Microstructure and Magnetic Properties of Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> Thin Films Prepared by Flash Evaporation Technique

An effort was made to develop semiconductor oxide-based room temperature dilute magnetic semiconductor (DMS) thin films based on wide band gap and transparent host lattice with transition metal substitution. The Sn\(_{\mathrm {1}-x}\)Ni\(_{x}\textit {O}_{\mathrm {2}}\) (\(x\,= \mathrm {0.00, 0.03, 0.05, 0.07, 0.10, and \,0.15}\)) thin film samples were prepared on glass substrates by flash evaporation technique. All the samples were shown single phase crystalline rutile structure of host SnO\(_{\mathrm {2}}\) with dominant (110) orientation. The Ni substitution promotes reduction of average crystallite size in SnO\(_{\mathrm {2}}\) as evidenced from the reduction of crystallite size from 40 (SnO\(_{\mathrm {2}}\)) to 20 nm (Sn\(_{\mathrm {0.85}}\)Ni\(_{\mathrm {0.15}}\textit {O}_{\mathrm {2}}\)). In the energy dispersive spectra as well as X-ray photoelectron spectra of all the samples show, the chemical compositions are close to stoichiometric with noticeable oxygen deficiency. The crystalline films were formed by coalescence of oval-shaped polycrystalline particles of 100 nm size as evidenced from the electron micrographs. The energy band gap of DMS films decreases from 4 (SnO\(_{\mathrm {2}}\)) to 3.8 eV (x \(=\) 0.05) with increase of Ni content. The magnetic hysteresis loops of all the samples at room temperature show soft ferromagnetic nature except for SnO\(_{\mathrm {2}}\) film. The SnO\(_{\mathrm {2}}\) films show diamagnetic nature and it converts into ferromagnetic upon substitution of 3 % Sn\(^{\mathrm {4+}}\) by Ni\(^{\mathrm {2+}}\). The robust intrinsic ferromagnetism (saturation magnetization, 21 emu/cm\(^{\mathrm {3}}\)). Further increase of Ni content weakens ferromagnetic strength due to Ni-O antiferromagnetic interactions among the nearest neighbour Ni ions via O\(^{\mathrm {2-}}\) ions. The observed magnetic properties were best described by bound magnetic polarons model.     

Simulating perfect channels with probabilistic lossy channels

We consider the problem of deciding whether an infinite-state system (expressed as a Markov chain) satisfies a correctness property with probability 1. This problem is, of course, undecidable for general infinite-state systems. We focus our attention on the model of probabilistic lossy channel systems consisting of finite-state processes that communicate over unbounded lossy FIFO channels. Abdulla and Jonsson have shown that safety properties are decidable while progress properties are undecidable for non-probabilistic lossy channel systems. Under assumptions of “sufficiently high” probability of loss, Baier and Engelen have shown how to check whether a property holds of probabilistic lossy channel system with probability 1. In this paper, we consider a model of probabilistic lossy channel systems, where messages can be lost only during send transitions. In contrast to the model of Baier and Engelen, once a message is successfully sent to channel, it can only be removed through a transition which receives the message. We show that checking whether safety properties hold with probability 1 is undecidable for this model. Our proof depends upon simulating a perfect channel, with a high degree of confidence, using lossy channels.     

Characterization of Fly Ash Sources in the Synthesis of Geopolymer

Silicon - Fly ash (FA) based geopolymers are affected by the reactive nature of FA, concentration and quantity of alkali activators and the curing conditions. However, for the geopolymer...     

A formal methods approach to medical device review

With software playing an increasingly important role in medical devices, regulatory agencies such as the US Food and Drug Administration need effective means for assuring that this software is safe and reliable. The FDA has been striving for a more rigorous engineering-based review strategy to provide this assurance. The use of mathematics-based techniques in the development of software might help accomplish this. However, the lack of standard architectures for medical device software and integrated engineering-tool support for software analysis make a science-based software review process more difficult. The research presented here applies formal modeling methods and static analysis techniques to improve the review process. Regulation of medical device software encompasses reviews of device designs (premarket review) and device performance (postmarket surveillance). The FDA's Center for Devices and Radiological Health performs the premarket review on a device to evaluate its safety and effectiveness. As part of this process, the agency reviews software development life-cycle artifacts for appropriate quality-assurance attributes, which tend to reveal little about the device software integrity.     

A case study on applying formal methods to medical devices: computer-aided resuscitation algorithm

The design and functional complexity of medical devices have increased during the past 50 years, evolving from the use of a metronome circuit for the initial cardiac pacemaker to functions that include electrocardiogram analysis, laser surgery, and intravenous delivery systems that adjust dosage based on patient feedback. As device functionality becomes more intricate, concerns arise regarding efficacy, safety, and reliability. It thus becomes imperative to adopt a standard or methodology to ensure that the possibility of any defect or malfunction in these devices is minimized. It is with these facts in view that regulatory bodies are interested in investigating mechanisms to certify safety-crictical medical devices. These organizations advocate the use of formal methods techniques to evaluate safety-critical medical systems. However, the use of formal methods is keenly debated, with most manufacturers claiming that they are arduous and time consuming.In this paper we describe our experience in analyzing the requirements documents for the computer-aided resuscitation algorithm (CARA) designed by the Resuscitative Unit of the Walter Reed Army Institute of Research (WRAIR). We present our observations from two different angles – that of a nonbeliever in formal methods and that of a practitioner of formal methods. For the former we catalog the effort required by a novice user of formal methods tools to carry out an analysis of the requirements documents. For the latter we address issues related to choice of designs, errors in discovered requirements, and the tool support available for analyzing requirements .     

Suprathreshold intrinsic dynamics of the human visual system

Intrinsic high-frequency neural activities have been observed in the visual system of several species, but their functional significance for visual perception remains a fundamental puzzle in cognitive neuroscience. Spatiotemporal integration in the human visual system acts as a low-pass filter and makes the psychophysical observation of high-frequency activities very difficult. A computational model of retino-cortical dynamics (RECOD) is used to derive experimental paradigms that allow psychophysical studies of high-frequency neural activities. A reduced-parameter version of the model is used to quantitatively relate psychophysical data collected in two of these experimental paradigms. Statistical analysis shows that the model's account of the variance in the data is, in general, highly significant. We suggest that psychophysically measured oscillations reflect intrinsic neuronal oscillations observed in the visual cortex.     

High-performance bottom electrode organic thin-film transistors

Pentacene-based organic field effect transistors (FETs) exhibit enormous potential as active elements in a number of applications. One significant obstacle to commercial application remains: no completely lithographic process exists for forming high-performance devices. Processing constraints prevent electrodes from being lithographically patterned once the semiconductor is deposited, but depositing the electrodes before the semiconductor leads to low-performance transistors. By using self-assembled monolayers (SAMs) to change the surface energy of the metal electrodes and morphology of the pentacene subsequently grown on the electrodes, high-performance transistors may be formed using a process compatible with lithographic definition of the source and drain electrodes     

Structural,linear and nonlinear optical,electrical and NBO reports on 4-aminopyridine-1-ium 4-aminobenzoate single crystal for SHG,optoelectronics and violet laser emission applications

Good quality NLO single crystal 4-aminopyridine-1-ium 4-aminobenzoate (4AP4AB) were grown by slow evaporation method. The Single crystal XRD analysis shows that the 4AP4AB compound belongs to the monoclinic system with non-centrosymmetric group C. Further, the molecular structure and vibrational assignments of the grown crystal were analysed by NMR and Fourier transform infrared (FT-IR) analysis. NBO analysis analysed inter and intramolecular interactions. Optical and thermal stabilities have been characterized by UV–Visible and DSC analysis. Linear optical parameters of the 4AP4AB crystal were quantified and listed by UV–visible study. Vicker's microhardness test at room temperature shows that the hardness number increases with increasing the load. The laser damage threshold (LDT) energy has been measured using an Nd:YAG laser. The impedance analysis recorded the dielectric response of the grown 4AP4AB crystal. The appearance of semicircle in Cole–Cole plot represents the dielectric relaxation and resistivity of the 4AP4AB crystal. Solid-state parameters of 4AP4AB were quantified and listed for the theoretical approaches.

     

Cure characteristics and mechanical properties of short nylon fiber‐reinforced nitrile rubber composites

Acrylonitrile butadiene rubber (NBR)‐based composites were prepared by incorporating short nylon fibers of different lengths and concentration into the matrix using a two‐roll mixing mill according to a base formulation. The curing characteristics of the samples were studied. The influence of fiber length, loading, and rubber crosslinking systems on the properties of the composites was analyzed. Surface morphology of the composites has been studied using Scanning Electron Microscopy (SEM). Addition of nylon fiber to NBR offers good reinforcement, and causes improvement in mechanical properties. A fiber length of 6 mm was found to be optimum for the best balance of properties. It has been found that at higher fiber loadings, composites show brittle‐type behavior. Composites vulcanized by the dicumyl peroxide (DCP) system were found to have better mechanical properties than that by the sulfur system. The swelling behavior of the composites in N,N‐dimethyl formamide has been analyzed for the swelling coefficient values. Composites vulcanized in the DCP system were found to have higher rubber volume fraction than that in the sulfur system, which indicates better rubber–fiber interaction in the former. The crosslink densities of various composites were also compared. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1023–1030, 2004