Passive Probe Research Articles

A passive probe for electrostatic charge density measurements

A probe has been developed to detect space charge density in flow streams. The probe not only measures the average space charge at a point, but also very small amplitude fluctuations up to 1 kHz. This electrostatic probe has a simple design and consists of a miniature central electrode and a hollow aerodynamically shaped shielding electrode for minimal flow disturbance. The high-frequency response of the probe and its simple design would make it desirable in many applications. Results of tests in a charged turbulent free jet flow of kerosene indicating the probe capabilities are presented.

A planar IrO multichannel stimulating electrode for use in neural prostheses

This paper describes a multisite stimulating probe capable of the precise delivery of sophisticated charge waveforms to neural structures on a chronic basis. The fabrication process for passive probes requires only four masks and is very high yield. Activated iridium oxide stimulating sites are shown to be compatible with the delivery of over 3 mC/cm 2/phase in biphasic charge-balanced operation. In order to minimize the number of external probe leads, on-chip circuitry has been defined to allow per-channel current control at the 8-bit level using serial input data and a total of five external leads.

Relationship between distention and absorption in rat intestine: II. Effects of volume and flow rate on transport

Studies in intact animals have shown that intestinal solute absorption may be enhanced with increasing intraluminal volume and flow rate, perhaps because of increases in functional absorptive surface area or perturbation of unstirred layers. We used single-pass perfusions of rat ileum, performed by simultaneously infusing and withdrawing at equal rates, to determine the separate effects of volume and flow rate on solute absorption at pressures between 3.0 and 12.5 cmH2O. Distention enhanced the absorption of passive probes (3H2O, urea), had no effect on the absorption of solutes transported by carrier mechanisms (d-glucose, l-alanine), and led to decreases in the net absorption of sodium and water whenever intraluminal pressure exceeded 10 cmH2O. Increasing flow rate enhanced the absorption of both glucose and 3H2O. However, the effects of increasing flow rate and distention on 3H2O were not additive. In the presence of higher filling volume, faster flow rate led to no further increases in 3H2O absorption; vice versa, at faster flow rate, no further increases in 3H2O absorption were noted when luminal volume was increased. We conclude that increased intraluminal volume enhances the absorption of solutes transported by passive but not carrier-mediated mechanisms, perhaps via augmentation of functional absorptive surface area. Increased flow rate and volume may increase the absorption of passively absorbed probes, in part, by a similar mechanism.

Coherence multiplexing of remote fibre optic fabry-perot sensing system

A monomode fibre optic coherence multiplexing sensor system incorporating passive miniature fibre optic probes is demonstrated using a coherence tuned local interferometer to sequentially interrogate the individual sensors. An example of its use as a high resolution relative point temperature measurement system is described with a range to resolution in excess of 10 4.

Shootdown: Flight 007 and the American Connection , and: The Target Is Destroyed (review)

BOOK REVIEWS 225 Wynia does provide insight into the incompetence and divisiveness ofthe military planners as well as their lack of preparedness for what is ostensibly their reason for existence, namely, protecting the national interest. Military officers, of all people, should know that if military adventurism is to be used to gain domestic support, the escapades must be successful. Junta leader General Leopoldo Galtieri and his associates used poor judgment in virtually every aspect of the invasion, from the actual decision to invade to the execution of the attack. The author then looks at the interaction among oligarchic factions and later, between the oligarchs, labor, and the military. Wynia observes a cyclical trend in Argentine politics, which was also noted by Rock. In essence, economic conditions determine who has the strongest voice in policy at a given time. The elites may tolerate a few years of populist policies that sought to redistribute wealth, but once inflation rises and investment drops, elites push for military intervention and subsequently introduce policies that are more growth-oriented. In the final chapter Wynia follows the rise of current President Raúl Alfonsm and his stunning victory in the election of 1983. He then analyzes — and praises strongly— Alfonsfn's management of the economic and political disaster he inherited from the military. Although the long-term results of his economic policies are as yet unknown, the political shrewdness he demonstrated in achieving their adoption as well as his tactful conduct of the trials of military leaders accused of human rights abuses show leadership abilities absent in Argentine leaders for many years. Alfonsfn's administrative ability and genuinely nonpartisan concern for Argentina make Wynia optimistic about the immediate prospects for democracy. This optimism is merited, but the resilience of democracy in Argentina will be severely tested when Alfonsm leaves office in 1989. At this time no promising successor to Alfonsm has emerged. The major illusion in Argentine politics is that a return to democracy is a panacea for all that ails the country; this is just not so. Wynia does not characterize the Argentine people as inherently antidemocratic (as some do) but rather as "maximizers" who are constantly trying to hedge their risks against the political and economic instability inherent in their system. It is largely their lack of confidence in compromise and democracy that causes Argentina's perennial instability. Shootdown: Flight 007 and the American Connection. By R.W. Johnson. New York: Viking Press, 1986. 335 pp. $18.95/cloth. The Target Is Destroyed. By Seymour Hersh. New York: Random House, 1986. 282 pp. $17.95/cloth. Reviewed by Michael Friend, M.A. candidate, SAIS. The controversy over the Soviet Union's destruction of Korean Air Lines flight 007 on 1 September 1983 is now well on its way to achieving equal status with "Who shot John F. Kennedy?" as the ultimate subject for flights of speculative ingenuity. R.W. Johnson's Shootdown and Seymour Hersh's The Target is Destroyed are, by one count, the fifth and sixth books in the 007 series, 226 SAIS REVIEW respectively, and if Hersh's book is not the equivalent of the single bullet theory, Johnson's work will tantalize anyone with a taste for conspiracy. In Shootdown, Johnson argues that the U.S. government, together with Korean Air Lines and (presumably) the Korean Central Intelligence Agency, arranged for flight 007 to penetrate Soviet airspace to act as a passive probe; this forced the Soviets to turn on their air defense systems, allowing U.S. listening stations and electronic intelligence aircraft to reap the benefits. Why send a civilian airliner? Because, says Johnson, the administration wished to avoid a U-2 incident and they did not think the Soviets would shoot at a civilian plane. The author is not deterred by the case of the 1978 shootdown of KAL flight 902, en route from Paris to Seoul, which apparently drifted off course near a major Soviet military base near Murmansk and was shot at and hit. More fortunate than flight 007, 902 managed a crash landing on a frozen lake in Karelia. Rather than ascribing the two incidents to mismanagement or poor pilot training, Johnson finds them highly...

Time-resolved impurity fluxes in the TEXTOR plasma edge

The internal configuration of the TEXTOR tokamak at Kernforschungsanlage (KFA) Jülich, Federal Republic of Germany, has been modified recently to include antennas for Ion Cyclotron Resonance Heating (ICRH) of the plasma. Passive deposition probe measurements of edge impurity fluxes were made for typical Ohmic discharges with this new liner configuration. The time-resolved behavior of impurities in the edge was determined as a function of radius and limiter position using rotating probe techniques. The dominant metallic impurities were found to be iron and the other components of stainless steel. Average deposited iron fluxes circulating along the field lines were found to be ∼1015/cm2 s at 5 cm behind the limiter radius. Radial profiles of the principal metallic impurities demonstrate a characteristic decrease with increasing radius outside the limiters and show an e-folding length of ∼1.9 cm. The limiting effects of the rf antenna are also evident in the radial profiles. Present results are compared with previous measurements of edge fluxes made prior to the modifications to the plasma-side liner of TEXTOR.

Impurity Flux Studies in the Limiter Shadow of the TEXTOR Tokamak

The temporal and radial dependence of the flux of impurity particles in the plasma scrape of layer in the TEXTOR tokamak is measured during a series of reproducible discharges by using passive collection probe techniques. Oxygen, titanium, chromium, iron and nickel impurities are detected. The flux of heavy impurities is observed to be reproducable. A typical peak value of the iron flux during a discharge is 2 · 1015 at./cm2 · s. No saturation effects of the measured amount of impurities on the probe surface is observed for surface densities of up to 5 · 1015 at./cm2, indicating that in this range losses due to possible release mechanisms of collected impurities are negligible. The e-folding length of the radial decay of the impurities detected on the probe surface is observed to vary with the discharge time. The value of the e-folding length is determined to be 20-30 mm at the flat top part of the discharge and about 13 mm at the end, for distances between 10 and 24 mm from the plasma edge.

Impurity measurements in the textor plasma edge using deposition probe techniques

Passive deposition probe techniques were used to characterize the impurities in the plasma edge region of the TEXTOR tokamak. Measurements were made as functions of radius, direction, and time using single crystal silicon collectors. Analysis of the probes was accomplished by Rutherford backscattering (RBS). The results indicate low impurity levels without impurity accumulation for 2.5 sec TEXTOR discharges.

Characterization of the TEXTOR plasma edge using deposition probe techniques

Carbon and single crystal silicon passive deposition probes were used to measure the characteristics of the plasma edge region of the TEXTOR tokamak. Analysis of the probes was done by Rutherford backscattering for impurities and nuclear reaction analysis and elastic recoil detection for hydrogen isotopes. Plasma fluxes and energies in the edge were measured using these techniques. The principal impurities in the plasma edge were determined and their behavior as a function of time and position was measured. Measurements were also made of in situ erosion rates. The results are compared with independent measurements of other plasma parameters to study possible impurity introduction mechanisms.

Impurity transport in the ASDEX edge plasma studied by a combination of passive and active probes with SIMS analysis

Radial profiles of impurity fluxes in the edge plasma of ASDEX are measured with collecting probes. Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) are used to analyse the collectors. The good agreement between the two methods indicates that the SIMS can be used as a new rapid analysis technique for large collectors. The impurity flux is found to decay exponentially with an e-folding length corresponding to the length of the flux tube in front of the probe, indicating that the flow is free streaming. Impurity ion temperatures are measured by means of an E × B analyser. A preliminary evaluation yields Fe ion temperatures of about 10 to 20 eV. Hence the cross field diffusion coefficient is estimated to be about 3 × 10 3 cm 2/s .

Probe measurements in the plasma boundary layer

A large variety of probes have been designed and used to improve our knowledge of the outermost plasma layer, the Scrape-Off-Layer (SOL). Such attempts are very instructive because the processes occurring in this region are barely known and because a precise knowledge of particle fluxes and temperatures is needed in order to correctly interpret plasma wall interactions. The probe systems are divided into two major groups. The first one includes the active probes, such as the Langmuir probes and particle analyzers, which work in real time, i.e., data is available during the discharge. The second group consists of passive probes, using specific collecting surfaces which are exposed to the discharge. Similar to a photographic plate, the surface keeps the information which is later “developed” using suitable surface analysis techniques. These probes are specifically used for high sensitivity studies such as impurity analysis. The aim of these probes is the measurement of plasma parameters. There is no comprehensive understanding of all involved processes so that plasma parameters can be deduced from experimental data. However, striking convergences are found between the data from different probes in different machines. Examples of agreements are the exponential decrease of ion fluxes with increasing distance from the plasma-edge and the different ion and electron temperatures in the SOL. A turbulent diffusion model is presented which gives a good description of the global particle confinement time and of the width of the SOL.

Singlet and Triplet Excitons as Probes for Chemical Reactivity

Abstract In most polynuclear hydrocarbons such as anthracane and its derivatives e.g. CH, CN, C1, OH compounds, photochemical reactivity is in direct competition with prompt fluorescence from the lowest singlet excited states. Accordingly, as reactivity proceeds the quantum yield of host emission decreases and products (guests) having different luminescence properties are formed. Thus the singlet exciton through its properties such as spectral distribution of emission, diffusion coefficient and lifetime may be considered an “active probe” for following such reactions. The triplet exciton on the other hand is not much involved in the reactivity of these systems and through its analogous properties is an efficient “passive probe” that allows us to study changes in the structure and chemical composition of the host-guest system as reactivity proceeds. The study of “dynamic” host-guest systems where the host: guest ratio is continually changing has its foundation in the vast literature available on similar “s...

A model passive probe for free atmosphere electric field measurements

A model of a passive probe for determination of electric field strength in the free atmosphere is developed. This model shows that the same probe can be used to determine mean monosigned ion conductivity and also conduction current density. Simulation of typical experimental conditions is used to derive the response to small altitude-dependent conductivity fluctuations. Results from a passive probe sounding indicate that conduction current density was nondivergent to (at least) 26 km and that small-scale conductivity fluctuations were only around ± 3% of the mean value.

Analysis of the penetrable space within the nucleus.

Radioactive glycogen molecules have been used as passive probes to compare cavity systems within nuclei and isolated chromatin. Isolated chromatin was found to possess a narrow range of microspaces with mean effective diameters between 4.0 and 4.5 nm (40 and 45 A) depending on shape assumptions. Intact nuclei contained a far larger class of free spaces with average diameters in the order of 11.0-15.0 nm. This clearly shows that DNase-I (diam. 4.1 nm) can penetrate and occupy a large proportion of nuclear space even though this enzyme does not readily attack the undisturbed nuclear structure. A structure which simulated the pattern of penetrability and incorporated other known properties of chromatin was used to explain this DNase-I resistance of intact nuclei in terms of an ordered, compact, local structure interspersed by much larger spaces. A system for this local packing is suggested and the functional implications of this type of organization considered.

Impedance approximations for resistive conductor cable

An asymptotic sequence of finite network approximations is obtained for the characteristic impedance at high frequencies of transmission line with constant series resistance. The model is relevant to the design of oscilloscope passive attenuator probes with nanosecond response time using low-capacitance cable with fine-resistance-wire centre conductor.

Nanosecond Passive Voltage Probes

Passive voltage probes with megohm input impedance at dc are traditionally understood as RC compensated dividers, but this is inadequate even for system rise times as slow as 100 ns. Qualitative understanding of faster probes is generally in terms of resistive damping of resonances, but this has been notably successful in practice only with the use of resistive conductor probe cable as introduced by Kobbe. This paper demonstrates that nanosecond probes can be understood and designed for a systematic transmission line viewpoint. The properties of the resistive conductor probe cable as a transmission line are an essential feature, and the original motivation for the use of resistive cable as damping of a resonance is seen to be largely irrelevant for nanosecond probes.

Experimental determination of the parameters of the field in the aperture of a sectorial horn by means of a passive probe

Experimental determination of the parameters of the field in the aperture of a sectorial horn by means of a passive probe

Transient heat transfer in human skin

Experiments are discussed which assess the influence of sudden, localized changes of thermal load on the conductance of human skin; the conductance is expected to change due to the thermal regulatory role of skin. The changes are produced by placing local areas of skin in contact with passive probes which are pre-heated or pre-cooled. It is found that the change in conductance is effectively independent of the surface temperature (and of the surface heat flux) to which the skin is exposed at the beginning of each test, for elapsed times exceeding one minute.

The Detonation Electric Effect

Electromagnetic signals have been found to originate from the wave fronts in detonating high explosives. The effect is that of small positive electric charge on the detonation front. For the liquid explosive, nitromethane, the amplitude of the detected signal increases smoothly as the wave approaches the detector. For particulate explosives there is superimposed on the signal a complex oscillatory pattern, the amplitude and frequency distribution of which are dependent on the kind of explosive, the particle size, and the presence of macroscopic disturbances of the detonation wave. Signal detection is achieved with an external passive probe, which has no effect on the explosive system under investigation and requires only a high-speed oscilloscope to record detonation events. These signals form the basis of a powerful new method for studying propagation times, initiation phenomena, and the structure of the detonation front.

Diffusion of Triplet Excitons in Anthracene Crystals

Diffusion of triplet excitons in anthracene crystals has been detected by time-dependent studies of the delayed blue fluorescence under varying spatial distribution of the exciting red light. The delayed fluorescence which results from triplet-triplet annihilation was used as a passive probe for detecting the triplets. The observed changes in the time dependence of the delayed fluorescence can be interpreted uniquely as due to triplet-exciton migration, and can be described by a diffusion equation. A diffusion constant of 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ was obtained for triplet diffusion in the $\mathrm{ab}$ plane of anthracene crystals at room temperature.