Mechanism of Exposure-Cracking of Rubbers. With a Review of the Influence of Ozone

1945 ◽  
Vol 18 (3) ◽  
pp. 504-556 ◽  
Author(s):  
R. G. Newton
Keyword(s):  
Surface Strain ◽  
Ozone Absorption ◽  
Surface Protection ◽  
Rate Of Growth ◽  
Retarding Effect ◽  
Actual Growth ◽  
Small Cracks ◽  
Formation Of Cracks ◽  
The Mean ◽  
Marked Resistance

Abstract “Exposure-cracking” is the fissuring which occurs when stretched rubber is placed in an atmosphere containing ozone, and is frequently wrongly described as “sun-cracking”. These cracks form in the rubber at right angles to the applied stress and must be distinguished from crazing, the fissures of which occur in an oxidized surface layer and may run in any direction. It is shown that there is a “critical elongation” at which cracking is maximal, but that the relation between the severity of cracking and the surface strain can be greatly modified by changes in the compounding ingredients. Butadiene type of rubbers do not differ greatly in resistance to exposure-cracking, whereas the Neoprene types and Thiokol-FA possess marked resistance. The only factors essential for the production of exposure-cracking are ozone and strain in the sample, and sufficient ozone must be present in the atmosphere to produce the deterioration observed. Light is not only unnecessary, but actually has a retarding effect on the production of cracks. Three different phenomena must be carefully distinguished (1) the rate of ozone attack ; (2) the rate of formation of cracks ; and (3) the rate of growth of cracks. The rate of formation of cracks increases with increase of strain until a maximum is reached at about 75 per cent elongation, but the mean rate of growth of cracks is most rapid at 20 per cent elongation because the surface strain is most persistent at this elongation. The actual growth of cracks has been studied microscopically, and it is shown that large cracks are formed by the coalescence of small cracks, and the collapse of neighboring ones. The rate of ozone absorption is considered, and speculations are advanced to explain the formation of cracks and their greater incidence at high strains. The course of ozone attack indicates that there is little likelihood of producing improvement in resistance by altering compounding ingredients such as fillers and antioxidants, and confirms that the most efficient methods will be based on some type of surface protection.

scholarly journals THE RATE OF GROWTH OF THE DAIRY COW

1921 ◽  
Vol 3 (5) ◽  
pp. 623-633 ◽  
Author(s):  
Samuel Brody ◽  
Arthur C. Ragsdale
Keyword(s):  
Dairy Cow ◽  
Growth Period ◽  
Holstein Cows ◽  
Rate Of Growth ◽  
Retarding Effect ◽  
Monomolecular Reaction ◽  
Pregnancy And Lactation

The growth period of the Jersey and Holstein cows is made up of at least three cycles, two extrauterine cycles with maxima at about 5 and 20 months of age, and one intrauterine cycle, the maximum of which has not yet been determined. The equation of an autocatalytic monomolecular reaction was found to give very good results when applied to the cycle having its maximum at about 5 months of age. The values obtained from this equation when applied to the cycle having the maximum at about 20 months of age were higher than the observed values probably due to the retarding effect of pregnancy and lactation on growth.

scholarly journals Stochastic analysis of field-scale heat advection in heterogeneous aquifers

2012 ◽  
Vol 16 (3) ◽  
pp. 641-648 ◽  
Author(s):  
C.-M. Chang ◽  
H.-D. Yeh
Keyword(s):  
Temperature Field ◽  
Heat Transport ◽  
Stochastic Analysis ◽  
Transport Model ◽  
Field Scale ◽  
Heat Advection ◽  
Rate Of Growth ◽  
Second Moments ◽  
Mean Temperature ◽  
The Mean

Abstract. Owing to the analogy between the solute and heat transport processes, it can be expected that the rate of growth of the spatial second moments of the heat flux in a heterogeneous aquifer over relatively large space scales is greater than that predicted by applying the classical heat transport model. The motivation of stochastic analysis of heat transport at the field scale is therefore to quantify the enhanced growth of the field-scale second moments caused by the spatially varying specific discharge field. Within the framework of stochastic theory, an effective advection-dispersion equation containing effective parameters (namely, the macrodispersion coefficients) is developed to model the mean temperature field. The rate of growth of the field-scale spatial second moments of the mean temperature field in the principal coordinate directions is described by the macrodispersion coefficient. The variance of the temperature field is also developed to characterize the reliability to be anticipated in applying the mean heat transport model. It is found that the heterogeneity of the medium and the correlation length of the log hydraulic conductivity are important in enhancing the field-scale heat advection, while the effective thermal conductivity plays the role in reducing the field-scale heat advection.

THE MECHANISM OF THE FORMATION OF CRACKS IN THE LASER-DEPOSITED NICKEL ALLOY SYSTEM NI–CR–B–SI ON THE SURFACE OF STRUCTURAL STEEL TYPE 30CGSA

2020 ◽  
pp. 3-10
Author(s):  
V. P. Morozov ◽  
Yu. G. Romanov
Keyword(s):  
High Temperature ◽  
Crack Formation ◽  
Alloy System ◽  
Powder Materials ◽  
High Temperature Region ◽  
Second Stage ◽  
Stage Of Development ◽  
Small Cracks ◽  
Formation Of Cracks ◽  
Technological Strength

The mechanism of crack formation in the deposited layers is investigated. In accordance with this mechanism, cracks are of the nature of “hot” cracks. The reasons that enhance crack formation during surfacing of powder materials of the Ni–Cr–B–Si system are examined and identified. Foci of “hot” small cracks are formed, as a rule, in the high-temperature region. At the second stage, the focus develops, developing into transcrystalline destruction. The second stage of development is associated with the process of accumulation of internal welding stresses in the area of the source. The main parameters that determine the technological strength of the metal during surfacing or welding are: the length of the temperature range of brittleness (TIC), the level of ductility of the metal in the TIC and the intensity of the shrinkage deformation of the metal in the TIC. It was established that it is possible to increase the service life of the restored product several times in comparison with the new part by eliminating cracks in the deposited layer.

scholarly journals A critical statistical study of experimental data on the effect of minute electric currents on the growth rate of the coleoptile of barley

1926 ◽  
Vol 99 (695) ◽  
pp. 122-130 ◽  
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Statistical Study ◽  
Pure Line ◽  
Similar Data ◽  
Electric Currents ◽  
Rate Of Growth ◽  
The Mean ◽  
Positive Results ◽  
Case Based

A study of the effect of very minute electric currents on the rate of growth of the coleoptile of barley was published recently by one of us (F. G. G.) in collaboration. In this paper the mean rate of a number of control coleoptiles was compared with the mean rate of a number exposed to a minute electric discharge. The growth rate of individual coleoptiles showed, naturally, considerable divergences, so the mean result was in each case based on the observation of a large number of coleoptiles, the increments of growth of individual coleoptiles being stated as percentages of the rate of growth during the first hour of observation. It was assumed that the distribution of growth rates in a comparatively large sample of a pure-line barley would conform with the normal distribution; the probable errors of the mean results were therefore calculated in the ordinary way. During the continuation of this work positive results have been obtained in further experimental sets, but a number of these, though significant in the mass, were individually without significance. This suggested that a careful statistical study of the data on which the results were based might show how the accuracy of the method could be increased. Such a study has accordingly been undertaken, and it seems probable that methods employed are likely to be of use in the treatment of similar data.

OBSERVATIONS ON FOETAL GROWTH IN MULTIPLE PREGNANCY IN MAN

1952 ◽  
Vol 8 (4) ◽  
pp. 386-401 ◽  
Author(s):  
THOMAS McKEOWN ◽  
R. G. RECORD
Keyword(s):  
Birth Weight ◽  
Multiple Pregnancy ◽  
Multiple Births ◽  
Experimental Animals ◽  
Litter Weight ◽  
Foetal Growth ◽  
Rate Of Growth ◽  
The Mean ◽  
The Times ◽  
Period Of Gestation

1. Observations on foetal growth in human pregnancy are recorded on 22,454 single, 325 twin, 249 triplet and 27 quadruplet maternities. 2. Mean birth weights of singletons, twins, triplets and quadruplets are respectively 7·43, 5·27, 4·00 and 3·07 lb. 3. For single, twin, triplet and quadruplet pregnancies, mean durations of gestation (in days) are 280·5, 261·6, 246·8 and 236·8. 4. Mean birth weight is greater for small than for large litters even when comparison is restricted to births delivered after the same period of gestation (see Table 4). 5. It is suggested that these observations, which are in accord with reports on experimental animals, raise two questions: (a) why is foetal growth retarded in multiple pregnancy during the last weeks of gestation? and (b) why is onset of labour earlier in multiple than in single pregnancy? 6. In consideration of 5 (a) it is shown that: (i) Mean foetal weight appears to be independent of litter size until about the 27th week of gestation. (ii) The rate of growth of multiple foetuses is slower than that of single foetuses from a stage of gestation which varies with size of litter as follows: quadruplets from about 26 weeks; triplets from 27 weeks; and twins from 30 weeks. In the case of singletons, foetal growth is linear between 30 and 36 weeks; after 36 weeks the rate of growth is reduced. (iii) At the times from which the respective rates of foetal growth are retarded, mean litter weights of twins, triplets and quadruplets are approximately the same. These mean litter weights (in lb.) are: quadruplets at 26 weeks, 7·6; triplets at 27 weeks, 6·9; twins at 30 weeks, 6·9. The mean weight of single births at 36 weeks is 6·5 lb. (iv) From the time that foetal growth is retarded, litter weight increment is approximately the same for every size of litter. Support is provided for the view that (a) retardation of foetal growth in large litters is attributable, at least in part, to crowding in the uterus (see Table 6); and (b) the restriction on foetal growth in the crowded uterus may be imposed by the placenta (see Table 7). 7. In consideration of 5 (b) it is shown that mean litter weights of singletons, twins, triplets and quadruplets at birth are respectively 7·43, 10·53, 12·00 and 12·28 lb. It is suggested that these observations are not inconsistent with the view that the early onset of labour in multiple pregnancy is due to distension of the uterus, if we suppose that the amount of distension which the uterus will tolerate during the last weeks of gestation decreases as pregnancy advances. 8. Mean litter weights of multiple births increase with birth order.

Midsummer stratospheric NO2 at latitude 45°S

1979 ◽  
Vol 57 (8) ◽  
pp. 1110-1117 ◽  
Author(s):  
A. W. Harrison
Keyword(s):  
New Zealand ◽  
Nitrogen Dioxide ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Absorption Bands ◽  
Ozone Absorption ◽  
Vertical Column ◽  
The Mean

Ground based measurements of stratospheric nitrogen dioxide during morning and evening twilight have been made at Lauder, New Zealand, 169°40′E longitude and 45°04′S latitude during January and February 1979. The analysis shows that ozone absorption overlying the nitrogen dioxide absorption bands cannot be ignored. After correcting for ozone absorption the mean vertical column abundance of nitrogen dioxide was found to be 2.9 × 1015 cm−2 (evening, solar zenith angle = 90°) and 1.1 × 1015 cm−2 (morning, solar zenith angle = 90°).

scholarly journals THE GROWTH AND DURATION OF LIFE OF CELOSIA CRISTATA SEEDLINGS AT DIFFERENT TEMPERATURES

1934 ◽  
Vol 17 (6) ◽  
pp. 763-781 ◽  
Author(s):  
Thomas I. Edwards ◽  
Raymond Pearl ◽  
Sophia A. Gould
Keyword(s):  
Growth Rate ◽  
Maximum Yield ◽  
Total Duration ◽  
Growth Curves ◽  
Growth Period ◽  
Hypocotyl Length ◽  
Rate Of Growth ◽  
Life Duration ◽  
Celosia Cristata ◽  
The Mean

Daily measurements of hypocotyl length were made on Celosia cristata seedlings cultured in darkness under aseptic conditions at six constant temperatures between 14.5° and 40.5°C. At 40.5° roots did not penetrate the agar and only the hypocotyls that were supported by the wall of the test tube could be measured. The growth curves were of the generalized logistic type, but of different degrees of skewness. The degree of symmetry of the growth curves was influenced by temperature. At the lower temperatures the maximal growth rate came relatively late in the grand period of growth; at successively higher temperatures it came progressively earlier. The mean total time rate of growth (millimeter per diem) was found to be a parabolic function of the temperature. The maximum rate of growth was found from the curve to be at 30.48°C. The maximum observed rate of growth, and the maximum yield, were found to be at 30°C. At all temperatures above 14.5° the maximum growth activity fell in the second quarter of the whole growth period. At all temperatures tested other than 30°, and at all parts of the growth cycle, the growth yield as measured by height of hypocotyl at any given equivalent point was less than at 30°. The total duration of life of the seedlings, and the duration of life after the end of the growth period (intermediate period) were inversely proportional to the mean total growth rate. The observations on Celosia cristata seedlings are thus in accord with the "rate of living" theory of life duration. The optimal temperature for life duration is the minimum temperature, within the range of these observations.

scholarly journals Entropy and Random Walk Trails Water Confinement and Non-Thermal Equilibrium in Photon-Induced Nanocavities

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1101 ◽  
Author(s):  
Vassilios Gavriil ◽  
Margarita Chatzichristidi ◽  
Dimitrios Christofilos ◽  
Gerasimos A. Kourouklis ◽  
Zoe Kollia ◽  
...  
Keyword(s):  
Random Walk ◽  
Thermal Equilibrium ◽  
Surface Strain ◽  
Molecular Water ◽  
Water Molecules ◽  
Escape Time ◽  
Thermal Equilibrium State ◽  
Surface Entropy ◽  
Molecular Confinement ◽  
The Mean

Molecules near surfaces are regularly trapped in small cavitations. Molecular confinement, especially water confinement, shows intriguing and unexpected behavior including surface entropy adjustment; nevertheless, observations of entropic variation during molecular confinement are scarce. An experimental assessment of the correlation between surface strain and entropy during molecular confinement in tiny crevices is difficult because strain variances fall in the nanometer scale. In this work, entropic variations during water confinement in 2D nano/micro cavitations were observed. Experimental results and random walk simulations of water molecules inside different size nanocavitations show that the mean escaping time of molecular water from nanocavities largely deviates from the mean collision time of water molecules near surfaces, crafted by 157 nm vacuum ultraviolet laser light on polyacrylamide matrixes. The mean escape time distribution of a few molecules indicates a non-thermal equilibrium state inside the cavity. The time differentiation inside and outside nanocavities reveals an additional state of ordered arrangements between nanocavities and molecular water ensembles of fixed molecular length near the surface. The configured number of microstates correctly counts for the experimental surface entropy deviation during molecular water confinement. The methodology has the potential to identify confined water molecules in nanocavities with life science importance.

Growth of Juvenile Chum Salmon (Oncorhynchus keta) Under Different Feeding Regimes

1969 ◽  
Vol 26 (6) ◽  
pp. 1631-1645 ◽  
Author(s):  
R. J. LeBrasseur
Keyword(s):  
Growth Rate ◽  
Chum Salmon ◽  
Oncorhynchus Keta ◽  
Rate Of Growth ◽  
Total Length ◽  
Chum Salmon Oncorhynchus Keta ◽  
Feeding Regimes ◽  
Size Groups ◽  
Juvenile Chum Salmon ◽  
The Mean

Juvenile chum salmon were fed on six different concentrations of size-selected zooplankton for 8 weeks. Zooplankton were caught daily and sorted through sieves into size-groups roughly as follows: 6–20 mm total length, mainly euphausiids; 2.5–4.5 mm, mainly copepods; and ≤ 1.5 mm, mainly small copepods. The rate of growth in weight of the fish was found to be dependent upon the concentration of the ration. Fish which were offered no food lost weight, and fish which were offered excess food increased in weight by 5.4% per day. The mean growth rate of the fish held on fixed rations ranged from 2.2 to 5.7% per day and was found to be independent of the type of prey. Electivity experiments showed that all the fish selected copepods 1.6–4.5 mm long in proportion to their abundance and rejected copepods ≤ 1.5 mm. The euphausiids were selected only by fish which had previously fed on euphausiids. The effect of variations in the availability of prey is discussed.

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