On the repulsive forces between charged colloid particles and on the theory of slow coagulation and stability of lyophobe sols.

1993 ◽  
Vol 43 (1-4) ◽  
pp. 15-27 ◽  
Author(s):  
B. Derjaguin
Author(s):  
Guan-Chung Ting ◽  
Kuang-Yuh Huang ◽  
Keng-Ning Chang

Bearings for high-speed rotors are the key component of dental handpieces. The friction induced by conventional ball bearings restricts its speed and reduces its efficiency. In order to significantly improve the efficiency of dental handpieces, a mini-type cartridge that integrates a turbine and a spindle with radial aerostatic bearings and axial passive magnetic bearings has been ingeniously designed and realized. Around the rotating spindle, there is a high-pressured air film built up by a pair of radial aerostatic bearings, and magnet rings are applied to create repulsive forces to axially support the rotating spindle. The high-pressured air film comes from the specifically designed separable orifice restrictors, which can be easily and precisely manufactured. Frictionless bearing effect can be achieved by aerostatic principle, and the magnetic principle is applied to create large repulsive force against the axial working force. A tri-directional air inlet is designed to reduce radial loading force of a spindle during working. The modularized form of the magneto-aerostatic bearing allows it to be easily assembled and replaced in the very compact space of a mini-type cartridge. Through analytical simulations with fluid-dynamics software (CFD) and experiments, the magneto-aerostatic bearing is optimized to bring out efficient performance in its limited space. The experiments have verified that its noise level is 15dB lower than the conventional cartridge with ball bearings, and its startup air pressure is reduced from 0.4 bar to 0.1 bar. Under the same operation conditions, the newly developed cartridge with magneto-aerostatic bearings creates twice higher speed than that of the conventional one.


1994 ◽  
Vol 72 (9-10) ◽  
pp. 633-638
Author(s):  
M. T. Attaf ◽  
D. Allab

In a previous work, the authors presented a semianalytical treatment of the electromagnetic field distribution in the case of a straight conductor carrying a sinusoidal current parallel to a thin conducting plate. The result of this investigation is extended here to the evaluation of the repulsive forces accompanying this type of electromagnetic interaction. The variation of such forces with geometric parameters is studied in the presence of a single conductor, and in the case of several conductors laying in a plane parallel to the surface of the material submitted to the induction phenomenon. The problem of lévitation in steady-state conditions is examined, in the light of this arrangement, for various conducting materials. Graphs illustrate the results obtained and make evident their practical interest particularly in the stationary case of magnetically levitated vehicles.


2011 ◽  
Vol 328-330 ◽  
pp. 547-550
Author(s):  
Gang Zheng ◽  
Ru Min Wang ◽  
Gao Yang Zhao ◽  
Zhong Yu

In this study, by using UV-visible adsorption spectrophotometer, ζ-potential analyzer and X-ray photo spectroscopy, the adsorption characteristics and surface electrochemical properties of WPS were studied in comparison with traditional naphthalene sulfonated formaldehyde condensates (FDN) whose dispersion ability mainly depends on electrostatic repulsive forces. WPS was prepared through free radical copolymerization in self-Single screw reactive extruder and synthesized from waste plexiglas and vinyl monomers by way of special extrusion modification. The results show that the adsorption of WPS and FDN on cement particle surface approximately conforms to Langmuir’s adsorption isotherm. The adsorption of WPS belongs to physical adsorption and its saturated adsorbed quantity was 5.38mg/g. When the dosage of WPS was 1 wt.% of cement, the thickness of the adsorption layer on the surface of cement particles was 61.2 nm. The ζ-potential of cement particle with WPS changed from positive (15 mV) to negative (-64.74mV) with its concentration increasing from 0 to 20 g/L and decreased from -65.19 to-39.82 mV (reducing by 38.9%) with its concentration of 10 g/L within 60 h.


Langmuir ◽  
2000 ◽  
Vol 16 (24) ◽  
pp. 9595-9603 ◽  
Author(s):  
Frank Caruso ◽  
Corinna Schüler

MRS Bulletin ◽  
1990 ◽  
Vol 15 (1) ◽  
pp. 41-47 ◽  
Author(s):  
Nikola Kallay

The adhesion of particles at solid surfaces in liquid media has attracted the attention of scientists because of its various applications as well as the theoretical significance of the processes involved. Early studies were characterized either by poorly defined systems or limited by the properties of a few morphologically well-defined model colloids, such as latex dispersions. Consequently, results were either of semiquantitative nature or were related to some specific cases, which eluded general conclusions. New methods for preparing uniform particles of different compositions, shapes, and sizes make it possible to approach the problem in a more comprehensive manner. For example, to demonstrate difficulties caused by polydispersity, it is sufficient to mention that the electrostatic interaction energy between a plane surface and a particle is approximately proportional to the particle radius, yet the rate of deposition depends exponentially on the height of the energy barrier.In principle, static and dynamic approaches may be employed in the study of particle adhesion. The static method yields the force required to detach an adhered particle, while kinetic investigations of attachment and detachment give the rates of the respective processes. Both methods offer information on the stability of the system in terms of the bond strength of adhered solids. For small colloid particles, which are the subject of thermal random Brownian motion, the dynamic approach is more appropriate. This article emphasizes the kinetics of deposition and detachment of small colloid particles in liquid media.


1989 ◽  
Vol 111 (2) ◽  
pp. 209-214 ◽  
Author(s):  
J. A. Tichy ◽  
K. A. Connor

The properties of magnetic bearings, particularly those based on repulsive forces due to eddy currents, are determined by a complex mixture of electrical and mechanical length and time scales. A perturbation solution for the magnetic field structure based on careful ordering of these parameters has permitted the effects of realistic gap geometries to be analyzed. The load capacity of eddy current journal bearings is found to be somewhat larger than previously predicted in an earlier paper which used magnetic fields based on constant gap size. The present results may be of interest to those concerned with calculating eddy currents in conventional attractive magnetic bearings.


2021 ◽  
Vol 50 (1) ◽  
Author(s):  
Berenike Maier

Biofilms are structured communities formed by a single or multiple microbial species. Within biofilms, bacteria are embedded into extracellular matrix, allowing them to build macroscopic objects. Biofilm structure can respond to environmental changes such as the presence of antibiotics or predators. By adjusting expression levels of surface and extracellular matrix components, bacteria tune cell-to-cell interactions. One major challenge in the field is the fact that these components are very diverse among different species. Deciphering how physical interactions within biofilms are affected by changes in gene expression is a promising approach to obtaining a more unified picture of how bacteria modulate biofilms. This review focuses on recent advances in characterizing attractive and repulsive forces between bacteria in correlation with biofilm structure, dynamics, and spreading. How bacteria control physical interactions to maximize their fitness is an emerging theme. Expected final online publication date for the Annual Review of Biophysics, Volume 50 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.


Author(s):  
A. Ya. Krasil’nikov ◽  
A. A. Krasil’nikov

The article considers the possibility of applying a standard method for calculating the repulsive force for a thick high-coercive permanent magnets from samarium-cobalt alloy in a magnetic system. The results of the research allowed us to introduce correction coefficients in the method of calculating the repulsive force in a magnetic system with such magnets, depending on the air gap between of them. It is shown that the repulsive forces of the North poles of permanent magnets differ from the repulsive forces of the South poles. The research was carried out with magnets manufactured by different enterprises. When calculating the repulsive force, the average value of the repulsive force between the North and South poles of magnets is found.


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