An Acoustic Emission Technique for Monitoring the Liquefied Natural Gas Cargo Tank

Increase in the market of supersized LNG (Liquefied Natural Gas) vessel, with doubled walled cargo tanks, has led to concerns regarding their safe operations. If both the primary and secondary wall of the cargo tank fails simultaneously, the hull of the vessel can be exposed to the LNG’s. This has the potential to cause brittle failure of the hull structure. This research presents a new Acoustic Emission (AE) technique that can be implemented to monitor the structural condition of the primary wall in the LNG cargo tank. The presented technique is able to provide information regarding critical damage so that appropriate maintenance can be carried out to avoid catastrophic failure. Acoustic Emission (AE) is a passive Non-Destructive Testing (NDT) technique, employed to identify critical damage in structures before failure can occur. Currently, AE monitoring is carried out by calculating the features of the waveform received by the AE sensor. User defined settings (i.e. timing and threshold) in the AE data acquisition system significantly affects many traditional AE features such as count, energy, centroid frequency, rise-time and duration. In AE monitoring, AE features are strongly related to the damage sources. Therefore, AE features, calculated due to inaccurate user defined acquisition settings can result in inaccurately classified damage sources. The new AE technique presented in this study is based on an AE feature of the waveform, which is independent of some user defined parameter (i.e. timing and threshold) used in the AE data acquisition system, unlike many traditional AE features. The presented AE feature is referred to as AE entropy in this research and is a measure of randomness in the waveform calculated using quadratic Renyi’s entropy. The effectiveness of AE entropy is evaluated by comparing it and traditional AE features under ideal conditions for a range of varying acquisition settings. Unlike the traditional feature, the AE entropy showed no variance with the acquisition settings and was effective in identifying different waveform shapes. The AE entropy was validated through fatigue and tensile tests on coupon specimens of austenitic stainless steel (material of the primary wall). The result suggested that AE entropy is effective in identifying the critical damages in austenitic stainless steel, irrespective of the data acquisition settings. Since AE entropy reduces the human involvement with the data acquisition system and can identify damages, it has the potential to be implemented in the commercial AE data acquisition system

A method for determining catalytic efficiency of surfaces

Catalytic efficiency calculations for surface heat flux and heat transfer during atmospheric reentr

Voluntary Participation in Organizational Decision-Making: A Model and an Experimental Test

This report was adapted from McMahon's doctoral dissertation, written at Michigan State University. It develops a theory and model for disagreement and consensus. This model has some features in common with a decision model by Camilleri, Berger, and Conner (1972). Results for 3 of 4 conditions were as predicted by the model. The technical report discusses some methodological issues of the tests, and suggests areas for further investigation, including studying the process in larger groups specifying the non-linear form of the relation between morale and participation

Permutative conversions in intuitionistic multiary sequent calculi with cuts

This work presents an extension with cuts of Schwichtenberg's multiary sequent calculus. We identify a set of permutative conversions on it, prove their termination and confluence and establish the permutability theorem. We present our sequent calculus as the typing system of the {\em generalised multiary $\lambda$-calculus} lambda-Jm, a new calculus introduced in this work. Lambda-Jm corresponds to an extension of $\lambda$-calculus with a notion of {\em generalised multiary application}, which may be seen as a function applied to a list of arguments and then explicitly substituted in another term. Proof-theoretically the corresponding typing rule encompasses, in a modular way, generalised eliminations of von Plato and Herbelin's head cuts.Fundação para a Ciência e a Tecnologia (FCT)

A calculus of multiary sequent terms

Multiary sequent terms were originally introduced as a tool for proving termination of permutative conversions in cut-free sequent calculus. This work develops the language of multiary sequent terms into a term calculus for the computational (Curry-Howard) interpretation of a fragment of sequent calculus with cuts and cut-elimination rules. The system, named generalised multiary lambda-calculus, is a rich extension of the lambda-calculus where the computational content of the sequent calculus format is explained through an enlarged form of the application constructor. Such constructor exhibits the features of multiarity (the ability of forming lists of arguments) and generality (the ability of prescribing a kind of continuation). The system integrates in a modular way the multiary lambda-calculus and an isomorphic copy of the lambda-calculus with generalised application LambdaJ (in particular, natural deduction is captured internally up to isomorphism). In addition, the system: (i) comes with permutative conversion rules, whose role is to eliminate the new features of application; (ii) is equipped with reduction rules --- either the mu-rule, typical of the multiary setting, or rules for cut-elimination, which enlarge the ordinary beta-rule. This paper establishes the meta-theory of the system, with emphasis on the role of the mu-rule, and including a study of the interaction of reduction and permutative conversions.Fundação para a Ciência e a Tecnologia (FCT

New orbital ephemerides for the dipping source 4U 1323-619: constraining the distance to the source

4U 1323-619 is a low mass X-ray binary system that shows type I X-ray bursts and dips. The most accurate estimation of the orbital period is 2.941923(36) hrs and a distance from the source that is lower than 11 kpc has been proposed. We aim to obtain the orbital ephemeris, the orbital period of the system, as well as its derivative to compare the observed luminosity with that predicted by the theory of secular evolution. We took the advantage of about 26 years of X-ray data and grouped the selected observations when close in time. We folded the light curves and used the timing technique, obtaining 12 dip arrival times. We fit the delays of the dip arrival times both with a linear and a quadratic function. We locate 4U 1323-619 within a circular area centred at RA (J2000)= 201.6543\degree and DEC (J2000)= -62.1358\degree with an associated error of 0.0002\degree, and confirm the detection of the IR counterpart already discussed in literature. We estimate an orbital period of P=2.9419156(6) hrs compatible with the estimations that are present in the literature, but with an accuracy ten times higher. We also obtain a constraint on the orbital period derivative for the first time, estimating $\dot{P}=(8\pm 13)\times 10^{-12}$ s/s. Assuming that the companion star is in thermal equilibrium in the lower main sequence, and is a neutron star of 1.4 M$_{\odot}$, we infer a mass of 0.28$\pm$0.03 M$_{\odot}$ for the companion star. Assuming a distance of 10 kpc, we obtained a luminosity of (4.3$\pm$0.5)$\times 10^{36}$ erg s$^{-1}$, which is not in agreement with what is predicted by the theory of secular evolution. Using a 3D extinction map of the K$_{s}$ radiation in our Galaxy, we obtain a distance of 4.2$^{+0.8}_{-0.7}$ kpc at 68\% confidence level. (Abridged)Comment: 10 pages, 8 figures, accepted for publication in Astronomy & Astrophysic

The puzzling symbiotic X-ray system 4U1700+24

Symbiotic X-ray binaries form a subclass of low-mass X-ray binary systems consisting of a neutron star accreting material from a red giant donor star via stellar wind or Roche lobe overflow. Only a few confirmed members are currently known; 4U 1700+24 is a good candidate as it is a relatively bright X-ray object, possibly associated with the late-type star V934 Her. We analysed the archive {\it XMM}-Newton and Swift/XRT observations of 4U 1700+24 in order to have a uniform high-energy ($0.3-10$ keV) view of the source. We confirmed the existence of a red-shifted O VIII Ly-$\alpha$ transition (already observed in the 2002 {\it XMM}-Newton data) in the high-resolution spectra collected via the RGS instruments. The red-shift of the line is found in all the analysed observations and, on average, it was estimated to be $\simeq 0.009$. We also observed a modulation of the centroid energy of the line on short time scales (a few days) and discuss the observations in the framework of different scenarios. If the modulation is due to the gravitational red-shift of the neutron star, it might arise from a sudden re-organization of the emitting $X$-ray matter on the scale of a few hundreds of km. Alternatively, we are witnessing a uni-polar jet of matter (with typical velocity of $1000-4000$ km s$^{-1}$) possibly emitted by the neutron star in an almost face-on system. The second possibility seems to be required by the apparent lack of any modulation in the observed $X$-ray light curve. We also note also that the low-resolution spectra (both {\it XMM}-Newton and Swift/XRT in the $0.3-10$ keV band) show the existence of a black body radiation emitted by a region (possibly associated with the neutron star polar cap) with typical size from a few tens to hundreds of meters. The size of this spot-like region reduces as the overall luminosity of 4U 1700+24 decreases.Comment: In press on A&

Study of the reflection spectrum of the LMXB 4U 1702-429

The source 4U 1702-429 (Ara X-1) is a low-mass X-ray binary system hosting a neutron star. Albeit the source is quite bright ( $\sim10^{37}$ erg s$^{-1}$) its broadband spectrum has never been studied. Neither dips nor eclipses have been observed in the light curve suggesting that its inclination angle is smaller than 60$^{\circ}$.We analysed the broadband spectrum of 4U 1702-429 in the 0.3-60 keV energy range, using XMM-Newton and INTEGRAL data, to constrain its Compton reflection component if it is present. After excluding the three time intervals in which three type-I X-ray bursts occurred, we fitted the joint XMM-Newton and INTEGRAL spectra obtained from simultaneous observations. A broad emission line at 6.7 keV and two absorption edges at 0.87 and 8.82 keV were detected. We found that a self-consistent reflection model fits the 0.3-60 keV spectrum well. The broadband continuum is composed of an emission component originating from the inner region of the accretion disc, a Comptonised direct emission coming from a corona with an electron temperature of $2.63 \pm 0.06$ keV and an optical depth $\tau=13.6 \pm 0.2$, and, finally, a reflection component. The best-fit indicates that the broad emission line and the absorption edge at 8.82 keV, both associated with the presence of \ion{Fe}{xxv} ions, are produced by reflection in the region above the disc with a ionisation parameter of $Log(\xi) \simeq 2.7$. We have inferred that the inner radius, where the broad emission line originates, is $64^{+52}_{-15}$ km, and the inner radius of the accretion disc is $39^{+6}_{-8}$ km. (Abridged)Comment: 9 pages, 9 figures, accepted for publication by A&