Ohm Resistance Research Articles

An Activity Promoting the Practice of Quantitative Literacy for Pre- and In-Service Teachers of Mathematics and Science

The purpose of this article is to describe a hands-on, laboratory activity that provided pre-service teachers in mathematics and science methods courses, and also some in-service mathematics teachers, with the opportunity to exercise quantitative literacy (QL) skills. The focus of the activity is electrical resistance, more particularly the resistance (in ohms) that is painted on small resistors by the use of color-coded bands, one of which is a band for % error. The activity consists of four parts. In the first, student teams familiarize themselves with the code, measure the ohmage of resistors for which the codes are visible, and compare their measurements with the labels. In the second part of the activity, the teams measure the ohmage of many resistors—all from the same batch—on which the code bands have been covered. In the third part, they decide what statistics to use to determine the code bands that should be on their resistors, make poster presentations of their predictions, and then compare their predictions with the actual label. At the end of the third part of the activity, the student teams discover that their predictions do not match the labels, and they are placed in a cognitive conflict. In the fourth part of the activity—the QL part—they integrate what they have learned about the nano-, micro-, and macroscopic structure of resistors and the statistical measures that they used with what they can find out about marketing practices to present a written argument explaining the discrepancy. Preand post-tests show that students learn statistical and resistor material associated with the activity, and qualitative assessment of their written explanations of the discrepancy show that students had various levels of success at integrating their mathematical understanding with the science and business context of this measurement activity.

Transient expression of red and yellow fluorescent protein vectors in HCT-8 cells ınfected with Cryptosporidium parvum

Electroporation in combination with the red and yellow fluorescent protein (RFP and YFP, respectively) reporter systems results in transient gene expression in HCT-8 cell lines infected and uninfected with Cryptosporidium parvum. Conditions are described allowing efficient electroporation of HCT-8 cell monolayers in a commercial electroporation device (180 kV/cm voltage, 250 microF capacitance, and 0 ohm (ohm) resistance resulting in a time constant of 0.4 ms.). Fluorescent microscopy showed that uninfected HCT-8 cell monolayers achieved higher gene transfer and expression efficiencies than HCT-8 cells infected with C. parvum under similar conditions. Real-time melting curve and quantitation analysis of reverse transcription polymerase chain reaction amplicons are presented for the detection of all mRNA sample levels. Our findings demonstrate that C. parvum infection of HCT-8 cells may negatively affect the transient expression of RFP and YFP plasmids. The focus of this study was to achieve transient expression of reporter genes in HCT-8 cell lines and provide the basis for further analyses of gene regulation in protozoan. These approaches may provide to understanding the feasibility of gene transfer and expression efficiencies HCT-8 cell cultures by RFP and YFP containing the CMV promoter; they could serve as tools for gene transfer in mammalian cell.

P-974: Characterization of human semen electrical resistance (ER) using the Fertilitrac© ovulation predictor device

The Biosense Fertilitrac © fertility monitor is an intravaginal personal medical device that measures electrical resistance (in ohms) of the vaginal epithelium. It is presently in clinical trials to assess its utility for predicting ovulation in women. We observed that presence of semen in the vagina following intercourse causes spikes in vaginal ER measurements. This may lead to bias in prediction of ovulation especially in couples who are advised to have intercourse at regular intervals to achieve a pregnancy.

06/01517 Pulsed laser deposition-assisted patterning of aligned carbon nanotubes modified by focused laser beam for efficient field emission: Saurakhiya, N. et al. Carbon, 2005, 43, (10), 2128–2133

In this study, the optimized conditions of electrophoretic deposition (application potential, application time and concentration of stable graphene oxide (GO) suspension) for development of ultra-thin graphene film on copper substrate are introduced. The current density and deposition efficiency analysis, Ohm resistance measurement, SEM, FTIR and AFM techniques were done on prepared samples. The electrical conductivity of graphene coated copper substrate was increased three times more than bare copper. All of the carried tests showed that by increasing the key parameters of EPD, the average thickness of electrodeposited GO layers are increased continually so that the GO concentration effect is the most evident factor. The minimum sheet resistance and average thickness of electrodeposited RGO layers with uniform wrinkled morphology are achieved at EPD conditions of 2 V in 10 s and annealed at 200 °C for 1 min. The results of this research manifested that the EPD technique is a promising route to a low cost and well controllable method to fabricate a very conductive electrode base for electro-optical devices.

Extracellular Signal-regulated Kinases 1/2 Control Claudin-2 Expression in Madin-Darby Canine Kidney Strain I and II Cells

The tight junction of the epithelial cell determines the characteristics of paracellular permeability across epithelium. Recent work points toward the claudin family of tight junction proteins as leading candidates for the molecular components that regulate paracellular permeability properties in epithelial tissues. Madin-Darby canine kidney (MDCK) strain I and II cells are models for the study of tight junctions and based on transepithelial electrical resistance (TER) contain "tight" and "leaky" tight junctions, respectively. Overexpression studies suggest that tight junction leakiness in these two strains of MDCK cells is conferred by expression of the tight junction protein claudin-2. Extracellular signal-regulated kinase (ERK) 1/2 activation by hepatocyte growth factor treatment of MDCK strain II cells inhibited claudin-2 expression and transiently increased TER. This process was blocked by the ERK 1/2 inhibitor U0126. Transfection of constitutively active mitogen-activated protein kinase/extracellular signal-regulated kinase kinase into MDCK strain II cells also inhibited claudin-2 expression and increased TER. MDCK strain I cells have higher levels of active ERK 1/2 than do MDCK strain II cells. U0126 treatment of MDCK strain I cells decreased active ERK 1/2 levels, induced expression of claudin-2 protein, and decreased TER by approximately 20-fold. U0126 treatment also induced claudin-2 expression and decreased TER in a high resistance mouse cortical collecting duct cell line (94D). These data show for the first time that the ERK 1/2 signaling pathway negatively controls claudin-2 expression in mammalian renal epithelial cells and provide evidence for regulation of tight junction paracellular transport by alterations in claudin composition within tight junction complexes.

Characterization of transition metal oxide ceramic material for continuous thermocouple and its use as NTC fire wire sensor

The ceramic powder prepared from the mixture of Mn 3O 4 and La 2O 3 have been characterized for NTC behavior and the same have been used as CT 2C (continuous thermocouple) sensor in the form of a thin metal cable to detect over-heating. These materials have mega ohm resistance at room temperature and showed exponential drop in resistance with the rise in temperature over a temperature range of 100–400 °C. It has been observed that as the concentration of La 2O 3 increases from 0 to 10% the NTC behavior drops from (400–260 °C) ±10%. The material was pressed into pellets and sintered at 700 °C for 3 h resulting in good bonding strength. Electrical characterization of the material was done by measuring the resistance over a temperature range of 100–400 °C. The material showed reproducible NTC characteristics over the temperature range 400, 370, 340, 280, and 260 °C with decreasing thermistor constant values ( B = 9588, 9210, 8500, 5170, 3330 K −1) and activation energy (Δ E = 826, 794, 733, 445, 287 meV), respectively. The decrease in activation energy of the ceramic powder with increase in La 2O 3 concentration makes it possible to fabricate thermal sensors which can be used in different temperature ranges. The microstructure was studied using SEM and evidence of a sintered body with grain size around 1 μm was observed in the material. XRD analysis indicated the single-phase tetragonal structure of the ceramic material. The process of using this ceramic material for fabrication of 10 ft continuous fire wire sensor has been explained.

Effect of deposition inhomogeneity on the Ohm resistance of thin electroless copper layers

The electric Ohm resistivity ρ of electroless Cu layers on glass substrates as a function of deposition thickness is studied. Deviations up to 200 times from the standard resistivity (ρ∞ (Cu) = 1.7 μΩ cm) below 100 nm deposition thickness reported in other papers are confirmed. A comparative analysis shows different reasons for the higher resistivity of thin electroless layers and evaporated ones. A diagram with variables taken from the so-called Fuchs theory correct for thin evaporated metallic layers quantitatively illustrates conductance differences of electroless and evaporated layers. It is supposed that at electroless layers the isolated areas of deposition as well as the strong branching of the conducting circuits play major role. Calculation of the relative resistivity ρ/ρ∞ of a real sample show good agreement with the proposed model.

VALIDITY OF BIOELECTRICAL IMPEDANCE EQUATIONS FOR ESTIMATING FAT-FREE WEIGHT IN LEAN FEMALES

The present study examined the validity of bioelectrical impedance (BIA) equations for estimating fat-free weight (FFW) in lean males (X +/- SD = 9.1 +/- 2.2% fat) by comparing the estimates with values obtained from underwater weighing. Sixty-eight Caucasian male volunteers served as subjects. Cross-validation analyses included examination of the constant error (CE), standard error of the estimate (SEE), r, and total error (TE). The results indicated that the equations of Oppliger et al. (16), which resulted in small TE (1.70 kg) and CE (-0.02 kg) values, most accurately estimated FFW. Simple linear regression showed that FFW was more highly correlated with body weight (BW) (r = 0.98, P < 0.0001) and resulted in a lower SEE (1.68 kg) than either height2/resistance (Ht2/R) (r = 0.81, P < 0.0001; SEE = 5.12 kg) or the independent variable (weight x resistance)/height2 [WR/Ht2] utilized by the manufacturer of the BIA analyzer (r = 0.15, P > 0.05; SEE = 8.59 kg). Multiple regression showed that when WR/Ht2, Ht2/R, resistance, body mass index, Ht2, and/or Ht was added to the prediction equation, which utilized BW alone, they accounted for less than 1% additional variance and reduced the SEE by < or = 0.16 kg. The results indicated that BW alone estimated FFW as accurately as any of the BIA equations in lean males.

超伝導入門 第３章 現象論

On basis of the Meissner effect, which assures the reversibility of the normal-superconducting state transition, thermodynamical relations describing the difference in superconducting and normal states were derived in the preceding chapter. In this chapter, a two-fluid theory is described where the free electrons in the superconducting state are assumed to be a mixture of superelectrons that flow freely without resistance and normal electrons that have Ohm resistance. The theory is phenomological in that the property of the superelectron is based on experiment and the theory does not attempt to describe the nature and origin of the superelectrons.

Construction, electroporatic transfer and expression of ZpβypGH and ZpβrtGH in zebrafish

Recombinant transformation vectors (ZPβypGH and ZpβrtGH) consisting of fish growth hormone cDNA, and a reporter geneβ-galactosidase driven by fish promoter (Zp) were constructed. Freshly fertilized eggs of zebrafish (Brachydanio rerio) were electroporated at optimum conditions (0.07 kV voltage; 25 μF capacitance; 8 ohm resistance and 2 pulses) in the presence of one of these transformation vectors (100 μg circular DNNml). In either cases 72% of the electroporated eggs successfully hatched, in comparison to the 85% hatchability of the control eggs. Genomic DNA extracted from fins of randomly chosenF0 individuals was screened (by Southern blot hybridization); the transgenes were retained in the host genome of all the randomly chosen adult transformants. Fin-positive presumptive founder parents were crossed with control counterparts and the DNA of randomly chosenF1 progenies was screened for germline transformation. Southern analysis of chosenF1 progenies revealed the persistence of ZPβypGH or ZpβrtGH in 53% of theF1 progenies. Southern analyses of chosenF1 progenies and the frequency (53% ofF1 ZpβrtGH and 53% ofF1 ZP{β}ypGH) of transmission revealed the degree of mosaicism inF0 transformants. Expression was confirmed from the 3–4 times elevated levels of activity of the reporter gene and 30–40% accelerated growth of transgenicF0 andF1 progenies.

The electrical resistance of enamel—dentine cylinders. Influence of NaCl content in storage solutions

Objectives: To investigate the influence of different electrolyte concentrations on the electrical resistance of sound human enamel-dentine cylinders in vitro. Methods: Forty cylinders of 3-mm diameter and 2-mm length were drilled from 40 extracted caries-free third molar teeth. For ease of handling the samples were fixed in Perspex discs by means of a cyanoacrylate-adhesive. An a.c. source (frequency 500 Hz, amplitude 1 μA) with a high internal resistance was applied. Only Ohm's resistance was measured. The resistance measurements on the samples were made after storage in distilled water, 0.16 mM NaCl, 1.6 mM NaCl, 16 mM NaCl and 160 mM NaCl for 24 h. Results: The mean resistance values were 2026 ± 152, 1835 ± 178, 1605 ± 364, 483 ± 265 and 60 ± 33 kΩ, respectively. All values were statistically significantly different (Wilcoxon test; P < 0.0001). Conclusion: It is concluded that the choice of electrolyte solution influences the resistance values of the enamel-dentine samples. This effect should be taken into account when measuring electrical resistances in vivo and in vitro.

Methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants

Beef females (547) were included in three experiments to evaluate methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants. In the first experiment, heifers not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule or 48 h after implant removal). In the second experiment, females not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule) or progesterone concentrations < 1.5 ng/mL at implant removal (inseminated 48 h after implant removal). In the third experiment, heifers not pregnant to the first insemination were identified for insemination via progesterone concentrations (as in experiment 2) or anterior vagina electrical resistance values < 81 ohm resistance 48 h after implant removal (inseminated after resistance measured). All methods of identifying and inseminating nonpregnant females were equally effective (P > 0.10) and did not effect (P > 0.10) calving rates from the first and second AI.

Electrical properties of polyethylene highly filled with carbon

Carbon-filled polyethylene composites were fabricated and tested to establish the practical lower limit of their electrical resistivity at room temperature and to investigate the trade-offs between low resistivity and the magnitude of the resistance anomaly (i.e., a large positive temperature coefficient of resistivity) that appears when such composites are heated through the polyethylene crystalline melting transition. Carbon blacks with large particle size and low surface area provided low-resistivity composites having large resistance anomalies. The largest resistance anomalies were found in composites that were well mixed, but the room-temperature resistivity also increased in composites that were cycled repetitively through the crystalline-melting transition. A mixture of carbon blacks of two different sizes provided a lower resistance than was found in a material with the same fill of only the coarser black. By controlling the composition and the processing, composites were made with room-temperature resistivities lower than 0.2 ohm cm and resistance changes of at least 2 orders of magnitude. A resistance change of as much as 5 orders of magnitude was obtained for composites with room-temperature resistivities of only 1 ohm cm.

BACTERIAL TRANSLOCATION ACROSS ENTEROCYTES

Due to the inherent limitations of in vivo studies, the cellular mechanisms underlying the process of bacterial translocation (BT) across the intestinal epithelial barrier are poorly understood. Thus, we have utilized the Caco-2 intestinal cell line to study this process. Caco-2 cells were grown to confluence on semipermeable membranes contained in the upper compartment of a 2 compartment system. Cellular confluence and tight junction integrity was verified by measurements of the transepithelial electrical resistance in ohms cm2.BT was measured by culturing the bacteria (nonpathogenic Escherichia coli) that were able to cross the Caco-2 monolayer and were present in the bottom compartment, as well as by monitoring the passage of 1-micron fluorescent beads. Caco-2 cells were pretreated with several metabolic inhibitors: 1.0 mM sodium azide (oxidative phosphorylation), 10 micrograms/ml nocodazole (microtubule), 10 microM phalloidine (microfilament), and 5.0 micrograms/ml cytochalasin D (microfilament). To investigate the mechanisms of BT. Both bacteria and fluorescent beads crossed the Caco-2 monolayer. Azide had no effect on BT, while both nocodazole (n = 17) and phalloidine (n = 14) significantly decreased translocation of E. coli versus control monolayers (p < .05). Cytochalasin D increased BT versus control membranes, however this was associated with loss of tight junction integrity (transepithelial electrical resistance decreased from 201 +/- 79 to 87 +/- 6.4). BT across Caco-2 cells appears to be a polar process which is to some extent microtubule- and microfilament-dependent.

Transformation of Acetobacter xylinum with plasmid DNA by electroporation

Genetic analysis of Acetobacter xylinum, a cellulose-synthesizing bacterium, has been limited by lack of a successful transformation method. Transformation of A. xylinum was attempted using two broad-host-range plasmids (pUCD2 and pRK248) and a variety of transformation methods. Methods using CaCl 2, freeze/thaw treatments, and polyethylene glycol were unsuccessful. Transformation of a cellulose-negative strain of A. xylinum with plasmid DNA has been achieved with high-voltage electroporation. Electroporation conditions of 25 μF capacitance, 2.5 kV, 400 ohms resistance, and pulse lengths of 6–8 ms were applied to a cell/DNA mixture in a 0.2-cm cuvette. Plasmid pUCD2 transformed at an efficiency of 10 6–10 7 transformants/μg DNA and pRK248 yielded 10 5 transformants/μg DNA. The frequency of transformation increased linearly with increasing DNA concentration, while transformation efficiency remained constant. pUCD2 was recovered from transformants following chloramphenicol amplification and observed by agarose gel electrophoresis. Both plasmids could be reisolated from Escherichia coli after back-transformation with alkaline lysis DNA preparations from Acetobacter transformants. Electro-transformation of A. xylinum with plasmid DNA suggests its potential use for analysis of the A. xylinum genome.

Antimony electrodes

Antimony electrodes are clinically useful because of their low cost and simple construction; they have no glass to break. There is only a few hundred ohms resistance between an antimony pH electrode and the reference electrode so that the voltage generated can be recorded with simple low-impedance recorders linked to microcomputers. We used antimony pH electrodes with silver-silver chloride electrodes applied to the skin to measure the gastric pH in vivo and obtained erroneously high values. Using an ion-permeable dialysis chamber to surround electrodes in vivo, we showed that the discrepancy was caused by interference from gastric transmucosal potential difference. To circumvent the interference, we used a combination electrode constructed by embedding a monocrystalline antimony electrode and a silver-silver chloride reference electrode in dental acrylic. Antimony pH electrodes calibrated with commercial pH buffers also gave erroneous readings in HCl solutions of known pH. The erroneous readings were due, in part, to organic complex-forming ligands or organic salts such as potassium phthalate present in commercial buffer solutions. Accurate pH calibration can be obtained with citrate or acetate buffers or by using a normogram to correct for the errors introduced with commercial buffers. The combination antimony pH electrode has a number of potential clinical and research applications and simplifies obtaining accurate and reliable pH data in vivo.

Development of an optimized system for electroporation of Listeria species

Electroporation was used to facilitate transformation of Listeria species with plasmid DNA. Optimal conditions for transformation of L. monocytogenes were a field strength of 8.5 kV/cm, 200 Ohms resistance, 25 microF capacitor with a time constant of 5 ms. With these conditions, 3.9 x 10(6) transformants/micrograms DNA were obtained. Under the same conditions, L. innocua and L. ivanovii exhibited a frequency of transformation similar to that of L. monocytogenes but a somewhat lower level was obtained with L. seeligeri.

Evaluation of a new defibrillation pathway—The tongue-epigastric route. I. Experimental studies in dogs

The purpose of this study was to determine the efficacy of a tongue-epigastric defibrillation route in anesthetized dogs. Ventricular fibrillation was induced by rectangular pulses passed down a transvenous catheter into the right ventricle. Three groups of dogs were studied. Group I (15 dogs) received shocks from a 12 cm2 tongue electrode, a 50 cm2 circular, gelled self-adhesive electrode pad placed on the epigastrium and standard transthoracic defibrillator paddle electrodes. Shocks were given at energy levels of 50 to 460 joules (delivered energy, 50 ohm resistance). The success of the tongue-epigastric shocks in achieving defibrillation, and the resistance and current flow were determined at each energy level and compared with the same energy shocks from the standard transthoracic electrodes. In Group II (five dogs), comparisons were made between the 12 cm2 tongue electrode used in the first group of dogs and a larger tongue electrode of 40 cm2. In Group III (five dogs), intracardiac current flow (potential gradient) with tongue-epigastric and standard transthoracic electrodes was studied. In Group I, defibrillation success with the tongue-epigastric electrodes ranged from no success at 50 to 100 joules to 83% success at 460 joules. With standard transthoracic electrodes, success rates ranged from 65% at 50 joules to 100% at 300 joules. At all energies tested, the resistance was significantly higher and current significantly lower using tongue-epigastric compared with transthoracic electrodes. The higher tongue-epigastric resistance is probably related to the longer interelectrode distance; the correlation between interelectrode distance (x, in centimeters) and resistance (y, in ohms) in these dogs was y = 2.2x + 29.6, r = 0.78.(ABSTRACT TRUNCATED AT 250 WORDS)

The automated multiparameter analyzer for cells (AMAC) IIA, a true bridge circuit Coulter-type electronic cell volume transducer.

A true bridge Coulter effect (electronic cell volume) transducer has been developed. All resistances of this bridge are now the result of current flow through saline channels. Contamination by electrode products including gas bubbles has been completely eliminated since both power electrodes are now remote from the flow chamber. Since the orifice is in series with an approximately 10 K ohm resistance generated by a gel-filled capillary and a displacement rheostat, it floats electrically, at virtual ground. The other side of the bridge consists of a fluid side-wire. Removing the power electrode from the orifice outlet makes possible downward flow and the use of a single outer sheath, and eliminates noise generated by gas bubbles which could possibly be trapped. It should now be possible to combine this design with that of the AMAC III square orifice, to produce an electro-optical sorter where all parameters are measured simultaneously. This true bridge circuit possesses the further advantage that noise due both to the power supply and to overvoltage at the power electrodes is common-mode rejected, and any drift due to changes in electrode polarization is eliminated. Preliminary experiments confirm results with the AMAC II that hemoglobinopathies can be recognized by the increased coefficient of variation (CV) of the erythrocyte spectra.

Properties of cadmium stannate films prepared by r.f. sputtering from powder targets

Abstract The composition, electrical conductivity and optical transmission of sputtered thin films of Cd2SnO4 were studied in relation to r.f. sputtering power and deposition rate and also in relation to the effects of post-deposition heat treatment. Sputtering conditions can be varied to give a stoichiometric cadmium:tin ratio in the film at which the conductivity is shown to have a maximum value. Design data are given relating the transmission of coated soda glass to film resistance in ohms per square.