Thermal Behavior in the Lens Process

Direct laser metal deposition processing is a promising manufacturing technology which could significantly impact the length oftime between initial concept and finished part. For adoption ofthis technology in the manufacturing environment, further understanding is required to ensure robust components with appropriate properties are routinelyfabricated. This requires a complete understanding ofthe thermal history.during part fabrication and control ofthis behavior. This paper will describe our research to understand the thermal behavior for the Laser Engineered Net Shaping (LENS) process!, where a component is fabricated by focusing a laser beam onto a substrate to create a molten pool in which powder particles are simultaneously injected to build each layer. The substrate is moved beneath the l~ser beam to deposit a thin cross section, thereby creating the desired geometry for each layer. After deposition of each layer, the powder delivery nozzle and focusing lens assembly is incremented in the positive Z-direction, thereby building a three dimensional component layer additively. It is important to control the thermal behavior to reproducibly fabricate parts. The ultimate intent is to monitor the thermal signatures and to incorporate sensors and feedback algorithms to control part fabrication. With appropriate control, the geometric properties (accuracy, surface finish, low warpage) as well as the materials' properties (e.g. strength, ductility) of a component can be dialed into the part through the fabrication parameters. Thermal monitoring techniques will be described, and their particular benefits highlighted. Preliminary details in correlating thermal behavior with processing results will be discussed.Mechanical Engineerin

Ferromagnetic resonance force microscopy on a thin permalloy film

Ferromagnetic Resonance Force Microscopy (FMRFM) offers a means of performing local ferromagnetic resonance. We have studied the evolution of the FMRFM force spectra in a continuous 50 nm thick permalloy film as a function of probe-film distance and performed numerical simulations of the intensity of the FMRFM probe-film interaction force, accounting for the presence of the localized strongly nonuniform magnetic field of the FMRFM probe magnet. Excellent agreement between the experimental data and the simulation results provides insight into the mechanism of FMR mode excitation in an FMRFM experiment.Comment: 9 pages, 2 figure

Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron System

We determine the spin susceptibility in a two dimensional electron system in GaAs/AlGaAs over a wide range of low densities from 2$\times10^{9}$cm$^{-2}$ to 4$\times10^{10}$cm$^{-2}$. Our data can be fitted to an equation that describes the density dependence as well as the polarization dependence of the spin susceptibility. It can account for the anomalous g-factors reported recently in GaAs electron and hole systems. The paramagnetic spin susceptibility increases with decreasing density as expected from theoretical calculations.Comment: 5 pages, 2 eps figures, to appear in PR

A Photometric Method for Quantifying Asymmetries in Disk Galaxies

A photometric method for quantifying deviations from axisymmetry in optical images of disk galaxies is applied to a sample of 32 face-on and nearly face-on spirals. The method involves comparing the relative fluxes contained within trapezoidal sectors arranged symmetrically about the galaxy center of light, excluding the bulge and/or barred regions. Such a method has several advantages over others, especially when quantifying asymmetry in flocculent galaxies. Specifically, the averaging of large regions improves the signal-to-noise in the measurements; the method is not strongly affected by the presence of spiral arms; and it identifies the kinds of asymmetry that are likely to be dynamically important. Application of this "method of sectors" to R-band images of 32 disk galaxies indicates that about 30% of spirals show deviations from axisymmetry at the 5-sigma level.Comment: 17 pages, 2 tables and 6 figures, uses psfig and AAS LaTex; to appear in A

A method to construct refracting profiles

We propose an original method for determining suitable refracting profiles between two media to solve two related problems: to produce a given wave front from a single point source after refraction at the refracting profile, and to focus a given wave front in a fixed point. These profiles are obtained as envelopes of specific families of Cartesian ovals. We study the singularities of these profiles and give a method to construct them from the data of the associated caustic.Comment: 12 pages, 5 figure

Light scattering study of the “pseudo-layer” compression elastic constant in a twist-bend nematic liquid crystal

The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or “pseudo-layers”, each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining “layer” compression and bending ought to be characterized by an effective layer compression elastic constant Beff and average director splay constant Keff1. The magnitude of Keff1 is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, Beff could differ substantially from the typical value of ∼10⁶ Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the “pseudo-layer” structure of the TB phase with Beff in the range 10³–10⁴ Pa. We show additionally that the temperature dependence of Beff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director

Abelian functions associated with a cyclic tetragonal curve of genus six

We develop the theory of Abelian functions defined using a tetragonal curve of genus six, discussing in detail the cyclic curve y^4 = x^5 + λ[4]x^4 + λ[3]x^3 + λ[2]x^2 + λ[1]x + λ[0]. We construct Abelian functions using the multivariate sigma-function associated with the curve, generalizing the theory of theWeierstrass℘-function. We demonstrate that such functions can give a solution to the KP-equation, outlining how a general class of solutions could be generated using a wider class of curves. We also present the associated partial differential equations satisfied by the functions, the solution of the Jacobi inversion problem, a power series expansion for σ(u) and a new addition formula

Quasiparticle entanglement: redefinition of the vacuum and reduced density matrix approach

A scattering approach to entanglement in mesoscopic conductors with independent fermionic quasiparticles is discussed. We focus on conductors in the tunneling limit, where a redefinition of the quasiparticle vacuum transforms the wavefunction from a manybody product state of noninteracting particles to a state describing entangled two-particle excitations out of the new vacuum. The approach is illustrated with two examples (i) a normal-superconducting system, where the transformation is made between Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system, where the transformation is made between electron quasiparticles and electron-hole pairs. This is compared to a scheme where an effective two-particle state is derived from the manybody scattering state by a reduced density matrix approach.Comment: Submitted to New Journal of Physics, Focused Issue on "Solid State Quantum Information". 19 pages, 7 figure

The Remarkable Be Star HD110432

HD110432 has gained considerable attention because it is a hard, variable X-ray source similar to gamma Cas. From time-serial echelle data obtained over two weeks during 2005 January and February, we find several remarkable characteristics in the star's optical spectrum. The line profiles show rapid variations on some nights which can be most likely be attributed to irregularly occurring and short-lived migrating subfeatures. Such features have only been observed to date in gamma Cas and AB Dor, two stars for which it is believed magnetic fields force circumstellar clouds to corotate over the stellar surface. The star's optical spectrum also exhibits a number of mainly FeII and HeI emission features with profiles typical of an optically thin disk viewed edge-on. Using spectral synthesis techniques, we find that its temperature is 9800K +/-300K, that its projected area is a remarkably large 100 stellar areas, and its emitting volume resides at a distance of 1 AU from the star. We also find that the star's absorption profiles extend to +/-1000 km/s, a fact which we cannot explain. Otherwise, HD110432 and gamma Cas share similarly peculiar X-ray and optical characteristics such as high X-ray temperature, erratic X-ray variability on timescales of a few hours, optical emission lines, and submigrating features in optical line profiles. Because of these similarities, we suggest that this star is a new member of a select class of "gamma Cas analogs."Comment: 31 pages, 9 figures, accepted by ApJ (3/20/06

Superposition in nonlinear wave and evolution equations

Real and bounded elliptic solutions suitable for applying the Khare-Sukhatme superposition procedure are presented and used to generate superposition solutions of the generalized modified Kadomtsev-Petviashvili equation (gmKPE) and the nonlinear cubic-quintic Schroedinger equation (NLCQSE).Comment: submitted to International Journal of Theoretical Physics, 23 pages, 2 figures, style change