Observations of directional gamma prime coarsening during engine operation

Two alloys with negative mismatch parameters, NASAIR 100 and a modified NASAIR 100 called Alloy 3 were run as turbine blades in an experimental ground based Garret TFE731 engine for up to 200 hr. The directional coarsening of gamma prime (rafting) that developed during engine testing was analyzed and compared to previous research from laboratory tests. The blades were found to be rafted normal to the centrifugal stress axis over much of the span, but near the surfaces, the blades were found to be rafted parallel to the centrifugal stress axis for certain cycles. Representative photomicrographs of the blades and the effects of stress and temperature on raft formation are shown

Using Rheo-Small-Angle Neutron Scattering to Understand How Functionalised Dipeptides Form Gels

We explore the use of rheo-small-angle neutron scattering as a method to collect structural information from neutron scattering simultaneously with rheology to understand how low-molecular-weight hydrogels form and behave under shear. We examine three different gelling hydrogel systems to assess what structures are formed and how these influence the rheology. Furthermore, we probe what is happening to the network during syneresis and why the gels do not recover after an applied strain. All this information is vital when considering gels for applications such as 3D-printing and injection

Strength Degradation of Sapphire Fibers During Pressure Casting of a Sapphire-Reinforced Ni-Base Superalloy

Transient-liquid-phase (TLP) bonding was used to fabricate a Haynes 230 Ni-base superalloy/sapphire fiber composite for high-temperature applications. Boron was used as a melting-point depressant for the Ni, to aid superalloy infiltration of the fibers. Preliminary study of the composite indicated an incomplete TLP bonding cycle. Therefore, microstructural and microchemical analyses were carried out to determine the TLP bonding mechanism. It was found that the TLP process did not occur under local thermodynamic equilibrium conditions at the solid/liquid interfaces, contrary to the primary assumption of conventional models, so a modified model for TLP bonding is proposed. The main differences between the proposed and the conventional models are: (a) the concentration of the melting-point depressant increases with time during isothermal solidification, (b) extensive boride segregation at grain boundaries and boride precipitation occurs within grains adjacent to the interlayer in the initial composite assembly, (c) because of the relatively high boron concentration in the interlayer, the TLP bonding cycle was incomplete, resulting in residual-liquid borides. To achieve ideal TLP bonding, four modifications are recommended: (i) use less boron, (ii) use finer sapphire fibers, (iii) create smaller initial grain sizes in the matrix and (iv) increase the homogenization time

Decuplet Baryon Structure from Lattice QCD

The electromagnetic properties of the SU(3)-flavor baryon decuplet are examined within a lattice simulation of quenched QCD. Electric charge radii, magnetic moments, and magnetic radii are extracted from the E0 and M1 form factors. Preliminary results for the E2 and M3 moments are presented giving the first model independent insight to the shape of the quark distribution in the baryon ground state. As in our octet baryon analysis, the lattice results give evidence of spin-dependent forces and mass effects in the electromagnetic properties. The quark charge distribution radii indicate these effects act in opposing directions. Some baryon dependence of the effective quark magnetic moments is seen. However, this dependence in decuplet baryons is more subtle than that for octet baryons. Of particular interest are the lattice predictions for the magnetic moments of $\Omega^-$ and $\Delta^{++}$ for which new recent experimental measurements are available. The lattice prediction of the $\Delta^{++}/p$ ratio appears larger than the experimental ratio, while the lattice prediction for the $\Omega^-/p$ magnetic moment ratio is in good agreement with the experimental ratio.Comment: RevTeX manuscript, 34 pages plus 21 figures (available upon request

On the Effect of Quantum Interaction Distance on Quantum Addition Circuits

We investigate the theoretical limits of the effect of the quantum interaction distance on the speed of exact quantum addition circuits. For this study, we exploit graph embedding for quantum circuit analysis. We study a logical mapping of qubits and gates of any $\Omega(\log n)$-depth quantum adder circuit for two $n$-qubit registers onto a practical architecture, which limits interaction distance to the nearest neighbors only and supports only one- and two-qubit logical gates. Unfortunately, on the chosen $k$-dimensional practical architecture, we prove that the depth lower bound of any exact quantum addition circuits is no longer $\Omega(\log {n})$, but $\Omega(\sqrt[k]{n})$. This result, the first application of graph embedding to quantum circuits and devices, provides a new tool for compiler development, emphasizes the impact of quantum computer architecture on performance, and acts as a cautionary note when evaluating the time performance of quantum algorithms.Comment: accepted for ACM Journal on Emerging Technologies in Computing System

Baryon Octet to Decuplet Electromagnetic Transitions

The electromagnetic transition moments of the $SU(3)$-flavor baryon octet to decuplet are examined within a lattice simulation of quenched QCD. The magnetic transition moment for the $N \; \gamma \to \Delta$ channel is found to be in agreement with recent experimental analyses. The lattice results indicate $\mu_{p \Delta} / \mu_p = 0.88(15)$. In terms of the Particle Data Group convention, $f_{M1} = 0.231(41)$ GeV${}^{-1/2}$ for $p \; \gamma \to \Delta^+$ transitions. Lattice predictions for the hyperon $M1$ transition moments agree with those of a simple quark model. However the manner in which the quarks contribute to the transition moments in the lattice simulation is different from that anticipated by quark model calculations. The scalar quadrupole form factor exhibits a behavior consistent with previous multipole analyses. The $E2/M1$ multipole transition moment ratios are also determined. The lattice results suggest $R_{EM} \equiv -{\cal G}_{E2}/{\cal G}_{M1} = +3\pm 8$ \% for $p \; \gamma \to \Delta^+$ transitions. Of particular interest are significant nonvanishing signals for the $E2/M1$ ratio in $\Xi^-$ and $\Sigma^-$ electromagnetic transitions.Comment: PostScript file, 37 pages including figures. U. MD PP #93-085, U. KY PP #UK/92-09, TRIUMF PP #TRI-PP-92-12

Tests of relativity using a microwave resonator

The frequencies of a cryogenic sapphire oscillator and a hydrogen maser are compared to set new constraints on a possible violation of Lorentz invariance. We determine the variation of the oscillator frequency as a function of its orientation (Michelson-Morley test) and of its velocity (Kennedy-Thorndike test) with respect to a preferred frame candidate. We constrain the corresponding parameters of the Mansouri and Sexl test theory to $\delta - \beta + 1/2 = (1.5\pm 4.2) \times 10^{-9}$ and $\beta - \alpha - 1 = (-3.1\pm 6.9) \times 10^{-7}$ which is equivalent to the best previous result for the former and represents a 30 fold improvement for the latter.Comment: 8 pages, 2 figures, submitted to Physical Review Letters (October 3, 2002

XMM Follow-Up Observations of Three Swift BAT-Selected Active Galactic Nuclei

We present XMM-Newton observations of three AGN taken as part of a hunt to find very heavily obscured Compton-thick AGN. For obscuring columns greater than 10^25 cm^-2, AGN are only visible at energies below 10 keV via reflected/scattered radiation, characterized by a flat power-law. We therefore selected three objects (ESO 417-G006, IRAS 05218-1212, and MCG -01-05-047) from the Swift BAT hard X-ray survey catalog with Swift X-ray Telescope XRT 0.5-10 keV spectra with flat power-law indices as candidate Compton-thick sources for follow-up observations with the more sensitive instruments on XMM-Newton. The XMM spectra, however, rule out reflection-dominated models based on the weakness of the observed Fe K-alpha lines. Instead, the spectra are well-fit by a model of a power-law continuum obscured by a Compton-thin absorber, plus a soft excess. This result is consistent with previous follow-up observations of two other flat-spectrum BAT-detected AGN. Thus, out of the six AGN in the 22-month BAT catalog with apparently flat Swift XRT spectra, all five that have had follow-up observations are not likely Compton-thick. We also present new optical spectra of two of these objects, IRAS 05218-1212 and MCG -01-05-047. Interestingly, though both these AGN have similar X-ray spectra, their optical spectra are completely different, adding evidence against the simplest form of the geometric unified model of AGN. IRAS 05218-1212 appears in the optical as a Seyfert 1, despite the ~8.5x10^22 cm^-2 line-of-sight absorbing column indicated by its X-ray spectrum. MCG -01-05-047's optical spectrum shows no sign of AGN activity; it appears as a normal galaxy.Comment: 18 pages including 4 figures, accepted by Ap