scholarly journals The molecular scattering of light in vapours and in liquids and its relation to the opalescence observed in the critical state

1922 ◽  
Vol 102 (715) ◽  
pp. 151-161 ◽  
Keyword(s):  
Critical Point ◽  
Critical State ◽  
Incident Light ◽  
Wave Length ◽  
Molecular Scattering ◽  
Avogadro’S Number ◽  
Quantitative Manner ◽  
The Mean ◽  
Good Agreement ◽  
Molecular Scattering Of Light

It has long been known that in the immediate vicinity of the critical state, many substances exhibit a strong and characteristic opalescence. In recent years, the phenomenon has been studied by Travers and Usher in the case of carefully purified CS 2 , SO 2 , and ether, by S. Young, by F. B. Young in the case of ether, and in a quantitative manner by Kammerlingh Onnes and Keesom in the case of ethylene. An explanation of the phenomenon on thermodynamic principles as due to the accidental deviations of density arising in the substance was put forward by Smoluchowski. He obtained an expression for the mean fluctuation of density in terms of the compressibility of the substance, and later, Einstein applied Maxwell’s equations of the electromagnetic field to obtain an expression for the intensity of the light scattered in consequence of such deviations of density. He showed that the fraction α of the incident energy scattered in the substance per unit volume is 8 π 3 /27 RT β ( μ 2 – 1) 2 ( μ 2 + 2) 2 /N λ 4 (1) In this, R and N are the gas constant and Avogadro’s number per grammolecule, β is the isothermal compressibility of the substance, μ is the refractive index and λ is the wave-length of the incident light. Keesom tested this formula over a range of 2·35° above the critical point of ethylene and found good agreement except very close to the critical point.

scholarly journals Interferometric measurements in the spectrum of the iron arc in air in the region λ 3100 — λ 3500

1931 ◽  
Vol 133 (822) ◽  
pp. 553-564 ◽  
Keyword(s):  
Wave Length ◽  
Systematic Difference ◽  
Vacuum Arc ◽  
International Astronomical Union ◽  
International Astronomical ◽  
Visible Part ◽  
Length Measurements ◽  
The Mean ◽  
Good Agreement ◽  
Made In

In a previous paper I gave the results of a set of wave-length measurements in the spectrum of the iron arc in the region λ 2300 to λ 3100. These measurements were carried out because it was found that previous measurements in this region were all rather unsatisfactory and gave results considerably higher than those calculated from levels determined from the wave-lengths recommended by the International Astronomical Union in 1928. My results confirm the values calculated from the I. A. U. Standards very satisfactorily, and also agree very well with the recent measurements of the vacuum arc by Burns and Walters. The apparatus was also used to measure a few lines in the visible part of the iron spectrum, and was shown to give results in excellent agreement with the values adopted by the I. A. U. in 1928. It was recommended by the I. A. U. that observations should be made in the region below λ 3400 for which there were no good modem measurements available. Accordingly the present work was undertaken to fill up the gap remaining and a set of 46 lines has been measured in the region λ 3100-λ 3500. The results are in very good agreement both with the I. A. U. calculated values and with the observed standards adopted by the I. A. U. in 1928, the mean systematic difference (J — I. A.) being only —0·0001 A. for 8 lines, while the mean accidental difference is ±0·0006 A. The agreement with the measurements of Babcock in the region λ 3370-λ 3500 is equally good, the mean systematic difference (J — B) being +0·0001 A. for eight lines, while the mean accidental difference is +0·0006 A.

scholarly journals The high-frequency resistance of superconducting tin

1940 ◽  
Vol 176 (967) ◽  
pp. 522-533 ◽  
Keyword(s):  
High Frequency ◽  
Skin Effect ◽  
Wave Length ◽  
Low Frequency ◽  
Mean Free Path ◽  
Low Frequencies ◽  
The Mean ◽  
Absolute Measurements ◽  
Eddy Current Heating ◽  
Good Agreement

The high-frequency resistance of tin in the superconducting state was measured at a wave-length of 20.5 cm. by a calorimetric method based on the principle of eddy-current heating. It was found that the resistance decreases gradually when the temperature falls below the transition point in contrast to the sudden drop in resistance peculiar to direct currents. An explanation of such a behaviour is given based on the assumption of the simultaneous presence of normal and superconducting electrons. Good agreement between theory and experiment was found. Absolute measurements of the conductivity in the normal state at low temperatures with both high and low frequencies were carried out, and it was found that at the temperature of liquid helium the conductivity for high frequency is considerably lower than for low frequency. This behaviour is possibly due to the fact that the mean free path of the electrons becomes larger than the penetration depth due to skin effect under the conditions of high conductivity and high frequency.

On overpotential and the photovoltaic process at polarized electrodes

1949 ◽  
Vol 199 (1058) ◽  
pp. 295-310 ◽  
Keyword(s):  
Incident Light ◽  
Wave Length ◽  
Electrode Reaction ◽  
Water Molecules ◽  
Adsorbed Hydrogen ◽  
Stationary Concentration ◽  
Rate Determining Step ◽  
Adsorbed Atoms ◽  
Complete Layer ◽  
Good Agreement

The acceleration of the electrodeposition of hydrogen and oxygen by light of wave-length from 4000 to 2000 A has been studied on different electrodes. The quantum efficiency of the photoreaction was determined as a function of the wave-length of the incident light and of the steady polarizing current. From these experiments it was concluded that the rate-determining step at these electrodes occurred after the discharge of the ions and that the overpotential corresponded to a stationary concentration of adsorbed atoms or radicals. It was further concluded that an electrode at which hydrogen is being evolved at a sensible rate is covered with a nearly complete layer of adsorbed hydrogen. The potential at which such evolution occurs is determined primarily by the negative potential necessary to displace adsorbed oxygen atoms or water molecules by hydrogen. Calculations of this potential, in the few cases where the necessary heats of adsorption are available, gave values in agreement with those observed experimentally. It was concluded that the rate-determining step on most cathodes, except platinum, was the electrochemical combination of an adsorbed atom with an ion in the double layer, and relations were obtained for the dependence of the overpotential on the current density and electrokinetic potential, which are in fairly good agreement with experiment. A similar mechanism is tentatively suggested for the electrode reaction at an anode at which oxygen is being evolved.

Computational Investigation of Different Turbulent Models When Predicting Airflow in an Enclosure

2008 ◽  
Author(s):  
Xi Wang ◽  
Hassan Naji ◽  
Ahmed Mezrhab
Keyword(s):  
Numerical Investigation ◽  
Turbulence Models ◽  
Turbulent Stress ◽  
Computational Investigation ◽  
Isothermal Case ◽  
The Mean ◽  
Turbulent Models ◽  
Rsm Model ◽  
Cold Case ◽  
Good Agreement

In the present study, a numerical investigation is carried out for an isothermal case, a hot case and a cold case with FLUENT code. Three turbulence models are considered: the k-ε realisable model, the RNG k-ε model and the RSM linear model. The obtained results are compared to experiments and show generally a good agreement for the mean velocities and temperatures, but less satisfactory for the turbulent stress. The performance of the RSM model is remarkable. Even if none of the models is able to give the exact experimental pattern on the map of turbulence, the RSM model seems able to predict such configuration.

Respiratory Exchange and Body Size in the Aldabra Giant Tortoise

1971 ◽  
Vol 55 (3) ◽  
pp. 651-665 ◽  
Author(s):  
G. M. HUGHES ◽  
R. GAYMER ◽  
MARGARET MOORE ◽  
A. J. WOAKES
Keyword(s):  
Body Weight ◽  
Body Size ◽  
Metabolic Rate ◽  
Relative Proportion ◽  
The Body ◽  
O2 Consumption ◽  
Weight Range ◽  
Testudo Hermanni ◽  
The Mean ◽  
Good Agreement

1. The O2 consumption and CO2 release of nine giant tortoises Testudo gigantea (weight range 118 g-35·5 kg) were measured at a temperature of about 25·5°C. Four European tortoises Testudo hermanni (weight range 640 g-2·16 kg) were also used. The mean RQ values obtained were 1·01 for T. gigantea and 0·97 for T. hermanni. These values were not influenced by activity or size. 2. The data was analysed by plotting log/log regression lines relating body weight to O2 consumption. Both maximum and minimum metabolic rates recorded for each individual T. gigantea showed a negative correlation with body weight. For active rates the relation was O2 consumption = 140·8W0·97, whereas for inactive animals O2 consumption = 45·47W0·82. 3. The maximum rates were obtained from animals that were observed to be active in the respirometer and the minimum rates from animals that remained quiet throughout. The scope for activity increased with body size, being 82 ml/kg/h for animals of 100 g and 103 ml/kg/h for 100 kg animals. The corresponding ratio between maximum and minimum rates increases from about 2 to 6 for the same weight range. 4. Values for metabolic rate in T. hermanni seem to be rather lower than in T. gigantea. Analysis of the relative proportion of the shell and other organs indicates that the shell forms about 31% of the body weight in adult T. hermanni but only about 18% in T. gigantea of similar size. The shell is not appreciably heavier in adult T. gigantea (about 20%). 5. Data obtained for inactive animals is in good agreement with results of other workers using lizards and snakes. Previous evidence suggesting that chelonians show no reduction in metabolic rate with increasing size is not considered to conflict with data obtained in the present work.

Correlation between the sea level muon spectrum and the primary nucleon spectrum using the Cocconi–Koester–Perkins model

1979 ◽  
Vol 57 (7) ◽  
pp. 921-925 ◽  
Author(s):  
A. K. Chakrabarti ◽  
A. K. Das ◽  
A. K. De
Keyword(s):  
Sea Level ◽  
Pion Production ◽  
Spectral Shape ◽  
Muon Spectrum ◽  
Proton Proton ◽  
Absolute Value ◽  
Nucleon Spectrum ◽  
Scaling Models ◽  
The Mean ◽  
Good Agreement

Using the recent ISR data of proton–proton interactions on the inclusive production of pions and nucleons, realistic values of the mean pion inelasticity Kπ and the mean nucleon inelasticity KT have been estimated. These values have been used for the derivation of the sea level differential muon spectrum from the primary nucleon spectrum and vice versa using the CKP model as an extension of the work presented in an earlier article. It is found that none of the measured primary nucleon spectra of Ryan, Ormes, and Balasubrahmanyan and Grigorov, Rapoport, and Shestoperov fit any of the precisely measured muon spectra of Ayre, Baxendale, Hume, Nandi, Thompson, and Whalley and Allkofer, Carstensen, and Dau in spectral shape or the absolute value. On the other hand good agreement between the derived muon spectra and the spectra of Allkofer et al. and Ayre et al. is found if the primary nucleon spectra of the forms, N(Ep) = (1.38 ± 0.08)Ep−2.59 and N(Ep) = (1.00 ± 0.10)Ep−2.55, respectively, are assumed. The first form is comparable with that obtained by Brooke, Hayman, Kamiya, and Wolfendale following more approximate but similar procedure. It is also not unjustified when compared with the measured primary all nuclei spectrum of Grigorov et al. in the light of suggestions made by Ellsworth, Ito, Macfall, Siohan, Streitmatter, Tonwar, Vishwanath, Yodh, and Balasubrahmanyan. By comparing the pion production spectra derived from the same primary nucleon spectrum but using the CKP and the scaling models, it is concluded that the results are sensitive to the model assumed for the collisions.

The continuous absorption of light in alkali-metal vapours

1953 ◽  
Vol 219 (1136) ◽  
pp. 89-101 ◽  
Keyword(s):  
Cross Section ◽  
Alkali Metals ◽  
Theoretical Calculations ◽  
Wave Length ◽  
Energy Difference ◽  
Continuous Absorption ◽  
Absorption Of Light ◽  
Sodium Vapour ◽  
Good Agreement ◽  
Dipole Length

The first section of this paper is an account of some experiments on the absorption of light in sodium vapour from the series limit at 2412 Å to about 1600 Å (an energy difference of 2·6 eV). The absorption cross-section at the limit is 11·6 ± 1·2 x 10 -20 cm 2 . The cross-section decreases giving a minimum of 1·3 ± 0·6 x 10 -20 cm 2 at 1900 Å and then increases to 1600 Å. A theoretical calculation by Seaton based on the dipole-length formula gives good agreement with the experiments at the series limit and also correctly predicts the wave-length for the minimum, but it predicts a significantly lower absorption at the minimum. The experiments described in the first section of the paper conclude a series on the absorption of light in the alkali metals. The second section consists of a general discussion of the results of these experiments and of their relation to theoretical calculations. There is good agreement between theory and experiment except in regard to the magnitude of the absorption at the minimum.

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