Direct current electric field

Electrodialysis. Electro dialysis processes transfer ions of dissolved salts across membranes, leaving purified water behind. Ion movement is induced by direct current electrical fields. A negative electrode (cathode) attracts cations, and a positive electrode (anode) attracts anions. Systems are compartmentalized in stacks by alternating cation and anion transfer membranes. Alternating compartments carry concentrated brine and purified permeate. Typically, 40—60% of dissolved ions are removed or rejected. Further improvement in water quaUty is obtained by staging (operation of stacks in series). ED processes do not remove particulate contaminants or weakly ionized contaminants, such as siUca. 

Of greater interest in recent years have been the peculiar piezolectric properties"" of polyfvinylidene fluoride). In 1969 it was observed" that stretched film of the polymer heated to 90°C and subsequently cooled to room temperature in a direct current electric field was 3-5 times more piezoelectric than crystalline quartz. It was observed that the piezolectric strain coefficients were higher in the drawn film and in the normal directions than in the direction transverse to the film drawing. 

Cooper, M.S., Schliwa, M. (1986). Motility of cultured fish epidermal cells in the presence and absence of direct current electric fields. J. Cell Biol. 102, 1384-1399. 

The pAf values of all functional groups of an amino acid dictate its net charge at a given pH. pi is the pH at which an amino acid bears no net charge and thus does not move in a direct current electrical field. 

Electroremediation is a method for the in situ removal of heavy-metal and organic compounds from low-permeability soils by the application of direct-current electric fields. These fields induce the transport of water and contaminants to wells where they are pumped to the surface. Massachusetts Institute of Technology (MIT) developed the Electroremediation technology, which is commercially available through Corrpro Companies Incorporated. 

In the quadrupole mass analyzer, focusing electrodes direct and accelerate the ionized fragments into a mass filter consisting of four cylindrical electrodes in a vacuum. Tire cylindrical electrodes establish a combination radio-frequency and direct-current electrical field that permits only those ions with a specific, selected mass-to-charge ratio to pass all the way through the filter. The rest of the ions impact die electrodes and do not travel to the exit. Varying the electrical field allows ions with other masses to pass through the filter. 

Figure 26-37 Separation of 2 000- to 23 000-Da DNA fragments by sieving through quartz pillars in a capillary electrophoresis channel on a quartz plate. [From N. Kaji, Y, Tezuka, Y. Takamura, M. Uedo. T. NisNmoto, H. Nakanishi, Y. Horiike. and Y. Baba, Separation of Long DNA Molecules by Quartz Nanopillar CNps Under a Direct Current Electric Field," Anal. Chem 2004, 76, IS.]...

Kaji, N., Tezuka, Y., Takamura, Y., Ueda, M., Nishimoto, T., Nakanishi, H., Horiike, Y., Baba, Y., Separation of long DNA molecules by quartz nanopillar chips under a direct current electric field. Anal. Chem. 2004, 76, 15-22. 

A second commonly used mass analyzer is the quadrupole. A quadrupole acts as a mass filter, allowing a certain mass-to-charge ratio of ions to be transmitted while filtering out all others. The quadrupole consists of a set of four electrodes positioned in an array. Superimposed radio frequency and direct current electric fields can be mutually tuned to allow transmission of ions of the selected mass-to-... 

A plasma is an efficient way to dissociate gas molecules to produce non-equilibnum concentrations of gas-phase species, such as the high concentrations of atomic hydrogen needed for diamond growth. Plasmas can be generated by a number of energy sources (microwave, radio-frequency, or direct-current electric fields), and can be either cold (non-isothermal, or nonequilibrium plasmas) or hot (isothermal, or equilibrium plasmas). The major characteristics of these plasmas are summarized in Table 3. 

Zhou DM, Chen HE, Chang L, Wang Y. (2007). Ryegrass uptake of soil Cu/Zn induced by EDTA/EDDS together with a vertical direct-current electrical field. Chemosphere 67(8) 1671-1676. 

V. Duzhko, K.D. Singer, Self-assembled fibers of a discotic phthalocyanine derivative internal structure, tailoring of geometry and alignment by a direct current electric field. J. Phys. Chem. C 111, 27-31 (2007)... 

Kaji N et al (2004) Separation of long DNA molecules by quartz nanopillar chips under a direct current electric field. Anal Chem 76(1) 15-22... 

An alternative method is electrokinetic focusing, which uses a direct current electric field (at high voltages of 1 kV) to focus particles and Uquids into a narrow stream. Typically, the sample fluid stream is driven along the central channel of a cross-shaped channel. As the sample enters the intersection, three fluid streams meet and the sample stream is focused into narrow stream. Dielectrophoresis (DEP) can also be used for sample focusing. DEP is the movement of polarized particles in a nonuniform electric field. This phenomenon is explained further in the next section. The main advantage of this... 

Lee CP, Chang HC, Wei ZH (2012) Charged droplet transportation under direct current electric fields as a cell carrier. Appl Phys Lett 101 014103... 

It has been observed that Pc derivatives 37 (Scheme 3.11) self-assemble out of solution into fibers with well-defined internal structure and controlled external geometry [109]. Floating Pc fibers have been shown to lie in a planar way onto an ITO substrate in the absence of an electric field. When the field is turned on, the planar fibers stand up with their long axes oriented along the direction of the electric field and hence perpendicular to the surface of ITO substrate. Strong interaction of the self-assembled fibers with the direct current electric field allows for their homeotropic or planar alignment on the conductive substrates for controlling the orientation. 

Hz in repetition rate), after increasing a direct-current electric field applied between the parallel Cu plates of electrodes, stable PLASLA is formed at an electric field of 400 V, which is inadequate to form DC-plasma (direct current plasma), which is formed by the direct discharge at a potential of 500 V without laser ablation. The oscilloscope trace of PLASLA luminescence signal in Fig. 1(b) indicates that plasma is formed by the first laser ablation, quenched by the next ablation, formed again by the third ablation, quenched again by the fourth ablation, and so on, indicating that the PLASLA formation and quenching completely synchronize with laser ablation. 

Further, it is possible to simultaneously manipulate the particles via DC-DEP as well as Unear electrophoresis in the same DC field. It should be noted that non-uniformities in the electric field are most effective when they occur over length scales comparable to a cell (< 10 p,m) in order for the cell to experience a significant dielectrophoretic force. Methods to embed insulators in the path of direct current electric field lines have varied. The next section wiU discuss these strategies. 

Tapscott et al. [7] have also examined electrostatic separation of spent abrasive. In this process, spent plastic abrasive is injected into a high-voltage, direct-current electric field. Material separation depends on the attraction of the particles for the electric field. In theory, metal contaminants can be separated from nonmetal blasting debris. In practice, Tapscott and colleagues reported, the process sometimes produced fractious with heavier metal couceutratious, but the separatiou was iusufficieut. Neither fractiou could be treated as uouhazardous waste. lu geueral, the results were erratic. 

Hammerick, K. E., A. W. James et al. 2010. Pulsed direct current electric fields enhance osteogenesis in adipose-derived stromal cells. Tissue Eng Part A 16(3) 917-31. 

If the coherent vibration of these dipoles is essential, the pulsing electric field is expected to be much more effective than the direct current electric field (DC field), as long as the coherent frequency components are contained. Therefore, the present study has been performed mainly with a pulsing electric field. 

---