摘要:

A combined long-term measurement and recording system for neurotransmission research of brain slices is presented in this study. This system, based on the IBM PC or compatible computer, is capable of simultaneously measuring and recording both single-unit neural electropotential signals and the electrochemical signals of neurotransmitter efflux from the same neuron in a brain slice for long periods of time (time limited largely by hard disk capacity, 100 h or more not being unreasonable with contemporary hardware) using a single carbon microelectrode for both measurements. The combined long-term recording system uses a simple switching circuit to switch periodically the single microelectrode between two data acquisition subsystems, one for electrochemical data and one for electrophysiological data. The simple switching circuit separates the electrophysiological signals and electrochemical signals, overcoming the traditional interference problem caused by the two different measuring techniques. Software designed for the proposed system allows easy reconstruction of the full time course of the compressed measured data and easy, simultaneous display of both types of signals on the same time scale. On-line and recorded displays are available. Test results of a practical implementation of the proposed system verify that the combined long-term recording system meets actual requirements for electrophysiological and neurochemical research. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148856

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager (EPRI) capable of detecting and imaging free radicals in biological objects is described. The magnetic field was 10 mT which corresponds to a resonance frequency of 300 MHz for paramagnetic species. Short pulses of 20–70 ns from the signal generator, with rise times of less than 4 ns, were generated using high speed gates, which after amplification to 283 Vpp, were deposited into a resonator containing the object of interest. Cylindrical resonators containing parallel loops at uniform spacing were used for imaging experiments. The resonators were maintained at the resonant frequency by tuning and matching capacitors. A parallel resistor and overcoupled circuit was used to achieveQvalues in the range 20–30. The transmit and receive arms were isolated using a transmit/receive diplexer. The dead time following the trailing edge of the pulse was about 450 ns. The first stage of the receive arm contained a low noise, high gain and fast recovery amplifier, suitable for detection of spin probes with spin-spin relaxation times(T2)in the order of &mgr;s. Detection of the induction signal was carried out by mixing the signals in the receiver arm centered around 300 MHz with a local oscillator at a frequency of 350 MHz. The amplified signals were digitized and summed using a 1 GHz digitizer/summer to recover the signals and enhance the signal-to-noise ratio (SNR). The time-domain signals were transformed into frequency-domain spectra, using Fourier transformation (FT). With the resonators used, objects of size up to5 cm3could be studied in imaging experiments. Spatial encoding of the spins was accomplished by volume excitation of the sample in the presence of static field gradients in the range of 1.0–1.5 G/cm. The spin densities were produced in the form of plane integrals and images were reconstructed using standard back-projection methods. The image resolution of the phantom objects containing the spin probe surrounded by lossy biologic medium was better than 0.2 mm with the gradients used. To examine larger objects at local sites, surface coils were used to detect and image spin probes successfully. The results from this study indicate the potential of rf FT EPR forin vivoapplications. In particular, rf FT EPR may provide a means to obtain physiologic information such as tissue oxygenation and redox status. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148857

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The measurement of short distances by interferometry using low coherence light is a potential option in the study of interfaces between intraocular elements. In this article we describe an experimental device to measure the distance between such interfacesin vitro. The procedure utilizes a Michelson interferometer to generate the probe beams together with a silicate photodetector system and a lock-in synchronous amplifier. The cornea and crystalline lens thickness of a rabbit eyeball are evaluated, as well as the human cornea in preservative solution. These tests indicate the method to be efficient, easy-to-handle, of high resolution and to present a signal-to-noise ratio of up to 12. We consider the possibility of its use in obtaining information about the degeneration of intraocular structures during the preservation process. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148867

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The design of servoloops for automating alignment and locking of long baseline gravitational wave detectors requires an accurate knowledge of the mechanical transfer function (TF) of the mirror suspensions. We present a suspended interferometric device devoted to the measurement of the TF of the multipendular seismic isolators of the VIRGO antenna. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148858

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Increasingly stringent environmental regulation imposed on both the military and civilian sectors has created a growing demand for alternative abatement methods for a variety of hazardous compounds. One alternative, the nonthermal plasma, shows promise of providing an efficient means for the destruction of dilute concentrations of hazardous air pollutants. The Dahlgren Laboratory of the Naval Surface Warfare Center has extensively investigated one type of nonthermal plasma discharge, the pulsed corona reactor, for the destruction of volatile organic compounds and chemical warfare agents. In this reactor, a fast rise time(∼10 ns),short duration(<100 ns),high-voltage pulse is repetitively delivered to a wire-cylinder electrode geometry, thereby producing a multitude of streamer discharges along its length. The resulting nonthermal plasma contains highly reactive chemical radicals which can interact with and destroy the hazardous molecules entrained in the ambient atmosphere flowing through the reactor volume. Increased electrical efficiency was obtained using a combination of high efficiency constant-current capacitor-charging, high repetition-rate spark gap switching, and resonant energy transfer to the reactor. Promising results have been obtained for toluene, methylene chloride, and dichlorodifluoromethane in air at concentrations of a few hundred parts per million. The device has been operated at voltages up to 30 kV, pulse repetition rates up to 1.4 kHz, and flow rates up to 60l/min. Detailed electrical measurements have been made to properly characterize the electrical properties of the pulsed corona reactor and to validate subsequent improvements in the reactor energy efficiency. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148859

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Definitive mineralogical identification of materials with x-ray diffraction and fluorescence on remote planetary probes requires the development of a rugged miniature x-ray source that complies with the mass, power, thermal, and electrical management constraints imposed by space missions. Conventional x-ray tubes are generally fragile, glass-envelope designs with heat-sensitive seals. They are too brittle and bulky for planetary missions, and usually require cumbersome and power-consuming cooling systems. Here we describe the development of a novel, rugged miniature x-ray source employing a ceramic BeO substrate upon which a metal target material is deposited. Conventional thermionic emission and high-voltage acceleration of electrons to strike the metal target material produce an x-ray yield comparable to conventional x-ray tubes. Thermal management of the x-ray source is achieved with the excellent heat transport properties of the BeO target substrate coupled with a passive heatpipe. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148860

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We conducted a study to estimate the impact that thermal variations and electronic drifts would have on the photometric stability of the multianode microchannel array (MAMA) detectors that are currently flying aboard the space telescope imaging spectrograph (STIS). Included in the present analysis is the expected impact of preferential aging of the microchannel plate due to prolonged concentrations of light in the same location. These data and analyses were used to examine the suitability of specified electronic tolerances to achieve a photometric accuracy of±1&percent;over a period of 1 week, but may be also useful should the spacecraft environment begin to vary. The original parameter tolerances were found to be adequate in most cases, although a few voltages did require somewhat better tolerance specifications. The present analysis indicates the sensitivity of the STIS MAMA detectors are reproducible over long periods of time to an accuracy of 0.62&percent; (0.33&percent; rms and 0.29&percent; systematic uncertainties) at an arbitrary location in the detector format. This result indicates the detectors are capable of obtaining data with a signal-to-noise ratio(S/N)≳200in a STIS2×2pixel optical resolution element, consistent with observed departures found in high-signal laboratory data. Even higher S/N levels have been demonstrated on orbit using techniques that move the spectral image around on the detector. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148861

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simple high-voltage gaseous switch designed to minimize the erosion of the discharge electrodes is described. The switch is triggered by ultraviolet radiation produced by a corona pulsed discharge. A pin-shaped auxiliary electrode, centered within an orifice made on the discharge surface of a hollow anode and connected to this electrode in series with an inductor, is used to promote the contraction of the discharge channel allowing it to penetrate the orifice. The switch has been tested by discharging capacitors of 5 and 40 nF at voltages and peak currents up to 16 kV and 8 kA, respectively. Negligible erosion of the electrodes was obtained. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148862

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Many commonly used PC-based data acquisition counter boards are specified to countregularly occurringevents at rates up to 7 MHz. Boards with this frequency limit begin to systematically and significantly underestimate the rate ofrandomly occurringevents occurring at average frequencies much lower than the specified 7 MHz rate due to the dead time of the counter. This report highlights the origin of this error and describes an easily constructed prescaler circuit that permits accurate event counting at rates up to, and even exceeding, the nominal speed of the counter. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148863

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simple method was applied to select a fundamental transverse electro-magnetic mode(TEM)00and a combination ofTEM00+TEM10modes using changeable cylindrical apertures inside the cavity close to the resonator mirrors. The experiment was carried out on a continuous waveCO2laser, with an internal resonator 3.6 m long and 2.4 cm in diameter. The experimental results were compared with some calculations, and reasonable agreement was observed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148864

出版商:AIP    

年代:1998

数据来源: AIP