S. Sharifian and S. M. Ahadi,
Volume 23, Issue 2 (1-2005)
Abstract
A variety of methods are used for speaker adaptation in speech recognition. In some techniques, such as MAP estimation, only the models with available training data are updated. Hence, large amounts of training data are required in order to have significant recognition improvements. In some others, such as MLLR, where several general transformations are applied to model clusters, the results are desirable for small training data, but with increasing training data, the performance improvement reaches the saturation lvel. In this paper, a new approach is introduced that makes use of the advantages of both mentioned techniques to improve the recognition rate. Here, the models with available training data are trained using MAP while
for those with insufficient training data, appropriate prior parameters for MAP estimation are found using MLLR. This technique has yielded better performance in comparison to either MAP or MLLR, in a system based on FARSDAT speech corpus.
B. Sharifian, G. H. Borhani, E. Mohammad Sharifi,
Volume 41, Issue 2 (Journal of Advanced Materials-Summer 2022)
Abstract
In this study, mechanically milled (MM) Al-24TiO2-20B2O3 powder in molten Al7075 matrix was used in order to fabricate in-situ TiB2 and Al2O3 reinforcements in Al7075 matrix. Differential thermal analysis (DTA) examination was adopted to find reaction temperature between milled Al, TiO2, and B2O3 powders. X-Ray Diffraction (XRD) patterns showed the existence of TiB2 and Al2O3 peaks (750 °C at Ar atmosphere) in MM powder. Scanning Electron Microscopy (SEM) results revealed the uniform distribution of TiO2 and B2O3 particles in the aluminum matrix. 6 wt.% MM powder was added to molten Al7075 at 750 °C. The molten Al7075/TiB2-Al2O3 composite was poured in copper mold. The stir casted composites were hot extruded at 465 °C with extrusion ratio of 6:1 and ram speed of 5 mm/s. The microstructures (optical microscopy and TEM) and mechanical properties (hardness and tensile testing) of samples were evaluated. TEM results showed that in-situ TiB2 nanoparticles were formed. The tensile strength of extruded Al7075/TiB2-Al2O3 composite was reached the value of 496 MPa. This result was around four times greater than that of the as cast Al7075 alloy.
