A Parametric study of gas sensing response of ZnO nanostructures and carbon nanotubes

Solid state chemical sensors are gaining popularity and finding extensive use in process control, environmental monitoring and residential safety. ZnO, a semiconducting metal oxide, and carbon nanotubes (CNTs) have attracted great interest over the years for their sensitivity to a variety of gases. Nanostructured sensing materials, such as nanowires, nanotubes and quantum dots offer an inherently high surface area, thus reducing operating temperatures and increasing sensitivity to low concentrations of analytes. In this work, ZnO nano-structures and CNTs have been tested as chemical sensors and a detailed study on the effect of different process parameters such as temperature, carrier gas flow, inter-electrode spacing, gas concentration and material properties on gas sensitivity is presented. Initial ZnO nanoparticles were prepared by a simple solution chemical process and characterized by Secondary Electron Microscopy (SEM) and Brunauer, Emmet and Teller (BET) Sorptometer to demonstrate the morphology and surface area respectively. The gas sensor platforms consisted of Pt inter-digitated fingers with a spacing of 10 μm. The sensor platform was dip-coated with ZnO nano-platelets suspended in terpineol to form a uniform film. Sensing was performed in a closed quartz chamber where, high purity N2 and dry industrial air were used as carrier and recovery gas respectively. Sensitivity of nano-platelets and porous films was measured for different concentrations of the analyte (H2). High response was observed at room temperature for H2 gas with sensitivities in excess 80% for 60ppm and about 55% for 80ppm of H2 gas at room temperature was observed for the nano-platelets and the porous films respectively. High sensitivity of the sensor at low temperatures is attributed to both the increased surface area of the porous ZnO nano-platelets and the presence of a Pt catalyst. Measurements at higher temperatures (150 °C) show even higher sensitivities, near 96% for a 20 ppm H2 concentration. Sensitivity with different gases and organic solvents was also measured at operating temperatures of 200oC. Values on the order of 60%, 42% and 29% for 315 PPM of CO, O2 and NH3 whereas sensitivity values of 77.76%, 70.26% and 38.43% for C2H5OH, CH3OH and H2O were recorded for concentration values approximating 500 PPM. The sensors depict incomplete recovery of resistance at room temperature. This effect is possibly due to the traces of elemental Zn in the material, which were not oxidized at the time of recovery. However, this effect was not observed at higher temperatures. Designed experiments conducted to understand effects of various device and process parameters show negative dependence of spacing on sensitivity with maximum effect of applied bias for lower concentration values. The sensitivity of the sensor was also recorded to increase with the increase in the number of electrodes. Higher sensitivity values nearing 70% were achieved with 30 IDEs for 60 PPM H2 when compared to 60% for 60 PPM of H2 with 20 IDEs. Interaction effects were observed and implemented to understand and model the behavior of the gas sensor. Sensitivity of arc produced CNTs was measured to various gases and organic solvents. Values on the order of 24% were observed at 80 PPM CO as compared to values of sensitivity about 15% for O2 and 3% for H2. Also, sensitivity value of 15% was measured for as low as 4 PPM of DMA which suggests the capability of PPB levels of DMA using CNTs. A brief comparison of sensitivity values achieved for ZnO nano-platelets and CNTs with similar analytes was also presented. Sensitivity to different analytes was measured using impedance spectroscopy for HiPCo produced SWCNT network. For experiments conducted with varying exposure time, sensitivity values nearing 6% for 0.01% (100 PPM) DMA for an exposure time of 25 minutes were recorded. Sensitivity values recorded for other solvents were 16.74%, 10.98%, 7.97%, 6.96% and 4.28% for concentration levels of 2.04%, 4.02%, 2.04%, 14% and 6.05% of NH3, IPA, CO, CH3OH and C2H5OH respectively. For experiments with varying concentration values of different analytes, higher response was observed for gaseous analytes. Results on the order of 15.27% and 3.82% were recorded for as low as 0.18% of both NH3 and CO. For the organic solvents, values approximating 2.64%, 2.36% and 0.10% for concentration levels of 0.29%, 0.92% and 0.42% of IPA, CH3OH and C2H5OH respectively. Results obtained with HiPCo produced SWCNT network at room temperature were comparable to the values of sensitivity shown by other researchers. Our future works entails correlating the sensitivity of the gas sensors to the material properties in addition to the device and the process parameters, with further development in methods for fabricating gas sensors and improvement in the selectivity of the sensor. For CNT based sensors, using as-grown multiwall carbon-nanotubes MWCNTs for gas sensor fabrication would be the next step in this research. In addition to developing standard fabrication techniques, further research is required for improving selectivity for different gases and organic solvents by decorating or filling CNTs with metal nano-particles or different groups of organic molecules. Also, future work will be focused to correlate sensitivity of HiPCo produced SWCNTs, Laser ablated SWCNTs and MWCNTs to their material properties

Interactive Proof Systems

The report is a compilation of lecture notes that were prepared during the course ``Interactive Proof Systems'' given by the authors at Tata Institute of Fundamental Research, Bombay. These notes were also used for a short course ``Interactive Proof Systems'' given by the second author at MPI, Saarbruecken. The objective of the course was to study the recent developments in complexity theory about interactive proof systems, which led to some surprising consequences on nonapproximability of NP hard problems. We start the course with an introduction to complexity theory and covered some classical results related with circuit complexity, randomizations and counting classes, notions which are either part of the definitions of interactive proof systems or are used in proving the above results. We define arthur merlin games and interactive proof systems, which are equivalent formulations of the notion of interactive proofs and show their equivalence to each other and to the complexity class PSPACE. We introduce probabilistically checkable proofs, which are special forms of interactive proofs and show through sequence of intermediate results that the class NP has probabilistically checkable proofs of very special form and very small complexity. Using this we conclude that several NP hard problems are not even weakly approximable in polynomial time unless P = NP

Descriptive Complexity of #P Functions

AbstractWe give a logic-based framework for defining counting problems and show that it exactly captures the problems in Valiant′s counting class #P. We study the expressive power of the framework under natural syntactic restrictions and show that some of the subclasses obtained in this way contain problems in #P with interesting computational properties. In particular, using syntactic conditions, we isolate a class of polynomial time computable #P problems and, also, a class in which every problem is approximable by a polynomial time randomized algorithm. These results set the foundation for further study of the descriptive complexity of the class #P. In contrast, we show, under reasonable complexity theoretic assumptions, that it is an undecidable problem to tell if a counting problem expressed in our framework is polynomial time computable or if it is approximable by a randomized polynomial time algorithm. Finally, we discuss some open problems which arise naturally from this work

A Common Fixed Point Theorem for Two Random Operators using Random Mann Iteration Scheme

Abstract: In this paper, we proved that if a random Mann iteration scheme is defined by two random operators is convergent under some contractive inequality the limit point is a common fixed point of each of two random operators in Banach space. Keywords: Mann iteration, fixed point, measurable mappings, Banach space. AMS Subject Classification: 47H10, 47H40

Strong Convergence Theorems for Strictly Asymptotically Pseudocontractive Mappings in Hilbert Spaces

We propose a new (CQ) algorithm for strictly asymptotically pseudo-contractive mappings and obtain a strong convergence theorem for this class ofmappings in the framework of Hilbert spaces.DOI : http://dx.doi.org/10.22342/jims.16.1.29.25-3

An Implicit Algorithm for a Family of Total Asymptotically Nonexpansive Mappings in CAT(0) Spaces

In this paper, we establish some strong convergence theorems of an implicit algorithm for a finite family of of total asymptotically nonexpansive mappings in the setting of CAT(0) spaces. Our results extend and generalize several recent results from the current existing literatures (see, e.g., [2, 9, 14, 16, 17, 25, 29])

Inhibition of Human Cervical Cancer Cell Growth by Ethanolic Extract of Boerhaavia diffusa Linn. (Punarnava) Root

In Indian traditional medicine, Boerhaavia diffusa (punarnava) roots have been widely used for the treatment of dyspepsia, jaundice, enlargement of spleen, abdominal pain and as an anti-stress agent. Pharmacological evaluation of the crude ethanolic extract of B. diffusa roots has been shown to possess antiproliferative and immunomodulatory properties. The extract of B. diffusa was studied for anti-proliferative effects on the growth of HeLa cells and for its effect on cell cycle. Bio-assays of extracts from B. diffusa root showed that a methanol : chloroform fraction (BDF 5) had an antiproliferative effect on HeLa cells. After 48 h of exposure, this fraction at a concentration of 200 μg mL−1 significantly reduced cell proliferation with visible morphological changes in HeLa cells. Cell cycle analysis suggests that antiproliferative effect of BDF 5 could be due to inhibition of DNA synthesis in S-phase of cell cycle in HeLa cells, whereas no significant change in cell cycle was detected in control cells. The fraction BDF 5 caused cell death via apoptosis as evident from DNA fragmentation and caspase-9 activation. Thus the extract has potential to be evaluated in detail to assess the molecular mechanism-mediated anticancer activities of this plant

Influence of key polymer attributes, manufacturing conditions and sintering on abuse deterrence of physical barrier type abuse deterrent formulations (ADF)

When sintering us used to treat tablet formulations containing polyethylene oxide (PEO), the polymer particles are able to form stronger bonds thereby increase tablet tensile strength. This increase in strength can make it more difficult for an abuser to break, chew, or grind opioid tablets. A mechanistic study was implemented to understand the key sintering factors that influence tensile strength

Predicting and grading the degree of difficulty of cochlear implant surgery by evaluating temporal bone using high resolution computed tomography and magnetic resonance imaging

Background: The current study was designed to assess the challenges that arise during cochlear implantation. Hence imaging based grading system, using a structured, 12-point scoring chart was developed with an aim to assess various anatomical factors of temporal bone helpful in contemplating complications involved in surgery and to assess various congenital and acquired abnormalities if detected during scan which can affect cochlear implant surgery.Methods: This was a descriptive study done on 60 patients with sensorineural hearing loss. They were evaluated preoperatively by using HRCT and MRI findings and subsequently underwent cochlear implantation. A 12-point scoring chart was developed based on imaging findings. Surgical times were noted in each case and each imaging point on the scoring chart was correlated with the surgical times.Results: Eleven out of 12 points in the scoring chart proved to be statistically significant in predicting the degree of difficulty of the surgical procedure. One point was not correlating with the surgical timings. Based on the grading system, in the present study, there were 37 patients (61.66%) classified as Grade 1, 16 patients (26.67%) classified as Grade 2 and 7 patients (11.67%) classified as Grade 3.Conclusions: These radiological image findings and its related grading system are relatively easy and quick to assess on readily available pre-operative temporal bone CT scan and MRI. They can form a pre-operative checklist that provides a formalized approach for the surgeons and, in particular surgical trainees, predict and, thus prepare for, potentially challenging cochlear implant cases