21,697 research outputs found
Analytical and Experimental Determination of FML Stiffness and Strength Properties.
The paper presents application of analytical methods of determining the mechanical
properties of Fibre Metal Laminates. Chosen micromechanical methods were employed
to predict elastic moduli and strength of FML panels. Prediction was conducted on
two levels i.e. micromechanics where properties of a single composite lamina (prepreg)
were analyzed, and macro–mechanics to determine properties of a full FML hybrid material.
The properties of a single GFR lamina were predicted by Rule of Mixture Method
(ROM), inverse Rule of Mixture Method with correction factor, Halpin Tsai Method,
Tsai Method and Wilczynski Method application. Properties of full 3–2 FML lay–up
were determined using the Rule of Mixtures. Analytical results were verified by experimental
tests. Tensile and bending test were performed on rectangular standard coupons
of 3–2 FMLs
A New Handle on de Sitter Compactifications
We construct a large new class of de Sitter (and anti de Sitter) vacua of
critical string theory from flux compactifications on products of Riemann
surfaces. In the construction, the leading effects stabilizing the moduli are
perturbative. We show that these effects self-consistently dominate over
standard estimates for further and quantum corrections, via
tuning available from large flux and brane quantum numbers.Comment: 26 pages, harvmac big. v2: Correction generalizing specific
ingredients required for tunable negative term; conclusions and structure of
potential unchange
Polystyrene-based nanocomposites with different fillers: fabrication and mechanical properties
The paper presents a comprehensive analysis of elastic properties of
polystyrene-based nanocomposites filled with different types of inclusions:
small spherical particles (SiO2 and Al2O3), alumosilicates (montmorillonite,
halloysite natural tubules and Mica) and carbon nanofillers (carbon black and
multi-walled carbon nanotubes). Composites were fabricated by melt technology.
The analysis of composite melts showed that the introduction of
Montmorillonite, Multi-walled carbon nanotubes, and Al2O3 particles provided an
increase in melt viscosity by an average of 2 to 5 orders of magnitude over the
pure polystyrene. Block samples of composites with different filler
concentrations were prepared, and their linear and nonlinear elastic properties
were studied. The introduction of more rigid particles led to a more profound
increase in the elastic modulus of the composite, with the highest rise of
about 80% obtained with carbon fillers. Carbon black particles provided also an
enhanced strength at break of about 20% higher than that of pure polystyrene.
The nonlinear elastic moduli of composites were shown to be more sensitive to
addition of filler particles to the polymer matrix than the linear ones. The
nonlinearity coefficient comprising the combination of linear and
nonlinear elastic moduli of a material demonstrated considerable changes
correlating with changes of the Young's modulus. The absolute value of
showed rise in 1.5-1.6 times in the CB- and HNT-containing composites as
compared to that of pure PS. The changes in nonlinear elasticity of fabricated
composites were compared with measurements of the parameters of bulk nonlinear
strain waves in them. Variations of wave velocity and decay decrement
correlated with observed enhancement of materials nonlinearity
Monodromy in the CMB: Gravity Waves and String Inflation
We present a simple mechanism for obtaining large-field inflation, and hence
a gravitational wave signature, from string theory compactified on twisted
tori. For Nil manifolds, we obtain a leading inflationary potential
proportional to phi^(2/3) in terms of the canonically normalized field phi,
yielding predictions for the tilt of the power spectrum and the
tensor-to-scalar ratio, and with 60
e-foldings of inflation; we note also the possibility of a variant with a
candidate inflaton potential proportional to phi^(2/5). The basic mechanism
involved in extending the field range -- monodromy in D-branes as they move in
circles on the manifold -- arises in a more general class of compactifications,
though our methods for controlling the corrections to the slow-roll parameters
require additional symmetries.Comment: 43 pages, latex. 4 figure
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