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Steady-state and Dynamic Probe Characteristics in a Low-density Plasma

Description: The problem with which this investigation is concerned is that of determining the steady-state and dynamic characteristics of the admittance of a metallic probe immersed in a laboratory plasma which has the low electron densities and low electron temperatures characteristic of the ionospheric plasma. The problem is separated into three related topics: the design and production of the laboratory plasma, the measurement of the steady-state properties of dc and very low frequency probe admittance, and the study of transient ion sheath effects on radio frequency probe admittance.
Date: December 1970
Creator: Bunting, William David
Partner: UNT Libraries
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New Methodology For Use in Rotating Field Nuclear MagneticResonance

Description: High-resolution NMR spectra of samples with anisotropicbroadening are simplified to their isotropic spectra by fast rotation ofthe sample at the magic angle 54.7 circ. This dissertation concerns thedevelopment of novel Nuclear Magnetic Resonance (NMR) methodologies basedwhich would rotate the magnetic field instead of the sample, rotatingfield NMR. It provides an over of the NMR concepts, procedures, andexperiments needed to understand the methodologies that will be used forrotating field NMR. A simple two-dimensional shimming method based onharmonic corrector rings which can provide arbitrary multiple ordershimming corrections were developed for rotating field systems, but couldbe used in shimming other systems as well. Those results demonstrate, forexample, that quadrupolar order shimming improves the linewidth by up toan order of magnitude. An additional order of magnitude reduction is inprinciple achievable by utilizing this shimming method for z-gradientcorrection and higher order xy gradients. A specialized pulse sequencefor the rotating field NMR experiment is under development. The pulsesequence allows for spinning away from the magic angle and spinningslower than the anisotropic broadening. This pulse sequence is acombination of the projected magic angle spinning (p-MAS) and magic angleturning (MAT) pulse sequences. This will be useful to rotating field NMRbecause there are limits on how fast a field can be spun and spin at themagic angle is difficult. One of the goals of this project is forrotating field NMR to be used on biological systems. The p-MAS pulsesequence was successfully tested on bovine tissue samples which suggeststhat it will be a viable methodology to use in a rotating field set up. Aside experiment on steering magnetic particle by MRI gradients was alsocarried out. Some movement was seen in these experiment, but for totalcontrol over steering further experiments would need to bedone.
Date: May 18, 2007
Creator: Jachmann, Rebecca C.
Partner: UNT Libraries Government Documents Department
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Physical Limitations on the Measurement of Transient Fields in Air and in Dissipative Media Using Electric and Magnetic Probes

Description: The properties of electric and magnetic probes for the measurement of transient electromagnetic fields in air and in dissipative media are discussed briefly, It is shown that the effective height of an electrically small loop is independent of the ambient medium. This is also virtually true for a thin electrically short dipole (or monopole). If the open-circuit voltage of a magnetic probe can be measured accurately, it is possible (in principle) to reconstruct the time history of the incident magnetic field, even if the loop is immersed in dissipative media of unknown characteristics. The time function of the open-circuit voltage of an electric probe is essentially a replica of the time history of the incident electric field. In some schemes, the probes are lumped impedance loaded, and the voltage drop across the load impedances is measured. The source impedances of the probes are then involved in the equivalent circuits of the receiving antennas, and the leading terms in the expressions for these impedances depend on the properties of the environment. If an electrically short monopole is base-loaded by a capacitor divider, the voltage wave appearing across any capacitor is a faithful reproduction of the time sequence of the incident electric field provided the measurement is made in air or other dielectric. (auth)
Date: November 1, 1963
Creator: Harrison, C. W., Jr.
Partner: UNT Libraries Government Documents Department
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Investigations of Probe Induced Perturbations in a Hall Thruster

Description: An electrostatic probe used to measure spatial plasma parameters in a Hall thruster generates perturbations of the plasma. These perturbations are examined by varying the probe material, penetration distance, residence time, and the nominal thruster conditions. The study leads us to recommendations for probe design and thruster operating conditions to reduce discharge perturbations, including metal shielding of the probe insulator and operation of the thruster at lower densities.
Date: August 12, 2002
Creator: Staack, D.; Raitses, Y. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department
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TiO2 Nanoparticles as a Soft X-ray Molecular Probe

Description: With the emergence of soft x-ray techniques for imaging cells, there is a pressing need to develop protein localization probes that can be unambiguously identified within the region of x-ray spectrum used for imaging. TiO2 nanocrystal colloids, which have a strong absorption cross-section within the "water-window" region of x-rays, areideally suited as soft x-ray microscopy probes. To demonstrate their efficacy, TiO2-streptavidin nanoconjugates were prepared and subsequently labeled microtubules polymerized from biotinylated tubulin. The microtubules were imaged using scanning transmission x-ray microscopy (STXM), and the TiO2 nanoparticle tags were specifically identified using x-ray absorption near edge spectroscopy (XANES). These experiments demonstrate that TiO2 nanoparticles are potential probes for protein localization analyses using soft x-ray microscopy.
Date: June 30, 2007
Creator: Larabell, Carolyn; Ashcroft, Jared M.; Gu, Weiwei; Zhang, Tierui; Hughes, Steven M.; Hartman, Keith B. et al.
Partner: UNT Libraries Government Documents Department
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Dependence of secondary electron image contrast of periodic objects upon probe diameter

Description: The effect of probe diameter upon secondary electron image contrast of periodic objects has been studied systematically. Interest in the topic arose following the observation of out-of-focus SEM images of conventional mesh support grids, where the basic periodicity was visible even with probe diameters many times the periodic spacing. The instrument used was a JEM-120CX/ASID operated in the SEM mode at low magnification with the objective lens off and other lenses in the free-control mode. The probe diameter at the specimen position was controlled by the continuously variable second condenser lens current. The first intermediate lens was focussed at the specimen position, thus allowing a determination of the probe diameter from the magnified shadow image, which could be photographed using the conventional TEM camera. The specimen used was a copper bar grid with spacings approx. = 125 ..mu..m.
Date: January 1, 1979
Creator: Bentley, J & Carpenter, R W
Partner: UNT Libraries Government Documents Department
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Design and analysis of mismatch probes for long oligonucleotide microarrays

Description: Nonspecific hybridization is currently a major concern with microarray technology. One of most effective approaches to estimating nonspecific hybridizations in oligonucleotide microarrays is the utilization of mismatch probes; however, this approach has not been used for longer oligonucleotide probes. Here, an oligonucleotide microarray was constructed to evaluate and optimize parameters for 50-mer mismatch probe design. A perfect match (PM) and 28 mismatch (MM) probes were designed for each of ten target genes selected from three microorganisms. The microarrays were hybridized with synthesized complementary oligonucleotide targets at different temperatures (e.g., 42, 45 and 50 C). In general, the probes with evenly distributed mismatches were more distinguishable than those with randomly distributed mismatches. MM probes with 3, 4 and 5 mismatched nucleotides were differentiated for 50-mer oligonucleotide probes hybridized at 50, 45 and 42 C, respectively. Based on the experimental data generated from this study, a modified positional dependent nearest neighbor (MPDNN) model was constructed to adjust the thermodynamic parameters of matched and mismatched dimer nucleotides in the microarray environment. The MM probes with four flexible positional mismatches were designed using the newly established MPDNN model and the experimental results demonstrated that the redesigned MM probes could yield more consistent hybridizations. Conclusions: This study provides guidance on the design of MM probes for long oligonucleotides (e.g., 50 mers). The novel MPDNN model has improved the consistency for long MM probes, and this modeling method can potentially be used for the prediction of oligonucleotide microarray hybridizations.
Date: August 15, 2008
Creator: Deng, Ye; He, Zhili; Van Nostrand, Joy D. & Zhou, Jizhong
Partner: UNT Libraries Government Documents Department
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High-resolution magnetic imaging and investigations of thin-film magnetism with spin-polarized electron, ion and atom probes. Progress report, November 1, 1994--October 31, 1995

Description: This is a progress report for the period 1 November, 1994 to 31 October, 1995. Research during this grant year includes: (1) Completion of the Spin-Polarized Electron Energy Loss Spectroscopy (SPEELS) research program. (2) Design of an improved and much more intense metastable atom source that can also be converted to a Rydberg atom beam, for continuing studies utilizing Spin-Polarized Metastable (Atom) Deexcitation Spectroscopy (SPMDS), and to initiate new investigations of interactions of Rydberg atoms with surfaces. (3) Development of a spin-polarized He{sup +} ion source for studies of ion-surface interaction dynamics and epitaxially grown magnetic films utilizing Spin-Polarized Ion Neutralization Spectroscopy (SPINS).
Date: April 1, 1995
Creator: Walters, G. K. & Dunning, F. B.
Partner: UNT Libraries Government Documents Department
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Diagnostic Setup for Characterization of Near-Anode Processes in Hall Thrusters

Description: A diagnostic setup for characterization of near-anode processes in Hall-current plasma thrusters consisting of biased and emissive electrostatic probes, high-precision positioning system and low-noise electronic circuitry was developed and tested. Experimental results show that radial probe insertion does not cause perturbations to the discharge and therefore can be used for accurate near-anode measurements.
Date: September 8, 2003
Creator: Dorf, L.; Raitses, Y. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department
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Electrostatic Probe with Shielded Probe Insulator Tube for Low Disturbing Plasma Measurements in Hall Thrusters

Description: Electrostatic probes are widely used to measure spatial plasma parameters of the quasi-neutral plasma in Hall thrusters and similar ExB electric discharge devices. Significant perturbations of the plasma, induced by such probes, can mask the actual physics involved in operation of these devices. In Hall thrusters, probe-induced perturbations can produce changes in the discharge current and plasma parameters on the order of their steady state values. These perturbations are explored by varying the material, penetration distance, and residence time of various probe designs. A possible cause of these perturbations appears to be the secondary electron emission, induced by energetic plasma electrons, from insulator ceramic tubes in which the probe wire is inserted. A new probe in which a low secondary electron emission material, such as metal, shields the probe ceramic tube, is shown to function without producing such large perturbations. A segmentation of this shield further prevents probe -induced perturbations, by not shortening the plasma through the conductive shield. In a set of experiments with a segmented shield probe, the thruster was operated in the input power range of 500-2.5 kW and discharge voltages of 200-500 V, while the probe-induced perturbations of the discharge current were below 4% of its steady state value in the region in which 90% of the voltage drop takes place.
Date: July 10, 2003
Creator: D. Staack, Y. Raitses, and N.J. Fisch
Partner: UNT Libraries Government Documents Department
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Development of Neutron Probes for Characterization of Hazardous Materials in the Sub-surface Medium

Description: Neutron probes are being developed at the Idaho National Engineering and Environmental Laboratory (INEEL) for the detection, identification and quantification of hazardous materials in the ground. Such materials include plutonium, uranium, americium, chlorine and fluorine. Both a Neutron Gamma (NG) probe and a Prompt Fission Neutron (PFN) probe are being developed. The NG probe is used primarily for nuclide identification and quantification measurements. The PFN is used mostly for the detection and measurement of fissile material, but also for the determination of thermal neutron macroscopic absorption cross sections of the various elements comprising the ground matrix. Calibration of these probes will be carried out at the INEEL using an indoor facility that has been designed for this activity.
Date: May 15, 2002
Creator: Keegan, R.P.; McGrath, C.A. & Lopez, J.C.
Partner: UNT Libraries Government Documents Department
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Compact Probe for Power Detection from the Narrow Side of the Waveguide

Description: Phased array antennas with high directivity have a variety of applications. One of their applications is in RF heating for magnetically confined plasma fusion research. Among these RF heating schemes, waveguide arrays with careful phase control on each waveguide can act as a phased array antenna to deliver megawatts of power for heating fusion plasmas in the lower-hybrid range of frequencies (1 GHz-10 GHz). In order to achieve compactness, it is common to stack reduced height waveguide together to form the waveguide array. As long as the delivered power does not cause arcing in the waveguide, the waveguide height can be quite small. Due to this confined space in a stack of reduced height waveguides, power detection of the incident and reflected wave in the reduced height waveguide is extremely difficult. A new compact probe, which employs current loops, to monitor the incident and reflected wave from the narrow side of the reduced height waveguide has been developed. Its theory and performance will be reported in this paper.
Date: May 2004
Creator: Kung, C. C.; Bernabei, S.; Gumbas, J.; Greenough, N.; Fredd, E.; Wilson, J. R. et al.
Partner: UNT Libraries Government Documents Department
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Microwave simulation of laser plasma interactions. Final report

Description: Various electron and ion current, electric field, and magnetic field probes were developed and tested during the course of the investigation. A three dimensional probe drive system was constructed in order to investigate two and three dimensional phenomena occurring in the microwave plasma interaction. In most of the experiments reported here, a 1 GHz, 40 kilowatt, pulsed rf source (Applied Microwave), was used. The antenna was a 20/sup 0/ horn. A dipole fed parabolic antenna system capable of producing a focussed microwave beam at 2.3 GHz was developed and bench tested. This system will be used in future investigations at higher power levels (E/sub 0//sup 2//8..pi..nkappaT > 1).
Date: May 14, 1977
Partner: UNT Libraries Government Documents Department
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Corrosion probes for fireside monitoring in coal-fired boilers

Description: Electrochemical corrosion rate (ECR) probes were constructed and exposed along with mass loss coupons in a N2/O2/CO2/H2O environment to determine ECR probe operating characteristics. Temperatures ranged from 450 to 600 C and both ECR probes and mass loss coupons were coated with ash. Results are presented in terms of the probe response to temperature, the measured zero baseline, and the quantitative nature of the probes. The effect of Stern-Geary constant and the choice of electrochemical technique used to measure the corrosion rate are also discussed. ECR probe corrosion rates were a function of time, temperature, and process environment and were found to be quantitative for some test conditions. Measured Stern-Geary constants averaged 0.0141 V/decade and the linear polarization technique was found to be more quantitative than the electrochemical noise technique.
Date: January 1, 2004
Creator: Covino, Bernard S., Jr.; Bullard, Sophie J.; Cramer, Stephen D.; Holcomb, Gordon R.; Ziomek-Moroz, Margaret; Eden, David A. (Intercorr International Inc.) et al.
Partner: UNT Libraries Government Documents Department
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Comparisons Between Experimental Measurments and Numerical Simulations of Spheromak Formation in SSPX

Description: Data from a recently installed insertable magnetic probe array in the Sustained Spheromak Physics Experiment (SSPX) [E. B. Hooper et al., Nucl. Fusion 39, 863 (1999)] is compared against NIMROD [C. R. Sovinec et al., J. Comp. Phys. 195, 355 (2004)], a full 3D resistive magnetohydrodynamic code that is used to simulate SSPX plasmas. The experiment probe consists of a linear array of chip inductors arranged in clusters that are spaced every 2 cm, and spans the entire machine radius at the flux conserver midplane. Both the experiment and the numerical simulations show the appearance, shortly after breakdown, of a column with a hollow current profile that precedes magnetic reconnection, a process essential to the formation of closed magnetic flux surfaces. However, there are differences between the experiment and the simulation in how the column evolves after it is formed. These differences are studied to help identify the mechanisms that eventually lead to closed-flux surfaces (azimuthally averaged) and flux amplification, which occur in both the experiment and the simulation.
Date: March 15, 2006
Creator: Romero-Talam?s, C. A.; Hooper, E. B.; Hill, D. N.; Cohen, B. I.; McLean, H. S.; Wood, R. D. et al.
Partner: UNT Libraries Government Documents Department
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Status of the Tandem Mirror Experiment-Upgrade (TMX-U) diagnostic system

Description: This paper presents the current status of the Tandem Mirror Experiment-Upgrade (TMX-U) diagnostics system. For the initial instruments active on TMX-U, the expansions or upgrades that have been implemented are outlined. For the newly added systems, more implementation details are presented.
Date: November 26, 1983
Creator: Coutts, G.W.; Coffield, F.E. & Hornady, R.S.
Partner: UNT Libraries Government Documents Department
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Design of the electromagnetic fluctuations diagnostic for MFTF-B

Description: The Electromagnetic Fluctuations (EMF) diagnostic will be used to monitor ion fluctuations which could be unstable in MFTF-B. Each probe assembly includes a high impedance electrostatic probe to measure potential fluctuations, and a group of nested, single turn loops to measure magnetic fluctuations in three directions. Eventually, more probes and loops will be added to each probe assembly for making more detailed measurements. The sensors must lie physically close to the plasma edge and are radially positionable. Also, probes at separate axial locations can be positioned to connect along the same magnetic field line. These probes are similar in concept to the rf probes used on TMX, but the high thermal load for 30-second shots on MFTF-B requires a water-cooled design along with temperature monitors. Each signal channel has a bandwidth of .001 to 150 MHz and is monitored by up to four different data channels which obtain amplitude and frequency information. This paper describes the EMF diagnostic and presents the detailed mechanical and electrical designs.
Date: November 28, 1983
Creator: House, P.A.; Goerz, D.A. & Martin, R.
Partner: UNT Libraries Government Documents Department
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Semiconductor Quantum Rods as Single Molecule FluorescentBiological Labels

Description: In recent years, semiconductor quantum dots have beenapplied with great advantage in a wide range of biological imagingapplications. The continuing developments in the synthesis of nanoscalematerials and specifically in the area of colloidal semiconductornanocrystals have created an opportunity to generate a next generation ofbiological labels with complementary or in some cases enhanced propertiescompared to colloidal quantum dots. In this paper, we report thedevelopment of rod shaped semiconductor nanocrystals (quantum rods) asnew fluorescent biological labels. We have engineered biocompatiblequantum rods by surface silanization and have applied them fornon-specific cell tracking as well as specific cellular targeting. Theproperties of quantum rods as demonstrated here are enhanced sensitivityand greater resistance for degradation as compared to quantum dots.Quantum rods have many potential applications as biological labels insituations where their properties offer advantages over quantumdots.
Date: May 29, 2006
Creator: Fu, Aihua; Gu, Weiwei; Boussert, Benjamine; Koski, Kristie; Gerion, Daniele; Manna, Liberato et al.
Partner: UNT Libraries Government Documents Department
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Several Combination Probes for Surveying Static and Total Pressure and Flow Direction

Description: Report presenting an investigation to provide a basis for the design of combination probes intended to survey the static and total pressure and direction of flow with special reference to subsonic turbo-machine testing. Static-pressure probes, yaw-element probes, claw-type yaw probes, and combination probes were tested in an 8-inch-diameter calibration tunnel. The factors that determine the sensitivity of claw-type yaw probes were determined from this test.
Date: November 1952
Creator: Schulze, Wallace M.; Ashby, George C., Jr. & Erwin, John R.
Partner: UNT Libraries Government Documents Department
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Theory and design of a pneumatic temperature probe and experimental results obtained in a high-temperature gas stream

Description: Report presenting a discussion of the basic theory of pneumatic temperature probes and deviations from the basic theory in practical applications. Design requirements and operating conditions are discussed. Results regarding calibration tests and high-temperature tests and results are provided.
Date: January 1957
Creator: Simmons, Frederick S. & Glawe, George E.
Partner: UNT Libraries Government Documents Department
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Radiation and recovery corrections and time constants of several chromel-alumel thermocouple probes in high-temperature, high-velocity gas streams

Description: Report presenting an experimental determination of radiation and recovery corrections and time constraints for several designs of shielded and unshielded thermocouple probes using chromel-alumel wire. Radiation and time constant data were obtained for Mach numbers from 0.3 to 0.9 and a range of static pressures and temperatures. Tables and graphs are presented which show the correction factors of the various designs to aid in selecting a probe for a particular application.
Date: October 1956
Creator: Glawe, George E.; Simmons, Frederick S. & Stickney, Truman M.
Partner: UNT Libraries Government Documents Department
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Reducing Plasma Perturbations with Segmented Metal Shielding on Electrostatic Probes

Description: Electrostatic probes are widely used to measure spatial plasma parameters in the quasi-neutral plasma created in Hall thrusters and similar E x B electric discharge devices. Significant perturbations of the plasma, induced by such probes, can mask the actual physics involved in operation of these devices. In an attempt to reduce these perturbations in Hall thrusters, the perturbations were examined by varying the component material, penetration distance, and residence time of various probe designs. This study leads us to a conclusion that secondary electron emission from insulator ceramic tubes of the probe can affect local changes of the plasma parameters causing plasma perturbations. A probe design, which consists of a segmented metal shielding of the probe insulator, is suggested to reduce these perturbations. This new probe design can be useful for plasma applications in which the electron temperature is sufficient to produce secondary electron emission by interaction of plasma electrons with dielectric materials.
Date: October 2, 2002
Creator: Staack, D.; Raitses, Y. & N.J., Fisch
Partner: UNT Libraries Government Documents Department
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A study of vacuum arc ion velocities using a linear set of probes

Description: The most likely velocity of ions moving away from vacuum arc cathode spots was measured using a set of probes along the path of plasma expansion. The goal was to determine how much, if any, change of the ion drift velocity occurs in the expanded plasma. The arc discharge current was perturbed to create plasma density markers whose travel is picked up by the set of probes. It was found that the perturbation with current oscillations did not result in consistent data because ion current maxima and minima are not only determined by the plasma production but by the transients of the arc pulse and by the asymmetry of the ion velocity distribution function. Perturbation with a short current spike was more conclusive. The ion velocity was measured to be slightly reduced with increasing distance from the cathode, which can be explained by collisions of ions with the background of neutrals. The ion velocity was increased when the arc current was increased, which correlated with enhanced arc voltage and power dissipation. The ion velocity could be enhanced when the plasma was produced in a non-uniform magnetic field.
Date: July 15, 2008
Creator: Hohenbild, Stefan; Grubel, Christoph; Yushkov, Georgy Yu.; Oks, Efim M. & Anders, Andre
Partner: UNT Libraries Government Documents Department
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