996 research outputs found
Coherent backscattering of ultrasound without a source
Full text linkCoherent backscattering is due to constructive interferences of reciprocal
paths and leads to an enhancement of the intensity of a multiply scattered
field near its source. To observe this enhancement an array of receivers is
conventionally placed close to the source. Our approach here is different. In a
first experiment, we recover the coherent backscattering effect (CBE) within an
array of sources and a distant receiver using time correlation of diffuse
fields. The enhancement cone has an excellent spatial resolution. The dynamics
of the enhancement factor is studied in a second experiment using correlation
of thermal phonons at the same ultrasonic frequencies, without any active
source
Melodies Of Scotland : Overture
Get PDFhttps://digitalcommons.library.umaine.edu/mmb-ps/1805/thumbnail.jp
The Role of State Committees in Developing a Conservation Education Program *
Full text linkPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72361/1/j.1949-8594.1959.tb08233.x.pd
On Slow Dynamic Elasticity at short times
Full text linkIt has been reported that slow dynamic nonlinear elastic relaxations, widely
thought to proceed in proportion to the logarithm of time since mechanical
conditioning ceases, recover at a diminished rate at early times, with a time
of transition that varies with the grain size of the material. Here we recount
new observations at short times, in the single bead system, in cement paste and
in sandstone and mortar. Notwithstanding the limits imposed by finite duration
ring down such that the effective instant of conditioning cessation is
imprecise, and the corresponding ambiguity as to the time that relaxation
begins, we find no reliable sign of such a transition, even in samples of large
grain size mortar similar to those described elsewhere as having clear and late
cutoffs.Comment: 10 pages, 16 figure
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