Baseline Noise Level Research Articles

Effects of aircraft noise on Pacific black brant and other geese in Alaska

In 1987, a study of the effects of aircraft noise on the behavior, distribution, and habitat use of Pacific black brant, Canadian geese, and emperor geese was initiated on the Alaska Peninsula and on the North Slope of Alaska. The objectives were to: (1) describe the behavioral responses of geese as an effect of noise from aircraft overflights; (2) record and examine noise associated with experimental overflights of fixed‐ and rotary‐wing aircraft and specific altitudes, airspeeds, and environmental conditions; (3) secure baseline noise levels for routine flights of nonexperimental aircraft; and (4) provide recommendations to government agencies for reduction or mitigation of any adverse impacts associated with aircraft noise to these populations of geese. Behavior of geese was monitored from remote locations prior to, during, and following level overflights along prescribed routes. Concurrently, 13‐oct sound exposure and maximum A‐weighted and sound levels of each aircraft were measured with a real time analyzer. Here, the design and preliminary results of the first of a multiyear study will be discussed.

Laminar profile of resistivity in frog retina.

Measurements of absolute transretinal resistance and of the relative resistance of the various retinal layers were obtained in the frog. The resistance of clamped sections of isolated retina was 66 omega . cm2, which results in an average resistivity (rho) between inner and outer limiting membranes of 5,050 omega . cm. In eyecups, relative resistances (obtained by passing constant currents across the retina) were assigned to specific layers of the retina with the aid of physiological criteria (e.g., depths of light-evoked field potentials, changes in extracellular K+ concentration, base-line noise level, and resistance). These relative resistances were then converted to absolute values, a calculation feasible because the region between inner and outer limiting membranes, which has the same structure in both isolated and eyecup retinas, could be specified during experiments. Resistivities (in omega . cm) for the retinal layers include 1) subretinal space, 970; 2) inner and outer nuclear layers, 6,800; and 3) inner plexiform layer, 1,750. The ganglion cell and optic nerve fiber layers were too thin to resolve individually, but rho of the two layers combined was 7,900. The outer plexiform layer was also too thin to reliably resolve, but its rho is likely the same as the inner plexiform layer. The extracellular space volume fraction (alpha) of the retinal layers was estimated from these rho s, and the following values were obtained: 1) subretinal space, 0.12; 2) outer and inner nuclear layers, 0.03; 3) inner and outer plexiform layers, 0.11; and 4) ganglion cell and optic nerve fiber layers, 0.02. The decreased rho and increased alpha of the inner plexiform layer and the subretinal space, compared with that of the nuclear layers, are expected from their anatomy. A consideration of these inhomogeneities is required in analyses of field potentials and of changes in extracellular ionic concentrations.

Effect of exercise in healthy men on QRS power spectrum.

The effect of exercise on the QRS power spectrum has not been evaluated. We hypothesized that increased conduction velocity with exercise might selectively increase high-frequency QRS potentials. Using a digital electrocardiograph (ECG) cart, a single bipolar chest lead was recorded in 21 healthy adult males at rest and then immediately after treadmill exercise. Fast Fourier transform analysis of the ECGs was performed using a 128-ms sampling window, including the QRS but not the P wave. Step discontinuities between PR and ST segments were minimized using a linear correction function to obviate artifactual increases in high-frequency content after exercise. The power spectrum plots of rest and exercise data showed an increase in the amplitude of high frequencies that could not be accounted for on the basis of noise contamination. For the frequency band between 187.5 and 250 Hz, the root-mean-square (RSM) voltage of exercise QRS complexes (10.0 +/- 3.6 micro V) was significantly (P less than 0.02) greater than that of rest QRS complexes (7.8 +/- 1.2). However, base-line noise level (computed over a 32-ms interval during the ST segment) was not different between rest and exercise over this high-frequency band. The same exercise protocol was also applied in 11 normal male subjects using an analog ECG cart. For the 187.5- to 250-Hz band, the RMS voltage of the QRS after exercise (13.0 +/- 1.8 micro V) was also significantly (P less than 0.01) greater than at rest (10.2 +/- 2.8) without any difference in ST segment noise level over the same frequency range. These data indicate that exercise causes an increase in the amplitude of high-frequency QRS potentials in healthy men.

Pupillary activity measured by reflected infra-red light

A simple, reliable and inexpensive device for continuously monitoring pupillary changes is described. It is an improved version of a device first suggested by L. Stark. Infra-red light is transmitted to the iris and reflected back onto the receiver. Consequently, the device is effective only if the eye is immobile. Pupillometer ouput was related linearly to measurements made directly from motion pictures of pupil mobility. Experimental data are presented which demonstrate the stable baseline and minimal noise levels of the pupillometer in a conditioning experiment using paralyzed cats.

Enforcement of a quantitative noise ordinance

Quantitative community noise ordinances are currently implemented in only a few municipal jurisdictions around the world. Comparative studies conducted by the Ontario Ministry of Environment show that significant differences exist in philosophy, law and measurement procedures between these jurisdictions, leading to varying interpretations of the allowable background (baseline) noise level for a given place and time of day. For legal purposes, the degree and quality of the offending noise excess above the allowable background (baseline) level must be determined quantitatively if this type of local community ordinance is to be enforced. Techniques for quantitative investigation of nuisance complaints due to common noise sources in the local community are discussed. Measurements, using some of the latest types of sound level measuring devices, are analyzed to suggest a rational solution to the problem.

Trace determination of beryllium oxide in biological samples by electron-capture gas chromatography.

Two preparations of beryllium oxide labeled with /sup 7/Be were synthesized by calcining at 500 deg C or 1600 deg C. Comparative radiochemical and gas chromatographic analyses of these oxides were made using two procedures. Direct dissolution-chelation of the oxides with concentrated trifluoroacetylacetone in ampoules followed by electron-capture gas chromatography of the resultant beryllium chelate suffered from interference by a trifluoroacetylacetone reaction product. A second method employed the dissolution of the oxides in dog blood and rat liver homogenate media by a hot 75% sodium hydroxide procedure. The beryllium from the dissolved oxide was then chelated by a low temperature reaction with trifluoroacetylacetone without forming an interfering product. Subsequent gas chromatographic analysis yielded recoveries averaging 105%; standard deviation = plus or minus 7%. The samples tested were limited to the 1.0-mg BeO/ml level by radioactivity, but the gas chromatographic base-line noise level was low enough to permit analyses of submicrogram quantities. (auth)