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[en] At present, there are many methods to identify the temperature and phase of a material using invasive techniques. However, most current methods require physical contact or implicit methods utilizing light reflectance of the specimen. In this paper, we present a nondestructive inspection method using ultrasonic wave technology that circumvents these disadvantages to identify phase change regions and infer the temperature state of a material. In the present study an experiment is performed to monitor the time of flight within a wax as it undergoes melting and the subsequent cooling. Results presented in this work show a clear relationship between a material’s speed of sound and its temperature. The phase change transition of the material is clear from the time of flight results, and in the case of the investigated material, this change in the material state occurs over a range of temperatures. The range of temperatures over which the wax material melts is readily identified by speed of sound represented as a function of material temperature. The melt temperature, obtained acoustically, is validated using Differential Scanning Calorimetry (DSC), which uses shifts in heat flow rates to identify phase transition temperature ranges. Lastly, the investigated ultrasonic NDE method has direct applications in many industries, including oil and gas, food and beverage, and polymer composites, in addition to many implications for future capabilities of nondestructive inspection of multi-phase materials.
[en] We have measured the collisional excitation cross sections for the 3d→4f and 3d→5f excitations in Au ions near the Ni-like charge state by using beam plasmas created in the Livermore electron beam ion trap EBIT-I. The cross sections have been experimentally determined at approximately 1, 2 and 3 keV above the threshold energy, ET, for the 3d→4f excitations (ET ~2.5 keV) and at approximately 0.1, 1 and 2 keV above the threshold energy for the 3d→5f excitations (ET ~3.3 keV). The cross section measurements were made possible by using the GSFC x-ray microcalorimeter at the Livermore EBIT facility. The absolute cross sections are determined from the ratio of the intensity of the collisionally excited bound-bound transitions to the intensity of the radiative recombination lines produced in EBIT-I plasmas. The effects of polarization and Auger decay channels are accounted for in the cross section determination. Measured cross sections are compared with those from HULLAC, DWS and FAC calculations. Finally, the measurements demonstrate that some errors exist in the calculated excitation cross sections.
[en] A high intensity polarized positron beam, as part of the JLAB 12 GeV program and the proposed electron-ion collider (EIC), can provide a unique opportunity for testing the Standard Model (SM) and probing for new physics. The combination of high luminosity with polarized electrons and positrons incident on protons and deuterons can isolate important effects and distinguish between possible new physics scenarios in a manner that will complement current experimental efforts. Here, a comparison of cross sections between polarized electron and positron beams will allow for an extraction of the poorly known weak neutral current coupling combination 2C3u - C3d and would complement the proposed plan for a precision extraction of the combination 2C2u - Cd at the EIC. Precision measurements of these neutral weak couplings would constrain new physics scenarios including Leptoquarks, R-parity violating supersymmetry, and electron and quark compositeness. The dependence of the charged current cross section on the longitudinal polarization of the positron beam will provide an independent probe to test the chiral structure of the electroweak interactions. A polarized positron can probe charged lepton flavor violation (CLFV) through a search for e+ → τ+ transitions in a manner that is independent and complementary to the proposed e- → τ- search at the EIC. A positron beam incident on an electron in a stationary nuclear target will also allow for a dark-photon (A') search via the annihilation process e+ + e- → A' + γ.
[en] In this talk I address two high impact physics programs that require the use of polarized and unpolarized positron beams in addition to using electron beams of the same energy. First, I address what will be gained from using positron beams in addition to electron beams in the extraction of the Compton Form Factors (CFFs) and generalized parton distributions (GPDs) from Deeply Virtual Compton Scattering (DVCS) on a proton target. Furthermore a second high impact science program I discuss an experimental scenario using unpolarized positrons to measure elastic scattering on protons in an effort to determine definitively the 2-photon exchange contributions in order to resolve a longstanding discrepancy in the determination of the proton’s electric and magnetic form factors.
[en] Laser-driven ramp wave compression experiments have been used to investigate the strength (flow stress) of tantalum and other metals at high pressures and high strain rates. Recently this kind of experiment has been used to assess the dependence of the strength on the average grain size of the material, finding no detectable variation with grain size. The insensitivity to grain size has been understood theoretically to result from the dominant effect of the high dislocation density generated at the extremely high strain rates of the experiment. Here we review the experiments and describe in detail the multiscale strength model used to simulate them. The multiscale strength model has been extended to include the effect of geometrically necessary dislocations generated at the grain boundaries during compatible plastic flow in the polycrystalline metal. Lastly, we use the extended model to make predictions of the threshold strain rates and grain sizes below which grain size strengthening would be observed in the laser-driven Rayleigh-Taylor experiments.
[en] Here, we present a density functional theory study of cerium deuterides, varying deuterium content and temperature. Results are discussed in relation to ejecta experiments recently described in [J. Dynam. Mat. Behav. 1, 12 (2017)]. Using quantum molecular dynamics, we calculate diffusion coefficients, radial distribution functions, and heat capacities of these materials. Properties are calculated over temperatures ranging from 500-4000K at near ambient pressure and at 2.37 fold compression. We find that deuterium diffusion occurs rapidly accross this temperature and compression region and that heat capacity calculations are in agreement with approximations made in experiments. For cerium metal, a comparison of self-diffusion coefficient and viscosity with experimental data and analytical models shows excellent agreement. Lastly, we discuss the stucture of cerium deuterides with respect to radial distribution functions and provide fitted equations for diffusion coefficients over temperature.
[en] Pions and kaons are, along with protons and neutrons, the main building blocks of nuclear matter. They are connected to the Goldstone modes of dynamical chiral symmetry breaking, the mechanism thought to generate all hadron mass in the visible universe. The distribution of the fundamental constituents, the quarks and gluons, is expected to be different in pions, kaons, and nucleons. However, experimental data are sparse. As a result, there has been persistent doubt about the behaviour of the pion's valence quark structure function at large Bjorken- and virtually nothing is known about the contribution of gluons. The Electron-Ion Collider (EIC) with an acceptance optimized for forward physics could provide access to structure functions over a larger kinematic region. This would allow for measurements testing if the origin of mass is encoded in the differences of gluons in pions, kaons, and nucleons, and measurements that could serve as a test of assumptions used in the extraction of structure functions and the pion and kaon form factors. Furthermore, measurements at an EIC would also allow to explore the effect of gluons at high x.