scholarly journals Heterogeneous Nucleation by Aggregates of Particles

1960 ◽  
Vol 13 (3) ◽  
pp. 584 ◽  
Author(s):  
RB Head ◽  
KL Sutherland
Keyword(s):  
Heterogeneous Nucleation ◽  
Fine Particles ◽  
Flat Surface ◽  
Phase Point ◽  
General Effect ◽  
Point Contacts ◽  
Active Particles ◽  
Line Contacts ◽  
New Phase ◽  
Number Of Particles

The induction of a new phase by fine particles of a nucleating substance is complicated not only by variation in sizes but also by aggregation. The general effect of aggregation is to decrease the total number of particles but to reduce the supercooling (or supersaturation) necessary for growth of a new phase. Point contacts appear to be more fruitful than do line contacts, although both may be able to cause a substance to be more active than a large flat surface of the substrate. If the contact between particles is not a specially favoured position for nucleation, the aerosol as a whole appears to contain a higher proportion of active particles because of the persistence of initially active particles and the loss of less active ones.

scholarly journals Image analysis to qualify soil erodibility into a wind tunnel

2018 ◽  
Vol 42 (3) ◽  
pp. 240-247
Author(s):  
Carlos Asensio ◽  
Emilio Rodríguez-Caballero ◽  
Francisco Jesús García-Navarro ◽  
José Antonio Torres
Keyword(s):  
Wind Tunnel ◽  
Wind Erosion ◽  
Particle Number ◽  
Fine Particles ◽  
Size Number ◽  
Main Effect ◽  
Trap Height ◽  
Natural Wind ◽  
Image Analyses ◽  
Number Of Particles

ABSTRACT A wind erosion research was carried out in a wind tunnel where sediment samples acquired were studied by an artificial vision camera. These images could be enlarged for further analysis. Image analyses were mainly colorimetry, number of particles present and their size. Soil wind erodibility was analyzed with the image analyses supported by other laboratory results. Anthrosols were the most erodible soils, whereas Calcisols showed the highest resistance to the erosive action of wind. Sediment characteristics show the influence of trap height with decreasing particle size, number and darkness as transport height increases. A two-factor ANOVA for main effect height showed that there were significant differences in particle number and size for sediments trapped 0-15 cm and 40-70 cm high. Soils could be grouped by differences in particle number and size at different heights into highly erodible Anthrosols and Leptosols, non-erodible Calcisols and Arenosols, in which fine particles were already depleted by natural wind erosion. Aggregation showed a similar pattern with decreasing values from Calcisols and Leptosols to Anthrosols and finally Arenosols, where only single sand grains were observed in adhesive traps.

Uniform Equations in the Inlet and Exit Zones of Heavily Loaded Point and Line Elastohydrodynamically Lubricated Contacts Involved in Various Steady Motions

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Ilya I. Kudish
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Lubrication Film ◽  
Lubricated Contacts ◽  
Asymptotic Equations ◽  
Line Contacts ◽  
Steady Motions ◽  
Numerical Approaches

Heavily loaded point elastohydrodynamically lubricated (EHL) contacts involved in steady purely transitional, skewed transitional, and transitional with spinning motions are considered. It is shown that in the central parts of the inlet and exit zones of such heavily loaded point EHL contacts the asymptotic equations governing the EHL problem along the lubricant flow streamlines for the above types of contact motions can be reduced to two sets of asymptotic equations: one in the inlet and one in the exit zones. The latter sets of equations are identical to the asymptotic equations describing lubrication process in the inlet and exit zones of the corresponding heavily loaded line EHL contact (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For each specific motion of a point contact, a separate set of formulas for the lubrication film thickness is obtained. For different types of contact motions, these film thickness formulas differ significantly (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For heavily loaded contacts, the discovered relationship between point and line EHL problems allows to apply to point contacts most of the results obtained for line contacts (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC; Kudish, I. I., and Covitch, M. J., 2010, Modeling and Analytical Methods in Tribology, Chapman and Hall/CRC).

scholarly journals Influence of Meteorology on Fine Particles Concentration in Vitória Metropolitan Region During Wintertime

2019 ◽  
Vol 34 (4) ◽  
pp. 459-470 ◽  
Author(s):  
Willian Lemker Andreão ◽  
Bruna Tuão Trindade ◽  
Antônio Paula Nascimento ◽  
Neyval Costa Reis Júnior ◽  
Maria de Fátima Andrade ◽  
...  
Keyword(s):  
High Pressure ◽  
Large Scale ◽  
Fine Particles ◽  
Metropolitan Region ◽  
World Health ◽  
Daily Maximum ◽  
Health Organization ◽  
Urban Sites ◽  
World Health Organization Guideline ◽  
Number Of Particles

Abstract Fine particles (PM2.5) are harmful to human health especially during periods of limited dispersion when the concentrations build up. This is a common occurrence in Southern Brazil in the dry season when high-pressure stationary systems inhibit vertical dispersion and reduce wind speed. The objective of this study was to evaluate the PM2.5 concentrations in the Region of Greater Vitória during the winter of 2013, and to assess the influence of the large-scale meteorological circulation on its concentration. An experimental campaign was carried out to determine the mass of PM2.5 at six urban sites and particle number concentration. The average PM2.5 concentrations varied from 9.70 μg m-3 to 14.36 μg m-3 with the average daily maximum reaching 29.35 μg m-3, exceeding the World Health Organization guideline (24-h average: 25 μg m-3). The particle size distribution showed a larger number of particles from 18 to 21 h (local time), indicating that the main vehicular emissions are the main sources. During the winter, rainfall associated with cold fronts were responsible for a decrease in the particulate concentrations. In contrast, the occurrence of high-pressure systems led to an increase in particle concentrations, due to stagnant conditions.

scholarly journals Enhanced Fluidity of ZL205A Alloy with the Combined Addition of Al–Ti–C and La

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6169
Author(s):  
Guowei Zhang ◽  
Zhaojie Wang ◽  
Jingwei Niu ◽  
Hong Xu ◽  
Xiaoyan Ren
Keyword(s):  
Grain Size ◽  
Heterogeneous Nucleation ◽  
Base Alloy ◽  
Microstructure Characterization ◽  
Solidification Range ◽  
Zl205a Alloy ◽  
Role Based ◽  
Fluidity Test ◽  
Number Of Particles

The effects of Al–Ti–C and La on the fluidity of a ZL205A alloy after separate and combined addition were studied by conducting a fluidity test. The fluidity of the ZL205A alloy first increased and then decreased with the increasing addition of Al–Ti–C and La; it peaked at 0.3% and 0.1% for Al–Ti–C and La, respectively. The combined addition of Al–Ti–C and La led to better fluidity, which increased by 74% compared with the base alloy. The affecting mechanism was clarified through microstructure characterization and a DSC test. The heterogeneous nucleation aided by Al–Ti–C and La, the number of particles in the melt, and the evolution of the solidification range all played a role. Based on the evolution of the fluidity and grain size, the optimal levels of Al–Ti–C and La leading to both high fluidity and small grain size were identified.

Contact Fatigue in Hard Steel Specimens with Point and line Contacts

1967 ◽  
Vol 9 (1) ◽  
pp. 67-71 ◽  
Author(s):  
P. H. Dawson
Keyword(s):  
Tensile Stress ◽  
Contact Zone ◽  
Elastic Limit ◽  
Contact Fatigue ◽  
Line Contact ◽  
Point Contacts ◽  
Hard Steel ◽  
Line Contacts ◽  
Tensile Strains ◽  
Ring Cracks

Kennedy and others have repeatedly loaded steel spheres together and produced ring cracks due to the radial tensile stress that exists at the edge of the contact zone. Merritt has pointed out that no such tensile stress exists in line contact. Tests similar to those of Kennedy have now been carried out both in line and point contacts. Both produced cracks. The cracks in line contact have been explained by residual tensile strains which develop near the edges of the contact zone when the elastic limit has been exceeded. A number of interesting features which appeared in the tests both with line and point contacts are noted.

Uniform Equations in the Inlet and Exit Zones of Heavily Loaded Point EHL Contacts Involved in Various Steady Motions

2014 ◽  
Author(s):  
Ilya I. Kudish
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Point Contacts ◽  
Lubrication Film ◽  
Asymptotic Equations ◽  
Lubricant Flow ◽  
Different Types ◽  
Line Contacts ◽  
Steady Motions ◽  
Ehl Contact

Heavily loaded point EHL contacts involved in steady purely transitional, skewed transitional, and transitional with spinning motions are considered. It is shown that in the central parts of the inlet and exit zones of such heavily loaded point EHL contacts the asymptotic equations governing the EHL problem along the lubricant flow streamlines for the above types of contact motions can be reduced to two sets of asymptotic equations: one in the inlet and one the exit zones. The latter sets of equations are identical to the asymptotic equations describing lubrication process in the inlet and exit zones of the corresponding heavily loaded line EHL contact [1]. For each specific motion of a point contact a separate set of formulas for the lubrication film thickness is obtained. For different types of contact motions these film thickness formulas differ significantly [1]. For heavily loaded contacts the discovered relationship between point and line EHL problems allow to apply to point contacts most of the results obtained for line contacts [1,2].

Nucleation Dynamics of Water Nanodroplets

2014 ◽  
Vol 20 (2) ◽  
pp. 407-415 ◽  
Author(s):  
Dipanjan Bhattacharya ◽  
Michel Bosman ◽  
Venkata R.S.S. Mokkapati ◽  
Fong Yew Leong ◽  
Utkur Mirsaidov
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Gold Nanoparticles ◽  
Heterogeneous Nucleation ◽  
Flat Surface ◽  
Nucleation And Growth ◽  
Length Scale ◽  
Transmission Electron ◽  
Nucleation Sites

AbstractThe origin of the condensation of water begins at the nanoscale, a length-scale that is challenging to probe for liquids. In this work we directly image heterogeneous nucleation of water nanodroplets by in situ transmission electron microscopy. Using gold nanoparticles bound to a flat surface as heterogeneous nucleation sites, we observe nucleation and growth of water nanodroplets. The growth of nanodroplet radii follows the power law: R(t)~(t−t0)β, where β~0.2−0.3.

scholarly journals Theoretical and Experimental Investigation on Friction in Lubricated Line Contacts with Different Materials and Textures in Presence of Wear

2016 ◽  
Vol 681 ◽  
pp. 142-154 ◽  
Author(s):  
Francesca Di Puccio ◽  
Enrico Ciulli
Keyword(s):  
Surface Roughness ◽  
Experimental Investigation ◽  
Friction Coefficient ◽  
Boundary Lubrication ◽  
Flat Surface ◽  
Surface Conditions ◽  
Lubrication Regimes ◽  
Line Contacts ◽  
Lubrication Conditions ◽  
Theoretical Procedure

An experimental investigation on the friction coefficient in line contacts under mixed and boundary lubrication regimes is described. Rectangular contacts between cylindrical specimens and the flat surface of discs of different material and surface roughness combinations were analyzed. Very low Stribeck numbers have been considered, resulting also in low dimensionless film thickness, so that the morphology of the surfaces and the material had a remarking role. In this work, the theoretical procedure for assessing the friction coefficient in the tested cases is described and compared to experimental results. Additionally, wear effects obtained in boundary lubrication conditions are shown. The surface conditions are put in relation with some particular trends of the friction coefficient obtained for certain combinations of materials and roughness.

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