Graph theoretic foundations of multibody dynamics

This second part of a two part paper uses concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The first part (Jain in Graph theoretic foundations of multibody dynamics. Part I. Structural properties, 2010) established the block-weighted adjacency (BWA) matrix structure of spatial operators associated with serial- and tree-topology multibody system dynamics, and introduced the notions of spatial kernel operators (SKO) and spatial propagation operators (SPO). This paper builds upon these connections to show that key analytical results and computational algorithms are a direct consequence of these structural properties and require minimal assumptions about the specific nature of the underlying multibody system. We formalize this notion by introducing the notion of SKO models for general tree-topology multibody systems. We show that key analytical results, including mass-matrix factorization, inversion, and decomposition hold for all SKO models. It is also shown that key low-order scatter/gather recursive computational algorithms follow directly from these abstract-level analytical results. Application examples to illustrate the concrete application of these general results are provided. The paper also describes a general recipe for developing SKO models. The abstract nature of SKO models allows for the application of these techniques to a very broad class of multibody systems.     

A compact spark pre-ionized pulser sustainer TE-CO<Subscript>2</Subscript> laser

A compact spark pre-ionized pulser sustainer TE-CO₂ laser that can produce an output energy of one joule with an overall efficiency of 12.4% is presented. Optical pulses have durations of 7.15 μs FWHM. Here, the laser uses all solid-state excitation (ASSE) circuit and the discharge formed between two uniform field electrodes placed 1.5 cm apart ultimately leads to a discharge volume of 50 cm × 1.5 cm × 1.5 cm     

3D Coordination Network of Ag(I) Ions with μ 3 -Bridging Melamine Ligands

Abstract  

A new 3D silver complex [Ag(mela)(H₂O)(NO₃)]_n (1) (mela = melamine or 2,4,6-triaminotriazine) is synthesized and characterized by single crystal X-ray diffraction, IR, and elemental analysis. The structural characterization shows that the compound crystallizes in space group C c, a = 8.181(2), b = 10.269(3) c = 11.347(3) ?, β = 105.88(2)°, Z = 4. Out of several structurally characterized transition metal compounds comprising melamine, the titled complex represents a rare example of μ ₃ -melamine coordination mode realized through the heterocycle nitrogen donors. The fluorescent property of complex 1 was investigated and the mechanism was validated by means of a density functional theory (DFT) calculation.     

Production of meso- and giga-porous zirconia particles — An improved multi-step particle aggregation process

Macro- and giga-porous zirconia supports were prepared from a 20% colloidal sol of zirconia (ZrO₂) by a combination of a polymer-induced colloid aggregation (PICA) process and the oil emulsion (OE) method. The effect of the pH of the initial sol on the size of the PICA particles, and subsequently on the final product, made by oil-emulsion assisted aggregation of the PICA particles was thoroughly investigated. Both the PICA and the OE methods were further optimized for performance. Particle morphology and porosity of the resultant particles were characterized by scanning electron microscopy, mercury intrusion-extrusion porosimetry, and nitrogen adsorption-desorption sorptometry. The supports were comprised of stable aggregates of 50-250 μm in size. The pore and throat size distributions showed narrow bi-modal distributions over two distinct size scales: 10-100 nm and 600-3000 nm. In addition, different combinations of aggregation techniques and porous supports prepared in previous steps for use in a subsequent aggregation were evaluated. Optimal amounts of zirconia sol and 10-100 micron porous spherical particles produced by the OE method in an earlier step were combined in an additional OE process to yield stable giga-porous supports. Porous zirconia particles obtained after calcination and sintering had particle sizes of 0.15-3.5 mm and multimodal pore and throat distributions over a range of 50 nm-8 μm.     

Model-based autonomous system for performing dexterous, human-level manipulation tasks

This article presents a model based approach to autonomous dexterous manipulation, developed as part of the DARPA Autonomous Robotic Manipulation Software (ARM-S) program. Performing human-level manipulation tasks is achieved through a novel combination of perception in uncertain environments, precise tool use, forceful dual-arm planning and control, persistent environmental tracking, and task level verification. Deliberate interaction with the environment is incorporated into planning and control strategies, which, when coupled with world estimation, allows for refinement of models and precise manipulation. The system takes advantage of sensory feedback immediately with little open-loop execution, attempting true autonomous reasoning and multi-step sequencing that adapts in the face of changing and uncertain environments. A tire change scenario utilizing human tools, discussed throughout the article, is used to described the system approach. A second scenario of cutting a wire is also presented, and is used to illustrate system component reuse and generality.     

Kruskal's Maximal Spanning Tree Algorithm for Optimizing Distribution Network Topology to Improve Voltage Stability

Abstract—Alteration of power network topology is often required to meet important objectives, such as restoring connectivity, minimizing power losses, maintaining stability, maximizing power transfer capability etc., and is achieved by switching of circuit breakers and other switching devices in the power network. Primary power distribution networks are often interconnected and meshed but should be transformed to radial topology to achieve various operational advantages. Distribution networks also need to be reconfigured after faults to restore power at all the load points. Reconfiguring a power network, however, is a complicated multi-constrained optimization problem, as there may exist many feasible switching combinations in a large power network. This article proposes a novel application of graph theory, supported by Kruskal's maximal spanning tree algorithm, to search for the optimal network topology and to optimally convert an interconnected meshed network into a radial system to achieve best operational characteristics, cost, and control. The proposed technique has been demonstrated on a 30-node primary distribution network originally having a mesh topology, and the results indicate significant performance improvement after transformation into optimal radial topology.     

Ultrafast excited state deactivation of doped porous anodic alumina membranes

Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the F?rster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.