Initial Time Delay Research Articles

Experimental measurements in a variable acoustics hall

The experimental measurement of some quantitative acoustic qualities of a variable acoustics concert hall, and their variation with absorber configuration, is discussed. The impulse response of the space, using a electric spark generator as a noise source, was recorded for each configuration at a variety of receiver locations. Digital analysis provided quantitative data for reverberation time, definition, initial time delay gap, and texture. The effect on these parameters of the amount and placement of absorbing material is shown.

4 Gbit/s direct modulation of 1.3 μm InGaAsP/InP semiconductor lasers

It is confirmed that the multiplexer and the semiconductor laser can be operated up to 4 Gbit/s with pseudorandom pulse pattern. The relaxation oscillation, pattern effect and tailing effect of the semiconductor laser are also studied. It is confirmed that eye degradation is predominantly due to fluctuation of initial time delay caused by pattern effect, and tailing effect and relaxation oscillation are not fatal factors of 4 Gbit/s modulation under proper bias conditions.

Sensitivity analysis of time-delay systems

A method is developed for the computation of general sensitivity coefficients of time-delay systems to the variation of initial data, control, time delays, and other parameters appearing in the differential-difference equations of retarded type. Using the variational approach, it is shown that integration of the adjoint equations is sufficient to determine all the effects of parameter variations from the nominal solution.

Multipurpose hall design—a new direction

In Beraneks evaluation of concert halls, he attributed 40% of the rating to his own discovery initial time delay gap, 30% to factors associated with reverberation time, and 16% to factors associated with loudness. Multipurpose halls following this design philosophy have emphasized the use of clouds to provide early reflections and moveable curtains behind partially open panels to vary the reverberation time at the expense of loudness, side reflections, and bass. Recent listener preference space sludies have attributed 47% of hall preference to factors associated with sound force, and 28% to factors associated with sensation definition and clearness (i.e., side and front reflections). The direction of this research points overwhelmingly to a return to smaller volume halls with strong side reflections even for multipurpose uses.

Delineation of geologic contacts by seismic refraction with application to the fault zone between the Thompson nickel belt and the Churchill Tectonic Province

Refracted P-wave and S-wave arrivals are studied from a fourfold multicoverage seismic experiment that has been conducted across a region that spans the contact between the Thompson nickel belt and the Churchill Province in northern Manitoba. A new technique for the calculation of accurate delay times and basement velocities for unreversed multicoverage data is introduced. In this technique, the times of rays between selected shots and receivers are combined to give initial delay time corrections and a subsequent iterative least-squares analysis yields the final delay time corrections and estimates of the basement P-wave velocities. The P-wave velocities correlate well with the basement geology and have been used to refine the location of the contact between the Moak Lake gneisses of the Thompson nickel belt and the Kisseynew gneisses of the Churchill Province. From the P-wave velocities and S-wave attenuation it is concluded that this contact is a fault zone.

Subjective preference tests for sound fields in concert halls simulated by the aid of a computer

In the context of optimal acoustic design of concert halls, preference tests for simulated sound fields with various combinations of early discrete reflections and subsequent reverberation were conducted and the results compared with objective parameters. The results show that lateral early reflections which yield a small value of the interaural cross correlation give more preferred judgments than do non-lateral ones. The most preferred initial time delay (or scale factor for the dimensions of concert halls) can be determined by the long-time autocorrelation function of a music motif and by the total amplitude of both early reflections and the subsequent reverberation. As a comprehensive design concept, an “overall preference” for listeners is introduced here from the preference results.

Subjectively optimal conditions of sound fields for recording and reproducing

Does the high fidelity sound reproduction system itself provides desired hearing conditions in a listening room? That is only a necessary condition, because sound fields in a recording room and/or a listening room affect on subjective preference. Results of subjective preference judgements of the synthesized sound fields reveal following optimal objectives, namely “Principle of Desire” of listeners [Y. Ando, J. Acoust. Soc. Am. 62, 1436–1441 (1977) and Y. Ando, 95th Meeting of Acoust. Soc. Am., Providence, paper JJI]: (1) Sound fields with a smaller value of the interaural crosscorrelation are always judged as preferred (Incoherence at the Two Ears). In order to obtain the small value of interaural cross correlation, the preferred direction of reflections is found in the range centered on ±55° in the azimuth to the listener. (2) The discrete reflection arriving after the direct sound is preferred, so that the initial time delay gap can be determined by the coherence of autocorrelation function of source signals and the level of reflections (Renewal of the Direct Sound). For example, a preferred scale factor for the dimensions of rooms exists for a given music source. Taking these points into consideration, it is possible to design a new sound system from recording to reproducing.

Pulse-response characteristics of position-sensitive photodetectors

A key factor in designing position-sensitive detectors operating through lateral photoeffects in semiconductors concerns the nature of the pulse response over the entire active area of the device. It is demonstrated that the limiting behavior can be approximated by means of a fundamental RC-filter time constant τ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> together with position-dependent initial delay times of up to 0.6τ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . A comparison with recorded pulse-response traces suggests that the time constant τ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of two-dimensional position-sensitive photodetectors takes on values of R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /π <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , where R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> is the backlayer sheet resistance, C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> the junction capacitance per unit area, and d the electrode separation. Illustrations of the dependence of pulse shape on spot position for representative ion-implanted silicon units are shown to substantiate the analysis in the context of evaluating position-sensitive photodetectors for applications involving very short laser pulses.

Multiple-electrode triggered vacuum gaps

Since the design criteria for reliable operation of a single gap at 300 kV are not well known, multiple-electrode triggered vacuum gaps were constructed. A six-gap structure was initially studied. It had excessive time delay in the initiation of the arc. Subsequently, a three-gap structure was built. Time delays in initiation of the arc were satisfactory, but the rate of rise of current was slow. In addition, voltage hold-off capability was marginal. To improve these characteristics, a low pressure of hydrogen, 7 to 25 mtorr, was added. Considerably improved firing characteristics and reliable voltage hold-off at 320 kV were obtained.

Approximations to α for diffusion transistors

The paper reviews, from the viewpoint of design engineers, various approximations to the common-base intrinsic current gain of junction transistors. The basis of this comparison is the familiar expression for α derived directly from the semiconductor diffusion and continuity equations.A 2-pole approximation is considered in detail. It is shown that both the sinusoidal and transient response predicted using this expression is in good agreement with that predicted using the exact theory. For most practical transistors the parameters of this approximation remain reasonably constant.In the response to a step function of emitter current, the 2-pole equation closely describes the initial time delay arising from the transit time of minority carriers across the base region. The collector response to unit charge inserted into the base in the form of σ function also gives good agreement with the results obtained from the exact theory.The various approximations are compared by graphical presentation of the results.

The kinetics of invertase action

A method of obtaining better fits to experimental curves for the hydrolysis of sucrose in the presence of invertase is found by assuming that the reaction is first-order, but that there is an initial time delay before this form is assumed. More rigorously, a system of two differential equations describing the reaction is established, assuming that the formation of enzyme-substrate complex is irreversible, and a solution is obtained relating, at any time, the concentration of the products, the total concentration of complex which has been formed in that time, and the time. This solution is compared with other equations for the reaction and is used to calculate reaction constants. Curves showing the concentration of complex existing at timet are given and are employed in calculating an “equivalent” enzyme concentration. This expression is discussed.