Reveal the underlying causes of dunes can sing.

World Scientific reports [tech.] Message: "thundered rumbled ... ... ... ..." - Marco Polo heard it in the Gobi Desert; Charles Darwin in Chile heard it; 100 years, physicists .always trying to uncover its secrets. .However, Sha Ming has been a mystery. .Now, scientists have carried out through the sand dunes of California Integrated acoustic and seismological study of internal structure of sand dunes proved that the frequency of a particular sound amplification quicksand. .<P> When the sand slide down from the steep side, some level of scattered sand dunes will be issued rumble. .Previous research that led to booming sand and sand may be due to the characteristics of the relevant, such as their size. .However, the California Institute of Technology in Pasadena (Caltech) graduate Nathalie Vriend and colleagues have given different answers. .In "Geophysical Research Letters" (Geophysical Research Letters) published a paper, they reported the sound of how the internal structure of sand dunes. .In Dumont Dunes - Death Valley National Park in southern California - and some sand dunes of western United States, the researchers placed a number of loudspeakers, the purpose is to record the rumble of booming sand. .They also set up a network of seismometers, which are usually used for seismic oil exploration. .Subsequently, a number of volunteers from sitting on the sand dunes to slide down the steep slope, as is the formation of the sand and eventually lead to slip Ming sand. .In order to investigate the internal structure of Mingsha Qiu, the researchers used a knife placed in the sand, a big hammer beating on a metal plate, and record the sand dunes at different positions in the flow speed. .</ P> <P> State Institute of Technology research team eventually found that the internal structure of booming sand and sand dunes close relationship between. .In summer, a large sand dunes can easily send bursts of rumble, this time there is a sand surface the outer layer thickness of 1.5 m, sound velocity here than it was in the external or internal sand in the air velocity must be slow .a lot. .The reason why sand dunes in the winter will not chirp, it is because of the low-velocity layer disappears. .The team believes that this low-velocity layer may play a "waveguide" role. .The waveguide can be above and below the sound speed layer inward reflection, which can be delivered effectively move the sand sound. .At the same time, due to the superposition between the frequency or the resonance effect, certain frequencies are amplified. .According to this theory to calculate the frequency characteristics of sound waves results agree with the observations of scientists. .The researchers believe that the reason that natural speakers with the disappearance of low-velocity layer in winter no longer exist, mostly due to more water into the sand dunes as a result the increase in the speed of sound. .</ P> <P> University of Michigan, Ann Arbor, says physicist Michael Bretz: "It looks like we are gradually find out the real reason for booming sand." He said, "This study provides us with a can .acceptable mechanism. "But his colleague, physicist Franco Nori thought:" In this complex problem, there are many different variables, the ripple effect of resonance is important, but it is not the only variable factor. " .In any case, sand boarding time fans have to come out to show their talents. .</ P> </ p>.