The fallen-stone sensor and snow-depth meter (which measures snowdepth on roads) have been developed for the purpose of traffic safety. The fallen-stone sensor uses an Si bulk microphone which detects pulsing vibrations, from a detection plate, which occur when the plate is struck by a stone. Noise and vibration from traffic will not be sensed due to the construction of the detection plate, while the pulsing vibration of a 2 g to 10 kg stone falling from a height of 1 meter can be sensed exactly by the plate. The snow-depth meter uses a 26 kHz ultrasonic tone burst wave, and the depth of snow on a road is measured by the reflection time. The accuracy of this snow-depth meter is + or - 2 to 3 cm, within a measurement range of 0 to 100 cm, with temperature correction for sound velocity.
Abstract. Neighbouring plants may affect volatile compound emissions of a focal plant and confer associational resistance or susceptibility. Associational resistance has been reported as a result of adsorption of neighbouring plant volatile and semivolatile compounds on focal plant foliage in field experiments. However, these associational effects in a natural ecosystem remain largely unknown. The effects of the presence and density of Rhododendron tomentosum (Rt) understorey on the volatile profile and herbivore density of mountain birch, Betula pubescens ssp. czerepanovii (MB) was investigated in a subarctic forest site. The monoterpene β-myrcene, sesquiterpene aromadendrene and sesquiterpene alcohols, palustrol and ledol were recovered from the foliage of MB trees that had Rt growing in the understorey. The number of Rt shoots growing directly under the MB trees correlated positively with the rate of recovery of adhered compounds and negatively with total MB emissions. Palustrol and β-myrcene recovery from MB leaves showed the highest positive correlation with Rt density. Recovery of adhered compounds was higher at lower sampling temperatures. Herbivory was at very low levels both in control and Rt plots. The proportion of foliage infected by a gall mites (Acalitus spp.) was positively correlated with the recovery of the adhered ledol and palustrol from MB foliage. These results indicate that understorey plant volatiles, both sesquiterpene and highly volatile monoterpenes, may adhere onto and be subsequently re-released from MB foliage at low temperatures during the subarctic growing season. The Rt density also plays an important role in the adherence and re-release rates of neighboring plant volatiles and may induce a response in MB volatile emission. Presence of Rt volatiles on MB foliage may make them more susceptible to gall mite infestation suggesting that high Rt density in the subarctic ecosystem may confer associational susceptibility to herbivores on MB.
The most important thing to be considered in manufacturing electret microphones is their endurance in all environments. Research so far has mainly considered the materials for the electret and their poling methods. There seems, however, to have been little study of the protection of the electret from actual environments. Viewed from the standpoint of us manufacturers, the matter to be considered is how to protect the electret from bad conditions and make them stable over a long time. Things that we should consider in connection with this problem are the structures fitting the objects in use, i.e., back-electrode electret, protection from dust, safety from humidity; optimum treatment; poling methods, and manufacturing processes to provide excellent durability. These questions are considered simultaneously. By these methods we have produced some electret microphones as commercial products. The above-mentioned methods are adopted for microphones of professional use; hand-free interphones; small hearing aid used under such bad conditions as sweat, high temperature, and shocks; and built-in microphones used in high temperature and high humidity. Thus we have found from the data of the market that by the methods outlined above, we can make electret microphones sufficiently stable.
