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Constant Voltage (constant + voltage)
Selected AbstractsSynergistic Effects of Iontophoresis and Jet Injector Pretreatment on the In-vitro Skin Permeation of Diclofenac and Angiotensin IIJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2000KENJI SUGIBAYASHI A non-needle syringe (jet injector) was utilized to increase skin permeation of drugs by iontophoresis. Briefly, physiological saline was initially flushed by the injector to make a pore in the stratum corneum of excised hairless rat skin, and the iontophoretic skin permeation of two model compounds, sodium diclofenac and angiotensin II, was followed using a 2-chamber diffusion cell. Constant voltage and constant current iontophoresis treatments were evaluated. Pretreatment using the jet injector alone resulted in about 13- and 22-fold increases in the steady-state flux of diclofenac and angiotensin II, respectively, through the skin, compared with non-treated controls. Jet injector pretreatment with constant voltage iontophoresis further enhanced skin permeation of diclofenac and angiotensin II, and the enhancement was also greater than that by constant voltage iontophoresis alone. Thus, a synergistic effect was observed. The ratio of enhancement was greater compared with the control. Jet injector pretreatment with constant current iontophoresis, however, did not always yield higher skin permeation of the drugs than injector pretreatment alone, although the lag time was shortened. The difference in the enhancement between the constant voltage- and constant current iontophoresis can be explained by the electric current through the excised skin. Constant current iontophoresis after a short period of constant voltage iontophoresis with multiple jet injector pretreatments may be the best way to increase drug permeability while preventing severe skin damage. [source] Pump-free and low-cost negative pressure sampling device for rapid sample loading in MCEELECTROPHORESIS, Issue 24 2009Hongmei Hu Abstract A pump-free and low-cost negative pressure sampling device for injecting well-defined non-biased sample plugs into the separation channel of MCE was developed. It was composed of a pipet bulb, a 3-way electromagnetic valve and a single voltage supply at constant voltage. A sub-atmospheric pressure was created by hand-pressing air out of the pipet bulb and retained in it by switching the 3-way electromagnetic valve at cutoff position. During the sample loading stage, the sub-atmospheric pressure in the pipet bulb was applied via a 3-way electromagnetic valve to the headspace of the sealed sample waste reservoir (SW). A pinched sample plug was formed at the channel intersection in less than 0.5,s. Once the 3-way electromagnetic valve was switched to connect SW to ambient atmosphere to release the vacuum in SW, electrophoresis separation was consequently activated under the electric potentials applied. Experimental results demonstrated the pump-free negative pressure sampling device worked well in a wide vacuum degree ranged from ,250 to ,30,mbar with a satisfactory analytical precision. The sample consumption for each cycle was calculated to be 51,12,nL under the sampling pressure. Theoretical deduction indicates that the volume of the pipet bulb can be further reduced to 1,mL, which is critical for minimizing the sampling device for MCE. [source] Analysis of sub-ppb levels of Fe(II), Co(II), and Ni(II) by electrokinetic supercharging preconcentration, CZE separation, and in-capillary derivatizationELECTROPHORESIS, Issue 20 2007Marek Urbanek Abstract The analysis of sub-ppb levels of Fe(II), Co(II), and Ni(II) in heat exchanger fluids of nuclear power plants is needed to monitor corrosion. A method involving preconcentration with electrokinetic supercharging (electrokinetic injection with transient ITP), CZE separation, and in-capillary derivatization with ortho -phenanthroline (o -Phe) for direct UV detection was thus developed. First, a multizone BGE was loaded into the capillary by successive hydrodynamic introduction of zones of (i) o -Phe-containing BGE, (ii) BGE for the zonal separation, and (iii) ammonium-based leading electrolyte. Metal cations were electrokinetically injected and stacked at the capillary inlet behind this last leading zone. Finally, a terminating electrolyte zone was hydrodynamically introduced. When a constant voltage was applied, metal ions kept on concentrating isotachophoretically, then separated in CZE mode, were complexed by migrating through an o -Phe zone, and finally detected by direct absorbance. To detect extremely thin peaks, it was attempted for the first time to focus the derivatization reagent by inducing a second transient ITP, before labeling analytes, already separated in CZE mode. With this arrangement, LODs were about 30,ppt in pure water. In heat exchanger fluid matrices containing 1000,ppm bore and 2,ppm lithium, only Fe(II) cation was detected among the three cations of interest at the 1,ppb level using the present method, and its LOD was about ten times higher, due to the lower loading rate during electrokinetic injection. [source] New Approach Toward Fast Response Light-Emitting Electrochemical Cells Based on Neutral Iridium Complexes via Cation TransportADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Tae-Hyuk Kwon Abstract Here, a new method is presented to increase the turn-on time and stability of light-emitting electrochemical cells (LECs). To this end, a neutral iridium complex (5) containing a pendant Na+ ion that is generally known to have a faster mobility in the solid film than bulky anions is introduced, instead of the classic ionic transition metal complex (iTMC) with counter anion (7). Synthesis, photophysical and electrochemical studies of these complexes are reported. In the device configuration of ITO/5 or 7+PEO (polyethylene oxide) (100,110,nm)/Au, as the voltage increases, complex 5 emits red light at ,3.6,V while complex 7 appears at ,5.6,V, although their electrochemical and photophysical gap are similar. Furthermore, at constant voltage, ,3,V, the turn-on time of complex 5 was less than 0.5,min, which is a 60-fold faster turn-on time compared to the iTMC (7) with PF6,. These results are presumably due to the faster delivery of the Na+ ions to the electrode compared to PF6, ions. Also, the device lifetime of complex 5 exhibits a six-fold increase in stability and a three-fold shorter time to reach maximum brightness at constant bias compared to the device made with complex 7. [source] Generating heat from conducting polypyrrole-coated PET fabricsADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005Akif Kaynak Abstract Heating effects in polypyrrole-coated polyethyleneterephthalate (PET)-Lycra® fabrics were studied. Chemical synthesis was employed to coat the PET fabrics by polypyrrole using ferric chloride as oxidant and antraquinone- 2-sulfonic acid (AQSA) and naphthalene sulfonic acid (NSA) as dopants. The coated fabrics exhibited reasonable electrical stability, possessed high electrical conductivity, and were effective in heat generation. Surface resistance of polypyrrole-coated fabrics ranged from approximately 150 to 500 ,/square. Different connections between conductive fabrics and the power source were examined. When subjected to a constant voltage of 24 V, the current transmitted through the fabric decreased about 10% in 72 h. An increase in resistance of conductive fabrics subjected to constant voltage was observed. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 194,207, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20040 [source] In vitro transdermal iontophoretic delivery of leuprolide,mechanisms under constant voltage applicationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2003Charu Kochhar Abstract The transdermal iontophoretic delivery of Leuprolide, a nonapeptide LHRH agonist was studied with the aim of understanding the mechanisms of iontophoresis. Permeation studies were carried out at pH 4.5 and 7.2, at which the average ionic valence of the drug molecule was roughly 2 and 1, respectively. Heat-separated human epidermal membrane was subjected to constant voltage within the range of 250 to 1000 mV during the iontophoretic phase. Iontophoretic enhancement at pH 7.2 was greated than at 4.5. A model for iontophoretic enhancement was developed that takes into consideration the membrane alterations caused by iontophoresis depicted as increased porosity and the permeation through lipid pathways of the stratum corneum. Model-based evaluation yielded that first, the porosity increased with the applied voltage to as much as three times the original at 1000 mV. Second, the lipid pathways contributed approx. 20% to the total permeation during the passive phase. Third, the electro-osmotic flow contributed significantly to the enhancement and its direction was from anode to cathode at pH 7.2 and the opposite at pH 4.5. The magnitude of the electro-osmotic flow was at pH 4.5 somewhat lower than at pH 7.2. Addition of a negatively charged water soluble peptide, Acetyl leucine leucinolyl phosphate as an adjuvant led to twofold increase in the enhancement factor at pH 4.5 and a decrease in the magnitude of the electro-osmotic flow from cathode to anode. Repeated iontophoretic applications of 250 mV on the same skin specimen resulted in same enhancement every time and did not cause any barrier alterations when applied for 1 h every 24 h, which was not the case if the duration between the two iontophoretic applications was only 3 h. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:84,96, 2003 [source] Synergistic Effects of Iontophoresis and Jet Injector Pretreatment on the In-vitro Skin Permeation of Diclofenac and Angiotensin IIJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2000KENJI SUGIBAYASHI A non-needle syringe (jet injector) was utilized to increase skin permeation of drugs by iontophoresis. Briefly, physiological saline was initially flushed by the injector to make a pore in the stratum corneum of excised hairless rat skin, and the iontophoretic skin permeation of two model compounds, sodium diclofenac and angiotensin II, was followed using a 2-chamber diffusion cell. Constant voltage and constant current iontophoresis treatments were evaluated. Pretreatment using the jet injector alone resulted in about 13- and 22-fold increases in the steady-state flux of diclofenac and angiotensin II, respectively, through the skin, compared with non-treated controls. Jet injector pretreatment with constant voltage iontophoresis further enhanced skin permeation of diclofenac and angiotensin II, and the enhancement was also greater than that by constant voltage iontophoresis alone. Thus, a synergistic effect was observed. The ratio of enhancement was greater compared with the control. Jet injector pretreatment with constant current iontophoresis, however, did not always yield higher skin permeation of the drugs than injector pretreatment alone, although the lag time was shortened. The difference in the enhancement between the constant voltage- and constant current iontophoresis can be explained by the electric current through the excised skin. Constant current iontophoresis after a short period of constant voltage iontophoresis with multiple jet injector pretreatments may be the best way to increase drug permeability while preventing severe skin damage. [source] Prediction of the location of stationary steady-state zone positions in counterflow isotachophoresis performed under constant voltage in a vortex-stabilized annular columnJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2007Schurie L. M. Harrison Abstract A theoretical model is presented and an analytical expression derived to predict the locations of stationary steady-state zone positions in ITP as a function of current for a straight channel under a constant applied voltage. Stationary zones may form in the presence of a countercurrent flow whose average velocity falls between that of a pure leader zone and of a pure trailer zone. A comparison of model predictions with experimental data from an anionic system shows that the model is able to predict the location of protein zones with reasonable accuracy once the ITP stack has formed. This result implies that an ITP stack can be precisely directed by the operator to specific positions in a channel whence portions of the stack can be removed or redirected for further processing or analysis. [source] Impact of varying pulse frequency and duration on muscle torque production and fatigue,MUSCLE AND NERVE, Issue 4 2007Chris M. Gregory PhD Abstract Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue. Muscle Nerve, 2007 [source] Magnetoelectric laminate based DC magnetic field sensorPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3 2008Makarand Karmarkar Abstract We report on a DC magnetic field sensor that utilizes magnetoelectric (ME) laminate composites. It consists of a ring-dot piezoelectric transformer laminated to a magnetostrictive disc. When a constant voltage is applied to the ring section of the piezoelectric layer at resonance, a stress is induced in the dot section. Then, if an external magnetic object is introduced in the vicinity of the dot section, the effective elastic stiffness is increased, altering the resonance frequency. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Porous anodic alumina thin films on Si: interface characterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008V. Gianneta Abstract Porous anodic alumina (PAA) thin films (thickness , 50nm) were fabricated on Si by anodization of thin Al films under constant voltage of 20 V in sulphuric acid aqueous solution. The films exhibit cylindrical vertical pores of diameter , 13,15 nm, arranged in hexagonal close packed structure. Electrochemical oxidation of the Si substrate through PAA, used as masking layer with openings in the pores, resulted in the formation of SiO2 dots at each pore tip. Two different kinds of films, namely with or without SiO2 dots at pore tips, were fabricated. In order to characterize the electrical quality of the interface of PAA thin films with Si, C-V and G-V measurements were performed on Metal-Insulator-Semiconductor (MIS) structures with Al metallization. The measurements were carried out in the voltage range +1.0 V to ,3.0 V in steps of 0.05 V and in the frequency range 1 MHz to 100 Hz. The typical form of C-V and G-V curves of a MIS structure was obtained. In order to determine the interface trap density Dit, C-f and G-f measurements were performed as a function of the applied gate voltage in the depletion region. Dit was evaluated following the Conductance Method (E. H. Nicollian, and J. R. Brews, MOS Physics and Technology (J. Wiley & Sons, New York, 1982), p. 222 [1]). Both types of samples exhibit values of Dit in the order of 1011 eV,1cm,2. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Protein Fractionation of Cowpea (Vigna unguiculata (L.) Walp) Leaf, Flower and Seed by Capillary Electrophoresis and Its Potential for Variety IdentificationCHINESE JOURNAL OF CHEMISTRY, Issue 4 2010Sirithon Siriamornpun Abstract The proteins of different faction of cowpea [Vigna unguiculata (L.) Walp] were fractionated by capillary electrophoresis (CE). The extracting solvent system was one of the most critical factors in the optimization exercise. To improve reproducibility, seed samples needed to be defatted with chloroform/methanol (V:V=2:1) as preferred prior to protein extraction. Proteins were extracted from seeds, leaves and flowers with 50% aqueous 1-propanol and separated on a 50 (m×20 cm fused silica capillary column using a UV detector at 200 nm. Separation was conducted at constant voltage (10 kV, 40°C), using iminodiacetic acid (pH 2.5) containing 0.05% hydroxypropylmethylcellulose (HPMC) and 20% acetonitile. The results showed that proteins extracted from all fraction of cowpea were successfully separated by CE in less than 20 min. Seed extracts provided the greatest number of eluted protein peaks, followed by flower and leaf, respectively. The seed-protein extracts provided unique CE patterns for different varieties; hence the seed was the tissue chosen as being most suitable for variety identification. As a result, an optimized procedure was developed to provide rapid identification of cowpea varieties, based on capillary electrophoregram patterns. [source] Electric current as a control variable in the electrospinning processPOLYMER ENGINEERING & SCIENCE, Issue 7 2006Ravikant Samatham In the electrospinning process submicron-diameter polymer fibers can be produced when a high potential difference is applied to a polymer drop suspended at the tip of a capillary. The electrospinning process is affected by a wide range of parameters, because of which controlling the properties of the fibers is difficult. This is the major hurdle in the development of practical applications of electrospun fibers along with its low productivity. Here we are proposing to use the electric current in the electrospinning process to control the "quality of the fibers". Electrospinning of a solution of polyacrylonitrile in dimethylformamide (PAN/DMF) was done by applying a programmed variable flow rate at different constant voltages. The electric current in the process was measured in real time. Four types of jet regimes were observed, electric current and the morphology of the fibers corresponding to these regimes were analyzed. A relation between the electric current, type of jet and morphology of the fibers has been established. The mechanical properties of electrospun fiber mats were also measured by a tensile testing method. POLYM. ENG. SCI. 46:954,959, 2006. © 2006 Society of Plastics Engineers [source] | |||||||||||||||||||