213 research outputs found
Covalent Rigid-Rod Organometallic Polymers with Alternating Transition Metal Clusters and Conjugated Spacers in the Main Chain
No full textThe first rigid-rod cluster-containing σ-alkynyl polymers E-[({Pt6}-CC-Ar-CC)]x-{Pt6}-E [(3), {Pt6} ) Pt6(μ-PBut2)4(CO)4, E ) end group; Mn ) 22 000-38 000] have been prepared by step-growth polycondensation of {Pt6}Cl2 and 1,4-didodecyl-2,5-diethynylbenzene (HCC-Ar-CCH) under Sono- gashira-type conditions. The monodisperse oligomers HCC-Ar-CC-({Pt6}CC-Ar-CC)x-{Pt6}-CC- Ar-CCH [(4) x ) 0; (11) x ) 2; (15) x ) 4] were also prepared by stepwise procedures, still based on Cu(I)-catalyzed dehydrohalogenation reactions. A red-shift of the UV-vis absorption centered at ca. 470 nm, on increasing chain length, suggests some degree of electron delocalization along the backbone
Roughness Based Passive Control Of Transition To Galloping Of A Circular Cylinder Undergoing Vortex Induced Vibrations
No full textFlow induced motion (FIM) is a naturally occurring fluid-structure interaction phenomenon, typically considered harmful to a wide variety of engineering structures. As a result, the majority of research in the field has been geared towards mitigating the occurrence of FIM. In 2005, Michael Bernitsas at the University of Michigan identified the energy harvesting potential of FIM\u27s, triggering a new line of research that instead focuses on augmenting it. Previous work by our group had tested the effectiveness of strips attached to the surface of a circular cylinder in augmenting FIM modes such as vortex induced vibrations (VIV) and galloping. The objective of the experimental results presented in this thesis is to develop a better understanding of the effect of strip surface on the incitation of galloping oscillations. Strip roughness ratios (ratio of the size of embedded roughness to the total strip thickness) ranging from 0% (smooth surface) to 100% (rough surface with zero thickness) were tested in addition to strip thickness ratios (ratio of strip thickness to cylinder diameter) ranging from 0.8% to 8.2%. At the higher roughness ratios, rough strips led to suppression of VIV and galloping amplitudes when compared to their smooth counterparts. However, with decreasing roughness ratio and increasing thickness, the effect of surface roughness became negligible in comparison to the smooth surface. We conclude that beyond a threshold values of strip thickness, the mechanistic impact of the strip (thickness) is the dominant parameter affecting the cylinder\u27s FIM response with no additional passive flow control possible by varying the surface roughness. At the lower threshold of thickness, neither the smooth nor the rough strips experienced galloping
Liquid extraction with immobilized liquids for product recovery from fermentation broths
No full textNowadays, many fermentation chemicals are produced at an industrial scale. Numerous technological improvements have been developed and implemented to achieve high quality and quantity of fermentation products. However, several drawbacks in fermentation processes still limit their application at an industrial level. In situ product removal (ISPR) is a potential alternative to overcome the conventional drawbacks of the fermentative processes, increasing the fermentation's productivity and reducing the separation steps for recovery and purification. Currently, liquid extraction has emerged as a promising separation technology for ISPR, with immobilized liquids such as membrane-assisted extraction and microchannel liquid membrane, due to the high mass transfer rates, scalability, easy integration, and efficiency. This chapter will discuss these technologies regarding their integration into fermentative processes
Chemical Characterization of Corydalis chaerophylla D.C. Extracts and Preliminary Evaluation of Their in Vitro and in Vivo Biological Properties
Get PDFGenus Corydalis is a rich source of isoquinoline alkaloids reported to having potential bioactivities. Corydalis chaerophylla collected from Nepal at an altitude of 2400-4800 m was extracted using hexane, methanol and chloroform as solvents. The resulting hexane, methanol and chloroform extracts were subjected to LC-DAD-MSn analysis to yield fifteen different alkaloids. To assess any potential pharmacological properties, antimicrobial activity against two Gram-positive, two Gram-negative bacterial strains and one fungal strain was assessed, revealing significant inhibitive action of the methanol and chloroform extracts. Of the extracts obtained using chloroform contained the highest content of phenolic compounds at 113 mg GAE/g, while the highest total flavonoid content was found for the hexane extract with a value of 46.45 mg QE/g. The chloroform extract also exhibited a considerable antioxidant activity at IC50 value, 261.5 +/- 3 mu g/mL, for the DPPH assay. Conversely, the methanol extract exhibited the highest LC50 value for Brine Shrimp cytotoxicity at 196 +/- 3 mu g/mL being least potential for the test. The methanol extract was found to be the most active against alpha-amylase inhibition with an IC50 of 51.52 +/- 2 mu g/mL. In an in vivo acute oral toxicity study against mice, methanol and chloroform extracts presented harmful effects with 1000.36 mg/kg BW and 515 mg/kg BW for LD50, respectively. By analyzing all the results of the solvents used, the chloroform extract was found to be the most active, a feature that will be used in future isolation procedures and other pharmacological tests
Continuous-time Single Network Adaptive Critic for Regulator Design of Nonlinear Control Affine Systems
No full textAn optimal control law for a general nonlinear system can be obtained by solving Hamilton-Jacobi-Bellman equation. However, it is difficult to obtain an analytical solution of this equation even for a moderately complex system. In this paper, we propose a continuoustime single network adaptive critic scheme for nonlinear control affine systems where the optimal cost-to-go function is approximated using a parametric positive semi-definite function. Unlike earlier approaches, a continuous-time weight update law is derived from the HJB equation. The stability of the system is analysed during the evolution of weights using Lyapunov theory. The effectiveness of the scheme is demonstrated through simulation examples
Implementation of a neural network based visual motor control algorithm for a 7 DOF redundant manipulator
No full textThis paper deals with visual-motor coordination of a 7 dof robot manipulator for pick and place applications. Three issues are dealt with in this paper - finding a feasible inverse kinematic solution without using any orientation information, resolving redundancy at position level and finally maintaining the fidelity of information during clustering process thereby increasing accuracy of inverse kinematic solution. A 3-dimensional KSOM lattice is used to locally linearize the inverse kinematic relationship. The joint angle vector is divided into two groups and their effect on end-effector position is decoupled using a concept called function decomposition. It is shown that function decomposition leads to significant improvement in accuracy of inverse kinematic solution. However, this method yields a unique inverse kinematic solution for a given target point. A concept called sub-clustering in configuration space is suggested to preserve redundancy during learning process and redundancy is resolved at position level using several criteria. Even though the training is carried out off-line, the trained network is used online to compute the required joint angle vector in only one step. The accuracy attained is better than the current state of art. The experiment is implemented in real-time and the results are found to corroborate theoretical findings. © 2008 IEEE
A Novel Geometry-based Algorithm for Robust Grasping in Extreme Clutter Environment
No full textThis paper looks into the problem of grasping unknown objects in a cluttered environment using a 3D point cloud data obtained from a range sensor or an RGBD sensor. The objective is to identify graspable regions and detect suitable grasp poses from a single view, possibly, partial 3D point cloud without any apriori knowledge of the object geometry. The problem is solved in two steps - first, identifying and segmenting various object surfaces and second, searching for suitable grasping handles on these surfaces by applying geometric constraints of the physical gripper. The first step is solved by using a modified version of region growing algorithm that uses a pair of thresholds for the smoothness constraint on local surface normals to find natural boundaries of object surfaces. In this process, a novel concept of edge point is introduced that allows us to segment between different surfaces of the same object. The second step is solved by converting a 6D pose detection problem into a 1D linear search problem by projecting 3D cloud points onto the principal axes of the surface segment obtained in the first step. The graspable handles are then localized by applying physical constraints of the gripper. The resulting method allows us to grasp all kinds of objects including rectangular or box-type objects with flat surfaces which is otherwise considered to be difficult in the grasping literature. The proposed method is simple and can be implemented in real-time and does not require any off-line training phase for computing these affordances. The improvements achieved is demonstrated through comparison with another state-of-the-art grasping algorithm on various publicly-available datasets. We also contribute a new grasping dataset for extreme clutter situations.</p
Numerical investigation of compressible flow through a curtain of fixed particles with an immersed boundary method
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