Martin Misakian

Equations for the Magnetic Field Produced by One or More Rectangular Loops of Wire in the Same Plane

Beginning with expressions for the vector potential, the equations for calculating the magnetic flux density from up to three rectangular loops of wire in the same plane are derived. The geometry considered is the same as that found in some walk-through metal detectors and electronic article surveillance systems. Equations for more or fewer loops can be determined by inspection. A computer program for performing the magnetic field calculation is provided in an appendix.

Electrostatic Influence on Ion Transport through the αHL Channel

The current-voltage relationship of a single Staphylococcus aureus α-hemolysin (αHL) channel is nonlinear, rectifying, and depends on the bulk pH and the ionic strength. The data are described qualitatively by a simple one-dimensional Nernst-Planck analysis in which the fixed charges inside and near the pore’s entrances affect the transport of ions through the channel. The distances of these fixed charges from one of the channel’s entrances are obtained from the channel’s crystal structure. The model demonstrates that rectification of monovalent ion flow through the αHL channel can be related to the asymmetry in the location of the ionizable amino acid side chains.

Human CD4+ lymphocytes for antigen quantification: Characterization using conventional flow cytometry and mass cytometry

To transform the linear fluorescence intensity scale obtained with fluorescent microspheres to an antibody bound per cell (ABC) scale, a biological cell reference material is needed. Optimally, this material should have a reproducible and tight ABC value for the expression of a known clinical reference biomarker. In this study, we characterized commercially available cryopreserved peripheral blood mononuclear cells (PBMCs) and two lyophilized PBMC preparations, Cyto‐Trol and PBMC–National Institute for Biological Standard and Control (NIBSC) relative to freshly prepared PBMC and whole blood samples. It was found that the ABC values for CD4 expression on cryopreserved PBMC were consistent with those of freshly obtained PBMC and whole blood samples. By comparison, the ABC value for CD4 expression on Cyto‐Trol is lower and the value on PBMC–NIBSC is much lower than those of freshly prepared cell samples using both conventional flow cytometry and CyTOF™ mass cytometry. By performing simultaneous surface and intracellular staining measurements on these two cell samples, we found that both cell membranes are mostly intact. Moreover, CD4+ cell diameters from both lyophilized cell preparations are smaller than those of PBMC and whole blood. This could result in steric interference in antibody binding to the lyophilized cells. Further investigation of the fixation effect on the detected CD4 expression suggests that the very low ABC value obtained for CD4+ cells from lyophilized PBMC–NIBSC is largely due to paraformaldehyde fixation; this significantly decreases available antibody binding sites. This study provides confirmation that the results obtained from the newly developed mass cytometry are directly comparable to the results from conventional flow cytometry when both methods are standardized using the same ABC approach. Published 2012 Wiley Periodicals, Inc.

Generation and measurement of dc electric fields with space charge

Characterization of the electrical environment in the vicinity of high voltage dc transmission lines requires measurement of a number of electrical parameters associated with the lines. These parameters include the electric field strength with significant space‐charge contributions. This report describes an experimental effort to generate known dc electric fields containing controlled amounts of space charge. An apparatus which has been built for this purpose is described, and two types of field probes currently used for transmission line field measurements are examined with the apparatus. Limitations on the operation of one type of probe in the presence of very large current densities are identified and discussed.

Influence of a dielectric barrier on the stochastic behaviour of Trichel-pulse corona

The influence of a solid polytetrafluorethylene (PTFE) dielectric barrier on the stochastic behaviour of negative (Trichel) pulse corona discharges in air is examined. This behavior is revealed from measurement of conditional and unconditional corona pulse-amplitude and pulse-time--separation distributions. The results indicate that the presence of a dielectric surface on the anode effectively reduces the electric field at the point electrode, but does not affect the occurrence of Trichel pulses, provided the point-to-plane gap spacing is greater than a critical value d/sub c/ which depends on the area of the dielectric and the applied voltage. As the gap spacing approaches d/sub c/, the effect of dielectric-surface charging by the corona introduces measurable memory effects indicated by correlations between pulse amplitude and time separation from the previous pulse. For spacings less than d/sub c/, detachable corona-pulse activity is quenched by the presence of a quasi-permanent surface charge on the dielectric. >

Time-resolved measurements of ion energy distributions and optical emissions in pulsed radio-frequency discharges

In pulse-modulated inductively coupled plasmas generated in CF4:Ar mixtures, a transition between a capacitive coupling mode (E mode) and an inductive coupling mode (H mode) was observed. For a pulsed plasma in a 50%CF4:50%Ar volume mixture with a peak rf power of 200 W at 13.56 MHz and a modulation frequency at 500 Hz with a duty cycle of 95%, the E→H mode transition occurs repetitively 0.75 ms after each rf pulse is applied. This long delay in the mode transition allows us to perform not only time-resolved measurements of optical emission and electrical characteristics but also time-resolved measurements of ion energy distributions at the grounded electrode. These measurements show that a relatively short rf off period can severely perturb the equilibrium plasma state and its recovery may take much longer than the rf off period.

Measurement of Ion Current Density at Ground Level in the Vicinity of High Voltage DC Transmission Lines

Sensors for measuring vertical current density at ground level near high voltage dc (HVDC) transmission lines are subject to error when the sensor is not in the ground plane. The magnitude of this error, for guarded and unguarded sensors, has been investigated using hoth dc electric fields with space charge and ac electric fields in a parallel plate facility. For conditions like those expected under HVDC transmission lines, the results obtained using ac and dc methods agreed to within experimental uncertainty. The measuired errors are as large as 25 percent for guarded sensors and significantly larger for unguarded sensors. Data for various sensor elevations and guarding are presented in graphs to aid the designer. Comparisons with results from an IEEE Working Group field day are also presented.

Miniature ELF electric field probe

A miniature ac electric field probe having direct electrical connections with its battery-operated electronics is described. Because its small size introduces little field perturbation, fields generated by relatively small electrode structures in laboratory environments can readily be characterized.

Ion fluxes and energies in inductively coupled radio-frequency discharges containing CHF3

Measurements of ion energy distributions, relative ion intensities, and absolute total ion current densities were made at the grounded electrode of an inductively coupled Gaseous Electronics Conference (GEC) radio-frequency reference cell for discharges generated in CHF3 and its mixtures with argon. In general, the dominant ion species detected were not due to direct ionization of the CHF3 feed gas. Results are presented for plasmas generated with and without a confining quartz annulus that has recently been used to extend the operating parameter range of inductively coupled GEC cells for certain etching gases. Compared to similar plasmas generated without the annulus, the presence of the ring increases the ion flux density by approximately a factor of 2, and increases the mean ion energies. The presence of the ring does not significantly affect the measured relative ion intensities.

Distributions of measurement error for three-axis magnetic field meters during measurements near appliances

Comparisons are made between the average magnetic flux density as it would be measured with a single-axis coil probe and the flux density at the center of the probe, assuming that the probe is oriented to measure the maximum field at that point. Probability distributions of the differences between the two quantities are calculated assuming a dipole magnetic field and are found to be asymmetric. The distributions are used to estimate the uncertainty for maximum magnetic field measurements at distances that are large compared with the dimensions of the field source.