scholarly journals Orientational instability of the director in a nematic cell caused by electro-induced anchoring modification

2021 ◽  
Vol 24 (1) ◽  
pp. 13601
Author(s):  
O.S. Tarnavskyy ◽  
M.F. Ledney
Keyword(s):  
Liquid Crystal ◽  
Negative Ions ◽  
The Other ◽  
Cell Surfaces ◽  
Positive Ions ◽  
Threshold Voltages ◽  
A Cell ◽  
Director Reorientation ◽  
Orientational Transitions

We theoretically investigate the threshold for the director reorientation from the homeotropic state to the hybrid homeotropic-planar state and vice versa in a cell filled with a flexoelectric nematic liquid crystal (NLC) subjected to an electric field. The liquid crystal is doped by a CTAB-like substance, a part of molecules of which dissociates into positive and negative ions. The anchoring on one of the cell surfaces is assumed to be strong and homeotropic, while the other surface can adsorb positive ions which play the role of an orienting surfactant for NLC molecules on this surface. At certain voltages, the orientational transitions in the bulk of the NLC are possible due to the changing conditions for the director on the adsorbing surface. We calculate respective threshold voltages as functions of anchoring parameters. The existence of the critical values of these parameters, beyond which the orientational transitions do not take place, is established.

The role of negative ions on the Jeans instability in a complex plasma in the presence of nonthermal positive ions

2006 ◽  
Vol 13 (10) ◽  
pp. 102904 ◽  
Author(s):  
Banamali Roy ◽  
Susmita Sarkar ◽  
Manoranjan Khan ◽  
M. R. Gupta
Keyword(s):  
Negative Ions ◽  
Complex Plasma ◽  
Positive Ions ◽  
Jeans Instability

Surface-Induced Flexoelectric Domains in Asymmetrically Strong-Weak Anchored MBBA Films

1982 ◽  
Vol 37 (4) ◽  
pp. 334-341
Author(s):  
H. P. Hinov
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Dielectric Anisotropy ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Surface Anchoring ◽  
Threshold Voltages ◽  
Domain Period ◽  
Cell Thickness

Abstract The longitudinal surface-induced flexoelectric domains, previously obtained in symmetrically weak-anchored nematic layers have been further investigated in asymmetrically strong-weak anchored MBBA layers. The threshold voltages indicating the onset of the flexoelectric instabilities are high for thin cells (d = 9 μm, Uth = 10 V) and small for thick cells (d = 150 μm, Uth =1.5 V). Pronounced minima in the curves p vs. d and Uth vs. d, where p is the domain period and d is the cell thickness, were obtained. The flexoelectric domains were replaced by electrohydrodynamic instabilities only in the case of strong azimuthal anchoring of the liquid crystal layer.The role of the sign and the value of the dielectric anisotropy, the homogeneity of the electric field as well as the asymmetry in the surface anchoring are discussed in detail.

scholarly journals Dissociation, recombination and attachment processes in the upper atmosphere II. The rate of recombination

1939 ◽  
Vol 170 (942) ◽  
pp. 322-340 ◽  
Keyword(s):  
Negative Ions ◽  
Neutral Molecule ◽  
Upper Atmosphere ◽  
The Other ◽  
Negative Ion ◽  
Neutral Atoms ◽  
Attachment Rate ◽  
Additional Advantage ◽  
Positive Ions ◽  
Positive Ion

The ionized regions of the upper atmosphere include, not only neutral atoms and molecules, electrons and positive ions, but also negative ions. Of these, electrons are alone effective in producing reflexion of wireless waves; so that an electron attached to a neutral molecule to form a negative ion is as effectively removed from active participation in these phenomena as one recombined with a positive ion to form a neutral molecule. The decay of electron density at night has been attributed by some authors to recombination with positive.ions and by others to attachment by neutral molecules. The first process is in agreement with the observed law of decay and has the additional advantage of making it easily possible to understand the formation of layers of concentrated ionization; on the other hand, the chance of attachment to a molecule per impact would have to be extremely small for the attachment rate to be negligible, since the number of collisions per second with neutral atoms is very much greater than with positive ions.

Dynamic of Surface-Mediated Director Reorientation in a Cell with Dye Doped Liquid Crystal

2004 ◽  
Vol 421 (1) ◽  
pp. 235-242 ◽  
Author(s):  
D. Fedorenko∗ ◽  
E. Ouskova ◽  
Yu. Reznikov ◽  
V. Reshetnyak ◽  
L. Lucchetti ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
A Cell ◽  
Director Reorientation

scholarly journals The effect of small traces of water vapour on the velocities of ions produced by Röntgen rays in air

1910 ◽  
Vol 84 (569) ◽  
pp. 173-181 ◽  
Keyword(s):  
Electric Field ◽  
Water Vapour ◽  
Lateral Diffusion ◽  
Negative Ions ◽  
Complete Removal ◽  
The Other ◽  
Electric Force ◽  
Dry Air ◽  
Positive Ions ◽  
Low Pressures

Some experiments by Prof. J. S. Townsend on the lateral diffusion of a narrow stream of ions moving in an electric field led to the conclusion that negative ions in perfectly dry air are much smaller than those in air containing a small quantity of moisture. It was consequently to be expected that the complete removal of water vapour would cause an increase in the velocity with which negative ions move under the influence of an electric field of force. At his suggestion the following investigation of the velocities of ions in air at low pressures was undertaken, and it was found that, while the complete removal of water vapour had only a small effect on the velocities of positive ions, yet the same cause increased the velocities of the negative ions by a factor varying between 2 and 30 for the range of pressures and electric forces used in the experiments. The method adopted was to let the ions travel between two gauzes under a known electric force for a time t and then to reverse the field. If v is the velocity of the ions and d is the distance between the gauzes, then ions starting from one gauze will reach the other if t ≮ d / v . If t is gradually decreased, it is possible to find, by means of an electrometer, when ions cease to reach the second gauze; when this happens v = d / t .

scholarly journals Characterisation of corona-generated ions used in a Neutral cluster and Air Ion Spectrometer (NAIS)

2011 ◽  
Vol 4 (2) ◽  
pp. 2099-2125 ◽  
Author(s):  
H. E. Manninen ◽  
A. Franchin ◽  
S. Schobesberger ◽  
A. Hirsikko ◽  
J. Hakala ◽  
...  
Keyword(s):  
Detection Limit ◽  
Size Range ◽  
Negative Ions ◽  
Neutral Cluster ◽  
Differential Mobility ◽  
Size Spectra ◽  
Mixing Ratios ◽  
Positive Ions ◽  
Concentration Of Ions

Abstract. We characterized size and chemical composition of ions generated by a corona-needle charger of a Neutral cluster and Air Ion Spectrometer (NAIS) by using a high resolution differential mobility analyzer and a time-of-flight mass spectrometer. Our study is crucial to verify the role of corona-generated ions in the particle size spectra measured with the NAIS, in which a corona charger is used to charge aerosol particles down to the size range overlapping with the size of generated ions. The size and concentration of ions produced by the corona discharging process depend both on corona voltage and on properties and composition of carrier gas. Negative ions were <1.6 nm (0.8 cm2 V−1 s−1 in mobility) in all tested gas mixtures (nitrogen, air with variable mixing ratios of water vapour), whereas positive ions were <1.7 nm (0.7 cm2 V−1 s−1. Electrical filtering of the corona-generated ions and not removing all charged particles plays an important role in determining the lowest detection limit. Based on our experiments, the lowest detection limit for the NAIS in the particle mode is between 2 and 3 nm.

scholarly journals PPARs and Adipose Cell Plasticity

PPAR Research ◽  
2007 ◽  
Vol 2007 ◽  
pp. 1-7 ◽  
Author(s):  
Louis Casteilla ◽  
Béatrice Cousin ◽  
Mamen Carmona
Keyword(s):  
Adipose Tissue ◽  
Adipocyte Differentiation ◽  
The Other ◽  
Relative Importance ◽  
Cell Plasticity ◽  
Adipose Cell ◽  
A Cell ◽  
Definition Of ◽  
Adipose Cells

Due to the importance of fat tissues in both energy balance and in the associated disorders arising when such balance is not maintained, adipocyte differentiation has been extensively investigated in order to control and inhibit the enlargement of white adipose tissue. The ability of a cell to undergo adipocyte differentiation is one particular feature of all mesenchymal cells. Up until now, the peroxysome proliferator-activated receptor (PPAR) subtypes appear to be the keys and essential players capable of inducing and controlling adipocyte differentiation. In addition, it is now accepted that adipose cells present a broad plasticity that allows them to differentiate towards various mesodermal phenotypes. The role of PPARs in such plasticity is reviewed here, although no definite conclusion can yet be drawn. Many questions thus remain open concerning the definition of preadipocytes and the relative importance of PPARs in comparison to other master factors involved in the other mesodermal phenotypes.

scholarly journals Teratocarcinoma stem cell adhesion: the role of divalent cations and a cell surface lectin.

1983 ◽  
Vol 96 (6) ◽  
pp. 1532-1537 ◽  
Author(s):  
L B Grabel ◽  
M S Singer ◽  
G R Martin ◽  
S D Rosen
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Cell Adhesion ◽  
Cell Surface ◽  
Divalent Cations ◽  
Intercellular Adhesion ◽  
The Other ◽  
Calcium Dependent ◽  
A Cell

We describe two additive systems of intercellular adhesion in teratocarcinoma stem cells (Nulli cell line). One component is divalent cation-dependent (Ca++ or Mg++) and the other involves a cell surface fucan/mannan-specific lectin, previously identified on stem cells by an erythrocyte rosetting assay. The existence of these two systems is inferred from the observation that reaggregation of stem cells was partially inhibited by the removal of divalent cations or by the presence of lectin inhibitors such as fucoidan, but reaggregation was completely blocked when the two conditions were combined. Our results are related to recent work describing a calcium-dependent system of intercellular adhesion in teratocarcinoma stem cells.

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