Robust Nearfield Wideband Beamforming Design Based on Adaptive-Weighted Convex Optimization

Nearfield wideband beamformers for microphone arrays have wide applications in multichannel speech enhancement. The nearfield wideband beamformer design based on convex optimization is one of the typical representatives of robust approaches. However, in this approach, the coefficient of convex optimization is a constant, which has not used all the freedom provided by the weighting coefficient efficiently. Therefore, it is still necessary to further improve the performance. To solve this problem, we developed a robust nearfield wideband beamformer design approach based on adaptive-weighted convex optimization. The proposed approach defines an adaptive-weighted function by the adaptive array signal processing theory and adjusts its value flexibly, which has improved the beamforming performance. During each process of the adaptive updating of the weighting function, the convex optimization problem can be formulated as a SOCP (Second-Order Cone Program) problem, which could be solved efficiently using the well-established interior-point methods. This method is suitable for the case where the sound source is in the nearfield range, can work well in the presence of microphone mismatches, and is applicable to arbitrary array geometries. Several design examples are presented to verify the effectiveness of the proposed approach and the correctness of the theoretical analysis

Prediction of structures and properties of 2,4,6-triamino-1,3,5-triazine-1,3,5-trioxide (MTO) and 2,4,6-trinitro-1,3,5-triazine-1,3,5-trioxide (MTO3N) green energetic materials from DFT and ReaxFF molecular modeling

2,4,6-Triamino-1,3,5-triazine-1,3,5-trioxide (MTO) and 2,4,6-trinitro-1,3,5-triazine-1,3,5-trioxide (MTO3N) were suggested by Klapötke et al. as candidates for green high energy density materials (HEDM), but a successful synthesis has not yet been reported. In order to predict the properties of these systems, we used quantum mechanics (PBE flavor of density functional theory) to predict the most stable conformations of MTO and MTO3N and their optimum packing into the most stable crystal structures. We found that MTO has the P2_1 space-group with a density of ρ = 1.92 g cm^(−3) while MTO3N has the P2_1/c space-group with a density of ρ = 2.10 g cm^(−3). The heats of reaction (ΔH_(rxn)) were computed to be 1036 kcal kg^(−1) for MTO, 1412 kcal kg^(−1) for MTO3N, and 1653 kcal kg^(−1) for a mixture of them. These properties are comparable to those of such other useful energetic materials as RDX (ρ = 1.80 g cm^(−3), ΔH_(rxn) = 1266 kcal kg^(−1)), HMX, and PETN, making MTO and MTO3N excellent candidates for environmentally friendly HEDMs. In addition, we predicted the stability of –NH_2, –NO, and –NO_2 groups in water solution. We also show that the ReaxFF-lg reactive FF leads to an accurate description of the structural properties of MTO and MTO3N crystals making it practical to carry out large-scale reactive molecular dynamics simulations practical for these systems to determine the sensitivity and performance (CJ point calculation and velocity) under shear, shock, and thermal loads

Comparison of preprocessing methods and storage times for touch DNA samples

Aim To select appropriate preprocessing methods for different substrates by comparing the effects of four different preprocessing methods on touch DNA samples and to determine the effect of various storage times on the results of touch DNA sample analysis. Method Hand touch DNA samples were used to investigate the detection and inspection results of DNA on different substrates. Four preprocessing methods, including the direct cutting method, stubbing procedure, double swab technique, and vacuum cleaner method, were used in this study. DNA was extracted from mock samples with four different preprocessing methods. The best preprocess protocol determined from the study was further used to compare performance after various storage times. DNA extracted from all samples was quantified and amplified using standard procedures. Results The amounts of DNA and the number of alleles detected on the porous substrates were greater than those on the non-porous substrates. The performances of the four preprocessing methods varied with different substrates. The direct cutting method displayed advantages for porous substrates, and the vacuum cleaner method was advantageous for non-porous substrates. No significant degradation trend was observed as the storage times increased. Conclusion Different substrates require the use of different preprocessing method in order to obtain the highest DNA amount and allele number from touch DNA samples. This study provides a theoretical basis for explorations of touch DNA samples and may be used as a reference when dealing with touch DNA samples in case work

Initial Decomposition of HMX Energetic Material from Quantum Molecular Dynamics and the Molecular Structure Transition of β- to δ-HMX

We demonstrate the use of quantum molecular dynamics to identify the β- to δ-molecular structure transition in bulk-phase HMX, which has been considered as the primary reason for the increased sensitivity in the thermal decomposition of HMX. Both physical and chemical changes accompany this transition, but no previous study has shown conclusively which specific change, or set of changes, is responsible. We find that the initial decomposition mechanism of HMX can explain this sensitivity issue. Our DFT simulations of the periodic system followed by detailed finite cluster calculations of the transition states find two distinct initial unimolecular reaction pathways in β-HMX that operate simultaneously. (1) For the HONO release reaction, β-HMX first transformed to an intermediate, in which one parallel N–NO_2 group transitions from chair to boat conformations with a low +1.2 kcal/mol barrier, followed by unimolecular HONO release (+42.8 kcal/mol barrier, rate-determining step). (2) For the NO_2 cleavage reaction, β-HMX first transforms to the δ-HMX structure in two steps, with low barriers of +1.9 and +7.6 kcal/mol for each step, followed by unimolecular NO_2 release (+31.3 kcal/mol barrier). Starting with δ-HMX, we find an initial unimolecular NO_2 cleavage and then an independent HONO release reaction with the barriers of +31.6 kcal/mol (NO_2 cleavage) and +38.9 kcal/mol (HONO release). We find that the constant proportional simulated initial structure transition temperature is 453 K, which is consistent with the experimental results (466 K)

Initial Decomposition Reactions of Bicyclo-HMX [BCHMX or cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole] from Quantum Molecular Dynamics Simulations

We investigated the initial chemical reactions of BCHMX [cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole] with the following procedure. First we used density functional theory molecular dynamics simulations (DFT-MD) on the periodic crystal to discover the initial reaction steps. This allowed us to determine the most important reactions through DFT-MD simulations at high temperatures. Then we started with the midpoint of the reaction (unimolecular or bimolecular) from the DFT-MD and carried out higher quality finite cluster DFT calculations to locate the true transition state of the reaction, followed by calculations along the reaction path to determine the initial and final states. We find that for the noncompressed BCHMX the nitro-aci isomerization reaction occurs earlier than the NO_2-releasing reaction, while for compressed BCHMX intermolecular hydrogen-transfer and bimolecular NO_2-releasing reactions occur earlier than the nitrous acid (HONO)-releasing reaction. At high pressures, the initial reaction involves intermolecular hydrogen transfer rather than intramolecular hydrogen transfer, and the intermolecular hydrogen transfer decreases the reaction barrier for release of NO_2 by ∼7 kcal/mol. Thus, the HONO-releasing reaction takes place more easily in compressed BCHMX. We find that this reaction barrier is 10 kcal/mol lower than the unimolecular NO_2 release and ∼3 kcal/mol lower than the bimolecular NO_2 release. This rationalizes the origin of the higher sensitivity of BCHMX compared to RDX (1,3,5-trinitrohexahydro-1,3,5-triazine) and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). We suggest changes in BCHMX that might help decrease the sensitivity by avoiding the intermolecular hydrogen-transfer and HONO-releasing reaction