Trajectory Tracking Control with Heterogeneous Input Delay in Multi-Agent System

In this paper we present a protocol to track a general trajectory for a multi-agent system in the presence of heterogeneous constant finite input delays. We consider two different multi-agent cases: agents with single-integrator and double-integrator dynamics. For the single-integrator case, we assume that the velocity along the desired trajectory is known to all agents for all time. Similar assumption is made only for the acceleration along the desired trajectory for the double-integrator case. It is assumed that at least one agent has the complete information about the desired trajectory for all time. The tracking strategy comprises of a consensus-based estimator and a simple independent tracking controller for each agent in the system. Only the state estimates are exchanged among the agents. The communication graph for the multi-agent system along with the desired trajectory has a rooted directed spanning tree with the desired trajectory being the root. The proposed tracking strategy ensures asymptotic convergence of the multi-agent system. The controller and estimator gains do not depend on the edge weights of the graph. The chosen controller gains of individual agent are bounded by their respective input delays. We present a particular form of control gains in order to achieve a desired possible exponential convergence rate and maximize the upper bound of the convergence rate for these selective gains. Finally, we present simulation results to substantiate the effectiveness of the proposed methodology. Comparison of the proposed strategy with the existing work in the literature show a better performance.     

Mechanical Properties and Nanocrystallization Behavior of Al-Ni-La Alloys

Rapidly solidified Al₈₉Ni₆La₅ ribbons were obtained by induction melting and ejecting the melt onto a rotating Cu wheel in an Ar atmosphere. The ribbons were investigated by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), microindentation, and nanoindentation techniques. The XRD and TEM studies revealed that the ribbon was fully amorphous; however, DSC did not show any glass transition. The alloy undergoes two stages of crystallization. The growth of fcc-Al is responsible for the first stage, and precipitation of Al₃Ni and Al₁₁La₃ is responsible for the second stage of crystallization. Microhardness of ribbons in the as-melt-spun, partially, and fully devitrified conditions was examined and subsequently correlated with evolved microstructure. Significant improvement in hardness was observed, with the progress of primary nanocrystallization, due to the effective barrier to shear band by a hard La-rich shell around the fcc-Al nanocrystals and enrichment of the remaining amorphous matrix by the solute elements. The pile up of materials in the form of semicircular shear bands was observed around all the indentations. During nanoindentation, it was observed that hardness and modulus values were initially increased and then decreased. The reasons for such observation were also discussed.     

Estimation of Heat and Hydrologic Budget of Upper Klamath Lake Oregon,USA Using Updated DLM-WQ Model

Estimation of lake hydrologic budgets is essential for sustainable water management due to increasing water demand and uncertainties related to climate change. The updated turbulent diffusion transfer algorithms were developed and incorporated in the DLM-WQ model developed at UC Davis to estimate the Upper Klamath Lake’s dynamics, and heat and hydrologic budget. The exchange coefficients for latent heat (C_EN), sensible heat (C_HN), and wind drag (C_D) of the turbulent diffusion model were calibrated using coefficient of correlation as the objective function. The agreement between estimated and measured lake water elevation and temperature are found to be excellent with correlation coefficients 0.99 and 0.95, respectively. The heat and hydrologic budgets are more sensitive to evaporative heat loss (35 %) than sensible heat exchanges (11 %). The stream inflow and lake outflow dominate the hydrologic budget with approximately 47 % due to stream inflow and approximately 44 % due to lake outflow. Precipitation directly on the lake and evaporation from the lake are only 3 % and 6 %, respectively. The lake mixes to the bottom sporadically during spring and summer. Estimated deep mixing for the period 1994–1996 shows the lake’s increasing stability without a deep mixing event for approximately 4 months during summer in 1996. Prolonged stratification in the hypereutrophic lake is expected to lead to hypoxia near the sediment surface resulting in exacerbation of existing ecological problems. The DLM-WQ model can be applied to a broad range of lakes/reservoirs with selection of appropriate C_EN and C_HN value for lake/reservoir dynamics and water resources planning evaluation.     

Multilayer inverse synthesis techniques for the analysis of mixed-mode inhomogeneities in composite and co-deposited dielectric coatings

It has been well established in recent times that mixed composite materials provide optical, mechanical, and stability advantages over pure dielectrics and ceramics. Such materials include fluoride and oxide compound mixtures that are co-evaporated or sputtered from pure or solid solutions of the composite starting materials. Mixed mode inhomogeneities are very typical to the growth of these composite and co-deposited films. When such conditions exist, the transmittance and reflectance spectra and even ellipsometric measurements get considerably modulated and extraction of optical constants from these measurements becomes extremely difficult. In these situations multilayer inverse techniques become the more appropriate and powerful approaches to derive not only various constants but also growth-dependent compositions in these films. In this work, a special multilayer inverse technique based on a powerful geometric approach along with the needle technique has been described to characterize such mixed-mode inhomogeneities.     

Semantic Sensor Web

Sensors are distributed across the globe leading to an avalanche of data about our environment. It is possible today to utilize networks of sensors to detect and identify a multitude of observations, from simple phenomena to complex events and situations. The lack of integration and communication between these networks, however, often isolates important data streams and intensifies the existing problem of too much data and not enough knowledge. With a view to addressing this problem, the Semantic Sensor Web (SSW) proposes that sensor data be annotated with semantic metadata that will both increase interoperability and provide contextual information essential for situational knowledge.     

Assessment of Creep Deformation,Damage, and Rupture Life of 304HCu Austenitic Stainless Steel Under Multiaxial State of Stress

The role of the multiaxial state of stress on creep deformation and rupture behavior of 304HCu austenitic stainless steel was assessed by performing creep rupture tests on both smooth and notched specimens of the steel. The multiaxial state of stress was introduced by incorporating circumferential U-notches of different root radii ranging from 0.25 to 5.00 mm on the smooth specimens of the steel. Creep tests were carried out at 973 K over the stress range of 140 to 220 MPa. In the presence of notch, the creep rupture strength of the steel was found to increase with the associated decrease in rupture ductility. Over the investigated stress range and notch sharpness, the strengthening was found to increase drastically with notch sharpness and tended toward saturation. The fractographic studies revealed the mixed mode of failure consisting of transgranular dimples and intergranular creep cavitation for shallow notches, whereas the failure was predominantly intergranular for relatively sharper notches. Detailed finite element analysis of stress distribution across the notch throat plane on creep exposure was carried out to assess the creep failure of the material in the presence of notch. The reduction in von-Mises stress across the notch throat plane, which was greater for sharper notches, increased the creep rupture strength of the material. The variation in fracture behavior of the material in the presence of notch was elucidated based on the von-Mises, maximum principal, and hydrostatic stresses. Electron backscatter diffraction analysis of creep strain distribution across the notch revealed localized creep straining at the notch root for sharper notches. A master curve for predicting creep rupture life under the multiaxial state of stress was generated considering the representative stress having contributions from both the von-Mises and principal stress components of the stress field in the notch throat plane. Rupture ductility was also predicted based on the multiaxial state of stress.     

Co(III) acetylacetonate-complex-initiated grafting of N-vinyl pyrrolidone on cellulose in aqueous media

The graft copolymerization of N-vinyl pyrrolidone (N-VP) onto cellulose was carried out with a cobalt acetylacetonate complex Co(acac)₃ as an initiator under a nitrogen atmosphere at 50 ± 0.1°C. The graft yield percentage (%G) obtained as a function of the concentrations of N-VP and Co(acac)₃ and the temperature was used to calculate various other grafting parameters and the grafting rate dependence on the concentrations of monomer, Co(acac)₃ and reaction temperature. The energy of activation (ΔE_a) for the grafting of N-VP onto cellulose was 22.7 kJ/mol within 40–60°C. The molecular weights of the grafted chains and homopolymers were determined viscometrically with a Ubbelohde-type viscometer. Graft yield (%G) in the presence of various additives such as sodium lauryl sulfate, cetyltrimethylammonium bromide, and methanol was studied, and the results are suitably explained. On the basis of the experimental results, a reaction scheme for graft copolymerization is proposed, and a kinetic rate expression is presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2286–2296, 2001     

Polymers from renewable resources. XIII. Interpenetrating polymer networks derived from castor oil–hexamethylene diisocyanate and polymethacrylamide

Several castor oil‐based polyurethanes (PUs) samples were synthesized using various diisocyanates such as hexamethylene diisocyanate (HMDI) with varying NCO/OH ratios. All the PUs were reacted with methacrylamide (MAM) using an ethylene glycol dimethacrylate (EGDM) crosslinker and benzoyl peroxide as an initiator. Thermogravimetric analysis of the polymers was followed using a computer analysis method for assigning the kinetic mechanism. The degradation steps are discussed in the light of kinetic parameters. The scanning electronic microscopy of some of the interpenetrating polymer networks (IPNs) were studied and the morphology was examined. The samples were subjected to wide‐angle X‐ray diffraction analysis. Ruland and Vonk's method was used to calculate the degree of crystallinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1349–1353, 2001     

Mechanistic modeling of cutting forces in micro-end-milling considering tool run out,minimum chip thickness and tooth overlapping effects

This work proposed an improved mechanistic model for prediction of cutting forces in micro-milling process. The combined influences of tool run out, trochoidal trajectory of the tool center, overlapping of tooth, edge radius and minimum chip thickness are incorporated in this model to realize the exact cutting phenomenon. Moreover, an improved undeformed chip thickness algorithm has been presented by considering tool run out, minimum chip thickness and trajectory of all passing teeth for one complete revolution of the tool instead of only the current tooth trajectory. For estimation of tool run out, a model based on the geometry of the two fluted end mill cutter has been developed. Effects of trochoidal trajectory of the tool center and tool run out are found to be significant as each tooth has a different chip load. Further, the effect of minimum chip thickness is found to be significant at lower feed value. The proposed model has been validated by micro-milling experiments on Ti6Al4V-titanium alloys using uncoated flat end mill cutter. The predicted cutting forces were found to be in good agreement with the experimental cutting forces in both feed and cross feed directions.