Ultrasonic Signal Attenuation in Engine Titanium Alloys

The titanium alloys used in rotating jet engine components present interesting UT inspection challenges. They have complicated, duplex, anisotropic structures which vary on several dimensional scales [1,2]. Individual metal crystallites with typical dimensions on the order of several microns comprise the fine scale structure (microstructure). Colonies of aligned crystallites, which develop from prior beta grains during cooling, can have dimensions of several millimeters and comprise the large scale structure (macrostructure). Cylindrical billets destined for use in rotating engine components are typically inspected using 5 MHz broadband transducers, with higher frequency inspections planned. Because macrostructure dimensions often exceed the sonic wavelength, sound beams can be distorted during propagation, leading to modifications of ultrasonic signals. These modifications are of two basic types: (1) identical reflectors at the same depth but located at different sites on a specimen produce different sonic echoes due to the influence of the local macrostructure (signal fluctuation); and (2) the average signal strength is different from the value it would have in a similar fine-grained material (signal attenuation)

Use of Electron Backscatter Diffraction in Understanding Texture and the Mechanisms of Backscattered Noise Generation in Titanium Alloys

Developing a quantitative understanding of ultrasonic beam propagation in engineering materials such as Ti-6A1-4V is important because flaw signals can be altered greatly by the macrostructure that the ultrasonic beam propagates through between the transducer and the flaw. Two consequences of the macrostructure are particularly important: 1) back scattered noise which competes with flaw signals and 2) forward scattered signals and the associated beam profile fluctuations which can modulate the strength of flaw signals [1,2,3], These effects are particularly important when ultrasonic beams are used to detect subtle defects such as unvoided, uncracked hard-alpha inclusions (regions with a high content of interstitial nitrogen or oxygen), because the flaw signal is inherently weak due to a small mismatch of acoustic impedance. Each of these effects is controlled by the inherently complex macrostructure which develops during routine processing. Current theories suggest that the most important physical feature which controls noise is the two-point correlation of elastic constants, which is in turn controlled by local variations in crystallographic orientation [4]. Therefore, in order to quantify the effects of the macrostructure on ultrasonic beam propagation, one must determine the elastic constants on a microscopic level with length scales less than the ultrasonic wavelength, approximately 600 μm at 10 MHz.</p

Detection of Gamma-Ray Emission from the Starburst Galaxies M82 and NGC 253 with the Large Area Telescope on Fermi

We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.Comment: Submitted to ApJ Letter

A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279

It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and gamma-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10^5 gravitational radii.Comment: Published in Nature issued on 18 February 2010. Corresponding authors: Masaaki Hayashida and Greg Madejsk

Fermi Large Area Telescope observations of PSR J1836+5925

The discovery of the gamma-ray pulsar PSR J1836+5925, powering the formerly unidentified EGRET source 3EG J1835+5918, was one of the early accomplishments of the Fermi Large Area Telescope (LAT). Sitting 25 degrees off the Galactic plane, PSR J1836+5925 is a 173 ms pulsar with a characteristic age of 1.8 million years, a spindown luminosity of 1.1$\times10^{34}$ erg s$^{-1}$, and a large off-peak emission component, making it quite unusual among the known gamma-ray pulsar population. We present an analysis of one year of LAT data, including an updated timing solution, detailed spectral results and a long-term light curve showing no indication of variability. No evidence for a surrounding pulsar wind nebula is seen and the spectral characteristics of the off-peak emission indicate it is likely magnetospheric. Analysis of recent XMM observations of the X-ray counterpart yields a detailed characterization of its spectrum, which, like Geminga, is consistent with that of a neutron star showing evidence for both magnetospheric and thermal emission.Comment: Accepted to Astrophysical Journa

Search for rare quark-annihilation decays, B --> Ds(*) Phi

We report on searches for B- --> Ds- Phi and B- --> Ds*- Phi. In the context of the Standard Model, these decays are expected to be highly suppressed since they proceed through annihilation of the b and u-bar quarks in the B- meson. Our results are based on 234 million Upsilon(4S) --> B Bbar decays collected with the BABAR detector at SLAC. We find no evidence for these decays, and we set Bayesian 90% confidence level upper limits on the branching fractions BF(B- --> Ds- Phi) Ds*- Phi)<1.2x10^(-5). These results are consistent with Standard Model expectations.Comment: 8 pages, 3 postscript figues, submitted to Phys. Rev. D (Rapid Communications

Measurement of the branching fraction for B−→D0K∗−B^- \to D^0 K^{*-}

We present a measurement of the branching fraction for the decay B- --> D0 K*- using a sample of approximately 86 million BBbar pairs collected by the BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the K*- through its decay to K0S pi-. We measure the branching fraction to be B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}

Observation and Interpretation of Microstructurally Induced Fluctuations of Back-Surface Signals and Ultrasonic Attenuation in Titanium Alloys

During ultrasonic inspection for flaws in engineering materials, it is important to understand the interactions between the inspecting beam and the microstructure in which flaws are embedded. It has been found that in certain materials such interactions can have dramatic effects on the characteristics of the beam as it propagates to and from a flaw and consequently can have deleterious effects on both flaw characterization and the probability of detection. It is well known that, the microstructure can backscatter energy, creating noise which can mask small flaws. In addition, a flaw signal can be attenuated by the removal of energy from the beam by absorption and scattering. Considerable progress has been made towards developing a theoretical understanding of these phenomena. For example, backscattered grain noise has been successfully modeled by Han and Thompson [1] for duplex microstructures that commonly occur in Ti-17 and Ti-6A1-4V alloys used in the rotating components of aircraft engines. In addition, attenuation has been modeled for randomly oriented, equiaxed, cubic microstructures [2], for textured, equiaxed, cubic, stainless-steel [3], and also for elongated textured microstructures [4]

Observation of a significant excess of π0π0\pi^{0}\pi^{0} events in B meson decays

We present an observation of the decay $B^{0} \to \pi^{0} \pi^{0}$ based on a sample of 124 million $B\bar{B}$ pairs recorded by the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We observe $46 \pm 13 \pm 3$ events, where the first error is statistical and the second is systematic, corresponding to a significance of 4.2 standard deviations including systematic uncertainties. We measure the branching fraction \BR(B^{0} \to \pi^{0} \pi^{0}) = (2.1 \pm 0.6 \pm 0.3) \times 10^{-6}, averaged over $B^{0}$ and $\bar{B}^{0}$ decays

Prospective Randomized Controlled Trial to Analyze the Effects of Intermittent Pneumatic Compression on Edema Following Autologous Femoropopliteal Bypass Surgery

Background: Patients who undergo autologous femoropopliteal bypass surgery develop postoperative edema in the revascularized leg. The effects of intermittent pneumatic compression (IPC) to treat and to prevent postreconstructive edema were examined in this study. Methods: In a prospective randomized trial, patients were assigned to one of two groups. All patients suffered from peripheral arterial disease, and all were subjected to autologous femoropopliteal bypass reconstruction. Patients in group 1 used a compression stocking (CS) above the knee exerting 18 mmHg (class I) on the leg postoperatively for 1 week (day and night). Patients in group 2 used IPC on the foot postoperatively at night for 1 week. The lower leg circumference was measured preoperatively and at five postoperative time points. A multivariate analysis was done using a mixed model analysis of variance. Results: A total of 57 patients were analyzed (CS 28; IPC 29). Indications for operation were severe claudication (CS 13; IPC 13), rest pain (10/5), or tissue loss (7/11). Revascularization was performed with either a supragenicular (CS 13; IPC10) or an infragenicular (CS 15; IPC 19) autologous bypass. Leg circumference increased on day 1 (CS/IPC): 0.4%/2.7%, day 4 (2.1%/6.1%), day 7 (2.5%/7.9%), day 14 (4.7%/7.3%), and day 90 (1.0%/3.3%) from baseline (preoperative situation). On days 1, 4, and 7 there was a significant difference in leg circumference between the two treatment groups. Conclusions: Edema following femoropopliteal bypass surgery occurs in all patients. For the prevention and treatment of that edema the use of a class I CS proved superior to treatment with IPC. The use of CS remains the recommended practice following femoropopliteal bypass surgery