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Powder Deposition and Sintering for a Two-Powder Approach to Solid Freeform Fabrication
A two-powder approach is presented where Fused Deposition modeling (FDM) is used to
create a thin shell in the shape of the part to be fabricated. The shell is filled with powder of the
part material and surrounded by a support powder that has a high sintering temperature. Upon
compressing and sintering the shelVpowder system in a uniaxial hot press, the polymer shell burns
out and the support powder compresses the part powder. The part powder consolidates into the
desired part while the support material remains in powder form and can be easily removed. This
paper presents results ofinitial experimental studies.Mechanical Engineerin
Light transmission through and its complete stoppage in an ultra slow wave optical medium
Light Wave transmission -- its compression, amplification, and the optical
energy storage -- in an Ultra Slow Wave Medium (USWM) is studied analytically.
Our phenomenological treatment is based entirely on the continuity equation for
the optical energy flux, and the well known distribution-product property of
Dirac delta-function. The results so obtained provide a clear understanding of
some recent experiments on light transmission and its complete stoppage in an
USWM.
Keywords : Ultra slow light, stopped light, slow wave medium, EIT.Comment: (single-column 5pages PDF). Simple class-room phenomenological model
of stopped light. Comments most welcom
Scaling of Fracture Strength in Disordered Quasi-Brittle Materials
This paper presents two main results. The first result indicates that in
materials with broadly distributed microscopic heterogeneities, the fracture
strength distribution corresponding to the peak load of the material response
does not follow the commonly used Weibull and (modified) Gumbel distributions.
Instead, a {\it lognormal} distribution describes more adequately the fracture
strengths corresponding to the peak load of the response. Lognormal
distribution arises naturally as a consequence of multiplicative nature of
large number of random distributions representing the stress scale factors
necessary to break the subsequent "primary" bond (by definition, an increase in
applied stress is required to break a "primary" bond) leading up to the peak
load. Numerical simulations based on two-dimensional triangular and diamond
lattice topologies with increasing system sizes substantiate that a {\it
lognormal} distribution represents an excellent fit for the fracture strength
distribution at the peak load. The second significant result of the present
study is that, in materials with broadly distributed microscopic
heterogeneities, the mean fracture strength of the lattice system behaves as
, and scales as as the lattice system size, , approaches
infinity.Comment: 24 pages including 11 figure
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