Direct detection and time-locked subsampling applied to pulsed electron paramagnetic resonance imaging

The application of direct time-locked subsampling (TLSS) to Fourier transform electron paramagnetic resonance (FT-EPR) spectroscopy at radio frequencies (rf) is described. With conventional FT-EPR spectroscopy, the high Larmor frequencies (L(f)) often necessitate the use of intermediate frequency (IF) stages to down convert the received free induction decay (FID) signal to a frequency that can be acquired with common data acquisition technology. However, our research focuses on in vivo studies, and consequently utilizes a FT-EPR system with a L(f) of 300 MHz. This relatively low frequency L(f), in conjunction with the advent of bandpass sampling analog-to-digital conversion and signal processing technologies, has enabled us to omit the IF stage in our FT-EPR system. With this in mind, TLSS techniques have been developed to directly sample the 300 MHz FID signal at a sampling rate of 80 MHz providing a signal bandwidth of 20 MHz. The required modifications to the data acquisition and processing system specific to this application are described. Custom software developed to control the EPR system setup, acquire the signals, and post process the data, is outlined. Data was acquired applying both coherent averaging and stochastic excitation sequences. The results of these experiments demonstrate digital down conversion of the 300 MHz FID signal to quadrature baseband. Direct FID TLSS eliminates many noise sources common in EPR systems employing traditional analog receiver techniques, such as the IF mixer stage in single channel systems, and the quadrature baseband mixer stage in dual channel systems.     

Interaction of nafion ionomers toward various solvents

Interactions of Nafion (Naf) ionomer with water, aqueous ethanol (EA), aqueous isopropyl alcohol (IPA), and aqueous ammonia were investigated by attenuated total reflectance (ATR)–infrared (IR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and computational modeling studies. Microstructural features by ATR–IR revealed the existence of hydrophilic interaction of Naf with all solvents. The Naf membranes formed hydrogen bonds with water, aqueous EA, and IPA. The incorporation of solvents on the Naf matrix impaired the crystallinity, which was highest in the case of IPA. Of all the microsolvated structures of Naf investigated, the formation of H₃O⁺ ions was evident; in addition, H₅O₂⁺ ions appeared in the alcohol–water mixture, and NH₄⁺ ions were observed in the water–ammonia mixture along with a direct ion pair with the SO₃^? group in Naf. Theoretical studies based on computational modeling disclosed that the interchain distance increased with enhanced interactions (hydrophobic interactions in particular), and this was in good agreement with the highest swelling ratio of the Naf membrane in aqueous IPA and EA solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ferritic steels for sodium-cooled fast reactors: Design principles and challenges

An overview of the current status of development of ferritic steels for emerging fast reactor technologies is presented in this paper. The creep-resistant 9–12Cr ferritic/martensitic steels are classically known for steam generator applications. The excellent void swelling resistance of ferritic steels enabled the identification of their potential for core component applications of fast reactors. Since then, an extensive knowledge base has been generated by identifying the empirical correlations between chemistry of the steels, heat treatment, structure, and properties, in addition to their in-reactor behavior. A few concerns have also been identified which pertain to high-temperature irradiation creep, embrittlement, Type IV cracking in creep-loaded weldments, and hard zone formation in dissimilar joints. The origin of these problems and the methodologies to overcome the limitations are highlighted. Finally, the suitability of the ferritic steels is re-evaluated in the emerging scenario of the fast reactor technology, with a target of achieving better breeding ratio and improved thermal efficiency.     

Analysis of multistage M[X]/GK/1 queue with different server’s interruptions and its application in energy consumption

ABSTRACT

In this paper, we consider multistage batch arrival, batch service (fixed batch size) queue having multiple vacation policy subject to server breakdown with the delayed repair. In addition, the server may extend the vacation at each vacation completion points and the server may renege during vacation and breakdown periods. Using the supplementary variable technique, transient and its corresponding steady-state solutions are derived. The results obtained are comprehended by using a numerical example.     

Dazzling cool white light emission from Ce3+/Sm3+ activated LBZ glasses for W-LED applications

We synthesized a batch of co-doped (Ce³⁺+Sm³⁺): LBZ glass specimens by melt quenching process and their structural and radiation properties were studied by employing XRD, FE-SEM, optical absorption, photoluminescence and lifetime measurements. UV–Vis–NIR absorption studies of the co-doped (Ce³⁺+Sm³⁺): LBZ glassy matrix displays pertinent bands of both Ce³⁺ and Sm³⁺ ions. Individually doped Sm³⁺: LBZ glass exhibit bright orange emission at 603?nm (⁴G_5/2 → ⁶H_7/2) under the excitation of 403?nm. Nevertheless, the luminescence intensities pertaining to Sm³⁺ were extraordinarily increased by co-doping with Ce³⁺ ions to Sm³⁺: LBZ glassy matrices because of energy transfer from Ce³⁺ to Sm³⁺. The fluorescence spectra of co-doped (Ce³⁺+Sm³⁺): LBZ exhibits characteristic emission bands of Ce³⁺ (441?nm, blue) and Sm³⁺ (603?nm, reddish orange) under the excitation of 362?nm. Decay curves of Ce³⁺ and Sm³⁺ ions in co-doped glass has been fitted to double exponential nature. The decreasing lifetime of donor ion and rising lifetime of acceptor ion in double doped glass could support the energy transfer from Ce³⁺ to Sm³⁺ ions in the host matrix. The CIE coordinates and CCT values were calculated for all the obtained co-doped glassy samples from their luminescence spectra. By adding Ce³⁺ ions to individually doped Sm³⁺: LBZ glass matrix, the emitting color changes from reddish orange to white light which resembles the energy transfer from Ce³⁺ to Sm³⁺ ions. These studies, perhaps implied that attained co-doped (Ce³⁺+Sm³⁺): LBZ glassy samples are potential materials for white lighting appliances.     

A misdirected route avoidance using random waypoint mobility model in wireless sensor network

Wireless Networks - In this paper, a novel method is proposed to reduce the number of route misdirection to increase network throughput. This method increases the network throughput by accurately...     

Effects of compressibility and transition to turbulence on flow through microchannels

A detailed experimental study of flow through long microchannels of hydraulic diameter ranging from 60.5 to 211 μm has been carried out. The internal pressure distribution along the length of the channel has been measured to analyze the local flow behaviour. The effects of compressibility and transition to turbulence occurring in the microchannel flow were investigated in detail. In addition, the resulting flow has been analyzed numerically using a commercially available CFD code, FLUENT. It has been shown that there are no special micro-scale effects, including early transition to turbulence at least in the present range of hydraulic diameters after the significant effects of compressibility are accounted appropriately.     

A matrix isolation FTIR investigation of laser-ablated uranium oxide in argon and nitrogen matrices

Uranium oxide was laser-ablated using the second harmonic of a Nd : YAG laser, and the products studied after trapping them in Ar and N₂ matrices. The species obtained in the Ar matrix were UO, UO₂ and UO₃, which represent the primary products of laser ablation. Charge transfer complexes, (UO ₂ ⁺ ) (O ₂ ⁻ ) and (UO ₂ ²⁺ )(O ₂ ²⁻ ) were also observed. In the N₂ matrix, in addition to the primary ablation products, reaction products with nitrogen were also observed; the prominent among them being UN₂ and NUO, together with their complexes with N₂. Charge transfer complexes were also seen in these experiments. Features due to NO, N₃ and N ₃ ⁻ were identified, which clearly point to the role of nitrogen in these reactions.     

Variant selection during nucleation and growth of γ-massive phase in TiAl-based intermetallic alloys

This work deals with the mechanisms of nucleation and growth of γ-massive phase in TiAl-based intermetallic alloys. In particular, it focuses on the process of variant selection operating at both stages of the transformation. Small γ-massive domains produced by rapid cooling are extensively characterized by high-resolution electron backscatter diffraction. This large data set allows a statistical analysis of nucleation sites, according to different crystallographic configurations. It is established that, whatever the nucleation sites, i.e., grain boundaries or triple junctions, a coherent facet is always found presenting a Blackburn orientation relationship (BOR) between the γ nucleus and the α parent grain. Moreover, some γ nuclei can additionally present another semicoherent facet with an approximate BOR with the α host grain. A new nucleation mechanism, called “co-nucleation”, is highlighted for this type of double-faceted nucleus. Variant selection during nucleation is discussed for both types of nuclei, in terms of minimization of interface energy. In addition, it is shown that growth of γ-massive domains from their initial nucleus always involves successive {1 1 1} twinning. Variant selection also occurs either at the nucleus growth stage or during the development of successive twin generations, and is discussed in terms of interphase boundary mobility.