Hydrothermal preparation and characterization of TiO2:AC composites

A new photocatalyst titania:activated carbon (TiO₂:AC) composite was prepared by impregnating anatase type TiO₂ nanoparticulates onto the activated carbon surface through a mild hydrothermal route. A varied ratio of TiO₂ to AC was considered for impregnation. As-prepared TiO₂:AC composite was characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET surface area and positron annihilation lifetime spectroscopy (PALS). Powder XRD results showed the persisting nature of anatase phase of TiO₂ deposited on the activated carbon surface. The BET, FTIR and PALS results revealed the impregnation threshold. The TiO₂ particulates were well adhered and uniformly dispersed on the carbon surface as confirmed by SEM.     

An approximation algorithm for state minimization in 2-MDFAs

In this paper, we analyze the problem of state minimization in a class of Finite State Automata called Two Start State Deterministic Finite State Automata (2-MDFAs). A 2-MDFA is similar to a deterministic finite state automaton (DFA), in that on a given input, each state has precisely one destination state; however, it differs from a DFA in that there are two start states. A string is accepted by a 2-MDFA if and only if there exists a transitional path from either start state to a finish state, on that string. Observe that 2-MDFAs provide a limited amount of non-determinism and hence investigating their properties from the perspective of state minimization is a worthwhile pursuit. In case of unbounded non-determinism, i.e., Non-deterministic finite state automata (NFAs), it is well-known that the state minimization problem is PSPACE-complete [Jiang and Ravikumar in Proceedings of the 18th International Colloquium on Automata, Languages and Programming, ICALP’91, Madrid, Spain, July 8–12, 1991] and further that such automata can be exponentially more succinct than DFAs [Meyer and Fischer in Proceedings of the 12th SWAT(Annual Symposium on switching and automata theory), pp 188-191, 1971]. Even in the case of 2-MDFAs, the minimization problem remains non-trivial; indeed, Malcher in Theor Comput Sci 327(3):375–390, 2004 shows that the corresponding decision problem is NP-complete. We focus on deriving approximability bounds for the state minimization problem in 2-MDFAs. Our main contribution in the current paper, is the design of an n-approximation algorithm for state minimization in 2-MDFAs, where n denotes the minimum number of states required to represent the input language as a 2-MDFA. We also present a proof that this bound is tight for our algorithm.The work of K. Subramani was supported in part by the Air-Force office of Scientific Research under Grant FA9550-06-1-0050     

Nano-structured CeO2 supported Cu-Pd bimetallic catalysts for the oxygen-assisted water–gas-shift reaction

The present work focuses on the development of novel Cu-Pd bimetallic catalysts supported on nano-sized high-surface-area CeO₂ for the oxygen-assisted water–gas-shift (OWGS) reaction. High-surface-area CeO₂ was synthesized by urea gelation (UG) and template-assisted (TA) methods. The UG method offered CeO₂ with a BET surface area of about 215 m²/g, significantly higher than that of commercially available CeO₂. Cu and Pd were supported on CeO₂ synthesized by the UG and TA methods and their catalytic performance in the OWGS reaction was investigated systematically. Catalysts with about 30 wt% Cu and 1 wt% Pd were found to exhibit a maximum CO conversion close to 100%. The effect of metal loading method and the influence of CeO₂ support on the catalytic performance were also investigated. The results indicated that Cu and Pd loaded by incipient wetness impregnation (IWI) exhibited better performance than that prepared by deposition–precipitation (DP) method. The difference in the catalytic activity was related to the lower Cu surface concentration, better Cu–Ce and Pd–Ce interactions and improved reducibility of Cu and Pd in the IWI catalyst as determined by the X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) studies. A direct relation between BET surface area of the CeO₂ support and CO conversion was also observed. The Cu-Pd bimetallic catalysts supported on high-surface-area CeO₂ synthesized by UG method exhibited at least two-fold higher CO conversion than the commercial CeO₂ or that obtained by TA method. The catalyst retains about 100% CO conversion even under extremely high H₂ concentration.     

Low temperature produced calcium-doped zinc oxide thick film via screen printing technique as thermal interface material in LED application

Pure and calcium-doped zinc oxide thick films were deposited on Aluminium substrate by screen printing technique using nanocrystalline powder synthesized from co-precipitation method. Shear thinning phenomenon with increment of shear rate was observed during the rheological analysis for all pastes. X-ray diffraction results confirmed the formation of ZnO with preferred orientation along (101) plane. Peak shifting to lower angle was observed upon increment of doping concentration of calcium. Crystallite size of doped ZnO powder decreased in the range (from 35.4 to 42.4 nm) from 116.1 nm of pure ZnO. Surface morphology analysed by FESEM had revealed the reduction of voids with increasing doping concentration up to 7 wt% of doping, followed by a slightly increase in the number of voids at 9 wt% doping. AFM analysis showed that the surface roughness of films exhibited a decreasing trend with the increase of calcium dopant until 7 wt% but became rougher at 9 wt%. Peaks shifting of ZnO to lower wavenumber revealed by FTIR study indicated that doping had affected the lattice structure of ZnO in the films. Thermal characterization showed the introduction of calcium dopant had increased the thermal resistance of the thick films. This led to a better junction temperature (T_j) of LED of 46.4?°C when compared with T_j of pure ZnO film at 47.3?°C.     

Analyzing restricted fragments of the theory of linear arithmetic

The theory of linear arithmetic (TLA), also known as the Theory of Rationals, is an extremely well-studied theory. It has been widely applied to a number of domains, including program verification and constraint specification. This paper discusses the computational complexities of two broad fragments of TLA, namely Quantified Linear Programs (QLPs) and Quantified Linear Implications (QLIs). These fragments are ideal for expressing specifications in real-time scheduling, and for modeling reactive systems. In this paper, we study the computational complexities of several variants of QLPs and QLIs. Our principal result shows that there exists a one-to-one correspondence between alternations in a class of QLIs and the complexity classes comprising the polynomial hierarchy PH. In other words, for each class of the PH, there exists a class of QLIs that is complete for that class. Our work mirrors the work in [L.J. Stockmeyer, The Polynomial-Time Hierarchy, Theoretical Computer Science, 3:1-22, 1977] which established the connection between the classes of PH and quantifier alternations in a Quantified Boolean Formula. Our results are surprising, since the variables in the fragments that we consider are continuous, as opposed to discrete.     

Optimal Length Resolution Refutations of Difference Constraint Systems

This paper is concerned with determining the optimal length resolution refutation (OLRR) of a system of difference constraints over an integral domain. The problem of finding short explanations for unsatisfiable difference constraint systems (DCS) finds applications in a number of design domains including program verification, proof theory, real-time scheduling and operations research. It is well-known that resolution refutation is a sound and complete procedure to establish the unsatisfiability of boolean formulas in clausal form. The literature has also established that a variant of the resolution procedure called Fourier-Motzkin elimination is a sound and complete procedure for establishing the unsatisfiability of linear constraint systems (LCS). Our work in this paper first establishes that every DCS has a short (polynomial in the size of the input) resolution refutation and then shows that there exists a polynomial time algorithm to compute the optimal size refutation. One of the consequences of our work is that the Minimum Unsatisfiable Subset (MUS) of a DCS can be computed in polynomial time; computing the MUS of an unsatisfiable constraint set is an extremely important aspect of certifying algorithms. This research was supported in part by a research grant from the Air-Force Office of Scientific Research under contract FA9550-06-1-0050 and in part by the National Science Foundation through Award CCF-0827397. A portion of this research was conducted at the Stanford Research Institute, where the author was a Visiting Fellow.     

Influence of Magnetic Nanoparticles on Surface Changes in CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Nerium Oleander Leaf Waste Activated Carbon Nanocomposite for Water Treatment

The paper reports on the successful use of the nano crystalline cobalt ferrite doped Nerium oleander leaf waste activated carbon (CoFe₂O₄/NOAC) synthesized by an urea assisted auto combustion technique to assess accurate kinetics and equilibrium parameters regarding the investigation of adsorption. The specific features of nano composite were investigated by various analytical techniques such as Scanning electron microscope with EDAX, powder X-ray diffraction study, BET surface area analysis, TG and DSC, Vibrating Sample Magnetometer. The BET analysis indicates that CoFe₂O₄ nano particles embedded in NOAC have increased the pore diameter for better adsorption. TG and DSC show the thermal stability of composite. The VSM study shows the Ferro magnetic behavior of nano composite which revealed that CoFe₂O₄/NOAC could be separated and retrieved easily by an external magnet after adsorption of AV49. The efficiency of adsorption of AV49 from aqueous solution was investigated through a series of batch experiments by using CoFe₂O₄/NOAC. The batch adsorption experiments showed the efficient removal on CoFe₂O₄/NOAC under optimum conditions such as pH 6.5, contact time-55 min and adsorbent dosage-50 mg. Adsorption kinetics—Pseudo first order and second order, Isotherms—Langmuir and Freundlich have been adapted to analyze the adsorption capacity. The results showed that the adsorption followed the pseudo second order kinetics and Langmuir isotherm equation is the best to describe the adsorption process. According to the thermodynamic study, it was very effective at higher temperatures also. The thermodynamic parameters ?G^o, ?H^o and ?S^o were also evaluated for this adsorption.     

Synthesis,spectral analysis,and catalytic activity of poly(aniline‐co‐congored)–metal oxide nanocomposites

Electrically conducting, water‐soluble fluorescent copolymer nanocomposites were synthesized by a solution polymerization method under different experimental conditions in the presence of CuO and V₂O₅ nanoparticles. The prepared copolymer nanocomposites were characterized with analytical tools, including Fourier transform infrared spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, and fluorescence emission spectroscopy. The order of copolymerization was determined on the basis of the UV–vis absorption spectra and fluorescence emission spectra. The copolymer–CuO nanocomposite system exhibited the highest electrical conductivity. The scanning electron microscopy image showed the presence of more CuO nanoparticles on the surface of the copolymer. Furthermore, the catalytic activity of the copolymer nanocomposites was tested for the reduction of p‐nitrophenol. All three types of polymer systems exhibited almost the same apparent rate constant values. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46469.     

Effect of Cesium Aluminate Nanofiller on Optical Properties of Polyvinyl Pyrrolidone Nanocomposite Films

The nanocomposite films of poly vinylpyrrolidone (PVP) with different amounts viz., 2, 4, 6 and 8?wt% of cesium aluminate (CsAlO₂) have been fabricated using solvent casting technique. The effect of nanofiller content on the optical properties of PVP/CsAlO₂ nanocomposite films has been established by UV-visible spectroscopy. The UV-visible transmittance studies revealed that the UV light absorbing nature of nanocomposite films with considerable visible transparency. The Fourier Transform Infrared (FTIR) spectral studies visualizes the effect of CsAlO₂ nanofiller on the structural behaviors of PVP, while optical studies reveals an obvious change in the electronic band structure leading to a significant reduction in optical band gaps. The scanning electron microscopic (SEM) studies establish the morphological changes in PVP matrix upon doping with CsAlO₂. The measured refractive index (RI) depends on the volume fraction of CsAlO₂ nanofiller and the result indicates that a substantial increase of RI values from 1.85 to 2.64 at wave length 360 nm. The dielectric studies, optical conductivity measurements and Urbach energy analysis also supports the dopant dependent optical property, tuning of PVP/CsAlO₂ nanocomposite films to enable effective material property engineering to suit specified application requirements.     

A complexity perspective on entailment of parameterized linear constraints

Extending linear constraints by admitting parameters allows for more abstract problem modeling and reasoning. A lot of focus has been given to conducting research that demonstrates the usefulness of parameterized linear constraints and implementing tools that utilize their modeling strength. However, there is no approach that considers basic theoretical tools related to such constraints that allow for reasoning over them. Hence, in this paper we introduce satisfiability with respect to polyhedral sets and entailment for the class of parameterized linear constraints. In order to study the computational complexities of these problems, we relate them to classes of quantified linear implications. The problem of satisfiability with respect to polyhedral sets is then shown to be co- $\mathbb{NP}$ hard. The entailment problem is also shown to be co- $\mathbb{NP}$ hard in its general form. Nevertheless, we characterize some subclasses for which this problem is in ?. Furthermore, we examine a weakening and a strengthening extension of the entailment problem. The weak entailment problem is proved to be $\mathbb{NP}$ complete. On the other hand, the strong entailment problem is shown to be co- $\mathbb{NP}$ hard.