The measurements of temperature dependence of thermal conductivity of silver for different fixed values of heat flux density (liquid helium temperature range)

1971 ◽  
Vol 4 (3) ◽  
pp. 779-785 ◽  
Author(s):  
J. Rafalowicz ◽  
K. Balcerek ◽  
B. Sujak ◽  
E. Pega
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Dependence ◽  
Liquid Helium ◽  
Flux Density ◽  
Heat Flux Density ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Temperature Range

Ortho and Paratritium

1963 ◽  
Vol 18 (2) ◽  
pp. 197-202 ◽  
Author(s):  
Edwin W. Albers ◽  
Paul Harteck ◽  
Robert R. Reeves
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Half Life ◽  
Solid Phase ◽  
Life Time ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Small Glass ◽  
Adsorbed Phase ◽  
Normal Hydrogen

KLAUS CLUSIUS zum 60. Geburtstag gewidmetNormal tritium was partially and totally converted to paratritium by adsorption on charcoal at liquid neon and liquid helium temperature. The experimentation was performed with 300 millicuries of tritium sealed in a small glass apparatus where the transformation could be performed and the paratritium concentration measured by thermal conductivity. In the adsorbed phase the conversion half-life time was one minute, about 24 times faster than normal hydrogen. In the solid phase the conversion half-life was in the order of 15 minutes. Both processes were much faster than expected.

Experimental Investigation of Radiative Transfer Between Metallic Surfaces at Cryogenic Temperatures

1970 ◽  
Vol 92 (3) ◽  
pp. 412-416 ◽  
Author(s):  
G. A. Domoto ◽  
R. F. Boehm ◽  
C. L. Tien
Keyword(s):  
Radiative Transfer ◽  
Liquid Helium ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Metallic Surfaces ◽  
Emitter Temperature ◽  
Temperature Range ◽  
Order Of Magnitude ◽  
Temperature Levels ◽  
Lower Temperature

Experimental measurements of the radiative heat flux between two parallel copper disks in the liquid-helium temperature range are presented. The temperature levels investigated were primarily for the higher temperature disk (emitter) at 10.0 deg K and 15.1 deg K and the lower temperature disk (receiver) at approximately 4.5 deg K. For the 15.1 deg K emitter temperature, the spacing was varied from 0.201 cm to 0.001 cm. For the 10 deg K emitter case, the spacing was varied from 0.044 cm to 0.005 cm. Experimental data at small spacings show a definite spacing dependence of radiative transfer which agree qualitatively with the predicted result. Based on the measurements at large spacings, an estimate of the total hemispherical emissivity for the copper surfaces in the liquid-helium temperature range indicates a value of 0.015, which is approximately one order of magnitude higher than predicted. The possible causes for the discrepancies are discussed.

Temperature-dependent phosphorescence spectra of Pd- and Pt-porphins and their applications

2008 ◽  
Vol 12 (11) ◽  
pp. 1201-1210 ◽  
Author(s):  
Mikalai M. Kruk ◽  
Aleksander S. Starukhin ◽  
Rafal Czerwieniec
Keyword(s):  
Liquid Helium ◽  
Metal Ion ◽  
Phosphorescence Spectrum ◽  
Liquid Helium Temperature ◽  
Triplet States ◽  
Helium Temperature ◽  
Temperature Range ◽  
The Matrix ◽  
The Given ◽  
Phosphorescence Spectra

In this paper the temperature dependence of radiative deactivation of Pd - and Pt -porphin triplet states in Shpol'skii matrices has been studied in the temperature range of 4.2-210 K. Dramatic changes in the phosphorescence spectra, with increasing temperature, were observed. It has been proposed that this is due to the inclusion of thermally activated states of the studied molecules in the processes of radiative deactivation of triplet states. For Pd -porphin the T 1 → S 0 emission is merely observed at liquid helium temperature. An increase in temperature leads to the activation of several radiative T i → S 0 transitions, so additional bands appear in the phosphorescence spectrum. In the case of Pt -porphin, temperature activation takes place as early as at liquid helium temperature. The degeneracy lifting of lowest T 1,2 states due to crystal field splitting was observed for both Pd - and Pt -porphins. The splitting value δ = ΔE( T 2 − T 1) has been measured in different matrices and the dependencies on both the metal ion in the given matrix and the matrix type for the given metal ion, have been revealed. The possibility of designing the luminescent molecular thermometers for cryogenic temperatures based on the high temperature sensitivity of the Pd - and Pt -porphin phosphorescence in n-alkane matrices, has been discussed. The workability of the dependence of Pd - and Pt -porphin phosphorescent properties on temperature in the design of the molecular thermometer family for the temperature range from a few K up to temperatures close to the melting point of n-alkane matrix (150-200 K) is demonstrated.

scholarly journals Determining Near-Surface Soil Heat Flux Density Using the Gradient Method: A Thermal Conductivity Model–Based Approach

2017 ◽  
Vol 18 (8) ◽  
pp. 2285-2295 ◽  
Author(s):  
Xiaoyang Peng ◽  
Joshua Heitman ◽  
Robert Horton ◽  
Tusheng Ren
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Flux Density ◽  
Gradient Method ◽  
Heat Flux Density ◽  
Soil Depth ◽  
Soil Heat Flux ◽  
Time Domain Reflectometry ◽  
Near Surface ◽  
Model Based

Abstract In the gradient method, soil heat flux density at a known depth G is determined as the product of soil thermal conductivity λ and temperature T gradient. While measuring λ in situ is difficult, many field studies readily support continuous, long-term monitoring of soil T and water content θ in the vadose zone. In this study, the performance of the gradient method is evaluated for estimating near-surface G using modeled λ and measured T. Hourly λ was estimated using a model that related λ to θ, soil bulk density ρb, and texture at 2-, 6-, and 10-cm depths. Soil heat flux Gm was estimated from modeled λ and measured T gradient (from thermocouples). The Gm results were evaluated with heat flux data GHP determined using independent measured λ and T gradient from heat-pulse probes. The λ model performed well at the three depths with 3.3%–7.4% errors. The Gm estimates were similar to GHP (agreed to within 15.1%), with the poorest agreement at the 2-cm soil depth, which was caused mainly by the relatively greater variability in ρb. Accounting for temporal variations in ρb (with core method) improved the accuracies of λ and Gm at the 2-cm depth. Automated θ monitoring approaches (e.g., time domain reflectometry), rather than gravimetric sampling, captured the temporal dynamics of near-surface λ and G well. It is concluded that with continuous θ and T measurements, the λ model–based gradient method can provide reliable near-surface G. Under conditions of soil disturbance or deformation, including temporally variable ρb, data improves the accuracy of G data.

scholarly journals Anomalous a.c. resistivity effect in Nb and Sn at high static fields in the liquid helium temperature range

1971 ◽  
Vol 34 (6) ◽  
pp. 321-323 ◽  
Author(s):  
L.J.M. van de Klundert ◽  
A. van Ardenne ◽  
L.C. van der Marel
Keyword(s):  
Liquid Helium ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Temperature Range

Resistivity of plutonium, neptunium and uranium due to the accumulation of radioactive self damage

1965 ◽  
Vol 284 (1398) ◽  
pp. 325-343 ◽  
Keyword(s):  
Crystal Structure ◽  
Temperature Dependence ◽  
Liquid Helium ◽  
Low Temperatures ◽  
Liquid Helium Temperature ◽  
Helium Temperature ◽  
Additive Resistance

An increase with time in resistivity occurs in plutonium at low temperatures as a result of radioactive self damage. The effect has been studied in experiments at liquid helium temperature lasting over 8000h and has been found to exist in the α , β and δ phases of the metal. In all cases the resistivity approaches saturation, the rates of increase depending on the crystal structure and isotropic content of the sample. In spite of wide differences in these rates the functional increase is roughly the same. The temperature dependence of the accumulated resistivities in all three modifications deviates very strongly from a simple additive resistance obeying Matthiesen’s rule. The resistivity of fully damaged α plutonium is almost temperature independent, becoming smaller than that of the undamaged specimen above about 50 °K. Measurements on neptunium and uranium 233 have also shown resistivity increases with time at helium temperatures, but the effect is too small to decide whether Matthiesen’s rule is obeyed in these metals. The observed effects have been discussed under the assumption that in plutonium scattering of electrons at low temperatures is mainly due to a co-operative phenomenon.

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