12,964 research outputs found
Scirtothrips perseae (Thysanoptera: Thripidae) : a new species infesting avocado in southern California
Scirtothrips perseae new species is described. It is a pest of avocado in southern California
Memory effect on the formation of drying cracks
We propose a model for the formation of drying cracks in a viscoplastic
material. In this model, we observe that when an external force is applied to a
viscoplastic material before drying, the material memorizes the effect of the
force as a plastic deformation. The formation of the drying cracks is
influenced by this plastic deformation. This outcome clarifies the result of a
recent experiments which demonstrated that a drying fracture pattern on a
powder-water mixture depends on the manner in which an external force is
applied before drying. We analytically express the position of the first crack
as a function of the strength of an external force applied before drying. From
the expression, we predict that there exists a threshold on the strength of the
force. When the force applied is smaller than the threshold, the first crack is
formed at the center of the mixture; however, when the force applied exceeds
the threshold, the position of the first crack deviates from the center. The
extent of the deviation increases as a linear function of the difference
between the strength of the force and the threshold.Comment: 9 pages, 9 figure
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