[en] The focus of this work was to develop thermally stable and mechanically strong polymer blend / composite systems for certain high impact applications. Two different commercially available polymers Polyamide (Nylon 6) and Polycarbonate (PC) were selected for this purpose. In order to improve the thermal and mechanical properties of Nylon, organically Modified clay was incorporated in the thermo-plastic matrix material. The uniform distribution and dispersion of clay was achieved by optimizing various parameters like temperature, time of mixing, torque during flush and cycle mode of operation of the co- rotating conical twin screw mini-extrusion machine. Duration of ten minutes under cycle mode at 250 degree C was found to be optimum for uniform exfoliation and distribution of organically modified clay platelets in the matrix. For the development of polycarbonate (PC) based nanocomposites with improved thermal and mechanical properties, Polymethylmethacrylate (PMMA) was blended in 5, 10 and 15 wt. % ratios with PC. Good miscibility in PC/PMMA blends was observed by melt blending them at 260 degree C for 20 minutes. The properties of the blends were further enhanced by incorporating 0.1, 0.2 and 0.3 wt. % of both pristine and carboxylic group (-COOH) functionalized carbon nanotubes (CNTs). While maintaining PC/PMMA blending ratios as 95/5 and 90/10, shear mixing of CNTs in the blend was carried out in the co-rotating conical twin screw extruder at 260 degree C for 20 minutes. Characterization of these composites was performed using FTIR, XRD, Dynamic thermo-mechanical analysis (DTMA) and mechanical testing using universal testing machine. The TMA and XRD results exhibited formation of miscible blends of PC/PMMA when melt blending is performed at 260 degree C for 20 minutes. Although miscible blends were achieved by incorporating up to 15 wt.% PMMA in PC, however, only the combination in 90/10 ratio of PC/PMMA and their composites were found to have high thermal stability and mechanical properties. Some lowering in the value of storage modulus was also noted that actually lowered due to incorporation of PMMA which was added to improve the toughness of polymer blend, was regained by inclusion of CNTs as reinforcing agent. The overall improvement in the properties was observed in pristine CNTs based composites. (author)

[en] A new generating function for the harmonic oscillator spherical basis is constructed from the Laguerre polynomials and spherical harmonics generating functions. Recurrence relations of interest for calculating the Talmi coefficients are discussed. A new expression for the Talmi-Moshinsky coefficients is presented. New relations which are useful from a practical point of view, between Talmi-Moshinsky coefficients are established

[en] We present a new approach for determining the Weyl invariants of unitary groups. Such an approach is based on the generating function of the basis of the representation fort unitary groups built in an earlier work. We obtain two expressions for the Weyl invariants, both including the parameters involved in the generating function. Coupling coefficients appear in one of the expressions. The comparison of the development of the two expressions allow the calculation of the coupling coefficients. The application of this approach to the calculation of the coupling coefficients for the direct product [lambda₁0] x [lambda₂μ₂] of SU (3) leads to an expression of the isoscalar factor where no summation occurs in contradistinction with the known expression for the coupling coefficients which involve five summation

[en] We construct the generating function of the Gel'fand basis for unitary as well as representation matrix elements. From these functions, we obtain via simple calculus, both the basis vectors and the representation matrix elements in the Gel'fand basis. The generating functions are obtained from two differents methods: the first one takes advantages of a property of the generating function showed in this paper and the second one, uses recurrence calculus for the chain GL(1,c) is contained in GL(2,c) is contained in ... is contained in GL(n,c)

[en] The method is developed and applied to the determination of Talmi's and Moshinsky-Smirnov's coefficients and to a study of the generating function of the Weyl invariants of SU(N) and of quasi-bosons developments

[en] Concerns have been raised in the literature on the suitability of time-independent methodologies (e.g., fault trees) for the reliability modeling of closed-loop control systems (CLCS), such as those used in nuclear power plants to maintain reactor vessel pressure and water level within allowed ranges. This paper (a) describes a methodology that utilizes CLCS simulator data for accurate dynamic reliability model construction and (b) illustrates the implementation of the methodology for the interval reliability analysis of high-pressure core spray system cooling of a boiling water reactor core following a small loss-of-coolant accident. The methodology is based on the modification of a dynamic modeling approach proposed earlier

[en] Age related degradation of nuclear power plant components and systems are of considerable concern because of the impact of such aging on plant safety. This paper presents the developments made in prioritizing and determining risk significance of aging and in the analyses of the light water reactor (LWR) operating data to quantify such effects. The approach developed to evaluate risk effects due to component and structural aging uses a probabilistic risk analysis (PRA) and component aging models. Linear and nonlinear aging behavior have been incorporated. Aging occurring after some minimum time, known as threshold, can also be handled. As an important part of the evaluations, maintenance and surveillance strategies can be explicitly evaluated to determine their effectiveness in controlling aging impacts on system unavailability, core melt frequency and public risk. Both point evaluations and uncertainty evaluations can be carried out, and detailed contributors to the aging effects can be identified and prioritized. For the applications, two NUREG 1150 PRAs, one pressurized-water reactor (PWR) and one boiling-water reactor (BWR), were used to calculate the average increase in core melt frequency due to aging of active components when a specific maintenance and surveillance program was employed. A NUREG has been issued (NUREG/CR-5510) detailing the methodology and the applications performed

[en] In this report, we present a screening study to identify environmental stressors for digital instrumentation and control (I ampersand C) systems in a nuclear power plant (NPP) which can be potentially risk-significant, and compare the hardware unavailability of such a system with that of its existing analog counterpart. The stressors evaluated are temperature, humidity, vibration, radiation, electro-magnetic interference (EMI), and smoke. The results of risk-screening for an example plant, subject to some bounding assumptions and based on relative changes in plant risk (core damage frequency impacts of the stressors), indicate that humidity, EMI from lightning, and smoke can be potentially risk-significant. Risk from other sources of EMI could not be evaluated for a lack of data. Risk from temperature appears to be insignificant as that from the assumed levels of vibrations. A comparison of the hardware unavailability of the existing analog Safety Injection Actuation System (SIAS) in the example plant with that of an assumed digital upgrade of the system indicates that system unavailability may be more sensitive to the level of redundancy in elements of the digital system than to the environmental and operational variations involved. The findings of this study can be used to focus activities relating to the regulatory basis for digital I ampersand C upgrades in NPPs, including identification of dominant stressors, data-gathering, equipment qualification, and requirements to limit the effects of environmental stressors. 30 refs., 8 figs., 26 tabs

No abstract available

[en] This work shows how easy one can deal with a huge number of gamma spectra. The method can be used for radiation monitoring. It is based on the macro feature of the windows XP connected to QBASIC software. The routine was used usefully in generating accurate results free from human errors. One hundred measured gamma spectra were fully analyzed in 10 minutes using our fast and automated method controlling the Genie 2000 gamma acquisition analysis software.