22,462 research outputs found

    Thermal barrier coating life-prediction model development

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    Life predictions are made for two types of strain-tolerant and oxidation-resistant Thermal Barrier Coating (TBC) systems produced by commercial coating suppliers to the gas turbine industry. The plasma-sprayed TBC system, composed of a low-pressure plasma spray (LPPS) applied oxidation-resistant NiCrAlY bond coating and an air-plasma-sprayed yttria (8 percent) partially stabilized zirconia insulative layer, is applied by both Chromalloy and Klock. The second type of TBC is applied by the electron-beam/physical vapor deposition process by Temescal. Thermomechanical and thermochemical testing of the program TBCs is in progress. A number of the former tests has been completed. Fracture mechanics data for the Chromalloy plasma-sprayed TBC system indicate that the cohesive toughness of the zirconia layer is increased by thermal cycling and reduced by high temperature exposure at 1150 C. Eddy current technology feasibility has been established with respect to nondestructively measuring zirconia layer thickness of a TBC system. High pressure turbine blades have been coated with program TBC systems for a piggyback test in a TFE731-5 turbofan factory engine test. Data from this test will be used to validate the TBC life models

    No-cloning theorem in thermofield dynamics

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    We discuss the relation between the no-cloning theorem from quantum information and the doubling procedure used in the formalism of thermofield dynamics (TFD). We also discuss how to apply the no-cloning theorem in the context of thermofield states defined in TFD. Consequences associated to mixed states, von Neumann entropy and thermofield vacuum are also addressed.Comment: 16 pages, 3 figure

    The Right Mutation Strength for Multi-Valued Decision Variables

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    The most common representation in evolutionary computation are bit strings. This is ideal to model binary decision variables, but less useful for variables taking more values. With very little theoretical work existing on how to use evolutionary algorithms for such optimization problems, we study the run time of simple evolutionary algorithms on some OneMax-like functions defined over Ω={0,1,,r1}n\Omega = \{0, 1, \dots, r-1\}^n. More precisely, we regard a variety of problem classes requesting the component-wise minimization of the distance to an unknown target vector zΩz \in \Omega. For such problems we see a crucial difference in how we extend the standard-bit mutation operator to these multi-valued domains. While it is natural to select each position of the solution vector to be changed independently with probability 1/n1/n, there are various ways to then change such a position. If we change each selected position to a random value different from the original one, we obtain an expected run time of Θ(nrlogn)\Theta(nr \log n). If we change each selected position by either +1+1 or 1-1 (random choice), the optimization time reduces to Θ(nr+nlogn)\Theta(nr + n\log n). If we use a random mutation strength i{0,1,,r1}ni \in \{0,1,\ldots,r-1\}^n with probability inversely proportional to ii and change the selected position by either +i+i or i-i (random choice), then the optimization time becomes Θ(nlog(r)(log(n)+log(r)))\Theta(n \log(r)(\log(n)+\log(r))), bringing down the dependence on rr from linear to polylogarithmic. One of our results depends on a new variant of the lower bounding multiplicative drift theorem.Comment: an extended abstract of this work is to appear at GECCO 201

    Blogging for Summative Assessment in Postgraduate Education

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    Blogging is widely regarded as a useful tool for reflection, articulation of ideas, and learning from peers - activities that support the formation of knowledge. Hence, blogging is often used in the formative stage of a module: Entries normally address curriculum topics for a particular week, so peer or tutor feedback works best with quick response times, before the curriculum journey moves on to new topics. Such a body of writing of course only develops with regular and consistent engagement. While engagement can be enforced by making a blogging activity mandatory, students would be better motivated if they had a more tangible return to their efforts. High quality formative feedback would provide such return, but at the cost of a high tutor workload. Embedding the blogging activity into the summative module assessment would provide an alternative motivation without overloading tutors

    Generation of pulse trains by current-controlled magnetic mirrors

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    The evolution of a spin-wave packet trapped between two direct current-carrying wires placed on the surface of a ferrite film is observed by Brillouin light scattering. The wires act as semi-transparent mirrors confining the packet. Because the spin-wave energy partially passes through these mirrors, trains of spin-wave packets are generated outside the trap. A numerical model of this process is presented and applied to the case when the current in the wires is dynamically controlled. This dynamical control of the mirror reflectivity provides new functionalities interesting for the field of spin-wave logic like that of a spin-wave memory cell.Comment: 4 pages, 3 figure

    Thermal barrier coating life prediction model development

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    Thermal barrier coatings (TBCs) for turbine airfoils in high-performance engines represent an advanced materials technology with both performance and durability benefits. The foremost TBC benefit is the reduction of heat transferred into air-cooled components, which yields performance and durability benefits. This program focuses on predicting the lives of two types of strain-tolerant and oxidation-resistant TBC systems that are produced by commercial coating suppliers to the gas turbine industry. The plasma-sprayed TBC system, composed of a low-pressure plasma-spray (LPPS) or an argon shrouded plasma-spray (ASPS) applied oxidation resistant NiCrAlY (or CoNiCrAlY) bond coating and an air-plasma-sprayed yttria (8 percent) partially stabilized zirconia insulative layer, is applied by Chromalloy, Klock, and Union Carbide. The second type of TBC is applied by the electron beam-physical vapor deposition (EB-PVD) process by Temescal

    Ground state overlap and quantum phase transitions

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    We present a characterization of quantum phase transitions in terms of the the overlap function between two ground states obtained for two different values of external parameters. On the examples of the Dicke and XY models, we show that the regions of criticality of a system are marked by the extremal points of the overlap and functions closely related to it. Further, we discuss the connections between this approach and the Anderson orthogonality catastrophe as well as with the dynamical study of the Loschmidt echo for critical systems.Comment: 5 pages. Version to be published, title change

    Low Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics

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    We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse, halo-like emission is detected from the center of the cluster at both frequencies. At 330 MHz the resolution of 90'' distinguishes this extended emission from previously known point sources. In addition to the halo and at a much lower level, outlying steep-spectrum emission regions straddle the cluster center and are seen only at 74 MHz. The location, morphology and spectrum of this emission are all highly suggestive of at least one, and possibly two cluster radio relics. Easily obtained higher resolution, higher sensitivity VLA observations at both frequencies are required to confirm the extended nature of the halo-like emission and the 74 MHz relic detections. However, since there is prior evidence that this cluster is or has recently been in the process of a major merger event, the possible discovery of relics in this system is of great interest in light of recent observational and theoretical evidence in favor of a merger-relic connection. We discuss the possible role the merger shock waves, which are seen in the X-ray emission, may have played in the formation of the halo and radio relics in A754.Comment: 15 pages including 4 figures. Accepted for publication by Ap

    The Environmental Law System of the Federal Republic of Germany

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    This paper presents a general overview of German environmental law, its principles, and its implementation. It briefly touches on the cultural and historical contexts in which this field of law evolved, as well as on its underlying policy. Being located in the center of Europe, Germany is tied into several systems of international relationships - regional, European, and global - that have to be examined with regard to their impact on German environmental law. Within the scope of this paper, the complex system of the legal obligations produced by these international relationships and German environmental law itself, consisting as it does of an agglomeration of very specific laws, can be considered only with regard to their essential features
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