40 CFR 205.54-2 - Sound data acquisition system.

Code of Federal Regulations, 2014 CFR

2014-07-01

... energy as the sinusoidal signal centered at 1000 Hz shall be no greater than 0.5 dB. A true rms voltmeter... described in IEC Publication 179, Precision Sound Level Meters. (v) Magnetic tape recorders. No requirements.... (3) General comments. (i) Calibrate tape recorders using the brand and type of magnetic tape used for...

40 CFR 205.54-2 - Sound data acquisition system.

Code of Federal Regulations, 2011 CFR

2011-07-01

... energy as the sinusoidal signal centered at 1000 Hz shall be no greater than 0.5 dB. A true rms voltmeter... described in IEC Publication 179, Precision Sound Level Meters. (v) Magnetic tape recorders. No requirements.... (3) General comments. (i) Calibrate tape recorders using the brand and type of magnetic tape used for...

Use of plant woody species electrical potential for irrigation scheduling

PubMed Central

Ríos-Rojas, Liliana; Morales-Moraga, David; Alcalde, José A; Gurovich, Luis A

2015-01-01

The electrical response of plants to environmental stimuli can be measured and quantitatively related to the intensity of several stimulating sources, like temperature, solar radiation, soil water content, evapotranspiration rates, sap flow and dendrometric cycles. These relations can be used to assess the influence of different environmental situations on soil water availability to plants, defined as a steady state condition between leaf transpirative flow and soil water flow to plant roots. A restricted soil water flow due to soil dryness can trigger water stress in plants, if the atmospheric evaporative demand is high, causing partial stomata closure as a physiological response to avoid plant dehydration; water stressed and unstressed plants manifest a differential electrical response. Real time plant electrical response measurements can anticipate actions that prevent the plant reaching actual stress conditions, optimizing stomata gas exchange and photosynthetic rates. An electrophysiological sensor developed in this work, allows remote real-time recording information on plant electrical potential (EP) in the field, which is highly related to EP measurements obtained with a laboratory Keithley voltmeter sensor used in an highly controlled experimental setup. Our electrophysiological sensor is a wireless, autonomous devise, which transmits EP information via Internet to a data server. Using both types of sensors (EP electrodes with a Keithley voltmeter and the electrophysiological sensor), we measured in real time the electrical responses of Persea americana and Prunus domestica plants, to induced water deficits. The differential response for 2 scenarios: irrigation and water restriction is identified by a progressive change in slope on the daily maximal and minimal electric signal values in stressed plants, and a zero-slope for similar signals for well-watered plants. Results show a correspondence between measured signals obtained by our electrophysiological sensor and the EP electrodes connected to the Keithley voltmeter in each irrigation stage. Also, both sensors show a daily cyclical signal (circadian cycle). PMID:25826257

Use of plant woody species electrical potential for irrigation scheduling.

PubMed

Ríos-Rojas, Liliana; Morales-Moraga, David; Alcalde, José A; Gurovich, Luis A

2015-01-01

The electrical response of plants to environmental stimuli can be measured and quantitatively related to the intensity of several stimulating sources, like temperature, solar radiation, soil water content, evapotranspiration rates, sap flow and dendrometric cycles. These relations can be used to assess the influence of different environmental situations on soil water availability to plants, defined as a steady state condition between leaf transpirative flow and soil water flow to plant roots. A restricted soil water flow due to soil dryness can trigger water stress in plants, if the atmospheric evaporative demand is high, causing partial stomata closure as a physiological response to avoid plant dehydration; water stressed and unstressed plants manifest a differential electrical response. Real time plant electrical response measurements can anticipate actions that prevent the plant reaching actual stress conditions, optimizing stomata gas exchange and photosynthetic rates. An electrophysiological sensor developed in this work, allows remote real-time recording information on plant electrical potential (EP) in the field, which is highly related to EP measurements obtained with a laboratory Keithley voltmeter sensor used in an highly controlled experimental setup. Our electrophysiological sensor is a wireless, autonomous devise, which transmits EP information via Internet to a data server. Using both types of sensors (EP electrodes with a Keithley voltmeter and the electrophysiological sensor), we measured in real time the electrical responses of Persea americana and Prunus domestica plants, to induced water deficits. The differential response for 2 scenarios: irrigation and water restriction is identified by a progressive change in slope on the daily maximal and minimal electric signal values in stressed plants, and a zero-slope for similar signals for well-watered plants. Results show a correspondence between measured signals obtained by our electrophysiological sensor and the EP electrodes connected to the Keithley voltmeter in each irrigation stage. Also, both sensors show a daily cyclical signal (circadian cycle).

Rapid testing of pulse transformers

NASA Technical Reports Server (NTRS)

Grillo, J.

1980-01-01

Quality-control testing of pulse transformers is speeded up by method for determining rise time and droop. Instead of using oscilloscope and square-wave generator to measure these characteristics directly, method uses voltmeter and sine-wave generator to measure them indirectly in about one-tenth time. Droop and rise time are determined by measuring input/output voltage ratio at just four frequencies.

Physics Demonstrations with the Arduino Board

ERIC Educational Resources Information Center

Kubínová, Štepánka; Šlégr, Jan

2015-01-01

In everyday praxis we often need to demonstrate measuring devices--such as thermometers, manometers and voltmeters--with large enough displays that they can easily be read from anywhere in the classroom. In some cases, computers with a measurement interface can be used as a substitute, but often this is not possible (for example in the lab or in…

A Different Approach to Studying the Charge and Discharge of a Capacitor without an Oscilloscope

ERIC Educational Resources Information Center

Ladino, L. A.

2013-01-01

A different method to study the charging and discharging processes of a capacitor is presented. The method only requires a high impedance voltmeter. The charging and discharging processes of a capacitor are usually studied experimentally using an oscilloscope and, therefore, both processes are studied as a function of time. The approach presented…

Measuring Multi-Megavolt Diode Voltages

NASA Astrophysics Data System (ADS)

Pereira, N. R.; Swanekamp, S. B.; Weber, B. V.; Commisso, R. J.; Hinshelwood, D. D.; Stephanakis, S. J.

2002-12-01

The voltage in high-power diodes can be determined by measuring the Compton electrons generated by the diode's bremsstrahlung radiation. This technique is implemented with a Compton-Hall (C-H) voltmeter that collimates the bremsstrahlung onto a Compton target and bends the emitted Compton electron orbits off to the side with an applied magnetic field off to Si pin diode detectors. Voltage is determined from the ratio of the Compton electron dose to the forward x-ray dose. The instrument's calibration and response are determined from coupled electron/photon transport calculations. The applicable voltage range is tuned by adjusting the position of the electron detector relative to the Compton target or by varying the magnetic field strength. The instrument was used to obtain time-dependent voltage measurements for a pinched-beam diode whose voltage is enhanced by an upstream opening switch. In this case, plasmas and vacuum electron flow from the opening switch make it difficult to determine the voltage accurately from electrical measurements. The C-H voltmeter gives voltages that are significantly higher than those obtained from electrical measurements but are consistent with measurements of peak voltage based on nuclear activation of boron-nitride targets.

Music Generated by a Zn/Cu Electrochemical Cell, a Lemon Cell, and a Solar Cell: A Demonstration for General Chemistry

ERIC Educational Resources Information Center

Cady, Susan G.

2014-01-01

The circuit board found in a commercial musical greeting card is used to supply music for electrochemical cell demonstrations. Similar to a voltmeter, the "modified" musical device is connected to a chemical reaction that produces electricity. The commercial 1 V battery inside the greeting card circuit board can be replaced with an…

Measuring Electrostatic Discharge

NASA Technical Reports Server (NTRS)

Smith, William C.

1987-01-01

Apparatus measures electrostatic-discharge properties of several materials at once. Allows samples charged either by friction or by exposure to corona. By testing several samples simultaneously, apparatus eliminates errors introduced by variations among test conditions. Samples spaced so they pass at intervals under either of two retractable arms. Samples are 2 inches wide along circular path. Arm tips and voltmeter probe are 6 inches from turntable center. Servocontrolled turntable speed constant within 0.1 percent.

Sensors and detectors based on superconducting devices. (Latest citations from the NTIS Bibliographic database). Published Search

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1993-10-01

The bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity wave experiments, geomagnetism, galvanometers, voltmeters, bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for SQUIDS (superconducting quantum interference devices). (Contains 250 citations and includes a subject term index and title list.)

SUNRAYCE 1995: Working safely with lead-acid batteries and photovoltaic power systems

NASA Astrophysics Data System (ADS)

Dephillips, M. P.; Moskowitz, P. D.; Fthenakis, V. M.

1994-05-01

This document is a power system and battery safety handbook for participants in the SUNRAYCE 95 solar powered electric vehicle program. The topics of the handbook include batteries, photovoltaic modules, safety equipment needed for working with sulfuric acid electrolyte and batteries, battery transport, accident response, battery recharging and ventilation, electrical risks on-board vehicle, external electrical risks, electrical risk management strategies, and general maintenance including troubleshooting, hydrometer check and voltmeter check.

USU AFOSR University Engineering Design Challenge Proposal

DTIC Science & Technology

2015-01-02

gauge, voltmeter, on/off switch Handle ◦ Aluminum, 7.5 in. wide Skirt ◦ EVA foam, abrasion resistant Friction strip ◦ Stealth Rubber 8 12/28/2014 5 Hose...0.962 Tensile Strength [Gpa] 3.2 2.9 1.103 Abrasion Resistance [cycles to failure] 286 83 3.446 Impact Resistance [Energy @ penetration, in-lbs] 125...combination of) terrain to extricate equipment and personnel in situations where the scene is actively on fire or burnt and have exposed sharp metallic

Sensors and detectors based on superconducting devices. (Latest citations from the Aerospace database). Published Search

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1993-09-01

The bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity wave experiments, geomagnetism and ocean bottom magnetic exploration, galvanometers and voltmeters, astronomical telescopes, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors. (Contains a minimum of 97 citations and includes a subject term index and title list.)

A new method of carboxyhaemoglobin determination.

PubMed Central

Sanderson, J H; Sotheran, M F; Stattersfield, J P

1978-01-01

A quick and accurate method of determining the concentration of carboxyhaemoglobin (COHb) in blood has been developed. The method uses a dual wavelength double beam spectrophotometer in the 1st derivative mode, linked to a digital voltmeter (DVM), with the two beams set 3 nm apart around an isobestic point of reduced haemoglobin (Hbred) and carboxyhaemoglobin at 579 nm. The 1st derivative mode measures the slope, and this slope is proportional to the concentration of COHb. PMID:629892

High resolution spectroscopic measurements of carbon dioxide and carbon monoxide

NASA Technical Reports Server (NTRS)

Chaney, L. W.

1972-01-01

A modified 1.83 meter Jarrell-Ash spectrometer is reported. The instrument was double passed and achieved a resolution of 0.05 cm at 15 micrometers. An integrating voltmeter was used to optimize the available integration time. Data were obtained in the 15 micrometer and 4.3 micrometer band of CO2 and the 4.6 micrometer and 2.3 micrometer bands of CO. The data are summarized and examples of typical spectra are given. All the data are stored on IBM cards.

Identification of elemental mercury in the subsurface

DOEpatents

Jackson, Dennis G

2015-01-06

An apparatus and process is provided for detecting elemental mercury in soil. A sacrificial electrode of aluminum is inserted below ground to a desired location using direct-push/cone-penetrometer based equipment. The insertion process removes any oxides or previously found mercury from the electrode surface. Any mercury present adjacent the electrode can be detected using a voltmeter which indicates the presence or absence of mercury. Upon repositioning the electrode within the soil, a fresh surface of the aluminum electrode is created allowing additional new measurements.

Mid-Term Progress Report on the Development of Army Closed Cycle Circulator (CCC) System.

DTIC Science & Technology

1979-09-20

installation of the rotor assembly. The compressor shaft is sealed with a Crane Type 28 Kinetic Wedge gas seal for positive static sealing. A unitized...Pressure ratio 1.91 Horsepower 134 R (Molecular weight 18.67) 82.76 The compressor is fitted with a Crane Packing Company Type 28 gas seal. This seal...simply reading a digital voltmeter which is hooked up to the anemometer. The only preparation that the anemometer requires is that the operating

Sensors and detectors based on superconducting devices. (Latest citations from the Compendex database). Published Search

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1993-02-01

The bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity wave experiments, geomagnetism and ocean bottom magnetic exploration, galvanometers and voltmeters, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for SQUIDS (superconducting quantum interference devices.) (Contains 250 citations and includes a subject term index and title list.)

Automated rejection of parasitic frequency sidebands in heterodyne-detection LIDAR applications

NASA Technical Reports Server (NTRS)

Esproles, Carlos; Tratt, David M.; Menzies, Robert T.

1989-01-01

A technique is described for the detection of the sporadic onset of multiaxial mode behavior of a normally single-mode TEA CO2 laser. The technique is implemented using primarily commercial circuit modules; it incorporates a peak detector that displays the RF detector output on a digital voltmeter, and a LED bar graph. The technique was successfully demonstrated with an existing coherent atmospheric LIDAR facility utilizing an injection-seeded single-mode TEA CO2 laser. The block schematic diagram is included.

Connecting to Thermocouples with Fewer Lead Wires

NASA Technical Reports Server (NTRS)

Goldsby, Jon C.

2003-01-01

A simple technique has been devised to reduce the number of lead wires needed to connect an array of thermocouples to the instruments (e.g., voltmeters) used to read their output voltages. Because thermocouple wires are usually made of expensive metal alloys, reducing the number of lead wires can effect a considerable reduction in the cost of such an array. Reducing the number of wires also reduces the number of terminals and the amount of space needed to accommodate the wires.

Vacuum Head Checks Foam/Substrate Bonds

NASA Technical Reports Server (NTRS)

Lloyd, James F.

1989-01-01

Electromechanical inspection system quickly gives measurements indicating adhesion, or lack thereof, between rigid polyurethane foam and aluminum substrate. Does not damage inspected article, easy to operate, and used to perform "go/no-go" evaluations or as supplement to conventional destructive pull-plug testing. Applies vacuum to small area of foam panel and measures distance through which foam pulled into vacuum. Probe head applied to specimen and evacuated through hose to controller/monitor unit. Digital voltmeter in unit reads deflection of LVDT probe head.

Sensors and detectors based on superconducting devices. July 1988-June 1989 (Citations from the COMPENDEX data base). Report for July 1988-June 1989

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1989-07-01

This bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity-wave experiments, geomagnetism and ocean-bottom magnetic exploration, galvanometers and voltmeters, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for SQUIDs (superconducting quantum interference devices.) (This updated bibliography contains 74 citations, all of which are new entries to the previous edition.)

Sensors and detectors based on superconducting devices. January 1970-June 1988 (Citations from the COMPENDEX data base). Report for January 1970-June 1988

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1989-07-01

This bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity-wave experiments, geomagnetism and ocean-bottom magnetic exploration, galvanometers and voltmeters, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for SQUIDs (superconducting quantum interference devices.) (This updated bibliography contains 394 citations, none of which are new entries to the previous edition.)

Sensors and detectors based on superconducting devices. July 1982-February 1989 (Citations from the EI Engineering Meetings data base). Report for July 1982-February 1989

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1989-04-01

This bibliography contains citations from conference proceedings concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity-wave experiments, geomagnetism and ocean bottom magnetic exploration, galvanometers and voltmeters, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for SQUIDS (superconducting quantum interference devices.) (Contains 115 citations fully indexed and including a title list.)

Sensors and detectors based on superconducting devices. January 1970-June 1988 (Citations from the Engineering Index data base). Report for January 1970-June 1988

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1988-07-01

This bibliography contains citations concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity-wave experiments, geomagnetism, and ocean-bottom magnetic exploration, galvanometers and voltmeters, and bolometers, and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for squids (superconducting quantum interference devices.) (This updated bibliography contains 394 citations, 71 of which are new entries to the previous edition.)

Quality assurance of reference standards from nine European solar-ultraviolet monitoring laboratories.

PubMed

Gröbner, Julian; Rembges, Diana; Bais, Alkiviadis F; Blumthaler, Mario; Cabot, Thierry; Josefsson, Weine; Koskela, Tapani; Thorseth, Trond M; Webb, Ann R; Wester, Ulf

2002-07-20

A program for quality assurance of reference standards has been initiated among nine solar-UV monitoring laboratories. By means of a traveling lamp package that comprises several 1000-W ANSI code DXW-type quartz-halogen lamps, a 0.1-ohm shunt, and a 6-1/2 digit voltmeter, the irradiance scales used by the nine laboratories were compared with one another; a relative uncertainty of 1.2% was found. The comparison of 15 reference standards yielded differences of as much as 9%; the average difference was less than 3%.

Device for measuring oxygen activity in liquid sodium

DOEpatents

Roy, P.; Young, R.S.

1973-12-01

A composite ceramic electrolyte in a configuration (such as a closed end tube or a plate) suitable to separate liquid sodium from a reference electrode with a high impedance voltmeter connected to measure EMF between the sodium and the reference electrode as a measure of oxygen activity in the sodium is described. The composite electrolyte consists of zirconiacalcia with a bonded layer of thoria-yttria. The device is used with a gaseous reference electrode on the zirconia-calcia side and liquid sodium on the thoria-yttria side of the electrolyte. (Official Gazette)

Sensors and detectors based on superconducting devices. July 1982-May 1990 (A Bibliography from the EI Engineering Meetings data base). Report for July 1982-May 1990

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-06-01

This bibliography contains citations from conference proceedings concerning gradiometers, magnetometers, and infrared detectors which use superconductors to improve sensitivity. Applications include biomagnetic measurements for medical studies, gravity wave experiments, geomagnetism and ocean bottom magnetic exploration, galvanometers and voltmeters, and bolometers and radiometers. Some articles refer to design considerations for cooling systems for the sensors and detectors, and fabrication techniques for squids (superconducting quantum interference devices.) (This updated bibliography contains 189 citations, 74 of which are new entries to the previous edition.)

Interim-Night Integrated Goggle Head Tracking System (I-Nights). Volume 1. Ground Test Summary

DTIC Science & Technology

1992-08-01

A/WDP _ DATE: I COORDINATION: NWC 04_______ DATE: 7914401 COORDINATION: USD/ YAGO DATE:9 4/ APPROVED BY: ESD/YAff-1DST j T [!1! / 624 TABLE OF CONTENTS...B/U YAGO ) Voltmeter 1 NWC Voltage Standard 1 NWC (CAL Lab) Soldering Iron 1 NWC O-Scope 1 NWC LPU-9D Life Preserver/ Surv. Vest 1 YAGO G-Suit (Large...1 YAGO Large Flight Boots 1 YAGO Ex-Large Flight Suit 1 YAGO ADAM #12 (Large) I Holloman ADAM I-NIGHTS Liners 3 (1 per vendor) AAMRL/BBM 5% Hybrid

[Age-related characteristics of the surface bioelectrical potential of human, canine and rat teeth and features of its distribution over the surface of the crown].

PubMed

Donskiĭ, G I; Pavliuchenko, O N; Palamarchuk, Iu N; Makarova, N Ia

1989-01-01

Using a digital electron voltmeter, bioelectrical potentials (BEPs) of dental crowns have been recorded in 180 patients, 36 dogs, and 93 white non-inbred rats. It has been established that the surface BEP is a marker of dental enamel maturation and does not depend on the species of mammals. On the other hand maturation processes differ in their rate on the cutting edge, equator, and neck: with advancing age algebraic difference between the magnitudes of surface BEPs decreases in humans and increases in dogs and rats.

An improved method for piezoelectric characterization of polymers for energy harvesting applications

NASA Astrophysics Data System (ADS)

Gusarova, E.; Gusarov, B.; Zakharov, D.; Bousquet, M.; Viala, B.; Cugat, O.; Delamare, J.; Gimeno, L.

2013-12-01

This work presents an improved method for measuring the direct piezoelectric voltage and energy of flexible polymers. Well-controlled stress is applied with a four-point bending system and voltage is measured in real open-circuit conditions. The presented method separates the piezoelectric part from the measurement part by introducing a mechanical switch, allowing instantaneous post-deformation discharge measurements. Oscilloscope and contact-less electrostatic voltmeter are compared. Direct piezoelectric measurements under open-circuit conditions have been performed on commercial PVDF (polyvinylidene fluoride) and its copolymers. Significant differences to data sheet values (close-circuit conditions) are reported and commented.

On performance of cylindrical dipole antenna in diagnostics of wave phenomena in space plasma

NASA Astrophysics Data System (ADS)

Kiraga, A.

Tubular and wire antennas have been employed since an advent of in situ measurements in space. It is generally accepted that they are well suited to recipe electromagnetic radiation from remote sources as well as divers local plasma emissions. Quasi thermal noise spectroscopy provides an example of well documented, both experimentally and theoretically, technique to study solar wind plasma. In many data sets of wave spectra, recorded with use of tubular or wire antennas at all altitudes inside a plasma sphere, there is pronounced, permanent, variable frequency spectral structure, routinely assigned to upper hybrid band (UHR) emissions. On the other hand, spectral structure, which could be assigned to upper hybrid band, is less pronounced and infrequent, in sets of wave spectra recorded in polar region with the use of spherical double probes. These apparently inconsistent observations have not drawn much attention of wave community. Assignment to UHR emission have been bolstered by theoretical plausibility, permanency in data sets, frequency verification with independent techniques and conviction that measurements were performed with good voltmeter with well known properties. It has been recognized that stray capacitance acts as a voltage divider and underestimates real voltage imposed on antenna. But in sufficiently dense and cold main plasma component, even short antenna is inductive in some frequency band below upper hybrid frequency. Stray capacitance and antenna inductance result in circuit resonance, which is very pronounced, if antenna resistance is low and input resistance is high. In such circumstances, a good voltmeter concept is very misleading. In this report we show that good voltmeter concept is not sufficient for interpretation of passive mode spectra recorded with tubular antenna on IK -19, APEX and CORONAS satellites. With orbit inclination of ~80deg and altitude range of 500-3000km, very divers plasmas were encountered, but distinct plasma emission within upper hybrid band do not show up. In equivalent circuit simulations, salient spectral characteristics can be matched and related to specific impedances. Equivalent circuit analysis was enforced by apparent difference between local plasma frequencies derived from onboard topside sounder data and frequencies of adjacent maximum in passive mode spectra. It has been subsequently verified and developed with the aid of impedance measurements, onboard sounder data and analysis of electron beam induced spectra. We show that circuit resonance can be neatly controlled to provide very low interference technique to monitor density of cold plasma. Circuit resonance monitoring, if properly coupled with impedance measurements and electron beam injection may be very useful, low interference tool for diagnostics of highly structured plasmas like those in auroral region.

Electric field changes on Au nanoparticles on semiconductor supports--the molecular voltmeter and other methods to observe adsorbate-induced charge-transfer effects in Au/TiO2 nanocatalysts.

PubMed

McEntee, Monica; Stevanovic, Ana; Tang, Wenjie; Neurock, Matthew; Yates, John T

2015-02-11

Infrared (IR) studies of Au/TiO2 catalyst particles indicate that charge transfer from van der Waals-bound donor or acceptor molecules on TiO2 to or from Au occurs via transport of charge carriers in the semiconductor TiO2 support. The ΔνCO on Au is shown to be proportional to the polarizability of the TiO2 support fully covered with donor or acceptor molecules, producing a proportional frequency shift in νCO. Charge transfer through TiO2 is associated with the population of electron trap sites in the bandgap of TiO2 and can be independently followed by changes in photoluminescence intensity and by shifts in the broad IR absorbance region for electron trap sites, which is also proportional to the polarizability of donors by IR excitation. Density functional theory calculations show that electron transfer from the donor molecules to TiO2 and to supported Au particles produces a negative charge on the Au, whereas the transfer from the Au particles to the TiO2 support into acceptor molecules results in a positive charge on the Au. These changes along with the magnitudes of the shifts are consistent with the Stark effect. A number of experiments show that the ∼3 nm Au particles act as "molecular voltmeters" in influencing ΔνCO. Insulator particles, such as SiO2, do not display electron-transfer effects to Au particles on their surface. These studies are preliminary to doping studies of semiconductor-oxide particles by metal ions which modify Lewis acid/base oxide properties and possibly strongly modify the electron-transfer and catalytic activity of supported metal catalyst particles.

Representative Electromagnetic Field Intensities Near the Clam Lake, Wisconsin and Republic, Michigan ELF (Extremely Low Frequency) Facilities.

DTIC Science & Technology

1984-01-01

wo 60 l s. 0 a -, 3" 0 . I, ,,. 0) 144 3.44 Y., 4 c 4 a ll.,m ._ - ,.,. .. ,. ,3k ,, -9 q𔃾!~ II W3 Q n o i i TIE 15 k USL . i jI O 1 A W.iW8 WA...stakes penetrate soil to a known depth at two points one meter apart. The potential difference between the stakes is measured with a tuned voltmeter to... soil below 100 microvolts per meter (Tables A-5, A-6 and A-12) are not listed. Variations were observed during measurements of such very low intensities

Computer Controlled Magnetotransport Setup for the Characterization of Semiconductor Thin Films

NASA Technical Reports Server (NTRS)

Ducoudray, G. O.; Collazo, R.; Martinez, A.

1997-01-01

We have considered a computer controlled magnetotransport setup using LabWindows environment. It allows for measurements of resistivity, Hall resistance, carrier concentration and charge mobility in semiconductor thin films using a van der Pauw configuration. The setup features an electromagnet (B = 0.7 Tesla) a 80486-DX 33 computer with a National Instrument AT-MIO 16 AD/DA and a GPIB interface board. A Keithely 224 current source and a Keithley 196 digital voltmeter were also used in the setup. Plans for the addition of capabilities to allow for magnetic field sweeping and the performance of measurements as a function of temperature will be presented.

Investigation of light scattering as a technique for detecting discrete soot particles in a luminous flame

NASA Technical Reports Server (NTRS)

1978-01-01

The practicability of using a classical light-scattering technique, involving comparison of angular scattering intensity patterns with theoretically determined Mie and Rayleight patterns, to detect discrete soot particles (diameter less than 50 nm) in premixed propane/air and propane/oxygen-helium flames is considered. The experimental apparatus employed in this investigation included a laser light source, a flat-flame burner, specially coated optics, a cooled photomultiplier detector, and a lock-in voltmeter readout. Although large, agglomerated soot particles were detected and sized, it was not possible to detect small, discrete particles. The limiting factor appears to be background scattering by the system's optics.

Electronic dendrometer

DOEpatents

Sauer, deceased, Ronald H.; Beedlow, Peter A.

1985-01-01

Disclosed is a dendrometer for use on soft stemmed herbaceous plants. The dendrometer uses elongated jaws to engage the plant stem securely but without appreciable distortion or collapse of the stem. A transducer made of flexible, noncorrodible and temperature stable material spans between the jaws which engage the plant stem. Strain gauges are attached at appropriate locations on a transducer member and are connected to a voltage source and voltmeter to monitor changes in plant stem size. A microprocessor can be used to integrate the plant stem size information with other relevant environmental parameters and the data can be recorded on magnetic tape or used in other data processing equipment.

The Electrostatic Gavimeter: An Alternative Way of Measuring Gravitational Acceleration

NASA Astrophysics Data System (ADS)

Kashinski, David

2005-03-01

In the past, Earth’s gravitational acceleration g has been measured in many ways, including the use of a pendulum as well as other models involving the use of a mass and a spring. We have designed a new method incorporating a spring with a capacitor and a voltmeter. This capacitor model still uses a hanging mass on a spring, but alters the method of determining the change in position of the spring due to the gravitational acceleration. We relate the change in position to the potential difference across the capacitor needed to cause a discharge through parallel plates. By relating this voltage directly to the gravitaional acceleration,a new method of measuring g is obtained.

Electrical Resistivity of Ten Selected Binary Alloy Systems.

DTIC Science & Technology

1981-04-01

100 m 2 L q2 2 J 4m v 2 1 ......... 13 I Here e , m, and v are the electronic charge, mass, and velocity, q is the screening parameter, and I is the...potentiometer method E Eddy current decay method wpik* -7 25 P Van der Pauw method R Rotating magnetic field method V Voltmeter and ammeter direct...r:~ 0; tz 0 hi~~ 0*~ . 0 . 6 0 M 0 0 % -0 0 e o C M -" I- I n WT 8 L a .44 44 -44 4 %. -~~ 0 0 0 0 U0. ii S 4. 0c .2 s , Q t 04 INN ) nW V W 33

SQUID picovoltometry of single crystal Bi2Sr2CaCu2O(8+delta) - Observation of the crossover from high-temperature Arrhenius to low-temperature vortex-glass behavior

NASA Astrophysics Data System (ADS)

Safar, H.; Gammel, P. L.; Bishop, D. J.; Mitzi, D. B.; Kapitulnik, A.

1992-04-01

A SQUID voltmeter has been used to measure current-voltage curves in untwinned crystals of Bi2Sr2CaCu2O(8+delta) as a function of temperature and magnetic field. The data show a clear crossover from high-temperature Arrhenius behavior to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z - 1) = 7 +/- 1 in this system are in accord with theoretical models and previous measurements in YBa2Cu3O7. The width of the critical region collapses below 2 T, reflecting the changing role of dimensionality with field.

Demodulator for carrier transducers

NASA Technical Reports Server (NTRS)

Roller, R. F. (Inventor)

1974-01-01

A carrier type transducer is supplied with a carrier wave via an audio amplifier, a filter, a frequency divider, and an oscillator. The carrier is modulated in accordance with the parameter being measured by the transducer and is fed to the input of a digital data system which may include a voltmeter. The output of the oscillator and the output of each stage of the divider are fed to an AND or a NAND gate and suitable variable and fixed delay circuits to the command input of the digital data system. With this arrangement, the digital data system is commanded to sample at the proper time so that the average voltage of the modulated carrier is measured. It may be utilized with ancillary circuitry for control of the parameter

Technical and commerical challenges in high Tc SQUIDs and their industrial applications

NASA Technical Reports Server (NTRS)

Lu, D. F.

1995-01-01

A SQUID is the most sensitive device for measuring changes in magnetic flux. Since its discovery in the sixties, scientists have made consistent efforts to apply SQUID's to various applications. Instruments that are the most sensitive in their respective categories have been built, such as SQUID DC susceptometer that is now manufactured by Quantum Design, pico-voltmeter which could measure 10(exp -14) volts, and gravitational wave detectors. One of the most successful applications of SQUID's is in magnetoencephalography, a non-invasive technique for investigating neuronal activity in the living human brain. This technique employs a multi-channel SQUID magnetometer that maps the weak magnetic field generated by small current when information is processed in brain, and its performance is marvelous.

Actinide-ion sensor

DOEpatents

Li, Shelly X; Jue, Jan-fong; Herbst, Ronald Scott; Herrmann, Steven Douglas

2015-01-13

An apparatus for the real-time, in-situ monitoring of actinide-ion concentrations. A working electrolyte is positioned within the interior of a container. The working electrolyte is separated from a reference electrolyte by a separator. A working electrode is at least partially in contact with the working electrolyte. A reference electrode is at least partially in contact with the reference electrolyte. A voltmeter is electrically connected to the working electrode and the reference electrode. The working electrolyte comprises an actinide-ion of interest. The separator is ionically conductive to the actinide-ion of interest. The separator comprises an actinide, Zr, and Nb. Preferably, the actinide of the separator is Am or Np, more preferably Pu. In one embodiment, the actinide of the separator is the actinide of interest. In another embodiment, the separator further comprises P and O.

Effects of coupling between sample and electrode on the electrical resistivity measurements of conductive samples

NASA Astrophysics Data System (ADS)

Lee, T. J.; Lee, S. K.

2015-12-01

A resistivity measurement system for conductive core samples has been setup using a high resolution nano-voltmeter. Using the system, in this study, various coupling effects between electrodes and the samples are discussed including contact resistance, lead resistance, temperature dependence, and heat produced within the samples by applied current. The lead resistance was over 10 times higher than the resistance of the conductive samples such as graphite or nichrome, even though the electrodes and lead lines were made of silver. Furthermore, lead resistance itself showed very strong temperature dependence, so that it is essential to subtract the lead resistance from the measured values at corresponding temperature. Minimization of contact resistance is very important, so that the axial loads are needed as big as possible unless the deformation of sample occurs.

Wind Tunnel Force Balance Calibration Study - Interim Results

NASA Technical Reports Server (NTRS)

Rhew, Ray D.

2012-01-01

Wind tunnel force balance calibration is preformed utilizing a variety of different methods and does not have a direct traceable standard such as standards used for most calibration practices (weights, and voltmeters). These different calibration methods and practices include, but are not limited to, the loading schedule, the load application hardware, manual and automatic systems, re-leveling and non-re-leveling. A study of the balance calibration techniques used by NASA was undertaken to develop metrics for reviewing and comparing results using sample calibrations. The study also includes balances of different designs, single and multi-piece. The calibration systems include, the manual, and the automatic that are provided by NASA and its vendors. The results to date will be presented along with the techniques for comparing the results. In addition, future planned calibrations and investigations based on the results will be provided.

Actuation stability test of the LISA pathfinder inertial sensor front-end electronics

NASA Astrophysics Data System (ADS)

Mance, Davor; Gan, Li; Weber, Bill; Weber, Franz; Zweifel, Peter

In order to limit the residual stray forces on the inertial sensor test mass in LISA pathfinder, √ it is required that the fluctuation of the test mass actuation voltage is within 2ppm/ Hz. The actuation voltage stability test on the flight hardware of the inertial sensor front-end electronics (IS FEE) is presented in this paper. This test is completed during the inertial sensor integration at EADS Astrium Friedrichshafen, Germany. The standard measurement method using voltmeter is not sufficient for verification, since the instrument low frequency √ fluctuation is higher than the 2ppm/ Hz requirement. In this test, by using the differential measurement method and the lock-in amplifier, the actuation stability performance is verified and the quality of the IS FEE hardware is confirmed by the test results.

Cadmium telluride photovoltaic radiation detector

DOEpatents

Agouridis, D.C.; Fox, R.J.

A dosimetry-type radiation detector is provided which employs a polycrystalline, chlorine-compensated cadmium telluride wafer fabricated to operate as a photovoltaic current generator used as the basic detecting element. A photovoltaic junction is formed in the wafer by painting one face of the cadmium telluride wafer with an n-type semi-conductive material. The opposite face of the wafer is painted with an electrically conductive material to serve as a current collector. The detector is mounted in a hermetically sealed vacuum containment. The detector is operated in a photovoltaic mode (zero bias) while DC coupled to a symmetrical differential current amplifier having a very low input impedance. The amplifier converts the current signal generated by radiation impinging upon the barrier surface face of the wafer to a voltage which is supplied to a voltmeter calibrated to read quantitatively the level of radiation incident upon the detecting wafer.

Sensitive method for characterizing liquid helium cooled preamplifier feedback resistors

NASA Technical Reports Server (NTRS)

Smeins, L. G.; Arentz, R. F.

1983-01-01

It is pointed out that the simple and traditional method of measuring resistance using an electrometer is ineffective since it is limited to a narrow and nonrepresentative range of terminal voltages. The present investigation is concerned with a resistor measurement technique which was developed to select and calibrate the Transimpedance Mode Amplifier (TIA) load resistors on the Infrared Astronomical Satellite (IRAS) for the wide variety of time and voltage varying signals which will be processed during the flight. The developed method has great versatility and power, and makes it possible to measure the varied and complex responses of nonideal feedback resistors to IR photo-detector currents. When employed with a stable input coupling capacitor, and a narrow band RMS voltmeter, the five input waveforms thouroughly test and calibrate all the features of interest in a load resistor and its associated TIA circuitry.

Temperature stability of transit time delay for a single-mode fibre in a loose tube cable

NASA Technical Reports Server (NTRS)

Bergman, L. A.; Eng, S. T.; Johnston, A. R.

1983-01-01

The effect of temperature on the transit-time delay of a loose-tube-type single-mode optical-fiber cable is investigated experimentally. A 1058-m length of cable was placed loosely coiled in an oven and used to connect a 820-nm single-mode laser diode to a high-speed avalanche-photodiode detector feeding a vector voltmeter; the signal was provided by a high-stability frequency-synthesized generator. Measurements were made every 2 C from -50 to 60 C and compared to those obtained with a 200-m lacquered bare fiber. The phase change of both fibers varied with temperature at a positive slope of 6-7 ppm/C. This value is significantly better than those reported for other cable types, suggesting the application of loose-fiber cables to long-haul gigabit digital transmissions or precision time-base distribution for VLBI.

Traceable Coulomb blockade thermometry

NASA Astrophysics Data System (ADS)

Hahtela, O.; Mykkänen, E.; Kemppinen, A.; Meschke, M.; Prunnila, M.; Gunnarsson, D.; Roschier, L.; Penttilä, J.; Pekola, J.

2017-02-01

We present a measurement and analysis scheme for determining traceable thermodynamic temperature at cryogenic temperatures using Coulomb blockade thermometry. The uncertainty of the electrical measurement is improved by utilizing two sampling digital voltmeters instead of the traditional lock-in technique. The remaining uncertainty is dominated by that of the numerical analysis of the measurement data. Two analysis methods are demonstrated: numerical fitting of the full conductance curve and measuring the height of the conductance dip. The complete uncertainty analysis shows that using either analysis method the relative combined standard uncertainty (k  =  1) in determining the thermodynamic temperature in the temperature range from 20 mK to 200 mK is below 0.5%. In this temperature range, both analysis methods produced temperature estimates that deviated from 0.39% to 0.67% from the reference temperatures provided by a superconducting reference point device calibrated against the Provisional Low Temperature Scale of 2000.

Cadmium telluride photovoltaic radiation detector

DOEpatents

Agouridis, Dimitrios C.; Fox, Richard J.

1981-01-01

A dosimetry-type radiation detector is provided which employs a polycrystalline, chlorine-compensated cadmium telluride wafer fabricated to operate as a photovoltaic current generator used as the basic detecting element. A photovoltaic junction is formed in the wafer by painting one face of the cadmium telluride wafer with an n-type semiconductive material. The opposite face of the wafer is painted with an electrically conductive material to serve as a current collector. The detector is mounted in a hermetically sealed vacuum containment. The detector is operated in a photovoltaic mode (zero bias) while DC coupled to a symmetrical differential current amplifier having a very low input impedance. The amplifier converts the current signal generated by radiation impinging upon the barrier surface face of the wafer to a voltage which is supplied to a voltmeter calibrated to read quantitatively the level of radiation incident upon the detecting wafer.

Current-based detection of nonlocal spin transport in graphene for spin-based logic applications

NASA Astrophysics Data System (ADS)

Wen, Hua; Zhu, Tiancong; Luo, Yunqiu Kelly; Amamou, Walid; Kawakami, Roland K.

2014-05-01

Graphene has been proposed for novel spintronic devices due to its robust and efficient spin transport properties at room temperature. Some of the most promising proposals require current-based readout for integration purposes, but the current-based detection of spin accumulation has not yet been developed. In this work, we demonstrate current-based detection of spin transport in graphene using a modified nonlocal geometry. By adding a variable shunt resistor in parallel to the nonlocal voltmeter, we are able to systematically cross over from the conventional voltage-based detection to current-based detection. As the shunt resistor is reduced, the output current from the spin accumulation increases as the shunt resistance drops below a characteristic value R*. We analyze this behavior using a one-dimensional drift-diffusion model, which accounts well for the observed behavior. These results provide the experimental and theoretical foundation for current-based detection of nonlocal spin transport.

Electric field measurements during the blowing snow in a cryogenic wind tunnel by a non-contact voltmeter

NASA Astrophysics Data System (ADS)

Sato, A.; Omiya, S.

2011-12-01

It is known that the average atmospheric electric field is +100V/m in fair weather (positive electric field vector points downward). An increase of atmospheric electric field is reported when the blowing snow occurred. This phenomenon is mainly explained by the fact that the blowing snow particles have negative charge in average. It is suggested that an electrostatic force, given by the product of the electric field and the charge of the particle, may influence the particle trajectory and change those movements, saltation and suspension. The purpose of this experiment is to clarify the characteristics of the electric field during blowing snow event. Experiments were carried out in the cryogenic wind tunnel of Snow and Ice Research Center, NIED. A non-contact voltmeter was used to measure the electric field. An artificial blowing snow was generated by a snow particle supply machine. The rolling brushes of the machine scratch the snow surface and supply snow particles into the airflow. This machine made it possible to supply the snow particles at an arbitrary rate. This experiment was conducted in the following experimental conditions; wind speed of 5 to 7 m/s (3 patterns), supply snow quantity of 8.7 to 34.9 g/m/s (4 patterns), air temperature of -10 degree Celsius, fetch of 10 m and hard snow surface. Measured electric field was all negative, which is opposite direction to the previous measurements. This means that the blowing snow particles had positive charges. The negative electric field tended to increase with increase of the wind speed and the mass flux. These results can be explained from the previous experiment by Omiya and Sato (2010). The snow particles gain positive charges by the friction with the rolling brush which is made from polypropylene, however the particles accumulate negative charges gradually with increase of the collisions to the snow surface. Probably, the positive charges might have remained on the snow particles that had passed over the measurement point. Moreover, it is thought that because the saltation length is longer when the wind speed is higher, fewer collision frequencies left the particles more positive charges. REFERENCE:Omiya and Sato(2010): Measurement of electrostatic charge of blowing snow particles in a wind tunnel focusing on collision frequency to the snow surface. Hokkaido University Collection of Scholarly and Academic Papers

Synthesis of Diopside by Solution Combustion Process Using Glycine Fuel

NASA Astrophysics Data System (ADS)

Sherikar, Baburao N.; Umarji, A. M.

Nano ceramic Diopside (CaMgSi2O6) powders are synthesized by Solution Combustion Process(SCS) using Calcium nitrate, Magnesium nitrate as oxidizer and glycine as fuel, fumed silica as silica source. Ammonium nitrate (AN) is used as extra oxidizer. Effect of AN on Diopside phase formation is investigated. The adiabatic flame temperatures are calculated theoretically for varying amount of AN according to thermodynamic concept and correlated with the observed flame temperatures. A “Multi channel thermocouple setup connected to computer interfaced Keithley multi voltmeter 2700” is used to monitor the thermal events during the process. An interpretation based on maximum combustion temperature and the amount of gases produced during reaction for various AN compositions has been proposed for the nature of combustion and its correlation with the characteristics of as synthesized powder. These powders are characterized by XRD, SEM showing that the powders are composed of polycrystalline oxides with crystallite size of 58nm to 74nm.

A simple device to illustrate the Einthoven triangle.

PubMed

Jin, Benjamin E; Wulff, Heike; Widdicombe, Jonathan H; Zheng, Jie; Bers, Donald M; Puglisi, Jose L

2012-12-01

The Einthoven triangle is central to the field of electrocardiography, but the concept of cardiac vectors is often a difficult notion for students to grasp. To illustrate this principle, we constructed a device that recreates the conditions of an ECG reading using a battery to simulate the electrical vector of the heart and three voltmeters for the main electrocardiographic leads. Requiring minimal construction with low cost, this device provides hands-on practice that enables students to rediscover the principles of the Einthoven triangle, namely, that the direction of the cardiac dipole can be predicted from the deflections in any two leads and that lead I + lead III = lead II independent of the position of heart's electrical vector. We built a total of 6 devices for classes of 30 students and tested them in the first-year Human Physiology course at the University of California-Davis School of Medicine. Combined with traditional demonstrations with ECG machines, this equipment demonstrated its ability to help medical students obtain a solid foundation of the basic principles of electrocardiography.

Accelerator characterization of the new ion beam facility at MTA Atomki in Debrecen, Hungary

NASA Astrophysics Data System (ADS)

Rajta, I.; Vajda, I.; Gyürky, Gy.; Csedreki, L.; Kiss, Á. Z.; Biri, S.; van Oosterhout, H. A. P.; Podaru, N. C.; Mous, D. J. W.

2018-02-01

In this work we present the 2 MV Tandetron accelerator manufactured by High Voltage Engineering Europa (HVEE), that was installed at MTA Atomki in Debrecen, Hungary in 2015. Furthermore, we report on the first performance test of the whole facility including the calibration of the terminal voltage using accurately known resonance energies of the 27Al(p, γ)28Si and 13C(p, γ)14N reactions, as well as neutron threshold energies of the 7Li(p,n)7Be and 13C(p,n)13N reactions. The accurate energy calibration of the generating voltmeter (GVM), the good energy stability of the accelerator as well as the low energy spread of the ion beam suited the requirements of nuclear astrophysics, resonance PIGE depth profiling and the nanoprobe beamline. We have investigated whether the terminal voltage reading depends on the insulating gas pressure, and how much the stripper gas pressure modifies the beam energy.

Instruction manual, optical effects module electronic controller and processor, model OEMCP

NASA Technical Reports Server (NTRS)

1975-01-01

The OEM-1 electronic module is discussed; it is comprised of four subsystems: the signal processing and display; the stepper motor controls; the chopper controls; and the dc-dc invertor. The OEM-1 module controls the sample wheel so that the relative transmittance of the samples can be compared to the clear aperture position. The 3-1/2 digit digital voltmeter displays the clear aperture signal level as well as the ratio of the remaining sample positions relative to the clear aperture position. The sample wheel position is decoded so that the signals and ratios can be correlated to the data. The OEM is automatically reset to the I sub o on initial turn-on and can be reset to the '0' position by actuating a front panel switch. The sample wheel can be interrupted to change samples or induce a longer integration time if desired by a front panel command. Integration times from 1 - 50 seconds are provided at the front panel, and BCD data for external interfacing is provided.

Development of mono-component and tri-component fibres 100% polymer based piezoelectric PVDF to harvest energy

NASA Astrophysics Data System (ADS)

Talbourdet, A.; Rault, F.; Cayla, A.; Cochrane, C.; Devaux, E.; Gonthier, A.; Lemort, G.; Campagne, C.

2017-10-01

A first study focused on the realization of a 100% Polyvinylidene fluoride woven fabric. The multi-filaments produced by melt spinning and studied by FTIR, X-Ray and DSC, were optimized in the β-phase, 97%, thanks drawing ratio of λ=5, and the processing temperature, 90°C. When the polar β-phase achieves a certain level in PVDF, the woven material is poling with fields up to about 6kV. DMA tests coupled to a Keithley voltmeter allow the solicitation of PVDF fabrics. A variation of voltage is obtained in compression, with a maximum output voltage of up to 2,3V. The other part of the study explains premises of a tricomponent fibre development, PEHD/PVDF/PA12. Two layers of conductive polymers acting as electrodes are placed on either side of the PVDF layer. The interfacial adhesion between the three different layers is analysed by SEM. The maximum stretch on melt spinning was fixed at 2.5 and the β-phase of the PVDF measured by X-Ray.

A simple device to illustrate the Einthoven triangle

PubMed Central

Jin, Benjamin E.; Wulff, Heike; Widdicombe, Jonathan H.; Zheng, Jie; Bers, Donald M.

2012-01-01

The Einthoven triangle is central to the field of electrocardiography, but the concept of cardiac vectors is often a difficult notion for students to grasp. To illustrate this principle, we constructed a device that recreates the conditions of an ECG reading using a battery to simulate the electrical vector of the heart and three voltmeters for the main electrocardiographic leads. Requiring minimal construction with low cost, this device provides hands-on practice that enables students to rediscover the principles of the Einthoven triangle, namely, that the direction of the cardiac dipole can be predicted from the deflections in any two leads and that lead I + lead III = lead II independent of the position of heart's electrical vector. We built a total of 6 devices for classes of 30 students and tested them in the first-year Human Physiology course at the University of California-Davis School of Medicine. Combined with traditional demonstrations with ECG machines, this equipment demonstrated its ability to help medical students obtain a solid foundation of the basic principles of electrocardiography. PMID:23209014

Neuronify: An Educational Simulator for Neural Circuits.

PubMed

Dragly, Svenn-Arne; Hobbi Mobarhan, Milad; Våvang Solbrå, Andreas; Tennøe, Simen; Hafreager, Anders; Malthe-Sørenssen, Anders; Fyhn, Marianne; Hafting, Torkel; Einevoll, Gaute T

2017-01-01

Educational software (apps) can improve science education by providing an interactive way of learning about complicated topics that are hard to explain with text and static illustrations. However, few educational apps are available for simulation of neural networks. Here, we describe an educational app, Neuronify, allowing the user to easily create and explore neural networks in a plug-and-play simulation environment. The user can pick network elements with adjustable parameters from a menu, i.e., synaptically connected neurons modelled as integrate-and-fire neurons and various stimulators (current sources, spike generators, visual, and touch) and recording devices (voltmeter, spike detector, and loudspeaker). We aim to provide a low entry point to simulation-based neuroscience by allowing students with no programming experience to create and simulate neural networks. To facilitate the use of Neuronify in teaching, a set of premade common network motifs is provided, performing functions such as input summation, gain control by inhibition, and detection of direction of stimulus movement. Neuronify is developed in C++ and QML using the cross-platform application framework Qt and runs on smart phones (Android, iOS) and tablet computers as well personal computers (Windows, Mac, Linux).

Design considerations for high-power VHF radar transceivers: Phase matching long coaxial cables using a cable radar

NASA Technical Reports Server (NTRS)

Johnson, P. E.; Ecklund, W. L.

1983-01-01

The Poker Flat 49.92-MHz MST radar uses 64 phase-controlled transmitters in individual shelters distributed throughout the antenna array. Phase control is accomplished by sampling the transmitted pulse at the directional coupler of each transmitter and sending the sample pulse back to a phase-control unit. This method requires phase matching 64 long (256 meter) coaxial cables (RG-213) to within several electrical degrees. Tests with a time domain reflectometer showed that attenuation of high frequency components in the long RG-213 cable rounded the leading edge of the reflected pulse so that the cables could only be measured to within 50 cm (about 45 deg at 49.92 MHz). Another measurement technique using a vector voltmeter to compare forward and reflected phase required a directional coupler with unattainable directivity. Several other techniques were also found lacking, primarily because of loss in the long RG-213 cables. At this point it was realized that what was needed was a simple version of the phase-coherent clear-air radar, i.e., a cable radar. The design and operation of this cable are described.

Characterization of transimpedance amplifier as optical to electrical converter on designing optical instrumentation

NASA Astrophysics Data System (ADS)

Hanto, D.; Ula, R. K.

2017-05-01

Optical to electrical converter is the main components for designing of the optical instrumentations. In addition, this component is also used as signal conditioning. This component usually consists of a photo detector and amplifier. In this paper, characteristics of commercial amplifiers from Thorlabs PDA50B-EC has been observed. The experiment was conducted by diode laser with power of -5 dBm and wavelength 1310 nm; the optical attenuator to vary optical power from 0 to 60 dB, optical to electrical converter from Thorlabs Amplifier PDA50B-EC; multimode optical fiber to guide the laser; and digital voltmeter to measure the output of converter. The results of the characterization indicate that each channel amplification has a non-linear correlation between optical and electrical parameter; optical conversion measurement range of 20-23 dB to full scale; and different measurement coverage area. If this converter will be used as a part component of optical instrumentation so it should be adjusted suitably with the optical power source. Then, because of the correlation equation is not linear so calculation to determine the interpretation also should be considered in addition to the transfer function of the optical sensor.

A Paramagnetic Molecular Voltmeter

PubMed Central

Surek, Jack T.; Thomas, David D.

2008-01-01

We have developed a general electron paramagnetic resonance (EPR) method to measure electrostatic potential at spin labels on proteins to millivolt accuracy. Electrostatic potential is fundamental to energy-transducing proteins like myosin, because molecular energy storage and retrieval is primarily electrostatic. Quantitative analysis of protein electrostatics demands a site-specific spectroscopic method sensitive to millivolt changes. Previous electrostatic potential studies on macromolecules fell short in sensitivity, accuracy and/or specificity. Our approach uses fast-relaxing charged and neutral paramagnetic relaxation agents (PRAs) to increase nitroxide spin label relaxation rate solely through collisional spin exchange. These PRAs were calibrated in experiments on small nitroxides of known structure and charge to account for differences in their relaxation efficiency. Nitroxide longitudinal (R1) and transverse (R2) relaxation rates were separated by applying lineshape analysis to progressive saturation spectra. The ratio of measured R1 increases for each pair of charged and neutral PRAs measures the shift in local PRA concentration due to electrostatic potential. Voltage at the spin label is then calculated using the Boltzmann equation. Measured voltages for two small charged nitroxides agree with Debye-Hückel calculations. Voltage for spin-labeled myosin fragment S1 also agrees with calculation based on the pK shift of the reacted cysteine. PMID:17964835

Neuronify: An Educational Simulator for Neural Circuits

PubMed Central

Hafreager, Anders; Malthe-Sørenssen, Anders; Fyhn, Marianne

2017-01-01

Abstract Educational software (apps) can improve science education by providing an interactive way of learning about complicated topics that are hard to explain with text and static illustrations. However, few educational apps are available for simulation of neural networks. Here, we describe an educational app, Neuronify, allowing the user to easily create and explore neural networks in a plug-and-play simulation environment. The user can pick network elements with adjustable parameters from a menu, i.e., synaptically connected neurons modelled as integrate-and-fire neurons and various stimulators (current sources, spike generators, visual, and touch) and recording devices (voltmeter, spike detector, and loudspeaker). We aim to provide a low entry point to simulation-based neuroscience by allowing students with no programming experience to create and simulate neural networks. To facilitate the use of Neuronify in teaching, a set of premade common network motifs is provided, performing functions such as input summation, gain control by inhibition, and detection of direction of stimulus movement. Neuronify is developed in C++ and QML using the cross-platform application framework Qt and runs on smart phones (Android, iOS) and tablet computers as well personal computers (Windows, Mac, Linux). PMID:28321440

Amplitude-Stabilized Oscillator for a Capacitance-Probe Electrometer

NASA Technical Reports Server (NTRS)

Blaes, Brent R.; Schaefer, Rembrandt T.

2012-01-01

A multichannel electrometer voltmeter that employs a mechanical resonator maintained in sustained amplitude-stabilized oscillation has been developed for the space-based measurement of an Internal Electrostatic Discharge Monitor (IESDM) sensor. The IESDM is new sensor technology targeted for integration into a Space Environmental Monitor (SEM) subsystem used for the characterization and monitoring of deep dielectric charging on spacecraft. Creating a stable oscillator from the mechanical resonator was achieved by employing magnetic induction for sensing the resonator s velocity, and forcing a current through a coil embedded in the resonator to produce a Lorentz actuation force that overcomes the resonator s dissipative losses. Control electronics employing an AGC loop provide conditions for stabilized, constant amplitude harmonic oscillation. The prototype resonator was composed of insulating FR4 printed-wireboard (PWB) material containing a flat, embedded, rectangular coil connected through flexure springs to a base PWB, and immersed in a magnetic field having two regions of opposite field direction generated by four neodymium block magnets. In addition to maintaining the mechanical movement needed for the electrometer s capacitor-probe transducer, this oscillator provides a reference signal for synchronous detection of the capacitor probe s output signal current so drift of oscillation frequency due to environmental effects is inconsequential.

Lockout/Tagout (LOTO) Simulator

NASA Technical Reports Server (NTRS)

Scheer, Jennifer

2011-01-01

The Lockout/Tagout (LOTO) Simulator is a portable training aid, or demonstration tool, designed to physically illustrate real-time critical-safety concepts of electrical lockout/tagout. The objective is to prevent misinterpretations of what is off and what is on during maintenance and repair of complex electrical systems. The simulator is designed in the form of a hinged box that opens up and stands on its own as an easel for demonstrations. On the outer face of the unit is a simulated circuit breaker box housing the switches. The breakers control the main power to the unit, a light bulb, and an electrical control cabinet. The light bulb is wired so that either of two breakers can provide power to it. When power is sent to the electrical control cabinet, a red indicator light illuminates. Inside the cabinet is the power supply from a personal computer. The power supply produces a 12-V dc output that is sent over to a small fan next to it, also from a computer, and an amber light on the front of the cabinet illuminates. A separate switch powers the fan on and off. The power supply is behind a plastic shield to protect against exposure to live conductors. Electrical banana jacks are mounted in the plastic shield to allow a voltmeter to be connected safely when opening the cabinet and taking a meter reading to verify de-energization as part of a simulation exercise. This LOTO simulator prototype is designed and fabricated as an all-in-one unit. All accessories can be stored inside the hinged case, and there is a handle on top for ease of transport. The circuit breaker labels attach with hook and loop fasteners so that they may be moved and changed to fit the training or demonstration scenario. The warning signs and labels on the electrical control box are magnetic, allowing for easy reconfiguration to emulate different equipment setups. A specially designed magnetic cover was made to disguise the indicator lights for demonstrations when these indicators are not used. The cover is disguised as an arc flash safety label that would typically be found on such a cabinet. One indicator light has a separate switch that can take it offline. This is to allow for demonstration to trainees on why it is important not to completely rely on indicator lights, but that they should always take a meter reading at the exposed conductors to absolutely verify de-energization before exposure. A clear plastic barrier and banana jacks inside the cabinet provide a safe way to plug in a voltmeter for demonstrations without exposure to the hazards of energized equipment. A small remote control unit is wired into the fan circuit. The remote allows the demonstrator to turn the fan on and off, provided that all of the breakers and switches leading to it are configured on as well. The remote feature was added in order to demonstrate the importance of starting the lockout/tagout task with energized equipment, then powering it down, isolating it, and locking it out to ensure that the correct breakers have been locked out.

Using self-potential housing technique to model water seepage at the UNHAS housing Antang area

NASA Astrophysics Data System (ADS)

Syahruddin, Muhammad Hamzah

2017-01-01

The earth's surface has an electric potential that is known as self-potentiall (SP). One of the causes of the electrical potential at the earth's surface is water seepage into the ground. Electrical potential caused by water velocity seepage into the ground known as streaming potential. How to model water seepage into the ground at the housing Unhas Antang? This study was conducted to answer these questions. The self-potential measurements performed using a simple digital voltmeter Sanwa brand PC500 with a precision of 0.01 mV. While the coordinates of measurements points are self-potential using Global Positioning System. Mmeasurements results thus obtained are plotted using surfer image distribution self-potential housing Unhas Antang. The self-potential data housing Unhas Antang processed by Forward Modeling methods to get a model of water infiltration into the soil. Housing Unhas Antang self-potential has a value of 5 to 23 mV. Self-potential measurements carried out in the rainy season so it can be assumed that the measurement results caused by the velocity water seepage into the ground. The results of modeling the velocity water seepage from the surface to a depth of 3 meters was 2.4 cm/s to 0.2 cm /s. Modeling results showed that the velocity water seepage of the smaller with depth.

Precision absolute-value amplifier for a precision voltmeter

DOEpatents

Hearn, W.E.; Rondeau, D.J.

1982-10-19

Bipolar inputs are afforded by the plus inputs of first and second differential input amplifiers. A first gain determining resistor is connected between the minus inputs of the differential amplifiers. First and second diodes are connected between the respective minus inputs and the respective outputs of the differential amplifiers. First and second FETs have their gates connected to the outputs of the amplifiers, while their respective source and drain circuits are connected between the respective minus inputs and an output lead extending to a load resistor. The output current through the load resistor is proportional to the absolute value of the input voltage difference between the bipolar input terminals. A third differential amplifier has its plus input terminal connected to the load resistor. A second gain determining resistor is connected between the minus input of the third differential amplifier and a voltage source. A third FET has its gate connected to the output of the third amplifier. The source and drain circuit of the third transistor is connected between the minus input of the third amplifier and a voltage-frequency converter, constituting an output device. A polarity detector is also provided, comprising a pair of transistors having their inputs connected to the outputs of the first and second differential amplifiers. The outputs of the polarity detector are connected to gates which switch the output of the voltage-frequency converter between up and down counting outputs.

Precision absolute value amplifier for a precision voltmeter

DOEpatents

Hearn, William E.; Rondeau, Donald J.

1985-01-01

Bipolar inputs are afforded by the plus inputs of first and second differential input amplifiers. A first gain determining resister is connected between the minus inputs of the differential amplifiers. First and second diodes are connected between the respective minus inputs and the respective outputs of the differential amplifiers. First and second FETs have their gates connected to the outputs of the amplifiers, while their respective source and drain circuits are connected between the respective minus inputs and an output lead extending to a load resister. The output current through the load resister is proportional to the absolute value of the input voltage difference between the bipolar input terminals. A third differential amplifier has its plus input terminal connected to the load resister. A second gain determining resister is connected between the minus input of the third differential amplifier and a voltage source. A third FET has its gate connected to the output of the third amplifier. The source and drain circuit of the third transistor is connected between the minus input of the third amplifier and a voltage-frequency converter, constituting an output device. A polarity detector is also provided, comprising a pair of transistors having their inputs connected to the outputs of the first and second differential amplifiers. The outputs of the polarity detector are connected to gates which switch the output of the voltage-frequency converter between up and down counting outputs.

Ground Simulations of Near-Surface Plasma Field and Charging at the Lunar Terminator

NASA Astrophysics Data System (ADS)

Polansky, J.; Ding, N.; Wang, J.; Craven, P.; Schneider, T.; Vaughn, J.

2012-12-01

Charging in the lunar terminator region is the most complex and is still not well understood. In this region, the surface potential is sensitively influenced by both solar illumination and plasma flow. The combined effects from localized shadow generated by low sun elevation angles and localized wake generated by plasma flow over the rugged terrain can generate strongly differentially charged surfaces. Few models currently exist that can accurately resolve the combined effects of plasma flow and solar illumination over realistic lunar terminator topographies. This paper presents an experimental investigation of lunar surface charging at the terminator region in simulated plasma environments in a vacuum chamber. The solar wind plasma flow is simulated using an electron bombardment gridded Argon ion source. An electrostatic Langmuir probe, nude Faraday probes, a floating emissive probe, and retarding potential analyzer are used to quantify the plasma flow field. Surface potentials of both conducting and dielectric materials immersed in the plasma flow are measured with a Trek surface potential probe. The conducting material surface potential will simultaneously be measured with a high impedance voltmeter to calibrate the Trek probe. Measurement results will be presented for flat surfaces and objects-on-surface for various angles of attack of the plasma flow. The implications on the generation of localized plasma wake and surface charging at the lunar terminator will be discussed. (This research is supported by the NASA Lunar Advanced Science and Exploration Research program.)

Ion Release and Galvanic Corrosion of Different Orthodontic Brackets and Wires in Artificial Saliva.

PubMed

Tahmasbi, Soodeh; Sheikh, Tahereh; Hemmati, Yasamin B

2017-03-01

To investigate the galvanic corrosion of brackets manufactured by four different companies coupled with stainless steel (SS) or nickel-titanium (NiTi) wires in an artificial saliva solution. A total of 24 mandibular central incisor Roth brackets of four different manufacturers (American Orthodontics, Dentaurum, Shinye, ORJ) were used in this experimental study. These brackets were immersed in artificial saliva along with SS or NiTi orthodontic wires (0.016'', round) for 28 days. The electric potential difference of each bracket/ wire coupled with a saturated calomel reference electrode was measured via a voltmeter and recorded constantly. Corrosion rate (CR) was calculated, and release of ions was measured with an atomic absorption spectrometer. Stereomicroscope was used to evaluate all samples. Then, samples with corrosion were further assessed by scanning electron microscope and energy-dispersive X-ray spectroscopy. Two-way analysis of variance was used to analyze data. Among ions evaluated, release of nickel ions from Shinye brackets was significantly higher than that of other brackets. The mean potential difference was significantly lower in specimens containing a couple of Shinye brackets and SS wire compared with other specimens. No significant difference was observed in the mean CR of various groups (p > 0.05). Microscopic evaluation showed corrosion in two samples only: Shinye bracket coupled with SS wire and American Orthodontics bracket coupled with NiTi wire. Shinye brackets coupled with SS wire showed more susceptibility to galvanic corrosion. There were no significant differences among specimens in terms of the CR or released ions except the release of Ni ions, which was higher in Shinye brackets.

Galvanic Corrosion of and Ion Release from Various Orthodontic Brackets and Wires in a Fluoride-containing Mouthwash.

PubMed

Tahmasbi, Soodeh; Ghorbani, Mohammad; Masudrad, Mahdis

2015-01-01

Background and aims. This study compared the galvanic corrosion of orthodontic wires and brackets from various manufacturers following exposure to a fluoride mouthwash. Materials and methods. This study was conducted on 24 lower central incisor 0.022" Roth brackets of four different commercially available brands (Dentaurum, American Orthodontics, ORJ, Shinye). These brackets along with stainless steel (SS) or nickel-titanium (NiTi) orthodontic wires (0.016", round) were immersed in Oral-B mouthwash containing 0.05% sodium fluoride for 28 days. The electric potential (EP) difference of each bracket-wire couple was measured with a Saturated Calomel Reference Electrode (Ag/AgCl saturated with KCl) via a voltmeter. The ions released in the electrolyte weremeasured with an atomic absorption spectrometer. All the specimens were assessed under a stereomicroscope and specimens with corrosion were analyzed with scanning electron microscopy (SEM). Data were analyzed using ANOVA. Results. The copper ions released from specimens with NiTi wire were greater than those of samples containing SS wire. ORJ brackets released more Cu ions than other samples. The Ni ions released from Shinye brackets were significantly more than those of other specimens (P < 0.05). Corrosion rate of brackets coupled with NiTi wires was higher than that of brackets coupled with SS wires. Light and electron microscopic observations showed greater corrosion of ORJ brackets. Conclusion. In fluoride mouthwash, Shinye and ORJ brackets exhibited greater corrosion than Dentaurum and American Orthodontics brackets. Stainless steel brackets used with NiTi wires showed greater corrosion and thus caution is recommended when using them.

Galvanic Corrosion of and Ion Release from Various Orthodontic Brackets and Wires in a Fluoride-containing Mouthwash

PubMed Central

Tahmasbi, Soodeh; Ghorbani, Mohammad; Masudrad, Mahdis

2015-01-01

Background and aims. This study compared the galvanic corrosion of orthodontic wires and brackets from various manufacturers following exposure to a fluoride mouthwash. Materials and methods. This study was conducted on 24 lower central incisor 0.022" Roth brackets of four different commercially available brands (Dentaurum, American Orthodontics, ORJ, Shinye). These brackets along with stainless steel (SS) or nickel-titanium (NiTi) orthodontic wires (0.016", round) were immersed in Oral-B mouthwash containing 0.05% sodium fluoride for 28 days. The electric potential (EP) difference of each bracket-wire couple was measured with a Saturated Calomel Reference Electrode (Ag/AgCl saturated with KCl) via a voltmeter. The ions released in the electrolyte weremeasured with an atomic absorption spectrometer. All the specimens were assessed under a stereomicroscope and specimens with corrosion were analyzed with scanning electron microscopy (SEM). Data were analyzed using ANOVA. Results. The copper ions released from specimens with NiTi wire were greater than those of samples containing SS wire. ORJ brackets released more Cu ions than other samples. The Ni ions released from Shinye brackets were significantly more than those of other specimens (P < 0.05). Corrosion rate of brackets coupled with NiTi wires was higher than that of brackets coupled with SS wires. Light and electron microscopic observations showed greater corrosion of ORJ brackets. Conclusion. In fluoride mouthwash, Shinye and ORJ brackets exhibited greater corrosion than Dentaurum and American Orthodontics brackets. Stainless steel brackets used with NiTi wires showed greater corrosion and thus caution is recommended when using them. PMID:26697148

Comparison of light-transmittance in dental tissues and dental composite restorations using incremental layering build-up with varying enamel resin layer thickness

PubMed Central

2018-01-01

Objectives To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness. Materials and Methods B1-colored natural teeth slabs were compared to dental restoration build-ups with A2D and B1E-colored nanofilled, supra-nanofilled, microfilled, and microhybrid composites. The enamel layer varied from 0.3, 0.5, or 1.2 mm thick, and the dentin layer was varied to provide a standardized 3.7 mm overall sample thickness (n = 10). All increments were light-cured to 16 J/cm2 with a multi-wave LED (Valo, Ultradent). Using a spectrophotometer, the samples were irradiated by an RGB laser beam. A voltmeter recorded the light output signal to calculate the light-transmittance through the specimens. The data were analyzed using 1-way analysis of variance followed by the post hoc Tukey's test (p = 0.05). Results Mean light-transmittance observed at thicker final layers of enamel were significantly lower than those observed at thinner final layers. Within 1.2 mm final enamel resin layer (FERL) thickness, all composites were similar to the dental tissues, with exception of the nanofilled composite. However, within 0.5 mm FERL thickness, only the supra-nanofilled composite showed no difference from the dental tissues. Within 0.3 mm FERL thickness, none of the composites were similar to the dental tissues. Conclusions The supra-nanofilled composite had the most similar light-transmittance pattern when compared to the natural teeth. However, for other composites, thicker FERL have a greater chance to match the light-transmittance of natural dental tissues. PMID:29765902

Controlled electrostatic methodology for imaging indentations in documents.

PubMed

Yaraskavitch, Luke; Graydon, Matthew; Tanaka, Tobin; Ng, Lay-Keow

2008-05-20

The electrostatic process for imaging indentations on documents using the ESDA device is investigated under controlled experimental settings. An in-house modified commercial xerographic developer housing is used to control the uniformity and volume of toner deposition, allowing for reproducible image development. Along with this novel development tool, an electrostatic voltmeter and fixed environmental conditions facilitate an optimization process. Sample documents are preconditioned in a humidity cabinet with microprocessor control, and the significant benefit of humidification above 70% RH on image quality is verified. Improving on the subjective methods of previous studies, image quality analysis is carried out in an objective and reproducible manner using the PIAS-II. For the seven commercial paper types tested, the optimum ESDA operating point is found to be at an electric potential near -400V at the Mylar surface; however, for most paper types, the optimum operating regime is found to be quite broad, spanning relatively small electric potentials between -200 and -550V. At -400V, the film right above an indented area generally carries a voltage which is 30-50V less negative than the non-indented background. In contrast with Seward's findings [G.H. Seward, Model for electrostatic imaging of forensic evidence via discharge through Mylar-paper path, J. Appl. Phys. 83 (3) (1998) 1450-1456; G.H. Seward, Practical implications of the charge transport model for electrostatic detection apparatus (ESDA), J. Forensic Sci. 44 (4) (1999) 832-836], a period of charge decay before image development is not required when operating in this optimal regime. A brief investigation of the role played by paper-to-paper friction during the indentation process is conducted using our optimized development method.

Designing low cost LED display for the billboard

NASA Astrophysics Data System (ADS)

Hong, Yi-Jian; Uang, Chii-Maw; Wang, Ping-Chieh; Ho, Zu-Sheng

2011-10-01

With quickly advance of the computer, microelectronics and photonics technologies, LED display panel becomes a new electronic advertising media. It can be used to show any information whatever characters or graphics. Most LED display panels are built of many Light-Emitting Diodes arranged in a matrix form. The display has many advantages such as low power, low cost, long life and high definition. Because the display panel is asked to show rich color, the LED display panel's driving system becomes very complex. The design methodology of LED display panel's driver becomes more and more important to meet the market requirements. Cost is always the most important issue in public market domain. In this paper, we report a design methodology of LED display panel's driver based on the microprocessor control unit (MCU) system and LED display controller IC, HT1632C, to control three colors, RGB, color LED display panel and the modular panel size is 24*16 in matrix form. The HT1632C is a memory mapping LED display controller, it can be used on many applications, such as digital clock, thermometer, counter, voltmeter or other instrumentation readouts. Three pieces of HT1632C are used to drive a 24*16 RGB LED display panel, in our design case. Each HT163C chip is used to control one of the R, G and B color. As the drive mode is driven in DC mode, the RGB display panel can create and totally of seven colors under the control of MCU. The MCU generates the control signal to drive HT1632C. In this study, the software design methodology is adopted with dynamic display principle. When the scan frequency is 60Hz, LED display panel will get the clear picture and be able to display seven colors.

Deconstructing and constructing innate immune functions using molecular sensors and actuators

NASA Astrophysics Data System (ADS)

Coutinho, Kester; Inoue, Takanari

2016-05-01

White blood cells such as neutrophils and macrophages are made competent for chemotaxis and phagocytosis -- the dynamic cellular behaviors that are hallmarks of their innate immune functions -- by the reorganization of complex biological circuits during differentiation. Conventional loss-of-function approaches have revealed that more than 100 genes participate in these cellular functions, and we have begun to understand the intricate signaling circuits that are built up from these gene products. We now appreciate: (1) that these circuits come in a variety of flavors -- so that we can make a distinction between genetic circuits, metabolic circuits and signaling circuits; and (2) that they are usually so complex that the assumption of multiple feedback loops, as well as that of crosstalk between seemingly independent pathways, is now routine. It has not escaped our notice, however, that just as physicists and electrical engineers have long been able to disentangle complex electric circuits simply by repetitive cycles of probing and measuring electric currents using a voltmeter, we might similarly be able to dissect these intricate biological circuits by incorporating equivalent approaches in the fields of cell biology and bioengineering. Existing techniques in biology for probing individual circuit components are unfortunately lacking, so that the overarching goal of drawing an exact circuit diagram for the whole cell -- complete with kinetic parameters for connections between individual circuit components -- is not yet in near sight. My laboratory and others have thus begun the development of a new series of molecular tools that can measurably investigate the circuit connectivity inside living cells, as if we were doing so on a silicon board. In these proceedings, I will introduce some of these techniques, provide examples of their implementation, and offer a perspective on directions moving forward.

Measurements of matric and water potentials in unsaturated tuff at Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thamir, F.; McBride, C.M.

1985-12-31

Two types of instruments were installed in a borehole in order to monitor matric and water potentials of various hydrogeologic units consisting of tuff. The borehole was drilled as part of a study to provide information to the US Department of Energy for their use in evaluating Yucca Mountain, Nevada, for a repository for high-level radioactive waste. Heat-dissipation probes were used to monitor matric potentials and thermocouple psychrometers were used to monitor water potentials. Two major concerns regarding the use of these instruments in deep boreholes are: (1) the effect of length of the lead wires, and (2) the inabilitymore » to recalibrate the instruments after installation. The length of the lead wire contributes to the source resistance and lead capacitance, which affects the signal settling time. Both instruments tested proved to be insensitive to lead-wire length, except when connected to smaller input-impedance data loggers. Thermocouple wires were more sensitive than heat-dissipation probe wires because of their greater resistance and quality of voltmeters used. Two thermocouple psychrometers were installed at every instrument station for backup and verification of data, because the instruments could not be recalibrated in situ. Multiple scanning rather than single-point scanning of the evaporation curve of a thermocouple psychrometer could give more reliable data, especially in differentiating between very wet and very dry environments. An isolated power supply needs to be used for each heat dissipation probe rather than a single power supply for a group of probes to avoid losing data from all probes when one probe malfunctions. This type of system is particularly desirable if the site is unattended by an operator for as long as a month. 20 refs., 13 figs., 2 tabs.« less

Comparison of light-transmittance in dental tissues and dental composite restorations using incremental layering build-up with varying enamel resin layer thickness.

PubMed

Rocha Maia, Rodrigo; Oliveira, Dayane; D'Antonio, Tracy; Qian, Fang; Skiff, Frederick

2018-05-01

To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness. B1-colored natural teeth slabs were compared to dental restoration build-ups with A2D and B1E-colored nanofilled, supra-nanofilled, microfilled, and microhybrid composites. The enamel layer varied from 0.3, 0.5, or 1.2 mm thick, and the dentin layer was varied to provide a standardized 3.7 mm overall sample thickness ( n = 10). All increments were light-cured to 16 J/cm 2 with a multi-wave LED (Valo, Ultradent). Using a spectrophotometer, the samples were irradiated by an RGB laser beam. A voltmeter recorded the light output signal to calculate the light-transmittance through the specimens. The data were analyzed using 1-way analysis of variance followed by the post hoc Tukey's test ( p = 0.05). Mean light-transmittance observed at thicker final layers of enamel were significantly lower than those observed at thinner final layers. Within 1.2 mm final enamel resin layer (FERL) thickness, all composites were similar to the dental tissues, with exception of the nanofilled composite. However, within 0.5 mm FERL thickness, only the supra-nanofilled composite showed no difference from the dental tissues. Within 0.3 mm FERL thickness, none of the composites were similar to the dental tissues. The supra-nanofilled composite had the most similar light-transmittance pattern when compared to the natural teeth. However, for other composites, thicker FERL have a greater chance to match the light-transmittance of natural dental tissues.

Molecular insight into the electrostatic membrane surface potential by 14n/31p MAS NMR spectroscopy: nociceptin-lipid association.

PubMed

Lindström, Fredrick; Williamson, Philip T F; Gröbner, Gerhard

2005-05-11

Exploiting naturally abundant (14)N and (31)P nuclei by high-resolution MAS NMR (magic angle spinning nuclear magnetic resonance) provides a molecular view of the electrostatic potential present at the surface of biological model membranes, the electrostatic charge distribution across the membrane interface, and changes that occur upon peptide association. The spectral resolution in (31)P and (14)N MAS NMR spectra is sufficient to probe directly the negatively charged phosphate and positively charged choline segment of the electrostatic P(-)-O-CH(2)-CH(2)-N(+)(CH(3))(3) headgroup dipole of zwitterionic DMPC (dimyristoylphosphatidylcholine) in mixed-lipid systems. The isotropic shifts report on the size of the potential existing at the phosphate and ammonium group within the lipid headgroup while the chemical shielding anisotropy ((31)P) and anisotropic quadrupolar interaction ((14)N) characterize changes in headgroup orientation in response to surface potential. The (31)P/(14)N isotropic chemical shifts for DMPC show opposing systematic changes in response to changing membrane potential, reflecting the size of the electrostatic potential at opposing ends of the P(-)-N(+) dipole. The orientational response of the DMPC lipid headgroup to electrostatic surface variations is visible in the anisotropic features of (14)N and (31)P NMR spectra. These features are analyzed in terms of a modified "molecular voltmeter" model, with changes in dynamic averaging reflecting the tilt of the C(beta)-N(+)(CH)(3) choline and PO(4)(-) segment. These properties have been exploited to characterize the changes in surface potential upon the binding of nociceptin to negatively charged membranes, a process assumed to proceed its agonistic binding to its opoid G-protein coupled receptor.

Rhinovirus disrupts the barrier function of polarized airway epithelial cells.

PubMed

Sajjan, Umadevi; Wang, Qiong; Zhao, Ying; Gruenert, Dieter C; Hershenson, Marc B

2008-12-15

Secondary bacterial infection following rhinovirus (RV) infection has been recognized in chronic obstructive pulmonary disease. We sought to understand mechanisms by which RV infection facilitates secondary bacterial infection. Primary human airway epithelial cells grown at air-liquid interface and human bronchial epithelial (16HBE14o-) cells grown as polarized monolayers were infected apically with RV. Transmigration of bacteria (nontypeable Haemophilus influenzae and others) was assessed by colony counting and transmission electron microscopy. Transepithelial resistance (R(T)) was measured by using a voltmeter. The distribution of zona occludins (ZO)-1 was determined by immunohistochemistry and immunoblotting. Epithelial cells infected with RV showed 2-log more bound bacteria than sham-infected cultures, and bacteria were recovered from the basolateral media of RV- but not sham-infected cells. Infection of polarized airway epithelial cell cultures with RV for 24 hours caused a significant decrease in R(T) without causing cell death or apoptosis. Ultraviolet-treated RV did not decrease R(T), suggesting a requirement for viral replication. Reduced R(T) was associated with increased paracellular permeability, as determined by flux of fluorescein isothiocyanate (FITC)-inulin. Neutralizing antibodies to tumor necrosis factor (TNF)-alpha, IFN-gamma and IL-1beta reversed corresponding cytokine-induced reductions in R(T) but not that induced by RV, indicating that the RV effect is independent of these proinflammatory cytokines. Confocal microscopy and immunoblotting revealed the loss of ZO-1 from tight junction complexes in RV-infected cells. Intranasal inoculation of mice with RV1B also caused the loss of ZO-1 from the bronchial epithelium tight junctions in vivo. RV facilitates binding, translocation, and persistence of bacteria by disrupting airway epithelial barrier function.

Coulomb interactions between cytoplasmic electric fields and phosphorylated messenger proteins optimize information flow in cells.

PubMed

Gatenby, Robert A; Frieden, B Roy

2010-08-11

Normal cell function requires timely and accurate transmission of information from receptors on the cell membrane (CM) to the nucleus. Movement of messenger proteins in the cytoplasm is thought to be dependent on random walk. However, Brownian motion will disperse messenger proteins throughout the cytosol resulting in slow and highly variable transit times. We propose that a critical component of information transfer is an intracellular electric field generated by distribution of charge on the nuclear membrane (NM). While the latter has been demonstrated experimentally for decades, the role of the consequent electric field has been assumed to be minimal due to a Debye length of about 1 nanometer that results from screening by intracellular Cl- and K+. We propose inclusion of these inorganic ions in the Debye-Huckel equation is incorrect because nuclear pores allow transit through the membrane at a rate far faster than the time to thermodynamic equilibrium. In our model, only the charged, mobile messenger proteins contribute to the Debye length. Using this revised model and published data, we estimate the NM possesses a Debye-Huckel length of a few microns and find this is consistent with recent measurement using intracellular nano-voltmeters. We demonstrate the field will accelerate isolated messenger proteins toward the nucleus through Coulomb interactions with negative charges added by phosphorylation. We calculate transit times as short as 0.01 sec. When large numbers of phosphorylated messenger proteins are generated by increasing concentrations of extracellular ligands, we demonstrate they generate a self-screening environment that regionally attenuates the cytoplasmic field, slowing movement but permitting greater cross talk among pathways. Preliminary experimental results with phosphorylated RAF are consistent with model predictions. This work demonstrates that previously unrecognized Coulomb interactions between phosphorylated messenger proteins and intracellular electric fields will optimize information transfer from the CM to the NM in cells.

Study of light transmission through gauze pad effected by blood or liquids to detect needle dislodgement.

PubMed

Takeuchi, Akihiro; Ishida, Kai; Morohoshi, Yasuo; Shinbo, Toshihiro; Hirose, Minoru; Ikeda, Noriaki

2010-02-01

Serious accidents during hemodialysis such as a large amount of blood loss are often caused by venous needle dislodgement. To develop a bleeding sensor based on a photo sensor for monitoring the needle sites, we studied effects of liquids and porcine blood on light transmission through a thin gauze pad with a basic photo sensor. The photo sensor consisted of an ordinary electrical circuit, a light emitting diode (LED, lambda max = 645 nm), a photo diode (PD), and a thin gauze pad placed between the LED and PD that were tightly attached to the edges of a plastic clip. The light transmitted through the gauze pad, soaked with liquids or porcine blood dropped on it, was measured with a digital voltmeter. The liquids were reverse osmosis water, physiological saline, glucose in water at 5, 10, 20, 40 and 50%, porcine plasma, and porcine blood (Hct 40, 30 and 20%). The liquids on a tight-weave gauze pad, significantly increased the voltage (light transmission) from 0.412 +/- 0.003 V (SD) to 0.794 +/- 0.025 V (minimum, by reverse osmosis water) and to 0.945 +/- 0.011 V (maximum, by 50% glucose). The porcine blood significantly decreased the voltage from 0.412 to 0.195 +/- 0.030 V in Hct 40%, to 0.334 +/- 0.035 in Hct 30%, to 0.397 +/- 0.007 V in Hct 20%. The higher the concentration of glucose, the more the light transmission increased. The higher concentration of Hct, the more the light transmission decreased. Similar results were also shown for the loose-weave pad. Using two types of gauze pads, we confirmed that liquids significantly increased light transmission through gauze pad, but porcine blood decreased light transmission. This opposite response can be used to distinguish liquids from blood on a gauze pad.

Uncertainty analysis of thermocouple measurements used in normal and abnormal thermal environment experiments at Sandia's Radiant Heat Facility and Lurance Canyon Burn Site.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakos, James Thomas

2004-04-01

It would not be possible to confidently qualify weapon systems performance or validate computer codes without knowing the uncertainty of the experimental data used. This report provides uncertainty estimates associated with thermocouple data for temperature measurements from two of Sandia's large-scale thermal facilities. These two facilities (the Radiant Heat Facility (RHF) and the Lurance Canyon Burn Site (LCBS)) routinely gather data from normal and abnormal thermal environment experiments. They are managed by Fire Science & Technology Department 09132. Uncertainty analyses were performed for several thermocouple (TC) data acquisition systems (DASs) used at the RHF and LCBS. These analyses apply tomore » Type K, chromel-alumel thermocouples of various types: fiberglass sheathed TC wire, mineral-insulated, metal-sheathed (MIMS) TC assemblies, and are easily extended to other TC materials (e.g., copper-constantan). Several DASs were analyzed: (1) A Hewlett-Packard (HP) 3852A system, and (2) several National Instrument (NI) systems. The uncertainty analyses were performed on the entire system from the TC to the DAS output file. Uncertainty sources include TC mounting errors, ANSI standard calibration uncertainty for Type K TC wire, potential errors due to temperature gradients inside connectors, extension wire uncertainty, DAS hardware uncertainties including noise, common mode rejection ratio, digital voltmeter accuracy, mV to temperature conversion, analog to digital conversion, and other possible sources. Typical results for 'normal' environments (e.g., maximum of 300-400 K) showed the total uncertainty to be about {+-}1% of the reading in absolute temperature. In high temperature or high heat flux ('abnormal') thermal environments, total uncertainties range up to {+-}2-3% of the reading (maximum of 1300 K). The higher uncertainties in abnormal thermal environments are caused by increased errors due to the effects of imperfect TC attachment to the test item. 'Best practices' are provided in Section 9 to help the user to obtain the best measurements possible.« less

Specific storage and hydraulic conductivity tomography through the joint inversion of hydraulic heads and self-potential data

NASA Astrophysics Data System (ADS)

Ahmed, A. Soueid; Jardani, A.; Revil, A.; Dupont, J. P.

2016-03-01

Transient hydraulic tomography is used to image the heterogeneous hydraulic conductivity and specific storage fields of shallow aquifers using time series of hydraulic head data. Such ill-posed and non-unique inverse problem can be regularized using some spatial geostatistical characteristic of the two fields. In addition to hydraulic heads changes, the flow of water, during pumping tests, generates an electrical field of electrokinetic nature. These electrical field fluctuations can be passively recorded at the ground surface using a network of non-polarizing electrodes connected to a high impedance (> 10 MOhm) and sensitive (0.1 mV) voltmeter, a method known in geophysics as the self-potential method. We perform a joint inversion of the self-potential and hydraulic head data to image the hydraulic conductivity and specific storage fields. We work on a 3D synthetic confined aquifer and we use the adjoint state method to compute the sensitivities of the hydraulic parameters to the hydraulic head and self-potential data in both steady-state and transient conditions. The inverse problem is solved using the geostatistical quasi-linear algorithm framework of Kitanidis. When the number of piezometers is small, the record of the transient self-potential signals provides useful information to characterize the hydraulic conductivity and specific storage fields. These results show that the self-potential method reveals the heterogeneities of some areas of the aquifer, which could not been captured by the tomography based on the hydraulic heads alone. In our analysis, the improvement on the hydraulic conductivity and specific storage estimations were based on perfect knowledge of electrical resistivity field. This implies that electrical resistivity will need to be jointly inverted with the hydraulic parameters in future studies and the impact of its uncertainty assessed with respect to the final tomograms of the hydraulic parameters.

Self-Nulling Lock-in Detection Electronics for Capacitance Probe Electrometer

NASA Technical Reports Server (NTRS)

Blaes, Brent R.; Schaefer, Rembrandt T.

2012-01-01

A multi-channel electrometer voltmeter that employs self-nulling lock-in detection electronics in conjunction with a mechanical resonator with noncontact voltage sensing electrodes has been developed for space-based measurement of an Internal Electrostatic Discharge Monitor (IESDM). The IESDM is new sensor technology targeted for integration into a Space Environmental Monitor (SEM) subsystem used for the characterization and monitoring of deep dielectric charging on spacecraft. Use of an AC-coupled lock-in amplifier with closed-loop sense-signal nulling via generation of an active guard-driving feedback voltage provides the resolution, accuracy, linearity and stability needed for long-term space-based measurement of the IESDM. This implementation relies on adjusting the feedback voltage to drive the sense current received from the resonator s variable-capacitance-probe voltage transducer to approximately zero, as limited by the signal-to-noise performance of the loop electronics. The magnitude of the sense current is proportional to the difference between the input voltage being measured and the feedback voltage, which matches the input voltage when the sense current is zero. High signal-to-noise-ratio (SNR) is achieved by synchronous detection of the sense signal using the correlated reference signal derived from the oscillator circuit that drives the mechanical resonator. The magnitude of the feedback voltage, while the loop is in a settled state with essentially zero sense current, is an accurate estimate of the input voltage being measured. This technique has many beneficial attributes including immunity to drift, high linearity, high SNR from synchronous detection of a single-frequency carrier selected to avoid potentially noisy 1/f low-frequency spectrum of the signal-chain electronics, and high accuracy provided through the benefits of a driven shield encasing the capacitance- probe transducer and guarded input triaxial lead-in. Measurements obtained from a 2- channel prototype electrometer have demonstrated good accuracy (|error| < 0.2 V) and high stability. Twenty-four-hour tests have been performed with virtually no drift. Additionally, 5,500 repeated one-second measurements of 100 V input were shown to be approximately normally distributed with a standard deviation of 140 mV.

Connecting Time and Frequency in the RC Circuit

NASA Astrophysics Data System (ADS)

Moya, A. A.

2017-04-01

Charging and discharging processes of a capacitor through a resistor, as well as the concept of impedance in alternating current circuits, are topics covered in introductory physics courses. The experimental study of the charge and discharge of a capacitor through a resistor is a well-established lab exercise that is used to introduce concepts such as exponential increase or decrease and time constant. Determining the time constant of the RC circuit has important practical applications because, for example, it can be used to measure unknown values of resistance or capacitance. The transient experiment can be done by using a voltmeter and stopwatch, signal generator and oscilloscope, or even low-cost data acquisition systems such as Arduino. An equivalent topic when studying alternating current circuits arises from the characterization of the impedance of the series or parallel combination of the capacitor and the resistor as a function of frequency. Determining the time constant of the RC circuit by means of impedance measurements for different frequencies is a known experimental technique that can be done using not only LCR meters but also basic instrumentation in the physics lab such as a signal generator, frequency counter, and multimeter. However, lab exercises dealing with RC circuits in alternating current usually focus on their use as filters, and the potential applications in the field of the electrical characterization of material systems are ignored. In this work, we describe a simple exercise showing how the time constant of the RC circuit can easily be determined in the introductory physics lab by means of impedance measurements as a function of frequency. This exercise allows students to learn experimental techniques that find application to characterize the time constants of the charge transport processes in material systems. Moreover, comparison of the time constants obtained from transient and frequency analysis allows us to relate the time and frequency domains, which plays a central role in the advanced analysis of electric circuits, once the concept of Laplace transform has been introduced in order to simplify the problem of dealing with differential equations in the time domain by converting them into algebraic equations within the frequency domain.

Magnetotransport in magnetic nanostructures

NASA Astrophysics Data System (ADS)

Panchula, Alex F.

The unifying theme of this dissertation is the exploration of novel magnetic thin film materials to improve our understanding of spin-dependent transport in such materials, especially with regard to their use in the nascent field of spin based devices. Such devices, which rely on controlling the electron's spin rather than its charge as in conventional micro-electronics, may be important for applications in sensing, memory and computation. This dissertation covers research performed at the IBM Almaden Research Center between 2000 and 2003. One class of spin-based devices are magnetic tunnel junctions (MTJs), which display large changes in resistance in small magnetic fields. This tunneling magnetoresistance (TMR) is derived from changes in the relative alignment of the magnetic moments of thin ferromagnetic layers which are separated by thin insulating layers. The tunneling current spin polarization (TSP) determines the magnitude of the TMR. For typical transition-metal ferromagnets and their alloys the TSP is ˜50% although it is anticipated that half-metals should display nearly 100%. Confirming theoretical predictions, MTJs with electrodes of magnetite and a conventional ferromagnet such as a CoFe alloy, display an inverted TMR, consistent with negatively spin polarized magnetite electrodes. However, the magnitude of TSP of -48% at low temperatures, is not much larger than that exhibited by conventional 3d transition metal ferromagnets. At high temperatures, transport through the MTJ is dominated by tunneling across the alumina tunnel barrier, while at low temperatures the bulk properties of the magnetite dominates at low bias voltage. Another class of half-metals, the semi-heuslers exhibit low TSP, most likely due to surface disorder and, as revealed in this work, the possible formation of MnSb. The MnSb alloys studied in MTJs are found to behave as typical ferromagnets with a small positive TMR. Also considered are MTJs whose barriers are comprised of the wide band-gap semiconductors, ZnSe and Cr2O3. These low barrier height materials show typical tunneling behavior, although the TMR is lower than found for wide-gap insulators. Finally, the development of a high precision SQUID based voltmeter for application to low resistance devices with the current perpendicular to the plane of the materials is outlined.

Inexpensive Ultrasound Demonstrations as Analogs of Radio Diffraction in the field : Huygens Probe Bistatic experiment on Titan and the Sea Interferometer (Invited)

NASA Astrophysics Data System (ADS)

Lorenz, R. D.

2013-12-01

The wave nature of electromagnetic radiation can be exploited in a number of astronomical and remote sensing methods, but is often challenging to visualize in the classroom. One approach with conveniently-inexpensive components is to use sound as an analog. Readily-available ultrasonic transducers at 40 kHz can be driven with a 555 oscillator and received intensity detected with an op-amp and visualized with a digital voltmeter, a lightbulb, or even acoustically. The wavelength of 9mm is convenient for tabletop experiments, with a relevant example being Lloyds Mirror, the interference of a direct wave from a source just above a surface with the reflected wave. As a distant receiver moves in angle through this interference pattern, a series of peaks and nulls in recorded intensity can be interpreted as the height of the transmitter and the reflectivity (i.e. with some assumptions, the roughness) of the reflecting surface. This $10 experiment will be demonstrated at the poster. Such an observation was (serendipitously) made in 2005 after the landing of the Huygens probe on the surface of Titan, where the radio signal measured by Cassini as it set on the horizon as seen from the probe underwent sharp dips in strength that were inverted into a precise measurement of the post-impact probe height. A similar technique in reverse was applied a half century earlier in early Australian radio astronomy to measure the position and width of astrophysical sources from a single clifftop antenna. Ultrasound can be convenient to emulate other radio work, exploiting Doppler effects and (for pulsed sources, like those used in rangers for amateur robotics) propagation time rather than diffraction. Some experiments on tracking Frisbees as an analog for measuring planetary winds by tracking descent probes, and on bistatic delay/Doppler scatterometry as in the CYGNSS GPS-based experiment to measure hurricane winds via sea state, will also be discussed. Huygens probe on the surface of Titan. The interference pattern constrained Titan surface properties Ultrasound pattern is a function of geometry and surface covering

Sandbox experiments on Uraninite Ore: ERT and SP measurments.

NASA Astrophysics Data System (ADS)

Singh, R. K.

2015-12-01

Nuclear energy, considering its own intrinsic merits, would be a leading source for meeting the energy requirement in present and future scenario. Concealed Uranium deposits under sedimentary cover, with poor surface indications calls for reorientation of survey with large inputs involving integrated geophysical approach. Sand Box experiments have been carried out over Uraninite ore. The tank is a glass fish tank (height 39 cm, length 75 cm, width 30 cm). It was filled with sand up to 35 cm high. The sand was saturated from below to minimize the entrapment of the gas bubbles. The average size for sand grains is ~ 0.295mm. The formation factor of the sand is 3.5, with a negligible surface conductivity because of the coarse nature of the sand grains. The dimension of considered Uraninite ore sample is 4cm x 4cm x 4cm. The depth of top of the ore sample is kept at 3cm. In this paper both resistivity and self-potential measurements were carried out for possible detection of Uraninite. The resistivity measurements were made with 64 non-polarizable electrodes using Electrical Resistivity Tomography (ERT) equipment of FlashRes Universal developed by ZZ Resistivity Imaging Pty. Ltd. We have used screws of length 3cm as electrodes. The separation between these electrodes are ~ 1cm. The resistivity tomography results clearly outlines the target Uraninite body. The resistivity tomography results also detects small heterogeneities associated with air bubbles possibly due to unsaturated pore spaces. SP measurements were made using two non-polarizing Pb/PbCl2 electrodes and a Fluke 289 voltmeter (sensitivity 0.001 mV, internal impedance 100 MOhm). The reference electrode was located on the corner of the sandbox. The other electrode was used to scan the electrical potential at the surface of the sand. SP measurements were made with a spacing of 3 cm over the same ERT profile. The SP results also shows a dip (or a low SP anomaly) over the target ore body sample. Thus, both SP and ERT results show the presence of Uraninite and could be used on the routine basis for possible detection of Uraninite.

Developing suitable methods for effective characterization of electrical properties of root segments

NASA Astrophysics Data System (ADS)

Ehosioke, Solomon; Phalempin, Maxime; Garré, Sarah; Kemna, Andreas; Huisman, Sander; Javaux, Mathieu; Nguyen, Frédéric

2017-04-01

The root system represents the hidden half of the plant which plays a key role in food production and therefore needs to be well understood. Root system characterization has been a great challenge because the roots are buried in the soil. This coupled with the subsurface heterogeneity and the transient nature of the biogeochemical processes that occur in the root zone makes it difficult to access and monitor the root system over time. The traditional method of point sampling (root excavation, monoliths, minirhizotron etc.) for root investigation does not account for the transient nature and spatial variability of the root zone, and it often disturbs the natural system under investigation. The quest to overcome these challenges has led to an increase in the application of geophysical methods. Recent studies have shown a correlation between bulk electrical resistivity and root mass density, but an understanding of the contribution of the individual segments of the root system to that bulk signal is still missing. This study is an attempt to understand the electrical properties of roots at the segment scale (1-5cm) for more effective characterization of electrical signal of the full root architecture. The target plants were grown in three different media (pot soil, hydroponics and a mixture of sand, perlite and vermiculite). Resistance measurements were carried out on a single segment of each study plant using a voltmeter while the diameter was measured using a digital calliper. The axial resistance was calculated using the measured resistance and the geometric parameters. This procedure was repeated for each plant replica over a period of 75 days which enabled us to study the effects of age, growth media, diameter and length on the electrical response of the root segments of the selected plants. The growth medium was found to have a significant effect on the root electrical response, while the effect of root diameter on their electrical response was found to vary among the plants. More work is still required to further validate these results and also to develop better systems to study the electrical behaviour of root segments. Findings from our review entitled "an overview of the geophysical approach to root investigation", suggest that SIP and EIT geophysical methods could be very useful for root investigations, thus more work is in progress to develop these systems for assessing the root electrical response at various scales.

Low Frequency Radio-wave System for subsurface investigation

NASA Astrophysics Data System (ADS)

Soldovieri, Francesco; Gennarelli, Gianluca; Kudelya, Anatoliy; Denisov, Alexander

2015-04-01

Low frequency radio-wave methods (RWM) allow subsurface investigations in terms of lithological structure characterization, detection of filtration flows of ground water, anthropogenic and natural cavities. In this contribution, we present a RWM that exploits two coils working at frequencies of few MHz as transmitting and receiving antennas. The basic principle of this inductive method is as follows. The primary alternating electromagnetic field radiated by the transmitting coil induces eddy currents in the subsurface mainly due to the conductivity anomalies. These eddy currents generate a secondary (scattered) magnetic field which overlaps to the incident magnetic field and is detected by the receiving coil. Despite the simple operation of the system, the complexity of the electromagnetic scattering phenomenon at hand must be properly modeled to achieve adequate performance. Therefore, an advanced data processing technique, belonging to the class of the inverse scattering approaches, has been developed by the authors in a full 3D geometry. The proposed method allows to deal with data collected on a scanning surface under a dipole inductive profiling (DIP) modality, where the transmitting/receiving coils are moved simultaneously with fixed offset (multi-bistatic configuration). The hardware, called Dipole Inductive Radio-wave System (DIRS), is composed by an electronic unit and transmitting and receiving loop antennas radiating at frequencies of few MHz (2-4 MHz), which are installed on theodolite supports. The compactness of DIRS and its robustness to external electromagnetic interference offers the possibility to perform geophysical research up to the depth of some tens of meters and under several types of ground and water surfaces, vegetation, and weather conditions. The light weight and small size of system (the single antenna with support weights about 5 kg and has a diameter of 0.5m) allows two operators to perform geophysical research without disturbing the surface integrity of investigated ground massif. The value of base and the value of voltage induced on the digital voltmeter of the receiver are stored in memory on a SD-card for a subsequent visualization and processing. Realistic cases of application of the DIRS system enhanced by the inverse scattering approach will be presented at the conference with regard to the geological characterization of a mine shaft and an archaeological site.

Polymer Electrolyte-Based Ambient Temperature Oxygen Microsensors for Environmental Monitoring

NASA Technical Reports Server (NTRS)

Hunter, Gary W.; Xu, Jennifer C.; Liu, Chung-Chiun

2011-01-01

An ambient temperature oxygen microsensor, based on a Nafion polymer electrolyte, has been developed and was microfabricated using thin-film technologies. A challenge in the operation of Nafion-based sensor systems is that the conductivity of Nafion film depends on the humidity in the film. Nafion film loses conductivity when the moisture content in the film is too low, which can affect sensor operation. The advancement here is the identification of a method to retain the operation of the Nafion films in lower humidity environments. Certain salts can hold water molecules in the Nafion film structure at room temperature. By mixing salts with the Nafion solution, water molecules can be homogeneously distributed in the Nafion film increasing the film s hydration to prevent Nafion film from being dried out in low-humidity environment. The presence of organics provides extra sites in the Nafion film to promote proton (H+) mobility and thus improving Nafion film conductivity and sensor performance. The fabrication of ambient temperature oxygen microsensors includes depositing basic electrodes using noble metals, and metal oxides layer on one of the electrode as a reference electrode. The use of noble metals for electrodes is due to their strong catalytic properties for oxygen reduction. A conducting polymer Nafion, doped with water-retaining components and extra sites facilitating proton movement, was used as the electrolyte material, making the design adequate for low humidity environment applications. The Nafion solution was coated on the electrodes and air-dried. The sensor operates at room temperature in potentiometric mode, which measures voltage differences between working and reference electrodes in different gases. Repeat able responses to 21-percent oxygen in nitrogen were achieved using nitrogen as a baseline gas. Detection of oxygen from 7 to 21 percent has also been demonstrated. The room-temperature oxygen micro sensor developed has extremely low power consumption (no heating for operation, no voltage applied to the sensor, only a voltmeter is needed to measure the output), is small in size, is simple to batch-fabricate, and is high in sensor yield. It is applicable in a wide humidity range, with improved operation in low humidity after the additives were added to the Nafion film. Through further improvement and development, the sensor can be used for aerospace applications such as fuel leak detection, fire detection, and environmental monitoring.

Aerosol domination of mesosheric ionization: In situ data spanning five decades

NASA Astrophysics Data System (ADS)

Hale, L.

Local mesospheric electrical phenomena are controlled by ionization production and recombination, and by electron attachment and detachment. These in turn are controlled by ionizing and detaching radiation, and by neutral atmosphere dynamics and chemistry, the latter frequently dominated by aerosol particles. Many detailed studies have been made of these phenomena for a gas phase atmosphere, but much less has been determined about the characteristics of aerosol particles, particularly those in the "invisible" range of order 10 nm. Aerosol dominates gas phase phenomena in many situations at all latitudes. The presence of larger particles at high latitudes has been known for over a century from the presence of "noctilucent clouds," and their variability has been inferred by Thomas, et al. (Nature v.337, 1989) from the relative absence of observations in earlier eras, before the massive release of industrial pollution. Studies of such particles are being well researched at the present time, and this paper is mainly concerned with "invisible" particles at lower latitudes. The presence of such particles was first inferred from a rocket launched at White Sands by Bourdeau, et al. in 1950 (JGR, 1959), and has been confirmed by many subsequent measurements (e.g. Hale, COSPAR, 1983). However the aerosol contributes to a variability so large (over six orders of magnitude in total conductivity at a single altitude) that it is difficult to study their variability with the limited amount of data (a few hundred rockets as compared to hundreds of thousands launched to measure temperature). One rocket series conducted during relatively "stationary" conditions without much chemistry or cosmic ray variat ions led to the conclusion that they were ice or water coated (Chesworth and Hale, v.1, GRL., 1974). The aerosol contributes to a very low nighttime conductivity that facilitates the penetration of ELF energy to about 80 km at night. Quasi static fields following- large lightning strokes provide the energy necessary to initiate the phenomena of "red sprites" in the mesosphere. "Slow tails" associated with the establishment of these fields propagate globally and comprise a few percent of the DC global circuit. Also, while travelling the globe in the earth-ionosphere cavity they "polarize" the magnetosphere depositing charge at the base of the conjugate ionosphere, sufficient to maintain the large "volt/meter" mesospheric fields (including hemispheric differences), observed by Russian and US groups (Hale, COSPAR, 2000). Examination of the data show that evaluation of long term secular changes, independent of many variables, can best be done in the DAYTIME by positive ion measurements at altitudes where free electrons dominate the conductivity.

Stress Tuning of Laser Crystals

NASA Technical Reports Server (NTRS)

Carty, Atherton A.

1995-01-01

The topic of stress tunable laser crystals is addressed in this study with the purpose of determining the piezo-optic coefficients of a new laser material. This data was collected using a quadruple pass birefringence technique because of its high degree of sensitivity relative to the other methods examined including fringe shift analysis using a Mach-Zender interferometer. A green He-Ne laser was passed through a light chopper and Glan-Thompson prism before entering a crystal of Erbium doped Yttrium Aluminum Garnet (Er:YAG) (used in order to validate the experimental technique). The Er:YAG crystal is mounted in a press mechanism and the laser is quadruple passed through test specimen before being returned through the prism and the orthogonally polarized portion of the beam measured with a optical sensor. At a later stage, the Er:YAG crystal was replaced with a new crystal in order to determine the piezo-optic coefficients of this uncharacterized material. The applied load was monitored with the use of a 50 lb. load cell placed in line with the press. Light transmission readings were taken using a lock-in amplifier while load cell measurements were taken with a voltmeter from a 5 volt, 0.5 amp power supply. Despite the fact that an effective crystal press damping system was developed, size limitations precluded the use of the complete system. For this reason, data points were taken only once per full turn so as to minimize the effect of non uniform load application on the collected data. Good correlation was found in the transmission data between the experimentally determined Er:YAG and the previously known peizo-optic constants of non-doped crystal with which it was compared. The variation which was found between the two could be accounted for by the aforementioned presence of Erbium in the experimental sample (for which exact empirical data was not known). The same test procedure was then carried out on a Yttrium Gallium Aluminum garnet (YGAG) for the purpose of establishing values of its unknown piezo-optic constant tensor using experimentally collected transmission data. Significant variation between the piezo-optic constants of YAG and YGAG crystals was found however, the excellent data correlation of separate experimental runs carried out on the YGAG sample demonstrates the validity of these results. The data collected during the stressing of the YGAG was of high quality, however the amount of data collected was somewhat limited by a fracture of YGAG specimen which undoubted altered the crystalline lattice structure and hence precluded any further testing.

DC Electric Field Measurement by the Double Probe System Aboard Geotail and its Simulation

NASA Astrophysics Data System (ADS)

Kasaba, Y.; Hayakawa, H.; Ishisaka, K.; Okada, T.; Matsuoka, A.; Mukai, T.; Okada, M.

2005-12-01

We summarize the characteristics of the DC electric field measurement by the double probe system, PANT and EFD-P, aboard Geotail. The accuracy and correction factors for the gain (effective length) and off-set, which depends on ambient plasma conditions, are provided. Accurate measurements of electric fields are essential for space plasma studies, for example, plasma convection, wave-particle interactions, violation of MHD approximation, etc. One typical measurement techniques is the 'Double Probe method', identical to that of a voltmeter: the potential difference between two top-hat probes [cf. Pedersen et al., 1984]. This method can measure electric fields passively and continuously in all plasma conditions. However, the accuracy of the measured electric field values is limited. The probe measurement is also subjected to the variable gain (effective length) of the probe antenna and the artificial offset of the measured values. Those depend on a) the disturbance from ambient plasma and b) the disturbance from the spacecraft and the probe itself. In this paper, we show the results of the characteristics of DC electric field measurement by the PANT probe and the EFD-P (Electric Field Detector - Probe technique) receiver aboard Geotail [Tsuruda et al., 1994], in order to evaluate the accuracy, gain, and offset controlled by ambient plasmas. We conclude that the Geotail electric field measurement by the double probe system has the accuracy 0.4 mV/m for Ex and 0.3 mV/m for Ey, after the correction of the gain and offset. In better conditions, accuracy of Ey is 0.2 mV/m. The potential accuracy would be better because those values are limited by the accuracy of the particle measurement especially in low density conditions. In practical use, the corrections by long-term variation and spacecraft potential are effective to refine the electric field data. The characteristics of long-term variation and the dependences on ambient plasma are not fully understood well, yet. Further works will be needed based on the calibrated LEP data after 1998. It will also cover the conditions rejected in this paper, i.e., low density regions, potential controlled period, electric field quasi-parallel to magnetic field, etc. The comparison with EFD-B (EFD - Beam technique) data will also be included in order to reject the ambiguity in particle observations. In addition, we are trying to establish the numerical model of the double probe system for the full-quantitative understanding of the effect of potential structure and photoelectron distributions. Those will be the basis for planned experiments, BepiColombo to Mercury, ERG to the inner magnetosphere, and the multi-spacecraft magnetospheric mission SCOPE.

Increasing Efficiency at the NTF by Optimizing Model AoA Positioning

NASA Technical Reports Server (NTRS)

Crawford, Bradley L.; Spells, Courtney

2006-01-01

The National Transonic Facility (NTF) at NASA Langley Research Center (LaRC) is a national resource for aeronautical research and development. The government, military and private industries rely on the capability of this facility for realistic flight data. Reducing the operation costs and keeping the NTF affordable is essential for aeronautics research. The NTF is undertaking an effort to reduce the time between data points during a pitch polar. This reduction is being driven by the operating costs of a cryogenic facility. If the time per data point can be reduced, a substantial cost savings can be realized from a reduction in liquid nitrogen (LN2) consumption. It is known that angle-of-attack (AoA) positioning is the longest lead-time item between points. In January 2005 a test was conducted at the NTF to determine the cause of the long lead-time so that an effort could be made to improve efficiency. The AoA signal at the NTF originates from onboard instrumentation then travels through a number of different systems including the signal conditioner, digital voltmeter, and the data system where the AoA angle is calculated. It is then fed into a closed loop control system that sets the model position. Each process along this path adds to the time per data point affecting the efficiency of the data taking process. Due to the nature of the closed loop feed back AoA control and the signal path, it takes approximately 18 seconds to take one pitch pause point with a typical AoA increment. Options are being investigated to reduce the time delay between points by modifying the signal path. These options include: reduced signal filtering, using analog channels instead of a digital volt meter (DVM), re-routing the signal directly to the AoA control computer and implementing new control algorithms. Each of these has potential to reduce the positioning time and together the savings could be significant. These timesaving efforts are essential but must be weighed against possible loss of data quality. For example, a reduction in filtering can introduce noise into the signal and using analog channels could result in some loss of accuracy. Data quality assessments need to be performed concurrently with timesaving techniques since data quality parameters are essential in maintaining facility integrity. This paper will highlight time saving efforts being undertaken or studied at the NTF. It will outline the instrumentation and computer systems involved in setting of the model pitch attitude then suggest changes to the process and discuss how these system changes would effect the time between data points. It also discusses the issue of data quality and how the potential efficiency changes in the system could affect it. Lastly, it will discuss the possibility of using an open loop control system and give some pros and cons of this method.

Alternative Energy Lessons in Scotland

NASA Astrophysics Data System (ADS)

Boyle, Julie

2010-05-01

In Scotland the new science curriculum for pupils aged 12 to 15 shall include the following outcomes: "Using my knowledge and understanding, I can express an informed view on a national or global environmental issue;" "I have participated in constructing a model to harness a renewable source of energy and can investigate how to optimise the output;" and "I can discuss why it is important to me and to the future of the world that alternatives to fossil fuels are developed." There will be an emphasis on creating lessons that will nurture responsible citizens, improve pupil engagement and allow students to develop their team working skills. To help teachers plan lessons to address this, the Scottish Schools Equipment Research Centre and Edinburgh University made teaching materials on four renewable energy resources. This poster describes how their suggested activities on solar cells, wind turbines, hydroelectric power stations and wave power were used in science lessons with twelve year old students. After an initial class discussion based on issues related to climate change and diminishing fossil fuel supplies, a workshop activity was carried out in three stages. The students were issued with a fact sheet about one of four imaginary islands (Skisdale, Cloudy Island, Surfsville and Sun City) and they were asked to work in teams to choose the most suitable method of generating electricity for their island. Issues such as costs, where it will be sited and environmental implications were considered. They were then asked to conduct practical activities by constructing and testing models for these forms of renewable energy. To conclude, they presented their proposal to the rest of the class with reasoned explanations. The kits used in the lessons can be purchased from Anderson Scientific (sales@andersonscientific.co.uk). The solar cells were simply connected to a voltmeter. The wind and hydroelectric groups used the same basic equipment. This was made using a small water bottle, insulating tape, a screwdriver, a connecting block, a solar motor, a plastic fan and thin wires. The only difference was that the wind groups were issued hairdryers and the hydroelectric groups worked at a sink. The wave turbine was constructed in a similar way using the bases from two 5 litre water bottles. Various investigations were conducted into the factors affecting the voltage produced. For instance, the effect of the distance from the light source, the area of the solar cell, the type of blades, the depth of water and the wind speed were studied. The lessons reinforced their understanding of ideas covered in Science and Geography, such as voltage, power, fair tests, compass directions and map contours. Students also had the opportunity to practise connecting electrical components in series and they consolidated their understanding of energy changes, observing that generators convert kinetic energy to electrical energy. The activities allowed students to learn the basics of how renewable energy technologies work. The tasks provided a hands-on experience of renewable energy being used to power small-scale electrical devices such as an LED. The students also gained an appreciation of the complex issues involved in planning and implementing renewable energy generation in the real world.

Development of an Electrochemistry Teaching Sequence using a Phenomenographic Approach

NASA Astrophysics Data System (ADS)

Rodriguez-Velazquez, Sorangel

Electrochemistry is the area of chemistry that studies electron transfer reactions across an interface. Chemistry education researchers have acknowledged that difficulties in electrochemistry instruction arise due to the level of abstraction of the topic, lack of adequate explanations and representations found in textbooks, and a quantitative emphasis in the application of concepts. Studies have identified conceptions (also referred to as misconceptions, alternative conceptions, etc.) about the electrochemical process that transcends academic and preparation levels (e.g., students and instructors) as well as cultural and educational settings. Furthermore, conceptual understanding of the electrochemical process requires comprehension of concepts usually studied in physics such as electric current, resistance and potential and often neglected in introductory chemistry courses. The lack of understanding of physical concepts leads to students. conceptions with regards to the relation between the concepts of redox reactions and electric circuits. The need for instructional materials to promote conceptual understanding of the electrochemical process motivated the development of the electrochemistry teaching sequence presented in this dissertation. Teaching sequences are educational tools that aim to bridge the gap between student conceptions and the scientific acceptable conceptions that instructors expect students to learn. This teaching sequence explicitly addresses known conceptions in electrochemistry and departs from traditional instruction in electrochemistry to reinforce students. previous knowledge in thermodynamics providing the foundation for the explicit relation of redox reactions and electric circuits during electrochemistry instruction. The scientific foundations of the electrochemical process are explained based on the Gibbs free energy (G) involved rather than on the standard redox potential values (E° ox/red) of redox half-reactions. Representations of the core concepts from discipline-specific models and theories serve as visual tools to describe reversible redox half-reactions at equilibrium, predict the spontaneity of the electrochemical process and explain interfacial equilibrium between redox species and electrodes in solution. The integration of physics concepts into electrochemistry instruction facilitated describing the interactions between the chemical system (e.g., redox species) and the external circuit (e.g., voltmeter). The "Two worlds" theoretical framework was chosen to anchor a robust educational design where the world of objects and events is deliberately connected to the world of theories and models. The core concepts in Marcus theory and density of states (DOS) provided the scientific foundations to connect both worlds. The design of this teaching sequence involved three phases; the selection of the content to be taught, the determination of a coherent and explicit connection among concepts and the development of educational activities to engage students in the learning process. The reduction-oxidation and electrochemistry chapters of three of the most popular general chemistry textbooks were revised in order to identify potential gaps during instruction, taking into consideration learning and teaching difficulties. The electrochemistry curriculum was decomposed into manageable sections contained in modules. Thirteen modules were developed and each module addresses specific conceptions with regard to terminology, redox reactions in electrochemical cells, and the function of the external circuit in electrochemical process. The electrochemistry teaching sequence was evaluated using a phenomenographic approach. This approach allows describing the qualitative variation in instructors' consciousness about the teaching of electrochemistry. A phenomenographic analysis revealed that the most relevant aspect of variation came from instructors' expertise. Participant A expertise (electrochemist) promoted in-depth discussions of fundamental theories and models that explain the electrochemical process while participant B expertise (general chemistry instruction) emphasized a coherent and explicit presentation of such theories and models to students. Other categories of variation were identified as: recognizing students' conceptions, the use of teaching resources and instructors' expectations for the teaching sequence. For example, while Participant B depended heavily on representations and explanations found in textbooks, participant A recognized misleading representations and oversimplified statements in general chemistry textbooks. Participant A was also more inclined to question the significance of some conceptions such as the correlation between the use of the term circuit and students' conceptions related to the movement of electrons in solution in an electrochemical cell. The electrochemistry teaching sequence in this dissertation fulfils each of the instructors' expectations with regards to the content that incorporated discipline-specific theories and models, explicit connections and flow among concepts, and addressing students' conceptions via the educational activities developed.

FOREWORD: Special issue on density

NASA Astrophysics Data System (ADS)

Fujii, Kenichi

2004-04-01

This special issue on density was undertaken to provide readers with an overview of the present state of the density standards for solids, liquids and gases, as well as the technologies developed for measuring density. This issue also includes topics on the refractive index of gases and on techniques used for calibrating hydrometers so that almost all areas concerned with density standards are covered in four review articles and seven original articles, most of which describe current research being conducted at national metrology institutes (NMIs). A review article was invited from the Ruhr-Universität Bochum to highlight research on the magnetic suspension densimeters. In metrology, the determinations of the volume of a weight and the density of air are of primary importance in establishing a mass standard because the effect of the buoyancy force of air acting on the weight must be known accurately to determine the mass of the weight. A density standard has therefore been developed at many NMIs with a close relation to the mass standard. Hydrostatic weighing is widely used to measure the volume of a solid. The most conventional hydrostatic weighing method uses water as a primary density standard for measuring the volume of a solid. A brief history of the determination of the density of water is therefore given in a review article, as well as a recommended value for the density of water with a specified isotopic abundance. The most modern technique for hydrostatic weighing uses a solid density standard instead of water. For this purpose, optical interferometers for measuring the diameters of silicon spheres have been developed to convert the length standard into the volume standard with a small uncertainty. A review article is therefore dedicated to describing the state-of-the-art optical interferometers developed for silicon spheres. Relative combined standard uncertainties of several parts in 108 have been achieved today for measuring the volume and density of silicon spheres. These technologies are currently being used not only for establishing a solid density standard, but also for determining the Avogadro constant by the x-ray crystal density method, where the density, molar mass and lattice constant of a silicon crystal are measured based on the definition of the SI units. Considering that much of the present research on the Avogadro constant has been undertaken to replace the present definition of the kilogram with a new definition based on a number of atoms, it is satisfying to note that the most accurate density standard may contribute to a new definition of the kilogram. Differential density measurements by hydrostatic weighing and by the pressure of flotation method developed for measuring the density differences between silicon crystals and solids are given in a review article and three original articles, where combined standard uncertainties of a few parts in 108 have been achieved in measuring relative density differences. These technologies are being used not only for the determination of the Avogadro constant, but also for evaluating defects in silicon crystals used in the semiconductor industry. Another important liquid used in the density standard is mercury because the pressured standard determined from mercury column barometers, the molar gas constant determined from an acoustic resonator, and the Josephson constant determined from a mercury voltmeter are all dependent on the density of mercury. A review article is therefore dedicated to an overview of the history, recommended value and recent progress in the measurement of the density of mercury. This special issue also features the technologies developed for measuring the thermodynamic properties of fluids. New instruments with a magnetic suspension balance have substantially improved the uncertainty in measuring the density of fluids at elevated pressures and temperatures. Two review articles and an original article are therefore dedicated to describing the history, principle and recent progress in magnetic suspension densimeters. When the diamagnetic properties of organic liquids are taken into account, an unprecedented uncertainty of a few parts in 106 can be achieved for density measurements at high pressures. The papers collected in this special issue reflect the general trends in research on density standards. I hope that this special issue will stimulate new directions of research in the density standard, and also help to create more accurate, reliable and convenient methods for many applications. Thanks are addressed to all the authors who have contributed to this special issue on density, to the referees who have given their time, and also to the former editor Professor Martin and the present editor Dr~Williams for their support and useful suggestions in collecting the articles.

The Complex Behaviour of High-Frequency Currents in Simple Circuits

PubMed Central

Bauwens, P.

1947-01-01

The fact that standing wave phenomena exist along transmission lines and loops conducting high-frequency electrical energy is responsible for effects of which therapeutic use can be made. A. Power measurements are made possible because parallel transmission lines behave as power transformers of which the ratio varies with the length of these lines. In a generator designed by the G.E.C. the dimensions of the lines are such that after a preliminary estimation of the impedance of the load in the treatment field, the sensitivity of the meter can be adjusted so that the meter subsequently registers in watts the power absorbed in this load. B. When using cable electrodes, in practice, the presence of strong electric fields between the antinodal portions of the loop as well as strong oscillating magnetic fields around the nodal portion gives rise to two distinct phenomena (fig. 6). Search for currents resulting from the electric field on the one hand, and for eddy currents due to the magnetic field on the other, was carried out at St. Thomas's Hospital, in liquid phantoms by means of a probe (fig. 5a) incorporating a small lamp capable of being rotated in every direction. Voltage measurements were recorded by matching its light intensity with that of a similar lamp in circuit with a variable resistance and a voltmeter (fig. 5b). When a portion of a cable electrode was coiled around a cylindrical vessel containing an electrolyte, the effects due to the two conditions could be dissociated. The following observations were made (fig. 7): (a) By using the nodal portions of the loop only, it was shown that only eddy currents are produced and that the lower the resistance of the electrolyte the more easily they are produced. They are strongest at the periphery and rapidly fall off away from it, as shown by the curves of the graph in fig. 8. (b) By using only the antinodal portions of the loop, coiled around the same vessel, coaxial or longitudinal currents can be demonstrated. It is interesting to note that these exist both at the periphery and at the centre. (c) When the whole cable is wound around the vessel, the concentration of the electrolyte becomes the factor determining the way in which the energy will be dissipated: (1) with tap-water, it is found that no eddy currents can be demonstrated whereas coaxial currents exist; (2) with strong saline solutions the converse holds good; (3) with electrolytes of intermediate concentration both types of currents can be shown to coexist at the periphery while at the centre only coaxial currents can be demonstrated. The fact that eddy currents and coaxial currents could be detected simultaneously and did not, as might be expected, give rise to a resultant, could only be explained by assuming that although eddy currents and coaxial currents coexisted as far as their effects on the pilot lamp were concerned, these two phenomena were not coincident as regards their phase relations. On examining the system more closely it became clear that the coaxial currents must be approximately 90 degrees out of phase with the eddy currents. By means of another type of probe (fig. 5c) for surface work, consisting of two metallic buttons mounted on an insulating strip and bridged by a small lamp, P3, similar to the one used throughout the investigations, it was possible to show that the same conditions existed in the body. It could be demonstrated that both coaxial and eddy currents occurred and that the predominance of one or the other type was dictated by conditions related to impedance. In the thigh just above the knee-joint, in most cases both currents could be demonstrated. It could also be shown that when half the cable was wound clockwise and the other half anticlockwise, so as to cancel the magnetic field between the two halves, no eddy currents existed. C. Present therapeutic applications of high-frequency currents involve the continuous dissipation of electrical energy in the load under treatment. Under these conditions the only detectable effect to which therapeutic value may be ascribed is the rise in temperature which results from heat production. This rise in temperature sets a limit to the power which can be used without risk of burns. Consequently effects other than thermal ones which might manifest themselves under higher intensities remain undetected. It is not possible to predict what would happen if, instead of treating tissues by means of sustained high-frequency electrical energy, tissues were subjected to intermittent radio-frequency pulses of very high intensity separated by silent periods of sufficient length to allow for the dissipation of heat. Those who have some technical knowledge of such matters will readily recognize an application of “Radar” technique in this. ImagesFig. 5 a, b, cFig. 9Fig. 10 PMID:19993665

The Complex Behaviour of High-Frequency Currents in Simple Circuits.

PubMed

Bauwens, P

1947-10-01

The fact that standing wave phenomena exist along transmission lines and loops conducting high-frequency electrical energy is responsible for effects of which therapeutic use can be made.A. Power measurements are made possible because parallel transmission lines behave as power transformers of which the ratio varies with the length of these lines. In a generator designed by the G.E.C. the dimensions of the lines are such that after a preliminary estimation of the impedance of the load in the treatment field, the sensitivity of the meter can be adjusted so that the meter subsequently registers in watts the power absorbed in this load.B. When using cable electrodes, in practice, the presence of strong electric fields between the antinodal portions of the loop as well as strong oscillating magnetic fields around the nodal portion gives rise to two distinct phenomena (fig. 6).Search for currents resulting from the electric field on the one hand, and for eddy currents due to the magnetic field on the other, was carried out at St. Thomas's Hospital, in liquid phantoms by means of a probe (fig. 5a) incorporating a small lamp capable of being rotated in every direction. Voltage measurements were recorded by matching its light intensity with that of a similar lamp in circuit with a variable resistance and a voltmeter (fig. 5b).When a portion of a cable electrode was coiled around a cylindrical vessel containing an electrolyte, the effects due to the two conditions could be dissociated. The following observations were made (fig. 7):(a) By using the nodal portions of the loop only, it was shown that only eddy currents are produced and that the lower the resistance of the electrolyte the more easily they are produced. They are strongest at the periphery and rapidly fall off away from it, as shown by the curves of the graph in fig. 8.(b) By using only the antinodal portions of the loop, coiled around the same vessel, coaxial or longitudinal currents can be demonstrated. It is interesting to note that these exist both at the periphery and at the centre.(c) When the whole cable is wound around the vessel, the concentration of the electrolyte becomes the factor determining the way in which the energy will be dissipated: (1) with tap-water, it is found that no eddy currents can be demonstrated whereas coaxial currents exist; (2) with strong saline solutions the converse holds good; (3) with electrolytes of intermediate concentration both types of currents can be shown to coexist at the periphery while at the centre only coaxial currents can be demonstrated.The fact that eddy currents and coaxial currents could be detected simultaneously and did not, as might be expected, give rise to a resultant, could only be explained by assuming that although eddy currents and coaxial currents coexisted as far as their effects on the pilot lamp were concerned, these two phenomena were not coincident as regards their phase relations. On examining the system more closely it became clear that the coaxial currents must be approximately 90 degrees out of phase with the eddy currents.By means of another type of probe (fig. 5c) for surface work, consisting of two metallic buttons mounted on an insulating strip and bridged by a small lamp, P(3), similar to the one used throughout the investigations, it was possible to show that the same conditions existed in the body. It could be demonstrated that both coaxial and eddy currents occurred and that the predominance of one or the other type was dictated by conditions related to impedance. In the thigh just above the knee-joint, in most cases both currents could be demonstrated. It could also be shown that when half the cable was wound clockwise and the other half anticlockwise, so as to cancel the magnetic field between the two halves, no eddy currents existed.C. Present therapeutic applications of high-frequency currents involve the continuous dissipation of electrical energy in the load under treatment. Under these conditions the only detectable effect to which therapeutic value may be ascribed is the rise in temperature which results from heat production. This rise in temperature sets a limit to the power which can be used without risk of burns. Consequently effects other than thermal ones which might manifest themselves under higher intensities remain undetected.It is not possible to predict what would happen if, instead of treating tissues by means of sustained high-frequency electrical energy, tissues were subjected to intermittent radio-frequency pulses of very high intensity separated by silent periods of sufficient length to allow for the dissipation of heat. Those who have some technical knowledge of such matters will readily recognize an application of "Radar" technique in this.

The Chemical and Educational Appeal of the Orange Juice Clock

NASA Astrophysics Data System (ADS)

Kelter, Paul B.; Carr, James D.; Johnson, Tanya; Mauricio Castro-Acuña, Carlos

1996-12-01

The Orange Juice Clock, in which a galvanic cell is made from the combination of a magnesium strip, a copper strip, and juice in a beaker, has been a popular classroom, conference, and workshop demonstration for nearly 10 years. It is widely enjoyed because it shows visually how chemistry - or more precisely, electrochemistry - is responsible for the very common phenomenon of a clock ticking. The chemistry of the process can also be understood on a variety of levels, from middle school (simple electron flow in a circuit, Ohm's law) and high school (reduction/oxidation and standard cell potentials) to first-year college (cell potential at nonideal conditions) and graduate school courses (overpotential and charge transfer across interfaces.) The discussion that follows considers the recent history, chemistry, and educational uses of the demonstration. The History The demonstration was devised by one of us (PK) in 1986, after reading an activity in Hubert Alyea's 1947 compendium of chemical demonstrations from this Journal (1). In that activity, Alyea hooked a magnesium strip to the negative battery terminal of an electric bell and hooked a copper strip to the positive terminal. He placed the loose ends of the strips into a 1M 2SO4 solution and the bell rang. After trying the demonstration, it seemed to make sense to modify the electrolyte to orange juice because it is safe, readily available, and would be a mixture in which the magnesium would oxidize more slowly than in sulfuric acid. Further, a clock was substituted for the bell because a clock is easier on the ears than a bell. A video of the orange-juice clock setup is given as Figure 1. Figure 1.The orange juice clock set up. Video of orange juice clock was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. The apparatus was presented in 1987 as part of a teacher workshop led by Irwin Talesnick, then of Queen's University in Canada. Talesnick, whose distinguished career has been characterized by seeing educational possibilities in so many things, created a modified version of the clock, with the atomic numbers of the elements representing the hours in the day (see Fig. 2) in his internationally popular workshops. Due largely to Talesnick's efforts, the orange juice clock is a standard demonstration in many chemistry programs and presentations. Figure 2.Irwin Talesnick represents the hours of the day by the corresponding elements in his clock. The Procedure This can be done as a demonstration or as an activity, although at about 10 per clock, expense does become an issue. There are no unusual safety precautions with this demonstration. We know of no accidents that have occurred with the orange juice clock. The demonstration requires: a single AA-cell battery-operated wall clock with a sweep-second hand a medium-sized beaker (600 mL is fine) enough orange juice or other electrolyte mixture or solution to fill the beaker about 2/3 full (tap water often works fine!) a 20-30-cm magnesium strip, coiled at one end or wrapped around a popsicle stick a 20-30-cm copper strip, coiled at one end alligator clips to connect the strips to the battery terminals on the clock a stand against which to lean the setup The demonstration is put together as shown in Figure 3. Connect the magnesium to the "-" contact of the clock and the copper to the "+" contact. Immerse the other ends of the strips into the solution. The clock will start to tick within a few seconds. If it does not work within a short period of time, check that the strips are well connected to the battery terminals, are hooked to the proper poles, and are not touching each other. The clock should keep reasonably close time (in orange juice) for a couple of days, or until the magnesium is nearly completely oxidized. Figure 3.A schematic of the orange juice clock seup. Video of orange juice clock. In video, the copper electrode is on the left and the magnesium electrode is on the right. Video was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. The Chemistry Basics When we ask students or precollege teacher groups about the reduction and oxidation reactions that are occurring, they invariably answer that the magnesium metal is being oxidized and the copper metal is being reduced. This response is important because we use it to impress upon students and workshop participants the importance of looking carefully at the system before giving what might seem like an obvious answer. The copper cannot be reduced because there is no copper ion in solution, and transition metals cannot be reduced to anions. Given what is actually in solution, participants can conclude that hydrogen ion can be reduced to molecular hydrogen (in orange juice) or that hydrogen in the water molecule is being reduced to molecular hydrogen (in hard tap water). In distilled water, the clock does not run because the internal resistance of the solution is too high, thus forcing the current to be very small. The reactions of interest are given as eqs 1-3: oxidation: Mg -> Mg2+ + 2e- Eo = 2.37 vs. SHE (1) reduction 2H+ + 2e- -> H2 Eo = 0.00 vs. SHE (2) (acid solution) reduction (water) 2H2O + 2e- -> H2 + 2OH- Eo = -0.8277 vs. SHE (3) where Eo = the voltage under standard conditions and SHE = standard hydrogen electrode. At standard conditions, under zero load (all activities equal to one and 298 K) the cell voltage should theoretically be 2.37 V in acid (pH = 1) and about 1.54 V in neutral solution, either of which is enough to allow the clock to run. It is important to remember the IUPAC convention for electrochemical cells: that voltage of the cell equals voltage of the cathodic half-cell minus voltage of the anodic half-cell. In this case, Eo = 0.00 V - (-2.37 V) = 2.37 V The standard free energy calculation is straightforward in each case (eq 4), DeltaGo = -nFEo in which n = number of moles of electrons transferred, as dictated by the stoichiometry of the reaction (in all reactions above, n = 2); F = Faraday's constant, 96,498 C per mole of electrons (it is useful to show students that this number is equal to the product of Avogadro's number and electron charge); and Eo = cell voltage under standard conditions (Eo = 2.37 V = 2.37 J/C in acid solution of pH = 1). In acid solution, DeltaG = -457,000 J = -4.57 kJ. The reaction is spontaneous (and there is enough current flow). The clock ticks. This represents an overview of the fundamental chemistry, suitable for a workshop, high school, or non-science first-year college audience. The discussion below considers some more advanced aspects of the demonstration, which make this an excellent demonstration for the first-year science majors' course as well as upper- and graduate-level analytical and electrochemistry courses. For Those Who Want More More advanced students can readily explore the parameters of the clock system beyond merely studying cell voltage at standard conditions. In this system, for example, two sources contribute to the oxidation of the magnesium electrode. One is the reaction with acid as part of the process that runs the clock. Also present is the reaction in acid solution that occurs irrespective of the electron flow used to run the clock, a process of corrosion that dissolves the metal without useful energy being obtained. It is possible to distinguish between the two and to determine, via Faraday's constant, the average current available to the clock in this system. Faraday's Constant and the Average Current Data for a typical determination are given in Table 1. The data were taken using a 0.3317-g magnesium strip that had been cleaned with steel wool. The magnesium and copper strips (the copper was cleaned by dipping in 1 M nitric acid for a few seconds) were placed in 400 mL of a commercial orange juice so that about 15 cm of each strip was above and 15 cm below the liquid line. About 5 cm of the magnesium strip was coiled. The clock was hooked up in the usual fashion. At 1-hour intervals, the mass of the magnesium wire was determined on an analytical balance. A digital multimeter was used to measure the voltage every hour and the current every other hour. The pH of the juice, initially 3.85 at 20 °C, was 3.93 at the end of the experiment, as measured with a portable pH meter. This is a typical result. A comparison system (called "no clock" in Table 1) was set up merely by putting a 0.3317-g strip of magnesium in 400 mL of orange juice. With this system we can exemplify a "corrosion process" where the anode and the cathode are in the same place. There is consumption of magnesium and evolution of molecular hydrogen but no useful current can be obtained. The mass of this magnesium strip was measured at 1-hour intervals. Faraday's constant, which relates coulombs to moles of electrons, can be used to calculate the approximate current available to the clock in this system. The current will not be constant because the H+ concentration (related to pH) is changing and also because the surface area and composition of the magnesium electrode change with time. The change is not necessarily regular, because although the surface is being oxidized, it is not smooth. The actual available surface area will therefore be considerably greater than the geometric surface. The mass of magnesium oxidized in the clock reaction over the 4-hour period is approximately equal to the change in grams of magnesium while running the clock minus the mass of magnesium oxidized in orange juice without the clock. Using the data from Table 1, grams Mg oxidized to run clock = approx. (0.3317 - 0.3089) - (0.3317 - 0.3136) = 0.0047 g Mg The average current can then be calculated via Faraday's constant: This is a rather simplistic way to get the current, but it shows well the use of Faraday's constant. The Value of Computer Interfacing - Exploring the Physics of Current/Voltage Measurements A more instructive measure of voltage vs. time, which opens up the activity to more interesting possibilities, was obtained by interfacing the clock to a Macintosh 8100/80 microcomputer via Vernier Corporation serial box interface hardware and software (see ref 2). This affordable (100-$250 per computer) interfacing package is being used in our first-year chemistry laboratories. The interfacing setup permitted data to be acquired at the much more meaningful rate of up to 50 points per second. It also permitted us to observe voltage variations with time while the strips in orange juice were hooked up to the clock. When data are taken 50 times per second rather than once every hour, the data take on new meaning. Figure 4 shows that there is a substantial drop in voltage each time the clock ticks. Figure 4.The observed voltage drop in the circuit corresponds to the ticking of the clock. The drop is due to the internal resistance of the orange juice solution. Video of orange juice clock connected to chart recorder demostrating voltage drop in the circuit as clock ticks. Video was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. This observation can be explained and can be predicted as part of a student activity, if we understand the nature of an open vs. a short circuit. A battery can, in concept, perform between two extreme points: an open circuit, in which the voltage (V) is at a maximum but there is no current (I), and a short circuit, in which the current is at a maximum but there is no voltage. A battery is best used at an intermediate point where the power, I xV, is a maximum. In summary (eqs 5-7): (5) Open Circuit: V = maximum and I = 0 (6) Short Circuit: I = maximum and V = 0 (7) Battery Use: I x V = power = maximum A 1.5-V battery has an open circuit potential of 1.5 volts. When the battery is working, however, the real voltage will be less than 1.5 V. This is due to the internal resistance of the battery. So the real voltage of the battery (Vreal) equals the open circuit voltage (Vopen) minus the voltage drop due to internal resistance in the battery. This drop is equal to the current passing through the circuit (I) multiplied by the internal resistance of the battery (Rint), as shown in eq 8: Vreal = Vopen - I x Rint (8) If the current passing is 0.002 A and the internal resistance of a 1.5-V battery is 50 Ohms, the real voltage is 1.4 V: Vreal = 1.5 V - (0.0020 A x 50 Ohms) = 1.4 V In this activity, in which we make a battery with a magnesium and a copper strip in orange juice, the juice itself provides the internal resistance in the battery. The key then to determining what the voltage drop should be is to find the internal resistance of the orange juice and then to find the current passing through the clock circuit. Students can determine the internal resistance of the orange juice by performing the following measurements. Note that the internal resistance of the orange juice is highly dependent upon how far apart the strips are in solution. The strips should be firmly taped, top and bottom, to the beaker. The data below were typical for 0.35-g Mg and 6.0-g Cu strips that were 4 cm apart in a 600-mL beaker with 400 mL of orange juice. The solution was not stirred. The area of the strips in solution was about 7.5 cm2 for the magnesium and about 15 cm2 for the copper. 1. Measure, using a high-impedance voltmeter, the voltage of the circuit using the voltmeter itself, rather than the clock, to complete the circuit. This will give a good approximation of the open circuit potential (the current is negligible, on the order of microamps if the voltmeter has MOhm resistance). In our setup Vopen = 1.772 V. 2. Attach a 1000-Ohm resistor across the circuit. Measure the voltage in parallel to the resistor. This voltage (1.037 V in our setup) will be equal to the current in the circuit x the resistance of 1000 Ohm. We can now solve for the current in this circuit: I = V/R = 1.037 V/1000 Ohm = 0.001037 A = 1.037 mA 3. The resistance of the orange juice is then calculated via the difference between the open circuit voltage (1.772 V) and the voltage with a known resistance (1.037 V). The difference, 1.772 - 1.037 = 0.735 V, equals the product of the circuit current and the resistance of the orange juice (ROJ), or ROJ = 0.735 V/0.001037 A = 708 Ohm 4. Finally, measure the current that the clock itself requires by hooking up in series an ammeter to the battery and the clock. The reading is not easy to take with an ammeter, which does not sample very often, and integrates across time. The computer interface works better for this. In our clock, a current of 0.49 mA was used. 5. The payoff comes at this point. The predicted voltage drop (I x Rint) can be calculated, voltage drop = I x Rint = 0.00049 A x 708 Ohm = 0.35 V Our observed voltage drops for this system were typically around 0.30 V. As a confirmation of the relationship of internal resistance to voltage drop, we placed the strips 1 mm apart in an orange by digging 2 holes in the orange and placing into the holes the coiled parts of the strips. We expected the voltage drop to be much higher than with the juice, due to the much higher internal resistance of the orange. Even when the strips were nearly touching, the drop was about 1 V. The Water Clock We discussed above the difference in the redox system when water is used rather than orange juice. Distilled water, which has a high internal resistance, will not permit the clock to run. However, hard tap water or distilled water with, for example, 1 g of table salt in 300 mL of water will work fine. As expected, because of the lower hydrogen ion concentration, the initial cell voltage is lower, typically around 1.45 V. The clock also ticks more slowly and more softly in water than in orange juice. In water, a black precipitate forms on the magnesium electrode and becomes more extensive with time. When the strip is removed from distilled water, and allowed to dry the precipitate turns white. Further student exploration on the precipitate might include designing experiments to find out if the precipitate is a carbonate or an oxide (from the hydroxide.) Non-Nernstian Considerations The systems above were always run without stirring because when setting up demonstrations, portability, simplicity, and expense are important, and the main concepts are as clear with a stir bar as without. We do note, however, that when the solution is constantly stirred, the rate of magnesium oxidation both with the clock setup and simply in solution is considerably faster than when the process is diffusion-limited. In fact, whereas the Mg strip will often last for several days in very dilute acid and overnight in orange juice when the solutions are not stirred, it will break off within 4 h when the solutions are stirred. Another important issue relates to our use of the Nernst equation to account for the potential developed in the system. This equation is very useful to assess chemistry at equilibrium conditions, but the orange juice clock is using an electric current and so is not at equilibrium. In our orange juice system, the Nernst equation (eq 9) is, in which E° = E°Mg - E°H2 - h and h = overpotential = difference in H2/H+ couple at a copper electrode minus that at platinum black. The hydrogen overpotential on a copper surface is typically 0.23 V. Another treatment of overpotential is given below. In our experiments, magnesium concentration and hydrogen activity were not measured or controlled; the pH was 3.85-3.93, as described above. The maximum theoretical potential of the electrode system is greater than that which is available to the clock when there is current flow. As described above, the potential drop is calculated as current ¥ internal resistance, equaling the "iR drop." This is why potentials are measured with a voltmeter, with a very high internal resistance, which draws very little current from the system. The measure of how far a system is from equilibrium is called the overpotential (h) h = actual potential minus potential at equilibrium This, along with the anodic and the cathodic components, the energy involved, and the temperature of the system are all dealt with using the Butler-Volmer equation, given as eq 10: I = io(e+Fh/2RT - e-Fh/2RT) (10) in which io is a specific constant for every system "electrode-electrolyte" and is called the "equilibrium exchange current." For this case, we have assumed the symmetry factor to be equal to 1/2. A detailed discussion of this factor is beyond the purpose of this paper, but can be found in ref 3. Questions To Raise with Students/Teacher Workshop Participants This demonstration can be a starting point for many concepts. It is especially powerful in showing how chemistry can be used beyond the chemistry laboratory. The primary question is "how is this system different from that in which redox occurs at one surface (such as a zinc strip placed in a solution of copper sulfate)?" The key with this electrochemical cell is that we are separating the anode from the cathode to take advantage of the electron flow (current) through an external wire and this current will give power to the clock or any other device. This is the essence of a battery. Other questions we often ask are: Is enough current produced to run a small electric motor? Light a light? Would the system work if we put Cu2+ ions into the solution? What would happen if we titrate the acid solution with a strong base while the clock is running? What happens to the voltage if we put Mg2+ into the system? Are the complex ions of Mg2+ with citric acid important to the potential value? What is the relationship between the clock ticking and different juices? Why is this relationship so? What are the reactions in the most popular commercial batteries? What is the chemical basis of rechargeable batteries? Related Activities We do this demonstration while studying electrochemistry during the second semester of the general chemistry sequence. In precollege teacher workshops, it is an important focus of an Operation Chemistry unit dealing with energy needs for living on board the space shuttle (4). A number of fairly safe activities work well as lead-in or follow-up material, as described in Table 2. Copies of these activities are available by writing to PK. Acknowledgments We wish to thank Walt Hancock and Jonathan Skean, along with our wonderful undergraduates Mickey Richards, Cory Emal, Julie Grundman, Jeff Atkins, and Darren Jack, for being there. Literature Cited 1. Alyea, H. N. Tested Demonstrations in General Chemistry, 1955-1956; American Chemical Society: Washington, DC, 1956. 2. Vernier Software, 8565 SW Beaverton Hillsdale Highway, Portland, OR 97225; phone (503) 297-5317. 3. Bockris, J.; Reddy, A. K. N. Modern Electrochemistry; Plenum: New York, 1970; Vol 2. 4. Kelter, P.; Hughes, K.; Murphy, A.; Roskos, P. J. Sci. Teacher Educ. 1995, 6, 57-59. 5. Tested Demonstrations in Chemistry; Gilbert, G., Ed.; American Chemical Society: Washington, DC, 1994; Vol. 1, #E-13. 6. Katz, D. A.; Willis, C. J. Chem. Educ. 1994, 71, 330-331. 7. Holmquist, D. D.; Volz, D. L. Chemistry with Computers;Vernier Software, Portland OR, 1994.

Fundamentals of Physics, Part 3 (Chapters 22-33)

NASA Astrophysics Data System (ADS)

Halliday, David; Resnick, Robert; Walker, Jearl

2004-03-01

Chapter 21. Electric Charge. Why do video monitors in surgical rooms increase the risk of bacterial contamination? 21-1 What Is Physics? 21-2 Electric Charge. 21-3 Conductors and Insulators. 21-4 Coulomb's Law. 21-5 Charge Is Quantized. 21-6 Charge Is Conserved. Review & Summary. Questions. Problems. Chapter 22. Electric Fields. What causes sprites, those brief .ashes of light high above lightning storms? 22-1 What Is Physics? 22-2 The Electric Field. 22-3 Electric Field Lines. 22-4 The Electric Field Due to a Point Charge. 22-5 The Electric Field Due to an Electric Dipole. 22-6 The Electric Field Due to a Line of Charge. 22-7 The Electric Field Due to a Charged Disk. 22-8 A Point Charge in an Electric Field. 22-9 A Dipole in an Electric Field. Review & Summary. Questions. Problems. Chapter 23. Gauss' Law. How can lightning harm you even if it do es not strike you? 23-1 What Is Physics? 23-2 Flux. 23-3 Flux of an Electric Field. 23-4 Gauss' Law. 23-5 Gauss' Law and Coulomb's Law. 23-6 A Charged Isolated Conductor. 23-7 Applying Gauss' Law: Cylindrical Symmetry. 23-8 Applying Gauss' Law: Planar Symmetry. 23-9 Applying Gauss' Law: Spherical Symmetry. Review & Summary. Questions. Problems. Chapter 24. Electric Potential. What danger does a sweater pose to a computer? 24-1 What Is Physics? 24-2 Electric Potential Energy. 24-3 Electric Potential. 24-4 Equipotential Surfaces. 24-5 Calculating the Potential from the Field. 24-6 Potential Due to a Point Charge. 24-7 Potential Due to a Group of Point Charges. 24-8 Potential Due to an Electric Dipole. 24-9 Potential Due to a Continuous Charge Distribution. 24-10 Calculating the Field from the Potential. 24-11 Electric Potential Energy of a System of Point Charges. 24-12 Potential of a Charged Isolated Conductor. Review & Summary. Questions. Problems. Chapter 25. Capacitance. How did a fire start in a stretcher being withdrawn from an oxygen chamber? 25-1 What Is Physics? 25-2 Capacitance. 25-3 Calculating the Capacitance. 25-4 Capacitors in Parallel and in Series. 25-5 Energy Stored in an Electric Field. 25-6 Capacitor with a Dielectric. 25-7 Dielectrics: An Atomic View. 25-8 Dielectrics and Gauss' Law. Review & Summary. Questions. Problems. Chapter 26. Current and Resistance. What precaution should you take if caught outdoors during a lightning storm? 26-1 What Is Physics? 26-2 Electric Current. 26-3 Current Density. 26-4 Resistance and Resistivity. 26-5 Ohm's Law. 26-6 A Microscopic View of Ohm's Law. 26-7 Power in Electric Circuits. 26-8 Semiconductors. 26-9 Superconductors. Review & Summary. Questions. Problems. Chapter 27. Circuits. How can a pit crew avoid a fire while fueling a charged race car? 27-1 What Is Physics? 27-2 "Pumping" Charges. 27-3 Work, Energy, and Emf. 27-4 Calculating the Current in a Single-Loop Circuit. 27-5 Other Single-Loop Circuits. 27-6 Potential Difference Between Two Points. 27-7 Multiloop Circuits. 27-8 The Ammeter and the Voltmeter. 27-9 RC Circuits. Review & Summary. Questions. Problems. Chapter 28. Magnetic Fields. How can a beam of fast neutrons, which are electrically neutral, be produced in a hospital to treat cancer patients? 28-1 What Is Physics? 28-2 What Produces a Magnetic Field? 28-3 The Definition of 736 :B. 28-4 Crossed Fields: Discovery of the Electron . 28-5 Crossed Fields: The Hall Effect. 28-6 A Circulating Charged Particle. 28-7 Cyclotrons and Synchrotrons. 28-8 Magnetic Force on a Current-Carrying Wire. 28-9 Torque on a Current Loop. 28-10 The Magnetic Dipole Moment. Review & Summary. Questions. Problems. Chapter 29. Magnetic Fields Due to Currents. How can the human brain produce a detectable magnetic field without any magnetic material? 29-1 What Is Physics? 29-2 Calculating the Magnetic Field Due to a Current. 29-3 Force Between Two Parallel Currents. 29-4 Ampere's Law. 29-5 Solenoids and Toroids. 29-6 A Current-Carrying Coil as a Magnetic Dipole. Review & Summary. Questions. Problems. Chapter 30. Induction and Inductance. How can the magnetic .eld used in an MRI scan cause a patient to be burned? 30-1 What Is Physics? 30-2 Two Experiments. 30-3 Faraday's Law of Induction. 30-4 Lenz's Law. 30-5 Induction and Energy Transfers. 30-6 Induced Electric Fields. 30-7 Inductors and Inductance. 30-8 Self-Induction. 30-9 RL Circuits. 30-10 Energy Stored in a Magnetic Field. 30-11 Energy Density of a Magnetic Field. 30-12 Mutual Induction. Review & Summary. Questions. Problems. Chapter 31. Electromagnetic Oscillations and Alternating Current. How did a solar eruption knock out the power-grid system of Quebec? 31-1 What Is Physics? 31-2 LC Oscillations, Qualitatively. 31-3 The Electrical-Mechanical Analogy. 31-4 LC Oscillations, Quantitatively. 31-5 Damped Oscillations in an RLC Circuit. 31-6 Alternating Current. 31-7 Forced Oscillations. 31-8 Three Simple Circuits. 31-9 The Series RLC Circuit. 31-10 Power in Alternating-Current Circuits. 31-11 Transformers. Review & Summary. Questions. Problems. Chapter 32. Maxwell's Equations; Magnetism of Matter. How can a mural painting record the direction of Earth's magnetic field? 32-1 What Is Physics? 32-2 Gauss' Law for Magnetic Fields. 32-3 Induced Magnetic Fields. 32-4 Displacement Current. 32-5 Maxwell's Equations. 32-6 Magnets. 32-7 Magnetism and Electrons. 32-8 Magnetic Materials. 32-9 Diamagnetism. 32-10 Paramagnetism. 32-11 Ferromagnetism. Review & Summary. Questions. Problems. Appendices. A. The International System of Units (SI). B. Some Fundamental Constants of Physics. C. Some Astronomical Data. D. Conversion Factors. E. Mathematical Formulas. F. Properties of the Elements. G. Periodic Table of the Elements. Answers to Checkpoints and Odd-Numbered Questions and Problems. Index.

Experimental Investigation of Pool Boiling Heat Transfer Enhancement in Microgravity in the Presence of Electric Fields

NASA Technical Reports Server (NTRS)

Herman, Cila

1999-01-01

In boiling high heat fluxes are possible driven by relatively small temperature differences, which make its use increasingly attractive in aerospace applications. The objective of the research is to develop ways to overcome specific problems associated with boiling in the low gravity environment by substituting the buoyancy force with the electric force to enhance bubble removal from the heated surface. Previous studies indicate that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50, as compared to values obtained for the same system without electric fields. The goal of our research is to experimentally explore the mechanisms responsible for EHD heat transfer enhancement in boiling in low gravity conditions, by visualizing the temperature distributions in the vicinity of the heated surface and around the bubble during boiling using real-time holographic interferometry (HI) combined with high-speed cinematography. In the first phase of the project the influence of the electric field on a single bubble is investigated. Pool boiling is simulated by injecting a single bubble through a nozzle into the subcooled liquid or into the thermal boundary layer developed along the flat heater surface. Since the exact location of bubble formation is known, the optical equipment can be aligned and focused accurately, which is an essential requirement for precision measurements of bubble shape, size and deformation, as well as the visualization of temperature fields by HI. The size of the bubble and the frequency of bubble departure can be controlled by suitable selection of nozzle diameter and mass flow rate of vapor. In this approach effects due to the presence of the electric field can be separated from effects caused by the temperature gradients in the thermal boundary layer. The influence of the thermal boundary layer can be investigated after activating the heater at a later stage of the research. For the visualization experiments a test cell was developed. All four vertical walls of the test cell are transparent, and they allow transillumination with laser light for visualization experiments by HI. The bottom electrode is a copper cylinder, which is electrically grounded. The copper block is heated with a resistive heater and it is equipped with 6 thermocouples that provide reference temperatures for the measurements with HI. The top electrode is a mesh electrode. Bubbles are injected with a syringe into the test cell through the bottom electrode. The working fluids presently used in the interferometric visualization experiments, water and PF 5052, satisfy requirements regarding thermophysical, optical and electrical properties. A 30kV power supply equipped with a voltmeter allows to apply the electric field to the electrodes during the experiments. The magnitude of the applied voltage can be adjusted either manually or through the LabVIEW data acquisition and control system connected to a PC. Temperatures of the heated block are recorded using type-T thermocouples, whose output is read by a data acquisition system. Images of the bubbles are recorded with 35mm photographic and 16mm high-speed cameras, scanned and analyzed using various software packages. Visualized temperature fields HI allows the visualization of temperature fields in the vicinity of bubbles during boiling in the form of fringes. Typical visualized temperature distributions around the air bubbles injected into the thermal boundary layer in PF5052 are shown. The temperature of the heated surface is 35 C. The temperature difference for a pair of fringes is approximately 0.05 C. The heat flux applied to the bottom surface is moderate, and the fringe patterns are regular. In the image a bubble penetrating the thermal boundary layer is visible. Because of the axial symmetry of the problem, simplified reconstruction techniques can be applied to recover the temperature field. The thermal plume developing above the heated surface for more intensive heating is shown. The temperature distribution in the liquid is clearly 3D, and tomographic techniques have to be applied to recover the temperature distribution in such a physical situation. A sequence of interferometric images showing the temperature distribution around the rising bubble, recorded with a high-speed camera is shown. Again, the temperature distribution is 3D, and a more complex approach to the evaluation, the tomographic reconstruction has to be taken. Measurement of the temperature distribution from the fringe pattern temperature distributions that yield important information regarding heat transfer are determined. Two algorithms that allow the quantitative evaluation of interferometric fringe patterns and the reconstruction of temperature fields during boiling have been developed at the Heat Transfer Laboratory of the Johns Hopkins University. In the first algorithm the bubble is assumed to be axially symmetrical, which significantly reduces the computational effort for quantifying the temperature distribution around the bubble. For this purpose the thermal boundary layer around the bubble is divided into equidistant concentric shells, and the refractive index is assumed to be constant in each of the shells. Since large temperature gradients are expected in the vicinity of the bubble during boiling, the deflection of the light beam cannot be neglected in boiling experiments. Since the exit angle of the light beam is known, this allows to account for the deflections and phase shifts outside the boundary layer (in the bulk fluid and in the windows of the test cell). Three dimensional temperature distributions in the vicinity of the bubble are reconstructed using tomographic techniques. In tomography, the measurement volume is sliced into 2D planes. In the present study these planes are parallel to the heated surface. The objective is to determine the values of the field parameter of interest in form of the field function in these 2D planes. The field parameter is the change of the refractive index of the liquid in the measurement volume caused by temperature changes. By superimposing data for many 2D planes recorded at the same time instant, the 3D temperature distribution in the measurement volume is recovered.

Electrical quantum standards and their role in the SI

NASA Astrophysics Data System (ADS)

Robinson, Ian; Georgakopoulos, Dimitrios

2012-12-01

The International System of Units, SI, is poised to make a quantum change and become a measurement system based entirely on the fundamental properties of the natural world. In the next version of the SI, the Planck constant h, the elementary charge e, the Avogadro constant NA and the Boltzmann constant k will be fixed, in addition to the already fixed values of the speed of light c and the ground state hyperfine splitting in caesium-133. As a result, six out of the seven base units of the SI will be based directly on true invariants of nature. A major part of this change has been enabled by the ready availability of electrical quantum standards of exquisite precision and mechanisms for using them to make measurements outside the electrical arena. The overall effect will be to eliminate the remaining imprecise definitions of physical units associated with the use of artefact standards and aid direct SI measurements without problems of scaling. Fixing the Planck constant and the elementary charge will have the effect of incorporating the best physical realizations of electrical quantities into the SI, providing a system of units fit for the 21st century. The purpose of this special feature is to review the status of electrical quantum standards and report the latest developments in those areas and their applications to other areas of metrology. The special feature coincides with the 50th anniversary of the seminal paper of Josephson, 'Possible new effects in superconductive tunnelling' [1], which established the basic physical principle upon which the quantum voltage standards are based. Josephson voltage standards are based on the inverse Josephson effect. When a junction of two superconducting electrodes, weakly linked through a thin insulator or a normal metal, is irradiated with a radiofrequency electromagnetic field of frequency f and is biased by a dc current, then the voltage across the junction is quantized (i.e. small changes in either the dc current or the power of the rf irradiation, or both, do not change the voltage). The value of this quantized Josephson voltage is equal to nfh/2e, where n is the quantum step of the current-voltage characteristic curve. In this special feature there are three papers on dc Josephson voltage standards. Solve and Stock review the programme conducted by the Bureau International des Poids et Mesures (BIPM) to perform on-site comparisons of Josephson voltage standards, and give a comprehensive analysis of the possible sources of errors of such comparisons. Behr et al summarize the developments of Josephson voltage standards at Physikalisch-Technische Bundesanstalt (PTB) and their applications in dc voltage and other areas of metrology. Finally, Georgakopoulos et al report a reduction, by a factor of a thousand, in the smallest voltage that can be generated by dc Josephson voltage standards. Although dc voltage standards are well established, significant challenges exist when extending this extremely precise technology to ac. There are two approaches to producing accurate ac voltages using the inverse Josephson effect: the programmable Josephson voltage standard (PJVS) and the pulse-driven ac voltage standard. The PJVS contains an array of Josephson junctions, organized into independently biased segments. By biasing chosen, binary-related, segments on the first quantum step (positive or negative) or zero, the array can be made to behave as a quantum digital to analogue converter. The PJVS approach can produce stepwise approximated sine waves with rms values of some volts, but it suffers from parasitic capacitances and inductances distributed in the different parts of the system and, more importantly, the voltage is not quantized during the finite transition time between successive voltage levels. Hence the output frequency of PJVS-based systems is limited to a few kilohertz. In this special feature, Jeanneret et al review the Josephson locked synthesizer, a PJVS-based system where the effect of transients between successive steps on the output voltage is reduced. This special feature also presents two applications of PJVS-based quantum voltage standards: the evaluation of conventional ac voltage standards based on thermal converters (Budovsky et al) and the measurement of the settling time of a high resolution digital voltmeter (Henderson et al). In the pulse-driven ac voltage standard, arbitrary voltages can be produced by modulating the rf irradiation of an array of Josephson junctions by a series of high frequency pulses, usually by means of Δ-Σ modulation. The output voltage of the array of junctions is a series of quantized voltage pulses that correspond to the desired waveform after the high frequency components are removed. The pulse-driven standard can operate at much higher frequencies than the PJVS. Eliminating the effects of parasitic impedances of the, necessarily long, connecting leads therefore becomes a significant challenge. In this special feature, van den Brom and Houtzager report a voltage lead correction technique. Quantum resistance standards are based on the quantum Hall effect in which the resistance of a two-dimensional electron gas in a strong magnetic field is quantized. The value of the quantized Hall resistance is h/ie2, where i is the number of the quantum step in the resistance-magnetic field curve. Quantum Hall resistance devices can be combined in series to form a resistive voltage divider with low uncertainty in the ratio. In this special feature, Domae et al report the realization of such a resistive voltage divider on a chip. Quantum Hall resistance standards have been routinely used at dc for over two decades. However, the operation of quantum Hall devices at ac is complicated by the flow of current in capacitances around the device, which can compromise measurement of its resistance. Schurr et al review the status of ac quantum Hall resistance standards and their role in the SI. Ohm's law can be applied to quantum realizations of voltage, resistance and current to test their consistency. Active research into this 'metrological triangle' is underway and, at present, there is no evidence to indicate a discrepancy at any level. However, work is continuing on current sources which utilize a countable flow of electrons (the electric current produced is proportional to ef, f being the operating frequency of the device), but the work has some way to go before the question of consistency can be resolved at levels approaching 1 part in 109. In this special feature, Scherer and Camarota review the state-of-the-art of metrological triangle experiments and Devoille et al report on the status of the metrological triangle experiment at the Laboratoire National de Métrologie et d'Essais (LNE), France. The availability of precise representations of the volt and the ohm based on quantum mechanics has enabled the watt balance, an apparatus which relates electrical and mechanical power, to link the kilogram to the Planck constant. This has paved the way for the proposed redefinition of the kilogram, the last artefact standard in the SI, in terms of a fixed value of the Planck constant. In the past few years a number of papers, e.g. [2, 3], have been published describing the working principles of the watt balance and the characteristics of the existing implementations of the experiment. The measurements of the principal quantities—mass, velocity, gravitational acceleration, resistance and voltage—are reasonably well documented but the ultimate precision of the apparatus depends on a number of techniques that are required to eliminate second-order effects. In this special feature, Robinson provides details of these general alignment techniques with special reference to the NPL Mark II watt balance. Acknowledgments We would like to thank the authors for supporting the special feature with their excellent contributions; the guardians of the quality of a scientific paper, the referees, for their valuable comments and suggestions; Professor Wuqiang Yang and the members of the editorial board of Measurement Science and Technology for their support. Finally, we would like to thank Dr Sharon D'Souza, James Dimond and all the editorial and publication staff at Measurement Science and Technology, for their help in making the special feature a reality. References [1] Josephson B D 1962 Possible new effects in superconductive tunnelling Phys. Lett. 1 251-3 [2] Li S, Han B, Li Z and Lan J 2012 Precisely measuring the Planck constant by electromechanical balances Measurement 45 1-13 [3] Stock M 2011 The watt balance: determination of the Planck constant and redefinition of the kilogram Phil. Trans. R. Soc. A 369 3936-53

BOOK REVIEW: The Current Comparator

NASA Astrophysics Data System (ADS)

Petersons, Oskars

1989-01-01

This 120-page book is a concise, yet comprehensive, clearly-written and well-illustrated monograph that covers the subject matter from basic principles through design, construction and calibration details to the principal applications. The book will be useful, as a primer, to the uninitiated and, as a reference book to the practitioner involved with transformer-type ratio devices. The length of the book and the style of presentation will not overburden any informed reader. The described techniques and the cited references are primarily from the work at the National Research Council, Canada (NRC). Any omissions, however, are not serious with respect to coverage of the subject matter, since most of the development work has been done at NRC. The role of transformers and transformer-like devices for establishing accurate voltage and current ratios has been recognized for over half a century. Transformer techniques were much explored and developed in the fifties and sixties for accuracy levels suitable for standards laboratories. Three-winding voltage transformers were developed for scaling of impedances in connection with the calculable Thompson Lampard capacitor; three-winding current transformers or current comparators were initially explored for the calibration of current transformers and later for specialized impedance measurements. Extensive development of the current comparator and its applications has been and is still being conducted at the NRC by a team that was started and, until his retirement, led by N L Kusters. The team is now led by W J M Moore. He and P N Miljanic, the authors of this book, have had the principal roles in the development of the current comparator. It is fortunate for the field of metrology that considerabe resources and a talented group of researchers were available to do this development along with mechanisms that were available to transfer this technology to a private sector instrument manufacturer and, thus, disseminate it world wide. One would hardly find a standards laboratory today without an instrument employing a current comparator. The NRC program, now nearing the end of its third decade, has resulted in a large number of papers in technical journals. The fact that the results of the current-comparator program are now documented in a well-written book is a most welcome development. The material in the book is well organized and divided into seven chapters. Chapter 1 deals very briefly with the historical aspects of the development, including related work in other organizations. Chapter 2 is the longest, occupying one third of the book. It presents the background theory; the definitions and origins of the errors; and the related concepts and devices including two-stage current transformers, electronic methods for improving the performance of current transformers, and null detectors. The idea of the current comparator is developed starting from Ampere's law; and then progressing to the practical realization of measuring the line integral of the magnetic field surrounding an electric current. Such an approach, as opposed to the more common methods of analyzing transformers, has a tutorial value in explaining how the current balance is achieved. Such analysis is intuitive for air-core sensing coils with infinitesimal cross-sections and uniform winding densities. The intuitive understanding, however, becomes less obvious when high-permeability magnetic cores are used. The subject of errors is discussed thoroughly. For errors of magnetic origin, ample experimental data are provided to support the hypothesis for the cause of such errors. The cause is discussed in a macroscopic sense (non-uniform effective permeability along the torus) without going into design and processing details which could be responsible for the non-uniformities. For capacitive errors, equations have been developed to compute them from geometrical considerations. Techniques are presented to reduce both types of errors shielding techniques for magnetic errors and magnetic-shield excitation for capacitive errors. The magnetic-shield-excitation technique leads naturally to two-stage transformer approaches, described in a small subchapter. Sensitivity of current comparators is discussed in terms of available signal levels for given excitations and current-comparator characteristics. The discussion, however, does not cover more basic limitations, such as inherent noise. A subchapter is devoted to electronically-aided current transformers. Although electronically-aided transformers are not in a strict sense current comparators, many of the design considerations and error sources are the same. Seven different circuits are presented with a brief qualitative discussion. The third chapter, covering design and construction, will be exceptionally valuable for someone needing basic information on how to construct a current comparator quickly. Indeed, all the necessary design, construction, and testing steps are presented in a well-illustrated 15-page chapter. The tests for shielding effectiveness discussed in this chapter and the knowledge of interwinding capacitances calculable from the equations in the previous chapter should enable one also to predict the limits of errors without an exhaustive and complete calibration. Chapter 4 is devoted to current-transformer calibration—the original objective for the current-comparator development work. The principal tool for this is the compensated current comparator, in effect a two-stage transformer operated in the current-comparator mode. The compensated current comparator is not only accurate but is also an extremely versatile device and, hence, deserves the attention that it receives in this book. Considerable space is devoted to the calibration of current comparators themselves using other current comparators in ratio-buildup (bootstrap) techniques. This information is more than most of the users will want since the pre-eminent feature of a current comparator is that errors can be made inherently negligible with proper construction techniques. Proper functioning can be verified by spot checks on a few ratios, and by indirect means. Complete calibration is useful, however, to verify the original design. A number of circuits incorporating compensated current comparators for current-transformer calibration are presented. Such circuits cover the calibration of current transformers normally encountered in electric-power transmission and distribution, from several amperes to several thousand amperes; cascaded circuits for very large currents up to 60,000 A; and special cases involving less-than-unity ratio (step-up) current transformers. Peripheral equipment such as ratio-sets and burdens are also discussed. This entire chapter is of great practical interest since much of the world's current-transformer calibration is performed using equipment described therein. The next two chapters, 5 and 6, deal with current-comparator applications in impedance-bridge circuits. High-voltage applications (described in Chapter 5) have been of great practical importance and indeed are the techniques of choice for a number of measurements. High-voltage bridge circuits are described for capacitance, inductance, voltage transformer ratio, and low-power-factor power measurements. Without going into much detail, the book mentions the particular characteristics required of current comparators in high-voltage bridge applications. Other components making up the bridge circuits are also described, as well as the calibration technique for the bridge. Limited in application but important in basic metrology is one particular low-voltage bridge, described in Chapter 6, for realization of ac power in terms of more basic SI units. Applications to ac resistance measurements and to realization of transconductance amplifiers are also included. Chapter 7, consisting of only eight pages, is devoted to direct-current comparators, although specific topics applicable to dc use are covered in earlier chapters. In relation to the number of dc vs ac instruments in use, the length of this chapter presents something of an imbalance. Nevertheless, in the limited number of pages, the authors have covered the principal direct-current comparator applications—the ratio device (dc comparator), the resistance bridge, and the potentiometer. More specialized instruments such as the differential voltmeter and the digital-to-analog converter are also mentioned. The unique feature of the dc comparator is the modulator-type balance detector. It is covered in Chapter 3 with current-comparator construction details. In conclusion, the technical depth and style of discussion, the material covered, the size of the volume, and the ample references suggest that the authors should satisfy most of the audience interested in current comparators. A possible exception might be those interested in extremely high accuracies (errors in the 10-8 to 10-9 range). The authors have selected the overall approach of presentation that is predominantly pragmatic rather than analytical. Metrologists unfamiliar with current comparators should be able, after a day's reading, to embark upon the construction of their own devices or upon the application of current comparators to their own measurement needs. The serious practioner will find the book valuable for the complete coverage of the subject and the bibliography. Also, most practitioners should find in the book a number of useful design, construction, or application tricks for their own use. At the present time, development activity on transformer-type ratio devices, including the current comparator, has subsided in comparison with the peak level of the sixties. For many applications, however, these devices remain the most accurate and sometimes the only viable instruments for scaling current and voltage. The applications include factory test systems and instruments for absolute electrical measurements. This situation is likely to continue for at least one more generation of metrologists. Thus, not only present but also future generations of metrologists will benefit from the book by not having to spend countless hours in "reinventing the wheel" or in searching scattered journal literature. One only wishes that other specialized fields of metrology could benefit from similar endeavors.

Revolution or flight from reality? The IoP Education Group Conference 1999

NASA Astrophysics Data System (ADS)

Dobson, Ken

1999-09-01

The 1999 Education Group Conference attracted some 60 teachers and educationalists to the salubrious outskirts of the city of Leicester on 2 3 July. The title of the conference was The ICT revolution: just how will ICT change my physics teaching? For those not au courant with current jargon ICT stands for Information and Communications Technology, or, in short, computers. ICT was certainly to the fore from the presenters, who practised what they preached. Every talk was delivered using Microsoft PowerPoint, obsolescent overhead projectors serving only as laptop stands. Animated slides, computer generated and controlled, were projected on to a screen and supplemented as required by (fairly) instant live excerpts from relevant computer programs. The theme of the conference was set by the opening discussion led by the trio PowerPoint, Ian Lawrence (chairman of the Institute of Physics Education Group) and Philip Britton (vice-chair). They gave us the slogan Physics first! with technology, however brilliant or politically correct, only significant and valuable insofar as it helped students learn physics. And learning is a social activity: any system that places one child in front of a computer screen for hours on end should be suspect. Much the same could be said of a voltmeter, of course, and the minimal situation must include a pair of students and a teacher as well as the apparatus. Another message: think of the computer system as just another piece of equipment whose use is determined by the learning task, not as an item that determines the task. Figure 1. Jason Wye, Secretary of the Education Group, opening the Conference. It may not be surprising that the level-headed delegates agreed whole-heartedly with these sentiments, but they were also supported and reinforced by all the speakers as the conference went on. The first speaker was Jerry Wellington, ex-physics teacher, now at the University of Sheffield. In his presentation `Multimedia in science teaching: friend or foe?', he gave us a useful overview (with `live' excerpts) of a number of multimedia CD-ROMs - the good, the bad and the ugly. The organizers arranged the programme so that each presentation was followed by group discussion about the points raised (or skated over) by the presenter, and Jerry, with customary efficiency, had listed these. In brief:

• Multimedia can be misleading, making science too clean and `easy' compared with messy experiments that don't always work.
• Many good CD-ROMs are American, with different spelling etc. Is this a problem?
• The best-selling CD-ROMs are revision aids: knowledge-rich, skill-poor, packaged as a commodity. They are used at home, with little or no teacher involvement. Good or bad?
• How `authentic' is learning via multimedia? A subtle point too deep to be considered here.
• Multimedia can be motivating: almost as good as TV - compared with the poor old teacher with a piece of chalk.