1,721,240 research outputs found
Pressure effects for crystal growth in a closed system
Full text linkWe analyze the growth of a crystal from its supercooled liquid in a closed domain (constrained growth), taking into account the effects due to the different densities ρs and ρl of the solid and liquid phases. We assume ρl>ρs, i.e., the liquid expands upon solidification. Then, the growth is contrasted by an increasing pressure, which results in a continuous decrease of the coexistence temperature and the effective supercooling. These phenomena have been simulated in two dimensions through a modified version of the classic phase-field model. We observe that for spherical growth the interface temperature reflects almost instantaneously the change of the coexistence temperature. For dendritic growth, we observed a relaxation time for the dendrite tip velocity and the tip radius which is comparable to the characteristic time of the process; however, after the first fast transient, the growth dynamics seems to follow the changing pressure with no appreciable lag. The onset of the morphological instability is slightly anticipated in respect to free growth
Advection flow effects in the growth of a free dendrite
Full text linkThe growth of a free dendrite into a supercooled liquid is simulated through a modified version of the phase-field model, which takes into account the advection flow due to the different densities ρs and ρl of the solid and liquid phases. The intensity of the flow is maximal at the dendrite tip and decays far from the surface of the crystal. At fixed undercooling, as the density ratio ρs/ρl increases, we observe a decrease of the tip velocity, while the tip radius increases. The Peclet number is shifted with respect to the pure diffusive value. The onset of the morphological instability, which is responsible for the origin of the dendrite from a growing circular germ, is slightly anticipated by the flow effects
JPEG encoder architectures for wireless networks
No full textWhile an old standard, the JPEG is still effective and used in many applications. Its relative simplicity is a clear advantage against its newest counterparts, i.e. the JPEG2000 and the JPEG XR, in many low-power scenarios. Moreover, features embedded in the JPEG2000 and the JPEG XR, such as the scalability of the image stream, can be added to the main JPEG core, making an encoder useful for example in a video surveillance wireless network. Nevertheless, the peculiar requirements of
wireless, low-power scenarios require a dedicated hardware design, and a careful choice of the hardware architecture. In this
work we developed several JPEG encoder architectures with full real-time reconfigurability, support for the restart intervals and
for a simple scalability mechanisms, the scan scheme. These features make the architectures suitable for the use in lowbandwidth, low-power wireless networks. The JPEG encoder architectures have been developed, evaluated and compared using a cycle-based SystemC model
Approximation of dynamical systems by continuous-time recurrent approximate identity neural networks
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