scholarly journals Which physics determines the location of the mean molecular weight minimum in red giants?

2014 ◽  
Vol 443 (2) ◽  
pp. 977-984 ◽  
Author(s):  
Ross P. Church ◽  
John Lattanzio ◽  
George Angelou ◽  
Christopher A. Tout ◽  
Richard J. Stancliffe
Keyword(s):  
Molecular Weight ◽  
Red Giants ◽  
The Mean ◽  
Mean Molecular Weight

scholarly journals Why Do Low-Mass Stars Become Red Giants?

2009 ◽  
Vol 26 (3) ◽  
pp. 203-208 ◽  
Author(s):  
Richard J. Stancliffe ◽  
Alessandro Chieffi ◽  
John C. Lattanzio ◽  
Ross P. Church
Keyword(s):  
Molecular Weight ◽  
Stellar Evolution ◽  
Energy Generation ◽  
Red Giants ◽  
Low Mass Stars ◽  
Change In The Mean ◽  
Low Mass ◽  
The Mean ◽  
Red Giant ◽  
Mean Molecular Weight

AbstractWe revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are discussed. We find that while a change in the mean molecular weight is necessary (but not sufficient) for a 1-M⊙ star to become a red giant, this is not the case in a star of 5 M⊙. It therefore seems that there may be more than one way to make a giant.

Study of the Preparation and Degradable Characteristics of CaCO3-PE Film

2012 ◽  
Vol 499 ◽  
pp. 85-89
Author(s):  
Xue Yong Zhou ◽  
Xiang Yun Liu ◽  
Lei Lu ◽  
Lei Gu ◽  
Jing Jing Liu
Keyword(s):  
Molecular Weight ◽  
Tensile Strength ◽  
Ultraviolet Light ◽  
Light Irradiation ◽  
Breaking Elongation ◽  
Average Tensile Strength ◽  
Ultraviolet Light Irradiation ◽  
Filling Method ◽  
The Mean ◽  
Mean Molecular Weight

The CaCO3-polyethylene (PE) film was prepared by filling method, and the filling amount of calcium carbonate in film was 20%(w/w). The effects of natural weathering, ultraviolet light irradiation on the tensile strength, breaking elongation and molecular weight of the CaCO3-PE film was investigated comparing with the photosensitizer-PE film. After being located in the open air for 30 d, the average tensile strength, average breaking elongation and the mean molecular weight of CaCO3-PE film decreased 80.6%, 99.3% and 25.3%, respectively, as for the photosensitizer-PE film, the corresponding items decreased 18.8%, 45.0% and 11.7%, respectively. After ultraviolet light irradiation for 120 h, the average tensile strength of CaCO3-PE film decreased 29.9%, the average tensile strength of the photosensitizer-PE film, however, increased 20.5%. The average breaking elongation of CaCO3-PE film and photosensitizer-PE film decreased 97.3% and 84.1% respectively, the mean molecular weight of both films decreased 66.7% and 26.6% respectively. After covered by soil for 200 d, the weight loss of the CaCO3-PE film and photosensitizer-PE was 2.15% and 0.22%, respectively. The results showed that the degradability of CaCO3-PE film is superior to the photosensitizer-PE film.

Chlorinated Rubber and Nitrogenous Plasticizers. I. Viscosity of Mixtures of Chlorinated Rubber and Anhydroformaldehyde Urethan

1957 ◽  
Vol 30 (1) ◽  
pp. 274-282
Author(s):  
Michele Giua ◽  
Corrado Mancini
Keyword(s):  
Molecular Weight ◽  
Molecular Weights ◽  
Mixed Solutions ◽  
Quantitative Basis ◽  
The Mean ◽  
Mean Molecular Weight

Abstract The viscosities of solutions of chlorinated rubber in chloroform and in toluene and of mixed solutions of chlorinated rubber and anhydroformaldehyde urethan in toluene were measured. From the data it was possible to determine in an approximate way the mean molecular weight of chlorinated rubber and the mean molecular weights, determined viscometrically, of the mixtures. From the results it was, in turn, possible to derive the α coefficient in the relation of Kuhn. The action of anhydroformaldehyde urethan on chlorinated rubber could then be considered on a quantitative basis.

The Structure of Elastomers and Their Reactivity

1951 ◽  
Vol 24 (1) ◽  
pp. 95-98
Author(s):  
A. S. Kuz'minskii ◽  
N. N. Lezhnev
Keyword(s):  
Molecular Weight ◽  
Methyl Groups ◽  
Side Chains ◽  
Double Bonds ◽  
Gutta Percha ◽  
Different Temperatures ◽  
Spatial Configurations ◽  
The Mean ◽  
Kinetics Of ◽  
Mean Molecular Weight

Abstract It has not yet been ascertained what constituent parts within the structure of various elastomers have the greatest influence on the reactivity of the elastomers. There are indications that the side chains, the presence of methyl groups acting as substitutes, and differences in spatial configurations, etc., all have definite effects. The present authors have investigated the oxidation of several different elastomers at different temperatures. The experiments were carried out both in the presence and in the absence of an inhibitor (phenyl-β-naphthylamine). The elastomers and the inhibitor were first carefully purified. The kinetics of autoxidations were studied volumetrically by means of an apparatus already described by one of the authors. A chainless molecular introduction of oxygen into the double bonds of the elastomer in the presence of the inhibitor was studied with the aid of our own previously described inhibitor methods. The study included the oxidation of butadiene elastomers containing different distributions of double bonds in the main and side chains, divinylstyrene rubber, and the hydrocarbons of natural rubber and gutta-percha. These products are distinguished by their different degrees of unsaturation, the number of side chains, the number of double bonds in both their main and side chains, the length of their molecular chains (the mean molecular weight), and their spatial configurations.

Chromatographic Fractionation of Some Synthetic Elastomers

1948 ◽  
Vol 21 (3) ◽  
pp. 682-683 ◽  
Author(s):  
Ivan Landler
Keyword(s):  
Molecular Weight ◽  
Cellulose Acetate ◽  
Active Carbon ◽  
Low Molecular Weight ◽  
High Polymer ◽  
Acrylonitrile Copolymer ◽  
Molecular Weights ◽  
The Mean ◽  
Mean Molecular Weight ◽  
Poor Solvent

Abstract Mark and Saito were the first to fractionate a high polymer (cellulose acetate) by chromatographic adsorption on blood carbon. They found that molecules of low molecular weight were adsorbed first, and that the mean molecular weight of the product which remained unadsorbed was higher than the original molecular weight. Levi and Giera confirmed this result, but did not succeed in fractionating Buna-S or polyisoprene, for these polymers were eluted by the solvent during the washing operation in the column. The present authors have carried out further experiments in this field with a study of three commercial synthetic elastomers, viz., GR-S (butadienestyrene copolymer), Perbunan-N (butadiene-acrylonitrile copolymer), and Visitanex (polyisobutylene). The polymer was adsorbed by starting with a poor solvent composed of a mixture of toluene and methanol ; the quantity of alcohol added was just below the threshold of precipitation. The adsorbent used was a mixture of 75 per cent of lamp black (80 square meters per gram) and 25 per cent of coarse active carbon. The latter served to prevent agglomeration of the lamp black. The adsorbent was divided into three layers, of 10 grams each. At the end of the tube was a filter of fritted glass. Filtration was carried out under pressure, the rate of flow thereby being maintained constant, The polymers were characterized by their intrinsic viscosities. The molecular weights which were estimated by means of the relation, found experimentally between the molecular weight and viscosity, are only approximate, for this relation holds true only for narrow fractions.

THE EFFECTS OF SINGLE LARGE INFUSIONS OF VARIOUS DEXTRAN SOLUTIONS ON HYPOVOLEMIC DOGS

1954 ◽  
Vol 32 (6) ◽  
pp. 670-678 ◽  
Author(s):  
Robert E. Semple
Keyword(s):  
Molecular Weight ◽  
Body Weight ◽  
Plasma Proteins ◽  
Total Plasma ◽  
Anesthetized Dogs ◽  
The Mean ◽  
Mean Molecular Weight ◽  
Dextran Molecule

Standardized bleeding procedures were carried out on anesthetized dogs. Some animals received no therapy, some infusions of saline, and some received dextran infusions at times that varied from immediately to three and one-half hours after hemorrhage. With no therapy, one of eight animals survived; with saline infusions, 4 of 13 survived; and with dextran 23 of 24 dogs survived. There was often wound bleeding after dextran; this was not seen in saline treated animals but dextran treated animals recovered rapidly and no other ill-effects were noted. Dextran infusions were quantitatively retained in the circulation for an appreciable time and the volume and pressure of the circulating fluid were effectively restored and maintained. The amount of dextran excreted in urine was inversely related to the mean molecular weight of the infused material and the quantity excreted was the same as that observed in normal animals. The rate of disappearance of dextran by other than the renal route did not vary with the mean molecular weight, and indicated that the dextran molecule is catabolized at from 4.9 to 8.6 mgm./hr./kgm. body weight. About 50% of total plasma proteins of animals was lost by the hemorrhage and was replaced, after dextran infusions, within four days. There was no evidence, after dextran infusions, of dextran storage in kidney, spleen, or liver.

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