Longer Travel Times Research Articles

A psychophysical estimate of the traveling‐wave delays in the human cochlea

Recent experiments using physiological means (such as recordings of action potentials in electrocochleography or studies of brainstem evoked responses to click stimuli) have allowed the accumulation of a first set of results on traveling‐wave delays in the human cochlea, but very few psychophysical results are available. We propose here a systematic psychophysical study. Two methods have been employed, both using pairs of short (2 ms) high‐frequency (F ⩾ 1000 Hz) stimuli, the frequency of the higher one (the reference) being fixed at 8000 Hz. Both methods are based on the determination of the advance that the lower frequency sound must have in order to make up for its longer travel time in the cochlea so that a subject will perceive the two sounds as simultaneous. Finally, we can propose a psychophysical estimate of traveling‐wave delays in the basal part of the human inner ear. The results are in very good agreement with those obtained in physiology.

On Lateral Dispersion Coefficients as Functions of Averaging Time

Abstract Plume dispersion coefficients are discussed in terms of single-particle and relative diffusion, and are investigated as functions of averaging time. To demonstrate the effects of averaging time on the relative importance of various dispersion processes, an observed lateral wind velocity spectrum is used to compute the lateral dispersion coefficients of total, single-particle and relative diffusion for various averaging times and plume travel times. The results indicate that for a 1 h averaging time the dispersion coefficient of a plume can be approximated by single-particle diffusion alone for travel times <250 s and by relative diffusion for longer travel times. Furthermore, it is shown that the power-law formula suggested by Turner for relating pollutant concentrations for other averaging times to the corresponding 15 min average is applicable to the present example only when the averaging time is less than 200 s and the travel time smaller than about 300 s. Since the turbulence spectrum used i...

Influence of cover slab diameter on solute travel time to wells

Travel times are computed for solute, moving by assumed piston flow, in steady state along streamlines in a phreatic (water table) aquifer in which a tube well is located to determine the influence of a well cover slab on the travel times. Flow nets are first computed by potential theory; then travel times along sets of streamlines are derived for 12 geometries. Parameters are cover slab radius, screened and unscreened casing depth, thickness of aquifer, well radius, and radius of influence. For example, for a well of cover slab radius 1.8 m, screened casing depth 0.5 m, unscreened casing depth 1.5 m, thickness of aquifer 6 m, well radius 0.6 m, and radius of influence 30 m, hydraulic conductivity 35 m/d, head difference across the system 0.15 m, and aquifer porosity 0.25, the travel time for solute injected at the edge of the cover slab to reach the well is 5.4 days, whereas solute introduced at the top of the aquifer next to the well pipe with no cover slab is 0.17 day (4.1 hours). The longer travel time, 5.4 days versus 0.17 day for ‘no cover slab,’ provides a longer time for biochemical and biophysical degradation of the solute, which may be pollutants as nitrates and acids originating from agriculture, industry, strip mines, sanitary landfills, or other groundwater pollution sources near a well.

アルミニウムおよび銅多結晶金属における超音波伝ぱ速度の応力依存性と３次弾性定数の測定

The third order elastic constants of polycrystalline aluminum (purity of 99.79%) and copper (purity of 99.98%) were determined by measuring their ultrasonic velocities under uniaxialy applied stress and the results were discussed by comparing with the previous data. The travel time of ultrasonic waves (5MHz) in a specimen of 10mm thickness was measured precisely with a sing-around system. The longitudinal and shear waves polarized parallel or perpendicular to the uniaxial stress axis were propagated perpendicular to the axis. Since the traveling time under zero stress varied slightly in the experiment, the traveling time was measured before and after periodical stress was applied and released rapidly. Elastic strains were below 200×10-6 in tension and compression and no plastic strains were observed.The results are summarized as follows:(1) The traveling time did not change linearly with applied stress. The deviation toward longer travel times was very large for copper both in tension and compression. However, the deviation for aluminum was a little. This is inferred to be the dislocation contribution.(2) To separate the measured traveling time change into two parts, one caused by the lattice anharmonicity and the other by dislocations, the measurements in both tensile and compressive conditions are needed.(3) The values of third order elastic constants measured for aluminum were in good agreement with the previous data, but not for copper. The present values, however, were most close to those calculated from the data of single crystal without containing dislocation contributions.

Access to usual source of care by race and income in ten urban areas.

In terms of less access to private sources of care (as distinguished from hospital-public clinics) and longer travel time to usual source of care, poverty areas are at a disadvantage. Within the ten areas studied, the poor have less access than the nonpoor, with access differences even greater between the races than between income groups. Blacks generally have less than whites when income differences are taken into account. Both the type of usual source of care and travel time appear to be related to differential utilizations of ambulatory care resources: persons reporting private sources of care and persons with shorter travel time to their usual source of care tend to make more physician visits in a year. Mechanisms for public financing of health care will not likely alleviate the problems of inaccessibility presented by poverty areas. It is in these areas of low access that public responsibility to organize and locate facilities will continue even after the advent of a fairly comprehensive payment mechanism for health care among the poor.

Waves from blasts recorded in Southern California

Records of five atomic explosions in Nevada and of a quarry blast of about 120,000 pounds of Dupont Nitramon at Corona, California, are investigated. The resulting travel times through the ground are combined with similar data reported previously. At a given station, records of different explosions near the same locality show great similarity. The following average velocities of longitudinal waves in Southern California are found: 5.9 km/sec below the sediments; a gradual or sudden increase to about 6.5km/sec near a depth of 6 km, and to about 6.9 km/sec near 10 km; about 8.2 km/sec below the Mohorovicic discontinuity at a depth of 35 to 40 km. A “low‐velocity layer” somewhere in the depth interval between 15 and 30 km has been inferred from earthquake data. This may prevent the finding of velocities from blast records for this depth range. No clear phase corresponding to in earthquake records is observed in blast records. This is to be expected if is a wave traveling along a low‐velocity channel approximately at the depth of foci of shallow earthquakes. The velocity of shear waves below the sediments is about 3.6 km/sec. Waves with such an apparent velocity recorded at distances between about 150 and over 400 km are possibly surface waves. Shear waves are usually relatively small in explosions.The recorded waves through the air include the direct sound waves, various types of waves with their highest points near 40 or 50 km, and waves with considerably longer travel times which have reached or passed through the low‐velocity layer near 80‐km elevation.