AM Techniques Research Articles

GABAB receptors increase intracellular calcium concentrations in chromaffin cells through two different pathways: Their role in catecholamine secretion

The activation of GABAB receptors of adrenal chomaffin cells produces an increase of [Ca2+]i measured by fura-2 AM techniques. GABAB agonists 3-aminopropylphosphinic acid or (-)baclofen, at concentrations of 0.5 mM, increased basal Ca2+ values 332 +/- 60.9 and 306 +/- 40.5 nM, respectively, in cells suspended in a 2.5 mM Ca2+ buffer. The GABAB-induced increase of [Ca2+]i seemed to have two different components. The first was due to an entry from the extracellular medium mainly through L-type voltage-dependent Ca2+ channels as the dihydropiridine nifedipine 50 microM was able to decrease it more than 60%, while omega-conotoxin, which blocks N-type channels, did not produce any change in the GABAB-evoked Ca2+ increment. The second component was due to a release of Ca2+ from intracellular pools and was about one-third of the total GABAB-induced increase of [Ca2+]i. GABAB receptors stimulated inositol 1,4,5-trisphosphate-sensitive and not the caffeine-sensitive Ca2+ store. In a low-Ca2+ buffer after treatment with 2 microM angiotensin II, neither 0.5 mM 3-APPA nor baclofen were able to produce an additional increase of [Ca2+]i, whereas 4 mM caffeine had no effect on GABAB response. This intracellular Ca2+ mobilization could be due to inositol 1,4,5-trisphosphate accumulation produced by the activation of GABAB receptors. In fact, the specific agonists after 10 minutes incubation produced a dose-dependent increase of inositol 1,4,5-trisphosphate. The maximal effect was obtained at 100 microM baclofen and 3-APPA, and it was 3.63 +/- 0.75 and 3.2 +/- 1.5 times the basal levels (7.3 +/- 0.3 pmol/10(6) cells), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Real-time analysis signal processor for ultrasonic nondestructive testing

Hilbert transform processors were developed to improve flaw detection in parts by sensing the rate of total energy arrival. Analytic signal processing is used to improve pulse resolution. A real-time analytic processor was built using single-sideband (SBB) AM techniques. An upper sideband processor using the filter method to maximize signal bandwidth and in which the lower sideband aliases was built. This processor has a transducer bandwidth of 0.5 to 20 MHz and can resolve echoes 90-ns apart. The spurious products of practical mixers and amplifiers make the aliased approach impractical due to high noise and distortion. By using a bandpass filter after the mixer, distortion is reduced. A processor built with a lower sideband filter method yielded the lowest distortion and noise. The lower sideband processor has a bandwidth of 2 to 42 MHz and can resolve echoes 60-ns apart. With a single-cycle tone-burst processor input, ringing in the IF filter causes temporal asymmetry of the output pulse, while ringing in the detector filter causes ringing in the output pulse. Performance is expected to improve through the design of optimized filters. The ringing is less with ultrasonic echoes, because they do not start and stop as abruptly as a tone burst.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Synthesis of arbitrary frequency domain transmitting pulses applicable to pulsed NMR instruments

The synthesis of specialized excitation waveforms for pulsed NMR spin systems is an integral part of many present-day NMR experiments. Methods in use include various types of constant amplitude rectangular rf pulse trains with controlled interpulse delay times, modulating amplitudes of the envelopes of a chain of rectangular pulses, special long pulse rectangular pulses, and recently, single sideband spectral selections for NMR imaging. This paper describes, in quantitative fashion with experimental results, analysis and implementation of a method to generate pulsed NMR excitation waveforms using AM and FM techniques which yield individual pulses with controllable frequency spectral distributions. Examples given are of simplified cases, but the extension to complex frequency distribution requirements is clear.

Communications: Single-sideband transmission for land mobile radio: From seven to ten times as many channels could be made available in existing VHF and UHF bands

It is suggested that from seven to ten times as many channels could be made available in existing VHF and UHF bands. FM, AM, and SSB modulation techniques combined with syllabic amplitude and frequency compandors are compared. In the 15- to 30-dB signal-to-noise ratios-the amplitude-compandored SSB system and the amplitude- and frequency-compandored SSB system provide the same or better quality reception than FM systems that have comparable transmitter power. Three to five channels of the narrow-band system can be used between the channels of the 25-kHz spaced FM channels without unacceptable interference on either system. Ten narrow-band channels can operate in the 25-kHz bandwidth if there are no FM channels present.