Pressure Rise Time Research Articles

Shock wave reflection in gas-liquid foams

Shock wave propagation in gas--liquid foams was studied in [I-5]. It was established in [I, 2] that plane shock waves in foams have developed relaxation zones with pressure rise times up to several milliseconds. Then with increase in intensity the parameters of incident, and especially reflected, waves deviate from the equilibrium parameters in a foam, calculated in the manner of [6], from the volume concentration of the condensed phase (c-phase). To describe the process of shock wave reflection in gas--liquid systems [4] proposed a model approach based on description of shock compression of a two-phase medium by a polytropy index K = I + (y -I)(I -c), where y is the adiabatic index of the Poisson gas phase, and c is the volume concentration of the c-phase. Despite this approach's satisfactory description of the experiments of [I, 2] on shock wave reflection in foam, use of K to explain observed shock wave attenuation in foam leads to severe divergence between experimental and calculated data [7, 8]. One of the causes of disagreement of calculated and experimental shock wave parameters in foam is apparently the presence of developed relaxation zones, comparable in size of the dimensions of the shock tube operating channels used in [I, 2, 5] for their generation. The present studies were performed in shock tubes which insured achievement of equilibrium parameter values behind the incident shock wave front. In addition to performing the experiments, the effect of volume fraction of the c-phase was analyzed, as was the validity of the assumptions of gas idealness and incompressibility of the c-phase normally employed in calculating incident and reflected shock wave parameters.

Vibrational excitation of molecules in a lattice due to shock induced molecular deformation

A simple formalism is developed to calculate the rate of internal vibrational excitation of a molecule in a lattice due to abrupt deformation of the bonds of the molecule as a result of the application of a shock pulse to the lattice. The excitation rate is calculated as a function of rise time of the pulse and peak pressure for the case of 1,3,5-trinitro, 1,3,5-triazocyclohexane. It is shown that large vibrational excitation rates can be achieved if the rise time of the shock pulse is in the order of the period of vibration of the bond. The possible role of this process in shock induced chemical reactions in solids is considered.

Fast pulsed gas valve

A fast valve which can inject gas pulses with durations from 25 to 400 μs into a vacuum system is described. Quantities up to 5 Torr l can be injected. A pressure rise time of ∼0.5 Torr/μs has been determined at the valve opening. A fast opening time is achieved by having a magnetically accelerated ring collide with a disk which is used as a vacuum seal. Gas pulse parameters have been measured with a fast ionization gauge.

Pressure-jump apparatus suitable for repetitive experiments

A repetitive pressure-jump apparatus has been devised and used for the measurement of a small relaxation effect in solution. Although the pressure rise time of the apparatus is inferior to the usual method, signal averaging has enhanced signal-to-noise ratio of the relaxation spectrum.

Fast valve for gas injection into vacuum

A simple, fast, reliable magnetically driven gas valve for use in plasma experiments is described. The pressure rise time has been measured to be approximately 1 Torr/mus at the valve opening.

Studies in infant behavioural audiometry. II. Six-week-old infants.

The behaviour of 90 clinically normal 6-week-old babies previously studied as neonates was video-recorded while they were presented with sequences of sound stimuli. The stimuli varied in sound pressure level, bandwidth and rise time, and included two voice signals and a no-sound (control) trial. Video records were made both for the whole body aspect and for a 3 1/2 X 'close-up' of the head. Later, the video records were shown to 6 observers who were allowed to see the babies for 10 s at each trial. The first 5 s was a prestimulus observation period, and the second 5 s usually contained a sound stimulus. Between the trials, the observers were given 20 s in which to record (i) prestimulus activity, (ii) confidence in response, and (iii) movement details (data for [iii] not reported here). Different segments of the baby's body were observed on different occasions as detailed in our neonatal report. The response confidence ratings were analysed, using aspects of signal detection theory, to show differences amongst various body segments (p less than 0.001), sound pressure levels (SPL) (p less than 0.001), band widths (BW) (p less than 0.001), and rise times (RT) (p less than 0.001). There were significant interactions between SPL and BW (p less than 0.05) and SPL X RT (p less than 0.001). The 3 factor interaction (SPL X BW X RT) was also significant (p less than 0.001). A 90-dB broad-spectrum noise band was by far the most effective stimulus. The response to different sound stimuli was affected by the baby's posture (lying or sitting) and by prestimulus activity state. The results are discussed in relation to our previous neonatal study.

Studies in infant behavioural audiometry. I. Neonates.

The behaviour of 93 clinically normal neonates was video-recorded while they were presented with sequences of sound stimuli which varied in sound pressure level, bandwidth and rise time and which included two voice signals and a no-sound (control) trial. Video records were made both for the whole body aspect and for a 3 1/2 X "close-up" of the head. Later, the video records were shown to 6 observers who were allowed to see the babies for 10 sec at each trial. The first 5 sec was a pre-stimulus observation period, and the second 5 sec usually contained a sound stimulus. Between the trials, the observers were given 20 sec in which to record (1) pre-stimulus activity, (2) confidence in response, and (3) movement details (data for (3) not reported here). For the whole-body aspect, observers were allowed to see (1) the whole body, (2) the head, arms and trunk, (3) the arms, trunk and legs, (4) the head only, (5) the arms and trunk only, or (6) the legs only, during different viewing sessions. For the head aspect, they could see (7) the whole head, (8) the head above the upper lip, or (9) the head below the upper lip. This segmentation was achieved by masking parts of the television screen with shutters. The response confidence ratings were analysed using aspects of signal detection theory to show differences amongst various body segments (p less than 0.001), sound pressure levels (p less than 0.001), bandwidths (p less than 0.001), and rise times (p less than 0.01). There were significant interactions between sound pressure level X bandwidth (p less than 0.001), sound pressure level X rise time (p less than 0.01), and bandwidth X rise time (p less than 0.001). A 90-dB broad-spectrum noiseband was by far the most effective stimulus. The response to different sound stimuli was differentially affected by pre-stimulus activity state. The results are discussed in relation to recent work on clinical screening techniques.

Functional explanation of differences in voice onset time and oral air pressure rise time for stops articulated at different distances from the vocal cords

It has been known since 1970 (Joseph Greenberg, Int. J. Am. Ling. 36, 123–145) that a positive correlation exists between voice onset time and distance of stop articulation from the vocal cords. Oral air pressure data tentatively support Greenberg's (1970) conjecture that the larger air cavity between the vocal cords and the point of closure in more anterior stops requires a longer time to build elevated air pressures than the cavity associated with more posterior stops: Prevoiced stops are released at comparable air pressure levels, while the number of glottal pulses occurring, and the time elapsing, as the pressure builds vary directly with the distance of the place of closure from the vocal cords. Air pressure rise times in voiceless stops, and in non‐prevoiced /b‐d‐g/, show a pattern of air pressure rise times comparable to that encountered in the prevoiced stops, suggesting that voiced stops and their prevoiced counterparts may be articulated according to the same internal schedule, or that VOT differences functionally induced in pre‐voiced stops may invade the internal organization of the speech production system.

Superselective left atrial cineangiocardiography.

A study of selective left atrial cineangiographic technique was undertaken to determine the diagnostic value and practicality of ECG-triggered intermittent systolic injections. One hundred intermittent systolic injections were performed in 83 infants, children and adults with mitral valvular lesions or congenital defects in the atrial or ventricular septum. A Contrac injector with short pressure rise time enabled rapid delivery of pre-selected flow rates and appropriate contrast volumes into the left atrium during one or repeated ventricular systolic periods. Systolic injection technique provides superior visualization of left atrial size and morphology with small injection volumes. There is superior visualization of left atrial outflow through the mitral valve or atrial septal defects due to accumulation of higher contrast gradients during the systolic atrial filling period. Better anatomic detail of contrast jet size and direction as well as more physiologic filling and washout of the atrium is obtained. Timeselective as well as anatomically selective injection technique results in significantly lower contrast volumes and a resultant increase in patient safety particularly important in pediatric patients with complicated congenital heart lesions.

Fundamental Research on Advanced Techniques for Sonic Boom Suppression

First Page

Alleviation of the Sonic Boom by Thermal Means

Previous studies suggest that reduction of SST sonic boom noise to levels acceptable to the public requires elimination of shocks and creation of pressure rise times of 10 msec or more at the ground. Because it appears impractical to lengthen the aircraft sufficiently to achieve this objective, a feasibility investigation of the use of heat to simulate a long body was undertaken. The large power requirement dictates the use of direct combustion of cheap fuel for this purpose, and practical considerations motivate off-axis heating. This can be accomplished in principle by the use of either a thermal spike with its axis parallel to the airstream or a thermal keel that extends downward from the aircraft.

A pneumatically operated `semi-dynamic' calibrator for pressure transducers

An air-operated device is described for observing the output of pressure transducers when subjected to pressure rise times such as those experienced in short-duration aerodynamic testing facilities (in particular, the hypersonic `gun' tunnel). Some results of its use with an unbonded strain gauge pressure transducer are presented.

CARDIOVASCULAR MANIFESTATIONS OF THE HURLER SYNDROME: HEMODYNAMIC AND ANGIOCARDIOGRAPHIC OBSERVATIONS IN 15 PATIENTS.

Hemodynamic observations in 15 cases of the Hunter-Hurler syndrome are reported. Required premedication was two to three times that usually needed. No major complications or deaths occurred. As a group, these individuals tend to have slight elevations of pulmonary artery pressures and more definite elevations of systemic arterial pressures. They generally have normal cardiac outputs and, thus, elevations of total systemic, total pulmonary, and pulmonary arteriolar resistances. In only one case was there clinical and angiocardiographic evidence of valvular involvement, that case having aortic insufficiency. In another case there was only angiocardiographic evidence of mitral insufficiency. Only one child was in congestive heart failure at the time of the study. There was no evidence of coronary artery disease. The ascending limb right ventricular pressure curve was frequently notched and the pressure rise time of the left ventricle (dp/dt) was low. No case had a congenital malformation of the heart. Those individuals who have normal vascular bed resistances appear to live longer than those who have elevated resistances early in life. The prognosis is also better for the male Hurler of the sex-linked variety than for those cases due to autosomal recessive inheritance.