesC for both fed and starved caterpillars (Q10=1-5). Indicative of diapause, late season caterpillars had depressed respiration rates which were less sensitive to temperature changes (Q10 approximately 1.5), while respiration rates for caterpillars that had spun hibernacula were even lower. G. groenlandica did not appear to demonstrate metabolic cold adaptation compared with other temperate lepidopteran larvae. The seasonal capacity to adjust metabolic rate rapidly in response to food consumption and temperature (which can be elevated by basking) may promote the efficient acquisition of energy during the brief (1 month) summer growing and feeding season, while conserving energy by entering diapause when conditions are less favorable. These adaptations, along with their long 15–20 year life cycle and the retention of freeze tolerance year-round, promote the survival of G. groenlandica in this harsh polar environment.

THERMODYNAMICALLY INVESTIGATIONS OF FREE RADICAL SCAVENGER POTENCY OF 1,2,4-TRIHYDROXYTHIOXANTHONE

2021 ◽  
Author(s):  
Svetlana R. Jeremić ◽  
Jelena R. Đorović Jovanović ◽  
Marijana S. Stanojević Pirković ◽  
Zoran S. Marković
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom Transfer ◽  
Free Radical Scavenger ◽  
Radical Scavenger ◽  
Homolytic Cleavage ◽  
Polar Environment ◽  
Thermodynamical Parameters ◽  
Plausible Mechanism ◽  
The One ◽  
Antioxidative Action

The operative mechanism of the antioxidative action of 1,2,4-trihydroxythioxanthone (TX) is investigated in this contribution. Conclusions are made based on enthalpy values, as thermodynamical parameters. All calculations are done using the M06-2X/6-311++G(d,p) level of theory. To imitate polar and non-polar environments, calculations are done in water and benzene as the medium. It is found that, among three possible radicals that TX can generate, the most stable is the one obtained by homolytic cleavage of the O-H group in position 4. It was found that HAT (Hydrogen Atom Transfer) is the most plausible mechanism for that purpose in benzene. On the other hand, the most favorable mechanism in water is SPLET (Sequential Proton Loss Electron Transfer). Here is estimated the capacity of TX to deactivate hydroxyl (HO●), hydroperoxyl (HOO●) and methylperoxyl radical (CH3OO●). It is found that TX can deactivate all three free radicals following HAT and SPLET reaction mechanisms competitively, in the polar and non-polar environment. SET-PT (Single-Electron Transfer followed by Proton Transfer) is the inoperative mechanism for radicals scavenging, in the polar and non-polar environment.

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