Actinide collisions for QED and superheavy elements with the time-dependent Hartree-Fock theory and the Balian-V\'en\'eroni variational principle

Collisions of actinide nuclei form, during very short times of few zs ($10^{-21}$ s), the heaviest ensembles of interacting nucleons available on Earth. Such collisions are used to produce super-strong electric fields by the huge number of interacting protons to test spontaneous positron-electron pair emission (vacuum decay) predicted by the quantum electrodynamics (QED) theory. Multi-nucleon transfer in actinide collisions could also be used as an alternative way to fusion in order to produce neutron-rich heavy and superheavy elements thanks to inverse quasifission mechanisms. Actinide collisions are studied in a dynamical quantum microscopic approach. The three-dimensional time-dependent Hartree-Fock (TDHF) code {\textsc{tdhf3d}} is used with a full Skyrme energy density functional to investigate the time evolution of expectation values of one-body operators, such as fragment position and particle number. This code is also used to compute the dispersion of the particle numbers (e.g., widths of fragment mass and charge distributions) from TDHF transfer probabilities, on the one hand, and using the Balian-Veneroni variational principle, on the other hand. A first application to test QED is discussed. Collision times in $^{238}$U+$^{238}$U are computed to determine the optimum energy for the observation of the vacuum decay. It is shown that the initial orientation strongly affects the collision times and reaction mechanism. The highest collision times predicted by TDHF in this reaction are of the order of $\sim4$ zs at a center of mass energy of 1200 MeV. According to modern calculations based on the Dirac equation, the collision times at $E_{cm}>1$ GeV are sufficient to allow spontaneous electron-positron pair emission from QED vacuum decay, in case of bare uranium ion collision. A second application of actinide collisions to produce neutron-rich transfermiums is discussed. A new inverse quasifission mechanism associated to a specific orientation of the nuclei is proposed to produce transfermium nuclei ($Z>100$) in the collision of prolate deformed actinides such as $^{232}$Th+$^{250}$Cf. The collision of the tip of one nucleus with the side of the other results in a nucleon flux toward the latter. The probability distributions for transfermium production in such a collision are computed. The produced nuclei are more neutron-rich than those formed in fusion reactions, thus, leading to more stable isotopes closer to the predicted superheavy island of stability. In addition to mass and charge dispersion, the Balian-Veneroni variational principle is used to compute correlations between $Z$ and $N$ distributions, which are zero in standard TDHF calculations.Comment: Proceeding of the FUSION11 conferenc

Henri Temianka Correspondence; (golabek)

This collection contains material pertaining to the life, career, and activities of Henri Temianka, violin virtuoso, conductor, music teacher, and author. Materials include correspondence, concert programs and flyers, music scores, photographs, and books.https://digitalcommons.chapman.edu/temianka_correspondence/3517/thumbnail.jp

Entstehung des Erdkerns: Laborexperimente und numerische Modelle zum Perkolationsmechanismus und zum Rayleigh-Taylor Diapirismus

Die vorliegende Arbeit behandelt das Forschungsthema der Entstehung des flüssigen Eisenkerns im Zentrum unseres Planeten. Dieses bislang wenig verstandene Gebiet ist reich an Fragestellungen, sowohl für Experimentatoren als auch für die Geodynamik. Es gibt sehr viele Arbeiten, die den Bildungsprozess experimentell untersuchen, jedoch wurde in den letzten Jahren die numerische Untersuchung in diesem Gebiet kaum vorangetrieben. Der experimentelle Teil der Arbeit stellt sich hierbei der aktuellen Frage nach der Perkolationsschwelle 1 von Eisenschmelze in der Silikatmatrix der Protoerde, während numerisch die Effekte von Potenzgesetzkriechen, Dissipation und Schmelzsegregation beim Absinken eines Eisendiapirs nach Ausbildung eines ersten flachen Magmaozeans in der Protoerde behandelt werden. Die genauen Fragestellungen könnnen dabei im letzten Abschnitt der Einleitung gefunden werden.The diploma thesis 'Formation of Earth's core: Laboratory experiments and numerical models for the percolation mechanism and the Rayleigh-Taylor instability' includes some laboratory experiments and numerical modelling which implement the percolation and Rayleigh-Taylor instability mechanisms. The laboratory experiments have been performed on a fertile peridotite with the addition of iron sulfide by the use of a centrifuge furnace in order to model a percolation flow. In some experiments in-situ performed electrical conductivity measurements have been done in order to access a connectivity of iron sulfide melts. The numerical experiments have been done with the use of a two-dimensional finite difference method applied to the sinking of iron diapirs through a silicate matrix in the case of the temperature and stress-dependent rheology. Peridotite samples containing different amounts of iron sulfide (5-15 vol%) were prepared from powders of the fertile peridotite and chemicals of Fe-FeS of the eutectic composition. They were placed in the centrifuge piston cylinder at the ETH Zürich to determine a percolation velocity of Fe-FeS through the peroditite matrix. It was found that the segregation velocity of Fe-FeS is far too slow in a partially molten silicate matrix to be accounted for the core formation alone. Additionally, the electrical conductivities of samples consisting of fertile peridotite and Fe-FeS were measured in-situ in order to revise the experimental results of Yoshino et al. (2003, 2004). These papers describe an interconnection threshold in a solid silicate matrix at about 5 vol% of iron sulfide. In the present work it was shown that more than 15 vol% Fe-FeS are needed to reach an interconnectivity of Fe-FeS in a peridotite matrix. In the numerical modelling the computer code FDCON was modified and extended to resolve more realistic cases for the evolution of the Rayleigh-Taylor instability at the top of a cold, undifferentiated and less dense protocore. This unstable gravitational configuration was used as a starting point in numerical models. Differing rheologic laws (temperatureindependent, temperature-dependent and power law) were used to explore the parameter space consisting of initial temperature and viscosity of the protocore and the non-dimensional temperature scaling factor of viscosity b to find a realistic scenario in an agreement with the Hf/W isotopic ages of the core in which the core formation is prescribed to be largely completed within the first 33 Ma (Kleine et al., 2002). It was found that only for b <= 10 the iron diapir is able to penetrate fast enough through the protocore and to fullfill the isotopic restrictions. The required central protocore temperature is in an good agreement with the numerical models performed by Merk et al. (2002), which included the heating during the accretion stage and heating due to the radioactive decay of a short-lived isotope 26Al. In a less advanced model without the application of a power law, it is shown that the dissipation plays only a second order role on the sinking depth of a diapir. Numerical experiments including the power law rheology may be useful in order to revise this result for a more realistic case. Finally, it was shown that the introducing of the melt effect in the calculation scheme is relevant to the core formation models due to the intensive development of stress-induced melt channelling in localities surrounding the incipient iron diapir. For simplicity an isothermal model with a temperature independent viscosity of a solid phase and with a rheology depending on a melt-fraction in the partially molten region surrounding a diapir was used. As a result of this model, the intensive development of iron-rich melt channels within a region approximately 2-3 times larger than a diapir size has been observed for sufficiently small melt retention numbers, i.e. the ratio of a Stokes sinking to a Darcy flow velocity. This mechanism enhanced the melt accumulation and accelerated the process of the core formation. The introduction of more realistic temperature profiles, the use of a power-law rheology and a stress-dependent porosity are possible in future numerical models which could lead to a better understanding of the core formation mechanism

Henri Temianka Correspondence; (golabek)

This collection contains material pertaining to the life, career, and activities of Henri Temianka, violin virtuoso, conductor, music teacher, and author. Materials include correspondence, concert programs and flyers, music scores, photographs, and books.https://digitalcommons.chapman.edu/temianka_correspondence/3516/thumbnail.jp

The Effectiveness Of Rational-Emotive Therapy In The Reduction Of Trait Anxiety Of College Undergraduate Students

The purpose of this study was to determine the effectiveness of Rational-Emotive Therapy (RET) in reducing levels of trait anxiety in undergraduates who enrolled in anxiety reduction workshops. S\u27s were 44 volunteer male and female students from the University of the Pacific who enrolled in either an independent study or a mini-course series of 8 sessions, and were assigned to one of the three randomly designated groups: Rational-Emotive Therapy (RET), Attention Placebo (AP), or No-Treatment (NT). The AP procedure consisted of exposure to various nutritional aspects of physical fitness which focused on vitamin and mineral intake. Two self-report measures, the State-Trait Anxiety Inventory (STAI) and the Multiple Affect Adjective Checklist (MAACL) were used, as well as a behavioral measure, the Anxiety Rating Scale (ARS), to assess the effectiveness of each treatment on anxiety. It was hypothesized that the self-report scales would reflect a decrease in anxiety which would be greatest for the RET treatment. The second hypothesis was that students in the RET treatment would show the greatest amount of anxiety reduction according to the behavioral measure. The third hypothesis stated that there would be no sex differentiation in anxiety reduction within any of the treatments. A two-way analysis of variance (ANOVA) on the difference scores was the method of statistical analysis for both of the self-report measures, and an analysis of co-variance (ANCOVA) on the difference scores was the method used for the behavioral measure, with alpha set at .05 for all analyses. Results showed that there was a significant difference, according to the STAI, in the effectiveness of anxiety reduction of the RET and AP groups. The MAACL failed to reveal any significant differences between treatments. The ARS did find significantly more effectiveness in anxiety reduction in the RET treatment over the two control groups. All instruments revealed no differences for sex differentiation in anxiety reduction within any of the treatments

The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals

The thermal history and internal structure of chondritic planetesimals, assembled before the giant impact phase of chaotic growth, potentially yield important implications for the final composition and evolution of terrestrial planets. These parameters critically depend on the internal balance of heating versus cooling, which is mostly determined by the presence of short-lived radionuclides (SLRs), such as aluminum-26 and iron-60, as well as the heat conductivity of the material. The heating by SLRs depends on their initial abundances, the formation time of the planetesimal and its size. It has been argued that the cooling history is determined by the porosity of the granular material, which undergoes dramatic changes via compaction processes and tends to decrease with time. In this study we assess the influence of these parameters on the thermo-mechanical evolution of young planetesimals with both 2D and 3D simulations. Using the code family I2ELVIS/I3ELVIS we have run numerous 2D and 3D numerical finite-difference fluid dynamic models with varying planetesimal radius, formation time and initial porosity. Our results indicate that powdery materials lowered the threshold for melting and convection in planetesimals, depending on the amount of SLRs present. A subset of planetesimals retained a powdery surface layer which lowered the thermal conductivity and hindered cooling. The effect of initial porosity was small, however, compared to those of planetesimal size and formation time, which dominated the thermo-mechanical evolution and were the primary factors for the onset of melting and differentiation. We comment on the implications of this work concerning the structure and evolution of these planetesimals, as well as their behavior as possible building blocks of terrestrial planets.Comment: 19 pages, 11 figures, 5 tables; accepted for publication in Icarus; for associated video files, see http://timlichtenberg.net/2015_porosity.html or http://dx.doi.org/10.1016/j.icarus.2016.03.00

Collision dynamics of two 238^{238}U atomic nuclei

Collisions of actinide nuclei form, during very short times of few $10^{-21}$ s, the heaviest ensembles of interacting nucleons available on Earth. Such very heavy ions collisions have been proposed as an alternative way to produce heavy and superheavy elements. These collisions are also used to produce super-strong electric fields by the huge number of interacting protons to test spontaneous positron-electron ($e^+e^-$) pair emission predicted by the quantum electrodynamics theory. The time-dependent Hartree-Fock theory which is a fully microscopic quantum approach is used to study collision dynamics of two $^{238}$U atomic nuclei. In particular, the role of nuclear deformation on collision time and on reaction mechanisms such as nucleon transfer is emphasized. These calculations are pessimistic in terms of transfermium elements ($Z>100$) production. However, the highest collision times ($\sim4\times10^{-21}$ s at 1200 MeV) should allow experimental signature of spontaneous $e^+e^-$ emission. Surprisingly, we also observe ternary fission due to purely dynamical effects.Comment: Accepted for publication in Physical Review Lette

Modification of icy planetesimals by early thermal evolution and collisions: Constraints for formation time and initial size of comets and small KBOs

Comets and small Kuiper belt objects are considered to be among the most primitive objects in the solar system as comets like C/1995 O1 Hale-Bopp are rich in highly volatile ices like CO. It has been suggested that early in the solar system evolution the precursors of both groups, the so-called icy planetesimals, were modified by both short-lived radiogenic heating and collisional heating. Here we employ 2D finite-difference numerical models to study the internal thermal evolution of these objects, where we vary formation time, radius and rock-to-ice mass fraction. Additionally we perform 3D SPH collision models with different impact parameters, thus considering both cratering and catastrophic disruption events. Combining the results of both numerical models we estimate under which conditions highly volatile ices like CO, CO2 and NH3 can be retained inside present-day comets and Kuiper belt objects. Our results indicate that for present-day objects derived from the largest post-collision remnant the internal thermal evolution controls the amount of remaining highly volatile ices, while for the objects formed from unbound post-collision material the impact heating is dominant. Finally we apply our results to present-day comets and Kuiper belt objects like 67P/Churyumov-Gerasimenko, C/1995 O1 Hale-Bopp and (486958) Arrokoth