Model for the structural changes occurring at low temperatures inPdDx

1981 ◽  
Vol 24 (1) ◽  
pp. 277-282 ◽  
Author(s):  
O. Blaschko ◽  
P. Fratzl ◽  
R. Klemencic
Keyword(s):  
Low Temperatures ◽  
Structural Changes

Nanoscale structure of amorphous solid water: What determines the porosity in ASW?

2019 ◽  
Vol 15 (S350) ◽  
pp. 368-369
Author(s):  
Sabrina Gärtner ◽  
Thomas F. Headen ◽  
Tristan G. A. Youngs ◽  
Catherine R. Hill ◽  
Natalia Pascual ◽  
...  
Keyword(s):  
Activation Energy ◽  
Pore Structure ◽  
Low Temperatures ◽  
Structural Changes ◽  
Amorphous Solid ◽  
Type Model ◽  
Star Forming ◽  
Star Forming Regions ◽  
Enhanced Mobility ◽  
Nanoscale Structure

AbstractThe pore structure of vapour deposited ASW is poorly understood, despite its importance to fundamental processes such as grain chemistry, cooling of star forming regions, and planet formation. We studied structural changes of vapour deposited D2O on intra-molecular to 30 nm length scales at temperatures ranging from 18 to 180 K and observed enhanced mobility from 100 to 150 K. An Arrhenius type model describes the loss of surface area and porosity with a common set of kinetic parameters. The low activation energy (428 K) is commensurate with van der Waals forces between nm-scale substructures in the ice. Our findings imply that water porosity will always change with time, even at low temperatures.

Structural changes in acclimated and unacclimated leaves during freezing and thawing

2004 ◽  
Vol 31 (1) ◽  
pp. 29 ◽  
Author(s):  
Marilyn C. Ball ◽  
Martin J. Canny ◽  
Chen X. Huang ◽  
Roger D. Heady
Keyword(s):  
Low Temperatures ◽  
Structural Changes ◽  
Living Cells ◽  
Evolutionary Significance ◽  
Intercellular Spaces ◽  
Freezing And Thawing ◽  
Specific Expansion ◽  
Intracellular Ice ◽  
Leaf Tissues ◽  
Leaf Survival

Freeze-induced damage to leaf tissues was studied at different states of acclimation to low temperatures in snow gum, Eucalyptus pauciflora Sieber ex Sprengel. Intact, attached leaves of plants grown under glasshouse or field conditions were frozen at natural rates (frost-freezing) and thawed under laboratory conditions. Leaves were cryo-fixed unfrozen, during frost-freezing or after thawing for observation in a cryo-scanning electron microscope. Frost-freezing in unacclimated tissues caused irreversible tissue damage consistent with tissue death. Intracellular ice formed in the cambium and phloem, killing the cells and leaving persistent gaps between xylem and phloem. Many other cells were damaged by frost-freeze-induced dehydration and failed to resorb water from thawed extracellular ice, leaving substantial amounts of liquid water in intercellular spaces. In contrast, acclimated leaves showed reversible tissue displacements consistent with leaf survival. In these leaves during freezing, massive extracellular ice formed in specific expansion zones within the midvein. On thawing, water was resorbed by living cells, restoring the original tissue shapes. Possible evolutionary significance of these expansion zones is discussed. Acclimated leaves showed no evidence of intracellular freezing, nor tissue lesions caused by extracellular ice. While the observations accord with current views of freeze-sensitivity and tolerance, cryo-microscopy revealed diverse responses in different tissue types.

Cis-Trans Isomerization in Natural Polyisoprenes

1960 ◽  
Vol 33 (2) ◽  
pp. 445-456 ◽  
Author(s):  
J. I. Cunneen
Keyword(s):  
Sulfur Dioxide ◽  
Natural Rubber ◽  
Ultraviolet Light ◽  
Low Temperatures ◽  
Structural Changes ◽  
Trans Isomers ◽  
Gutta Percha ◽  
Trans Isomerization ◽  
Cis And Trans Isomers ◽  
Cis And Trans

Abstract The cis and trans isomers of many simple olefins and conjugated polyolefins can be interconverted by the action of heat, light, and various catalysts, and in many such systems the changes in geometric configuration can be readily followed and the isomers separated and identified. Previous attempts to isomerize natural rubber and gutta-percha by treatment with ultraviolet light and various chemicals gave no detectable cis-trans isomerization, and in general configurational changes in unconjugated polyolefins have been unknown until recently when Golub converted the cis-1,4 units in polybutadiene into the corresponding trans units. This isomerization was achieved by irradiation of the cis-polymer with ultraviolet light in the presence of various organic bromides and sulfur compounds, but apparently this method did not isomerize natural rubber. In attempts to retard the rate of crystallization of natural rubber at moderately low temperatures—i.e., −10° to −40° C—by the attachment of side groups which would interfere with the molecular packing, it was observed that very small amounts of thiol acids were remarkably effective. This suggested that structural changes other than simply the attachment of side groups were occurring in the polyisoprene molecule. Recently it was found that thiol acids could interconvert the cis and trans forms of a simple trialkyl ethylene—e.g., 3-methylpent-2-ene—and subsequently, the isomerization of natural rubber and gutta-percha by these reagents was also observed. Following this, natural rubber, gutta-percha, squalene and cis and trans forms of 3-methylpent-2-ene have also been isomerized by treatment with sulfur dioxide and allied compounds; this work, including an investigation of the physical properties of the vulcanizates obtained from some of the isomerized polyisoprenes, is described in the present paper.

scholarly journals An Antiviral Compound That Blocks Structural Transitions of Poliovirus Prevents Receptor Binding at Low Temperatures

2000 ◽  
Vol 74 (8) ◽  
pp. 3929-3931 ◽  
Author(s):  
Alan W. Dove ◽  
Vincent R. Racaniello
Keyword(s):  
Receptor Binding ◽  
Low Temperatures ◽  
Structural Changes ◽  
Cellular Receptor ◽  
Structural Transitions ◽  
Wild Type ◽  
Antiviral Compound

ABSTRACT Drugs such as WIN51711 that inhibit picornavirus replication are thought to block poliovirus infectivity by binding to the capsid and preventing structural transitions required for uncoating. We examined the activity of WIN51711 at temperatures where capsid flexibility is thought to be decreased. Below 37°C, WIN51711 inhibits the binding of wild-type poliovirus to cells but does not affect the binding of a poliovirus mutant which is believed to undergo structural transitions more readily. These results suggest that the poliovirus capsid must undergo structural changes to bind to its cellular receptor.

scholarly journals The Structure of Ferroselite, FeSe2, at Pressures up to 46 GPa and Temperatures down to 50 K: A Single-Crystal Micro-Diffraction Analysis

Crystals ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 289 ◽  
Author(s):  
Barbara Lavina ◽  
Robert Downs ◽  
Stanislav Sinogeikin
Keyword(s):  
Single Crystal ◽  
Low Temperatures ◽  
Diamond Anvil Cell ◽  
Structural Changes ◽  
High Pressures ◽  
Structural Instability ◽  
Crystal Structure Analysis ◽  
Ambient Conditions ◽  
Diamond Anvil

We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe2, was studied under high pressures up to 46 GPa and low temperatures, down to 50 K using single-crystal microdiffraction techniques. High pressures and low temperatures were generated using a diamond anvil cell and a cryostat respectively. We found no evidences of structural instability in the explored P-T space. The deformation of the orthorhombic lattice is slightly anisotropic. As expected, the compressibility of the Se-Se dumbbell, the longer bond in the structure, is larger than that of the Fe-Se bonds. There are two octahedral Fe-Se bonds, the short bond, with multiplicity two, is slightly more compressible than the long bond, with multiplicity four; as a consequence the octahedral tetragonal compression slightly increases under pressure. We also achieved a robust structural analysis of ferroselite at low temperature in the diamond anvil cell. Structural changes upon temperature decrease are small but qualitatively similar to those produced by pressure.

Anomalies in the temperature dependence of the yield stress of metals at low temperatures

1983 ◽  
Vol 61 (11) ◽  
pp. 1528-1530 ◽  
Author(s):  
S. M. Raza
Keyword(s):  
Low Temperature ◽  
Temperature Dependence ◽  
Yield Stress ◽  
Low Temperatures ◽  
Structural Changes ◽  
Zero Point ◽  
Quantum Effects ◽  
Enhancement Effect ◽  
Polycrystalline Nickel ◽  
Creep Equation

Yield stress "anomalies" have been studied in polycrystalline nickel at low temperatures. Both quantum effects and structural changes below 0.1–0.2 of the Debye temperature contribute to low-temperature anomalies in the temperature dependence of the yield stress. The anomalies appear to be basically a consequence of the effect of zero-point vibrations on the rates of transition in the localized process of activation. An attempt is made to explain the anomalies by introducing a "strain-enhancement" effect, i.e., f(T), semiempirically in the logrithmic creep equation [Formula: see text] where Teff = T0 + AT2 (T0 and A are constants), which allows for quantum effects below a certain temperature.

scholarly journals An In-Silico Comparative Study of Lipases from the Antarctic Psychrophilic Ciliate Euplotes focardii and the Mesophilic Congeneric Species Euplotes crassus: Insight into Molecular Cold-Adaptation

Marine Drugs ◽  
2021 ◽  
Vol 19 (2) ◽  
pp. 67
Author(s):  
Guang Yang ◽  
Matteo Mozzicafreddo ◽  
Patrizia Ballarini ◽  
Sandra Pucciarelli ◽  
Cristina Miceli
Keyword(s):  
Amino Acid ◽  
Low Temperatures ◽  
In Silico ◽  
Cold Adaptation ◽  
Structural Changes ◽  
Hydrolytic Enzymes ◽  
Industrial Applications ◽  
Euplotes Crassus ◽  
Ciliate Species ◽  
The Antarctic

Cold-adapted enzymes produced by psychrophilic organisms have elevated catalytic activities at low temperatures compared to their mesophilic counterparts. This is largely due to amino acids changes in the protein sequence that often confer increased molecular flexibility in the cold. Comparison of structural changes between psychrophilic and mesophilic enzymes often reveal molecular cold adaptation. In the present study, we performed an in-silico comparative analysis of 104 hydrolytic enzymes belonging to the family of lipases from two evolutionary close marine ciliate species: The Antarctic psychrophilic Euplotes focardii and the mesophilic Euplotes crassus. By applying bioinformatics approaches, we compared amino acid composition and predicted secondary and tertiary structures of these lipases to extract relevant information relative to cold adaptation. Our results not only confirm the importance of several previous recognized amino acid substitutions for cold adaptation, as the preference for small amino acid, but also identify some new factors correlated with the secondary structure possibly responsible for enhanced enzyme activity at low temperatures. This study emphasizes the subtle sequence and structural modifications that may help to transform mesophilic into psychrophilic enzymes for industrial applications by protein engineering.

scholarly journals Dynamics of Freezing and Warming of Soft Tissues with Short-Term Eff ect on Skin with Cryoapplicator

2020 ◽  
Vol 30 (4) ◽  
pp. 359-368
Author(s):  
Gennady Kovalov ◽  
◽  
Eduard Gordiyenko ◽  
Yulia Fomenko ◽  
Galyna Shustakova ◽  
...  
Keyword(s):  
Temperature Field ◽  
Thermal Imaging ◽  
Low Temperatures ◽  
Structural Changes ◽  
Soft Tissues ◽  
Short Term ◽  
Zone Diameter ◽  
Intraoperative Control ◽  
Stable Stage ◽  
Morbid Growth

The paper presents the analysis of possibilities and limitations of using the thermal imaging to monitor the dynamics of temperature field caused by a short-term cryoablation of skin. It is shown that the method allows to remote and intraoperative control the dynamics of the freezing zone diameter as well as to estimate the current diameter of primary cryonecrosis zone. The diameter of primary cryonecrosis zone for this type of tissues reaches 13 mm, which makes it possible to destroy small morbid growth by low temperatures even with a short-term (30 s) croexposure. The using of this method to monitor the process of natural warming has shown the presence of long quasi-stable stage in dynamics of the freezing zone diameter with a slight change in the temperature field. This fact is likely due to structural changes in frozen tissues.

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