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

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 $\Omega = \{0, 1, \dots, r-1\}^n$. More precisely, we regard a variety of problem classes requesting the component-wise minimization of the distance to an unknown target vector $z \in \Omega$. 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 $1/n$, 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 $\Theta(nr \log n)$. If we change each selected position by either $+1$ or $-1$ (random choice), the optimization time reduces to $\Theta(nr + n\log n)$. If we use a random mutation strength $i \in \{0,1,\ldots,r-1\}^n$ with probability inversely proportional to $i$ and change the selected position by either $+i$ or $-i$ (random choice), then the optimization time becomes $\Theta(n \log(r)(\log(n)+\log(r)))$, bringing down the dependence on $r$ 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

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

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

Performance of a centrifugal pump running in inverse mode

This paper presents the functional characterization of a centrifugal pump used as a turbine. It shows the characteristics of the machine involved at several rotational speeds, comparing the respective flows and heads. In this way, it is possible to observe the influence of the rotational speed on efficiency, as well as obtaining the characteristics at constant head and runaway speed. Also, the forces actuating on the impeller were studied. An uncertainty analysis was made to assess the accuracy of the results. The research results indicate that the turbine characteristics can be predicted to some extent from the pump characteristics, that water flows out of the runner free of swirl flow at the best efficiency point, and that radial stresses are lower than in pump mode

Frequency-dependent reflection of spin waves from a magnetic inhomogeneity induced by a surface DC-current

The reflectivity of a highly localized magnetic inhomogeneity is experimentally studied. The inhomogeneity is created by a dc-current carrying wire placed on the surface of a ferrite film. The reflection of propagating dipole-dominated spin-wave pulses is found to be strongly dependent on the spin-wave frequency if the current locally increases the magnetic field. In the opposite case the frequency dependence is negligible.Comment: 3 pages, 3 figure

Design Of SRF Cavities With Cell Profiles Based On Bezier Splines

Elliptical cavities have been a standard in SRF linac technology for 30 years. In this work, we present a novel approach [1] using Bezier spline profile curves. By using different degrees of spline curves, the number of free parameters can be varied to suit a given problem endcell tuning, basecell figures of merit , thus leading to a high flexibility of the spline approach. As a realistic example, a cubic spline SRF multicell cavity geometry is calculated and the figures of merit are optimized for the operational mode. We also present an outline for HOM endcell optimization that can be realized using available 2D solver

Preparation of pure and mixed polarization qubits and the direct measurement of figures of merit

Non-classical joint measurements can hugely improve the efficiency with which certain figures of merit of quantum systems are measured. We use such a measurement to determine a particular figure of merit, the purity, for a polarization qubit. In the process we highlight some of subtleties involved in common methods for generating decoherence in quantum optics.Comment: 5 pages, 3 figures, 1 tabl

Alternative Approaches for HOM Damped Cavities

In this paper, we present two different ideas that may be useful for design and simulation of superconducting radio frequency cavities. To obtain longitudinal and transverse voltages resp. shunt impedances in cavities without rotational symmetry, one or two integration paths are often used to get an approximate difference relation for the transverse voltage of higher order modes HOMs . The presented approach uses a multipole decomposition that is valid in vicinity of the central axis to compute voltage multipole decomposition directly for paths of arbitrary number and position. Elliptical cavities have been a standard in SRF linac technology for 30 years. We present another approach to base cell geometry based on Bezier splines that is much more flexible in terms of optimization, while reaching equal performance level