Modelling of Chevron electrothermal actuator and its performance analysis

Microsystem Technologies - In this work, a Chevron electrothermal actuator is designed and its analytical model is developed. Chevron actuator works on the principle of Joules heating effect and...     

Decentralized and adaptive control of multiple nonholonomic robots for sensing coverage

This work deals with decentralized control of multiple nonholonomic mobile sensors for optimal coverage of a given area for sensing purposes. We assume a density function over the region to be covered, which can be viewed as a probability density of the phenomena to be sensed. The density function is unknown but assumed to be linearly parameterized with unknown parameter weights. We consider a second‐order dynamic model for the mobile agents and derive decentralized adaptive control laws to achieve optimal coverage of the region. We then consider the case where the dynamic model of the agents are not fully known, and then develop parameter adaptation laws to achieve the optimal coverage objective. We test the derived algorithms using simulations and compare our proposed controllers with kinematics‐based controllers. We find that the feedback control design based on the dynamic model performs significantly better than controllers solely relying on kinematic models. Furthermore, for the unknown dynamics case, our controller outperforms the nonadaptive controller with poor initial parameter estimates.     

Immunoregulation of Macrophages by Controlling Winding and Unwinding of Nanohelical Ligands

Developing materials with the capability of changing their innate features can help to unravel direct interactions between cells and ligand-displaying features. This study demonstrates the grafting of magnetic nanohelices displaying cell-adhesive Arg-Gly-Asp (RGD) ligand partly to a material surface. These enable nanoscale control of rapid winding (“W”) and unwinding (“UW”) of their nongrafted portion, such as directional changes in nanohelix unwinding (lower, middle, and upper directions) by changing the position of a permanent magnet while keeping the ligand-conjugated nanohelix surface area constant. The unwinding (“UW”) setting cytocompatibility facilitates direct integrin recruitment onto the ligand-conjugated nanohelix to mediate the development of paxillin adhesion assemblies of macrophages that stimulate M2 polarization using glass and silicon substrates for in vitro and in vivo settings, respectively, at a single cell level. Real time and in vivo imaging are demonstrated that nanohelices exhibit reversible unwinding, winding, and unwinding settings, which modulate time-resolved adhesion and polarization of macrophages. It is envisaged that this remote, reversible, and cytocompatible control can help to elucidate molecular-level cell–material interactions that modulate regenerative/anti-inflammatory immune responses to implants.     

Nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> composite synthesized by sol–gel technique: powder processing and microstructure

Al₂O₃–ZrO₂ composite gel powder was prepared by sol–gel route. The gel precursor compositions were preferred to achieve yield of 5–15 mol% zirconia after calcination of respective powders. The precursor gel was characterized by Differential Thermal Analysis (DTA)/Thermo Gravimetric (TG), IR and X-ray Diffraction study (XRD). The analysis reveal the gel contained pseudoboehmite and amorphous Zr(OH)₄, which was decomposed in three and two stages respectively. The phase transformation of alumina during calcination followed the sequence of pseudoboehmite → bayerite → boehmite → γ-Al₂O₃ → θ-Al₂O₃ → α-Al₂O₃, while that of ZrO₂ follows amorphous ZrO₂ → t-ZrO₂ → (t + m) ZrO₂. Fourier Transform Infrared Spectroscopy (FTIR) studies showed that the number of M–OH and M–O bond increases with zirconia due to a change in the cationic charge of the composite powder. Transmission Electron Microscopy (TEM) photograph of calcined powder exhibited the presence of dispersed as well as agglomerated nano sized spherical particles. SEM and Electron Probe Microscope Analysis (EPMA) confirmed the near uniform distribution of zirconia particles in the alumina matrix.     

Biodegradable film. IV. Printability study on biodegradable film

A starch‐based biodegradable (BD) low density polyethylene (LDPE) film can be directly printable without any corona treatment, unlike virgin LDPE film. Such a film shows poor adhesion and nail scratch resistance of the ink on the printed area of the film. In order to increase the adhesion and nail scratch resistance of the ink on the printed BD film, grafting of acrylonitrile onto the BD film is carried out. The polyacrylonitrile grafted BD film shows better adhesion, nail scratch resistance, and printability. The printability of the polyacrylonitrile grafted BD film is comparable to the conventional corona treated LDPE film. The extent of printability is a function of the surface smoothness, as well as the optimum percentage of grafting on the biodegradable film. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1273–1277, 2001     

Arbitrary branched and intersecting cracks with the extended finite element method

Extensions of a new technique for the finite element modelling of cracks with multiple branches, multiple holes and cracks emanating from holes are presented. This extended finite element method (X‐FEM) allows the representation of crack discontinuities and voids independently of the mesh. A standard displacement‐based approximation is enriched by incorporating discontinuous fields through a partition of unity method. A methodology that constructs the enriched approximation based on the interaction of the discontinuous geometric features with the mesh is developed. Computation of the stress intensity factors (SIF) in different examples involving branched and intersecting cracks as well as cracks emanating from holes are presented to demonstrate the accuracy and the robustness of the proposed technique. Copyright © 2000 John Wiley & Sons, Ltd.     

Antimony polymers. III. Flame retardant behavior of chloroprene and natural rubber vulcanizates with antimony polymer

The antimony-containing polymer of bisphenol-A (BPA) and triphenyl antimony dinitrate was used as a flame retardant (FR) for chloroprene rubber (CR) and natural rubber (NR). The flame retardancy of this additive was monitored by the limiting oxygen index (LOI) measurements of the rubber vulcanizates and compared with that for antimony trioxide used as a FR additive. The thermogravimetric analysis (TGA) of the vulcanizates has also been studied. A structure flammability relationship has been established. The effect of this FR additive on physical properties of the vulcanizates undergoing heat aging and solvent leaching has also been evaluated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 927–935, 1998     

A new rigid rodlike colored poly(amide hydrazide): Thermal,optical anisotropic,and mechanical behavior

A new aromatic all-para oriented poly(amide hydrazide) containing an azo group in the main chain was prepared by reacting a symmetric diamine containing a preformed hydrazide group, viz., N,N′-bis(4-aminobenzoyl)hydrazine (BABH), with 4,4′-azobenzoyl chloride (ADBC). The thermal behavior of the polymer was studied by TGA and DSC in air and nitrogen. Films of the polymer were prepared by two processes, viz., wet and dry processes, by using its solution in DMAc containing LiCl. The optical anisotropy, surface morphology, and tensile properties of the films were studied. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1211–1215, 1997     

Chemical modification of LDPE film

Low‐density polyethylene (LDPE) film was chemically modified by chromic acid treatment to generate polar groups on the surface. The film samples were etched by chromic acid with variation of temperature at a constant time (30 min) and variation of time at a constant temperature (room temperature = 26°C). The variation of weight and thickness of the film samples before and after etching was measured. The surface morphology of the etched films was studied by Scanning Electron Microscopy (SEM). IR and XPS analysis revealed the introduction of polar groups like  COOH, 〉CO,  SO₃H on the etched LDPE film surface, which exhibited improved printability. Etching also enhanced adhesion with epoxy resin. The mechanical properties of the laminates of the two specimens of the same film sample with epoxy resin were also measured. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1041–1048, 1999     

Analysis of Metallurgical and Mechanical Properties of Continuous and Pulsed Current Gas Tungsten Arc Welded Alloy C-276 with Duplex Stainless Steel

The present work investigates the microstructure and mechanical properties of alloy C-276 fabricated by continuous and pulsed current gas tungsten arc welding process and by employing ER2553 filler wire. Optical and scanning electron microscopic analyses were carried out to study the microstructures of weldments produced. Energy dispersive X-ray spectroscopy (EDS) was performed to investigate the formation of secondary phases in the weldments. The results disclosed that pulsed current gas tungsten arc welding showed refined microstructure compared to continuous current gas tungsten arc welding. SEM/EDS analysis revealed the segregation of Mo in the weld interface regions in both the welding techniques. The extent of microsegregation reduced the strength and toughness of the weld joint compared to the base metal. Bend test revealed cracks in the weld interface region in both the weldments.