scholarly journals Metamorphism of Dry Snow as a Result of Temperature Gradient and Vapor Density Differences

1983 ◽  
Vol 4 ◽  
pp. 3-9 ◽  
Author(s):  
E. E. Adams ◽  
R. L. Brown
Keyword(s):  
Temperature Gradient ◽  
Heat Conduction Equation ◽  
Temperature Gradients ◽  
Large Temperature ◽  
Local Minima ◽  
Vapor Density ◽  
Snow Density ◽  
Local Maxima ◽  
The Difference

A heat conduction equation for the determination of the temperature profile in a snowpack is developed. The magnitude of the temperature gradient tends to increase as the snow surface is approached, with local minima through layers of high snow density and local maxima above and below these layers. Calculations are made of the difference in vapor density in the pore and over the ice grain surfaces which border the pore. In the presence of sufficient temperature and temperature gradient, faceted crystals will develop near the top of the pore, as ice is sublimed away from the surfaces in the lower region. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is demonstrated to be enhanced at warm temperatures and large temperature gradients in low density snow.

scholarly journals Metamorphism of Dry Snow as a Result of Temperature Gradient and Vapor Density Differences

1983 ◽  
Vol 4 ◽  
pp. 3-9 ◽  
Author(s):  
E. E. Adams ◽  
R. L. Brown
Keyword(s):  
Temperature Gradient ◽  
Heat Conduction Equation ◽  
Temperature Gradients ◽  
Large Temperature ◽  
Local Minima ◽  
Vapor Density ◽  
Snow Density ◽  
Local Maxima ◽  
The Difference

A heat conduction equation for the determination of the temperature profile in a snowpack is developed. The magnitude of the temperature gradient tends to increase as the snow surface is approached, with local minima through layers of high snow density and local maxima above and below these layers. Calculations are made of the difference in vapor density in the pore and over the ice grain surfaces which border the pore. In the presence of sufficient temperature and temperature gradient, faceted crystals will develop near the top of the pore, as ice is sublimed away from the surfaces in the lower region. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is demonstrated to be enhanced at warm temperatures and large temperature gradients in low density snow.

XXV.—The Determination of Temperature Gradients over the Greenland Ice Sheet by Optical Methods

1957 ◽  
Vol 64 (4) ◽  
pp. 381-397
Author(s):  
R. A. Hamilton
Keyword(s):  
Temperature Gradient ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temperature Gradients ◽  
Lower Atmosphere ◽  
Optical Methods ◽  
Snow Surface ◽  
Vertical Angle ◽  
Gradient Measurements

SynopsisThe temperature gradient in the lower atmosphere can be directly determined by measuring the optical refractive index of the air. This method is suitable for use on the Greenland ice sheet where errors introduced by water vapour are small, and where the strong solar radiation reflected by the snow surface makes it difficult to measure temperature differences over height differences of about I metre.The refraction was measured by observing the apparent vertical angle of each of a set of targets at distances up to 4 km. from a theodolite. The refraction was found to vary linearly with the distance of the target. The true vertical angle to the targets was determined when a second theodolite was available and reciprocal sights could be taken with it from the site of target to the fixed theodolite. The true vertical angle varied with time due to slow descent of the theodolite as the firn slumped; a correction for this was made. The standard error of the temperature gradient measurements was about 1.5 × 10−2 C.° per metre. It is considered that the method could be developed and improved so that over a range of only 100 metres temperature gradients could be measured to an accuracy of about 0·1° C. per metre.

scholarly journals Parameterization of the shear strength of faceted crystals during equi-temperature metamorphism

2011 ◽  
Vol 52 (58) ◽  
pp. 111-118 ◽  
Author(s):  
Hiroyuki Hirashima ◽  
Osamu Abe ◽  
Atsushi Sato
Keyword(s):  
Shear Strength ◽  
Temperature Gradient ◽  
Empirical Equation ◽  
Large Temperature ◽  
Strength Increase ◽  
Bottom Temperature ◽  
Snow Density ◽  
Snow Layer ◽  
Empirical Relationships ◽  
Temperature Conditions

AbstarctChanges in the shear strength of faceted crystals were measured and parameterized under equi-temperature conditions in the laboratory. The air temperature and bottom temperature of the snow layer were controlled to create a large temperature gradient for 8.8 days to make faceted crystals. Subsequently, the temperature gradient was eliminated and the snow was kept under equi-temperature conditions (–5°C and –10°C) for 55 days. During the experiments, the snow density and shear strength were measured six times. The measured shear strength was compared with two empirical relationships based on density. One of these relationships addresses the strength of round grains, whereas the other refers to faceted grains. The measured shear strength approached the calculated value for faceted crystals when the temperature gradient was large, whereas it approached that for rounded grains after the temperature gradient was removed. The dry snow metamorphism factor (DSM factor), which expresses the developmental stage of faceted crystals, was used to model the shear strength increase under equi-temperature conditions. The DSM factor indicates shear strength using an empirical equation based on rounded grains or faceted crystals. It is approximately 0 for rounded grains and 1 for faceted crystals. It decreased from 1.04 to 0.84 and 0.79 at –10°C and –5°C, respectively, in 55 days. These results were incorporated into the numerical snowpack model SNOWPACK, which successfully reproduced the experimentally observed increase in shear strength under equi-temperature conditions.

End Thermal Stresses in a Long Circular Rod

1968 ◽  
Vol 35 (2) ◽  
pp. 267-273 ◽  
Author(s):  
W. H. Chu ◽  
F. T. Dodge
Keyword(s):  
Temperature Gradient ◽  
General Solution ◽  
Thermal Stresses ◽  
Linear Interpolation ◽  
Temperature Gradients ◽  
Characteristic Functions ◽  
Large Temperature ◽  
End Effect ◽  
Title Problem ◽  
Characteristic Values

The title problem is solved by the method of collocation utilizing complex nonorthogonal characteristic functions. It is shown that the characteristic values can be obtained by repeated linear interpolation without much difficulty. Ten roots are given for the case of Poisson’s ratio equaling 0.3. For large temperature gradients, an example is given which shows high end stresses. The general solution due to the end effect dies down at the rate of exp (–2.722 z/a) or faster, but its magnitude depends on the steepness of the temperature gradient. This paper also shows that the Saint-Venant principle may not always be sufficient, that the end stress could be critical, and that, therefore, it should be calculated.

scholarly journals Determination of Mobility and Charge Carriers Concentration from Ionic Conductivity in Sodium Germanate Glasses above and below Tg

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Marcio Luis Ferreira Nascimento
Keyword(s):  
Ionic Conductivity ◽  
Charge Carrier ◽  
Formation Enthalpy ◽  
Large Temperature ◽  
Complete Test ◽  
Ionic Displacement ◽  
The Difference ◽  
And Migration ◽  
Positively Charged

The ionic conductivity and viscous flow data of xNa2O·(1−x)GeO2, 0.05<x<0.296, have been collected in a large temperature range, below and above their glass transition temperatures (Tg). A microscopic model is proposed, assuming that the ionic displacement would result from the migration of interstitial positively charged cationic pairs whose concentration is an activated function of temperature. Below Tg, their migration is also an activated mechanism, but a “free volume” would prevail above this temperature. This discontinuity in the migration mechanism justifies a Dienes-Macedo-Litovitz (DML) relationship to be representative of conductivity data above Tg and an Arrhenius law below. According to this model, the enthalpy deduced by the fit of high temperature data using a DML equation would correspond to the charge carrier formation, whose migration enthalpy, below Tg, could be deduced by the difference between the activation energy measured in the Arrhenius domain and the charge carrier formation enthalpy. To reduce the number of adjustable parameters numerical values were physically justified. We also applied a complete test for conductivity below Tg, using the so-called weak electrolyte model, splitting activation enthalpy EσA into formation and migration enthalpies and also explaining the variation of pre-exponential term of conductivity with composition.

scholarly journals A Note for Probabilistic Model of Polymer Crystallization in Temperature Gradients

Crystals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 538
Author(s):  
Chunlei Ruan ◽  
Yunlong Lv
Keyword(s):  
Temperature Gradient ◽  
Crystallization Kinetics ◽  
Probabilistic Model ◽  
Polymer Crystallization ◽  
Temperature Gradients ◽  
Kinetics Model ◽  
Gradient Field ◽  
Conversion Degree ◽  
Avrami Equation ◽  
Large Temperature

A polymer crystallization kinetics model is the most important way to characterize the crystallization rate of polymers. Because polymers are poor heat conductors, the cooling of thick-walled shapes results in temperature gradients. Piorkowska (Piorkowska, E. J. Appl. Polym. Sci., 2002, 86: 1351–1362.) derived the probabilistic analytical model of polymer crystallization in temperature gradients based on the Avrami equation. However, there are some misunderstandings when using this model. Here, isotactic polypropylene (iPP) is chosen as a model polymer and its crystallization is studied in a temperature gradient field. Based on the results of the Monte Carlo method, the probabilistic model methodology is discussed. The results show that when the product has a large temperature gradient and a large temperature difference, the probabilistic model cannot be used directly; instead, it is necessary to use the average probabilistic model. This means that the sample should be divided into several smaller parts and the probabilistic model used separately for each small part. The values are then averaged to obtain the mean conversion degree of the melt into spherulites for the whole product. The effects of the division number are also discussed. The goal of the present paper is to better understand the polymer crystallization kinetics model in terms of temperature gradients.

Role of substrate shape on thermal energy transmission in robotized wire and arc additive manufacturing

2019 ◽  
Vol 25 (7) ◽  
pp. 1285-1294 ◽  
Author(s):  
Rong Li ◽  
Jun Xiong
Keyword(s):  
Additive Manufacturing ◽  
Temperature Gradient ◽  
Thermal Energy ◽  
Molten Pool ◽  
Temperature Gradients ◽  
Maximum Temperature ◽  
Large Temperature ◽  
Energy Transmission ◽  
Content Type ◽  
Thin Walled

Purpose The purpose of this study is to present how the thermal energy transmission of circular parts produced in robotized gas metal arc (GMA)-based additive manufacturing was affected by the substrate shape through finite element analysis, including distributions of thermal energy and temperature gradient in the molten pool and deposited layers. Design/methodology/approach Three geometric shapes, namely, square, rectangle and round were chosen in simulation, and validation tests were carried out by corresponding experiments. Findings The thermal energy conduction ability of the deposited layers is the best on the round substrate and the worst on the rectangular substrate. The axial maximum temperature gradients in the molten pool along the deposition path with the round substrate are the largest during the deposition process. At the deposition ending moment, the circumferential temperature gradients of all layers with the round substrate are the largest. A large temperature gradient usually stands for a good heat conduction condition. Altogether, the round substrate is more suitable for the fabrication of circular thin-walled parts. Originality/value The predicted thermal distributions of the circular thin-walled part with various substrate shapes are helpful to understand the influence of substrate shape on the thermal energy transmission behavior in GMA-based additive manufacturing.

scholarly journals Temperature gradient and initial snow density as controlling factors in the formation and structure of hard depth hoar

2002 ◽  
Vol 48 (163) ◽  
pp. 485-494 ◽  
Author(s):  
W. Tad Pfeffer ◽  
Randy Mrugala
Keyword(s):  
Temperature Gradient ◽  
Initial Density ◽  
Controlling Factors ◽  
High Density ◽  
Temperature Gradients ◽  
Two Dimensional ◽  
Snow Density ◽  
Solid Type

AbstractWe investigate how temperature gradient and initial density influence depth-hoar growth in snow and seek to better define the range of conditions under which cohesive, or hard, depth hoar forms. Samples of 400 kg m−3sieved snow were exposed to temperature gradients of 20–80°C m−1, and samples of four different densities were exposed to a 40°C m temperature gradient. Following exposure to temperature gradients, penetrometer tests were made on samples to determine the presence of solid and/or hard depth hoar. Grain bond orientation was analyzed in section planes by two-dimensional stereological techniques where hard depth hoar developed. Results indicate that hard cohesive depth hoar forms from rounded-grain snow having a density of 400 kg m−3or greater, following exposure to a temperature gradient of 20°C m−1or greater. Hard depth hoar appears to consist of solid-type depth-hoar grains connected by necks, with vertically preferred directions of grain elongation and organization of grain-to-grain chains. This work corroborates Atikaya’s (1974) results, but extends his observation of formation of hard depth hoar to weaker temperature gradients for high-density snow. Our results also indicate that hard depth hoar is composed of faceted solid-type (anhedral) grains.

FRACTIONAL DETERMINATIONS OF URINARY 17-KETOSTEROIDS IN HYPEREMESIS GRAVIDARUM

1962 ◽  
Vol 41 (1) ◽  
pp. 123-128 ◽  
Author(s):  
Pentti A. Järvinen ◽  
Sykkö Pesonen ◽  
Pirkko Väänänen
Keyword(s):  
Hyperemesis Gravidarum ◽  
First Trimester ◽  
Control Group ◽  
Before And After ◽  
Daily Urine ◽  
First Trimester Of Pregnancy ◽  
The Difference

ABSTRACT The fractional determination of 17-ketosteroids in the daily urine was performed in nine cases of hyperemesis gravidarum and in four control cases, in the first trimester of pregnancy both before and after corticotrophin administration. The excretion of total 17-KS is similar in the two groups. Only in the hyperemesis group does the excretion of total 17-KS increase significantly after corticotrophin administration. The fractional determination reveals no difference between the two groups of patients with regard to the values of the fractions U (unidentified 17-KS), A (androsterone) and Rest (11-oxygenated 17-KS). The excretion of dehydroepiandrosterone is significantly higher in the hyperemesis group than in the control group. The excretion of androstanolone seems to be lower in the hyperemesis group than in the control group, but the difference is not statistically significant. The differences in the correlation between dehydroepiandrosterone and androstanolone in the two groups is significant. The high excretion of dehydroepiandrosterone and low excretion of androstanolone in cases of hyperemesis gravidarum is a sign of adrenal dysfunction.

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