Variations in mid-ocean ridge CO2 emissions driven by glacial cycles

The geological record shows links between glacial cycles and volcanic productivity, both subaerially and at mid-ocean ridges. Sea-level-driven pressure changes could also affect chemical properties of mid-ocean ridge volcanism. We consider how changing sea-level could alter the CO2 emissions rate from mid-ocean ridges, on both the segment and global scale. We develop a simplified transport model for a highly incompatible element through a homogenous mantle; variations in the melt concentration the emission rate of the element are created by changes in the depth of first silicate melting. The model predicts an average global mid-ocean ridge CO2 emissions-rate of 53 Mt/yr, in line with other estimates. We show that falling sea level would cause an increase in ridge CO2 emissions with a lag of about 100 kyrs after the causative sea level change. The lag and amplitude of the response are sensitive to mantle permeability and plate spreading rate. For a reconstructed sea-level time series of the past million years, we predict variations of up to 12% (7 Mt/yr) in global mid-ocean ridge CO2 emissions. The magnitude and timing of the predicted variations in CO2 emissions suggests a potential role for ridge carbon emissions in glacial cycles

Mathematical Modelling of Tyndall Star Initiation

The superheating that usually occurs when a solid is melted by volumetric heating can produce irregular solid-liquid interfaces. Such interfaces can be visualised in ice, where they are sometimes known as Tyndall stars. This paper describes some of the experimental observations of Tyndall stars and a mathematical model for the early stages of their evolution. The modelling is complicated by the strong crystalline anisotropy, which results in an anisotropic kinetic undercooling at the interface; it leads to an interesting class of free boundary problems that treat the melt region as infinitesimally thin

Viscoelastic mechanics of tidally induced lake drainage in the Amery grounding zone

Drainage of supraglacial lakes through hydrofractures plays an important role in lubricating the ice--bedrock interface and causing ice-shelf collapse. For supraglacial lakes in Antarctic grounding zones, the effect of their drainage, which is complicated by the grounding line dynamics, is of great importance for understanding ice-sheet mass loss and ice-shelf vulnerability. Recently, a series of supraglacial lake drainage events through hydrofractures was observed in the Amery Ice Shelf grounding zone, East Antarctica, but the mechanism inducing hydrofracture was not determined. Here we explore the potential tidal contribution to hydrofracture propagation with a modelling approach. We model the viscoelastic tidal response of a marine ice sheet and hydrofracture propagation under tidal stress. Our results show that ocean tides and lake-water pressure together control supraglacial lake drainage through hydrofractures in the grounding zone. We give a model-based criterion that predicts supraglacial lake drainage based on observations of daily maximum tidal amplitude and lake depth. Our model-based criterion agrees with remotely sensed data, indicating the importance of tidal flexure to processes associated with hydrofracturing such as supraglacial lake drainage, rifting and calving.Comment: 23 pages, 8 figure

Full-Scale Wind-Tunnel Study of the Effect of Nacelle Shape on Cooling Drag

Tests were made in the Ames 40 by 80 ft Wind Tunnel of a semispan wing with a nacelle (no propeller) from a typical, general aviation twin-engine aircraft. Measurements were made of the effect on drag of the flow of cooling air through the nacelle. Internal and external nacelle pressures were measured. It was found that the cooling airflow accounts for about 13% of the total estimated airplane drag during both cruise and climb. The now of cooling air through the nacelle accounts for 30% of the airflow drag component during cruise and 42% during climb; the balance, in both cruise and climb, is attributed to [he external shape of the nacelle. It was suggested that improvements could possibly be made by relocating both the inlet and the outlet for the cooling air

Histone H2AX Is Phosphorylated at Sites of Retroviral DNA Integration but Is Dispensable for Postintegration Repair

The histone variant H2AX is rapidly phosphorylated (denoted {gamma}H2AX) in large chromatin domains (foci) flanking double strand DNA (dsDNA) breaks that are produced by ionizing radiation or genotoxic agents and during V(D)J recombination. H2AX-deficient cells and mice demonstrate increased sensitivity to dsDNA break damage, indicating an active role for {gamma}H2AX in DNA repair; however, {gamma}H2AX formation is not required for V(D)J recombination. The latter finding has suggested a greater dependence on {gamma}H2AX for anchoring free broken ends versus ends that are held together during programmed breakage-joining reactions. Retroviral DNA integration produces a unique intermediate in which a dsDNA break in host DNA is held together by the intervening viral DNA, and such a reaction provides a useful model to distinguish {gamma}H2AX functions. We found that integration promotes transient formation of {gamma}H2AX at retroviral integration sites as detected by both immunocytological and chromatin immunoprecipitation methods. These results provide the first direct evidence for the association of newly integrated viral DNA with a protein species that is an established marker for the onset of a DNA damage response. We also show that H2AX is not required for repair of the retroviral integration intermediate as determined by stable transduction. These observations provide independent support for an anchoring model for the function of {gamma}H2AX in chromatin repair

Label-free shotgun proteomics and metabolite analysis reveal a significant metabolic shift during citrus fruit development.

Label-free LC-MS/MS-based shot-gun proteomics was used to quantify the differential protein synthesis and metabolite profiling in order to assess metabolic changes during the development of citrus fruits. Our results suggested the occurrence of a metabolic change during citrus fruit maturation, where the organic acid and amino acid accumulation seen during the early stages of development shifted into sugar synthesis during the later stage of citrus fruit development. The expression of invertases remained unchanged, while an invertase inhibitor was up-regulated towards maturation. The increased expression of sucrose-phosphate synthase and sucrose-6-phosphate phosphatase and the rapid sugar accumulation suggest that sucrose is also being synthesized in citrus juice sac cells during the later stage of fruit development

The interferon-inducible antiviral protein Daxx is not essential for interferon-mediated protection against avian sarcoma virus

BACKGROUND: The antiviral protein Daxx acts as a restriction factor of avian sarcoma virus (ASV; Retroviridae) in mammalian cells by promoting epigenetic silencing of integrated proviral DNA. Although Daxx is encoded by a type I (α/β) interferon-stimulated gene, the requirement for Daxx in the interferon anti-retroviral response has not been elucidated. In this report, we describe the results of experiments designed to investigate the role of Daxx in the type I interferon-induced anti-ASV response. FINDINGS: Using an ASV reporter system, we show that type I interferons are potent inhibitors of ASV replication. We demonstrate that, while Daxx is necessary to silence ASV gene expression in the absence of interferons, type I interferons are fully-capable of inducing an antiviral state in the absence of Daxx. CONCLUSIONS: These results provide evidence that Daxx is not essential for the anti-ASV interferon response in mammalian cells, and that interferons deploy multiple, redundant antiviral mechanisms to protect cells from ASV

Tail pinch induced stress-arousal facilitates brain stimulation reward

Adult male Sprague Dawley rats with chronic access to self stimulation were subjected to handling, tail pinch, or left undisturbed. Tail pinch increased responding for positive reinforcement while the other conditions did not. The stress related properties of tail pinch may therefore facilitate responding in the present and other situations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23691/1/0000661.pd

Stress, behavioral arousal, and open field activity--A reexamination of emotionality in the rat

The effects of stress upon emotionality, and of emotionality upon the open field activity of rats have now been studied for over four decades. Controversy remains however regarding the degree to which stress alters behavior, and the direction of that change. One reason for this is the absence of an adequate behavioral definition of stress. The present series of experiments demonstrates a standard relatively nontraumatic stress induction procedure which may be used in conjunction with open field testing. Pre-exposure to moderately intense light and white noise facilitated open field activity as measured by initial activity, lowered defecation scores, and supplementary measures (rearing, grooming, center field penetration). Further parametric, psychoendocrine, and pharmacological studies characterized the nature of the facilitation, its time course, and its modification by other manipulations. Our results suggest the initial behavioral response to stress in an open field is activation. Previous studies may have differed in their results relating stress and behavior because of subtle procedural distinctions, some of which may be identified using the present technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23706/1/0000678.pd