Absorption-Fluctuation Theorem for Nuclear Reactions: Brink-Axel, Incomplete Fusion and All That

We discuss the connection between absorption, averages and fluctuations in nuclear reactions. The fluctuations in the entrance channel result in the compound nucleus, Hauser-Feshbach, cross section, the fluctuations in the intermediate channels, result in modifications of multistep reaction cross sections, while the fluctuations in the final channel result in hybrid cross sections that can be used to describe incomplete fusion reactions. We discuss the latter in details and comment on the validity of the assumptions used in the develpoment of the Surrogate method. We also discuss the theory of multistep reactions with regards to intermediate state fluctuations and the energy dependence and non-locality of the intermediate channels optical potentials.Comment: 9 pages. Contribution to the International Workshop on Compound-Nuclear Reactions and Related Topics (CNR*2007), October 22-26, 2007, Fish Camp, California. To be published in AIP Proceedings (Editor Jutta Escher

Further testing and development of simulation models for UT inspections of armor

In previous work we introduced an approach for simulating ultrasonic pulse/echo immersion inspections of multi-layer armor panels. Model inputs include the thickness, density, velocity and attenuation of each armor layer, the focal properties of the transducer, and a measured calibration signal. The basic model output is a response-versus-time waveform (ultrasonic A-scan) which includes echoes from all interfaces including those arising from reverberations within layers. Such A-scans can be predicted both for unflawed panels and panels containing a large disbond at any given interface. In this paper we continue our testing of the simulation software, applying it now to an armor panel consisting of SiC ceramic tiles fully embedded in a titanium-alloy matrix. An interesting specimen of such armor became available in which some tile/metal interfaces appear to be well bonded, while others have disbonded areas of various sizes. We compare measured and predicted A-scans for UT inspections, and also demonstrate an extension of the model to predict ultrasonic C-scans over regions containing a small, isolated disbond

Predicting ultrasonic grain noise in polycrystals: A Monte Carlo model

A Monte Carlo technique is described for predicting the ultrasonic noise backscattered from the microstructure of polycrystalline materials in a pulse/echo immersion inspection. Explicit results are presented for equiaxed, randomly oriented aggregates of either cubic or hexagonal crystallites. The model is then tested using measured noise signals. Average and peak noise levels and the distribution of the noise voltages are studied as the density of grains changes

Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol and hydroquinone

Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S1 (\u3c0\u3c0*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S1potential surface. In catechol, the overall S1 state lifetime was observed to be 12.1 ps, which is 1\u20132 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S1 state and the close lying S2 (\u3c0\u3c3*) state, which is dissociative along the O\u2013H stretching coordinate. Further evidence of this S1/S2 interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.Peer reviewed: YesNRC publication: Ye

Seismic Evaluation of Highway Bridges - Phase 1

The primary objective of the study was to establish the guidelines for screening, assessing, and ranking Indiana bridges for seismic upgrade. The outcome of the study is a complete strategy for the detailed structural assessment of Indiana highway bridges subjected to seismic forces. The structural evaluation is conducted using a nonlinear time-history analysis of the bridge for simulated or actual records. The specific soil conditions at the site are accounted in terms of the ground motion. From the time history analysis the maximum structural response including displacements, bending moments, shear and axial forces are computed. A weighted evaluation of the ratio of expected demand to available capacity is conducted next. A seismic rating is established based on the weighted evaluation. The bridges are classified into three different categories: high, moderate and low seismic risk. In the case of bridges falling in the high and moderate categories, the weighted seismic rating can be used to establish strengthening needs. The same type of analysis could be used to evaluate different strengthening schemes. In the case where the bridge inventory is substantial, the proposed strategy in this study would be more effective helped by a preliminary first level screening of the bridge population. Several first level screening procedures available in the United States are evaluated in this study. First level screening procedures are used in the qualitative ranking of seismic bridges with respect to seismic risk. They are simplified methods for use in extensive highway networks and are the first steps in a comprehensive evaluation strategy. The Indiana Department of Transportation has conducted a preliminary first level screening of the bridge population in the southern part of the state. Several bridges have been identified as presenting a high level of seismic risk. The approach proposed in this study could be used to further refine the preliminary ranking, and to evaluate different strengthening schemes. It must be pointed out that the soil-structure interaction of bridge structures is a developing area. Many questions remain to be answered regarding the proper modeling of the foundation and the surrounding soil. The proposed evaluation strategy can be improved by means of a field evaluation of dynamic characteristics of a representative sample of bridge foundations and soil conditions in the critical southern part of the state

Anisotropic Gauss-Hermite Beam Model Applied to through-Transmission Inspections of Delaminations in Composite Plates

Manufactured parts containing composite materials can present challenging ultrasonic inspection problems. The inherent anisotropy of such materials acts to distort propagating ultrasonic beams, leading in turn to an associated distortion of defect images. Such distortions complicate the task of estimating the physical dimensions of a defect from its ultrasonic image. In the present work we demonstrate how these difficulties can be overcome by appropriately modelling the ultrasonic inspection process, and using the model to analyze defect images. To illustrate the approach, we consider a normal incidence through-transmission inspection of a flat uniaxial composite plate with an internal delamination. We begin by reviewing our model of the inspection process which incorporates the Gauss-Hermite model for beam propagation in anisotropic materials. The inspection model requires as inputs certain parameters which characterize the transducers, and others which characterize the composite material. We demonstrate how these parameters can be obtained from simple beam-mapping experiments. We then present experimental C-scan images of a seeded circular delamination in a composite plate, and compare these to images predicted by the model. Finally, we demonstrate how the model can be used to accurately size a delamination from its ultrasonic image

Ultrasonic NDE Techniques for Integrally Fabricated Rotors

Solid-state bonding methods, e.g., diffusion bonding and pressure welding, are becoming common manufacture and repair techniques for gas turbine engine components. Effective NDE inspection techniques are crucial to the utilization of this approach due to the high stresses on the bond plane associated with jet engine operation. Recently we have examined ultrasonic techniques for assessing bond quality including leaky Rayleigh waves and critical angle longitudinal waves[1], for which the illuminating waves are nearly normal to the bond plane, and longitudinal waves at near grazing incidence to the bond[1]. Based upon preliminary theoretical analyses[1,2] of ultrasonic reflectivity from imperfect interfaces, it was found that the reflection coefficient for both longitudinal and shear waves increases to unity as the incident angle approaches grazing[1]. In contrast, the bond reflection coefficients for near normal incidence can be quite small, depending upon the degree of imperfection of the bond. A second drawback to the first two approaches mentioned is that surface roughness of the blade can cause scattering noise which dominates the signals reflected from the bond. The grazing incidence technique suffers less from these problems since the probe is oriented nearly normal to the surface of the blade and the interaction of the beam with the surface is minimized

The Host Galaxy of the Broad Absorption Line QSO PG 1700+518 and Its Ring Galaxy Companion: NICMOS 1.6 Micron Imaging

The 1.6 μm Near Infrared Camera and Multiobject Spectrometer image of the broad absorption line QSO PG 1700+518 clearly resolves the QSO host galaxy and a ringlike companion. The companion is most likely a ring galaxy produced in a collision with the QSO galaxy ~5×10^7 yr ago. The morphology of the PG 1700+518 system is very similar to IRAS 04505-2958 (Boyce et al. 1996). Both objects were identified in a sample of eight QSOs selected by "warm" far-IR colors and extreme IR luminosities (Low et al. 1988). All eight QSOs show signs of strong interaction, and the presence of two head-on colliding systems in this sample may suggest that small impact parameters favor the energizing of IR-luminous QSOs

3,6,9,16,19,22-Hexaaza­tricyclo­[22.2.2.211,14]­triaconta-1(27),11 (30),12,14(29),24(28),25-hexa­ene hexa­kis(p-toluene­sulfonate) dihydrate

In the title compound, C24H44N6 6+·6C7H7O3S−·2H2O, the macrocycle crystallizes in its hexa­protonated form, accompanied by six p-toluene­sulfonate ions and two water mol­ecules, and lies on an inversion center. The three independent p-toluene­sulfonate anions and their inversion equivalents at (1 − x, 1 − y, 1 − z) are linked to the macrocyclic cation through N—H⋯O hydrogen bonds. Of these, two p-toluene­sulfonate ions are located on opposite sides of the macrocyclic plane and are linked to bridgehead N atoms via N—H⋯O hydrogen bonds. The remaining four p-toluene­sulfonate ions bridge two adjacent macrocyclic cationic units through N—H⋯O hydrogen bonding involving other N atoms, forming a chain along the a axis. The water mol­ecules, which could not be located and may be disordered, do not inter­act with the macrocycle; however, they form hydrogen bonds with anions