Determination of electronic polarizabilities of ions in orthosilicates

Pohl, Douglas G.; Eck, J. C.; Klaska, K.‐H.

doi:10.1107/s0567739478002119

Cited by 8 publications

(3 citation statements)

References 4 publications

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“…Pohl and Hawk (1966) have demonstrated the separation of viable and nonviable yeast cells using this technique in the last decade. It has also been extended to other biological cells, including canine thrombocytes, red blood cells, chloroplasts, mitochondria and bacteria (Pohl et al 1978). Cabrera and Yeager have presented a microfluidic flow cell for bacterial concentration utilizing electrokinetic effects (Cabrera and Yeager 2001).…”

Section: Introductionmentioning

confidence: 99%

“…This refers to the interaction of non-uniform electric field with polarization charges induced in any electrically neutral particle which results in differential forces and selective trapping over the electrodes causing the non homogenous electric field (Voldman et al 2000). It is a prominent technique widely used for manipulation and separation of large particles like cells (Pohl et al 1978). Pohl and Hawk (1966) have demonstrated the separation of viable and nonviable yeast cells using this technique in the last decade.…”

Section: Introductionmentioning

confidence: 99%

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Dielectrophoresis assisted concentration of micro-particles and their rapid quantitation based on optical means

Ghubade

Mandal

Chaudhury

et al. 2009

Biomed Microdevices

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The detection and counting of micro particles having sizes comparable to biological entities can provide a tremendous impetus to rapid diagnostics and clinical applications. MEMS technology has already been used in capture and detection of such micron size entities in miniscule concentrations. For this purpose a concentration step is normally added prior to the detection process. A variety of methodologies are used for quantization of such micron size particles/entities including change in permittivity, medium impedance, magnetic permeability and other means. Although optical studies have been extensively performed prior to this, it has not been used for quantization of the micro particles. We have designed, developed and characterized a MEMS counter which captures micron size fluorescent beads using delectrophoresis (DEP) and monitors their accumulation in a 12 μm x 230 μm size channel and monitors this accumulation as growth of overall fluorescence. The field is generated by a set of finely placed interdigitated microelectrodes. As we apply an alternating voltage at 10 V(pp) for a range of different frequencies we are able to capture the flowing beads and concentrate them by several orders of magnitude. This is also followed by their quantification in terms of growing fluorescence signal. For quantitating the fluorescence values a CCD (charge couple device) module fitted over an inverted fluorescence microscope is used that visualizes the whole capture process and a Labview based image acquisition software simultaneously calculates the signal intensity over these frames and arranges it temporally. Our work will have tremendous utility in developing a rapid bacterial counting procedure and will be a valuable tool in microbiological laboratories.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dielectrophoresis assisted concentration of micro-particles and their rapid quantitation based on optical means

Ghubade

Mandal

Chaudhury

et al. 2009

Biomed Microdevices

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show abstract

“…There are however additional difficulties with every improved model, leading to the conclusion that the problem of too many coefficients and not enough data cannot be easily removed. As pointed out by a number of authors (Spangenberg, 1923;Fajans & Joos, 1924;Born & Heisenberg, 1924;Bragg, 1925;Batsanov, 1966;Pohl, 1978;Pohl, Eck & Klaska, 1978) the polarizability of the anions varies with the size of the cation. Specifically, small cations tend to reduce the polarizability of the anions.…”

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confidence: 99%

Point-dipole theory and optical birefringence of calcite-type carbonates

Pohl¹,

Ram²

1979

Acta Cryst Sect A

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A critical survey of the literature has revealed that recent structure determinations and optical data are available for only three calcite-type carbonates: calcite, rhodochrosite and magnesite. For these structures, the limitations of the pointdipole approximation are discussed.The point-dipole model was introduced by Bragg (1924) to explain quantitatively the birefringence of calcite and aragonite with respect to the crystal structures. In this approach optical anisotropy arises from differences in dipole-dipole coupling along different crystallographic directions. This source of anisotropy is connected with the Lorentz-factor tensor. In addition, however, optical anisotropy may arise from an intrinsic anisotropy in the constituent ions. In this case electronic polarizability tensors should be considered.In order to investigate the relation between atomic arrangement and double refraction, the crystals of carbonates have been used repeatedly. The latest studies are those given by Isherwood &James (1976) andPohl (1978). In his paper Pohl (1978) has developed a method to determine the electronic polarizabilities of ions from structural and optical data by a least-squares fit. The method is based on Bragg's (1924) model of point dipoles and on an exact calculation of Lorentz-factor tensors. This model satisfactorily accounts for the double refraction of aragonite-type carbonates. In the present paper we discuss the application of the method to calcite-type carbonates.Structural parameters of only three calcite-type carbonates have been determined: calcite (Chessin, Hamilton & Post, 1965), rhodochrosite (Brown & Forsyth, 1967) and magnesite (Oh, Morikawa, Iwai & Aoki, 1973). Optical constants are given by Winchell & Winchell (1964). Application of Pohl's (1978) method yields the electronic polariz- Bragg's (1924) ideas, the birefringence arises from the oxygens within the isolated COl-groups: the stronger the birefringence the stronger the influence of the O z-ions on each other. Strengthening of the oxygen interaction can take place in two ways. Firstly, the distance between the carbon and oxygen can be diminished. Secondly, the polarizability of the oxygen ion can be increased. Since the C-O distance is fixed according to the structure determination, only an increased polarizability of the 0 2-ion remains. However, this results in an increased mean refractivity which in return is compensated by a smaller polarizability of the cation, thus explaining the above results.To overcome the shortcomings encountered with the Bragg model of point dipoles, two improvements may be considered. Firstly, the point dipoles can be positioned outside the atomic centers, because the outer electrons responsible for the optical effects may have a center of gravity distinct from that determined by X-rays. Secondly, an intrinsic anisotropy can be allocated to the polarizability of the ions. Both of these improvements involve the introcluction of at least one extra parameter. Thus the number of adjustable parameters will exce...

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Olivines, their polymorphs and related silicates (Text, tables)

Burzo

Landolt-Börnstein - Group III Condensed Matter

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Determination of electronic polarizabilities of ions in orthosilicates

Cited by 8 publications

References 4 publications

Dielectrophoresis assisted concentration of micro-particles and their rapid quantitation based on optical means

Dielectrophoresis assisted concentration of micro-particles and their rapid quantitation based on optical means

Point-dipole theory and optical birefringence of calcite-type carbonates

Olivines, their polymorphs and related silicates (Text, tables)

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