Scanning electron microscopy investigation of bio-polymer composites morphology

The development of nano-composite materials puts higher demand on morphological analysis techniques. The bio-nano-composite material systems is among the most challenging nano-composite materials for morphology characterization due to its sensitivity to damage, complex molecular conformations and nano-structures. The aim of this project is to provide a nanometer resolution and convenient chemical mapping tool based on scanning electron microscope (SEM) and electron spectroscopy for complex bio-composite systems. This would combine the backscattered electron and secondary electron techniques based on the angle-selection and energy-filtering methods. Theoretical electron behavior in the SEM is calculated using Monte Carlo simulations for reference. This SEM technique is validated and applied on representative artificial and natural bio-composite systems. Poly(N-isopropylacrylamide) (PNIPAM) composite material is a family of widely applied temperature-responsive bio-materials. The phase separation and morphology in PNIPAM nano-composites can affect the bio-compatibility of material system. Silk fiber is a well known natural bio-material with exceptional properties as well as a model hierarchical material system. The organization of nano-repeating unit in silk is expected to be a key factor in the mechanical property formation. Direct chemical mapping of this organization was not available up to now in convenient methods. Our SEM techniques (secondary electron hyperspectral imaging, SEHI) were validated and applied for mapping of these bio-materials and provided high-resolution chemical characterization of their nano-structures. The application of SEM techniques were further extended to different silk fibers and artificial silk materials. Such experiment validated the complex fine structure of secondary electron spectra measured on silk materials. The comparison of the electron spectra in different silk materials suggested a possible reflection of protein conformation in secondary electron spectra and this may be exploited for characterization of such complex materials in future applications. In summary, SEM analysis technique using electron selective detection methods capable of nano-resolution chemical characterization were validated and applied on nano-bio-composite materials. These techniques show great potential for morphological analysis in complex and sensitive composite materials in the future

Adaptive RAKE receiver structures for ultra wide-band systems

Ultra wide band (UWB) is an emerging technology that recently has gained regulatory approval. It is a suitable solution for high speed indoor wireless communications due to its promising ability to provide high data rate at low cost and low power consumption. Another benefit of UWB is its ability to resolve individual multi-path components. This feature motivates the use of RAKE multi-path combining techniques to provide diversity and to capture as much energy as possible from the received signal. Potential future and rule limitation of UWB, lead to two important characteristics of the technology: high bit rate and low emitting power. Based on the power emission limit of UWB, the only choice for implementation is the low level modulation technology. To obtain such a high bit rate using low level modulation techniques, significant inter-symbol interference (ISI) is unavoidable. Three N (N means the numbers of fingers) fingers RAKE receiver structures are proposed: the N-selective maximal ratio combiner (MRC), the N-selective MRC receiver with least-mean-square (LMS) adaptive equalizer and the N-selective MRC receiver with LMS adaptive combiner. These three receiver structures were all simulated for N=8, 16 and 32. Simulation results indicate that ISI is effectively suppressed. The 16-selective MRC RAKE receiver with LMS adaptive combiner demonstrates a good balance between performance, computation complexity and required length of the training sequence. Due to the simplicity of the algorithm and a reasonable sampling rate, this structure is feasible for practical VLSI implementations

Calculations of Magnetic Exchange Interactions in Mott--Hubbard Systems

An efficient method to compute magnetic exchange interactions in systems with strong correlations is introduced. It is based on a magnetic force theorem which evaluates linear response due to rotations of magnetic moments and uses a novel spectral density functional framework combining our exact diagonalization based dynamical mean field and local density functional theories. Applications to spin waves and magnetic transition temperatures of 3d metal mono--oxides as well as high--T_{c} superconductors are in good agreement with experiment

Attention-Based Models for Text-Dependent Speaker Verification

Attention-based models have recently shown great performance on a range of tasks, such as speech recognition, machine translation, and image captioning due to their ability to summarize relevant information that expands through the entire length of an input sequence. In this paper, we analyze the usage of attention mechanisms to the problem of sequence summarization in our end-to-end text-dependent speaker recognition system. We explore different topologies and their variants of the attention layer, and compare different pooling methods on the attention weights. Ultimately, we show that attention-based models can improves the Equal Error Rate (EER) of our speaker verification system by relatively 14% compared to our non-attention LSTM baseline model.Comment: Submitted to ICASSP 201

An efficient identity-based group signature scheme over elliptic curves

Group signatures allow every authorized member of a group to sign on behalf of the underlying group. Anyone except the group manager is not able to validate who generates a signature for a document. A new identity-based group signature scheme is proposed in this paper. This scheme makes use of a bilinear function derived from Weil pairings over elliptic curves. Also, in the underlying composition of group signatures there is no exponentiation computation modulo a large composite number. Due to these ingredients of the novel group signatures, the proposed scheme is efficient with respect to the computation cost in signing process. In addition, this paper comes up with a security proof against adaptive forgeability