High concentration of atmospheric 14C during the Younger Dryas cold episode

Nature ◽  
1995 ◽  
Vol 377 (6548) ◽  
pp. 414-417 ◽  
Author(s):  
Tomasz Goslar ◽  
Maurice Arnold ◽  
Edouard Bard ◽  
Tadeusz Kuc ◽  
Mieczysław F. Pazdur ◽  
...  
Keyword(s):  
Younger Dryas ◽  
High Concentration ◽  
Cold Episode

scholarly journals Routing of meltwater from the Laurentide Ice Sheet during the Younger Dryas cold episode

Nature ◽  
1989 ◽  
Vol 341 (6240) ◽  
pp. 318-321 ◽  
Author(s):  
Wallace S. Broecker ◽  
James P. Kennett ◽  
Benjamin P. Flower ◽  
James T. Teller ◽  
Sue Trumbore ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Younger Dryas ◽  
Laurentide Ice Sheet ◽  
Cold Episode

scholarly journals Sea level fingerprinting of the Bering Strait flooding history detects the source of the Younger Dryas climate event

2020 ◽  
Vol 6 (9) ◽  
pp. eaay2935 ◽  
Author(s):  
T. Pico ◽  
J. X. Mitrovica ◽  
A. C. Mix
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Younger Dryas ◽  
The Arctic ◽  
Bering Strait ◽  
Land Bridge ◽  
Climate Event ◽  
Ice Retreat ◽  
Cold Episode ◽  
Continental Ice Sheets

During the Last Glacial Maximum, expansive continental ice sheets lowered globally averaged sea level ~130 m, exposing a land bridge at the Bering Strait. During the subsequent deglaciation, sea level rose rapidly and ultimately flooded the Bering Strait, linking the Arctic and Pacific Oceans. Observational records of the Bering Strait flooding have suggested two apparently contradictory scenarios for the timing of the reconnection. We reconcile these enigmatic datasets using gravitationally self-consistent sea-level simulations that vary the timing and geometry of ice retreat between the Laurentide and Cordilleran Ice Sheets to the southwest of the Bering Strait to fit observations of a two-phased flooding history. Assuming the datasets are robust, we demonstrate that their reconciliation requires a substantial melting of the Cordilleran and western Laurentide Ice Sheet from 13,000 to 11,500 years ago. This timing provides a freshwater source for the widely debated Younger Dryas cold episode (12,900 to 11,700 years ago).

A Multiproxy Investigation of Late-Glacial Climate and Vegetation Change at Pine Ridge Pond, Southwest New Brunswick, Canada

1994 ◽  
Vol 42 (3) ◽  
pp. 316-327 ◽  
Author(s):  
André J. Levesque ◽  
Les C. Cwynar ◽  
Ian R. Walker
Keyword(s):  
Vegetation Change ◽  
Birch Pollen ◽  
Younger Dryas ◽  
Late Glacial ◽  
Coarse Sand ◽  
Tree Pollen ◽  
Pine Ridge ◽  
Dwarf Birch ◽  
Armeria Maritima ◽  
Cold Episode

AbstractPollen, plant macrofossil, chironomid, and lithological analyses of late-glacial sediment from Pine Ridge Pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes; initially by a brief and moderate cold episode (the Killarney Oscillation), followed shortly by the Younger Dryas. The Killarney Oscillation, AMS 14C dated at between 11,290 and 10,960 yr B.P., is characterized by abrupt and simultaneous increases in Betula (birch) pollen and Betula glandulosa (dwarf birch) macrofossils and a decline in tree pollen. The Younger Dryas is distinguished by the reversion of a short-lived closed Picea (spruce) forest to a prolonged forest-tundra stage (ca. 10, 820 to 9500(?) yr B.P.), during which macrofossils of arctic/alpine plants such as Salix herbaces, Cassiope hypnoides, Armeria maritima, and Thalictrum alpinum make their sole late-glacial appearance. Chironomid-inferred summer surface-water temperatures indicate a cooling of approximately 8 and 12°C during the Killarney Oscillation and Younger Dryas, respectively, and coarse-sand analysis indicates increased erosion on the landscape during these same intervals.

Cytomembrane Preservation in Tissue Dehydrated Only With Glutaraldehyde and Epon 812 Resin

1973 ◽  
Vol 31 ◽  
pp. 320-321
Author(s):  
Daniel C. Pease
Keyword(s):  
Diffraction Pattern ◽  
X Ray Diffraction ◽  
High Concentration ◽  
Unpublished Study ◽  
X Ray ◽  
Sectioned Material

A previous study demonstrated that tissue could be successfully infiltrated with 50% glutaraldehyde, and then subsequently polymerized with urea to create an embedment which retained cytomembrane lipids in sectioned material. As a result, the 180-190 Å periodicity characteristic of fresh, mammalian myelin was preserved in sections, as was a brilliant birefringence, and the capacity to bind OsO4 vapor in the hydrophobic bilayers. An associated (unpublished) study, carried out in co-operation with Drs. C.K. Akers and D.F. Parsons, demonstrated that the high concentration of glutaraldehyde (and urea) did not significantly alter the X-ray diffraction pattern of aldehyde-fixed, myelin. Thus, by itself, 50% glutaraldehyde has little effect upon cytomembrane systems and can be used with confidence for the first stages of dehydration.

Effects of carbamylcholine on chick embryo aggregate retina cell cultures

1988 ◽  
Vol 46 ◽  
pp. 350-351
Author(s):  
Glenn M. Cohen ◽  
Radharaman Ray
Keyword(s):  
Cell Cultures ◽  
Single Cells ◽  
Retinal Cell ◽  
Cell Aggregates ◽  
High Concentration ◽  
In Ovo ◽  
Sterile Culture ◽  
Retinal Tissue ◽  
Synaptic Junctions ◽  
And Control

Retinal,cell aggregates develop in culture in a pattern similar to the in ovo retina, forming neurites first and then synapses. In the present study, we continuously exposed chick retinal cell aggregates to a high concentration (1 mM) of carbamylcholine (carbachol), an acetylcholine (ACh) analog that resists hydrolysis by acetylcholinesterase (AChE). This situation is similar to organophosphorus anticholinesterase poisoning in which the ACh level is elevated at synaptic junctions due to inhibition of AChE, Our objective was to determine whether continuous carbachol exposure either damaged cholino- ceptive neurites, cell bodies, and synaptic elements of the aggregates or influenced (hastened or retarded) their development.The retinal tissue was isolated aseptically from 11 day embryonic White Leghorn chicks and then enzymatically (trypsin) and mechanically (trituration) dissociated into single cells. After washing the cells by repeated suspension and low (about 200 x G) centrifugation twice, aggregate cell cultures (about l0 cells/culture) were initiated in 1.5 ml medium (BME, GIBCO) in 35 mm sterile culture dishes and maintained as experimental (containing 10-3 M carbachol) and control specimens.

The Fine Structure of Phloem Cells

1985 ◽  
Vol 43 ◽  
pp. 632-635
Author(s):  
James Cronshaw
Keyword(s):  
Structural Studies ◽  
High Concentration ◽  
Long Distance ◽  
Phloem Tissue ◽  
Sieve Elements ◽  
Long Distance Transport ◽  
P Protein ◽  
Companion Cells ◽  
Electron Microscopical ◽  
Distance Transport

Long distance transport in plants takes place in phloem tissue which has characteristic cells, the sieve elements. At maturity these cells have sieve areas in their end walls with specialized perforations. They are associated with companion cells, parenchyma cells, and in some species, with transfer cells. The protoplast of the functioning sieve element contains a high concentration of sugar, and consequently a high hydrostatic pressure, which makes it extremely difficult to fix mature sieve elements for electron microscopical observation without the formation of surge artifacts. Despite many structural studies which have attempted to prevent surge artifacts, several features of mature sieve elements, such as the distribution of P-protein and the nature of the contents of the sieve area pores, remain controversial.

Tem analysis of multiple-energy arsenic implanted and Rta'd silicon

1987 ◽  
Vol 45 ◽  
pp. 246-247
Author(s):  
R.A. Herring
Keyword(s):  
Device Fabrication ◽  
High Concentration ◽  
Tem Analysis ◽  
Defect Clusters ◽  
High Fluences ◽  
Small Defect ◽  
Before And After ◽  
The Matrix ◽  
The Difference ◽  
Factor Type

Rapid thermal annealing (RTA) of ion-implanted Si is important for device fabrication. The defect structures of 2.5, 4.0, and 6.0 MeV As-implanted silicon irradiated to fluences of 2E14, 4E14, and 6E14, respectively, have been analyzed by electron diffraction both before and after RTA at 1100°C for 10 seconds. At such high fluences and energies the implanted As ions change the Si from crystalline to amorphous. Three distinct amorphous regions emerge due to the three implantation energies used (Fig. 1). The amorphous regions are separated from each other by crystalline Si (marked L1, L2, and L3 in Fig. 1) which contains a high concentration of small defect clusters. The small defect clusters were similar to what had been determined earlier as being amorphous zones since their contrast was principally of the structure-factor type that arises due to the difference in extinction distance between the matrix and damage regions.

Influence of nascent polypeptide positive charges on translation dynamics

2020 ◽  
Vol 477 (15) ◽  
pp. 2921-2934
Author(s):  
Rodrigo D. Requião ◽  
Géssica C. Barros ◽  
Tatiana Domitrovic ◽  
Fernando L. Palhano
Keyword(s):  
Mrna Decay ◽  
Translation Termination ◽  
Published Data ◽  
Translation Efficiency ◽  
Amino Acid Residues ◽  
High Concentration ◽  
Strong Argument ◽  
Translation Arrest ◽  
Exit Tunnel ◽  
Positively Charged

Protein segments with a high concentration of positively charged amino acid residues are often used in reporter constructs designed to activate ribosomal mRNA/protein decay pathways, such as those involving nonstop mRNA decay (NSD), no-go mRNA decay (NGD) and the ribosome quality control (RQC) complex. It has been proposed that the electrostatic interaction of the positively charged nascent peptide with the negatively charged ribosomal exit tunnel leads to translation arrest. When stalled long enough, the translation process is terminated with the degradation of the transcript and an incomplete protein. Although early experiments made a strong argument for this mechanism, other features associated with positively charged reporters, such as codon bias and mRNA and protein structure, have emerged as potent inducers of ribosome stalling. We carefully reviewed the published data on the protein and mRNA expression of artificial constructs with diverse compositions as assessed in different organisms. We concluded that, although polybasic sequences generally lead to lower translation efficiency, it appears that an aggravating factor, such as a nonoptimal codon composition, is necessary to cause translation termination events.

Measurement of the Platelet Response to Laser- induced Microvascular Injury

1974 ◽  
Vol 32 (02/03) ◽  
pp. 704-713 ◽  
Author(s):  
F. N McKenzie ◽  
K.-E Arfors ◽  
N. A Matheson
Keyword(s):  
Inhibitory Effect ◽  
Microvascular Blood Flow ◽  
Platelet Response ◽  
High Concentration ◽  
Platelet Activity ◽  
Microvascular Injury ◽  
Arterial Blood ◽  
Proximal Site ◽  
Adenosine Phosphates

SummaryA study has been made of the biochemical factors underlying the platelet response to laser-induced microvascular injury. A platelet aggregating substance is produced at sites of laser-induced injury which markedly stimulates platelet activity at a site of injury inflicted a short distance downstream. Distal sites of injury are not similarly influenced if the distance between the injuries is increased or if the proximal site no longer shows platelet-stimulating activity. The stimulating effect of an adjacent proximal injury on platelet activity at a distal site is inhibited by local intra-arterial infusion of adenosine. Measurements of arterial blood pressure and microvascular blood flow velocity during adenosine infusion showed that its inhibitory effect on platelet activity is largely independent of its vasodilator properties. The effect of infusion of different adenosine phosphates (AMP, ADP, ATP) was also studied. Very small amounts of ADP markedly stimulated platelet activity and the emboli formed were similar to those normally produced at sites of laser injury. At high concentration AMP inhibited while ATP stimulated platelet activity in vivo. The results emphasise the fundamental role of ADP as a mediator of the platelet response at sites of laser- induced microvascular injury.

Sign in / Sign up

Export Citation Format

Share Document