High Drift Rates Research Articles

Observations on the stability of thermistors

This paper investigates the long-term stability of three different types of thermistor with room-temperature resistances ranging from 80 to 150 kΩ. Precision measurements of thermistor resistance and temperature were made in a thermal environment controlled to ±3 μK. Measurements took place in between periods of limited thermal cycling and also during 100 days at constant temperature. Mechanical shock and strain appear to be the cause of the high drift rates observed in some thermistors; the majority of the thermistors were, however, very stable, with drift rates around 0.1 mK per 100 days and were unaffected by thermal cycling. Such low drift rates indicate that certain thermistors could be used as convenient temperature transfer standards with a reproducibility in the submillikelvin range.

The lateral effect of oscillation of peripheral luminance gratings on the foveal increment threshold

A black-and-white grating oscillating in the peripheral visual field reduces the visibility of a foveal test spot in the center of a uniform, white background disk. Visibility attains a minimum at an oscillation frequency of 4 Hz, but it fails to attain a similar minimum when the grating drifts slowly at a rate of 4 c/sec. Only when high drift rates and sudden reversals of direction (jerks) are used with the drifting grating does one obtain a noticeable decrease in visibility. As the diameter of the background disk increases, the reduction of test spot visibility decreases. These findings are compared to similar parametric variations in the strength of the neurophysiologically measured “periphery-effect” of single neurons.

Migrations ofLeptophlebia vespertina L.andL. marginata L.(Ins.: Ephemeroptera) in the estuary of a coastal stream

Abstract Investigations carried out in a coastal stream flowing to the Northern Bothnian Sea (Angeran, 63°35'N, 19°50'E) have shown a high drift rate of mayfly nymphs towards the coastal areas. The nymphal development takes place in the estuaries with low salinity (conductivity between 47 and 9800 μS; salinity between 0 and 4–5%0). After the emergence (May/June) the adults fly from the coastal areas to lay their eggs in the stream biotope in the Angeran. There thus appears to be a colonization cycle between the coastal stream and adjacent coastal areas. The migration movements of downstream drift and the compensatory upstream directed flight are interpreted as asurvival strategy of the species concerned.

S-bursts in Jupiter's decametric radio spectra

Dynamic spectra of Jupiter's S-bursts are observed with sweep-frequency and multi-channel receivers operating at frequency ranges 21–30 and 20.85–23.20 MHz, respectively. Spectra obtained with time resolutions of 0.2, 0.02, and 0.004 s are compared, the frequency resolution being 50 kHz. The most normal appearance of S-bursts is in trains with a frequency range of the order of 1 MHz. Narrow-band Strains also occur. Narrow-band L-emissions in region B are often associated with S-bursts, obviously in the manner described by Flagget al. (1976). Synoptic spectral observations indicate that region B for S-bursts exhibits a drift in longitude similar to that for L-bursts. The Io phase profile for S-bursts has a maximum in the vicinity of 80° in region B and 230° in region C. S-bursts observed in 1976 have higher drift rates than those compiled by Krauscheet al. (1976). Region C bursts have simpler spectra and lower drift rates than region B bursts.

Spatial frequency channels in the human visual system: Effects of luminance and pattern drift rate

Recent evidence indicates that the human visual system contains multiple channels, with each channel sensitive to a different narrow range of spatial frequency. In this study the sensitivity of these channels for patterns at low mean luminance or high drift rate is measured by the effect of adaptation to sinusoidal gratings on the contrast thresholds for sinusoidal gratings. The channels do not behave in the way expected from retinal ganglion cell physiology; rather, they remain selectively sensitive to narrow ranges of spatial frequency even when the luminance is low or the drift rate high.

Light Control of Aquatic Insect Activity and Drift

Investigations on aquatic insect activity, measured as drift in an artificial stream system with rigid light and temperature conditions, demonstrated a light—controlled, labile, exogenously—mediated activity rhythm. A threshold value for light, incident at the water surface, which when decreased led to high drift rates, and when increased suppressed activity, was determined to lie between 10—3 and 10—4 ft—c (10—2 and 10—3 lux). Preliminary experiments showed variations in wavelength to have little effect on the activity patterns of the insects.

Geothermal Exploration for Ground Water

Since 1961, precise ground-temperature measurements have been made at shallow depth in a number of geological terranes and climates. The objective has been to investigate the effectiveness of shallow geothermal techniques in geological exploration. The thermal sensors used are thermistors individually calibrated to within .02°C. It was found that shallow-earth temperatures can be related to the occurrence of ground water. Shallow, moving ground water produces low temperatures and low annual drift rates, due to damping of the annual temperature wave. Conversely, dry shallow bedrock, because of higher conductivity and lower specific heat, produces relatively higher temperatures and higher drift rates. Other permutations of observed temperature and drift rate reflect intermediate conditions of bedrock and ground-water distribution. As a case study, the geothermal survey of Johnson Valley is described. This is a closed basin system in southern California, which shows a direct relationship between ground temperature and depth to water as measured in wells.

Growth of Germanium for Lithium Drift Detectors

The germanium for lithium drift germanium detectors should have the following properties: 1. High lithium drift rate. 2. Low reverse current during the drifting process - particularly for high temperature drifting. 3. Minimal lithium precipation during drifting. 4. Capability of fabrication into detectors exhibiting (a) Low noise reverse currents at high bias voltages (b) A minimum of carrier trapping. Germanium grown in a hydrogen atmosphere exhibits most of these desirable qualities. Measurements of ρ, τ, dislocation density, Hall mobility, conductivity, and IR absorption on both hydrogen grown and normally grown crystals have been made for correlation with detector properties. These measurements and the details of the hydrogen growth process are discussed.

Effect of Light Intensity on the Drift of Stream Invertebrates

Various experiments were conducted in a small Minnesota stream to determine the effect of light intensity on the circadian rhythms in drift of two aquatic invertebrates, the nymph of the mayfly Baetis vagans McDunnough and the amphipod Gammarus pseudolimnaeus Bousfield. Experiments included 1) artifical light in an exclosure which insured that experimental conditions were applied only to the organisms on the stream bottom area in the exclosure, 2) artificial light in the open stream, and 3) artificially produced darkness in an exclosure. A threshold of light intensity which, decreasing, initiated high drift rates and which, increasing, caused cessation of drift, was about 0.1 ft—c (1 lux) for both species. Continuous artificial light above the threshold level for an entire night period, and also for 4 consecutive days, depressed the normal high nocturnal drift rates in the exclosure to near daytime levels; on the fifth night in the exclosure, in darkness, drift was much higher than normal. Continuous artifical light for an entire night period on an open stream riffle also greatly depressed noctural drift. In another open stream experiment, in which organisms drifted from darkness onto a lighted riffle, some settled to the bottom as evidenced by depressed nocturnal drift rates, while other drifted through the light and off the riffle. The effect of shortened and lengthened “night” periods, produced by artificial light and darkness respectively, was to shift the circadian pattersn of drift correspondingly. Rapidly alternating periods (15 min) of light and darkness in the exclosure produced correspondingly alternating drift, with drift rates high in darkness and low in light. When the normal day—night cycle of light was reversed with artificial light and darkness, the phases of the circadian rhythm in drift were also reversed. Observed circadian rhythms in drift appear exogenously controlled; if an endogenous rhythm exists at all, it is very weak and is influenced strongly by environmental light conditions.

Diurnal Periodicity in the Drift of Stream Invertebrates

Many aquatic animals exhibit diurnal periodicity in activity. In lakes the daily vertical migrations of crustaceans, rotifers, and the insect Chaoborus have been the subject of many studies (Bainbridge 1961, Pennak 1944, Berg 1937). Although similar phenomena might be expected in streams, little has been reported. Moon (1940), who studied the colonization by invertebrates of bottom materials set out in trays, reported greater activity at night than during the day in both a lake and a stream. It is reasonable to postulate that changes in activity among stream organisms would be manifested in changes in the drift rate (defined as the quantity of organisms drifting downstream per unit time per unit of stream width), but published studies on drift either have not undertaken measurement of drift rates during hours of darkness or have not distinguished between night and daytime drift rates (Needham 1928, Lennon 1941, Dendy 1944, Mullor 1954, Waters 1961). However, Lennon (personal communication) observed in his study greater activity of stream insects at night and believed that in his 24-hour drift samples the immatures were collected mostly at night. Also, in a personal communication, G. R. Alexander, Michigan Department of Conservation, stated that in his drift studies (as yet unpublished), there appeared to be peaks in drift rate in the evening and again in early morning. Prior to the present study, ecological investigations in the summer of 1959 included drift measurements out of an exclosure set into a stream bottom; much higher drift rates were observed at night than during daylight hours. Subsequent observations, both from an exclosure and in the open stream, confirmed the daily changes as regularly occurring events. The purpose of the present study was to document more intensively this phenomenon of diurnal periodicity in the drift rate. I would like to express appreciation to Robert J. Knapp for his conscientious assistance in the field; to many students, especially George A. Swanson, for the extensive work of sorting and analyzing the samples in the laboratory; and to Roy C. Arnold on whose property the field work was conducted, and who generously offered his cooperation and facilities. The study was assisted by National Science Foundation research grant No. F 9935.