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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Dimensional analysis on microscale gas breakdown with electric field nonuniformity and positive space charge effects

A dimensional method was employed to evaluate the microscale gas breakdown characteristics at atmospheric pressure, resulting in a universal breakdown curve applicable to different types of gases (e.g., Ar, Xe, Ne, and N2). As the gap distance decreases, the breakdown mode transitions from ion-induced secondary electron emission to the field emission regime. In the field emission regime, the positive space charge effect becomes more significant. We discovered that incorporating the positive space charge effect in the field emission regime can be achieved by modifying the local electric field enhancement factor β. Consequently, we propose an effective electric field enhancement factor, βeff, which scales linearly with β, to accurately reproduce the breakdown curve while considering the positive space charge effect. This proposed approach significantly simplifies the numerical model. Additionally, we examined the effects of gas pressure, gap distance, cathode properties (e.g., work function and secondary electron emission coefficient), and electric field nonuniformity.

Physics↗
NASA NTRS1978

The calibration of photographic and spectroscopic films: 1: A microscopic analysis of IIaO films. 2: The effects of agitation and soaking on IIaO films. 3: The effects of electric field on IIaO films. 4: The effects of X-ray radiation on IIaO films

The grain structure of the emulsion using both reflected and transmission light was examined along with the effects of soaking. The effect of a static charge by a Tesla-coil, and the effects of airport equipment, and dental X-rays on the film were also analyzed.

Hammond, E. C., Jr.↗
NASA NTRS1995

A universal steady state I-V relationship for membrane current

A purely electrical mechanism for the gating of membrane ionic channel gives rise to a simple I-V relationship for membrane current. Our approach is based on the known presence of gating charge, which is an established property of the membrane channel gating. The gating charge is systematically treated as a polarization of the channel protein which varies with the external electric field and modifies the effective potential through which the ions migrate in the channel. Two polarization effects have been considered: 1) the up or down shift of the whole potential function, and 2) the change in the effective electric field inside the channel which is due to familiar effect of the effective reduction of the electric field inside a dielectric body because of the presence of surface charges on its surface. Both effects are linear in the channel polarization. The ionic current is described by a steady state solution of the Nernst-Planck equation with the potential directly controlled by the gating charge system. The solution describes reasonably well the steady state and peak-current I-V relationships for different channels, and when applied adiabatically, explains the time lag between the gating charge current and the rise of the ionic current. The approach developed can be useful as an effective way to model the ionic currents in axons, cardiac cells and other excitable tissues.

NASA Discipline Regulatory Physiology↗
NASA NTRS1989

Bounds on current collection from the far field by plasma clouds in the ionosphere

Plasma clouds can enhance the collection of current to a charged body in the ionosphere in two ways. The first is by providing a large collection area for ionospheric electrons to be collected. The second is by ionization of neutral gas in the vicinity of the plasma cloud. The collection of electrons across a magnetic field is examined, and it is shown that the effective collection area is limited to the region of the cloud where the magnetic field effects are overwhelmed by the electric field effects from the charged body. Upper and lower bounds are obtained for the radius of the core region where the electric field influence dominates. From these, upper and lower bounds are obtained for the current collection.

Hastings, D. E.↗
NASA NTRS2003

Effects Of Electric Field On Hydrocarbon-Fueled Flames

It has been observed that flames are susceptible to electric fields that are much weaker than the breakdown field strength of the flame gases. When an external electric field is imposed on a flame, the ions generated in the flame reaction zone drift in the direction of the electric forces exerted on them. The moving ions collide with the neutral species and change the velocity distribution in the affected region. This is often referred to as ionic wind effect. In addition, the removal of ions from the flame reaction zone can alter the chemical reaction pathway of the flame. On the other hand, the presence of space charges carried by moving ions affects the electric field distribution. As a result, the flame often changes its shape, location and color once an external electric field is applied. The interplay between the flame movement and the change of electric field makes it difficult to determine the flame location for a given configuration of electrodes and fuel source. In normal gravity, the buoyancy-induced flow often complicates the problem and hinders detailed study of the interaction between the flame and the electric field. In this work, the microgravity environment established at the 2.2 Second Drop Tower at the NASA Glenn Research Center is utilized to effectively remove the buoyant acceleration. The interaction between the flame and the electric field is studied in a one-dimensional domain. A specially designed electrode makes flame current measurements possible; thus, the mobility of ions, ion density, and ionic wind effect can be evaluated.

Yuan, Z.-G.↗
NASA NTRS1972

Random walk study of electron motion in helium in crossed electromagnetic fields

Random walk theory, previously adapted to electron motion in the presence of an electric field, is extended to include a transverse magnetic field. In principle, the random walk approach avoids mathematical complexity and concomitant simplifying assumptions and permits determination of energy distributions and transport coefficients within the accuracy of available collisional cross section data. Application is made to a weakly ionized helium gas. Time of relaxation of electron energy distribution, determined by the random walk, is described by simple expressions based on energy exchange between the electron and an effective electric field. The restrictive effect of the magnetic field on electron motion, which increases the required number of collisions per walk to reach a terminal steady state condition, as well as the effect of the magnetic field on electron transport coefficients and mean energy can be quite adequately described by expressions involving only the Hall parameter.

Englert, G. W.↗
DOE OSTI2020

Investigating the effect of electric fields on lead halide perovskites by scanning tunneling microscopy

Lead halide perovskites have emerged as promising absorber materials over the last decade to increase the efficiency of photovoltaics beyond its current limits. However, to further optimize the performance of perovskites, more detailed studies need to be performed which allow for the correlation of film morphology and local electronic properties at the nanoscale. In this paper, we present a scanning tunneling microscopy (STM) approach to probe the effect of an applied electric field of a methylammonium formamidinium lead triiodide perovskite thin film on the film response by current-voltage spectroscopy, current imaging tunneling spectroscopy, differential conductance mapping and X-ray absorption spectroscopy (XAS) by means of synchrotron X-ray STM (SX-STM). We find a strong correlation between the measurement conditions and the obtained current-voltage characteristics when imaging under opposite applied bias polarities. In particular, we find similarities to already observed poling effects for perovskites which result in either a positively or negatively charged interface due to ion and vacancy migration. Our results provide insight into the influence of measurement conditions such as bias polarity on the performance assessment of perovskite thin films by STM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effect of an electric field on liquid helium scintillation produced by fast electrons

The dependence on applied electric field (0–40 kV/cm) of the scintillation light produced by fast electrons and α particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution of the Debye-Smoluchowski equation, we show that the apparent temperature dependence for electrons can be explained by the time required for geminate pairs to recombine relative to the detector signal integration time. This finding indicates that the spatial distribution of secondary electrons with respect to their geminate partners possesses a heavy, non-Gaussian tail at larger separations and has a dependence on the energy of the primary ionization electron. Here, we discuss the potential application of this result to pulse shape analysis for particle detection and discrimination.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Microsecond Pulsed Electric Fields: An Effective Way to Selectively Target and Radiosensitize Medulloblastoma Cancer Stem Cells

Cancer stem cells constitute an endless reserve for the maintenance and progression of tumors, and they could be the reason for conventional therapy failure. New therapeutic strategies are necessary to specifically target them. In this context, microsecond pulsed electric fields have been selected to expose D283Med cells, a human medulloblastoma cell line resulted to be rich in cancer stem cells, and normal human astrocytes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗