Changes In Signal Level Research Articles

Investigation of the contact charge transfer absorption of organic solvents with oxygen for use in oxygen determination

The contact charge transfer (CCT) absorption spectra of dimethylsulphoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), ethanol, methanol, water, benzene (Bz), N, N'-diethylaniline (DEA), N, N'-dimethyl- p-toluidine (DMT) and N, N'-diethyl- p-toluidine with molecular oxygen have been investigated. These solvents form strong ultraviolet/visible CCT absorption spectra with intensities that are related to the partial pressure of the applied oxygen. DMSO, DMF, DMA, Bz, DEA and DMT are shown to form 1:1 molecular contact complexes with molecular oxygen. A simple oxygen sensing system is described using CCT absorption spectroscopy of DMT at a wavelength of 400 nm, with a gas flow rate of 60 cm 3 min −1 through the solvent in a cuvette with a pathlength of 1 cm. Inexpensive plastic fibres are used to relay the light from a xenon lamp source to the cuvette and back to a photo-detector. The response of the sensing system to changes in oxygen concentration is reversible, non-linear and in good agreement with the Beer-Lambert law. The most sensitive response region is from 0 to 20% O 2 with a change in signal level of about 35%. The solvent used shows no deterioration in performance over a long period and can be used to determine gaseous oxygen concentrations from 0 to 100%. It does not respond to carbon dioxide.

Classification of the temporal discharge patterns of single auditory neurons in the frog superior olivary nucleus

Temporal discharge patterns of neurons in the superior olivary nucleus (SON) of the northern leopard frog ( Rana pipiens pipiens) were studied by evaluating peri-stimulus time histograms and interspike interval histograms generated from responses to tone bursts at the neuron's characteristic frequency and at 10 dB above neuron's characteristic threshold. Four basic discharge patterns were observed, i.e., primary-like, phasic-burst, phasic, and pauser. Additionally, within each class, different neurons exhibited further subtle differences in temporal discharge patterns and thus subclasses were distinguishable. For most SON neurons, changes in signal level did not affect the discharge pattern. However, there were a few notable exceptions. The firing pattern of 12% of SON neurons changed from one class to another with a change in signal level. Two-thirds of phasic-burst neurons showed increased regularity (i.e., chopping pattern) in their discharges as the signal level was increased. The majority of SON neurons showed monotonic rate-level functions, but one-fourth gave non-monotonic rate-level functions. The presence of a fairly large number of non-monotonic units in the frog SON suggests an additional role of this nucleus in information processing beyond the simple coding of stimulus level. The discharge patterns displayed by SON neurons resembled those seen in the frog cochlear nucleus and in the mammalian superior olivary complex.

Method for transmitting an audio signal with an improved signal to noise ratio

A method of transmitting an audio signal wherein the audio signal is partitioned into successive (in time) blocks by means of time windows, the signal parts contained in the blocks are converted to short-time frequency spectrums by transformation, subsequently the short-time frequency spectrums are coded on the basis of psycho-acoustical masking laws and are transmitted. The received coded signals are decoded, the short-time frequency spectrum signals are brought back into the time domain through re-transformation, and finally the blocks present in the time domain are assembled. Moreover, the blocks are partitioned into sub-blocks and, in case of signal level changes from one block to the other which exceed a predetermined value, the signal parts in the sub-blocks are subjected to a compression prior to transformation and to a complementary expansion after the re-transformation. To improve the signal-to-noise ratio, the signal is amplified and/or attenuated in the sub-blocks during the compression dependent on the average signal powers in the respective sub-blocks.

Effects of antenna pointing errors on the design of heterodyne optical intersatellite communications

In the optical intersatellite communication system using a heterodyne detection, the signal level changes by the pointing error of the receiving antenna on the satellite in addition to the pointing error of the transmitting antenna of another satellite. Further, since these antenna pointing errors cause the unavailable state of the optical channel, the unavailability will become a problem. However, to date, nothing has been reported on link design which reflects the unavailability by considering the pointing errors of both the transmitting and receiving antennas. In this paper, equations for the burst error rate are derived by means of the probability density function of the pointing error distributions of the transmitting and receiving antennas. With this burst error rate, the unavailability is computed. Hence, a link design reflecting the unavailability can be carried out by taking into consideration the pointing errors of the transmitting and receiving antennas at the same time. Further, a link design example is presented in the case where the facing satellites have identical communication systems.

A neuronal model of classical conditioning

A neuronal model of classical conditioning is proposed. The model is most easily described by contrasting it with a still influential neuronal model first analyzed by Hebb (1949). It is proposed that the Hebbian model be modified in three ways to yield a model more in accordance with animal learning phenomena. First, instead of correlating pre- and postsynaptic levels of activity, changes in pre- and postsynaptic levels of activity should be correlated to determine the changes in synaptic efficacy that represent learning. Second, instead of correlating approximately simultaneous pre- and postsynaptic signals, earlier changes in presynaptic signals should be correlated with later changes in postsynaptic signals. Third, a change in the efficacy of a synapse should be proportional to the current efficacy of the synapse, accounting for the initial positive acceleration in the S-shaped acquisition curves observed in animal learning. The resulting model, termed a drive-reinforcement model of single neuron function, suggests that nervous system activity can be understood in terms of two classes of neuronal signals: drives that are defined to be signal levels and reinforcers that are defined to be changes in signal levels. Defining drives and reinforcers in this way, in conjunction with the neuronal model, suggests a basis for a neurobiological theory of learning. The proposed neuronal model is an extension of the Sutton-Barto (1981) model, which in turn can be seen as a temporally refined extension of the Rescorla-Wagner (1972) model. It is shown that the proposed neuronal model predicts a wide range of classical conditioning phenomena, including delay and trace conditioning, conditioned and unconditioned stimulus duration and amplitude effects, partial reinforcement effects, interstimulus interval effects, second-order conditioning, conditioned inhibition, extinction, reacquisition effects, backward conditioning, blocking, overshadowing, compound conditioning, and discriminative stimulus effects. The neuronal model also eliminates some inconsistencies with the experimental evidence that occur with the Rescorla-Wagner and Sutton-Barto models. Implications of the neuronal model for animal learning theory, connectionist and neural network modeling, artificial intelligence, adaptive control theory, and adaptive signal processing are discussed. It is concluded that real-time learning mechanisms that do not require evaluative feedback from the environment are fundamental to natural intelligence and may have implications for artificial intelligence. Experimental tests of the model are suggested.

Stimulus parameters governing confusion effects in forward masking

Confusion effects in forward masking occur when the listener has difficulty discriminating a suprathreshold signal from the preceding masker. Confusion effects were examined for “pulsing” forward maskers composed of repeated bursts of a sinusoid followed by a sinusoidal signal. Differences between the level, frequency, and duration of the signal and an individual masker pulse, as well as offset—onset delay were varied to determine the change necessary to resolve confusion. For maskers composed of 20-ms pulses, changes in signal level of 1–5 dB or in signal frequency or 20–30 Hz resolved confusion. For maskers composed of 10-, 20-, or 40-ms pulses, the signal delay necessary to resolve confusion increased with masker-pulse duration but was typically less than 10 ms. For these three pulsing maskers, signal durations less than one half or greater than twice the masker-pulse duration were necessary to resolve confusion. [Work supported by NSF, NIH, and the University of Nebraska.]

Sensitivity of predicted effectiveness of a paging system to design criteria

The expected effectiveness of an industrial paging system for presentation of emergency messages has been evaluated in terms of sentence intelligibility (SI). The evaluation was based on the Speech Transmission Index concept developed by Houtgast and Steeneken [J. Acoust. Soc. Am. 67, 318–326 (1980)]. Changes in SI were evaluated for 17 paging system locations with nominal signal‐to‐noise ratios ranging from −21 to +15 dB and reverberation times ranging from 0.3 to 1.6 s. The change in signal level required to achieve a design goal of 90% and 97% SI was evaluated as a function of (1) the average age of the listeners (30 or 40 years), (2) the percentage (50% or 90%) of this age group who would achieve the desired SI, and (3) the number of message repetitions. The primary result is to point out that the influence on required signal level of message repetitions was found to be at least as important as the other factors. This influence is not included in the usual engineering methods for evaluating communication systems. Conflicts between alternate prediction models for the effect of message repetition according to current signal detection theory and earlier experimental work are considered.

Effect of Geophysical Disturbances on Ionospheric Radio Wave Propagation and Emergency Communication

Some results of a study of the effect of geophysical disturbance due to solar flares, thunderstorms and meteor showers on the ionospheric radio wave propagation characteristics in the entire frequency range of radio communication ranging from VLF to HF, are presented. The results reveal that a fadeout in one band may be accompanied by an enhancement or no change of signal level in other band, and thus indicate the possibility of evolving an interband frequency diversity system involving VLF, LF, MF and HF bands to cope with the fadeouts associated with different geophysical disturbances.

Response of hot wire anemometer probes to a stream of air bubbles in a water flow

The response of a hot wire anemometer in bubbly two-phase air-water flow was studied. For the conventional hot wire design and operation at low overheat, it was found that the sensor does not enter the bubble completely, thus making measurements inside the bubble virtually impossible. This is due to a liquid film which attaches to the wire. For small bubbles it results in splitting of the bubble into two. Three types of interactions are identified-direct, glancing and partial hits. Direct and glancing hits result in identical signal level changes and hence discrimination between bubble and no-bubble signals, whereas partial hits give considerably reduced signal level changes. Application of such measurements to determination of local void fraction by use of signal probability density plots is also considered.

Auditory informational masking

Masking is typically defined in terms of the threshold change in signal level resulting from the presence of a neighboring noise. By contrast with “energetic” masking, informational masking is defined in terms of the threshold change in statistical structure resulting from the presence of a neighboring signal of the same amplitude. Forward masking, backward masking, combined masking, etc., may be defined in terms of the temporal relations of the neighboring to the informational sequences. Forward informational masking is shown to be appreciably smaller than backward or combined informational masking. The threshold change in statistical structure tends to be proportional to the ratio of the durations of the neighboring to the informational sequences.

Phase-shift compensation of limiter amplifiers

Phase shift in limiters with signal level changes is a calculable consequence of waveshape distortion and can be eliminated by providing suitable low-frequency response to compensate for restricted high-frequency response.

A 5 to 50 MHz Direct-Reading Phase Meter with Hundredth-Degree Precision

The subject phase meter provides a direct, level-insensitive indication of the relative phase angle between two RF signals in the frequency range from 5 to 50 MHz. It has an inherent phase resolution capability of greater than 0.001°, although the present design is limited by stability, noise, and spurious responses to an accuracy of about ±0.01°. The instrument utilizes the well-known technique of measuring phase in terms of the time between the zero crossings of two sinusoidal signals, using an electronic counter for time-measuring and display. A considerable advance in angular resolution, accuracy, and operational ease over any known previous instrumentation has been achieved by a painstaking combination of such key factors as highly level-insensitive zero-crossing detectors, extremely linear RF/IF amplifiers and mixers, and multiperiod averaging of the numerical readout. Verification of the hundredth-degree accuracy for all phase angles, operating levels, and frequencies is a problem comparable in magnitude to the development of the meter itself. For cases where the signal level is essentially constant, a relatively simple verification procedure is described. Verification of meter insensitivity to signal level changes requires the availability of a phase-calibrated RF attenuator.

The active adaptive antenna array system

The active adaptive antenna array system (AAAAS) is a self-focusing antenna array. Phase-lock loop-type circuits are used to automatically adjust the phases of signals received on the elemental antennas of the array so that the received signals can all be added in phase or coherently. The AAAAS is active in that it automatically searches for, locks onto and tracks a source. Furthermore, the system 1) is adaptive to changes in antenna spacing, 2) is adaptive to changes in signal level and noise spectral density, 3) uses the incoming signal to automatically and electronically collimate the antenna array beam and 4) can have its aperture amplitude distribution readily changed. A theoretical study and detailed description of two particular configurations of the AAAAS is given. The theory of operation of the system has been experimentally verified on a simulated system in which audio frequencies were used.

Amplitude Contour Display of Sound Spectrograms

Sound spectrographs typically displayed complex signals, such as speech, on teledeltos (facsimile) paper with frequency and time plotted along the ordinate and abscissa, and shades of gray to indicate the relative intensity of the frequency components. The gray scale is usually limited by the teledeltos paper to a marking range of 12 dB, whereas the signal may have amplitude variations of 40 to 50 db. A voltage quantizer has been designed which will plot equal-level contours in the frequency/time plane. The equal-level plateaus were selected at 6-dB intervals over a 42-db range. Gray-scale compression is also obtained as a by-product of this quantizer to shade each contour level such that a 42-dB change in signal level causes a 12-dB change in marking voltage. A discussion of the design and operating principles is given so that one can incorporate the circuit into a spectrograph or modify the circuit for other applications.

The Application of Linear Servo Theory to the Design of AGC Loops

An analytical technique for designing automatic gain control (AGC) circuits is presented. This technique is directly applicable to high-gain high-performance radio receiving equipment. Use of this technique permits the designer to specify the performance of the AGC system completely with respect to step changes in signal level, ramp changes in signal level, frequency response, receiver gain error as a function of receiver noise, etc., before the receiver is constructed and tested. When used in conjunction with the statistical filter theory the technique has been used to synthesize optimal AGC systems when the characteristics of the signal and noise are appropriately defined. The mathematical derivation of the closed-loop equations is presented. The resulting expressions are simple and easy to understand by anyone acquainted with linear servo theory. Furthermore, the underlying assumptions used in theory have been tested experimentally, and the close agreement between theory and experiment attests the usefulness of the design technique.