Results 301 to 310 of about 292,669 (354)
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Solid State Phenomena, 2006
Gas quenching in vacuum furnaces is an increasingly attractive option because it has a low environmental impact and the least distortion of parts being treated. Whilst nitrogen is by far the most common quenching gas, helium is a viable option where higher cooling rates are required, particularly for carburised components.
Paul Stratton +2 more
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Gas quenching in vacuum furnaces is an increasingly attractive option because it has a low environmental impact and the least distortion of parts being treated. Whilst nitrogen is by far the most common quenching gas, helium is a viable option where higher cooling rates are required, particularly for carburised components.
Paul Stratton +2 more
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Polarizability of Helium and Gas Metrology
Physical Review Letters, 2007Using a quasispherical, microwave cavity resonator, we measured the refractive index of helium to deduce its molar polarizability A(epsilon) in the limit of zero density. We obtained (A(epsilon,meas) - A(epsilon,theory))/A(epsilon) = (-1.8 +/- 9.1) x 10(-6), where the standard uncertainty (9.1 ppm) is a factor of 3.3 smaller than that of the best ...
J. W. SCHMIDT +3 more
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Transitions to turbulence in helium gas
Physical Review A, 1987Experimental study in gaseous helium at low temperature (4 K) of thermal convection up to a Rayleigh number $R={10}^{11}$. Three regimes are observed, a chaotic state up to $R=2.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$, a soft-turbulence state up to $R=4\ifmmode\times\else\texttimes\fi{}{10}^{7}$, and then a hard-turbulence state.
B. Castaing, Albert Libchaber, F. Heslot
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Diffusion of hydrogen atoms in helium gas and helium atoms in hydrogen gas
Physical Review A, 2002The potential of Meyer and Frommhold describing the interaction between hydrogen and helium atoms is used to calculate the diffusion coefficients of hydrogen atoms in helium gas and helium atoms in hydrogen gas as functions of temperature, taking into account higher-order corrections of transport theory.
Alexander Dalgarno, H. K. Chung
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Turbulent convection in helium gas
Physica D: Nonlinear Phenomena, 1992Abstract Various changes in measured signals were observed in thermal convective experiments of low-temperature helium gas, indicating that there are more than one turbulent states in the system. The more recently observed transition occurs at a Rayleigh number of about 1011, within the hard turbulence regime.
Albert Libchaber +3 more
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Diffusion of positrons in helium gas
Journal of Physics B: Atomic and Molecular Physics, 1977The caution describing diffusion of positrons in helium gas is solved with the scattering and annihilation data previously obtained by Humberston (1973), and Campeanu and Humberston (1975) to obtain the positron annihilation rate under various conditions of temperature and electric field strength and for various initial velocity distributions.
Radu I. Campeanu, J W Humberston
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Helium in Natural Gas in the Witwatersrand [PDF]
Nature, 1958 DURING a visit to the Union of South Africa in the spring of 1957 I observed escapes of natural gas associated with faults and fissures in the underground workings of some of the gold–uranium mines of the Witwatersrand.
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Oxygen and helium gas mixtures for dyspnoea
Current Opinion in Supportive & Palliative Care, 2007Recent reports of the benefits of helium/oxygen gas mixtures (heliox) use for the relief of dyspnoea and exercise limitation have stimulated interest in the use of heliox in the palliation of dyspnoea especially in chronic obstructive pulmonary disease patients.
Sam H Ahmedzai, Elizabeth A. Laude
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Turbulence in helium-gas free convection
Physical Review A, 1989Results on a Rayleigh-B\'enard experiment in helium gas at 5 K in a cylindrical cell of aspect ratio 1 are presented. The Rayleigh number spans a range from ${10}^{5}$ to ${10}^{12}$. A large-scale coherent flow is observed via the correlation of two adjacent temperature probes.
Albert Libchaber +2 more
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Helium, Cryogenics and Natural Gas
Financial Analysts Journal, 1964(1964). Helium, Cryogenics and Natural Gas. Financial Analysts Journal: Vol. 20, No. 2, pp. 109-114.
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