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  • 1
    Electronic Resource
    Electronic Resource
    Efficient switchless multi-Joule TE-CO2 laser (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1404-1407 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Switchless mode operation of a pulse TE-CO2 laser is reported. The system has provided an output energy of 7 J at atmospheric pressure from a discharge volume of 3 cm×3.3 cm×42 cm with an efficiency of 8%. Under long pulse loading, it has provided 3.5 J in a 5 μs pulse at an efficiency of 7% at a pressure of 500 mbar. The elimination of the high voltage switch from the main discharge circuit has resulted in a simple and inexpensive laser system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142457
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  • 2
    Electronic Resource
    Electronic Resource
    Femtoampere current reference stable over atmospheric temperatures (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3231-3232 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Calibration of ultralow current ammeters deployed in atmospheric ion counters requires stable current references operating at high source impedance. Using standard precision components, this current reference generates equal bipolar currents of nominally ±500 fA, cyclically for 32 s each. The currents were found to be stable to 2 fA over the temperature range −20 to 20 °C, typical of atmospheric conditions. The output current is delivered via a capacitor, and by arranging for the capacitor to be guarded at ground potential when the system is not generating a current, the reference can be permanently connected to an electrometer with minimal leakage. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304859
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  • 3
    Electronic Resource
    Electronic Resource
    Multimode electrometer for atmospheric ion measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4683-4685 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A computer-controlled electrometer capable of either high impedance voltage measurements or femtoampere current measurements has been developed. It is intended for use with a Gerdien ion counter in atmospheric temperatures. Temperature variations can cause significant thermal errors arising from offset voltage and bias current changes that compromise the measurements. Use of high impedance switching permits the offset voltage and input bias currents of the electrometer to be measured, and allows regular software compensations to be applied in both modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327303
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  • 4
    Electronic Resource
    Electronic Resource
    A noise-rejecting current amplifier for surface atmospheric ion flux measurements (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3563-3565 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Large area electrodes are required to determine atmospheric charge fluxes at the earth's surface. These also act as antennas for power line hum, swamping the small atmospheric electric signals. A battery-powered head-amplifier resolving 0.025 pA is described here, which uses active compensation to substantially cancel the interference, allowing the atmospheric charge fluxes to be resolved in the presence of the interference. The overall response is nominally −100 mV/pA, with 30 dB of 50 Hz rejection. The head amplifier can drive a low impedance line. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148323
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  • 5
    Electronic Resource
    Electronic Resource
    Novel magnetic-spiker sustainer excitation circuit for a multijoule TE CO2 laser (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2175-2179 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Successful operation of a multijoule output TE CO2 laser using a new magnetic-spiker sustainer excitation circuit is reported. The use of the new excitation circuit has resulted in a significant reduction (∼90%) in the amount of sustainer pulse energy that has to pass through the magnetic switch. In addition, the new circuit technique allows operation of the discharge at reduced voltage (∼50%) and extends the range of excitation current pulse durations (up to ∼7 μs) over which arc-free discharges can be formed. The laser has produced a typical output of 5 J at an overall efficiency of ∼13% from a helium-free gas mixture at a pressure of 400 mbar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144722
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  • 6
    Electronic Resource
    Electronic Resource
    Novel discharge circuit for a multijoule TEA CO2 laser (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 563-566 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel discharge circuit that reduces significantly the amount of energy conducted by the switch in a TEA CO2 laser is reported. We demonstrate this circuit on a working multijoule TEA CO2 laser in which the switch is shown to conduct typically only 5% of the total input pulse energy. The laser has worked reliably in gas mixtures that place stringent demands on the discharge and circuit. It has produced an output of 7 J at an efficiency of 9.6% using a CO2:N2:He (1:1:4) gas mixture at atmospheric pressure and further using a helium-free gas mixture (CO2:N2:H2 at 400 mbar) it has produced a maximum efficiency of 14.6% for an output of 7.8 J. The great simplicity and high efficiency of the new discharge circuit allow it to be incorporated in the existing laser designs with minimal modifications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145118
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature-compensated meteorological barometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1909-1910 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Meteorological measurements of surface pressure to better than 1 mbar are routinely required in surface pressures of typically 1000 mbar, and detecting small pressure changes is important for forecasting. An inexpensive pressure sensor provides the basis of a barometer suitable for such general meteorological use. Signal-conditioning circuitry has been added to allow typical surface sea-level pressure variations to be resolved to 0.1 mbar using a ±5 V 12-bit analog to digital system. The sensor excitation voltage is shown to track the sensor's temperature closely, and this is extracted to provide a temperature-compensation signal. When combined with a nonlinearity correction system and a digital display, this gives a portable barometer capable of reading to ±0.5 mbar (over the range of 930–1020 mbar) for temperatures between 0 and 25 °C. The final display reading includes the temperature compensation by using a panel meter in ratio mode. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150549
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  • 8
    Electronic Resource
    Electronic Resource
    An antenna electrometer system for atmospheric electrical measurements (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1599-1603 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A ±300 V dynamic range, battery-powered, and inexpensive electrometer system is described that has been used with passive horizontal wire antennas to measure the atmospheric electric potential at 1 and 2 m above the earth's surface. Input currents drawn by the electrometer circuit are of order femtoamperes, and a guard drive output is provided to minimize leakage. The implementation of the passive wire antenna is described, using rigorous insulation and signal guarding, together with results obtained in fair weather conditions. Linearity of the portable electrometer over the input range is demonstrated to be comparable with a commercial laboratory electrometer, and the antenna potential can be determined to within a few volts in the fair weather electric field. Several such portable systems can be cheaply combined, sharing a common high tension supply, to measure the profile of the atmospheric electrical potential above the surface, at a remote site. Damage to the electrometer sustained in electrical storms can be cheaply repaired. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147932
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  • 9
    Electronic Resource
    Electronic Resource
    MATERNAL PLASMA UNCONJUGATED OESTROGENS IN EARLY HUMAN PREGNANCY (1980)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 87 (1980), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The plasma levels of unconjugated oestrone (El), oestradiol (E2) and oestriol (E3) were determined by radioimmunoassay, twice weekly in 21 subjects from the earliest detection of pregnancy up to 16 weeks gestation where possible. Normal ranges for the three oestrogens were established using data from 15 subjects who had a normal pregnancy, including one sampled throughout the cycle of conception. The six other subjects comprised a twin pregnancy, two who aborted and three who received progestogen therapy, and their oestrogen levels were compared with the normal ranges. El and E2 levels showed a steady increase over the period of study with E2 levels exceeding those of El. E3 levels remained low (in many cases less than 50 pg/ml) until week 13 when levels began to rise steadily. In a caseof twin pregnancy, El and E2 levels only became significantly elevated when compared with single pregnancies from week 15. There were differing oestrogen trends in two patients who aborted. In a patient with an incomplete abortion, levels only dropped significantly after abortion had occurred, whereas, in a patient with a complete abortion, a gradual and progressive fall in El and E2 levels was observed. The levels of El and E2 for the three subjects receiving progestogen therapy did not differ significantly from those of the normal subjects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1980.tb04602.x
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  • 10
    Electronic Resource
    Electronic Resource
    MATERNAL PLASMA ANDROGENS IN EARLY HUMAN PREGNANCY (1980)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 87 (1980), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Mean maternal plasma levels of testosterone, androstenedione, and 5 α-dihydro-testosterone were established from 4 to 16 weeks gestation from twice-weekly blood samples taken from 15 pregnant women. All three hormone levels were raised when compared with the non-pregnant state. There were significant differences in mean maternal plasma testosterone levels at 4 to 5 and 7 to 8 weeks gestation, when comparing women carrying male and female fetuses. Androstenedione levels in a twin pregnancy were increased throughout and testosterone levels were more than 1 SD above the mean from week 15. Steroid levels fell late in the two women who aborted. Hormone levels in three women being given progestogens were within normal limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1980.tb04603.x
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