scholarly journals Changes in microstructure of snow under large deformations

1991 ◽  
Vol 37 (126) ◽  
pp. 193-202 ◽  
Author(s):  
Michael Q. Edens ◽  
Robert L. Brown
Keyword(s):  
Grain Size ◽  
Free Surface ◽  
Coordination Number ◽  
Surface Area ◽  
Unit Volume ◽  
Compression Tests ◽  
Confined Compression ◽  
Neck Length ◽  
Volume Measurements ◽  
Free Surface Area

AbstractA set of microstructural variables is selected to characterize the behavior of snow. Corresponding mathematical relations from quantitative stereology theory are presented along with relations and techniques required for numerical evaluation. An experimental investigation is carried out to determine changes in these variables for snow subjected to large compressive deformations. The micro-structural variables studied included coordination number, grain-size, bond radius, neck length, pore-size, free surface area and grains/unit volume. Measurements at several stages of deformation are used to evaluate the changes in the microstructure as functions of deformation. Microstructure measurements of six snow samples subjected to confined compression tests are presented for pre-compressed and compressed states, corresponding to final stresses of 0.387, 0.77 and 1.55 MPa. Grain-size and bond radius were found to go through finite changes during compression, although the variation of bond radius was more complicated in nature. The coordination number and number of bonds/unit volume were found to go through large changes during compression, while specific free surface area was found to increase by 100% due to grain- and bond-fracture processes. No discernible patterns of change in neck length could be found in the experiments. A close relationship between some of the microstructural variables and the stress response of the material was observed. These results serve to contribute to the presently available data and understanding of the microstructural behavior of snow.

scholarly journals Changes in microstructure of snow under large deformations

1991 ◽  
Vol 37 (126) ◽  
pp. 193-202 ◽  
Author(s):  
Michael Q. Edens ◽  
Robert L. Brown
Keyword(s):  
Grain Size ◽  
Free Surface ◽  
Coordination Number ◽  
Surface Area ◽  
Unit Volume ◽  
Compression Tests ◽  
Confined Compression ◽  
Neck Length ◽  
Volume Measurements ◽  
Free Surface Area

AbstractA set of microstructural variables is selected to characterize the behavior of snow. Corresponding mathematical relations from quantitative stereology theory are presented along with relations and techniques required for numerical evaluation. An experimental investigation is carried out to determine changes in these variables for snow subjected to large compressive deformations. The micro-structural variables studied included coordination number, grain-size, bond radius, neck length, pore-size, free surface area and grains/unit volume. Measurements at several stages of deformation are used to evaluate the changes in the microstructure as functions of deformation. Microstructure measurements of six snow samples subjected to confined compression tests are presented for pre-compressed and compressed states, corresponding to final stresses of 0.387, 0.77 and 1.55 MPa. Grain-size and bond radius were found to go through finite changes during compression, although the variation of bond radius was more complicated in nature. The coordination number and number of bonds/unit volume were found to go through large changes during compression, while specific free surface area was found to increase by 100% due to grain- and bond-fracture processes. No discernible patterns of change in neck length could be found in the experiments. A close relationship between some of the microstructural variables and the stress response of the material was observed. These results serve to contribute to the presently available data and understanding of the microstructural behavior of snow.

Improved Methods of Obtaining Clean Larvae of Haemonchus contortus

1963 ◽  
Vol 37 (4) ◽  
pp. 251-254 ◽  
Author(s):  
M. G. Christie ◽  
J. E. Patterson
Keyword(s):  
Free Surface ◽  
Surface Area ◽  
Haemonchus Contortus ◽  
Water Repellent ◽  
Optimum Conditions ◽  
Infective Larvae ◽  
Mucous Coat ◽  
Third Stage ◽  
Free Surface Area ◽  
Improved Methods

A pellet of sheep faeces containing eggs of Haemonchus contortus forms an adequate environment for the development of those eggs to third stage infective larvae, provided that it is kept moist. Observation shows a concentration of developing larvae on the external mucous coat of the pellet. These data suggest that optimum conditions for development would occur when pellets are separated one from another and standing on a water repellent surface, thus presenting the maximum free surface area and minimum opportunity for aggregation and hence of over crowding. The best method of recovering the infective larvae would be one that obtained larvae free from contamination without requiring them to expend energy in separating themselves from the contamination.

scholarly journals The effect of differing types of cloth and of contamination by non-feed nitrogen on intestinal digestion estimates using porous synthetic-fibre bags in a cow

1990 ◽  
Vol 63 (2) ◽  
pp. 221-229 ◽  
Author(s):  
Tuomo Varvikko ◽  
Aila Vanhatalo
Keyword(s):  
Free Surface ◽  
Chemical Composition ◽  
Pore Size ◽  
Surface Area ◽  
Dry Matter ◽  
Synthetic Fibre ◽  
Aqueous Suspension ◽  
Barley Straw ◽  
Intestinal Digestion ◽  
Free Surface Area

The influence of free surface area and pore size of a synthetic-fibre bag, and flow of intestinal substances into the bag, on the intestinal digestion estimates by the nylon-bag method of dry matter (DM), neutral detergent fibre (NDF), nitrogen, NDF-N and feed 15N was studied using a non-lactating cow fed on hay supplemented with barley and oats at maintenance level. The bags containing 15N-labelled ground ryegrass (Lolium perenne), barley, barley straw or rapeseed (Brassica napus) straw were introduced into the duodenum through a T-shaped cannula and collected from the faeces. Also, the disappearance of N from the bag was related to the true intestinal N digestion by comparing it with the net loss between duodenum and faeces of 15N in ryegrass introduced into the duodenum in an aqueous suspension. It was noted that the bag cloth often significantly affected both disappearance values and the subsequent chemical composition of the residues. Re-analysing part of the data as a 2x2 factorial (free surface x pore size) suggested that free surface area was often more important than pore size as a determinant of both disappearance values and chemical composition. Lower apparent (Kjeldahl N) than true (15N) feed N disappearance from the bag suggested a notable proportion of non-feed N in the residues, especially with fibrous feeds with low N. With ryegrass, 15N net loss within the intestine was lower than 15N disappearance from the bags. It was concluded that disappearance of Kjeldahl N is an underestimate of feed N disappearance from bags, but may possibly be an overestimate of the true intestinal digestion of feed N.

Assessment of the free surface area of magnesia-supported magnesium ferrite particles using selective oxygen chemisorption

1992 ◽  
Vol 27 (2) ◽  
pp. 343-350 ◽  
Author(s):  
D. E. Stobbe ◽  
F. R. Van Buren ◽  
A. J. Orbons ◽  
A. J. Van Dillen ◽  
J. W. Geus
Keyword(s):  
Free Surface ◽  
Surface Area ◽  
Magnesium Ferrite ◽  
Oxygen Chemisorption ◽  
Free Surface Area

Late Thrombogenicity of Grafts in the Venous System

1987 ◽  
Vol 2 (1) ◽  
pp. 29-36
Author(s):  
Gunnar Plate ◽  
Larry H. Hollier ◽  
Mrinal K. Dewanjee ◽  
Michael P. Kaye
Keyword(s):  
Free Surface ◽  
Surface Area ◽  
Half Life ◽  
Venous System ◽  
Long Term Results ◽  
Microscopic Appearance ◽  
Endothelial Seeding ◽  
Vein Grafts ◽  
Autogenous Vein ◽  
Free Surface Area

Although some previous experiments have demonstrated encouraging early results with venous vascular prosthesis, the long-term results have not been sufficiently investigated. The late thrombogenicity of 12 autogenous vein grafts and eight polytetrafluoroethylene (PTFE) grafts, three of which had been subjected to endothelial seeding, was evaluated 6 months after implantation in the canine venous system by determination of the survival time of the indium-labelled autogenous platelets and of the light and electron microscopic appearance of the graft-to-blood interface. Twelve dogs receiving autogenous vein grafts had a platelet half-life of 64 ± 13 (mean ± s.d.) hours and a completely thrombus-free internal graft surface covered by a smooth endothelium. The platelet half-life in five dogs with non-seeded PTFE grafts was significantly ( P < 0.01) shorter (44 ± 11h). The PTFE-to-blood interface consisted of a 100- to 170-μm-thick pseudointima with a thrombus-free surface area of 25-90% and substantial endothelial coverage in only two animals. Three dogs receiving endothelial-seeded PTFE grafts had a platelet half-life of 38, 46 and 53h, respectively, a 10- to 80-μm-thick pseudointima covered with typical endothelium, and a thrombus-free surface area of 90-100%. Our results demonstrate that PTFE grafts are still thrombogenic at 6 months following implantation in the canine venous system. Therefore, additional measures are required to maintain graft patency. Our limited experience with endothelial seeding does not allow any definite conclusions, but our findings indicate that this procedure might be beneficial.

Effects of resolution on the measurement of grain ‘size’

1985 ◽  
Vol 49 (353) ◽  
pp. 539-546 ◽  
Author(s):  
R. Dearnley
Keyword(s):  
Grain Size ◽  
Image Analysis ◽  
Grain Boundary ◽  
Surface Area ◽  
Unit Volume ◽  
Fractal Dimensions ◽  
Size Analysis ◽  
Automatic Image Analysis ◽  
Fine Grained ◽  
Kinetics Of

AbstractMeasurements of fine-grained dolerites by optical automatic image analysis are used to illustrate the effects of magnification and resolution on the values obtained for grain ‘size’, grain boundary length, surface area per unit volume, and other parameters. Within the measured range of optical magnifications (× 26 to × 3571) and resolutions (1.20 × 10−3 cm to 8.50 × 10−6 cm), it is found that the values of all grain parameters estimated by chord size analysis vary with magnification. These results are interpreted in terms of the concepts of ‘fractal dimensions’ introduced by Mandelbrot (1967, 1977). For some comparative purposes the fractal relationships may be of little significance as relative changes of size, surface area, and other parameters can be expressed adequately at given magnification(s). But for many studies, for instance in kinetics of grain growth, the actual diameter or surface area per unit volume is an important dimension. The consequences are disconcerting and suggest that it may be difficult in some instances to specify the ‘true’ measurements of various characteristics of fine-grained aggregates.

scholarly journals SIZING AND EXPERIMENTAL STUDY OF A SOLAR STILL FOR THE PRODUCTIVITY OF WATER DESALINATION IN SOUTH-WEST OF ALGERIA – BECHAR: التصميم والدراسة التجريبية لجهاز التقطير الشمسي لإنتاجية تحلية المياه في جنوب غرب الجزائر – بشار

2020 ◽  
Vol 4 (4) ◽  
Author(s):  
Abdelkarim Maamar Abdelkader, Bounegta Bachir Mohammed
Keyword(s):  
Drinking Water ◽  
Free Surface ◽  
Surface Area ◽  
Evaporation Rate ◽  
Salt Content ◽  
Experimental Studies ◽  
Water Desalination ◽  
Solar Still ◽  
Free Surface Area ◽  
The Third World

Algeria, like many countries belonging mostly to the Third World, has considerable water resources saline (salt content ranging between 1500 and 2000 ppm, exceeding the required standards for drinking water and therefore unfit for consumption). We must therefore think of making use these huge reserves interested in desalination techniques. The stain majored is therefore to achieve a distiller solar plan which meets these needs in drinking water. The absorber surface of the modified solar still is coated with black enamel paint and covered with copper chips. The evaporation rate of the water in the solar still is directly proportional to the exposure area of the water. Thus the productivity of the solar still increases with the free surface area of the water in the basin. The distillate yield was found to have improved considerably, especially when the water depth was high. The study also indicated some design features that would further enhance the improvement in output due to the modification made, the evaporation rate is proportional to the temperature of the free surface area of the water only. A general model based on heat transfer balances in each component of the system was developed to predict the mass of freshwater. The efficiency of this still was about 65% and can produce about 5.13 l/m2 per day, experimental studies and the outcomes are discussed in the article. We propose a new design of the cascading solar desalination still with obstacles and preheating of inlet water.

scholarly journals Enzyme activities of rumen particles and feed samples incubatedin situwith differing types of cloth

1998 ◽  
Vol 79 (2) ◽  
pp. 161-168 ◽  
Author(s):  
Pekka Huhtanen ◽  
Aila Vanhatalo ◽  
Tuomo Varvikko
Keyword(s):  
Free Surface ◽  
Pore Size ◽  
Microbial Activity ◽  
Surface Area ◽  
Enzyme Activities ◽  
Xylanase Activity ◽  
General Assumption ◽  
Free Surface Area ◽  
Highly Correlated

Three ruminally cannulated non-lactating dairy cows were used to investigate the effects of six different bag cloth types with pore size (μm): free surface area (%) ratios of 200: 45, 41: 33, 16: 5, 10: 2, 6: 5 and 1: 2 respectively on the disappearance of grass silage DM and neutral-detergent fibre (NDF), and on particle-associated carboxymethylcellulase (EC3.2.1.4; CMCase) and xylanase (EC3.2.1.8) activties extracted from feed residues. Another objective was to compare microbial activity inside the bags and in rumen ingesta. Rumen incubation periods were 3, 6, 12, 24, 48 and 96 h. DM and NDF disappearance and particle-associated enzyme activities were greatly reduced with the smaller pore size and/or open surface area. Re-analysing some of the data as a 2 x 2 factorial (pore size x free surface area) indicated that, generally, free surface area rather than pore size affected the disappearance of feed components and particle-associated enzyme activities. Enzyme activities were highly correlated with NDF disappearance at 6–48 h of incubation. Cumulative area under CMCase and xylanase activity curves explained 0·79 and 0·88 of the variation in NDF disappearance when different cloth type and 6–48 h incubation data were combined. Weighted mean enzyme activities inside the bags were less than 0·35 those in rumen ingesta. The highest activity values inside the bags (24 or 48 h) were less than 0·50 those found in rumen ingesta. The lower microbial activity inside the bags explains the slower rates of NDF digestion reported within situtechniques than with rumen evacuation techniques. The general assumption of similar microbial activity inside the bags and in rumen ingesta is not justified by the present results, and caution must be taken in interpretingin situresults quantitatively for feed evaluation systems.

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