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.

Dielectric Loss in Li- and Na-Swept α-Quartz and the Effect of Irradiation

1983 ◽  
Vol 24 ◽  
Author(s):  
J. Toulouse ◽  
A.S. Nowick
Keyword(s):  
Dielectric Loss ◽  
Low Temperature ◽  
Low Temperatures ◽  
Quantum Effects ◽  
Frequency Stability ◽  
Distorted Tetrahedron ◽  
High Quality ◽  
Quartz Crystals ◽  
Alkali Ions ◽  
Synthetic Crystals

ABSTRACTAlkali ions, which compensate for substitional Al3+, play an important role in the frequency stability of α-quartz crystals. In this work, low temperature dielectricloss measurements (between 2.9 and 300 K) are carried out on crystals that have been “swept” so as to introduce either Li+ or Na+. High quality synthetic crystals as well as natural crystals are employed. The well known loss peaks due to Al-Na pairs are further explored and similar peaks due to Al-Li are sought after but not found. It is concluded that the Al-Li pair is oriented along the C2 -axis of the A104 distorted tetrahedron. After irradiation, large peaks are observed at very low temperatures both in Li+- and Na+-containing crystals. These peaks, which are distorted below ∼6 K due to the onset of quantum effects, may originate in alkali centers produced when alkali ions are liberated by the irradiation.

scholarly journals Low-temperature rheology of calcite

2019 ◽  
Vol 221 (1) ◽  
pp. 129-141 ◽  
Author(s):  
Michael K Sly ◽  
Arashdeep S Thind ◽  
Rohan Mishra ◽  
Katharine M Flores ◽  
Philip Skemer
Keyword(s):  
Low Temperature ◽  
Yield Stress ◽  
Low Temperatures ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Polycrystalline Sample ◽  
Small Scale ◽  
Indentation Hardness ◽  
Micropillar Compression ◽  
Flow Laws

SUMMARY Low-temperature plastic rheology of calcite plays a significant role in the dynamics of Earth's crust. However, it is technically challenging to study plastic rheology at low temperatures because of the high confining pressures required to inhibit fracturing. Micromechanical tests, such as nanoindentation and micropillar compression, can provide insight into plastic rheology under these conditions because, due to the small scale, plastic deformation can be achieved at low temperatures without the need for secondary confinement. In this study, nanoindentation and micropillar compression experiments were performed on oriented grains within a polycrystalline sample of Carrara marble at temperatures ranging from 23 to 175 °C, using a nanoindenter. Indentation hardness is acquired directly from nanoindentation experiments. These data are then used to calculate yield stress as a function of temperature using numerical approaches that model the stress state under the indenter. Indentation data are complemented by uniaxial micropillar compression experiments. Cylindrical micropillars ∼1 and ∼3 μm in diameter were fabricated using a focused ion beam-based micromachining technique. Yield stress in micropillar experiments is determined directly from the applied load and micropillar dimensions. Mechanical data are fit to constitutive flow laws for low-temperature plasticity and compared to extrapolations of similar flow laws from high-temperature experiments. This study also considered the effects of crystallographic orientation on yield stress in calcite. Although there is a clear orientation dependence to plastic yielding, this effect is relatively small in comparison to the influence of temperature.

Peotoemission Study of Si (001) Surfaces Exposed to as Flux

1989 ◽  
Vol 148 ◽  
Author(s):  
H. Okumura ◽  
K. Miki ◽  
K. Sakamoto ◽  
T. Sakamoto ◽  
S. Misawa ◽  
...  
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Electronic Structures ◽  
Low Temperatures ◽  
Dimer Model ◽  
Surface And Interface ◽  
High And Low Temperatures ◽  
Interface Structures ◽  
Temperature Sample

ABSTRACTPhotoemission spectra (XPS and UPS) of As-covered Si (001) surfaces prepared at high (>600ºC) and low (<450ºC) temperatures and GaAs epilayers subsequently grown on them were measured without exposing to air. It was found that the surface electronic structures of As/Si prepared at the low temperature are different from those of the high temperature sample, the spectra of which can be interpreted as a symmetric dimer model. Differences were also observed between the GaAs epilayers on the As—covered Si surfaces prepared at the high and low temperatures. The temperature dependence of the surface and interface structures are discussed.

scholarly journals Low-temperature behaviour of the engine oil

2013 ◽  
Vol 61 (6) ◽  
pp. 1763-1767 ◽  
Author(s):  
Vojtěch Kumbár ◽  
Artüras Sabaliauskas
Keyword(s):  
Low Temperature ◽  
Temperature Dependence ◽  
Low Temperatures ◽  
Kinematic Viscosity ◽  
Engine Oil ◽  
Economic Losses ◽  
Temperature Behaviour ◽  
Engine Oils ◽  
Theoretical Assumptions ◽  
Automobile Engines

The behaviour of engine oil is very important. In this paper has been evaluated temperature dependence kinematic viscosity of engine oils in the low temperatures. Five different commercially distributed engine oils (primarily intended for automobile engines) with viscosity class 0W–40, 5W–40, 10W–40, 15W–40, and 20W–40 have been evaluated. The temperature dependence kinematic viscosity has been observed in the range of temperature from −15 °C to 15 °C (for all oils). Considerable temperature dependence kinematic viscosity was found and demonstrated in case of all samples, which is in accordance with theoretical assumptions and literature data. Mathematical models have been developed and tested. Temperature dependence dynamic viscosity has been modeled using a polynomials 3rd and 4th degree. The proposed models can be used for prediction of flow behaviour of oils. With monitoring and evaluating we can prevent technical and economic losses.

scholarly journals Modification of placenta blood serum proteins under low temperature effect

2013 ◽  
Vol 59 (2) ◽  
pp. 219-234
Author(s):  
O.V. Falko ◽  
N.G. Zemlianskykh ◽  
O.V. Lipina ◽  
O.S. Procopyuk
Keyword(s):  
Low Temperature ◽  
Blood Serum ◽  
Low Temperatures ◽  
Structural Changes ◽  
Serum Proteins ◽  
Protein Structures ◽  
Aggregate Formation ◽  
Low Temperature Storage ◽  
Blood Serum Proteins ◽  
Temperature Storage

Changes in environmental physical and chemical factors upon freeze-thawing and low temperature storage of biological samples can result in impairments of protein structures. This work specifies spontaneous and diamide-induced protein aggregations of placenta blood serum stored at -20° and -196°C during 2 years with SDS-PAGE. It was shown that storage of placenta blood serum at low temperatures did not cause any quantitative and qualitative changes in fraction distribution of proteins denatured with SDS in comparison to the native samples which were not frozen. Application of b-mercaptoethanol revealed that placenta blood serum proteins upon freeze-thawing did not form spontaneous aggregates linked by disulphide bridges. Oxidation of amino acid sulfhydryl groups induced by diamide and accompanied by high molecular aggregate formation proved to be a quite effective way for indirect estimation of structural changes in protein upon low temperature effects. In samples thawed after low temperature storage the protein aggregation with 4 mM diamide was significantly higher than in native serum. These discrepancies between native and frozen-thawed samples are stipulated by impairments of protein structure under low temperature and increased in accessibility of reactive SH-groups of proteins for oxidation with diamide. Structural changes in placenta blood serum proteins, which caused by low temperatures and revealed by elevated sensibility to diamide-induced aggregate formation, did not depend on temperature (-20° и -196°C) and storage terms (2 years and 3 weeks). They reflect protein reaction to freeze-thawing processes and could be sequence of ice crystal formation which takes place in unprotected media.

SPIN FLUCTUATIONS IN TCo2 STUDIED BY RESISTIVITY AND THERMOPOWER EXPERIMENTS (T = Y, Lu, Sc, Hf, Zr, Ce)

1993 ◽  
Vol 07 (01n03) ◽  
pp. 370-373 ◽  
Author(s):  
N. BARANOV ◽  
E. BAUER ◽  
E. GRATZ ◽  
R. HAUSER ◽  
A. MARKOSYAN ◽  
...  
Keyword(s):  
Low Temperature ◽  
Specific Heat ◽  
Temperature Dependence ◽  
Temperature Region ◽  
Low Temperatures ◽  
Spin Fluctuations ◽  
General Tendency ◽  
Electronic Specific Heat ◽  
Temperature Dependent

The temperature dependence of the resistivity and the thermopower in the region from 4.2K up to 1000K for the six isostructural paramagnetic compounds TCo 2 (T=Y, Lu, Sc, Hf, Zr, Ce) is studied. The resistivity ρ (T) follows a T 2 dependence at low temperatures in all these compounds. Plotting the A values into an A vs. γ2 diagram shows that YCo 2, LuCo 2, and ScCo 2 are spinfluctuation systems (A and γ denote the coefficients in ρ (T) = ρ0 + AT 2 and that of the electronic specific heat, respectively) HfCo 2 and ZrCo 2 do not fit into this general tendency in the ( A , γ2)-diagram. The temperature dependent thermopower S(T) in YCo 2, LuCo 2 and ScCo 2 exhibits a pronounced minimum in the low temperature region. These minima are obviously connected with the existence of spin fluctuations (paramagnon-drag). Spin fluctuations in HfCo 2 and ZrCo 2 are less important. This we conclude also from the ten times smaller A-values and the missing minimum in the thermopower at low temperatures.

scholarly journals Collective proton transfer in ordinary ice: local environments, temperature dependence and deuteration effects

2017 ◽  
Vol 19 (4) ◽  
pp. 2623-2635 ◽  
Author(s):  
Christof Drechsel-Grau ◽  
Dominik Marx
Keyword(s):  
Low Temperature ◽  
Proton Transfer ◽  
Temperature Dependence ◽  
Quantum Effects ◽  
Local Environments ◽  
Nuclear Quantum Effects

Ordinary ice at low temperature: what about collective nuclear quantum effects in its chiral six rings?

scholarly journals Temperature-dependence of open-complex formation at two Escherichia coli promoters with extended −10 sequences

1996 ◽  
Vol 317 (1) ◽  
pp. 305-311 ◽  
Author(s):  
Helen D. BURNS ◽  
Tamara A. BELYAEVA ◽  
Stephen J. W. BUSBY ◽  
Stephen D. MINCHIN
Keyword(s):  
Escherichia Coli ◽  
Low Temperature ◽  
Complex Formation ◽  
Temperature Dependence ◽  
Low Temperatures ◽  
Dna Fragments ◽  
Promoter Sequences ◽  
E Coli ◽  
Base Sequences ◽  
Open Complex Formation

We have studied the formation of open complexes between purified RNA polymerase from Escherichia coli and DNA fragments carrying the galP1 promoter, a promoter with an extended -10 region. Unusually, these complexes are formed readily at low temperatures. This low-temperature opening is unaffected by deletions of either upstream or downstream promoter sequences. We conclude that low-temperature open-complex formation is due to specific base sequences in and just upstream of the extended -10 region. In contrast, open complexes are not formed at low temperatures with DNA fragments carrying the E. coli cysG promoter, which also has an extended -10 region. This demonstrates that an extended -10 sequence alone is not sufficient for low-temperature opening. Additionally, we report the temperature dependence of a hybrid galP1–cysG promoter, the related galP2 and galP3 promoters and a derivative of galP1 with an improved -10 hexamer sequence.

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