Ellipsoidal Techniques for Reachability Analysis of Discrete-Time Linear Systems

This paper describes the computation of reach sets for discrete-time linear control systems with time-varying coefficients and ellipsoidal bounds on the controls and initial conditions. The algorithms construct external and internal ellipsoidal approximations that touch the reach set boundary from outside and from inside. Recurrence relations describe the time evolution of these approximations. An essential part of the paper deals with singular discrete-time linear systems     

Preparation and characterization of carbon-encapsulated iron nanoparticles and their catalytic activity in the hydrogenation of levulinic acid

This study describes the synthesis of carbon-encapsulated iron nanoparticles using an ultrasonic method and also investigates their catalytic activity. These nanoparticles have been prepared using ultrasonic irradiation followed by annealing at various temperatures. As the annealing temperature of as-prepared α-Fe₂O₃ nanoparticles increased, the sample transformed into γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles via the reduction process without requiring any additional reducing agents such as H₂ gas, thus, creating a carbon shell surrounding the nanoparticles. By controlling the experimental conditions, Fe nanoparticles of various sizes can be formed with diameters in the range 100–800 nm; these nanoparticles are tightly encapsulated by 20-nm-thick carbon shells. Because of their high saturation magnetization 212 emu g^?1, the carbon-encapsulated Fe nanoparticles can be used for magnetic resonance imaging with a dramatically enhanced efficiency compared to commercially available T ₂ contrast agents. Moreover, the carbon-encapsulated Fe nanoparticles showed its superior catalytic activity and reusability for the hydrogenation of biomass-derived levulinic acid to GVL (99.6 %) in liquid phase.     

Multifunctional plasmonic Ag-hematite nano-dendrite electro-catalysts for methanol assisted water splitting: Synergism between silver nanoparticles and hematite dendrites

Hydrogen is the most environment friendly fuel and has the largest energy density but still much away from being a viable technology due to the cost associated with its production on-site on-demand. However, hydrogen production via water splitting could become potential commercial technology by designing new catalyst materials with low cost, desired surface structures and properties that govern hydrogen evolution reaction (HER) activity and stability. Here, we report the methanol assisted electrochemical water splitting using silver nanoparticles decorated hematite (Ag-hematite) dendrite nanostructures. Ag-hematite nano-dendrites prepared via two different methods viz. chemical co-precipitation and hydrothermal treatment are analysed and compared for their potential applications towards methanol assisted water splitting. It is found that Ag-hematite nano-dendrites prepared by chemical precipitation method shows much better activity as compared to both the parent materials (i.e. Ag NPs and hematite nano-dendrites) as well as Ag-hematite nano-dendrites synthesized by hydrothermal treatment. A baseline study showing the influence of methanol concentration, catalyst, catalyst support, and operating mode has been established. The analysis of the system was carried out as a function of onset potentials and kinetic parameters, including the Tafel slopes and exchange current densities. The effect of electrochemical promotion was investigated to see if it can increase the efficiency and performance of H₂ production through electrochemical processes. The observed electro-catalytic enhancement could be attributed to the synergistic effect of hematite dendrites, larger surface area of dendrite structure leading to higher loading of Ag NPs on the surface of HDs. Moreover, the endurance study was performed to check the stability of the presented electrocatalyst in acidic medium under both dark and light illumination conditions which shows that the presented composite catalyst is stable for minimum 100 scans even under light illumination with no signs of photo-corrosion.     

Impressed Current Cathodic Protection of Low Carbon Steel in Conjunction with Conducting Polyaniline based Paint Coating

Protection of Metals and Physical Chemistry of Surfaces - Epoxy, Fusion bonded epoxy and conducting polyaniline based paints were applied on low carbon steel sample. Conducting polyaniline and...     

Using channel state dependent packet scheduling to improve TCPthroughput over wireless LANs

In recent years, a variety of mobile computers equipped with wireless communication devices have become popular. These computers use applications and protocols, originally developed for wired desktop hosts, to communicate over wireless channels. Unlike wired networks, packets transmitted on wireless channels are often subject to burst errors which cause back to back packet losses. In this paper we study the effect of burst packet errors and error recovery mechanisms employed in wireless MAC protocols on the performance of transport protocols such as TCP. Most wireless LAN link layer protocols recover from packet losses by retransmitting lost segments. When the wireless channel is in a burst error state, most retransmission attempts fail, thereby causing poor utilization of the wireless channel. Furthermore, in the event of multiple sessions sharing a wireless link, FIFO packet scheduling can cause the HOL blocking effect, resulting in unfair sharing of the bandwidth. This observation leads to a new class of packet dispatching methods which explicitly take wireless channel characteristics into consideration in making packet dispatching decisions. We compare a variety of channel state dependent packet (CSDP) scheduling methods with a view towards enhancing the performance of transport layer sessions. Our results indicate that by employing a CSDP scheduler at the wireless LAN device driver level, significant improvement in channel utilization can be achieved in typical wireless LAN configurations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preclinical In Vitro Model to Assess the Changes in Permeability and Cytotoxicity of Polarized Intestinal Epithelial Cells during Exposure Mimicking Oral or Intravenous Routes: An Example of Arsenite Exposure

The gastrointestinal tract (GIT) is exposed to xenobiotics, including drugs, through both: local (oral) and systemic routes. Despite the advances in drug discovery and in vitro pre-clinical models, there is a lack of appropriate translational models to distinguish the impact of these routes of exposure. Changes in intestinal permeability has been observed in different gastrointestinal and systemic diseases. This study utilized one such xenobiotic, arsenic, to which more than 200 million people around the globe are exposed via their food, drinking water, work environment, soil, and air. The purpose of this study was to establish an in vitro model to mimic gastrointestinal tract exposure to xenobiotics via oral or intravenous routes. To achieve this, we compared the route (mimicking oral and intravenous exposure to GIT and the dose response (using threshold approach) of trivalent and pentavalent inorganic arsenic species on the permeability of in vitro cultured polarized T84 cells, an example of intestinal epithelial cells. Arsenic treatment to polarized T84 cells via the apical and basolateral compartment of the trans-well system reflected oral or intravenous routes of exposure in vivo, respectively. Sodium arsenite, sodium arsenate, dimethyl arsenic acid sodium salt (DMA^V), and disodium methyl arsonate hydrate (MMA^V) were assessed for their effects on intestinal permeability by measuring the change in trans-epithelial electrical resistance (TEER) of T-84 cells. Polarized T-84 cells exposed to 12.8 µM of sodium arsenite from the basolateral side showed a marked reduction in TEER. Cytotoxicity of sodium arsenite, as measured by release of lactate dehydrogenase (LDH), was increased when cells were exposed via the basolateral side. The mRNA expression of genes related to cell junctions in T-84 cells was analyzed after exposure with sodium arsenite for 72 h. Changes in TEER correlated with mRNA expression of focal-adhesion-, tight-junction- and gap-junction-related genes (upregulation of Jam2, Itgb3 and Notch4 genes and downregulation of Cldn2, Cldn3, Gjb1, and Gjb2). Overall, exposure to sodium arsenite from the basolateral side was found to have a differential effect on monolayer permeability and on cell-junction-related genes as compared to apical exposure. Most importantly, this study established a preclinical human-relevant in vitro translational model to assess the changes in permeability and cytotoxicity during exposure, mimicking oral or intravenous routes.     

Multilayered large‐area WO3 films on sheet and mesh‐type stainless steel substrates for photoelectrochemical hydrogen generation

The objective of this study is to demonstrate the significant improvement in the photoelectrochemical (PEC) hydrogen generation by a photoanode owing to the increased surface area of the substrate. In this work, multilayered tungsten oxide (WO₃) films have been successfully synthesized onto the large‐area sheet (9 × 9cm²) and mesh (1 × 20cm²) ‐type stainless steel (SS) substrates using screen printing and brush painting methods, respectively. All the WO₃ films are porous and nanocrystalline (30–80 nm) in nature with a monoclinic crystal structure as revealed from X‐ray diffraction and scanning electron microscopy studies. The PEC water splitting study is performed under simulated 1 SUN illumination (AM1.5 G) in a typical two‐electrode cell configuration with WO₃ photoanode and Pt wire immersed in 0.5 M H₂SO₄ electrolyte. The photocurrent as well as hydrogen generation rate for WO₃ photoanodes coated on the plane SS sheet substrate is relatively low and showed minimal change with increasing film thickness. On the other hand, the photocurrent as well as the hydrogen generation is enhanced by a 3–4 fold degree for the WO₃ photoanodes coated on SS mesh. We attribute such efficient water splitting to the increment in the filling factor of the WO₃ material due to the large effective surface area of the SS mesh as compared to the SS sheet substrate. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimisation of opportunistic maintenance of a multi-component system considering the effect of failures on quality and production schedule: A case study

For a manufacturing equipment, any unplanned breakdown during the production period results into a high production loss. To keep the manufacturing facilities in good condition, preventive maintenance is planned. However, because of limited time and availability of resources, not all the system components can be or need to be repaired/replaced during a planned opportunity. Hence, the unplanned breakdowns can also be considered as an opportunity to do the maintenance activities for other components to take the advantage of economic dependency in multi-component system. However, when the system is under maintenance, it is very conservative to take the decision of maintenance actions on the components because of limited available time and resources. For such situation, this paper consider an opportunistic maintenance model for a multi-component system to take maintenance decision with a constraint on available time and the system availability requirements. The maintenance decisions for each component involves one of the three actions namely, repair, replace or do nothing to achieve the target availability with minimum maintenance cost. The model also considers the effect of component failures on the quality of product being manufactured as well as the production schedule on the machine. The cost of rejections is considered in the total failure cost along with the maintenance and downtime costs. The production schedule delay factor is considered as a constraint for the maintenance decision to account for the effect on production schedule delay. The optimal solution for the model is obtained using three solution methodologies namely simulated annealing, genetic algorithm and sequence heuristics. Using a real-life example of high pressure die casting machine, the opportunistic maintenance approach is demonstrated and results are discussed.     

Microstructure determination and thermal studies of n‐acryloylcarbazole/vinyl acetate copolymers

Copolymers of N‐acryloylcarbazole (A) and vinyl acetate (V) were synthesized by bulk polymerization using benzoyl peroxide (BPO) as free‐radical initiator at 65°C in different in‐feed ratios. The composition of the copolymer was determined by ¹H‐NMR spectrum. The comonomer reactivity ratios, determined by Kelen–Tudos (KT) and nonlinear error‐in‐variables (EVM) methods, were r_A= 16.75 ± 1.38, r_V = 0.015 ± 0.002, and r_A = 16.36, r_V = 0.015, respectively. Complete spectral assignments of the ¹H and ¹³C{¹H} NMR spectra of the copolymers were done by the help of distortionless enhancement by polarization transfer (DEPT) and two‐dimensional NMR techniques such as heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). The methine and methylene carbon resonances were found to be compositional as well as configurational sensitive. The signals obtained were broad pertaining to the restricted rotation of bulky carbazole group. The thermal stability and glass‐transition temperatures (T_g) of the copolymers were found to be dependant on polymer composition and characteristic of rotational rigidity of the polymer chain. Variation in the values of T_g with the copolymer composition was found to be in good agreement with theoretical values obtained from Johnston and Barton equations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2720–2733, 2007