33,184 research outputs found
Morphology and thermal conductivity of model organic aerogels
The intersection volume of two independent 2-level cut Gaussian random fields
is proposed to model the open-cell microstructure of organic aerogels. The
experimentally measured X-ray scattering intensity, surface area and solid
thermal conductivity of both polymeric and colloidal organic aerogels can be
accounted for by the model.Comment: 5 pages. RevTex with 4 encapsulated figures. Higher resolution
figures have been submitted for publication. To be published in Phys. Rev. E
(Rapid Comm.). email, [email protected]
What affects the freezing behaviors of cement-based porous materials: The role of the unfrozen liquid-like layer
A key factor that affects freeze-thaw damages of cement-based porous materials (CBPMs) is the amount of the freezable water confined in the pores that generate large internal pressures during freezing. Taking account of an unfrozen liquid-like layer (ULLL) between ice crystals and pore wall, this paper investigates deformations of a saturated CBPM specimen under freezing with different thickness values of the ULLL. To bridge the macro strains and the local pressure exerted on the pore wall of the material, the thermodynamic equilibrium between the water and ice, and a poroelastic approach were adopted. The hydraulic pressure by volume change as phase transition takes place in the pores, the fusion pressure by energy change as ice forms and penetrates through the thin pores and the hydrothermal pressure by TEC discrepancies between the pore fluids and solid substrate dominate the internal freezing stress. The obtained results reveal that the ULLL plays an important role on the estimation of the amount of ice crystals confined in the pores, and thus influences the pore pressures and deformations of the CBPM specimen used. Appropriate model of the ULLL helps to decrease the deviations between the predicted strains and the experimental data
Quasi-long range order in glass states of impure liquid crystals, magnets, and superconductors
In this review we consider glass states of several disordered systems:
vortices in impure superconductors, amorphous magnets, and nematic liquid
crystals in random porous media. All these systems can be described by the
random-field or random-anisotropy O(N) model. Even arbitrarily weak disorder
destroys long range order in the O(N) model. We demonstrate that at weak
disorder and low temperatures quasi-long range order emerges. In
quasi-long-range-ordered phases the correlation length is infinite and
correlation functions obey power dependencies on the distance. In pure systems
quasi-long range order is possible only in the lower critical dimension and
only in the case of Abelian symmetry. In the presence of disorder this type of
ordering turns out to be more common. It exists in a range of dimensions and is
not prohibited by non-Abelian symmetries.Comment: 32 page
Nonequilibrium Green's function approach to mesoscopic thermal transport
We present a formulation of a nonequilibrium Green's function method for
thermal current in nanojunction atomic systems with nonlinear interactions.
This first-principle approach is applied to the calculation of the thermal
conductance in carbon nanotube junctions. It is shown that nonlinearity already
becomes important at low temperatures. Nonlinear interactions greatly suppress
phonon transmission at room temperature. The peak of thermal conductance is
found to be around 400K, in good agreement with experiments. High-order phonon
scattering processes are important for diffusive heat transport.Comment: 4 pages, 4 figure
- …