22,462 research outputs found
Thermal barrier coating life-prediction model development
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
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
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
. More precisely, we regard a variety of
problem classes requesting the component-wise minimization of the distance to
an unknown target vector . 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 , 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 . If we change each selected position
by either or (random choice), the optimization time reduces to
. If we use a random mutation strength with probability inversely proportional to and change
the selected position by either or (random choice), then the
optimization time becomes , bringing down
the dependence on 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
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
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
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
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
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
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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