The Reaction Mass Biped: Geometric Mechanics and Control

Inverted Pendulum based reduced order models offer many valuable insights into the much harder problem of bipedal locomotion. While they help in understanding leg behavior during walking, they fail to capture the natural balancing ability of humans that stems from the variable rotational inertia on the torso. In an attempt to overcome this limitation, the proposed work introduces a Reaction Mass Biped (RMB). It is a generalization of the previously introduced Reaction Mass Pendulum (RMP), which is a multi-body inverted pendulum model with an extensible leg and a variable rotational inertia torso. The dynamical model for the RMB is hybrid in nature, with the roles of stance leg and swing leg switching after each cycle. It is derived using a variational mechanics approach, and is therefore coordinate-free. The RMB model has thirteen degrees of freedom, all of which are considered to be actuated. A set of desired state trajectories that can enable bipedal walking in straight and curved paths are generated. A control scheme is then designed for asymptotically tracking this set of trajectories with an almost global domain-of-attraction. Numerical simulation results confirm the stability of this tracking control scheme for different walking paths of the RMB. Additionally, a discrete dynamical model is also provided along-with an appropriate Geometric Variational Integrator (GVI). In contrast to non-variational integrators, GVIs can better preserve energy terms for conservative mechanical systems and stability properties (achieved through energy-like lyapunov functions) for actuated systems.     

Polarizer superstrate and SRR‐loaded high‐gain dual band dual polarized waveguide slot array antenna

This article presents a high‐gain dual band dual polarized waveguide slot array antenna. Three split ring resonators (SRRs) are placed on the transverse plane of a slotted waveguide at uniform distance to achieve dual band response whereas a polarizer superstrate has been used to change the linear polarization of the lower band to circular polarization. Ansys HFSS 14.0 has been used for simulation and optimization purpose. Proposed antenna shows two 10 dB return loss bandwidth covering the frequency range 8.41‐8.88 and 9.31‐10.43 GHz, respectively. The lower band offers a circular polarization and upper band offers a linear polarization.     

Comparative performance evaluation of carbon dot-based paper immunoassay on Whatman filter paper and nitrocellulose paper in the detection of HIV infection

Carbon dots synthesized from citric acid and ethylene diamine by a one-step hydrothermal technique were used to develop a carbon dot-based paper immunoassay (CDPIA) for rapid detection of HIV-1 p24 antigen. In the present study, the 96-well template was hand patterned using a wax pencil, as a prototype method, on two types of paper, (1) Whatman filter paper and (2) nitrocellulose paper. The sandwich immunoassay was performed on both paper microplates for detection of HIV-1 p24 antigen which is an early marker of HIV infection. The detection range was from 10 μg/mL to 1 ng/mL for the Whatman filter paper while the nitrocellulose paper exhibited a higher range from 10 μg/mL to 250 pg/mL. CDPIA on the nitrocellulose paper (CDNIA) exhibited a fourfold increase in sensitivity and reduced the assay time by threefold compared with CDPIA on Whatman paper (CDWIA). HIV-negative and HIV-positive plasma samples were tested using CDNIA for the presence of HIV-1 p24 antigen. This immunoassay exhibited no false-positive and false-negative results with the clinical samples tested. This simple and sensitive paper-based HIV-1 p24 antigen assay may be useful in preventing HIV transmission by blood transfusion in resource-limited settings by reducing the antibody negative, infectious window period in blood donors and for early diagnosis of HIV infected individuals where nucleic acid-based testing is not practical or feasible.     

The influence of alkali pretreatments in lyocell resin finishing—Resin distribution and mechanical properties

Lyocell fabric samples were pretreated with NaOH and KOH and resin finished. The treated samples were tested to determine the influence of alkali pretreatments on the tenacity, abrasion resistance, and crease recovery of resin‐finished lyocell. Alkali pretreatments resulted in a higher surface concentration of the crosslinking reagent in fabrics, leading to lowered crease recovery and abrasion resistance. The pretreatments also exerted a deleterious influence on the tensile strength in resin‐finished samples. However, the differential distribution of crosslinking reagent within the textile structure does not appear to be the only factor responsible for the changes observed in substrate properties; other factors also appear to be responsible for the results observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3596–3601, 2006     

Building 3D visual maps of interior space with a new hierarchical sensor fusion architecture

It is now generally recognized that sensor-fusion is the best approach to the accurate construction of environment maps by a sensor-equipped mobile robot. Typically, range data collected with a range sensor is combined with the reflectance data obtained from one or more cameras mounted on the robot.In much of the past work on sensor fusion in hierarchical approaches to map construction, the fusion was carried out only at the lowest level of the hierarchy. As a result, in those approaches, only the fused data was made available to the higher levels in the hierarchy. This implied that any errors caused by sensor fusion would propagate upwards into the higher level representations of an interior map. Our work, on the other hand, checks for consistency between the data elements produced by the different sensors at all levels of the hierarchy. This consistency checking is carried out with the help of an interval-based representation of uncertainties in the sensor data.In addition to demonstrating that our approach to the fusion of range and image data results in dense 3D maps of the interior space, we also provide validation of our overall framework by presenting a set of loop closure results. These results demonstrate that our overall errors in the maps remain small (within 0.91% of the distance traveled for map construction) even when the robot has to traverse over large loops inside a building.     

Image compression and data integrity in confocal microscopy

To manage large volumes of image data generated routinely using real-time confocal microscopy, compressing image data using a lossy algorithm prior to sustained video rate transferring and/or storing is proposed. Test criteria for determining the acceptability of uncompressed data, both qualitatively and quantitatively, are described, and an empirical demonstration of the use of lossy compression in data management is provided. It is found that, if appropriately used, the lossy compression scheme could retain all the useful information in the data while providing better compression ratios (memory for the original/ memory for the compressed) when compared with a lossless scheme.     

Dielectric properties study of surface engineered nano$$\hbox {TiO}_{2}$$/epoxy composites

Nanodielectrics are promising materials that can efficiently store a large amount of electrical energy that are desirable for many electronic and power devices. Control of polymer–particle interface in nanodielectrics is very critical in not only obtaining the improved quality of dispersion but also in altering the dielectric properties. Various surface modifying agents with linear (alkyl), aromatic (phenyl) and extended aromatic (naphthyl) chemical nature were employed at the epoxy–nano\(\hbox {TiO}_{2}\) interface. All the surface-modifying agents were successful in passivating the nanoparticles surface and in obtaining the improved quality of polymer–particle dispersion and improved glass transition temperature comparatively. However, all the surface modifiers were not successful in obtaining the improved dielectric properties of the nanodielectrics, especially dielectric breakdown resistance. Only the extended aromatic group at the polymer–particle interface, which is more electron withdrawing in electronic nature than phenyl and alkyl structures, was successful in improving the dielectric breakdown resistance. Thus, the choice of surface-modifying agent based on its chemical and electronic nature is very important in optimizing the dielectric properties of nanodielectrics. Naphthyl phosphate-modified nano\(\hbox {TiO}_{2}\)–epoxy composite films of \(\sim \)90–100 \(\upmu \)m thick at 5 vol% particle concentration yielded higher dielectric breakdown resistance than pure epoxy polymer and thereby resulted in about 90% higher electrical energy storage density than the pure epoxy film.     

Guest‐Molecule‐Directed Assembly of Mesostructured Nanocomposite Polymer/Organoclay Hydrogels

Given the urgent need for soft materials with high functional value, hydrogels based on the integrative assembly of organic polymers and nanoscale inorganic building blocks—so‐called nanocomposite polymer hydrogels—offer a generic approach to swollen hybrid networks with tuneable and synergistic properties. Here, we report a new approach to assembling nanocomposite polymer hydrogels with multiple levels of structural complexity and enhanced functionality by using nanoscale integration of mesostructured inorganic building blocks capable of sequestering and releasing drugs (ibuprofen, aspirin, naproxen) and enzymes (glucose oxidase). The viscoelastic materials are produced by noncovalent crosslinking of poly(vinylpyrrolidone) in the presence of low amounts (1–5 wt%) of an exfoliated synthetic organoclay that undergoes in situ guest‐molecule‐directed self‐assembly. The hydrogels can be moulded into shape‐persistent, free‐standing objects that are stable between pH values of 4 to 11 and self‐heal when damaged. Significantly, the mesostructured nanocomposite polymer hydrogels, which can be reversibly dried and reconstituted in the form of highly swollen materials, exhibit sustained drug release and can be recharged and reused. The results provide important guidelines for developing new multifunctional nanocomposite polymer hydrogels based on the concerted self‐assembly of inorganic building blocks with mesostructured interiors.